TRAY MOUNTAIN ROADLESS AREA, GEORGIA.

USGS Publications Warehouse

Nelson, Arthur E.; Chatman, Mark L.

1984-01-01

A mineral survey indicates that the Tray Mountain Roadless Area, Georgia has little promise for the occurrence of metallic mineral resources. Rocks underlying the Tray Mountain Roadless Area are suitable for crushed rock or aggregate; however, other sources for these materials are available closer to present markets. There is a possibility for the occurrence of hydrocarbon resources underlying the area at great depth, but no hydrocarbon potential was identified. Detailed studies are needed to establish the presence or absence and mineral-resource potential of olivine, nickel, cobalt, and chrome in the two mafic-ultramafic bodies in the Hayesville thrust sheet. The cause of the lead anomaly in pan concentrate samples taken from the southwest part of the roadless area has not been established; the mineral residence and source of the anomaly remain to be determined.

Extrusional Tectonics over Plate Corner: an Example in Northern Taiwan

NASA Astrophysics Data System (ADS)

Lu, Chia-Yu; Lee, Jian-Cheng; Li, Zhinuo; Lee, Ching-An; Yeh, Chia-Hung

2016-04-01

In northern Taiwan, contraction, transcurrent shearing, block rotation and extension are four essential tectonic deformation mechanisms involved in the progressive deformation of this arcuate collision mountain belt. The neotectonic evolution of the Taiwan mountain belt is mainly controlled not only by the oblique convergence between the Eurasian plate and the Philippine Sea plate but also the corner shape of the plate boundary. Based on field observations and analyses, and taking geophysical data (mostly GPS) and experimental modelling into account, we interpret the curved belt of northern Taiwan as a result of of contractional deformation (with compression, thrust-sheet stacking & folding, back thrust duplex & back folding) that induced vertical extrusion, combined with increasing transcurrent & rotational deformation (with transcurrent faulting, bookshelf-type strike-slip faulting and block rotation) that induced transcurrent/rotational extrusion and extension deformation which in turn induced extensional extrusion. As a consequence, a special type of extrusional folds was formed in association with contractional, transcurrent & rotational and extensional extrusions subsequently. The extrusional tectonics in northern Taiwan reflect a single, albeit complicated, regional pattern of deformation. The crescent-shaped mountain belt of Northeastern Taiwan develops in response to oblique indentation by an asymmetric wedge indenter, retreat of Ryukyu trench and opening of the Okinawa trough.

Extrusional Tectonics at Plate Corner: an Example in Northern Taiwan

NASA Astrophysics Data System (ADS)

Lu, C. Y.; Lee, J. C.; Li, Z.; Yeh, C. H.; Lee, C. A.

2015-12-01

In northern Taiwan, contraction, transcurrent shearing, block rotation and extension are four essential tectonic deformation mechanisms involved in the progressive deformation of this arcuate collision mountain belt. The neotectonic evolution of the Taiwan mountain belt is mainly controlled not only by the oblique convergence between the Eurasian plate and the Philippine Sea plate but also the corner shape of the plate boundary. Based on field observations and analyses, and taking geophysical data (mostly GPS) and experimental modelling into account, we interpret the curved belt of northern Taiwan as a result of of contractional deformation (with compression, thrust-sheet stacking & folding, back thrust duplex & back folding) that induced vertical extrusion, combined with increasing transcurrent & rotational deformation (with transcurrent faulting, bookshelf-type strike-slip faulting and block rotation) that induced transcurrent/rotational extrusion and extension deformation which in turn induced extensional extrusion. As a consequence, a special type of extrusional folds was formed in association with contractional, transcurrent & rotational and extensional extrusions subsequently. The extrusional tectonics in northern Taiwan reflect a single, albeit complicated, regional pattern of deformation. The crescent-shaped mountain belt of Northeastern Taiwan develops in response to oblique indentation by an asymmetric wedge indenter and opening of the Okinawa trough at plate corner.

Structural evidence for northeastward movement on the Chocolate Mountains Thrust, southeasternmost California

USGS Publications Warehouse

Dillon, J.T.; Haxel, G.B.; Tosdal, R.M.

1990-01-01

The Late Cretaceous Chocolate Mountains Thrust of southeastern California and southwestern Arizona places a block of Proterozoic and Mesozoic continental crust over the late Mesozoic continental margin oceanic sedimentary and volcanic rocks of the Orocopia Schist. The Chocolate Mountains Thrust is interpreted as a thrust (burial, subduction) fault rather than a low-angle normal fault. An important parameter required to understand the tectonic significance of the Chocolate Mountains and related thrusts is their sense of movement. The only sense of movement consistent with collective asymmetry of the thrust zone folds is top to the northeast. Asymmetric microstructures studied at several localities also indicate top to the northeast movement. Paleomagnetic data suggest that the original sense of thrusting, prior to Neogene vertical axis tectonic rotation related to the San Andreas fault system, was northward. Movement of the upper plate of the chocolate Mountains thrust evidently was continentward. Continentward thrusting suggests a tectonic scenario in which an insular or peninsular microcontinental fragment collided with mainland southern California. -from Authors

First-order control of syntectonic sedimentation on crustal-scale structure of mountain belts

NASA Astrophysics Data System (ADS)

Erdős, Zoltán.; Huismans, Ritske S.; van der Beek, Peter

2015-07-01

The first-order characteristics of collisional mountain belts and the potential feedback with surface processes are predicted by critical taper theory. While the feedback between erosion and mountain belt structure has been fairly extensively studied, less attention has been given to the potential role of synorogenic deposition. For thin-skinned fold-and-thrust belts, recent studies indicate a strong control of syntectonic deposition on structure, as sedimentation tends to stabilize the thin-skinned wedge. However, the factors controlling basement deformation below fold-and-thrust belts, as evident, for example, in the Zagros Mountains or in the Swiss Alps, remain largely unknown. Previous work has suggested that such variations in orogenic structure may be explained by the thermotectonic "age" of the deforming lithosphere and hence its rheology. Here we demonstrate that sediment loading of the foreland basin area provides an additional control and may explain the variable basement involvement in orogenic belts. When examining the role of sedimentation, we identify two end-members: (1) sediment-starved orogenic systems with thick-skinned basement deformation in an axial orogenic core and thin-skinned deformation in the bordering forelands and (2) sediment-loaded orogens with thick packages of synorogenic deposits, derived from the axial basement zone, deposited on the surrounding foreland fold-and-thrust belts, and characterized by basement deformation below the foreland. Using high-resolution thermomechanical models, we demonstrate a strong feedback between deposition and crustal-scale thick-skinned deformation. Our results show that the loading effects of syntectonic sediments lead to long crustal-scale thrust sheets beneath the orogenic foreland and explain the contrasting characteristics of sediment-starved and sediment-loaded orogens, showing for the first time how both thin- and thick-skinned crustal deformations are linked to sediment deposition in these orogenic systems. We show that the observed model behavior is consistent with observations from a number of natural orogenic systems.

Stable isotopic evidence for fluid flow and fluid/rock interaction during thrust faulting in Pumpkin Valley shale and Rome Formation, east Tennessee

DOE Office of Scientific and Technical Information (OSTI.GOV)

Butler, B.K.; Haase, C.S.

1989-08-01

The Pumpkin Valley Shale and the underlying Rome Formation form the lower portions of the Copper Creek and White Oak Mountain thrust sheets in east Tennessee. The Pumpkin Valley Shale consists of shale and mudstone with subordinate amounts of interbedded siltstone. The Rome Formation is composed predominantly of sandstone with interbedded shale and siltstone toward the base of the formation. The percentage of illite increases from 20% to over 80% of the bulk clay mineralogy toward the base of the section. Porosity is occluded by quartz, phyllosilicate, and calcite cements. Both formations contain calcite-filled and, less commonly, quartz-filled Alleghenian fracturesmore » and joints.« less

Progressive deformation and superposed fabrics related to Cretaceous crustal underthrusting in western Arizona, U.S.A.

USGS Publications Warehouse

Laubach, S.E.; Reynolds, S.J.; Spencer, J.E.; Marshak, S.

1989-01-01

In the Maria fold and thrust belt, a newly recognized E-trending Cretaceous orogenic belt in the southwestern United States, ductile thrusts, large folds and superposed cleavages record discordant emplacement of crystalline thrust sheets across previously tilted sections of crust. Style of deformation and direction of thrusting are in sharp contrast to those of the foreland fold-thrust belt in adjacent segments of the Cordillera. The net effect of polyphase deformation in the Maria belt was underthrusting of Paleozoic and Mesozoic metasedimentary rocks under the Proterozoic crystalline basement of North America. The structure of the Maria belt is illustrated by the Granite Wash Mountains in west-central Arizona, where at least four non-coaxial deformation events (D1-D4) occurred during the Cretaceous. SSE-facing D1 folds are associated with S-directed thrusts and a low-grade slaty cleavage. D1 structures are truncated by the gently-dipping Hercules thrust zone (D2), a regional SW-vergent shear zone that placed Proterozoic and Jurassic crystalline rocks over upturned Paleozoic and Mesozoic supracrustal rocks. Exposures across the footwall margin of the Hercules thrust zone show the progressive development of folds, cleavage and metamorphism related to thrusting. D3 and D4 structures include open folds and spaced cleavages that refold or transect D1 and D2 folds. The D2 Hercules thrust zone and a D3 shear zone are discordantly crosscut by late Cretaceous plutons. ?? 1989.

Chronology of paleozoic metamorphism and deformation in the Blue Ridge thrust complex, North Carolina and Tennessee

DOE Office of Scientific and Technical Information (OSTI.GOV)

Goldberg, S.A.; Dallmeyer, R.D.

1997-05-01

The Blue Ridge province in northwestern North Carolina and northeastern Tennessee records a multiphase collisional and accretionary history from the Mesoproterozoic through the Paleozoic. To constrain the tectonothermal evolution in this region, radiometric ages have been determined for 23 regionally metamorphosed amphibolites, granitic gneisses, and pelitic schists and from mylonites along shear zones that bound thrust sheets and within an internal shear zone. The garnet ages from the Pumpkin Patch a thrust sheet (458, 455, and 451 Ma) are similar to those from the structurally overlying Spruce Pine thrust sheet (460, 456, 455, and 450 Ma). Both thrust sheets exhibitmore » similar upper amphibolite-facies conditions. Because of the high closure temperature for garnet, the garnet ages are interpreted to date growth at or near the peak of Taconic metamorphism. Devonian metamorphic ages are recognized in the Spruce Pine thrust sheet, where Sm-Nd and Rb-Sr garnet ages of 386 and 393 Ma and mineral isochron ages of 397 {+-} 14 and 375 {+-} 27 Ma are preserved. Hornblendes record similar {sup 40}Ar/{sup 39}Ar, Sm-Nd, and Rb-Sr ages of 398 to 379 Ma. Devonian {sup 40}Ar/{sup 39}Ar hornblende ages are also recorded in the structurally lower Pumpkin Patch thrust sheet. The Devonian mineral ages are interpreted to date a discrete tectonothermal event, as opposed to uplift and slow cooling from an Ordovician metamorphic event. The Mississippian mylonitization is interpreted to represent thrusting and initial assembly of crystalline sheets associated with the Alleghanian orogeny. The composite thrust stack of the Blue Ridge complex was subsequently thrust northwestward along the Linville Falls fault during middle Alleghanian orogeny (about 300 Ma).« less

Structural evidence for northeastward movement on the Chocolate Mountains thrust, southeasternmost Calfornia

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dillon, J.T.; Haxel, G.B.; Tosdal, R.M.

1990-11-10

The Late Cretaceous Chocolate Mountains thrust of southeastern California and southwestern Arizona places a block of Proterozoic and Mesozoic continental crust over the late Mesozoic continental margin oceanic sedimentary and volcanic rocks of the regionally distinctive Orocopia Schist. The Chocolate Mountains thrust is interpreted as a thrust (burial, subduction) fault rather than a low-angle normal (exhumation, unroofing, uplift) fault. The Chocolate Mountains thrust zone contains sparse to locally abundant mesoscopic asymmetric folds. Fabric relations indicate that these folds are an integral part of and coeval with the thrust zone. On a lower hemisphere equal-area plot representing the orientation and sensemore » of asymmetry of 80 thrust zone folds from 36 localities, spread over an area 60 by 10 km, Z folds plot northwest of and S folds plot southeast of a northeast-southwest striking vertical plane of overall monoclinic symmetry. The only sense of movement consistent with the collective asymmetry of the thrust zone folds is top to the northeast. Paleomagnetic data suggest that the original sense of thrusting, prior to Neogene vertical axis tectonic rotation related to the San Andreas fault system, was northward. The essential point is that movement of the upper plate of the Chocolate Mountains thrust evidently was continentward. Continentward thrusting suggests a tectonic scenario in which an insular or peninsular microcontinental fragment collided with mainland southern California. Alternative tectonic models involving subduction of the Orocopia Schist eastward beneath continental southern California circumvent the suture problem but are presently not supported by any direct structural evidence.« less

Was Himalayan normal faulting triggered by initiation of the Ramgarh-Munsiari Thrust?

USGS Publications Warehouse

Robinson, Delores M.; Pearson, Ofori N.

2013-01-01

The Ramgarh–Munsiari thrust is a major orogen-scale fault that extends for more than 1,500 km along strike in the Himalayan fold-thrust belt. The fault can be traced along the Himalayan arc from Himachal Pradesh, India, in the west to eastern Bhutan. The fault is located within the Lesser Himalayan tectonostratigraphic zone, and it translated Paleoproterozoic Lesser Himalayan rocks more than 100 km toward the foreland. The Ramgarh–Munsiari thrust is always located in the proximal footwall of the Main Central thrust. Northern exposures (toward the hinterland) of the thrust sheet occur in the footwall of the Main Central thrust at the base of the high Himalaya, and southern exposures (toward the foreland) occur between the Main Boundary thrust and Greater Himalayan klippen. Although the metamorphic grade of rocks within the Ramgarh–Munsiari thrust sheet is not significantly different from that of Greater Himalayan rock in the hanging wall of the overlying Main Central thrust sheet, the tectonostratigraphic origin of the two different thrust sheets is markedly different. The Ramgarh–Munsiari thrust became active in early Miocene time and acted as the roof thrust for a duplex system within Lesser Himalayan rocks. The process of slip transfer from the Main Central thrust to the Ramgarh–Munsiari thrust in early Miocene time and subsequent development of the Lesser Himalayan duplex may have played a role in triggering normal faulting along the South Tibetan Detachment system.

Early history and reactivation of the rand thrust, southern California

NASA Astrophysics Data System (ADS)

Postlethwaite, Clay E.; Jacobson, Carl E.

The Rand thrust of the Rand Mountains in the northwestern Mojave Desert separates an upper plate of quartz monzonite and quartzofeldspathic to amphibolitic gneiss from a lower plate of metagraywacke and mafic schist (Rand Schist). The Rand thrust is considered part of the regionally extensive Vincent/Chocolate Mountain thrust system, which is commonly believed to represent a Late Cretaceous subduction zone. The initial direction of dip and sense of movement along the Vincent/Chocolate Mountain thrust are controversial. Microfabrics of mylonites and quartzites from the Rand Mountains were analyzed in an attempt to determine transport direction for this region, but the results are ambiguous. In addition, the southwestern portion of the Rand thrust was found to have been reactivated as a low-angle normal fault after subduction. Reactivation might have occurred shortly after subduction, in which case it could account for the preservation of high-pressure mineral assemblages in the Rand Schist, or it could be related to mid-Tertiary extension in the western United States. In either event, the reactivation might be responsible for the complicated nature of the microfabrics. The Rand Schist exhibits an inverted metamorphic zonation. Isograds in the schist are not significantly truncated by the reactivated segment of the Rand thrust. This indicates that other segments of the Vincent/Chocolate Mountain thrust should be re-evaluated for the possibility of late movement, even if they show an apparently undisturbed inverted metamorphic zonation.

Thrusting and back-thrusting as post-emplacement kinematics of the Almora klippe: Insights from Low-temperature thermochronology

NASA Astrophysics Data System (ADS)

Patel, R. C.; Singh, Paramjeet; Lal, Nand

2015-06-01

Crystalline klippen over the Lesser Himalayan Sequence (LHS) in the Kumaon and Garhwal regions of NW-Himalaya, are the representative of southern portion of the Main Central Thrust (MCT) hanging wall. These were tectonically transported over the juxtaposed thrust sheets (Berinag, Tons and Ramgarh) of the LHS zone along the MCT. These klippen comprise of NW-SE trending synformal folded thrust sheet bounded by thrusts in the south and north. In the present study, the exhumation histories of two well-known klippen namely Almora and Baijnath, and the Ramgarh thrust sheet, in the Kumaon and Garhwal regions vis-a-vis Himalayan orogeny have been investigated using Apatite Fission Track (AFT) ages. Along a ~ 60 km long orogen perpendicular transect across the Almora klippe and the Ramgarh thrust sheet, 16 AFT cooling ages from the Almora klippe and 2 from the Ramgarh thrust sheet have been found to range from 3.7 ± 0.8 to 13.2 ± 2.7 Ma, and 6.3 ± 0.8 to 7.2 ± 1.0 Ma respectively. From LHS meta-sedimentary rocks only a single AFT age of 3.6 ± 0.8 Ma could be obtained. Three AFT ages from the Baijnath klippe range between 4.7 ± 0.5 and 6.6 ± 0.8 Ma. AFT ages and exhumation rates of different klippen show a dynamic coupling between tectonic and erosion processes in the Kumaon and Garhwal regions of NW-Himalaya. However, the tectonic processes play a dominant role in controlling the exhumation. Thrusting and back thrusting within the Almora klippe and Ramgarh thrust sheet are the post-emplacement kinematics that controlled the exhumation of the Almora klippe. Combining these results with the already published AFT ages from the crystalline klippen and the Higher Himalayan Crystalline (HHC), the kinematics of emplacement of the klippen over the LHS and exhumation pattern across the MCT in the Kumaon and Garhwal regions of NW-Himalaya have been investigated.

Geologic map of the Hogback Mountain quadrangle, Lewis and Clark and Meagher Counties, Montana

USGS Publications Warehouse

Reynolds, Mitchell W.

2003-01-01

The geologic map of the Hogback Mountain quadrangle, scale 1:24,000, was made as part of the Montana Investigations Project to provide new information on the stratigraphy, structure, and geologic history of an area in the geologically complex southern part of the Montana disturbed belt. In the Hogback Mountain area, rocks ranging in age from Middle Proterozoic through Cretaceous are strongly folded within and under thrust plates of equivalent rocks. Continental rocks of successive thrust plates have been telescoped eastward over a buttress of the stable continent. Erosional remnants of Oligocene andesitic basalt lie on highest surfaces eroded across the strongly deformed older rocks; younger erosion has dissected the terrain deeply, producing Late Tertiary and Quaternary deposits of alluvium, colluvium, and local landslide debris in the valleys and canyons. Different stratigraphic successions are exposed at different structural levels across the quadrangle. In the northeastern part of the quadrangle at the lowest structural level, rocks of the Upper Mississippian Big Snowy Group, including the Kibbey Formation and the undivided Otter and Heath Formations, the overlying Pennsylvanian Amsden and undivided Quadrant and Phosphoria Formations, the Ellis Group, and the Kootenai Formation, are folded and broken by thrust faults. The next higher structural level, the Avalanche Butte thrust plate, exposes strongly folded and, in places, attenuated strata of Cambrian (Flathead Sandstone, Wolsey Shale, Meagher Limestone, and undivided Pilgrim Formation and Park Shale), Devonian (Maywood Formation, Jefferson Formation, and most of the Three Forks Formation), and Mississippian (uppermost part of the Three Forks Formation and Lodgepole and Mission Canyon Limestones) ages. The overlying Hogback Mountain thrust plate contains strongly folded rocks ranging in age from the Middle Proterozoic Greyson Formation to the Upper and Lower Mississippian Mission Canyon Limestone and Cretaceous diorite sills. The highest structural level, the Moors Mountain thrust plate, contains the Middle Proterozoic Greyson and Newland Formations and discontinuous Upper Proterozoic diabase sills. Rocks are complexly folded and faulted across the quadrangle. At the lowest level in the northeastern part of the quadrangle, Upper Mississippian and younger strata are folded along northwest-trending axes and broken by thrust faults that at outcrop level displace the same rocks. The central core of the quadrangle is formed by the Avalanche Butte thrust plate, which contains recumbently folded and thrust faulted Paleozoic rocks. A succession of four tight recumbent folds within the plate have axial traces that trend northwest and north-northwest, and that are both arched and downfolded along east- and northeast-trending axes. Carbonate rocks of the Mission Canyon and Lodgepole Limestones in the upper part of the Avalanche Butte thrust plate exposed in the canyon of Trout Creek are folded and attenuated in stacked east-directed recumbent folds that developed as a succession of folded duplex thrust slices. The exposed remnant of the next higher structural level, the Hogback Mountain thrust plate, contains northeast- and east-trending folds that are inverted on the upper overturned limb of a younger northwest-trending recumbent fold. The Hogback Mountain thrust fault is itself folded and, in its northernmost exposures, is overturned to dip west beneath the overlying Moors Mountain thrust plate. During post-middle Tertiary deformation, the Hogback Mountain thrust fault moved as a normal fault, down on the east. The structurally highest Moors Mountain thrust plate rests on the Avalanche Butte thrust plate in the southwestern part of the quadrangle and across both the Avalanche Butte and Hogback Mountain thrust plates along the northwest edge of the quadrangle. In the central eastern part of the map area, the edge of a large klippen of the Moors Mounta

Stratigraphic relations and U-Pb geochronology of the Upper Cretaceous upper McCoy Mountains Formation, southwestern Arizona

USGS Publications Warehouse

Tosdal, R.M.; Stone, P.

1994-01-01

A previously unrecognized angular unconformity divides the Jurassic and Cretaceous McCoy Mountains Formation into a lower and an upper unit in the Dome Rock Mountains and Livingston Hills of western Arizona. The intraformation unconformity in the McCoy Mountains Formation developed where rocks of the lower unit were deformed adjacent to the southern margin of the Maria fold and thrust belt. The upper unit of the formation is interpreted as a foreland-basin deposit that was shed southward from the actively rising and deforming fold and thrust belt. The apparent absence of an equivalent unconformity in the McCoy Mountains Formation in adjacent California is presumably a consequence of the observed westward divergence of the outcrop belt from the fold and thrust belt. Tectonic burial beneath the north-vergent Mule Mountains thrust system in the latest Late Cretaceous (~70 Ma) marked the end of Mesozoic contractile deformation in the area. -from Authors

Geologic Map of the Sulphur Mountain Quadrangle, Park County, Colorado

USGS Publications Warehouse

Bohannon, Robert G.; Ruleman, Chester A.

2009-01-01

The main structural element in the Sulphur Mountain quadrangle is the Elkhorn thrust. This northwest-trending fault is the southernmost structure that bounds the west side of the Late Cretaceous and early Tertiary Front Range basement-rock uplift. The Elkhorn thrust and the Williams Range thrust that occurs in the Dillon area north of the quadrangle bound the west flank of the Williams Range and the Front Range uplift in the South Park area. Kellogg (2004) described widespread, intense fracturing, landsliding, and deep-rooted scarps in the crystalline rocks that comprise the upper plate of the Williams Range thrust. The latter thrust is also demonstrably a low-angle structure upon which the fractured bedrock of the upper plate was translated west above Cretaceous shales. Westward thrusting along the border of the Front Range uplift is probably best developed in that area. By contrast, the Elkhorn in the Sulphur Mountain quadrangle is poorly exposed and occurs in an area of relatively low relief. The thrust also apparently ends in the central part of the quadrangle, dying out into a broad area of open, upright folds with northwest axes in the Sulphur Mountain area.

Emplacement history of a thrust sheet based on analysis of pressure solution cleavage and deformed fossils

DOE Office of Scientific and Technical Information (OSTI.GOV)

Protzman, G.M.; Mitra, G.

The emplacement history of a thrust sheet is recorded by the strain accumulated in its hanging wall and footwall. Detailed studies of second order structures and analysis of strain due to pressure solution and plastic deformation allow the authors to determine the deformation history of the Meade thrust in the Idaho - Wyoming thrust belt. Emplacement of the Meade thrust was accompanied by the formation of a series of second order in echelon folds in the footwall. Temporal relations based on detailed structural studies show that these folds, which are confined to the Jurassic Twin Creek Formation, formed progressively inmore » front of the advancing Meade thrust and were successively truncated and overridden by footwall imbricates of the Meade thrust. The Twin Creek Formation in both the hanging wall and footwall of the Meade thrust is penetratively deformed, with a well developed pressure solution cleavage. In addition, plastic strain is recorded by deformed Pentacrinus within fossil hash layers in the Twin Creek. Much of this penetrative deformation took place early in the history of the thrust sheet as layer parallel shortening, and the cleavage and deformed fossils behaved passively during subsequent folding and faulting. The later stages of deformation may be sequentially removed through balancing techniques to track successive steps in the deformation. This strain history, which is typical of an internal thrust sheet, is partly controlled by the lithologies involved, timing between successive thrusts, and the amount of interaction between major faults.« less

Geologic map of the Lockwood Valley Quadrangle, Ventura County, California

USGS Publications Warehouse

Kellogg, Karl S.

2001-01-01

The Lockwood Valley quadrangle is located in the western Transverse Ranges of California, about 10 km southwest of Frazier Park. It includes the western flank of Frazier Mountain, southern Lockwood Valley, and a region of the Los Padres National Forest near northern Piru Creek. The oldest rocks are mostly biotite augen gneiss, in the hanging wall of the Frazier Mountain thrust and in a large body south of the thrust. A U-Pb zircon age for the gneiss is 1690+5 Ma (W. Premo, unpublished data). Two Cretaceous intrusive rocks are named the quartz monzonite of Sheep Creek and the coarse-grained granodiorite of Lockwood Peak. A U-Pb zircon age on the latter is 76.05+0.22 Ma (W. Premo, unpublished data). The northeastern edge of a large Eocene marine basin, comprising the sandstones, shales, and conglomerates of the Juncal Formation, occupies the southwestern 25 percent of the quadrangle. Miocene fluvial rocks, including coarse boulder conglomerates, sandstones, and shale, of the Caliente Formation crop out mostly in the northwestern part of the quadrangle. Commercially exploitable Lockwood Clay unconformably overlies the Caliente, which, in turn, is overlain by the mostly fluvial Pliocene Quatal Formation. Two major south-directed thrusts, the Frazier Mountain thrust and the South Frazier Mountain thrust, place crystalline rocks over Miocene and Pliocene sedimentary rocks. The South Frazier Mountain thrust is transected by the newly recognized, north-directed Lockwood Peak reverse fault. In addition, the newly recognized south-directed Yellowjacket thrust displaces rocks of the Pliocene Quatal Formation.

Reevaluating the age of the Walden Creek Group and the kinematic evolution of the western Blue Ridge, southern Appalachians

USGS Publications Warehouse

Thigpen, J. Ryan; Hatcher, Robert D.; Kah, Linda C.; Repetski, John E.

2016-01-01

An integrated synthesis of existing datasets (detailed geologic mapping, geochronologic, paleontologic, geophysical) with new paleontologic and geochemical investigations of rocks previously interpreted as part of the Neoproterozoic Walden Creek Group in southeastern Tennessee suggest a necessary reevaluation of the kinematics and structural architecture of the Blue Ridge Foothills. The western Blue Ridge of Tennessee, North Carolina, and Georgia is composed of numerous northwest-directed early and late Paleozoic thrust sheets, which record pronounced variation in stratigraphic/structural architecture and timing of metamorphism. The detailed spatial, temporal, and kinematic relationships of these rocks have remained controversial. Two fault blocks that are structurally isolated between the Great Smoky and Miller Cove-Greenbrier thrust sheets, here designated the Maggies Mill and Citico thrust sheets, contain Late Ordovician-Devonian conodonts and stable isotope chemostratigraphic signatures consistent with a mid-Paleozoic age. Geochemical and paleontological analyses of Walden Creek Group rocks northwest and southeast of these two thrust sheets, however, are more consistent with a Late Neoproterozoic (550–545 Ma) depositional age. Consequently, the structural juxtaposition of mid-Paleozoic rocks within a demonstrably Neoproterozoic-Cambrian succession between the Great Smoky and Miller Cove-Greenbrier thrust sheets suggests that a simple foreland-propagating thrust sequence model is not applicable in the Blue Ridge Foothills. We propose that these younger rocks were deposited landward of the Ocoee Supergroup, and were subsequently plucked from the Great Smoky fault footwall as a horse, and breached through the Great Smoky thrust sheet during Alleghanian emplacement of that structure.

Syntectonic Fluid-Rock Interactions Involving Surficial Waters in the Sevier Thrust Belt, Tendoy Mountains, Southwest Montana

NASA Astrophysics Data System (ADS)

Johnson, A. C.; Anastasio, D. J.; Bebout, G. E.

2002-05-01

Calcite veins and Mississippian carbonates from the Sevier thrust front record syntectonic meteoric fluid infiltration and hydrocarbon migration. The Tendoy and Four Eyes Canyon thrust sheets were emplaced onto the western margin of the Late Cretaceous Western Interior Seaway \\{WIS\\}. Low salinity \\{Tice = -0.6° C to +3.6° C\\} and low temperature \\{110° C +/- 10\\} fluids interacted with hanging-wall carbonates at a depth of 5km. Most veins have single or multiple generations of varying apertures, composed predominately of large euhedral crystals with some finer grained layers and protolith inclusions. Orientation analysis of mutually cross-cutting, high-angle vein sets suggest development concurrent with Four Eyes Canyon thrusting but prior to Tendoy thrusting. These vein sets are generally cut by later synfolding bed-parallel shear veins. Reactivation of both the bed-parallel and bed-perpendicular vein sets \\{strike parallel and strike perpendicular\\} in the Four Eyes Canyon thrust sheet occurred subsequent to Sevier compression, creating wide, coarse crystalline veins that often transect Sevier structures. Oxygen and Carbon isotope analyses of veins allow for reconstruction of fluid-rock interactions during thrust sheet emplacement and later reactivation. All veins and variably deformed host-rocks were microsampled and analyzed for δ 18OV-SMOW and δ 13CV-PDB. Small Tendoy veins \\{1mm-1cm wide\\} have calcite δ 18O values of +8.9 to +28.8‰ and calculated fluid \\{as H2O\\} of -8.3 to +11.6‰ \\{100° C\\}, -7.3 to +12.6‰ \\{110° C\\}, and -6.3 to +13.6‰ \\{120° C\\}. Four Eyes Canyon veins \\{1cm-3m wide\\} have calcite δ 18O values of +5.9 to +17.0‰ and calculated fluid of -11.3 to -0.2‰ \\{100° C\\}, -10.3 to +0.8‰ \\{110° C\\}, and -9.3 to +1.8‰ \\{120° C\\}. While there is significant variation in δ 18O there is relatively little systematic variation seen in δ 13C. Protolith carbonate has δ 18O values of +22.2‰ +/- 3.2; and some multi-layered veins are more depleted in δ 18O in earlier-formed generations. For three sites in the Lost River Range \\{LRR\\}, Idaho, the calculated minimum fluid δ 18O is -7.5‰ \\{+150 to +250° C\\} \\{Bebout et al., 2001; GRL\\}. Although the uncertainty of the regional temperature is large, when assuming a temperature of 110° C +/- 10 the Tendoy has a minimum calculated δ 18O H2O value of -8.3 to -6.3‰ and the Four Eyes Canyon has a minimum calculated δ 18O H2O value of -11.3 to -9.3‰ . These fluid O-isotope compositions are similar to the minimum H2O δ 18O calculated for the LRR sites - all pointing to infiltration of the thrust sheets by meteoric waters, possibly relatively nearshore meteoric waters with isotopic compositions strongly influenced by the nearby WIS. Surficial fluids possibly infiltrated into the thrust sheets by topographic recharge and migrated updip towards the foreland, mixing to varying degrees with more deeply roused fluids. Smaller veins and longer travel times and distances favored more extensive fluid-rock interaction and thus more rock-controlled fluid compositions. Microfractures in veins healed by hydrocarbons indicate that hydrocarbons migrated with freshwater fluids. Calcite veins record a dynamic history of fluid pathways and fluid flow as permeability evolved during thrust emplacement.

Thrust-induced collapse of mountains-an example from the "Big Bend" region of the San Andreas Fault, western transverse ranges, California

USGS Publications Warehouse

Kellogg, Karl S.

2005-01-01

Mount Pinos and Frazier Mountain are two prominent mountains just south of the San Andreas fault in the western Transverse Ranges of southern California, a region that has undergone rapid Quaternary contraction and uplift. Both mountains are underlain, at least in part, by thrusts that place granitic and gneissic rocks over sedimentary rocks as young as Pliocene. Broad profiles and nearly flat summits of each mountain have previously been interpreted as relicts of a raised erosion surface. However, several features bring this interpretation into question. First, lag or stream gravels do not mantle the summit surfaces. Second, extensive landslide deposits, mostly pre?Holocene and deeply incised, mantle the flanks of both mountains. Third, a pervasive fracture and crushed?rock network pervades the crystalline rocks underlying both mountains. The orientation of the fractures, prominent in roadcuts on Mount Pinos, is essentially random. 'Hill?and?saddle' morphology characterizes ridges radiating from the summits, especially on Mount Pinos; outcrops are sparse on the hills and are nonexistent in the saddles, suggesting fractures are concentrated in the saddles. Latest movement on the thrusts underlying the two mountain massifs is probably early Quaternary, during which the mountains were uplifted to considerably higher (although unknown) elevations than at present. A model proposes that during thrusting, ground accelerations in the hanging wall, particularly near thrust tips, were high enough to pervasively fracture the hanging?wall rocks, thereby weakening them and producing essentially an assemblage of loose blocks. Movement over flexures in the fault surface accentuated fracturing. The lowered shear stresses necessary for failure, coupled with deep dissection and ongoing seismic activity, reduced gravitational potential by spreading the mountain massifs, triggering flanking landslides and producing broad, flat?topped mountains. This study developed from mapping in the western Transverse Ranges as part of the U.S. Geological Survey's Southern California Areal Mapping Project (SCAMP).

A reevaluation of the age of the Vincent-Chocolate Mountains thrust system, southern California

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jacobsen, C.E.; Barth, A.P.

1993-04-01

The Vincent-Chocolate Mountains (VCM) thrust superposes Mesozoic arc plutons and associated Precambrian country rock above subduction-related Pelona-Orocopia schist. The thrust is disrupted in many areas by postmetamorphic deformation, but appears to be intact in the San Gabriel Mountains. Two Rb-Sr mineral-isochron ages from Pelona Schist and mylonite in the San Gabriel Mountains led Ehlig (1981) to conclude that the original thrusting event occurred at c. 60 Ma. However, biotite K-Ar ages determined by Miller and Morton (1980) for upper plate in the same area caused Dillon (1986) to reach a different conclusion. The biotite ages range mainly from 74--60 Mamore » and increase structurally upward from the VCM thrust. Dillon (1986) inferred that the age gradient was due to uplift and cooling of the upper plate during underthrusting of Pelona Schist. This would indicate that the VCM thrust was at least 74 Ma in age. An alternative to the interpretation of Dillon (1986) is that the biotite age gradient largely predates the VCM thrust. Upward heat flow, leading to older ages at higher structural levels, could have resulted from either static cooling of Cretaceous plutons or uplift and erosion induced by crustal thickening during possible west-directed intra-arc thrusting at c. 88--78 Ma (May and Walker, 1989). Subsequent underthrusting of Pelona Schist would establish a cold lower boundary to the crust and cause the closure of isotopic systems in the base of the upper plate. A 60 Ma time of thrusting is also suggested by two amphibole [sup 40]Ar/[sup 39]Ar ages from the Pelona Schist of the San Gabriel Mountains. Peak metamorphic temperature in this area was below 480 C and amphibole ages should thus indicate time of crystallization rather than subsequent cooling. Four phengite [sup 40]Ar/[sup 39]Ar ages of 55--61 Ma from Pelona Schist and mylonite indicate rapid cooling from peak metamorphic temperatures, consistent with subduction refrigeration.« less

Extensional faulting in the southern Klamath Mountains, California

USGS Publications Warehouse

Schweickert, R.A.; Irwin, W.P.

1989-01-01

Large northeast striking normal faults in the southern Klamath Mountains may indicate that substantial crustal extension occurred during Tertiary time. Some of these faults form grabens in the Jurassic and older bedrock of the province. The grabens contain continental Oligocene or Miocene deposits (Weaverville Formation), and in two of them the Oligocene or Miocene is underlain by Lower Cretaceous marine formations (Great Valley sequence). At the La Grange gold placer mine the Oligocene or Miocene strata dip northwest into the gently southeast dipping mylonitic footwall surface of the La Grange fault. The large normal displacement required by the relations at the La Grange mine is also suggested by omission of several kilometers of structural thickness of bedrock units across the northeast continuation of the La Grange fault, as well as by significant changes in bedrock across some northeast striking faults elsewhere in the Central Metamorphic and Eastern Klamath belts. The Trinity ultramafic sheet crops out in the Eastern Klamath terrane as part of a broad northeast trending arch that may be structurally analogous to the domed lower plate of metamorphic core complexes found in eastern parts of the Cordillera. The northeast continuation of the La Grange fault bounds the southeastern side of the Trinity arch in the Eastern Klamath terrane and locally cuts out substantial lower parts of adjacent Paleozoic strata of the Redding section. Faults bounding the northwestem side of the Trinity arch generally trend northeast and juxtapose stacked thrust sheets of lower Paleozoic strata of the Yreka terrane against the Trinity ultramafic sheet. Geometric relations suggest that the Tertiary extension of the southern Klamath Mountains was in NW-SE directions and that the Redding section and the southern part of the Central Metamorphic terrane may be a large Tertiary allochthon detached from the Trinity ultramafic sheet. Paleomagnetic data indicate a lack of rotation about a vertical axis during the extension. We propose that the Trinity ultramafic sheet is structurally analogous to a metamorphic core complex; if so, it is the first core complex to be described that involves ultramafic rocks. We infer that Mesozoic terrane accretion produced a large gravitational instability in the crust that spread laterally during Tertiary extension

Structural analysis of the Lombard thrust sheet and adjacent areas in the Helena salient, southwest Montana, USA

NASA Astrophysics Data System (ADS)

Whisner, Stephen C.; Schmidt, Christopher J.; Whisner, Jennifer B.

2014-12-01

The Helena salient is a prominent craton-convex curve in the Cordillera thrust belt of Montana, USA. The Lombard thrust sheet is the primary sheet in the salient. Structural analysis of fold trends, cleavage attitudes, and movement on minor faults is used to better understand both the geometry of the Lombard thrust and the kinematic development of the salient. Early W-E to WNW-ENE shortening directions in the Lombard sheet are indicated by fold trends in the center of the thrust sheet. The same narrow range of shortening directions is inferred from kinematic analysis of movement on minor faults and the orientations of unrotated cleavage planes along the southern lateral ramp boundary of the salient. As the salient developed, the amount and direction of shortening were locally modified as listric detachment faults rotated some tight folds to the NW, and as right-lateral simple shear, caused by lock-up and folding of the Jefferson Canyon fault above the lateral ramp, rotated other folds northeastward. Where the lateral ramp and frontal-oblique ramp intersect, folds were rotated back to the NW. Our interpretation of dominant W-E to WNW-ESE shortening in the Lombard sheet, later altered by local rotations, supports a model of salient formation by primary parallel transport modified by interactions with a lateral ramp.

Tabletop Tectonics: Diverse Mountain Ranges Using Flour and Graphite

NASA Astrophysics Data System (ADS)

Davis, D. M.

2006-12-01

It has been recognized for some time that the frontal deformation zones where plates converge (foreland fold- and-thrust belts on continents and accretionary wedges at subduction zones) involve shortening over a decoupling layer, or decollement. A simple but successful way of explaining many aspects of their behavior is called the critical Coulomb wedge model, which regards these contractional wedges as analogous to the wedge-shaped mass of soil accreted in front of a bulldozer, or the wedge of snow that piles up in front of a snow plow. The shape and deformation history of the accreted wedge of soil or snow will depend upon the frictional strength of the material being plowed up and the surface over which it is being plowed. The same is true of `bulldozer' wedges consisting of many km thick piles of sediment at convergent plate margins. Using flour (or powdered milk), sandpaper, graphite, transparency sheets, and athletic field marker chalk, manipulated with sieves, brushes, pastry bags and blocks and sheets of wood, it is possible to demonstrate a wide variety of processes and tectonic styles observed at convergent plate boundaries. Model fold-and-thrust belts that behave like natural examples with a decollement that is strong (e.g., in rock without high pore fluid pressure) or weak (e.g., in a salt horizon or with elevated pore fluid pressure) can be generated simply by placing wither sandpaper or graphite beneath the flour that is pushed across the tabletop using a block of wood (the strong basement and hiterland rocks behind the fold-thrust belt). Depending upon the strength of the decollement, the cross-sectional taper of the deforming wedge will be thin or broad, the internal deformation mild or intense, and the structures either close to symmetric or strongly forward-vergent, just as at the analogous natural fold-thrust belts. Including a horizontal sheet of wood or Plexiglas in front of the pushing block allows generation of an accretionary wedge, outer-are high, and forearc basin, just as over a subduction zone. Any dark material emplaced (a pastry bag works well) atop the experiment before deformation in the form of football-field `hash marks' every 10 cm allows for easy calculation of strain distribution at any time during or after the experiment. Finally, the entire orogen can be excavated using a plastic photocopier transparency sheet. If the original set-up included occasional thin layers of red and blue field marker chalk within sedimentary column (the rest of which consists of white flour or powdered milk), excavation reveals (quite colorfully) many internal details of the fold-thrust belts that have been generated.

The geology of a part of Acadia and the nature of the Acadian orogeny across Central and Eastern Maine

USGS Publications Warehouse

Tucker, R.D.; Osberg, P.H.; Berry, H.N.

2001-01-01

The zone of Acadian collision between the Medial New England and Composite Avalon terranes is well preserved in Maine. A transect from northwest (Rome) to southeast (Camden) crosses the eastern part of Medial New England comprising the Central Maine basin, Liberty-Orrington thrust sheet, and Fredericton trough, and the western part of Composite Avalon, including the Graham Lake, Clarry Hill, and Clam Cove thrust sheets. U-Pb geochronology of events before, during, and after the Acadian orogeny helps elucidate the nature and distribution of tectonostrati& graphic belts in this zone and the timing of some Acadian events in the Northern Appalachians. The Central Maine basin consists of sedimentary and volcanic rocks of Middle Ordovician (???470 to ???460 Ma) age overlain with probable conformity by latest Ordovician(?) through earliest Devonian marine rift and flysch sedimentary rocks; these are intruded by weakly to undeformed plutonic rocks of Early and Middle Devonian age (???399??378 Ma). The Fredericton trough consists of Early Silurian gray pelite and sandstone to earliest Late Silurian calcareous turbidite, deformed and variably metamorphosed prior to the emplacement of Late Silurian (???422 Ma) and Early to Late Devonian (???418 to ???368 Ma) plutons. The Liberty-Orrington thrust sheet consists of Cambrian(?)-Ordovician (>???474 to ???469 Ma and younger) clastic sedimentary and volcanic rocks intruded by highly deformed Late Silurian (???424 to ???422 Ma) and Devonian (???418 to ???389 Ma) plutons, possibly metamorphosed in Late Silurian time (prior to ???417 Ma), and metamorphosed to amphibolite facies in Early to Middle Devonian time (???400 to ???381 Ma). The Graham Lake thrust sheet contains possible Precambrian rocks, Cambrian sedimentary rocks with a volcanic unit dated at ???503 Ma, and Ordovician rocks with possible Caradocian Old World fossils, metamor& phosed and deformed in Silurian time and intruded by mildly to undeformed Late Silurian (???421 Ma) and Late Devonian (???371 to ???368 Ma) plutons. The Clarry Hill thrust sheet consists of poorly studied, highly metamorphosed Cambrian(?) rocks. The Clam Cove thrust sheet contains highly deformed Precambrian limestone, shale, sandstone, and conglomerate, metamorphosed to epidote amphibolite facies and intruded by a mildly deformed pluton dated at ???421 Ma. Metamorphism, deformation, and voluminous intrusive igneous activity of Silu& rian age are common to both the most southeastern parts of Medial New England and the thrust sheets of Composite Avalon. In contrast to Medial New England, the thrust sheets of Composite Avalon show only modest effects of Devonian deformation and metamorphism. Regional stratigraphic relations, paleontologic findings, and U-Pb geochronology suggest that the Graham Lake, Clarry Hill, and Clam Cove thrust sheets are far-traveled allochthons that were widely separated from Medial New England in the Silurian.

Origin and implications of a thrust-bound gypsiferous unit along the western edge of Jabal Sumeini, northern Oman Mountains

NASA Astrophysics Data System (ADS)

Cooper, David J. W.; Ali, Mohammed Y.; Searle, Michael P.

2018-04-01

The Oman Mountains comprise a series of thrust sheets of Neo-Tethyan oceanic rocks that were emplaced onto the Arabian continental margin during obduction of the Semail Ophiolite during the Late Cretaceous. Three separate groups of anomalous gypsiferous bodies intrude the allochthonous units along faults over a distance of about 150 km in the Hawasina Window, Jabal Qumayrah and Jabal Sumeini. The bodies at Jabal Sumeini form a band about 4 km long and up to 100 m wide along a late-stage thrust that restacks the allochthon over a post-emplacement Maastrichtian-Palaeogene sedimentary succession. The gypsum shows evidence of flow-folding and contains numerous clasts and rafts of a range of quartzose sandstones, but with only a minor component from carbonates from the Neo-Tethyan Sumeini Group in the hanging-wall. Palaeogene limestones from the footwall succession are essentially absent. Strontium isotope ratios are high and intersect with the open ocean-water reference curve for the Late Cambrian-Ordovician and Late Miocene-Pliocene. They are also noticeably higher than the ratios from the two other gypsiferous outcrop areas in the Oman Mountains and from outcrops of Ediacaran-Early Cambrian salt domes in central Oman. However, the regional stratigraphy points towards a source of the gypsum from either an Ediacaran-Early Cambrian Ara Group salt basin or from the Lower Fars Formation (Early-Middle Miocene), and derivation of the sandstone clasts and rafts from thick Lower Palaeozoic clastic sequences. The discrepancy with the ages inferred from the strontium isotope data can be attributed to deposition of the gypsum in restricted conditions not in equilibrium with the prevailing ocean water. Two models are presented, for an Ediacaran-Early Cambrian and an Early-Middle Miocene source. While the latter cannot be wholly discounted, the stratigraphic and structural context point more strongly towards an Ediacaran-Early Cambrian Ara Group source of the gypsum. This was extruded along deep-rooted Late Cretaceous thrust faults that were reactivated during a period of Cenozoic compression, incorporating Lower Palaeozoic sandstone clasts from adjacent strata during extrusion, or during an earlier phase of possible halokinesis. This is consistent with existing models for the emplacement of the other two identified groups of gypsiferous bodies in the Oman Mountains and provides further evidence for the presence of smaller evaporite basins between the major Hormuz and central/ southern Oman salt basins.

Describing earthquakes potential through mountain building processes: an example within Nepal Himalaya

NASA Astrophysics Data System (ADS)

Zhang, Zhen; Zhang, Huai; Shi, Yaolin; Mary, Baptiste; Wang, Liangshu

2016-04-01

How to reconcile earthquake activities, for instance, the distributions of large-great event rupture areas and the partitioning of seismic-aseismic slips on the subduction interface, into geological mountain building period is critical in seismotectonics. In this paper, we try to scope this issue within a typical and special continental collisional mountain wedge within Himalayas across the 2015 Mw7.8 Nepal Himalaya earth- quake area. Based on the Critical Coulomb Wedge (CCW) theory, we show the possible predictions of large-great earthquake rupture locations by retrieving refined evolutionary sequences with clear boundary of coulomb wedge and creeping path inferred from interseismic deformation pattern along the megathrust-Main Himalaya Thrust (MHT). Due to the well-known thrusting architecture with constraints on the distribution of main exhumation zone and of the key evolutionary nodes, reasonable and refined (with 500 yr interval) thrusting sequences are retrieved by applying sequential limit analysis (SLA). We also use an illustration method-'G' gram to localize the relative positions of each fault within the tectonic wedge. Our model results show that at the early stage, during the initial wedge accumulation period, because of the small size of mountain wedge, there's no large earthquakes happens in this period. Whereas, in the following stage, the wedge is growing outward with occasionally out-of-sequence thrusting, four thrusting clusters (thrusting 'families') are clarified on the basis of the spatio-temporal distributions in the mountain wedge. Thrust family 4, located in the hinterland of the mountain wedge, absorbed the least amount of the total convergence, with no large earthquakes occurrence in this stage, contributing to the emplacement of the Greater Himalayan Complex. The slips absorbed by the remnant three thrust families result in large-great earthquakes rupturing in the Sub-Himalaya, Lesser Himalaya, and the front of Higher Himalaya. The portion rupturing in Sub-Himalaya is mainly great Himalaya earthquakes (M>8), with enough energy to rupture the whole MHT, while the thrusting family 2 and 3 will cause mainly large earthquakes. The averaged lifespan of single segment (inclined short lines) is growing from the deformation front to the hinterland, while the occurrence frequency is just in the opposite way. Thrusting slips in family 1-3 will enhance the coulomb wedge development resulting in mountain building. Note that, all the large earthquake behaviors described in this paper is a statistical characteristic, just the tendency distribution on the MHT in one interval. Although our research domain is a section of the Nepal Himalaya, the treatment proposed in this paper has universality in continental collisional orogenic belt which having the same interseismic pattern. We also summary the differences of seismogenic zones in oceanic subduction zone (Cascadia subduction zone) and arc-continental subduction zone (Taiwan area). The different types of interseismic pattern(mechanical patterns) are the controlling factors controlling seismic potential on megathrust and thus impacting the mountain building history.

Large-scale glacitectonic deformation in response to active ice sheet retreat across Dogger Bank (southern central North Sea) during the Last Glacial Maximum

NASA Astrophysics Data System (ADS)

Phillips, Emrys; Cotterill, Carol; Johnson, Kirstin; Crombie, Kirstin; James, Leo; Carr, Simon; Ruiter, Astrid

2018-01-01

High resolution seismic data from the Dogger Bank in the central southern North Sea has revealed that the Dogger Bank Formation records a complex history of sedimentation and penecontemporaneous, large-scale, ice-marginal to proglacial glacitectonic deformation. These processes led to the development of a large thrust-block moraine complex which is buried beneath a thin sequence of Holocene sediments. This buried glacitectonic landsystem comprises a series of elongate, arcuate moraine ridges (200 m up to > 15 km across; over 40-50 km long) separated by low-lying ice marginal to proglacial sedimentary basins and/or meltwater channels, preserving the shape of the margin of this former ice sheet. The moraines are composed of highly deformed (folded and thrust) Dogger Bank Formation with the lower boundary of the deformed sequence (up to 40-50 m thick) being marked by a laterally extensive décollement. The ice-distal parts of the thrust moraine complex are interpreted as a "forward" propagating imbricate thrust stack developed in response to S/SE-directed ice-push. The more complex folding and thrusting within the more ice-proximal parts of the thrust-block moraines record the accretion of thrust slices of highly deformed sediment as the ice repeatedly reoccupied this ice marginal position. Consequently, the internal structure of the Dogger Bank thrust-moraine complexes can be directly related to ice sheet dynamics, recording the former positions of a highly dynamic, oscillating Weichselian ice sheet margin as it retreated northwards at the end of the Last Glacial Maximum.

Earthquakes, geodesy, and the structure of mountain belts

NASA Astrophysics Data System (ADS)

Allen, Mark; Walters, Richard; Nissen, Ed

2015-04-01

Most terrestrial mountain belts are the topographic expression of thrust faulting and folding, which are how the continents deform in compression. Fold-and-thrust belts are therefore a global phenomenon, in existence since at least the onset of plate tectonics. They are typically described as wedge-shaped zones of deformation, overlying a basal low-angle thrust fault (≤10o dip). Here we use earthquake focal mechanisms and geodetic data from active continental fold-and-thrust belts worldwide, to test these concepts. We find that widespread, seismogenic, low-angle thrusting at the base of a wedge occurs only in the Himalayas, New Guinea, Talesh and far-eastern Zagros, which are plausibly underthrust by strong plates. In other ranges there is no focal mechanism evidence for a basal low-angle thrust, and well-constrained hypocentre depths are typically <20 km. Available geodetic data show that active deformation is focussed on a single, low-angle thrust in the Himalayas and New Guinea, but distributed in other ranges for which there are sufficient observations. We suggest that the more common style of deformation approximates to pure shear, with a brittle lid overlying the rest of the plate, where ductile or plastic deformation predominates. Interpretations of both active and ancient mountain belts will need re-evaluation in the light of these results.

'Passive-roof' duplex geometry in the frontal structures of the Kirthar and Sulaiman mountain belts, Pakistan

NASA Astrophysics Data System (ADS)

Banks, C. J.; Warburton, J.

Exploration for hydrocarbons over the past few years has greatly improved our understanding of the geometry of frontal mountain belt structures. In this study we introduce and discuss the concept of the 'Passive-roof duplex', using as the main example the Kirthar and Sulaiman Ranges in the Baluchistan Province of Pakistan. Structures similar to those described here have been recognized previously in other mountain belts, and they appear to exist as a common feature in many more frontal regions of mountain belts. Our example of a Passive-roof duplex which we describe from Pakistan is compared briefly with similar structures reported by others. The Passive-roof duplex is here defined as a duplex whose roof thrust has backthrust sense ( Passive-roof thrust) and whose roof sequence (those rocks lying above the roof thrust) remains relatively 'stationary' during foreland directed piggy-back style propagation of horses within the duplex.

Transverse tectonic structural elements across Himalayan mountain front, eastern Arunachal Himalaya, India: Implication of superposed landform development on analysis of neotectonics

NASA Astrophysics Data System (ADS)

Bhakuni, S. S.; Luirei, Khayingshing; Kothyari, Girish Ch.; Imsong, Watinaro

2017-04-01

Structural and morphotectonic signatures in conjunction with the geomorphic indices are synthesised to trace the role of transverse tectonic features in shaping the landforms developed along the frontal part of the eastern Arunachal sub-Himalaya. Mountain front sinuosity (Smf) index values close to one are indicative of the active nature of the mountain front all along the eastern Arunachal Himalaya, which can be directly attributed to the regional uplift along the Himalayan Frontal Thrust (HFT). However, the mountain front is significantly sinusoidal around junctions between HFT/MBT (Main Boundary Thrust) and active transverse faults. The high values of stream length gradient (SL) and stream steepness (Ks) indices together with field evidence of fault scarps, offset of terraces, and deflection of streams are markers of neotectonic uplift along the thrusts and transverse faults. This reactivation of transverse faults has given rise to extensional basins leading to widening of the river courses, providing favourable sites for deposition of recent sediments. Tectonic interactions of these transverse faults with the Himalayan longitudinal thrusts (MBT/HFT) have segmented the mountain front marked with varying sinuosity. The net result is that a variety of tectonic landforms recognized along the mountain front can be tracked to the complex interactions among the transverse and longitudinal tectonic elements. Some distinctive examples are: in the eastern extremity of NE Himalaya across the Dibang River valley, the NW-SE trending mountain front is attenuated by the active Mishmi Thrust that has thrust the Mishmi crystalline complex directly over the alluvium of the Brahmaputra plains. The junction of the folded HFT and Mishmi Thrust shows a zone of brecciated and pulverized rocks along which transverse axial planar fracture cleavages exhibit neotectonic activities in a transverse fault zone coinciding with the Dibang River course. Similarly, the transverse faults cut the mountain front along the Sesseri, Siluk, Siku, Siang, Mingo, Sileng, Dikari, and Simen rivers. At some such junctions, landforms associated with the active right-lateral strike-slip faults are superposed over the earlier landforms formed by transverse normal faults. In addition to linear transverse features, we see evidence that the fold-thrust belt of the frontal part of the Arunachal Himalaya has also been affected by the neotectonically active NW-SE trending major fold known as the Siang antiform that again is aligned transverse to the mountain front. The folding of the HFT and MBT along this antiform has reshaped the landscape developed between its two western and eastern limbs running N-S and NW-SE, respectively. The transverse faults are parallel to the already reported deep-seated transverse seismogenic strike-slip fault. Therefore, a single take home message is that any true manifestation of the neotectonics and seismic hazard assessment in the Himalayan region must take into account the role of transverse tectonics.

Apatite Fission Track Constraints On The Denudational History Of The Bielsa And Millares Plutons, West-Central Pyrenees, Spain

NASA Astrophysics Data System (ADS)

Schwabe, E.; Fitzgerald, P. G.; Munoz, J. A.; Baldwin, S. L.

2006-12-01

The Pyreneean orogen extends for ~ 440 km from the Bay of Biscay to the Mediterranean Sea, forming a WNW-ESE topographic barrier between France and Spain. The mountain belt, formed by the Late Cretaceous-Early Miocene oblique collision and partial subduction of the Iberian Plate beneath the European Plate. Restored and balanced cross sections show a decrease in crustal shortening from ~165 km in the central Pyrenees to ~ 50 km in the Cantabrian margin, further to the west. The variation in shortening and crustal style is due to the decrease westward in convergence and differences in inherited geometry of pre- existing extensional faults. We propose the variation must also be reflected in the denudation record, with relative timing of the main denudational events younging to the west, as well as the magnitude and rates of denudation decreasing westward. In this study we analyze AFT data collected from vertical profiles on the southern flank of the mountains in the west-central Pyrenees. The results constrain the relative timing of structures between the central and west-central Pyrenees. AFTT data from the Bielsa and Millares massifs, located in the Bielsa and Millares thrust sheets on the southern flank of the axial zone, west-central Pyrenees yield AFT ages from 30 to 20 Ma. The data, including constraints from inverse thermal modeling, indicate denudation at rates ca. 300 m/my underway in the middle Oligocene, slowing in the Miocene. Denudation is likely related to erosion following thrusting during which the granites were transported within the south-vergent Bielsa and Millares thrust sheets. The Late Oligocene-Early Miocene AFT PAZ has since been exhumed to its present elevation. In form, results are similar to those from the central Pyrenees (Fitzgerald et al., 1999) but that Oligocene denudation in the west-central Pyrenees occurred later, was slower, and of reduced magnitude when compared to extremely rapid Oligocene denudation recorded ~50 km east in the central Pyrenees. There, as demonstrated in results from the Maladeta profile, denudation in the Early Oligocene is extremely rapid (km/my) followed by a slowing or cessation of exhumation. The Miocene PAZ preserved in both profiles suggests a similar post- orogenic history most likely related to filling and subsequent re-excavation of the Ebro Basin.

Paleomagnetic evidence for rapid vertical-axis rotations during thrusting in an active collision zone, northeastern Papua New Guinea

NASA Astrophysics Data System (ADS)

Weiler, Peter D.; Coe, Robert S.

1997-06-01

A paleomagnetic study of three thrust sheets of the fold and thrust belt north of the Ramu-Markham Fault Zone (RMFZ) indicates very rapid vertical-axis rotations, with differential declination anomalies related to tectonic transport of thrust units. Data from this investigation indicate depositional ages straddling the Brunhes-Matuyama reversal (780 ka) for the Leron Formation in Erap Valley. Net counterclockwise, vertical-axis rotations as great as 90° since 1 Ma have occurred locally in the Erap Valley area. These rotations appear to be kinematically related to shear across a tear fault within the foreland fold and thrust belt of the colliding Finisterre Arc, which in turn is aligned with and may be structurally controlled by a major fault in the lower plate. These data indicate that vertical-axis rotations occurred during thrusting; consequently, the actual rotation rate is likely several times higher than the calculated minimum rate. Such very rapid rotations during thrust sheet emplacement may be more common in fold and thrust belts than is presently recognized. Anisotropy of magnetic susceptibility data yields foliated fabrics with subordinate, well-grouped lineations that differ markedly in azimuth in the three thrust sheets. The susceptibility lineations are rendered parallel by the same bedding-perpendicular rotations used to restore the paleomagnetic remanence to N-S thus independently confirming the rapid rotations. The restored lineations are perpendicular to the direction of tectonic transport, and the minimum susceptibility axes are streaked perpendicular to the lineation. We interpret these anisotropy of magnetic susceptibility data as primary sedimentary fabrics modified by weak strain accompanying foreland thrusting.

Constraints on the tectonics of the Mule Mountains thrust system, southeast California and southwest Arizona

USGS Publications Warehouse

Tosdal, R.M.

1990-01-01

The Mule Mountains thrust system crops out discontinuously over a 100-km-strike length in this Blythe-Quartzsite region. Along the thrust system, middle and upper crustal metamorphic and plutonic rocks of Proterozoic and Mesozoic age are thrust N-NE (015??-035??) over a lower plate metamorphic terrane. Stratigraphic, petrologic, and Pb isotopic ties for Jurassic granitoids and for Jurassic(?) and Cretaceous sedimentary rocks across the various parts of the thrust system indicate that related crustal blocks are superposed and preclude it from having large displacements. Deformation occurred under low greenschist facies metamorphic conditions in the upper crust. Movement along the thrust system was probably limited to no more than a few tens of kilometers and occurred between 79??2 Ma and 70??4 Ma. Results suggest that the thrust system forms the southern boundary of the narow zone of Cretaceous intracratonic deformation, and it is one of the last tectonic events in the zone prior to regional cooling. -from Author

Crustal structure of Wrangellia and adjacent terranes inferred from geophysical studies along a transect through the northern Talkeetna Mountains

USGS Publications Warehouse

Glen, J.M.G.; Schmidt, J.; Pellerin, L.; McPhee, D.K.; O'Neill, J. M.

2007-01-01

Recent investigations of the Talkeetna Mountains in south-central Alaska were undertaken to study the region's framework geophysics and to reinterpret structures and crustal composition. Potential field (gravity and magnetic) and magnetotelluric (MT) data were collected along northwest-trending profiles as part of the U.S. Geological Survey's Talkeetna Mountains transect project. The Talkeetna Mountains transect area comprises eight 1:63,360 quadrangles (???9500 km2) in the Healy and Talkeetna Mountains 1?? ?? 3?? sheets that span four major lithostratigraphic terranes (Glen et al., this volume) including the Wrangellia and Peninsular terranes and two Mesozoic overlap assemblages inboard (northwest) of Wrangellia. These data were used here to develop 21/2-dimensional models for the three profiles. Modeling results reveal prominent gravity, magnetic, and MT gradients (???3.25 mGal/ km, ???100nT/km, ???300 ohm-m/km) corresponding to the Talkeetna Suture Zone-a first-order crustal discontinuity in the deep crust that juxtaposes rocks with strongly contrasting rock properties. This discontinuity corresponds with the suture between relatively dense magnetic crust of Wrangellia (likely of oceanic composition) and relatively less dense transitional crust underlying Jurassic to Cretaceous flysch basins developed between Wrangellia and North America. Some area of the oceanic crust beneath Wrangellia may also have been underplated by mafic material during early to mid-Tertiary volcanism. The prominent crustal break underlies the Fog Lakes basin approximately where theTalkeetna thrust faultwaspreviouslymappedas a surface feature. Potential fieldand MT models, however, indicate that the Talkeetna Suture Zone crustal break along the transect is a deep (2-8 km), steeply west-dipping structure-not a shallow east-dipping Alpine nappe-like thrust. Indeed, most of the crustal breaks in the area appear to be steep in the geophysical data, which is consistent with regional geologic mapping that indicates that most of the faults are steep normal, reverse, strike-slip, or oblique-slip faults. Mapping further indicates that many of these features, which likely formed during Jurassic and Cretaceous time, such as the Talkeetna Suture Zone have reactivated inTertiary time (O'Neill et al., 2005). Copyright ?? 2007 The Geological Society of America.

The Neoacadian orogenic core of the souther Appalachians: a Geo-traverse through the migmatitic inner Piedmont from the Brushy Mountains to Lincolnton, North Carolina

USGS Publications Warehouse

Merschat, Arthur J.; Hatcher, Robert D.; Byars, Heather E.; Gilliam, William G.; Eppes, Martha Cary; Bartholomew, Mervin J.

2012-01-01

The Inner Piedmont extends from North Carolina to Alabama and comprises the Neoacadian (360–345 Ma) orogenic core of the southern Appalachian orogen. Bordered to west by the Blue Ridge and the exotic Carolina superterrane to the east, the Inner Piedmont is cored by an extensive region of migmatitic, sillimanite-grade rocks. It is a composite of the peri-Laurentian Tugaloo terrane and mixed Laurentian and peri-Gondwanan affinity Cat Square terrane, which are exposed in several gentle-dipping thrust sheets (nappes). The Cat Square terrane consists of Late Silurian to Early Devonian pelitic schist and metagraywacke intruded by several Devonian to Mississippian peraluminous granitoids, and juxtaposed against the Tugaloo terrane by the Brindle Creek fault. This field trip through the North Carolina Inner Piedmont will examine the lithostratigraphies of the Tugaloo and Cat Square terranes, deformation associated with Brindle Creek fault, Devonian-Mississippian granitoids and charnockite of the Cat Square terrane, pervasive amphibolite-grade Devonian-Mississippian (Neoacadian) deformation and metamorphism throughout the Inner Piedmont, and existence of large crystalline thrust sheets in the Inner Piedmont. Consistent with field observations, geochronology and other data, we have hypothesized that the Carolina superterrane collided obliquely with Laurentia near the Pennsylvania embayment during the Devonian, overrode the Cat Square terrane and Laurentian margin, and squeezed the Inner Piedmont out to the west and southwest as an orogenic channel buttressed against the footwall of the Brevard fault zone.

The evolution of the Piedemonte Llanero petroleum system, Cordillera Oriental, Colombia (2) Reservoir petrography & petroleum geochemistry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Piggott, N.; Vear, A.; Warren, E.A.

1996-08-01

Detailed quantification of cements and rock texture, fluid inclusion microthermometry, thermal maturity data, oil-source rock correlations and structural restorations have been integrated to reveal the porosity and hydrocarbon charge evolution of reservoirs in the Piedemonte Llanero thrustbelt of Colombia. Active exploration of deeply buried structures in different thrust sheets of the Piedemonte Llanero has encountered quartz arenites of widely varying average porosities (4-15%). Porosity has been reduced by mechanical compaction and quartz cementation during burial, and by pressure solution during structural deformation. The relative importance and timing of these processes varies between thrust sheets controlling the observed porosity variation. Thermalmore » maturity data indicate that all thrust sheets have been deeply buried and uplifted in several stages of compression. Detailed structural restorations indicate significant differences in the burial histories of individual thrust sheets. Oil-source rock correlations suggest two major hydrocarbon components in the thrustbelt: a Late Cretaceous oil-prone source and a Tertiary oil- and gas-prone source. Initial generation charged early structures leading to partial inhibition of quartz cementation. For most structures quartz cementation predated major hydrocarbon migration. Average quartz cementation temperature is uniform within a structure, but varies between thrust sheets. These variations appear to reflect differences in burial depths during quartz cementation rather than variations in timing. Integration of all data reveals a complex but predictable evolution of porosity and hydrocarbon charge in both space and time which is being applied to current exploration in the Piedemonte Llanero and is relevant to thrustbelt exploration elsewhere.« less

The age of the Keystone thrust: laser-fusion 40Ar/39Ar dating of foreland basin deposits, southern Spring Mountains, Nevada

USGS Publications Warehouse

Fleck, R.J.; Carr, M.D.

1990-01-01

Nonmarine sedimentary and volcaniclastic foreland-basin deposits in the Spring Mountains are cut by the Contact and Keystone thrusts. These synorogenic deposits, informally designated the Lavinia Wash sequence by Carr (1980), previously were assigned a Late Jurassic to Early Cretaceous(?) age. New 40Ar.39Ar laser-fusion and incremental-heating studies of a tuff bed in the Lavinia Wash sequence support a best estimate age of 99.0 ?? 0.4 Ma, indicating that the Lavinia Wash sequence is actually late Early Cretaceous in age and establishing a maximum age for final emplacement of the Contact and Keystone thrust plates consistent with the remainder of the Mesozoic foreland thrust belt. -from Authors

Duplex development and abandonment during evolution of the Lewis thrust system, southern Glacier National Park, Montana

NASA Astrophysics Data System (ADS)

Yin, An; Kelty, Thomas K.; Davis, Gregory A.

1989-09-01

Geologic mapping in southern Glacier National Park, Montana, reveals the presence of two duplexes sharing the same floor thrust fault, the Lewis thrust. The westernmost duplex (Brave Dog Mountain) includes the low-angle Brave Dog roof fault and Elk Mountain imbricate system, and the easternmost (Rising Wolf Mountain) duplex includes the low-angle Rockwell roof fault and Mt. Henry imbricate system. The geometry of these duplexes suggests that they differ from previously described geometric-kinematic models for duplex development. Their low-angle roof faults were preexisting structures that were locally utilized as roof faults during the formation of the imbricate systems. Crosscutting of the Brave Dog fault by the Mt. Henry imbricate system indicates that the two duplexes formed at different times. The younger Rockwell-Mt. Henry duplex developed 20 km east of the older Brave Dog-Elk Mountain duplex; the roof fault of the former is at a higher structural level. Field relations confirm that the low-angle Rockwell fault existed across the southern Glacier Park area prior to localized formation of the Mt. Henry imbricate thrusts beneath it. These thrusts kinematically link the Rockwell and Lewis faults and may be analogous to P shears that form between two synchronously active faults bounding a simple shear system. The abandonment of one duplex and its replacement by another with a new and higher roof fault may have been caused by (1) warping of the older and lower Brave Dog roof fault during the formation of the imbricate system (Elk Mountain) beneath it, (2) an upward shifting of the highest level of a simple shear system in the Lewis plate to a new decollement level in subhorizontal belt strata (= the Rockwell fault) that lay above inclined strata within the first duplex, and (3) a reinitiation of P-shear development (= Mt. Henry imbricate faults) between the Lewis thrust and the subparallel, synkinematic Rockwell fault.

Lateral ramps in the folded Appalachians and in overthrust belts worldwide; a fundamental element of thrust-belt architecture

USGS Publications Warehouse

Pohn, Howard A.

2000-01-01

Lateral ramps are zones where decollements change stratigraphic level along strike; they differ from frontal ramps, which are zones where decollements change stratigraphic level perpendicular to strike. In the Appalachian Mountains, the surface criteria for recognizing the subsurface presence of lateral ramps include (1) an abrupt change in wavelength or a termination of folds along strike, (2) a conspicuous change in the frequency of mapped faults or disturbed zones (extremely disrupted duplexes) at the surface, (3) long, straight river trends emerging onto the coastal plain or into the Appalachian Plateaus province, (4) major geomorphic discontinuities in the trend of the Blue Ridge province, (5) interruption of Mesozoic basins by cross-strike border faults, and (6) zones of modern and probable ancient seismic activity. Additional features related to lateral ramps include tectonic windows, cross-strike igneous intrusions, areas of giant landslides, and abrupt changes in Paleozoic sedimentation along strike. Proprietary strike-line seismic-reflection profiles cross three of the lateral ramps that were identified by using the surface criteria. The profiles confirm their presence and show their detailed nature in the subsurface. Like frontal ramps, lateral ramps are one of two possible consequences of fold-and-thrust-belt tectonics and are common elements in the Appalachian fold-and-thrust belt. A survey of other thrust belts in the United States and elsewhere strongly suggests that lateral ramps at depth can be identified by their surface effects. Lateral ramps probably are the result of thrust sheet motion caused by continued activation of ancient cratonic fracture systems. Such fractures localized the transform faults along which the continental segments adjusted during episodes of sea-floor spreading.

Limited fluid in carbonate-shale hosted thrust faults of the Rocky Mountain Fold-and-Thrust Belt (Sun River Canyon, Montana)

NASA Astrophysics Data System (ADS)

OBrien, V. J.; Kirschner, D. L.

2001-12-01

It is widely accepted that fluids play a fundamental role in the movement of thrust faults in foreland fold-and-thrust belts. We have begun a combined structure-geochemistry study of faults in the Rocky Mountain fold-and-thrust belt in order to provide more insight into the occurrence and role(s) of fluid in the deformation of thrust faults. We focus on faults exposed in the Sun River Canyon of Montana, an area that contains some of the best exposures of the Rocky Mountain fold-and-thrust belt in the U.S. Samples were collected from two well exposed thrusts in the Canyon -- the Diversion and French thrusts. Both faults have thrust Mississippian dolostones over Cretaceous shales. Displacement exceeds several kilometers. Numerous small-displacement, subsidiary faults characterize the deformation in the hanging wall carbonates. The footwall shales accommodated more penetrative deformation, resulting in well developed foliation and small-scale folds. Stable isotope data have been obtained from host rock samples and veins from these faults. The data delimit an arcuate trend in oxygen-carbon isotope space. Approximately 50 host rock carbonate samples from the hanging walls have carbon and oxygen isotope values ranging from +3 to 0 and 28 to 19 per mil, respectively. There is no apparent correlation between isotopic values and distance from thrust fault at either locality. Fifteen samples of fibrous slickensides on small-displacement faults in the hanging walls have similar carbon and lower oxygen isotope values (down to 16 per mil). And 15 veins that either post-date thrusting or are of indeterminate origin have carbon and oxygen isotope values down to -3 and12 per mil, respectively. The isotopic data collected during the initial stages of this project are similar to some results obtained several hundred kilometers north in the Front Ranges of the Canadian Rockies (Kirschner and Kennedy, JGR 2000) and in carbonate fold-thrust belts of the Swiss Helvetic Alps and Italian Apennines. These data are consistent with limited infiltration of fluid through fractures and minor faults into hanging walls of large-displacement thrust faults.

Understanding continental megathrust earthquake potential through geological mountain building processes: an example in Nepal Himalaya

NASA Astrophysics Data System (ADS)

Zhang, Huai; Zhang, Zhen; Wang, Liangshu; Leroy, Yves; shi, Yaolin

2017-04-01

How to reconcile continent megathrust earthquake characteristics, for instances, mapping the large-great earthquake sequences into geological mountain building process, as well as partitioning the seismic-aseismic slips, is fundamental and unclear. Here, we scope these issues by focusing a typical continental collisional belt, the great Nepal Himalaya. We first prove that refined Nepal Himalaya thrusting sequences, with accurately defining of large earthquake cycle scale, provide new geodynamical hints on long-term earthquake potential in association with, either seismic-aseismic slip partition up to the interpretation of the binary interseismic coupling pattern on the Main Himalayan Thrust (MHT), or the large-great earthquake classification via seismic cycle patterns on MHT. Subsequently, sequential limit analysis is adopted to retrieve the detailed thrusting sequences of Nepal Himalaya mountain wedge. Our model results exhibit apparent thrusting concentration phenomenon with four thrusting clusters, entitled as thrusting 'families', to facilitate the development of sub-structural regions respectively. Within the hinterland thrusting family, the total aseismic shortening and the corresponding spatio-temporal release pattern are revealed by mapping projection. Whereas, in the other three families, mapping projection delivers long-term large (M<8)-great (M>8) earthquake recurrence information, including total lifespans, frequencies and large-great earthquake alternation information by identifying rupture distances along the MHT. In addition, this partition has universality in continental-continental collisional orogenic belt with identified interseismic coupling pattern, while not applicable in continental-oceanic megathrust context.

Reinterpretation of Mesozoic and Cenozoic tectonic events, Mountain Pass area, northeastern San Bernardino County, California

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nance, M.A.

1993-04-01

Detailed mapping, stratigraphic structural analysis in the Mountain Pass area has resulted in a reinterpretation of Mesozoic and Cenozoic tectonic events in the area. Mesozoic events are characterized by north vergent folds and thrust faults followed by east vergent thrusting. Folding created two synclines and an anticline which were than cut at different stratigraphic levels by subsequent thrust faults. Thrusting created composite tectono-stratigraphic sections containing autochthonous, para-autothonous, and allochthonous sections. Normal faults cutting these composite sections including North, Kokoweef, White Line, and Piute fault must be post-thrusting, not pre-thrusting as in previous interpretations. Detailed study of these faults results inmore » differentiation of at least three orders of faults and suggest they represent Cenozoic extension correlated with regional extensional events between 11 and 19 my. Mesozoic stratigraphy reflects regional orogenic uplift, magmatic activity, and thrusting. Inclusion of Kaibab clasts in the Chinle, Kaibab and Chinle clasts in the Aztec, and Chinle, Aztec, and previously deposited Delfonte Volcanics clasts in the younger members of the Delfonte Volcanics suggest regional uplift prior to the thrusting of Cambrian Bonanza King over Delfonte Volcanics by the Mescal Thrust fault. The absence of clasts younger than Kaibab argues against pre-thrusting activity for the Kokoweef fault.« less

Basement thrust sheets in the Clearwater orogenic zone, central Idaho and western Montana

NASA Astrophysics Data System (ADS)

Skipp, Betty

1987-03-01

The Clearwater orogenic zone in central Idaho and western Montana contains at least two major northeast-directed Cordilleran thrust plates of Early Proterozoic metasedimentary and metaigneous rocks that overrode previously folded Middle Proterozoic rocks of the Belt basin in Cretaceous time. The northeastward migration of the resultant thickened wedge of crustal material combined with Cretaceous subduction along the western continental margin produced a younger northern Bitterroot lobe of the Idaho batholith relative to an older southern Atlanta lobe. Eocene extensional unroofing and erosion of the Bitterroot lobe has exposed the roots of the thick Cordilleran thrust sheets.

Computational Validation of a Two-Dimensional Semi-Empirical Model for Inductive Coupling in a Conical Pulsed Inductive Plasma Thruster

NASA Technical Reports Server (NTRS)

Hallock, Ashley K.; Polzin, Kurt A.

2011-01-01

A two-dimensional semi-empirical model of pulsed inductive thrust efficiency is developed to predict the effect of such a geometry on thrust efficiency. The model includes electromagnetic and gas-dynamic forces but excludes energy conversion from radial motion to axial motion, with the intention of characterizing thrust efficiency loss mechanisms that result from a conical versus a at inductive coil geometry. The range of conical pulsed inductive thruster geometries to which this model can be applied is explored with the use of finite element analysis. A semi-empirical relation for inductance as a function of current sheet radial and axial position is the limiting feature of the model, restricting the applicability as a function of half cone angle to a range from ten degrees to about 60 degrees. The model is nondimensionalized, yielding a set of dimensionless performance scaling parameters. Results of the model indicate that radial current sheet motion changes the axial dynamic impedance parameter at which thrust efficiency is maximized. This shift indicates that when radial current sheet motion is permitted in the model longer characteristic circuit timescales are more efficient, which can be attributed to a lower current sheet axial velocity as the plasma more rapidly decouples from the coil through radial motion. Thrust efficiency is shown to increase monotonically for decreasing values of the radial dynamic impedance parameter. This trend indicates that to maximize the radial decoupling timescale should be long compared to the characteristic circuit timescale.

Coseismic and blind fault of the 2015 Pishan Mw 6.5 earthquake: Implications for the sedimentary-tectonic framework of the western Kunlun Mountains, northern Tibetan Plateau

NASA Astrophysics Data System (ADS)

Lu, Renqi; Xu, Xiwei; He, Dengfa; Liu, Bo; Tan, Xibin; Wang, Xiaoshan

2016-04-01

On 3 July 2015, the Mw 6.5 Pishan earthquake occurred in the western Kunlun Mountains front, at the northern margin of the Tibetan Plateau. To reveal the sedimentary-tectonic framework of the seismically active structure, three high-resolution seismic reflection profiles and well drilling data were collected for seismic interpretation. The western Kunlun Mountains and Tarim Basin have two gypseous detachments and one basement detachment that control the tectonic framework and structural deformation. The upper gypseous detachment (D1) is in the lower Paleocene, and the middle gypseous detachment (D2) is in the Middle to Lower Cambrian. A Neogene shallow thrust system is developing above D1 and includes the Zepu fault (F2) and Mazar Tagh fault (F3). A deep thrust system is developing between D1 and D2 and forms a large-scale structural wedge beneath the western Kunlun Mountains front. The Pishan Mw 6.5 earthquake was triggered on a frontal blind fault of this deep thrust system. The lower detachment is in the Proterozoic basement (D3), which extends into the Tarim Basin and develops another deep thrust (F4) beneath the F3 belt. D1, D2, D3, and the Tiekelike fault (F1) merge together at depth. Crustal shortening of the western Kunlun Mountains front continues for approximately 54 km. Two tectonic evolutionary stages have occurred since the Miocene according to sedimentary unconformity, axial analysis, and fault interpretation. The results of this study indicate a regime of episodic growth of the western Kunlun Mountains and Tarim Basin during the Cenozoic.

Thrust Breakdown Characteristics of Conventional Propellers

DTIC Science & Technology

2007-09-01

extends beyond the trailing edge of the blade . These sheets violently collapse as the blade moves out of the wake deficit produced by the hull. This...thrust breakdown, vibration, noise , erosion and blade damage. Propellers operating with enough cavitation to cause thrust breakdown can experience...7 Figure 5. Sensitivity of thrust reduction to harmonic content in wake (Prop 5491) .................. 8 Figure 6. Comparison of

Growth of the Zagros Fold-Thrust Belt and Foreland Basin, Northern Iraq, Kurdistan

NASA Astrophysics Data System (ADS)

Koshnaw, Renas; Horton, Brian; Stockli, Daniel; Barber, Douglas; Ghalib, Hafidh; Dara, Rebwar

2016-04-01

The Zagros orogenic belt in the Middle Eastern segment of the Alpine-Himalayan system is among the youngest seismically active continental collision zones on Earth. However, due to diachronous and incremental collision, the precise ages and kinematics of shortening and deposition remain poorly understood. The Kurdistan region of the Zagros fold-thrust belt and foreland basin contains well-preserved Neogene wedge-top and foredeep deposits that include clastic nonmarine fill of the Upper Fars, Lower Bakhtiari, and Upper Bakhtiari Formations. These deposits record significant information about orogenic growth, fold-thrust dynamics, and advance of the deformation front. Thermochronologic and geochronologic data from thrust sheets and stratigraphic archives combined with local earthquake data provide a unique opportunity to address the linkages between surface and subsurface geologic relationships. This research seeks to constrain the timing and geometry of exhumation and deformation by addressing two key questions: (1) Did the northwestern Zagros fold-thrust belt evolve from initial thin-skinned shortening to later thick-skinned deformation or vice-versa? (2) Did the fold-thrust belt advance steadily under critical/supercritical wedge conditions involving in-sequence thrusting or propagate intermittently under subcritical conditions with out-of-sequence deformation? From north to south, apatite (U-Th)/He ages from the Main Zagros Thrust, the Mountain Front Flexure (MFF), and additional frontal thrusts suggest rapid exhumation by ~10 Ma, ~5 Ma, and ~8 Ma respectively. Field observations and seismic sections indicate progressive tilting and development of growth strata within the Lower Bakhtiari Formation adjacent to the frontal thrusts and within the Upper Bakhtiari Formation near the MFF. In the Kurdistan region of Iraq, a regional balanced cross section constrained by new thermochronometric results, proprietary seismic reflection profiles, and earthquake hypocenters suggest prolonged thin-skinned shortening in sequence from north to south followed by a thick-skinned out-of-sequence MFF deformation and intermittent hinterland uplift postdating initial collision. Magnetostratigraphic analyses of Dinarta wedge-top deposits and Kifri foredeep deposits constrain accumulation of the Upper Fars-Lower Bakhtiari synorogenic succession to 12.5-5 Ma. These findings suggest that temporal and spatial shifts in upper-crustal modes of deformation in the Kurdistan segment of the Zagros orogenic belt strongly influenced patterns of topographic growth, landscape development, and resulting foreland basin stratigraphy.

Basement thrust sheets in the Clearwater orogenic zone, central Idaho and western Montana ( USA).

USGS Publications Warehouse

Skipp, B.

1987-01-01

The Clearwater orogenic zone in central Idaho and W Montana contains at least 2 major NE-directed Cordilleran thrust plates of Early Proterozoic metasedimentary and metaigneous rocks that overrode previously folded Middle Proterozoic rocks of the Belt basin in Cretaceous time. The northeastward migration of the resultant thickened wedge of crustal material combined with Cretaceous subduction along the W continental margin produced a younger N Bitterroot lobe of the Idaho batholith relative to an older S Atlanta lobe. Eocene extensional unroofing and erosion of the Bitterroot lobe has exposed the roots of the thick Cordilleran thrust sheets.-Author

Along-strike continuity of structure, stratigraphy, and kinematic history in the Himalayan thrust belt: The view from Northeastern India

NASA Astrophysics Data System (ADS)

DeCelles, P. G.; Carrapa, B.; Gehrels, G. E.; Chakraborty, T.; Ghosh, P.

2016-12-01

The Himalaya consists of thrust sheets tectonically shingled together since 58 Ma as India collided with and slid beneath Asia. Major Himalayan structures, including the South Tibetan Detachment (STD), Main Central Thrust (MCT), Lesser Himalayan Duplex (LHD), Main Boundary Thrust (MBT), and Main Frontal Thrust (MFT), persist along strike from northwestern India to Arunachal Pradesh near the eastern end of the orogenic belt. Previous work suggests significant basement involvement and a kinematic history unique to the Arunachal Himalaya. We present new geologic and geochronologic data to support a regional structural cross section and kinematic restoration of the Arunachal Himalaya. Large Paleoproterozoic orthogneiss bodies (Bomdila Gneiss) previously interpreted as Indian basement have ages of 1774-1810 Ma, approximately 50 Ma younger than Lesser Himalayan strata into which their granitic protoliths intruded. Bomdila Gneiss is therefore part of the Lesser Himalayan cover sequence, and no evidence exists for basement involvement in the Arunachal Himalaya. Minimum shortening in rocks structurally beneath the STD is 421 km. The MCT was active during the early Miocene; STD extension overlapped MCT shortening and continued until approximately 15-12 Ma; and growth of the LHD began 11 Ma, followed by slip along the MBT (post-7.5 Ma) and MFT (post-1 Ma) systems. Earlier thrusting events involved long-distance transport of strong, low-taper thrust sheets, whereas events after 12-10 Ma stacked smaller, weaker thrust sheets into a steeply tapered orogenic wedge dominated by duplexing. A coeval kinematic transition is observed in other Himalayan regions, suggesting that orogenic wedge behavior was controlled by rock strength and erodibility.

The Gamburtsev mountains and the origin and early evolution of the Antarctic Ice Sheet.

PubMed

Bo, Sun; Siegert, Martin J; Mudd, Simon M; Sugden, David; Fujita, Shuji; Xiangbin, Cui; Yunyun, Jiang; Xueyuan, Tang; Yuansheng, Li

2009-06-04

Ice-sheet development in Antarctica was a result of significant and rapid global climate change about 34 million years ago. Ice-sheet and climate modelling suggest reductions in atmospheric carbon dioxide (less than three times the pre-industrial level of 280 parts per million by volume) that, in conjunction with the development of the Antarctic Circumpolar Current, led to cooling and glaciation paced by changes in Earth's orbit. Based on the present subglacial topography, numerical models point to ice-sheet genesis on mountain massifs of Antarctica, including the Gamburtsev mountains at Dome A, the centre of the present ice sheet. Our lack of knowledge of the present-day topography of the Gamburtsev mountains means, however, that the nature of early glaciation and subsequent development of a continental-sized ice sheet are uncertain. Here we present radar information about the base of the ice at Dome A, revealing classic Alpine topography with pre-existing river valleys overdeepened by valley glaciers formed when the mean summer surface temperature was around 3 degrees C. This landscape is likely to have developed during the initial phases of Antarctic glaciation. According to Antarctic climate history (estimated from offshore sediment records) the Gamburtsev mountains are probably older than 34 million years and were the main centre for ice-sheet growth. Moreover, the landscape has most probably been preserved beneath the present ice sheet for around 14 million years.

The Junction of Hellenic and Cyprus Arcs: a Detailed Study of the Morphology and Neogene Tectonic Evolution of the Anaximander Mountains

NASA Astrophysics Data System (ADS)

Cranshaw, J.; Aksu, A.; Hall, J.; Cifci, G.; Dondurur, D.; Yaltirak, C.

2009-05-01

The Anaximander Mountains are enigmatic highs located at the complex corner that links the Cyprus and Hellenic Arcs in the eastern Mediterranean. They are made up of several different highs: Anaximander (sensu stricto), Anaxagoras and Anaximenes. Previous work had shown that rock samples from the Anaximander Mountain have affinity with rocks exposed on land nearby in southern Turkey. This had been explained by rifting of the Mountain away from Turkey. In contrast to that, our interpretation of around 1750 km of high-resolution multi-channel seismic reflection data acquired in 2001 showed that Anaximander Mountain is part of a broadly south-verging Miocene thrust system associated with relative southward motion of the Tauride Mountains in southern Turkey. Post-Miocene motion also involves thrusting but is accompanied by transpression and rotation. The 3-dimensional nature of the geology makes mapping of the linkage of structures difficult, so we collected an additional 500 km of multi-channel seismic reflection data acquired in 2007, extending our 2001 survey further southwards into the Mediterranean Ridge. These new profiles are shot in a grid oblique to that obtained in 2001, such that the new profile intersections provide a basis for better correlation of the earlier data. We are testing our earlier interpretation through processing and interpretation of these new profiles. Here, we present examples of the new profiles and give first indications of how our earlier interpretation is broadly corroborated by the new data, but with minor adjustments. Anaximenes Mountain is imaged to the south of our previously- mapped area and is characterized as a large south-verging thrust lifting pre-Messinian strata by up to 2 km in a 12-km wide pop-up structure. Internally, Anaximenes is dissected by several splays from the bounding thrusts.

The junction of Hellenic and Cyprus arcs: a detailed study of the morphology and Neogene tectonic evolution of the Anaximander Mountains

NASA Astrophysics Data System (ADS)

Cranshaw, J.; Aksu, A.; Hall, J.; Çifçi, G.; Dondurur, D.; Yaltırak, C.

2009-04-01

The Anaximander Mountains are enigmatic highs located at the complex corner that links the Cyprus and Hellenic Arcs in the eastern Mediterranean. They are made up of several different highs: Anaximander (sensu stricto), Anaxagoras and Anaximenes. Previous work had shown that rock samples from the Anaximander Mountain have affinity with rocks exposed on land nearby in southern Turkey. This had been explained by rifting of the Mountain away from Turkey. In contrast to that, our interpretation of around 1750 km of high-resolution multi-channel seismic reflection data acquired in 2001 showed that Anaximander Mountain is part of a broadly south-verging Miocene thrust system associated with relative southward motion of the Tauride Mountains in southern Turkey. Post-Miocene motion also involves thrusting but is accompanied by transpression and rotation. The 3-dimensional nature of the geology makes mapping of the linkage of structures difficult, so we collected an additional 500 km of multi-channel seismic reflection data acquired in 2007, extending our 2001 survey further southwards into the Mediterranean Ridge. These new profiles are shot in a grid oblique to that obtained in 2001, such that the new profile intersections provide a basis for better correlation of the earlier data. We are testing our earlier interpretation through processing and interpretation of these new profiles. Here, we present examples of the new profiles and give first indications of how our earlier interpretation is broadly corroborated by the new data, but with minor adjustments. Anaximenes Mountain is imaged to the south of our previously-mapped area and is characterized as a large south-verging thrust lifting pre-Messinian strata by up to 2 km in a 12-km wide pop-up structure. Internally, Anaximenes is dissected by several splays from the bounding thrusts.

Integrating GIS-based geologic mapping, LiDAR-based lineament analysis and site specific rock slope data to delineate a zone of existing and potential rock slope instability located along the grandfather mountain window-Linville Falls shear zone contact, Southern Appalachian Mountains, Watauga County, North Carolina

USGS Publications Warehouse

Gillon, K.A.; Wooten, R.M.; Latham, R.L.; Witt, A.W.; Douglas, T.J.; Bauer, J.B.; Fuemmeler, S.J.

2009-01-01

Landslide hazard maps of Watauga County identify >2200 landslides, model debris flow susceptibility, and evaluate a 14km x 0.5km zone of existing and potential rock slope instability (ZEPRSI) near the Town of Boone. The ZEPRSI encompasses west-northwest trending (WNWT) topographic ridges where 14 active/past-active rock/weathered rock slides occur mainly in rocks of the Grandfather Mountain Window (GMW). The north side of this ridgeline is the GMW / Linville Falls Fault (LFF) contact. Sheared rocks of the Linville Falls Shear Zone (LFSZ) occur along the ridge and locally in the valley north of the contact. The valley is underlain principally by layered granitic gneiss comprising the Linville Falls/Beech Mountain/Stone Mountain Thrust Sheet. The integration of ArcGIS??? - format digital geologic and lineament mapping on a 6m LiDAR (Light Detecting and Ranging) digital elevation model (DEM) base, and kinematic analyses of site specific rock slope data (e.g., presence and degree of ductile and brittle deformation fabrics, rock type, rock weathering state) indicate: WNWT lineaments are expressions of a regionally extensive zone of fractures and faults; and ZEPRSI rock slope failures concentrate along excavated, north-facing LFF/LFSZ slopes where brittle fabrics overprint older metamorphic foliations, and other fractures create side and back release surfaces. Copyright 2009 ARMA, American Rock Mechanics Association.

New Insight into the Role of Tectonics versus Gravitational Deformation in Development of Surface Ruptures along the Ragged Mountain Fault, Katalla, Alaska USA: Applications of High-Resolution Three-Dimensional Terrain Models

NASA Astrophysics Data System (ADS)

Heinlein, S. N.; Pavlis, T. L.; Bruhn, R. L.; McCalpin, J. P.

2017-12-01

This study evaluates a surface structure using 3D visualization of LiDAR and aerial photography then analyzes these datasets using structure mapping techniques. Results provide new insight into the role of tectonics versus gravitational deformation. The study area is located in southern Alaska in the western edge of the St. Elias Orogen where the Yakutat microplate is colliding into Alaska. Computer applications were used to produce 3D terrain models to create a kinematic assessment of the Ragged Mountain fault which trends along the length of the east flank of Ragged Mountain. The area contains geomorphic and structural features which are utilize to determine the type of displacement on the fault. Previous studies described the Ragged Mountain fault as a very shallow (8°), west-dipping thrust fault that reactivated in the Late Holocene by westward-directed gravity sliding and inferred at least 180 m of normal slip, in a direction opposite to the (relative) eastward thrust transport of the structure inferred from stratigraphic juxtaposition. More recently this gravity sliding hypothesis has been questioned and this study evaluates one of these alternative hypotheses; that uphill facing normal fault-scarps along the Ragged Mountain fault trace represent extension above a buried ramp in a thrust and is evaluated with a fault-parallel flow model of hanging-wall folding and extension. Profiles across the scarp trace were used to illustrate the curvature of the topographic surfaces adjacent to the scarps system and evaluate their origin. This simple kinematic model tests the hypothesis that extensional fault scarps at the surface are produced by flexure above a deeper ramp in a largely blind thrust system. The data in the context of this model implies that the extensional scarp structures previously examined represent a combination of erosionally modified features overprinted by flexural extension above a thrust system. Analyses of scarp heights along the structure are combined with the model to suggest a decrease in Holocene slip from south to north along the Ragged Mountain fault from 11.3 m to 0.2 m, respectively.

Formation of fold-and-thrust belts on Venus by thick-skinned deformation

NASA Astrophysics Data System (ADS)

Zuber, M. T.; Parmentier, E. M.

1995-10-01

ON Venus, fold-and-thrust belts—which accommodate large-scale horizontal crustal convergence—are often located at the margins of kilometre-high plateaux1-5. Such mountain belts, typically hundreds of kilometres long and tens to hundreds of kilometres wide, surround the Lakshmi Planum plateau in the Ishtar Terra highland (Fig. 1). In explaining the origin of fold-and-thrust belts, it is important to understand the relative importance of thick-skinned deformation of the whole lithosphere and thin-skinned, large-scale overthrusting of near-surface layers. Previous quantitative analyses of mountain belts on Venus have been restricted to thin-skinned models6-8, but this style of deformation does not account for the pronounced topographic highs at the plateau edge. We propose that the long-wavelength topography of these venusian fold-and-thrust belts is more readily explained by horizontal shortening of a laterally heterogeneous lithosphere. In this thick-skinned model, deformation within the mechanically strong outer layer of Venus controls mountain building. Our results suggest that lateral variations in either the thermal or mechanical structure of the interior provide a mechanism for focusing deformation due to convergent, global-scale forces on Venus.

Constraints on the tectonics of the Mule Mountains Thrust System, southeast California and southwest Arizona

NASA Astrophysics Data System (ADS)

Tosdal, Richard M.

1990-11-01

The Mule Mountains thrust system crops out discontinuously over a 100-km-strike length in the Blythe-Quartzsite region of southeast California and southwest Arizona. Along the thrust system, middle and upper crustal metamorphic and plutonic rocks of Proterozoic and Mesozoic age are thrust north-northeastward (015° to 035°) over a lower plate metamorphic terrane that formed part of the Proterozoic North American craton, its Paleozoic sedimentary rock cover, overlying Mesozoic volcanic and sedimentary rocks, and the intruding Jurassic and Cretaceous granitic rocks. Stratigraphic, petrologic, and Pb isotopic ties for Jurassic granitoids and for Jurassic(?) and Cretaceous sedimentary rocks across the various parts of the thrust system indicate that related crustal blocks are superposed and preclude it from having large displacements. The thick-skinned thrust system is structurally symmetrical along its length with a central domain of synmetamorphic thrust faults that are flanked by western and eastern domains where lower plate synclines underlie the thrusts. Deformation occurred under low greenschist facies metamorphic conditions in the upper crust. Movement along the thrust system was probably limited to no more than a few tens of kilometers and occurred between 79±2 Ma and 70±4 Ma. The superposition of related rocks and the geometry of the thrust system preclude it from being a major tectonic boundary of post-Middle Jurassic age, as has been previously proposed. Rather, the thrust system forms the southern boundary of the narrow zone of Cretaceous intracratonic deformation, and it is one of the last tectonic events in the zone prior to regional cooling.

Structural framework of a major intracontinental orogenic termination zone: The easternmost Tien Shan, China

USGS Publications Warehouse

Cunningham, D.; Owen, L.A.; Snee, L.W.; Li, Ji

2003-01-01

The Barkol Tagh and Karlik Tagh ranges of the easternmost Tien Shan are a natural laboratory for studying the fault architecture of an active termination zone of a major intracontinental mountain range. Barkol and Karlik Tagh and lesser ranges to the north are bounded by active thrust faults that locally deform Quaternary sediments. Major thrusts in Karlik Tagh connect along strike to the east with the left-lateral Gobi-Tien Shan Fault System in SW Mongolia. From a Mongolian perspective. Karlik Tagh represents a large restraining bend for this regional strike-slip fault system, and the entire system of thrusts and strike-slip faults in the Karlik Tagh region defines a horsetail splay fault geometry. Regionally, there appears to be a kinematic transition from thrust-dominated deformation in the central Tien Shan to left-lateral transpressional deformation in the easternmost Tien Shan. This transition correlates with a general eastward decrease in mountain belt width and average elevation and a change in the angular relationship between the NNE-directed maximum horizontal stress in the region and the pre-existing basement structural grain, which is northwesterly in the central Tien Shan (orthogonal to SHmax) but more east-west in the eastern Tien Shan (acute angular relationship with SHmax . Ar-Ar ages indicate that major range-bounding thrusts in Barkol and Karlik Tagh are latest Permian-Triassic ductile thrust zones that underwent brittle reactivation in the Late Cenozoic. It is estimated that the modern mountain ranges of the extreme easternmost Tien Shan could have been constructed by only 10-15 km of Late Cenozoic horizontal shortening.

Intrinsic And Extrinsic Controls On Unsteady Deformation Rates, Northern Apennine Mountains, Italy

NASA Astrophysics Data System (ADS)

Anastasio, D. J.; Gunderson, K. L.; Pazzaglia, F. J.; Kodama, K. P.

2017-12-01

The slip rates of faults in the Northern Apennine Mountains were unsteady at 104-105 year timescales during the Neogene and Quaternary. Fault slip rates were recovered from growth strata and uplifted fluvial terraces associated with the Salsomaggiore, Quatto Castella, and Castevetro fault-related folds, sampled along the Stirone, Enza, and Panaro Rivers, respectively. The forelimb stratigraphy of each anticline was dated using rock magnetic-based cyclostratigraphy, which varies with Milankovitch periodicity, multispecies biostratigraphy, magnetostratigraphy, OSL luminescence dating, TCN burial dating, and radiocarbon dating of uplifted and folded fluvial terraces. Fault slip magnitudes were constrained with trishear forward models. We observed decoupled deformation and sediment accumulation rates at each structure. From 3.5Ma deformation of a thick and thin-skinned thrusts was temporally variable and controlled by intrinsic rock processes, whereas, the more regional Pede-Apenninic thrust fault, a thick-skinned thrust underlying the mountain front, was likely activated because of extrinsic forcing from foreland basin sedimentation rate accelerations since 1.4Ma. We found that reconstructed slip rate variability increased as the time resolution increased. The reconstructed slip history of the thin-skinned thrust faults was characterized relatively long, slow fold growth and associated fault slip, punctuated by shorter, more rapid periods limb rotation, and slip on the underlying thrust fault timed asynchronously. Thrust fault slip rates slip rates were ≤ 0.1 to 6 mm/yr at these intermediate timescales. The variability of slip rates on the thrusts is likely related to strain partitioning neighboring faults within the orogenic wedge. The studied structures slowed down at 1Ma when there was a switch to slower synchronous fault slip coincident with orogenic wedge thickening due to the emplacement of the out of sequence Pene-Apenninic thrust fault that was emplaced at 1.4±0.7 mm/yr. Both tectonic control and climate controlled variability on syntectonic sedimentation was observed in the growth sections.

Effects of structural heterogeneity on frictional heating from biomarker thermal maturity analysis of the Muddy Mountain thrust, Nevada, USA

NASA Astrophysics Data System (ADS)

Coffey, G. L.; Savage, H. M.; Polissar, P. J.; Rowe, C. D.

2017-12-01

Faults are generally heterogeneous along-strike, with changes in thickness and structural complexity that should influence coseismic slip. However, observational limitations (e.g. limited outcrop or borehole samples) can obscure this complexity. Here we investigate the heterogeneity of frictional heating determined from biomarker thermal maturity and microstructural observations along a well-exposed fault to understand whether coseismic stress and frictional heating are related to structural complexity. We focus on the Muddy Mountain thrust, Nevada, a Sevier-age structure that has continuous exposure of its fault core and considerable structural variability for up to 50 m, to explore the distribution of earthquake slip and temperature rise along strike. We present new biomarker thermal maturity results that capture the heating history of fault rocks. Biomarkers are organic molecules produced by living organisms and preserved in the rock record. During heating, their structure is altered systematically with increasing time and temperature. Preliminary results show significant variability in thermal maturity along-strike at the Muddy Mountain thrust, suggesting differences in coseismic temperature rise on the meter- scale. Temperatures upwards of 500°C were generated in the principal slip zone at some locations, while in others, no significant temperature rise occurred. These results demonstrate that stress or slip heterogeneity occurred along the Muddy Mountain thrust at the meter-scale and considerable along-strike complexity existed, highlighting the importance of careful interpretation of whole-fault behavior from observations at a single point on a fault.

The East Antarctic Ice Sheet and the Gamburtsev Subglacial Mountains (Invited)

NASA Astrophysics Data System (ADS)

Bell, R. E.; Studinger, M.; Ferraccioli, F.; Damaske, D.; Finn, C.; Braaten, D. A.; Fahnestock, M. A.; Jordan, T. A.; Corr, H.; Elieff, S.; Frearson, N.; Block, A. E.; Rose, K.

2009-12-01

Models of the onset of glaciation in Antarctica routinely document the early growth of the ice sheet on the summit of the Gamburtsev Subglacial Mountains in the center of the East Antarctic Craton. While ice sheet models replicate the formation of the East Antarctic ice sheet 35 million years ago, the age, evolution and structure of the Gamburtsev Mountains remain completely unresolved. During the International Polar Year scientists from seven nations have launched a major collaborative program (AGAP) to explore the Gamburtsev Subglacial Mountains buried by the East Antarctic ice sheet and bounded by numerous subglacial lakes. The AGAP umbrella is a multi-national, multi-disciplinary effort and includes aerogeophysics, passive seismology, traverse programs and will be complimented by future ice core and bedrock drilling. A major new airborne data set including gravity; magnetics; ice thickness; SAR images of the ice-bed interface; near-surface and deep internal layers; and ice surface elevation is providing insights into a more dynamic East Antarctica. More than 120,000 km of aerogeophysical data have been acquired from two remote field camps during the 2008/09 field season. AGAP effort was designed to address several fundamental questions including: 1) What role does topography play in the nucleation of continental ice sheets? 2) How do tectonic processes control the formation, distribution, and stability of subglacial lakes? The preliminary analysis of this major new data set indicated these 3000m high mountains are deeply dissected by a dendritic system. The northern margin of the mountain range terminates against the inland extent of the Lambert Graben. Evidence of the onset of glaciation is preserved as cirques and U shaped valleys along the axis of the uplifted massifs. The geomorphology reflects the interaction between the ice sheet and the Gamburtsev Mountains. Bright reflectors in the radar data in the deep valleys indicate the presence of water that has the potential to influence ice sheet flow. Crevassing and disrupted internal layers are present in the deep ice found in the inland extent of the Lambert Graben. Preliminary analysis indicates both a more dynamic East Antarctic ice sheet and a more complex tectonic evolution for East Antarctica.

Mesozoic contractile and extensional structures in the Boyer Gap area, northern Dome Rock Mountains, Arizona

DOE Office of Scientific and Technical Information (OSTI.GOV)

Boettcher, S.S.

1993-04-01

Mesozoic polyphase contractile and superposed ductile extensional structures affect Proterozoic augen gneiss, Paleozoic metasedimentary rocks, and Jurassic granitoids in the Boyer Gap area of the northern Dome Rock Mtns, W-central Arizona. The nappe-style contractile structures are preserved in the footwall of the Tyson Thrust shear zone, which is one of the structurally lowest thrust faults in the E-trending Jurassic and Cretaceous Maria fold and thrust belt. Contractile deformation preceded emplacement of Late Cretaceous granite (ca 80 Ma, U-Pb zircon) and some may be older than variably deformed Late Jurassic leucogranite. Specifically, detailed structural mapping reveals the presence of a km-scalemore » antiformal syncline that apparently formed as a result of superposition of tight to isoclinal, south-facing folds on an earlier, north-facing recumbent fold. The stratigraphic sequence of metamorphosed Paleozoic cratonal strata is largely intact in the northern Dome Rock Mtns, such that overturned and upright stratigraphic units can be distinguished. A third phase of folding in the Boyer Gap area is distinguished by intersection lineations that are folded obliquely across the hinges of open to tight, sheath folds. The axial planes of the sheet folds are subparallel to the mylonitic foliation in top-to-the-northeast extensional shear zones. The timing of ductile extensional structures in the northern Dome Rock is constrained by [sup 40]Ar/[sup 39]Ar isochron ages of 56 Ma and 48 Ma on biotite from mylonitic rocks in both the hanging wall and footwall of the Tyson Thrust shear zone. The two early phases of folding are the dominant mechanism by which shortening was accommodated in the Boyer Gap area, as opposed to deformation along discrete thrust faults with large offset. All of the ductile extensional structures are spectacularly displayed at an outcrop scale but are not of sufficient magnitude to obliterate the km-scale Mesozoic polyphase contractile structures.« less

Temperature micro-mapping and redox conditions of a chlorite zoning pattern in green-schist facies fault zone

NASA Astrophysics Data System (ADS)

Trincal, Vincent; Lanari, Pierre; Lacroix, Brice; Buatier, Martine D.; Charpentier, Delphine; Labaume, Pierre; Muñoz, Manuel

2014-05-01

Faults are major discontinuities driving fluid flows and playing a major role in precipitation of ore deposits. Mineral paragenesis and crystal chemistry depend on Temperature (T) condition, fluid composition but also on the redox environment of precipitation. The studied samples come from the Pic de Port Vieux thrust sheet, a minor thrust sheet associated to Gavarnie thrust fault zone (Central Pyrenees). The Pic de Port Vieux Thrust sheet comprises a 1-20 meter thick layer of Triassic red beds and mylonitized Cretaceous limestone. The thrust sheet is affected by faults and cleavage; the other important deformation product is a set of veins filled by quartz and chlorite. Microstructural and mineralogical investigations were performed based on the previous work of Grant (1992). The crystallization of chlorite is syn-tectonic and strongly controlled by the fluid circulation during the Gavarnie thrust sheet emplacement. Chlorite precipitated in extension veins, crack-seal shear veins or in open cavities. The chlorite filling the open cavities occurs as pseudo-uniaxial plates arranged in rosette-shaped aggregates. These aggregates appear to have developed as a result of radial growth of the chlorite platelets. According to point and microprobe X-ray images, these chlorites display oscillatory chemical zoning patterns with alternating iron rich and magnesium rich bands. The chlorite composition ranges from Fe rich pole (Si2.62Al1.38O10(Al1.47Fe1.87Mg2.61)6(OH)8) to Mg rich pole (Si2.68Al1.31O10(Al1.45Fe1.41Mg3.06)6(OH)8). In metamorphic rocks, zoning pattern or rimmed minerals results for varying P or T conditions and can be used to unravel the P-T history of the sample. In the present study, temperature maps are derived from standardized microprobe X-ray images using the program XMapTools (Lanari et al 2014). The (Fe3+/Fetot) value in chlorite was directly measured using μXANES spot analyses collected at the Fe-K edge. The results indicate a homogeneous temperature of 300-350° C throughout the crystallization. This result excludes the T as the main parameter to explain the Fe and Mg zoning patterns. Several other origins can be proposed and discussed in order to understand zoning patterns such as fluid chemistry, pressure, pH or redox variations of the fluid. Grant, N.T., 1992. Post-emplacement extension within a thrust sheet from the central Pyrenees. Journal of the Geological Society 149, 775-792. Lanari, P., Vidal, O., De Andrade, V., Dubacq, B., Lewin, E., Grosch, E.G., Schwartz, S., 2014. XMapTools: A MATLAB©-based program for electron microprobe X-ray image processing and geothermobarometry. Computers & Geosciences 62, 227-240.

Pliocene episodic exhumation and the significance of the Munsiari thrust in the northwestern Himalaya

NASA Astrophysics Data System (ADS)

Stübner, Konstanze; Grujic, Djordje; Dunkl, István; Thiede, Rasmus; Eugster, Patricia

2018-01-01

The Himalayan thrust belt comprises three in-sequence foreland-propagating orogen-scale faults, the Main Central thrust, the Main Boundary thrust, and the Main Frontal thrust. Recently, the Munsiari-Ramgarh-Shumar thrust system has been recognized as an additional, potentially orogen-scale shear zone in the proximal footwall of the Main Central thrust. The timing of the Munsiari, Ramgarh, and Shumar thrusts and their role in Himalayan tectonics are disputed. We present 31 new zircon (U-Th)/He ages from a profile across the central Himachal Himalaya in the Beas River area. Within a ∼40 km wide belt northeast of the Kullu-Larji-Rampur window, ages ranging from 2.4 ± 0.4 Ma to 5.4 ± 0.9 Ma constrain a distinct episode of rapid Pliocene to Present exhumation; north and south of this belt, zircon (U-Th)/He ages are older (7.0 ± 0.7 Ma to 42.2 ± 2.1 Ma). We attribute the Pliocene rapid exhumation episode to basal accretion to the Himalayan thrust belt and duplex formation in the Lesser Himalayan sequence including initiation of the Munsiari thrust. Pecube thermokinematic modelling suggests exhumation rates of ∼2-3 mm/yr from 4-7 to 0 Ma above the duplex contrasting with lower (<0.3 mm/yr) middle-late Miocene exhumation rates. The Munsiari thrust terminates laterally in central Himachal Pradesh. In the NW Indian Himalaya, the Main Central thrust zone comprises the sheared basal sections of the Greater Himalayan sequence and the mylonitic 'Bajaura nappe' of Lesser Himalayan affinity. We correlate the Bajaura unit with the Ramgarh thrust sheet in Nepal based on similar lithologies and the middle Miocene age of deformation. The Munsiari thrust in the central Himachal Himalaya is several Myr younger than deformation in the Bajaura and Ramgarh thrust sheets. Our results illustrate the complex and segmented nature of the Munsiari-Ramgarh-Shumar thrust system.

Constraints on the tectonics of the Mule Mountains thrust system, southeast California and southwest Arizona

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tosdal, R.M.

1990-11-10

The Mule Mountains thrust system crops out discontinuously over a 100-km-strike length in the Blythe-Quartzsite region of southeast California and southwest Arizona. Along the thrust system, middle and upper crustal metamorphic and plutonic rocks of Proterozoic and Mesozoic age are thrust north-northeastward (015{degree} to 035{degree}) over a lower plate metamorphic terrane that formed part of the Proterozoic North American craton, its Paleozoic sedimentary rock cover, overlying Mesozoic volcanic and sedimentary rocks, and the intruding Jurassic and Cretaceous granitic rocks. Stratigraphic, petrologic, and Pb isotopic ties for Jurassic granitoids and for Jurassic( ) and Cretaceous sedimentary rocks across the various partsmore » of the thrust system indicate that related crustal blocks are superposed and preclude it from having large displacements. The thick-skinned thrust system is structurally symmetrical along its length with a central domain of synmetamorphic thrust faults that are flanked by western and eastern domains where lower plate domains where lower plate synclines underlie the thrusts. Deformation occurred under low greenschist facies metamorphic conditions in the upper crust. Movement along the thrust system was probably limited to no more than a few tens of kilometers and occurred between 79{plus minus}2 Ma and 70{plus minus}4 Ma. The superposition of related rocks and the geometry of the thrust system preclude it from being a major tectonic boundary of post-Middle Jurassic age, as has been previously proposed. Rather, the thrust system forms the southern boundary of the narrow zone of Cretaceous intracratonic deformation, and it is one of the last tectonic events in the zone prior to regional cooling.« less

New Structural Interpretation of the Central Confusion Range, Western Utah, Based On Balanced Cross Sections

NASA Astrophysics Data System (ADS)

Yezerski, D.; Greene, D. C.

2009-12-01

The Confusion Range is a topographically low mountain range in the Basin and Range of west-central Utah, located east of and in the hanging wall of the Snake Range core complex. Previous workers have used a gravity sliding model to interpret the Confusion Range as a large structural trough or synclinorium (e.g. Hose, 1977). Based on existing mapping (Hose, 1965; Hintze, 1974) and new field data, we use balanced and restored cross sections to reinterpret the structure of the Confusion Range as an east-vergent fold-and-thrust belt formed during the Sevier Orogeny. The Confusion Range consists of Cambro-Ordovician through Triassic strata, with predominantly thick-bedded, competent carbonate rocks in the lower Paleozoic (lPz) section and incompetent shales and thin-bedded carbonates in the upper Paleozoic (uPz) section. The contrasting mechanical behavior of these stratigraphic sections results in faulted folds within uPz carbonates above detachments in shale-rich units, deforming in response to ramp-flat thrust faulting of the underlying lPz units. East of the axis of the Conger Mountain (Mtn) syncline, we attribute the increase in structural elevation of lPz rocks to a subsurface thrust sheet consisting of lPz strata that advanced eastward via a high-angle ramp from a lower detachment in the Kanosh Shale to an upper detachment in the Pilot Shale. The doubling of lPz strata that resulted continues through the eastern Confusion Range where a series of small-displacement thrust faults comprising the Kings Canyon thrust system gently tilt strata to the west. In the Conger Range, west of the Conger Mtn syncline, our analysis focuses on reinterpreting the geometrically unlikely folding depicted in previous cross sections as more admissible, fault-cored, asymmetric, detached folding. In our interpretation, resistance created by a steeply-dipping thrust ramp in the lPz section west of Conger Mtn resulted in folding of uPz strata into an east-vergent anticline. Continued east-vergent contraction against the ramp resulted in the west-dipping limb of the anticline, consisting of Ely Limestone, developing into an overturned, west-vergent, synclinal backfold detached in the Chainman Shale. Further contraction exceeded the fold capacity of the detachment fold and resulted in the formation of the Browns Wash fault as an east-vergent thrust fault. The Browns Wash fault is a key component in the development of the present structural geometry, emplacing a west-vergent overturned syncline (detachment fold) in the hanging wall against an east-vergent overturned syncline (footwall syncline) in the footwall. Further west, underlying the western Conger Range and Buckskin Hills, lPz strata are exposed in what we interpret to be a ramp anticline overlying a subsurface thrust ramp. This interpretation implies a lateral ramp separating lPz rocks in the Buckskin Hills from uPz rocks exposed in the Knoll Hill anticline to the north. UPz and Mesozoic strata exposed to the west on the edge of Snake Valley were emplaced by a Tertiary west-dipping normal fault that truncated the west limb of the ramp anticline.

Boundary element analysis of active mountain building and stress heterogeneity proximal to the 2015 Nepal earthquake

NASA Astrophysics Data System (ADS)

Thompson, T. B.; Meade, B. J.

2015-12-01

The Himalayas are the tallest mountains on Earth with ten peaks exceeding 8000 meters, including Mt. Everest. The geometrically complex fault system at the Himalayan Range Front produces both great relief and great earthquakes, like the recent Mw=7.8 Nepal rupture. Here, we develop geometrically accurate elastic boundary element models of the fault system at the Himalayan Range Front including the Main Central Thrust, South Tibetan Detachment, Main Frontal Thrust, Main Boundary Thrust, the basal detachment, and surface topography. Using these models, we constrain the tectonic driving forces and frictional fault strength required to explain Quaternary fault slip rate estimates. These models provide a characterization of the heterogeneity of internal stress in the region surrounding the 2015 Nepal earthquake.

Publications - PIR 2015-6 | Alaska Division of Geological & Geophysical

Science.gov Websites

content DGGS PIR 2015-6 Publication Details Title: Geologic map of the Talkeetna Mountains C-4 Quadrangle ., Freeman, L.K., and Lande, L.L., 2015, Geologic map of the Talkeetna Mountains C-4 Quadrangle and adjoining Sheets Sheet 1 Geologic map of the Talkeetna Mountains C-4 Quadrangle and adjoining areas, central Alaska

Foreland structure - Beartooth Mountains, Montana and Wyoming

DOE Office of Scientific and Technical Information (OSTI.GOV)

Clark, D.M.

1996-06-01

Analysis of public drilling records from the AMOCO Beartooth Number 1 and 1 A sidetrack boreholes (SW1/4, SE1/4, Section 19, T.8 S., R.20 E., Carbon County, Montana) continues. Several additional inferences are made about this large foreland structure, and subsequent interpretation of the structural model of the northeast corner of the Beartooth Mountain Block and structural relationship with the Big Horn Basin. The structure is described as a large recumbent to sub-horizontal, synclinal fold with the overturned upper limb out diagonally by the Beartooth Thrust or Thrust Zone and a complex thrust fault zone below the Beartooth Thrust. The singlemore » recorded dip angle and direction of the Beartooth Thrust at depth was 19 degrees to the northwest(?). The dipmeter dip angle on the Beartooth Thrust, 19 degrees, validates foreland structural theory of decreasing dip angles at a vertical depth of 8,232 feet (2,509 m), in the Precambrian crystalline basement. The northwest dip direction may be attributable to secondary structural folding. The record of northwest, southeast, and southwest dip of bedding surfaces and faults in sections of the overturned upper limb, in both boreholes, suggests possible, less intense secondary folding, after thrust fault deformation. Given the overall geometry of this large foreland structure, there is little doubt that the average direction of maximum principal stress (sigma 1) was oriented in a northeast - southwest direction.« less

Geological and Geographical Atlas of Colorado and portions of adjacent territory

USGS Publications Warehouse

Hayden, Ferdinand Vandeveer; Bien, Julius

1881-01-01

Sheets I-IV are triangulations, drainage, land classification, and geologic maps of Colorado west of longitude 102°, on the scale of 12 miles to the inch. Sheets V-XVI are topographic (contour) and geologic maps of Colorado and adjacent States, between meridians 104° 30' and 109° 30' and parallels 36° 45' and 40° 30', on the scale of 4 miles to the inch. Sheets XVII and XVIII contain three geologic sections across the State, west of the longitude 104° 30'. Sheets XIX and XX are panoramic views of the Pikes Peak group, Sawatch Range, central portion of West Elk Mountains, Twin Lakes, southwestern border of the Mesa Verde, San Juan Mountains, and La Plata Mountains.

Geological and Geographical Atlas of Colorado and portions of adjacent territory

USGS Publications Warehouse

Hayden, Ferdinand Vandeveer; Bien, Julius

1877-01-01

Sheets I-IV are triangulations, drainage, land classification, and geologic maps of Colorado west of longitude 102°, on the scale of 12 miles to the inch. Sheets V-XVI are topographic (contour) and geologic maps of Colorado and adjacent States, between meridians 104° 30' and 109° 30' and parallels 36° 45' and 40° 30', on the scale of 4 miles to the inch. Sheets XVII and XVIII contain three geologic sections across the State, west of the longitude 104° 30'. Sheets XIX and XX are panoramic views of the Pikes Peak group, Sawatch Range, central portion of West Elk Mountains, Twin Lakes, southwestern border of the Mesa Verde, San Juan Mountains, and La Plata Mountains.

Extent and architecture of major fault systems between northern Victoria Land and the eastern margin of the Wilkes Subglacial Basin (East Antarctica)

NASA Astrophysics Data System (ADS)

Armadillo, E.; Ferraccioli, F.; Balbi, P.; Bozzo, E.

2013-12-01

Terrane bounding and intra-terrane faults of the Ross Orogen in East Antarctica are linked to several phases of Cambrian to Ordovician age subduction and accretion along the active paleo-Pacific margin of Gondwana. Here we compile and analyse new enhanced aeromagnetic anomaly images over the Northern Victoria Land (NVL) segment of the Ross Orogen and the eastern margin of the Wilkes Subglacial Basin (WSB) that help constrain the extent and structural architecture of these fault systems and enable us re-assess their tectonic evolution. Long-wavelength magnetic lows and residual Bouguer gravity highs are modelled as several-km thick inverted sedimentary basins of early Cambrian(?) age. Tectonic inversion occurred along major thrust faults during the late stages of the Ross Orogen, forming a major high-grade pop-up structure within the central Wilson Terrane, flanked by lower grade rocks. The Prince Albert Fault System can now be recongnised as being located to the west of the Exiles Thrust fault system rather than representing its southern continuation. Relatively thin sheets of mylonitic sheared granitoids and possible ultramafic lenses are associated with the late-Ross (ca 480 Ma) Exiles Thrust fault system, while significantly larger and thicker batholiths were emplaced along the Prince Albert Fault System. Recent zircon U-Pb dating over small exposures of gabbro-diorites within the Prince Albert Mountains to the south lead us to propose that this part of the magmatic arc was emplaced during an earlier phase of subduction (~520 Ma or older?), compared to the late-Ross intrusions to the east. Whether the Prince Albert Fault System was indeed a major cryptic suture in early Cambrian times (Ferraccioli et al., 2002, GRL) remains speculative, but possible. Our aeromagnetic interpretation leads us to conclude that these inherited terrane bounding and intra-terrane fault systems of the Ross Orogen exerted a key influence on Cenozoic tectonic blocks and faults of the Transantarctic Mountains, and that the eastern margin of the WSB adjacent to NVL was also strongly controlled by a complex array of major intraplate strike-slip fault systems.

The role of Mesozoic sedimentary basin tapers on the formation of Cenozoic crustal shortening structures and foredeep in the western Sichuan Basin, China

NASA Astrophysics Data System (ADS)

Wang, M.

2017-12-01

The foreland basin records important clues of tectonic and sedimentary process of mountain-building, thus to explore its dynamic mechanism on the formation is an important issue of the mountain-basin interaction. The Longmen Shan fold-and-thrust belt and its adjacent Sichuan basin located in the eastern margin of Tibetan Plateau, are one of the most-concerned regions of studying modern mountain-building and seismic process, and are also a natural laboratory of studying the dynamics of the formation and development of foreland basin. However, it still need further explore on the mechanics of the development of the Cenozoic foreland basin and thrust-belts in the western Sichuan Basin. The Longmen Shan thrust belt has experienced multi-stages of tectonics evolution, foreland basin formation and topography growth since Late Triassic, and whether the early formed basin architecture and large Mesozoic sedimentary basin taper can influence the formation and development of the Cenozoic foreland basin and thrust belts? To solve these issues, this project aim to focus on the Cenozoic foreland basin and internal crustal shortening structures in the western Sichuan basin, on the basis of growth critical wedge taper theory. We will reconstruct the shape of multi-phases of sedimentary basin tapers, the temporal-spatial distribution of crustal shortening and thrusting sequences, and analyze the control mechanism of Mesozoic sedimentary basin taper on the formation of Cenozoic foreland basins, and final explore the interaction between the tectonics geomorphology, stress field and dynamic propagation of foreland basin.

Crustal structure and tectonics of the Hidaka Collision Zone, Hokkaido (Japan), revealed by vibroseis seismic reflection and gravity surveys

NASA Astrophysics Data System (ADS)

Arita, Kazunori; Ikawa, Takashi; Ito, Tanio; Yamamoto, Akihiko; Saito, Matsuhiko; Nishida, Yasunori; Satoh, Hideyuki; Kimura, Gaku; Watanabe, Teruo; Ikawa, Takeshi; Kuroda, Toru

1998-05-01

This study is the first integrated geological and geophysical investigation of the Hidaka Collision Zone in southern Central Hokkaido, Japan, which shows complex collision tectonics with a westward vergence. The Hidaka Collision Zone consists of the Idon'nappu Belt (IB), the Poroshiri Ophiolite Belt (POB) and the Hidaka Metamorphic Belt (HMB) with the Hidaka Belt from west to east. The POB (metamorphosed ophiolites) is overthrust by the HMB (steeply eastward-dipping palaeo-arc crust) along the Hidaka Main Thrust (HMT), and in turn, thrusts over the Idon'nappu Belt (melanges) along the Hidaka Western Thrust (HWT). Seismic reflection and gravity surveys along a 20-km-long traverse across the southern Hidaka Mountains revealed hitherto unknown crustal structures of the collision zone such as listric thrusts, back thrusts, frontal thrust-and-fold structures, and duplex structures. The main findings are as follows. (1) The HMT, which dips steeply at the surface, is a listric fault dipping gently at a depth of ˜7 km beneath the eastern end of the HMB, and cutting across the lithological boundaries and schistosity of the Hidaka metamorphic rocks. (2) A second reflector is detected 1 km below the HMT reflector. The intervening part between these two reflectors is inferred to be the POB, which is only little exposed at the surface. This inference is supported by the high positive Bouguer anomalies along the Hidaka Mountains. (3) The shallow portion of the IB at the front of the collision zone has a number of NNE-dipping reflectors, indicative of imbricated fold-and-thrust structures. (4) Subhorizontal reflectors at a depth of 14 km are recognized intermittently at both sides of the seismic profile. These reflectors may correspond to the velocity boundary (5.9-6.6 km/s) previously obtained from seismic refraction profiling in the northern Hidaka Mountains. (5) These crustal structures as well as the back thrust found in the eastern end of the traverse represent characteristics of collisional tectonics resulting from the two collisional events since the Early Tertiary.

The thrust belt in Southwest Montana and east-central Idaho

USGS Publications Warehouse

Ruppel, Edward T.; Lopez, David A.

1984-01-01

The leading edge of the Cordilleran fold and thrust in southwest Montana appears to be a continuation of the edge of the Wyoming thrust belt, projected northward beneath the Snake River Plain. Trces of the thrust faults that form the leading edge of the thrust belts are mostly concealed, but stratigraphic and structural evidence suggests that the belt enters Montana near the middle of the Centennial Mountains, continues west along the Red Rock River valley, and swings north into the Highland Mountains near Butte. The thrust belt in southwest Montana and east-central Idaho includes at least two major plates -- the Medicine Lodge and Grasshopper thrust plates -- each of which contains a distinctive sequence of rocks, different in facies and structural style from those of the cratonic region east of the thrust belt. The thrust plates are characterized by persuasive, open to tight and locally overturned folds, and imbricate thrust faults, structural styles unusual in Phanerozoic cratonic rocks. The basal decollement zones of the plates are composed of intensely sheared, crushed, brecciated, and mylonitized rocks, the decollement at the base of the Medicine Lodge plate is as much as 300 meters thick. The Medicine Lodge and Grasshopper thrust plates are fringed on the east by a 10- to 50-kilometer-wide zone of tightly folded rocks cut by imbricate thrust fauls, a zone that forms the eastern margin of the thrust belt in southwest Montana. The frontal fold and thrust zone includes rocks that are similar to those of the craton, even though they differ in details of thickness, composition, or stratigraphic sequence. The zone is interpreted to be one of terminal folding and thrusting in cratonic rocks overridden by the major thrust plates from farther west. The cratonic rocks were drape-folded over rising basement blocks that formed a foreland bulge in front of the thrust belt. The basement blocks are bounded by steep faults of Proterozoic ancestry, which also moved as tear faults during thrusting, and seem to have controlled the curving patterns of salients and reentrants at the leading edge of the thrust belt. Radiometric and stratiographic evidence shows that the thrust belt was in its present position by about 75 million year go.

Reprocessing and Interpretation of Vintage Seismic Reflection Data: Evidence for the Tectonic History of the Rocky Mountain Trench, Northwest Montana.

NASA Astrophysics Data System (ADS)

Porter, M.; Speece, M. A.; Rutherford, B. S.; Constenius, K. N.

2014-12-01

In 1983 Techno, Inc. collected five seismic reflection profiles in the region between Whitefish, Montana and the United States-Canada border. The poulter method was used to gather four of these profiles and one profile was collected using a vibroseis source. We are currently reprocessing these data in order to construct a regional geological interpretation. The profiles cover a key position in the hinterland of the Cordillera in the lee of the Lewis thrust salient where the east-northeast verging Lewis thrust fault system translated (horizontal displacement >100 km) and inverted a thick, strong slab of primarily Belt-Purcell rocks out of a deep Precambrian depositional basin onto a cratonic platform. In this event, Belt-Purcell rocks were thrust over complexly imbricated Phanerozoic strata in the foreland. Late Mesozoic compressional deformation was followed by Cenozoic extensional collapse of the over-thickened Cordillera and subsequent basin and range style deformation that produced an array of northwest trending grabens. Three of the seismic profiles cross the Rocky Mountain Trench; the Trench is a linear structure of regional dimension that is an expression of the extensional fragmentation of the Cordillera. Strong reflections, interpreted as sills encased within Lower Belt rocks (encountered in the Arco-Marathon 1 Paul Gibbs borehole), outline the complexly folded and faulted structure of the eastern limb of the Purcell anticlinorium. East of the Rocky Mountain Trench stratified reflections within Belt rocks clearly outline the Wigwam Thrust. Beneath the Whitefish Range, an apparent inflection in the strongly reflective basal Cambrian veneer marks the westerly increase in dip of the Rocky Mountain Basal Detachment. The dip contrast between the foreland and hinterland might be a manifestation of the tectonic loading of the Belt basin margin and the loading might have localized extension across the Rocky Mountain Trench.

The sup 40 Ar/ sup 39 Ar geochronology of the Pelona schist and related rocks, southern California

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jacobson, C.E.

1990-01-10

Seventeen {sup 40}Ar/{sup 39}Ar ages for hornblende, celadonitic muscovite, and biotite from the Pelona, Orocopia, Rand, and Portal Ridge (POR) schists range from 39 to 85 Ma. Two muscovites and one hornblende from the Rand Schist have ages of 72 to 74 Ma, indistinguishable from the K-Ar age of 74 Ma for hornblende from a posttectonic granodiorite that intrudes the schist, but younger than the 70 Ma U-Pb age of the intrusion. Four muscovite and two hornblende ages for schist and mylonite from the East Fork area of the San Gabriel Mountains range from 55 to 61 Ma. Concordance ofmore » schist and upper plate ages confirms structural and metamorphic evidence that the Vincent thrust in the San Gabriel Mountains has not undergone significant postmetamorphic disruption. Ages from the Orocopia Mountains are 75 Ma for hornblende from nonmylonitic upper plate, 52 Ma for muscovite from structurally high Orocopia Schist that is mylonitic, and 41 Ma for muscovite from nonmylonitic Orocopia Schist. These are consistent with field evidence that the Orocopia thrust is a postmetamorphic normal fault. Muscovite and hornblende from the Gavilan Hills have ages of 48 to 50 Ma, younger than ages from the San Gabriel Mountains but similar to schist ages from the Orocopia Mountains. The geochronologic and structural complexities of the Vincent, Chocolate Mountains, Orocopia, and Rand thrusts imply that previously cited northeastward vergence may not relate to prograde metamorphism (subduction) of the POR schists. The data indicate substantial uplift of the POR schists prior to middle Tertiary detachment faulting, which confirms other geochronologic evidence of uplift in southern California and southern Arizona during the Late Cretaceous-early Tertiary.« less

Co-seismic ruptures of the 12 May 2008, Ms 8.0 Wenchuan earthquake, Sichuan: East-west crustal shortening on oblique, parallel thrusts along the eastern edge of Tibet

USGS Publications Warehouse

Liu-Zeng, J.; Zhang, Z.; Wen, L.; Tapponnier, P.; Sun, Jielun; Xing, X.; Hu, G.; Xu, Q.; Zeng, L.; Ding, L.; Ji, C.; Hudnut, K.W.; van der Woerd, J.

2009-01-01

The Ms 8.0, Wenchuan earthquake, which devastated the mountainous western rim of the Sichuan basin in central China, produced a surface rupture over 200??km-long with oblique thrust/dextral slip and maximum scarp heights of ~ 10??m. It thus ranks as one of the world's largest continental mega-thrust events in the last 150??yrs. Field investigation shows clear surface breaks along two of the main branches of the NE-trending Longmen Shan thrust fault system. The principal rupture, on the NW-dipping Beichuan fault, displays nearly equal amounts of thrust and right-lateral slip. Basin-ward of this rupture, another continuous surface break is observed for over 70??km on the parallel, more shallowly NW-dipping Pengguan fault. Slip on this latter fault was pure thrusting, with a maximum scarp height of ~ 3.5??m. This is one of the very few reported instances of crustal-scale co-seismic slip partitioning on parallel thrusts. This out-of-sequence event, with distributed surface breaks on crustal mega-thrusts, highlights regional, ~ EW-directed, present day crustal shortening oblique to the Longmen Shan margin of Tibet. The long rupture and large offsets with strong horizontal shortening that characterize the Wenchuan earthquake herald a re-evaluation of tectonic models anticipating little or no active shortening of the upper crust along this edge of the plateau, and require a re-assessment of seismic hazard along potentially under-rated active faults across the densely populated western Sichuan basin and mountains. ?? 2009 Elsevier B.V.

The Lewis thrust fault and related structures in the Disturbed Belt, northwestern Montana

USGS Publications Warehouse

Mudge, Melville Rhodes; Earhart, Robert L.

1980-01-01

The classical Lewis thrust fault in Glacier National Park has now been mapped 125 km south of the park to Steamboat Mountain, where the trace dies out in folded middle Paleozoic rocks. The known length of the fault is 452 km, extending northward from Steamboat Mountain to a point 225 km into Canada, where the fault also dies out in Paleozoic rocks. At the south end, the surface expression of the Lewis thrust begins in a shear zone in folded Mississippian rocks. To the north, the thrust progressively cuts downsection into Proterozoic Y (Belt) rocks near Glacier National Park. Displacement on the Lewis plate increases northward from approximately 3 km on an easterly trending hinge line at the West Fork of the Sun River to a postulated 65 km at the southern edge of the park, where the stratigraphic throw is about 6,500 m. Present data indicate the thrust formed during very late Paleocene to very early Eocene time. The Lewis thrust and related structures, the Hoadley thrust and the Continental Divide syncline, probably formed concurrently under the same stress field. The northern limit of the trace of the Hoadley thrust is within the lower portion of the Lewis plate, about 28 km north of where the Lewis thrust develops, and the Hoadley extends for at least 125 km to the south. Displacement of the Hoadley increases southward from about 1 km at the hinge line to an inferred 70 km near its known southern extent. If our inference is correct, the Hoadley is nearly the southern mirror image of the Lewis to the north. The Continental Divide syncline, a doubly plunging, broad, northerly trending open fold that is about 120 km long, is a major fold within the Lewis plate.

Stratigraphy and structural setting of Upper Cretaceous Frontier Formation, western Centennial Mountains, southwestern Montana and southeastern Idaho

USGS Publications Warehouse

Dyman, T.S.; Tysdal, R.G.; Perry, W.J.; Nichols, D.J.; Obradovich, J.D.

2008-01-01

Stratigraphic, sedimentologic, and palynologic data were used to correlate the Frontier Formation of the western Centennial Mountains with time-equivalent rocks in the Lima Peaks area and other nearby areas in southwestern Montana. The stratigraphic interval studied is in the middle and upper parts (but not uppermost) of the formation based on a comparison of sandstone petrography, palynologic age data, and our interpretation of the structure using a seismic line along the frontal zone of the Centennial Mountains and the adjacent Centennial Valley. The Frontier Formation is comprised of sandstone, siltstone, mudstone, limestone, and silty shale in fluvial and coastal depositional settings. A distinctive characteristic of these strata in the western Centennial Mountains is the absence of conglomerate and conglomeratic sandstone beds. Absence of conglomerate beds may be due to lateral facies changes associated with fluvial systems, a distal fining of grain size, and the absence of both uppermost and lower Frontier rocks in the study area. Palynostratigraphic data indicate a Coniacian age for the Frontier Formation in the western Centennial Mountains. These data are supported by a geochronologic age from the middle part of the Frontier at Lima Peaks indicating a possible late Coniacian-early Santonian age (86.25 ?? 0.38 Ma) for the middle Frontier there. The Frontier Formation in the western Centennial Mountains is comparable in age and thickness to part of the Frontier at Lima Peaks. These rocks represent one of the thickest known sequences of Frontier strata in the Rocky Mountain region. Deposition was from about 95 to 86 Ma (middle Cenomanian to at least early Santonian), during which time, shoreface sandstone of the Telegraph Creek Formation and marine shale of the Cody Shale were deposited to the east in the area now occupied by the Madison Range in southwestern Montana. Frontier strata in the western Centennial Mountains are structurally isolated from other Cretaceous rocks in the region and are part of the Lima thrust sheet that lies at the leading edge of the Sevier-style overthrusting in this part of southwestern Montana and adjacent southeastern Idaho.

Thrust-ridge paleodepositional model for the Upper Freeport coal bed and associated clastic facies, Upper Potomac coal field, Appalachian Basin, U.S.A.

USGS Publications Warehouse

Belt, Edward S.; Lyons, P.C.

1990-01-01

Two differential depositional sequences are recognized within a 37-m-thick lowermost section of the Conemaugh Group of Late Pennsylvanian (Westphalian D) age in the southern part of the Upper Potomac coal field (panhandle of Maryland and adjacent West Virginia). The first sequence is dominated by the Upper Freeport coal bed and zone (UF); the UF consists of a complex of interfingered thick coal beds and mudrocks. The UF underlies the entire 500 km2 study area (approximately 40 km in a NE-SW direction). The second sequence is dominated by medium- to coarse-grained sandstone and pebbly sandstone. They were deposited in channel belts that cut into and interfingered laterally with mudrock and fine- to medium-grained sandstone facies of floodbasin and crevasse-lobe origin. Thin lenticular coals occur in the second sequence. Nowhere in the study area does coarse-grained sandstone similar to the sandstone of the channel belts of the second sequence occur within the UF. However, 20 km north of the study area, coarse channel belts are found that are apparently synchronous with the UF (Lyons et al., 1984). The southeastern margin of the study are is bounded by the Allegheny Front. Between it and the North Mountain thrust (75 km to the southeast), lie at least eight other thrusts of unknown extent (Wilson, 1887). All these thrusts are oriented northwest; Devonian and older strata are exposed at the surface between the Allegheny Front and the North Mountain thrust. A blind-thrust ridge model is proposed to explain the relation of the two markedly depositional sequences to the thrusts that lie to the southeast of the Upper Potomac coal field. This model indicates that thrust ridges diverted coarse clastics from entering the swamp during a period when the thick Upper Freeport peat accumulated. Anticlinal thrust ridges and associated depressions are envisioned to have developed parallel to the Appalachian orogen during Middle and early Late Pennsylvanian time. A blind thrust developed from one of the outboard ridges, and it was thrust farther outboard ahead of the main body of the orogen. Sediment derived from the orogen was diverted into a sediment trap inboard of the ridge (Fig. 1). The ridge prevented sediment from entering the main peat-forming swamp. Sediment shed from the orogen accumulated in the sediment trap was carried out of the ends of the trap by steams that occupied the shear zone at the ends of the blind-thrust ridge (Fig. 1). Remnants of blind-thrust ridges occurs in the Sequatchie Valley thrust and the Pine Mountain thrust of the southern Appalachians. The extent, parallel to the orogen, of the thick areally extensive UF coal is related to the length of the blind-thrust ridge that, in turn, controlled the spacing of the river-derived coarse clastics that entered the main basin from the east. Further tectonism caused the thrust plane to emerge to the surface of the blind-thrust ridge. Peat accumulation was then terminated by the rapid erosion of the blind-thrust ridge and by the release of trapped sediment behind it. The peat was buried by sediments from streams from closely spaced channel belts] with intervening floodbasins. The model was implications for widespread peat (coal) deposits that developed in tropical regions, a few hundred kilometers inland from the sea during Pennsylvanian time (Belt and Lyons, 1989). ?? 1990.

Biostratigraphy and structure of paleozoic host rocks and their relationship to Carlin-type gold deposits in the Jerritt Canyon mining district, Nevada

USGS Publications Warehouse

Peters, S.G.; Armstrong, A.K.; Harris, A.G.; Oscarson, R.L.; Noble, P.J.

2003-01-01

The Jerritt Canyon mining district in the northern Independence Range, northern Nevada, contains multiple, nearly horizontal, thrust masses of platform carbonate rocks that are exposed in a series of north- to northeast-elongated, tectonic windows through rocks of the Roberts Mountains allochthon. The Roberts Mountains allochthon was emplaced during the Late Devonian to Early Mississippian Antler orogeny. These thrust masses contain structurally and stratigraphically controlled Carlin-type gold deposits. The gold deposits are hosted in tectonically truncated units of the Silurian to Devonian Hanson Creek and Roberts Mountains Formations that lie within structural slices of an Eastern assemblage of Cambrian to Devonian carbonate rocks. In addition, these multiply thrust-faulted and folded host rocks are structurally interleaved with Mississippian siliciclastic rocks and are overlain structurally by Cambrian to Devonian siliciclastic units of the Roberts Mountains allochthon. All sedimentary rocks were involved in thrusting, high-angle faulting, and folding, and some of these events indicate substantial late Paleozoic and/or Mesozoic regional shortening. Early Pennsylvanian and late Eocene dikes also intrude the sedimentary rocks. These rocks all were uplifted into a northeast-trending range by subsequent late Cenozoic Basin and Range faulting. Eocene sedimentary and volcanic rocks flank part of the range. Pathways of hydrothermal fluid flow and locations of Carlin-type gold orebodies in the Jerritt Canyon mining district were controlled by structural and host-rock geometries within specific lithologies of the stacked thrust masses of Eastern assemblage rocks. The gold deposits are most common proximal to intersections of northeast-striking faults, northwest-striking dikes, and thrust planes that lie adjacent to permeable stratigraphic horizons. The host stratigraphic units include carbonate sequences that contained primary intercrystalline permeability, which provided initial pathways for fluid flow and later served as precipitation sites for ore minerals. Alteration, during, and perhaps prior to mineralization, enhanced primary permeability by dissolution, by removal of calcite, and by formation of dolomite. Ore-stage sulfide minerals and alteration minerals commonly precipitated in pore spaces among dolomite grains. Microveinlets and microbrecciation in zones of intense alteration also provided networks of secondary permeability that further enhanced fluid flux and produced additional sites for ore deposition.

Laramide structure of the central Sangre de Cristo Mountains and adjacent Raton Basin, southern Colorado

USGS Publications Warehouse

Lindsey, D.A.

1998-01-01

Laramide structure of the central Sangre de Cristo Mountains (Culebra Range) is interpreted as a system of west-dipping, basement-involved thrusts and reverse faults. The Culebra thrust is the dominant structure in the central part of the range; it dips 30 -55?? west and brings Precambrian metamorphic base-ment rocks over unmetamorphosed Paleozoic rocks. East of the Culebra thrust, thrusts and reverse faults break the basement and overlying cover rocks into north-trending fault blocks; these boundary faults probably dip 40-60?? westward. The orientation of fault slickensides indicates oblique (northeast) slip on the Culebra thrust and dip-slip (ranging from eastward to northward) movement on adjacent faults. In sedimentary cover rocks, east-vergent anticlines overlie and merge with thrusts and reverse faults; these anticlines are interpreted as fault-propagation folds. Minor east-dipping thrusts and reverse faults (backthrusts) occur in both the hanging walls and footwalls of thrusts. The easternmost faults and folds of the Culebra Range form a continuous structural boundary between the Laramide Sangre de Cristo highland and the Raton Basin. Boundary structures consist of west-dipping frontal thrusts flanked on the basinward side by poorly exposed, east-dipping backthrusts. The backthrusts are interpreted to overlie structural wedges that have been emplaced above blind thrusts in the basin margin. West-dipping frontal thrusts and blind thrusts are interpreted to involve basement, but backthrusts are rooted in basin-margin cover rocks. At shallow structural levels where erosion has not exposed a frontal thrust, the structural boundary of the basin is represented by an anticline or monocline. Based on both regional and local stratigraphic evidence, Laramide deformation in the Culebra Range and accompanying synorogenic sedimentation in the western Raton Basin probably took place from latest Cretaceous through early Eocene time. The earliest evidence of uplift and erosion of a highland is the appearance of abundant feldspar in the Late Cretaceous Vermejo Formation. Above the Vermejo, unconformities overlain by conglomerate indicate continued thrusting and erosion of highlands from late Cretaceous (Raton) through Eocene (Cuchara) time. Eocene alluvial-fan conglomerates in the Cuchara Formation may represent erosion of the Culebra thrust block. Deposition in the Raton Basin probably shifted north from New Mexico to southern Colorado from Paleocene to Eocene time as movement on individual thrusts depressed adjacent segments of the basin.

Shorter intervals between great earthquakes near Sendai: Scour ponds and a sand layer attributable to A.D. 1454 overwash

NASA Astrophysics Data System (ADS)

Sawai, Yuki; Namegaya, Yuichi; Tamura, Toru; Nakashima, Rei; Tanigawa, Koichiro

2015-06-01

A sparsely documented tsunami in 1454 may subdivide the recurrence interval between the 869 and 2011 tsunamis near Sendai, as judged from geomorphic, stratigraphic, and archival evidence. Pond-filled breaches cut across beach ridges on century-old topographic maps. The basal pond deposit in one of these breaches postdates 1454. Stratigraphy on Sendai Plain includes a sand sheet that contains marine and brackish diatoms. Radiocarbon ages suggest that the sheet dates to 1406-1615 (2σ), and written records for this interval in Tohoku mention a tsunami in 1454. The inferred inundation extended 1.0-2.5 km inland from an approximate medieval shoreline. Simulated tsunamis that best account for the sand sheet require a thrust earthquake of moment magnitude 8.4 or larger. If the sand sheet represents the 1454 tsunami, the two most recent intervals between great thrust earthquakes in Sendai region spanned 585 and 557 years.

A viscoelastic strain energy principle expressed in fold thrust belts and other compressional regimes

NASA Astrophysics Data System (ADS)

Patton, Regan L.; Watkinson, A. John

2005-07-01

A mathematical folding theory for stratified viscoelastic media in layer parallel compression is presented. The second order fluid, in slow flow, is used to model rock rheological behavior because it is the simplest nonlinear constitutive equation exhibiting viscoelastic effects. Scaling and non-dimensionalization of the model system reveals the presence of Weissenberg number ( Wi), defined as a ratio of time scales τ*/( H*/ V*). V*/ H* is the strain rate (s -1) imposed by an assumed far field velocity V* acting on a layer of thickness H*, while τ* (s) is related to the relaxation of normal stresses. Our most significant finding is a transitional behavior as Wi→½, which is independent of the viscosity contrast. A change of variables shows that lengths associated with this transition are scaled by a parameter α=[(1-2 Wi)/(1+2 Wi)] 1/2, which is inversely proportional to local strain energy. On this basis a scaling law representing a distribution of non-dimensional wavelengths (wavelength/layer thickness) is derived. Geologically this is consistent with a transition from folding to faulting, as observed in fold-thrust belts. Folding, a distributed deformation scaling as Wi-1, is found to be energetically favored at non-dimensional wavelengths ranging from about three to seven. Furthermore, the transition from folding to faulting, a localized deformation scaling as ( αWi) -1, is predicted at a non-dimensional wavelength of about seven. These findings are consistent with measurements of thrust sheets in the Sawtooth Mountains of western Montana, USA and other fold-thrust belts. A review of the literature reveals a similar distribution of non-dimensional wavelengths spanning a wide range of observational scales in compressional deformation. Specific examples include lithospheric scale folding in the central Indian Basin and microscopic scale failure of ice columns between splay microcracks in laboratory studies.

JPRS Report, Soviet Union, Aviation and Cosmonautics, No. 7, July 1987.

DTIC Science & Technology

1988-01-14

CONTENTS u JANUARY ms Improvement in Elements of Combat Potential Traced [I. Sviridov] 1 More Realistic Pilot Training Under Mountain Conditions Urged...training commenced. The arriv- ing Soviet aviators became familiar with a new flight area for them and improved their skills in mountain flights...withstand the thrust of the units of the Edelweiss Division which had been specially trained for fighting in mountain areas. But they firmly

Late Oligocene to present contractional structure in and around the Susitna basin, Alaska—Geophysical evidence and geological implications

USGS Publications Warehouse

Saltus, Richard W.; Stanley, Richard G.; Haeussler, Peter J.; Jones, James V.; Potter, Christopher J.; Lewis, Kristen A.

2016-01-01

The Cenozoic Susitna basin lies within an enigmatic lowland surrounded by the Central Alaska Range, Western Alaska Range (including the Tordrillo Mountains), and Talkeetna Mountains in south-central Alaska. Some previous interpretations show normal faults as the defining structures of the basin (e.g., Kirschner, 1994). However, analysis of new and existing geophysical data shows predominantly (Late Oligocene to present) thrust and reverse fault geometries in the region, as previously proposed by Hackett (1978). A key example is the Beluga Mountain fault where a 50-mGal gravity gradient, caused by the density transition from the igneous bedrock of Beluga Mountain to the >4-km-thick Cenozoic sedimentary section of Susitna basin, spans a horizontal distance of ∼40 km and straddles the topographic front. The location and shape of the gravity gradient preclude a normal fault geometry; instead, it is best explained by a southwest-dipping thrust fault, with its leading edge located several kilometers to the northeast of the mountain front, concealed beneath the shallow glacial and fluvial cover deposits. Similar contractional fault relationships are observed for other basin-bounding and regional faults as well. Contractional structures are consistent with a regional shortening strain field inferred from differential offsets on the Denali and Castle Mountain right-lateral strike-slip fault systems.

Prograde evolution of the Scottish Caledonides and tectonic implications

NASA Astrophysics Data System (ADS)

Ashley, Kyle T.; Thigpen, J. Ryan; Law, Richard D.

2015-05-01

Recent thermometric analyses of samples collected in thrust-parallel structural transects across the Scandian (435-415 Ma) orogenic wedge in northwest Scotland provide a comprehensive characterization of the synorogenic retro-wedge thermal architecture. However, the paucity of petrologically-important metamorphic mineral phases (e.g., staurolite, Al-silicates) has limited investigation of pressure-temperature (P-T) histories, which hinders our ability to examine the nature of orogen-scale kinematic and thermal coupling. New data collected along a foreland-to-hinterland transect from the Moine to the Naver thrust sheets provides additional constraints for characterizing the prograde metamorphic evolution. In addition, we characterized Ti diffusion profiles in quartz inclusions in garnet to constrain duration of metamorphic heating. These results are used to develop coupled kinematic-thermal models of Scandian orogenic evolution. Early garnet core growth conditions are constrained by isopleth intersections, with peak P-T estimates determined by conventional exchange and net transfer thermobarometry and thermodynamic calculations. Most samples follow normal prograde heating and burial profiles, with peak conditions of 450 °C and 5.0 kbar in the immediate hanging wall to the Moine thrust, increasing in temperature and pressure to 733 °C and 9.5 kbar in the immediate hanging wall to the Naver thrust. These normal prograde pressure trajectories are interpreted to reflect burial of incipient thrust sheets beneath the overriding wedge at the leading edge of the orogen. Prograde heating coeval with burial is interpreted to result from surface-directed isotherm perturbation due to thrust-related advection in the overriding wedge. One exception to this is a sample from the top of the Moine thrust sheet, where prograde heating occurs during decompression (540 °C and 8.1 kbar to 590 °C and 7.0 kbar). In this case, the short lag times between motion on the Moine and Ben Hope thrusts may have limited advectionary heating until after exhumation associated with motion on the underlying Moine thrust was underway. Ti diffusion profiles in quartz inclusions in garnet suggest the near-peak thermal evolution of these rocks occurred over very short time scales (< 200,000 years). While most of the garnets are inferred to be Scandian in age, we document evidence for pre-Scandian garnet cores in structurally higher (more hinterland positioned) samples that must have grown under higher temperatures. In the hanging wall of the Moine thrust, high grossular garnets with estimated formation conditions > 9 kbar are probably of detrital origin.

Numerical modeling of fold-and-thrust belts: Applications to Kuqa foreland fold belt, China

NASA Astrophysics Data System (ADS)

Yin, H.; Morgan, J. K.; Zhang, J.; Wang, Z.

2009-12-01

We constructed discrete element models to simulate the evolution of fold-and-thrust belts. The impact of rock competence and decollement strength on the geometric pattern and deformation mechanics of fold-and-thrust belts has been investigated. The models reproduced some characteristic features of fold-and-thrust belts, such as faulted detachment folds, pop-ups, far-traveled thrust sheets, passive-roof duplexes, and back thrusts. In general, deformation propagates farther above a weak decollement than above a strong decollement. Our model results confirm that fold-and-thrust belts with strong frictional decollements develop relatively steep and narrow wedges formed by closely spaced imbricate thrust slices, whereas fold belts with weak decollements form wide low-taper wedges composed of faulted detachment folds, pop-ups, and back thrusts. Far-traveled thrust sheets and passive-roof duplexes are observed in the model with a strong lower decollement and a weak upper detachment. Model results also indicate that the thickness of the weak layer is critical. If it is thick enough, it acts as a ductile layer that is able to flow under differential stress, which helps to partition deformation above and below it. The discrete element modeling results were used to interpret the evolution of Kuqa Cenozoic fold-and-thrust belt along northern Tarim basin, China. Seismic and well data show that the widely distributed Paleogene rock salt has a significant impact on the deformation in this area. Structures beneath salt are closely spaced imbricate thrust and passive-roof duplex systems. Deformation above salt propagates much farther than below the salt. Faults above salt are relatively wide spaced. A huge controversy over the Kuqa fold-and-thrust belt is whether it is thin-skinned or thick-skinned. With the insights from DEM results, we suggest that Kuqa structures are mostly thin-skinned with Paleogene salt as decollement, except for the rear part near the backstop, where the faults below the salt are thick-skinned and involve the Paleozoic basement. We think that most basement-involved sub-salt faults, if not all, formed later than the above salt-detached thin-skinned structures.

Geologic Map of the Eastern Three-Quarters of the Cuyama 30' x 60' Quadrangle, California

USGS Publications Warehouse

Kellogg, Karl S.; Minor, Scott A.; Cossette, Pamela M.

2008-01-01

The map area encompasses a large part of the western Transverse Ranges and southern Coast Ranges of southern California. The San Andreas fault (SAF) cuts the northern part of the map. The area south of the SAF, about 80 percent of the map area, encompasses several distinct tectonic blocks bounded by major thrust or reverse faults, including the Santa Ynez fault, Big Pine fault (and structurally continuous Pine Mountain fault), Tule Creek fault, Nacimiento fault, Ozena fault, Munson Creek fault, Morales fault, and Frazier Mountain Thrust System. Movement on these faults is as old as Miocene and some faults may still be active. In addition, the Paleocene Sawmill Mountain Thrust south of the SAF and the Pastoria Thrust north of the SAF place Cretaceous and older crystalline rocks above Pelona Schist (south of the SAF) and Rand Schist (north of the SAF). South of the SAF, each tectonic block contains a unique stratigraphy, reflecting either large-scale movement on bounding faults or different depositional environments within each block. On Mount Pinos and Frazier Mountain, intrusive and metamorphic rocks as old as Mesoproterozoic, but including voluminous Cretaceous granitoid rocks, underlie or are thrust above non-marine sedimentary rocks as old as Miocene. Elsewhere, marine and non-marine sedimentary rocks are as old as Cretaceous, dominated by thick sequences of both Eocene and Cretaceous marine shales and sandstones. Middle Miocene to early Oligocene volcanic rocks crop out in the Caliente Hills (part of Caliente Formation) and south of Mount Pinos (part of the Plush Ranch Formation). Fault-bounded windows of Jurassic Franciscan Complex ophiolitic rocks are evident in the southwest corner of the area. North of the SAF, marine and non-marine sedimentary rocks as old as Eocene and Miocene volcanic rocks overlie a crystalline basement complex. Basement rocks include Cretaceous intrusive rocks that range from monzogranite to diorite, and Jurassic to late Paleozoic intrusive and metamorphic rocks. The Jurassic to late Paleozoic intrusive rocks include diorite, gabbro, and ultramafic rocks, and the metasedimentary rocks include marble, quartzite, schist, and gneiss.

Flower-strucutre deformation pattern of theTian Shan mountains as revealed by Late Quaternary geological and modern Geodesy slip rates

NASA Astrophysics Data System (ADS)

Wu, C.; Zhang, P.; Zheng, W.; Wang, H.; Zhang, Z.; Ren, Z.; Zheng, D.; Yu, J.; Wu, G.

2017-12-01

The deformation pattern and strain distribution of the Tian Shan is a hot issue.Previous studies mainly focus on the thrust-fold systems on both sides of Tian Shan, the strike-slip faults within the mountains are rarely reported. The understanding about the deformation characteristics of Tian Shan is not complete for lacking information of these strike-slip faults.Our studies show the NEE trending structures of Maidan fault and Nalati fault in the southwestern Tian Shan are all active during the Holence. These faults are characterized by sinistral strike-slip and thrust movement. The minimum average sinistral strike-slip rate of the Maidan fault is 1.07 ± 0.13 mm/yr. During the late Quaternary, the average shortening rate and sinistral strike-slip rate of the Nalati fault are 2.1 ±0.4 mm/yr and 2.56 ±0.25 mm/yr, respectively . In the interior of the Tian Shan area, two groups of strike-slip faults were developed. The NEE trending faults with sinistral strike-slipmovement, and the NWW trending faults with dextral strike-slip movement show the shape of "X"in geometrical structure. The piedmont thrust faults and the thrust strike-slip faults in the interior mountain constitute the tectonic framework of Tian Shan. Threegroups of active fault systems are the main seismogenic and geological structures, which control the current tectonic deformation pattern of Tian Shan (Figure 1). GPS observation data also showthe similar deformation characteristics with the geological results (Figures 2, 3). In addition to the crustal shortening, there is a certain strike-slip shear movement in the interior of the Tian Shan.The strike-slip rate defined by the geological and GPS data is approximately consistent with each other near the same longitude. We suggest the two groups of strike-slip faults in the interior of mountains is a set of conjugate structures. The whole Tian Shan forms a large flower-structure in a profile view. The complete tectonic deformation of the Tian Shan mountains consists ofthe shortening deformationof the N-S direction and the lateral extrusion of the E-W direction (Figure 2). The late Cenozoic deformation of the Tian Shan mountains is due to the northward subduction of Tarim Block. Although the activedeformation of the Tian Shan decrease eastward, the geological sturcutrein eastern Tian Shan is similar.

Along-strike variations of structural styles in the imbricated Molasse of Salzburg and Upper Austria: a 3-D seismic perspective

NASA Astrophysics Data System (ADS)

Hinsch, Ralph; Linzer, Hans-Gert

2010-05-01

At the southern border of the Northern Alpine Foreland Basin syntectonic deposits (Molasse Sediments) are partly incorporated into Alpine contractional deformation. Along the alpine chain style and timing of this deformation varies significantly. In this study we use one of the largest European on-shore 3-D seismic datasets, spanning the Molasse basin of Upper Austria and Salzburg states, to investigate the along-strike structural architecture of the alpine deformation front. In the Austrian Part of the Molasse basin, foredeep sedimentation started in Upper-Eocene times (Wagner, 1996). The sediments cover the European margin, consisting of a crystalline basement covered by variously thick Mesozoic sediments (Nachtmann und Wagner, 1987). In Oligocene to Lower Miocene times, syntectonic foredeep sedimentation took place in a deep marine environment, comprising an axial channel system (Linzer 2001, DeRuig and Hubbard, 2006). Parts of these syntectonic sediments are subsequently affected by the advancing thrust wedge. Within the study area, three distinct fold-and-thrust belt segments of different structural architecture can be defined. 1) The Perwang Imbricates are a promontory mostly situated in Salzburg at the border to Germany. Complexly deformed small thrust sheets evolve above a detachment horizon situated in Late Cretaceous shaly marls in Oligocene times. Syntectonic piggy-back and thrust top basins evolve (Covault et al. 2008), which are partly affected by subsequent Miocene overthrusting. 2) The Regau Segment is the area west of the Perwang lobe. It is dominated by few number of thrust sheets in the Molasse sediments. Instead, over-thrusting by the alpine wedge (pre-deformed Flysch and Helvetic thrust sheets) dominates. 3) The Sierning Imbricates segment is located further to the east, at the border of Upper Austria to Lower Austria. The structural inventory of this thrust belt is comprises varying numbers of thrust sheets along strike (1-5), ramp-flat-ramp geometries, tear faults as well as belt-parallel strike-slip faults. The differences in structural style along strike are interpreted to be caused by pre-deformational conditions (sediment thickness and distribution of potential decollement horizons) and varying tectonic pulses. Covault, J.A., Hubbard, S.M., Graham, S.A., Hinsch, R. and Linzer, H., 2008, Turbidite-reservoir architecture in complex foredeep-margin and wedge-top depocenters, Tertiary Molasse foreland basin system, Austria, Marine and Petroleum Geology, V26/3, 379-396 De Ruig, M. J., and Hubbard, S. M., 2006. Seismic facies and reservoir characteristics of a deep marine channel belt in the Molasse foreland basin. AAPG Bulletin, v. 90, p. 735-752 Linzer, H.-G., 2001, Cyclic channel systems in the Molasse foreland basin of the Eastern Alps- the effects of Late Oligocene foreland thrusting and Early Miocene lateral escape. AAPG Bulletin, 85, 118. Nachtmann, W., Wagner, L., 1987.Mesozoic and Early Tertiary evolution of the Alpine Foreland in Upper Austria and Salzburg, Austria. Tectonophysics, 137, 61-76 Wagner, L. R., 1996. Stratigraphy and hydrocarbons in the Upper Austrian Molasse Foredeep (active margin). In:Wessely, G., Liebl, W. (Eds.), Oil and Gas in Alpidic Thrustbelts and Basins of Central and Eastern Europe. EAGE Special Pub. 5, pp. 217-235.

Thrust Belt Architecture of the Central and Southern Western Foothills of Taiwan

NASA Astrophysics Data System (ADS)

Rodriguez, F.; Wiltschko, D.

2006-12-01

A structural model of the central and southern Western Foothills Fold and Thrust Belt (WFFTB) was constructed from serial balanced cross sections using available surface, drill, seismic and thermochronologic data. The WFFTB is composed of four main thrust sheets with minor splays. On the east, the Tulungwan fault, which separates the sedimentary rocks of the WFFTB from the low grade meta-sediments of the Slate Belt, evolves from a basement cored fold in the north (around 24°10' N) where the conformable contact between foothills sediments and meta-sediments from the Slate Belt on its western flank is present. At this point the tip of the fault is below the unconformity and the displacement amount is small. To the south this fault breaks the back limb of the fold and gains displacement, and continues gaining displacement to the south. The next thrust sheet to the west includes the Schuantung, Fenghuangchan, Luku, Tatou, Hopiya, and Pingchi faults. This fault system is interpreted as characterized by a long flat with small ramps along a Miocene detachment, not a series of imbricates, as it has been interpreted before. The next thrust sheet to the west is the Chulungupu-Chukou-Lunhou, this system appears to gain displacement to the south as the Schuantung fault system decreases in amount of displacement. The Chulungpu-Chukou-Lunhou fault system contains a wide monocline in the central foothills related with the Chulungpu fault and two wide synclines in the southern part, the Yuching and Tinpligling synclines. Modeling of these two last structures shows that both are uplifted with respect to the regional level above a wide and flat feature; the footwall of the Lunhou fault is a monocline. A geometric solution to lift the Lunhou system involves a major fault-bend-fold anticline with a long ramp and a detachment at ~13 km of depth. It explains, 1) the frontal monocline, which is the from limb of this fault-bend- fold, 2) the minor structures associated with minor back-thrusts and wedging, and 3) the uplift of the structures above the regional level over a wide anticlinal crest. The last thrust system toward the west shows a series of structures which closely associated with the Peikang high implying that the structures are either inversion structures or new thrust faults whose ramps are located in pre-existing normal faults.

Fold-to-fault progression of a major thrust zone revealed in horses of the North Mountain fault zone, Virginia and West Virginia, USA

USGS Publications Warehouse

Orndorff, Randall C.

2012-01-01

The method of emplacement and sequential deformation of major thrust zones may be deciphered by detailed geologic mapping of these important structures. Thrust fault zones may have added complexity when horse blocks are contained within them. However, these horses can be an important indicator of the fault development holding information on fault-propagation folding or fold-to-fault progression. The North Mountain fault zone of the Central Appalachians, USA, was studied in order to better understand the relationships of horse blocks to hanging wall and footwall structures. The North Mountain fault zone in northwestern Virginia and eastern panhandle of West Virginia is the Late Mississippian to Permian Alleghanian structure that developed after regional-scale folding. Evidence for this deformation sequence is a consistent progression of right-side up to overturned strata in horses within the fault zone. Rocks on the southeast side (hinterland) of the zone are almost exclusively right-side up, whereas rocks on the northwest side (foreland) of the zone are almost exclusively overturned. This suggests that the fault zone developed along the overturned southeast limb of a syncline to the northwest and the adjacent upright limb of a faulted anticline to the southeast.

Origin of a major cross-element zone: Moroccan Rif

NASA Astrophysics Data System (ADS)

Morley, C. K.

1987-08-01

Alpine age (Oligocene-Miocene) deformation in the western Mediterranean formed the Rif mountain belt of northern Morocco. A linear east-northeast-west-southwest trend of cross elements from Jebah (Mediterranean coast) to Arbaoua (near the Atlantic coast) extends through several thrust sheets in the western Rif. The cross elements are manifest as a lateral ramp, the northern limit of a large culmination, and they affect syntectonic turbidite sandstone distribution. Gravity anomalies indicate that the cross-element zone is coincident with a transition zone from normal thickness to thinner continental crust. It is suggested that an early Mesozoic strike-slip fault system related to rifting of North America from North Africa caused a strong east-northeast-west-southwest, basement block-fault trend to form on the normal thickness side of the thick-to-thin continental crustal transition zone. This trend later influenced the position of the Alpine age cross-element zone that traverses several different Mesozoic and Tertiary basins, inverted during the Alpine deformation.

Origin of a major cross-element zone: Moroccan Rif

DOE Office of Scientific and Technical Information (OSTI.GOV)

Morley, C.K.

1987-08-01

Alpine age (Oligocene-Miocene) deformation in the western Mediterranean formed the Rif mountain belt of northern Morocco. A linear east-northeast-west-southwest trend of cross elements from Jebah (Mediterranean coast) to Arbaoua (near the Atlantic coast) extends through several thrust sheets in the western Rif. The cross elements are manifest as a lateral ramp, the northern limit of a large culmination, and they affect syntectonic turbidite sandstone distribution. Gravity anomalies indicate that the cross-element zone is coincident with a transition zone from normal thickness to thinner continental crust. It is suggested that an early Mesozoic strike-slip fault system related to rifting of Northmore » America from North Africa caused a strong east-northeast-west-southwest, basement block-fault trend to form on the normal thickness side of the thick-to-thin continental crustal transition zone. This trend later influenced the position of the Alpine age cross-element zone that traverses several different Mesozoic and Tertiary basins, inverted during the Alpine deformation.« less

Interseismic Strain Accumulation Across Metropolitan Los Angeles: Puente Hills Thrust

NASA Astrophysics Data System (ADS)

Argus, D.; Liu, Z.; Heflin, M. B.; Moore, A. W.; Owen, S. E.; Lundgren, P.; Drake, V. G.; Rodriguez, I. I.

2012-12-01

Twelve years of observation of the Southern California Integrated GPS Network (SCIGN) are tightly constraining the distribution of shortening across metropolitan Los Angeles, providing information on strain accumulation across blind thrust faults. Synthetic Aperture Radar Interferometry (InSAR) and water well records are allowing the effects of water and oil management to be distinguished. The Mojave segment of the San Andreas fault is at a 25° angle to Pacific-North America plate motion. GPS shows that NNE-SSW shortening due to this big restraining bend is fastest not immediately south of the San Andreas fault across the San Gabriel mountains, but rather 50 km south of the fault in northern metropolitan Los Angeles. The GPS results we quote next are for a NNE profile through downtown Los Angeles. Just 2 mm/yr of shortening is being taken up across the San Gabriel mountains, 40 km wide (0.05 micro strain/yr); 4 mm/yr of shortening is being taken up between the Sierra Madre fault, at the southern front of the San Gabriel mountains, and South Central Los Angeles, also 40 km wide (0.10 micro strain/yr). We find shortening to be more evenly distributed across metropolitan Los Angeles than we found before [Argus et al. 2005], though within the 95% confidence limits. An elastic models of interseismic strain accumulation is fit to the GPS observations using the Back Slip model of Savage [1983]. Rheology differences between crystalline basement and sedimentary basin rocks are incorporated using the EDGRN/EDCMP algorithm of Wang et al. [2003]. We attempt to place the Back Slip model into the context of the Elastic Subducting Plate Model of Kanda and Simons [2010]. We find, along the NNE profile through downtown, that: (1) The deep Sierra Madre Thrust cannot be slipping faster than 2 mm/yr, and (2) The Puente Hills Thrust and nearby thrust faults (such as the upper Elysian Park Thrust) are slipping at 9 ±2 mm/yr beneath a locking depth of 12 ±5 km (95% confidence limits). Incorporating sedimentary basin rock either reduces the slip rate by 10 per cent or increases the locking rate by 20 per cent. The 9 mm/yr rate for the Puente Hills Thrust and nearby faults exceeds the cumulative 3-5 mm/yr rate estimated using paleoseismology along the Puente Hills Thrust (1.2-1.6 mm/yr, Dolan et al. 2003), upper Elysian Park Thrust (0.6-2.2 mm/yr, Oskin et al. 2000), and western Compton Thrust (1.2 mm/yr, Leon et al. 2009], though all the paleoseismic estimates are minimums. We infer that M 7 earthquakes in northern metropolitan Los Angeles may occur more frequently that previously thought.

Geochemistry and field geology of shoshonitic magmas in the Late Cretaceous foreland fold and thrust belt of southwestern Montana: Results from the North Doherty Mountain Intrusive Complex

NASA Astrophysics Data System (ADS)

Beranek, L. P.; Burton, B. R.; Ihinger, P. D.

2002-12-01

The North Doherty Mountain Intrusive Complex (NDMIC) is one of several satellite plutons related to the areally extensive Boulder batholith of southwestern Montana. The Boulder batholith comprises multiple plutons and intrusive phases, and the magmatism has long been thought to be the result of subduction due to its calc-alkaline granodioritic composition. The batholith is situated in the Helena salient, which differs from other parts of the North American Cordilleran foreland because there, magmatism spatially and temporally overlaps with deformation in the foreland fold and thrust belt. The North Doherty Mountain Intrusive Complex (NDMIC) is one of several satellite plutons related to the Boulder batholith and represents an ideal microcosm of the batholith for petrogenetic and structural studies because it exposes both mafic and felsic units and was emplaced in the limb of a major thrust related fold. We present new geologic mapping and detailed trace element geochemical analyses to show that the entire mafic-to-felsic suite of rocks in the NDMIC are cogenetic and shoshonitic in character. Shoshonites are unusual magmas that are distinguished by their high concentrations of K, Rb, Sr, Ba, Zr, and Th contents, and are thought to represent partial melting at great depths within the mantle wedge above a subducting slab. The presence of shoshonitic magma in the Cordilleran foreland fold and thrust belt provides important clues into the nature of the formation of this unusual magma type and can provide insights into our understanding of magmatism in foreland structural settings.

Geology of the Northern Part of the Harcuvar Complex, West-Central Arizona

USGS Publications Warehouse

Bryant, Bruce; Wooden, J.L.

2008-01-01

In west-central Arizona near the northeast margin of the Basin and Range Province, the Rawhide detachment fault separates Tertiary and older rocks lacking significant effects of Tertiary metamorphism from Precambrian, Paleozoic, and Mesozoic rocks in the Harcuvar metamorphic core complex below. Much of the northern part of the Harcuvar complex in the Buckskin and eastern Harcuvar Mountains is layered granitic gneiss, biotite gneiss, amphibolite, and minor pelitic schist that was probably deformed and metamorphosed in Early Proterozoic time. In the eastern Buckskin Mountains, Early and Middle Proterozoic plutons having U-Pb zircon ages of 1,683?6.4 mega-annum (Ma) and 1,388?2.3 Ma, respectively, intruded the layered gneiss. Small plutons of alkaline gabbro and diorite intruded in Late Jurassic time. A sample of mylonitized diorite from this unit has a U-Pb zircon age of 149?2.8 Ma. In the Early Cretaceous, amphibolite facies regional metamorphism was accompanied by partial melting and formation of migmatite. Zircon from a granitic layer in migmatitic gneiss in the eastern Harcuvar Mountains has a U-Pb age of 110?3.7 Ma. In the Late Cretaceous, sills and plutons of the granite of Tank Pass were emplaced in both the Buckskin and eastern Harcuvar Mountains. In the Buckskin Mountains those intrusions are locally numerous enough to form an injection migmatite. A pluton of this granite crops out over almost half the area of the eastern Harcuvar Mountains. Paleozoic and Mesozoic sedimentary rocks were caught as slices along south-vergent Cretaceous thrusts related to the Maria fold and thrust belt and were metamorphosed beneath a thick sheet of Proterozoic crustal rocks. Inception of volcanism and basin formation in upper-plate rocks indicates that regional extension started at about 26 Ma, in late Oligocene. The Swansea Plutonic Suite, composed of rocks ranging from gabbro to granite, intruded the lower-plate rocks in the Miocene and Oligocene(?). Granite and a gabbro from the suite have a U-Pb zircon age of 21.86?0.60 Ma. Previously published 40Ar/39Ar ages of hornblende suggest that some of the Swansea Suite is Oligocene. The felsic rocks contain numerous inclusions ranging from porphyritic granite to porphyritic granodiorite. A sample from one inclusion has a U-Pb zircon age of 1,409?6.3 Ma. A discordia line for the U-Pb zircon data from the Swansea Plutonic Suite has an upper intercept at 1,408?3.4 Ma. The Swansea Plutonic Suite probably formed by interaction between mantle material and plutonic rocks at least as old as Middle Proterozoic. An irregular layer in the middle crust, which is thickest under and adjacent to the Buckskin Mountains, may be the level where that interaction took place. During extensional deformation these rocks and all the older rocks were displaced southwest from beneath the rocks of the Colorado Plateau transition zone below an area extending 50?80 kilometers northeast of the Buckskin Mountains as far as Bagdad, Arizona, or beyond. At that time the rocks were variably mylonitized, and a northeast-trending lineation formed. Much of the evidence for the complex sequence of structural events preserved in these rocks in the western Harcuvar Mountains has been obliterated in the northern Harcuvar complex by Miocene deformation.

Integrating seismic reflection and geological data and interpretations across an internal basement massif: The southern Appalachian Pine Mountain window, USA

USGS Publications Warehouse

McBride, J.H.; Hatcher, R.D.; Stephenson, W.J.; Hooper, R.J.

2005-01-01

The southern Appalachian Pine Mountain window exposes 1.1 Ga Grenvillian basement and its metasedimentary Paleozoic(?) cover through the allochthonous Inner Piedmont. The issue of whether the crustal block inside the window was either transported above the master Appalachian (late Alleghanian) de??collement or is an autochthonous block that was overridden by the de??collement has been debated for some time. New detrital zircon geochronologic data from the cover rocks inside the window suggest this crustal block was derived from Gondwana but docked with Laurentia before the Alleghanian event. Reprocessed deep seismic reflection data from west-central Georgia (pre- and poststack noise reduction, amplitude variation analysis, and prestack depth migration) indicate that a significant band of subhorizontal reflections occurs almost continuously beneath the window collinear with the originally recognized de??collement reflections north of the window. A marked variation in the de??collement image, from strong and coherent north of the window to more diffuse directly beneath the window, is likely a partial consequence of the different geology between the Inner Piedmont and the window. The more diffuse image beneath the window may also result from imaging problems related to changes in topography and fold of cover (i.e., signal-to-noise ratio). Two alternative tectonic models for the Pine Mountain window can partially account for the observed variation in the de??collement reflectivity. (1) The Pine Mountain block could be truncated below by a relatively smooth continuation of the de??collement. The window would thus expose an allochthonous basement duplex or horse-block thrust upward from the south along the Late Proterozoic rifted continental margin. (2) The window represents localized exhumation of autochthonous basement and cover along a zone of distributed intrabasement shearing directly beneath the window. Either model is viable if only reflector geometry is considered; model (1) is favored if both geometry and kinematics of Blue Ridge-Piedmont thrust sheet emplacement are incorporated. In either model, the southern margin of the window merges to the west with the Iapetan early Alleghanian Central Piedmont suture, which juxtaposes North American-affinity Piedmont rocks to the north and exotic Panafrican rocks of the Carolina (Avalon) terrane to the south. Immediately south of the window, this suture dips southward and merges in the lower crust with the late Alleghanian suture joining the Appalachians with Gondwana. ?? 2005 Geological Society of America.

Structural analysis using thrust-fault hanging-wall sequence diagrams: Ogden duplex, Wasatch Range, Utah

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schirmer, T.W.

1988-05-01

Detailed mapping and cross-section traverses provide the control for structural analysis and geometric modeling of the Ogden duplex, a complex thrust system exposed in the Wasatch Mountains, east of Ogden, Utah. The structures consist of east-dipping folded thrust faults, basement-cored horses, lateral ramps and folds, and tear faults. The sequence of thrusting determined by means of lateral overlap of horses, thrust-splay relationships, and a top-to-bottom piggyback development is Willard thrust, Ogden thrust, Weber thrust, and Taylor thrust. Major decollement zones occur in the Cambrian shales and limestones. The Tintic Quartzite is the marker for determining gross geometries of horses. Thismore » exposed duplex serves as a good model to illustrate the method of constructing a hanging-wall sequence diagram - a series of longitudinal cross sections that move forward in time and space, and show how a thrust system formed as it moved updip over various footwall ramps. A hanging wall sequence diagram also shows the complex lateral variations in a thrust system and helps to locate lateral ramps, lateral folds, tear faults, and other features not shown on dip-oriented cross sections. 8 figures.« less

Significance of the precambrian basement and late Cretaceous thrust nappes on the location of tertiary ore deposits in the Oquirrh Mountains, Utah

USGS Publications Warehouse

Tooker, Edwin W.

2005-01-01

The Oquirrh Mountains are located in north central Utah, in the easternmost part of the Basin and Range physiographic province, immediately south of the Great Salt Lake. The range consists of a northerly trending alignment of peaks 56 km long. Tooele and Rush Valleys flank the Oquirrh Mountains on the western side and Salt Lake and Cedar Valleys lie on the eastern side. The world class Bingham mine in the central part of the range hosts disseminated copper-bearing porphyry, skarn, base-and precious-metal vein and replacement ore deposits. The district includes the outlying Barneys Canyon disseminated-gold deposits. Disseminated gold in the Mercur mining district in the southern part of the range has become exhausted. The Ophir and Stockton base- and precious-metal mining districts in the range north of Mercur also are inactive. A geologic map of the range (Tooker and Roberts, 1998), available at a scale of 1:50,000, is a summation of U.S. Geological Survey (USGS) studies. Information about the range and its mining areas is scattered. This report summarizes map locations, new stratigraphic and structural data, and reexamined data from an extensive published record. Unresolved controversial geological interpretations are considered, and, for the first time, the complete geological evidence provides a consistent regional basis for the location of the ore deposits in the range. The geological setting and the siting of mineral deposits in the Oquirrh Mountains began with the formation of a Precambrian craton. Exposures of folded Proterozoic basement rocks of the craton, in the Wasatch Mountains east of Salt Lake City, were accreted and folded onto an Archean crystalline rock terrane. The accretion suture lies along the north flank of the Uinta Mountains. The western part of the accreted block was offset to northern Utah along a north-trending fault lying approximately along the Wasatch Front (Nelson and others, 2002), thereby creating a prominant basement barrier or buttress east of the Salt Lake area. The accretion suture along the north flank of the Uinta Anticline overlaps an earlier Precambrian east-west mobile zone, the Uinta trend (Erickson, 1976, Bryant and Nichols, 1988 and John, 1989), which extends westward across western Utah and into Nevada. A trace of the trend underlies the middle part of the Oquirrh Mountains. Its structure is recognized by disrupted Paleozoic stratigraphic units and fold and fault evidence of thrust faulting, intermittent local uplift and erosion, the alignment of Tertiary intrusives and associated ore deposits. Geologic readjustments along the trend continued intermittently through the Paleozoic, Cenozoic, Tertiary, and the development of clastic deposits along the shores of Pleistocene Lake Bonneville. Paleozoic sedimentary rocks were deposited on the craton platform shelf in westernmost Utah and eastern Nevada as the shelf subsided gradually and differentially. Debris was shed into two basins separated by the uplifted Uinta trend, the Oquirrh Basin on the south and Sublette Basin on the north. Sediments were derived from the craton to the east, the Antler orogenic zone on the west (Roberts, 1964), and locally from uplifted parts of the trend itself. Thick accumulations of clastic calcareous quartzite, shale, limestone, and dolomite of Lower and Upper Paleozoic ages are now exposed in the Oquirrh Mountains, the result of thrust faults. Evidence of decollement thrust faults in in the Wasatch Mountains during the Late Cretaceous Sevier orogeny, recognized by Baker and others (1949) and Crittenden (1961, is also recognized in the Oquirrh Mountains by Roberts and others (1965). During the late Cretaceous Sevier Orogeny, nappes were thrust sequentially along different paths from their western hinterland to the foreland. Five distinct nappes converged over the Uinta trend onto an uplifted west-plunging basement buttress east of the Oquirrh Mountains area: the Pass Canyon, Bingham,

Water, energy, and biogeochemical budgets investigation at Panola Mountain research watershed, Stockbridge, Georgia; a research plan

USGS Publications Warehouse

Huntington, T.G.; Hooper, R.P.; Peters, N.E.; Bullen, T.D.; Kendall, Carol

1993-01-01

The Panola Mountain Research Watershed (PMRW), located in the Panola Mountain State Conservation Park near Stockbridge, Georgia has been selected as a core research watershed under the Water, Energy and Biogeochemical Budgets (WEBB) research initiative of the U.S. Geological Survey (USGS) Global Climate Change Program. This research plan describes ongoing and planned research activities at PMRW from 1984 to 1994. Since 1984, PMRW has been studied as a geochemical process research site under the U.S. Acid Precipitation Thrust Program. Research conducted under this Thrust Program focused on the estimation of dry atmospheric deposition, short-term temporal variability of streamwater chemistry, sulfate adsorption characteristics of the soils, groundwater chemistry, throughfall chemistry, and streamwater quality. The Acid Precipitation Thrust Program continues (1993) to support data collection and a water-quality laboratory. Proposed research to be supported by the WEBB program is organized in 3 interrelated categories: streamflow generation and water-quality evolution, weathering and geochemical evolution, and regulation of soil-water chemistry. Proposed research on streamflow generation and water-quality evolution will focus on subsurface water movement, its influence in streamflow generation, and the associated chemical changes of the water that take place along its flowpath. Proposed research on weathering and geochemical evolution will identify the sources of cations observed in the streamwater at Panola Mountain and quantify the changes in cation source during storms. Proposed research on regulation of soil-water chemistry will focus on the poorly understood processes that regulate soil-water and groundwater chemistry. (USGS)

Distribution of garnet grain sizes and morphologies across the Moine Supergroup, northern Scottish Caledonides

NASA Astrophysics Data System (ADS)

Ashley, Kyle T.; Thigpen, J. Ryan; Law, Richard D.

2016-04-01

Garnet is used in a wide range of geologic studies due to its important physical and chemical characteristics. While the mineral is useful for thermobarometry and geochronology constraints and can often be correlated to deformation and fabric development, difficulties remain in making meaningful interpretations of such data. In this study, we characterize garnet grain sizes and crystal morphologies from 141 garnet-bearing metasedimentary rock samples collected from the northern part of the Moine Supergroup in the Scottish Caledonides. Larger, euhedral crystals are indicative of prograde metamorphic growth and are typically associated with the most recent phase of orogenesis (Scandian, ˜430 Ma). Small, rounded ("pin-head") garnets are interpreted as detrital in origin. A subhedral classification is more subjective and is used when garnets contains portions of straight boundaries but have rounded edges or rims that have been altered through retrograde metamorphic reactions. From our collection, 88 samples contain anhedral garnets (maximum measured grain size d = 0.46 ± 0.21 mm), 34 bear subhedral garnets (d = 2.0 ± 1.0 mm), and the remaining 19 samples contain garnets with euhedral grains (d = 4.4 ± 2.6 mm). Plotting the distribution of garnets relative to the mapped thrust contacts reveals an abrupt change in morphology and grain size when traced from the Moine thrust sheet across the Ben Hope and Sgurr Beag thrusts into the higher-grade, more hinterland-positioned thrust sheets. The dominance of anhedral garnets in the Moine thrust sheet suggests that these grains should not be used for peak P - T estimation associated with relatively low temperature (<500 ° C) Scandian metamorphism, as they are likely detrital in origin and contain protolith chemical signatures that would not have been reset due to sluggish diffusivities at greenschist facies temperatures. However, chemical and isotopic data from these grains may provide information into the provenance of these metasediments. A thermal/chemical break must occur at the Ben Hope thrust, because hanging wall garnets contain euhedral (Scandian?) rims that are distinct from the garnet grains observed in the underlying Moine thrust sheet. In addition to morphology, the propensity of garnet to include minerals during growth makes it a useful phase for obtaining a historical perspective on growth conditions. The distribution and chemistries of minerals included/encapsulated by garnet was studied for various samples to gain insight into metamorphic evolution and to distinguish garnets that likely contain multiple generations of growth. Although our results are specific to the Caledonides of northern Scotland, this work highlights the general necessity of a comprehensive petrographic assessment of garnet grains in advance of interpreting large suits of garnet-derived thermodynamic and geochronologic data.

SHEEP MOUNTAIN WILDERNESS STUDY AREA, WYOMING.

USGS Publications Warehouse

Houston, Robert S.; Patten, Lowell L.

1984-01-01

On the basis of a mineral survey the Sheep Mountain Wilderness study area in Wyoming was determined to offer little promise for metallic mineral resources. There is a probable potential for oil and gas resources in a small part of the study area along its northeast margin. Geophysical studies, such as reflection seismic profiling would help define the oil and gas potential in fault-controlled structures, such as those beneath the thrust fault that crops out along the east flank of Sheep Mountain.

Crustal implications of bedrock geology along the Trans-Alaska Crustal Transect (TACT) in the Brooks Range, northern Alaska

USGS Publications Warehouse

Moore, Thomas E.; Wallace, W.K.; Mull, C.G.; Adams, K.E.; Plafker, G.; Nokleberg, W.J.

1997-01-01

Geologic mapping of the Trans-Alaska Crustal Transect (TACT) project along the Dalton Highway in northern Alaska indicates that the Endicott Mountains allochthon and the Hammond terrane compose a combined allochthon that was thrust northward at least 90 km in the Early Cretaceous. The basal thrust of the combined allochthon climbs up section in the hanging wall from a ductile shear zone, in the south through lower Paleozoic rocks of the Hammond terrane and into Upper Devonian rocks of the Endicott Mountains allochthon at the Mount Doonerak antiform, culminating in Early Cretaceous shale in the northern foothills of the Brooks Range. Footwall rocks north of the Mount Doonerak antiform are everywhere parautochthonous Permian and Triassic shale of the North Slope terrane rather than Jurassic and Lower Cretaceous strata of the Colville Basin as shown in most other tectonic models of the central Brooks Range. Stratigraphic and structural relations suggest that this thrust was the basal detachment for Early Cretaceous deformation. Younger structures, such as the Tertiary Mount Doonerak antiform, deform the Early Cretaceous structures and are cored by thrusts that root at a depth of about 10 to 30 km along a deeper detachment than the Early Cretaceous detachment. The Brooks Range, therefore, exposes (1) an Early Cretaceous thin-skinned deformational belt developed during arc-continent collision and (2) a mainly Tertiary thick-skinned orogen that is probably the northward continuation of the Rocky Mountains erogenic belt. A down-to-the-south zone of both ductile and brittle normal faulting along the southern margin of the Brooks Range probably formed in the mid-Cretaceous by extensional exhumation of the Early Cretaceous contractional deformation. copyright. Published in 1997 by the American Geophysical Union.

A thrust-sheet propulsion concept using fissionable elements

NASA Technical Reports Server (NTRS)

Moeckel, W. E.

1976-01-01

A space propulsion concept is proposed and analyzed which consists of a thin sheet coated on one side with fissionable material, so that nuclear power is converted directly into propulsive power. Thrust is available both from ejected fission fragments and from thermal radiation. Optimum thicknesses are determined for the active and substrate layers. This concept is shown to have potential mission capability (in terms of velocity increments) superior to that of all other advanced propulsion concepts for which performance estimates are available. A suitable spontaneously fissioning material such as Cf254 could provide an extremely high-performance first stage beyond earth orbit. In contrast with some other advanced nuclear propulsion concepts, there is no minimum size below which this concept is infeasible.

A thrust-sheet propulsion concept using fissionable elements

NASA Technical Reports Server (NTRS)

Moeckel, W. E.

1976-01-01

A space propulsion concept is proposed and analyzed which consists of a thin sheet coated on one side with fissionable material, so that nuclear power is converted directly into propulsive power. Thrust is available both from ejected fission fragments and from thermal radiation. Optimum thicknesses are determined for the active and substrate layers. This concept is shown to have potential mission capability (in terms of velocity increments) superior to that of all other advanced propulsion concepts for which performance estimates are available. A suitable spontaneously fissioning material such as Cf-254 could provide an extremely high-performance first stage beyond earth orbit. In contrast with some other advanced nuclear propulsion concepts, there is no minimum size below which this concept is infeasible.

Airborne gamma-ray spectrometer and magnetometer survey, Durango A, B, C, and D, Colorado. Volume I. Detail area. Final report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Not Available

1983-01-01

An airborne combined radiometric and magnetic survey was performed for the Department of Energy (DOE) over the Durango A, Durango B, Durango C, and Durango D Detail Areas of southwestern Colorado. The Durango A Detail Area is within the coverage of the Needle Mountains and Silverton 15' map sheets, and the Pole Creek Mountain, Rio Grande Pyramid, Emerald Lake, Granite Peak, Vallecito Reservoir, and Lemon Reservoir 7.5' map sheets of the National Topographic Map Series (NTMS). The Durango B Detail Area is within the coverage of the Silverton 15' map sheet and the Wetterhorn Peak, Uncompahgre Peak, Lake City, Redcloudmore » Peak, Lake San Cristobal, Pole Creek Mountain, and Finger Mesa 7.5' map sheets of the NTMS. The Durango C Detail Area is within the coverage of the Platoro and Wolf Creek Pass 15' map sheets of the NTMS. The Durango D Detail Area is within the coverage of the Granite Lake, Cimarrona Peak, Bear Mountain, and Oakbrush Ridge 7.5' map sheets of the NTMS. Radiometric data were corrected for live time, aircraft and equipment background, cosmic background, atmospheric radon, Compton scatter, and altitude dependence. The corrected data were statistically evaluated, gridded, and contoured to produce maps of the radiometric variables, uranium, potassium, and thorium; their ratios; and the residual magnetic field. These maps have been analyzed in order to produce a multi-variant analysis contour map based on the radiometric response of the individual geological units. A geochemical analysis has been performed, using the radiometric and magnetic contour maps, the multi-variant analysis map, and factor analysis techniques, to produce a geochemical analysis map for the area.« less

Frontal compression along the Apennines thrust system: The Emilia 2012 example from seismicity to crustal structure

NASA Astrophysics Data System (ADS)

Chiarabba, Claudio; De Gori, Pasquale; Improta, Luigi; Lucente, Francesco Pio; Moretti, Milena; Govoni, Aladino; Di Bona, Massimo; Margheriti, Lucia; Marchetti, Alessandro; Nardi, Anna

2014-12-01

The evolution of the Apennines thrust-and-fold belt is related to heterogeneous process of subduction and continental delamination that generates extension within the mountain range and compression on the outer front of the Adria lithosphere. While normal faulting earthquakes diffusely occur along the mountain chain, the sparse and poor seismicity in the compressional front does not permit to resolve the ambiguity that still exists about which structure accommodates the few mm/yr of convergence observed by geodetic data. In this study, we illustrate the 2012 Emilia seismic sequence that is the most significant series of moderate-to-large earthquakes developed during the past decades on the compressional front of the Apennines. Accurately located aftershocks, along with P-wave and Vp/Vs tomographic models, clearly reveal the geometry of the thrust system, buried beneath the Quaternary sediments of the Po Valley. The seismic sequence ruptured two distinct adjacent thrust faults, whose different dip, steep or flat, accounts for the development of the arc-like shape of the compressional front. The first shock of May 20 (Mw 6.0) developed on the middle Ferrara thrust that has a southward dip of about 30°. The second shock of May 29 (Mw 5.8) ruptured the Mirandola thrust that we define as a steep dipping (50-60°) pre-existing (Permo-Triassic) basement normal fault inverted during compression. The overall geometry of the fault system is controlled by heterogeneity of the basement inherited from the older extension. We also observe that the rupture directivity during the two main-shocks and the aftershocks concentration correlate with low Poisson ratio volumes, probably indicating that portions of the fault have experienced intense micro-damage.

Uplifting model of the Longmenshan mountain in the eastern margin of Tibetan plateau

NASA Astrophysics Data System (ADS)

Zhang, S.; Ding, R.; Mao, C.

2010-12-01

Longmenshan mountain is a vivid manifestation of the Cenozoic orogenesis in the eastern margin of the Tibetan plateau, and a key to understand the geodynamics of eastward extending of the plateau. Thus the uplift mechanism of Longmenshan mountain became a hot spot issue of geosciences about the Tibetan plateau. Two entirely different hypotheses, i.e., crustal shortening and lower crustal channel flow, were put forward, but the solution is open. Further discussion need our deeper understanding about the uplifting features of the Longmenshan mountain. Fortunately, the uplifting processes were recorded objectively by peneplains and river landforms. We first analysed the peneplains and pediplanes of Longmenshan mountain and its surrounding areas, and surveyed the terraces of Dadu river running across the mountain. Then we studied the uplifting features of the study areas in late Cenozoic time on the basis of landform geometries. Finaly we discussed the possible mechanisms for the uplifting. There are two levels of peneplains whose peneplanations may begin in early Cenozoic time and end at late Miocene when the final fluctuations of elevations were possibly less than one kilometers. The valley of Dadu river is incised into the peneplains and has a staircase of no less than ten levels of terraces. The highest terrace is a strath which was contemporary with the pediplane in the piedmont formed in late Pliocene or in early Pleistocene. Due to their originally flat features, the peneplains and the strath terraces were used as datum planes for judging neotectonic deformations. Since late Miocene, the southeastern side of Longmenshan mountain has been dominated by thrust-faulting with a total vertical displacement of about 4500 m against the Sichuan basin, meantime the northwest side has been maintained flexural uplift with syncline hinge approximately following the Longriba fault. As a landform barrier between Tibetan plateau and Sichuan basin, the crest lines of the mountain are about 500 to 1000 m higher than the hinterland surface on the west side. In a word, Longmenshan mountain has been formed by the combination of eastern-wing thrusting and west-wing flexing which are attested by the deformation of the Tertiary peneplains and the longitudinal profiles of Quaternary strath terraces of Dadu river. The possible mechanisms for the uplifting of the mountain are the fault-bend folding of the upper crust, the upwelling of plastic lower crust , and crustal isostasy induced by surface erosion. In the light of the existence of longitudinal thrust faults or reversely strike-slip fault along the eastern and western wings of Longmenshan mountain, and no finding of longitudinal extensional faults there, fault-bend folding is proposed to be the leading factor.

Permian deposition in the north central Brooks Range, Alaska Constraints for tectonic reconstructions

USGS Publications Warehouse

Adams, K.E.; Mull, C.G.; Crowder, R.K.

1997-01-01

Two opposing tectonic models have been offered to explain the regional structural relations in the north central Brooks Range fold-thrust belt of northern Alaska. The first suggests that rocks of the northern Endicott Mountains were thrust from south to north over the area of the present Mount Doonerak high and are therefore highly allochthonous. The second implies that the rocks of the northern Endicott Mountains were deposited in a basin that lay north of the Mount Doonerak high and later were thrust a short distance southward onto the northern flank of the high and are thus parautochthonous. To provide stratigraphic constraints for these models, this study examines Permian facies of the north central Brooks Range. Permian rocks in the north central Brooks Range comprise a thin (40 to 160 m thick), fining-upward succession of clastic, storm-influenced shelf deposits. When the rocks of the northern Endicott Mountains are restored south of the Mount Doonerak area, a minimum distance of 80 km, the Permian deposits grade systematically from distal facies (Siksikpuk Formation) in the southwest to proximal facies (Echooka Formation) in the northeast. Facies trends in the reconstructed Permian basin include, from southwest to northeast, (1) an increase in carbonate content and corresponding decrease in silica content, (2) a general darkening and thickening of shaley intervals, (3) an increase in proximal features of storm beds, including coarser, thicker, more abundant, and more closely spaced beds, and (4) an increase in abundance and diversity of the faunal assemblage with a corresponding decrease in age. These stratigraphic relations imply that rocks of the northern Endicott Mountains are allochthonous and structurally overlie a proximal stratigraphic succession similar to that exposed in the Mount Doonerak area and northeastern Brooks Range. Copyright 1997 by the American Geophysical Union.

Possible reactivation of the Vincent-Chocolate Mountains thrust in the Gavilan Hills area, southeasternmost California

DOE Office of Scientific and Technical Information (OSTI.GOV)

Oyarzabal, F.R.; Jacobson, C.E.; Haxel, G.B.

The Late Cretaceous-early Tertiary Orocopia Schist (OS) of southeasternmost California consists of metamorphosed continental margin sedimentary and basaltic rocks, overlain by an upper plate of continental crust along the Vincent-Chocolate Mountains fault (VCMF). Previous analysis of late folds and shear band in OS and upper plate in the Gavilan Hills and adjacent ares indicated that the direction of transport of the upper plate was northeastward. This has been considered evidence of a SW dipping subduction zone, along which an outboard continental fragment was sutured to North America. Another view is that the VCMF was formed by underplating of the OSmore » in an Andean continental margin, and that the NE-vergent late structures formed during uplift of the OS. The authors' continuing work in the Gavilan Hills confirm the NE sense of vergence but suggests a more complex structural history. The schist is characterized by refolded folds, shear bands, and two penetrative lineations. An older lineation that ranges from N10[degree]E to N30[degree]E is widespread in the area, but is more evident at low structural levels. A second lineation ranges from N40[degree]E to N70[degree]E and is strongly developed in rocks near the VCMF. The complex folding pattern, presence of mylonitic schist, relative thinness of upper-plate mylonite, and possible retrogressive character of the shear bands suggest that the VCMF in the Gavilan Hills area may have been reactivated after original thrusting. The VCMF in the Gavilan Hills is intermediate in character between the probable subduction thrust in the San Gabriel Mountains and the reactivated faults in the Orocopia Mountains and areas surrounding the Gavilan Hills.« less

Contributions of gravity and field data on the structural scheme updating of the Tellian domain and its foreland (Nefza-Bizerte region, northern Tunisia)

NASA Astrophysics Data System (ADS)

Essid, El Mabrouk; Kadri, Ali; Balti, Hadhemi; Gasmi, Mohamed; Zargouni, Fouad

2018-03-01

The Nefza-Bizerte region, eastern part of the Tunisian Alpine chain, covers the thrust sheets domain called the Tell and its Atlassic foreland. The deep structures under the Tellian thrust sheets are not enough explored. The structural interpretation of magmatic rocks, Triassic outcrops and the depressions are still a subject of discussion. In this work, we intend to investigate deep faults and their eventual role in magmatism and Triassic salt setting up and to explain the depression genesis. Analysis of the Bouguer anomaly map and its derivatives reveals the main gravity lineaments, organized in major NE- and NW-trending systems. The NE-trending system, dipping towards the NW, is the main component of the structural scheme and has controlled the tectonic evolution of this area. After the immobilization of the Tellian thrust sheets during the uppermost Langhian, the Tell and its Atlassic foreland were affected by the Tortonian compressive event with a NW-trending maximum horizontal stress. The reverse kinematics of the NE-trending deep-seated faults created at their front continental environments filled later by post-nappes Neogene deposits. After the early Pleistocene, a NNW-directed compressional stress regime deformed the post-nappes Neogene series and generated NW-trending grabens. This coexistence of compression-extension continues until present day.

Depositional settings, correlation, and age carboniferous rocks in the western Brooks Range, Alaska

USGS Publications Warehouse

Dumoulin, Julie A.; Harris, Anita G.; Blome, Charles D.; Young, Lorne E.

2004-01-01

The Kuna Formation (Lisburne Group) in northwest Alaska hosts the Red Dog and other Zn-Pb-Ag massive sulfide deposits in the Red Dog district. New studies of the sedimentology and paleontology of the Lisburne Group constrain the setting, age, and thermal history of these deposits. In the western and west-central Brooks Range, the Lisburne Group includes both deep- and shallow-water sedimentary facies and local volcanic rocks that are exposed in a series of thrust sheets or allochthons. Deep-water facies in the Red Dog area (i.e., the Kuna Formation and related rocks) are found chiefly in the Endicott Mountains and structurally higher Picnic Creek allochthons. In the Red Dog plate of the Endicott Mountains allochthon, the Kuna consists of at least 122 m of thinly interbedded calcareous shale, calcareous spiculite, and bioclastic supportstone (Kivalina unit) overlain by 30 to 240 m of siliceous shale, mudstone, calcareous radiolarite, and calcareous lithic turbidite (Ikalukrok unit). The Ikalukrok unit in the Red Dog plate hosts all massive sulfide deposits in the area. It is notably carbonaceous, is generally finely laminated, and contains siliceous sponge spicules and radiolarians. The Kuna Formation in the Key Creek plate of the Endicott Mountains allochthon (60–110 m) resembles the Ikalukrok unit but is unmineralized and has thinner carbonate layers that are mainly organic-rich dolostone. Correlative strata in the Picnic Creek allochthon include less shale and mudstone and more carbonate (mostly calcareous spiculite). Conodonts and radiolarians indicate an age range of Osagean to early Chesterian (late Early to Late Mississippian) for the Kuna in the Red Dog area. Sedimentologic, faunal, and geochemical data imply that most of the Kuna formed in slope and basin settings characterized by anoxic or dysoxic bottom water and by local high productivity.

Exhumation history of the West Kunlun Mountains, northwestern Tibet: Evidence for a long-lived, rejuvenated orogen

NASA Astrophysics Data System (ADS)

Cao, Kai; Wang, Guo-Can; Bernet, Matthias; van der Beek, Peter; Zhang, Ke-Xin

2015-12-01

How and when the northwestern Tibetan Plateau originated and developed upon pre-existing crustal and topographic features is not well understood. To address this question, we present an integrated analysis of detrital zircon U-Pb and fission-track double dating of Cenozoic synorogenic sediments from the Kekeya and Sanju sections in the southwestern Tarim Basin. These data help establishing a new chronostratigraphic framework for the Sanju section and confirm a recent revision of the chronostratigraphy at Kekeya. Detrital zircon fission-track ages present prominent Triassic-Early Jurassic (∼250-170 Ma) and Early Cretaceous (∼130-100 Ma) static age peaks, and Paleocene-Early Miocene (∼60-21 Ma) to Eocene-Late Miocene (∼39-7 Ma) moving age peaks, representing source exhumation. Triassic-Early Jurassic static peak ages document unroofing of the Kunlun terrane, probably related to the subduction of Paleotethys oceanic lithosphere. In combination with the occurrence of synorogenic sediments on both flanks of the Kunlun terrane, these data suggest that an ancient West Kunlun range had emerged above sea level by Triassic-Early Jurassic times. Early Cretaceous fission-track peak ages are interpreted to document exhumation related to thrusting along the Tam Karaul fault, kinematically correlated to the Main Pamir thrust further west. Widespread Middle-Late Mesozoic crustal shortening and thickening likely enhanced the Early Mesozoic topography. Paleocene-Early Eocene fission-track peak ages are presumably partially reset. Limited regional exhumation indicates that the Early Cenozoic topographic and crustal pattern of the West Kunlun may be largely preserved from the Middle-Late Mesozoic. The Main Pamir-Tam Karaul thrust belt could be a first-order tectonic feature bounding the northwestern margin of the Middle-Late Mesozoic to Early Cenozoic Tibetan Plateau. Toward the Tarim basin, Late Oligocene-Early Miocene steady exhumation at a rate of ∼0.9 km/Myr is likely related to initial thrusting of the Tiklik fault and reactivation of the Tam Karaul thrust. Thrusting together with upper crustal shortening in the mountain front indicates basinward expansion of the West Kunlun orogen at this time. This episode of exhumation and uplift, associated with magmatism across western Tibet, is compatible with a double-sided lithospheric wedge model, primarily driven by breakoff of the Indian crustal slab. Accelerated exhumation of the mountain front at a rate of ∼1.1 km/Myr since ∼15 Ma supports active compressional deformation at the margins of the northwestern Tibetan Plateau. We thus propose that the West Kunlun Mountains are a long-lived topographic unit, dating back to Triassic-Early Jurassic times, and have experienced Middle-Late Mesozoic to Early Cenozoic rejuvenation and Late Oligocene-Miocene expansion.

Ordovician and Silurian Phi Kappa and Trail Creek formations, Pioneer Mountains, central Idaho; stratigraphic and structural revisions, and new data on graptolite faunas

USGS Publications Warehouse

Dover, James H.; Berry, William B.N.; Ross, Reuben James

1980-01-01

Recent geologic mapping in the northern Pioneer Mountains combined with the identification of graptolites from 116 new collections indicate that the Ordovician and Silurian Phi Kappa and Trail Creek Formations occur in a series of thrust-bounded slices within a broad zone of imbricate thrust faulting. Though confirming a deformational style first reported in a 1963 study by Michael Churkin, our data suggest that the complexity and regional extent of the thrust zone were not previously recognized. Most previously published sections of the Phi Kappa and Trail Creek Formations were measured across unrecognized thrust faults and therefore include not only structural repetitions of graptolitic Ordovician and Silurian rocks but also other tectonically juxtaposed lithostratigraphic units of diverse ages as well. Because of this discovery, the need to reconsider the stratigraphic validity of these formations and their lithology, nomenclature, structural distribution, facies relations, and graptolite faunas has arisen. The Phi Kappa Formation in most thrust slices has internal stratigraphic continuity despite the intensity of deformation to which it was subjected. As revised herein, the Phi Kappa Formation is restricted to a structurally repeated succession of predominantly black, carbonaceous, graptolitic argillite and shale. Some limy, light-gray-weathering shale occurs in the middle part of the section, and fine-grained locally pebbly quartzite is present at the base. The basal quartzite is here named the Basin Gulch Quartzite Member of the Phi Kappa. The Phi Kappa redefined on a lithologic basis represents the span of Ordovician time from W. B. N. Berry's graptolite zones 2-4 through 15 and also includes approximately 17 m of lithologically identical shale of Early and Middle Silurian age at the top. The lower contact of the formation as revised is tectonic. The Phi Kappa is gradationally overlain by the Trail Creek Formation as restricted herein. Most of the coarser clastic rocks reported in previously measured sections of the Phi Kappa, as well as the sequence along Phi Kappa Creek from which the name originates, are excluded from the Phi Kappa as revised and are reassigned to two structural plates of Mississippian Copper Basin Formation; other strata now excluded from the formation are reassigned to the Trail Creek Formation and to an unnamed Silurian and Devonian unit. As redefined, the Phi Kappa Formation is only about 240 m thick, compared with the 3,860 m originally estimated, and it occupies only about 25 percent of the outcrop area previously mapped in 1930 by H. G. Westgate and C. P. Ross. Despite this drastic reduction in thickness and the exclusion of the rocks along Phi Kappa Creek, the name Phi Kappa is retained because of widely accepted prior usage to denote the Ordovician graptolitic shale facies of central Idaho, and because the Phi Kappa Formation as revised is present in thrust slices on Phi Kappa Mountain, at the head of Phi Kappa Creek. The lithic and faunal consistency of this unit throughout the area precludes the necessity for major facies telescoping along individual faults within the outcrop belt. However, tens of kilometers of tectonic shortening seems required to juxtapose the imbricated Phi Kappa shale facies with the Middle Ordovician part of the carbonate and quartzite shale sequence of east central Idaho. The shelf rocks are exposed in the Wildhorse structural window of the northeastern Pioneer Mountains, and attain a thickness of at least 1,500 m throughout the region north and east of the Pioneer Mountains. The Phi Kappa is in direct thrust contact on intensely deformed medium- to high-grade metamorphic equivalents of the same shelf sequence in the Pioneer window at the south end of the Phi Kappa-Trail Creek outcrop belt. Along East Pass, Big Lake, and Pine Creeks, north of the Pioneer Mountains, some rocks previously mapped as Ramshorn Slate are lithologically and faunally equivalent to the P

Interseismic coupling, seismic potential and earthquake recurrence on the southern front of the Eastern Alps (NE Italy)

NASA Astrophysics Data System (ADS)

Cheloni, Daniele; D'Agostino, Nicola; Selvaggi, Giulio

2014-05-01

The interaction of the African, Arabian, and Eurasia plates in the "greater" Mediterranean region yields to a broad range of tectonic processes including active subduction, continental collision, major continental strike-slip faults and "intra-plate" mountain building. In this puzzling region the convergence between Adria microplate and Eurasia plate is partly or entirely absorbed within the South-Eastern Alps, where the Adriatic lithosphere underthrusts beneath the mountain belt. Historical seismicity and instrumentally recorded earthquakes show thrust faulting on north-dipping low-angle faults in agreement with geological observations of active mountain building and active fold growing at the foothills of the South-Eastern Alps. In this study, we use continuous GPS observations to document the geodetic strain accumulation across the South-Eastern Alps (NE Italy). We estimate the pattern of interseismic coupling on the intra-continental collision north-dipping thrust faults that separate the Eastern Alps and the Venetian-Friulian plain using the back-slip approach and discuss the seismic potential and earthquake recurrence. Comparison between the rigid-rotation predicted motion and the shortening observed across the studied area indicates that the South-Eastern Alpine thrust front absorbs about 80% of the total convergence rate between the Adria microplate and Eurasia plate. The modelled thrust fault is currently locked from the surface to a depth of approximately 10 km. The transition zone between locked and creeping portions of the fault roughly corresponds with the belt of microseismicity parallel and to the north of the mountain front. The estimated moment deficit rate is 1.27±0.14×10^17 Nm/yr. The comparison between the estimated moment deficit and that released historically by the earthquakes suggests that to account for the moment deficit the following two factors or their combination should be considered: (1) a significant part of the observed interseismic coupling is released aseismically by folding or creeping; (2) infrequent "large" events with long return period (>1000 years) and with magnitudes larger than the value assigned to the largest historical events (Mw≡6.7).

Effect of Inductive Coil Geometry and Current Sheet Trajectory of a Conical Theta Pinch Pulsed Inductive Plasma Accelerator

NASA Technical Reports Server (NTRS)

Hallock, Ashley K.; Polzin, Kurt A.; Bonds, Kevin W.; Emsellem, Gregory D.

2011-01-01

Results are presented demonstrating the e ect of inductive coil geometry and current sheet trajectory on the exhaust velocity of propellant in conical theta pinch pulsed induc- tive plasma accelerators. The electromagnetic coupling between the inductive coil of the accelerator and a plasma current sheet is simulated, substituting a conical copper frustum for the plasma. The variation of system inductance as a function of plasma position is obtained by displacing the simulated current sheet from the coil while measuring the total inductance of the coil. Four coils of differing geometries were employed, and the total inductance of each coil was measured as a function of the axial displacement of two sep- arate copper frusta both having the same cone angle and length as the coil but with one compressed to a smaller size relative to the coil. The measured relationship between total coil inductance and current sheet position closes a dynamical circuit model that is used to calculate the resulting current sheet velocity for various coil and current sheet con gura- tions. The results of this model, which neglects the pinching contribution to thrust, radial propellant con nement, and plume divergence, indicate that in a conical theta pinch ge- ometry current sheet pinching is detrimental to thruster performance, reducing the kinetic energy of the exhausting propellant by up to 50% (at the upper bound for the parameter range of the study). The decrease in exhaust velocity was larger for coils and simulated current sheets of smaller half cone angles. An upper bound for the pinching contribution to thrust is estimated for typical operating parameters. Measurements of coil inductance for three di erent current sheet pinching conditions are used to estimate the magnetic pressure as a function of current sheet radial compression. The gas-dynamic contribution to axial acceleration is also estimated and shown to not compensate for the decrease in axial electromagnetic acceleration that accompanies the radial compression of the plasma in conical theta pinches.

Inception of the Laurentide Ice Sheet using asynchronous coupling of a regional atmospheric model and an ice model

NASA Astrophysics Data System (ADS)

Birch, L.; Cronin, T.; Tziperman, E.

2017-12-01

The climate over the past 0.8 million years has been dominated by ice ages. Ice sheets have grown about every 100 kyrs, starting from warm interglacials, until they spanned continents. State-of-the-art global climate models (GCMs) have difficulty simulating glacial inception, or the transition of Earth's climate from an interglacial to a glacial state. It has been suggested that this failure may be related to their poorly resolved local mountain topography, due to their coarse spatial resolution. We examine this idea as well as the possible role of ice flow dynamics missing in GCMs. We investigate the growth of the Laurentide Ice Sheet at 115 kya by focusing on the mountain glaciers of Canada's Baffin Island, where geologic evidence indicates the last inception occurred. We use the Weather Research and Forecasting model (WRF) in a regional, cloud-resolving configuration with resolved mountain terrain to explore how quickly Baffin Island could become glaciated with the favorable yet realizable conditions of 115 kya insolation, cool summers, and wet winters. Using the model-derived mountain glacier mass balance, we force an ice sheet model based on the shallow-ice approximation, capturing the ice flow that may be critical to the spread of ice sheets away from mountain ice caps. The ice sheet model calculates the surface area newly covered by ice and the change in the ice surface elevation, which we then use to run WRF again. Through this type of iterated asynchronous coupling, we investigate how the regional climate responds to both larger areas of ice cover and changes in ice surface elevation. In addition, we use the NOAH-MP Land model to characterize the importance of land processes, like refreezing. We find that initial ice growth on the Penny Ice Cap causes regional cooling that increases the accumulation on the Barnes Ice Cap. We investigate how ice and topography changes on Baffin Island may impact both the regional climate and the large-scale circulation.

Scale independence of décollement thrusting

USGS Publications Warehouse

McBride, John H.; Pugin, Andre J.M.; Hatcher, Robert D.

2007-01-01

Orogen-scale décollements (detachment surfaces) are an enduring subject of investigation by geoscientists. Uncertainties remain as to how crustal convergence processes maintain the stresses necessary for development of low-angle fault surfaces above which huge slabs of rock are transported horizontally for tens to hundreds of kilometers. Seismic reflection profiles from the southern Appalachian crystalline core and several foreland fold-and-thrust belts provide useful comparisons with high-resolution shallow-penetration seismic reflection profiles acquired over the frontal zone of the Michigan lobe of the Wisconsinan ice sheet northwest of Chicago, Illinois. These profiles provide images of subhorizontal and overlapping dipping reflections that reveal a ramp-and-flat thrust system developed in poorly consolidated glacial till. The system is rooted in a master décollement at the top of bedrock. These 2–3 km long images contain analogs of images observed in seismic reflection profiles from orogenic belts, except that the scale of observation in the profiles in glacial materials is two orders of magnitude less. Whereas the décollement beneath the ice lobe thrust belt lies ∼70 m below thrusted anticlines having wavelengths of tens of meters driven by an advancing ice sheet, seismic images from overthrust terranes are related to lithospheric convergence that produces décollements traceable for thousands of kilometers at depths ranging from a few to over 10 km. Dual vergence or reversals in vergence (retrocharriage) that developed over abrupt changes in depth to the décollement can be observed at all scales. The strikingly similar images, despite the contrast in scale and driving mechanism, suggest a scale- and driving mechanism–independent behavior for décollement thrust systems. All these systems initially had the mechanical properties needed to produce very similar geometries with a compressional driving mechanism directed subparallel to Earth's surface. Subduction-related accretionary complexes also produce thrust systems with similar geometries in semi- to unconsolidated materials.

Structural Mapping of Paterae and Mountains on Io: Implications for Crustal Stresses and Feature Evolution

NASA Astrophysics Data System (ADS)

Ahern, A.; Radebaugh, J.; Christiansen, E. H.; Harris, R. A.

2015-12-01

Paterae and mountains are some of the most distinguishing and well-distributed surface features on Io, and they reveal the role of tectonism in Io's crust. Paterae, similar to calderas, are volcano-tectonic collapse features that often have straight margins. Io's mountains are some of the highest in the solar system and contain linear features that reveal crustal stresses. Paterae and mountains are often found adjacent to one another, suggesting possible genetic relationships. We have produced twelve detailed regional structural maps from high-resolution images of relevant features, where available, as well as a global structural map from the Io Global Color Mosaic. The regional structural maps identify features such as fractures, lineations, folds, faults, and mass wasting scarps, which are then interpreted in the context of global and regional stress regimes. A total of 1048 structural lineations have been identified globally. Preliminary analyses of major thrust and normal fault orientations are dominantly 90° offset from each other, suggesting the maximum contractional stresses leading to large mountain formation are not a direct result of tidal extension. Rather, these results corroborate the model of volcanic loading of the crust and global shortening, leading to thrust faulting and uplift of coherent crustal blocks. Several paterae, such as Hi'iaka and Tohil, are found adjacent to mountains inside extensional basins where lava has migrated up normal faults to erupt onto patera floors. Over time, mass wasting and volcanic resurfacing can change mountains from young, steep, and angular peaks to older, gentler, and more rounded hills. Mass wasting scarps make up 53% of all features identified. The structural maps highlight the significant effect of mass wasting on Io's surface, the evolution of mountains through time, the role of tectonics in the formation of paterae, and the formation of mountains through global contraction due to volcanism.

Roaring Fork Motor Nature Trail, Title Sheet Great Smoky ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

Roaring Fork Motor Nature Trail, Title Sheet - Great Smoky Mountains National Park Roads & Bridges, Roaring Fork Motor Nature Trail, Between Cherokee Orchard Road & U.S. Route 321, Gatlinburg, Sevier County, TN

Numerical simulations of the Cordilleran ice sheet through the last glacial cycle

NASA Astrophysics Data System (ADS)

Seguinot, Julien; Rogozhina, Irina; Stroeven, Arjen P.; Margold, Martin; Kleman, Johan

2016-03-01

After more than a century of geological research, the Cordilleran ice sheet of North America remains among the least understood in terms of its former extent, volume, and dynamics. Because of the mountainous topography on which the ice sheet formed, geological studies have often had only local or regional relevance and shown such a complexity that ice-sheet-wide spatial reconstructions of advance and retreat patterns are lacking. Here we use a numerical ice sheet model calibrated against field-based evidence to attempt a quantitative reconstruction of the Cordilleran ice sheet history through the last glacial cycle. A series of simulations is driven by time-dependent temperature offsets from six proxy records located around the globe. Although this approach reveals large variations in model response to evolving climate forcing, all simulations produce two major glaciations during marine oxygen isotope stages 4 (62.2-56.9 ka) and 2 (23.2-16.9 ka). The timing of glaciation is better reproduced using temperature reconstructions from Greenland and Antarctic ice cores than from regional oceanic sediment cores. During most of the last glacial cycle, the modelled ice cover is discontinuous and restricted to high mountain areas. However, widespread precipitation over the Skeena Mountains favours the persistence of a central ice dome throughout the glacial cycle. It acts as a nucleation centre before the Last Glacial Maximum and hosts the last remains of Cordilleran ice until the middle Holocene (6.7 ka).

Static investigation of two fluidic thrust-vectoring concepts on a two-dimensional convergent-divergent nozzle

NASA Technical Reports Server (NTRS)

Wing, David J.

1994-01-01

A static investigation was conducted in the static test facility of the Langley 16-Foot Transonic Tunnel of two thrust-vectoring concepts which utilize fluidic mechanisms for deflecting the jet of a two-dimensional convergent-divergent nozzle. One concept involved using the Coanda effect to turn a sheet of injected secondary air along a curved sidewall flap and, through entrainment, draw the primary jet in the same direction to produce yaw thrust vectoring. The other concept involved deflecting the primary jet to produce pitch thrust vectoring by injecting secondary air through a transverse slot in the divergent flap, creating an oblique shock in the divergent channel. Utilizing the Coanda effect to produce yaw thrust vectoring was largely unsuccessful. Small vector angles were produced at low primary nozzle pressure ratios, probably because the momentum of the primary jet was low. Significant pitch thrust vector angles were produced by injecting secondary flow through a slot in the divergent flap. Thrust vector angle decreased with increasing nozzle pressure ratio but moderate levels were maintained at the highest nozzle pressure ratio tested. Thrust performance generally increased at low nozzle pressure ratios and decreased near the design pressure ratio with the addition of secondary flow.

Measurement of hydrodynamic force generation by swimming dolphins using bubble DPIV.

PubMed

Fish, Frank E; Legac, Paul; Williams, Terrie M; Wei, Timothy

2014-01-15

Attempts to measure the propulsive forces produced by swimming dolphins have been limited. Previous uses of computational hydrodynamic models and gliding experiments have provided estimates of thrust production by dolphins, but these were indirect tests that relied on various assumptions. The thrust produced by two actively swimming bottlenose dolphins (Tursiops truncatus) was directly measured using digital particle image velocimetry (DPIV). For dolphins swimming in a large outdoor pool, the DPIV method used illuminated microbubbles that were generated in a narrow sheet from a finely porous hose and a compressed air source. The movement of the bubbles was tracked with a high-speed video camera. Dolphins swam at speeds of 0.7 to 3.4 m s(-1) within the bubble sheet oriented along the midsagittal plane of the animal. The wake of the dolphin was visualized as the microbubbles were displaced because of the action of the propulsive flukes and jet flow. The oscillations of the dolphin flukes were shown to generate strong vortices in the wake. Thrust production was measured from the vortex strength through the Kutta-Joukowski theorem of aerodynamics. The dolphins generated up to 700 N during small amplitude swimming and up to 1468 N during large amplitude starts. The results of this study demonstrated that bubble DPIV can be used effectively to measure the thrust produced by large-bodied dolphins.

Palinspastic reconstruction of the Alpine thrust belt at the Alpine-Carpathian transition - A geological Sudoku

NASA Astrophysics Data System (ADS)

Beidinger, A.; Decker, K.; Zamolyi, A.; Hölzel, M.; Hoprich, M.; Strauss, P.

2009-04-01

The palinspastic reconstruction of the Austroalpine thrust belt is part of the project Karpatian Tectonics, which is funded by OMV Austria. The objective is to reconstruct the evolution of the thrust belt through the Early to Middle Miocene in order to obtain information on the palaeogeographic position of the Northern Calcareous Alps (NCA) in the region of the present Vienna Basin. A particular goal of the study is to constrain the position of reservoir rocks within the Rhenodanubic Flysch units and the NCA with respect to the autochthonous Malmian source rocks overlying the European basement below the Alpine-Carpathian thrust wedge, and to constrain the burial history of these source rocks. Reconstruction uses regional 2D seismic lines crossing from the European foreland into the fold-thrust belt, 3D seismic data covering the external thrust sheets, and lithostratigraphic data from a total of 51 selected wells, which were drilled and provided by OMV Austria. The main criterion, whether a well was suitable for palinspastic reconstruction or not, was its penetration of Alpine thrust sheets down to the Autochthonous Molasse of the foreland. Additional wells, which do not penetrate the entire Alpine thrust complex but include the Allochthonous Molasse or the external Alpine-Carpathian nappes (Waschberg and Roseldorf thrust unit, Rhenodanubic Flysch nappes) in their well path, were also taken into account. The well data in particular comprise stratigraphic information on the youngest overthrust sediments of the different thrust units and the underlying Autochthonous foreland Molasse. These data allow constraining the timing of thrust events in the allochthonous thrust units and overthrusting of the Autochthonous Molasse. In the particular case of overthrust Autochthonous Molasse, additionally to the timing of overthrusting, which can be derived from the youngest overthrust sediments, the palaeogeographic position of the Alpine Carpathian thrust front could directly be inferred from well data for the specific time period. By further utilization of geological maps, geological cross sections and two regional c. 80 km long composite 2D seismic sections through the external Alpine thrusts, the positions of major thrusts could be approximated for five time slices. This procedure was applied for the front of the allochthonous Molasse units, the floor thrust of the Roseldorf thrust unit, the Waschberg thrust unit and the frontal thrusts of the Rhenodanubic Flysch and the NCA. In addition, several out-of-sequence thrusts within the Waschberg unit, the Molasse unit, the Rhenodanubic Flysch and the Calcareous Alps (floor thrust of the NCA and two internal thrusts) were taken into account. The reconstruction results in 5 palinspastic maps for the time slices early Egerian (25 Ma), early Eggenburgian (20 Ma), Ottnangian (17.5 Ma), Lower Karpatian (16.5 Ma) and the Karpatian/ Badenian stage boundary (16 Ma). Convergence rates, which were calculated for the four intervening time intervals, range from about 3 mm/yr to 5 mm/yr. These values compare well with estimated convergence rates reconstructed for the Miocene in the western Eastern Alps (Schmid et al., 1996), as well as with plate tectonic constraints on Tertiary convergence rates (Dewey et al., 1989). Dewey, J., Helman, M.L., Turco, E., Hutton, D.H.W.&Knott, S.D., 1989. Kinematics of the western Mediterranean, in: N.P. Coward, D. Dietrich & R.G. Park (eds.), Alpine Tectonics, Geol. Soc. Spec. Publ., 45: 265-283. Schmid, S.M., Pfiffner, O.A., Frotzheim, N., Schönborn, G. & Kissling, E., 1996. Geophysical-geological transect and tectonic evolution of the Swiss-Italian Alps. Tectonics, 15: 1036-1064.

1957 Gobi-Altay, Mongolia, earthquake as a prototype for southern California's most devastating earthquake

USGS Publications Warehouse

Bayarsayhan, C.; Bayasgalan, A.; Enhtuvshin, B.; Hudnut, K.W.; Kurushin, R.A.; Molnar, P.; Olziybat, M.

1996-01-01

The 1957 Gobi-Altay earthquake was associated with both strike-slip and thrust faulting, processes similar to those along the San Andreas fault and the faults bounding the San Gabriel Mountains just north of Los Angeles, California. Clearly, a major rupture either on the San Andreas fault north of Los Angeles or on the thrust faults bounding the Los Angeles basin poses a serious hazard to inhabitants of that area. By analogy with the Gobi-Altay earthquake, we suggest that simultaneous rupturing of both the San Andreas fault and the thrust faults nearer Los Angeles is a real possibility that amplifies the hazard posed by ruptures on either fault system separately.

Thin‐ or thick‐skinned faulting in the Yakima fold and thrust belt (WA)? Constraints from kinematic modeling of the saddle mountains anticline

USGS Publications Warehouse

Casale, Gabriele; Pratt, Thomas L.

2015-01-01

The Yakima fold and thrust belt (YFTB) deforms the Columbia River Basalt Group flows of Washington State. The YFTB fault geometries and slip rates are crucial parameters for seismic‐hazard assessments of nearby dams and nuclear facilities, yet there are competing models for the subsurface fault geometry involving shallowly rooted versus deeply rooted fault systems. The YFTB is also thought to be analogous to the evenly spaced wrinkle ridges found on other terrestrial planets. Using seismic reflection data, borehole logs, and surface geologic data, we tested two proposed kinematic end‐member thick‐ and thin‐skinned fault models beneath the Saddle Mountains anticline of the YFTB. Observed subsurface geometry can be produced by 600–800 m of heave along a single listric‐reverse fault or ∼3.5  km of slip along two superposed low‐angle thrust faults. Both models require decollement slip between 7 and 9 km depth, resulting in greater fault areas than sometimes assumed in hazard assessments. Both models require initial slip much earlier than previously thought and may provide insight into the subsurface geometry of analogous comparisons to wrinkle ridges observed on other planets.

Folding kinematics expressed in fracture patterns: An example from the Anti-Atlas fold belt, Morocco

NASA Astrophysics Data System (ADS)

Ismat, Zeshan

2008-11-01

The Anti-Atlas fold belt, Morocco, formed during the same Variscan collisional event that produced the Valley-and-Ridge fold-thrust belt of the Appalachian mountains. Both are external belts of the Appalachian-Ouachita-Mauritanides chain and at the map scale have very similar topographic expressions. The Anti-Atlas, however, consists of map-scale folds that are buckle-related, detachment folds, whereas the Valley-and-Ridge folds developed in response to imbricate thrusting. For this reason, the Anti-Atlas is referred to as a fold belt rather than a fold-thrust belt. This paper examines Variscan folding processes in the Anti-Atlas Mountains. Folding in some layers occurred by sliding along a penetrative network of mesoscale fractures, i.e. cataclastic flow, during buckling. Layer-parallel shortening fractures were reactivated in the later stages of folding to accommodate limb rotation. Although 'boutonnieres', i.e. basement uplifts, punctuate the fold belt, the fracture patterns indicate that the uplifts failed to provide any 'bending' component. Folding is also interpreted to occur under low to moderate confining pressures because the fracture network includes conjugate shear fractures with very small (˜20°) dihedral angles.

Tonalite and trondhjemite plutonism in the western Chugach Mountains, so. Alaska: an example of near trench magmatism

DOE Office of Scientific and Technical Information (OSTI.GOV)

Monteverde, D.; Pavlis, T.

1985-01-01

In the northern Chugach Mountains of southern Alaska a suite of granitoid plutons were emplaced in a near-trench setting in mid-Early Cretaceous time. The plutons intrude both the then continental edge marked by Jurassic igneous and metamorphic rocks of the Peninsular terrane and the accretionary prism composed of the Early Cretaceous McHugh Complex. Field, petrographic and geochemical data classify the plutonic rocks as ranging from a hornblende-biotite tonalite to a biotite trondjhemite. Most of the rocks are post-metamorphic and show hypidiomorphic granular textures. Locally, however, the rocks are weakly foliated and quartz shows grain size reduction (serrate textures) indicative ofmore » minor ductile strain; suggesting some strain following emplacement. Geochemically, Harker variation diagrams show a linear variation as related to silica content: MgO, FeO total, TiO/sub 2/, and CaO and Al/sub 2/O/sub 3/ decrease while Na/sub 2/O, K/sub 2/O, MnO and P/sub 2/O/sub 5/ maintain constant percentages with increasing silica content. Chemical ranges include: SiO/sub 2/ 61.98 to 74.90%, Al/sub 2/O/sub 3/ 19.35 to 14.25%, CaO 6.93 to 2.23%, Na/sub 2/O averages 4.33%, K/sub 2/O averages 0.91%. The rocks are a high Al/sub 2/O/sub 3/ (calcic.) trondjhemite of Barker (1979). Most of the rocks are strongly peraluminous (>1.1% corundum normative); garnet crystals show equilibrium textures without reaction rims; and stable isotope analysis of a small sample suite show significant /sup 08/O enrichment (>9.6 per mil SMOW). Two possible petrographic models fit the data. The entail a fractional crystallization-assimilation model and a partial melting of a low temperature hydrothermally altered basalt. The tectonic mechanism responsible for this unusual event is elusive but two models are allowable: 1) a ridge-trench encounter; and 2) melting along thrust planes during initiation of subduction - a mechanism analogous to melting along great crystalline thrust sheets.« less

An Antarctic stratigraphic record of step-wise ice-sheet growth through the Eocene-Oligocene transition

NASA Astrophysics Data System (ADS)

Passchier, S.; Ciarletta, D. J.; Miriagos, T.; Bijl, P.; Bohaty, S. M.

2016-12-01

The Antarctic cryosphere plays a critical role in the ocean-atmosphere system, but its early evolution is still poorly known. With a near-field record from Prydz Bay, Antarctica, we conclude that Antarctic continental ice-sheet growth commenced with the EOT-1 "precursor" glaciation, during a time of Subantarctic surface ocean cooling and a decline in atmospheric pCO2. Prydz Bay lies downstream of a major East Antarctic ice-sheet drainage system and the Gamburtsev Mountains, a likely nucleation point for the first ice sheets. Its sedimentary records uniquely constrain the timing of ice-sheet advance onto the continental shelf. We investigate a detrital record extracted from three Ocean Drilling Program drill holes in Prydz Bay within a new depositional and chronological framework spanning the late Eocene to early Oligocene ( 36-33 Ma). The chemical index of alteration (CIA) and the S-index, calculated from the major element geochemistry of bulk samples, yield estimates of chemical weathering intensities and mean annual temperature (MAT) on the East Antarctic continent. We document evidence for late Eocene mountain glaciation along with transient warm events at 35.8-34.8 Ma. These data and our sedimentological analyses confirm the presence of ephemeral mountain glaciers on East Antarctica during the late Eocene between 35.9 and 34.4 Ma. Furthermore, we document the stepwise climate cooling of the Antarctic hinterland from 34.4 Ma as the ice sheet advanced towards the edges of the continent during EOT-1. The youngest part of our data set correlates to the time interval of the Oi-1 glaciation, when the ice-sheet in Prydz Bay extended to the outer shelf. Cooling and ice growth on Antarctica was spatially variable and ice sheets formed under declining pCO2. These results point to complex ice sheet - atmosphere - ocean - solid-earth feedbacks.

Interpretation of the Seattle uplift, Washington, as a passive-roof duplex

USGS Publications Warehouse

Brocher, T.M.; Blakely, R.J.; Wells, R.E.

2004-01-01

We interpret seismic lines and a wide variety of other geological and geophysical data to suggest that the Seattle uplift is a passive-roof duplex. A passive-roof duplex is bounded top and bottom by thrust faults with opposite senses of vergence that form a triangle zone at the leading edge of the advancing thrust sheet. In passive-roof duplexes the roof thrust slips only when the floor thrust ruptures. The Seattle fault is a south-dipping reverse fault forming the leading edge of the Seattle uplift, a 40-km-wide fold-and-thrust belt. The recently discovered, north-dipping Tacoma reverse fault is interpreted as a back thrust on the trailing edge of the belt, making the belt doubly vergent. Floor thrusts in the Seattle and Tacoma fault zones, imaged as discontinuous reflections, are interpreted as blind faults that flatten updip into bedding plane thrusts. Shallow monoclines in both the Seattle and Tacoma basins are interpreted to overlie the leading edges of thrust-bounded wedge tips advancing into the basins. Across the Seattle uplift, seismic lines image several shallow, short-wavelength folds exhibiting Quaternary or late Quaternary growth. From reflector truncation, several north-dipping thrust faults (splay thrusts) are inferred to core these shallow folds and to splay upward from a shallow roof thrust. Some of these shallow splay thrusts ruptured to the surface in the late Holocene. Ages from offset soils in trenches across the fault scarps and from abruptly raised shorelines indicate that the splay, roof, and floor thrusts of the Seattle and Tacoma faults ruptured about 1100 years ago.

Quaternary geologic map of the Havre 1° x 2° quadrangle

USGS Publications Warehouse

Compilations by Fullerton, David S.; Colton, Roger B.; Bush, Charles A.

2012-01-01

The Havre quadrangle encompasses approximately 16,084 km2 (6,210 mi2). The northern boundary is the Montana/Saskatchewan (U.S./Canada) boundary. The quadrangle is in the Northern Plains physiographic province and it includes parts of the Bearpaw Mountains, the Little Rocky Mountains, and the Boundary Plateau. The primary river is the Milk River. The ancestral Missouri River was diverted south of the Bearpaw Mountains by a Laurentide ice sheet. The fill in the buried ancestral valley at and southwest of Havre contains a complex stratigraphy of fluvial, glaciofluvial, ice-contact, glacial, lacustrine, and eolian deposits. The old valley east of Havre now is occupied by the Milk River. The map units are surficial deposits and materials, not landforms. Deposits that comprise some constructional landforms (e.g., ground-moraine deposits, end-moraine deposits, stagnation-moraine deposits, all composed of till) are distinguished for purposes of reconstruction of glacial history. Surficial deposits and materials are assigned to 24 map units on the basis of genesis, age, lithology or composition, texture or particle size, and other physical, chemical, and engineering characteristics. It is not a map of soils that are recognized in engineering geology, or of substrata or parent materials in which pedologic or agronomic soils are formed. Glaciotectonic (ice-thrust) structures and deposits are mapped separately, represented by a symbol. On the glaciated plains and on the Boundary Plateau the surficial deposits are glacial, ice-contact, glaciofluvial, catastrophic flood, alluvial, lacustrine, eolian, and colluvial deposits. In the Bearpaw Mountains and Little Rocky Mountains beyond the limit of Quaternary glaciation they are fluvial, colluvial, and mass-wasting deposits and residual materials. Tills of late Wisconsin and Illinoian ages are represented by map units. Tills of two pre-Illinoian glaciations are not mapped but are widespread in the subsurface and are identified in stratigraphic sections. Thirteen stratigraphic sections document a complex glacial and interglacial history in the quadrangle. Pliocene continental glaciation possibly is represented by erratic blocks of garnet gneiss and pegmatite from the Canadian Shield, perched high on drainage divides in the western Bearpaw Mountains. Glacial striations on bedrock, two boulder trains, and linear ice-molded landforms (primarily drumlins) indicate the possible presence of an east-southeast flowing ice stream in the Havre glacial lobe during late Wisconsin glaciation.

How to build the Eiger: Surface expression of litho-tectonic preconditioning

NASA Astrophysics Data System (ADS)

Mair, David; Lechmann, Alessandro; Schlunegger, Fritz

2017-04-01

The north face of the Eiger has exerted a strong attraction on alpinists, but also on geologists during the past decades, mainly because of its triangular, nearly vertical shape. We build on this tradition and investigate the relationship between the shape of this mountain and its underlying lithology, and its history of folding and thrusting. To this extent, we constructed a geometric 3D geological model of the Eiger-Moench-Jungfrau mountain chain in the central Swiss Alps. We proceeded through compilations of geological maps that we combined with new mapping in the field and collection of structural data such as the orientation of lineaments and faults. The model itself was constructed by interpolation of interfaces between geological formations, thrust- and fold-geometries between several NW-SE running, balanced, cross-sections. In addition, new geological data from the Jungfraubahn railway tunnel was used to verify surface data and improve the resulting model in the depth. The analyzed units of the Hercynian crystalline basement of the Aar massif and the Mesozoic cover rocks of the Helvetics form a foliated and thrusted stack. Multiple ductile structure sets bear witness of Alpine deformation and are dominant amid the mark of later brittle deformation across the whole mountain. There are two major outcomes of this analysis. First, the thrust contact between two stacks, which comprise a foliated basement and cover rocks, are responsible for the shape and overall architecture of the Eiger and its famous north face. Second, the high-resolution 3D structural model paired with petrological data shows that second-order, horizontally aligned morphological steps in the north face are related to the foliation within the bedrock. We suspect the inherited fabric significantly modified the susceptibility to erosion mechanisms which in turn further amplified the morphological differences (expressed in e.g. terrain roughness or slope).

Near-Surface and High Resolution Seismic Imaging of the Bennett Thrust Fault in the Indio Mountains of West Texas

NASA Astrophysics Data System (ADS)

Vennemann, Alan

My research investigates the structure of the Indio Mountains in southwest Texas, 34 kilometers southwest of Van Horn, at the UTEP (University of Texas at El Paso) Field Station using newly acquired active-source seismic data. The area is underlain by deformed Cretaceous sedimentary rocks that represent a transgressive sequence nearly 2 km in total stratigraphic thickness. The rocks were deposited in mid Cretaceous extensional basins and later contracted into fold-thrust structures during Laramide orogenesis. The stratigraphic sequence is an analog for similar areas that are ideal for pre-salt petroleum reservoirs, such as reservoirs off the coasts of Brazil and Angola (Li, 2014; Fox, 2016; Kattah, 2017). The 1-km-long 2-D shallow seismic reflection survey that I planned and led during May 2016 was the first at the UTEP Field Station, providing critical subsurface information that was previously lacking. The data were processed with Landmark ProMAX seismic processing software to create a seismic reflection image of the Bennett Thrust Fault and additional imbricate faulting not expressed at the surface. Along the 1-km line, reflection data were recorded with 200 4.5 Hz geophones, using 100 150-gram explosive charges and 490 sledge-hammer blows for sources. A seismic reflection profile was produced using the lower frequency explosive dataset, which was used in the identification of the Bennett Thrust Fault and additional faulting and folding in the subsurface. This dataset provides three possible interpretations for the subsurface geometries of the faulting and folding present. However, producing a seismic reflection image with the higher frequency sledge-hammer sourced dataset for interpretation proved more challenging. While there are no petroleum plays in the Indio Mountains region, imaging and understanding subsurface structural and lithological geometries and how that geometry directs potential fluid flow has implications for other regions with petroleum plays.

Evidence for the stability of the West Antarctic Ice Sheet divide for 1.4 million years

NASA Astrophysics Data System (ADS)

Hein, Andrew S.; Woodward, John; Marrero, Shasta M.; Dunning, Stuart A.; Steig, Eric J.; Freeman, Stewart P. H. T.; Stuart, Finlay M.; Winter, Kate; Westoby, Matthew J.; Sugden, David E.

2016-02-01

Past fluctuations of the West Antarctic Ice Sheet (WAIS) are of fundamental interest because of the possibility of WAIS collapse in the future and a consequent rise in global sea level. However, the configuration and stability of the ice sheet during past interglacial periods remains uncertain. Here we present geomorphological evidence and multiple cosmogenic nuclide data from the southern Ellsworth Mountains to suggest that the divide of the WAIS has fluctuated only modestly in location and thickness for at least the last 1.4 million years. Fluctuations during glacial-interglacial cycles appear superimposed on a long-term trajectory of ice-surface lowering relative to the mountains. This implies that as a minimum, a regional ice sheet centred on the Ellsworth-Whitmore uplands may have survived Pleistocene warm periods. If so, it constrains the WAIS contribution to global sea level rise during interglacials to about 3.3 m above present.

Deformation of the Roberts Mountains Allochthon in north-central Nevada

USGS Publications Warehouse

Evans, James George; Theodore, Ted G.

1978-01-01

During the Antler orogeny in Late Devonian and Early Mississippian time, early and middle Paleozoic siliceous rocks, largely chert and sha1e, were thrust eastward for 90 to 160 km over coexisting carbonate rocks. Minor and major structures of two small areas of the allochthon at Battle Mountain and in the southern Tuscarora Mountains were studied in order to characterize the deformation and test the consistency of the movement plan with respect to the large eastward displacement. In the Battle Mountain area, the lower Paleozoic Scott Canyon and Valmy Formations were deformed in the Antler orogeny but were unaffected by later tectonism during late Paleozoic or early Mesozoic. In the southern Tuscarora Mountains area, the Ordovician and Silurian siliceous rocks deformed in the Antler Orogeny were deformed by later, possibly Mesozoic, folding and thrusting. Most of the minor folding visible in the allochthon is in the cheret, but proportionally more of the strain was taken up in the shale and argillite, both poorly exposed but predominant rock types. Most minor folds, concentric in form, plunge at small angles to the north-northeast and south-southwest with steeply dipping or vertical axial planes. The b-fabric axis, parallel to these folds, is identical apparently to the B-kinematic axis. The horizontal component of tectonic shortening of the allochthon, N. 70?-75? W. both in the Battle Mountain area and in the southern Tuscarora Mountains area, is therefore consistent with an eastward direction of movement of the allochthon. Folds with west- northwest trends locally present in the allochthon, may have formed in the direction of tectonic transport. In the southern Tuscarora Mountains, local strain in and below the allochthon was different from the prevailing strain in the allochthon, and tectonic shortening was locally at large angles to the accepted direction of movement of the allochthon.

Geochronology and geology of late Oligocene through Miocene volcanism and mineralization in the western San Juan Mountains, Colorado

USGS Publications Warehouse

Bove, Dana J.; Hon, Ken; Budding, Karin E.; Slack, John F.; Snee, Lawrence W.; Yeoman, Ross A.

2001-01-01

This paper presents 25 new 40Ar/39Ar dates from the main calc-alkaline ash-flow sheets and related younger plutons of the western San Juan volcanic field, the ash-flow sheets of the Lake City caldera cycle, and veins and other altered rocks in the Lake City region. The goal of the study was to produce similar quality 40Ar/39Ar ages to those currently published for the eastern and central San Juan Mountains. These new data provide a much more precise chronological framework for interpreting durations of events and their relationship to mineralization than do previously published conventional K-Ar dates for the western San Juan Mountains.

Origin and tectonic significance of a Mesozoic multi-layer over-thrust system within the Yangtze Block (South China)

NASA Astrophysics Data System (ADS)

Yan, Dan-Ping; Zhou, Mei-Fu; Song, Hong-Lin; Wang, Xin-Wen; Malpas, John

2003-01-01

In the Yangtze Block (South China), a well-developed Mesozoic thrust system extends through the Xuefeng and Wuling mountains in the southeast to the Sichuan basin in the northwest. The system comprises both thin- and thick-skinned thrust units separated by a boundary detachment fault, the Dayin fault. To the northwest, the thin-skinned belt is characterized by either chevron anticlines and box synclines to the northwest or chevron synclines to the southeast. The former structural style displays narrow exposures for the cores of anticlines and wider exposures for the cores of synclines. Thrust detachments occur along Silurian (Fs) and Lower Cambrian (Fc) strata and are dominantly associated with the anticlines. To the southeast, this style of deformation passes gradually into one characterized by chevron synclines with associated principal detachment faults along Silurian (Fs), Cambrian (Fc) and Lower Sinian (Fz) strata. There are, however, numerous secondary back thrusts. Therefore, the thin-skinned belt is like the Valley and Ridge Province of the North American Applachian Mountains. The thick-skinned belt structurally overlies the thin-skinned belt and is characterized by a number of klippen including the Xuefeng and Wuling nappes. It is thus comparable to the Blue Ridge Province of Appalachia. The structural pattern of this thrust system in South China can be explained by a model involving detachment faulting along various stratigraphic layers at different stages of its evolution. The system was developed through a northwest stepwise progression of deformation with the earliest delamination along Lower Sinian strata (Fz). Analyses of balanced geological cross-sections yield about 18.1-21% (total 88 km) shortening for the thin-skinned unit and at least this amount of shortening for the thick-skinned unit. The compressional deformation from southeast to northwest during Late Jurassic to Cretaceous time occurred after the westward progressive collision of the Yangtze Block with the North China Block and suggests that the orogenic event was intracontinental in nature.

Role of Neogene Exhumation and Sedimentation on Critical-Wedge Kinematics in the Zagros Orogenic Belt, Northeastern Iraq, Kurdistan

NASA Astrophysics Data System (ADS)

Koshnaw, R. I.; Horton, B. K.; Stockli, D. F.; Barber, D. E.; Tamar-Agha, M. Y.; Kendall, J. J.

2014-12-01

The Zagros orogenic belt and foreland basin formed during the Cenozoic Arabia-Eurasia collision, but the precise histories of shortening and sediment accumulation remain ambiguous, especially at the NW extent of the fold-thrust belt in Iraqi Kurdistan. This region is characterized by well-preserved successions of Cenozoic clastic foreland-basin fill and deformed Paleozoic-Mesozoic hinterland bedrock. The study area provides an excellent opportunity to investigate the linkage between orogenic wedge behavior and surface processes of erosion and deposition. The aim of this research is to test whether the Zagros orogenic wedge advanced steadily under critical to supercritical wedge conditions involving in-sequence thrusting with minimal erosion or propagated intermittently under subcritical condition involving out-of-sequence deformation with intense erosion. These endmember modes of mountain building can be assessed by integrating geo/thermochronologic and basin analyses techniques, including apatite (U-Th)/He thermochronology, detrital zircon U-Pb geochronology, stratigraphic synthesis, and seismic interpretations. Preliminary apatite (U-Th)/He data indicate activation of the Main Zagros Fault (MZF) at ~10 Ma with frontal thrusts initiating at ~8 Ma. However, thermochronometric results from the intervening Mountain Front Flexure (MFF), located between the MZF and the frontal thrusts, suggest rapid exhumation at ~6 Ma. These results suggest that the MFF, represented by the thrust-cored Qaradagh anticline, represents a major episode of out-of-sequence deformation. Detrital zircon U-Pb analyses from the Neogene foreland-basin deposits show continuous sediment derivation from sources to the NNE in Iraq and western Iran, suggesting that out-of-sequence thrusting did not significantly alter sedimentary provenance. Rather, intense hinterland erosion and recycling of older foreland-basin fill dominated sediment delivery to the basin. The irregular distribution of thermochronologic ages, hinterland growth, extensive erosion, and recycled sediment in the Neogene foreland basin imply that the Zagros orogenic wedge in the Iraqi Kurdistan region largely developed under subcritical wedge conditions.

40Ar/39Ar dates from alkaline intrusions of the northern Crazy Mountains, south-central Montana

NASA Astrophysics Data System (ADS)

Harlan, S. S.

2005-05-01

The Crazy Mountains basin of south-central Montana is a complex foreland basin that formed during the interaction of thin-skinned, decollement-style folds of the Montana thrust belt and the basement-involved folds and thrust faults of the Rocky Mountain foreland province. Near the depositional center of the basin, synorogenic strata of the Paleocene Fort Union Formation have been intruded and locally thermally metamorphosed by strongly alkaline to subalkaline Tertiary intrusive rocks. The subalkaline rocks are found mostly in the southern Crazy Mountains and form stocks (Big Timber stock, Loco Mountain stock), radiating dikes and sills. With the exception of the Ibex Mountain sill (?), the alkaline rocks are restricted to the northern Crazy Mountains. New 40Ar/39Ar dates are reported from the strongly alkaline rocks, including the Comb Creek stock and dike swarm, the Ibex Mountain sill(?), and sills from the Robinson anticline intrusive complex. The alkaline rocks of the Robinson anticline intrusive complex are exposed in the easternmost folds of the Cordilleran fold and thrust belt, but despite their arcuate and apparently folded map geometry they have been shown to post-date folding. Hornblende from a trachyte sill in the Robinson anticline intrusive complex yielded a relatively simple age spectrum with a weighted mean of 50.61 ± 0.14 Ma (2σ), which probably records the age of sill emplacement. Nepheline syenite and mafic nepheline syenites of the Comb Creek stock and a dike from its radial dike swarm, two sills from the Robinson antlicline intrusive complex, and the Ibex Mountains sill(?) gave biotite plateau dates ranging from 50.03 to 50.22 Ma, with 2σ errors of ± 0.11 to 0.19 Ma. Because these dates are from fairly small, hypabyssal intrusions, they must have cooled quickly and thus these dates closely approximate the emplacement age of the intrusions. These data indicate that the strongly alkaline intrusions were emplaced during a fairly restricted interval of time at about 50.1 Ma. The dates from the alkaline rocks are somewhat older than dates from the subalkaline Big Timber stock in the southern Crazy Mountains, which gave biotite 40Ar/39Ar dates of about 49.3 Ma (du Bray and Harlan, 1996). However, because these dates represent cooling through closure temperatures of about 350° C, they are minimum estimates for the age of the stock. The limited span of 40Ar/39Ar dates between the alkaline and subalkaline rocks of the Crazy Mountains intrusions (i.e., 50.6 to 49.2 Ma) indicates that the magmas represented by these different geochemical groups were closely associated in both time and space, with emplacement occurring in as little as 1.5 Ma. On a regional scale, the 49-51 Ma age is similar to that of most of the igneous centers of the Central Montana alkalic province and is coeval with the peak of widespread volcanism in the Absaroka-Gallatin volcanic field immediately to the south of the Crazy Mountains Basin.

SSTAC/ARTS Review of the Draft Integrated Technology Plan (ITP). Volume 2: Propulsion Systems

NASA Technical Reports Server (NTRS)

1991-01-01

The topics addressed are: (1) space propulsion technology program overview; (2) space propulsion technology program fact sheet; (3) low thrust propulsion; (4) advanced propulsion concepts; (5) high-thrust chemical propulsion; (6) cryogenic fluid management; (7) NASA CSTI earth-to-orbit propulsion; (8) advanced main combustion chamber program; (9) earth-to-orbit propulsion turbomachinery; (10) transportation technology; (11) space chemical engines technology; (12) nuclear propulsion; (13) spacecraft on-board propulsion; and (14) low-cost commercial transport.

Uniquely Acquired Vintage Seismic Reflection Data Reveal the Stratigraphic and Tectonic History of the Montana Disturbed Belt, USA

NASA Astrophysics Data System (ADS)

Speece, M. A.; Link, C. A.; Stickney, M.

2011-12-01

In 1983 and 1984 Techco of Denver, Colorado, acquired approximately 302 linear kilometers of two-dimensional (2D) seismic reflection data in Flathead and Lake Counties, Montana, USA, as part of an initiative to identify potential drilling targets beneath the Swan and Whitefish Mountain Ranges and adjacent basins of northwestern Montana. These seismic lines were collected in the Montana Disturbed Belt (MDB) or Montana thrust belt along the western edge of Glacier National Park in mountainous terrain with complicated subsurface structures including thrust faults and folds. These structures formed during the Laramide Orogeny as sedimentary rocks of the Precambrian Belt Supergroup were thrust eastward. Later, during the Cenozoic, high-angle normal faults produced prominent west-facing mountain scarps of the Mission, Swan and Whitefish mountains. The 1983 data set consisted of two profiles of 24-fold (96-channels) Vibroseis data and four profiles of 24-fold (96-channels) helicopter-assisted dynamite data. The dynamite data were collected using the Poulter Method in which explosives were placed on poles and air shots were recorded. The 1983 dynamite profiles extend from southwest to northeast across the Whitefish Mountain Range to the edge of Glacier National Park and the Vibroseis data were collected along nearby roadways. The 1984 data set consists of four profiles of 30-fold (120-channels) helicopter-assisted dynamite data that were also collected using the Poulter Method. The 1984 profiles cross the Swan Mountain Range between Flathead Lake and Glacier National Park. All of these data sets were recently donated to Montana Tech and subsequently recovered from nine-track tape. Conventionally processed seismic stacked sections from the 1980s of these data show evidence of a basement decollement that separates relatively undeformed basement from overlying structures of the MDB. Unfortunately, these data sets have not been processed using modern seismic processing techniques including linear noise suppression of the air wave and ground roll, refraction statics, and prestack migration. Reprocessing of these data using state-of-the-art seismic reflection processing techniques will provide a detailed picture of the stratigraphy and tectonic framework for this region. Moreover, extended correlations of the Vibroseis records to Moho depths might reveal new insights on crustal thickness and provide a framework for understanding crustal thickening during the Laramide Orogeny as well as later Cenozoic extension.

Neogene compressional deformation and possible thrust faulting in southwest Dominican Republic

NASA Technical Reports Server (NTRS)

Golombek, M. P.; Goreau, P.; Dixon, T. H.

1985-01-01

Analysis of regional and high resolution remote sensing data coupled with detailed field investigations indicates Neogene compressional deformation in the southwest Dominican Republic. Airborne synthetic aperture radar data and high resolution near infrared photography show folds in Tertiary sediments and possible thrust fault scarps implying NE to SW compression in the region. Large road cuts through the scarps allow study of otherwise poorly accessible, heavily vegetated karst terrain. Deformation increases toward scrap fronts where small bedding-plane thrust faults become more numerous. Analysis of mesoscopic faults with slickensides indicates compression oriented between N to S and E to W. The lowermost scarp has highly sheared fault breccia and undeformed frontal talus breccias implying it is the basal thrust into which the higher thrust faults sole. Thus, the scarps probably formed in a regional NE to SW compressional stress regime and are the toes of thrust sheets. Previous workers have suggested that these scarps are ancient shorelines. However, the gross morphology of the scarps differs substantially from well known erosional terraces on the north coast.

Method of constructing dished ion thruster grids to provide hole array spacing compensation

NASA Technical Reports Server (NTRS)

Banks, B. A. (Inventor)

1976-01-01

The center-to-center spacings of a photoresist pattern for an array of holes applied to a thin metal sheet are increased by uniformly stretching the thin metal sheet in all directions along the plane of the sheet. The uniform stretching is provided by securely clamping the periphery of the sheet and applying an annular force against the face of the sheet, within the periphery of the sheet and around the photoresist pattern. The technique is used in the construction of ion thruster grid units where the outer or downstream grid is subjected to uniform stretching prior to convex molding. The technique provides alignment of the holes of grid pairs so as to direct the ion beamlets in a direction parallel to the axis of the grid unit and thereby provide optimization of the available thrust.

Plateau growth around the Changma Basin in NE Tibet

NASA Astrophysics Data System (ADS)

Vernon, Rowan; Cunningham, Dickson; Zhang, Jin; England, Richard

2014-05-01

The Qilian Mountains form one of the most actively uplifting regions of the northeastern Tibetan Plateau and provide an opportunity to study the ongoing, intermediate stages of plateau growth. The crust of the Qilian Mountains consists of an orogenic collage of mid-Proterozoic to mid-Palaeozoic island arc terranes accreted to the North China Craton during the Palaeozoic. NE-directed compression related to the Indo-Asian collision began in the Early Neogene, uplifting fold-thrust mountain ranges which splay south-eastwards from the sinistral northeast-trending Altyn Tagh Fault (ATF). In this study, we investigate the post-Oligocene tectonic evolution of the northern margin of the Tibetan Plateau around the Changma Basin, at the very northeast corner of the Plateau, where the ATF forms a triple junction with the frontal Qilian Shan thrust. Our research involves synthesis of previous geological and geophysical data, remote sensing analysis and field mapping of structures along key transects. The Changma Basin is a relatively low intra-montane basin in the northeast Tibetan Plateau that is receiving alluvial infill from surrounding ranges, but is also being drained by the Su Le River, one of the largest river systems in the northeast Tibetan Plateau. The basin is also internally deforming and inverting along fault and fold zones, as well as being overthrust along some of its margins. Where older basement trends are parallel to neotectonic faults, some reactivation is inferred and locally documented through field observations. Otherwise, the post-Oligocene thrust and oblique-slip faults which are responsible for uplifting various basement blocks and inverting the Changma Basin appear discordant to nearby basement trends. Range-bounding thrust faults with the greatest along-strike continuity and relief generation are assumed to have the largest displacements, whereas other intra-range thrusts that bound uplifted limestone blocks are assumed to have lower amounts of displacement. Structural transects reveal a lack of intra-range reactivation of inherited structures or fabrics, concentrating uplift on the lithologically-controlled intra-range thrust faults and the major range-bounding thrust and oblique-slip faults. Northeast of the Changma Basin, in the Qilian Shan foreland, an east-trending belt of low folds and faulted ridges along the ATF marks the structural continuation of the Yumen Shan range. We find that uplift and growth of northeastern Tibet is complex with local variations in structural vergence, degree of strain partitioning, fault reactivation and basin inversion. This complexity reflects both the buttressing effect of the rigid Archaean basement directly to the north and the variation in the structural trends and lithologies of the Qilian basement, as well as the competition between uplift and erosion in the region.

Active folding and thrusting in North Africa: A framework for a seismotectonic model of the Atlas Mountains

NASA Astrophysics Data System (ADS)

Meghraoui, Mustapha; Maouche, Said; Timoulali, Youssef; Bouhadad, Youcef; Bouaziz, Samir

2013-04-01

Large earthquakes in the Atlas Mountains of North Africa are often generated on thrust or reverse faults. For inland faults, surface ruptures and long-term active tectonics appear as a thrust escarpment and fold-related faulting visible in the field and using remote sensing images, or measured using space-borne geodesy (GPS or INSAR). For coastal faults, major uplifts of late Quaternary marine terraces and folding with steplike morphology are exposed indicating the incremental development of coastal active deformation. We have investigated the similarities and differences between different active fault-related folding along the Africa - Eurasia convergent plate boundary. These active structures are seismogenic and the striking case studies are the 1960 Agadir (Mw 5.9), the 1954 Orleansville (Mw 6.7), the 1980 El Asnam (Mw 7.3), the 1992 Gafsa (Mw 5.3), the 1999 Ain Temouchent (Mw 6.0), and the 2003 Zemmouri (Mw 6.8) earthquakes. From paleoseismic investigations the El Asnam active fold shows 0.6 to 1.0 mm/yr uplift rate. West of Algiers on the Sahel anticline, the levelling of uplifted successive coastal benches and notches document the incremental folding uplift with ~ 0.84 - 1.2 mm/yr uplift rate in the last 120-140 ka. The relatively fast folding growth during late Pleistocene and Holocene in the Atlas Mountains attests for the significance of earthquake activity and the importance of convergent movements between Africa and Eurasia in the Western Mediterranean. This work is prepared in the framework of the UNESCO (SIDA) - IGCP Project 601 "Seismotectonics and Seismic Hazards in Africa".

Structural analysis and tectonic evolution of the eastern Binalud Mountains, NE Iran

NASA Astrophysics Data System (ADS)

Sheikholeslami, M. R.; Kouhpeyma, M.

2012-10-01

The Binalud Mountains are situated in the south of the Kopeh Dagh as a transitional zone between the Alborz and Central Iran zones. The Palaeotethys suture of the north Iran is located in this area. The Binalud Mountains consists of relatively thick successions of sedimentary, metamorphic and igneous rocks. The earliest deformation, a polyphase synmetamorphic deformation which occurred entirely in ductile conditions, is distinguished in the metamorphic rocks of the eastern part. D1, D2 and D3 deformation phases are related to this deformation. The D4 deformation affected the area after a period of sedimentation and erosion. The thrust faults of the central and southern part of the eastern Binalud were classified as structures related to the D5 tectonic event. From the geodynamic point of view, in Late Palaeozoic times the studied area formed an oceanic trench generated by the subduction of the Palaeotethys oceanic lithosphere beneath the Turan Plate. In the Late Triassic, the Early Cimmerian Event resulted in a collisional type orogeny generating a transpression polyphase deformation and the metamorphism of Permian and older sediments. Following this collision, granite intrusions were emplaced in the area and caused contact metamorphism. The exhumation and erosion of the rocks deformed and metamorphosed during Early Cimmerian Event caused the formation of molassic type sediments in a Rhaetian-Lias back arc basin. The continuation of convergence between the Turan and Iran Plates caused the metamorphism of these sediments and their transformation to phyllite and meta-sandstone. During Late Mesozoic and Early Cenozoic times, the convergence between Central Iran and Turan Plates continued and a NE compression caused folding of the Cretaceous and older rocks in the Kopeh Dagh area. In the Binalud area this deformation caused the generation of several thrust fault systems with S to SW vergence, resulting in a thrusting of Palaeozoic and Mesozoic successions on each other and on the Neogene sediments at the southern border of the Binalud Mountains.

Cordilleran front range structural features in northwest Montana interpreted from vintage seismic reflection data

NASA Astrophysics Data System (ADS)

Porter, Mason C.; Rutherford, Bradley S.; Speece, Marvin A.; Mosolf, Jesse G.

2016-04-01

Industry seismic reflection data spanning the Rocky Mountain Cordillera front ranges of northwest Montana were reprocessed and interpreted in this study. Five seismic profiles represent 160 km of deep reflection data collected in 1983 that span the eastern Purcell anticlinorium, Rocky Mountain Trench (RMT), Rocky Mountain Basal Décollement (RMBD), and Lewis thrust. The data were reprocessed using modern techniques including refraction statics, pre-stack time migration (PSTM), and pre- and post-stack depth migration. Results indicate the RMBD is 8-13 km below the Earth's surface and dip 3-10° west. Evidence for the autochthonous Mesoproterozoic Belt and basal Cambrian rocks beneath the RMBD is present in all of the profiles and appears to extend east of the RMT. The Lewis thrust was identified in the seismic profiles and appears to sole into the RMBD east of the RMT. The RMT fault system has a dip displacement of 3-4 km and forms a half graben filled with 1 km of unconsolidated Tertiary sedimentary deposits. The RMT and adjacent Flathead fault systems are interpreted to be structurally linked and may represent a synthetic, en echelon fault system.

Predicting orogenic wedge styles as a function of analogue erosion law and material softening

NASA Astrophysics Data System (ADS)

Mary, Baptiste C. L.; Maillot, Bertrand; Leroy, Yves M.

2013-10-01

The evolution of a compressive frictional wedge on a weak, frictional and planar décollement, subjected to frontal accretion, is predicted with a two step method called sequential limit analysis. The first step consists in finding, with the kinematic approach of limit analysis, the length of the active décollement and the dips of the emerging ramp and of the conjugate shear plane composing the emerging thrust fold. The second step leads to a modification of the geometry, first, because of the thrust fold development due to compression and, second, because of erosion. Erosion consists in removing periodically any material above a fictitious line at a selected slope, as done in analogue experiments. This application of sequential limit analysis generalizes the critical Coulomb wedge theory since it follows the internal deformation development. With constant frictional properties, the deformation is mostly diffuse, a succession of thrust folds being activated so that the topographic slope reaches exactly the theoretical, critical value. Frictional weakening on the ramps results in a deformation style composed of thrust sheets and horses. Applying an erosion slope at the critical topographic value leads to exhumation in the frontal, central, or rear region of the wedge depending on the erosion period and the weakening. Erosion at slopes slightly above or below the critical value results in exhumation toward the foreland or the hinterland, respectively, regardless of the erosion period. Exhumation is associated with duplexes, imbricate fans, antiformal stacks, and major backthrusting. Comparisons with sandbox experiments confirm that the thickness, dips, vergence, and exhumation of thrust sheets can be reproduced with friction and erosion parameters within realistic ranges of values.

Complex thrusting at the toe of the Nankai accretionary prism, NanTroSEIZE Kumano transect

NASA Astrophysics Data System (ADS)

Moore, G. F.; Park, J.; Kodaira, S.; Kaneda, Y.

2009-12-01

Seismic reflection data collected over the past 10 years by the Institute for Research on Earth Evolution (IFREE) of Japan Agency for Marine Earth Science and Technology (JAMSTEC) image a zone of complex thrusting at the toe of the Nankai accretionary prism south of Kii Peninsula, Honshu, Japan. The frontal part of the Nankai prism west of Shionomisaki Canyon (SC) at ~136° E, including the Muroto and Ashizuri Transects off Shikoku, is generally formed of imbricate thrusts with spacing of ~ 1-3 km that dip ~25-35° landward and sole into a prominent décollement. Out-of-sequence thrusts (OOSTs) are usually restricted to the landward margin of this imbricate thrust zone. East of SC, in the Kumano Transect area, the imbricate thrust zone is bounded on its seaward edge by a frontal thrust block that is ~5-6 km wide and consists of several OOSTs. The frontal thrust dips ~5-10° under this ~2-4 km thick block, emplacing this thrust sheet over the trench floor. The number and character of thrusts within the frontal thrust block vary laterally along strike. The 2006 Kumano 3D seismic data set images details of one segment of this complex frontal thrust block. Out-of-sequence faulting has led to underplating of several smaller thrust slices and movement along oblique ramps has led to a complex pattern of faulting that cannot be recognized in even closely-spaced 2D seismic lines. The frontal thrust block is further modified by subduction of seamounts and ridges that have caused large slumps of material from the block.

Regional metamorphism in the Condrey Mountain Quadrangle, north-central Klamath Mountains, California

USGS Publications Warehouse

Hotz, Preston Enslow

1979-01-01

A subcircular area of about 650 km 2 in northern California and southwestern Oregon is occupied by rocks of the greenschist metamorphic facies called the Condrey Mountain Schist. This greenschist terrane is bordered on the east and west by rocks belonging to the amphibolite metamorphic facies that structurally overlie and are thrust over the Condrey Mountain Schist. The amphibolite facies is succeeded upward by metavolcanic and metasedimentary rocks belonging to the greenschist metamorphic facies. The Condrey Mountain Schist is composed predominantly of quartz-muscovite schist and lesser amounts of actinolite-chlorite schist formed by the metamorphism of graywacke and spilitic volcanic rocks that may have belonged to the Galice Formation of Late Jurassic age. Potassium-argon age determinations of 141?4 m.y. and 155?5 m.y. obtained on these metamorphic rocks seem to be incompatible with the Late Jurassic age usually assigned the Galice. The rocks that border the amphibolite facies are part of an extensive terrane of metavolcanic and metasedimentary rocks belonging to the western Paleozoic and Triassic belt. The metavolcanic rocks include some unmetamorphosed spilite but are mostly of the greenschist metamorphic facies composed of oligoclase (An15-20) and actinolite with subordinate amounts of chlorite and clinozoisiteepidote. The interbedded sedimentary rocks are predominantly argillite and slaty argillite, less commonly siliceous argillite and chert, and a few lenticular beds of marble. On the south, high-angle faults and a tabular granitic pluton separate the greenschist metavolcanic terrane from the amphibolite facies rocks; on the east, nonfoliated amphibolite is succeeded upward, apparently conformably, by metasedimentary rocks belonging to the greenschist metavolcanic terrane. In the southern part of Condrey Mountain quadrangle, an outlier of a thrust plate composed of the Stuart Fork Formation overlies the metavolcanic and metasedimentary rocks. The Stuart Fork in this region is composed of siliceous phyllite and phyllitic quartzite and is believed to be the metamorphosed equivalent of rocks over which it is thrust. In the Yreka-Fort Jones area, potassium-argon determinations on mica from the blueschist facies in the Stuart Fork gave ages of approximately 220 m.y. (Late Triassic) for the age of metamorphism. Rocks of the amphibolite facies structurally overlie the Condrey Mountain Schist along a moderate to steeply dipping thrust fault. The amphibolite terrane is composed of amphibolite and metasedimentary rocks in approximately equal amounts accompanied by many bodies of serpentinite and a number of gabbro and dioritic plutons. Most of the amphibolite is foliated, but some is nonfoliated; the nonfoliated amphibolite has an amphibolite mineralogy and commonly a relict volcanic rock texture. The nonfoliated amphibolite occurs on the southern and eastern borders of the amphibolite terrane between the areas offoliated amphibolite and the overly ing metavolcanic and metasedimentary rocks. Hornblende and plagioclase (An30-35) are the characteristic minerals, indicating that the rocks are of the almandine-amphibolite metamorphic facies. The metasedimentary rocks interbedded with the amphibolites include siliceous schist and phyllite, minor quartzite, and subordinate amounts of marble. Potassium-argon age dates obtained on hornblende from foliated amphibolite yield ages of 146?4 and 148? 4 m.y., suggesting a Late Jurassic metamorphic episode. Mafic and ultramafic rocks are widespread in the amphibolite terrane but are almost entirely absent from the area of greenschist facies metavolcanic and metasedimentary rocks. The ultramafic rocks, predominantly serpentinite, occur as a few large bodies and many small tabular concordant bodies interleaved with the foliated rocks. The ultramafic rocks include harzburgite and d1lIlite and their serpentinized equivalents. In the Condrey Mountain quadrangle, probably more t

Analogue modeling of 3-D structural segmentation in fold-and-thrust belts: interactions between frictional and viscous provinces in foreland basins

NASA Astrophysics Data System (ADS)

Borderie, Sandra; Graveleau, Fabien; Witt, César; Vendeville, Bruno C.

2016-04-01

Accretionary wedges are generally segmented both across and along strike because of diverse factors including tectonic and stratigraphic inheritance. In fold-and-thrust belts, along-strike stratigraphic changes in the foreland sequence are classically observed and cause a curvature of the deformation front. Although the parameters controlling this curvature are well documented, the structural interactions and mutual influences between adjacent provinces are much less analyzed. To investigate this question, we deformed analogue models in a compressional box equipped with digital cameras and a topographic measurement apparatus. Models where shortened above a basal frictional detachment (glass microbeads) and segmentation was tested by having a region in which we added an interbedded viscous level (silicone polymer) within the sedimentary cover (dry sand). By changing the number (2 or 3) and the relative width of the purely frictional and viscous provinces, our goal was to characterize geometrically and kinematically the interactions between the viscous and the purely frictional provinces. We used a commercial geomodeller to generate 3-D geometrical models. The results indicate that regardless of the relative width of the purely frictional vs. viscous provinces, the deformation style in the frictional province is not influenced by the presence of the adjacent viscous province. On the contrary, the structural style and the deformation kinematics in the viscous province is significantly impacted by the presence or absence of an adjacent purely frictional province. At first order, the deformation style in the viscous province depends on its width, and three structural styles can be defined along strike. Far from the frictional area, structures are primarily of salt-massif type, and they do not seem to be influenced by the frictional wedge province. Towards the frictional province, deformation changes gradually to a zone of purely forethrusts (foreland verging), and finally to a highly faulted zone with both fore- and backthrusts (hinterland verging). In addition, a kinematic analysis indicates that narrow viscous provinces are strongly influenced by the presence of an adjacent frictional province. Indeed, propagation of shallow thrusts occurs in sequence and the deformation front reaches lately the external décollement pinchout. On the contrary, the deformation front of the wide viscous provinces propagates rapidly to the external décollement pinchout, then younger thrusts form out of sequence. Along-strike segmentation also affects the deep structures (thrusts detaching on the basal frictional décollement). In the viscous province, the presence of an upper viscous décollement opposes the advance of the basal deformation front. There, the rear of the wedge is characterized by imbrications of thrusts sheets (antiformal stacks), and the deep deformation front is convex towards the hinterland. Our experiments allow to better understand the dynamics of salt-controlled fold-and-thrust belts such as in the Huallaga (Peru) and Kuqa (China) basins or the Franklin Mountains (NW Canada).

Multistory duplexes with forward dipping roofs, north central Brooks Range, Alaska

USGS Publications Warehouse

Wallace, W.K.; Moore, Thomas E.; Plafker, G.

1997-01-01

The Endicott Mountains allochthon has been thrust far northward over the North Slope parautochthon in the northern Brooks Range. Progressively younger units are exposed northward within the allochthon. To the south, the incompetent Hunt Fork Shale has thickened internally by asymmetric folds and thrust faults. Northward, the competent Kanayut Conglomerate forms a duplex between a floor thrust in Hunt Fork and a roof thrust in the Kayak Shale. To the north, the competent Lisburne Group forms a duplex between a floor thrust in Kayak and a roof thrust in the Siksikpuk Formation. Both duplexes formed from north vergent detachment folds whose steep limbs were later truncated by south dipping thrust faults that only locally breach immediately overlying roof thrusts. Within the parautochthon, the Kayak, Lisburne, and Siksikpuk-equivalent Echooka Formation form a duplex identical to that in the allochthon. This duplex is succeeded abruptly northward by detachment folds in Lisburne. These folds are parasitic to an anticlinorium interpreted to reflect a fault-bend folded horse in North Slope "basement," with a roof thrust in Kayak and a floor thrust at depth. These structures constitute two northward tapered, internally deformed wedges that are juxtaposed at the base of the allochthon. Within each wedge, competent units have been shortened independently between detachments, located mainly in incompetent units. The basal detachment of each wedge cuts upsection forward (northward) to define a wedge geometry within which units dip regionally forward. These dips reflect forward decrease in internal structural thickening by forward vergent folds and hindward dipping thrust faults. Copyright 1997 by the American Geophysical Union.

State of balance of the cryosphere

NASA Technical Reports Server (NTRS)

Van Der Veen, C. J.

1991-01-01

Available observations and mass balance estimates of the cryosphere are summarized. Problems discussed include mountain glaciers, the Greenland ice sheet, the Antarctic ice sheet, conventional glacier measurement techniques, and satellite applications in glacier mass balance studies. It is concluded that the interior part of the Greenland ice sheet is thickening or in near equilibrium. Estimates of the mass balance of the Antarctic ice sheet suggest that it is positive, although the error limits allow for a slightly negative balance.

1. Title Sheet; Door Profiles; Roof Truss, Protestant Chapel; Mess ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

1. Title Sheet; Door Profiles; Roof Truss, Protestant Chapel; Mess Hall/Corridor Window Jamb; Circular Stair Newel Post and Balustrade - National Home for Disabled Volunteer Soldiers - Battle Mountain Sanitarium, Mess Hall, 500 North Fifth Street, Hot Springs, Fall River County, SD

Neogene Tectonics of Part of the Junction of Cyprus and Hellenic Arcs in the Eastern Mediterranean Sea

NASA Astrophysics Data System (ADS)

Küçük, H. M.; Dondurur, D.; ćifçi, G.; Gürçay, S.; Hall, J.; Yaltırak, C.; Aksu, A. E.

2012-04-01

The junction between the Hellenic and Cyprus Arcs is one of the tectonically most active regions of the eastern Mediterranean. This junction developed in association with convergence between the African and Eurasian Plates, and the re-organization of the smaller Aegean-Anatolian and Arabian Microplates. Recent studies have shown that the predominant Miocene deformation process in the eastern Mediterranean is compressional tectonism. However, many studies have also shown that the strain is partitioned in the Pliocene-Quaternary and the area displays regions dominated by compression, strike slip and extensional tectonism. The junction between the Hellenic and Cyprus Arcs exhibits complex morphological features including submarine mountains, rises, ridges and trenches. Approximately 600 km of high resolution 72-channel seismic profiles were collected from the junction of Cyprus and Hellenic Arcs using a 450 m long 6.25 m hydrophone spacing streamer and a seven gun array with a 200 cubic inch total volume. This project was part of the joint scientific venture between Dokuz Eylül University (Turkey) and Memorial University of Newfoundland (Canada), and was funded by TÜBITAK and NSERC. The study area includes the southwestern Antalya Basin and the Anaxagoras Mountain of the larger Anaximander Mountains. The multichannel data were processed both at Dokuz Eylül and Memorial University of Newfoundland, using the Landmark Graphics ProMAX software, with automatic gain control, short-gap deconvolution, velocity analysis, normal move-out correction, stack, filter (typically 50-200 Hz bandpass), f-k time migration, and adjacent trace sum. Despite the fact that the source volume was modest, reflections are imaged to 2-3 s two-way time below seabed, even in 2 km water depth. The processed seismic reflection profiles show that there are three distinct sedimentary units, separated by two prominent markers: the M-reflector separates the Pliocene-Quaternary from the underlying Messinian evaporite successions, and the N-reflector separates the Messinian evaporite successions from the pre-Messinian Miocene sediments. Interpretation of the data clearly shows that the Miocene and Pliocene-Quaternary tectonic frameworks of the Anaxagoras Mountain are dominated by thrust faults. These major faults in turn, control all of the sedimentary structures observed over the submarine mountain. These thrusts display E-W trending map traces and show southerly vergence. The seismic profiles across the southwestern margin of the Antalya Basin, immediately north of the Anaxagoras Mountain show the presence of numerous upright anticlines and their intervening synclines. These structures are interpreted as salt-cored anticlines. Although mud volcanoes and diapiric structures have also been observed in the area, the normal-move-out velocities suggest that these structures are indeed cored by evaporites. The western margin of the Anaxagoras Mountain is delineated by a profound lineation which separates it from the Anaximander Mountains in the west. In the seismic reflection profiles, this lineation appears to be controlled by NE-SW-trending and mainly west-verging thrusts. The tip points of these thrusts lie at the depositional surface, and their trajectories can be traced well below 4-5 seconds. It is speculated that this prominent and somewhat arcuate boundary defines a crustal scale structure that links the Anaximander Mountains to the Antalya Basin. If so, it might have a sinistral strike slip component, possibly associated with the clockwise rotation of the Anaxagoras Mountain. The acoustic basement is located at approximately 5-6 s in the seismic reflection profiles from the Antalya Basin, and is interpreted to include Miocene-Oligocene sediments. A short seismic profile from the eastern side of Finike basin shows that Pliocene-Quaternary thickness of Finike Basin is more than in the Antalya Basin. The fact that no unequivocal evaporite successions are observed in the Finike Basin is puzzling and requires that the Finike Basin either remained above the depositional surface during the Messinian or was isolated from the eastern Mediterranean Sea.

Palaeoglaciology of the Central European Uplands - a link between the former ice masses over the Alps and Scandinavia

NASA Astrophysics Data System (ADS)

Hauzenberger, B.; Fickert, T.

2009-04-01

The Central European Uplands are located northeast of the Alps along the western edge of the Czech border. A horseshoe shaped range of low mountains contains the Bavarian Forest Mountains, the Fichtel Mountains, the Erz Mountains and the Giant Mountains, with highest summit altitudes ranging from 1051 m a.s.l. (Fichtel Mountains) to 1603 m a.s.l. (Giant Mountains). The location north of the Alps makes these mountains highly interesting as a possible link between the Scandinavian ice sheet and the Alps. Although the glacial traces of the Central European Uplands have been investigated for more than 100 years, the glacial history is still elusive. While the highest mountains (the Bavarian Forest and the Giant Mountains) hold evidence of valley glaciers, the lower mountains (the Fichtel and the Erz Mountains) lack unambiguous glacial traces. As a first step towards a palaeoglaciological reconstruction for the Central European Uplands, we present a digital map of glacier termini with elevation data from the SRTM elevation model, compiled from previous investigations of the area. The glacial map of the Central European Uplands presents the pattern of glacial traces over an extensive area in central Europe and forms the basis for reconstructing the extent of former glaciers. We compare the glacial evidence with modern day climate data (from the high resolution WorldClim database), from which we can estimate the climate change needed to produce Central European Upland glaciers. The glacial traces of the Central European Uplands hold information on past climate of the region and this may be a key to link the glacial record of the Alps with the Scandinavian ice sheet.

Control on frontal thrust progression by the mechanically weak Gondwana horizon in the Darjeeling-Sikkim Himalaya

NASA Astrophysics Data System (ADS)

Ghosh, Subhajit; Bose, Santanu; Mandal, Nibir; Das, Animesh

2018-03-01

This study integrates field evidence with laboratory experiments to show the mechanical effects of a lithologically contrasting stratigraphic sequence on the development of frontal thrusts: Main Boundary Thrust (MBT) and Daling Thrust (DT) in the Darjeeling-Sikkim Himalaya (DSH). We carried out field investigations mainly along two river sections in the DSH: Tista-Kalijhora and Mahanadi, covering an orogen-parallel stretch of 20 km. Our field observations suggest that the coal-shale dominated Gondwana sequence (sandwiched between the Daling Group in the north and Siwaliks in the south) has acted as a mechanically weak horizon to localize the MBT and DT. We simulated a similar mechanical setting in scaled model experiments to validate our field interpretation. In experiments, such a weak horizon at a shallow depth perturbs the sequential thrust progression, and causes a thrust to localize in the vicinity of the weak zone, splaying from the basal detachment. We correlate this weak-zone-controlled thrust with the DT, which accommodates a large shortening prior to activation of the weak zone as a new detachment with ongoing horizontal shortening. The entire shortening in the model is then transferred to this shallow detachment to produce a new sequence of thrust splays. Extrapolating this model result to the natural prototype, we show that the mechanically weak Gondwana Sequence has caused localization of the DT and MBT in the mountain front of DSH.

Ice Surface Morphology and Flow on Malaspina Glacier, Alaska: Implications for Regional Tectonics in the Saint Elias Orogen

NASA Technical Reports Server (NTRS)

Cotton, Michelle M.; Bruhn, Ronald L.; Sauber, Jeanne; Burgess, Evan; Forster, Richard R.

2014-01-01

The Saint Elias Mountains in southern Alaska are located at a structural syntaxis where the coastal thrust and fold belt of the Fairweather plate boundary intersects thrust faults and folds generated by collision of the Yakutat Terrane. The axial trace of this syntaxis extends southeastward out of the Saint Elias Mountains and beneath Malaspina Glacier where it is hidden from view and cannot be mapped using conventional methods. Here we examine the surface morphology and flow patterns of Malaspina Glacier to infer characteristics of the bedrock topography and organization of the syntaxis. Faults and folds beneath the eastern part of the glacier trend northwest and reflect dextral transpression near the terminus of the Fairweather fault system. Those beneath the western part of the glacier trend northeast and accommodate folding and thrust faulting during collision and accretion of the Yakutat Terrane. Mapping the location and geometry of the structural syntaxis provides important constraints on spatial variations in seismicity, fault kinematics, and crustal shortening beneath Malaspina Glacier, as well as the position of the collisional deformation front within the Yakutat Terrane. We also speculate that the geometrical complexity of intersecting faults within the syntaxis formed a barrier to rupture propagation during two regional Mw 8.1earthquakes in September 1899.

Reconnaissance investigation of the Lisburne Group in the Cobblestone Creek area, Chandler Lake quadrangle, Alaska

USGS Publications Warehouse

Dumoulin, Julie A.; Whalen, Michael T.; Edited by Wartes, M. A.; Decker, P. L.

2015-01-01

A reconnaissance investigation of the Carboniferous Lisburne Group in the Cobblestone Creek area, Chandler Lake Quadrangle, yields insights into its resource potential and regional relations. Locally porous vuggy dolostone with hydrocarbon reservoir potential occurs in the lower Lisburne in the three most southerly of five thrust sheets, and contains traces of dead oil in two of these sheets. The dolostones are coarse crystalline, commonly cross-bedded, and at least in part of Osagean (late Early Mississippian) age; they have pelmatozoan grainstone protoliths that likely formed in sand shoals of the midramp to inner ramp. Similar, coeval porous dolostones occur in the Lisburne from Skimo Creek to Itkillik Lake, ~70 km west and 10 km east of the Cobblestone Creek area, respectively. We also examined the uppermost Lisburne Group at several localities in the Cobblestone Creek area, mainly in the northernmost thrust sheet where the rocks are as young as Morrowan (Early Pennsylvanian). Cobblestone sections contain more supportstone than equivalent strata at Skimo Creek, and overlying Permian successions also differ between the two areas. These lithologic contrasts may reflect different rates of tectonically controlled subsidence, and (or) changes in sediment input, along the late Paleozoic continental margin.

Glaciotectonic deformation associated with the Orient Point-Fishers Island moraine, westernmost Block Island Sound: further evidence of readvance of the Laurentide ice sheet

USGS Publications Warehouse

Poppe, Lawrence J.; Oldale, Robert N.; Foster, David S.; Smith, Shepard M.

2012-01-01

High-resolution seismic-reflection profiles collected across pro-glacial outwash deposits adjacent to the circa 18 ka b.p. Orient Point–Fishers Island end moraine segment in westernmost Block Island Sound reveal extensive deformation. A rhythmic seismic facies indicates the host outwash deposits are composed of fine-grained glaciolacustrine sediments. The deformation is variably brittle and ductile, but predominantly compressive in nature. Brittle deformation includes reverse faults and thrust faults that strike parallel to the moraine, and thrust sheets that extend from beneath the moraine. Ductile deformation includes folded sediments that overlie undisturbed deposits, showing that they are not drape features. Other seismic evidence for compression along the ice front consists of undisturbed glaciolacustrine strata that dip back toward and underneath the moraine, and angular unconformities on the sea floor where deformed sediments extend above the surrounding undisturbed correlative strata. Together, these ice-marginal glaciotectonic features indicate that the Orient Point–Fishers Island moraine marks a significant readvance of the Laurentide ice sheet, consistent with existing knowledge for neighboring coeval moraines, and not simply a stillstand as previously reported.

Antarctica and Its Ice Sheet: Knowledge Gained During the IGY/IGC

NASA Astrophysics Data System (ADS)

Bentley, C. R.

2006-12-01

At the end of World War II, the interior of Antarctica, with the exception of the mountains south of the Ross Ice Shelf, was still terra incognita. It was described simply as a nearly continuous high plateau. Even less was known about the ice thickness; the eminent glacial geologist, Richard Foster Flint, believed it "unlikely that the ice thickness exceeds 2000 feet except very locally; probably its average thickness is considerably less." Then in the late 1940's and early 1950's, seismic sounding in Greenland by the Expéditions Polaires Françaises and in Queen Maud Land by the Norwegian-British-Swedish Antarctic Expedition, 1949-52, revealed that, inland of the coastal mountains, the beds in both regions lie close to sea level. This led to a reappraisal of the Antarctic ice sheet, such that the prescient glaciologist, Robert P. Sharp, could predict, on the eve of the IGY, that "between 3000 and 4000 meters of ice will be found" in East Antarctica and that "work during IGY will establish an average thickness for Antarctic inland ice in excess of 1600 m." Seismic and gravity soundings on oversnow traverses conducted by eight countries during the IGY and the succeeding IGC showed Sharp to be basically correct, but there were major surprises, such as the vast Gamburtsev Subglacial Mountains, completely hidden by the ice in central East Antarctica, and the equally vast Byrd Subglacial Basin beneath much of the West Antarctic ice sheet, so deep that roughly half the ice in the region lies below sea level. There were major discoveries on and above the surface too, such as the huge size of the Filchner/Ronne Ice Shelf, and the very existence of the Ellsworth and Pensacola Mountains, the former including the highest peak on the continent. Further, the fundamental difference between the crustal structures of East and West Antarctica became clear. A summary paper published in 1960, looking primarily at West Antarctica where the main U.S. activity lay, could conclude that 1) the bed of most of the West Antarctic ice sheet (including the ice shelves) lies below sea level; 2) the Byrd Subglacial Basin represents a fundamental division between the geological provinces of Marie Byrd Land, the Ellsworth Mountains, and the Transantarctic Mountains; 3) the crust of West Antarctica is continental in character and is in approximate isostatic equilibrium, but is only about 30 km thick; and 4) the ice sheet in West Antarctica originated separately in Marie Byrd Land and the Ellsworth-Whitmore-Horlick highland, expanded and converged to form an ice shelf over the open water between them, which then thickened to form the present grounded ice sheet. Thus the background was well laid for all the advances of the last 50 years.

Conodont and Radiolarian Data from the De Long Mountains Quadrangle and Adjacent Areas, Northern Alaska

USGS Publications Warehouse

Dumoulin, Julie A.; Harris, Anita G.; Blome, Charles D.; Young, Lorne E.

2006-01-01

INTRODUCTION This report presents biostratigraphic data from 289 collections at 189 localities in the De Long Mountains, Misheguk Mountain, and Noatak quadrangles (fig. 1); most of these data have never been previously published. The collections were made during studies of the Red Dog massive sulfide deposit in 1998?2004 and in support of regional mapping projects in 1979, 1981, 1983, and 1997?98. The collections?mostly conodonts and some radiolarians?tightly constrain the age of many stratigraphic units of Devonian through Triassic age exposed within the study area, and provide additional data on the depositional environments and thermal history of these rocks. The data are presented in a series of tables, organized by fossil type, stratigraphic unit, and location. Tables 1?12 contain conodont data, mostly from the De Long Mountains quadrangle. All of these collections were initially examined, or were reevaluated, from 1997 through 2004, and complete faunal lists are given for all samples. Table 13 lists ages and conodont color alteration indices (CAIs) of 27 collections from 24 localities in the Noatak quadrangle; updated faunal lists were not prepared for these samples. Radiolarian data?all from the De Long Mountains quadrangle?are given in table 14; these collections were analyzed between 1998 and 2003. Collection localities are shown in four maps (sheets 1, 2). Map 1 (sheet 1) shows all outcrop samples from the De Long Mountains and western Misheguk Mountain quadrangle (locs. 1-121). Maps 2?4 (sheets 1, 2) show all drill hole sample localities; samples come from the Su-Lik deposit and in and around the Anarraaq deposit (map 2, locs. 122?135), in and adjacent to the Red Dog deposits (Paalaaq, Aqqaluk, Main, and Qanaiyaq) (map 3, locs. 136?158), and from drill holes along the Port Road in the Noatak quadrangle (map 4, locs. 159?160). Map 4 (sheet 2) also shows all outcrop samples from the Noatak quadrangle (locs. 161?189). The text summarizes the lithofacies, age, and biofacies of the Paleozoic and Mesozoic stratigraphic units that produced the fossil collections presented in the tables. Many of the data for the Lisburne Group are taken from Dumoulin and others (2004). Plates 1?4 illustrate important conodonts from the collections listed herein, as well as from coeval collections in the Howard Pass quadrangle; information about the Howard Pass conodonts is given in Table 15.

Evidence for the stability of the West Antarctic Ice Sheet divide for 1.4 million years

PubMed Central

Hein, Andrew S.; Woodward, John; Marrero, Shasta M.; Dunning, Stuart A.; Steig, Eric J.; Freeman, Stewart P. H. T.; Stuart, Finlay M.; Winter, Kate; Westoby, Matthew J.; Sugden, David E.

2016-01-01

Past fluctuations of the West Antarctic Ice Sheet (WAIS) are of fundamental interest because of the possibility of WAIS collapse in the future and a consequent rise in global sea level. However, the configuration and stability of the ice sheet during past interglacial periods remains uncertain. Here we present geomorphological evidence and multiple cosmogenic nuclide data from the southern Ellsworth Mountains to suggest that the divide of the WAIS has fluctuated only modestly in location and thickness for at least the last 1.4 million years. Fluctuations during glacial–interglacial cycles appear superimposed on a long-term trajectory of ice-surface lowering relative to the mountains. This implies that as a minimum, a regional ice sheet centred on the Ellsworth-Whitmore uplands may have survived Pleistocene warm periods. If so, it constrains the WAIS contribution to global sea level rise during interglacials to about 3.3 m above present. PMID:26838462

Development of Archean crust in the Wind River Mountains, Wyoming

NASA Technical Reports Server (NTRS)

Frost, C. D.; Koesterer, M. E.; Koesterer, M. E.; Koesterer, M. E.; Koesterer, M. E.

1986-01-01

The Wind River Mountains are a NW-SE trending range composed almost entirely of high-grade Archean gneiss and granites which were thrust to the west over Phanerozoic sediments during the Laramide orogeny. Late Archean granites make up over 50% of the exposed crust and dominates the southern half of the range, while older orthogneisses and magnatites form most of the northen half of the range. Locally these gneisses contain enclaves of supracrustal rocks, which appear to be the oldest preserved rocks in the range. Detailed work in the Medina Mountain area of the central Wind River Mountains and reconnaissance work throughout much of the northern part of the range has allowed definition of the sequence of events which marked crustal development in this area. The sequence of events are described.

Cenozoic volcanic centers in the New Mexico segment of the Pedregosa Basin: constraints on oil and gas exploration in southwestern New Mexico. Final report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Elston, W.E.

1983-01-01

Located in the southwestern corner of New Mexico, southern Hidalgo County occupies a segment of the Pedregosa sedimentary basin and is crossed by a belt of Laramide thrust faults. These factors favor accumulations of oil and gas. The present investigation has documented a constraint on probable oil and gas accumulations, the occurrence of major mid-Tertiary Valles-type ash-flow cauldrons and indications of underlying plutons. Indications of cauldrons have been found in the following ranges: in the southern Pyramid Mountains (Muir cauldron), south-central Peloncillo Mountains (Rodeo cauldron), Gaudalupe Mountains (Geronimo Trail cauldron), Sierra San Luis (San Luis cauldron), Southern Animas Mountains (Tullous,more » Animas Peak, Cowboy Rim cauldrons), Central Animas Mountains (Juniper cauldron), and Apache Hills (Apache cauldron). No indications of cauldrons or other major volcanic centers have been found in the southeastern corner of Hidalgo County, including the southern Sierra Rica, Big Hatchet Mountains, Alamo Hueco Mountains, and Dog Mountains. These cauldron-free areas offer the most favorable prospects for petroleum exploration.« less

An alternative hypothesis for the mid-Paleozoic Antler orogeny in Nevada

USGS Publications Warehouse

Ketner, Keith B.

2012-01-01

A great volume of Mississippian orogenic deposits supports the concept of a mid-Paleozoic orogeny in Nevada, and the existence and timing of that event are not questioned here. The nature of the orogeny is problematic, however, and new ideas are called for. The cause of the Antler orogeny, long ascribed to plate convergence, is here attributed to left-lateral north-south strike-slip faulting in northwestern Nevada. The stratigraphic evidence originally provided in support of an associated regional thrust fault, the Roberts Mountains thrust, is now known to be invalid, and abundant, detailed map evidence testifies to post-Antler ages of virtually all large folds and thrust faults in the region. The Antler orogeny was not characterized by obduction of the Roberts Mountains allochthon; rocks composing the "allochthon" essentially were deposited in situ. Instead, the orogeny was characterized by appearance of an elongate north-northeast-trending uplift through central Nevada and by two parallel flanking depressions. The eastern depression was the Antler foreland trough, into which sediments flowed from both east and west in the Mississippian. The western depression was the Antler hinterland trough into which sediments also flowed from both east and west during the Mississippian. West of the hinterland trough, across a left-lateral strike-slip fault, an exotic landmass originally attached to the northwestern part of the North American continent was moved southward 1700 km along a strike-slip fault. An array of isolated blocks of shelf carbonate rocks, long thought to be autochthonous exposures in windows of the Roberts Mountains allochthon, is proposed here as an array of gravity-driven slide blocks dislodged from the shelf, probably initiated by the Late Devonian Alamo impact event.

Style of Cenozoic extensional deformation in the central Beaverhead Mountains, Idaho-Montana

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kellogg, K.S.

1993-04-01

Cenozoic extension in the upper Medicine Lodge Creek area in the Beaverhead Mountains was accommodated along numerous low- to high-angle, west-facing normal faults. These faults have repeated moderately east-dipping (by 20--40[degree]) Tertiary rocks that are as old as the Eocene Medicine Lodge Volcanics and that include conformably overlying Miocene and Oligocene conglomerate, tuffaceous sandstone, siltstone, and limestone; a reasonable restoration of Tertiary faulting suggests that the region has extended about 20 percent. At least one normal fault soles into the Late Cretaceous Cabin thrust, one of at least four major Cordilleran thrusts in the Beaverhead Mountains and the Tendoy Mountainsmore » immediately to the east. The Cabin thrust places enigmatic quartzite (age is between Middle Proterozoic and Lower Cambrian) and Archean gneiss above Mississippian to Ordovician rocks. The formation of the north-northwest-trending upper Medicine Lodge Valley was controlled mostly by low-angle normal faults along its east side, where Eocene volcanics and overlying sedimentary rocks dip about 25[degree] eastward against Archean rocks. Faceted spurs are prominent but no scarps are visible, suggesting that last movement is pre-Holocene. Other large-displacement normal faults at higher elevations show relatively little topographic expression. The Late Proterozoic or Cambrian Beaverhead impact structure, defined by wide-spread shatter-coning, pseudotachylite formation, and localized brecciation, make interpretation of some extensive breccia zones in Archean rocks along the east side of Medicine Lodge Valley problematic. The proximity of the breccias to Tertiary normal faults makes a Tertiary age attractive, yet the breccias are older than pseudotachylite interpreted to have been produced by the impact.« less

Structural architecture of the central Brooks Range foothills, Alaska

USGS Publications Warehouse

Moore, Thomas E.; Potter, Christopher J.; O'Sullivan, Paul B.

2002-01-01

Five structural levels underlie the Brooks Range foothills, from lowest to highest: (1) autochthon, at a depth of ~9 km; (2) Endicott Mountains allochthon (EMA), thickest under the northern Brooks Range (>15 km) and wedging out northward above the autochthon; (3) higher allochthons (HA), with a composite thickness of 1.5+ km, wedging out northward at or beyond the termination of EMA; (4) Aptian-Albian Fortress Mountain Formation (FM), deposited unconformably on deformed EMA and HA and thickening northward into a >7-km-thick succession of deformed turbidites (Torok Formation); (5) gently folded Albian-Cenomanian deltaic deposits (Nanushuk Group). The dominant faulting pattern in levels 2-3 is thin-skinned thrusting and thrust-related folds formed before deposition of Cretaceous strata. These structures are cut by younger steeply south-dipping reverse faults that truncate and juxtapose structural levels 1-4 and expose progressively deeper structural levels to the south. Structural levels 4-5 are juxtaposed along a north-dipping zone of south-vergent folds and thrusts. Stratigraphic and fission-track age data suggest a kinematic model wherein the foothills belt was formed first, by thrusting of HA and EMA as deformational wedges onto the regionally south-dipping authochon at 140-120Ma. After deposition of FM and Torok during mid-Cretaceous hinterland extension and uplift, a second episode of contractional deformation at 60 Ma shortened the older allochthonous deformational wedges (EMA, HA) and overlying strata on north-vergent reverse faults. To the north, where the allochthons wedge out, shortening caused duplexing in the Torok and development of a triangle zone south of the Tuktu escarpment.

Neotectonic inversion of the Hindu Kush-Pamir mountain region

USGS Publications Warehouse

Ruleman, C.A.

2011-01-01

The Hindu Kush-Pamir region of southern Asia is one of Earth's most rapidly deforming regions and it is poorly understood. This study develops a kinematic model based on active faulting in this part of the Trans-Himalayan orogenic belt. Previous studies have described north-verging thrust faults and some strike-slip faults, reflected in the northward-convex geomorphologic and structural grain of the Pamir Mountains. However, this structural analysis suggests that contemporary tectonics are changing the style of deformation from north-verging thrusts formed during the initial contraction of the Himalayan orogeny to south-verging thrusts and a series of northwest-trending, dextral strike-slip faults in the modern transpressional regime. These northwest-trending fault zones are linked to the major right-lateral Karakoram fault, located to the east, as synthetic, conjugate shears that form a right-stepping en echelon pattern. Northwest-trending lineaments with dextral displacements extend continuously westward across the Hindu Kush-Pamir region indicating a pattern of systematic shearing of multiple blocks to the northwest as the deformation effects from Indian plate collision expands to the north-northwest. Locally, east-northeast- and northwest-trending faults display sinistral and dextral displacement, respectively, yielding conjugate shear pairs developed in a northwest-southeast compressional stress field. Geodetic measurements and focal mechanisms from historical seismicity support these surficial, tectono-morphic observations. The conjugate shear pairs may be structurally linked subsidiary faults and co-seismically slip during single large magnitude (> M7) earthquakes that occur on major south-verging thrust faults. This kinematic model provides a potential context for prehistoric, historic, and future patterns of faulting and earthquakes.

Middle to Late Jurassic Tectonic Evolution of the Klamath Mountains, California-Oregon

NASA Astrophysics Data System (ADS)

Harper, Gregory D.; Wright, James E.

1984-12-01

The geochronology, stratigraphy, and spatial relationships of Middle and Late Jurassic terranes of the Klamath Mountains strongly suggest that they were formed in a single west-facing magmatic arc built upon older accreted terranes. A Middle Jurassic arc complex is represented by the volcanic rocks of the western Hayfork terrane and consanguineous dioritic to peridotitic plutons. New U/Pb zircon dates indicate that the Middle Jurassic plutonic belt was active from 159 to 174 Ma and is much more extensive than previously thought. This plutonic belt became inactive just as the 157 Ma Josephine ophiolite, which lies west and structurally below the Middle Jurassic arc, was generated. Late Jurassic volcanic and plutonic arc rocks (Rogue Formation and Chetco intrusive complex) lie outboard and structurally beneath the Josephine ophiolite; U/Pb and K/Ar age data indicate that this arc complex is coeval with the Josephine ophiolite. Both the Late Jurassic arc complex and the Josephine ophiolite are overlain by the "Galice Formation," a Late Jurassic flysch sequence, and are intruded by 150 Ma dikes and sills. The following tectonic model is presented that accounts for the age and distribution of these terranes: a Middle Jurassic arc built on older accreted terranes undergoes rifting at 160 Ma, resulting in formation of a remnant arc/back-arc basin/island arc triad. This system collapsed during the Late Jurassic Nevadan Orogeny (150 Ma) and was strongly deformed and stacked into a series of east-dipping thrust sheets. Arc magmatism was active both before and after the Nevadan Orogeny, but virtually ceased at 140 Ma.

Records of past ice sheet fluctuations in interior East Antarctica

USGS Publications Warehouse

Liu, Xiaohan; Huang, Feixin; Kong, Ping; Fang, Aimin; Li, Xiaoli

2007-01-01

The results of a land-based multi-disciplinary study of the past ice surface elevation in the Grove Mountains of interior East Antarctica support a dynamic evolution of the East Antarctic Ice Sheet (EAIS). Moraine boulders of sedimentary rocks and spore pollen assemblage imply a significant shrinkage of the EAIS, with its margin retreating south of the Grove Mountains (~450 km south of recent coast line) before the middle Pliocene. The exposure ages indicate that the ice sheet subsequently re-advanced, with the ice surface rising locally at least 450 m higher than today. It then went back down constantly from before 2.3 Ma to 1.6 Ma. The glacial topography and existence of soil show that the ice surface fluctuation continued since the early Quaternary, but with highest levels never exceeding ~100 m higher than today.

Extensional collapse along the Sevier Desert reflection, northern Sevier Desert basin, western United States

NASA Astrophysics Data System (ADS)

Coogan, James C.; Decelles, Peter G.

1996-10-01

Newly released and previously published seismic reflection data from the northern Sevier Desert basin provide a complete seismic transect between the tilted western margin of the basin and the eastern breakaway zone. When tied to well and surface age data, the transect delineates a continuum of extensional fault and basin fill geometries that developed between late Oligocene and Pleistocene time across the basin. A minimum of 18 km of top-to-the-west normal displacement is estimated across the Sevier Desert from only the most conspicuous growth geometries and offsets across listric normal faults that sole downward into the Sevier Desert reflection (SDR). The SDR clearly marks a normal fault zone beneath the entire basin, where stratal truncations are imaged for 50% of the 39 km length of the reflection east of the Cricket Mountains block. Restoration of extensional displacement along this entire 39 km fault length is necessary to reconstruct the pre-Oligocene configuration and erosion level of Sevier thrust sheets across the Sevier Desert area. The SDR normal fault zone underlies the former topographic crest of the Sevier orogenic belt, where it accommodated extensional collapse after cessation of regional contractile tectonism.

Fault dating in the Canadian Rocky Mountains: Evidence for late Cretaceous and early Eocene orogenic pulses

USGS Publications Warehouse

van der Pluijm, B.A.; Vrolijk, P.J.; Pevear, D.R.; Hall, C.M.; Solum, J.

2006-01-01

Fault rocks from the classic Rocky Mountain foreland fold-and-thrust belt in south-western Canada were dated by Ar analysis of clay grain-size fractions. Using X-ray diffraction quantification of the detrital and authigenic component of each fraction, these determinations give ages for individual faults in the area (illite age analysis). The resulting ages cluster around 72 and 52 Ma (here called the Rundle and McConnell pulses, respectively), challenging the traditional view of gradual forward progression of faulting and thrust-belt history of the area. The recognition of spatially and temporally restricted deformation episodes offers field support for theoretical models of critically stressed wedges, which result in geologically reasonable strain rates for the area. In addition to regional considerations, this study highlights the potential of direct dating of shallow fault rocks for our understanding of upper-crustal kinematics and regional tectonic analysis of ancient orogens. ?? 2006 Geological Society of America.

Thin-skinned tectonics in the Central Basin of the Iranian Plateau in the Semnan area, Central Iran

NASA Astrophysics Data System (ADS)

Bouzari, Soheila; Konon, Andrzej; Koprianiuk, Marek; Julapour, Ali A.

2013-01-01

During continent-continent convergence of the Arabian and Eurasian plates, and after the late Eocene inversion of a back-arc rift, the Iranian Plateau underwent broad subsidence resulting in the formation of the Central Basin (Morley et al., 2009). New 2D seismic data acquired by National Iranian Oil Company (NIOC) in the NW-SW-trending arm of the Central Basin suggest that during the main stage of shortening (middle-late? Miocene to Pliocene), strain concentrations resulted in the development of the thin-skinned Kuh-e-Gachab, Kuh-e-Gugerd, Garmsar and Sorkh-e-Kuh structures. These structures are built of Oligocene-Miocene/Pliocene(?) rocks belonging to the Lower Red, Qom and Upper Red formations. Seismic data suggest that one of these structures comprises the south-verging Kuh-e-Gachab anticline, which is bounded by the N-dipping Kuh-e-Gachab thrust and cored by a complex array of thrust sheets forming a triangle zone. During the deformation process, two salt evaporate levels played a significant role as detachment horizons. The main detachment horizon was rooted within the Lower Red Formation, whereas the second detachment horizon was located along evaporites belonging to the Upper Red Formation. Variations in the thin-skinned style of deformation between the larger triangle zone in the western part of the Kuh-e-Gachab structure contrasts with less shortening in the smaller triangle zone to the east. This suggests that the change resulted from the increase of thickness of the mobile detachment horizon to the east. Contraction deformations are still active south of the Alborz Mountains, which is confirmed by GPS data and present-day seismicity.

A Wrench fault system and nappe emplacement in Southern Kenya and Northern Tanzania.- A key area for Pan-African continental collision in East Africa?

NASA Astrophysics Data System (ADS)

Bauernhofer, A.; Wallbrecher, E.; Hauzenberger, C.; Fritz, H.; Loizenbauer, J.; Hoinkes, G.; Muhongo, S.; Mathu, E.

2003-04-01

In the Voi Area of Southern Kenya, the granulite facies rocks of the Taita Hills and the Tsavo East National Park (Galana River) can be divided into three structural domains: The Galana-East unit consists of an intercalation of flat lying metapelites and marbles of continental margin origin. These metasediments can be traced further east to the Umba Steppe (Between Mombasa and Tanga). Galana-West consists of a N-S oriented wrench fault zone with vertical foliation planes and horizontal stretching lineation. Numerous shear sense indicators always show sinistral shear sense. Amphibolites of MORB affinity are involved in this wrench fault zone. To the west, this zone is bordered by calc-alkaline metatonalites of the Sagala Hills. The westernmost unit consists of the Taita Hills. They form an imbricated pile of southwestward thrusted nappe sheets containing metapelites, marbles, and ultramafics. The Taita Hills may be explained as part of an accretionary wedge. Southwestward nappe thrusting is also the prominent structure in the Pare and Usambara Mountains of Northern Tanzania. The following model may may explain these observations: The Southern Kenya -- Northern Tanzania section of the Mozambique Belt is the result of continental collision tectonics. Remnants of an island arc and of an accretionary wedge that occur at least in the Voi area may be part of a former subduction zone. An oceanic domain between an eastern passive continental margin and a western terrane, now represented by the Tanzanian granulite belt has been closed incorporating island arc and accretionary wedge material. Oblique convergence of two continental blocks is suggested from wrench tectonics. The age of convergent tectonics is 530 -- 580 Ma, dated by Sm-Nd garnet-whole rock analysis. This is interpreted as the age of peak metamorphism.

Geometry and kinematics of the fold-thrust belt and structural evolution of the major Himalayan fault zones in the Darjeeling -- Sikkim Himalaya, India

NASA Astrophysics Data System (ADS)

Bhattacharyya, Kathakali

The Darjeeling-Sikkim Himalaya lies in the eastern part of the Himalayan fold-thrust belt (FTB) in a zone of high arc-perpendicular convergence between the Indian and Eurasian plates. In this region two distinct faults form the Main Central thrust (MCT), the structurally higher MCT1 and the lower MCT2; both these faults have translated the Greater Himalayan hanging wall rocks farther towards the foreland than in the western Himalaya. The width of the sub-MCT Lesser Himalayan rocks progressively decreases from the western Himalaya to this part of the eastern Himalaya, and as a result, the width of the FTB is narrower in this region compared to the western Himalaya. Our structural analysis shows that in the Darjeeling-Sikkim Himalaya the sub-MCT Lesser Himalayan duplex is composed of two duplex systems and has a more complex geometry than in the rest of the Himalayan fold-thrust belt. The structurally higher Dating duplex is a hinterland-dipping duplex; the structurally lower Rangit duplex varies in geometry from a hinterland-dipping duplex in the north to an antiformal stack in the middle and a foreland-dipping duplex in the south. The MCT2 is the roof thrust of the Daling duplex and the Ramgarh thrust is the roof thrust of the Rangit duplex. In this region, the Ramgarh thrust has a complex structural history with continued reactivation during footwall imbrication. The foreland-dipping component of the Rangit duplex, along with the large displacement associated with the reactivation of the Ramgarh thrust accounts for the large translation of the MCT sheets in the Darjeeling-Sikkim Himalaya. The growth of the Lesser Himalayan duplex modified the final geometry of the overlying MCT sheets, resulting in a plunge culmination that manifests itself as a broad N-S trending "anticline" in the Darjeeling-Sikkim Himalaya. This is not a "river anticline" as its trace lies west of the Teesta river. A transport parallel balanced cross section across this region has accommodated a total minimum shortening of ˜502 km (˜82%) south of the South Tibetan Detachment system (STDS). Based on this shortening, the average long-term shortening rate is estimated to be ˜22mm/yr in this region. The available shortening estimates from different parts of the Himalayan arc show significant variations in shortening, but based on the present available data, it is difficult to evaluate the primary cause for this variation. The shortening in the Himalayan fold-thrust belt (FTB) is highest in the middle of the Himalayan arc (western Nepal) and progressively decreases towards the two syntaxes. Although the width of the Lesser Himalayan belt decreases in the eastern Himalaya, the Lesser Himalayan shortening percentage remains approximately similar to that in the Nepal Himalaya. In addition, the shortening accommodated within the Lesser Himalayan duplex progressively increases from the western to the eastern Himalaya where it accommodates nearly half of the total shortening. The regional restorations suggest that the width of the original Lesser Himalayan basin may have played an important role in partitioning the shortening in the Himalayan FTB. In addition, the retrodeformed cross section in the Darjeeling-Sikkim Himalaya provides insights into the palinspastic reconstruction of the Gondwana basin of Peninsular India, suggesting that this basin extended ˜150 km northward of its present northernmost exposure in this region. The balanced cross section suggests that each of the MCT sheets has undergone translation of ≥100km in this region. Although a regional scale flat-on-flat relationship is seen in the MCT sheets, there is a significant variation in overburden from the trailing portion to the leading edge of the MCT due to the geometry of the tapered crystalline orogenic wedge. Microstructural studies from three segments of the MCT2 fault zone suggest that the MCT2 zone has undergone strain softening by different mechanisms along different portions of its transport-parallel length, mainly as a result of changing overburden conditions. This regional strain softening provides a suitable explanation for the large translation of ≥100 km along a relatively thin MCT2 fault zone in the Darjeeling-Sikkim Himalaya.

DOE Office of Scientific and Technical Information (OSTI.GOV)

McCollum, L.B.; Buchanan, J.P.; McCollum, M.B.

The Antler orogeny is a textbook example of a Paleozoic mountain building and crustal shortening event in western North America. A relatively complex geologic history of the type Antler at Battle Mountain, Nevada, is interpreted as distinct thrust plates of Lower Cambrian Scott Canyon Formation, Upper Cambrian Harmony Sandstone, and Ordovician Valmy Formation, overlain unconformably by the Middle Pennsylvanian Battle Formation. Mississippian crustal deformation and emplacement of the Roberts Mountain thrust have previously been thought to characterize the Antler orogen. Detailed sedimentology studies of the Scott Canyon and Harmony, and the relationship with the overlying Battle Formation at the typemore » section of the Antler orogeny, cast doubt on the previously accepted geologic history. The Scott Canyon is an interbedded sequence of pillow basalts, Late Devonian radiolarian cherts, and mudstone debris flows with numerous limestone olistoliths, many containing undescribed archaeocyathid fauna. The contact of the Harmony with the Battle Formation appears channeled, but otherwise conformable, and the Battle has been interpreted as an alluvial fan facies. The paleoenvironmental interpretation of these sediments is that the Scott Canyon was deposited upon a Late Devonian active continental margin setting, with prograding fan deposits of the Harmony Sandstone, overlain by Middle Pennsylvanian fanglomerates of the Battle Formation. This conformable sequence appears to preclude any major uplift within the type Antler orogen.« less

Variable exhumation rates and variable displacement rates: Documenting recent slowing of Himalayan shortening in western Bhutan

USGS Publications Warehouse

McQuarrie, Nadine; Tobgay, Tobgay; Long, Sean P.; Reiners, Peter W.; Cosca, Michael A.

2014-01-01

We link exhumational variability in space and time to the evolving geometry of the Himalayan fold–thrust belt in western Bhutan. By combining new and published geochronologic and thermochronologic data we document the burial age, peak temperatures and complete cooling history from 20 Ma to the present over an across-strike distance of ∼125 km. These integrated cooling curves highlight windows of fast exhumation that vary spatially and temporally. We propose that pulses of fast exhumation are a result of structures that facilitate the vertical motion of material, illustrated in sequentially-restored cross sections. Due to a range of permissible geometries at depth, we explore and evaluate the impact of geometry on kinematics and rates of deformation. The linked cooling history and cross sections provide estimates of both magnitude and timing of thrust sheet displacement and highlight temporal variability in potential shortening rates. Structural and chronologic data illustrate a general north to south progression of Himalayan deformation, with emplacement of the Main Central thrust (MCT), Paro thrust and Shumar thrust by 12 to no later than 9 Ma. Two different geometries and kinematic scenarios for the Lesser Himalayan duplex are proposed. A north to south propagating duplex system requires that the southern portion of that system, south of the MCT, deformed and cooled by 9 Ma, leaving only the southernmost thrust sheets, including the Main Boundary and Main Frontal thrusts, to deform between 9 and 0 Ma. This limited post 9 Ma shortening would necessitate a marked slowdown in convergence accommodated on the Main Himalayan thrust. A two-tiered duplex system, which allows for the Paro window duplex and the southern Baxa duplex to form simultaneously, permits duplex formation and accompanying exhumation until 6 Ma. Limited cooling from ∼200 °C to the surface post 6 Ma suggests either a decrease in shortening rates from 6 to 0 Ma or that duplex formation and exhumation are temporally decoupled. Our combined cooling curves highlight that the youngest cooling ages may not mark the fastest thrusting rates or the window of fastest exhumation. Instead, temporal variations in exhumation are best viewed through identifying transients in exhumation rate. We suggest that the strongest control on exhumation magnitude and variability is fold–thrust belt geometry, particularly the locations and magnitudes of footwall ramps, which can change over 10ʼs of km distance. Balanced cross sections predict the location and magnitude of these ramps and how they vary in space and time, providing an untapped potential for testing permissible cross-section geometries and kinematics against measured cooling histories.

Using erosion associated with glaciovolcanic features to document the existence of pre-LGM ice-sheets: examples from the Kawdy Plateau, northern British Columbia

NASA Astrophysics Data System (ADS)

Dunnington, Gwen; Edwards, Benjamin R.; Ryane, Chanone; Russell, James K.; Lasher, Gregory K.

2010-05-01

One of the most significant difficulties with understanding terrestrial Pleistocene climate change is that the depositional record of ancient ice sheets is frequently destroyed by successive glaciations. Given their resistance to erosion, glaciovolcanic features provide unique opportunities at which to look for evidence of multiple glaciations. Evidence from the Kawdy Plateau (KP) region of northern British Columbia is consistent with the presence of multiple ice sheets covering the Canadian Cordillera over the past 2 Ma and derives from two sources: features interpreted as having formed by glacial scouring of bedrock, and the state of preservation for six glaciovolcanic edifices (Kawdy Mountain, Tutsingale Mountain, Nuthinaw Mountain, Meehaz Mountain, Tanker tuya, Horseshoe tuya) located on the plateau. Detailed measurements of glacial mega-grooves/striations on bedrock in the eastern part of the plateau, along with similar features on two different edifices (Tutsingale Mountain and Tanker tuya), are consistent with ice movement in three distinctly different azimuths: 21-59 degrees; 60-88 degrees; 88-92 degrees. The scours may indicate the presence of at least three separate glaciers flowing in different directions over the KP, separated by enough time to allow the previous glacier to melt entirely and expose the plateau floor to continued erosion. Cross-cutting relationships and quality of preservation indicate that the group trending between 88-92° across the plateau and tuyas is the oldest, the group trending 21-59° is younger than that, and a group trending 60-88° is the youngest, presumably related to ice flow during the Last Glacial Maximum (LGM). Drumlinoid features on the plateau floor and on top of Horseshoe Tuya indicate that despite this 71° variation in orientation direction of scours across the entire area, the general direction of ice movement across the plateau has always been in an east-to-west or northeast-to-southwest direction. The states of erosion for all six of the KP glaciovolcanic edifices are consistent with extensive glaciation. Besides the glacial features noted above, at least three of the edifices (Kawdy Mountain, Tanker tuya, Horseshoe tuya) show evidence for extensive morphological modification. Although the core of Kawdy Mountain is made of erosion-resistant palagonitized volcanic breccia and intrusions, its core has been eviscerated and now has a long, northeasterly trending cirque-like valley. Horseshoe tuya appears to have lost almost half of its original volume into a north-facing, cirque-like feature. The aerial footprint of Tanker tuya is consistent with erosion of more than half of the original edifice, and its lower stratigraphy may contain at least one pre-LGM glacial diamicton. We believe that these observations indicate that the Cordilleran Ice Sheet (CIS) did not remain constant and intact during the Pleistocene, but fluctuated between periods of thick, low-elevation ice cover and more sparse, high-elevation cover. Evidence for multi-stage continental glaciation has important implications for the reconstruction of the history of the Cordilleran ice sheet, correlation with the marine Pleistocene climate record, and constraints on the paleoclimate factors which influenced terrestrial ice sheet development.

Crustal shortening and structural architecture of the Interandean and Subandean zones of southern Bolivia (21°S): Constraints from a new balanced cross section

NASA Astrophysics Data System (ADS)

Anderson, R. B.; Long, S. P.; Horton, B. K.; Calle, A.; Ramirez, V.

2015-12-01

Structural insights obtained from balanced cross sections, including thrust belt geometry, location of footwall ramps, and crustal shortening estimates, provide key information for testing model predictions of orogen dynamics (e.g., Cordilleran cyclicity, critical taper theory). New results from geologic mapping along an east-west transect in the central Andes are integrated with existing geophysical data to construct a balanced cross section across the Interandean (IAZ) and Subandean (SAZ) zones of southern Bolivia at 21°S, in order to define thrust belt geometry and estimate crustal shortening. The IAZ consists of a doubly vergent zone of 2-4 km-thick thrust sheets of mainly Silurian-Devonian rocks, which are structurally elevated ~10 km relative to equivalent SAZ levels to the east. Notably, our proposed IAZ geometry differs from published geometries that lack significant west-directed backthrusts. The SAZ is defined by regional-scale, fault-bend folds (10-20 km wavelength, 4-6 km amplitude) that exhume rocks as deep as Carboniferous above a 10-12 km-deep regional décollement in Silurian rocks. Previous studies have interpreted IAZ and SAZ shortening to be balanced by slip on two separate basement megathrust sheets at depth. We estimate 151 km (44%) of total east-west shortening in the IAZ (71 km) and SAZ (80 km), which is similar to a previous estimate (144 km, 42%). Importantly, our estimate of SAZ shortening restores the leading edge of the basement thrust sheet feeding displacement into the SAZ back to a corresponding footwall ramp that is constrained by a seismic reflection profile 90 km along strike to the south. Our shortening magnitudes are similar to nearby estimates to the north and south, which range between 60-86 km for the SAZ and 43-96 km for the IAZ. Future work will continue the cross section westward into the Eastern Cordillera hinterland, and explore potential variations in the geometry and style of basement deformation.

Geophysical interpretations of the Libby thrust belt, northwestern Montana

USGS Publications Warehouse

Kleinkopf, M. Dean; with sections by Harrison, Jack Edward; Stanley, W.D.

1997-01-01

Interpretations of gravity and aeromagnetic anomaly data, supplemented by results from two seismic reflection profiles and five magnetotelluric soundings, were used to study buried structure and lithology of the Libby thrust belt of northwestern Montana. The gravity anomaly data show a marked correlation with major structures. The Purcell anticlinorium and the Sylvanite anticline are very likely cored by stacks of thrust slices of dense crystalline basement rocks that account for the large gravity highs across these two structures. Gravity anomaly data for the Cabinet Mountains Wilderness show a string of four broad highs. The principal magnetic anomaly sources are igneous intrusive rocks, major fault zones, and magnetite-bearing sedimentary rocks of the Ravalli Group. The most important magnetic anomalies in the principal study area are five distinct positive anomalies associated with Cretaceous or younger cupolas and stocks.

Modern Uplift of the Transantarctic Mountains: Preliminary Results of an Autonomous GPS Array

NASA Technical Reports Server (NTRS)

Raymond, C. A.; Heflin, M. B.; Ivins, E. R.; James, T. S.

1998-01-01

An autonomous GPS array is being implemented in the Transantarctic Mountains, sponsored by NSF and NASA, for the purpose of measuring uplift resulting from post-glacial rebound (PGR). The rebound of the solid earth due to unloading of ice since the Last Glacial Maximum is expected to dominate the measured uplift for most of West Antarctica, dwarfing the signals due to present-day ice sheet mass balance changes and tectonic motion, as long as mantle viscosity is greater than about 10(exp 20) Pa-s. Predicted uplift patterns have been calculated for a range of model scenarios, which illustrate how the uplift pattern might distinguish between different-sized ice sheets and deglaciation histories as represented by the competing models. The scenarios considered by James and Ivins (1998) include ICE-3G, CLIMAP and a variation of the CLIMAP model by Denton et al. For these models, peak uplift rates occur in the Transantarctic Mountains, and differences between models is often large there. Thus, the Transantarctic Mountains are an ideal place to obtain uplift measurements to constrain deglaciation models.

The magnitude 6.7 Northridge, California, earthquake of 17 January 1994

USGS Publications Warehouse

Jones, L.; Aki, K.; Boore, D.; Celebi, M.; Donnellan, A.; Hall, J.; Harris, R.; Hauksson, E.; Heaton, T.; Hough, S.; Hudnut, K.; Hutton, K.; Johnston, M.; Joyner, W.; Kanamori, H.; Marshall, G.; Michael, A.; Mori, J.; Murray, M.; Ponti, D.; Reasenberg, P.; Schwartz, D.; Seeber, L.; Shakal, A.; Simpson, R.; Thio, H.; Tinsley, J.; Todorovska, M.; Trifunac, M.; Wald, D.; Zoback, M.L.

1994-01-01

The most costly American earthquake since 1906 struck Los Angeles on 17 January 1994. The magnitude 6.7 Northridge earthquake resulted from more than 3 meters of reverse slip on a 15-kilometer-long south-dipping thrust fault that raised the Santa Susana mountains by as much as 70 centimeters. The fault appears to be truncated by the fault that broke in the 1971 San Fernando earthquake at a depth of 8 kilometers. Of these two events, the Northridge earthquake caused many times more damage, primarily because its causative fault is directly under the city. Many types of structures were damaged, but the fracture of welds in steel-frame buildings was the greatest surprise. The Northridge earthquake emphasizes the hazard posed to Los Angeles by concealed thrust faults and the potential for strong ground shaking in moderate earthquakes.The most costly American earthquake since 1906 struck Los Angeles on 17 January 1994. The magnitude 6.7 Northridge earthquake resulted from more than 3 meters of reverse slip on a 15-kilometer-long south-dipping thrust fault that raised the Santa Susana mountains by as much as 70 centimeters. The fault appears to be truncated by the fault that broke in the 1971 San Fernando earthquake at a depth of 8 kilometers. Of these two events, the Northridge earthquake caused many times more damage, primarily because its causative fault is directly under the city. Many types of structures were damaged, but the fracture of welds in steel-frame buildings was the greatest surprise. The Northridge earthquake emphasizes the hazard posed to Los Angeles by concealed thrust faults and the potential for strong ground shaking in moderate earthquakes.

Deformation during terrane accretion in the Saint Elias orogen, Alaska

USGS Publications Warehouse

Bruhn, R.L.; Pavlis, T.L.; Plafker, G.; Serpa, L.

2004-01-01

The Saint Elias orogen of southern Alaska and adjacent Canada is a complex belt of mountains formed by collision and accretion of the Yakutat terrane into the transition zone from transform faulting to subduction in the northeast Pacific. The orogen is an active analog for tectonic processes that formed much of the North American Cordillera, and is also an important site to study (1) the relationships between climate and tectonics, and (2) structures that generate large- to great-magnitude earthquakes. The Yakutat terrane is a fragment of the North American plate margin that is partly subducted beneath and partly accreted to the continental margin of southern Alaska. Interaction between the Yakutat terrane and the North American and Pacific plates causes significant differences in the style of deformation within the terrane. Deformation in the eastern part of the terrane is caused by strike-slip faulting along the Fairweather transform fault and by reverse faulting beneath the coastal mountains, but there is little deformation immediately offshore. The central part of the orogen is marked by thrusting of the Yakutat terrane beneath the North American plate along the Chugach-Saint Elias fault and development of a wide, thin-skinned fold-and-thrust belt. Strike-slip faulting in this segment may he localized in the hanging wall of the Chugach-Saint Elias fault, or dissipated by thrust faulting beneath a north-northeast-trending belt of active deformation that cuts obliquely across the eastern end of the fold-and-thrust belt. Superimposed folds with complex shapes and plunging hinge lines accommodate horizontal shortening and extension in the western part of the orogen, where the sedimentary cover of the Yakutat terrane is accreted into the upper plate of the Aleutian subduction zone. These three structural segments are separated by transverse tectonic boundaries that cut across the Yakutat terrane and also coincide with the courses of piedmont glaciers that flow from the topographic backbone of the Saint Elias Mountains onto the coastal plain. The Malaspina fault-Pamplona structural zone separates the eastern and central parts of the orogen and is marked by reverse faulting and folding. Onshore, most of this boundary is buried beneath the western or "Agassiz" lobe of the Malaspina piedmont glacier. The boundary between the central fold-and-thrust belt and western zone of superimposed folding lies beneath the middle and lower course of the Bering piedmont glacier. ?? 2004 Geological Society of America.

Preliminary geologic map of the San Guillermo Mountain Quadrangle, Ventura County, California

USGS Publications Warehouse

Minor, S.A.

1999-01-01

New 1:24,000-scale geologic mapping in the Cuyama 30' x 60' quadrangle, in support of the USGS Southern California Areal Mapping Project (SCAMP), is contributing to a more complete understanding of the stratigraphy, structure, and tectonic evolution of the complex junction area between the NW-striking Coast Ranges and EW-striking western Transverse Ranges. The 1:24,000-scale geologic map of the San Guillermo Mountain quadrangle is one of six contiguous 7 1/2' quadrangle geologic maps in the eastern part of the Cuyama map area being compiled for a more detailed portrayal and reevaluation of geologic structures and rock units shown on previous geologic maps of the area (e.g., Dibblee, 1979). The following observations and interpretations are based on the new San Guillermo Mountain geologic compilation: (1) The new geologic mapping in the northern part of the San Guillermo Mountain quadrangle allows for reinterpretation of fault architecture that bears on potential seismic hazards of the region. Previous mapping had depicted the eastern Big Pine fault (BPF) as a northeast-striking, sinistral strike-slip fault that extends for 30 km northeast of the Cuyama River to its intersection with the San Andreas fault (SAF). In contrast the new mapping indicates that the eastern BPF is a thrust fault that curves from a northeast strike to an east strike, where it is continuous with the San Guillermo thrust fault, and dies out further east about 15 km south of the SAF. This redefined segment of the BPF is a south-dipping, north-directed thrust, with dominantly dip slip components (rakes > 60 deg.), that places Middle Eocene marine rocks (Juncal and Matilija Formations) over Miocene through Pliocene(?) nonmarine rocks (Caliente, Quatal, and Morales Formations). Although a broad northeast-striking fault zone, exhibiting predominantly sinistral components of slip (rakes < 45 deg.), extends to the SAF as previously mapped, the fault zone does not connect to the southwest with the BPF but instead curves into a southwest-directed thrust fault system a short distance north of the BPF. Oligocene to Pliocene(?) nonmarine sedimentary and volcanic rocks of the Plush Ranch, Caliente, and Morales(?) Formations are folded on both sides of this fault zone (informally named the Lockwood Valley fault zone [LVFZ] on the map). South-southeast of the LVFZ overturned folds have southward vergence. Several moderate-displacement (< 50 m), mainly northwest-dipping thrust and reverse faults, exhibiting mostly sinistral-oblique slip, flank and strike parallel to the overturned folds. The fold vergence and thrust direction associated with the LVFZ is opposite to that of the redefined BPF, providing further evidence that the two faults are distinct structures. These revised fault interpretations bring into question earlier estimates of net sinistral strike-slip displacement of as much as 13 km along the originally defined eastern BPF, which assumed structural connection with the LVFZ. Also, despite sparse evidence for repeated Quaternary movement on the LVFZ (e.g., Dibblee, 1982), the potential for a large earthquake involving coseismic slip on both the LVFZ and the central BPF to the southwest may not be as great as once believed. (2) Several generations of Pleistocene and younger dissected alluvial terrace and fan deposits sit at various levels above modern stream channels throughout the quadrangle. These deposits give testimony to the recent uplift and related fault deformation that has occurred in the area. (3) A vast terrane of Eocene marine sedimentary rocks (Juncal and Matilija Formations and Cozy Dell Shale) exposed south of the Big Pine fault forms the southern two-thirds of the San Guillermo Mountain quadrangle. Benthic foraminifers collected from various shale intervals within the Juncal Formation indicate a Middle Eocene age (Ulatisian) for the entire formation (K. McDougall, unpub. data, 1998) and deposition at paleodepths as great as 2,000 m (i.e., lowe

Storage and release of organic carbon from glaciers and ice sheets

NASA Astrophysics Data System (ADS)

Hood, Eran; Battin, Tom J.; Fellman, Jason; O'Neel, Shad; Spencer, Robert G. M.

2015-02-01

Polar ice sheets and mountain glaciers, which cover roughly 11% of the Earth's land surface, store organic carbon from local and distant sources and then release it to downstream environments. Climate-driven changes to glacier runoff are expected to be larger than climate impacts on other components of the hydrological cycle, and may represent an important flux of organic carbon. A compilation of published data on dissolved organic carbon from glaciers across five continents reveals that mountain and polar glaciers represent a quantitatively important store of organic carbon. The Antarctic Ice Sheet is the repository of most of the roughly 6 petagrams (Pg) of organic carbon stored in glacier ice, but the annual release of glacier organic carbon is dominated by mountain glaciers in the case of dissolved organic carbon and the Greenland Ice Sheet in the case of particulate organic carbon. Climate change contributes to these fluxes: approximately 13% of the annual flux of glacier dissolved organic carbon is a result of glacier mass loss. These losses are expected to accelerate, leading to a cumulative loss of roughly 15 teragrams (Tg) of glacial dissolved organic carbon by 2050 due to climate change -- equivalent to about half of the annual flux of dissolved organic carbon from the Amazon River. Thus, glaciers constitute a key link between terrestrial and aquatic carbon fluxes, and will be of increasing importance in land-to-ocean fluxes of organic carbon in glacierized regions.

Storage and release of organic carbon from glaciers and ice sheets

USGS Publications Warehouse

Hood, Eran; Battin, Tom J.; Fellman, Jason; O'Neel, Shad; Spencer, Robert G. M.

2015-01-01

Polar ice sheets and mountain glaciers, which cover roughly 11% of the Earth's land surface, store organic carbon from local and distant sources and then release it to downstream environments. Climate-driven changes to glacier runoff are expected to be larger than climate impacts on other components of the hydrological cycle, and may represent an important flux of organic carbon. A compilation of published data on dissolved organic carbon from glaciers across five continents reveals that mountain and polar glaciers represent a quantitatively important store of organic carbon. The Antarctic Ice Sheet is the repository of most of the roughly 6 petagrams (Pg) of organic carbon stored in glacier ice, but the annual release of glacier organic carbon is dominated by mountain glaciers in the case of dissolved organic carbon and the Greenland Ice Sheet in the case of particulate organic carbon. Climate change contributes to these fluxes: approximately 13% of the annual flux of glacier dissolved organic carbon is a result of glacier mass loss. These losses are expected to accelerate, leading to a cumulative loss of roughly 15 teragrams (Tg) of glacial dissolved organic carbon by 2050 due to climate change — equivalent to about half of the annual flux of dissolved organic carbon from the Amazon River. Thus, glaciers constitute a key link between terrestrial and aquatic carbon fluxes, and will be of increasing importance in land-to-ocean fluxes of organic carbon in glacierized regions.

Caledonian evolution of the Moine Supergroup: Prograde garnet growth and context for quartz fabric-based deformation thermometry

NASA Astrophysics Data System (ADS)

Law, Richard; Ashley, Kyle; Thigpen, Ryan

2014-05-01

Despite the detailed Caledonian structural/tectonic framework developed for the Moine Supergroup of northern Scotland, debate continues over the tectonic processes that drove metamorphism. Rapid temporal evolution of the metamorphic sequence has led some geologists to suggest that crustal thickening alone cannot provide sufficient heat flow to reach the metamorphic grades observed. Rather, they postulate that large-scale contact metamorphism or initial heating in an extensional, back-arc setting is required. We present coupled petrographic analyses and forward phase stability modeling for quantifying prograde metamorphic evolution in pelite horizons dispersed across the Caledonian thrust sheets. Results suggest garnet growth was syn-kinematic during prograde decompression. Rutile and ilmenite inclusions in garnet cores and rims, respectively, support this claim, while chemical profiles and crystal morphology argue against a detrital origin for these garnet grains. The observed clockwise P-T path for these garnets is incompatible with extensional or contact metamorphic models (would require counter-clockwise paths). Rather, the P-T data suggests advection of isotherms during thrusting as the dominant mechanism for metamorphism (Thigpen et al., 2013). Recent studies in other orogens (e.g., Spear et al., 2012) suggest that heating over long time scales under mid-crustal conditions may not be needed to reach the metamorphic grades observed. Therefore the structurally higher, more hinterland Caledonian thrust sheets may have reached peak metamorphism in a much shorter time period than previously expected. The paucity of pelitic horizons across the foreland-positioned Moine thrust sheet has previously limited insight into the prograde evolution of these rocks. However, the dominance of quartz-rich units has allowed the thermal structure of the thrust sheet to be evaluated using quartz c-axis fabric opening angle-based deformation thermometry. Microstructures in the pelites sampled indicate that garnet (rim) growth is syn-kinematic with respect to the Scandian (mid-Silurian) deformation fabrics. Deformation temperatures indicated by quartz fabric opening angles are very similar to temperatures of metamorphism constrained using pseudosection and petrographic data from adjacent pelite horizons. This suggests that the deformation- and petrology-based data sets are providing information on the same thermal event. These results support the use of quartz deformation thermometry in obtaining thermal profiles across tectonic units where rock types (usually pelites), with metamorphic mineral assemblages suitable for petrology-based thermometry, are not present. Thigpen, J.R., Law, R.D., Loehn, C.L., Strachan, R.A., Tracy, R.J., Lloyd, G.E., Roth, B.L., and Brown, S.J., 2013, Thermal structure and tectonic evolution of the Scandian orogenic wedge, Scottish Caledonides: integrating geothermometry, deformation temperatures and conceptual kinematic-thermal models, J. Metamorphic Geol., 31, 813-842. Spear, F.S., Ashley, K.T., Webb, L.E., and Thomas, J.B., 2012, Ti diffusion in quartz inclusions: implications for metamorphic time scales, Contrib. Mineral Petrol., 164, 977-986.

Constraints on ice volume changes of the WAIS and Ross Ice Shelf since the LGM based on cosmogenic exposure ages in the Darwin-Hatherton glacial system of the Transantarctic Mountains

NASA Astrophysics Data System (ADS)

Fink, David; Storey, Bryan; Hood, David; Joy, Kurt; Shulmeister, James

2010-05-01

Quantitative assessment of the spatial and temporal scale of ice volume change of the West Antarctic ice sheet (WAIS) and Ross Ice Shelf since the last glacial maximum (LGM) ~20 ka is essential to accurately predict ice sheet response to current and future climate change. Although global sea level rose by approximately 120 metres since the LGM, the contribution of polar ice sheets is uncertain and the timing of any such contribution is controversial. Mackintosh et al (2007) suggest that sectors of the EAIS, similar to those studied at Framnes Mountains where the ice sheet slowly calves at coastal margins, have made marginal contributions to global sea-level rise between 13 and 7 ka. In contrast, Stone et al (2003) document continuing WAIS decay during the mid-late Holocene, raising the question of what was the response of the WAIS since LGM and into the Holocene. Terrestrial evidence is restricted to sparse coastal oasis and ice free mountains which archive limits of former ice advances. Mountain ranges flanking the Darwin-Hatherton glaciers exhibit well-defined moraines, weathering signatures, boulder rich plateaus and glacial tills, which preserve the evidence of advance and retreat of the ice sheet during previous glacial cycles. Previous studies suggest a WAIS at the LGM in this location to be at least 1,000 meters thicker than today. As part of the New Zealand Latitudinal Gradient Project along the Transantarctic, we collected samples for cosmogenic exposure dating at a) Lake Wellman area bordering the Hatherton Glacier, (b) Roadend Nunatak at the confluence of the Darwin and Hatherton glaciers and (c) Diamond Hill which is positioned at the intersection of the Ross Ice Shelf and Darwin Glacier outlet. While the technique of exposure dating is very successful in mid-latitude alpine glacier systems, it is more challenging in polar ice-sheet regions due to the prevalence of cold-based ice over-riding events and absence of outwash processes which removes glacially transported debris. Our glacial geomorphic survey from ice sheet contact edge (~850 masl) to mountain peak at 1600 masl together with a suite of 10Be and 26Al exposure ages, documents a pre-LGM ice volume at least 800 meters thicker than current ice levels which was established at least 2 million years ago. However a complex history of exposure and re-exposure of the ice free regions in this area is seen in accordance with advance and retreat of the ice sheets that feeds into the Darwin -Hatherton system. A cluster of mid-altitude boulders, located below a prominent moraine feature mapped previously as demarcating the LGM ice advance limits, have exposure ages ranging from 30 to 40 ka. Exposure ages for boulders just above the ice contact range from 1to 19 ka and allow an estimate of inheritance. Hence, we conclude that LGM ice volume was not as large as previously estimated and actually little different from what is observed today. These results raise rather serious questions about the implications of a reduced WAIS at the LGM, its effect on the development of the Ross Ice Shelf, and how the Antarctic ice sheets respond to global warming. J. O. Stone et al., Science v299, 99 (2003). A. Mackintosh, D. White, D. Fink, D. Gore et al, Geology, v 35; 551-554 (2007).

Pre-, syn-, and postcollisional stratigraphic framework and provenance of upper triassic-upper cretaceous strata in the northwestern talkeetna mountains, alaska

USGS Publications Warehouse

Hampton, B.A.; Ridgway, K.D.; O'Neill, J. M.; Gehrels, G.E.; Schmidt, J.; Blodgett, R.B.

2007-01-01

Mesozoic strata of the northwestern Talkeetna Mountains are located in a regional suture zone between the allochthonous Wrangellia composite terrane and the former Mesozoic continental margin of North America (i.e., the Yukon-Tanana terrane). New geologic mapping, measured stratigraphic sections, and provenance data define a distinct three-part stratigraphy for these strata. The lowermost unit is greater than 290 m thick and consists of Upper Triassic-Lower Jurassic mafic lavas, fossiliferous limestone, and a volcaniclastic unit that collectively we informally refer to as the Honolulu Pass formation. The uppermost 75 m of the Honolulu Pass formation represent a condensed stratigraphic interval that records limited sedimentation over a period of up to ca. 25 m.y. during Early Jurassic time. The contact between the Honolulu Pass formation and the overlying Upper Jurassic-Lower Cretaceous clastic marine strata of the Kahiltna assemblage represents a ca. 20 m.y. depositional hiatus that spans the Middle Jurassic and part of Late Jurassic time. The Kahiltna assemblage may to be up to 3000 m thick and contains detrital zircons that have a robust U-Pb peak probability age of 119.2 Ma (i.e., minimum crystallization age/maximum depositional age). These data suggest that the upper age of the Kahiltna assemblage may be a minimum of 10-15 m.y. younger than the previously reported upper age of Valanginian. Sandstone composition (Q-43% F-30% L-27%-Lv-71% Lm-18% Ls-11%) and U-Pb detrital zircon ages suggest that the Kahiltna assemblage received igneous detritus mainly from the active Chisana arc, remnant Chitina and Talkeetna arcs, and Permian-Triassic plutons (Alexander terrane) of the Wrangellia composite terrane. Other sources of detritus for the Kahiltna assemblage were Upper Triassic-Lower Jurassic plutons of the Taylor Mountains batholith and Devonian-Mississippian plutons; both of these source areas are part of the Yukon-Tanana terrane. The Kahiltna assemblage is overlain by previously unrecognized nonmarine strata informally referred to here as the Caribou Pass formation. This unit is at least 250 m thick and has been tentatively assigned an Albian-Cenomanian-to-younger age based on limited palynomorphs and fossil leaves. Sandstone composition (Q-65% F-9% L-26%-Lv-28% Lm-52% Ls-20%) from this unit suggests a quartz-rich metamorphic source terrane that we interpret as having been the Yukon-Tanana terrane. Collectively, provenance data indicate that there was a fundamental shift from mainly arc-related sediment derivation from sources located south of the study area during Jurassic-Early Cretaceous (Aptian) time (Kahiltna assemblage) to mainly continental margin-derived sediment from sources located north and east of the study area by Albian-Cenomanian time (Caribou Pass formation). We interpret the threepart stratigraphy defined for the northwestern Talkeetna Mountains to represent pre- (the Honolulu Pass formation), syn- (the Kahiltna assemblage), and post- (the Caribou Pass formation) collision of the Wrangellia composite terrane with the Mesozoic continental margin. A similar Mesozoic stratigraphy appears to exist in other parts of south-central and southwestern Alaska along the suture zone based on previous regional mapping studies. New geologic mapping utilizing the three-part stratigraphy interprets the northwestern Talkeetna Mountains as consisting of two northwest-verging thrust sheets. Our structural interpretation is that of more localized thrust-fault imbrication of the three-part stratigraphy in contrast to previous interpretations of nappe emplacement or terrane translation that require large-scale displacements. Copyright ?? 2007 The Geological Society of America.

Effect of Inductive Coil Geometry on the Thrust Efficiency of a Microwave Assisted Discharge Inductive Plasma Accelerator

NASA Technical Reports Server (NTRS)

Hallock, Ashley; Polzin, Kurt; Emsellem, Gregory

2012-01-01

Pulsed inductive plasma thrusters [1-3] are spacecraft propulsion devices in which electrical energy is capacitively stored and then discharged through an inductive coil. The thruster is electrodeless, with a time-varying current in the coil interacting with a plasma covering the face of the coil to induce a plasma current. Propellant is accelerated and expelled at a high exhaust velocity (O(10-100 km/s)) by the Lorentz body force arising from the interaction of the magnetic field and the induced plasma current. While this class of thruster mitigates the life-limiting issues associated with electrode erosion, pulsed inductive plasma thrusters require high pulse energies to inductively ionize propellant. The Microwave Assisted Discharge Inductive Plasma Accelerator (MAD-IPA) [4, 5] is a pulsed inductive plasma thruster that addressees this issue by partially ionizing propellant inside a conical inductive coil via an electron cyclotron resonance (ECR) discharge. The ECR plasma is produced using microwaves and permanent magnets that are arranged to create a thin resonance region along the inner surface of the coil, restricting plasma formation, and in turn current sheet formation, to a region where the magnetic coupling between the plasma and the inductive coil is high. The use of a conical theta-pinch coil is under investigation. The conical geometry serves to provide neutral propellant containment and plasma plume focusing that is improved relative to the more common planar geometry of the Pulsed Inductive Thruster (PIT) [2, 3], however a conical coil imparts a direct radial acceleration of the current sheet that serves to rapidly decouple the propellant from the coil, limiting the direct axial electromagnetic acceleration in favor of an indirect acceleration mechanism that requires significant heating of the propellant within the volume bounded by the current sheet. In this paper, we describe thrust stand measurements performed to characterize the performance (specific impulse, thrust efficiency) of the MAD-IPA thruster. Impulse data are obtained at various pulse energies, mass flow rates and inductive coil. geometries. Dependencies on these experimental parameters are discussed in the context of the current sheet formation and electromagnetic plasma acceleration processes.

Source Parameters for Moderate Earthquakes in the Zagros Mountains with Implications for the Depth Extent of Seismicity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Adams, A; Brazier, R; Nyblade, A

2009-02-23

Six earthquakes within the Zagros Mountains with magnitudes between 4.9 and 5.7 have been studied to determine their source parameters. These events were selected for study because they were reported in open catalogs to have lower crustal or upper mantle source depths and because they occurred within an area of the Zagros Mountains where crustal velocity structure has been constrained by previous studies. Moment tensor inversion of regional broadband waveforms have been combined with forward modeling of depth phases on short period teleseismic waveforms to constrain source depths and moment tensors. Our results show that all six events nucleated withinmore » the upper crust (<11 km depth) and have thrust mechanisms. This finding supports other studies that call into question the existence of lower crustal or mantle events beneath the Zagros Mountains.« less

Using U-Th-Pb petrochronology to determine rates of ductile thrusting: Time windows into the Main Central Thrust, Sikkim Himalaya

NASA Astrophysics Data System (ADS)

Mottram, Catherine M.; Parrish, Randall R.; Regis, Daniele; Warren, Clare J.; Argles, Tom W.; Harris, Nigel B. W.; Roberts, Nick M. W.

2015-07-01

Quantitative constraints on the rates of tectonic processes underpin our understanding of the mechanisms that form mountains. In the Sikkim Himalaya, late structural doming has revealed time-transgressive evidence of metamorphism and thrusting that permit calculation of the minimum rate of movement on a major ductile fault zone, the Main Central Thrust (MCT), by a novel methodology. U-Th-Pb monazite ages, compositions, and metamorphic pressure-temperature determinations from rocks directly beneath the MCT reveal that samples from 50 km along the transport direction of the thrust experienced similar prograde, peak, and retrograde metamorphic conditions at different times. In the southern, frontal edge of the thrust zone, the rocks were buried to conditions of 550°C and 0.8 GPa between 21 and 18 Ma along the prograde path. Peak metamorphic conditions of 650°C and 0.8-1.0 GPa were subsequently reached as this footwall material was underplated to the hanging wall at 17-14 Ma. This same process occurred at analogous metamorphic conditions between 18-16 Ma and 14.5-13 Ma in the midsection of the thrust zone and between 13 Ma and 12 Ma in the northern, rear edge of the thrust zone. Northward younging muscovite 40Ar/39Ar ages are consistently 4 Ma younger than the youngest monazite ages for equivalent samples. By combining the geochronological data with the >50 km minimum distance separating samples along the transport axis, a minimum average thrusting rate of 10 ± 3 mm yr-1 can be calculated. This provides a minimum constraint on the amount of Miocene India-Asia convergence that was accommodated along the MCT.

Detrital Thermochronology Record of the Local-to-Extraregional Provenance Shift Recorded by the Northern Peninsular Ranges Forearc

NASA Astrophysics Data System (ADS)

Flores, M.; Shulaker, D. Z.

2016-12-01

Previously measured detrital zircon U-Pb age distributions have revealed that Late Cretaceous to Eocene forearc strata in the Santa Ana mountains region experienced a dramatic shift in sedimentary provenance from a 125-90 Ma northern Peninsular Ranges batholith (PRB) source region along the continental margin to a cratonal source area intruded by Late Cretaceous (85-75 Ma) plutons within the continental interior (western Sonora). To improve our understanding of the timing and magnitude of denudation prior to, and during this local to extraregional provenance shift, we have measured new detrital K-feldspar 40Ar/39Ar total fusion and zircon U-Pb age distributions from forearc sandstones. Our combined crystallization age and thermal history results confirm two pulses of rapid denudation of the PRB. These include a syn-batholith phase (Cenomanian) and a post-batholithic (Maastrichtian to Paleocene) phase attributed to shallow subduction. The new data require that significant (5-10 km) syn-batholithic erosional denudation of the northern PRB had already occurred by ca. 95 Ma and that post-emplacement denudation of the PRB accelerated again during the Maastrichtian with the eastern PRB providing the bulk of the detritus. Our new results demonstrate that deposition of the Paleocene Silverado Fm. occurred during a transitional period. Sand reaching the forearc during the Paleocene was derived from both the heavily denuded eastern PRB with additional input supplied either from Late Cretaceous plutons of northwestern Sonoran region and/or similar plutons emplaced in thrust sheets atop PRB basement within the Santa Rosa Mountains. In contrast, the Eocene Santiago Fm. was nearly entirely derived from extraregional sources that supplied abundant late Cretaceous (75-85 Ma) and Proterozoic (1.4 & 1.7 Ga) detritus with virtually no PRB-derived sediment detected.

Quantifying the role of mantle forcing, crustal shortening and exogenic forcing on exhumation of the North Alpine Foreland Basin

NASA Astrophysics Data System (ADS)

von Hagke, C.; Luijendijk, E.; Hindle, D.

2017-12-01

In contrast to the internal zones of orogens, where the stacking of thrust sheets can overwhelm more subtle signals, foreland basins can record long-wavelength subsidence or uplift signals caused by mantle processes. We use a new and extensive compilation of geological and thermochronology data from the North Alpine Foreland Basin to understand the dynamics of foreland basins and their interaction with surface and geodynamic processes. We quantify cooling and exhumation rates in the basin by combining published and new vitrinite reflectance, apatite fission track and U-Th/He data with a new inverse burial and thermal history model, pybasin. No correlation is obvious between inferred cooling and exhumation rates and elevation, relief or tectonics. Uncertainty analysis shows that thermochronometers can be explained by cooling starting as early as the Miocene or as late as the Pleistocene. We compare derived temperature histories to exhumation estimates based on the retro-deformation of Molasse basin and the Jura mountains, and to exhumation caused by drainage reorganization and incision. Drainage reorganization can explain at most 25% of the observed cooling rates in the basin. Tectonic transport of the basin's sediments over the inclined basement of the alpine foreland as the Jura mountains shortened can explain part of the cooling signal in the western part of the basin. However, overall a substantial amount of cooling and exhumation remains unexplained by known tectonic and surface processes. Our results document basin wide exhumation that may be related to slab roll-back or other lithospheric processes. We suggest that new (U-Th)/He data from key areas close to the Alpine front may provide better constraints on the timing of exhumation.

Southern montane populations did not contribute to the recolonization of West Siberian Plain by Siberian larch (Larix sibirica): a range-wide analysis of cytoplasmic markers.

PubMed

Semerikov, Vladimir L; Semerikova, Svetlana A; Polezhaeva, Maria A; Kosintsev, Pavel A; Lascoux, Martin

2013-10-01

While many species were confined to southern latitudes during the last glaciations, there has lately been mounting evidence that some of the most cold-tolerant species were actually able to survive close to the ice sheets. The contribution of these higher latitude outposts to the main recolonization thrust remains, however, untested. In the present study, we use the first range-wide survey of genetic diversity at cytoplasmic markers in Siberian larch (Larix sibirica; four mitochondrial (mt) DNA loci and five chloroplast (cp) DNA SSR loci) to (i) assess the relative contributions of southern and central areas to the current L. sibirica distribution range; and (ii) date the last major population expansion in both L. sibirica and adjacent Larix species. The geographic distribution of cpDNA variation was uninformative, but that of mitotypes clearly indicates that the southernmost populations, located in Mongolia and the Tien-Shan and Sayan Mountain ranges, had a very limited contribution to the current populations of the central and northern parts of the range. It also suggests that the contribution of the high latitude cryptic refugia was geographically limited and that most of the current West Siberian Plain larch populations likely originated in the foothills of the Sayan Mountains. Interestingly, the main population expansion detected through Approximate Bayesian Computation (ABC) in all four larch species investigated here pre-dates the LGM, with a mode in a range of 220,000-1,340,000 years BP. Hence, L. sibirica, like other major conifer species of the boreal forest, was strongly affected by climatic events pre-dating the Last Glacial Maximum. © 2013 John Wiley & Sons Ltd.

Chapter C in Geological Survey research 1967

USGS Publications Warehouse

1967-01-01

Low-grade metamorphic rocks of the blueschist facies grade upward to the sole of a great thrust fault along the eastern margin of the Coast Ranges in northern California and southwestern Oregon. The gradation is defined by three textural zones of increasing reconstitution in metagraywacke, and by two metamorphic mineral zones, lawsonite and pumpellyite. The metagraywacke of textural zones 1 and 2 is clearly Franciscan Formation on the basis of lithology and age, and grades into thoroughly reconstituted rocks of textural zone 3 that herein are named the South Fork Mountain Schist. The blueschist probably formed in a zone of cataclasis and anomalously high water pressures under the thrust fault, rather than in the generally postulated zone of extreme depth of burial. Water in excess of that required to form pumpellyite and lawsonite was available for serpentinization of ultramafic rocks emplaced in the thrust fault.

Correlation of the Klamath Mountains and Sierra Nevada

USGS Publications Warehouse

Irwin, William P.

2003-01-01

This report graphically portrays the broadly parallel tectonic development of the Klamath Mountains and Sierra Nevada from early Paleozoic to Early Cretaceous time. It is dedicated to J.S. Diller of the U.S. Geological Survey who, during his pioneer field studies a century ago, recognized significant similarities between these two important provinces. The report is based mainly on the numerous published reports of the field and laboratory studies by various geologists and students during the last century, and to a lesser extent on my own field work which has been substantial in the Klamath Mountains but minimal in the Sierra Nevada. For brevity, required by the format of this report, little of the extensive literature pertaining to these two provinces is referenced. This report is preliminary in nature and was prepared as an aid to further study of the tectonic relations between the Klamath Mountains and Sierra Nevada. This report consists of two sheets: Sheet 1, Map showing accreted terranes and plutons of the Klamath Mountains and Sierra Nevada, and Sheet 2, Successive accretionary episodes of the Klamath mountains and northern part of Sierra Nevada, showing related plutonic, volcanic, and metamorphic events. The map on Sheet 1 was compiled and modified from two Open-File maps (Irwin and Wooden, 1999 and 2001) which had been compiled and modified mainly from Jennings (1977), Harwood (1992), Irwin (1994), Jayko (1988), Graymer and Jones (1994), Edelman and Sharp (1989), Schweickert and others (1999), Saucedo and Wagner(1992), Saleeby and Sharp (1980), Wagner and others (1981), and various other sources. For detailed lists of the sources for the isotopic age data used in Sheets 1 and 2, see Irwin and Wooden (1999 and 2001). On Sheet 2, the accretionary episodes are shown sequentially from left to right in two tiers of figures. Episodes for the Klamath Mountains are in the upper tier; correlative episodes of the Sierra Nevada are directly below in the lower tier. The sequence shown for the Klamath Mountains is modified from Irwin and Mankinen (1998) and Irwin and Wooden (1999). The episodes are named for the accreting terranes of the Klamath Mountains, but those names may not be suitable for reference to the correlative episodes of the Sierra Nevada. In the figure for each episode, a heavy black line represents the active suture that separated oceanic crustal rocks on the left from the earlier accreted terranes on the right. Plutons are particularly useful for timing the accretionary episodes. The preaccretionary plutons, which commonly represent the roots of oceanic volcanic arcs, are shown in the accreting oceanic crustal rocks to the left of the heavy black line. The accretionary plutons consist of rock that has been subducted and remobilized as magma during the accretionary process and injected into an overlying earlier accreted terrane on the right of the heavy black line. Thus, isotopic dating of the accretionary plutons (preferably U/Pb dates measured on zircon extracted from the plutonic rock) provides a useful basis for assigning ages to the accretionary episodes. Many plutons are rootless at depth, as they tend to be truncated by the subduction zone sutures of younger accreting terranes. Volcanic deposits resulting from accretionary episodes apparently are uncommon except for those deposited on the backstop terranes. In the Klamath Mountains, the Eastern Klamath terrane, which consists of the Yreka, Trinity and Redding subterranes, was the backstop for the Central Metamorphic and younger accretionary episodes, and displays a remarkable record of sedimentation, volcanism and plutonism from Silurian-Devonian to Jurassic time. In the Sierra Nevada, the correlative backstop was the Northern Sierra terrane which shows a similar long record of volcanism in the Taylorsville, Permian, and Jurassic volcanic arc sequences. During some accretionary episodes the subducting oceanic rocks were dynamically metamorphosed to schist along the suture zone beneath the overriding accreted terranes. Examples of this in the Klamath Mountains are the Devonian Salmon and Abrams Schists of the Central Metamorphic terrane, the Triassic(?) schist of the Fort Jones terrane , and the Early Cretaceous South Fork Mountain Schist that structurally underlies Klamath Mountains terranes along much of the western edge of the province. The Fort Jones terrane and South Fork Mountains Schist were metamorphosed under blueschist-facies conditions. In the Sierra Nevada, schist that is correlative with the Central Metamorphic terrane is present in patches along the Feather River terrane (see Hacker and Peacock, 1990); the Triassic(?) Red Ant Schist is correlative with the Fort Jones terrane; but a correlative of the South Fork Mountain Schist is not present. In addition to the similarities in the sequences of accretion, plutonism, volcanism, and metamorphism, strong ties between the two provinces are also provided by paleontologic data. The Permian McCloud fusulinid fauna of the Redding subterrane also is present in the Northern Sierra terrane. Rare Tethyan fusulinids are found in Permian limestone of the Eastern Hayfork terrane of the Klamath Mountains and also in limestone blocks in the Central Belt of the Sierra Nevada. Ichthyosaur fossils have been collected from the Triassic of both the Redding subterrane and Northern Sierra terrane. Jurassic ammonites and the pelecypod Buchia concentrica occur in both the Galice Formation of the western Klamath Mountains and the Mariposa Formation of the western Sierra Nevada. Events that preceded the Central Metamorphic episode prior to Silurian-Devonian time are not clearly understood and are not shown in the succession of diagrams on Sheet 2. The oldest rocks of the Klamath Mountains are Neoproterozic and they predate the Central Metamorphic episode by possibly a hundred million years or more. They include ophiolitic rocks of the Trinity subterrane and the Antelope Mountain Quartzite of the Yreka subterrane (see Mankinen and others, 2002). In the Sierra Nevada, correlatives of the ancient ophiolitic rocks may be part of the Feather River terrane. Although Neoproterozoic fossils have not yet been found in the Sierra Nevada, petrologic study shows the quartzite of the Lang sequence is closely similar to the Antelope Mountain Quartzite (see Bond and Devay, 1980). Correlation of the two quartzite formations is also suggested by the similarity of their positions in the accretionary sequence.

High sedimentation rates and thrust fault modulation: Insights from ocean drilling offshore the St. Elias Mountains, southern Alaska

NASA Astrophysics Data System (ADS)

Worthington, Lindsay L.; Daigle, Hugh; Clary, Wesley A.; Gulick, Sean P. S.; Montelli, Aleksandr

2018-02-01

The southern Alaskan margin offshore the St. Elias Mountains has experienced the highest recorded offshore sediment accumulation rates globally. Combined with high uplift rates, active convergence and extensive temperate glaciation, the margin provides a superb setting for evaluating competing influences of tectonic and surface processes on orogen development. We correlate results from Integrated Ocean Drilling Program (IODP) Expedition 341 Sites U1420 and U1421 with regional seismic data to determine the spatial and temporal evolution of the Pamplona Zone fold-thrust belt that forms the offshore St. Elias deformation front on the continental shelf. Our mapping shows that the pattern of active faulting changed from distributed across the shelf to localized away from the primary glacial depocenter over ∼300-780 kyrs, following an order-of-magnitude increase in sediment accumulation rates. Simple Coulomb stress calculations show that the suppression of faulting is partially controlled by the change in sediment accumulation rates which created a differential pore pressure regime between the underlying, faulted strata and the overlying, undeformed sediments.

Foreshock occurrence rates before large earthquakes worldwide

USGS Publications Warehouse

Reasenberg, P.A.

1999-01-01

Global rates of foreshock occurrence involving shallow M ??? 6 and M ??? 7 mainshocks and M ??? 5 foreshocks were measured, using earthquakes listed in the Harvard CMT catalog for the period 1978-1996. These rates are similar to rates ones measured in previous worldwide and regional studies when they are normalized for the ranges of magnitude difference they each span. The observed worldwide rates were compared to a generic model of earthquake clustering, which is based on patterns of small and moderate aftershocks in California, and were found to exceed the California model by a factor of approximately 2. Significant differences in foreshock rate were found among subsets of earthquakes defined by their focal mechanism and tectonic region, with the rate before thrust events higher and the rate before strike-slip events lower than the worldwide average. Among the thrust events a large majority, composed of events located in shallow subduction zones, registered a high foreshock rate, while a minority, located in continental thrust belts, measured a low rate. These differences may explain why previous surveys have revealed low foreshock rates among thrust events in California (especially southern California), while the worldwide observations suggest the opposite: California, lacking an active subduction zone in most of its territory, and including a region of mountain-building thrusts in the south, reflects the low rate apparently typical for continental thrusts, while the worldwide observations, dominated by shallow subduction zone events, are foreshock-rich.

Palaeomagnetic evidence for post-thrusting tectonic rotation in the Southeast Pyrenees, Spain

NASA Astrophysics Data System (ADS)

Keller, P.; Lowrie, W.; Gehring, A. U.

1994-12-01

The structural framework of the Southeast Pyrenees led to two conflicting interpretations—thrust tectonics vs. wrench tectonics—to explain the geometry of this mountain range. In the present study palaeomagnetic data are presented in an attempt to resolve this conflict. The data reveal different magnetisation directions that indicate tectonic rotations about vertical axes. By means of a regionally homogeneous pattern of rotation, three tectonic units could be distinguished in the Southeast Pyrenees. The Internal Unit in the north reveals no rotation since the Permian. The External Unit to the south shows anticlockwise rotation of 25°, younger than the Early Oligocene. The Pedraforca Unit, placed on the External Unit, shows 57° clockwise rotation which can be assigned to the Neogene. The anticlockwise rotation of the External Unit can be explained by differential compression during the last phase of Pyrenean thrusting, whereas the clockwise rotation of the Pedraforca Unit can be interpreted by post-thrusting tectonics. The rotation pattern of the Southeast Pyrenees provides evidence for both Cretaceous to Paleogene N-S compression and Neogene right-lateral wrench tectonics.

Recent development of a jet-diffuser ejector

NASA Technical Reports Server (NTRS)

Alperin, M.; Wu, J. J.

1980-01-01

The paper considers thrust augmenting ejectors in which the processes of mixing and diffusion are partly carried out downstream of the ejector solid surfaces. A jet sheet surrounding the periphery of a widely diverging diffuser prevents separation and forms a gaseous, curved surface to provide effective diffuser ratio and additional length for mixing of primary and induced flows. Three-dimensional potential flow methods achieved a large reduction in the length of the associated solid surface; primary nozzle design further reduced the volume required by the jet-diffuser ejectors, resulting in thrust augmentation in excess of two, and an overall length of about 2 1/2 times the throat width.

Two new ductile microscopic shear sense indicators from the Oman Mountains

NASA Astrophysics Data System (ADS)

Scharf, Andreas; Mattern, Frank; Pracejus, Bernhard

2017-04-01

The new shear sense indicators were observed in two different tectonic settings. The first one occurs in mylonitized Jurassic limestone on the northern flank of the Jebel Akhdar Dome (eastern Oman Mountains) and is associated with top-to-the-NNE extension. The second one was discovered in mylonitized plagiogranite (trondhjemite) with vertical to subvertical foliation and strike-slip deformation within harzburgite of the Semail Ophiolite in Wadi Fizh (northwestern Oman Mountains). The carbonate mylonite displays shear planes, in thin, flat and parallel laminations with a compositional aspect as there are alternations between pure calcite laminae and dark laminae of accumulated limestone impurities (iron compounds, clay). Despite the fact that the carbonate mylonite is associated with extension, the shear sense criterion is linked to top-to-the-NNE microthrusts, involving shortening of the dark laminae. The thrusts form an acute angle in relation to the lamination. Thrusting between segments of these, microthrusts created pull-aparts whose voids remained temporarily open cavities but were eventually filled with drusy calcite cement. The shear sense is revealed by (1) the shortening and related imbrication of the thrust laminae, (2) the pull-apart structures and (3) drag folds at either end of the microthrusts. The shear is also confirmed by independent ductile and brittle macroscopic shear sense criteria in the same outcrop, such as drag folds, Riedel shears and mineral steps. These new shear sense fabrics measure approximately 0.5mm in width and 1mm in length. The mylonitized granite contains large (2mm long axis) plagioclase porphyroclasts. We encountered a rotated plagioclase crystal whose twin lamellae have been dragged by the rotational motion during high-temperature conditions. Drag folds occur on either end of the lamellae/crystal. As a result an "S" shape is produced by counterclockwise rotation and sinistral shear, respectively. The observed shear sense is confirmed by synthetically sheared K-feldspar and feldspar porphyroclast systems. "Z" shapes are expected to develop in case of opposite rotation and shearing.

Structural implications of an offset Early Cretaceous shoreline in northern California

USGS Publications Warehouse

Jones, D.L.; Irwin, W.P.

1971-01-01

Recognition of a nonmarine to marine transition in sedimentary rocks at Glade Creek and Big Bar in the southern Klamath Mountains permits reconstruction of the approximate position of a north-trending Early Cretaceous (Valanginian) shoreline. At the southern end of the Klamath Mountains, the shoreline is displaced 60 mi or more to the east by a west-northwest-trending fault zone. South of this fault zone the shoreline is buried at a much lower level beneath late Cenozoic rocks in the Great Valley. This large displacement probably is the result of differential movement along a system of left-lateral tear faults in the upper plate of the Coast Range thrust. The westward bulge of the Klamath arc also may have resulted from this faulting, as the amount and direction of the bulge is comparable with the displacement of the Valanginian shoreline.Basal clastic strata at both Glade Creek and Big Bar contain abundant fresh-water or brackish-water clams, many of which consist of unabraded paired valves. These are conformably overlain by Valanginian marine strata containing Buchia crassicollis solida.The position of the Valanginian shoreline beneath the Great Valley cannot be directly observed because it is buried by thick late Cenozoic deposits. However, its approximate westernmost limit must lie between the outcrop belt of marine strata on the west side of the valley and drill holes to basement on the east side, in which equivalent strata are absent.Franciscan rocks containing Valanginian fossils occur 10 mi southwest of Glade Creek, but these are deep-water marine eugeosynclinal rocks that were deposited far to the west of the shoreline. The deformation responsible for the displacement of the Valanginian shoreline and juxtaposition of the Franciscan rocks and Klamath Mountain basement rocks involved eastward under-thrusting of the Franciscan beneath the Coast Range thrust contemporaneous with differential movement along tear faults within the upper plate.

Major, trace element and stable isotope geochemistry of synorogenic breccia bodies, Ellsworth Mountains, Antarctica

USGS Publications Warehouse

Craddock, J.P.; McGillion, M.S.; Webers, G.F.

2007-01-01

Cambrian carbonates in the Heritage Range of the Ellsworth Mountains, West Antarctica host a series of carbonate-rich breccia bodies that formed contemporaneously with the Permian Gondwanide orogen. The breccia bodies had a three-stage genesis, with the older breccias containing Cambrian limestone (and marble) clasts supported by calcite, whereas the younger breccias are nearly clast-free and composed entirely of matrix calcite. Breccia clasts, calcite matrix and detrital matrix samples were analyzed using x-ray fluorescence (major and trace elements), x-ray diffraction, and stable isotopes (C, O) and suggest that the breccias formed as part of a closed geochemical system, at considerable depth, within the Cambrian limestone host as the Ellsworth Mountains deformed into a fold-and-thrust belt along the margin of Gondwana

Interpretation of recent gravity profiles over the ophiolite belt, Northern Oman Mountains, United Arab Emirates

NASA Astrophysics Data System (ADS)

Khattab, M. M.

1993-04-01

The compiled Bouguer gravity anomaly map over parts of the ophiolite rocks of the Northern Oman Mountains suggests the existence of three partially serpentinized nappes: two along the Gulf of Oman coast with axes near Dadnah, near Fujira and the third 17 km SSE of Masafi. Modeling of the subsurface geology, beneath two gravity profiles (Diba-Kalba and Masafi-Fujira), is based on the occurrence (field evidence) of multiphase low-angle thrusting of the members of the Tethyan lithosphere in northern and Oman Mountains. An assumed crustal model at the Arabian continental margin, beneath the Masafi-Fujira profile, is made to explain an intense gravity gradient. Gravity interpretation is not inconsistent with a gliding mechanism for obduction of the ophiolite on this part of the Arabian continental margin.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Montgomery, S.L.

Recent discovery of natural gas in sandstones of the Jackfork Group of southeastern Oklahoma has led to revised interpretations of hydrocarbon potential in the Ouachita thrust province of eastern Oklahoma. Jackfork reservoirs consist of fine to very fine grained, submarine-fan lobe sandstones with low matrix permeability and porosity. Production is dependent upon natural fractures, enhanced in most cases by artificial stimulation. Individual wells have produced at rates of 1.3-5.7 Mcf per day and possess estimated reserves in the range of 2.0-7.6 Gcf. Hyperbolic decline suggests gas contribution from the matrix, possibly due to the presence of microfractures. Drilling has concentratedmore » on two subsidiary thrust blocks in the hanging wall of the Ti Valley thrust, southern Latimer County. However, recent outcrop, petrographic, and sedimentological analyses have shown that traditional depositional models of the Jackfork are overly limited and that potential Jackfork reservoirs exist across a broad area to the south of the current play. Such analyses have revealed the existence of thick, medium-coarse-grained channel sequences at a number of localities in the Lynn Mountain syncline. Similar sequences may also exist well to the south, in the Boktukola syncline, where thick sand intervals have been identified. Petrographic study of samples from the Lynn Mountain syncline suggests that channel sequences may have significantly higher reservoir quality than is found in productive Jackfork sandstones to the north. Traditional assumptions postulating low regional hydrocarbon potential for the Jackfork therefore stand in need of revision.« less

Surface mass balance of Greenland mountain glaciers and ice caps

NASA Astrophysics Data System (ADS)

Benson, R. J.; Box, J. E.; Bromwich, D. H.; Wahr, J. M.

2009-12-01

Mountain glaciers and ice caps contribute roughly half of eustatic sea-level rise. Greenland has thousands of small mountain glaciers and several ice caps > 1000 sq. km that have not been included in previous mass balance calculations. To include small glaciers and ice caps in our study, we use Polar WRF, a next-generation regional climate data assimilation model is run at grid resolution less than 10 km. WRF provides surface mass balance data at sufficiently high resolution to resolve not only the narrow ice sheet ablation zone, but provides information useful in downscaling melt and accumulation rates on mountain glaciers and ice caps. In this study, we refine Polar WRF to simulate a realistic surface energy budget. Surface melting is calculated in-line from surface energy budget closure. Blowing snow sublimation is computed in-line. Melt water re-freeze is calculated using a revised scheme. Our results are compared with NASA's Gravity Recovery and Climate Experiment (GRACE) and associated error is calculated on a regional and local scale with validation from automated weather stations (AWS), snow pits and ice core data from various regions along the Greenland ice sheet.

Ice Elevation Changes in the Ellsworth Mountains, Antarctica Using Multiple Cosmogenic Nuclides

NASA Astrophysics Data System (ADS)

Marrero, S.; Hein, A.; Sugden, D.; Woodward, J.; Dunning, S.; Reid, K.

2014-12-01

Well-dated geologic data points provide important indicators that can be used for the reconstruction of ice sheet dynamics and as constraints in ice sheet models predicting future change. Cosmogenic nuclides, which accumulate in rocks exposed at the earth's surface, can be used to directly date the exposure age of the rock surfaces that have been created through glacial erosion or deposition. The technique requires a detailed understanding of the local geomorphology as well as awareness of the post-depositional processes that may affect the interpretation of exposure ages. Initial surface exposure ages (10Be, 26Al, 21Ne, and 36Cl ) from local limestone bedrock and other glacially deposited exotic lithologies provide a history spanning from 0 to 1.1 Ma in the Patriot, Independence, and Marble Hills in the southern Ellsworth Mountains, Antarctica. Using the new surface exposure ages combined with geomorphological mapping, we will discuss the implications for the glacial history of the southern Ellsworth Mountains.

Using Multiple Cosmogenic Nuclides to Investigate Ice Elevation Changes in the Ellsworth Mountains, Antarctica

NASA Astrophysics Data System (ADS)

Marrero, Shasta; Hein, Andy; Sugden, David; Woodward, John; Dunning, Stuart; Freeman, Stewart; Shanks, Richard

2015-04-01

Well-dated geologic data points provide important indicators that can be used for the reconstruction of ice sheet dynamics and as constraints in ice sheet models predicting future change. Cosmogenic nuclides, which accumulate in rocks exposed at the earth's surface, can be used to directly date the exposure age of the rock surfaces that have been created through glacial erosion or deposition. The technique requires a detailed understanding of the local geomorphology as well as awareness of the post-depositional processes that may affect the interpretation of exposure ages. Surface exposure ages (10Be, 26Al, 21Ne, and 36Cl) from local limestone bedrock and other glacially deposited exotic lithologies provide a history spanning from 0 to more than 1 million years in the Patriot, Independence, and Marble Hills in the southern Ellsworth Mountains, Antarctica. Using the new surface exposure ages combined with geomorphological mapping, we will discuss the implications for the glacial history of the southern Ellsworth Mountains.

Geologic map of the central San Juan caldera cluster, southwestern Colorado

USGS Publications Warehouse

Lipman, Peter W.

2006-01-01

The San Juan Mountains are the largest erosional remnant of a composite volcanic field that covered much of the southern Rocky Mountains in middle Tertiary time. The San Juan field consists mainly of intermediate-composition lavas and breccias, erupted about 35-30 Ma from scattered central volcanoes (Conejos Formation) and overlain by voluminous ash-flow sheets erupted from caldera sources. In the central San Juan Mountains, eruption of at least 8,800 km3 of dacitic-rhyolitic magma as nine major ash flow sheets (individually 150-5,000 km3) was accompanied by recurrent caldera subsidence between 28.3 Ma and about 26.5 Ma. Voluminous andesitic-dacitic lavas and breccias erupted from central volcanoes prior to the ash-flow eruptions, and similar lava eruptions continued within and adjacent to the calderas during the period of more silicic explosive volcanism. Exposed calderas vary in size from 10 to 75 km in maximum dimension; the largest calderas are associated with the most voluminous eruptions.

Fuels planning: science synthesis and integration; environmental consequences fact sheet 05: prescriptions and fire effects

Treesearch

Melanie Miller

2004-01-01

Fuels planning: science synthesis and integration; environmental consequences fact sheet 5: prescriptions and fire effects. Miller, Melanie. 2004. Res. Note RMRS-RN-23-5-WWW. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. 2 p. While our understanding of the causes for variation in postfire effects is increasing, burn...

268. Photocopy of drawing (1981 piping drawing by StearnsRoger Incorporated) ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

268. Photocopy of drawing (1981 piping drawing by Stearns-Roger Incorporated) ATLAS H CONVERSION; PLANS, SECTIONS, AND DETAILS FOR THE LIQUID OXYGEN PIPING AND THRUST SECTION HEATER DUCT, SHEET 517-P2 - Vandenberg Air Force Base, Space Launch Complex 3, Launch Pad 3 East, Napa & Alden Roads, Lompoc, Santa Barbara County, CA

CASA Fact Sheet.

ERIC Educational Resources Information Center

National Court Appointed Special Advocate Association, Seattle WA.

Each year nearly 400,000 children in the United States are thrust into court through no fault of their own. Often these children also become victims of the United States' overburdened child welfare system. A Court Appointed Special Advocate (CASA) volunteer is a trained citizen who is appointed by a judge to represent the best interests of a child…

Late Wisconsin and early holocene glacial history, inner Ross Embayment, Antarctica

NASA Technical Reports Server (NTRS)

Denton, George H.; Bockheim, James G.; Wilson, Scott C.; Stuiver, Minze

1991-01-01

Lateral drift sheets of outlet glaciers that pass through the Transantarctic Mountains constrain past changes of the huge Ross ice drainage system of the Antarctic Ice Sheet. Drift stratigraphy suggests correlation of Reedy III (Reedy Glacier), Beardmore, Britannia (Hatherton/Darwin Glaciers), Ross Sea (McMurdo Sound), and younger (Terra Nova Bay) drifts; radiocarbon dates place the outer limits of Ross Sea drift in late Wisconsin time at 24,000 to 13,000 yr B.P. Outlet glacier profiles from these drifts constrain late Wisconsin ice sheet surface elevations. Within these constraint, two extreme late Wisconsin reconstructions are given of the Ross ice drainage system. Both show little elevation change of the polar plateau coincident with extensive ice shelf grounding along the inner Ross Embayment. However, in the central Ross Embayment, one reconstruction shows floating shelf ice, where as the other shows a grounded ice sheet. Massive late Wisconsin/Holocene recession of grounded ice from the western Ross Embayment, which was underway at 13,040 yr B.P. and completed by 6600 to 6020 yr B.P., was accompanied by little change in plateau ice levels inland of the Transantarctic Mountains.

A middle Pleistocene through middle Miocene moraine sequence in the central Transantarctic Mountains, Antarctica

NASA Astrophysics Data System (ADS)

Balter, A.; Bromley, G. R.; Balco, G.; Thomas, H.; Jackson, M. S.

2017-12-01

Ice-free areas at high elevation in the central Transantarctic Mountains preserve extensive moraine sequences and drift deposits that comprise a geologic record of former East Antarctic Ice Sheet thickness and extent. We are applying cosmogenic-nuclide exposure dating to determine the ages of these moraine sequences at Roberts Massif and Otway Massif, at the heads of the Shackleton and Beardmore Glaciers, respectively. Moraines at these sites are for the most part openwork boulder belts characteristic of deposition by cold-based ice, which is consistent with present climate and glaciological conditions. To develop our chronology, we collected samples from 30 distinct ice-marginal landforms and have so far measured >100 3He, 10Be, and 21Ne exposure ages. Apparent exposure ages range from 1-14 Ma, which shows that these landforms record glacial events between the middle Pleistocene and middle Miocene. These data show that the thickness of the East Antarctic Ice Sheet in this region was similar to or thicker than present for long periods between the middle Miocene and today. The time range represented by these moraine sequences indicates that they may also provide direct geologic evidence for East Antarctic Ice Sheet behavior during past periods of warmer-than-present climate, specifically the Miocene and Pliocene. As the East Antarctic Ice Sheet is the largest ice sheet on earth, understanding its sensitivity to warm-climate conditions is critical for projections of ice sheet behavior and sea-level rise in future warm climates.

Extensional reactivation of the Chocolate Mountains subduction thrust in the Gavilan Hills of southeastern California

USGS Publications Warehouse

Oyarzabal, F.R.; Jacobson, C.E.; Haxel, G.B.

1997-01-01

The NE vergent Chocolate Mountains fault of south-eastern California has been interpreted as either a subduction thrust responsible for burial and prograde metamorphism of the ensimatic Orocopia Schist or as a normal fault involved in the exhumation of the schist. Our detailed structural analysis in the Gavilan Hills area provides new evidence to confirm the latter view. A zone of deformation is present at the top of the Orocopia Schist in which lineations are parallel to those in the upper plate of the Chocolate Mountains fault but oblique to ones at relatively deep levels in the schist. Both the Orocopia Schist and upper plate contain several generations of shear zones that show a transition from crystalloblastic through mylonitic to cataclastic textures. These structures formed during retrograde metamorphism and are considered to record the exhumation of the Orocopia Schist during early Tertiary time as a result of subduction return flow. The Gatuna fault, which places low-grade, supracrustal metasediments of the Winterhaven Formation above the gneisses of the upper plate, also seems to have been active at this time. Final unroofing of the Orocopia Schist occurred during early to middle Miocene regional extension and may have involved a second phase of movement on the Gatuna fault. Formation of the Chocolate Mountains fault during exhumation indicates that its top-to-the-NE sense of movement provides no constraint on the polarity of the Orocopia Schist subduction zone. This weakens the case for a previous model involving SW dipping subduction, while providing support for the view that the Orocopia Schist is a correlative of the Franciscan Complex.

Deep crustal structure of the UAE-Oman mountain belt from seismic and gravity data

NASA Astrophysics Data System (ADS)

Pilia, S.; Tanveer, M.; Ali, M.; Watts, A. B.; Searle, M. P.; Keats, B. S.

2016-12-01

The UAE-Oman mountains constitute a 700 km long, 50 km wide compressional orogenic belt that developed during the Cenozoic on an underlying extensional Tethyan rifted margin. It contains the world's largest and best-exposed thrust sheet of oceanic crust and upper mantle (Semail Ophiolite), which was obducted onto the Arabian rifted continental margin during the Late Cretaceous. Although the shallow structure of the UAE-Oman mountain belt is reasonably well known through the exploitation of a diverse range of techniques, information on deeper structure remains little. Moreover, the mechanisms by which dense oceanic crustal and mantle rocks are emplaced onto less dense and more buoyant continental crust are still controversial and remain poorly understood. The focus here is on an active-source seismic and gravity E-W transect extending from the UAE-mountain belt to the offshore. Seismic refraction data were acquired using the survey ship M/V Hawk Explorer, which was equipped with a large-volume airgun array (116 liters). About 400 air gun shots at 50-second time interval were recorded on land by eight broadband seismometers. In addition, reflection data were acquired at 20 seconds interval and recorded by a 5-km-long multichannel streamer. Results presented here include an approximately 85 km long (stretching about 35 km onshore and 50 km offshore) P-wave velocity crustal profile derived by a combination of forward modelling and inversion of both diving and reflected wave traveltimes using RAYINVR software. We employ a new robust algorithm based on a Monte Carlo approach (VMONTECARLO) to address the velocity model uncertainties. We find ophiolite seismic velocities of about 5.5 km/s, underlain by a thin layer of slower material (about 4.5 km/s). Furthermore, the velocity model reveals a Moho depth that rises from ca 30 km in the west to ca 20 km in the east. A poststack depth-migrated profile (about 50 km long) coincident with the offshore part of the refraction profile shows a thick sequence (up to 6 km) of seaward dipping sediments that are offset by a number of listric (normal) faults, some of which intersect the seabed and so reflect recent tectonic activity. The trend of the Bouguer anomaly provides further constraints on the deeper structure of the margin and appears to confirm the presence of a stretched crust.

The Dandridge-Vonore Fault Zone in the Eastern Tennessee Seismic Zone (and Rejuvenation of the Smokies?)

NASA Astrophysics Data System (ADS)

Cox, R. T.; Hatcher, R. D., Jr.; Forman, S. L.; Gamble, E. D. S.; Warrell, K. F.

2017-12-01

The eastern Tennessee seismic zone (ETSZ) trends 045o from NE Alabama and NW Georgia through Tennessee to SE Kentucky, and seismicity is localized 5-26 km deep in the basement. The ETSZ is the second most seismically active region in North America east of the Rocky Mountains, although no historic earthquakes larger than Mw 4.8 have been recorded here. Late Quaternary paleoiseismic evidence suggests that the ETSZ is capable of M7+ earthquakes and that neotectonic faults may have significantly influenced the regional relief. We have identified an 80 km-long, 060o-trending corridor in eastern Tennessee that contains collinear northeast-striking thrust, strike-slip, and normal Quaternary faults with displacements of 1-2 m, herein termed the Dandridge-Vonore fault zone (DVFZ). French Broad River alluvium in the northeast DVFZ near Dandridge, TN, is displaced by a 050o-striking, SE-dipping thrust fault and by a set of related fissures that record at least two significant post 25 ka paleo-earthquakes. Southwest of Dandridge near Alcoa, TN, a 060o-striking, SE-dipping thrust fault cuts Little River alluvium and records two significant post-15 ka paleo-earthquakes. Farther southwest at Vonore, colluvium with alluvial cobbles is thrust >1 m by a 057o-striking, steeply SE-dipping fault that may also have a significant strike-slip component, and Little Tennessee River alluvium is dropped >2 m along a 070o- striking normal fault. The DVFZ partly overlaps and is collinear with a local trend of maximum seismicity that extends 30 km farther SW of the DVFZ (as currently mapped), for a total length of 110 km. The DVFZ is coincident with a steep gradient in S-wave velocities (from high velocity on the SE to low velocity on the NW) at mid-crustal depths of 20 to 24 km, consistent with a fault and source zone at hypocentral depths in the crystalline basement. Moreover, the DVFZ parallels the NW foot of Blue Ridge Mountains, and the sense of thrusting at all sites of Quaternary faulting in the DVFZ is consistent with uplift of the Blue Ridge.

A transect through the base of the Bronson Hill Terrane in western New Hampshire

USGS Publications Warehouse

Walsh, Gregory J.; Valley, Peter M.; Sicard, Karri R.; Thompson, Thelma Barton; Thompson, Peter J.

2012-01-01

This trip will present the preliminary results of ongoing bedrock mapping in the North Hartland and Claremont North 7.5-minute quadrangles in western New Hampshire. The trip will travel from the Lebanon pluton to just north of the Sugar River pluton (Fig. 1) with the aim of examining the lower structural levels of the Bronson Hill anticlinorium (BHA), and the nature of the boundary with the rocks of the Connecticut Valley trough (CVT). Spear and others (2002, 2003, 2008) proposed that western New Hampshire was characterized by five major faults bounding five structural levels including, from lowest to highest, the “chicken yard line”, Western New Hampshire Boundary Thrust, Skitchewaug nappe, Fall Mountain nappe, and Chesham Pond nappe. Lyons and others (1996, 1997) showed the lowest level cored by the Cornish nappe and floored by the Monroe fault. Thompson and others (1968) explained the geometry of units by folding without major thrust faults, and described the second level as the Skitchewaug nappe. This trip will focus on the two lowest levels which we have revised to call the Monroe and Skitchewaug Mountain thrust sheets. Despite decades of geologic mapping in the northeastern United States at various scales, little 1:24,000-scale (or larger scale) modern bedrock mapping has been published for the state of New Hampshire. In fact, of the New England states, New Hampshire contains the fewest published, modern bedrock geologic maps. Conversely, adjacent Vermont has a relatively high percentage of modern bedrock maps due to focused efforts to create a new state-wide bedrock geologic map over the last few decades. The new Vermont map (Ratcliffe and others, 2011) has identified considerable gaps in our knowledge of the bedrock geology in adjacent New Hampshire where published maps are, in places, more than 50 years old and at scales ranging from 1:62,500 to 1:250,000. Fundamental questions remain concerning the geology across the Connecticut River, especially in regards to the stratigraphy of the BHA and CVT, and the distribution, or even existence, of faults ranging in age from Devonian to Mesozoic (e.g., Spear and others, 2008; McWilliams and others, 2010; Walsh and others, 2010). Questions to ponder on this trip include, but are not limited to: 1) Is the Bronson Hill anticlinorium allochthonous? 2) What is the crust beneath the Bronson Hill anticlinorium? 3) Is there a “Big Staurolite nappe” as proposed by Spear and others (2002, 2003, 2008)? 4) What is the role of Taconic, Acadian, and Alleghanian orogenesis in the tectonic development of the region? Modern 1:24,000-scale mapping is the first step towards answering these questions. Mapping will be supplemented by modern geochronology and geochemistry as this project develops. We plan to share some of our provisional results during this field trip.

Team Teaching and Cooperative Groups in Abstract Algebra: Nurturing a New Generation of Confident Mathematics Teachers

ERIC Educational Resources Information Center

Grassl, R.; Mingus, T. T. Y.

2007-01-01

Experiences in designing and teaching a reformed abstract algebra course are described. This effort was partially a result of a five year statewide National Science Foundation (NSF) grant entitled the Rocky Mountain Teacher Enhancement Collaborative. The major thrust of this grant was to implement reform in core mathematics courses that would…

Effect of footwall structures on kinematic evolution of dominant thrusts from hinterland of an orogenic wedge: Insights from Sikkim Himalayan FTB

NASA Astrophysics Data System (ADS)

Ghosh, Pritam; Bhattacharyya, Kathakali

2017-04-01

Deformation profile of a thrust sheet is generally characterized by a dominance of simple-shear toward the base and pure-shear higher up. In this study, we attempt to examine the effect of underlying footwall structure on the evolution of such a deformation profile with time. We focus on two dominant thrusts of the Sikkim Himalayan FTB, the northern most Main Central thrust (MCT) and its major footwall thrust, the Pelling thrust (PT). The MCT and the PT sheets are folded in an E-W trending antiform-synform pair by the growth of the underlying Lesser Himalayan duplex. The PT acts as the roof thrust of the duplex. The coarse-grained, quartzo-feldspathic gneissic protoliths transform into quartz-mica mylonite forming ˜1170m thick amphibolite facies MCT zone and ˜938m thick greenschist facies PT zone. Due to the forelandward progression of deformation front, the overlying MCT foliation is superposed by the underlying PT foliation. Within both the fault zones, quartz has undergone grain-size reduction dominantly by dislocation creep, and feldspar by fracturing mechanism. Interestingly, microfracturing is more dominant in MCT zone than in the PT zone. Additionally, pressure solution is significantly higher in the PT zone than in the MCT. Thus, there is a spatial variation in deformation mechanisms within the MCT and PT zones. Based on recrystallized quartz grain-sizes, we estimate deformation temperatures of ˜430˚ C-510˚ C and ˜400˚ C-430˚ C within the MCT and the PT, respectively. Both quartz and feldspar grains record a higher flattening strain in the MCT zone than in the PT zone. We infer fracturing and pressure solution accommodated a significant amount of strain, thereby under-representing the viscoplastic strain. Estimation of kinematic vorticity from two different incremental strain markers, namely oblique-fabric and subgrains, indicate both the MCT and the PT zones record a progressively higher pure-shear dominated deformation with time. The PT zone records a higher pure-shear than the MCT zone. Therefore, integration of structural geometry, microstructure and kinematic data suggest that the PT fault zone records the effect of footwall duplex more prominently than the MCT fault zone. We attribute the temporal evolution toward a pure-shear dominated deformation within the PT zone due to the growth of the underlying Lesser Himalayan duplex.

Structural profile reconstructions and thermal metamorphic evolution in the slate belt of southern Hsuehshan Range in the active Taiwan mountain belt

NASA Astrophysics Data System (ADS)

Wu, Yu; Chen, Chih-Tung; Lee, Jian-Cheng; Shyu, J. Bruce H.

2017-04-01

The fate of passive continental margin in collisional orogens is crucial in understanding tectonic evolution of mountain belts. The active arc-continent collision of Taiwan is considered as a model case in studying mountain building processes, and largely consists of deformed margin basement and cover series. Among the whole orogeny belt, the slate belt of the Hsuehshan Range (HR) is a prominent large-scale pop-up structural on the prowedge part of the orogen, and is composed of metamorphosed Eocene to Miocene sediments which experienced only the Neogene Taiwan orogeny after diagenesis in margin graben. Characterizing the metamorphic history of the HR is essential for reconstructing its geological evolution during the mountain building processes. However, previous studies were mostly focused on northern and central HR, structural investigation coupled with metamorphic documentation in the southern part of HR, which is the most active part of the orogeny belt, is therefore targeted in this work. Since carbonaceous material is common in pelitic protolith of HR slates, the Raman spectrum of carbonaceous material (RSCM) measuring the rock peak temperature is chosen for quantitative thermal metamorphic documentation. In this study, we reconstruct a geological structural profile in western central Taiwan across the prowedge part of the mountain belt containing the southern HR by combining the surface geological data, well log records and published seismic reflection profiles. Although most of the existing data are concentrated in the fold-and-thrust belt, they are now reinforced by new field structural measurements and RSCM samples in the southern HR. In total 27 RSCM samples were collected along 2 transects perpendicular to the average strike with a dense interval about 2 km. The results allow us to map peak temperature distribution across southern HR, and provide new constraints for structural profile reconstruction and reappraisal of the structural evolution of the HR and neighboring fold-and-thrust belt. As shown in the previous thermal metamorphic investigation, we expected that southern HR strata acquired highest temperature during its burial stage than the orogenic stage like their central HR counterparts, thus experiencing mostly retrograde metamorphism in the entire mountain building processes.

Inherited crustal features and tectonic blocks of the Transantarctic Mountains: An aeromagnetic perspective (Victoria Land, Antarctica)

NASA Astrophysics Data System (ADS)

Ferraccioli, F.; Bozzo, E.

1999-11-01

Aeromagnetic images covering a sector of the Transantarctic Mountains in Victoria Land as well as the adjacent Ross Sea are used to study possible relationships between tectonic blocks along the Cenozoic and Mesozoic West Antarctic rift shoulder and prerift features inherited mainly from the Paleozoic terranes involved in the Ross Orogen. The segmentation between the Prince Albert Mountains block and the Deep Freeze Range-Terra Nova Bay region is related to an inherited NW to NNW ice-covered boundary, which we name the "central Victoria Land boundary." It is interpreted to be the unexposed, southern continuation of the Ross age back arc Exiles thrust system recognized at the Pacific coast. The regional magnetic high to the west of the central Victoria Land boundary is attributed to Ross age calc-alkaline back arc intrusives forming the in-board Wilson "Terrane," thus shifting the previously interpreted Precambrian "shield" at least 100 km farther to the west. The high-frequency anomalies of the Prince Albert Mountains and beneath the Polar Plateau show that this region was extensively effected by Jurassic tholeiitic magmatism; NE to NNE trending magnetic lineations within this pattern could reflect Cretaceous and/or Cenozoic faulting. The western and eastern edges of the Deep Freeze Range block, which flanks the Mesozoic Rennick Graben, are marked by two NW magnetic lineaments following the Priestley and Campbell Faults. The Campbell Fault is interpreted to be the reactivated Wilson thrust fault zone and is the site of a major isotopic discontinuity in the basement. To the east of the Campbell Fault, much higher amplitude magnetic anomalies reveal mafic-ultramafic intrusives associated with the alkaline Meander Intrusive Group (Eocene-Miocene). These intrusives are likely genetically linked to the highly uplifted Southern Cross Mountains block. The NW-SE trends crossing the previously recognized ENE trending Polar 3 Anomaly offshore of the Southern Cross Mountains are probably linked to Cenozoic reactivation of the Paleozoic Wilson-Bowers suture zone as proposed from recent seismic interpretations. The ENE trend of the anomaly may also be structural, and if so, it could reflect an inherited fault zone of the cratonal margin.

Tectono-sedimentary evolution of salt controlled minibasin in a fold-an-thrust belt setting Example from the Sivas Basin Turkey and physical model.

NASA Astrophysics Data System (ADS)

Kergaravat, Charlie; Ribes, Charlotte; Darnault, Romain; Callot, Jean-Paul; Ringenbach, Jean-Claude

2017-04-01

The aim of this study is to present the influence of regional shortening on the evolution of a minibasin province and the associated foldbelt geometry based on a natural example, the Sivas Basin, then compared to a physical experiment. The Sivas Basin in the Central Anatolian Plateau (Turkey) is a foreland fold-and-thrust belt, displaying in the central part a typical wall and basin province characterized by spectacularly exposed minibasins, separated by continuous steep-flanked walls and diapirs over a large area (45x25 km). The advance of the orogenic wedge is expressed within the second generation of minibasins by a shortening-induced squeezing of diapirs. Network of walls and diapirs evolve form polygonal to linear pattern probably induced by the squeezing of pre-existing evaporite walls and diapirs, separating linear primary minibasins. From base to top of secondary minibasins, halokinetic structures seem to evolve from small-scale objects along diapir flanks, showing hook and wedges halokinetic sequences, to large stratigraphic wedging, megaflap and salt sheets. Minibasins show progressively more linear shape at right angle to the regional shortening and present angular unconformities along salt structures related to the rejuvenation of pre-existing salt diapirs and walls probably encouraged by the shortening tectonic regime. The advance of the fold-and-thrust belts during the minibasins emplacement is mainly expressed during the late stage of minibasins development by a complex polygonal network of small- and intermediate-scale tectonic objects: (1) squeezed evaporite walls and diapirs, sometimes thrusted forming oblique or vertical welds, (2) allochthonous evaporite sheets, (3) thrusts and strike-slip faults recording translation and rotation of minibasins about vertical axis. Some minibasins are also tilted, with up to vertical position, associated with both the salt expulsion during minibasins sinking, recorded by large stratigraphic wedge, and the late thrust faults developments. The influence of the regional shortening deformation seems to be effective when the majority of the evaporite is remobilized toward the foreland. Results of scaled physical experiments, where continuous shortening is applied during minibasins emplacement, closely match with the deformation patterns observed in the Sivas minibasins. Shortening induce deformations such as translation of minibasins basinward, strike-slip fault zones along minibasin margin, rejuvenation of silicon walls and diapirs, emergence of silicon glaciers and rotation of minibasins along vertical and horizontal axis.

New structural and stratigraphic insights for northwestern Pakistan from field and Landsat Thematic Mapper data

USGS Publications Warehouse

Robinson, J.; Beck, R.; Gnos, E.; Vincent, R.K.

2000-01-01

The remote Waziristan region of northwestern Pakistan includes outcrops of the India-Asia suture zone. The excellent exposure of the Waziristan ophiolite and associated sedimentary lithosomes and their inaccessibility made the use of Landsat Thematic Mapper (TM) data desirable in this study. Landsat TM data were used to create a spectral ratio image of bands 3/4, 5/4, and 7/5, displayed as red, green, and blue, respectively, and a principal component analysis image of bands 4, 5, and 7 (RGB). These images were interpreted in the context of available geologic maps, limited field work, and biostratigraphic, lithostratigraphic, and radiometric data. They were used to create a coherent geologic map of Waziristan and cross section of the area that document five tectonic units in the region and provide a new and more detailed tectonic history for the region. The lowest unit is comprised of Indian shelf sediments that were thrust under the Waziristan ophiolite. The ophiolite has been tectonically shuffled and consists of two separate tectonic units. The top thrust sheet is a nappe comprised of distal Triassic to Lower Cretaceous Neotethyan sediments that were underthrust during the Late Cretaceous by the ophiolite riding on Indian shelf strata. The uppermost unit contains unconformable Tertiary and younger strata. The thrust sheets show that the Waziristan ophiolite was obducted during Late Cretaceous time and imply that the Paleocene and Eocene deformation represents collision of India with the Kabul block and/or Asia.

On the lag time between internal strain and basement involved thrust induced exhumation: The case of the Colombian Eastern Cordillera

NASA Astrophysics Data System (ADS)

Mora, Andrès; Blanco, Vladimir; Naranjo, Julian; Sanchez, Nelson; Ketcham, Richard A.; Rubiano, Jorge; Stockli, Daniel F.; Quintero, Isaid; Nemčok, Michal; Horton, Brian K.; Davila, Hamblet

2013-07-01

Thrust sheets accumulate internal strain before they start moving along discrete fault planes. However, there are no previous studies evaluating the time difference between initiation of strain and fault displacement. In this paper we use observations from the Eastern Cordillera of Colombia to evaluate this interval. We utilize multiple thermochronometers and paleothermometers to refine the timing of deformation. Based on these new data we build time-temperature path estimates that together with geometric outcrop-based structural analysis and fluid inclusions allow us to assign relative timing to features associated with strain, such as cleavage, veins and certain types of fractures, and compare that with the timing of thrusting. We find that cleavage was only formed close to maximum paleotemperatures, almost coeval with the onset of thrust-induced denudation by the Late Oligocene. The corresponding structural level of fold-related veins suggest that they were formed later but still when the country rocks were at temperatures higher than 160 °C, mostly during the Early Miocene and still coexisted with the latest stages of cleavage formation. Our data show that the main period of strain hardening was short (probably a few million years) and occurred before first-order basement thrusting was dominant, but was associated with second-order folding.

Latest Cretaceous-Paleogene basin development and resultant sedimentation patterns in the thrust belt and broken foreland of central Utah

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lawton, T.F.; Franczyk, K.J.; Pitman, J.K.

1990-05-01

Latest Cretaceous tectonism in central and east-central Utah formed several intermontane basins both atop thrust sheets and between the thrust front and basement-involved uplifts in the former foreland basin. The upper Campanian Castlegate Sandstone and its inferred western equivalents were the last strata deposited prior to segmentation of the foreland basin. Thereafter, eastward transport of the thrust allochthon uplifted the most proximal part of the Castlegate depositional wedge. West of the thrust front, small intermontane basins formed on the allochthon. Sediment was transported into these basins from both eastern and western sources. In each basin, facies grade from basin-margin conglomeraticmore » alluvial fan deposits to basin-interior flood-plain and lacustrine deposits within a few kilometers. These intermontane basins existed from latest Campanian through the late Paleocene, and may have been transported a short distance eastward as they formed. East of the thrust front in the latest Campanian and contemporaneous with basin formation on the allochthon, a northward-northeastward-flowing big river system transported sediment into the foreland basin from feldspar-rich source areas southwest of the study area. Subsequently, major movement of the San Rafael uplift in the very late Campanian or early Maastrichtian gave rise to an intermontane basin between the thrust front and the San Rafael uplift. Northwestward-flowing, pebble-bearing braided rivers deposited the oldest sediments in this basin prior to an influx from the south and southwest of sediment that formed a thick Maastrichtian clastic sequence. In contrast to deposition in basins on the allochthon, deposition east of the thrust front in the Paleocene was intermittent and restricted to rapidly shifting centers of basin subsidence.« less

Solar treatments for reducing survival of mountain pine beetle in infested ponderosa and lodgepole pine logs

Treesearch

Jose F. Negron; Wayne A. Shepperd; Steve A. Mata; John B. Popp; Lance A. Asherin; Anna W. Schoettle; John M. Schmid; David A. Leatherman

2001-01-01

Three experiments were conducted to evaluate the use of solar radiation for reducing survival of mountain pine beetle populations in infested logs. Ponderosa pine logs were used in experiments 1 and 2 and lodgepole pine logs were used in experiment 3. Experiment 1 comprised three treatments: (1) one-layer solar treatment without plastic sheeting and logs rotated one-...

National Program for Inspection of Non-Federal Dams. Highland Lake North Outlet (NH 00238), NHWRB 245.07, Merrimack River Basin, Washington, New Hampshire. Phase I Inspection Report.

DTIC Science & Technology

1978-08-01

appropriate portion of the USGS Lovewell Mountain quadrangle shown previously. Shedd Brook eventually flows into the Contoocook River. (b) Description...Washington Date: September 19, 1967 The North Outlet is shown on the USGS Quadrangle sheet at Lovewells Mountain. It is located about 1000 feet north of a

Evidence of rapid Cenozoic uplift of the shoulder escarpment of the Cenozoic West Antarctic rift system and a speculation on possible climate forcing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Behrendt, J.C.; Cooper, A.

1991-04-01

The Cenzoic West Antarctic rift system, characterized by Cenozoic bimodal alkalic volcanic rocks, extends over a largely ice-covered area, from the Ross Sea nearly to the Bellingshausen Sea. It is bounded on one side by a spectacular 4-to 5-km-high rift-shoulder scarp (maximum bedrock relief 5 to 7 km) from northern Victoria Land-Queen Maud Mountains to the Ellsworth-Whitmore-Horlick Mountains. Jurassic tholeiites crop out with the late Cenozoic volcanic rocks along the section of the Transantarctic Mountains from northern Victoria Land to the Horlick Mountains. The Cenozoic rift shoulder diverges here from the Jurassic tholeiite trend, and the tholeiites are exposed discontinuouslymore » along the lower elevation (1-2 km) section of the Transantarctic Mountains to the Weddell Sea. Various lines of evidence, no one of which is independently conclusive, lead the authors (as others have also suggested) to interpret the following. The Transantarctic Mountains part of the rift shoulder (and probably the entire shoulder) has been rising since about 60 Ma, at episodic rates of {approximately}1 km/m.y., most recently since mid-Pliocene time, rather than continuously at the mean rate of 100m/m.y. Uplift rates vary along the scarp, which is cut by transverse faults. The authors speculate that this uplift may have climatically forced the advance of the Antarctic ice sheet since the most recent warm period. They suggest a possible synergistic relation between episodic tectonism, mountain uplift, and volcanism in the Cenozoic West Antarctic rift system and waxing and waning of the Antarctic ice sheet beginning about earliest Oligocene time.« less

Evidence of rapid Cenozoic uplift of the shoulder escarpment of the Cenozoic West Antarctic rift system and a speculation on possible climate forcing

NASA Astrophysics Data System (ADS)

Behrendt, John C.; Cooper, Alan

1991-04-01

The Cenozoic West Antarctic rift system, characterized by Cenozoic bimodal alkalic volcanic rocks, extends over a largely ice-covered area, from the Ross Sea nearly to the Bellingshausen Sea. It is bounded on one side by a spectacular 4- to 5-km-high rift-shoulder scarp (maximum bedrock relief 5 to 7 km) from northern Victoria Land-Queen Maud Mountains to the Ellsworth-Whitmore-Horlick Mountains. Jurassic tholeiites crop out with the late Cenozoic volcanic rocks along the section of the Transantarctic Mountains from northern Victoria Land to the Horlick Mountains. The Cenozoic rift shoulder diverges here from the Jurassic tholeiite trend, and the tholeiites are exposed discontinuously along the lower elevation (1-2 km) section of the Transantarctic Mountains to the Weddell Sea. Various lines of evidence, no one of which is independently conclusive, lead us (as othershave also suggested) to interpret the following. The Transantarctic Mountains part of the rift shoulder (and probably the entire shoulder) has been rising since about 60 Ma, at episodic rates of ˜1 km/m.y., most recently since mid-Pliocene time, rather than continuously at the mean rate of 100 m/m.y. Uplift rates vary along the scarp, which is cut by transverse faults. We speculate that this uplift may have climatically forced the advance of the Antarctic ice sheet since the most recent warm period. We suggest a possible synergistic relation between episodic tectonism, mountain uplift, and volcanism in the Cenozoic West Antarctic rift system and waxing and waning of the Antarctic ice sheet beginning about earliest Oligocene time.

Deglaciation of the northwestern White Mountains, New Hampshire

USGS Publications Warehouse

Thompson, W.B.; Fowler, B.K.; Dorion, C.C.

1999-01-01

The mode of deglaciation in the northwestern White Mountains of New Hampshire has been controversial since the mid 1800's. Early workers believed that active ice deposited the Bethlehem Moraine complex in the Ammonoosuc River basin during recession of the last ice sheet. In the 1930's this deglaciation model was replaced by the concept of widespread simultaneous stagnation and downwastage of Late Wisconsinan ice. The present authors reexamined the Bethlehem Moraine complex and support the original interpretation of a series of moraines deposited by active ice. We found other moraine clusters of similar age to the northeast in the Johns River and Israel River basins. Ice-marginal deposits that probably correlate with the Bethlehem Moraine also occur west of Littleton. The Bethlehem Moraine complex and equivalent deposits in adjacent areas were formed by readvance and oscillatory retreat of the Connecticut Valley lobe of the Laurentide Ice Sheet. This event is called the Littleton-Bethlehem Readvance. Throughout the study area, sequences of glaciolacustrine deposits and meltwater drainage channels indicate progressive northward recession of the glacier margin. Radiocarbon dates from nearby New England and Quebec suggest that the ice sheet withdrew from this part of the White Mountains between about 12,500 and 12,000 14C yr BP. We attribute the Littleton-Bethlehem Readvance to a brief climatic cooling during Older Dyas time, close to 12,000 BP.

Anomalous concentrations of gold, silver, and other metals in the Mill Canyon area, Cortez quadrangle, Eureka and Lander Counties, Nevada

USGS Publications Warehouse

Elliott, James E.; Wells, John David

1968-01-01

The Mill Canyon area is in the eastern part of the Cortez window of the Roberts Mountains thrust belt in the Cortez quadrangle, north-central Nevada. Gold and silver ores have been mined from fissure veins in Jurassic quartz monzonite and in the bordering Wenban Limestone of Devonian age. Geochemical data show anomalies of gold, silver, lead, zinc, copper, arsenic, antimony, mercury, and tellurium. Geologic and geochemical studies indicate that a formation favorable for gold deposition, the Roberts Mountains Limestone of Silurian age, may be found at depth near the mouth of Mill Canyon.

Assessment of East Antarctic ice flow directions, ice grounding events, and glacial thermal regime across the middle Miocene climate transition from the ANDRILL-SMS and CRP drill holes

NASA Astrophysics Data System (ADS)

Passchier, S.; Hauptvogel, D.; Hansen, M.; Falk, C.; Martin, L.

2010-12-01

Here we present a synthesis of early and middle Miocene ice sheet development based on facies analyses and multiple compositional studies on the AND-2A and CRP drillcores from the Ross Sea, ca. 10 km off the coast of East Antarctica. The middle Miocene is characterized by one of the three largest shifts in deep-sea oxygen isotope records. During this time the East Antarctic ice sheet became dry-based at high elevation in the Transantarctic Mountains and advanced across the Ross Sea continental shelf to create widespread glacial unconformities. However, detailed proxy records also indicate that ice development was complex and may have occurred in a stepwise fashion, instead of one major episode. Our analyses of “grounded ice” diamictites from both the CRP and AND-2A cores show a significant change in composition across the middle Miocene transition. More detailed analyses of the stratigraphic distribution of facies, heavy mineral provenance, particle size, and major and trace element geochemistry in AND-2A show that relatively large polythermal ice-sheets similar in size to the modern were already present between 17.6 and 17.1 Ma. These results are in agreement with proxy records suggesting that Antarctic ice volumes were larger than today’s volume during the Mi-1b glaciation. Between 17.1 and 15.6-14.9 Ma, a predominance of iceberg debris sourced from the Ferrar Group in the Transantarctic Mountains suggests vigorous glacial erosion and fjord incision by East Antarctic outlet glaciers. The facies characteristics and comparison with compositional data from Neogene tills in the Transantarctic Mountains further suggest that the East Antarctic ice sheet may have been smaller than today during the Miocene climatic optimum (~17-15 Ma) with ice possibly reaching sea level only near the central Transantarctic Mountains. Advance of the grounding line and the development of glacial flow patterns compatible with a larger ice sheet than the modern commenced between 15.6 and 14.7 Ma and was established prior to 14.2 Ma. These results suggest an earlier onset of Antarctic ice growth across the middle Miocene climate transition than is generally inferred from geochemical proxy records.

Evolution of the Alpine Tethys (Sava) suture zone in Fruška Gora Mountains (N Serbia): from orogenic building to tectonic omissions

NASA Astrophysics Data System (ADS)

Toljić, Marinko; Matenco, Liviu; ĐErić, Nevenka; Milivojević, Jelena; Gerzina, Nataša.; Stojadinović, Uros

2010-05-01

The Fru\\vska Gora Mountains in northern Serbia offers an unique opportunity to study the Cretaceous-Eocene evolution of the NE part of the Dinarides, which is largely covered elsewhere beneath the thick Miocene sediments of the Pannonian basin, deposited during the back-arc collapse associated with the subduction and roll-back recorded in the external Carpathians. The structural grain of the Fru\\vska Gora Mountains is the one of a large scale antiform, exposing a complex puzzle of highly deformed metamorphic rocks in its centre and Triassic-Miocene sequence of non-metamorphosed sediments, ophiolites and volcanics along its flanks. The metamorphic rocks were the target of structural investigations coupled with paleontological dating (conodonts, palynomorphs and radiolarians) in an effort to unravel the geodynamic evolution of an area thought to be located near the suture zone between the Tisza upper plate and the Adriatic lower plate, i.e. the Sava subduction zone of the Dinarides (e.g., Pamic, 2002; Schmid et al., 2008). The existence of this subduction zone was previously inferred here by local observations, such as metamorphosed Mesozoic sediments containing Middle Triassic conodonts (Đurđanović, 1971) or Early Cretaceous blue schists metamorphism (123±5 Ma, Milovanović et al., 1995). The metamorphic sequence is characterized by a Paleozoic age meta-sedimentary basement which contains palynomorphs of Upper Paleozoic - Carboniferous age and a meta-sedimentary and meta-volcanic sequence which contain a succession of contrasting metamorphosed lithologies such sandstones, black limestones, shallow water white limestones, basic volcanic sequences, deep nodular limestiones, radiolarites, meta-ophiolites and turbiditic sequences. The lower part of the sequence is contrastingly similar with the Triassic cover of the Drina-Ivanijca thrust sheet and its metamorphosed equivalent observed in the Kopaonik and Studenica series (Schefer et al., in press). This observation is supported by the newly found micro-fauna of Upper Triassic in age in the meta-sandstones associated with meta-volcanics on the SW slopes of the mountain. The upper part of the sequence display metamorphosed "flysh"-type of sequences and meta-basalts. In these deposits, slightly metamorphosed siliciclastics (lithic sandstones with volcanic-derived clasts) previously interpreted as Upper Jurassic mélange have proved to contain Upper Cretaceous palynomorphs. Among the rocks exposed in the metamorphic core of the mountains, the SW slope of Fru\\vska Gora offers the optimal locality for the study of the kinematic evolution. Here, four phases of folding have been mapped, being associated mainly with large-scale regional contraction. The first phase is characterized by isoclinal folding, with reconstructed SW vergence. The second generation of E-W oriented and coaxial folds is asymmetric and is up to metres in size, displaying a south vergence and has largely refolded the previous generation. The third event was responsible for the formation of upright folds, yet again E-W oriented, re-folding earlier structures. The first two phases of folding are associated with metamorphic conditions, while the third was apparently near the transition with the brittle domain. The relationship with a fourth folding event observed also in the non-metamorphosed clastic-carbonate rocks is rather uncertain, but is apparently associated with the present day antiformal structure of the Fuska Gora Mountains. Interestingly, the metamorphosed Triassic and Upper Cretaceous carbonatic-clastic sequence in the core of the antiform is in structural contact along the antiformal flanks with Lower-Middle Triassic and Upper Cretaceous-Paleogene sediments which display the same facies, but these are not metamorphosed. This demonstrates a large scale tectonic omission along the flanks of the Fru\\vska Gora antiform, 9-10km of rocks being removed by what we speculatively define as an extensional detachment exhuming the metamorphic core. This detachment has been subsequently folded into the present-day antiformal geometry of the Fru\\vska Gora Mountains. These findings demonstrate that the metamorphic and non-metamorphic Upper Cretaceous - Paleogene clastic-carbonate sediments belongs to the main Alpine Tethys (Sava) subduction zone of the Dinarides. The Paleozoic-Triassic metamorphic and non-metamorphic rocks belong to the distal Adriatic lower plate, or more precisely to the Jadar-Kopaonik composite thrust sheet (Schmid et al., 2008), while the layer of serpentinized peridotite found at their contact most probably belongs to the Western Vardar ophiolites obducted over the Adriatic plate during Late Jurassic - Earliest Cretaceous. The distal Jadar-Kopaonik composite unit was partly affected by strong contractional deformation and a Late Eocene greenschist facies metamorphism during the main phase of subduction and collision, similarly to what has been observed elsewhere in the Dinarides (Pamić, 2002; Schefer et al., in press). A Miocene phase of core-complex formation was responsible for the large tectonic omission observed, being probably followed by the formation of a wide open antiformal structure during the Pliocene-Quaternary inversion of the Pannonian basin.

Geomorphic evidence of Quaternary tectonics within an underlap fault zone of southern Apennines, Italy

NASA Astrophysics Data System (ADS)

Giano, Salvatore Ivo; Pescatore, Eva; Agosta, Fabrizio; Prosser, Giacomo

2018-02-01

A composite seismic source, the Irpinia - Agri Valley Fault zone, located in the axial sector of the fold-and-thrust belt of southern Apennines, Italy, is investigated. This composite source is made up of a series of nearly parallel, NW-striking normal fault segments which caused many historical earthquakes. Two of these fault segments, known as the San Gregorio Magno and Pergola-Melandro, and the fault-related mountain fronts, form a wedge-shaped, right-stepping, underlap fault zone. This work is aimed at documenting tectonic geomorphology and geology of this underlap fault zone. The goal is to decipher the evidence of surface topographic interaction between two bounding fault segments and their related mountain fronts. In particular, computation of geomorphic indices such as mountain front sinuosity (Smf), water divide sinuosity (Swd), asymmetry factor (AF), drainage basin elongation (Bs), relief ratio (Rh), Hypsometry (HI), normalized steepness (Ksn), and concavity (θ) is integrated with geomorphological analysis, the geological mapping, and structural analysis in order to assess the recent activity of the fault scarp sets recognized within the underlap zone. Results are consistent with the NW-striking faults as those showing the most recent tectonic activity, as also suggested by presence of related slope deposits younger than 38 ka. The results of this work therefore show how the integration of a multidisciplinary approach that combines geomorphology, morphometry, and structural analyses may be key to solving tectonic geomorphology issues in a complex, fold-and-thrust belt configuration.

Early Jurassic extensional inheritance in the Lurestan region of the Zagros fold-and-thrust belt, Iran.

NASA Astrophysics Data System (ADS)

Tavani, Stefano; Parente, Mariano; Vitale, Stefano; Puzone, Francesco; Erba, Elisabetta; Bottini, Cinzia; Morsalnejad, Davoud; Mazzoli, Stefano

2017-04-01

It has long been recognized that the tectonic architecture of the Zagros mountain belt was strongly controlled by inherited structures previously formed within the Arabian plate. These preexisting features span in age from the pre-Cambrian to the Mesozoic, showing different trends and deformation styles. Yet, these structures are currently not fully understood. This uncertainty is partly related with the paucity of exposures, which rarely allows a direct observation of these important deformation features. The Lurestan Province of Iran provides a remarkable exception, since it is one of the few places of the Zagros mountain belt where exposures of Triassic and Jurassic rocks are widespread. In this area we carried out structural observations on Mesozoic extensional structures developed at the southern margin of the Neo-Tethyan basin. Syn-sedimentary extensional faults are hosted within the Triassic-Cretaceous succession, being particularly abundant in the Jurassic portion of the stratigraphy. Early to Middle Jurassic syn-sedimentary faults are observed in different paleogeographic domains of the area, and their occurrence is coherent with the subsequent transition from shallow-water to deep-sea basin environments, observed in a wide portion of the area. Most of the thrusts exposed in the area may indeed be interpreted as reactivated Jurassic extensional faults, or as reverse faults whose nucleation was controlled by the location of preexisting normal faults, as a result of positive inversion during crustal shortening and mountain building.

Inheritance, Variscan tectonometamorphic evolution and Permian to Mesozoic rejuvenations in the metamorphic basement complexes of the Romanian Carpathians revealed by monazite microprobe geochronology

NASA Astrophysics Data System (ADS)

Săbău, Gavril; Negulescu, Elena

2014-05-01

Monazite U-Th-Pb chemical dating reaches an acceptable compromise between precision and accuracy on one side, and spatial resolution and textural constraints on the other side. Thus it has a powerful potential in testing the coherence of individual metamorphic basement units, and enabling correlations among them. Yet, sensitivity and specificity issues in monazite response to thermotectonic events, especially in the case of superposed effects, remain still unclear. Monazite dating at informative to detailed scale in the main metamorphic basement units of the Carpathians resulted in complex age spectra. In the main, the spectra are dominated by the most pervasive thermal and structural overprint, as checked against independent geochronological data. Post-peak age resetting is mostly present, but statistically subordinate. Resetting in case of superposed events is correlated with the degree of textural and paragenetic overprinting, inheritances being always indicated by more or less well-defined age clusters. The lack of relict ages correlating with prograde structural and porphyroblast zonation patterns is indicative for juvenile formations. Age data distribution in the Carpathians allowed distinction of pre-Variscan events, syn-metamorphic Variscan tectonic stacking of juvenile and reworked basement, post-Variscan differential tectonic uplift, as well as prograde metamorphic units ranging down to Upper Cretaceous ages. In the South Carpathians, the Alpine Danubian domain consists of several Variscan and Alpine thrust sheets containing a metamorphic complex dominated by Upper Proterozoic to Lower Cambrian metamorphic and magmatic ages (Lainici-Păiuş), and several complexes with metamorphic overprints ranging from Carboniferous to Lower Permian. Any correlation among these units, as well as geotectonic models placing a Lower Paleozoic oceanic domain between pre-existing Lainici-Păiuş and Drăgşan terranes are precluded by the age data. Other basement of the South Carpathians contain lower Paleozoic or older units intruded by Ordovician granitoids, imbricated with juvenile Variscan slivers, the structural sequence differing in individual basement complexes. So, in the Leaota Massif the lowermost term of the sequence is prograde Variscan, tectonically overlain by reworked lower Paleozoic gneisses, supporting thrust sheets with very low- to low-grade Variscan schists. In the Făgăraş Massif a lower Paleozoic (Cumpăna) complex bearing a strong Variscan overprint, straddles Variscan juvenile rocks, and the lowermost visible structural level is assumed by upper Carboniferous to Permian juvenile medium-grade metamorphic schists. In the Lotru Metamorphic Suite of the Alpine Getic Nappe, the Variscan stacking is overprinted by post-orogenic differential uplift, documented by the correlation among younging ages, structural and metamorphic low-pressure overprints, recording often higher metamorphic temperatures. The most spectacular structure is Upper Jurassic in age, contains high-grade metamorphic rocks and peraluminous anatectic granitoids, is outlined by a deformed boundary evolving from ductile to brittle regime during cooling, and induces a thermal overprint in the neighbouring rocks. In the basement units thrust over the Getic Nappe, the Sibişel unit yielded Permian prograde peak metamorphic ages and Triassic post-peak overprints, while an adjacent gneissic unit (Laz) delivered an exclusively Cretaceous age pattern. Unexpectedly young metamorphic ages resulted also for the East Carpathians and the Apuseni Mountains. While most of the ages obtained so far correspond to Variscan retrogression of older basement units, the lowermost structural unit of the infra-Bucovinian nappe system in the East Carpathians yielded Upper Cretaceous metamorphic ages in apparently monometamorphic medium-grade schists. In the Apuseni Mountains, schists of the Baia de Arieş Unit display an Upper Jurassic age spectrum, corresponding to a clearly prograde medium-grade event. The ages recorded not only question some of the currently accepted correlations among basement units, but urge to reconsideration of the way in which the basement-cover relationships are interpreted and extrapolated.

Palinspastic reconstruction of southeastern California and southwestern Arizona for the middle Miocene

NASA Technical Reports Server (NTRS)

Richard, Stephen M.

1992-01-01

A paleogeographic reconstruction of southeastern California and southwestern Arizona at 10 Ma was made based on available geologic and geophysical data. Clockwise rotation of 39 deg was reconstructed in the eastern Transverse Ranges, consistent with paleomagnetic data from late Miocene volcanic rocks, and with slip estimates for left-lateral faults within the eastern Transverse Ranges and NW-trending right lateral faults in the Mojave Desert. This domain of rotated rocks is bounded by the Pinto Mountain fault on the north. In the absence of evidence for rotation of the San Bernardino Mountains or for significant right slip faults within the San Bernardino Mountains, the model requires that the late Miocene Pinto Mountain fault become a thrust fault gaining displacement to the west. The Squaw Peak thrust system of Meisling and Weldon may be a western continuation of this fault system. The Sheep Hole fault bounds the rotating domain on the east. East of this fault an array of NW-trending right slip faults and south-trending extensional transfer zones has produced a basin and range physiography while accumulating up to 14 km of right slip. This maximum is significantly less than the 37.5 km of right slip required in this region by a recent reconstruction of the central Mojave Desert. Geologic relations along the southern boundary of the rotating domain are poorly known, but this boundary is interpreted to involve a series of curved strike slip faults and non-coaxial extension, bounded on the southeast by the Mammoth Wash and related faults in the eastern Chocolate Mountains. Available constraints on timing suggest that Quaternary movement on the Pinto Mountain and nearby faults is unrelated to the rotation of the eastern Transverse Ranges, and was preceded by a hiatus during part of Pliocene time which followed the deformation producing the rotation. The reconstructed Clemens Well fault in the Orocopia Mountains, proposed as a major early Miocene strand of the San Andreas fault, projects eastward towards Arizona, where early Miocene rocks and structures are continuous across its trace. The model predicts a 14 deg clockwise rotation and 55 km extension along the present trace of the San Andreas fault during late Miocene and early Pliocene time. Palinspastic reconstructions of the San Andreas system based on this proposed reconstruction may be significantly modified from current models.

Influence of soil development on the geomorphic evolution of landscapes: An example from the Transverse Ranges of California

NASA Astrophysics Data System (ADS)

Eppes, M. C.; McFadden, L. D.; Matti, J.; Powell, R.

2002-03-01

Soil development can significantly influence the topographic evolution of a tectonically deforming mountain piedmont. Faults and folds associated with the North Frontal thrust system deform piedmont sediments of variable compositions along the north flank of the San Bernardino Mountains. The topographic expressions of folds with similar structural characteristics diverge appreciably, primarily as a function of differences in sediment composition and associated soil development. Soils with petrocalcic horizons in limestone- rich deposits are resistant to erosion, and anticlinal folds form prominent ridges. Folds forming in granite-derived deposits with argillic soil horizons are eroded and/or buried and are therefore topographically less pronounced. We propose that these landform contrasts can be explained by differences in soil-controlled hydrologic and erosion characteristics of deposits without calling upon changes in tectonic style along the mountain front.

Geological and geomorphological insights into Antarctic ice sheet evolution.

PubMed

Sugden, David E; Bentley, Michael J; O Cofaigh, Colm

2006-07-15

Technical advances in the study of ice-free parts of Antarctica can provide quantitative records that are useful for constraining and refining models of ice sheet evolution and behaviour. Such records improve our understanding of system trajectory, influence the questions we ask about system stability and help to define the ice-sheet processes that are relevant on different time-scales. Here, we illustrate the contribution of cosmogenic isotope analysis of exposed bedrock surfaces and marine geophysical surveying to the understanding of Antarctic ice sheet evolution on a range of time-scales. In the Dry Valleys of East Antarctica, 3He dating of subglacial flood deposits that are now exposed on mountain summits provide evidence of an expanded and thicker Mid-Miocene ice sheet. The survival of surface boulders for approximately 14Myr, the oldest yet measured, demonstrates exceptionally low rates of subsequent erosion and points to the persistence and stability of the dry polar desert climate since that time. Increasingly, there are constraints on West Antarctic ice sheet fluctuations during Quaternary glacial cycles. In the Sarnoff Mountains of Marie Byrd Land in West Antarctica, 10Be and 26Al cosmogenic isotope analysis of glacial erratics and bedrock reveal steady thinning of the ice sheet from 10400 years ago to the present, probably as a result of grounding line retreat. In the Antarctic Peninsula, offshore analysis reveals an extensive ice sheet at the last glacial maximum. Based on radiocarbon dating, deglaciation began by 17000cal yr BP and was complete by 9500cal yr BP. Deglaciation of the west and east sides of the Antarctic Peninsula ice sheet occurred at different times and rates, but was largely complete by the Early Holocene. At that time ice shelves were less extensive on the west side of the Antarctic Peninsula than they are today. The message from the past is that individual glacier drainage basins in Antarctica respond in different and distinctive ways to global climate change, depending on the link between regional topography and climate setting.

Sediment Volume Record of Paleogene-Neogene Transantarctic Mountains Erosion and Landscape Modification, McMurdo Sound Region, Antarctica

NASA Astrophysics Data System (ADS)

Hall, T.; Wilson, T. J.; Henrys, S.; Speece, M. A.

2016-12-01

The interplay of tectonics and climate is recorded in the sedimentary strata within Victoria Land Basin, McMurdo Sound, Antarctica. Patterns of Cenozoic sedimentation are documented from interpretation of seismic reflection profiles calibrated by drillhole data in McMurdo Sound, and these patterns provide enhanced constraints on the evolution of the coupled Transantarctic Mountains-West Antarctic Rift System and on ice sheet advance/retreat through multiple climate cycles. The research focuses on shifts from warm based to cold based ice sheets through the variable climate and ice sheet conditions that characterized the early to middle Miocene. The study seeks to test the view that cold based ice sheets in arid, polar deserts minimally erode the landscape by calculating sediment volumes for critical climatic intervals. Revised seismic mapping through McMurdo Sound has been completed, utilizing the seismic stratigraphic framework first established by Fielding et al. (2006) and new reflectors marking unconformities identified from the AND-2A core (Levy et al., 2016). Reflector age constraints are derived by tying surfaces to the Cape Roberts Project, CIROS-1, and AND-2A drillholes. Seismic facies coupled with AND-2A core provenance information provides insight into depositional mechanisms and ice sheet behavior. Seismic facies transitions occur across the major unconformity surfaces in the AND-2A core. Sediment volume calculations for subareas within McMurdo Sound where reflectors are most continuous indicate substantial decreases in preserved sediment volume between the Oligocene and Early Miocene sequences, and between the early and mid-Miocene sequences. Sediment volumes, used in combination with an ice sheet model in a backstacking procedure, provide constraints on landscape modification and further understanding of how landscapes erode under warm and cold based ice sheet regimes.

The MIS 3 maximum of the Torres del Paine and Última Esperanza ice lobes in Patagonia and the pacing of southern mountain glaciation

NASA Astrophysics Data System (ADS)

García, Juan-Luis; Hein, Andrew S.; Binnie, Steven A.; Gómez, Gabriel A.; González, Mauricio A.; Dunai, Tibor J.

2018-04-01

The timing, structure and termination of the last southern mountain glaciation and its forcing remains unclear. Most studies have focused on the global Last Glacial Maximum (LGM; 26.5-19 ka) time period, which is just part of the extensive time-frame within the last glacial period, including Marine Isotope Stages 3 and 4. Understanding the glacial fluctuations throughout the glacial period is a prerequisite for uncovering the cause and climate mechanism driving southern glaciation and the interhemispheric linkages of climate change. Here, we present an extensive (n = 65) cosmogenic 10Be glacier chronology derived from moraine belts marking the pre-global LGM extent of the former Patagonian Ice Sheet in southernmost South America. Our results show the mountain ice sheet reached its maximum extent at 48.0 ± 1.8 ka during the local LGM, but attained just half this extent at 21.5 ± 1.8 ka during the global LGM. This finding, supported by nearby glacier chronologies, indicates that at orbital time scales, the southern mid-latitude glaciers fluctuated out-of-phase with northern hemisphere ice sheets. At millennial time-scales, our data suggest that Patagonian and New Zealand glaciers advanced in unison with cold Antarctic stadials and reductions in Southern Ocean sea surface temperatures. This implies a southern middle latitudes-wide millennial rhythm of climate change throughout the last glacial period linked to the north Atlantic by the bipolar seesaw. We suggest that winter insolation, acting alongside other drivers such as the strength and/or position of the southern westerlies, controlled the extents of major southern mountain glaciers such as those in southernmost South America.

Geologic map of the Ennis 30' x 60' quadrangle, Madison and Gallatin Counties, Montana

USGS Publications Warehouse

Kellogg, Karl S.; Williams, Van S.

1998-01-01

The Ennis 1:100,000 quadrangle lies within both the Laramide (Late Cretaceous to early Tertiary) foreland province of southwestern Montana and the northeastern margin of the middle to late Tertiary Basin and Range province. The oldest rocks in the quadrangle are Archean high-grade gneiss, and granitic to ultramafic intrusive rocks that are as old as about 3.0 Ga. The gneiss includes a supracrustal assemblage of quartz-feldspar gneiss, amphibolite, quartzite, and biotite schist and gneiss. The basement rocks are overlain by a platform sequence of sedimentary rocks as old as Cambrian Flathead Quartzite and as young as Upper Cretaceous Livingston Group sandstones, shales, and volcanic rocks. The Archean crystalline rocks crop out in the cores of large basement uplifts, most notably the 'Madison-Gravelly arch' that includes parts of the present Tobacco Root Mountains and the Gravelly, Madison, and Gallatin Ranges. These basement uplifts or blocks were thrust westward during the Laramide orogeny over rocks as young as Upper Cretaceous. The thrusts are now exposed in the quadrangle along the western flanks of the Gravelly and Madison Ranges (the Greenhorn thrust and the Hilgard fault system, respectively). Simultaneous with the west-directed thrusting, northwest-striking, northeast-side-up reverse faults formed a parallel set across southwestern Montana; the largest of these is the Spanish Peaks fault, which cuts prominently across the Ennis quadrangle. Beginning in late Eocene time, extensive volcanism of the Absorka Volcanic Supergroup covered large parts of the area; large remnants of the volcanic field remain in the eastern part of the quadrangle. The volcanism was concurrent with, and followed by, middle Tertiary extension. During this time, the axial zone of the 'Madison-Gravelly arch,' a large Laramide uplift, collapsed, forming the Madison Valley, structurally a complex down-to-the-east half graben. Basin deposits as thick as 4,500 m filled the graben. Pleistocene glaciers sculpted the high peaks of the mountain ranges and formed the present rugged topography.

Geologic map of the Ennis 30' x 60' quadrangle, Madison and Gallatin Counties, Montana, and Park County, Wyoming

USGS Publications Warehouse

Kellogg, Karl S.; Williams, Van S.

2000-01-01

The Ennis 1:100,000 quadrangle lies within both the Laramide (Late Cretaceous to early Tertiary) foreland province of southwestern Montana and the northeastern margin of the middle to late Tertiary Basin and Range province. The oldest rocks in the quadrangle are Archean high-grade gneiss, and granitic to ultramafic intrusive rocks that are as old as about 3.0 Ga. The gneiss includes a supracrustal assemblage of quartz-feldspar gneiss, amphibolite, quartzite, and biotite schist and gneiss. The basement rocks are overlain by a platform sequence of sedimentary rocks as old as Cambrian Flathead Quartzite and as young as Upper Cretaceous Livingston Group sandstones, shales, and volcanic rocks. The Archean crystalline rocks crop out in the cores of large basement uplifts, most notably the 'Madison-Gravelly arch' that includes parts of the present Tobacco Root Mountains and the Gravelly, Madison, and Gallatin Ranges. These basement uplifts or blocks were thrust westward during the Laramide orogeny over rocks as young as Upper Cretaceous. The thrusts are now exposed in the quadrangle along the western flanks of the Gravelly and Madison Ranges (the Greenhorn thrust and the Hilgard fault system, respectively). Simultaneous with the west-directed thrusting, northwest-striking, northeast-side-up reverse faults formed a parallel set across southwestern Montana; the largest of these is the Spanish Peaks fault, which cuts prominently across the Ennis quadrangle. Beginning in late Eocene time, extensive volcanism of the Absorka Volcanic Supergroup covered large parts of the area; large remnants of the volcanic field remain in the eastern part of the quadrangle. The volcanism was concurrent with, and followed by, middle Tertiary extension. During this time, the axial zone of the 'Madison-Gravelly arch,' a large Laramide uplift, collapsed, forming the Madison Valley, structurally a complex down-to-the-east half graben. Basin deposits as thick as 4,500 m filled the graben. Pleistocene glaciers sculpted the high peaks of the mountain ranges and formed the present rugged topography.

Development of a glacially dominated shelf-slope-fan system in tectonically active southeast Alaska: Results of IODP Expedition 341 core-log-seismic integrated studies at glacial cycle resolution

NASA Astrophysics Data System (ADS)

Gulick, Sean; Jaeger, John; Mix, Alan; Swartz, John; Worthington, Lindsay; Reece, Robert

2014-05-01

Collision of the Yakutat microplate with North American formed the St. Elias Mountains in coastal Gulf of Alaska. While the tectonic driver for orogenesis has been ongoing since the Miocene, results from the Integrated Ocean Drilling Program Expedition 341 suggests that direct climatic perturbation of active orogenesis through glacial erosion is non-linear. Geophysical studies of the glaciated continental margin, slope, and adjacent deep-sea Surveyor Fan allow examination of the glaciated orogen from source to sink. Using high-resolution and crustal-scale seismic data and through comparison with other glaciated margins, we can identify key diagnostic seismic morphologies and facies indicative of glacial proximity and sediment routing. Expedition drilling results calibrated these images suggesting a timeline for initial advances of the Cordilleran ice sheet related glacial systems onto the shelf and a further timeline for the development of ice streams that reach the shelf edge. Comparisons can be made within this single margin between evolution of the tectonic-glacial system where erosion and sediment transport are occurring within a fold and thrust belt versus on a more stable shelf region. Onshore the Bering-Bagley glacial system in the west flows across the Yakataga fold and thrust belt, allowing examination of whether glacial erosion can cause tectonic feedbacks, whereas offshore the Bering-Bagley system interacts with the Pamplona Zone thrusts in a region of significant sediment accommodation. Results from Expedition 341 imply that timing of glacial advance to the shelf edge in this region may be driven by the necessity of filling up the accommodation through aggradation followed by progradation and thus is autogenic. In contrast the Malaspina-Hubbard glacial system to the east encountered significantly less accommodation and more directly responded to climatic forcing including showing outer shelf glacial occupation since the mid-Pleistocene transition-MPT to 100 kyr glacial-interglacial cycles. Examination of the sink for both of these systems, which includes the Surveyor Fan and Aleutian Trench wedge, demonstrates a clear climatic driver for sediment flux to the deep sea. The first appearance of ice-rafted debris at our distal drill site closely approximates the start of the Pleistocene and a doubling of sediment accumulation accompanies the MPT. Converting sediment volumes just within the deep-sea sinks back to erosion rates in the orogen and correlating with changes in exhumation rates from thermochronology demonstrates a lack of accelerated tectonic response to the intensification of Northern Hemisphere glaciations at the start of the Pleistocene but increased shortening and exhumation of sediments at the MPT. The form of tectonic response differs between out-of-sequence thrusting or antiformal stacking within the fold and thrust belt to the west and a near vertical advection of material in a tectonic aneurysm in the core of the orogen to the east.

Geologic and geophysical maps of the Las Vegas 30' x 60' quadrangle, Clark and Nye counties, Nevada, and Inyo County, California

USGS Publications Warehouse

Page, William R.; Lundstrom, Scott C.; Harris, Anita G.; Langenheim, V.E.; Workman, Jeremiah B.; Mahan, Shannon; Paces, James B.; Dixon, Gary L.; Rowley, Peter D.; Burchfiel, B.C.; Bell, John W.; Smith, Eugene I.

2005-01-01

Las Vegas and Pahrump are two of the fastest growing cities in the US, and the shortage of water looms as among the greatest future problems for these cities. These new maps of the Las Vegas 30 x 60-minute quadrangle provide a geologic and geophysical framework and fundamental earth science database needed to address societal issues such as ground water supply and contamination, surface flood, landslide, and seismic hazards, and soil properties and their changing impact by and on urbanization. The mountain ranges surrounding Las Vegas and Pahrump consist of Mesozoic, Paleozoic and Proterozoic rocks. A majority of these rocks are Paleozoic carbonate rocks that are part of Nevada's carbonate rock aquifer province. The Spring Mountains represent a major recharge site in the province, where maximum altitude is 3,632 m (Charleston Peak) above sea level. Rocks in the Sheep and Las Vegas Ranges and Spring Mountains contain correlative, northeast-striking, southeast-verging thrust faults that are part of the Cretaceous, Sevier orogenic belt. These thrusts were offset during the Miocene by the Las Vegas Valley shear system (LVVSZ). We conducted new mapping in the Blue Diamond area, highlighting refined work on the Bird Spring thrust, newly studied ancient landslides, and gravity-slide blocks. We conducted new mapping in the Las Vegas Range and mapped previously unrecognized structures such as the Valley thrust and fold belt; recognition of these structures has led to a refined correlation of Mesozoic thrust faults across the LVVSZ. New contributions in the quadrangle also include a greatly refined stratigraphy of Paleozoic bedrock units based on conodont biostragraphy. We collected over 200 conodont samples in the quadrangle and established stratigraphic reference sections used to correlate units across the major Mesozoic thrust faults. Quaternary deposits cover about half of the map area and underlie most of the present urbanized area. Deposits consist of large coalescing alluvial fans that grade downslope to extensive areas of fine-grained sediment indicative of groundwater-discharge during the Pleistocene. In the central areas of Las Vegas and Pahrump valleys, Quaternary fault scarps associated with past ground-water discharge deposits suggest a genetic relationship. In collaboration with NBMG and University of Nevada, a variety of ages of gravelly alluvium are newly mapped using surficial characteristics and soil development, along with reassessment of previously published mapping during compilation. Reconnaissance geochronology (thermoluminescence and U-series) of eolian and authigenic components of surficial and buried soils and spring deposits is applied to test hypotheses of geomorphic and hydrologic response to climate change over the past 100 k.y.). The major structure in the Las Vegas quadrangle is the LVVSZ. Because the LVVSZ is concealed by thick basin-fill deposits of Quaternary and Tertiary age, it was characterized primarily based on geophysics. Likewise, the newly described State line fault system in Pahrump Valley has also been characterized by geophysics, where geophysically inferred structures correlate remarkably with surface structures defined by our new geologic mapping in the Mound Spring and Hidden Hills Ranch 7.5-minute quadrangles.

Late Archean greenstone tectonics: Evidence for thermal and thrust-loading lithospheric subsidence from stratigraphic sections in the Slave Province, Canada

NASA Technical Reports Server (NTRS)

Kidd, W. S. F.; Kusky, T. M.; Bradley, D. C.

1988-01-01

How late Archean tectonics could be seen to have operated in the Slave Province is illustrated. Lithospheric thinning and stretching, with the formation of rifted margins (to continental or island arc fragments), and lithospheric flexural loading of the kind familiar in arcs and mountain belts could be discerned.

Age and tectonic setting of Mesozoic metavolcanic and metasedimentary rocks, northern White Mountains, California

NASA Astrophysics Data System (ADS)

Hanson, R. Brooks; Saleeby, Jason B.; Fates, D. Gilbert

1987-11-01

Mesozoic metavolcanic and metasedimentary rocks in the northern White Mountains, eastern California and western Nevada, are separated from lower Paleozoic and Precambrian rocks by Jurassic and Cretaceous plutons. The large stratigraphic hiatus across the plutons is called the Barcroft structural break. Recent mapping and new U/Pb zircon ages of 154 +3/-1 Ma and 137 ±1 Ma. from an ash-flow tuff and a hypabyssal intrusion, respectively, indicate that part of the Mesozoic section and the Barcroft structural break are younger than the 160 165 Ma Barcroft Granodiorite, in contrast to previous interpretations. The Barcroft Granodiorite has been thrust westward over most of the Mesozoic section. It is everywhere in fault contact with overturned metasedimentary rocks on the west side of the range, rocks which were previously thought to be upright and the oldest part of the Mesozoic section. The McAfee Creek Granite, which has a 100 ±1 Ma U/Pb zircon age, postdates thrusting; therefore, the Barcroft structural break is primarily Early Cretaceous in age. *Present addresses: Hanson—Department of Mineral Sciences, Smithsonian Institution, Washington, D.C. 20560; Fates—Dames & Moore, 455 S. Figueroa Street, Suite 3504, Los Angeles, California 90074

Isotopic complexities and the age of the Delfonte volcanic rocks, eastern Mescal Range, southeastern California: Stratigraphic and tectonic implications

USGS Publications Warehouse

Fleck, R.J.; Mattinson, J.M.; Busby, C.J.; Carr, M.D.; Davis, G.A.; Burchfiel, B.C.

1994-01-01

Combined U-Pb zircon, Rb-Sr, 40Ar/39Ar laser-fusion, and conventional K-Ar geochronology establish a late Early Cretaceous age for the Delfonte volcanic rocks. U-Pb zircon analyses define a lower intercept age of 100.5 ± 2 Ma that is interpreted as the crystallization age of the Delfonte sequence. Argon studies document both xenocrystic contamination and postemplacement Ar loss. Rb-Sr results from mafic lavas at the base of the sequence demonstrate compositionally correlated variations in initial 87Sr/86Sr ratios (Sri) from 0.706 for basalts to 0.716 for andesitic compositions. This covariation indicates substantial mixing of subcontinental lithosphere with Proterozoic upper crust. Correlations between Rb/Sr and Sri may result not only in pseudoisochrons approaching the age of the crustal component, but also in reasonable but incorrect apparent ages approaching the true age.Ages obtained in this study require that at least some of the thrust faulting in the Mescal Range-Clark Mountain portion of the foreland fold-and-thrust belt occurred later than ca. 100 Ma and was broadly contemporaneous with emplacement of the Keystone thrust plate in the Spring Mountains to the northeast. Comparison of the age and Rb-Sr systematics of ash-flow tuff boulders in the synorogenic Lavinia Wash sequence near Goodsprings, Nevada, with those of the Delfonte volcanic rocks supports a Delfonte source for the boulders. The 99 Ma age of the Lavinia Wash sequence is nearly identical to the Delfonte age, requiring rapid erosion, transport, and deposition following Delfonte volcanism.

A P-T path for amphibolites from the metamorphic sole of the Dinaride ophiolite zone in Bosnia

NASA Astrophysics Data System (ADS)

Balen, D.; Massonne, H. J.

2016-12-01

The Dinarides, an Alpine-cycle mountain chain in SE Europe, originated along the margin of the Adriatic microplate. It is characterized by complex fold, thrust, and imbricate structures and partially dismembered ophiolites forming significant parts of the Dinarides. In the Krivaja-Konjuh ultramafic massif (KKUM; Bosnia) tectonic peridotite (spinel lherzolite) occurs as NE deeping thrust sheets underlain by gradually decreasing high- to low-grade metamorphic sole rocks (up to 1200 m thick). The sole rocks originated from cumulus gabbro and peridotites and are mainly composed of granulite and amphibolite varieties with various proportions of amphibole, plagioclase, pyroxenes, garnet, and quartz. These rocks vary in textures (granoblastic, porphyroblastic and nematoblastic) and grain size. Conventional thermobarometry of garnet- and clinopyroxene-bearing amphibolites directly beneath the contact to the overlying peridotite resulted in peak pressure (P) - temperature (T) conditions of 11-12 kbar (depth of 35-40 km) and 745-830°C. Those amphibolites without clinopyroxene experienced peak conditions of 7 kbar and 630°C, whereas the lowermost-grade amphibolites yielded peak temperatures of 550°C only. The obtained values can be related to a geothermal gradient of 21-25 °C/km. P-T pseudosections, contoured by mineral isopleths, combined with chemical zonation of garnet, elucidated by X-ray mapping, and the study of the succession of accessory Ti-minerals (Ilmenite->Rutile->Titanite) suggest a composite P-T path characterized by pressure decrease accompanied by temperature increase. This path can be interpreted in the frame of late Jurassic to early Cretaceous regional geodynamic processes that involve collision at the edge of the Adriatic microplate, subduction and underplating of mafic cumulus rocks under the hot upper mantle part of the KKUM and finally subsequent erosional events. Support by the Croatian Science Foundation (IP-2014-09-9541) is acknowledged.

Relation between relief and crustal structure in the Cantabrian Mountains (Spain) using DEM-GIS analysis

NASA Astrophysics Data System (ADS)

Llana-Fúnez, Sergio; Rodríguez-Rodríguez, Laura; Ballesteros, Daniel; María Díaz-Díaz, Luis; Valenzuela, Pablo; López-Fernández, Carlos; José Domínguez-Cuesta, María; Meléndez, Mónica; Jiménez-Sánchez, Montserrat; Fernández-Viejo, Gabriela

2017-04-01

The Cantabrian Mountains show a linear E-W trend parallel to the northern coast of Iberia peninsula, from the Pyrenees to Galicia, where it looses its trend and linearity. The western end of the linear segment of the orogen coincides with a change in the style of structures, accommodating the N-S shortening during the convergence between Europe and Iberia plates. We study the relief of the 230 km-long segment of the linear range between the Cantabria and Galicia re- gions, up to 2,650 m altitude. The bulk trend of the orogeny is controlled by the orientation of alpine thrusts that accommodate the shortening in relation to plate convergence. The Alpine Orogeny produced crustal thickening and the present day topography. Crustal thickness varies from 30 km in Eastern Cantabrian Mountains to 45-55 km at the Middle part of these mountains. The collision between European and African plates localized in northern Iberia from the Eocene to Oligocene and later migrated to southern Iberia during the Miocene. No major tectonic convergence was accommodated in the Cantabrians Mountains since the Oligocene, entering the orogen an erosional phase since then. The GIS-analysis present here, using 5 and 25 m-resolution DEMs by the Spanish National Geographical Institute, aims to identify the major features and to characterize the overall relief of the Cantabrians Mountains. In our preliminary approach, we present swath profiles, major river basins, watershed, longitudinal profiles of major rivers and hypsometric curves from selected areas that cover the studied orogen segment. Major tectonic structures control the location and orientation of the main watershed of the mountain range, but also the orientation of some local watersheds, e.g. associated to the Llanera thrust or the Ventaniella (strike-slip) fault. An unexpected result is that the average altitude along the water divide is 1,500 m, regardless of the large differences in crustal thickness along the study area. Most longitudinal river profiles running south to north lack knick points in relation to relief forming tectonic structures, indicative of the predominance of fluvial erosional system postdating tectonics. An emerged coastal wave-cut platform dipping gently towards the West, a slight increase in maximum mountain altitude to the east and slight increase in river incision also towards the East may indicate that a gradient in erosion and in up-lifting exists increasing from West to East. This is consistent with an overall increase of crustal thickness along this direction.

Kinematic evolution of a regional-scale gravity-driven deepwater fold-and-thrust belt: The Lamu Basin case-history (East Africa)

NASA Astrophysics Data System (ADS)

Cruciani, F.; Barchi, M. R.; Koyi, H. A.; Porreca, M.

2017-08-01

The deepwater fold-and-thrust belts (DWFTBs) are geological structures recently explored thanks to advances in offshore seismic imaging by oil industry. In this study we present a kinematic analysis based on three balanced cross-sections of depth-converted, 2-D seismic profiles along the offshore Lamu Basin (East African passive margin). This margin is characterized by a regional-scale DWFTB (> 450 km long), which is the product of gravity-driven contraction on the shelf that exhibits complex structural styles and differing amount of shortening along strike. Net shortening is up to 48 km in the northern wider part of the fold-and-thrust belt (≈ 180 km), diminishing to < 15 km toward the south, where the belt is markedly narrower (≈ 50 km). The three balanced profiles show a shortening percentage around 20% (comparable with the maximum values documented in other gravity-driven DWFTBs), with a significant variability along dip: higher values are achieved in the outer (i.e. down-dip) portion of the system, dominated by basinward-verging, imbricate thrust sheets. Fold wavelength increases landward, where doubly-verging structures and symmetric detachment folds accommodate a lower amount of shortening. Similar to other cases, a linear and systematic relationship between sedimentary thickness and fold wavelength is observed. Reconstruction of the rate of shortening through time within a fold-and-thrust belt shows that after an early phase of slow activation (Late Cretaceous), > 95% of net shortening was produced in < 10 Myr (during Paleocene). During this acme phase, which followed a period of high sedimentation rate, thrusts were largely synchronous and the shortening rate reached a maximum value of 5 mm/yr. The kinematic evolution reconstructed in this study suggests that the structural evolution of gravity-driven fold-and-thrust belts differs from the accretionary wedges and the collisional fold-and-thrust belts, where thrusts propagate in-sequence and shortening is uniformly accommodated along dip.

Significant strain accumulation between the deformation front and landward out-of-sequence thrusts in accretionary wedge of SW Taiwan revealed by cGPS and SAR interferometry

NASA Astrophysics Data System (ADS)

Tsai, M. C.

2017-12-01

High strain accumulation across the fold-and-thrust belt in Southwestern Taiwan are revealed by the Continuous GPS (cGPS) and SAR interferometry. This high strain is generally accommodated by the major active structures in fold-and-thrust belt of western Foothills in SW Taiwan connected to the accretionary wedge in the incipient are-continent collision zone. The active structures across the high strain accumulation include the deformation front around the Tainan Tableland, the Hochiali, Hsiaokangshan, Fangshan and Chishan faults. Among these active structures, the deformation pattern revealed from cGPS and SAR interferometry suggest that the Fangshan transfer fault may be a left-lateral fault zone with thrust component accommodating the westward differential motion of thrust sheets on both side of the fault. In addition, the Chishan fault connected to the splay fault bordering the lower-slope and upper-slope of the accretionary wedge which could be the major seismogenic fault and an out-of-sequence thrust fault in SW Taiwan. The big earthquakes resulted from the reactivation of out-of-sequence thrusts have been observed along the Nankai accretionary wedge, thus the assessment of the major seismogenic structures by strain accumulation between the frontal décollement and out-of-sequence thrusts is a crucial topic. According to the background seismicity, the low seismicity and mid-crust to mantle events are observed inland and the lower- and upper- slope domain offshore SW Taiwan, which rheologically implies the upper crust of the accretionary wedge is more or less aseimic. This result may suggest that the excess fluid pressure from the accretionary wedge not only has significantly weakened the prism materials as well as major fault zone, but also makes the accretionary wedge landward extension, which is why the low seismicity is observed in SW Taiwan area. Key words: Continuous GPS, SAR interferometry, strain rate, out-of-sequence thrust.

Debris-Flow Hazards within the Appalachian Mountains of the Eastern United States

USGS Publications Warehouse

Wieczorek, Gerald F.; Morgan, Benjamin A.

2008-01-01

Tropical storms, including hurricanes, often inflict major damage to property and disrupt the lives of people living in coastal areas of the Eastern United States. These storms also are capable of generating catastrophic landslides within the steep slopes of the Appalachian Mountains. Heavy rainfall from hurricanes, cloudbursts, and thunderstorms can generate rapidly moving debris flows that are among the most dangerous and damaging type of landslides. This fact sheet explores the nature and occurrence of debris flows in the central and southern Appalachian Mountains, which extend from central Pennsylvania to northern Alabama.

Pressure-Temperature Studies and Structural Setting of Amphibolite-Grade Rocks Within the Easternmost Indus-Ysangpo Suture Zone and Forearc Complex (Tidding Formation), N. Indo-Burma Ranges of N.E. India

NASA Astrophysics Data System (ADS)

Braza, M.; Haproff, P. J.

2016-12-01

The easternmost extension of the Indus-Ysangpo suture (IYS) and Xigaze forearc complex, the Tidding Formation of northeastern India, remains the least-studied sequence representing closure of the Neotethys ocean and syn-tectonic sedimentation. In this study, we present P-T determinations coupled with detrital zircon U-Pb geochronology and detailed geologic mapping to uncover the depositional and metamorphic history of Tidding suture and forearc rocks during Himalayan orogenesis. Four mica schists were sampled from successive NW-SE-striking thrust sheets within the Dibang Valley of Arunachal Pradesh (N.E. India), southwest of the easternmost L. Cretaceous Gangdese batholith. Use of the garnet-muscovite-biotite-plagioclase (GMBP) thermobarometer and Ti-in-biotite thermometer on schist sample PH-1-8-13-26 yield peak conditions of 627 ± 28°C and 10.4 ± 1.1 kbar. Similarly, use of the garnet-biotite Fe-Mg exchange thermometer and garnet-aluminosilicate-silica-plagioclase (GASP) barometer yield 644 ± 50°C and 12 ± 1 kbar for schist sample PH-11-14-15-24 within the same thrust sheet. Both samples contain recrystallized quartz along grain boundaries and garnets contain no significant compositional zoning. At structurally lower levels, garnet chlorite schist (PH-1-8-13-8) sampled from the Mayodia klippe records peak temperatures below 650°C. Garnets display growth zoning, with increasing Mn and decreasing Fe and Mg from rim to core. Application of the Ti-in-biotite thermometer to a mafic schist (PH-1-3-13-1B) within the Mayodia klippe near a southwestward-directed thrust yields a peak temperature of 679 ± 24°C. Our study reveals metamorphism of IYS rocks occurred at deep crustal levels (>30 km) during northward Neotethys subduction. Suture rocks were subsequently exhumed by orogen-scale N-dipping thrusts during growth of the easternmost Himalayan orogen.

Late Cretaceous-Cenozoic subduction-collision history of the Southern Neotethys: new evidence from the Çağlayancerit area, SE Turkey

NASA Astrophysics Data System (ADS)

Akıncı, Ahmet Can; Robertson, Alastair H. F.; Ünlügenç, Ulvi Can

2016-01-01

Evidence of the subduction-collision history of the S Neotethys is well exposed in the frontal part of the SE Anatolian thrust belt and the adjacent Arabian continental margin. The foreland succession in the study area begins with Eocene shelf carbonates, ranging from shallow marine to deeper marine, without sedimentary input from the Tauride continent to the north. After a regional hiatus (Oligocene), sedimentation resumed during the Early Miocene with terrigenous gravity-flow deposition in the north (Lice Formation) and shallow-marine carbonates further south. Clastic detritus was derived from the Tauride continent and oceanic accretionary material. The base of the overriding Tauride allochthon comprises ophiolite-derived debris flows, ophiolite-related mélange and dismembered ophiolitic rocks. Above this, the regional-scale Bulgurkaya sedimentary mélange (an olistostrome) includes blocks and dismembered thrust sheets of metamorphic rocks, limestone and sandstone, which include Late Cretaceous and Eocene foraminifera. The matrix is mainly strongly deformed Eocene-Oligocene mudrocks, hemipelagic marl and sandstone turbidites. The thrust stack is topped by a regionally extensive thrust sheet (Malatya metamorphic unit), which includes greenschist facies marble, calcschist, schist and phyllite, representing Tauride continental crust. Beginning during the Late Mesozoic, the S Neotethys subducted northwards beneath a backstop represented by the Tauride microcontinent (Malatya metamorphic unit). Ophiolites formed within the S Neotethys and accreted to the Tauride active margin. Large-scale sedimentary mélange developed along the Tauride active margin during Eocene-Oligocene. On the Arabian margin, a sedimentary hiatus and tilting (Oligocene) is interpreted to record initial continental collision. The Early Miocene terrigenous gravity flows represent a collision-related flexural foreland basin. Southward overthrusting of the Tauride allochthon took place during Early-Middle Miocene. Associated regional uplift triggered large-scale alluvial deposition. The foreland folded and faulted in response to suture zone tightening (Late Miocene). Left-lateral strike slip characterised the Plio-Pleistocene.

Seismotectonics of the Pamir

NASA Astrophysics Data System (ADS)

Schurr, Bernd; Sippl, Christian; Yuan, Xiaohui; Mechie, James; Lothar, Ratschbacher

2013-04-01

The Pamir Mountains form a complex orographic node north of the western Himalayan Syntaxis. Due to the Pamir's remote location, crustal tectonics of the region is not well studied. We report new data on distribution and kinematics of crustal earthquakes in the Pamir and its surroundings. Our data set stems from a deployment of seismometers between 2008-2010 that covered the SW Tien Shan, Pamir and Tajik basin. We detected and carefully relocated several thousand crustal earthquakes that are confined to the uppermost 20 km of the crust and thereby clearly separated from Pamir's unique intermediate depth seismicity. For the larger earthquakes (M<3) we use both full waveform inversion and first motion polarities to determine source mechanisms. A string of earthquakes outlines the thrust system along the northern Pamir's perimeter. In the east, where the Pamir collides with the Tien Shan, the M6.7 Nura earthquake activated several faults. Whereas the main shock shows almost pure reverse faulting on a south dipping thrust, many aftershocks also show sinistral strike-slip faulting along a NE striking lineamnet. In the centre, where the Pamir overthrusts the intramontane Alai valley, micro-seismicity recedes southward from the Frontal and Trans Alai thrust systems. The largest of these earthquakes show mostly strike-slip mechanisms. Further west, where the Pamir thrust system bends southward, earthquakes show thrust mechanisms again with strikes following the oroclinal structures. Inside the Pamir a NE striking lineament runs from the eastern end of Lake Sarez across Lake Kara Kul to the Pamir thrust system. Source mechanisms along the lineament are sinistral strike slip and transtensional. This lineament approximately separates the deeply incised western Pamir, which shows significant seismic deformation, from the relatively aseismic eastern Pamir. In the western Pamir earthquakes cluster along approximately the Vanch valley and near Lake Sarez. Diffuse seismicity is also visible beneath the SW Pamir's basement domes. Source mechanisms exhibit mostly sinistral strike slip faulting on NE striking or conjugate planes indicating north-south compression and east-west extension. At the Pamir's western margin, where the mountains merge into the Tajik basin's fold and thrust belt, we observe numerous earthquakes with mechanisms exhibiting EW slip on subhorizontal planes. We interpret this as movement along the Jurassic evaporite decollement that detaches the sedimentary section from the basement. Our data indicate that in the western Pamir NS compression is accommodated by westward escape, i.e. the western Pamir is pushed into the Tajik depression ontop of a weak evaporite detachment. This is in accordance with the observed GPS displacement vectors rotating anticlockwise from NS to EW when traversing from the eastern Pamir into the Tajik depression.

The Eocene-Miocene tectonic evolution of the Rif chain (Morocco): new data from the Jebha area

NASA Astrophysics Data System (ADS)

D'Assisi Tramparulo, Francesco; Ciarcia, Sabatino; El Ouaragli, Bilal; Vitale, Stefano; Najib Zaghloul, Mohamed

2016-04-01

Keywords: structural analysis, tectonics, shear bands, Miocene, Jebha Fault The Jebha area, located in the Central Rif, is a key sector to understand the orogenic evolution of the Rif chain. Here, the left lateral Jebha-Chrafate transfer fault, allowed, in the Miocene time, the westward migration of the internal thrust front. The structural analysis of the area revealed a complex tectonic history. The Eocene orogenic pulse produced the tectonic stacking of the Ghomaride thrust sheets. During the late Aquitanian and Langhian, under a dominant ENE-WSW shortening, imbrication of several Internal Dorsale Calcaire slices occurred. The following orogenic stage, characterized by a main SE tectonic transport, allowed the External Dorsale Calcaire to overthrust the Maghrebian Flysch Basin Units by means of a dominant thin-skinned tectonics. Synchronously with the buttressing following the collision of the allochthonous wedge against the External Rif domain, an out-of-sequence thrusting stage involved the Ghomaride and Dorsale Calcaire Units and a general back-thrusting deformed the entire tectonic pile. A renewal of the NE-SW shortening produced strike-slip faults and SW-verging folds and finally a radial extension affected the whole chain.

Seismicity of the Earth 1900–2010 Himalaya and vicinity

USGS Publications Warehouse

Turner, Bethan; Jenkins, Jennifer; Turner, Rebecca; Parker, Amy; Sinclair, Alison; Davies, Sian; Hayes, Gavin P.; Villaseñor, Antonio; Dart, Rirchard L.; Tarr, Arthur C.; Furlong, Kevin P.; Benz, Harley M.

2013-01-01

Seismicity in the Himalaya region predominantly results from the collision of the India and Eurasia continental plates, which are converging at a relative rate of 40–50 mm/yr. Northward underthrusting of India beneath Eurasia generates numerous earthquakes and consequently makes this area one of the most seismically hazardous regions on Earth. The surface expression of the plate boundary is marked by the foothills of the north-south trending Sulaiman Range in the west, the Indo-Burmese Arc in the east, and the east-west trending Himalaya Front in the north of India. Along the western margin of the India plate, relative motions between India and Eurasia are accommodated by strike-slip, reverse, and oblique-slip faulting resulting in the complex Sulaiman Range fold and thrust belt, and the major translational Chaman Fault in Afghanistan. Beneath the Pamir‒Hindu Kush Mountains of northern Afghanistan, earthquakes occur to depths as great as 200 km as a result of remnant lithospheric subduction. Further north again, the Tian Shan is a seismically active intra-continental mountain belt defined by a series of east-west trending thrust faults thought to be related to the broad footprint of the India-Eurasia collision. Tectonics in northern India are dominated by motion along the Main Frontal Thrust and associated thrust faults of the India-Eurasia plate boundary, which have resulted in a series of large and devastating earthquakes in (and prior to) the 20th century. The Tibetan Plateau to the north of the main plate boundary is a broad region of uplift associated with the India-Eurasia collision, and is cut by a series of generally east-west trending strike-slip faults. These include the Kunlun, Haiyuan, and the Altyn Tagh faults, all of which are left-lateral structures, and the Kara-Koram right-lateral fault. Throughout the plateau, thrust faults accommodate the north-south compressional component of crustal shortening associated with the ongoing collision of India and Eurasia, while strike-slip and normal faults accommodate east-west extension. To the east, The Longmen Shan thrust belt marks the eastern margin of the Tibetan Plateau separating the complex tectonics of the plateau region from the relatively undeformed Sichuan Basin. Further south, the left-lateral Xiangshuihe-Xiaojiiang, right-lateral Red River and right-lateral Sagaing strike-slip fault systems accommodate deformation along the eastern margin of the India plate. Deep earthquakes have also occurred in the Indo-Burmese Arc region, thought to be an expression of eastward-directed subduction of the India plate, though whether subduction is ongoing is still debated.

Oil prospects of Cuba

DOE Office of Scientific and Technical Information (OSTI.GOV)

Marrero-Faz, M.; Hernandezperez, G.

The Cuban Archipelago is an Early Tertiary thrust belt derived from the Collision of the Cretaceous volcanic arc from the South with the North American continental margin (Jurassic- Cretaceous). The main characteristics of the hydrocarbon potential of Cuba are: (1) Widespread existence of Jurassic-Cretaceous source rocks and active process of generation of different types of oils; (2) Hydrocarbons are reservoired in a wide range of rock types most commonly in thrusted, fractured carbonates of Jurassic to Cretaceous age. This kind of reservoir is the most important in Cuba; (3) High density in area of different types of traps, being themore » most important hinterland dipping thrust sheet play; and (4) Migration and trapping of hydrocarbons mainly in Eocene. Migration is supposed to be mostly lateral. Vertical migration is not excluded in the South and also in some part of the North Province. There still remains a significant number of untested, apparently valid exploration plays in both on- and offshore areas of Cuba.« less

The Influence of fold and fracture development on reservoir behavior of the Lisburne Group of northern Alaska

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wesley K. Wallace; Catherine L. Hanks; Jerry Jensen: Michael T. Whalen

2004-07-01

The Carboniferous Lisburne Group is a major carbonate reservoir unit in northern Alaska. The Lisburne is folded and thrust faulted where it is exposed throughout the Brooks Range, but is relatively undeformed in areas of current production in the subsurface of the North Slope. The objectives of this study were to develop a better understanding of four major aspects of the Lisburne: (1) The geometry and kinematics of folds and their truncation by thrust faults. (2) The influence of folding on fracture patterns. (3) The influence of deformation on fluid flow. (4) Lithostratigraphy and its influence on folding, faulting, fracturing,more » and reservoir characteristics. Symmetrical detachment folds characterize the Lisburne in the northeastern Brooks Range. In contrast, Lisburne in the main axis of the Brooks Range is deformed into imbricate thrust sheets with asymmetrical hangingwall anticlines and footwall synclines. The Continental Divide thrust front separates these different structural styles in the Lisburne and also marks the southern boundary of the northeastern Brooks Range. Field studies were conducted for this project during 1999 to 2001 in various locations in the northeastern Brooks Range and in the vicinity of Porcupine Lake, immediately south of the Continental Divide thrust front. Results are summarized below for the four main subject areas of the study.« less

Locating Pleistocene Refugia: Comparing Phylogeographic and Ecological Niche Model Predictions

DTIC Science & Technology

2007-07-01

the nature of the paleoclimatic layers currently available. Mountain ranges or large ice sheets are reflected in climate layers, as they present major...environmental gradients running both north-south (latitu- dinal) and east to west (North American mountain ranges). To assure that the test could be...Conceived and designed the experiments: RG EW. Analyzed the data: RG EW. Other: Contributed to project planning: SP AN. Provided data layers: AP RH

Mountain building on Io driven by deep faulting

USGS Publications Warehouse

Bland, Michael T.; McKinnon, William B

2016-01-01

Jupiter’s volcanic moon Io possesses some of the highest relief in the Solar System: massive, isolated mountain blocks that tower up to 17 km above the surrounding plains. These mountains are likely to result from pervasive compressive stresses induced by subsidence of the surface beneath the near-continual emplacement of volcanic material. The stress state that results from subsidence and warming of Io’s lithosphere has been investigated in detail1, 2, 3, 4; however, the mechanism of orogenesis itself and its effect on regional tectonism and volcanism has not been firmly established. Here we present viscoelastic–plastic finite element simulations demonstrating that Io’s mountains form along deep-seated thrust faults that initiate at the base of the lithosphere and propagate upward. We show that faulting fundamentally alters the stress state of Io’s lithosphere by relieving the large volcanism-induced subsidence stresses. Notably, in the upper portion of the lithosphere, stresses become tensile (near-zero differential stress). A number of processes are therefore altered post-faulting, including magma transport through the lithosphere, interactions with tidal stresses and potentially the localization of mountain formation by thermoelastic stresses. We conclude that Io’s mountains form by a unique orogenic mechanism, compared with tectonic processes operating elsewhere in the Solar System.

Paleozoic and mesozoic evolution of East-Central California

USGS Publications Warehouse

Stevens, C.H.; Stone, P.; Dunne, G.C.; Greene, D.C.; Walker, J.D.; Swanson, B.J.

1997-01-01

East-central California, which encompasses an area located on the westernmost part of sialic North America, contains a well-preserved record of Paleozoic and Mesozoic tectonic events that reflect the evolving nature of the Cordilleran plate margin to the west. After the plate margin was formed by continental rifting in the Neoproterozoic, sediments comprising the Cordilleran miogeocline began to accumulate on the subsiding passive margin. In east-central California, sedimentation did not keep pace with subsidence, resulting in backstepping of a series of successive carbonate platforms throughout the early and middle Paleozoic. This phase of miogeoclinal development was brought to a close by the Late Devonian-Early Mississippian Antler orogeny, during the final phase of which oceanic rocks were emplaced onto the continental margin. Subsequent Late Mississippian-Pennsylvanian faulting and apparent reorientation of the carbonate platform margin are interpreted to have been associated with truncation of the continental plate on a sinistral transform fault zone. In the Early Permian, contractional deformation in east-central California led to the development of a narrow, uplifted thrust belt flanked by marine basins in which thick sequences of deep-water strata accumulated. A second episode of contractional deformation in late Early Permian to earliest Triassic time widened and further uplifted the thrust belt and produced the recently identified Inyo Crest thrust, which here is correlated with the regionally significant Last Chance thrust. In the Late Permian, about the time of the second contractional episode, extensional faulting created shallow sedimentary basins in the southern Inyo Mountains. In the El Paso Mountains to the south, deformation and plutonism record the onset of subduction and arc magmatism in late Early Permian to earliest Triassic time along this part of the margin. Tectonism had ceased in most of east-central California by middle to late Early Triassic time, and marine sediment deposited on the subsiding continental shelf overlapped the previously deformed Permian rocks. Renewed contractional deformation, probably in the Middle Triassic, is interpreted to be associated with emplacement of the Golconda allochthon onto the margin of the continent. This event, which is identified with certainty in the Sierra Nevada, also may have significantly affected rocks in the White and Inyo Mountains to the east. Subduction and arc magmatism that created most of the Sierra Nevada batholith began in the Late Triassic and lasted through the remainder of the Mesozoic. During this time, the East Sierran thrust system (ESTS) developed as a narrow zone of intense, predominantly E-vergent contractional deformation along the eastern margin of the growing batholith. Activity on the ESTS took place over an extended part of Mesozoic time, both before and after intrusion of voluminous Middle Jurassic plutons, and is interpreted to have been mechanically linked to emplacement of the batholith. Deformation on the ESTS and magmatism in the Sierra Nevada both ended prior to the close of the Cretaceous.

A dynamic early East Antarctic Ice Sheet suggested by ice-covered fjord landscapes.

PubMed

Young, Duncan A; Wright, Andrew P; Roberts, Jason L; Warner, Roland C; Young, Neal W; Greenbaum, Jamin S; Schroeder, Dustin M; Holt, John W; Sugden, David E; Blankenship, Donald D; van Ommen, Tas D; Siegert, Martin J

2011-06-02

The first Cenozoic ice sheets initiated in Antarctica from the Gamburtsev Subglacial Mountains and other highlands as a result of rapid global cooling ∼34 million years ago. In the subsequent 20 million years, at a time of declining atmospheric carbon dioxide concentrations and an evolving Antarctic circumpolar current, sedimentary sequence interpretation and numerical modelling suggest that cyclical periods of ice-sheet expansion to the continental margin, followed by retreat to the subglacial highlands, occurred up to thirty times. These fluctuations were paced by orbital changes and were a major influence on global sea levels. Ice-sheet models show that the nature of such oscillations is critically dependent on the pattern and extent of Antarctic topographic lowlands. Here we show that the basal topography of the Aurora Subglacial Basin of East Antarctica, at present overlain by 2-4.5 km of ice, is characterized by a series of well-defined topographic channels within a mountain block landscape. The identification of this fjord landscape, based on new data from ice-penetrating radar, provides an improved understanding of the topography of the Aurora Subglacial Basin and its surroundings, and reveals a complex surface sculpted by a succession of ice-sheet configurations substantially different from today's. At different stages during its fluctuations, the edge of the East Antarctic Ice Sheet lay pinned along the margins of the Aurora Subglacial Basin, the upland boundaries of which are currently above sea level and the deepest parts of which are more than 1 km below sea level. Although the timing of the channel incision remains uncertain, our results suggest that the fjord landscape was carved by at least two iceflow regimes of different scales and directions, each of which would have over-deepened existing topographic depressions, reversing valley floor slopes.

Numerical modeling of mountain formation on Io

NASA Astrophysics Data System (ADS)

Turtle, E. P.; Jaeger, W. L.; McEwen, A. S.; Keszthelyi, L.

2000-10-01

Io has ~ 100 mountains [1] that, although often associated with patera [2], do not appear to be volcanic structures. The mountains are up to 16 km high [3] and are generally isolated from each other. We have performed finite-element simulations of the formation of these mountains, investigating several mountain building scenarios: (1) a volcanic construct due to heterogeneous resurfacing on a coherent, homogeneous lithosphere; (2) a volcanic construct on a faulted, homogeneous lithosphere; (3) a volcanic construct on a faulted, homogeneous lithosphere under compression induced by subsidence due to Io's high resurfacing rate; (4) a faulted, homogeneous lithosphere under subsidence-induced compression; (5) a faulted, heterogeneous lithosphere under subsidence-induced compression; and (6) a mantle upwelling beneath a coherent, homogeneous lithosphere under subsidence-induced compression. The models of volcanic constructs do not produce mountains similar to those observed on Io. Neither do those of pervasively faulted lithospheres under compression; these predict a series of tilted lithospheric blocks or plateaus, as opposed to the isolated structures that are observed. Our models show that rising mantle material impinging on the base of the lithosphere can focus the compressional stresses to localize thrust faulting and mountain building. Such faults could also provide conduits along which magma could reach the surface as is observed near several mountains. [1] Carr et al., Icarus 135, pp. 146-165, 1998. [2] McEwen et al., Science 288, pp. 1193-1198, 2000. [3] Schenk and Bulmer, Science 279, pp. 1514-1517, 1998.

Stratiform zinc-lead mineralization in Nasina assemblage rocks of the Yukon-Tanana Upland in east-central Alaska

USGS Publications Warehouse

Dusel-Bacon, Cynthia; Bressler, Jason R.; Takaoka, Hidetoshi; Mortensen, James K.; Oliver, Douglas H.; Leventhal, Joel S.; Newberry, Rainer J.; Bundtzen, Thomas K.

1998-01-01

The Yukon-Tanana Upland of east-central Alaska and Yukon comprises thrust sheets of ductilely deformed metasedimentary and metaigneous rocks of uncertain age and origin that are overlain by klippen of weakly metamorphosed oceanic rocks of the Seventymile-Slide Mountain terrane, and intruded by post-kinematic Early Jurassic, Cretaceous and Tertiary granitoids. Metamorphosed continental margin strata in the Yukon-Tanana Upland of east-central Alaska are thought to be correlative, on the basis of stratigraphic similarities and sparse Mississippian U-Pb zircon and fossil ages (Mortensen, 1992), with middle Paleozoic metasedimentary and metavolcanic rocks in the eastern Alaska Range and in western and southeastern Yukon. Furthermore, rocks in the northern Yukon-Tanana Upland may correlate across the Tintina fault with unmetamorphosed counterparts in the Selwyn Basin (Murphy and Abbott, 1995). Volcanic-hosted (VMS) and sedimentary exhalative (sedex) massive sulfide occurrences are widely reported for these other areas (green-colored unit of fig. 1) but, as yet, have not been documented in the Alaskan part of the Yukon-Tanana Upland. Recent discoveries of VMS deposits in Devono-Mississippian metavolcanic rocks in the Finlayson Lake area of southeastern Yukon (Hunt, 1997) have increased the potential for finding VMS deposits in rocks of similar lithology and age in the Yukon-Tanana Upland of Alaska. Restoration of 450 km of early Tertiary dextral movement along the Tintina fault juxtaposes these two areas.

Tectonic controls on large landslide complex: Williams Fork Mountains near Dillon, Colorado

USGS Publications Warehouse

Kellogg, K.S.

2001-01-01

An extensive (~ 25 km2) landslide complex covers a large area on the west side of the Williams Fork Mountains in central Colorado. The complex is deeply weathered and incised, and in most places geomorphic evidence of sliding (breakaways, hummocky topography, transverse ridges, and lobate distal zones) are no longer visible, indicating that the main mass of the slide has long been inactive. However, localized Holocene reactivation of the landslide deposits is common above the timberline (at about 3300 m) and locally at lower elevations. Clasts within the complex, as long as several tens of meters, are entirely of crystalline basement (Proterozoic gneiss and granitic rocks) from the hanging wall of the Laramide (Late Cretaceous to Early Tertiary), west-directed Williams Range thrust, which forms the western structural boundary of the Colorado Front Range. Late Cretaceous shale and sandstone compose most footwall rocks. The crystalline hanging-wall rocks are pervasively fractured or shattered, and alteration to clay minerals is locally well developed. Sackung structures (trenches or small-scale grabens and upslope-facing scarps) are common near the rounded crest of the range, suggesting gravitational spreading of the fractured rocks and oversteepening of the mountain flanks. Late Tertiary and Quaternary incision of the Blue River Valley, just west of the Williams Fork Mountains, contributed to the oversteepening. Major landslide movement is suspected during periods of deglaciation when abundant meltwater increased pore-water pressure in bedrock fractures. A fault-flexure model for the development of the widespread fracturing and weakening of the Proterozoic basement proposes that the surface of the Williams Range thrust contains a concave-downward flexure, the axis of which coincides approximately with the contact in the footwall between Proterozoic basement and mostly Cretaceous rocks. Movement of brittle, hanging-wall rocks through the flexure during Laramide deformation pervasively fractured the hanging-wall rocks. ?? 2001 Elsevier Science B.V. All rights reserved.

The tectonometamorphic evolution of the Apuseni Mountains (Romania): Geodynamic constraints for the evolution of the Alps-Carpathians-Dinaride system of orogens

NASA Astrophysics Data System (ADS)

Reiser, Martin; Schuster, Ralf; Fügenschuh, Bernhard

2015-04-01

New structural, thermobarometric and geochronological data allow integrating kinematics, timing and intensity of tectonic phases into a geodynamic model of the Apuseni Mountain, which provides new constraints for the evolution of the Alps-Carpathians-Dinaride system of orogens. Strong differences in terms of deformation directions between Early and Late Cretaceous events provide new constraints on the regional geodynamic evolution during the Cretaceous. Geochronological and structural data evidence a Late Jurassic emplacement of the South Apuseni Ophiolites on top of the Biharia Nappe System (Dacia Mega-Unit), situated in an external position at the European margin. Following the emplacement of the ophiolites, three compressive deformation phases affected the Apuseni Mountains during Alpine orogeny: a) NE-directed in-sequence nappe stacking and regional metamorphic overprinting under amphibolite-facies conditions during the Early Cretaceous ("Austrian Phase"), b) NW-directed thrusting and folding, associated with greenschist-facies overprinting, during the early Late Cretaceous ("Turonian Phase") and c) E-W internal folding together with brittle thrusting during the latest Cretaceous ("Laramian Phase"). Major tectonic unroofing and exhumation at the transition from Early to Late Cretaceous times is documented through new Sm-Nd Grt, Ar-Ar Ms and Rb-Sr Bt ages from the study area and resulted in a complex thermal structure with strong lateral and vertical thermal gradients. Nappe stacking and medium-grade metamorphic overprinting during the Early Cretaceous exhibits striking parallels between the evolution of the Tisza-Dacia Mega-Units and the Austroalpine Nappes (ALCAPA Mega-Unit) and evidences a close connection. However, Late Cretaceous tectonic events in the study area exhibit strong similarities with the Dinarides. Thus, the Apuseni Mountains represent the "missing link" between the Early Cretaceous Meliata subduction (associated with obduction of ophiolites) and the Neotethys subduction during Late Cretaceous times.

The western limits of the Seattle fault zone and its interaction with the Olympic Peninsula, Washington

USGS Publications Warehouse

A.P. Lamb,; L.M. Liberty,; Blakely, Richard J.; Pratt, Thomas L.; Sherrod, B.L.; Van Wijk, K.

2012-01-01

We present evidence that the Seattle fault zone of Washington State extends to the west edge of the Puget Lowland and is kinemati-cally linked to active faults that border the Olympic Massif, including the Saddle Moun-tain deformation zone. Newly acquired high-resolution seismic reflection and marine magnetic data suggest that the Seattle fault zone extends west beyond the Seattle Basin to form a >100-km-long active fault zone. We provide evidence for a strain transfer zone, expressed as a broad set of faults and folds connecting the Seattle and Saddle Mountain deformation zones near Hood Canal. This connection provides an explanation for the apparent synchroneity of M7 earthquakes on the two fault systems ~1100 yr ago. We redefi ne the boundary of the Tacoma Basin to include the previously termed Dewatto basin and show that the Tacoma fault, the southern part of which is a backthrust of the Seattle fault zone, links with a previously unidentifi ed fault along the western margin of the Seattle uplift. We model this north-south fault, termed the Dewatto fault, along the western margin of the Seattle uplift as a low-angle thrust that initiated with exhu-mation of the Olympic Massif and today accommodates north-directed motion. The Tacoma and Dewatto faults likely control both the southern and western boundaries of the Seattle uplift. The inferred strain trans-fer zone linking the Seattle fault zone and Saddle Mountain deformation zone defi nes the northern margin of the Tacoma Basin, and the Saddle Mountain deformation zone forms the northwestern boundary of the Tacoma Basin. Our observations and model suggest that the western portions of the Seattle fault zone and Tacoma fault are com-plex, require temporal variations in principal strain directions, and cannot be modeled as a simple thrust and/or backthrust system.

Seismicity of the Earth 1900–2010 Middle East and vicinity

USGS Publications Warehouse

Jenkins, Jennifer; Turner, Bethan; Turner, Rebecca; Hayes, Gavin P.; Davies, Sian; Dart, Richard L.; Tarr, Arthur C.; Villaseñor, Antonio; Benz, Harley M.

2013-01-01

No fewer than four major tectonic plates (Arabia, Eurasia, India, and Africa) and one smaller tectonic block (Anatolia) are responsible for seismicity and tectonics in the Middle East and surrounding region. Geologic development of the region is a consequence of a number of first-order plate tectonic processes that include subduction, large-scale transform faulting, compressional mountain building, and crustal extension. In the east, tectonics are dominated by the collision of the India plate with Eurasia, driving the uplift of the Himalaya, Karakorum, Pamir and Hindu Kush mountain ranges. Beneath the Pamir‒Hindu Kush Mountains of northern Afghanistan, earthquakes occur to depths as great as 200 km as a result of remnant lithospheric subduction. Along the western margin of the India plate, relative motions between India and Eurasia are accommodated by strike-slip, reverse, and oblique-slip faulting, resulting in the complex Sulaiman Range fold and thrust belt, and the major translational Chaman Fault in Afghanistan. Off the south coasts of Pakistan and Iran, the Makran trench is the surface expression of active subduction of the Arabia plate beneath Eurasia. Northwest of this subduction zone, collision between the two plates forms the approximately 1,500-km-long fold and thrust belts of the Zagros Mountains, which cross the whole of western Iran and extend into northeastern Iraq. Tectonics in the eastern Mediterranean region are dominated by complex interactions between the Africa, Arabia, and Eurasia plates, and the Anatolia block. Dominant structures in this region include: the Red Sea Rift, the spreading center between the Africa and Arabia plates; the Dead Sea Transform, a major strike-slip fault, also accommodating Africa-Arabia relative motions; the North Anatolia Fault, a right-lateral strike-slip structure in northern Turkey accommodating much of the translational motion of the Anatolia block westwards with respect to Eurasia and Africa; and the Cyprian Arc, a convergent boundary between the Africa plate to the south, and Anatolia Block to the north.

Map of normal faults and extensional folds in the Tendoy Mountains and Beaverhead Range, Southwest Montana and eastern Idaho

USGS Publications Warehouse

Janecke, S.U.; Blankenau, J.J.; VanDenburg, C.J.; VanGosen, B.S.

2001-01-01

Compilation of a 1:100,000-scale map of normal faults and extensional folds in southwest Montana and adjacent Idaho reveals a complex history of normal faulting that spanned at least the last 50 m.y. and involved six or more generations of normal faults. The map is based on both published and unpublished mapping and shows normal faults and extensional folds between the valley of the Red Rock River of southwest Montana and the Lemhi and Birch Creek valleys of eastern Idaho between latitudes 45°05' N. and 44°15' N. in the Tendoy and Beaverhead Mountains. Some of the unpublished mapping has been compiled in Lonn and others (2000). Many traces of the normal faults parallel the generally northwest to north-northwest structural grain of the preexisting Sevier fold and thrust belt and dip west-southwest, but northeastand east-striking normal faults are also prominent. Northeaststriking normal faults are subparallel to the traces of southeast-directed thrusts that shortened the foreland during the Laramide orogeny. It is unlikely that the northeast-striking normal faults reactivated fabrics in the underlying Precambrian basement, as has been documented elsewhere in southwestern Montana (Schmidt and others, 1984), because exposures of basement rocks in the map area exhibit north-northwest- to northwest-striking deformational fabrics (Lowell, 1965; M’Gonigle, 1993, 1994; M’Gonigle and Hait, 1997; M’Gonigle and others, 1991). The largest normal faults in the area are southwest-dipping normal faults that locally reactivate thrust faults (fig. 1). Normal faulting began before middle Eocene Challis volcanism and continues today. The extension direction flipped by about 90° four times.

Changes in mountain glacier systems and the distribution of main climatic parameters on the territory of Russia (second part of the XX -beginning of the XXI century).

NASA Astrophysics Data System (ADS)

Tatiana, K.; Nosenko, G.; Popova, V.; Muraviev, A.; Nikitin, S.; Chernova, L.

2017-12-01

Mountain glaciers are vital sources of water worldwide to many densely-populated regions. Most glaciers are now shrinking, resulting in variable water supplies and sustained sea level rise. Rapid glacier change threatens water, energy and food security. Further glacier mass loss is likely in response to recent climate change, driven by global increases in air temperatures and the production of atmospheric pollutants. However, high altitudes and rugged topography generate regional weather systems that complicate the investigation of the relationship between climate and glacier change. Predictive models need to move beyond the state-of-the-art to couple advanced climate models with accurate representations of glacier processes, and more detailed and reliable data describing the state of mountain glaciers are required to constrain these models, both from monitoring individual glaciers and regional remote-sensing observations. Glaciation exists on the territory of Russia for thousands of years. At present both mountain glaciers and continental ice sheets are present there. Continental ice sheets are located on islands and archipelagoes of Russian Arctic region and mountain glaciers are wide-spread on continental part of the country where it currently covers the area of about 3,480,000 km². Now there are 18 mountain glacier regions on the territory of Russia. We present recent data on glaciers state and changes in mountain regions of Russia based on remote sensing and in situ studies and distribution of main climatic parameters that affect the existence of glaciers: summer air temperature, winter precipitations and maximum value of snow thickness. Acknowledgements. This presentation includes the results of research project № 0148-2014-0007 of the Research Plan of the Institute of Geography, RAS and research project supported by the Russian Geographical Society (grant number 05/2017/RGS-RFBR).

New Orogenic Model for Taiwan Collision Zone Inferred From Three-dimensional P- and S-wave Velocity Structures and Seismicity

NASA Astrophysics Data System (ADS)

Nagai, S.; Hirata, N.; Sato, H.

2008-12-01

The island of Taiwan is located in the site of ongoing arc-continent collision zone between the Philippine Sea Plate (PSP) and the Eurasian Plate (EUP). Numerous geophysical and geological studies are done in and around Taiwan to develop various models to explain the tectonic processes in the Taiwan region. However, their details have not been known enough, especially under the Central Range. We suggest a new orogenic model for Taiwan orogeny, named 'Upper Crustal Stacking Model', inferred from our tomographic images using three temporary seismic networks with the Central Weather Bureau Seismic Network. These three temporary networks are the aftershock observation after the 1999 Chi-Chi Taiwan earthquake and two dense array observations across central and southern Taiwan, respectively. Tomographic images by the double-difference tomography [Zhang and Thurber, 2003] show a lateral alternate variation of high- and low-velocity, which are well correlated to surface geology and separated by east-dipping boundaries. These images have reliable high-resolution by dense arrays to be able to discuss this alternate variation. We found three high-velocity zones (> 6.0km/s). The westernmost zone corresponds to the subducting EUP. Other two zones are located beneath the Hsuehshan Range and the Eastern Central Range with trends of eastward dipping, respectively. And, we could image low-velocity zone located beneath Backbone Range between the two high-velocity zones clearly. We interpret that these east-dipping high- and low-velocity zones can be divided into two layered blocks and the subducting EUP, each of which consists of a high-velocity body under low-velocity one. Layered blocks can be interpreted as stacked thrust sheets between the subducting EUP and the Northern Luzon Arc, a part of PSP. These thrust sheets are parts of upper- and mid-crust detached from the subducting EUP. The model of continental subduction followed by buoyancy-driven exhumation can explain the existence of stacked thrust sheets. Thus we propose a new orogenic model, as referred to as the 'Upper Crustal Stacking Model'.

Complex layering of the Orange Mountain Basalt: New Jersey, USA

NASA Astrophysics Data System (ADS)

Puffer, John H.; Block, Karin A.; Steiner, Jeffrey C.; Laskowich, Chris

2018-06-01

The Orange Mountain Basalt of New Jersey is a Mesozoic formation consisting of three units: a single lower inflated sheet lobe about 70 m thick (OMB1), a middle pillow basalt about 10 to 20 m thick (OMB2), and an upper compound pahoehoe flow about 20 to 40 m thick (OMB3). The Orange Mountain Basalt is part of the Central Atlantic Magmatic Province. Quarry and road-cut exposures of OMB1 near Paterson, New Jersey, display some unusual layering that is the focus of this study. OMB1 exposures displays the typical upper crust, core, and basal crust layers of sheet lobes but throughout the Patterson area also display distinct light gray layers of microvesicular basalt mineralized with albite directly over the basal crust and under the upper crust. The lower microvesicular layer is associated with mega-vesicular diapirs. We propose that the upper and lower microvesicular layers were composed of viscous crust that was suddenly quenched before it could devolatilize immediately before the solidification of the core. During initial cooling, the bottom of the basal layer was mineralized with high concentrations of calcite and albite during a high-temperature hydrothermal event. Subsequent albitization, as well as zeolite, prehnite, and calcite precipitation events, occurred during burial and circulation of basin brine heated by recurring Palisades magmatism below the Orange Mountain Basalt. Some of the events experienced by the Orange Mountain Basalt are unusual and place constraints on the fluid dynamics of thick flood basalt flows in general. The late penetration of vesicular diapirs through the entire thickness of the flow interior constrains its viscosity and solidification history.

Paleomagnetic study of an active arc-continent collision, Finisterre Arc Terrane, Papua New Guinea

NASA Astrophysics Data System (ADS)

Weiler, Peter Donald

1999-12-01

This dissertation includes 3 studies from the active collision zone between the Finisterre volcanic arc and Papua New Guinea. Chapter 1 is a paleomagnetic study of thrust sheets of the fold and thrust belt north of the Ramu-Markham suture indicating very rapid vertical-axis rotations related to tectonic transport of thrust units. Our data indicate that rotations as great as 90° since 1 Ma have occurred locally in the Erap Valley area. Such rapid rotations during thrust sheet emplacement may be more common in fold and thrust belts than is presently recognized. Anisotropy of magnetic susceptibility (AMS) lineations are rendered parallel by the same rotations used to restore the paleomagnetic remanence to N-S thus independently confirming the rapid rotations. In Chapter 2, we compare the AMS fabrics from the Erap Valley with microscopic shape fabrics obtained through digital image analysis. We find that the orientations of principal axes found by the two techniques agree very well, but that the maximum and intermediate axes of the magnetic fabric are inverted relative to the grain shape. We interpret the shape fabric as a primary depositional fabric, and the magnetic fabric as the result of a weak tectonic strain overprinting a depositional fabric. Thus, comparison of these fabrics detects the earliest transition from depositional to tectonic strain fabric. Finally, in Chapter 3, we turn to larger scale paleomagnetic results from the colliding Finisterre Arc. Hemipelagic rocks possess a syn-collisional remagnetization indicating a clockwise rotation of the colliding terrane through about 40° in post-Miocene time. Decreasing paleomagnetic declination anomalies as a function of along-strike distance in the Finisterre Terrane, analyzed by our preferred model of a linear remagnetization and a migrating Euler pole, suggests an average rotation rate of 8°/Ma. Thus, we propose that the rotation results from a rigid-body rotation of the Finisterre Terrane rather than from sequential docking of independently colliding blocks. We examine models of a syn-collisional remagnetization with both fixed and migrating Euler poles, and suggest that the Euler pole describing Bismarck/Australia plate motion may have migrated 675 km through post-Miocene time to its present location at the collision suture.

Low-temperature thermochronology of the Laramide Ranges and eastward translation of shortening in the Sevier Belt, Wyoming, Utah and Montana

NASA Astrophysics Data System (ADS)

Peyton, Sara Lynn

This dissertation contains two studies that use very different techniques to investigate the Mesozoic and Cenozoic tectonics of the western USA. The first study investigates shortening in the Sevier thrust belt of northeast Utah and southwest Wyoming using cross sections and seismic reflection data. The second study investigates the low-temperature thermochronology of the Laramide Ranges using apatite (U-Th)/He dating. We used cross sections and seismic reflection data to investigate bed length discrepancies within the hanging wall of the Absaroka thrust in the Sevier thrust belt of northeast Utah and southwest Wyoming. Restoration of cross sections suggests that there was ˜8-14 km of pre-Absaroka-thrust shortening above the Jurassic Preuss salt detachment, but not below it, in the hanging wall of the Absaroka thrust. Reflection seismic data over the hanging wall of the Crawford thrust show that the Crawford thrust is not offset along the Preuss salt detachment, indicating that the additional shortening on the Absaroka plate was transferred east before main movement on the Crawford thrust. Although early displacement on the Crawford thrust cannot be ruled out as the cause of the extra shortening, surface and subsurface geology suggests slip from the western thrust system (Willard and Lost Creek thrusts) was transferred several tens of kilometers east along the Jurassic Preuss salt detachment between ˜102-90 Ma, to the future location of the Absaroka thrust hanging wall. The lack of deformation of the Crawford thrust on the seismic data, along with shortening and extension estimates from cross sections, also indicate that the magnitude of Paleocene and post-early Eocene shortening on the Medicine Butte thrust was essentially offset by subsequent extension on the middle Eocene to late Oligocene Almy-Acocks normal-fault system. For the second study in this dissertation, we dated 91 borehole and surface samples from Laramide-age, basement-cored uplifts of the Rocky Mountain foreland (Wind River, Beartooth, Bighorn and Laramie Ranges) and the Uncompahgre Uplift using the apatite (U-Th)/He system. Apatite (U-Th)/He ages generally decrease with increasing subsurface depth (decreasing elevation) and most samples show age dispersion ranging from tens to hundreds of Myr. Additionally, several samples show correlations between apatite (U-Th)/He age and effective U concentration (eU = [U] + 0.235[Th]) of the crystal, indicating that radiation damage has affected He diffusivity, and hence (U-Th)/ He age. Many surface and near-surface samples have apatite (U-Th)/He ages that are older than corresponding apatite fission-track ages. Forward modeling of Laramide-type thermal histories using a radiation damage diffusion model showed that (U-Th)/He ages may be widely dispersed, and may be older than corresponding apatite fission-track ages within a fossil He partial retention zone. Most of our samples, however, do not show the correlation between (U-Th)/He age and eU predicted by radiation damage diffusion models. We investigated the influence of both grain size and eU content and show that the effects of grain size can obscure (U-Th)/ He age-eU correlations and, similarly, the effect of eU variation can obscure (U-Th)/ He age-grain size correlations. (U-Th)/He ages that are older than fission-track ages from high peaks in the Wind River Range, and from some samples from the Beartooth Range, are most likely the result of He implantation from high eU phases. Best-fit thermal histories from the inversion of age-eU pairs were extrapolated to other elevations to create model age-elevation profiles for a range of eU concentrations. These model profiles approximate our real data. Inverse modeling of (U-Th)/He age data suggests that rapid exhumation within the Laramide province likely began earlier in the Bighorn Mountains (before ˜71 Ma) than the Beartooth Range (before ˜58 Ma), and that the borehole at the northern end of the Laramie Range penetrated a fault sliver at depth.

Evidence for Crustal-Scale Imbrication and non-Equilibrium Topography in the Southern Central Range, Taiwan

NASA Astrophysics Data System (ADS)

Byrne, T. B.; Huang, C.; Ouimet, W. B.; Rau, R.; Hsieh, M.; Lee, Y.

2011-12-01

We integrate a suite of new and recently re-interpreted profiles of the 3-D crustal velocity structure from the southern Central Range of Taiwan with geomorphic data from the range and propose that the topography is supported by a crustal-scale, west-verging thrust. The extent and geometry of the thrust is indicated by contours of P-wave velocity that are progressively overturned from south to north, placing high Vp rocks above low Vp rocks. The interpreted thrust dips gently east (15-20 degrees) and carries pre-Tertiary metamorphic rocks and Eocene to Miocene rocks with a well-developed slaty cleavage in its hanging wall. The thrust is interpreted to cut up section to the west and link with the basal detachment of the fold-and-thrust belt. Leveling data1 along the South Cross-Island Highway also suggest that the thrust is active. Along-strike profiles suggest that the thrust is propagating southward, consistent with a progressive decrease in mean elevation and an increase in reset apatite fission track ages from north to south. The hanging wall of the propagating thrust also correlates with anomalous areas of low topographic relief that straddle the crest of the southern part of the range. The areas of low relief are fringed by stream channels with relatively high stream gradient indexes and do not appear related to weaker rock types, glacial erosion, or lower rock uplift rates along the range crest. We propose that the surfaces represent relict topography that formed prior to a recent acceleration in rock uplift rate, consistent with the presence of a propagating, crustal-scale thrust in the subsurface. Taken together, these results raise questions about the notion of steady state topography and critically tapered wedges in Taiwan. 1) Ching, Kuo-En, Hsieh, M.-L., Johnson, K. M., Chen, K-H., Rau, R.-J., Yang M., Modern vertical deformation rates and mountain building in Taiwan from precise leveling and continuous GPS observations, 2000-2008, in press, JGR.

Publications - MP 157 | Alaska Division of Geological & Geophysical Surveys

Science.gov Websites

Alaska, containing the communities of Fairbanks, Fort Yukon, and Eagle, scale 1:500,000 (79.0 M) Sheet 7 ; Mineral Prospect; Mountain Leather; Tremolite; Ultramafic; geoscientificInformation Top of Page Department

15 Years of GRACE Earth Observations

NASA Image and Video Library

2017-03-15

For 15 years, the GRACE mission has unlocked mysteries of how water moves around our planet. It gave us the first view of underground aquifers from space, and shows how fast polar ice sheets and mountain glaciers are melting.

Psoroptic scabies

USGS Publications Warehouse

Lange, R.E.; Thorne, E. Tom; Kingston, Newton; Jolly, William R.; Bergstrom, Robert C.

1982-01-01

Scabies, caused by mites of the genus Psoroptes, is widespread in free-ranging desert bighorn sheet, Rocky Mountain bighorn sheep, elk, and white-tailed deer. It has been identified on captive mule deer and may have been present on bison.

Geologic map of the Nelson quadrangle, Lewis and Clark County, Montana

USGS Publications Warehouse

Reynolds, Mitchell W.; Hays, William H.

2003-01-01

The geologic map of the Nelson quadrangle, scale 1:24,000, was prepared as part of the Montana Investigations Project to provide new information on the stratigraphy, structure, and geologic history of an area in the geologically complex southern part of the Montana disturbed belt. In the Nelson area, rocks ranging in age from Middle Proterozoic through Cretaceous are exposed on three major thrust plates in which rocks have been telescoped eastward. Rocks within the thrust plates are folded and broken by thrust faults of smaller displacement than the major bounding thrust faults. Middle and Late Tertiary sedimentary and volcaniclastic rocks unconformably overlie the pre-Tertiary rocks. A major normal fault displaces rocks of the western half of the quadrangle down on the west with respect to strata of the eastern part. Alluvial and terrace gravels and local landslide deposits are present in valley bottoms and on canyon walls in the deeply dissected terrain. Different stratigraphic successions are exposed at different structural levels across the quadrangle. In the northeastern part, strata of the Middle Cambrian Flathead Sandstone, Wolsey Shale, and Meagher Limestone, the Middle and Upper Cambrian Pilgrim Formation and Park Shale undivided, the Devonian Maywood, Jefferson, and lower part of the Three Forks Formation, and Lower and Upper Mississippian rocks assigned to the upper part of the Three Forks Formation and the overlying Lodgepole and Mission Canyon Limestones are complexly folded and faulted. These deformed strata are overlain structurally in the east-central part of the quadrangle by a succession of strata including the Middle Proterozoic Greyson Formation and the Paleozoic succession from the Flathead Sandstone upward through the Lodgepole Limestone. In the east-central area, the Flathead Sandstone rests unconformably on the middle part of the Greyson Formation. The north edge, northwest quarter, and south half of the quadrangle are underlain by a succession of rocks that includes not only strata equivalent to those of the remainder of the quadrangle, but also the Middle Proterozoic Newland, Greyson, and Spokane Formations, Pennsylvanian and Upper Mississippian Amsden Formation and Big Snowy Group undivided, the Permian and Pennsylvanian Phosphoria and Quadrant Formations undivided, the Jurassic Ellis Group and Lower Cretaceous Kootenai Formation. Hornblende diorite sills and irregular bodies of probable Late Cretaceous age intrude Middle Proterozoic, Cambrian and Devonian strata. No equivalent intrusive rocks are present in structurally underlying successions of strata. In this main part of the quadrangle, the Flathead Sandstone cuts unconformably downward from south to north across the Spokane Formation into the upper middle part of the Greyson Formation. Tertiary (Miocene?) strata including sandstone, pebble and cobble conglomerate, and vitric crystal tuff underlie, but are poorly exposed, in the southeastern part of the quadrangle where they are overlain by late Tertiary and Quaternary gravel. The structural complexity of the quadrangle decreases from northeast to southwest across the quadrangle. At the lowest structural level (Avalanche Butte thrust plate) exposed in the canyon of Beaver Creek, lower and middle Paleozoic rocks are folded in northwest-trending east-inclined disharmonic anticlines and synclines that are overlain by recumbently folded and thrust faulted Devonian and Mississippian rocks. The Mississippian strata are imbricated adjacent to the recumbent folds. In the east-central part of the quadrangle, a structurally overlying thrust plate, likely equivalent to the Hogback Mountain thrust plate of the Hogback Mountain quadrangle adjacent to the east (Reynolds, 20xx), juxtaposes recumbently folded Middle Proterozoic and unconformably overlying lower Paleozoic rocks on the complexly folded and faulted rocks of the Avalanche Butte thrust plate. The highest structural plate, bounded below

Deformation along the leading edge of the Maiella thrust sheet in central Italy

NASA Astrophysics Data System (ADS)

Aydin, Atilla; Antonellini, Marco; Tondi, Emanuele; Agosta, Fabrizio

2010-09-01

The eastern forelimb of the Maiella anticline above the leading edge of the underlying thrust displays a complex system of fractures, faults and a series of kink bands in the Cretaceous platform carbonates. The kink bands have steep limbs, display top-to-the-east shear, parallel to the overall transport direction, and are brecciated and faulted. A system of pervasive normal faults, trending sub-parallel to the strike of the mechanical layers, accommodates local extension generated by flexural slip. Two sets of strike-slip faults exist: one is left-lateral at a high angle to the main Maiella thrust; the other is right-lateral, intersecting the first set at an acute angle. The normal and strike-slip faults were formed by shearing across bed-parallel, strike-, and dip-parallel pressure solution seams and associated splays; the thrust faults follow the tilted mechanical layers along the steeper limb of the kink bands. The three pervasive, mutually-orthogonal pressure solution seams are pre-tilting. One set of low-angle normal faults, the oldest set in the area, is also pre-tilting. All other fault/fold structures appear to show signs of overlapping periods of activity accounting for the complex tri-shear-like deformation that developed as the front evolved during the Oligocene-Pliocene Apennine orogeny.

The 1987 Whittier Narrows, California, earthquake: A Metropolitan shock

NASA Astrophysics Data System (ADS)

Hauksson, Egill; Stein, Ross S.

1989-07-01

Just 3 hours after the Whittier Narrows earthquake struck, it became clear that a heretofore unseen geological structure was seismically active beneath metropolitan Los Angeles. Contrary to initial expectations of strike-slip or oblique-slip motion on the Whittier fault, whose north end abuts the aftershock zone, the focal mechanism of the mainshock showed pure thrust faulting on a deep gently inclined surface [Hauksson et al., 1988]. This collection of nine research reports spans the spectrum of seismological, geodetic, and geological investigations carried out as a result of the Whittier Narrows earthquake. Although unseen, the structure was not unforeseen. Namson [1987] had published a retrodeformable geologic cross section (meaning that the sedimentary strata could be restored to their original depositional position) 100 km to the west of the future earthquake epicenter in which blind, or subsurface, thrust faults were interpreted to be active beneath the folded southern Transverse Ranges. Working 25 km to the west, Hauksson [1987] had also found a surprising number of microearthquakes with thrust focal mechanisms south of the Santa Monica mountains, another clue to a subsurface system of thrust faults. Finally, Davis [1987] had presented a preliminary cross section only 18 km to the west of Whittier Narrows that identified as "fault B" the thrust that would rupture later that year. Not only was the earthquake focus and its orientation compatible with the 10-15 km depth and north dipping orientation of Davis' proposed thrust, but fault B appears to continue beneath the northern flank of the Los Angeles basin, skirting within 5 km of downtown Los Angeles, an area of dense commercial high-rise building development. These results are refined and extended by Davis et al. [this issue].

Structure of the western Rif (Morocco): Possible hydrocarbon plays

DOE Office of Scientific and Technical Information (OSTI.GOV)

Flinch, J.

1995-08-01

Seismic data offshore and onshore northwestern Morocco (i.e. Atlantic margin, Rharb Basin, Rif foothills) provided a detailed picture of the Western Rif Cordillera. The most external units of the folded-belt consist of allochthonous Cretaceous and Neogene strongly deformed sediments that constitute a westward-directed accretionary wedge. The structure of the accretionary wedge consist of a complex set of thrust and normal faults. The inner part of the study area consist of NW-SE trending thrust faults, partially exposed in the foothills of the Western Rif. Proceeding towards the foreland, thrust faults are offset by low-angle extensional detachments characterized by anastomosing extensional horses.more » Widespread extension overlying the accretionary wedge defines a Late Neogene episode of extensional collapse. Extension is not characterized by localized conventional half-grabens but consists of a complex extensional system with variable orientation. Locally shale ridges and toe-thrusts characterized by rear extension and frontal compression define a set of mixed extensional-compressional satellite basins that significantly differ from conventional thrust-related piggy-back basins. Satellite basins are filled with Upper Tortonian to Pliocene sediments. Shallow fields of biogenic gas are present in this Upper Neogene succession of the satellite basins. The frontalmost part of the wedge consist of WNW-ESE trending thrust imbricates. A flexural basin (foredeep) developed as a result of the accretionary prism loading. The foredeep basin discordantly overlies thinn Cretaceous and Lower-Middle Miocene shallow-water sediments that indistinctly cover Plaeozoic basement rocks and Triassic half-grabens. Pre-foredeep units are related to rifting and passive margin development of the Atlantic Ocean. East from the Rharb Basin the Rif Cordillera is essentially unexplored. Few scattered seismic sections display subsurface ramp anticlines similar to those exposed in the mountain belt.« less

How the structural architecture of the Eurasian continental margin affects the structure, seismicity, and topography of the south central Taiwan fold-and-thrust belt

NASA Astrophysics Data System (ADS)

Brown, Dennis; Alvarez-Marron, Joaquina; Biete, Cristina; Kuo-Chen, Hao; Camanni, Giovanni; Ho, Chun-Wei

2017-07-01

Studies of mountain belts worldwide show that along-strike changes are common in their foreland fold-and-thrust belts. These are typically caused by processes related to fault reactivation and/or fault focusing along changes in sedimentary sequences. The study of active orogens, like Taiwan, can also provide insights into how these processes influence transient features such as seismicity and topography. In this paper, we trace regional-scale features from the Eurasian continental margin in the Taiwan Strait into the south central Taiwan fold-and-thrust belt. We then present newly mapped surface geology, P wave velocity maps and sections, seismicity, and topography data to test the hypothesis of whether or not these regional-scale features of the margin are contributing to along-strike changes in structural style, and the distribution of seismicity and topography in this part of the Taiwan fold-and-thrust belt. These data show that the most important along-strike change takes place at the eastward prolongation of the upper part of the margin necking zone, where there is a causal link between fault reactivation, involvement of basement in the thrusting, concentration of seismicity, and the formation of high topography. On the area correlated with the necking zone, the strike-slip reactivation of east northeast striking extensional faults is causing sigmoidal offset of structures and topography along two main zones. Here basement is not involved in the thrusting; there is weak focusing of seismicity and localized development of topography. We also show that there are important differences in structure, seismicity, and topography between the margin shelf and its necking zone.

Foreshock occurrence before large earthquakes

USGS Publications Warehouse

Reasenberg, P.A.

1999-01-01

Rates of foreshock occurrence involving shallow M ??? 6 and M ??? 7 mainshocks and M ??? 5 foreshocks were measured in two worldwide catalogs over ???20-year intervals. The overall rates observed are similar to ones measured in previous worldwide and regional studies when they are normalized for the ranges of magnitude difference they each span. The observed worldwide rates were compared to a generic model of earthquake clustering based on patterns of small and moderate aftershocks in California. The aftershock model was extended to the case of moderate foreshocks preceding large mainshocks. Overall, the observed worldwide foreshock rates exceed the extended California generic model by a factor of ???2. Significant differences in foreshock rate were found among subsets of earthquakes defined by their focal mechanism and tectonic region, with the rate before thrust events higher and the rate before strike-slip events lower than the worldwide average. Among the thrust events, a large majority, composed of events located in shallow subduction zones, had a high foreshock rate, while a minority, located in continental thrust belts, had a low rate. These differences may explain why previous surveys have found low foreshock rates among thrust events in California (especially southern California), while the worldwide observations suggests the opposite: California, lacking an active subduction zone in most of its territory, and including a region of mountain-building thrusts in the south, reflects the low rate apparently typical for continental thrusts, while the worldwide observations, dominated by shallow subduction zone events, are foreshock-rich. If this is so, then the California generic model may significantly underestimate the conditional probability for a very large (M ??? 8) earthquake following a potential (M ??? 7) foreshock in Cascadia. The magnitude differences among the identified foreshock-mainshock pairs in the Harvard catalog are consistent with a uniform distribution over the range of observation.

Sea level change: lessons from the geologic record

USGS Publications Warehouse

,

1995-01-01

Rising sea level is potentially one of the most serious impacts of climatic change. Even a small sea level rise would have serious economic consequences because it would cause extensive damage to the world's coastal regions. Sea level can rise in the future because the ocean surface can expand due to warming and because polar ice sheets and mountain glaciers can melt, increasing the ocean's volume of water. Today, ice caps on Antarctica and Greenland contain 91 and 8 percent of the world's ice, respectively. The world's mountain glaciers together contain only about 1 percent. Melting all this ice would raise sea level about 80 meters. Although this extreme scenario is not expected, geologists know that sea level can rise and fall rapidly due to changing volume of ice on continents. For example, during the last ice age, about 18,000 years ago, continental ice sheets contained more than double the modem volume of ice. As ice sheets melted, sea level rose 2 to 3 meters per century, and possibly faster during certain times. During periods in which global climate was very warm, polar ice was reduced and sea level was higher than today.

Structural and petrographic constraints on the stratigraphy of the Lapataia Formation, with implications for the tectonic evolution of the Fuegian Andes

NASA Astrophysics Data System (ADS)

Cao, Sebastián J.; Torres Carbonell, Pablo J.; Dimieri, Luis V.

2018-07-01

The structure of the Fuegian Andes central belt is characterized by a first phase of peak metamorphism and ductile deformation, followed by a brittle-ductile thrusting phase including juxtaposition of different (first phase) structural levels; both related to the closure and inversion of the Late Jurassic-Early Cretaceous Rocas Verdes basin. The second phase involved thrust sheets of pre-Jurassic basement, as well as Upper Jurassic and Lower Cretaceous units from the volcanic-sedimentary fill of the basin. Rock exposures in the Parque Nacional Tierra del Fuego reveal a diversity of metamorphic mineral assemblages, dynamic recrystallization grades and associated structures, evidencing a variety of protoliths and positions in the crust during their orogenic evolution. Among the units present in this sector, the Lapataia Formation portrays the higher metamorphic grade reported in the Argentine side of the Fuegian Andes, and since no precise radiometric ages have been established to date, its stratigraphic position remains a matter of debate: the discussion being whether it belongs to the pre-Jurassic basement, or the Upper Jurassic volcanic/volcaniclastic initial fill of the Rocas Verdes basin. The mapping and petrographic/microstructural study of the Lapataia Formation and those of undoubtedly Mesozoic age, allow to characterize the former as a group of rocks with great lithological affinity with the Upper Jurassic metamorphic rocks found elsewhere in the central belt of the Fuegian Andes. The main differences in metamorphic grade are indebted to its deformation at deeper crustal levels, but during the same stages than the Mesozoic rocks. Accordingly, we interpret the regional structure to be associated with the stacking of thrust sheets from different structural levels through the emplacement of a duplex system during the growth of the Fuegian Andes.

Ouachitas need more exploratory drilling

USGS Publications Warehouse

Suneson, Neil H.; Campbell, Jock A.

1990-01-01

The Ouachita Mountains in southeastern Oklahoma and western Arkansas are part of a mostly buried late Paleozoic fold and thrust belt that extends from Alabama to northern Mexico. The principal hydrocarbon reservoirs in the Ouachita tectonic province can be subdivided into those that produce natural gas from shallow-water units and those that produce oil and/or natural gas from deep-water units. They can also be divided into those that are fractured and those that produce from primary pore spaces or vugs. The first successful oil well in the Ouachita Mountains was drilled in 1913 or 1914. Since the discovery of the Redden field, over 800 oil and gas wells have been drilled in the Ouachita tectonic province in Oklahoma. Yet, most of the region remains little explored.

Development of Improved Rhenium Coatings for Fluorine Engine Thrust Chambers. [hydrazine-fluorine rocket engines

NASA Technical Reports Server (NTRS)

Barton, K. J.; Yurkewycz, R.; Harada, Y.; Daniels, I.

1981-01-01

Coating trials were undertaken to evaluate the application of rhenium to carbon-carbon composite sheet by plasma spraying. Optimum spray parameters and coating thickness were identified for production of coatings free from continuous defects and with adequate adherence to the substrate. A tungsten underlayer was not beneficial and possibly detracted from coating integrity. Stress calculations indicated that the proposed operating cycle of the rocket engine would not cause spalling of the rhenium coating. Calculations indicated that permeation of gases through the coating would not be significant during the expected life of the thrust chamber. The feasibility of applying rhenium coatings by laser melting was also studied. Poor wetting of the composite surface by the liquid rhenium precluded production of uniform coatings. Borate/carborate fluxes did not improve wetting characteristics.

HAER COLO,1COMCI,2A (sheet 1 of 2) Highline Canal, Sand ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

HAER COLO,1-COMCI,2A- (sheet 1 of 2) - Highline Canal, Sand Creek Lateral, Beginning at intersection of Peoria Street & Highline Canal in Arapahoe County (City of Aurora), Sand Creek lateral Extends 15 miles Northerly through Araphoe County, City & County of Denver, & Adams County to its end point, approximately 1/4 mile Southest of intersectioin of D Street & Ninth Avenue in Adams County (Rocky Mountain Arsenal, Commerce City Vicinity), Commerce City, Adams County, CO

HAER COLO,1COMCI,2A (sheet 2 of 2) Highline Canal, Sand ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

HAER COLO,1-COMCI,2A- (sheet 2 of 2) - Highline Canal, Sand Creek Lateral, Beginning at intersection of Peoria Street & Highline Canal in Arapahoe County (City of Aurora), Sand Creek lateral Extends 15 miles Northerly through Araphoe County, City & County of Denver, & Adams County to its end point, approximately 1/4 mile Southest of intersectioin of D Street & Ninth Avenue in Adams County (Rocky Mountain Arsenal, Commerce City Vicinity), Commerce City, Adams County, CO

West-directed thrusting south of the eastern Himalayan syntaxis indicates clockwise crustal flow at the indenter corner during the India-Asia collision

NASA Astrophysics Data System (ADS)

Haproff, Peter J.; Zuza, Andrew V.; Yin, An

2018-01-01

Whether continental deformation is accommodated by microplate motion or continuum flow is a central issue regarding the nature of Cenozoic deformation surrounding the eastern Himalayan syntaxis. The microplate model predicts southeastward extrusion of rigid blocks along widely-spaced strike-slip faults, whereas the crustal-flow model requires clockwise crustal rotation along closely-spaced, semi-circular right-slip faults around the eastern Himalayan syntaxis. Although global positioning system (GPS) data support the crustal-flow model, the surface velocity field provides no information on the evolution of the India-Asia orogenic system at million-year scales. In this work, we present the results of systematic geologic mapping across the northernmost segment of the Indo-Burma Ranges, located directly southeast of the eastern Himalayan syntaxis. Early research inferred the area to have experienced either right-slip faulting accommodating northward indentation of India or thrusting due to the eastward continuation of the Himalayan orogen in the Cenozoic. Our mapping supports the presence of dip-slip thrust faults, rather than strike-slip faults. Specifically, the northern Indo-Burma Ranges exposes south- to west-directed ductile thrust shear zones in the hinterland and brittle fault zones in the foreland. The trends of ductile stretching lineations within thrust shear zones and thrust sheets rotate clockwise from the northeast direction in the northern part of the study area to the east direction in the southern part of the study area. This clockwise deflection pattern of lineations around the eastern Himalayan syntaxis mirrors the clockwise crustal-rotation pattern as suggested by the crustal-flow model and contemporary GPS velocity field. However, our finding is inconsistent with discrete strike-slip deformation in the area and the microplate model.

Thrusting Rates in the Early Eocene from the Sevier Hinterland, Idaho, USA

NASA Astrophysics Data System (ADS)

Anastasio, D. J.; Latta, D.; Kodama, K. P.; Idleman, B. D.

2011-12-01

The terminal motion on the Wildhorse thrust system was reconstructed from the Smiley Creek Formation in eastern Idaho, USA (UTM coordinates 11T 739950 m E, 4865190 m N). During the last 100 m of fault slip the calculated slip rate varied between 0.05 to 1.2 mm/yr averaged over time intervals of 300-800 kyrs. The emergent thrust fault overrode proximal fault scarp colluvium deposited as water poor debris flows and was buried by braided stream sheet flood facies sourced by out-of-sequence thrust motion further west. Paleomagnetic data (~100 cores from 27 horizons spaced ~5-60 m apart) showed both normal and reversed directions during progressive step-wise thermal demagnetization to 670° C. Principal component analysis was used to calculate characteristic remanent magnetization directions from which sample polarities were assigned. Correlation of the Smiley Creek Formation to the Geomagnetic Polarity Timescale requires an age older than 49.39±0.27 (n=7) Ma determined by 40Ar/39Ar dating of overlying Challis Volcanic samples and younger than 57±9 Ma, the youngest U/Pb zircon age from an included andesite cobble from a near by Smiley Creek conglomerate exposure (11T 766548 m E, 4874382 m N). The favored magnetostratigraphic correlation is most consistent with expected terrestrial fan facies accumulation rates, the reversal pattern, and calculated paleopole positions. The 183 m of Smiley Creek Formation west of Stag Creek, Idaho was deposited in 4.48 myrs during polarity chrons 24.3n to 23n2n. The terminal emplacement of the Wildhorse thrust was associated with the development of the Pioneer Metamorphic Core complex in the hinterland of the Montana Recess of the Idaho-Wyoming-Montana thrust belt.

SparkJet Actuators for Flow Control

DTIC Science & Technology

2007-03-01

volume. The ceramic component is inserted between a stainless steel holder and a threaded brass cap with a jewel orifice installed in the face (Fig. 3...single sheet of stainless steel shim stock. This metal structure is oriented vertically and clamped at the top and bottom in a Lexan® fixture. The...Laser interferometer arrangement for measuring thrust stand vibrations. In addition to a high natural frequency, the rigid design of the steel

Active Tectonics of Himalayan Faults/Thrusts System in Northern India on the basis of recent & Paleo earthquake Studies

NASA Astrophysics Data System (ADS)

Kumar, S.; Biswal, S.; Parija, M. P.

2016-12-01

The Himalaya overrides the Indian plate along a decollement fault, referred as the Main Himalayan Thrust (MHT). The 2400 km long Himalayan mountain arc in the northern boundary of the Indian sub-continent is one of the most seismically active regions of the world. The Himalayan Frontal Thrust (HFT) is characterized by an abrupt physiographic and tectonic break between the Himalayan front and the Indo-Gangetic plain. The HFT represents the southern surface expression of the MHT on the Himalayan front. The tectonic zone between the Main Boundary Thrust (MBT) and the HFT encompasses the Himalayan Frontal Fault System (HFFS). The zone indicates late Quaternary-Holocene active deformation. Late Quaternary intramontane basin of Dehradun flanked to the south by the Mohand anticline lies between the MBT and the HFT in Garhwal Sub Himalaya. Slip rate 13-15 mm/yr has been estimated on the HFT based on uplifted strath terrace on the Himalyan front (Wesnousky et al. 2006). An out of sequence active fault, Bhauwala Thrust (BT), is observed between the HFT and the MBT. The Himalayan Frontal Fault System includes MBT, BT, HFT and PF active fault structures (Thakur, 2013). The HFFS structures were developed analogous to proto-thrusts in subduction zone, suggesting that the plate boundary is not a single structure, but series of structures across strike. Seismicity recorded by WIHG shows a concentrated belt of seismic events located in the Main Central Thrust Zone and the physiographic transition zone between the Higher and Lesser Himalaya. However, there is quiescence in the Himalayan frontal zone where surface rupture and active faults are reported. GPS measurements indicate the segment between the southern extent of microseismicity zone and the HFT is locked. The great earthquake originating in the locked segment rupture the plate boundary fault and propagate to the Himalaya front and are registered as surface rupture reactivating the fault in the HFFS.

The San Gabriel mountains bright reflective zone: Possible evidence of young mid-crustal thrust faulting in southern California

USGS Publications Warehouse

Ryberg, T.; Fuis, G.S.

1998-01-01

During the Los Angeles Region Seismic Experiment (LARSE), a reflection/retraction survey was conducted along a line extending northeastward from Seal Beach, California, to the Mojave Desert, crossing the Los Angeles basin and San Gabriel Mountains. Shots and receivers were spaced most densely through the San Gabriel Mountains for the purpose of obtaining a combined reflection and refraction image of the crust in that area. A stack of common-midpoint (CMP) data reveals a bright reflective zone, 1-s thick, that dominates the stack and extends throughout most of the mid-crust of the San Gabriel Mountains. The top of this zone ranges in depth from 6 s (???18-km depth) in the southern San Gabriel Mountains to 7.5 s (???23-km depth) in the northern San Gabriel Mountains. The zone bends downward beneath the surface traces of the San Gabriel and San Andreas faults. It is brightest between these two faults, where it is given the name San Gabriel Mountains 'bright spot' (SGMBS). and becomes more poorly defined south of the San Gabriel fault and north of the San Andreas fault. The polarity of the seismic signal at the top of this zone is clearly negative, and our analysis suggests it represents a negative velocity step. The magnitude of the velocity step is approximately 1.7 km/s. In at least one location, an event with positive polarity can be observed 0.2 s beneath the top of this zone, indicating a thickness of the order of 500 m for the low-velocity zone at this location. Several factors combine to make the preferred interpretation of this bright reflective zone a young fault zone, possibly a 'master' decollement. (1) It represents a significant velocity reduction. If the rocks in this zone contain fluids, such a reduction could be caused by a differential change in fluid pressure between the caprock and the rocks in the SGMBS; near-lithostatic fluid pressure is required in the SGMBS. Such differential changes are believed to occur in the neighborhood of active fault zones, where 'fault-valve' action has been postulated. Less likely alternative explanations for this velocity reduction include the presence of magma and a change in composition to serpentinite or metagraywacke. (2) It occurs at or near the brittle-ductile transition, at least in the southern San Gabriel Mountains, a possible zone of concentrated shear. (3) A thin reflection rising from its top in the southern San Gabriel Mountains projects to the hypocenter of the 1987 M 5.9 Whittier Narrows earthquake, a blind thrust-fault earthquake with one focal plane subparallel to the reflection. Alternatively, one could argue that the bends or disruptions in the reflective zone seen at the San Gabriel and San Andreas faults are actually offsets and that the reflective zone is therefore an older feature, possibly an older fault zone. ?? 1998 Elsevier Science B.V. All rights reserved.

Geology of the Yucca Mountain region

USGS Publications Warehouse

Stuckless, J.S.; O'Leary, Dennis W.

2006-01-01

Yucca Mountain has been proposed as the site for the nation's first geologic repository for high-level radioactive waste. This chapter provides the geologic framework for the Yucca Mountain region. The regional geologic units range in age from late Precambrian through Holocene, and these are described briefly. Yucca Mountain is composed dominantly of pyroclastic units that range in age from 11.4 to 15.2 Ma. The proposed repository would be constructed within the Topopah Spring Tuff, which is the lower of two major zoned and welded ash-flow tuffs within the Paintbrush Group. The two welded tuffs are separated by the partly to nonwelded Pah Canyon Tuff and Yucca Mountain Tuff, which together figure prominently in the hydrology of the unsaturated zone. The Quaternary deposits are primarily alluvial sediments with minor basaltic cinder cones and flows. Both have been studied extensively because of their importance in predicting the long-term performance of the proposed repository. Basaltic volcanism began ca. 10 Ma and continued as recently as ca. 80 ka with the eruption of cones and flows at Lathrop Wells, ???10 km south-southwest of Yucca Mountain. Geologic structure in the Yucca Mountain region is complex. During the latest Paleozoic and Mesozoic, strong compressional forces caused tight folding and thrust faulting. The present regional setting is one of extension, and normal faulting has been active from the Miocene through to the present. There are three major local tectonic domains: (1) Basin and Range, (2) Walker Lane, and (3) Inyo-Mono. Each domain has an effect on the stability of Yucca Mountain. ?? 2007 Geological Society of America. All rights reserved.

Latest Pleistocene to Holocene Thrusting Recorded by a Flight of Strath Terraces in the Eastern Qilian Shan, NE Tibetan Plateau

NASA Astrophysics Data System (ADS)

Xiong, Jianguo; Li, Youli; Zhong, Yuezhi; Lu, Honghua; Lei, Jinghao; Xin, Weilin; Wang, Libo; Hu, Xiu; Zhang, Peizhen

2017-12-01

At the eastern Qilian Shan mountain front in the NE Tibetan Plateau, the Minle-Damaying Fault (MDF), the southernmost fault of the North Frontal Thrust (NFT) system, has previously been proposed as an inactive structure during the Holocene. Here we present a detailed record of six strath terraces of the Xie River that document the history of active deformation of the MDF. One optically stimulated luminescence dating sample constrains abandonment of the highest terrace T6 at 12.7 ± 1.4 ka. The formation ages of the lower terraces (T4-T1) are dated by AMS 14C dating. The cumulative vertical offsets of the MDF recorded by these terraces are determined as 12.2 ± 0.4 m (T6), 8.0 ± 0.4 m (T5), 6.4 ± 0.4 m (T4), 4.6 ± 0.1 m (T3), and 3.2 ± 0.2 m (T1c) by an unmanned aerial vehicle system, respectively. A long-term vertical slip rate of the MDF of 0.9 ± 0.2 mm/yr is then estimated from the above data of terrace age and vertical offset by a linear regression. Assuming that the fault dip of 35 ± 5° measured at the surface is representative for the depth-averaged fault dip, horizontal shortening rates of 0.83-1.91 mm/yr are inferred for the MDF. Our new data show that the proximal fault (the MDF) of the NFT system at the eastern Qilian Shan mountain front has remained active when the deformation propagated basinward, a different scenario from that observed at both the western and central Qilian Shan mountain front.

Thin-skinned tectonics of the Upper Ojai Valley and Sulphur Mountain area, Ventura basin, California

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huftile, G.J.

1991-08-01

By integrating surface mapping with subsurface well data and drawing cross sections and subsurface maps, the geometry of shallow structures and their geologic history of the Upper Ojai Valley of California can be reconstructed. The geometry of shallow structures, the geologic history, and the location of earthquake foci then offer constraints on the deep structure of this complex area. The Upper Ojai Valley is a tectonic depression between opposing reverse faults. Its northern border is formed by the active, north-dipping San Cayetano fault, which has 6.0 km of stratigraphic separation in the Silverthread area of the Ojai oil field andmore » 2.6 km of stratigraphic separation west of Sisar Creek. The fault dies out farther west in Ojai Valley, where the south-vergent shortening is transferred to a blind thrust. The southern border of the Upper Ojai Valley is formed by the Quaternary Lion fault set, which dips south and merges into the Sisar decollement within the south-dipping, ductile, lower Miocene Rincon formation. By the middle Pleistocene, the Sulphur Mountain anticlinorium and the Big Canyon syncline began forming as a fault-propagation fold; the fault-propagation fold is rooted in the Sisar decollement, a passive backthrust rising from a blind thrust at depth. The formation of the Sulphur Mountain anticlinorium was followed closely by the ramping of the south-dipping Lion fault set to the surface over the nonmarine upper Pleistocene Saugus Formation. To the east, the San Cayetano fault overrides and folds the Lion Fault set near the surface. Area-balancing of the deformation shows shortening of 15.5 km, and suggests a 17 km depth to the brittle-ductile transition.« less

Restoration of the Cretaceous uplift of the Harz Mountains, North Germany: evidence for the geometry of a thick-skinned thrust

NASA Astrophysics Data System (ADS)

Tanner, David C.; Krawczyk, Charlotte M.

2017-04-01

Reverse movement on the Harz Northern Boundary Fault was responsible for the Late Cretaceous uplift of the Harz Mountains in northern Germany. Using the known geometry of the surface position and dip of the fault, and a published cross section of the Base Permian horizon, we show that it is possible to predict the probable shape of the fault at depth, down to a detachment level. We use the `inclined-shear' method with constant heave and argue that a shear angle of 30° was most likely. In this case, the detachment level is at a depth of ca. 25 km. Kinematic restoration of the Harz Mountains using this fault geometry does not produce a flat horizon, rather it results in a ca. 4 km depression. Airy-Heiskanen isostatic equilibrium adjustment of the Harz Mountains restores the Base Permian horizon to the horizontal, as well as raising the Moho to a depth of 32 km, a typical value for northern Germany. Restoration also causes a rotation of tectonic fabrics within the Harz Mountains of about 11° clockwise. We show that this model geometry is very good fit to the interpreted DEKORP BASIN 9601 deep seismic profile.

Pennsylvanian-Permian tectonism in the Great Basin: The Dry Mountain trough and related basins

DOE Office of Scientific and Technical Information (OSTI.GOV)

Snyder, W.S.; Spinosa, C.; Gallegos, D.M.

1991-02-01

Pennsylvanian-Permian tectonism affected the continental margin of western North America from the Yukon to the Mojave Desert. Specific signatures of this tectonism include local angular unconformities, regional disconformities, renewed outpouring of clastic debris from a reactivated Antler and related highlands, and development of deeper water basins with anoxic sediments deposited below wave base. The basins formed include Ishbel trough (Canada), the Wood River basin (Idaho), Cassia basin, Ferguson trough, Dry Mountain trough (all Nevada), and unnamed basins in Death Valley-Mojave Desert region. The Dry Mountain trough (DMT) was initiated during early Wolfcampian and received up to 1,200 m of sedimentmore » by the late Leonardian. The lower contact is a regional unconformity with the Ely Limestone, or locally with the Diamond Peak or Vinini formations. Thus, following a period of localized regional uplift that destroyed the Ely basin, portions of the uplifted and exposed shelf subsided creating the Dry Mountain trough. Evidence suggesting a tectonic origin for the DMT includes (1) high subsidence rates (60-140 m/m.y.); (2) renewed influx of coarse clastic debris from the Antler highlands: (3) possible pre-Early Permian folding, thrusting, and tilting within the highlands; and (4) differential subsidence within the Dry Mountain trough, suggesting the existence of independent fault blocks.« less

Large-scale deformation related to the collision of the Aleutian Arc with Kamchatka

USGS Publications Warehouse

Gesit, Eric L.; Scholl, David W.

1994-01-01

The far western Aleutian Island Arc is actively colliding with Kamchatka. Westward motion of the Aleutian Arc is brought about by the tangential relative motion of the Pacific plate transferred to major, right-lateral shear zones north and south of the arc. Early geologic mapping of Cape Kamchatka (a promontory of Kamchatka along strike with the Aleutian Arc) revealed many similarities to the geology of the Aleutian Islands. Later studies support the notion that Cape Kamchatka is the farthest west Aleutian “island” and that it has been accreted to Kamchatka by the process of arc-continent collision. Deformation associated with the collision onshore Kamchatka includes gravimetrically determined crustal thickening and formation of a narrow thrust belt of intensely deformed rocks directly west of Cape Kamchatka. The trend of the thrust faults is concave toward the collision zone, indicating a radial distribution of maximum horizontal compressive stress. Offshore, major crustal faults trend either oblique to the Kamchatka margin or parallel to major Aleutian shear zones. These offshore faults are complex, accommodating both strike-slip and thrust displacements as documented by focal mechanisms and seismic reflection data. Earthquake activity is much higher in the offshore region within a zone bounded to the north by the northernmost Aleutian shear zone and to the west by an apparent aseismic front. Analysis of focal mechanisms in the region indicate that the present-day arc-continent “contact zone” is located directly east of Cape Kamchatka. In modeling the dynamics of the collision zone using thin viscous sheet theory, the rheological parameters are only partially constrained to values of n (the effective power law exponent) ≥ 3 and Ar(the Argand number) ≤ 30. These values are consistent with a forearc thermal profile of Kamchatka, previously determined from heat flow modeling. The thin viscous sheet modeling also indicates that onshore thrust faulting is a consequence, not only of compressive stresses resulting from the west directed collision, but also of sediment-induced coupling of the subducting Pacific plate.

Sandstone provenance and tectonic evolution of the Xiukang Mélange from Neotethyan subduction to India-Asia collision (Yarlung-Zangbo suture, south Tibet)

NASA Astrophysics Data System (ADS)

An, Wei; Hu, Xiumian; Garzanti, Eduardo

2016-04-01

The Xiukang Mélange of the Yarlung-Zangbo suture zone in south Tibet documents low efficiency of accretion along the southern active margin of Asia during Cretaceous Neotethyan subduction, followed by final development during the early Paleogene stages of the India-Asia collision. Here we investigate four transverses in the Xigaze area (Jiding, Cuola Pass, Riwuqi and Saga), inquiry the composition in each transverse, and present integrated petrologic, U-Pb detrital-zircon geochronology and Hf isotope data on sandstone blocks. In fault contact with the Yarlung-Zangbo Ophiolite to the north and the Tethyan Himalaya to the south, the Xiukang mélange can be divided into three types: serpentinite-matrix mélange composed by broken Yarlung-Zangbo Ophiolite, thrust-sheets consisting mainly chert, quartzose or limestone sheets(>100m) with little intervening marix, and mudstone-matrix mélange displaying typical blocks-in-matrix texture. While serpentinite-matrix mélange is exposed adjacent to the ophiolite, distributions of thrust-sheets and blocks in mudstone-matrix mélange show along-strike diversities. For example, Jiding transverse is dominant by chert sheets and basalt blocks with scarcely sandstone blocks, while Cuola Pass and Saga transverses expose large amounts of limestone/quartzarenite sheets in the north and volcaniclastic blocks in the south. However, turbidite sheets and volcaniclastic blocks are outcropped in the north Riwuqi transverse with quartzarenite blocks preserved in the south. Three groups of sandstone blocks/sheets with different provenance and depositional setting are distinguished by their petrographic, geochronological and isotopic fingerprints. Sheets of turbiditic quartzarenite originally sourced from the Indian continent were deposited in pre-Cretaceous time on the northernmost edge of the Indian passive margin and eventually involved into the mélange at the early stage of the India-Asia collision. Two distinct groups of volcaniclastic-sandstone blocks were derived from the central Lhasa block and Gangdese magmatic arc. One group was deposited in the trench and/or on the trench slope of the Asian margin during the early Late Cretaceous, and the other group in a syn-collisional basin just after the onset of the India-Asia collision in the Early Eocene. The largely erosional character of the Asian active margin in the Late Cretaceous is indicated by the scarcity of off-scraped trench-fill deposits and the relatively small subduction complex developed during limited episodes of accretion. The Xiukang Mélange was finally structured in the Late Paleocene/Eocene, when sandstone of both Indian and Asian origin were progressively incorporated tectonically in the suture zone of the nascent Himalayan Orogen.

Crustal velocity structure and earthquake processes of Garhwal-Kumaun Himalaya: Constraints from regional waveform inversion and array beam modeling

NASA Astrophysics Data System (ADS)

Negi, Sanjay S.; Paul, Ajay; Cesca, Simone; Kamal; Kriegerowski, Marius; Mahesh, P.; Gupta, Sandeep

2017-08-01

In order to understand present day earthquake kinematics at the Indian plate boundary, we analyse seismic broadband data recorded between 2007 and 2015 by the regional network in the Garhwal-Kumaun region, northwest Himalaya. We first estimate a local 1-D velocity model for the computation of reliable Green's functions, based on 2837 P-wave and 2680 S-wave arrivals from 251 well located earthquakes. The resulting 1-D crustal structure yields a 4-layer velocity model down to the depths of 20 km. A fifth homogeneous layer extends down to 46 km, constraining the Moho using travel-time distance curve method. We then employ a multistep moment tensor (MT) inversion algorithm to infer seismic moment tensors of 11 moderate earthquakes with Mw magnitude in the range 4.0-5.0. The method provides a fast MT inversion for future monitoring of local seismicity, since Green's functions database has been prepared. To further support the moment tensor solutions, we additionally model P phase beams at seismic arrays at teleseismic distances. The MT inversion result reveals the presence of dominant thrust fault kinematics persisting along the Himalayan belt. Shallow low and high angle thrust faulting is the dominating mechanism in the Garhwal-Kumaun Himalaya. The centroid depths for these moderate earthquakes are shallow between 1 and 12 km. The beam modeling result confirm hypocentral depth estimates between 1 and 7 km. The updated seismicity, constrained source mechanism and depth results indicate typical setting of duplexes above the mid crustal ramp where slip is confirmed along out-of-sequence thrusting. The involvement of Tons thrust sheet in out-of-sequence thrusting indicate Tons thrust to be the principal active thrust at shallow depth in the Himalayan region. Our results thus support the critical taper wedge theory, where we infer the microseismicity cluster as a result of intense activity within the Lesser Himalayan Duplex (LHD) system.

The anatomy of a major late-stage thrust and implications for models of late-stage collisional orogenesis in the Caledonian crust of northern Scandinavia

NASA Astrophysics Data System (ADS)

Anderson, Mark; Hames, Willis; Stokes, Alison

2010-05-01

Within the stack of Caledonian crystalline thrust sheets of northern Scandinavia, a single amphibolite facies lithotectonic unit, the Småtinden nappe, is identified as a major, basement-coupled ("stretching") shear zone. This dominantly pelitic unit achieved peak metamorphic conditions of 535-550°C and 8-9kbars, and the stretching geometry suggests that this most likely occurred in response to overthrusting of a hot, pre-assembled Caledonian thrust stack. Along-strike variations in microstructural geometries and patterns of mineral zoning in widely developed porphyroblast phases suggest, however, subsequent strain partitioning within the zone during late-stage decoupling of the thrust stack from the basement along major out-of-sequence thrusts. Large parts of the nappe are characterised by relatively late, static growth preserving concordant Si-Se relationships, and typically symmetrical external fabrics consistent with formation under dominantly pure shear conditions. In the Salangen area, however, the nappe is characterised by early garnet growth, with discordant Si-Se relationships and asymmetric external fabric geometries consistent with formation during ESE-directed simple shear. Remarkably consistent thermometric estimates from chlorites in both regimes (post- and syn-shearing) suggest that out-of-sequence ramping occurred at temperatures in the range 370-400 ̊C, within the typical range of blocking temperatures for argon retention in muscovite. 40Ar-39Ar dating of muscovites from S-C fabrics in the out-of-sequence shear zone suggest that late-stage thrusting occurred during the middle-late Devonian (ca. 395-375 Ma). Hanging-wall and footwall geometries coupled with these radiometric dates indicate that the development of these late thrusts closely relates to reactivation of pre-Caledonian Baltic basement during the Devonian (400-370 Ma). East-west contraction during the upper end of this time frame is peculiar considering that this was the period of large magnitude and rapid extension in western Norway.

A generalized vortex theory of the screw propeller and its application

NASA Technical Reports Server (NTRS)

Reissner, Hans

1940-01-01

The vortex theory as presented by the author in earlier papers has been extended to permit the solution of the following problems: (1) the investigation of the relation between thrusts and torque distribution and energy loss as given by the induction of helical vortex sheets and by the parasite drag; (2) the checking of the theorem of Betz of the rigidly behaving helical vortex sheet of minimum induced energy loss; (3) the extension of the theory of the screw propeller of minimum energy loss for the inclusion of parasite-drag distribution along the blades. A simple system of diagrams has been developed to systematize the design of airplane propellers for a wide range of parasite-drag distribution along the blades.

Paleomagnetism and magnetic fabric of the Eastern Cordillera of Colombia: Evidence for oblique convergence and non-rotational reactivation of a Mesozoic intra-continental rift

NASA Astrophysics Data System (ADS)

Jiménez Díaz, G.; Speranza, F.; Faccenna, C.; Bayona, G.; Mora, A.

2012-12-01

The Eastern Cordillera of Colombia (EC) is a double-verging mountain system inverting a Mesozoic rift, and bounded by major reverse faults that locally involve crystalline and metamorphic Precambrian-Lower Paleozoic basement rocks, as well as Upper Paleozoic-Cenozoic sedimentary and volcanic sequences. In map view the EC is a curved mountain belt with a regional structural strike that ranges from NNE in the southern part to NNW in the northern part. The origin of its curvature has not been studied or discussed so far. We report on an extensive paleomagnetic and anisotropy of magnetic susceptibility (AMS) investigation of the EC, in order to address to test its non-rotational vs. oroclinal nature. Fifty-eight sites were gathered from Cretaceous to Miocene marine and continental strata, both from the southern and northern parts of the EC; additionally, we examined the southern Maracaibo plate, at the junction between the Santander Massif and the Merida Andes of Colombia (Cucuta zone). Twenty-three sites reveal no rotation of the EC range with respect to stable South America. In contrast, a 35°±9° clockwise rotation is documented in four post-Miocene magnetically overprinted sites from the Cucuta zone. Magnetic lineations from AMS analysis do not trend parallel to the chain, but are oblique to the main strike of the orogenic belt. By also considering GPS evidence of a ~1 cm/yr ENE displacement of central-western Colombia accommodated by the EC, we suggest that the late Miocene-recent deformation occurred by a ENE oblique convergence reactivating a NNE rift zone. Our data show that the EC is a non-rotational chain, and that the locations of the Mesozoic rift and the mountain chain roughly correspond. One possible solution is that the oblique shortening is partitioned in pure dip-slip shear characterizing thick-skinned frontal thrust sheets (well-known along both chain fronts), and by range-parallel right-lateral strike-slip fault(s), which have not been identified yet and likely occur in the axial part of the EC. The clockwise rotation in the Cucuta zone reflects late Cenozoic and ongoing right-lateral strike-slip displacement occurring along buried faults parallel to the Boconó fault system, possibly connected with the right-lateral faults inferred along the axial part of the EC.

Deep crustal structure of the northeastern margin of the Arabian plate from seismic and gravity data

NASA Astrophysics Data System (ADS)

Pilia, Simone; Ali, Mohammed; Watts, Anthony; Keats, Brook; Searle, Mike

2017-04-01

The United Arab Emirates-Oman mountains constitute a 700 km long, 50 km wide compressional orogenic belt that developed during the Cainozoic on an underlying extensional Tethyan rifted margin. It contains the world's largest and best-exposed thrust sheet of oceanic crust and upper mantle (Semail Ophiolite), which was obducted onto the Arabian rifted continental margin during the Late Cretaceous. Although the shallow structure of the UAE-Oman mountain belt is reasonably well known through the exploitation of a diverse range of techniques, information on deeper structure remains little. Moreover, the mechanisms by which dense oceanic crustal and mantle rocks are emplaced onto less dense and more buoyant continental crust are still controversial and remain poorly understood. The focus here is on an active-source seismic and gravity E-W transect extending from the UAE-mountain belt to the offshore. Seismic refraction data were acquired using the survey ship M/V Hawk Explorer, which was equipped with a large-volume airgun array (7060 cubic inches, 116 liters). About 400 air gun shots at 50-second time interval were recorded on land by eight broadband seismometers. In addition, reflection data were acquired at 20 seconds interval and recorded by a 5-km-long multichannel streamer. Results presented here include an approximately 85 km long (stretching about 35 km onshore and 50 km offshore) P-wave velocity crustal profile derived by a combination of forward modelling and inversion of both diving and reflected wave traveltimes using RAYINVR software. We employ a new robust algorithm based on a Monte Carlo approach (VMONTECARLO) to address the velocity model uncertainties. We find ophiolite seismic velocities of about 5.5 km/s and a thick sedimentary package in the offshore. Furthermore, the velocity model reveals a highly stretched crust with the Moho discontinuity lying at about 20 km. A prestack depth-migrated profile (about 50 km long) coincident with the offshore part of the refraction profile shows a thick sequence (up to about 10 km) of seaward dipping sediments that are offset by a number of listric (normal) faults, some of which intersect the seabed and so reflect recent tectonic activity. The trend of the Bouguer anomaly provides further constraints on the deeper structure of the margin and appears to confirm the presence of a stretched crust.

Interseismic coupling, seismic potential, and earthquake recurrence on the southern front of the Eastern Alps (NE Italy)

NASA Astrophysics Data System (ADS)

Cheloni, D.; D'Agostino, N.; Selvaggi, G.

2014-05-01

Here we use continuous GPS observations to document the geodetic strain accumulation across the South-Eastern Alps (NE Italy). We estimate the interseismic coupling on the intracontinental collision thrust fault and discuss the seismic potential and earthquake recurrence. We invert the GPS velocities using the back slip approach to simultaneously estimate the relative angular velocity and the degree of interseismic coupling on the thrust fault that separates the Eastern Alps and the Venetian-Friulian plain. Comparison between the rigid rotation predicted motion and the shortening observed across the area indicates that the South-Eastern Alpine thrust front absorbs about 70% of the total convergence between the Adria and Eurasia plates. The coupling is computed on a north dipping fault following the continuous external seismogenic thrust front of the South-Eastern Alps. The modeled thrust fault is currently locked from the surface to a depth of ≈10 km. The transition zone between locked and creeping portions of the fault roughly corresponds with the belt of microseismicity parallel and to the north of the mountain front. The estimated moment deficit rate is 1.3 ± 0.4 × 1017 Nm/yr. The comparison between the estimated moment deficit and that released historically by the earthquakes suggests that to account for the moment deficit the following two factors or their combination should be considered: (1) a significant part of the observed interseismic coupling is released aseismically and (2) infrequent "large" events with long return period (> 1000 years) and with magnitudes larger than the value assigned to the largest historical events (Mw≈ 6.7).

Crustal structure and evolution of the Pyrenean-Cantabrian belt: A review and new interpretations from recent concepts and data

NASA Astrophysics Data System (ADS)

Teixell, A.; Labaume, P.; Ayarza, P.; Espurt, N.; de Saint Blanquat, M.; Lagabrielle, Y.

2018-01-01

This paper provides a synthesis of current data and interpretations on the crustal structure of the Pyrenean-Cantabrian orogenic belt, and presents new tectonic models for representative transects. The Pyrenean orogeny lasted from Santonian ( 84 Ma) to early Miocene times ( 20 Ma), and consisted of a spatial and temporal succession of oceanic crust/exhumed mantle subduction, rift inversion and continental collision processes at the Iberia-Eurasia plate boundary. A good coverage by active-source (vertical-incidence and wide-angle reflection) and passive-source (receiver functions) seismic studies, coupled with surface data have led to a reasonable knowledge of the present-day crustal architecture of the Pyrenean-Cantabrian belt, although questions remain. Seismic imaging reveals a persistent structure, from the central Pyrenees to the central Cantabrian Mountains, consisting of a wedge of Eurasian lithosphere indented into the thicker Iberian plate, whose lower crust is detached and plunges northwards into the mantle. For the Pyrenees, a new scheme of relationships between the southern upper crustal thrust sheets and the Axial Zone is here proposed. For the Cantabrian belt, the depth reached by the N-dipping Iberian crust and the structure of the margin are also revised. The common occurrence of lherzolite bodies in the northern Pyrenees and the seismic velocity and potential field record of the Bay of Biscay indicate that the precursor of the Pyrenees was a hyperextended and strongly segmented rift system, where narrow domains of exhumed mantle separated the thinned Iberian and Eurasian continental margins since the Albian-Cenomanian. The exhumed mantle in the Pyrenean rift was largely covered by a Mesozoic sedimentary lid that had locally glided along detachments in Triassic evaporites. Continental margin collision in the Pyrenees was preceded by subduction of the exhumed mantle, accompanied by the pop-up thrust expulsion of the off-scraped sedimentary lid above. To the west, oceanic subduction of the Bay of Biscay under the North Iberian margin is supported by an upper plate thrust wedge, gravity and magnetic anomalies, and 3D inclined sub-crustal reflections. However, discrepancies remain for the location of continent-ocean transitions in the Bay of Biscay and for the extent of oceanic subduction. The plate-kinematic evolution during the Mesozoic, which involves issues as the timing and total amount of opening, as well as the role of strike-slip drift, is also under debate, discrepancies arising from first-order interpretations of the adjacent oceanic magnetic anomaly record.

Crustal shortening followed by extensional collapse of the Cordilleran orogenic belt in northwestern Montana: Evidence from vintage seismic reflection profiles acquired in the Swan Range and Swan Valley

NASA Astrophysics Data System (ADS)

Rutherford, B. S.; Speece, M. A.; Stickney, M. C.; Mosolf, J. G.

2013-12-01

Reprocessing of one 24-fold (96 channel) and four 30-fold (120 channel) 2D seismic reflection profiles have revealed crustal scale reflections in the Swan Range and adjacent Swan River Valley of northwestern Montana. The five reprocessed profiles constitute 142.6 of the 303.3 linear km acquired in 1983-84 by Techo of Denver, Colorado. The four 30-fold profiles used helicopter-assisted dynamite shooting (Poulter method) and the 24-fold profile used the Vibroseis method. Acquisition parameters were state of the art for the time. The Swan Range lies east of the Rocky Mountain Trench and is part of the Cordilleran foreland thrust belt where the Lewis thrust system emplaced a thick slab of Proterozoic Belt Supergroup strata eastward and over Paleozoic and Mesozoic rocks during the Late Cretaceous to early Paleocene Laramide orogeny. Deeply drilled borehole data are absent within the study area; however, we generated a synthetic seismogram from the Arco-Marathon 1 Paul Gibbs well (total depth=5418 m), located approximately 70 km west of the reprocessed profiles, and correlated the well data to surface seismic profiles. Large impedance contrasts in the log data are interpreted to be tholeiitic Moyie sills within the Prichard Formation argillite (Lower Belt), which produce strong reflection events in regional seismic sections and result in highly reflective, east-dipping events in the reprocessed profiles. We estimate a depth of 10 km (3 to 3.5 seconds) to the basal detachment of the Lewis thrust sheet. The décollement lies within Belt Supergroup strata to the west of the Swan River Valley before contacting unreflective, west-dipping crystalline basement beneath the Swan Range--a geometry that results in a wedge of eastward-thinning, autochthonous Belt rocks. Distinct fault-plane signatures from the west-dipping, range-bounding Swan fault--produced by extensional collapse of the over-thickened Cordillera--are not successfully imaged. However, reflections from Cenozoic half-graben fill suggest up to 1.5 km of Cenozoic basin filling sediments are present. Refraction tomography velocity modeling of distinct refracted arrivals, prevalent in the gathers, constrain a half-graben geometry for the Swan Valley. Signal attenuation within the low-velocity valley fill make correlation of reflectors at the depth of the décollement impossible underneath the Swan Valley. Prestack depth migration of the sections is anticipated to improve geometric constraints on major structural features of the Swan Range and Swan Valley.

Active deformation and seismicity in the Southern Alps (Italy): The Montello hill as a case study

NASA Astrophysics Data System (ADS)

Danesi, Stefania; Pondrelli, Silvia; Salimbeni, Simone; Cavaliere, Adriano; Serpelloni, Enrico; Danecek, Peter; Lovati, Sara; Massa, Marco

2015-06-01

The Montello anticline is a morphotectonic feature of the east pede-mountain of the South Alpine Chain in northern Italy, which lies ca. 40 km northwest of Venice, Italy. The purpose of this study is to characterize the present-day crustal deformation and seismotectonics of the Montello area through multi-parametric geophysical observations. We used new data obtained from the installation of a temporary network of 12 seismic stations and 6 GPS sites. The GPS observations indicate that there is ~ 1 mm/yr shortening across the Montello thrust. Sites located north of the Montello thrust front deviate from the ~ NNW-ward Adria-Eurasia convergence direction, as they are constrained by a relative rotation pole in northwestern Italy that has a NNE-ward motion trend. Over 18 months, seismographic recordings allowed us to locate 142 local seismic events with Ml 0.5-3.5 with good reliability (rms < 0.5). After cross-correlation analysis, we classified 42 of these events into six clusters, with cross-correlation thresholds > 0.80. The source focal solutions indicate that: (i) there is thrusting seismic activity on the basal, sub-horizontal, portion of the Montello structure; and (ii) strike-slip source kinematics prevail on the western edge of the Montello hill. Our observations on the source mechanisms and the measured crustal deformation confirm that the Montello thrust is tectonically active.

The Junction of Hellenic and Cyprus Arcs: the Bey Daglari Lineament, Offshore Termination of the Antalya Basin

NASA Astrophysics Data System (ADS)

Gogacz, A.; Hall, J.; Cifci, G.; Yasar, D.; Kucuk, M.; Yaltirak, C.; Aksu, A.

2009-05-01

The Antalya Basin is one of a series of basins that sweep along the Cyprus Arc in the forearc region between the (formerly) volcanic Tauride Mountains on Turkey in the north and the subduction zone and associated suture between the African plate and the Aegean-Anatolian microplate in the eastern Mediterranean, south of Cyprus. Miocene contraction occurs widely on southwest verging thrusts. Pliocene-Quaternary structures vary from extension/transtension in the northeast, adjacent to the Turkish coastline, to transpression in the southwest, farther offshore. All these structures are truncated at the northwest end of the Antalya Basin by a broad zone of NNE-SSW-trending transverse structure that appears to represent a prolongation of the extreme easterly transform end of the Hellenic arc. Our mapping suggests that this broad zone links the Hellenic Arc with the Isparta Angle in southern Turkey, which we suggest is an earlier location of the junction of Hellenic and Cyprus Arcs: the junction migrated to the southwest over time, as the Hellenic Arc rolled back. The Turkish coastline turns from parallel to the Antalya Basin structures in the east to a N-S orientation, cutting across the trend of the Antalya Basin. The Antalya Complex and the Bey Dağları Mountains provide a spectacular backdrop to this edge of the offshore basin. Somewhere offshore lies the structural termination of the Antalya Basin. In 2001, we acquired around 400 km of high-resolution multi-channel seismic reflection data across the western end of the Antalya Basin to explore the nature of the termination, which we call the Bey Dağları lineament. We present a selection of the seismic profiles with interpretation of the nature and Neogene history of the lineament. Landward of the N-S-trending coastline, ophiolites of the Antalya Complex are exposed in a series of westerly-verging thrust slivers that extend to the carbonate sequences of the Bey Dağları Mountains. Our seismic data indicate that N-S trending west- and east-verging thrusts define a transpressional continental margin. The shelf is underlain by a prominent angular unconformity between overlying shallow-dipping Pliocene-Quaternary sediments and underlying, easterly- dipping ?Miocene sediments.

Source and tectonic implications of tonalite-trondhjemite magmatism in the Klamath Mountains

USGS Publications Warehouse

Barnes, C.G.; Petersen, S.W.; Kistler, R.W.; Murray, R.; Kays, M.A.

1996-01-01

In the Klamath Mountains, voluminous tonalite-trondhjemite magmatism was characteristic of a short period of time from about 144 to 136 Ma (Early Cretaceous). It occurred about 5 to l0 m.y. after the ??? 165 to 159 Ma Josephine ophiolite was thrust beneath older parts of the province during the Nevadan orogeny (thrusting from ??? 155 to 148 Ma). The magmatism also corresponds to a period of slow or no subduction. Most of the plutons crop out in the south-central Klamath Mountains in California, but one occurs in Oregon at the northern end of the province. Compositionally extended members of the suite consist of precursor gabbroic to dioritic rocks followed by later, more voluminous tonalitic and trondhjemitic intrusions. Most plutons consist almost entirely of tonalite and trondhjemite. Poorlydefined concentric zoning is common. Tonalitic rocks are typically of the Iow-Al type but trondhjemites are generally of the high-Al type, even those that occur in the same pluton as low-Al tonalite??. The suite is characterized by low abundances of K2O, Rb, Zr, and heavy rare earth elements. Sr contents are generally moderate ( ???450 ppm) by comparison with Sr-rich arc lavas interpreted to be slab melts (up to 2000 ppm). Initial 87Sr/ 86Sr, ??18O, and ??Nd are typical of mantle-derived magmas or of crustally-derived magmas with a metabasic source. Compositional variation within plutons can be modeled by variable degrees of partial melting of a heterogeneous metabasaltic source (transitional mid-ocean ridge to island arc basalt), but not by fractional crystallyzation of a basaltic parent. Melting models require a residual assemblage of clinopyroxene+garnet??plagioclase??amphibole; residual plagioclase suggests a deep crustal origin rather than melting of a subducted slab. Such models are consistent with the metabasic part of the Josephine ophiolite as the source. Because the Josephine ophiolite was at low T during Nevadan thrusting, an external heat source was probably necessary to achieve significant degrees of melting; heat was probably extracted from mantle-derived basaltic melts, which were parental to the mafic precursors of the tonalite-trondhjemite suite. Thus, under appropriate tectonic and thermal conditions, heterogeneous mafic crustal rocks can melt to form both low- and high-Al tonalitic and trondhjemitic magmas; slab melting is not necessary.

Role of Fluids in Mechanics of Overthrust Faulting on Titan

NASA Astrophysics Data System (ADS)

Liu, Z.; Radebaugh, J.; Harris, R. A.; Christiansen, E. H.

2013-12-01

Since Cassini has unveiled Titan's surface, its mountains have been commonly associated with contractional tectonism. However, in order to form contractional structures on icy satellites, relatively large stresses are required. The stress required to form contractional structures on Ganymede and Europa is 3-8 times that required for extensional features. Sources of such stresses probably do not exist for most icy satellites. Therefore, a paradox has emerged, wherein no stress source is known that is large enough to produce the contractional structures observed on Titan. A possible solution for the strength paradox is inspired by Hubbert and Rubey (1959) who demonstrated how high fluid pressures reduce the normal stress along a fault plane, therefore significantly reducing frictional resistance to thrusting. Since liquid hydrocarbons have been identified on Titan's surface and may flow in the subsurface, we speculate that fluid pressures associated with liquid hydrocarbons in the subsurface significantly reduce the shear strength of the icy crust and enable contractional structures to form without the requiring large stresses. We use critical wedge theory, which is a mechanism for driving fold-and-thrust belt formation, to test if the slope angles of mountains and crustal conditions with estimated fluid pressures favor the formation of fold-thrust belts on Titan. We evaluated 6 mountain belts with available Cassini SARTopo data using critical wedge calculations. The slopes of 10 traces from valley floors to summits are between 0.4 and 2.5 degrees. We use the measured slopes with varying friction coefficients and fluid pressures to calculate the range of dip angles. The results yielded 840 dip angle values, 689 (82%) of which were in a reasonable range, and consistent with fold belt formation in critical wedge settings. We conclude that crustal liquids have played a key role in Titan's tectonic history. Our results highlight the significance of fluids in planetary lithospheres and have implications for tectonics on all solid bodies that may have fluid in their lithospheres, now or in the past. Reference: Hubbert, M. K. & Rubey, W. W. Role of fluid pressure in mechanics of overthrust faulting I. Mechanics of fluid-filled porous solids and its application to overthrust faulting. Geol. Soc. Am. Bull. 70, 2, 115-166 (1959).

Terrestrial ice streams-a view from the lobe

USGS Publications Warehouse

Jennings, C.E.

2006-01-01

The glacial landforms of Minnesota are interpreted as the products of the lobate extensions of ice streams that issued from various ice sheds within the Laurentide Ice Sheet. Low-relief till plains, trough-shaped lowlands, boulder pavements, and streamlined forms make up the subglacial landsystem in Minnesota that is interpreted as having been formed by streaming ice. Extremely uniform tills are created subglacially in a way that remains somewhat mysterious. At the ice margins, thrust moraines and hummocky stagnation topography are more common than single-crested, simple moraines if the ice lobes had repeated advances. Subglacial drainage features are obscure up-ice but are present down-ice in the form of tunnel valleys, eskers, Spooner hills, and associated ice-marginal fans. Ice streaming may occur when basal shear stress is lowered as a result of high subglacial water pressure. Subglacial conditions that allow the retention of water will allow an ice lobe to extend far beyond the ice sheet as long as the ice shed also supports the advance by supplying adequate ice. Even with adequate ice flux, however, the advance of an ice lobe may be terminated, at least temporarily, if the subglacial water is drained, through tunnel valleys or perhaps a permeable substrate. Thrust moraines, and ice stagnation topography will result from sudden drainage. Although climate change is ultimately responsible for the accumulation of ice in the Laurentide Ice Sheet, the asynchronous advances and retreats of the ice lobes in the mid-continent are strongly overprinted by the internal dynamics of individual ice streams as well as the interaction of ice sheds, which obscure the climate signal. ?? 2005 Elsevier B.V. All rights reserved.

Paleoseismology at high latitudes: Seismic disturbance of upper Quaternary deposits along the Castle Mountain fault near Houston, Alaska

USGS Publications Warehouse

Haeussler, Peter J.; Best, Timothy C.; Waythomas, Christopher F.

2002-01-01

Most paleoseismic studies are at low to moderate latitudes. Here we present results from a high-latitude (61°30′ N) trenching study of the Castle Mountain fault in south-central Alaska. This fault is the only one known in the greater Anchorage, Alaska, area with historical seismicity and a Holocene fault scarp. It strikes east-northeast and cuts glacial and postglacial sediments in an area of boreal spruce-birch forest, shrub tundra, and sphagnum bog. The fault has a prominent vegetation lineament on the upthrown, north side of the fault. Nine trenches were logged across the fault in glacial and postglacial deposits, seven along the main trace, and two along a splay. In addition to thrust and strike-slip faulting, important controls on observed relationships in the trenches are the season in which faulting occurred, the physical properties of the sediments, liquefaction, a shallow water table, soil-forming processes, the strength of the modern root mat, and freeze-thaw processes. Some of these processes and physical properties are unique to northern-latitude areas and result in seismic disturbance effects not observed at lower latitudes.The two trenches across the Castle Mountain fault splay exposed a thrust fault and few liquefaction features. Radiocarbon ages of soil organic matter and charcoal within and overlying the fault indicate movement on the fault at ca. 2735 cal. (calendar) yr B.P. and no subsequent movement. In the remaining seven trenches, surface faulting was accompanied by extensive liquefaction and a zone of disruption 3 m or more wide. The presence of numerous liquefaction features at depths of <0.5–1.0 m indicates faulting when the ground was not frozen—i.e., from about April to October. Sandy-matrix till, sand, silt, gravel, and pebbly peat were injected up to the base of the modern soil, but did not penetrate the interlocking spruce-birch root mat. The strength of the root mat prohibited development of a nonvegetated scarp face and colluvial wedge. In only one trench did we observe a discrete fault plane with measurable offset. It lay beneath a 2-m-thick carapace of liquefied sand and silt and displayed a total of 0.9–1.85 m of thrust motion since deposition of the oldest deposits in the trenches at ca. 13,500 yr B.P. We found liquefaction ejecta on paleosols at only one other trench, where there were bluejoint (Calamagrostis canadensis) tussocks that lacked an extensive root mat. From crosscutting relationships, we interpret three paleoliquefaction events on the main trace of the Castle Mountain fault: 2145–1870, 1375–1070, and 730–610 cal. yr B.P. These four earthquakes on the Castle Mountain fault in the past ∼2700 yr indicate an average recurrence interval of ∼700 yr. As it has been 600–700 yr since the last significant earthquake, a significant (magnitude 6–7) earthquake in the near future may be likely. Paleoseismic data indicate that the timing and recurrence interval of megathrust earthquakes is similar to the timing and recurrence interval of Castle Mountain fault earthquakes, suggesting a possible link between faulting on the megathrust and on “crustal” structures.

Applied geochemistry, geology and mineralogy of the northernmost Carlin trend, Nevada

USGS Publications Warehouse

Theodore, T.G.; Kotlyar, B.B.; Singer, D.A.; Berger, V.I.; Abbott, E.W.; Foster, A.L.

2003-01-01

Investigations in the northernmost Carlin trend were undertaken to advance understanding of the geochemical signatures and genesis of precious metal deposits in the trend. Two fundamental geologic relationships near the trend significantly affect regional geochemical distributions: a remarkably intact lower Paleozoic stratigraphic sequence of siliceous rocks in the upper plate of the middle Paleozoic Roberts Mountains thrust, and the widespread repetition of rocks high in the upper plate during late Paleozoic thrusting that thickens the cover above mineralized rock in the lower plate. A compilation of previously published chemical analyses of 440 stream sediment samples and 115 rocks from two 7 1/2-minute quadrangles, as well as new chemical analyses of approximately 1,000 drill core samples in a 1,514 m (4,970 ft) hole through the Rodeo Creek deposit were used to construct three-dimensional element distribution models that highlight metal zonation in the mineralized systems. The Rodeo Creek deposit comprises deep Ag base-metal ?? Au-mineralized rock below the Roberts Mountains thrust and contains an unusually high Ag/Au ratio greater than 30. Stacked geochemical halos related to the deposit are confined to the lower plate of the Roberts Mountains thrust and include two horizons of Hg, Cu, and Zn anomalies-as much as 180 m above the deposit-that mostly result from mercurian sphalerite. Extremely subtle indications of mineralization in the upper plate of the Roberts Mountains thrust above the deposit include arsenopyrite overgrowths on small pyrite crystals in 50- to 75-??m-wide clay-carbonate veinlets that lack alteration halos, arsenical rims on small disseminated crystal of recrystallized diagenetic pyrite, and partial replacement of diagenetic pyrite by tennantite. Some of these minerals contain anomalously high Au. However, these As-(Au)-bearing rocks most likely represent another locus of largely untested mineralized rock rather than distal halos related to either the Rodeo Creek or the nearby Dee and Storm gold deposits. Application of micromineralogic techniques helped to identify mineral assemblages that are specific to mineralization and provided an empirical foundation for interpretations of geochemical halos in the Carlin trend. District-scale geochemical patterns of several elements in stream sediments and surface rocks coincide with the northernmost Carlin trend and can be used to explore for Carlin-type deposits. Concentrations of elevated As and Sb in stream sediments (as much as 54 ppm As) have northwest-elongate lobate patterns that clearly outline the trend across a width of approximately 4 km. Arsenic contents of exposed rocks (as much as 90 ppm As) strongly correlate with As contents of derivative stream sediments, and rock contents of Sb show a somewhat lesser but nonetheless strong and similar correspondence. Factor analysis of stream-sediment data shows that those factor scores that are correlated with As, Sb, Au, and Pb also are high along the trend and suggest that mineralized rocks may be present. Although As was not detected by scanning electron microscope-energy dispersive spectrometer (SEM-EDS) studies in heavy mineral concentrates of high-As stream sediments in the Carlin trend, X-ray absorption near-edge spectra (XANES) of selected light fractions of stream sediment samples indicate that Al-bearing phases, such as gibbsite, amorphous Al oxyhydroxides, or aluminosilicate clay minerals host most of the As(V). The best fit, visually and in terms of the lowest residual, was obtained by a model compound of As(V) sorbed to gibbsite. Thus, most As in stream sediments derived from altered rock within the Carlin trend apparently is contained in light fractions. The geochemical character of young, unconsolidated, postmineral deposits that cover mineralized rocks on the Carlin trend partly results from mineralized sources along the trend. Concentration of As in the Miocene Carlin Formation shows an exceptio

Deglacial history of the Pensacola Mountains, Antarctica from glacial geomorphology and cosmogenic nuclide surface exposure dating

NASA Astrophysics Data System (ADS)

Bentley, M. J.; Hein, A. S.; Sugden, D. E.; Whitehouse, P. L.; Shanks, R.; Xu, S.; Freeman, S. P. H. T.

2017-02-01

The retreat history of the Antarctic Ice Sheet is important for understanding rapid deglaciation, as well as to constrain numerical ice sheet models and ice loading models required for glacial isostatic adjustment modelling. There is particular debate about the extent of grounded ice in the Weddell Sea embayment at the Last Glacial Maximum, and its subsequent deglacial history. Here we provide a new dataset of geomorphological observations and cosmogenic nuclide surface exposure ages of erratic samples that constrain the deglacial history of the Pensacola Mountains, adjacent to the present day Foundation Ice Stream and Academy Glacier in the southern Weddell Sea embayment. We show there is evidence of at least two glaciations, the first of which was relatively old and warm-based, and a more recent cold-based glaciation. During the most recent glaciation ice thickened by at least 450 m in the Williams Hills and at least 380 m on Mt Bragg. Progressive thinning from these sites was well underway by 10 ka BP and ice reached present levels by 2.5 ka BP, and is broadly similar to the relatively modest thinning histories in the southern Ellsworth Mountains. The thinning history is consistent with, but does not mandate, a Late Holocene retreat of the grounding line to a smaller-than-present configuration, as has been recently hypothesized based on ice sheet and glacial isostatic modelling. The data also show that clasts with complex exposure histories are pervasive and that clast recycling is highly site-dependent. These new data provide constraints on a reconstruction of the retreat history of the formerly-expanded Foundation Ice Stream, derived using a numerical flowband model.

Crustal Structure of the Iran Region from In-Country and Ground-Truth Data

DTIC Science & Technology

2008-09-30

thickness in the region (e.g., Mokhtari et al., 2004), and these data will be utilized in our Pn tomography both as constraints and for validation of...Vergne, and M. Mokhtari (2006). Seismological evidence for crustal-scale thrusting in the Zagros mountain belt (Iran), Geophys. J Int. 166: 227-237...for understanding the deformation history of the Arabian-Eurasian collision. Geophvs. J. Int. 172: 1179-1187. Mokhtari , M., A. M. Farahbod, C. Lindholm

Structural controls on Carlin-type gold mineralization in the gold bar district, Eureka County, Nevada

USGS Publications Warehouse

Yigit, O.; Nelson, E.P.; Hitzman, M.W.; Hofstra, A.H.

2003-01-01

The Gold Bar district in the southern Roberts Mountains, 48 km northwest of Eureka, Nevada, contains one main deposit (Gold Bar), five satellite deposits, and other resources. Approximately 0.5 Moz of gold have been recovered from a resource of 1,639,000 oz of gold in Carlin-type gold deposits in lower plate, miogeoclinal carbonate rocks below the Roberts Mountains thrust. Host rocks are unit 2 of the Upper Member of the Devonian Denay Formation and the Bartine Member of the McColley Canyon Formation. Spatial and temporal relations between structures and gold mineralization indicate that both pre-Tertiary and Tertiary structures were important controls on gold mineralization. Gold mineralization occurs primarily along high-angle Tertiary normal faults, some of which are reactivated reverse faults of Paleozoic or Mesozoic age. Most deposits are localized at the intersection of northwest- and northeast-striking faults. Alteration includes decalcification, and to a lesser extent, silicification along high-angle faults. Jasperoid (pervasive silicification), which formed along most faults and in some strata-bound zones, accounts for a small portion of the ore in every deposit. In the Gold Canyon deposit, a high-grade jasperoid pipe formed along a Tertiary normal fault which was localized along a zone of overturned fault-propagation folds and thrust faults of Paleozoic or Mesozoic age.

Paleoseismology of a newly discovered scarp in the Yakima fold-and-thrust belt, Kittitas County, Washington

USGS Publications Warehouse

Barnett, Elizabeth A.; Sherrod, Brian L.; Norris, Robert; Gibbons, Douglas

2013-01-01

The Boylston Mountains anticlinal ridge is one of several that are cored by rocks of the Columbia River Basalt Group and, with the interceding synclinal valleys, constitute the Yakima fold-and-thrust belt of central Washington. Lidar data acquired from the U.S. Army's Yakima Training Center reveal a prominent, northwest-side-up, 65°- to 70°-trending, 3- to 4-meter-high scarp that cuts across the western end of the Boylston Mountains, perpendicular to the mapped anticline. The scarp continues to the northeast from the ridge on the southern side of Park Creek and across the low ridges for a total length of about 3 kilometers. A small stream deeply incises its flood plain where it projects across Johnson Canyon. The scarp is inferred to be late Quaternary in age based on its presence on the modern landscape and the incised flood-plain sediments in Johnson Canyon. Two trenches were excavated across this scarp. The most informative of the two, the Horned Lizard trench, exposed shallow, 15.5-Ma Grande Ronde Basalt, which is split by a deep, wide crack that is coincident with the base of the scarp and filled with wedges of silty gravels that are interpreted to represent at least two generations of fault colluvium that offset a buried soil.

Global glacier and ice sheet surface velocities derived from 31 years of Landsat imagery

NASA Astrophysics Data System (ADS)

Gardner, A. S.; Scambos, T. A.; Fahnestock, M. A.

2016-12-01

Glaciers and ice sheets are contributing substantial volumes of water to the world's oceans due to enhanced melt resulting from changes in ocean and atmospheric conditions and respective feedbacks. Improving understanding of the processes leading to accelerated rates of ice loss is necessary for reducing uncertainties sea level projections. One key to doing this is to assemble and analyze long records of glacier change that characterize grounded ice response to changes in driving stress, buttressing, and basal conditions. As part of the NASA funded GO_LIVE project we exploit 31 years of Landsat imagery to construct detailed time histories of global glacier velocities. Early exploration of the dataset reveals the diversity of information to be gleaned: sudden tidewater glacier speedups in the Antarctic Peninsula, rifting of Antarctic ice shelves, high variability in velocities near glacier grounding lines, frequent surge activity in the mountainous regions of Alaska and High Mountain Asia, and the slowdown of land-terminating valley glaciers in Arctic Canada and elsewhere.

Evidence of rapid Cenozoic uplift of the shoulder escarpment of the Cenozoic West Antarctic rift system and a speculation on possible climate forcing

USGS Publications Warehouse

Behrendt, John C.; Cooper, A.

1991-01-01

The Cenozoic West Antarctic rift system, characterized by Cenozoic bimodal alkalic volcanic rocks, extends over a largely ice-covered area, from the Ross Sea nearly to the Bellingshausen Sea. Various lines of evidence lead to the following interpretation: the transantarctic Mountains part of the rift shoulder (and probably the entire shoulder) has been rising since about 60 Ma, at episodic rates of ~1 km/m.y., most recently since mid-Pliocene Time, rather than continuously at the mean rate of 100 m/m.y. Uplift rates vary along the scarp, which is cut by transverse faults. It is speculated that this uplift may have climatically forced the advance of the Antarctic ice sheet since the most recent warm period. A possible synergistic relation is suggested between episodic tectonism, mountain uplift, and volcanism in the Cenozoic West Antarctic rift system and waxing and waning of the Antarctic ice sheet beginning about earliest Oligocene time. 

Oroclines - a century of discourse about curved mountain belts (Petrus Peregrinus Medal Lecture)

NASA Astrophysics Data System (ADS)

Van der Voo, Rob

2014-05-01

Exactly a century ago, in early 2014, a discussion appeared in the Journal of Geology by William H. Hobbs entitled "Mechanics of formation of arcuate mountains". In it, he notes how the concept of nappes "has now overcome all opposition in Switzerland" and, presumably in other countries just as much. With horizontal transport so central to the nappe concept, this must have paved the way for the idea that emplacement of trust sheets may have involved rotations. Where such rotations form a coherent regional pattern, a curved mountain belt may be the result. While the paper by Hobbs does not mention the word orocline, and while the dynamics of the situation is not yet illuminated, one must give credit to him for his foresights. The term "orocline" was introduced by S. Warren Carey of Tasmania in 1955, as part of a kinematic analysis of rhomb- and triangle-shaped basins and curved mountain belts. When the displacements involved in the analysis are undone, as he did, for instance, in the western Mediterranean, a grand scheme of simple convergent and divergent patterns emerges. Noteworthy is, of course, the fact that this mobilistic analysis preceded plate tectonics by more than a decade. From Carey (although not exactly in his words) we have inherited the definition of orocline, as "a thrust belt or orogen that is curved in map-view due to it having been bent or buckled about a vertical axis of rotation". Because oroclinal bending involves rotations, the declinations of paleomagnetic studies can be utilized to support and quantify them, and early efforts were already made in the 1960's and early 1970's to do so (e.g., Krs in the Carpathians; Ries & Shackleton in Cantabria; Roy, Opdyke & Irving in the Central Appalachians; Packer & Stone in Alaska). Curved mountain belts everywhere were subsequently investigated, and typically shown by paleomagnetists to be of the oroclinal variety. Few curved belts turned out to be curved from the start. Because these studies were generally carried out in fold- and trust-belts, the allochthony of the rotated limbs of the thin-skinned belts implied transport above a basal décollement plane located in the upper crust. Some examples of these thin-skinned oroclines will be given. However, in recent years oroclines have also been proposed as resulting from buckling of ribbon continents (e.g., Panama; D'Entrecasteaux) with the noteworthy Great Alaskan Terrane Wreck, as discussed by Stephen Johnston of the University of Victoria, as prime example. And oroclines of truly continental dimensions have been presented on the basis of paleomagnetic and structural data in Hercynian Europe and Asia (the Kazakhstan and Mongol-Okhotsk oroclines). Because most of the fold- and trust-belt oroclines contain thick carbonate formations; paleomagnetists frequently find that these have been remagnetized in geological episodes that are coeval with mountain building nearby in time and space. A connection between remagnetization and clay diagenesis is a possibility that is currently being investigated. If this is shown to be the case, the last word on oroclines will not have been printed.

Double salt décollements: Effect of pinch-out overlapping in experimental thrust wedges

NASA Astrophysics Data System (ADS)

Santolaria, P.; Vendeville, B.; Graveleau, F.; Casas, A.; Soto, R.

2013-12-01

The presence of one or more evaporitic horizons acting as detachment levels in fold-and-thrust belts is common. Numerous works have dealt with the analysis of the role played by basal detachments on the deformation style of fold-and-thrust belts, but less attention has been paid to the interaction between two décollements and strain transfer between them. In this study, 10 sand-silicone analogue experiments with two detachment levels and different stratigraphic pinch-out configurations were carried out: the basal décollement was located hinterlandwards, and the upper one was located forelandwards, with or without geographic underlap or overlap. These geometrical arrangements simulate evaporites deposited in foreland basins progressively involved in shortening. To analyze their influence on the geometry and kinematics of thrust wedges, we tested successively the following parameters: i) the amount of vertical overlapping between the two décollement pinch-outs, ii) the total amount of shortening, and iii) the geometry of the intermediate décollement (pinch-out line parallel or oblique with respect to the pinch-out line of the basal décollement). All experiments were quantitatively monitored by carrying DEM (Digital Elevation Models) and PIV (Particle Image Velocimetry) measurements. All models had a similar style: (i) an inner domain, characterized by a thicker sand cover, with three forward verging thrusts rooted in the basal décollement, (ii) an outer domain with thinner sand cover, whose deformation pattern was characterized by 2 to 6 structures detaching on the upper décollement and (iii) a 'step zone' located between the inner and outer domains having varying geometry and kinematics. In longer-lived models, structures were reworked and salt migration deformed the early emplaced folds and thrusts. Our experimental results point out that the amount of vertical overlapping between the two décollement pinch outs is a first order parameter that conditions not only the geometry and deformation of the 'step zone', but also the geometry and kinematics of the entire thrust wedge. Comparison with the foreland fold-and-thrust belt from the Southeastern Pyrenees, where deformation is transferred from the Triassic evaporites to Eocene-Oligocene evaporitic horizons deposited in front of the advancing Pyrenean thrust sheets, supports the experimental results and validates their interpretation.

Découverte d'un chevauchement d'âge quaternaire au sud de la Grande Kabylie (Algérie)

NASA Astrophysics Data System (ADS)

Boudiaf, Azzedine; Philip, Hervé; Coutelle, Alain; Ritz, Jean-François

1999-03-01

In the Maghreb, the southern border of the Kabylie (Algeria) mountains is considered as an aseismic region. The detailed study of the historical seismicity of this region shows moderate seismic activity (M 1 = 5.0) which is not coherent with the observed tectonic deformations. However, an analysis of the morphology on Landsat image, aerial photos and the topography shows Quaternary deformations in the southern side of the "Kabylie massifs" (Algeria). These deformations are interpreted as reactivation of Miocene thrust faults. The tectonic Quaternary scarps are more spectacular in the Bouira and Tazmalt region and might be associated with successive strong earthquakes (M = 7.0). Therefore, this major active thrust fault observed in this region, as in many intraplate regions, poses the problem of the long return period of seismic activity in this zone. Elsevier, Paris

Application of High Resolution Topography and Remote Sensing: Imagery to the Kinematics of Fold-and-Thrust Belts

NASA Technical Reports Server (NTRS)

Rubin, Charles

1997-01-01

This report summarizes one year of funding for NASA contract NAGW-3691, Application of High Resolution Topography and Remote Sensing: Imagery to the Kinematics of Fold-and-Thrust Belts. I never received year three from NASA. The funds were to support on going tectonic and topographic studies along the front of the central Transverse Ranges and expand the topographic studies to the north. Below are results from the first two years of actual funds that I received from NASA (see attached Federal Cash Transaction Reports). The main focus of this contract was to define and understand the major tectonic processes affecting the formation and evolution of the topography in convergent tectonic settings. The results will be used to test ongoing space-based geodetic measurements and will be compared with present-day seismicity in the central Transverse Ranges and adjacent basins. Two major factors that controls topography in active regions are (1) tectonic uplift due to fault-normal compression and (2) subsequent erosion. The central Transverse and Temblor Ranges are excellent regions for these focused topographic studies. The tectonic processes leading to the mountain building are relatively straightforward and thus are easy to model. Available evidence suggests that the topography in this region is relatively young, - 3.5 Ma or less. In addition,, erosional processes may be relatively easier to model compared to larger and more ancient mountain belts. For example, in larger mountain belts, topographic relief may cause significant orographic effects and high elevation may result in part of the topography located above snowline. Both factors complicate interpretation of erosional processes that may be controlled by elevation. Mountain ranges that are significantly older may have experienced a much wider variety of erosional or climatic conditions over their lifetime. While erosion rates have certainly not been consistent in the Transverse or Temblor ranges over its 3.5 Ma lifetime, we are sure that the region was spared the Pleistocene glaciation that affected parts of the Sierra Nevada Range.

A new Late Cretaceous paleomagnetic pole from the Adel Mountains, west central Montana

NASA Astrophysics Data System (ADS)

Gunderson, Jay A.; Sheriff, Steven D.

1991-01-01

North America's apparent polar wander path has been poorly defined between the mid-Cretaceous and Paleocene reference pole positions. Existing data allowed 13° of apparent polar motion over about 22 m.y. (87-65 Ma) roughly coinciding with the beginning of Laramide deformation (˜80 Ma). We report on a paleomagnetic study of the Adel Mountain Volcanic rocks to refine the North American apparent polar wander path for this interval. The shonkinite rocks of the Adel Mountain Volcanic field are on the eastern edge of the Cretaceous-Paleocene fold and thrust belt; some of these structures disturb the western edge of the volcanic pile. We obtained two new K-Ar dates from the Adel rocks. One date, on biotite ( from a shonkinite dike that crosscuts most of the volcanic rocks, is 71.2±2.7 Ma. The other, a whole rock date from a flow deep in the volcanic pile, is 81.1±3.5 Ma. We collected six to nine paleomagnetic samples from each of 34 sites in roadcuts and natural outcrops of flows, dikes, and laccoliths. Positive fold and conglomerate tests, along with alternating field and thermal demagnetization, indicate that our characteristic remanent directions are primary magnetizations acquired before Late Cretaceous to Paleocene thrust belt deformation. Averaging the virtual geomagnetic poles from 26 reliable sites, all of normal polarity, yields a paleopole at 82.2°N, 209.9°E (α95 = 6.80°, k = 18.38). This pole is concordant with the Paleocene reference pole (82.0°N, 170.2°E, α95 = 3.5°, k = 18.6 (Diehl et al., 1983)) and is 11.6° from the Globerman and Irving (1988) mid-Cretaceous pole at 71°N, 196°E. The youngest information in the Cretaceous stillstand pole is from the Niobrara Formation (Shive and Frerichs, 1974) at about 85-89 Ma. If we take the average age of the Adel Mountain Volcanics to be 76 Ma, then ˜12° of apparent polar motion occurred between 87 Ma and 76 Ma. Thus, rapid apparent polar motion correlates well with the onset of Laramide deformation.

Effect of Inductive Coil Geometry on the Operating Characteristics of a Pulsed Inductive Plasma Accelerator

NASA Technical Reports Server (NTRS)

Hallock, Ashley K.; Polzin, Kurt A.; Kimberlin, Adam C.

2012-01-01

Operational characteristics of two separate inductive thrusters with coils of different cone angles are explored through thrust stand measurements and time-integrated, un- filtered photography. Trends in impulse bit measurements indicate that, in the present experimental configuration, the thruster with the inductive coil possessing a smaller cone angle produced larger values of thrust, in apparent contradiction to results of a previous thruster acceleration model. Areas of greater light intensity in photographs of thruster operation are assumed to qualitatively represent locations of increased current density. Light intensity is generally greater in images of the thruster with the smaller cone angle when compared to those of the thruster with the larger half cone angle for the same operating conditions. The intensity generally decreases in both thrusters for decreasing mass ow rate and capacitor voltage. The location of brightest light intensity shifts upstream for decreasing mass ow rate of propellant and downstream for decreasing applied voltage. Recognizing that there typically exists an optimum ratio of applied electric field to gas pressure with respect to breakdown efficiency, this result may indicate that the optimum ratio was not achieved uniformly over the coil face, leading to non-uniform and incomplete current sheet formation in violation of the model assumption of immediate formation where all the injected propellant is contained in a magnetically-impermeable current sheet.

Effect of Inductive Coil Geometry on the Operating Characteristics of an Inductive Pulsed Plasma Thruster

NASA Technical Reports Server (NTRS)

Hallock, Ashley K.; Polzin, Kurt A.; Kimberlin, Adam C.; Perdue, Kevin A.

2012-01-01

Operational characteristics of two separate inductive thrusters with conical theta pinch coils of different cone angles are explored through thrust stand measurements and time- integrated, unfiltered photography. Trends in impulse bit measurements indicate that, in the present experimental configuration, the thruster with the inductive coil possessing a smaller cone angle produced larger values of thrust, in apparent contradiction to results of a previous thruster acceleration model. Areas of greater light intensity in photographs of thruster operation are assumed to qualitatively represent locations of increased current density. Light intensity is generally greater in images of the thruster with the smaller cone angle when compared to those of the thruster with the larger half cone angle for the same operating conditions. The intensity generally decreases in both thrusters for decreasing mass flow rate and capacitor voltage. The location of brightest light intensity shifts upstream for decreasing mass flow rate of propellant and downstream for decreasing applied voltage. Recognizing that there typically exists an optimum ratio of applied electric field to gas pressure with respect to breakdown efficiency, this result may indicate that the optimum ratio was not achieved uniformly over the coil face, leading to non-uniform and incomplete current sheet formation in violation of the model assumption of immediate formation where all the injected propellant is contained in a magnetically-impermeable current sheet.

Landform Evolution of the Zanskar Valley, Ladakh Himalaya.

NASA Astrophysics Data System (ADS)

Chahal, P.; Kumar, A.; Sharma, P.; Sundriyal, Y.; Srivastava, P.

2017-12-01

Zanskar River flow from south-west to north-east, perpendicularly through Higher Himalayan crystalline sequences, Tethyan sedimentary sequences, and Indus Molasses; and finally merge with the Indus River at Nimu. Geologically, the Indus valley is bounded by Ladakh Batholith in the north and highly folded and thrusted Zanskar mountain ranges in the south. Sedimentary sequences of Zanskar ranges are largely of continental origin, which were uplifted and deformed via several north verging thrusts, where Zanskar counter thrust, Choksti and Indus-Bazgo thrusts are important thrust zone, and there is atleast 36 km of crustal shortening in the Zanskar section which continued from middle Miocene to the late Pleistocene. This shortening is accommodated mainly by north or north-east directed Zanskar backthrusts. Two major tributaries of Zanskar: Tsrapchu and Doda, flow in the headwaters, along the strike of South Tibetan Detachment System (STDs), an east-west trending regional fault. The present study incorporate field sedimentology, geomorphology and chronology of landform associated with Zanskar valley. In the upper Zanskar, alluvial fan, valley fill and strath terraces configured the major landforms with paleo-lake deposits­­­ in the area between the fans. The lower catchment, at the confluence of Zanskar and Indus rivers, exhibit mainly valley fill terraces and strath terraces. Chronology suggests diachronous aggradation in the upper and lower Zanskar catchments. In the upper Zanskar large scale valley aggradation took place with simultaneously fan progradation and flooding events from 45-15 ka. Luminescence chronology of the lower Zanskar indicates aggradation from 145-55 ka and 18-12 ka. The two aggradation basins are separated by a deep V-shaped gorge which is approximately 60 km long. The longitudinal profile of the Zanskar River shows several local convexities marking knick point zone, which suggests tectonically controlled topography.

Late Cenozoic transpressional mountain building directly north of the Altyn Tagh Fault in the Sanweishan and Nanjieshan, North Tibetan Foreland, China

NASA Astrophysics Data System (ADS)

Cunningham, Dickson; Zhang, Jin; Li, Yanfeng

2016-09-01

For many tectonicists, the structural development of the northern Tibetan Plateau stops at the Altyn Tagh Fault (ATF). This study challenges that assumption. Structural field observations and remote sensing analysis indicate that the Sanweishan and Nanjieshan basement cored ridges of the Archean Dunhuang Block, which interrupt the north Tibetan foreland directly north of the ATF, are bound and cut by an array of strike-slip, thrust and oblique-slip faults that have been active in the Quaternary and remain potentially active. The Sanweishan is a SE-tilted block that is bound on its NW margin by a steep south-dipping thrust fault that has also accommodated sinistral strike-slip displacements. The Nanjieshan consists of parallel, but offset basement ridges that record NNW and SSE thrust displacements and sinistral strike-slip. Regional folds characterize the extreme eastern Nanjieshan and appear to have formed above blind thrust faults which break the surface further west. Previously published magnetotelluric data suggest that the major faults of the Sanweishan and Nanjieshan ultimately root to the south within conductive zones that are inferred to merge into the ATF. Therefore, although the southern margin of the Dunhuang Block focuses significant deformation along the ATF, the adjacent cratonic basement to the north is also affected. Collectively, the ATF and structurally linked Sanweishan and Nanjieshan fault array represent a regional asymmetric half-flower structure that is dominated by non-strain partitioned sinistral transpression. The NW-trending Dengdengshan thrust fault system near Yumen City appears to define the northeastern limit of the Sanweishan-Nanjieshan block, which may be regionally viewed as the most northern, but early-stage expression of Tibetan Plateau growth into a slowly deforming, mechanically stiff Archean craton.

Dynamics of erosion in a compressional mountain range revealed by 10Be paleoerosion rates

NASA Astrophysics Data System (ADS)

Val, P.; Hoke, G. D.; Fosdick, J. C.; Wittmann, H.

2015-12-01

The temporal evolution of erosion over million-year timescales is key to understanding the evolution of mountain ranges and adjacent fold-and-thrust belts. While models of orogenic wedge evolution predict an instantaneous response of erosion to pulses of rock uplift, stream-power based landscape evolution models predict catchment-wide erosion maxima that lag behind a rock uplift pulse. Here, we explore the relationships between rock uplift, erosion, and sediment deposition in the Argentine Precordillera fold-and-thrust belt at 30°S where extensive previous work documents deformation, climate and sediment accumulation histories. Sandstone samples spanning 8.8 to 1.8 Ma were collected from the previously dated wedge-top (Iglesia) and foredeep basins (Bermejo) for quartz purification and 10Be extraction. 10Be concentrations due to burial and exhumation were estimated and subtracted from the measured concentrations and yielded the inherited 10Be concentrations, which were then corrected for sample magnetostratigraphic age. The inherited concentrations were then used to calculate paleoerosion rates. We modeled various pre-burial and post-burial exposure scenarios in order to assess potential sources of uncertainty in the recovered paleoerosion rates. The modeling results reveal that pre-burial and post-burial exposure periods only marginally affect our results. By combining the 10Be-derived paleoerosion rates and geomorphic observations with detrital zircon provenance, we document the isolation of the wedge-top basin, which was later reconnected by an upstream migrating pulse of erosion in a process that was directly controlled by thrust activity and base level. The data further indicate that the attainment of maximum upland erosion rates lags maximum rates of deformation and subsidence over million-year timescales. The magnitudes and causes of the erosional delays shed new light on the catchment erosional response to tectonic deformation and rock uplift in orogenic wedges.

Recurrent eruption and subsidence at the Platoro caldera complex, southeastern San Juan volcanic field, Colorado: New tales from old tuffs

USGS Publications Warehouse

Lipman, P.W.; Dungan, M.A.; Brown, L.L.; Deino, A.

1996-01-01

Reinterpretation of a voluminous regional ash-flow sheet (Masonic Park Tuff) as two separate tuff sheets of similar phenocryst-rich dacite erupted from separate source calderas has important implications for evolution of the multicyclic Platoro caldera complex and for caldera-forming processes generally. Masonic Park Tuff in central parts of the San Juan field, including the type area, was erupted from a concealed source at 28.6 Ma, but widespread tuff previously mapped as Masonic Park Tuff in the southeastern San Juan Mountains is the product of the youngest large-volume eruption of the Platoro caldera complex at 28.4 Ma. This large unit, newly named the "Chiquito Peak Tuff," is the last-erupted tuff of the Treasure Mountain Group, which consists of at least 20 separate ash-flow sheets of dacite to low-silica rhyolite erupted from the Platoro complex during a 1 m.y. interval (29.5-28.4 Ma). Two Treasure Mountain tuff sheets have volumes in excess of 1000 km3 each, and five more have volumes of 50-150 km3. The total volume of ash-flow tuff exceeds 2500 km3, and caldera-related lavas of dominantly andesitic composition make up 250-500 km3 more. A much greater volume of intermediate-composition magma must have solidified in subcaldera magma chambers. Most preserved features of the Platoro complex - including postcollapse asymmetrical trap-door resurgent uplift of the ponded intracaldera tuff and concurrent infilling by andesitic lava flows - postdate eruption of the Chiquito Peak Tuff. The numerous large-volume pre-Chiquito Peak ash-flow tuffs document multiple eruptions accompanied by recurrent subsidence; early-formed caldera walls nearly coincide with margins of the later Chiquito Peak collapse. Repeated syneruptive collapse at the Platoro complex requires cumulative subsidence of at least 10 km. The rapid regeneration of silicic magmas requires the sustained presence of an andesitic subcaldera magma reservoir, or its rapid replenishment, during the 1 m.y. life span of the Platoro complex. Either case implies large-scale stoping and assimilative recycling of the Tertiary section, including intracaldera tuffs.

Fold-Thrust mapping using photogrammetry in Western Champsaur basin, SE France

NASA Astrophysics Data System (ADS)

Totake, Y.; Butler, R.; Bond, C. E.

2016-12-01

There is an increasing demand for high-resolution geometric data for outcropping geological structures - not only to test models for their formation and evolution but also to create synthetic seismic visualisations for comparison with subsurface data. High-resolution 3D scenes reconstructed by modern photogrammetry offer an efficient toolbox for such work. When integrated with direct field measurements and observations, these products can be used to build geological interpretations and models. Photogrammetric techniques using standard equipment are ideally suited to working in the high mountain terrain that commonly offers the best outcrops, as all equipment is readily portable and, in the absence of cloud-cover, not restricted to the meteorological and legal restrictions that can affect some airborne approaches. The workflows and approaches for generating geological models utilising such photogrammetry techniques are the focus of our contribution. Our case study comes from SE France where early Alpine fore-deep sediments have been deformed into arrays of fold-thrust complexes. Over 1500m vertical relief provides excellent outcrop control with surrounding hillsides providing vantage points for ground-based photogrammetry. We collected over 9,400 photographs across the fold-thrust array using a handheld digital camera from 133 ground locations that were individually georeferenced. We processed the photographic images within the software PhotoScan-Pro to build 3D landscape scenes. The built photogrammetric models were then imported into the software Move, along with field measurements, to map faults and sedimentary layers and to produce geological cross sections and 3D geological surfaces. Polylines of sediment beds and faults traced on our photogrammetry models allow interpretation of a pseudo-3D geometry of the deformation structures, and enable prediction of dips and strikes from inaccessible field areas, to map the complex geometries of the thrust faults and deformed strata in detail. The resultant structural geometry of the thrust zones delivers an exceptional analogue to inaccessible subsurface fold-thrust structures which are often challenging to obtain a clear seismic image.

Geologic and Fossil Locality Maps of the West-Central Part of the Howard Pass Quadrangle and Part of the Adjacent Misheguk Mountain Quadrangle, Western Brooks Range, Alaska

USGS Publications Warehouse

Dover, James H.; Tailleur, Irvin L.; Dumoulin, Julie A.

2004-01-01

The map depicts the field distribution and contact relations between stratigraphic units, the tectonic relations between major stratigraphic sequences, and the detailed internal structure of these sequences. The stratigraphic sequences formed in a variety of continental margin depositional environments, and subsequently underwent a complexde formational history of imbricate thrust faulting and folding. A compilation of micro and macro fossil identifications is included in this data set.

Shear zones bounding the central zone of the Limpopo Mobile Belt, southern Africa

NASA Astrophysics Data System (ADS)

McCouri, Stephen; Vearncombe, Julian R.

Contrary to previously suggested north-directed thrust emplacement of the central zone of the Limpopo mobile belt, we present evidence indicating west-directed emplacement. The central zone differs from the marginal zones in rock types, structural style and isotopic signature and is an allochthonous thrust sheet. It is bounded in the north by the dextral Tuli-Sabi shear zone and in the south by the sinistral Palala shear zone which are crustal-scale lateral ramps. Published gravity data suggest that the lateral ramps are linked at depth and they probably link at the surface, in a convex westward frontal ramp, in the vicinity of longitude 26°30'E in eastern Botswana. Two phases of movement, the first between 2.7 and 2.6 Ga and the second between 2.0 and 1.8 Ga. occurred on both the Tuli-Sabi and the Palala shear zones.

Non-cylindrical fold growth in the Zagros fold and thrust belt (Kurdistan, NE-Iraq)

NASA Astrophysics Data System (ADS)

Bartl, Nikolaus; Bretis, Bernhard; Grasemann, Bernhard; Lockhart, Duncan

2010-05-01

The Zagros mountains extends over 1800 km from Kurdistan in N-Iraq to the Strait of Hormuz in Iran and is one of the world most promising regions for the future hydrocarbon exploration. The Zagros Mountains started to form as a result of the collision between the Eurasian and Arabian Plates, whose convergence began in the Late Cretaceous as part of the Alpine-Himalayan orogenic system. Geodetic and seismological data document that both plates are still converging and that the fold and thrust belt of the Zagros is actively growing. Extensive hydrocarbon exploration mainly focuses on the antiforms of this fold and thrust belt and therefore the growth history of the folds is of great importance. This work investigates by means of structural field work and quantitative geomorphological techniques the progressive fold growth of the Permam, Bana Bawi- and Safeen- Anticlines located in the NE of the city of Erbil in the Kurdistan region of Northern Iraq. This part of the Zagros fold and thrust belt belongs to the so-called Simply Folded Belt, which is dominated by gentle to open folding. Faults or fault related folds have only minor importance. The mechanical anisotropy of the formations consisting of a succession of relatively competent (massive dolomite and limestone) and incompetent (claystone and siltstone) sediments essentially controls the deformation pattern with open to gentle parallel folding of the competent layers and flexural flow folding of the incompetent layers. The characteristic wavelength of the fold trains is around 10 km. Due to faster erosion of the softer rock layers in the folded sequence, the more competent lithologies form sharp ridges with steeply sloping sides along the eroded flanks of the anticlines. Using an ASTER digital elevation model in combination with geological field data we quantified 250 drainage basins along the different limbs of the subcylindrical Permam, Bana Bawi- and Safeen- Anticlines. Geomorphological indices of the drainage basins (spacing and elongation ratio, circularity index and shape factor) of different parts in the fore and back-limb of the anticlines demonstrate that the basins have a low maturity and that fold growth is still highly active. Most importantly, the results of this geomorphological investigations demonstrates that the subcylindrical folds have developed from several non-cylindrical embryonic folds, which have merged during progressive fold growth.

Paleomagnetic Results for Eocene Volcanic Rocks from Northeastern Washington and the Tertiary Tectonics of the Pacific Northwest

NASA Astrophysics Data System (ADS)

Fox, Kenneth F., Jr.; Beck, Myrl E., Jr.

1985-04-01

The direction of remanent magnetization for 102 sites in Eocene volcanic and volcaniclastic rocks of the O'Brien Creek Formation, Sanpoil Volcanics, and Klondike Mountain Formation suggests approximately 25° of clockwise rotation of a 100 by 200 km area in northeastern Washington. The volcanic rocks consist chiefly of rhyodacite and quartz latite flows, with intercalated ash flow tuff and volcaniclastic layers. These rocks have been sampled at 102 sites distributed among five volcanotectonic depressions: the Toroda Creek, Republic, Keller, and First Thought grabens and the Spokane-Enterprise lineament. The volcanic rocks probably range in age from 55 m.y. to about 48 m.y., and the 50- to 48-m.y.-old volcanic rocks within this suite appear to be rotated as much as the older rocks. Previous investigators have shown that 40-m.y.-old and younger plutonic rocks of northwestern Washington are not rotated; hence we infer that the north-central Washington rocks were rotated to their present declination between 48 and 40 m.y. B.P. (during the middle and/or late Eocene). During early Eocene time this region was extended in a westward direction through crustal necking, gneiss-doming, diking, and graben formation. Internal deformation of the region related to this crustal extension was extreme, but most bedrock units that were formed concurrent with the crustal extension were probably in place prior to the rotation; hence we infer that the rotation was chiefly accommodated by movement on faults peripheral to the sampled area. Faults active during Paleogene time appear to define boundaries of a triangular crustal block (the Sanpoil block), encompassing much of northeastern Washington, northern Idaho, northwestern Montana, and adjacent parts of British Columbia. The faults include the Laramide thrusts of the Rocky Mountain thrust belt, the strike-slip faults of the Lewis and Clark line, and strike-slip faults of the Straight Creek-Fraser zone. We suggest that during early Eocene time the Sanpoil block was extended westward through crustal necking and dilation and then during the middle Eocene was rotated clockwise and thrust over the craton in a final stage of Laramide thrusting. The "motor" driving these deformations presumably was interaction of North America with oceanic lithosphere off its western margin; such interaction probably involved right-oblique underthrusting and dextral shear.

Deformation Front Development at the Northeast Margin of the Tainan Basin, Tainan-Kaohsiung Area, Taiwan

NASA Astrophysics Data System (ADS)

Huang, Shiuh-Tsann; Yang, Kenn-Ming; Hung, Jih-Hao; Wu, Jong-Chang; Ting, Hsin-Hsiu; Mei, Wen-Wei; Hsu, Shiang-Horng; Lee, Min

2004-03-01

The geological setting south of the Tsengwen River and the Tsochen Fault is the transitional zone between the Tainan foreland basin and Manila accretionary wedge in Southwestern Taiwan. This transitional zone is characterized by the triangle zone geological model associated with back thrusts that is quite unique compared to the other parts of the Western foreland that are dominated by thrust imbrications. The Hsinhua structure, the Tainan anticline, and the offshore H2 anticline are the first group of major culminations in the westernmost part of the Fold-and-Thrust belt that formed during the Penglay Orogeny. Structures in the the Tainan and Kaohsiung areas provide important features of the initial mountain building stage in Western Taiwan. A deeply buried basal detachment with ramp-flat geometry existed in the constructed geological sections. A typical triangle is found by back thrusting, such as where the Hsinhua Fault cuts upsection of the Upper Pliocene and Pleistocene from a lower detachment along the lower Gutingkeng Formation. The Tainan structure is a southward extension of the Hinhua Fault and has an asymmetric geometry of gentle western and steep eastern limbs. Our studies suggest that the Tainan anticline is similar to the structure formed by the Hsinhua Fault. Both are characterized by back thrusts and rooted into a detachment about 5 km deep. The triangle zone structure stops at H2 anticline offshore Tainan and beyond the west of it, All the structures are replaced by rift tectonic settings developed in the passive continental margin. On the basal detachment, a major ramp interpreted as a tectonic discontinuity was found in this study. Above the northeastern end of the major ramp of basal detachment, the Lungchuan Fault is associated with a triangle system development, while at the southwestern end a thrust wedge is present. It could be deduced that a thrust wedge intrudes northwestward. The area below the major ramp, or equivalent to the trailing edge of the basal detachment, mud diapers often occur in relation to the thickest deposits of the Gutingkeng Formation and caused by the mechanism of detachment folding

Kinematics and Seismotectonics of the Montello Thrust Fault (Southeastern Alps, Italy) Revealed by Local GPS and Seismic Networks

NASA Astrophysics Data System (ADS)

Serpelloni, E.; Anderlini, L.; Cavaliere, A.; Danesi, S.; Pondrelli, S.; Salimbeni, S.; Danecek, P.; Massa, M.; Lovati, S.

2014-12-01

The southern Alps fold-and-thrust belt (FTB) in northern Italy is a tectonically active area accommodating large part of the ~N-S Adria-Eurasia plate convergence, that in the southeastern Alps ranges from 1.5 to 2.5 mm/yr, as constrained by a geodetically defined rotation pole. Because of the high seismic hazard of northeastern Italy, the area is well monitored at a regional scale by seismic and GPS networks. However, more localized seismotectonic and kinematic features, at the scale of the fault segments, are not yet resolved, limiting our knowledge about the seismic potential of the different fault segments belonging to the southeastern Alps FTB. Here we present the results obtained from the analysis of data collected during local seismic and geodetic experiments conducted installing denser geophysical networks across the Montello-Bassano-Belluno system, a segment of the FTB that is presently characterized by a lower sismicity rate with respect to the surrounding domains. The Montello anticline, which is the southernmost tectonic features of the southeastern Alps FTB (located ~15 km south of the mountain front), is a nice example of growing anticline associated with a blind thrust fault. However, how the Adria-Alps convergence is partitioned across the FTB and the seismic potential of the Montello thrust (the area has been struck by a Mw~6.5 in 1695 but the causative fault is still largely debated) remained still unresolved. The new, denser, GPS data show that this area is undergoing among the highest geodetic deformation rates of the entire south Alpine chain, with a steep velocity gradient across the Montello anticline. The earthquakes recorded during the experiment, precisely relocated with double difference methods, and the new earthquake focal mechanisms well correlate with available information about sub-surface geological structures and highlight the seismotectonic activity of the Montello thrust fault. We model the GPS velocities using elastic dislocations embedded in a kinematic block model approach, which suggest that the Montello thrust fault is weakly coupled with respect to surrounding segments of the southernmost thrust system. Future works will include the integration of InSAR data and the densification/improvement of the geodetic infrastructure.

Reconnaissance geology of the Central Mastuj Valley, Chitral State, Pakistan

USGS Publications Warehouse

Stauffer, Karl W.

1975-01-01

The Mastuj Valley in Chitral State is a part of the Hindu Kush Range, and is one of the structurally most complicated areas in northern Pakistan. Sedimentary rocks ranging from at least Middle Devonian to Cretaceous, and perhaps Early Tertiary age lie between ridge-forming granodiorite intrusions and are cut by thrust faults. The thrust planes dip 10? to 40? to the north- west. Movement of the upper thrust plates has been toward the southeast relative to the lower blocks. If this area is structurally typical of the Hindu-Kush and Karakoram Ranges, then these mountains are much more tectonically disturbed than previously recorded, and suggest compression on a scale compatible with the hypothesis that the Himalayan, Karakoram, and Hindu Kush Ranges form part of a continental collision zone. The thrust faults outline two plates consisting of distinctive sedimentary rocks. The lower thrust plate is about 3,000 feet thick and consists of the isoclinally folded Upper Cretaceous to perhaps lower Tertiary Reshun Formation. It has overridden the Paleozoic metasedimentary rocks of the Chitral Slate unit. This thrust plate is, in turn, overridden by an 8,000-foot thick sequence consisting largely of Devonian to Carboniferous limestones and quartzites. A key factor in the tectonic processes has been the relatively soft and plastic lithology of the siltstone layers in the Reshun Formation which have acted as lubricants along the principal thrust faults, where they are commonly found today as fault slices and smears. The stratigraphic sequence, in the central Mastuj Valley was tentatively divided into 9 mapped units. The fossiliferous shales and carbonates of the recently defined Shogram Formation and the clastlcs of the Reshun Formation have been fitted into a sequence of sedimentary rocks that has a total thick- ness of at least 13,000 feet and ranges in age from Devonian to Neogene. Minerals of potential economic significance include antimony sulfides which have been mined elsewhere in Chitral, the tungstate, scheelite, which occurs in relatively high concentrations in heavy-mineral fractions of stream sands, and an iron-rich lateritic rock.

Section of Morgan formation, Pennsylvanian, at Split Mountain in Dinosaur National Monument, Uintah County, Utah

USGS Publications Warehouse

McCann, Franklin T.; Raman, Norman D.; Henbest, Lloyd G.

1946-01-01

Extension of the oil pool in the Weber sandstone (Pennsylvanian), in the Rangely oil field, Rio Blanco County, Colorado, subsequent to the completion of the filed work on which Preliminary Chart 16 is based, has stimulated special interest in the beds beneath that sandstone as potential oil reservoirs. In compliance with the demand for additional information concerning these beds, a detailed description of the sequence immediately underlying the Weber sandstone at Split Mountain, Utah, is here given. That part of Split Mountain where the section was measured is approximately 35 airline miles northwest of the town of Rangely. The section itself is shown graphically and somewhat generalized in column 8, sheet 2, Preliminary Chart 16. A more detailed graphic section is presented in the accompanying column section.

The Lamu Basin deepwater fold-and-thrust belt: An example of a margin-scale, gravity-driven thrust belt along the continental passive margin of East Africa

NASA Astrophysics Data System (ADS)

Cruciani, Francesco; Barchi, Massimiliano R.

2016-03-01

In recent decades, advances in seismic processing and acquisition of new data sets have revealed the presence of many deepwater fold-and-thrust belts (DW-FTBs), often developing along continental passive margins. These kinds of tectonic features have been intensively studied, due to their substantial interest. This work presents a regional-scale study of the poorly explored Lamu Basin DW-FTB, a margin-scale, gravity-driven system extending for more than 450 km along the continental passive margin of Kenya and southern Somalia (East Africa). A 2-D seismic data set was analyzed, consisting of both recently acquired high-quality data and old reprocessed seismic profiles, for the first detailed structural and stratigraphic interpretation of this DW-FTB. The system originated over an Early to mid-Cretaceous shale detachment due to a mainly gravity-spreading mechanism. Analysis of synkinematic strata indicates that the DW-FTB was active from the Late Cretaceous to the Early Miocene, but almost all of the deformation occurred before the Late Paleocene. The fold-and-thrust system displays a marked N-S variation in width, the northern portion being more than 150 km wide and the southern portion only a few dozen kilometers wide; this along-strike variation is thought to be related to the complex tectonosedimentary evolution of the continental margin at the Somalia-Kenya boundary, also reflected in the present-day bathymetry. Locally, a series of volcanic edifices stopped the basinward propagation of the DW-FTB. A landward change in the dominant structural style, from asymmetric imbricate thrust sheets to pseudo-symmetric detachment folds, is generally observed, related to the landward thickening of the detached shales.

Flight Mechanics and Control Requirements for a Modular Solar Electric Tug Operating in Earth-Moon Space

NASA Astrophysics Data System (ADS)

Woodcock, Gordon; Wingo, Dennis

2006-01-01

A modular design for a solar-electric tug was analyzed to establish flight control requirements and methods. Thrusters are distributed around the periphery of the solar array. This design enables modules to be berthed together to create a larger system from smaller modules. It requires a different flight mode than traditional design and a different thrust direction scheme, to achieve net thrust in the desired direction, observe thruster pointing constraints that avoid plume impingement on the tug, and balance moments. The array is perpendicular to the Sun vector for maximum electric power. The tug may maintain a constant inertial attitude or rotate around the Sun vector once per orbit. Either non-rotating or constant angular velocity rotation offers advantages over the conventional flight mode, which has highly variable roll rates. The baseline single module has 12 thrusters: two 2-axis gimbaling main thrusters, one at each ``end'', and two back-to-back Z axis thrusters at each corner of the array. Thruster pointing and throttling were optimized to maximize net thrust effectiveness while observing constraints. Control design used a spread sheet with Excel Solver to calculate nominal thruster pointing and throttling. These results are used to create lookup tables. A conventional control system generates a thruster pointing and throttling overlay on the nominals to maintain active attitude control. Gravity gradients can cause major attitude perturbations during occultation periods if thrust is off during these periods. Thrust required to maintain attitude is about 4% of system rated power. This amount of power can be delivered by a battery system, avoiding the performance penalty if chemical propulsion thrusters were used to maintain attitude.

Paleomagnetism of the Wyoming Craton: A Pre-Laurentian Puzzle

NASA Astrophysics Data System (ADS)

Kilian, T.; Chamberlain, K.; Mitchell, R. N.; Evans, D. A.; Bleeker, W.; Lecheminant, A. N.

2010-12-01

The Archean Wyoming craton is mostly buried beneath Phanerozoic sediments in the Rocky Mountains of the west central United States. Exposures of the craton are entirely in thrust-bounded Laramide uplifts and contain numerous swarms of Neoarchean-Proterozoic mafic dikes. U-Pb ages from these dikes include ~2685 Ma from a dike in the Owl Creek Mountains (Frost et al., 2006) as well as another in the Bald Mountain region of the Bighorn Mountains (this study), ~2170 Ma from the Wind River Mountain quartz diorite (Harlan et al., 2003), ~2110 Ma from a dike in the Granite Mountains (Bowers and Chamberlain, 2006), ~2010 Ma from a Kennedy dike in the Laramie Range (Cox et al., 2000), and ~780 Ma for dikes in the Beartooth and Teton Mountains (Harlan et al., 1997). These possible age ranges of magmatic events will allow a detailed comparison with other cratons, especially Superior and Slave. Prior to the assembly of Laurentia, Wyoming may have been connected with Slave in supercraton Sclavia (Bleeker, 2003; Frost et al., 2007), or alternatively, Wyoming may have been attached to the present southern margin of Superior in the supercraton Superia, as judged by similarities of the thrice-glaciated Huronian and Snowy Pass sedimentary successions (Roscoe and Card, 1993). Paleomagnetic results will be presented from over 150 dikes in the Wyoming craton. All dikes were from the basement uplifts of the Beartooth Mountains, Bighorn Mountains, Owl Creek Mountains, Granite Mountains, Ferris Mountains and Laramie Range. Dikes range in widths from 1 to >100 meters, and trends vary across all orientations. Stable remanence is observed in majority of sites with at least 8 different directions from the various uplifts. Structural corrections are applied when necessary to restore shallowly dipping Cambrian strata to horizontal. The paleomagnetic study is being integrated with precise U-Pb geochronology of dikes that bear stable remanence directions. Results will eventually allow a comparison of results from both Slave and Superior cratons throughout the Archean and Proterozoic. The data will test the prior connections, or lack thereof, among the Archean cratons in Laurentia, and help assess whether there was a supercontinent during the Archean-Proterozoic transition.

Preliminary Geologic Map of the Little Piute Mountains, California; a Digital Database

USGS Publications Warehouse

Howard, Keith A.; Dennis, Michael L.; Karlstrom, Karl; Phelps, Geoffrey A.

1997-01-01

Introduction The Little Piute Mountains in the eastern Mojave Desert expose a series of folds and thrust faults involving metamorphosed Paleozoic strata (Miller and others, 1982; Stone and others, 1983). Detailed mapping of these structures was undertaken to help elucidate regional Mesozoic structural evolution. Earlier geologic maps were prepared by Cooksley (1960a,b,c,d, generalized by Bishop, 1964) and Stone and others (1983). Deformed and metamorphosed Paleozoic and Triassic rocks form a stratal succession that was originally deposited in shallow seas on the North American craton. Based on lithologic sequence the units are correlated with unmetamorphosed equivalents 200 km to the northeast in the Grand Canyon, Arizona, and 35-50 km to the west in the Marble, Ship, and Providence Mountains, California (Stone and others, 1983). The Paleozoic sequence rests nonconformably on a heterogeneous basement of polydeformed Early Proterozoic gneiss (Miller and others, 1982; Wooden and Miller, 1990). Triassic and older rocks were deformed, metamorphosed to staurolite or andalusite grade, and intruded concordantly at their base by Late Cretaceous granodiorite (Miller and others, 1982).

Preliminary Geologic Map of the the Little Piute Mountains, San Bernardino County, California

USGS Publications Warehouse

Howard, Keith A.; Dennis, Michael L.; Karlstrom, Karl E.; Phelps, Geoffrey A.

1995-01-01

Introduction The Little Piute Mountains in the eastern Mojave Desert expose a series of folds and thrust faults involving metamorphosed Paleozoic strata (Miller and others, 1982; Stone and others, 1983). Detailed mapping of these structures was undertaken to help elucidate regional Mesozoic structural evolution. Earlier geologic maps were prepared by Cooksley (1960a,b,c,d, generalized by Bishop, 1964) and Stone and others (1983). Deformed and metamorphosed Paleozoic and Triassic rocks form a stratal succession that was originally deposited in shallow seas on the North American craton. Based on lithologic sequence the units are correlated with unmetamorphosed equivalents 200 km to the northeast in the Grand Canyon, Arizona, and 35-50 km to the west in the Marble, Ship, and Providence Mountains, California (Stone and others, 1983). The Paleozoic sequence rests nonconformably on a heterogeneous basement of polydeformed Early Proterozoic gneiss (Miller and others, 1982; Wooden and Miller, 1990). Triassic and older rocks were deformed, metamorphosed to staurolite or andalusite grade, and intruded concordantly at their base by Late Cretaceous granodiorite (Miller and others, 1982).

Mini-MITEE: Ultra Small, Ultra Light NTP Engines for Robotic Science and Manned Exploration Missions

NASA Astrophysics Data System (ADS)

Powell, James; Maise, George; Paniagua, John

2006-01-01

A compact, ultra lightweight Nuclear Thermal Propulsion (NTP) engine design is described with the capability to carry out a wide range of unique and important robotic science missions that are not possible using chemical or Nuclear Electric Propulsion (NEP). The MITEE (MInature ReacTor EnginE) reactor uses hydrogeneous moderator, such as solid lithium-7 hydride, and high temperature cermet tungsten/UO2 nuclear fuel. The reactor is configured as a modular pressure tube assembly, with each pressure tube containing an outer annual shell of moderator with an inner annular region of W/UO2 cermet fuel sheets. H2 propellant flows radially inwards through the moderator and fuel regions, exiting at ~3000 K into a central channel that leads to a nozzle at the end of the pressure tube. Power density in the fuel region is 10 to 20 megawatts per liter, depending on design, producing a thrust output on the order of 15,000 Newtons and an Isp of ~1000 seconds. 3D Monte Carlo neutronic analyses are described for MITEE reactors utilizing various fissile fuel options (U-235, U-233, and Am242m) and moderators (7LiH and BeH2). Reactor mass ranges from a maximum of 100 kg for the 7LiH/U-235 option to a minimum of 28 kg for the BeH2/Am-242 m option. Pure thrust only and bi-modal (thrust plus electric power generation) MITEE designs are described. Potential unique robotic science missions enabled by the MITEE engine are described, including landing on Europa and exploring the ice sheet interior with return of samples to Earth, hopping to and exploring multiple sites on Mars, unlimited ramjet flight in the atmospheres of Jupiter, Saturn, Uranus, and Neptune and landing on, and sample return from Pluto.

Identification of new NE-trending deep-seated faults and tectonic pattern updating in northern Tunisia (Mogodos-Bizerte region), insights from field and seismic reflection data

NASA Astrophysics Data System (ADS)

Essid, El Mabrouk; Kadri, Ali; Inoubli, Mohamed Hedi; Zargouni, Fouad

2016-07-01

The northern Tunisia is occupied by the Tellian domain constituent the eastern end of the Maghrebides, Alpine fold-thrust belt. Study area includes partially the Tellian domain (Mogodos belt) and its foreland (Bizerte region). Most of this region outcrops consist of Numidian thrust sheet flysch attributed to the lower Oligocene-Burdigalian. In the study area, the major fault systems are still subject of discussion. The Numidian nappe structure, the distribution of basalt and Triassic outcrops within and at the front of this Tellian domain deserve more explanation. In this work we intend to update the structural scheme and the tectonic evolution of the northern Tunisia, taking into account salt tectonics and magmatism. The updated tectonic evolution will be integrated in the geodynamic framework of the Central Mediterranean. For this purpose, we have analyzed morphologic, seismic and structural data. The compilation of the results has allowed the identification of new regional NE-trending faults dipping towards the NW: the Bled el Aouana-Bizerte, the Sejnane-Ras Enjla and the Oued el Harka faults. They correspond to the reactivation of deep-seated normal faults splaying on the Triassic evaporites. This fault system constitutes the main component of the northern Tunisia structural scheme and has influenced its tectonic evolution marked by the main following stages. The Tellian thrust-sheets were immobilized at the uppermost Langhian. During the major Tortonian NW-trending compressive phase, these faults were reactivated with reverse kinematics and controlled the distribution of the post-nappes Neogene continental deposits. At the early Pleistocene, a compressive NNW-trending event has reactivated again these faults with sinistral-reverse movements and deformed the post-nappes Neogene series. Late Quaternary to Actual, the tectonic regime continues to be compressive with a NNW-trending maximum horizontal stress.

Mini-MITEE: Ultra Small, Ultra Light NTP Engines for Robotic Science and Manned Exploration Missions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Powell, James; Maise, George; Paniagua, John

2006-01-20

A compact, ultra lightweight Nuclear Thermal Propulsion (NTP) engine design is described with the capability to carry out a wide range of unique and important robotic science missions that are not possible using chemical or Nuclear Electric Propulsion (NEP). The MITEE (MInature ReacTor EnginE) reactor uses hydrogeneous moderator, such as solid lithium-7 hydride, and high temperature cermet tungsten/UO2 nuclear fuel. The reactor is configured as a modular pressure tube assembly, with each pressure tube containing an outer annual shell of moderator with an inner annular region of W/UO2 cermet fuel sheets. H2 propellant flows radially inwards through the moderator andmore » fuel regions, exiting at {approx}3000 K into a central channel that leads to a nozzle at the end of the pressure tube. Power density in the fuel region is 10 to 20 megawatts per liter, depending on design, producing a thrust output on the order of 15,000 Newtons and an Isp of {approx}1000 seconds. 3D Monte Carlo neutronic analyses are described for MITEE reactors utilizing various fissile fuel options (U-235, U-233, and Am242m) and moderators (7LiH and BeH2). Reactor mass ranges from a maximum of 100 kg for the 7LiH/U-235 option to a minimum of 28 kg for the BeH2/Am-242 m option. Pure thrust only and bi-modal (thrust plus electric power generation) MITEE designs are described. Potential unique robotic science missions enabled by the MITEE engine are described, including landing on Europa and exploring the ice sheet interior with return of samples to Earth, hopping to and exploring multiple sites on Mars, unlimited ramjet flight in the atmospheres of Jupiter, Saturn, Uranus, and Neptune and landing on, and sample return from Pluto.« less

Synthrusting deposition of the Pennsylvanian and Permian Strathearn Formation, Northern Carlin Trend, Nevada

USGS Publications Warehouse

Theodore, T.G.; Berger, V.I.; Singer, D.A.; Harris, A.G.; Stevens, C.H.

2004-01-01

The middle Upper Pennsylvanian and middle Lower Permian Strathearn Formation belongs to the overlap assemblage of the Antler orogen in Nevada. At Beaver Peak, near the Carlin Trend of gold deposits, it contains synorogenic conglomerate deposits associated with emplacement of a regionally extensive, 1-km-thick tectonic wedge that is floored by the Coyote thrust. Normal marine conodont biofacies throughout the Strathearn Formation suggest middle shelf or deeper, depositional environments. The allochthon floored by the Coyote thrust has been thrust above a middle Upper Pennsylvanian, lower conglomerate unit of the Strathearn Formation. A middle Lower Permian upper conglomerate unit, the highest unit recognized in the Strathearn Formation, as well as similarly aged dolomitic siltstone, onlap directly onto Ordovician quartzarenite of the Vinini Formation that makes up most of the Coyote allochthon. Quartz grains and quartzarenite fragments of variable roundness and shape in the conglomerate units were derived from the presently adjoining tectonic lobe of mostly quartzarenite that advanced southeast (present geographic coordinates) during the late Paleozoic into the developing Strathearn basin. Chert fragments in the conglomerates probably were derived mostly from Devonian Slaven Chert, including a widespread thick me??lange unit of the Slaven Chert in the footwall of the Coyote thrust.Lithologic and shape ratio data from approximately 4200 clasts at 17 sites of the two major conglomerate units in the Strathearn Formation at Beaver Peak are roughly similar in that they contain only chert and quartzarenite clasts, and chert clasts predominate in both units. They differ in the relative proportion of the two lithologies whereby quartzarenite clasts increase sixfold in the upper unit (middle Lower Permian) versus its content in the lower conglomerate unit. Relations at the unconformity between the upper conglomerate unit and its underlying quartzarenite shows quartzarenite fragments actually breaking away from an immediately subjacent source. Ordovocian quartzarenite, which forms a tectonically uplifted wedge with the Coyote thrust at its base, became a source region for much of the quartzarenite detritus deposited preferentially in the upper parts of the Strathearn Formation. The conglomerate units of the Strathearn Formation temporally bracket emplacement of the Coyote thrust. Thrusting related to contractional reactivation of the Robert Mountains thrust system largely was completed by middle Early Permian. ?? 2004 Published by Elsevier B.V.

Upper crustal mechanical stratigraphy and the evolution of thrust wedges: insights from sandbox analogue experiments

NASA Astrophysics Data System (ADS)

Milazzo, Flavio; Storti, Fabrizio; Nestola, Yago; Cavozzi, Cristian; Magistroni, Corrado; Meda, Marco; Salvi, Francesca

2016-04-01

Crustal mechanical stratigraphy i.e. alternating mechanically weaker and stronger layers within the crust, plays a key role in determining how contractional deformations are accommodated at convergent plate boundaries. In the upper crust, evaporites typically provide preferential décollement layers for fault localization and foreland ward propagation, thus significantly influencing evolution of thrust-fold belts in terms of mechanical balance, geometries, and chronological sequences of faulting. Evaporites occur at the base of many passive margin successions that underwent positive inversion within orogenic systems. They typically produce salient geometries in deformation fronts, as in the Jura in the Northern Alps, the Salakh Arch in the Oman Mountains, or the Ainsa oblique thrust-fold belt in the Spanish Pyrenees. Evaporites frequently occur also in foredeep deposits, as in the Apennines, the Pyrenees, the Zagros etc. causing development of additional structural complexity. Low-friction décollement layers also occur within sedimentary successions involved in thrust-fold belts and they contribute to the development of staircase fault trajectories. The role of décollement layers in thrust wedge evolution has been investigated in many experimental works, particularly by sandbox analogue experiments that have demonstrated the impact of basal weak layers on many first order features of thrust wedges, including the dominant fold vergence, the timing of fault activity, and the critical taper. Some experiments also investigated on the effects of weak layers within accreting sedimentary successions, showing how this triggers kinematic decoupling of the stratigraphy above and below the décollements, thus enhancing disharmonic deformation. However, at present a systematic experimental study of the deformation modes of an upper crustal mechanical stratigraphy consisting of both low-friction and viscous décollement layers is still missing in the specific literature. In this contribution we present the results of such a study, where a three-décollement mechanical stratigraphy has been deformed in the sandbox at the same boundary conditions. Different rheological properties were assigned to the three décollements in different experiments, up to testing all possible mechanical stratigraphies. Implications on thrust propagation and slip rate history and cross-sectional thrust wedge architecture are discussed and compared with natural cases.

Reconciling deep seismic refraction and reflection data from the grenvillian-appalachian boundary in western New England

USGS Publications Warehouse

Hughes, S.; Luetgert, J.H.; Christensen, N.I.

1993-01-01

The Grenvillian-Appalachian boundary is characterized by pervasive mylonitic deformation and retrograde alteration of a suite of imbricated allochthonous and parautochthonous gneisses that were thrust upon the Grenvillian continental margin during the lower Paleozoic. Seismic reflection profiling across this structural boundary zone reveals prominent dipping reflectors interpreted as overthrust basement slices (parautochthons) of the Green Mountain Anticlinorium. In contrast, a seismic refraction study of the Grenvillian-Appalachian boundary reveals a sub-horizontally layered seismic velocity model that is difficult to reconcile with the pronounced sub-vertical structures observed in the Green mountains. A suite of rock samples was collected from the Green Mountain Anticlinorium and measured at high pressures in the laboratory to determine the seismic properties of these allochthonous and parautochthonous gneisses. The laboratory-measured seismic velocities agree favorably with the modelled velocity structure across the Grenvillian-Appalachian boundary suggesting that the rock samples are reliable indicators of the rock mass as whole. Samples of the parautochthonous Grenvillian basement exposed in the Green Mountains have lower velocities, by about 0.5 km/s, than lithologically equivalent units exposed in the eastern Adirondack Highlands. Velocity reduction in the Green Mountain parautochthons can be accounted for by retrograde metamorphic alteration (hydration) of the paragneisses. Seismic anisotropies, ranging from 2 to 12%, in the mylonitized Green Mountain paragneisses may also contribute to the observation of lower seismic velocities, where the direction of ray propagation is normal to the foliation. The velocity properties of the Green Mountain paragneisses are thus insufficiently different from the mantling Appalachian allochthons to permit their resolution by the Ontario-New York-New England seismic refraction profile. ?? 1993.

Snow and ice in a changing hydrological world.

USGS Publications Warehouse

Meier, M.F.

1983-01-01

Snow cover on land (especially in the Northern Hemisphere) and sea ice (especially in the Southern Hemisphere) vary seasonally, and this seasonal change has an important affect on the world climate because snow and sea ice reflect solar radiation efficiently and affect other heat flow processes between atmosphere and land or ocean. Glaciers, including ice sheets, store most of the fresh water on Earth, but change dimensions relatively slowly. There is no clear evidence that the glacier ice volume currently is declining, but more needs to be known about mountain glacier and ice sheet mass balances. -from Author

Reflector for efficient coupling of a laser beam to air or other fluids

DOEpatents

Kare, Jordin T.

1992-01-01

A reflector array is disclosed herein that provides a controlled region or regions of plasma breakdowns from a laser beam produced at a remotely-based laser source. The plasma may be applied to produce thrust to propel a spacecraft, or to diagnose a laser beam, or to produce shockwaves. The spacecraft propulsion system comprises a reflector array attached to the vehicle. The reflector array comprises a plurality of reflectors spaced apart on a reflective surface, with each reflector acting as an independent focusing mirror. The reflectors are spaced closely together to form a continuous or partially-continuous surface. The reflector array may be formed from a sheet of reflective material, such as copper or aluminum. In operation, a beam of electromagnetic energy, such as a laser beam, is directed at the reflectors which focus the reflected electromagnetic energy at a plurality of regions off the surface. The energy concentrated in the focal region causes a breakdown of the air or other fluid in the focal region, creating a plasma. Electromagnetic energy is absorbed in the plasma and it grows in volume, compressing and heating the adjacent fluid thereby providing thrust. Laser pulses may be applied repetitively. After each such thrust pulse, fresh air can be introduced next to the surface either laterally, or through a perforated surface. If air or some other gas or vapor is supplied, for example from a tank carried on board a vehicle, this invention may also be used to provide thrust in a vacuum environment.

Soro West: A non-seismically defined, fault cut-off prospect in the Papuan Fold and Thrust Belt, Papua New Guinea

DOE Office of Scientific and Technical Information (OSTI.GOV)

Robinson, W.F.; Swift, C.M. Jr.

Soro West is a fault cut-off prospect located in the frontal portion of the Papuan Fold and Thrust Belt. Prospective Toro and Imburu sandstones are interpreted to be in the hanging wall of the Soro Thrust. Truncation against the thrust, both updip and through lateral ramps, provides the trapping mechanism. The Soro West Prospect was defined using geological, geochemical, remote sensing, and geophysical data. The definition and location of the trap is a primary risk and work was focused on this aspect. Surface geological data (lithology, strikes, and dips) topography and synthetic aperture radar imagery were incorporated into the evaluation.more » Statistical curvature analysis techniques helped define the shape of the structure and the locations of the lateral ramps. Strontium isotope analyses of Darai Limestone surface samples refined erosional levels using a locally-derived reference curve. Severe karst precludes the acquisition of coherent surface seismic data, so the primary geophysical tool used was magnetotellurics (MT). A detailed, pre-survey feasibility study defined expected responses from alternative structural models. The MT data demonstrated that the limestone at surface is underlain by thick conductive clastics and not another Darai Limestone sheet. The data also constrained the range of fault cut-off positions significantly. Multiple, three-dimensionally consistent, restorable alternative structural models were created using results from all analyses. These led to a positive assessment of the prospect and an exploratory test is to be drilled in 1996.« less

Geologic and geophysical maps of the eastern three-fourths of the Cambria 30' x 60' quadrangle, central California Coast Ranges

USGS Publications Warehouse

Graymer, R.W.; Langenheim, V.E.; Roberts, M.A.; McDougall, Kristin

2014-01-01

The Cambria 30´ x 60´ quadrangle comprises southwestern Monterey County and northwestern San Luis Obispo County. The land area includes rugged mountains of the Santa Lucia Range extending from the northwest to the southeast part of the map; the southern part of the Big Sur coast in the northwest; broad marine terraces along the southwest coast; and broadvalleys, rolling hills, and modest mountains in the northeast. This report contains geologic, gravity anomaly, and aeromagnetic anomaly maps of the eastern three-fourths of the 1:100,000-scale Cambria quadrangle and the associated geologic and geophysical databases (ArcMap databases), as well as complete descriptions of the geologic map units and the structural relations in the mapped area. A cross section is based on both the geologic map and potential-field geophysical data. The maps are presented as an interactive, multilayer PDF, rather than more traditional pre-formatted map-sheet PDFs. Various geologic, geophysical, paleontological, and base map elements are placed on separate layers, which allows the user to combine elements interactively to create map views beyond the traditional map sheets. Four traditional map sheets (geologic map, gravity map, aeromagnetic map, paleontological locality map) are easily compiled by choosing the associated data layers or by choosing the desired map under Bookmarks.

Paleozoic-involving thrust array in the central Sierras Interiores (South Pyrenean Zone, Central Pyrenees): regional implications

NASA Astrophysics Data System (ADS)

Rodriguez, L.; Cuevas, J.; Tubía, J. M.

2012-04-01

This work deals with the structural evolution of the Sierras Interiores between the Tena and Aragon valleys. The Sierras Interiores is a WNW-trending mountain range that bounds the South Pyrenean Zone to the north and that is characterized by a thrust-fold system with a strong lithological control that places preferably decollements in Triassic evaporites. In the studied area of the Sierras Interiores Cenomanian limestones cover discordantly the Paleozoic rocks of the Axial Zone because there is a stratigraphic lacuna developed from Triassic to Late Cretaceous times. A simple lithostratigraphy of the study area is made up of Late Cenomanian to Early Campanian limestones with grey colour and massive aspect in landscape (170 m, Lower calcareous section), Campanian to Maastrichtian brown coloured sandstones (400-600 m, Marboré sandstones) and, finally, Paleocene light-coloured massive limestones (130-230 m), that often generate the higher topographic levels of the Sierras Interiores due to their greater resistance to erosion. Above the sedimentary sequence of the Sierras Interiores, the Jaca Basin flysch succession crops out discordantly. Based on a detailed mapping of the studied area of the Sierras Interiores, together with well and structural data of the Jaca Basin (Lanaja, 1987; Rodríguez and Cuevas, 2008) we have constructed a 12 km long NS cross section, approximately parallel to the movement direction deduced for this region (Rodríguez et al., 2011). The main structure is a thrust array made up of at least four Paleozoic-involving thrusts (the deeper thrust system) of similar thickness in a probably piggyback sequence, some of which are blind thrusts that generate fold-propagation-folds in upper levels. The higher thrust of the thrust array crops out duplicating the lower calcareous section all over the Sierras Interiores. The emplacement of the deeper thrust system generated the tightness of previous structures: south directed piggyback duplexes (the upper thrust system) affecting the Marboré sandstones and the Paleocene limestones, deformed by angular south-vergent folds and their related axial plane foliation. The transect explained above clearly summarizes the alpine evolution of northern part of the Sierras Interiores. Moreover, well data available indicate the presence of two thrust soled in the lower calcareous section covering Triassic evaporites at 5 km depth and 8 km to the south of the Sierras Interiores. Because the Triassic evaporites constitute a main decollement level in the South Pyrenean Zone, the deeper thrust system is associated to the emplacement of the Gavarnie nappe. Lanaja, J.M., 1987, Contribución de la exploración petrolífera al conocimiento de la Geología de España, IGME, Madrid, 465 p. Rodríguez, L., Cuevas, J., 2008. Geogaceta 44, 51-54. Rodríguez, L., Cuevas, J., Tubia, J.M., 2011. Geophysical Research Abstracts 13, 2273.

Kinematic Evolution of the North-Tehran Fault (NTF), Alborz Mountains, Iran

NASA Astrophysics Data System (ADS)

Landgraf, A.; Ballato, P.; Strecker, M. R.; Shahpasandzadeh, M.; Friedrich, A.; Tabatabaei, S. H.

2007-12-01

The ENE-to NW-striking NTF is an active frontal thrust that delimits the Alborz Mountain range to the south with an up to 2000 m topographic break with respect to the adjacent Tehran plain. Eocene rocks of the Alborz range are thrusted over Neogene and Quaternary sediments of the alluvial Tehran embayment. The fault consists of right- stepping segments and merges to the east with the active Mosha-Fasham strike-slip fault (MFF). The complex tectonic history, involving changes in the direction of SHmax, has resulted in a composite tectonic landscape with inherited topographic and fault-kinematic fingerprints along the NTF. We therefore used a combination of fault-kinematic measurements and geomorphic observations to unravel the temporal tectonic evolution of this fault. Presently, the NTF is virtually inactive, although the tectonically overprinted landforms reflect tectonic activity on longer time scales during the Quaternary. Being located adjacent north of the Tehran megacity, there is thus considerable interest to decipher its youngest tectonic evolution and to better understand the relation with other fault systems. Our fault kinematic study has revealed an early dextral kinematic history for the NTF. Dextral strike-slip and oblique reverse faulting took place during NW-oriented shortening. The overall fault-geometry of the NTF suggests that it has evolved in relation to dextral transpression along the MFF. This early kinematic regime was superseded by NE-oriented shortening, associated with sinistral-oblique thrusting along the fault segments. Fault linkage between the semi-independent ENE-striking NTF-segments and NW-striking thrusts (Emamzadeh Davud Fault [EDF], Purkan Vardij Thrust [PVT], NTF-prolongation) point towards an evolution into a nascent transpressional duplex. In this scenario the NTF segments constitute lateral ramps and the NW-striking faults act as frontal ramps. Topographic residuals, as an expression of high-uplift zones, indicate that the central segment of the NTF, incorporating the EDF was most effective in accommodating oblique convergence during this time. However, subtle knickpoints in the longitudinal river profiles crossing the PVT may indicate a relatively recent transfer of deformation onto this block. The youngest manifestations of deformation along the NTF, however, are left-lateral and normal faulting. This youngest phase of activity is documented by numerous striated and rotated conglomeratic clasts, meter-scale fault gouge zones with shear-sense indicators of oblique normal faulting, and multiple colluvial wedges with drag phenomena. Rupture traces and filled extensional cracks reaching the surface also document the seismogenic nature of these features. Since recent left-lateral transtension is also known from neighboring faults, e.g., the eastern MFF, our observations suggest that this youngest phase of tectonic activity of the NTF is a regional phenomenon, rather than the result of locally-determined geometries.

Coseismic fold scarp associated with historic earthquakes upon the Yoro active blind thrust, the Nobi-Ise fault zone, central Japan

NASA Astrophysics Data System (ADS)

Ishiyama, T.; Mueller, K.; Togo, M.

2004-12-01

We present structural models constrained by tectonic geomorphology, surface geologic mapping, shallow borehole transects and a high-resolution S-wave seismic reflection profile to define the kinematic evolution of a coseismic fold scarp along the Nobi-Ise fault zone (NIFZ). The NIFZ is an active intraplate fault system in central Japan, and consists of a 110-km-long array of active, east-verging reverse faults. Fold scarps along the Yoro fault are interpreted as produced during a large historic blind-thrust earthquake. The Yoro Mountains form the stripped core of the largest structure in the NIFZ and expose Triassic-Jurassic basement that are thrust eastward over a 2-km-thick sequence of Pliocene-Pleistocene strata deposited in the Nobi basin. This basement-cored fold is underlain by an active blind thrust that is expressed as late Holocene fold scarps along its eastern flank. Drilling investigations across the fold scarp at a site near Shizu identified at least three episodes of active folding associated with large earthquakes on the Yoro fault. Radiocarbon ages constrain the latest event as having occurred in a period that contains historical evidence for a large earthquake in A.D. 1586. A high resolution, S-wave seismic reflection profile at the same site shows that the topographic fold scarp coincides with the projected surface trace of the synclinal axis, across which the buried, early Holocene to historic sedimentary units are folded. This is interpreted to indicate that the structure accommodated coseismic fault-propagation folding during the A.D. 1586 blind thrust earthquake. Flexural-slip folding associated with secondary bedding-parallel thrusts may also deform late Holocene strata and act to consume slip on the primary blind thrust across the synclinal axial surfaces. The best-fitting trishear model for folded ca. 13 ka gravels deposited across the forelimb requires a 28\\deg east-dipping thrust fault. This solution suggests that a 4.2 mm/yr of slip rate has been accommodated on the Yoro fault during the late Holocene, with an average vertical rate of 1.9 mm/yr. This is consistent with longer-term slip rates calculated by a structural relief across a ca. 7.3 ka volcanic ash horizon (1.6 mm/yr), and ca. 110 ka innerbay clays (1.3 mm/yr) deposited across the forelimb. Our trishear model is thus able to account for the bulk of the folding history accommodated at shorter millennial timescales, suggesting that this technique may be used to adequately define slip rates on blind thrust faults.

Magnetotail particle dynamics and transport

NASA Technical Reports Server (NTRS)

Speiser, Theodore W.

1995-01-01

The main thrust of our research is to study the consequences of particle dynamics in the current sheet region of the magnetotail. The importance of understanding particle dynamics, in and near current sheets, cannot be over estimated, especially in light of NASA's recent interest in developing global circulation models to predict space weather. We have embarked on a long-term study to investigate the electrical resistance due to chaotic behavior, compare this resistance to inertial effects, and relate it to that resistance required in MHD modeling for reconnection to proceed. Using a single-particle model and observations, we have also found that a neutral line region can be remotely sensed. We plan to evaluate other cases of satellite observations near times of substorm onset to elucidate the relationship between the temporal development of a near-Earth neutral line and onset.

Lithospheric buckling and far-foreland deformation during the Laramide and Appalachian orogenies

NASA Astrophysics Data System (ADS)

Tikoff, B.; Siddoway, C. S.

2017-12-01

Major intraplate tectonics within North America (Laurentia) occurs during times of major orogenesis along the plate margins. During mountain building, typical structures of the hinterland are an orogenic plateau and fold-and-thrust belts, while in the far foreland (intraplate) areas long-wavelength ( 200 km or longer) folds and fault-reactivation features form. Long-wavelength folds are evident in both the Appalachian and Laramide orogenic forelands, with the stratigraphy recording the timing of the uplift. This contribution examines the model of lithospheric buckling - periodic folding associated with a horizontal endload on the edge of the plate - based on scaled, physical experiments and corroborated by numerical models. The Laramide (75-55 Ma) intraplate orogen in the classical location in Wyoming contains basement-cored arches spaced 200 km apart, for which the mechanism of uplift is questioned. Seismic evidence obtained for the Bighorn uplift, Wyoming, obtained by the EarthScope Bighorn project, shows an upwarp of the Moho beneath, but oblique to the trend of the surface exposure of the basement arch. Both the surface and Moho exhibit approximately the same structural relief. The seismic data exhibit no evidence for a regionally continuous decollement, nor is there evidence of rotation of structural markers within these features, of the type that is observed in the detached fold-and-thrust belt. The intraplate region affected by long-wavelength folding includes western Wyoming, with continuation of some features across the E-W-oriented Cheyenne belt (e.g., Rock Springs-Douglas Creek arch), Colorado Plateau, and High Plains east of the Rocky Mountains, where surface and subsurface structures display a series of anticlinal arches ("plains-type" folds). Appalachian mountain building also caused long-wavelength folding, with a spacing consistent with lithospheric buckling, mostly associated with the Devonian Acadian orogeny. The Laramide arches in the High Plains seem to occur on arches inherited from the Appalachian orogeny, suggesting the permanence of these lithospheric buckles once they have formed.

Physical Limits on Hmax, the Maximum Height of Glaciers and Ice Sheets

NASA Astrophysics Data System (ADS)

Lipovsky, B. P.

2017-12-01

The longest glaciers and ice sheets on Earth never achieve a topographic relief, or height, greater than about Hmax = 4 km. What laws govern this apparent maximum height to which a glacier or ice sheet may rise? Two types of answer appear possible: one relating to geological process and the other to ice dynamics. In the first type of answer, one might suppose that if Earth had 100 km tall mountains then there would be many 20 km tall glaciers. The counterpoint to this argument is that recent evidence suggests that glaciers themselves limit the maximum height of mountain ranges. We turn, then, to ice dynamical explanations for Hmax. The classical ice dynamical theory of Nye (1951), however, does not predict any break in scaling to give rise to a maximum height, Hmax. I present a simple model for the height of glaciers and ice sheets. The expression is derived from a simplified representation of a thermomechanically coupled ice sheet that experiences a basal shear stress governed by Coulomb friction (i.e., a stress proportional to the overburden pressure minus the water pressure). I compare this model to satellite-derived digital elevation map measurements of glacier surface height profiles for the 200,000 glaciers in the Randolph Glacier Inventory (Pfeffer et al., 2014) as well as flowlines from the Greenland and Antarctic Ice Sheets. The simplified model provides a surprisingly good fit to these global observations. Small glaciers less than 1 km in length are characterized by having negligible influence of basal melt water, cold ( -15C) beds, and high surface slopes ( 30 deg). Glaciers longer than a critical distance 30km are characterized by having an ice-bed interface that is weakened by the presence of meltwater and is therefore not capable of supporting steep surface slopes. The simplified model makes predictions of ice volume change as a function of surface temperature, accumulation rate, and geothermal heat flux. For this reason, it provides insights into both past and future global ice volume changes.

The petrology, structure and geochemistry of an Archean terrane in the North Snowy Block, Beartooth Mountains, Montana

NASA Astrophysics Data System (ADS)

Mogk, D. W.

1984-12-01

Six major rock units in the North Snowy Block in an Archean mobile belt are recognized between all units representing discontinuities in metamorphic grade, structural style, geochemistry, and isotopic ages. Four of the units occur in NE trending linear belts; the Basement Gneiss; the phyllitic Davis Creek Schist; the mount cowen augen gneis; the Paragneiss unit. Overlying the linear units is the 3.2 Ga old Pine Creek Nappe Complex, an isoclinally folded, middle to upper amphibolite facies, thrust nappe consisting of the Barney Creek Amphibolite, George Lake Marble and Jewel Quartzite. The highest structural units, including a thick sequence of upper amphibolite grade supracrustal rocks and a lower section of injected 3.4 Ga old granitic to tonalitic migmatitic rocks were emplaced on the Columbine Thrust. It is shown that there was secular variation in tectonic style in the Archean of southwest Montana. Three stages are recognized: (1) melting of ancient matic crust produced trondhjemitic continental nuclei; (2) numerous ensialic basins were created and destroyed, resulting in high grade metamorphism and mignatization of supracrustal rocks; and (3) contemporary style plate tectonics resulted in generation of large volumes of andesities and calc-alkaline granitic rocks, transcurrent faulting, and thrust faulting.

A Mountain Child: An Active Learning Pack for 9-13 Year Olds.

ERIC Educational Resources Information Center

Lyle, Sue; Jenkins, Alyson

This resource packet includes a teacher's guide, reproducible student activity sheets, a simulation game: "Life with the Incas", and a poster. The resource presents a cross-curricular thematic approach to the United Kingdom's National Curriculum. The materials look at the Andes and the Andean people, the Quechuan, who live in the…

Chlorine-36 and 14C chronology support a limited last glacial maximum across central Chukotka, northeastern Siberia, and no Beringian ice sheet

USGS Publications Warehouse

Brigham-Grette, J.; Gualtieri, L.M.; Glushkova, O.Y.; Hamilton, T.D.; Mostoller, D.; Kotov, A.

2003-01-01

The Pekulney Mountains and adjacent Tanyurer River valley are key regions for examining the nature of glaciation across much of northeast Russia. Twelve new cosmogenic isotope ages and 14 new radiocarbon ages in concert with morphometric analyses and terrace stratigraphy constrain the timing of glaciation in this region of central Chukotka. The Sartan Glaciation (Last Glacial Maximum) was limited in extent in the Pekulney Mountains and dates to ???20,000 yr ago. Cosmogenic isotope ages > 30,000 yr as well as non-finite radiocarbon ages imply an estimated age no younger than the Zyryan Glaciation (early Wisconsinan) for large sets of moraines found in the central Tanyurer Valley. Slope angles on these loess-mantled ridges are less than a few degrees and crest widths are an order of magnitude greater than those found on the younger Sartan moraines. The most extensive moraines in the lower Tanyurer Valley are most subdued implying an even older, probable middle Pleistocene age. This research provides direct field evidence against Grosswald's Beringian ice-sheet hypothesis. ?? 2003 Elsevier Science (USA). All rights reserved.

From nappe stacking to extensional detachments at the contact between the Carpathians and Dinarides - The Jastrebac Mountains of Central Serbia

NASA Astrophysics Data System (ADS)

Erak, Dalibor; Matenco, Liviu; Toljić, Marinko; Stojadinović, Uroš; Andriessen, Paul A. M.; Willingshofer, Ernst; Ducea, Mihai N.

2017-07-01

Reactivation of inherited nappe contacts is a common process in orogenic areas affected by back-arc extension. The amount of back-arc extension is often variable along the orogenic strike, owing to the evolution of arcuated mountain chains during stages of rapid slab retreat. This evolution creates low rates of extension near rotation poles, where kinematics and interplay with the pre-existing orogenic structure are less understood. The amount of Miocene extension recorded by the Pannonian Basin of Central Europe decreases SE-wards along the inherited Cretaceous - Paleogene contact between the Dinarides and Carpathian Mountains. Our study combines kinematic data obtained from field and micro-structural observations assisted with fission track thermochronological analysis and U-Pb zircon dating to demonstrate a complex poly-phase evolution in the key area of the Jastrebac Mountains of Serbia. A first event of Late Cretaceous exhumation was followed by latest Cretaceous - Eocene thrusting and magmatism related to a continental collision that sutured the accretionary wedge containing contractional trench turbidites. The suture zone was subsequently reactivated and exhumed by a newly observed Miocene extensional detachment that lasted longer in the Jastrebac Mountains when compared with similar structures situated elsewhere in the same structural position. Such extensional zones situated near the pole of extensional-driven rotation favour late stage truncations and migration of extension in a hanging-wall direction, while directions of tectonic transport show significant differences in short distances across the strike of major structures.

Fluvial-Deltaic Strata as a High-Resolution Recorder of Fold Growth and Fault Slip

NASA Astrophysics Data System (ADS)

Anastasio, D. J.; Kodama, K. P.; Pazzaglia, F. P.

2008-12-01

Fluvial-deltaic systems characterize the depositional record of most wedge-top and foreland basins, where the synorogenic stratigraphy responds to interactions between sediment supply driven by tectonic uplift, climate modulated sea level change and erosion rate variability, and fold growth patterns driven by unsteady fault slip. We integrate kinematic models of fault-related folds with growth strata and fluvial terrace records to determine incremental rates of shortening, rock uplift, limb tilting, and fault slip with 104-105 year temporal resolution in the Pyrenees and Apennines. At Pico del Aguila anticline, a transverse dècollement fold along the south Pyrenean mountain front, formation-scale synorogenic deposition and clastic facies patterns in prodeltaic and slope facies reflect tectonic forcing of sediment supply, sea level variability controlling delta front position, and climate modulated changes in terrestrial runoff. Growth geometries record a pinned anticline and migrating syncline hinges during folding above the emerging Guarga thrust sheet. Lithologic and anhysteretic remanent magnetization (ARM) data series from the Eocene Arguis Fm. show cyclicity at Milankovitch frequencies allowing detailed reconstruction of unsteady fold growth. Multiple variations in limb tilting rates from <8° to 28°/my over 7my are attributed to unsteady fault slip along the roof ramp and basal dècollement. Along the northern Apennine mountain front, the age and geometry of strath terraces preserved across the Salsomaggiore anticline records the Pleistocene-Recent kinematics of the underlying fault-propagation fold as occurring with a fixed anticline hinge, a rolling syncline hinge, and along-strike variations in uplift and forelimb tilting. The uplifted intersection of terrace deposits documents syncline axial surface migration and underlying fault-tip propagation at a rate of ~1.4 cm/yr since the Middle Pleistocene. Because this record of fault slip coincides with the well-known large amplitude oscillations in global climate that contribute to the filling and deformation of the Po foreland, we hypothesize that climatically-modulated surface processes are reflected in the observed rates of fault slip and fold growth.

Growth and erosion of mountain ranges at the northeastern margin of Tibet

NASA Astrophysics Data System (ADS)

Hetzel, Ralf; Palumbo, Luigi; Giese, Jörg; Guo, Jianming

2010-05-01

The hypothesis that mountain belts may reach a steady state, in which rock uplift is balanced by erosion, has been supported by numerous field studies and numerical models. The early evolution of mountain ranges, however, and especially the relation between fault growth and topographic response has received little attention. By using a space-for-time substitution we illustrate how active thrust faults and small, fault-bounded mountain ranges evolve into mature mountain chains that will ultimately be incorporated into the laterally growing Tibetan Plateau. At an early stage of development, when faults propagate laterally, slip rates are constant along strike [1-3]. As long as no significant topographic relief has developed, tectonic uplift is at least an order of magnitude faster than the rate of erosion [2,4]. During progressive relief growth and the establishment of drainage basins, erosion of the rising mountain ranges becomes more important, but the studied ranges are still in a pre-steady state and continue to grow both vertically and laterally [5]. During this stage the rate of erosion is linearly correlated to the mean hillslope gradient and the mean local relief, if differences in lithology or rock strength are negligible [6]. The rate of relief growth may be inferred from the difference between local erosion rates on ridge crests and catchment-wide denudation rates [7] - the latter may be taken as a surrogate for the rate of river incision. As hillslopes approach a threshold value, landsliding becomes the dominant process of mass transport and erosion rates increase non-linearly with slope. Once a steady state has been reached, the erosion rate is equal to the rate of rock uplift. A key problem is how the rate of rock uplift can be quantified in such regions, because the stochastic distribution of landslides causes the denudation rates inferred from 10Be in river sediment to be highly variable [8]. References [1] Hetzel et al. (2004). Implications of the fault scaling law for the growth of topography: Mountain ranges in the broken foreland of NE Tibet. Terra Nova 16, 157-162. [2] Hetzel et al. (2002). Low slip rates and long-term preservation of geomorphic features in Central Asia. Nature 417, 428-432. [3] Hetzel et al. (2004). Late Pleistocene/Holocene slip rate of the Zhangye thrust (Qilian Shan, China) and implications for the active growth of the northeastern Tibetan Plateau, Tectonics 23, TC6006, doi:10.1029/2004TC001653. [4] Goethals et al. (2009). Determining the impact of faulting on the rate of erosion in a low-relief landscape: A case study using in situ produced 21Ne on active normal faults in the Bishop Tuff, California. Geomorphology 103, 401-413. [5] Palumbo et al. (2009). Deciphering the rate of mountain growth during topographic presteady state: an example from the NE margin of the Tibetan Plateau. Tectonics 28, TC4017, doi:10.1029/2009TC002455. [6] Palumbo et al. (in press). Topographic and lithologic control on catchment-wide denudation rates derived from cosmogenic 10Be in two mountain ranges at the margin of NE Tibet. Geomorphology, doi:10.1016/j.geomorph.2009.11.019. [7] Meyer et al. (in press). Determining the growth rate of topographic relief using in situ-produced 10Be: A case study in the Black Forest, Germany. Earth and Planetary Science Letters. [8] Densmore et al. (2009). Spatial variations in catchment-averaged denudation rates from normal fault footwalls. Geology 37, 1139-1142.

Formation of fold and thrust belts on Venus due to horizontal shortening of a laterally heterogeneous lithosphere

NASA Technical Reports Server (NTRS)

Zuber, M. T.; Parmentier, E. M.; Neumann, G. A.

1994-01-01

An outstanding question relevant to understanding the tectonics of Venus is the mechanism of formation of fold and thrust belts, such as the mountain belts that surround Lakshmi Planum in western Ishtar Terra. These structures are typically long (hundreds of km) and narrow (many tens of km), and are often located at the margins of relatively high (km-scale) topographic rises. Previous studies have attempted to explain fold and thrust belts in various areas of Venus in the context of viscous and brittle wedge theory. However, while wedge theory can explain the change in elevation from the rise to the adjacent lowland, it fails to account for a fundamental aspect of the deformation, i.e., the topographic high at the edge of the rise. In this study we quantitatively explore the hypothesis that fold and thrust belt morphology on Venus can alternatively be explained by horizontal shortening of a lithosphere that is laterally heterogeneous, due either to a change in thickness of the lithosphere or the crust. Lateral heterogeneities in lithosphere structure may arise in response to thermal thinning or extensive faulting, while variations in crustal thickness may arise due to either spatially variable melting of mantle material or by horizontal shortening of the crust. In a variable thickness lithosphere or crust that is horizontally shortened, deformation will tend to localize in the vicinity of thickness heterogeneity, resulting in a higher component of dynamic topography there as compared to elsewhere in the shortening lithosphere. This mechanism may thus provide a simple explanation for the topographic high at the edge of the rise.

Formation of fold and thrust belts on Venus due to horizontal shortening of a laterally heterogeneous lithosphere

NASA Astrophysics Data System (ADS)

Zuber, M. T.; Parmentier, E. M.; Neumann, G. A.

1994-03-01

An outstanding question relevant to understanding the tectonics of Venus is the mechanism of formation of fold and thrust belts, such as the mountain belts that surround Lakshmi Planum in western Ishtar Terra. These structures are typically long (hundreds of km) and narrow (many tens of km), and are often located at the margins of relatively high (km-scale) topographic rises. Previous studies have attempted to explain fold and thrust belts in various areas of Venus in the context of viscous and brittle wedge theory. However, while wedge theory can explain the change in elevation from the rise to the adjacent lowland, it fails to account for a fundamental aspect of the deformation, i.e., the topographic high at the edge of the rise. In this study we quantitatively explore the hypothesis that fold and thrust belt morphology on Venus can alternatively be explained by horizontal shortening of a lithosphere that is laterally heterogeneous, due either to a change in thickness of the lithosphere or the crust. Lateral heterogeneities in lithosphere structure may arise in response to thermal thinning or extensive faulting, while variations in crustal thickness may arise due to either spatially variable melting of mantle material or by horizontal shortening of the crust. In a variable thickness lithosphere or crust that is horizontally shortened, deformation will tend to localize in the vicinity of thickness heterogeneity, resulting in a higher component of dynamic topography there as compared to elsewhere in the shortening lithosphere. This mechanism may thus provide a simple explanation for the topographic high at the edge of the rise.

Contrasting terrace systems of the lower Moulouya river as indicator of crustal deformation in NE Morocco

NASA Astrophysics Data System (ADS)

Rixhon, Gilles; Bartz, Melanie; El Ouahabi, Meriam; Szemkus, Nina; Brückner, Helmut

2017-02-01

The Moulouya river has the largest catchment in Morocco and drains an area characterized by active crustal deformation during the Late Cenozoic due to the N-S convergence between the African and Eurasian plates. As yet, its Pleistocene terrace sequence remains poorly documented. Our study focuses on the lowermost reach of the river in north-eastern Morocco, which drains the Zebra-Triffa sedimentary basin directly upstream of the estuary. New field observations, measurements and sedimentological data reveal contrasting fluvial environments on each side of a newly identified, W-E striking thrust zone disrupting the sedimentary basin. On the one hand, long-lasting fluvial aggradation, materialized by 37 m-thick stacked terraces, has occurred in the footwall of the thrust. On the other hand, the hanging wall is characterized by a well-preserved terrace staircase, with three Pleistocene terrace levels. Whilst the identification of this thrust zone question some previous interpretations about the local (hydro-)geology, it is consistent with the statement that most of the Plio-Quaternary deformation in the eastern Rif mountains has concentrated in this region of Morocco. Our new data and interpretations also agree with morphometric indicators showing that the whole Moulouya catchment is at desequilibrium state (i.e. several knickzones in its longitudinal profile), showing several knickzones in its longitudinal profile, is at disequilibrium state. We also suggest that the knickzone in the Beni Snassen gorge, located directly upstream of the Zebra-Triffa sedimentary basin, could (partly) result from a transient fluvial reaction to Late Cenozoic thrusting activity and correlated uplift in the hanging wall.

Mountain Peaks

NASA Image and Video Library

2014-11-10

Mountain peaks through the ice cover on Thurston Island off of western Antarctica as seen on the IceBridge flight on Nov. 5, 2014. Image Credit: NASA/Jim Yungel NASA’s Operation IceBridge collected some rare images on a flight out of Punta Arenas, Chile on Nov. 5, 2014, on a science flight over western Antarctica dubbed Ferrigno-Alison-Abbott 01. The crew snapped a few shots of a calving front of the Antarctic ice sheet. This particular flight plan was designed to collect data on changes in ice elevation along the coast near the Ferrigno and Alison ice streams, on the Abbot Ice Shelf, and grounded ice along the Eights Coast.

Seismic images of a tectonic subdivision of the Greenville Orogen beneath lakes Ontario and Erie

USGS Publications Warehouse

Forsyth, D. A.; Milkereit, B.; Davidson, A.; Hanmer, S.; Hutchinson, Deborah R.; Hinze, W. J.; Mereu, R.F.

1994-01-01

New seismic data from marine air-gun and Vibroseis profiles in Lake Ontario and Lake Erie provide images of subhorizontal Phanerozoic sediments underlain by a remarkable series of easterly dipping reflections that extends from the crystalline basement to the lower crust. These reflections are interpreted as structural features of crustal-scale subdivisions within the Grenville Orogen. Broadly deformed, imbricated, and overlapping thrust sheets within the western Central Metasedimentary Belt are succeeded to the west by a complex zone of easterly dipping, apparent thrust faults that are interpreted as a southwest subsurface extension of the boundary zone between the Central Metasedimentary Belt and the Central Gneiss Belt. The interpreted Central Metasedimentary Belt boundary zone has a characteristic magnetic anomaly that provides a link from the adjacent ends of lakes Ontario and Erie to structures exposed 150 km to the north. Less reflective, west-dipping events are interpreted as structures within the eastern Central Gneiss Belt. The seismic interpretation augments current tectonic models that suggest the exposed ductile structures formed at depth as a result of crustal shortening along northwest-verging thrust faults. Relatively shallow reflections across the boundary region suggest local, Late Proterozoic extensional troughs containing post-Grenville sediments, preserved possibly as a result of pre-Paleozoic reactivation of basement structures.

The Mountains of Io: Global and Geological Perspectives from Voyager and Galileo

NASA Technical Reports Server (NTRS)

Schenk, Paul; Hargitai, Henrik; Wilson, Ronda; McEwen, Alfred; Thomas, Peter; Bredekamp, Joe (Technical Monitor)

2001-01-01

To search for local and global scale geologic associations that may be related to the internal dynamics of Io, we have completed a global catalog of all mountains and volcanic centers. We have identified 115 mountain structures (covering approx. 3% of the surface) and 541 volcanic centers, including paterae (calderas and dark spots) and shield volcanoes. The average length of an Ionian mountain is 157 km, with the longest being 570 km. The mean height of Ionian mountains is 6.3 km, and the highest known mountain is Boosaule Montes (17.5 +/- 3 km). Five basic morphologic types of mountains have been identified; mesa, plateau peak, ridge, and massif. Very few mountains bear any physical similarity. to classic volcanic landforms, but many resemble flatiron mountains on Earth and are interpreted as tilted crustal blocks. This would be consistent with the hypothesis that most mountains are thrust blocks formed as a result of compressive stresses built up in the lower crust due to the global subsidence of volcanic layers as they are buried over time. More than one mechanism may be responsible for all Ionian mountains, however. The proximity of some mountains to paterae may indicate a direct link between some mountains and volcanism, although it is not always clear which came first. In contrast to earlier studies, a pronounced bimodal pattern is observed in the global distribution of both mountains and volcanic centers. The regions of highest areal densities of volcanic centers are near the sub- and anti-Jovian regions, but are offset roughly 90deg in longitude from the two, regions of greatest concentration of mountains. This anticorrelation may indicate the overprinting of a second stress field on the global compressive stresses due to subsidence. The bimodal distribution of volcanic centers and mountains is consistent with models of asthenospheric tidal heating and internal convection developed by Tackley et al.Over regions of mantle upwelling, compressive stresses in the lower crust induced by global subsidence might be reduced, encouraging volcanism and discouraging mountain building. In regions of mantle downwelling, these compressive stresses in the lower crust might be increased, discouraging volcanism and encouraging mountain building. Alternatively, the global pattern may be related to possible (but undocumented) nonsynchronous rotation of lo, which would produce two regions each of compression and extension in the crust. Evidence of layering and of mass wasting, including landslides, block sliding, debris aprons and downslope creep, on Ionian mountains suggests that the crust of Io is essentially a layered stack of partially consolidated volcanic lavas and plume deposits, becoming more consolidated with depth. The lower crust especially may also be ductily deformed, punctuated by volcanic intrusions and faulting at paterae, and broken into blocks, some of which have been uplifted to form mountains.

Polyphase tertiary fold-and-thrust tectonics in the Belluno Dolomites: new mapping, kinematic analysis, and 3D modelling

NASA Astrophysics Data System (ADS)

Chistolini, Filippo; Bistacchi, Andrea; Massironi, Matteo; Consonni, Davide; Cortinovis, Silvia

2014-05-01

The Belluno Dolomites are comprised in the eastern sector of the Southern Alps, which corresponds to the fold-and-thrust belt at the retro-wedge of the Alpine collisional orogen. They are characterized by a complex and polyphase fold-and-thrust tectonics, highlighted by multiple thrust sheets and thrust-related folding. We have studied this tectonics in the Vajont area where a sequence of Jurassic, Cretaceous and Tertiary units have been involved in multiple deformations. The onset of contractional tectonics in this part of the Alps is constrained to be Tertiary (likely Post-Eocene) by structural relationships with the Erto Flysch, whilst in the Mesozoic tectonics was extensional. We have recognized two contractional deformation phases (D1 and D2 in the following), of which only the second was mentioned in previous studies of the area and attributed to the Miocene Neoalpine event. D1 and D2 are characterized by roughly top-to-WSW (possibly Dinaric) and top-to-S (Alpine) transport directions respectively, implying a 90° rotation of the regional-scale shortening axis, and resulting in complex thrust and fold interference and reactivation patterns. Geological mapping and detailed outcrop-scale kinematic analysis allowed us to characterize the kinematics and chronology of deformations. Particularly, relative chronology was unravelled thanks to (1) diagnostic fold interference patterns and (2) crosscutting relationships between thrust faults and thrust-related folds. A km-scale D1 syncline, filled with the Eocene Erto Flysch and "decapitated" by a D2 thrust fault, provides the best map-scale example of crosscutting relationships allowing to reconstruct the faulting history. Due to the strong competence contrast between Jurassic carbonates and Tertiary flysch, in this syncline spectacular duplexes were also developed during D2. In order to quantitatively characterize the complex interference pattern resulting from two orthogonal thrusting and folding events, we performed a dip-domain analysis that allowed to categorize the different fold limbs and reduce the uncertainty in the reconstruction of the fault network topology in map view. This enabled us to reconstruct a high-quality, low-uncertainty 3D structural and geological model, which unambiguously proves that deformations with a top-to-WSW Dinaric transport direction propagate farther to the west than previously supposed in this part of the Southern Alps. Our new structural reconstruction of the Vajont valley have also clarified the structural control on the 1963 catastrophic landslide (which caused over 2000 losses). Besides being a challenging natural laboratory for testing analysis and modelling methodologies to be used when reconstructing in 3D this kind of complex interference structures, the Vajont area also provides useful clues on the still-enigmatic structures in the frontal part of the Friuli-Venetian Southern Alps, buried in the Venetian Plain foredeep. These include active seismogenic thrust-faults and, at the same time, represent a growing interest for the oil industry.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brumbaugh, William D.; Cook, Kenneth L.

During the summers of 1975 and 1976, a gravity survey was conducted in the Cove Fort - Sulphurdale KGRA and north Mineral Mountains area, Millard and Beaver counties, Utah. The survey consisted of 671 gravity stations covering an area of about 1300 km{sup 2}, and included two orthogonal gravity profiles traversing the area. The gravity data are presented as a terrain-corrected Bouguer gravity anomaly map with a contour interval of 1 mgal and as an isometric three-dimensional gravity anomaly surface. Selected anomaly separation techniques were applied to the hand-digitized gravity data (at 1-km intervals on the Universal Transverse Mercator grid)more » in both the frequency and space domains, including Fourier decomposition, second vertical derivative, strike-filter, and polynomial fitting analysis, respectively. Residual gravity gradients of 0.5 to 8.0 mgal/km across north-trending gravity contours observed through the Cove Fort area, the Sulphurdale area, and the areas east of the East Mineral Mountains, along the west flanks of the Tushar Mountains, and on both the east and west flanks of the north Mineral Mountains, were attributed to north-trending Basin and Range high-angle faults. Gravity highs exist over the community of Black Rock area, the north Mineral Mountains, the Paleozoic outcrops in the east Cove Creek-Dog Valley-White Sage Flats areas, the sedimentary thrust zone of the southern Payant Range, and the East Mineral Mountains. The gravity lows over north Milford Valley, southern Black Rock Desert, Cunningham Wash, and northern Beaver Valley are separated from the above gravity highs by steep gravity gradients attributed to a combination of crustal warping and faulting. A gravity low with a closure of 2 mgal corresponds with Sulphur Cove, a circular topographic features containing sulphur deposits.« less

Reflector for efficient coupling of a laser beam to air or other fluids

DOEpatents

Kare, J.T.

1992-10-06

A reflector array is disclosed herein that provides a controlled region or regions of plasma breakdowns from a laser beam produced at a remotely-based laser source. The plasma may be applied to produce thrust to propel a spacecraft, or to diagnose a laser beam, or to produce shock waves. The spacecraft propulsion system comprises a reflector array attached to the vehicle. The reflector array comprises a plurality of reflectors spaced apart on a reflective surface, with each reflector acting as an independent focusing mirror. The reflectors are spaced closely together to form a continuous or partially-continuous surface. The reflector array may be formed from a sheet of reflective material, such as copper or aluminum. In operation, a beam of electromagnetic energy, such as a laser beam, is directed at the reflectors which focus the reflected electromagnetic energy at a plurality of regions off the surface. The energy concentrated in the focal region causes a breakdown of the air or other fluid in the focal region, creating a plasma. Electromagnetic energy is absorbed in the plasma and it grows in volume, compressing and heating the adjacent fluid thereby providing thrust. Laser pulses may be applied repetitively. After each such thrust pulse, fresh air can be introduced next to the surface either laterally, or through a perforated surface. If air or some other gas or vapor is supplied, for example from a tank carried on board a vehicle, this invention may also be used to provide thrust in a vacuum environment. 10 figs.

East Antarctic rifting triggers uplift of the Gamburtsev Mountains

USGS Publications Warehouse

Ferraccioli, F.; Finn, Carol A.; Jordan, Tom A.; Bell, Robin E.; Anderson, Lester M.; Damaske, Detlef

2011-01-01

The Gamburtsev Subglacial Mountains are the least understood tectonic feature on Earth, because they are completely hidden beneath the East Antarctic Ice Sheet. Their high elevation and youthful Alpine topography, combined with their location on the East Antarctic craton, creates a paradox that has puzzled researchers since the mountains were discovered in 1958. The preservation of Alpine topography in the Gamburtsevs may reflect extremely low long-term erosion rates beneath the ice sheet, but the mountains’ origin remains problematic. Here we present the first comprehensive view of the crustal architecture and uplift mechanisms for the Gamburtsevs, derived from radar, gravity and magnetic data. The geophysical data define a 2,500-km-long rift system in East Antarctica surrounding the Gamburtsevs, and a thick crustal root beneath the range. We propose that the root formed during the Proterozoic assembly of interior East Antarctica (possibly about 1 Gyr ago), was preserved as in some old orogens and was rejuvenated during much later Permian (roughly 250 Myr ago) and Cretaceous (roughly 100 Myr ago) rifting. Much like East Africa, the interior of East Antarctica is a mosaic of Precambrian provinces affected by rifting processes. Our models show that the combination of rift-flank uplift, root buoyancy and the isostatic response to fluvial and glacial erosion explains the high elevation and relief of the Gamburtsevs. The evolution of the Gamburtsevs demonstrates that rifting and preserved orogenic roots can produce broad regions of high topography in continental interiors without significantly modifying the underlying Precambrian lithosphere.

Pest Fact Sheet 2007: Southern Pine Beetle prevention initiative: Working for healthier forests

Treesearch

R-8 and Southern Research Station U.S. Department of Agriculture Forest Service Forest Health Protection

2007-01-01

From 1999 to 2003, southern pine beetle (SPB) caused unprecedented damage to pine forests in southern Appalachian mountains. These losses severely impacted the natural resource base that supports the South's tourism and wood-based manufacturing industries and also destroyed the habitat of threatened and endangered species, such as the red-cockaded woodpecker....

Strike up Student Interest through Song: Technology and Westward Expansion

ERIC Educational Resources Information Center

Steele, Meg

2014-01-01

Sheet music, song lyrics, and audio recordings may not be the first primary sources that come to mind when considering ways to teach about changes brought about by technology during westward expansion, but these sources engage students in thought provoking ways. In this article the author presents a 1917 photograph of Mountain Chief, of the Piegan…

Active fold-thrust belts in the foreland of eastern Tibet, the Longquan and Xiongpu anticlines in Sichuan, China

NASA Astrophysics Data System (ADS)

Lee, Jian-Cheng; Chan, Yu-Chang; Lu, Chia-Yu; Chen, Chih-Tung; Chu, Hao-Tsu; Liu, Yuiping; Li, Jianzhong

2016-04-01

The 2008 M7.9 Wenchuan earthquake ruptured from the Longmenshan fault system, which is the frontal thrust system in eastern Tibet. Further east toward the foreland area in the Sichuan basin, it sits two anticlinal structures, the Longquan and Xiongpu anticlines, which trends sub-parallel to the Longmenshan range with a distance of about 70-100 km to the mountain front. It is widely considered that these two anticlinal features are attributed to propagation of the eastward extrusion of the eastern Tibetan plateau, similar to the stress system the Wenchuan earthquake. In this study, we carried out field investigations on these two active anticlinal structures in order to characterize the bulk deformation of the anticlines. We also conducted fracture analysis and fault-slip data analysis, in an attempt to characterize the fracture developments of the rock and the paleostress states related to the faulting events associated growth of the anticlines. We thus constructed a series of geological cross sections along these two anticlines. Our results show that the Longquan anticline is characterized by pop up structure with a dominant west-vergent thrust (i.e., backthrust) on the western limb. On the other hand to the eastern limb, an east-vergent thrust only well developed in the middle part of the anticline and die out toward the north and the south. For the Xiongpu anticline, it is characterized by a pre-dominant west-vergent backthrust system without developing an east-vergent thrust. A strike-slip fault and a series of N-S-trending pop-up thrusts cut across the Xiongpu anticline indicate a rather complex stress system with two dominant compression directions, NW-SE and E-W, subsequently or alternatively affected the area. Finally, the fracture analysis revealed that 2-3 pre-dominant bedding-perpendicular fracture sets are commonly developed in the massive sandstone layers. Most of them seemingly are of the characteristics of the mode I open joint, without clear relationship with the stress system associated with the regional anticlinal growth.

Tectonically controlled relief evolution in the Northern Tien Shan and Junggar Alatau from the Eocene to the Present

NASA Astrophysics Data System (ADS)

Seib, N.; Kley, J.; Voigt, T.; Kober, M.

2012-04-01

The Cenozoic Tien Shan and Junggar Alatau mountains developed on the southern part of the Paleozoic Altaid orogen as a far-field effect of the collision of the Indian and Eurasian plates. Highland terrain, active seismicity, and fast GPS-derived motions are evidence of rapid ongoing mountain growth today. Variations in relief energy, hight-to-width ratio of ranges and apatite fission track (AFT) exhumation ages suggest they rose at different times. The strong dissection of the higher ridges (heights of up to 2km), indicates an earlier onset and higher rates of uplift. At the other end of the spectrum are low, little dissected ridges. According to AFT ages, exhumation in the Junggar Range began at 9 Ma (Jolivet et al., 2010), circa 11 Ma in the central Kyrgyz Range (Sobel et al., 2006) and 10 Ma in the Terskey Alatau. An AFT age of the low Sogety range is 77 Ma, suggesting that the Cenozic exhumation of the ridge was insufficient to expose rocks from below c.3 km depth. The synclinal lows between the basement highs preserve Cenozoic strata of Eocene to Quaternary age, probably deposited in a once continuous basin (the Ili Basin) and recording the entire history of Tien Shan uplift. Facies pattern of proximal alluvial fans are strictly related to the recent higher mountain areas in the north and in the south. During Middle Miocene, a large lake developed in the basin center. Up to the Middle Miocene sedimentation was accompanied by normal faulting of small magnitude. The main Cenozoic folding and thrusting occurred after that time and before deposition of the Chorgos formation. Shortening was accommodated by reactivation of inherited basement structures, by a switch to reverse or strike-slip motion on normal faults, and the nucleation of new thrusts. The majority of faults which emplace basement rocks over upper Cenozoic sediments dip steeply at angles of 60-70˚, and some have throws of more than 200 m. They are marked by topographic steps and contrasting morphology across them. This first phase of deformation was followed by erosional leveling. Well-consolidated caliche layers indicate an extended period of stable soil formation in a (semi-)arid climate. Renewed shoting and uplift led to river incision and the formation of terraces and gave rise to new active faults, but their displacements are still low due to their short lifespans. These faults are presently expressed at the surface as fold scarps. The scarps are underlain by flexures affected in places by small thrust faults. Some of them, judging by their directions, are probably reactivating Miocene faults. The differences in the timing of range uplift, the progression of Cenozoic folding and the location of the young flexures all indicate migration of thrusting and folding from the borders of the Ili basin toward its center. A similar pattern of tectonic activity shifting from the flanking ridges toward the basin center was also observed in the Issyk-Kul basin (Korzhenkov, et al., 2007).

Geologic isolation of nuclear waste at high latitudes: the role of ice sheets

USGS Publications Warehouse

Person, M.; McIntosh, J.; Iverson, N.; Neuzil, C.E.; Bense, V.

2012-01-01

Geologic isolation of high-level nuclear waste from the biosphere requires special consideration in countries at high latitudes (>40°N) owing to the possibility of future episodes of continental glaciation (Talbot 1999). It is now widely recognized that Pleistocene continental glaciations have had a profound effect on rates of sediment erosion (Cuffey & Paterson 2010) and deformation including tectonic thrusting (Pedersen 2005) as well as groundwater flow (Person et al. 2007; Lemieux et al. 2008a,b,c). In addition, glacial mechanical loads may have generated anomalous, or fossil, pore pressures within certain clay-rich confining units (e.g. Vinard et al. 2001). Because high-level nuclear wastes must be isolated from the biosphere as long as 1 million years (McMurry et al. 2003), the likelihood of one or more continental ice sheets overrunning high-latitude sites must be considered.

Restoration of the Cretaceous uplift of the Harz Mountains, North Germany: Evidence for thick-skinned thrusting

NASA Astrophysics Data System (ADS)

Tanner, David C.; Krawczyk, Charlotte M.

2017-04-01

Fault prediction and kinematic restoration are useful tools to firstly determine the likely geometry of a fault at depth and secondly restore the pre-deformation state to discover, for instance, paleogeometry. The inclined-shear method with constant slip uses the known geometry of the surface position and dip of the fault and the geometries of the hanging and footwall beds to predict the probable shape of the fault at depth, down to a detachment level. We use this method to determine the geometry of the Northern Harz Boundary Fault in northern Germany that was responsible for the uplift of the Harz Mountains during Late Cretaceous inversion. A shear angle of 30° was most likely in this case, as indicated by geological and geophysical data. This suggests that the detachment level is at a depth of ca. 25 km. Kinematic restoration of the Harz Mountains using this fault geometry does not produce a flat horizon, rather it results in a 3.5 km depression. Restoration also causes a rotation of fabrics within the Harz Mountains of approximately 11° clockwise. Airy-Heiskanen isostatic equilibrium adjustment reduces the depression to ca. 1 km depth, as well as raising the Moho from 41 to 36 km depth. We show that this model geometry is also a very good fit to the interpreted DEKORP BASIN 9601 deep seismic profile.

Evidence of Vertical and Horizontal Motions on Venus: Maxwell Montes

NASA Astrophysics Data System (ADS)

Ansan, V.; Vergely, P.

1995-01-01

Based on full-resolution Magellan radar images, the detailed structural analysis of central Ishtar Terra (Venus) provides new insight to the understanding of the Venusian tectonics. Ishtar Terra, centered on 65° N latitude and 0° E longitude includes a high plateau. Lakshmi Planum, surrounded by highlands, the most important being Maxwell Montes to the East. Structural analysis has been performed with classical remote-sensing methods. Folds and faults identified on radar images were reported on structural map. Their type and distribution allowed to define the style of the crustal deformation and the context in which these structures formed. This analysis shows that Lakshmi Planum formed under a crustal stretching associated with a volcanic activity. This area then became a relatively steady platform, throughout the formation of Maxwell Montes mountain belt. Maxwell Montes is characterized by a series of NNW-SSE trending thrust faults dipping to the East, formed during a WSW-ESE horizontal shortening. In its NW quarter, the mountain belt shows a disturbed deformation controlled by pre-existing grabens and old vertical crustal fault zone. The deformation of this area is characterized by a shortening of cover above a flat detachment zone, with a progressive accommodation to the southwest. All these tectonic structures show evidence of horizontal and vertical crustal movements on Venus, with subsidence, mountain belt raise, West regional overthrusting of this mountain belt, and regional shear zone.

Geologic Map of the Denver West 30' x 60' Quadrangle, North-Central Colorado

USGS Publications Warehouse

Kellogg, Karl S.; Shroba, Ralph R.; Bryant, Bruce; Premo, Wayne R.

2008-01-01

The Denver West quadrangle extends east-west across the entire axis of the Front Range, one of numerous uplifts in the Rocky Mountain region in which Precambrian rocks are exposed. The history of the basement rocks in the Denver West quadrangle is as old as 1,790 Ma. Along the east side of the range, a sequence of sedimentary rocks as old as Pennsylvanian, but dominated by Cretaceous-age rocks, overlies these ancient basement rocks and was upturned and locally faulted during Laramide (Late Cretaceous to early Tertiary) uplift of the range. The increasingly coarser grained sediments up section in rocks of latest Cretaceous to early Tertiary age record in remarkable detail this Laramide period of mountain building. On the west side of the range, a major Laramide fault (Williams Range thrust) places Precambrian rocks over Cretaceous sedimentary rocks. The geologic history of the quadrangle, therefore, can be divided into four major periods: (1) Proterozoic history, (2) Pennsylvanian to pre-Laramide, Late Cretaceous history, (3) Late Cretaceous to early Tertiary Laramide mountain building, and (4) post-Laramide history. In particular, the Quaternary history of the Denver West quadrangle is described in detail, based largely on extensive new mapping.

WEST AND EAST PALISADES ROADLESS AREAS, IDAHO AND WYOMING.

USGS Publications Warehouse

Oriel, Steven S.; Benham, John R.

1984-01-01

Studies of the West and East Palisades Roadless Areas, which lie within the Idaho-Wyoming thrust belt, document structures, reservoir formations, source beds, and thermal maturities comparable to those in producing oil and gas field farther south in the belt. Therefore, the areas are highly favorable for the occurrence of oil and gas. Phosphate beds of appropriate grade within the roadless areas are thinner and less accessible than those being mined from higher thrust sheets to the southwest; however, they contain 98 million tons of inferred phosphate rock resources in areas of substantiated phosphate resource potential. Sparsely distributed thin coal seams occur in the roadless areas. Although moderately pure limestone is present, it is available from other sources closer to markets. Geochemical anomalies from stream-sediment and rock samples for silver, copper, molydenum, and lead occur in the roadless areas but they offer little promise for the occurrence of metallic mineral resources. A possible geothermal resource is unproven, despite thermal phenomena at nearby sites.

Assessment of Appalachian basin oil and gas resources: Carboniferous Coal-bed Gas Total Petroleum System: Chapter G.1 in Coal and petroleum resources in the Appalachian basin: distribution, geologic framework, and geochemical character

USGS Publications Warehouse

Milici, Robert C.; Ruppert, Leslie F.; Ryder, Robert T.

2014-01-01

Trap formation began with the deposition of the peat deposits during the Mississippian and continued into the Late Pennsylvanian and Permian, when strata of the Appalachian Plateaus were deformed during the Alleghanian orogeny. The seals are the connate waters that occupy fractures and larger pore spaces within the coal beds, as well as the fine-grained, siliciclastic sedimentary strata that are intercalated with the coal. The critical moment for the petroleum system occurred during the Alleghanian orogeny, when deformation resulted in the geologic structures in the eastern part of the Appalachian basin that enhanced fracture porosity within the coal beds. In places, burial by thrust sheets (thrust loading) in the Valley and Ridge physiographic province may have resulted in the additional generation of thermogenic coalbed methane in the Pennsylvania Anthracite region and in the semianthracite deposits of Virginia and West Virginia, although other explanations have been offered.

Reinterpretation of ADOCH and COCORP Seismic Reflection Data with Constraints from Detailed Forward Modeling of Potential Field Data - Implications for Laurentia-Peri-Gondwana Suture

NASA Astrophysics Data System (ADS)

Duff, P.; Kellogg, J. N.

2017-12-01

To better constrain the structure of the Laurentian - Peri-Gondwana suture zone, maps and a 2-dimensional regional cross-section model constrained by seismic data and surface geology have been developed by forward and inverse modeling the aeromagnetic and gravity fields. The Central Piedmont Suture (CPS), the boundary between the Laurentian Inner Piedmont and the Peri-Gondwanan Carolina terrane is a low-angle thrust fault ( 30°) ramping up from an Alleghanian mid-crustal detachment at depths of about 12 km. ADCOH and COCORP seismic data image anticlinal structures in the footwalls of the Hayesville thrust and the CPS, above the Alleghanian decollement. The footwall rocks have previously been interpreted as Paleozoic shelf strata on the basis of sub-horizontal seismic reflectors; however, the high densities required to fit the observed gravity anomaly suggest that the folded footwall reflectors may need to be reinterpreted as horse blocks or duplex structures of Grenvillian basement. The Appalachian paired gravity anomaly can be explained by an increase in crustal thickness and a decrease in upper crustal density moving northwestward from the Carolina Terrane toward the Appalachian core. A change in lower crustal density is not required, so that Grenville basement rocks may extend farther to the southeast than previously thought. The 5 to 10 km of Alleghanian uplift and exhumation predicted by P-T crystallization data compiled in this paper can be easily accommodated by thrusting on four major low-angle thrust systems: Great Smoky Mountain Thrust (GSMT), Hayesville, Brevard, and CPS. Unroofing of metamorphic core complexes by normal faulting may therefore not be required to explain the observed exhumation. Alleghanian collision along the southeastern Appalachian margin was predominately orthogonal to strike consistent with the previous reconstructions that call for the counter-clockwise rotation of Gondwanan West Africa, creating head-on collision in the southern Appalachians and at least 370 km of shortening.

Potential earthquake faults offshore Southern California, from the eastern Santa Barbara Channel south to Dana Point

USGS Publications Warehouse

Fisher, M.A.; Sorlien, C.C.; Sliter, R.W.

2009-01-01

Urban areas in Southern California are at risk from major earthquakes, not only quakes generated by long-recognized onshore faults but also ones that occur along poorly understood offshore faults. We summarize recent research findings concerning these lesser known faults. Research by the U.S. Geological Survey during the past five years indicates that these faults from the eastern Santa Barbara Channel south to Dana Point pose a potential earthquake threat. Historical seismicity in this area indicates that, in general, offshore faults can unleash earthquakes having at least moderate (M 5-6) magnitude. Estimating the earthquake hazard in Southern California is complicated by strain partitioning and by inheritance of structures from early tectonic episodes. The three main episodes are Mesozoic through early Miocene subduction, early Miocene crustal extension coeval with rotation of the Western Transverse Ranges, and Pliocene and younger transpression related to plate-boundary motion along the San Andreas Fault. Additional complication in the analysis of earthquake hazards derives from the partitioning of tectonic strain into strike-slip and thrust components along separate but kinematically related faults. The eastern Santa Barbara Basin is deformed by large active reverse and thrust faults, and this area appears to be underlain regionally by the north-dipping Channel Islands thrust fault. These faults could produce moderate to strong earthquakes and destructive tsunamis. On the Malibu coast, earthquakes along offshore faults could have left-lateral-oblique focal mechanisms, and the Santa Monica Mountains thrust fault, which underlies the oblique faults, could give rise to large (M ??7) earthquakes. Offshore faults near Santa Monica Bay and the San Pedro shelf are likely to produce both strike-slip and thrust earthquakes along northwest-striking faults. In all areas, transverse structures, such as lateral ramps and tear faults, which crosscut the main faults, could segment earthquake rupture zones. ?? 2009 The Geological Society of America.

Preliminary digital geologic maps of the Mariposa, Kingman, Trona, and Death Valley Sheets, California

DOE Office of Scientific and Technical Information (OSTI.GOV)

D`Agnese, F.A.; Faunt, C.C.; Turner, A.K.

1995-10-01

Parts of four 1:250,000-scale geologic maps by the California Department of Natural Resources, Division of Mines and Geology have been digitized for use in hydrogeologic characterization. These maps include the area of California between lat. 35{degree}N; Long. 115{degree}W and lat. 38{degree}N, long. 118{degree}W of the Kingman Sheet (Jennings, 1961), Trona Sheet (Jennings and others, 1962), Mariposa Sheet (Strand, 1967), and Death Valley Sheet (Streitz and Stinson, 1974). These digital maps are being released by the US Geological Survey in the ARC/INFO Version 6.1 Export format. The digitized data include geologic unit boundaries, fault traces, and identity of geologic units. Themore » procedure outlined in US Geological Survey Circular 1054 (Soller and others, 1990) was sued during the map construction. The procedure involves transferring hard-copy data into digital format by scanning manuscript maps, manipulating the digital map data, and outputting the data. Most of the work was done using Environmental Systems Research Institute`s ARC/INFO software. The digital maps are available in ARC/INFO Rev. 6.1 Export format, from the USGS, Yucca Mountain Project, in Denver, Colorado.« less

A Classic Test of the Hubbert-Rubey Weakening Mechanism: M7.6 Thrust-Belt Earthquake Taiwan

NASA Astrophysics Data System (ADS)

Yue, L.; Suppe, J.

2005-12-01

The Hubbert-Rubey (1959) fluid-pressure hypothesis has long been accepted as a classic solution to the problem of the apparent weakness of long thin thrust sheets. This hypothesis, in its classic form argues that ambient high pore-fluid pressures, which are common in sedimentary basins, reduce the normalized shear traction on the fault τb/ρ g H = μb(1-λb) where λb=Pf/ρ g H is the normalized pore-fluid pressure and μb is the coefficient of friction. Remarkably, there have been few large-scale tests of this classic hypothesis. Here we document ambient pore-fluid pressures surrounding the active frontal thrusts of western Taiwan, including the Chulungpu thrust that slipped in the 1999 Mw7.6 Chi-Chi earthquake. We show from 3-D mapping of these thrusts that they flatten to a shallow detachment at about 5 km depth in the Pliocene Chinshui Shale. Using critical-taper wedge theory and the dip of the detachment and surface slope we constrain the basal shear traction τb/ρ g H ≍ 0.1 which is substantially weaker than common lab friction values of of Byerlee's law (μb= 0.85-0.6). We have determined the pore-fluid pressures as a function of depth in 76 wells, based on in-situ formation tests, sonic logs and mud densities. Fluid pressures are regionally controlled stratigraphically by sedimentary facies. The top of overpressures is everywhere below the base of the Chinshui Shale, therefore the entire Chinshui thrust system is at ambient hydrostatic pore-fluid pressures (λb ≍ 0.4). According to the classic Hubbert-Rubey hypothesis the required basal coefficient of friction is therefore μb ≍ 0.1-0.2. Therefore the classic Hubbert & Rubey mechanism involving static ambient excess fluid pressures is not the cause of extreme fault weakening in this western Taiwan example. We must look to other mechanisms of large-scale fault weakening, many of which are difficult to test.

New insights into seismic faulting during the 2008 Mw7.9 Wenchuan earthquake

NASA Astrophysics Data System (ADS)

Li, H.; Wang, H.; Si, J.; Sun, Z.; Pei, J.; Lei, Z.; He, X.

2017-12-01

The WFSD project was implemented promptly after the 2008 Mw 7.9 Wenchuan earthquake. A series of research results on the seismogenic structure, fault deformation, sliding mechanism and fault healing have been obtained, which provide new insights into seismic faulting and mechanisms of the Wenchuan earthquake. The WFSD-1 and -2 drilling core profiles reveal that the Longmen Shan thrust belt is composed of multiple thrust sheets. The 2008 Wenchuan earthquake took place in such tectonic setting with strong horizontal shortening. The two ruptured faults have different deformation mechanisms. The Yingxiu-Beichuan fault (YBF) is a stick-slip fault characterized by fault gouge with high magnetic susceptibility, Guanxian-Anxian fault (GAF) with creeping features and characterized by fault gouge with low magnetic susceptibility. Two PSZs were found in WFSD-1 and -2 cores in the southern segment of YBF. The upper PSZ1 is a low-angle thrust fault characterized by coseisimc graphitization with an extremely low frictional coefficient. The lower PSZ2 is an oblique dextral-slip thrust fault characterized by frictional melt lubrication. In the northern segment of YBF, the PSZ in WFSD-4S cores shows a high-angle thrust feature with fresh melt as well. Therefore, the oblique dextral-slip thrust faulting with frictional melt lubrication is the main faulting of Wenchuan earthquake. Fresh melt with quenching texture was formed in Wenchuan earthquake implying vigorous fluid circulation occurred during the earthquake, which quenched high-temperature melt, hamper the aftermost fault slip and welding seismic fault. Therefore, fluids in the fault zone not only promotes fault weakening, but also suppress slipping in theWenchuan earthquake. The YBF has an extremely high hydraulic diffusivity (2.4×10-2 m2s-1), implying a vigorous fluid circulation in the Wenchuan fault zone. the permeability of YBF has reduced 70% after the shock, reflecting a rapid healing for the YBF. However, the water level has not changed in the WFSD-3 borehole drilled through GAF, indicating an unchanged permeability. These results are of great significance to understanding the seismogenic mechanisms and earthquake cycle for the Wenchuan earthquake.

Lithospheric Structure of the Zagros and Alborz Mountain Belts (Iran) from Seismic Imaging

NASA Astrophysics Data System (ADS)

Paul, A.; Hatzfeld, D.; Kaviani, A.; Tatar, M.

2008-12-01

We present a synthesis of the results of two dense temporary passive seismic experiments installed for a few months across Central Zagros for the first one, and from North-western Zagros to Alborz for the second one. On both transects, the receiver function analysis shows that the crust has an average thickness of ~ 43 km beneath the Zagros fold-and-thrust belt and the Iranian plateau. The crust is thicker in the back side of the Main Zagros Reverse Fault (MZRF), with a larger maximum Moho depth in Central Zagros (69 ± 2 km) than in North-western Zagros (56 ± 2 km). To reconcile Bouguer anomaly data and Moho depth profile of Central Zagros, we proposed that the thickening is related to overthrusting of the Arabian margin by Central Iran on the MZRF considered as a major thrust fault rooted at Moho depth. The better-quality receiver functions of NW Zagros display clear conversions on a low-velocity channel which cross-cuts the whole crust from the surface trace of the MZRF to the Moho on 250-km length. Waveform modeling shows that the crustal LVZ is ~ 10-km thick with a S-wave velocity 8-30 % smaller than the average crustal velocity. We interpret the low-velocity channel as the trace of the thrust fault and the suture between the Arabian and the Iranian lithospheres. We favour the hypothesis of the LVZ being due to sediments of the Arabian margin dragged to depth during the subduction of the Neotethyan Ocean. At upper mantle depth, we find shield-like shear-wave velocities in the Arabian upper-mantle, and lower velocities in the Iranian shallow mantle (50-150 km) which are likely due to higher temperature. The lack of a high-velocity anomaly in the mantle northeast of the MZRF suture suggests that the Neotethian oceanic lithosphere is now detached from the Arabian margin. The crust of the Alborz mountain range is not thickened in relation with its high elevations, but its upper mantle has low P-wave velocities.

Tectonic evolution of the central Brooks Range mountain front: Evidence from the Atigun Gorge region

USGS Publications Warehouse

Mull, C.G.; Glenn, R.K.; Adams, K.E.

1997-01-01

Atigun Gorge, at the northern front of the eastern Endicott Mountains, contains well-exposed rocks of the upper part of the Endicott Mountains allochthon and rocks of the structurally higher Picnic Creek or Ipnavik River allochthon. These allochthons contain rocks as young as Early Cretaceous (Valanginian) and are separated by a nearly vertical fault zone that contains exotic blocks of Triassic and Jurassic chert and silicified mudstone. Siliceous rocks of this type are not present in the Endicott Mountains allochthon but are characteristic of the Picnic Creek, Ipnavik River, and some of the other allochthons that structurally overlie the Endicott Mountains allochthon in the central and western Brooks Range. These exotic blocks, therefore indicate that structurally higher rocks of either the Picnic Creek or Ipnavik River allochthon were emplaced during the Early Cretaceous and are preserved along the northern flank of the eastern Endicott Mountains. The deformed thickness of this higher allochthon in the subsurface north of the mountains is unknown but probably exceeds 2 kilometers. Similar relations are mapped east of Atigun Gorge in an area of structural transition from the eastern Endicott Mountains into the northern Philip Smith Mountains, which are formed by the parautochthonous North Slope stratigraphic assemblage. The allochthonous rocks at the mountain front are regionally unconformably overlain by proximal Lower Cretaceous (Albian) foredeep conglomerate at the southern flank of the Colville basin, but at Atigun Gorge, the base of these deposits is interpreted as a possible back thrust at a triangle zone. Conglomerate clasts in the foredeep deposits are dominantly chert, mafic igneous rock, and other lithologies characteristic of the Picnic Creek and Ipnavik River allochthons and scattered clasts from the Endicott Mountains allochthon. The conglomerates show that the chert-rich allochthonous rocks and the Endicott Mountains allochthon were emplaced in the north-central Brooks Range by large-scale crustal shortening (>300 km) between the Valanginian and Albian (??135 to ??112 Ma). This orogenic event significantly postdates early stages of Brooks Range orogeny but predates later stages of orogeny documented by stratigraphic and apatite fission-track data. These relations reduce the magnitude of shortening inferred at the triangle zone at the Brooks Range mountain front. The outcrop data suggest that some of the strata preserved at a structurally low level north of the mountain front and visible in the seismic data of the Trans-Alaska Crustal Transect (TACT) may consist of clastic sedimentary rocks of the structurally higher Picnic Creek or Ipnavik River allochthon. Copyright 1997 by the American Geophysical Union.

Modelling water flow under glaciers and ice sheets

PubMed Central

Flowers, Gwenn E.

2015-01-01

Recent observations of dynamic water systems beneath the Greenland and Antarctic ice sheets have sparked renewed interest in modelling subglacial drainage. The foundations of today's models were laid decades ago, inspired by measurements from mountain glaciers, discovery of the modern ice streams and the study of landscapes evacuated by former ice sheets. Models have progressed from strict adherence to the principles of groundwater flow, to the incorporation of flow ‘elements’ specific to the subglacial environment, to sophisticated two-dimensional representations of interacting distributed and channelized drainage. Although presently in a state of rapid development, subglacial drainage models, when coupled to models of ice flow, are now able to reproduce many of the canonical phenomena that characterize this coupled system. Model calibration remains generally out of reach, whereas widespread application of these models to large problems and real geometries awaits the next level of development. PMID:27547082

Self-folding origami at any energy scale

NASA Astrophysics Data System (ADS)

Pinson, Matthew B.; Stern, Menachem; Carruthers Ferrero, Alexandra; Witten, Thomas A.; Chen, Elizabeth; Murugan, Arvind

2017-05-01

Programmable stiff sheets with a single low-energy folding motion have been sought in fields ranging from the ancient art of origami to modern meta-materials research. Despite such attention, only two extreme classes of crease patterns are usually studied; special Miura-Ori-based zero-energy patterns, in which crease folding requires no sheet bending, and random patterns with high-energy folding, in which the sheet bends as much as creases fold. We present a physical approach that allows systematic exploration of the entire space of crease patterns as a function of the folding energy. Consequently, we uncover statistical results in origami, finding the entropy of crease patterns of given folding energy. Notably, we identify three classes of Mountain-Valley choices that have widely varying `typical' folding energies. Our work opens up a wealth of experimentally relevant self-folding origami designs not reliant on Miura-Ori, the Kawasaki condition or any special symmetry in space.

Windblown Pliocene diatoms and East Antarctic Ice Sheet retreat

PubMed Central

Scherer, Reed P.; DeConto, Robert M.; Pollard, David; Alley, Richard B.

2016-01-01

Marine diatoms in tillites along the Transantarctic Mountains (TAMs) have been used to suggest a diminished East Antarctic Ice Sheet (EAIS) during Pliocene warm periods. Updated ice-sheet modelling shows significant Pliocene EAIS retreat, creating marine embayments into the Wilkes and Aurora basins that were conducive to high diatom productivity and rapid accumulation of diatomaceous sediments. Here we show that subsequent isostatic uplift exposed accumulated unconsolidated marine deposits to wind erosion. We report new atmospheric modelling utilizing Pliocene climate and derived Antarctic landscapes indicating that prevailing mid-altitude winds transported diatoms towards the TAMs, dominantly from extensive emerged coastal deposits of the Aurora Basin. This result unifies leading ideas from competing sides of a contentious debate about the origin of the diatoms in the TAMs and their link to EAIS history, supporting the view that parts of the EAIS are vulnerable to relatively modest warming, with possible implications for future sea-level rise. PMID:27649516

Modelling water flow under glaciers and ice sheets.

PubMed

Flowers, Gwenn E

2015-04-08

Recent observations of dynamic water systems beneath the Greenland and Antarctic ice sheets have sparked renewed interest in modelling subglacial drainage. The foundations of today's models were laid decades ago, inspired by measurements from mountain glaciers, discovery of the modern ice streams and the study of landscapes evacuated by former ice sheets. Models have progressed from strict adherence to the principles of groundwater flow, to the incorporation of flow 'elements' specific to the subglacial environment, to sophisticated two-dimensional representations of interacting distributed and channelized drainage. Although presently in a state of rapid development, subglacial drainage models, when coupled to models of ice flow, are now able to reproduce many of the canonical phenomena that characterize this coupled system. Model calibration remains generally out of reach, whereas widespread application of these models to large problems and real geometries awaits the next level of development.

Kinematics and Ophiolite obduction in the Gerania and Helicon Mountains, central Greece

NASA Astrophysics Data System (ADS)

Kaplanis, A.; Koukouvelas, I.; Xypolias, P.; Kokkalas, S.

2013-06-01

New structural, petrofabric and palaeostress data from the Beotia area (central Greece) were used to investigate the tectonic evolution of the suture zone between the External (Parnassus microplate) and Internal Hellenides (Pelagonian microplate). Petrofabric studies of ultramafic rocks were done using conventional U-stage analysis and the electron backscatter diffraction (EBSD) technique. Detailed structural analysis enabled us to distinguish three main deformation phases that took place from the Triassic to the Eocene. Triassic-Jurassic deformation is related to continental rifting and the progressive formation of an ocean basin. Ophiolites formed above a westward-dipping supra-subduction zone (SSZ) in the Early-Late Jurassic. Trench-margin collision resulted in the southeastward emplacement of the ophiolite nappe over the Pelagonian margin. There is also evidence for a north-westward thrusting of ophiolitic rocks over the Gerania and Helicon units during Berriasian time. This latter tectonic process is closely related to the deposition of "Beotian flysch" into a foreland basin. An extensional phase of deformation accompanied by shallow-water carbonate sedimentation is documented in the Upper Cretaceous. Later, during Paleocene the area was subjected to a compressional deformation phase characterised by SW-directed thrusting and folding, as well as NE-verging backthrusts and backfolds. Our proposed geotectonic model suggests the consumption of the ocean between the Parnassus and Pelagonian microplates. This model includes Late Jurassic eastward ophiolite obduction followed by Early Cretaceous west directed ophiolite thrusting.

Origin of the megabreccias in the Katanga Copperbelt (D.R.Congo)

NASA Astrophysics Data System (ADS)

Cailteux, Jacques L. H.; Muchez, Philippe; De Cuyper, Jana; Dewaele, Stijn; De Putter, Thierry

2018-04-01

The megabreccias in the Katanga part of the Neoproterozoic Central African Copperbelt contain up to several km-long blocks and fragments of the Mines Subgroup which host most of the stratiform Cu-Co deposits. New observations, particularly on cores from boreholes drilled at Luiswishi indicate three types of fracturing: 1) brittle post-folding in the Mines Subgroup; 2) hydraulic; and 3) ductile in soft incompetent siltstones of the R.A.T. and Dipeta subgroups. These fracturing phases dislocated the Roan succession into blocks and fragments and, in particular, clearly showed that there is an evolution from an in situ hydraulic fracturing, to a heterometric brecciation implying some movement and abrasion of the fragments. The process points to significant compression, and was accompanied by fluid expulsion and precipitation of dolomite after decompression. Fluid inclusion microthermometry in dolomite grains shows that the fluids were of high salinity and high temperature, suggesting dissolution of evaporites most likely contained in the Roan sedimentary pile. These saline fluids allowed the fluidization of the breccias, facilitating the displacement of the nappes, pinching out (extrusion-like) megabreccias along thrust-faults, and resulting in intrusion of breccias between the blocks or into large fractures. Breccias between the blocks are clearly identified as friction breccias. They contain a fine material, as part of the matrix, resulting from abrasion of the fragments during transportation. Abrasion and attrition explain the rounding of the fragments. A late cementation phase from less saline and lower temperature fluids suggests the addition of meteoric water in the system, and the mixing with the ambient fluids. The minimum burial depth of the meteoric water incursion is estimated at 2.8 km. Such under-saturated fluids may have contributed to the dissolution of residual evaporites and of the evaporitic material from the Kiubo rocks at the base of the nappes, and led to further brecciation, possibly explaining the multi-phase features of the breccia. The megabreccias occur at the base of the thrusts sheets and are marked by thrust-fault zones. Results of the study support a process of formation of the megabreccias related to a fold-and-trust event, and invalidate a syn-orogenic sedimentary origin as an olistostrome formed by subaqueous conglomeratic debris flows and clastic syn-orogenic sediments. They also contradict a pure salt tectonic hypothesis that propose the extrusions and enlargements of allochthonous evaporites-gigabreccia before the Lufilian deformation. However, the model is compatible with a "fluid behaviour" of pressured saline fluids trapped in folds and/or thrust sheets, and resulting from evaporites dissolution at variable depth.

SHINING ROCK WILDERNESS, NORTH CAROLINA.

USGS Publications Warehouse

Lesure, Frank G.; Dunn, Maynard L.

1984-01-01

The Shining Rock Wilderness, in the Blue Ridge Mountains of Haywood County, North Carolina, is underlain by complexly folded mica gneiss and schist of Precambrian age. A mineral-resource survey determined that two commodities, quartz as a source of silica (SiO//2) and gneiss and schist suitable for common building stone and crushed rock, are present in large quantities. Demonstrated resources of silica occur at Shining Rock Mountain and small amounts of sheet muscovite (mica) and scrap mica are present at about 10 localities. Until deep drilling is done to test the results of the seismic studies, no estimate of the potential for gas can be made, but the presence of gas cannot be totally discounted.

Fuels planning: science synthesis and integration; economic uses fact sheet 09: Mechanical treatment costs

Treesearch

Rocky Mountain Research Station USDA Forest Service

2005-01-01

Although fuel reduction treatments are widespread, there is great variability and uncertainty in the cost of conducting treatments. Researchers from the Rocky Mountain Research Station, USDA Forest Service, have developed a model for estimating the per-acre cost for mechanical fuel reduction treatments. Although these models do a good job of identifying factors that...

Glacio-Seismotectonics: Ice Sheets, Crustal Deformation and Seismicity

NASA Technical Reports Server (NTRS)

Sauber, Jeanne; Stewart, Iain S.; Rose, James

2000-01-01

The last decade has witnessed a significant growth in our understanding of the past and continuing effects of ice sheets and glaciers on contemporary crustal deformation and seismicity. This growth has been driven largely by the emergence of postglacial rebound models (PGM) constrained by new field observations that incorporate increasingly realistic rheological, mechanical, and glacial parameters. In this paper, we highlight some of these recent field-based investigations and new PGMs, and examine their implications for understanding crustal deformation and seismicity during glaciation and following deglaciation. The emerging glacial rebound models outlined in the paper support the view that both tectonic stresses and glacial rebound stresses are needed to explain the distribution and style of contemporary earthquake activity in former glaciated shields of eastern Canada and Fennoscandia. However, many of these models neglect important parameters, such as topography, lateral variations in lithospheric strength and tectonic strain built up during glaciation. In glaciated mountainous terrains, glacial erosion may directly modulate tectonic deformation by resetting the orogenic topography and thereby providing an additional compensatory uplift mechanism. Such effects are likely to be important both in tectonically active orogens and in the mountainous regions of glaciated shields.

Neogene shortening and exhumation of the Zagros fold-thrust belt and foreland basin in the Kurdistan region of northern Iraq

NASA Astrophysics Data System (ADS)

Koshnaw, Renas I.; Horton, Brian K.; Stockli, Daniel F.; Barber, Douglas E.; Tamar-Agha, Mazin Y.; Kendall, Jerome J.

2017-01-01

The Zagros fold-thrust belt in the Kurdistan region of Iraq encroached southward toward a rapidly subsiding Neogene foreland basin and was later partitioned by out-of-sequence shortening focused along the Mountain Front Flexure (MFF), as defined by new low-temperature thermochronologic, stratigraphic, and provenance results. Apatite (U-Th)/He ages document rapid deformation advance from the Main Zagros Fault to southern frontal structures (Kirkuk, Shakal, and Qamar thrusts) at 10-8 Ma, followed by potential basement-involved out-of-sequence development of the MFF (Qaradagh anticline) by 5 Ma. Distinct shifts in detrital zircon U-Pb provenance signatures for Neogene foreland basin fill provide evidence for drainage reorganization during fold-thrust belt advance. U-Pb age spectra and petrologic data from the Injana (Upper Fars) Formation indicate derivation from a variety of Eurasian, Pan-African, ophiolitic and Mesozoic-Cenozoic volcanic terranes, whereas the Mukdadiya (Lower Bakhtiari) and Bai-Hasan (Upper Bakhtiari) Formations show nearly exclusive derivation from the Paleogene Walash-Naopurdan volcanic complex near the Iraq-Iran border. Such a sharp cutoff in Eurasian, Pan-African, and ophiolitic sources is likely associated with drainage reorganization and tectonic development of the geomorphic barrier formed by the MFF. As a result of Zagros crustal shortening, thickening and loading, the Neogene foreland basin developed and accommodated an abrupt influx of fluvial clastic sediment that contains growth stratal evidence of synkinematic accumulation. The apparent out-of-sequence pattern of upper crustal shortening in the hinterland to foreland zone of Iraqi Kurdistan suggests that structural inheritance and the effects of synorogenic erosion and accumulation are important factors influencing the irregular and episodic nature of orogenic growth in the Zagros.

Architectural evidence of dune collapse in the Navajo Sandstone, Zion National Park, Utah

NASA Astrophysics Data System (ADS)

Ford, Colby; Bryant, Gerald; Nick, Kevin E.

2016-10-01

The Canyon Overlook Trail of Zion National Park follows an outcrop of Navajo Sandstone, which displays a uniquely well-exposed assemblage of features associated with failure of the lee face of a large eolian dune, and run-out over an expanse of interdune sediments downwind of that bedform. Exposed features include dramatic folds in the interdune succession and a stacked series of thrust sheets incorporating both interdune and overlying dune deposits. Thrust surfaces display consistent strikes, parallel to those of undeformed foresets, and incorporate zones of brittle failure and fluid deformation, including folds overturned in the direction of foreset dip. These features correspond to predictions made by a previous researcher's model of dune collapse, formulated from less fortuitously exposed architectures in the Navajo Sandstone. Unlike the previous model, however, this site preserves distinct indications that the bulk of deformed material accumulated above the level of the contemporary interdune surface, in an aggradational succession. Paleotopographic reconstruction, based on preserved facies relationships at this site, indicates the presence of a large dune, partially encroached upon a well-developed wet interdune succession, made up of two half-meter carbonate mud layers, separated by a meter of medium-grained sand. Trapping of pore water pressure between these mud layers during liquefaction reduced shear strength in this interval, facilitating the collapse of the lee face of the upwind dune into the interdune area, and transmitted resultant shear forces to distal portions of the interdune expanse, in the shallow subsurface. Shear failure developed along bedding planes in the horizontally laminated carbonate muds, which provided both lubrication of the shear surfaces and structural support for the preservation of coherent thrust sheets during production of an imbricated succession of shear zones in the toe portion of the slump. Individual shear surfaces exposed in this outcrop extend for up to 50 m along strike and dip north up to 55°. Upturned mud layers in the toe of the slump resisted deflation, promoting preservation of an irregular interdune topography, over which the reorganized dune ultimately advanced.

The Dauki Thrust Fault and the Shillong Anticline: An incipient plate boundary in NE India?

NASA Astrophysics Data System (ADS)

Ferguson, E. K.; Seeber, L.; Steckler, M. S.; Akhter, S. H.; Mondal, D.; Lenhart, A.

2012-12-01

The Shillong Massif is a regional contractional structure developing across the Assam sliver of the Indian plate near the Eastern Syntaxis between the Himalaya and Burma arcs. Faulting associated with the Shillong Massif is a major source of earthquake hazard. The massif is a composite basement-cored asymmetric anticline and is 100km wide, >350km long and 1.8km high. The high relief southern limb preserves a Cretaceous-Paleocene passive margin sequence despite extreme rainfall while the gentler northern limb is devoid of sedimentary cover. This asymmetry suggests southward growth of the structure. The Dauki fault along the south limb builds this relief. From the south-verging structure, we infer a regional deeply-rooted north-dipping blind thrust fault. It strikes E-W and obliquely intersects the NE-SW margin of India, thus displaying three segments: Western, within continental India; Central, along the former passive margin; and Eastern, overridden by the west-verging Burma accretion system. We present findings from recent geologic fieldwork on the western and central segments. The broadly warped erosional surface of the massif defines a single anticline in the central segment, east of the intersection with the hinge zone of the continental margin buried by the Ganges-Brahmaputra Delta. The south limb of the anticline forms a steep topographic front, but is even steeper structurally as defined by the Cretaceous-Eocene cover. Below it, Sylhet Trap Basalts intrude and cover Precambrian basement. Dikes, presumably parallel to the rifted margin, are also parallel to the front, suggesting thrust reactivation of rift-related faults. Less competent Neogene clastics are preserved only near the base of the mountain front. Drag folds in these rocks suggest north-vergence and a roof thrust above a blind thrust wedge floored by the Dauki thrust fault. West of the hinge zone, the contractional structure penetrates the Indian continent and bifurcates. After branching into the Dapsi Fault, the Dauki Fault continues westward as the erosion-deposition boundary combined with a belt of N-S shortening. The Dapsi thrust fault strikes WNW across the Shillong massif and dips NNE. It is mostly blind below a topographically expressed fold involving basement and passive-margin cover. Recent fieldwork has shown that the fault is better exposed in the west, where eventually Archean basement juxtaposes folded and steeply dipping fluvial sediment. Both Dauki and Dapsi faults probably continue beyond the Brahmaputra River, where extreme fluvial processes mask them. The area between the two faults is a gentle southward monocline with little or no shortening. Thus uplift of this area stems from slip on the Dauki thrust fault, not from pervasive shortening. The Burma foldbelt overrides the Shillong Plateau and is warped but continuous across the eastern segment of the Dauki fault. The Haflong-Naga thrust front north of the Dauki merges with the fold-thrust belt in the Sylhet basin to the south, despite >150km of differential advance due to much greater advance of the accretionary prism in the basin. Where the Dauki and Haflong-Naga thrusts cross, the thrust fronts are nearly parallel and opposite vergence. We trace a Dauki-related topographic front eastward across the Burma Range. This and other evidence suggest that the Dauki Fault continues below the foldbelt.

Preliminary Geologic Map of the White Sulphur Springs 30' x 60' Quadrangle, Montana

USGS Publications Warehouse

Reynolds, Mitchell W.; Brandt, Theodore R.

2006-01-01

The geologic map of the White Sulphur Springs quadrangle, scale 1:100,000, was made as part of the Montana Investigations Project to provide new information on the stratigraphy, structure, and geologic history of the geologically complex area in west-central Montana. The quadrangle encompasses about 4,235 km2 (1,635 mi2), across part of the Smith River basin, the west end of the Little Belt Mountains, the Castle Mountains, and the upper parts of the basins of the North Forks of the Smith and Musselshell Rivers and the Judith River. Geologically the quadrangle extends across the eastern part of the Helena structural salient in the Rocky Mountain thrust belt, a segment of the Lewis and Clark tectonic zone, west end of the ancestral central Montana uplift, and the southwest edge of the Judith basin. Rocks and sediments in the White Sulphur Springs quadrangle are assigned to 88 map units on the basis of rock or sediment type and age. The oldest rock exposed is Neoarchean diorite that is infolded with Paleoproterozoic metamorphic rocks including gneiss, diorite, granite, amphibolite, schist, and mixed metamorphic rock types. A thick succession of the Mesoproterozoic Belt Supergroup unconformably overlies the metamorphic rocks and, in turn, is overlain unconformably by Phanerozoic sedimentary and volcanic rocks. Across most of the quadrangle, the pre-Tertiary stratigraphic succession is intruded by Eocene dikes, sills, and plutons. The central part of the Little Belt Mountains is generally underlain by laccoliths and sheet-like bodies of quartz monzonite or dacite. Oligocene andesitic basalt flows in the western and southern part of the quadrangle document both the configuration of the late Eocene erosional surfaces and the extent of extensional faulting younger than early Oligocene in the area. Pliocene, Miocene, and Oligocene strata, mapped as 11 units, consist generally of interbedded sand, gravel, and tuffaceous sedimentary rock. Quaternary and Quaternary-Tertiary sediments rest across the older Cenozoic deposits and across all older rocks. The Quaternary and Quaternary-Tertiary deposits generally are gravels that mantle broad erosional surfaces on the flanks of the mountains, gravels in stream channels, and colluvium and landslide deposits on hill sides. Glacial deposits, representing at least two stages of glaciation, are present in the northern part of the Little Belt Mountains. The geologic structure of much of the northwest part of the quadrangle is a broad uplift, in the core of which the Paleoproterozoic and Neoarchean metamorphic rocks are exposed. Down plunge to the east, the succession of Phanerozoic sedimentary rocks define an east-trending arch, cored locally by Mesoproterozoic strata of the Belt Supergroup. The north flank of the arch dips steeply north as a monocline. Stratigraphic relations among Mississippian, Pennsylvanian, and Jurassic strata document the recurrent uplift and erosion on that north flank. The broader arch of the Little Belt Mountains reflects the west plunge of the ancestral Central Montana uplift. The eastern extension of the Lewis and Clark tectonic zone is exposed in the southern half of the quadrangle where the Volcano Valley fault zone curves from west to southeast as a reverse fault along which the latest movement is up on the south side. The fault zone ends in an anticline in the south-central margin of the quadrangle. Stratigraphic overlap of Phanerozoic strata over the truncated edges of Mesoproterozoic units documents that the area of the eastern terminus of the fault zone was tectonically recurrently active. Northeast trending strike-slip faults displace Mesoproterozoic rocks in the northwest and south-central parts of the quadrangle. Several of those faults are overlain unconformably by the Middle Cambrian Flathead Sandstone. Other north-east and west-trending faults across the central part of the quadrangle are intruded by middle Eocene plutons. You

History of research on glaciation in the White Mountains, New Hampshire (U.S.A.)

USGS Publications Warehouse

Thompson, W.B.

1999-01-01

The glacial geology of the White Mountains in New Hampshire has been the subject of many investigations since the 1840's. A series of controversies evolved during this period. First was the question of what geologic processes were responsible for eroding the bedrock and depositing the cover of surficial sediments. By the 1860's, the concept of glaciation replaced earlier theories invoking floods and icebergs. Research in the late 1800's concerned the relative impact of continental versus local glaciation. Some workers believed that surficial deposits in northern New Hampshire were the product of valley glaciers radiating from the White Mountains, but in the early 1900's continental glaciation was established as the most important process across the region. Debate over the extent and timing of alpine glaciation in the Presidential Range has continued until recent years. The most intensely argued topic has been the manner in which the Late Wisconsinan ice sheet withdrew from the White Mountains: whether by rapid stagnation and downwastage, or by progressive retreat of a still-active ice margin. The stagnation model became popular in the 1930's and was unchallenged until the late 1900's. Following a research hiatus lasting over 40 years, renewed interest in the glacial history of the White Mountains continues to inspire additional work.

Two-phase unsaturated flow at Yucca Mountain, Nevada: A report on current understanding

NASA Astrophysics Data System (ADS)

Pruess, Karsten

Thick unsaturated zones in semi-arid regions have some unique attributes that are favorable for long-term isolation of hazardous wastes. The disposal concept at Yucca Mountain takes advantage of low ambient water fluxes. Evaluation of site suitability must be based on an understanding of two-phase (liquid-gas) fluid flow and heat transfer processes in a heterogeneous, fractured rock mass. A large body of relevant knowledge has been accumulated in various fields, including petroleum and geothermal reservoir engineering, chemical engineering, civil engineering, and soil science. Complications at Yucca Mountain arise from the partly episodic and localized nature of water seepage in fracture networks. This limits the applicability of spatial and temporal averaging, and poses great challenges for numerical modeling. Significant flow and heat transfer effects may occur in the gas phase. Observations of natural and man-made chemical tracers as well as controlled field experiments have provided much useful information on mass transport at Yucca Mountain, including the occurrence of fast preferential flow. It is now clear that fracture-matrix interactions are considerably weaker than would be expected from a concept of water flowing in fractures as areally extensive sheets. The Yucca Mountain system is expected to be quite robust in coping with larger seepage rates, as may occur under future more pluvial climatic conditions.

Basal Freeze-on: An Active Component of Hydrology from the Ice Divide to the Margin

NASA Astrophysics Data System (ADS)

Bell, R. E.; Tinto, K. J.; Abdi, A.; Creyts, T. T.; Wolovick, M.; Das, I.; Ferraccioli, F.; Csatho, B. M.

2012-12-01

Subglacial hydrology is considered a key control of ice sheet dynamics. Here we show that basal freeze-on is a process that can terminate basal hydrologic networks both in the interior of East Antarctica and at the margins of the Greenland Ice Sheet. Basal freeze-on modifies the ice thickness, ice structure, and ice rheology and therefore must be considered in developing accurate understanding of how hydrology interacts with ice dynamics. In East Antarctica, the freeze-on process follows well-defined hydrologic networks within Gamburtsev Mountain valleys. The steep mountain topography strongly controls the routing of the subglacial water. Ice surface slope drives the water up the mountain valleys and freeze-on occurs at the valley heads. Freeze-on ice is characterized by distinct basal radar reflectors that emerge from the hydrologic network. Evidence that these spatially coherent reflectors demark accreted ice is the upward deflection of the overlying internal layers accompanied by thickening of base of the ice sheet. Individual accretion bodies can be 25 km wide across flow, 100 km along flow with average thicknesses of ~500m although the maximum thickness is 1100m. Regional accumulation rates near the accretion sites average 4cm/yr with low ice velocity (1.5 m/yr). The volume of the ice enclosed by the accretion ice reflectors is 45-1064 km3. The accretion occurs beneath 2200-3000m thick ice and has been persistent for at least 50,000yr. Other basal reflectors in northern Greenland appear in radar from NASA's Icebridge mission and CRESIS. To identify freeze-on ice, we use specific criteria: reflectors must originate from the bed, must be spatially continuous from line to line and the meteoric stratigraphy is deflected upward. The absence of coincident gravity anomalies indicates these reflectors define distinct packages of ice rather than frozen sediment or off-nadir subglacial topography. In the Petermann Glacier Catchment, one of the largest in northern Greenland, we have identified 14 distinct basal ice packages over a wide region. The accumulation rate (~17 cm/yr) and ice velocity (~5-200m/yr) are higher than East Antarctica. These accretion bodies are 10-50 km wide, up to 940m thick and can be traced up to 140 km. The volume of the ice enclosed by the accretion ice reflector units is ~70-300 km3. We estimate that the freeze-on process in Petermann has been active for at least 6,000yr. Water has been mapped beneath much of the Greenland ice sheet and adjacent to the inland freeze-on site flat bright reflectors are interpreted as basal water. The onset of fast flow in Petermann Glacier is associated with the development of the thickest unit of freeze-on ice. Other areas of Greenland also have basal freeze-on ice. North of Jakobshavn Isbrae where the ice sheet is ~1000 m thick, evidence exists for a nearly 10 km wide, 200 m thick unit of basal ice in airborne radar. Located close to the site where basal freeze-on outcrops at the ice sheet margin at Pakitsoq, this unit may be the result of freeze-on of water draining from a supraglacial lake. Basal freeze-on is a critical component of subglacial hydrology. The evidence for large scale freeze-on East Antarctica and many areas of Greenland indicates widespread modification of the base of the ice sheet by basal hydrology.

The impact of dynamic topography on the bedrock elevation and volume of the Pliocene Antarctic Ice Sheet

NASA Astrophysics Data System (ADS)

Austermann, Jacqueline; Pollard, David; Mitrovica, Jerry X.; Moucha, Robert; Forte, Alessandro M.; DeConto, Robert M.

2015-04-01

Reconstructions of the Antarctic ice sheet over long timescales (i.e. Myrs) require estimates of bedrock elevation through time. Ice sheet models have accounted, with varying levels of sophistication, for changes in the bedrock elevation due to glacial isostatic adjustment (GIA), but they have neglected other processes that may perturb topography. One notable example is dynamic topography, the deflection of the solid surface of the Earth due to convective flow within the mantle. Numerically predicted changes in dynamic topography have been used to correct paleo shorelines for this departure from eustasy, but the effect of such changes on ice sheet stability is unknown. In this study we use numerical predictions of time-varying dynamic topography to reconstruct bedrock elevation below the Antarctic ice sheet during the mid Pliocene warm period (~3 Ma). Moreover, we couple this reconstruction to a three-dimensional ice sheet model to explore the impact of dynamic topography on the evolution of the Antarctic ice sheet since the Pliocene. Our modeling indicates significant uplift in the area of the Transantarctic Mountains (TAM) and the adjacent Wilkes basin. This predicted uplift, which is at the lower end of geological inferences of uplift of the TAM, implies a lower elevation of the basin in the Pliocene. Relative to simulations that do not include dynamic topography, the lower elevation leads to a smaller Antarctic Ice Sheet volume and a more significant retreat of the grounding line in the Wilkes basin, both of which are consistent with offshore sediment core data. We conclude that reconstructions of the Antarctic Ice Sheet during the mid-Pliocene warm period should be based on bedrock elevation models that include the impact of both GIA and dynamic topography.

Basin-mountain structures and hydrocarbon exploration potential of west Junggar orogen in China

NASA Astrophysics Data System (ADS)

Wu, X.; Qi, X.; Zheng, M.

2015-12-01

Situated in northern Xinjiang, China, in NE-SW trend, West Junggar Orogen is adjacent to Altai fold belt on the north with the Ertix Fault as the boundary, North Tianshan fold belt on the south with the Ebinur Lake Strike-slip Fault as the boundary, and the Junggar Basin on the southeast with Zaire-Genghis Khan-Hala'alat fold belt as the boundary. Covering an area of about 10×104 km2 in China, there are medium and small intermontane basins, Burqin-Fuhai, Tacheng, Hefeng and Hoxtolgay, distributing inside the orogen. Tectonically West Junggar Orogen lies in the middle section of the Palaeo-Asian tectonic domain where the Siberia, Kazakhstan and Tarim Plates converge, and is the only orogen trending NE-SW in the Palaeo-Asian tectonic domain. Since the Paleozoic, the orogen experienced pre-Permian plate tectonic evolution and post-Permian intra-plate basin evolution. Complex tectonic evolution and multi-stage structural superimposition not only give rise to long term controversial over the basin basement property but also complex basin-mountain coupling relations, structures and basin superimposition modes. According to analysis of several kinds of geological and geophysical data, the orogen was dominated by compressive folding and thrust napping from the Siberia plate in the north since the Late Paleozoic. Compressive stress weakened from north to south, corresponding to subdued vertical movement and enhanced horizontal movement of crustal surface from north to south, and finally faded in the overthrust-nappe belt at the northwest margin of the Junggar Basin. The variation in compressive stress is consistent with the surface relief of the orogen, which is high in the north and low in the south. There are two kinds of basin-mountain coupling relationships, i.e. high angle thrusting and overthrusting and napping, and two kinds of basin superimposition modes, i.e. inherited and progressive, and migrating and convulsionary modes. West Junggar orogen has rich oil and gas shows. Tacheng Basin, north faulted fold belt in the Heshituoluogai basin, and Hongyan fault bench zone in north Ulungur Depression in the Junggar Basin are promising areas for hydrocarbon exploration.

Normal Faulting in the 1923 Berdún Earthquake and Postorogenic Extension in the Pyrenees

NASA Astrophysics Data System (ADS)

Stich, Daniel; Martín, Rosa; Batlló, Josep; Macià, Ramón; Mancilla, Flor de Lis; Morales, Jose

2018-04-01

The 10 July 1923 earthquake near Berdún (Spain) is the largest instrumentally recorded event in the Pyrenees. We recover old analog seismograms and use 20 hand-digitized waveforms for regional moment tensor inversion. We estimate moment magnitude Mw 5.4, centroid depth of 8 km, and a pure normal faulting source with strike parallel to the mountain chain (N292°E), dip of 66° and rake of -88°. The new mechanism fits into the general predominance of normal faulting in the Pyrenees and extension inferred from Global Positioning System data. The unique location of the 1923 earthquake, near the south Pyrenean thrust front, shows that the extensional regime is not confined to the axial zone where high topography and the crustal root are located. Together with seismicity near the northern mountain front, this indicates that gravitational potential energy in the western Pyrenees is not extracted locally but induces a wide distribution of postorogenic deformation.

Tertiary tilting and dismemberment of the laramide arc and related hydrothermal systems, Sierrita Mountain, Arizona

USGS Publications Warehouse

Stavast, W.J.A.; Butler, R.P.; Seedorff, E.; Barton, M.D.; Ferguson, C.A.

2008-01-01

Multiple lines of evidence, including new and published geologic mapping and paleomagnetic and geobarometric determinations, demonstrate that the rocks and large porphyry copper systems of the Sierrita Mountains in southern Arizona were dismembered and tilted 50?? to 60?? to the south by Tertiary normal faulting. Repetition of geologic features and geobarometry indicate that the area is segmented into at least three major structural blocks, and the present surface corresponds to oblique sections through the Laramide plutonic-hydrothermal complex, ranging in paleodepth from ???1 to ???12 km. These results add to an evolving view of a north-south extensional domain at high angles to much extension in the southern Basin and Range, contrast with earlier interpretations that the Laramide systems are largely upright and dismembered by thrust faults, highlight the necessity of restoring Tertiary rotations before interpreting Laramide structural and hydrothermal features, and add to the broader understanding of pluton emplacement and evolution of porphyry copper systems. ?? 2008 Society of Economic Geologists, Inc.

Fracture density and grain size controls on the relief structure of threshold landscapes

NASA Astrophysics Data System (ADS)

DiBiase, R.; Rossi, M. W.; Neely, A.

2015-12-01

A central goal in geomorphology is to untangle the competing controls of climate, tectonics, and rock strength on the topography and relief structure of mountain ranges. This is important for deciphering the history of climate and tectonics encoded in landscapes, predicting natural hazards, and quantifying critical zone processes. Incorporating rock strength into landscape evolution models has been a particularly challenging problem, because the factors that determine rock strength vary in importance depending on process. Here we propose a mechanism of hillslope-channel coupling by which tectonically-induced fracturing influences the relief structure of steep, rocky "threshold" landscapes by leading to A) increased fracture density in exposed bedrock outcrops, thereby limiting hillslope relief, and B) decreased grain size of channel bed material, thereby reducing the magnitude of fluvial incision thresholds and increasing the erosional efficiency of bedrock rivers. To test this hypothesis, we compare two contrasting landscapes in southern California—the eastern San Gabriel Mountains and the northern San Jacinto Mountains. The eastern San Gabriel Mountains rise 2 km in relief and exhibit high uplift and erosion rates due to active faulting along the Cucamonga thrust fault. Although bedrock on hillslopes is common, the exposed granitic and metamorphic basement rock is highly fractured at the decimeter or finer scale, and river channels are mantled with a thin layer of gravel-cobble alluvium. The northern San Jacinto Mountains, 80 km to the southeast, experience similar mean runoff and daily runoff variability, and are underlain by similar bedrock. Yet, despite an absence of active faulting, and erosion rates slower than the eastern San Gabriel Mountains by a factor of 5, the northern San Jacinto Mountains preserve one of the steepest escarpments in the contiguous US (2-3 km high), characterized by massive bedrock outcrops on hillslopes with meter-scale or larger fracture spacing, and a resulting channel network mantled with large boulders. Preliminary analyses suggest that fracture spacing and bed material grain size in threshold landscapes are tightly coupled, and influence the steepness of hillslopes and channels that control the relief structure of mountain ranges in a predictable manner.

Seasonal changes in ground-water quality and ground-water levels and directions of ground-water movement in southern Elmore County, southwestern Idaho, including Mountain Home Air Force Base, 1990-1991

USGS Publications Warehouse

Young, H.W.; Parliman, D.J.; Jones, Michael L.

1992-01-01

The study area is located in southern Elmore County, southwestern Idaho, and includes the Mountain Home Air Force Base located approximately 10 mi southwest of the city of Mountain Home. Chemical analyzes have been made periodically since the late 1940's on water samples from supply wells on the Air Force Base. These analyses indicate increases in specific conductance and in concentrations of nitrogen compounds, chloride, and sulfate. The purposes of this report, which was prepared in cooperation with the Department of the Air Force, are to describe the seasonal changes in water quality and water levels and to depict the directions of ground-water movement in the regional aquifer system and perched-water zones. Although data presented in this report are from both the regional ground-water system and perched-water zones, the focus is on the regional system. A previous study by the U.S. Geological Survey (Parliman and Young, 1990) describes the areal changes in water quality and water levels during the fall of 1989. During March, July, and October 1990, 141 wells were inventoried and depth to water was measured. Continuous water-level recorders were installed on 5 of the wells and monthly measurements of depth to water were made in 17 of the wells during March 1990 through February 1991. Water samples from 33 wells and 1 spring were collected during the spring and fall of 1990 for chemical analyses. Samples also were collected monthly from 11 of those wells during April to September 1990 (table 1). Selected well-construction and water-use data and measurements of depth to water for 141 wells are given in table 2 (separated sheets in envelope). Directions of ground-water movement and selected hydrographs showing seasonal fluctuations of water levels in the regional ground-water system and perched-water zones are shown on sheet 2. Changes in water levels in the regional ground-water system during March to October 1990 are shown on sheet 2.

Lutetian arc-type magmatism along the southern Eurasian margin: New U-Pb LA-ICPMS and whole-rock geochemical data from Marmara Island, NW Turkey

NASA Astrophysics Data System (ADS)

Ustaömer, P. Ayda; Ustaömer, Timur; Collins, Alan S.; Reischpeitsch, Jörg

2009-07-01

The rocks of Turkey, Greece and Syria preserve evidence for the destruction of Tethys, the construction of much of the continental crust of the region and the formation of the Tauride orogenic belt. These events occurred between the Late Cretaceous and Miocene, but the detailed evolution of the southern Eurasian margin during this period of progressive continental accretion is largely unknown. Marmara Island is a basement high lying at a key location in the Cenozoic Turkish tectonic collage, with a Palaeogene suture zone to the south and a deep Eocene sedimentary basin to the north. North-dipping metamorphic thrust sheets make up the island and are interlayered with a major metagranitoid intrusion. We have dated the intrusion by Laser Ablation ICP-MS analysis of U and Pb isotopes on zircon separates to 47.6 ± 2 Ma. We also performed major- and trace-elemental geochemical analysis of 16 samples of the intrusion that revealed that the intrusion is a calc-alkaline, metaluminous granitoid, marked by Nb depletion relative to LREE and LIL-element enrichment when compared to ocean ridge granite (ORG). We interpret the metagranitoid sill as a member of a mid-Eocene magmatic arc, forming a 30 km wide and more than 200 km long arcuate belt in NW Turkey that post-dates suturing along the İzmir-Ankara-Erzincan Suture zone. The arc magmatism was emplaced at the early stages of mountain building, related to collision of Eurasia with the Menderes-Taurus Platform in early Eocene times. Orogenesis and magmatism loaded the crust to the north creating coeval upward-deepening marine basins partially filled by volcanoclastic sediments.

CHATTAHOOCHEE ROADLESS AREA, GEORGIA.

USGS Publications Warehouse

Nelson, Arthur E.; Welsh, Robert A.

1984-01-01

A mineral survey indicates that the Chattahoochee Roadless Area, Georgia, offers little promise for the occurrence of mineral resources even though gold, mica, sillimanite, soapstone, dunite, chromite, and nickel have been mined nearby, and source rocks for these commodities are present in the roadless area. Granite gneiss, gneiss, schist, and metasandstone in the roadless area are suitable for stone, crushed rock, or aggregate; however, other sources for these materials are available outside the roadless area, closer to present markets. The potential for the occurrence of hydrocarbons (probably gas) beneath the thick regional thrust sheets in this area cannot be adequately evaluated from available data.

NASA programs in advanced sensors and measurement technology for aeronautical applications

NASA Astrophysics Data System (ADS)

Conway, Bruce A.

NASA involvement in the development, implementation, and experimental use of advanced aeronautical sensors and measurement technologies is presently discussed within the framework of specific NASA research centers' activities. The technology thrusts are in the fields of high temperature strain gages and microphones, laser light-sheet flow visualization, LTA, LDV, and LDA, tunable laser-based aviation meteorology, and fiber-optic CARS measurements. IR thermography and close-range photogrammetry are undergoing substantial updating and application. It is expected that 'smart' sensors will be increasingly widely used, especially in conjunction with smart structures in aircraft and spacecraft.

Offshore Tectonics of the St. Elias Mountains: Insights from Ocean Drilling and Seismic Stratigraphy on the Yakutat Shelf

NASA Astrophysics Data System (ADS)

Worthington, L. L.; Gulick, S. P. S.; Montelli, A.; Jaeger, J. M.; Zellers, S.; Walczak, M. H.; Mix, A. C.

2015-12-01

Ongoing collision of the Yakutat (YAK) microplate with North America (NA) in southern Alaska has driven orogenesis of the St. Elias Mountains and the advance of the offshore deformation front to the southeast. The offshore St. Elias fold-thrust belt records the complex interaction between collisional tectonics and glacial climate variability, providing insight for models of orogenesis and the evolution of glacial depocenters. Glacial erosion and deposition have provided sediment that constructed the upper continental shelf, much of which has been reincorporated into the orogenic wedge through offshore faulting and folding. We integrate core and downhole logging data from IODP Expedition 341 (Sites U1420 and U1421) drilled on the Yakutat shelf and slope with high-resolution and regional seismic profiles to investigate the coupled structural and stratigraphic evolution of the St. Elias margin. Site U1420 lies on the Yakutat shelf within the Bering Trough, a shelf-crossing trough that is within primary depocenter for Bering Glacier sediments. Two faults underlie the glacial packages and have been rendered inactive as the depositional environment has evolved, while faulting elsewhere on the shelf has initiated. Site U1421 lies on the current continental slope, within the backlimb of an active thrust that forms part of the modern YAK-NA deformation front. At each of these sites, we recovered glacigenic diamict (at depths up to ~1015 m at Site U1420), much of which is younger than 0.3 Ma. Age models within the trough indicated that initiation of active deformation away from the Bering Trough depocenter likely occurred since 0.3 Ma, suggesting that possible tectonic reorganization due to mass redistribution by glacial processes can occur at time scales on the order of 100kyr-1Myr.

Morphologic expression of Quaternary deformation in the northwestern foothills of the Ysyk-Köl basin, Tien Shan

NASA Astrophysics Data System (ADS)

Korjenkov, A. M.; Povolotskaya, I. E.; Mamyrov, E.

2007-03-01

The Tien Shan is one of the most active intracontinental mountain belts exhibiting numerous examples of Quaternary fault-related folding. To provide insight into the deformation of the Quaternary intermontane basins, the territory of the northwestern Ysyk-Köl region, where the growing Ak-Teke Anticline divided the piedmont apron of alluvial fans, is studied. It is shown that the Ak-Teke Hills are a sharply asymmetric anticline, which formed as a result of tectonic uplift and erosion related to motions along the South Ak-Teke Thrust Fault. The tectonic uplift gave rise to the local deviation of the drainage network in front of the northern limb of the fold. Optical (luminescent) dating suggests that the tectonic uplifting of the young anticline and the antecedent downcutting started 157 ka ago. The last upthrow of the high floodplain of the Toru-Aygyr River took place 1300 years ago. The structure of the South Ak-Teke Fault is examined by means of seismologic trenching and shallow seismic profiling across the fault. A laser tachymeter is applied to determine the vertical deformation of alluvial terraces in the Toru-Aygyr River valley at its intersection with the South Ak-Teke Fault. The rates of vertical deformation and an inferred number of strong earthquakes, which resulted in the upthrow of Quaternary river terraces of different ages, are calculated. The study territory is an example of changes in fluvial systems on growing folds in piedmont regions. As a result of shortening of the Earth’s crust in the mountainous belt owing to thrusting, new territories of previous sedimentation are involved in emergence. The tectonic activity migrates with time from the framing ridges toward the axial parts of intramontane basins.

Thermal consequences of thrust faulting: simultaneous versus successive fault activation and exhumation

NASA Astrophysics Data System (ADS)

ter Voorde, M.; de Bruijne, C. H.; Cloetingh, S. A. P. L.; Andriessen, P. A. M.

2004-07-01

When converting temperature-time curves obtained from geochronology into the denudation history of an area, variations in the isotherm geometry should not be neglected. The geothermal gradient changes with depth due to heat production and evolves with time due to heat advection, if the deformation rate is high. Furthermore, lateral variations arise due to topographic effects. Ignoring these aspects can result in significant errors when estimating denudation rates. We present a numerical model for the thermal response to thrust faulting, which takes these features into account. This kinematic two-dimensional model is fully time-dependent, and includes the effects of alternating fault activation in the upper crust. Furthermore, any denudation history can be imposed, implying that erosion and rock uplift can be studied independently to each other. The model is used to investigate the difference in thermal response between scenarios with simultaneous compressional faulting and erosion, and scenarios with a time lag between rock uplift and denudation. Hereby, we aim to contribute to the analysis of the mutual interaction between mountain growth and surface processes. We show that rock uplift occurring before the onset of erosion might cause 10% to more than 50% of the total amount of cooling. We applied the model to study the Cenozoic development of the Sierra de Guadarrama in the Spanish Central System, aiming to find the source of a cooling event in the Pliocene in this region. As shown by our modeling, this temperature drop cannot be caused by erosion of a previously uplifted mountain chain: the only scenarios giving results compatible with the observations are those incorporating active compressional deformation during the Pliocene, which is consistent with the ongoing NW-SE oriented convergence between Africa and Iberia.

Tectonics of the North American Cordillera near the Fortieth Parallel

USGS Publications Warehouse

King, P.B.

1978-01-01

The North American Cordillera near the Fortieth Parallel consists of the following tectonic units: 1. (A) To the east is a reactivated cratonic area, in the Southern Rocky Mountains and Colorado Plateau, in which the supracrustal rocks (Cambrian to Cretaceous) were broadly deformed during the late Cretaceous-Paleocene Laramide orogeny, and the Precambrian basement was raised in folds of wide amplitude. 2. (B) West of it is a miogeosynclinal belt, in the eastern Great Basin, in which a thick sequence of Paleozoic carbonates and related deposits was thrust eastward along low-angle faults during the middle to late Cretaceous Sevier orogeny. The miogeosyncline is the downwarped western margin of the original North American continent, and its rocks accumulated on Precambrian basement. 3. (C) Beyond is a eugeosynclinal belt, in the western Great Basin, in which Paleozoic graywackes, cherts, and volcanics were thrust easteastward along low-angle faults during several Paleozoic orogenies - the mid-Paleozoic Antler orogeny which produced the Roberts thrust on the east, and the end-Paleozoic Sonoma orogeny which produced the Golconda thrust farther west. The Paleozoic eugeosynclinal rocks accumulated on oceanic basement. They are overlapped from the west by Triassic and Jurassic shelf deposits, which pass westward into eugeosynclinal deposits. 4. (D) A volcanic island-arc belt existed on the sites of the Sierra Nevada in Paleozoic and early Mesozoic time, which produced thick bodies of sediments and volcanics. During the mid-Mesozoic Nevadan orogeny these were steeply deformed and thrust westward over subduction zones, and were intruded by granitic rocks that rose from the upper mantle to form great batholiths. 5. (E) West of the Sierra Nevada, in the Great Valley, is a great sedimentary embankment of later Mesozoic flysch or turbidite, largely younger than the supracrustal rocks of the Sierra Nevada and the Nevadan orogeny. It was formed of the erosional products of the supracrustal and granitic rocks of the Sierra Nevada. 6. (F) This sequence is, in turn, thrust westward over the Mesozoic Franciscan terrane of the Coast Ranges, which forms the westernmost belt of the Cordillera, and which is being treated in other papers in this symposium. The net effect of the prolonged events that produced the Cordillera in this segment has been the addition of successive tectonic belts to the North American continent at the expense of the Pacific Ocean basin during Phanerozoic time. ?? 1978.

Tectonic evolution and hydrocarbon accumulation in the Yabulai Basin, western China

NASA Astrophysics Data System (ADS)

Zheng, Min; Wu, Xiaozhi

2014-05-01

The Yabulai petroliferous basin is located at the north of Hexi Corridor, western China, striking NEE and covering an area of 1.5×104 km2. It is bounded on the south by Beidashan Mountain to the Chaoshui Basin, on the east by Bayanwulashan Mountain to the Bayanhaote Basin, and on the northwest by Yabulai Mountain to the Yingen-Ejinaqi Basin. It is a Meso-cenozoic compressive depression residual basin. In view of regional geotectonics, the Yabulai basin sits in the middle-southern transition belt of Arershan massif in North China Craton. Driven by Indosinian movement at the late Triassic, two near EW normal faults were developed under the regional extensional stress along the northern fringe of Beidashan Mountain and the southern fringe of Yabulai Mountain front in the Arershan massif, forming the embryonic form of the Yabulai rift lake basin. Since Yanshan period, the Yabulai basin evolved in two major stages: Jurassic rift lake basin and Cretaceous rift lake basin. During early Yanshan period, EW striking Yabulai tensional rift was formed. Its major controlling fault was Beidashan normal fault, and the depocenter was at the south of this basin. During middle Yanshan period, collision orogenesis led to sharp uplift at the north of this basin where the middle-lower Jurassic formations were intensely eroded. During late Yanshan period, the Alashan massif and its northern area covered in an extensional tectonic environment, and EW striking normal faults were generated at the Yabulai Mountain front. Such faults moved violently and subsided quickly to form a new EW striking extensional rift basin with the depocenter at the south of Yabulai Mountain. During Himalayan period, the Alashan massif remained at a SN horizontal compressional tectonic environment; under the compressional and strike slip actions, a NW striking and south dipping thrusting nappe structure was formed in the south of the Yabulai basin, which broke the Beidashan normal fault to provide the echelon fault system and finally present the current structural framework of "east uplift and west depression, south faulted and north overlapping". The Yabulai basin presented as a strike-slip pull-apart basin in Mesozoic and a compressional thrusting depression basin in Cenozoic. Particularly, the Mesozoic tectonic units were distributed at a big included angle with the long axis of the basin, while the Cenozoic tectonic units were developed in a basically consistent direction with the long axis. The sags are segmented. Major subsiding sags are located in the south, where Mesozoic Jurassic-Cretaceous systems are developed, with the thickest sedimentary rocks up to 5300m. Jurassic is the best developed system in this basin. Middle Jurassic provides the principal hydrocarbon-bearing assemblage in this basin, with Xinhe Fm. and Qingtujing Fm. dark mudstone and coal as the source rocks, Xinhe Fm. and Qingtujing Fm. sandstones as the reservoir formation, and Xinhe Fm. mudstones as the cap rocks. However, the early burial and late uplifting damaged the structural framework of the basin, thus leading to the early violent compaction and tightness of Jurassic sandstone reservoir and late hydrocarbon maturity. So, tectonic development period was unmatched to hydrocarbon expulsion period of source rocks. The hydrocarbons generated were mainly accumulated near the source rocks and entrapped in reservoir. Tight oil should be the major exploration target, which has been proved by recent practices.

ICDP drilling in the Scandinavian Caledonides: the SDDP-COSC project

NASA Astrophysics Data System (ADS)

Lorenz, Henning; Juhlin, Christopher; Gee, David; Pascal, Christophe; Tsang, Chin-Fu; Pedersen, Karsten; Rosberg, Jan-Erik

2013-04-01

The Swedish Deep Drilling Program (SDDP) Collisional Orogeny in the Scandinavian Caledonides (COSC) project is a multidisciplinary investigation of the Scandian mountain belt. Cenozoic uplift of the Scandes has exposed a lower- to middle-crustal level section through this Himalaya-type orogen, providing unique opportunities to better understand not only the Caledonides, but also on-going orogeny and the earthquake-prone environments of modern mountains belts. COSC will also contribute to our knowledge of mountain belt hydrology, provide the first information about deep thermal gradients for paleoclimate modeling and potential geothermal energy resources, contribute new information about the deep biosphere, and improve our understanding of the Cenozoic uplift history of the Scandes. The drilling program targets the far-traveled (> 400 km) allochthons of the Scandinavian Caledonides and their emplacement across the Baltoscandian foreland basin onto the platform of continent Baltica. Two 2.5 km deep holes are planned. COSC-1, to be drilled in the summer of 2013, will target the high-grade metamorphic complex of the Seve Nappes (SNC) and its contact to underlying allochthons. COSC-2 will start in the lower thrust sheets, pass through the basal décollement and investigate the character of the deformation in the underlying basement. An international science team, including expertise on Himalaya-Tibet and other young orogens, is running the science program. New high-resolution reflection seismic data provide excellent images of the upper crust. Alternative interpretations of the reflectors' origin, particularly those in the basement, will be tested. The site of COSC-1 is based on a 3D geological model, constructed from surface geology, recent and vintage regional reflection seismic profiles, regional and local gravity data, and high-resolution aeromagnetics, acquired recently by the Geological Survey of Sweden. The drilling will be carried out utilising the new Swedish scientific drilling infrastructure, located at Lund University, an Atlas Copco CT20 diamond core-drilling rig, with versatile drilling equipment (see EGU2012-7379), providing the ideal platform for core-drilling to 2.5 km depths. Existing drilling, sampling and testing techniques (e.g. triple-tube core drilling for best core quality) will need to be adapted to highly variable lithologies and new techniques will be developed, as necessary. COSC-1 drilling operations and the directly related on-site investigations are financed by ICDP and the Swedish Research Council. All drill cores will be transferred to the core repository of the Geological Survey of Sweden, and a sampling party will be announced later this year. Researchers who want to participate in COSC and contribute their expertise are encouraged to inform us of their interests.

Seismic images of a Grenvillian terrane boundary

USGS Publications Warehouse

Milkereit, B.; Forsyth, D. A.; Green, A.G.; Davidson, A.; Hanmer, S.; Hutchinson, Deborah R.; Hinze, W. J.; Mereu, R.F.

1992-01-01

A series of gently dipping reflection zones extending to mid-crustal depths is recorded by seismic data from Lakes Ontario and Erie. These prominent reflection zones define a broad complex of southeast-dipping ductile thrust faults in the interior of the Grenville orogen. One major reflection zone provides the first image of a proposed Grenvillian suture—the listric boundary zone between allochthonous terranes of the Central Gneiss and Central Metasedimentary belts. Curvilinear bands of reflections that may represent "ramp folds" and "ramp anticlines" that originally formed in a deep crustal-scale duplex abut several faults. Vertical stacking of some curvilinear features suggests coeval or later out-of-sequence faulting of imbricated and folded thrust sheets. Grenvillian structure reflections are overlain by a thin, wedge-shaped package of shallow-dipping reflections that probably originates from sediments deposited in a local half graben developed during a period of post-Grenville extension. This is the first seismic evidence for such extension in this region, which could have occurred during terminal collapse of the Grenville orogen, or could have marked the beginning of pre-Appalachian continental rifting.

A remote sensing study of active folding and faulting in southern Kerman province, S.E. Iran

NASA Astrophysics Data System (ADS)

Walker, Richard Thomas

2006-04-01

Geomorphological observations reveal a major oblique fold-and-thrust belt in Kerman province, S.E. Iran. The active faults appear to link the Sabzevaran right-lateral strike-slip fault in southeast Iran to other strike-slip faults within the interior of the country and may provide the means of distributing right-lateral shear between the Zagros and Makran mountains over a wider region of central Iran. The Rafsanjan fault is manifest at the Earth's surface as right-lateral strike-slip fault scarps and folding in alluvial sediments. Height changes across the anticlines, and widespread incision of rivers, are likely to result from hanging-wall uplift above thrust faults at depth. Scarps in recent alluvium along the northern margins of the folds suggest that the thrusts reach the surface and are active at the present-day. The observations from Rafsanjan are used to identify similar late Quaternary faulting elsewhere in Kerman province near the towns of Mahan and Rayen. No instrumentally recorded destructive earthquakes have occurred in the study region and only one historical earthquake (Lalehzar, 1923) is recorded. In addition GPS studies show that present-day rates of deformation are low. However, fault structures in southern Kerman province do appear to be active in the late Quaternary and may be capable of producing destructive earthquakes in the future. This study shows how widely available remote sensing data can be used to provide information on the distribution of active faulting across large areas of deformation.

Retrodeformable cross sections and Oak Ridge fault, Ventura basin, California

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yeats, R.S.; Huftile, G.F.

1988-03-01

A retrodeformable (balanced) cross section is constructed such that stratified rocks are restored to their undeformed state without loss or gain of bed length or bed thickness. Ductile strata may be area-balanced if original thickness is known. Near Ventura, folds in Pliocene-Pleistocene turbidites and Miocene-early Pliocene shales (Rincon, Monterey, Sisquoc) overlie an unfolded competent Paleogene sequence. The basal decollement of the foldbelt is in the ductile Rincon Formation (lower Miocene). The overlying Sulphur Mountain, Ventura Avenue, San Miguelito, and Rincon anticlines are fault-propagation folds developing from south-dipping, largely late Quaternary frontal ramp thrusts (Sisar-Big Canyon-Lion fault set, Barnard fault set,more » padre Juan fault, and C-3 fault, respectively) that rise from the decollement. Cross-section balancing shows that the overlying fold-thrust belt has shortened 2.5-6 km more than subjacent Paleogene competent strata. This excess bed length is taken up in the Paleogene sequence on the Oak Ridge fault as a ramp from the brittle-plastic transition zone through the upper crust. This implies that the basal decollement is the frontal active thrust of the Oak Ridge fault. The decollement dies out southeast of a line between Timber Canyon oil field and the west end of Oak Ridge, possibly because of decreased ductility in the Miocene decollement sequence due to appearance of sandstone interbeds. Farther southeast, late Quaternary displacement concentrated on the Oak Ridge fault itself at rates greater than 10 mm/year.« less

Regional Landscape Response to Wedge-Top Basin Formation

NASA Astrophysics Data System (ADS)

Ruetenik, G.; Moucha, R.; Hoke, G. D.; Val, P.

2017-12-01

Wedge-top basins are the result of regionally variable uplift along thrust faults downstream of a mountain range and provide an ideal environment to study the regional stream and surface response to local variations in rock uplift. In this study, we simulate the formation and evolution of a wedge-top basin using a landscape evolution model. In line with a previous study, we find that during deformation in the fold-and-thrust belt adjacent to a wedge-top basin, both channel slope and erosion rates are reduced, and these changes propagate as a wave of low erosion into the uplands. For a uniform background uplift rate, this reduced rate of erosion results in a net surface uplift and a decreased slope within and upstream of the wedge-top basin. Following the eventual breach of the basin's bounding thrust belt, a wave of high erosion propagates through the basin and increases the channel slope. We expand upon previous studies by testing our model against a wide range of model parameters, although in general we find that the onset of increased erosion can be delayed by up to several million years. The amount of surface uplift is highly dependent on flexural isostasy and therefore it is heavily influenced by the elastic thickness and erodbility parameters. Observed paleoerosion rates in a paired wedge-top foreland sequence in the Argentine Precordillera reveal similar histories of paleo-erosion, and present day stream profiles show evidence that support model outcomes.

Near-field tsunami inferred from numerical modeling of medieval overwash at Anegada, British Virgin Islands

NASA Astrophysics Data System (ADS)

Wei, Y.; Ten Brink, U. S.; Atwater, B. F.; Tuttle, M. P.; Robert, H.; Feuillet, N.; Jennifer, W.; Fuentes, Z.

2012-12-01

In a comparison among numerical models of storms and tsunamis, only tsunami waves of nearby origin manage to wash over an area where coral heads of medieval age are scattered hundreds of meters inland from the north shore of Anegada, British Virgin Islands. This low-lying island faces the Puerto Rico Trench 120 km to the north. The island's north shore, fringed by a coral reef 100-1200 m offshore, displays geological evidence for two levels of overwash. The medieval overwash, dated to AD 1200-1450, was the higher one. It is evidenced by scores of coral boulders scattered hundreds of meters inland. Some of them crossed the area of the modern storm berm at Soldier Wash, continued across a broad limestone rise 3-4 m above sea level, and came to rest on lower ground farther inland. Coral heads in four other areas, also medieval or older, came to rest hundreds of meters inland from beach ridges now 2-4 m above sea level. The later, lower-elevation overwash, dated to AD 1650-1800, laid down a sheet of sand and shell that extends as much as 1.5 km inland. The hypothetical causes for each event, tested by numerical modeling, include (1) category IV and V hurricanes that differ in surge and wave heights; (2) the 1755 Lisbon earthquake or hypothetical medieval predecessor, at M 8.7 and M 9.0; (3) M 8.4 thrust earthquake along the Puerto Rico Trench between Hispaniola and Anegada; (4) M 8.7 thrust along the Puerto Rico Trench between Tortola and Antigua; (5) M 8.0 earthquake from normal faulting on the outer rise north of Anegada. The model output includes extent of onshore flooding, depth and velocity of overland flow, and energy lost by tsunami and hurricane waves as they cross the reef and continue across a shallow subtidal flat to Anegada's north shore. For the medieval overwash, the modeling is most conclusive in testing various explanations for the coral boulders inland of Soldier Wash. The simulated hurricane waves do not wash inland of the storm berm; the height of storm surge level is limited by deep water offshore, and the waves lose energy by breaking on the reef. As for the hypothesized tsunami sources, the Soldier Wash evidence is explained only by the M 8.7 interplate-thrust source along the eastern Puerto Rico Trench (4) or the outer-rise source north of Anegada (5). The M 8.7 interplate-thrust source may be inconsistent with recent GPS measurements [1], in which case the likely source is normal faulting on the outer rise (L = 132 km, W = 45 km, depth = 7.5 km, dip = 60°, strike = 110°, rake = -90°, slip = 7.1 m). The 1755 Lisbon tsunami may explain the sand-and-shell sheet from 1650-1800, with two caveats: (1) the sheet extends farther inland than does the modeled inundation from a Lisbon source smaller than M 9.0; and (2) neither of the Lisbon sources tested corresponds to mapped faults offshore Iberia (the modeled Lisbon sources strike NNW-SSE to account for flooding and damage elsewhere in the Caribbean [2]). In the hurricane models, the reef and the subtidal flats behind it dissipate too much wave energy from the storms to explain even the low-elevation overwash of 1650-1800. COMPANION ABSTRACTS: Geological evidence overview (Atwater), coral-boulder ages (Weil Accardo). REFERENCES: [1] GRL 39 (2012), L10304. [2] Marine Geology (2009), 264, 109-122.

Variable shortening on the Main Frontal Thrust in Nepal

NASA Astrophysics Data System (ADS)

Almeida, R. V.; Hubbard, J.; Lee, Y. S.; Liberty, L. M.; Paudel, L.; Shrestha, A.; Sapkota, S. N.; Joshi, G.

2017-12-01

The Main Frontal Thrust (MFT) is the youngest, most active, and southernmost thrust system in the Himalaya. It is located in the footwall of the Main Boundary thrust (MBT), deforming Miocene to Pliocene age Siwalik Group rocks. Although often considered a single, continuous fault, in reality as many as four subparallel faults, spaced 5-30 km apart, make up this fault system. Estimates of total shortening across the MFT for eastern and central Nepal vary from 15 to 40 km, based on cross-sections and surface measurements. However, when the same methods are applied, shortening does not vary significantly along strike (Hirschmiller et al., 2014), suggesting contrasting methodologies rather than a difference in interpreted along strike structural history. Based on high resolution seismic reflection imaging, we present new interpretations of total shortening recorded by the MFT system in central vs. eastern Nepal (200 km apart), together with a detailed transect of field observations in central Nepal. Our structural interpretations demonstrate that the geological shortening recorded on the MFT ranges from >20 km in central Nepal to <1 km in far eastern Nepal. Geodetic measurements show only a slight decrease in interseismic convergence from central (15±1 mm/yr) to eastern Nepal (14±1 mm/yr) and therefore cannot explain this dramatic difference (Lindsey et al., in prep). Taken at face value, these results imply that the MBT must have been much more recently active in eastern Nepal ( 70 ka) than central Nepal ( 1.4 Ma). We propose an alternative model that does not require this dramatic difference in the age of the MFT. As one end-member, it is indeed possible that the MFT may have broken forward much more recently in the east. However, it is also possible that older MFT thrust sheets have formed, and then have been consumed as the MBT passively slid south in the hanging wall of the MFT. Distinguishing between these models is important not only for understanding the evolution of the MBT and MFT, but also plays a critical role in assessing the current geometry and earthquake hazard associated with the Main Himalayan Thrust, the décollement that underlies the entire system (e.g., Hubbard et al., 2016). We explore the implications of these two end-member models and identify ways in which each model could be tested.

Characterization of Fluid Transfer Properties in a Transpressive Fault System: Chaîne des Matheux Fold-and-Thrust Belt and Enriquillo-Plantain Garden Fault Zone - Haiti

NASA Astrophysics Data System (ADS)

Wessels, R.; Ellouz-Zimmermann, N.; Rosenberg, C.; Hamon, Y.; Battani, A.; Bellahsen, N.; Deschamps, R.; Leroy, S. D.; Momplaisir, R.

2016-12-01

The NW - SE trending Chaîne des Matheux (CdM) comprises the onshore frontal thrust sheet of the SW-verging Haitian fold-and-thrust belt (HFTB). The HFTB's active deformation front is covered by sediments of the Cul-de-Sac plain and is bounded on the south by the E - W trending left-lateral Enriquillo-Plantain Garden fault zone (EPGFZ). Seismicity down to the junction between the two systems has been recorded during the 12 January 2010 Mw 7.0 Léogâne earthquake. Stratigraphic, structural and kinematic field data on a transect from the CdM to the EPGFZ indicate (N)NE - (S)SW oriented shortening, which is partitioned over 1) (N)NE-dipping oblique thrusts rooted in Cretaceous basement, 2) decollement levels in both latest Cretaceous and Paleogene limestones, and 3) by strike-slip and positive flower structures along the EPGFZ. We investigated the geometry and kinematics of both fault and fracture systems, which was coupled with sampling and analysis of fluid-derived mineralizations to constrain the timing and geological evolution. C & O isotope and whole-rock analyses have been performed to characterize the geochemistry of the source of these fluids. Raman spectroscopy and fluid-inclusion analyses has been applied to selected samples to comprehend the local burial history. Fluid and gas seepages along fault planes are qualitative indicators for transfer properties between different fault segments and their connectivity with deeper crustal or mantle reservoirs. Relative timing of structures in the CdM coupled with cathodoluminescence (CL) microscopy reveals three deformation phases, characterized by associated calcite veins that precipitated from oxidizing meteoric fluids. The deeply rooted frontal CdM thrust lacks mineralization, but fluids expelled from along-strike natural springs registered He and Ne isotope ratios suggesting a strong mantle-derived component. CL microscopy results on calcite veins from the EPGFZ's fault core imply fluid circulation in an episodically `open' system under a reducing environment. He and Ne isotope ratios from fluids derived along the EPGFZ suggest a significant, but less pronounced, mantle-derived component compared to the frontal thrust of the CdM. The above results indicate a change in fluid transfer properties over time for this transpressive system.

Foreland crustal structure of the New York recess, northeastern United States

USGS Publications Warehouse

Herman, G.C.; Monteverde, D.H.; Schlische, R.W.; Pitcher, D.M.

1997-01-01

A new structural model for the northeast part of the Central Appalachian foreland and fold-and-thrust belt is based on detailed field mapping, geophysical data, and balanced cross-section analysis. The model demonstrates that the region contains a multiply deformed, parautochthonous fold-and-thrust system of Paleozoic age. Our interpretations differ from previous ones in which the entire region north of the Newark basin was considered to be allochthonous. The new interpretation requires a substantial decrease in Paleozoic tectonic shortening northeastward from adjacent parts of the Central Appalachian foreland and illustrates the common occurrence of back-thrusting within the region. During early Paleozoic time northern New Jersey consisted of a Taconic orogenic foreland in which cover folds (F1) involved lower Paleozoic carbonate and flysch overlying Middle Proterozoic basement. F1 folds are open and upright in the foreland and more gently inclined to recumbent southeastward toward the trace of the Taconic allochthons. F1 structures were cut and transported by a fold-and-thrust system of the Allegheny orogeny. This thrust system mostly involves synthetic faults originating from a master decollement rooted in Proterozoic basement. Antithetic faults locally modify early synthetic overthrusts and S1 cleavage in lower Paleozoic cover and show out-of-sequence structural development. The synthetic parts of the regional thrust system are bounded in the northwestern foreland by blind antithetic faults interpreted from seismic-reflection data. This antithetic faulting probably represents Paleozoic reactivation of Late Proterozoic basement faults. Tectonic contraction in overlying cover occurred by wedge faulting where synthetic and antithetic components of the foreland fault system overlap. S2 cleavage in the Paleozoic cover stems from Alleghanian shortening and flattening and commonly occurs in the footwall of large overthrust sheets. Paleozoic structures in Proterozoic basement include fault blocks bounded by high-angle faults and low- to moderate-angle shear zones that locally produce overlying cover folds. Broad and open folds in basement probably reflect shear-zone displacement of subhorizontal foliation. Our cross-section interpretations require limited involvement of lower Paleozoic cover folds in the footwalls of major overthrust faults. Palinspastic restoration of F1 folds produces an arched passive-margin sequence. The tectonic contraction for the Valley and Ridge province and southeastern Pocono Plateau is about 25 km, and tectonic wedge angles are 8??-11??.

Tectonic triggering of slump sheets in the Upper Cretaceous carbonate succession of the Porto Selvaggio area (Salento peninsula, southern Italy): Synsedimentary tectonics in the Apulian Carbonate Platform

NASA Astrophysics Data System (ADS)

Mastrogiacomo, G.; Moretti, M.; Owen, G.; Spalluto, L.

2012-08-01

Soft-sediment deformation structures crop out in the Upper Cretaceous carbonate succession in Porto Selvaggio cove in the western Salento peninsula, Apulian foreland, southern Italy. The deformed interval is about 13 m thick and occurs between shallow-water limestones and dolostones formed in peritidal and shallow subtidal environments. It comprises well-bedded grey mudstones interlayered with dark grey laminated microbioclastic wackestones characterized by couplets of closely spaced dark and bright laminae marked by the parallel orientation of calcareous microbioclasts and thin-shelled bivalves. The low biological diversity, scarcity of burrowing biota, and presence of a well preserved fish fauna provide evidence of anoxic conditions occurring in morphological depressions within the platform, and a stagnant, stratified water body affected by weak bottom currents, indicating the sudden development of a localised and short-lived intraplatform basin. Two soft-sediment deformation horizons (slump sheets) separated by undeformed limestones with similar facies occur in this part of the succession. The lower, thicker slump sheet (1.0-1.3 m thick) contains asymmetric and box folds. Well-developed décollement surfaces (locally containing thick brecciated zones) cut the folds, forming small-scale thrust-sheets and indicating mixed plastic to brittle behaviour. The upper, thinner slump sheet (0.25-0.35 m thick) contains only asymmetric folds, indicating plastic behaviour only. The differences in deformation style are attributed to differences in facies. Measurements of fold-axis orientations in the slump sheets show that they moved in similar directions, recording the development of a local, gently dipping palaeoslope. Autogenic (internal) trigger mechanisms are ruled out by a detailed consideration of facies. The slump sheets were triggered by allogenic, tectonic effects, either the weakening of sediment by seismic activity or the tectonically induced steepening of slopes, or a combination of both. Tectonically induced steepening is consistent with localised and sudden vertical facies changes related to the creation of an intraplatform basin. The occurrence of slump sheets in carbonate platform successions is unusual since carbonate platforms are normally associated with shelves or low-angle ramps.

10Be surface exposure dating reveals strong active deformation in the central Andean backarc interior

NASA Astrophysics Data System (ADS)

García Morabito, Ezequiel; Terrizzano, Carla; Zech, Roland; Willett, Sean; Yamin, Marcela; Haghipour, Negar; Wuethrich, Lorenz; Christl, Marcus; María Cortes, José; Ramos, Victor

2016-04-01

Understanding the deformation associated with active thrust wedges is essential to evaluate seismic hazard. How is active faulting distributed throughout the wedge, and how much deformation is taken up by individual structures? We address these questions for our study region, the central Andean backarc of Argentina. We combined a structural and geomorphological approach with surface exposure dating (10Be) of alluvial fans and strath terraces in two key localities at ~32° S: the Cerro Salinas, located in the active orogenic front of the Precordillera, and the Barreal block in the interior of the Andean mountain range. We analysed 22 surface samples and 6 depth profiles. At the thrust front, the oldest terrace (T1) yields an age of 100-130 ka, the intermediate terrace (T2) between 40-95 ka, and the youngest terrace (T3) an age of ~20 ka. In the Andean interior, T1´ dates to 117-146 ka, T2´ to ~70 ka, and T3´ to ~20 ka, all calculations assuming negligible erosion and using the scaling scheme for spallation based on Lal 1991, Stone 2000. Vertical slip rates of fault offsets are 0.3-0.5 mm/yr and of 0.6-1.2 mm/yr at the thrust front and in the Andean interior, respectively. Our results highlight: i) fault activity related to the growth of the Andean orogenic wedge is not only limited to a narrow thrust front zone. Internal structures have been active during the last 150 ka, ii) deformation rates in the Andean interior are comparable or even higher that those estimated and reported along the emerging thrust front, iii) distribution of active faulting seems to account for unsteady state conditions, and iv) seismic hazards may be more relevant in the internal parts of the Andean orogen than assumed so far. References Lal, D., 1991: Cosmic ray labeling of erosion surfaces: In situ nuclide production rates and erosion models. Earth and Planetary Science Letters 104: 424-439. Stone, J.O., 2000: Air pressure and cosmogenic isotope production. Journal of Geophysical Research 105 (B10): 23753-23759

Crustal thickness variations in the Zagros continental collision zone (Iran) from joint inversion of receiver functions and surface wave dispersion

NASA Astrophysics Data System (ADS)

Tatar, M.; Nasrabadi, A.

2013-10-01

Variations in crustal thickness in the Zagros determined by joint inversion of P wave receiver functions (RFs) and Rayleigh wave group and phase velocity dispersion. The time domain iterative deconvolution procedure was employed to compute RFs from teleseismic recordings at seven broadband stations of INSN network. Rayleigh wave phase velocity dispersion curves were estimated employing two-station method. Fundamental mode Rayleigh wave group velocities for each station is taken from a regional scale surface wave tomographic imaging. The main variations in crustal thickness that we observe are between stations located in the Zagros fold and thrust belt with those located in the Sanandaj-Sirjan zone (SSZ) and Urumieh-Dokhtar magmatic assemblage (UDMA). Our results indicate that the average crustal thickness beneath the Zagros Mountain Range varies from ˜46 km in Western and Central Zagros beneath SHGR and GHIR up to ˜50 km beneath BNDS located in easternmost of the Zagros. Toward NE, we observe an increase in Moho depth where it reaches ˜58 km beneath SNGE located in the SSZ. Average crustal thickness also varies beneath the UDMA from ˜50 km in western parts below ASAO to ˜58 in central parts below NASN. The observed variation along the SSZ and UDMA may be associated to ongoing slab steepening or break off in the NW Zagros, comparing under thrusting of the Arabian plate beneath Central Zagros. The results show that in Central Iran, the crustal thickness decrease again to ˜47 km below KRBR. There is not a significant crustal thickness difference along the Zagros fold and thrust belt. We found the same crystalline crust of ˜34 km thick beneath the different parts of the Zagros fold and thrust belt. The similarity of crustal structure suggests that the crust of the Zagros fold and thrust belt was uniform before subsidence and deposition of the sediments. Our results confirm that the shortening of the western and eastern parts of the Zagros basement is small and has only started recently.

Landforms along transverse faults parallel to axial zone of folded mountain front, north-eastern Kumaun Sub-Himalaya, India

NASA Astrophysics Data System (ADS)

Luirei, Khayingshing; Bhakuni, S. S.; Negi, Sanjay S.

2017-02-01

The shape of the frontal part of the Himalaya around the north-eastern corner of the Kumaun Sub-Himalaya, along the Kali River valley, is defined by folded hanging wall rocks of the Himalayan Frontal Thrust (HFT). Two parallel faults (Kalaunia and Tanakpur faults) trace along the axial zone of the folded HFT. Between these faults, the hinge zone of this transverse fold is relatively straight and along these faults, the beds abruptly change their attitudes and their widths are tectonically attenuated across two hinge lines of fold. The area is constituted of various surfaces of coalescing fans and terraces. Fans comprise predominantly of sandstone clasts laid down by the steep-gradient streams originating from the Siwalik range. The alluvial fans are characterised by compound and superimposed fans with high relief, which are generated by the tectonic activities associated with the thrusting along the HFT. The truncated fan along the HFT has formed a 100 m high-escarpment running E-W for ˜5 km. Quaternary terrace deposits suggest two phases of tectonic uplift in the basal part of the hanging wall block of the HFT dipping towards the north. The first phase is represented by tilting of the terrace sediments by ˜30 ∘ towards the NW; while the second phase is evident from deformed structures in the terrace deposit comprising mainly of reverse faults, fault propagation folds, convolute laminations, flower structures and back thrust faults. The second phase produced ˜1.0 m offset of stratification of the terrace along a thrust fault. Tectonic escarpments are recognised across the splay thrust near south of the HFT trace. The south facing hill slopes exhibit numerous landslides along active channels incising the hanging wall rocks of the HFT. The study area shows weak seismicity. The major Moradabad Fault crosses near the study area. This transverse fault may have suppressed the seismicity in the Tanakpur area, and the movement along the Moradabad and Kasganj-Tanakpur faults cause the neotectonic activities as observed. The role of transverse fault tectonics in the formation of the curvature cannot be ruled out.

Geometry and kinematics of Majiatan Fold-and-thrust Belt, Western Ordos Basin: implication for Tectonic Evolution of North-South Tectonic Belt

NASA Astrophysics Data System (ADS)

He, D.

2017-12-01

The Helan-Chuandian North-South Tectonic Belt crossed the central Chinese mainland. It is a boundary of geological, geophysical, and geographic system of Chinese continent tectonics from shallow to deep, and a key zone for tectonic and geomorphologic inversion during Mesozoic to Cenozoic. It is superimposed by the southeastward and northeastward propagation of Qinghai-Tibet Plateau in late Cenozoic. It is thus the critical division for West and East China since Mesozoic. The Majiatan fold-and-thrust belt (MFTB), locating at the central part of HCNSTB and the western margin of Ordos Basin, is formed by the tectonic evolution of the Helan-Liupanshan Mountains. Based on the newly-acquired high-resolution seismic profiles, deep boreholes, and surface geology, the paper discusses the geometry, kinematics, and geodynamic evolution of MFTB. With the Upper Carboniferous coal measures and the pre-Sinian ductile zone as the detachments, MFTB is a multi-level detached thrust system. The thrusting was mainly during latest Jurassic to Late Cretaceous, breaking-forward in the foreland, and resulting in a shortening rate of 25-29%. By structural restoration, this area underwent extension in Middle Proterozoic to Paleozoic, which can be divided into three phases of rifting such as Middle to Late Proterozoic, Cambiran to Ordovician, and Caboniferous to early Permian. It underwent compression since Late Triassic, including such periods as Latest Triassic, Late Jurassic to early Cretaceous, Late Cretaceous to early Paleogene, and Pliocene to Quaternary, with the largest shortening around Late Jurassic to early Cretaceous period (i.e. the mid-Yanshanian movement by the local name). However, trans-extension since Eocene around the Ordos Basin got rise to the formation the Yingchuan, Hetao, and Weihe grabens. It is concluded that MFTB is the leading edge of the intra-continental Helan orogenic belt, and formed by multi-phase breaking-forward thrusting during Late Jurassic to Cretaceous. During Cenozoic, MFTB is moderately modified by the northeastward compression due to the NE propagation of Qinghai-Tibet Plateau, and distinctly superimposed by the Yingchuan half-graben. North-South Tectonic Belt underwent a full cycle from extension during Middle Proterozoic to Paleozoic to compression since late Triassic.

The Inskip Formation, the Harmony Formation, and the Havallah Sequence of Northwestern Nevada - An Interrelated Paleozoic Assemblage in the Home of the Sonoma Orogeny

USGS Publications Warehouse

Ketner, Keith B.

2008-01-01

An area between the towns of Winnemucca and Battle Mountain in northwestern Nevada, termed the arkosic triangle, includes the type areas of the middle to upper Paleozoic Inskip Formation and Havallah sequence, the Upper Devonian to Mississippian Harmony Formation, the Sonoma orogeny, and the Golconda thrust. According to an extensive body of scientific literature, the Havallah sequence, a diverse assemblage of oceanic rocks, was obducted onto the continent during the latest Permian or earliest Triassic Sonoma orogeny by way of the Golconda thrust. This has been the most commonly accepted theory for half a century, often cited but rarely challenged. The tectonic roles of the Inskip and Harmony Formations have remained uncertain, and they have never been fully integrated into the accepted theory. New, and newly interpreted, data are incompatible with the accepted theory and force comprehensive stratigraphic and tectonic concepts that include the Inskip and Harmony Formations as follows: middle to upper Paleozoic strata, including the Inskip, Harmony, and Havallah, form an interrelated assemblage that was deposited in a single basin on an autochthonous sequence of Cambrian, Ordovician, and lowest Silurian strata of the outer miogeocline. Sediments composing the Upper Devonian to Permian sequence entered the basin from both sides, arkosic sands, gravel, limestone olistoliths, and other detrital components entered from the west, and quartz, quartzite, chert, and other clasts from the east. Tectonic activity was expressed as: (1) Devonian uplift and erosion of part of the outer miogeocline; (2) Late Devonian depression of the same area, forming a trough, probably fault-bounded, in which the Inskip, Harmony, and Havallah were deposited; (3) production of intraformational and extrabasinal conglomerates derived from the basinal rocks; and (4) folding or tilting of the east side of the depositional basin in the Pennsylvanian. These middle to upper Paleozoic deposits were compressed in the Jurassic, causing east-verging thrusts in the eastern part of the depositional basin (Golconda thrust) and west-verging thrusts and folds in the western part. Hypotheses involving a far-traveled allochthon that was obducted from an ocean or back-arc basin are incompatible with modern observations and concepts.

Geologic Map of the Clark Peak Quadrangle, Jackson and Larimer Counties, Colorado

USGS Publications Warehouse

Kellogg, Karl S.; Ruleman, Chester A.; Shroba, Ralph R.; Braddock, William A.

2008-01-01

The Clark Peak quadrangle encompasses the southern end of the Medicine Bow Mountains and the northernmost end of the Mummy Range. The Continental Divide traverses the map area and Highway 14 cross the Divide at Cameron Pass, in the southeastern corner of the map. Approximately the eastern half of the map, and a few areas to the west, are underlain by Early Proterozoic plutonic and metamorphic rocks. Most of these basement rocks are part of the ~1,715 Ma Rawah batholith, composed mostly of pinkish, massive to moderately foliated monzogranite and granodiorite intruded by numerous, large pegmatite- aplite bodies. The metamorphic rocks, many of which form large inclusions in the granitic rocks of the Rawah batholith, include biotite-hornblende gneiss, hornblende gneiss, amphibolite, and biotite schist. The crystalline basement rocks are thrust westward along the Medicine Bow thrust over a sequence of sedimentary rocks as old as the Upper Permian Satanka Shale. The Satanka Shale, Middle and Lower Triassic Chugwater group, and a thin sandstone tentatively correlated with the Lower Jurassic and Upper Triassic Jelm Formation are combined as one map unit. This undivided unit is overlain sequentially upward by the Upper Jurassic Sundance Formation, Upper Jurassic Morrison Formation, Lower Cretaceous Dakota Group, Upper and Lower Cretaceous Benton Group, Upper Cretaceous Niobrara Formation, and the Eocene and Paleocene Coalmont Formation. The Late Cretaceous to early Eocene Medicine Bow thrust is folded in places, and several back thrusts produced a complicated thrust pattern in the south part of the map. Early Oligocene magmatism produced rhyolite tuff, dacite and basalt flows, and intermediate dikes and small stocks. A 40Ar/39Ar date on sanidine from one rhyolite tuff is ~28.5 Ma; a similar whole-rock date on a trachybasalt is ~29.6 Ma. A very coarse, unsorted probably pre-Quaternary ridge-top diamicton crops out in the southern part of the quadrangle. Numerous glacial deposits (mostly of Pinedale age), rock glaciers, block-slope deposits, landslide deposits, talus deposits, fan deposits, colluvium, and alluvium comprise the surficial deposits of the map area.

A balanced water layer concept for subglacial hydrology in large scale ice sheet models

NASA Astrophysics Data System (ADS)

Goeller, S.; Thoma, M.; Grosfeld, K.; Miller, H.

2012-12-01

There is currently no doubt about the existence of a wide-spread hydrological network under the Antarctic ice sheet, which lubricates the ice base and thus leads to increased ice velocities. Consequently, ice models should incorporate basal hydrology to obtain meaningful results for future ice dynamics and their contribution to global sea level rise. Here, we introduce the balanced water layer concept, covering two prominent subglacial hydrological features for ice sheet modeling on a continental scale: the evolution of subglacial lakes and balance water fluxes. We couple it to the thermomechanical ice-flow model RIMBAY and apply it to a synthetic model domain inspired by the Gamburtsev Mountains, Antarctica. In our experiments we demonstrate the dynamic generation of subglacial lakes and their impact on the velocity field of the overlaying ice sheet, resulting in a negative ice mass balance. Furthermore, we introduce an elementary parametrization of the water flux-basal sliding coupling and reveal the predominance of the ice loss through the resulting ice streams against the stabilizing influence of less hydrologically active areas. We point out, that established balance flux schemes quantify these effects only partially as their ability to store subglacial water is lacking.

The Ellsworth Mountains: critical and enduringly enigmatic

USGS Publications Warehouse

Dalziel, I.W.D.

2007-01-01

The elevation (~5000m) is high for an early Mesozoic fold belt. Thermal uplift could have been initiated during Jurassic-Cretaceous block rotation and Weddell Sea opening and continued into the Cenozoic. The history of glaciation provides input for models of ice loading and unloading. Measurements of present-day uplift test these models and help assess change in the mass of the ice sheet and hence in global sea level.

Receiver functions from west Antarctica; crust and mantle properties from POLENET

NASA Astrophysics Data System (ADS)

Aster, R. C.; Chaput, J. A.; Hansen, S. E.; Nyblade, A.; Wiens, D. A.; Huerta, A. D.; Wilson, T. J.; Anandakrishnan, S.

2011-12-01

We use receiver functions to extract crustal thickness and mantle transition zone depths across a wide extent of West Antarctica and the Transantarctic mountains using POLENET data, including recently recovered data from a 14-station West Antarctic Rift Zone transect. An adaptive approach for generating and analyzing P-receiver functions over ice sheets and sedimentary basins (similar to Winberry and Anandakrishnan, 2004) is applied using an extended time multitaper deconvolution algorithm and forward modeling synthetic seismogram fitting. We model P-S receiver functions via a layer stripping methodology (beginning with the ice sheet, if present), and fit increasingly longer sections of synthetic receiver functions to model the multiples observed in the data derived receiver functions. We additionally calculate S-P receiver functions, which provide complementary structural constraints, to generate consistent common conversion point stacks to image crustal and upper mantle discontinuities under West Antarctica. Crust throughout West Antarctica is generally thin (23-29 km; comparable to the U.S. Basin and Range) with relative thickening under the Marie Byrd Land volcanic province (to 32 km) and the Transantarctic Mountains. All constrained west Antarctic crust is substantially thicker than that in the vicinity of Ross Island, where crust as thin as 17 km is inferred in the Terror Rift region.

Intraplate extensional tectonics of the eastern Basin-Range Inferencess on structural style from seismic reflection data, regional tectonics, and thermal-mechanical models of brittle-ductile deformation

NASA Technical Reports Server (NTRS)

Smith, R. B.; Bruhn, R. L.

1984-01-01

Using 1500 km of industry-released seismic reflection data, surface geology, velocity models from refraction data, and earthquake data, the large extensional structures in the crust of the eastern Basin-Range and its transition into the Middle Rocky Mountains and Colorado Plateau have been studied. It is suggested that the close spatial correlation between normal faults and thrust fault segmentation along the Wasatch Front reflects major east-trending structural and lithological boundaries inherited from tectonic processes associated with the evolution of the cordilleran miogeocline, which began in the Precambrian.

1. U.S. Route 250 grade separation structure. This reinforced concrete, ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

1. U.S. Route 250 grade separation structure. This reinforced concrete, rigid frame structure was built in 1941. Its relatively flat arch provided maximum useful clearance in a short span and the physics of the design eliminated the need for extensive abutments to contain the thrust of traditional arches, making it ideally suited as a grade separation structure. BLRI designers made extensive use of theses bridges for crossing small streams and creeks, and grade separation structures, ornamenting them with a rustic stone facade. View is of the south-southeast elevation. - Blue Ridge Parkway, Between Shenandoah National Park & Great Smoky Mountains, Asheville, Buncombe County, NC

Saturn Apollo Program

NASA Image and Video Library

1963-01-01

Smokeless flame juts from the diffuser of a unique vacuum chamber in which the upper stage rocket engine, the hydrogen fueled J-2, was tested at a simulated space altitude in excess of 60,000 feet. The smoke you see is actually steam. In operation, vacuum is established by injecting steam into the chamber and is maintained by the thrust of the engine firing through the diffuser. The engine was tested in this environment for start, stop, coast, restart, and full-duration operations. The chamber was located at Rocketdyne's Propulsion Field Laboratory, in the Santa Susana Mountains, near Canoga Park, California. The J-2 engine was developed by Rocketdyne for the Marshall Space Flight Center.

New aerogeophysical data reveal the extent of the Weddell Sea Rift beneath the Institute and Möller ice streams

NASA Astrophysics Data System (ADS)

Jordan, T. A.; Ferraccioli, F.; Siegert, M. J.; Ross, N.; Corr, H.; Bingham, R. G.; Rippin, D. M.; Le Brocq, A. M.

2011-12-01

Significant continental rifting associated with Gondwana breakup has been widely recognised in the Weddell Sea region. However, plate reconstructions and the extent of this rift system onshore beneath the West Antarctic Ice Sheet (WAIS) are ambiguous, due to the paucity of modern geophysical data across the Institute and Möller ice stream catchments. Understanding this region is key to unravelling Gondwana breakup and the possible kinematic links between the Weddell Sea and the West Antarctic Rift System. The nature of the underlying tectonic structure is also critical, as it provides the template for ice-flow draining ~20% of the West Antarctic Ice Sheet (WAIS). During the 2010/11 Antarctic field season ~25,000 km of new airborne radar, aerogravity and aeromagnetic data were collected to help unveil the crustal structure and geological boundary conditions beneath the Institute and Möller ice streams. Our new potential field maps delineate varied subglacial geology beneath the glacial catchments, including Jurassic intrusive rocks, sedimentary basins, and Precambrian basement rocks of the Ellsworth Mountains. Inversion of airborne gravity data reveal significant crustal thinning directly beneath the faster flowing coastal parts of the Institute and Möller ice streams. We suggest that continental rifting focussed along the Weddell Sea margin of the Ellsworth-Whitmore Mountains block, providing geological controls for the fast flowing ice streams of the Weddell Sea Embayment. Further to the south we suggest that strike-slip motion between the East Antarctica and the Ellsworth-Whitmore Mountains block may provide a kinematic link between Cretaceous-Cenozoic extension in the West Antarctic Rift System and deformation in the Weddell Sea Embayment.

Aerogeophysical evidence for complex subglacial geology below the Rutford drainage basin,WestAntarctica

NASA Astrophysics Data System (ADS)

Jones, P.; Ferraccioli, F.; Corr, H.; Smith, A. M.; King, E.; Vaughan, D.

2003-12-01

A significant part of the West Antarctic Ice Sheet appears to be imposed upon a complex and still largely unknown continental rift system, perhaps featuring sedimentary basins, thin crust and high heat flow. Subglacial geology has been postulated to strongly modulate the dynamics and stability of the ice sheet itself. Specifically, recent aerogeophysics collected over central West Antarctica at edge of the Whitmore Mountains crustal block show that narrow subglacial rift basins with thick sedimentary infill may control the onsets and lateral margins of ice streams. The British Antarctic Survey flew an aerogeophysical survey during the 2001-02 field season: the main aim was to investigate what factors control the location and dynamics of the onset region of the Rutford Ice stream. Airborne radar, aerogravity and aeromagnetic data were simultaneously collected over the drainage basin of the Rutford Ice Stream. The new bedrock elevation grid for the area shows that the Rutford Ice Stream is constrained by a deep bedrock trough with a N-S to NE-SW trend. The onset region appears however to lie within an E-W bedrock trough at the edge of the Ellsworth Mountains crustal block. Bouguer gravity maps do not reveal typical signatures for a coincident deep rift basin at this location. However, a sharp NE-SW trending gradient, likely separating crustal blocks with contrasting crustal thickness is revealed. Aeromagnetic data image NE-SW trends north of the Rutford Ice Stream. In the onset region, these trends appear to be truncated by a NNW-SSE trend, lying on strike with the Ellsworth Mountains. Hence, the new aerogeophysical data suggests greater complexity in the subglacial geology and structure of an onset region of an ice stream compared to previous investigations.

Uplift of the Transantarctic Mountains and the bedrock beneath the East Antarctic ice sheet

USGS Publications Warehouse

ten Brink, Uri S.; Hackney, R.I.; Bannister, S.; Stern, T.A.; Makovsky, Y.

1997-01-01

In recent years the Transantarctic Mountains (TAM), the largest noncontractional mountain belt in the world, have become the focus of modelers who explained their uplift by a variety of isostatic and thermal mechanisms. A problem with these models is a lack of available data to compare with model predictions. We report here the results of a 312-km-long geophysical traverse conducted in 1993/1994 in the hinterland of the TAM. Using detailed subglacial topography and gravity measurements, we confirm the origin of the TAM as a flexural uplift of the edge of East Antarctica. Using an elastic model with a free edge, we can jointly fit the topography and the gravity with a plate having an elastic thickness of 85 ?? 15 km and a preuplift elevation of 700 ?? 50 m for East Antarctica. Using a variety of evidence, we argue that the uplift is coincident with a relatively minor tectonic event of transtensional motion between East and West Antarctica during the Eocene rather than the Late Cretaceous rifting event that created the Ross Embayment. We suggest that this transtensional motion caused the continuous plate to break, which created an escarpment that significantly increased the rates of erosion and exhumation. Results from the geophysical traverse also extend our knowledge of the bedrock geology from the exposures within the TAM to the ice covered interior. Our interpretation suggests that the Ferrar flood basalts extend at least 100 km westward under the ice. The Beacon Supergroup of Paleozoic and Mesozoic sediments thins gradually under the ice and its reconstructed thickness is reminiscent of profiles of foreland basins. Finally, there is no indication in the gravity field for an incomplete rebound due to significant melting of the East Antarctic ice sheet since the last glacial period.

Crew Launch Vehicle (CLV) Upper Stage Configuration Selection Process

NASA Technical Reports Server (NTRS)

Davis, Daniel J.; Coook, Jerry R.

2006-01-01

The Crew Launch Vehicle (CLV), a key component of NASA's blueprint for the next generation of spacecraft to take humans back to the moon, is being designed and built by engineers at NASA s Marshall Space Flight Center (MSFC). The vehicle s design is based on the results of NASA's 2005 Exploration Systems Architecture Study (ESAS), which called for development of a crew-launch system to reduce the gap between Shuttle retirement and Crew Exploration Vehicle (CEV) Initial Operating Capability, identification of key technologies required to enable and significantly enhance these reference exploration systems, and a reprioritization of near- and far-term technology investments. The Upper Stage Element (USE) of the CLV is a clean-sheet approach that is being designed and developed in-house, with element management at MSFC. The USE concept is a self-supporting cylindrical structure, approximately 115' long and 216" in diameter, consisting of the following subsystems: Primary Structures (LOX Tank, LH2 Tank, Intertank, Thrust Structure, Spacecraft Payload Adaptor, Interstage, Forward and Aft Skirts), Secondary Structures (Systems Tunnel), Avionics and Software, Main Propulsion System, Reaction Control System, Thrust Vector Control, Auxiliary Power Unit, and Hydraulic Systems. The ESAS originally recommended a CEV to be launched atop a four-segment Space Shuttle Main Engine (SSME) CLV, utilizing an RS-25 engine-powered upper stage. However, Agency decisions to utilize fewer CLV development steps to lunar missions, reduce the overall risk for the lunar program, and provide a more balanced engine production rate requirement prompted engineers to switch to a five-segment design with a single Saturn-derived J-2X engine. This approach provides for single upper stage engine development for the CLV and an Earth Departure Stage, single Reusable Solid Rocket Booster (RSRB) development for the CLV and a Cargo Launch Vehicle, and single core SSME development. While the RSRB design has changed since the CLV Project's inception, the USE design has remained essentially a clean-sheet approach. Although a clean-sheet upper stage design inherently carries more risk than a modified design, it does offer many advantages: a design for increased reliability; built-in extensibility to allow for commonality/growth without major redesign; and incorporation of state-of-the-art materials, hardware, and design, fabrication, and test techniques and processes to facilitate a potentially better, more reliable system. Because consideration was given in the ESAS to both clean-sheet and modified USE designs, this paper will highlight the advantages and disadvantages of both approaches and provide a detailed discussion of trades/selections made that led to the final upper stage configuration.

Tectonic setting and hydrocarbon habitat of external Carpathian basins in Romania

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dicea, O.; Morariu, D.C.

1993-09-01

During the Alpine evolution of Romania, two distinct depositional areas evolved in the external zones of the Carpathians: the Paleogene flysch and Neogene Molasse basin of the eastern Carpathians, and the Paleogene and Neogene Molasse basin of the southern Carpathians. Both basins were compressionally deformed during the Neogene, giving rise to the development of a succession of nappes and thrust sheets. The internal elements of the external Carpathians corresponding to the Tarcau and marginal folds nappes and the external elements forming the sub-carpathian nappe and foredeep were thrusted over significant distances onto the European platform. Intense exploration of the externalmore » Carpathian thrustbelt has led to the discovery of more than 100 oil and gas pools. Reservoirs are provided by Oligocene, Burdigalian, Sarmatian, and Pliocene clastic rocks. A prolific hydrocarbon charge is derived from regionally distributed Oligocene oil source rocks. Traps are mainly of the structural type and involve faulted anticlines, [open quotes]scale folds,[close quotes] and compressional structures modified by salt; stratigraphic pinch-out and unconformity related traps play a secondary role. On the basis of selected examples, the development and distribution of hydrocarbon pools will be discussed in terms of thrust kinematics and the structure of different platform blocks. The philosophy of past exploration activities will be reviewed, and both success cases and failures will be discussed. Remaining oil and gas plays, aimed at shallow as well as at deep objectives, will be highlighted.« less

Office of Science and Technology&International Year EndReport - 2005

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bodvarsson, G.S.

2005-10-27

Source Term, Materials Performance, Radionuclide Getters, Natural Barriers, and Advanced Technologies, a brief introduction in each section describes the overall organization and goals of each program area. All of these areas have great potential for improving our understanding of the safety performance of the proposed Yucca Mountain repository, as processes within these areas are generally very conservatively represented in the Total System Performance Assessment. In addition, some of the technology thrust areas in particular may enhance system efficiency and reduce risk to workers. Thus, rather modest effort in the S&T Program could lead to large savings in the lifetime repositorymore » total cost and significantly enhanced understanding of the behavior of the proposed Yucca Mountain repository, without safety being compromised, and in some instances being enhanced. An overall strength of the S&T Program is the significant amount of integration that has already been achieved after two years of research. As an example (illustrated in Figure 1), our understanding of the behavior of the total waste isolation system has been enhanced through integration of the Source Term, Materials Performance, and Natural Barriers Thrust areas. All three thrust areas contribute to the integration of different processes in the in-drift environment. These processes include seepage into the drift, dust accumulation on the waste package, brine formation and precipitation on the waste package, mass transfer through the fuel cladding, changes in the seepage-water chemical composition, and transport of released radionuclides through the invert and natural barriers. During FY2005, each of our program areas assembled a team of external experts to conduct an independent review of their respective projects, research directions, and emphasis. In addition, the S&T Program as a whole was independently reviewed by the S&T Programmatic Evaluation Panel. As a result of these reviews, adjustments to the S&T Program will be implemented in FY2006 to ensure that the Program is properly aligned with OCRWM's priorities. Also during FY2005, several programmatic documents were published, including the Science and Technology Program Strategic Plan, the Science and Technology Program Management Plan, and the Science and Technology Program Plan. These and other communication products are available on the OCRWM web site under the Science and Technology section (http://www.ocrwm.doe.gov/osti/index.shtml).« less

Constraining the Uplift History of the Jabal Akhdar and Saih Hatat Culminations, Al Hajar Mountains, Oman, with Fission Track and (U-Th)/He Ages

NASA Astrophysics Data System (ADS)

Hansman, R. J.; Ring, U.; Thomson, S. N.; Den Brok, B.; Stübner, K.

2016-12-01

We constrain the timing of the enigmatic uplift history of the Al Hajar Mountains in Oman by apatite (U-Th)/He and fission-track (AHe and AFT), as well as zircon (U-Th)/He (ZHe) ages. Our data show differential cooling between the two major culminations of the mountain range, which are separated by the Semail gap, a major NNE-oriented depression in the Al Hajar Mountains. In the up to 3 km high Jabal Akhdar Culmination west of the Semail Gap AHe sample mean ages range between 35.5 ± 4.3 Ma and 23.9 ± 8.8 Ma (1σ errors), AFT ages range 51 ± 4 to 32 ± 2 Ma (1σ errors), and ZHe sample mean ages range 50.6 ± 16.7 to 46.1 ± 7.1 Ma (1σ errors). Whereas, in the Saih Hatat Culmination to the east AHe ages range from 23.6 ± 1.7 Ma to 15.7 ± 4.1 Ma, AFT ages range 73 ± 10 to 57 ± 4 Ma, and ZHe ages range 70.6 ± 10.8 Ma through to 58.8 ± 1.8 Ma. These data demonstrate that the uplift initiated at 45 Ma and had ceased by 15 Ma, climaxing between 40 to 35 Ma. In addition, U-Pb dating of calcite tectonics also supports N-S shortening at 40 to 35 Ma. We propose that the Semail gap is a west-dipping thrust, which uplifted the Jabal Akhdar Culmination in the hanging-wall but hardly affected the Saih Hatat Culmination in the footwall. During mountain uplift, the Al Hajar Mountains were located at least 600 km outboard of the current Eurasia-Arabia subduction/collision zone on the continental margin of the downgoing Arabian Plate. We therefore conclude that the uplift of the Al Hajar Mountains preceded the Zagros collisional event by at least 15 Myr and were not causally related to the Zagros collision and Makran subduction.

Reconstructing the last Irish Ice Sheet 2: a geomorphologically-driven model of ice sheet growth, retreat and dynamics

NASA Astrophysics Data System (ADS)

Greenwood, Sarah L.; Clark, Chris D.

2009-12-01

The ice sheet that once covered Ireland has a long history of investigation. Much prior work focussed on localised evidence-based reconstructions and ice-marginal dynamics and chronologies, with less attention paid to an ice sheet wide view of the first order properties of the ice sheet: centres of mass, ice divide structure, ice flow geometry and behaviour and changes thereof. In this paper we focus on the latter aspect and use our new, countrywide glacial geomorphological mapping of the Irish landscape (>39 000 landforms), and our analysis of the palaeo-glaciological significance of observed landform assemblages (article Part 1), to build an ice sheet reconstruction yielding these fundamental ice sheet properties. We present a seven stage model of ice sheet evolution, from initiation to demise, in the form of palaeo-geographic maps. An early incursion of ice from Scotland likely coalesced with local ice caps and spread in a south-westerly direction 200 km across Ireland. A semi-independent Irish Ice Sheet was then established during ice sheet growth, with a branching ice divide structure whose main axis migrated up to 140 km from the west coast towards the east. Ice stream systems converging on Donegal Bay in the west and funnelling through the North Channel and Irish Sea Basin in the east emerge as major flow components of the maximum stages of glaciation. Ice cover is reconstructed as extending to the continental shelf break. The Irish Ice Sheet became autonomous (i.e. separate from the British Ice Sheet) during deglaciation and fragmented into multiple ice masses, each decaying towards the west. Final sites of demise were likely over the mountains of Donegal, Leitrim and Connemara. Patterns of growth and decay of the ice sheet are shown to be radically different: asynchronous and asymmetric in both spatial and temporal domains. We implicate collapse of the ice stream system in the North Channel - Irish Sea Basin in driving such asymmetry, since rapid collapse would sever the ties between the British and Irish Ice Sheets and drive flow configuration changes in response. Enhanced calving and flow acceleration in response to rising relative sea level is speculated to have undermined the integrity of the ice stream system, precipitating its collapse and driving the reconstructed pattern of ice sheet evolution.

The Pinjaur dun (intermontane longitudinal valley) and associated active mountain fronts, NW Himalaya: Tectonic geomorphology and morphotectonic evolution

NASA Astrophysics Data System (ADS)

Singh, Vimal; Tandon, S. K.

2008-12-01

The Himalayan orogenic belt, formed as a result of collision tectonic processes, shows abundant evidence of neotectonic activity, active tectonics, and the occurrence of historical earthquakes. Its frontal deformation zone is characterized, in some segments, by intermontane longitudinal valleys (duns). Such frontal segments of the Himalaya are marked by the occurrence of multiple mountain fronts. In one such segment of the foothills of the NW Himalaya, the Pinjaur dun is developed and marked by three mountain fronts: MF1A and MF1B associated with the southernmost Himalayan Frontal Thrust (HFT), MF2 associated with the Sirsa fault, and MF3 associated with the Barsar thrust along the southern margin of the relatively higher main part of the sub-Himalaya. Geomorphic responses to the tectonic activity of these and related structural features have been analyzed through the use of geomorphic indices, drainage density, stream longitudinal profiles, drainage anomalies, and hypsometric analysis. Also, fault and fold growth and their expression on landform development was studied using a combination of surface profiles and field observations. The values of valley floor width to height ratio ( Vf) for valleys associated with MF1 ranged between 0.07 and 0.74, and for valleys associated with MF2 ranged from 1.02-5.12. Vf for the four major valleys associated with MF1B ranged from 1.1-1.7. The asymmetry factor for 26 drainage basins related to MF1A indicate these have developed under the influence of a transverse structure. These results taken together with those obtained from the Hack profiles and SL index values, hypsometry, drainage density, and drainage anomalies suggest that the faults associated with the mountain fronts and related structures are active. Active tectonics and neotectonic activity have led to the formation of four surfaces in the Pinjaur dun. In addition, an important drainage divide separating the Sirsa and Jhajara drainage networks also developed in the intermontane valley. Surface profile analysis helped in deciphering the growth history of the fault bend fold structures of the outermost Siwalik hills. The effects of tectonic activity on the proximal part of the Indo-Gangetic plains are interpreted from the remarkable river deflections that are aligned linearly over tens of kilometers in a zone about 10 km south of the HFT. Based on these integrated structural and tectonic geomorphological approaches, a morphotectonic evolutionary model of the dun has been proposed. This model highlights the role of uplift and growth history of the fault bend fold structures of the outermost Siwalik hills on (i) the depositional landforms and drainage development of the Pinjaur dun, and (ii) valley development of the outermost Siwalik hills. Importantly, this study postulates the formation of an incipient mountain front that is evolving ahead of the HFT and the outermost Siwalik hills in the Indo-Gangetic plains.

Chemistry of water collected from an unventilated drift, Yucca Mountain, Nevada

USGS Publications Warehouse

Marshall, B.D.; Oliver, T.A.; Peterman, Z.E.

2007-01-01

Water samples (referred to as puddle water samples) were collected from the surfaces of a conveyor belt and plastic sheeting in the unventilated portion of the Enhanced Characterization of the Repository Block (ECRB) Cross Drift in 2003 and 2005 at Yucca Mountain, Nevada. The chemistry of these puddle water samples is very different than that of pore water samples from borehole cores in the same region of the Cross Drift or than seepage water samples collected from the Exploratory Studies Facility tunnel in 2005. The origin of the puddle water is condensation on surfaces of introduced materials and its chemistry is dominated by components of the introduced materials. Large CO2 concentrations may be indicative of localized chemical conditions induced by biologic activity. ?? 2007 Materials Research Society.

Gravity constraints on the geometry of the Big Bend of the San Andreas Fault in the southern Carrizo Plains and Pine Mountain egion

NASA Astrophysics Data System (ADS)

Altintas, Ali Can

The goal of this project is to combine gravity measurements with geologic observations to better understand the "Big Bend" of the San Andreas Fault (SAF) and its role in producing hydrocarbon-bearing structures in the southern Central Valley of California. The SAF is the main plate boundary structure between the Pacific and North American plates and accommodates ?35 mm/yr of dextral motion. The SAF can be divided into three main parts: the northern, central and southern segments. The boundary between the central and southern segments is the "Big Bend", which is characterized by an ≈30°, eastward bend. This fault curvature led to the creation of a series of roughly east-west thrust faults and the transverse mountain ranges. Four high-resolution gravity transects were conducted across locations on either side of the bend. A total of 166 new gravity measurements were collected. Previous studies suggest significantly inclined dip angle for the San Andreas Fault in the Big Bend area. Yet, our models indicate that the San Andreas Fault is near vertical in the Big Bend area. Also gravity cross-section models suggest that flower structures occur on either side of the bend. These structures are dominated by sedimentary rocks in the north and igneous rocks in the south. The two northern transects in the Carrizo plains have an ≈-70 mgal Bouguer anomaly. The SAF has a strike of ≈315° near these transects. The northern transects are characterized by multiple fault strands which cut marine and terrestrial Miocene sedimentary rocks as well as Quaternary alluvial valley deposits. These fault strands are characterized by ?6 mgal short wavelength variations in the Bouguer gravity anomaly, which correspond to low density fault gouge and fault splays that juxtapose rocks of varying densities. The southern transects cross part of the SAF with a strike of 285°, have a Bouguer anomaly of ≈-50 mgal and are characterized by a broad 15 mgal high. At this location the rocks on either side of the fault are Proterozoic - Cretaceous metamorphic or/and plutonic rocks. Previous work based on geologic mapping hypothesized the existence of a shallow, low angle Abel Mountain Thrust in which crystalline rocks were thrust over Miocene sedimentary rocks, near Apache Saddle. However, gravity models indicate the crystalline rocks are vertically extensive and form a positive flower structure bounded by high angle faults. Also, based on the thickness of fault adjacent sedimentary cover, the gravity models suggest a minimum exhumation of 5-6 km for crystalline rocks in the south. Assuming exhumation began with the switch from the transtensional San Gabriel Fault to transpressional San Andreas Fault at approximately 5 Ma, this indicates exhumation rates of 1 km/Ma. Overall, the broad gravity highs observed along the southern transects are due to uplift of basement rocks in this area.

The plane problem of the flapping wing

NASA Technical Reports Server (NTRS)

Birnbaum, Walter

1954-01-01

In connection with an earlier report on the lifting vortex sheet which forms the basis of the following investigations this will show how the methods developed there are also suitable for dealing with the air forces for a wing with a circulation variable with time. The theory of a propulsive wing flapping up and down periodically in the manner of a bird's wing is developed. This study shows how the lift and its moment result as a function of the flapping motion, what thrust is attainable, and how high is the degree of efficiency of this flapping propulsion unit if the air friction is disregarded.

Investigation of the Vortex Tab. M.S. Thesis

NASA Technical Reports Server (NTRS)

Hoffler, K. D.

1985-01-01

An investigation was made into the drag reduction capability of vortex tabs on delta wing vortex flaps. The vortex tab is an up-deflected leading edge portion of the vortex flap. Tab deflection augments vortex suction on the flap, thus improving its thrust, but the tab itself is drag producing. Whether a net improvement in the drag reduction can be obtained with vortex tabs, in comparison with plane vortex flaps of the same total area, was the objective of this investigation. Wind tunnel tests were conducted on two models, and analytical studies were performed on one of them using a free vortex sheet theory.

The 2011 Mineral, Virginia, earthquake and its significance for seismic hazards in eastern North America: overview and synthesis

USGS Publications Warehouse

Horton, J. Wright; Chapman, Martin C.; Green, Russell A.

2015-01-01

The earthquake and aftershocks occurred in crystalline rocks within Paleozoic thrust sheets of the Chopawamsic terrane. The main shock and majority of aftershocks delineated the newly named Quail fault zone in the subsurface, and shallow aftershocks defined outlying faults. The earthquake induced minor liquefaction sand boils, but notably there was no evidence of a surface fault rupture. Recurrence intervals, and evidence for larger earthquakes in the Quaternary in this area, remain important unknowns. This event, along with similar events during historical time, is a reminder that earthquakes of similar or larger magnitude pose a real hazard in eastern North America.

Disposal of Chemical Agent Identification Sets at Rocky Mountain Arsenal, Colorado. Volume 2. Appendices A-D

DTIC Science & Technology

1983-08-01

N ENTER UNIT NURSER YOU ARE USING FOR THE DATA TAPE 11 FIGURE A-20 A-15 PMOMR TO P"IN? PROCES: DATA SHEET - DECOMED PIC CONTRL INSERT DATA TAPE IN...EXCHANGE/COOLER 70 CONTROL PANEL1 ACTUATORPFEELER 71 TV MONITOR 2 MOTOR 72 CART TOP3 PUMP 73 CIRCUIT BREAKER 4 VALVE 74 5 BELT 75 LIGHT6 SEAL 76 MIRAN 807

Worldwide Emerging Environmental Issues Affecting the U.S. Military. March 2007 Report

DTIC Science & Technology

2007-03-01

some existent climate regions (mainly in tropical mountain areas, Amazon and Indonesian rainforests , and towards the poles) and the prospects of...ice sheets and floating sea ice. Military Implications: In view of the increasing importance of the Arctic in military planning and the oil reserves...95080 4.2 Malacca Straits Need Increased Protection from Various Security Threats The Malacca Strait, one of the most important shipping lanes in the

Late extension in compressional wedges above a weak, viscous décollement: results from analogue modeling

NASA Astrophysics Data System (ADS)

Borderie, Sandra; Vendeville, Bruno C.; Graveleau, Fabien; Witt, César

2016-04-01

Extension during convergence is a structural process commonly encountered in different geodynamic settings, such as accretionary wedges subjected to tectonic erosion, or mountain belts undergoing post-orogenic collapse. This has been investigated with experimental models at the scale of doubly-vergent wedges (Haq and Davis 2008; Bonini et al. 2000, Buck and Sokoutis 1994) but not thoroughly at the scale of fold-and-thrust belts. During an experimental investigation carried out on the behavior of segmented fold-and-thrust belts induced by stratigraphic inheritance in the foreland series (Borderie et al., EGU this session), unexpected shallow normal faulting occurred. The models comprised one basal frictional décollement (glass microbeads) and one upper viscous décollement embedded in the cover (silicone polymer). Extension took place during the late stages of the experiments and it was localized at the transition zone between the rear domain of the wedge and the frontal fold-and-thrust belt that detached on the upper viscous décollement. Normal faults strike parallel to the compressional structures and mainly dip toward the foreland. They root in the viscous décollement. Through a series of parametrized experiments dedicated to constrain the timing of formation of these extensional structures, we could evidence that these normal faults appear once the bulk shortening in the rear domain has created enough uplift of the internal zone by antiformal stacking and enough forelandward tilting of the upper viscous décollement. These two latter mechanisms are direct consequences of the whole wedge dynamics that links the thrust fault dynamics in the upper shallow sedimentary sequence and the thrust dynamics of the deep subsalt basement. The occurrence of this extension depends on the initial position of the upper viscous décollement and notably the position of the internal pinchout relative to the position of the backstop. Additional tests have also demonstrated that this extension is prevented by surface processes and notably sedimentation. We compare our experimental findings with natural examples of extensional features in various fold-and-thrust belts and accretionary features across the world (e.g. the Mediterranean ridge). References: Bonini, Marco, Dimitrios Sokoutis, Genene Mulugeta, and Emmanouil Katrivanos. 2000. "Modelling Hanging Wall Accommodation above Rigid Thrust Ramps." Journal of Structural Geology 22 (8): 1165-79. Borderie, Sandra, Fabien Graveleau, Cesar Witt and Bruno C. Vendeville. 2016. "Analogue modeling of 3-D structural segmentation in fold-and-thrust belts: interactions between frictional and viscous provinces in foreland basins." Gephys. Res. Abstr., 18, EGU2016-Vienne. Buck, W Roger, and Dimitrios Sokoutis. 1994. "Analogue Model of Gravitational Collapse and Surface Extension during Continental Convergence." Nature 369: 737-40. Haq, Saad SB, and Dan M. Davis. 2008. "Extension during Active Collision in Thin-Skinned Wedges: Insights from Laboratory Experiments." Geology 36 (6): 475-78.

Extensive massive basal-ice structures in West Antarctica relate to ice-sheet anisotropy and ice-flow

NASA Astrophysics Data System (ADS)

Ross, N.; Bingham, R. G.; Corr, H. F. J.; Siegert, M. J.

2016-12-01

Complex structures identified within both the East Antarctic and Greenland ice sheets are thought to be generated by the action of basal water freezing to the ice-sheet base, evolving under ice flow. Here, we use ice-penetrating radar to image an extensive series of similarly complex basal ice facies in West Antarctica, revealing a thick (>500 m) tectonised unit in an area of cold-based and relatively slow-flowing ice. We show that major folding and overturning of the unit perpendicular to ice flow elevates deep, warm ice into the mid ice-sheet column. Fold axes align with present ice flow, and axis amplitudes increase down-ice, suggesting long-term consistency in the direction and convergence of flow. In the absence of basal water, and the draping of the tectonised unit over major subglacial mountain ranges, the formation of the unit must be solely through the deformation of meteoric ice. Internal layer radar reflectivity is consistently greater parallel to flow compared with the perpendicular direction, revealing ice-sheet crystal anisotropy is associated with the folding. By linking layers to the Byrd ice-core site, we show the basal ice dates to at least the last glacial cycle and may be as old as the last interglacial. Deformation of deep-ice in this sector of WAIS, and potentially elsewhere in Antarctica, may be caused by differential shearing at interglacial-glacial boundaries, in a process analogous to that proposed for interior Greenland. The scale and heterogeneity of the englacial structures, and their subsequent impact on ice sheet rheology, means that the nature of ice flow across the bulk of West Antarctica must be far more complex that is currently accounted for by any numerical ice sheet model.

Melt-induced speed-up of Greenland ice sheet offset by efficient subglacial drainage.

PubMed

Sundal, Aud Venke; Shepherd, Andrew; Nienow, Peter; Hanna, Edward; Palmer, Steven; Huybrechts, Philippe

2011-01-27

Fluctuations in surface melting are known to affect the speed of glaciers and ice sheets, but their impact on the Greenland ice sheet in a warming climate remains uncertain. Although some studies suggest that greater melting produces greater ice-sheet acceleration, others have identified a long-term decrease in Greenland's flow despite increased melting. Here we use satellite observations of ice motion recorded in a land-terminating sector of southwest Greenland to investigate the manner in which ice flow develops during years of markedly different melting. Although peak rates of ice speed-up are positively correlated with the degree of melting, mean summer flow rates are not, because glacier slowdown occurs, on average, when a critical run-off threshold of about 1.4 centimetres a day is exceeded. In contrast to the first half of summer, when flow is similar in all years, speed-up during the latter half is 62 ± 16 per cent less in warmer years. Consequently, in warmer years, the period of fast ice flow is three times shorter and, overall, summer ice flow is slower. This behaviour is at odds with that expected from basal lubrication alone. Instead, it mirrors that of mountain glaciers, where melt-induced acceleration of flow ceases during years of high melting once subglacial drainage becomes efficient. A model of ice-sheet flow that captures switching between cavity and channel drainage modes is consistent with the run-off threshold, fast-flow periods, and later-summer speeds we have observed. Simulations of the Greenland ice-sheet flow under climate warming scenarios should account for the dynamic evolution of subglacial drainage; a simple model of basal lubrication alone misses key aspects of the ice sheet's response to climate warming.

Tropical tales of polar ice: evidence of Last Interglacial polar ice sheet retreat recorded by fossil reefs of the granitic Seychelles islands

NASA Astrophysics Data System (ADS)

Dutton, Andrea; Webster, Jody M.; Zwartz, Dan; Lambeck, Kurt; Wohlfarth, Barbara

2015-01-01

In the search for a record of eustatic sea level change on glacial-interglacial timescales, the Seychelles ranks as one of the best places on the planet to study. Owing to its location with respect to the former margins of Northern Hemisphere ice sheets that wax and wane on orbital cycles, the local-or relative-sea level history is predicted to lie within a few meters of the globally averaged eustatic signal during the Last Interglacial period. We have surveyed and dated Last Interglacial fossil corals to ascertain peak sea level and hence infer maximum retreat of polar ice sheets during this time interval. We observe a pattern of gradually rising sea level in the Seychelles between ˜129 and 125 thousand years ago (ka), with peak eustatic sea level attained after 125 ka at 7.6 ± 1.7 m higher than present. After accounting for thermal expansion and loss of mountain glaciers, this sea-level budget would require ˜5-8 m of polar ice sheet contribution, relative to today's volume, of which only ˜2 m came from the Greenland ice sheet. This result clearly identifies the Antarctic ice sheet as a significant source of melt water, most likely derived from one of the unstable, marine-based sectors in the West and/or East Antarctic ice sheet. Furthermore, the establishment of a +5.9 ± 1.7 m eustatic sea level position by 128.6 ± 0.8 ka would require that partial AIS collapse was coincident with the onset of the sea level highstand.

From thrusting to transpressional tectonics in the Aghdarband Basin (NE Iran): evidence for Cimmerian oblique convergence

NASA Astrophysics Data System (ADS)

Zanchi, Andrea; Balini, Marco; Ghassemi, Mohammad Reza; Zanchetta, Stefano

2010-05-01

The Aghdarband Basin, consisting of a strongly deformed arc-related Triassic marine succession, is a key-area for the study of the Cimmerian events, as it is unconformably covered by mid-Jurassic gently folded sediments entirely sealing the Cimmerian compressive structures. The basin developed during part of the Triassic in a highly mobile tectonic context suggested by abrupt facies variations and local unconformities. In addition, syn-sedimentary tectonic activity is testified by the occurrence of carbonate olistholiths in the deepest parts of the basin. The marine succession, spanning from Olenekian to lowermost Carnian, shows at the base continental conglomerates andsandstones, as well as basaltic lava flows, possibly of Early Triassic age. They are followed by the shallow water Sefid Kuh Limestone, in which an intraformational unconformity has been now identified. This unit is locally covered by deep-water limestones of the Nazarkardeh Fm. which interfinger with slope facies of the Sefid Kuh Limestone. The volcaniclastic sandstone layers of the Sina Fm follow up-section with a deep unconformity, marked in several places by deep erosion and tilting of the underlying units. The Sina Fm. is in turn unconformably covered by the coal bearing shales of the Miankhui Fm., with a Norian-Rhaetian age testified by plant megafossils, marking the end of marine sedimentation and of volcanic-arc activity. The Triassic units are overthrusted to the south by Upper Palaeozoic siliciclastic successions showing in some cases a LG metamorphic imprint. They largely include the Qara Geithan Fm. consisting of granitic rocks, acidic to basic volcanics, and locally also large blocks of Permian bioclastic limestones derived from the erosion of the Palaeotethys accretionary wedge, exposed south of Aghdarband. The whole succession of the Aghdarband Basin, including the unconformable Miankhui Fm., is deeply involved in a north-verging thrust stack which interacts in the northern part of the area with an important strike-slip shear zone. Several tectonic units have been recognized within the Triassic succession, causing repetitions of the whole stratigraphic succession. Two main thrust sheets are exposed in the southern part of the basin under the Upper Palaeozoic thrust stack. Thrust faults and folds consistently show a N-directed tectonic transport, suggested by dip-slip motion along S-dipping reverse faults and axial plane geometry. Deformation occurred at shallow levels taking to the formation of cataclastic shear zones and to disjunctive and pencil cleavage in the shale layers of the succession. The thrust sheets comprise the Miankhui Fm. which shows a thick basal coal layer (up to 10 m) deeply excavated at the Aghdarband Mine. Nice examples of coal-related tectonics are exposed in open pits and tunnels of the mine. Intensive deformation of the coal, forming complex shear zones with s-c bands, causes the décollement of the Miankhui beds which show intensive tectonic thickening and repetitions mainly caused by polyphase thrust imbrications and disharmonic folding. The northernmost part of the Triassic basin shows a very complex setting, with traspressional structures given by vertical strike-slip faults and closed to tight folds with steeply plunging axes. According to our new data, up to four tectonic slices can be distinguished in this complex area. This structural zone is directly bounded to the north by severely deformed LG metamorphic rocks resulting from a volcaniclastic succession with Devonian and Carboniferous marble layers. Systematic asymmetry of major and parasitic folds, as well as rotation and torsion of axial surfaces indicate a general left-lateral transpressional regime, whereas kinematic indicators along the main fault planes show both left- and right-lateral motions. According to our relative chronology, dextral movements follow in time the sinistral ones reactivating previous Cimmerian structures and displacing also the surrounding Jurassic to Neogene succession of Kopeh Dagh in relatively recent times. Fold analyses along the area of interaction between thrust structure and the transpressional zone suggest an intricate interference pattern between thrust-related folds and strike-slip brittle shear zones, suggesting that the latter caused a strong reorientation of previously formed folds. The extension of the traspressional zone, which can be followed for some 20 km across the study area, indicates that important left-lateral movements, roughly parallel to the orientation of the convergence zone, were active during the last stages of the Late Triassic Cimmerian event, in contrast to what indicated by previous authors in the Mashhad area.

Drainage reorganization during mountain building in the river system of the Eastern Cordillera of the Colombian Andes

NASA Astrophysics Data System (ADS)

Struth, Lucía; Babault, Julien; Teixell, Antonio

2015-12-01

The Eastern Cordillera of Colombia is a thick-skinned thrust-fold belt that is characterized by two topographic domains: (1) the axial zone, a high altitude plateau (the Sabana de Bogotá, 2500 masl) with low local relief and dominated by longitudinal rivers, and (2) the Cordillera flanks, where local relief exceeds 1000 m and transverse rivers dominate. On the basis of an analysis of digital topography and river parameters combined with a review of paleodrainage data, we show that the accumulation of shortening and crustal thickening during the Andean orogeny triggered a process of fluvial reorganization in the Cordillera. Owing to a progressive increase of the regional slope, the drainage network evolves from longitudinal to transverse-dominated, a process that is still active at present. This study provides the idea of progressive divide migration toward the inner part of the mountain belt, by which the area of the Sabana de Bogotá plateau is decreasing, the flanks increase in area, and ultimately transverse rivers will probably dominate the drainage of the Cordillera.

Glaciers in the Himalayan Mountains taken from Atlantis during STS-106

NASA Image and Video Library

2000-09-16

STS106-705-009 (8-20 September 2000) --- One of the STS-106 crew members on board the Space Shuttle Atlantis used a handheld 70mm camera to photograph this image of Qogir Feng (8,611 meters), which appears at the far upper left in this view of the northwestern Karakoram Range. Also called K2 or Mt. Godwin Austen, the mountain is the second highest peak in the world. The Tarim sedimentary basin borders the range on the north and the Lesser Himalayas on the south. Melt waters from vast glaciers, such as those south and east of K2, feed agriculture in the valleys (dark green) and contribute significantly to the regional fresh-water supply. The Karakoram Range lies along the southern edge of the Eurasian tectonic plate and is made up of ancient sedimentary rocks (more than 390 million years old, according to geologists studying the shuttle imagery). Those strata were folded and thrust-faulted, and granite masses were intruded, say the geologists, when the Indo-Pakistan plate collided with Eurasia, beginning more than 100 million years ago.