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Sample records for age metamorphic history

  1. Tectonic evolution of forearc nappes of the active Banda arc-continent collision: Origin, age, metamorphic history and structure of the Lolotoi Complex, East Timor

    NASA Astrophysics Data System (ADS)

    Standley, Carl E.; Harris, Ron

    2009-12-01

    An integrated multidisciplinary investigation of the Lolotoi Complex of East Timor (Timor Leste) indicates that it is part of the Banda forearc that was metamorphosed and rapidly exhumed during the Eocene and accreted to the NW Australian continental margin during Late Miocene to present arc-continent collision. Greenschist, graphitic phyllite, quartz-mica schist, amphibolite and pelitic schist dominate metamorphic rock types. Mineral, whole rock, and trace element geochemical analyses of metabasites indicate protolith compositions consistent with tholeiitic basalt and basaltic andesite with mixed MORB and oceanic arc affinities. Metapelite schist is mostly composed of metasedimentary units derived from mafic to intermediate rocks with oceanic to continental volcanic arc provenance. Thermobarometric calculations show peak metamorphic conditions of 530 °C to 680 °C for garnet-biotite pairs and amphibole, and peak pressures of 5 to 10 kbar for garnet-aluminosilicate-quartz-plagioclase assemblages. Peak metamorphism occurred at 45.36 ± 0.63 Ma, as indicated by Lu-Hf analyses of garnet. Detrital zircon grains have a U/Pb age distribution with spikes at 663, 120 and 87 Ma, which is typical of detrital zircon ages throughout the Great Indonesian Arc of Asia, but is distinct from Australian affinity units. These data indicate deposition and later metamorphism occurred after 87 Ma. Structural analyses of the metamorphic rocks and their sedimentary and volcanic cover units reveals 5-6 deformational phases of alternating shortening and extension. There is little to no evidence of strike-slip deformation. Phases 1-4 are inferred as pre-Oligocene from age determinations. Phases 5 and 6 are most likely related to latest Miocene to Pliocene nappe emplacement and Pliocene to present collisional deformation. Kinematic indicators show mostly top to the SE directed shortening and top to the south and SE extension. Structural mapping indicates that the Lolotoi Complex and some of

  2. U-Pb garnet, sphene, monazite, and rutile ages: Implications for the duration of high-grade metamorphism and cooling histories, Adirondack Mts. , New York

    SciTech Connect

    Mezger, K.; Rawnsley, C.M.; Hanson, G.N. ); Bohlen, S.R. )

    1991-05-01

    Garnet ages for the Lowlands range from 1,168-1,127 Ma, those from the central and southern Highlands from 1,154-1,013 Ma. Metamorphism in the Highlands may not have occurred as a single event but rather in several discrete thermal pulses. An age of 1,153 {plus minus} 3 Ma was determined for garnets in the syn-regional metamorphic contact aureole of the Diana syenite, consistent with that of the syenite intrusion, 1 155 {plus minus} 4 Ma. Garnets just outside the contact aureole give an age of 1,168 {plus minus} 6 Ma. In the Lowlands, monazite yielded an age of 1,161 {plus minus} 1 Ma, rutiles yielded ages of 1,005 {plus minus} 2 Ma and 953 {plus minus} 4 Ma, and sphene ages range from 1,156 to 1,103 Ma. In the Highlands, monazite yielded an age of 1,033 {plus minus} 1 Ma, rutiles yielded ages of 911 {plus minus} 2 Ma and 885 {plus minus} 2 and sphenes from 1,033 Ma to 991 Ma. The rutile and monazite ages indicate that both terranes cooled at time-integrated rates of ca. 1.5C/Ma for at least 150 Ma following the last phase of high-grade metamorphism. The Lowlands cooled to ca. 400C by ca. 1,000 Ma and the Highlands by ca. 900 Ma. The mineral ages indicate that metamorphic pressures and temperatures recorded by thermobarometry correspond to conditions attained polychronically over 150 Ma or more. Mineral ages combined with temperature estimates for peak metamorphism indicate that the closure temperature for the U-Pb system is >800C in garnet, 640-730C in monazite, and 500-670C in sphene.

  3. Cathodoluminescence of diamond as an indicator of its metamorphic history

    NASA Astrophysics Data System (ADS)

    Kopylova, Maya; Bruce, Loryn; Longo, Micaela; Ryder, John; Dobrzhinetskaya, Larissa

    2010-05-01

    Diamond displays a supreme resistance to chemical and mechanical weathering, ensuring its survival through complex and prolonged crustal processes, including metamorphism and exhumation. For these reasons, volcanic sources and secondary and tertiary collectors for detrital placer diamonds, like Ural or Bingara diamonds, may be difficult to determine. If metamorphic processes leave their marks on diamond, they can be used to reconstruct crustal geologic processes and ages of primary diamondiferous volcanics. Four diamond suites extracted from metamorphic rocks have been characterized using optical CL, infrared and CL spectroscopy, and photoluminescence at the liquid nitrogen temperature. The studied diamonds are from the ~2.7 Ga sedimentary conglomerate and lamprophyric breccia metamorphosed in the greenschist facies (Wawa, Northern Ontario, Canada) during the 2.67 Ga Kenoran orogeny, and from the ultra-high pressure (UHP) terranes of Kokchetav (Kazakhstan) and Erzgebirge (Germany) exhumated in the Paleozoic. Wawa diamonds (Type IaAB and Type II) displayed green, yellow, orange, and red CL colours controlled by the CL emittance at 520, 576 nm, and between 586 and 664 nm. The UHP terranes diamonds show much weaker CL; few luminescent stones display CL peaks at 395, 498, 528 nm and a broad band at 580-668 nm. In contrast, most common diamonds found in unmetamorphosed rocks, i.e. octahedrally grown Type IaAB stones, luminescence blue emitting light at ~415-440 nm and 480-490 nm. There is a noticeable difference between cathodoluminescence of these diamonds and diamonds in metamorphic rocks. The studied diamonds that experienced metamorphism show a shift of CL emission to longer wavelengths (above 520 nm) and to green, yellow and red CL colours. Photoluminescence has the high resolution necessary to assign luminescence to specific optical centers of diamond. Diamonds in metamorphic rocks contain H3 (pairs of substitutional nitrogen atoms separated by a vacancy) and NVo

  4. Thermal history of a metamorphic core complex

    NASA Technical Reports Server (NTRS)

    Dokka, R. K.; Mahaffie, M. J.; Snoke, A. W.

    1985-01-01

    Fission track (FT) thermochronology studies of lower plate rocks of the Ruby Mountains-East Humbolt Range metamorphic core complex provide important constraints on the timing an nature of major middle Tertiary extension of northeast Nevada. Rocks analyzed include several varieties of mylonitic orthogneiss as well as amphibolitic orthognesses from the non-mylonitic infrastructural core. Oligocene-age porphyritic biotite granodiorite of the Harrison Pass pluton was also studied. The minerals dated include apatite, zircon, and sphene and were obtained from the same rocks that have been previously studied. FT ages are concordant and range in age from 26.4 Ma to 23.8 Ma, with all showing overlap at 1 sigma between 25.4 to 23.4 Ma. Concordancy of all FT ages from all structural levels indicates that the lower plate cooled rapidly from temperatures above approx. 285 C (assumed sphene closure temperature (2)) to below approx. 150 C (assumed apatite closure temperature) near the beginning of the Miocene. This suggests that the lower plate cooled at a rate of at least approx. 36 deg C/Ma during this event. Rapid cooling of the region is considered to reflect large-scale tectonic denudation (intracrustal thinning), the vertical complement to intense crustal extension. FT data firmly establish the upper limit on the timing of mylonitization during detachment faulting and also coincide with the age of extensive landscape disruption.

  5. Protolith age and deformation history of high grade metamorphic rocks from the roots of a continental magmatic arc: the Central Gneiss Complex, British Columbia, Canada

    NASA Astrophysics Data System (ADS)

    MacLeod, D.; Pearson, D. M.

    2014-12-01

    The Central Gneiss Complex, located in western British Columbia, preserves mid and lower crustal igneous and metasedimentary rocks that yield insight into deformational and thermal processes at the roots of a continental magmatic arc. The complex primarily consists of gneiss interpreted as a volcanic sequence with calcareous interlayers and lesser clastic metasedimentary rocks. Cretaceous U-Pb zircon ages from granulite-facies equivalent rocks in the core of the complex hint at rapid burial following deposition. However, a Permian or older crinoid fossil found in one locality (Hill, 1985) requires the presence of some late Paleozoic or early Mesozoic material. A new U-Pb zircon age (313±5 Ma; LA-ICPMS) from ~10 km west of this fossil locality is interpreted to record volcanism. We also conducted focused structural and geochronological analysis at higher structural levels in the northeastern Central Gneiss Complex to positively identify sedimentary lithologies with which to document the early structural history of the complex prior to early Cenozoic rapid exhumation. In this area, a subhorizontal shear zone forms the boundary between mainly clastic metasedimentary rocks and the widespread metavolcanic and carbonate rocks where an important stretched pebble conglomerate has been previously documented. In the footwall of the shear zone, flattening fabrics transition structurally upward into E-W trending stretching lineations, lineation-parallel isoclinal fold axes, and boudinage that record E-W stretching and major shear strain near the contact. S-C fabrics and shear bands yield a top to the east sense of shear. Where observed, a shallowly dipping, ~15 m thick zone of cataclasite forms the lithologic contact and overprints the shear zone. Sills and dikes record ongoing but localized magmatism throughout deformation and steep NE striking brittle normal faults crosscut all features. Ongoing work will further constrain the protolith age of these rocks, the timing of

  6. Lunar anorthosite 15415 - Texture, mineralogy, and metamorphic history.

    NASA Technical Reports Server (NTRS)

    James, O. B.

    1972-01-01

    Lunar anorthosite 15415 consists almost entirely of anorthite (homogeneous anorthite 96.6 molecule percent), with accessory diopsidic augite and traces of hypersthene, ilmenite, and a silica mineral. The rock has had a complex metamorphic history. The texture reflects at least two episodes of shearing (followed by intense and partial recrystallization, respectively), one episode of cataclastic deformation, and one or more episodes of shattering and fragmentation.

  7. Lunar anorthosite 15415: texture, mineralogy, and metamorphic history.

    PubMed

    James, O B

    1972-01-28

    Lunar anorthosite 15415 consists almost entirely of anorthite (homogeneous anorthite 96.6 molecule percent), with accessory diopsidic augite and traces of hypersthene, ilmenite, and a silica mineral. The rock has had a complex metamorphic history. The texture reflects at least two episodes of shearing (followed by intense and partial recrystallization, respectively), one episode of cataclastic deformation, and one or more episodes of shattering and fragmentation. PMID:17731367

  8. Lunar anorthosite 15415: Texture, mineralogy, and metamorphic history

    USGS Publications Warehouse

    James, O.B.

    1972-01-01

    Lunar anorthosite 15415 consists almost entirely of anorthite (homogeneous anorthite 96.6 molecule percent), with accessory diopsidic augite and traces of hypersthene, ilmenite, and a silica mineral. The rock has had a complex metamorphic history. The texture reflects at least two episodes of shearing (followed by intense and partial recrystallization, respectively), one episode of cataclastic deformation, and one or more episodes of shattering and fragmentation.

  9. Age, temperature and pressure of metamorphism in the Tasriwine Ophiolite Complex, Sirwa, Morocco

    NASA Astrophysics Data System (ADS)

    Samson, S. D.; Inglis, J.; Hefferan, K. P.; Admou, H.; Saquaque, A.

    2013-12-01

    Sm-Nd garnet-whole rock geochronology and phase equilbria modeling have been used to determine the age and conditions of regional metamorphism within the Tasriwine ophiolite complex,Sirwa, Morocco. Pressure and temperature estimates obtained using a NaCaKFMASHT phase diagram (pseudosection) and garnet core and rim compositions predict that garnet growth began at ~0.72GPa and ~615°C and ended at ~0.8GPa and ~640°C. A bulk garnet Sm-Nd age of 645.6 × 1.6 Ma, calculated from a four point isochron that combines whole rock, garnet full dissolution and two successively more aggressive partial dissolutions, provides a precise date for garnet formation and regional metamorphism. The age is nearly 20 million years younger than a previous age estimate of regional metamorphism of 663 × 14 Ma based upon a SHRIMP U-Pb date from rims on zircon from the Irri migmatite. The new data provide further constraints on the age and nature of regional metamorphism in the Anti-Atlas mountains and emphasizes that garnet growth during regional metamorphism may not necessarily coincide with magmatism/anatexis which predominate the signature witnessed by previous U-Pb studies. The ability to couple PT estimates for garnet formation with high precision Sm- Nd geochronology highlights the utility of garnet studies for uncovering the detailed metamorphic history of the Anti-Atlas mountain belt.

  10. Rb-Sr age of the Shergotty achondrite and implications for metamorphic resetting of isochron ages

    NASA Technical Reports Server (NTRS)

    Nyquist, L. E.; Bogard, D. D.; Wooden, J.; Bansal, B.; Wiesmann, H.; Mckay, G.

    1979-01-01

    The age of the Shergotty achondrite is determined by Rb-Sr isotope analysis and the metamorphic resetting of isochron ages, which is presumed to have occurred during a shock event in the history of the meteorite, is discussed. The isochron best fitting the Rb-Sr evolution diagram is found to correspond to an age of 165 million years, with an initial Sr-87/Sr-86 value of 0.72260. Different apparent ages obtained by the K-Ar and Sm-Nd methods are interpreted in terms of a model which quantifies the degree of resetting of internal isochron ages by low temperature solid state diffusion. On the basis of these considerations, it is concluded that Shergotty crystallized from a melt 650 million years ago, was shock heated to 300 to 400 C after its parent body was involved in a collision 165 million years ago, and was first exposed to cosmic rays two million years ago.

  11. Geospeedometry and the metamorphic history of the Late Cretaceous Chiwaukum Schist, west central Washington state

    SciTech Connect

    Evans, D.A. . Div. of Geological and Planetary Sciences); Lasaga, A.C.; Ague, J.J.; Brandon, M.T. . Dept. of Geology and Geophysics)

    1993-04-01

    The Chiwaukum Schist on the NE side of the Late Cretaceous Mount Stuart batholith (MSB) shows evidence of a low-P contact metamorphism, followed by a higher-P amphibolite-facies regional metamorphism (Evans and Berti, 1986). Samples were collected from this contact zone in order to quantify the time-temperature history of the schist using the geospeedometry method of Lasaga (1983). Pseudomorphic textures and garnet-aluminosilicate-plagioclase (GASP) geobarometry within some samples show an increase in pressure during crystal growth, consistent with the interpretation of Evans and Berti (1986), that regional metamorphism followed intrusion of the MSB. Geospeedometry exploits the kinetics of diffusion associated with the thermo-barometric exchange reactions in order to determine the retrograde cooling history of a metamorphic rock. This technique was applied using Fe-Mg diffusion between garnet and biotite as defined by that geothermometer. Modeling results indicate that the region was exhumed and cooled from about 22 km and 610 C to about 8 km and 525 C, in a period of about 2.5 Myr. The average exhumation rate is 5.6 km/Myr. These results are consistent with existing isotopic ages, which indicate that the northeast MSB was intruded at about 95 Ma (K/Ar hornblende and U/Pb zircon) and that the Chiwaukum Schist cooled through temperatures of about 350 C at 86 to 83 Ma (K/Ar muscovite). Rapid unroofing appears to follow shortly after the climax of crustal thickening within the Cascade metamorphic core and may be related to erosional and/or tectonic denudation within a mountainous collisional orogen.

  12. Proterozoic metamorphism and uplift history of the north-central Laramie Mountains, Wyoming, USA

    USGS Publications Warehouse

    Patel, S.C.; Frost, B.R.; Chamberlain, K.R.; Snyder, G.L.

    1999-01-01

    The Laramie Mountains of south-eastern Wyoming contain two metamorphic domains that are separated by the 1.76 Ga. Laramie Peak shear zone (LPSZ). South of the LPSZ lies the Palmer Canyon block, where apatite U-Pb ages are c. 1745 Ma and the rocks have undergone Proterozoic kyanite-grade Barrovian metamorphism. In contrast, in the Laramie Peak block, north of the shear zone, the U-Pb apatite ages are 2.4-2.1 Ga, the granitic rocks are unmetamorphosed and supracrustal rocks record only low-T amphibolite facies metamorphism that is Archean in age. Peak mineral assemblages in the Palmer Canyon block include (a) quartz-biotite-plagioclase-garnet-staurolite-kyanite in the pelitic schists; (b) quartz-biotite-plagioclase-low-Ca amphiboles-kyanite in Mg-Al-rich schists, and locally (c) hornblende-plagioclase-garnet in amphibolites. All rock types show abundant textural evidence of decompression and retrograde re-equilibration. Notable among the texturally late minerals are cordierite and sapphirine, which occur in coronas around kyanite in Mg-Al-rich schists. Thermobarometry from texturally early and late assemblages for samples from different areas within the Palmer Canyon block define decompression from > 7 kbar to < 3 kbar. The high-pressure regional metamorphism is interpreted to be a response to thrusting associated with the Medicine Bow orogeny at c. 1.78-1.76 Ga. At this time, the north-central Laramie Range was tectonically thickened by as much as 12 km. This crustal thickening extended for more than 60 km north of the Cheyenne belt in southern Wyoming. Late in the orogenic cycle, rocks of the Palmer Canyon block were uplifted and unroofed as the result of transpression along the Laramie Peak shear zone to produce the widespread decompression textures. The Proterozoic tectonic history of the central Laramie Range is similar to exhumation that accompanied late-orogenic oblique convergence in many Phanerozoic orogenic belts.

  13. Radiometric ages related to the timing of Paleozoic metamorphism and deformation in the Blue Ridge of northwestern North Carolina

    SciTech Connect

    Goldberg, S.A. . Dept. of Geology); Dallmeyer, R.D. . Dept. of Geology)

    1992-01-01

    Thrust sheets within the Blue Ridge (BR) of northwestern NC record different Paleozoic tectonic histories, recognized on the basis of detailed field and petrographic studies. Ar-40/Ar-39, Rb-Sr, Sm-Nd, and U-Pb data are reported on mineral separates, part of an ongoing study to define the ages of Paleozoic metamorphism and deformation within various segments of the Blue Ridge. East of the Gossan Lead fault in vicinity of the Grandfather Mountain window, the BR consists mainly of amphibolite and pelitic schist. These rocks record ordovician Sm-Nd ages, Devonian Rb-Sr ages, and Mississippian Ar-40/Ar-39 ages. A Sm-Nd mineral isochron based on hornblende, plagioclase, and sphene from an amphibolite defines an age of 465 [+-] 35 Ma. Rb-Sr data from an amphibolite of similar metamorphic grade yields Devonian mineral ages ranging from 365--408 Ma. Muscovite separates in associated pelitic schists record Ar-40/Ar-39 plateau ages of 324 [+-] 1 and 329 [+-] 1 Ma. The ages are interpreted to reflect extensive Paleozoic tectonothermal activity in eastern Blue Ridge sequences, commencing with high-grade Ordovician metamorphism, isotopic resetting in the Devonian associated with granitic intrusions, followed by further re-equilibration associated with Alleghanian thrusting. In contrast, thrust sheets from the westernmost BR exhibit low metamorphic grades and record mainly Taconic ages of metamorphism. Preliminary analysis suggests that only the easternmost thrust sheets of northwestern NC experienced thermal resetting during the Devonian.

  14. Mesoproterozoic syntectonic garnet within Belt Supergroup metamorphic tectonites: Evidence of Grenville-age metamorphism and deformation along northwest Laurentia

    USGS Publications Warehouse

    Nesheim, T.O.; Vervoort, J.D.; McClelland, W.C.; Gilotti, J.A.; Lang, H.M.

    2012-01-01

    Northern Idaho contains Belt-Purcell Supergroup equivalent metamorphic tectonites that underwent two regional deformational and metamorphic events during the Mesoproterozoic. Garnet-bearing pelitic schists from the Snow Peak area of northern Idaho yield Lu-Hf garnet-whole rock ages of 1085??2. Ma, 1198??79. Ma, 1207??8. Ma, 1255??28. Ma, and 1314??2. Ma. Garnet from one sample, collected from the Clarkia area, was micro-drilled to obtain separate core and rim material that produced ages of 1347??10. Ma and 1102??47. Ma. The core versus rim ages from the micro-drilled sample along with the textural and spatial evidence of the other Lu-Hf garnet ages indicate two metamorphic garnet growth events at ~. 1330. Ma (M1) and ~. 1080. Ma (M2) with the intermediate ages representing mixed ages. Some garnet likely nucleated and grew M1 garnet cores that were later overgrown by younger M2 garnet rims. Most garnet throughout the Clarkia and Snow Peak areas are syntectonic with a regional penetrative deformational fabric, preserved as a strong preferred orientation of metamorphic matrix minerals (e.g., muscovite and biotite). The syntectonic garnets are interpreted to represent one regional, coeval metamorphic and deformation event at ~. 1080. Ma, which overlaps in time with the Grenville Orogeny. The older ~. 1330. Ma ages may represent an extension of the East Kootenay Orogeny described in western Canada. These deformational and metamorphic events indicate that western Laurentia (North America) was tectonically active in the Mesoproterozoic and during the assembly of the supercontinent Rodinia. ?? 2011 Elsevier B.V.

  15. Mesoproterozoic syntectonic garnet within Belt Supergroup metamorphic tectonites: Evidence of Grenville-age metamorphism and deformation along northwest Laurentia

    NASA Astrophysics Data System (ADS)

    Nesheim, Timothy O.; Vervoort, Jeffrey D.; McClelland, William C.; Gilotti, Jane A.; Lang, Helen M.

    2012-03-01

    Northern Idaho contains Belt-Purcell Supergroup equivalent metamorphic tectonites that underwent two regional deformational and metamorphic events during the Mesoproterozoic. Garnet-bearing pelitic schists from the Snow Peak area of northern Idaho yield Lu-Hf garnet-whole rock ages of 1085 ± 2 Ma, 1198 ± 79 Ma, 1207 ± 8 Ma, 1255 ± 28 Ma, and 1314 ± 2 Ma. Garnet from one sample, collected from the Clarkia area, was micro-drilled to obtain separate core and rim material that produced ages of 1347 ± 10 Ma and 1102 ± 47 Ma. The core versus rim ages from the micro-drilled sample along with the textural and spatial evidence of the other Lu-Hf garnet ages indicate two metamorphic garnet growth events at ~ 1330 Ma (M1) and ~ 1080 Ma (M2) with the intermediate ages representing mixed ages. Some garnet likely nucleated and grew M1 garnet cores that were later overgrown by younger M2 garnet rims. Most garnet throughout the Clarkia and Snow Peak areas are syntectonic with a regional penetrative deformational fabric, preserved as a strong preferred orientation of metamorphic matrix minerals (e.g., muscovite and biotite). The syntectonic garnets are interpreted to represent one regional, coeval metamorphic and deformation event at ~ 1080 Ma, which overlaps in time with the Grenville Orogeny. The older ~ 1330 Ma ages may represent an extension of the East Kootenay Orogeny described in western Canada. These deformational and metamorphic events indicate that western Laurentia (North America) was tectonically active in the Mesoproterozoic and during the assembly of the supercontinent Rodinia.

  16. Petrochronological investigations to unravel the tectono-metamorphic history of Alpine subduction (Briançonnais, Queyras, Western Alps)

    NASA Astrophysics Data System (ADS)

    Lanari, Pierre

    2015-04-01

    The study of the tectonic and metamorphic history of the Alpine metamorphic belt involving oceanic and continental subduction processes requires knowledge of detailed Pressure-Temperature-time-deformation (P-T-t-ɛ) paths recorded by different tectono-metamorphic units across the belt. This task is particularly challenging in low-grade rocks, e.g. metapelites, (a) for thermobarometry, and (b) for geochronology. Metapelites at greenschist facies metamorphic conditions show a narrow spectrum of metamorphic minerals, notably quartz, chlorite and K-white mica, in addition to commonly detrital relics inherited from previous metamorphic rocks. To obtain reliable P-T estimates, a multi-method approach is required, which usefully combines Raman study of Carbonaceous Material (RSCM), chemical analysis in standardized X-ray maps, and multi-equilibrium inverse thermodynamic modelling of chlorite and white mica. In order to be able to link each assemblage to a specific metamorphic stage and determine the time scales and rates of metamorphism, it is critical to use in situ dating techniques. In this study, high-resolution geochronology was conducted including single-grain 40Ar/39Ar dating (step heating), where possible in combination with U-Th-Pb age-dating of allanite by LA-ICP-MS analysis. In the French western Alps, the Briançonnais zone is a remnant of the continental subduction wedge, while the Liguro-Piedmontais zone is a fossil oceanic subduction wedge. Metapelites from these two complexes were investigated to constrain the individual P-T-t paths recorded in each tectonic slice. This study focussed on deciphering four tectono-metamorphic units in the Briançonnais zone: (B1) The Internal basement; (B2) the Lower and (B3) Upper Zone Houillère; (B4) the Mesozoic Nappe Stack. These continental units recorded green-schist Alpine metamorphic conditions. In the Liguro-Piedmontais zone, five tectono-metamorphic units are identified: (LP1) the Péouvou; (LP2) Saint-Véran; (LP

  17. Age of granites of Wrangel Island metamorphic complex

    NASA Astrophysics Data System (ADS)

    Luchitskaya, Marina; Sergeev, Sergey; Sokolov, Sergey; Tuchkova, Marianna

    2014-05-01

    Within huge arctic shelf of Eastern-Siberian and Chukchi seas the metamorphic basement (Wrangel complex, Berri Formation) is exposed only on the Wrangel Island. There are different points of views on the age of metamorphic rocks of Wrangel complex (Berri Formation): (1) Neoproterozoic (Kameneva, 1970; Ageev, 1979; Kos'ko et al., 1993, 2003), (2) Devonian (Til'man et al., 1964, 1970; Ganelin, 1989). Metamorphic basement is represented by stratified complex, composed of dislocated metavolcanic, metavolcaniclastic and metasedimentary rocks (schists, metasandstones, metaconglomerated) with single lenses and layers of carbonate rocks (Wrangel Island…, 2003). Among basement rocks in the central part of Wrangel Island there are felsic intrusive bodies. They form small tabular bodies from tens centimeters to 70-80 meters in thickness, rarely dikes and small stocks (up to 20 x 30 m) and are composed of granite-porphyres, rarely muscovite porphyr-like granites and granosyenites (Wrangel Island…, 2003). The age of intrusions allow to determine the age of basement formation. Earlier the age of intrusions was determined by different methods and correlated to the boundary between Neoproterozoic and Paleozoic: K-Ar 570-603 Ma, Pb-Pb 590±50 Ma (S.M. Pavlov, Institute of Precambrian Geology and Geochronology, USSR Academy of Sciences), Rb-Sr 475±31 Ma (I.M.Vasil'eva, Institute of Precambrian Geology and Geochronology, USSR Academy of Sciences), U-Pb 609, 633, 677 Ma (Geological Survey of Canada) (Wrangel Island…, 2003; Kos'ko et al., 1993; Cecile et al., 1991). In the lower part of metamorphic rocks of Wrangel complex there are conformable tabular bodies of gneissosed and foliated granitoides. The latter are meramorphosed and transformed in biotite-muscovite-feldspar-quartz-sericite and muscovite-feldspar-quartz-sericite gneisses and schists, where relics of primary minerals (quartz, plagioclase, potassium feldspar, rarely biotite and muscovite) and equigranular granitic

  18. Quantitative determination of metamorphic reaction history : mass balance relations between groundmass and mineral inclusion assemblages in metamorphic rocks

    NASA Astrophysics Data System (ADS)

    Whitney, Donna L.; Lang, Helen M.; Ghent, Edward D.

    1995-07-01

    Qualitative and quantitative information about metamorphic reaction history and PT paths may be obtained from mineral inclusions in garnet by comparing the mineralogy, distribution, and compositions of paragenetically-related inclusions with minerals in the groundmass assemblage. Using the algebraic technique of singular value decomposition (SVD), we document mass balance relations between inclusion and groundmass assemblages in metapelitic rocks from two metamorphic terranes that experienced different peak metamorphic conditions, and whose transition from inclusion to groundmass assemblage records different PT path segments relative to peak conditions. We calculate mass balances relating an inclusion assemblage consisting in part of armored relics of chloritoid to groundmass mineral assemblages in a kyanite-staurolite mica schist from the Solitude Range, British Columbia, and an inclusion assemblage of kyanite, staurolite, and rutile to groundmass minerals in a sillimanite-cordierite gneiss from the Skagit Gneiss, North Cascade Range, Washington. Mass balances for each rock are consistent with reaction histories inferred from petrographic observations. In the Solitude Range schist, the results of mass balance calculations are consistent with the growth of staurolite and garnet at the expense of chloritoid during prograde metamorphism and suggest that chlorite, although not preserved as an inclusion, was involved in initial staurolite growth. In the Skagit sillimanite gneiss, mass balance relations exist between the inclusion suite, which formed during high pressure metamorphism, and the associated groundmass assemblage, which equilibrated at high temperature but much lower pressure. Mass balance does not exist between the groundmass of the Skagit sillimanite gneiss and the groundmass of a nearby kyanite-staurolite schist that has been proposed as a possible lower-grade equivalent of the sillimanite-bearing rocks. These results indicate that, although compositional

  19. Thermal history of chondrites - Hot accretion vs. metamorphic reheating

    NASA Technical Reports Server (NTRS)

    Haack, Henning; Taylor, G. J.; Scott, E. R. D.; Keil, Klaus

    1992-01-01

    The thermal evolution of chondrules is investigated for the stages including primary heating through accretion to parent-body processing to determine whether the chondrules could be hot during accretion. Theoretical attention is given to whether chondrites of different petrologic types could have originated by means of hot accretion or metamorphic reheating. Data are presented from cooling-rate experiments and from calculations of heat retention required for the hot-accretion scenario. The accretion of chondrules hotter than 800 C is shown to be inconsistent with constraints on chondrule thermal evolution, in particular the slow cooling environment of chondrules vs the apparent cooling of chondrites in cold environments. It is argued that petrologic chondrites are formed by cold accretion and subsequently by metamorphic heating.

  20. The age and petrography of two Luna 20 fragments and inferences for widespread lunar metamorphism.

    NASA Technical Reports Server (NTRS)

    Podosek, F. A.; Huneke, J. C.; Gancarz, A. J.; Wasserburg, G. J.

    1973-01-01

    Ages were determined by the Ar-40/Ar-39 method on two metaclastic rocks returned from the lunar highlands north of Mare Fecunditatis by the Luna 20 probe. Both samples gave very well-defined argon retention ages of 3.90 plus or minus 0.04 AE which are indistinguishable from each other within a resolution of 0.02 AE. Both fragments, 22006 and 22007, are highly recrystallized polymict breccias; there is no evidence of radiogenic Ar-40, and the age almost surely dates the time of recrystallization. The cosmic ray exposure ages of these fragments are similar and high: 900 million years for 22006, 1300 million years for 22007. 22007 also contains substantial trapped argon with a high Ar-40/Ar-36. The Luna 20 results greatly extend the area of the moon's surface exhibiting a well-defined record of metamorphism at 3.9 AE. So far, lunar history in the interval from 4.6 to 3.9 AE is not preserved in the ages of surface rocks. This obliteration suggests lunar-wide metamorphic conditions occurring or terminating at this time as a result of major impacts.

  1. The Silurian to Permian history of a metamorphic core complex in Lofoten, northern Scandinavian Caledonides

    NASA Astrophysics Data System (ADS)

    Steltenpohl, Mark G.; Hames, Willis E.; Andresen, Arild

    2004-02-01

    The Lofoten archipelago exposes Precambrian Baltic basement and Caledonian allochthonous sequences within a 1000 km long chain of gravity and magnetic highs and structural culminations along the extended, British and Norwegian continental shelf. Previous regional geophysical studies indicate that post-Caledonian extension and development of the northern Norwegian shelf occurred during broadly defined Carboniferous-Permian, Cretaceous-Jurassic, and early Tertiary events. Structures related to these events are known to young westward. We report field, structural, and 40Ar/39Ar thermochronologic data from rocks exposed in Lofoten that further define the history and style of post-Caledonian extension. The islands of southwest Lofoten also represent the most outboard exposures of Caledonian basement in northern Norway that presumably formed the middle to deep crustal core of the orogen. Metasedimentary rocks and penetratively deformed basement in Lofoten record high-grade Silurian-Devonian metamorphism and top-to-the-east (hereinafter tops-east) thrusting followed by episodes of Late Devonian to Early Carboniferous, tops-west, ductile extension which progressed into oblique left-slip movements. The structural style and timing of Silurian contraction in this area are remarkably similar to that determined for the more forelandward areas on the mainland, ˜120 km to the east, supporting the inference that distal parts of the Baltic continental margin that were once deeply subducted are presently exposed in Lofoten. The timings of post-Devonian structural events that affected rocks in Lofoten are partially constrained by the ages of unconformities and strata known to be preserved in graben flanking the Lofoten culmination. The radiometric age and structural data presented in this study, in combination with stratigraphic constraints, suggest a westward progression through time of extensional deformation over a protracted interval of Silurian to Permian time. The latest

  2. Single or Multiphase Metamorphic History of the Nordfjord Ultrahigh-Pressure Province, Western Norway?

    NASA Astrophysics Data System (ADS)

    Young, D. J.; Kylander-Clark, A. R.; Gehrels, G. E.; Hacker, B. R.

    2010-12-01

    Deciphering the metamorphic evolution of exposed ancient high/ultrahigh-pressure terranes yields important insights into the tectonic processes hidden beneath active continental collision belts. In particular, continuing controversy exists over the age and tectonic significance of multiple, broadly syn-orogenic, eclogite-, granulite- and amphibolite-facies metamorphic episodes that have been identified by numerous workers in both ancient and modern orogens. Do these episodes represent discrete tectonic events, changing boundary conditions, or simply asynchronous equilibrium within a continuous kinematic framework? The Nordfjord area of western Norway was subducted to depths >100 km during the Devonian Scandian orogeny, and exhumed rapidly thereafter. Peak metamorphic grade increases steadily from high-P amphibolite facies south of Nordfjord, to coesite-eclogite facies north and westward. This transition is not disrupted by any significant structural or metamorphic breaks, and thus likely results from in-situ prograde metamorphism. Yet two ages of eclogite-facies metamorphism are known from this region: in southern parts of the transition, TIMS U/Pb dating of multigrain zircon fractions from a fine-grained mafic eclogite (2.3 GPa, 600°C) yield a discord with a lower intercept of 414±4 Ma (MSWD=1.1). Farther north within the UHP zone, however, TIMS dating of two zircon grains from a coarser-grained, higher temperature (˜700°C) eclogite return a concordant weighted mean age of 405±2 Ma (MSWD=0.96). Determining the relative age(s) of metamorphic episodes in the Nordfjord region has relied on dating scattered, rare mafic eclogite. Yet the volumetrically dominant granodioritic and granitic gneiss country rocks, which mostly retain amphibolite-facies assemblages, may offer a more continuous database to elucidate the significance of spatial variations in metamorphic age. Populations of small zircons (<50-80 microns) from seven samples of felsic gneiss were analyzed

  3. The age of deep, steep continental subduction in the NW Himalaya: Relating zircon growth to metamorphic history. Comment on: “The onset of India-Asia continental collision: Early, steep subduction required by the timing of UHP metamorphism in the western Himalaya” by Mary L. Leech, S. Singh, A.K. Jain, Simon L. Klemperer and R.M. Manickavasagam, Earth and Planetary Science Letters 234 (2005) 83-97

    NASA Astrophysics Data System (ADS)

    O'Brien, Patrick J.

    2006-05-01

    Leech et al. [Mary L. Leech, S. Singh, A.K. Jain, Simon L. Klemperer and R.M. Manickavasagam, Earth and Planetary Science Letters 234 (2005) 83-97], present 3 clusters of ages for growth stages in zircon from quartzo-feldspathic gneisses hosting coesite-bearing eclogite from the Tso Morari Complex, NW India. These age clusters, from oldest to youngest, are interpreted to represent the age of ultrahigh-pressure metamorphism, a subsequent eclogite facies overprint and a later amphibolite facies retrogression and require subduction of Indian crust to have started earlier than previously accepted. However, no petrographic evidence, such as inclusions in the zircons relating to particular metamorphic events, is presented to substantiate the proposed sequence of metamorphic stages. Previously published data from eclogites of the same area indicate that coesite-eclogite is not the first but at least the second eclogite facies stage. In addition, the newly proposed time interval between coesite-eclogite and the amphibolite facies overprint is longer than previously indicated by diffusion modelling of natural garnet-garnet couples in eclogite. Neither the age of ultrahigh-pressure metamorphism nor the timing of initiation of subduction is reliably constrained by the presented data.

  4. Age and metamorphism of some massive sulflde deposits in Virginia, North Carolina and Tennessee

    USGS Publications Warehouse

    Kinkel, A.R., Jr.; Thomas, H.H.; Marvin, R.F.; Walthall, F.G.

    1965-01-01

    Isotopic ages of vein and wall-rock samples have been determined on five massive sulflde deposits of the southern Appalachians. Vein mineral ages of about 1100 m.y. indicate that some ore bodies formed at least as early as the Grenville metamorphism, and probably soon after the formation of the enclosing gneiss and schist. Present textures of the ore were formed during subsequent metamorphic periods at about 450 m.y. and 300 to 330 m.y. ago. ?? 1965.

  5. 40Ar/39Ar and K-Ar data bearing on the metamorphic and tectonic history of western New England.

    USGS Publications Warehouse

    Sutter, J.F.; Ratcliffe, N.M.; Mukasa, S.B.

    1985-01-01

    40Ar/39Ar ages of coexisting biotite and hornblende from Proterozoic Y gneisses of the Berkshire and Green Mt massifs, as well as 40Ar/39Ar and K/Ar mineral and whole-rock ages from Palaeozoic metamorphic rocks, suggest that the thermal peaks for the dominant metamorphic recrystallization in western New England occurred 465 + or - 5 m.y. (Taconian). 40Ar/39Ar age data from a poorly-defined terrain along the eastern strip of the area suggests that the area has been retrograded during a metamorphism that peaked at least 376 + or - 5 m.y. (Acadian). Available age and petrological data from western New England indicate the presence of at least three separate metamorphic-structure domains of Taconic age: 1) a small area of relict high-P and low-T metamorphism, 2) a broad area of normal Barrovian metamorphism from chlorite to garnet grade characterized by a gentle metamorphic gradient and, 3) a rather narrow belt of steep-gradient, Barrovian series metamorphic rocks. Areas of maximum metamorphic intensity within the last domain coincide with areas of maximum crustal thickening in the later stage of Taconic orogeny. -L.di H

  6. Peak metamorphic temperature and thermal history of the Southern Alps (New Zealand)

    NASA Astrophysics Data System (ADS)

    Beyssac, O.; Cox, S. C.; Vry, J.; Herman, F.

    2016-04-01

    The Southern Alps orogen of New Zealand results from late Cenozoic convergence between the Indo-Australian and Pacific plates and is one of the most active mountain belts in the world. Metamorphic rocks carrying a polymetamorphic legacy, ranging from low-greenschist to high-grade amphibolites, are exhumed in the hanging wall of the Alpine Fault. On a regional scale, the metamorphic grade has previously been described in terms of metamorphic zones and mineral isograds; application of quantitative petrology being severely limited owing to unfavorable quartzofeldspathic lithologies. This study quantifies peak metamorphic temperatures (T) in a 300 × 20 km area, based on samples forming 13 transects along-strike from Haast in the south to Hokitika in the north, using thermometry based on Raman spectroscopy of carbonaceous material (RSCM). Peak metamorphic T decreases across each transect from ≥ 640 °C locally in the direct vicinity of the Alpine Fault to less than 330 °C at the drainage divide 15-20 km southeast of the fault. Thermal field gradients exhibit a degree of similarity from the southernmost to the northernmost transects, are greater in low-grade semischist than high-grade schist, are affected by folding or discontinuous juxtaposition of metamorphic zones, and contain limited information on crustal-scale geothermal gradients. Temperatures derived by RSCM thermometry are slightly (≤ 50 °C) higher than those derived by traditional quantitative petrology using garnet-biotite thermometry and THERMOCALC modeling. The age of RSCM T appears to be mostly pre-Cenozoic over most of the area except in central Southern Alps (Franz Josef-Fox area), where the amphibolite facies schists have T of likely Cenozoic age. The RSCM T data place some constraints on the mode of exhumation along the Alpine Fault and have implications for models of Southern Alps tectonics.

  7. Long and complex thermal history of the Song Chay metamorphic dome (Northern Vietnam) by multi-system geochronology

    NASA Astrophysics Data System (ADS)

    Roger, Francoise; Leloup, Philippe Hervé; Jolivet, Marc; Lacassin, Robin; Trinh, Phan Trong; Brunel, Maurice; Seward, Diane

    2000-06-01

    Multi-system geochronology was used to unravel the long and complex thermal history of the Song Chay range (Northern Vietnam), a high-grade granitic and metamorphic dome in the vicinity of the Cenozoic, Ailao Shan-Red River fault zone. It was considered to be Proterozoic South China basement, but its geological history was basically unknown. Scattered field observations suggest three episodes of high-temperature deformation: firstly at the time of granite emplacement, secondly a décollement with top to the north shear and thirdly anticlinal doming of the foliations formed during the two first stages. P- T estimates suggest that metamorphism coeval with the second deformation phase culminated at ˜580°C and ˜4.5 kbar (˜16 km depth). Multi-system geochronology is applied to a two-micas granite sample, slightly deformed within the décollement. U/Pb dating of zircon yields an age of 428±5 Ma (±2 σ) interpreted as the time of granite crystallization within the South China 'Caledonian' belt. Rb/Sr on white micas and biotite yields ages of 206±10 Ma and 176±5.3 Ma, respectively (2 σ), whereas 39Ar/ 40Ar ages of the same minerals are 210±9 and 190±8 Ma (2 σ). These ages suggest an Upper Triassic episode of rapid cooling interpreted as due to doming a few million years after the end of movement on the décollement. The K-feldspar irregular 39Ar/ 40Ar age spectrum can, to the first order, be explained by a cooling history with two episodes of rapid cooling: one at ˜140 Ma and a second around 41 to 25 Ma. Apatite fission tracks central age (33.6±3.6 Ma, 1 σ) confirms a Tertiary rapid cooling event interpreted as the final exhumation of the Song Chay dome.

  8. Larval history influences post-metamorphic condition in a coral-reef fish.

    PubMed

    Hamilton, Scott L

    2008-12-01

    Upon settlement, many fishes undergo an energetically costly metamorphic period that requires substantial nutritional reserves. Larval growth and the accumulation of lipids prior to metamorphosis are likely to influence growth and survival following this critical period. On the Caribbean island of St. Croix, I investigated relationships between larval growth, early life-history characteristics, and post-metamorphic lipid content in the bluehead wrasse Thalassoma bifasciatum. Lipid reserves remaining after metamorphosis were positively related (r2 = 0.62) to the width of the metamorphic band; thus, this otolith-derived trait may be used to estimate the condition at emergence of survivors collected at some later time. In contrast, pelagic larval duration, average larval growth, and otolith size at settlement were negatively related to post-metamorphic lipid content. Interestingly, the trend for slower growth among fish in good condition was not consistent over the entire pelagic larval duration. Analyses of daily larval growth histories indicated that fish with high lipid reserves grew rapidly in the last week prior to settlement, but relatively slowly during the early phases of larval life; those emerging with low lipid concentrations, however, displayed strikingly opposite patterns. These contrasting patterns of growth and energy storage were consistent at two sites and over three recruitment events. Otolith chemistry data suggested that differences in growth histories and body condition were consistent with the hypothesis of larval development in distinct oceanic environments (characterized by Pb concentration); but, within a water mass, differences reflected life-history trade-offs between growth and energy storage. The results have implications for understanding the processes driving juvenile survival, which may be condition dependent. PMID:18836749

  9. Thermoluminescence constraints on the metamorphic, shock, and brecciation history of basaltic meteorites

    NASA Technical Reports Server (NTRS)

    Batchelor, J. D.; Sears, Derek W. G.

    1991-01-01

    The metamorphic, shock, and brecciation history of 18 eucrites, 13 howardites, 6 diogenites, and 15 mesosiderites is investigated via induced thermoluminescence measurements performed on them. The eucrites show a 15-fold range of TL sensitivities, which correlate with petrographic indicators of metamorphic intensity. The temperature of the dominant TL peak observed for basaltic meteorites, and experiments in which four eucrites with diverse petrographic properties were annealed at various temperatures in the laboratory, suggests that the metamorphic equilibration temperatures for most basaltic meteorites were not more than 800 C. Assuming this temperature was typical of conditions during metamorphism, then burial depths for type-above-5 eucrites were greater than 350 m and less than 50 m for type-2 eucrites. Since TL peak temperatures are related to the degree of disorder in the Al, Si chain in feldspar, the present data provide independent evidence for very slow cooling rates for mesosiderites and for the slower cooling rates for some cumulate eucrites relative to equilibrated noncumulate eucrites.

  10. Age and tectonic implications of some low-grade metamorphic rocks from the Yucatan Channel

    USGS Publications Warehouse

    Vedder, J.G.; MacLeod, N.S.; Lanphere, M.A.; Dillon, William P.

    1973-01-01

    Phyllite and marble dredged from the lower part of the continental slope between Cuba and the Yucatan Peninsula seem to support the contention that a pre-early Tertiary metamorphic belt extends from the western Greater Antilles into northern Central America. The minimum K-Ar ages derived from the samples suggest that the metamorphic event was pre-Late Cretaceous, and evaluation of the K-Ar data implies that this metamorphic event is not older than Late Jurassic. Greater antiquity, however, is inferred from structural and stratigraphic relations in British Honduras, where the latest regional metamorphic event was post-Early Permian and pre-Middle Jurassic.  Rifting and extension related to plate motions along the British Honduras Quintana Roo margin through Mesozoic and earliest Cenozoic time presumably would preclude extensive regional metamorphism, permitting only limited development of schistose rocks there during that interval. The timing of metamorphic events in western Cuba is uncertain, but a pre-Middle Jurassic episode possibly is reflected in the phyllite and marble terranes of Isla de Pinos and Sierra de Trinidad. Local incipient metamorphism of Early and Middle Jurassic strata in the Sierra de los Organos may have resulted from severe tectonism that began in Late Cretaceous time and diminished in the Eocene.

  11. Age and duration of eclogite-facies metamorphism, North Qaidam HP/UHP terrane, Western China

    USGS Publications Warehouse

    Mattinson, C.G.; Wooden, J.L.; Liou, J.G.; Bird, D.K.; Wu, C.L.

    2006-01-01

    Amphibolite-facies para-and orthogneisses near Dulan, at the southeast end of the North Qaidam terrane, enclose minor eclogite and peridotite which record ultra-high pressure (UHP) metamorphism associated with the Early Paleozoic continental collision of the Qilian and Qaidam microplates. Field relations and coesite inclusions in zircons from paragneiss suggest that felsic, mafic, and ultramafic rocks all experienced UHP metamorphism and a common amphibolite-facies retrogression. SHRIMP-RG U-Pb and REE analyses of zircons from four eclogites yield weighted mean ages of 449 to 422 Ma, and REE patterns (flat HREE, no Eu anomaly) and inclusions of garnet, omphacite, and rutile indicate these ages record eclogite-facies metamorphism. The coherent field relations of these samples, and the similar range of individual ages in each sample suggests that the ???25 m.y. age range reflects the duration of eclogite-facies conditions in the studied samples. Analyses from zircon cores in one sample yield scattered 433 to 474 Ma ages, reflecting partial overlap on rims, and constrain the minimum age of eclogite protolith crystallization. Inclusions of Th + REE-rich epidote, and zircon REE patterns are consistent with prograde metamorphic growth. In the Lu??liang Shan, approximately 350 km northwest in the North Qaidam terrane, ages interpreted to record eclogite-facies metamorphism of eclogite and garnet peridotite are as old as 495 Ma and as young as 414 Ma, which suggests that processes responsible for extended high-pressure residence are not restricted to the Dulan region. Evidence of prolonged eclogite-facies metamorphism in HP/UHP localities in the Northeast Greenland eclogite province, the Western Gneiss Region of Norway, and the western Alps suggests that long eclogite-facies residence may be globally significant in continental subduction/collision zones.

  12. Annealing studies of the thermoluminescence of meteorites and implications for their metamorphic history

    SciTech Connect

    Guimon, R.K.

    1986-01-01

    The application of thermoluminescence to study metamorphism in the type 3 ordinary chondrites and five CAI from the Allende meteorite is explored. It has been found that the changes in the shape of the TL curve provide insight into the thermal history of the meteorites and meteoritic components. It is also shown that for ordinary chondrites, the TL sensitivity depends on the amount of feldspar present which, in turn, is governed by the intensity of metamorphism experienced. A type 3.4 ordinary chondrite shows changes in the peak temperature and width occurred upon annealing. These parameters showed a discontinuous increase after annealing at 800/sup 0/C; the peak temperature jumped from 130 to 200/sup 0/C and peak width increased from 90 to 150/sup 0/C. These changes in the TL emission characteristics suggest that type 3.3-3.5 ordinary chondrites have a low-feldspar as the dominant TL phosphor and > 3.5 have high feldspar as the phosphor. Thermoluminescence therefore provides a means of paleothermometry. In addition, experiments were performed aimed at causing the crystallization of feldspar in mesostasis glass in an attempt to reproduce the trends of increasing TL sensitivity with metamorphism. At high temperatures and longer annealing times, increases in TL sensitivity by factors of up to 40 were observed.

  13. Exotic metamorphic terranes in the Caledonides: Tectonic history of the Dalradian block, Scotland

    NASA Astrophysics Data System (ADS)

    Bluck, B. J.; Dempster, T. J.

    1991-11-01

    The Dalradian block, a part of the Precambrian metamorphic basement of Scotland, is thought to be exotic to Laurentia, having a provenance in Gondwana. In contrast to the rest of the Laurentian margin, which from ca. 700 to 530 Ma was undergoing extension, the Dalradian block was undergoing severe compression ca. 590 Ma. At the time of splitting of the Late Proterozoic supercontinent, both Gondwana and Laurentia shared a common history of extension; however, at ca. 670 Ma Gondwana converted to a destructive margin and underwent compression, whereas Laurentia remained in extension and passive to 500-510 Ma. The Dalradian block had two major phases of metamorphism and deformation, one in Gondwana, and the other in Laurentia. The second phase of classical Barrovian metamorphism may have been produced by thickening due to emplacement of ophiolitic and other nappes, rather than the earlier internal nappe structures. Late-stage ductile folding in the Moine basement to the north may be related to the final emplacement of the Dalradian block onto Laurentia.

  14. Metamorphic history and geodynamic significance of the Early Cretaceous Sabzevar granulites (Sabzevar structural zone, NE Iran)

    NASA Astrophysics Data System (ADS)

    Nasrabady, M.; Rossetti, F.; Theye, T.; Vignaroli, G.

    2011-11-01

    The Iranian ophiolites are part of the vast orogenic suture zones that mark the Alpine-Himalayan convergence zone. Few petrological and geochronological data are available from these ophiolitic domains, hampering a full assessment of the timing and regimes of subduction zone metamorphism and orogenic construction in the region. This paper describes texture, geochemistry, and the pressure-temperature path of the Early Cretaceous mafic granulites that occur within the Tertiary Sabzevar ophiolitic suture zone of NE Iran. Whole rock geochemistry indicates that the Sabzevar granulites are likely derived from a MORB-type precursor. They are thus considered as remnants of a dismembered dynamo-thermal sole formed during subduction of a back-arc basin (proto-Sabzevar Ocean) formed in the upper-plate of the Neotethyan slab. The metamorphic history of the granulites suggests an anticlockwise pressure-temperature loop compatible with burial in a hot subduction zone, followed by cooling during exhumation. Transition from a nascent to a mature stage of oceanic subduction is the geodynamic scenario proposed to accomplish for the reconstructed thermobaric evolution. When framed with the regional scenario, results of this study point to diachronous and independent tectonic evolutions of the different ophiolitic domains of central Iran, for which a growing disparity in the timing of metamorphic equilibration and of pressure-temperature paths can be expected to emerge with further investigations.

  15. Coupling thermodynamic modeling and high-resolution in situ LA-ICP-MS monazite geochronology: evidence for Barrovian metamorphism late in the Grenvillian history of southeastern Ontario

    NASA Astrophysics Data System (ADS)

    McCarron, Travis; Gaidies, Fred; McFarlane, Christopher R. M.; Easton, R. Michael; Jones, Peter

    2014-12-01

    The Flinton Group is a greenschist to upper amphibolite facies package of metasediments in southeastern Ontario that was metamorphosed during the Ottawan Orogeny. Thermodynamic modeling of metapelitic mineral assemblages suggests an increase in peak conditions of metamorphism across the 40 km wide study area from 3.5 to 7.9 kbar and 540 to 715 °C. Garnet isopleth thermobarometry applied to the cores of compositionally zoned porphyroblasts reveals remarkably similar P-T conditions of initial crystallization at approximately 3.7-4.0 kbar and 512-520 °C, corresponding to a relatively high geothermal gradient of ca. 34-45 °C km-1. It is inferred from modeling and reaction textures that metamorphism was along Barrovian P-T paths. Major and trace element zoning in garnet from one sample records a complex growth history as evidenced by major and trace element zoning and the distribution of xenotime, allanite and monazite inclusions. High-resolution (6 μm) LA-ICP-MS U-Pb geochronology performed on monazite in the rock matrix and included in the outer 150 μm of garnet rim-ward of a Y annulus revealed an age of 976 ± 4 Ma. The age is interpreted to reflect monazite growth at the expense of allanite and apatite late in garnet's growth history over the P-T interval 4.5-6.8 kbar and 540-640 °C. This new age estimate for near peak metamorphism fits well into the regional framework but is significantly younger than previously reported ages for Ottawan metamorphism. Based on microstructures this new age suggests that compressional tectonics were operating much later in the history of the Grenville of southeastern Ontario than previously thought.

  16. Structural, metamorphic and magmatic history of the Mondon¯edo nappe (Hercynian belt, NW Spain)

    NASA Astrophysics Data System (ADS)

    Bastida, F.; Martinez-Catalan, J. R.; Pulgar, J. A.

    The Mondon¯edo nappe is one of the main units in the internal zone of the Hercynian belt in the Iberian Peninsula. It consists of low to medium grade metasediments, late Precambrian and Palaeozoic in age, folded by large D1 E-verging recumbent structures, and thrusted several tens of km towards the east during a D2 deformation episode. At the base of the thrust sheet, a shear zone of up to 3 km thick was developed. Granitoid bodies, which were intruded after D1 and before or during D2, were deformed in this basal zone. The geometry of D1 and D2 structures and that of the isograds are described, as well as the relationships between metamorphism and deformation. A structural evolution is inferred which shows an episode of generalized ductile deformation ( D1) followed by another in which the deformation tended to concentrate in a subhorizontal ductile shear zone ( D2) and culminated with the thrusting along an important fracture. The shear zone originated in a thermally softened level which, according to metamorphic data, was at temperatures in the range 550-600°C. The structural, metamorphic and magmatic features of the Mondon¯edo nappe suggest a relationship with a crustal scale overthrusting of the continental mass to which the nappe belongs. This could be a consequence of the collision against another continental mass to the west.

  17. Petrology and metamorphic history of metapelites in the Boehls Butte quadrangle, northern Idaho

    SciTech Connect

    Carey, J.W.; Rice, J.M.

    1985-01-01

    Metapelitic rocks in the Goat Mountain area record a pre-Beltian anatectic event and two later metamorphic events correlated to the M2 and M3 events observed by Lang and Rice. The co-occurrence of all three aluminosilicates is the result of M2 kyanite-sillimanite growth and M3 andalusite growth. The conditions of M2 metamorphism are estimated at 675 +/- 50/sup 0/C and 9.3 +/- 1.5 kb as determined from a variety of geothermo/barometers. M2 AFM mineral assemblages include Grt-Bt-Ky+/-Sil+/-Str and Crd-Bt-Ky+/-Sil. Partitioning of Mg and Fe in garnet and staurolite is normal (K/sub D/ > 1) for relict staurolite enclosed by aluminosilicate or muscovite and reversed (K/sub D/ < 1) for apparently stable staurolite and staurolite occurring as inclusions in garnet. Cordierite occurs as an overgrowth of kyanite; a texture which cannot be explained by reactions among the coexisting minerals. The texture may be explained by prograde consumption of chlorite or consumption of garnet upon decompression. The M3 event had limited effect on M2 mineral assemblages but resulted in crenulation and brittle deformation of M2 fabrics. The M3 event occurred during uplift and cooling following the M2 event. The M3 event is correlated to uplift of the Idaho batholith implying a Cretaceous age of M2 metamorphism.

  18. A Tale of Two Plutons: Using Monazite to Reconstruct the Fluid History of Contact Metamorphic Aureoles

    NASA Astrophysics Data System (ADS)

    Ayers, J. C.; Crombie, S.; Miller, C.; Luo, Y.; Loflin, M.

    2006-12-01

    The rare earth phosphate monazite can be a powerful tool for characterizing the timing and spatial extent of fluid infiltration during contact metamorphism. We used an ion microprobe to investigate how wallrock monazite responded to the intrusion of two different granitic plutons, the Cretaceous Birch Creek Pluton (BCP) in the White Mountains of eastern California and the Miocene Searchlight pluton in southern Nevada. The contact metamorphic aureoles of both plutons contain monazite and display evidence of alteration by acidic magmatic fluids (sericitization). Contact metamorphism occurred at conditions under which monazite in granitic systems has been shown to be susceptible to hydrothermal alteration: mildly acidic fluids at temperatures of ~250-400C and pressures of ~0.15-0.4 GPa. Monazite from the hydrothermal aureole of the BCP records the infiltration of magmatic fluids into the Early Cambrian Deep Spring Formation (DSF) containing metaquartzites and metasandstones. Monazites in the DSF < 0.6 km from the contact show patchy zoning and have Th-Pb ages and oxygen isotope compositions similar to monazites in the Birch Creek granite but different from monazites > 0.6 km from the contact, suggesting that they dissolved and reprecipitated in infiltrating magmatic fluids. In contrast, the stable isotope compositions of monazites and host rocks (Proterozoic gneisses and the Cretaceous Ireteba granite) on the flanks of the Searchlight pluton do not show evidence of hydrothermal alteration, even though many of the monazites display patchy zoning and ages corresponding to the Searchlight intrusion. The Searchlight gold-silver-copper mining district is primarily located in the roof of the Searchlight intrusion, which contains rocks that were intensely hydrothermally altered but contain no monazite. Searchlight magmatic fluids were strongly focused into the roof zone, with little or no fluid escaping out the sides of the Searchlight pluton during crystallization. Monazite

  19. Resetting of RbSr ages of volcanic rocks by low-grade burial metamorphism

    USGS Publications Warehouse

    Asmeroma, Y.; Damon, P.; Shafiqullah, M.; Dickinson, W.R.; Zartman, R.E.

    1991-01-01

    We report a nine-point RbSr whole-rock isochron age of 70??3 Ma (MSWD 3.97) for Mid-Jurassic volcanic rocks. The same rocks have also been dated by the UThPb method on zircon, giving a crystallization age of 166 ?? 11 Ma, over twice as old as the RbSr age. The data demonstrate that whole-rock RbSr ages of volcanic rocks, even lava flows with SiO2 content as low as 57 wt.%, are susceptible to complete resetting. The rocks range in composition from rhyodacite tuffs to andesite lavas. The complete breakdown of all major minerals that contain Rb and Sr resulted in an alteration mineral assemblage consisting of phengite, albite, secondary quartz, and minor amounts of chlorite and epidote. Phengite is the K-bearing product of the breakdown of biotite and K-feldspar. Pressure during low-grade metamorphism of the volcanic rocks, estimated from phengite composition to have been in the range of 4 to 6 kbar, points to thrust-related burial as the main cause of resetting. Consequently, such reset isochrons may date large-scale events such as regional thrusting and metamorphism. The coherent resetting of the RbSr isochron suggests large-scale pervasive fluid movement during thrust-related burial metamorphism. ?? 1991.

  20. Thermal history of the H-chondrite parent body: Implications for metamorphic grade and accretionary time-scales

    NASA Astrophysics Data System (ADS)

    Monnereau, Marc; Toplis, Michael J.; Baratoux, David; Guignard, Jérémy

    2013-10-01

    Multiple temperature-age constraints for eight H-chondrite samples have been used to provide insight into the thermal history of their parent-body through combination with numerical models of thermal evolution assuming internal heating by 26Al and conductive cooling. The effect of spreading accretion out over time is the principal focus of this work. A wide range of body size and date of accretion is systematically tested for different values of accretion rate in order to quantify and illustrate the parameter space that is consistent with the available thermo-chronological data. We conclude that the H-chondrite samples considered have a thermal history consistent with a parent body that at some stage had a concentric 'onion-shell' internal structure. That body had a radius no larger than 130 km, and accretion most probably took place over a time interval on the order of 0.0-0.2 Myr, approximately 2 Myr after CAI condensation. In any case, the time interval of accretion is unlikely to have been more than 0.5 Myr supporting evidence in favour of rapid accretion, possibly through reassembly of the fragments of an earlier generation of bodies. Furthermore, the H-chondrites studied here are inferred to have come from a wide depth range within the body where they experienced metamorphism, indicating that preservation of the onion-shell structure is unlikely. The presence of an insulating regolith does not modify this conclusion, as appropriate thermal histories for the three H6 samples considered cannot be reproduced at depths near the surface. Asteroid 6-Hebe may be the parent body of the H-chondrites, but the high bulk density of the latter is difficult to reconcile with a 'rubble-pile' structure of pure H-chondrite material. Finally, optimized thermal histories are used to constrain the temperatures characterizing boundaries between petrological types (800, 1000, and 1140 K for the H3/4, H4/5, and H5/6 boundaries respectively). In detail, the type 6 samples studied

  1. New U-Pb Age and Trace Element Composition of Young Metamorphic Zircon Rims from the UHP Tso Morari Complex, NW Himalaya, Distinguishes Peak from Retrograde Metamorphism

    NASA Astrophysics Data System (ADS)

    Leech, M. L.; Coble, M. A.; Singh, S.; Guillot, S.; Jain, A. K.

    2014-12-01

    The ultrahigh-pressure (UHP) Tso Morari Complex (TMC) sits in the footwall of the Indus-Yarlung suture zone in the NW Himalaya. The timing of metamorphism during subduction and exhumation in the complex is critical to constraining the age of the India-Asia collision. de Sigoyer et al. (2000) and Leech et al. (2005) reported mean U-Pb ages for thin outer rims of sectioned zircon between 55 ± 6 Ma and 53.3 ± 0.7 Ma, respectively, for the age of peak UHP through retrograde metamorphism, and Leech et al. (2005) used these data to calculate the minimum age for the start of continental subduction at 57 ± 1 Ma. Recently published results for the TMC have reignited debate on the age of metamorphism and thus, the timing of India-Asia collision. We used the same TM38 sample analyzed for the results described in Leech et al. (2005) and performed new SIMS U-Pb depth-profiling analyses to target only the outermost ~1.5 micron rims of zircon. Our results yield a mean age of 44.9 ± 0.7 Ma; adjacent spots for REE analyses yielded positive, enriched HREE profiles with negative Eu anomalies and corresponding Ti-in-zircon temperatures of ~550° to 680° C. Sharp boundaries between zircon domains are clearly resolved with CL and BSE imaging of TM38 zircons, and there is a large age difference between rims and protolith core ages; any mixing during depth-profiling through rims is clear. The positive HREE profiles imply the period of zircon growth in the TMC at c. 45 Ma to be retrograde. We suggest that the 47-43 Ma peak ages and flat heavy REE profiles with no Eu anomaly recently reported by Donaldson et al. (2013) on sectioned zircons, and interpreted as the age of UHP metamorphism of the TMC, may actually represent mixing between zircon rims and cores. The Leech et al. (2005) collision age of 57 ± 1 Ma assumed the TMC represents the leading edge of India. However, numerical modeling of Warren et al. (2008) suggests all exhumed material is derived from the central part of the pro

  2. U-Pb ages for sphene in a contact metamorphic zone.

    NASA Technical Reports Server (NTRS)

    Hanson, G. N.; Catanzaro, E. J.; Anderson, D. H.

    1971-01-01

    U-Pb ages have been determined on sphene concentrates from the 2700 my old Giants Range Granite at varying distances from the contact with the 1100 my old Duluth gabbro. As the contact is approached the sphene ages become more discordant and plot along a chord between 1100 and 2700 my on a concordia diagram. The U-Pb ages for sphene in the contact aureole are more resistant to thermal metamorphism than are K-Ar ages for hornblende and biotite. The resistance relative to U-Pb ages for zircon is more difficult to interpret because the zircon U-Pb ages may have become discordant prior to or after 1100 my ago, whereas the U-Pb ages for sphene appear to have had episodic discordance only at 1100 my ago.

  3. Metamorphic conditions and CHIME monazite ages of Late Eocene to Late Oligocene high-temperature Mogok metamorphic rocks in central Myanmar

    NASA Astrophysics Data System (ADS)

    Maw Maw Win; Enami, Masaki; Kato, Takenori

    2016-03-01

    The high temperature (T)/pressure (P) regional Mogok metamorphic belt is situated in central Myanmar, and is mainly composed of pelitic gneisses, amphibolites, marbles, and calc-silicate rocks. The garnet-biotite-plagioclase-sillimanite-quartz assemblage and its partial system suggest equilibrium P/T conditions of 0.6-1.0 GPa/780-850 °C for the peak metamorphic stage, and 0.3-0.5 GPa/600-680 °C for the exhumation and hydration stage. Monazite grains show complex compositional zoning consisting of three segments-I, II, and III. Taking into consideration the monazite zoning and relative misfit curves, the calculated chemical Th-U-total Pb isochron method (CHIME) monazite age data (284 spot analyses) indicated four age components: 49.3 ± 2.6-49.9 ± 7.9, 37.8 ± 1.0-38.1 ± 1.7, 28.0 ± 0.8-28.8 ± 1.6, and 23.7 ± 1.3 Ma (2σ level). The ages of the Late Eocene and Late Oligocene epochs were interpreted as the peak metamorphic stage of upper-amphibolite and/or granulite facies and the postdated hydration stage, respectively.

  4. Thermal histories of CO3 chondrites - Application of olivine diffusion modelling to parent body metamorphism

    NASA Technical Reports Server (NTRS)

    Jones, Rhian H.; Rubie, David C.

    1991-01-01

    The petrologic sequence observed in the CO3 chondrite group has been suggested to be the result of thermal metamorphism on a parent body. A model developed to examine the possibility that chondrule and matrix olivines equilibrated in situ, during parent body metamorphism is presented. The model considers Fe-Mg interdiffusion between chondrule and matrix olivines. Zoning profiles comparable to those observed in chondrule olivines from partially equilibrated members of the series are reproduced successfully. Metamorphism of CO3 chondrites on a parent body is therefore a viable model for the observed equilibration. Results indicate that peak metamorphic temperatures experienced by the CO3 chondrites were around 500 C, and that the range of peak temperatures between unequilibrated and equilibrated subtypes was relatively narrow, around 100 C.

  5. Tectono-metamorphic history of southern New Hampshire and southeastern Vermont

    SciTech Connect

    Chamberlain, C.P.; Lyons, J.B.; Thompson, J.B. Jr.; Rosenfeld, J.L.; Downie, E.

    1985-01-01

    A major boundary between two Acadian metamorphic terranes is marked by a band of low-grade rocks in the Connecticut River valley coinciding with the Monroe Line (ML) and separating higher-grade rocks in two distinct lithostratigraphic terranes. To the west, Cambro-Devonian rocks in the Vermont sequence overlie Grenvillian basement, whereas to the east a different Cambro-Dev. sequence rests upon Hadrynian basement. These terranes were assembled no later than the early Devonian. The eastern terrane, consisting of the Bronson Hill Anticlinorium(BHA) and Merrimack Synclinorium (MS), is bounded on the east by the older Massabesic Gneiss (650-480 my) and Ord (.) Merrimack Group. This southeastern terrane was in contact with the MS by the early Devonian because there is no break in metamorphism across the terrane boundary. Metamorphism in the western terrane (Vermont) is synkinematic and peaks in the Staur-Ky zone. The earliest metamorphism is believed to be Taconian and represents the thermal decay of relict blueschist metamorphism observed to the northwest and the accretion of an island-arc. The earliest metamorphism in the eastern terrane (BHA-MS) is Acadian and is associated with nappe formation and synkinematic plutons. Continued Acadian crustal shortening in the MS resulted in a pressure increase (from 3.8 to 7 kb), with rocks reaching peak metamorphism in the Sil-Mus up to Kspar-Cord zones. The authors suggest that this high-grade metamorphism was the result of a high transient heat flux initiated by crustal stretching in the MS during the Silurian and early Devonian when 8 km of clastics were deposited in a rapidly subsiding trough.

  6. The Sutter's Mill meteorite: Thermoluminescence data on thermal and metamorphic history

    NASA Astrophysics Data System (ADS)

    Sears, Derek W.; Beauford, Robert

    2014-11-01

    A piece of the Sutter's Mill meteorite, fragment SM2-1d, has been examined using thermoluminescence techniques to better understand its thermal and metamorphic history. The sample had very weak but easily measureable natural and induced thermoluminescence (TL) signals; the signal-to-noise ratio was better than 10. The natural TL was restricted to the high-temperature regions of the glow curve suggesting that the meteorite had been heated to approximately 300 °C within the time it takes for the TL signal to recover from a heating event, probably within the last 105 years. It is possible that this reflects heating during release from the parent body, close passage by the Sun, or heating during atmospheric passage. Of these three options, the least likely is the first, but the other possibilities are equally likely. It seems that temperatures of approximately 300 °C reached 5 or 6 mm into the meteorite, so that all but one of the small Sutter's Mill stones have been heated. The Dhajala normalized induced TL signal for SM2-1d is comparable to that of type 3.0 chondrites and is unlike normal CM chondrites, the class it most closely resembles, which do not have detectable TL sensitivity. The shape of the induced TL curve is comparable to other low-type ordinary, CV, and CO chondrites, in that it has a broad hummocky structure, but does not resemble any of them in detail. This suggests that Sutter's Mill is a unique, low-petrographic-type (3.0) chondrite.

  7. Carboniferous U-Pb age of the Sebago batholith, southwestern Maine: metamorphic and tectonic implications.

    USGS Publications Warehouse

    Aleinikoff, J.H.; Moench, R.H.; Lyons, J.B.

    1985-01-01

    Two phases (pink and white granite) of the Sebago batholith have been dated by the U/Pb zircon method. The age of both phases is 325 m.y. Zircon in the pink phase has been reset in intrusion of the Pleasant Mountain stock approx 114 m.y. ago. Zircon in the white phase lost lead only recently. Metamorphic isograds in the vicinity of the batholith approximately parallel its shape, and may be at least partly Hercynian in age. Cooling and uplift of the Sebago batholith appear to have followed a complicated path involving little or no uplift in the Middle Carboniferous to Middle Permian, rapid cooling from 275 to 225 m.y. ago, and a slow cooling since Middle Triassic. Different rates of cooling may be related to changes in the tectonic regime.-L.C.H.

  8. K-Ar ages of allochthonous mafic and ultramafic complexes and their metamorphic aureoles, Western Brooks Range, Alaska

    SciTech Connect

    Boak, J.L.; Turner, D.L.; Wallace, W.K.; Moore, T.E.

    1985-04-01

    New K-Ar ages from allochthonous mafic and ultramafic complexes of the western Brooks Range (Brooks Range ophiolite) show that igneous rocks yielded ages nearly identical to those of underlying metamorphic aureole rocks. Dated rocks of the Misheguk igneous sequence from Tumit Creek consist of (1) hornblende gabbro with minor greenschist and lower grade alteration, hornblende age 147.2 +/- 4.4 Ma; and (2) hornblende-bearing diorite, also slightly altered, age 155.8 +/- 4.7 Ma. Both samples come from presumed higher levels of the Misheguk sequence. Dated samples of metamorphic aureole rocks come from outcrops near Kismilot Creek and lie structurally beneath the Iyikrok Mountain peridotite body. The rocks consist of amphibolite and garnet-bearing biotite-hornblende gneiss considered to be metamorphosed Copter igneous sequence and related sedimentary rocks. Hornblende ages are 154.2 +/- 4.6 Ma and 153.2 +/- 4.6 Ma. metamorphism is clearly related to the structurally overlying perioditite, as the degree of alteration decreases downward. The authors suggest that the K-Ar ages of these rocks represent the effects of thermal metamorphism post-dating igneous crystallization, and are related to tectonic emplacement of the complex. Earlier K-Ar data on igneous rocks give similar ages and have been interpreted as reflecting tectonothermal events. The age of igneous crystallization of the mafic and ultramafic rocks of the Misheguk igneous sequence remains uncertain.

  9. Metamorphic facies map of Southeastern Alaska; distribution, facies, and ages of regionally metamorphosed rocks

    USGS Publications Warehouse

    Dusel-Bacon, Cynthia; Brew, D.A.; Douglass, S.L.

    1996-01-01

    Nearly all of the bedrock in Southeastern Alaska has been metamorphosed, much of it under medium-grade conditions during metamorphic episodes that were associated with widespread plutonism. The oldest metamorphisms affected probable arc rocks near southern Prince of Wales Island and occurred during early and middle Paleozoic orogenies. The predominant period of metamorphism and associated plutonism occurred during Early Cretaceous to early Tertiary time and resulted in the development of the Coast plutonic-metamorphic complex that extends along the inboard half of Southeastern Alaska. Middle Tertiary regional thermal metamorphism affected a large part of Baranof Island.

  10. The West African Mauritanid metamorphic suite of Proterozoic age in the subsurface of peninsular Florida and environs

    SciTech Connect

    Winston, G.O.

    1993-03-01

    A high and low-grade Gondwanan metamorphic terrane is revealed by 14 wells in Florida and environs. Two high-grade metamorphics (gneiss and schist) are located in central Florida and are probably Early Proterozoic in age. The 12 other wells contain low-grade metamorphic suites, principally composed of inter-bedded argillites, acid volcanics and quartzites belonging to the Mauritanid sequence of West Africa. These suites are present in south Georgia, north Florida and offshore; a 3,975-foot section was penetrated in one well. These widespread metamorphic rocks are probably the terrane into which the Cambrian Osceola granite of central Florida was intruded. The two grades of metamorphics represent Early and Late Proterozoic episodes of sedimentation, each followed by metamorphism and erosion. Lower Ordovician to Devonian sediments were deposited on this terrane in southern Georgia and northern Florida. In the Early Jurassic, volcanics completely covered southern Florida, concealing the nature of the old underlying surface. Younger Mesozoic sediments eventually buried the entire Pre-Cambrian-Lower Jurassic terrane.

  11. Thermal history of the Maramureş area (Northern Romania) constrained by zircon fission track analysis: Cretaceous metamorphism and Late Cretaceous to Paleocene exhumation

    NASA Astrophysics Data System (ADS)

    Gröger, Heike R.; Tischler, Matthias; Fügenschuh, Bernhard; Schmid, Stefan M.

    2013-10-01

    This study presents zircon fission track data from the Bucovinian nappe stack (northern part of the Inner Eastern Carpathians, Rodna Mountains) and a neighbouring part of the Biharia nappe system (Preluca massif) in order to unravel the thermal history of the area and its structural evolution by integrating the fission track data with published data on the tectonic and sedimentary evolution of the area. The increase of metamorphic temperatures towards the SW detected by the zircon fission track data suggests SW-wards increasing tectonic overburden (up to at least 15 km) and hence top NE thrusting. Sub-greenschist facies conditions during the Alpine metamorphic overprint only caused partial annealing of fission tracks in zircon in the external main chain of the Central Eastern Carpathians. Full annealing of zircon points to at least 300 °C in the more internal elements (Rodna Mountains and Preluca massif). The zircon fission track central and single grain ages largely reflect Late Cretaceous cooling and exhumation. A combination of fission track data and stratigraphic constraints points to predominantly tectonic differential exhumation by some 7-11 km, connected to massive Late Cretaceous extension not yet detected in the area. Later events such as the latest Cretaceous ("Laramian") juxtaposition of the nappe pile with the internal Moldavides, causing exhumation by erosion, re-burial by sedimentation and tectonic loading during the Cenozoic had no impact on the zircon fission track data; unfortunately it prevented a study of the low temperature part of the Late Cretaceous exhumation history.

  12. Modelling of the thermal history of metamorphic zoning in the Connemara region (western Ireland)

    NASA Astrophysics Data System (ADS)

    Reverdatto, V. V.; Polyansky, O. P.

    2004-02-01

    The Connemara region of the Irish Caledonides is a classic example of regional-scale metamorphism of low pressure and high temperature. This terrane is considered as part of a fold belt comprising metasedimentary and metavolcanic rocks that are correlated with the Neoproterozoic-Lower Paleozoic Dalradian Supergroup of Scotland. In mid-Ordovician time, the extensive and high-temperature metamorphism was superimposed on the Dalradian rocks resulting in the Connemara zoning. The key feature of the zoning is elevated horizontal thermal gradient of ca. 14 °C/km. Geological data and geochronological evidence point to a causative link between metamorphism and associated magmatic intrusions, and a brief period of development for the metamorphic zoning. Magmatic intrusion into the middle part of continental crust is treated as a most plausible source of heat for metamorphism, and other conjectures as to the origin of the zoning (flow of hot fluid through the permeable rocks, fracture conduit flushed by flowing magma) are believed to be improbable. To examine in sufficient detail the problem of the nature of heat source, a series of appropriate calculations have been performed to reach the best agreement between the observed and simulated spatial distribution of maximum temperatures at different times. The mathematical modelling shows that the temperature-spatial structure of the Connemara zoning is best explained by the model version based on mid-crustal heating above the upper contact of magmatic intrusive body gently curved and tilted at an angle between 20° and 40°, with an initial temperature of the magma appropriate to a basaltic melt. The model estimate of total lifetime of the temperature anomaly in the crust is of the order of 5-6 Ma. In general, this is in rather good agreement with the currently available evidence of geochronological duration of metamorphism and magmatism in Connemara.

  13. Monazite Growth from the Eocene to the Miocene: New Interpretations of the Metamorphic History of Greater Himalayan Rocks in the Eastern Himalaya

    NASA Astrophysics Data System (ADS)

    Gordon, S. M.; Kauffman, R.; Gonzales-Clayton, B.; Long, S. P.; Kylander-Clark, A. R.

    2015-12-01

    Across the Himalaya, mid- to lower-crustal Greater-Himalayan (GH) rocks have been exhumed during active continent-continent collision. In the eastern Himalaya within Bhutan, GH rocks are divided into an upper and lower level by an intra-GH shear zone, the Kakthang thrust (KT). To decipher the metamorphic, melt-crystallization and exhumation history of the GH rocks exposed above and below the KT, monazite from metapelites and migmatites was dated and trace elements were analyzed by laser-ablation, split-stream ICPMS. The trace elements from the monazite were used to track when the rocks were at near-peak conditions (based on the depletion of HREE and the likely presence of garnet during monazite growth) versus likely undergoing initial exhumation and garnet breakdown (based on an increase in HREE). Samples were collected from two N-S transects that cross the KT in central and eastern Bhutan. The eastern transect reveals a progressive younging of near-peak metamorphism within the GH, with dates of ca. 23-20 Ma for the structurally-highest sample versus ca. 18-16 Ma in the structurally-lowest sample. The youngest dates from all structural levels of the eastern Bhutan metapelites are 13-15 Ma; the same analyses yield higher HREE abundances, suggesting garnet breakdown during their (re)crystallization. The migmatites yield ca. 14-16 Ma melt-crystallization ages, consistent with the GH having undergone cooling and initial exhumation to cause garnet breakdown by ca. 15 Ma. In comparison, the central Bhutan transect reveals older near-peak metamorphic ages, with garnet-stable monazite populations at ca. 48­-46 Ma within the KT zone, ca. 38-30 Ma for rocks in the middle of the upper-GH, and ca. 25-22 Ma for the structurally-highest sample. Youngest monazites from the central Bhutan transect that yield growth or recrystallization at garnet-unstable conditions range from ca. 17-26 Ma. These results suggest earlier metamorphism and exhumation of GH rocks in central Bhutan

  14. Metamorphic evolution of the Rechnitz metamorphic core complex in relation to the Neogene Pannonian basin, Eastern Alps: Constraints from Ar-Ar white mica ages

    NASA Astrophysics Data System (ADS)

    Cao, Shuyun; Neubauer, Franz; Genser, Johann; Bernroider, Manfred; Friedl, Gertrude

    2015-04-01

    The exhumation of Cordilleran-type metamorphic core complexes (MCC) is generally related to largely contemporaneous collapse-type sedimentary basins (mainly halfgrabens). Here, we investigate the example of the Rechnitz MCC, which formed by Miocene orogen-parallel extension within the Neogene Pannonian basin. The Rechnitz MCC is located on the South Burgenland basement High within the western part of the Neogene Pannonian basin, with the Styrian basin in the west and the Danube basin in the east. The Rechnitz MCC is metamorphosed within greenschist facies conditions (maximum temperature of 430 °C) ideal for Ar-Ar white mica dating. For the first time, we undertook an extensive survey of 40Ar/39Ar white mica dating combined with microfabrics and electron microprobe compositional data and we compare the new data with major evolutionary stages of adjacent sedimentary basins, mainly based on re-evaluation of existing reflection seismic lines. The internal structure of the Rechnitz window is characterized by two tectonic cover nappes, a lower nappe with distal continental affinity, and an upper nappe representing the infilling of an oceanic basin. Both within greenschist facies metamorphic conditions and few blueschists were found in the northwestern part of the upper nappe. We found a number of distinct white mica age spectra: (1) A sample from the northwesternmost upper nappe yield a staircase pattern ranging from 14.8 ± 0.9 Ma to 41.5 ± 1.0 Ma. We interpret the older age is minimum age of high-pressure metamorphism and the younger age as age of overprint during extensional exhumation. (2) A number of samples from the western part, independent from positions within the nappes yield plateau ages between 20 and maximum 23 Ma and are variably affected by a younger thermal overprint between 13 and 15 Ma. (3) The eastern and lower units show plateau-like patterns with plateau ages of 17 - 19 Ma with a majority at ca. 18 Ma and a single younger outlier at ca. 16 Ma. Some

  15. Metamorphic history of a high-grade blueschist exotic block from the Franciscan complex, California.

    USGS Publications Warehouse

    Moore, Diane E.

    1984-01-01

    A tectonic block (approx 6 m in diameter) in the NE Diablo Range shows evidence of three episodes of retrograde blueschist-facies metamorphism + or - deformation under progressively declining P-T conditions. Retrograde metamorphism began with the tectonic incorporation of fragments of the original metamorphic terrain into serpentinite, which provided Mg-bearing fluids for the reactions of both the first and second retrograde events. There is extensive CaCO3 veining which matches that of the associated metasediments. In the third retrograde event, aragonite crystallized, accompanied by lawsonite, chlorite, jadeitic pyroxene and crossite. Such tectonic blocks may have originally formed in a pre-Franciscan subduction zone setting; fragments of blueschist and eclogite from this metamorphic terrain were tectonically incorporated in a serpentinite diapir and developed alteration zones against the enclosing ultramafic rock. When the serpentinite reached the Earth's surface, such blocks were transferred to the Franciscan as detritus and were then re-subducted and metamorphosed along with their associated sedimentary sequences.-R.A.H.

  16. Chemical and physical studies of type 3 chondrites 12: The metamorphic history of CV chondrites and their components

    NASA Technical Reports Server (NTRS)

    Guimon, R. Kyle; Symes, Steven J. K.; Sears, Derek W. G.

    1995-01-01

    The induced thermoluminescence (TL) properties of 16 CV and CV-related chondrites, four CK chondrites and Renazzo (CR2) have been measured in order to investigate their metamorphic history. The petrographic, mineralogical and bulk compositional differences among the CV chondrites indicate that the TL sensitivity of the approximately 130 C TL peak is reflecting the abundance of ordered feldspar, especially in chondrule mesostasis, which in turn reflects parent-body metamorphism. The TL properties of 18 samples of homogenized Allende powder heated at a variety of times and temperatures, and cathodoluminescence mosaics of Axtell and Coolidge, showed results consistent with this conclusion. Five refractory inclusions from Allende, and separates from those inclusions, were also examined and yielded trends reflecting variations in mineralogy indicative of high peak temperatures (either metamorphic or igneous) and fairly rapid cooling. The CK chondrites are unique among metamorphosed chondrites in showing no detectable induced TL, which is consistent with literature data that suggests very unusual feldspar in these meteorites. Using TL sensitivity and several mineral systems and allowing for the differences in the oxidized and reduced subgroups, the CV and CV-related meteorites can be divided into petrologic types analogous to those of the ordinary and CO type 3 chondrites. Axtell, Kaba, Leoville, Bali, Arch and ALHA81003 are type 3.0-3.1, while ALH84018, Efremovka, Grosnaja, Allende and Vigarano are type 3.2-3.3 and Coolidge and Loongana 001 are type 3.8. Mokoia is probably a breccia with regions ranging in petrologic type from 3.0 to 3.2. Renazzo often plots at the end of the reduced and oxidized CV chondrite trends, even when those trends diverge, suggesting that in many respects it resembles the unmetamorphosed precursors of the CV chondrites. The low-petrographic types and low-TL peak temperatures of all samples, including the CV3.8 chondrites, indicates metamorphism

  17. Geology and geochronology of granitoid and metamorphic rocks of late Archean age in northwestern Wisconsin

    USGS Publications Warehouse

    Sims, P.K.; Peterman, Z.E.; Zartman, R.E.; Benedict, F.C.

    1985-01-01

    Granitoid rocks of the Puritan Quartz Monzonite and associated biotite gneiss and amphibolite in northwestern Wisconsin compose the southwestern part of the Puritan batholith of Late Archean age. They differ from rocks in the Michigan segment of the batholith in having been deformed by brittle-ductile deformation and partly recrystallized during shearing accompanying development of the midcontinent rift system of Keweenawan (Middle Proterozoic) age. Granitoid rocks ranging in composition from granite to tonalite are dominant in the Wisconsin part of the batholith. To the north of the Mineral Lake fault zone, they are massive to weakly foliated and dominantly of granite composition, whereas south of the fault zone they are more strongly foliated and mainly of tonalite composition. Massive granite, leucogranite, and granite pegmatite cut the dominant granitoid rocks. Intercalated with the granitoid rocks in small to large conformable bodies are biotite gneiss, amphibolite, and local tonalite gneiss. Metagabbro dikes of probable Early Proterozoic age as much as 15 m thick cut the Archean rocks. Rubidium-strontium whole-rock data indicate a Late Archean age for the granitoids and gneisses, but data points are scattered and do not define a single isochron. Zircon from two samples of tonalitic gneiss for uranium-thorium-Iead dating define a single chord on a concordia diagram, establishing an age of 2,735?16 m.y. The lower intercept age of 1,052?70 m.y. is in close agreement with rubidium-strontium and potassium-argon biotite ages from the gneisses. Two episodes of deformation and metamorphism are recorded in the Archean rocks. Deformation during the Late Archean produced a steep west-northwest-oriented foliation and gently plunging fold axes and was accompanied by low amphibolite-facies metamorphism of the bedded rocks. A younger deformation resulting from largely brittle fracture was accompanied by retrogressive metamorphism; this deformation is most evident adjacent

  18. Sr-isotopic composition of marbles from the Puerto Galera area (Mindoro, Philippines): additional evidence for a Paleozoic age of a metamorphic complex in the Philippine island arc

    SciTech Connect

    Knittel, U.; Daniels, U.

    1987-02-01

    The Sr-isotopic composition of marbles from the Puerto Galera area (Mindoro, Philippines) is compatible with either a Tertiary or a Paleozoic age. The former is considered as unlikely because nonmetamorphic sediments of that age overlie the metamorphic complex. This implies that the metamorphic complex does not represent the basement of the Philippine arc but is an accreted terrane.

  19. Timing of HP metamorphism in the Schistes Lustrés of Alpine Corsica: New Lu-Hf garnet and lawsonite ages

    NASA Astrophysics Data System (ADS)

    Vitale Brovarone, Alberto; Herwartz, Daniel

    2013-07-01

    Alpine Corsica is crucial in understanding Western Mediterranean geodynamics. Available paleotectonic models attribute the high-pressure terrains of Corsica to the Western Alps (east dipping subduction), or to the Apennines (west-dipping subduction) or to a flip from one to the other subduction zone. Constraints on the timing of high-pressure metamorphism in Alpine Corsica are sparse and ages range from Late Cretaceous to Late Eocene. This represents a major point of debate. Here we present high-precision garnet Lu-Hf ages for three samples from the highest grade, Lawsonite-eclogite unit yielding ages of 34.23 ± 1.6 Ma; 34.11 ± 0.89 Ma, 34.65 ± 0.55 Ma. In addition to the well-established garnet dating, we employed lawsonite Lu-Hf analyses on a lawsonite-bearing (garnet-free) metagabbro from the neighboring lawsonite-blueschist unit that yielded an age of 37.5 ± 1.3 Ma. Because metamorphic temperatures of the eclogite-facies samples (ca. 500-550 °C) are below the Lu-Hf closure temperature in garnet and since the eclogitic garnet displays a core-to-rim increase in Mn concentrations typical of prograde zoning, we attribute the above Lu-Hf ages to prograde subduction metamorphism. Similarly, the age of lawsonite in the blueschist-facies unit can be safely referred to prograde-peak conditions based on the available clockwise metamorphic path. The slightly older age of the lawsonite-blueschist sample suggests a diachronous timing in the achievement of high-pressure conditions in the eclogite and in the blueschist facies units. Since both units are thought to derive from a former ocean-continent transition zone, our geochronological data provide precise time constraints to the subduction history of Alpine Corsica in the frame of the Western Mediterranean geodynamics. Our data provide Late Eocene ages for the subduction event in Corsica, which are significantly younger than previously published Cretaceous ages. This calls for partial revision of the current

  20. Exploiting Quartz to Constrain Pressure-Temperature-time-Deformation Histories in Metamorphic Rocks Through Recent Innovations in Thermobarometry and Geospeedometry

    NASA Astrophysics Data System (ADS)

    Ashley, Kyle; Law, Richard; Thomas, Jay; Caddick, Mark; Stahr, Donald, III

    2013-04-01

    Despite the abundance of quartz in continental crust, it has only recently been exploited for thermobarometric purposes. We are using trace element content, cathodoluminescence (CL) characteristics, fabric properties, extent of recrystallization, elastic properties and chemical diffusivities of quartz to better understand the pressure-temperature-time-deformation (P - T - t - D) histories of metamorphic rocks. The Ti-in-quartz thermobarometer has significant potential for unveiling important information on the metamorphic history of rocks, since quartz is commonly present in multiple microstructural settings (e.g. matrix, veins, inclusions) and zoning may be present in single crystals that reveal information about the reequilibration, recrystallization and growth histories of quartz. CL imaging provides a qualitative way to obtain such information, and provides a domainal framework for targeted quantitative analyses. We illustrate such analyses with examples from Vermont, India and Greece. A recent study in metapelites from central-eastern Vermont revealed crystals that have low Ti cores (interpreted to be preserved early prograde growth), with mantles that grade to higher Ti, attributed to temperature increase during fabric development and liberation of Si during crenulation cleavage development in the micaceous matrix. Low-Ti overgrowth rims that form sharp boundaries with these graded mantles may be later retrograde overgrowths. Forward modeling the expected volume of quartz present in the rock in P - T space may be implemented to confirm periods of quartz production/precipitation and dissolution. Rocks from the Sutlej Valley (north-west India) have matrix quartz grains with triple junction grain boundaries indicating extensive recovery. CL imaging, however, reveals high Ti ribbons that may be indicative of chemically-preserved paleo-microstructures. At the temperatures and metamorphic rates experienced by these samples, grain boundaries during recovery may not

  1. Metamorphic and age constraints on tectono-thermal reworking in the western H.U. Sverdrupfjella: A new crustal evolution model for Western Dronning Maud Land, Antarctica

    NASA Astrophysics Data System (ADS)

    Grosch, Eugene; Frimmel, Hartwig; Abu-Alam, Tamer; Košler, Jan

    2014-05-01

    Western Dronning Maud Land (WDML) of East Antarctica is argued to consist of two major crustal domains, namely the low-grade Archaean Kalahari-Grunehogna Craton and the high-grade Maud belt (e.g. Grantham et al., 1995; Jacobs et al. 2008). The geodynamic and tectono-thermal crustal evolution histories of these two proposed domains remain a debated topic in Rodinia and Gondwana reconstructions. In this study we conducted a petrological and metamorphic comparison of Mesoproterozoic metabasic rocks on the eastern margin of the Archaean Grunehogna Craton and the adjacent westernmost Maud Belt, across a major structural discontinuity known as the Pencksökket-Jutulstraumen Discontinuity (PJD). As such we evaluate to what extent the two domains of WDML represent independent crustal growth and metamorphic histories. Metamorphic constraints on low-grade rocks on the eastern Grunehogna craton record greenschist facies conditions of T = 340 ± 25oC and P = 2.9 ± 0.8 kbar. The high-grade PT-constraint of T =700 ± 30oC and P = 9.0 ± 2 kbar for the western extreme of the Maud Belt, derived from garnet-hornblende-plagioclase-quartz geothermobarometry and phase diagram modeling in PERPLEX, is very similar to that reported for the eastern Maud Belt and thus, does not support the concept of a westward decreasing metamorphic field gradient within the Maud Belt as previously proposed. Laser-ablation-ICP-MS U-Pb dating of titanite in a hornblende-plagioclase-quartz symplectite (after garnet breakdown), yielded a Pan-African age for high-grade metamorphism in the westernmost Maud belt, which overlaps with the age of tectonic decompression in the eastern Maud Belt. The new U-Pb age data argues against previous models that invoke only late-Mesoproterozoic high-grade metamorphism in the western Maud Belt. The new petrological data indicate that the inferred sub-glacial boundary (PJD) between the Grunehogna Craton and the Maud Belt, represents a major metamorphic hiatus as a Pan

  2. K-Ar ages of metamorphic rocks at the base of the Samail ophiolite, Oman

    SciTech Connect

    Lanphere, M.A.

    1981-04-10

    Hornblendes from amphiobolities in the sheet of metamorphic rocks beneath the peridotite member of the Samail ophiolite and phyllites farther from the peridotite contact have weighted mean /sup 40/Ar//sup 39/Ar total fusion ages of 90.0 +- 3.0 m.y. and 79.5 +- 3.0 m.y., respectively. The amphibolities represent the first tectonic slice welded to the base of the Samail ophiolite after it was detached from the Tethyan oceanic crust. Formation of the amphiobolities occurred no more than 3 to 7 m.y. after crystallization of plagiogranite in the ophiolite. The phyllites represent another tectonic slice of ocean floor sediments welded to the ophiolite as it was transported further from the Tethyan spreading axis. The K-Ar ages suggest, assuming a half-spreading rate of 2 to 5 cm/yr, that detachment of the Samail ophiolite and formation of amphibolite facies rocks occurred no more than 60 to 350 km from spreading center. Using the same spreading rate, one can calculate a minimum half width of 300 to 750 km for the Tethyan Ocean during the Late Cretaceous.

  3. The problem of the age and structural position of the Blyb metamorphic complex (Fore Range zone, Great Caucasus) granitoids.

    NASA Astrophysics Data System (ADS)

    Kamzolkin, Vladimir; Latyshev, Anton; Ivanov, Stanislav

    2016-04-01

    The Blyb metamorphic complex (BMC) of the Fore Range zone is one of the most high-grade metamorphosed element of the Great Caucasus fold belt. Determination of the timing and the mechanism of formation of the Fore Range fold-thrust structures are not possible without investigation of the BMC located at the basement of its section. At the same time, the conceptions about its structure and age are outdated and need revision. Somin (2011) determined the age of the protolith and metamorphism of the Blyb complex as the Late Devonian - Early Carboniferous. We have recently shown that the BMC has not the dome, as previously thought, but nappe structure (Vidjapin, Kamzolkin, 2015), and is metamorphically coherent with the peak metamorphism pressures up to 22 kbar (Kamzolkin et al., 2015; Konilov et al., 2013). Considering the age and structure of the Blyb complex it is necessary to revise the age of granitoid intrusions and their relations with gneisses and schists, which constitute the main part of the section of the complex. Most authors (Gamkrelidze, Shengelia, 2007; Lavrischev, 2002; Baranov, 1967) adheres to Early Paleozoic age of intrusives, which is doubtful, considering the younger age of metamorphic rocks. We suppose, that the intrusive bodies broke through a BMC nappe structure during the exhumation of the complex (Perchuk, 1991) at the Devonian - Carboniferous boundary. Seemingly, the massive monzodiorites body (Lavrischev, 2002), intruding garnet-muscovite schists and amphibolite gneisses of the Blyb complex and cut by the Main Caucasian fault (MCF), are younger. Given the timing of termination of the MCF movement activity as the Middle Jurassic (Greater Caucasus..., 2005), their age should be in the Early Carboniferous - Middle Jurassic interval. At the same time, on the modern geological map (Lavrischev, 2002) monzodiorites body is assigned to the Middle Paleozoic. The study of the BMC granitoids and monzodiorites will help in determining of the mechanism and

  4. Mesozoic thermal history and timing of structural events for the Yukon-Tanana Upland, east-central Alaska: 40Ar/39Ar data from metamorphic and plutonic rocks

    USGS Publications Warehouse

    Dusel-Bacon, C.; Lanphere, M.A.; Sharp, W.D.; Layer, P.W.; Hansen, V.L.

    2002-01-01

    We present new 40Ar/39Ar ages for hornblende, muscovite, and biotite from metamorphic and plutonic rocks from the Yukon-Tanana Upland, Alaska. Integration of our data with published 40Ar/39Ar, kinematic, and metamorphic pressure (P) and temperature (T) data confirms and refines the complex interaction of metamorphism and tectonism proposed for the region. The oldest metamorphic episode(s) postdates Middle Permian magmatism and predates the intrusion of Late Triassic (215-212 Ma) granitoids into the Fortymile River assemblage (Taylor Mountain assemblage of previous papers). In the eastern Eagle quadrangle, rapid and widespread Early Jurassic cooling is indicated by ???188-186 Ma 40Ar/39Ar plateau ages for hornblende from plutons that intrude the Fortymile River assemblage, and for metamorphic minerals from the Fortymile River assemblage and the structurally underlying Nasina assemblage. We interpret these Early Jurassic ages to represent cooling resulting from northwest-directed contraction that emplaced the Fortymile River assemblage onto the Nasina assemblage to the north as well as the Lake George assemblage to the south. This cooling was the final stage of a continuum of subduction-related contraction that produced crustal thickening, intermediate- to high-P metamorphism within both the Fortymile River assemblage and the structurally underlying Lake George assemblage, and Late Triassic and Early Jurassic plutonism in the Fortymile River and Nasina assemblages. Although a few metamorphic samples from the Lake George assemblage yield Jurassic 40Ar/39Ar cooling ages, most yield Early Cretaceous 40Ar/39Ar ages: hornblende ???135-115 Ma, and muscovite and biotite ???110-108 Ma. We interpret the Early Cretaceous metamorphic cooling, in most areas, to have resulted from regional extension and exhumation of the lower plate, previously tectonically thickened during Early Jurassic and older convergence.

  5. Interpretation of ages of arc magmatism, metamorphism, and collisional tectonics in the taconian orogen of western New England

    USGS Publications Warehouse

    Ratcliffe, N.M.; Hames, W.E.; Stanley, R.S.

    1998-01-01

    Available geochronologic ages of volcanic and intrusive rocks of the Taconian arc complex of western New England suggest that the Shelburne Falls and Bronson Hill arcs are not temporally or spatially discrete. Arc activity ranges from earliest Ordovician to Silurian. Activity in the Early and Middle Ordovician coincided with outboard accretionary tectonics and metamorphism that was contemporaneous with the older igneous activity in the Shelburne Falls arc and Bronson Hill arcs. Activity at about 455 to 445 Ma coincides with the collisional stage of the Taconian orogeny that affected Caradocian and older rocks of the Laurentian margin. The 455 to 445 Ma range for the collisional stage of Taconian orogeny in western New England is bracketed by biostratigraphic ages of sedimentary rocks formed on the Laurentian margin and 40Ar/39Ar ages of prograde hornblende formed during Taconian metamorphism. The previous 40Ar/39Ar age estimate of 465 Ma for this collisional and metamorphic event is now known to be too old because this age violates the age of metasedimentary rocks involved in the collisional tectonics. Acceptance of the newer 40Ar/39Ar age estimates of 445 to 450 Ma for Taconian metamorphism during collision establishes the contemporaneity with arc activity in the Bronson Hill arc. Taken together these data support the concept of a long-lived volcanic arc terrane(s) that prograded oceanward. Collision with this time-composite arc terrane(s) in the Caradocian produced the Taconian orogeny rather than the collision of a separate and smaller arc called the "Shelburne Falls arc" by Karabinos and others (1998).

  6. A Petrographic History of Martian Meteorite ALH84001: Two Shocks and an Ancient Age

    NASA Technical Reports Server (NTRS)

    Treiman, Allan H.

    1995-01-01

    ALH84001 is an igneous meteorite, an orthopyroxenite of martian origin. It contains petrographic evidence of two shock metamorphic events, separated by thermal and chemical events. The evidence for two shock events suggests that ALH84001 is ancient and perhaps a sample of the martian highlands. From petrography and mineral chemistry, the history of ALH84001 must include: crystallization from magma, a first shock (impact) metamorphism, thermal metamorphism, low-temperature chemical alteration, and a second shock (impact) metamorphism. Originally, ALH84001 was igneous, an orthopyroxene-chromite cumulate. In the first shock event, the igneous rock was cut by melt-breccia or cataclastic veinlets, now bands of equigranular fine-grained pyroxene and other minerals (crush zones). Intact fragments of the cumulate were fractured and strained (now converted to polygonized zones). The subsequent thermal metamorphism (possibly related to the first shock) annealed the melt-breccia or cataclastic veinlets to their present granoblastic texture and permitted chemical homogenization of all mineral species present. The temperature of metamorphism was at least 875 C, based on mineral thermometers. Next, Mg-Fe-Ca carbonates and pyrite replaced plagioclase in both clasts and granular bands, producing ellipsoidal carbonate globules with sub-micron scale compositional stratigraphy, repeated identically in all globules, The second shock event produced microfault offsets of carbonate stratigraphy and other mineral contacts, radial fractures around chromite and maskelynite, and strain birefringence in pyroxene. Maskelynite could not have been preserved from the first shock event, because it would have crystallized back to plagioclase. The martian source area for ALH84001 must permit this complex, multiple impact history. Very few craters on young igneous surfaces are on or near earlier impact features. It is more likely that ALH84001 was ejected from an old igneous unit (Hesperian or

  7. Metamorphic history of LP/HT migmatites from the Bavarian Unit (Bohemian Massif)

    NASA Astrophysics Data System (ADS)

    Sorger, Dominik; Hauzenberger, Christoph; Linner, Manfred; Iglseder, Christoph

    2016-04-01

    Granulite facies migmatites are commonly observed in the Bavarian Unit which were formed during a late Variscan (post 330 Ma) LP-HT overprint. This event is related to a delamination of mantle lithosphere and subsequent asthenospheric upwelling. Most of these rocks underwent high degrees of melting forming meta- and diatexites. Former work in the Sauwald area, Upper Austria, by Tropper et al. (2006) determined metamorphic conditions of 700-800°C and 0.4-0.5 Gpa. In this study samples were taken along the (1) Danube valley (west of Linz), from the (2) Lichtenberg area (north of Linz), the (3) Bad Leonfelden area (west of the Rodl Fault) and the (4) Sauwald area (south of the river Danube). Biotite and plagioclase bearing migmatite is very common and occurs all over the investigated area. These rocks are the product of intensive melting (anatexite) and formed at conditions of ~650-700°C and 0.25-0.45 Gpa. Scarce outcrops of garnet bearing Al-rich migmatitic metapelites occur along the Danube valley. The formation of the migmatitc texture with well-developed leucosomes (K-feldspar, plagioclase, quartz) and melanosomes (garnet, cordierite, sillimanite, spinel, ilmenite, ± biotite) indicate high temperature metamorphism. Most of the garnet grains show a homogenous iron-rich composition and form generally an almandine-pyrope (Xalm=0.78-0.80, Xprp=0.16-0.18) solid solution with minor contents of grossular and spessartine (Xgrs=0.028-0.032, Xsps=0.020-0.024). Large garnet porphyroblasts (up to 1cm in size) display a distinct chemical zoning, especially in grossular component. Elevated homogeneous grossular content in the core is followed discontinously by low grossular content at the rim indicating a two stage growth. Garnet core and rim also display different mineral inclusions. Thermobarometric calculations using garnet core compositions with inclusions and garnet rim compositions with matrix phases as well as pseudosection calculations allow the reconstruction of a P

  8. Two-dimensional numerical modeling of tectonic and metamorphic histories at active continental margins

    NASA Astrophysics Data System (ADS)

    Gerya, Taras; Stöckhert, Bernhard

    2006-04-01

    : (a) an accretionary complex of low-grade metamorphic sedimentary material; (b) a wedge of mainly continental crust, with medium-grade HP metamorphic overprint, wound up and stretched in a marble cake fashion to appear as nappes with alternating upper and lower crustal provenance, and minor oceanic or hydrated mantle interleaved material; (c) a megascale melange composed of high-pressure and ultrahigh-pressure metamorphic oceanic and continental crust, and hydrated mantle, all extruded from the subduction channel; (d) zone represents the upward tilted frontal part of the remaining upper plate lid in the case of a weak upper crust. The shape of the P T paths and the time scales correspond to those typically recorded in orogenic belts. Comparison of the numerical results with the European Alps reveals some similarities in their gross structural and metamorphic pattern exposed after collision. A similar structure may be developed at depth beneath the forearc of the Andes, where the importance of subduction erosion is well documented, and where a strong upper crust forms a stable lid.

  9. Protracted tectono-metamorphic history of the SE Superior Province : contribution of 40Ar/39Ar thermochronology in the Abitibi-Opatica contact zone, Québec, Canada

    NASA Astrophysics Data System (ADS)

    Daoudene, Yannick; Tremblay, Alain; Ruffet, Gilles; Leclerc, François; Goutier, Jean

    2015-04-01

    of an important sub-vertical shearing deformation as expected if it was a major upper plate-lower plate boundary. Furthermore, the contact does not present significant metamorphic break between the two domains, but a progressive increasing of metamorphism toward the OSP, from greenschist- to amphibolite-facies conditions. Based on these structural and metamorphic characteristics, we suggest that the OSP exposes the deepest rocks at outcrop of an ASP-OSP crust in the study area. Regionally, the 40Ar/39Ar ages acquired during this study indicate that the ASP-OSP contact records a protracted metamorphic history that started around 2685 Ma. The structural and isotopic age data suggest that, from ~2685 Ma to ~2632 Ma, the deepest level of the ASP and the underlying OSP reached amphibolite-facies metamorphic conditions and that regional deformation was accommodated by an overall horizontal shortening and sub-vertical transfers of crustal material. Subsequently, the cooling of these crustal rocks was accompanied by strain localisation, which led to the development of oblique strike-slip shear zones from ~2600 Ma, when the lateral flowing of crustal material became predominant. Our 40Ar/39Ar data compared with metamorphic ages documented in adjacent areas of the Superior Province suggests that the peak and duration of regional metamorphism might have been coeval over a large region. This rather favours a mode of pervasive deformation as expected in vertical tectonics.

  10. Mineral inclusions in zircons of S-type granite: implications for high pressure metamorphism history of meta-sedimentary rocks in the Huai'an terrain, North China Craton

    NASA Astrophysics Data System (ADS)

    Wang, Haozheng; Zhang, Huafeng; Zhai, Mingguo; Cui, Xiahong

    2016-04-01

    The Paleoproterozoic evolution of North China Craton (NCC) arises many argument as geologists have different viewpoints on the distribution and metamorphic history of mafic granulites and granulite facies meta-sedimentary rocks. To provide more evidence of constraining the metamorphic history of granulite facies meta-sedimentary rocks, we select granulite facies meta-sedimentary rocks and co-existing S-type granite in the Huai'an terrain to make a deep research. Magmatic zircons derived from the S-type granite reveal the magmatic age of ˜1.95 Ga and metamorphic age of ˜1.85 Ga with ɛHf(t) value of -4.5 - -0.5. The ɛHf(t) value of S-type granite and relict of garnet-sillimanite gneiss suggest that the S-type granite is generated by melting of meta-sedimentary rocks. Zircons with ages of ˜1.95 Ga and ˜1.85 Ga have the mineral inclusions of Ky + Qz + Ru + Pl and these mineral inclusions are determined by method of Laser-Raman. The ˜1.95 Ga magmatic zircons with inclusions of Ky + Qz + Ru + Pl suggest that meta-sedimentary rocks have mineral assemblages Ky + Qz + Ru + Pl. However, previous studies in the Huai'an terrain showed that almost granulite facies metamorphic condition of meta-sedimentary rocks were regarded as medium pressure by considering the Sill + Grt + Bt + Pl + Qz + Ru + Kf. Presence of kyanite instructs that meta-sedimentary rocks may experience high pressure granulite facies metamorphism. According to pseudosection calculation by using effective bulk composition of garnet-sillimanite gneiss, mineral assemblage of Grt + Ky + Pl + Bt + Qz + Ru + Kf is regarded as the peak stage of high pressure metamorphism. This mineral assemblage is occurred at field of 1033 - 1123 K and 9 - 15 Kbar and the peak pressure is around 11 - 13 Kbar, determined by the XMg and XCa isopleths of garnet. This P-T result is consistent with peak condition of high pressure mafic granulite. Considering the ˜1.95 Ga magmatic age of S-type granite generated by decompression

  11. Different radiation and metamorphic history of the Kainsaz CO 3.2 chondrules

    NASA Technical Reports Server (NTRS)

    Kashkarov, L. L.; Kalinina, G. V.

    1993-01-01

    Track and thermoluminescence parameters in chondrules from the Kainsaz CO 3.2 chondrite have been studied. Obtained results elucidate their individual shock-thermal history and the early pre-accretion stage of the meteorite parent body formation.

  12. Age constraints on felsic intrusions, metamorphism and gold mineralisation in the Palaeoproterozoic Rio Itapicuru greenstone belt, NE Bahia State, Brazil

    USGS Publications Warehouse

    Mello, E.F.; Xavier, R.P.; McNaughton, N.J.; Hagemann, S.G.; Fletcher, I.; Snee, L.

    2006-01-01

    U-Pb sensitive high resolution ion microprobe mass spectrometer (SHRIMP) ages of zircon, monazite and xenotime crystals from felsic intrusive rocks from the Rio Itapicuru greenstone belt show two development stages between 2,152 and 2,130 Ma, and between 2,130 and 2,080 Ma. The older intrusions yielded ages of 2,152??6 Ma in monazite crystals and 2,155??9 Ma in zircon crystals derived from the Trilhado granodiorite, and ages of 2,130??7 Ma and 2,128??8 Ma in zircon crystals derived from the Teofila??ndia tonalite. The emplacement age of the syntectonic Ambro??sio dome as indicated by a 2,080??2-Ma xenotime age for a granite dyke probably marks the end of the felsic magmatism. This age shows good agreement with the Ar-Ar plateau age of 2,080??5 Ma obtained in hornblendes from an amphibolite and with a U-Pb SHRIMP age of 2,076??10 Ma in detrital zircon crystals from a quartzite, interpreted as the age of the peak of the metamorphism. The predominance of inherited zircons in the syntectonic Ambro??sio dome suggests that the basement of the supracrustal rocks was composed of Archaean continental crust with components of 2,937??16, 3,111??13 and 3,162??13 Ma. Ar-Ar plateau ages of 2,050??4 Ma and 2,054??2 Ma on hydrothermal muscovite samples from the Fazenda Brasileiro gold deposit are interpreted as minimum ages for gold mineralisation and close to the true age of gold deposition. The Ar-Ar data indicate that the mineralisation must have occurred less than 30 million years after the peak of the metamorphism, or episodically between 2,080 Ma and 2,050 Ma, during uplift and exhumation of the orogen. ?? Springer-Verlag 2006.

  13. The effect of thermal resetting and recrystallisation on white mica 40Ar/39Ar ages during retrograde metamorphism on Syros, Greece

    NASA Astrophysics Data System (ADS)

    Uunk, Bertram; Wijbrans, Jan; Brouwer, Fraukje

    2015-04-01

    White mica 40Ar/39Ar dating is a proven powerful tool for constraining timing of metamorphism, deformation and exhumation. However, in high-pressure metamorphic rocks, dating often results in wide age ranges which are not in agreement with constraints from other isotopic systems, indicating that geological and chemical processes complicate straightforward 40Ar/39Ar dating. In this research project, white mica ages from rocks of the Cycladic Blueschist Unit on Syros, Greece with contrasting rheology and strain mechanisms are compared, in order to better understand the role of deformation, recrystallization and fluid flow on 40Ar/39Ar ages of white mica during retrograde metamorphism. Resulting ages vary along different sections on the island, inconsistent with other isotopic constraints on eclogite-blueschist metamorphism (55-50 Ma) and greenschist overprinting (41-30 Ma). Two end-member models are possible: 1) Results represent continuous crystallization of white mica while moving from blueschist to greenschist conditions in the metamorphic P-T loop, or 2) white mica equilibrated in eclogite-blueschist conditions and their diffusion systematics were progressively perturbed during greenschist overprinting. The single grain fusion analyses yielded contrasting age distributions, which indicate contrasts in degree of re-equilibration during retrograde metamorphism. Step wise heating of larger grain populations resulted in flat plateau shapes, providing no evidence for partial resetting. Electron microprobe measurements of Si per formula unit, as a proxy for pressure during crystallisation, do not explain age variation within sections or on the island scale. The previously unreported north-south age trend and age ranges per sample, as shown only in the 40Ar/39Ar system of the metapelitic and marble lithologies, contains key information that will allow us to test between different scenarios for age formation. Excess argon infiltration at this stage seems to have been of

  14. Chondrite thermal histories from Low-CA pyroxene microstructures: Autometamorphism versus prograde metamorphism revisited

    NASA Technical Reports Server (NTRS)

    Brearley, Adrian J.; Jones, Rhian H.; Papike, J. J.

    1993-01-01

    In order to constrain the thermal histories of chondritic meteorites, a detailed study of the microstructures of low-Ca pyroxenes produced experimentally and in types 4 and 5 ordinary chondrites was carried out. Cooling experiments on synthetic MgSiO3 at cooling rates between 2 and 10000 C/hr from the protopyroxene stability field into that of orthopyroxene (OPX) were performed and the products of these experiments were annealed for a variety of annealing times. There are clear microstructural differences between samples which were cooled and those which were subsequently annealed. A comparison of the microstructures observed in the experimental samples with those in H4-5 ordinary chondrites shows that they cannot have experienced a single stage cooling history, as proposed for the autometamorphism model.

  15. On the timing of high-pressure metamorphism in Alpine Corsica: the first Lu-Hf garnet and lawsonite ages

    NASA Astrophysics Data System (ADS)

    Vitale Brovarone, A.; Herwartz, D.; Castelli, D.; Malavieille, J.

    2012-04-01

    Timing of HP metamorphism in Alpine Corsica is highly debated. Controversial biostratigraphic and radiometric constraints results in a poor understanding of the evolution of Alpine Corsica and its meaning in the Western Mediterranean dynamics. Age estimates provided by means of several techniques (e.g. Ar-Ar, Sa-Nd, U-Pb) vary form Late Cretaceous to Late Eocene. Some authors favor a Late Cretaceous peak metamorphism under HP conditions followed by Late Eocene and Early Oligocene blueschist and greenschist retrogression, respectively. Others favor a Late Eocene peak metamorphism and consider the older estimates as affected by analytical inaccuracy. In order to unravel this debate, we provide new Lu-Hf constraints on garnet and lawsonite from the lawsonite-eclogite and lawsonite-blueschist units of Alpine Corsica, which represent a part of the so-called Schistes Lustrés complex. The two investigated units are interpreted to represent remnants of the former Corsican ocean-continent transition zone [2]. As Lu concentrates in the cores of the selected minerals during the early stages of growth and blocking temperatures are high, this method provides robust insight on the timing of prograde/peak metamorphism [1]. Garnet and lawsonite separated form three lawsonite-eclogite samples yield systematic Late Eocene ages at ~ 34 Ma, while lawsonite from the lawsonite-blueschist unit yields a slightly older age at ~ 37 Ma. These data are in agreement with U-Pb data on zircon from the lawsonite-eclogite unit (~ 34 Ma) [3], but are in contrast with a recent U-Pb estimate on the Corsican continental margin unit metamorphosed under blueschist condition, yielding an age of ~ 55 Ma [4]. These discrepancies indicate a complex paleogeographic setting and a diachronous metamorphic evolution along the Corsican ocean-continent transition zone. The Late Eocene HP metamorphism in the Schistes Lustrés of Alpine Corsica also provides important constraints in the evolution of the Alps

  16. Exhumation history of the eastern Periadriatic fault - linkage to the Tauern metamorphic core complex

    NASA Astrophysics Data System (ADS)

    Heberer, Bianca; Neubauer, Franz; Dunkl, István; Genser, Johann

    2014-05-01

    Indentation of rigid blocks into rheologically weak orogens is generally associated with lateral and vertical extrusion of rocks. In this study, we report an example from the Eastern Alps, in which subvertical extrusion of crustal blocks associated with exhumation in distant areas is connected by a transfer fault, which likely corresponds to a block boundary in the deeper crust or even lithosphere. We applied apatite (U-Th)/He (AHe) dating to Triassic granites and Oligocene tonalites from the Karawanken plutonic belts located in the immediate vicinity of the eastern Periadriatic fault near the Austrian-Slovenian border. The eastern Periadriatic fault is segmented into three portions: a straight segment west of the Hochstuhl-Möll Valley (HVM) fault system, a central segment between the NW-trending HVM and Lavant Valley faults with a Neogene positive flower structure separating the north-vergent North Karawanken from the south-vergent South Karawanken unit, and an eastern segment largely buried underneath Neogene Pannonian basin sediments. In the central segment, the Periadriatic fault is dextrally displaced by the HVM and Lavant Valley faults and the North Karawanken unit is thrust over the Neogene flexural, intra-orogenic Klagenfurt basin, which contains sediments ranging from Sarmatian (ca. 11 Ma) to Pliocene or possibly even Quaternary. In the central segment, we find AHe ages mostly ranging from 6 to 9 Ma. This is in contrast to older ages west of the HVM directly at the PAF, where an age of 20 ± 1 Ma has been found. The basement north of the Klagenfurt basin yields also older AHe and apatite fission track ages ranging from c. 25 to 30 Ma. This age pattern confirms and constrains the positive flower structure as an area of young exhumation. Young AHe ages similar to the central segment of the eastern Periadriatic fault were reported from the Tauern window (Foeken et al., 2007; Wölfler et al., 2012). We suggest that the HVM fault system acts as a transfer

  17. Extensional versus compressional settings for metamorphism: Garnet chronometry and pressure-temperature-time histories in the Moine Supergroup, northwest Scotland

    NASA Astrophysics Data System (ADS)

    Vance, D.; Strachan, R. A.; Jones, K. A.

    1998-10-01

    Identification of the tectonic setting for metamorphism is often extremely difficult in complex polymetamorphic terranes where individual tectonothermal events are obscured by later thermal and structural reorganizations. The traditional approach is to use mineral parageneses to outline the nature of the pressure-temperature-time path, but assigning an age to that path remains a challenge. In this case study, pressure-temperature data show that garnet in pelites of the polymetamorphic Moine Supergroup of northwest Scotland grew during compressional tectonics. In addition, the Sm-Nd systematics of these garnets demonstrate that growth occurred in the interval 820 790 Ma and was thus coeval with crustal melting documented as ca. 800 Ma. The heat source for the latter event has previously been postulated to be related to extension, but here we provide the first substantive evidence for a collisional orogeny at this time. These data further demonstrate the utility of garnet chronometry in identifying the timing and nature of particular tectonothermal events in polymetamorphic settings. In addition, the data show that the period between Grenville collision and supercontinent assembly in the North Atlantic region ca. 1000 1100 Ma, and rifting and continental breakup ca. 750 Ma was not as quiescent as previously envisaged. Late Proterozoic orogenesis is likely to have resulted from the closure of aborted continental rifts and/or minor oceanic tracts within the Grenville supercontinent prior to final rifting and supercontinent dispersal.

  18. Metamorphic P-T conditions and CO2 influx history of medium-grade metapelites from Karakorum, Trans-Himalaya, India

    NASA Astrophysics Data System (ADS)

    Sachan, Himanshu K.; Santosh, M.; Prakash, Divya; Kharya, Aditya; Chandra Singh, P.; Rai, Santosh K.

    2016-07-01

    The medium grade metapelites of Pangong-Tso area in the trans-Himalayan region underwent sillimanite-grade metamorphism initiated during the Cretaceous, associated with the collision of the Kohistan arc and the Indian plate with Asia. This paper present results from a petrological and fluid inclusion study to understand the metamorphic P-T conditions and fluid history of these rocks. The calculated phase equilibria in the Na2O-CaO-K2O-FeO-MgO-MnO-Al2O3-SiO2-H2O-TiO2 (NCKFMMnASHT) system suggest P-T conditions of 8 kbar and 650 °C for the peak metamorphic event. Primary fluid inclusions occur in staurolite and garnet, whereas quartz carries mostly secondary fluid inclusions. The trapped fluids in primary inclusions show initial melting temperatures in the range of -56.9 to -56.6 °C, suggesting nearly pure CO2 composition. The secondary fluids are of mixed carbonic-aqueous nature. The re-equilibrated inclusions show annular morphology as well as necking phenomena. The CO2 isochores for the primary inclusions indicate pressures of 6.1-6.7 kbar, suggesting that the CO2-rich fluids were trapped during post-peak exhumation of the rocks, or that synmetamorphic carbonic fluids underwent density reversal during isothermal decompression. The secondary CO2-H2O fluids must have been trapped during the late exhumation stage, as their isochores define further lower pressures of 4.8 kbar. The morphology of re-equilibrated fluid inclusions and the rapid decrease in pressure are consistent with a near-isothermal decompression trajectory following the peak metamorphism. The carbonic fluids were probably derived locally from decarbonation reactions of the associated carbonate rocks during metamorphism or from a deep-seated reservoir through Karakorum fault.

  19. Contrast in stress-strain history during exhumation between high- and ultrahigh-pressure metamorphic units in the Western Alps: Microboudinage analysis of piemontite in metacherts

    NASA Astrophysics Data System (ADS)

    Omori, Yasutomo; Barresi, Antonello; Kimura, Nozomi; Okamoto, Atsushi; Masuda, Toshiaki

    2016-08-01

    Our analyses of microboudinage structures of piemontite grains embedded within six samples of metachert, one collected from an ultrahigh-pressure (UHP) metamorphic unit at Lago di Cignana in Italy of the Western Alps, and the other five from surrounding high-pressure (HP) metamorphic units in Italy and France, have revealed that the structures are all symmetrical in type, and were presumably produced in coaxial strain fields. Stress-strain analyses of the microboudinaged grains revealed significant contrasts in the stress and strain histories of the UHP and HP metamorphic units, with the differential stress recorded by the UHP sample being unequivocally lower than that recorded by the five HP samples. In addition, our analyses showed that the UHP sample underwent stress-relaxation during microboudinage, whereas the five HP samples did not. On the basis of these observations and analyses we discuss the mechanical decoupling of the UHP and HP units that led to different histories in differential stress between the units during exhumation of the Western Alps.

  20. The CO chondrites: Major recent Antarctic finds, their thermal and radiation history, and describing the metamorphic history of members of the class

    NASA Astrophysics Data System (ADS)

    Sears, Derek W. G.

    2016-09-01

    Thermoluminescence (TL) properties of 29 CO chondrites from the Miller Range (MIL) and five chondrites from the Dominion Range (DOM) have been measured. MIL has a relatively strong natural TL signal (19.6 ± 14.7 krad), while some of the DOM samples have a very weak natural TL signal (<1 krad) whereas others resemble the MIL meteorites. I argue that MIL and some of the DOM samples had a normal perihelion (∼1.0 AU) and terrestrial age of ∼450-700 ka, while some of the DOM samples have a terrestrial age of ∼100 ka but a perihelion of ∼0.8 AU. The DOM meteorites also show considerable heterogeneity in their induced TL properties, also suggesting that the DOM fragments represent more than one fall. The induced TL data for the MIL samples studied here are consistent with them all being from a single fragmented meteorite. Small (50 mg) chips have TL properties similar to 500 mg chips, so that the smaller chips are representative, although samples taken from original masses less than ∼2 g have low natural TL suggesting that they were heated during atmospheric fall. The properties of CO chondrites are reviewed in terms of their petrologic types. Correlations between TL sensitivity, the most quantitative technique for evaluating metamorphic alteration in CO chondrites, and data for olivine composition and heterogeneity, matrix composition, inert gas content, metal composition (Ni, Co, and Cr in the kamacite), bulk carbon, C and O isotopes, graphite ordering, spectral reflectance at 0.8 μm, and textural characteristics of the ameboid olivine and Ca-rich inclusions are examined. The petrographic types appear to be largely metamorphic in origin with perhaps a minor role for metasomatism. Contrary to recent proposals it is here argued that petrologic type definitions should (1) be specific enough to be meaningful, but broad enough to be simple in application and robust to new developments, (2) be descriptive and not interpretative, (3) should not oversimplify and

  1. Metamorphic fluids and uplift-erosion history of a portion of the Kapuskasing structural zone, Ontario, as deduced from fluid inclusions

    NASA Technical Reports Server (NTRS)

    Rudnick, R. L.; Ashwal, L. D.; Henry, D. J.

    1983-01-01

    Fluid inclusions can be used to determine the compositional evolution of fluids present in high grade metamorphic rocks (Touret, 1979) along with the general P-T path followed by the rocks during uplift and erosion (Hollister et al., 1979). In this context, samples of high grade gneisses from the Kapuskasing structural zone (KSZ, Fig. 1) of eastern Ontario were studied in an attempt to define the composition of syn- and post-metamorphic fluids and help constrain the uplift and erosion history of the KSZ. Recent work by Percival (1980), Percival and Card (1983) and Percival and Krogh (1983) shows that the KSZ represents lower crustal granulites that form the lower portion of an oblique cross section through the Archean crust, which was up faulted along a northeast striking thrust fault. The present fluid inclusion study places constraints upon the P-T path which the KSZ followed during uplift and erosion.

  2. Mixing of rocks of differing metamorphic histories within a subduction channel of upper mantle depth exposed on the Ohmachi Seamount, Izu-Bonin Arc

    NASA Astrophysics Data System (ADS)

    Ueda, H.; Usuki, T.; Imayama, T.; Hirauchi, K.

    2011-12-01

    Common occurrences of high-P/T metamorphic oceanic rocks in serpentinite melange suggest that deep portions of subduction channel could act as conduits both of subduction and exhumation transports. Metamorphic analysis of these rocks can provide information on modes of material transport along the subduction interfaces. Serpentinites exposed on the Ohmachi Seamount in Izu-Bonin arc contain minor amounts of metabasites, and their occurrence in sea floor and its least fractured nature imply to record primary structures and components of an intraoceanic subduction channel in upper mantle depths. Here we report metamorphic histories of some representative rocks. A garnet -zoisite amphibolite (R12) contains relics of eclogite-facies minerals. Its amphibole composition changed from hornblende presumably of non-eclogite stage I, via stage II when it merged to actinolite, to hornblende again in the final amphibolite stage III. The eclogite facies relic minerals co-occur with actinolitic hornblende of the stage II. This change suggests an anticlockwise path with cooling before decompression. A garnet-epidote amphibolite (D6-1) has glaucophane inclusions in garnet, suggesting a clockwise path with heating from blueschist to amphibolite facies before exhumation. Serpentinites show cooling from spinel peridotite via upper to lower amphibolite grades. Absence of high-pressure (e.g. Ti-clinohumite) and low-pressure (e.g. anthophyllite) minerals and occurrence of minor Tlc+Ol assemblage imply their medium pressure origins. Common deformation structures suggest that the serpentinites were juxtaposed with amphibolites being decompressed. Comparing rocks described above, the subduction channel exposed in the Ohmachi Seamount is regarded as a mixture of rocks of differing metamorphic histories. This implies that significant temporal or spatial variation in mode of material transport occur in a single subduction channel.

  3. New U-Pb ages from dykes cross-cutting the Demirci metamorphics, NW Turkey: Implications for multiple orogenic events

    NASA Astrophysics Data System (ADS)

    Sen, Fatih; Koral, Hayrettin; Peytcheva, Irena

    2016-04-01

    A high-grade metamorphic sequence in the Sünnice Mountains, Bolu, NW Turkey, is represented by migmatitic quartzo-feldspathic gneisses in amphibolite facies called the Demirci metamorphics/paragneisses, and a sequence of low-grade meta-volcanics containing meta-andesites with minor meta-rhyolites and meta-sedimentary rocks called the Yellice meta-volcanics. They are intruded by the Dirgine granite with an age of Upper Ediacaran (576-565 Ma) and are considered a part of the İstanbul-Zonguldak Tectonic Unit. The Demirci paragneisses are also intruded by a number of dykes in various directions, traditionally considered without radiometric dating to have been emplaced in a single magmatic phase in the Eocene related to post-collision regime of the Anatolide-Tauride platform. Mafic-intermediate-felsic dykes cross-cutting the Demirci paragneisses have been investigated in maps of 1/1000 scale, and their U-Pb zircon age, major-trace element and kinematic data have been obtained. The mafics dykes cross-cutting the Yellice meta-volcanics, equivalents of those in the Demirci paragneisses, occur in N400-500E orientations and have calc-alkaline basalt compositions with a subduction signature. The intermediate dykes occur in N650W, N800W orientations and have calc-alkaline basaltic andesite to andesitic compositions with a subduction signature. Some felsics occur in N150W and N800E orientations and have calc-alkaline dacitic compositions with a collisional tectonic setting. Other calc-alkaline granitic dykes occur in N750E orientation and calc-alkaline granitic compositions with a subduction signature. U-Pb LA-ICP-MS dating of zircons yield ages from 485.7±3.6 Ma (i.e. Cambro-Ordovician) for N800E trending dacite dykes; 443.0±5.4 Ma (i.e. Ordovician-Silurian) for N150W trending dacite dykes; 301.0±1.6 Ma (i.e. Upper Pennsylvanian-Carboniferous) for N650W trending basaltic andesite dykes; 268.2±2.4 Ma (i.e. Guadalupian-Permian) for N40-500E trending basalt dykes; 262.9±3

  4. Metamorphic facies map of Alaska

    SciTech Connect

    Dusel-Bacon, C.; O-Rourke, E.F.; Reading, K.E.; Fitch, M.R.; Klute, M.A.

    1985-04-01

    A metamorphic-facies of Alaska has been compiled, following the facies-determination scheme of the Working Group for the Cartography of the Metamorphic Belts of the World. Regionally metamorphosed rocks are divided into facies series where P/T gradients are known and into facies groups where only T is known. Metamorphic rock units also are defined by known or bracketed age(s) of metamorphism. Five regional maps have been prepared at a scale of 1:1,000,000; these maps will provide the basis for a final colored version of the map at a scale of 1:2,500,000. The maps are being prepared by the US Geological Survey in cooperation with the Alaska Division of Geological and Geophysical Surveys. Precambrian metamorphism has been documented on the Seward Peninsula, in the Baird Mountains and the northeastern Kuskokwim Mountains, and in southwestern Alaska. Pre-Ordovician metamorphism affected the rocks in central Alaska and on southern Prince of Wales Island. Mid-Paleozoic metamorphism probably affected the rocks in east-central Alaska. Most of the metamorphic belts in Alaska developed during Mesozoic or early Tertiary time in conjuction with accretion of many terranes. Examples are Jurassic metamorphism in east-central Alaska, Early Cretaceous metamorphism in the southern Brooks Range and along the rim of the Yukon-Kovyukuk basin, and late Cretaceous to early Tertiary metamorphism in the central Alaska Range. Regional thermal metamorphism was associated with multiple episodes of Cretaceous plutonism in southeastern Alaska and with early Tertiary plutonism in the Chugach Mountains. Where possible, metamorphism is related to tectonism. Meeting participants are encouraged to comment on the present version of the metamorphic facies map.

  5. High-pressure metamorphic age and significance of eclogite-facies continental fragments associated with oceanic lithosphere in the Western Alps (Etirol-Levaz Slice, Valtournenche, Italy)

    NASA Astrophysics Data System (ADS)

    Fassmer, Kathrin; Obermüller, Gerrit; Nagel, Thorsten J.; Kirst, Frederik; Froitzheim, Nikolaus; Sandmann, Sascha; Miladinova, Irena; Fonseca, Raúl O. C.; Münker, Carsten

    2016-05-01

    The Etirol-Levaz Slice in the Penninic Alps (Valtournenche, Italy) is a piece of eclogite-facies continental basement sandwiched between two oceanic units, the blueschist-facies Combin Zone in the hanging wall and the eclogite-facies Zermatt-Saas Zone in the footwall. It has been interpreted as an extensional allochthon from the continental margin of Adria, emplaced onto ultramafic and mafic basement of the future Zermatt-Saas Zone by Jurassic, rifting-related detachment faulting, and later subducted together with the future Zermatt-Saas Zone. Alternatively, the Etirol-Levaz Slice could be derived from a different paleogeographic domain and be separated from the Zermatt-Saas Zone by an Alpine shear zone. We present Lu-Hf whole rock-garnet ages of two eclogite samples, one from the center of the unit and one from the border to the Zermatt-Saas Zone below. These data are accompanied by a new geological map of the Etirol-Levaz Slice and the surrounding area, as well as detailed petrology of these two samples. Assemblages, mineral compositions and garnet zoning in both samples indicate a clockwise PT-path and peak-metamorphic conditions of about 550-600 °C/20-25 kbar, similar to conditions proposed for the underlying Zermatt-Saas Zone. Prograde garnet ages of the two samples are 61.8 ± 1.8 Ma and 52.4 ± 2.1 Ma and reflect different timing of subduction. One of these is significantly older than published ages of eclogite-facies metamorphism in the Zermatt-Saas Zone and thus contradicts the hypothesis of Mesozoic emplacement. The occurrence of serpentinite and metagabbro bodies possibly derived from the Zermatt-Saas Zone inside the Etirol-Levaz Slice suggests that the latter is a tectonic composite. The basement slivers forming the Etirol-Levaz Slice and other continental fragments were subducted earlier than the Zermatt-Saas Zone, but nonetheless experienced similar pressure-temperature histories. Our results support the hypothesis that the Zermatt-Saas Zone and the

  6. The Age and Geodynamic Evolution of the Metamorphic sole rocks from Izmir-Ankara-Erzıncan suture zone (Northern-Turkey)

    NASA Astrophysics Data System (ADS)

    Melih Çörtük, Rahmi; Faruk Çelik, Ömer; Özkan, Mutlu; Sherlock, Sarah C.; Marzoli, Andrea; Altıntaş, İsmail Emir; Topuz, Gültekin

    2016-04-01

    The İzmir-Ankara-Erzincan suture zone in northern Turkey is one of the major tectonic zones separating the Pontides to the North from the Anatolide-Tauride block and Kı rşehir Massif to the South. The accretionary complex of the İzmir-Ankara-Erzincan suture zone, near Artova, is composed mainly of peridotites with varying degree serpentinization, metamorphic rocks, basalt, sandstones, pelagic and neritic limestones. The metamorphic rocks are represented by amphibolite, garnet micaschit, calc-schist and marble. The metamorphic rocks were interpreted as the metamorphic sole rocks. Because; (i) They are tectonically located beneath the serpentinized peridotites. (ii) Foliation planes of both the amphibolites and mantle tectonites are parallel to each other. (iii) The metamorphic rocks are crosscut by non-metamorphic dolerite dikes which exhibite Nb and Ta depletion relative to Th enrichment on the N-MORB normalized multi-element spider diagram. The dolerite dikes display flat REE patterns (LaN/YbN=0.85-1.24). These geochemical signatures of the dolerite dikes are indicative of subduction component during their occurrences. Geochemical observations of the amphibolites suggest E-MORB- and OIB-like signatures (LaN/SmN= 1.39-3.14) and their protoliths are represented by basalt and alkali basaltic rocks. Amphiboles from the amphibolites are represented by calcic amphiboles (magnesio-hornblende, tchermakite and tremolite) and they yielded 40Ar-39Ar ages between 157.8 ± 3.6 Ma and 139 ± 11 Ma. These cooling ages were interpreted to be the intra-oceanic subduction/thrusting time of the İzmir-Ankara-Erzincan oceanic domain. This study was funded by TÜBİTAK (Project no: 112Y123).

  7. Review of metamorphic and kinematic data from Internal Crystalline Massifs (Western Alps): PTt paths and exhumation history

    NASA Astrophysics Data System (ADS)

    Gasco, Ivano; Gattiglio, Marco; Borghi, Alessandro

    2013-01-01

    Detailed geological mapping combined with micro-structural and petrological investigation allowed to clarify the tectono-metamorphic relationships between continental and oceanic units transition in the Penninic domain of the Western Alps. The three study areas (Gressoney, Orco and Susa sections) take into consideration the same structural level across the axial metamorphic belt of the Western Italian Alps, i.e., a geological section across the Internal Crystalline Massifs vs Piedmont Zone boundary. The units outcropping in these areas can be grouped into two Tectonic Elements according to their tectono-metamorphic evolution. The Lower Tectonic Element (LTE) consists of the Internal Crystalline Massifs and the Lower Piedmont Zone (Zermatt-Saas like units), both showing well preserved eclogite facies relics. Instead, the Upper Tectonic Element (UTE) consists of the Upper Piedmont Zone (Combin like units) lacking evidence of eclogite facies relics. In the Lower Tectonic Element two main Alpine tectono-metamorphic stages were identified: M1/D1 developed under eclogite facies conditions and M2/D2 is related to the development of the regional foliation under greenschist to epidote-albite amphibolite facies conditions. In the Upper Tectonic Element the metamorphic stage M1/D1 developed under bluschist to greenschist facies conditions and M2/D2 stage under greenschist facies conditions. These two Tectonic Elements are separated by a tectonic contact of regional importance generally developed along the boundary between the Lower and the Upper Piedmont zone under greenschist facies conditions. PT data compared to geochronology indicate that the first exhumation of ICM can be explained by buoyancy forces acting along the subduction channel that occurred during the tectonic coupling between the continental and oceanic eclogite units. These buoyancy forces vanished at the base of the crust where the density difference between the subducted crustal units and the surroundings

  8. The Taili-Yiwulüshan metamorphic core complex corridor: Diachronous exhumation and relationships to the adjacent basins based on new 40Ar/39Ar and (U-Th-Sm)/He mineral ages

    NASA Astrophysics Data System (ADS)

    Liang, Chenyue; Neubauer, Franz; Liu, Yongjiang; Genser, Johann; Dunkl, István; Heberer, Bianca; Jin, Wei; Zeng, Zuoxun; Li, Weimin; Wen, Quanbo; Li, Jing

    2015-04-01

    The Xingcheng-Taili ductile shear zone (western Liaoning Province in China) formed during latest Jurassic to Early Cretaceous crustal extension of the eastern North China craton, and exhumed low to medium metamorphic grade Archean, Upper Triassic and Upper Jurassic granitic rocks. The Mesozoic Yiwulüshan metamorphic core complex (Yiwulüshan MCC) is dominated by a NNE-SSW elongated dome with a left-lateral shear zone, which is located in the northeastern part of Xingcheng-Taili ductile shear zone, and combine as Taili-Yiwulüshan metamorphic core complex corridor. To the east, it is bounded by the NNE-trending Cretaceous to Eocene Liaohe basin (the northern extension of the Bohai Bay basin), and to the west by the Cretaceous-aged Fuxin-Yixian basin, which could potentially interpreted as supra-detachment basins. Here, we present results from a multi-method thermochronological study and coupled with structural investigations and sections of adjacent supra-detachment basins, which constrain the timing of regional deformation as well as the cooling history and exhumation processes of the low- to middle-grade metamorphic complex in the Taili-Yiwulüshan MCC corridor, in order to understand the mode of lithospheric scale reactivation, extension and thinning of the North China craton. The new40Ar/39Ar muscovite, biotite, K-feldspar and (U-Th)/He apatite ages from granitic rocks help constrain the thermal evolution during its exhumation. The thermochronologic studies have shown at least three stages of exhumation and cooling from late Jurassic to Eocene in Xingcheng-Taili shear zone should be distinguished, e.g., ~ 150-130 Ma, 130-115 Ma and 115-52 Ma, respectively. Diachronous onset and subsequent parallel cooling and exhumation characterize the early thermal history. The Yiwulüshan MCC has a similar exhumation history from 135 to 97 Ma with a similar cooling history. The development of Taili-Yiwulüshan MCC corridor is associated with synkinematic emplacement

  9. Metamorphism of tectonic terranes in the eastern marginal zone of the Appalachian orogen, New England

    SciTech Connect

    Hepburn, J.C.; Olszewski, W.J.; Guidotti, C.V.

    1985-01-01

    Southeastern New England is subdivided into three major fault bounded tectonic terranes, each with a distinctive metamorphic history. The easternmost, the Avalon Terrane, has generally been metamorphosed no higher than the lower greenschist facies. Evidence for pre-Alleghanian metamorphism includes a Proterozoic Z(.) event, contact metamorphism adjacent to Ord.-Dev. alkaline plutons, and granulite facies crustal xenoliths in Mesozoic dikes. To the west the Nashoba Terrane has been deformed and polymetamorphosed to the sill. and 2nd sill. zones between approximately 415 and 450 m.y., based on ages of associated granitic and migmatitic rocks. 730 m.y. assumed basement gneisses (fish Brook) have likely experienced Late PC metamorphism. In the Merrimack Trough, here including the Massabesic Gneiss, the metamorphic grade ranges from the greenschist facies on the east to the 2nd sillimanite zones on the west toward the Massabesic. The two metamorphic events present here must predate the intrusion of the Exeter Diorite (473 m.y .), indicating one or both may be PC. To the east, the fault bounded Rye Formation has also experienced two pre- 470 m.y. metamorphisms (and -sill.) However, the terrane east of the Turtle Head Fault Zone (THFZ) has many similarities to the Boston Platform including general (Late PC.) lower greenschist metamorphism. Also, the area between the Norumbega FZ and the THFZ has experienced high grade metamorphism of probable Silurian age and thus may be similar to the Nashoba Terrane.

  10. Mesozoic and Cenozoic thermal history of the eastern Mojave Desert, California and western Arizona, with emphasis on the Old Woman Mountains area and the Chemehuevi metamorphic core complex

    SciTech Connect

    Foster, D.A.

    1989-01-01

    Mesozoic thickening and Cenozoic extension resulted in the juxtaposition of upper and middle crustal rocks in the eastern Mojave Desert, southeastern California and western Arizona. The application of {sup 40}Ar/{sup 39}Ar thermochronology and petrology/thermobarometry to rocks in this region provides information about the timing and nature of thrusting, plutonism, metamorphism, denudation, and detachment faulting. Orogenesis culminated during the Late Cretaceous when rocks exposed in the Old Woman-Piute, Chemehuevi, and Sacramento Mountains attained temperatures > 500C. High grade metamorphism of the Old Woman Mountains area was caused by the intrusion of the Old Woman-Piute batholith at 73 {plus minus} 1 Ma; Cretaceous mineral assemblages in Proterozoic pelites increase in grade from greenschist to upper amphibolite facies, and {sup 40}Ar/{sup 39}Ar hornblende ages from Proterozoic amphibolites decrease in age from {approximately} 1,600 Ma to 73 {plus minus} 1 Ma, in the direction of 73 Ma plutons. Pluton emplacement and metamorphism occurred at 3 to 3.5 kbars and 400 > 600C in the Piute Mountains, and 3.5 to 4.5 kbars and 530 to > 650C in the Old Woman Mountains. Following the Cretaceous, the eastern Mojave Desert underwent a period of cooling at a rate of 2 to 10C/Ma between 65 and 25 Ma. By 30 Ma rocks exposed in the Old Woman-Piute, Marble Ship, Clipper and Turtle Mountains were below {approximately} 100C. {sup 40}/{sup 39}Ar ages from the Sacramento Mountains suggest that mylonitization caused by the onset of regional extension occurred at 23 {plus minus} 1 Ma. When extension started in the Chemehuevi Mountains, rocks exposed in the southwestern and northeastern portions of footwall to the Chemehuevi detachment fault were at {approximately} 180C and {approximately} 350C, respectively which suggests that this fault initiated at a dip of 5 to 30{degree}.

  11. The age of oceanic crust and of HP/LT-metamorphism on Syros (Cyclades, Greece) based on Lu-Hf geochronology and geochemistry

    NASA Astrophysics Data System (ADS)

    Lagos, M.; Münker, C.; Tomaschek, F.; Ballhaus, C.; Scherer, E. E.

    2003-04-01

    The ages of protolith formation and high pressure metamorphism of blueschist facies rocks in the Cyclades (Greece) are not completely constrained because they rely largely on U-Pb zircon geochronology plus Rb-Sr, and Ar-Ar cooling ages rather than direct dating of the high pressure assemblage. To adress this question further, we examined a meta-igneous sequence, which occurs in a dismembered meta-ophiolite belt in northern Syros. The sequence was subjected to blueschist-eclogite facies metamorphism at pressures of 16 kbar and temperatures up to 480^oC and forms part of the Cycladic Lower Unit. All examined samples were taken from one coherent mélange block at the Grizzas locality, comprising a complete compositional spectrum from mafic to felsic. Lu-Hf dating of WR-Grt-Omph in two samples yields ages between 47 and 51 Ma, overlapping with U-Pb-SHRIMP ages of ca. 52 Ma that were obtained from metamorphic zircons [1]. Such zircons are frequently found as inclusions in peak metamorphic garnet. Hence, both Lu-Hf and U-Pb ages most likely date garnet growth and peak metamorphism on Syros because the closure temperature of Lu-Hf in Grt is probably above 540^oC [2]. Such temperatures were not reached during HP-metamorphism on Syros. Major and trace element patterns indicate that the protoliths of the examined sequence are cogenetic and related by fractional crystallization. ɛHf(t) at 80 Ma range from +12.4 to +13.8, consistent with inferences from trace element patterns that suggest deposition of the Grizzas metavolcanics in a back-arc environment. The 176Hf/177Hf and 176Lu/177Hf of 11 whole rock samples define an errorchrone of 63±37 Ma (2σ). The errorchrone provides an upper limit of 100 Ma for the protolith age of the Grizzas sequence, implying that the oceanic crust on Syros was formed in the Upper Cretaceous. There is an older zircon generation (ca. 80 Ma) in Grizzas [1] that displays grossly different trace element characteristics than the 50 Ma old population

  12. Deformation and thermal histories of ordinary chondrites: Evidence for post-deformation annealing and syn-metamorphic shock

    NASA Astrophysics Data System (ADS)

    Ruzicka, Alex; Hugo, Richard; Hutson, Melinda

    2015-08-01

    We show that olivine microstructures in seven metamorphosed ordinary chondrites of different groups studied with optical and transmission electron microscopy can be used to evaluate the post-deformation cooling setting of the meteorites, and to discriminate between collisions affecting cold and warm parent bodies. The L6 chondrites Park (shock stage S1), Bruderheim (S4), Leedey (S4), and Morrow County (S5) were affected by variable shock deformation followed by relatively rapid cooling, and probably cooled as fragments liberated by impact in near-surface settings. In contrast, Kernouvé (H6 S1), Portales Valley (H6/7 S1), and MIL 99301 (LL6 S1) appear to have cooled slowly after shock, probably by deep burial in warm materials. In these chondrites, post-deformation annealing lowered apparent optical strain levels in olivine. Additionally, Kernouvé, Morrow County, Park, MIL 99301, and possibly Portales Valley, show evidence for having been deformed at an elevated temperature (⩾800-1000 °C). The high temperatures for Morrow County can be explained by dynamic heating during intense shock, but Kernouvé, Park, and MIL 99301 were probably shocked while the H, L and LL parent bodies were warm, during early, endogenically-driven thermal metamorphism. Thus, whereas the S4 and S5 chondrites experienced purely shock-induced heating and cooling, all the S1 chondrites examined show evidence for static heating consistent with either syn-metamorphic shock (Kernouvé, MIL 99301, Park), post-deformation burial in warm materials (Kernouvé, MIL 99301, Portales Valley), or both. The results show the pitfalls in relying on optical shock classification alone to infer an absence of shock and to construct cooling stratigraphy models for parent bodies. Moreover, they provide support for the idea that "secondary" metamorphic and "tertiary" shock processes overlapped in time shortly after the accretion of chondritic planetesimals, and that impacts into warm asteroidal bodies were

  13. Archean metamorphic sequence and surfaces, Kangerdlugssuaq Fjord, East Greenland

    NASA Technical Reports Server (NTRS)

    Kays, M. A.

    1986-01-01

    The characteristics of Archean metamorphic surfaces and fabrics of a mapped sequence of rocks older than about 3000 Ma provide information basic to an understanding of the structural evolution and metamorphic history in Kangerdlugssuaq Fjord, east Greenland. This information and the additional results of petrologic and geochemical studies have culminated in an extended chronology of Archean plutonic, metamorphic, and tectonic events. The basis for the chronology is considered, especially the nature of the metamorphic fabrics and surfaces in the Archean sequence. The surfaces, which are planar mineral parageneses, may prove to be mappable outside Kangerdlugssuaq Fjord, and if so, will be helpful in extending the events that they represent to other Archean sequences in east Greenland. The surfaces will become especially important reference planes if the absolute ages of their metamorphic assemblages can be determined in at least one location where strain was low subsequent to their recrystallization. Once an isochron is obtained, the dynamothermal age of the regionally identifiable metamorphic surface is determined everywhere it can be mapped.

  14. New insights into the history and origin of the southern Maya block, SE Mexico: U-Pb-SHRIMP zircon geochronology from metamorphic rocks of the Chiapas massif

    USGS Publications Warehouse

    Weber, Bodo; Iriondo, Alexander; Premo, Wayne R.; Hecht, Lutz; Schaaf, Peter

    2007-01-01

    The histories of the pre-Mesozoic landmasses in southern México and their connections with Laurentia, Gondwana, and among themselves are crucial for the understanding of the Late Paleozoic assembly of Pangea. The Permian igneous and metamorphic rocks from the Chiapas massif as part of the southern Maya block, México, were dated by U–Pb zircon geochronology employing the SHRIMP (sensitive high resolution ion microprobe) facility at Stanford University. The Chiapas massif is composed of deformed granitoids and orthogneisses with inliers of metasedimentary rocks. SHRIMP data from an anatectic orthogneiss demonstrate that the Chiapas massif was part of a Permian (∼ 272 Ma) active continental margin established on the Pacific margin of Gondwana after the Ouachita orogeny. Latest Permian (252–254 Ma) medium- to high-grade metamorphism and deformation affected the entire Chiapas massif, resulting in anatexis and intrusion of syntectonic granitoids. This unique orogenic event is interpreted as the result of compression due to flat subduction and accretionary tectonics. SHRIMP data of zircon cores from a metapelite from the NE Chiapas massif yielded a single Grenvillian source for sediments. The majority of the zircon cores from a para-amphibolite from the SE part of the massif yielded either 1.0–1.2 or 1.4–1.5 Ga sources, indicating provenance from South American Sunsás and Rondonian-San Ignacio provinces.

  15. The origin and age of the metamorphic sole from the Rogozna Mts., Western Vardar Belt: New evidence for the one-ocean model for the Balkan ophiolites

    NASA Astrophysics Data System (ADS)

    Borojević Šoštarić, S.; Palinkaš, A. L.; Neubauer, F.; Cvetković, V.; Bernroider, M.; Genser, J.

    2014-04-01

    This study brings new geochronological and petrochemical data from the metamorphic sole beneath the Rogozna Mts., Western Vardar ophiolite belt. The Rogozna metamorphic sole is located at the base of a serpentinite nappe and consists of amphibolites and talc-chlorite schists. The Rogozna amphibolites are medium- to fine-grained rocks with nematoblastic texture and pronounced foliation. They consist of green amphibole (~ 70 vol.%) with variable silica contents (6.4 to 7.8 Si apfu), as well as Mg# (molMg/[Mg + Fetot]; 0.53 to 0.77) and variably albitized plagioclase (~ 30 vol.%; Ab24-Ab98). Amphibolites are overprinted by a retrograde assemblage containing actinolite, epidote, clinoclore, sericite, chlorite, and magnetite. The amphibolites formed due to metamorphism of two basaltic suites: subalkaline/tholeiitic and alkaline. Subalkaline/tholeiitic amphibolites possess low Zr, Nb, Y, Th, Hf, TiO2, and P2O5 values and a LREE-depleted pattern, typical for the N-MORB (normal mid ocean ridge basalt) to BAB (back-arc basalt) origin. Alkaline amphibolites show elevated concentrations of Zr, Nb, Y, Th, Hf, TiO2, and P2O5 with a LREE-enriched pattern typically displayed by OIB (ocean island basalt). Amphibolites were crystallized during intra-oceanic thrusting at temperatures between 685 °C and 765 °C and at a depth of 12-17 km. 40Ar/39Ar cooling ages of amphibole, ranging from 165 to 170 Ma, slightly postdate the sole formation. Talc-chlorite schists are related to retrograde greenschist-facies metamorphism. They consist of Fe-rich talc and Cr-rich chlorite (peninite-diabantite) pseudomorphs after amphibole and MORB-type Cr-Al spinel, surrounded by Al- and Mg-poor ferrit chromite. The occurrence of ferrit chromite is related to earlier, amphibolite facies metamorphism. Chlorite pseudomorphs after amphibole were formed at 300-410 °C.

  16. Nitrogen-isotope compositions of metasedimentary rocks in the Catalina Schist, California: Implications for metamorphic devolatilization history

    NASA Astrophysics Data System (ADS)

    Bebout, Gray E.; Fogel, Marilyn L.

    1992-07-01

    In the Catalina Schist subduction-zone metamorphic complex (California), metasedimentary rocks show a decrease in N concentration and an increase in δ15Nair with increasing metamorphic grade. Lowest-grade lawsonite-albite rocks contain 632 ± 185 ppm N with δ 15N = +1.9 ± 0.6‰ , whereas highgrade amphibolite equivalents contain 138 ± 76 ppm N with δ 15N = +4.3 ± 0.8‰ . Loss of N accompanied devolatilization reactions that evolved H 2O-rich C-O-H-S-N fluids through consumption of chlorite and phengitic white mica and production of mineral assemblages containing muscovite, biotite, garnet and kyanite. Whole-rock N concentrations of up to 200 ppm in veins and pegmatites produced during high- P/T metamorphism reflect the redistribution of N during devolatilization and partial melting of the metasedimentary rocks. Bulk fluid-rock N-isotope fractionations ( Δ15N = δ15Nfluid - δ15Nrock) of -1.5 ± 1‰ were calculated with the Rayleigh distillation equation, taking into account variability in rock composition by comparison of samples with similar K 2O concentrations. These fractionations are similar to but slightly lower than published calculated fractionations for N 2-NH 4+ exchange at the temperature range of 350-600°C over which most of the devolatilization occurred in the Catalina Schist (approximately -3.4 to -2.25‰). The N systematics appear to be explained by N 2-NH 4+ exchange and a devolatilization process intermediate in behavior to batch volatilization and Rayleigh distillation. The observed shifts in N concentration and δ15N cannot be explained by NH 3-NH 4+ exchange at these temperatures using the equilibrium models. The distillation devolatilization process implicated in this study may govern the behavior of other trace elements partitioned into hydrous fluids during devolatilization (e.g., B, Cs, U). Similarity of the calculated fluid δ15N( ~ -1.5 to +5.5‰) with compositions of natural gases inferred to be derived from metasedimentary

  17. Constraints on Age of India-Asia Collision and Pre-Collisional Subduction Metamorphism from the Sangsang Region, South Central Tibet

    NASA Astrophysics Data System (ADS)

    Borneman, N.; Hodges, K. V.; Van Soest, M. C.; Wartho, J. A.

    2014-12-01

    A common feature of continental collision zones is the entrainment of ophiolitic and subduction complex rock units. The crystallization and metamorphic ages of these units provide important constraints on both subduction zone evolution and the maximum age of ophiolite obduction. Ophiolites and subduction complexes have been well described in the Yarlung Tsangpo suture zone (YTSZ), but thus far relatively few high-pressure, low-temperature metamorphic assemblages from within the suture zone have been documented and successfully dated. Here we present structural, petrologic, and chronologic data from a recently discovered subduction complex occurrence of high-pressure (blueschist facies) rocks along the YTSZ in south central Tibet (29.31º N, 86.68º E). Mapping of the complex based on ASTER satellite image analysis as well as field work enabled the identification of four major lithostratigaphic units; from structurally highest to lowest, they are: 1) forarc affinity Chengdoi sandstones 2) a variably serpentinized ophiolitic fragment; 3) a structural mélange of blueschist-facies metabasic and metaclastic rocks; and 4) sandstones containing serpentinite and rutile detritus. The second and third of these tectonostratigraphic units are separated by thrust faults, whereas the Chengdoi sandstones unconformably overlie the ophiolitic fragment. We interpret the thrust separating the blueschists from the ophiolites as a paleo-subduction zone that dips northward when the entire section is rotated to restore the Chengdoi formation to horizontal. The subduction complex is further disrupted by oblique faults, including some with apparent normal sense offset that may be pre-collisional, intraoceanic normal faults. U/Pb zircon dating of the blueschist facies metavlocanic rocks implies a ca. 111 Ma protolith age, while a ca. 65 Ma 40Ar/39Ar amphibole date from one blueschist sample is interpreted as representing a close approximation of the timing of high-pressure metamorphism

  18. History of the Calendar : In Different Countries Through the Ages

    NASA Astrophysics Data System (ADS)

    Saha, M. N.; Lahiri, N. C.

    This volume contains Part of the Report of the Calendar Reform Committee appointed by the Council of Scientific and Industrial Research (CSIR) on history of the Calendar in different countries through the Ages.

  19. Thermal history of low metamorphic grade Paleoproterozoic sedimentary rocks of the Penokean orogen, Lake Superior region: Evidence for a widespread 1786 Ma overprint based on xenotime geochronology

    USGS Publications Warehouse

    Vallini, D.A.; Cannon, W.F.; Schulz, K.J.; McNaughton, N.J.

    2007-01-01

    Paleoproterozoic strata in northern Michigan, Wisconsin, and Minnesota were deposited between 2.3 and 1.75 Ga within the rifted margin and subsequent foreland basin of the Penokean orogen. These strata show evidence for multiple regional metamorphic events previously attributed entirely to the Penokean orogeny (1875-1835 Ma). Metasandstones from the Marquette Range Supergroup and the Animikie, Mille Lacs, and North Range Groups were sampled at multiple localities across Minnesota, Wisconsin and Michigan for metamorphic xenotime suitable for in situ SHRIMP U-Pb geochronology. All samples are from the northern Penokean foreland basin where the metamorphic grade is greenschist to sub-greenschist and the strata are virtually undeformed. Xenotime U-Pb ages in these samples have a bimodal population with means of 1786 ?? 4 Ma (n = 32) and 1861 ?? 10 Ma (n = 9). Xenotime of both ages are contained in metasandstones from the basal Chocolay Group in Michigan and Wisconsin and the Mille Lacs Group and North Range Groups in Minnesota. The older age records a regional low-temperature thermal event that is slightly older than the overlying Menominee Group in Michigan and the Animikie Group in Minnesota and Ontario. This 1861 Ma event coincides with regional uplift that led to the formation of the unconformity between the Menominee Group and the overlying Baraga Group in Michigan; hence xenotime growth must have occurred at shallow burial depths. Younger units from the Menominee and Baraga Groups in Michigan and the Animikie Group in Minnesota, record only the 1786 Ma event. A dominant 1800-1790 Ma metamorphic monazite population that overprints Penokean-interval monazite has been documented within amphibolite- to granulite-facies rocks immediately north of the Niagara Fault Zone within the vicinity of gneiss domes and granitic plutons. In contrast, the 1786 Ma xenotime ages are from low-grade, virtually undeformed rocks 50-150 km from the high-grade zones and thus do not appear

  20. Passive absolute age and temperature history sensor

    SciTech Connect

    Robinson, Alex; Vianco, Paul T.

    2015-11-10

    A passive sensor for historic age and temperature sensing, including a first member formed of a first material, the first material being either a metal or a semiconductor material and a second member formed of a second material, the second material being either a metal or a semiconductor material. A surface of the second member is in contact with a surface of the first member such that, over time, the second material of the second member diffuses into the first material of the first member. The rate of diffusion for the second material to diffuse into the first material depends on a temperature of the passive sensor. One of the electrical conductance, the electrical capacitance, the electrical inductance, the optical transmission, the optical reflectance, or the crystalline structure of the passive sensor depends on the amount of the second material that has diffused into the first member.

  1. Paleoproterozoic layered PGE-bearing Monchetundra pluton, Kola Peninsula: Sm-Nd age of metamorphic alteration of mafic rocks

    NASA Astrophysics Data System (ADS)

    Kunakkuzin, E. L.; Serov, P. A.; Bayanova, T. B.; Nerovich, L. I.; Borisenko, E. S.

    2015-09-01

    The aim of this work is Sm-Nd study of metamorphic alteration of massive gabbronorites from the Monchetundra pluton. The mafic rocks of the pluton are unevenly metamorphosed up to amphibolite facies with the formation of garnet, hornblende, and other minerals. The presence of garnet is a distinctive feature of this pluton in comparison with other Paleoproterozoic PGE-bearing plutons of the eastern part of the Baltic shield: Mt. General'skaya, Fedorovo-Pana, Imandra lopolith, and Monchepluton [9]. The degree of metamorphic alteration of rocks increases near the faults, the largest of which is Monchetundra fault separating the studied pluton from the Monchepluton. This fault was formed about 1.9-2.0 Ga ago according to Sm-Nd and Rb-Sr mineral isochrons for minerals from metagabbro-anorthosites of the M1 well.

  2. The genetic history of Ice Age Europe.

    PubMed

    Fu, Qiaomei; Posth, Cosimo; Hajdinjak, Mateja; Petr, Martin; Mallick, Swapan; Fernandes, Daniel; Furtwängler, Anja; Haak, Wolfgang; Meyer, Matthias; Mittnik, Alissa; Nickel, Birgit; Peltzer, Alexander; Rohland, Nadin; Slon, Viviane; Talamo, Sahra; Lazaridis, Iosif; Lipson, Mark; Mathieson, Iain; Schiffels, Stephan; Skoglund, Pontus; Derevianko, Anatoly P; Drozdov, Nikolai; Slavinsky, Vyacheslav; Tsybankov, Alexander; Cremonesi, Renata Grifoni; Mallegni, Francesco; Gély, Bernard; Vacca, Eligio; Morales, Manuel R González; Straus, Lawrence G; Neugebauer-Maresch, Christine; Teschler-Nicola, Maria; Constantin, Silviu; Moldovan, Oana Teodora; Benazzi, Stefano; Peresani, Marco; Coppola, Donato; Lari, Martina; Ricci, Stefano; Ronchitelli, Annamaria; Valentin, Frédérique; Thevenet, Corinne; Wehrberger, Kurt; Grigorescu, Dan; Rougier, Hélène; Crevecoeur, Isabelle; Flas, Damien; Semal, Patrick; Mannino, Marcello A; Cupillard, Christophe; Bocherens, Hervé; Conard, Nicholas J; Harvati, Katerina; Moiseyev, Vyacheslav; Drucker, Dorothée G; Svoboda, Jiří; Richards, Michael P; Caramelli, David; Pinhasi, Ron; Kelso, Janet; Patterson, Nick; Krause, Johannes; Pääbo, Svante; Reich, David

    2016-06-01

    Modern humans arrived in Europe ~45,000 years ago, but little is known about their genetic composition before the start of farming ~8,500 years ago. Here we analyse genome-wide data from 51 Eurasians from ~45,000-7,000 years ago. Over this time, the proportion of Neanderthal DNA decreased from 3-6% to around 2%, consistent with natural selection against Neanderthal variants in modern humans. Whereas there is no evidence of the earliest modern humans in Europe contributing to the genetic composition of present-day Europeans, all individuals between ~37,000 and ~14,000 years ago descended from a single founder population which forms part of the ancestry of present-day Europeans. An ~35,000-year-old individual from northwest Europe represents an early branch of this founder population which was then displaced across a broad region, before reappearing in southwest Europe at the height of the last Ice Age ~19,000 years ago. During the major warming period after ~14,000 years ago, a genetic component related to present-day Near Easterners became widespread in Europe. These results document how population turnover and migration have been recurring themes of European prehistory. PMID:27135931

  3. Late Cretaceous Localized Crustal Thickening as a Primary Control on the 3-D Architecture and Exhumation Histories of Cordilleran Metamorphic Core Complexes

    NASA Astrophysics Data System (ADS)

    Gans, P. B.; Wong, M.

    2014-12-01

    The juxtaposition of mylonitic mid-crustal rocks and faulted supracrustal rocks in metamorphic core complexes (MMCs) is usually portrayed in 2 dimensions and attributed to a single event of large-scale slip ± isostatic doming along a low-angle "detachment fault"/ shear zone. This paradigm does not explain dramatic along strike (3-D) variations in slip magnitude, footwall architecture, and burial / exhumation histories of most MMCs. A fundamental question posed by MMCs is how did their earlier thickening and exhumation histories influence the geometric evolution and 3-D slip distribution on the subsequent detachment faults? New geologic mapping and 40Ar/39Ar thermochronology from the Snake Range-Kern Mts-Deep Creek Mts (SKDC) complex in eastern Nevada offer important insights into this question. Crustal shortening and thickening by large-scale non-cylindrical recumbent folds and associated thrust faults during the late Cretaceous (90-80 Ma) resulted in deep burial (650°C, 20-25 km) of the central part of the footwall, but metamorphic grade decreases dramatically to the N and S in concert with decreasing amplitude on the shortening structures. Subsequent Paleogene extensional exhumation by normal faulting and ESE-directed mylonitic shearing is greatest in areas of maximum earlier thickening and brought highest grade rocks back to depths of~10-12 km. After ≥15 Ma of quiescence, rapid E-directed slip initiated along the brittle Miocene Snake Range detachment at 20 Ma and reactivated the Eocene shear zone. The ≥200°C gradient across the footwall at this time implies that the Miocene slip surface originated as a moderately E-dipping normal fault. This Miocene slip surface can be tracked for more than 100 km along strike, but the greatest amount of Miocene slip also coincides with parts of the footwall that were most deeply buried in the Cretaceous. These relations indicate that not only is the SKDC MMC a composite feature, but that the crustal welt created by

  4. Zircon ages of metamorphic and magmatic rocks within peridotite-bearing mélanges: Crucial time constraints on early Carboniferous extensional tectonics in the Chinese Tianshan

    NASA Astrophysics Data System (ADS)

    Jian, Ping; Kröner, Alfred; Jahn, Bor-ming; Liu, Dunyi; Zhang, Wei; Shi, Yuruo; Ma, Huadong

    2013-07-01

    We dated and geochemically characterized peridotite-bearing mélanges in the Chinese South Tianshan and within the Main Tianshan Shear Zone. The Yushugou-Tonghuashan mélange in the Chinese South Tianshan exposes a tectonic juxtaposition of a diapirically emplaced metaperidotite (predominantly lherzolite) massif with a high-grade metamorphic terrane (ca. 10 km long; protolith age ≥ ca. 445-466 Ma). Metamorphic zircons of a mafic granulite (εNd(t) = 5.0) yielded a weighted mean 206Pb/238U age of 341 ± 8 Ma that we interpret as the time of granulite-facies metamorphism. The youngest zircon rims of an intermediate granulite (εNd(t) = - 4.3) have a mean age of 332 ± 13 Ma that records a retrogressive metamorphic event. These ages determine the timing (ca. 341-332 Ma) of mantle diapirism through continental crust. A dolerite dike (εNd(t) = 2.3) emplaced into metaperidote has a crystallization age of 335 ± 5 Ma, that, on the basis of geochemistry, we interpret as representing E-MORB-OIB magmatism that accompanied mantle diapirism. An undeformed pink granite (εNd(t) = - 3.6) intrudes the mélange matrix and has an emplacement age of 324 ± 5 Ma, thus providing an upper time limit for a tectonic movement that led to mélange formation. The older time limit of deformation (ca. 362-352 Ma) is constrained by the youngest ages of thermo-tectonically modified zircons in a mylonitized metagabbro and a foliated meta-andesite. Magmatic zircons in the meta-andesite (εNd(t) = - 3.3) and a dacite (εNd(t) = - 5.6) have eruption ages of 433 ± 4 Ma and 435 ± 3 Ma that date formation of the mélange matrix. A microgabbro dike (εNd(t) = 10.0) cutting metasediments (i.e. mélange matrix) has an emplacement age of 279 ± 3 Ma and contains abundant zircon xenocrysts ranging in age from Archean to late Paleozoic. Similarly, a dolerite dike, a meta-andesite, an intermediate granulite, and a metagabbro all contain inherited Precambrian to Paleozoic zircons. We accordingly conclude

  5. Re-Os ages for Archean molybdenite and pyrite, Kuittila-Kivisuo, Finland and Proterozoic molybdenite, Kabeliai, Lithuania: Testing the chronometer in a metamorphic and metasomatic setting

    USGS Publications Warehouse

    Stein, H.J.; Sundblad, K.; Markey, R.J.; Morgan, J.W.; Motuza, G.

    1998-01-01

    Seven 187Re-187Os ages were determined for molybdenite and pyrite samples from two well-dated Precambrian intrusions in Fennoscandia to examine the sustainability of the Re-Os chronometer in a metamorphic and metasomatic setting. Using a new 187Re decay constant (1.666 x 10-11y-1) with a much improved uncertainty (??0.31%), we determined replicate Re-Os ages for molybdenite and pyrite from the Kuittila and Kivisuo prospects in easternmost Finland and for molybdenite from the Kabeliai prospect in southernmost Lithuania. These two localities contain some of the oldest and youngest plutonic activity in Fennoscandia and are associated with newly discovered economic Au mineralization (Ilomantsi, Finland) and a Cu-Mo prospect (Kabeliai, Lithuania). Two Re-Os ages for veinhosted Kabeliai molybdenite average 1486 ?? 5 Ma, in excellent agreement with a 1505 ?? 11 Ma U-Pb zircon age for the hosting Kabeliai granite pluton. The slightly younger age suggests the introduction of Cu-Mo mineralization by a later phase of the Kabeliai magmatic system. Mean Re-Os ages of 2778 ?? 8 Ma and 2781 ?? 8 Ma for Kuittila and Kivisuo molybdenites, respectively, are in reasonable agreement with a 2753 ?? 5 Ma weighted mean U-Pb zircon age for hosting Kuittila tonalite. These Re-Os ages agree well with less precise ages of 2789 ?? 290 Ma for a Rb-Sr whole-rock isochron and 2771 ?? 75 Ma for the average of six Sm-Nd T(DM) model ages for Kuittila tonalite. Three Re-Os analyses of a single pyrite mineral separate, from the same sample of Kuittila pluton that yielded a molybdenite separate, provide individual model ages of 2710 ?? 27, 2777 ?? 28, and 2830 ?? 28 Ma (Re = 17.4, 12.1, and 8.4 ppb, respectively), with a mean value of 2770 ?? 120 Ma in agreement with the Kuittila molybdenite age. The Re and 187Os abundances in these three pyrite splits are highly correlated (r = 0.9994), and provide a 187Re-187Os isochron age of 2607 ?? 47 Ma with an intercept of 21 ppt 187Os (MSWD = 1.1). It appears

  6. The Inextricable Link between Age and Criminal History in Sentencing

    ERIC Educational Resources Information Center

    Bushway, Shawn D.; Piehl, Anne Morrison

    2007-01-01

    In sentencing research, significant negative coefficients on age research have been interpreted as evidence that actors in the criminal justice system discriminate against younger people. This interpretation is incomplete. Criminal sentencing laws generally specify punishment in terms of the number of past events in a defendant's criminal history.…

  7. Metamorphic belts of Anatolia

    NASA Astrophysics Data System (ADS)

    Oberhänsli, Roland; Prouteau, Amaury; Candan, Osman; Bousquet, Romain

    2015-04-01

    Investigating metamorphic rocks from high-pressure/low-temperature (HP/LT) belts that formed during the closure of several oceanic branches, building up the present Anatolia continental micro-plate gives insight to the palaeogeography of the Neotethys Ocean in Anatolia. Two coherent HP/LT metamorphic belts, the Tavşanlı Zone (distal Gondwana margin) and the Ören-Afyon-Bolkardağ Zone (proximal Gondwana margin), parallel their non-metamorphosed equivalent (the Tauride Carbonate Platform) from the Aegean coast in NW Anatolia to southern Central Anatolia. P-T conditions and timing of metamorphism in the Ören-Afyon-Bolkardağ Zone (>70?-65 Ma; 0.8-1.2 GPa/330-420°C) contrast those published for the overlying Tavşanlı Zone (88-78 Ma; 2.4 GPa/500 °C). These belts trace the southern Neotethys suture connecting the Vardar suture in the Hellenides to the Inner Tauride suture along the southern border of the Kirşehir Complex in Central Anatolia. Eastwards, these belts are capped by the Oligo-Miocene Sivas Basin. Another HP/LT metamorphic belt, in the Alanya and Bitlis regions, outlines the southern flank of the Tauride Carbonate Platform. In the Alanya Nappes, south of the Taurides, eclogites and blueschists yielded metamorphic ages around 82-80 Ma (zircon U-Pb and phengite Ar-Ar data). The Alanya-Bitlis HP belt testifies an additional suture not comparable to the northerly Tavşanlı and Ören-Afyon belts, thus implying an additional oceanic branch of the Neotethys. The most likely eastern lateral continuation of this HP belt is the Bitlis Massif, in SE Turkey. There, eclogites (1.9-2.4 GPa/480-540°C) occur within calc-arenitic meta-sediments and in gneisses of the metamorphic (Barrovian-type) basement. Zircon U-Pb ages revealed 84.4-82.4 Ma for peak metamorphism. Carpholite-bearing HP/LT metasediments representing the stratigraphic cover of the Bitlis Massif underwent 0.8-1.2 GPa/340-400°C at 79-74 Ma (Ar-Ar on white mica). These conditions compares to the Tav

  8. Rock relationships in the Mogok metamorphic belt, Tatkon to Mandalay, central Myanmar

    NASA Astrophysics Data System (ADS)

    Mitchell, A. H. G.; Htay, Myint Thein; Htun, Kyaw Min; Win, Myint Naing; Oo, Thura; Hlaing, Tin

    2007-03-01

    The Mogok metamorphic belt (MMB), over 1450 km long and up to 40 km wide, consists of regionally metamorphosed rocks including kyanite and sillimanite schists and granites lying along the Western margin of the Shan Plateau in central Myanmar and continuing northwards to the eastern Himalayan syntaxis. Exposures in quarries allow correlation of Palaeozoic meta-sedimentary, early Mesozoic meta-igneous and late Mesozoic intrusive rocks within a 230 km long northerly-trending segment of the MMB, from Tatkon to Kyanigan north of Mandalay, and with the Mogok gemstone district 100 km to the northeast. Relationships among the metamorphic and intrusive rocks, with sparse published radiometric age controls, indicate at least two metamorphic events, one before and one after the intrusion of Late Jurassic to early Cretaceous calc-alkaline rocks. These relationships can be explained by either of two possible tectonic histories. One, constrained by correlation of mid-Permian limestones across Myanmar, requires early Permian and early Jurassic regional metamorphic events, prior to an early Tertiary metamorphism, in the western part of but within a Shan-Thai - western Myanmar block. The second, not compatible with a single laterally continuous Permian limestone, requires pre-Upper Jurassic regional metamorphism and orogenic gold mineralization in the Mergui Group and western Myanmar, early Cretaceous collision of an east-facing Mergui-western Myanmar island arc with the Shan Plateau, and early Tertiary metamorphism in the MMB related to reversal in tectonic polarity following the arc-Plateau collision.

  9. Integrating field, microstructures, magnetic fabrics, metamorphic studies to establish Yavapai-Mazatazal-aged syntectonic pluton emplacement and strain localization in the Tusas Mountains, New Mexico

    NASA Astrophysics Data System (ADS)

    Davis, P.; Kruckenberg, S. C.

    2012-12-01

    Paleoproterozoic metamorphic rocks in the northern Tusas Mountains of New Mexico record the conditions of deposition, deformation and tectonic processes during assembly and stabilization of these rocks to the southern margin of the Laurentian craton. Metasedimentary and metavolcanic supracrustal rocks of the Vadito and Hondo groups comprise the majority of exposures, detrital zircon from within these units constrain the age of deposition ca. 1.70 Ga. - the Yavapai-Mazatazal temporal orogenic boundary. P-T conditions are ~425-600 C and 4-6 kbars. Two pervasive fold and fabric events are regionally displayed that have been locally modified by a third deformation event. Regional constraints on tectonism timing are mixed, with recent work showing that tectonism occurred ca. 1.4 Ga. Two orthogneiss bodies, the Tres Piedras (TP) and Tusas Mountain (TM) granites, were emplaced into supracrustal host rocks at ca. 1.69 Ga. Several datasets that include mapping and characterization of metamorphic assemblages, EBSD microstructural analysis, and anisotropy of magnetic susceptibility analyses suggest that emplacement was syntectonic. Metamorphic assemblages show a field-gradient that is roughly concentric to the TP and TM plutons from greenschist facies (ca. 400-425 C) in the distant country rock, to upper amphibolite facies (ca. 650 C) near the pluton contacts. This is a new discovery for the region, as most of northern New Mexico displays a regional amphibolite facies signature. Quartz and feldspar microstructures suggest that the body of both plutons record non-coaxial deformation from near solidus to high-T conditions (>600 C). Muscovite inclusions in cm-scale euhedral microcline grains are aligned with S1, and isoclinal folds in the TP lack an axial planar fabric. Measurement of the anisotropy of magnetic susceptibility (AMS) suggest that the orientation of magmatic fabrics within these plutons are consistent with principal regional fabrics (D1) recorded in the

  10. Constraints on the metamorphic history of a mélange complex within the easternmost Himalayan orogen, northern Indo-Burma Range, based on P-T pseudosection and thermobarometric studies.

    NASA Astrophysics Data System (ADS)

    Haproff, P. J.; Yin, A.

    2015-12-01

    Despite many petrologic and structural studies surrounding the eastern Himalayan syntaxis, P-T histories of metamorphic rocks within the northern Indo-Burman mélange of the easternmost Himalayas remain largely unknown. We present metamorphic P-T conditions of three schists from successive thrust sheets related to generation of the Himalayan orogen, based on mineral assemblage thermobarometry and pseudosection phase diagrams. Use of the garnet-muscovite-biotite-plagioclase thermobarometer and Ti-in-biotite thermometer yield peak conditions of 676 ± 78°C and 10.6 ± 1.3 kbar for schist (PH-1-8-13-26) thrust atop metavolcanics, mafic schist, and ultramafics of the Indus-Ysangpo suture zone (IYSZ). Within this sample, quartz is recrystallized along grain boundaries and garnets contain no significant compositional zoning. Pseudosections constructed from bulk-rock composition and equilibrium mineral assemblages yield a clockwise P-T path with similar peak garnet amphibolite conditions. At structurally lower levels, garnet chlorite schist (PH-1-8-13-8) from a thrust klippe of the IYSZ record 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 klippe near a southwestward-directed thrust yields a peak temperature of 679 ± 24°C. Our study reveals a complex metamorphic history throughout the northern Indo-Burman mélange zone that likely records metamorphism at deep crustal levels during thrust motion and growth of the Himalayan orogen around the northeastern corner of India.

  11. Distinguishing among major controls on the apparent thermal and barometric structure of metamorphic belts

    SciTech Connect

    Day, H.W.

    1985-01-01

    The apparent thermal and barometric structures of metamorphosed terrains are expressed in the map patterns of isograds and bathograds. Geographic variation in the apparent P,T of peak metamorphism may be the result of: (1) differences in the amount of tectonic thickening (2) variation in the thermal properties of the lithosphere or (3) differential uplift across the mountain belt. Oversimplified tectonic models of a burial and uplift event, combined with simple physical models for the conductive transfer of heat, have normally been used. The results suggest that the relative roles of the three large scale controls on metamorphism may be distinguished. In mountain belts having variable tectonic thickening, apparent isotherms and isobars of peak metamorphism are parallel. Geographic variation in either thermal properties or uplift history, by contrast, leads to patterns of intersecting apparent isobars and isotherms (e.g.. the New England Appalachians). In terrains that experienced rapid and differential uplift, the most rapidly uplifted portions show the shortest cooling times, the least discordance between apparent mineral ages, and the lowest pressures at peak metamorphism and no necessary correlation between metamorphic grade and cooling time (e.g.. the Alps). In contrast, in terrains with large variations in either thermal parameters or tectonic thickening, long cooling times are directly associated with the highest metamorphic temperatures and the least discordance between apparent mineral ages (e.g.. the Scottish Highlands).

  12. Thermal metamorphism of mantle chromites and the stability of noble-metal nanoparticles

    NASA Astrophysics Data System (ADS)

    González-Jiménez, José M.; Reich, Martin; Camprubí, Antoni; Gervilla, Fernando; Griffin, William L.; Colás, Vanessa; O'Reilly, Suzanne Y.; Proenza, Joaquín A.; Pearson, Norman J.; Centeno-García, Elena

    2015-08-01

    The Loma Baya complex in south-western Mexico is a volume of chromitite-bearing oceanic mantle that records a complex metamorphic history, defined by a first stage of hydrous metamorphism overprinted by a short-lived thermal event associated with an Eocene granite intrusion. During the hydrous metamorphism, the primary magmatic chromite-olivine assemblage was replaced by a secondary, porous intergrowth of Fe2+-rich chromite and chlorite. The heat supplied by an Eocene-age granite intrusion reversed the hydration reaction, producing chromite rims with perfectly developed crystal faces. This third-generation chromite is in equilibrium with highly magnesian (neoformed) olivine and defines a chemical trend analogous to the original magmatic one. The preservation of both reactions in the Loma Baya chromitite provides compelling evidence that the hydration of chromite can be reversed by either prograde metamorphism or any heating event, confirming previous thermodynamic predictions. Understanding these complex features is of particular interest due to the fact that changes in temperature and variable degrees of fluid/rock interaction during metamorphism and intrusion have also significantly affected the chromite-hosted IPGE carrier phases. Here, we propose that the metamorphic fluids involved in the hydrous metamorphism have caused the desulphurization of laurite RuS2, releasing minute particles of Ru-Os-Ir alloys <50 nm in diameter. The following short-lived thermal event that promoted dehydration in the chromitite had the opposite effect on nanoparticle stability, producing a significant coarsening of metal nanoparticles to dimensions larger than a micron. Based on such observations, we argue that IPGE nanoparticles can be exsolved and grown (or coarsen) from sulphide matrices during prograde metamorphism or heating and not exclusively upon cooling under magmatic conditions as it has been previously suggested. These results provide new insights on the relevant role of

  13. Ar-39-Ar-40 Ages of Euerites and the Thermal History of Asteroid 4-Vesta

    NASA Technical Reports Server (NTRS)

    Bogard, Donald D.; Garrison, Daniel H.

    2002-01-01

    Eucrite meteorites are igneous rocks that derive from a large asteroid, probably 4 Vesta. Prior studies have shown that after eucrites formed, most were subsequently metamorphosed to temperatures up to equal to or greater than 800 C, and much later many were brecciated and heated by large impacts into the parent body surface. The uncommon basaltic, unbrecciated eucrites also formed near the surface but presumably escaped later brecciation, whereas the cumulate eucrites formed at depth where metamorphism may have persisted for a considerable period. To further understand the complex HED parent body thermal history, we determined new Ar-39-Ar-40 ages for nine eucrites classified as basaltic but unbrecciated, six eucrites classified as cumulate, and several basaltic-brecciated eucrites. Relatively precise Ar-Ar ages of two cumulate eucrites (Moama and EET87520) and four unbrecciated eucrites give a tight cluster at 4.48 +/1 0.01 Gyr. Ar-Ar ages of six additional unbrecciated eucrites are consistent with this age, within their larger age uncertainties. In contrast, available literature data on Pb-Pb isochron ages of four cumulate eucrites and one unbrecciated eucrite vary over 4.4-4.515 Gyr, and Sm-147 - Nd-143 isochron ages of four cumulate and three unbrecciated eucrites vary over 4.41-4.55 Gyr. Similar Ar-Ar ages for cumulate and unbrecciated eucrites imply that cumulate eucrites do not have a younger formation age than basaltic eucrites, as previously proposed. Rather, we suggest that these cumulate and unbrecciated eucrites resided at depth where parent body temperatures were sufficiently high to cause the K-Ar and some other chronometers to remain open diffusion systems. From the strong clustering of Ar-Ar ages at approximately 4.48 Gyr, we propose that these meteorites were excavated from depth in a single large impact event approximately 4.48 Gyr ago, which quickly cooled the samples and started the K-Ar chronometer. A large (approximately 460 km) crater

  14. Ar-Ar ages and thermal histories of enstatite meteorites

    NASA Astrophysics Data System (ADS)

    Bogard, Donald D.; Dixon, Eleanor T.; Garrison, Daniel H.

    2010-05-01

    Compared with ordinary chondrites, there is a relative paucity of chronological and other data to define the early thermal histories of enstatite parent bodies. In this study, we report 39Ar-40Ar dating results for five EL chondrites: Khairpur, Pillistfer, Hvittis, Blithfield, and Forrest; five EH chondrites: Parsa, Saint Marks, Indarch, Bethune, and Reckling Peak 80259; three igneous-textured enstatite meteorites that represent impact melts on enstatite chondrite parent bodies: Zaklodzie, Queen Alexandra Range 97348, and Queen Alexandra Range 97289; and three aubrites, Norton County, Bishopville, and Cumberland Falls Several Ar-Ar age spectra show unusual 39Ar recoil effects, possibly the result of some of the K residing in unusual sulfide minerals, such as djerfisherite and rodderite, and other age spectra show 40Ar diffusion loss. Few additional Ar-Ar ages for enstatite meteorites are available in the literature. When all available Ar-Ar data on enstatite meteorites are considered, preferred ages of nine chondrites and one aubrite show a range of 4.50-4.54Ga, whereas five other meteorites show only lower age limits over 4.35-4.46Ga. Ar-Ar ages of several enstatite chondrites are as old or older as the oldest Ar-Ar ages of ordinary chondrites, which suggests that enstatite chondrites may have derived from somewhat smaller parent bodies, or were metamorphosed to lower temperatures compared to other chondrite types. Many enstatite meteorites are brecciated and/or shocked, and some of the younger Ar-Ar ages may record these impact events. Although impact heating of ordinary chondrites within the last 1Ga is relatively common for ordinary chondrites, only Bethune gives any significant evidence for such a young event.

  15. Magmatic and metamorphic belts and plutonic-metamorphic complexes of southeastern Alaska

    SciTech Connect

    Brew, D.A.; Himmelberg, G.R.; Ford, A.B.; Loney, R.A. . Branch of Alaskan Geology Univ. of Missouri, Columbia, MO . Dept. of Geology)

    1993-04-01

    The Cordilleran orogen in southeastern Alaska includes 24 distinct magmatic belts, ranging in age from Cambrian to Holocene, that are defined by map relations, lithology, age, and chemical composition. The youngest magmatic features are Quaternary-age pre- and post-glacial volcanic rocks that occur in three major fields in the region, as well as in isolated locations. Cenozoic magmatic features consist of four major and three minor belts. The major Tkope-Portland Peninsula belt of Oligocene age includes both volcanic and plutonic rocks. The major calcalkalic Coast Mountains belt of early and middle Eocene age is the single largest magmatic feature of the region. Early Tertiary and latest Cretaceous magmatism is represented by the major calcalkalic great tonalite sill belt, a remarkable long and narrow feature along the west side of the Coast Mountains. Cretaceous and Jurassic intrusive rocks occur in five major belts and two minor belts in the region and Paleozoic intrusive rocks occur in four major and two minor belts. The three major plutonic-metamorphic complexes (PMC), from east to west, are: the Coast PMC in the Coast Mountains; the Glacier Bay-Chichag of plutonic complex (Chugach MC) in the northern outer islands. The Coast PMC records dynamothermal and regional contact metamorphic events related to regional plutonism within several juxtaposed terranes; its lengthy and complicated history is related to the Late Cretaceous collision of the Alexander and Wrangellia terranes and the Gravina overlap assemblage to the west against the Yukon prong and Stikine terrane to the east. The relatively simple Glacier Bay PC history is recorded as the roots of a Late Jurassic through late Early Cretaceous island arc that probably developed during the early stages of the above tectonic event. The complicated Chugach MC history developed during and after the Late Cretaceous collision of the Chugach terrane with the Wrangellia and Alexander terranes.

  16. SHRIMP U-Pb age and high temperature conditions of the collisional metamorphism in the Várzea do Capivarita Complex: Implications for the origin of Pelotas Batholith, Dom Feliciano Belt, southern Brazil

    NASA Astrophysics Data System (ADS)

    Philipp, Ruy Paulo; Bom, Francisco Molina; Pimentel, Márcio Martins; Junges, Sérgio Luiz; Zvirtes, Gustavo

    2016-03-01

    The Várzea do Capivarita Complex is composed of pelitic gneisses with subordinate calc-silicate rock, marble and rare quartzite. It is part of the neoproterozoic Dom Feliciano Belt, in southern Brazil. The gneisses are associated to veins and tabular leucogranite bodies, which are the product of anatexis of the pelitic gneiss. The paragneisses of the Várzea do Capivarita Complex are tectonically juxtaposed to orthogneisses of the Arroio dos Ratos Complex. This complex is exposed as megaxenoliths in granites of the Encruzilhada do Sul Suite and as smaller fragments in the Quitéria and Cordilheira Granites, all part of the Pelotas Batholith. The metamorphic foliation is oriented to N30°W, with dips between 35 and 55° to the SW and mineral lineation is suborizontal with rake ranging from 15° to 30° and down dip to NW and SE, suggesting deformation associated with a transpressive system. Based on the paragenesis garnet-cordierite-sillimanite-biotite, metamorphism occurred at 720-820° C and pressure of 8-9 kbar, characterizing it as of intermediate pressure and high temperature series. Zircon grains of one sample of garnet-cordierite-sillimanite-biotite gneiss and one of peraluminous leucogranite was dated by the U-Pb SHRIMP method. The paragneiss metamorphic zircon yielded an age of 619 ± 4.3 Ma interpreted as an age of the main metamorphic event, whereas igneous zircon grains from the leucogranite indicates that magma crystallization took place at 620 ± 6.3 Ma. The main metamorphic foliation (S2) of the paragneiss and the leucogranite magmatic foliation (S0) are parallel to each other, indicating that they were formed during the same event. This suggests that anatexis of the paragneisses of the Várzea do Capivarite Complex generated the peraluminous leucogranites right after the climax of the collisional metamorphism.

  17. Ar-Ar and I-Xe Ages and the Thermal History of IAB Meteorites

    NASA Technical Reports Server (NTRS)

    Bogard, Donald D.; Garrison, Daniel H.; Takeda, Hiroshi

    2004-01-01

    Studies of several samples of the large Caddo County IAB iron meteorite reveal andesitic material, enriched in Si, Nay Al and Ca, which is essentially unique among meteorites. This material is believed to have formed from a chondritic source by partial melting and to have further segregated by grain coarsening. Such an origin implies extended metamorphism of the IAB parent body. New Ar-39-Ar-40 ages for silicate from three different Caddo samples are consistent with a common age of 4.50- 4.51 Gyr ago. Less well defined Ar-Ar degassing ages for inclusions from two other IABs, EET8333 and Udei Station, are approx.4.32 Gyr, whereas the age for Campo del Cielo varies considerably over approx.3.23-4.56 Gyr. New I-129-Xe-129 ages for Caddo County and EET8333 are 4561.9 +/-0.1 Myr and 4560-4563 Myr, respectively, relative to an age of 4566 Myr for Shallowater. Considering all reported Ar-Ar ages for IABs and related winonaites, the range is approx.4.32-4.53 Gyr, but several IABs give similar Ar ages of 4.50-4.52 Gyr. We interpret these older ages to represent cooling after the time of last significant metamorphism on the parent body, and the younger ages to represent later Ar-40 diffusion loss. These older Ar-Ar ages are similar to Sm-Nd and Rb-Sr isochron ages reported in the literature for Caddo County. Considering the possibility that IAB parent body formation was followed by impact disruption, reassembly, and metamorphism (e.g., Benedix et al. 2000), the time of the post-assembly metamorphism may have been as late as approx.4.53 Gyr ago. However, precise I-Xe ages reported for some IABs define a range of ages of approx.4560 to approx.4576 My. The older I-Xe ages exceed the oldest precise radiometric ages of meteorites, appear unrealistic, and suggest a bias in the calibration of all I-Xe ages. But even with such a bias, the I-Xe ages of IABs cannot easily be reconciled with the much younger Ar-Ar and Sm-Nd ages and with cooling rates deduced from Ni concentration

  18. Ar-Ar and I-Xe Ages and the Thermal History of IAB Meteorites

    NASA Technical Reports Server (NTRS)

    Bogard, Donald D.; Garrison, Daniel H.; Takeda, Hiroshi

    2004-01-01

    Studies of several samples of the large Caddo County IAB iron meteorite reveal andesitic material, enriched in Si, Na, Al and Ca, which is essentially unique among meteorites. This material is believed to have formed from a chondritic source by partial melting and to have further segregated by grain coarsening. Such an origin implies extended metamorphism of the IAB parent body. New Ar-39-Ar-40 ages for silicate from three different Caddo samples are consistent with a common age of 4.50-4.51 Gyr ago. Less well defined Ar-Ar degassing ages for inclusions from two other IABs, EET8333 and Udei Station, are approx.4.32 Gyr, whereas the age for Campo del Cielo varies considerably over approx.3.23-4.56 Gyr. New I-129-Xe-129 ages for Caddo County and EET8333 are 4561.9+/-0.1 Myr and 4560- 4563 Myr, respectively, relative to an age of 4566 Myr for Shallowater. Considering all reported Ar-Ar ages for IABs and related winonaites, the range is approx.4.32-4.53 Gyr, but several IABs give similar Ar ages of 4.50-4.52 Gyr. We interpret these older ages to represent cooling after the time of last significant metamorphism on the parent body, and the younger ages to represent later Ar-40 diffusion loss. These older Ar-Ar ages are similar to Sm-Nd and Rb-Sr isochron ages reported in the literature for Caddo County. Considering the possibility that IAB parent body formation was followed by impact disruption, reassembly, and metamorphism (e.g., Benedix et al. 2000), the time of the post-assembly metamorphism may have been as late as approx.4.53 Gyr ago. However, precise I-Xe ages reported for some IABs define a range of ages of approx.4560 to approx.4576 Myr. The older I-Xe ages exceed the oldest precise radiometric ages of meteorites, appear unrealistic, and s,uggest a bias in the calibration of all I-Xe ages. But even with such a bias, the I-Xe ages of IABs cannot easily be reconciled with the much younger Ar-Ar and Sm-Nd ages and with cooling rates deduced from Ni concentration

  19. Ar-Ar and I-Xe Ages and the Thermal History of IAB Meteorites

    NASA Technical Reports Server (NTRS)

    Bogard, Donald D.; Garrison, Daniel H.; Takeda, Hiroshi

    2005-01-01

    Studies of several samples of the large Caddo County IAB iron meteorite reveal andesitic material, enriched in Si, Na, Al and Ca, which is essentially unique among meteorites. This material is believed to have formed from a chondritic source by partial melting and to have further segregated by grain coarsening. Such an origin implies extended metamorphism of the IAB parent body. New Ar-39- Ar-40 ages for silicate from three different Caddo samples are consistent with a common age of 4.50-4.51 Gyr ago. Less well defined Ar-Ar degassing ages for inclusions from two other IABs, EET8333 and Udei Station, are approx.4.32 Gyr, whereas the age for Campo del Cielo varies considerably over approx.3.23-4.56 Gyr. New I-129-Xe-129 ages for Caddo County and EET8333 are 4557.9+/-0.1 Myr and 4557-4560 Myr, respectively, relative to an age of 4562.3 Myr for Shallowater. Considering all reported Ar-Ar degassing ages for IABs and related winonaites, the range is approx.4.32-4.53 Gyr, but several IABs give similar Ar ages of 4.50-4.52 Gyr. We interpret these older Ar ages to represent cooling after the time of last significant metamorphism on the parent body, and the younger ages to represent later 40Ar diffusion loss. The older Ar-Ar ages for IABs are similar to Sm-Nd and Rb-Sr isochron ages reported in the literature for Caddo County. Considering the possibility that IAB parent body formation was followed by impact disruption, reassembly, and metamorphism (e.g., Benedix et al. 2000), the Ar-Ar ages and IAB cooling rates deduced from Ni concentration profiles in IAB metal (Herpfer et al., 1994) are consistent if the time of the post-assembly metamorphism was as late as approx.4.53 Gyr ago. However, I-Xe ages reported for some IABs define much older ages of approx.4558-4566 Myr, which cannot easily be reconciled with the much younger Ar-Ar and Sm-Nd ages. An explanation for the difference in radiometric ages of IABs may reside in combinations of the following: a) I-Xe ages have very

  20. Ar-Ar and I-XE Ages and the Thermal History of IAB Meteorites

    NASA Technical Reports Server (NTRS)

    Bogard, Donald D.; Garrison, Daniel H.; Takeda, Hiroshi

    2006-01-01

    Studies of several samples of the large Caddo County IAB iron meteorite reveal andesitic material, enriched in Si, Na, Al and Ca which is essentially unique among meteorites. This material is believed to have formed from a chondritic source by partial melting and to have further segregated by grain coarsening. Such an origin implies extended metamorphism of the IAB parent body. New Ar-39- Ar-40 ages for silicate from three different Caddo samples are consistent with a common age of 4.50- 4.51 Gyr ago. Less well defined Ar-Ar degassing ages for inclusions from two other IABs, EET8333 and Udei Station, are approx. 4.32 Gyr, whereas the age for Campo del Cielo varies considerably over approx. 3.23-4.56 Gyr. New I-129-Xe-129 ges for Caddo County and EET8333 are 4561.9 plus or minus 0.1 Myr and 4560-4563 Myr, respectively, relative to an age of 4566 Myr for Shallowater. Considering all reported Ar-Ar ages for IABs and related winonaites, the range is approx. 4.32-4.53 Gyr, but several IABs give similar Ar ages of 4.50-4.52 Gyr. We interpret these older ages to represent cooling after the time of last significant metamorphism on the parent body, and the younger ages to represent later 40Ar diffusion loss. These older Ar-Ar ages are similar to Sm-Nd and Rb-Sr isochron ages reported in the literature for Caddo County. Considering the possibility that IAB parent body formation was followed by impact disruption, reassembly, and metamorphism (e.g., Benedix et al. 2000), the time of the postassembly metamorphism may have been as late as approx. 4.53 Gyr ago. However, precise I-Xe ages reported for some IABs define a range of ages of approx. 4560 to approx. 4576 Myr. The older I-Xe ages exceed the oldest precise radiometric ages of meteorites, appear unrealistic, and suggest a bias in the calibration of all I-Xe ages. But even with such a bias, the I-Xe ages of IABs cannot easily be reconciled with the much younger Ar-Ar and Sm-Nd ages and with cooling rates deduced from Ni

  1. Acting Out History from the Ice Age to the Modern Age.

    ERIC Educational Resources Information Center

    Mattioli, Denee J.; Drake, Frederick

    1999-01-01

    Addresses the teaching methods of Michael Welch, a seventh grade teacher, who incorporates the humanities, such as drama and literature, into his history classroom in order to help students learn to question, think analytically, solve problems, and make decisions. Summarizes a particular unit on the Ice Age. (CMK)

  2. Natural history of aging in Cornelia de Lange syndrome.

    PubMed

    Kline, Antonie D; Grados, Marco; Sponseller, Paul; Levy, Howard P; Blagowidow, Natalie; Schoedel, Christianne; Rampolla, Joni; Clemens, Douglas K; Krantz, Ian; Kimball, Amy; Pichard, Carmen; Tuchman, David

    2007-08-15

    Observations about the natural history of aging in Cornelia de Lange syndrome (CdLS) are made, based on 49 patients from a multidisciplinary clinic for adolescents and adults. The mean age was 17 years. Although most patients remain small, obesity may develop. Gastroesophageal reflux persists or worsens, and there are early long-term sequelae, including Barrett esophagus in 10%; other gastrointestinal findings include risk for volvulus, rumination, and chronic constipation. Submucous cleft palate was found in 14%, most undetected before our evaluation. Chronic sinusitis was noted in 39%, often with nasal polyps. Blepharitis improves with age; cataracts and detached retina may occur. Decreased bone density is observed, with occasional fractures. One quarter have leg length discrepancy and 39% scoliosis. Most females have delayed or irregular menses but normal gynecologic exams and pap smears. Benign prostatic hypertrophy occurred in one male prior to 40 years. The phenotype is variable, but there is a distinct pattern of facial changes with aging. Premature gray hair is frequent; two patients had cutis verticis gyrata. Behavioral issues and specific psychiatric diagnoses, including self-injury, anxiety, attention-deficit disorder, autistic features, depression, and obsessive-compulsive behavior, often worsen with age. This work presents some evidence for accelerated aging in CdLS. Of 53% with mutation analysis, 55% demonstrate a detectable mutation in NIPBL or SMC1A. Although no specific genotype-phenotype correlations have been firmly established, individuals with missense mutations in NIPBL and SMC1A appear milder than those with other mutations. Based on these observations, recommendations for clinical management of adults with CdLS are made. PMID:17640042

  3. LIFE HISTORY. Age-related mortality explains life history strategies of tropical and temperate songbirds.

    PubMed

    Martin, Thomas E

    2015-08-28

    Life history theory attempts to explain why species differ in offspring number and quality, growth rate, and parental effort. I show that unappreciated interactions of these traits in response to age-related mortality risk challenge traditional perspectives and explain life history evolution in songbirds. Counter to a long-standing paradigm, tropical songbirds grow at similar overall rates to temperate species but grow wings relatively faster. These growth tactics are favored by predation risk, both in and after leaving the nest, and are facilitated by greater provisioning of individual offspring by parents. Increased provisioning of individual offspring depends on partitioning effort among fewer young because of constraints on effort from adult and nest mortality. These growth and provisioning responses to mortality risk finally explain the conundrum of small clutch sizes of tropical birds. PMID:26315435

  4. Timing and duration of garnet granulite metamorphism in magmatic arc crust, Fiordland, New Zealand

    USGS Publications Warehouse

    Stowell, H.; Tulloch, A.; Zuluaga, C.; Koenig, A.

    2010-01-01

    Pembroke Granulite from Fiordland, New Zealand provides a window into the mid- to lower crust of magmatic arcs. Garnet Sm-Nd and zircon U-Pb ages constrain the timing and duration of high-P partial melting that produced trondhjemitic high Sr/Y magma. Trace element zoning in large, euhedral garnet is compatible with little post growth modification and supports the interpretation that garnet Sm-Nd ages of 126.1??2.0 and 122.6??2.0. Ma date crystal growth. Integration of the garnet ages with U-Pb zircon ages elucidates a history of intrusion(?) and a protracted period of high-temperature metamorphism and partial melting. The oldest zircon ages of 163 to 150. Ma reflect inheritance or intrusion and a cluster of zircon ages ca. 134. Ma date orthopyroxene-bearing mineral assemblages that may be magmatic or metamorphic in origin. Zircon and garnet ages from unmelted gneiss and garnet reaction zones record garnet granulite facies metamorphism at 128 to 126. Ma. Peritectic garnet and additional zircon ages from trondhjemite veins and garnet reaction zones indicate that garnet growth and partial melting lasted until ca. 123. Ma. Two single fraction garnet ages and young zircon ages suggest continued high-temperature re-equilibration until ca. 95. Ma. Phase diagram sections constrain orthopyroxene assemblages to <0.6 GPa @ 650??C, peak garnet granulite facies metamorphic conditions to 680-815??C @ 1.1-1.4. GPa, and a P-T path with a P increase of???0.5. GPa. These sections are compatible with water contents???0.28wt.%, local dehydration during garnet granulite metamorphism, and <0.3. GPa P increases during garnet growth. Results demonstrate the utility of integrated U-Pb zircon and Sm-Nd garnet ages, and phase diagram sections for understanding the nature, duration, and conditions of deep crustal metamorphism and melting. Geochronologic and thermobarometric data for garnet granulite indicate that thickening of arc crust, which caused high-pressure metamorphism in northern

  5. Zircon U-Pb ages, Hf isotope data, and tectonic implications of Early-Middle Triassic granitoids in the Ailaoshan high-grade metamorphic belt of Southeast Tibet

    NASA Astrophysics Data System (ADS)

    Wu, Wenbin; Liu, Junlai; Chen, Xiaoyu; Zhang, Lisheng

    2016-05-01

    The Ailaoshan tectonic belt, where the effects of the Paleo-Tethyan ocean evolution and Indian-Eurasian plate collision are superimposed, is one of the most significant geological discontinuities in western Yunnan province of southeast Tibet. An Ailaoshan micro-block within the belt is bounded by the Ailaoshan suture zone to the west and the Red River Fault to the east, and consists of low- and high-grade metamorphic belts. Late Permian-Middle Triassic granitoids that are widely distributed to the west of the Ailaoshan suture zone and within the Ailaoshan micro-block may yield significant information on the Tethyan tectonic evolution of the Ailaoshan tectonic belt. This study reports new LA-ICP-MS zircon U-Pb geochronology and Hf isotope data of four granitoids from the Ailaoshan high-grade metamorphic belt. Zircon grains from the Yinjie granitoid do not have inherited cores and yield a weighted mean U-Pb age of 247.1 ± 2.0 Ma. The zircon ɛ Hf(t) values range from 7.8 to 12.1, and Hf model ages from 775 to 546 Ma, indicating that the granitoid was derived from juvenile crust. The rims of zircons from the Majie and Yuanjiang granitoids yield weighted mean U-Pb ages of 239.5 ± 1.8 and 237.9 ± 2.6 Ma, respectively, whereas the cores yield ages of 1608-352 Ma. The ɛ Hf(t) values of zircon rims range from -20.4 to -5.3, yielding Hf model ages from 2557 to 1606 Ma and suggesting that the source magma of the Majie and Yuanjiang granitoids was derived from ancient crust. An additional granitoid located near the Majie Village yields a zircon U-Pb age of 241.2 ± 1.0 Ma. Based on our geochronological and geochemical data, combined with geological observations, we propose that the Ailaoshan micro-block was derived from the western margin of the Yangtze block, and is comparable to the Zhongzan and Nam Co micro-blocks. The presence of late Permian mafic rocks with rift-related geochemical characteristics within the Ailaoshan micro-block, together with granitoids derived

  6. History of allergy in the middle ages and renaissance.

    PubMed

    Ring, Johannes

    2014-01-01

    In the Middle Ages little innovative medical literature came from Western Europe. The Greek-Roman tradition with the scriptures of Hippocrates and Galenos was preserved in Byzantium and then in the Middle East by Arabic medicine; it then returned to Europe in Latin translations mostly made in Italy and Spain. There were innovative developments in Arabic medicine also with regard to the history of allergy, especially with the first description of 'rose fever', which is described as very similar in symptomatology to hay fever. Under Arabic influence, the first medical university in Salerno was famous for its well-known text Tacuinum sanitatis in which a description of asthma can be found. With the beginning of renaissance new developments were also registered in Europe, with new observations and a new way of thinking. PMID:24925380

  7. Upper Cretaceous exhumation of the western Rhodope Metamorphic Province (Chalkidiki Peninsula, northern Greece)

    NASA Astrophysics Data System (ADS)

    Kydonakis, Konstantinos; Gallagher, Kerry; Brun, Jean-Pierre; Jolivet, Marc; Gueydan, Frédéric; Kostopoulos, Dimitrios

    2014-06-01

    The Vertiskos Unit of northern Greece is an elongated basement belt with a complex poly-metamorphic history. It extends from Greece (Chalkidiki peninsula), to the south, up to Serbia, in the north, and arguably represents the westernmost part of the Rhodope Metamorphic Province (northern Greece to southern Bulgaria). The Vertiskos Unit experienced a medium pressure lower amphibolite-facies metamorphic overprint during the Alpine Orogeny. The available medium-temperature geochronology implies that it remained at temperature of approximately 300°C (or slightly higher) during Lower Cretaceous. In order to constrain its post-Lower Cretaceous thermal history, until near-surface exposure, we applied apatite fission track analysis. The central ages obtained range from 68.5 ± 3.8 to 46.6 ± 3.6 Ma (uppermost Cretaceous to Middle Eocene) and mean track lengths between 13 and 13.5 µm. We applied two inverse thermal modeling approaches using either each sample independently (high degree of freedom in the thermal history, better data fit) or all samples together interpreting them as a vertical profile (simpler thermal history, worse data fit). Irrespective of the modeling approach, we conclude that the bulk thermal history of the Vertiskos Unit crosses the high-temperature limit of the apatite partial annealing zone by the uppermost Cretaceous and reaches near-surface conditions as early as lower/middle Eocene. These results contrast with the thermal history of the other domains of the Rhodope Metamorphic Province further east (namely the Southern Rhodope Core Complex and the Northern Rhodope Complex) and establish the Vertiskos basement complex as the oldest exhumed coherent basement fragment of the Rhodope Metamorphic Province and Greece.

  8. Class Struggles: Teaching History in the Postmodern Age.

    ERIC Educational Resources Information Center

    Wilton, Shirley

    1999-01-01

    Describes Generation X students. Believes that teaching history to Generation X requires rebuilding the connections between community college teachers and four year schools that invent the "new history." Discusses how teachers can use the new history, "reflexive methodology," pictures from art history, and storytelling in the postmodern classroom.…

  9. Age of the Druksiai-Polotsk deformation zone, Lithuania: a U-Pb dating of metamorphic titanite

    NASA Astrophysics Data System (ADS)

    Vejelyte, Irma; Bogdanova, Svetlana; Salnikova, Ekaterina

    2010-05-01

    The studied Druksiai-Polotsk deformation zone (DPDZ) transects the East Lithuanian Domain (ELD), representing the southern margin of the major Polotsk-Kurzeme zone of faulting in the Baltic-Belarus region. The DPDZ is of 35-40 km wide, E-W trending, and marked well by linear gravity and magnetic anomalies. The crystalline rocks within the DPDZ are granulites, biotite granites, and migmatites, the latter consisting of amphibole-plagioclase paleo- and mesosomes, and plagioclase-quartz-biotite±microcline±amphibole neosomes. Because of ductile shearing gneisses, augen mylonites, mylonites and ultramylonites were produced while tectonic breccias and pseudotachyllite were formed by later brittle deformation. According to geophysical data and the surface morphology of the crystalline basement, a horst-graben structure have recognized along the DPDZ. The graben is filled with Vendian, Cambrian, Ordovician, Silurian and Devonian deposits. A U-Pb dating of titanite from an augen granitoid mylonite in the DPDZ has yielded a concordant age of 1534±9 Ma. This light brown titanite follows the folation in the host rock and was obviously formed during retrogression from amphibolite- to epidote-amphibolite facies and coeval mylonitization. Shear zones of the same age are known in southern and central Sweden and in NE Poland. These E-W trending deformation zones accommodate both mafic and granitoid intrusions and are probably related to an extensional period in the Mesoproterozoic evolution in the western part of the East European Craton. This is a contribution to the project "The Precambrian structure of Baltica as a control of its recent environment and evolution" of the Visby Programme supported by the Swedish Institute and the Lithuanian State Science and Studies Foundation.

  10. New U-Pb and Sm-Nd isotope data of the age of formation and metamorphic alteration of the Kandalaksha-Kolvitsa gabbro-anorthosite complex (Baltic Shield)

    NASA Astrophysics Data System (ADS)

    Steshenko, Ekaterina; Bayanova, Tamara; Serov, Pavel; Chashchin, Viktor

    2016-04-01

    The aim of this research was to study the isotope U-Pb age of zircon and rutile and Sm-Nd (rock forming and sulphide minerals) in Kandalaksha-Kolvitsa gabbro-anorthosite complex. Kandalaksha-Kolvitsa gabbro-anorthosite complex is located in the N-E part of Baltic shield and consists of three parts. Marginal zone (mesocratic metanorite) lies at the base of the massif. Main zone is composed of leucocratic metagabbro. The upper zone is alteration of mataanorthosite and leucocratic metagabbro. All rocks were subjected to granulate metamorphism. New U-Pb and Sm-Nd isotopic and geochronological data for the rocks of the Kandalaksha-Kolvitsa Paleoproterozoic gabbro-anorthosite complex is presented. For the first time single zircon grains from metagabbros of Kolvitsa massif were dated 2448±5 Ma, using U-Pb method with an artificial 205Pb tracer. Sm-Nd isotopic age of the metamorphic minerals apatite, garnet and sulphide WR Kolvitsa array is 1985 ± 17 Ma, which is interpreted granulite metamorphism. Two fractions of single zircons from anorthosite of the Kandalaksha massif gave U-Pb age 2450± 3 Ma. Leucocratic gabbro-norite (Kandalaksha massif) were dated by U-Pb on single zircon, with age up to 2230±10 Ma. This age reflects the time of granulite metamorphism according to data of [1]. Two fractions of rutile from anorthosite of the Kandalaksha massif have been analyzed by U-Pb method and reflect age of 1700 ± 10 Ma. It is known that the closure temperature of U-Pb system rutile 400-450 ° C [2], thus cooling of the massif to these temperatures was about 1.7 Ga. These data suggested two stages of metamorphic transformations of the massif. Sm-Nd research Kandalaksha massif reflected the age of the high-temperature metasomatic transformations -1887 ± 37 Ma. Time of regional fluid processing - 1692 ± 71 Ma. A model Sm-Nd age metagabbros Kolvitsa massif is 3.3 Ga with a negative value ɛNd = -4.6, which corresponds to the most likely primary enriched mantle reservoir of

  11. {sup 40}Ar/{sup 39}Ar thermochronology and thermobarometry of metamorphism, plutonism, and tectonic denudation in the Old Woman Mountains area, California

    SciTech Connect

    Foster, D.A.; Miller, C.F.; Harrison, T.M.; Hoisch, T.D.

    1992-02-01

    Discrimination of individual tectonometamorphic events in polymetamorphosed terranes requires a comprehensive understanding of the relative timing and conditions of metamorphism and plutonism. We have applied a combination of {sup 40}Ar/{sup 39} Ar thermochronology, petrology, and thermobarometry to reconstruct the complex Early Proterozoic through early Cenozoic tectonic and metamorphic evolution of continental crust in the Old Woman Mountains area, southeastern California. Strong Mesozoic thermal events obscure the earlier history in much of the Old Woman Mountains area. In those areas where Early Proterozoic rocks underwent only lower-greenschist-facies metamorphism during the Mesozoic, thermobarometry of pelitic schists indicates that Proterozoic metamorphism occurred at 9 to 11 kbar and {approximately}700 {degrees}C. {sup 40}Ar/{sup 39}Ar ages of hornblende from samples of interbedded Proterozoic amphibolite indicate that this high-grade metamorphism took place before 1600 Ma. The relatively high-pressure conditions of Early Proterozoic metamorphism in the Old Woman Mountains area contrast with the low-pressure granulite-facies metamorphism that occurred elsewhere in the Mojave Desert at this time. {sup 40}Ar/{sup 39}Ar analyses of hornblende from Proterozoic rocks within Mesozoic shear zones and hornblende barometry from Jurassic intrusive rocks suggest that tectonism and burial of Paleozoic strata to >10 km began between 170 and 150 Ma. This tectonism resulted in regional greenschist-facies metamorphism. Late-stage mineral assemblages in Proterozoic and Paleozoic pelitic rocks in the Old Woman Mountains area indicate an increase in metamorphic grade from greenschist to upper amphibolite facies toward Later Cretaceous Plutons of the 73 Ma Old Woman-Piute batholith. Barometric calculations from garnet-bearing metamorphic rocks suggest that this Cretaceous metamorphism took place at 3.5 to 5.0 kbar in the Old Woman Mountains. 68 refs., 11 figs., 3 tabs.

  12. Shock Metamorphism of the Dhofar 378 Basaltic Shergottite

    NASA Technical Reports Server (NTRS)

    Mikouchi, T.; McKay, G.

    2006-01-01

    Shock metamorphism is one of the most fundamental processes in the history of Martian meteorites, especially shergottites, which affect their mineralogy and chronology. The formation of "maskelynite" from plagioclase and shock melts is such major mineralogical effects. Dhofar 378 is one of the recently found desert shergottites that is mainly composed of plagioclase and pyroxene. This shergottite is important because of its highly shocked nature and unique plagioclase texture, and thus has a great potential for assessing a "shock" age of shergottites. We have been working on a combined study of mineralogy and chronology of the same rock chip of Dhofar 378. This abstract reports its mineralogical part.

  13. Canada basin: age and history of its continental margin

    SciTech Connect

    Sweeney, J.F.

    1985-02-01

    Presently available age controls suggest that the Canada basin formed during the Cretaceous Period between about 131 and 79 Ma. The opening process began with continental breakup that may have involved all parts of the North American polar margin at about the same time. The opening was completed by the formation of oceanic crust during the extended Cretaceous interval of normal geomagnetic polarity. Features characteristics of continental breakup, insofar as they are known, show systematic regional differences. From Brock to Axel Heiberg Island, continental breakup was associated with an extended (100 + Ma) stratigraphic hiatus and, northeastward from Ellef Ringnes Island, with extensive tholeiitic igneous activity. From Banks Island to northeastern Alaska, the breakup interval was abbreviated (20-30 Ma), and sparse igneous activity occurred. These differences can be produced by changes in the rate and/or amount of crustal stretching during margin formation and would imply relatively faster or more stretching northeast of Brock island. A continental margin of fixed age, exhibiting the indicated pattern of crustal stretching, could be produced along the trailing edge of a rotating block (Arctic Alaska terrane AA) with its pivot near the Mackenzie delta. When the rotation is restored, however, geological discrepancies are evident between Devonian and older rocks across the conjugate margins, suggesting an earlier history of drifting for the AA. Early Paleozoic correlations appear improved if the AA is placed, polar margin to polar margin, against northern Ellesmere Island and Greenland, where in the middle Paleozoic, it was sheared sinistrally along the Canadian margin to its pre-rotated position opposite Banks Island.

  14. Zircon U-Pb ages, Hf isotopes and geochemistry of the schists, gneisses and granites in Delbar Metamorphic-Igneous Complex, SE of Shahrood (Iran): Implications for Neoproterozoic geodynamic evolutions of Central Iran

    NASA Astrophysics Data System (ADS)

    Balaghi Einalou, Maryam; Sadeghian, Mahmoud; Zhai, Minggou; Ghasemi, Habibollah; Mohajjel, Mohammad

    2014-10-01

    The Delbar Metamorphic-Igneous Complex (DMIC) consists of the medium to high-grade metamorphic rocks and granites - leucogranites is located in the Biarjmand region, in Central Iran. U-Pb dating of the gneisses yielded the ages of 546 ± 3.7-547 ± 6.8 Ma similar to the crystallization ages of leucogranites (541 ± 4.7-547 ± 11 Ma) are consistent to the Late Ediacaran-Early Cambrian ages of Cadomian magmatic arc (∼545 Ma). The 206Pb/238U ages of the detrital zircons from the mica-schists sample are from 551 ± 5.1-549 ± 5.1 Ma. The youngest ages of the meta-pelitic protolith have 10 Ma age intervals compared to the granites emplacement age, which indicates rapid Late Precambrian crustal recycling involving erosion, burial, metamorphism to partial melting of the continental crust in less than ca. 10 Ma. These rapid crustal evolutions were related to the final collision and amalgamation of Gondwana, the Rheic Ocean clouser and coeval paleotethys opening at the end of the Avalonian-Cadomian orogeny. The studied granites are similar to the volcanic arc granitoids and originated from the crustal source in an active continental margin based on the geochemical characteristics and Hf isotopes data. Exhumation of the DMIC Complex, is marked by deposition of Lower Jurassic conglomerates contains pebbles of basement rocks. These rocks were interrupted by mafic swarms dikes that have generated in a back arc extensional setting related to the Neotethys subduction under the Central Iran at the 152 ± 35 Ma (Middle-Late Jurassic) based on the U-Pb apatite dating.

  15. The history of a continent from U-Pb ages of zircons from Orinoco River sand and Sm-Nd isotopes in Orinoco basin river sediments

    USGS Publications Warehouse

    Goldstein, S.L.; Arndt, N.T.; Stallard, R.F.

    1997-01-01

    We report SHRIMP U-Pb ages of 49 zircons from a sand sample from the lower Orinoco River, Venezuela, and Nd model ages of the fine sediment load from the main river and tributaries. The U-Pb ages reflect individual magmatic or metamorphic events, the Sm-Nd model ages reflect average crustal-residence ages of the sediment sources. Together they allow delineation of the crust-formation history of the basement precursors of the sediments. The U-Pb ages range from 2.83 to 0.15 Ga, and most are concordant or nearly so. Discrete age groupings occur at ??? 2.8, ??? 2.1, and ??? 1.1 Ga. The oldest group contains only three samples but is isolated from its closest neighbors by a ??? 600 Ma age gap. Larger age groupings at ??? 2.1 and ??? 1.1 Ga make up about a third and a quarter of the total number of analyses, respectively. The remaining analyses scatter along concordia, and most are younger than 1.6 Ga. The ??? 2.8 and ??? 2.1 Ga ages correspond to periods of crust formation of the Imataca and Trans-Amazonian provinces of the Guyana Shield, respectively, and record intervals of short but intensive continental growth. These ages coincide with ??? 2.9 and ??? 2.1 Ga Nd model ages of sediments from tributaries draining the Archean and Proterozoic provinces of the Guyana Shield, respectively, indicating that the U-Pb ages record the geological history of the crystalline basement of the Orinoco basin. Zircons with ages corresponding to the major orogenies of the North Atlantic continents (the Superior at ??? 2.7 Ga and Hudsonian at 1.7-1.9 Ga) were not found in the Orinoco sample. The age distribution may indicate that South and North America were separated throughout their history. Nd model ages of sediments from the lower Orinoco River and Andean tributaries are ??? 1.9 Ga, broadly within the range displayed by major rivers and dusts. This age does not coincide with known thermal events in the region and reflects mixing of sources with different crust-formation ages. The

  16. Pressure-temperature evolution of Neoproterozoic metamorphism in the Welayati Formation (Kabul Block), Afghanistan

    NASA Astrophysics Data System (ADS)

    Collett, Stephen; Faryad, Shah Wali

    2015-11-01

    The Welayati Formation, consisting of alternating layers of mica-schist and quartzite with lenses of amphibolite, unconformably overlies the Neoarchean Sherdarwaza Formation of the Kabul Block that underwent Paleoproterozoic granulite-facies and Neoproterozoic amphibolite-facies metamorphic events. To analyze metamorphic history of the Welayati Formation and its relations to the underlying Sherdarwaza Formation, petrographic study and pressure-temperature (P-T) pseudosection modeling were applied to staurolite- and kyanite-bearing mica-schists, which crop out to the south of Kabul City. Prograde metamorphism, identified by inclusion trails and chemical zonation in garnet from the micaschists indicates that the rocks underwent burial from around 6.2 kbar at 525 °C to maximum pressure conditions of around 9.5 kbar at temperatures of around 650 °C. Decompression from peak pressures under isothermal or moderate heating conditions are indicated by formation of biotite and plagioclase porphyroblasts which cross-cut and overgrow the dominant foliation. The lack of sillimanite and/or andalusite suggests that cooling and further decompression occurred in the kyanite stability field. The results of this study indicate a single amphibolite-facies metamorphism that based on P-T conditions and age dating correlates well with the Neoproterozoic metamorphism in the underlying Sherdarwaza Formation. The rocks lack any paragenetic evidence for a preceding granulite-facies overprint or subsequent Paleozoic metamorphism. Owing to the position of the Kabul Block, within the India-Eurasia collision zone, partial replacement of the amphibolite-facies minerals in the micaschist could, in addition to retrogression of the Neoproterozoic metamorphism, relate to deformation associated with the Alpine orogeny.

  17. Timing of Proterozoic deformation, plutonism, and metamorphism in the Los Pinos Mountains, Central New Mexico

    SciTech Connect

    Shastri, L.L. . Dept. of Geology); Bowring, S.A. )

    1992-01-01

    Geochronologic, structural, and metamorphic studies within the Los Pinos Mountains (LPM), central NM provide new insights into the Proterozoic geologic history of this area. The LPM consist of a NE-trending, NW-dipping sequence of complexly deformed amphibolites and felsic schists. These have been intruded by a pervasively deformed granitic pluton. Two predominant deformational fabrics exist in the LPM. S1 is an early northwest-trending foliation, commonly parallel to compositional layering, which is folded about S2. S2 is axial planar foliation to tight to isoclinal folds and is the regional NE-trending fabric. Other fabrics and complex fold interference patterns may be related to localized strain partitioning around granitic bodies. A network of granitic dikes associated with the pluton crosscuts S2 but contains a weak foliation parallel to S2, suggesting synkinematic intrusion of the dikes. Regional metamorphism in the LPM took place at upper greenschist to lower amphibolite facies. Electron microprobe traverses of garnets show compositional variation indicative of growth zoning. No abrupt changes in composition representative of multiple metamorphic events are observed. Garnet-biotite geothermometry yields average rim temperatures of 454 [+-] 50 C. U-Pb geochronology of zircons from amphibolite, granite, and a granite dike indicates essentially the same age for all three units (1.66 Ga). The amphibolite contains abundant zircons which have complex morphologies typical of metamorphic growth; however, an igneous origin cannot yet be precluded. Spheres from the same amphibolite yield a near concordant age of 1.62 Ga. Thus, deformation, plutonism, and possibly the peak of metamorphism, were coeval at ca. 1.66 Ga, with metamorphism cooling through the blocking temperature of sphene at 1.62 Ga. The LPM are similar to other mountain ranges in south-central New Mexico where 1.66 Ga ages have been reported.

  18. The timing of metamorphism in the Odenwald-Spessart basement, Mid-German Crystalline Zone

    NASA Astrophysics Data System (ADS)

    Will, T. M.; Schulz, B.; Schmädicke, E.

    2016-07-01

    New in situ electron microprobe monazite and white mica 40Ar/39Ar step heating ages support the proposition that the Odenwald-Spessart basement, Mid-German Crystalline Zone, consists of at least two distinct crustal terranes that experienced different geological histories prior to their juxtaposition. The monazite ages constrain tectonothermal events at 430 ± 43 Ma, 349 ± 14 Ma, 331 ± 16 Ma and 317 ± 12 Ma/316 ± 4 Ma, and the 40Ar/39Ar analyses provide white mica ages of 322 ± 3 Ma and 324 ± 3 Ma. Granulite-facies metamorphism occurred in the western Odenwald at c. 430 and 349 Ma, and amphibolite-facies metamorphism affected the eastern Odenwald and the central Spessart basements between c. 324 and 316 Ma. We interpret these data to indicate that the Otzberg-Michelbach Fault Zone, which separates the eastern Odenwald-Spessart basement from the Western Odenwald basement, is part of the Rheic Suture, which marks the position of a major Variscan plate boundary separating Gondwana- and Avalonia-derived crustal terranes. The age of the Carboniferous granulite-facies event in the western Odenwald overlaps with the minimum age of eclogite-facies metamorphism in the adjacent eastern Odenwald. The granulite- and eclogite-facies rocks experienced contrasting pressure-temperature paths but occur in close spatial proximity, being separated by the Rheic Suture. As high-pressure and high-temperature metamorphisms are of similar age, we interpret the Odenwald-Spessart basement as a paired metamorphic belt and propose that the adjacent high-pressure and high-temperature rocks were metamorphosed in the same subduction zone system. Juxtaposition of these rocks occurred during the final stages of the Variscan orogeny along the Rheic Suture.

  19. Metamorphic and geochemical evolution of an amphibolite layer in the Chugach Metamorphic Complex (Alaska)

    NASA Astrophysics Data System (ADS)

    Bruand, E.; Gasser, D.; Stuewe, K.

    2010-12-01

    metapelites of the CMC (Bruand et al., 2010) which has pointed out much higher pressure (5 to 13kb) than previously believed (~3kb; Sisson et al., 1989). We integrate our new petrological and geochemical data to the geodynamic history of the CMC and test different geodynamic models to explain the presence of such an amphibolite layer in southern Alaska: seamount subduction, ridge subduction and obduction. Bruand E, Gasser D & Stüwe K, 2010. Metamorphic evolution and new PT estimates for the Chugach Metamorphic Complex (Alaska) - implications for the ridge subduction model. In review. JMG. Lull J & Plafker G 1990. Geochemistry and Paleotectonic Implications of Metabasaltic Rocks in the Valdez Group, Southern Alaska. In: Dover J, Galloway J (eds) Geological Studies in Alaska by the U.S. Geological Survey, 1946, 29-38. Sisson V, Hollister L & Onstott, 1989. Petrologic and age constraints on the origin of a low-pressure/high-temperature metamorphic complex, Southern Alaska. JGR, 94, 4392-4410.

  20. Teaching History in a Post-Industrial Age

    ERIC Educational Resources Information Center

    Bianchetti, Ann

    2004-01-01

    As a social studies teacher, the author emphasizes the story of history (sticking to the facts as much as they are known) and the human qualities of the players. Middle school kids are in the throes of exploring self-identity and attempting to define their worlds. They love drama, and history provides plenty of it. The author finds that teaching…

  1. Post-metamorphic brecciation in type 3 ordinary chondrites

    NASA Technical Reports Server (NTRS)

    Scott, E. R. D.; Mccoy, T. J.; Keil, K.

    1993-01-01

    Type 3.1-3.9 ordinary chondrites can be divided into two kinds: those in which the compositions of chondrule silicates are entirely consistent with metamorphism of type 3.0 material, and those in which the computational heterogeneity appears to be too extreme for in situ metamorphism. We present petrologic data for three LL3 chondrites of the second kind--Ngawi, ALH A77278 (both type 3.6), and Hamlet (type 3.9)--and compare these data with results for the first kind of LL3-4 chondrites. Given that chondrules form in the nebula and that metamorphic equilibration occurs in asteroids, our new data imply that Ngawi, A77278, Hamlet, and many other type 3 ordinary chondrites are post-metamorphic breccias containing materials with diverse metamorphic histories; they are not metamorphic rocks or special kinds of 'primitive breccias.' We infer also that metamorphism to type 3.1-3.9 levels produces very friable material that is easily remixed into breccias and lithified by mild shock. Thus, petrologic types and subtypes of chondrites indicate the mean metamorphic history of the ingredients, not the thermal history of the rock. The metamorphic history of individual type 1 or 2 porphyritic chondrules in type 3 breccias is best derived from olivine and pyroxene analyses and the data of McCoy et al. for unbrecciated chondrites. The new chondrule classification schemes of Sears, DeHart et al., appears to provide less information about the original state and metamorphic history of individual porphyritic chondrules and should not replace existing classification schemes.

  2. Post-metamorphic brecciation in type 3 ordinary chondrites

    NASA Astrophysics Data System (ADS)

    Scott, E. R. D.; McCoy, T. J.; Keil, K.

    1993-03-01

    Type 3.1-3.9 ordinary chondrites can be divided into two kinds: those in which the compositions of chondrule silicates are entirely consistent with metamorphism of type 3.0 material, and those in which the computational heterogeneity appears to be too extreme for in situ metamorphism. We present petrologic data for three LL3 chondrites of the second kind--Ngawi, ALH A77278 (both type 3.6), and Hamlet (type 3.9)--and compare these data with results for the first kind of LL3-4 chondrites. Given that chondrules form in the nebula and that metamorphic equilibration occurs in asteroids, our new data imply that Ngawi, A77278, Hamlet, and many other type 3 ordinary chondrites are post-metamorphic breccias containing materials with diverse metamorphic histories; they are not metamorphic rocks or special kinds of 'primitive breccias.' We infer also that metamorphism to type 3.1-3.9 levels produces very friable material that is easily remixed into breccias and lithified by mild shock. Thus, petrologic types and subtypes of chondrites indicate the mean metamorphic history of the ingredients, not the thermal history of the rock. The metamorphic history of individual type 1 or 2 porphyritic chondrules in type 3 breccias is best derived from olivine and pyroxene analyses and the data of McCoy et al. for unbrecciated chondrites. The new chondrule classification schemes of Sears, DeHart et al., appears to provide less information about the original state and metamorphic history of individual porphyritic chondrules and should not replace existing classification schemes.

  3. Martian Meteorite Ages and Implications for Martian Cratering History

    NASA Technical Reports Server (NTRS)

    Nyquist, Laurence E.

    2006-01-01

    New radiometrically determined ages of Martian meteorites add to the growing number with crystallization ages < 1.4 Ga. The observation of mainly geologically young ages for the Martian meteorites, the only exception being the 4.5 Ga ALH84001 [1], is paradoxical when viewed in context of a Martian surface thought to be mostly much older as inferred from the surface density of meteorite craters [2]. There appears to be at least a twofold difference between the observed ages of Martian meteorites and their expected ages as inferred from the ages of Martian surfaces obtained from crater densities.

  4. Metamorphism in mesosiderites

    NASA Technical Reports Server (NTRS)

    Delaney, J. S.; Prinz, M.; Harlow, G. E.; Nehru, C. E.

    1982-01-01

    Previous studies of mesosiderites have identified a metamorphic overprint in these meteorites. However, the effects and implications of this overprint have not yet been explored in detail. The present study documents several important textural and chemical features of the mesosiderites. The components of mesosiderites are examined, taking into account orthopyroxenites, olivine in clasts, mesosiderite mafic clasts, and metal. The characteristics of the silicate matrix of the mesosiderites is explored, and textural and chemical evidence of metamorphism is discussed, giving attention to coronas on olivine clasts, overgrowths on Mg-pyroxene clasts, rims on iron rich pyroxene grains, poikiloblasts of plagioclase, and resorption of clasts. Aspects of redox formation of merrillite are considered along with the causes and the implications of metamorphism. It is found that metamorphism has radically changed the texture of the silicate fraction of the mesosiderites.

  5. Color Me Metamorphic.

    ERIC Educational Resources Information Center

    Birdd, Donald L.

    1990-01-01

    Described are five activities using crayons to demonstrate the rock cycle including weathering, erosion and sedimentation, and sedimentary, metamorphic, and igneous rock formation. Discussed are materials, procedures, and probable results. (CW)

  6. Plate tectonics: Metamorphic myth

    NASA Astrophysics Data System (ADS)

    Korenaga, Jun

    2016-01-01

    Clear evidence for subduction-induced metamorphism, and thus the operation of plate tectonics on the ancient Earth has been lacking. Theoretical calculations indicate that we may have been looking for something that cannot exist.

  7. Petrology of metamorphic rocks

    SciTech Connect

    Suk, M.

    1983-01-01

    ''Petrology of Metamorphic Rocks'' reviews Central European opinions about the origin and formation of metamorphic rocks and their genetic systems, confronting the works of such distinguished European scientists as Rosenbusch, Becke, Niggli, Sander, Eskola, Barth and others with present-day knowledge and the results of Soviet and American investigations. The initial chapters discuss the processes that give rise to metamorphic rocks, and the main differences between regional metamorphism and other types of alterations, the emphasis being laid on the material characteristic of the processes of metamorphism, metasomatism and ultrametamorphism. Further chapters give a brief characterization of research methods, together with a detailed genetic classification based on the division of primary rocks into igneous rocks, sediments and ore materials. The effects of metamorphic alterations and those of the properties of the primary rocks are analyzed on the basis of examples taken chiefly from the Bohemian Massif, the West Carpathians, other parts of the European Variscides, from the crystalline Scandinavian Shelf in Norway and Finland, and from the Alps. Typical examples are documented by a number of charts, photographs and petrographical - particularly petrochemical - data.

  8. Late Cretaceous to Paleocene metamorphism and magmatism in the Funeral Mountains metamorphic core complex, Death Valley, California

    USGS Publications Warehouse

    Mattinson, C.G.; Colgan, J.P.; Metcalf, J.R.; Miller, E.L.; Wooden, J.L.

    2007-01-01

    Amphibolite-facies Proterozoic metasedimentary rocks below the low-angle Ceno-zoic Boundary Canyon Detachment record deep crustal processes related to Meso-zoic crustal thickening and subsequent extension. A 91.5 ?? 1.4 Ma Th-Pb SHRIMP-RG (sensitive high-resolution ion microprobe-reverse geometry) monazite age from garnet-kyanite-staurolite schist constrains the age of prograde metamorphism in the lower plate. Between the Boundary Canyon Detachment and the structurally deeper, subparallel Monarch Spring fault, prograde metamorphic fabrics are overprinted by a pervasive greenschist-facies retrogression, high-strain subhorizontal mylonitic foliation, and a prominent WNW-ESE stretching lineation parallel to corrugations on the Boundary Canyon Detachment. Granitic pegmatite dikes are deformed, rotated into parallelism, and boudinaged within the mylonitic foliation. High-U zircons from one muscovite granite dike yield an 85.8 ?? 1.4 Ma age. Below the Monarch Spring fault, retrogression is minor, and amphibolite-facies mineral elongation lineations plunge gently north to northeast. Multiple generations of variably deformed dikes, sills, and leucosomal segregations indicate a more complex history of partial melting and intrusion compared to that above the Monarch Spring fault, but thermobarometry on garnet amphibolites above and below the Monarch Spring fault record similar peak conditions of 620-680 ??C and 7-9 kbar, indicating minor (<3-5 km) structural omission across the Monarch Spring fault. Discordant SHRIMP-RG U-Pb zircon ages and 75-88 Ma Th-Pb monazite ages from leucosomal segregations in paragneisses suggest that partial melting of Proterozoic sedimentary protoliths was a source for the structurally higher 86 Ma pegmatites. Two weakly deformed two-mica leucogranite dikes that cut the high-grademetamorphic fabrics below the Monarch Spring fault yield 62.3 ?? 2.6 and 61.7 ?? 4.7 Ma U-Pb zircon ages, and contain 1.5-1.7 Ga cores. The similarity of metamorphic

  9. Timing and heat sources for the Barrovian metamorphism, Scotland

    NASA Astrophysics Data System (ADS)

    Viete, Daniel R.; Oliver, Grahame J. H.; Fraser, Geoff L.; Forster, Marnie A.; Lister, Gordon S.

    2013-09-01

    New SHRIMP U/Pb zircon ages of 472.2 ± 5.8 Ma and 471.2 ± 5.9 Ma are presented for the age of peak metamorphism of Barrovian migmatites. 40Ar/39Ar ages for white mica from the Barrovian metamorphic series are presented, and are recalculated using recently-proposed revisions to the 40K decay constants to allow more precise and accurate comparison with U/Pb ages. The 40Ar/39Ar ages are found to vary systematically with increasing metamorphic grade, between c. 465 Ma for the biotite zone and c. 461 Ma for the sillimanite zone. There is no evidence for any significant metamorphic heating during the first 15 Myr of the Grampian Orogeny (before c. 473 Ma) or the final 4 Myr (after c. 465 Ma). The Barrovian metamorphism occurred over a period of ~ 8 Myr within the ~ 27-Myr Grampian Orogeny. The Barrovian metamorphism records punctuated heating, was temporally and spatially associated with large-scale bimodal magmatism, and developed within crust that was not overthickened. The temporally distinct nature of the Barrovian metamorphic episode within the Grampian Orogeny, and its heating pattern and tectonic context, are not consistent with significant heat contribution from thermal equilibration of overthickened crust. Rather, the Barrovian metamorphism records a transient phase of crustal thermal disequilibrium during the Grampian Orogeny. Temporal and spatial association with Grampian bimodal magmatism is consistent with production of the Barrovian metamorphic series within the middle crust as the result of advection of heat from the lower crust and/or mantle. The Barrovian metamorphic series - the classic example of ‘orogenic regional metamorphism’ - did not form in response to crustal thickening and thermal relaxation, but appears to record large-scale contact metamorphism.

  10. The History Walk: Integrated Multi-Age Learning.

    ERIC Educational Resources Information Center

    Morris, Ronald V.

    2000-01-01

    This article describes a learning activity, the Texas History Walk, in which third- and seventh-grade gifted students learn about life in the 1870s on the Texas frontier. The younger students interact with the actors, seventh graders role-playing characters of the 1870s. Benefits of the activity include its interdisciplinary nature, the cross-age…

  11. "High-grade burial metamorphism of sedimentary mélange, Shoo Fly Complex, central Sierra Nevada, California"

    NASA Astrophysics Data System (ADS)

    Mendoza, Y.; Wakabayashi, J.

    2013-12-01

    The Shoo Fly Complex, California is a subduction complex metamorphosed at lower greenschist facies in much of the northern Sierra Nevada. Central Sierra Nevada exposures include higher grade assemblages. Previous studies have interpreted the higher grade rocks as gneissic granitoids representing the roots of a Paleozoic arc. Recent field work in the North Fork Mokelumne River drainage, shows that high-grade and low-grade metamorphic rocks were derived from similar subduction complex protoliths. The Shoo Fly in this region consists of mostly phyllite (metasiltstone, metasandstone, metachert), with some metabasite, and metaultramafic blocks. There is a metamorphic gradient from west to east in the field area, transitioning from sub to lower greenschist facies (white mica only) to middle and upper green schist facies (biotite) within the phyllites to amphibolite/upper amphibolite/granulite grade mica schists, gneisses, and amphibolites This gradient occurs across a zone about 1.5 km wide and this gradient is about 5 km west of the contact between the Shoo Fly Complex and plutons of the Sierra Nevada batholith. The higher-grade rocks do not have an apparent west-east metamorphic gradient. Accordingly the high-grade metamorphism does not appear to be a consequence of either contact metamorphism or raised regional geothermal gradients connected with the batholith. This conclusion is consistent with the fact that published metamorphic ages from probable correlative rocks within the central Sierra are much older than the Sierra Nevada batholith. Protoliths for the higher grade rocks appear identical to the lower grade rocks, for metaclastic rocks dominate with subordinate metacherts, metabasites, and metaultramafic rocks. The latter are represented by tremolite-talc schists. In the lower grade rocks some of the metabasite and metaultramafic blocks exhibit a higher grade of metamorphism than the surrounding metaclastic rocks and metacherts. Amphibolite and tremolite schist

  12. No Paleozoic metamorphics in Palawan (the Philippines)? Evidence from single grain U-Pb dating of detrital zircons

    NASA Astrophysics Data System (ADS)

    Walia, Monika; Knittel, Ulrich; Suzuki, Shigeyuki; Chung, Sun-Lin; Pena, Rolando E.; Yang, Tsanyao Frank

    2012-06-01

    The Palawan Continental Terrane (PCT) is a fragment of the margin of SE China that drifted south as a result of the Cenozoic opening of the South China Sea. This fragment is of great interest as it may contain a record of the early history of the continental margin of SE China that is not exposed on the mainland. The age and potential correlations of meta-sediments exposed on Palawan Island, Philippines, with those exposed on the other islands of Philippine Archipelago and Asia are a long standing problem of the geology of this island. Given the presence of non-metamorphic sedimentary sequences of Permian and Triassic age in the northern part of the island, a Paleozoic age was inferred for the metamorphics but recently also a younger age for these rocks was considered possible. U/Pb dating of detrital zircons by the laser-ablation ICP-MS method reveals the presence of 80-98 Ma old zircons in all of the usually distinguished units, hence despite significant differences in degree of metamorphism and tectonic deformation, all meta-sediments appear to be of late Cretaceous or younger age. Thus, in principle, these clastic rocks could be overly derived from the older sequences. However, the relatively higher degree of metamorphism of the younger rocks suggests a tectonic contact with the older sequences.

  13. Petrology, chemistry, age and irradiation history of Luna 24 samples

    NASA Technical Reports Server (NTRS)

    Wasserburg, G. J.; Papanastassiou, D. A.; Mcculloch, M. T.; Huneke, J. C.; Dymek, R. F.; Depaolo, D. J.; Chodos, A. A.; Albee, A. L.; Radicati Di Brozolo, F.

    1978-01-01

    The results of petrological, chemical, isotopic age determination and irradiation studies of sample 24170 from the 170 cm depth of the regolith core returned from Mare Crisium by Luna 24 are presented. The sample is found to be comprised of fragments from a single igneous rock, with mineralogical evidence indicating it to be a mare basalt. The crystallization age is determined by Sm-Nd and Ar(40)-Ar(39) ages to be 3.30 AE, establishing the presence of relatively young flows. All soil samples show low trace element compositions with minimum contamination by KREEPUTh-rich materials. Rb-Sr and Sm-Nd relations reflect the absence of significant fractionation at ages younger than 4.5 AE. One soil sample shows extremely large neutron capture effects, imposing a new lower limit to the neutron production rate in the regolith and requiring the addition of irradiated materials from depth.

  14. The role of male age, sperm age and mating history on fecundity and fertilization success in the hide beetle.

    PubMed Central

    Jones, Therésa M.; Elgar, Mark A.

    2004-01-01

    Models of age-related mate choice predict female preference for older males as they have proven survival ability. However, these models rarely address differences in sperm age and male mating history when evaluating the potential benefits to females from older partners. We used a novel experimental design to assess simultaneously the relative importance of these three parameters in the hide beetle, Dermestes maculatus. In a two-part experiment we first explored age-related male mating success and subsequently examined the consequences of male age, sperm age and male mating history on female fecundity and fertilization success. In a competitive mating environment, intermediate-age males gained significantly higher mating success than younger or older males. To test the consequences for females of aged-related male mating success, a second set of females were mated to males varying in age (young, intermediate-age and old), in numbers of matings and in timing of the most recent mating. We found that male age had a significant impact on female fecundity and fertilization success. Females mated to intermediate-age males laid more eggs and attained consistently higher levels of fertilization success than females with young and old mates. A male's previous mating history determined his current reproductive effort; virgin males spent longer in copula than males with prior mating opportunities. However, differences in copulation duration did not translate into increased fecundity or fertilization success. There was also little evidence to suggest that fertilization success was dependent on the age of a male's sperm. The experiment highlights the potential direct benefits accrued by females through mating with particular aged males. Such benefits are largely ignored by traditional viability models of age-related male mating success. PMID:15306356

  15. Evolution of a Neoproterozoic suture in the Iberian Massif, Central Portugal: New U-Pb ages of igneous and metamorphic events at the contact between the Ossa Morena Zone and Central Iberian Zone

    NASA Astrophysics Data System (ADS)

    Henriques, S. B. A.; Neiva, A. M. R.; Ribeiro, M. L.; Dunning, G. R.; Tajčmanová, L.

    2015-04-01

    A Neoproterozoic suture is exposed at the contact between the Ossa Morena Zone and the Central Iberian Zone, in the Iberian Massif (Central Portugal), the westernmost segment of the European Variscides. Although, the Cadomian magmatic and tectonometamorphic events have been previously documented, their timing is still poorly constrained, particularly in the inner zones of the suture. We used geochronological (ID-TIMS U-Pb) data to establish the sequence of events, isotopic (Rb-Sr, Sm-Nd) data to characterize the magmatic sources and thermodynamic modelling to determine the maximum P-T conditions attained during the Cadomian metamorphism. The first event, in the future Ossa Morena Zone, is the onset of island arc magmatism represented mainly by tholeiites with a MORB signature. Their igneous crystallization age is unknown, but they are older than ca. 539 Ma. This magmatic activity was accompanied by deposition of fine-grained sediments in a Neoproterozoic basin. The second event is the evolution of the Cadomian magmatic arc in different stages. The earliest magmatic stage occurs at ca. 692 Ma, which is the oldest igneous age known in the Ossa Morena Zone. It is followed by the generation of subalkaline and peraluminous protoliths at ca. 569 Ma, with the isotopic signature of old crustal sources. The final phase of the arc magmatism (ca. 548-544 Ma) involved mainly partial melting of continental crust. The range of the main magmatic activity must have been between ca. 569 Ma and ca. 544 Ma as mentioned for other areas in the Ossa Morena Zone. A major metamorphic event, recorded in metamorphic monazite, zircon and titanite at ca. 540 Ma, attained upper amphibolite facies conditions close to the transition to granulite facies (7-8 kbar and 640-660 °C). It represents the continental arc accretion of the Ossa Morena Zone with the Iberian Autochthon passive margin (future Central Iberian Zone). The Early Ordovician rocks (ca. 483-477 Ma) were generated from depleted and

  16. Geologic and Geochronologic Studies of the Early Proterozoic Kanektok Metamorphic Complex of Southwestern Alaska

    USGS Publications Warehouse

    Turner, Donald L.; Forbes, Robert B.; Aleinikoff, John N.; McDougall, Ian; Hedge, Carl E.; Preface by: Wilson, Frederic H.; Layer, Paul W.; Hults, Chad P.

    2009-01-01

    having been partially reset during the late Mesozoic thermal event. 40Ar/39Ar incremental heating experiments suggest metamorphism occurred at least 1.2 b.y. ago but do not exhibit high temperature plateau ages significantly older than the 40Ar/39Ar total fusion ages of these samples. The age spectra are much more uniform than expected from a terrane with such a complex thermal history, perhaps caused by the small grain size of the samples which may possibly be less than the effective Ar diffusion radii of the analyzed hornblendes.

  17. U-Pb zircon and CHIME monazite dating of granitoids and high-grade metamorphic rocks from the Eastern and Peninsular Thailand - A new report of Early Paleozoic granite

    NASA Astrophysics Data System (ADS)

    Kawakami, T.; Nakano, N.; Higashino, F.; Hokada, T.; Osanai, Y.; Yuhara, M.; Charusiri, P.; Kamikubo, H.; Yonemura, K.; Hirata, T.

    2014-07-01

    also share the similar plutono-metamorphic history with the Khanom and the Hub-Kapong to Pran Buri areas. This suggests that these three areas belong to the Sibumasu block, and the Sibumasu block records similar plutono-metamorphic history from Northern to Peninsular Thailand. Relative abundance of oceanic components in the Khao Chao gneiss, their Late Triassic magmatic ages, and the Early Jurassic metamorphic ages prefer the interpretation that the Khao Chao gneiss belongs to the Sukhothai Arc.

  18. Politics as Social History: Political Cartoons in the Gilded Age.

    ERIC Educational Resources Information Center

    Edwards, Rebecca

    1999-01-01

    Provides analyses of four political cartoons in order to suggest approaches to Gilded Age politics that reveal key issues, such as gender, religion, and ethnicity, as well as the struggles over material resources in a stratified economy. Maintains that political cartoons assist students in understanding the ideology of a past era. (CMK)

  19. One-dimensional thermal modelling of Acadian metamorphism in southern Vermont, USA

    USGS Publications Warehouse

    Armstrong, T.R.; Tracy, R.J.

    2000-01-01

    One-dimensional thermal (1DT) modelling of an Acadian (Devonian) tectonothermal regime in southern Vermont, USA, used measured metamorphic pressures and temperatures and estimated metamorphic cooling ages based on published thermobarometric and geochronological studies to constrain thermal and tectonic input parameters. The area modelled lies within the Vermont Sequence of the Acadian orogen and includes: (i) a western domain containing garnet-grade pre-Silurian metasedimentary and metavolcanic rocks from the eastern flank of an Acadian composite dome structure (Rayponda-Sadawga Dome); and (ii) an eastern domain containing similar, but staurolite- or kyanite-grade, rocks from the western flank of a second dome structure (Athens Dome), approximately 10 km farther east. Using reasonable input parameters based on regional geological, petrological and geochronological constraints, the thermal modelling produced plausible P-T paths, and temperature-time (T-t) and pressure-time (P-t) curves. Information extracted from P-T-t modelling includes values of maximum temperature and pressure on the P-T paths, pressure at maximum temperature, predicted Ar closure ages for hornblende, muscovite and K-feldspar, and integrated exhumation and cooling rates for segments of the cooling history. The results from thermal modelling are consistent with independently obtained pressure, temperature and Ar cooling age data on regional metamorphism in southern Vermont. Modelling results provide some important bounding limits on the physical conditions during regional metamorphism, and indicate that the pressure contemporaneous with the attainment of peak temperature was probably as much as 2.5 kbar lower than the actual maximum pressure experienced by rocks along various particle paths. In addition, differences in peak metamorphic grade (garnet-grade versus staurolite-grade or kyanite-grade) and peak temperature for rocks initially loaded to similar crustal depths, differences in calculated

  20. Distribution and characteristics of metamorphic belts in the south- eastern Alaska part of the North American Cordillera

    USGS Publications Warehouse

    Brew, D.A.; Himmelberg, G.R.; Loney, R.A.; Ford, A.B.

    1992-01-01

    The Cordilleran orogen in south-eastern Alaska includes 14 distinct metamorphic belts that make up three major metamorphic complexes, from east to west: the Coast plutonic-metamorphic complex; the Glacier Bay-Chichagof plutonic-metamorphic complex; and the Chugach plutonic-metamorphic complex. Each of these complexes is related to a major subduction event. The metamorphic history of the Coast complex is lengthy and is related to the Late Cretaceous collision of the Alexander and Wrangellia terranes and the Gravina overlap assemblage to the west against the Stikine terrane to the east. The metamorphic history of the Glacier Bay-Chichagof complex is relatively simple and is related to the roots of a Late Jurassic to late Early Cretaceous island arc. The metamorphic history of the Chugach is complicated and developed during and after the Late Cretaceous collision of the Chugach terrane with the Wrangellia and Alexander terranes. -from Authors

  1. 40Ar/39Ar age-spectrum data for hornblende, biotite, white mica, and K-feldspar samples from metamorphic rocks in the Great Smoky Mountains of North Carolina and Tennessee

    USGS Publications Warehouse

    Kunk, Michael J.; McAleer, Ryan

    2011-01-01

    This report contains reduced 40Ar/39Ar data of hornblende, biotite, white mica and (or) sericite, and potassium-feldspar mineral separates and phyllite groundmass samples from metamorphic rocks of the Great Smoky Mountains in North Carolina and Tennessee. Included in this report are information on the location of the samples and a brief description of the samples. The data contained herein are not interpreted in a geological context, and care should be taken by users unfamiliar with argon isotopic data in the use of these results. No geological meaning is implied for any of the apparent ages presented below, and many of the individual apparent ages are not geologically meaningful. This report is primarily a detailed source document for subsequent publications that will integrate these data into a geological context. All the samples in this report were collected in and around the Great Smoky Mountain National Park in western North Carolina and eastern Tennessee.

  2. Prostate cancer and consistency of reporting sexual histories in men over age 50.

    PubMed

    Dennis, L K; Ritchie, J M; Resnick, M I

    2005-01-01

    We conducted an in-person interview to examine the reliability of reported sexual histories among men over age 50 y with and without prostate cancer. Marriage and cohabitation were used as memory cues to recall sexual activity. High correlations on test-retest for questions evaluating sexual histories suggest reliable answers for most factors, and specifically for age at first sexual activity, and lifetime number of sexual partners. Low correlations were seen for ill-defined and socially undesirable items. These data suggest that men consistently report most measures of sexual activity when using marriage and cohabitation as memory cues to recall sexual histories. PMID:15983628

  3. History of a Bronze Age tell and its environment

    NASA Astrophysics Data System (ADS)

    Kovács, Gabriella; Füleky, György; Vicze, Magdolna

    2016-04-01

    Százhalombatta-Földvár is the most excessively researched Bronze Age tell site in Hungary. Parallel to the investigation of the settlement structure and activity patterns the changes of the landscape and the effect of human alteration is also studied. Significant changes of the landscape can be detected from the Bronze Age until the recent natural and cultural heritage protection of the area. Archaeological, soil analytical and thin section soil micromorphological methods are used to reconstruct the past 4000 years of the tell and its immediate surroundings. Prior to the Bronze Age the area was covered by forest vegetation, so the initial settling could only be realised after deforestation (2000 BC). The result of the soil corings and the prepared soil thin sections are solid proves of this action. It also became evident that at some areas - so far it seems that at locales where house floors were laid for the very first time - even the topsoil was removed so intensively that only the B horizon of the relict forest soil can be found. This observation needs to be further tested outside the habitation area to define the horizontal extension of the forest clearance and the topsoil removal. The northern side of the settlement is bordered by a natural erosion gully. At 2000 BC it was just a natural depression, but by 1500 BC it was deepened to serve as a fortification ditch. Around 1200 BC the ditch started to be filled in and by 1000 BC it was refilled to such an extent that its surface was utilised again. At about 600 BC (Late Iron Age) a smaller inner rampart was erected on the southern side of the ditch for inner separation. Not much is known about the Roman period of this area (200 AD) but the remnants of a watchtower indicate their presence. During the 18th century AD the area was used for grape cultivation and later for hobby gardens up until the protection of the area in the late 20th century. Since then species of the original vegetation started to grow back

  4. Aging Aircraft Transparencies: AN Italian Air Force Fleet Case History

    NASA Astrophysics Data System (ADS)

    Caucci, D.; Aiello, L.; Bagnoli, F.; Bernabei, M.

    2008-08-01

    Aircraft acrylic transparencies are structural components that must withstand flight and ground loads. Crazing occurrence, known as Environmental Stress Cracking (ESC), causes their substitution during aircraft maintenance operations. This form of aging is mainly a physical phenomenon due to the interaction of transparencies base material with an active liquid and leads craze formation at lower stress that would be required in air. In this paper, an extensive phenomenon of network ESC occurred on transparencies of many aircrafts operating in the same fleet was investigated. Cover application while parking was found to be the critical aspect in crazing appearance, thus acting as physical shield for condensed water and heat transferring.

  5. From the Axial Age to the New Age: Religion as a Dynamic of World History.

    ERIC Educational Resources Information Center

    Tucker, Carlton H.

    In order to broaden student understanding of past and contemporary situations, the world history survey course needs to consider religion as a vehicle through which history moves. The course proposal includes prehistory and paleolithic times to contemporary Islamic culture. The course is thematic and comparative in orientation, but moves through…

  6. Thrust involvement of metamorphic rocks, southwestern Brooks Range, Alaska

    SciTech Connect

    Till, A.B.; Schmidt, J.M.; Nelson, S.W. )

    1988-10-01

    Most models for the tectonic history of the western Brooks Range treat Proterozoic and lower Paleozoic metamorphic rocks exposed in the southern part of the range as passive structural basement vertically uplifted late in the Mesozoic orogenic episode. Mapping in the metamorphic rocks shows that they can de divided into two structurally and metamorphically distinct belts, both of which were folded and thrust during the orogeny. Recognition of these belts and the nature of the contact separating them is critical to construction of accurate tectonic models of the Brooks Range fold and thrust belt.

  7. Searching for the Kinkeepers: Historian Gender, Age, and Type 2 Diabetes Family History

    ERIC Educational Resources Information Center

    Giordimaina, Alicia M.; Sheldon, Jane P.; Kiedrowski, Lesli A.; Jayaratne, Toby Epstein

    2015-01-01

    Kinkeepers facilitate family communication and may be key to family medical history collection and dissemination. Middle-aged women are frequently kinkeepers. Using type 2 diabetes (T2DM) as a model, we explored whether the predicted gender and age effects of kinkeeping can be extended to family medical historians. Through a U.S. telephone survey,…

  8. Ubiquitous brecciation after metamorphism in equilibrated ordinary chondrites

    NASA Technical Reports Server (NTRS)

    Scott, E. R. D.; Lusby, D.; Keil, K.

    1985-01-01

    Ten objects with aberrant Fe/(Fe + Mg) ratios have been found in apparently unbrecciated types 4-6 H and L chondrites. Since the Fe/(Fe + Mg) ratios of these objects are incompatible with the metamorphic history of the host chondrites, it is concluded that a high proportion of ordinary chondrites are breccias that were lithified after peak metamorphism. This is consistent with the results of Scott (1984), who concluded that most type three ordinary chondrites are breccias of materials with diverse thermal histories, even though they do not show prominent brecciation. It is found that the classification scheme of Van Schmus and Wood (1967) does not identify chondrites with similar thermal histories; the petrologic type of a chondrite is only a measure of the average thermal history of its ingredients. Chondrite and achondrite breccias are also compared in order to understand how brecciation of chondrites after metamorphism is so well camouflaged.

  9. Effects of psychiatric history on cognitive performance in old-age depression

    PubMed Central

    Pantzar, Alexandra; Atti, Anna Rita; Bäckman, Lars; Laukka, Erika J.

    2015-01-01

    Cognitive deficits in old-age depression vary as a function of multiple factors; one rarely examined factor is long-term psychiatric history. We investigated effects of psychiatric history on cognitive performance in old-age depression and in remitted persons. In the population-based Swedish National Study on Aging and Care in Kungsholmen study, older persons (≥60 years) without dementia were tested with a cognitive battery and matched to the Swedish National Inpatient Register (starting 1969). Participants were grouped according to current depression status and psychiatric history and compared to healthy controls (n = 96). Group differences were observed for processing speed, attention, executive functions, and verbal fluency. Persons with depression and psychiatric inpatient history (n = 20) and late-onset depression (n = 49) performed at the lowest levels, whereas cognitive performance in persons with self-reported recurrent unipolar depression (n = 52) was intermediate. Remitted persons with inpatient history of unipolar depression (n = 38) exhibited no cognitive deficits. Heart disease burden, physical inactivity, and cumulative inpatient days modulated the observed group differences in cognitive performance. Among currently depressed persons, those with inpatient history, and late onset performed at the lowest levels. Importantly, remitted persons showed no cognitive deficits, possibly reflecting the extended time since the last admission (m = 15.6 years). Thus, the present data suggest that cognitive deficits in unipolar depression may be more state- than trait-related. Information on profiles of cognitive performance, psychiatric history, and health behaviors may be useful in tailoring individualized treatment. PMID:26175699

  10. Shock metamorphism of Elephant Moraine A79001: Implications for olivine-ringwoodite transformation and the complex thermal history of heavily shocked Martian meteorites

    NASA Astrophysics Data System (ADS)

    Walton, Erin L.

    2013-04-01

    Lithology A of Martian meteorite Elephant Moraine (EET) A79001 contains fragments entrained within a 100 μm-thick shear-induced shock vein. These fragments, the shock vein matrix and walls of olivine along the vein, as well as shock deformation and transformation in rock-forming minerals in the bulk rock, were investigated using scanning electron microscopy, the electron microprobe and Raman spectroscopy. The presence of ringwoodite, the spinel-structured high-pressure (Mg,Fe)2SiO4 polymorph, has been confirmed in EETA79001 for the first time. Ringwoodite occurs within and around the shock vein, exhibiting granular and lamellar textures. In both textures ringwoodite consists of ˜500 nm size distinct grains. Ringwoodite lamellae are 115 nm to 1.3 μm wide. Planar fractures in olivine provided sites for heterogeneous nucleation of ringwoodite. Analyses performed on the largest grains (⩾1 μm) show that ringwoodite is consistently higher in iron (Fa27.4-32.4) relative to surrounding olivine (Fa25.1-267.7), implying that there was Fe-Mg exchange during their transformation, and therefore their growth was diffusion-controlled. In the shock environment, diffusion takes place dynamically, i.e., with concurrent deformation and grain size reduction. This results in enhanced diffusion rates (⩾10-8 m2/s) over nm - μm distances. Shock deformation in host rock minerals including strong mosaicism, pervasive fracturing, polysynthetic twinning (pyroxene only), extensive shock melting, local transformation of olivine to ringwoodite, and complete transformation of plagioclase to maskelynite in the bulk rock, indicate that EETA79001 was strongly shocked. The short shock duration (0.01 s) combined with a complex thermal history, resulted in crystallization of the 100 μm thick shock vein in EETA79001 during the pressure release, and partial back-transformation of ringwoodite to olivine. Based on the pressure stabilities of clinopyroxene + ringwoodite, crystallization at the

  11. First evidence of the Ellesmerian metamorphism on Svalbard

    NASA Astrophysics Data System (ADS)

    Kośmińska, Karolina; Majka, Jarosław; Manecki, Maciej; Schneider, David A.

    2016-04-01

    The Ellesmerian fold-and-thrust belt is exposed in the High Arctic from Ellesmere Island in the east, through North Greenland, to Svalbard in the west (e.g. Piepjohn et al., 2015). It developed during Late Devonian - Early Carboniferous, and overprinted older (mainly Caledonian) structures. It is thought that this fold-and-thrust belt was formed due to collision of the Pearya Terrane and Svalbard with the Franklinian Basin of Laurentia. Traditionally, the Ellesmerian fold-and-thrust belt comprises a passive continental margin affected by foreland deformation processes, but the exact larger scale tectonic context of this belt is disputable. It is partly because the Eocene Eurekan deformation superimposed significantly the Ellesmerian structures, thus making the reconstruction of the pre-Eurekan history very difficult. Here we present for the first time evidence for Ellesmerian metamorphism within the crystalline basement of Svalbard. These rocks are exposed in the Pinkie unit on Prins Karls Forland (W-Svalbard), which exhibits tectonic contacts with the overlying sequences. The Pinkie unit is mainly composed of strongly deformed lithologies such as laminated quartzites, siliciclastic rocks and garnet-bearing mica schists. Detrital zircon dating yielded ages as young as Neoproterozoic (0.95-1.05 Ga), thus the Pinkie unit is considered to be Neoproterozoic (Kośmińska et al., 2015a). The M1 assemblages and D1 structures are affected by D2 mylonitization (cf. Faehnrich et al., 2016, this meeting). Petrological characterization and Th-U-total Pb chemical monazite dating have been performed on the Pinkie metapelites. These rocks exhibit an apparent inverted Barrovian metamorphic sequence, within which three metamorphic zones have been distinguished: garnet+staurolite+muscovite+biotite, garnet+staurolite+kyanite+muscovite+biotite, garnet+kyanite+muscovite+biotite. The P-T estimates using the QuiG barometry coupled with thermodynamic modelling revealed that the

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

    SciTech Connect

    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 exhibit 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).

  13. The baboon model (Papio hamadryas) of fetal loss: Maternal weight, age, reproductive history and pregnancy outcome

    PubMed Central

    Schlabritz-Loutsevitch, Natalia; Moore, Charleen M.; Lopez-Alvarenga, Juan Carlos; Dunn, Betty G.; Dudley, Donald; Hubbard, Gene B.

    2010-01-01

    Background Several risk factors are associated with the incidence of human stillbirths. The prevention of stillbirths in women is a pressing clinical problem. Methods We reviewed 402 pathology records of fetal loss occurring in a large baboon (Papio spp.) colony during a 15-year period. Clinical histories of 565 female baboons with one or more fetal losses during a 20-year period were analyzed for weight, age, and reproductive history. Results Fetal loss was most common at term (35.57%) and preterm (28.61%) and less common in the first half of gestation (11.20%) and post-term (5.22%). Greater maternal weight, older age, history of stillbirth and higher parity were independent predictors for stillbirth. An exponential increase in the incidence of fetal loss was observed beginning at age 14 years in baboons. Conclusion Fetal loss and maternal risk factors associated with stillbirths in baboons were similar to those documented in women. PMID:19017195

  14. Prevalence and Sociodemographic Determinants of Hypertension History among Women in Reproductive Age in Ghana

    PubMed Central

    Nyarko, Samuel H.

    2016-01-01

    Background. Hypertension is a global health problem. Yet, studies on hypertension rarely focus on women in Ghana. The purpose of this study is to ascertain the prevalence and sociodemographic determinants of hypertension history among Ghanaian women in reproductive age. Methods. This study used data from the 2014 Ghana Demographic and Health Survey. Bivariate and logistic regression analyses were carried out to ascertain the prevalence and determinants of hypertension history among the respondents. Results. The study found that the overall prevalence of hypertension history among the respondents was 7.5%; however, there were vast variations within most of the sociodemographic categories. Age, level of education, marital status, work status, and wealth status had a significant relationship with hypertension history among the respondents. Women in advanced age groups, highly educated, married, and widowed/divorced/separated, nonworking women, and women from wealthy households were at higher risk of having hypertension history. Conclusion. Myriads of sociodemographic factors determine the hypertension history of women in Ghana. It is therefore essential to target medical and psychosocial hypertension interventions at Ghanaian women in the higher risk groups. PMID:27200184

  15. Modelling Metamorphism by Abstract Interpretation

    NASA Astrophysics Data System (ADS)

    Dalla Preda, Mila; Giacobazzi, Roberto; Debray, Saumya; Coogan, Kevin; Townsend, Gregg M.

    Metamorphic malware apply semantics-preserving transformations to their own code in order to foil detection systems based on signature matching. In this paper we consider the problem of automatically extract metamorphic signatures from these malware. We introduce a semantics for self-modifying code, later called phase semantics, and prove its correctness by showing that it is an abstract interpretation of the standard trace semantics. Phase semantics precisely models the metamorphic code behavior by providing a set of traces of programs which correspond to the possible evolutions of the metamorphic code during execution. We show that metamorphic signatures can be automatically extracted by abstract interpretation of the phase semantics, and that regular metamorphism can be modelled as finite state automata abstraction of the phase semantics.

  16. Fluid-driven metamorphism

    NASA Astrophysics Data System (ADS)

    Jamtveit, B.; Ulven, O. I.; Malthe-Sorenssen, A.

    2014-12-01

    Metamorphic processes in the Earth crust are almost invariably associated with fluid migration. Many lines of evidence suggest that fluid migration is intimately coupled both to the metamorphic reactions, and to associated deformation processes. Petrologic arguments suggest that all granulite facies and most amphibolite facies rocks are essentially dry (no free fluid phase) at normal geothermal gradients outside periods of heating-produced fluid generation. In addition, except at high pressure - low temperature condition, fluid-consuming reactions leads to an increase in solid volume and a potential clogging of any initial pore space. Hence, fluid migration in medium and high-grade metamorphic rocks is in general associated with some porosity producing process. Porosity generation may occur by either chemical or mechanical processes. In systems with high fluid fluxes, porosity may be produced by dissolution and transport of mass out of the system. Such fluxes can normally only be sustained over short length scales and limited time scales. In systems where the infiltrating fluid is far from equilibrium with the rock matrix, mechanical porosity generation can arise from local stresses generated by the volume change of volatilization reactions. Furthermore, it has become increasingly clear that crustal rocks may be under significant tectonic stress, even far from plate tectonic boundaries. In situations where the rocks are close to critically stressed, any stress perturbations caused by reaction driven changes in solid volume or fluid pressure gradients may lead to dilatant deformation and porosity production on a scale much larger than the characteristic length scales of the reacting rock units. Field observations, experimental studies and modeling results will be presented that focus on reaction driven porosity generation in systems subject to variable initial differential stresses.

  17. Evolvability of an avian life history trait declines with father's age.

    PubMed

    Kim, S-Y; Drummond, H; Torres, R; Velando, A

    2011-02-01

    Studies of laboratory organisms have suggested that parental age affects the genetic variance of offspring traits. This effect can engender age-specific variance in genetic contributions to evolutionary change in heritable traits under directional selection, particularly in age-structured populations. Using long-term population data of the blue-footed booby (Sula nebouxii), we tested whether genetic variance of recruiting age varies with parental age. Using robust quantitative genetic models fitted to pedigree, we found a significant genotype-by-paternal age interaction for recruiting age. Genetic potential for adaptive change in recruiting age was greater in progeny of young (age 1-6 years) fathers (males: CV(A)=6.68; females: CV(A)=7.59) than those of middle age (7-9 years) fathers (males: CV(A) = 4.64; females: CV(A)=5.08) and old (10-14 years) fathers (CV(A)=0 for both sexes). Therefore, parental age dependence of heritable variance, in addition to age-related variation in survival and fecundity, should affect the strength of natural selection for evolutionary changes. Our results provide rare evidence for the influence of parental age on the evolutionary potential of a life history trait in a wild population. PMID:21044208

  18. Metamorphic Testing for Cybersecurity

    PubMed Central

    Chen, Tsong Yueh; Kuo, Fei-Ching; Ma, Wenjuan; Susilo, Willy; Towey, Dave; Voas, Jeffrey

    2016-01-01

    Testing is a major approach for the detection of software defects, including vulnerabilities in security features. This article introduces metamorphic testing (MT), a relatively new testing method, and discusses how the new perspective of MT can help to conduct negative testing as well as to alleviate the oracle problem in the testing of security-related functionality and behavior. As demonstrated by the effectiveness of MT in detecting previously unknown bugs in real-world critical applications such as compilers and code obfuscators, we conclude that software testing of security-related features should be conducted from diverse perspectives in order to achieve greater cybersecurity. PMID:27559196

  19. Bushveld-aged fluid flow, peak metamorphism, and gold mobilization in the Witwatersrand basin, South Africa: Constraints from in situ SHRIMP U-Pb dating of monazite and xenotime

    NASA Astrophysics Data System (ADS)

    Rasmussen, Birger; Fletcher, Ian R.; Muhling, Janet R.; Mueller, Andreas G.; Hall, Greg C.

    2007-10-01

    In situ U-Pb dating of monazite and xenotime in gold reefs and unmineralized greenschist facies sedimentary rocks from the Witwatersrand basin, South Africa, reveals two episodes of tectonothermal activity. A major event between 2.06 and 2.03 Ga is recorded in the Wit-watersrand and Transvaal Supergroups in the northwestern and central basin, and broadly coincides with the ca. 2.06 Ga Bushveld event. In the central and southern basin, a previously unrecognized event has been dated between 2.14 and 2.12 Ga. The widespread geographic and stratigraphic occurrence of Bushveld-aged monazite and xenotime, including both auriferous reefs and unmineralized strata, indicates that metamorphism and fluid flow associated with magmatism was pervasive, affecting most of the succession (>10 km thick) in the central and northern parts of the basin. The metamorphic phosphate dates, which are younger away from the complex, indicate a lag of 20-30 m.y. between emplacement and phosphate growth in the central basin (˜100 km south), suggesting that heat related to magmatism was transferred southward at an average rate of 3-5 mm yr-1. The absence of 2.06-2.03 Ga phosphates in the Welkom goldfield at the southern end of the basin implies that Bushveld-related heating and fluid flow did not affect this part of the basin. The intergrowth of ca. 2.045 Ga monazite with gold in quartz-pebble conglomerate from the West Rand goldfield indicates that fluid flow related to the Bushveld event caused mobilization of gold in the Witwatersrand basin.

  20. Meeting Report: International Symposium on the Genetics of Aging and Life History II.

    PubMed

    Artan, Murat; Hwang, Ara B; Lee, Seung V; Nam, Hong Gil

    2015-06-01

    The second International Symposium on the Genetics of Aging and Life History was held at the campus of Daegu Gyeongbuk Institute of Science and Technology (DGIST), Daegu, South Korea, from May 14 to 16, 2014. Many leading scientists in the field of aging research from all over the world contributed to the symposium by attending and presenting their recent work and thoughts. The aim of the symposium was to stimulate international collaborations and interactions among scientists who work on the biology of aging. In the symposium, the most recent and exciting work on aging research was presented, covering a wide range of topics, including the genetics of aging, age-associated diseases, and cellular senescence. The work was conducted in various organisms, includingC. elegans, mice, plants, and humans. Topics covered in the symposium stimulated discussion of novel directions for future research on aging. The meeting ended with a commitment for the third International Symposium on the Genetics of Aging and Life History, which will be held in 2016. PMID:26115541

  1. Moderate pressure metamorphism and anatexis due to anorthosite intrusion, western Adirondack Highlands, New York

    NASA Astrophysics Data System (ADS)

    Florence, F. P.; Darling, R. S.; Orrell, S. E.

    1995-10-01

    Garnet-sillimanite-biotite gneiss near Port Leyden, in the western Adirondack Highlands, New York, contains mineral assemblages and textures that formed during high temperature metamorphism and anatexis at mid-crustal pressures. Evidence for melting includes thin, plagioclase-rich veins, sieve textures in biotite, and the presence of small, euhedral garnet neoblasts. Hercynite-silicate equilibria in combination with the solidus for biotite dehydration melting indicate metamorphic pressure was between 4 and 6.4 kbar at the temperature of melting (ca. 735° C). The gneiss is intruded by a small, discordant Fe-Ti oxide-apatite (nelsonite) dike. Reported field occurrences of nelsonite demonstrate its common association with anorthosite plutons. Although no anorthosite bodies are exposed in the Port Leyden region, the presence of nelsonite is evidence of anorthositic magmatism in the western Adirondacks. Post-intrusion metamorphism has caused partial apatite recrystallization and produced a weak foliated texture in the dike. U-Pb ages from zircon and monazite from both the gneiss and the nelsonite dike indicate that these rocks experienced a complex, polymetamorphic history that we interpret to reflect two thermal episodes. An older event is recorded by discordant zircons in the gneiss, which indicate a minimum age of 1129±6 Ma. A linear best fit to the data yields an upper intercept at 1166±53 Ma. This range of ages coincides with anorthosite-suite magmatism in the Adirondacks. A minimum zircon age of 1104±3 Ma was obtained from the nelsonite dike. Lead-loss or late zircon crystallization at about 1020 Ma affected the U-Pb systematics of zircon in the dike. Monazite ages from both rocks also indicate high temperature metamorphism (>700° C) between 1040 and 960 Ma. The older zircon ages and textural relations in the metapelite are viewed as evidence for anatexis at ca. 1150 Ma, and the presence of nelsonite suggests that the intrusion of anorthosite was coincident

  2. High-resolution garnet chronometry and the rates of metamorphic processes

    NASA Astrophysics Data System (ADS)

    Burton, Kevin W.; Keith O'Nions, R.

    1991-12-01

    Garnets in an amphibolite-facies metasediment from Sulitjelma, North Norway yield precise and concordant Sm sbnd Nd, U sbnd Pb and Rb sbnd Sr ages that relate directly to the pressure ( P) and temperature ( T) conditions of mineral growth. Differential mineral reaction between graphitic and non-graphitic layers within this sample preserves a record of the P-T and time ( t) history experienced during Barrovian regional metamorphism. Garnets in graphitic layers grew during prograde metamorphism at 462 ± 16°C and 5.2 ± 0.5 kbar under conditions of low aH 2O , and yield indistinguishable 147Sm sbnd 143Nd and 238U sbnd 206Pb ages of 434.1 ± 1.2 Ma and 433.9 ± 1.0 Ma, respectively. In contrast, garnet growth in adjacent graphite-free layers did not occur until P-T conditions of 540 ± 18°C and 8.0 ± 1.0 kbar were attained, with continued growth in response to minor heating and decompression with final matrix equilibration at 544 ± 16°C and 7.0 ± 1.0 kbar. The inclusion-free garnet rims in this assemblage record indistinguishable 147Sm sbnd 143Nd and 238U sbnd 206Pb ages of 424.6 ± 1.2 Ma and 423.4± 1.7 Ma, respectively. These results provide precise estimates for average heating and burial rates during prograde metamorphism of 8.6 -4.4+7.5°C Ma -1 and 0.8 -0.5+0.9 km Ma -1, respectively. Rb and Sr exchange between coexisting silicates in the graphite-free assemblage continued for some 37 Ma after the "peak" of metamorphism, and require an average cooling rate of about 4.0°C Ma -1 during uplift. These results illustrate a clear relationship between reaction history and the timing of mineral growth and provide definitive constraints on the rates of thermal and tectonic processes accompanying regional metamorphism.

  3. Meeting Report: International Symposium on the Genetics of Aging and Life History II

    PubMed Central

    Lee, Seung‐Jae V.; Nam, Hong Gil

    2015-01-01

    The second International Symposium on the Genetics of Aging and Life History was held at the campus of Daegu Gyeongbuk Institute of Science and Technology (DGIST), Daegu, South Korea, from May 14 to 16, 2014. Many leading scientists in the field of aging research from all over the world contributed to the symposium by attending and presenting their recent work and thoughts. The aim of the symposium was to stimulate international collaborations and interactions among scientists who work on the biology of aging. In the symposium, the most recent and exciting work on aging research was presented, covering a wide range of topics, including the genetics of aging, age‐associated diseases, and cellular senescence. The work was conducted in various organisms, including C. elegans, mice, plants, and humans. Topics covered in the symposium stimulated discussion of novel directions for future research on aging. The meeting ended with a commitment for the third International Symposium on the Genetics of Aging and Life History, which will be held in 2016. PMID:26115541

  4. History vs. snapshot: how slab morphology relates to slab age evolution

    NASA Astrophysics Data System (ADS)

    Garel, Fanny; Goes, Saskia; Davies, Rhodri; Davies, Huw; Lallemand, Serge; Kramer, Stephan; Wilson, Cian

    2016-04-01

    The age of the subducting plate at the trench ("slab age") spans a wide range, from less than 10 Myr in Central and South America to 150 Myr in the Marianas. The morphology of subducting slab in the upper mantle is also very variable, from slabs stagnating at the top of the lower mantle to slabs penetrating well beyond 1000 km depth. People have looked rather unsucessfully for correlations between slab morphology and subduction parameters, including age at the trench, on the basic assumption that old (thick) plates are likely to generate a large slab pull force that would influence slab dip. Thermo-mechanical models reveal complex feedbacks between temperature, strain rate and rheology, and are able to reproduce the evolution of plate ages as a function of time, subducting plate velocity and trench velocity. In particular, we show how initially young subducting plates can rapidly age at the surface because of a slow sinking velocity. As a consequence, different slab morphologies can exhibit similar ages at the trench provided that subduction history is different. We illustrate how models provide insights into Earth subduction zones for which we have to consider their history (evolution of trench velocity, relative plate ages at time of initiation) in order to unravel their present-day geometry.

  5. Formation Ages of the Apollo 16 Regolith Breccias: Implications for Accessing the Bombardment History of the Moon

    NASA Technical Reports Server (NTRS)

    Joy, K. H.; Kring, D. A.; Bogard, D. D.; Zolensky, M. E.; McKay, D. S.

    2010-01-01

    Regolith breccias are lithified samples of the regolith that have been fused together by impact shock and thermal metamorphism. In lunar regolith samples, the ratio of trapped 40Ar/36Ar is a useful indicator of antiquity and can be used to model the closure age/lifithication event of the regolith (i.e. the apparent time when Ar became trapped [1]), thus providing an important insight into specific times when that regolith was interacting with the the dynamic inner solar system space environment [2-4].

  6. Mesozoic age of the Gilyui Metamorphic Complex in the junction zone of the Selenga-Stanovoi and Dzhugdzhur-Stanovoi superterranes, Central Asian fold belt

    NASA Astrophysics Data System (ADS)

    Velikoslavinskii, S. D.; Kotov, A. B.; Kovach, V. P.; Larin, A. M.; Sorokin, A. A.; Sorokin, A. P.; Tolmacheva, E. V.; Salnikova, E. B.; Wang, K. L.; Jahn, B. M.; Cung, S. L.

    2016-06-01

    The Gilyui Complex includes sedimentary and volcanic rocks metamorphosed to amphibolite and epidote-amphibolite facies, which constitute blocks confined to the main structural sutures of the Dzhugdzhur-Stanovoi superterrane in the Central Asian fold belt. In recent stratigraphic scales, they are considered as being Neoarchean in age with Nd model age values of 1.5-3.0 Ga. The youngest detrital zircons from metamorphosed mudstone of the Gilyui Complex yield a date of 285 ± 4 Ma, which determines the lower age limit for the formation of its protolith. The age of crystallization of rhyolites from the Gilyui Complex is determined to be 231 ± 4 Ma. If the rhyolites form volcanic flow units or sills, the Gilyui Complex is approximately 230 Ma or 231 ± 4 to 285 ± 4 Ma old, respectively.

  7. Shock metamorphism of ordinary chondrites

    NASA Technical Reports Server (NTRS)

    Stoeffler, Dieter; Keil, Klaus; Scott, Edward R. D.

    1991-01-01

    This study proposes a revised petrographic classification of progressive stages of shock metamorphism of 26 ordinary chondrites. Six stages of shock (S1 to S6) are defined on the basis of shock effects in olivine and plagioclase as recognized by thin section microscopy, and the characteristic shock effects of each shock stage are described. It is concluded that shock effects and the sequence of progressively increasing degrees of shock metamorphosis are very similar in H, L, and LL groups. Differences in the frequency distribution of shock stages are relatively minor. It is suggested that the collisional histories of the H, L, and LL parent bodies were similar. Petrologic type-3 chondrites are deficient in stages S4 and S6 and, with increasing petrologic type, the frequency of stages S4 to S6 increases. It is suggested that the more porous and volatile-rich Type-3 chondrites are subject to melting at a lower shock pressure than the nonporous chondrites of higher petrologic type. Stage S3 is the most abundant in nearly all petrologic types.

  8. Stratigraphic and structural implications of conodont and detrital zircon U-Pb ages from metamorphic rocks of the Coldfoot terrane, Brooks Range, Alaska

    USGS Publications Warehouse

    Moore, T.E.; Aleinikoff, J.N.; Harris, A.G.

    1997-01-01

    New paleontologic and isotopic data from the Emma Creek and Marion Creek schists of the Coldfoot terrane, Arctic Alaska superterrane, central Brooks Range, suggest Devonian and possibly younger ages of deposition for their sedimentary protoliths. Conodonts from marble of the Emma Creek schist, intruded by a roughly 392 Ma orthogneiss, are late Lochkovian (early Early Devonian, between about 408 and 396 Ma) and Silurian to Devonian at two other locations. Spherical to oblong detrital zircons from quartz-mica schist of the overlying Marion Creek schist yield mostly discordant U-Pb data suggestive of provenance ages of 3.0, 2.0-1.8, and 1.5-1.4 Ga; however, several euhedral grains of zircon from Marion Creek quartz-mica schist have concordant U-Pb ages from 370 to 360 Ma. The Marion Creek schist in our study area therefore is at least 26 m.y. younger than the Emma Creek schist. The age data imply that the protolith of the Emma Creek schist is age correlative with Devonian carbonate rocks in the Hammond and North Slope terranes, whereas the Marion Creek schist is age correlative with Upper Devonian and Lower Mississippian clastic sedimentary rocks of the Endicott Group in the Endicott Mountains terrane and shale and carbonate units in the De Long Mountains and Sheenjek River terranes. Consequently, tectonic models restoring the entire Coldfoot terrane beneath partly or wholly coeval rocks of the Hammond, Endicott Mountains, De Long Mountains, and Sheenjek River terranes of the Arctic Alaska superterrane require revision. Alternative reconstructions, including restoration of the Coldfoot terrane inboard of the Endicott Mountains terrane or outboard of the De Long Mountains and Sheenjek River terranes are plausible but require either larger amounts of shortening than previously suggested or indicate problematic facies relations. copyright. Published in 1997 by the American Geophysical Union.

  9. Ostwald ripening of clays and metamorphic minerals

    USGS Publications Warehouse

    Eberl, D.D.; Srodon, J.; Kralik, M.; Taylor, B.E.; Peterman, Z.E.

    1990-01-01

    Analyses of particle size distributions indicate that clay minerals and other diagenetic and metamorphic minerals commonly undergo recrystallization by Ostwald ripening. The shapes of their particle size distributions can yield the rate law for this process. One consequence of Ostwald ripening is that a record of the recrystallization process is preserved in the various particle sizes. Therefore, one can determine the detailed geologic history of clays and other recrystallized minerals by separating, from a single sample, the various particle sizes for independent chemical, structural, and isotopic analyses.

  10. Role of Family Resources and Paternal History of Substance Use Problems in Psychosocial Adjustment among School-Aged Children

    ERIC Educational Resources Information Center

    Peleg-Oren, Neta; Rahav, Giora; Teichman, Meir

    2009-01-01

    The present study examines the role of family resources (parenting style and family cohesion) and paternal history of substance abuse on the psychosocial adjustment of their school-aged children. Data were collected from 148 children aged 8-11 (72 of fathers with history of substance use disorder, 76 children of fathers with no substance use…

  11. [Beyond the asylum -An other view on the history of psychiatry in the modern age].

    PubMed

    Fauvel, Aude

    2015-07-01

    If one thinks medicine, madness and the past, one image immediately pops into mind: that of the mental asylum. Following the famous work by Michel Foucault, Madness and Civilization: A History of Insanity in the Age of Reason, many historians have thus considered that the medicalization of insanity in the modern age had mostly led to a "great confinement" and a greater segregation of all individuals deemed mentally unfit during the "asylum era': However, new research demonstrates that this classic narrative of the psychiatric past needs to be revised. It discloses that, ever since the 191h century, a whole other medical culture existed as a challenge to asylums, a culture that advocated the integration of the mad and fought to disassociate psychiatry from the dominant model of confinement all throughout the occidental world. This article aims at presenting the results of these historical works that depict another aspect of the psychiatric history, exploring "boarding out" practices, instead of asylum ones. PMID:26111838

  12. Iron Age and Anglo-Saxon genomes from East England reveal British migration history

    PubMed Central

    Schiffels, Stephan; Haak, Wolfgang; Paajanen, Pirita; Llamas, Bastien; Popescu, Elizabeth; Loe, Louise; Clarke, Rachel; Lyons, Alice; Mortimer, Richard; Sayer, Duncan; Tyler-Smith, Chris; Cooper, Alan; Durbin, Richard

    2016-01-01

    British population history has been shaped by a series of immigrations, including the early Anglo-Saxon migrations after 400 CE. It remains an open question how these events affected the genetic composition of the current British population. Here, we present whole-genome sequences from 10 individuals excavated close to Cambridge in the East of England, ranging from the late Iron Age to the middle Anglo-Saxon period. By analysing shared rare variants with hundreds of modern samples from Britain and Europe, we estimate that on average the contemporary East English population derives 38% of its ancestry from Anglo-Saxon migrations. We gain further insight with a new method, rarecoal, which infers population history and identifies fine-scale genetic ancestry from rare variants. Using rarecoal we find that the Anglo-Saxon samples are closely related to modern Dutch and Danish populations, while the Iron Age samples share ancestors with multiple Northern European populations including Britain. PMID:26783965

  13. Iron Age and Anglo-Saxon genomes from East England reveal British migration history.

    PubMed

    Schiffels, Stephan; Haak, Wolfgang; Paajanen, Pirita; Llamas, Bastien; Popescu, Elizabeth; Loe, Louise; Clarke, Rachel; Lyons, Alice; Mortimer, Richard; Sayer, Duncan; Tyler-Smith, Chris; Cooper, Alan; Durbin, Richard

    2016-01-01

    British population history has been shaped by a series of immigrations, including the early Anglo-Saxon migrations after 400 CE. It remains an open question how these events affected the genetic composition of the current British population. Here, we present whole-genome sequences from 10 individuals excavated close to Cambridge in the East of England, ranging from the late Iron Age to the middle Anglo-Saxon period. By analysing shared rare variants with hundreds of modern samples from Britain and Europe, we estimate that on average the contemporary East English population derives 38% of its ancestry from Anglo-Saxon migrations. We gain further insight with a new method, rarecoal, which infers population history and identifies fine-scale genetic ancestry from rare variants. Using rarecoal we find that the Anglo-Saxon samples are closely related to modern Dutch and Danish populations, while the Iron Age samples share ancestors with multiple Northern European populations including Britain. PMID:26783965

  14. The Western Sierras Pampeanas: Protracted Grenville-age history (1330-1030 Ma) of intra-oceanic arcs, subduction-accretion at continental-edge and AMCG intraplate magmatism

    NASA Astrophysics Data System (ADS)

    Rapela, C. W.; Pankhurst, R. J.; Casquet, C.; Baldo, E.; Galindo, C.; Fanning, C. M.; Dahlquist, J. M.

    2010-01-01

    New U-Pb SHRIMP zircon ages combined with geochemical and isotope investigation in the Sierra de Maz and Sierra de Pie de Palo and a xenolith of the Precordillera basement (Ullún), provides insight into the identification of major Grenville-age tectonomagmatic events and their timing in the Western Sierras Pampeanas. The study reveals two contrasting scenarios that evolved separately during the 300 Ma long history: Sierra de Maz, which was always part of a continental crust, and the juvenile oceanic arc and back-arc sector of Sierra de Pie de Palo and Ullún. The oldest rocks are the Andino-type granitic orthogneisses of Sierra de Maz (1330-1260 Ma) and associated subalkaline basic rocks, that were part of an active continental margin developed in a Paleoproterozoic crust. Amphibolite facies metamorphism affected the orthogneisses at ca. 1175 Ma, while granulite facies was attained in neighbouring meta-sediments and basic granulites. Interruption of continental-edge magmatism and high-grade metamorphism is interpreted as related to an arc-continental collision dated by zircon overgrowths at 1170-1230 Ma. The next event consisted of massif-type anorthosites and related meta-jotunites, meta-mangerites (1092 ± 6 Ma) and meta-granites (1086 ± 10 Ma) that define an AMCG complex in Sierra de Maz. The emplacement of these mantle-derived magmas during an extensional episode produced a widespread thermal overprint at ca. 1095 Ma in neighbouring country rocks. In constrast, juvenile oceanic arc and back-arc complexes dominated the Sierra de Pie de Palo-Ullún sector, that was fully developed ca. 1200 Ma (1196 ± 8 Ma metagabbro). A new episode of oceanic arc magmatism at ˜1165 Ma was roughly coeval with the amphibolite high-grade metamorphism of Sierra de Maz, indicating that these two sectors underwent independent geodynamic scenarios at this age. Two more episodes of arc subduction are registered in the Pie de Palo-Ullún sector: (i) 1110 ± 10 Ma orthogneisses and

  15. Association of Family History of Epilepsy with Earlier Age Onset of Juvenile Myoclonic Epilepsy

    PubMed Central

    2016-01-01

    Objective Juvenile myoclonic epilepsy (JME) is supposedly the most frequent subtype of idiopathic generalized epilepsies (IGE). The aim of this study was to determine the prevalence of JME and comparison of patients’ demographics as well as timeline of the disease between positive family history epileptic patients (PFHE) and negative family history epileptic patients (NFHE) among sample of Iranian epileptic patients. Materials & Methods From Feb. 2006 to Oct. 2009, 1915 definite epileptic patients (873 females) referred to epilepsy clinics in Isfahan, central Iran, were surveyed and among them, 194 JME patients were diagnosed. JME was diagnosed by its specific clinical and EEG criteria. Patients were divided into two groups as PFHE and NFHE and data were compared between them. Results JME was responsible for 10% (194 patients) of all types of epilepsies. Of JME patients, 53% were female. In terms of family history of epilepsy, 40% were positive. No significant differences was found between PFHE and NFHE groups as for gender (P>0.05). Age of epilepsy onset was significantly earlier in PFHE patients (15 vs. 22 yr, P<0.001). Occurrence of JME before 18 yr old among PFHE patients was significantly higher (OR=2.356, P=0.007). Conclusion A family history of epilepsy might be associated with an earlier age of onset in patients with JME. PMID:27247579

  16. The history of bronchial asthma from the ancient times till the Middle Ages.

    PubMed

    Cserháti, E

    2004-01-01

    The aim of the paper is to give an overview of the knowledge on asthma through the history of mankind. The text begins with ancient China and it is finished with the medicine of Middle Age. During this time, a lot of theories came and this appeared about the etiology and therapy of the disease. The paper is giving a short description of the changing medical views during this very long period including China, Egypt Greco-roman period, Mesopotamia, the Hebrews, the physicians of India, the pre-Columbian medicine in the America and the Arabic world, and partly the European medicine of the Middle Ages. PMID:16438118

  17. Genomic basis of aging and life-history evolution in Drosophila melanogaster.

    PubMed

    Remolina, Silvia C; Chang, Peter L; Leips, Jeff; Nuzhdin, Sergey V; Hughes, Kimberly A

    2012-11-01

    Natural diversity in aging and other life-history patterns is a hallmark of organismal variation. Related species, populations, and individuals within populations show genetically based variation in life span and other aspects of age-related performance. Population differences are especially informative because these differences can be large relative to within-population variation and because they occur in organisms with otherwise similar genomes. We used experimental evolution to produce populations divergent for life span and late-age fertility and then used deep genome sequencing to detect sequence variants with nucleotide-level resolution. Several genes and genome regions showed strong signatures of selection, and the same regions were implicated in independent comparisons, suggesting that the same alleles were selected in replicate lines. Genes related to oogenesis, immunity, and protein degradation were implicated as important modifiers of late-life performance. Expression profiling and functional annotation narrowed the list of strong candidate genes to 38, most of which are novel candidates for regulating aging. Life span and early age fecundity were negatively correlated among populations; therefore, the alleles we identified also are candidate regulators of a major life-history trade-off. More generally, we argue that hitchhiking mapping can be a powerful tool for uncovering the molecular bases of quantitative genetic variation. PMID:23106705

  18. Zircon SHRIMP U-Pb dating for gneisses in northern Dabie high T/ P metamorphic zone, central China: Implications for decoupling within subducted continental crust

    NASA Astrophysics Data System (ADS)

    Liu, Yi-Can; Li, Shu-Guang; Xu, Shu-Tong

    2007-06-01

    Zircon SHRIMP U-Pb ages and cathodoluminescence (CL) images reveal that most zircon separated from two tonalitic gneiss samples in the northern Dabie high T/ P metamorphic zone (NDZ) have four different domains: (1) inherited core, with clear oscillatory zoning, low- P mineral inclusions and high Th/U ratios, indicating the Neoproterozoic age of the protolith; (2) inner-mantle, with homogeneous CL intensity, low Th/U ratios of ≤ 0.09 and occasionally ultrahigh pressure metamorphic (UHPM) mineral inclusions such as diamond, garnet and rutile, which defined a weighted mean 206Pb/ 238U age of 218 ± 3 Ma, corresponding to the age of ultrahigh-pressure metamorphism; (3) outer-mantle with lower Th/U ratio and retrograde mineral inclusions, which yields a retrogressive age of 191 ± 5 Ma; and (4) rim, which is black luminescence, with relatively high Th/U ratios of 0.12-0.40 and a weighted mean 206Pb/ 238U age of 126 ± 5 Ma, indicating an overprint of the Early Cretaceous migmatization. Consequently, four discrete and meaningful age groups have been identified. Remarkably, the U-Pb ages of both UHPM zircon and retrograded metamorphic zircon from the NDZ are significantly younger than the U-Pb ages of 238 ± 3 Ma-230 ± 4 Ma for UHPM zircon and U-Th-Pb ages of 218 ± 1.2 Ma-209 ± 3 Ma for rutile and monazite overgrowths (representing the cooling or retrograded metamorphic time corresponding to amphibolite-facies) from the southern Dabie UHPM zone (SDZ), respectively. Combined with reported ages for UHPM rocks from the NDZ, SDZ and Huangzhen low- T eclogite zone (HZ), we found that the metamorphic ages of these three UHPM units in the Dabie orogen gradually decrease from south to north. This age distribution suggests that the three UHPM units represent 3 exhumed crustal slices, which are decoupled from each other and have different subduction and exhumation histories. Firstly, the subducted Huangzhen crustal slice was detached from the underlying subducted continental

  19. Metamorphic and stratigraphic constraints on the evolution of the Santa Catalina Mountains metamorphic core complex, Arizona

    SciTech Connect

    Palais, D.G.; Peacock, S.M. )

    1990-01-10

    Contact metamorphic mineral assemblages in the Santa Catalina Mountains metamorphic core complex constrain the emplacement depth of the metaluminous Late Cretaceous Leatherwood quartz diorite to between 7.5 and 14 km (2-3.8 kbar). The peraluminous Eocene Wilderness granite is constrained to have been emplaced at depths of less than 14 km. Stratigraphic and tectonic considerations are consistent with emplacement of both the Leatherwood quartz diorite and Wilderness granite at upper crustal levels. Published igneous thermobarometry (Anderson et al., 1988), although in approximate agreement with the metamorphic and tectonostratigraphic estimates for the depth of emplacement of the Wilderness granite, suggests that the Leatherwood quartz diorite was emplaced at depths of {approximately} 21 km (5.6 kbar) or greater. The discrepancy between the different emplacement estimates may reflect ambiguities associated with interpretations of the results from each technique. Igneous barometric assemblages may reflect conditions experienced during a period of crystallization during ascent of the magma through the crust (i.e., ponding of the magma). Alternatively, emplacement of the voluminous Wilderness granite and associated plutons may have entirely overprinted earlier Leatherwood-related contact metamorphism. The proposed upper crustal emplacement of the Leatherwood quartz diorite is consistent with the observation that Laramide-age crustal thickening in southeast Arizona probably did not exceed 8 km.

  20. Zircon Messengers Reveal the Age and History of Great Basin Crust, Kern Mountains, Nevada

    NASA Astrophysics Data System (ADS)

    Gottlieb, E. S.; Miller, E. L.; Wooden, J. L.

    2011-12-01

    Results of SHRIMP-RG analyses of complexly zoned zircons from muscovite-bearing granitic rocks exposed in the Kerns Mountains of East-Central Nevada constrain the timing, duration, and loci of zircon growth within the interior of the U.S. Cordillera during Late Cretaceous through Eocene time. The Kern Mountains are an exhumed block of greenschist to amphibolite facies metamorphosed miogeoclinal rocks that were pervasively intruded by the Late Cretaceous Tungstonia granite pluton and the Eocene Skinner Canyon and Uvada plutons (Best et al., 1974). Euhedral zircons separated from a coarse-grained (2-3 cm) muscovite-bearing phase of the Tungstonia pluton exhibit complex cathodeluminescence (CL) zonation. Sub-angular to sub-rounded cores with highly variable CL are overgrown by oscillatory-zoned zircon which in turn is rimmed by dark CL zircon (U>5000 ppm). A weighted mean Pb/U age of 70.2±0.9 Ma (n=20, MSWD=2.5) obtained from the oscillatory-zoned zircon coincides with the end of Cretaceous peak metamorphism at shallow crustal levels. Pb/U ages from core zones (n=18) predominantly are 0.9-1.4 Ga (n=11; 7 of which <15% discordant) or 2.4-2.7 Ga (n=5; 1 of which <15% discordant), consistent with ages of detrital zircons within the Late Proterozoic McCoy Creek Group exposed in adjacent ranges. A previously undated muscovite-bearing dike in Skinner Canyon yielded a texturally complex population of subhedral zircon grains. CL imaging of these grains reveals fragmental, ghost-like cores surrounded by irregularly shaped overgrowth zones with diffuse boundaries which are rimmed by oscillatory-zoned zircon. Both oscillatory zoned and gradational rim areas (n=32) yielded Late Cretaceous to Eocene ages. Twelve spots define the age of intrusion at 41.7±0.3 Ma (MSWD=1.8), consistent with the local onset of Eocene magmatism. An older period of zircon growth from ~75-45 Ma, coincident with the proposed duration of the Laramide shallow slab, is defined by zircon with flat to

  1. Grampian high-pressure-granulite-facies metamorphism of the Slishwood Division, NW Ireland and its enigmatic eclogite-facies precursor

    NASA Astrophysics Data System (ADS)

    Daly, J. S.; Flowerdew, M. J.; Whitehouse, M. J.

    2012-04-01

    The Slishwood Division of NW Ireland is located along the SW margin of the Grampian belt, whose metamorphism and deformation is generally attributed to the collision of outboard magmatic arcs with the Laurentian continental margin during the c. 470 Ma Grampian Orogeny. The unusual metamorphic history of the Slishwood Division (with eclogite-facies and later high-pressure-granulite-facies assemblages) is a unique feature of the Grampian belt and has long been regarded as evidence for pre-Caledonian tectonism, possibly of Grenvillian age. Detrital zircon U-Pb dating of Slishwood Division metasediments shows that they were deposited after c. 926 Ma, ruling out a Grenville event. A maximum age for the eclogite-facies event is provided by a U-Pb zircon age of 596 ± 6 Ma for a suite of metabasite intrusives, which exhibit varying degrees of decompression from eclogite- to high pressure granulite-facies or amphibolite-facies assemblages accompanied by the development of migmatitic leucosomes. Zircons in these leucosomes yield U-Pb zircon ages of c. 470 Ma identical to metamorphic zircons in a relatively dry partially decompressed eclogite. Following polyphase deformation, migmatitic leucosomes in metasediments crystallized under high pressure granulite-facies conditions during sinistral transtension. Dating these leucosomes has been challenging because the majority of zircons within them are inherited and generally only thin (< 15 μm) euhedral magmatic zircon overgrowths are present. Careful targeting with the ion microprobe yields U-Pb ages of c. 470 Ma, consistent with a U-Pb zircon age of c. 470 Ma from a cross-cutting granite pegmatite. In addition the high pressure granulite facies mineral fabrics are cut by tonalite bodies also dated at 470 Ma (ref. 1). Based on these results, we interpret the Slishwood Division as a Neoproterozoic metasedimentary sequence deposited after c. 926 Ma on what became a microcontinental fragment that detached from Laurentia during the

  2. Age and zircon inheritance of eastern Blue Ridge plutons, southwestern North Carolina and northeastern Georgia, with implications for magma history and evolution of the southern Appalachian origin

    SciTech Connect

    Miller, C.F.; Hatcher, R.D. Jr.; Ayers, J.C.; Coath, C.D.; Harrison, T.M.

    2000-02-01

    High-resolution ion microprobe analysis of zircon has provided ages for previously undated plutons of the high-grade eastern Blue Ridge of northeastern Georgia and southwestern North Carolina. These data, together with backscattered electron imaging, reveal the presence of nearly ubiquitous inherited cores of highly variable age and magmatic rims that have experienced variable Pb loss, thus making interpretation of conventional U-Pb analyses very difficult. Ion probe rim analyses indicate that the plutons were emplaced during both the mod-Ordovician and mid-Devonian. Zircons from all intrusions have predominantly 1.0 to 1.25 Ga cores (Grenvillian). In addition, both Devonian and Ordovician plutons have smaller populations of Late Proterozoic-early Paleozoic (0.5--0.75 Ga), Middle Proterozoic (1.4 Ga), and Late Archean (2.6--2.9 Ga) cores. The ubiquitous, round cores and thick magmatic rims suggest significant resorption and then protracted growth within the melts. Zircon saturation temperatures based on whole-rock ({approximately}melt) Zr concentrations are lower than expected for magma generation (710--760 C). Zirconium concentrations may not reflect saturation at maximum temperature, if melting was very rapid (<{approximately}10{sup 5} yrs), or if zircon cores represent grains that were shielded from melt inside host grains for much of the magmatic history. Ages of magmatic and inherited zones of zircon from the plutons demonstrate that similar crust underlay the eastern Blue Ridge during both Taconian and Acadian orogenies, that there was no single episode of voluminous magmatism, and that metamorphism and deformation began before 470 Ma and continued after 370 Ma. These plutons do not constitute a significant convergence-related arc, though it is possible that they represent a displaced part of an arc that lies primarily to the east (in the Inner Piedmont?).

  3. New [sup 40]Ar/[sup 39]Ar mica ages from eastern New Hampshire and southern Maine: Implications for the exhumation history of the region

    SciTech Connect

    Lux, D.R.; West, D.P. Jr. . Dept. of Geological Science)

    1993-03-01

    It has long been recognized that micas from the high-grade metamorphic terrane of Maine and New Hampshire have anomalously young K-Ar ages. Furthermore, ages show systematic spatial patterns. Samples from western New Hampshire are youngest and become progressively older towards the east. In the Kearsarge-Central Maine Synclinorium (KCMS) of western Maine, ages are oldest along the northern terminus of high grade metamorphism and become progressively younger towards the southwest. In order to understand this peculiar relationship, micas from 20 sites in eastern New Hampshire and southern Maine were dated by the [sup 40]Ar/[sup 39]Ar method. The following relationships are observed: (1) Micas from the KCMS of southern New Hampshire have Permo-Carboniferous ages and coexisting micas are highly discordant, (2) micas from within or very near the Massabesic Gneiss Complex have young ages ([approximately]240--250 Ma) and show little to no discordance, (3) with one exception, micas from south of the Sebago batholith in Maine are also young ([approximately]240--250 Ma) and show little to no discordance. North of the Sebago batholith the transition to older micas is gradual. Mica ages from the Massabesic Gneiss Complex are younger than in surrounding regions and the transition to older ages roughly coincides with the Campbell Hill and Flint Hill faults. Outside the zone of young micas, cooling curves are concave upward for the same temperature interval. The young micas are concordant indicating rapid cooling but they are [approximately]40 Ma younger than the time of Late Paleozoic metamorphism. Therefore the young ages cannot be explained by rapid post-metamorphic cooling. The authors believe the accelerated cooling is the result of regional tectonic exhumation related to the earliest stages of rifting associated with opening of the Atlantic.

  4. The Utilization of Local History in Teaching American Religious History: A Gilded Age and Progressive Era North Dakota Case Study

    ERIC Educational Resources Information Center

    Price, Christopher Neal

    2013-01-01

    Teachers of college-level courses on American religious history generally leave out the importance of local and regional histories when telling the story of religion in America. The study of local history provides a fertile ground for understanding broad national trends in a local context. This dissertation focuses upon a little-studied religious…

  5. Fission track studies of xenolithic chondrites - Implications regarding brecciation and metamorphism

    NASA Technical Reports Server (NTRS)

    Kothari, B. K.; Rajan, R. S.

    1982-01-01

    Fission tracks in phosphates from one gas-poor chondrite and three gas-rich ones are studied to determine their thermal history and brecciation time scales. Model fission track ages are calculated for given track densities due to Pu-244 and U-238; track densities and uranium measurements for whitlockite are shown, and possible sources of the tracks are mentioned. Details of track density and uranium measurements are discussed for each meteorite separately. Whitlockites from all the meteorites give model fission track ages of 4.4 Gyr assuming a Pu/U ratio at 4.55 Gyr of 0.045. The final brecciation event definitely did not reset the track clock in phosphates of one meteor and probably not in another two. It is concluded that the observed fission track ages date the end of metamorphic cooling in the meteorite parent bodies and support the planetesimal model for the formation of xenolithic chondrites.

  6. Genetic modifiers and subtypes in schizophrenia: investigations of age at onset, severity, sex and family history.

    PubMed

    Bergen, Sarah E; O'Dushlaine, Colm T; Lee, Phil H; Fanous, Ayman H; Ruderfer, Douglas M; Ripke, Stephan; Sullivan, Patrick F; Smoller, Jordan W; Purcell, Shaun M; Corvin, Aiden

    2014-04-01

    Schizophrenia is a genetically and clinically heterogeneous disorder. Genetic risk factors for the disorder may differ between the sexes or between multiply affected families compared to cases with no family history. Additionally, limited data support a genetic basis for variation in onset and severity, but specific loci have not been identified. We performed genome-wide association studies (GWAS) examining genetic influences on age at onset (AAO) and illness severity as well as specific risk by sex or family history status using up to 2762 cases and 3187 controls from the International Schizophrenia Consortium (ISC). Subjects with a family history of schizophrenia demonstrated a slightly lower average AAO that was not significant following multiple testing correction (p=.048), but no differences in illness severity were observed by family history status (p=.51). Consistent with prior reports, we observed earlier AAO (p=.005) and a more severe course of illness for men (p=.002). Family history positive analyses showed the greatest association with KIF5C (p=1.96×10(-8)), however, genetic risk burden overall does not differ by family history. Separate association analyses for males and females revealed no significant sex-specific associations. The top GWAS hit for AAO was near the olfactory receptor gene OR2K2 (p=1.52×10(-7)). Analyses of illness severity (episodic vs. continuous) implicated variation in ST18 (p=8.24×10(-7)). These results confirm recognized demographic relationships but do not support a simplified genetic architecture for schizophrenia subtypes based on these variables. PMID:24581549

  7. Genetic modifiers and subtypes in schizophrenia: Investigations of age at onset, severity, sex and family history

    PubMed Central

    Bergen, Sarah E.; O’Dushlaine, Colm T.; Lee, Phil H.; Fanous, Ayman H.; Ruderfer, Douglas M.; Ripke, Stephan; Sullivan, Patrick F.; Smoller, Jordan W.; Purcell, Shaun M.; Corvin, Aiden

    2015-01-01

    Schizophrenia is a genetically and clinically heterogeneous disorder. Genetic risk factors for the disorder may differ between the sexes or between multiply affected families compared to cases with no family history. Additionally, limited data support a genetic basis for variation in onset and severity, but specific loci have not been identified. We performed genome-wide association studies (GWAS) examining genetic influences on age at onset (AAO) and illness severity as well as specific risk by sex or family history status using up to 2762 cases and 3187 controls from the International Schizophrenia Consortium (ISC). Subjects with a family history of schizophrenia demonstrated a slightly lower average AAO that was not significant following multiple testing correction (p = .048), but no differences in illness severity were observed by family history status (p = .51). Consistent with prior reports, we observed earlier AAO (p = .005) and a more severe course of illness for men (p = .002). Family history positive analyses showed the greatest association with KIF5C (p = 1.96 × 10−8), however, genetic risk burden overall does not differ by family history. Separate association analyses for males and females revealed no significant sex-specific associations. The top GWAS hit for AAO was near the olfactory receptor gene OR2K2 (p = 1.52 × 10−7). Analyses of illness severity (episodic vs. continuous) implicated variation in ST18 (p = 8.24 × 10−7). These results confirm recognized demographic relationships but do not support a simplified genetic architecture for schizophrenia subtypes based on these variables. PMID:24581549

  8. Interactive effects of working memory and trial history on Stroop interference in cognitively healthy aging.

    PubMed

    Aschenbrenner, Andrew J; Balota, David A

    2015-03-01

    Past studies have suggested that Stroop interference increases with age; however the robustness of this effect after controlling for processing speed has been questioned. Both working memory (WM) and the congruency of the immediately preceding trial have also been shown to moderate the magnitude of Stroop interference. Specifically, interference is smaller both for individuals with higher working memory capacity and following an incongruent trial. At present, it is unclear whether and how these 3 variables (age, WM and previous congruency) interact to predict interference effects in the standard Stroop color-naming task. We present analyses of Stroop interference in a large database of Stroop color-naming trials from a lifespan sample of well-screened, cognitively healthy, older adults. Our results indicated age-related increases in interference (after controlling for processing speed) that were exaggerated for individuals with low WM. This relationship between age and WM occurred primarily when the immediately preceding trial was congruent. Following an incongruent trial, interference increased consistently with age, regardless of WM. Taken together, these results support previous accounts of multiple mechanisms underlying control in the Stroop task and provide insight into how each component is jointly affected by age, WM, and trial history. PMID:25602489

  9. Motor system alterations in retired former athletes: the role of aging and concussion history

    PubMed Central

    2013-01-01

    Background Retired athletes with a history of sports concussions experience cognitive and motor declines with aging, and the risk of severe neurodegenerative conditions is magnified in this population. The present study investigated the effects of aging on motor system metabolism and function in former university-level athletes who sustained their last concussion several decades prior to testing. Methods To test the hypothesis that age and remote concussions induce functional as well as metabolic alterations of the motor system, we used proton magnetic resonance spectroscopy to detect metabolic abnormalities in the primary motor cortex and the serial reaction time task (SRTT) to evaluate motor learning. Results Our results indicate that motor learning is significantly reduced in former concussed athletes relative to controls. In addition, glutamate/H2O ratio in M1 was disproportionately reduced in concussed athletes with advancing age and was found to strongly correlate with motor learning impairments. Conclusion Findings from this study provide evidence that the acquisition of a repeated motor sequence is compromised in the aging concussed brain and that its physiological underpinnings could implicate disproportionate reductions of M1 glutamate concentrations with advancing age. PMID:23972282

  10. Application of Lu-Hf garnet dating to unravel the relationships between deformation, metamorphism and plutonism: An example from the Prince Rupert area, British Columbia

    NASA Astrophysics Data System (ADS)

    Wolf, David E.; Andronicos, Christopher L.; Vervoort, Jeffery D.; Mansfield, Michael R.; Chardon, Dominique

    2010-04-01

    The tectonic history of the Prince Rupert area is marked by profound crustal thickening from thrusting that produced inverted metamorphic field gradients and transpression in crustal-scale shear zones. Syn-tectonic garnet in the Prince Rupert area has Lu-Hf ages of 102.6 ± 3.7 Ma and 108.3 ± 4.1 Ma (2 σ). Porphyroblast-matrix relationships in these samples, and samples from the same outcrops, indicate syn-tectonic garnet growth. These relationships imply that the garnet ages directly date the development of the metamorphic foliations. A third sample of migmatitic garnet amphibolite from the contact aureole of the 94-90 Ma Ecstall pluton had complex isotope systematics interpreted to indicate a garnet growth episode ˜ 105 Ma, similar to the ages obtained from the other samples and a growth or equilibration event at ˜ 94 Ma during pluton emplacement. The data show that the older Lu-Hf garnet ages date prograde metamorphism during foliation development and modification during pluton emplacement. The Ecstall pluton was emplaced 10 to 15 m.y. after regional metamorphism and thrust stacking in the Prince Rupert area. In order to place our samples in a regional tectonic context we compare our results to patterns of regional deformation, metamorphism and plutonism throughout the North American Cordillera in the time period between 110 and 85 Ma. Contractional and transpressional deformation occurred throughout much of the North American Cordillera at this time, from southeastern Alaska to the Baja Peninsula in Mexico. Left-lateral transpression dominated the Canadian Cordillera, whereas, right-lateral transpression affected areas south of the Idaho-Salmon River suture zone, including the Sierra Nevada batholith. This reversal in kinematics in the northern and southern cordillera within coeval magmatic belts appears to be a first-order feature of the geology of the North American Cordillera during the Cretaceous.

  11. Health maintenance in school-aged children: Part I. History, physical examination, screening, and immunizations.

    PubMed

    Riley, Margaret; Locke, Amy B; Skye, Eric P

    2011-03-15

    The goals of the well-child examination in school-aged children (kindergarten through early adolescence) are promoting health, detecting disease, and counseling to prevent injury and future health problems. A complete history should address any concerns from the patient and family and screen for lifestyle habits, including diet, physical activity, daily screen time (e.g., television, computer, video games), hours of sleep per night, dental care, and safety habits. School performance can be used for developmental surveillance. A full physical examination should be performed; however, the U.S. Preventive Services Task Force recommends against routine scoliosis screening and testicular examination. Children should be screened for obesity, which is defined as a body mass index at or above the 95th percentile for age and sex, and resources for comprehensive, intensive behavioral interventions should be provided to children with obesity. Although the evidence is mixed regarding screening for hypertension before 18 years of age, many experts recommend checking blood pressure annually beginning at three years of age. The American Academy of Pediatrics recommends vision and hearing screening annually or every two years in school-aged children. There is insufficient evidence to recommend screening for dyslipidemia in children of any age, or screening for depression before 12 years of age. All children should receive at least 400 IU of vitamin D daily, with higher doses indicated in children with vitamin D deficiency. Children who live in areas with inadequate fluoride in the water (less than 0.6 ppm) should receive a daily fluoride supplement. Age-appropriate immunizations should be given, as well as any missed immunizations. PMID:21404978

  12. Settlement and landscape history of the Northern Franconian Jura during the Bronze and Iron Ages

    NASA Astrophysics Data System (ADS)

    Kothieringer, Katja; Lambers, Karsten; Seregély, Timo; Schäfer, Andreas

    2014-05-01

    This paper describes the results of initial archaeological and geoarchaeological fieldwork in the Northern Franconian Jura between the cities of Bayreuth and Bamberg. Our research aims at the reconstruction of settlement patterns and strategies of land use during the Metal Ages (Bronze Age and Iron Age) in the catchment area of the river Weismain. The project is designed as a case study for research into the settlement and landscape history of a rural region of the Central German Uplands during the last two millennia before our era. During the Bronze Age and Iron Age (about 2.100 BC to 30 BC), the Northern Franconian Jura must have been densely populated, as evidenced by numerous burial monuments, prominent hillforts like the Staffelberg, and ritual places on the Jurassic plateau. However, little is known about small rural settlements and hamlets which would have accounted for most of the settlement activity in the region. Thus, we lack the most important element for understanding the cultural history and development of the region as well as the consequences of human impact on the landscape. This impact must have induced changes in vegetation and subsequent erosion processes, leading to the formation of geoarchives like colluvial layers. During our initial fieldwork we identified such colluvial layers in depressions on the Jurassic plateau or at footslope positions. As radiocarbon datings of charcoal fragments showed, some of them date from the Metal Ages. The type is wood of these charcoal fragments is oak, which recently only occurs sporadically in mixed forests with beeches. The quantification of the shift of sediments from the plateau to the valleys will be the next important step of geoarchaeological research. Thus, investigations both on the plateau and in the river valleys will accompany archaeological survey. Apart from landscape reconstruction, they will also provide information on the state of preservation and the conditions for identifying archaeological

  13. Relating Major Silicates and Monazite Growth in Metamorphic Rocks: Application to the Upper Granite Gorge (Grand Canyon, USA)

    NASA Astrophysics Data System (ADS)

    Allaz, J.; Williams, M. L.; Jercinovic, M. J.

    2010-12-01

    Relating deformation and metamorphic conditions with time is a major goal in tectonic studies. The challenge is to find suitable minerals to be dated, and to associate them with specific events and with pressure and temperature (PT) conditions. Monazite has proven to be an excellent chronometer for dating stages in a tectonic history. It contains very little common lead, is highly retentive, and it can be dated by electron microprobe at very high spatial resolution. In addition, it commonly preserves different growth stages in distinct compositional domains that can be identified via EPMA mapping. However, its growth history and relation with major silicate assemblages and reactions are usually poorly constrained. The growth of monazite can be related to the petrology of major silicate assemblages in metamorphic rocks if reactions forming specific monazite compositional domains can be identified and geochemically linked to silicate assemblages. This is accomplished here through use of thermobarometric tools, mainly TWQ [1] for determination of PT-conditions and THERIAK-DOMINO for pseudo-sections [2]. The composition of each monazite domain is then obtained, and microprobe ages using the technique described in [3] are obtained. The next step currently being developed is to identify the metamorphic reaction responsible for each monazite growth stage. The area selected for this study is the Upper Granite Gorge of the Grand Canyon (USA). Paleoproterozoic basement crops out in this area, characterized by a segmented, block-type architecture consisting of km-scale blocks of granitic and psammitic/pelitic rocks, separated by shear zones. Previous work [4] reveals constant P but variable T from block to block. At least one block preserves a T-gradient from upper greenschist to granulite facies. Compositional mapping of hundreds of monazite grains in several samples, revealed a complex growth history within and between samples. Analysis is currently in progress. First

  14. Exposure age and erosional history of an upland planation surface in the US Atlantic Piedmont

    USGS Publications Warehouse

    Stanford, S.D.; Seidl, M.A.; Ashley, G.M.

    2000-01-01

    The upland planation surface in the Piedmont of central New Jersey consists of summit flats, as much as 130 km2 in area, that truncate bedding and structure in diabase, basalt, sandstone, mudstone and gneiss. These flats define a low-relief regional surface that corresponds in elevation to residual hills in the adjacent Coastal Plain capped by a fluvial gravel of late Miocene age. A Pliocene fluvial sand is inset 50 m below the upland features. These associations suggest a late Miocene or early Pliocene age for the surface. To assess exposure age and erosional history, a 4??4 m core of clayey diabase saprolite on a 3 km2 remnant of the surface was sampled at six depths for atmospherically produced cosmogenic 10Be. The measured inventory, assuming a deposition rate of 1??3 x 106 atoms cm-2 a-1, yields a minimum exposure age of 227 000 years, or, assuming continuous surface erosion, a constant erosion rate of 10 m Ma-1. Because the sample site lies about 60 m above the aggradation surface of the Pliocene fluvial deposit, and itself supports a pre-Pliocene fluvial gravel lag, this erosion rate is too high. Rather, episodic surface erosion and runoff bypassing probably have produced an inventory deficit. Reasonable estimates of surface erosion (up to 10 m) and bypassing (up to 50 per cent of total precipitation) yield exposure ages of as much as 6??4 Ma. These results indicate that (1) the surface is probably of pre-Pleistocene age and has been modified by Pleistocene erosion, and (2) exposure ages based on 10Be inventories are highly sensitive to surface erosion and runoff bypassing. Copyright (C) 2000 John Wiley and Sons, Ltd.

  15. Using quantitative phase petrology to understand metamorphism

    NASA Astrophysics Data System (ADS)

    White, Richard

    2015-04-01

    Quantitative phase petrology has become one of the mainstay methods for interpreting metamorphic rocks and processes. Its increased utility has been driven by improvements to end-member thermodynamics, activity-composition relationships and computer programs to undertake calculations. Such improvements now allow us to undertake calculations in increasingly complex chemical systems that more closely reflect those of rocks. Recent progress in activity-composition (a-x) relationships is aimed at developing suites of a-x relationships in large chemical systems that are calibrated together, which will allow a more direct application of the method to metamorphic rocks. In addition, considerable progress has been made in how quantitative phase diagrams can be used to understand features, including chemical potential diagrams for reaction textures, methods for fractionating bulk compositions and methods for modelling open system processes. One feature of calculated phase diagrams is that they present us with a great amount of information, such as mineral assemblages, mineral proportions, phase compositions, volume or density etc. An important aspect to using this information is to understand the potential uncertainties associated with these, which are significant. These uncertainties require that calculated phase diagrams be used with caution to interpret observed features in rocks. Features such as mineral zoning and reaction textures should still be interpreted in a semi-quantitative way, even if based on a fully quantitative diagram. Exercises such as the interpretation of reaction overstepping based on relating phase diagrams to observed mineral core compositions are likely to give spurious results given the infelicities in existing a-x models. Despite these limitations, quantitative phase petrology remains the most useful approach to interpreting the metamorphic history of rocks in that it provides a theoretical framework in which to interpret observed features rather

  16. The eastern limit of Acadian high grade metamorphism in northern New England: Implications for the location of the Acadian Suture''

    SciTech Connect

    West, D.P. Jr. . Dept. of Geological Sciences)

    1993-03-01

    Identifying the eastern limit of Acadian high grade metamorphism in New England is complicated by the presence of pre-Devonian high grade relics, locally intense Late Paleozoic thermal overprints, and post-metamorphic faults. New [sup 40]Ar/[sup 39]Ar mineral ages from along the eastern margin of high grade metamorphism in Maine and New Hampshire help delineate the eastern limit of Devonian amphibolite facies metamorphism thereby placing constraints on the location of the Acadian suture. In New Hampshire, Acadian high grade metamorphism extends southeast at least as far as the Campbell Hill fault and perhaps as far as the Flint Hill fault. New [sup 40]Ar/[sup 39]Ar hornblende ages and previously published U-Pb monazite ages from the Massabesic Gneiss Complex are Permian indicating high grade Alleghanian metamorphism. New [sup 40]Ar/[sup 39]Ar hornblende ages from the Rye Formation, although complicated by excess argon, are considerably older, indicating an earlier Pre-Silurian amphibolite facies metamorphism affected these rocks. North of Portland, [sup 40]Ar/[sup 39]Ar hornblende ages east of the Norumbega Fault Zone from high grade rocks of the Casco Bay Group have ages that range from Middle Devonian to Early Carboniferous, consistent with diachronous cooling following Acadian metamorphism. Further northeast, in upper amphibolite facies rocks of the Passagassawakeag Gneiss, new [sup 40]Ar/[sup 39]Ar hornblende ages range from 385--395 Ma suggesting that these rocks were also affected by high grade Acadian metamorphism.

  17. Large impact crater histories of Mars: The effect of different model crater age techniques

    NASA Astrophysics Data System (ADS)

    Robbins, Stuart J.; Hynek, Brian M.; Lillis, Robert J.; Bottke, William F.

    2013-07-01

    Impact events that produce large craters primarily occurred early in the Solar System's history because the largest bolides were remnants from planetary formation. Determining when large impacts occurred on a planetary surface such as Mars can yield clues to the flux of material in the early inner Solar System which, in turn, can constrain other planetary processes such as the timing and magnitude of resurfacing and the history of the martian core dynamo. We have used a large, global planetary database in conjunction with geomorphologic mapping to identify craters superposed on the rims of 78 larger craters with diameters D ⩾ 150 km on Mars, ≈78% of which have not been previously dated in this manner. The densities of superposed craters with diameters larger than 10, 16, 25, and 50 km, as well as isochron fits were used to derive model crater ages of these larger craters and basins from which we derived an impact flux. In discussing these ages, we point out several internal inconsistencies of crater-age modeling techniques and chronology systems and, all told, we explain why we think isochron-fitting is the most reliable indicator of an age. Our results point to a mostly obliterated crater record prior to ˜4.0 Ga with the oldest preserved mappable craters on Mars dating to ˜4.3-4.35 Ga. We have used our results to constrain the cessation time of the martian core dynamo which we found to have occurred between the formation of Ladon and Prometheus basins, approximately 4.06-4.09 Ga. We also show that, overall, surfaces on Mars older than ˜4.0-4.1 Ga have experienced >1 km of resurfacing, while those younger than ˜3.8-3.9 Ga have experienced significantly less.

  18. Women in American History: A Series. Book Two, Women in the Ages of Expansion and Reform 1820-1860.

    ERIC Educational Resources Information Center

    Sanders, Beverly

    The document, one in a series of four on women in American history, discusses women in the ages of expansion and reform (1820-1860). Designed to supplement U.S. history textbooks, the book is presented in six chapters. Chapter I describes the "true woman," an ideal cultivated by women writers, educators, and magazine editors. The four virtues were…

  19. Petrology and Geochronology of High-Grade Metamorphic Rocks from Cedros Island, Baja California, Mexico

    NASA Astrophysics Data System (ADS)

    Gonzales, D.; Leech, M. L.

    2014-12-01

    High-grade metamorphic rocks exposed on Cedros Island, Baja California, Mexico, record the Mesozoic subduction history of western North America. Blocks of amphibolite, blueschist, and eclogite crop out in a serpentinite-matrix mélange on the southeast and southwestern parts of Cedros Island. Amphibolite blocks contain Amp + Ep + Ab + Chl ± Ms ± Grt ± Ttn ± Qz; blueschist blocks have the assemblage Na-Amp + Ms + Lw + Qz ± Ttn ± Grt ± Jd ± Chl; and eclogite blocks are comprised primarily of Omp + Grt with retrograde Na-Amp + Ms + Lw. Blueschists from Cedros have been dated using 40Ar/39Ar step-heating of white mica and sodic amphiboles that yield ages from 103 ± 4 Ma to 94.9 ± 1.1 Ma, respectively, that represent cooling during exhumation. Apatite fission-track dating gives ages from 32 ± 4 Ma to 22 ± 3 Ma that record exhumation through the upper crust. Related Mesozoic subduction zone rocks of the Franciscan Complex crop out in a serpentinite-matrix mélange along coastal northern California. The Franciscan rocks are older, yielding 40Ar/39Ar step-heating ages of hornblende from amphibolite ranging from 159 to 156 Ma and represent an older part of the subduction history of the oceanic Farallon plate along western North America. I will determine the prograde and peak metamorphic P-T conditions for these high-grade rocks using petrography, mineral chemistries, and isochemical phase diagram modeling with Perple_X to generate complete P-T paths. I will then supplement these data with Sm-Nd and Lu-Hf geochronology for these high-grade Cedros rocks to evaluate their subduction/exhumation history, and develop a tectonic model for these southernmost Franciscan-type rocks. Ultimately, I will compare my results to Franciscan rocks in northern California to better understand the Mesozoic subduction margin of western North America.

  20. Natural history of age-related lobular involution and impact on breast cancer risk.

    PubMed

    Radisky, Derek C; Visscher, Daniel W; Frank, Ryan D; Vierkant, Robert A; Winham, Stacey; Stallings-Mann, Melody; Hoskin, Tanya L; Nassar, Aziza; Vachon, Celine M; Denison, Lori A; Hartmann, Lynn C; Frost, Marlene H; Degnim, Amy C

    2016-02-01

    Age-related lobular involution (LI) is a physiological process in which the terminal duct lobular units of the breast regress as a woman ages. Analyses of breast biopsies from women with benign breast disease (BBD) have found that extent of LI is negatively associated with subsequent breast cancer development. Here we assess the natural course of LI within individual women, and the impact of progressive LI on breast cancer risk. The Mayo Clinic BBD cohort consists of 13,455 women with BBD from 1967 to 2001. The BBD cohort includes 1115 women who had multiple benign biopsies, 106 of whom had developed breast cancer. Within this multiple biopsy cohort, the progression of the LI process was examined by age at initial biopsy and time between biopsies. The relationship between LI progression and breast cancer risk was assessed using standardized incidence ratios and by Cox proportional hazards analysis. Women who had multiple biopsies were younger age and had a slightly higher family history of breast cancer as compared with the overall BBD cohort. Extent of LI at subsequent biopsy was greater with increasing time between biopsies and for women age 55 + at initial biopsy. Among women with multiple biopsies, there was a significant association of higher breast cancer risk among those with involution stasis (lack of progression, HR 1.63) as compared with those with involution progression, p = 0.036. The multiple biopsy BBD cohort allows for a longitudinal study of the natural progression of LI. The majority of women in the multiple biopsy cohort showed progression of LI status between benign biopsies, and extent of progression was highest for women who were in the perimenopausal age range at initial biopsy. Progression of LI status between initial and subsequent biopsy was associated with decreased breast cancer risk. PMID:26846985

  1. Psychosocial Adjustment in School-age Girls With a Family History of Breast Cancer

    PubMed Central

    Bradbury, Angela R.; Patrick-Miller, Linda; Schwartz, Lisa; Egleston, Brian; Sands, Colleen Burke; Chung, Wendy K.; Glendon, Gord; McDonald, Jasmine A.; Moore, Cynthia; Rauch, Paula; Tuchman, Lisa; Andrulis, Irene L.; Buys, Saundra S.; Frost, Caren J.; Keegan, Theresa H.M.; Knight, Julia A.; Terry, Mary Beth; John, Esther M.; Daly, Mary B.

    2016-01-01

    OBJECTIVE Understanding how young girls respond to growing up with breast cancer family histories is critical given expansion of genetic testing and breast cancer messaging. We examined the impact of breast cancer family history on psychosocial adjustment and health behaviors among >800 girls in the multicenter LEGACY Girls Study. METHODS Girls aged 6 to 13 years with a family history of breast cancer or familial BRCA1/2 mutation (BCFH+), peers without a family history (BCFH−), and their biological mothers completed assessments of psychosocial adjustment (maternal report for 6- to 13-year-olds, self-report for 10- to 13-year-olds), breast cancer–specific distress, perceived risk of breast cancer, and health behaviors (10- to 13-year-olds). RESULTS BCFH+ girls had better general psychosocial adjustment than BCFH− peers by maternal report. Psychosocial adjustment and health behaviors did not differ significantly by self-report among 10- to 13-year-old girls. BCFH+ girls reported higher breast cancer–specific distress (P = .001) and were more likely to report themselves at increased breast cancer risk than BCFH− peers (38.4% vs 13.7%, P < .001), although many girls were unsure of their risk. In multivariable analyses, higher daughter anxiety was associated with higher maternal anxiety and poorer family communication. Higher daughter breast cancer–specific distress was associated with higher maternal breast cancer-specific distress. CONCLUSIONS Although growing up in a family at risk for breast cancer does not negatively affect general psychosocial adjustment among preadolescent girls, those from breast cancer risk families experience greater breast cancer–specific distress. Interventions to address daughter and mother breast cancer concerns and responses to genetic or familial risk might improve psychosocial outcomes of teen daughters. PMID:26482668

  2. Urban neighbourhood unemployment history and depressive symptoms over time among late middle age and older adults

    PubMed Central

    Wight, Richard G; Aneshensel, Carol S; Barrett, Christopher; Ko, Michelle; Chodosh, Joshua; Karlamangla, Arun S

    2013-01-01

    Background Little is known about how a neighbourhood’s unemployment history may set the stage for depressive symptomatology. This study examines the effects of urban neighbourhood unemployment history on current depressive symptoms and subsequent symptom trajectories among residentially stable late middle age and older adults. Contingent effects between neighbourhood unemployment and individual-level employment status (ie, cross-level interactions) are also assessed. Methods Individual-level survey data are from four waves (2000, 2002, 2004 and 2006) of the original cohort of the nationally representative US Health and Retirement Study. Neighbourhoods are operationalised with US Census tracts for which historical average proportion unemployed between 1990 and 2000 and change in proportion unemployed between 1990 and 2000 are used to characterise the neighbourhood’s unemployment history. Hierarchical linear regressions estimate three-level (time, individual and neighbourhood) growth models. Results Symptoms in 2000 are highest among those residing in neighbourhoods characterised by high historical average unemployment beginning in 1990 and increasing unemployment between 1990 and 2000, net of a wide range of socio-demographic controls including individual-level employment status. These neighbourhood unemployment effects are not contingent upon individual-level employment status in 2000. 6-year trajectories of depressive symptoms decrease over time on average but are not significantly influenced by the neighbourhood’s unemployment history. Conclusions Given the current US recession, future studies that do not consider historical employment conditions may underestimate the mental health impact of urban neighbourhood context. The findings suggest that exposure to neighbourhood unemployment earlier in life may be consequential to mental health later in life. PMID:22918896

  3. The Kokchetav Massif, Kazakhstan: "Type locality" of diamond-bearing UHP metamorphic rocks

    NASA Astrophysics Data System (ADS)

    Schertl, H.-P.; Sobolev, N. V.

    2013-02-01

    kbar at temperatures of about 950-1000 °C. Some zircon separates show inherited Proterozoic cores and 537-530 Ma UHP metamorphic mantle zones. Several Ar-Ar-ages on micas scatter around 529-528 and 521-517 Ma and reflect different stages of the exhumation history. Migmatization occurred during exhumation at about 526-520 Ma. Isotopic studies on calcsilicate rocks confirm a metasedimentary origin: δ18O values of garnet and clinopyroxene of a layered calcsilicate rock rule out the possibility having a primitive mantle protolith. Similar studies on eclogites indicate their basaltic protolith having experienced water-rock interaction prior to UHP metamorphism. A number of unique mineralogical findings have been made on Kokchetav UHP rocks. K-feldspar exsolutions in clinopyroxene demonstrate that potassium can be incorporated into the cpx-structure under upper mantle pressures. Other significant observations are coesite exsolutions in titanite, quartz-rods in cpx, the discovery of K-tourmaline as well as new minerals like kokchetavite, a hexagonal polymorph of K-feldspar and kumdykolite, an orthorhombic polymorph of albite. The Kokchetav UHP rocks represent a unique and challenging stomping ground for geoscientists of various disciplines. From crystallography, petrology and geochemistry to geophysics and geodynamics/geotectonics - it concerns all who are interested in the diverse metamorphic processes under upper mantle conditions.

  4. Geochemical, geochronological characterization and tectonic setting of the metamorphic rocks from the Biga Peninsula, NW Turkey

    NASA Astrophysics Data System (ADS)

    Şengün, F.; Tunç, Ä.°. O.; Yiǧitbaş, E.

    2012-04-01

    The Biga Peninsula in the northwest Turkey is one of the world's important natural laboratories to study geochronology due to having complex geology. The Biga Peninsula has different metamorphic basements including Kazdağ Massif, Çamlıca metamorphics, Kemer metamorphics and Karadağ Massif under cover of the Cenozoic volcano-sedimentary association. The Çamlıca metamorphic assemblage are one of the most critical regions for understanding of the geology of northwestern Turkey. The Çamlıca metamorphic association located on the westernmost part of Turkey is mainly composed of the Andıktası formation, the Dedetepe formation and the Salihler formation, from bottom to top. Metasedimentary rocks of the Çamlıca metamorphics have high SiO2 and medium Al2O3 and TiO2 values. The protolith of these metasediments is arkose-subarkose and greywacke. However, whole-rock geochemistry for the HP eclogite/blueschist within the Çamlıca metamorphics suggests that their protolith was basalt with high TiO2 and K2O-Na2O content and Nb/Y ratios. REE pattern and trace element contents of the HP eclogite/blueschist similar to typical MORB based on tectonic discrimination diagrams. The metavolcanic rocks occurring on the lowest part of the Çamlıca metamorphicassociation has andesitic composition with calc-alkaline character. All metavolcanic rocks in this unit cluster within the volcanic arc field. Zircon grains from metavolcanic rocks and HP eclogite/blueschists were dated by LA-ICPMS. Zircon ages of two metavolcanic samples yielded 328.6 ± 3.5 Ma and 343.2 ± 2.6 Ma, respectively. These ages are interpreted as the time of protolith crystallization of metavolcanic rocks. Moreover, zircon ages from HP eclogite/blueschist yielded 338 ± 1.8 Ma (Early Carboniferous) which is interpreted as the age of protolith crystallization of HP eclogite/blueschist. Geochemical and isotopic data indicate that Early Carboniferous Variscan ages within the Sakarya Zone may form the eastern

  5. Demographic patterns of Ferocactus cylindraceus in relation to substrate age and grazing history

    USGS Publications Warehouse

    Bowers, Janice E.

    1997-01-01

    Three subpopulations of Ferocactus cylindraceus, a short-columnar cactus of the Sonoran and Mojave deserts, were sampled in Grand Canyon, Arizona, USA, at sites representing a range of substrate ages and different grazing histories. Age-height relations were determined from annual growth, then used to estimate probable year of establishment for each cohort. Eight years between 1944 and 1992 were especially favorable for establishment. Six of these 8 years coincided with El Nino-Southern Oscillation conditions, indicating that as for many woody plants in arid regions, somewhat unusual climatic conditions are necessary if populations are to replace themselves. Comparison of age structures showed that established and developing populations have somewhat different dynamics in that the rate of population increase was slowest on the youngest terrace. On the ancient terraces, about half the plants were less than 25 years old. Plants older than 40 years were few; however the oldest plants in the study (about 49 years) grew on the ancient terraces. On the recent terrace, 76% of the subpopulation was 25 years or younger, and the oldest living plant was about 36 years of age. The age structures of subpopulations on grazed and ungrazed sites also differed markedly. On ungrazed sites, subpopulations were more or less at equilibrium, with enough young plants to replace old ones as they died. In contrast, the subpopulation on the grazed site was in a state of marked disequilibrium. Grazing before 1981 largely extirpated a palatable subshrub that was probably an important nurse plant. Until the shrub population at Indian Canyon recovers from decades of burro grazing, a rebound in E cylindraceus establishment is not to be expected.

  6. Subsidence in Gorontalo Bay, Sulawesi (Indonesia) and metamorphic core complex exhumation on land

    NASA Astrophysics Data System (ADS)

    Pezzati, Giovanni; Hennig, Juliane; Advokaat, Eldert; Hall, Robert; Burgess, Peter; Perez-Gussinye, Marta

    2015-04-01

    Gorontalo Bay is a semi-enclosed sea between the North and East Arms of Sulawesi. It is surrounded by land on three sides, separating a northern volcanic province from metamorphic rocks to the south and west, and ophiolites to the southeast. In the western part of Gorontalo Bay there are two sub-basins: the northern Tomini Basin and the southern Poso Basin, which have different histories. This study presents a new geological interpretation of western Gorontalo Bay, based on recent multibeam and 2D seismic data and field observations on land. In Tomini Basin six major seismic sequences (Units A to F) have a total thickness of more than 5 sec TWT. Ages are based on correlation with events on land. A major unconformity above Basement Unit A is interpreted to be the result of an Early Miocene collision. Unit A subsided from the Early Miocene, with deposition of Units B and C largely in a deep marine environment. There was regional uplift in the Middle Miocene followed by renewed subsidence resulting in shallow marine depositional environments in which carbonate platforms developed (Units D-E). Subsidence accelerated during the deposition of Unit E, causing back-stepping of the shelf edge, formation of pinnacle reefs and then drowning of the carbonate platforms, leading to the present depths of 2 km in the basin centre with a thin clastic cover (Unit F). North of Tomini Basin, the Malino Metamorphic Complex exposes strongly deformed mid-crustal rocks which record Middle Miocene extension accommodated by low angle shear zones. A second phase of rapid uplift and extension recorded in these rocks occurred in the Pliocene-Pleistocene, and was accommodated by high angle normal faulting. Poso Basin is younger than Tomini Basin and it occupies the southern part of western Gorontalo Bay. The deeper part of its sedimentary sequence is probably the time equivalent of Unit D in Tomini Basin. Immediately south of Poso Basin, on land, is a large metamorphic core complex. Seismic

  7. Prolonged Eclogite-Facies Metamorphism: Evidence From Geochronology and Trace Element Geochemistry, North Qaidam UHP Terrane, NW China

    NASA Astrophysics Data System (ADS)

    Mattinson, C. G.; Wooden, J. L.; Mazdab, F. K.; Liou, J. G.; Bird, D. K.; Wu, C.

    2006-12-01

    Amphibolite-facies felsic gneisses near Dulan, at the southeast end of the North Qaidam terrane, enclose minor (<10 vol%) eclogite and peridotite which record ultra-high pressure (UHP) metamorphism. Field relations, and coesite inclusions in zircons from paragneiss suggest that felsic, mafic, and ultramafic rocks all experienced UHP metamorphism and a common amphibolite-facies retrogression. SHRIMP-RG U-Pb and REE analyses of zircons from four eclogites yield weighted mean ages of 449--422 Ma; REE patterns (flat HREE, no Eu anomaly) and inclusions of garnet, omphacite, and rutile indicate that these ages record eclogite-facies metamorphism. Trace element variations in zircon are similar to core-to-rim trace element zoning of coexisting garnet revealed by LA-ICP-MS analysis. The coherent field relations, and the similar range of individual ages in each sample suggests that the ~25 m.y. age range reflects the duration of eclogite-facies conditions. Ti-in-zircon thermometry results show considerable spread, but may suggest cooling from 650-700°C (442--449 Ma) to 600-650°C (433--422 Ma). One group of zircons yields 770--810°C temperatures, possibly related to granulite-facies overprinting during exhumation. In contrast to Ti-in-zircon, Zr- in-rutile thermometry yields tightly clustered results of 590°C for all four eclogites and one 426 ± 4 Ma paragneiss. The ~25 m.y. duration as well as possible cooling during eclogite-facies metamorphism suggests the UHP rocks decoupled from the downgoing plate, and were refrigerated by continued, structurally deeper subduction. In the Lüliang Shan (350 km NW) in the North Qaidam terrane, eclogite and garnet peridotite ages of 414-- 495 Ma suggest that this locality also records a protracted eclogite-facies history. Evidence of prolonged eclogite-facies metamorphism in other HP/UHP localities (Greenland, Norway, Alps, Dabie-Sulu) suggests that eclogite-facies residence times of >15--25 m.y. may be globally significant in

  8. Controlling for Landform Age When Determining the Settlement History of the Kuril Islands

    PubMed Central

    MacInnes, Breanyn; Fitzhugh, Ben; Holman, Darryl

    2014-01-01

    Archaeological investigations of settlement patterns in dynamic landscapes can be strongly biased by the evolution of the Earth’s surface. The Kuril Island volcanic arc exemplifies such a dynamic landscape, where landscape-modifying geological forces were active during settlement, including sea-level changes, tectonic emergence, volcanic eruptive processes, coastal aggradation, and dune formation. With all these ongoing processes, in this paper we seek to understand how new landscape formation in the Holocene might bias archaeological interpretations of human settlement in the Kurils. Resolving this issue is fundamental to any interpretation of human settlement history derived from the distribution and age of archaeological sites from the region. On the basis of a comparison of landform ages and earliest archaeological occupation ages on those landforms, we conclude that landform creation did not significantly bias our aggregate archaeological evidence for earliest settlement. Some sections of the archipelago have larger proportions of landform creation dates closer to archaeological evidence of settlement and undoubtedly some archaeological sites have been lost to geomorphic processes. However, comparisons between regions reveal comparable archaeological establishment patterns irrespective of geomorphic antiquity. PMID:25684855

  9. Accessing probable thermal histories through dispersed, partially-reset zircon (U-Th)/He ages

    NASA Astrophysics Data System (ADS)

    Powell, Jeremy; Schneider, David

    2016-04-01

    exhibited by the datasets. We do not recommend selecting only the youngest dates from samples or averaging (U-Th)/He dates, as these methods do not acknowledge the complexity of the (U-Th)/He system and potentially exclude non-obvious, but equally probable, geologic scenarios. To this extent, using the vertical profile approach to assess exhumation rates from cooling age data may also provide an inaccurate result if the strata have not been buried to sufficient temperatures to completely reset any prior thermal history. As an alternative, we analyzed more grains from individual samples and combine data from similar structural regions to assess regional trends in thermal history. We believe that this approach does an appropriate job of acknowledging the errors and assumptions involved in the technique while providing meaningful information on thermal history of a region. Thermal modeling of the Mackenzie Mountains data reveals that (1) a substantial sedimentary package was deposited following the Devonian and removed during Permo-Triassic cooling, and (2) the Cordilleran deformation front propagated through the study area from the Albian to the Paleocene, with a moderate increase in cooling rates between 75-67 Ma in the southwest, and 60-55 Ma at the deformation front.

  10. Alpine Corsica Metamorphic Core Complex

    NASA Astrophysics Data System (ADS)

    Fournier, Marc; Jolivet, Laurent; Goffé, Bruno; Dubois, Roland

    1991-12-01

    Alpine Corsica is an example where superficial nonmetamorphic allochtonous units rest upon a highly strained metamorphic complex. Early ductile deformation under high pressure-low temperature (HP-LT) conditions is due to the westward thrusting of oceanic material onto a continental basement as shown by previous studies. New thermobarometric estimates yield minimal peak HP-LT metamorphism conditions of 11 kbar at 400°C. The early deformation is overprinted by a ductile deformation with an eastward sense of shear postdating or contemporaneous with mineral recrystallizations in the greenschist facies conditions. Early compressive thrust contacts are reworked as east dipping ductile normal faults and the less competent units display only eastward shear criteria. The upper units are affected by an extensional brittle deformation, and east dipping brittle normal faults bound to the west the early to middle Miocene Saint-Florent half-graben. The greenschist metamorphic event lasted until 33 Ma, which is contemporaneous with the beginning of the extension in the Liguro-Provençal basin. We interpret the second deformation stage as the result of a ductile extension following the overthickening of the crust due to the westward thrusting. Extension reduces the thickness of the crust so that upper units free from early P-T conditions are brought into close contact with a HP-LT metamorphic core complex. The geometry of the late extension is controlled by that of the early compressive thrust.

  11. Early planetary metamorphism in chondritic meteorites

    NASA Astrophysics Data System (ADS)

    Hanan, B. B.; Tilton, G. R.

    1985-07-01

    The record of early events in the solar system is presently sought, together with information on the isotopic composition of primordial lead, in the lead isotope relations of whole rock and separated phases of Mezo-Madaras (L3) and Sharps (H3) chondrites; the respective ages of 4.48 and 4.47 billion years are not significantly changed when Canyon Diablo troilite lead is included in the data sets, suggesting that the initial Pb isotopic composition in both meteorites was the same as that in the troilite. The 4.48 billion year age, which is younger than the well established 4.54-4.56 billion years of the Allende chondrite and Angra dos Reis achondrite, appears to date an early metamorphic event rather than the formation of the chondrites.

  12. Testosterone related to age and life-history stages in male baboons and geladas.

    PubMed

    Beehner, Jacinta C; Gesquiere, Laurence; Seyfarth, Robert M; Cheney, Dorothy L; Alberts, Susan C; Altmann, Jeanne

    2009-10-01

    Despite significant advances in our knowledge of how testosterone mediates life-history trade-offs, this research has primarily focused on seasonal taxa. We know comparatively little about the relationship between testosterone and life-history stages for non-seasonally breeding species. Here we examine testosterone profiles across the life span of males from three non-seasonally breeding primates: yellow baboons (Papio cynocephalus or P. hamadryas cynocephalus), chacma baboons (Papio ursinus or P. h. ursinus), and geladas (Theropithecus gelada). First, we predict that testosterone profiles will track the reproductive profiles of each taxon across their respective breeding years. Second, we evaluate age-related changes in testosterone to determine whether several life-history transitions are associated with these changes. Subjects include males (>2.5 years) from wild populations of each taxon from whom we had fecal samples for hormone determination. Although testosterone profiles across taxa were broadly similar, considerable variability was found in the timing of two major changes: (1) the attainment of adult levels of testosterone and (2) the decline in testosterone after the period of maximum production. Attainment of adult testosterone levels was delayed by 1 year in chacmas compared with yellows and geladas. With respect to the decline in testosterone, geladas and chacmas exhibited a significant drop after 3 years of maximum production, while yellows declined so gradually that no significant annual drop was ever detected. For both yellows and chacmas, increases in testosterone production preceded elevations in social dominance rank. We discuss these differences in the context of ecological and behavioral differences exhibited by these taxa. PMID:19712676

  13. Testosterone related to age and life-history stages in male baboons and geladas

    PubMed Central

    Beehner, Jacinta C.; Gesquiere, Laurence; Seyfarth, Robert M.; Cheney, Dorothy L.; Alberts, Susan C.; Altmann, Jeanne

    2013-01-01

    Despite significant advances in our knowledge of how testosterone mediates life-history trade-offs, this research has primarily focused on seasonal species. We know comparatively little about the relationship between testosterone and life-history stages for non-seasonally breeding species. Here we examine testosterone profiles across the lifespan of males from three non-seasonally breeding primates: yellow baboons (Papio cynocephalus or P. hamadryas cynocephalus), chacma baboons (Papio ursinus or P. h. ursinus), and geladas (Theropithecus gelada). First, we predict that testosterone profiles will track the reproductive profiles of each taxon across their respective breeding years. Second, we evaluate age-related changes in testosterone to determine whether several life-history transitions are associated with these changes. Subjects include males (>2.5 years) from wild populations of each taxon from whom we had fecal samples for hormone determination. Although testosterone profiles across species were broadly similar, considerable variability was found in the timing of two major changes: (1) the attainment of adult levels of testosterone, and (2) the decline in testosterone after the period of maximum production. Attainment of adult testosterone levels was delayed by one year in chacmas compared with yellows and geladas. With respect to the decline in testosterone, geladas and chacmas exhibited a significant drop after three years of maximum production, while yellows declined so gradually that no significant annual drop was ever detected. For both yellows and chacmas, increases in testosterone production preceded elevations in social dominance rank. We discuss these differences in the context of ecological and behavioral differences exhibited by these taxa. PMID:19712676

  14. Apoptosis: its origin, history, maintenance and the medical implications for cancer and aging

    NASA Astrophysics Data System (ADS)

    Kaczanowski, Szymon

    2016-06-01

    Programmed cell death is a basic cellular mechanism. Apoptotic-like programmed cell death (called apoptosis in animals) occurs in both unicellular and multicellular eukaryotes, and some apoptotic mechanisms are observed in bacteria. Endosymbiosis between mitochondria and eukaryotic cells took place early in the eukaryotic evolution, and some of the apoptotic-like mechanisms of mitochondria that were retained after this event now serve as parts of the eukaryotic apoptotic machinery. Apoptotic mechanisms have several functions in unicellular organisms: they include kin-selected altruistic suicide that controls population size, sharing common goods, and responding to viral infection. Apoptotic factors also have non-apoptotic functions. Apoptosis is involved in the cellular aging of eukaryotes, including humans. In addition, apoptosis is a key part of the innate tumor-suppression mechanism. Several anticancer drugs induce apoptosis, because apoptotic mechanisms are inactivated during oncogenesis. Because of the ancient history of apoptosis, I hypothesize that there is a deep relationship between mitochondrial metabolism, its role in aerobic versus anaerobic respiration, and the connection between apoptosis and cancer. Whereas normal cells rely primarily on oxidative mitochondrial respiration, most cancer cells use anaerobic metabolism. According to the Warburg hypothesis, the remodeling of the metabolism is one of the processes that leads to cancer. Recent studies indicate that anaerobic, non-mitochondrial respiration is particularly active in embryonic cells, stem cells, and aggressive stem-like cancer cells. Mitochondrial respiration is particularly active during the pathological aging of human cells in neurodegenerative diseases. According to the reversed Warburg hypothesis formulated by Demetrius, pathological aging is induced by mitochondrial respiration. Here, I advance the hypothesis that the stimulation of mitochondrial metabolism leads to pathological aging.

  15. Apoptosis: its origin, history, maintenance and the medical implications for cancer and aging.

    PubMed

    Kaczanowski, Szymon

    2016-01-01

    Programmed cell death is a basic cellular mechanism. Apoptotic-like programmed cell death (called apoptosis in animals) occurs in both unicellular and multicellular eukaryotes, and some apoptotic mechanisms are observed in bacteria. Endosymbiosis between mitochondria and eukaryotic cells took place early in the eukaryotic evolution, and some of the apoptotic-like mechanisms of mitochondria that were retained after this event now serve as parts of the eukaryotic apoptotic machinery. Apoptotic mechanisms have several functions in unicellular organisms: they include kin-selected altruistic suicide that controls population size, sharing common goods, and responding to viral infection. Apoptotic factors also have non-apoptotic functions. Apoptosis is involved in the cellular aging of eukaryotes, including humans. In addition, apoptosis is a key part of the innate tumor-suppression mechanism. Several anticancer drugs induce apoptosis, because apoptotic mechanisms are inactivated during oncogenesis. Because of the ancient history of apoptosis, I hypothesize that there is a deep relationship between mitochondrial metabolism, its role in aerobic versus anaerobic respiration, and the connection between apoptosis and cancer. Whereas normal cells rely primarily on oxidative mitochondrial respiration, most cancer cells use anaerobic metabolism. According to the Warburg hypothesis, the remodeling of the metabolism is one of the processes that leads to cancer. Recent studies indicate that anaerobic, non-mitochondrial respiration is particularly active in embryonic cells, stem cells, and aggressive stem-like cancer cells. Mitochondrial respiration is particularly active during the pathological aging of human cells in neurodegenerative diseases. According to the reversed Warburg hypothesis formulated by Demetrius, pathological aging is induced by mitochondrial respiration. Here, I advance the hypothesis that the stimulation of mitochondrial metabolism leads to pathological aging

  16. Ar-Ar and I-Xe Ages of Caddo County and Thermal History of IAB Iron Meteorites

    NASA Technical Reports Server (NTRS)

    Bogard, Donald D.; Garrison, Daniel H.; Takeda, Hiroshi

    2005-01-01

    Inclusions in IAB iron meteorites include non-chondritic silicate and those with more primitive chondritic silicate composition. Coarse-grained gabbroic material rich in plagioclase and diopside occurs in the Caddo County IAB iron meteorite and represents a new type of chemically differentiated, extra-terrestrial, andesitic silicate. Other parts of Caddo contain mostly andesitic material. Caddo thus exhibits petrologic characteristics of parent body metamorphism of a chondrite-like parent and inhomogeneous segregation of melts. Proposed IAB formation models include parent body partial melting and fractional crystallization or incomplete differentiation due to internal heat sources, and impact/induced melting and mixing. Benedix et al. prefer a hybrid model whereby the IAB parent body largely melted, then underwent collisional breakup, partial mixing of phases, and reassembly. Most reported 129I- Xe-129 ages of IABs are greater than 4.56 Gyr and a few are greater than or = 4.567 Gyr. These oldest ages exceed the 4.567 Gyr Pb-Pb age of Ca, Al-rich inclusions in primitive meteorites,

  17. Penecontemporaneous metamorphism, fragmentation, and reassembly of ordinary chondrite parent bodies

    NASA Technical Reports Server (NTRS)

    Grimm, R. E.

    1985-01-01

    The thermal histories of ordinary chondrites and the canonical internal heating or onion shell models, which predict an inverse relation between the petrologic type of chondrites and the metallographic cooling rate, are reviewed. The thermal and accretional requirements of the 'metamorphosed planetesimal' model proposed by Scott and Rajan (1981) are analyzed, and an alternative model consistent with the metallographic cooling rate constraints is suggested in which ordinary chondrite parent bodies are collisionally fragmented and then rapidly reassembled before metamorphic heat has been dissipated.

  18. Resource allocation as a driver of senescence: life history tradeoffs produce age patterns of mortality.

    PubMed

    Davison, Raziel; Boggs, Carol L; Baudisch, Annette

    2014-11-01

    We investigate the effects of optimal time and resource allocation on age patterns of fertility and mortality for a model organism with (1) fixed maximum lifespan, (2) distinct juvenile and adult diets, and (3) reliance on nonrenewable resources for reproduction. We ask when it is optimal to tolerate starvation vs. conserve resources and then examine the effects of these decisions on adult mortality rates. We find that (1) age-related changes in tradeoffs partition the life cycle into as many as four discrete phases with different optimal behavior and mortality patterns, and (2) given a cost of reproduction, terminal investment can produce a signal of actuarial senescence. Also, given limitations imposed by non-replenishable resources, individuals beginning adult life with more replenishable resources do not necessarily live longer, since they can engage in capital breeding and need not defer reproduction to forage; low reproductive overheads and low costs of starvation also encourage capital breeding and may lead to earlier terminal investment and earlier senescence. We conclude that, even for species with qualitatively similar life histories, differences in physiological, behavioral and environmental tradeoffs or constraints may strongly influence optimal allocation schedules and produce variation in mortality patterns and life expectancy. PMID:25051533

  19. The northern coast plutonic-metamorphic complex, southeastern Alaska and northwestern British Columbia

    NASA Astrophysics Data System (ADS)

    Brew, D. A.; Ford, A. B.

    The northern Coast plutonic-metamorphic complex is but one segment of an 8,000-km-long batholithic complex that extends the length of the North American Cordillera from Baja, California to the Aleutian Islands. Different segments of the Cordilleran batholithic complex have significantly different features. This report documents the main characteristics and inferred evolutionary history of the northern Coast plutonic-metamorphic complex that should facilitate comparisons between segments.

  20. Mapping of high pressure metamorphics in the As Sifah region, NE Oman using ASTER data

    NASA Astrophysics Data System (ADS)

    Rajendran, Sankaran; Nasir, Sobhi

    2015-02-01

    The high pressure metamorphic zone of As Sifah area in the Saih Hatat window, NE Oman plays a vital role to study global tectonic setting, metamorphism, transport direction and age of initial ophiolite emplacement. Scientists and researchers are keen in determining the protolith, structural evolution, and timing and metamorphic conditions of the Saih Hatat area. In this study, mapping of the metamorphic zone and discrimination of associated rock formations occurred in the As Sifah region is carried out using visible and near infrared-shortwave infrared (VNIR-SWIR) spectral bands of Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and well known image processing methods such as image decorrelation, Principal Component Analysis (PCA) and Spectral Angel Mapper (SAM). The study delineated the region of metamorphic zone and discriminated the different metamorphic and carbonate rocks of the study area characterized by hydroxyl (OH) and carbonate bearing minerals. The assessment of accuracy for the occurrence and spatial distribution of major lithological units provided the overall accuracy of 96.06% with Kappa Coefficient = 0.95 in the matrix of Maximum Likelihood (ML) and compared with the Spectral Angle Mapper (SAM) and Spectral Information Divergence (SID) algorithms. The occurrence of such minerals are detected and confirmed by SAM supervised classification method. The study also describes the spectral character of metamorphic and carbonates minerals. The metamorphic zone and associated rock types interpreted over the images are verified in the field and checked for their occurrences and spatial distributions. The occurrence of CO3 bearing carbonate minerals and OH bearing metamorphic minerals are confirmed further under microscope, XRD analysis and PIMA spectral measurements in the laboratory studies. The study proved sensor capability of ASTER to discriminate metamorphic rocks from associated formations and detection of different mineral

  1. Permo-Triassic and Paleoproterozoic metamorphism related to continental collision in Yangpyeong, South Korea

    NASA Astrophysics Data System (ADS)

    Oh, Chang Whan; Imayama, Takeshi; Lee, Seung Yeol; Yi, Sang-Bong; Yi, Keewook; Lee, Byung Choon

    2015-02-01

    Gneisses and migmatites exposed in the Yangpyeong area in the northern Gyeonggi Massif provide insight into the Paleoproterozoic and Triassic metamorphic events in South Korea. Garnet-biotite gneiss and sillimanite-garnet-biotite gneiss in the western part of the area reveal Paleoproterozoic metamorphism (1888-1871 Ma) at P-T conditions of 760-820 °C and 8-10 kbar and 710-750 °C and 5-7 kbar, respectively. These rocks were overprinted by low-P/T type metamorphism (590-650 °C, 3-4 kbar) during the Triassic (ca. 237 Ma). In contrast, a cordierite-rich migmatite near the post-collisional Triassic igneous complex in the eastern part of the area was strongly metamorphosed during the Triassic (ca. 235 Ma) at 750-790 °C and 7-8 kbar. The similar Triassic ages in the western and eastern areas suggest that low-P/T type metamorphism occurred as a second stage of regional metamorphism, which is characterized by the production of cordierite with an irregularly shaped garnet. The metamorphic grade of the Triassic metamorphism decreases spatially towards the west from granulite facies to amphibolite facies metamorphic conditions, and the Paleoproterozoic metamorphism is well preserved in the western part with low grade Triassic metamorphism. The new discovery of the Triassic metamorphic event in the Yangpyeong area, in addition to the previously reported Triassic post-collision igneous event, supports the idea that the continental collision belt between the North and South China blocks extends from the Hongseong area into the Odesan area through the Yangpyeong area in South Korea.

  2. Three Dimensional Petrography of Kernouve: A Story of Vein Formation, Compaction, and Metamorphism

    SciTech Connect

    Friedrich, J.M.; Ruzicka, A.; Ebel, D.S.; Thostenson, J.; Rudolph, R.A.; Rivers, M.L.; Macke, R.J.; Britt, D.T.

    2012-03-26

    Metallic veins in ordinary chondrites, like those found in Kernouve (H5, S1), have been attributed to impact or shock processes on the parent body. However, Kernouve is widely known to exhibit few traditional signs of shock loading and has a very old {sup 39}Ar-{sup 40}Ar age (4.46 Ga), making the significance of vein formation in Kernouve unclear. One possibility is early vein formation followed by partial obliteration due to thermal metamorphism. We examine this scenario here. The metal vein in Kernouve can be explained as a pre-metamorphic shock-induced structure, given the evidence for current weak compaction and low shock stage. However, it is not clear how one explains high porosity and low shock stage if the meteorite experienced early shock sufficiently strong to mobilize metal into a vein-like structure. Some combination of unusual conditions during shock (e.g. high temperatures) or mobility of metal during metamorphism may be needed. One possible mechanism occurring early on the H chondrite parent body follows: blocks of slightly indurated but porous material were disturbed by an impact which caused a physical concentration of metallic phases akin to slickensides. Shearing of these materials caused the warm, ductile metal grains to be concentrated on rock surfaces. This process would have imparted the rocks with indicators cited by as shock induced. This event happened early in the history of the chondrite otherwise shearing forces would have imparted a preferred orientation upon the metal grains. Subsequent annealing due to radiogenic heating erased any preferential orientation and further coalesced the vein metal. The final compaction of the material occurred yielding the porosity seen in the samples today. The material escaped other major shock episodes.

  3. Metamorphic evolution of pelitic-semipelitic granulites in the Kon Tum massif (south-central Vietnam)

    NASA Astrophysics Data System (ADS)

    Tích, Vu Van; Leyreloup, Andrey; Maluski, Henry; Lepvrier, Claude; Lo, Chinh-hua; Vượng, Nguyễn V.

    2013-09-01

    Pelitic and semipelitic anatectic granulites form one of the major lithological units in Kan Nack complex of the Kon Tum massif (in south-central Vietnam), which comprises HT metamorphic and magmatic rocks including granulites and charnockites is classically regarded as the older part of the Gondwana-derived Indosinia terrain. Metamorphic evolution study of pelitic granulite, the most abundant among granulites exposed in this massif, facilitates to understand that tectonic setting take place during the Indosinian time. The paragenetic assemblages, mineral chemistry, thermobarometry and P-T evolution path of pelitic-semipelitic granulites from Kon Tum massif has been studied in detail. Petrographic feature demonstrates that the pelitic granulite experienced prograde history, from pregranulitic conditions in the amphibolite facies up to the peak granulitic assemblages. Successive prograde reactions led to the temperature-climax giving rise to assemblages with cordierite-hercynite and cordierite-hercynite-K-feldspar. Then, as attested by the mineralogic association occurring in cordieritic coronas, these rocks have been affected by retrograde conditions coeval with a decrease of the pressure. Thermobarometic results show that the highest temperature obtained by ksp/pl thermometry is 850 °C and the highest pressure obtained by GASP (Garnet Alumino-Silicate Plagioclase) is 7.8 kbar. The obtained clockwise P-T evolution path involving heating decompression, then nearly isothermal decompression and nearly isobar cooling conditions shows that high temperature-low pressure metamorphism of the studied pelitic anatectic granulites of Kan Nack complex occurred possibly in extensional setting during the Indosinian orogeny of 260-240 Ma in age.

  4. Exhumation history of the NW Indian Himalaya revealed by fission track and 40Ar/39Ar ages

    USGS Publications Warehouse

    Schlup, M.; Steck, A.; Carter, A.; Cosca, M.; Epard, J.-L.; Hunziker, J.

    2011-01-01

    New fission track and Ar/Ar geochronological data provide time constraints on the exhumation history of the Himalayan nappes in the Mandi (Beas valley) - Tso Morari transect of the NW Indian Himalaya. Results from this and previous studies suggest that the SW-directed North Himalayan nappes were emplaced by detachment from the underthrusted upper Indian crust by 55. Ma and metamorphosed by ca. 48-40. Ma. The nappe stack was subsequently exhumed to shallow upper crustal depths (<10. km) by 40-30. Ma in the Tso Morari dome (northern section of the transect) and by 30-20. Ma close to frontal thrusts in the Baralacha La region. From the Oligocene to the present, exhumation continued slowly.Metamorphism started in the High Himalayan nappe prior to the Late Oligocene. High temperatures and anatexis of the subducting upper Indian crust engendered the buoyancy-driven ductile detachment and extrusion of the High Himalayan nappe in the zone of continental collision. Late extrusion of the High Himalayan nappe started about 26. Ma ago, accompanied by ductile extensional shearing in the Zanskar shear zone in its roof between 22 and 19. Ma concomitant with thrusting along the basal Main Central Thrust to the south. The northern part of the nappe was then rapidly exhumed to shallow depth (<10. km) between 20 and 6. Ma, while its southern front reached this depth at 10-5. Ma. ?? 2010 Elsevier Ltd.

  5. Zircon and monazite response to prograde metamorphism in the Reynolds Range, central Australia

    NASA Astrophysics Data System (ADS)

    Rubatto, Daniela; Williams, Ian S.; Buick, Ian S.

    2001-01-01

    We report an extensive field-based study of zircon and monazite in the metamorphic sequence of the Reynolds Range (central Australia), where greenschist- to granulite-facies metamorphism is recorded over a continuous crustal section. Detailed cathodoluminescence and back-scattered electron imaging, supported by SHRIMP U-Pb dating, has revealed the different behaviours of zircon and monazite during metamorphism. Monazite first recorded regional metamorphic ages (1576 ± 5 Ma), at amphibolite-facies grade, at ˜600 °C. Abundant monazite yielding similar ages (1557 ± 2 to 1585 ± 3 Ma) is found at granulite-facies conditions in both partial melt segregations and restites. New zircon growth occurred between 1562 ± 4 and 1587 ± 4 Ma, but, in contrast to monazite, is only recorded in granulite-facies rocks where melt was present (≥700 °C). New zircon appears to form at the expense of pre-existing detrital and inherited cores, which are partly resorbed. The amount of metamorphic growth in both accessory minerals increases with temperature and metamorphic grade. However, new zircon growth is influenced by rock composition and driven by partial melting, factors that appear to have little effect on the formation of metamorphic monazite. The growth of these accessory phases in response to metamorphism extends over the 30 Ma period of melt crystallisation (1557-1587 Ma) in a stable high geothermal regime. Rare earth element patterns of zircon overgrowths in leucosome and restite indicate that, during the protracted metamorphism, melt-restite equilibrium was reached. Even in the extreme conditions of long-lasting high temperature (750-800 °C) metamorphism, Pb inheritance is widely preserved in the detrital zircon cores. A trace of inheritance is found in monazite, indicating that the closure temperature of the U-Pb system in relatively large monazite crystals can exceed 750-800 °C.

  6. In the Age of the Web: Strategies for Building a Collection of Primary Sources for European History from the Middle Ages to the Eighteenth Century.

    ERIC Educational Resources Information Center

    Saenger, Paul

    2003-01-01

    Describes efforts by the Newberry Library (Chicago) to obtain original source materials for studying the literature and history of western Europe from the Middle Ages to the eighteenth century. Discusses joint acquisitions with higher education institutions; acquisition of rare book collections from religious colleges and seminaries; and…

  7. The Natural History of Insomnia in the Ibadan Study of Ageing

    PubMed Central

    Gureje, Oye; Oladeji, Bibilola Damilola; Abiona, Taiwo; Makanjuola, Victor; Esan, Oluyomi

    2011-01-01

    Study Objectives: To determine the incidence and risk factors for insomnia among an under-studied population of elderly persons in Sub-Saharan Africa. Setting: Eight contiguous predominantly Yoruba-speaking states in south-west and north-central Nigeria representing about 22% of the national population. Participants: 1307 elderly community-dwelling persons, aged 65 years and older. Measurements: Face-to-face assessment with the Composite International Diagnostic Interview, version 3 (CIDI.3) in 2007 and 12 months later in 2008 to determine the occurrence and risk factors of incident and persistent insomnia, defined as syndrome or symptom. Results: The incidence of insomnia syndrome in 2008 at 12 months was 7.97% (95% CI, 6.60–9.60), while that of insomnia symptom was 25.68% (22.68–28.66). Females were at elevated risk for both syndrome and symptom. Among persons with insomnia symptom or syndrome at the baseline, 47.36% (95% CI 43.07–51.68) continued to have it one year later. Decreasing economic status was associated with increasing incidence of insomnia. Persons with chronic medical conditions at baseline were at increased risk for new onset of insomnia. Compared to persons with the lowest body mass index (BMI) (< 18.5), those with higher BMI were at elevated risk for persistence of their insomnia, with those in the obese range (≥ 30) having a 4-fold risk. Conclusions: There is a high incidence and chronicity of insomnia in this elderly population. Persons with chronic health conditions are particularly at risk of new onset as well as persistence of insomnia. Citation: Gureje O; Oladeji BD; Abiona T; Makanjuola V; Esan O. The natural history of insomnia in the Ibadan Study of Ageing. SLEEP 2011;34(7):965-973. PMID:21731147

  8. The history of mare volcanism in the Orientale Basin: Mare deposit ages, compositions and morphologies

    NASA Technical Reports Server (NTRS)

    Kadel, S. D.; Greeley, R.; Neukum, G.; Wagner, R.

    1993-01-01

    The eruptive history of mare basalts in the Orientale Basin has been studied, using Lunar Orbiter 4 high-resolution photographs, Zond 8 photographs, and recently acquired Galileo EM-1 multispectral images. This work represents a refined set of compositional data incorporating the use of a linear mixing model for mare compositions, crater count data, and a comprehensive morphologic analysis of Orientale Basin mare deposits. Evidence for multiple eruptive episodes has been found, with compositions ranging from medium- to high-Ti basalt (less than 4 to greater than 6 wt. percent TiO2). Eruptive styles included flood, rille-forming, and shield-forming eruptions. Impact crater densities of mare units in the Orientale Basin enable determination of the ages of these deposits, using the method of Neukum et al. Earliest eruptions of mare basalt in the basin occurred at greater than or equal to 3.80 Ga and the latest eruptions occurred at about 2.3-2.5 Ga. Hence, mare volcanism occurred over a period of nearly 1.5 Ga.

  9. Low-rhenium molybdenite by metamorphism in northern Sweden: Recognition, genesis, and global implications

    NASA Astrophysics Data System (ADS)

    Stein, Holly J.

    2006-04-01

    Re-Os dating of molybdenite is an accurate means to date intrusions and intrusion-related ore deposits using the model age or isochron approach. But, molybdenite has a new niche in the greenschist- to granulite-facies metamorphic environment. Re-Os ages for metamorphic molybdenite may be used to construct regional metamorphic histories. Age significance and accuracy are established by analyzing multiple molybdenite separates extracted from single, petrographically-characterized molybdenite occurrences. In this study, twelve geologically distinct molybdenite-bearing samples from two small Mo districts in northern Sweden trace a 150 m.y. Paleoproterozoic Svecofennian metamorphic history from ˜1900 to 1750 Ma. These data reveal a little-known, widespread and protracted, Late Svecofennian anatexis in northern Sweden. The Kåtaberget Mo-(Cu, F) deposit is located in the Moskosel granite batholith north of the economically-renown Skellefte district. Four different molybdenite samples from outcrop at Kåtaberget indicate an intrusion age of 1895 ± 6 Ma with the formation of later pegmatite-aplite at 1875 ± 6 Ma. The Allebuoda (Björntjärn) and Munka Mo-(W) deposits in the Rappen district are represented by three outcrop and five drill core samples of molybdenite-bearing aplite-pegmatite-granite. These two deposits were previously described as intrusion-related Climax-type Mo mineralization. Re-Os ages for molybdenites from these deposits range from 1865 to 1750 Ma and, significantly, Re concentrations are markedly low, extending to the sub-ppm level. Age agreement within the deposits is conspicuously lacking, whereas, with one exception, age agreement within any single sample (geologic occurrence), as established by analysis of additional molybdenite separates, is very good. These data, together with fundamental geologic observations discussed in this paper, suggest that Mo-(W) mineralization in northern Sweden is not intrusion-related, but the local product of

  10. Geographical variation in reproductive ageing patterns and life-history strategy of a short-lived passerine bird.

    PubMed

    Balbontín, Javier; Møller, A P; Hermosell, I G; Marzal, A; Reviriego, M; de Lope, F

    2012-11-01

    We investigated differences in ageing patterns in three measures of breeding performance in populations of barn swallows Hirundo rustica L. from Spain and Denmark differing in breeding latitude and hence migration distance and duration of the breeding season. We found differences in ageing patterns between populations. Generally, young (i.e. yearling) and old females (i.e. ≥ 5 years of age) laid their first eggs later and produced smaller clutches than middle-aged females (i.e. 2-4 years of age) in both populations. The southernmost population (i.e. Spanish) showing the shorter migratory distance experienced a greater within-individual increase in timing of breeding and clutch size in early life and a greater within-individual decrease in laying date but not in clutch size during senescence compared with the northernmost population (i.e. Danish). We also found that the number of fledglings produced annually was related to the age of the two members of the breeding pairs with pairs composed of young and old females performing less well than breeding pairs composed of middle-aged females. We did not find reproductive senescence for the age of the male while controlling for the age of the female on the number of fledglings produced annually by the breeding pair. Differential survival between individuals did not explain age effects on laying date or annual clutch size in neither population. However, the increase in the number of fledglings produced annually with age was partly explained by the disappearance of poor-quality members of the pairs, mainly poor-quality males. Age-related breeding success (i.e. number of fledglings) was similar for barn swallows from Spain and Denmark. Therefore, the study of ageing patterns and life-history strategies in free-ranging animals from more than a single population can throw new light on life-history theory, population dynamics and evolutionary studies of senescence. PMID:22994532

  11. Organic nitrogen chemistry during low-grade metamorphism

    USGS Publications Warehouse

    Boudou, J.-P.; Schimmelmann, A.; Ader, M.; Mastalerz, Maria; Sebilo, M.; Gengembre, L.

    2008-01-01

    Most of the organic nitrogen (Norg) on Earth is disseminated in crustal sediments and rocks in the form of fossil nitrogen-containing organic matter. The chemical speciation of fossil Norg within the overall molecular structure of organic matter changes with time and heating during burial. Progressive thermal evolution of organic matter involves phases of enhanced elimination of Norg and ultimately produces graphite containing only traces of nitrogen. Long-term chemical and thermal instability makes the chemical speciation of Norg a valuable tracer to constrain the history of sub-surface metamorphism and to shed light on the subsurface biogeochemical nitrogen cycle and its participating organic and inorganic nitrogen pools. This study documents the evolutionary path of Norg speciation, transformation and elimination before and during metamorphism and advocates the use of X-ray photoelectron spectroscopy (XPS) to monitor changes in Norg speciation as a diagnostic tool for organic metamorphism. Our multidisciplinary evidence from XPS, stable isotopes, traditional quantitative coal analyses, and other analytical approaches shows that at the metamorphic onset Norg is dominantly present as pyrrolic and pyridinic nitrogen. The relative abundance of nitrogen substituting for carbon in condensed, partially aromatic systems (where N is covalently bonded to three C atoms) increases exponentially with increasing metamorphic grade, at the expense of pyridinic and pyrrolic nitrogen. At the same time, much Norg is eliminated without significant nitrogen isotope fractionation. The apparent absence of Rayleigh-type nitrogen isotopic fractionation suggests that direct thermal loss of nitrogen from an organic matrix does not serve as a major pathway for Norg elimination. Instead, we propose that hot H, O-containing fluids or some of their components gradually penetrate into the carbonaceous matrix and eliminate Norg along a progressing reaction front, without causing nitrogen

  12. Metamorphism, alteration, and timing of mineralization at Hemlo, Ontario

    SciTech Connect

    Ferreira, M.C.; Fyfe, W.S.

    1985-01-01

    Relative age discrimination between metamorphic and mineralizing processes related to Archean gold deposits is often equivocal. The mineralogy and/or stability range of hydrothermal alteration assemblages in and around the deposits are, in most cases, similar to the low grade metamorphic assemblages characteristic of their host sequences. At Hemlo, the distinction is made easier by the relatively high metamorphic rank recorded in the host rocks. From a regional perspective, the mineralization at Hemlo sits in a highly deformed zone flanked by intermediate to mafic volcanic rocks in the footwall, and clastic to volcaniclastic (sensu lato) rocks in the hanging wall. Amphibolite facies assemblages in both hanging wall and footwall are progressively altered, via hydrolysis and hydration, to greenschist facies assemblages. The extent and intensity of alteration increase towards the mineralization. Accordingly, alteration and mineralization at Hemlo postdate peak metamorphic conditions. Whereas structurally enhanced permeability may have played an important role in facilitating access to mineralizing solutions, gold deposition was probably controlled by host rock composition and reactivity. Gold precipitation may have been triggered by an increase in hydrogen ion activity of mineralizing solutions related to white mica replacement of aluminosilicates.

  13. Why do women stop reproducing before menopause? A life-history approach to age at last birth.

    PubMed

    Towner, Mary C; Nenko, Ilona; Walton, Savannah E

    2016-04-19

    Evolutionary biologists have long considered menopause to be a fundamental puzzle in understanding human fertility behaviour, as post-menopausal women are no longer physiologically capable of direct reproduction. Menopause typically occurs between 45 and 55 years of age, but across cultures and history, women often stop reproducing many years before menopause. Unlike age at first reproduction or even birth spacing, a woman nearing the end of her reproductive cycle is able to reflect upon the offspring she already has-their numbers and phenotypic qualities, including sexes. This paper reviews demographic data on age at last birth both across and within societies, and also presents a case study of age at last birth in rural Bangladeshi women. In this Bangladeshi sample, age at last birth preceded age at menopause by an average of 11 years, with marked variation around that mean, even during a period of high fertility. Moreover, age at last birth was not strongly related to age at menopause. Our literature review and case study provide evidence that stopping behaviour needs to be more closely examined as an important part of human reproductive strategies and life-history theory. Menopause may be a final marker of permanent reproductive cessation, but it is only one piece of the evolutionary puzzle. PMID:27022074

  14. New terrace ages better constrain the uplift history for the Mejillones Peninsula, northern Chile

    NASA Astrophysics Data System (ADS)

    Liermann, Ariane; Dunai, Tibor; Binnie, Steven; Heinze, Stefan; Dewald, Alfred; Victor, Pia; González, Gabriel

    2013-04-01

    The Mejillones Peninsula is a promontory extending spectacularly from the northern Chilean coastline. The peninsula is marked by well preserved marine terraces extending from just above sea-level to greater than 400 m. These staircased planar expressions result from a combination of glacioeustatic sea-level fluctuation and tectonic uplift. It has been shown by several studies that such terraces are formed during interglacial marine high-stands and are preserved because of abandonment in intervening sea-level low-stands. Post Mid Pleistocene transition high-stands (MIS 1 to 19) were within 10 m of the current sea-level (Siddall et al. 2006). We present cosmogenic 10Be exposure ages from marine pebbles deposited on the surface of the terraces when they were at sea-level in order to constrain the uplift history of the northwestern highland part of the peninsula. Based on the mean age (n=10) of the oldest terrace measured (~140 m) we obtain an average uplift rate of ~0.3 m/ka for the last ~465 ka. This average uplift rate can be subdivided into a recent slower and an older, more rapid rate. The average uplift rate between ~465 and ~280 ka was ~0.6 m/ka, and based on the observed linear increase in age with altitude the uplift was steady throughout this period. However, for the last ~280 ka we calculate a slower uplift rate of ~0.1 m/ka. Tracing the surface expressions of the marine terraces northwards we observe an anomalous increase of >100 m elevation over length-scales of ~2 km. This suggests different amounts of tectonic uplift for adjacent regions within the northern part of the peninsula. From a single terrace surface (288m) in the more elevated region we measured an exposure age of ~405 ka, compatible with the temporal framework of uplift defined by the lower elevation ages. However, the higher altitude of this terrace, in comparison to the adjacent, lower region suggests a more rapid rate of uplift (~0.7 m/ka) and thus differential uplift within the northern

  15. Oxidation during metamorphism of the ordinary chondrites

    NASA Technical Reports Server (NTRS)

    Mcsween, Harry Y., Jr.; Labotka, Theodore C.

    1993-01-01

    It is suggested that some current concepts about the conditions of metamorphism in ordinary chondrites may be flawed. These meteorites display small systematic variations in the oxidation state of Fe. Evidence is presented that oxidation of Fe is linked to metamorphic grade in types 4-6 ordinary chondrites. This conclusion is at variance with a commonly accepted model for chondrite metamorphism that assumes Fe reduction by graphite.

  16. Metamorphic and volcanic quartz of the siliciclastic Tipuma Formation, West Papua, Indonesia: an insight into Triassic palaeogeography of northern Australia

    NASA Astrophysics Data System (ADS)

    Gunawan, Indra; Hall, Robert; Augustsson, Carita

    2013-04-01

    The origin and Triassic evolution of the Bird's Head of West Papua has been a subject of active discussion. Many interpretations have been proposed for the Triassic evolution, from active margin to passive margin models. The Bird's Head region is underlain by Australian continental crust and has a relatively complete stratigraphy from Palaeozoic to Recent. The Tipuma Formation is a Mesozoic siliciclastic sequence and a potentially important reservoir. Its sedimentation may record parts of the region's Mesozoic tectonic history, including several phases of rifting. Little is known about the variations in lithologies and their composition, and nothing is known about its provenance. The Tipuma Formation is dominated by red to cream well-bedded mudstone, sandstone and conglomerate. It rests unconformably on the Kemum Formation and is overlain by the Cretaceous Jass Formation. It is difficult to assess the depositional age of the Tipuma Formation due to the absence of fossils. The suggested Triassic age is based solely on its stratigraphic position. The Tipuma Formation was previously thought to be deposited in a stable continental setting. Detrital modes indicate acid plutonic, metamorphic, and recycled sedimentary source rocks for the Tipuma Formation sandstones. Angular volcanic quartz and elongate euhedral zircons suggest a contribution from previously unrecognised contemporaneous acid volcanics. New interpretations suggest that the widespread Permo-Triassic volcanic activity in the Bird's Head was caused by subduction associated with an Andean-type active margin and that the Tipuma Formation was deposited in a fluvial setting close to the volcanic arc. Cathodoluminescence (CL) characteristics of quartz depend on variations in temperature, pressure, and geochemical environment during crystal growth and subsequent events. The CL colour spectra of quartz can be correlated with the formation conditions of the quartz. They can therefore be used as a provenance indicator

  17. [An outline on the phylogenetic history of metazoa aging phenomenon (to the study of creating a common metazoa aging theory)].

    PubMed

    Boĭko, A G; Labas, Iu A; Gordeeva, A V

    2010-01-01

    The evolution of aging phenomenon in Metazoa was from the very beginning developing from potentially immortal forms to those more prone to aging. Potential immortality is an ancestral feature gradually lost in the course of evolution; at the same time aging and death resulting from aging are not obligatory but highly desirable property of existence of Metazoa with gamogenesis; this is a prerequisite of evolutionary progress as it facilitates species formation processes accelerating phylogenetic groups radiation and thus gives certain outlying evolutionary advantages, namely, accelerating the evolutionary process and the speed of substitution of one species by others. The main principle of aging phenomenon evolution is as follows: it's the substitution of internal factors of death of nonaging Metazoa with external ones programmed in genome. Aging mechanisms add up to limitation of repairing and regeneration capabilities of adult phenotype and/or by extermination of the whole pool of stem cells or its part only. Aging is a holistic process and it can't be drawn down to one of the known cellular processes which in their turn can't be the initial trigger of this process that is programmed in the genome in a vague form (there is no aging program as it is): if at some stage of ontogenesis the reparation mechanism disablement is genetically programmed then this is really the aging phenomenon programming. Mainly full or partial postmitotic design of an organism is programmed, and it is in its turn a factor securing the "harmfulness" of cellular mechanisms, decreasing the physiological potential of an organism with age. By this it increases the chances of mortality among Metazoa species. On the whole the presented material points to the fact that to develop a common aging theory of Metazoa we don't have to substantially replenish the database of biological science, but we need a new understanding of known facts, which determine the initial cognitive position. PMID:20586245

  18. Archean gold mineralization and metamorphism: timing constraints from precise U-Pb dating

    SciTech Connect

    Colvine, A.C.; Corfu, F.; Davis, D.W.; Stott, G.M.

    1985-01-01

    Gold mineralization is tightly constrained to an event closely following establishment of peak metamorphic condition, in all areas of the Superior Province of Canada where precise dating has been applied to defined field relationships. In the Abitibi and Wabigoon Subprovinces of the Southern Superior Domain, peak metamorphism caused by major batholith emplacement is consistently >2685 Ma and affects Archean supracrustal units of all ages (mainly >2700 Ma). Gold is commonly hosted by felsic stocks, dated at a specific age in the Abitibi Belt (2688-2684 Ma), and is therefore close to or younger than peak metamorphism. Dateable units crosscutting mineralization are extremely rare, but at Shebandowan and Mine Centre dated field relationships bracket the maximum and minimum age of mineralization between 2689 - 2684 and 2692 - 2686 Ma, respectively. While the metamorphic event in the Northern Superior Domain is approximately 20 my older, relative timing of gold mineralization is identical. At Red Lake, gold is hosted by units ranging in age from 2990-2718 Ma, all metamorphosed at >2704 Ma. Peak metamorphic minerals are retrograded by alteration during gold localization and mineralization is cut by a 2704 Ma dyke. These data show that gold mineralization was the product of a tectonic event during the latest Archean which involved major plutonism, deformation and metamorphism.

  19. Evidence for an age-dependent influence of environmental variations on a long-lived seabird's life-history traits.

    PubMed

    Pardo, Deborah; Barbraud, Christophe; Authier, Matthieu; Weimerskirch, Henri

    2013-01-01

    Theoretical and empirical studies have highlighted the effects of age on several life-history traits in wild populations. There is also increasing evidence for environmental effects on their demographic traits. However, quantifying how individuals differentially respond to environmental variations according to their age remains a challenge in ecology. In a population of Black-browed Albatrosses monitored during 43 years, we analyzed how life-history traits varied according to age, and whether individuals of different ages responded in different ways to environmental conditions. To do so, we: (1) examined how age affected seven life-history traits, (2) investigated differences in temporal variance of demographic traits between age classes, and (3) tested for age-dependent effects of climate and fisheries covariates on demographic traits. Overall, there was a tendency for traits to improve during the first years of life (5-10 years), to peak and remain stable at middle age (10-30 years), and decline at old ages. At young ages, survival and reproductive parameters increased, except offspring body condition at fledging, suggesting that younger parents had already acquired good foraging capacities. However, they suffered from inexperience in breeding as suggested by their higher breeding failures during incubation. There was evidence for reproductive and actuarial senescence. In particular, breeding success and offspring body condition declined abruptly, suggesting altered foraging capacities of old individuals. Middle-aged individuals had the lowest temporal variance of demographic traits. Although this is predicted by the theory of environmental canalization, it could also results from a higher susceptibility of young and old birds due to their respective inexperience and senescence. The highest temporal variances were found in old individuals. Survival was significantly influenced by sea surface temperatures in the foraging zone of this albatross population during

  20. Progressive low pressure metamorphism of metapelitic rocks from the Casco Bay area, southwestern Maine

    SciTech Connect

    Grover, T.W. . Dept. of Geology and Geophysics); Lang, H.M. . Dept. of Geology and Geography); Gordon, T.M. . Dept. of Geology and Geophysics)

    1993-03-01

    A prograde sequence of metapelitic rocks occurs in the Casco Bay area, southwestern Maine. Excellent exposure along the coast of Orrs Island, Harpswell Neck, and Small Point have allowed for the delineation of several metamorphic zones which show an increase in metamorphic grade from west to east across the area. These zones are, in order of increasing metamorphic grade, a garnet zone, a staurolite zone, a staurolite + andalusite zone and a sillimanite [plus minus] andalusite [plus minus] staurolite zone. The widespread occurrence of coexisting andalusite + sillimanite in the highest grade portion of the area, along with the presence of andalusite [plus minus] sillimanite veins on Hermit Island suggest peak metamorphism was near the andalusite-sillimanite transition. Staurolite is also found in apparent textural equilibrium in many of the sillimanite-bearing samples. Metamorphic pressures and temperatures were determined using the approach of Gordon. Peak temperatures range from [approx] 440C in garnet zone rocks to [approx] 510C in sillimanite [plus minus] andalusite zone rocks. Metamorphic pressures are [approx] 3-3.5 kbars. These P-T estimates are consistent with those determined using GeO-Calc. In contrast with the static style of metamorphism reported in central and western Maine, metamorphism in the Casco Bay area, located east of the Norumbega Fault, was synchronous with deformation. The same sequence of porphyroblast growth reported for the Orrs Island-Harpswell Neck area is also found in the Small Point area, suggesting the same metamorphic event affected the entire region. However, coarse grained muscovite pseudomorphs after andalusite or staurolite in rocks with stable andalusite and staurolite are found in the Small Point area suggesting these rocks have a polymetamorphic history. Evidence for polymetamorphism is not found elsewhere in the area.

  1. Resolving the Youngest Episode of Zircon Rim Growth with High-Spatial Resolution SIMS: U-Pb Ages and Trace Element Analyses from <1 um Thick Metamorphic Zircon Rims from the Zanskar Shear Zone and Tso Morari UHP Complex, NW Himalaya

    NASA Astrophysics Data System (ADS)

    Coble, M. A.; Leech, M. L.

    2014-12-01

    Dating the youngest phase of metamorphic or magmatic zircon growth by in-situ techniques on sectioned zircons can be challenging when rims are only a few microns thick; in the worst case, geologically meaningless measurements result from mixing between different age and/or compositional growth domains. This is especially true for zircons from the Zanskar Shear Zone and Tso Morari UHP Complex, NW Himalaya, which contain Eocene to Miocene rims that grew over Paleozoic and Proterozoic protolith cores during peak and retrograde metamorphism. These metamorphic rims are typically only 0.5 to 3.0 microns thick and require high-spatial resolution to resolve. We used the SHRIMP-RG ion-microprobe to perform new U-Pb depth-profiling analyses on zircon surfaces (non-polished) pressed into indium metal. Zircons from a leucogranite dike from Malung Tokpo along the Zanskar Shear Zone, which have 2000-5000 ppm U rims, were selected for detailed depth-profiling to evaluate the depth-resolution by SIMS for U-Pb and trace element analyses. Due to the high U concentration, we were able to decrease the primary beam intensity (sputter rate) and the count times for U and Pb isotopes, and increase the number of cycles through the run-table (45 peak-hopping scans). As a result, each cycle yielded a 0.04 micron depth-resolved zircon age and trace element composition. The youngest 13 scans yielded a U-Pb age of 21.3 ± 0.5 Ma, representing a 0.6 micron rim with uniform U, Th, and Hf concentrations. At 1.15 microns, the primary beam sputtered into a ~600 Ma core; this older age is complicated by the fact that it reflects mixing between the bottom of the sputter volume and the Miocene ages of the pit margins and rim, because the diameter of the spot tends to increase with time. Trace element analyses on zircon surfaces from the Tso Morari UHP Complex are highly reproducible, showing enriched HREE profiles with negative Eu anomalies - a result that is difficult to reproduce by analyses of

  2. Using Age-Based Life History Data to Investigate the Life Cycle and Vulnerability of Octopus cyanea

    PubMed Central

    Herwig, Jade N.; Depczynski, Martial; Roberts, John D.; Semmens, Jayson M.; Gagliano, Monica; Heyward, Andrew J.

    2012-01-01

    Octopus cyanea is taken as an unregulated, recreationally fished species from the intertidal reefs of Ningaloo, Western Australia. Yet despite its exploitation and importance in many artisanal fisheries throughout the world, little is known about its life history, ecology and vulnerability. We used stylet increment analysis to age a wild O. cyanea population for the first time and gonad histology to examine their reproductive characteristics. O. cyanea conforms to many cephalopod life history generalisations having rapid, non-asymptotic growth, a short life-span and high levels of mortality. Males were found to mature at much younger ages and sizes than females with reproductive activity concentrated in the spring and summer months. The female dominated sex-ratios in association with female brooding behaviours also suggest that larger conspicuous females may be more prone to capture and suggests that this intertidal octopus population has the potential to be negatively impacted in an unregulated fishery. Size at age and maturity comparisons between our temperate bordering population and lower latitude Tanzanian and Hawaiian populations indicated stark differences in growth rates that correlate with water temperatures. The variability in life history traits between global populations suggests that management of O. cyanea populations should be tailored to each unique set of life history characteristics and that stylet increment analysis may provide the integrity needed to accurately assess this. PMID:22912898

  3. Oman metamorphic sole formation reveals early subduction dynamics

    NASA Astrophysics Data System (ADS)

    Soret, Mathieu; Agard, Philippe; Dubacq, Benoît; Plunder, Alexis; Ildefonse, Benoît; Yamato, Philippe; Prigent, Cécile

    2016-04-01

    Metamorphic soles correspond to m to ~500m thick tectonic slices welded beneath most of the large-scale ophiolites. They typically show a steep inverted metamorphic structure where the pressure and temperature conditions of crystallization increase upward (from 500±100°C at 0.5±0.2 GPa to 800±100°C at 1.0±0.2 GPa), with isograds subparallel to the contact with the overlying ophiolitic peridotite. The proportion of mafic rocks in metamorphic soles also increases from the bottom (meta-sediments rich) to the top (approaching the ophiolite peridotites). These soles are interpreted as the result of heat transfer from the incipient mantle wedge toward the nascent slab (associated with large-scale fluid transfer and possible shear heating) during the first My of intra-oceanic subduction (as indicated by radiometric ages). Metamorphic soles provide therefore major constraints on early subduction dynamics (i.e., thermal structure, fluid migration and rheology along the nascent slab interface). We present a detailed structural and petrological study of the metamorphic sole from 4 major cross-sections along the Oman ophiolite. We show precise pressure-temperature estimates obtained by pseudosection modelling and EBSD measurements performed on both the garnet-bearing and garnet-free high-grade sole. Results allow quantification of the micro-scale deformation and highlight differences in pressure-temperature-deformation conditions between the 4 different locations, showing that the inverted metamorphic gradient through the sole is not continuous in all locations. Based on these new constraints, we suggest a new tectonic-petrological model for the formation of metamorphic soles below ophiolites. This model involves the stacking of several homogeneous slivers of oceanic crust leading to the present-day structure of the sole. In this view, these thrusts are the result of rheological contrasts between the sole and the peridotite as the plate interface progressively cools down

  4. Fi Investigations On Hp-Rocks From The Lower Engadine Window New Insights On Its Late Tectono-Metamorphic Evolution

    NASA Astrophysics Data System (ADS)

    Bertle, R. J.; Götzinger, M. A.; Koller, F.

    2003-04-01

    acknowledged. References: BERTLE, R. J. 2000: Zur Geologie und Geochronologie um Alp Trida (Samnaun/Schweiz) einschließlich ingenieurgeologischer Fragen der Gebirgsauflösung und des Permafrosts. - Unpubl. Msc-Thesis. Univ. Wien, 395 S. BOUSQUET, R., GOFFÉ, B., VIDAL, O., OBERHÄNSLI, R. & PATRIAT, M. 2002: The tectono-metamorphic history of the Valaisan domain from the Western to the Central Alps: new constraints on the evolution of the Alps. - Geol. Soc. America Bull., 114/2, S. 207-225. KÜSTER, M. &STÖCKHERT, B. 1997: Density changes of fluid inclusions in high-pressure low-temperature metamorphic rocks from Crete: A thermobarometric approach based on the creep strength of the host minerals. Lithos, 41, S. 151-167. MATTMÜLLER, C. R. 1996: Geometrische Untersuchung des Inntalgewölbes. - Jahrb. Geol. B.-A., 139/1, S. 45-69, Wien 1996. RING, U. 1989: Tectonogenesis of the Penninic/Austroalpine Boundary Zone: The Arosa Zone (Grisons Rätikon area, Swiss-Austrian Alps). - Unpubl. Phd.-Thesis., 177 p., Tübingen. STOECKHERT, B., RÖSSNER, G., KÜSTER, M., HEIDER, M., GUNDLACH, K. &RICHTER, D.K. 1990: High-Pressure Metamorphism of the Mesozoic Sediments in the Lower Engadine Window, Eastern Alps. - Terra Abstracts, 2, S. 34, 1990. THÖNI, M. 1981: Degree and Evolution of the Alpine Metamorphism in the Austroalpine Unit W of the Hohe Tauern in the light of K/Ar and Rb/Sr Age Determinations on Micas. - Jahrb. Geol. B.-A., 124/1, S. 111-174, Wien 1981.

  5. 160 Ma of magmatic/hydrothermal and metamorphic activity in the Gällivare area: Re-Os dating of molybdenite and U-Pb dating of titanite from the Aitik Cu-Au-Ag deposit, northern Sweden

    NASA Astrophysics Data System (ADS)

    Wanhainen, Christina; Billström, Kjell; Martinsson, Olof; Stein, Holly; Nordin, Roger

    2005-12-01

    Host rocks to the Aitik Cu-Au-Ag deposit in northern Sweden are strongly altered and deformed Early Proterozoic mica(-amphibole) schists and gneisses. The deposit is characterised by numerous mineralisation styles, vein and alteration types. Four samples were selected for Re-Os molybdenite dating and 12 samples for U-Pb titanite dating in order to elucidate the magmatic/hydrothermal and metamorphic history following primary ore deposition in the Aitik Cu-Au-Ag deposit. Samples represent dyke, vein and alteration assemblages from the ore zone, hanging wall and footwall to the deposit. Re-Os dating of molybdenite from deformed barite and quartz veins yielded ages of 1,876±10 Ma and 1,848±8 Ma, respectively. A deformed pegmatite dyke yielded a Re-Os age of 1,848±6 Ma, and an undeformed pegmatite dyke an age of 1,728±7 Ma. U-Pb dating of titanite from a diversity of alteration mineral associations defines a range in ages between 1,750 and 1,805 Ma with a peak at ca. 1,780 Ma. The ages obtained, together with previous data, bracket a 160-Ma (1,890-1,730 Ma) time span encompassing several generations of magmatism, prograde to peak metamorphism, and post-peak cooling; events resulting in the redistribution and addition of metals to the deposit. This multi-stage evolution of the Aitik ore body suggests that the deposit was affected by several thermal events that ultimately produced a complex ore body. The Re-Os and U-Pb ages correlate well with published regional Re-Os and U-Pb age clusters, which have been tied to major magmatic, hydrothermal, and metamorphic events. Primary ore deposition at ca. 1,890 Ma in connection with intrusion of Haparanda granitoids was followed by at least four subsequent episodes of metamorphism and magmatism. Early metamorphism at 1,888-1,872 Ma overlapping with Haparanda (1,890-1,880 Ma) and Perthite-monzonite (1,880-1,870 Ma) magmatism clearly affected the Aitik area, as well as late metamorphism and Lina magmatism at 1,810-1,774 Ma and

  6. Perspectives on elasmobranch life-history studies: a focus on age validation and relevance to fishery management.

    PubMed

    Cailliet, G M

    2015-12-01

    Life-history (age, growth, age validation, reproduction and demography) studies of elasmobranchs date back to the middle of the last century with major early contributions made by British fishery scientists. As predicted by Holden in the early 1970s, many sharks and rays can be vulnerable to fishery mortality because they grow slowly, mature late in life, reproduce infrequently, have relatively low fecundities and can have relatively long life spans. As has now been found, however, not all species exhibit these traits. Also, ageing structures (neural arches and caudal thorns), other than vertebrae and spines, have since been evaluated. Various methods for validating age and growth estimates have been developed and tested on numerous species of elasmobranchs. These include tag-recapture analyses, oxytetracycline injections, centrum or spine edge and marginal increment analyses, and bomb radiocarbon dating of calcified structures. Application of these techniques has sometimes not only validated relatively slow growth and long life span estimates, but also has produced other results. A brief historical perspective on the applications and limitations of these techniques for elasmobranchs is provided, along with a discussion of selected species for which these techniques worked well, did not work at all or have produced variable and conflicting results. Because many fishery management techniques utilize age or stage-specific information, often through demographic analyses, accurate information on the life histories of fished populations, especially age validation, is extremely important for the fishery management of these cartilaginous fishes. PMID:26709208

  7. Metamorphic geology: Why should we care?

    NASA Astrophysics Data System (ADS)

    Tajcmanova, Lucie; Moulas, Evangelos; Vrijmoed, Johannes

    2016-04-01

    Estimation of pressure-temperature (P-T) from petrographic observations in metamorphic rocks has become a common practice in petrology studies during the last 50 years. This data then often serves as a key input in geodynamic reconstructions and thus directly influences our understanding of lithospheric processes. Such an approach might have led the metamorphic geology field to a certain level of quiescence. Obtaining high-quality analytical data from metamorphic rocks has become a standard part of geology studies. The numerical tools for geodynamic reconstructions have evolved to a great extend as well. Furthermore, the increasing demand on using the Earth's interior for sustainable energy or nuclear waste disposal requires a better understanding of the physical processes involved in fluid-rock interaction. However, nowadays, metamorphic data have apparently lost their importance in the "bigger picture" of the Earth sciences. Interestingly, the suppression of the metamorphic geology discipline limits the potential for understanding the aforementioned physical processes that could have been exploited. In fact, those phenomena must be considered in the development of new generations of fully coupled numerical codes that involve reacting materials with changing porosity while obeying conservation of mass, momentum and energy. In our contribution, we would like to discuss the current role of metamorphic geology. We will bring food for thoughts and specifically touch upon the following questions: How can we revitalize metamorphic geology? How can we increase the importance of it? How can metamorphic geology contribute to societal issues?

  8. What shall I do now? State-dependent variations of life-history traits with aging in Wandering Albatrosses.

    PubMed

    Pardo, Deborah; Barbraud, Christophe; Weimerskirch, Henri

    2014-02-01

    Allocation decisions depend on an organism's condition which can change with age. Two opposite changes in life-history traits are predicted in the presence of senescence: either an increase in breeding performance in late age associated with terminal investment or a decrease due to either life-history trade-offs between current breeding and future survival or decreased efficiency at old age. Age variation in several life-history traits has been detected in a number of species, and demographic performances of individuals in a given year are influenced by their reproductive state the previous year. Few studies have, however, examined state-dependent variation in life-history traits with aging, and they focused mainly on a dichotomy of successful versus failed breeding and non-breeding birds. Using a 50-year dataset on the long-lived quasi-biennial breeding wandering albatross, we investigated variations in life-history traits with aging according to a gradient of states corresponding to potential costs of reproduction the previous year (in ascending order): non-breeding birds staying at sea or present at breeding grounds, breeding birds that failed early, late or were successful. We used multistate models to study survival and decompose reproduction into four components (probabilities of return, breeding, hatching, and fledging), while accounting for imperfect detection. Our results suggest the possible existence of two strategies in the population: strict biennial breeders that exhibited almost no reproductive senescence and quasi-biennial breeders that showed an increased breeding frequency with a strong and moderate senescence on hatching and fledging probabilities, respectively. The patterns observed on survival were contrary to our predictions, suggesting an influence of individual quality rather than trade-offs between reproduction and survival at late ages. This work represents a step further into understanding the evolutionary ecology of senescence and its

  9. What shall I do now? State-dependent variations of life-history traits with aging in Wandering Albatrosses

    PubMed Central

    Pardo, Deborah; Barbraud, Christophe; Weimerskirch, Henri

    2014-01-01

    Allocation decisions depend on an organism's condition which can change with age. Two opposite changes in life-history traits are predicted in the presence of senescence: either an increase in breeding performance in late age associated with terminal investment or a decrease due to either life-history trade-offs between current breeding and future survival or decreased efficiency at old age. Age variation in several life-history traits has been detected in a number of species, and demographic performances of individuals in a given year are influenced by their reproductive state the previous year. Few studies have, however, examined state-dependent variation in life-history traits with aging, and they focused mainly on a dichotomy of successful versus failed breeding and non-breeding birds. Using a 50-year dataset on the long-lived quasi-biennial breeding wandering albatross, we investigated variations in life-history traits with aging according to a gradient of states corresponding to potential costs of reproduction the previous year (in ascending order): non-breeding birds staying at sea or present at breeding grounds, breeding birds that failed early, late or were successful. We used multistate models to study survival and decompose reproduction into four components (probabilities of return, breeding, hatching, and fledging), while accounting for imperfect detection. Our results suggest the possible existence of two strategies in the population: strict biennial breeders that exhibited almost no reproductive senescence and quasi-biennial breeders that showed an increased breeding frequency with a strong and moderate senescence on hatching and fledging probabilities, respectively. The patterns observed on survival were contrary to our predictions, suggesting an influence of individual quality rather than trade-offs between reproduction and survival at late ages. This work represents a step further into understanding the evolutionary ecology of senescence and its

  10. Effects of magmatic and metamorphic volatiles on the evolution of fluid-rock interactions and fluid pressure during contact metamorphism

    SciTech Connect

    Hanson, R.B. )

    1992-01-01

    Finite difference models of hydrothermal flow around a cooling intrusion that include fluid production from the magma during crystallization and from wall rocks during heating are used to investigate the evolution of fluid pressure and fluid-rock interactions during the contact metamorphism. For a granodiorite intrusion with a width of 9 km and releasing just 1: H[sub 2]O linearly during crystallization, fluid production elevates fluid pressures to lithostatic values above and adjacent to the intrusion when permeabilities are less than 1 [mu]D (10[sup [minus]18] m[sup 2]). Alternatively, hydrofracturing resulting from fluid production would be sufficient to create and maintain a time-averaged permeability of 1 [mu]D for 50,000 years: permeability decreases gradually with time afterward until the magma crystallizes (350,000 years). In detail, the history depends strongly on how fluids are released from the crystallizing magma. The effect is comparable to that obtained for devolatilization of 5% H[sub 2]O by weight over heating of 400 C in adjacent wall rocks. Fluid production dominates other mechanisms for elevating fluid pressures such as thermal expansion of pore fluids or ductile strain. In models with both magmatic and metamorphic fluids, fluid flow is outward from the inner aureole for much of the cooling history at wall-rock permeabilities of [le]100 [mu]D. Extensive up-temperature flow is not predicted. The evolution of flow is such that magmatic fluids can initially dominate fluid-rock interactions in a plume above the intrusion, although the timing of interaction of magmatic and metamorphic waters is sensitive to the detailed devolatilization histories. Initial pore fluids rapidly become insignificant in the overall fluid budget. Surface or external fluids infiltrate only late in the cooling history, as rocks within a few kilometers of the intrusion are cooling.

  11. An outline of tectonic, igneous, and metamorphic events in the Goshute-Toano Range between Silver Zone Pass and White Horse Pass, Elko County, Nevada; a history of superposed contractional and extensional deformation

    USGS Publications Warehouse

    Ketner, Keith Brindley; Day, Warren C.; Elrick, Maya; Vaag, Myra K.; Zimmerman, Robert A.; Snee, Lawrence W.; Saltus, Richard W.; Repetski, John E.; Wardlaw, Bruce R.; Taylor, Michael E.; Harris, Anita G.

    1998-01-01

    Seven kinds of fault-bounded tracts are described. One of the tracts provides a good example of Mesozoic contractional folding and faulting; six exemplify various aspects of Miocene extensional faulting. Massive landslide deposits resulting from Tertiary faulting are described. Mesozoic intrusive rocks and extensive exposures of Miocene volcanic rocks are described and dated. The age ranges of stratigraphic units were based on numerous conodont collections, and ages of igneous rocks were determined by argon/argon and fission-track methods. The geologic complexity of the Goshute-Toano Range provides opportunities for many additional productive structural studies.

  12. Koolen metamorphic complex, NE Russia: Implications for the tectonic evolution of the Bering Strait region

    NASA Astrophysics Data System (ADS)

    Akinin, Vyacheslav V.; Gelman, Mikhail L.; Sedov, Boris M.; Amato, Jeffrey M.; Millwer, Elizabeth L.; Toro, Jaime; Calvert, Andrew T.; Fantini, Riccardo M.; Wright, James E.; Natal'in, Boris A.

    Structural culminations of midcrustal metamorphic rocks are found on both sides of the Bering Strait in Alaska and Russia and occur within a magmatic belt of Cretaceous age. Geologic mapping in the Koolen Lake-Lavrentia Bay region of the Chukchi Peninsula, Russia, outlines the basic relations between deformation, metamorphism, and magmatism in one of these structural culminations, the Koolen metamorphic complex. Here, a 10-15 km-thick, southwest dipping structural succession of gneisses and high-grade metamorphic rocks is exposed. The succession consists of a lower sequence of granitic gneisses and an upper sequence of biotite-rich gneisses, quartzofeldspathic gneisses, lesser amphibolite and marble, and gneisses and schists with an increasing abundance of intercalated marble and calc-silicate units toward the top. All rocks are strongly foliated and exhibit north-south trending stretching lineations. Deformation occurred during sillimanite-grade metamorphism concurrent with partial melting of the crust. Metamorphic conditions varied from 7 to 3 kbar and from 700°C-500°C. Three fractions of monazite from a deformed pegmatite yielded ages of 104 Ma. Igneous monazite from undeformed biotite granite yielded a U-Pb age of 94 Ma, indicating peak metamorphism and deformation is Cretaceous. Relations in the Koolen complex are similar to those in the Kigluaik gneiss dome, Seward Peninsula, Alaska, where upper amphibolite to granulite facies metamorphism and deformation occurred between ~105 and 90 Ma. Our findings,together with regional relations, suggest that wholesale crustal extension or extensional collapse of the crust affected this region, perhaps during Pacific-ward migration of subduction. The results do not support large amounts of east-west shortening between North America and Russia predicted by poles of rotation related to opening of the North Atlantic in the Late Cretaceous and Tertiary.

  13. The Dark Ages of Education and a New Hope: Teaching Native American History in Maine Schools

    ERIC Educational Resources Information Center

    Loring, Donna

    2009-01-01

    In 2001, the author wrote legislation that required all public schools in Maine to teach Maine Indian history. On June 14 of that year, Gov. Angus King signed "An Act to Require Maine Native American History and Culture in Maine's Schools" into law--the first of its kind in the U.S. What makes the law unique is its requirement that specific topics…

  14. CARBONACEOUS MATTER PRECURSORS AND METAMORPHIC CONDITIONS IN THERMALLY PROCESSED CHONDRITES

    NASA Astrophysics Data System (ADS)

    Quirico, E.; Montagnac, G.; Rouzaud, J.; Bonal, L.; Bourot-Denise, M.; Duber, S.; Reynard, B.

    2009-12-01

    Unravelling the origin of carbonaceous matter in pristine chondrites requires the understanding of the effect of post-accretion processes. In chondrites of petrologic type 3, thermal metamorphism modified to various extents the composition and structure of carbonaceous matter. Interestingly, this process controls the degree of structural order of carbonaceous matter, and clues on the thermal history of the parent body may be recovered from the physico-chemical study of carbonaceous matter. Following this framework, geothermometers based on Raman spectrometry of carbonaceous matter and covering a wide range of temperatures (100-650 °C) have been developed over recent years, both on terrestrial rocks and chondrites. While Raman data have been largely interpreted in terms of temperature, they are also the fingerprint of certain metamorphic conditions, especially in the low temperature range relevant to poorly ordered carbonaceous matter. This study investigates the Raman spectra of two series of chondritic carbonaceous matter and coal samples formed from different precursors and under different metamorphic conditions. The Raman spectra of Polyaromatic Carbonaceous Matter (PCM) from 42 chondrites and 27 coal samples, measured with visible (514 nm) and ultra-violet (244 nm) excitation wavelengths, are analyzed. The Raman spectra of low rank coals and chondrites of petrologic types 1 and 2, which contain the more disordered PCM, reflect the distinct carbon structures of their precursors. The 514 nm Raman spectra of high rank coals and chondrites of petrologic type 3 exhibit continuous and systematic spectral differences reflecting different carbon structures present during the metamorphism event. They result from differences in the chemical structures of the precursors concerning for instance the reticulation of polyaromatic units or an abundance of ether functional groups, or possibly from a lack of carbonization processes to efficiently expel oxygen heteroatoms, due

  15. Metamorphism and partial melting of ordinary chondrites: Calculated phase equilibria

    NASA Astrophysics Data System (ADS)

    Johnson, T. E.; Benedix, G. K.; Bland, P. A.

    2016-01-01

    Constraining the metamorphic pressures (P) and temperatures (T) recorded by meteorites is key to understanding the size and thermal history of their asteroid parent bodies. New thermodynamic models calibrated to very low P for minerals and melt in terrestrial mantle peridotite permit quantitative investigation of high-T metamorphism in ordinary chondrites using phase equilibria modelling. Isochemical P-T phase diagrams based on the average composition of H, L and LL chondrite falls and contoured for the composition and abundance of olivine, ortho- and clinopyroxene, plagioclase and chromite provide a good match with values measured in so-called equilibrated (petrologic type 4-6) samples. Some compositional variables, in particular Al in orthopyroxene and Na in clinopyroxene, exhibit a strong pressure dependence when considered over a range of several kilobars, providing a means of recognising meteorites derived from the cores of asteroids with radii of several hundred kilometres, if such bodies existed at that time. At the low pressures (<1 kbar) that typify thermal metamorphism, several compositional variables are good thermometers. Although those based on Fe-Mg exchange are likely to have been reset during slow cooling, those based on coupled substitution, in particular Ca and Al in orthopyroxene and Na in clinopyroxene, are less susceptible to retrograde diffusion and are potentially more faithful recorders of peak conditions. The intersection of isopleths of these variables may allow pressures to be quantified, even at low P, permitting constraints on the minimum size of parent asteroid bodies. The phase diagrams predict the onset of partial melting at 1050-1100 °C by incongruent reactions consuming plagioclase, clinopyroxene and orthopyroxene, whose compositions change abruptly as melting proceeds. These predictions match natural observations well and support the view that type 7 chondrites represent a suprasolidus continuation of the established petrologic

  16. Role of family resources and paternal history of substance use problems in psychosocial adjustment among school-aged children.

    PubMed

    Peleg-Oren, Neta; Rahav, Giora; Teichman, Meir

    2008-01-01

    The present study examines the role of family resources (parenting style and family cohesion) and paternal history of substance abuse on the psychosocial adjustment of their school-aged children. Data were collected from 148 children aged 8-11 (72 of fathers with history of substance use disorder, 76 children of fathers with no substance use problems) and their mothers. Results draw attention to the differences between the subjective experiences of the child and those of the mother, and by indicating that the effect of the interaction between the father's and the mother's control parenting style on the child's psychosocial outcome is greater than the sum total of influences of each of them separately. PMID:19157043

  17. Shock metamorphism of carbonaceous chondrites

    NASA Technical Reports Server (NTRS)

    Scott, Edward R. D.; Keil, Klaus; Stoeffler, Dieter

    1992-01-01

    Shock effects were studied in 69 carbonaceous chondrites, including CM2, CO3, CV3, ungrouped C2-C4, and CK4-6 chondrites, using optical microscopy of thin sections. It is shown that the classification scheme of Stoeffler et al. (1991) for the progressive stages of shock metamorphism in ordinary chondrites is also applicable to carbonaceous chondrites. On the basis of shock effects in olivine, the 69 carbonaceous chondrites could be assigned to four shock stage, S1 to S4. The CM2 and CO3 groups were found to be the least shocked chondrite groups, whereas the CK4-6 and CV3 were the most strongly shocked groups.

  18. Complex Histories of Two Lunar Zircons as Evidenced by their Internal Structures and U-Pb Ages

    NASA Technical Reports Server (NTRS)

    Pidgeon, R. T.; Nemchin, A. A.; Meyer, Charles

    2006-01-01

    The U-Pb dating of lunar zircon by ion-microprobe provides a robust technique for investigating the timing of lunar events [1,2]. However, we have now identified two cases where the U-Pb systems in a single zircon show more than one age. These complex zircons provide new opportunities for extending our knowledge on the timing of events in the early history of the Moon.

  19. Early, steep subduction of India beneath Asia required by timing of UHP metamorphism

    NASA Astrophysics Data System (ADS)

    Leech, M. L.; Klemperer, S. L.; Singh, S.; Jain, A. K.

    2004-12-01

    Ultrahigh-pressure (UHP) rocks in the NW Himalaya are the youngest on earth, and allow testing of critical questions of UHP formation and exhumation and the India-Asia collision. The Tso Morari Complex (TMC) is a UHP subduction zone complex in eastern Ladakh in the western Himalaya, south of the Indus-Tsangpo suture zone. New U-Pb SHRIMP data from zircon shows the TMC has a Proterozoic protolith with a Pan-African history, and defines three stages in the Eocene history of the TMC, hence constraining the timing of collision, subduction, and exhumation in the western Himalaya. Our precise new single zircon U-Pb ages indicate that UHP eclogite-facies metamorphism occurred at 53.3±0.7 Ma followed by a HP eclogite-facies event at 50.0±0.6 Ma, and amphibolite-facies metamorphism at 47.5±0.5 Ma. Retrograde zircon growth may result from dehydration reaction-related fluids evolved during exhumation; the intermittent presence of these fluids would allow zircon crystallization during exhumation that would document the changing P-T conditions. Today India subducts beneath Tibet at an angle of only c. 10° ; at this low angle, rocks must travel over 500 km along the subduction thrust to reach the depth of c. 100 km required for UHP metamorphism. Initial collision of India with Asia, based on stratigraphic and paleomagnetic data, is widely cited as being at 55±1 Ma. Here we show that Indian rocks reached UHP depths at 53.3±0.7 Ma. Given the fast India-Asia convergence rate of 69 km/m.y., our result implies an earlier onset of collision (c. 57 Ma) and that UHP rocks must have traveled a short, hence steep path into the mantle. We infer that early continental subduction was at a steep angle, probably vertical, comparable to modern continental subduction in the Hindu Kush.

  20. UHP metamorphism in Greece: Petrologic data from the Rhodope Mountains

    NASA Astrophysics Data System (ADS)

    Baziotis, I. P.; Mposkos, E.; Krohe, A.; Wawrzenitz, N. H.; Liu, Y.; Taylor, L. A.

    2012-12-01

    Metamorphic rocks contain invaluable information for understanding the orogenic mechanisms of a tectonic regime. It is now well recorded and recognized that subduction of oceanic lithosphere and collision of continental blocks can result in sinking of subducted rocks to deeper levels than normal (>100 km). Further, the discovery of coesite and diamond in apparently regionally metamorphosed rocks provoked issues, for returning these rocks to the surface relatively fast, thereby preserving the UHP conditions. These UHPM terrains have been identified in more than twenty provinces worldwide. In Greece, UHPM rocks occur in the Rhodope area, one of the major tectono-metamorphic units located in NE Greece. This region consists of different metamorphic complexes involved in the Alpine collisional history between the Eurasian and African plates (e.g., Krohe & Mposkos, 2002-Geol Soc London Spec Pub, 204, 151). In Rhodope, a Jurassic UHP metamorphism is confirmed in the uppermost Kimi and the underlying Sidironero complexes (Mposkos & Kostopoulos, 2001- EPSL, 192, 497; Perraki et al., 2004-5th ISEMG, T2-35, 2006- EPSL, 241, 672; Liati, 2005- Con Min Pet, 150, 608; Bauer et al., 2007- Lithos, 99, 207). UHP metamorphism is evidenced by the presence of octahedral microdiamond inclusions (3 to 10 μm) in protective garnets, within the metapelitic gneisses. Microdiamonds probably formed from a supercritical fluid under extreme P-T conditions. The latter is strengthened by the presence of composite inclusions consisting of CO2, calcite, and microdiamonds. Other UHP indicators include: 1) quartz rods and rutile needle exsolutions in metapelitic garnet, suggesting a former titaniferous super-silicic (majoritic) garnet formed at P >4GPa; 2) oriented quartz lamellae in eclogitic clinopyroxene having been exsolved from a former super-silicic UHP precursor; and 3) coesite pseudomorphs in garnet, where radial cracks around multi-crystalline-quartz aggregates are indicative of the former

  1. The timing of tertiary metamorphism and deformation in the Albion-Raft River-Grouse Creek metamorphic core complex, Utah and Idaho

    USGS Publications Warehouse

    Strickland, A.; Miller, E.L.; Wooden, J.L.

    2011-01-01

    The Albion-Raft River-Grouse Creek metamorphic core complex of southern Idaho and northern Utah exposes 2.56-Ga orthogneisses and Neoproterozoic metasedimentary rocks that were intruded by 32-25-Ma granitic plutons. Pluton emplacement was contemporaneous with peak metamorphism, ductile thinning of the country rocks, and top-to-thewest, normal-sense shear along the Middle Mountain shear zone. Monazite and zircon from an attenuated stratigraphic section in the Middle Mountain were dated with U-Pb, using a SHRIMP-RG (reverse geometry) ion microprobe. Zircons from the deformed Archean gneiss preserve a crystallization age of 2532 ?? 33 Ma, while monazites range from 32.6 ?? 0.6 to 27.1 ?? 0.6 Ma. In the schist of the Upper Narrows, detrital zircons lack metamorphic overgrowths, and monazites produced discordant U-Pb ages that range from 52.8 ?? 0.6 to 37.5 ?? 0.3 Ma. From the structurally and stratigraphically highest unit sampled, the schist of Stevens Spring, narrow metamorphic rims on detrital zircons yield ages from 140-110 Ma, and monazite grains contained cores that yield an age of 141 ??2 Ma, whereas rims and some whole grains ranged from 35.5 ?? 0.5 to 30.0 ?? 0.4 Ma. A boudinaged pegmatite exposed in Basin Creek is deformed by the Middle Mountains shear zone and yields a monazite age of 27.6 ?? 0.2 Ma. We interpret these data to indicate two periods of monazite and metamorphic zircon growth: a poorly preserved Early Cretaceous period (???140 Ma) that is strongly overprinted by Oligocene metamorphism (???32-27 Ma) related to regional plutonism and extension. ?? 2011 by The University of Chicago.

  2. 40Ar/39Ar thermochronology of mesoproterozoic metamorphism in the Colorado Front Range

    USGS Publications Warehouse

    Shaw, C.A.; Snee, L.W.; Selverstone, J.; Reed, J.C., Jr.

    1999-01-01

    A low-pressure metamorphic episode in the Colorado Front Range has been identified by the presence of staurolite, andalusite, cordierite, and garnet porphyroblasts overprinting earlier assemblages. The overprinting assemblages and reaction textures are most consistent with porphyroblast growth on a prograde metamorphic path with peak temperatures exceeding ~525??C. Twenty-eight 40Ar/39Ar dates on hornblende, muscovite, biotite, and microcline were used to infer the age and thermal conditions of metamorphism. Muscovite and biotite 40Ar/39Ar ages fall mainly in the interval 1400-1340 Ma, consistent with cooling through the closure temperature interval of micas (~400??-300??C) after about 1400 Ma. In contrast, hornblende apparent ages (T(c)~500??-550??C) between 1600 and 1390 Ma reflect variable retention of radiogenic argon. Forward modeling of argon diffusion shows that the distribution of hornblende and mica ages is consistent with the partial resetting of argon systematics ca. 1400 Ma by a thermal pulse reaching maximum temperatures around 550??C and decaying within <20 m.yr. These temperatures match the conditions inferred from the overprinting assemblage; thus, muscovite and biotite ages are interpreted to date the cooling phase of this metamorphic event. This late metamorphism is broadly coeval with the intrusion of ca. 1400-Ma granitic plutons in the study area and throughout the southwestern United States. However, thermal effects are observed far from pluton margins, suggesting pervasive, regional crustal heating rather than restricted contact metamorphism. Our results suggest that ca. 1400-Ma metamorphism and plutonism are manifestations of a regional thermal episode that both partially melted the lower crust and pervasively metamorphosed middle crustal rocks.

  3. Contrasting Metamorphic Record of Heat Production Anomalies in the Penokean Orogen of Northern Michigan.

    PubMed

    Attoh

    2000-05-01

    It is proposed that the contrasting metamorphic mineral assemblages of the isolated amphibolite facies metamorphic highs in the Penokean orogen of northern Michigan may be caused by different heat production rates in the Archean basement. This hypothesis is based on concentrations of K, U, and Th in the Archean basement gneisses and Paleoproterozoic metasediments that indicate significant contribution of radiogenic heating during Penokean metamorphism. Heat production was anomalously high ( approximately 10.6 µWm-3) where andalusite-bearing mineral assemblages indicate that high temperatures were attained at shallow crustal levels ( approximately 550 degrees -600 degrees C at approximately 3 kbar). In contrast, where exposed metamorphic rocks indicate peak temperatures of 600 degrees -650 degrees C at 6-7 kbar, heat production in the Archean basement was lower ( approximately 3.7 µWm-3). The effect of heat production rates on the metamorphic pressure-temperature paths was tested with numerical thermal models. The calculations show (1) that if the heat production rate, where andalusite-bearing assemblages formed, was significantly <6.0 µWm-3, the estimated pressure at peak temperatures (PTmax) would be much higher and lie in the sillimanite or kyanite stability fields; and (2) differences between PTmax estimates for the metamorphic highs based on thermobarometry can be reproduced if thermal history involved significant crustal thickening as well as moderate unroofing rates. PMID:10769161

  4. High neuroticism at age 20 predicts history of mental disorders and low self-esteem at age 35.

    PubMed

    Lönnqvist, Jan-Erik; Verkasalo, Markku; Mäkinen, Seppo; Henriksson, Markus

    2009-07-01

    The authors assessed whether neuroticism in emerging adulthood predicts mental disorders and self-esteem in early adulthood after controlling for possible confounding variables. A sample of 69 male military conscripts was initially assessed at age 20 and again as civilians at age 35. The initial assessment included a psychiatric interview, objective indicators of conscript competence, an intellectual performance test, and neuroticism questionnaires. The follow-up assessment included a Structured Clinical Interview for DSM-IV (SCID; First, Spitzer, Gibbon, & Williams, 1996) and the Rosenberg Self-Esteem Scale (Rosenberg, 1965). Neuroticism predicted future mental disorders and low self-esteem beyond more objective indicators of adjustment. The results support the use of neuroticism as a predictor of future mental disorders, even over periods of time when personality is subject to change. PMID:19267331

  5. Neoarchean metamorphism recorded in high-precision Sm-Nd isotope systematics of garnets from the Jack Hills (Western Australia)

    NASA Astrophysics Data System (ADS)

    Eccles, K. A.; Baxter, E. F.; Mojzsis, S. J.; Marschall, H.; Williams, M. L.; Jercinovic, M. J.

    2013-12-01

    Studies of metasedimentary rocks from the Jack Hills, which host Earth's oldest known detrital minerals, have focused on zircon and occasionally monazite or xenotime, but no attention has been directed toward one of the most common mineral markers of metamorphism: garnet. Garnet can provide a record of the post-depositional, prograde metamorphic history of Archean metasedimentary rocks. Additionally, the use of a newly developed detrital garnet dating technique [1,2] may reveal information about pre-depositional metamorphism that could address lingering questions about the nature and timing of Earth's earliest tectonometamorphic events. Here we investigate garnet from the Jack Hills metasedimentary rocks to test whether they record in situ metamorphism or are a detrital relict of even older metamorphic events. We identified garnet in two bulk quartz-pebble conglomerate samples collected from the 'discovery' outcrop at Eranondoo Hill in the Jack Hills of Western Australia. Electron microprobe analyses of polished grains and SEM measurements of unpolished grain surfaces are consistent, revealing garnet composition indicative of a single generation/population of predominantly almandine-spessartine solid solution (~10-35% mole fraction spessartine). Compositional maps of garnet grains reveal little zoning and no discontinuities, most consistent with a single growth event. Dating Jack Hills' garnet via the Sm-Nd system is possible due to continued development of small sample analysis techniques, including running NdO+ TIMS analyses with Ta2O5 activator [3] permitting <50 ppm 2 sigma analytical precision on a 400pg in-house standard and continued improvement in blanks (<15pg full procedural blanks). Additionally, employing a nondestructive chemical prescreening technique (tabletop SEM) allows for grouping of multiple grains based on chemical similarity. Final Nd loads in the 450-750pg range routinely yield dates with precisions <×10Ma for two point isochrons between

  6. Potential contributions of metamorphic petrology studies in an ultra-deep drillhole in the southern Appalachians

    SciTech Connect

    Speer, J.A.

    1985-01-01

    The proposed, ultra-deep hole in the southeast U.S. will penetrate allochthonous, medium- to high-grade metamorphic rocks of the Inner Piedmont and Blue Ridge thrust sheets. It is anticipated that the hole will then encounter autochthonous low-grade, metasedimentary cover rocks before bottoming out in crystalline Precambrian basement rocks. Metamorphic petrology in the recent past has concentrated on unraveling the physical and chemical history (P, T, X/sub fluid/, etc.) of metamorphic rocks. The techniques that have been developed are ideally suited to the study of relatively limited samples from drill core. Detailed studies of the allochthonous and autochthonous rocks from the drillhole, combined with comparable studies of the surface rocks, by metamorphic petrologists experimented with these approaches, would give a 3-dimensional picture of the PTX evolution in the region of the ultra-deep hole, and thus an idea of the geometrical, chemical, and physical changes the rocks experienced. This would place constraints on conditions of the rocks before and after thrusting and thus any tectonic models of thrusting in the southern Appalachians. With limited sampling this could be a problem, with more complete sampling it will be an advantage. The metamorphic petrology of the rocks will provide basic support for the other studies of the drill core and drillhole, most notably geochronology and stable isotopes. It should not be forgotten that in addition to the historical metamorphism, the expected, present-day conditions in the drillhole are those of burial metamorphism. The hole will present an excellent opportunity to study such active metamorphic conditions.

  7. Metamorphic probing of subduction dynamics and rheology

    NASA Astrophysics Data System (ADS)

    Agard, Philippe

    2015-04-01

    Understanding subduction dynamics and rheology, and particularly the role of fluids and deformation, strongly relies on integrated tectonic, petrological and geochemical studies able to retrieve from our most direct and reliable natural probes (i.e., preserved metamorphic assemblages) their pressure-temperature-time (P-T-t) evolution. I first provide two examples of such integrated studies that allow tracking rock trajectories and exhumation dynamics in subduction zones -- thanks to the considerable progress made over the last ten years on estimating P-T-t conditions. The Oman example shows how EPMA mapping and the detailed study of local, low-temperature equilibria help constrain the behaviour and dynamics of upper crustal units during continental subduction, demonstrating the importance of slicing, accretion at depths of ~30 km and short-lived tectonic expulsion. In the Western Alps, the extensive coverage of field exposures by means of the Raman Spectrometry of carbonaceous matter and by dedicated pseudosection modelling allows to identify the existence of tens of km long, fairly continuous slices of downgoing slab exhumed from similar eclogitic depths (~80 km), and to assess the role of the overall fluid content in enabling their exhumation/preservation. I then illustrate how metamorphic rocks can provide ideal probes (though still partly to be improved) to address key, large-scale tectonic processes and not 'simply' histories, and do stress the importance of adequate field-based data acquisition. Three examples (and present-day limitations) are reviewed here: (1) The regional-scale exhumation of blueschists from the downdip end of the seismogenic zone across thousands of kilometers along the Neotethys (at ~1-1.5 GPa, 350°C) is a major geodynamic event providing insights into changes in interplate mechanical coupling and subduction dynamics. (2) Eclogite breccias recently reported in the Monviso area (W. Alps) allow constraining short-term processes involving

  8. Quantitative estimates of metamorphic equilibria: Tallassee synform, Dadeville belt, Alabama's Inner Piedmont

    SciTech Connect

    Drummond, M.S.; Neilson, M.J. . Dept. of Geology)

    1993-03-01

    The Tallassee synform is the major structural feature in the western part of the Dadeville belt. This megascopic F2 structure folds amphibolite (Ropes Creek Amphibolite) and metasedimentary units (Agricola Schist, AS), as well as tonalitic (Camp Hill Gneiss, CHG), granitic (Chattasofka Creek Gneiss, CCG), and mafic-ultramafic plutons (Doss Mt. and Slaughters suites). Acadian-age prograde regional metamorphism preceded the F2 folding event, producing the pervasive S1 foliation and metamorphic recrystallization. Prograde mineralogy in the metapelites and metagraywackes of the AS includes garnet, biotite, muscovite, plagioclase, kyanite, sillimanite, and epidote. The intrusive rocks, both felsic and mafic-ultramafic, are occasionally garnetiferous and provide suitable mineral assemblages for P-T evaluation. The AS yields a range of T-P from 512--635C and 5.1--5.5 kb. Muscovite from the AS exhibits an increase in Ti content from 0.07 to 0.15 Ti/22 O formula unit with progressively increasing T's from 512 to 635C. This observation is consistent with other studies that show increasing Ti content with increasing grade. A CHG sample records an average metamorphic T-P of 604C and 5.79 kb. Hornblende-garnet pairs from a Doss Mt. amphibolite sample provides an average metamorphic T of 607C. These data are consistent with regional Barrovian-type middle to upper amphibolite facies metamorphism for the Tallassee synform. Peak metamorphism is represented by kyanite-sillimanite zone conditions and localized migmatization of the AS. The lithotectonic belts bounding the Dadeville belt to the NW and SE are the eastern Blue Ridge and Opelika belts. Studies have shown that these belts have also experienced Acadian-age amphibolite facies metamorphism with comparable P-T estimates to those presented here. These data suggest that the eastern Blue Ridge and Inner Piedmont of AL experienced the same pervasive dynamothermal Barrovian-type metamorphic episode during Acadian orogenesis.

  9. Differential effects of age and history of hypertension on regional brain volumes and iron

    PubMed Central

    Rodrigue, Karen M.; Haacke, E. Mark; Raz, Naftali

    2010-01-01

    Aging affects various structural and metabolic properties of the brain. However, associations among various aspects of brain aging are unclear. Moreover, those properties and associations among them may be modified by age-associated increase in vascular risk. In this study, we measured volume of brain regions that vary in their vulnerability to aging and estimated local iron content via T2* relaxometry. In 113 healthy adults (19–83 years old), we examined prefrontal cortex (PFC), primary visual cortex (VC), hippocampus (HC), entorhinal cortex (EC), caudate nucleus (Cd), and putamen (Pt). In some regions (PFC, VC, Cd, Pt) age-related differences in iron and volume followed similar patterns. However, in the medial temporal structures, volume and iron content exhibited different age trajectories. Whereas age-related volume reduction was mild in HC and absent in EC, iron content evidenced significant age-related declines. In hypertensive participants significantly greater iron content was noted in all examined regions. Thus, iron content as measured by T2* may be a sensitive index of regional brain aging and may reveal declines that are more prominent than gross anatomical shrinkage. PMID:20923707

  10. Sex differences in cognitive ageing: testing predictions derived from life-history theory in a dioecious nematode.

    PubMed

    Zwoinska, Martyna K; Kolm, Niclas; Maklakov, Alexei A

    2013-12-01

    Life-history theory maintains that organisms allocate limited resources to different traits to maximize fitness. Learning ability and memory are costly and known to trade-off with longevity in invertebrates. However, since the relationship between longevity and fitness often differs between the sexes, it is likely that sexes will differentially resolve the trade-off between learning and longevity. We used an established associative learning paradigm in the dioecious nematode Caenorhabditis remanei, which is sexually dimorphic for lifespan, to study age-related learning ability in males and females. In particular, we tested the hypothesis that females (the shorter-lived sex) show higher learning ability than males early in life but senesce faster. Indeed, young females outperformed young males in learning a novel association between an odour (butanone) and food (bacteria). However, while learning ability and offspring production declined rapidly with age in females, males maintained high levels of these traits until mid-age. These results not only demonstrate sexual dimorphism in age-related learning ability but also suggest that it conforms to predictions derived from the life-history theory. PMID:24120565

  11. Thermal metamorphism. [of chondrite parent bodies

    NASA Technical Reports Server (NTRS)

    Mcsween, Harry Y., Jr.; Sears, Derek W. G.; Dodd, Robert T.

    1988-01-01

    Most chondrites have experienced thermal metamorphism, resulting in changes in texture, mineralogy and possibly chemical composition. The physical conditions for metamorphism range from approximately 400 to 1000 C at low lithostatic pressure. Metamorphism may have resulted from decay of short-lived radionuclides, electromagnetic induction or accretion of hot materials. Several thermal models for chondrite parent bodies have been proposed. The least metamorphosed type-3 chondrites probably carry the most information about the early solar system, but even these have been affected to some degree by thermal processing.

  12. Studying Local History in the Digital Age: The Story of Asaph Perry

    ERIC Educational Resources Information Center

    Lee, John K.; Clarke, W. Guy

    2004-01-01

    In this article, the authors speak of an encounter they had in which they discovered some forgotten and unused historical resources hidden in a storage closet at the Cherokee County Georgia Historical Society. From these resources, they were able to weave an intriguing narrative encompassing people and events in history. They hope their story will…

  13. Using Simulations to Teach Middle Grades U.S. History in an Age of Accountability

    ERIC Educational Resources Information Center

    DiCamillo, Lorrei; Gradwell, Jill M.

    2012-01-01

    In this year-long qualitative study we explore the case of two eighth grade U.S. History teachers who use simulations on a regular basis to teach heterogeneously-grouped students in a high-stakes testing environment. We describe the purposes the teachers espoused for implementing simulations and provide detailed portraits of three types of…

  14. Learning US History in an Age of Globalization and Transnational Migration

    ERIC Educational Resources Information Center

    An, Sohyun

    2009-01-01

    This paper examines US Korean youth's perspectives on US history and the impact of their sociocultural backgrounds, particularly their migration status, on their historical interpretations. Based on in-depth interviews with 42 US Korean high school students, the study opens up the question of diversity within an ethnic group, while it also begins…

  15. Sleep Problems in Chinese School-Aged Children with a Parent-Reported History of ADHD

    ERIC Educational Resources Information Center

    Li, Shenghui; Jin, Xinming; Yan, Chonghuai; Wu, Shenghu; Jiang, Fan; Shen, Xiaoming

    2009-01-01

    Objective: The objective was to survey the prevalence of parent-reported ADHD diagnosis and to assess its associations with sleep problems among urban school-aged children in China. Method: A random sample of 20,152 school-aged children participated in a cross-sectional survey in eight cities of China. A parent-administered questionnaire and the…

  16. Adolescents' Age Preferences for Dating Partners: Support for an Evolutionary Model of Life-History Strategies.

    ERIC Educational Resources Information Center

    Kenrick, Douglas T.; And Others

    1996-01-01

    Explored sex differences in adolescent preference for older versus younger mates. Found that teenage males were willing to date females of a wide age range, whereas teenage females prefer dating males from their own age to several years older. Data suggested viewing development of sex differences in dating partner preference from the perspective…

  17. The Moderating Effect of Age on the 12-Month Prevalence of Anxiety and Depressive Disorders in Adults with a Lifetime History of Cancer

    PubMed Central

    Simning, Adam; Conwell, Yeates; Mohile, Supriya G.; van Wijngaarden, Edwin

    2013-01-01

    Objectives To determine how age may modulate the association of a history of cancer with a 12-month history of anxiety and depressive disorders. Design Population-based, cross-sectional surveys. Setting The Collaborative Psychiatric Epidemiology Surveys (CPES) occurred in the United States and were conducted in 2001-2003. Participants CPES included 16,423 adult participants, of whom 702 reported a cancer history. Measurements The Composite International Diagnostic Interview evaluated the presence of a 12-month history of anxiety and depressive disorders. Results Among those with a cancer history, older adults (≥ 60 years old) were less likely than younger adults (18-59 years old) to have a 12-month history of an anxiety or depressive disorder. Compared to their peers without cancer, younger adults with a cancer history had more anxiety (23.8% vs. 13.9%) and depressive (16.0% vs. 9.5%) disorders, whereas older adults with a cancer history had lower levels of anxiety (3.7% vs. 6.3%) and depressive (1.9% vs. 3.9%) disorders. In multivariable modeling, there was a statistically significant interaction between age group and cancer history, with the risk for anxiety and depressive disorders elevated in the younger age group with a cancer history (OR=5.84 and OR=6.13, respectively), but decreased in the older age group with a cancer history (OR=0.55 and OR=0.45). Conclusions Our findings suggest that there is considerable age-dependent variation with regard to anxiety and depressive disorders in adults with a cancer history. Investigation of the mechanisms contributing to this apparent age differential in risk could have important mental illness treatment implications in this population. PMID:24080385

  18. Cosmic-Ray-Exposure Ages of Diogenites and the Collisional History of the HED Parent Body or Bodies

    NASA Technical Reports Server (NTRS)

    Welten, K. C.; Lindner, L.; vanderBorg, K.; Loeken, T.; Scherer, P.; Schultz, L.

    1996-01-01

    Cosmic-ray-exposure ages of meteorites provide information on the collisional history of their parent bodies and the delivery mechanism of meteorites to Earth. The exposure-age distributions of ordinary chondrites show distinct patterns for H, L, and LL types, consistent with their origin on different parent bodies. The exposure-age distributions of howardites, eucrites. and diogenites (HEDS) show a common pattern with major peaks at 22 Ma and 38 Ma This provides additional evidence for a common origin of the HED meteorites, possibly 4 Vesta, although orbital dynamics calculations showed that the delivery of meteorites from Vesta to Earth is difficult. However, the discovery of several kilometer-sized Vesta-like asteroids in the region between Vesta and the 3:1 resonance suggested that these seem more likely parent bodies of the HEDs than Vesta itself. This implies that the exposure-age clusters may represent samples of several parent bodies. Therefore, the near-absence of diogenites with ages <20 Ma might be of interest for the composition of these kilometer-sized fragments of Vesta. Here we present cosmic-ray-exposure ages of 20 diogenites, including 9 new meteorites. In addition, we calculate the probability for each peak to occur by chance, assuming a constant production rate of HED fragments.

  19. Development of inverted metamorphic isograds in the western metamorphic belt, Juneau, Alaska

    USGS Publications Warehouse

    Himmelberg, G.R.; Brew, D.A.; Ford, A.B.

    1991-01-01

    An inverted metamorphic gradient is preserved in the western metamorphic belt near Juneau, Alaska. Detailed mapping of pelitic single-mineral isograds, systematic changes in mineral assemblages, and silicate geothermometry indicate that thermal peak metamorphic conditions increase structurally upward over a distance of about 8 km. Silicate geobarometry suggests that the thermal peak metamorphism occurred under pressures of 9-11 kbar. Our preferred interpretation of the cause of the inverted gradient is that it formed during compression of a thickened wedge of relatively wet and cool rocks in response to heat flow associated with the formation and emplacement of tonalite sill magma. -from Authors

  20. Offense history and recidivism in three victim-age-based groups of juvenile sex offenders.

    PubMed

    Kemper, Therese Skubic; Kistner, Janet A

    2007-12-01

    This study compared subgroups of juvenile sex offenders (JSOs) who victimized children (child offenders), peers (peer offenders), or both children and peers (mixed offenders) on sexual and nonsexual offense history, treatment outcomes, and recidivism to determine if these are distinct and valid subgroups. Though the group of mixed offenders was small, results showed that they exhibited a more diverse and more physically intrusive sexual offense history than the other JSOs and were less likely to successfully complete treatment. Sexual and nonsexual recidivism rates of mixed offenders did not differ from the other subgroups despite subgroup differences in juvenile sexual and nonsexual criminal records. However, differences in sexual recidivism rates of child versus peer offenders were found when the mixed offenders were either excluded from the sample or combined with child offenders. The results highlight the need to include mixed offenders in future research examining the etiology of sexual offending, treatment, and recidivism of JSOs. PMID:17952596

  1. Early Tertiary Anaconda metamorphic core complex, southwestern Montana

    USGS Publications Warehouse

    O'Neill, J. M.; Lonn, J.D.; Lageson, D.R.; Kunk, M.J.

    2004-01-01

    A sinuous zone of gently southeast-dipping low-angle Tertiary normal faults is exposed for 100 km along the eastern margins of the Anaconda and Flint Creek ranges in southwest Montana. Faults in the zone variously place Mesoproterozoic through Paleozoic sedimentary rocks on younger Tertiary granitic rocks or on sedimentary rocks older than the overlying detached rocks. Lower plate rocks are lineated and mylonitic at the main fault and, below the mylonitic front, are cut by mylonitic mesoscopic to microscopic shear zones. The upper plate consists of an imbricate stack of younger-on-older sedimentary rocks that are locally mylonitic at the main, lowermost detachment fault but are characteristically strongly brecciated or broken. Kinematic indicators in the lineated mylonite indicate tectonic transport to the east-southeast. Syntectonic sedimentary breccia and coarse conglomerate derived solely from upper plate rocks were deposited locally on top of hanging-wall rocks in low-lying areas between fault blocks and breccia zones. Muscovite occurs locally as mica fish in mylonitic quartzites at or near the main detachment. The 40Ar/39Ar age spectrum obtained from muscovite in one mylonitic quartzite yielded an age of 47.2 + 0.14 Ma, interpreted to be the age of mylonitization. The fault zone is interpreted as a detachment fault that bounds a metamorphic core complex, here termed the Anaconda metamorphic core complex, similar in age and character to the Bitterroot mylonite that bounds the Bitterroot metamorphic core complex along the Idaho-Montana state line 100 km to the west. The Bitterroot and Anaconda core complexes are likely components of a continuous, tectonically integrated system. Recognition of this core complex expands the region of known early Tertiary brittle-ductile crustal extension eastward into areas of profound Late Cretaceous contractile deformation characterized by complex structural interactions between the overthrust belt and Laramide basement uplifts

  2. Ortigalita Peak gabbro, Franciscan complex: U-Pb dates of intrusion and high-pressure low-temperature metamorphism

    NASA Astrophysics Data System (ADS)

    Mattinson, James M.; Echeverria, Lina M.

    1980-12-01

    Paleontological and isotopic age data from the Franciscan complex in the Ortigalita Peak quadrangle, Diablo Range, California, provide new insight into the tectonic evolution of at least part of the Franciscan complex. Graywacke, shale, pillowed greenstone, and chert in the quadrangle were deposited in Late Jurassic (Tithonian) time, about 135 to 150 m.y. ago, on the basis of radiolaria. These rocks then were incorporated in an accretionary wedge prior to the intrusion of gabbroic magma 95 m.y. ago (U-Pb dating on zircons). Subduction (metamorphism of gabbro and surrounding sedimentary rocks to blueschist grade) closely followed intrusion at about 92 m.y. ago (U-Pb dating on metamorphic titanite and “plagioclase” = albite + pumpellyite ± quartz). The brief interval between intrusion and subduction confirms the idea that the gabbro was intruded into the accretionary wedge, essentially at the site of plate convergence. The much longer interval (about 40 to 55 m.y.) between deposition and subduction reveals that the Franciscan had a long presubduction history and provides a time frame within which more speculative concepts such as extensive northward translation of the Franciscan must be constrained.

  3. Detrital U-Pb Zircon Dating of the Cenozoic Metamorphic Terrane in Taiwan Orogenic Belt and its Tectonic Implication

    NASA Astrophysics Data System (ADS)

    Tsai, W.; Lee, Y.

    2011-12-01

    The Taiwan orogen resulted from the collision between the Philippine Sea plate and Eurasia plate since 6.5 Ma and comprises four geologic provinces. From east to west, they are the Coastal Range, the Backbone Range, the Hsuehshan Range, and the Western Foothills. The Coastal Range belongs to Philippine Sea plate. The Backbone Range and Hsuehshan Range are metamorphic terrane are composed of Cenozoic metamorphic terrane and pre-Tertianay metamorphic basement. The Cenozoic metamorphic terrane are lack of fossil and cut by several major faults that results in hard to obtain deposition age and stratigraphic correlation relationship. Here we analysis of more than 3000 grains of detrital U-Pb zircon ages to obtain the age spectrum from Eocene to Miocene metamorphic terrane. The major ages of the Eocene strata are less than 500 Ma; on the contrast the Miocene strata have high percentage of 1800 Ma. Instead of older ages (>100Ma) we found several groups of young U-Pb zircon age, ~39 Ma, ~ 44Ma, ~50 Ma in Eocene strata and 22~25 Ma in Miocene strata which are related with Cenozoic magmatism events in continental margin of Eurasia Plate. This young U-Pb zircon ages indicates the strata age should be younger or similar with these ages. The Eocene strata have been cut by several thrust faults and separated into different blocks. The metamorphic grade increases from west to east of the blocks. The U-Pb Zircon ages indicate the deposition age of the Eocene strata are similar (40Ma) but with different metamorphic grade across the major thrust fault that infers that those thrust faults are preexisting normal faults and are reactive as thrust fault during recently deformation. We also found that the major tectonic boundary "Lishan fault" is unconformity rather than faulting relationship.

  4. Fluid-absent metamorphism in the Adirondacks

    NASA Astrophysics Data System (ADS)

    Valley, J. W.

    Results on late Proterozoic metamorphism of granulite in the Adirondacks are presented. There more than 20,000 sq km of rock are at granulite facies. Low water fugacites are implied by orthopyroxene bearing assemblages and by stability of k'spar-plag-quartz assemblages. After mentioning the popular concept of infiltration of carbon dioxide into Precambrian rocks and attendent generation of granulite facies assemblages, several features of Adirondack rocks pertinent to carbon dioxide and water during their metamorphism are summarized: wollastonite occurs in the western lowlands; contact metamorphism by anorthosite preceeding granulite metamorphism is indicated by oxygen isotopes. Oxygen fugacity lies below that of the QFM buffer; total P sub water + P sub carbon dioxide determined from monticellite bearing assemblages are much less than P sub total (7 to 7.6 kb). These and other features indicate close spatial association of high- and low-P sub carbon dioxide assemblages and that a vapor phase was not present during metamorphism. Thus Adirondack rocks were not infiltrated by carbon dioxide vapor. Their metamorphism, at 625 to 775 C, occurred either when the protoliths were relatively dry or after dessication occurred by removal of a partial melt phase.

  5. Fluid-absent metamorphism in the Adirondacks

    NASA Technical Reports Server (NTRS)

    Valley, J. W.

    1986-01-01

    Results on late Proterozoic metamorphism of granulite in the Adirondacks are presented. There more than 20,000 sq km of rock are at granulite facies. Low water fugacites are implied by orthopyroxene bearing assemblages and by stability of k'spar-plag-quartz assemblages. After mentioning the popular concept of infiltration of carbon dioxide into Precambrian rocks and attendent generation of granulite facies assemblages, several features of Adirondack rocks pertinent to carbon dioxide and water during their metamorphism are summarized: wollastonite occurs in the western lowlands; contact metamorphism by anorthosite preceeding granulite metamorphism is indicated by oxygen isotopes. Oxygen fugacity lies below that of the QFM buffer; total P sub water + P sub carbon dioxide determined from monticellite bearing assemblages are much less than P sub total (7 to 7.6 kb). These and other features indicate close spatial association of high- and low-P sub carbon dioxide assemblages and that a vapor phase was not present during metamorphism. Thus Adirondack rocks were not infiltrated by carbon dioxide vapor. Their metamorphism, at 625 to 775 C, occurred either when the protoliths were relatively dry or after dessication occurred by removal of a partial melt phase.

  6. A rift-related origin for regional medium-pressure, high-temperature metamorphism

    NASA Astrophysics Data System (ADS)

    Tucker, Naomi M.; Hand, Martin; Payne, Justin L.

    2015-07-01

    Crustal-scale exhumation during the Alice Springs Orogeny (c. 450-320 Ma) in central Australia has exposed a region of medium-pressure, high-temperature metasedimentary and metabasic rocks that comprise the Harts Range Group (HRG). Similarities in the detrital zircon age spectra between the HRG and surrounding unmetamorphosed, intraplate late Neoproterozoic-Cambrian basin sequences suggest that the HRG is a highly metamorphosed equivalent of these successions. Calculated phase equilibria modelling and thermobarometry constrain peak metamorphic conditions to ˜ 880 °C and 10.5 kbar, and ˜ 680 °C and 5.5-8.0 kbar, in the structurally lowest and highest parts of the HRG, respectively. Metamorphic conditions also indicate that burial occurred along a near-linear moderately-high apparent thermal gradient, recorded by the prograde development of andalusite-bearing mineral assemblages at shallower structural levels. Prograde and peak metamorphism was associated with voluminous intrusive and extrusive mafic magmatism, the development of a coarse layer-parallel fabric and north-directed normal shear-sense kinematics. Collectively, these point to an extensional regime. Furthermore, burial and metamorphism at c. 480-460 Ma was concurrent with a shallow epicontinental marine environment and ongoing sedimentation in central Australia. Accordingly, the deep burial, metamorphism and deformation of the HRG to mid-lower crustal depths (˜ 20- 35 km) must be justified in the context of the broader intraplate basin evolution at this time. It is difficult to reconcile medium-pressure, high-temperature metamorphism of the HRG with deep burial by tectonic overthickening which is commonly assumed to be the case. In contrast, metamorphism of the HRG seems more compatible with burial within a deep rift-style basin driven by high heat flow and mafic magmatism, suggesting that regional medium-pressure metamorphic terranes are not necessarily reflective of compressional thickening of the

  7. Magmatism and metamorphism linked to the accretion of continental blocks south of the Hindu Kush, Afghanistan

    NASA Astrophysics Data System (ADS)

    Faryad, Shah Wali; Collett, Stephen; Petterson, Mike; Sergeev, Sergey A.

    2013-08-01

    Metamorphic basement rocks in the southern part of the Western Hindu Kush at contact with the Kabul and Helmand crustal blocks were investigated to elucidate pressure-temperature variation and relative time relations among different metamorphic rocks. The rocks are represented by Proterozoic amphibolite facies para-/orthogneisses and migmatites with low-grade Paleozoic volcano-sedimentary sequences. Major- and trace-element geochemistry from two orthogneiss bodies and geochronological data, including new SHRIMP analyses on zircon from one of these bodies shows that they are derived from granitic rocks that related to two different magmatic arcs of Triassic and Cretaceous ages. The Triassic granites are common in the Western Hindu Kush where they intrude basement units; the Cretaceous granitic belt crosses the Afghan Central blocks south of the Hindu Kush Mountains. Three different metamorphic events have been distinguished in the southern part of Western Hindu Kush. Based on an unconformity between basement units and Carboniferous cover sequences, the first two amphibolite and greenschist facies metamorphic events are Proterozoic and Pre-Carboniferous in age respectively. The third metamorphism was recognized in Triassic and Cretaceous granitic rocks near to contact with the Kabul Block. It is of Eocene age and reached medium pressure amphibolite facies conditions. This event is genetically linked to the collision of India and Eurasia which produced a series of trans-Afghan Central block magmatic arcs and crustal scale deformation.

  8. Life-history differences in age-dependent expressions of multiple ornaments and behaviors in a lekking bird.

    PubMed

    Kervinen, Matti; Lebigre, Christophe; Alatalo, Rauno V; Siitari, Heli; Soulsbury, Carl D

    2015-01-01

    Age is a major factor explaining variation in life-history traits among individuals with typical patterns of increasing trait values early in life, maximum trait expression, and senescence. However, age-dependent variation in the expressions of sexually selected traits has received less attention, although such variation underpins differences in male competitive abilities and female preference, which are central to sexual selection. In contrast to previous studies focusing on single traits, we used repeated measures of seven sexually selected morphological and behavioral traits in male black grouse (Tetrao tetrix) to quantify the effects of age and life span on their expressions and quantified this variation in relation to male reproductive effort. Trait expression increased with age, but long-lived males had a slower increase and delayed maxima in trait values compared with short-lived males. There was evidence of terminal investment (increasing trait values during the last breeding season) in some traits and senescence in all traits. These trait dynamics were largely explained by the timing of male peak lekking effort. This study shows that fully understanding the variation in sexually selected traits and fitness benefits associated with sexual selection requires accounting for the complex interaction among individual age, life span, and the timing of individuals' investment in reproduction. PMID:25560550

  9. Ages of flow units in the far eastern maria and implications for basin-filling history

    NASA Technical Reports Server (NTRS)

    Boyce, J. M.; Jonnson, D. A.

    1978-01-01

    The spatial distribution of major units of uniform relative age exposed in the far eastern maria and Mare Humorum was determined using a crater density mapping technique. Correlation of crater densities and radiometric ages of Apollo and Luna landing sites provided estimates of the absolute ages for the units. The combination of such data with relative age data from previous crater morphology studies produced a complete map of the distribution of major age units in the lunar near-side maria. The map shows that there are young (2.5 + or - 0.5 billion years old) mare basalts in the eastern maria, although most young flows occur in the western maria. The vents for the young flows generally are found along the edges of basins. Because old mare units (greater than 3.5 billion years old) are also commonly found around the edges of the basins, it is suggested that the basins were subsiding during filling, probably as a result of isostatic compensation due to the weight of the lava.

  10. [History and poetry in women's biological twilight: menopause and old age].

    PubMed

    Cruz y Hermida, Julio

    2011-01-01

    This is a poetical and historical approach to the last biological stages of the evolutive development of women, namely menopause and old age. It starts with the passages found in Egyptian Papirii such as Ebers or Smith, dated 1500-2000 BC, which describe, among other symptoms, the sweating and hig body temperatures caused by the diminishing hormon secretion of the ovaries. Other important works on the subject, some of them written in the 20th century and some others composed before that date, are also quoted, such as the Edad Crítica (Critical Age) by Dr. Marañon. The final stage of a woman's life, old age, is presented through the famous sonet "Alfa y Omega" (Alpha and Omega) by poet Manuel Machado. Using poetical strokes, the author conveys an image of the many phisiopatological consequences of old age in women: osteoporosis, genital prolapse, urine incontinence and "wrinkles" ("old age is neither shown by white hair nor by wrinkles but by the heart"). The work finishes with the famous statement uttered by Napoleon Bona-parte: "God wanted to be a writer: Man is His prose; His poetry, Women". The same poetry that Dr. Cruz y Hermida has found through the complexities of the evolutive process of feminine biology. PMID:23350338

  11. The discovery and significance of the northeastern Jiangxi Province ophiolite (NEJXO), its metamorphic peridotite and associated high temperature-high pressure metamorphic rocks

    NASA Astrophysics Data System (ADS)

    Guoqing, Zhou

    The NEJXO with a N.E.-S.W. elongation occurs in the mid-Lower Qigong Group, under which lies the Jiuling Group (1401 Ma) and above which lies the Shangshu Group (817 ± 87 Ma), so that the age of NEJXO is defined to be Proterozoic between 1401 Ma and 817 ± 87 Ma. The sediments of the Jiuling Group show evidence of continental derivation, but the Qigong Group and Shangshu Group are characterised by CA volcanic rocks and probably represent a gradually growing island-arc. Thus, we regard the NEJXO as occurring in a back-island-arc basin between the ancient continent and the island-arc. On the whole, the main members of dismembered ophiolite are all present. The metamorphic periodotite present in them, is considered to be especially important, because it may be the sole representative of the older mantle present and it differs from those younger. The high-T metamorphic rocks associated with the NEJXO are various hornstones and melilite marble, whereas the high-P metamorphic rocks are aragonite-jadeite-glaucophane schist and schistose lawsonite marble. From the fact that high-P metamorphism was superimposed on the high-T metamorphic rocks, it may be suggested that early tension (at opening stage) and late compression (at closing stage) occurred during the development of the basin.

  12. Syn-extensional plutonism and peak metamorphism in the albion-raft river-grouse creek metamorphic core complex

    USGS Publications Warehouse

    Strickland, A.; Miller, E.L.; Wooden, J.L.; Kozdon, R.; Valley, J.W.

    2011-01-01

    The Cassia plutonic complex (CPC) is a group of variably deformed, Oligocene granitic plutons exposed in the lower plate of the Albion-Raft River- Grouse Creek (ARG) metamorphic core complex of Idaho and Utah. The plutons range from granodiorite to garnet-bearing, leucogranite, and during intrusion, sillimanite- grade peak metamorphism and ductile attenuation occurred in the country rocks and normal-sense, amphibolite-grade deformation took place along the Middle Mountain shear zone. U-Pb zircon geochronology from three variably deformed plutons exposed in the lower plate of the ARG metamorphic core complex revealed that each zircon is comprised of inherited cores (dominantly late Archean) and Oligocene igneous overgrowths. Within each pluton, a spread of concordant ages from the Oligocene zircon overgrowths is interpreted as zircon recycling within a long-lived magmatic system. The plutons of the CPC have very low negative whole rock ??Nd values of -26 to -35, and initial Sr values of 0.714 to 0.718, consistent with an ancient, crustal source. Oxygen isotope ratios of the Oligocene zircon overgrowths from the CPC have an average ??18O value of 5.40 ?? 0.63 permil (2SD, n = 65) with a slight trend towards higher ??18O values through time. The ??18O values of the inherited cores of the zircons are more variable at 5.93 ?? 1.51 permil (2SD, n = 29). Therefore, we interpret the plutons of the CPC as derived, at least in part, from melting Archean crust based on the isotope geochemistry. In situ partial melting of the exposed Archean basement that was intruded by the Oligocene plutons of the CPC is excluded as the source for the CPC based on field relationships, age and geochemistry. Correlations between Ti and Hf concentrations in zircons from the CPC suggest that the magmatic system may have become hotter (higher Ti concentration in zircon) and less evolved (lower Hf in zircon concentration) through time. Therefore, the CPC represents prolonged or episodic magmatism

  13. Social life histories: jackdaw dominance increases with age, terminally declines and shortens lifespan

    PubMed Central

    Verhulst, Simon; Geerdink, Moniek; Salomons, H. Martijn; Boonekamp, Jelle J.

    2014-01-01

    Behaviour may contribute to changes in fitness prospects with age, for example through effects of age-dependent social dominance on resource access. Older individuals often have higher dominance rank, which may reflect a longer lifespan of dominants and/or an increase in social dominance with age. In the latter case, increasing dominance could mitigate physiological senescence. We studied the social careers of free-living jackdaws over a 12 year period, and found that: (i) larger males attained higher ranks, (ii) social rank increased with age within individuals, and (iii) high-ranked individuals had shorter lifespan suggesting that maintaining or achieving high rank and associated benefits comes at a cost. Lastly, (iv) social rank declined substantially in the last year an individual was observed in the colony, and through its effect on resource access this may accelerate senescence. We suggest that behaviour affecting the ability to secure resources is integral to the senescence process via resource effects on somatic state, where behaviour may include not only social dominance, but also learning, memory, perception and (sexual) signalling. Studying behavioural effects on senescence via somatic state may be most effective in the wild, where there is competition for resources, which is usually avoided in laboratory conditions. PMID:25100696

  14. Integrating Teaching about the Little Ice Age with History, Art, and Literature.

    ERIC Educational Resources Information Center

    Glenn, William Harold

    1996-01-01

    Discusses climate change during the Little Ice Age as experienced during several historical events, including the settlement and demise of the Norse Greenland colonies, the landing of the Pilgrims at Plymouth, and both the Battle of Trenton and Washington's encampment at Valley Forge during the American Revolution. Associated artistic and literary…

  15. History of the USDA Human Nutrition Research Center on Aging at Tufts University

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The Jean Mayer United States Department of Agriculture Human Nutrition Research Center on Aging at Tufts University, while quite a mouthful, is aptly named, since it has contributed substantially to the legacy of Jean Mayer, to the scientific stature of the USDA and, in Atwater’s tradition, to the d...

  16. School-Age Prework Experiences of Young People with a History of Specific Language Impairment

    ERIC Educational Resources Information Center

    Durkin, Kevin; Fraser, Jill; Conti-Ramsden, Gina

    2012-01-01

    Young people with specific language impairment (SLI) are at risk for poorer outcomes with respect to employment in adulthood, yet little is known of how early school-age prework experiences prepare them for the job market. This study examined whether young people with SLI engage in similar types of early work experiences as their typically…

  17. Teaching the Nuclear Age: A History Institute for Teachers. Footnotes. Volume 14, Number 5

    ERIC Educational Resources Information Center

    Kuehner, Trudy

    2009-01-01

    On March 28-29, 2009, FPRI's Wachman Center hosted 43 teachers from across the country for a weekend of discussion on teaching the nuclear age. In his opening remarks, Walter A. McDougall observed that although students today are not made to crawl under their desks in air raid drills, that atomic power remains, and it is still necessary to raise a…

  18. Unroofing history of a suture zone in the Himalaya of Pakistan by means of fission-track annealing ages

    USGS Publications Warehouse

    Zeitler, P.K.; Tahirkheli, R.A.K.; Naeser, C.W.; Johnson, N.M.

    1982-01-01

    The uplift history of the Swat Valley and Hazara region of northwestern Pakistan has been established using 22 fission-track dates on apatite, zircon and sphene. A major fault, the Main Mantle Thrust (MMT) strikes east-west across the Swat Valley, separates regions of markedly differing fission-track age regimesm, and may be a suture zone separating an extinct island arc terrane on the north from the Indian plate to the south. Fission-track ages ranging from about 55 to 58 m.y. for sphene, 18 to 53 m.y. for zircon, and 9 to 17 m.y. for apatite were obtained from the region north of the MMT. To the south the fission-track age ranges are 20 to 25 m.y. for sphene, 17 to 26 m.y. for zircon, and 16 to 23 m.y. for apatite. Disparate zircon and sphene ages on each side of the MMT imply different cooling histories for each side of the fault prior to 15 m.y. Similar apatite ages on both sides of the fault imply similar cooling histories during the past 15 m.y. This may indicate that faulting ceased by 15 m.y. Mean uplift rates have been derived from the fission-track data using mainly the mineral-pair method. Uplift rates in the region north of the MMT increased from 0.07 to 0.20 mm/yr during the period 55 to 15 m.y. South of the fault, uplift rates averaged in excess of 0.70 mm/yr for the period 25 to 15 m.y. During the past 15 m.y. uplift across the MMT in the Swat Valley showsno discontinuities, ranging from 0.16 mm/yr in the south to 0.39 mm/yr in the north. A plausible interpretation for the fission-track uplift data has the MMT verging to the south with overthrusting taking place at a depth between 3.5 and 6.0 km, juxtaposing two terranes that were originally separated by a substantial, but unknown distance. In this model, regional uplift followed cessation of faulting just prior to 15 m.y. ?? 1982.

  19. Diffuse white matter tract abnormalities in clinically normal ageing retired athletes with a history of sports-related concussions

    PubMed Central

    Tremblay, Sebastien; Henry, Luke C.; Bedetti, Christophe; Larson-Dupuis, Camille; Gagnon, Jean-François; Evans, Alan C.; Théoret, Hugo; Lassonde, Maryse

    2014-01-01

    Sports-related concussions have been shown to lead to persistent subclinical anomalies of the motor and cognitive systems in young asymptomatic athletes. In advancing age, these latent alterations correlate with detectable motor and cognitive function decline. Until now, the interacting effects of concussions and the normal ageing process on white matter tract integrity remain unknown. Here we used a tract-based spatial statistical method to uncover potential white matter tissue damage in 15 retired athletes with a history of concussions, free of comorbid medical conditions. We also investigated potential associations between white matter integrity and declines in cognitive and motor functions. Compared to an age- and education-matched control group of 15 retired athletes without concussions, former athletes with concussions exhibited widespread white matter anomalies along many major association, interhemispheric, and projection tracts. Group contrasts revealed decreases in fractional anisotropy, as well as increases in mean and radial diffusivity measures in the concussed group. These differences were primarily apparent in fronto-parietal networks as well as in the frontal aspect of the corpus callosum. The white matter anomalies uncovered in concussed athletes were significantly associated with a decline in episodic memory and lateral ventricle expansion. Finally, the expected association between frontal white matter integrity and motor learning found in former non-concussed athletes was absent in concussed participants. Together, these results show that advancing age in retired athletes presenting with a history of sports-related concussions is linked to diffuse white matter abnormalities that are consistent with the effects of traumatic axonal injury and exacerbated demyelination. These changes in white matter integrity might explain the cognitive and motor function declines documented in this population. PMID:25186429

  20. Permo-Carboniferous granitoids with Jurassic high temperature metamorphism in Central Pontides, Northern Turkey

    NASA Astrophysics Data System (ADS)

    Gücer, Mehmet Ali; Arslan, Mehmet; Sherlock, Sarah; Heaman, Larry M.

    2016-04-01

    likely that peak metamorphism took place during the Jurassic as reflected by the U-Pb zircon ages (199-158 Ma) and also 40Ar/39Ar from hornblende/biotite (163-152 Ma). The four biotite 40Ar/39Ar average ages from the rock samples are ca. 156 Ma, suggesting that the metamorphic rocks cooled to 350-400 °C at ca. 156 Ma. Conclusively, the Devrekani metamorphic rocks can be ascribed as products of Permo-Carboniferous continental arc magmatism overprinted by Jurassic metamorphism in the northern Central Pontides.

  1. Pre-Cenozoic metamorphism and deformation of Lesser Himalayan rocks in central Nepal

    NASA Astrophysics Data System (ADS)

    Martin, A. J.; Copeland, P.

    2009-12-01

    Many previous studies have found pre-Cenozoic Lesser Himalayan muscovite 40Ar/39Ar dates, often accompanied by poorly-defined age plateaus produced during step heating. In the Annapurna Range of central Nepal, we find that muscovite from two of seven studied Lesser Himalayan rocks yields pre-Cenozoic dates. Muscovite from a Lesser Himalayan sample from the Marsyangdi river valley has a poorly defined plateau at c. 90 Ma and a total gas age of c. 97 Ma and muscovite from a Lesser Himalayan sample from the Modi Khola valley also has a poorly defined plateau, in this sample at c. 95 Ma, and a total gas age of c. 241 Ma. There are at least two possible interpretations of the tectonic significance of these dates. One option is that cooling or muscovite growth below the closure temperature occurred at c. 95 Ma (or perhaps at c. 240 Ma). Problems with this explanation include the very wide range of pre-Cenozoic dates found in different samples from multiple studies and the absence of other evidence for mid-Cretaceous tectonism and metamorphism. Our preferred interpretation is that our pre-Cenozoic dates and corresponding poor plateaus from step-heating result from muscovite growth and cooling at some time prior to 95 Ma followed by partial Ar loss during Cenozoic Himalayan metamorphism to a peak temperature below the closure temperature for Ar in muscovite of about 350 °C. The Lesser Himalayan sample from the Modi Khola valley bears garnet and reached peak metamorphic conditions of 9±2 kbar at 560±70 °C. Because the peak temperature during Cenozoic metamorphism did not exceed about 350 °C, garnet growth and metamorphism to the peak recorded conditions must have occurred prior to the Cenozoic Himalayan orogeny. Spiraling Y and Cr zoning in these garnets and deflected external foliation rule out pre- and post-tectonic garnet growth, respectively, revealing that deformation and foliation formation accompanied the pre-Cenozoic metamorphism of these Lesser Himalayan rocks

  2. Low-grade, M1 metamorphism of the western metamorphic belt near Juneau, Alaska

    SciTech Connect

    Himmelberg, G.R. . Dept. of Geology); Brew, D.A.; Ford, A.B. )

    1993-04-01

    The western metamorphic belt is part of the Coast plutonic-metamorphic complex of western Canada and southeastern Alaska that developed as a result of tectonic overlap and/or compressional thickening of crustal rocks during collision of the Alexander terrane and Gravina assemblage on the west against the Yukon Prong and Stikine terranes to the east. Sub-greenschist to lower greenschist facies metabasalts exposed along the west end of the western metamorphic belt near Juneau, Alaska record the earliest metamorphic event (M1). These low-grade rocks are gradational with younger, higher-grade assemblages that define an inverted metamorphic gradient (metamorphic event M5). The most common metamorphic mineral assemblages are chlorite-epidote-actinolite with or without pumpellyite and stilpnomelane. There is no systematic distribution of metamorphic mineral assemblages in the study area, and all assemblages are in the pumpellyite-actinolite facies near the transition to the lower greenschist facies. Different low-variance assemblages can be attributed to minor differences in pressure, temperature, or X[sub CO[sub 2

  3. Metamorphism and aqueous alteration in low petrographic type ordinary chondrites

    NASA Technical Reports Server (NTRS)

    Xie, T.; Lipschutz, M. E.; Sears, D. W. G.; Guimon, R. K.; Jie, Lu; Benoit, P. H.; O'D. Alexander, C. M.; Wright, Ian; Pillinger, C.; Morse, A. D.; Hutchison, Robert

    1995-01-01

    In order to investigate the relative importance of dry metamorphism and aqueous alteration in the history of chondruies, chondruies were hand-picked from the Semarkona (petrographic type 3.0), Bishunpur (3. 1), Chainpur (3.4), Dhajala (3.8) and Allegan (5) chondrites, and matrix samples were extracted from the first three ordinary chondrites. The thermoluminescence (TL) properties of all the samples were measured, and appropriate subsets of the samples were analyzed by electron-microprobe and radiochemical neutron activation and the water and H-isotopic composition determined. The TL data for chondrules from Semarkona and Bishunpur scatter widely showing no unambiguous trends, although group B1 chondrules tend to have lower sensitivities and lower peak temperatures compared with group A5 chondrules. It is argued that these data reflect the variety of processes accompanying chondrule formation. The chondrules show remarkably uniform contents of the highly labile elements, indicating mineralogical control on abundance and volatile loss from silicates and loss and recondensation of mobile chalcophiles and siderophiles in some cases. Very high D/H values (up to approx. 8000% SMOW) are observed in certain Semarkona chondrules, a confirmation of earlier work. With increasing petrographic type, mean TL sensitivities of the chondrules increase, the spread of values within an individual meteorite decreases, and peak temperatures and peak widths show trends indicating that the TL is mainly produced by feldspar and that dry, thermal metamorphism is the dominant secondary process experienced by the chondrules. The TL sensitivities of matrix samples also increase with petrographic type. Chainpur matrix samples show the same spread of peak temperatures and peak widths as Chainpur chondruies, indicating metamorphism-related changes in the feldspar are responsible for the TL of the matrix. The TL data for the Semarkona and Bishunpur matrix samples provide, at best, only weak

  4. Teaching Igneous and Metamorphic Petrology Through Guided Inquiry Projects

    NASA Astrophysics Data System (ADS)

    McMillan, N. J.

    2003-12-01

    Undergraduate Petrology at New Mexico State University (GEOL 399) has been taught using three, 5-6 week long projects in place of lectures, lab, and exams for the last six years. Reasons for changing from the traditional format include: 1) to move the focus from identification and memorization to petrologic thinking; 2) the need for undergraduate students to apply basic chemical, structural, and field concepts to igneous and metamorphic rocks; 3) student boredom in the traditional mode by the topic that has captivated my professional life, in spite of my best efforts to offer thrilling lectures, problems, and labs. The course has three guided inquiry projects: volcanic, plutonic, and pelitic dynamothermal. Two of the rock suites are investigated during field trips. Each project provides hand samples and thin sections; the igneous projects also include whole-rock major and trace element data. Students write a scientific paper that classifies and describes the rocks, describes the data (mineralogical and geochemical), and uses data to interpret parameters such as tectonic setting, igneous processes, relationship to phase diagrams, geologic history, metamorphic grade, metamorphic facies, and polymetamorphic history. Students use the text as a major resource for self-learning; mini-lectures on pertinent topics are presented when needed by the majority of students. Project scores include evaluation of small parts of the paper due each Friday and participation in peer review as well as the final report. I have found that petrology is much more fun, although more difficult, to teach using this method. It is challenging to be totally prepared for class because students are working at different speeds on different levels on different aspects of the project. Students enjoy the course, especially the opportunity to engage in scientific investigation and debate. A significant flaw in this course is that students see fewer rocks and have less experience in rock classification

  5. Chemical and physical studies of type 3 chondrites. VIII - Thermoluminescence and metamorphism in the CO chondrites

    NASA Technical Reports Server (NTRS)

    Keck, Bradly D.; Sears, Derek W. G.

    1987-01-01

    A possible relationship between the thermoluminescence (TL) properties of CO chondrites and their metamorphic history was investigated by measuring the TL properties of seven normal CO chondrites and of the Colony and the Allan Hills A77307 (ALHA 77307) CO-related chondrites. With the exception of Colony and ALHA 77307, whose maximum induced TL emission is at approximately 350 C, the CO chondrites were found to exhibit two TL peaks: a 130 C and a 250 C peaks. Among the CO chondrites, the 130 C peak showed a 100-fold range in TL sensitivity and was found to correlate with various metamorphism-related phenomena, such as silicate heterogeneity, metal composition, and McSween's metamorphic subtypes. The peak at 250 did not show these correlations and, with exception of Colony, showed little variation.

  6. The combined effects of bacterial symbionts and aging on life history traits in the pea aphid, Acyrthosiphon pisum.

    PubMed

    Laughton, Alice M; Fan, Maretta H; Gerardo, Nicole M

    2014-01-01

    While many endosymbionts have beneficial effects on hosts under specific ecological conditions, there can also be associated costs. In order to maximize their own fitness, hosts must facilitate symbiont persistence while preventing symbiont exploitation of resources, which may require tight regulation of symbiont populations. As a host ages, the ability to invest in such mechanisms may lessen or be traded off with demands of other life history traits, such as survival and reproduction. Using the pea aphid, Acyrthosiphon pisum, we measured survival, lifetime fecundity, and immune cell counts (hemocytes, a measure of immune capacity) in the presence of facultative secondary symbionts. Additionally, we quantified the densities of the obligate primary bacterial symbiont, Buchnera aphidicola, and secondary symbionts across the host's lifetime. We found life history costs to harboring some secondary symbiont species. Secondary symbiont populations were found to increase with host age, while Buchnera populations exhibited a more complicated pattern. Immune cell counts peaked at the midreproductive stage before declining in the oldest aphids. The combined effects of immunosenescence and symbiont population growth may have important consequences for symbiont transmission and maintenance within a host population. PMID:24185857

  7. The frequency of aneuploidy in cultured lymphocytes is correlated with age and gender but not with reproductive history.

    PubMed Central

    Nowinski, G P; Van Dyke, D L; Tilley, B C; Jacobsen, G; Babu, V R; Worsham, M J; Wilson, G N; Weiss, L

    1990-01-01

    The clinical significance of low numbers of aneuploid cells in routine cytogenetic studies of cultured lymphocytes is not always clear. We compared the frequencies of chromosome loss and gain among five groups of subjects whose karyotypes were otherwise normal; these groups were (1) subjects studied because of multiple miscarriages, (2) parents of live borns with autosomal trisomy, (3) subjects studied because they had a relative with Down syndrome, (4) an age-matched control group of phenotypically normal adults studied for other reasons (e.g., parent of a dysmorphic child or member of a translocation family), and (5) other mostly younger and phenotypically abnormal subjects who could not be assigned to the first four groups (e.g., individuals with multiple congenital anomalies or mental retardation). No significant age, sex, or group effects were observed for autosomal loss (hypodiploidy) or gain (hyperdiploidy). Autosomal loss was inversely correlated with relative chromosome length, but autosomal gain was not. Sex-chromosome gain was significantly more frequent in females than in males, but sex-chromosome loss was not significantly different between the sexes. Significant age effects were observed for both gain and loss of sex chromosomes. When age and sex were accounted for, the frequencies of sex-chromosome loss and gain were not significantly different among the five clinical groups. In general, low numbers of aneuploid cells are not clinically important when observed in blood chromosome preparations of subjects studied because of multiple miscarriages or a family history of autosomal trisomy. PMID:2339703

  8. UHP metamorphism in the Western Mediterranean : A tale of a Tethys fragment (Edough Massif, NE Algeria) and its geodynamic consequences

    NASA Astrophysics Data System (ADS)

    Bruguier, Olivier; Bosch, Delphine; Caby, Renaud; Fernandez, Laure; Abdallah, Nachida; Arnaud, Nicolas; Hammor, Dalila; Laouar, Rabah; Mechati, Medhi; Monié, Patrick; Ouabadi, Aziouz; Toubal, Abder

    2016-04-01

    The Edough Massif of NE Algeria is part of the Maghrebides, a peri-Mediterranean Alpine belt that extends from Morocco to Tunisia. The belt resulted mainly from the eastward retreat of the Tethyan slab and from the drift of continental fragments, some of which finally collided with the north African margin. In this study we report the recent discovery of metamorphic diamonds (5-30 μm in size) included in a garnet megacryst and identified by Raman spectroscopy and the characteristic sharp band at 1332 cm‑1 for crystalline diamond. The studied megacryst was taken from a weathered actinolitite horizon inserted within a major mylonite-ultramylonite band, which outcrops at the base of an allochtonous oceanic unit thrust onto the African paleomargin. The host garnet is almandine-dominant with a sharp increase in grossular component in the rim and is rich in exsolution of small acicular rutile needles. Major and trace elements show a gradual but significant zonation from core to rim characterized by a decrease in HREE, Y and Mn, typical of a prograde growth in a closed system. Trace element analyses of large prismatic rutile (up to 300 μm) indicate that the host metamorphic rock was a mafic protolith of MORB affinity and the Zr-in-rutile thermometry indicates a temperature range of 724-778°C for rutile growth. U-Pb analyses of these large rutile crystals provide an age of 32.4 ± 3.3 Ma interpreted as dating the prograde subduction stage of the mafic protolith. Minute zircons (≤ 30μm), disseminated in the garnet, display a multifaceted appearance and low Th/U ratios consistent with a metamorphic origin. The lack of HREE depletion in these zircons indicates that their metamorphic growth was not coeval with garnet. U-Pb analyses and Ti-in-zircon thermometry indicate they nucleated at 20.9 ± 2.2 Ma during near isothermal decompression related to exhumation of the UHP units. This study allows bracketing the age of UHP metamorphism in the Western Mediterranean to the

  9. The value of age and medical history for predicting colorectal cancer and adenomas in people referred for colonoscopy

    PubMed Central

    2011-01-01

    Background Colonoscopy is an invasive and costly procedure with a risk of serious complications. It would therefore be useful to prioritise colonoscopies by identifying people at higher risk of either cancer or premalignant adenomas. The aim of this study is to assess a model that identifies people with colorectal cancer, advanced, large and small adenomas. Methods Patients seen by gastroenterologists and colorectal surgeons between April 2004 and December 2006 completed a validated, structured self-administered questionnaire prior to colonoscopy. Information was collected on symptoms, demographics and medical history. Multinomial logistic regression was used to simultaneously assess factors associated with findings on colonoscopy of cancer, advanced adenomas and adenomas sized 6 -9 mm, and ≤ 5 mm. The area under the curve of ROC curve was used to assess the incremental gain of adding demographic variables, medical history and symptoms (in that order) to a base model that included only age. Results Sociodemographic variables, medical history and symptoms (from 8,204 patients) jointly provide good discrimination between colorectal cancer and no abnormality (AUC 0.83), but discriminate less well between adenomas and no abnormality (AUC advanced adenoma 0.70; other adenomas 0.67). Age is the dominant risk factor for cancer and adenomas of all sizes. Having a colonoscopy within the last 10 years confers protection for cancers and advanced adenomas. Conclusions Our models provide guidance about which factors can assist in identifying people at higher risk of disease using easily elicited information. This would allow colonoscopy to be prioritised for those for whom it would be of most benefit. PMID:21899773

  10. ERBB4 Polymorphism and Family History of Psychiatric Disorders on Age-Related Cortical Changes in Healthy Children

    PubMed Central

    Douet, Vanessa; Chang, Linda; Lee, Kristin; Ernst, Thomas

    2015-01-01

    Background Genetic variations in ERBB4 were associated with increased susceptibility for schizophrenia (SCZ) and bipolar disorders (BPD). Structural imaging studies showed cortical abnormalities in adolescents and adults with SCZ or BPD. However, less is known about subclinical cortical changes or the influence of ERBB4 on cortical development. Methods 971 healthy children (ages 3–20 years old; 462 girls and 509 boys) were genotyped for the ERBB4-rs7598440 variants, had structural MRI, and cognitive evaluation (NIH Toolbox ®). We investigated the effects of ERBB4 variants and family history of SCZ and/or BPD (FH) on cortical measures and cognitive performances across ages 3–20 years using a general additive model. Results Variations in ERBB4 and FH impact differentially the age-related cortical changes in regions often affected by SCZ and BPD. The ERBB4-TT-risk genotype children with no FH had subtle cortical changes across the age span, primarily located in the left temporal lobe and superior parietal cortex. In contrast, the TT-risk genotype children with FH had more pronounced age-related changes, mainly in the frontal lobes compared to the non-risk genotype children. Interactive effects of age, FH and ERBB4 variations were also found on episodic memory and working memory, which are often impaired in SCZ and BPD. Conclusions Healthy children carrying the risk-genotype in ERBB4 and/or with FH had cortical measures resembling those reported in SCZ or BPD. These subclinical cortical variations may provide early indicators for increased risk of psychiatric disorders and improve our understanding of the effect of the NRG1–ERBB4 pathway on brain development. PMID:25744101

  11. Implications of IODP Expedition 349 Age Results for the Spreading History of the South China Sea

    NASA Astrophysics Data System (ADS)

    Briais, Anne

    2016-04-01

    The International Ocean Discovery Program (IODP) Expedition 349 in the South China Sea drilled three sites (U1431, U1433, and U1434) into the basaltic crustal basement near the fossil spreading center in the East and Southwest Subbasins. These results provided age constraints on the termination of seafloor spreading in the South China Sea (SCS) basin. Shipboard biostratigraphic analysis of microfossils from the sediment immediately above or between flows in the basaltic basement indicates early Miocene ages: 16.7-17.6 Ma for Site U1431 in the East Subbasin, ~18-21 Ma for Site U1433 in the Southwest Subbasin. Since Expedition 349, Ar/Ar dating of basalt samples from these two sites have confirmed these ages in the east, and have provided an age of 17 Ma in the Southwest. The similarity in crustal age between sites suggests that the last stages of spreading have been coeaval in both the East and Southwest Subbasins, forming a single mid-ocean ridge system with a series of transform faults and discontinuities between the two subbasins. Expedition 349 also drilled Site U1435 on a bathymetric high along the northwestern continent-ocean boundary. Onboard core description, biostratigraphy and magnetostratigraphy revealed that sediment at this site shows a sharp discontinuity at about 33 Ma, interpreted to represent the breakup unconformity and date the beginning of seafloor spreading in the East Subbasin. The results of IODP Exp. 349, as well as results from deep-towed magnetic surveys, thus imply that oceanic seafloor spreading in the SCS, from 33 to ~16-18 Ma, is coeval with a large part of the left-lateral motion along the Ailao Shan-Red River Fault Zone (dated 34 to 17 Ma). This episode of the extension of the South China Sea basin is therefore more likely driven by the extrusion of the Indochina tectonic block resulting from the collision of India with Eurasia than by the subduction of a proto-South China Sea to the south.

  12. Metamorphic fluid flow - a question of scale, crustal depth and bulk rock composition

    SciTech Connect

    Tracy, R.J.; Rye, D.M.

    1985-01-01

    Recent studies have indicated that certain metamorphic rocks interacted with significant volumes of aqueous fluid during their time-integrated mineral reaction history. Rather than demonstrating that pervasive fluid flow is general in metamorphic rocks, these documented cases instead suggest the likelihood of pronounced to extreme channelization of through-going in fluids in deep-seated metamorphic terranes (P>3 kbar). In rocks more shallowly buried, and therefore under low lithostatic stress, pervasive flow along grain boundaries and open microfractures probably occurred, as at Skye and the Skaergaard Complex. In higher pressure metamorphic environments, documented cases of high fluid/rock ratio make a strong case for flow channelized in veins or in impure marble aquifers where pore space and permeability were created by decarbonation reactions driven by infiltration of aqueous fluid. The source of this fluid may commonly be traced to a nearby wet granitic intrusion or quartz vein. As long as the pressurized source of aqueous fluid continued, outward flow was possible as fluid held open the intergranular pore space which was created only at the infiltration/reaction front where a reduction in solid volume accompanied reaction. Cessation or interruption of fluid flow would allow the pore space to close due to porous-rock strength being exceeded by lithostatic stress. Pervasive flow or aqueous fluid in deepseated metamorphic terranes is therefore probably limited to carbonate-bearing lithologies adjacent to sources of major volumes of fluid; otherwise, fluid flow is likely to be localized in fractures or veins.

  13. 40Ar/39Ar impact ages and time-temperature argon diffusion history of the Bunburra Rockhole anomalous basaltic achondrite

    NASA Astrophysics Data System (ADS)

    Jourdan, Fred; Benedix, Gretchen; Eroglu, Ela.; Bland, Phil. A.; Bouvier, Audrey.

    2014-09-01

    The Bunburra Rockhole meteorite is a brecciated anomalous basaltic achondrite containing coarse-, medium- and fine-grained lithologies. Petrographic observations constrain the limited shock pressure to between ca. 10 GPa and 20 GPa. In this study, we carried out nine 40Ar/39Ar step-heating experiments on distinct single-grain fragments extracted from the coarse and fine lithologies. We obtained six plateau ages and three mini-plateau ages. These ages fall into two internally concordant populations with mean ages of 3640 ± 21 Ma (n = 7; P = 0.53) and 3544 ± 26 Ma (n = 2; P = 0.54), respectively. Based on these results, additional 40Ar/39Ar data of fusion crust fragments, argon diffusion modelling, and petrographic observations, we conclude that the principal components of the Bunburra Rockhole basaltic achondrite are from a melt rock formed at ∼3.64 Ga by a medium to large impact event. The data imply that this impact generated high enough energy to completely melt the basaltic target rock and reset the Ar systematics, but only partially reset the Pb-Pb age. We also conclude that a complete 40Ar∗ resetting of pyroxene and plagioclase at this time could not have been achieved at solid-state conditions. Comparison with a terrestrial analog (Lonar crater) shows that the time-temperature conditions required to melt basaltic target rocks upon impact are relatively easy to achieve. Ar data also suggest that a second medium-size impact event occurred on a neighbouring part of the same target rock at ∼3.54 Ga. Concordant low-temperature step ages of the nine aliquots suggest that, at ∼3.42 Ga, a third smaller impact excavated parts of the ∼3.64 Ga and ∼3.54 Ga melt rocks and brought the fragments together. The lack of significant impact activity after 3.5 Ga, as recorded by the Bunburra Rockhole suggests that (1) either the meteorite was ejected in a small secondary parent body where it resided untouched by large impacts, or (2) it was covered by a porous heat

  14. Evidence for multiple metamorphic events in the Adirondack Mountains, N. Y

    SciTech Connect

    McLelland, J.; Lochhead, A.; Vyhnal, C.

    1988-05-01

    Field evidence consisting of: (1) rotated, foliated xenoliths, (2) country rock foliation truncated by isoclinally folded igneous intrusions bearing granulite facies assemblages document one, or more, early dynamothermal event(s) of regional scale and high grade. Early metamorphism resulted in pronounced linear and planar fabric throughout the Adirondacks and preceded the emplacement of the anorthosite-mangerite-charnockite-granite-alaskite (AMCA) suite which contains xenoliths of the metamorphosed rocks. Olivine metagabbros, believed to be approximately contemporaneous with the AMCA-suite, also crosscut and contain xenoliths of, strongly foliated metasediments. These intrusive rocks caused contact metamorphism in the metasediments which locally exhibit both anatectite and restite assemblages. Subsequently, this already complex framework underwent three phases of folding, including an early recumbent isoclinical event, and was metamorphosed to granulite facies P,T conditions. The age of the early metamorphism cannot yet be narrowly constrained, but isotopic results suggest that it may be as young as approx. 1200 Ma or older than approx. 1420 Ma. U-Pb zircon ages indicate emplacement of the AMCA-(metagabbro)-suite in the interval 1160-1130 Ma and place the peak of granulite facies metamorphism between 1070-1025 Ma. The anorogenic character of the AMCA-suite, and the occurrence of metadiabase dike swarms within it, are further evidence of the separate nature of the metamorphic events that precede and postdate AMCA emplacement.

  15. Dating Subduction Zone Metamorphism with Garnet and Lawsonite Geochronology

    NASA Astrophysics Data System (ADS)

    Mulcahy, S. R.; Vervoort, J. D.

    2013-12-01

    Lawsonite [CaAl2Si2O7(OH)2 H2O] is a critical index mineral for high- to ultrahigh-pressure metamorphism associated with subduction. Lawsonite is an important carrier of water into the mantle, a likely contributor to subduction zone seismicity, and a bearer of trace elements that link metamorphism to arc magmatism. Due to its limited pressure-temperature stability, lawsonite can serve as a powerful petrogenetic indicator of specific metamorphic events. Lu-Hf dating of lawsonite, therefore provides a potentially powerful new tool for constraining subduction zone processes in a pressure-temperature window where few successful geochronometers exist. Broad application of lawsonite Lu-Hf geochronology requires constraining the role of pressure-temperature path, lawsonite forming reactions, and the Lu and Hf systematics within lawsonite and other blueschist facies minerals. We are working to address the role of the metamorphic path on the applicability of lawsonite Lu-Hf geochronology within the Franciscan Complex of California. The Franciscan Complex preserves mafic high-grade exotic blocks in melange that underwent a counterclockwise pressure-temperature path wherein garnet, which strongly partitions heavy rare-earth elements, formed prior to lawsonite. Coherent mafic rocks within the Franciscan Complex, however, underwent a clockwise pressure-temperature path and lawsonite growth occurred prior to garnet. We sampled exotic blocks of garnet-hornblendite, garnet-epidote amphibolite, garnet-epidote blueschist, and lawsonite blueschist from the Berkeley Hills and Tiburon Peninsula of California. We collected four samples from coherent lawsonite blueschist across the lawsonite-pumpellyite-epidote isograds in Ward Creek, near Cazadero California. High-grade blocks give ages similar to existing Franciscan geochronology: multi-stage garnet in hornblendite gives the following ages: 171×1.3 Ma (MSWD 2.8) for the core and 159.4×0.9 Ma (MSWD 2.0) for the corresponding rim; 166

  16. Zircon SHRIMP U-Pb dating of metamorphic complexes in the conjunction of the Greater and Lesser Xing'an ranges, NE China: Timing of formation and metamorphism and tectonic implications

    NASA Astrophysics Data System (ADS)

    Miao, Laicheng; Zhang, Fuqin; Zhu, Mingshuai; Liu, Dunyi

    2015-12-01

    Metamorphic complexes, including the Luomahu, Xinkailing and Fengshuigouhe groups, are scattered in the conjunction of the Greater and the Lesser Xing'an ranges, NE China, and have long been interpreted to represent the Precambrian basement of the so-called "Xing'an" and "Songnen" blocks although reliable evidence is lacking. Thin-section examination and mineral assemblage indicate that the protoliths of these metamorphic rocks are mainly meta-sedimentary and meta-volcanic rocks and have experienced greenschist- to amphibolite-facies metamorphism and strong deformation. Zircon SHRIMP U-Pb dating results of the metamorphic complexes and associated pre- or syn-kinematic veins constrained the formation and metamorphic ages of the Luomahuo Group at 175 ± 3 Ma and 159 ± 3 Ma, the Xingkailing Group at 200 ± 2 Ma and 158 ± 3 Ma, and the Fengshuigouhe Group at between 230-310 Ma and 170 ± 3 Ma, respectively. Additionally, all these rocks contain some Late Paleozoic detrital or inherited zircons with ages between 290-390 Ma, but no Precambrian, even if Early Paleozoic, age information was detected from these metamorphic rocks. These new data suggest that the metamorphic complexes were formed during Mesozoic-Late Paleozoic period, rather than in Precambrian as previously inferred, and that all of them underwent metamorphism and deformation during Middle Jurassic between 170-160 Ma. Consequently, these metamorphic complexes are not basement rocks of the so-called Precambrian continental blocks. Instead, there are likely metamorphosed Late Paleozoic-Mesozoic accretionary complexes and/or arc terranes. These results, in combination with published data, illustrate an overall young trend from north to south in the tectonic evolution of the northern Xing'an region. Significantly, the Jurassic (170-160 Ma) metamorphism and deformation event firstly identified by this study from the metamorphic complexes likely recorded the coinstantaneous Mongol-Okhotsk collisional and

  17. Lessons from history: Surviving old age during The Great Depression in the United States.

    PubMed

    Matthews, Sarah H; Dunkle, Ruth E

    2013-12-01

    This paper focuses on 30 couples who received a pension and other services from two private trusts in Detroit, Michigan beginning in 1929 or 1930. Results of the qualitative analysis of case files, which contain notes recorded chronologically for 17 of the couples and then surviving spouses, provide a portrait of older couples' lives prior to a partner's death, circumstances surrounding the death, and changes in the social support systems of widows and widowers until their deaths. Close examination of the experiences of these couples is a reminder of how old age and widowhood were experienced prior to the enactment of public pensions and health insurance in the United States. PMID:24300066

  18. The progenitors of quiescent galaxies at z~2: precision ages and star-formation histories from WFC3/IR spectroscopy

    NASA Astrophysics Data System (ADS)

    Barro, Guillermo

    2013-10-01

    The important "adolescent" epoch at redshifts z 1 to 2 bridges a universe of "adult" galaxies at z<1 to an earlier "childhood" period z>2 when galaxies were dramatically different. During this transition, the early quenching of star formation and later enlargement of compact quiescent galaxies since z 2 remain key unsolved mysteries. We have identified a population of compact star-forming galaxies at 2.5 whose structural properties and number densities suggest an evolutionary connection with the first quiescent galaxies. But demonstrating full consistency between progenitor to descendant populations requires high-precision redshifts, ages, and star formation histories to make reliable links in time. We thus propose adding a 56 orbit G102 survey to GOODS-North. The G102 grism meets the required spectral resolution to resolve stellar population ages and connect progenitors to quiescent galaxies, and perfectly bridges the gap for galaxies at 1ages and star formation histories between their cores and outskirts during the transition era. Given its high value for legacy science, the new data will have no proprietary period.

  19. Zircon response to high-grade metamorphism as revealed by U-Pb and cathodoluminescence studies

    NASA Astrophysics Data System (ADS)

    Siebel, W.; Shang, C. K.; Thern, E.; Danišík, M.; Rohrmüller, J.

    2012-11-01

    Correct interpretation of zircon ages from high-grade metamorphic terrains poses a major challenge because of the differential response of the U-Pb system to metamorphism, and many aspects like pressure-temperature conditions, metamorphic mineral transformations and textural properties of the zircon crystals have to be explored. A large (c. 450 km2) coherent migmatite complex was recently discovered in the Bohemian Massif, Central European Variscides. Rocks from this complex are characterized by granulite- and amphibolite-facies mineral assemblages and, based on compositional and isotopic trends, are identified as the remnants of a magma body derived from mixing between tonalite and supracrustal rocks. Zircon crystals from the migmatites are exclusively large (200-400 μm) and yield 207Pb/206Pb evaporation ages between 342-328 Ma and single-grain zircon fractions analysed by U-Pb ID-TIMS method plot along the concordia curve between 342 and 325 Ma. High-resolution U-Pb SHRIMP analyses substantiate the existence of a resolvable age variability and yield older 206Pb/238U ages (342-330 Ma, weighted mean age = 333.6 ± 3.1 Ma) for inner zone domains without relict cores and younger 206Pb/238U ages (333-320 Ma, weighted mean age = 326.0 ± 2.8 Ma) for rim domains. Pre-metamorphic cores were identified only in one sample (206Pb/238U ages at 375.0 ± 3.9, 420.3 ± 4.4 and 426.2 ± 4.4 Ma). Most zircon ages bracket the time span between granulite-facies metamorphism in the Bohemian Massif (~345 Ma) and the late-Variscan anatectic overprint (Bavarian phase, ~325 Ma). It is argued that pre-existing zircon was variously affected by these metamorphic events and that primary magmatic growth zones were replaced by secondary textures as a result of diffusion reaction processes and replacement of zircon by dissolution and recrystallization followed by new zircon rim growth. Collectively, the results show that the zircons equilibrated during high-grade metamorphism and record

  20. Age-Related Changes in Segmental Body Composition by Ethnicity and History of Weight Change across the Adult Lifespan.

    PubMed

    Tian, Simiao; Morio, Béatrice; Denis, Jean-Baptiste; Mioche, Laurence

    2016-01-01

    This study assessed age-related changes in body composition (specifically in trunk fat and appendicular lean masses), with consideration of body mass index (BMI) at age 20 years (BMI reference age, "BMIref"), ethnicity and lifetime weight change history. A cross-sectional dual-energy X-ray absorptiometry-based dataset was extracted from the U.S. National Health and Nutrition Examination Survey (NHANES) 1999-2004. Only European-American and African-American subjects were used (2705 men, 2527 women). For each gender and ethnicity, 6 analytic cases were considered, based on three BMIref categories (normal, overweight and obese, being 22, 27 and 30 kg/m², respectively) and two weight contexts (stable weight or weight gain across the lifespan). A nonparametric model was developed to investigate age-related changes in body composition. Then, parametric modelling was developed for assessing BMIref- and ethnicity-specific effects during aging. In the stable weight, both genders' and ethnicities' trunk fat (TF) increased gradually; body fat (BF) remained stable until 40 years and increased thereafter; trunk lean (TL) remained stable, but appendicular lean (APL) and body lean (BL) declined from 20 years. In the weight gain context, TF and BF increased at a constant rate, while APL, TL and BL increased until 40-50 years, and then declined slightly. Compared with European-American subjects of both genders, African-American subjects had lower TF and BF masses. Ethnic differences in body composition were quantified and found to remain constant across the lifespan. PMID:27529269

  1. Age-Related Changes in Segmental Body Composition by Ethnicity and History of Weight Change across the Adult Lifespan

    PubMed Central

    Tian, Simiao; Morio, Béatrice; Denis, Jean-Baptiste; Mioche, Laurence

    2016-01-01

    This study assessed age-related changes in body composition (specifically in trunk fat and appendicular lean masses), with consideration of body mass index (BMI) at age 20 years (BMI reference age, “BMIref”), ethnicity and lifetime weight change history. A cross-sectional dual-energy X-ray absorptiometry-based dataset was extracted from the U.S. National Health and Nutrition Examination Survey (NHANES) 1999–2004. Only European-American and African-American subjects were used (2705 men, 2527 women). For each gender and ethnicity, 6 analytic cases were considered, based on three BMIref categories (normal, overweight and obese, being 22, 27 and 30 kg/m2, respectively) and two weight contexts (stable weight or weight gain across the lifespan). A nonparametric model was developed to investigate age-related changes in body composition. Then, parametric modelling was developed for assessing BMIref- and ethnicity-specific effects during aging. In the stable weight, both genders’ and ethnicities’ trunk fat (TF) increased gradually; body fat (BF) remained stable until 40 years and increased thereafter; trunk lean (TL) remained stable, but appendicular lean (APL) and body lean (BL) declined from 20 years. In the weight gain context, TF and BF increased at a constant rate, while APL, TL and BL increased until 40–50 years, and then declined slightly. Compared with European-American subjects of both genders, African-American subjects had lower TF and BF masses. Ethnic differences in body composition were quantified and found to remain constant across the lifespan. PMID:27529269

  2. Diverging Histories of the Liberty Creek and Iceberg Lake Blueschist Bodies, south central Alaska

    NASA Astrophysics Data System (ADS)

    Day, E. M.; Pavlis, T. L.; Amato, J. M.

    2011-12-01

    New studies of the Liberty Creek and Iceberg Lake blueschist bodies of south central Alaska indicate that despite structural similarities, these blueschist bodies are derived from a different protolith and were metamorphosed to blueschist facies at distinctly different times. Both blueschists are located just south of the Border Ranges Fault (BRF) within outcrop belts of the McHugh Complex, a low-grade mélange assemblage that is now known from detrital zircon studies to consist of two distinct assemblages: a Jurassic to Earliest Cretaceous assemblage and a Late Cretaceous assemblage. The BRF is a megathrust system that represents the Late Triassic-Early Jurassic initiation of southern Alaskan subduction. Large scale (1:24,000) mapping revealed similar fabric overprint histories, epitomized by a previously undescribed youngest vertical N-S trending crenulation cleavage in both blueschist bodies which implies a structural correlation despite their separation of ~100 kilometers along strike. Despite structural similarities detrital zircon studies show that the Liberty Creek and Iceberg Lake blueschists do not have a similar maximum age of deposition. Thirteen samples from the Iceberg Lake blueschist were processed, none of which produced detrital zircons. Samples from the McHugh Complex greenschists that surround the Iceberg Lake blueschist produced numerous zircons indicating a Late Jurassic (~160 Ma) maximum age of deposition. Three out of sixteen samples from the Liberty creek blueschist produced detrital zircons indicating maximum depositional ages ranging from Late Jurassic (~160.1 Ma, n=64 grains; ~152.25 Ma, n=68 grains) to Early Cretaceous (~137.1 Ma, n=95 grains). The Late Jurassic dates are consistent with maximum depositional ages determined by Amato and Pavlis (2010) for McHugh Complex rocks along Turnagain Arm near Anchorage, AK. Sisson and Onstott (1986) reported a metamorphic cooling age of 185 Ma for the Iceberg Lake blueschist, thus, although no

  3. The age of the martian meteorite Northwest Africa 1195 and the differentiation history of the shergottites

    SciTech Connect

    Symes, S; Borg, L; Shearer, C; Irving, A

    2007-04-05

    Samarium-neodymium isotopic analyses of unleached and acid-leached mineral fractions from the recently identified olivine-bearing shergottite Northwest Africa 1195 yield a crystallization age of 348 {+-} 19 Ma and an {var_epsilon}{sub Nd}{sup 143} value of +40.1 {+-} 1.3. Maskelynite fractions do not lie on the Sm-Nd isochron and appear to contain a martian surface component with low {sup 147}Sm/{sup 144}Nd and {sup 143}Nd/{sup 144}Nd ratios that was added during shock. The Rb-Sr system is disturbed and does not yield an isochron. Terrestrial Sr appears to have affected all of the mineral fractions, although a maximum initial {sup 87}Sr/{sup 86}Sr ratio of 0.701614 {+-} 16 is estimated by passing a 348 Ma reference isochron through the maskelynite fraction that is least affected by contamination. The high initial {var_epsilon}{sub Nd}{sup 143} value and the low initial {sup 87}Sr/{sup 86}Sr ratio, combined with the geologically young crystallization age, indicate that Northwest Africa 1195 is derived from a source region characterized by a long-term incompatible element depletion. The age and initial Sr and Nd isotopic compositions of Northwest Africa 1195 are very similar to those of Queen Alexandra Range 94201, indicating these samples were derived from source regions with nearly identical Sr-Nd isotopic systematics. These similarities suggest that these two meteorites share a close petrogenetic relationship and might have been erupted from a common volcano. The meteorites Yamato 980459, Dar al Gani 476, Sayh al Uhaymir 005/008, and Dhofar 019 also have relatively old ages between 474-575 Ma and trace element and/or isotopic systematics that are indicative of derivation from incompatible-element-depleted sources. This suggests that the oldest group of meteorites is more closely related to one another than they are to the younger meteorites that are derived from less incompatible-element-depleted sources. Closed-system fractional crystallization of this suite of

  4. Is the onset of the 6th century 'dark age' in Maya history related to explosive volcanism?

    NASA Astrophysics Data System (ADS)

    Nooren, Kees; Hoek, Wim Z.; Van der Plicht, Hans; Sigl, Michael; Galop, Didier; Torrescano-Valle, Nuria; Islebe, Gerald; Huizinga, Annika; Winkels, Tim; Middelkoop, Hans; Van Bergen, Manfred

    2016-04-01

    Maya societies in Southern Mexico, Guatemala and Belize experienced a 'dark age' during the second half of the 6th century. This period, also known as the 'Maya Hiatus', is characterized by cultural downturn, political instability and abandonment of many sites in the Central Maya Lowlands. Many theories have been postulated to explain the occurrence of this 'dark age' in Maya history. A possible key role of a large volcanic eruption in the onset of this 'dark age' will be discussed. Volcanic deposits recovered from the sedimentary archive of lake Tuspán and the Usumacinta-Grijalva delta were studied in detail and the combination of multiple dating techniques allowed the reconstruction of the timing of a large 6th century eruption. Volcanic glass shards were fingerprinted to indicate the source volcano and high resolution pollen records were constructed to indicate the environmental impact of the eruption. Results are compared with available archaeological data and causality with the disruption of Maya civilization will be evaluated.

  5. The Mythology of Metamorphic Fluid Expulsion

    NASA Astrophysics Data System (ADS)

    Connolly, James

    2010-05-01

    Regional metamorphism occurs in an ambiguous rheological regime between the brittle upper crust and ductile sub-lithospheric mantle. This ambiguous position has allowed two schools of thought to develop concerning the nature of metamorphic fluid flow. The classical school holds that metamorphic rocks are inviscid and that any fluid generated by devolatilization is squeezed out of rocks as rapidly as it is produced. According to this school permeability is a dynamic property and fluid flow is upward. In contrast the modern school, selectively uses concepts from upper crustal hydrology that presume implicitly, if not explicitly, that rocks are rigid or, at most, brittle. For the modern school, the details of crustal permeability determine fluid flow and as these details are poorly known almost anything is possible. Reality, to the extent that is reflected by field studies, offers some support to both schools. In particular, evidence of significant lateral and chanellized fluid flow are consistent with flow in rigid media, while evidence for short (104 - 105 y) grain-scale fluid rock interaction during much longer metamorphic events, suggests that reaction-generated grain-scale permeability is sealed rapidly by compaction; a phenomenon that is also essential to prevent extensive retrograde metamorphism. These observations provide a compelling argument for recognizing in conceptual models for metamorphic fluid flow that rocks are neither inviscid nor rigid, but have finite strength. The surprising result of this strength is that the steady state solutions for fluid flow in porous compacting media require that fluid expulsion is channeled into waves of fluid-filled porosity. The waves develop on a characteristic length scale known as the viscous compaction length, δ, that is also the length scale for lateral fluid flow. In this context, porosity refers to any hydraulically connected void space present on spatial scales

  6. Geochronology and geochemistry of zircon from the northern Western Gneiss Region: Insights into the Caledonian tectonic history of western Norway

    NASA Astrophysics Data System (ADS)

    Gordon, Stacia M.; Whitney, Donna L.; Teyssier, Christian; Fossen, Haakon; Kylander-Clark, Andrew

    2016-03-01

    The Western Gneiss Region (WGR) of Norway is divided by the Møre-Trøndelag shear zone (MTSZ) into a southern region that contains domains of Caledonian ultrahigh-pressure (UHP) metamorphic rocks (> 2.5 GPa) and a northern area of similar Caledonian-aged rocks that record a maximum pressure reported thus far of ~1.5 GPa. Although both regions contain similar lithologies (primarily migmatitic quartzofeldspathic gneiss containing mafic lenses) and structural relationship of basement rocks to infolded nappes, this difference in maximum pressure implies a difference in tectonic history (continental subduction south of the shear zone, none to the north) and raises questions about the role of the MTSZ in the metamorphic history (including exhumation) of the WGR. Previous geochronology results indicated a difference in timing of peak metamorphism (older in north, younger in south). In order to better understand the tectonic history of the northern WGR and the MTSZ, and in particular the late- to post-Caledonian tectonic history, U-Pb zircon geochronology and trace-element abundances were obtained using the split-stream, laser-ablation ICPMS technique from metabasaltic lenses and migmatitic quartzofeldspathic host rocks from the structurally lowest exposed region of the northern WGR (Roan Peninsula basement), as well as leucosomes from an intercalated portion of the Seve Nappe Complex and a pegmatite in the MTSZ. Zircon from Roan gneiss and metabasite yield metamorphic ages of ca. 410-406 Ma, and zircon from a variety of migmatite samples (foliation-parallel leucosome to dikes) indicate melt crystallization at ca. 410 to 405 Ma. The Seve Nappe leucosomes yield only early Caledonian dates that cluster at ca. 437 Ma and ca. 465 Ma, suggesting that the allochthons in this region did not experience (or record) the same Scandian tectonic history as the basement rocks. Zircon from a weakly deformed pegmatite dike within the MTSZ crystallized at ca. 404 Ma, indicating that this

  7. Detrital zircon geochronology of the Tananao Metamorphic Complex, Taiwan

    NASA Astrophysics Data System (ADS)

    Huang, Y. C.; Chen, W. S.; Feng, H. T.; Liu, C. H.; Chung, S. L.; Lee, Y. H.

    2014-12-01

    The oldest rock of the Tananao Metamorphic Complex exposed at the Backbone Range which consists of marble, schist, and gneiss. According to the stratigraphy and structural analysis, the Complex in the ascending order can be divided into Chiuchu Marble, Paiyang Schist with Kuyuan Schist, and Pilu Formation. Based on Sr isotope dating, it is speculated that the formation age of Chiuchu Marble is closed to 250±20 Ma. Using the zircon U-Pb dating, the magnetic age of gneiss (I-type granite) yields 105- 86 Ma. The stratigraphic age of schist is difficult to define because of fossils are poorly-preserved. In our study, we use the detrital zircon U-Pb dating, by LA-ICPMS, to yield the maximum depositional age of the schist formation. We analyze fifteen samples in this study. The depositional age of the Kuyuan and Paiyang Schists would be not older than late Cretaceous, and the depositional age of the Pilu Formation may have formed in late Cretaceous and younger than Kuyuan and Paiyang Schists. Results from the above mentioned, we are interpreted as the tectonic setting of the Tananao Metamorpic Complex. The region was located on a passive continental margin that formed carbonate platform deposits during the late Permian period. The clastic sediments were unconformably deposited on Chiuchu Marble during the early Cretaceous. Then the paleo-Pacific plate subducted to the Cathaysia Block forming the granite at about 105-86 Ma. Afterwards, the clastic sediments were deeply buried caused by continuing subduction formed as schist rock. The metamorphic event is known as the Nanao orogeny.

  8. Removing the effects of metamorphism from the Neoproterozoic carbon isotope record: a case study on Islay, western Scotland

    NASA Astrophysics Data System (ADS)

    Skelton, Alasdair

    2016-04-01

    The Port Askaig Formation on Islay, western Scotland is the first discovered tillite (glacial sediment) of Neoproterozoic age. This formation is sandwiched between carbonate rocks which preserve an extreme negative carbon isotope excursion. This so called "Islay anomaly" has been correlated with other such anomalies worldwide and together with the tillites has been cited as evidence of major (worldwide) glaciation events. During subsequent mountain building, this carbonate-tillite- carbonate sequence has been folded, producing a major en-echelon anticlinal fold system. Folding was accompanied by metamorphism at greenschist facies conditions which was, in turn, accompanied by metamorphic fluid flow. Mapping of the δ18O and δ13C values of these carbonate rocks reveals that metamorphic fluids were channelled through the axial region of the anticlinal fold. The metamorphic fluid was found to have a highly negative δ13C value, which was found to be in equilibrium with metamorphosed graphitic mudstones beneath the carbonate-tillite-carbonate sequence. Devolatilisation of these mudstones is therefore a likely source of this metamorphic fluid. Removal of the effects of metamorphic fluid flow on δ13C values recorded by metamorphosed carbonate rocks on Islay allows us to re-evaluate the isotopic evidence used to reconstruct Neoproterozoic climate. We are able to show that extreme negative δ13C values can partly be attributed to metamorphic fluid flow.

  9. Ti diffusion in quartz inclusions: implications for metamorphic time scales

    NASA Astrophysics Data System (ADS)

    Spear, Frank S.; Ashley, Kyle T.; Webb, Laura E.; Thomas, Jay B.

    2012-12-01

    Quartz inclusions in garnet from samples collected from the staurolite zone in central New England are zoned in cathodoluminescence (CL). The CL intensity is interpreted to be a proxy for Ti concentration and the zoning attributed to Ti diffusion into the quartz grains driven by Ti exchange between quartz and enclosing garnet as a function of changing temperature. The CL zoning has been interpreted using a numerical diffusion model to constrain the time scales over which the diffusion has occurred. Temperature-time histories are sensitive to the presumed peak temperature but not to other model parameters. The total time of the metamorphic heating and cooling cycle from around 450 °C to the peak temperature (550-600 °C) back to 450 °C is surprisingly short and encompasses only 0.2-2 million years for peak temperatures of 600-550 °C. The metamorphism was accompanied by large-scale nappe and dome formation, and it is suggested that this occurred as a consequence of in-sequence thrusting resulting in a mid-crustal ductile duplex structure.

  10. Extent, age, and resurfacing history of the northern smooth plains on Mercury from MESSENGER observations

    NASA Astrophysics Data System (ADS)

    Ostrach, Lillian R.; Robinson, Mark S.; Whitten, Jennifer L.; Fassett, Caleb I.; Strom, Robert G.; Head, James W.; Solomon, Sean C.

    2015-04-01

    MESSENGER orbital images show that the north polar region of Mercury contains smooth plains that occupy ~7% of the planetary surface area. Within the northern smooth plains (NSP) we identify two crater populations, those superposed on the NSP ("post-plains") and those partially or entirely embayed ("buried"). The existence of the second of these populations is clear evidence for volcanic resurfacing. The post-plains crater population reveals that the NSP do not exhibit statistically distinguishable subunits on the basis of crater size-frequency distributions, nor do measures of the areal density of impact craters reveal volcanically resurfaced regions within the NSP. These results suggest that the most recent outpouring of volcanic material resurfaced the majority of the region, and that this volcanic flooding emplaced the NSP over a relatively short interval of geologic time, perhaps 100 My or less. Stratigraphic embayment relationships within the buried crater population, including partial crater flooding and the presence of smaller embayed craters within the filled interiors of larger craters and basins, indicate that a minimum of two episodes of volcanic resurfacing occurred. From the inferred rim heights of embayed craters, we estimate the NSP to be regionally 0.7-1.8 km thick, with a minimum volume of volcanic material of 4 × 106 to 107 km3. Because of the uncertainty in the impact flux at Mercury, the absolute model age of the post-plains volcanism could be either ∼3.7 or ∼2.5 Ga, depending on the chronology applied.

  11. THE STAR FORMATION AND NUCLEAR ACCRETION HISTORIES OF NORMAL GALAXIES IN THE AGES SURVEY

    SciTech Connect

    Watson, Casey R.; Kochanek, Christopher S.; Forman, William R.; Hickox, Ryan C.; Jones, Christine J.; Kenter, Almus T.; Murray, Steve S.; Vikhlinin, Alexey; Fazio, Giovani G.; Green, Paul J.; Brown, Michael J. I.; Brand, Kate; Dey, Arjun; Jannuzi, Buell T.; Rieke, Marcia; Eisenstein, Daniel J.; McNamara, Brian R.; Shields, Joseph C.

    2009-05-10

    We combine IR, optical, and X-ray data from the overlapping, 9.3 deg{sup 2} NOAO Deep Wide-Field Survey, AGN and Galaxy Evolution Survey (AGES), and XBooetes Survey to measure the X-ray evolution of 6146 normal galaxies as a function of absolute optical luminosity, redshift, and spectral type over the largely unexplored redshift range 0.1 {approx}< z {approx}< 0.5. Because only the closest or brightest of the galaxies are individually detected in X-rays, we use a stacking analysis to determine the mean properties of the sample. Our results suggest that X-ray emission from spectroscopically late-type galaxies is dominated by star formation, while that from early-type galaxies is dominated by a combination of hot gas and active galactic nucleus (AGN) emission. We find that the mean star formation and supermassive black hole accretion rate densities evolve like {approx}(1 + z){sup 3{+-}}{sup 1}, in agreement with the trends found for samples of bright, individually detectable starburst galaxies and AGN. Our work also corroborates the results of many previous stacking analyses of faint source populations, with improved statistics.

  12. Women healers of the middle ages: selected aspects of their history.

    PubMed Central

    Minkowski, W L

    1992-01-01

    The stellar role of women as healers during the Middle Ages has received some attention from medical historians but remains little known or appreciated. In the three centuries preceding the Renaissance, this role was heightened by two roughly parallel developments. The first was the evolution of European universities and their professional schools that, for the most part, systematically excluded women as students, thereby creating a legal male monopoly of the practice of medicine. Ineligible as healers, women waged a lengthy battle to maintain their right to care for the sick and injured. The 1322 case of Jacqueline Felicie, one of many healers charged with illegally practicing medicine, raises serious questions about the motives of male physicians in discrediting these women as incompetent and dangerous. The second development was the campaign--promoted by the church and supported by both clerical and civil authorities--to brand women healers as witches. Perhaps the church perceived these women, with their special, often esoteric, healing skills, as a threat to its supremacy in the lives of its parishioners. The result was the brutal persecution of unknown numbers of mostly peasant women. Images p290-a p291-a PMID:1739168

  13. Proterozoic metamorphism in the Neoarchean Kabul Block, Afghanistan

    NASA Astrophysics Data System (ADS)

    Collett, Stephen; Wali Faryad, Shah

    2015-04-01

    The Kabul Block is an elongate crustal fragment that is situated within a tectonic zone known as the Afghan Central Blocks, which form at the triple junction between the Indian, Eurasian, and Arabian plates. Unique amongst the Afghan Central Blocks, the Kabul Block contains quantifiably Precambrian basement rocks. Recent U/Pb SHRIMP analysis of zircons from the lowermost basement formations (the Sherdarwaza and Khair Khana) indicated the presence of a small Neoarchean component (~2700 Ma), while the majority of zircon cores yielded ages of 2200-2500 Ma. The Sherdarwaza and Khair Khana Formations consist predominantly of migmatites and orthogneisses that reached granulite-facies conditions. Conventional geothermobarometry and phase equilibria modelling on well preserved granulite-facies assemblages indicate that the rocks reached peak conditions in excess of 850°C and up to 7 kbar. U/Pb SHRIMP dating of zircon rims in addition to Th/U dating of monazite inclusions in garnet suggest that this event occurred in the late Paleoproterozoic (1800-1900 Ma). The granulite-facies assemblages are overprinted by a younger amphibolite-facies metamorphism, and are unconformably overlain by amphibolite-facies rocks belonging to younger formations (the Kharog and Welayati) that lack paragenetic evidence for a preceding high-grade metamorphism. The Welayati formation crops-out extensively in the south of Kabul City and consists of a variety of mica-schists and garnet-amphibolites, which contain textural relations suitable for the construction of a pressure-temperature (P-T) path. Inclusion assemblages in porphyroblastic garnet yield P-T conditions of around 525°C and 6 kbar. Chemical zonation in the garnet and phase equilibria modelling indicates that from this point garnet grew during a pressure increase of ~3.5 kbar over a temperature increase of ~125°C. A subsequent period of near isothermal decompression over ~2 kbar is confirmed by the growth of plagioclase, kyanite, and

  14. A prospective study of cognitive health in the elderly (Oregon Brain Aging Study): effects of family history and apolipoprotein E genotype.

    PubMed Central

    Payami, H; Grimslid, H; Oken, B; Camicioli, R; Sexton, G; Dame, A; Howieson, D; Kaye, J

    1997-01-01

    The oldest old are the fastest-growing segment of our population and have the highest prevalence of dementia. Little is known about the genetics of cognitive health in the very old. The aim of this study was to determine whether the genetic risk factors for Alzheimer disease (AD)--namely, apolipoprotein E (APOE) epsilon4 allele and a family history of dementia-continue to be important factors in the cognitive health of the very old. Case-control studies suggest that the effect of genetic factors diminishes at age >75 years. The present prospective study provided evidence to the contrary. We studied 114 Caucasian subjects who were physically healthy and cognitively intact at age 75 years and who were followed, for an average of 4 years, with neurological, psychometric, and neuroimaging examinations. Excellent health at entry did not protect against cognitive decline. Incidence of cognitive decline rose sharply with age. epsilon4 and a family history of dementia (independent of epsilon4) were associated with an earlier age at onset of dementia. Subjects who had epsilon4 or a family history of dementia had a ninefold-higher age-specific risk for dementia than did those who had neither epsilon4 nor a family history of dementia. These observations suggest that the rate of cognitive decline increases with age and that APOE and other familial/genetic factors influence the onset age throughout life. PMID:9106542

  15. P- T- t evolution of eclogite/blueschist facies metamorphism in Alanya Massif: time and space relations with HP event in Bitlis Massif, Turkey

    NASA Astrophysics Data System (ADS)

    Çetinkaplan, Mete; Pourteau, Amaury; Candan, Osman; Koralay, O. Ersin; Oberhänsli, Roland; Okay, Aral I.; Chen, Fukun; Kozlu, Hüseyin; Şengün, Fırat

    2016-01-01

    The Alanya Massif, which is located to the south of central Taurides in Turkey, presents a typical nappe pile consisting of thrust sheets with contrasting metamorphic histories. In two thrust sheets, Sugözü and Gündoğmuş nappes, HP metamorphism under eclogite (550-567 °C/14-18 kbar) and blueschist facies (435-480 °C/11-13 kbar) conditions have been recognized, respectively. Whereas the rest of the Massif underwent MP metamorphism under greenschist to amphibolite facies (525-555 °C/6.5-7.5 kbar) conditions. Eclogite facies metamorphism in Sugözü nappe, which consists of homogeneous garnet-glaucophane-phengite schists with eclogite lenses is dated at 84.8 ± 0.8, 84.7 ± 1.5 and 82 ± 3 Ma (Santonian-Campanian) by 40Ar/39Ar phengite, U/Pb zircon and rutile dating methods, respectively. Similarly, phengites in Gündoğmuş nappe representing an accretionary complex yield 82-80 Ma (Campanian) ages for blueschist facies metamorphism. During the exhumation, the retrograde overprint of the HP units under greenschist-amphibolite facies conditions and tectonic juxtaposition with the Barrovian units occurred during Campanian (75-78 Ma). Petrological and geochronological data clearly indicate a similar Late Cretaceous tectonometamorphic evolution for both Alanya (84-75 Ma) and Bitlis (84-72 Ma) Massifs. They form part of a single continental sliver ( Alanya- Bitlis microcontinent), which was rifted from the southern part of the Anatolide-Tauride platform. The P- T- t coherence between two Massifs suggests that both Massifs have been derived from the closure of the same ocean ( Alanya- Bitlis Ocean) located to the south of the Anatolide-Tauride block by a northward subduction. The boundary separating the autochthonous Tauride platform to the north from both the Alanya and Bitlis Massifs to the south represents a suture zone, the Pamphylian- Alanya- Bitlis suture.

  16. Blueschist metamorphism in the Yreka-Fort Jones area, Klamath Mountains, California

    USGS Publications Warehouse

    Hotz, Preston E.

    1973-01-01

    Blueschist is plentiful in the Yreka-Fort Jones area, eastern Klamath Mountains, adjacent to a belt of serpentinite that marks the boundary between two fundamental lithologic units, an eastern belt of early Paleozoic sedimentary and metamorphic rocks, and a western greenstone-chert assemblage of late Paleozoic and Triassic(?) age. The blueschists, which contain lawsonite and glaucophane or crossite, occur with phyllitic quartzite and siliceous phyllite of the Stuart Fork Formation, which is overthrust northwestward on the greenstone-chert terrane. The blueschist facies metamorphism probably was synchronous with Middle and Late Jurassic metamorphism of the Stuart Fork Formation. The blueschist-serpentinite terrane possibly marks the site of collision between the eastern Klamath plate and an oceanic western Paleozoic and Triassic plate.

  17. Social consequences of ethanol: Impact of age, stress, and prior history of ethanol exposure.

    PubMed

    Varlinskaya, Elena I; Spear, Linda P

    2015-09-01

    The adolescent period is associated with high significance of interactions with peers, high frequency of stressful situations, and high rates of alcohol use. At least two desired effects of alcohol that may contribute to heavy and problematic drinking during adolescence are its abilities to both facilitate interactions with peers and to alleviate anxiety, perhaps especially anxiety seen in social contexts. Ethanol-induced social facilitation can be seen using a simple model of adolescence in the rat, with normal adolescents, but not their more mature counterparts, demonstrating this ethanol-related social facilitation. Prior repeated stress induces expression of ethanol-induced social facilitation in adults and further enhances socially facilitating effects of ethanol among adolescent rats. In contrast, under normal circumstances, adolescent rats are less sensitive than adults to the social inhibition induced by higher ethanol doses and are insensitive to the socially anxiolytic effects of ethanol. Sensitivity to the socially anxiolytic effects of ethanol can be modified by prior stress or ethanol exposure at both ages. Shortly following repeated restraint or ethanol exposure, adolescents exhibit social anxiety-like behavior, indexed by reduced social preference, and enhanced sensitivity to the socially anxiolytic effects of ethanol, indexed through ethanol-associated reinstatement of social preference in these adolescents. Repeated restraint, but not repeated ethanol, induces similar effects in adults as well, eliciting social anxiety-like behavior and increasing their sensitivity to the socially anxiolytic effects of acute ethanol; the stressor also decreases sensitivity of adults to ethanol-induced social inhibition. The persisting consequences of early adolescent ethanol exposure differ from its immediate consequences, with males exposed early in adolescence, but not females or those exposed later in adolescence, showing social anxiety-like behavior when tested

  18. Intermediate P/T-type regional metamorphism of the Isua Supracrustal Belt, southern west Greenland: The oldest Pacific-type orogenic belt?

    NASA Astrophysics Data System (ADS)

    Arai, Tatsuyuki; Omori, Soichi; Komiya, Tsuyoshi; Maruyama, Shigenori

    2015-11-01

    The 3.7-3.8 Ga Isua Supracrustal Belt (ISB), southwest Greenland, might be the oldest accretionary complex on Earth. Regional metamorphism of the ISB has a potential to constrain the tectonothermal history of the Earth during the Eoarchean. Chemical and modal analyses of metabasite in the study area (i.e., the northeast part of the ISB) show that the metamorphic grade increases from greenschist facies in the northern part of the study area to amphibolite facies in the southern part. To determine the precise metamorphic P-T ranges, isochemical phase diagrams of minerals of metabasite were made using Perple_X. A synthesis of the estimated metamorphic P-T ranges of the ISB indicates that both the metamorphic pressure and temperature increase systematically to the south in the study area from 3 kbar and 380 °C to 6 kbar and 560 °C. The monotonous metamorphic P-T change suggests that the northeast part of the ISB preserves regional metamorphism resulting from the subduction of an accretionary complex although the ISB experienced metamorphic overprints during the Neoarchean. Both the presence of the regional metamorphism and an accretionary complex having originating at subduction zone suggest that the ISB may be the oldest Pacific-type orogenic belt. The progressive metamorphism can be considered as a record of intermediate-P/T type geothermal gradient at the subduction zone in the Eoarchean. Intermediate-P/T type geothermal gradient is typical at the current zones of subducting young oceanic crust, such as in the case of the Philippine Sea Plate in the southwest part of Japan. Considering the fact that almost all metamorphisms in the Archean are greenschist-amphibolite facies, the intermediate-P/T type geothermal gradient at the ISB might have been worldwide in the Archean. This would indicate that the subduction of young micro-plates was common because of the vigorous convection of hot mantle in the Archean.

  19. Platy Hematite and Metamorphism on Mars

    NASA Technical Reports Server (NTRS)

    Lane, M. D.; Morris, R. V.; Hartmann, W. K.; Christensen, P. R.; Mertzman, S. A.

    2002-01-01

    Emissivity spectra of Sinus Meridiani, Mars suggest that the hematite consists of platy particles that occur as consolidated, schistose lenses or loose, platy particles. This platy hematite may have originated as a result of burial metamorphism. Additional information is contained in the original extended abstract.

  20. Chemical demineralization of different metamorphic grade coals

    SciTech Connect

    Yusupov, T.S.; Shumskaya, L.G.; Burdukov, A.P.

    2009-07-15

    The paper analyzes a process of deep mineralization of various metamorphic grade coals pre-ground in different destructive units, namely, in centrifugal-planetary mill and disintegrator. Coal dispergation in higher energy intensive mills greatly enhances inorganic component extraction to acidic solutions. This is explained by distortion of crystal structure and amorphization of minerals under various kinds and different intensity mechanical actions.

  1. Metamorphic conditions in the Ashe Metamorphic Suite, North Carolina Blue Ridge

    SciTech Connect

    McSween, H.Y. Jr. ); Abbott, R.N.; Raymond, L.A. )

    1989-12-01

    Taconian metamorphism of mafic rocks in the Ashe Metamorphic Suite can be characterized by reference to an isograd corresponding to the reaction bio + epi = hbl + gar, which separates rocks into two zones of low-variance assemblages. Temperatures and pressures estimated from mineral exchange geothermometers and a barometer suggest that this reaction occurred at approximately 600-650C and 7.5 kbar. Phase equilibria between biotite and hornblende, as well as the sharpness of the mapped isograd, indicate that the reaction is discontinuous. Inferred differences in metamorphic grade between Ashe amphibolites and mafic dikes in the underlying basement suggest that these units are in faulted contact. Isograd patterns in pelitic rocks suggest an elongated domal uplift that developed after metamorphism and thrusting, the core of which is exposed in the adjacent Grandfather Mountain window.

  2. Geospeedometry in the inverted metamorphic gradient of the Nestos Thrust Zone in central Rhodope (Northern Greece)

    NASA Astrophysics Data System (ADS)

    Cioldi, Stefania; Moulas, Evangelos; Burg, Jean-Pierre

    2015-04-01

    Thrust tectonics and inverted metamorphic gradients are major consequences of large and likely fast movements of crustal segments in compressional environments. The purpose of this study is to investigate the tectonic setting and the timescale of inverted metamorphic zonations related to crustal-scale thrusting. The aim is to contribute understanding the link between mechanical and thermal evolution of major thrust zones and to clarify the nature and the origin of orogenic heat. The Rhodope metamorphic complex (Northern Greece) is interpreted as a part of the Alpine-Himalaya orogenic belt and represents a collisional system with an association of both large-scale thrusting and pervasive exhumation tectonics. The Nestos Shear Zone overprints the suture boundary with a NNE-dipping pile of schists displaying inverted isograds. The inverted metamorphic zones start from chlorite-muscovite grade at the bottom and reach kyanite-sillimanite grades with migmatites in the upper structural levels. In order to reconstruct the thermo-tectonic evolution of inverted metamorphic zonation, reliable geochronological data are essential. 40Ar/39Ar geochronology with step-heating technique on white mica from micaschists provided a temporal resolution with the potential to characterize shearing. 40Ar/39Ar dating across the Nestos Shear Zone yields Late Eocene-Early Oligocene (40-30 Ma) cooling (~400-350° C) ages, which correspond to local thermo-deformation episodes linked to late and post-orogenic intrusions. U-Pb Sensitive High Resolution Ion Microprobe (SHRIMP) zircon geochronology on leucosomes from migmatitic orthogneisses were considered to estimate the age of peak metamorphic conditions, contemporaneous with anatexis. U-Pb ages of zircon rims specify regional partial melting during the Early Cretaceous (160-120 Ma). This is in disagreement with previous assertions, which argued that the formation of leucosomes in this region is Late Eocene (42-35 Ma) and implied multiple

  3. Magmas, Mushes and Mobility: Thermal Histories of Magma Reservoirs from Combined U-Series and Diffusion Ages

    NASA Astrophysics Data System (ADS)

    Cooper, K. M.; Rubin, A. E.; Schrecengost, K.; Kent, A. J.; Huber, C.

    2014-12-01

    The thermal conditions of magma storage control many aspects of the dynamics of a magma reservoir system. For example, the temperature of magma storage directly relates to the crystallinity, and magmas stored at relatively low temperatures in a crystal mush (more than 40-50% crystalline) must be remobilized (e.g., by heating) before they can be erupted. A better understanding of the duration of magma storage at largely-liquid vs. largely-solid conditions is thus critical to understanding crustal magmatic processes such as magma mixing and for quantifying the hazard potential of a given volcano. Although mineral thermometry reflects the conditions of crystal growth or equilibration, these may not correspond to the thermal conditions of crystal storage. The duration of crystal storage at high temperatures can be quantified by comparing U-series crystal ages with the time scales over which disequilibrium trace-element profiles in the same crystals would be erased by diffusion. In the case of Mount Hood, OR, such a comparison for the two most recent eruptions shows that <12% of the total lifetime of plagioclase crystals (minimum 21 kyr) was spent at temperatures high enough that the magma would be easily mobilized. Partial data sets for other systems suggest such behavior is common, although the diffusion and U-series ages in these cases are from different samples and may not be directly comparable. We will present preliminary data combining U-series dating and diffusion timescales on the same samples for other volcanic systems (e.g., Lassen Volcanic Center, Mount St. Helens, Okataina Volcanic Center, New Zealand). Combining these data with numerical models offers additional insights into the controls on the conditions of storage. In addition, extension of this approach to combining U-Th ages with time scales of Li diffusion in zircon offers a promising new method to quantify thermal histories of silicic reservoir systems.

  4. New geochemical and geochronological data constraining metamorphism of the Tavşanlı Zone, NW Turkey

    NASA Astrophysics Data System (ADS)

    Aydın, Halil Can; Özdamar, Şenel

    2016-04-01

    The Tavşanlı Zone is a high-grade metamorphic belt, representing subduction and exhumation between the Sakarya Zone and the Afyon-Bolkardaǧ Zone in Western Anatolia. The Sivrihisar area of the Tavşanlı Zone comprises Paleozoic metamorphic rocks including sedimentary and magmatic origanated; Eocene granites; Neogene sedimentary rocks and alluvium. Metasedimantary rocks are composed of marble, schist and quartzite. Metamagmatics are gneiss and metabazites. This study presents new and precise, whole-rock chemistry; phengite-40Ar/39Ar age data from this area to constrain the high pressure (HP)-low temperature (LT) metamorphism of the Tavşanlı Zone. 40Ar/39Ar dating of two phengite samples from schists gave plateau ages between 82,5 ± 0,14 and 83,29 ± 0,22 Ma, which are interpreted as the metamorphic age of these schists, and as the age of metamorphism affected the Tavşanlı Zone. Also these ages constrain the timing of the closure of the Neo-Tethys.

  5. Degree of equilibration of eucritic pyroxenes and thermal metamorphism of the earliest planetary crust

    SciTech Connect

    Takeda, Hiroshi; Graham, A.L. Natural History Museum, London )

    1991-06-01

    The pyroxenes in two new monomict eucrites from Antarctica, Yamato 791186 and Yamato 792510, have been studied and compared with those of other Antarctic and non-Antarctic eucrites. The purpose of this study is to identify compositional and textural relationship shown by these pyroxenes which may be used as indicators of the thermal history of the meteorite. An attempt is made, using petrographic and compositional criteria, to distinguish between the initial cooling history and subsequent thermal events. It is suggested that it is possible to identify stages of thermal 'metamorphism' which may be used to indicate the conditions on the surface and crust of the parent body. A picture of the geological setting of the HED (Howardites, Eucrites, Diogenites) parent body is proposed, for which thermal metamorphism by impact heating is an important process. 22 refs.

  6. Unraveling P-T-Time-Fluids Paths: in-situ Geochronology Combined with Oxygen Isotopes in Metamorphic Rocks

    NASA Astrophysics Data System (ADS)

    Rubatto, D.; Angiboust, S.

    2014-12-01

    Geochronology of metamorphic rocks aims to determine pressure-temperature-time paths. The development of in-situ oxygen isotope analysis by ion microprobe permits to add fluid evolution to metamorphic histories. Accurate oxygen isotope analysis requires matrix-matched standards and, for chemically complex minerals, also appropriate matrix corrections. We will report on recent progresses on the analysis of oxygen isotopes in monazite, allanite and garnet using the SHRIMP ion microprobe. Zircon is a prime candidate for retrieving the oxygen composition of the pre-metamorphic protolith, as inherited zircons are preserved in many high-grade rocks. Metamorphic zircon rims that differ from the cores in δ18O offer insight into the origin of the fluid and the timing as well as degree of fluid-rock interaction. Garnet is another exceptional recorder of multiple metamorphic stages. Highly zoned garnets are found in a variety of eclogite-facies rocks and they can preserve dramatic oxygen isotopic variations (differences of a few to 10 δ18O ‰ within single crystal). Garnet and zircons from eclogite-facies metamorphic veins and shear zones within the metamorphosed Lago Superiore Unit from the Monviso ophiolite (W. Alps) have distinct growth zones with different oxygen isotopes composition. The shift in oxygen isotopes between the magmatic zircon core and the metamorphic zircon rim testifies to metasomatism by fluids equilibrated with serpentinites. The oxygen isotopes zoning in garnet confirms large scale fluid metasomatism concentrated in shear zones. It also indicates that some major shear zones from the Monviso ophiolitic sequence possibly underwent two stages of metasomatism, an event before or during early subduction and a later stage at around 550°C/2.5 GPa at peak pressure metamorphism.

  7. Revealing the significance and polyphase tectonothermal evolution of a major metamorphic unit in an orogen: the central Sanandaj-Sirjan zone, Zagros Mts., Iran

    NASA Astrophysics Data System (ADS)

    Shakerardakani, Farzaneh; Neubauer, Franz; Genser, Johann; Liu, Xiaoming; Dong, Yunpeng; Monfaredi, Behzad; Benroider, Manfred; Finger, Fritz; Waitzinger, Michael

    2016-04-01

    environment. The Darijune gabbro with the mean U-Pb zircon age of 170.2 ± 3.1 Ma postdates greenschist facies-grade metamorphism. This age marks the beginning of the initial subduction of Neotethyan oceanic in a continental arc setting. The best average P-T estimates for the metamorphic mineral assemblages of the Galeh-Doz orthogneiss range between 600 ± 50 °C at 2 ± 0.8 kbar. The subsequent cooling history after an amphibolite facies-grade metamorphism has been constrained with 40Ar-39Ar amphibole ages of plateau ages between 240-260 Ma. The estimate P-T conditions for the Carboniferous metagabbro from core (580 ± 50 °C, 4.0 ± 0.8 kbar) to rim (700 ± 20 °C, 7.5 ± 0.7 kbar) are in favor of a prograde P-T path. The new 40Ar-39Ar mineral ages integrated with structural field and microfabric studies reveals that the amphibolite-grade Carboniferous metagabbro indicate a Late Carboniferous age of amphibolite-grade metamorphism associated with ductile deformation of the new-detected Galeh-Doz nappe (Galeh-Doz orthogneiss and Amphibolite-Metagabbro unit). In the same unit, two lenses of metapelite including a garnet-muscovite-biotite schist give a P-T estimate of garnet cores from 640 ± 20 °C at 6.2 ± 0.8 kbar and garnet rims from 680 ± 20 °C at 7.2 ± 1.0 kbar, as well as garnet-biotite schist that yield lower P-T conditions, which vary from 620 °C at 5.5 ± 0.5 kbar in garnet cores to 600 ± 30 °C at 4.0 ± 1.0 kbar in garnet rims. Chemical monazite ages from garnet micaschists are at 322 ± 28 Ma. 40Ar-39Ar experiments on white mica in the first and second types yield staircase patterns from ca. 36 to 170 Ma and a plateau age of 137.84 ± 0.65 Ma, respectively. Taking all data together, we suggest that amphibolite-grade metamorphism is Carboniferous and is overprinted by two events: (1) during Late Jurassic- Cretaceous during ductile dextral transpressive nappe emplacement of the Galeh-Doz nappe over the June complex (peak conditions of greenschist facies

  8. Landscape history and land-use dependent soil erosion in central Bosnia from the Bronze Age to Medieval Times

    NASA Astrophysics Data System (ADS)

    Wolters, Steffen; Enters, Dirk; Bittmann, Felix

    2010-05-01

    The inland areas of the northwestern Balkan peninsula and in particular of Bosnia and Herzegovina are poor in natural archives suitable for the reconstruction of past environmental changes and vegetation history. Consequently, palaeoenvironmental analyses are scarce with only three palynological studies available dating back to 1973, 1956 and 1934. Central Bosnia, however, is rich in archaeological heritage, featuring numerous prehistoric settlement sites along the river Bosna starting in the early Neolithic. This generates the need for palaeoenvironmental reconstructions to support and complement recent archaeological research in this area. Here we present results from a 450 cm gyttja-peat sequence from Seoce Jezero, a small mire located at 600 m NN on a plateau above a tributary of the river Bosna 30 km northwest of Sarajevo (central Bosnia). Fourteen AMS C-14 dates provide a robust time-depth-relationship which covers natural and anthropogenic environmental changes at Seoce Jezero from the Bronze Age to early Medieval Times. Pollen, macrofossil and geochemical analyses of 167 samples produce a high resolution record of land-use and vegetation change up to a half-decadal time scale. The palaeoenvironmental record starts ca. 1800 BC (3750 cal. BP) and reveals an initially relatively undisturbed landscape dominated by Fagus- and Quercus-Carpinus woodland. Anthropogenic influence is clearly visible from 1400 BC (3350 cal. BP) onwards and comprises woodland clearances, pasturing and crop cultivation. Pollen analyses confirm several consecutive phases of different land-use character and intensity. Phases of high land-use pressure culminated at the transition Bronze Age/Iron Age (1100 BC), the late Iron Age (400 BC), late Roman times (AD 300) and from AD 700 onwards. In between, stages of forest regeneration could be detected, most pronounced in the period between 70 BC and AD 150 (2020-1800 cal. BP), when anthropogenic influence virtually ceased. Whereas land use in

  9. Thermal history and extensional exhumation of a high-temperature crystalline complex (Hırkadağ Massif, Central Anatolia)

    NASA Astrophysics Data System (ADS)

    Lefebvre, Côme; Kalijn Peters, M.; Wehrens, Philip C.; Brouwer, Fraukje M.; van Roermund, Herman L. M.

    2015-12-01

    The Central Anatolian Crystalline Complex (CACC) is a large continental domain exposed in central Turkey that was affected by high temperature metamorphism during the Late Cretaceous. As a result of this event, Paleozoic sediments became metamorphosed, initially under Barrovian conditions, then overprinted locally by high temperature-low pressure metamorphism, and intruded by widespread batholiths. In this study we focus on the crystalline Hırkadağ Massif located in the central part of the CACC, where we applied an integrated approach involving metamorphic, structural and geochronological analysis in order to elucidate its tectonic history from burial to exhumation. Our metamorphic study reveals that conditions of metamorphism reached ~ 7-8 kbar/700 °C and were relatively homogeneous at the scale of the Hırkadağ Massif. Coeval with the regional metamorphism, the rocks were intensely deformed as reflected by isoclinal folding, the development of a pervasive foliation and top-to-the-SE shearing. This was followed by decompression to pressures of ~ 3-4 kbar at 800 °C, which may be linked to the emplacement of local granodioritic intrusions at ~ 77 Ma. Subsequent cooling of the Hırkadağ high-grade metamorphic and intrusive rocks is indicated by 40Ar/39Ar cooling ages of 68.8 ± 0.9 Ma (biotite) and 67.0 ± 1.2 Ma (potassium feldspar). Evidence for tectonic exhumation has been identified within the marbles at the NE margin of the Hırkadağ Massif, in the form of discrete protomylonitic and mylonitic shear bands showing a consistent N40-60 top-to-NE sense of shear. Further east, the contact between brecciated mylonitic marbles and non-metamorphic conglomerates preserves the typical structural features of an upper-crustal detachment fault. Restoration of the Hırkadağ Massif and the CACC to their late Cretaceous configuration suggests that the LP-HT metamorphism, magmatism and extensional structures evolved as a result of the development and exhumation of a ~ N

  10. Blueschist-facies metamorphism related to regional thrust faulting

    USGS Publications Warehouse

    Blake, M.C., Jr.; Irwin, W.P.; Coleman, R.G.

    1969-01-01

    Rocks of the blueschist (glaucophane schist) facies occur throughout the world in narrow tectonic belts associated with ultramafic rocks. In the Coast Range province of California, blueschist rocks are devloped in the eugeosynclinal Franciscan Formation of Late Mesozoic age. The blueschist rocks form a narrow belt for more than 800 km along the eastern margin of this province and commonly are separated from rocks of an overlying thrust plate by serpentinite. Increasing metamorphism upward toward the thrust fault is indicated mineralogically by a transition from pumpellyite to lawsonite and texturally by a transition from metagraywacke to schist. The blueschist metamorphism probably occurred during thrusting in a zone of anomalously high water pressure in the lower plate along the sole of the thrust fault. This tectonic mode of origin for blueschist differs from the generally accepted hypothesis involving extreme depth of burial. Other belts of blueschist-facies rocks, including the Sanbagawa belt of Japan, the marginal synclinal belt of New Zealand, and the blueschist-ultramafic belts of Venezuela, Kamchatka, Ural mountains, and New Caledonia have similar geologic relations and might be explained in the same manner. ?? 1969.

  11. Zoning and recrystallization of phengitic micas: implications for metamorphic equilibration

    NASA Astrophysics Data System (ADS)

    Dempster, T. J.

    1992-02-01

    White micas (phengites) in the metasediments of the Scottish Dalradian display a large range of compositions within single samples. The variations in the composition of these phengites are strongly controlled by their structural age, with early fabrics containing a paragonite-poor, celadonite-rich phengite whereas in later fabrics the micas are generally paragonite-rich and celadonite-poor. Retrograde phengite growth, identified using back scattered electron imaging, occurs as celadonite-rich rims on micas within all existing fabrics and appears to be preferentially developed along existing white mica-plagioclase grain boundaries. The presence of these chemically distinct phengite populations within single samples implies that chemical exchange between the individual micas was inefficient. It is proposed that diffusion-controlled exchange reactions in phengites have relatively high closure temperatures below which major element exchange is effectively impossible. This closed system behaviour of micas questions the ease with which phengites may equilibrate with other phases during prograde greenschist and lower amphibolite facies metamorphism. Many of the chemical variations preserved in phengites from such metamorphic rocks may reflect deformation/recrystallization controlled equilibria.

  12. Impact Metamorphism of Subsurface Organic Matter on Mars: A Potential Source for Methane and Surface Alteration

    NASA Technical Reports Server (NTRS)

    Oehler, D. Z.; Allen, C. C.; McKay, D. S.

    2005-01-01

    Reports of methane in the Martian atmosphere have spurred speculation about sources for that methane [1-3]. Discussion has centered on cometary/ meteoritic delivery, magmatic/mantle processes, UV-breakdown of organics, serpentinization of basalts, and generation of methane by living organisms. This paper describes an additional possibility: that buried organic remains from past life on Mars may have been generating methane throughout Martian history as a result of heating associated with impact metamorphism.

  13. Raman spectroscopy of carbon and solid bitumens in sedimentary and metamorphic rocks.

    PubMed

    Jehlicka, Jan; Urban, Ondrej; Pokorný, Jan

    2003-08-01

    Different types of carbonaceous matter from rocks display Raman spectral features which knowledge permits to obtain structural information of these materials. Application of Raman microspectroscopy to investigate kerogen, bitumen, fossils, highly carbonified amorphous carbon as well as graphite from different environments is reviewed. Differences in Raman spectra and structural differences between carbonaceous samples differing in their metamorphic history are discussed on the basis of new data. PMID:12909147

  14. KAr and {40Ar }/{39}Ar study of metamorphic rocks associated with the Oman ophiolite: Tectonic implications

    NASA Astrophysics Data System (ADS)

    Montigny, R.; Le Mer, O.; Thuizat, R.; Whitechurch, H.

    1988-09-01

    K-Ar analyses on extracted minerals are reported for a variety of metamorphic rocks associated with the Sumail ophiolite. Amphibolites lying at the sole of the ophiolite yield ages of 95-100 Ma, which are viewed as reflecting times of crystallization. High-pressure metamorphics of the Saih Hatat reveal complex results: white micas range in age from 80 to 131 Ma whereas blue amphiboles indicate ages that are systematically lower than those of coexisting white micas. Investigation of a few white micas by the {40Ar }/{39Ar } step heating method yields rather intricate age spectra, featuring low apparent ages in the first and the last stages of gas release and high apparent ages in between. Two explanations can be equally envisaged for these convex-upward age spectra. The first is the mixing of two generations of micas, corresponding to two main metamorphisms. The first one ( M1) is a low- to medium-temperature, high-pressure event which conceivably occurred between 130 and 114 m.y. ago. The second ( M2) overprints M1 and has produced rocks typical of the greenschist facies. It took place 80 m.y. ago and also affected the sole of the ophiolites. The second is the presence of excess argon in mica mixtures with complex degassing properties. Thus, the two metamorphic phases identified by microscopic inspection are not significantly different in age. They occurred in the 70-80 Ma interval. Moreover, K-Ar dates on amphibole from gabbroic dikes intersecting the peridotites suggest that they are genetically linked to the mafic part of the ophiolites. Assuming that metamorphism is a tracer of tectonic events, we view the infraophiolitic amphibolites as the result of an intraoceanic thrusting which took place near a spreading center. Nevertheless, the uncertainty as to the age of the blueschist metamorphism precludes the possibility of indicating a timetable, based on metamorphic ages, for the motion shift of Africa relative to Eurasia during the Late Cretaceous. A tentative

  15. Meteoric water in metamorphic core complexes

    NASA Astrophysics Data System (ADS)

    Teyssier, Christian; Mulch, Andreas

    2015-04-01

    The trace of surface water has been found in all detachment shear zones that bound the Cordilleran metamorphic core complexes of North America. DeltaD values of mica fish in detachment mylonites demonstrate that these synkinematic minerals grew in the presence of meteoric water. Typically deltaD values are very negative (-120 to -160 per mil) corresponding to deltaD values of water that are < -100 per mil given the temperature of water-mica isotopic equilibration (300-500C). From British Columbia (Canada) to Nevada (USA) detachment systems bound a series of core complexes: the Thor-Odin, Valhalla, Kettle-Okanogan, Bitterroot -Anaconda, Pioneer, Raft River, Ruby Mountain, and Snake Range. The bounding shear zones range in thickness from ~100 m to ~1 km, and within the shear zones, meteoric water signature is recognized over 10s to 100s of meters beneath the detachment fault. The age of shearing ranges generally from Eocene in the N (~50-45 Ma) to Oligo-Miocene in the S (25-15 Ma). DeltaD water values derived from mica fish in shear zones are consistent with supradetachment basin records of the same age brackets and can be used for paleoaltimetry if coeval isotopic records from near sea level are available. Results show that a wave of topography (typically 4000-5000 m) developed from N to S along the Cordillera belt from Eocene to Miocene, accompanied by the propagation of extensional deformation and volcanic activity. In addition, each detachment system informs a particular extensional detachment process. For example, the thick Thor-Odin detachment shear zone provides sufficient age resolution to indicate the downward propagation of shearing and the progressive incorporation of footwall rocks into the hanging wall. The Kettle detachment provides a clear illustration of the dependence of fluid circulation on dynamic recrystallization processes. The Raft River system consists of a thick Eocene shear zone that was overprinted by Miocene shearing; channels of meteoric

  16. Metamorphic sole formation, emplacement and blueschist overprint: early obduction dynamics witnessed by W. Turkey ophiolites

    NASA Astrophysics Data System (ADS)

    Plunder, Alexis; Agard, Philippe; Chopin, Christian; Soret, Mathieu; Okay, Aral; Whitechurch, Hubert

    2016-04-01

    Western Turkey, with a >200 km long-belt of unmetamorphosed ophiolite overlying continental lithosphere is one or even the largest obducted ophiolite on Earth and therefore a key example to study obduction and early subduction dynamics. All Western Turkish ophiolite fragments are considered as part of the same Neotethyan branch resulting of a long-lived continental subduction (or underthrusting). Synchronous (ca. ~ 93 Ma) metamorphic sole formation and preservation at the base of most of the Turkish ophiolite fragments support this single event and place a strong constraint on the age of subduction initiation. Metamorphic soles are indeed generally considered to have formed during the early and hot subduction zone at 25 ± 10 km depths and welded to the overriding oceanic lithosphere. In Western Turkey however (as for most places worldwide) a systematic study of the pressure-temperature conditions with modern thermobarometric tools is generally lacking, and fundamental mechanisms of formation or accretion to the upper plate are poorly (if at all) constrained. We herein reappraise Western Turkish metamorphic soles focusing on the following points and issues: (i) detailed structures of metamorphic sole and other subduction derived units, petrological evolution and refined pressure-temperature conditions; peak pressure-temperature conditions of metamorphic sole were estimated using garnet, clinopyroxene, amphibole and plagioclase as the peak paragenesis at 10.5 ± 2 kbar and 800 ± 50°C based on pseudosections using the Theriak/Domino package (ii) the rather unique (and enigmatic) blueschist facies overprint found in places was investigated in terms of structural position and pressure-temperature conditions. Conditions of overprint were estimated around 12 kbar and 425 °C from the presence of glaucophane, lawsonite, jadeite and garnet overgrowing the amphibolite-facies assemblage. This field-based study provides clues to mechanisms of metamorphic sole underplating

  17. Age and genesis of precious metals deposits, Buffalo Hump district, central Idaho: implications for depth of emplacement of quartz veins.

    USGS Publications Warehouse

    Lund, K.; Snee, L.W.; Evans, K.V.

    1986-01-01

    Three samples (metamorphic country rock, Idaho batholith granite, and auriferous quartz vein) were dated by the 40Ar/39Ar age spectrum technique. The lode deposits are Cretaceous (71 m.y.); their cooling histories and depths of emplacement, inferred from the age spectra, are evidence for the granite plutons and the lode deposits having been emplaced at the same 40-9 km depth and being genetically related. Thus, the Idaho batholith is not barren, and at least two precious-metal mineralizing events, Cretaceous and Eocene in age, occur in central Idaho. Class differences between the two ages of deposits, of style, alteration and mineralogy, are suggested. -G.J.N.

  18. Carbonic metamorphism, granulites and crustal growth

    NASA Technical Reports Server (NTRS)

    Newton, R. C.; Smith, J. V.; Windley, B. F.

    1980-01-01

    Stabilization of early crust against melting by high radioactivity and against resorption into the mantle by fast convective overturn requires that water and heat producers were flushed upwards within 50 Myr of accretion. Creation of a refractory base of granulite by metamorphism associated with CO2 vapour explains CO2-rich fluid inclusions in ancient high-grade rocks, minor-element depletions and local phenomena of arrested development of charnockite in Precambrian terrains. The hot-spot and plate-tectonic models of Precambrian crustal evolution lead to different schemes for CO2 delivery to continental roots. New tectonic concepts may be needed to explain carbonic metamorphism and other features of early crustal evolution.

  19. Heat transfer by fluids in granulite metamorphism

    NASA Technical Reports Server (NTRS)

    Morgan, Paul; Ashwal, Lewis D.

    1988-01-01

    The thermal role of fluids in granulite metamorphism was presented. It was shown that for granulites to be formed in the middle crust, heat must be advected by either magma or by volatile fluids, such as water or CO2. Models of channelized fluid flow indicate that there is little thermal difference between channelized and pervasive fluid flow, for the same total fluid flux, unless the channel spacing is of the same order or greater than the thickness of the layer through which the fluids flow. The volumes of volatile fluids required are very large and are only likely to be found associated with dehydration of a subducting slab, if volatile fluids are the sole heat source for granulite metamorphism.

  20. Shape Metamorphism Using p-Laplacian Equation

    SciTech Connect

    Cong, Ge; Esser, Mehmet; Parvin, Bahram; Bebis, George

    2004-05-19

    We present a new approach for shape metamorphism, which is a process of gradually changing a source shape (known) through intermediate shapes (unknown) into a target shape (known). The problem, when represented with implicit scalar function, is under-constrained, and regularization is needed. Using the p-Laplacian equation (PLE), we generalize a series of regularization terms based on the gradient of the implicit function, and we show that the present methods lack additional constraints for a more stable solution. The novelty of our approach is in the deployment of a new regularization term when p --> infinity which leads to the infinite Laplacian equation (ILE). We show that ILE minimizes the supremum of the gradient and prove that it is optimal for metamorphism since intermediate solutions are equally distributed along their normal direction. Applications of the proposed algorithm for 2D and 3D objects are demonstrated.

  1. Age of the Dawson Arkose, southwestern Air Force Academy, Colorado, and implications for the uplift history of the Front Range

    SciTech Connect

    Kluth, C.F.; Nelson, S.N. )

    1988-01-01

    An angular unconformity within the synorogenic Dawson Arkose (Late Cretaceous-Eocene) is preserved and exposed in areas south of Denver, Colorado, along the eastern side of the Front Range uplift. In the southwestern part of the Air Force Academy, the basal Dawson is concordant with the underlying Laramie and Fox Hills formations and dips 72-84{degree} eastward. Above an intraformational angular unconformity, younger units of the Dawson dip 24{degree}-46{degree} eastward. Smaller angular unconformities (10{degree}{plus minus}), and beds with gradually decreasing dip occur higher in the Dawson section. Rocks above the largest unconformity contain a rich palynomorph assemblage of Late Maestrichtain age. These data indicate that approximately 30{degree}-40{degree}, and possibly as much as approximately 70{degree}, of tilting of the underlying rocks occurred during the Late Maestrichtian (66-70 Ma). It is also possible that approximately 30{degree}-40{degree} of the tilting of the Late Cretaceous rocks occurred between latest Maestrichtian and Eocene (approximately 45 Ma). These results suggest that the transition from a tectonically quiet marine environment to a non-marine, tectonically active condition took place rapidly, probably within a few million years. When combined with published data, the authors study indicates that the Front Range has different tectonic histories on its eastern and its western side, and that the deformation is diachronous along the strike of the eastern side of the Front Range.

  2. The analysis of chemical zoning in a garnet population: Determination of the P-T-t path of Grenvillian metamorphism in southeastern Ontario

    NASA Astrophysics Data System (ADS)

    McCarron, T.; Gaidies, F.

    2013-12-01

    Growth zoning developed in a population of garnet porphyroblasts of a metapelite from the Grenville Province of southeastern Ontario has been used to infer the metamorphic P-T-t history of the garnet-bearing rock. The sample is a garnet-biotite-staurolite bearing schist of the Flinton Group, a package of metasediments in southeastern Ontario metamorphosed during the Grenville Orogeny between ca. 1080-980 Ma. Characterization of the garnet population with high-resolution X-ray micro-computed tomography revealed a unimodal, slightly positively skewed crystal size distribution (CSD). A representative set of garnet porphyroblasts ranging from 4000 to 200 μm in diameter from the different size classes of the CSD were centrally sectioned. Electron probe micro analyses across the centrally sectioned garnet porphyroblasts revealed decreasing Xsps and Xgrs and increasing Xalm and Xpyp from core to rim consistent with growth zoning. Garnet growth simulations with THERIA_G (Gaidies et al., 2008) successfully reproduced the observed growth zoning in the differently sized grains allowing to derive a significant part of the rock's metamorphic P-T-t history. Large porphyroblasts of the population were used to determine a clockwise P-T path over the interval 3.7 to 5.9 kbar and 512 to 615°C whereas modification of growth zoning via intracrystalline diffusion in relatively small porphyroblasts was used to infer an average heating rate of 2°C Ma-1. This suggests a timescale of ca. 53 Ma for garnet growth and an average growth rate of 30 μm Ma-1. Using LA-ICP-MS U-Pb geochronology, a major age population at 977×4 Ma was identified for metamorphic monazite commonly included in the outer 200 μm of the garnet grains. That age is interpreted to represent monazite growth at the expense of allanite and apatite late in garnet's growth history providing an absolute calibration for the relative timescales predicted through THERIA_G modeling. Gaidies, F., de Capitani, C. & Abart, R

  3. Ultrahigh-temperature metamorphism under isobaric heating: New evidence from the North China Craton

    NASA Astrophysics Data System (ADS)

    Yang, Qiong-Yan; Santosh, M.; Tsunogae, Toshiaki

    2014-12-01

    The Khondalite Belt within Inner Mongolia Suture Zone (IMSZ) in the North China Craton (NCC) preserves evidence for extreme crustal metamorphism under ultra-high temperature (UHT) conditions at ca. 1.92 Ga, associated with the subduction-collision tectonics between the Yinshan and Ordos Blocks. Here we report a new locality in Hongsigou where cordierite- and spinel-bearing granulites record UHT metamorphism. The prograde, peak, and retrograde mineral assemblages in these pelitic granulites have been identified based on petrography and mineral chemistry as: Bt1 + Grt1 + Sil1 + Kfs1 + Pl1 + Ilm + Qtz1, Grt1 + Sil2 + Kfs2 + Pl2 + Spl + Ilm + Qtz2 + Liq, and Crd + Grt2 + Sil3 + Kfs2 + Pl2 + Ilm + Qtz2 respectively. The peak metamorphic conditions of the pelitic granulite were estimated as 930-1050 °C and 6.5-7.5 kbar based on pseudosection analysis in the system NCKFMASHTO, suggesting extreme thermal metamorphism. We report LA-ICPMS zircon U-Pb data from the granulite which show weighted mean 207Pb/206Pb age of 1881 ± 6.6 Ma, marking the timing of UHT metamorphism. Lu-Hf analyses of the zircons show εHf(t) values within a restricted range of -4.2 to 0.3 and together with Hf model ages, a Paleoproterozoic arc magmatic source is inferred for the detrital zircons. The estimated P-T path for the UHT granulite suggests isobaric heating followed by cooling and decompression along a clockwise trajectory, different from the anti-clockwise P-T paths defined in earlier studies for the 1.92 Ga UHT rocks from the IMSZ. The younger age and the isobaric heating trajectory suggest that the Hongsigou UHT rocks are related to heat input from underplated mafic magmas following continental collision.

  4. PTt path in metamorphic rocks of the Khoy region (northwest Iran) and their tectonic significance for Cretaceous Tertiary continental collision

    NASA Astrophysics Data System (ADS)

    Azizi, H.; Moinevaziri, H.; Mohajjel, M.; Yagobpoor, A.

    2006-06-01

    Metamorphic rocks in the Khoy region are exposed between obducted ophiolites to the southwest and sedimentary rocks of Precambrian-Paleozoic age to the northeast. The Qom formation (Oligocene-Miocene) with a basal conglomerate transgressively overlies all of these rocks. The metamorphic rocks consist of both metasediments and metabasites. The metasediments are micaschist, garnet-staurolite schist and garnet-staurolite sillimanite schist with some meta-arkose, marble and quartzite. The metabasites are metamorphosed to greenschist and amphibolite facies from a basaltic and gabbroic protolith of tholeiitic and calc-alkaline rocks. Geothermobarometry based on the equivalence of minerals stability and their paragenesis in these rocks and microprobe analyses by several different methods indicate that metamorphism occurred in a temperature range between 450 and 680 °C at 5.5 and 7.5 kb pressure. Rims of minerals reveal a considerable decrease of pressure (<2 kb) and insignificant decrease of temperature. The PTt path of this metamorphism is normal. The MFG line passes above the triple junction of Al 2SiO 5 polymorphs, and the average geothermal gradient during metamorphism was from 27 to 37 °C/km, which is more concordant with the temperature regime of collision zones. We infer that crustal thickening during post-Cretaceous (possibly Eocene) collision of the Arabian plate and the Azerbaijan-Albourz block was the main factor that caused the metamorphism in the studied area.

  5. Strontium and neodymium isotopic variations in early Archean gneisses affected by middle to late Archean high-grade metamorphic processes: West Greenland and Labrador

    NASA Technical Reports Server (NTRS)

    Collerson, K. D.; Mcculloch, M. T.; Bridgwater, D.; Mcgregor, V. R.; Nutman, A. P.

    1986-01-01

    Relicts of continental crust formed more than 3400 Ma ago are preserved fortuitously in most cratons. The cratons provide the most direct information about crust and mantle evolutionary processes during the first billion years of Earth history. In view of their polymetamorphic character, these terrains are commonly affected by subsequent tectonothermal events. Hence, their isotope systematics may be severely disturbed as a result of bulk chemical change or local isotopic homogenization. This leads to equivocal age and source information for different components within these terrains. The Sr and Nd isotopic data are presented for early Archean gneisses from the North Atlantic Craton in west Greenland and northern Labrador which were affected by younger metamorphic events.

  6. A polyphase metamorphic evolution for the Xitieshan paragneiss of the north Qaidam UHP metamorphic belt, western China: In-situ EMP monazite- and U-Pb zircon SHRIMP dating

    NASA Astrophysics Data System (ADS)

    Zhang, Cong; van Roermund, Herman; Zhang, Lifei; Spiers, Chris

    2012-04-01

    In-situ electron microprobe (EMP) U-Th-Pb monazite-, sensitive high-resolution ion microprobe (SHRIMP) zircon analyses, metamorphic phase equilibrium (Domino/Theriak)- and geothermobarometric calculations are performed on kyanite/sillimanite-bearing garnet biotite gneisses forming part of the dominant rock association in the Xitieshan ultra-high pressure metamorphic belt, north Qaidam, western China. Results are consistent with the following complex polyphase tectono-metamorphic evolution. The kyanite/sillimanite bearing garnet biotite gneisses contain monazite ages of 938 ± 23 Ma and zircon SHRIMP ages of 945 ± 7 Ma, referring to a Neoproterozoic metamorphism, i.e. similar to the age of the Jinning orogeny in the Yangtze block of southern China. This correlation suggests that the paragneiss has affinities with the Yangtze block (South China block). The Neoproterozoic monazites were found inside coarse grained porphyroblastic garnets containing amphibolite facies mineral inclusion assemblages. The kyanite/sillimanite-bearing garnet biotite gneisses also contain early Paleozoic monazite ages of 422-425 Ma and 455-460 Ma, detected in amphibolite facies mineral assemblages associated with matrix minerals. Using phase equilibrium- and geothermobarometric calculations, PT conditions of 560-610 °C/5.8-7.0 kbar and 610-675 °C/4.6-6.5 kbar were calculated respectively for both amphibolite facies assemblages. The early Paleozoic ages of 422-425 Ma and 455-460 Ma were detected in 8 monazite grains from the investigated paragneiss samples. Based on the Y and Eu contents variation of the early Paleozoic monazite domains (measured by EMP), the 422-425 Ma monazite ages are interpreted to have formed during an amphibolite facies tectono-metamorphic overprint that post-dates (U)HP metamorphism and can thus be related to exhumation of previously deeply subducted rocks. Alternatively, the 455-460 Ma monazite ages are interpreted to represent the age of the prograde subduction

  7. Prograde Metamorphism recorded in Antarctic Granulite

    NASA Astrophysics Data System (ADS)

    Marschall, H.; Pauly, J.; Chatterjee, N.; Monteleone, B.; Meyer, H. P.

    2015-12-01

    High-grade metamorphic rocks provide an archive of tectonic processes and record conditions in the deep roots of orogenic belts. Granulites typically preserve chemical and mineralogical evidence of the peak temperature to which crustal rocks may be subjected, and they commonly preserve a multitude of textural and chemical features that allow a rather detailed reconstruction of their cooling and exhumation. More rarely, however, is it possible to reconstruct parts of the prograde path, which would allow a reconstruction of the loading and heating of the rocks. Access to the prograde P-T path and the rates and durations involved in granulite formation would provide important constraints on the convergence part of orogenic processes. Here we investigated a sample of felsic granulite from the H.U. Sverdrupfjella, which is part of the high-grade Maud Belt (East Antarctica). Peak-metamorphic conditions of approximately 925 °C and 1.45 GPa persisted for a maximum of circa 14 million years and were attained shortly after 570 Ma. In addition to the short-lived temperature peak, zircon preserved evidence for protracted granulite facies conditions with temperatures above 800 °C persisting for approximately 40 million years. Constraints on prograde metamorphism are recorded by garnet that preserved pre-peak metamorphic growth zones, by Ti zonation in zircon and by rutile inclusions in garnet. Zr-in-rutile thermometry using rutile included in different generations of garnet is used to reconstruct the prograde P-T path documenting burial followed by heating to ultra-high temperatures at peak pressures. Complementary, Ti zonation in prograde cores of zircon grains document and date heating, whereas younger zircon rims show again lower Ti-in-zircon temperatures and date the retrograde stages of metamorphism. The highest T is recorded in rutile, but not in zircon, consistent with the dissolution rather than growth of zircon at ultra-high temperatures. The clockwise loading

  8. Disturbance of isotope systematics in meteorites during shock and thermal metamorphism and implications for shergottite chronology

    SciTech Connect

    Gaffney, A M; Borg, L E; Asmerom, Y

    2008-12-10

    Shock and thermal metamorphism of meteorites from differentiated bodies such as the Moon and Mars have the potential to disturb chronometric information contained in these meteorites. In order to understand the impact-related mechanisms and extent of disturbance to isochrons, we undertook experiments to shock and heat samples of 10017, a 3.6 billion year old lunar basalt. One sub-sample was shocked to 55 GPa, a second subsample was heated to 1000 C for one week, and a third sub-sample was maintained as a control sample. Of the isotope systems analyzed, the Sm-Nd system was the least disturbed by shock or heat, followed by the Rb-Sr system. Ages represented by the {sup 238}U-{sup 206}Pb isotope system were degraded by shock and destroyed with heating. In no case did either shock or heating alone result in rotated or reset isochrons that represent a spurious age. In some cases the true crystallization age of the sample was preserved, and in other cases age information was degraded or destroyed. Although our results show that neither shock nor thermal metamorphism alone can account for the discordant ages represented by different isotope systems in martian meteorites, we postulate that shock metamorphism may render a meteorite more susceptible than unshocked material to subsequent disturbance during impact-related heating or aqueous alteration on Mars or Earth. The combination of these processes may result in the disparate chronometric information preserved in some meteorites.

  9. Fluid heterogeneity during granulite facies metamorphism in the Adirondacks: stable isotope evidence

    USGS Publications Warehouse

    Valley, J.W.; O'Neil, J.R.

    1984-01-01

    The preservation of premetamorphic, whole-rock oxygen isotope ratios in Adirondack metasediments shows that neither these rocks nor adjacent anorthosites and gneisses have been penetrated by large amounts of externally derived, hot CO2-H2O fluids during granulite facies metamorphism. This conclusion is supported by calculations of the effect of fluid volatilization and exchange and is also independently supported by petrologic and phase equilibria considerations. The data suggest that these rocks were not an open system during metamorphism; that fluid/rock ratios were in many instances between 0.0 and 0.1; that externally derived fluids, as well as fluids derived by metamorphic volatilization, rose along localized channels and were not pervasive; and thus that no single generalization can be applied to metamorphic fluid conditions in the Adirondacks. Analyses of 3 to 4 coexisting minerals from Adirondack marbles show that isotopic equilibrium was attained at the peak of granulite and upper amphibolite facies metamorphism. Thus the isotopic compositions of metamorphic fluids can be inferred from analyses of carbonates and fluid budgets can be constructed. Carbonates from the granulite facies are on average, isotopically similar to those from lower grade or unmetamorphosed limestones of the same age showing that no large isotopic shifts accompanied high grade metamorphism. Equilibrium calculations indicate that small decreases in ??18O, averaging 1 permil, result from volatilization reactions for Adirondack rock compositions. Additional small differences between amphibolite and granulite facies marbles are due to systematic lithologie differences. The range of Adirondack carbonate ??18O values (12.3 to 27.2) can be explained by the highly variable isotopic compositions of unmetamorphosed limestones in conjunction with minor 18O and 13C depletions caused by metamorphic volatilization suggesting that many (and possibly most) marbles have closely preserved their

  10. Differentiating Detrital and Metamorphic Monazite in Greenschist-Facies Sandstones From the Witwatersrand Supergroup

    NASA Astrophysics Data System (ADS)

    Muhling, J. R.; Rasmussen, B.

    2009-05-01

    Monazite is a robust and reliable geochronometer of low-temperature metamorphic and hydrothermal events. It is a widespread accessory phase in sedimentary rocks metamorphosed at prehnite-pumpellyite to lower greenschist facies grade, and also in a range of hydrothermal ore deposits. Its ability to date multiple fluid-flow events in low-grade metasedimentary belts has been largely neglected, possibly because of a misconception that it is rare in these rocks and possibly because of misidentification of metamorphic monazite grains as detrital. Both detrital and metamorphic monazites are present in sandstone and conglomerate from the Witwatersrand Supergroup but can be distinguished by their occurrence, chemistry and age. Detrital grains were unstable during regional greenschist-facies metamorphism, and show evidence for a number of destructive reactions dependent on bulk rock composition and the original composition of the monazite. In quartz sandstone and conglomerate, detrital grains were present in heavy mineral bands with pyrite, zircon and chromite. The monazite grains have been pseudomorphed by intergrowths of apatite, florencite and Th-silicate, as well as matrix muscovite and chlorite. In some samples, Th-silicate forms only minute specks but in others it forms larger prismatic crystals that comprise up to 2% of some pseudomorphs. These variations may reflect differences in the original compositions of the detrital grains. In other samples detrital monazite cores, dated at 2.8-3.0 Ga, are enclosed within 2.04 Ga metamorphic rims. These composite grains formed by dissolution and reprecipitation of monazite during metamorphism. The cores and rims have distinctly different compositions, and the metamorphic rims show pronounced zoning of REE. In more calcic sandstone monazite occurs in heavy mineral bands with chromite, zircon, rutile, pyrite, apatite, Th-silicate, allanite and baddeleyite. These sandstones are notably rich in Ca-bearing minerals such as epidote

  11. 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

  12. Metamorphic and thermal evolution of large contact aureoles - lessons from the Bushveld Igneous Complex

    NASA Astrophysics Data System (ADS)

    Waters, D.

    2012-04-01

    Large igneous intrusions crystallise, cool, and transfer heat out into their host rocks. The thermal structure of the resulting aureole can be mapped as a series of assemblage zones and isograds, and can in principle be modelled on the assumption that heat transfer is dominantly by conduction. The local peak of contact metamorphism occurs later in time with increasing distance from the igneous contact. The importance of fluids as a metamorphic/metasomatic agent or heat transfer mechanism depends on volatile contents of magma and country rock, and on the geometry of the intrusion. Many of these features are spectacularly illustrated by the aureole beneath the mafic Rustenburg Layered Suite of the Bushveld Complex, which was emplaced at ca. 2060 Ma sub-concordantly into the shale-quartzite succession of the Pretoria Group in the Transvaal Basin. The layered suite reaches a thickness of at least 8 km, and the metamorphic aureole extends 4 km or more downwards into the "floor" of the intrusion. The great extent and relative absence of deformation make this a remarkable natural laboratory for studying the fundamental processes of metamorphism. In quantifying the thermal history, however, a number of second-order factors need to be taken into account. The first relates to the markedly different thermal properties of the major quartzite and shale units, and the second to the importance of endothermic metamorphic reactions in shale units relative to the quartzites. Further insights into metamorphic processes arise from the exquisite detail of poikiloblast growth microstructures preserved in graphite-poor metapelites of the Timeball Hill and Silverton Formations, 2.5 to 3.5 km beneath the igneous contact. These allow a detailed reconstruction of the time sequence of mineral growth and replacement, revealing a marked overlap of the growth intervals of porphyroblastic staurolite, cordierite, biotite, garnet and andalusite at the expense of muscovite, chlorite and chloritoid

  13. U-Th age distribution of coral fragments from multiple rubble ridges within the Frankland Islands, Great Barrier Reef: Implications for past storminess history

    NASA Astrophysics Data System (ADS)

    Liu, Entao; Zhao, Jian-xin; Feng, Yue-xing; Leonard, Nicole D.; Clark, Tara R.; Roff, George

    2016-07-01

    Prograded coral rubble ridges have been widely used as archives for reconstructing long-term storm or storminess history. Chronologies of ridge systems in previous studies are often based on a limited number of low-resolution radiocarbon or optically-stimulated luminescence (OSL) ages per ridge (usually only one age per ridge), which carry intrinsic age uncertainties and make interpretation of storm histories problematic. To test the fidelity of storm ridges as palaeo-storm archives, we used high-precision U-Th dating to examine whether different samples from a single ridge are temporally constrained. We surveyed three transects of ridge systems from two continental islands (Normanby Island and High Island) within the Frankland Islands, Great Barrier Reef (GBR), and obtained 96 U-Th dates from coral rubble samples collected from within and between different ridges. Our results revealed significant differences in age ranges between the two islands. The steeper and more defined rubble ridges present on Normanby Island revealed that the majority of U-Th ages (over 60%) from a single ridge clustered within a narrow age range (∼100 years). By contrast, the lower and less defined ridges on High Island, which were more likely formed during both storm and non-storm high-energy events, revealed significant scatter in age distribution (>>200 years) with no notable clustering. The narrower age ranges obtained from the steeper and more defined rubble ridges suggest that previous approaches of using either limited samples from a single ridge or low-precision dating methods to establish chronologies are generally valid at centennial to millennial timescales, although caution must be taken to use such approaches for storm history reconstruction on shorter timescales (e.g. decadal). The correlation between U-Th mortality ages of coral rubble and historical stormy periods highlights the possibility of using coral rubble age distribution from rubble ridges to reconstruct the long

  14. Telemagmatic metamorphism superimposed on regional metamorphism: Evidence from coals in central China

    SciTech Connect

    Tang, Y. . Dept. of Geological Sciences)

    1993-02-01

    Coal (Lower Permian No. 1) in north-central Henan province, central China, exhibits a zoned rank distribution. The rank varies between high-volatile bituminous and anthracite. Highest rank coal occurs in a northwest-southeast trending zone that cuts across the center of the study area. Coal rank decreases from this central zone towards both the northeast and southwest. Core data indicate that the anthracite is currently overlain by over 4,600 m of sedimentary cover, which represents more or less continuous sedimentation during the Permian and Triassic. In the lower rank area to the southwest, erosion has removed all but approximately 1,000 m of strata. The rank distribution in this area has been attributed to regional metamorphism by previous workers as the higher coal rank coincides with the thicker strata. However, this study reveals that anthracite in the area has a much higher vitrinite reflectance, between 3--6% (Ro max, in oil), with some locations exhibiting reflectances greater than 6%. Petrographically, the anthracite is characterized by well developed pores (5--10 [mu]m in diameter) and mosaic structure. It is suggested that the higher heat flow is due to the presence of deep-seated plutons. It is proposed that coal metamorphism in this area involved three stages: (1) Pre-orogenic (early Permian-late Triassic). Regional metamorphism produced coals of subbituminous to high-volatile bituminous rank; (2) Orogenic (early Jurassic-late Cretaceous). Telemagmatic metamorphism resulted in zones of higher rank coal (medium volatile through anthracite rank); (3) Post-orogenic (Tertiary-Quaternary). Shallow burial depth due to the tectonic uplift followed by erosion had a negligible effect on coal rank. It is suggested, therefore, that coalification in this area is the result of regional metamorphism overprinted by telemagmatic metamorphism.

  15. The digital global geologic map of Mars: chronostratigraphic ages, topographic and crater morphologic characteristics, and updated resurfacing history

    USGS Publications Warehouse

    Tanaka, K.L.; Robbins, S.J.; Fortezzo, C.M.; Skinner, J.A., Jr.; Hare, T.M.

    2014-01-01

    A new global geologic map of Mars has been completed in a digital, geographic information system (GIS) format using geospatially controlled altimetry and image data sets. The map reconstructs the geologic history of Mars, which includes many new findings collated in the quarter century since the previous, Viking-based global maps were published, as well as other discoveries that were made during the course of the mapping using new data sets. The technical approach enabled consistent and regulated mapping that is appropriate not only for the map's 1:20,000,000 scale but also for its widespread use by diverse audiences. Each geologic unit outcrop includes basic attributes regarding identity, location, area, crater densities, and chronostratigraphic age. In turn, units are grouped by geographic and lithologic types, which provide synoptic global views of material ages and resurfacing character for the Noachian, Hesperian, and Amazonian periods. As a consequence of more precise and better quality topographic and morphologic data and more complete crater-density dating, our statistical comparisons identify significant refinements for how Martian geologic terrains are characterized. Unit groups show trends in mean elevation and slope that relate to geographic occurrence and geologic origin. In comparison with the previous global geologic map series based on Viking data, the new mapping consists of half the number of units due to simpler, more conservative and globally based approaches to discriminating units. In particular, Noachian highland surfaces overall have high percentages of their areas now dated as an epoch older than in the Viking mapping. Minimally eroded (i.e., pristine) impact craters ≥3 km in diameter occur in greater proportion on Hesperian surfaces. This observation contrasts with a deficit of similarly sized craters on heavily cratered and otherwise degraded Noachian terrain as well as on young Amazonian surfaces. We interpret these as reflecting the

  16. The digital global geologic map of Mars: Chronostratigraphic ages, topographic and crater morphologic characteristics, and updated resurfacing history

    NASA Astrophysics Data System (ADS)

    Tanaka, K. L.; Robbins, S. J.; Fortezzo, C. M.; Skinner, J. A.; Hare, T. M.

    2014-05-01

    A new global geologic map of Mars has been completed in a digital, geographic information system (GIS) format using geospatially controlled altimetry and image data sets. The map reconstructs the geologic history of Mars, which includes many new findings collated in the quarter century since the previous, Viking-based global maps were published, as well as other discoveries that were made during the course of the mapping using new data sets. The technical approach enabled consistent and regulated mapping that is appropriate not only for the map's 1:20,000,000 scale but also for its widespread use by diverse audiences. Each geologic unit outcrop includes basic attributes regarding identity, location, area, crater densities, and chronostratigraphic age. In turn, units are grouped by geographic and lithologic types, which provide synoptic global views of material ages and resurfacing character for the Noachian, Hesperian, and Amazonian periods. As a consequence of more precise and better quality topographic and morphologic data and more complete crater-density dating, our statistical comparisons identify significant refinements for how Martian geologic terrains are characterized. Unit groups show trends in mean elevation and slope that relate to geographic occurrence and geologic origin. In comparison with the previous global geologic map series based on Viking data, the new mapping consists of half the number of units due to simpler, more conservative and globally based approaches to discriminating units. In particular, Noachian highland surfaces overall have high percentages of their areas now dated as an epoch older than in the Viking mapping. Minimally eroded (i.e., pristine) impact craters ≥3 km in diameter occur in greater proportion on Hesperian surfaces. This observation contrasts with a deficit of similarly sized craters on heavily cratered and otherwise degraded Noachian terrain as well as on young Amazonian surfaces. We interpret these as reflecting the

  17. Formation of Neoproterozoic metamorphic complex during oblique convergence (Eastern Desert, Egypt)

    NASA Astrophysics Data System (ADS)

    Fritz, H.; Wallbrecher, E.; Khudeir, A. A.; Abu el Ela, F.; Dallmeyer, D. R.

    1996-10-01

    Major portions of the Pan-African Orogen in the Eastern Desert of Egypt were formed by island-arc accretion in the Neoproterozoic. These areas are characterized by their lack of major crustal thickening. Metamorphic core complexes occur parallel to the strike of the Eastern Desert Orogen. These domes exhibit polyphase metamorphism and deformation in contrast to the structurally overlying nappes which include ophiolitic melanges and island-arc volcanic rocks. These nappes show northwest directed, orogen-parallel thrusting in the internal parts and west to southwest directed imbrication in the external parts of the orogen. Structures related to exhumation of the metamorphic core complexes partition into different displacement paths localized within a crustal-scale wrench corridor of the Najd fault system. Northwest trending orogen-parallel, sinistral strike-slip faults define the western and eastern margins of the domes. North and south dipping low-angle normal faults developed along the northern and southern margins of the domes and form extensional bridges between them. {40Ar}/{39Ar} ages obtained from syntectonic muscovites within the shear zones gave Neoproterozoic ages of 595.9±0.5 and 588.2±0.3 Ma. The synchronous activity of strike-slip and normal faults suggests a regional east-west shortening which was accomodated by deep-level basal decollement beneath the metamorphic core complexes and a coeval northwest-southeast, orogen-parallel extension. This extension was accompanied by intramontane molasse sedimentation and emplacement of calc-alkaline plutons. Since the rapid exhumation of gneisses in the core complexes cannot be explained by thickening of the crust, the authors favour a model which calls for enhanced heat flow along the Najd fault system which would have enabled the formation of syn-extensional plutonism and triggered the exhumation of the metamorphic core complexes. Lateral buoyancy forces were concentrated within the Najd wrench corridor and

  18. The Relative Importance of Family History, Gender, Mode of Onset, and Age at Onset in Predicting Clinical Features of First-Episode Psychotic Disorders.

    PubMed

    Compton, Michael T; Berez, Chantal; Walker, Elaine F

    2014-11-01

    Objective: Family history of psychosis, gender, mode of onset, and age at onset are considered prognostic factors important to clinicians evaluating first-episode psychosis; yet, clinicians have little guidance as to how these four factors differentially predict early-course substance abuse, symptomatology, and functioning. We conducted a "head-to-head comparison" of these four factors regarding their associations with key clinical features at initial hospitalization. We also assessed potential interactions between gender and family history with regard to age at onset of psychosis and symptom severity.Methods: Consecutively admitted first-episode patients (n=334) were evaluated in two studies that rigorously assessed a number of early-course variables. Associations among variables of interest were examined using Pearson correlations, ÷2 tests, Student's t-tests, and 2x2 factorial analyses of variance.Results: Substance (nicotine, alcohol, and cannabis) abuse and positive symptom severity were predicted only by male gender. Negative symptom severity and global functioning impairments were predicted by earlier age at onset of psychosis. General psychopathology symptom severity was predicted by both mode of onset and age at onset. Interaction effects were not observed with regard to gender and family history in predicting age at onset or symptom severity.Conclusions: The four prognostic features have differential associations with substance abuse, domains of symptom severity, and global functioning. Gender and age at onset of psychosis appear to be more predictive of clinical features at the time of initial evaluation (and thus presumably longer-term outcomes) than the presence of a family history of psychosis and a more gradual mode of onset. PMID:25367167

  19. Deciphering cryptic P-T-d-t histories in the western Thor-Odin dome, Monashee Mountains, Canadian Cordillera: A key to unravelling pre-Cordilleran tectonic signatures

    NASA Astrophysics Data System (ADS)

    Spalla, M. Iole; Zanoni, Davide; Williams, Paul F.; Gosso, Guido

    A detailed structural and metamorphic study along a transect from the core of the Thor-Odin dome to its western margin (South-eastern Canadian Cordillera) has allowed the reconstruction of the P-T-d-t history estimating PT changes, during successive fabric development. The dome comprises a recumbently-folded and transposed Proterozoic high-grade basement and Late Proterozoic-Palaeozoic metasedimentary cover, characterised by a regional foliation (S T). An inferred, nearly-isothermal decompressional path, from a maximum depth of ca. 40 km, transgresses the "maximum relaxed geotherm", consistent with exhumation during lithospheric extension. Contrasting pre-S T PT conditions indicate that different units followed different PT paths before S T development. Traces of these early and variable structural and metamorphic re-equilibration steps are preserved in meter-scale boudins and granular-scale domains poorly affected by transposition. The various paths represent events, from Palaeoproterozoic to Proterozoic Rodinia break up, to Jurassic-Cretaceous convergence and final exhumation in the Eocene. Much of the deformational and metamorphic history may have been accumulated before onset of S T. However, the early structural history is overprinted, and mineral assemblages and their relative ages are mostly obscured by S T development. A glimpse of the earlier geologic history is possible only by combining micro-structural analysis and PT estimates.

  20. A new approach to quantification of metamorphism using ultra-small and small angle neutron scattering

    NASA Astrophysics Data System (ADS)

    Anovitz, Lawrence M.; Lynn, Gary W.; Cole, David R.; Rother, Gernot; Allard, Lawrence F.; Hamilton, William A.; Porcar, Lionel; Kim, Man-Ho

    2009-12-01

    In this paper we report the results of a study using small angle and ultra-small angle neutron scattering techniques (SANS and USANS) to examine the evolution of carbonates during contact metamorphism. Data were obtained from samples collected along two transects in the metamorphosed Hueco limestone at the Marble Canyon, Texas, contact aureole. These samples were collected from the igneous contact out to ˜1700 m. Scattering curves obtained from these samples show mass fractal behavior at low scattering vectors, and surface fractal behavior at high scattering vectors. Significant changes are observed in the surface and mass fractal dimensions as well as the correlation lengths (pore and grain sizes), surface area to volume ratio and surface Gibbs Free energy as a function of distance, including regions of the aureole outside the range of classic metamorphic petrology. A change from mass-fractal to non-fractal behavior is observed at larger scales near the outer boundary of the aureole that implies significant reorganization of pore distributions early in the metamorphic history. Surface fractal results suggest significant smoothing of grain boundaries, coupled with changes in pore sizes. A section of the scattering curve with a slope less than -4 appears at low- Q in metamorphosed samples, which is not present in unmetamorphosed samples. A strong spike in the surface area to volume ratio is observed in rocks near the mapped metamorphic limit, which is associated with reaction of small amounts of organic material to graphite. It may also represent an increase in pore volume or permeability, suggesting that a high permeability zone forms at the boundary of the aureole and moves outwards as metamorphism progresses. Neutron scattering data also correlate well with transmission electron microscopic (TEM) observations, which show formation of micro- and nanopores and microfractures during metamorphism. The scattering data are, however, quantifiable for a bulk rock in a

  1. A new approach to quantification of metamorphism using ultra-small and small angle neutron scattering.

    SciTech Connect

    Anovitz, Lawrence {Larry} M; Lynn, Gary W; Cole, David R

    2009-12-01

    In this paper we report the results of a study using small angle and ultra-small angle neutron scattering techniques (SANS and USANS) to examine the evolution of carbonates during contact metamorphism. Data were obtained from samples collected along two transects in the metamorphosed Hueco limestone at the Marble Canyon, Texas, contact aureole. These samples were collected from the igneous contact out to {approx}1700 m. Scattering curves obtained from these samples show mass fractal behavior at low scattering vectors, and surface fractal behavior at high scattering vectors. Significant changes are observed in the surface and mass fractal dimensions as well as the correlation lengths (pore and grain sizes), surface area to volume ratio and surface Gibbs Free energy as a function of distance, including regions of the aureole outside the range of classic metamorphic petrology. A change from mass-fractal to non-fractal behavior is observed at larger scales near the outer boundary of the aureole that implies significant reorganization of pore distributions early in the metamorphic history. Surface fractal results suggest significant smoothing of grain boundaries, coupled with changes in pore sizes. A section of the scattering curve with a slope less than -4 appears at low-Q in metamorphosed samples, which is not present in unmetamorphosed samples. A strong spike in the surface area to volume ratio is observed in rocks near the mapped metamorphic limit, which is associated with reaction of small amounts of organic material to graphite. It may also represent an increase in pore volume or permeability, suggesting that a high permeability zone forms at the boundary of the aureole and moves outwards as metamorphism progresses. Neutron scattering data also correlate well with transmission electron microscopic (TEM) observations, which show formation of micro- and nanopores and microfractures during metamorphism. The scattering data are, however, quantifiable for a bulk rock

  2. Sequential Development of Interfering Metamorphic Core Complexes: Numerical Experiments and Comparison to the Cyclades, Greece

    NASA Astrophysics Data System (ADS)

    Tirel, C.; Gautier, P.; van Hinsbergen, D.; Wortel, R.

    2007-12-01

    The Cycladic extensional province (Greece) contains classical examples of metamorphic core complexes (MCCs), where exhumation was accommodated along multiple interfering and/or sequentially developed syn- and antithetic extensional detachment zones. Previous studies on the development of MCCs did not take into account the possible interference between multiple and closely spaced MCCs. In the present study, we have performed new lithosphere-scale experiments in which the deformation is not a priori localized so as to explore the conditions of the development of several MCCs in a direction parallel to extension. In a narrow range of conditions, MCCs are closely spaced, interfere with each other, and develop in sequence. From a comparison between numerical results and geological observations, we find that the Cyclades metamorphic core complexes are in good agreement with the model in terms of Moho geometry and depth, kinematic and structural history, timing and duration of core complex formation and metamorphic history. We infer that, for Cycladic MCC-type to develop, an initial crustal thickness prior to the onset of post-orogenic extension between 40 and 44 km, a boundary velocity close to 2 cm/yr and an initial thermal lithospheric thickness of about 60 km are required. The latter may be explained by a significant heating due to delamination of subducting continental crust or vigorous small-scale thermal convection.

  3. New evidence for polyphase metamorphism of glaucophane schist and eclogite exotic blocks in the Franciscan Complex, California and Oregon

    USGS Publications Warehouse

    Moore, Diane E.; Blake, M.C., Jr.

    1989-01-01

    The early metamorphic history of high-grade exotic blocks in the Franciscan Complex may be more complicated than previously supposed. The different assemblages of high-grade glaucophane schists, eclogite, amphibolite and hornblende schist are commonly considered to have formed at the same time from essentially unmetamorphosed oceanic crust. However, new textural and mineralogical data presented here suggest that high-grade glaucophane schist and eclogite have replaced an earlier epidote-amphibolite facies assemblage that is identical to the primary assemblages in many of the hornblende-rich blocks. At least some of the hornblende-rich blocks may therefore be well-preserved remnants of the earlier metamorphism. Comparison of the mineral assemblages and element partititioning in the mixed-assemblage blocks suggests that the glaucophane schist and eclogite metamorphism took place at slightly lower temperatures but at the same or higher pressures than the earlier, hornblende-forming stage. -Authors

  4. Making MetPetDB a tool for reconnaissance studies of metamorphism and metamorphic rocks

    NASA Astrophysics Data System (ADS)

    Hallett, B. W.; Spear, F. S.; Horkley, L. K.; Adali, S.; Fox, P. A.

    2012-12-01

    Recent data mining efforts have significantly increased the coverage and quantity of published data that form the foundation of MetPetDB: the Database for Metamorphic Petrology. Mineral assemblage, metamorphic grade, geochemical mineral and whole rock analyses, and image data from over 600 published papers have been compiled and uploaded, with focus on a number of particularly well-studied metamorphic belts of regional extent. As a result of data mining efforts in the past several years, MetPetDB now contains data for over 9,000 samples, over 10,000 mineral and whole rock (major or trace element) analyses, and over 20,000 images including maps, thin section scans, photomicrographs, SE and BSE images, and X-ray maps. These data are available for searching and download, exportable in spreadsheets and/or as placemark layers in a Google Earth .kml file. Each Google Earth placemark contains a link to the full data available through MetPetDB's web interface. The improved spatial coverage provides a starting point for a geoscientist to rapidly gather sample and geochemical data for a growing inventory of distinct metamorphic belts. Regional searches can be performed by choosing a user-defined bounding box, or any of a number of bounding polygons that delineate distinct metamorphic belts, such as the Greenland Caledonides, or the Bohemian Massif. MetPetDB is a tool for researchers to share, compile, and organize sample information, both published and unpublished, enabling production of a dynamic GIS to aid in planning field work, producing geologic maps, or making inventory of geochemical data for metamorphic rocks. In addition to regional queries, published metamorphic rock samples with non-spatial commonalities may be queried and compiled using MetPetDB. For example, a petrologist with an interest in the equilibrium exchange of yttrium between garnet and monazite at mid-crustal conditions could easily find garnet with a certain range of yttrium content in amphibolite

  5. Hinterland-to-foreland structural evolution of the base of the Himalayan metamorphic core, west Nepal

    NASA Astrophysics Data System (ADS)

    Braden, Z.; Godin, L.; Yakymchuk, C.; Kellett, D.; Cottle, J. M.

    2015-12-01

    The base of the Himalayan metamorphic core is a folded reverse-sense shear zone exposed extensively along its transport direction. In west Nepal, along-transport exposures show a transition in structural style from hinterland to foreland, and sampled quartzite and pelite show variations in thermobarometry, quartz crystallographic preferred orientation (CPO), monazite Th-Pb ages and 40Ar/39Ar thermochronology. In the hinterland region, the shear zone yields a deformation temperature gradient from > 700°C at the top of the shear zone down to 400°C at the base. Metamorphic grade also decreases downwards through the shear zone. Muscovite 40Ar/39Ar ages are ca. 6 Ma. In the transition zone separating hinterland and foreland on the north flank of the Karnali klippe, a comparable structural section yields a deformation temperature gradient that similarly decreases down structural level from ~700 to 500°C. Muscovite 40Ar/39Ar dating yield ca. 14-12 Ma cooling ages. In-situ monazite geochronology indicates prograde metamorphism at ca. 43-34 Ma and melt crystallization at ca. 26-18 Ma. In the foreland, deformation is not strictly brittle; CPO analyses on sheared quartzite on the south flank of the Karnali klippe suggest deformation temperatures decreasing from 500 to 400°C downwards through the shear zone. Muscovite from the foreland yields 40Ar/39Ar ages of ca. 17 Ma. Deformation temperatures decrease marginally from hinterland to foreland and structurally downward within the shear zone, and estimates suggest ductile deformation prevails well into the foreland. Hinterland 40Ar/39Ar muscovite ages in west Nepal are anomalously young, and are possibly related to recent exhumation due to the SE-propagating mid-Miocene Gurla Mandhata-Humla system. Alternatively, they could be linked to the activation of a young duplex in the footwall of the Himalayan metamorphic core due to along-strike variation in geometry of the Main Himalayan thrust ramp.

  6. Strain-collapsed metamorphic isograds in a sillimanite gneiss dome, Seward Peninsula, Alaska

    SciTech Connect

    Miller, E.L.; Calvert, A.T.; Little, T.A. )

    1992-06-01

    Unusually closely spaced Barrovian series isograds have been described along the flanks of the Kigluaik Mountains, Seward Peninsula, Alaska, where they separate a high-grade gneiss complex intruded by granites of Cretaceous age from surrounding, regionally developed, blueschist to greenschist facies rocks. Structural mapping of the transition zone between the two metamorphic types indicates that their juxtaposition was aided by significant syn- to late-metamorphic solid-state flow that served to attenuate the overlying rock column and thus collapse the field metamorphic gradient. On the basis of field relations, structural data, petrography, and geochronologic data, strain appears to have accompanied the rapid (adiabatic) rise of high-temperature rocks from several tens of kilometers to less than 10 km depth during the Cretaceous, in an event younger than the unrelated to high-P metamorphism. Granite-cored gneiss domes on the Seward Peninsula may have formed during extension of previously thickened continental crust, resulting in the {approximately}35-km-thick crust and near-sea-level elevations of the region today.

  7. Using Family Health History for Chronic Disease Prevention in the Age of Genomics: Translation to Health Education Practice

    ERIC Educational Resources Information Center

    Hanson, Carl; Novilla, Lelinneth; Barnes, Michael; De La Cruz, Natalie; Meacham, Aaron

    2007-01-01

    Advances in the field of human genomics have important implications for the prevention of chronic disease. In response to these advancements, public health professionals--including health educators--must become competent in the principles underlying the interface between genomics and the use of family health history. Family health history captures…

  8. Evolution of the Eastern Karakoram Metamorphic Complex, Ladakh, NW India, and its relationship to magmatism and regional tectonics

    NASA Astrophysics Data System (ADS)

    Wallis, David; Phillips, R. J.; Lloyd, G. E.

    2014-06-01

    The eastern Karakoram terrane, NW India, records crustal evolution in the core of the Himalayan-Tibetan orogen. Recent debate has centred on whether prograde metamorphism, anatexis and leucogranite emplacement were the result of localised shear heating and magma advection within the Karakoram Fault Zone (KFZ) or instead predate the KFZ and were the result of regional tectonometamophic events. Inclusions within andalusite porphyroblasts that grew during 15.7 Ma leucogranite emplacement have fabrics that are random or discordant to the KFZ matrix foliation, indicating that the KFZ initiated after this time. Therefore, earlier anatexis and metamorphism are the result of regional metamorphic events. Amphibole-plagioclase thermobarometry on a c. 17 Ma migmatite melanosome, later exhumed within a transpressional zone of the KFZ, shows that melting occurred at 688 °C and 522 MPa. Amphibolites record an older kyanite-grade metamorphic event that occurred at 677-736 °C and 875-1059 MPa. Metapelites also record a kyanite-grade event which is constrained by Ti-in-biotite thermometry to have occurred at 622 °C and > 650 MPa. The tectonometamorphic history of the eastern Karakoram correlates closely with that of the central Karakoram away from the KFZ. This correlation supports the interpretation that metamorphism and anatexis were regional in extent and also indicates a limited offset of < 150 km on the KFZ.

  9. Sedimentologic to metamorphic processes recorded in the high-pressure/low-temperature Mesozoic Rosetta Marble of Anatolia

    NASA Astrophysics Data System (ADS)

    Scheffler, F.; Oberhänsli, R.; Pourteau, A.; Immenhauser, A.; Candan, O.

    2016-01-01

    Anatolia's high-pressure metamorphic belts are characterized in part by a Neotethyan stratigraphic succession that includes a mid-Cretaceous hemi-pelagic marble sequence. This unit contains, towards its stratigraphic top, dm-to-m-long radiating calcitic rods forming rosette-like textures. Here, we refer to these features as "Rosetta Marble". The remarkable textural similarity of non-metamorphic selenite crystals and radiating calcite rods in the Rosetta Marble strongly suggests that these textures represent pseudomorphs after selenites. Metamorphosed hemi-pelagic limestones, dominated by Rosetta selenite pseudomorphs, are alternating with siliceous meta-sediments containing relictic radiolaria tests. This stratigraphic pattern is indicative of transient phases characterized by evaporites precipitated from basinal brines alternating with non-evaporative hemi-pelagic deposition from normal-marine seawater. The regional distribution of Rosetta Marble exposures over 600 km is indicative of basin-scale evaporitic intervals. High-pressure, low-temperature metamorphism of these rocks is witnessed by Sr-rich (up to 3500 ppm), fibrous calcite pseudomorphs after aragonite and isolated aragonite inclusions in quartz. Peak metamorphic conditions of 1.2 GPa and 300-350 °C are attested by high-Si white mica thermobarometry. The Rosetta Marble case example examines the potential to unravel the complete history from deposition to diagenesis and metamorphism of meta-sedimentary rocks.

  10. Metamorphism of the ca. 3800 Ma supracrustal rocks at Isua, West Greenland: implications for early Archaean crustal evolution

    NASA Astrophysics Data System (ADS)

    Boak, Jeremy L.; Dymek, Robert F.

    1982-06-01

    A detailed mineralogical and petrological study has been carried out on samples from two clastic metasedimentary lithologies from the ˜ 3800 Ma Isua Supracrustal Belt, West Greenland. Semipelitic to pelitic "garnet-biotite schist" contains the limiting AKFM assemblage: muscovite-biotite-garnet-staurolite (+ quartz + plagioclase + ilmenite), whereas "muscovite-biotite gneiss", derived from felsic volcanogenic graywacke, locally contains kyanite (+ quartz+ plagioclase + Ca-, Mn-rich garnet). Temperatures calculated from Fe-Mg partitioning between coexisting garnet- biotite indicate equilibration for garnet coresat T ˜550°C, and ˜460°C for garnet rims. We interpret the higher T as a minimum estimate for prograde regional metamorphism which we argue occurred before 3600 Ma, whereas the lower T reflects later retrogression as indicated by the development of chlorite ± sericite in many samples. The presence of kyanite as the stable aluminosilicate polymorph, combined with phase assemblage data, indicate P ˜5 kbar during prograde metamorphism, and a depthof burial of at least 15 km. The Isua supracrustals are the oldest comprehensively dated rocks on Earth, and the metamorphic mineral assemblages reported here constitute the earliest direct record of thermal regimes in Archaean crust. Therefore, characterization of the metamorphic history of the Isua region places an important constraint on models of early Earth history. Our data and observations indicate that prograde regional metamorphism at Isua occurred at conditions which are considered "normal" for an orogenic system, with a metamorphic thermal gradient ˜35°C/km. Moreover, our results contraindicate the universal occurrence of "thin" Archaean crust and excessively "steep" crustal thermal gradients as proposed by some investigators. Such conclusion appears at odds with estimates for higher terrestrial heat production during the early Archaean, but can be resolved by appealing to more rapid convection and

  11. Reconstruction of the metamorphic evolution of the Hamadan high-grade metapelites, Sanandaj-Sirjan Zone, western Iran

    NASA Astrophysics Data System (ADS)

    Monfaredi, Behzad; Hauzenberger, Christoph; Neubauer, Franz; Schulz, Bernhard; Shakerardakani, Farzaneh; Genser, Johann; Halama, Ralf

    2016-04-01

    C, suggesting that garnet growth is the result of two growth cycles. Despite textural differences, U-Th-Pb monazite geochronology revealed similar ages between 168 ± 11 Ma and 149 ± 19 Ma for schistose/hornfels rocks, which is within the same timeframe of the Alvand pluton intrusion. 40Ar-39Ar white mica age patterns yielded total gas ages ranging from 80 to 70 Ma over the entire transect. Microfabrics indicate formation of the foliation during garnet growth, which is followed subsequently by a retrogression to chlorite. Consequently, the Ar-Ar ages most likely indicate the final stage of foliation formation and accompanying cooling of the Hamadan complex to less than ca. 425 ± 25 °C (argon retention temperature in white mica). Temperature-time paths from all accessible mineral ages suggest, therefore, slow cooling and exhumation within two episodes toward the contact. Since absence or lack of plutonic rocks in the higher-grade sillimanite-bearing rocks and irregular metamorphic zones, we postulate that the Alvand batholith extends at shallow levels below the entire basement or is disturbed by shearing or a large number of smaller granitoid intrusions are hidden below the surface at mid- to upper-crustal depths. References Mahmoudi, S., Corfu, F., Masoudi, F., Mehrabi, B., Mohajjel, M., 2011. U-Pb dating and emplacement history of granitoid plutons in the northern Sanandaj-Sirjan Zone, Iran. J. Asian Earth Sci. 41, 238-249. Moynihan, D. P., Pattison, D. R. M., 2013. An automated method for the calculation of P-T paths from garnet zoning, with application to metapelitic schist from the Kootenay Arc, British Columbia, Canada. J. Metamorphic Geol. 31, 525-548. Shahbazi, H., Siebel,W., Pourmoafee, M., Ghorbani, M., Sepahi, A.A., Shang, C.K., Vosoughi Abedini, M., 2010. Geochemistry and U-Pb zircon geochronology of the Alvand plutonic complex in Sanandaj-Sirjan Zone (Iran): new evidence for Jurassic magmatism. J. Asian Earth Sci. 9, 668-683.

  12. Metamorphism of the Chugach Metamorphic Complex, (Alaska). New pressure estimates question the ridge subduction context.

    NASA Astrophysics Data System (ADS)

    Bruand, Emilie; Gasser, Deta; Kurt, Stuewe; Beyssac, Olivier

    2010-05-01

    The Chugach Metamorphic Complex (CMC, Alaska) is a 200 km long and 10-50 km wide complex and is part of an active accretionary prism. According to the sparse existing literature, the complex is believed to be a low-pressure high-temperature terrain (400-650°C and ~3kb) with a migmatitic inner core (~5-10 km) and schist rims surrounded by phyllite (Sisson et al., 1988). Such low pressure conditions are not common in a subduction zone setting and the formation of the complex is thus attributed to the subduction of a ridge during the Eocene (~ 50 my). This contribution presents detailed petrological work from the region to show that the metamorphism occurred at much higher pressures than previously believed. We focus on the petrology of calcareous metapelites from 4 different N-S transects across the complex from west to east (each being 10 to 30 km wide). Several PT thermobarometric tools are used including average PT determination using THERMOCALC, garnet-biotite thermometry and RSCM (graphite) thermometers using Raman spectroscopy. In addition to these methods, several thermodynamic pseudosections were calculated. Our calculations show that the metamorphic conditions vary between 550°C and 3-4 kbar in the north of the complex to >700°C and 7-9 kbar in the south. In the central part of the complex these conditions appear to be attributable to a single metamorphic event that occurred around 50 my. However, in some locations near major granitic intrusions that penetrate the regions two events are observed: 1) a first one characterised by temperatures around 550°C followed by 2) a hotter contact metamorphism (>640°C). Earlier studies have interpreted the supposed low-pressure conditions of the CMC (considered to be no more than 3 kbar) to be connected to a ridge subduction geodynamic context. Within our interpretation, the hypothesis of a ridge subduction context is not needed and indeed appears questionable. In fact, a simple subduction context following by a

  13. The eruptive history of the Tequila volcanic field, western Mexico: ages, volumes, and relative proportions of lava types

    NASA Astrophysics Data System (ADS)

    Lewis-Kenedi, Catherine B.; Lange, Rebecca A.; Hall, Chris M.; Delgado-Granados, Hugo

    2005-06-01

    The eruptive history of the Tequila volcanic field (1600 km2) in the western Trans-Mexican Volcanic Belt is based on 40Ar/39Ar chronology and volume estimates for eruptive units younger than 1 Ma. Ages are reported for 49 volcanic units, including Volcán Tequila (an andesitic stratovolcano) and peripheral domes, flows, and scoria cones. Volumes of volcanic units ≤1 Ma were obtained with the aid of field mapping, ortho aerial photographs, digital elevation models (DEMs), and ArcGIS software. Between 1120 and 200 kyrs ago, a bimodal distribution of rhyolite (~35 km3) and high-Ti basalt (~39 km3) dominated the volcanic field. Between 685 and 225 kyrs ago, less than 3 km3 of andesite and dacite erupted from more than 15 isolated vents; these lavas are crystal-poor and show little evidence of storage in an upper crustal chamber. Approximately 200 kyr ago, ~31 km3 of andesite erupted to form the stratocone of Volcán Tequila. The phenocryst assemblage of these lavas suggests storage within a chamber at ~2 3 km depth. After a hiatus of ~110 kyrs, ~15 km3 of andesite erupted along the W and SE flanks of Volcán Tequila at ~90 ka, most likely from a second, discrete magma chamber located at ~5 6 km depth. The youngest volcanic feature (~60 ka) is the small andesitic volcano Cerro Tomasillo (~2 km3). Over the last 1 Myr, a total of 128±22 km3 of lava erupted in the Tequila volcanic field, leading to an average eruption rate of ~0.13 km3/kyr. This volume erupted over ~1600 km2, leading to an average lava accumulation rate of ~8 cm/kyr. The relative proportions of lava types are ~22 43% basalt, ~0.4 1% basaltic andesite, ~29 54% andesite, ~2 3% dacite, and ~18 40% rhyolite. On the basis of eruptive sequence, proportions of lava types, phenocryst assemblages, textures, and chemical composition, the lavas do not reflect the differentiation of a single (or only a few) parental liquids in a long-lived magma chamber. The rhyolites are geochemically diverse and were likely

  14. A review of the plate convergence history of the East Anatolia-Transcaucasus region during the Variscan: Insights from the Georgian basement and its connection to the Eastern Pontides

    NASA Astrophysics Data System (ADS)

    Rolland, Y.; Hässig, M.; Bosch, D.; Meijers, M. J. M.; Sosson, M.; Bruguier, O.; Adamia, Sh.; Sadradze, N.

    2016-05-01

    This article summarizes the geodynamic evolution of the Variscan to Mesozoic Tethyan subduction history, based on a review of geochronological data from Eastern Anatolia and the Lesser Caucasus, and new isotopic ages for the Georgian crystalline basements. The geological history of the basements of Georgia (Transcaucasus) and NE Turkey (eastern Pontides) appears to be similar and provides evidence for a continuously active continental margin above a north-dipping subduction since at least the Lower Jurassic. New La-ICPMS U-Pb ages from the Georgian basement provide further evidence for the derivation of the Transcaucasus and its western continuation (the eastern Pontides) from Gondwana. A migmatized granodiorite provides preserved magmatic zircon cores with an age of 474 ± 3 Ma, while the age of migmatization is constrained by its 343 ± 2 Ma metamorphic rims. Metamorphism is synchronous with widespread I-type granites that were emplaced at 335 ± 8 Ma in the neighbouring Dzirula massif, and in the eastern Pontides. These U-Pb ages are in close agreement with recently obtained Ar/Ar ages from biotites and muscovites from metamorphic schists and U-Pb ages ranging from 340 to 330 Ma in the Georgian basement. The narrow range of ages suggests that the Variscan LP-HT metamorphic event in the eastern Pontides and Georgia was of short duration and likely related to mantle-derived intrusives. Furthermore, we suggest that (1) rifting of the Pontides-Transcaucasus block (PTB) from Gondwana at 450-350 Ma could have been driven by roll-back of the south-dipping Rheic slab, (2) that the main metamorphic and coeval magmatic events are related to the accretion of the PTB to the Eurasian margin at c. 350 Ma, while the source of magmatism is ascribed to slab detachment of the south-dipping slab at 340 Ma and that (3) three subduction zones may have been contemporaneously active in the Tethyan domain during the Jurassic: (i) the Lesser Caucasus South Armenian Block (SAB) shares a

  15. Aging.

    PubMed

    Park, Dong Choon; Yeo, Seung Geun

    2013-09-01

    Aging is initiated based on genetic and environmental factors that operate from the time of birth of organisms. Aging induces physiological phenomena such as reduction of cell counts, deterioration of tissue proteins, tissue atrophy, a decrease of the metabolic rate, reduction of body fluids, and calcium metabolism abnormalities, with final progression onto pathological aging. Despite the efforts from many researchers, the progression and the mechanisms of aging are not clearly understood yet. Therefore, the authors would like to introduce several theories which have gained attentions among the published theories up to date; genetic program theory, wear-and-tear theory, telomere theory, endocrine theory, DNA damage hypothesis, error catastrophe theory, the rate of living theory, mitochondrial theory, and free radical theory. Although there have been many studies that have tried to prevent aging and prolong life, here we introduce a couple of theories which have been proven more or less; food, exercise, and diet restriction. PMID:24653904

  16. Aging

    PubMed Central

    Park, Dong Choon

    2013-01-01

    Aging is initiated based on genetic and environmental factors that operate from the time of birth of organisms. Aging induces physiological phenomena such as reduction of cell counts, deterioration of tissue proteins, tissue atrophy, a decrease of the metabolic rate, reduction of body fluids, and calcium metabolism abnormalities, with final progression onto pathological aging. Despite the efforts from many researchers, the progression and the mechanisms of aging are not clearly understood yet. Therefore, the authors would like to introduce several theories which have gained attentions among the published theories up to date; genetic program theory, wear-and-tear theory, telomere theory, endocrine theory, DNA damage hypothesis, error catastrophe theory, the rate of living theory, mitochondrial theory, and free radical theory. Although there have been many studies that have tried to prevent aging and prolong life, here we introduce a couple of theories which have been proven more or less; food, exercise, and diet restriction. PMID:24653904

  17. Testing exhumation models using PTt paths: an Alpine perspective based on deformation ages

    NASA Astrophysics Data System (ADS)

    Reddy, S.; Butler, R.; Wheeler, J.; Cliff, B.; Freeman, S.; Biggs, A.

    2005-12-01

    Geochronological data are now commonly used to establish the timing and rates of exhumation of high pressure metamorphic rocks, critical for testing geodynamic models of orogenic belts. Such approaches must be used with care. Ages of peak pressure metamorphic assemblages allied to younger cooling ages give a general insight into the rates of exhumation when tied to PT paths. However, the results of this workflow are difficult to relate to the kinematic history and therefore maybe of limited use in the critical testing of exhumation models. An alternative strategy is to date directly synkinematic mineral phases in characterised deformation zones. Examples are drawn from the deformed and variably subducted "European" continental crust now exposed in the Western Alps to illustrate this, chiefly using Rb-Sr mica dating, applied to greenschist facies shear zones. Some structures are synchronously active for c. 100km along strike (e.g. the regional "retrocharriage" shear system of the Eastern Brianconnais: 34 Ma). However, UHP terrains of the basement massifs attained peak pressures and were exhumed diachronously (38 Ma - 32 Ma). These results indicate that tectono-metamorphic histories based on single orogenic transects may give misleading pictures of geodynamic evolution. In an Alpine context it appears that exhumation of UHP and shallower parts of the evolving continental subduction channel occurred as variably detached flakes rather than relate to the dynamics of larger scale plate processes.

  18. Thermoluminescence of Antarctic meteorites: A rapid screening technique for terrestrial age estimation, pairing studies and identification of specimens with unusual prefall histories

    NASA Technical Reports Server (NTRS)

    Sutton, S. R.; Walker, R. M.

    1986-01-01

    Thermoluminescence (TL) is a promising technique for rapid screening of the large numbers of Antarctic meteorites, permitting identification of interesting specimens that can then be studied in detail by other, more definite techniques. Specifically, TL permits determination of rough terrestrial age, identification of potential paired groups and location of specimens with unusual pre-fall histories. Meteorites with long terrestrial ages are particularly valuable for studying transport and weathering mechanisms. Pairing studies are possible because TL variations among meteorites are large compared to variations within individual objects, especially for natural TL. Available TL data for several L3 fragments, three of which were paired by other techniques, are presented as an example of the use of TL parameters in pairing studies. Additional TL measurements, specifically a blind test, are recommended to satisfactorily establish the reliability of this pairing property. The TL measurements also identify fragments with unusual pre-fall histories, such an near-Sun orbits.

  19. Maximum sedimentation ages and provenance of metasedimentary rocks from Tinos Island, Cycladic blueschist belt, Greece

    NASA Astrophysics Data System (ADS)

    Hinsken, Tim; Bröcker, Michael; Berndt, Jasper; Gärtner, Claudia

    2015-10-01

    U-Pb zircon ages of five metasedimentary rocks from the Lower Unit on Tinos Island (Cycladic blueschist belt, Greece) document supply of detritus from various Proterozoic, Paleozoic and Mesozoic source rocks as well as post-depositional metamorphic zircon formation. Essential features of the studied zircon populations are Late Cretaceous (70-80 Ma) maximum sedimentation ages for the lithostratigraphic succession above the lowermost dolomite marble, significant contributions from Triassic to Neoproterozoic source rocks, minor influx of detritus recording Paleoproterozoic and older provenance (1.9-2.1, 2.4-2.5 and 2.7-2.8 Ga) and a lack or paucity of zircons with Mesoproterozoic ages (1.1-1.8 Ga). In combination with biostratigraphic evidence, the new dataset indicates that Late Cretaceous or younger rocks occur on top of or very close to the basal Triassic metacarbonates, suggesting a gap in the stratigraphic record near the base of the metamorphic succession. The time frame for sediment deposition is bracketed by the youngest detrital zircon ages (70-80 Ma) and metamorphic overgrowths that are related to high-pressure/low-temperature overprinting in the Eocene. This time interval possibly indicates a significant difference to the sedimentation history of the southern Cyclades, where Late Cretaceous detrital zircons have not yet been detected.

  20. Crustal channel flows: 2. Numerical models with implications for metamorphism in the Himalayan-Tibetan orogen

    NASA Astrophysics Data System (ADS)

    Jamieson, Rebecca A.; Beaumont, Christopher; Medvedev, Sergei; Nguyen, Mai H.

    2004-06-01

    Results from a thermal-mechanical model (HT1) that includes midcrustal channel flow are compatible with many features of the Himalayan-Tibetan system. Radioactive self-heating and rheological weakening of thickened model orogenic crust lead to the formation of a hot, low-viscosity midcrustal channel and a broad plateau. Channel material, corresponding to the Greater Himalayan Sequence (GHS), flows outward from beneath the plateau in response to topographically induced differential pressure. At the plateau flank it is exhumed by focused surface denudation and juxtaposed with cooler, newly accreted material corresponding to the Lesser Himalayan Sequence (LHS). The model channel is bounded by coeval thrust and normal sense ductile shear zones, interpreted to represent the Main Central Thrust (MCT) zone and South Tibetan Detachment system, respectively. Inverted metamorphism associated with the model MCT zone results from distributed ductile shear along the MCT and extrusion of the hot channel. A variety of model P-T-t path styles, resembling those observed in the GHS and LHS, are produced for points traveling through contrasting tectonic regimes that coexist in different parts of the model. Predicted times of peak metamorphism, cooling, and erosion of metamorphic facies are generally compatible with observations, although model GHS cooling ages are too young. The times of M1 and M2 metamorphic "events" observed in the GHS correspond to model times of maximum burial and maximum heating, respectively. The results highlight the need to integrate tectonics and metamorphism in continental collision models and demonstrate the importance of lateral transport of both heat and material in large hot orogens.

  1. A key extensional metamorphic complex reviewed and restored: The Menderes Massif of western Turkey

    NASA Astrophysics Data System (ADS)

    van Hinsbergen, Douwe J. J.

    2010-09-01

    This paper provides a review of the structure and metamorphism of the Menderes Massif in western Turkey, and subsequently a map-view restoration of its Neogene unroofing history. Exhumation of this massif — among the largest continental extensional provinces in the world — is generally considered to have occurred along extensional detachments with a NE-SW stretching direction. Restoration of the early Miocene history, however, shows that these extensional detachments can only explain part of the exhumation history of the Menderes Massif, and that NE-SW stretching can only be held accountable for half, or less, of the exhumation. Restoration back to ˜ 15 Ma is relatively straightforward, and is mainly characterised by a previously reported 25-30° vertical axis rotation difference between the northern Menderes Massif, and the Southern Menderes Massif and overlying HP nappes, Lycian Nappes and Bey Dağları about a pivot point close to Denizli. To the west of this pole, the rotation was accommodated by exhumation of the Central Menderes core complex since middle Miocene times, and to the east probably by shortening. At the end of the early Miocene, the Menderes Massif formed a rectangular, NE-SW trending tectonic window of ˜ 150 × 100 km. Geochronology suggests unroofing between ˜ 25 and 15 Ma. The north-eastern Menderes Massif was exhumed along the early Miocene Simav detachment, over a distance of ≤ 50 km. The accommodation of the remainder of the exhumation is enigmatic, but penetrative NE-SW stretching lineations throughout the Menderes Massif suggest a prominent role of NE-SW extension. This, however, requires that the eastern margin of the Menderes Massif, bordering a region without significant extension, is a transform fault with an offset of ˜ 150 km, cutting through the Lycian Nappes. For this, there is no evidence. The Lycian Nappes — a non-metamorphic stack of sedimentary thrust slices and an overlying ophiolite and ophiolitic mélange

  2. Pregnancy history and current use of contraception among women of reproductive age in Burundi, Kenya, Rwanda, Tanzania and Uganda: analysis of demographic and health survey data

    PubMed Central

    Bakibinga, Pauline; Matanda, Dennis J; Ayiko, Rogers; Rujumba, Joseph; Muiruri, Charles; Amendah, Djesika; Atela, Martin

    2016-01-01

    Objective To examine the relationship between pregnancy history and the use of contraception among women of reproductive age (15–49 years) in East Africa. Methods Demographic and Health Surveys data from Burundi (2010), Kenya (2008–2009), Rwanda (2010), Tanzania (2010) and Uganda (2011) were used in the analysis. Logistic regression was used to determine the effects of women's pregnancy history on their use of contraception. Setting Burundi, Kenya, Rwanda, Tanzania and Uganda. Participants 3226, 2377, 4396, 3250 and 2596 women of reproductive age (15–49 years) from Burundi, Kenya, Rwanda, Tanzania and Uganda, respectively, were included in the analysis. Results Women who had experienced a mistimed pregnancy were more likely to use a modern contraceptive method during their most recent sexual encounter in Kenya, Rwanda, Burundi and Uganda. Other significant correlates of women's contraceptive use were: desire for more children, parity, household wealth, maternal education and access information through radio. In-country regional differences on use of modern contraceptive methods were noted across five East African countries. Conclusions Women's birth histories were significantly associated with their decision to adopt a modern contraceptive method. This highlights the importance of considering women's birth histories, especially women with mistimed births, in the promotion of contraceptive use in East Africa. Variations as a result of place of residency, educational attainment, access to family planning information and products, and wealth ought to be addressed in efforts to increase use of modern contraceptive methods in the East African region. PMID:26966059

  3. Offspring Provisioning Explains Clone-Specific Maternal Age Effects on Life History and Life Span in the Water Flea, Daphnia pulex.

    PubMed

    Plaistow, Stewart J; Shirley, Christopher; Collin, Helene; Cornell, Stephen J; Harney, Ewan D

    2015-09-01

    Genetic inheritance underpins evolutionary theories of aging, but the role that nongenetic inheritance plays is unclear. Parental age reduces the life span of offspring in a diverse array of taxa but has not been explained from an evolutionary perspective. We quantified the effect that maternal age had on the growth and maturation decisions, life history, rates of senescence, and life span of offspring from three Daphnia pulex clones collected from different populations. We then used those data to test general hypotheses proposed to explain maternal age effects on offspring life span. Three generations of breeding from young or old mothers produced dramatic differences in the life histories of fourth-generation offspring, including significant reductions in life span. The magnitude of the effect differed between clones, which suggests that genetic and nongenetic factors ultimately underpin trait inheritance and shape patterns of aging. Older parents did not transmit a senescent state to their offspring. Instead, offspring from older ancestors had increased early-life reproductive effort, which resulted in an earlier onset of reproductive senescence, and an increased rate of actuarial senescence, which shortened their life span. Our results provide a clear example of the need to consider multiple inheritance mechanisms when studying trait evolution. PMID:26655355

  4. Permian basic magmatism, Upper Eocene and Lower Oligocene metamorphism in the Furgg zone (Western Alps)

    NASA Astrophysics Data System (ADS)

    Liati, A.; Gebauer, D.; Froitzheim, N.

    2003-04-01

    The Furgg zone (Western Alps) separates the Monte Rosa nappe from the Bernhard and Zermatt nappes. It consists mainly of a schist-, leucocratic gneiss-, quartzite- and metacarbonate-matrix containing boudins of amphibolitised eclogites. Controversial views exist on the nature, origin and extent of the Furgg zone (cf. Dal Piaz, 2001). We dated by SHRIMP (GSC, Ottawa) magmatic and metamorphic zircon domains of a metabasite in the area of Stockknubel (north of the western part of the Monte Rosa nappe). This metabasite is a strongly retrogressed eclogite occurring in form of a boudin, ca. 1 m long, within leucocratic schists. Based on cathodoluminescence (CL)-imaging, zircons from this rock consist of large oscillatory zoned (magmatic) domains surrounded by metamorphic (recrystallisation) rims, bright in CL, with ghost oscillatory zoning. Bright CL-domains are irregularly dispersed also inside the magmatic domains, due to fluid circulation along fractures during metamorphism(s). Eight spot analyses on the magmatic domains yield a Permian weighted mean age at 269 ± 3 Ma (95% c.l.), corresponding to the crystallisation time of the gabbroic protolith of this metabasite. This age is in agreement with a ca. 272 Ma age reported for the crystallisation of an orthogneiss at Mattmark (farther east in the Furgg zone; Liati et al., 2001), as well as for Monte Rosa granites. The new Permian protolith age of the metabasic rock in Stockknubel, together with a 510 ± 5 Ma age reported for an eclogite boudin from the eastern part of the Furgg zone, is in agreement with the 'mélange hypothesis' for the origin of the Furgg zone (e.g. Froitzheim, 2001). 11 spot analyses on metamorphic domains indicate a strong influence of the Lepontine event at 31.5 ± 1.0 Ma (weighted mean of 8 analyses), accompanied by influx of high amounts of fluids. Of great interest are metamorphic rim analyses at ca. 38-39 Ma, together with a series of data scattering between this and the ca. 31.5 Ma age. The

  5. Ion microprobe (SHRIMP) dating of detrital zircon grains from quartzites of the Eckergneiss Complex, Harz Mountains (Germany): implications for the provenance and the geological history

    NASA Astrophysics Data System (ADS)

    Geisler, Thorsten; Vinx, Roland; Martin-Gombojav, Nergui; Pidgeon, Robert T.

    2005-07-01

    The Eckergneiss Complex (EGC) is a geologically unique medium- to high-grade metamorphic unit within the Rhenohercynian domain of the Mid-European Variscides. A previously, poorly defined conventional lower U Pb intercept age of about 560 Ma from detrital zircons of metasedimentary rocks has led to speculations about an East Avalonian affinity of the EGC. In order to unravel the provenance and to constrain the age of the sediment protolith, we carried out sensitive high-resolution ion microprobe U Pb analyses on detrital zircons from five different EGC quartzite occurrences. The obtained age spectrum indicates a SW Baltica provenance of the detritus. Sveconorwegian ages between 0.9 1.2 Ga are particularly well represented by analyses from metamorphic recrystallization/alteration zones penetrating into igneous zircon. Cadomian (Pan-African) ages, which might reflect a metamorphic event, could not be substantiated. Instead, zircons of igneous origin yielded concordant Lower Devonian and Silurian ages of 410±10, 419±10, and 436±6 Ma (1σ), implying that sedimentation of the EG protolith must have taken place after 410±10 Ma. The lower age limit of the EGC metamorphism is constrained by 295 Ma intrusion ages of the adjacent, nonmetamorphosed Harzburg Gabbronorite and Brocken Granite. Sedimentation and metamorphism must thus have taken place between about 410 Ma and 295 Ma. Given that this time span coincides with most of the sedimentation within the virtually nonmetamorphosed (lowest grade) Rhenohercynian in the Harz Mountains, including the direct vicinity of the EGC, along with the high-grade metamorphism, the EGC can hardly be seen as uplifted local basement. A possible candidate for the root region is an easterly, concealed marginal segment of the Rhenohercynian domain of the Variscides, which is tectonically overridden and suppressed by the Mid-German Crystalline Rise during continent collision. However, based on the concept of strike-slip movement of Variscan

  6. Inverted Regional Metamorphism in the Coaxially Refolded Tonga Formation: Evidence for Cretaceous Accretional Tectonics in the Cascades Crystalline Core

    NASA Astrophysics Data System (ADS)

    Jensen, L. A.; Lebit, H. D.; Paterson, S. R.; Miller, R. B.; Vernon, R. H.

    2008-12-01

    lower-grade equivalent of the Chiwaukum Schist, as protoliths of each unit are also similar. Exposure of the Evergreen fault is limited, but the observed structural and metamorphic relationships suggest that it is a late, east-dipping reverse fault that places the deeper, higher-grade Chiwaukum Schist structurally adjacent to the lower-grade Tonga Formation. Though the Tonga formation exposes, at different crustal levels, multiple stages of deformation and metamorphism, a single foliation dominates the meso-scale rock fabric. It is inferred that this fabric accumulates over the entire strain history, departing from a strong ~layer-parallel anisotropy/fabric related to the initial isoclinal folding episode.

  7. Metamorphism of eucrite meteorites studied quantitatively using induced thermoluminescence

    NASA Technical Reports Server (NTRS)

    Batchelor, J. David; Sears, Derek W. G.

    1991-01-01

    Induced thermoluminescence studies provide a new and quantitative means of determining relative metamorphic intensities for eucrite meteorites, the simplest and most ancient products of basaltic volcanism. Using this technique, it is shown that the eucrites constitute a continuous metamorphic series and not, as commonly assumed, two groups of metamorphosed and nonmetamorphosed meteorites. It is suggested that the method may have applications to other basalts.

  8. A Simulated Research Problem for Undergraduate Metamorphic Petrology.

    ERIC Educational Resources Information Center

    Amenta, Roddy V.

    1984-01-01

    Presents a laboratory problem in metamorphic petrology designed to simulate a research experience. The problem deals with data on scales ranging from a geologic map to hand specimens to thin sections. Student analysis includes identifying metamorphic index minerals, locating their isograds on the map, and determining the folding sequence. (BC)

  9. Timing of middle Paleozoic (Acadian) metamorphism in the southern Appalachians: K-Ar studies in the Talladega belt, Alabama

    SciTech Connect

    Kish, S.A. )

    1990-07-01

    The Talladega belt of Alabama and Georgia is located at the southernmost exposed part of the southern Appalachian orogen and is one of the westernmost metamorphic terranes in this part of the orogen. The presence of the Lower Devonian Jemison Chert of the Talladega Group provides a maximum age for the timing of greenschist facies metamorphism and penetrative slaty cleavage formation in this terrane. Six slate collected form upper Precambrian( )-Lower Cambrian, and Silurian( )-Devonian rocks of the Talladega belt have an average K-Ar age of 399 {plus minus} 17 Ma. This age is interpreted to be the approximate time of regional greenschist facies metamorphism. The timing of metamorphism in the Talladega belt is similar to the age of the Acadian orogeny in the Maritime and northern Appalachians. Unlike the accreted nature of the Acadian terranes in the northern Appalachians, the Talladega belt appears to have been part of the early to middle Paleozoic cratonic margin of North America. The results of this study indicate that Acadian dynamothermal events extended into parts of the Laurentian margin in the southern Appalachians. Paleozoic igneous activity in the southern Appalachians was less extensive compared with the voluminous Acadian plutonism of the northern Appalachians; however, synkinematic to postkinematic Devonian plutons are present in the central and western parts of the orogen.

  10. Pseudotachylyte in the Tananao Metamorphic Complex, Taiwan: Occurrence and dynamic phase changes of fossil earthquakes

    NASA Astrophysics Data System (ADS)

    Chu, Hao-Tsu; Hwang, Shyh-Lung; Shen, Pouyan; Yui, Tzen-Fu

    2012-12-01

    Pseudotachylyte veins and cataclasites were studied in the mylonitized granitic gneiss of the Tananao Metamorphic Complex at Hoping, Eastern Taiwan. The aphanitic pseudotachylyte veins vary in thickness, ranging from millimeters to about 1 cm. Field and optical microscopic observations show that such pseudotachylyte veins cut across cataclasites, which, in turn, transect the mylonitized granitic gneiss. Scanning electron microscopic images also show that both the pseudotachylyte veins and the cataclasites have been metasomatized by a K-rich fluid, resulting in the replacement of Na-plagioclase by K-feldspar (veins). Analytical electron microscopic observations reveal further details of physical and chemical changes (mainly fragmentation, dislocations, cleaving-healing with inclusions and relic voids, and retention of high-temperature albite) of quartz and feldspar in crushed grains. Pseudotachylytes occur as dark veins having a higher content of chlorite-biotite, clinozoisite-epidote and titanite fragments than cataclasites. These veins, coupled with hematite/jarosite-Fe-rich amorphous shell/carbonaceous material, indicate that crushing, healing/sintering, and inhomogeneous melt/fluid infiltration involving incipient and intermediate/high temperature melt patches, before and/or contemporaneous with the metasomatic K-rich fluid, prevailed in a coupled or sequential manner in the faulting event to form nonequilibrium phase assemblage. The chlorite-biotite, carbonaceous material and other nanoscale minerals could be vulnerable in future earthquakes under the influence of water. The timing of the formation of these pseudotachylyte veins should be later than the area's age of mylonitization of granitic gneiss of approximately 4.1-3.0 Ma (Wang et al., 1998). The formation of pseudotachylytes registers the fossil earthquakes during early stages in the exhumation history of the uplifting Taiwan Mountain belt since the Plio-Pleistocene Arc-Continent collision.

  11. Pb and Zn release from crustal sediments during metamorphism

    NASA Astrophysics Data System (ADS)

    Hammerli, Johannes; Spandler, Carl; Oliver, Nick; Sossi, Paolo; Dipple, Greg

    2015-04-01

    Our understanding of the genesis of Pb-Zn ore systems is currently limited by a lack of knowledge about from where these metals are sourced. While it is generally agreed that the temperature and salinity of fluids play a crucial role in mobilizing metals, the importance of the composition of the source lithologies is poorly constrained. Furthermore, fluid-rock processes that lead to element mobility are yet to be fully understood, especially in metamorphic environments. To address these gaps in our knowledge we examine metal distribution and mobility in rocks from a prograde metamorphic sequence of the Mt Lofty Ranges, South Australia, where temperatures range from ~300 to 700˚C at ~3.5 to 5 kbar. This regional metamorphic belt underwent regional up-temperature fluid flow, which allowed for favourable conditions for enhanced element mobility. By studying the distribution and concentration of Pb and Zn on both bulk-rock and mineral scales, in combination with bulk rock Zn-isotope data, we can monitor the behaviour of these elements during pressure and temperature changes. Our results show that in staurolite-absent siliciclastic metasedimentary rocks, biotite contains >80% of the bulk rock Zn, as well as a considerable proportion of the total Pb, irrespective of the metamorphic grade. Pervasive fluid flow during metamorphism through these metasedimentary rocks led to a continuous depletion of Pb and Zn on a mineral and bulk-rock scale, resulting in a mobilization of ~80% of the bulk-rock Zn and ~50% of the bulk-rock Pb, mainly through reactions involving biotite. We calculated that a minimum of 2.7Mt of Pb and 27Mt of Zn was mobilized/lost in the high-grade metamorphic zone (200 km2). Halogen contents of apatite and biotite and bulk-rock Zn isotope data provide evidence that Cl-rich metamorphic fluids were important for metal transport. Hence, fluid flow accompanying metamorphism of typical sedimentary rocks can mobilize base metals to the degree required to form

  12. Fluid flow and chemical reaction kinetics in metamorphic systems

    SciTech Connect

    Lasaga, A.C.; Rye, D.M. )

    1993-05-01

    The treatment and effects of chemical reaction kinetics during metamorphism are developed along with the incorporation of fluid flow, diffusion, and thermal evolution. The interplay of fluid flow and surface reaction rates, the distinction between steady state and equilibrium, and the possible overstepping of metamorphic reactions are discussed using a simple analytic model. This model serves as an introduction to the second part of the paper, which develops a reaction model that solves the coupled temperature-fluid flow-chemical composition differential equations relevant to metamorphic processes. Consideration of stable isotopic evidence requires that such a kinetic model be considered for the chemical evolution of a metamorphic aureole. A general numerical scheme is discussed to handle the solution of the model. The results of this kinetic model allow us to reach several important conclusions regarding the factors controlling the chemical evolution of mineral assemblages during a metamorphic event. 41 refs., 19 figs., 5 tabs.

  13. Isothermal densification and metamorphism of new snow

    NASA Astrophysics Data System (ADS)

    Schleef, S.; Loewe, H.; Schneebeli, M.

    2012-12-01

    The interplay between overburden stress and surface energy induced growth and coarsening is relevant for the densification of snow and porous ice at all densities. The densification of new snow is amenable to high precision experiments on short time scales. To this end we investigate the coupling of densification and metamorphism of new snow via time-lapse tomography experiments in the laboratory. We compare the evolution of density, strain, and specific surface area to previous long-time metamorphism experiments of snow and creep of polycrystalline ice. Experimental conditions are tailored to the requirements of time-lapse tomography and the measurements are conducted under nearly isothermal conditions at -20°C with a duration of two days. Images were taken with temporal resolution of a few hours which reveal precise details of the microstructure evolution due to sintering and compaction. We used different crystal shapes of natural new snow and snow samples obtained by sieving crystals grown in a snowmaker in the laboratory. To simulate the effect of overburden stress due to an overlying snowpack additional weights were applied to the sample. As expected we find an influence of the densification rate on initial density and overburden stress. We calculated strain rates and identified a transient creep behavior with a similar power law for all crystal types which substantially differs from the Andrade creep of polycrystalline ice. As a main result we found that the evolution of the specific surface area is independent of the density and follows a unique decay form for all measurements of each crystal type. The accuracy of the measurements allows to obtain a decay exponent for the SSA which is the same as previously obtained from the long-time regime during isothermal metamorphism after several months. Our preliminary results for all available types of new snow suggest a correlation between the initial density and SSA. We also find snow samples which coincide in

  14. High-pressure amphibolite facies dynamic metamorphism and the Mesozoic tectonic evolution of an ancient continental margin, east- central Alaska

    USGS Publications Warehouse

    Dusel-Bacon, C.; Hansen, V.L.; Scala, J.A.

    1995-01-01

    Ductilely deformed amphibolite facies tectonites comprise two adjacent terranes in east-central Alaska: the northern, structurally higher Taylor Mountain terrane and the southern, structurally lower Lake George subterrane of the Yukon-Tanana terrane. The pressure, temperature, kinematic and age data are interpreted to indicate that the metamorphism of the Taylor Mountain terrane and Lake George subterrane took place during different phases of a latest Palaeozoic through early Mesozoic shortening episode resulting from closure of an ocean basin now represented by klippen of the Seventymile-Slide Mountain terrane. High- to intermediate-pressure metamorphism of the Taylor Mountain terrane took place within a SW-dipping (present-day coordinates) subduction system. High- to intermediate-pressure metamorphism of the Lake George subterrane and the structural contact zone occurred during NW-directed overthrusting of the Taylor Mountain, Seventymile-Slide Mountain and Nisutlin terranes, and imbrication of the continental margin in Jurassic time. -from Authors

  15. Structure and thermochronology of the metamorphic core of the Brooks Range, Alaska

    NASA Astrophysics Data System (ADS)

    Toro, Jaime

    1999-11-01

    Detailed field studies were undertaken in two key areas of the Central Belt of the Brooks Range: (1) the north flank of Mt. Igikpak in the Survey Pass Quadrangle and (2) in the Shishakshinovik Pass area in the eastern Ambler River Quadrangle. In both areas structural, stratigraphic, petrologic, 40Ar/39Ar, apatite fission-track and U-Pb data were used to constrain the kinematic and thermal history of metamorphic rocks of those areas. North of the Mt. Igikpak massif a crustal section ˜15 km thick is exposed. There are upper greenschist facies rocks in the deeper portions, and very low grade metamorphic rocks at higher structural levels. Two foliations are found: a higher grade relict S1 fabric and a lower grade S 2 fabric that controls the metamorphic layering. 40Ar/ 39Ar analyses from S1 white mica in the low-grade rocks at the northern end of the transect indicate that peak M1 metamorphism occurred before ˜112 Ma. We ascribe M1 to shortening that occurred during collision of an island arc against the Arctic Alaska margin. S 2 involved the retrogression of earlier assemblages. Kinematic indicators on S2 are top-to-the-north. A rapid cooling event from 500 +/- 50°C to 300 +/- 50°C took place between ˜98 and ˜90 Ma. The driving mechanism for ductile deformation during S2, and for rapid cooling documented by our thermochronologic data, was probably the gravitational collapse of the core of the orogen, over-thickened during the preceding collision. At Shishakshinovik Pass there are Mississippian Lisburne Group strata surrounded by metamorphic rocks typical of the Central Belt of the Brooks Range. All the rocks at Shishakshinovik Pass are intensely deformed, so that one cannot distinguish between an autochthonous and an allochthonous sequence. Furthermore the Mississippian rocks, instead of being attached to the underlying basement, are in the hanging wall of a northwest dipping shear zone. Based on the variations in metamorphic grade and the 40Ar/ 39Ar

  16. UHT granulite-facies metamorphism in Rogaland, S Norway, is polyphase in nature

    NASA Astrophysics Data System (ADS)

    Laurent, Antonin; Duchene, Stéphanie; Bingen, Bernard; Seydoux-Guillaume, Anne-Magali; Bosse, Valérie

    2016-04-01

    Propensity of metamorphic assemblages to remain metastable after melt extraction complicates singularly the petrologist's task to discriminate between a single granulite-facies P-T path and a polyphase one. Using an integrated petrological and in-situ geochronological approach in key rock-samples, we reconstruct the pressure-temperature-time path of Sveconorwegian metamorphism across a 30 km-wide metamorphic gradient ranging from upper amphibolite facies to ultra-high temperature (UHT) granulite-facies in Rogaland, S. Norway. Thermodynamic modelling of phase equilibria in the Na2O-CaO-K2O-FeO-MgO-Al2O3-SiO2-H2O-Ti2O-O2 chemical system (PerpleX code) are carried out with an emphasis on moderately oxidized, spinel-bearing assemblages resulting from either garnet or sapphirine breakdown. Geochronological U-(Th)-Pb data acquired on both monazite (LA-ICP-MS) and zircon (SIMS) are complemented by minor- and trace-elements signatures of both minerals, to monitor REE distribution through time and to evaluate garnet apparition or demise. Coupling field, petrological and geochronological data lead to a polyphase metamorphic history, lasting about 100 My. The onset of regional granulite facies metamorphism at 1035 Ma is associated with the emplacement of large volumes of granitic magmas in the amphibolite to granulite facies transition zone. In the deeper part of the crustal section, localized sapphirine-bearing restitic lithologies testify to UHT temperatures (900‑920 °C). These conditions were reached at ca. 1010 Ma following a tight clockwise P-T path associated with minor exhumation (7 to 5.5 kbar) and subsequent cooling to 700 °C. A distinct thermal episode, initiated at ca. 950 Ma, reached UHT granulite-facies conditions with the intrusion of massif-type anorthosite plutons at ca. 930 Ma producing a 5-km wide aureole. The aureole is delimited by the presence of osumilite in high Fe-Al rocks yielding quantitative estimates of 900-950 °C at a maximum pressure of 5

  17. Age and geomorphic history of Meteor Crater, Arizona, from cosmogenic 36Cl and 14C in rock varnish

    USGS Publications Warehouse

    Phillips, F.M.; Zreda, M.G.; Smith, S.S.; Elmore, D.; Kubik, P.W.; Dorn, R.I.; Roddy, D.J.

    1991-01-01

    Using cosmogenic 36Cl buildup and rock varnish radiocarbon, we have measured the exposure age of rock surfaces at Meteor Crater, Arizona. Our 36Cl measurements on four dolomite boulders ejected from the crater by the impact yield a mean age of 49.7 ?? 0.85 ka, which is in excellent agreement with an average age of 49 ?? 3 ka obtained from thermoluminescence studies on shock-metamorphosed dolomite and quartz. These ages are supported by undetectably low 14C in the oldest rock varnish sample. ?? 1991.

  18. Metamorphic zoning and geodynamic evolution of an inverted crustal section (Karakorum margin, N Pakistan), evidence for two metamorphic events

    NASA Astrophysics Data System (ADS)

    Rolland, Y.; Carrio-Schaffhauser, E.; Sheppard, S. M. F.; Pêcher, A.; Esclauze, L.

    2006-04-01

    The Karakorum Range comprises a crustal section of marbles and metapelites provi