Blueschist metamorphism and its tectonic implication of Late Paleozoic-Early Mesozoic metabasites in the mélange zones, central Inner Mongolia, China

NASA Astrophysics Data System (ADS)

Zhang, Jinrui; Wei, Chunjing; Chu, Hang

2015-01-01

Blueschists in central Inner Mongolia are distributed as layers and blocks in mélanges including the southern zone in Ondor Sum area and the northern zone in Manghete and Naomuhunni areas. They have been attributed to the subduction of Early Paleozoic oceanic crust. Blueschists from Ondor Sum and Naomuhunni are characterized by occurrence of sodic amphibole coexisting with epidote, albite, chlorite, calcic amphibole (in Ondor Sum) and muscovite (in Naomuhunni). Blueschists in Manghete contain porphyroblastic albite with inclusions of garnet and epidote in a matrix dominated by calcic-sodic amphibole, epidote, chlorite, albite and muscovite. Phase equilibria modeling for three blueschist samples using pseudosection suggest that the AlM2 contents in sodic amphibole can be used as a good barometer in the limited assemblage involving sodic amphibole + actinolite + epidote + chlorite + albite + quartz under pressures <4-6 kbar, while this barometer is largely influenced by temperature and bulk Fe2O3 contents in the actinolite-absent assemblage sodic amphibole + epidote + chlorite + albite + quartz of higher pressure and the AlM2 contents are not pressure-controlled in the albite-absent assemblage sodic amphibole + epidote + chlorite + quartz under pressures > 7-10 kbar. In the sodic amphibole-bearing assemblages, the NaM4 contents in sodic amphibole mainly decrease as temperature rises, being a potential thermometry. The calculated pseudosections constrain the P-T conditions of blueschists to be 3.2-4.2 kbar/355-415 °C in Ondor Sum, 8.2-9.0 kbar/455 °C-495 °C in Manghete and 6.6-8.1 kbar/420-470 °C in Naomuhunni. These P-T estimates indicate a rather high geothermal gradient of 18-25 °C/km for the blueschist metamorphism, being of intermediate P/T facies series. Available zircon U-Pb age data suggests that the protoliths of blueschists were formed later than Late Paleozoic-Early Mesozoic and metamorphosed soon afterwards. An alternative interpretation for the

Paleomagnetism of Early Paleozoic Rocks from the de Long Archipelago and Tectonics of the New Siberian Islands Terrane

NASA Astrophysics Data System (ADS)

Metelkin, D. V.; Chernova, A. I.; Matushkin, N. Y.; Vernikovskiy, V. A.

2017-12-01

The De Long archipelago is located to the north of the Anjou archipelago as a part of a large group between the Laptev Sea and the East Siberian Sea - the New Siberian Islands and consists of Jeannette Island, Bennett Island and Henrietta Island. These islands have been shown to be part of a single continental terrane, whose tectonic history was independent of other continental masses at least since the Ordovician. Paleomagnetic and precise geological data for the De Long archipelago were absent until recently. Only in 2013 special international field trips to the De Long Islands could be organized and geological, isotope-geochronological and paleomagnetic studies were carried out.On Jeannette Island a volcanic-sedimentary sequence intruded by mafic dikes was described. The age of these dikes is more likely Early Ordovician, close to 480 Ma, as evidenced by the results of our 40Ar/39Ar and paleomagnetic investigations of the dolerites as well as the result from detrital zircons in the host rocks published before. On Bennett Island, there are widespread Cambrian-Ordovician mainly terrigenous rocks. Paleomagnetic results from these rocks characterize the paleogeographic position of the De Long archipelago at 465 Ma and perhaps at 530 Ma, although there is no evidence for the primary origin of magnetization for the latter. On Henrietta Island the Early Cambrian volcanic-sedimentary section was investigated. A paleomagnetic pole for 520 Ma was obtained and confirmed by new 40Ar/39Ar results. Adding to our previous paleomagnetic data for the Anjou archipelago the extended variant of the apparent polar wander path for the New Siberian Island terrane was created. The established paleolatitudes define its location in the equatorial and subtropical zone no higher than 40 degrees during the Early Paleozoic. Because there are no good confirmations for true polarity and related geographic hemisphere we present two possibilities for tectonic reconstruction. But both these

A New Model of the Early Paleozoic Tectonics and Evolutionary History in the Northern Qinling, China

NASA Astrophysics Data System (ADS)

Dong, Yunpeng; Zhang, Guowei; Yang, Zhao; Qu, Hongjun; Liu, Xiaoming

2010-05-01

The Qinling Orogenic Belt extends from the Qinling Mountains in the west to the Dabie Mountains in the east. It lies between the North China and South China Blocks, and is bounded on the north by the Lushan fault and on the south by the Mianlue-Bashan-Xiangguang fault (Zhang et al., 2000). The Qinling Orogenic Belt itself is divided into the North and South Qinling Terranes by the Shangdan suture zone. Although the Shangdan zone is thought to represent the major suture separating the two blocks, there still exists debate about the timing and mechanism of convergence between these two blocks. For instance, some authors suggested an Early Paleozoic collision between the North China Block and South China Block (Ren et al., 1991; Kroner et al., 1993; Zhai et al., 1998). Others postulated left-lateral strike-slip faulting along the Shangdan suture at ca. 315 Ma and inferred a pre-Devonian collision between the two blocks (Mattauer et al., 1985; Xu et al., 1988). Geochemistry of fine-grained sediments in the Qinling Mountains was used to argue for a Silurian-Devonian collision (Gao et al., 1995). A Late Triassic collision has also been proposed (Sengor, 1985; Hsu et al., 1987; Wang et al., 1989), based on the formation of ultrahigh-pressure metamorphic rocks in the easternmost part of the Qinling Orogenic Belt at ~230 Ma (e.g., Li et al., 1993; Ames et al., 1996). Paleomagnetic data favor a Late Triassic-Middle Jurassic amalgamation of the North China and South China Blocks (Zhao and Coe, 1987; Enkin et al., 1992). It is clear that most authors thought that the Qinling Mountains are a collisional orogen, even they have different methods about the timing of the orogeny. Based on new detailed investigations, we propose a new model of the Early Paleozoic Tectonics and Evolutionary History between the North China and South China Blocks along the Shangdan Suture. The Shangdan suture is marked by a great number of ophiolites, island-arc volcanic rocks and other related rock

Geochronological framework of the early Paleozoic Bainaimiao Cu-Mo-Au deposit, NE China, and its tectonic implications

NASA Astrophysics Data System (ADS)

Zhou, Zhen-Hua; Mao, Jing-Wen; Ma, Xing-Hua; Che, He-Wei; Ou'yang, He-Gen; Gao, Xu

2017-08-01

The Bainaimiao Cu-Mo-Au deposit of NE China is an important ore deposit in the middle section of the northern margin of the North China Craton. The early Paleozoic Bainaimiao Group is the main ore-hosting rock. The mineralization at the deposit shows features of porphyry alteration and late-stage orogenesis and transformation. Zircon LA-ICP-MS U-Pb age data indicate that the ages of the Third and Fifth formations of the Bainaimiao Group are 492.7 ± 2.9 Ma (MSWD = 0.53) and 488.9 ± 3.1 Ma (MSWD = 0.92), respectively. The age of quartz diorite that intrudes the Bainaimiao Group is 459.3 ± 6.4 Ma (MSWD = 2.20). Molybdenite samples from massive Cu-Mo-bearing ores and quartz veins in the southern ore belt yield a Re-Os isochron age of 438.2 ± 2.7 Ma (MSWD = 0.16), which is consistent with the Re-Os isochron age of molybdenite in the northern ore belt, implying that the two ore belts belong to the same mineralization system. Muscovite from a post-magmatic Cu-Mo-bearing quartz-calcite vein yields an Ar-Ar isochron age of 422.5 ± 3.9 Ma (MSWD = 0.64) with an initial 40Ar/36Ar ratio of 286 ± 21. The well-defined plateau age of the muscovite is 422.4 ± 2.6 Ma (MSWD = 0.05), which represents the time of the post-magmatic orogenic transformation event. Based on our new age data and previous findings, we propose that the Bainaimiao Cu-Mo-Au deposit formed in an active continental margin setting and experienced four stages of ore mineralization: (1) a Late Cambrian-Middle Ordovician volcanic-sedimentary stage; (2) a Late Ordovician porphyry mineralization stage; (3) a Late Silurian regional metamorphism stage; and (4) an orogenic transformation stage. Subhedral and euhedral Paleoproterozoic (2402-1810 Ma) inherited zircons indicate that the Bainaimiao Group has a tectonic affinity with the North China Craton. The Central Asian Orogenic Belt, which is closely related to the complex closure of the Paleo-Asian Ocean, is favorable for prospecting for Paleozoic porphyry Cu

Carboniferous - Early Permian magmatic evolution of the Bogda Range (Xinjiang, NW China): Implications for the Late Paleozoic accretionary tectonics of the SW Central Asian Orogenic Belt

NASA Astrophysics Data System (ADS)

Wali, Guzalnur; Wang, Bo; Cluzel, Dominique; Zhong, Linglin

2018-03-01

The Late Paleozoic magmatic evolution of the Bogda Range (Chinese North Tianshan) is important for understanding the accretionary history of the Central Asian Orogenic Belt. We investigated the Carboniferous and Lower Permian volcanic and sedimentary sequences of the Daheyan section, southern Bogda Range, and present new zircon U-Pb ages and whole-rock geochemical data for the volcanic rocks. One Carboniferous rhyolite is dated at 298 ± 8 Ma; a Permian basalt yielded many Proterozoic zircon xenocrysts, and its maximum age (∼297 Ma) is constrained by the detrital zircon ages of the sandstone that stratigraphically underlies it. These volcanic rocks belong to calc-alkaline series. We further synthesize previous geochronological, geochemical and isotopic data of magmatic and sedimentary rocks in the Bogda Range. The available data indicate that the magmatism occurred continuously from 350 Ma to 280 Ma. A comprehensive analysis allows us to propose that: (1) the Carboniferous to Early Permian magmatic rocks of the Bogda Range generally show consistent arc-type features; (2) increasing mantle input through time suggests intra-arc extension in a supra-subduction zone; (3) the localized occurrence of Early Permian alkaline pillow basalts and deep water sediments close to the major shear zone advocate a transtensional crustal thinning during the transition from Carboniferous convergence to Early Permian transcurrent tectonics; (4) occurrence of a large number of Proterozoic zircon xenocrysts in the Late Paleozoic magmatic rocks, and Proterozoic detrital zircons in the coeval clastic sediments suggest a continental or transitional basement of the Bogda Arc; (5) subduction in the Bogda area terminated prior to the deposition of Middle Permian terrestrial sediments.

Reworked crustal of early Paleozoic WuYi Orogen revealed by receiver function data

NASA Astrophysics Data System (ADS)

Wei, Y.; Duan, Y.; Tian, X.; Zhao, Y.

2017-12-01

Intraplate orogenic belt, which occurs at the rigid and undeformable plate interiors, is a distinct new type of orogen rather than an interplate or plate marginal orogenic belt, whose deformation occurs exclusively at plate margins. Therefore, intraplate orogenic belts are the most obvious exception to the plate-tectonic paradigm, they are uncommon in Earth's history. The early Paleozoic Wuyi orogen in South China is one of the few examples of intraplate orogen, and is a key to understanding the process of intraplate orogenesis and global early Paleozoic geodynamics. In this study, we select teleseismic records from 45 mobile linear seismic stations deployed in Wuyi Mountain and 58 permanent stations setting in Jiangxi and Fujian provinces, from January 2011 to December 2012, and calculate the crustal thickness and average crustal Vp/Vs ratio using the H-κ stacking method. The main results include the following: 1) the crustal average Poission's ratio shows an increase tendency from land to sea, the interior of Wuyi orogen belt with an low ration less than 0.23, and the coastline with high ration which is up to 0.28, which indicate a very heterogeneous crustal structure and composition in Wuyi orogen and coast belt. 2) the crustal thickness ranges 28-34 km and shows a tendency of thinning from inland to coast in the region of SE China margin, which maight mean the eastern Eurasia lithospheric is extension and thinning induced by the subducted paleo-Pacific slab. To conclusion, we assume that Wuyi orogen experienced upper crustal thickening, lower crust and lithosphere delamination during the early Paleozoic orogeny, and lithosphere extension in Mesozoic. This research is founded by the Natural Science Foundation of China (41174052 and 41604048).

Collision of the Tacheng block with the Mayile-Barleik-Tangbale accretionary complex in Western Junggar, NW China: Implication for Early-Middle Paleozoic architecture of the western Altaids

NASA Astrophysics Data System (ADS)

Zhang, Ji'en; Xiao, Wenjiao; Luo, Jun; Chen, Yichao; Windley, Brian F.; Song, Dongfang; Han, Chunming; Safonova, Inna

2018-06-01

Western Junggar in NW China, located to the southeast of the Boshchekul-Chingiz (BC) Range and to the north of the Chu-Balkhash-Yili microcontinent (CBY), played a key role in the architectural development of the western Altaids. However, the mutual tectonic relationships have been poorly constrained. In this paper, we present detailed mapping, field structural geology, and geochemical data from the Barleik-Mayile-Tangbale Complex (BMTC) in Western Junggar. The Complex is divisible into Zones I, II and III, which are mainly composed of Cambrian-Silurian rocks. Zone I contains pillow lava, siliceous shale, chert, coral-bearing limestone, sandstone and purple mudstone. Zone II consists of basaltic lava, siliceous shale, chert, sandstone and mudstone. Zone III is characterized by basalt, chert, sandstone and mudstone. These rocks represent imbricated ocean plate stratigraphy, which have been either tectonically juxtaposed by thrusting or form a mélange with a block-in-matrix structure. All these relationships suggest that the BMTC is an Early-Middle Paleozoic accretionary complex in the eastern extension of the BC Range. These Early Paleozoic oceanic rocks were thrust onto Silurian sediments forming imbricate thrust stacks that are unconformably overlain by Devonian limestone, conglomerate and sandstone containing fossils of brachiopoda, crinoidea, bryozoa, and plant stems and leaves. The tectonic vergence of overturned folds in cherts, drag-related curved cleavages and σ-type structures on the main thrust surface suggests top-to-the-NW transport. Moreover, the positive εNd(t) values of volcanic rocks from the Tacan-1 drill-core, and the positive εHf(t) values and post-Cambrian ages of detrital zircons from Silurian and Devonian strata to the south of the Tacheng block indicate that its basement is a depleted and juvenile lithosphere. And there was a radial outward transition from coral-bearing shallow marine (shelf) to deep ocean (pelagic) environments, and from

An exhumed Late Paleozoic canyon in the rocky mountains

USGS Publications Warehouse

Soreghan, G.S.; Sweet, D.E.; Marra, K.R.; Eble, C.F.; Soreghan, M.J.; Elmore, R.D.; Kaplan, S.A.; Blum, M.D.

2007-01-01

Landscapes are thought to be youthful, particularly those of active orogenic belts. Unaweep Canyon in the Colorado Rocky Mountains, a large gorge drained by two opposite-flowing creeks, is an exception. Its origin has long been enigmatic, but new data indicate that it is an exhumed late Paleozoic landform. Its survival within a region of profound late Paleozoic orogenesis demands a reassessment of tectonic models for the Ancestral Rocky Mountains, and its form and genesis have significant implications for understanding late Paleozoic equatorial climate. This discovery highlights the utility of paleogeomorphology as a tectonic and climatic indicator. ?? 2007 by The University of Chicago. All rights reserved.

Paleoclimatic and paleomagnetic constraints on the Paleozoic reconstructions of south China, north China and Tarim

NASA Astrophysics Data System (ADS)

Shangyou, Nie

1991-10-01

Paleomagnetic and paleoclimatic data provide the most useful latitudinal constraints for plate reconstructions. Distributions through the Paleozoic of five types of climatically sensitive sediments (coals, evaporites, reefs, dolomites and limestones) for south China, north China and Tarim are shown on 15 maps that include 1578 reliable data points. These paleoclimatic data agree reasonably well with available paleomagnetic directions, although significant divergence between the two exists for the Early Paleozoic. These data indicate the following: (1) South China was in low latitudes during the entire Paleozoic, with a subtropical position in the Cambrian. (2) North China also remained near the equator in the Early and Late Paleozoic, except for the Ordovian and the Late Permian when extensive evaporites suggest slightly higher latitudinal positions, while its Middle Paleozoic position is uncertain due to the missing stratigraphie record. (3) In south China, local tectonics appears to have played a dominant role in determining paleogeography and therefore marine sedimentation, especially after the Late Ordovician-Early Silurian, because the areal coverage of marine sediments through time is distinctly different from what would be expected from published global sea-level curves. (4) Paleoclimatic and paleomagnetic data are compatible with biogeographic data which suggest that south China was part of eastern Gondwana in the Early Paleozoic, but was widely separated from Gondwana in the Late Paleozoic, and the split between the two probably happened in the Devonian, giving rise to a major break-up unconformity in central south China.

Facies patterns and conodont biogeography in Arctic Alaska and the Canadian Arctic Islands: Evidence against juxtaposition of these areas during early Paleozoic time

USGS Publications Warehouse

Dumoulin, Julie A.; Harris, A.G.; Bradley, D.C.; De Freitas, T. A.

2000-01-01

Differences in lithofacies and biofacies suggest that lower Paleozoic rocks now exposed in Arctic Alaska and the Canadian Arctic Islands did not form as part of a single depositional system. Lithologic contrasts are noted in shallow- and deep-water strata and are especially marked in Ordovician and Silurian rocks. A widespread intraplatform basin of Early and Middle Ordovician age in northern Alaska has no counterpart in the Canadian Arctic, and the regional drowning and backstepping of the Silurian shelf margin in Canada has no known parallel in northern Alaska. Lower Paleozoic basinal facies in northern Alaska are chiefly siliciclastic, whereas resedimented carbonates are volumetrically important in Canada. Micro- and macrofossil assemblages from northern Alaska contain elements typical of both Siberian and Laurentian biotic provinces; coeval Canadian Arctic assemblages contain Laurentian forms but lack Siberian species. Siberian affinities in northern Alaskan biotas persist from at least Middle Cambrian through Mississippian time and appear to decrease in intensity from present-day west to east. Our lithologic and biogeographic data are most compatible with the hypothesis that northern Alaska-Chukotka formed a discrete tectonic block situated between Siberia and Laurentia in early Paleozoic time. If Arctic Alaska was juxtaposed with the Canadian Arctic prior to opening of the Canada basin, biotic constraints suggest that such juxtaposition took place no earlier than late Paleozoic time.

The distribution, geochronology and geochemistry of early Paleozoic granitoid plutons in the North Altun orogenic belt, NW China: Implications for the petrogenesis and tectonic evolution

NASA Astrophysics Data System (ADS)

Meng, Ling-Tong; Chen, Bai-Lin; Zhao, Ni-Na; Wu, Yu; Zhang, Wen-Gao; He, Jiang-Tao; Wang, Bin; Han, Mei-Mei

2017-01-01

Abundant early Paleozoic granitoid plutons are widely distributed in the North Altun orogenic belt. These rocks provide clues to the tectonic evolution of the North Altun orogenic belt and adjacent areas. In this paper, we report an integrated study of petrological features, U-Pb zircon dating, in situ zircon Hf isotope and whole-rock geochemical compositions for the Abei, 4337 Highland and Kaladawan Plutons from north to south in the North Altun orogenic belt. The dating yielded magma crystallization ages of 514 Ma for the Abei Pluton, 494 Ma for the 4337 Highland Pluton and 480-460 Ma for the Kaladawan Pluton, suggesting that they are all products of oceanic slab subduction because of the age constraint. The Abei monzogranites derived from the recycle of Paleoproterozoic continental crust under low-pressure and high-temperature conditions are products of subduction initiation. The 4337 Highland granodiorites have some adakitic geochemical signatures and are sourced from partial melting of thickened mafic lower continental crust. The Kaladawan quartz diorites are produced by partial melting of mantle wedge according to the positive εHf(t) values, and the Kaladawan monzogranite-syenogranite are derived from partial melting of Neoproterozoic continental crust mixing the juvenile underplated mafic material from the depleted mantle. These results, together with existing data, provide significant information about the evolution history of oceanic crust subduction during the 520-460 Ma. The initiation of subduction occurred during 520-500 Ma with formation of Abei Pluton; subsequent transition from steep-angle to flat-slab subduction at ca.500 Ma due to the arrival of buoyant oceanic plateaus, which induces the formation of 4337 Highland Pluton. With ongoing subduction, the steep-angle subduction system is reestablished to cause the formation of 480-460 Ma Kaladawan Pluton. Meanwhile, it is this model that account for the temporal-spatial distribution of these early

Geochronology and geochemistry of late Paleozoic-early Mesozoic igneous rocks of the Erguna Massif, NE China: Implications for the early evolution of the Mongol-Okhotsk tectonic regime

NASA Astrophysics Data System (ADS)

Li, Yu; Xu, Wen-Liang; Wang, Feng; Tang, Jie; Zhao, Shuo; Guo, Peng

2017-08-01

We undertook geochemical and geochronological studies on late Paleozoic-early Mesozoic igneous rocks from the Erguna Massif with the aim of constraining the early evolution of the Mongol-Okhotsk tectonic regime. Zircon crystals from nine representative samples are euhedral-subhedral, display oscillatory growth zoning, and have Th/U values of 0.14-6.48, indicating a magmatic origin. U-Pb dating of zircon using SIMS and LA-ICP-MS indicates that these igneous rocks formed during the Late Devonian (∼365 Ma), late Carboniferous (∼303 Ma), late Permian (∼256 Ma), and Early-Middle Triassic (246-238 Ma). The Late Devonian rhyolites, together with coeval A-type granites, formed in an extensional environment related to the northwestwards subduction of the Heihe-Nenjiang oceanic plate. Their positive εHf(t) values (+8.4 to +14.4) and Hf two-stage model ages (TDM2 = 444-827 Ma) indicate they were derived from a newly accreted continental crustal source. The late Carboniferous granodiorites are geochemically similar to adakites, and their εHf(t) values (+10.4 to +12.3) and Hf two-stage model ages (TDM2 = 500-607 Ma) suggest they were sourced from thickened juvenile lower crustal material, this thickening may be related to the amalgamation of the Erguna-Xing'an and Songnen-Zhangguangcai Range massifs. Rocks of the late Permian to Middle Triassic suite comprise high-K calc-alkaline monzonites, quartz monzonites, granodiorites, and monzogranites. These rocks are relatively enriched in light rare earth elements and large ion lithophile elements, and depleted in heavy rare earth elements and high field strength elements. They were emplaced, together with coeval porphyry-type ore deposits, along an active continental margin where the Mongol-Okhotsk oceanic plate was subducting beneath the Erguna Massif.

Tectonic context of the penetrative fracture system origin in the Early Paleozoic shale complex (Baltic Basin, Poland/Sweden).

NASA Astrophysics Data System (ADS)

Jarosiński, Marek; Gluszynski, Andrzej; Bobek, Kinga; Dyrka, Ireneusz

2017-04-01

Characterization of natural fracture and fault pattern play significant role for reservoir stimulation design and evaluation of its results. Having structural observations limited to immediate borehole surrounding it is a common need to build up a fracture model of reservoir in a range of stimulation reservoir volume or even beyond. To do this we need both a 3D seismic model and a consistent concept of the regional tectonic evolution. We present the result of integrated tectonic study in several deep boreholes target the Lower Paleozoic shale complex of Baltic Basin (BB), combined with analysis of 3D seismic survey and outcrop screening in Scania (Swedish part of the BB). During deposition of shale complex in the Ordovician and Silurian the research area was located 200-300 km away from the continental margin of Baltica involved in the Caledonian collision with the Eastern Avalonia. This distance allowed the shale complex to avoid significant tectonic deformation. Regional seismic cross section reveals the general pattern of the BB infill characteristic for the foreland basin underwent post-collisional isostatic rebound. Due to stress changes in collisional context the shale complex was cross-cut by steep, mostly inverse faults trending NW-SE and NE-SW. The fault zones oriented NW-SE are associated with an array of en echelon faults characteristic for strike-slip displacement. In our interpretation, these faults of Silurian (Wenlock) age create pattern of the regional pop-up structure, which is simultaneously involved in the plate flexure extension. Seismic attributes (e.g. curvature or ant tracking) highlight lineaments which mostly mimic the faults orientation. However, attributes show also some artefacts that come from regular array of seismic sources and receivers, which mimic the orthogonal joint system. Structural observations on borehole core lead us to conclusion that regular, orthogonal fracture system developed after maximum burial of the complex

Timing of tectonic evolution of the East Kunlun Orogen, Northern Tibet Plateau

NASA Astrophysics Data System (ADS)

Dong, Yunpeng

2017-04-01

The East Kunlun Orogen, located at the northern Tibet Plateau, represents the western segment of the Central China Orogenic Belt which was formed by amalgamation of the North China blocks and South China blocks. It is a key to understanding the formation of Eastern Asian continent as well as the evolution of the Pangea supercontinent. Based on detailed geological mapping, geochemical and geochronological investigations, the orogen is divided into three main tectonic belts, from north to south, including the Northern Qimantagh, Central Kunlun and Southern Kunlun Belts by the Qimantagh suture, Central Kunlun suture and South Kunlun fault. The Qimantagh suture is marked by the Early Paleozoic ophiolites outcropped in the Yangziquan, Wutumeiren, and Tatuo areas, which consist mainly of peridotites, gabbros, diabases and basalts. Besides, the ophiolite in the Wutumeiren is characterized by occurring anorthosite while the ophiolite in the Tatuo occurring chert. The basalts and diabases from both Yaziquan and Tatuo areas display depletion of Nb, Ta, P and Ti, and enrichment of LILE, suggesting a subduction related tectonic setting. LA-ICP-MS zircon U-Pb age of 421 Ma for the diabase represents the formation age of the Yaziquan ophiolite, while the U-Pb ages of 490 Ma and 505 Ma for gabbro and anorthosite, respectively, constrain the formation age of the Tatuo ophiolite. The basaltic rocks in the Wutumeiren area display flat distribution of HFSEs (such as Nb, Ta, K, La, Ce, Pr, Nd, Zr, Sm, Eu, Ti, Dy, Y, Yb and Lu) and slightly enrichment in LREEs, while the peridotites showing depletion in MREEs. The LA-ICP-MS zircon U-Pb age of 431 Ma for the gabbro represents the formation age of the Wutumeiren ophiolite. Together with regional geology, we suggest herewith a back-arc basin tectonic setting during ca. 505-421 Ma at least for the Qimantagh suture. The Central Kunlun suture is represented by the ophiolite in the Wutuo area, which is characterized by depletion of Nb, Ta, P

A model for the evolution of the Earth's mantle structure since the Early Paleozoic

NASA Astrophysics Data System (ADS)

Zhang, Nan; Zhong, Shijie; Leng, Wei; Li, Zheng-Xiang

2010-06-01

the African superplume structure can be formed before ˜230 Ma (i.e., ˜100 Myr after the assembly of Pangea). Particularly, the last 120 Myr plate motion plays an important role in generating the African superplume. Our models have implications for understanding the global-scale magmatism, tectonics, mantle dynamics, and thermal evolution history for the Earth since the Early Paleozoic.

The Timan-Pechora Basin province of northwest Arctic Russia; Domanik, Paleozoic total petroleum system

USGS Publications Warehouse

Lindquist, Sandra J.

1999-01-01

The Domanik-Paleozoic oil-prone total petroleum system covers most of the Timan-Pechora Basin Province of northwestern Arctic Russia. It contains nearly 20 BBOE ultimate recoverable reserves (66% oil). West of the province is the early Precambrian Eastern European craton margin. The province itself was the site of periodic Paleozoic tectonic events, culminating with the Hercynian Uralian orogeny along its eastern border. The stratigraphic record is dominated by Paleozoic platform and shelf-edge carbonates succeeded by Upper Permian to Triassic molasse siliciclastics that are locally present in depressions. Upper Devonian (Frasnian), deep marine shale and limestone source rocks ? with typically 5 wt % total organic carbon ? by middle Mesozoic time had generated hydrocarbons that migrated into reservoirs ranging in age from Ordovician to Triassic but most focused in Devonian and Permian rocks. Carboniferous structural inversions of old aulacogen borders, and Hercynian (Permian) to Early Cimmerian (Late Triassic to Early Jurassic) orogenic compression not only impacted depositional patterns, but also created and subsequently modified numerous structural traps within the province.

Late Paleozoic tectonic evolution of the Central Asian Orogenic Belt: Constraints from multiple arc-basin systems in Altai-Junggar area, NW China

NASA Astrophysics Data System (ADS)

Li, D.

2015-12-01

In this study, we report results from integrated geological, geophysical and geochemical investigations on the Wulungu Depression of the Junggar Basin to understand the Late Paleozoic continental growth of the Junggar area and its amalgamation history with the Altai terrane, within the broad tectonic evolution of the Altai-Junggar area. Based on seismic and borehole data, the Wulungu Depression can be divided into two NW-trending tectonic units by southward thrust faults. The Suosuoquan Sag is composed of gray basaltic andesite, andesite, tuff, tuffaceous sandstone and tuffite, and the overlying Early Carboniferous volcano-sedimentary sequence with lava gushes and marine sediments from a proximal juvenile provenance, compared to the andesite in the Hongyan High. The SIMS Zircon U-Pb ages for andesites from Late Paleozoic strata indicate that these volcanics in Suosuoquan Sag and Hongyan High erupted at 376.3Ma and 313.4Ma, respectively. Most of the intermediate-mafic volcanic rocks exhibit calc-alkaline affinity, low initial 87Sr/86Sr and positive ɛNd(t) and ɛHf(t) values. Furthermore, these rocks have high Th/Yb and low Ce/Pb and La/Yb ratios as well as variable Ba/Th and Ba/La ratios. These features imply that the rocks were derived from partial melting of a mantle wedge metasomatized by subduction-related components in an island arc setting. The basin filling pattern and the distribution of island arc-type volcanics and their zircon Hf model ages with the eruptive time suggest that the Wulungu Depression represents an island arc-basin system with the development of a Carboniferous retro-arc basin. The gravity and magnetic anomaly data suggest that Altai-Junggar area incorporates three arc-basin belts from north to south: the Karamaili-Luliang-Darbut, Yemaquan-Wulungu, and Dulate-Fuhai-Saur. The recognition of the Wulungu arc-basin system demonstrates that the northern Junggar area is built by amalgamation of multiple Paleozoic linear arcs and accretionary

Petrogenesis and tectonic implications of the Early Paleozoic granites in the western segment of the North Qilian orogenic belt, China

NASA Astrophysics Data System (ADS)

Wang, Nan; Wu, Cai-Lai; Lei, Min; Chen, Hong-Jie

2018-07-01

Early Paleozoic granitic magmatism in the North Qilian orogenic belt records a complete Wilson cycle and provides critical geological clues for unraveling the regional tectonic history. In this study, we report the results of zircon U-Pb ages, Hf isotopic analysis and systematic whole-rock geochemical data for the Late Ordovician Hongliuhe granite and Early Silurian Qingshan monzogranite in the western segment of the North Qilian orogenic belt to constrain their emplacement ages, petrogenesis, and regional evolution history. U-Pb dating reveals that the Hongliuhe granite was emplaced around 453-452 Ma, and the Qingshan monzogranite was emplaced about 440-438 Ma. A geochemical study shows that the two granites belong to the calc-alkaline to high-K calc-alkaline series. The Hongliuhe granite shows adakitic and peraluminous features, while the Qingshan monzogranite belongs to metaluminous to weak peraluminous granites. Zircons in the Hongliuhe granite show εHf(t) values ranging from -15.1 to +11.7 with two-stage Hf model ages (tDM2) of 687-2398 Ma, whereas zircons in the Qingshan monzogranite show εHf(t) values ranging from +5.7 to +11.0 with two-stage Hf model ages from 814 to 1057 Ma. The geochemical characteristics indicate that the Hongliuhe granite was a transitional I/S-type granite and was generated from a thickened lower crust with the addition of minor Paleo- to Mesoproterozoic crustal materials, which left a rutile + garnet + pyroxene ± plagioclase residue. The Qingshan monzogranite formed from the partial melting of mafic crust with minor mantle-derived materials, and the fractionation of Ti-bearing phases, apatite and pyroxene occurred during the magma's evolution, which left an amphibole and plagioclase residue. We infer that the Hongliuhe granite formed during the northward subduction of the North Qilian Ocean, while the Qingshan monzogranite was generated during the post-collision stage between the Qilian and Alxa blocks. This observation indicates

Paleozoic to early Cenozoic cooling and exhumation of the basement underlying the eastern Puna plateau margin prior to plateau growth

NASA Astrophysics Data System (ADS)

Insel, N.; Grove, M.; Haschke, M.; Barnes, J. B.; Schmitt, A. K.; Strecker, M. R.

2012-12-01

Constraining the pre-Neogene history of the Puna plateau is crucial for establishing the initial conditions that attended the early stage evolution of the southern extent of the Andean plateau. We apply high- to low-temperature thermochronology data from plutonic rocks in northwestern Argentina to quantify the Paleozoic, Mesozoic and early Tertiary cooling history of the Andean crust. U-Pb crystallization ages of zircons indicate that pluton intrusion occurred during the early mid-Ordovician (490-470 Ma) and the late Jurassic (160-150 Ma). Lower-temperature cooling histories from 40Ar/39Ar analyses of K-feldspar vary substantially. Basement rocks underlying the western Puna resided at temperatures below 200°C (<6 km depth) since the Devonian (˜400 Ma). In contrast, basement rocks underlying the southeastern Puna were hotter (˜200-300°C) throughout the Paleozoic and Jurassic and cooled to temperatures of <200°C by ˜120 Ma. The southeastern Puna basement records a rapid cooling phase coeval with active extension of the Cretaceous Salta rift at ˜160-100 Ma that we associate with tectonic faulting and lithospheric thinning. The northeastern Puna experienced protracted cooling until the late Cretaceous with temperatures <200°C during the Paleocene. Higher cooling rates between 78 and 55 Ma are associated with thermal subsidence during the postrift stage of the Salta rift and/or shortening-related flexural subsidence. Accelerated cooling and deformation during the Eocene was focused within a narrow zone along the eastern Puna/Eastern Cordillera transition that coincides with Paleozoic/Mesozoic structural and thermal boundaries. Our results constrain regional erosion-induced cooling throughout the Cenozoic to have been less than ˜150°C, which implies total Cenozoic denudation of <6-4 km.

Reconstruction of an early Paleozoic continental margin based on the nature of protoliths in the Nome Complex, Seward Peninsula, Alaska

USGS Publications Warehouse

Till, Alison B.; Dumoulin, Julie A.; Ayuso, Robert A.; Aleinikoff, John N.; Amato, Jeffrey M.; Slack, John F.; Shanks, W.C. Pat

2014-01-01

The Nome Complex is a large metamorphic unit that sits along the southern boundary of the Arctic Alaska–Chukotka terrane, the largest of several micro continental fragments of uncertain origin located between the Siberian and Laurentian cratons. The Arctic Alaska–Chukotka terrane moved into its present position during the Mesozoic; its Mesozoic and older movements are central to reconstruction of Arctic tectonic history. Accurate representation of the Arctic Alaska–Chukotka terrane in reconstructions of Late Proterozoic and early Paleozoic paleogeography is hampered by the paucity of information available. Most of the Late Proterozoic to Paleozoic rocks in the Alaska–Chukotka terrane were penetratively deformed and recrystallized during the Mesozoic deformational events; primary features and relationships have been obliterated, and age control is sparse. We use a variety of geochemical, geochronologic, paleontologic, and geologic tools to read through penetrative deformation and reconstruct the protolith sequence of part of the Arctic Alaska–Chukotka terrane, the Nome Complex. We confirm that the protoliths of the Nome Complex were part of the same Late Proterozoic to Devonian continental margin as weakly deformed rocks in the southern and central part of the terrane, the Brooks Range. We show that the protoliths of the Nome Complex represent a carbonate platform (and related rocks) that underwent incipient rifting, probably during the Ordovician, and that the carbonate platform was overrun by an influx of siliciclastic detritus during the Devonian. During early phases of the transition to siliciclastic deposition, restricted basins formed that were the site of sedimentary exhalative base-metal sulfide deposition. Finally, we propose that most of the basement on which the largely Paleozoic sedimentary protolith was deposited was subducted during the Mesozoic.

A-type granitoid in Hasansalaran complex, northwestern Iran: Evidence for extensional tectonic regime in northern Gondwana in the Late Paleozoic

NASA Astrophysics Data System (ADS)

Azizi, Hossein; Kazemi, Tahmineh; Asahara, Yoshihiro

2017-07-01

The Hasansalaran plutonic complex is one of the main intrusive bodies with a wide range of granite, monzonite, diorite and syenite that crop out in northwest Iran. This body includes Paleozoic granitoids that are surrounded and cut by Cretaceous granitoids. Zircon U-Pb age dating shows that the crystallization of this body occurred at 360 Ma ago in the Early Carboniferous. Whole rock compositions of the investigated intrusive body, show high contents of Ga (11.1-76.3 ppm), Zr (73.5-1280 ppm), Zn (43.7-358 ppm), Y(17.9-177 ppm), enrichment of rare earth elements (REEs) together with high Ga/Al ratios and a strong Eu negative anomaly, fairly consistent with typical A-type signature. The low εNd(t = 360 Ma) value (< + 3) and high variation of 87Sr/86Sr(initial) ratios are evidence of the role of the continental component for the evolution of A-type granitoids in the Hasansalaran area. Because of the high contents of Ta, Yb, Nb and Y, all samples are plotted in the within-plate tectonic regime without interfering oceanic released fluids in the subduction zone. These high Nb content rocks (37.2-342 ppm without one sample) are classified as A1-type granitoids. Based on the distribution of A1- and A2-type granitoids in the Late Paleozoic in northwest Iran, the existence of some gabbroic rocks with tholeiitic to alkali composition and a long gap for magmatic activities in the area from 550 to 360 Ma (approximately 180 my.a.) between the Zagros and Tabriz faults, we suggest a new thematic model for evolution of northwest Iran in the Late Paleozoic. Based on our model, the upwelling of a mantle plume, probably due to the proto-Tethys oceanic rollback activity beneath northern Gondwana, had a crucial role in the uplifting of the continental crust and resulted in the crystallization of A-type granitoids with some gabbroic rocks in northwest Iran.

Late Paleozoic transpression in Buenos Aires and northeast Patagonia ranges, Argentina

NASA Astrophysics Data System (ADS)

Rossello, E. A.; Massabie, A. C.; López-Gamundí, O. R.; Cobbold, P. R.; Gapais, D.

1997-12-01

, immediately west of the Sierras Australes. In the Sierras Septentrionales of Buenos Aires, Precambrian through early Paleozoic deposits of La Tinta, Sierras Bayas, Las Aguilas and Balcarce Formations rest on Precambrian crystalline basement of the La Plata craton. These exposed rocks are affected by subordinate, right lateral wrench faulting; some thrusting indicates tectonic transport toward the NE. In northeast Patagonia (Sierra Grande region) synkinematic deformation of early Permian (261 ± 5 Ma, {Rb}/{Sr} whole rock) age has been identified in Silurian metasediments of the Sierra Grande Formation. Bands of deformation in Sierra Grande quartzites indicate right lateral wrenching in a N-S direction. Contraction in a NE-SW direction is evidenced by folding. Three stages of tectonic evolution can be discerned for the above regions: (1) Early Paleozoic platform sedimentation, punctuated by episodes of accelerated subsidence during the Silurian and early Devonian, as shown by transgressive episodes, (2) late Paleozoic sedimentation and deformation, and (3) Meso-Cenozoic extensional inversion due to the South Atlantic opening. The late Paleozoic sedimentation and deformation (stage 2) includes late Carboniferous-earliest Permian glacial deposits of the Sierras Australes and Colorado offshore basin, deposited during an initial phase of extension, and cratonward foreland subsidence triggered sedimentation of the synorogenic deposits of the Permian Tunas Formation. Tuffs are intercalated in the upper half of this unit. These tuffs are associated with the silicic volcanism along the Andes and Patagonia (Choiyoi magmatic province) that peaked between the late early Permian and late Permian. Likewise, the first widespread appearance of tuffs in the Karoo basin is in the Whitehill Formation, of late early Permian (260 Ma) age. The deformation described in this paper can be considered as part of a large scale intracontinental deformation in SW Gondwanaland inboard of an Andean

The distribution and tectonic framework of Late Paleozoic volcanoes in the Junggar basin and its adjacent area, NW China

NASA Astrophysics Data System (ADS)

Mao, X.; Li, J. H.

2012-04-01

We analyse the distribution and characteristics of 145 late Paleozoic volcanoes in north Xinjiang, NW China, including 32 volcanoes on the edge of the Junggar basin. These volcanoes are clustered and can be divided into calderas, volcanic domes, and volcanic necks. There are also 85 volcanoes inside the Junggar basin, which are dominantly distributed in the Ke-Bai fractured zone of the northwestern margin of Junggar Basin, 4 depressions (Dongdaohaizi Depression, Dishuiquan Depression, Sannan Depression and Wucaiwan Depression) and 7 uplifts (Baijiahai uplift, Beisantai uplift, Dibei uplift, Dinan uplift, Sangequan uplift, Shixi uplift and Xiayan uplift). The volcanoes inside the basin are principally controlled by Hercynian Fault Systems, along NE and nearly EW trending faults and most developed in the interjunctions of the faults. The long modification by late-stage weathering and leaching made the volcanoes difficult to identify. Remaining volcanic landforms, changing trends of the volcanic lithofacies and the typical volcanic rock, such as the crypto- explosive breccia, are the typical marks of the late Paleozoic volcanoes in the field; and the concealed volcanic edifices are identified by the techniques of seismic identification, such as seismic slicing, analysis of the attribute and tectonic trend plane. The ages of the volcanic rocks are focused on from 340 Ma to 320Ma and from 300 Ma to 295 Ma, corresponding to the subducting periods of West Junggar and East Junggar. From early Carboniferous to late Carboniferous, the volcanic activities in Junggar Basin and its adjacent areas show a variation trend from undersea to continental, from deep water to shallow water and from continental margin to intracontinental.

The petrogenesis of sodic granites in the Niujuanzi area and constraints on the Paleozoic tectonic evolution of the Beishan region, NW China

NASA Astrophysics Data System (ADS)

Yu, Jiyuan; Guo, Lin; Li, Jianxing; Li, Yanguang; Smithies, Robert H.; Wingate, Michael T. D.; Meng, Yong; Chen, Shefa

2016-07-01

Ordovician to Devonian sodic granites dominate the newly recognized Luotuojuan composite granite in the Lebaquan-Luotuojuan-Niujuanzi region of Beishan, along the southern margin of the Central Asian Orogenic Belt in NW China. The granites include sodic (K2O/Na2O > 0.5) tonalites with low Y (< 7 ppm), Yb (< 0.7 ppm), high Sr/Y (> 68) that formed during at least two events at c. 435 and c. 370-360 Ma. Their compositions are consistent with high-pressure melting of basaltic crust, although relatively non-radiogenic Nd isotope compositions (εNd(t) + 0.9) require some crustal assimilation. The interpretation that these granites reflect melts of a subducted slab (i.e. adakite) is supported by independent local and regional geological evidence for an oceanic subduction-accretion setting, including a long history of calc-alkaline magmatism and the identification of a series of early Paleozoic ophiolite belts. Other sodic granites forming the Luotuojuan composite granite are mainly quartz-diorite and granodiorite formed between c. 391 and c. 360 Ma. These rocks are not adakites, having Sr concentrations and Sr/Y ratios too low and Y and Yb concentrations too high. They are low- to medium-K calc-alkaline rocks more typical of magmas derived through melting in a subduction modified mantle wedge. Compositional changes from sodic to potassic granites, over time frames consistent with subduction processes, suggest at least two separate cycles, or pulses, of hot subduction in the Lebaquan-Luotuojuan-Niujuanzi region. Although early Paleozoic adakites have been inferred to exist elsewhere in the Beishan region, many of the reported adakitic rocks have compositions inconsistent with melting of subducted oceanic lithosphere and so tectonic interpretation of hot subduction might not be valid in these cases. A study of regional granite data also shows not only that adakite magmatism does not extend into the Permian but that if subduction-accretion processes extended into the late

Geochronological and sedimentological evidences of Panyangshan foreland basin for tectonic control on the Late Paleozoic plate marginal orogenic belt along the northern margin of the North China Craton

NASA Astrophysics Data System (ADS)

Li, Jialiang; Zhou, Zhiguang; He, Yingfu; Wang, Guosheng; Wu, Chen; Liu, Changfeng; Yao, Guang; Xu, Wentao; Zhao, Xiaoqi; Dai, Pengfei

2017-08-01

There is a wide support that the Inner Mongolia Palaeo-uplift on the northern margin of the North China Craton has undergone an uplifting history. However, when and how did the uplift occurred keeps controversial. Extensive field-based structural, metamorphic, geochemical, geochronological and geophysical investigations on the Inner Mongolia Palaeo-uplift, which suggested that the Inner Mongolia Palaeo-uplift was an uplifted region since the Early Precambrian or range from Late Carboniferous-Early Jurassic. The geochemical characteristics of the Late Paleozoic to Early Mesozoic intrusive rocks indicated that the Inner Mongolia Palaeo-uplift was an Andean-type continental margin that is the extensional tectonic setting. To address the spatial and temporal development of the Inner Mongolia Palaeo-uplift, we have carried out provenance analysis of Permian sedimentary rocks which collected from the Panyangshan basin along the northern margin of the North China Craton. The QFL diagram revealed a dissected arc-recycled orogenic tectonic setting. Moreover, the framework grains are abundant with feldspar (36-50%), indicating the short transport distance and unstable tectonic setting. Detrital zircon U-Pb analysis ascertained possible provenance information: the Precambrian basement ( 2490 and 1840 Ma) and continental arc magmatic action ( 279 and 295 Ma) along the northern margin of the North China Craton. The projection in rose diagrams of the mean palaeocurrent direction, revealing the SSW and SSE palaeoflow direction, also shows the provenance of the Panyangshan basin sources mainly from the Inner Mongolia Palaeo-uplift. The andesite overlying the Naobaogou Formation has yielded U-Pb age of 277.3 ± 1.4 Ma. The additional dioritic porphyry dike intruded the Naobaogou and Laowopu Formations, which has an emplacement age of 236 ± 1 Ma. The above data identify that the basin formed ranges from Early Permian to Middle Triassic (277-236 Ma). Accordingly, the Inner Mongolia

Geochronological and sedimentological evidences of Panyangshan foreland basin for tectonic control on the Late Paleozoic plate marginal orogenic belt along the northern margin of the North China Craton

NASA Astrophysics Data System (ADS)

Li, Jialiang; Zhou, Zhiguang; He, Yingfu; Wang, Guosheng; Wu, Chen; Liu, Changfeng; Yao, Guang; Xu, Wentao; Zhao, Xiaoqi; Dai, Pengfei

2018-06-01

There is a wide support that the Inner Mongolia Palaeo-uplift on the northern margin of the North China Craton has undergone an uplifting history. However, when and how did the uplift occurred keeps controversial. Extensive field-based structural, metamorphic, geochemical, geochronological and geophysical investigations on the Inner Mongolia Palaeo-uplift, which suggested that the Inner Mongolia Palaeo-uplift was an uplifted region since the Early Precambrian or range from Late Carboniferous-Early Jurassic. The geochemical characteristics of the Late Paleozoic to Early Mesozoic intrusive rocks indicated that the Inner Mongolia Palaeo-uplift was an Andean-type continental margin that is the extensional tectonic setting. To address the spatial and temporal development of the Inner Mongolia Palaeo-uplift, we have carried out provenance analysis of Permian sedimentary rocks which collected from the Panyangshan basin along the northern margin of the North China Craton. The QFL diagram revealed a dissected arc-recycled orogenic tectonic setting. Moreover, the framework grains are abundant with feldspar (36-50%), indicating the short transport distance and unstable tectonic setting. Detrital zircon U-Pb analysis ascertained possible provenance information: the Precambrian basement ( 2490 and 1840 Ma) and continental arc magmatic action ( 279 and 295 Ma) along the northern margin of the North China Craton. The projection in rose diagrams of the mean palaeocurrent direction, revealing the SSW and SSE palaeoflow direction, also shows the provenance of the Panyangshan basin sources mainly from the Inner Mongolia Palaeo-uplift. The andesite overlying the Naobaogou Formation has yielded U-Pb age of 277.3 ± 1.4 Ma. The additional dioritic porphyry dike intruded the Naobaogou and Laowopu Formations, which has an emplacement age of 236 ± 1 Ma. The above data identify that the basin formed ranges from Early Permian to Middle Triassic (277-236 Ma). Accordingly, the Inner Mongolia

Provenance analysis of the Late Paleozoic sedimentary rocks in the Xilinhot Terrane, NE China, and their tectonic implications

NASA Astrophysics Data System (ADS)

Han, Jie; Zhou, Jian-Bo; Wilde, Simon A.; Song, Min-Chun

2017-08-01

The Xilinhot Terrane is located in the eastern segment of the Central Asian Orogenic Belt in NE China, and is a key to a hotly debated issue on the Paleozoic tectonic evolution of this giant progenic belt. To constrain the tectonic evolution of the Xilinhot Terrane in the Late Paleozoic, we undertook zircon U-Pb dating and geochemical analyses of the Zhesi and Benbatu formations in the Suolun and Xi Ujimqin areas in the Xilinhot Terrane. Samples of the Benbatu Formation yield detrital zircon U-Pb ages ranging from 2659 Ma to 316 Ma, with four age populations at: 2659-1826 Ma, 1719-963 Ma, 590-402 Ma, and 396-316 Ma, whereas samples from the Zhesi Formation yield detrital zircon U-Pb ages ranging from 1967 Ma to 250 Ma, with four age populations at: 1967-1278 Ma, 971-693 Ma, 561-403 Ma, and 399-250 Ma. The age groups of both the Benbatu and Zhesi formations in the Xilinhot Terrane are similar to those in other parts of the Central Asian Orogenic Belt (CAOB). This evidence indicates that the Xilinhot Terrane is a microcontinent, and not an accretionary complex as previously thought. Furthermore, the youngest zircon grains in the Benbatu and Zhesi formations yield weighted mean 206Pb/238U ages of 322 ± 12 Ma (MSDW = 0.12, n = 4) and 257 ± 2.8 Ma (MSDW = 1.6, n = 8), respectively. Combined with fossil data, our new data suggest that the Benbatu and Zhesi formations in the Xilinhot Terrane were possibly deposited at ∼322 Ma and ∼257 Ma, respectively. Based on the provenance of the Carboniferous-Permian sandstones came from the blocks of NE China, we speculate that the Xilinhot Terrane is the western part of the Songliao block.

Paleogeography of the upper Paleozoic basins of southern South America: An overview

NASA Astrophysics Data System (ADS)

Limarino, Carlos O.; Spalletti, Luis A.

2006-12-01

The paleogeographic evolution of Late Paleozoic basins located in southern South America is addressed. Three major types of basins are recognized: infracratonic or intraplate, arc-related, and retroarc. Intraplate basins (i.e., Paraná, Chaco-Paraná, Sauce Grande-Colorado, and La Golondrina) are floored by continental or quasi-continental crust, with low or moderate subsidence rates and limited magmatic and tectonic activity. Arc-related basins (northern and central Chile, Navidad-Arizaro, Río Blanco, and Calingasta-Uspallata basins and depocenters along Chilean Patagonia) show a very complex tectonic history, widespread magmatic activity, high subsidence rates, and in some cases metamorphism of Late Paleozoic sediments. An intermediate situation corresponds to the retroarc basins (eastern Madre de Dios, Tarija, Paganzo, and Tepuel-Genoa), which lack extensive magmatism and metamorphism but in which coeval tectonism and sedimentation rates were likely more important than those in the intraplate region. According to the stratigraphic distribution of Late Paleozoic sediments, regional-scale discontinuities, and sedimentation pattern changes, five major paleogeographic stages are proposed. The lowermost is restricted to the proto-Pacific and retroarc basins, corresponds to the Mississippian (stage 1), and is characterized by shallow marine and transitional siliciclastic sediments. During stage 2 (Early Pennsylvanian), glacial-postglacial sequences dominated the infracratonic (or intraplate) and retroarc basins, and terrigenous shallow marine sediments prevailed in arc-related basins. Stage 3 (Late Pennsylvanian-Early Cisuralian) shows the maximum extension of glacial-postglacial sediments in the Paraná and Sauce Grande-Colorado basins (intraplate region), whereas fluvial deposits interfingering with thin intervals of shallow marine sediments prevailed in the retroarc basins. To the west, arc-related basins were dominated by coastal to deep marine conditions

Geometry and kinematics of Majiatan Fold-and-thrust Belt, Western Ordos Basin: implication for Tectonic Evolution of North-South Tectonic Belt

NASA Astrophysics Data System (ADS)

He, D.

2017-12-01

The Helan-Chuandian North-South Tectonic Belt crossed the central Chinese mainland. It is a boundary of geological, geophysical, and geographic system of Chinese continent tectonics from shallow to deep, and a key zone for tectonic and geomorphologic inversion during Mesozoic to Cenozoic. It is superimposed by the southeastward and northeastward propagation of Qinghai-Tibet Plateau in late Cenozoic. It is thus the critical division for West and East China since Mesozoic. The Majiatan fold-and-thrust belt (MFTB), locating at the central part of HCNSTB and the western margin of Ordos Basin, is formed by the tectonic evolution of the Helan-Liupanshan Mountains. Based on the newly-acquired high-resolution seismic profiles, deep boreholes, and surface geology, the paper discusses the geometry, kinematics, and geodynamic evolution of MFTB. With the Upper Carboniferous coal measures and the pre-Sinian ductile zone as the detachments, MFTB is a multi-level detached thrust system. The thrusting was mainly during latest Jurassic to Late Cretaceous, breaking-forward in the foreland, and resulting in a shortening rate of 25-29%. By structural restoration, this area underwent extension in Middle Proterozoic to Paleozoic, which can be divided into three phases of rifting such as Middle to Late Proterozoic, Cambiran to Ordovician, and Caboniferous to early Permian. It underwent compression since Late Triassic, including such periods as Latest Triassic, Late Jurassic to early Cretaceous, Late Cretaceous to early Paleogene, and Pliocene to Quaternary, with the largest shortening around Late Jurassic to early Cretaceous period (i.e. the mid-Yanshanian movement by the local name). However, trans-extension since Eocene around the Ordos Basin got rise to the formation the Yingchuan, Hetao, and Weihe grabens. It is concluded that MFTB is the leading edge of the intra-continental Helan orogenic belt, and formed by multi-phase breaking-forward thrusting during Late Jurassic to Cretaceous

Late Paleozoic tectonics of the Solonker Zone in the Wuliji area, Inner Mongolia, China: Insights from stratigraphic sequence, chronology, and sandstone geochemistry

NASA Astrophysics Data System (ADS)

Shi, Guanzhong; Song, Guangzeng; Wang, Hua; Huang, Chuanyan; Zhang, Lidong; Tang, Jianrong

2016-09-01

The geology in the Wuliji area (including the Enger Us and Quagan Qulu areas) is important for understanding the Late Paleozoic tectonics of the Solonker Zone. Ultramafic/mafic rocks in the Enger Us area, previously interpreted as an ophiolitic suture, are actually lava flows and sills in a Permian turbiditic sequence and a small body of fault breccia containing serpentinite. Subduction zone features, such as accretionary complexes, magmatic arc volcanics or LP/HP metamorphism are absent. Early Permian N-MORB mafic rocks and Late Permian radiolarian cherts accompanied by turbidites and tuffeous rocks indicate a deep water setting. In the Quagan Qulu area, outcrops of the Late Carboniferous to Permian Amushan Formation are composed of volcano-sedimenary rocks and guyot-like reef limestone along with a Late Permian volcano-sedimentary unit. A dacite lava in the Late Permian volcano-sedimentary unit yields a zircon U-Pb age of 254 Ma. The gabbros in the Quagan Qulu area are intruded into the Amushan Formation and caused contact metamorphism of country rocks. Sandstones in the Upper Member of the Amushan Formation contain detrital clasts of volcanic fragments and mineral clasts of crystalline basement rocks (i.e. biotite, muscovite and garnet). Geochemical analysis of volcaniclastic sandstones shows a magmatic affinity to both continental island arc (CIA) and active continental margin (ACM) tectonic settings. A Late Permian incipient rift setting is suggested by analyzing the lithostratigraphic sequence and related magmatism in the Wuliji area. The volcano-sedimentary rocks in the Wuliji area experienced a nearly N-S shortening that was probably related to the Early Mesozoic nearly N-S compression well developed in other areas close to the Wuliji area.

Sequential filling of a late paleozoic foreland basin

USGS Publications Warehouse

Mars', J. C.; Thomas, W.A.

1999-01-01

Through the use of an extensive data base of geophysical well logs, parasequence-scale subdivisions within a late Paleozoic synorogenic clastic wedge resolve cycles of sequential subsidence of a foreland basin, sediment progradation, subsidence of a carbonate shelf edge, diachronously subsiding discrete depositional centers, and basinwide transgression. Although temporal resolution of biostratigraphic markers is less precise in Paleozoic successions than in younger basins, parasequence-scale subdivisions provide more detailed resolution within marker-defined units in Paleozoic strata. As an example, the late Paleozoic Black Warrior basin in the foreland of the Ouachita thrust belt is filled with a synorogenic clastic wedge, the lower part of which intertongues with the fringe of a cratonic carbonate facie??s in the distal part of the basin. The stratal geometry of one tongue of the carbonate facie??s (lower tongue of Bangor Limestone) defines a ramp that grades basinward into a thin black shale. An overlying tongue of the synorogenic clastic wedge (lower tongue of Parkwood Formation) consists of cyclic delta and delta-front deposits, in which parasequences are defined by marine-flooding surfaces above coarsening- and shallow ing-upward successions of mudstone and sandstone. Within the lower Parkwood tongue, two genetic stratigraphie sequences (A and B) are defined by parasequence offlap and downlap patterns and are bounded at the tops by basinwide maximum-flooding surfaces. The distribution of parasequences within sequences A and B indicates two cycles of sequential subsidence (deepening) and progradation, suggesting subsidence during thrust advance and progradation during thrust quiescence. Parasequence stacking in sequences A and B also indicates diachronous differential tectonic subsidence of two discrete depositional centers within the basin. The uppermost sequence (C) includes reworked sandstones and an overlying shallow-marine limestone, a vertical succession

Early Paleozoic magmatic events in the eastern Klamath Mountains, northern California

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

Wallin, E.T.; Mattinson, J.M.; Potter, A.W.

1988-02-01

New U-Pb zircon ages for nine samples of tonalite and pegmatitic trondhjemite from the Trinity ophiolite and associated melange reveal a complex history of magmatic activity extending back into the earliest Cambrian, much older than previously believed. Earlier investigations, based on limited data, recognized lower Paleozoic crustal elements in the eastern Klamath terrane (EKT) ranging in age from Middle Ordovician to Early to Middle Devonian. The new work in the Yreka-Callahan area of the EKT confirms the Ordovician (440-475 Ma) and younger ages, but reveals for the first time the presence of tonalitic rocks that crystallized during a narrow timemore » interval at about 565-570 Ma. The authors also recognize younger, Late Silurian magmatism at 412 Ma. In the context of available mapping, these ages indicate that the Trinity ophiolite is broadly polygenetic because parts of it yield crystallization ages that span approximately 150 m.y. Superjacent dismembered units of probable early Paleozoic age may be tectonostratigraphically equivalent to the Sierra City melange in the northern Sierra Nevada.« less

Ogaden Basin subsidence history: Another key to the Red Sea-Gulf of Aden tectonic puzzle

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

Pigott, J.D.; Neese, D.; Carsten, G.

1995-08-01

Previous work has attempted to understand the tectonic evolution of the Red Sea-Gulf of Aden region through a focus upon plate kinematics and reconstruction of plate interactions in a two dimensional sense. A significant complement to the three dimensional puzzle can be derived from a critical examination of the vertical component, tectonic subsidence analysis. By removing the isostatic contributions of sediment loading and unloading, and fluctuations in sea level, the remaining thermal-mechanical contribution to a basin`s subsidence can be determined. Such an analysis of several Ogaden Basin wells reveals multiple pulses of tectonic subsidence and uplift which correspond to far-fieldmore » tectonic activities in the Red Sea and Gulf of Aden. One of the more dramatic is a Jurassic tectonic pulse circa 145-130 m.a., and a later extensional event which correlates to a major subsidence event ubiquitous through-out the Gulf of Aden, related to Gondwana Land breakup activities. Tectonic uplift during the Tertiary coincides with early Red Sea rifting episodes. Such activities suggest the Ogaden Basin has been a relatively stable East African cratonic basin, but with heating-extension events related to nearby plate interactions. In terms of hydrocarbon generation, the use of steady state present day geothermal gradients, coupled with subsidence analysis shows that potential Paleozoic and Mesozoic source rocks initiated generation as early as the Jurassic. The generating potential of Paleozoic source rocks would only be exacerbated by later heating events. Furthermore, cooling and tectonic uplift during the Tertiary would tend to arrest on-going hydrocarbon generation for Jurassic source rocks in the Ogaden area.« less

Paleozoic subduction complex and Paleozoic-Mesozoic island-arc volcano-plutonic assemblages in the northern Sierra terrane

USGS Publications Warehouse

Hanson, Richard E.; Girty, Gary H.; Harwood, David S.; Schweickert, Richard A.

2000-01-01

This field trip provides an overview of the stratigraphic and structural evolution of the northern Sierra terrane, which forms a significant part of the wall rocks on the western side of the later Mesozoic Sierra Nevada batholith in California. The terrane consists of a pre-Late Devonian subduction complex (Shoo Fly Complex) overlain by submarine arc-related deposits that record the evolution of three separate island-arc systems in the Late Sevonian-Early Mississippian, Permian, and Late Triassic-Jurassic. The two Paleozoic are packages and the underlying Shoo Fly Complex have an important bearing on plate-tectonic processes affecting the convergent margin outboard of the Paleozoic Cordilleran miogeocline, although their original paleogeographic relations to North America are controversial. The third arc package represents an overlap assemblage that ties the terrane to North America by the Late Triassic and helps constrain the nature and timing of Mesozoic orogenesis. Several of the field-trip stops examine the record of pre-Late Devonian subduction contained in the Shoo Fly Complex, as well as the paleovolcanology of the overlying Devonian to Jurassic arc rocks. Excellent glaciated exposures provide the opportunity to study a cross section through a tilted Devonian volcano-plutonic association. Additional stops focus on plutonic rocks emplaced during the Middle Jurassic arc magmatism in the terrane, and during the main pulse of Cretaceous magmatism in the Sierra Nevada batholith to the east.

Supra-subduction zone extensional magmatism in Vermont and adjacent Quebec: Implications for early Paleozoic Appalachian tectonics

USGS Publications Warehouse

Kim, J.; Coish, R.; Evans, M.; Dick, G.

2003-01-01

Metadiabasic intrusions of the Mount Norris Intrusive Suite occur in fault-bounded lithotectonic packages containing Stowe, Moretown, and Cram Hill Formation lithologies in the northern Vermont Rowe-Hawley belt, a proposed Ordovician arc-trench gap above an east-dipping subduction zone. Rocks of the Mount Norris Intrusive Suite are characteristically massive and weakly foliated, have chilled margins, contain xenoliths, and have sharp contacts that both crosscut and are parallel to early structural fabrics in the host metasedimentary rocks. Although the mineral assemblage of the Mount Norris Intrusive Suite is albite + actinolite + epidote + chlorite + calcite + quartz, intergrowths of albite + actinolite are probably pseudomorphs after plagioclase + clinopyroxene. The metadiabases are subalkaline, tholeiitic, hypabyssal basalts with preserved ophitic texture. A backarc-basin tectonic setting for the intrusive suite is suggested by its LREE (light rare earth element) enrichment, negative Nb-Ta anomalies, and Ta/Yb vs. Th/Yb trends. Although no direct isotopic age data are available, the intrusions are broadly Ordovician because their contacts are clearly folded by the earliest Acadian (Silurian-Devonian) folds. Field evidence and geochemical data suggest compelling along-strike correlations with the Coburn Hill Volcanics of northern Vermont and the Bolton Igneous Group of southern Quebec. Isotopic and stratigraphic age constraints for the Bolton Igneous Group bracket these backarc magmas to the 477-458 Ma interval. A tectonic model that begins with east-dipping subduction and progresses to outboard west-dipping subduction after a syncollisional polarity reversal best explains the intrusion of deformed metamorphosed metasedimentary rocks by backarc magmas.

Sedimentary record of late Paleozoic to Recent tectonism in central Asia — analysis of subsurface data from the Turan and south Kazak domains

NASA Astrophysics Data System (ADS)

Thomas, J. C.; Cobbold, P. R.; Shein, V. S.; Le Douaran, S.

1999-11-01

The Turan and south Kazak domains (TSK) are in central Asia, between the Caspian Sea and the Tien Shan. The area is covered by sediments, deposited since the Late Permian during a series of tectonic events closely related to the history of two oceanic domains, Paleotethys and Neotethys. Sedimentary basins on the TSK therefore provide constraints on the tectonic development of the southern margin of Eurasia since the Late Permian. Our study is based on structure-contour maps and isopach maps of five key stratigraphic markers, of Late Permian to Tertiary age. Isopach maps help locate major faults and delimit sedimentary basins, providing information on vertical motions and, in some instances, horizontal motions. Subsidence associated with extension appears to have dominated the TSK, from the Late Permian to the Eocene. The extension may have been of back-arc type in southern Eurasia, next to the active margin, where the Paleotethys and Neotethys successively subducted toward the north. Here, sedimentary basins are both wide and deep (up to 15 km). During the Mesozoic, two compressional events of regional significance occurred in association with accretion of continental blocks at the southern margin of Eurasia. The first one, at the end of the Triassic, led to strong selective inversion of basins over the Turan domain. The second one, during the Late Jurassic-Early Cretaceous, had weaker effects. Since the Oligocene, following collision of both India and Arabia with Eurasia, inversion has become more generalized and compressional basins have formed on the TSK. Throughout the entire history of development of the TSK, from the Late Permian to the Tertiary, structures of Paleozoic and early Mesozoic age have exerted a strong control on sedimentation and especially on the location of depocenters. The south Kazak domain has registered little subsidence, in comparison with the Turan domain, where some basins have become very deep.

Late cretaceous extensional tectonics and associated igneous activity on the northern margin of the Gulf of Mexico Basin

NASA Technical Reports Server (NTRS)

Bowen, R. L.; Sundeen, D. A.

1985-01-01

Major, dominantly compressional, orogenic episodes (Taconic, Acadian, Alleghenian) affected eastern North America during the Paleozoic. During the Mesozoic, in contrast, this same region was principally affected by epeirogenic and extensional tectonism; one episode of comparatively more intense tectonic activity involving extensive faulting, uplift, sedimentation, intrusion and effusion produced the Newark Series of eposits and fault block phenomena. This event, termed the Palisades Disturbance, took place during the Late Triassic - Earliest Jurassic. The authors document a comparable extensional tectonic-igneous event occurring during the Late Cretaceous (Early Gulfian; Cenomanian-Santonian) along the southern margin of the cratonic platform from Arkansas to Georgia.

Tectonics and hydrocarbon potential of the Barents Megatrough

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

Baturin, D.; Vinogradov, A.; Yunov, A.

1991-08-01

Interpretation of geophysical data shows that the geological structure of the Eastern Barents Shelf, named Barents Megatrough (BM), extends sublongitudinally almost from the Baltic shield to the Franz Josef Land archipelago. The earth crust within the axis part of the BM is attenuated up to 28-30 km, whereas in adjacent areas its thickness exceeds 35 km. The depression is filled with of more than 15 km of Upper Paleozoic, Mesozoic, and Cenozoic sediments overlying a folded basement of probable Caledonian age. Paleozoic sediments, with exception of the Upper Permian, are composed mainly of carbonates and evaporites. Mesozoic-Cenozoic sediments are mostlymore » terrigenous. The major force in the development of the BM was due to extensional tectonics. Three rifting phases are recognizable: Late Devonian-Early Carboniferous, Early Triassic, and Jurassic-Early Cretaceous. The principal features of the geologic structure and evolution of the BM during the late Paleozoic-Mesozoic correlate well with those of the Sverdup basin, Canadian Arctic. Significant quantity of Late Jurassic-Early Cretaceous basaltic dikes and sills were intruded within Triassic sequence during the third rifting phase. This was probably the main reason for trap disruption and hydrocarbon loss from Triassic structures. Lower Jurassic and Lower Cretaceous reservoir sandstones are most probably the main future objects for oil and gas discoveries within the BM. Upper Jurassic black shales are probably the main source rocks of the BM basin, as well as excellent structural traps for hydrocarbon fluids from the underlying sediments.« less

The pre-Mesozoic tectonic unit division of the Xing-Meng orogenic belt (XMOB)

NASA Astrophysics Data System (ADS)

Xu, Bei; Zhao, Pan

2014-05-01

According to the viewpoint that the paleo-Asian ocean closed by the end of early Paleozoic and extended during the late Paleozoic, a pre-Mesozoic tectonic unit division has been suggested. Five blocks and four sutures have been recognized in the pre-Devonia stage, the five blocks are called Erguna (EB), Xing'an (XB), Airgin Sum-Xilinhot (AXB), Songliao-Hunshandak (SHB) and Jiamusi (JB) blocks and four sutures, Xinlin-Xiguitu (XXS), Airgin Sum-Xilinhot-Heihe (AXHS), Ondor Sum-Jizhong-Yanji (OJYS) and Mudanjiang (MS) sutures. The EB contains the Precambrian base with the ages of 720-850Ma and ɛHf(T)=+2.5to +8.1. The XB is characterized by the Paleoproterozoic granitic gneiss with ɛHf(T)=-3.9 to -8.9. Several ages from 1150 to 1500 Ma bave been acquired in the AXB, proving presence of old block that links with Hutag Uul block in Mongolia to the west. The Paleoproterozoic (1.8-1.9Ga) and Neoproterozoic (750-850Ma) ages have been reported from southern and eastern parts of the SHB, respectively. As a small block in east margin of the XMOB, the JB outcrops magmatite and granitic gneiss bases with ages of 800-1000Ma. The XXS is marked by blueschists with zircon ages of 490-500Ma in Toudaoqiao village, ophiolites in Xiguitu County and granite with ages of about 500Ma along the northern segment of XXS. The AXHS is characterized by the early Paleozoic arc magmatic rocks with ages from 430Ma to 490Ma, mélange and the late Devonia molass basins, which indicates a northward subduction of the SHB beneath the AXB during the early-middle Paleozoic. The OJYS is composed of the early Paleozoic volcanic rocks, diorites and granites with ages of 425-475Ma, blueschists, ophiolitic mélange, the late Silurian flysch and Early-Middle Devonian molasses in western segment, granites (420-450Ma) in middle segment, and plagiogranites (443Ma) and the late Silurian molasses in eastern segment. This suture was caused by a southward subduction of the SHB beneath the North China block. The MS

Detrital zircon ages in Korean mid-Paleozoic meta-sandstones (Imjingang Belt and Taean Formation): Constraints on tectonic and depositional setting, source regions and possible affinity with Chinese terranes

NASA Astrophysics Data System (ADS)

Han, Seokyoung; de Jong, Koen; Yi, Keewook

2017-08-01

Sensitive High-Resolution Ion Microprobe (SHRIMP) U-Th-Pb isotopic data of detrital zircons from mature, quartz-rich meta-sandstones are used to constrain possible tectonic affinities and source regions of the rhythmically layered and graded-bedded series in the Yeoncheon Complex (Imjingang Belt) and the correlative Taean Formation. These metamorphic marine turbidite sequences presently occur along the Paleoproterozoic (1.93-1.83 Ga) Gyeonggi Massif, central Korea's main high-grade metamorphic gneiss terrane. Yet, detrital zircons yielded highly similar multimodal age spectra with peaks that do not match the age repartition in these basement rocks, as late (1.9-1.8 Ga) and earliest (∼ 2.5 Ga) Paleoproterozoic detrital modes are subordinate but, in contrast, Paleozoic (440-425 Ma) and Neoproterozoic (980-920 Ma) spikes are prominent, yet the basement essentially lacks lithologies with such ages. The youngest concordant zircon ages in each sample are: 378, 394 and 423 Ma. The maturity of the meta-sandstones and the general roundness of zircons of magmatic signature, irrespective of their age, suggest that sediments underwent considerable transport from source to sink, and possibly important weathering and recycling, which may have filtered out irradiation-weakened metamorphic zircon grains. In combination with these isotopic data, presence of a low-angle ductile fault contact between the Yeoncheon Complex and the Taean Formation and the underlying mylonitized Precambrian basement implies that they are in tectonic contact and do not have a stratigraphic relationship, as often assumed. Consequently, in all likelihood, both meta-sedimentary formations: (1) are at least of early Late Devonian age, (2) received much of their detritus from distant (reworked) Silurian-Devonian and Early Neoproterozoic magmatic sources, not present in the Gyeonggi Massif, (3) and not from Paleoproterozoic crystalline rocks of this massif, or other Korean Precambrian basement terranes, and

Paleozoic Orogens of Mexico and the Laurentia-Gondwana Connections: an Update

NASA Astrophysics Data System (ADS)

Ortega-Gutierrez, F.

2009-05-01

The present position of Mexico in North America and the fixist tectonic models that prevailed prior to the seventies of the past century, have considered the main Paleozoic tectonic systems of Mexico as natural extensions of the orogens that fringed the eastern and southern sides of the Laurentian craton. Well known examples of pre-Mesozoic orogens in Mexico are the Oaxacan, Acatlan, and Chiapas polymetamorphic terranes, which have been correlated respectively with the Grenville and Appalachian-Ouachitan orogens of eastern North America. Nonetheless, several studies conducted during the last decade in these Mexican orogenic belts, have questioned their Laurentian connections, regarding northwestern Gondwana instead as the most plausible place for their birth and further tectonic evolution. This work pretends to approach the problem by briefly integrating the massive amount of new geological information, commonly generated through powerful dating methods such as LA-ICPM-MS on detrital zircon of sedimentary and metasedimentary units in the Paleozoic crustal blocks, which are widely exposed in southern and southeastern Mexico. The Acatlan Complex bears the closest relationships to the Appalachian orogenic system because it shows thermotectonic evidence for opening and closure of the two main oceans involved in building the Appalachian mountains in eastern Laurentia, whereas two other Paleozoic terranes in NW and SE Mexico, until recently rather geologically unknown, may constitute fundamental links between the Americas for the last-stage suturing and consolidation of western Pangea. The buried basement of the Yucatan platform (400,000 squared km) on the other hand, remains as one of the most relevant problems of tectonostratigraphic correlations across the Americas, because basement clasts from the Chicxulub impact ejecta reveal absolute and Nd-model ages that suggest close Gondwanan affinities. Major changes in the comprehension of the Paleozoic orogens in Mexico

Hydrothermal zebra dolomite in the Great Basin, Nevada--attributes and relation to Paleozoic stratigraphy, tectonics, and ore deposits

USGS Publications Warehouse

Diehl, S.F.; Hofstra, A.H.; Koenig, A.E.; Emsbo, P.; Christiansen, W.; Johnson, Chad

2010-01-01

In other parts of the world, previous workers have shown that sparry dolomite in carbonate rocks may be produced by the generation and movement of hot basinal brines in response to arid paleoclimates and tectonism, and that some of these brines served as the transport medium for metals fixed in Mississippi Valley-type (MVT) and sedimentary exhalative (Sedex) deposits of Zn, Pb, Ag, Au, or barite. Numerous occurrences of hydrothermal zebra dolomite (HZD), comprised of alternating layers of dark replacement and light void-filling sparry or saddle dolomite, are present in Paleozoic platform and slope carbonate rocks on the eastern side of the Great Basin physiographic province. Locally, it is associated with mineral deposits of barite, Ag-Pb-Zn, and Au. In this paper the spatial distribution of HZD occurrences, their stratigraphic position, morphological characteristics, textures and zoning, and chemical and stable isotopic compositions were determined to improve understanding of their age, origin, and relation to dolostone, ore deposits, and the tectonic evolution of the Great Basin. In northern and central Nevada, HZD is coeval and cogenetic with Late Devonian and Early Mississippian Sedex Au, Zn, and barite deposits and may be related to Late Ordovician Sedex barite deposits. In southern Nevada and southwest California, it is cogenetic with small MVT Ag-Pb-Zn deposits in rocks as young as Early Mississippian. Over Paleozoic time, the Great Basin was at equatorial paleolatitudes with episodes of arid paleoclimates. Several occurrences of HZD are crosscut by Mesozoic or Cenozoic intrusions, and some host younger pluton-related polymetallic replacement and Carlin-type gold deposits. The distribution of HZD in space (carbonate platform, margin, and slope) and stratigraphy (Late Neoproterozoic Ediacaran-Mississippian) roughly parallels that of dolostone and both are prevalent in Devonian strata. Stratabound HZD is best developed in Ediacaran and Cambrian units, whereas

Geochemistry and geochronology of the blueschist in the Heilongjiang Complex and its implications in the late Paleozoic tectonics of eastern NE China

NASA Astrophysics Data System (ADS)

Ge, Mao-hui; Zhang, Jin-jiang; Liu, Kai; Ling, Yi-yun; Wang, Meng; Wang, Jia-min

2016-09-01

The Paleozoic to early Mesozoic tectonic framework and evolution of Northeast China, especially the Jiamusi block and its related structural belts, are highly debated. In this paper, geochemical, geochronological and isotopic analyses were carried out on the blueschist in the Heilongjiang Complex to address these issues. The Heilongjiang Complex defines the suture belt between the Jiamusi block and the Songliao block in NE China, and the blueschist is a major composition for this complex, coexisting with mafic-ultramafic rocks, greenschist, quartzite and mica schist. The blueschist has a mineral association of sodic amphibole, epidote, chlorite, phengite, albite and quartz with accessory phases of apatite, titanite, zircon and ilmenite. Together with the lithological association, the major and trace element compositions present that the protoliths of the blueschist can be divided into the alkaline and tholeiitic basalts and have OIB affinities, formed in an ocean island setting, indicated by the (La/Yb) N values of 3.57 - 11.54, and the (La/Sm) N values of 0.69 - 3.64. The high and positive εNd (t) values of + 3.7 to + 9.0, and relative enrichment in Nb (vs. Th) and Ta (vs. U) show that both the alkaline and tholeiitic basalts may be derived from the asthenospheric mantle with insignificant crustal contamination. Magmatic zircons from the blueschist in Yilan area yield a 206Pb/238U age of 281 ± 3 Ma, interpreted as its protolithic age. The youngest ages of 200 Ma of the detrital zircons in the associated mica schist from Mudanjiang area place constraints on the timing of metamorphism for the blueschist. These indicate that a big ocean existed between the Jiamusi and Songliao blocks at least since the early Permian, and the blueschist formed since the late Triassic to late Jurassic by the subduction of this ocean. Such an ocean during the Permian - Jurassic is difficult to be interpreted by the tectonic evolution of the Paleo-Asian Ocean.

An Intracratonic Record of North American Tectonics

NASA Astrophysics Data System (ADS)

Lovell, Thomas Rudolph

Investigating how continents change throughout geologic time provides insight into the underlying plate tectonic process that shapes our world. Researchers aiming to understand plate tectonics typically investigate records exposed at plate margins, as these areas contain direct structural and stratigraphic information relating to tectonic plate interaction. However, these margins are also susceptible to destruction, as orogenic processes tend to punctuate records of plate tectonics. In contrast, intracratonic basins are long-lived depressions located inside cratons, shielded from the destructive forces associated with the plate tectonic process. The ability of cratonic basins to preserve sedimentological records for extended periods of geologic time makes them candidates for recording long term changes in continents driven by tectonics and eustacy. This research utilizes an intracratonic basin to better understand how the North American continent has changed throughout Phanerozoic time. This research resolves geochronologic, thermochronologic, and sedimentologic changes throughout Phanerozoic time (>500 Ma) within the intracratonic Illinois Basin detrital record. Core and outcrop sampling provide the bulk of material upon which detrital zircon geochronologic, detrital apatite thermochronologic, and thin section petrographic analyses were performed. Geochronologic evidence presented in Chapters 2 and 3 reveal the Precambrian - Cretaceous strata of the intracratonic Illinois Basin yield three detrital zircon U-Pb age assemblages. Lower Paleozoic strata yield ages corresponding to predominantly cratonic sources (Archean - Mesoproterozoic). In contrast, Middle - Upper Paleozoic strata have a dominant Appalachian orogen (Neoproterozoic - Paleozoic) signal. Cretaceous strata yield similar ages to underlying Upper Paleozoic strata. We conclude that changes in the provenance of Illinois Basin strata result from eustatic events and tectonic forcings. This evidence

The evolution of Phanerozoic seawater - Isotope paleothermometry finds consensus on Early Paleozoic warmth and constant seawater δ18O

NASA Astrophysics Data System (ADS)

Grossman, E. L.; Henkes, G. A.; Passey, B. H.; Shenton, B.; Yancey, T. E.; Perez-Huerta, A.

2015-12-01

Evolution of metazoan life is closely linked to the Phanerozoic evolution of ocean temperatures and chemistry. Oxygen isotopic evidence for early Phanerozoic paleotemperatures has been equivocal, with decreasing δ18O values with age being interpreted as warmer early oceans, decreasing seawater δ18O with age, or increasing diagenetic alteration in older samples. Here we compare an updated compilation of oxygen isotope data for carbonate and phosphate fossils and microfossils (Grossman, 2012, Geol. Time Scale, Elsevier, 195-220) with a compilation of new and existing clumped isotope data. Importantly, these data are curated based on sample preservation with special consideration given to screening techniques, and tectonic and burial history. Burial history is critical in the preservation of carbonate clumped isotope temperatures in particular, which can undergo reordering in the solid state. We use a model derived for reordering kinetics (Henkes et al., 2014, Geochim. Cosmochim. Acta 139:362-382) to screen clumped isotope data for the effects of solid-state burial alteration. With minor but significant exceptions (Late Cretaceous, Early Triassic), average δ18O values (4 m.y. window, 2 m.y. steps) for post-Devonian brachiopods, belemnites, and foraminifera, representing tropical-subtropical surface ocean conditions, yield average isotopic temperatures below 30°C (assuming a seawater δ18O value [ -1‰ VSMOW] of an "ice-free" world). In contrast, Ordovician to Devonian data show sustained temperatures of 35-40°C. Likewise, isotopic paleotemperatures from conodont apatite, known to be resistant to isotopic exchange, follow the same pattern. Clumped isotope data derived from Paleozoic brachiopod shells that experienced minimal burial (< 100 °C) and <1% reordering according to the taxon-specific clumped isotope reordering model yield typical temperatures of 25-30°C for the Carboniferous, and 35-40°C for the Ordovician-Silurian. Inserting clumped temperatures and

Late paleozoic base and precious metal deposits, East Tianshan, Xinjiang, China: Characteristics and geodynamic setting

USGS Publications Warehouse

Mao, J.; Goldfarb, R.J.; Wang, Y.; Hart, C.J.; Wang, Z.; Yang, J.

2005-01-01

The East Tianshan is a remote Gobi area located in eastern Xinjiang, northwestern China. In the past several years, a number of gold, porphyry copper, and Fe(-Cu) and Cu-Ag-Pb-Zn skarn deposits have been discovered there and are attracting exploration interest. The East Tianshan is located between the Junggar block to the north and early Paleozoic terranes of the Middle Tianshan to the south. It is part of a Hercynian orogen with three distinct E-W-trending tectonic belts: the Devonian-Early Carboniferous Tousuquan-Dananhu island arc on the north and the Carboniferous Aqishan - Yamansu rift basin to the south, which are separated by rocks of the Kanggurtag shear zone. The porphyry deposits, dated at 322 Ma, are related to the late evolutionary stages of a subduction-related oceanic or continental margin arc. In contrast, the skarn, gold, and magmatic Ni-Cu deposits are associated with post-collisional tectonics at ca. 290-270 Ma. These Late Carboniferous - Early Permian deposits are associated with large-scale emplacement and eruption of magmas possibly caused by lithosphere delamination and rifting within the East Tianshan.

Precambrian Continent Arctida: A New Kinematic Reconstruction of Late Precambrian - Early Paleozoic Arctida U Europe (baltia) Collision

NASA Astrophysics Data System (ADS)

Borisova, T. P.; Guertseva, M. V.; Egorov, A. Ju.; Kononov, M. V.; Kouznetsov, N. B.

In according to L.P.Zonenshain and L.M.Natapov (1988, 1990), different size conti- nental blocks locating at the margins and inside of present-day Arctic ocean composed the hypothetical early Paleozoic paleocontinent Arctida. The blocks are Kara block (north part of Taymir peninsula, Severnaja Zemlja archipelago and Franz Joseph Land archipelago), north part of Alaska (northward Bruks ridge), Chukchi block, Novosi- birsky block (Novosibirskiye islands together their shelves), several fragments north- ward to the Innuitian orogen (north parts of Peary Land and Ellesmere Island), and Lomonosov ridgeSs block. In the previous kinematic reconstruction it was believed that Arctida as a whole collided with north flanks of Laurentia (Innuitian margin) and Europe (Baltia, Barentsia margin) in middle Paleozoic time. Later, the Arctida (been a fragment of supercontinent Pangea) was fragmented due to a spreading in the Arctic ocean and north part of Atlantic ocean in late Mesozoic and Cenozoic times. Then ArctidaSs fragments were accreted to the Eurasia and North America conti- nents. During the last decade "AEROGEOLOGIA" company has been gathered new data (geologic, stratigraphical, paleomagnetic, and others) of Russian Arctic sector and Svalbard. The data were summarized into "Paleogeographical Atlas for the Rus- sian Arctic sector and Svalbard from Vendian to Jurassic times" (see Abstact SE1.04, ID-NR: EGS02-A-02453). An analyzing of the maps for Vend and Cambrian times allows us to reconsider a few stages of kinematic scenario of late Precambrian - early Paleozoic Arctida U Europe collision. 1) Old interpretation: Arctida was considered as an isolated paleocontinent during early Paleozoic time. New interpretation: during the early Paleozoic Arctida together Europe (Baltia) were assembled into a paleo- continent named us Arcteurope. This conclusion is based on excellent coincidence of Paleozoic paleomagnetic poles of the Kara block (which is a part of Arctida) and Europe

Late Paleozoic orogeny in Alaska's Farewell terrane

USGS Publications Warehouse

Bradley, D.C.; Dumoulin, Julie A.; Layer, P.; Sunderlin, D.; Roeske, S.; McClelland, B.; Harris, A.G.; Abbott, G.; Bundtzen, T.; Kusky, T.

2003-01-01

Evidence is presented for a previously unrecognized late Paleozoic orogeny in two parts of Alaska's Farewell terrane, an event that has not entered into published scenarios for the assembly of Alaska. The Farewell terrane was long regarded as a piece of the early Paleozoic passive margin of western Canada, but is now thought, instead, to have lain between the Siberian and Laurentian (North American) cratons during the early Paleozoic. Evidence for a late Paleozoic orogeny comes from two belts located 100-200 km apart. In the northern belt, metamorphic rocks dated at 284-285 Ma (three 40Ar/39Ar white-mica plateau ages) provide the main evidence for orogeny. The metamorphic rocks are interpreted as part of the hinterland of a late Paleozoic mountain belt, which we name the Browns Fork orogen. In the southern belt, thick accumulations of Pennsylvanian-Permian conglomerate and sandstone provide the main evidence for orogeny. These strata are interpreted as the eroded and deformed remnants of a late Paleozoic foreland basin, which we name the Dall Basin. We suggest that the Browns Fork orogen and Dall Basin comprise a matched pair formed during collision between the Farewell terrane and rocks to the west. The colliding object is largely buried beneath Late Cretaceous flysch to the west of the Farewell terrane, but may have included parts of the so-called Innoko terrane. The late Paleozoic convergent plate boundary represented by the Browns Fork orogen likely connected with other zones of plate convergence now located in Russia, elsewhere in Alaska, and in western Canada. Published by Elsevier B.V.

Evidence for a Battle Mountain-Eureka crustal fault zone, north-central Nevada, and its relation to Neoproterozoic-Early Paleozoic continental breakup

USGS Publications Warehouse

Grauch, V.J.S.; Rodriguez, B.D.; Bankey, V.; Wooden, J.L.

2003-01-01

Combined evidence from gravity, radiogenic isotope, and magnetotelluric (MT) data indicates a crustal fault zone that coincides with the northwest-trending Battle Mountain-Eureka (BME) mineral trend in north-central Nevada, USA. The BME crustal fault zone likely originated during Neoproterozoic-Early Paleozoic rifting of the continent and had a large influence on subsequent tectonic events, such as emplacement of allochthons and episodic deformation, magmatism, and mineralization throughout the Phanerozoic. MT models show the fault zone is about 10 km wide, 130-km long, and extends from 1 to 5 km below the surface to deep crustal levels. Isotope data and gravity models imply the fault zone separates crust of fundamentally different character. Geophysical evidence for such a long-lived structure, likely inherited from continental breakup, defies conventional wisdom that structures this old have been destroyed by Cenozoic extensional processes. Moreover, the coincidence with the alignment of mineral deposits supports the assertion by many economic geologists that these alignments are indicators of buried regional structures.

Late Paleozoic paleolatitude and paleogeography of the Midland basin, Texas

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

Walker, D.A.; Golonka, J.; Reid, A.M.

1992-04-01

During the Late Pennsylvanian through Early Permian, the Midland basin was located in the low latitudes. In the Desmoinesian (Strawn), the basin was astride the equator; during the Missourian (Canyon), the center of the basin had migrated northward so it was located at 1-2N latitude. In the Virgilian (Cisco), the basin center was located around 2-4N latitude, and by the Wolfcampian, it was positioned at around 4-6N latitude. From the Desmoinesian (312 Ma) through the Missourian (306 Ma), the relative motion of the basin was 63NE. Later during the Virgilian (298 Ma) to Wolfcampian (280 Ma), the direction of motionmore » was 24NE. This change in motion reflects a major tectonic event, occurring between the Missourian and Virgilian, that greatly modifed the movement of the Laurentian (North American) plate. At that time, Laurentia had collided with Gondwana and become part of the supercontinent Pangea. Throughout the late Paleozoic, Laurentia was rotated so the Midland basin was oriented 43{degree} northeast from its current setting. Late Paleozoic paleogeography and paleolatitude controlled the direction of prevailing winds and ocean currents, thereby influencing the distribution of carbonate facies in the Midland basin. Present prevailing winds and ocean currents have been shown to have a major impact on modern carbonate sedimentation and facies distribution in Belize, the Bahamas and Turks, and Caicos. A clearer understanding of how late Paleozoic latitude and geography affected sedimentation helps explain and predict the distribution of carbonates throughout the Midland basin.« less

Tectonics of the North American Cordillera near the Fortieth Parallel

USGS Publications Warehouse

King, P.B.

1978-01-01

The North American Cordillera near the Fortieth Parallel consists of the following tectonic units: 1. (A) To the east is a reactivated cratonic area, in the Southern Rocky Mountains and Colorado Plateau, in which the supracrustal rocks (Cambrian to Cretaceous) were broadly deformed during the late Cretaceous-Paleocene Laramide orogeny, and the Precambrian basement was raised in folds of wide amplitude. 2. (B) West of it is a miogeosynclinal belt, in the eastern Great Basin, in which a thick sequence of Paleozoic carbonates and related deposits was thrust eastward along low-angle faults during the middle to late Cretaceous Sevier orogeny. The miogeosyncline is the downwarped western margin of the original North American continent, and its rocks accumulated on Precambrian basement. 3. (C) Beyond is a eugeosynclinal belt, in the western Great Basin, in which Paleozoic graywackes, cherts, and volcanics were thrust easteastward along low-angle faults during several Paleozoic orogenies - the mid-Paleozoic Antler orogeny which produced the Roberts thrust on the east, and the end-Paleozoic Sonoma orogeny which produced the Golconda thrust farther west. The Paleozoic eugeosynclinal rocks accumulated on oceanic basement. They are overlapped from the west by Triassic and Jurassic shelf deposits, which pass westward into eugeosynclinal deposits. 4. (D) A volcanic island-arc belt existed on the sites of the Sierra Nevada in Paleozoic and early Mesozoic time, which produced thick bodies of sediments and volcanics. During the mid-Mesozoic Nevadan orogeny these were steeply deformed and thrust westward over subduction zones, and were intruded by granitic rocks that rose from the upper mantle to form great batholiths. 5. (E) West of the Sierra Nevada, in the Great Valley, is a great sedimentary embankment of later Mesozoic flysch or turbidite, largely younger than the supracrustal rocks of the Sierra Nevada and the Nevadan orogeny. It was formed of the erosional products of the

Paleomagnetism and tectonics of the Southern Tarim Basin, northwestern China

NASA Astrophysics Data System (ADS)

Gilder, Stuart; Zhao, Xixi; Coe, Robert; Meng, Zifang; Courtillot, Vincent; Besse, Jean

1996-10-01

We report Late Carboniferous, Permian, and early Tertiary paleomagnetic data from the southern Tarim basin. Prefolding magnetizations were isolated in each case. The Late Carboniferous-Permian and early Tertiary poles lie at 64.6°N, 166.5°E, A95 = 6.3° and 58.1°N, 202.0°E, A95 = 12.7°, respectively. The Late Jurassic to early Tertiary (J3-E1) paleolatitudes of Tarim and several basins throughout central Asia are similar, yet significantly (10° to 20°) shallower than those predicted by the Eurasian apparent polar wander path. Resolving this discrepancy remains a major problem in Asian paleomagnetism. Discordance of the late Paleozoic poles from Tarim and Siberia suggest that Tarim has rotated about 30° counterclockwise with respect to Siberia since the Permian. Where paleomagnetic samples of both Late Carboniferous to Early Triassic (C3-T1) and J3-E1 ages were collected from the same area of Tarim, a great circle passes through the means of the poles and the sampling locality. This suggests that (1) only a difference in inclination (and not declination) distinguishes the two data sets, and (2) vertical axis block rotations of the C3-E1 strata occurred after E1. Although based on data of lesser quality, the mean Early to Middle Jurassic (J1-2) pole from Tarim differs significantly from the Eurasian reference pole, requiring radical tectonic solutions to resolve them. The Tarim J1-2 pole is indistinguishable from both the mean J3-E1 and C3-T1 poles. The similarity of all the poles and the analogous tectonic setting of present-day central Asia to that of the late Paleozoic in eastern North America raises the question whether all the data from Tarim are overprinted.

Early Paleozoic paleogeography of the northern Gondwana margin: new evidence for Ordovician-Silurian glaciation

NASA Astrophysics Data System (ADS)

Semtner, A.-K.; Klitzsch, E.

1994-12-01

During the Early Paleozoic, transgressions and the distribution of sedimentary facies on the northern Gondwana margin were controlled by a regional NNW-SSE to almost north-south striking structural relief. In Early Silurian times, a eustatic highstand enabled the sea to reach its maximum southward extent. The counterclockwise rotation of Gondwana during the Cambrian and Early Ordovician caused the northern Gondwana margin to shift from intertropical to southern polar latitudes in Ordovician times. Glacial and periglacial deposits are reported from many localities in Morocco, Algeria, Niger, Libya, Chad, Sudan, Jordan and Saudi Arabia. The Late Ordovician glaciation phase was followed by a period of a major glacioeustatic sea-level rise in the Early Silurian due to the retreat of the ice-cap. As a consequence of the decreasing water circulation in the basin centers (Central Arabia, Murzuk- and Ghadames basins), highly bituminous euxinic shales were deposited. These shales are considered to be the main source rock of Paleozoic oil and gas deposits in parts of Saudi Arabia, Libya and Algeria. The following regression in the southern parts of the Early Silurian sea was probably caused by a second glacial advance, which was mainly restricted to areas in Chad, Sudan and Niger. Evidence for glacial activity and fluvioglacial sedimentation is available from rocks overlying the basal Silurian shale in north-east Chad and north-west Sudan. The Early Silurian ice advance is considered to be responsible for the termination of euxinic shale deposition in the basin centers.

Devonian paleomagnetism of the North Tien Shan: Implications for the middle-Late Paleozoic paleogeography of Eurasia

NASA Astrophysics Data System (ADS)

Levashova, Natalia M.; Mikolaichuk, Alexander V.; McCausland, Philip J. A.; Bazhenov, Mikhail L.; Van der Voo, Rob

2007-05-01

The Ural-Mongol belt (UMB), between Siberia, Baltica and Tarim, is widely recognized as the locus of Asia's main growth during the Paleozoic, but its evolution remains highly controversial, as illustrated by the disparate paleogeographic models published in the last decade. One of the largest tectonic units of the UMB is the Kokchetav-North Tien Shan Domain (KNTD) that stretches from Tarim in the south nearly to the West Siberian Basin. The KNTD comprises several Precambrian microcontinents and numerous remnants of Early Paleozoic island arcs, marginal basins and accretionary complexes. In Late Ordovician time, all these structures had amalgamated into a single contiguous domain. Its paleogeographic position is of crucial importance for elucidating the Paleozoic evolution of the UMB in general and of the Urals in particular. The Aral Formation, located in Kyrgyzstan in the southern part of the KNTD, consists of a thick Upper Devonian (Frasnian) basalt-andesite sequence. Paleomagnetic data show a dual-polarity characteristic component (Dec/Inc = 286° / + 56°, α95 = 9°, k = 21, N = 15 sites). The primary origin of this magnetization is confirmed by a positive test on intraformational conglomerates. We combine this result with other Paleozoic data from the KNTD and show its latitudinal motion from the Late Ordovician to the end of the Paleozoic. The observed paleolatitudes are found to agree well with the values extrapolated from Baltica to a common reference point (42.5°N, 73°E) in our sampling area for the entire interval; hence coherent motion of the KNTD and Baltica is strongly indicated for most of the Paleozoic. This finding contradicts most published models of the UMB evolution, where the KNTD is separated from Baltica by a rather wide Ural Ocean containing one or more major plate boundaries. An exception is the model of Şengör and Natal'in [A.M.C. Şengör, B.A. Natal'in, Paleotectonics of Asia: fragments of a synthesis, in: A. Yin and M. Harrison (eds

Structural features of northern Tarim basin: Implications for regional tectonics and petroleum traps

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

Dong Jia; Juafu Lu; Dongsheng Cai

1998-01-01

The rhombus-shaped Tarim basin in northwestern China is controlled mainly by two left-lateral strike-slip systems: the northeast-trending Altun fault zone along its southeastern side and the northeast-trending Aheqi fault zone along its northwestern side. In this paper, we discuss the northern Tarim basin`s structural features, which include three main tectonic units: the Kalpin uplift, the Kuqa depression, and the North Tarim uplift along the northern margin of the Tarim basin. Structural mapping in the Kalpin uplift shows that a series of imbricated thrust sheets have been overprinted by strike-slip faulting. The amount of strike-slip displacement is estimated to be 148more » km by restoration of strike-slip structures in the uplift. The Kuqa depression is a Mesozoic-Cenozoic foredeep depression with well-developed flat-ramp structures and fault-related folds. The Baicheng basin, a Quaternary pull-apart basin, developed at the center of the Kuqa depression. Subsurface structures in the North Tarim uplift can be divided into the Mesozoic-Cenozoic and the Paleozoic lithotectonic sequences in seismic profiles. The Paleozoic litho-tectonic sequence exhibits the interference of earlier left-lateral and later right-lateral strike-slip structures. Many normal faults in the Mesozoic-Cenozoic litho-tectonic sequence form the negative flower structures in the North Tarim uplift; these structures commonly directly overlie the positive flower structures in the Paleozoic litho-tectonic sequence. The interference regions of the northwest-trending and northeast-trending folds in the Paleozoic tectonic sequence have been identified to have the best trap structures. Our structural analysis indicates that the Tarim basin is a transpressional foreland basin rejuvenated during the Cenozoic.« less

Hot-field tectonics

NASA Astrophysics Data System (ADS)

Zonenshain, L. P.; Kuzmin, M. I.; Bocharova, N. Yu.

1991-12-01

Intraplate, hot spot related volcanic occurrences do not have a random distribution on the Earth's surface. They are concentrated in two large regions (up to 10,000 km in diameter), the Pacific and the African, and two smaller areas (2000-3000 km in diameter), the Central Asian and the Tasmanian. These regions are considered as manifestations of hot fields in the mantle, whereas the regions lying in between are expressions of cold fields in the mantle. Large-scale anomalies coincide with the hot fields: topographic swells, geoid highs, uplifts of the "asthenospheric table", inferred heated regions in the lowermost mantle according to seismic tomographic images, geochemical anomalies showing the origin of volcanics from undepleted mantle sources. Hot fields are relatively stable features, having remained in the same position on the Earth's surface during the last 120 Ma, although they have other configurations and other positions in the Late Paleozoic and Early Mesozoic. Available data show that two main hot fields (Pacific and African) are possibly moving one with respect to the other, converging along the Eastern Pacific subduction system and diverging along that of the Western Pacific. If so, well-known differences between these subduction systems can also be connected with related displacement of the hot fields. Hot fields are assumed to correspond to upwelling branches of mantle and rather deep mantle convection, and cold fields to downwelling branches. Thus, hot fields can be regarded as expressions of deeper tectonics, comparative to the plate tectonics, which is operating in the upper layers of the Earth. We call it hot-field tectonics. Plate tectonics is responsible for the opening and closure of oceans and for the formation of orogenic belts, whereas hot-field tectonics accounts for a larger cyclicity of the Earth's evolution and for amalgamation and break up of Pangea-type supercontinents. Hot-field tectonics seems to be the only process to have existed

Relations between extensional tectonics and magmatism within the Southern Oklahoma aulacogen

NASA Technical Reports Server (NTRS)

Mcconnell, D. A.; Gilbert, M. C.

1985-01-01

Variations in the geometry, distribution and thickness of Cambrian igneous and sedimentary units within southwest Oklahoma are related to a late Proterozoic - early Paleozoic rifting event which formed the Southern Oklahoma aulacogen. These rock units are exposed in the Wichita Mountains, southwest Olkahoma, located on the northern margin of a Proterozoic basin, identified in the subsurface by COCORP reflection data. Overprinting of the Cambrian extensional event by Pennyslvanian tectonism obsured the influence of pre-existing basement structures and contrasting basement lithologies upon the initial development of the aulacogen.

A comparative study of diversification events: the early Paleozoic versus the Mesozoic

NASA Technical Reports Server (NTRS)

Erwin, D. H.; Valentine, J. W.; Sepkoski, J. J. Jr; Sepkoski JJ, J. r. (Principal Investigator)

1987-01-01

We compare two major long-term diversifications of marine animal families that began during periods of low diversity but produced strikingly different numbers of phyla, classes, and orders. The first is the early-Paleozoic diversification (late Vendian-Ordovician; 182 MY duration) and the other the Mesozoic phase of the post-Paleozoic diversification (183 MY duration). The earlier diversification was associated with a great burst of morphological invention producing many phyla, classes, and orders and displaying high per taxon rates of family origination. The later diversification lacked novel morphologies recognized as phyla and classes, produced fewer orders, and displayed lower per taxon rates of family appearances. The chief difference between the diversifications appears to be that the earlier one proceeded from relatively narrow portions of adaptive space, whereas the latter proceeded from species widely scattered among adaptive zones and representing a variety of body plans. This difference is believed to explain the major differences in the products of these great radiations. Our data support those models that hold that evolutionary opportunity is a major factor in the outcome of evolutionary processes.

Neoproterozoic-Early Paleozoic Peri-Pacific Accretionary Evolution of the Mongolian Collage System: Insights From Geochemical and U-Pb Zircon Data From the Ordovician Sedimentary Wedge in the Mongolian Altai

NASA Astrophysics Data System (ADS)

Jiang, Y. D.; Schulmann, K.; Kröner, A.; Sun, M.; Lexa, O.; Janoušek, V.; Buriánek, D.; Yuan, C.; Hanžl, P.

2017-11-01

Neoproterozoic to early Paleozoic accretionary processes of the Central Asian Orogenic Belt have been evaluated so far mainly using the geology of ophiolites and/or magmatic arcs. Thus, the knowledge of the nature and evolution of associated sedimentary prisms remains fragmentary. We carried out an integrated geological, geochemical, and zircon U-Pb geochronological study on a giant Ordovician metasedimentary succession of the Mongolian Altai Mountains. This succession is characterized by dominant terrigenous components mixed with volcanogenic material. It is chemically immature, compositionally analogous to graywacke, and marked by significant input of felsic to intermediate arc components, pointing to an active continental margin depositional setting. Detrital zircon U-Pb ages suggest a source dominated by products of early Paleozoic magmatism prevailing during the Cambrian-Ordovician and culminating at circa 500 Ma. We propose that the Ordovician succession forms an "Altai sedimentary wedge," the evolution of which can be linked to the geodynamics of the margins of the Mongolian Precambrian Zavhan-Baydrag blocks. This involved subduction reversal from southward subduction of a passive continental margin (Early Cambrian) to the development of the "Ikh-Mongol Magmatic Arc System" and the giant Altai sedimentary wedge above a north dipping subduction zone (Late Cambrian-Ordovician). Such a dynamic process resembles the tectonic evolution of the peri-Pacific accretionary Terra Australis Orogen. A new model reconciling the Baikalian metamorphic belt along the southern Siberian Craton with peri-Pacific Altai accretionary systems fringing the Mongolian microcontinents is proposed to explain the Cambro-Ordovician geodynamic evolution of the Mongolian collage system.

Eclogite-facies metamorphism in impure marble from north Qaidam orogenic belt: Geodynamic implications for early Paleozoic continental-arc collision

NASA Astrophysics Data System (ADS)

Chen, Xin; Xu, Rongke; Schertl, Hans-Peter; Zheng, Youye

2018-06-01

In the North Qaidam ultrahigh-pressure (UHP) metamorphic belt, impure marble and interbedded eclogite represent a particular sedimentary provenance and tectonic setting, which have important implications for a controversial problem - the dynamic evolution of early Paleozoic subduction-collision complexes. In this contribution, detailed field work, mineral chemistry, and whole-rock geochemistry are presented for impure marble to provide the first direct evidence for the recycling of carbonate sediments under ultrahigh-pressures during subduction and collision in the Yuka terrane, in the North Qaidam UHP metamorphic belt. According to conventional geothermobarometry, pre-peak subduction to 0.8-1.3 GPa/485-569 °C was followed by peak UHP metamorphism at 2.5-3.3 GPa/567-754 °C and cooling to amphibolite facies conditions at 0.6-0.7 GPa/571-589 °C. U-Pb dating of zircons from impure marble reveals a large group with ages ranging from 441 to 458 Ma (peak at 450 Ma), a smaller group ranging from 770 to 1000 Ma (peak at 780 Ma), and minor >1.8 Ga zircon aged ca. 430 Ma UHP metamorphism. The youngest detrital zircons suggest a maximum depositional age of ca. 442 Ma and a burial rate of ca. 1.0-1.1 cm/yr when combined with P-T conditions and UHP metamorphic age. The REE and trace element patterns of impure marble with positive Sr and U anomalies, negative high field strength elements (Nb, Ta, Zr, Hf, and Ti), and Ce anomalies imply that the marble had a marine limestone precursor. Impure marble intercalated with micaschist and eclogite was similar to limestone and siltstone protoliths deposited in continental fore-arc or arc setting with basic volcanic activity. Therefore, the Yuka terrane most likely evolved in a continental island arc setting during the Paleozoic. These data suggest that metasediments were derived from a mixture of Proterozoic continental crust and juvenile early Paleozoic oceanic and/or island arc crust. In addition, their protoliths were likely

Geochemistry of Early Paleozoic boninites from the Central Qilian block, Northwest China: Constraints on petrogenesis and back-arc basin development

NASA Astrophysics Data System (ADS)

Gao, Zhong; Zhang, Hong-Fei; Yang, He; Luo, Bi-Ji; Guo, Liang; Xu, Wang-Chun; Pan, Fa-Bin

2018-06-01

Early Paleozoic boninites occur in the Central Qilian orogenic belt, Northwest China. Their petrogenesis provides insights into lithosphere process and tectonic evolution of the Qilian block. In this paper, we carry out a study of geochronological, geochemical and Sr-Nd isotopic compositions for the Early Paleozoic boninites in the Lajishan area of the Central Qilian block. The Lajishan boninites (∼483 Ma) have high Al2O3/TiO2 (36.7-64.7) and CaO/TiO2 (31.1-49.6) ratios, and high MgO (7.86-10.47 wt%), Cr (439-599 ppm) and Ni (104-130 ppm) contents, indicating that the boninites result from a refractory mantle source. They are depleted in high field-strength elements (HFSE) and enriched in large ion lithophile elements (LILE), coupled with slightly high initial 87Sr/86Sr values of 0.7059-0.7074 and low εNd(t) values of -1.05 to +2.66, indicating that the mantle source was metasomatized by subducted slab-derived components. We found that an assemblage of low-Ca group and high-Ca group boninites occurred in the Lajishan belt. The high-Ca group boninites were derived from relatively fertile mantle with slightly higher melting degree, whereas the low-Ca group boninites were generated by partial melting of more refractory mantle wedge peridotites with slightly lower melting degree. The assemblage of low-Ca group and high-Ca group boninites reveals that the low-Ca group boninites were generated by the further melting of the more refractory mantle source after the segregation of the high-Ca group boninitic magmas in response to the back-arc basin opening. In the light of reported boninites worldwide, a diagram of Zr/Y vs. CaO/Al2O3 is used to identify boninites in fore-arc and back-arc regions. We suggest that the Lajishan boninites represent the products of back-arc basin development in response to the northward subduction of the Qaidam-West Qinling ocean slab.

Paleozoic and mesozoic evolution of East-Central California

USGS Publications Warehouse

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

1997-01-01

East-central California, which encompasses an area located on the westernmost part of sialic North America, contains a well-preserved record of Paleozoic and Mesozoic tectonic events that reflect the evolving nature of the Cordilleran plate margin to the west. After the plate margin was formed by continental rifting in the Neoproterozoic, sediments comprising the Cordilleran miogeocline began to accumulate on the subsiding passive margin. In east-central California, sedimentation did not keep pace with subsidence, resulting in backstepping of a series of successive carbonate platforms throughout the early and middle Paleozoic. This phase of miogeoclinal development was brought to a close by the Late Devonian-Early Mississippian Antler orogeny, during the final phase of which oceanic rocks were emplaced onto the continental margin. Subsequent Late Mississippian-Pennsylvanian faulting and apparent reorientation of the carbonate platform margin are interpreted to have been associated with truncation of the continental plate on a sinistral transform fault zone. In the Early Permian, contractional deformation in east-central California led to the development of a narrow, uplifted thrust belt flanked by marine basins in which thick sequences of deep-water strata accumulated. A second episode of contractional deformation in late Early Permian to earliest Triassic time widened and further uplifted the thrust belt and produced the recently identified Inyo Crest thrust, which here is correlated with the regionally significant Last Chance thrust. In the Late Permian, about the time of the second contractional episode, extensional faulting created shallow sedimentary basins in the southern Inyo Mountains. In the El Paso Mountains to the south, deformation and plutonism record the onset of subduction and arc magmatism in late Early Permian to earliest Triassic time along this part of the margin. Tectonism had ceased in most of east-central California by middle to late Early

The Brahmaputra tale of tectonics and erosion: Early Miocene river capture in the Eastern Himalaya

NASA Astrophysics Data System (ADS)

Bracciali, Laura; Najman, Yani; Parrish, Randall R.; Akhter, Syed H.; Millar, Ian

2015-04-01

The Himalayan orogen provides a type example on which a number of models of the causes and consequences of crustal deformation are based and it has been suggested that it is the site of a variety of feedbacks between tectonics and erosion. Within the broader orogen, fluvial drainages partly reflect surface uplift, different climatic zones and a response to crustal deformation. In the eastern Himalaya, the unusual drainage configuration of the Yarlung Tsangpo-Brahmaputra River has been interpreted either as antecedent drainage distorted by the India-Asia collision (and as such applied as a passive strain marker of lateral extrusion), latest Neogene tectonically-induced river capture, or glacial damming-induced river diversion events. Here we apply a multi-technique approach to the Neogene paleo-Brahmaputra deposits of the Surma Basin (Bengal Basin, Bangladesh) to test the long-debated occurrence and timing of river capture of the Yarlung Tsangpo by the Brahmaputra River. We provide U-Pb detrital zircon and rutile, isotopic (Sr-Nd and Hf) and petrographic evidence consistent with river capture of the Yarlung Tsangpo by the Brahmaputra River in the Early Miocene. We document influx of Cretaceous-Paleogene zircons in Early Miocene sediments of the paleo-Brahmaputra River that we interpret as first influx of material from the Asian plate (Transhimalayan arc) indicative of Yarlung Tsangpo contribution. Prior to capture, the predominantly Precambrian-Paleozoic zircons indicate that only the Indian plate was drained. Contemporaneous with Transhimalayan influx reflecting the river capture, we record arrival of detrital material affected by Cenozoic metamorphism, as indicated by rutiles and zircons with Cenozoic U-Pb ages and an increase in metamorphic grade of detritus as recorded by petrography. We interpret this as due to a progressively increasing contribution from the erosion of the metamorphosed core of the orogen. Whole rock Sr-Nd isotopic data from the same samples

Parallel Extension Tectonics (PET): Early Cretaceous tectonic extension of the Eastern Eurasian continent

NASA Astrophysics Data System (ADS)

Liu, Junlai; Ji, Mo; Ni, Jinlong; Guan, Huimei; Shen, Liang

2017-04-01

The present study reports progress of our recent studies on the extensional structures in eastern North China craton and contiguous areas. We focus on characterizing and timing the formation/exhumation of the extensional structures, the Liaonan metamorphic core complex (mcc) and the Dayingzi basin from the Liaodong peninsula, the Queshan mcc, the Wulian mcc and the Zhucheng basin from the Jiaodong peninsula, and the Dashan magmatic dome within the Sulu orogenic belt. Magmatic rocks (either volcanic or plutonic) are ubiquitous in association with the tectonic extension (both syn- and post-kinematic). Evidence for crustal-mantle magma mixing are popular in many syn-kinematic intrusions. Geochemical analysis reveals that basaltic, andesitic to rhyolitic magmas were generated during the tectonic extension. Sr-Nd isotopes of the syn-kinematic magmatic rocks suggest that they were dominantly originated from ancient or juvenile crust partly with mantle signatures. Post-kinematic mafic intrusions with ages from ca. 121 Ma to Cenozoic, however, are of characteristic oceanic island basalts (OIB)-like trace element distribution patterns and relatively depleted radiogenic Sr-Nd isotope compositions. Integrated studies on the extensional structures, geochemical signatures of syn-kinematic magmatic rocks (mostly of granitic) and the tectono-magmatic relationships suggest that extension of the crust and the mantle lithosphere triggered the magmatisms from both the crust and the mantle. The Early Cretaceous tectono-magmatic evolution of the eastern Eurasian continent is governed by the PET in which the tectonic processes is subdivided into two stages, i.e. an early stage of tectonic extension, and a late stage of collapse of the extended lithosphere and transformation of lithospheric mantle. During the early stage, tectonic extension of the lithosphere led to detachment faulting in both the crust and mantle, resulted in the loss of some of the subcontinental roots, gave rise to

Mantle contribution and tectonic transition in the Aqishan-Yamansu Belt, Eastern Tianshan, NW China: Insights from geochronology and geochemistry of Early Carboniferous to Early Permian felsic intrusions

NASA Astrophysics Data System (ADS)

Du, Long; Long, Xiaoping; Yuan, Chao; Zhang, Yunying; Huang, Zongying; Wang, Xinyu; Yang, Yueheng

2018-04-01

Late Paleozoic is a key period for the accretion and collision of the southern Central Asian Orogenic Belt (CAOB). Here, we present new zircon U-Pb ages, whole-rock geochemistry and Sr-Nd isotopic compositions for four Late Paleozoic felsic plutons in Eastern Tianshan (or Tienshan in some literatures) in order to constrain the tectonic evolution of the southern CAOB. The granodioritic pluton and its dioritic enclaves were synchronously formed in the Early Carboniferous (336 ± 3 Ma and 335 ± 2 Ma, respectively). These rocks are depleted in Nb, Ta and Ti, and enriched in Rb, Ba, Th and U related to the primitive mantle, which show typical features of arc rocks. They both have similar Sr-Nd isotopic ratios to those granitic rocks from the eastern Central Tianshan Block and have the latest Mesoproterozoic two stage Nd model ages (TDM2) (1111-1195 Ma for the granodioritic pluton and 1104-1108 Ma for the enclaves, respectively), indicating that their source magmas may have been derived from the Mesoproterozoic crust. The albitophyric pluton was also emplaced in the Early Carboniferous (333 ± 3 Ma). Rocks of this pluton have similar εNd(t) values (-0.69 to -0.37) and TDM2 ages (1135-1161 Ma) to those of the granodioritic rocks, suggest similar crustal source for both types of rocks. In contrast, the K-feldspar granitic and monzonitic plutons were emplaced in the Early Permian (292 ± 3 Ma and 281 ± 2 Ma, respectively). Samples of the K-feldspar granitic pluton have high K2O + Na2O, FeO/MgO, Ga/Al, HFSE (e.g., Zr and Hf) and low CaO, Sr and Ba, exhibiting characteristics of A2-type granites, which probably emplaced in a post-collisional extension environment. They have higher εNd(t) values (+2.77 to +3.27) and more juvenile TDM2 ages (799-841 Ma) than the Early Carboniferous plutons, suggesting that they were derived from relatively younger crustal sources. The monzonitic granites are metaluminous to weakly peraluminous with A/CNK ranging from 0.93 to 1.05, and have

Timing, petrogenesis and tectonic setting of the Late Paleozoic gabbro-granodiorite-granite intrusions in the Shalazhashan of northern Alxa: Constraints on the southernmost boundary of the Central Asian Orogenic Belt

NASA Astrophysics Data System (ADS)

Shi, Xingjun; Wang, Tao; Zhang, Lei; Castro, Antonio; Xiao, XuChang; Tong, Ying; Zhang, Jianjun; Guo, Lei; Yang, Qidi

2014-11-01

The Late Paleozoic tectonic setting and location of the southernmost boundary of the Central Asian Orogenic Belt (CAOB) with respect to the Alxa Block or Alxa-North China Craton (ANCC) are debated. This paper presents new geochronological, petrological, geochemical and zircon Hf isotopic data of the Late Paleozoic intrusions from the Shalazhashan in northern Alxa and discusses the tectonic setting and boundary between the CAOB and ANCC. Using zircon U-Pb dating, intrusions can be broadly grouped as Late Carboniferous granodiorites (~ 301 Ma), Middle Permian gabbros (~ 264 Ma) and granites (~ 266 Ma) and Late Permian granodiorites, monzogranites and quartz monzodiorites (254-250 Ma). The Late Carboniferous granodiorites are slightly peraluminous and calcic. The remarkably high zircon Hf isotopes (εHf(t) = + 6-+ 10) and characteristics of high silica adakites suggest that these granodiorites were mainly derived from "hot" basaltic slab-melts of the subducted oceanic crust. The Middle Permian gabbros exhibited typical cumulate textures and were derived from the partial melting of depleted mantle. The Middle Permian granites are slightly peraluminous with high-K calc-alkaline and low εHf(t) values from - 0.9 to + 2.9. These granites were most likely derived from juvenile materials mixed with old crustal materials. The Late Permian granodiorites, monzogranites and quartz monzodiorites are characterized as metaluminous to slightly peraluminous, with variable Peacock alkali-lime index values from calc-alkalic to alkali-calcic. These rocks were mainly derived from juvenile crustal materials, as evidenced by their high εHf(t) values (+ 3.3 to + 8.9). The juvenile sources of the above intrusions in the Shalazhashan are similar to those of the granitoids from the CAOB but distinct from the granitoids within the Alxa Block. These findings suggest that the Shalazhashan Zone belongs to the CAOB rather than the Alxa Block and that its boundary with the Alxa block can be

Two contrasting late Paleozoic magmatic episodes in the northwestern Chinese Tianshan Belt, NW China: Implication for tectonic transition from plate convergence to intra-plate adjustment during accretionary orogenesis

NASA Astrophysics Data System (ADS)

Wang, Xiangsong; Cai, Keda; Sun, Min; Xiao, Wenjiao; Xia, Xiaoping; Wan, Bo; Bao, Zihe; Wang, Yannan

2018-03-01

Late Carboniferous to Early Permian is a critical period for the final amalgamation of the Central Asian Orogenic Belt (CAOB). However, as most of the accreted terranes of the CAOB are unclear in tectonic nature and origin, the timing and processes of their mutual amalgamation have been poorly constrained. To understand assembly of the West Junggar Terrane with the Yili Block, a suite of the late Paleozoic magmatic rocks, including ignimbrite, rhyolite and granite, in northwestern Chinese Tianshan Belt were studied for their petrogenesis and tectonic implications. Our new results of secondary ion mass spectrometry (SIMS) zircon U-Pb dating reveal two separate magmatic episodes, ca. 300 Ma volcanism (ignimbrite and rhyolite) and ca. 288 Ma plutonsim (biotite granite). Geochemically, for the ca. 300 Ma volcanism, the ignimbrites have low SiO2 (65.8-71.5 wt.%) and Mg# (6-13) values, and exhibit arc affinity with significantly enriched in large ion lithophile elements (LILE) and depleted in high field strength elements (HFSE) such as Nb, Ta and Ti. The whole-rock εNd(t) and zircon εHf(t) values range from +6.9 to +7.0 and +9.9 to +14.1 respectively, indicating a juvenile basaltic lower crustal origin. Rhyolites have slightly high SiO2 (72.7-74.0 wt.%) and K2O (3.86-4.53 wt.%) contents, high zircon δ18O (11.67-13.23‰) values, and low whole-rock εNd(t) (+2.9 to +3.8) and zircon εHf(t) (+2.8 to +10.0) values, which may suggest sediment involvements during magma generation. In contrast, for the ca. 288 Ma plutonism, the biotite granites have obviously higher SiO2 (74.7-75.5 wt.%) contents and whole-rock εNd(t) (+7.7 to +8.8), zircon εHf(t) (+9.8 to +12.7), and lower zircon δ18O (5.99-6.84‰) values, than those of the ca. 300 Ma volcanic rocks, which are consistent with signatures of juvenile magma source. According to our estimates of zircon saturation temperatures, together with their contrasting genesis, we attribute the formation of ca. 300 Ma high

Early Paleozoic development of the Maine-Quebec boundary Mountains region

USGS Publications Warehouse

Gerbi, C.C.; Johnson, S.E.; Aleinikoff, J.N.; Bedard, J.H.; Dunning, G.R.; Fanning, C.M.

2006-01-01

Pre-Silurian bedrock units played key roles in the early Paleozoic history of the Maine-Quebec Appalachians. These units represent peri-Laurentian material whose collision with the craton deformed the Neoproteozoic passive margin and initiated the Appalachian mountain-building cycle. We present new field, petrological, geochronological, and geochemical data to support the following interpretations related to these units. (1) The Boil Mountain Complex and Jim Pond Formation do not represent part of a coherent ophiolite. (2) Gabbro and tonalite of the Boil Mountain Complex intruded the Chain Lakes massif at ca. 477 Ma. (3) The Skinner pluton, an arc-related granodiorite, intruded the Chain Lakes massif at ca. 472 Ma. (4) The Attean pluton, with a reconfirmed age of ca. 443 Ma, is unrelated to Early Ordovician orogenesis. (5) The most likely timing for the juxtaposition of the Jim Pond Formation and the Boil Mountain Complex was during regional Devonian deformation. These interpretations suggest that the Boundary Mountains were once part of a series of arcs extending at least from central New England through Newfoundland. ?? 2006 NRC Canada.

Late Paleozoic magmatism in South China: Oceanic subduction or intracontinental orogeny?

NASA Astrophysics Data System (ADS)

Liu, Q.; Yu, J.; Zhao, G.

2013-12-01

The significant late Paleozoic magmatism has been widely recognized in the East Asian Blocks, which sheds a light on the assembly and break-up of the Pangea supercontinent. As one of major components in East Asia, however, the South China Block (SCB) does not have much late Paleozoic magmatism recognized. Here we report a gneissic granite intrusion in northeastern Fujian Province, eastern SCB. It is a S-type granite characterized by high K2O and Al2O3, and low SiO2 and Na2O with a high A/CNK ratio of 1.22. Zircons with stubby morphology from this gneissic granite yield 206Pb/238U ages ranging from 326 Ma to 301 Ma with a weighted average age of 313×4 Ma, and negative epsilonHf(t) values from -8.35 to -1.74 with two-stage Hf model ages of 1.43 to 1.84 Ga. This S-type granite was probably originated from late Paleoproterozoic crust during an intracontinental orogeny, not under oceanic subduction. Integrated with previous results on the paleogeographic reconstruction of the SCB, the nature of Paleozoic basins, Early Permian volcanism and U-Pb-Hf isotope of detrital zircons from the late Paleozoic to early Mesozoic sedimentary rocks, our data support a late Paleozoic orogeny in the SCB, which may have included Late Carboniferous (340-310 Ma) compressive episode and Early Permian (287-270 Ma) post-orogenic or intraplate extensive episode. Our interpretation is consistent with the late Paleozoic orogenic events recognized in other Pangea microcontinents, and thus provides a window for the reconstruction of Pangea. Acknowledgements: NSFC (41190070, 41190075)

Geochemistry and Geochronology of the Heilongjiang Complex and Its Implications in the Late Paleozoic Tectonics of Eastern NE China

NASA Astrophysics Data System (ADS)

GE, M.; Zhang, J.; Liu, K.; Ling, Y.; Wang, M.; Wang, J.

2016-12-01

The Paleozoic to early Mesozoic tectonic framework of Northeast China, especially the Jiamusi block and its related structural belts, are highly debated. In this contribution, geochemical, geochronological and isotopic analyses were carried out on the basalts in the Heilongjiang complex to address these issues. The Heilongjiang complex defines the suture belt between the Jiamusi block and the Songliao block in Northeast China, and the blueschist is a major composition for this complex, coexisting with ultramafic rocks, amphibolite, greenschist, quartzite and mica schist. The blueschist has a mineral association of sodic amphibole, epidote, chlorite, phengite, albite and quartz with accessory phases of apatite, titanite, zircon and ilmenite. Together with the lithological association, the geochemical results present that the protoliths of the blueschist can be divided into the alkaline and tholeiitic basalts and have OIB affinities, formed in an ocean island setting, indicated by the (La/Yb) N values of 3.57 - 11.54, and the (La/Sm) N values of 0.69 - 3.64. The high and positive ɛNd (t) values of + 3.7 to +9.0, and relative enrichment in Nb and Ta show that both the alkaline and tholeiitic basalts may be derived from the asthenospheric mantle. Magmatic zircons from the blueschist in Yilan area yield a 206Pb/238U age of 281 - 288 Ma, interpreted as its protolithic age. The amphibolite from Xiachengzi area has a zircon U-Pb age of 248 ± 4 Ma, interpreted as its protolith age and has N-MORB affinities, supported by (La/Yb)N ratios of 0.60-0.89 and (La/Sm)N of 0.62-0.84, and high ɛNd (t) values ranging from + 7.8 to + 9.5, deriving from a depleted mantle source. A new 40Ar/39Ar amphibole plateau age of 195 ± 3 Ma and a youngest age of 200 Ma of the detrital zircons from Heilongjiang complex are reported to constrain the metamorphic age of the Heilongjiang complex. In addition, a huge north-south trending granitic belt generated from 174 Ma - 200 Ma has been

Tectonic sequence stratigraphy, Early Permian Dry Mountain trough, east-central Nevada

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

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

1991-06-01

The Early Permian Dry Mountain trough (DMT) of east-central Nevada is one of several tectonic basins and associated uplifts that developed along the continenetal margin during the latest Pennsylvanian-Early Permian Dry Mountain tectonic phase. The sequence stratigraphy reflects a combination of eustatic sea level changes and tectonic uplift or subsidence. Fewer than one to only a few million years separate the development of sequence boundaries within the DMT. At this scale, differences among published eustasy curves preclude their use as definitive tools to identify eustatically controlled sequence boundaries. Nevertheless, available data indicate several pulses of tectonism affected sedimentation within themore » DMT. The authors are attempting to develop criteria to distinguish tectonic from eustatic sequence boundaries. Detailed biostratigraphic data are required to provide an independent check on the correlation of sequence boundaries between measured sections. For example, the same age boundary may reflect tectonic uplift in one part of the basin and subsidence in another. The uplift may or may not result in subaerial exposure and erosion. For those boundaries that do not result from subaerial exposure, lithofacies and biofacies analyses are required to infer relative uplift (water depth decrease) or subsidence (water depth increase). There are inherent resolution limitations in both the paleontologic and sedimentologic methodologies. These limitations, combined with those of eustasy curves, dictate the preliminary nature of their results.« less

Geochemistry and chronology of the early Paleozoic diorites and granites in the Huangtupo volcanogenic massive sulfide (VMS) deposit, Eastern Tianshan, NW China: Implications for petrogenesis and geodynamic setting

NASA Astrophysics Data System (ADS)

Zheng, Jiahao; Chai, Fengmei; Feng, Wanyi; Yang, Fuquan; Shen, Ping

2018-03-01

The Eastern Tianshan orogen contains many late Paleozoic porphyry Cu and magmatic Cu-Ni deposits. Recent studies demonstrate that several early Paleozoic volcanogenic massive sulfide (VMS) Cu-polymetallic and porphyry Cu deposits were discovered in the northern part of Eastern Tianshan. This study presents zircon U-Pb, whole-rock geochemical, and Sr-Nd isotopic data for granites and diorites from the Huangtupo VMS Cu-Zn deposit, northern part of the Eastern Tianshan. Our results can provide constraints on the genesis of intermediate and felsic intrusions as well as early Paleozoic geodynamic setting of the northern part of Eastern Tianshan. LA-ICP-MS zircon U-Pb analyses suggest that the granites and diorites were formed at 435 ± 2 Ma and 440 ± 2 Ma, respectively. Geochemical characteristics suggest that the Huangtupo granites and diorites are metaluminous rocks, exhibiting typical subduction-related features such as enrichment in LILE and LREE and depletion in HFSE. The diorites have moderate Mg#, positive εNd(t) values (+6.4 to +7.3), and young Nd model ages, indicative of a depleted mantle origin. The granites exhibit mineral assemblages and geochemical characteristics of I-type granites, and they have positive εNd(t) values (+6.7 to +10.2) and young Nd model ages, suggesting a juvenile crust origin. The early Paleozoic VMS Cu-polymetallic and porphyry Cu deposits in the northern part of Eastern Tianshan were genetically related. The formation of the early Paleozoic magmatic rocks as well as VMS and porphyry Cu deposits in the northern part of Eastern Tianshan was due to a southward subduction of the Junggar oceanic plate.

The Pennsylvanian-early permian bird spring carbonate shelf, Southeastern California: Fusulinid biostratigraphy, paleogeographic evolution, and tectonic implications

USGS Publications Warehouse

Stevens, C.H.; Stone, P.

2007-01-01

transported eastward on the Last Chance thrust. By middle Sakmarian (middle middle Wolfcampian) time (within Fusulinid Zone 4), emplacement of the Last Chance allochthon was complete, and subsidence caused by thrust loading had resulted in development of a new turbidite basin (Darwin Basin) along the former western part of the Bird Spring Shelf. At the same time, farther east into the craton, paralic facies began prograding westward, so that the youngest fusulinid-bearing limestones on the shelf in this area become progressively younger to the west. Eventually, in Artinskian to Kungurian (late Wolfcampian to Leonardian) time (Fusulinid Zones 5 and 6), deposition of fusulinid-bearing limestone on the shelf was restricted to a marginal belt between the prograding paralic facies to the east and the Darwin Basin to the west. Development of the Keeler Basin in Pennsylvanian to earliest Permian time was approximately coeval with collision between South America-Africa (Gondwana) and North America (Laurentia) on the Ouachita-Marathon orogenic belt. This basin developed inboard of a northwest-trending, sinistral fault zone that truncated the continental margin. Later, in the Early Permian, the Last Chance allochthon, which was part of a northeast-trending belt of deformation that extended into northeastern Nevada, was emplaced. This orogenic belt probably was driven by convergence at the continental margin to the northwest. This work adds significant detail to existing interpretations of the late Paleozoic as a time of major tectonic instability on the continental margin of southeastern California as it changed from a relatively passive margin that had characterized most of the Paleozoic to an active convergent margin that would characterize the Mesozoic. ?? 2007 The Geological Society of America. All rights reserved.

Petrogenesis of the Pd-rich intrusion at Salt Chuck, Prince of Wales island: an early Paleozoic Alaskan-type ultramafic body

USGS Publications Warehouse

Loney, R.A.; Himmelberg, G.R.

1992-01-01

The early Paleozoic Salt Chuck intrusion has petrographic and chemical characteristics that are similar to those of Cretaceous Alaskan-type ultramafic-mafic bodies. The intrusion is markedly discordant to the structure of the early Paleozoic Descon Formation, in which it has produced a rather indistinct contact aureole a few meters wide. Mineral assemblages, sequence of crystallization, and mineral chemistry suggest that the intrusion crystallized under low pressures (~2 kbar) with oxidation conditions near those of the NNO buffer, from a hydrous, silica-saturated, orthopyroxene-normative parental magma. The Salt Chuck deposit was probably formed by a two-stage process: 1) a stage of magmatic crystallization in which the sulfides and PGE accumulated in a disseminated manner in cumulus deposits, possibly largely in the gabbro, and 2) a later magmatic-hydrothermal stage during which the sulfides and PGE were remobilized and concentrated in veins and fracture-fillings. In this model, the source of the sulfides and PGE was the magma that produced the Salt Chuck intrusion. -from Authors

Late Tharsis tectonic activity and implications for Early Mars

NASA Astrophysics Data System (ADS)

Bouley, S.; Baratoux, D.; Paulien, N.; Missenard, Y.; Saint-Bezar, B.

2017-12-01

Constraining the timing of Tharsis volcanism is critical to understanding the planet's evolution including its climate, surface environment and mantle dynamics. The tectonic history of the Tharsis bulge was previously documented from the distribution and ages of related tectonic features [1]. Here we revisit the ages of 7493 Tharsis-related tectonic features based on their relationship with stratigraphic units defined in the new geological map [2]. Conversely to previous tectonic mapping [1], which suggested that Tharsis growth was nearly achieved during the Noachian, we find a protracted growth of Tharsis during the Hesperian. Faulting at Tempe Terra, Claritas and Coracis Fossae and Thaumasia Planum confirms that tectonic deformation started during the Noachian. Accumulated tectonic deformation was maximum in the Early Hesperian for compressional strain (Solis, Lunae and Ascuris Planum) and extended over time from Noachian to Amazonian for extensional strain (Noctis Labyrinthus and Fossae, Sinai Planum and Tractus, Ulysses and Fortuna fossae, Alba Patera). This new scenario is consistent with a protracted growth of Tharsis dome during the Hesperian and with the timing a large Tharsis-driven true polar wander post-dating the incision of Late Noachian/Hesperian valley networks[3]. References:[1] Anderson et al. JGR-Planets 106, E9, 20,563-20,585 (2001).[2] Tanaka, K.L. et al. Geologic map of Mars (2014). [3] Bouley et al. Nature doi:10.1038 (2016)

Early Earth plume-lid tectonics: A high-resolution 3D numerical modelling approach

NASA Astrophysics Data System (ADS)

Fischer, R.; Gerya, T.

2016-10-01

Geological-geochemical evidence point towards higher mantle potential temperature and a different type of tectonics (global plume-lid tectonics) in the early Earth (>3.2 Ga) compared to the present day (global plate tectonics). In order to investigate tectono-magmatic processes associated with plume-lid tectonics and crustal growth under hotter mantle temperature conditions, we conduct a series of 3D high-resolution magmatic-thermomechanical models with the finite-difference code I3ELVIS. No external plate tectonic forces are applied to isolate 3D effects of various plume-lithosphere and crust-mantle interactions. Results of the numerical experiments show two distinct phases in coupled crust-mantle evolution: (1) a longer (80-100 Myr) and relatively quiet 'growth phase' which is marked by growth of crust and lithosphere, followed by (2) a short (∼20 Myr) and catastrophic 'removal phase', where unstable parts of the crust and mantle lithosphere are removed by eclogitic dripping and later delamination. This modelling suggests that the early Earth plume-lid tectonic regime followed a pattern of episodic growth and removal also called episodic overturn with a periodicity of ∼100 Myr.

Thermochronologic constraints on post-Paleozoic tectonic evolution of the central Transantarctic Mountains, Antarctica

NASA Astrophysics Data System (ADS)

Fitzgerald, Paul G.

1994-08-01

Built upon the roots of a compressive orogenic belt of late Proterozoic-early Paleozoic age and once adjacent to North America, the present-day Transantarctic Mountains (TAM) represent a rift flank, resulting from episodic uplift in the Cretaceous and Cenozoic. Fault blocks are discernible in present-day topography and subglacial morphology. Fission track results give information on differential block movement (uplift and denudation) and are important in constraining models for the uplift of the range. Apatite fission track thermochronology on samples collected from the central TAM record a complex thermotectonic history for this region over the past 350 m.y. Apatite ages in the Miller Range vary from ˜250 to ˜350 Ma and are from an exhumed apatite partial annealing zone formed following cooling of Cambro-Ordovician granitoids. A period of Cretaceous denudation (≲2 km), beginning at ˜115 Ma, is recorded at Moody Nunatak on the inland side of the TAM. Near the coast, samples along the Beardmore Glacier record rapid cooling indicative of denudation initiated in the early Cenozoic (˜50 Ma). The amount of uplift ˜70 km inland of the coast in the Queen Alexandra Range since the early Cenozoic is ˜7 km, with the likelihood of an additional ˜3 km at the coast. Eastward facing topographic escarpments in the Queen Alexandra Range mark the likely position of steeply dipping normal faults, which offset the apatite ages. Apatite ages on the east side of the Beardmore Glacier mouth are generally younger (average 27 Ma) than on the west side (average 33 Ma), reflecting greater denudation. Assumptions made regarding the use of an assumed paleogeothermal gradient are tested with available geologic evidence. The fission track data neither conflict with nor confirm paleobotanical evidence from the Sirius Group in the central TAM which suggests significant surface uplift (2-3 km) of the TAM since the Pliocene. Results build upon the available fission track database along the

MEVTV Workshop on Early Tectonic and Volcanic Evolution of Mars

NASA Technical Reports Server (NTRS)

Frey, H. (Editor)

1988-01-01

Although not ignored, the problems of the early tectonic and volcanic evolution of Mars have generally received less attention than those later in the evolution of the planet. Specifically, much attention was devoted to the evolution of the Tharsis region of Mars and to the planet itself at the time following the establishment of this major tectonic and volcanic province. By contrast, little attention was directed at fundamental questions, such as the conditions that led to the development of Tharsis and the cause of the basic fundamental dichotomy of the Martian crust. It was to address these and related questions of the earliest evolution of Mars that a workshop was organized under the auspices of the Mars: Evolution of Volcanism, Tectonism, and Volatiles (MEVTV) Program. Four sessions were held: crustal dichotomy; crustal differentiation/volcanism; Tharsis, Elysium, and Valles Marineris; and ridges and fault tectonics.

Cenozoic Tectonic Activity of the "Passive" North America Margin: Evidence for Cenozoic Activity on Mesozoic or Paleozoic Faults

NASA Astrophysics Data System (ADS)

Nedorub, O. I.; Knapp, C. C.

2012-12-01

The tectonic history of the Eastern North American Margin (ENAM) incorporates two cycles of continental assembly, multiple pulses of orogeny, rifting, and post-rift geodynamic evolution. This is reflected in the heterogeneous lithosphere of the ENAM which contains fault structures originated in Paleozoic to Mesozoic eras. The South Georgia Rift basin is probably the largest Mesozoic graben within its boundaries that is associated with the breakup of Pangea. It is composed of smaller sub-basins which appear to be bounded by high-angle normal faults, some of which may have been inverted in late Cretaceous and Cenozoic eras. Paleozoic structures may have been reactivated in Cenozoic time as well. The ENAM is characterized by N-NE maximum horizontal compressive stress direction. This maximum compressional stress field is sub-parallel to the strike of the Atlantic Coast province fault systems. Camden, Augusta, Allendale, and Pen Branch faults are four of the many such reactivated faults along the southern part of ENAM. These faults are now buried under the 0-400 m of loosely consolidated Cretaceous and Cenozoic age sediments and thus are either only partially mapped or currently not recognized. Some of the objectives of this study are to map the subsurface expression and geometry of these faults and to investigate the post Cretaceous deformation and possible causes of fault reactivation on a passive margin. This study employs an integrated geophysical approach to investigate the upper 200 m of identified locations of the above mentioned faults. 2-D high-resolution shallow seismic reflection and refraction methods, gravity surveys, GPR, 2-D electrical resistivity and well data are used for analyses and interpretation. Preliminary results suggest that Camden fault shows signs of Cenozoic reactivation through an approximately 30 m offset NW side up mainly along a steeply dipping fault zone in the basal contact of Coastal Plain sediments with the Carolina Piedmont. Drill

"Taconic" arc magmatism in the central Brooks Range, Alaska: New U-Pb zircon geochronology and Hf isotopic data from the lower Paleozoic Apoon assemblage of the Doonerak fenster

NASA Astrophysics Data System (ADS)

Strauss, J. V.; Hoiland, C. W.; Ward, W.; Johnson, B.; McClelland, W.

2015-12-01

The Doonerak fenster in the central Brooks Range, AK, exposes an important package of early Paleozoic volcanic and sedimentary rocks called the Apoon assemblage, which are generally interpreted as para-autochthonous basement to the Mesozoic-Cenozoic Brookian fold-thrust belt. Recognition in the 1970's of a major pre-Mississippian unconformity within the window led to correlations between Doonerak and the North Slope (sub-) terrane of the Arctic Alaska Chukotka microplate (AACM); however, the presence of arc-affinity volcanism and the apparent lack of pre-Mississippian deformation in the Apoon assemblage makes this link tenuous and complicates Paleozoic tectonic reconstructions of the AACM. Previous age constraints on the Apoon assemblage are limited to a handful of Middle Cambrian-Silurian paleontological collections and five K-Ar and 40Ar/39Ar hornblende ages from mafic dikes ranging from ~380-520 Ma. We conducted U-Pb geochronologic and Hf isotopic analyses on igneous and sedimentary zircon from the Apoon assemblage to test Paleozoic links with the North Slope and to assess the tectonic and paleogeographic setting of the Doonerak region. U-Pb analyses on detrital zircon from Apoon rocks yield a spectrum of unimodal and polymodal age populations, including prominent age groups of ca. 420-490, 960-1250, 1380­-1500, 1750-1945, and 2650-2830 Ma. Hf isotopic data from the ca. 410-490 Ma age population are generally juvenile (~7-10 ɛHf), implying a distinct lack of crustal assimilation during Ordovician-Silurian Doonerak arc magmatism despite its proximity to a cratonic source terrane as indicated by an abundance of Archean and Proterozoic zircon in the interbedded siliciclastic strata. These data are in stark contrast to geochronological data from the non-Laurentian portions of the AACM, highlighting a prominent tectonic boundary between Laurentian- and Baltic-affinity rocks at the Doonerak window and implying a link to "Taconic"-age arc magmatism documented along

Provenance and detrital zircon geochronologic evolution of lower Brookian foreland basin deposits of the western Brooks Range, Alaska, and implications for early Brookian tectonism

USGS Publications Warehouse

Moore, Thomas; O'Sullivan, Paul B.; Potter, Christopher J.; Donelick, Raymond A.

2015-01-01

The Upper Jurassic and Lower Cretaceous part of the Brookian sequence of northern Alaska consists of syntectonic deposits shed from the north-directed, early Brookian orogenic belt. We employ sandstone petrography, detrital zircon U-Pb age analysis, and zircon fission-track double-dating methods to investigate these deposits in a succession of thin regional thrust sheets in the western Brooks Range and in the adjacent Colville foreland basin to determine sediment provenance, sedimentary dispersal patterns, and to reconstruct the evolution of the Brookian orogen. The oldest and structurally highest deposits are allochthonous Upper Jurassic volcanic arc–derived sandstones that rest on accreted ophiolitic and/or subduction assemblage mafic igneous rocks. These strata contain a nearly unimodal Late Jurassic zircon population and are interpreted to be a fragment of a forearc basin that was emplaced onto the Brooks Range during arc-continent collision. Synorogenic deposits found at structurally lower levels contain decreasing amounts of ophiolite and arc debris, Jurassic zircons, and increasing amounts of continentally derived sedimentary detritus accompanied by broadly distributed late Paleozoic and Triassic (359–200 Ma), early Paleozoic (542–359 Ma), and Paleoproterozoic (2000–1750 Ma) zircon populations. The zircon populations display fission-track evidence of cooling during the Brookian event and evidence of an earlier episode of cooling in the late Paleozoic and Triassic. Surprisingly, there is little evidence for erosion of the continental basement of Arctic Alaska, its Paleozoic sedimentary cover, or its hinterland metamorphic rocks in early foreland basin strata at any structural and/or stratigraphic level in the western Brooks Range. Detritus from exhumation of these sources did not arrive in the foreland basin until the middle or late Albian in the central part of the Colville Basin.These observations indicate that two primary provenance areas provided

Paleozoic Hydrocarbon-Seep Limestones

NASA Astrophysics Data System (ADS)

Peckmann, J.

2007-12-01

To date, five Paleozoic hydrocarbon-seep limestones have been recognized based on carbonate fabrics, associated fauna, and stable carbon isotopes. These are the Middle Devonian Hollard Mound from the Antiatlas of Morocco [1], Late Devonian limestone lenses with the dimerelloid brachiopod Dzieduszyckia from the Western Meseta of Morocco [2], Middle Mississippian limestones with the dimerelloid brachiopod Ibergirhynchia from the Harz Mountains of Germany [3], Early Pennsylvanian limestones from the Tantes Mound in the High Pyrenees of France [4], and Late Pennsylvanian limestone lenses from the Ganigobis Shale Member of southern Namibia [5]. Among these examples, the composition of seepage fluids varied substantially as inferred from delta C-13 values of early diagenetic carbonate phases. Delta C-13 values as low as -50 per mil from the Tantes Mound and -51 per mil from the Ganigobis limestones reveal seepage of biogenic methane, whereas values of -12 per mil from limestones with Dzieduszyckia associated with abundant pyrobitumen agree with oil seepage. Intermediate delta C-13 values of carbonate cements from the Hollard Mound and Ibergirhynchia deposits probably reflect seepage of thermogenic methane. It is presently very difficult to assess the faunal evolution at seeps in the Paleozoic based on the limited number of examples. Two of the known seeps were typified by extremely abundant rhynchonellide brachiopods of the superfamily Dimerelloidea. Bivalve mollusks and tubeworms were abundant at two of the known Paleozoic seep sites; one was dominated by bivalve mollusks (Hollard Mound, Middle Devonian), another was dominated by tubeworms (Ganigobis Shale Member, Late Pennsylvanian). The tubeworms from these two deposits are interpreted to represent vestimentiferan worms, based on studies of the taphonomy of modern vestimentiferans. However, this interpretation is in conflict with the estimated evolutionary age of vestimentiferans based on molecular clock methods

On the temporal evolution of long-wavelength mantle structure of the Earth since the early Paleozoic

NASA Astrophysics Data System (ADS)

Zhong, Shijie; Rudolph, Maxwell L.

2015-05-01

The seismic structure of the Earth's lower mantle is characterized by a dominantly degree-2 pattern with the African and Pacific large low shear velocity provinces (i.e., LLSVP) that are separated by circum-Pacific seismically fast anomalies. It is important to understand the origin of such a degree-2 mantle structure and its temporal evolution. In this study, we investigated the effects of plate motion history and mantle viscosity on the temporal evolution of the lower mantle structure since the early Paleozoic by formulating 3-D spherical shell models of thermochemical convection. For convection models with realistic mantle viscosity and no initial structure, it takes about ˜50 Myr to develop dominantly degree-2 lower mantle structure using the published plate motion models for the last either 120 Ma or 250 Ma. However, it takes longer time to develop the mantle structure for more viscous mantle. While the circum-Pangea subduction in plate motion history models promotes the formation of degree-2 mantle structure, the published pre-Pangea plate motions before 330 Ma produce relatively cold lower mantle in the African hemisphere and significant degree-1 structure in the early Pangea (˜300 Ma) or later times, even if the lower mantle has an initially degree-2 structure and a viscosity as high as 1023 Pas. This suggests that the African LLSVP may not be stationary since the early Paleozoic. With the published plate motion models and lower mantle viscosity of 1022 Pas, our mantle convection models suggest that the present-day degree-2 mantle structure may have largely been formed by ˜200 Ma.

Early impact basins and the onset of plate tectonics. Ph.D. Thesis - Maryland Univ.

NASA Technical Reports Server (NTRS)

Frey, H.

1977-01-01

The fundamental crustal dichotomy of the Earth (high and low density crust) was established nearly 4 billion years ago. Therefore, subductable crust was concentrated at the surface of the Earth very early in its history, making possible an early onset for plate tectonics. Simple thermal history calculations spanning 1 billion years show that the basin forming impact thins the lithosphere by at least 25%, and increases the sublithosphere thermal gradients by roughly 20%. The corresponding increase in convective heat transport, combined with the highly fractured nature of the thinned basin lithosphere, suggest that lithospheric breakup or rifting occurred shortly after the formation of the basins. Conditions appropriate for early rifting persisted from some 100,000,000 years following impact. We suggest a very early stage of high temperature, fast spreading "microplate" tectonics, originating before 3.5 billion years ago, and gradually stabilizing over the Archaean into more modern large plate or Wilson Cycle tectonics.

Tectonic isolation from regional sediment sourcing of the Paradox Basin

NASA Astrophysics Data System (ADS)

Smith, T. M.; Saylor, J.; Sundell, K. E.; Lapen, T. J.

2017-12-01

The Appalachian and Ouachita-Marathon mountain ranges were created by a series of tectonic collisions that occurred through the middle and late Paleozoic along North America's eastern and southern margins, respectively. Previous work employing detrital zircon U-Pb geochronology has demonstrated that fluvial and eolian systems transported Appalachian-derived sediment across the continent to North America's Paleozoic western margin. However, contemporaneous intraplate deformation of the Ancestral Rocky Mountains (ARM) compartmentalized much of the North American western interior and mid-continent. We employ lithofacies characterization, stratigraphic thickness, paleocurrent data, sandstone petrography, and detrital zircon U-Pb geochronology to evaluate source-sink relationships of the Paradox Basin, which is one of the most prominent ARM basins. Evaluation of provenance is conducted through quantitative comparison of detrital zircon U-Pb distributions from basin samples and potential sources via detrital zircon mixture modeling, and is augmented with sandstone petrography. Mixing model results provide a measure of individual source contributions to basin stratigraphy, and are combined with outcrop and subsurface data (e.g., stratigraphic thickness and facies distributions) to create tectonic isolation maps. These maps elucidate drainage networks and the degree to which local versus regional sources influence sediment character within a single basin, or multiple depocenters. Results show that despite the cross-continental ubiquity of Appalachian-derived sediment, fluvial and deltaic systems throughout much of the Paradox Basin do not record their influence. Instead, sediment sourcing from the Uncompahgre Uplift, which has been interpreted to drive tectonic subsidence and formation of the Paradox Basin, completely dominated its sedimentary record. Further, the strong degree of tectonic isolation experienced by the Paradox Basin appears to be an emerging, yet common

New age constraints on the palaeoenvironmental evolution of the late Paleozoic back-arc basin along the western Gondwana margin of southern Peru

NASA Astrophysics Data System (ADS)

Boekhout, F.; Reitsma, M. J.; Spikings, R.; Rodriguez, R.; Ulianov, A.; Gerdes, A.; Schaltegger, U.

2018-03-01

The tectonic evolution of the western Gondwana margin during Pangaea amalgation is recorded in variations in the Permo-Carboniferous back-arc basin sedimentation of Peru. This study provides the first radiometric age constraints on the volcanic and sedimentary sequences of south-central eastern Peru up to the western-most tip of Bolivia, and now permits the correlation of lateral facies variations to the late Paleozoic pre-Andean orogenic cycle. The two phases of Gondwanide magmatism and metamorphism at c. 315 Ma and c. 260 Ma are reflected in two major changes in this sedimentary environment. Our detrital U-Pb zircon ages demonstrate that the timing of Ambo Formation deposition corroborates the Late Mississipian age estimates. The transition from the Ambo to the Tarma Formation around the Middle Pennsylvanian Early Gondwanide Orogeny (c. 315 Ma) represents a relative deepening of the basin. Throughout the shallow marine deposits of the Tarma Formation evidence for contemporaneous volcanism becomes gradually more pronounced and culminates around 312 - 309 Ma. Continuous basin subsidence resulted in a buildup of platform carbonates of the Copacabana Formation. Our data highlights the presence of a previously unrecognized phase of deposition of mainly fluvial sandstones and localized volcanism (281-270 Ma), which we named ´Oqoruro Formation'. This sedimentary succession was previously miss-assigned to the so-called Mitu Group, which has recently been dated to start deposition in the Middle Triassic (∼245-240 Ma). The emersion of this marine basin coincides with the onset of a major plutonic pulse related to the Late Gondwanide Orogeny (c. 260). Exhumation lead to the consequent retreat of the epeiric sea to the present-day sub-Andean region, and the coeval accumulation of the fluvial Oqoruro Formation in south eastern Peru. These late Paleozoic palaeoenvironmental changes in the back-arc basins along the western Gondwana margin of southern reflect changes in

Tectonic and neotectonic framework of the Yucca Mountain Region

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

Schweickert, R.A.

1992-09-30

Highlights of major research accomplishments concerned with the tectonics and neotectonics of the Yucca Mountain Region include: structural studies in Grapevine Mountains, Bullfrog Hills, and Bare Mountain; recognition of significance of pre-Middle Miocene normal and strike-slip faulting at Bare Mountain; compilation of map of quaternary faulting in Southern Amargosa Valley; and preliminary paleomagnetic analysis of Paleozoic and Cenozoic units at Bare Mountain.

Tectonic map of Uruguay

NASA Astrophysics Data System (ADS)

Sanchez Bettucci, L.; Oyhantcabal, P.

2008-05-01

A compilation of available data about the geology of Uruguay allowed the definition of its main events and tectonic units. Based on a critical revision of different tectonic hypothesis found in the literature, a parsimonious tectonic evolution schema is presented, in the context of Western Gondwana. The tectonic map illustrates the general features of the structure and main tectonic units of Uruguay. The Precambrian shield, cropping out in the South and Southeast of the country is an Archean to Paleoprtoerozoic basement divided in three main tectonostratigraphic terrranes: the Piedra Alta (PAT) a juvenile Paleoproterozoic unit not reworked by later events; the Nico Pérez (NPT) a complex unit composed of several blocks where Archean to Mesoproterozoic events are recognised. The NPT was strongly reworked by Neoproterozoic (Brasiliano) orogeny. The Dom Feliciano Belt cropping out in eastern Uruguay is related to Western Gondwana amalgamation. Different tectonic settings are considered: pre-Brasiliano Basement inliers; supracrustal successions representing the evolution from a back- arc to a foreland basin; a magmatic arc; and post-collisional basins and related magmatism. In lower Paleozoic the Paraná foreland basin was generated as a consequence of orogenic events. The sedimentary successions in Uruguay include continental to shallow marine deposits where the influence of carboniferous to Permian glacial episode is recorded. The Mesozoic record is characterised by the influence of extension related to the break-up of Gondwana and the formation of the Atlantic Ocean: huge amounts of tholeiitic basalt were erupted (near 30.000 km3 in Uruguay), followed by cretaceous sediments in the northern area of the country while in the south-east, bimodal magmatism and sediments of the same age are associated to rift basins. The Cenozoic is characterised by tectonic quiescence. Subsidence is only observed in the western region (Chaco-Paraná Basin) and in the east (Laguna Mer

Stratigraphy and Mesozoic–Cenozoic tectonic history of northern Sierra Los Ajos and adjacent areas, Sonora, Mexico

USGS Publications Warehouse

Page, William R.; Gray, Floyd; Iriondo, Alexander; Miggins, Daniel P.; Blodgett, Robert B.; Maldonado, Florian; Miller, Robert J.

2010-01-01

Geologic mapping in the northern Sierra Los Ajos reveals new stratigraphic and structural data relevant to deciphering the Mesozoic–Cenozoic tectonic evolution of the range. The northern Sierra Los Ajos is cored by Proterozoic, Cambrian, Devonian, Mississippian, and Pennsylvanian strata, equivalent respectively to the Pinal Schist, Bolsa Quartzite and Abrigo Limestone, Martin Formation, Escabrosa Limestone, and Horquilla Limestone. The Proterozoic–Paleozoic sequence is mantled by Upper Cretaceous rocks partly equivalent to the Fort Crittenden and Salero Formations in Arizona, and the Cabullona Group in Sonora, Mexico.Absence of the Upper Jurassic–Lower Cretaceous Bisbee Group below the Upper Cretaceous rocks and above the Proterozoic–Paleozoic rocks indicates that the Sierra Los Ajos was part of the Cananea high, a topographic highland during the Late Jurassic and Early Cretaceous. Deposition of Upper Cretaceous rocks directly on Paleozoic and Proterozoic rocks indicates that the Sierra Los Ajos area had subsided as part of the Laramide Cabullona basin during Late Cretaceous time. Basal beds of the Upper Cretaceous sequence are clast-supported conglomerate composed locally of basement (Paleozoic) clasts. The conglomerate represents erosion of Paleozoic basement in the Sierra Los Ajos area coincident with development of the Cabullona basin.The present-day Sierra Los Ajos reaches elevations of greater than 2600 m, and was uplifted during Tertiary basin-and-range extension. Upper Cretaceous rocks are exposed at higher elevations in the northern Sierra Los Ajos and represent an uplifted part of the inverted Cabullona basin. Tertiary uplift of the Sierra Los Ajos was largely accommodated by vertical movement along the north-to-northwest-striking Sierra Los Ajos fault zone flanking the west side of the range. This fault zone structurally controls the configuration of the headwaters of the San Pedro River basin, an important bi-national water resource in the US

The Myszkow porphyry copper-molybdenum deposit, Poland

USGS Publications Warehouse

Chaffee, M.A.; Eppinger, R.G.; Lason, K.; Slosarz, J.; Podemski, M.

1994-01-01

The porphyry copper-molybdenum deposit at Myszkow, south-central Poland, lies in the Cracow-Silesian orogenic belt, in the vicinity of a Paleozoic boundary between two tectonic plates. The deposit is hosted in a complex that includes early Paleozoic metasedimentary rocks intruded in the late Paleozoic by a predominantly granodioritic pluton. This deposit exhibits many features that are typical of porphyry copper deposits associated with calc-alkaline intrusive rocks, including ore- and alteration-mineral suites, zoning of ore and alteration minerals, fluid-inclusion chemistry, tectonic setting, and structural style of veining. Unusual features of the Myszkow deposit include high concentrations of tungsten and the late Paleozoic (Variscan) age. -Authors

Petrogenesis of the NE Gondwanan uppermost Ediacaran-Lower Cretaceous siliciclastic sequence of Jordan: Provenance, tectonic, and climatic implications

NASA Astrophysics Data System (ADS)

Amireh, Belal S.

2018-04-01

Detrital framework modes of the NE Gondwanan uppermost Ediacaran-Lower Cretaceous siliciclastic sequence of Jordan are determined employing the routine polarized light microscope. The lower part of this sequence constitutes a segment of the vast lower Paleozoic siliciclastic sheet flanking the northern Gondwana margin that was deposited over a regional unconformity truncating the outskirts of the East African orogen in the aftermath of the Neoproterozoic amalgamation of Gondwana. The research aims to evaluate the factors governing the detrital light mineral composition of this sandstone. The provenance terranes of the Arabian craton controlled by plate tectonics appear to be the primary factor in most of the formations, which could be either directly inferred employing Dickinson's compositional triangles or implied utilizing the petrographic data achieved and the available tectonic and geological data. The Arabian-Nubian Shield constitutes invariably the craton interior or the transitional provenance terrane within the NE Gondwana continental block that consistently supplied sandy detritus through northward-flowing braided rivers to all the lower Paleozoic formations. On the other hand, the Lower Cretaceous Series received siliciclastic debris, through braided-meandering rivers having same northward dispersal direction, additionally from the lower Paleozoic and lower-middle Mesozoic platform strata in the Arabian Craton. The formations making about 50% of the siliciclastic sequence represent a success for Dickinson's plate tectonics-provenance approach in attributing the detrital framework components primarily to the plate tectonic setting of the provenance terranes. However, even under this success, the varying effects of the other secondary sedimentological and paleoclimatological factors are important and could be crucial. The inapplicability of this approach to infer the appropriate provenance terranes of the remaining formations could be ascribed either to the

Unroofing history of Late Paleozoic magmatic arcs within the ``Turan Plate'' (Tuarkyr, Turkmenistan)

NASA Astrophysics Data System (ADS)

Garzanti, E.; Gaetani, M.

2002-07-01

Stratigraphic, sedimentologic and petrographic data collected on the Kizilkaya sedimentary succession (Western Turkmenistan) demonstrate that the "Turan Plate" consists in fact of an amalgamation of Late Paleozoic to Triassic continental microblocks separated by ocean sutures. In the Kizilkaya area, an ophiolitic sequence including pyroxenite, gabbro, pillow basalt and chert, interpreted as the oceanic crust of a back-arc or intra-arc basin, is tectonically juxtaposed against volcaniclastic redbeds documenting penecontemporaneous felsic arc magmatism (Amanbulak Group). A collisional event took place around ?mid-Carboniferous times, when oceanic rocks underwent greenschist-facies metamorphism and a thick volcaniclastic wedge, with pyroclastic rocks interbedded in the lower part, accumulated (Kizilkaya Formation). The climax of orogenic activity is testified by arid fanglomerates shed from the rapid unroofing of a continental arc sequence, including Middle-Upper Devonian back-reef carbonates and cherts, and the underlying metamorphic and granitoid basement rocks (Yashmu Formation). After a short period of relative quiescence, renewed tectonic activity is indicated by a conglomeratic sequence documenting erosion of a sedimentary and metasedimentary succession including chert, sandstone, slate and a few carbonates. A final stage of rhyolitic magmatism took place during rapid unroofing of granitoid basement rocks (Kizildag Formation). Such a complex sequence of events recorded by the Kizilkaya episutural basin succession documents the stepwise assemblage of magmatic arcs and continental fragments to form the Turan microblock collage during the Late Paleozoic. Evolution of detrital modes is compatible with that predicted for juvenile to accreted and unroofed crustal blocks. The deposition of braidplain lithic arkoses in earliest Triassic time indicates that strong subsidence continued after the end of the volcanic activity, possibly in retroarc foreland basin settings

Geochemistry, geochronology, and Sr-Nd isotopic compositions of Permian volcanic rocks in the northern margin of the North China Block: implications for the tectonic setting of the southeastern Central Asian Orogenic Belt

NASA Astrophysics Data System (ADS)

Ji, Zejia; Zhang, Zhicheng; Chen, Yan; Li, Ke; Yang, Jinfu; Qian, Xiaoyan

2018-02-01

The southeastern part of the Central Asian Orogenic Belt (CAOB), which records the collision of the North China Block (NCB) with the South Mongolian microcontinent, is a key area for reconstructing the tectonic history of the CAOB. Controversy persists regarding the timing of the final structural amalgamation of the region; therefore, it remains unclear whether the Late Paleozoic thick volcanic successions were generated in a subduction or post-orogenic environment. Redefining the age of the formation and analyzing the geochemical compositions of these volcanic rocks can provide clues regarding the regional tectonic evolution during the Late Paleozoic and place constraints on the closure time of the Paleo-Asian Ocean. In this study, we present geochemical, geochronologic, and Sr-Nd isotopic data for 29 volcanic rock samples from the Elitu Formation in Xianghuangqi, central Inner Mongolia. The Elitu volcanic rocks have latest early-to-middle Permian ages between 272 and 268 Ma. Most of the mafic-intermediate and felsic rocks show K-normal and high-K calc-alkaline characteristics. Melting is considered to be due to large scale upwelling of the metasomatic lithospheric mantle and different degrees of melting of the thickened lower crust. The northern margin of the NCB, which represents the southeastern boundary of the CAOB, records transtensional and, subsequently, extensional tectonics associated with late Carboniferous to middle Permian volcanic activity.

Plate Tectonism on Early Mars: Diverse Geological and Geophysical Evidence

NASA Technical Reports Server (NTRS)

Dohm, J. M.; Maruyama, S.; Baker, V. R.; Anderson, R. C.; Ferris, Justin C.; Hare, Trent M.

2002-01-01

Mars has been modified by endogenic and exogenic processes similar in many ways to Earth. However, evidence of Mars embryonic development is preserved because of low erosion rates and stagnant lid convective conditions since the Late Noachian. Early plate tectonism can explain such evidence. Additional information is contained in the original extended abstract.

MEVTV study: Early tectonic evolution of Mars: Crustal dichotomy to Valles Marineris

NASA Technical Reports Server (NTRS)

Frey, Herbert V.; Schultz, Richard A.

1990-01-01

Several fundamental problems were addressed in the early impact, tectonic, and volcanic evolution of the martian lithosphere: (1) origin and evolution of the fundamental crustal dichotomy, including development of the highland/lowland transition zone; (2) growth and evolution of the Valles Marineris; and (3) nature and role of major resurfacing events in early martian history. The results in these areas are briefly summarized.

Tectonics of Antarctica

USGS Publications Warehouse

Hamilton, W.

1967-01-01

Antarctica consists of large and wholly continental east Antarctica and smaller west Antarctica which would form large and small islands, even after isostatic rebound, if its ice cap were melted. Most of east Antarctica is a Precambrian Shield, in much of which charnockites are characteristic. The high Transantarctic Mountains, along the Ross and Weddell Seas, largely follow a geosyncline of Upper Precambrian sedimentary rocks that were deformed, metamorphosed and intruded by granitic rocks during Late Cambrian or Early Ordovician time. The rocks of the orogen were peneplained, then covered by thin and mostly continental Devonian-Jurassic sediments, which were intruded by Jurassic diabase sheets and overlain by plateau-forming tholeiites. Late Cenozoic doming and block-faulting have raised the present high mountains. Northeastern Victoria Land, the end of the Transantarctic Mountains south of New Zealand, preserves part of a Middle Paleozoic orogen. Clastic strata laid unconformably upon the Lower Paleozoic plutonic complex were metamorphosed at low grade, highly deformed and intruded by Late Devonian or Early Carboniferous granodiorites. The overlying Triassic continental sedimentary rocks have been broadly folded and normal-faulted. Interior west Antarctica is composed of miogeosynclinal clastic and subordinate carbonate rocks which span the Paleozoic Era and which were deformed, metamorphosed at generally low grade, and intruded by granitic rocks during Early Mesozoic time and possibly during other times also. Patterns of orogenic belts, if systematic, cannot yet be defined; but fragmentation and rotation of crustal blocks by oroclinal folding and strike-slip faulting can be suggested. The Ellsworth Mountains, for example, consist of Cambrian-Permian metasedimentary rocks that strike northward toward the noncorrelative and latitudinally striking Mesozoic terrane of the Antarctic Peninsula in one direction and southward toward that of the Lower Paleozoic: terrane

A new Triassic shortening-extrusion tectonic model for Central-Eastern Asia: Structural, geochronological and paleomagnetic investigations in the Xilamulun Fault (North China)

NASA Astrophysics Data System (ADS)

Zhao, Pan; Faure, Michel; Chen, Yan; Shi, Guanzhong; Xu, Bei

2015-09-01

At the northern margin of the North China Block (NCB), the Xilamulun Fault (XMF) is a key belt to decipher the tectonic evolution of Central-Eastern Asia, as it records the Paleozoic final closure of the Paleo-Asian Ocean, and localizes a Late Triassic intracontinental deformation. In this study, structural analysis, 40Ar-39Ar dating, and paleomagnetic studies were performed to investigate the kinematics of the XMF and to further discuss its Triassic geodynamic significance in the Central-Eastern Asia framework after the Paleozoic Central Asian Orogenic evolution. The structural analyses reveal two phases of ductile deformation. The first one (D1), which displays N-verging and E-W trending folds, is related to the Early Paleozoic collisional event between the NCB and the Songliao-Hunshandake Block (SHB). The second phase (D2) displays a high-angle foliation and a pervasive sub-horizontal E-W stretching lineation with kinematic criteria indicative of dextral strike-slip shearing. The 40Ar-39Ar dating on mylonitic granite places the main shearing event around 227-209 Ma. This D2 shearing is coeval with that of the dextral strike-slip Bayan Obo-Chifeng Fault (BCF) and the Chicheng-Fengning-Longhua Fault to the south, which together constitute a dextral shearing fault system on the northern margin of the NCB during the Late Triassic. The paleomagnetic study performed on the Middle Permian Guangxingyuan pluton, located between the XMF and BCF, documents a local clockwise rotation of this pluton with respect to the NCB and SHB. Our multidisciplinary study suggests an NNW-SSE shortening and strike-slip shearing dominated tectonic setting on the northern margin of the NCB during the Late Triassic. Combining the contemporaneous dextral strike-slip movements of the XMF and BCF in northern China and the sinistral strike-slip movement of East Gobi Fault (EGF) in southeastern Mongolia with the large-scale tectonic framework, a Late Triassic NNW-SSE shortening-eastward extrusion

A new Triassic shortening-extrusion tectonic model for Central-EasternAsia: Structural, geochronological and paleomagnetic investigations in the Xilamulun Fault (North China)

NASA Astrophysics Data System (ADS)

Zhao, Pan; Faure, Michel; Chen, Yan; Xu, Bei

2017-04-01

At the northern margin of the North China Block (NCB), the Xilamulun Fault (XMF) is a key belt to decipher the tectonic evolution of Central-Eastern Asia, as it records the Paleozoic final closure of the Paleo-Asian Ocean, and localizes a Late Triassic intracontinental deformation. In this study, structural analysis, 40Ar-39Ar dating, and paleomagnetic studies were performed to investigate the kinematics of the XMF and to further discuss its Triassic geodynamic significance in the Central-Eastern Asia framework after the Paleozoic Central Asian Orogenic evolution. The structural analyses reveal two phases of ductile deformation. The first one (D1), which displays N-verging and E-W trending folds, is related to the Early Paleozoic collisional event between the NCB and the Songliao-Hunshandake Block (SHB). The second phase (D2) displays a high-angle foliation and a pervasive sub-horizontalE-W stretching lineation with kinematic criteria indicative of dextral strike-slip shearing. The 40Ar-39Ar dating on mylonitic granite places the main shearing event around 227-209 Ma. This D2 shearing is coeval with that of the dextral strike-slip Bayan Obo-Chifeng Fault (BCF) and the Chicheng-Fengning-Longhua Fault to the south, which together constitute a dextral shearing fault system on the northern margin of the NCB during the Late Triassic. The paleomagnetic study performed on the Middle Permian Guangxingyuan pluton, located between the XMF and BCF, documents a local clockwise rotation of this pluton with respect to the NCB and SHB. Our multidisciplinary study suggests anNNW-SSE shortening and strike-slip shearing dominated tectonic setting on the northern margin of the NCB during the Late Triassic. Combining the contemporaneous dextral strike-slip movements of the XMF and BCF in northern China and the sinistral strike-slip movement of East Gobi Fault (EGF) in southeastern Mongolia with the large-scale tectonic framework, a Late Triassic NNW-SSE shortening-eastward extrusion

A New Paleozoic Symmoriiformes (Chondrichthyes) from the Late Carboniferous of Kansas (USA) and Cladistic Analysis of Early Chondrichthyans

PubMed Central

Pradel, Alan; Tafforeau, Paul; Maisey, John G.; Janvier, Philippe

2011-01-01

Background The relationships of cartilaginous fishes are discussed in the light of well preserved three-dimensional Paleozoic specimens. There is no consensus to date on the interrelationship of Paleozoic chondrichthyans, although three main phylogenetic hypotheses exist in the current literature: 1. the Paleozoic shark-like chondrichthyans, such as the Symmoriiformes, are grouped along with the modern sharks (neoselachians) into a clade which is sister group of holocephalans; 2. the Symmoriiformes are related to holocephalans, whereas the other Paleozoic shark-like chondrichthyans are related to neoselachians; 3. many Paleozoic shark-like chondrichthyans, such as the Symmoriiformes, are stem chondrichthyans, whereas stem and crown holocephalans are sister group to the stem and crown neoselachians in a crown-chondrichthyan clade. This third hypothesis was proposed recently, based mainly on dental characters. Methodology/Principal Findings On the basis of two well preserved chondrichthyan neurocrania from the Late Carboniferous of Kansas, USA, we describe here a new species of Symmoriiformes, Kawichthys moodiei gen. et sp. nov., which was investigated by means of computerized X-ray synchrotron microtomography. We present a new phylogenetic analysis based on neurocranial characters, which supports the third hypothesis and corroborates the hypothesis that crown-group chondrichthyans (Holocephali+Neoselachii) form a tightly-knit group within the chondrichthyan total group, by providing additional, non dental characters. Conclusions/Significance Our results highlight the importance of new well preserved Paleozoic fossils and new techniques of observation, and suggest that a new look at the synapomorphies of the crown-group chondrichthyans would be worthwhile in terms of understanding the adaptive significance of phylogenetically important characters. PMID:21980367

A new paleozoic Symmoriiformes (Chondrichthyes) from the late Carboniferous of Kansas (USA) and cladistic analysis of early chondrichthyans.

PubMed

Pradel, Alan; Tafforeau, Paul; Maisey, John G; Janvier, Philippe

2011-01-01

The relationships of cartilaginous fishes are discussed in the light of well preserved three-dimensional Paleozoic specimens. There is no consensus to date on the interrelationship of Paleozoic chondrichthyans, although three main phylogenetic hypotheses exist in the current literature: 1. the Paleozoic shark-like chondrichthyans, such as the Symmoriiformes, are grouped along with the modern sharks (neoselachians) into a clade which is sister group of holocephalans; 2. the Symmoriiformes are related to holocephalans, whereas the other Paleozoic shark-like chondrichthyans are related to neoselachians; 3. many Paleozoic shark-like chondrichthyans, such as the Symmoriiformes, are stem chondrichthyans, whereas stem and crown holocephalans are sister group to the stem and crown neoselachians in a crown-chondrichthyan clade. This third hypothesis was proposed recently, based mainly on dental characters. On the basis of two well preserved chondrichthyan neurocrania from the Late Carboniferous of Kansas, USA, we describe here a new species of Symmoriiformes, Kawichthys moodiei gen. et sp. nov., which was investigated by means of computerized X-ray synchrotron microtomography. We present a new phylogenetic analysis based on neurocranial characters, which supports the third hypothesis and corroborates the hypothesis that crown-group chondrichthyans (Holocephali+Neoselachii) form a tightly-knit group within the chondrichthyan total group, by providing additional, non dental characters. Our results highlight the importance of new well preserved Paleozoic fossils and new techniques of observation, and suggest that a new look at the synapomorphies of the crown-group chondrichthyans would be worthwhile in terms of understanding the adaptive significance of phylogenetically important characters.

Tectonic implications of facies patterns, Lower Permian Dry Mountain trough, east-central Nevada

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

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

1991-02-01

Paleozoic tectonism is indicated by a study of a west-east facies analysis transect across the northern portion of the Lower Permian Dry Mountain trough (DMT). In an attempt to characterize the Early Permian basin-filling sequences, three broadly recognizable facies packages have been identified across the DMT: the western margin facies and the central basin facies of the DMT and an eastern shelf facies. In the western margin facies of the basin, pulses of tectonic activity are recorded at McCloud Spring in the Sulphur Springs Range. Here, shallow open-marine carbonate overlies eroded Vinini Formation and, in turn, is unconformably overlain bymore » basinal marine carbonate. An unconformity also marks the contact with the overriding prograding coarse clastic facies. These abrupt transitions suggest the sediments were deposited in a tectonically active area where they preservation of Waltherian sequences is unlikely to occur. Similarly abrupt transitions are evident in the western part of the central basin facies. At Portuguese Springs n the Diamond Range, a thin basal marine conglomerate delineates Lower Permian sedimentation over the Pennsylvanian Ely Formation. Coarsening-upward basinal carbonate strata of pelagic, hemipelagic, and turbidite components overlie the basal conglomerate. this progression of sediments is unconformably overlain by a subaerial sequence of coarse clastic deposits. Within the eastern part of the central basin facies in the Maverick Spring Range, the Lower Permian sediments are open-marine siltstone, wackestone, packstone, and grainstone. The sediments are assigned to a gradually sloping ramp, indicating the effects of tectonism on this margin of the basin were subdued.« less

Paleozoic tectonic evolution of the Dananhu-Tousuquan island arc belt, Eastern Tianshan: Constraints from the magmatism of the Yuhai porphyry Cu deposit, Xinjiang, NW China

NASA Astrophysics Data System (ADS)

Wang, Yunfeng; Chen, Huayong; Han, Jinsheng; Chen, Shoubo; Huang, Baoqiang; Li, Chen; Tian, Qinglei; Wang, Chao; Wu, Jianxin; Chen, Mingxia

2018-03-01

pyroxene diorite shows slight enrichments in LREEs ((La/Yb)N = 2.04-2.55), Ba, U, K and Pb, weak depletions in Nb, Ta and Ti, elevated Th/U ratios, and low Ni contents and Ce/Pb ratios. Integrating with the regional tectonic evolution, we suggest that the pyroxene diorite was likely originated from the partial melting of depleted mantle metasomatized by subducted slab-derived fluids. In addition, crustal contamination likely occurred when the pyroxene diorite magma traversed the continental crust. Integrating our new results with published works on the early Paleozoic Dananhu-Tousuquan and Bogeda-Haerlike island arc belts, we propose that the Yuhai quartz diorite may have formed in a subduction setting related to the N-dipping subduction of the North Tianshan oceanic plate. The younger Yuhai granite was likely generated by the bipolar subduction of the North Tianshan oceanic plate, which formed both of the Dananhu-Tousuquan belt to the north and the Aqishan-Yamansu belt to the south. The youngest Yuhai pyroxene diorite was likely formed under a post-collisional extension setting after the Dananhu-Tousuquan and Aqishan-Yamansu belts had collided.

A hypothesis for Proterozoic-Phanerozoic supercontinent cyclicity, with implications for mantle convection, plate tectonics and Earth system evolution

NASA Astrophysics Data System (ADS)

Grenholm, Mikael; Scherstén, Anders

2015-11-01

We present a conceptual model for supercontinent cycles in the Proterozoic-Phanerozoic Eons. It is based on the repetitive behavior of C and Sr isotopes in marine carbonates and U-Pb ages and εHf of detrital zircons seen during the Neoproterozoic-Paleozoic and Paleoproterozoic Eras, respectively. These records are considered to reflect secular changes in global tectonics, and it is hypothesized that the repetitive pattern is caused by the same type of changes in global tectonics. The fundamental premise of this paper is that such repetitive changes should also be recorded in orogenic belts worldwide. This carries the implication that Neoproterozoic-Paleozoic orogenic belts should have Paleoproterozoic equivalents. It is proposed that this is the case for the East African, Uralides and Ouachita-Alleghanian orogens, which have Paleoproterozoic analogs in the West African-Amazon, Laurentian and East European cratons, respectively. The Neoproterozoic-Paleozoic orogenic belts are not isolated features but occur in a specific global context, which correspond to the relatively well-constrained Neoproterozoic break-up of Rodinia, and the subsequent Late Paleozoic assembly of Pangea. The existence of Paleoproterozoic equivalents to Neoproterozoic-Paleozoic orogens requires that the same cycle defined the Paleoproterozoic. We therefore hypothesize that there were Paleoproterozoic supercontinents equivalent to Rodinia and Pangea, and that Proterozoic-Phanerozoic supercontinents are comprised of two basic types of configurations, equivalent to Rodinia (R-type) and Pangea (P-type). The Paleoproterozoic equivalent of Rodinia is likely the first supercontinent to have formed, and Proterozoic-Phanerozoic supercontinent cycles are therefore defined by R- to R-type cycles, each lasting approximately 1.5 Gyr. We use this cyclic pattern as a framework to develop a conceptual model that predicts the configuration and cycles of Proterozoic-Phanerozoic supercontinents, and their

Late Mesozoic tectonics of the Southern-Thai Peninsula: from transpression to basins opening

NASA Astrophysics Data System (ADS)

Sautter, Benjamin; Pubellier, Manuel; Menier, David

2015-04-01

The petroleum basins of the Southern Thailand Peninsula are poorly known and their final geometry is controlled by the Tertiary stress variations applied on pre-existing Paleozoic and Mesozoic basement structures. From the end of Mesozoic times, the arrival of Indian plate was accomodated by transpressionnal deformation along the Western Margin of Sunda Plate. Evidences of this strain are the motions along several regional strike Slip Faults (Sagaing, Three Pagodas, Mae Ping, Red River, Ranong and Klong Marui Faults) as well as compressional features (folds and thrusts) evidenced onshore. Due to changes in the boundary forces, these structures were reactivated during the Tertiary, leading to the opening of basins in this part of Sundaland. We present a structural analysis based on geomorphology, fieldwork and seismic interpretation of the Southern Thai Peninsula with emphasis on the deformation's style onshore from Ranong to Satun and offshore from Eastern Mergui to Songhkla. By analyzing morphostructures and drainage anomalies from Digital Elevation Model (SRTM and ASTER), we highlight a predominance of N-S structures in the Southern Thai Peninsula: both in the granitic belt and in the sedimentary cover. The Triassic-Jurassic (Indosinian) post-collision granitic belt is intensely fractured, with 2 penetrative directions: N140 and N50. On both sides, the sedimentary units appear folded at a large wavelength (~20km). On most of the studied outcrops, Triassic to Early Cretaceous series are gently tilted and weakly fractured whereas the Paleozoic ones shows intense fracturation and steep dipping beds. Moreover, all the Paleozoic stratas display a constant N-S S1 which does not appear in the Mezosoic sediments. Althought most of the post-Mesozoic sediments do not crop out due to thick vegetal cover, several Tertiary basins can be easily seen from seismic data both onshore and offshore. These data suggest that rifting started in the Eocene and was accommodated by large

Integrated interpretation of geophysical data of the Paleozoic structure in the northwestern part of the Siljan Ring impact crater, central Sweden

NASA Astrophysics Data System (ADS)

Muhamad, Harbe; Juhlin, Christopher; Malehmir, Alireza; Sopher, Daniel

2018-01-01

The Siljan Ring impact structure is the largest known impact structure in Europe and is Late Devonian in age. It contains a central uplift that is about 20-30 km in diameter and is surrounded by a ring-shaped depression. The Siljan area is one of the few areas in Sweden where the Paleozoic sequence has not been completely eroded, making it an important location for investigation of the geological and tectonic history of Baltica during the Paleozoic. The Paleozoic strata in this area also provide insight into the complex deformation processes associated with the impact. In this study we focus on the northwestern part of the Siljan Ring, close to the town of Orsa, with the main objective of characterizing the subsurface Paleozoic succession and uppermost Precambrian crystalline rocks along a series of seismic reflection profiles, some of which have not previously been published. We combine these seismic data with gravity and magnetic data and seismic traveltime tomography results to produce an integrated interpretation of the subsurface in the area. Our interpretation shows that the Paleozoic sequence in this area is of a relatively constant thickness, with a total thickness typically between 300 and 500 m. Faulting appears to be predominantly extensional, which we interpret to have occurred during the modification stage of the impact. Furthermore, based on the geophysical data in this area, we interpret that the impact related deformation to differ in magnitude and style from other parts of the Siljan Ring.

Early Mesozoic paleogeography and tectonic evolution of the western United States: Insights from detrital zircon U-Pb geochronology, Blue Mountains Province, northeastern Oregon

USGS Publications Warehouse

LaMaskin, Todd A.; Vervoort, J.D.; Dorsey, R.J.; Wright, J.E.

2011-01-01

This study assesses early Mesozoic provenance linkages and paleogeographic-tectonic models for the western United States based on new petrographic and detrital zircon data from Triassic and Jurassic sandstones of the "Izee" and Olds Ferry terranes of the Blue Mountains Province, northeastern Oregon. Triassic sediments were likely derived from the Baker terrane offshore accretionary subduction complex and are dominated by Late Archean (ca. 2.7-2.5 Ga), Late Paleoproterozoic (ca. 2.2-1.6 Ga), and Paleozoic (ca. 380-255 Ma) detrital zircon grains. These detrital ages suggest that portions of the Baker terrane have a genetic affinity with other Cordilleran accretionary subduction complexes of the western United States, including those in the Northern Sierra and Eastern Klamath terranes. The abundance of Precambrian grains in detritus derived from an offshore complex highlights the importance of sediment reworking. Jurassic sediments are dominated by Mesozoic detrital ages (ca. 230-160 Ma), contain significant amounts of Paleozoic (ca. 290, 380-350, 480-415 Ma), Neoproterozoic (ca. 675-575 Ma), and Mesoproterozoic grains (ca. 1.4-1.0 Ga), and have lesser quantities of Late Paleoproterozoic grains (ca. 2.1-1.7 Ga). Detrital zircon ages in Jurassic sediments closely resemble well-documented age distributions in transcontinental sands of Ouachita-Appalachian provenance that were transported across the southwestern United States and modified by input from cratonal, miogeoclinal, and Cordilleran-arc sources during Triassic and Jurassic time. Jurassic sediments likely were derived from the Cordilleran arc and an orogenic highland in Nevada that yielded recycled sand from uplifted Triassic backarc basin deposits. Our data suggest that numerous Jurassic Cordilleran basins formed close to the Cordilleran margin and support a model for moderate post-Jurassic translation (~400 km) of the Blue Mountains Province. ?? 2011 Geological Society of America.

Detrital-zircon geochronology of Paleozoic sedimentary rocks in the Hangay Hentey basin, north-central Mongolia: Implications for the tectonic evolution of the Mongol Okhotsk Ocean in central Asia

NASA Astrophysics Data System (ADS)

Kelty, Thomas K.; Yin, An; Dash, Batulzii; Gehrels, George E.; Ribeiro, Angela E.

2008-04-01

Understanding the development of the Central Asian Orogenic System (CAOS), which is the largest Phanerozoic accretionary orogen in the world, is critical to the determination of continental growth mechanisms and geological history of central Asia. A key to unraveling its geological history is to ascertain the origin and tectonic setting of the large flysch complexes that dominate the CAOS. These complexes have been variably interpreted as deep-marine deposits that were accreted onto a long-evolving arc against large continents to form a mega-accretionary complex or sediments trapped in back-arc to fore-arc basins within oceanic island-arc systems far from continents. To differentiate the above models we conducted U-Pb geochronological analyses of detrital-zircon grains from turbidites in the composite Hangay-Hentey basin of central Mongolia. This basin was divided by a Cenozoic fault system into the western and eastern sub-basins: the Hangay Basin in the west and Hentey basin in the east. This study focuses on the Hentey basin and indicates two groups of samples within this basin: (1) a southern group that were deposited after the earliest Carboniferous (˜ 339 Ma to 354 Ma) and a northern group that were deposited after the Cambrian to Neoproterozoic (˜ 504 Ma to 605 Ma). The samples from the northern part of the basin consistently contain Paleoproterozoic and Archean zircon grains that may have been derived from the Tuva-Mongol massif and/or the Siberian craton. In contrast, samples from the southern part of the basin contain only a minor component of early Paleozoic to Neoproterozoic zircon grains, which were derived from the crystalline basement bounding the Hangay-Hentey basin. Integrating all the age results from this study, we suggest that the Hangay-Hentey basin was developed between an island-arc system with a Neoproterozoic basement in the south and an Andean continental-margin arc in the north. The initiation of the southern arc occurred at or after the

A Cambrian mixed carbonate-siliciclastic platform in SW Gondwana: evidence from the Western Sierras Pampeanas (Argentina) and implications for the early Paleozoic paleogeography of the proto-Andean margin

NASA Astrophysics Data System (ADS)

Ramacciotti, Carlos D.; Casquet, César; Baldo, Edgardo G.; Galindo, Carmen; Pankhurst, Robert J.; Verdecchia, Sebastián O.; Rapela, Carlos W.; Fanning, Mark

2018-05-01

The Western Sierras Pampeanas (WSP) of Argentina record a protracted geological history from the Mesoproterozoic assembly of the Rodinia supercontinent to the early Paleozoic tectonic evolution of SW Gondwana. Two well-known orogenies took place at the proto-Andean margin of Gondwana in the Cambrian and the Ordovician, i.e., the Pampean (545-520 Ma) and Famatinian (490-440 Ma) orogenies, respectively. Between them, an extensive continental platform was developed, where mixed carbonate-siliciclastic sedimentation occurred. This platform was later involved in the Famatinian orogeny when it underwent penetrative deformation and metamorphism. The platform apparently extended from Patagonia to northwestern Argentina and the Eastern Sierras Pampeanas, and has probable equivalents in SW Africa, Peru, and Bolivia. The WSP record the outer (deepest) part of the platform, where carbonates were deposited in addition to siliciclastic sediments. Detrital zircon U-Pb SHRIMP ages from clastic metasedimentary successions and Sr-isotope compositions of marbles from the WSP suggest depositional ages between ca. 525 and 490 Ma. The detrital zircon age patterns further suggest that clastic sedimentation took place in two stages. The first was sourced mainly from re-working of the underlying Neoproterozoic metasedimentary rocks and the uplifted core of the early Cambrian Pampean orogen, without input from the Paleoproterozoic Río de la Plata craton. Sediments of the second stage resulted from the erosion of the still emerged Pampean belt and the Neoproterozoic Brasiliano orogen in the NE with some contribution from the Río de la Plata craton. An important conclusion is that the WSP basement was already part of SW Gondwana in the early Cambrian, and not part of the exotic Precordillera/Cuyania terrane, as was previously thought.

Late Paleozoic to Cenozoic reconstruction of the Arctic

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

Smith, D.G.

1985-04-01

The plate tectonic evolution of the Arctic is reassessed in the context of the known histories of the North Atlantic and North Pacific Oceans, and of the tectono-stratigraphic development of the lands around the Arctic Ocean. Computer map-drawing facilities were used to provide geometrical constraints on the reconstructions, which are presented to in the form of eight palinispatic maps. Stratigraphic similarities among presently dispersed continental areas identify fragments of a former Barents plate. Collision of this plate with the Euramerican plate was the cause of the Late Devonian Ellesmerian orogeny. In later Paleozoic time, the Siberian continent also joined Pangeamore » by collision with the combined Barents and Euramerican plates along the Ural-Taymyr suture. The Mesozoic-Cenozoic history of the Arctic is concerned with the fragmentation and dispersal of the former Barents plate, as well as the accretion of new continental fragments from the Pacific.« less

Paleozoic and Lower Mesozoic magmas from the eastern Klamath Mountains (North California) and the geodynamic evolution of northwestern America

NASA Astrophysics Data System (ADS)

Lapierre, H.; Brouxel, M.; Albarede, F.; Coulin, C.; Lecuyer, C.; Martin, P.; Mascle, G.; Rouer, O.

1987-09-01

The Paleozoic to Early Mesozoic geology of the eastern Klamath Mountains (N California) is characterized by three major magmatic events of Ordovician, Late Ordovician to Early Devonian, and Permo-Triassic ages. The Ordovician event is represented by a calc-alkalic island-arc sequence (Lovers Leap Butte sequence) developed in the vicinity of a continental margin. The Late Ordovician to Early Devonian event consists of the 430-480 Ma old Trinity ophiolite formed during the early development of a marginal basin, and a series of low-K tholeiitic volcanic suites (Lovers Leap Basalt—Keratophyre unit, Copley and Balaklala Formations) belonging to intraoceanic island-arcs. Finally, the Permo-Triassic event gave rise to three successives phases of volcanic activity (Nosoni, Dekkas and Bully Hill) represented by the highly differentiated basalt-to-rhyolite low-K tholeiitic series of mature island-arcs. The Permo-Triassic sediments are indicative of shallow to moderate depth in an open, warm sea. The geodynamic evolution of the eastern Klamath Mountains during Paleozoic to Early Mesozoic times is therefore constrained by the geological, petrological and geochemical features of its island-arcs and related marginal basin. A consistent plate-tectonic model is proposed for the area, consisting of six main stages: (1) development during Ordovician times of a calc-alkalic island-arc in the vicinity of a continental margin; (2) extrusion during Late Ordovician to Silurian times of a primitive basalt-andesite intraoceanic island-arc suite, which terminated with boninites, the latter suggest rifting in the fore-arc, followed by the breakup of the arc; (3) opening and development of the Trinity back-arc basin around 430-480 Ma ago; (4) eruption of the Balaklala Rhyolite either in the arc or in the fore-arc, ending in Early Devonian time with intrusion of the 400 Ma Mule Mountain stock; (5) break in volcanic activity from the Early Devonian to the Early Permian; and (6) development of

The Juchatengo complex: an upper-level ophiolite assemblage of late Paleozoic age in Oaxaca, southern Mexico

NASA Astrophysics Data System (ADS)

Grajales-Nishimura, José Manuel; Ramos-Arias, Mario Alfredo; Solari, Luigi; Murillo-Muñetón, Gustavo; Centeno-García, Elena; Schaaf, Peter; Torres-Vargas, Ricardo

2018-04-01

The Juchatengo complex (JC) suite is located between the Proterozoic Oaxacan complex to the north and the Xolapa complex to the south, and was amalgamated by late Paleozoic magmatism. It consists of mafic and sedimentary rocks that have oceanic affinities, with internal pseudostratigraphic, structural and metamorphic characteristics, which resemble a typical upper-level ophiolite assemblage. New U-Pb zircon and previous hornblende K-Ar analyses yield ages of ca. 291-313 Ma (U-Pb) for plagiogranites and ca. 282-277 Ma for tonalites intruding the entire sequence, including pelagic sediments at the top, with a maximum deposition age of ca. 278 Ma and noteworthy local provenance. These data constrain the age of the JC to the Late Pennsylvanian-Early Permian period. Hf isotopic analyses obtained from zircons in the JC plagiogranite and tonalite show that they come from a similar primitive mantle source (176Hf/177Hf: 0.282539-0.283091; ƐHf(t): + 3.2 to + 15.0). ƐHf(t) values from near 0 to - 2.8 in the tonalites indicate a contribution from the continental crust. Trace elements and REE patterns in whole rock and zircons point to a primitive mantle source for differentiated mafic, plagiogranite dykes and tonalitic plutons. Geochronological and geochemical data address the generation of new oceanic crust above the subduction zone, probably in a backarc setting. In this tectonic scenario, the JC ophiolite originated due to the convergence of the paleo-Pacific plate below the already integrated Oaxacan and Acatlán complexes in western Pangea. The dextral displacement places the deformation in a transtensional regime during the late Paleozoic age.

Early to Middle Ordovician back-arc basin in the southern Appalachian Blue Ridge: characteristics, extent, and tectonic significance

USGS Publications Warehouse

Tull, James; Holm-Denoma, Christopher S.; Barineau, Clinton I.

2014-01-01

Fault-dismembered segments of a distinctive, extensive, highly allochthonous, and tectonically significant Ordovician (ca. 480–460 Ma) basin, which contains suites of bimodal metavolcanic rocks, associated base metal deposits, and thick immature deep-water (turbiditic) metasediments, occur in parts of the southern Appalachian Talladega belt, eastern Blue Ridge, and Inner Piedmont of Alabama, Georgia, and North and South Carolina. The basin's predominantly metasedimentary strata display geochemical and isotopic evidence of a mixed provenance, including an adjacent active volcanic arc and a provenance of mica (clay)-rich sedimentary and felsic plutonic rocks consistent with Laurentian (Grenvillian) upper-crustal continental rocks and their passive-margin cover sequences. Geochemical characteristics of the subordinate intercalated bimodal metavolcanic rocks indicate formation in a suprasubduction environment, most likely a back-arc basin, whereas characteristics of metasedimentary units suggest deposition above Neoproterozoic rift and outer-margin lower Paleozoic slope and rise sediments within a marginal basin along Ordovician Laurentia's Iapetus margin. This tectonic setting indicates that southernmost Appalachian Ordovician orogenesis (Taconic orogeny) began as an extensional accretionary orogen along the outer margin of Laurentia, rather than in an exotic (non-Laurentian) arc collisional setting. B-type subduction polarity requires that the associated arc-trench system formed southeast of the palinspastic position of the back-arc basin. This scenario can explain several unique features of the southern Appalachian Taconic orogen, including: the palinspastic geographic ordering of key tectonic elements (i.e., back-arc, arc, etc.), and a lack of (1) an obducted arc sensu stricto on the Laurentian margin, (2) widespread Ordovician regional metamorphism, and (3) Taconic klippen to supply detritus to the Taconic foreland basin.

Shale hydrocarbon reservoirs: some influences of tectonics and paleogeography during deposition: Chapter 2

USGS Publications Warehouse

Eoff, Jennifer D

2014-01-01

Fundamental to any of the processes that acted during deposition, however, was active tectonism. Basin type can often distinguish self-sourced shale plays from other types of hydrocarbon source rocks. The deposition of North American self-sourced shale was associated with the assembly and subsequent fragmentation of Pangea. Flooded foreland basins along collisional margins were the predominant depositional settings during the Paleozoic, whereas deposition in semirestricted basins was responsible along the rifted passive margin of the U.S. Gulf Coast during the Mesozoic. Tectonism during deposition of self-sourced shale, such as the Upper Jurassic Haynesville Formation, confined (re)cycling of organic materials to relatively closed systems, which promoted uncommonly thick accumulations of organic matter.

Paleozoic magmatism and porphyry Cu-mineralization in an evolving tectonic setting in the North Qilian Orogenic Belt, NW China

NASA Astrophysics Data System (ADS)

Qiu, Kun-Feng; Deng, Jun; Taylor, Ryan D.; Song, Kai-Rui; Song, Yao-Hui; Li, Quan-Zhong; Goldfarb, Richard J.

2016-05-01

The NWW-striking North Qilian Orogenic Belt records the Paleozoic accretion-collision processes in NW China, and hosts Paleozoic Cu-Pb-Zn mineralization that was temporally and spatially related to the closure of the Paleo Qilian-Qinling Ocean. The Wangdian Cu deposit is located in the eastern part of the North Qilian Orogenic Belt, NW China. Copper mineralization is spatially associated with an altered early Paleozoic porphyritic granodiorite, which intruded tonalites and volcaniclastic rocks. Alteration zones surrounding the mineralization progress outward from a potassic to a feldspar-destructive phyllic assemblage. Mineralization consists mainly of quartz-sulfide stockworks and disseminated sulfides, with ore minerals chalcopyrite, pyrite, molybdenite, and minor galena and sphalerite. Gangue minerals include quartz, orthoclase, biotite, sericite, and K-feldspar. Zircon LA-ICPMS U-Pb dating of the ore-bearing porphyritic granodiorite yielded a mean 206Pb/238U age of 444.6 ± 7.8 Ma, with a group of inherited zircons yielding a mean U-Pb age of 485 ± 12 Ma, consistent with the emplacement age (485.3 ± 6.2 Ma) of the barren precursor tonalite. Rhenium and osmium analyses of molybdenite grains returned model ages of 442.9 ± 6.8 Ma and 443.3 ± 6.2 Ma, indicating mineralization was coeval with the emplacement of the host porphyritic granodiorite. Rhenium concentrations in molybdenite (208.9-213.2 ppm) suggest a mantle Re source. The tonalities are medium-K calc-alkaline. They are characterized by enrichment of light rare-earth elements (LREEs) and large-ion lithophile elements (LILEs), depletion of heavy rare-earth elements (HREEs) and high-field-strength elements (HFSEs), and minor negative Eu anomalies. They have εHf(t) values in the range of +3.6 to +11.1, with two-stage Hf model ages of 0.67-1.13 Ga, suggesting that the ca. 485 Ma barren tonalites were products of arc magmatism incorporating melts from the mantle wedge and the lithosphere. In contrast, the

Detrital zircon U-Pb geochronology, Lu-Hf isotopes and REE geochemistry constrains on the provenance and tectonic setting of Indochina Block in the Paleozoic

NASA Astrophysics Data System (ADS)

Wang, Ce; Liang, Xinquan; Foster, David A.; Fu, Jiangang; Jiang, Ying; Dong, Chaoge; Zhou, Yun; Wen, Shunv; Van Quynh, Phan

2016-05-01

In situ U-Pb geochronology, Lu-Hf isotopes and REE geochemical analyses of detrital zircons from Cambrian-Devonian sandstones in the Truong Son Belt, central Vietnam, are used to provide the information of provenance and tectonic evolution of the Indochina Block. The combined detrital zircon age spectra of all of the samples ranges from 3699 Ma to 443 Ma and shows with dominant age peaks at ca. 445 Ma and 964 Ma, along with a number of age populations at 618-532 Ma, 1160-1076 Ma, 1454 Ma, 1728 Ma and 2516 Ma. The zircon age populations are similar to those from time equivalent sedimentary sequences in continental blocks disintegrated from the East Gondwana during the Phanerozoic. The younger zircon grains with age peaks at ca. 445 Ma were apparently derived from middle Ordovician-Silurian igneous and metamorphic rocks in Indochina. Zircons with ages older than about 600 Ma were derived from other Gondwana terrains or recycled from the Precambrian basement of the Indochina Block. Similarities in the detrital zircon U-Pb ages suggest that Paleozoic strata in the Indochina, Yangtze, Cathaysia and Tethyan Himalayas has similar provenance. This is consistent with other geological constrains indicating that the Indochina Block was located close to Tethyan Himalaya, northern margin of the India, and northwestern Australia in Gondwana.

The Influence of the Ufimian Tectonic Concentric Structure on the Hydrocarbon Migration and Ore Genesis

NASA Astrophysics Data System (ADS)

Filippov, V. A.

2018-01-01

The Ufimian tectonic concentric structure (UTC) is a regional structure with concentric and zonal structure of the internal gravity field. In the Neoproterozoic this structure was at higher hypsometric level relative to the Bashkir Meganticlinorium. The most significant uplift of this tectonic concentric structure happened at the beginning of the Karatau time ( 825 Ma) and was accompanied by the formation of a ring fractured zone, favorable for hydrocarbon migration from the Lower Riphean black shales. Due to this, bitumens with higher Mo content in the Neoproterozoic and Paleozoic deposits are confined spatially to this zone. The bitumenosity of the Neoproterozoic deposits on the southern slope of the Ufimian tectonic concentric structure could have contributed to the formation of complex Cu-Ag-Mo-Re ores (copper sands) at the upper boundary of terrigenous red deposits of the Zilmerdak Formation. Positive structures identified in the Neoproterozoic deposits near the margin of the Ufimian tectonic concentric structure are considered to be promising for searching for hydrocarbon fields.

The Links Between the Formation of the Gulf of Mexico and the Late Proterozoic to Mesozoic Tectonic Evolution of Southern North America

NASA Astrophysics Data System (ADS)

Keller, G. R.; Mickus, K. L.; Gurrola, H.; Harry, D. L.; Pulliam, J.

2016-12-01

A full understanding of the Gulf of Mexico's geologic history depends on understanding the tectonic framework along the southern margin of North America. The first step in establishing this framework was the breakup of Laurentia during the Early Paleozoic. At least one tectonic block rifted away from Laurentia's southern margin at this time, and is interpreted to be presently located in Argentina. Rifting resulted in a sinuous margin consisting of alternating ridge and transform segments extending from the southeastern U.S. across Texas into northern Mexico. The Paleozoic margin is associated with a clearly defined gravity high, and ends in the trend of this high are associated with intersections of ridge and transform segments along the margin. By the end of the Paleozoic, continental assembly via the Appalachian-Ouachita orogeny added new terranes to the eastern and southern margins of Laurentia and the assembly of the supercontinent Pangea was complete. Triassic through Late Jurassic opening of the Gulf of Mexico (GOM) created a complex margin, initially mobilizing several crustal blocks that were eventually left behind on the North American margin as seafloor spreading developed within the Gulf and the Yucatan block separated and rotated into its current position. Recent deep seismic reflection profiles along the northern margin of the GOM show that rifted continental crust extends offshore for 250 km before the oceanic crust of the Gulf of Mexico is encountered. Our group has worked to produce four integrated models of the lithospheric structure based upon reflection, refraction, and teleseismic data acquired across this margin integrated with gravity, magnetic, geologic and drilling data. These models define a complex zone of crustal thinning along the Gulf Coastal plain of Texas that is covered by up to 10km of primarily Cretaceous and younger sedimentary rocks. To the east along the coastal plain region, we have defined two large crustal blocks that were

Linking the southern West Junggar terrane to the Yili Block: Insights from the oldest accretionary complexes in West Junggar, NW China

NASA Astrophysics Data System (ADS)

Ren, Rong; Han, Bao-Fu; Guan, Shu-Wei; Liu, Bo; Wang, Zeng-Zhen

2018-06-01

West Junggar is known to tectonically correlate with East Kazakhstan; however, the tectonic link of the southern West Junggar terrane to adjacent regions still remains uncertain. Here, we examined the oldest accretionary complexes, thus constraining its tectonic evolution and link during the Early-Middle Paleozoic. They have contrasting lithologic, geochemical, and geochronological features and thus, provenances and tectonic settings. The Laba Unit was derived from the Late Ordovician-Early Devonian continental arc system (peaking at 450-420 Ma) with Precambrian substrate, which formed as early as the Early Devonian and metamorphosed during the Permian; however, the Kekeshayi Unit was accumulated in an intra-oceanic arc setting, and includes the pre-Late Silurian and Late Silurian subunits with or without Precambrian sources. Integrated with the regional data, the southern West Junggar terrane revealed a tectonic link to the northern Yili Block during the Late Silurian to Early Devonian, as suggested by the comparable Precambrian zircon age spectra between the southern West Junggar terrane and the micro-continents in the southern Kazakhstan Orocline, the proximal accumulation of the Laba Unit in the continental arc atop the Yili Block, and the sudden appearance of Precambrian zircons in the Kekeshayi Unit during the Late Silurian. This link rejects the proposals of the southern West Junggar terrane as an extension of the northern Kazakhstan Orocline and the Middle Paleozoic amalgamation of West Junggar. A new linking model is thus proposed, in which the southern West Junggar terrane first evolved individually, and then collided with the Yili Block to constitute the Kazakhstan continent during the Late Silurian. The independent and contrasting intra-oceanic and continental arcs also support the Paleozoic archipelago-type evolution of the Central Asian Orogenic Belt.

Biostratigraphy and petrography of upper Paleozoic rocks of Sierra Las Pintas, northern Baja California

NASA Astrophysics Data System (ADS)

Navas-Parejo, Pilar; Lara-Peña, R. Aaron; Torres-Martínez, Miguel Angel; Martini, Michelangelo

2018-07-01

A transported crinoid fauna is herein described for the first time in the Paleozoic succession cropping out in the Sierra Las Pintas, northern Baja California, northwestern Mexico. The fossil association includes Heterostelechus texanus Moore and Jeffords, Preptopremnum laeve? Moore and Jeffords, and Mooreanteris perforatus Moore and Jeffords, which indicates a Middle Pennsylvanian-early Permian time-averaged age. The studied area corresponds with the northernmost outcrop of definitely late Paleozoic deep-water facies in northwestern Mexico and the southern United States. Petrographic analyses indicate that the studied metasandstones were primarily derived from high-grade metamorphic rocks and from a shallow-water platform environment dominated by crinoid meadows. These results allow the correlation of the studied metasedimentary rocks with the Carboniferous Rancho Nuevo Formation of the Sonora allochthon, which crops out in central Sonora. The Sonora allochthon includes an Early Ordovician-Late Pennsylvanian sedimentary succession that was deposited in the oceanic basin located south of the Laurentian craton. Therefore, upper Paleozoic metasedimentary rocks of the Sierra Las Pintas were deposited along the same continental margin of Laurentia as those rocks in the Sonora allochthon, and were mostly derived from metamorphic rocks of the continental craton and by the typical Carboniferous encrinites, which characterize the shallow-water rocks of central and northern Sonora.

New tectonic concept of the Arctic region evolution

NASA Astrophysics Data System (ADS)

Petrov, O. V.; Morozov, A.; Grikurov, G.; Shokalsky, S.; Kashubin, S.; Sobolev, N. V.; Petrov, E.

2012-12-01

The international project "Atlas of Geological Maps of Circumpolar Arctic at 1:5 million scale" was launched in 2003. It was initiated by geological surveys of Circum-Arctic states with active support from the UNESCO Commission for the Geological Map of the World (CGMW). This work engages a number of scientists from national academies of sciences and universities. As of today, international working groups have accomplished the compilation of geological, magnetic and gravity maps at 1:5 million scale. Upon completion of those basic maps, it became possible to undertake the compilation of the Tectonic Map of the Arctic - TeMAr. The final draft of this map is being demonstrated at GeoExpo here in Brisbane. Analysis of the new tectonic map clearly shows the Neoproterozoic - Paleozoic - late Mesozoic Paleoasian oceanic structures. Among those structures are the Neoproterozoic Timan Orogen, the Baikalian fold basement in the Pre-Yenisey zone and the collisional systems of Uralides and Kimmerides whose age becomes successively younger northward from Late Carboniferous - Early Permian to Triassic - Jurassic. Seismic and isotope-geochemistry data recently obtained on Lomonosov Ridge and Mendeleev Rise suggest the possibility that Neoproterozoic-Mesozoic orogenic structures of the High Arctic may incorporate isolated blocks of Early Precambrian continental crust. The north-directed decrease of age refers not only to orogenies caused by gradual closing of the Asian paleo-ocean but also to post-orogenic rift-related processes superposed on continental crust and reflected in the first place in the formation of LIPs. This is well exemplified by transition from the Early Triassic Siberian trap province to Triassic West Siberian province and then to Late Jurassic - Cretaceous, locally Cenozoic basaltic province of the High Arctic. The center of the Canadian Basin so far remains enigmatic: it was probably formed by seafloor spreading that could follow intensive Jurassic-Early

A- and I-type metagranites from the North Shahrekord Metamorphic Complex, Iran: Evidence for Early Paleozoic post-collisional magmatism

NASA Astrophysics Data System (ADS)

Badr, Afsaneh; Davoudian, Ali Reza; Shabanian, Nahid; Azizi, Hossein; Asahara, Yoshihiro; Neubauer, Franz; Dong, Yunpeng; Yamamoto, Koshi

2018-02-01

The North Shahrekord Metamorphic Complex (NSMC) of the central Sanandaj-Sirjan Zone (SaSZ) consists of metagranitoid bodies, which were metamorphosed within high pressure-low temperature conditions. Whole rock chemistry shows relatively high amounts of SiO2 (65-77 wt%) and Al2O3 (12-15 wt%), low amounts of Nb, P, Sr, Ti, a high ratio of Ga/Al (4-9) and a negative Eu anomaly. The chemical compositions of metagranites are reasonably similar to A- and I-type granites. U-Pb zircon ages of three samples of metagranites indicate that crystallization of the granites occurred at 521.6 ± 9.1 to 513.5 ± 8.5 Ma, Middle Cambrian. The initial 87Sr/86Sr and 143Nd/144Nd ratios of samples vary from 0.7057-0.7239 and 0.511801-0.511890, respectively. High initial 87Sr/86Sr ratios and low εNd(t) values (- 3.39 to - 1.07) associated with high ratios of 206Pb/204Pb(t) = 17.8557-18.8045, 207Pb/204Pb(t) = 15.6721-15.7220, and 208Pb/204Pb(t) = 37.7490-38.4468 infer a significant contribution of continental crust in generating the source magma of the metagranite bodies. The results reveal that the metagranites were mainly produced through mixing of basaltic melts with components similar to metasedimentary sources. The new results show that crystallization of the metagranites occurred in Early Paleozoic times and much earlier than break-up and drifting of the SaSZ from the Arabian plate, suggesting that the metagranites were mainly produced in the western Iran after the closure of the Proto-Tethys Ocean. This model is consistent with the previously suggested models for formation of an Early Paleozoic granitoid belt along the northern rim of Gondwana.

Recent advances on the tectonic and magmatic evolution of the Greater Tibetan Plateau: A special issue in honor of Prof. Guitang Pan

NASA Astrophysics Data System (ADS)

Zhu, Di-Cheng; Chung, Sun-Lin; Niu, Yaoling

2016-02-01

The Greater Tibetan Plateau, also known in China as the Qinghai-Tibet Plateau or the Qingzang Plateau, is a tectonic amalgamation of numbers of continental collision events from the northwest in the early Paleozoic to the southwest in the Cenozoic (cf. Dewey et al., 1988; Pan et al., 2012; Yin and Harrison, 2000). These collision events resulted in orogenic belts that record the prolonged albeit complex histories of opening and closing of Tethyan ocean basins and associated tectonic and magmatic responses (cf. Chung et al., 2005; Pan et al., 2012; Song et al., 2014; Yin and Harrison, 2000; Zhu et al., 2013, 2015). Although many aspects related to these events have been recently synthesized with elegance by Pan et al. (2012) and Zhu et al. (2013) using data and observations made available since 2000, many scientific questions, such as the duration of oceanic basins, the collisional and accretionary processes of different terranes, the processes responsible for crustal growth, and the mechanisms for economic mineralization, remain underdeveloped and require further investigations with additional data.

Elucidating tectonic events and processes from variably tectonized conglomerate clast detrital geochronology: examples from the Hongliuhe Formation in the southern Central Asian Orogenic Belt, NW China

NASA Astrophysics Data System (ADS)

Cleven, Nathan; Lin, Shoufa; Davis, Donald; Xiao, Wenjiao; Guilmette, Carl

2017-04-01

This work expands upon detrital zircon geochronology with a sampling and analysis strategy dating granitoid conglomerate clasts that exhibit differing degrees of internal ductile deformation. As deformation textures within clastic material reflect the variation and history of tectonization in the source region of a deposit, we outline a dating methodology that can provide details of the provenance's tectonomagmatic history from deformation-relative age distributions. The method involves bulk samples of solely granitoid clasts, as they are representative of the magmatic framework within the provenance. The clasts are classified and sorted into three subsets: undeformed, slightly deformed, and deformed. LA-ICPMS U-Pb geochronology is performed on zircon separates of each subset. Our case study, involving the Permian Hongliuhe Formation in the southern Central Asian Orogenic Belt, analyzes each of the three clast subsets, as well as sandstone detrital samples, at three stratigraphic levels to yield a profile of the unroofed provenance. The age spectra of the clast samples exhibit different, wider distributions than sandstone samples, considered an effect of proximity to the respective provenance. Comparisons of clast data to sandstone data, as well as comparisons between stratigraphic levels, yield indications of key tectonic processes, in addition to the typical characteristics provided by detrital geochronology. The clast data indicates a minimal lag time, implying rapid exhumation rates, whereas sandstone data alone would indicate a 90 m.y. lag time. Early Paleozoic arc building episodes appear as Ordovician peaks in sandstone data, and Silurian-Devonian peaks in clast data, indicating a younging of magmatism towards the proximal provenance. A magmatic hiatus starts in the Devonian, correlating with the latest age of deformed clasts, interpreted as timing of collisional tectonics. Provenance interpretation using the correlations seen between the clast and sandstone

Paleozoic magmatism and porphyry Cu-mineralization in an evolving tectonic setting in the North Qilian Orogenic Belt, NW China

USGS Publications Warehouse

Qiu, Kun-Feng; Deng, Jun; Taylor, Ryan D.; Song, Kai-Rui; Song, Yao-Hui; Li, Quan-Zhong; Goldfarb, Richard J.

2016-01-01

The NWW-striking North Qilian Orogenic Belt records the Paleozoic accretion–collision processes in NW China, and hosts Paleozoic Cu–Pb–Zn mineralization that was temporally and spatially related to the closure of the Paleo Qilian-Qinling Ocean. The Wangdian Cu deposit is located in the eastern part of the North Qilian Orogenic Belt, NW China. Copper mineralization is spatially associated with an altered early Paleozoic porphyritic granodiorite, which intruded tonalites and volcaniclastic rocks. Alteration zones surrounding the mineralization progress outward from a potassic to a feldspar-destructive phyllic assemblage. Mineralization consists mainly of quartz-sulfide stockworks and disseminated sulfides, with ore minerals chalcopyrite, pyrite, molybdenite, and minor galena and sphalerite. Gangue minerals include quartz, orthoclase, biotite, sericite, and K-feldspar. Zircon LA-ICPMS U–Pb dating of the ore-bearing porphyritic granodiorite yielded a mean 206Pb/238U age of 444.6 ± 7.8 Ma, with a group of inherited zircons yielding a mean U–Pb age of 485 ± 12 Ma, consistent with the emplacement age (485.3 ± 6.2 Ma) of the barren precursor tonalite. Rhenium and osmium analyses of molybdenite grains returned model ages of 442.9 ± 6.8 Ma and 443.3 ± 6.2 Ma, indicating mineralization was coeval with the emplacement of the host porphyritic granodiorite. Rhenium concentrations in molybdenite (208.9–213.2 ppm) suggest a mantle Re source. The tonalities are medium-K calc-alkaline. They are characterized by enrichment of light rare-earth elements (LREEs) and large-ion lithophile elements (LILEs), depletion of heavy rare-earth elements (HREEs) and high-field-strength elements (HFSEs), and minor negative Eu anomalies. They have εHf(t) values in the range of +3.6 to +11.1, with two-stage Hf model ages of 0.67–1.13 Ga, suggesting that the ca. 485 Ma barren tonalites were products of arc magmatism incorporating melts from the mantle wedge and

Tectono-thermal evolution of the southwestern Alxa Tectonic Belt, NW China: Constrained by apatite U-Pb and fission track thermochronology

NASA Astrophysics Data System (ADS)

Song, Dongfang; Glorie, Stijn; Xiao, Wenjiao; Collins, Alan S.; Gillespie, Jack; Jepson, Gilby; Li, Yongchen

2018-01-01

The Central Asian Orogenic Belt (CAOB) is regarded to have undergone multiple phases of intracontinental deformation during the Meso-Cenozoic. Located in a key position along the southern CAOB, the Alxa Tectonic Belt (ATB) connects the northernmost Tibetan Plateau with the Mongolian Plateau. In this paper we apply apatite U-Pb and fission track thermochronological studies on varieties of samples from the southwestern ATB, in order to constrain its thermal evolution. Precambrian bedrock samples yield late Ordovician-early Silurian ( 430-450 Ma) and late Permian ( 257 Ma) apatite U-Pb ages; the late Paleozoic magmatic-sedimentary samples yield relatively consistent early Permian ages from 276 to 290 Ma. These data reveal that the ATB experienced multiple Paleozoic tectono-thermal events, as the samples passed through the apatite U-Pb closure temperature ( 350-550 °C). We interpret these tectonic events to record the long-lived subduction-accretion processes of the Paleo-Asian Ocean during the formation of the southern CAOB, with possible thermal influence of the Permian Tarim mantle plume. Apatite fission track (AFT) data and thermal history modelling reveal discrete low-temperature thermal events for the ATB, inducing cooling/reheating through the AFT partial annealing zone ( 120-60 °C). During the Permian, the samples underwent rapid cooling via exhumation or denudation from deep crustal levels to temperatures < 200 °C. Subsequent thermal events in the Triassic were thought to be associated with the final amalgamation of the CAOB or the closure of the Paleotethys. During the Jurassic-Cretaceous the study area experienced heating by burial, followed by renewed cooling, which may be related with the construction and subsequent collapse of the Mongol-Okhotsk Orogeny, or the Lhasa-Eurasia collision and subsequent slab break-off. These results indicate that the ATB may have been stable after late Cretaceous in contrast to the Qilian Shan and Tianshan. Finally, our

A synthesis of Jurassic and Early Cretaceous crustal evolution along the southern margin of the Arctic Alaska–Chukotka microplate and implications for defining tectonic boundaries active during opening of Arctic Ocean basins

USGS Publications Warehouse

Till, Alison B.

2016-01-01

A synthesis of Late Jurassic and Early Cretaceous collision-related metamorphic events in the Arctic Alaska–Chukotka microplate clarifies its likely movement history during opening of the Amerasian and Canada basins. Comprehensive tectonic reconstructions of basin opening have been problematic, in part, because of the large size of the microplate, uncertainties in the location and kinematics of structures bounding the microplate, and lack of information on its internal deformation history. Many reconstructions have treated Arctic Alaska and Chukotka as a single crustal entity largely on the basis of similarities in their Mesozoic structural trends and similar late Proterozoic and early Paleozoic histories. Others have located Chukotka near Siberia during the Triassic and Jurassic, on the basis of detrital zircon age populations, and suggested that it was Arctic Alaska alone that rotated. The Mesozoic metamorphic histories of Arctic Alaska and Chukotka can be used to test the validity of these two approaches.A synthesis of the distribution, character, and timing of metamorphic events reveals substantial differences in the histories of the southern margin of the microplate in Chukotka in comparison to Arctic Alaska and places specific limitations on tectonic reconstructions. During the Late Jurassic and earliest Cretaceous, the Arctic Alaska margin was subducted to the south, while the Chukotka margin was the upper plate of a north-dipping subduction zone or a zone of transpression. An early Aptian blueschist- and greenschist-facies belt records the most profound crustal thickening event in the evolution of the orogen. It may have resulted in thicknesses of 50–60 km and was likely the cause of flexural subsidence in the foredeep of the Brooks Range. This event involved northern Alaska and northeasternmost Chukotka; it did not involve central and western Chukotka. Arctic Alaska and Chukotka evolved separately until the Aptian thickening event, which was likely a

Paleozoic Assemblage of the Northern Sierra Terrane: New Geochronology And Geochemical Data From the Stitching Late Devonian - Early Carboniferous Bowman Lake Batholith, and Associated Rocks

NASA Astrophysics Data System (ADS)

Powerman, V.; Hanson, R. E.; Girty, G.; Tretiakov, A.

2016-12-01

Previous study (Grove et al., 2008) of detrital zircon ages and the timing of magmatism within the Northern Sierra terrane (NST) suggest that it is exotic relative to western Laurentia, and link it to the Paleozoic Arctic Realm, Baltica and Caledonides. NST is a composite terrane in the North America Cordillera, consisting of four distinct allochthons, thrusted upon each other. As a first step towards the understanding of the origin and tectonic development of the NST we have undertaken the SHRIMP-RG U-Pb zircon dating of the rocks from granites, granodiorites, trondhjemites, tonalites and hypabyssal intrusions, composing the Bowman Lake batholith. The batholith stitches the allochthons of the NST and its crystallization age signifies the timing of juxtaposition SHRIMP-RG analyses from 14 samples yielded an age range of ca. 352-369 Ma, which overlaps the Devonian-Mississipian boundary and constrains the minimum age for amalgamation. Additionally, we have acquired multiple XRF data, favoring the island arc provenance of the Bowman Lake batholith Batholith. Previously proposed ties between NST and Robert Mountains allochthon seem unlikely because the latter was accreted onto the western miogeocline of Laurentia during the Late Dev.-Early Miss. while the NST was most probably still situated within the Arctic Realm. This work has been supported by the grant #14.Z50.31.0017 of the Government of the Russian Federation and by the Russian Foundation for Basic Research grant #15-55-10055. We are grateful to Stanford-USGS SHRIMP-RG center, and personally to Marty Grove and Elizabeth Miller.

Tectonic Recycling in the Paleozoic Ouachita Assemblage from U-Pb Detrital Zircon Studies

NASA Astrophysics Data System (ADS)

Gleason, J. D.; Gehrels, G. E.; Finney, S. C.

2001-05-01

The Paleozoic Ouachita deep-marine clastic sedimentary assemblage records a complex provenance over the course of its 200 m.y. history, with evidence for mixed sources and multiple dispersal paths. Combined neodymium and U-Pb detrital zircon work has established that most of the assemblage in Arkansas and Oklahoma is derived from Laurentian sources, meaning that regardless of the multiple pathways by which sediment was delivered to Ouachita seafloor, the material had its ultimate origin on the North American continent. More detailed work is in progress to elucidate specific dispersal paths, in particular for the middle to late Ordovician when a major change in provenance is recorded, and during the Carboniferous when voluminous turbidites entered the basin. We sampled three formations for U-Pb detrital zircon studies: the lower Middle Ordovician Blakely Sandstone, the Upper Ordovician/Lower Silurian Blaylock Sandstone, and the Pennsylvanian Jackfork Group. Individual zircon ages from these units document a major change in provenance between deposition of the Blakely Sandstone and Blaylock Sandstone, which is also reflected in the neodymium isotopic signature. Both units have a large population of Grenvillian-age zircons (1.0-1.2 Ga), and a less abundant population of 1.3-1.4 Ga zircons likely derived from sources in the mid-continent region. The Blakely Sandstone also contains abundant Archean zircons (2.5-2.7 Ga, likely derived from the Superior Province), and one grain apparently derived from the Penokean orogen (1.9 Ga). Zircon morphology (highly rounded, spherical), combined with the pure quartz sandstone lithology of the Blakely Sandstone, indicates very mature sedimentary sources. We conclude that zircons from this source were recycled ultimately from source terranes in the North American craton. This is reinforced by neodymium isotopes (eNd = -15), paleocurrents (from the north) and olistoliths (1.3 Ga granites), the latter indicating that Blakely turbidites

Foreland crustal structure of the New York recess, northeastern United States

USGS Publications Warehouse

Herman, G.C.; Monteverde, D.H.; Schlische, R.W.; Pitcher, D.M.

1997-01-01

A new structural model for the northeast part of the Central Appalachian foreland and fold-and-thrust belt is based on detailed field mapping, geophysical data, and balanced cross-section analysis. The model demonstrates that the region contains a multiply deformed, parautochthonous fold-and-thrust system of Paleozoic age. Our interpretations differ from previous ones in which the entire region north of the Newark basin was considered to be allochthonous. The new interpretation requires a substantial decrease in Paleozoic tectonic shortening northeastward from adjacent parts of the Central Appalachian foreland and illustrates the common occurrence of back-thrusting within the region. During early Paleozoic time northern New Jersey consisted of a Taconic orogenic foreland in which cover folds (F1) involved lower Paleozoic carbonate and flysch overlying Middle Proterozoic basement. F1 folds are open and upright in the foreland and more gently inclined to recumbent southeastward toward the trace of the Taconic allochthons. F1 structures were cut and transported by a fold-and-thrust system of the Allegheny orogeny. This thrust system mostly involves synthetic faults originating from a master decollement rooted in Proterozoic basement. Antithetic faults locally modify early synthetic overthrusts and S1 cleavage in lower Paleozoic cover and show out-of-sequence structural development. The synthetic parts of the regional thrust system are bounded in the northwestern foreland by blind antithetic faults interpreted from seismic-reflection data. This antithetic faulting probably represents Paleozoic reactivation of Late Proterozoic basement faults. Tectonic contraction in overlying cover occurred by wedge faulting where synthetic and antithetic components of the foreland fault system overlap. S2 cleavage in the Paleozoic cover stems from Alleghanian shortening and flattening and commonly occurs in the footwall of large overthrust sheets. Paleozoic structures in Proterozoic

Metamorphism, Plate Tectonics, and the Supercontinent Cycle

NASA Astrophysics Data System (ADS)

Brown, Michael

Granulite facies ultrahigh temperature metamorphism (G-UHTM) is documented in the rock record predominantly from Neoarchean to Cambrian; G-UHTM facies series rocks may be inferred at depth in younger, particularly Cenozoic orogenic systems. The first occurrence of G-UHTM in the rock record signifies a change in geodynamics that generated transient sites of very high heat flow. Many G-UHTM belts may have developed in settings analogous to modern continental backarcs. On a warmer Earth, the cyclic formation of supercontinents and their breakup, particularly by extroversion, which involved destruction of ocean basins floored by thinner lithosphere, may have generated hotter continental backarcs than those associated with the modern Pacific rim. Medium-temperature eclogite, high-pressure granulite metamorphism (E-HPGM), is also first recognized in the Neoarchean rock record and occurs at intervals throughout the Proterozoic and Paleozoic rock record. E-HPGM belts are complementary to G-UHTM belts and are generally inferred to record subduction-to-collision orogenesis. Blueschists become evident in the Neoproterozoic rock record; they record the low thermal gradients associated with modern subduction. Lawsonite blueschists and eclogites (high-pressure metamorphism, HPM) and ultrahigh pressure metamorphism (UHPM) characterized by coesite (±lawsonite) or diamond are predominantly Phanerozoic phenomena. HPM-UHPM registers the low thermal gradients and deep subduction of continental crust during the early stage of the collision process in Phanerozoic subduction-to-collision orogens. Although perhaps counterintuitive, many HPM-UHPM belts appear to have developed by closure of small ocean basins in the process of accretion of a continental terrane during a period of supercontinent introversion (Wilson cycle ocean basin opening and closing). A duality of metamorphic belts—reflecting a duality of thermal regimes—appears in the record only since the Neoarchean Era. A

Pacing of Paleozoic macroevolutionary rates by Milankovitch grand cycles.

PubMed

Crampton, James S; Meyers, Stephen R; Cooper, Roger A; Sadler, Peter M; Foote, Michael; Harte, David

2018-05-29

Periodic fluctuations in past biodiversity, speciation, and extinction have been proposed, with extremely long periods ranging from 26 to 62 million years, although forcing mechanisms remain speculative. In contrast, well-understood periodic Milankovitch climate forcing represents a viable driver for macroevolutionary fluctuations, although little evidence for such fluctuation exists except during the Late Cenozoic. The reality, magnitude, and drivers of periodic fluctuations in macroevolutionary rates are of interest given long-standing debate surrounding the relative roles of intrinsic biotic interactions vs. extrinsic environmental factors as drivers of biodiversity change. Here, we show that, over a time span of 60 million years, between 9 and 16% of the variance in biological turnover (i.e., speciation probability plus species extinction probability) in a major Early Paleozoic zooplankton group, the graptoloids, can be explained by long-period astronomical cycles (Milankovitch "grand cycles") associated with Earth's orbital eccentricity (2.6 million years) and obliquity (1.3 million years). These grand cycles modulate climate variability, alternating times of relative stability in the environment with times of maximum volatility. We infer that these cycles influenced graptolite speciation and extinction through climate-driven changes to oceanic circulation and structure. Our results confirm the existence of Milankovitch grand cycles in the Early Paleozoic Era and show that known processes related to the mechanics of the Solar System were shaping marine macroevolutionary rates comparatively early in the history of complex life. We present an application of hidden Markov models to macroevolutionary time series and protocols for the evaluation of statistical significance in spectral analysis.

Delineation of tectonic provinces of New York state as a component of seismic-hazard evaluation

USGS Publications Warehouse

Fakundiny, R.H.

2004-01-01

Seismic-hazard evaluations in the eastern United States must be based on interpretations of the composition and form of Proterozoic basement-rock terranes and overlying Paleozoic strata, and on factors that can cause relative movements among their units, rather than Phanerozoic orogenic structures, which may be independent of modern tectonics. The tectonic-province concept is a major part of both probabilistic and deterministic seismic-hazard evaluations, yet those that have been proposed to date have not attempted to geographically correlate modern earthquakes with regional basement structure. Comparison of basement terrane (megablock) boundaries with the spatial pattern of modern seismicity may lead to the mechanically sound definition of tectonic provinces, and thus, better seismic-hazard evaluation capability than is currently available. Delineation of megablock boundaries will require research on the many factors that affect their structure and movement. This paper discusses and groups these factors into two broad categories-megablock tectonics in relation to seismicity and regional horizontal-compressive stresses, with megablock tectonics divided into subcategories of basement, overlying strata, regional lineaments, basement tectonic terranes, earthquake epicenter distribution, and epeirogeny, and compressive stresses divided into pop-ups and the contemporary maximum horizontal-compressive stress field. A list presenting four to nine proposed research topics for each of these categories is given at the end.

The Inskip Formation, the Harmony Formation, and the Havallah Sequence of Northwestern Nevada - An Interrelated Paleozoic Assemblage in the Home of the Sonoma Orogeny

USGS Publications Warehouse

Ketner, Keith B.

2008-01-01

An area between the towns of Winnemucca and Battle Mountain in northwestern Nevada, termed the arkosic triangle, includes the type areas of the middle to upper Paleozoic Inskip Formation and Havallah sequence, the Upper Devonian to Mississippian Harmony Formation, the Sonoma orogeny, and the Golconda thrust. According to an extensive body of scientific literature, the Havallah sequence, a diverse assemblage of oceanic rocks, was obducted onto the continent during the latest Permian or earliest Triassic Sonoma orogeny by way of the Golconda thrust. This has been the most commonly accepted theory for half a century, often cited but rarely challenged. The tectonic roles of the Inskip and Harmony Formations have remained uncertain, and they have never been fully integrated into the accepted theory. New, and newly interpreted, data are incompatible with the accepted theory and force comprehensive stratigraphic and tectonic concepts that include the Inskip and Harmony Formations as follows: middle to upper Paleozoic strata, including the Inskip, Harmony, and Havallah, form an interrelated assemblage that was deposited in a single basin on an autochthonous sequence of Cambrian, Ordovician, and lowest Silurian strata of the outer miogeocline. Sediments composing the Upper Devonian to Permian sequence entered the basin from both sides, arkosic sands, gravel, limestone olistoliths, and other detrital components entered from the west, and quartz, quartzite, chert, and other clasts from the east. Tectonic activity was expressed as: (1) Devonian uplift and erosion of part of the outer miogeocline; (2) Late Devonian depression of the same area, forming a trough, probably fault-bounded, in which the Inskip, Harmony, and Havallah were deposited; (3) production of intraformational and extrabasinal conglomerates derived from the basinal rocks; and (4) folding or tilting of the east side of the depositional basin in the Pennsylvanian. These middle to upper Paleozoic deposits were

Slowing extrusion tectonics: Lowered estimate of post-Early Miocene slip rate for the Altyn Tagh fault

USGS Publications Warehouse

Yue, Y.; Ritts, B.D.; Graham, S.A.; Wooden, J.L.; Gehrels, G.E.; Zhang, Z.

2004-01-01

Determination of long-term slip rate for the Altyn Tagh fault is essential for testing whether Asian tectonics is dominated by lateral extrusion or distributed crustal shortening. Previous slip-history studies focused on either Quaternary slip-rate measurements or pre-Early Miocene total-offset estimates and do not allow a clear distinction between rates based on the two. The magmatic and metamorphic history revealed by SHRIMP zircon dating of clasts from Miocene conglomerate in the Xorkol basin north of the Altyn Tagh fault strikingly matches that of basement in the southern Qilian Shan and northern Qaidam regions south of the fault. This match requires that the post-Early Miocene long-term slip rate along the Altyn Tagh fault cannot exceed 10 mm/year, supporting the hypothesis of distributed crustal thickening for post-Early Miocene times. This low long-term slip rate and recently documented large pre-Early Miocene cumulative offset across the fault support a two-stage evolution, wherein Asian tectonics was dominated by lateral extrusion before the end of Early Miocene, and since then has been dominated by distributed crustal thickening and rapid plateau uplift. ?? 2003 Elsevier B.V. All rights reserved.

Tethys and the evolution in Afghanistan: tectonics and mineral resources

NASA Astrophysics Data System (ADS)

Okaya, N.; Onishi, C. T.; Mooney, W. D.

2009-12-01

The tectonic history and mineral resources of Afghanistan are related to the closing of the Paleo-Tethys Ocean and the opening of the Neo-Tethys Ocean. As part of this process, oceanic sediments and continental fragments were accreted onto northern Afghanistan during the Mesozoic Cimmerian orogeny. Deposits in the Paleo-Tethys Ocean iare presently represented by a thick sequence of Paleozoic sedimentary rocks within the Tajik/Turan block, part of the Eurasian continent in northern Afghanistan. The accreted micro-continents of the Cimmerian orogeny include: (1) the Farah block, (2) the Helmand block and (3) the exotic Kabul block. Later, during the Cretaceous, the East Nuristan island arc and the intra-oceanic island arc of Kohistan were sutured. Major faults in Afghanistan include: (1) the Herat fault, an E-W suture zone between the Eurasia continent and the terrains of the Cimmerian orogeny; (2) the N-S Punjao suture located between the Farah and Helmand blocks; and (3) the NE-SW oriented Chaman fault, part of a transpressional plate boundary located near the border with Pakistan. Such a complex blend of geology and tectonics gives host to abundant mineral resources. We summarize the tectonic evolution of Afghanistan in a series of lithospheric cross-sections, beginning at about 400 Ma., and identify the mineral resources in the context of the regional tectonics.

Shifting locus of carbonate sedimentation and the trajectory of Paleozoic pCO2

NASA Astrophysics Data System (ADS)

Husson, J. M.; Peters, S. E.

2016-12-01

The burial of calcium carbonate is a determinant of planetary habitability, dictated by CO2 input to the surface environment and rates of chemical weathering. An important source of CO2 is the metamorphism of carbon-bearing sediments, which is responsive to the locus of sedimentation. For example, deep sea sediments are prone to recycling as sea floor is consumed at convergent margins; by contrast, sediments deposited on continental crust can be stable for billions of years.The predominant feature in the empirical sedimentary rock record, as measured by Macrostrat (https://macrostrat.org) and global geological syntheses, is a step-wise increase in continental sedimentation at the Neoproterozoic-Paleozoic transition. Although early Paleozoic carbonate volumes are sufficient to account for a CO2 flux 5x greater than present, Proterozoic continental burial fluxes were likely below the modern estimate. This observation implies that most carbonate sedimentation in the Proterozoic took place on the deep sea floor. The establishment of persistent, widespread continental flooding during the Paleozoic shifted the locus of carbonate sedimentation to continental interiors. A major implication of this shift is that CO2 flux declined during the Paleozoic as carbonate-laden Precambrian seafloor was metamorphosed and recycled. This prediction is consistent with independent proxy records and our model for Phanerozoic carbonate burial. An important corollary is that as carbonate-rich Precambrian seafloor was progressively destroyed, the carbonate content of deep sea sediments decreased concordantly because Paleozoic continents effectively captured global alkalinity fluxes. This process culminated near the Permian/Triassic, with metamorphic CO2 flux at a Phanerozoic minimum and the global ocean uniquely unbuffered against acidification. Such a condition could enhance the environmental effects of transient CO2 injections. Because the mid-Mesozoic appearance of pelagic calcifiers and

Philippine microplate tectonics and hydrocarbon exploration

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

Gallagher, J.J. Jr.

1986-07-01

Hydrocarbon traps in the Philippine Islands developed during a long, complex history of microplate tectonics. Carbonate and clastic stratigraphic traps formed during Mesozoic and early Cenozoic rifting and drifting. Hydrocarbons, generated in deep rift basins, migrated to the traps during drifting. Later Cenozoic compressional tectonic activity and concomitant faulting enhanced some traps and destroyed others. Seismic data offshore from Palawan Island reveal the early trap histories. Later trap histories can be interpreted from seismic, outcrop, and remote-sensing data. Understanding the microplate tectonic history of the Philippines is the key to interpreting trap histories.

High-resolution sequence stratigraphy of lower Paleozoic sheet sandstones in central North America: The role of special conditions of cratonic interiors in development of stratal architecture

USGS Publications Warehouse

Runkel, Anthony C.; Miller, J.F.; McKay, R.M.; Palmer, A.R.; Taylor, John F.

2007-01-01

Well-known difficulties in applying sequence stratigraphic concepts to deposits that accumulated across slowly subsiding cratonic interior regions have limited our ability to interpret the history of continental-scale tectonism, oceanographic dynamics of epeiric seas, and eustasy. We used a multi-disciplinary approach to construct a high-resolution stratigraphic framework for lower Paleozoic strata in the cratonic interior of North America. Within this framework, these strata proved readily amenable to modern sequence stratigraphic techniques that were formulated based on successions along passive margins and in foreland basins, settings markedly different from the cratonic interior. Parasequences, parasequence stacking patterns, systems tracts, maximum flooding intervals, and sequence-bounding unconformities can be confidently recognized in the cratonic interior using mostly standard criteria for identification. The similarity of cratonic interior and foreland basin successions in size, geometry, constituent facies, and local stacking patterns of nearshore parasequences is especially striking. This similarity indicates that the fundamental processes that establish shoreface morphology and determine the stratal expression of retreat and progradation were likewise generally the same, despite marked differences in tectonism, physiography, and bathymetry between the two settings. Our results do not support the widespread perception that Paleozoic cratonic interior successions are so anomalous in stratal geometries, and constitute such a poor record of time, that they are poorly suited for modern sequence stratigraphic analyses. The particular arrangement of stratal elements in the cratonic interior succession we studied is no more anomalous or enigmatic than the variability in architecture that sets all sedimentary successions apart from one another. Thus, Paleozoic strata of the cratonic interior are most appropriately considered as a package that belongs in a

The revised tectonic history of Tharsis

NASA Astrophysics Data System (ADS)

Bouley, Sylvain; Baratoux, David; Paulien, Nicolas; Missenard, Yves; Saint-Bézar, Bertrand

2018-04-01

Constraining the timing of the emplacement of the volcano-tectonic province of Tharsis is critical to understanding the evolution of mantle, surface environment and climate of Mars. The growth of Tharsis had exerted stresses on the lithosphere, which were responsible for tectonic deformation, previously mapped as radial or concentric faults. Insights into the emplacement history of Tharsis may be gained from an analysis of the characteristics and ages of these tectonic features. The number, total length, linear density of extensional or compressional faults in the Tharsis region and deformation rates are reported for each of the following 6 stages: Early and Middle Noachian (stage 1); Late Noachian (stage 2); Early Hesperian (stage 3); Late Hesperian (stage 4), Early Amazonian (stage 5) and Middle Amazonian to Late Amazonian (stage 6). 8571 Tharsis-related tectonic features (radial or concentric to the center of Tharsis) were assigned to one of these periods of time based on their relationship with stratigraphic units defined in the most recent geological map. Intense faulting at Tempe Terra, Claritas and Coracis Fossae and Thaumasia Planum confirms that tectonic deformation started during the Noachian. However, we report a peak in both compressive and extensive rates of deformation during the Early Hesperian whereas the quantitative indicators for compressional and extensional tectonics vary within less than one order of magnitude from the Late Noachian to the Late Hesperian. These observations indicate a protracted growth of Tharsis during the first quarter of Mars evolution and declining from 3 Gyrs ago.

Petrogenesis of granitoids and associated xenoliths in the early Paleozoic Baoxu and Enping plutons, South China: Implications for the evolution of the Wuyi-Yunkai intracontinental orogen

NASA Astrophysics Data System (ADS)

Yu, Yang; Huang, Xiao-Long; Sun, Min; He, Peng-Li

2018-05-01

The early Paleozoic Wuyi-Yunkai orogen was associated with extensive felsic magmatic activities and the orogenic core was mainly distributed in the Yunkai and Wugong domains located in the western Cathaysia block and in the Wuyi domain located in the central part of the Cathaysia block. In order to investigate the evolution of the Wuyi-Yunkai orogen, elemental and Sr-Nd isotopic analyses were performed for granites from the Baoxu pluton in the Yunkai domain and from the Enping pluton in the central part of the Cathaysia block. The Baoxu pluton consists of biotite granite with abundant xenoliths of gneissic granite, granodiorite and diorite, and the Enping pluton is mainly composed of massive granodiorite. Biotite granites (441 ± 5 Ma) and gneissic granite xenolith (443 ± 4 Ma) of the Baoxu pluton are all weakly peraluminous (A/CNK = 1.05-1.10). They show high Sr/Y and La/Yb ratios and have negative bulk-rock εNd(t) values (-7.0 to -4.4), which are similar to coeval gneissic S-type granites in the Yunkai domain and were probably derived from dehydration melting of a sedimentary source with garnet residue in the source. Granodiorites (429 ± 3 Ma) from Enping and granodiorite xenolith (442 ± 4 Ma) from Baoxu are metaluminous and have REE patterns with enriched light REE and flat middle to heavy REE, possibly generated by the dehydration melting of an igneous basement at middle to lower crustal level. Diorite xenolith from Baoxu is ultrapotassic (K2O = 4.9 wt%), has high contents of MgO (7.0 wt%), Cr (379 ppm) and Ni (171 ppm) and shows pronounced negative Nb, Ta and Ti anomalies. This xenolith also has negative εNd(t) value (-3.6) and low Rb/Ba and high Ba/Sr ratios, and is thus interpreted to be derived from an enriched lithospheric mantle with the breakdown of phlogopite. Early Paleozoic I- and S-type granites in the Wuyi-Yunkai orogen mostly have negative εNd(t) values and do not have juvenile components, consistent with genesis by an intracontinental

The Paleozoic ichthyofauna of the Amazonas and Parnaíba basins, Brazil

NASA Astrophysics Data System (ADS)

Figueroa, Rodrigo Tinoco; Machado, Deusana Maria da Costa

2018-03-01

The Brazilian Paleozoic ichthyofauna from the Parnaíba and Amazonas basins regard a sparsely known diversity, including chondrichthyans and acanthodians, besides some osteichthyan remains. This work proposes a revision of the fossil material from these two sedimentary basins and synthesizes the morphological aspect of such material trying to understand the influences of those fossils to the paleontology of the region, comparing the Brazilian fossils with other gondwanan faunas. The Brazilian Paleozoic fish fauna shows great resemblance to those of Bolivia, especially during the Devonian. Many of the Acanthodian spines from the Manacapuru Formation (Amazonas Basin), and the Pimenteira Formation (Parnaíba Basin), are comparable to the taxa found in Bolivia. The lack of more Placoderm remains in the Brazilian outcrops is similar to the low diversity of this group in Bolivia, when compared to other South American and Euramerican localities. The most diverse Brazilian ichthyofauna is encountered in the Permian Pedra de Fogo Formation where numerous chondrichthyans and 'paleopterygians' remains are found, together with dipnoans and actinistians. Despite the apparent lack of more representative Paleozoic ichthyofaunas in Brazil, the available material that ranges from Lower Devonian to early Permian from Brazil bears important taxa that could address valuable taxonomic and biogeographic informations.

Reported middle Paleozoic fossils and new geochronological data from the southern and central Appalachians: Disposable outrageous hypothesis or justification for major revision of tectonic history

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

Hatcher, R.D. Jr.

Recently published interpretations of fossil fragments from the Walden Creek Group (Ocoee Supergroup) suggesting that these rocks are middle Paleozoic (Devonian to Early Carboniferous), and new geochronological data that yield late Paleozoic age dates on rocks and major faults in the Blue Ridge and piedmont, if taken alone, would permit speculation that most of the deformation and metamorphism affecting this part of the orogen is Alleghanian. The two Ordovician clastic wedges (Sevier, Llanvirn, and Martinsburg, Caradoc-Ashgill) and the Carboniferous-Permian wedge(s), along with many radiometric ages on plutons, indicate uplift and sediment dispersal from the interior of the southern and centralmore » Appalachians (SCA) that may have resulted from Taconian and Alleghanian deformation. Combining the reproducible fossil evidence, including that from Alabama and a recently discovered crinoid fragment from the upper part of the Murphy belt sequence, with the most current geochronological data requires that peak metamorphism and penetrative deformation be at least Devonian or younger at the southwestern end of the orogen, and Late Ordovician or younger in the Carolinas and northern Georgia. Zircon ages reported from large thrust and dextral strike-slip faults bounding the Pine Mountain window indicate all of the faults there may be Alleghanian, except the younger sinistral Mesozoic faults, and requires that both metamorphism and penetrative deformation there also be Alleghanian. As in New England, the southern Appalachian Alleghanian metamorphic core is now known to be much more extensive. The older data require that the Taconian and perhaps the Acadian orogenies were significant events in the SCA, but these new data reconfirm the dominance of Alleghanian continent-continent collision processes here.« less

Early Miocene Tectonic Activity in the western Ross Sea (Antarctica)

NASA Astrophysics Data System (ADS)

Sauli, C.; Sorlien, C. C.; Busetti, M.; Geletti, R.; De Santis, L.

2012-12-01

In the framework of the Rossmap Italian PNRA work objectives to compile extended and revised digital maps of the main unconformities in Ross Sea, Antarctica, much additional seismic reflection data, that were not available to previous ANTOSTRAT compilation, were incorporated into a new ROSSMAP interpretation. The correlation across almost all of Ross Sea, from DSDP Site 270 and Site 272 in Eastern Basin to northern Victoria Land Basin, of additional early Miocene and late Oligocene horizons that were not part of ANTOSTRAT allows interpretations to be made of fault activity and glacial erosion or deposition at a finer time resolution. New conclusions include that extensional or transtensional fault activity within the zone between Victoria Land Basin and Northern Basin, initiated by 23 Ma or earlier, and continued after 18 Ma. Steep parallel-striking faults in southern Victoria Land Basin display both reverse and normal separation of 17.5 Ma (from Cape Roberts Program-core 1) and post-16 Ma horizons, suggesting an important strike-slip component. This result may be compared with published papers that proposed post-17 Ma extension in southern Victoria Land Basin, 16-17 Ma extension in the AdareTrough, north of the Ross Sea continental shelf, but no Miocene extension affecting the Northern Basin (Granot et al., 2010). Thus, our evidence for extension through the early Miocene is significant to post-spreading tectonic models. Reference Granot R., Cande S. C., Stock J. M., Davey F. J. and Clayton R. W. (2010) Postspreading rifting in the Adare Basin, Antarctica: Regional tectonic consequences. Geochem. Geophys. Geosyst., 8, Q08005, doi:10.1029/2010GC003105.

EAG Eminent Speaker: Two types of Archean continental crust: plume and plate tectonics on early Earth

NASA Astrophysics Data System (ADS)

Van Kranendonk, M. J.

2012-04-01

Over 4.5 billion years, Earth has evolved from a molten ball to a cooler planet with large continental plates, but how and when continents grew and plate tectonics started remain poorly understood. In this paper, I review the evidence that 3.5-3.2 Ga continental nuclei of the Pilbara (Australia) and Kaapvaal (southern Africa) cratons formed as thick volcanic plateaux over hot, upwelling mantle and survived due to contemporaneous development of highly depleted, buoyant, unsubductable mantle roots. This type of crust is distinct from, but complimentary to, high-grade gneiss terranes, as exemplified by the North Atlantic Craton of West Greenland, which formed through subduction-accretion tectonics on what is envisaged as a vigorously convecting early Earth with small plates. Thus, it is proposed that two types of crust formed on early Earth, in much the same way as in modern Earth, but with distinct differences resulting from a hotter Archean mantle. Volcanic plateaux provided a variety of stable habitats for early life, including chemical nutrient rich, shallow-water hydrothermal systems and shallow marine carbonate platforms.

Latest Neoproterozoic basin inversion of the Beardmore Group, central Transantarctic Mountains, Antarctica

NASA Astrophysics Data System (ADS)

Goodge, John W.

1997-08-01

Structural and age relationships in Beardmore Group rocks in the central Transantarctic Mountains of Antarctica indicate that they experienced a single deformation in latest Neoproterozoic to early Paleozoic time. New structural data contrast with earlier suggestions that Beardmore rocks record two orogenic deformations, one of the early Paleozoic Ross orogeny and a distinct earlier tectonic event of presumed Neoproterozoic age referred to as the Beardmore orogeny. In the Nimrod Glacier area, Beardmore metasedimentary rocks contain only a single set of geometrically related regional structures associated with the development of upright, large- and small-scale flexural-slip folds. Deformation of Beardmore strata involved west directed contraction of modest regional strain at relatively high crustal levels. Existing ages of detrital zircons from the Cobham and Goldie formations constrain Beardmore Group deposition to be younger than ˜600 Ma. This is significantly younger than previous age estimates and suggests that Beardmore deposition may be closely linked to a latest Neoproterozoic East Antarctic rift margin. The lack of structural evidence for polyphase deformation and the relatively young depositional age for the Beardmore Group thus raises the question of a temporally and/or technically unique Beardmore orogeny. Here I suggest that Beardmore shortening may be related to tectonic inversion of East Antarctic marginal-basin strata because of localized compression during proto-Pacific seafloor spreading. Basin inversion is but one stage in a protracted Ross tectonic cycle of rifting, tectonic inversion, subduction initiation, and development of a mature convergent continental margin during latest Neoproterozoic and early Paleozoic time. The term "Beardmore orogeny" has little meaning as an event of orogenic status, and it should be abandoned. Recognition of this latest Neoproterozoic history reinforces the view that the broader Ross orogeny was not a single event

Paleozoic and Mesozoic deformations in the central Sierra Nevada, California

USGS Publications Warehouse

Nokleberg, Warren J.; Kistler, Ronald Wayne

1980-01-01

Analysis of structural and stratigraphic data indicates that several periods of regional deformation, consisting of combined folding, faulting, cataclasis, and regional metamorphism, occurred throughout the central Sierra Nevada during Paleozoic and Mesozoic time. The oldest regional deformation occurred alono northward trends during the Devonian and Mississippian periods in most roof pendants containing lower Paleozoic metasedimentary rocks at the center and along the crest of the range. This deformation is expressed in some roof pendants by an angular unconformity separating older thrice-deformed from younger twice-deformed Paleozoic metasedimentary rocks. The first Mesozoic deformation, which consisted of uplift and erosion and was accompanied by the onset of Andean-type volcanism during the Permian and Triassic, is expressed by an angular unconformity in several roof pendants from the Saddlebag Lake to the Mount Morrison areas. This unconformity is defined by Permian and Triassic andesitic to rhyolitic metavolcanic rocks unconformably overlying more intensely deformed Pennsylvanian, Permian(?), and older metasedimentary rocks. A later regional deformation occurred during the Triassic along N. 20?_30? W. trends in Permian and Triassic metavolcanic rocks of the Saddlebag Lake and Mount Dana roof pendants, in upper Paleozoic rocks of the Pine Creek roof pendant, and in the Calaveras Formation of the western metamorphic belt; the roof pendants are crosscut by Upper Triassic granitic rocks of the Lee Vining intrusive epoch. A still later period of Early and Middle Jurassic regional deformation occurred along N. 30?-60? E. trends in upper Paleozoic rocks of the Calaveras Formation of the western metamorphic belt. A further period of deformation was the Late Jurassic Nevadan orogeny, which occurred along N. 20?_40? W. trends in Upper Jurassic rocks of the western metamorphic belt that are crosscut by Upper Jurassic granitic rocks of the Yosemite intrusive epoch

Structural-tectonic zoning of the Arctic

NASA Astrophysics Data System (ADS)

Petrov, Oleg; Sobolev, Nikolay; Morozov, Andrey; Shokalsky, Sergey; Kashubin, Sergey; Grikurov, Garrik; Tolmacheva, Tatiana; Rekant, Pavel; Petrov, Evgeny

2017-04-01

Structural-tectonic zoning of the Arctic is based on the processing of geological and geophysical data and bottom sampling materials produced within the project "Atlas of Geological Maps of the Circumpolar Arctic." Zoning of the Arctic territories has been conducted taking into account the Earth's crust types, age of consolidated basement, and features of geological structure of the sedimentary cover. Developed legend for the zoning scheme incorporates five main groups of elements: continental and oceanic crust, folded platform covers, accretion-collision systems, and provinces of continental cover basalts. An important feature of the structural-tectonic zoning scheme is designation of continental crust in the central regions of the Arctic Ocean, the existence of which is assumed on the basis of numerous geological data. It has been found that most of the Arctic region has continental crust with the exception of the Eurasian Basin and the central part of the Canada Basin, which are characterized by oceanic crust type. Thickness of continental crust from seismic data varies widely: from 30-32 km on the Mendeleev Rise to 18-20 km on the Lomonosov Ridge, decreasing to 8-10 km in rift structures of the Podvodnikov-Makarov Basin at the expense of reduction of the upper granite layer. New data confirm similar basement structure on the western and eastern continental margins of the Eurasian oceanic basin. South to north, areas of Neoproterozoic (Baikalian) and Paleozoic (Ellesmerian) folding are successively distinguished. Neoproterozoic foldbelt is observed in Central Taimyr (Byrranga Mountains). Continuation of this belt in the eastern part of the Arctic is Novosibirsk-Chukchi fold system. Ellesmerian orogen incorporates the northernmost areas of Taimyr and Severnaya Zemlya, wherefrom it can be traced to the Geofizikov Spur of the Lomonosov Ridge and further across the De Long Archipelago and North Chukchi Basin to the north of Alaska Peninsula and in the Beaufort Sea

Assessment of Paleozoic terrane accretion along the southern central Andes using detrital zircon geochronology

NASA Astrophysics Data System (ADS)

McKenzie, R.; Horton, B. K.; Fuentes, F.; Fosdick, J. C.; Capaldi, T.; Stockli, D. F.; Alvarado, P. M.

2015-12-01

Two distinct Paleozoic terranes known as Cuyania and Chilenia occupy the southern central Andes of Argentina and Chile. Because the proposed terrane boundaries coincide with major structural elements of the modern Andean system at 30-36°S, it is important to understand their origins and potential role in guiding later Andean deformation. The Cuyania terrane of western Argentina encompasses the Precordillera (PC) and a thick-skinned thrust block of the western Sierras Pampeanas, persisting southward to the San Rafael Basin (SRB). Although recently challenged, Cuyania has been long considered a piece of southern Laurentia that rifted away during the early Cambrian and collided with the Argentine margin during the Ordovician. Chilenia is situated west of Cuyania and includes the Frontal Cordillera (FC) and Andean magmatic arc. This less-studied terrane was potentially accreted during an enigmatic Devonian orogenic event. We present new detrital zircon U-Pb age data from siliciclastic sedimentary rocks that span the entire Paleozoic to Triassic from the FC, PC, and SRB. Cambrian rocks of the PC exhibit similar zircon age distributions with prominent ~1.4 and subordinate ~1.1 Ga populations, which are distinct from other Paleozoic strata. Plutonic rocks with these ages are common in southern Laurentia, whereas ~1.4 Ga zircons are uncommon in South American age distributions. This supports a Laurentian origin for Cuyania in isolation from Argentina during the Cambrian. Upper Paleozoic strata from the PC, FC, and SRB all yield similar age data suggesting shared provenance across the proposed Cuyania-Chilenia suture. Age distributions also notably lack Devonian-age grains. The regional paucity of Devonian plutonic rocks and detrital zircon casts doubt on a possible arc system between these terranes at this time, a key requisite for the mid-Paleozoic transfer and accretion of Chilenia to the Argentine margin. Collectively, these data question the precise boundaries of the

Early to Middle Jurassic tectonic evolution of the Bogda Mountains, Northwest China: Evidence from sedimentology and detrital zircon geochronology

NASA Astrophysics Data System (ADS)

Ji, Hongjie; Tao, Huifei; Wang, Qi; Qiu, Zhen; Ma, Dongxu; Qiu, Junli; Liao, Peng

2018-03-01

The Bogda Mountains, as an important intracontinental orogenic belt, are situated in the southern part of the Central Asian Orogenic Belt (CAOB), and are a key area for understanding the Mesozoic evolution of the CAOB. However, the tectonic evolution of the Bogda Mountains remains controversial during the Mesozoic Era, especially the Early to Middle Jurassic Periods. The successive Lower to Middle Jurassic strata are well preserved and exposed along the northern flank of the Western Bogda Mountains and record the uplift processes of the Bogda Mountains. In this study, we analysed sedimentary facies combined with detrital zircon U-Pb geochronology at five sections of Lower to Middle Jurassic strata to detect the tectonic evolution and changes of provenance in the Bogda area. During Early to Middle Jurassic times, the fluvial, deltaic and lacustrine environments dominated in the western section of the Bogda area. The existence of Early Triassic peak age indicates that the Bogda Mountains did not experience uplift during the period of early Badaowan Formation deposition. The Early Triassic to Late Permian granitoid plutons and Carboniferous volcanic rocks from the Barkol and Santanghu areas were the main provenances. The significant change in the U-Pb age spectrum implies that the Eastern Bogda Mountains initiated uplift in the period of late Badaowan Formation deposition, and the Eastern Junggar Basin and the Turpan-Hami Basin were partially partitioned. The Eastern Bogda Mountains gradually became the major provenance. From the period of early Sangonghe to early Toutunhe Formations deposition, the provenance of the sediments and basin-range frame were similar to that of late Badaowan. However, the Eastern Bogda Mountains suffered intermittent uplift three times, and successive denudation. The uplifts respectively happened in early Sangonghe, late Sangonghe to early Xishanyao, and late Xishanyao to early Toutunhe. During the deposition stage of Toutunhe Formation, a

North American Paleozoic land snails with a summary of other Paleozoic nonmarine snails

USGS Publications Warehouse

Solem, Alan; Yochelson, Ellis Leon

1979-01-01

Land snails from the Paleozoic of North America are known from the coal fields of eastern Canada, from the Dunkard basin west of the Allegheny Mountains, and from the western margin of the Illinois basin. The earliest finds were made about 125 years ago; essentially no new information has been recorded for a century. Large collections of Anthracopupa from the Dunkard basin sparked inquiry into the land snails from the other two areas. Studies using the SEM (scanning electron microscope) have provided considerable insight into microdetails of shell structure, which allow systematic assignment of these gastropods. All may be assigned to extant families, except one, for which insufficient material allows only superfamily assignment. The prosobranch Dawsonella is confirmed as being a terrestrial neritacean gastropod. To date, it is known only from the upper Middle Pennsylvanian of Illinois and Indiana. All the other Paleozoic land snails are stylommatophoran pulmonates; their current classification as nonmarine cyclophoraceans is not correct. Restudy of material from the Joggins section of Nova Scotia indicates that representatives of two ordinal groups of pulmonates appeared simultaneously in upper Lower Pennsylvanian strata; the oldest land prosobranch is found in only very slightly younger rocks. Zonites (Conulus) priscus is reassigned to the new genus Protodiscus in the extant family Discidae. Dendropupa is placed within the family Enidae, Anthraaopupa is placed in the family Tornatellinidae, and 'Pupa' bigsbii is assigned to the superfamily Pupillacea. All four of these family-level taxa are diverse and belong to two orders within the superorder Stylommatophora, heretofore considered a derived rather than an ancestral stock. Anthracopupa ohioensis Whitfield is a highly variable species, and two other species Naticopsis (?) diminuta and A.(?) dunkardona, both named by Stauffer and Schroyer, are placed in synonymy with it. To obtain taxonomic data to support the

Rotational and accretionary evolution of the Klamath Mountains, California and Oregon, from Devonian to present time

USGS Publications Warehouse

Irwin, William P.; Mankinen, Edward A.

1998-01-01

The purpose of this report is to show graphically how the Klamath Mountains grew from a relatively small nucleus in Early Devonian time to its present size while rotating clockwise approximately 110°. This growth occurred by the addition of large tectonic slices of oceanic lithosphere, volcanic arcs, and melange during a sequence of accretionary episodes. The Klamath Mountains province consists of eight lithotectonoic units called terranes, some of which are divided into subterranes. The Eastern Klamath terrane, which was the early Paleozoic nucleus of the province, is divided into the Yreka, Trinity, and Redding subterranes. Through tectonic plate motion, usually involving subduction, the other terranes joined the early Paleozoic nucleus during seven accretionary episodes ranging in age from Early Devonian to Late Jurassic. The active terrane suture is shown for each episode by a bold black line. Much of the western boundary of the Klamath Mountains is marked by the South Fork and correlative faults along which the Klamath terranes overrode the Coast Range rocks during an eighth accretionary episode, forming the South Fork Mountain Schist in Early Cretaceous time.

Phanerozoic polyphase orogenies recorded in the northeastern Okcheon Belt, Korea from SHRIMP U-Pb detrital zircon and K-Ar illite geochronologies

NASA Astrophysics Data System (ADS)

Jang, Yirang; Kwon, Sanghoon; Song, Yungoo; Kim, Sung Won; Kwon, Yi Kyun; Yi, Keewook

2018-05-01

We present the SHRIMP U-Pb detrital zircon and K-Ar illite 1Md/1M and 2M1 ages, suggesting new insight into the Phanerozoic polyphase orogenies preserved in the northeastern Okcheon Belt, Korea since the initial basin formation during Neoproterozoic rifting through several successive contractional orogens. The U-Pb detrital zircon ages from the Early Paleozoic strata of the Taebaeksan Zone suggest a Cambrian maximum deposition age, and are supported by trilobite and conodont biostratigraphy. Although the age spectra from two sedimentary groups, the Yeongwol and Taebaek Groups, show similar continuous distributions from the Late Paleoproterozoic to Early Paleozoic ages, a Grenville-age hiatus (1.3-0.9 Ga) in the continuous stratigraphic sequence from the Taebaek Group suggests the existence of different peripheral clastic sources along rifted continental margin(s). In addition, we present the K-Ar illite 1Md/1M ages of the fault gouges, which confirm fault formation/reactivation during the Late Cretaceous to Early Paleogene (ca. 82-62 Ma) and the Early Miocene (ca. 20-18 Ma). The 2M1 illite ages, at least those younger than the host rock ages, provide episodes of deformation, metamorphism and hydrothermal effects related to the tectonic events during the Devonian (ca.410 Ma) and Permo-Triassic (ca. 285-240 Ma). These results indicate that the northeastern Okcheon Belt experienced polyphase orogenic events, namely the Okcheon (Middle Paleozoic), Songrim (Late Paleozoic to Early Mesozoic), Daebo (Middle Mesozoic) and Bulguksa (Late Mesozoic to Early Cenozoic) Orogenies, reflecting the Phanerozoic tectonic evolution of the Korean Peninsula along the East Asian continental margin.

Kinematics and age of Early Tertiary trench parallel volcano-tectonic lineaments in southern Mexico: Tectonic implications

NASA Astrophysics Data System (ADS)

Martini, M.; Ferrari, L.; Lopez Martinez, M.; Cerca Martinez, M.; Serrano Duran, L.

2007-05-01

We present new geological, structural, and geochronological data that constrain the timing and geometry of Early Tertiary strike slip deformation in southwestern Mexico and its relation with the concurrent magmatic activity. Geologic mapping in Guerrero and Michoacan States documented two regional WNW trending volcano-tectonic lineaments sub parallel to the present trench. The southernmost lineament runs for ~140 km from San Miguel Totolapan area (NW Guerrero) to Sanchiqueo (SE Michoacan), and passes through Ciudad Altamirano. Its southeastern part is marked by the alignment of at least eleven silicic to intermediate major domes as well as by the course of the Balsas River. The northwestern part of the lineament is characterized by ductile left lateral shear zones in Early Tertiary plutonic rocks observed in the Rio Chiquito valley. Domes near Ciudad Altamirano are unaffected by ductile shearing and yielded a ~42 Ma 40Ar/39Ar age, setting a minimum age for this deformation. The northern volcano-tectonic lineament runs for ~190 km between the areas of Huitzuco in northern Guerrero and the southern part of the Tzitzio fold in eastern Michoacan. The Huautla, Tilzapotla, Taxco, La Goleta and Nanchititla silicic centers (all in the range 37-34 Ma) are emplaced along this lineament, which continues to the WNW trough a mafic dike swarm exposed north of Tiquicheo (37-35 Ma) and the Purungueo subvolcanic body (~42 Ma). These rocks, unaffected by ductile shearing, give a minimum age of deformation similar to the southern Totolapan-Sanquicheo lineament. Post ~42 Ma deformation is essentially brittle and is characterized by several left lateral and right lateral transcurrent faults with typical Riedel patterns. Other trench-parallel left lateral shear zones active in pre-Oligocene times were recently reported in western Oaxaca. The recognizing of Early Tertiary trench-parallel and left-lateral ductile shearing in internal areas of southern Mexico suggest a field of widely

Devonian brachiopods of southwesternmost laurentia: Biogeographic affinities and tectonic significance

USGS Publications Warehouse

Boucot, A.J.; Poole, F.G.; Amaya-Martinez, R.; Harris, A.G.; Sandberg, C.A.; Page, W.R.

2008-01-01

associated worm tubes in the Los Pozos Formation of the Sonora allochthon in central Sonora are also found in strati-form-barite facies in the upper Upper Devonian (Famennian) part of the Slaven Chert in the Roberts Mountains allochthon (upper plate) of central and western Nevada. Although these brachiopods and worm tubes occur in similar depositional settings along the margin of Laurentia in Mexico, they occur in allochthons that exhibit different tectonic styles and times of emplacement. Thus, the allochthons containing the brachiopods and worm tubes in Sonora and Nevada are parts of separate orogenic belts and have different geographic settings and tectonic histories. Devonian facies belts and faunas in northern Mexico indicate a continuous continental shelf along the entire southern margin of Laurentia. These data, in addition to the continuity of the late Paleozoic Ouachita-Marathon-Sonora orogen across northern Mexico, contradict the early Late Jurassic Mojave-Sonora megashear as a viable hypothesis for large-magnitude offset (600-1100 km) of Proterozoic through Middle Jurassic rocks from California to Sonora. ?? 2008 The Geological Society of America.

Facies interfingering and synsedimentary tectonics on late Ladinian-early Carnian carbonate platforms (Dolomites, Italy)

NASA Astrophysics Data System (ADS)

Keim, Lorenz; Brandner, Rainer

2001-11-01

A stratigraphic model for carbonate platform evolution in the Dolomites during the late Ladinian-early Carnian is presented. New light on pre-Raibl growth of individual carbonate platforms of the western Dolomites was shed by biostratigraphic data combined with a revised lithostratigraphy. At the Schlern, Langkofel and Sella, the carbonate factory (Upper Schlern Dolomite) remained productive into the lowermost Carnian (Cordevolian = Aon Zone), and caused a levelling-out of the former steep platform-to-basin relief. In the eastern Dolomites, platforms were producing till basal Julian 2 (Austriacum Zone). At the Sella and Langkofel, the sedimentation pattern after deposition of the Upper Schlern Dolomite was strongly influenced by synsedimentary tectonics. A first phase of extensional tectonics led to local fissures, block-tilting, graben structures and breccia deposits. Composition and fabric of the reworked clasts argue for local-source sediments and short transport distances. The extensional structures are sealed by sediments of Lower Carnian age. Two facies belts (Schlernplateau beds and Dürrenstein Dolomite), which interfinger at the western side of the Sella, reflect the shallow marine environment with terrigenous-volcanoclastic input in the western Dolomites. A second generation of breccias at the Sella documents local fracturing of the Dürrenstein and Upper Schlern Dolomite. Depositional environments across the western and eastern Dolomites were largely dependent on differential subsidence. The sediments of early Carnian age on top of the Schlern platform are a few metres thick only, whereas, in the eastern Dolomite, up to 400-m-thick carbonate sediments ('Richthofen reef' and Settsass platform) were deposited. The most incomplete stratigraphic record is present at the Mendel platform in the west, where Ladinian volcanics are unconformably overlain by late Carnian 'Raibl beds'. The increase in sediment thickness towards the eastern Dolomites becomes partly

Paleomagnetic and Tectonic studies in Uruguay: a brief synthesis of the last decade

NASA Astrophysics Data System (ADS)

Sanchez Bettucci, L.

2013-05-01

The paleomagnetic studies in Uruguay have been applied as a complementary tool to geological studies. Paleomagnetic data can be very useful for geodynamic reconstructions, fundamentally for determine the latitudinal tectonic transport, rotations of crustal blocks. This technique has been applied to Paleoproterozoic, Neoproterozoic and Paleozoic units. The geology of the Uruguayan territory is divided into four tectonic units of Uruguay that include a) the Piedra Alta tectonostratigraphic terrane (PATT) and b) Nico Pérez tectonostratigraphic terrane (NPTT), separated by the Sarandí del Yí high-strain zone. Both terranes are well exposed in the Río de La Plata craton (RPC) and have paleoproterozoic ages, the last was reworked in Neoproterozoic times (metacraton). The most thoroughly investigated Neoproterozoic sections are located in the eastern and southeastern regions of Uruguay. The c) Dom Feliciano Belt shows a tectonic evolution from back-arc to foreland basin characterized by fold-and-thrust, thick-skinned belts developed during the Brasiliano/Pan-African orogenic cycle. And finally d) The high metamorphic grade Punta del Este terrane where its most notable feature is their African affinity. There is a significant shortage of geochemical and geochronological data for the existing geological complexity.

Petrogenesis and tectonic implications of the Early Carboniferous to the Late Permian Barleik plutons in the West Junggar (NW China)

NASA Astrophysics Data System (ADS)

Liu, Bo; Han, Bao-Fu; Ren, Rong; Chen, Jia-Fu; Wang, Zeng-Zhen; Zheng, Bo

2017-02-01

The Paleozoic accretionary orogenesis and continental crustal growth in Central Asia are thought to have close relationship with the evolution of the Paleo-Asian Ocean (PAO). The well-exposed plutons in the northern Barleik Mountains of the West Junggar region, NW China, may provide essential insights into the evolution of the Junggar Ocean, a branch of the PAO, and mechanism of continental crustal growth. Our work on the Barleik plutons indicates an early suite of 324-320 Ma diorite and a late suite of 314-259 Ma quartz syenite and granitic porphyry. All the plutons are characterized by high-K calc-alkaline to shoshonitic signatures, varying depletion in Nb, Ta, Sr, P, Eu, and Ti, low initial 87Sr/86Sr ratios (0.70241-0.70585), strongly positive εNd(t) values (+ 5.7-+7.7), and young one-stage Nd model ages (390-761 Ma), suggesting that they resulted from different batches of magma that were produced by fractional crystallization of a metasomatized mantle source with minor crustal contamination. The diorite is coeval with the youngest arc magmatic rocks, indicating a subduction-related origin. By contrast, the quartz syenite and granitic porphyry are geochemically similar to A2-type granites, with high Zr, Ga, and FeOT/[FeOT + MgO], and are coeval with the widespread plutons in the West Junggar. This, together with the occurrence of Late Carboniferous fluvial deposits and the lack of < 320 Ma ophiolitic and subduction-related metamorphic lithologies, definitively indicates a post-collisional setting after the closure of the Junggar Ocean. Slab breakoff accompanied by asthenospheric upwelling and basaltic underplating is a possible geodynamic process that is responsible for the post-collisional magmatism and vertical crustal growth in the region. Thus a tectonic switch from subduction to post-collision started at the end of the Early Carboniferous ( 320 Ma), probably as a result of the final closure of the Junggar Ocean.

Extending Whole-earth Tectonics To The Terrestrial Planets

NASA Astrophysics Data System (ADS)

Baker, V. R.; Maruyama, S.; Dohm, J. M.

Based on the need to explain a great many geological and geophysical anomalies on Mars, and stimulated by the new results from the Mars Global Surveyor Mission, we propose a conceptual model of whole-EARTH (Episodic Annular Revolving Thermal Hydrologic) tectonics for the long-term evolution of terrestrial planets. The theory emphasizes (1) the importance of water in planetary evolution, and (2) the physi- cal transitions in modes of mantle convection in relation to planetary heat produc- tion. Depending on their first-order geophysical parameters and following accretion and differentiation from volatile-rich planetessimals, terrestrial planets should evolve through various stages of mantle convection, including magma ocean, plate tectonic, and stagnant lid processes. If a water ocean is able to condense from the planet's early steam atmosphere, an early regime of plate tectonics will follow the initial magma ocean. This definitely happened on earth, probably on Mars, and possibly on Venus. The Mars history led to transfer of large amounts of water to the mantle during the pe- riod of heavy bombardment. Termination of plate tectonics on Mars during the heavy bombardment period led to initiation of superplumes at Tharsis and Elysium, where long-persistent volcanism and water outbursts dominated much of later Martian his- tory. For Venus, warming of the early sun made the surface ocean unstable, eliminating its early plate-tectonic regime. Although Venus now experiences stagnant-lid convec- tion with episodic mantle overturns, the water subducted to its lower mantle during the ancient plate-tectonic regime manifests itself in the initation of volatile-rich plumes that dominate its current tectonic regime.

Late Jurassic - Early Cretaceous convergent margins of Northeastern Asia with Northwestern Pacific and Proto-Arctic oceans

NASA Astrophysics Data System (ADS)

Sokolov, Sergey; Luchitskaya, Marina; Tuchkova, Marianna; Moiseev, Artem; Ledneva, Galina

2013-04-01

Continental margin of Northeastern Asia includes many island arc terranes that differ in age and tectonic position. Two convergent margins are reconstructed for Late Jurassic - Early Cretaceous time: Uda-Murgal and Alazeya - Oloy island arc systems. A long tectonic zone composed of Upper Jurassic to Lower Cretaceous volcanic and sedimentary rocks is recognized along the Asian continent margin from the Mongol-Okhotsk thrust-fold belt on the south to the Chukotka Peninsula on the north. This belt represents the Uda-Murgal arc, which was developed along the convergent margin between Northeastern Asia and Northwestern Meso-Pacific. Several segments are identified in this arc based upon the volcanic and sedimentary rock assemblages, their respective compositions and basement structures. The southern and central parts of the Uda-Murgal island arc system were a continental margin belt with heterogeneous basement represented by metamorphic rocks of the Siberian craton, the Verkhoyansk terrigenous complex of Siberian passive margin and the Koni-Taigonos late Paleozoic to early Mesozoic island arc with accreted oceanic terranes. At the present day latitude of the Pekulney and Chukotka segments there was an ensimatic island arc with relicts of the South Anyui oceanic basin in backarc basin. Alazeya-Oloy island arc systems consists of Paleozoic and Mesozoic complexes that belong to the convergent margin between Northeastern Asia and Proto-Artic Ocean. It separated structures of the North American and Siberian continents. The Siberian margin was active whereas the North American margin was passive. The Late Jurassic was characterized by termination of a spreading in the Proto-Arctic Ocean and transformation of the latter into the closing South Anyui turbidite basin. In the beginning the oceanic lithosphere and then the Chukotka microcontinent had been subducted beneath the Alazeya-Oloy volcanic belt

Chondrites isp. Indicating Late Paleozoic Atmospheric Anoxia in Eastern Peninsular India

PubMed Central

Bhattacharya, Biplab; Banerjee, Sudipto

2014-01-01

Rhythmic sandstone-mudstone-coal succession of the Barakar Formation (early Permian) manifests a transition from lower braided-fluvial to upper tide-wave influenced, estuarine setting. Monospecific assemblage of marine trace fossil Chondrites isp. in contemporaneous claystone beds in the upper Barakar succession from two Gondwana basins (namely, the Raniganj Basin and the Talchir Basin) in eastern peninsular India signifies predominant marine incursion during end early Permian. Monospecific Chondrites ichnoassemblage in different sedimentary horizons in geographically wide apart (~400 km) areas demarcates multiple short-spanned phases of anoxia in eastern India. Such anoxia is interpreted as intermittent falls in oxygen level in an overall decreasing atmospheric oxygenation within the late Paleozoic global oxygen-carbon dioxide fluctuations. PMID:24616628

Stitching the western Piedmont of Virginia: Early Paleozoic tectonic history of the Ellisville Pluton and the Potomac and Chopawamsic Terranes

USGS Publications Warehouse

Hughes, K. S.; Hibbard, J. P.; Sauer, R.T.; Burton, William C.

2014-01-01

The theme of the 2014 Virginia Geological Field Conference is the tectonic development, economic geology, and seismicity of the western Piedmont of Louisa County, Virginia. It is timely for the conference to turn its attention here, for during the past decade these aspects of western Piedmont geology have garnered the renewed attention of researchers. In terms of regional tectonics, it has been hypothesized that the major structure in the region, the Chopawamsic fault system, represents the most significant boundary in the Appalachian orogen, the main Iapetan suture (Hibbard et al., 2014). Economically, recent elevated market values of metals— particularly that of gold—has spurred reconsideration of the economic geology of the western Piedmont. Finally, the August 23, 2011, M5.8 earthquake, with its epicenter in our field area, startled the North American east coast and has revived awareness of the seismic potential of the region. This renewed interest in the geology of the western Piedmont of north-central Virginia has led to new detailed bedrock mapping, detailed surficial mapping, high-resolution UPb TIMS zircon geochronology, U-Pb LA-ICPMS detrital zircon geochronology, radiogenic isotope geochemistry, major/minor/REE geochemistry, and geophysical studies (e.g. Bailey et al., 2005, 2008; Bailey and Owens, 2012: Berti et al., 2012; Burton et al., 2014; Burton, in progress; Harrison, 2012; Horton et al., 2010, in press; Hughes, 2010, 2014; Hughes et al., 2013a, 2013b, 2014, in press a, in press b; Malenda, in progress; Owens et al., 2013; Spears and Gilmer 2012; Spears et al. 2013, Terblanche, 2013; Terblanche and Nance, 2012). A host of institutions have taken part in the research, including North Carolina State University, the Virginia Department of Mines, Minerals, and Energy, the U.S. Geological Survey, Virginia Tech, Lehigh University, and the College of William and Mary. Many of these investigations remain active. The majority of the data presented

Spreading continents kick-started plate tectonics.

PubMed

Rey, Patrice F; Coltice, Nicolas; Flament, Nicolas

2014-09-18

Stresses acting on cold, thick and negatively buoyant oceanic lithosphere are thought to be crucial to the initiation of subduction and the operation of plate tectonics, which characterizes the present-day geodynamics of the Earth. Because the Earth's interior was hotter in the Archaean eon, the oceanic crust may have been thicker, thereby making the oceanic lithosphere more buoyant than at present, and whether subduction and plate tectonics occurred during this time is ambiguous, both in the geological record and in geodynamic models. Here we show that because the oceanic crust was thick and buoyant, early continents may have produced intra-lithospheric gravitational stresses large enough to drive their gravitational spreading, to initiate subduction at their margins and to trigger episodes of subduction. Our model predicts the co-occurrence of deep to progressively shallower mafic volcanics and arc magmatism within continents in a self-consistent geodynamic framework, explaining the enigmatic multimodal volcanism and tectonic record of Archaean cratons. Moreover, our model predicts a petrological stratification and tectonic structure of the sub-continental lithospheric mantle, two predictions that are consistent with xenolith and seismic studies, respectively, and consistent with the existence of a mid-lithospheric seismic discontinuity. The slow gravitational collapse of early continents could have kick-started transient episodes of plate tectonics until, as the Earth's interior cooled and oceanic lithosphere became heavier, plate tectonics became self-sustaining.

Tectonic Evolution of the Careón Ophiolite (Northwest Spain): A Remnant of Oceanic Lithosphere in the Variscan Belt.

PubMed

Díaz García F; Arenas; Martínez Catalán JR; González del Tánago J; Dunning

1999-09-01

Analysis of the Careón Unit in the Ordenes Complex (northwest Iberian Massif) has supplied relevant data concerning the existence of a Paleozoic oceanic lithosphere, probably related to the Rheic realm, and the early subduction-related events that were obscured along much of the Variscan belt by subsequent collision tectonics. The ophiolite consists of serpentinized harzburgite and dunite in the lower section and a crustal section made up of coarse-grained and pegmatitic gabbros. An Early Devonian zircon age (395+/-2 Ma, U-Pb) was obtained in a leucocratic gabbro. The whole section was intruded by numerous diabasic gabbro dikes. Convergence processes took place shortly afterward, giving rise to a mantle-rooted synthetic thrust system, with some coeval igneous activity. Garnet amphibolite, developed in metamorphic soles, was found discontinuously attached to the thrust fault. The soles graded downward to epidote-amphibolite facies metabasite and were partially retrogressed to greenschist facies conditions. Thermobarometric estimations carried out at a metamorphic sole (T approximately 650 degrees C; P approximately 11.5 kbar) suggested that imbrications developed in a subduction setting, and regional geology places this subduction in the context of an early Variscan accretionary wedge. Subduction and imbrication of oceanic lithosphere was followed by underthrusting of the Gondwana continental margin.

Silurian to Early Carboniferous plate tectonic model of Central Europe

NASA Astrophysics Data System (ADS)

Golonka, Jan; Barmuta, Jan; Barmuta, Maria

2014-05-01

The presented plate tectonic model focuses on Silurian to Early Carboniferous evolution of Central Europe with special attention given to the Sudetes region (north and north-east part of the Bohemian Massif). During our studies, we tested alternative models focused on the position of the Armorican terranes, known as the Armorican Terrane Assembly (ATA) (e.g.: Matte, 2001) and tried to refine the existing reconstructions, which describe Armorica as an individual continent during the Late Silurian and Devonian (e.g. Lewandowski, 2003, Winchester, 2002). Our plate tectonic model depict that these small blocks were scattered along the northern margin of Gondwana, where they formed the "Armorican Spour" as suggested by Kroner and Romer (2013). The seaways were present between blocks. Because of the north dipping subduction zone along the southern margin of the Laurussia continent the back-arc basin and island arc were formed. The narrowing of the Rheic ocean led to the complicated collision of Gondwana and Laurussia. Three main stages of this event can be distinguished: (1) collision of the Armorican Spour with the Laurussian island arc, (2) back-arc basin closure, (3) final Gondwana and Laurussian collision. Those stages correlate well with Variscan Subduction Zone System proposed by Kroner and Romer (2013). Interactive modeling performed in GPlates, shows that the presented model is valid from kinematic and geometrical point of view. Kroner U., Romer R., L., 2013, Two plates - many subduction zones: the Variscan orogeny reconsidered. Gondwana Research, 24: 298-329. Lewandowski M., 2003, Assembly of Pangea: Combined paleomagnetic and paleoclimatic approach, Advances in Geophysics, 46: 199-236 Matte P., 2001, The Variscan collage and orogeny (480 290 Ma) and the tectonic definition of the Armorica microplate: a review. Terra Nova, 13: 122¨C128. Winchester J., A., The Pace TMR Network Team, 2002, Palaeozoic amalgamation of Central Europe: new results from recent

Deformation of the Roberts Mountains Allochthon in north-central Nevada

USGS Publications Warehouse

Evans, James George; Theodore, Ted G.

1978-01-01

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

Paleozoic mafic-intermediate intrusions (320-287 Ma) in the Kalatongke area, southern Altai, NW China: Products of protracted magmatism in a convergent tectonic setting

NASA Astrophysics Data System (ADS)

Qian, Zhuangzhi; Duan, Jun; Li, Chusi; Xu, Gang; Feng, Yanqing; Ren, Meng

2018-06-01

Numerous small mafic-intermediate intrusions are present in the Kalatongke area in the southern part of the Paleozoic Altai Orogenic Belt, NW China. Previous studies reveal that most of these intrusions were emplaced at ∼287 Ma, broadly coeval with the eruption of alkaline flood basalts at ⩽282 Ma in the Tarim Craton. The similar ages have led some researchers to believe that the Tarim flood basalts and the Kalatongke mafic-intermediate intrusions are related to the same mantle plume. New and existing geochronological and geochemical data for the mafic-intermediate intrusions in the Kalatongke area together do not support such interpretation. Most of the intrusions in this small area (4.5 × 2 km) were emplaced at ∼287 Ma but our new data reveal that older intrusive rocks with zircon U-Pb ages from 290 ± 1.5 to 320 ± 2 Ma are also present. The temporal and spatial distribution of these intrusions does not show a hotspot track as expected by the mantle plume model. The intrusive rocks have similar Nd-Hf isotope compositions (εNd = 3-9, εHf = 15-19) and are all characterized by light REE enrichments relative to heavy REE, plus pronounced negative Nb-Ta anomalies. The oldest intrusion (∼320 Ma) also shows negative Zr-Hf anomalies, which are common in arc basalts but absent in continental flood basalts. The results of mixing calculations based on Sr-Nd-Hf isotopes and selected trace elements (Th, Nb and Yb) indicate that the parental magmas for these intrusions were all enriched in Th and depleted in Nb prior to crustal contamination, similar to the magmas generated in a convergent tectonic setting from subduction to post-subduction elsewhere in the world. The results from this study remind us that temporal correlation is not a reliable tool to determine the size of a mantle plume.

Sedimentary petrography of the Early Proterozoic Pretoria Group, Transvaal Sequence, South Africa: implications for tectonic setting

NASA Astrophysics Data System (ADS)

Schreiber, U. M.; Eriksson, P. G.; van der Neut, M.; Snyman, C. P.

1992-11-01

Sandstone petrography, geochemistry and petrotectonic assemblages of the predominantly clastic sedimentary rocks of the Early Proterozoic Pretoria Group, Transvaal Sequence, point to relatively stable cratonic conditions at the beginning of sedimentation, interrupted by minor rifting events. Basement uplift and a second period of rifting occurred towards the end of Pretoria Group deposition, which was followed by the intrusion of mafic sill swarms and the emplacement of the Bushveld Complex in the Kaapvaal Craton at about 2050 Ma, the latter indicating increased extensional tectonism, and incipient continental rifting. An overall intracratonic lacustrine tectonic setting for the Pretoria Group is supported by periods of subaerial volcanic activity and palaeosol formation, rapid sedimentary facies changes, significant arkosic sandstones, the presence of non-glacial varves and a highly variable mudrock geochemistry.

S-type granite from the Gongpoquan arc in the Beishan Orogenic Collage, southern Altaids: Implications for the tectonic transition

NASA Astrophysics Data System (ADS)

Wang, Xinyu; Yuan, Chao; Zhang, Yunying; Long, Xiaoping; Sun, Min; Wang, Lixing; Soldner, Jeremie; Lin, Zhengfan

2018-03-01

Voluminous Paleozoic intrusions occur in the Beishan Orogenic Collage (BOC) and their genesis and tectonic background are important to reconstruct the accretion-collision processes in the southernmost Altaids. Paleozoic is an important period for arc development in the BOC, where the Gongpoquan and Huaniushan arcs are located. There are two pulses of magmatism in the Huaniushan and Gongpoquan arcs, i.e., the ca. 470-423 Ma I-type and ca. 424-395 Ma S- and A-type granitoids. In this study, we focus on two peraluminous granitic plutons in the Gongpoquan arc, i.e., the Baitoushan muscovite granite and Haergen two-mica granite, aiming at unraveling their petrogenesis and tectonic background. Zircon LA-ICP-MS U-Pb dating yields emplacement ages of ca. 409-395 Ma and ca. 409 Ma for the Baitoushan and Haergen plutons, respectively. Both the granitic plutons are strongly peraluminous with A/CNK ratios of 1.10-1.20, indicative of S-type affinities. The rocks are characterized by high SiO2 and K2O contents with high CaO/Na2O ratios. Moreover, the rocks possess low MgO contents, Rb/Sr and Rb/Ba ratios, together with their relatively high initial 87Sr/86Sr ratios (0.7139-0.7152) and less radiogenic εNd(t) values (-3.15 to -5.17), implying a clay-poor and plagioclase-rich crustal source. Compared with earlier pulse of arc-related magmatism (ca. 470-423 Ma), the latter pulse of magmatism (ca. 424-395 Ma) consists mainly of "normal granite" characterized by higher SiO2 (>66%) and K2O contents, weaker fractionated REE patterns and lower δEu values, and gabbroic to dioritic intrusions are only sporadic. Moreover, the granitoids of the latter pulse show variable but more crust-like Sr-Nd isotopic compositions ((87Sr/86Sr)0 = 0.7038-0.7327; εNd(t) = -6.70 to +0.33) than the earlier ones ((87Sr/86Sr)0 = 0.7024-0.7080; εNd(t) = -2.56 to +8.86), indicating that the Early Devonian (ca. 424-395 Ma) experienced extensive crustal melting with minor involvement of mantle materials

Lower paleozoic of Baltic Area

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

Haselton, T.M.; Surlyk, F.

The Baltic Sea offers a new and exciting petroleum play in northwestern Europe. The Kaliningrad province in the Soviet Union, which borders the Baltic Sea to the east, contains an estimated 3.5 billion bbl of recoverable oil from lower Paleozoic sandstones. To the south, in Poland, oil and gas fields are present along a trend that projects offshore into the Baltic. Two recent Petrobaltic wells in the southern Baltic have tested hydrocarbons from lower Paleozoic sandstone. Minor production comes from Ordovician reefs on the Swedish island of Gotland in the western Baltic. The Baltic synclise, which began subsiding in themore » late Precambrian, is a depression in the East European platform. Strate dip gently to the south where the Baltic Synclise terminates against a structurally complex border zone. Depth to the metamorphosed Precambrian basement is up to 4,000 m. Overlying basement is 200-300 m of upper Precambrian arkosic sandstone. The Lower Cambrian consists of shallow marine quartzites. During Middle and Late Camnbrian, restricted circulation resulted in anoxic conditions and the deposition of Alum shale. The Lower Ordovician consists of quartzites and shale. The Upper Ordovician includes sandstones and algal reefs. The Silurian contains marginal carbonates and shales. For the last 25 years, exploration in northwest Europe has concentrated on well-known Permian sandstone, Jurassic sandstone, and Cretaceous chalk plays. Extrapolation of trends known and exploited in eastern Europe could open an entirely new oil province in the lower Paleozoic in the Baltic.« less

Pennsylvanian and Early Permian paleogeography of east-central California: Implications for the shape of the continental margin and the timing of continental truncation

NASA Astrophysics Data System (ADS)

Stone, Paul; Stevens, Calvin H.

1988-04-01

Pennsylvanian and Early Permian paleogeographic features in east-central California include a southeast-trending carbonate shelf edge and turbidite basin that we infer paralleled a segment of the western margin of the North American continent. This segment of the continental margin was oblique to an adjoining segment on the north that trended southwestward across Nevada into easternmost California. We propose that the southeast-trending segment of the margin originated by tectonic truncation of the originally longer southwest-trending segment in Early or Middle Pennsylvanian to late Early Permian time, significantly earlier than a previously hypothesized Late Permian or Early Triassic continental truncation event. We interpret the truncating structure to have been a sinistral transform fault zone along which a continental fragment was removed and carried southeastward into the Caborca-Hermosillo region of northern Mexico, where it is now represented by exposures of Late Proterozoic and Paleozoic miogeoclinal rocks.

Deformational history of part of the Acatlán Complex: Late Ordovician Early Silurian and Early Permian orogenesis in southern Mexico

NASA Astrophysics Data System (ADS)

Malone, J. R.; Nance, R. D.; Keppie, J. D.; Dostal, J.

2002-10-01

The Paleozoic Acatlán Complex of southern Mexico comprises polydeformed metasedimentary, granitoid, and mafic-ultramafic rocks variously interpreted as recording the closure of the Iapetus, Rheic, and Ouachitan Oceans. The complex is tectonically juxtaposed on its eastern margin against Grenville-age gneisses (Oaxacan Complex) that are unconformably overlain by Lower Paleozoic strata containing fossils of Gondwanan affinity. A thick siliciclastic unit (Chazumba and Cosoltepec Formations) at the base of the complex is considered part of a Lower Paleozoic accretionary prism with a provenance that isotopically resembles the Oaxacan Complex. This unit is tectonically overridden by a locally eclogitic mafic-ultramafic unit interpreted as a westward-obducted ophiolite, the emplacement of which was synchronous with mylonitic granitoid intrusion at ca. 440 Ma. Both units are unconformably overlain by a deformed volcano-sedimentary sequence (Tecomate Formation) attributed to a volcanic arc of presumed Devonian age. Deformed granitoids in contact with this sequence have been dated at ca. 371 (La Noria granite) and 287 Ma (Totoltepec pluton). Three phases of penetrative deformation (D 1-3) affect the Cosoltepec Formation; the last two correlate with two penetrative deformational phases that affect the Tecomate Formation. D 1 is of unknown kinematics but predates deposition of the Tecomate Formation and likely records obduction at ca. 440 Ma (Acatecan orogeny). A folded foliation in the Totoltepec pluton appears to record both deformational phases in the Tecomate Formation, bracketing D 2 and D 3 between 287 Ma and the deposition of the nonconformably overlying Leonardian Matzitzi Formation. D 2 records north-south dextral transpression and south-vergent thrusting and is attributed to the collision of Gondwana and southern Laurentia (Ouachitan orogeny) at ca. 290 Ma, the kinematics being consistent with the northward motion of Mexico that is required by most continental

Petrologic implications of plate tectonics.

PubMed

Yoder, H S

1971-07-30

Petrologists can make significant contributions to the plate tectonic concept. Fixing the stability fields of the principal rock types involved will provide the limits of pressure and temperature of the various environments. Experimental determination of the partition coefficients of the trace elements will be helpful. Studies of the partial melting behavior of possible parental materials in the absence and presence of water, especially the undersaturated region, will contribute to the understanding of magma production. Experimental observations on the rheological properties of the peridotites below and just above the solidus will lead to a better evaluation of the convective mechanism. Measurement of the fundamental properties of rocks, such as the density of solids and liquids at high pressures and temperatures, would contribute to understanding the concepts of diapiric rise, magma segregation, and the low-velocity zone. Broader rock sampling of the oceanic areas of all environments will do much to define the petrologic provinces. The field petrologist specializing in the Paleozoic regions and Precambrian shields can contribute by examining those regions for old plate boundaries and devising new criteria for their recognition.

Charon tectonics

PubMed Central

Beyer, Ross A.; Nimmo, Francis; McKinnon, William B.; Moore, Jeffrey M.; Binzel, Richard P.; Conrad, Jack W.; Cheng, Andy; Ennico, K.; Lauer, Tod R.; Olkin, C.B.; Robbins, Stuart; Schenk, Paul; Singer, Kelsi; Spencer, John R.; Stern, S. Alan; Weaver, H.A.; Young, L.A.; Zangari, Amanda M.

2017-01-01

New Horizons images of Pluto’s companion Charon show a variety of terrains that display extensional tectonic features, with relief surprising for this relatively small world. These features suggest a global extensional areal strain of order 1% early in Charon’s history. Such extension is consistent with the presence of an ancient global ocean, now frozen. PMID:28919640

Thin and layered subcontinental crust of the great Basin western north America inherited from Paleozoic marginal ocean basins?

USGS Publications Warehouse

Churkin, M.; McKee, E.H.

1974-01-01

The seismic profile of the crust of the northern part of the Basin and Range province by its thinness and layering is intermediate between typical continental and oceanic crust and resembles that of marginal ocean basins, especially those with thick sedimentary fill. The geologic history of the Great Basin indicates that it was the site of a succession of marginal ocean basins opening and closing behind volcanic arcs during much of Paleozoic time. A long process of sedimentation and deformation followed throughout the Mesozoic modifying, but possibly not completely transforming the originally oceanic crust to continental crust. In the Cenozoic, after at least 40 m.y. of quiescence and stable conditions, substantial crustal and upper-mantle changes are recorded by elevation of the entire region in isostatic equilibrium, crustal extension resulting in Basin and Range faulting, extensive volcanism, high heat flow and a low-velocity mantle. These phenomena, apparently the result of plate tectonics, are superimposed on the inherited subcontinental crust that developed from an oceanic origin in Paleozoic time and possibly retained some of its thin and layered characteristics. The present anomalous crust in the Great Basin represents an accretion of oceanic geosynclinal material to a Precambrian continental nucleus apparently as an intermediate step in the process of conversion of oceanic crust into a stable continental landmass or craton. ?? 1974.

Archean greenstone-tonalite duality: Thermochemical mantle convection models or plate tectonics in the early Earth global dynamics?

NASA Astrophysics Data System (ADS)

Kerrich, Robert; Polat, Ali

2006-03-01

Mantle convection and plate tectonics are one system, because oceanic plates are cold upper thermal boundary layers of the convection cells. As a corollary, Phanerozoic-style of plate tectonics or more likely a different version of it (i.e. a larger number of slowly moving plates, or similar number of faster plates) is expected to have operated in the hotter, vigorously convecting early Earth. Despite the recent advances in understanding the origin of Archean greenstone-granitoid terranes, the question regarding the operation of plate tectonics in the early Earth remains still controversial. Numerical model outputs for the Archean Earth range from predominantly shallow to flat subduction between 4.0 and 2.5 Ga and well-established steep subduction since 2.5 Ga [Abbott, D., Drury, R., Smith, W.H.F., 1994. Flat to steep transition in subduction style. Geology 22, 937-940], to no plate tectonics but rather foundering of 1000 km sectors of basaltic crust, then "resurfaced" by upper asthenospheric mantle basaltic melts that generate the observed duality of basalts and tonalities [van Thienen, P., van den Berg, A.P., Vlaar, N.J., 2004a. Production and recycling of oceanic crust in the early earth. Tectonophysics 386, 41-65; van Thienen, P., Van den Berg, A.P., Vlaar, N.J., 2004b. On the formation of continental silicic melts in thermochemical mantle convection models: implications for early Earth. Tectonophysics 394, 111-124]. These model outputs can be tested against the geological record. Greenstone belt volcanics are composites of komatiite-basalt plateau sequences erupted from deep mantle plumes and bimodal basalt-dacite sequences having the geochemical signatures of convergent margins; i.e. horizontally imbricated plateau and island arc crust. Greenstone belts from 3.8 to 2.5 Ga include volcanic types reported from Cenozoic convergent margins including: boninites; arc picrites; and the association of adakites-Mg andesites- and Nb-enriched basalts. Archean cratons

Shoshonitic- and adakitic magmatism of the Early Paleozoic age in the Western Kunlun orogenic belt, NW China: Implications for the early evolution of the northwestern Tibetan plateau

NASA Astrophysics Data System (ADS)

Wang, Jian; Hattori, Keiko; Liu, Jianguo; Song, Yue; Gao, Yongbao; Zhang, Han

2017-08-01

The Western Kunlun orogenic belt in the northwestern margin of the Tibetan plateau contains two magmatic belts; early Paleozoic belt in the northern part of Western Kunlun Terrane (WKT), and early Mesozoic belt in the southern part of WKT. Both formed from northward subduction of the Paleo-Tethys. The early Paleozoic belt contains large Datong and Qiukesu igneous complexes and many smaller plutons. The Datong complex is mainly composed of dark-colored porphyritic syenite and monzonite with minor light-colored dykes of granite and monzonite. The dark-colored rocks are characterized by moderate SiO2 (58.2-69.3 wt.%), and high Al2O3 (15.3-17.1 wt.%), total alkali (Na2O + K2O = 8.07-10.2 wt.%) and ratios of K2O/Na2O (0.77-1.83). They plot in "shoshonite" field, and show high abundances of LILE including LREE ((La/Yb)n = 15.4-26.2; mean 20.2) with pronounced negative anomalies of Nb-Ta-P-Ti in normalized trace elemental patterns and weak negative anomalies of Eu (δEu = 2Eun/(Smn + Gdn) = 0.68-0.80). The light-colored rocks contain slightly higher concentrations of SiO2 (60.3-72.0 wt.%), similar Al2O3 (14.7-17.6 wt.%), and slightly lower total alkalis (6.57-9.14 wt.%) than dark-colored rocks. They show adakitic geochemical signatures with low Y (5.80-17.2 ppm) and Yb (0.63-1.59 ppm), and high Sr/Y (> 40). U-Pb zircon dating indicates that shoshonitic rocks and adakitic dykes formed at 444 Ma to 443 Ma, and a separate small adakitic plug at 462 Ma. The mean εHf(t) values of zircon range from - 1.6 to - 0.94 (n = 14) with TDM2 of 1.5 Ga for shoshonitic rocks and εHf(t) values from - 1.8 to + 0.72 (n = 12) with TDM2 of 1.4 to 1.5 Ga for adakitic rocks. Shoshonitic rocks show initial 87Sr/86Sr and εNd(t) of 0.7092-0.7100 and - 3.9 to - 3.2, respectively, and adakitic rocks yield initial 87Sr/86Sr and εNd(t) of 0.7099-0.7134 and - 3.6 to - 3.1, respectively. Similar Sr, Nd, and Hf isotope compositions for the shoshonitic and adakitic rocks suggest similar ancient rocks

Mesozoic intra-arc tectonics in the NE Mojave Desert, CA

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

Stephens, K.A.; Schermer, E.R.; Walker, J.D.

1993-04-01

Field and U-Pb zircon geochronological data from the Tiefort Mts. (TM) and surrounding areas in the NE Mojave Desert provide new constraints on Precambrian to Paleozoic paleogeography and Mesozoic intra-arc tectonics. Amphibolite facies metasediments appear to correlate with lower Paleozoic miogeoclinal sequences. Coarse-grained K-feldspar augen gneiss occurs in sharp contact with the metasedimentary rocks; U-Pb dating yields a 1393[+-]12 Ma age. This gneiss is interpreted to represent cratonal basement of North America. A texturally and compositionally heterogeneous amphibolite-facies monzonitic complex which intrudes the basement and metasediments yields a mid-Jurassic age. Felsite and biotite granite that intrude the foliated monzonitic complexmore » locally contain the mylonitic fabric and appear to be syn-late kinematic. Undeformed pegmatite, granite, and microdiorite appear as dikes throughout the region. Vertical silicic dikes at southern TM trend N5-25E and are dated at 148[+-]14 Ma, coeval with the Independence dike swarm (IDS). Similar dikes that occur at TM trend N60-80E. Undeformed granite cross-cuts the foliated monzonite; some granitic rocks cut dikes of the IDs and are likely to be Cretaceous in age. The E- to SE-vergence and mid-late Jurassic age of ductile shear zones in the TM region are similar to that in nearby parts of the East Sierra Thrust System (ESTS). If NE and NNE dikes are IDS-equivalent, this implies clockwise, vertical-axis rotation of 30[degree]--90[degree] by younger structures. The authors interpret this to be related to late Cenozoic strike-slip faults. Restoration of folds and the IDS to the regional NW trend results in top to the E to NE sense of shear during Jurassic deformation. Deformation in the TM and areas to the north connects the ESTS from the Garlock fault to the central Mojave region indicating a region in which mid-crustal levels of the arc and cratonal basement experienced contractional tectonism during mid

Tectonic Evolution of the Jurassic Pacific Plate

NASA Astrophysics Data System (ADS)

Nakanishi, M.; Ishihara, T.

2015-12-01

We present the tectonic evolution of the Jurassic Pacific plate based on magnetic anomly lineations and abyssal hills. The Pacific plate is the largest oceanic plate on Earth. It was born as a microplate aroud the Izanagi-Farallon-Phoenix triple junction about 192 Ma, Early Jurassic [Nakanishi et al., 1992]. The size of the Pacific plate at 190 Ma was nearly half that of the present Easter or Juan Fernandez microplates in the East Pacific Rise [Martinez et at, 1991; Larson et al., 1992]. The plate boundary surrounding the Pacific plate from Early Jurassic to Early Cretaceous involved the four triple junctions among Pacific, Izanagi, Farallon, and Phoenix plates. The major tectonic events as the formation of oceanic plateaus and microplates during the period occurred in the vicinity of the triple junctions [e.g., Nakanishi and Winterer, 1998; Nakanishi et al., 1999], implying that the study of the triple junctions is indispensable for understanding the tectonic evolution of the Pacific plate. Previous studies indicate instability of the configuration of the triple junctions from Late Jurassic to Early Cretaceous (155-125 Ma). On the other hand, the age of the birth of the Pacific plate was determined assuming that all triple junctions had kept their configurations for about 30 m.y. [Nakanishi et al., 1992] because of insufficient information of the tectonic history of the Pacific plate before Late Jurassic.Increase in the bathymetric and geomagnetic data over the past two decades enables us to reveal the tectonic evolution of the Pacific-Izanagi-Farallon triple junction before Late Jurassic. Our detailed identication of magnetic anomaly lineations exposes magnetic bights before anomaly M25. We found the curved abyssal hills originated near the triple junction, which trend is parallel to magnetic anomaly lineations. These results imply that the configuration of the Pacific-Izanagi-Farallon triple junction had been RRR before Late Jurassic.

Stratigraphy of lower to middle Paleozoic rocks of northern Nevada and the Antler orogeny

USGS Publications Warehouse

Ketner, Keith B.

2013-01-01

Commonly accepted concepts concerning the lower Paleozoic stratigraphy of northern Nevada are based on the assumption that the deep-water aspects of Ordovician to Devonian siliceous strata are due to their origin in a distant oceanic environment, and their presence where we find them is due to tectonic emplacement by the Roberts Mountains thrust. The concept adopted here is based on the assumption that their deep-water aspects are the result of sea-level rise in the Cambrian, and all of the Paleozoic strata in northern Nevada are indigenous to that area. The lower part of the Cambrian consists mainly of shallow-water cross-bedded sands derived from the craton. The upper part of the Cambrian, and part of the Ordovician, consists mainly of deep-water carbonate clastics carried by turbidity currents from the carbonate shelf in eastern Nevada, newly constructed as a result of sea-level rise. Ordovician to mid-Devonian strata are relatively deep-water siliceous deposits, which are the western facies assemblage. The basal contact of this assemblage on autochthonous Cambrian rocks is exposed in three mountain ranges and is clearly depositional in all three. The western facies assemblage can be divided into distinct stratigraphic units of regional extent. Many stratigraphic details can be explained simply by known changes in sea level. Upper Devonian to Mississippian strata are locally and westerly derived orogenic clastic beds deposited disconformably on the western facies assemblage. This disconformity, clearly exposed in 10 mountain ranges, indicates regional uplift and erosion of the western facies assemblage and absence of local deformation. The disconformity represents the Antler orogeny.

A Cenozoic tectonic model for Southeast Asia - microplates and basins

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

Maher, K.A.

1995-04-01

A computer-assisted Cenozoic tectonic model was built for Southeast Asia and used to construct 23 base maps, 2 to 6 million years apart. This close temporal spacing was necessary to constrain all the local geometric shifts in a consistent and geologically feasible fashion. More than a hundred individual blocks were required to adequately treat Cenozoic microplate processes at a basic level. The reconstructions show tectonic evolution to be characterized by long periods of gradual evolution, interrupted by brief, widespread episodes of reorganization in fundamental plate geometries and kinematics. These episodes are triggered by major collisions, or by accumulation of smallermore » changes. The model takes into account difficulties inherent in the region. The Pacific and Indo-Australian plates and their predecessors have driven westward and northward since the late Paleozoic, towards each other and the relatively stationary backstop of Asia. Southeast Asia is therefore the result of a long-lived, complex process of convergent tectonics, making it difficult to reconstruct tectonic evolution as much of the continental margin and sea floor spreading record was erased. In addition, the region has been dominated by small-scale microplate processes with short time scales and internal deformation, taking place in rapidly evolving and more ductile buffer zones between the major rigid plate systems. These plate interaction zones have taken up much of the relative motion between the major plates. Relatively ephemeral crustal blocks appear and die within the buffer zones, or accrete to and disperse from the margins of the major plate systems. However, such microplate evolution is the dominant factor in Cenozoic basin evolution. This detailed testonic model aids in comprehension and prediction of basin development, regional hydrocarbon habitat, and petroleum systems.« less

Towards a Holistic Model for the Tectonic Evolution of the North China Craton

NASA Astrophysics Data System (ADS)

Kusky, T. M.; Polat, A.; Windley, B. F.; Wang, J.; Deng, H.

2016-12-01

The North China Craton (NCC) consists of distinctly different tectonic elements assembled during the late Archean - early Proterozoic. We propose a new tectonic evolution of the NCC. The Eastern Block (EB) consists of small microblocks that resemble a collage of accreted arc-rocks from a sutured archipelago similar to the SW Pacific, accreted between 2.6 and 2.7 Ga. An Atlantic-type margin developed on the western side of the EB by 2.5 Ga, and a >1,300 km long arc/accretionary prism collided with this passive margin at 2.5 Ga, obducting ophiolites and ophiolitic mélanges, and forming a foreland basin. This was followed by arc-polarity reversal, and injection of mantle wedge-derived melts. By 2.43 Ga, the ocean behind the accreted arc closed through the collision of an oceanic plateau. Rifting of the amalgamated craton followed at 2.4-2.35 Ga, with a failed rift arm preserved in the center of the craton, and two that successfully made an ocean along the northern margin. By 2.3 Ga an arc built on older cratonic material collided with this passive margin which soon converted to an Andean-type margin. Andean margin tectonics affected much of the craton from 2.3-1.9 Ga, forming a broad E-W swath of continental margin magmas, and retro-arc sedimentary basins including a superimposed basin over the passive margin on the northern margin. From 1.88-1.79 Ga the craton experienced a craton-wide granulite facies metamorphism and basement reactivation event with high-pressure granulites and eclogites in the north, and medium-pressure granulites across the craton. Early Proterozoic granulites and anatectic melts were generated by high-grade metamorphism and partial melting at mid-crustal levels beneath a collisionally-thickened plateau. This collision of the NCC on its northern margin was with the Columbia (Nuna) Continent. The NCC broke out in the period 1753-1673 Ma, as indicated by the formation of a suite of anorthosite, mangerite, charnockite, and alkali-feldspar granites

Final report. [Mesozoic tectonic history of the northeastern Great Basin (Nevada)

NASA Technical Reports Server (NTRS)

Zamudio, Joe

1993-01-01

In eastern Nevada and western Utah is an extensive terrane that has experienced a complex tectonic history of Mesozoic deformation and superposed Tertiary extension. The Mesozoic tectonic history of this area has been the subject of controversy for the past twenty or more years. The debate has centered on whether major Mesozoic geologic structures were due to compressional or extensional tectonic regimes. The goal of our research was to decipher the deformational history of the area by combining detailed geologic mapping, remote sensing data analysis, and U-Pb and K-Ar geochronology. This study area includes the Dolly Varden Mountains and adjacent Currie Hills, located in the semi-arid environment of the northeastern Great Basin in Nevada. Vegetation cover in the Dolly Varden Mountains typically ranges from about 10 percent to 50 percent, with some places along drainages and on high, north-facing slopes where vegetation cover approaches 100 percent. Sagebrush is found at less vegetated lower elevations, whereas pinon pine and juniper are prevalent above 2,000 meters. A variety of geologic materials is exposed in the study area. A sequence of Late Paleozoic and Triassic sedimentary rocks includes limestone, dolomite, chert, sandstone, siltstone and shale. A two-phase granitic stock, called the Melrose, intruded these rocks, resulting in metamorphism along the intrusive contact. Tertiary volcanic rocks cover most of the eastern part of the Dolly Varden Mountains and low-lying areas in the Currie Hills.

A paleozoic pangaea.

PubMed

Boucot, A J; Gray, J

1983-11-11

Paleozoic paleogeographies should be consistent with all available, reliable data. However, comparison of three different Devonian paleogeographies that are based largely or wholly on the data of remanent magnetism show them to be inconsistent in many regards. When these three paleogeographies are provided with possible ocean surface current circulation patterns, and have added to them lithofacies and biogeographic data, they also are shown to be inconsistent with such data. A pangaeic reconstruction positioned in the Southern Hemisphere permits the lithofacies and biogeographical data to be reconciled in a plausible manner.

Effect of basement structure and salt tectonics on deformation styles along strike: An example from the Kuqa fold-thrust belt, West China

NASA Astrophysics Data System (ADS)

Neng, Yuan; Xie, Huiwen; Yin, Hongwei; Li, Yong; Wang, Wei

2018-04-01

The Kuqa fold-thrust belt (KFTB) has a complex thrust-system geometry and comprises basement-involved thrusts, décollement thrusts, triangle zones, strike-slip faults, transpressional faults, and pop-up structures. These structures, combined with the effects of Paleogene salt tectonics and Paleozoic basement uplift form a complex structural zone trending E-W. Interpretation and comprehensive analysis of recent high-quality seismic data, field observations, boreholes, and gravity data covering the KFTB has been performed to understand the characteristics and mechanisms of the deformation styles along strike. Regional sections, fold-thrust system maps of the surface and the sub-salt layer, salt and basement structure distribution maps have been created, and a comprehensive analysis of thrust systems performed. The results indicate that the thrust-fold system in Paleogene salt range can be divided into five segments from east to west: the Kela-3, Keshen, Dabei, Bozi, and Awate segments. In the easternmost and westernmost parts of the Paleogene salt range, strike-slip faulting and basement-involved thrusting are the dominant deformation styles, as basement uplift and the limits of the Cenozoic evaporite deposit are the main controls on deformation. Salt-core detachment fold-thrust systems coincide with areas of salt tectonics, and pop-up, imbricate, and duplex structures are associated with the main thrust faults in the sub-salt layer. Distribution maps of thrust systems, basement structures, and salt tectonics show that Paleozoic basement uplift controlled the Paleozoic foreland basin morphology and the distribution of Cenozoic salt in the KFTB, and thus had a strong influence on the segmented structural deformation and evolution of the fold-thrust belt. Three types of transfer zone are identified, based on the characteristics of the salt layer and basement uplift, and the effects of these zones on the fault systems are evaluated. Basement uplift and the boundary of

Paleozoic carbonate buildup (reef) inventory, central and southeastern Idaho

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

Isaacson, P.E.

1987-08-01

Knowledge of central and southeastern Idaho's Paleozoic rocks to date suggest that three styles of buildup (reef) complexes occur in Late Devonian, Mississippian, and Pennsylvanian-Permian time. The Late Devonian Jefferson Formation has stromatoporoid and coral (both rugosan and tabulate) organisms effecting a buildup in the Grandview Canyon vicinity; Early Mississippian Waulsortian-type mud mounds occur in the Lodgepole formation of southeastern Idaho; there are Late Mississippian Waulsortian-type mounds in the Surrett Canyon Formation of the Lost River Range; and cyclic Pennsylvanian-Permian algal and hydrozoan buildups occur in the Juniper gulch Member of the Snaky Canyon Formation in the Arco Hills andmore » Lemhi Range. Late Devonian (Frasnian) carbonates of the Jefferson formation show buildup development on deep ramp sediments.« less

Tectono-thermal Evolution of the Lower Paleozoic Petroleum Source Rocks in the Southern Lublin Trough: Implications for Shale Gas Exploration from Maturity Modelling

NASA Astrophysics Data System (ADS)

Botor, Dariusz

2018-03-01

The Lower Paleozoic basins of eastern Poland have recently been the focus of intensive exploration for shale gas. In the Lublin Basin potential unconventional play is related to Lower Silurian source rocks. In order to assess petroleum charge history of these shale gas reservoirs, 1-D maturity modeling has been performed. In the Łopiennik IG-1 well, which is the only well that penetrated Lower Paleozoic strata in the study area, the uniform vitrinite reflectance values within the Paleozoic section are interpreted as being mainly the result of higher heat flow in the Late Carboniferous to Early Permian times and 3500 m thick overburden eroded due to the Variscan inversion. Moreover, our model has been supported by zircon helium and apatite fission track dating. The Lower Paleozoic strata in the study area reached maximum temperature in the Late Carboniferous time. Accomplished tectono-thermal model allowed establishing that petroleum generation in the Lower Silurian source rocks developed mainly in the Devonian - Carboniferous period. Whereas, during Mesozoic burial, hydrocarbon generation processes did not develop again. This has negative influence on potential durability of shale gas reservoirs.

Neoproterozoic, Paleozoic, and Mesozoic granitoid magmatism in the Qinling Orogen, China: Constraints on orogenic process

NASA Astrophysics Data System (ADS)

Wang, Xiaoxia; Wang, Tao; Zhang, Chengli

2013-08-01

The Qinling Orogen is one of the main orogenic belts in Asia and is characterized by multi-stage orogenic processes and the development of voluminous magmatic intrusions. The results of zircon U-Pb dating indicate that granitoid magmatism in the Qinling Orogen mainly occurred in four distinct periods: the Neoproterozoic (979-711 Ma), Paleozoic (507-400 Ma), and Early (252-185 Ma) and Late (158-100 Ma) Mesozoic. The Neoproterozoic granitic magmatism in the Qinling Orogen is represented by strongly deformed S-type granites emplaced at 979-911 Ma, weakly deformed I-type granites at 894-815 Ma, and A-type granites at 759-711 Ma. They can be interpreted as the products of respectively syn-collisional, post-collisional and extensional setting, in response to the assembly and breakup of the Rodinia supercontinent. The Paleozoic magmatism can be temporally classified into three stages of 507-470 Ma, 460-422 Ma and ˜415-400 Ma. They were genetically related to the subduction of the Shangdan Ocean and subsequent collision of the southern North China Block and the South Qinling Belt. The 507-470 Ma magmatism is spatially and temporally related to ultrahigh-pressure metamorphism in the studied area. The 460-422 Ma magmatism with an extensive development in the North Qinling Belt is characterized by I-type granitoids and originated from the lower crust with the involvement of mantle-derived magma in a collisional setting. The magmatism with the formation age of ˜415-400 Ma only occurred in the middle part of the North Qinling Belt and is dominated by I-type granitoid intrusions, and probably formed in the late-stage of a collisional setting. Early Mesozoic magmatism in the study area occurred between 252 and 185 Ma, with the cluster in 225-200 Ma. It took place predominantly in the western part of the South Qinling Belt. The 250-240 Ma I-type granitoids are of small volume and show high Sr/Y ratios, and may have been formed in a continental arc setting related to subduction

Paleozoic-Mesozoic boundary in the Berry Creek Quadrangle, northwestern Sierra Nevada, California

USGS Publications Warehouse

Hietanen, Anna Martta

1977-01-01

Structural and petrologic studies in the Berry Creek quadrangle at the north end of the western metamorphic belt of the Sierra Nevada have yielded new information that helps in distinguishing between the chemically similar Paleozoic and Mesozoic rocks. The distinguishing features are structural and textural and result from different degrees of deformation. Most Paleozoic rocks are strongly deformed and thoroughly recrystallized. Phenocrysts in meta volcanic rocks are granulated and drawn out into lenses that have sutured outlines. In contrast, the phenocrysts in the Mesozoic metavolcanic rocks show well-preserved straight crystal faces, are only slightly or not at all granulated, and contain fewer mineral inclusions than do those in the Paleozoic rocks. The groundmass in the Paleozoic rocks is recrystallized to a fairly coarse grained albite-epidote-amphibole-chlorite rock, whereas in the Mesozoic rocks the groundmass is a very fine grained feltlike mesh with only spotty occurrence of well-recrystallized finegrained albite-epidote-chlorite-actinolite rock. Primary minerals, such as augite, are locally preserved in the Mesozoic rocks but are altered to a mixture of amphibole, chlorite, and epidote in the Paleozoic rocks. In the contact aureoles of the plutons, and within the Big Bend fault zone, which crosses the area parallel to the structural trends, all rocks are thoroughly recrystallized and strongly deformed. Identification of the Paleozoic and Mesozoic rocks in these parts of the area was based on the continuity of the rock units in the field and on gradual changes in microscopic textures toward the plutons.

Paleozoic oil/gas shale reservoirs in southern Tunisia: An overview

NASA Astrophysics Data System (ADS)

Soua, Mohamed

2014-12-01

During these last years, considerable attention has been given to unconventional oil and gas shale in northern Africa where the most productive Paleozoic basins are located (e.g. Berkine, Illizi, Kufra, Murzuk, Tindouf, Ahnet, Oued Mya, Mouydir, etc.). In most petroleum systems, which characterize these basins, the Silurian played the main role in hydrocarbon generation with two main 'hot' shale levels distributed in different locations (basins) and their deposition was restricted to the Rhuddanian (Lllandovery: early Silurian) and the Ludlow-Pridoli (late Silurian). A third major hot shale level had been identified in the Frasnian (Upper Devonian). Southern Tunisia is characterized by three main Paleozoic sedimentary basins, which are from North to South, the southern Chotts, Jeffara and Berkine Basin. They are separated by a major roughly E-W trending lower Paleozoic structural high, which encompass the Mehrez-Oued Hamous uplift to the West (Algeria) and the Nefusa uplift to the East (Libya), passing by the Touggourt-Talemzane-PGA-Bou Namcha (TTPB) structure close to southern Tunisia. The forementioned major source rocks in southern Tunisia are defined by hot shales with elevated Gamma ray values often exceeding 1400 API (in Hayatt-1 well), deposited in deep water environments during short lived (c. 2 Ma) periods of anoxia. In the course of this review, thickness, distribution and maturity maps have been established for each hot shale level using data for more than 70 wells located in both Tunisia and Algeria. Mineralogical modeling was achieved using Spectral Gamma Ray data (U, Th, K), SopectroLith logs (to acquire data for Fe, Si and Ti) and Elemental Capture Spectroscopy (ECS). The latter technique provided data for quartz, pyrite, carbonate, clay and Sulfur. In addition to this, the Gamma Ray (GR), Neutron Porosity (ΦN), deep Resistivity (Rt) and Bulk Density (ρb) logs were used to model bulk mineralogy and lithology. Biostratigraphic and complete

The diversification of Paleozoic fire systems and fluctuations in atmospheric oxygen concentration

PubMed Central

Scott, Andrew C.; Glasspool, Ian J.

2006-01-01

By comparing Silurian through end Permian [≈250 million years (Myr)] charcoal abundance with contemporaneous macroecological changes in vegetation and climate we aim to demonstrate that long-term variations in fire occurrence and fire system diversification are related to fluctuations in Late Paleozoic atmospheric oxygen concentration. Charcoal, a proxy for fire, occurs in the fossil record from the Late Silurian (≈420 Myr) to the present. Its presence at any interval in the fossil record is already taken to constrain atmospheric oxygen within the range of 13% to 35% (the “fire window”). Herein, we observe that, as predicted, atmospheric oxygen levels rise from ≈13% in the Late Devonian to ≈30% in the Late Permian so, too, fires progressively occur in an increasing diversity of ecosystems. Sequentially, data of note include: the occurrence of charcoal in the Late Silurian/Early Devonian, indicating the burning of a diminutive, dominantly rhyniophytoid vegetation; an apparent paucity of charcoal in the Middle to Late Devonian that coincides with a predicted atmospheric oxygen low; and the subsequent diversification of fire systems throughout the remainder of the Late Paleozoic. First, fires become widespread during the Early Mississippian, they then become commonplace in mire systems in the Middle Mississippian; in the Pennsylvanian they are first recorded in upland settings and finally, based on coal petrology, become extremely important in many Permian mire settings. These trends conform well to changes in atmospheric oxygen concentration, as predicted by modeling, and indicate oxygen levels are a significant control on long-term fire occurrence. PMID:16832054

Strain partitioning in the footwall of the Somiedo Nappe: structural evolution of the Narcea Tectonic Window, NW Spain

NASA Astrophysics Data System (ADS)

Gutiérrez-Alonso, Gabriel

1996-10-01

The Somiedo Nappe is a major thrust unit in the Cantabrian Zone, the external foreland fold and thrust belt of the North Iberian Variscan orogen. Exposed at the Narcea Tectonic Window are Precambrian rocks below the basal decollement of the Somiedo Nappe, which exhibit a different deformation style than the overlying Paleozoic rocks above the basal decollement. During Variscan deformation, folding and widespread subhorizontal, bedding-parallel decollements were produced in the hanging wall within the Paleozoic rocks. Vertical folding, with related axial-planar cleavage at a high angle to the decollement planes, developed simultaneously in the upper Proterozoic Narcea Slates of the footwall, below the detachment. The relative magnitude of finite strain, measured in the footwall rocks, diminishes towards the foreland. These observations indicate that (1) significant deformation may occur in the footwall of foreland fold and thrust belts, (2) the shortening mechanism in the footwall may be different from that of the hanging wall, and (3) in this particular case, the partitioning of the deformation implies the existence of a deeper, blind decollement surface contemporaneous with the first stages of the foreland development, that does not crop out in the region. This implies a significant shortening in the footwall, which must be taken into account when restoration and balancing of cross-sections is attempted. A sequential diagram of the evolution of the Narcea Tectonic Window with a minimum shortening of 85 km is proposed, explaining the complete Variscan evolution of the foreland to hinterland transition in the North Iberian Variscan orogen.

Architecture and evolution of an Early Permian carbonate complex on a tectonically active island in east-central California

USGS Publications Warehouse

Stevens, Calvin H.; Magginetti, Robert T.; Stone, Paul

2015-01-01

The newly named Upland Valley Limestone represents a carbonate complex that developed on and adjacent to a tectonically active island in east-central California during a brief interval of Early Permian (late Artinskian) time. This lithologically unique, relatively thin limestone unit lies within a thick sequence of predominantly siliciclastic rocks and is characterized by its high concentration of crinoidal debris, pronounced lateral changes in thickness and lithofacies, and a largely endemic fusulinid fauna. Most outcrops represent a carbonate platform and debris derived from it and shed downslope, but another group of outcrops represents one or possibly more isolated carbonate buildups that developed offshore from the platform. Tectonic activity in the area occurred before, probably during, and after deposition of this short-lived carbonate complex.

Tectonic study of the extension of the New Madrid fault zone near its intersection with the 38th parallel lineament

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

Braile, L.W.; Hinze, W.J.; Sexton, J.L.

1982-06-01

Gravity, magnetic, geologic, and seismicity data have been combined in a seismotectonic analysis of the New Madrid seismic zone. Previous studies have presented evidence for several rift zones in this area (Upper Mississippi enmbayment), including the Reelfoot rift, a late precambrian-early Paleozoic failed arm which extends north-northeast from the ancient continental margin. We suggest that the northern terminus of the Reelfoot rift forms a rift complex, with arms extending northeast into southwestern Indiana, northwest along the Mississippi River, and east into western Kentucky, which appears to correlate well with the seismicity in the area. This correlation suggests that faults associatedmore » with this rift complex are being reactivated in the contemporary stress field (east-northeast compression). If this interpretation is valid, it represents a seismotectonic model which can be used to predict the extent of future seismicity in the New Madrid seismic zone. The proposed rift complex also provides a coherent model for the tectonic development of this region of the North American midcontinent.« less

Lithostratigraphic, conodont, and other faunal links between lower Paleozoic strata in northern and central Alaska and northeastern Russia

USGS Publications Warehouse

Dumoulin, Julie A.; Harris, Anita G.; Gagiev, Mussa; Bradley, Dwight C.; Repetski, John E.

2002-01-01

Lower Paleozoic platform carbonate strata in northern Alaska (parts of the Arctic Alaska, York, and Seward terranes; herein called the North Alaska carbonate platform) and central Alaska (Farewell terrane) share distinctive lithologic and faunal features, and may have formed on a single continental fragment situated between Siberia and Laurentia. Sedimentary successions in northern and central Alaska overlie Late Proterozoic metamorphosed basement; contain Late Proterozoic ooid-rich dolostones, Middle Cambrian outer shelf deposits, and Ordovician, Silurian, and Devonian shallow-water platform facies, and include fossils of both Siberian and Laurentian biotic provinces. The presence in the Alaskan terranes of Siberian forms not seen in wellstudied cratonal margin sequences of western Laurentia implies that the Alaskan rocks were not attached to Laurentia during the early Paleozoic.The Siberian cratonal succession includes Archean basement, Ordovician shallow-water siliciclastic rocks, and Upper Silurian–Devonian evaporites, none of which have counterparts in the Alaskan successions, and contains only a few of the Laurentian conodonts that occur in Alaska. Thus we conclude that the lower Paleozoic platform successions of northern and central Alaska were not part of the Siberian craton during their deposition, but may have formed on a crustal fragment rifted away from Siberia during the Late Proterozoic. The Alaskan strata have more similarities to coeval rocks in some peri-Siberian terranes of northeastern Russia (Kotelny, Chukotka, and Omulevka). Lithologic ties between northern Alaska, the Farewell terrane, and the peri-Siberian terranes diminish after the Middle Devonian, but Siberian afµnities in northern and central Alaskan biotas persist into the late Paleozoic.

Inventory of Neoproterozoic and Paleozoic strata in Sonora, Mexico

USGS Publications Warehouse

Stewart, John H.; Poole, Forrest G.

2002-01-01

This compilation is an inventory of all known outcrops of Neoproterozoic and Paleozoic strata in Sonora, Mexico. We have not attempted an interpretation of the regional stratigraphic or structural setting of the strata. Brief summaries of the stratigraphic setting of the Sonora rocks are given in Poole and Hayes (1971), Rangin (1978), Stewart and others (1984, 1990), and Poole and Madrid (1986; 1988b). More specific information on the setting of strata of specific ages are given by Stewart and others (2002) for the Neoproterozoic and Cambrian; by Poole and others (1995a) for Ordovician shelf strata; by Poole and others (1995b) for Ordovician deep-water openbasin strata; by Poole and others (1997, 1998, 2000a) for Silurian strata; and by Poole and others (2000a) for Mississippian strata. Other reports that discuss regional aspects of Paleozoic stratigraphy include López-Ramos (1982), Peiffer-Rangin, (1979, 1988), Pérez-Ramos (1992), and Stewart and others (1997, 1999a). Structurally, the major Paleozoic feature of Sonora is the Sonora allochthon, consisting of deep-water (eugeoclinal) strata emplaced in the Permian over shelf (miogeoclinal) deposits (Poole and others, 1995a,b; Poole and Perry, 1997; 1998). The emplacement structure is generally considered to be a major Permian continental margin thrust fault that emplaced the deep-water rocks northward over shelf (miogeoclinal) deposits. An alternate interpretation has been presented by Stewart and others (2002). He proposed that the emplacement of the Sonora allochthon was along a major Permian transpressional structure that was primarily a strike-slip fault with only a minor thrust component . The Mojave-Sonora megashear has been proposed to disrupt Neoproterozoic and Paleozoic trends in Sonora. This feature is a hypothetical, left-lateral, northwest-striking fault extending across northern Sonora and the southwestern United States (Silver and Anderson, 1974; Anderson and Schmidt, 1983). It is proposed to have

Paleozoic–early Mesozoic gold deposits of the Xinjiang Autonomous Region, northwestern China

USGS Publications Warehouse

Rui, Zongyao; Goldfarb, Richard J.; Qiu, Yumin; Zhou, T.; Chen, R.; Pirajno, Franco; Yun, Grace

2002-01-01

The late Paleozoic–early Mesozoic tectonic evolution of Xinjiang Autonomous Region, northwestern China provided a favorable geological setting for the formation of lode gold deposits along the sutures between a number of the major Eastern Asia cratonic blocks. These sutures are now represented by the Altay Shan, Tian Shan, and Kunlun Shan ranges, with the former two separated by the Junggar basin and the latter two by the immense Tarim basin. In northernmost Xinjiang, final growth of the Altaid orogen, southward from the Angara craton, is now recorded in the remote mid- to late Paleozoic Altay Shan. Accreted Early to Middle Devonian oceanic rock sequences contain typically small, precious-metal bearing Fe–Cu–Zn VMS deposits (e.g. Ashele). Orogenic gold deposits are widespread along the major Irtysh (e.g. Duyolanasayi, Saidi, Taerde, Kabenbulake, Akexike, Shaerbulake) and Tuergen–Hongshanzui (e.g. Hongshanzui) fault systems, as well as in structurally displaced terrane slivers of the western Junggar (e.g. Hatu) and eastern Junggar areas. Geological and geochronological constraints indicate a generally Late Carboniferous to Early Permian episode of gold deposition, which was coeval with the final stages of Altaid magmatism and large-scale, right-lateral translation along older terrane-bounding faults. The Tian Shan, an exceptionally gold-rich mountain range to the west in the Central Asian republics, is only beginning to be recognized for its gold potential in Xinjiang. In this easternmost part to the range, northerly- and southerly-directed subduction/accretion of early to mid-Paleozoic and mid- to late Paleozoic oceanic terranes, respectively, to the Precambrian Yili block (central Tian Shan) was associated with 400 to 250 Ma arc magmatism and Carboniferous through Early Permian gold-forming hydrothermal events. The more significant resulting deposits in the terranes of the southern Tian Shan include the Sawayaerdun orogenic deposit along the Kyrgyzstan

Global-scale tectonic patterns on Pluto

NASA Astrophysics Data System (ADS)

Matsuyama, I.; Keane, J. T.; Kamata, S.

2016-12-01

The New Horizons spacecraft revealed a global-scale tectonic pattern on the surface of Pluto which is presumably related to its formation and early evolution. Changes in the rotational and tidal potentials, expansion, and loading can generate stresses capable of producing global-scale tectonic patterns. The current alignment of Sputnik Planum with the tidal axis suggests a reorientation of Pluto relative to the rotation and tidal axes, or true polar wander. This reorientation can be driven by mass loading associated with Sputnik Planum. We developed a general theoretical formalism for the calculation of tectonic patterns due to a variety of process including true polar wander, loading, and expansion. The formalism is general enough to be applicable to non-axisymmetric loads. We illustrate that the observed global-scale tectonic pattern can be explained by stresses generated by true polar wander, Sputnik Planum loading, and expansion.

Evolution of the Sibişel Shear Zone (South Carpathians): A study of its type locality near Răşinari (Romania) and tectonic implications

NASA Astrophysics Data System (ADS)

Ducea, Mihai N.; Negulescu, Elena; Profeta, Lucia; Sǎbǎu, Gavril; Jianu, Denisa; Petrescu, Lucian; Hoffman, Derek

2016-09-01

The Sibişel Shear Zone is a 1-3 km wide, ductile shear zone located in the South Carpathian Mountains, Romania. In the Rășinari area, the ductile shear zone juxtaposes amphibolite facies rocks of the Lotru Metamorphic Suite against greenschist facies rocks of the Râuşorul Cisnădioarei Formation. The first represents the eroded remnants of Peri-Gondwanan arcs formed between the Neoproterozoic-Silurian (650-430 Ma), regionally metamorphosed to amphibolite facies during the Variscan orogeny (350-320 Ma). The second is composed of metasedimentary and metavolcanic Neoproterozoic-Ordovician (700-497 Ma) assemblages of mafic to intermediate bulk composition also resembling an island arc metamorphosed during the Ordovician (prior to 463 Ma). Between these lie the epidote amphibolite facies mylonitic and ultramylonitic rocks of the Sibișel Formation, a tectonic mélange dominated by mafic actinolite schists attenuated into a high strain ductile shear zone. Mineral Rb-Sr isochrons document the time of juxtaposition of the three domains during the Permian to Early Triassic ( 290-240 Ma). Ductile shear sense indicators suggest a right lateral transpressive mechanism of juxtaposition; the Sibişel shear zone is a remnant Permo-Triassic suture between two Early Paleozoic Gondwanan terranes. A zircon and apatite U-Th/He age transect across the shear zone yields Alpine ages (54-90 Ma apatite and 98-122 Ma zircon); these data demonstrate that the exposed rocks were not subjected to Alpine ductile deformation. Our results have significant implications for the assembly of Gondwanan terranes and their docking to Baltica during Pangea's formation. Arc terranes free of Variscan metamorphism existed until the Early Triassic, emphasizing the complex tectonics of terrane amalgamation during the closure of Paleotethys.

Paleozoic shale gas resources in the Sichuan Basin, China

USGS Publications Warehouse

Potter, Christopher J.

2018-01-01

The Sichuan Basin, China, is commonly considered to contain the world’s most abundant shale gas resources. Although its Paleozoic marine shales share many basic characteristics with successful United States gas shales, numerous geologic uncertainties exist, and Sichuan Basin shale gas production is nascent. Gas retention was likely compromised by the age of the shale reservoirs, multiple uplifts and orogenies, and migration pathways along unconformities. High thermal maturities raise questions about gas storage potential in lower Paleozoic shales. Given these uncertainties, a new look at Sichuan Basin shale gas resources is advantageous. As part of a systematic effort to quantitatively assess continuous oil and gas resources in priority basins worldwide, the US Geological Survey (USGS) completed an assessment of Paleozoic shale gas in the Sichuan Basin in 2015. Three organic-rich marine Paleozoic shale intervals meet the USGS geologic criteria for quantitative assessment of shale gas resources: the lower Cambrian Qiongzhusi Formation, the uppermost Ordovician Wufeng through lowermost Silurian Longmaxi Formations (currently producing shale gas), and the upper Permian Longtan and Dalong Formations. This study defined geologically based assessment units and calculated probabilistic distributions of technically recoverable shale gas resources using the USGS well productivity–based method. For six assessment units evaluated in 2015, the USGS estimated a mean value of 23.9 tcf (677 billion cubic meters) of undiscovered, technically recoverable shale gas. This result is considerably lower than volumes calculated in previous shale gas assessments of the Sichuan Basin, highlighting a need for caution in this geologically challenging setting.

Geochemistry, zircon U-Pb dating and Hf isotopies composition of Paleozoic granitoids in Jinchuan, NW China: Constraints on their petrogenesis, source characteristics and tectonic implication

NASA Astrophysics Data System (ADS)

Zeng, Renyu; Lai, Jianqing; Mao, Xiancheng; Li, Bin; Ju, Peijiao; Tao, Shilong

2016-05-01

Granitoids are widely distributed in Jinchuan at the southwestern margin of the North China plate, which is also an important area of mineral deposits. The research subject of this article are two Paleozoic granitoids, a cataclastic syenogranite and a granodiorite porphyry. This study presents whole rock geochemistry and zircon U-Pb-Hf isotope data for the two granitoids to determine their petrogenesis, source characteristics and tectonic significance. The cataclastic syenogranite is characterized by metaluminous composition with high potassium, and LaN/YbN from 39 to 48. The composition with strong negative Eu anomalies and Zircon saturation temperatures (TZr) from 947 to 1072 °C classify this intrusion as an A-type granite. The granodiorite porphyry is metaluminous with high sodium, sub-alkaline, LaN/YbN ratios from 27 to 32. These I-type intrusions have no Eu anomalies and TZr ranges from 818 to 845 °C. Both the cataclastic syenogranite and granodiorite porphyry show enrichment of LREE and LILE and depletion of HREE and HFSE, except Hf and Zr. Using single zircon LA-ICP-MS U-Pb dating, the emplacement age of the cataclastic syenogranite and granodiorite porphyry are determined at 433.4 ± 3.7 Ma and 361.7 ± 4.6 Ma, respectively. Zircons from the cataclastic syenogranits have uniform negative εHf(t) values (-11 ± 0.5 to -9 ± 0.5), implying the involvement of an old Palaeoproterozoic crustal source in magma genesis. The zircons from the granodiorite porphyry have εHf(t) values that range from -8 ± 1.0 to +10 ± 0.6, suggesting heterogeneous source materials involving both juvenile and ancient crust reworked crustal components. Based on the geological significance of granites at the southwestern margin of the North China plate, the closure of the North Qilian Ocean occurred at ∼444 Ma. Geochemical features suggest that the cataclastic syenogranite and granodiorite porphyry formed in an intraplate extensional and compressional setting, respectively. Hence

Tectonic history of the Illinois basin

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

Kolata, D.R.; Nelson, J.W.

1990-05-01

The Illinois basin began as a failed rift that developed during breakup of a supercontinent approximately 550 Ma. A rift basin in the southernmost part of the present Illinois basin subsided rapidly and filled with about 3,000 m of probable Early and Middle Cambrian sediments. By the Late Cambrian, the rift-bounding faults became inactive and a broad relatively slowly subsiding embayment, extending well beyond the rift and open to the Iapetus Ocean, persisted through most of the Paleozoic Era. Widespread deformation swept through the proto-Illinois basin beginning in the latest Mississippian, continuing to the end of the Paleozoic Era. Upliftmore » of basement fault blocks resulted in the formation of many major folds and faults. The timing of deformation and location of these structures in the forelands of the Ouachita and Alleghanian orogenic belts suggest that much of the deformation resulted from continental collision between North America and Gondwana. The associated compressional stress reactivated the ancient rift-bounding faults, upthrusting the northern edge of a crustal block approximately 1,000 m within the rift. Concurrently, dikes (radiometrically dated as Early Permian), sills, and explosion breccias formed in or adjacent to the reactivated rift. Subsequent extensional stress, probably associated with breakup of Pangea, caused the crustal block within the rift to sink back to near its original position. High-angle, northeast- to east-west-trending normal faults, with as much as 1,000 m of displacement, formed in the southern part of the basin. These faults displace some of the northwest trending Early Permian dikes. Structural closure of the southern end of the Illinois basin was caused by uplift of the Pascola arch sometime between the Late Pennsylvanian and Late Cretaceous.« less

Late Proterozoic-Paleozoic evolution of the Arctic Alaska-Chukotka terrane based on U-Pb igneous and detrital zircon ages: Implications for Neoproterozoic paleogeographic reconstructions

USGS Publications Warehouse

Amato, J.M.; Toro, J.; Miller, E.L.; Gehrels, G.E.; Farmer, G.L.; Gottlieb, E.S.; Till, A.B.

2009-01-01

The Seward Peninsula of northwestern Alaska is part of the Arctic Alaska-Chukotka terrane, a crustal fragment exotic to western Laurentia with an uncertain origin and pre-Mesozoic evolution. U-Pb zircon geochronology on deformed igneous rocks reveals a previously unknown intermediate-felsic volcanic event at 870 Ma, coeval with rift-related magmatism associated with early breakup of eastern Rodinia. Orthogneiss bodies on Seward Peninsula yielded numerous 680 Ma U-Pb ages. The Arctic Alaska-Chukotka terrane has pre-Neoproterozoic basement based on Mesoproterozoic Nd model ages from both 870 Ma and 680 Ma igneous rocks, and detrital zircon ages between 2.0 and 1.0 Ga in overlying cover rocks. Small-volume magmatism occurred in Devonian time, based on U-Pb dating of granitic rocks. U-Pb dating of detrital zircons in 12 samples of metamorphosed Paleozoic siliciclastic cover rocks to this basement indicates that the dominant zircon age populations in the 934 zircons analyzed are found in the range 700-540 Ma, with prominent peaks at 720-660 Ma, 620-590 Ma, 560-510 Ma, 485 Ma, and 440-400 Ma. Devonian- and Pennsylvanian-age peaks are present in the samples with the youngest detrital zircons. These data show that the Seward Peninsula is exotic to western Laurentia because of the abundance of Neoproterozoic detrital zircons, which are rare or absent in Lower Paleozoic Cordilleran continental shelf rocks. Maximum depositional ages inferred from the youngest detrital age peaks include latest Proterozoic-Early Cambrian, Cambrian, Ordovician, Silurian, Devonian, and Pennsylvanian. These maximum depositional ages overlap with conodont ages reported from fossiliferous carbonate rocks on Seward Peninsula. The distinctive features of the Arctic Alaska-Chukotka terrane include Neoproterozoic felsic magmatic rocks intruding 2.0-1.1 Ga crust overlain by Paleozoic carbonate rocks and Paleozoic siliciclastic rocks with Neoproterozoic detrital zircons. The Neoproterozoic ages are

Cenozoic intraplate tectonics in Central Patagonia: Record of main Andean phases in a weak upper plate

NASA Astrophysics Data System (ADS)

Gianni, G. M.; Echaurren, A.; Folguera, A.; Likerman, J.; Encinas, A.; García, H. P. A.; Dal Molin, C.; Valencia, V. A.

2017-11-01

Contraction in intraplate areas is still poorly understood relative to similar deformation at plate margins. In order to contribute to its comprehension, we study the Patagonian broken foreland (PBF) in South America whose evolution remains controversial. Time constraints of tectonic events and structural characterization of this belt are limited. Also, major causes of strain location in this orogen far from the plate margin are enigmatic. To unravel tectonic events, we studied the Cenozoic sedimentary record of the central sector of the Patagonian broken foreland (San Bernardo fold and thrust belt, 44°30‧S-46°S) and the Andes (Meseta de Chalia, 46°S) following an approach involving growth-strata detection, U-Pb geochronology and structural modeling. Additionally, we elaborate a high resolution analysis of the effective elastic thickness (Te) to examine the relation between intraplate contraction location and variations in lithospheric strength. The occurrence of Eocene growth-strata ( 44-40 Ma) suggests that contraction in the Andes and the Patagonian broken foreland was linked to the Incaic phase. Detection of synextensional deposits suggests that the broken foreland collapsed partially during Oligocene to early Miocene. During middle Miocene times, the Quechua contractional phase produced folding of Neogene volcanic rocks and olistostrome deposition at 17 Ma. Finally, the presented Te map shows that intraplate contraction related to Andean phases localized preferentially along weak lithospheric zones (Te < 15 km). Hence, the observed strain distribution in the PBF appears to be controlled by lateral variations in the lithospheric strength. Variations in this parameter could be related to thermo-mechanical weakening produced by intraplate rifting in Paleozoic-Mesozoic times.

Late Mesozoic and possible early Tertiary accretion in western Washington State: the Helena-Haystack melange and the Darrington- Devils Mountain fault zone

USGS Publications Warehouse

Tabor, R.W.

1994-01-01

The Helena-Haystack melange (HH melange) and coincident Darrington-Devils Mountain fault zone (DDMFZ) in northwestern Washington separate two terranes, the northwest Cascade System (NWCS) and the western and eastern melange belts (WEMB). The two terranes of Paleozoic and Mesozoic rocks superficially resemble each other but record considerable differences in structural and metamorphic history. The HH melange is a serpentinite-matrix melange containing blocks of adjacent terranes but also exotic blocks. The HH melange must have formed between early Cretaceous and late middle Eocene time, because it contains tectonic clasts of early Cretaceous Shuksan Greenschist and is overlain by late middle Eocene sedimentary and volcanic rocks. The possible continuation of the DDMFZ to the northwest as the San Juan and the West Coast faults on Vancouver Island suggests that the structure has had a major role in the emplacement of all the westernmost terranes in the Pacific Northwest. -from Author

The Neoproterozoic-Paleozoic Arctic Margins: early stages of geodynamic evolution and plate reconstructions

NASA Astrophysics Data System (ADS)

Vernikovsky, V. A.; Metelkin, D. V.; Vernikovskaya, A. E.; Matushkin, N. Yu.; Lobkovsky, L. I.; Shipilov, E. V.

2012-04-01

Available data on the existence of Precambrian metamorphic complexes among the main structures of the Arctic led to the suggestion that a large continental mass existed between Laurentia, Baltica and Siberia - an Arctic continent, more often called Arctida (Zonenshain, Natapov, 1987). It is inferred that as an independent continental mass Arctida was formed after the breakup of Rodinia, and in general it can have a pre-Grenvillian (including Grenvillian) basement age. The breakup of this mass and the collision of its fragments with adjacent cratons led to the formation of heterochronous collisional systems. Arctida probably included the Kara, Novosibirsk, Alaska-Chukotka blocks, the blocks of northern Alaska and the submerged Lomonosov Ridge, small fragments of the Inuit fold belt in the north of Greenland and the Canadian archipelago, the structures of the Svalbard and maybe the Timan-Pechora plates. However the inner structure of this paleocontinent, the mutual configuration of the blocks and its evolution in the Neoproterozoic-Paleozoic is still a matter of discussion. The most accurate way of solving these issues is by using paleomagnetic data, but those are nonexistent for most of the defined blocks. Reliable paleomagnetic determinations for the Neoproterozoic-Paleozoic time interval we are concerned with are available only for fragments of an island arc from Central Taimyr, which are 960 m.y. old (Vernikovsky et al., 2011) and for which the paleomagnetic pole is very close to the pole of Siberia from (Pavlov et al., 2002), and of the Kara microcontinent. This includes three paleomagnetic poles for 500, 450 and 420 Ma (Metelkin et al., 2000; Metelkin et al., 2005). It is those data that made up the basis of the presented paleotectonic reconstructions along with an extensive paleomagnetic database for the cratons of Laurentia, Baltica, Siberia and Gondwana. The paleogeographic position of the cratons is corrected (within the confidence levels for the

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

USGS Publications Warehouse

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

2003-01-01

The Jerritt Canyon mining district in the northern Independence Range, northern Nevada, contains multiple, nearly horizontal, thrust masses of platform carbonate rocks that are exposed in a series of north- to northeast-elongated, tectonic windows through rocks of the Roberts Mountains allochthon. The Roberts Mountains allochthon was emplaced during the Late Devonian to Early Mississippian Antler orogeny. These thrust masses contain structurally and stratigraphically controlled Carlin-type gold deposits. The gold deposits are hosted in tectonically truncated units of the Silurian to Devonian Hanson Creek and Roberts Mountains Formations that lie within structural slices of an Eastern assemblage of Cambrian to Devonian carbonate rocks. In addition, these multiply thrust-faulted and folded host rocks are structurally interleaved with Mississippian siliciclastic rocks and are overlain structurally by Cambrian to Devonian siliciclastic units of the Roberts Mountains allochthon. All sedimentary rocks were involved in thrusting, high-angle faulting, and folding, and some of these events indicate substantial late Paleozoic and/or Mesozoic regional shortening. Early Pennsylvanian and late Eocene dikes also intrude the sedimentary rocks. These rocks all were uplifted into a northeast-trending range by subsequent late Cenozoic Basin and Range faulting. Eocene sedimentary and volcanic rocks flank part of the range. Pathways of hydrothermal fluid flow and locations of Carlin-type gold orebodies in the Jerritt Canyon mining district were controlled by structural and host-rock geometries within specific lithologies of the stacked thrust masses of Eastern assemblage rocks. The gold deposits are most common proximal to intersections of northeast-striking faults, northwest-striking dikes, and thrust planes that lie adjacent to permeable stratigraphic horizons. The host stratigraphic units include carbonate sequences that contained primary intercrystalline permeability, which

The tectonics of Venus: An overview

NASA Technical Reports Server (NTRS)

Solomon, Sean C.

1992-01-01

While the Pioneer Venus altimeter, Earth-based radar observatories, and the Venera 15-16 orbital imaging radars provided views of large-scale tectonic features on Venus at ever-increasing resolution, the radar images from Magellan constitute an improvement in resolution of at least an order of magnitude over the best previously available. A summary of early Magellan observations of tectonic features on Venus was published, but data available at that time were restricted to the first month of mapping and represented only about 15 percent of the surface of the planet. Magellan images and altimetry are now available for more than 95 percent of the Venus surface. Thus a more global perspective may be taken on the styles and distribution of lithospheric deformation on Venus and their implications for the tectonic history of the planet.

Faulting at Thebes Gap, Mo. -Ill. : Implications for New Madrid tectonism

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

Harrison, R.W.; Schultz, A.P.

1992-01-01

Recent geologic mapping in the Thebes Gap area has identified numerous NNE- and NE-striking faults having a long-lived and complex structural history. The faults are located in an area of moderate recent seismicity at the northern margin of the Mississippi embayment, approximately 45 km north of the New Madrid seismic zone. Earliest deformation occurred along dextral strike-slip faults constrained as post-Devonian and pre-Cretaceous. Uplift and erosion of all Carboniferous strata suggest that this faulting is related to development of the Pascola arch (Ouachita orogeny). This early deformation is characterized by strongly faulted and folded Ordovician through Devonian rocks overlain inmore » places with angular unconformity by undeformed Cretaceous strata. Elsewhere, younger deformation involves Paleozoic, Cretaceous, Paleocene, and Eocene formations. These units have experienced both minor high-angle normal faulting and major, dextral strike-slip faulting. Quaternary-Tertiary Mounds Gravel is also involved in the latest episode of strike-slip deformation. Enechelon north-south folds, antithetic R[prime] shears, and drag folds indicate right-lateral motion. Characteristic positive and negative flower structures are commonly revealed in cross section. Right-stepping fault strands have produced pull-apart basins where Ordovician, Silurian, Devonian, Cretaceous, and Tertiary units are downdropped several hundreds of meters and occur in chaotic orientations. Similar fault orientations and kinematics, as well as recent seismicity and close proximity, clearly suggest a structural relationship between deformation at Thebes Gap and tectonism associated with the New Madrid area.« less

Thick-skinned tectonics in a Late Cretaceous-Neogene intracontinental belt (High Atlas Mountains, Morocco): The flat-ramp fault control on basement shortening and cover folding

NASA Astrophysics Data System (ADS)

Fekkak, A.; Ouanaimi, H.; Michard, A.; Soulaimani, A.; Ettachfini, E. M.; Berrada, I.; El Arabi, H.; Lagnaoui, A.; Saddiqi, O.

2018-04-01

Most of the structural studies of the intracontinental High Atlas belt of Morocco have dealt with the central part of the belt, whose basement does not crop out. Here we study the Alpine deformation of the North Subatlas Zone, which is the part of the Western High Atlas (WHA) Paleozoic Massif that involves both Paleozoic basement units and remnants of their Mesozoic-Cenozoic cover formations. Our aim is to better constrain the geometry and kinematics of the basement faults during the Alpine shortening. Based on detail mapping, satellite imagery and field observations, we describe an array of sub-equatorial, transverse and oblique faults between the WHA Axial Zone and the Haouz Neogene basin. They define a mosaic of basement blocks pushed upon one another and upon the Haouz basement along the North Atlas Fault (NAF). The Axial Zone makes up the hanging-wall of the Adassil-Medinet Fault (AMF) south of this mosaic. The faults generally presents flat-ramp-flat geometry linked to the activation of multiple décollement levels, either within the basement where its foliation is subhorizontal or within favourable cover formations (Jurassic evaporites, Lower Cretaceous silty red beds, Upper Cretaceous evaporitic marls, Neogene basal argillites). The occurrence of the North Atlas detachment (NAD) allowed folded pop-up units to develop in front of the propagating NAF. Shortening began as early as the Campanian-Maastrichtian along the AMF. The direction of the maximum horizontal stress rotated from NNE-SSW to NNW-SSE from the Maastrichtian-Paleocene to the Neogene. The amount of shortening reaches 20% in the Azegour transect. This compares with the shortening amount published for the central-eastern High Atlas, suggesting that similar structures characterize the Paleozoic basement all along the belt. The WHA thick-skinned tectonics evokes that of the frontal Sevier belt and of the external Western Alps, although with a much minor pre-inversion burial.

Early Paleozoic dioritic and granitic plutons in the Eastern Tianshan Orogenic Belt, NW China: Constraints on the initiation of a magmatic arc in the southern Central Asian Orogenic Belt

NASA Astrophysics Data System (ADS)

Du, Long; Long, Xiaoping; Yuan, Chao; Zhang, Yunying; Huang, Zongying; Sun, Min; Zhao, Guochun; Xiao, Wenjiao

2018-03-01

Early Paleozoic dioritic and granitic plutons in the Eastern Tianshan Orogenic Belt (ETOB) have been studied in order to constraint the initiation of a magmatic arc formed in this region. Zircon U-Pb dating indicates that two dioritic plutons in the northern ETOB were generated in the Late Ordovician (452 ± 4 Ma) and the Early Silurian (442 ± 3 Ma), respectively. Diorites from the two plutons are characterized by enrichments in large ion lithophile elements (LILE) and highly incompatible elements, with depletions in high field strength elements (HSFE) displaying typical geochemical features of a subduction-related origin. They have positive εNd(t) values (+5.08-+6.58), relatively young Nd model ages (TDM = 0.71-1.08 Ga), with Ta/Yb (0.05-0.09) and Nb/Ta ratios (12.06-15.19) similar to those of depleted mantle, suggesting a juvenile mantle origin. Their high Ba/La (13.3-35.9), low Th/Yb (0.72-2.02), and relatively low Ce/Th (4.57-14.7) and Ba/Th (47.8-235) ratios indicate that these diorites were probably produced by partial melting of a depleted mantle wedge metasomatized by both subducted sediment-derived melts and slab-derived aqueous fluids. Zircon U-Pb dating of a granitic pluton in the northern ETOB yielded a Late Ordovician intrusion age of 447 ± 5 Ma. Granites from this pluton show calc-alkaline compositions with geochemical characteristics of I-type granites. They also show positive εNd(t) values (+6.49-+6.95) and young Nd model ages (TDM = 0.69-0.87 Ga), indicating that the granites were most likely derived from juvenile lower crust. Our new dating results on the dioritic and granitic plutons suggest that arc-type magmatism in the northern ETOB began prior to or at the Late Ordovician (452-442 Ma). In addition, north-dipping subduction of the Kangguertage oceanic lithosphere may account for the arc-type magmatism and the geodynamic process of the ETOB in the Early Paleozoic.

Permian-Early Triassic tectonics and stratigraphy of the Karoo Supergroup in northwestern Mozambique

NASA Astrophysics Data System (ADS)

Bicca, Marcos Müller; Philipp, Ruy Paulo; Jelinek, Andrea Ritter; Ketzer, João Marcelo Medina; dos Santos Scherer, Claiton Marlon; Jamal, Daúd Liace; dos Reis, Adriano Domingos

2017-06-01

The Gondwana continent was the base of great basin inception, sedimentation and magmatism throughout the Cambrian to Middle Jurassic periods. The northwestern Mozambique igneous and metamorphic basement assemblages host the NW-trending Moatize Minjova Basin, which has great economic potential for coal and gas mining. This rift basin was activated by an S-SW stress field during the Early Permian period, as constrained by regional and field scale structural data. Tectonically induced subsidence in the basin, from the reactivation of NW-SE and NNE-SSW regional structures is well recorded by faults, folds and synsedimentary fractures within the Early Late Permian Moatize Formation. NW-SE, N-S and NE-SW field structures consist of post-Karoo reactivation patterns related to a NNE-SSW extension produced by the Pangea breakup and early inception stages of the Great East African Rift System. The Early Late Permian sequences of the Moatize-Minjova Basin are composed of fluvial meandering, coal-bearing beds of the Moatize Formation, which comprises mostly floodplain, crevasse splay and fluvial channel lithofacies associations, deposited in a cyclic pattern. This sequence was overlapped by a multiple-story, braided fluvial plain sequence of the Matinde Formation (Late Permian - Early Triassic). Lithofacies associations in the Matinde Formation and its internal relationships suggest deposition of poorly channelized braided alluvial plain in which downstream and probably lateral accretion macroforms alternate with gravity flow deposits. NW paleoflow measurements suggest that Permian fluvial headwaters were located somewhere southeast of the study area, possibly between the African and Antarctic Precambrian highlands.

Provenance of Carboniferous sedimentary rocks in the northern margin of Dabie Mountains, central China and the tectonic significance: constraints from trace elements, mineral chemistry and SHRIMP dating of zircons

NASA Astrophysics Data System (ADS)

Li, Renwei; Li, Shuangying; Jin, Fuquan; Wan, Yusheng; Zhang, Shukun

2004-04-01

A suite of slightly metamorphosed Carboniferous sedimentary strata occurs in the northern margin of the Dabie Mountains, central China. It consists, in ascending order, of the upper Huayuanqiang Formation (C 1), the Yangshan Formation (C 1), the Daorenchong Formation (C 1-2), the most widely distributed Huyoufang Formation (C 2) and the Yangxiaozhuang Formation (C 2). The provenance of the Carboniferous sedimentary rocks is constrained by the integration of trace elements, detrital mineral chemistry and sensitive high resolution ion microprobe (SHRIMP) dating of detrital zircons, which can help to understand the connection between the provenance and the Paleozoic tectonic evolution of the Qinling-Dabie Orogen. The trace element compositions indicate that the source terrain was probably a continental island arc. Detrital tourmalines were mainly derived from aluminous and Al-poor metapelites and metapsammites, and some are sourced from Li-poor granitoids, pegmatites and aplites. Detrital garnets, found only in the uppermost Huyoufang Formation, are almandine and Mn-almandine garnets, indicating probable sources mainly from garnetiferous schists, and partly from granitoid rocks. The detrital white K-micas are muscovitic in the Huayuanqiang, Daorenchong and Huyoufang Formations, and phengitic with Si contents (p.f.u.) from 3.20 up to max. 3.47-3.53 in the uppermost Huyoufang and the Yangxiaozhuang Formations, a meta-sedimentary source. Major components in the detrital zircon age structure for the Huyoufang Formation range from 506 to 363 Ma, centering on ˜400 and ˜480 Ma, which is characteristic of the Qinling and Erlangping Groups in the Qinling and Tongbai Mountains, central China. Evidently, the major source of the Carboniferous sedimentary rocks in the northern margin of Dabie Mountains was from the southern margin of the Sino-Korean Craton represented by the Qinling and Erlangping Groups. The source area was an island-arc system during the Early Paleozoic that

Late Alpine to recent thick-skinned tectonics of the central Swiss Molasse Basin, Canton of Bern, Switzerland

NASA Astrophysics Data System (ADS)

Mock, Samuel; Allenbach, Robin; Wehrens, Philip; Reynolds, Lance; Kurmann-Matzenauer, Eva; Michael, Salomè; Herwegh, Marco

2017-04-01

The Swiss Molasse Basin (SMB) forms part of the North Alpine Foreland Basin. It is a typical peripheral foreland basin, which developed in Paleogene and Neogene times in response to flexural bending of the European lithosphere induced by the orogenic loading of the advancing Alpine thrust wedge. The tectonics of the SMB and the role of Paleozoic and Mesozoic structures are still poorly understood. It is widely accepted that during the main deformation phase of the Jura fold-and-thrust belt, the SMB was riding piggy-back above a major detachment horizon situated within Triassic evaporites. In recent years it has been observed that the Jura fold-and-thrust belt is today deforming in a thick-skinned tectonic style. As for the western and central SMB, most authors still argue in favor of a classical foreland type, thin-skinned style of deformation. Based on the geological 3D modeling of seismic interpretations, we present new insights into the structural configuration of the central SMB. Revised and new interpretations of 2D reflection seismic data from the 1960s to the 1980s reveal a major strike-slip fault zone affecting not only the Mesozoic and Cenozoic cover, but also the crystalline basement beneath. The fault zone reactivated late Paleozoic synsedimentary normal faults bounding a Permo-Carboniferous trough. Basement-involved thrusting observed in the southern part of the SMB seems to be controlled by the presence of slightly inverted Permo-Carboniferous troughs as well. These observations, combined with a compiled structural map and the distribution of recent earthquake hypocenters suggest a late stage, NNW-SSE directed, compressional thick-skinned and strike-slip dominated tectonic activity of the central SMB, post-dating the main deformation phase of the Jura fold-and-thrust belt. This still ongoing deformation might be related to the slab rollback of the European plate and the associated lower crustal delamination as recently suggested by Singer et al. (2014

The Anarak, Jandaq and Posht-e-Badam metamorphic complexes in central Iran: New geological data, relationships and tectonic implications

NASA Astrophysics Data System (ADS)

Bagheri, Sasan; Stampfli, Gérard M.

2008-04-01

The Anarak, Jandaq and Posht-e-Badam metamorphic complexes occupy the NW part of the Central-East Iranian Microcontinent and are juxtaposed with the Great Kavir block and Sanandaj-Sirjan zone. Our recent findings redefine the origin of these complexes, so far attributed to the Precambrian-Early Paleozoic orogenic episodes, and now directly related to the tectonic evolution of the Paleo-Tethys Ocean. This tectonic evolution was initiated by Late Ordovician-Early Devonian rifting events and terminated in the Triassic by the Eocimmerian collision event due to the docking of the Cimmerian blocks with the Asiatic Turan block. The "Variscan accretionary complex" is a new name we proposed for the most widely distributed metamorphic rocks connected to the Anarak and Jandaq complexes. This accretionary complex exposed from SW of Jandaq to the Anarak and Kabudan areas is a thick and fine grain siliciclastic sequence accompanied by marginal-sea ophiolitic remnants, including gabbro-basalts with a supra-subduction-geochemical signature. New 40Ar/ 39Ar ages are obtained as 333-320 Ma for the metamorphism of this sequence under greenschist to amphibolite facies. Moreover, the limy intercalations in the volcano-sedimentary part of this complex in Godar-e-Siah yielded Upper Devonian-Tournaisian conodonts. The northeastern part of this complex in the Jandaq area was intruded by 215 ± 15 Ma arc to collisional granite and pegmatites dated by ID-TIMS and its metamorphic rocks are characterized by some 40Ar/ 39Ar radiometric ages of 163-156 Ma. The "Variscan" accretionary complex was northwardly accreted to the Airekan granitic terrane dated at 549 ± 15 Ma. Later, from the Late Carboniferous to Triassic, huge amounts of oceanic material were accreted to its southern side and penetrated by several seamounts such as the Anarak and Kabudan. This new period of accretion is supported by the 280-230 Ma 40Ar/ 39Ar ages for the Anarak mild high-pressure metamorphic rocks and a 262 Ma U

Volcano-tectonic evolution of the Castle Mountains: 22 to 14 MA

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

Capps, R.C.

1993-04-01

The alkali-calcic Castle Mountains Volcanic rocks (CMV) are host to major gold mineralization. They are located about 100 km south of Las Vegas, Nevada and are on the boundary between the Basin and Range Province and Colorado River extensional corridor (35[degree]18 minutes 45 seconds N, 115[degree]05 minutes 10 seconds W). New data show the following chronology. 22 Ma. A regional rhyolite ash-flow tuff, the Castle Mountain Tuff member, was deposited on a Proterozoic-Paleozoic basement of low relief. <22 Ma - > 17 Ma. Normal faulting (N30--60[degree]W, 60--65[degree]NE) formed half-grabens. Latite and basalt flows, minor ash-flow tuffs, lahars and sediments (Jacksmore » Well member - JW) were deposited unconformably. JW magmas are enriched in light REE compared to the younger CMV. <17 Ma to 15.5 Ma. Oxidizing upper portions (796 C) of a shallowly emplaced silicic melt erupted to form the high-silica rhyolite dome complexes and intrusives (Linder Peak member - LP) of the NNE-striking Castle Mountains. NW-striking transverse structures caused discontinuities in strike direction of the subvolcanic intrusive and domes and helped form a synvolcanic depression. During a hiatus in volcanism, early Hart Peak member (HP) sediments were deposited marginal to the Castle Mountains. Major gold mineralization and widespread hydrothermal alteration occurred at about 15.5 Ma. 16 Ma to 14 Ma. Early HP volcaniclastic sediments, rhyolite pyroclastic-surge tuff, and basaltic flows, were deposited during late hydrothermal alteration and then fractured and displaced by NNE-striking normal faults, especially in the eastern and northeastern CMV. < 14 Ma. Tectonically significant flat-lying boulder conglomerate and unconformably overlying, largely andesitic flows fill depressions in the Castle Mountains and the Piute Range to the east.« less

Detrital Record of Phanerozoic Tectonics in Iran: Evidence From U-Pb Zircon Geochronology

NASA Astrophysics Data System (ADS)

Horton, B. K.; Gillis, R. J.; Stockli, D. F.; Hassanzadeh, J.; Axen, G. J.; Grove, M.

2004-12-01

Ion-microprobe U-Pb ages of 91 detrital zircon grains supplement ongoing investigations of the tectonic history of Iran, a critical region bridging the gap between the Alpine and Himalayan orogenic belts. These data improve understanding of the distribution of continental blocks during a complex history of Late Proterozoic (Pan-African) crustal growth, Paleozoic passive-margin sedimentation, early Mesozoic collision with Eurasia, and Cenozoic collision with Arabia. U-Pb analyses of detrital zircon grains from four sandstone samples (two Lower Cambrian, one uppermost Triassic-Lower Jurassic, one Neogene) collected from the Alborz mountains of northern Iran reveal a spectrum of ages ranging from 50 to 2900 Ma. Most analyses yield concordant to moderately discordant ages. The Lower Cambrian Lalun and Barut sandstones yield age distribution peaks at approximately 550-650, 1000, and 2500 Ma, consistent with a Gondwanan source area presently to the south and west in parts of Iran and the Arabian-Nubian shield (Saudi Arabia and northwestern Africa). The uppermost Triassic-Lower Jurassic Shemshak Formation exhibits a broad range of U-Pb ages, including peaks of approximately 200-260, 330, 430, 600, and 1900 Ma, requiring a Eurasian source area presently to the north and east in the Turan plate (Turkmenistan and southwestern Asia). Neogene strata display both the youngest and oldest ages (approximately 50 and 2900 Ma) of any samples, a result of substantial sedimentary recycling of older Phanerozoic cover rocks. Because the youngest zircon ages for three of the four samples are indistinguishable from their stratigraphic (depositional) ages, these data suggest rapid exhumation and help constrain the termination age of Late Proterozoic-Early Cambrian (Pan-African) orogenesis and the timing of the Iran-Eurasia collision.

Geologic map and upper Paleozoic stratigraphy of the Marble Canyon area, Cottonwood Canyon quadrangle, Death Valley National Park, Inyo County, California

USGS Publications Warehouse

Stone, Paul; Stevens, Calvin H.; Belasky, Paul; Montañez, Isabel P.; Martin, Lauren G.; Wardlaw, Bruce R.; Sandberg, Charles A.; Wan, Elmira; Olson, Holly A.; Priest, Susan S.

2014-01-01

This geologic map and pamphlet focus on the stratigraphy, depositional history, and paleogeographic significance of upper Paleozoic rocks exposed in the Marble Canyon area in Death Valley National Park, California. Bedrock exposed in this area is composed of Mississippian to lower Permian (Cisuralian) marine sedimentary rocks and the Jurassic Hunter Mountain Quartz Monzonite. These units are overlain by Tertiary and Quaternary nonmarine sedimentary deposits that include a previously unrecognized tuff to which we tentatively assign an age of late middle Miocene (~12 Ma) based on tephrochronologic analysis, in addition to the previously recognized Pliocene tuff of Mesquite Spring. Mississippian and Pennsylvanian rocks in the Marble Canyon area represent deposition on the western continental shelf of North America. Mississippian limestone units in the area (Tin Mountain, Stone Canyon, and Santa Rosa Hills Limestones) accumulated on the outer part of a broad carbonate platform that extended southwest across Nevada into east-central California. Carbonate sedimentation was interrupted by a major eustatic sea-level fall that has been interpreted to record the onset of late Paleozoic glaciation in southern Gondwana. Following a brief period of Late Mississippian clastic sedimentation (Indian Springs Formation), a rise in eustatic sea level led to establishment of a new carbonate platform that covered most of the area previously occupied by the Mississippian platform. The Pennsylvanian Bird Spring Formation at Marble Canyon makes up the outer platform component of ten third-order (1 to 5 m.y. duration) stratigraphic sequences recently defined for the regional platform succession. The regional paleogeography was fundamentally changed by major tectonic activity along the continental margin beginning in middle early Permian time. As a result, the Pennsylvanian carbonate shelf at Marble Canyon subsided and was disconformably overlain by lower Permian units (Osborne Canyon and

The global record of local iron geochemical data from Proterozoic through Paleozoic basins

NASA Astrophysics Data System (ADS)

Sperling, E. A.; Wolock, C.; Johnston, D. T.; Knoll, A. H.

2013-12-01

Iron-based redox proxies represent one of the most mature tools available to sedimentary geochemists. These techniques, which benefit from decades of refinement, are based on the fact that rocks deposited under anoxic conditions tend to be enriched in highly-reactive iron. However, there are myriad local controls on the development of anoxia, and no local section is an exemplar for the global ocean. The global signal must thus be determined using techniques like those developed to solve an analogous problem in paleobiology: the inference of global diversity patterns through time from faunas seen in local stratigraphic sections. Here we analyze a dataset of over 4000 iron speciation measurements (including over 600 de novo analyses) to better understand redox changes from the Proterozoic through the Paleozoic Era. Preliminary database analyses yield interesting observations. We find that although anoxic water columns in the middle Proterozoic were dominantly ferruginous, there was a statistical tendency towards euxinia not seen in early Neoproterozoic or Ediacaran data. Also, we find that in the Neoproterozoic oceans, oxic depositional environments-the likely home for early animals-have exceptionally low pyrite contents, and by inference low levels of porewater sulfide. This runs contrary to notions of sulfide stress on early metazoans. Finally, the current database of iron speciation data does not support an Ediacaran or Cambrian oxygenation event. This conclusion is of course only as sharp as the ability of the Fe-proxy database to track dissolved oxygen and does not rule out the possibility of a small-magnitude change in oxygen. It does suggest, however, that if changing pO2 facilitated animal diversification it did so by a limited rise past critical ecological thresholds, such as seen in the modern Oxygen Minimum Zones benthos. Oxygen increase to modern levels thus becomes a Paleozoic problem, and one in need of better sampling if a database approach is to be

Sedimentological constraints on the initial uplift of the West Bogda Mountains in Mid-Permian.

PubMed

Wang, Jian; Cao, Ying-Chang; Wang, Xin-Tong; Liu, Ke-Yu; Wang, Zhu-Kun; Xu, Qi-Song

2018-01-23

The Late Paleozoic is considered to be an important stage in the evolution of the Central Asian Orogenic Belt (CAOB). The Bogda Mountains, a northeastern branch of the Tianshan Mountains, record the complete Paleozoic history of the Tianshan orogenic belt. The tectonic and sedimentary evolution of the west Bogda area and the timing of initial uplift of the West Bogda Mountains were investigated based on detailed sedimentological study of outcrops, including lithology, sedimentary structures, rock and isotopic compositions and paleocurrent directions. At the end of the Early Permian, the West Bogda Trough was closed and an island arc was formed. The sedimentary and subsidence center of the Middle Permian inherited that of the Early Permian. The west Bogda area became an inherited catchment area, and developed a widespread shallow, deep and then shallow lacustrine succession during the Mid-Permian. At the end of the Mid-Permian, strong intracontinental collision caused the initial uplift of the West Bogda Mountains. Sedimentological evidence further confirmed that the West Bogda Mountains was a rift basin in the Carboniferous-Early Permian, and subsequently entered the Late Paleozoic large-scale intracontinental orogeny in the region.

Carboniferous volcanic rocks associated with back-arc extension in the western Chinese Tianshan, NW China: Insight from temporal-spatial character, petrogenesis and tectonic significance

NASA Astrophysics Data System (ADS)

Su, Wenbo; Cai, Keda; Sun, Min; Wan, Bo; Wang, Xiangsong; Bao, Zihe; Xiao, Wenjiao

2018-06-01

The Yili-Central Tianshan Block, as a Late Paleozoic major continental silver of the Central Asian Orogenic Belt, holds a massive volume of Carboniferous volcanic rocks, occurring as subparallel magmatic belts. However, the petrogenesis and tectonic implications of these volcanic rocks remain enigmatic. This study compiled isotopic age data for mapping their temporal-spatial character, and conducted petrogenetic study of these magmatic belts, aiming to understand their tectonic implications. Our compiled dataset reveals four magmatic belts in the Yili-Central Tianshan Block, including the Keguqinshan-Tulasu belt and the Awulale belt in the north, and the Wusun Mountain belt and the Haerk-Nalati belt in the south. In addition, our new zircon U-Pb dating results define two significant Early Carboniferous eruptive events (ca. 355-350 Ma and 325 Ma) in the Wusun Mountain belt. Volcanic rocks of the early significant eruptive event (ca. 355-350 Ma) in the Wusun Mountain comprise basalt, trachy-andesite, andesite, dacite and rhyolite, which are similar to the typical rock assemblage of a continental arc. Their positive εNd(t) values (+0.3 to +1.5) and relatively high Th/Yb and Nb/Yb ratios suggest the derivation from a mantle source with additions of slab-derived components. The gabbroic dykes and rhyolites of the late volcanic event (ca. 325 Ma) form a bimodal rock association, and they show alkaline features, with relatively low Th/Yb and Th/Nb ratios, and higher positive εNd(t) values (εNd(t) = +3.3-+5.0). It is interpreted that the gabbroic dykes and rhyolites may have been derived from mantle and juvenile crustal sources, respectively. The isotopic and trace elemental variations with time elapse of the Wusun Mountain magmatic belt show an important clue for strengthening depletion of the magma sources. Considering the distinctive temporal-spatial character of the Carboniferous volcanic rocks, two separate subduction systems in the southern and northern margins of

Late Cretaceous-Early Eocene Climate Change Linked to Tectonic Eevolution of Neo-Tethyan Subduction Systems

NASA Astrophysics Data System (ADS)

Jagoutz, O. E.; Royden, L.; Macdonald, F. A.

2015-12-01

In this presentation we demonstrate that the two tectonic events in the late Cretaceous-Early Tertiary triggered the two distinct cooling events that followed the Cretaceous Thermal Maximum (CTM). During much of the Cretaceous time, the northern Neo Tethyan ocean was dominated by two east-west striking subduction system. Subduction underneath Eurasia formed a continental arc on the southern margin of Eurasia and intra oceanic subduction in the equatorial region of the Neo Tethys formed and intra oceanic arc. Beginning at ~85-90 Ma the western part of the TTSS collided southward with the Afro-Arabian continental margin, terminating subduction. This resulted in southward obduction of the peri-Arabian ophiolite belt, which extends for ~4000 km along strike and includes the Cypus, Semail and Zagros ophiolites. At the same time also the eastern part of the TTS collided northwards wit Eurasia. After this collisional event, only the central part of the subduction system remained active until it collided with the northern margin of the Indian continent at ~50-55 Ma. The collision of the arc with the Indian margin, over a length of ~3000 km, also resulted in the obduction of arc material and ophiolitic rocks. Remnants of these rocks are preserved today as the Kohistan-Ladakh arc and ophiolites of the Indus-Tsangpo suture zone of the Himalayas. Both of these collision events occurred in the equatorial region, near or within the ITCZ, where chemical weathering rates are high and are contemporaneous with the onset of the global cooling events that mark the end of the CTM and the EECO. The tectonic collision events resulted in a shut down of subduction zone magmatism, a major CO2 source and emplacement of highly weatherable basaltic rocks within the ITCZ (CO2 sink). In order to explore the effect of the events in the TTSS on atmospheric CO2, we model the potential contribution of subduction zone volcanism (source) and ophiolite obduction (sink) to the global atmospheric CO2

On volcanism and thermal tectonics on one-plate planets

NASA Technical Reports Server (NTRS)

Solomon, S. C.

1978-01-01

For planets with a single global lithospheric shell or 'plate', the thermal evolution of the interior affects the surface geologic history through volumetric expansion and the resultant thermal stress. Interior warming of such planets gives rise to extensional tectonics and a lithospheric stress system conductive to widespread volcanism. Interior cooling leads to compressional tectonics and lithospheric stresses that act to shut off surface volcanism. On the basis of observed surface tectonics, it is concluded that the age of peak planetary volume, the degree of early heating, and the age of youngest major volcanism on the one-plate terrestrial planets likely decrease in the order Mercury, Moon, Mars.

The impact of fire on the Late Paleozoic Earth system

PubMed Central

Glasspool, Ian J.; Scott, Andrew C.; Waltham, David; Pronina, Natalia; Shao, Longyi

2015-01-01

Analyses of bulk petrographic data indicate that during the Late Paleozoic wildfires were more prevalent than at present. We propose that the development of fire systems through this interval was controlled predominantly by the elevated atmospheric oxygen concentration (p(O2)) that mass balance models predict prevailed. At higher levels of p(O2), increased fire activity would have rendered vegetation with high-moisture contents more susceptible to ignition and would have facilitated continued combustion. We argue that coal petrographic data indicate that p(O2) rather than global temperatures or climate, resulted in the increased levels of wildfire activity observed during the Late Paleozoic and can, therefore, be used to predict it. These findings are based upon analyses of charcoal volumes in multiple coals distributed across the globe and deposited during this time period, and that were then compared with similarly diverse modern peats and Cenozoic lignites and coals. Herein, we examine the environmental and ecological factors that would have impacted fire activity and we conclude that of these factors p(O2) played the largest role in promoting fires in Late Paleozoic peat-forming environments and, by inference, ecosystems generally, when compared with their prevalence in the modern world. PMID:26442069

The impact of fire on the Late Paleozoic Earth system.

PubMed

Glasspool, Ian J; Scott, Andrew C; Waltham, David; Pronina, Natalia; Shao, Longyi

2015-01-01

Analyses of bulk petrographic data indicate that during the Late Paleozoic wildfires were more prevalent than at present. We propose that the development of fire systems through this interval was controlled predominantly by the elevated atmospheric oxygen concentration (p(O2)) that mass balance models predict prevailed. At higher levels of p(O2), increased fire activity would have rendered vegetation with high-moisture contents more susceptible to ignition and would have facilitated continued combustion. We argue that coal petrographic data indicate that p(O2) rather than global temperatures or climate, resulted in the increased levels of wildfire activity observed during the Late Paleozoic and can, therefore, be used to predict it. These findings are based upon analyses of charcoal volumes in multiple coals distributed across the globe and deposited during this time period, and that were then compared with similarly diverse modern peats and Cenozoic lignites and coals. Herein, we examine the environmental and ecological factors that would have impacted fire activity and we conclude that of these factors p(O2) played the largest role in promoting fires in Late Paleozoic peat-forming environments and, by inference, ecosystems generally, when compared with their prevalence in the modern world.

Tectonic Evolution of the Çayirhan Neogene Basin (Ankara), Central Turkey

NASA Astrophysics Data System (ADS)

Behzad, Bezhan; Koral, Hayrettin; İşb&idot; l, Duygu; Karaaǧa; ç, Serdal

2016-04-01

Çayırhan (Ankara) is located at crossroads of the Western Anatolian extensional region, analogous to the Basin and Range Province, and suture zone of the Neotethys-Ocean, which is locus of the North Anatolian Transform since the Late Miocene. To the north of Çayırhan (Ankara), a Neogene sedimentary basin comprises Lower-Middle Miocene and Upper Miocene age formations, characterized by swamp, fluvial and lacustrine settings respectively. This sequence is folded and transected by neotectonic faults. The Sekli thrust fault is older than the Lower-Middle Miocene age formations. The Davutoǧlan fault is younger than the Lower-Middle Miocene formations and is contemporaneous to the Upper Miocene formation. The Çatalkaya fault is younger than the Upper Miocene formation. The sedimentary and tectonic features provide information on mode, timing and evolution of this Neogene age sedimentary basin in Central Turkey. It is concluded that the region underwent a period of uplift and erosion under the influence of contractional tectonics prior to the Early-Middle Miocene, before becoming a semi-closed basin under influence of transtensional tectonics during the Early-Middle Miocene and under influence of predominantly extensional tectonics during the post-Late Miocene times. Keywords: Tectonics, Extension, Transtension, Stratigraphy, Neotectonic features.

Generation and Initiation of Plate Tectonics on Terrestrail Planets

NASA Astrophysics Data System (ADS)

Foley, Bradford J.

The question of why plate tectonics occurs on Earth, but not on the other planets of our solar system, is one of the most fundamental issues in geophysics and planetary science. I study this problem using numerical simulations of mantle convection with a damage-grainsize feedback (grain-damage) to constrain the conditions necessary for plate tectonics to occur on a terrestrial planet, and how plate tectonics initiates. In Chapter 2, I use numerical simulations to determine how large a viscosity ratio, between pristine lithosphere and mantle, damage can offset to allow mobile (plate-like) convection. I then use the numerical results to formulate a new scaling law to describe the boundary between stagnant lid and plate-like regimes of mantle convection. I hypothesize that damage must reduce the viscosity of shear zones in the lithosphere to a critical value, equivalent to the underlying mantle viscosity, in order for plate tectonics to occur, and demonstrate that a scaling law based on this hypothesis reproduces the numerical results. For the Earth, damage is efficient in the lithosphere and provides a viable mechanism for the operation of plate tectonics. I apply my theory to super-Earths and map out the transition between plate-like and stagnant lid convection with a "planetary plate-tectonic phase" diagram in planet size-surface temperature space. Both size and surface temperature are important, with plate tectonics being favored for larger, cooler planets. This gives a natural explanation for Earth, Venus, and Mars, and implies that plate tectonics on exoplanets should correlate with size, incident solar radiation, and atmospheric composition. In Chapters 3 and 4 I focus on the initiation of plate tectonics. In Chapter 3, I develop detailed scaling laws describing plate speed and heat flow for mantle convection with grain-damage across a wide parameter range, with the intention of applying these scaling laws to the early Earth in Chapter 4. Convection with grain

Accretionary history of the Altai-Mongolian terrane: perspectives from granitic zircon U-Pb and Hf-isotope data

NASA Astrophysics Data System (ADS)

Cai, Keda; Sun, Min; Xiao, Wenjiao

2014-05-01

The Central Asian Orogenic Belt (CAOB) consists of many tectonic terranes with distinct origin and complicated evolutionary history. Understanding of individual block is crucial to reconstruct the geodynamic history of the gigantic accetionary collage. This study presents zircon U-Pb ages and Hf isotopes for the granitoid rocks in the Russian Altai mountain range (including Gorny Altai, Altai-Mongolian terrane and CTUS suture zone between them), in order to clarify the timing of granitic magmatism, source nature, continental crustal growth and tectonic evolution. Our dating results suggest that granitic magmatism of the Russian Altai mountain range occurred in three major episodes including 445~429 Ma, 410~360 Ma and ~241 Ma. Most of the zircons within the Paleozoic granitoids present comparable positive ɛHf(t) values and Neoproterozoic crustal model ages, which favor the interpretation that the juvenile crustal materials produced in the early stage of CAOB were probably dominant sources for the Paleozoic magmatism in the region. The inference is also supported by widespread occurrence of short-lived juvenile materials including ophiolites, seamount relics and arc assemblages in the north CAOB. Consequently, the Paleozoic massive granitic rocks maybe not represent continental crustal growth at the time when they were emplaced, but rather record reworking of relatively juvenile Proterozoic crustal rocks although mantle-derived mafic magma was possibly involved to sever as heat engine during granitic magma generation. The Early Triassic granitic intrusion may be product in an intra-plate environment, as the case of same type rocks in the adjacent areas. The positive ɛHf(t) values (1.81~7.47) and corresponding Hf model ages (0.80~1.16 Ga) together with evidence of petrology are consistent with the interpretation that the parental magma of the Triassic granitic intrusion was produced from enriched mantle-derived sources under an usually high temperature condition

Tethys- and Atlas-related deformations in the Triassic Basin, Algeria

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

Jackson, J.S.; Moore, S.R.; Quarles, A.I.

1995-08-01

Petroleum provinces of Algeria can be divided into Paleozoic and Mesozoic domains. Paleozoic basins are located on the Gondwanaland paleo-continent where the last significant tectonic episode is ascribed to the Late Paleozoic Hercynian Orogeny. Mesozoic basins are located on the south margin of the Neo-Tethyan seaway. These basins were subject to varying degrees of contractional deformation during the Cenozoic Atlas Orogeny. The Triassic Basin of Algeria is a Tethyan feature located above portions of the Paleozoic Oued M`ya and Ghadames Basins. Paleozoic strata are deeply truncated at the Hercynian Unconformity on a broad arch between the older basins. This ismore » interpreted to reflect rift margin rebound during Carboniferous time. Continental Lower Triassic sediments were deposited in a series of northeast trending basins which opened as the Neo-Tethys basin propagated from east to west between Africa and Europe. Middle Triassic marine transgression from the east resulted in evaporate deposition persisting through the Early Jurassic. Passive margin subsidence associated with carbonate marine deposition continued through the Early Cretaceous. Several zones of coeval wrench deformation cross the Atlas and adjoining regions. In the Triassic Basin, inversion occurred before the end of the Early Cretaceous. This episode created discrete uplifts, where major hydrocarbon accumulations have been discovered, along northeast trending lineaments. During the Eocene, the main phase of the Atlas Orogeny produced low amplitude folding of Jurassic and Cretaceous sediments. The folds detach within the Triassic-Jurassic evaporate interval. Many of these folds have been tested without success, as the deeper reservoirs do not show structural closure.« less

A new reconstruction of the Paleozoic continental margin of southwestern North America: Implications for the nature and timing of continental truncation and the possible role of the Mojave-Sonora megashear

USGS Publications Warehouse

Stevens, C.H.; Stone, P.; Miller, J.S.

2005-01-01

Data bearing on interpretations of the Paleozoic and Mesozoic paleogeography of southwestern North America are important for testing the hypothesis that the Paleozoic miogeocline in this region has been tectonically truncated, and if so, for ascertaining the time of the event and the possible role of the Mojave-Sonora megashear. Here, we present an analysis of existing and new data permitting reconstruction of the Paleozoic continental margin of southwestern North America. Significant new and recent information incorporated into this reconstruction includes (1) spatial distribution of Middle to Upper Devonian continental-margin facies belts, (2) positions of other paleogeographically significant sedimentary boundaries on the Paleozoic continental shelf, (3) distribution of Upper Permian through Upper Triassic plutonic rocks, and (4) evidence that the southern Sierra Nevada and western Mojave Desert are underlain by continental crust. After restoring the geology of western Nevada and California along known and inferred strike-slip faults, we find that the Devonian facies belts and pre-Pennsylvanian sedimentary boundaries define an arcuate, generally south-trending continental margin that appears to be truncated on the southwest. A Pennsylvanian basin, a Permian coral belt, and a belt of Upper Permian to Upper Triassic plutons stretching from Sonora, Mexico, into westernmost central Nevada, cut across the older facies belts, suggesting that truncation of the continental margin occurred in the Pennsylvanian. We postulate that the main truncating structure was a left-lateral transform fault zone that extended from the Mojave-Sonora megashear in northwestern Mexico to the Foothills Suture in California. The Caborca block of northwestern Mexico, where Devonian facies belts and pre-Pennsylvanian sedimentary boundaries like those in California have been identified, is interpreted to represent a missing fragment of the continental margin that underwent ???400 km of left

Late Cambrian - Early Ordovician turbidites of Gorny Altai (Russia): Compositions, sources, deposition settings, and tectonic implications

NASA Astrophysics Data System (ADS)

Kruk, Nikolai N.; Kuibida, Yana V.; Shokalsky, Sergey P.; Kiselev, Vladimir I.; Gusev, Nikolay I.

2018-06-01

The Cambrian-Ordovician transition was the time of several key events in the history of Central Asia. They were the accretion of Mariana-type island arc systems to the Siberian continent, the related large-scale orogeny and intrusions of basaltic and granitic magma and the formation of a huge turbidite basin commensurate with the Bengal Gulf basin in the western part of the Central Asian orogenic belt (CAOB). The structure of the basin, as well as the sources and environments of deposition remain open to discussion. This paper presents new major- and trace-element data on Late-Cambrian-Early Ordovician turbidites from different parts of the Russian Altai and a synthesis of Nd isotope composition and ages of detrital zircons. The turbidites share chemical similarity with material shed from weathered continental arcs. Broad variations of CIA (39-73) and ICV (0.63-1.66) signatures in sandstones suggest origin from diverse sources and absence of significant sorting. Trace elements vary considerably and have generally similar patterns in rocks from different terranes. On the other hand, there are at least two provinces according to Nd isotope composition and age of detrital zircons. Samples from eastern Russian Altai contain only Phanerozoic zircons and have Nd isotope ratios similar to those in Early Cambrian island arcs (εNdt + 4.4… + 5.4; TNd(DM)-2-st = 0.8-0.9 Ga). Samples from central, western, and southern parts of Russian Altai contain Precambrian zircons (some as old as Late Archean) and have a less radiogenic Nd composition (εNdt up to -3.6; TNd(DM)-2-st up to 1.5 Ga). The chemical signatures of Late Cambrian to Early Ordovician turbidites indicate a provenance chemically more mature than the island arc rocks, and the presence of zircons with 510-490 Ma ages disproves their genetic relation with island arcs. The turbidite basin formed simultaneously with peaks of granitic and alkali-basaltic magmatism in the western Central Asian orogen and resulted from

Sensitivity of Seawater Oxygen Isotopes to Climatic and Tectonic Boundary Conditions in an Early Paleogene Simulation with GISS ModelE-R

NASA Technical Reports Server (NTRS)

Roberts, Christopher D.; LeGrande, Allegra N.; Tripati, Aradhna K.

2011-01-01

An isotope-enabled ocean-atmosphere general circulation model (GISS ModelE -R) is used to estimate the spatial gradients of the oxygen isotopic composition of seawater (delta O-18(sub sw), where delta is the deviation from a known reference material in per mil) during the early Paleogene (45.65 Ma). Understanding the response of delta O-18(sub sw) to changes in climatic and tectonic boundary conditions is important because records of carbonate delta O-18 document changes in hydrology, as well as changes in temperature and global ice -volume. We present results from an early Paleogene configuration of ModelE -R which indicate that spatial gradients of surface ocean delta O-18(sub sw) during this period could have been significantly different to those in the modern ocean. The differences inferred from ModelE -R are sufficient to change early Paleogene sea surface temperature estimates derived from primary carbonate delta O-18 signatures by more than +/-2 C in large areas of the ocean. In the North Atlantic, Indian, and Southern Oceans, the differences in d18Osw inferred from our simulation with ModelE -R are in direct contrast with those from another d18O ]tracing model study which used different, but equally plausible, early Paleogene boundary conditions. The large differences in delta O-18(sub sw) between preindustrial and early Paleogene simulations, and between models, emphasizes the sensitivity of d18Osw to climatic and tectonic boundary conditions. For this reason, absolute estimates of Eocene/ Paleocene temperature derived from carbonate delta O-18 alone are likely to have larger uncertainties than are usually assumed.

Tectonic assembly of Gondwana

NASA Astrophysics Data System (ADS)

Rogers, John J. W.; Unrug, Raphael; Sultan, Mohamed

1995-01-01

The Paleozoic assembly of Pangea, with Gondwana as its southern half, completed the last full cycle of growth and dispersal of supercontinents during earth history. This assembly apparently resulted from reorganization of a preceding supercontinent (Rodinia) that existed at ˜1000 Ma. In addition to Laurentia and fragments that formed nuclei for Europe and Asia, the rifting of Rodinia produced: (1) East Gondwana, consisting largely of Western Australia, India, East Antarctica, and possibly part of southern Africa; and (2) various smaller fragments that converged to form West Gondwana, consisting of most of Africa and South America. East Gondwana appears to have been a stable block at a time no younger than ˜1000 Ma and possibly older. West Gondwana accreted largely in the latest Proterozoic and early Paleozoic by closure of the Pharusian Ocean in the north, the Adamaster Ocean in the south, and the ANEKT/Mozambique Ocean between West and East Gondwana. The assembly process was diachronous along numerous mobile belts, accompanied by syn- and post-collisional shearing and magmatism, and led to development of successor basins and rifts. Uncertainties in the timing and mechanism of assembly of Gondwana greatly limit our understanding of the supercontinent cycle. Thus, we propose investigations of Gondwana to determine more precisely the nature and age of apparent cratonic blocks, the locations and ages of orogenic belts, the configuration of former ocean basins, the significance of transcontinental shears, the extent of reactivation of older terranes, and the relationship of Gondwana to North America. Detailed knowledge of the assembly of Gondwana should also provide information on its relationship to other major processes such as mantle evolution and atmospheric, oceanic, and biologic changes.

Quantitative Hydraulic Models Of Early Land Plants Provide Insight Into Middle Paleozoic Terrestrial Paleoenvironmental Conditions

NASA Astrophysics Data System (ADS)

Wilson, J. P.; Fischer, W. W.

2010-12-01

Fossil plants provide useful proxies of Earth’s climate because plants are closely connected, through physiology and morphology, to the environments in which they lived. Recent advances in quantitative hydraulic models of plant water transport provide new insight into the history of climate by allowing fossils to speak directly to environmental conditions based on preserved internal anatomy. We report results of a quantitative hydraulic model applied to one of the earliest terrestrial plants preserved in three dimensions, the ~396 million-year-old vascular plant Asteroxylon mackei. This model combines equations describing the rate of fluid flow through plant tissues with detailed observations of plant anatomy; this allows quantitative estimates of two critical aspects of plant function. First and foremost, results from these models quantify the supply of water to evaporative surfaces; second, results describe the ability of plant vascular systems to resist tensile damage from extreme environmental events, such as drought or frost. This approach permits quantitative comparisons of functional aspects of Asteroxylon with other extinct and extant plants, informs the quality of plant-based environmental proxies, and provides concrete data that can be input into climate models. Results indicate that despite their small size, water transport cells in Asteroxylon could supply a large volume of water to the plant's leaves--even greater than cells from some later-evolved seed plants. The smallest Asteroxylon tracheids have conductivities exceeding 0.015 m^2 / MPa * s, whereas Paleozoic conifer tracheids do not reach this threshold until they are three times wider. However, this increase in conductivity came at the cost of little to no adaptations for transport safety, placing the plant’s vegetative organs in jeopardy during drought events. Analysis of the thickness-to-span ratio of Asteroxylon’s tracheids suggests that environmental conditions of reduced relative

Oceanic crust within the paleozoic Granjeno Schist, northeastern Mexico. Remnants of the Rheic and paleo-Pacific Ocean.

NASA Astrophysics Data System (ADS)

Torres Sanchez, Sonia Alejandra; Augustsson, Carita; Rafael Barboza Gudiño, Jose; Jenchen, Uwe; Torres Sanchez, Dario; Aleman Gallardo, Eduardo; Abratis, Michael

2015-04-01

Late Paleozoic metamorphic rocks in Mexico are related to the Laurentia-Gondwana collision in Carboniferous time, during Pangaea amalgamation. Vestiges of the Mexican Paleozoic continental configuration are present in the Granjeno Schist, the metamorphic basement of the Sierra Madre Oriental. Field work and petrographic analysis reveal that the Granjeno Schist comprises metamorphic rocks with both sedimentary (psammite, pelite, turbidite, conglomerate, black shale) and igneous (tuff, lava flows, pillow lava and ultramafic bodies) protoliths. The chlorite geothermometer and the presence of phengite in the metasedimentary units as well as 40Ar/39Ar ages on metavolcanic and metaultramafic rocks indicate that the Granjeno Schist was metamorphosed under sub-greenschist to greenschist facies with temperatures ranging from 250-345°C with 2.5 kbar during Carboniferous time (330±30 Ma). The presence of metabasalt, metacumulate, serpentinite and talc bodies suggests an oceanic tectonic setting for the evolution of the Granjeno Schist. Serpetinite rocks have mesh, granular and ribbon textures which indicate recrystallization and metasomatic events. The serpentinite rocks are enriched in the very large incompatible elements Cs, U, and Zr and depleted in Ba, Sr, Pb, Zr and Ce. Normalized REE patterns (LaN/YbN = 0.51 - 19.95 and LaN/SmN = 0.72 - 9.08) of the serpentinite and talc/soapstone are characteristic of peridotite from both suprasubduction and mid-ocean ridge zones. Serpentinite from the Granjeno Schist have spinel content which can reveal different stages of evolution in host serpentinite. The composition of chromite indicates that they belong to podiform chromite that may have crystallized from mid-ocean ridge magma. Al-chromite in the serpentinite is characterized by #Cr 0.48 to 0.55, which indicates a depleted mantle source affected by 17 to 18% of partial melting. The ferritchromite has #Cr values of 0.93 to 1.00 which indicates a metamorphic origin. Our study

Why is understanding when Plate Tectonics began important for understanding Earth?

NASA Astrophysics Data System (ADS)

Korenaga, J.

2015-12-01

Almost all kinds of geological activities on Earth depend critically on the operation of plate tectonics, but did plate tectonics initiate right after the solidification of a putative magma ocean, or did it start much later, e.g., sometime during the Archean? This problem of the initiation of plate tectonics in the Earth history presents us a unique combination of observational and theoretical challenges. Finding geological evidence for the onset of plate tectonics is difficult because plate tectonics is a dynamic process that continuously destroys a remnant of the past. We therefore need to rely on more secondary traces, the interpretation of which often involves theoretical considerations. At the same time, it is still hard to predict, on a firm theoretical ground, when plate tectonics should have prevailed, because there is no consensus on why plate tectonics currently takes place on Earth. Knowing when plate tectonics began is one thing, and understanding why it did so is another. The initiation of plate tectonics is one of the last frontiers in earth science, which encourages a concerted effort from both geologists and geophysicists to identify key geological evidence and distinguish between competing theories of early Earth evolution. Such an endeavor is essential to arrive at a self-contained theory for the evolution of terrestrial planets.

This dynamic earth: the story of plate tectonics

USGS Publications Warehouse

Kious, W. Jacquelyne; Tilling, Robert I.

1996-01-01

In the early 1960s, the emergence of the theory of plate tectonics started a revolution in the earth sciences. Since then, scientists have verified and refined this theory, and now have a much better understanding of how our planet has been shaped by plate-tectonic processes. We now know that, directly or indirectly, plate tectonics influences nearly all geologic processes, past and present. Indeed, the notion that the entire Earth's surface is continually shifting has profoundly changed the way we view our world.People benefit from, and are at the mercy of, the forces and consequences of plate tectonics. With little or no warning, an earthquake or volcanic eruption can unleash bursts of energy far more powerful than anything we can generate. While we have no control over plate-tectonic processes, we now have the knowledge to learn from them. The more we know about plate tectonics, the better we can appreciate the grandeur and beauty of the land upon which we live, as well as the occasional violent displays of the Earth's awesome power.This booklet gives a brief introduction to the concept of plate tectonics and complements the visual and written information in This Dynamic Planet (see Further reading), a map published in 1994 by the U.S. Geological Survey (USGS) and the Smithsonian Institution. The booklet highlights some of the people and discoveries that advanced the development of the theory and traces its progress since its proposal. Although the general idea of plate tectonics is now widely accepted, many aspects still continue to confound and challenge scientists. The earth-science revolution launched by the theory of plate tectonics is not finished.

Erosion-tectonics feedbacks in shaping the landscape: An example from the Mekele Outlier (Tigray, Ethiopia)

NASA Astrophysics Data System (ADS)

Sembroni, Andrea; Molin, Paola; Dramis, Francesco; Faccenna, Claudio; Abebe, Bekele

2017-05-01

An outlier consists of an area of younger rocks surrounded by older ones. Its formation is mainly related to the erosion of surrounding rocks which causes the interruption of the original continuity of the rocks. Because of its origin, an outlier is an important witness of the paleogeography of a region and, therefore, essential to understand its topographic and geological evolution. The Mekele Outlier (N Ethiopia) is characterized by poorly incised Mesozoic marine sediments and dolerites (∼2000 m in elevation), surrounded by strongly eroded Precambrian and Paleozoic rocks and Tertiary volcanic deposits in a context of a mantle supported topography. In the past, studies about the Mekele outlier focused mainly in the mere description of the stratigraphic and tectonic settings without taking into account the feedback between surface and deep processes in shaping such peculiar feature. In this study we present the geological and geomorphometric analyses of the Mekele Outlier taking into account the general topographic features (slope map, swath profiles, local relief), the river network and the principal tectonic lineaments of the outlier. The results trace the evolution of the study area as related not only to the mere erosion of the surrounding rocks but to a complex interaction between surface and deep processes where the lithology played a crucial role.

From P-T-age to secular change and global tectonic regimes (or Essene in reverse - from granulites to blueschists and eclogites over time)

NASA Astrophysics Data System (ADS)

Brown, M.

2006-12-01

Essene's contributions began pre-plate tectonics more than 40 years ago; they range from mineralogy to tectonics, from experiments and thermobarometry to elements and isotopes, and from the Phanerozoic to the Precambrian. Eric is a true polymath! Assessing the P-T conditions and age distribution of crustal metamorphism is an important step in evaluating secular change in tectonic regimes and geodynamics. In general, Archean rocks exhibit moderate-P - moderate-to-high-T facies series metamorphism (greenstone belts and granulite terranes); neither blueschists nor any record of deep continental subduction and return are documented and only one example of granulite facies ultrahigh-temperature metamorphism is reported. Granulite facies ultrahigh temperature metamorphism (G-UHTM) is documented in the rock record predominantly from Neoarchean to Cambrian, although G-UHTM facies series rocks may be inferred at depth in younger orogenic systems. The first occurrence of G-UHTM in the rock record signifies a change in geodynamics that generated transient sites of very high heat flow. Many G-UHTM belts may have developed in settings analogous to modern continental backarcs. On a warmer Earth, the formation and breakup of supercontinents, particularly by extroversion, which involved destruction of ocean basins floored by thinner lithosphere, may have generated hotter continental backarcs than those around the modern Pacific rim. Medium-temperature eclogite - high-pressure granulite metamorphism (E-HPGM) also is first recognized in the Neoarchean rock record, and occurs at intervals throughout the Proterozoic and Paleozoic rock record. E- HPGM belts are complementary to G-UHTM belts, and are generally inferred to record subduction-to-collision orogenesis. Blueschists become evident in the Neoproterozoic rock record; lawsonite blueschists and eclogites (high-pressure metamorphism, HPM), and ultrahigh pressure metamorphism (UHPM) characterized by coesite or diamond are

Tectonism

NASA Image and Video Library

2011-10-24

This image from NASA 2001 Mars Odyssey spacecraft shows evidence of tectonic stresses that deform and fracture rocks and planetary surfaces. Right angles seen here are a good indication that the feature was formed by tectonic stresses.

Mayer Kangri metamorphic complexes in Central Qiangtang (Tibet, western China): implications for the Triassic-early Jurassic tectonics associated with the Paleo-Tethys Ocean

NASA Astrophysics Data System (ADS)

Wang, Yixuan; Liang, Xiao; Wang, Genhou; Yuan, Guoli; Bons, Paul D.

2018-03-01

The Mesozoic orogeny in Central Qiangtang Metamorphic Belt, northern Tibet, provides important insights into the geological evolution of the Paleo-Tethys Ocean. However, the Triassic-early Jurassic tectonics, particularly those associated with the continental collisionstage, remains poorly constrained. Here we present results from geological mapping, structural analysis, P-T data, and Ar-Ar geochronology of the Mayer Kangri metamorphic complex. Our data reveal an E-W-trending, 2 km wide dome-like structure associated with four successive tectonic events during the Middle Triassic and Early Jurassic. Field observations indicate that amphibolite and phengite schist complexes in this complex are separated from the overlying lower greenschist mélange by normal faulting with an evident dextral shearing component. Open antiform-like S2 foliation of the footwall phengite schist truncates the approximately north-dipping structures of the overlying mélange. Microtextures and mineral chemistry of amphibole reveal three stages of growth: Geothermobarometric estimates yield temperatures and pressures of 524 °C and 0.88 GPa for pargasite cores, 386 °C and 0.34 GPa for actinolite mantles, and 404 °C and 0.76 GPa for winchite rims. Peak blueschist metamorphism in the phengite schist occurred at 0.7-1.1 GPa and 400 °C. Our Ar-Ar dating of amphibole reveals rim-ward decreasing in age bands, including 242.4-241.2 Ma, ≥202.6-196.8, and 192.9-189.8 Ma. The results provide evidence for four distinct phases of Mesozoic tectonic evolution in Central Qiangtang: (1) northward oceanic subduction beneath North Qiangtang ( 244-220 Ma); (2) syn-collisional slab-break off (223-202 Ma); (3) early collisional extension driven by buoyant extrusion flow from depth ( 202.6-197 Ma); and (4) post-collision contraction and reburial (195.6-188.7 Ma).

Stratigraphy and paleogeographic significance of a Late Pennsylvanian to Early Permian channeled slope sequence in the Darwin Basin, southern Darwin Hills, east-central California

USGS Publications Warehouse

Stevens, Calvin H.; Stone, Paul; Magginetti, Robert T.; Ritter, Scott M.

2015-01-01

The complex stratigraphy of late Paleozoic rocks in the southern Darwin Hills consists of regionally extensive Mississippian and Early to Middle Pennsylvanian rocks overlain by latest Pennsylvanian to Early Permian rocks, herein called the Darwin Hills sequence. Deposition of this latter sequence marked the beginning of the Darwin Basin. In Mississippian time, a carbonate platform prograded westward over slightly older slope deposits. In the Late Mississippian this platform was exposed to erosion and siliciclastic sediments were deposited. In Early to Middle Pennsylvanian time the area subsided, forming a west-facing ramp that was subjected to deformation and erosion in Middle or early Late Pennsylvanian time. Later this area was tilted westward and deep-water sediments were deposited on this slope. In latest Pennsylvanian to earliest Permian time, a major channel was cut through the older Pennsylvanian rocks and into the Upper Mississippian strata. This channel was gradually filled with increasingly finer grained, deep-water sediment as the area evolved into a basin floor by Early Permian (Sakmarian) time. Expansion of the Darwin Basin in Artinskian time led to a second phase of deposition represented by strata of the regionally extensive Darwin Canyon Formation. The geology in this small area thus documents tectonic events occurring during the early development of the Darwin Basin.

Lithospheric mantle structure beneath Northern Scotland: Pre-plume remnant or syn-plume signature?

NASA Astrophysics Data System (ADS)

Knapp, J.

2003-04-01

Upper mantle reflectors (Flannan and W) beneath the northwestern British Isles are some of the best-known and most-studied examples of preserved structure within the continental mantle lithosphere, and are spatially coincident with the surface location of early Iceland plume volcanism in the British Tertiary Province. First observed on BIRPS (British Institutions Reflection Profiling Syndicate) marine deep seismic reflection profiles in the early 1980's, these reflectors have subsequently been imaged and correlated on additional reflection and refraction profiles in the offshore area of northern and western Scotland. The age and tectonic significance of these reflectors remains a subject of wide debate, due in part to the absence of robust characterization of the upper mantle velocity structure in this tectonically complex area. Interpretations advanced over the past two decades for the dipping Flannan reflector range from fossilized subduction complex to large-scale extensional shear zone, and span ages from Proterozoic to early Mesozoic. Crustal geology of the region records early Paleozoic continental collision and late Paleozoic to Mesozoic extension. Significant modification of the British lithosphere in early Tertiary time, including dramatic thinning and extensive basaltic intrusion associated with initiation and development of the Iceland plume, suggests either (1) an early Tertiary age for the Flannan reflector or (2) preservation of ancient features within the mantle lithosphere despite such pervasive modification. Exisitng constraints are consistent with a model for early Tertiary origin of the Flannan reflector as the downdip continuation of the Rockall Trough extensional system of latest Cretaceous to earliest Tertiary age during opening of the northern Atlantic Ocean and initiation of the Iceland plume. Lithopsheric thinning beneath present-day northern Scotland could have served to focus the early expression of plume volcanism (British Tertiary

Plate tectonics on the Earth triggered by plume-induced subduction initiation.

PubMed

Gerya, T V; Stern, R J; Baes, M; Sobolev, S V; Whattam, S A

2015-11-12

Scientific theories of how subduction and plate tectonics began on Earth--and what the tectonic structure of Earth was before this--remain enigmatic and contentious. Understanding viable scenarios for the onset of subduction and plate tectonics is hampered by the fact that subduction initiation processes must have been markedly different before the onset of global plate tectonics because most present-day subduction initiation mechanisms require acting plate forces and existing zones of lithospheric weakness, which are both consequences of plate tectonics. However, plume-induced subduction initiation could have started the first subduction zone without the help of plate tectonics. Here, we test this mechanism using high-resolution three-dimensional numerical thermomechanical modelling. We demonstrate that three key physical factors combine to trigger self-sustained subduction: (1) a strong, negatively buoyant oceanic lithosphere; (2) focused magmatic weakening and thinning of lithosphere above the plume; and (3) lubrication of the slab interface by hydrated crust. We also show that plume-induced subduction could only have been feasible in the hotter early Earth for old oceanic plates. In contrast, younger plates favoured episodic lithospheric drips rather than self-sustained subduction and global plate tectonics.

Tectonics of Precambrian basement along the Pacific margin of Antarctica and relation to western North America

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

Goodge, J.W.; Hansen, V.L.; Walker, N.W.

1993-02-01

High-grade metamorphic rocks of the Precambrian Nimrod Group (NG) constitute one of few cratonal basement exposures in the Transantarctic Mountains. These rocks represent an outlier of the East Antarctic craton, evolved as part of Gondwana and pre-Gondwana (Rodinia) supercontinents. Despite pervasive, high-strain ductile deformation at T [>=] 650 C, they preserve petrologic and geochronologic evidence of an earlier history. Sm-Nd model ages from several NG lithologies, including that of a [approximately]1.7 Ga orthogneiss, range from about 2.7--2.9 Ga; these ages reflect both sedimentary and magmatic derivation from Archean crust. Individual detrital zircon U-Pb ages (about 1.7--2.6 Ga) from NG quartzitesmore » indicate clastic input from Archean to Paleoproterozoic source terrains. The Sm-Nd and U-Pb ages are reminiscent of both the Yavapai-Mazatzal (1.6--1.8 Ga) and Wyoming (> 2.5 Ga) provinces in western North America. U-Pb ages from syn-tectonic metaigneous and pelitic NG tectonites indicate that this basement complex was re-worked by the major ductile deformation in latest neoproterozoic to Early Cambrian time. Supracrustal assemblages that lie outboard of the Nimrod craton include Neoproterozoic graywacke, impure carbonate, and minor mafic volcanics (Beardmore Group), and Cambrian to Lower Ordovician carbonate and siliciclastic rocks (Byrd Group). Neoproterozoic ([approximately]750 Ma) rifting along the proto-Pacific margin of East Antarctica is reflected by deposition of Beardmore turbidites and coeval mafic magmatism. Latest Neoproterozoic to early Paleozoic orogenesis occurred along a left-oblique convergent plate margin of East Antarctica is reflected by deposition of Beardmore turbidites and coeval mafic magmatism.« less

Transverse tectonic zonation of Cuba and its significance for oil exploration

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

Levchenko, V.A.

The Laramide structures of Cuba and its continental shelf, which are oriented sublatitudinally, are divided into variously elevated blocks by transverse faults of submeridional strike, movements along which have occurred since the end of the Paleozoic. This division, inherited from the region's pre-Mesozoic stage of development, has determined the heterogeneous composition of the Cuban geosyncline's folded basement, which may be characterized by an alternation of areas of Paleozoic uplifts and intervening grabens filled with metamorphosed deposits of Early and Middle Jurassic and Triassic age, and also areas of oceanic crust. In the concluding phase of the Laramide orogeny, there weremore » northward strike-slip movements of individual blocks in the central part of Cuba. The oil potential of Cuba is associated mainly with the depressed blocks, above which the section through the Mesozoic deposits may be presumed to be more complete. The best potential for finding oil exists in the zones of the transverse regional faults along which there may have been both lateral and vertical migration of oil hydrocarbons in the stages of crustal upwarp and extension.« less

Redescription of Bellerophon asiaticus Wirth (Early Triassic: Gastropoda) from China, and a survey of Triassic Bellerophontacea.

USGS Publications Warehouse

Yochelson, E.Y.; Yin, Hongfu

1985-01-01

The bilaterally symmetrical gastropod Bellerophon asiaticus Wirth is redescribed from specimens collected in Guizhou Province, PRC. The species is reassigned to Retispira, a common late Paleozoic taxon. Retispira is another example of a Paleozoic gastropod genus that crossed the era boundary. Associated pelecypods that date these Guizhou occurrences as Early Triassic are well known species in PRC and are illustrated. Both Bellerophon and Euphemites probably occur in the Early Triassic, though the quality of illustrations leaves some uncertainty; the existence of Stachella in the Triassic is more problematic. There was no dramatic reduction of the Bellerophontacea from their abundance and diversity in the Permian. It may be a general phenomenon that most late Paleozoic family-level and many generic-level taxa of gastropods were unaffected by the late Permian 'crisis'. from Authors

The potential of paleozoic nonmarine trace fossils for paleoecological interpretations

USGS Publications Warehouse

Maples, C.G.; Archer, A.W.

1989-01-01

Many Late Paleozoic environments have been interpreted as marine because of the co-occurrence of supposedly exclusively marine trace fossils. Beginning in the Late Ordovician, however, nonmarine trace-fossil diversity increased throughout the Paleozoic. This diversification of nonmarine organisms and nonmarine trace fossils was especially prevalent in Devonian and later times. Diversification of freshwater organisms is indicated by the large number of freshwater fish, arthropods, annelids and molluscs that had developed by the Carboniferous. In addition to diverse freshwater assemblages, entirely terrestrial vertebrate and invertebrate ecosystems had developed by the Devonian. This rapid diversification of freshwater and terrestrial organisms is inherently linked to development and diversification of land plants and subsequent shedding of large quantities of organic detritus in nonmarine and marginal-marine areas. Nearshore marine organisms and their larvae that are able to tolerate relatively short periods of lowered salinities will follow salt-water wedges inland during times of reduced freshwater discharge. Similarly, amphidromous marine organisms will migrate periodically inland into nonmarine environments. Undoubtedly, both of these processes were active in the Paleozoic. However, both processes are restricted to stream/distributary channels, interdistributary bays, or estuaries. Therefore, the presence of diverse trace-fossil assemblages in association with floodplain deposits is interpreted to reflect true nonmarine adaptation and diversity. Conversely, diverse trace-fossil assemblages in association with stream/distributary channel deposits, interdistributary-bay deposits, or estuarine deposits may reflect migration of salt-water wedges inland, or migration of marine organisms into freshwater environments (amphidromy), or both. ?? 1989.

Closure Time of the Junggar-Balkhash Ocean: Constraints From Late Paleozoic Volcano-Sedimentary Sequences in the Barleik Mountains, West Junggar, NW China

NASA Astrophysics Data System (ADS)

Liu, Bo; Han, Bao-Fu; Chen, Jia-Fu; Ren, Rong; Zheng, Bo; Wang, Zeng-Zhen; Feng, Li-Xia

2017-12-01

The Junggar-Balkhash Ocean was a major branch of the southern Paleo-Asian Ocean. The timing of its closure is important for understanding the history of the Central Asian Orogenic Belt. New sedimentological and geochronological data from the Late Paleozoic volcano-sedimentary sequences in the Barleik Mountains of West Junggar, NW China, help to constrain the closure time of the Junggar-Balkhash Ocean. Tielieketi Formation (Fm) is dominated by littoral sediments, but its upper glauconite-bearing sandstone is interpreted to deposit rapidly in a shallow-water shelf setting. By contrast, Heishantou Fm consists chiefly of volcanic rocks, conformably overlying or in fault contact with Tielieketi Fm. Molaoba Fm is composed of parallel-stratified fine sandstone and sandy conglomerate with graded bedding, typical of nonmarine, fluvial deposition. This formation unconformably overlies the Tielieketi and Heishantou formations and is conformably covered by Kalagang Fm characterized by a continental bimodal volcanic association. The youngest U-Pb ages of detrital zircons from sandstones and zircon U-Pb ages from volcanic rocks suggest that the Tielieketi, Heishantou, Molaoba, and Kalagang formations were deposited during the Famennian-Tournaisian, Tournaisian-early Bashkirian, Gzhelian, and Asselian-Sakmarian, respectively. The absence of upper Bashkirian to Kasimovian was likely caused by tectonic uplifting of the West Junggar terrane. This is compatible with the occurrence of coeval stitching plutons in the West Junggar and adjacent areas. The Junggar-Balkhash Ocean should be finally closed before the Gzhelian, slightly later or concurrent with that of other ocean domains of the southern Paleo-Asian Ocean.

Disentangling the control of tectonics, eustasy, trophic conditions and climate on shallow-marine carbonate production during the Aalenian-Oxfordian interval: From the western France platform to the western Tethyan domain

NASA Astrophysics Data System (ADS)

Andrieu, Simon; Brigaud, Benjamin; Barbarand, Jocelyn; Lasseur, Eric; Saucède, Thomas

2016-11-01

The objective of this work is to improve our understanding of the processes controlling changes in the architecture and facies of intracontinental carbonate platforms. We examined the facies and sequence stratigraphy of Aalenian to Oxfordian limestones of western France. Seventy-seven outcrop sections were studied and thirty-one sedimentary facies identified in five depositional environments ranging from lower offshore to backshore. Platform evolution was reconstructed along a 500 km cross-section. Twenty-two depositional sequences were identified on the entire western France platform and correlated with European third-order sequences at the biozone level, demonstrating that eustasy was the major factor controlling the cyclic trend of accommodation. The tectonic subsidence rate was computed from accommodation measurements from the Aalenian to the Oxfordian in key localities. Tectonism controlled the sedimentation rate and platform architecture at a longer time scale. Tectonic subsidence triggered the demise of carbonate production at the Bathonian/Callovian boundary while the uplift made possible the recovery of carbonate platform from Caen to Le Mans during the mid Oxfordian. Topography of the Paleozoic basement mainly controlled lateral variations of paleodepth within the western France platform until the mid Bathonian. A synthesis of carbonate production in the western Tethyan domain at that time was conducted. Stages of high carbonate production during the Bajocian/Bathonian and the middle to late Oxfordian are synchronous with low δ13C, high eccentricity intervals, and rather dry climate promoting (1) evaporation and carbonate supersaturation, and (2) oligotrophic conditions. Periods of low carbonate production during the Aalenian and from the middle Callovian to early Oxfordian correlate with high δ13C and low eccentricity intervals, characterized by wet climate and less oligotrophic conditions. Such conditions tend to diminish growth potential of carbonate

Elevated lateral stress in unlithified sediment, Midcontinent, United States - geotechnical and geophysical indicators for a tectonic origin

USGS Publications Warehouse

Woolery, E.W.; Schaefer, J.A.; Wang, Z.

2003-01-01

Indirect and direct geotechnical measurements revealed the presence of high lateral earth pressure (Ko) in shallow, unlithified sediment at a site in the northernmost Mississippi embayment region of the central United States. Results from pile-load and pressuremeter tests showed maximum Ko values greater than 10; however, the complex geologic environment of the Midcontinent made defining an origin for the anomalous Ko based solely on these measurements equivocal. Although in situ sediment characteristics indicated that indirect tectonic or nontectonic geologic mechanisms that include transient overburden loads (e.g., fluvial deposition/erosion, glacial advance/retreat) and dynamic shear loads (e.g., earthquakes) were not the dominant cause, they were unable to provide indicators for a direct tectonic generation. Localized stresses induced anthropogenically by the geotechnical field tests were also considered, but ruled out as the primary origin. A high-resolution shear-wave (SH) reflection image of geologic structure in the immediate vicinity of the test site revealed compression-style neotectonism, and suggested that the elevated stress was a tectonic manifestation. Post-Paleozoic reflectors exhibit a Tertiary (?) structural inversion, as evidenced by post-Cretaceous fault displacement and pronounced positive folds in the hanging wall of the interpreted faults. The latest stratigraphic extent of the stress effects (i.e., all measurements were in the Late Cretaceous to Tertiary McNairy Formation), as well as the relationship of stress orientation with the orientation of local structure and regional stress, remain unknown. These are the subjects of ongoing studies. ?? 2003 Elsevier Science B.V. All rights reserved.

Late Paleozoic closure of the Ob-Zaisan Ocean along the Irtysh/Chara shear zone and implications for arc amalgamation and oroclinal bending in the western Central Asian Orogenic Belt

NASA Astrophysics Data System (ADS)

Li, Pengfei; Sun, Min; Rosenbaum, Gideon

2016-04-01

The Irtysh/Chara Shear Zone is one of the largest strike-slip systems in the Central Asian Orogenic Belt (CAOB). It records collisional processes of the peri-Siberian orogenic system with the West Junggar-Kazakhstan-Tianshan orogenic system following the closure of the Ob-Zaisan Ocean, but the exact timing of these events remains enigmatic. We conducted detailed structural analysis along the Irtysh Shear Zone (NW China), which together with new geochronological data allows us to reconstruct the tectonic evolution during the final closure of the Ob-Zaisan Ocean. Our results showed that subduction-accretion processes lasted at least until the Late Carboniferous in the Chinese Altai and the East/West Junggar. The subsequent arc amalgamation is characterized by a cycle of crustal thickening, orogenic collapse and transpressional thickening. On a larger scale, the West Junggar- Kazakhstan -Tianshan orogenic system defines a U-shape oroclinal structure (e.g. Xiao et al., 2010). A major phase of oroclinal bending that involved ~110° rotation may have occurred during the Late Devonian to Early Carboniferous (Levashova et al., 2012). Previous authors have linked oroclinal bending with the late Paleozoic amalgamation of the western CAOB, and proposed that a quasi-linear West Junggar- Kazakhstan -Tianshan orogenic system was buckled during the convergence of the Siberian and Tarim cratons following the closure of the Ob-Zaisan Ocean (in the north) and the South Tianshan Ocean (in the south) (e.g. Abrajevitch et al., 2008). This model, however, is not supported by our new data that constrain the closure of the Ob-Zaisan Ocean to the Late Carboniferous. Alternatively, we propose that oroclinal bending may have involved two phases of bending, with the ~110° rotation in the Late Devonian to Early Carboniferous possibly associated with trench retreat. Further tightening may have occurred in response to the convergence of the Siberian and Tarim cratons during the Late

Cretaceous and Paleogene granitoid suites of the Sikhote-Alin area (Far East Russia): Geochemistry and tectonic implications

NASA Astrophysics Data System (ADS)

Grebennikov, Andrei V.; Khanchuk, Alexander I.; Gonevchuk, Valeriy G.; Kovalenko, Sergey V.

2016-09-01

The Mesozoic and Cenozoic geological history of NE Asia comprises alternating episodes of subduction or transform strike-slip movement of the oceanic plate along the continental margin of Eurasia. This sequence resulted in the regular generation of granitoid suites that are characterized by different ages, compositions, and tectonic settings. The Hauterivian-Aptian orogenic stage of the Sikhote-Alin, associated with the strike-slip displacement of the early Paleozoic continental blocks, the successive deformation of the Jurassic and Early Cretaceous terranes, and the injection of the earliest S-type granitoids. During late Albian, the area underwent syn-strike-slip compression caused by collision with the Aptian island arc and resulted in the injection of voluminous magmas of calc-alkaline magnesian (S- and I-type) and alkali-calcic ferroan (A-type) granitoids into syn-faulting compressional and extensional basins, respectively. Northwestward to westward movement of the Izanagi Plate resulted in the initiation of frontal subduction of the Paleo-Pacific Plate during the Cenomanian-Maastrichtian. In turn, this resulted in the generation of plateau-forming ignimbrites and their intrusive analogs formed from metaluminous I-type felsic magmas. Paleocene-Eocene magmatism in the Sikhote-Alin area commenced after the termination of subduction in a rifting regime related to strike-slip movement of the oceanic plate relative to the continent. The break-off of the subducted plate and the injection of oceanic asthenospheric material into the subcontinental lithosphere resulted in the eruption of lamproites and fayalite rhyolites, and coeval intrusions of gabbro and alkali feldspar granites (A-type). The A-type granitic-rocks and coeval gabbro-monzonites are considered to be reliable indicators of the transform continental margin geodynamic settings.

Tectonics and soil edaphics as controls on animal migrations and early human inhabitance in the Kenya Rift

NASA Astrophysics Data System (ADS)

Kübler, Simon; Rucina, Stephen; Reynolds, Sally; Fürgut, Felix; Bailey, Geoffrey; King, Geoffrey

2017-04-01

Animal movements in the tectonically active East African Rift Valley today are influenced by a combination of topography and soil nutrient distribution (soil edaphics). These patterns would have been the same in the past when hominins inhabited the area. Our study in the Kenya Rift shows that soil edaphics and active rift structures play a key role in present day animal movements as well as the for the location of early hominin sites. We carried out field analysis at Olorgesailie and Kariandusi, two key hominin sites in the southern and central Kenya Rift, respectiveley. Based on studying the relationship between the geology, tectonics and soil development we identified 'good' and 'bad' regions both in terms of edaphics and accessibility for grazing animals. We further sampled a large number of soils that developed on the volcanic bedrock and sediments of the region and interviewed the local Maasai shepherds to learn about present-day good and bad grazing sites. Ultimately, we created palaeoenvironmental and spatio-temporal reconstructions for interpreting human land use and exploitation of large mammals in the Kenya Rift for the relevant time frame of approximately 1 Ma BP. At Olorgesailie the hominin site is located in lacustrine sediments at the southern edge of a playa that extends north and northwest of Mt. Olorgesailie. The lakebeds are now tilted and eroded by motion on two north-south striking faults. The lake was trapped by volcanic flows and alluvial fans from Mt. Olorgesailie and was released by the fault motion leading to deep river incision and exposure of the site. To the west and the north steep fault scarps bound the playa forming a natural barrier for animals. Field observations and information from local shepherds suggest that the abundant trachytes at the valley floor produce poor soils whereas the soils developed on lacustrine and alluvial sediments close to the hominin site provide much more attractive grazing sites for present-day animals

Mountain building processes during continent continent collision in the Uralides

NASA Astrophysics Data System (ADS)

Brown, D.; Juhlin, C.; Ayala, C.; Tryggvason, A.; Bea, F.; Alvarez-Marron, J.; Carbonell, R.; Seward, D.; Glasmacher, U.; Puchkov, V.; Perez-Estaun, A.

2008-08-01

Since the early 1990's the Paleozoic Uralide Orogen of Russia has been the target of a significant research initiative as part of EUROPROBE and GEODE, both European Science Foundation programmes. One of the main objectives of these research programmes was the determination of the tectonic processes that went into the formation of the orogen. In this review paper we focus on the Late Paleozoic continent-continent collision that took place between Laurussia and Kazakhstania. Research in the Uralides was concentrated around two deep seismic profiles crossing the orogen. These were accompanied by geological, geophysical, geochronological, geochemical, and low-temperature thermochronological studies. The seismic profiles demonstrate that the Uralides has an overall bivergent structural architecture, but with significantly different reflectivity characteristics from one tectonic zone to another. The integration of other types of data sets with the seismic data allows us to interpret what tectonic processes where responsible for the formation of the structural architecture, and when they were active. On the basis of these data, we suggest that the changes in the crustal-scale structural architecture indicate that there was significant partitioning of tectonothermal conditions and deformation from zone to zone across major fault systems, and between the lower and upper crust. Also, a number of the structural features revealed in the bivergent architecture of the orogen formed either in the Neoproterozoic or in the Paleozoic, prior to continent-continent collision. From the end of continent-continent collision to the present, low-temperature thermochronology suggests that the evolution of the Uralides has been dominated by erosion and slow exhumation. Despite some evidence for more recent topographic uplift, it has so far proven difficult to quantify it.

The structural evolution of the Ghadames and Illizi basins during the Paleozoic, Mesozoic and Cenozoic: Petroleum implications

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

Gauthier, F.J.; Boudjema, A.; Lounis, R.

1995-08-01

The Ghadames and Illizi basins cover the majority of the eastern Sahara of Algeria. Geologicaly, this part of the Central Saharan platform has been influenced by a series of structural arches and {open_quotes}moles{close_quotes} (continental highs) which controlled sedimentation and structure through geologic time. These features, resulting from and having been affected by nine major tectonic phases ranging from pre-Cambrian to Tertiary, completely bound the Ghadames and Illizi Basins. During the Paleozoic both basins formed one continuous depositional entity with the Ghadames basin being the distal portion of the continental sag basin where facies and thickness variations are observed over largemore » distances. It is during the Mesozoic-Cenozoic that the Ghadames basin starts to evolve differently from the Illizi Basin. Eustatic low-stand periods resulted in continental deposition yielding the major petroleum-bearing reservoir horizons (Cambrian, Ordovician, Siluro-Devonian and Carboniferous). High-stand periods corresponds to the major marine transgressions covering the majority of the Saharan platform. These transgressions deposited the principal source rock intervals of the Silurian and Middle to Upper Devonian. The main reservoirs of the Mesozoic and Cenozoic are Triassic sandstone sequences which are covered by a thick evaporite succession forming a super-seal. Structurally, the principal phases affecting this sequence are the extensional events related to the breakup of Pangea and the Alpine compressional events. The Ghadames and Illizi basins, therefore, have been controlled by a polphase tectonic history influenced by Pan African brittle basement fracturing which resulted in complex structures localized along the major basin bounding trends as well as several subsidiary trends within the basin. These trends, as demonstrated with key seismic data, have been found to contain the majority of hydrocarbons trapped.« less

Paleozoic strata of the Dyckman Mountain area, northeastern Medfra quadrangle, Alaska: A section in Geologic studies in Alaska by the U.S. Geological Survey, 1998

USGS Publications Warehouse

Dumoulin, Julie A.; Bradley, Dwight C.; Harris, Anita G.

2000-01-01

Paleozoic rocks in the Dyckman Mountain area (northeastern Medfra quadrangle; Farewell terrane) include both shallowand deep-water lithologies deposited on and adjacent to a carbonate platform. Shallow-water strata, which were recognized by earlier workers but not previously studied in detail, consist of algal-laminated micrite and skeletal-peloidal wackestone, packstone, and lesser grainstone. These rocks are, at least in part, of Early and (or) Middle Devonian age but locally could be as old as Silurian; they accumulated in shallow subtidal to intertidal settings with periodically restricted water circulation. Deepwater facies, reported here for the first time, are thin, locally graded beds of micrite and calcisiltite and subordinate thick to massive beds of lime grainstone and conglomerate. Conodonts indicate an age of Silurian to Middle Devonian; the most tightly dated intervals are early Late Silurian (early to middle Ludlow). These strata formed as hemipelagic deposits, turbidites, and debris flows derived from shallow-water lithologies of the Nixon Fork subterrane. Rocks in the Dyckman Mountain area are part of a broader facies belt that is transitional between the Nixon Fork carbonate platform to the west and deeper water, basinal lithologies (Minchumina “terrane”) to the east. Transitional facies patterns are complex because of Paleozoic shifts in the position of the platform margin, Mesozoic shortening, and Late Cretaceous-Tertiary disruption by strike-slip faulting.

Post-carboniferous tectonics in the Anadarko Basin, Oklahoma: Evidence from side-looking radar imagery

NASA Technical Reports Server (NTRS)

Nielsen, K. C.; Stern, R. J.

1985-01-01

The Anadarko Basin of western Oklahoma is a WNW-ESE elongated trough filled with of Paleozoic sediments. Most models call for tectonic activity to end in Pennsylvanian times. NASA Shuttle Imaging Radar revealed a distinctive and very straight lineament set extending virtually the entire length of the Anadarko Basin. The lineaments cut across the relatively flat-lying Permian units exposed at the surface. The character of these lineaments is seen most obviously as a tonal variation. Major streams, including the Washita and Little Washita rivers, appear to be controlled by the location of the lineaments. Subsurface data indicate the lineaments may be the updip expression of a buried major fault system, the Mountain View fault. Two principal conclusions arise from this analysis: (1) the complex Mountain View Fault system appears to extend southeast to join the Reagan, Sulphur, and/or Mill Creek faults of the Arbuckle Mountains, and (2) this fault system has been reactivated in Permian or younger times.

Source characteristics and tectonic setting of mafic-ultramafic intrusions in North Xinjiang, NW China: Insights from the petrology and geochemistry of the Lubei mafic-ultramafic intrusion

NASA Astrophysics Data System (ADS)

Chen, Bao-Yun; Yu, Jin-Jie; Liu, Shuai-Jie

2018-05-01

The newly discovered Lubei sulfide-bearing mafic-ultramafic intrusion forms the western extension of the Huangshan-Jin'erquan mafic-ultramafic intrusion belt in East Tianshan, NW China. The Lubei intrusion comprises hornblende peridotite, lherzolite, and harzburgite in its southern portion, gabbro in its middle portion, and hornblende gabbro in its northern portion. Intrusive relationships indicate that three magma pulses were involved in the formation of the intrusion, and that they were likely evolved from a common primitive magma. Estimated compositions of the Lubei primitive magma are similar to those of island arc calc-alkaline basalt except for the low Na2O and CaO contents of the Lubei primitive magma. This paper reports on the mineral compositions, whole-rock major and trace element contents, and Rb-Sr and Sm-Nd isotopic compositions of the Lubei intrusion, and a zircon LA-MC-ICP-MS U-Pb age for hornblende gabbro. The Lubei intrusion is characterized by enrichment in large-ion lithophile elements, depletion in high-field-strength elements, and marked negative Nb and Ta anomalies, with enrichment in chondrite-normalized light rare earth elements. It exhibits low (87Sr/86Sr)i ratios of 0.70333-0.70636 and low (143Nd/144Nd)i ratios of 0.51214-0.51260, with positive εNd values of +4.01 to +6.33. LA-ICP-MS U-Pb zircon ages yielded a weighted-mean age of 287.9 ± 1.6 Ma for the Lubei intrusion. Contemporaneous mafic-ultramafic intrusions in different tectonic domains in North Xinjiang show similar geological and geochemical signatures to the Lubei intrusion, suggesting a source region of metasomatized mantle previously modified by hydrous fluids from the slab subducted beneath the North Xinjiang region in the early Permian. Metasomatism of the mantle was dominated by hydrous fluids and was related to subduction of the Paleo-Asian oceanic lithosphere during the Paleozoic. Sr-Nd-Pb isotopic compositions suggest that the mantle source was a mixture of depleted mid

Plate tectonic history of the Arctic

NASA Technical Reports Server (NTRS)

Burke, K.

1984-01-01

Tectonic development of the Arctic Ocean is outlined, and geological maps are provided for the Arctic during the mid-Cenozoic, later Cretaceous, late Jurassic, early Cretaceous, early Jurassic and late Devonian. It is concluded that Arctic basin history is moulded by the events of the following intervals: (1) continental collision and immediately subsequent rifting and ocean formation in the Devonian, and continental rifting ocean formation, rapid rotation of microcontinents, and another episode of collision in the latest Jurassic and Cretaceous. It is noted that Cenozoic Arctic basin formation is a smaller scale event superimposed on the late Mesozoic ocean basin.

Episodic Cenozoic volcanism and tectonism in the Andes of Peru

USGS Publications Warehouse

Noble, D.C.; McKee, E.H.; Farrar, E.; Petersen, U.

1974-01-01

Radiometric and geologic information indicate a complex history of Cenozoic volcanism and tectonism in the central Andes. K-Ar ages on silicic pyroclastic rocks demonstrate major volcanic activity in central and southern Peru, northern Chile, and adjacent areas during the Early and Middle Miocene, and provide additional evidence for volcanism during the Late Eocene. A provisional outline of tectonic and volcanic events in the Peruvian Andes during the Cenozoic includes: one or more pulses of igneous activity and intense deformation during the Paleocene and Eocene; a period of quiescence, lasting most of Oligocene time; reinception of tectonism and volcanism at the beginning of the Miocene; and a major pulse of deformation in the Middle Miocene accompanied and followed through the Pliocene by intense volcanism and plutonism. Reinception of igneous activity and tectonism at about the Oligocene-Miocene boundary, a feature recognized in other circum-Pacific regions, may reflect an increase in the rate of rotation of the Pacific plate relative to fixed or quasifixed mantle coordinates. Middle Miocene tectonism and latest Tertiary volcanism correlates with and probably is genetically related to the beginning of very rapid spreading at the East Pacific Rise. ?? 1974.

The tectonic evolution of the Irtysh tectonic belt: New zircon U-Pb ages of arc-related and collisional granitoids in the Kalaxiangar tectonic belt, NW China

NASA Astrophysics Data System (ADS)

Hong, Tao; Klemd, Reiner; Gao, Jun; Xiang, Peng; Xu, Xing-Wang; You, Jun; Wang, Xin-Shui; Wu, Chu; Li, Hao; Ke, Qiang

2017-02-01

Precise geochronological constraints of the Irtysh tectonic belt situated between the Saur Island Arc and the Altay Terrane are crucial to a better understanding of the tectonic evolution of the Central Asian Orogenic Belt (CAOB). Recently, we discovered repeatedly deformed arc-related and collisional granitoids in the Kalaxiangar tectonic belt (KTB), which is located in the eastern part of the Irtysh tectonic belt. In this study, we report new whole-rock geochemical, zircon U-Pb and Hf isotopic data of the arc-related and collisional granitoids. Our data reveal that 1) arc-related granodioritic porphyries formed at ca. 382-374 Ma. Recrystallized zircon grains from a (ultra-)mylonitic granodiorite of the Laoshankou zone in the southern KTB display a U-Pb age of ca. 360 Ma; 2) syn-collisional granodioritic porphyries, which distribute along faults and parallel to the cleavage, were emplaced at ca. 367-356 Ma, with εHf(t) values varying from + 7.8 to + 14.2 and Hf model ages from 873 to 459 Ma; 3) a post-collisional A-type granodioritic porphyry, which crosscuts the NW-NNW trending schistosity of the metasedimentary country rocks at a low angle, has an age of ca. 324-320 Ma, while the εHf(t) values range from + 7.6 to + 14.4 with Hf model ages from 850 to 416 Ma; 4) post-collisional strike-slip A-type granite dykes, exposed along strike-slip faults, gave ages between 287 and 279 Ma, whereas the εHf(t) values range from + 4.9 to + 12.7 and the Hf model ages from 995 to 500 Ma; and 5) A-type biotite granite dykes, which intruded along conjugate tension joints, have ages of 274-271 Ma, and εHf(t) values from + 1.5 to + 13.2 with Hf model ages from 1196 to 454 Ma. Consequently, we propose that the collision between the Saur Island Arc and the Altay Terrane occurred in the Early Carboniferous (ca. 367-356 Ma) and the subsequent post-collisional tectonic process continued to the Late Carboniferous (ca. 324-320 Ma). It is further suggested that the Irtysh tectonic belt

Mesozoic evolution of the northeast African shelf margin, Libya and Egypt

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

Aadland, R.K.; Schamel, S.

1988-08-01

The present tectonic features of the northeast African shelf margin between the Nile delta and the Gulf of Sirte are products of (1) precursory late Paleozoic basement arches, (2) early Mesozoic rifting and plate separation, and (3) Late Cretaceous structural inversion. Isopach and structural maps, cross sections, and sediment accumulation (geohistory) curves constructed from 89 wells in the Western Desert and 27 wells in northeastern Libya depict the structural and stratigraphic development of the northeast African shelf margin.

Incorporation of New and Old Tectonics Concepts Into a Modern Course in Tectonics.

ERIC Educational Resources Information Center

Hatcher, Robert D., Jr.

1983-01-01

Describes a graduate-level tectonics course which includes the historical basis for modern tectonics concepts and an in-depth review of pros/cons of plate tectonics. Tectonic features discussed include: ocean basins; volcanic arcs; continental margins; continents; orogenic belts; foreland fold and thrust belts; volcanic/plutonic belts of orogens;…

The Cottage Grove fault system (Illinois Basin): Late Paleozoic transpression along a Precambrian crustal boundary

USGS Publications Warehouse

Duchek, A.B.; McBride, J.H.; Nelson, W.J.; Leetaru, H.E.

2004-01-01

The Cottage Grove fault system in southern Illinois has long been interpreted as an intracratonic dextral strike-slip fault system. We investigated its structural geometry and kinematics in detail using (1) outcrop data, (2) extensive exposures in underground coal mines, (3) abundant borehole data, and (4) a network of industry seismic reflection profiles, including data reprocessed by us. Structural contour mapping delineates distinct monoclines, broad anticlines, and synclines that express Paleozoic-age deformation associated with strike slip along the fault system. As shown on seismic reflection profiles, prominent near-vertical faults that cut the entire Paleozoic section and basement-cover contact branch upward into outward-splaying, high-angle reverse faults. The master fault, sinuous along strike, is characterized along its length by an elongate anticline, ???3 km wide, that parallels the southern side of the master fault. These features signify that the overall kinematic regime was transpressional. Due to the absence of suitable piercing points, the amount of slip cannot be measured, but is constrained at less than 300 m near the ground surface. The Cottage Grove fault system apparently follows a Precambrian terrane boundary, as suggested by magnetic intensity data, the distribution of ultramafic igneous intrusions, and patterns of earthquake activity. The fault system was primarily active during the Alleghanian orogeny of Late Pennsylvanian and Early Permian time, when ultramatic igneous magma intruded along en echelon tensional fractures. ?? 2004 Geological Society of America.

Metallogenesis and tectonics of the Russian Far East, Alaska, and the Canadian Cordillera

USGS Publications Warehouse

Nokleberg, Warren J.; Bundtzen, Thomas K.; Eremin, Roman A.; Ratkin, Vladimir V.; Dawson, Kenneth M.; Shpikerman, Vladimir I.; Goryachev, Nikolai A.; Byalobzhesky, Stanislav G.; Frolov, Yuri F.; Khanchuk, Alexander I.; Koch, Richard D.; Monger, James W.H.; Pozdeev, Anany I.; Rozenblum, Ilya S.; Rodionov, Sergey M.; Parfenov, Leonid M.; Scotese, Christopher R.; Sidorov, Anatoly A.

2005-01-01

The Proterozoic and Phanerozoic metallogenic and tectonic evolution of the Russian Far East, Alaska, and the Canadian Cordillera is recorded in the cratons, craton margins, and orogenic collages of the Circum-North Pacific mountain belts that separate the North Pacific from the eastern North Asian and western North American Cratons. The collages consist of tectonostratigraphic terranes and contained metallogenic belts, which are composed of fragments of igneous arcs, accretionary-wedge and subduction-zone complexes, passive continental margins, and cratons. The terranes are overlapped by continental-margin-arc and sedimentary-basin assemblages and contained metallogenic belts. The metallogenic and geologic history of terranes, overlap assemblages, cratons, and craton margins has been complicated by postaccretion dismemberment and translation during strike-slip faulting that occurred subparallel to continental margins. Seven processes overlapping in time were responsible for most of metallogenic and geologic complexities of the region (1) In the Early and Middle Proterozoic, marine sedimentary basins developed on major cratons and were the loci for ironstone (Superior Fe) deposits and sediment-hosted Cu deposits that occur along both the North Asia Craton and North American Craton Margin. (2) In the Late Proterozoic, Late Devonian, and Early Carboniferous, major periods of rifting occurred along the ancestral margins of present-day Northeast Asia and northwestern North America. The rifting resulted in fragmentation of each continent, and formation of cratonal and passive continental-margin terranes that eventually migrated and accreted to other sites along the evolving margins of the original or adjacent continents. The rifting also resulted in formation of various massive-sulfide metallogenic belts. (3) From about the late Paleozoic through the mid-Cretaceous, a succession of island arcs and contained igneous-arc-related metallogenic belts and tectonically paired

Early Paleozoic high-Mg granodiorite from the Erlangping unit, North Qinling orogen, central China: Partial melting of metasomatic mantle during the initial back-arc opening

NASA Astrophysics Data System (ADS)

Abdallsamed, Mohammed I. M.; Wu, Yuan-Bao; Zhang, Wenxiang; Zhou, Guangyan; Wang, Hao; Yang, Saihong

2017-09-01

This study discussed the petrological classification, petrogenesis, and tectonic significance of early Paleozoic high-Mg granodiorite from the Erlangping unit, in the North Qinling orogen. To achieve this target, we conducted integrated investigation of in situ zircon U-Pb dating, whole-rock geochemical, as well as Sr-Nd-Hf-O isotopic compositions for the Kanfenggou pluton from the Erlangping unit. LA-ICP-MS zircon dating for the Kanfenggou samples yields U-Pb ages of 442.9 ± 6.2 and 438.0 ± 6.7 Ma, suggesting that the pluton was emplaced at ca. 440 Ma. Whole-rock geochemical compositions of the samples display intermediate SiO2 (60.48-64.67 wt%) and K2O (1.21 to 2.10 wt%), but high Al2O3 (15.44 to 16.51 wt%) and Na2O (4.01 to 4.81 wt%) contents. The granodiorite samples are characterized by elevated MgO ranging from 2.30 to 3.44 wt% and Mg# values of 53.35to 56.66, implying they are high-Mg granodiorites. They are characterized by very high Ba (524-1132 ppm) and Sr (684-980 ppm) contents, but depleted in HREE, and high (La/Yb)N ratios of 6.34 to 16.5 and slightly negative to weak positive Eu anomalies (Eu/Eu* = 0.68-1.09). These evidence that the Kanfenggou pluton belongs to the sanukitoid series. The high-Mg granodiorite samples exhibit a mantle signature with high Mg# values (53.35-56.66), Cr (45.8 to 93.3 ppm) and Ni (28.2 to 48.2 ppm) contents, but enriched in LILE, pointing to an enriched mantle source. The samples show relatively depleted radiogenic isotopic compositions with initial 87Sr/86Sr ratios varying from 0.7044 to 0.7047, εNd(t) values from 0.31 to 4.21, and zircon εHf (t) values from 7.3 to 8.3. The zircons have a mean δ18O value of 5.20 ± 0.17 ‰. Based on the trace element geochemical features, the metasomatic agent was suggested to be the fluids generated from dehydration of subducted slab. Therefore, we suggest two-stage processes for the formation of the Erlangping high-Mg granodiorites: (1) interaction between slab fluids and mantle

Formation of modern and Paleozoic stratiform barite at cold methane seeps on continental margins

USGS Publications Warehouse

Torres, M.E.; Bohrmann, G.; Dube, T.E.; Poole, F.G.

2003-01-01

Stratiform (bedded) Paleozoic barite occurs as large conformable beds within organic- and chert-rich sediments; the beds lack major sulfide minerals and are the largest and most economically significant barite deposits in the geologic record. Existing models for the origin of bedded barite fail to explain all their characteristics: the deposits display properties consistent with an exhalative origin involving fluid ascent to the seafloor, but they lack appreciable polymetallic sulfide minerals and the corresponding strontium isotopic composition to support a hydrothermal vent source. A new mechanism of barite formation, along structurally controlled sites of cold fluid seepage in continental margins, involves barite remobilization in organic-rich, highly reducing sediments, transport of barium-rich fluids, and barite precipitation at cold methane seeps. The lithologic and depositional framework of Paleozoic and cold seep barite, as well as morphological, textural, and chemical characteristics of the deposits, and associations with chemosymbiotic fauna, all support a cold seep origin for stratiform Paleozoic barite. This understanding is highly relevant to paleoceanographic and paleotectonic studies, as well as to economic geology.

Assessment of Appalachian Basin Oil and Gas Resources: Utica-Lower Paleozoic Total Petroleum System

USGS Publications Warehouse

Ryder, Robert T.

2008-01-01

The Utica-Lower Paleozoic Total Petroleum System (TPS) is an important TPS identified in the 2002 U.S. Geological Survey (USGS) assessment of undiscovered, technically recoverable oil and gas resources in the Appalachian basin province (Milici and others, 2003). The TPS is named for the Upper Ordovician Utica Shale, which is the primary source rock, and for multiple lower Paleozoic sandstone and carbonate units that are the important reservoirs. Upper Cambrian through Upper Silurian petroleum-bearing strata that constitute the Utica-Lower Paleozoic TPS thicken eastward from about 2,700 ft at the western margin of the Appalachian basin to about 12,000 ft at the thrust-faulted eastern margin of the Appalachian basin. The Utica-Lower Paleozoic TPS covers approximately 170,000 mi2 of the Appalachian basin from northeastern Tennessee to southeastern New York and from central Ohio to eastern West Virginia. The boundary of the TPS is defined by the following geologic features: (1) the northern boundary (from central Ontario to northeastern New York) extends along the outcrop limit of the Utica Shale-Trenton Limestone; (2) the northeastern boundary (from southeastern New York, through southeastern Pennsylvania-western Maryland-easternmost West Virginia, to northern Virginia) extends along the eastern limit of the Utica Shale-Trenton Limestone in the thrust-faulted eastern margin of the Appalachian basin; (3) the southeastern boundary (from west-central and southwestern Virginia to eastern Tennessee) extends along the eastern limit of the Trenton Limestone in the thrust-faulted eastern margin of the Appalachian basin; (4) the southwestern boundary (from eastern Tennessee, through eastern Kentucky, to southwestern Ohio) extends along the approximate facies change from the Trenton Limestone with thin black shale interbeds (on the east) to the equivalent Lexington Limestone without black shale interbeds (on the west); (5) the northern part of the boundary in southwestern Ohio

Polyphase tectonics at the southern tip of the Manila trench, Mindoro-Tablas Islands, Philippines

NASA Astrophysics Data System (ADS)

Marchadier, Yves; Rangin, Claude

1990-11-01

The southern termination of the Manila trench within the South China Sea continental margin in Mindoro is marked by a complex polyphase tectonic fabric in the arc-trench gap area. Onshore Southern Mindoro the active deformation front of the Manila trench is marked by parallel folds and thrusts, grading southward to N50° W-trending left-lateral strike-slip faults. This transpressive tectonic regime, active at least since the Late Pliocene, has overprinted the collision of an Early Miocene volcanic arc with the South China Sea continental margin (San Jose platform). The collision is postdated by deposition of the Late Miocene-Early Pliocene elastics of the East Mindoro basin. The tectonic and geological framework of this arc, which overlies a metamorphic basement and Eocene elastics, suggests that it was built on a drifted block of the South China Sea continental margin.

Depositional environments and tectonic significance of the Wajid Sandstone of southern Saudi Arabia

NASA Astrophysics Data System (ADS)

Dabbagh, Mohamed E.; Rogers, John J. W.

The Wajid Sandstone, of probable Early Paleozoic age, rests disconformably on crystalline rocks of the southern part of the Arabian shield. Scattered outcrops extend over an area about 450 km north-south and 300 km east-west. The southern part of the formation, near the Yemen border, consists of fluvial sandstones and very minor siltstones and silty shales. The fluvial origin is demonstrated by the presence of fining-upward cycles, channels, trough cross bedding, and absence of all organic traces. The northern part of the outcrop area consists of internally homogeneous, tabular cross-bedded, horizontally bedded sandstones apparently formed in a shallow marine environment. These marine rocks contain trace fossils broadly similar to Skolithos. Abundant cross bedding in both facies of the Wajid indicates a northward transport direction, toward what is now the center of the Arabian shield. The southern part of the Arabian shield, which was cratonized about 500 to 600 Ma ago (Pan-African age), was apparently still a depositional area receiving sediments from a southern source in Early Paleozoic time. Other, older, shields also show a tendency to be areas of deposition shortly after their apparent age of stabilization, becoming sources of clastic sediments only after several hundreds of millions of years. The conversion from basin to uplifted source may indicate a prolonged process of shield maturation after initial stabilization.

Initiation of plate tectonics from post-magma ocean thermochemical convection

NASA Astrophysics Data System (ADS)

Foley, Bradford J.; Bercovici, David; Elkins-Tanton, Linda T.

2014-11-01

Leading theories for the presence of plate tectonics on Earth typically appeal to the role of present day conditions in promoting rheological weakening of the lithosphere. However, it is unknown whether the conditions of the early Earth were favorable for plate tectonics, or any form of subduction, and thus, how subduction begins is unclear. Using physical models based on grain-damage, a grainsize-feedback mechanism capable of producing plate-like mantle convection, we demonstrate that subduction was possible on the Hadean Earth (hereafter referred to as proto-subduction or proto-plate tectonics), that proto-subduction differed from modern day plate tectonics, and that it could initiate rapidly. Scaling laws for convection with grain-damage show that though either higher mantle temperatures or higher surface temperatures lead to slower plates, proto-subduction, with plate speeds of ≈1.75 cm/yr, can still be maintained in the Hadean, even with a CO2 rich primordial atmosphere. Furthermore, when the mantle potential temperature is high (e.g., above ≈2000 K), the mode of subduction switches to a "sluggish subduction" style, where downwellings are drip like and plate boundaries are diffuse. Finally, numerical models of post-magma ocean mantle convection demonstrate that proto-plate tectonics likely initiates within ˜100 Myr of magma ocean solidification, consistent with evidence from Hadean zircons. After the initiation of proto-subduction, non-plate-tectonic "sluggish subduction" prevails, giving way to modern style plate tectonics as both the mantle interior and climate cool. Hadean proto-subduction may hasten the onset of modern plate tectonics by drawing excess CO2 out of the atmosphere and cooling the climate.

The main features of the Uralian Paleozoic magmatism and the epioceanic nature of the orogen

NASA Astrophysics Data System (ADS)

Fershtater, G. B.

2013-02-01

The 2000 km Uralian Paleozoic orogen is situated on the western flank of the Uralo-Mongolian folded belt. It is characterized by an abundant variety of magmatic rocks and related ore deposits. Uralian Paleozoic magmatism is entirely subduction-related. It is proposed that the Uralian orogen represents a cold mobile belt in which the mantle temperature was 200 to 500 °C cooler than in the adjacent areas; a situation which is similar to the modern West Pacific Triangle Zone including Indonesia, the Philippine Islands, and southern Asia. During the course of the geological evolution of the Uralian orogen, the nature of the magmatism has changed from basic rocks of indisputable mantle origin (460-390 Ma) to mantle-crust gabbro-granitic complexes (370-315 Ma) followed by pure crustal granite magmatism (290-250 Ma). This order in rock type and age reflects the evolution of Paleozoic magmatic complexes from the beginning of subduction to the final stages of the orogen development.

Underpressure in Mesozoic and Paleozoic rock units in the Midcontinent of the United States

USGS Publications Warehouse

Nelson, Philip H.; Gianoutsos, Nicholas J.; Drake, Ronald

2015-01-01

Potentiometric surfaces for Paleozoic strata, based on water well levels and selected drill-stem tests, reveal the control on hydraulic head exerted by outcrops in eastern Kansas and Oklahoma. From outcrop in the east, the westward climb of hydraulic head is much less than that of the land surface, with heads falling so far below land surface that the pressure:depth ratio in eastern Colorado is less than 5.7 kPa/m (0.25 psi/ft). Permian evaporites separate the Paleozoic hydrogeologic units from a Lower Cretaceous (Dakota Group) aquifer, and a highly saline brine plume pervading Paleozoic units in central Kansas and Oklahoma is attributed to dissolution of Permian halite. Underpressure also exists in the Lower Cretaceous hydrogeologic unit in the Denver Basin, which is hydrologically separate from the Paleozoic units. The data used to construct the seven potentiometric surfaces were also used to construct seven maps of pressure:depth ratio. These latter maps are a function of the differences among hydraulic head, land-surface elevation, and formation elevation. As a consequence, maps of pressure:depth ratio reflect the interplay of three topologies that evolved independently with time. As underpressure developed, gas migrated in response to the changing pressure regime, most notably filling the Hugoton gas field in southwestern Kansas. The timing of underpressure development was determined by the timing of outcrop exposure and tilting of the Great Plains. Explorationists in western Kansas and eastern Colorado should not be surprised if a reservoir is underpressured; rather, they should be surprised if it is not.

The Pan-African nappe tectonics in the Shackleton Range

USGS Publications Warehouse

Buggisch, W.; Kleinschmidt, G.

2007-01-01

In memory of Campbell Craddock: When J. Campbell Craddock (1972) published his famous 1:5 000 000 map of the Geology of Antarctica, he established major units such as the East Antarctic Craton, the early Palaeozoic Ross, the Mesozoic Ellsworth, and the Cenozoic Andean orogens. It is already evident from this map, that the strike of the Ellsworth Mountains and the Shackleton Range is perpendicular to palaeo-Pacific and modern Pacific margins. While the Ellsworth-Whitmore block is classified as a rotated terrane, the Ross-aged orogen of the Shackleton Range requires another interpretation. The discovery of extended tectonic nappes with south directed transport in the southern Shackleton Range and west transport in the north established a plate tectonic scenery with a subduction dominated Ross Orogen in the Transantarctic Mountains and a transpressive tectonic regime in the Shackleton Range during the final closing of the Mozambique Ocean.

Tectonic Geomorphology.

ERIC Educational Resources Information Center

Bull, William B.

1984-01-01

Summarizes representative quantitative tectonic-geomorphology studies made during the last century, focusing on fault-bounded mountain-front escarpments, marine terraces, and alluvial geomorphic surfaces (considering stream terraces, piedmont fault scarps, and soils chronosequences). Also suggests where tectonic-geomorphology courses may best fit…

Migmatization and low-pressure overprinting metamorphism as record of two pre-Cretaceous tectonic episodes in the Santander Massif of the Andean basement in northern Colombia (NW South America)

NASA Astrophysics Data System (ADS)

Zuluaga, C. A.; Amaya, S.; Urueña, C.; Bernet, M.

2017-03-01

crystallization of modified partial melts contrast with several other leucosomes that were injected; however, in some cases the melts crystallized as injected leucosomes show consistent geochemistry with partial melting of lithologies geochemically similar to the ones observed in the unit. The migmatization and the low pressure metamorphic overprint are related here to two main tectonic events: an early Paleozoic tectonic pulse produced by subduction of the oceanic crust of the Iapetus Ocean beneath northwestern Gondwana, and an Upper Triassic to Lower Jurassic tectonic pulse produced by subduction of oceanic crust of the proto-Pacific ocean beneath western Pangaea.

Martian plate tectonics

NASA Astrophysics Data System (ADS)

Sleep, N. H.

1994-03-01

The northern lowlands of Mars have been produced by plate tectonics. Preexisting old thick highland crust was subducted, while seafloor spreading produced thin lowland crust during late Noachian and Early Hesperian time. In the preferred reconstruction, a breakup margin extended north of Cimmeria Terra between Daedalia Planum and Isidis Planitia where the highland-lowland transition is relatively simple. South dipping subduction occured beneath Arabia Terra and east dipping subduction beneath Tharsis Montes and Tempe Terra. Lineations associated with Gordii Dorsum are attributed to ridge-parallel structures, while Phelegra Montes and Scandia Colles are interpreted as transfer-parallel structures or ridge-fault-fault triple junction tracks. Other than for these few features, there is little topographic roughness in the lowlands. Seafloor spreading, if it occurred, must have been relatively rapid. Quantitative estimates of spreading rate are obtained by considering the physics of seafloor spreading in the lower (approx. 0.4 g) gravity of Mars, the absence of vertical scarps from age differences across fracture zones, and the smooth axial topography. Crustal thickness at a given potential temperature in the mantle source region scales inversely with gravity. Thus, the velocity of the rough-smooth transition for axial topography also scales inversely with gravity. Plate reorganizations where young crust becomes difficult to subduct are another constraint on spreading age. Plate tectonics, if it occurred, dominated the thermal and stress history of the planet. A geochemical implication is that the lower gravity of Mars allows deeper hydrothermal circulation through cracks and hence more hydration of oceanic crust so that more water is easily subducted than on the Earth. Age and structural relationships from photogeology as well as median wavelength gravity anomalies across the now dead breakup and subduction margins are the data most likely to test and modify hypotheses

Tectonic exhumation and boundary structure of the Kokchetav HP - UHP metamorphic belt (Northern Kazakhstan): constraints from 40Ar/39Ar geochronology

NASA Astrophysics Data System (ADS)

Zhimulev, Fedor; de Grave, Johan; Travin, Aleksey; Buslov, Mikhail

2010-05-01

The Kokchetav metamorphic belt (KMB) is part of the Early Paleozoic orogenic belt of Northern Kazakhstan and constitutes one of the most famous, classical ultra-high pressure (UHP) metamorphic terranes. The KMB mainly consists of gneisses, mica schists and eclogites. These were formed by Cambrian continental subduction and associated metamorphism of the Precambrian Kokchetav microcontinent and subsequent exhumation of fragments of this metamorphosed continental crust. Several subterranes can be distinguished in the KMB: Barchi, Kumdi-Kol, Sulu-Tube, Enbek-Berlyk, Kulet and Borovoe. These subterranes differ not only in rock composition or in genetic pT conditions, but also in the age of the individual metamorphic events, including the timing of peak, and regressive stages. Most geochronological data indicate a Cambrian age of UHP and HP metamorphism and subsequent exhumation of the KMB. However, there is no field evidence of Cambrian geodynamic processes in the region: Cambrian sediments, volcanic rocks, or large magmatic bodies are completely absent in the KMB setting. The youngest geochronological information in the KMB was obtained on the garnet-mica schists from the Enbek-Berlyk subterrane. The 40Ar/39Ar ages of the muscovite from these schists lies in the range of 490 to 475 Ma (mainly 480-485 Ma). All 40Ar/39Ar stepwise heating experiments yield well-defined plateau and isochron ages. This age is considered to represent the time of emplacement of various heterogeneous nappes, including nappes that consist of HP - UHP metamorphic rocks, to upper crustal levels. To the north, the Kokchetav HP - UHP metamorphic belt is bounded by the Northern Kokchetav tectonic zone (NKTZ). This zone includes thin nappes of (1) Palaeo-Mesoproterozoic gneiss of the metamorphic basement of the Kokchetav microcontinent and Neoproterozoic meta-sandstones and dolomites of its deformed sedimentary cover, (2) pre-Ordovician volcanic rocks of island-arc affinity, (3) Early Ordovician

Environmental trends in extinction during the Paleozoic

NASA Technical Reports Server (NTRS)

Sepkoski, J. John, Jr.

1987-01-01

Extinction intensities calculated from 505 Paleozoic marine assemblages divided among six environmental zones and 40 stratigraphic intervals indicate that whole communities exhibit increasing extinction offshore but that genera within individual taxonomic classes tend to have their highest extinction onshore. The offshore trend at the community level results from a concentration of genera in classes with low characteristic extinction rates in nearshore environments. This finding is consistent with the ecologic expectation that organisms inhabiting unpredictably fluctuating environments should suffer more extinction than counterparts living under more predictably equitable conditions.

Age and provenance constraints on seismically-determined crustal layers beneath the Paleozoic southern Central Asian Orogen, Inner Mongolia, China

NASA Astrophysics Data System (ADS)

Jian, Ping; Kröner, Alfred; Shi, Yuruo; Zhang, Wei; Liu, Yaran; Windley, Brian F.; Jahn, Bor-ming; Zhang, Liqao; Liu, Dunyi

2016-06-01

We present 110 ages and 51 in-situ δ18O values for zircon xenocrysts from a post-99 Ma intraplate basaltic rock suite hosted in a subduction-accretion complex of the southern Central Asian Orogenic Belt in order to constrain a seismic profile across the Paleozoic Southern Orogen of Inner Mongolia and the northern margin of the North China Craton. Two zircon populations are recognized, namely a Phanerozoic group of 70 zircons comprising granitoid-derived (ca. 431-99 Ma; n = 31; peak at 256 Ma), meta-granitoid-derived (ca. 449-113 Ma; n = 24; peak at 251 Ma) and gabbro-derived (436-242 Ma; n = 15; peaks at 264 and 244 Ma) grains. Each textural type is characterized by a distinct zircon oxygen isotope composition and is thus endowed with a genetic connotation. The Precambrian population (2605-741 Ma; n = 40) exhibits a prominent age peak at 2520 Ma (granulite-facies metamorphism) and four small peaks at ca. 1900, 1600, and 800 Ma. Our new data, together with literature zircon ages, significantly constrain models of three seismically-determined deep crustal layers beneath the fossil subduction zone-forearc along the active northern margin of the North China Craton, namely: (1) an upper arc crust of early to mid-Paleozoic age, intruded by a major Permian-Triassic composite granitoid-gabbroic pluton (8-20 km depth); (2) a middle crust, predominantly consisting of mid-Meso- to Neoproterozoic felsic and mafic gneisses; and (3) a lower crust composed predominantly of late Archean granulite-facies rocks. We conclude that the Paleozoic orogenic crust is limited to the upper crustal level, and the middle to lower crust has a North China Craton affinity. Furthermore, integrating our data with surface geological, petrological and geochronological constraints, we present a new conceptual model of orogenic uplift, lithospheric delamination and crustal underthrusting for this key ocean-continent convergent margin.

Three stages in the Late Paleozoic to Triassic magmatism of southwestern Gondwana, and the relationships with the volcanogenic events in coeval basins

NASA Astrophysics Data System (ADS)

Sato, Ana María; Llambías, Eduardo J.; Basei, Miguel A. S.; Castro, Carlos E.

2015-11-01

The intermediate to acid Choiyoi Magmatic Province is the most conspicuous feature along the Late Paleozic continental margin of southwestern Gondwana, and is generally regarded as the possible source for the widespread ash fall deposits interlayered with sedimentary sequences in the adjacent Gondwana basins. The Choiyoi magmatism is geologically constrained between the early Permian San Rafael orogenic phase and the Triassic extensional Huarpica phase in the region of Argentine Frontal Cordillera, Precordillera and San Rafael Block. In order to better assess the Choiyoi magmatism in Argentine Frontal Cordillera, we obtained 6 new LA-ICPMS U-Pb ages between 278.8 ± 3.4 Ma and 252.5 ± 1.9 Ma from plutonic rocks of the Colangüil Batholith and an associated volcanic rock. The global analysis of age data compiled from Chilean and Argentine Late Paleozoic to Triassic outcrops allows us to identify three stages of magmatism: (1) pre-Choiyoi orogenic magmatism, (2) Choiyoi magmatism (286-247 Ma), and (3) post-Choiyoi magmatism related to extensional tectonics. In the Choiyoi stage is there an eastward shift and expansion of the magmatism to the southeast, covering an extensive region that defines the Choiyoi magmatic province. On the basis of comparison with the ages from volcanogenic levels identified in the coeval Gondwana basins, we propose: (a) The pre-Choiyoi volcanism from the Paganzo basin (320-296 Ma) probably has a local source in addition to the Frontal Cordillera region. (b) The pre-Choiyoi and Choiyoi events identified in the Paraná basin (304-275 Ma) are likely to have their source in the Chilean Precordillera. (c) The early stage of the Choiyoi magmatism found in the Sauce Grande basin (284-281 Ma) may have come from the adjacent Las Matras to Chadileuvú blocks. (d) The pre-Choiyoi and Choiyoi events in the Karoo basins (302-253 Ma) include the longest Choiyoi interval, and as a whole bear the best resemblance to the age records along the Chilean and

The Implementation of 2-D Resistivity Method in Verifying Paleozoic Aquifer Properties at Bukit Chondong, Perlis (Malaysia)

NASA Astrophysics Data System (ADS)

Maslinda, Umi; Nordiana, M. M.; Bery, A. A.; Afiq Saharudin, Muhamad; Hisham, Hazrul; Taqiuddin, Z. M.; Sulaiman, Nabila; Nur Amalina, M. K. A.; Nordiana, A. N.

2017-04-01

The research was conducted using 2-D resistivity in verifying Paleozoic aquifer. Since most geologic materials behave as electrical insulators, surface measurements of earth resistivity are controlled by the electrolytic ability of interstitial water. The subsurface distribution of water is controlled by the porosity of the formations. The study area is at Bukit Chondong, Beseri, Perlis. Bukit Chondong is made of sedimentary rock which mostly is sandstone. Bukit Chondong is from uppermost of the Kubang Pasu Formation that represented by a thick unit of grey mudstone interbedded with sandstone. The Kubang Pasu Formation was influenced by shallow marine during the early age. Paleocurrent and fossils traces were found on the mudstone at the study area. The area is suspected to be a Paleozoic aquifer because the sandstone can be a productive aquifer with diffuse flow. The water movement in sandstone is through the fractures and joints. Most of the water stores and transmits in sandstone. The interbedded sandstone and mudstone is one of the aquifer characteristic. Sandstone and mudstone are water-bearing rocks and low-permeable rocks respectively. The data was processed according to the geological information of the study area since there was an outcrop. The study area have low resistivity value which both sandstone and mudstone give less than 800 Ohm-m due to the water content (Sulphide and clay).

Tectonic evolution of the northern African margin in Tunisia from paleostress data and sedimentary record

NASA Astrophysics Data System (ADS)

Bouaziz, Samir; Barrier, Eric; Soussi, Mohamed; Turki, Mohamed M.; Zouari, Hédi

2002-11-01

A reconstruction of the tectonic evolution of the northern African margin in Tunisia since the Late Permian combining paleostress, tectonic stratigraphic and sedimentary approaches allows the characterization of several major periods corresponding to consistent stress patterns. The extension lasting from the Late Permian to the Middle Triassic is contemporaneous of the rifting related to the break up of Pangea. During Liassic times, regional extensional tectonics originated the dislocation of the initial continental platform. In northern Tunisia, the evolution of the Liassic NE-SW rifting led during Dogger times to the North African passive continental margin, whereas in southern Tunisia, a N-S extension, associated with E-W trending subsiding basins, lasted from the Jurassic until the Early Cretaceous. After an Upper Aptian-Early Albian transpressional event, NE-SW to ENE-WSW trending extensions prevailed during Late Cretaceous in relationship with the general tectonic evolution of the northeastern African plate. The inversions started in the Late Maastrichtian-Paleocene in northern Tunisia, probably as a consequence of the Africa-Eurasia convergence. Two major NW-SE trending compressions occurred in the Late Eocene and in the Middle-Late Miocene alternating with extensional periods in the Eocene, Oligocene, Early-Middle Miocene and Pliocene. The latter compressional event led to the complete inversion of the basins of the northwestern African plate, originating the Maghrebide chain. Such a study, supported by a high density of paleostress data and including complementary structural and stratigraphic approaches, provides a reliable way of determining the regional tectonic evolution.

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

NASA Astrophysics Data System (ADS)

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

1994-12-01

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

From Plate Tectonic to Continental Dynamics

NASA Astrophysics Data System (ADS)

Molnar, P. H.

2017-12-01

By the early 1970s, the basics of plate tectonics were known. Although much understanding remained to be gained, as a topic of research, plate tectonics no longer defined the forefront of earth science. Not only had it become a foundation on which to build, but also the methods used to reveal it became tools to take in new directions. For me as a seismologist studying earthquakes and active processes, the deformation of continents offered an obvious topic to pursue. Obviously examining the deformation of continents and ignoring the widespread geologic evidence of both ongoing and finite deformation of crust would be stupid. I was blessed with the opportunity to learn from and collaborate with two of the best, Paul Tapponnier and Clark Burchfiel. Continental deformation differed from plate tectonics both because deformation was widespread but more importantly because crust shortens (extends) horizontally and thickens (thins), processes that can be ignored where plate tectonics - the relative motion of rigid plates - occurs. Where a plate boundary passes into a continent, not only must the forces that move plates do work against friction or other dissipative processes, but where high terrain is created, they must also do work against gravity, to create gravitational potential energy in high terrain. Peter Bird and Kenneth Piper and Philip England and Dan McKenzie showed that a two-dimensional thin viscous sheet with vertically averaged properties enabled both sources of resistance to be included without introducing excessive complexity and to be scaled by one dimensionless number, what the latter pair called the Argand number. Increasingly over the past thirty years, emphasis has shifted toward the role played by the mantle lithosphere, because of both its likely strength and its negative buoyancy, which makes it gravitationally unstable. Despite progress since realizing that rigid plates (the essence of plate tectonics) provides a poor description of continental

Tectonic map of Indonesia: A progress report

USGS Publications Warehouse

Hamilton, Warren Bell

1970-01-01

Orogeny, volcanism, and seismicity are now intensely active in Indonesia. Many Dutch tectonists--Brouwer, Umbgrove, van Bemifielen, Smit4Sibinga, Vening Meinesz, Westerveld, and others--recognized that this complex cluster of islands represents an early stage in the evolution of orogenic belts. Not until Indonesia is understood can we comprehend the Alps. This report summarizes some aspects of work to date on the Tectonic Map of Indonesia. The preparation of this map is a joint project of the Geological Survey of Indonesia and the United States Geological Survey, sponsored by the Government of Indonesia and the United States Agency for International Development. The Tectonic Map of Indonesia will be published at a scale of 1:5,000,000. Adjacent regions in other countries will be included to provide a broader context. The map limits presently envisaged are the parallels of 12° N. and 15° S., and the meridians of 91° and 148° E. Tectonic features will be shown in many colors and patterns. Bathymetry is being newly compiled, and will be shown with contours and shades of blue. Figure 1 shows the islands of Indonesia.

Paleozoic evolution of active margin basins in the southern Central Andes (northwestern Argentina and northern Chile)

NASA Astrophysics Data System (ADS)

Bahlburg, H.; Breitkreuz, C.

The geodynamic evolution of the Paleozoic continental margin of Gondwana in the region of the southern Central Andes is characterized by the westward progression of orogenic basin formation through time. The Ordovician basin in the northwest Argentinian Cordillera Oriental and Puna originated as an Early Ordovician back-arc basin. The contemporaneous magmatic arc of an east-dipping subduction zone was presumably located in northern Chile. In the back-arc basin, a ca. 3500 meter, fining-up volcaniclastic apron connected to the arc formed during the Arenigian. Increased subsidence in the late Arenigian allowed for the accomodation of large volumes of volcaniclastic turbidites during the Middle Ordovician. Subsidence and sedimentation were caused by the onset of collision between the para-autochthonous Arequipa Massif Terrane (AMT) and the South American margin at the Arenigian-Llanvirnian transition. This led to eastward thrusting of the arc complex over its back-arc basin and, consequently, to its transformation into a marine foreland basin. As a result of thrusting in the west, a flexural bulge formed in the east, leading to uplift and emergence of the Cordillera Oriental shelf during the Guandacol Event at the Arenigian-Llanvirnian transition. The basin fill was folded during the terminal collision of the AMT during the Oclóyic Orogeny (Ashgillian). The folded strata were intruded post-tectonically by the presumably Silurian granitoids of the "Faja Eruptiva de la Puna Oriental." The orogeny led to the formation of the positive area of the Arco Puneño. West of the Arco Puneño, a further marine basin developed during the Early Devonian, the eastern shelf of which occupied the area of the Cordillera Occidental, Depresión Preandina, and Precordillera. The corresponding deep marine turbidite basin was located in the region of the Cordillera de la Costa. Deposition continued until the basin fill was folded in the early Late Carboniferous Toco Orogeny. The basin

The Cannery Formation--Devonian to Early Permian arc-marginal deposits within the Alexander Terrane, Southeastern Alaska

USGS Publications Warehouse

Karl, Susan M.; Layer, Paul W.; Harris, Anita G.; Haeussler, Peter J.; Murchey, Benita L.

2011-01-01

cherts on both Admiralty and Kupreanof Islands contain radiolarians as young as Permian, the age of the Cannery Formation is herein extended to Late Devonian through early Permian, to include the early Permian rocks exposed in its type locality. The Cannery Formation is folded and faulted, and its stratigraphic thickness is unknown but inferred to be several hundred meters. The Cannery Formation represents an extended period of marine deposition in moderately deep water, with slow rates of deposition and limited clastic input during Devonian through Pennsylvanian time and increasing argillaceous, volcaniclastic, and bioclastic input during the Permian. The Cannery Formation comprises upper Paleozoic rocks in the Alexander terrane of southeastern Alaska. In the pre-Permian upper Paleozoic, the tectonic setting of the Alexander terrane consisted of two or more evolved oceanic arcs. The lower Permian section is represented by a distinctive suite of rocks in the Alexander terrane, which includes sedimentary and volcanic rocks containing early Permian fossils, metamorphosed rocks with early Permian cooling ages, and intrusive rocks with early Permian cooling ages, that form discrete northwest-trending belts. After restoration of 180 km of dextral displacement of the Chilkat-Chichagof block on the Chatham Strait Fault, these belts consist, from northeast to southwest, of (1) bedded chert, siliceous argillite, volcaniclastic turbidites, pillow basalt, and limestone of the Cannery Formation and the Porcupine Slate of Gilbert and others (1987); (2) greenschist-facies Paleozoic metasedimentary and metavolcanic rocks that have Permian cooling ages; (3) silty limestone and calcareous argillite interbedded with pillow basalt and volcaniclastic rocks of the Halleck Formation and the William Henry Bay area; and (4) intermediate-composition and syenitic plutons. These belts correspond to components of an accretionary complex, contemporary metamorphic rocks, forearc-basin deposits,

Burning experiments and late Paleozoic high O2 levels

NASA Astrophysics Data System (ADS)

Wildman, R.; Essenhigh, R.; Berner, R.; Hickey, L.; Wildman, C.

2003-04-01

The Paleozoic rise of land plants brought about increased burial of organic matter and a resulting increase in atmospheric oxygen concentrations. Levels as high as 30-35% O2 may have been reached during the Permo-Carboniferous (Berner and Canfield, 1989; Berner, 2001). However, burning experiments based solely on paper (Watson, 1978) have challenged these results, the claim being that if the oxygen made up more than 25% of the atmosphere, the frequency and intensity of forest fires would increase sufficiently to prevent the continued existence of plant life. Thus, since plants have persisted, it is possible that fires served as a negative feedback against excessive oxygen levels. An initial study of Paleozoic wildfire behavior via thermogravimetric analysis (TGA) was conducted under ambient and enriched oxygen conditions to simulate present and ancient atmospheres. The tests focused on natural fuels, specifically tree leaves and wood, tree fern fibers, and sphagnum peat-moss, simulating Permo-Carboniferous upland and swampland ecosystems, respectively. Three conclusions are: (1) enriched oxygen increases the rate of mass loss during burning; (2) fuel chemistry (cellulose vs. lignin) influences burning patterns; and (3) in geometrically heterogeneous fuels, geometry affects burning rate significantly. Both geometrically and chemically, paper resists fire poorly; thus, we found that it loses its mass at lower temperatures than forest materials and is therefore a poor proxy for Paleozoic ecosystems. Further study of Paleozoic wildfire spread behavior is currently being conducted. Fires are lit using pine dowels, which allow for reproducible fuel density. Steady-state, one-dimensional flame-spread is measured with thermocouples anchored two inches above the fuel bed. Both oxygen concentration of the air supply to the fire and moisture content of the fuels are varied, as we suspect that these are two main controls of wildfire spread. Burning fuels of varying moisture

Late paleozoic fusulinoidean gigantism driven by atmospheric hyperoxia.

PubMed

Payne, Jonathan L; Groves, John R; Jost, Adam B; Nguyen, Thienan; Moffitt, Sarah E; Hill, Tessa M; Skotheim, Jan M

2012-09-01

Atmospheric hyperoxia, with pO(2) in excess of 30%, has long been hypothesized to account for late Paleozoic (360-250 million years ago) gigantism in numerous higher taxa. However, this hypothesis has not been evaluated statistically because comprehensive size data have not been compiled previously at sufficient temporal resolution to permit quantitative analysis. In this study, we test the hyperoxia-gigantism hypothesis by examining the fossil record of fusulinoidean foraminifers, a dramatic example of protistan gigantism with some individuals exceeding 10 cm in length and exceeding their relatives by six orders of magnitude in biovolume. We assembled and examined comprehensive regional and global, species-level datasets containing 270 and 1823 species, respectively. A statistical model of size evolution forced by atmospheric pO(2) is conclusively favored over alternative models based on random walks or a constant tendency toward size increase. Moreover, the ratios of volume to surface area in the largest fusulinoideans are consistent in magnitude and trend with a mathematical model based on oxygen transport limitation. We further validate the hyperoxia-gigantism model through an examination of modern foraminiferal species living along a measured gradient in oxygen concentration. These findings provide the first quantitative confirmation of a direct connection between Paleozoic gigantism and atmospheric hyperoxia. © 2012 The Author(s). Evolution© 2012 The Society for the Study of Evolution.

Polygenetic Karsted Hardground Omission Surfaces in Lower Silurian Neritic Limestones: a Signature of Early Paleozoic Calcite Seas

NASA Astrophysics Data System (ADS)

James, Noel P.; Desrochers, André; Kyser, Kurt T.

2015-04-01

Exquisitely preserved and well-exposed rocky paleoshoreline omission surfaces in Lower Silurian Chicotte Formation limestones on Anticosti Island, Quebec, are interpreted to be the product of combined marine and meteoric diagenesis. The different omission features include; 1) planar erosional bedding tops, 2) scalloped erosional surfaces, 3) knobs, ridges, and swales at bedding contacts, and 4) paleoscarps. An interpretation is proposed that relates specific omission surface styles to different diagenetic-depositional processes that took place in separate terrestrial-peritidal-shallow neritic zones. Such processes were linked to fluctuations in relative sea level with specific zones of diagenesis such as; 1) karst corrosion, 2) peritidal erosion, 3) subtidal seawater flushing and cementation, and 4) shallow subtidal deposition. Most surfaces are interpreted to have been the result of initial extensive shallow-water synsedimentary lithification that were, as sea level fell, altered by exposure and subaerial corrosion, only to be buried by sediments as sea level rose again. This succession was repeated several times resulting in a suite of recurring polyphase omission surfaces through many meters of stratigraphic section. Synsedimentary cloudy marine cements are well preserved and are thus interpreted to have been calcitic originally. Aragonite components are rare and thought to have to have been dissolved just below the Silurian seafloor. Large molluscs that survived such seafloor removal were nonetheless leached and the resultant megamoulds were filled with synsedimentary calcite cement. These Silurian inner neritic-strandline omission surfaces are temporally unique. They are part of a suite of marine omission surfaces that are mostly found in early Paleozoic neritic carbonate sedimentary rocks. These karsted hardgrounds formed during a calcite-sea time of elevated marine carbonate saturation and extensive marine cement precipitation. The contemporaneous greenhouse

Upper Paleozoic Marine Shale Characteristics and Exploration Prospects in the Northwestern Guizhong Depression, South China

NASA Astrophysics Data System (ADS)

Zhu, Zhenhong; Yao, Genshun; Lou, Zhanghua; Jin, Aimin; Zhu, Rong; Jin, Chong; Chen, Chao

2018-05-01

Multiple sets of organic-rich shales developed in the Upper Paleozoic of the northwestern Guizhong Depression in South China. However, the exploration of these shales is presently at a relatively immature stage. The Upper Paleozoic shales in the northwestern Guizhong Depression, including the Middle Devonian Luofu shale, the Nabiao shale, and the Lower Carboniferous Yanguan shale, were investigated in this study. Mineral composition analysis, organic matter analysis (including total organic carbon (TOC) content, maceral of kerogen and the vitrinite reflection (Ro)), pore characteristic analysis (including porosity and permeability, pore type identification by SEM, and pore size distribution by nitrogen sorption), methane isothermal sorption test were conducted, and the distribution and thickness of the shales were determined, Then the characteristics of the two target shales were illustrated and compared. The results show that the Upper Paleozoic shales have favorable organic matter conditions (mainly moderate to high TOC content, type I and II1 kerogen and high to over maturity), good fracability potential (brittleness index (BI) > 40%), multiple pore types, stable distribution and effective thickness, and good methane sorption capacity. Therefore, the Upper Paleozoic shales in the northern Guizhong Depression have good shale gas potential and exploration prospects. Moreover, the average TOC content, average BI, thickness of the organic-rich shale (TOC > 2.0 wt%) and the shale gas resources of the Middle Devonian shales are better than those of the Lower Carboniferous shale. The Middle Devonian shales have better shale gas potential and exploration prospects than the Lower Carboniferous shales.

Early cretaceous topographic growth of the Lhasaplano, Tibetan plateau: Constraints from the Damxung conglomerate

NASA Astrophysics Data System (ADS)

Wang, Jian-Gang; Hu, Xiumian; Garzanti, Eduardo; Ji, Wei-Qiang; Liu, Zhi-Chao; Liu, Xiao-Chi; Wu, Fu-Yuan

2017-07-01

Constraining the timing of early topographic growth on the Tibetan plateau is critical for any models of India-Asia collision, Himalayan orogeny and subsequent plateau development in the Cenozoic. Stratigraphic, sedimentological and provenance analysis of the Lower Cretaceous red-beds of the Damxung Conglomerate provide new key information to reconstruct the paleogeography and the tectonic evolution of the Lhasa terrane at the time. The over 700-m-thick Damxung Conglomerate documents distal alluvial fan to braidplain sedimentation passing upward to proximal alluvial fan sedimentation. Deposition began near sea level, as documented by limestone beds occurring at the base of the unit. Zircon U-Pb dating of interbedded tuff layers constrain deposition age at ca. 111 Ma. Abundance of volcanic clasts, Cretaceous U-Pb ages and Hf isotopes of detrital zircons yielding mainly negative ɛHf(t) values together with paleocurrent data indicate an active volcanic source located in the North Lhasa subterrane. Pre-Mesozoic-aged zircon, recycled quartz and (meta) sedimentary rock fragments increase up-section, indicating progressive erosional exhumation of the Paleozoic sedimentary/metasedimentary basement. The Damxung Conglomerate thus records a significant uplift and unroofing stage in the source region, implying initial topographic growth on the Lhasa terrane at early Albian time. Early Cretaceous topographic growth on the Lhasa terrane is supported by the stratigraphic record in the Linzhou basin, the Xigaze forearc basin and the southern Nima basin. In contrast, marine strata in the central-western Lhasa terrane lasted until the early Cenomanian (ca. 96 Ma), indicating diachronous marine regression on the Lhasa terrane from east to west.

Sedimentary and tectonic evolution of the southern Qiangtang basin: Implications for the Lhasa-Qiangtang collision timing

NASA Astrophysics Data System (ADS)

Ma, Anlin; Hu, Xiumian; Garzanti, Eduardo; Han, Zhong; Lai, Wen

2017-07-01

The Mesozoic stratigraphic record of the southern Qiangtang basin in central Tibet records the evolution and closure of the Bangong-Nujiang ocean to the south. The Jurassic succession includes Toarcian-Aalenian shallow-marine limestones (Quse Formation), Aalenian-Bajocian feldspatho-litho-quartzose to feldspatho-quartzo-lithic sandstones (shallow-marine Sewa Formation and deep-sea Gaaco Formation), and Bathonian outer platform to shoal limestones (Buqu Formation). This succession is truncated by an angular unconformity, overlain by upper Bathonian to lower Callovian fan-delta conglomerates and litho-quartzose to quartzo-lithic sandstones (Biluoco Formation) and Callovian shoal to outer platform limestones (Suowa Formation). Sandstone petrography coupled with detrital-zircon U-Pb and Hf isotope analysis indicate that the Sewa and Gaaco formations contain intermediate to felsic volcanic detritus and youngest detrital zircons (183-170 Ma) with ɛHf(t) ranging widely from +13 to -25, pointing to continental-arc provenance from igneous rocks with mixed mantle and continental-crust contributions. An arc-trench system thus developed toward the end of the Early Jurassic, with the southern Qiangtang basin representing the fore-arc basin. Above the angular unconformity, the Biluoco Formation documents a change to dominant sedimentary detritus including old detrital zircons (mainly >500 Ma ages in the lower part of the unit) with age spectra similar to those from Paleozoic strata in the central Qiangtang area. A major tectonic event with intense folding and thrusting thus took place in late Bathonian time (166 ± 1 Ma), when the Qiangtang block collided with another microcontinental block possibly the Lhasa block.

Phanerozoic tectonic evolution of the Circum-North Pacific

USGS Publications Warehouse

Nokleberg, Warren J.; Parfenov, Leonid M.; Monger, James W.H.; Norton, Ian O.; Khanchuk, Alexander I.; Stone, David B.; Scotese, Christopher R.; Scholl, David W.; Fujita, Kazuya

2000-01-01

The Phanerozoic tectonic evolution of the Circum-North Pacific is recorded mainly in the orogenic collages of the Circum-North Pacific mountain belts that separate the North Pacific from the eastern part of the North Asian Craton and the western part of the North American Craton. These collages consist of tectonostratigraphic terranes that are composed of fragments of igneous arcs, accretionary-wedge and subduction-zone complexes, passive continental margins, and cratons; they are overlapped by continental-margin-arc and sedimentary-basin assemblages. The geologic history of the terranes and overlap assemblages is highly complex because of postaccretionary dismemberment and translation during strike-slip faulting that occurred subparallel to continental margins.We analyze the complex tectonics of this region by the following steps. (1) We assign tectonic environments for the orogenic collages from regional compilation and synthesis of stratigraphic and faunal data. The types of tectonic environments include cratonal, passive continental margin, metamorphosed continental margin, continental-margin arc, island arc, oceanic crust, seamount, ophiolite, accretionary wedge, subduction zone, turbidite basin, and metamorphic. (2) We make correlations between terranes. (3) We group coeval terranes into a single tectonic origin, for example, a single island arc or subduction zone. (4) We group igneous-arc and subduction- zone terranes, which are interpreted as being tectonically linked, into coeval, curvilinear arc/subduction-zone complexes. (5) We interpret the original positions of terranes, using geologic, faunal, and paleomagnetic data. (6) We construct the paths of tectonic migration. Six processes overlapping in time were responsible for most of the complexities of the collage of terranes and overlap assemblages around the Circum-North Pacific, as follows. (1) During the Late Proterozoic, Late Devonian, and Early Carboniferous, major periods of rifting occurred along

Mesozoic and Cenozoic exhumation history of the SW Iberian Variscides inferred from low-temperature thermochronology

NASA Astrophysics Data System (ADS)

Vázquez-Vílchez, Mercedes; Jabaloy-Sánchez, Antonio; Azor, Antonio; Stuart, Finlay; Persano, Cristina; Alonso-Chaves, Francisco M.; Martín-Parra, Luis Miguel; Matas, Jerónimo; García-Navarro, Encarnación

2015-11-01

The post-Paleozoic tectonothermal evolution of the SW Iberian Variscides is poorly known mainly due to the scarce low-temperature geochronological data available. We have obtained new apatite fission-tracks and apatite (U-Th)/He ages to constrain the Mesozoic and Cenozoic tectonic evolution of this portion of the Iberian Massif located just north of the Betic-Rif Alpine orogen. We have obtained nine apatite fission-track ages on samples from Variscan and pre-Variscan granitoids. These ages range from 174.4 (± 10.8) to 54.1 (± 4.9) Ma, with mean track lengths between 10.3 and 13.9 μm. We have also performed 5 (U-Th)/He datings on some of the same samples, obtaining ages between 74.6 (± 1.6) and 18.5 (± 1.4) Ma. Time-temperature path modeling of these low-temperature geochronological data leads us to envisage four post-Paleozoic tectonically controlled exhumation episodes in the SW Iberian Variscides. Three of these episodes occurred in Mesozoic times (Middle Triassic to Early Jurassic, Early Cretaceous, and Late Cretaceous) at rates of ≈ 1.1 to 2.5 °C Ma- 1, separated by periods with almost no cooling. We relate these Mesozoic cooling events to the formation of important marginal reliefs during the rifting and opening of the central and northern Atlantic realm. The fourth exhumation episode occurred in Cenozoic times at rates of ≈ 3.2 to 3.6 °C Ma- 1, being only recorded in samples next to faults with topographic escarpments. These samples cooled below 80 °C at ≈ 20 Ma at rates of 3-13 °C Ma- 1 due to roughly N-S oriented compressional stresses affecting the whole Iberian plate, which, in the particular case of SW Iberia, reactivated some of the previous Late Paleozoic thrusts.

The Grand St Bernard-Briançonnais Nappe System and the Paleozoic Inheritance of the Western Alps Unraveled by Zircon U-Pb Dating

NASA Astrophysics Data System (ADS)

Bergomi, M. A.; Dal Piaz, G. V.; Malusà, M. G.; Monopoli, B.; Tunesi, A.

2017-12-01

The continental crust involved in the Alpine orogeny was largely shaped by Paleozoic tectono-metamorphic and igneous events during oblique collision between Gondwana and Laurussia. In order to shed light on the pre-Alpine basement puzzle disrupted and reamalgamated during the Tethyan rifting and the Alpine orogeny, we provide sensitive high-resolution ion microprobe U-Pb zircon and geochemical whole rock data from selected basement units of the Grand St Bernard-Briançonnais nappe system in the Western Alps and from the Penninic and Lower Austroalpine units in the Central Alps. Zircon U-Pb ages, ranging from 459.0 ± 2.3 Ma to 279.1 ± 1.1 Ma, provide evidence of a complex evolution along the northern margin of Gondwana including Ordovician transtension, Devonian subduction, and Carboniferous-to-Permian tectonic reorganization. Original zircon U-Pb ages of 371 ± 0.9 Ma and 369.3 ± 1.5 Ma, from calc-alkaline granitoids of the Grand Nomenon and Gneiss del Monte Canale units, provide the first compelling evidence of Late Devonian orogenic magmatism in the Alps. We propose that rocks belonging to these units were originally part of the Moldanubian domain and were displaced toward the SW by Late Carboniferous strike-slip faulting. The resulting assemblage of basement units was disrupted by Permian tectonics and by Mesozoic opening of the Alpine Tethys. Remnants of the Moldanubian domain became either part of the European paleomargin (Grand Nomenon unit) or part of the Adriatic paleomargin (Gneiss del Monte Canale unit), to be finally accreted into the Alpine orogenic wedge during the Cenozoic.

Synthesis of late Paleozoic and Mesozoic eolian deposits of the Western Interior of the United States

USGS Publications Warehouse

Blakey, R.C.; Peterson, F.; Kocurek, G.

1988-01-01

include the Jurassic part of the Wingate Sandstone and the Navajo-Aztec-Nugget complex and coeval deposits in the arc terrain to the south and west of the Colorado Plateau. Major Middle Jurassic deposits include the Page Sandstone on the Colorado Plateau and the widespread Entrada Sandstone, Sundance Formation, and coeval deposits. Less extensive eolian deposits occur in the Carmel Formation, Temple Cap Sandstone, Romana Sandstone and Moab Tongue of the Entrada Sandstone, mostly on the central and western Colorado Plateau. Upper Jurassic eolian deposits include the Bluff Sandstone Member and Recapture Member of the Morrison Formation and Junction Creek Sandstone, all of the Four Corners region, and smaller eolian deposits in the Morrison Formation of central Wyoming and apparently coeval Unkpapa Sandstone of the Black Hills. Late Paleozoic and Mesozoic eolian deposits responded to changing climatic, tectonic and eustatic controls that are documented elsewhere in this volume. All of the eolian deposits are intricately interbedded with non-eolian deposits, including units of fluvial, lacustrine and shallow-marine origin, clearly dispelling the myth that eolian sandstones are simple sheet-like bodies. Rather, these units form some of the most complex bodies in the stratigraphic record. ?? 1988.

Mid-Cenozoic tectonic and paleoenvironmental setting of the central Arctic Ocean

USGS Publications Warehouse

O'Regan, M.; Moran, K.; Backman, J.; Jakobsson, M.; Sangiorgi, F.; Brinkhuis, Henk; Pockalny, Rob; Skelton, Alasdair; Stickley, Catherine E.; Koc, N.; Brumsack, Hans-Juergen; Willard, Debra A.

2008-01-01

Drilling results from the Integrated Ocean Drilling Program's Arctic Coring Expedition (ACEX) to the Lomonosov Ridge (LR) document a 26 million year hiatus that separates freshwater-influenced biosilica-rich deposits of the middle Eocene from fossil-poor glaciomarine silty clays of the early Miocene. Detailed micropaleontological and sedimentological data from sediments surrounding this mid-Cenozoic hiatus describe a shallow water setting for the LR, a finding that conflicts with predrilling seismic predictions and an initial postcruise assessment of its subsidence history that assumed smooth thermally controlled subsidence following rifting. A review of Cenozoic tectonic processes affecting the geodynamic evolution of the central Arctic Ocean highlights a prolonged phase of basin-wide compression that ended in the early Miocene. The coincidence in timing between the end of compression and the start of rapid early Miocene subsidence provides a compelling link between these observations and similarly accounts for the shallow water setting that persisted more than 30 million years after rifting ended. However, for much of the late Paleogene and early Neogene, tectonic reconstructions of the Arctic Ocean describe a landlocked basin, adding additional uncertainty to reconstructions of paleodepth estimates as the magnitude of regional sea level variations remains unknown.

Improving global paleogeography since the late Paleozoic using paleobiology

NASA Astrophysics Data System (ADS)

Cao, Wenchao; Zahirovic, Sabin; Flament, Nicolas; Williams, Simon; Golonka, Jan; Dietmar Müller, R.

2017-12-01

Paleogeographic reconstructions are important to understand Earth's tectonic evolution, past eustatic and regional sea level change, paleoclimate and ocean circulation, deep Earth resources and to constrain and interpret the dynamic topography predicted by mantle convection models. Global paleogeographic maps have been compiled and published, but they are generally presented as static maps with varying map projections, different time intervals represented by the maps and different plate motion models that underlie the paleogeographic reconstructions. This makes it difficult to convert the maps into a digital form and link them to alternative digital plate tectonic reconstructions. To address this limitation, we develop a workflow to restore global paleogeographic maps to their present-day coordinates and enable them to be linked to a different tectonic reconstruction. We use marine fossil collections from the Paleobiology Database to identify inconsistencies between their indicative paleoenvironments and published paleogeographic maps, and revise the locations of inferred paleo-coastlines that represent the estimated maximum transgression surfaces by resolving these inconsistencies. As a result, the consistency ratio between the paleogeography and the paleoenvironments indicated by the marine fossil collections is increased from an average of 75 % to nearly full consistency (100 %). The paleogeography in the main regions of North America, South America, Europe and Africa is significantly revised, especially in the Late Carboniferous, Middle Permian, Triassic, Jurassic, Late Cretaceous and most of the Cenozoic. The global flooded continental areas since the Early Devonian calculated from the revised paleogeography in this study are generally consistent with results derived from other paleoenvironment and paleo-lithofacies data and with the strontium isotope record in marine carbonates. We also estimate the terrestrial areal change over time associated with

Continental tectonics in the aftermath of plate tectonics

NASA Technical Reports Server (NTRS)

Molnar, Peter

1988-01-01

It is shown that the basic tenet of plate tectonics, rigid-body movements of large plates of lithosphere, fails to apply to continental interiors. There, buoyant continental crust can detach from the underlying mantle to form mountain ranges and broad zones of diffuse tectonic activity. The role of crustal blocks and of the detachment of crustal fragments in this process is discussed. Future areas of investigation are addressed.

Geologic map of Mészáros revisited: Pioneering tectonic mapping of the Transdanubian Range in the early 1980s

NASA Astrophysics Data System (ADS)

Zámolyi, A.; Horváth, F.; Kovács, G.; Timár, G.; Székely, B.

2009-04-01

Rocks, even in tectonically active areas are very solid compared to the changes within the scientific theories that occured especially in Eastern Europe as the political landscape changed and the separation into socialist and capitalist countries started to fade. While in Western Europe, Wegener's mobilistic approach gained widespread acceptance in the 1960-ies, in the countries of Eastern Europe (partly due to political reasons) fixistic ideas were supported. Despite the fact that most important early concepts in Hungarian tectonics were born about a century ago as a results of exploration of the Lake Balaton and its surroundings conducted by Lajos Lóczy, initiatives to integrate various geodynamic observations were rare exceptions in the second half of the 20th century. The high priority of economic geologic prospection in order to find raw materials resulted in an enormous amount of observations. In the central Transdanubian Range (TR), hosting bauxite, coal and manganese deposits, extensive surveying was carried out according to fixistic tectonic concepts. Although the recognition of faults was of vital importance in mining, mapped faults were rarely integrated into a global geodynamic model. A pioneering approach was presented by Mészáros (1983), who compiled a 1: 100 000 scale structural and economic-geologic map of large parts of TR. The map focuses on the Bakony hills that are of key importance for the geodynamic understanding of the formation of PB. TR forms inselbergs with well preserved outcrops, which is rare in PB, thus allowing for direct measurements of fault striations and fault plane orientations. Prinz (1926) maintained the theory that the TR is a rigid block and named it Tisia block. An alternative to this approach was the monograph of Uhlig (1907) proposing mobilistic concepts. Csontos et al (1991) reviewed the evolution of neogene stress-fields in the Carpatho-Pannonian region observing microtectonic faults in TR. The authors conclude that

Structural evolution of the Irtysh Shear Zone: implication for the Late Paleozoic amalgamation of multiple arc systems in Central Asia

NASA Astrophysics Data System (ADS)

Li, Pengfei; Sun, Min; Rosenbaum, Gideon

2015-04-01

The NW-SE Irtysh Shear Zone represents a major tectonic boundary in the Central Asian Orogenic Belt, recording the amalgamation history between the peri-Siberian orogenic system and the Kazakhstan orogenic system. The structural evolution and geodynamics of this shear zone is still poorly documented. Here we present new structural data complemented by chronological data in an attempt to unravel the geodynamic significance of the Irtysh Shear Zone in the context of accretion history of the Central Asian Orogenic Belt. Our results show three episodes of deformation for the shear zone. D1 foliation is locally recognized in low strain area and recorded by garnet inclusions, whereas D2 is represented by a sub-horizontal fabric and related NW-SE lineation. D3 is characterized by a transpersonal deformation event, to form a series of NW-SE mylonitic belts with sinistral kinematics, and to overprint D2 fabric forming regional-scale NW-SE upright folds. A paragneiss sample from the shear zone yielded the youngest detrital zircon peaks in the late Carboniferous, placing a maximum age constraint on the deformation, which overlaps in time with the late Paleozoic collision between the Chinese Altai and the intraoceanic arc system of the East Junggar and West Junggar. We interpret three episodes of deformation to represent orogenic thickening (D1), collapse (D2) and thickening (D3) in response to this collisional event. Sinistral shearing (D3) together with the coeval dextral shearing in the Tianshan accommodate eastward extrusion of the Kazakhstan orogenic system during the late Paleozoic amalgamation of the Central Asian Orogenic Belt. Acknowledgements: This study was financially supported by the Major Basic Research Project of the Ministry of Science and Technology of China (Grant: 2014CB440801), Hong Kong Research Grant Council (HKU705311P and HKU704712P), National Science Foundation of China (41273048, 41273012) and a HKU CRCG grant. The work is a contribution of the Joint

Assessment of Paleozoic shale gas resources in the Sichuan Basin of China, 2015

USGS Publications Warehouse

Potter, Christopher J.; Schenk, Christopher J.; Charpentier, Ronald R.; Gaswirth, Stephanie B.; Klett, Timothy R.; Leathers, Heidi M.; Brownfield, Michael E.; Mercier, Tracey J.; Tennyson, Marilyn E.; Pitman, Janet K.

2015-10-14

Using a geology-based assessment methodology, the U.S. Geological Survey estimated a mean of 23.9 trillion cubic feet of technically recoverable shale gas resources in Paleozoic formations in the Sichuan Basin of China.

Plate tectonics drive tropical reef biodiversity dynamics.

PubMed

Leprieur, Fabien; Descombes, Patrice; Gaboriau, Théo; Cowman, Peter F; Parravicini, Valeriano; Kulbicki, Michel; Melián, Carlos J; de Santana, Charles N; Heine, Christian; Mouillot, David; Bellwood, David R; Pellissier, Loïc

2016-05-06

The Cretaceous breakup of Gondwana strongly modified the global distribution of shallow tropical seas reshaping the geographic configuration of marine basins. However, the links between tropical reef availability, plate tectonic processes and marine biodiversity distribution patterns are still unknown. Here, we show that a spatial diversification model constrained by absolute plate motions for the past 140 million years predicts the emergence and movement of diversity hotspots on tropical reefs. The spatial dynamics of tropical reefs explains marine fauna diversification in the Tethyan Ocean during the Cretaceous and early Cenozoic, and identifies an eastward movement of ancestral marine lineages towards the Indo-Australian Archipelago in the Miocene. A mechanistic model based only on habitat-driven diversification and dispersal yields realistic predictions of current biodiversity patterns for both corals and fishes. As in terrestrial systems, we demonstrate that plate tectonics played a major role in driving tropical marine shallow reef biodiversity dynamics.

The influence of mantle refertilisation on the formation of TTGs in a plume-lid tectonics setting

NASA Astrophysics Data System (ADS)

Fischer, R.; Gerya, T.

2017-12-01

Higher amounts of radiogenic elements and leftover primordial heat in the early Earth both contribute to the increased temperature in the Earth's interior and it is mainly this increased mantle potential temperature that controls the dynamics of the crust and upper mantle and the predominant style of tectonics in the Early Earth. The increased upper mantle temperature precludes the modern plate tectonics regime and stabilizes another type of global tectonics often called plume-lid tectonics (Fischer and Gerya, 2016) or 'plutonic squishy lid' tectonics(Rozel et al., 2017). Plume-lid tectonics is dominated by intrusive mantle-derived magmatism which results in a thickening of the overlaying crust. The overthickened basaltic crust is transformed into eclogite and episodically recycled back into the mantle. Melt extraction from hydrated partially molten basaltic crust leads to the production of primordial tonalite-trondhjemite-granodiorite (TTG) continental crust. TTGs make up over half of the Archean crust and can be classied into low-, medium- and high-pressure types (Moyen, 2011). Field studies show that the three different types (low-, medium- and high-pressure) appear in a ratio of 20%, 60% and 20% (Moyen, 2011). Numerical models of plume-lid tectonics generally agree very well with these values (Rozel et al., 2017) but also show that the ratio between the three different TTG types varies greatly during the two phases of the plume-lid tectonics cycle: growth phase and overturn phase. Melt productivity of the mantle decreases rapidly after removal of the garnet and clinopyroxene components. Addition of new garnet and clinopyroxene-rich material into the harzburgitic residue should lead to a refertilised lherzolite which could potentially yield new melt (Bédard, 2006). Mixing of eclogite drips back into the mantle can lead to the geochemical refertilisation of already depleted mantle and allow for further extraction of melt (Bédard, 2006). We will explore this

Exotic island arc Paleozoic terranes on the eastern margin of Gondwana: Geochemical whole rock and zircon U-Pb-Hf isotope evidence from Barry Station, New South Wales, Australia

NASA Astrophysics Data System (ADS)

Manton, Ryan J.; Buckman, Solomon; Nutman, Allen P.; Bennett, Vickie C.

2017-08-01

Early Paleozoic intra-oceanic terranes crop out along the Peel-Manning Fault System, in the southern New England Orogen, NSW Australia. These are the Cambrian ophiolitic Weraerai terrane and the Siluro-Devonian island arc Gamilaroi terrane. There has been debate whether these terranes formed at the Gondwana margin or if they are intra-oceanic, and were accreted to Gondwana later in the Paleozoic. Major-trace-REE elemental data indicate Weraerai terrane formed in a supra-subduction environment. Rare zircons extracted from Weraerai terrane gabbro-plagiogranite suites at Barry Station yield a U-Pb zircon date of 504.9 ± 3.5 Ma with initial εHf values of + 11.1 indicating a juvenile source. Amphibole-bearing felsic dykes and net-vein complexes are also found within the gabbro with a U-Pb zircon date of 503.2 ± 5.7 Ma and initial εHf values of + 11.6. These are coeval in age with their host rocks and we propose they represent partial melts of the mafic crust during the circulation of seawater. The Gamilaroi trondhjemites of prehnite-pumpellyite-greenschist metamorphic grade terrane yielded very few zircons with an age of 413 ± 8.7 Ma. Zircon initial εHf values range from + 5.0 to + 2.9, indicating an input from an evolved crustal source, unlike the purely oceanic Weraerai terrane. Gamilaroi terrane trondhjemites are enriched in LREE have low K2O and K2O/Na2O ratios and strong negative Nb anomalies consistent with supra-subduction zone environments. Multiple subduction zones may well have existed within the Panthalassa Ocean during the early-mid Paleozoic with the Weraerai-Gamilaroi being accreted onto the Gondwanan margin during the latest Devonian.

The rise and fall of late Paleozoic trilobites of the United States

USGS Publications Warehouse

Brezinski, D.K.

1999-01-01

Based on range data and generic composition, four stages of evolution are recognized for late Paleozoic trilobites of the contiguous United States. Stage 1 occurs in the Lower Mississippian (Kinderhookian-Osagean) and is characterized by a generically diverse association of short-ranging, stenotopic species that are strongly provincial. Stage 2 species are present in the Upper Mississippian and consist of a single, eurytopic, pandemic genus, Paladin. Species of Stage 2 are much longer-ranging than those of Stage 1, and some species may have persisted for as long as 12 m.y. Stage 3 is present within Pennsylvanian and Lower Permian strata and consists initially of the eurytopic, endemic genera Sevillia and Ameura as well as the pandemic genus Ditomopyge. During the middle Pennsylvanian the very long-ranging species Ameura missouriensis and Ditomopyge scitula survived for more than 20 m.y. During the late Pennsylvanian and early Permian, a number of pandemic genera appear to have immigrated into what is now North America. Stage 4 is restricted to the Upper Permian (late Leonardian-Guadalupian) strata and is characterized by short-ranging, stenotopic, provincial genera. The main causal factor controlling the four-stage evolution of late Paleozoic trilobites of the United States is interpreted to be eustacy. Whereas Stage 1 represents an adaptive radiation developed during the Lower Mississippian inundation of North America by the Kaskaskia Sequence, Stage 2 is present in strata deposited during the regression of the Kaskaskia sea. Stage 3 was formed during the transgression and stillstand of the Absaroka Sequence and, although initially endemic, Stage 3 faunas are strongly pandemic in the end when oceanic circulation patterns were at a maximum. A mid-Leonardian sea-level drop caused the extinction of Stage 3 fauna. Sea-level rise near the end of the Leonardian and into the Guadalupian created an adaptive radiation of stentopic species of Stage 4 that quickly became

Tectonic Mechanism for the Mid-Cretaceous - Early Paleogene Intraplate Magmatism from the Gulf of Mexico to Northwestern Canada

NASA Astrophysics Data System (ADS)

Liu, Y.; Murphy, M. A.; Snow, J. E.; van Wijk, J.; Cannon, J. M.; Parsons, C.

2017-12-01

Tectonic mechanisms have remained controversial for a number of intraplate igneous suites of mid-Cretaceous - early Paleogene age across North America. They span the northern Gulf of Mexico (GoM), through Arkansas and Kansas in the US, to Saskatchewan and Northwestern Territories in Canada, resembling a belt that is located 1000+ km inboard from, and aligned sub-parallel to, the western margin of North America. The northern GoM magmatism is characterized by lamproites, carbonatites, nephelinites, with other alkaline rocks, whereas the rest igneous provinces are dominated by kimberlites. Their geochemical signatures, in general, point to a sub-lithospheric mantle origin. Hypotheses that explain the tectonic origin of these magmatic rocks include: (1) hotspots and mantle plumes, (2) edge-driven convection, (3) lithospheric reactivation, and (4) low-angle subduction. Evaluation based on our integration of published geological and geophysical data shows that contradictions exist in each model between observations and predictions. To explain this plate-scale phenomenon, we propose that the Farallon slab may have stagnated within or around the mantle transition zone during the Early Cretaceous, with its leading edge reaching ca. 1600 km inland beneath the North American plate. Dehydration and decarbonation of the slab produces sporadic, dense, low-degree partial melts at the mantle transition zone depths. As the slab descends into the lower mantle, Rayleigh-Taylor instabilities are induced at slab edges, causing passive upwelling that brings alkali-rich carbonate silicate melts to the base of the overriding plate. Subsequently, the North American lithosphere with varying thicknesses, discontinuities, and compositions interacts with the rising partial melts, generating a spectrum of igneous rocks. Fragments of the once-stagnated slab may still be detectable in the lower mantle beneath eastern US in seismic tomography models. This study highlights a profound plate

Emergence of silicic continents as the lower crust peels off on a hot plate-tectonic Earth

NASA Astrophysics Data System (ADS)

Chowdhury, Priyadarshi; Gerya, Taras; Chakraborty, Sumit

2017-09-01

The rock record and geochemical evidence indicate that continental recycling has been occurring since the early history of the Earth. The stabilization of felsic continents in place of Earth's early mafic crust about 3.0 to 2.0 billion years ago, perhaps due to the initiation of plate tectonics, implies widespread destruction of mafic crust during this time interval. However, the physical mechanisms of such intense recycling on a hotter, (late) Archaean and presumably plate-tectonic Earth remain largely unknown. Here we use thermomechanical modelling to show that extensive recycling via lower crustal peeling-off (delamination but not eclogitic dripping) during continent-continent convergence was near ubiquitous during the late Archaean to early Proterozoic. We propose that such destruction of the early mafic crust, together with felsic magmatism, may have caused both the emergence of silicic continents and their subsequent isostatic rise, possibly above the sea level. Such changes in the continental character have been proposed to influence the Great Oxidation Event and, therefore, peeling-off plate tectonics could be the geodynamic trigger for this event. A transition to the slab break-off controlled syn-orogenic recycling occurred as the Earth aged and cooled, leading to reduced recycling and enhanced preservation of the continental crust of present-day composition.

Triassic metasediments in the internal Dinarides (Kopaonik area, southern Serbia): stratigraphy, paleogeographic and tectonic significance

NASA Astrophysics Data System (ADS)

Schefer, Senecio; Egli, Daniel; Missoni, Sigrid; Bernoulli, Daniel; Fügenschuh, Bernhard; Gawlick, Hans-Jürgen; Jovanović, Divna; Krystyn, Leopold; Lein, Richard; Schmid, Stefan M.; Sudar, Milan N.

2010-04-01

Strongly deformed and metamorphosed sediments in the Studenica Valley and Kopaonik area in southern Serbia expose the easternmost occurrences of Triassic sediments in the Dinarides. In these areas, Upper Paleozoic terrigenous sediments are overlain by Lower Triassic siliciclastics and limestones and by Anisian shallow-water carbonates. A pronounced facies change to hemipelagic and distal turbiditic, cherty metalimestones (Kopaonik Formation) testifies a Late Anisian drowning of the former shallow-water carbonate shelf. Sedimentation of the Kopaonik Formation was contemporaneous with shallow-water carbonate production on nearby carbonate platforms that were the source areas of diluted turbidity currents reaching the depositional area of this formation. The Kopaonik Formation was dated by conodont faunas as Late Anisian to Norian and possibly extends into the Early Jurassic. It is therefore considered an equivalent of the grey Hallstatt facies of the Eastern Alps, the Western Carpathians, and the Albanides-Hellenides. The coeval carbonate platforms were generally situated in more proximal areas of the Adriatic margin, whereas the distal margin was dominated by hemipelagic/pelagic and distal turbiditic sedimentation, facing the evolving Neotethys Ocean to the east. A similar arrangement of Triassic facies belts can be recognized all along the evolving Meliata-Maliac-Vardar branch of Neotethys, which is in line with a ‘one-ocean-hypothesis’ for the Dinarides: all the ophiolites presently located southwest of the Drina-Ivanjica and Kopaonik thrust sheets are derived from an area to the east, and the Drina-Ivanjica and Kopaonik units emerge in tectonic windows from below this ophiolite nappe. On the base of the Triassic facies distribution we see neither argument for an independent Dinaridic Ocean nor evidence for isolated terranes or blocks.

Provenance analysis on detrital zircons from the back-arc Arivechi basin: Implications for the Upper Cretaceous tectonic evolution of northern Sonora and southern Arizona

NASA Astrophysics Data System (ADS)

Rodríguez-Castañeda, José Luis; Ortega-Rivera, Amabel; Roldán-Quintana, Jaime; Espinoza-Maldonado, Inocente Guadalupe

2018-07-01

In the Arivechi region of eastern Sonora, northwestern Mexico, mountainous exposures of Upper Cretaceous rocks that contain monoliths within coarse sedimentary debris are enigmatic, in a province of largely Late Cretaceous continental-margin arc rocks. The rocks sequence in the study area are grouped in two Upper Cretaceous units: the lower Cañada de Tarachi and the younger El Potrero Grande. Detrital zircons collected from three samples of the Cañada de Tarachi and El Potrero Grande units have been analyzed for U-Pb ages to constrain their provenance. These ages constrain the age of the exposed rocks and provide new insights into the geological evolution of eastern Sonora Cretaceous rocks. The detrital zircon age populations determined for the Cañada de Tarachi and El Potrero Grande units contain distinctive Precambrian, Paleozoic, and Mesozoic zircon ages that provide probable source areas which are discussed in detail constraining the tectonic evolution of the region. Comparison of these knew ages with published data suggests that the source terranes, that supplied zircons to the Arivechi basin, correlate with Proterozoic, Paleozoic and Mesozoic domains in southern California and Baja California, northern Sonora, southern Arizona and eastern Chihuahua. The provenance variation is vital to constrain the source of the Cretaceous rocks in eastern Sonora and support a better understanding of the Permo-Triassic Cordilleran Magmatic Arc in the southwestern North America.

Early Cretaceous stratigraphy, paleontology, and sedimentary tectonics in Paris overthrust foredeep (western Wyoming and southeastern Idaho) compared with Quaternary features of indo-gangetic plain

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

Dorr, J.A. Jr.

1983-08-01

Fluviatile clastics of the nonmarine, early Cretaceous Gannett and Wayan groups were deposited on wet alluvial megafans and on intervening interfan piedmont slopes which declined eastward into more poorly drained lowlands from a western highland source area uplifted episodically by movements of the Paris overthrust. Lacustrine episodes of deposition intercalated Peterson and Draney limestones with Gannett fluvial clastics. Westward marine transgressions (Skull Creek, Mowry) intercalated mixed lacustrine and brackish facies (Smiths and Cokedale formations) into Wayan fluviatile clastics. Newly discovered fossil vertebrate and invertebrate materials (all fragmentary but identifiable) include: Gannett Group - large reptiles including turtles; Thomas Fork Formationmore » - freshwater gastropods and unionid pelecypods, gastroliths, two types of turtles, large reptilian fragments (dinosaur), and abundant dinosaur eggshell fragments; Wayan Formation - perennially aquatic snails, turtles, unidentifiable large reptiles, two types of crocodilians, an iguanodontid dinosaur (Tenontosaurus), an ankylosaurian dinosaur, a large ornithopod dinosaur, gastroliths, abundant and ubiquitous dinosaur eggshell fragments (numerous types and sizes), and miscellaneous unidentifiable small vertebrate bone fragments. A census of analogous modern reptile reproductive behaviors supports the conclusion that the Wayan, and probably also the Gannett, alluvial fan environments were used as upland breeding grounds by dinosaurs and perhaps other reptiles. Comparison of these Early Cretaceous data with observations on the tectonic setting, sedimentology, and biology of the Quaternary indo-gangetic plain suggests many close analogies between the two sedimentary tectonic settings.« less

A problematic early tetrapod from the Mississippian of Nevada

USGS Publications Warehouse

Thomson, K.S.; Shubin, N.S.; Poole, F.G.

1998-01-01

We report here the discovery of a new taxon of Paleozoic tetrapod from the Late Mississippian of Nevada (330-340 Ma). It has a unique vertebral column with principal centra having vertical anterior and posterior faces, ventrally incomplete accessory centra located antero-dorsally in each centrum, and enlarged presacral/sacral vertebrae. The head and pectoral girdle were not preserved but the large femur, robust pelvic girdle and enlarged sacral vertebrae possibly indicate a terrestrial mode of life. This new form significantly extends the western geographic range of known Mississippian tetrapods. It presents a mosaic of primitive and derived features, indicating that continued revision of traditional accounts of vertebral homology and the early diversifications of Paleozoic tetrapods will be necessary.

Late-Paleozoic-Mesozoic deformational and deformation related metamorphic structures of Kuznetsk-Altai region

NASA Astrophysics Data System (ADS)

Zinoviev, Sergei

2014-05-01

Kuznetsk-Altai region is a part of the Central Asian Orogenic Belt. The nature and formation mechanisms of the observed structure of Kuznetsk-Altai region are interpreted by the author as the consequence of convergence of Tuva-Mongolian and Junggar lithospheric block structures and energy of collision interaction between the blocks of crust in Late-Paleozoic-Mesozoic period. Tectonic zoning of Kuznetsk-Altai region is based on the principle of adequate description of geological medium (without methods of 'primary' state recovery). The initial indication of this convergence is the crust thickening in the zone of collision. On the surface the mechanisms of lateral compression form a regional elevation; with this elevation growth the 'mountain roots' start growing. With an approach of blocks an interblock elevation is divided into various fragments, and these fragments interact in the manner of collision. The physical expression of collision mechanisms are periodic pulses of seismic activity. The main tectonic consequence of the block convergence and collision of interblock units is formation of an ensemble of regional structures of the deformation type on the basis of previous 'pre-collision' geological substratum [Chikov et al., 2012]. This ensemble includes: 1) allochthonous and autochthonous blocks of weakly deformed substratum; 2) folded (folded-thrust) systems; 3) dynamic metamorphism zones of regional shears and main faults. Characteristic of the main structures includes: the position of sedimentary, magmatic and PT-metamorphic rocks, the degree of rock dynamometamorphism and variety rock body deformation, as well as the styles and concentrations of mechanic deformations. 1) block terranes have weakly elongated or isometric shape in plane, and they are the systems of block structures of pre-collision substratum separated by the younger zones of interblock deformations. They stand out among the main deformation systems, and the smallest are included into the

Studies in geophysics: Active tectonics

NASA Technical Reports Server (NTRS)

1986-01-01

Active tectonics is defined within the study as tectonic movements that are expected to occur within a future time span of concern to society. Such movements and their associated hazards include earthquakes, volcanic eruptions, and land subsidence and emergence. The entire range of geology, geophysics, and geodesy is, to some extent, pertinent to this topic. The needs for useful forecasts of tectonic activity, so that actions may be taken to mitigate hazards, call for special attention to ongoing tectonic activity. Further progress in understanding active tectonics depends on continued research. Particularly important is improvement in the accuracy of dating techniques for recent geologic materials.

Ages of the Xinghuadukou Group in the Erguna Block, NE China

NASA Astrophysics Data System (ADS)

Liu, X.; Hou, W.

2016-12-01

The Xinghuadukou group is outcropped in the Erguna block (EB) of NE China, which is an important component of the eastern segment of the Central Asian Orogenic Belt (CAOB). This group was previously classified as Paleoproterozoic in age. However, recent studies reported Paleozoic ages from the meta-volcanic rocks, Paleoproterozoic to Neoarchean detrital zircon ages from the meta-sedimentary rocks and Neoproterozoic ages from the granitoids. The tectonic affinity of the EB is still debated. In order to clarify the aforementioned issues, 19 samples were collected from the Xinghuadukou group from the Mohe region in NE China. All samples underwent gneiss facies metamorphism, including two-mica granitic gneiss and quartz biotite gneiss. Based on the protolith discrimination diagram of Si—(al+fm)-(c+alk) system, 7 samples originated from sedimentary rocks and the other 12 of igneous origin. The orthogneiss samples were plotted as diorite, granodiorite and granite respectively in TAS, showing felsic character (SiO2 57% - 74%). One orthogneiss and one paragneiss samples were chosen to conduct the LA-ICP-MS U-Pb zircon age analysis. Apart from one zircon with the age of 742 Ma shows evident metamorphic rim, all zircons from the orthogneiss show euhedral to subhedral prismatic shape and typical concentric or oscillatory structure indicating the igneous origin. The concordant age of 2478±26 Ma was generated, indicating the existence of the near Archean basement of the EB. The detrital zircons from the paragneiss produced age populations cluster at 0.6, 0.8, 1.9, 2.6 and 2.7 Ga, lacking of the Grenville event age. The youngest zircon age is 395 Ma, taken as the maximum depositional age of the sedimentary protolith. According to the new data obtained, it is suggested that the Xinghuadukou group comprises the early Paleoproterozoic granite-gneiss, which proves the granitic basement of the Erguna block. The sedimentary rocks formed overlying the basement during the early

Plate Tectonics on Earth-like Planets: Implications for Habitability

NASA Astrophysics Data System (ADS)

Noack, L.; Breuer, D.

2011-12-01

tectonics regime. References [1] Parnell, J. (2004): Plate tectonics, surface mineralogy, and the early evolution of life. Int. J. Astrobio. 3(2): 131-137. [2] Rosing, M.T.; D.K. Bird, N.H. Sleep, W. Glassley, and F. Albar (2006): The rise of continents - An essay on the geologic consequences of photosynthesis. Palaeogeography, Palaeoclimatology, Palaeoecology 232 (2006) 99-11. [3] Stamenkovic, V.; D. Breuer and T. Spohn (2011): Thermal and transport properties of mantle rock at high pressure: Applications to super-Earths. Submitted to Icarus. [4] Valencia, D., R.J. O'Connell and D.D. Sasselov (2007): Inevitability of plate tectonics on super-Earths. Astrophys. J. Let. 670(1): 45-48. [5] O'Neill, C. and A. Lenardic (2007). Geological consequences of super-sized Earths. GRL 34: 1-41.

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

NASA Astrophysics Data System (ADS)

Tosdal, Richard M.

1990-11-01

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

Tectonic Plates of China

DTIC Science & Technology

1977-04-01

C. Sun and Ta-iang Teng Contractor: University of Southern California Principal Investigator: Professor Ta-liang Teng (213) 746-6124 Contract Number...83 i" I. INTRODUCTION Over the vast Chinese mainland, one of the most interesting and dynamic regions of the world, complex tectonics, coupled with...west Pacific and the Alpine- Himalaya tectonic belts, the multitude of Chinese tectonic com- plexities is evident from its enormous topographic relief

Plate tectonics drive tropical reef biodiversity dynamics

PubMed Central

Leprieur, Fabien; Descombes, Patrice; Gaboriau, Théo; Cowman, Peter F.; Parravicini, Valeriano; Kulbicki, Michel; Melián, Carlos J.; de Santana, Charles N.; Heine, Christian; Mouillot, David; Bellwood, David R.; Pellissier, Loïc

2016-01-01

The Cretaceous breakup of Gondwana strongly modified the global distribution of shallow tropical seas reshaping the geographic configuration of marine basins. However, the links between tropical reef availability, plate tectonic processes and marine biodiversity distribution patterns are still unknown. Here, we show that a spatial diversification model constrained by absolute plate motions for the past 140 million years predicts the emergence and movement of diversity hotspots on tropical reefs. The spatial dynamics of tropical reefs explains marine fauna diversification in the Tethyan Ocean during the Cretaceous and early Cenozoic, and identifies an eastward movement of ancestral marine lineages towards the Indo-Australian Archipelago in the Miocene. A mechanistic model based only on habitat-driven diversification and dispersal yields realistic predictions of current biodiversity patterns for both corals and fishes. As in terrestrial systems, we demonstrate that plate tectonics played a major role in driving tropical marine shallow reef biodiversity dynamics. PMID:27151103

Tectonics of Europa

NASA Astrophysics Data System (ADS)

Kattenhorn, S. A.; Hurford, T. A.

2007-12-01

This review of Europan tectonics previews a chapter of the forthcoming text "Europa". After the Voyager flyby of the icy moon Europa in 1979, models were developed that attributed pervasive surface fracturing to the effects of tidal forcing due to the gravitational pull of Jupiter. The late 1990s Galileo mission returned high resolution coverage of the surface, allowing a diverse range of tectonic features to be identified. Subsequent description, interpretation, and modeling of these features has resulted in significant developments in five key themes: (1) What drives the tectonics? (2) What are the formation mechanisms of the various types of tectonic features? (3) What are the implications for a subsurface ocean? (4) What is the nature and thickness of the ice shell? (5) Is Europa currently tectonically active? We highlight key developments pertaining to these fundamental issues, focusing on the following elements: (1) Many fracture patterns can be correlated with theoretical stress fields induced by diurnal tidal forcing and long-term effects of nonsynchronous rotation of the ice shell; however, these driving mechanisms alone cannot explain all fracturing. The tectonic fabric has likely been affected by additional contributing effects: tidal despinning, orbital evolution, interior differentiation, polar wander, finite obliquity, stresses due to shell thickening, endogenic forcing by convection and diapirism, and secondary effects driven by strike-slip faulting and plate flexure. (2) Due to the prevalence of global tension, a low lithostatic gradient, and the inherent weakness of ice, tectonic features likely have predominantly extensional primary formation mechanisms (e.g. surface fractures, ridges, and normal faults). There has been no categorical documentation of fracture development by compressive shearing. Even so, the constantly changing nature of the tidal stress field results in shearing reactivation of cracks being important for the morphologic and

Archean inheritance in zircon from late Paleozoic granites from the Avalon zone of southeastern New England: an African connection

USGS Publications Warehouse

Zartman, R.E.; Don, Hermes O.

1987-01-01

In southeastern New England the Narragansett Pier Granite locally intrudes Carboniferous metasedimentary rocks of the Narragansett basin, and yields a monazite UPb Permian emplacement age of 273 ?? 2 Ma. Zircon from the Narragansett Pier Granite contains a minor but detectable amount of an older, inherited component, and shows modern loss of lead. Zircon from the late-stage, aplitic Westerly Granite exhibits a more pronounced lead inheritance -permitting the inherited component to be identified as Late Archean. Such old relict zircon has not been previously recognized in Proterozoic to Paleozoic igneous rocks in New England, and may be restricted to late Paleozoic rocks of the Avalon zone. We suggest that the Archean crustal component reflects an African connection, in which old Archean crust was underplated to the Avalon zone microplate in the late Paleozoic during collision of Gondwanaland with Avalonia. ?? 1987.

Cenozoic Tectonic Evolution of Northeast China and Surrounding Areas Reproduced by Slab Subduction Models

NASA Astrophysics Data System (ADS)

Yang, T.; Moresi, L. N.; Zhao, D.; Sandiford, D.

2017-12-01

Northeast China lies at the continental margin of the western Pacific subduction zone where the Pacific Plate subducts beneath the Eurasia Plate along the Kuril-Japan trench during the Cenozoic, after the consumption of the Izanagi Plate. The Izanagi Plate and the Izanagi-Pacific mid-ocean ridge recycled to the mantle beneath Eurasia before the early Cenozoic. Plate reconstructions suggest that (1) age of the incoming Pacific Plate at the trench increases with time; (2) convergence rate between the Pacific and Eurasia Plates increased rapidly from the late Eocene to the early Miocene. Northeast China and surrounding areas suffered widespread extension and magmatism during the Cenozoic, culminating in the opening of the Japan Sea and the rifting of the Baikal Rift Zone. The Japan Sea opened during the early Miocene and kept spreading until the late Miocene, since when compression tectonics gradually prevailed. The Baikal Rift Zone underwent slow extension in the Cenozoic but its extension rate has increased rapidly since the late Miocene. We investigate the Cenozoic tectonic evolution of Northeast China and surrounding areas with geodynamic models. Our study suggests that the rapid aging of the incoming Pacific Plate at the subduction zone leads to the increase of plate convergence and trench motion rates, and explains the observed sequence of regional tectonic events. Our geodynamic model, which reproduces the Cenozoic regional tectonic events, predicts slab morphology and stress state consistent with seismic observations, including over 1000 km of slab stagnant in the transition zone, and the along-dip principal compressional stress direction. Our model requires a value of the 660 km phase transition Clapeyron slope of -2.5 MPa/K to reproduce the stagnant slab and tectonic events in the study region. This suggests that the Pacific slab is hydrated in the transition zone, explaining geochemical characteristics of some regional Cenozoic igneous rocks which were

Easy handling of tectonic data: the programs TectonicVB for Mac and TectonicsFP for Windows™

NASA Astrophysics Data System (ADS)

Ortner, Hugo; Reiter, Franz; Acs, Peter

2002-12-01

TectonicVB for Macintosh and TectonicsFP for Windows TM operating systems are two menu-driven computer programs which allow the shared use of data on these environments. The programs can produce stereographic plots of orientation data (great circles, poles, lineations). Frequently used statistical procedures like calculation of eigenvalues and eigenvectors, calculation of mean vector with concentration parameters and confidence cone can be easily performed. Fault data can be plotted in stereographic projection (Angelier and Hoeppener plots). Sorting of datasets into homogeneous subsets and rotation of tectonic data can be performed in interactive two-diagram windows. The paleostress tensor can be calculated from fault data sets using graphical (calculation of kinematic axes and right dihedra method) or mathematical methods (direct inversion or numerical dynamical analysis). The calculations can be checked in dimensionless Mohr diagrams and fluctuation histograms.

Tectonic framework of Turkish sedimentary basins

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

Yilmaz, P.O.

1988-08-01

Turkey's exploration potential primarily exists in seven onshore (Southeast Turkey platform, Tauride platform, Pontide platform, East Anatolian platform, Interior, Trace, and Adana) basins and four offshore (Black Sea, Marmara Sea, Aegean Sea, and Mediterranean Sea) regional basins formed during the Mesozoic and Tertiary. The Mesozoic basins are the onshore basins: Southeast Turkey, Tauride, Pontide, East Anatolian, and Interior basins. Due to their common tectonic heritage, the southeast Turkey and Tauride basins have similar source rocks, structural growth, trap size, and structural styles. In the north, another Mesozoic basin, the Pontide platform, has a much more complex history and very littlemore » in common with the southerly basins. The Pontide has two distinct parts; the west has Paleozoic continental basement and the east is underlain by island-arc basement of Jurassic age. The plays are in the upper Mesozoic rocks in the west Pontide. The remaining Mesozoic basins of the onshore Interior and East Anatolian basins are poorly known and very complex. Their source, reservoir, and seal are not clearly defined. The basins formed during several orogenic phases in mesozoic and Tertiary. The Cenozoic basins are the onshore Thrace and Adana basins, and all offshore regional basins formed during Miocene extension. Further complicating the onshore basins evolution is the superposition of Cenozoic basins and Mesozoic basins. The Thrace basin in the northwest and Adana basin in the south both originate from Tertiary extension over Tethyan basement and result in a similar source, reservoir, and seal. Local strike-slip movement along the North Anatolian fault modifies the Thrace basin structures, influencing its hydrocarbon potential.« less

Kinematics and 40Ar/ 39Ar geochronology of the Gaoligong and Chongshan shear systems, western Yunnan, China: Implications for early Oligocene tectonic extrusion of SE Asia

NASA Astrophysics Data System (ADS)

Wang, Yuejun; Fan, Weiming; Zhang, Yanhua; Peng, Touping; Chen, Xinyue; Xu, Yigang

2006-06-01

The Gaoligong and Chongshan shear systems (GLSS and CSSS) in western Yunnan, China, have similar tectonic significance to the Ailaoshan-Red River shear system (ASRRSS) during the Cenozoic tectonic development of the southeastern Tibetan syntaxis. To better understand their kinematics and the Cenozoic tectonic evolution of SE Asia, this paper presents new kinematic and 40Ar/ 39Ar geochronological data for these shear systems. All the structural and microstructural evidence indicate that the GLSS is a dextral strike-slip shear system while the CSSS is a sinistral strike-slip shear system, and both were developed under amphibolite- to greenschist-grade conditions. The 40Ar/ 39Ar dating of synkinematic minerals revealed that the strike-slip shearing on the GLSS and CSSS at least began at ˜ 32 Ma, possibly coeval with the onset of other major shear systems in SE Asia. The late-stage shearing on the GLSS and CSSS is dated at ˜ 27-29 Ma by the biotite 40Ar/ 39Ar ages, consistent with that of the Wang Chao shear zone (WCSZ), but ˜ 10 Ma earlier than that of the ASRRSS. The dextral Gaoligong shear zone within the GLSS may have separated the India plate from the Indochina Block during early Oligocene. Combined with other data in western Yunnan, we propose that the Baoshan/Southern Indochina Block escaped faster southeastward along the CSSS to the east and the GLSS to the west than the Northern Indochina Block along the ASRRSS, accompanying with the obliquely northward motion of the India plate during early Oligocene (28-36 Ma). During 28-17 Ma, the Northern Indochina Block was rotationally extruded along the ASRRSS relative to the South China Block as a result of continuously impinging of the India plate.

Sand fairway mapping as a tool for tectonic restoration in orogenic belts

NASA Astrophysics Data System (ADS)

Butler, Rob

2016-04-01

The interplay between regional subsidence mechanisms and local deformation associated with individual fold-thrust structures is commonly investigated in neotectonic subaerial systems using tectonic geomorphology. Taking these approaches back into the early evolution of mountain belts is difficult as much of the key evidence is lost through erosion. The challenge is to develop appropriate tools for investigating these early stages of orogenesis. However, many such systems developed under water. In these settings the connections between regional and local tectonics are manifest in complex bathymetry. Turbidity currents flowing between and across these structures will interact with their substrate and thus their deposits, tied to stratigraphic ages, can chart tectonic evolution. Understanding the depositional processes of the turbidity currents provides substantial further insight on confining seabed geometry and thus can establish significant control on the evolution of bathymetric gradients and continuity through basins. However, reading these records commonly demands working in structurally deformed terrains that hitherto have discouraged sedimentological study. This is now changing. Sand fairway mapping provides a key approach. Fairway maps chart connectivity between basins and hence their relative elevation through time. Larger-scale tectonic reconstructions may be tested by linking fairway maps to sand composition and other provenance data. More detailed turbidite sedimentology provides substantial further insight. In confined turbidite systems, it is the coarser sand component that accumulates in the deeper basin with fines fractionated onto the flanks. Flow bypass, evidenced by abrupt breaks in grading within individual event beds, can be used to predict sand fraction distribution down fairways. Integrating sedimentology into fairway maps can chart syntectonic slope evolution and thus provide high resolution tools equivalent to those in subaerial tectonic

Correlation of Late Precambrian and Paleozoic events in the East European platform and the adjacent paleooceanic domains

NASA Astrophysics Data System (ADS)

Kheraskova, T. N.; Volozh, Yu. A.; Antipov, M. P.; Bykadorov, V. A.; Sapozhnikov, R. B.

2015-01-01

The correlation of geological events and structure-forming processes occurring contemporaneously in the inner parts of cratons and the adjacent paleooceanic basins is discussed in order to understand the effects of these processes on sedimentation and structural rearrangements. For this purpose, a series of paleodynamic reconstructions of the Riphean, Vendian, and Paleozoic epicontinental basins of the East European Platform and zones of their transition to marginal basins of the same age once situated in the Ural, Timan, Caucasus, Scandinavian fold regions and in the Scythian-Turan Plate have been performed on the basis of the available original and published data combined with interpretation of seismic profiles. As a result, a set of structural-facies maps of this territory have been compiled for several time intervals from the Late Riphean to Early Permian.

Jurassic cooling ages in Paleozoic to early Mesozoic granitoids of northeastern Patagonia: 40Ar/39Ar, 40K-40Ar mica and U-Pb zircon evidence

NASA Astrophysics Data System (ADS)

Martínez Dopico, Carmen I.; Tohver, Eric; López de Luchi, Mónica G.; Wemmer, Klaus; Rapalini, Augusto E.; Cawood, Peter A.

2017-10-01

Patagonia during the Early Jurassic (Sinemurian-Pliensbachian) was responsible for the partial (re)exhumation of the mid-crustal Paleozoic basement along reactivated discrete NE-SW to ENE-WSW lineaments and the resetting of isotopic systems. These new thermochronological data indicate that Early Permian magmatic rocks of the Nahuel Niyeu block were below 300 °C for ca. 20 Ma prior to the onset of the main magmatic episode of the Late Permian to Triassic igneous and metaigneous rocks of the Yaminué block.

The origin and development of plains-type folds during the cretaceous in Central and western Kansas

USGS Publications Warehouse

Merriam, D.F.; Forster, A.

2000-01-01

Kansas is part of the Central Stable Region of North America. Structural movement on this part of the craton has been mainly the result of tectonism in nearby areas. Response to the outside tectonic forces, transmitted through the rigid Precambrian basement, has been vertical adjustment. Differential movement along an indigenous fault/fracture pattern in the basement created displaced blocks over which the later sediments were draped by differential compaction. After initial formation of this structural regimen in late Mississippian-early Pennsylvanian time, continued movement of the basement blocks gave rise to the plains-type folds so prevalent in the U.S. Midcontinent. The incremental movement continues through the late Paleozoic, Mesozoic, and Tertiary until today. This paper demonstrates the Cretaceous development of some of these structures in central and western Kansas.

Seismic evidence for change of the tectonic regime in Messinian, northern Marmara Sea, Turkey

NASA Astrophysics Data System (ADS)

Alp, Hakan; Vardar, Denizhan; Alpar, Bedri; Ustaömer, Timur

2018-01-01

New Chirp seismic data collected from the northern margin of the Marmara Sea in June 2015 and previous Sparker seismic profiles recorded in 1999 suggest a change in tectonic regime in Messinian. New tectonic lineaments and fault segments were detected at offshore the Çekmece lagoons region that is located on one of the possible water corridors with the Paratethys. The faults only affect the older seismic unit (U1), which can be best outlined on the Chirp data. The E-W trending fault offshore Avcılar (OAF) borders the northern edge of a tightly folded sedimentary zone. The NNE-SSW trending fault, namely the Büyükçekmece Fault (BF), passing through the Büyükçekmece Bay, follows a buried valley. Its evolution must be related to the development of the Early Miocene - Early Pliocene Thrace-Eskişehir fault zone (TEFZ). BF and OAF indicate old tectonic activities in the region, which continued to the North Anatolian fault becoming the most dominant tectonic element in the region. The upper surface of the stratigraphic unit U1 and its terraces define the thickness of younger deposits (U2), which is thinner in the middle of the shelf. The morphology of the tightly folded zone controls those terraces, which correspond to the Bakırköy Formation and Kıraç member on land. The topmost parts of the terraces must have been eroded during sea level low-stands and cutting of the paleo-valleys. There is no evidence of any tectonic deformation or active fault in the younger seismic unit (U2).

Geomorphology, tectonics, and exploration

NASA Technical Reports Server (NTRS)

Sabins, F. F., Jr.

1985-01-01

Explorationists interpret satellite images for tectonic features and patterns that may be clues to mineral and energy deposits. The tectonic features of interest range in scale from regional (sedimentary basins, fold belts) to local (faults, fractures) and are generally expressed as geomorphic features in remote sensing images. Explorationists typically employ classic concepts of geomorphology and landform analysis for their interpretations, which leads to the question - Are there new and evolving concepts in geomorphology that may be applicable to tectonic analyses of images?

A new model for early Earth: heat-pipe cooling

NASA Astrophysics Data System (ADS)

Webb, A. G.; Moore, W. B.

2013-12-01

In the study of heat transport and lithospheric dynamics of early Earth, current models depend upon plate tectonic and vertical tectonic concepts. Plate tectonic models adequately account for regions with diverse lithologies juxtaposed along ancient shear zones, as seen at the famous Eoarchean Isua supracrustal belt of West Greenland. Vertical tectonic models to date have involved volcanism, sub- and intra-lithospheric diapirism, and sagduction, and can explain the geology of the best-preserved low-grade ancient terranes, such as the Paleoarchean Barberton and Pilbara greenstone belts. However, these models do not offer a globally-complete framework consistent with the geologic record. Plate tectonics models suggest that paired metamorphic belts and passive margins are among the most likely features to be preserved, but the early rock record shows no evidence of these terranes. Existing vertical tectonics models account for the >300 million years of semi-continuous volcanism and diapirism at Barberton and Pilbara, but when they explain the shearing record at Isua, they typically invoke some horizontal motion that cannot be differentiated from plate motion and is not a salient feature of the lengthy Barberton and Pilbara records. Despite the strengths of these models, substantial uncertainty remains about how early Earth evolved from magma ocean to plate tectonics. We have developed a new model, based on numerical simulations and analysis of the geologic record, that provides a coherent, global geodynamic framework for Earth's evolution from magma ocean to subduction tectonics. We hypothesize that heat-pipe cooling offers a viable mechanism for the lithospheric dynamics of early Earth. Our numerical simulations of heat-pipe cooling on early Earth indicate that a cold, thick, single-plate lithosphere developed as a result of frequent volcanic eruptions that advected surface materials downward. The constant resurfacing and downward advection caused compression as the

Gravity study of Libya;Evaluation and Integration with Geological Data

NASA Astrophysics Data System (ADS)

Ben Suleman, abdunnur; Saheel, Ahmed

2016-04-01

Libya is located on the Mediterranean foreland of the African Shield and covers an area of approximately 1.8 million square kilometers. Since Early Paleozoic time, Libya has been a site of deposition of large sheets of continental clastics and several transgressions and regressions by the seas with consequent accumulations of a wide variety of sedimentary rocks. Several tectonic cycles affected the area and shaped the geological setting of the country. However, the regional geology and the structural framework have been highly influenced by the Caledonian, Hercynian, and Alpine tectonic events. As a result, a total of seven sedimentary basins, namely Ghadames, Murzuq, Al Kufra, Al Butnan, Sirt, and the Offshore Pelagian Basin, were developed and were separated by intervening uplifts and platforms ( Gargaf, Tibesti, Nafusah and Cyrenaica platform). Apart from Sirt and the offshore basins, all the above mentioned basins are active since Early Paleozoic time and received several thousand feet of sediments. The capability of providing regional information on the structure of sedimentary basins makes gravity mapping, in conjunction with geological information, potentially powerful tools. In this study we used gravity mapping as our primary tool of investigation however, we also used all available geological information to better understand the regional tectonics. The gravity dataset that were used in the Gravity compilation project of Libya is not homogenous. As a result, some irregularities, apparent spikes or misties, and large shifts were obtained and were taken into consideration. Evaluation of gravity Maps of Libya and their integration with geological data provide a better understanding of the role that gravity mapping plays in the geological exploration of sedimentary basins. Results confirm the known Sirt Basin regional tectonic elements and the possible presence of NW-SE lateral wrench tectonics, crossing Ajdabiya Trough at the center of Sirt Basin. The

The development of floristic provinciality during the Middle and Late Paleozoic

USGS Publications Warehouse

Wnuk, C.

1996-01-01

Phytogeographic reconstructions have been published for most Paleozoic series since the Pr??i??doli??, but there have been few attempts to synthesize this data into a comprehensive review of the characteristics and causes of the changing phytogeographic patterns for the whole Paleozoic history of the vascular flora. Existing floristic analyses have been compiled in this manuscript and the resulting data are used to reconstruct the evolution of floristic provinces since the Silurian. The earliest plant fossil records indicate that provinciality was characteristic of terrestrial vascular plant distributions right from the beginning of terrestrial colonization by vascular plants. This interpretation differs markedly from the views of many workers who still maintain that pre-Upper Carboniferous floras were uniform and cosmopolitan in distribution. Three of the four major phytogeographic units, i.e. Angara, Euramerica, and Gondwana, can be recognized in the earliest fossil floras. The fourth unit, Cathaysia, differentiated from Euramerica during the late Upper Carboniferous. Phytogeographic differentiation occurs in direct response to climatic gradients and physiographic barriers. As these gradients and barriers change, provincial boundaries expand and contract, fragment, reassemble and reassort. Phytogeographic units are dynamic through time. ?? 1996 Elsevier Science B.V. All rights reserved.

Petrogenesis of the ∼500 Ma Fushui mafic intrusion and Early Paleozoic tectonic evolution of the Northern Qinling Belt, Central China

NASA Astrophysics Data System (ADS)

Shi, Yu; Pei, Xiaoli; Castillo, Paterno R.; Liu, Xijun; Ding, Haihong; Guo, Zhichao

2017-06-01

The Fushui mafic intrusion in the Qinling orogenic belt (QOB) is composed of meta-gabbro, meta-gabbro-diorite, diorite, and syenite. Most of these rocks are metamorphosed under the upper greenschist facies to lower amphibolite facies metamorphism. Zircon separates from eight samples have LA-ICP-MS U-Pb ages of 497-501 Ma which are taken to be the emplacement age of magmas that formed the Fushui intrusion. Most of the zircon grains exhibit negative εHf values, correspond to TDM2 model ages of late Paleoproterozoic-early Mesoproterozoic or Neoproterozoic and suggest that the mafic rocks were most probably derived from mafic melts produced by partial melting of a previously metasomatized lithospheric mantle. The intrusion is not extensively contaminated by crustal materials and most chemical compositions of rocks are not modified during the greenschist to amphibolite-facies metamorhism. Rocks from the intrusion have primitive mantle-normalized trace element patterns with significant enrichment in light-REE and large ion lithophile elements (LILE) and depletion in high field-strength elements (HFSE). On the basis of the trace element contents, the Fushui intrusion was derived from parental magmas generated by <10% partial melting of both phlogopite-lherzolite and garnet-lherzolite mantle sources. These sources are best interpreted to be in a subduction-related arc environment and have been modified by fluids released from a subducting slab. The formation of the Fushui intrusion was related to the subduction of the Paleotethyan Shangdan oceanic lithosphere at ∼500 Ma.

Global plate boundary evolution and kinematics since the late Paleozoic

NASA Astrophysics Data System (ADS)

Matthews, Kara J.; Maloney, Kayla T.; Zahirovic, Sabin; Williams, Simon E.; Seton, Maria; Müller, R. Dietmar

2016-11-01

Many aspects of deep-time Earth System models, including mantle convection, paleoclimatology, paleobiogeography and the deep Earth carbon cycle, require high-resolution plate motion models that include the evolution of the mosaic of plate boundaries through time. We present the first continuous late Paleozoic to present-day global plate model with evolving plate boundaries, building on and extending two previously published models for the late Paleozoic (410-250 Ma) and Mesozoic-Cenozoic (230-0 Ma). We ensure continuity during the 250-230 Ma transition period between the two models, update the absolute reference frame of the Mesozoic-Cenozoic model and add a new Paleozoic reconstruction for the Baltica-derived Alexander Terrane, now accreted to western North America. This 410-0 Ma open access model provides a framework for deep-time whole Earth modelling and acts as a base for future extensions and refinement. We analyse the model in terms of the number of plates, predicted plate size distribution, plate and continental root mean square (RMS) speeds, plate velocities and trench migration through time. Overall model trends share many similarities to those for recent times, which we use as a first order benchmark against which to compare the model and identify targets for future model refinement. Except for during the period 260-160 Ma, the number of plates (16-46) and ratio of "large" plates (≥ 107.5 km2) to smaller plates ( 2.7-6.6) are fairly similar to present-day values (46 and 6.6, respectively), with lower values occurring during late Paleozoic assembly and growth of Pangea. This temporal pattern may also reflect difficulties in reconstructing small, now subducted oceanic plates further back in time, as well as whether a supercontinent is assembling or breaking up. During the 260-160 Ma timeframe the model reaches a minima in the number of plates, in contrast to what we would expect during initial Pangea breakup and thus highlighting the need for refinement

A bibliography of Paleozoic Crustacea from 1698 to 1889, including a list of North American species and a systematic arrangement of genera

USGS Publications Warehouse

Vogdes, Anthony Wayne

1890-01-01

The sole object of this bulletin is to give a general view of the literature on the Paleozoic Crustacea and to aid students and paleontologists in their researches. It is the result of more or less constant work during the past ten years.In its compilation I have examined almost every reference before recording it; those not so examined are indicated by a star (*) following the title.For convenience, the subject-matter has been arranged as follows:Part I. List of authors, including a brief index of the genera described in each work. Part II. A catalogue of the North American Paleozoic trilobites. Part III. The non-trilobitic Paleozoic Crustacea, with a list of the species.

Paleobiogeography, high-resolution stratigraphy, and the future of Paleozoic biostratigraphy: Fine-scale diachroneity of the Wenlock (Silurian) conodont Kockelella walliseri

USGS Publications Warehouse

Cramer, Bradley D.; Kleffner, Mark A.; Brett, Carlton E.; McLaughlin, P.I.; Jeppsson, Lennart; Munnecke, Axel; Samtleben, Christian

2010-01-01

The Wenlock Epoch of the Silurian Period has become one of the chronostratigraphically best-constrained intervals of the Paleozoic. The integration of multiple chronostratigraphic tools, such as conodont and graptolite biostratigraphy, sequence stratigraphy, and ??13Ccarb chemostratigraphy, has greatly improved global chronostratigraphic correlation and portions of the Wenlock can now be correlated with precision better than ??100kyr. Additionally, such detailed and integrated chronostratigraphy provides an opportunity to evaluate the fidelity of individual chronostratigraphic tools. Here, we use conodont biostratigraphy, sequence stratigraphy and carbon isotope (??13Ccarb) chemostratigraphy to demonstrate that the conodont Kockelella walliseri, an important guide fossil for middle and upper Sheinwoodian strata (lower stage of the Wenlock Series), first appears at least one full stratigraphic sequence lower in Laurentia than in Baltica. Rather than serving as a demonstration of the unreliability of conodont biostratigraphy, this example serves to demonstrate the promise of high-resolution Paleozoic stratigraphy. The temporal difference between the two first occurrences was likely less than 1million years, and although it is conceptually understood that speciation and colonization must have been non-instantaneous events, Paleozoic paleobiogeographic variability on such short timescales (tens to hundreds of kyr) traditionally has been ignored or considered to be of little practical importance. The expansion of high-resolution Paleozoic stratigraphy in the future will require robust biostratigraphic zonations that embrace the integration of multiple chronostratigraphic tools as well as the paleobiogeographic variability in ranges that they will inevitably demonstrate. In addition, a better understanding of the paleobiogeographic migration histories of marine organisms will provide a unique tool for future Paleozoic paleoceanography and paleobiology research. ?? 2010

Remnant colloform pyrite at the haile gold deposit, South Carolina: A textural key to genesis

USGS Publications Warehouse

Foley, N.; Ayuso, R.A.; Seal, R.R.

2001-01-01

Auriferous iron sulfide-bearing deposits of the Carolina slate belt have distinctive mineralogical and textural features-traits that provide a basis to construct models of ore deposition. Our identification of paragenetically early types of pyrite, especially remnant colloform, crustiform, and layered growth textures of pyrite containing electrum and pyrrhotite, establishes unequivocally that gold mineralization was coeval with deposition of host rocks and not solely related to Paleozoic tectonic events. Ore horizons at the Haile deposit, South Carolina, contain many remnants of early pyrite: (1) fine-grained cubic pyrite disseminated along bedding; (2) fine- grained spongy, rounded masses of pyrite that may envelop or drape over pyrite cubes; (3) fragments of botryoidally and crustiform layered pyrite, and (4) pyritic infilling of vesicles and pumice. Detailed mineral chemistry by petrography, microprobe, SEM, and EDS analysis of replaced pumice and colloform structures containing both arsenic compositional banding and electrum points to coeval deposition of gold and the volcanic host rocks and, thus, confirms a syngenetic origin for the gold deposits. Early pyrite textures are present in other major deposits of the Carolina slate belt, such as Ridgeway and Barite Hill, and these provide strong evidence for models whereby the sulfide ores formed prior to tectonism. The role of Paleozoic metamorphism was to remobilize and concentrate gold and other minerals in structurally prepared sites. Recognizing the significance of paragenetically early pyrite and gold textures can play an important role in distinguishing sulfide ores that form in volcanic and sedimentary environments from those formed solely by metamorphic processes. Exploration strategies applied to the Carolina slate belt and correlative rocks in the eastern United States in the Avalonian basement will benefit from using syngenetic models for gold mineralization.

Accretion and exhumation at a Variscan active margin, recorded in the Saxothuringian flysch

NASA Astrophysics Data System (ADS)

Schäfer, J.; Neuroth, H.; Ahrendt, H.; Dörr, W.; Franke, W.

The Saxothuringian flysch basin, on the north flank of the Central European Variscides, was fed and eventually overthrust by the northwestern, active margin of the Tepla-Barrandian terrane. Clast spectra, mineral composition and isotopic ages of detrital mica and zircon have been analyzed in order to constrain accretion and exhumation of rocks in the orogenic wedge. The earliest clastic sediments preserved are of early Famennian age (ca. 370Ma). They are exposed immediately to the NW of the suture, and belong to the par-autochthon of the foreland. Besides ultramafic (?ophiolite) material, these rocks contain clasts derived from Early Paleozoic continental slope sediments, originally deposited at the NW margin of the Saxothuringian basin. These findings, together with the paleogeographic position of the Famennian clastics debris on the northwestern passive margin, indicate that the Saxothuringian narrow ocean had been closed by that time. Microprobe analyses of detrital hornblendes suggest derivation from the ``Randamphibolit'' unit, now present in the middle part of the Saxothuringian allochthon (Münchberg nappes). Detrital zircons of metamorphic rocks formed a little earlier (ca. 380Ma) indicate rapid recycling at the tectonic front. The middle part of the flysch sequence (ca. early to middle Viséan), both in the par-autochthon and in the allochthon, contains abundant clasts of Paleozoic rocks derived from the northwestern slope and rise, together with debris of Cadomian basement, 500-Ma granitoids and 380Ma (early Variscan) crystalline rocks. All of these source rocks were still available in the youngest part of the flysch (c. middle to late Viséan), but some clasts record, in addition, accretion of the northwestern shelf. Our findings permit deduction of minimum rates of tectonic shortening well in excess of 10-30mm per year, and rates of exhumation of ca. 3mm/a, and possibly more.

Mesozoic architecture of a tract of the European-Iberian continental margin: Insights from preserved submarine palaeotopography in the Longobucco Basin (Calabria, Southern Italy)

NASA Astrophysics Data System (ADS)

Santantonio, Massimo; Fabbi, Simone; Aldega, Luca

2016-01-01

The sedimentary successions exposed in northeast Calabria document the Jurassic-Early Cretaceous tectonic-sedimentary evolution of a former segment of the European-Iberian continental margin. They are juxtaposed today to units representing the deformation of the African and Adriatic plates margins as a product of Apenninic crustal shortening. A complex pattern of unconformities reveals a multi-stage tectonic evolution during the Early Jurassic, which affected the facies and geometries of siliciclastic and carbonate successions deposited in syn- and post-rift environments ranging from fluvial to deep marine. Late Sinemurian/Early Pliensbachian normal faulting resulted in exposure of the Hercynian basement at the sea-floor, which was onlapped by marine basin-fill units. Shallow-water carbonate aprons and reefs developed in response to the production of new accommodation space, fringing the newborn islands which represent structural highs made of Paleozoic crystalline and metamorphic rock. Their drowning and fragmentation in the Toarcian led to the development of thin caps of Rosso Ammonitico facies. Coeval to these deposits, a thick (> 1 km) hemipelagic/siliciclastic succession was sedimented in neighboring hanging wall basins, which would ultimately merge with the structural high successions. Footwall blocks of the Early Jurassic rift, made of Paleozoic basement and basin-margin border faults with their onlapping basin-fill formations, are found today at the hanging wall of Miocene thrusts, overlying younger (Middle/Late Jurassic to Late Paleogene) folded basinal sediments. This paper makes use of selected case examples to describe the richly diverse set of features, ranging from paleontology to sedimentology, to structural geology, which are associated with the field identification of basin-margin unconformities. Our data provide key constraints for restoring the pre-orogenic architecture of a continental margin facing a branch of the Liguria-Piedmont ocean in the

Land plants, weathering, and Paleozoic climatic evolution

NASA Astrophysics Data System (ADS)

Goddéris, Yves; Maffre, Pierre; Donnadieu, Yannick; Carretier, Sébastien

2017-04-01

At the end of the Paleozoic, the Earth plunged into the longest and most severe glaciation of the Phanerozoic eon (Montanez et al., 2013). The triggers for this event (called the Late Paleozoic Ice Age, LPIA) are still debated. Based on field observations and laboratory experiments showing that CO2 consumption by rock weathering is enhanced by the presence of plants, the onset of the LPIA has been related to the colonization of the continents by vascular plants in the latest Devonian. By releasing organic acids, concentrating respired CO2 in the soil, and by mechanically breaking rocks with their roots, land plants may have increased the weatherability of the continental surfaces. The "greening" of the continents may also have contributed to an enhanced burial of organic carbon in continental sedimentary basins, assuming that lignin decomposers have not yet evolved (Berner, 2004). As a consequence, CO2 went down, setting the conditions for the onset of the LPIA. This scenario is now widely accepted in the scientific community, and reinforces the feeling that biotic evolutionary steps are main drivers of the long-term climatic evolution. Although appealing, this scenario suffers from some weaknesses. The timing of the continent colonization by vascular plants was achieved in the late Devonian, several tens of million years before the onset of the LPIA (Davies and Gibling, 2013). Second, lignin decomposer fungi were present at the beginning of the Carboniferous, 360 million years ago while the LPIA started around 340-330 Ma (Nelsen et al., 2016). Land plants have also decreased the continental albedo, warming the Earth surface and promoting runoff. Weathering was thus facilitated and CO2 went down. Yet, temperature may have stayed constant, the albedo change compensating for the CO2 fall (Le Hir et al., 2010). From a modelling point of view, the effect of land plants on CO2 consumption by rock weathering is accounted for by forcing the weatherability of the

Paleomagnetic tests for tectonic reconstructions of the Late Jurassic-Early Cretaceous Woyla Group, Sumatra

NASA Astrophysics Data System (ADS)

Advokaat, Eldert; Bongers, Mayke; van Hinsbergen, Douwe; Rudyawan, Alfend; Marshal, Edo

2017-04-01

SE Asia consists of multiple continental blocks, volcanic arcs and suture zones representing remnants of closing ocean basins. The core of this mainland is called Sundaland, and was formed by accretion of continental and arc fragments during the Paleozoic and Mesozoic. The former positions of these blocks are still uncertain but reconstructions based on tectonostratigraphic, palaeobiogeographic, geological and palaeomagnetic studies indicate the continental terranes separated from the eastern margin of Gondwana. During the mid-Cretaceous, more continental and arc fragments accreted to Sundaland, including the intra-oceanic Woyla Arc now exposed on Sumatra. These continental fragments were derived from Australia, but the former position of the Woyla Arc is unconstrained. Interpretations on the former position of the Woyla Arc fall in two end-member groups. The first group interprets the Woyla Arc to be separated from West Sumatra by a small back-arc basin. This back arc basin opened in the Late Jurassic, and closed mid-Cretaceous, when the Woyla Arc collided with West Sumatra. The other group interprets the Woyla Arc to be derived from Gondwana, at a position close to the northern margin of Greater India in the Late Jurassic. Subsequently the Woyla Arc moved northwards and collided with West Sumatra in the mid-Cretaceous. Since these scenarios predict very different plate kinematic evolutions for the Neotethyan realm, we here aim to place paleomagnetic constraints on paleolatitudinal evolution of the Woyla Arc. The Woyla Arc consists mainly of basaltic to andesitic volcanics and dykes, and volcaniclastic shales and sandstones. Associated limestones with volcanic debris are interpreted as fringing reefs. This assemblage is interpreted as remnants of an Early Cretaceous intra-oceanic arc. West Sumatra exposes granites, surrounded by quartz sandstones, shales and volcanic tuffs. These sediments are in part metamorphosed. This assemblage is interpreted as a Jurassic-Early

Persistent and widespread occurrence of bioactive quinone pigments during post-Paleozoic crinoid diversification

PubMed Central

Wolkenstein, Klaus

2015-01-01

Secondary metabolites often play an important role in the adaptation of organisms to their environment. However, little is known about the secondary metabolites of ancient organisms and their evolutionary history. Chemical analysis of exceptionally well-preserved colored fossil crinoids and modern crinoids from the deep sea suggests that bioactive polycyclic quinones related to hypericin were, and still are, globally widespread in post-Paleozoic crinoids. The discovery of hypericinoid pigments both in fossil and in present-day representatives of the order Isocrinida indicates that the pigments remained almost unchanged since the Mesozoic, also suggesting that the original color of hypericinoid-containing ancient crinoids may have been analogous to that of their modern relatives. The persistent and widespread occurrence, spatially as well as taxonomically, of hypericinoid pigments in various orders during the adaptive radiation of post-Paleozoic crinoids suggests a general functional importance of the pigments, contributing to the evolutionary success of the Crinoidea. PMID:25730856

Crustal structure beneath the Paleozoic Parnaíba Basin revealed by airborne gravity and magnetic data, Brazil

USGS Publications Warehouse

de Castroa, David L.; Fuck, Reinhardt A.; Phillips, Jeffrey D.; Vidotti, Roberta M.; Bezerra, Francisco H. R.; Dantas, Elton L.

2014-01-01

The Parnaíba Basin is a large Paleozoic syneclise in northeastern Brazil underlain by Precambrian crystalline basement, which comprises a complex lithostructural and tectonic framework formed during the Neoproterozoic–Eopaleozoic Brasiliano–Pan African orogenic collage. A sag basin up to 3.5 km thick and 1000 km long formed after the collage. The lithologic composition, structure, and role in the basin evolution of the underlying basement are the focus of this study. Airborne gravity and magnetic data were modeled to reveal the general crustal structure underneath the Parnaíba Basin. Results indicate that gravity and magnetic signatures delineate the main boundaries and structural trends of three cratonic areas and surrounding Neoproterozoic fold belts in the basement. Triangular-shaped basement inliers are geophysically defined in the central region of this continental-scale Neoproterozoic convergence zone. A 3-D gravity inversion constrained by seismological data reveals that basement inliers exhibit a 36–40.5 km deep crustal root, with borders defined by a high-density and thinner crust. Forward modeling of gravity and magnetic data indicates that lateral boundaries between crustal units are limited by Brasiliano shear zones, representing lithospheric sutures of the Amazonian and São Francisco Cratons, Tocantins Province and Parnaíba Block. In addition, coincident residual gravity, residual magnetic, and pseudo-gravity lows indicate two complex systems of Eopaleozoic rifts related to the initial phase of the sag deposition, which follow basement trends in several directions.

Petrogenesis and tectonic implications of an Early Jurassic magmatic arc from South to East China Seas

NASA Astrophysics Data System (ADS)

Zhang, L.; Xu, C.

2017-12-01

Granite and diorite samples by drilling in northeastern South China Sea (SCS) and southwestern East China Sea (ECS) contribute key information to understanding tectonic regime of South China Block in Jurassic time. SIMS and LA-ICPMS U-Pb zircon analyses yield ages ranging from 195±2 Ma to 198±1 Ma for samples from well LF3511 in SCS, and an age of 187±1 Ma for the sample from well ESC635 in ECS. They are low temperature I-type granitoids with strongly enriched fluid-mobile elements and depleted Nb-Ta features, indicating subduction arc-related magmatism in their origin. Sr-Nd isotopic compositions for samples from SCS ((87Sr/86Sr)i=0.705494-0.706623, ɛNdt=-0.9 to +2.2) and sample from ECS ((87Sr/86Sr)i=0.705200, ɛNdt=1.1) suggest an affinity with evolved mantle-derived melts. The granitoids found from NE SCS, SE Taiwan to the SW ECS could spatially define an Early Jurassic NE-SW-trending Dongsha-Talun-Yandang low-temperature magmatic arc zone along the East Asian continental margin, paired with Jurassic accretionary complexes exposed in SW Japan, E Taiwan to the W Philippines. Its geodynamic context is associated with oblique subduction of the paleo-Pacific slab beneath Eurasia, as a mechanism responsible for early Jurassic lithospheric extension with magmatism in the South China Block.

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

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

Tosdal, R.M.

1990-11-10

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

Active tectonics

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

Not Available

1986-01-01

This study is part of a series of Studies in Geophysics that have been undertaken for the Geophysics Research Forum by the Geophysics Study Committee. One purpose of each study is to provide assessments from the scientific community to aid policymakers in decisions on societal problems that involve geophysics. An important part of such assessments is an evaluation of the adequacy of current geophysical knowledge and the appropriateness of current research programs as a source of information required for those decisions. The study addresses our current scientific understanding of active tectonics --- particularly the patterns and rates of ongoing tectonicmore » processes. Many of these processes cannot be described reasonably using the limited instrumental or historical records; however, most can be described adequately for practical purposes using the geologic record of the past 500,000 years. A program of fundamental research focusing especially on Quaternary tectonic geology and geomorphology, paleoseismology, neotectonics, and geodesy is recommended to better understand ongoing, active tectonic processes. This volume contains 16 papers. Individual papers are indexed separately on the Energy Database.« less

Early Tertiary Anaconda metamorphic core complex, southwestern Montana

USGS Publications Warehouse

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

Paleogeography, Paleo-drainage Systems, and Tectonic Reconstructions of Eocene Northern South America Constrained by U-Pb Detrital Zircon Geochronology

NASA Astrophysics Data System (ADS)

Xie, X.; Mann, P.; Escalona, A.

2008-12-01

Thick, Eocene to Miocene clastic sedimentary basins are widespread across on- and offshore northern South America and have been identified using seismic reflection data in offshore basins of the Leeward Antilles, the Lesser Antilles arc and forearc, and the Barbados accretionary prism. Several 3 to12-km-thick Paleogene depocenters occur in shelf to deep basinal settings along the offshore margins of Venezuela, Trinidad and Tobago, and Barbados. Previous studies proposed that the proto-Orinoco River has been the single fluvial source for these distal, continentally-derived sandstone units along northern Venezuela as part of the early Eocene to Miocene, proto-Maracaibo fluvial-deltaic system that emanated from the northern Andes of western Venezuela and Colombia. Those distal sandstones were displaced eastward with the movement of the Caribbean plate by several hundred kilometers and are now found in basins and islands of the southeastern Caribbean region. We collected nine Eocene age sandstone samples from well cores and outcrops along the northern South America margin, including Lake Maracaibo, Trinidad and Tobago, and Barbados Island. In total, 945 single detrital zircon grains were analyzed using LA-ICP-MS. The objective is to reconstruct the paleogeography, paleo-drainage system, and tectonic history during Eocene time. New data show that the Eocene Misoa Formation of Lake Maracaibo was characterized by a mixture of Precambrian, Paleozoic, and Mesozoic ages matching age provinces from eastern Cordillera and the Guayana Shield, which is consistent with previous proto-Orinoco River model flowing from the western Amazonian region of Colombia and Brazil through the Maracaibo basin into the area of western Falcon basin. However, coeval Eocene samples from Barbados and Trinidad show a much different age population dominated by Precambrian matching the eastern part of the Guyana shield to the south, which suggests that the western onland system and eastern offshore

Plate tectonic model for the oligo-miocene evolution of the western Mediterranean

NASA Astrophysics Data System (ADS)

Cohen, Curtis R.

1980-10-01

This paper outlines a plate tectonic model for the Oligo-Miocene evolution of the western Mediterranean which incorporates recent data from several tectonic domains (Corsica, Sardinia, the Kabylies, Balearic promontory, Iberia, Algero-Provençal Basin and Tunisian Atlas). Following late Mesozoic anticlockwise rotation of the Iberian peninsula (including the Balearic promontory and Sardinia), late Eocene collision occurred between the Kabylies and Balearic promontory forming a NE-trending suture with NW-tectonic polarity. As a result of continued convergence between the African and European plates, a polarity flip occurred and a southward-facing trench formed south of the Kabylie—Balearic promontory suture. During late Oligocene time an E-W-trending arc and marginal basin developed behind the southward-facing trench in the area of the present-day Gulf of Lion. Opening of this basin moved the Corsica—Sardinia—Calabria—Petit Kabylie—Menorca plate southward, relative to the African plate. Early Miocene back-arc spreading in the area between the Balearic promontory and Grand Kabylie emplaced the latter in northern Algeria and formed the South Balearic Basin. Coeval with early Miocene back-arc basin development, the N-S-extension in the Gulf of Lion marginal basin changed to a more NW-SE direction causing short-lived extension in the area of the present-day Valencia trough and a 30° anticlockwise rotation of the Corsica-Sardinia-Calabria—Petit Kabylie plate away from the European plate. Early—middle Miocene deformation along the western Italian and northeastern African continental margins resulted from this rotation. During the early late Miocene (Tortonian), spreading within a sphenochasm to the southwest of Sardinia resulted in the emplacement of Petit Kabylie in northeastern Algeria.

Testing the limits of Paleozoic chronostratigraphic correlation via high-resolution (13Ccarb) biochemostratigraphy across the Llandovery–Wenlock (Silurian) boundary: Is a unified Phanerozoic time scale achievable?

USGS Publications Warehouse

Cramer, Bradley D.; Loydell, David K.; Samtleben, Christian; Munnecke, Axel; Kaljo, Dimitri; Mannik, Peep; Martma, Tonu; Jeppsson, Lennart; Kleffner, Mark A.; Barrick, James E.; Johnson, Craig A.; Emsbo, Poul; Joachimski, Michael M.; Bickert, Torsten; Saltzman, Matthew R.

2010-01-01

The resolution and fidelity of global chronostratigraphic correlation are direct functions of the time period under consideration. By virtue of deep-ocean cores and astrochronology, the Cenozoic and Mesozoic time scales carry error bars of a few thousand years (k.y.) to a few hundred k.y. In contrast, most of the Paleozoic time scale carries error bars of plus or minus a few million years (m.y.), and chronostratigraphic control better than ??1 m.y. is considered "high resolution." The general lack of Paleozoic abyssal sediments and paucity of orbitally tuned Paleozoic data series combined with the relative incompleteness of the Paleozoic stratigraphic record have proven historically to be such an obstacle to intercontinental chronostratigraphic correlation that resolving the Paleozoic time scale to the level achieved during the Mesozoic and Cenozoic was viewed as impractical, impossible, or both. Here, we utilize integrated graptolite, conodont, and carbonate carbon isotope (??13Ccarb) data from three paleocontinents (Baltica, Avalonia, and Laurentia) to demonstrate chronostratigraphic control for upper Llando very through middle Wenlock (Telychian-Sheinwoodian, ~436-426 Ma) strata with a resolution of a few hundred k.y. The interval surrounding the base of the Wenlock Series can now be correlated globally with precision approaching 100 k.y., but some intervals (e.g., uppermost Telychian and upper Shein-woodian) are either yet to be studied in sufficient detail or do not show sufficient biologic speciation and/or extinction or carbon isotopic features to delineate such small time slices. Although producing such resolution during the Paleozoic presents an array of challenges unique to the era, we have begun to demonstrate that erecting a Paleozoic time scale comparable to that of younger eras is achievable. ?? 2010 Geological Society of America.

A review of the sedimentology of the Early Proterozoic Pretoria Group, Transvaal Sequence, South Africa: implications for tectonic setting

NASA Astrophysics Data System (ADS)

Eriksson, P. G.; Schreiber, U. M.; van der Neut, M.

The sedimentary rocks of the Early Proterozoic Pretoria Group form the floor rocks to teh 2050 M.a. Bushveld Complex. An overall alluvial fan-fan-delta - lacustrine palaeoenvironmental model is postulated for the Pretoria Group. This model is compatible with a continental half-graben tectonic setting, with steep footwall scarps on the southern margin and a lower gradient hanging wall developed to the north. The latter provided much of the basin-fill detritus. It is envisaged that the southern boundary fault system migrated southwards by footwall collapse as sedimentation continued. Synsedimentary mechanical rifting, associated with alluvial and deltaic sedimentation (Rooihoogte-Strubenkop Formations) was followed by thermal subsidence, with concomitant transgressive lacustrine deposition (Daspoort-Magaliesberg Formations). The proposed half-graben basin was probably related to the long-lived Thabazimbi-Murchison and Sugarbush-Barberton lineaments, which bound the preserved outcrops of the Pretoria Group.

Widespread effects of middle Mississippian deformation in the Great Basin of western North America

USGS Publications Warehouse

Trexler, J.H.; Cashman, P.H.; Cole, J.C.; Snyder, W.S.; Tosdal, R.M.; Davydov, V.I.

2003-01-01

Stratigraphic analyses in central and eastern Nevada reveal the importance of a deformation event in middle Mississippian time that caused widespread deformation, uplift, and erosion. It occurred between middle Osagean and late Meramecian time and resulted in deposition of both synorogenic and postorogenic sediments. The deformation resulted in east-west shortening, expressed as east-vergent folding and east-directed thrusting; it involved sedimentary rocks of the Antler foredeep as well as strata associated with the Roberts Mountains allochthon. A latest Meramecian to early Chesterian unconformity, with correlative conformable lithofacies changes, postdates this deformation and occurs throughout Nevada. A tectonic highland-created in the middle Mississippian and lasting into the Pennsylvanian and centered in the area west and southwest of Carlin, Nevada- shed sediments eastward across the Antler foreland, burying the unconformity. Postorogenic strata are late Meramecian to early Chesterian at the base and are widespread throughout the Great Basin. The tectonism therefore occurred 20 to 30 m.y. after inception of the Late Devonian Antler orogeny, significantly extending the time span of this orogeny or representing a generally unrecognized orogenic event in the Paleozoic evolution of western North America. We propose a revised stratigraphic nomenclature for Mississippian strata in Nevada, based on detailed age control and the recognition of unconformities. This approach resolves the ambiguity of some stratigraphic names and emphasizes genetic relationships within the upper Paleozoic section. We take advantage of better stratigraphic understanding to propose two new stratigraphic units for southern and eastern Nevada: the middle Mississippian Gap Wash and Late Mississippian Captain Jack Formations.

History and Evolution of Precambrian plate tectonics

NASA Astrophysics Data System (ADS)

Fischer, Ria; Gerya, Taras

2014-05-01

Plate tectonics is a global self-organising process driven by negative buoyancy at thermal boundary layers. Phanerozoic plate tectonics with its typical subduction and orogeny is relatively well understood and can be traced back in the geological records of the continents. Interpretations of geological, petrological and geochemical observations from Proterozoic and Archean orogenic belts however (e.g., Brown, 2006), suggest a different tectonic regime in the Precambrian. Due to higher radioactive heat production the Precambrian lithosphere shows lower internal strength and is strongly weakened by percolating melts. The fundamental difference between Precambrian and Phanerozoic tectonics is therefore the upper-mantle temperature, which determines the strength of the upper mantle (Brun, 2002) and the further tectonic history. 3D petrological-thermomechanical numerical modelling experiments of oceanic subduction at an active plate at different upper-mantle temperatures show these different subduction regimes. For upper-mantle temperatures < 175 K above the present day value a subduction style appears which is close to present day subduction but with more frequent slab break-off. At upper-mantle temperatures 175 - 250 K above present day values steep subduction continues but the plates are weakened enough to allow buckling and also lithospheric delamination and drip-offs. For upper-mantle temperatures > 250 K above the present day value no subduction occurs any more. The whole lithosphere is delaminating and due to strong volcanism and formation of a thicker crust subduction is inhibited. This stage of 200-250 K higher upper mantle temperature which corresponds roughly to the early Archean (Abbott, 1994) is marked by strong volcanism due to sublithospheric decompression melting which leads to an equal thickness for both oceanic and continental plates. As a consequence subduction is inhibited, but a compressional setup instead will lead to orogeny between a continental

Formation of cratonic lithosphere during the initiation of plate tectonics

NASA Astrophysics Data System (ADS)

Moresi, L. N.; Beall, A.; Cooper, C. M.

2017-12-01

The Earth's oldest near-surface material, the cratonic crust, is typically underlain by unusually thick Archean lithosphere (<300 km). This cratonic lithosphere likely thickened in a high compressional stress environment. Mantle convection in the hotter Archean Earth would have imparted relatively low stresses on the lithosphere, whether or not tectonics was operating, so a high stress signal from the early Earth is paradoxical. We propose that a rapid transition, from a stagnant lid Earth to the onset of plate tectonics, generated the high stresses required to thicken the cratonic lithosphere. Numerical calculations are used to demonstrate that an existing buoyant and strong layer, representing harzburgite and felsic crust, can thicken and stabilize during the lid-breaking event. The peak compressional stress experienced by lithosphere is 3-4 higher than for the stagnant lid or mobile lid regimes immediately before and after. It is plausible that the cratonic lithosphere has still not returned to this high stress-state, explaining its stability. The lid-breaking thickening event reproduces craton features previously attributed to subduction: thrust structures, assembled crustal fragments and transport of basaltic upper crust to depths required to generate felsic melt. Palaeoarchean `pre-tectonic' structures can also survive the lid-breaking event, acting as strong crustal rafts. Together, the results indicate that the signature of a catastrophic switch, from a stagnant lid Earth to the initiation of plate tectonics, has been captured and preserved in the unusual characteristics of cratonic crust and lithosphere.

Early Holocene to present landscape dynamics of the tectonic lakes of west-central Mexico

NASA Astrophysics Data System (ADS)

Castillo, Miguel; Muñoz-Salinas, Esperanza; Arce, José Luis; Roy, Priyadarsi

2017-12-01

Paleoclimatic reconstructions from lake sediments of central Mexico indicate that the environmental conditions in the Holocene have oscillated from cool-dry to warm-wet, thus, landscape erosion rates have been modified accordingly. The Cenozoic tectonics and volcanic activity of west-central Mexico have produced a set of lakes in warmer and drier conditions compared to lakes of central Mexico. Nevertheless, the Holocene landscape dynamics for this area remains understudied. Using age-depth models, OSL and multi-element chemistry analysis of sediments in the lakes of San Marcos and Sayula we explore the landscape dynamics from early Holocene present of west-central Mexico. Our results indicate that the sedimentation rates in San Marcos Lake notably increased from 240 yr BP to the present. Since AD 1950 the sedimentation rate in Sayula Lake rose fourfold the rates of the last 2000 years. Analysis of OSL and chemistry of major elements of sediments indicates that IRSL/BLSL strongly correlates with Ti/Al (R2 = 0.93) and with the mean monthly rainfall (R2 = 0.70). We propose that the IRSL/BLSL can be used as a proxy to infer past changes in landscape dynamics. Analysis of climatic data from the 1950s to present indicates that rainfall, and consequently water runoff, is enhanced in summers free of ENSO conditions. Extreme one-day rainfall can, however, exceed mean seasonal rainfall and occur in all phases of ENSO. Droughts are particularly severe in the phase of La Niña. Our results indicate that the erosion rate in San Marcos Lake was high from ∼8000 to ∼7000 yr BP in a period coinciding with the advance and recession of glaciers in Central Mexico, however, the erosion rates in the last 165 years have surpassed the rates of the early to mid-Holocene. By constraining the age of sediment and using environmental proxies such as the Ti/Al and IRSL/BLSL from lake sediments of Sayula and San Marcos we present the first model of landscape dynamics of this part of Mexico

Plate tectonics, habitability and life

NASA Astrophysics Data System (ADS)

Spohn, Tilman; Breuer, Doris

2016-04-01

weathering of possible land surfaces and a biosphere could set up a CO2 sink that would further stabilize the temperature. As long as the planet keeps degassing CO2 at a sufficient rate, CO2 recycling through the mantle may not be required. However, this would require a sufficiently oxidized planet early on. If not sufficiently oxidized during accretion and core formation, oxidization of the planet would require cycling of matter between surface and interior reservoirs. Oxidization of an initially reduced Earth interior with the help of plate tectonics has been cited as a possible mechanism to allow the building up of oxygen in the terrestrial atmosphere around 2.3Ga b.p. (e.g., Catling and Claire, 2005), a pre-requisite for more evolved eukaryotic life. The oxidization would diminish a sink in the oxygen budget of the atmosphere by lowering the rate of outgassing of chemically reducing gases from the interior. Clearly, plate tectonics is a mechanism more potent of keeping a planet habitable and allow evolution of the biosphere than alternative concepts such as crust delamination. Catling, DC, Claire DW (2005), EPSL, 237, 1-20 Elkins-Tanton, L (2015) AGU Fall Meeting Abstract Tosi, N et al. (2016) EGU Abstract

Palaeozoic and Mesozoic tectonic implications of Central Afghanistan

NASA Astrophysics Data System (ADS)

Sliaupa, Saulius; Motuza, Gediminas

2017-04-01

The field and laboratory studies were carried out in Ghor Province situated in the central part of Afghanistan. It straddles juxtaposition of the Tajik (alternatively, North Afghanistan) and Farah Rod blocks separated by Band-e-Bayan zone. The recent studies indicate that Band-e-Bayan zone represents highly tectonised margin of the Tajik block (Motuza, Sliaupa, 2016). The Band-e-Bayan zone is the most representative in terms of sedimentary record. The subsidence trends and sediment lithologies suggest the passive margin setting during (Cambrian?) Ordovician to earliest Carboniferous times. A change to the foredeep setting is implied in middle Carboniferous through Early Permian; the large-thickness flysh-type sediments were derived from continental island arc provenance, as suggested by chemical composition of mudtstones. This stage can be correlated to the amalgamation of the Gondwana supercontinent. The new passive-margin stage can be inferred in the Band-e-Bayan zone and Tajik blocks in the Late Permian throughout the early Late Triassic that is likely related to breaking apart of Gondwana continent. A collisional event is suggested in latest Triassic, as seen in high-rate subsidence associating with dramatic change in litholgies, occurrence of volcanic rocks and granidoid intrusions. The continental volcanic island arc derived (based on geochemical indices) terrigens prevail at the base of Jurassic that were gradually replaced by carbonate platform in the Middle Jurassic pointing to cessation of the tectonic activity. A new tectonic episode (no deposition; and folding?) took place in the Tajik and Band-e-Bayan zone in Late Jurassic. The geological section of the Farah Rod block, situated to the south, is represented by Jurassic and Cretaceous sediments overlain by sporadic Cenozoic volcanic-sedimentary succession. The lower part of the Mesozoic succession is composed of terrigenic sediments giving way to upper Lower Cretaceous shallow water carbonates implying

Mantle structure and tectonic history of SE Asia

NASA Astrophysics Data System (ADS)

Hall, Robert; Spakman, Wim

2015-09-01

that detached in the Early Miocene such as the Sula slab, now found in the lower mantle north of Lombok, and the Proto-South China Sea slab now at depths below 700 km curving from northern Borneo to the Philippines. Based on our tectonic model we interpret virtually all features seen in upper mantle and lower mantle to depths of at least 1200 km to be the result of Cenozoic subduction.

Tectonic models for Yucca Mountain, Nevada

USGS Publications Warehouse

O'Leary, Dennis W.

2006-01-01

Performance of a high-level nuclear waste repository at Yucca Mountain hinges partly on long-term structural stability of the mountain, its susceptibility to tectonic disruption that includes fault displacement, seismic ground motion, and igneous intrusion. Because of the uncertainty involved with long-term (10,000 yr minimum) prediction of tectonic events (e.g., earthquakes) and the incomplete understanding of the history of strain and its mechanisms in the Yucca Mountain region, a tectonic model is needed. A tectonic model should represent the structural assemblage of the mountain in its tectonic setting and account for that assemblage through a history of deformation in which all of the observed deformation features are linked in time and space. Four major types of tectonic models have been proposed for Yucca Mountain: a caldera model; simple shear (detachment fault) models; pure shear (planar fault) models; and lateral shear models. Most of the models seek to explain local features in the context of well-accepted regional deformation mechanisms. Evaluation of the models in light of site characterization shows that none of them completely accounts for all the known tectonic features of Yucca Mountain or is fully compatible with the deformation history. The Yucca Mountain project does not endorse a preferred tectonic model. However, most experts involved in the probabilistic volcanic hazards analysis and the probabilistic seismic hazards analysis preferred a planar fault type model. ?? 2007 Geological Society of America. All rights reserved.

Inferred Early Permian Arc Rifting in Bogda Mountain, Southernmost of the Central Asia Orogenic Belt: Evidence from a Peperite Bearing Volcano-Sedimentary Succession

NASA Astrophysics Data System (ADS)

Memtimin, M.; Guo, Z.

2017-12-01

Late Paleozoic tectonic history, especially Carboniferous-Permian periods, of the Central Asia Orogenic Belt (CAOB) is considered to be the turning point for the termination of terrane amalgamation and closure of the Paleoasian Ocean. However, the debate about the paleoenvironment and tectonic setting of the region during the period is still not resolved. In this study, we report a set of volcano-sedimentary sequence in the Bogda Mountain of the southernmost of CAOB, which is associated with contemporaneous subaqueous emplacement of and interaction between mafic lava and carbonate sediments. The succession contains four distinct facies including closely packed pillow basalts, pillow basalts with interstitial materials, hyaloclastites and peperites. We discuss their formation and emplacement mechanism, interaction between hot magma-water/unconsolidated sediments and thermal metamorphism during the interaction. Textural features of the sequence, especially hyaloclastites and peperites, provide clear evidence for in situ autofragmentation of lava flows, synvolcanic sedimentation of carbonates, fuel coolant interaction when hot magma bulldozed into wet unconsolidated sediments, and represent autochthonous origin of the succession. Lateral transition of the lithofacies indicate a progressively deepening subaqueous environment, resembling a stepwise evolution from early stage of volcanic intrusion with lower lava flux in shallower water level to increasingly subsiding basin with more lava flux in greater depth. Previous studies determined that the mafic magma was intruded around the Carboniferous-Permian boundary ( 300Ma), and geochemical studies showed the magma was originated from dry depleted mantle with little crustal contamination. Nevertheless, the succession was thought to be fault related allochthones formation which was transferred in as part of a Carboniferous intraplate arc. Combining our findings with the previous study results, we propose a new model to

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

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

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

1991-02-01

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

North-South contraction of the mojave block and strike-slip tectonics in southern california.

PubMed

Bartley, J M; Glazner, A F; Schermer, E R

1990-06-15

The Mojave block of southern California has undergone significant late Cenozoic north-south contraction. This previously unappreciated deformation may account for part of the discrepancy between neotectonic and plate-tectonic estimates of Pacific-North American plate motion, and for part of the Big Bend in the San Andreas fault. In the eastern Mojave block, contraction is superimposed on early Miocene crustal extension. In the western Mojave block, contractional folds and reverse faults have been mistaken for extensional structures. The three-dimensional complexity of the contractional structures may mean that rigid-block tectonic models of the region based primarily on paleomagnetic data are unreliable.

Tectonic insight based on anisotropy of magnetic susceptibility and compaction studies in the Sierras Australes thrust and fold belt (southwest Gondwana boundary, Argentina)

NASA Astrophysics Data System (ADS)

Arzadún, Guadalupe; Tomezzoli, Renata N.; Cesaretti, Nora N.

2016-04-01

The Sierras Australes fold and thrust belt (Buenos Aires Province, Argentina) was in the southwestern Gondwanaland margin during the Paleozoic. The Tunas Formation (Permian) is exposed along the eastern part of it and continues eastward beneath the Claromecó Basin. Anisotropy of magnetic susceptibility (AMS) and compaction studies are described and compared with previous paleomagnetic studies with the aim of determining direction and magnitude of the main stresses acting during the sedimentation of the Tunas Formation. The anisotropy ellipsoids are triaxial with oblate or prolate shapes, reflecting different stages of layer parallel shortening during the evolution of the basin. Kmax axes trend NW-SE, parallel to the fold axes, while Kmin move from a horizontal (base) to a vertical orientation at the top of the succession, showing a change from a tectonic to almost a sedimentary fabric. The magnitude of anisotropy and compaction degree decreases toward the top of the succession. The AMS results are consistent with the outcrop structural observations and the compaction and paleomagnetic data. Regional pattern indicates a compression from the SW along this part of Gondwana, with a migration of the orogenic front and attenuation toward the NE in the foreland basin during the Upper Paleozoic. This deformation, locally assigned to the San Rafael noncollisional orogenic phase, is the result of the latitudinal movements toward the Equator of Gondwana (southern plates) and Laurentia (northern plates) during the Permian. This movement is the result of a rearrangement of the microplates that collided with Gondwana during the Late Devonian, to configure Pangea during the Triassic.

Earthquakes and plate tectonics

USGS Publications Warehouse

Spall, H.

1977-01-01

An explanation is to be found in plate tectonics, a concept which has revolutionized thinking in the Earth sciences in the last 10 years. The theory of plate tectonics combines many of the ideas about continental drift (originally proposed in 1912 by Alfred Wegener in Germany) and sea-floor spreading (suggested originally by Harry Hess of Princeton University). 

Tectonics and petroleum prospects in Bangladesh

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

Chowdhury, A.N.

1995-07-10

Bangladesh is a part of the Bengal basin, bordered to the west and northwest by Jurassic-early Cretaceous volcanic trap rocks of the Rajmahal Hills, underlain by Precambrian shield and Gondwana sediments. The Bengal basin is the largest delta basin (approximately 23,000 sq miles) in the world, at the confluence of the Ganges and Brahmaputra rivers. The deep sea fan complex that is being built outward into the Bay of Bengal has in excess of 12 km of sediments. Rate of sediment transportation within the basin, from the Himalayas and the mountains and hills to the north, east, and west, exceedsmore » 1 billion tons/year. The tectonic and sedimentary history of Bangladesh is favorable for hydrocarbon accumulation. The basin is an underexplored region of 207,000 sq km where only 52 exploratory wells have been drilled with a success rate of more than 30%. In addition to the folded belt in the east, where gas and some oil have been found, the Garo-Rajmahal gap to the north and the deep sea fan to the south merit detailed exploration using state of the art technology. The paper describes the tectonics, sedimentation, petroleum prospects, and seismic surveys.« less

Eolian Signal of the Onset of the Late Paleozoic Ice Age in North America Re-Deposited and Preserved As Paleo-Cave Sediments, Southwestern Colorado, U.S.a.

NASA Astrophysics Data System (ADS)

Evans, J. E.; Soreghan, M. J.

2014-12-01

The Molas Formation is a loessite consisting of reddish silt of Early Pennsylvanian (Bashkirian) age. U-Pb age spectra of accessory zircons indicate long-distance (>2000 km) transport from the Grenville province in northeastern North America plus sources from the peri-Gondwanan terranes in southeastern North America and local sources in the Ancestral Rocky Mountains uplift. These eolian sediments formed a blanket deposit <30 m thick above a paleokarst landscape in southwestern Colorado, infilling solution valleys and burying karst towers developed on the underlying Mississippian (Tournaisian-Visean) Leadville Limestone. The loessite is an eolian signal for the probable onset of glaciation at multiple locations in tectonically uplifted mountainous areas in North America. However, the loessite is easily eroded and has low preservation potential. Prior to lithification, significant amounts of the loess were remobilized and transported into the underlying karst system. As paleo-cave deposits, encased in limestone and dolostone, the silt-rich deposits have a higher preservation potential, and the eolian signal of the onset of the Late Paleozoic Ice Age in North America is still recognizable. However, the following signal modification processes need to be understood: (1) source area weathering and pedogenesis; (2) land-atmosphere transfer processes; (3) deposition effects of paleotopography, vegetation and moisture conditions, and infiltration into open fractures and/or the matrix of colluvium; (4) remobilization by surface runoff into open fractures and/or groundwater piping/sapping processes in loess soils; (5) transport into vadose and phreatic karst passageways by episodic ("streamflood") hydrologic events, forming event deposits (debrites, inundites, and jointites); (6) breakout dome collapse (forming interbedded cave sediments, karst breccias, and speleothems); (7) lithification and diagenesis; (8) post-lithification modification including pervasive hydrothermal

Evidence for Late-Paleozoic brine migration in Cambrian carbonate rocks of the central and southern Appalachians: Implications for Mississippi Valley-type sulfide mineralization

USGS Publications Warehouse

Hearn, P.P.; Sutter, J.F.; Belkin, H.E.

1987-01-01

Many Lower Paleozoic limestones and dolostones in the Valley and Ridge province of the central and southern Appalachians contain 10 to 25 weight percent authigenic potassium feldspar. This was considered to be a product of early diagenesis, however, 40Ar 39Ar analyses of overgrowths on detrital K-feldspar in Cambrian carbonate rocks from Pennsylvania, Maryland, Virginia, and Tennessee yield Late Carboniferous-Early Permian ages (278-322 Ma). Simple mass balance calculations suggest that the feldspar could not have formed isochemically, but required the flux of multiple pore volumes of fluid through the rocks, reflecting regional fluid migration events during the Late-Paleozoic Alleghanian orogeny. Microthermometric measurements of fluid inclusions in overgrowths on detrital K-feldspar and quartz grains from unmineralized rocks throughout the study area indicate homogenization temperatures from 100?? to 200??C and freezing point depressions of -14?? to -18.5??C (18-21 wt.% NaCl equiv). The apparent similarity of these fluids to fluid inclusions in ore and gangue minerals of nearby Mississippi Valley-type (MVT) deposits suggests that the regional occurrences of authigenic K-feldspar and MVT mineralization may be genetically related. This hypothesis is supported by the discovery of authigenic K-feldspar intergrown with sphalerite in several mines of the Mascot-Jefferson City District, E. Tennessee. Regional potassic alteration in unmineralized carbonate rocks and localized occurrences of MVT mineralization are both explainable by a gravity-driven flow model, in which deep brines migrate towards the basin margin under a hydraulic gradient established during the Alleghanian orogeny. The authigenic K-feldspar may reflect the loss of K during disequilibrium cooling of the ascending brines. MVT deposits are probably localized manifestations of the same migrating fluids, occurring where the necessary physical and chemical traps are present. ?? 1987.

Revisions to the original extent of the Devonian Shale-Middle and Upper Paleozoic Total Petroleum System

USGS Publications Warehouse

Enomoto, Catherine B.; Rouse, William A.; Trippi, Michael H.; Higley, Debra K.

2016-04-11

Technically recoverable undiscovered hydrocarbon resources in continuous accumulations are present in Upper Devonian and Lower Mississippian strata in the Appalachian Basin Petroleum Province. The province includes parts of New York, Pennsylvania, Ohio, Maryland, West Virginia, Virginia, Kentucky, Tennessee, Georgia, and Alabama. The Upper Devonian and Lower Mississippian strata are part of the previously defined Devonian Shale-Middle and Upper Paleozoic Total Petroleum System (TPS) that extends from New York to Tennessee. This publication presents a revision to the extent of the Devonian Shale-Middle and Upper Paleozoic TPS. The most significant modification to the maximum extent of the Devonian Shale-Middle and Upper Paleozoic TPS is to the south and southwest, adding areas in Tennessee, Georgia, Alabama, and Mississippi where Devonian strata, including potential petroleum source rocks, are present in the subsurface up to the outcrop. The Middle to Upper Devonian Chattanooga Shale extends from southeastern Kentucky to Alabama and eastern Mississippi. Production from Devonian shale has been established in the Appalachian fold and thrust belt of northeastern Alabama. Exploratory drilling has encountered Middle to Upper Devonian strata containing organic-rich shale in west-central Alabama. The areas added to the TPS are located in the Valley and Ridge, Interior Low Plateaus, and Appalachian Plateaus physiographic provinces, including the portion of the Appalachian fold and thrust belt buried beneath Cretaceous and younger sediments that were deposited on the U.S. Gulf Coastal Plain.

The effects of internal heating and large scale climate variations on tectonic bi-stability in terrestrial planets

NASA Astrophysics Data System (ADS)

Weller, M. B.; Lenardic, A.; O'Neill, C.

2015-06-01

We use 3D mantle convection and planetary tectonics models to explore the links between tectonic regimes and the level of internal heating within the mantle of a planet (a proxy for thermal age), planetary surface temperature, and lithosphere strength. At both high and low values of internal heating, for moderate to high lithospheric yield strength, hot and cold stagnant-lid (single plate planet) states prevail. For intermediate values of internal heating, multiple stable tectonic states can exist. In these regions of parameter space, the specific evolutionary path of the system has a dominant role in determining its tectonic state. For low to moderate lithospheric yield strength, mobile-lid behavior (a plate tectonic-like mode of convection) is attainable for high degrees of internal heating (i.e., early in a planet's thermal evolution). However, this state is sensitive to climate driven changes in surface temperatures. Relatively small increases in surface temperature can be sufficient to usher in a transition from a mobile- to a stagnant-lid regime. Once a stagnant-lid mode is initiated, a return to mobile-lid is not attainable by a reduction of surface temperatures alone. For lower levels of internal heating, the tectonic regime becomes less sensitive to surface temperature changes. Collectively our results indicate that terrestrial planets can alternate between multiple tectonic states over giga-year timescales. Within parameter space regions that allow for bi-stable behavior, any model-based prediction as to the current mode of tectonics is inherently non-unique in the absence of constraints on the geologic and climatic histories of a planet.

Regional geology and tectonics

USGS Publications Warehouse

Nokleberg, Warren J.; Bundtzen, Thomas K.; Nokleberg, Warren J.; Price, Raymond A.; Scholl, David W.; Stone, David B.

2017-01-01

This chapter describes the regional geology and tectonic origins of the major geologic units for the Northern Cordillera. The goals of the chapter are to: (1) provide a summary and regional overview of this vast region that contains a complicated geologic history; and (2) describe the major geologic units and tectonic events that cover a broad geologic time span from the Proterozoic to the Holocene (Recent).

Linking craton stability and deep earth processes using thermochronology; a case study in the Superior Province of the Canadian Shield.

NASA Astrophysics Data System (ADS)

Sturrock, C. P.; Flowers, R. M.; Zhong, S.; Metcalf, J. R.; Kohn, B. P.

2017-12-01

Ancient, cratonic continental interiors are often presumed to be stable in the long term, neither accumulating nor shedding significant amounts of overlying sediment. However, recent low-temperature thermochronologic work suggests that such long term stability is an overly simplistic view and that forces besides plate tectonics, such as dynamic topography, may play a significant role. New apatite (U-Th)/He (AHe) and apatite fission track (AFT) data from Archean-Proterozoic basement rocks along a 1400km NW-SE transect in the Superior Province of the Canadian Shield record a spatially variable thermal history for the craton in Paleozoic through the end of Mesozoic time. Dates range from 600­­­­­­±60 Ma (AHe) and 529­±48 Ma (AFT) in the west to 184±14 Ma (AHe) and 174±9 Ma (AFT) in the east. Tectonic activity within the Superior Province ceased by 1.8 Ga, with the latest activity at the margins ending at 1 Ga. Widespread resetting of both AHe and AFT systems post 1 Ga is most likely due to regional scale burial at one or more times since the Cambrian. The temperature sensitivity of the AHe and AFT systems (30-90°C and 60-120°C, respectively) require at least a few km of burial across the craton that has since been stripped away. Preliminary inverse thermal history models, utilizing geologic constraints and radiation damage effects on He diffusion in apatite, indicate significant reheating in the Paleozoic-early Mesozoic (37 to >120°C) and a possible lesser reheating event since the mid Mesozoic (<100°C). Making the simplified assumption of a 25°C/km geothermal gradient and 0°C surface temperature, burial in some areas must have been at least 2-5km in the Paleozoic and was <4km in the Mesozoic. These burial and denudation patterns do not correlate with global sea level changes, making dynamic topography a good candidate for a driving mechanism. New AHe data from kimberlites emplaced in the early to mid-Jurassic will provide an important new constraint

An enigmatic source of hematitic carbonate beds containing vast amounts of iron oxidizers in a paleozoic metamorphic complex, South Hungary, Geresd-Hills, Ófalu.

NASA Astrophysics Data System (ADS)

Jáger, Viktor; Dabi, Gergely; Menyhárt, Adrienn

2013-04-01

neptunian dykes, their age must be younger than the paleozoic metamorphic event. They must be older than the Early Cretaceous dyke emplacement in the region, based on cross-cutting relation with limonite stained calcite veins, related to the volcanic activity (Dabi et al., 2011) In this region (Tisza-megaunit) continental rift-related alkali basaltic submarine volcanism was widespread during the Early Cretaceous epoch, when hypabyssal basaltic bodies (intrusive pillow basalts) intruded into unconsolidated sediments. Along these magmatic bodies low temperature hydrothermal circulation of seawater hydrolyzed basaltic glass and mafic minerals, and huge amount of Fe(II) was released and got into the lime mud that was saturated with anaerobic water, where iron oxidizing microorganisms thrived (Jáger et al., 2012).We propose a very similar paleoenvironmental model for Ófalu occurence, where low temperature, reductive iron-rich hydrothermal fluids penetrated soft sediments and contributed to the flourishing of iron-oxidizers. Due to subsequent tectonic events, these iron-rich sediments got into the fissures of the Ófalu metamorphic complex. This model is strenghtened by some borehole and outcrops where the Lower Cretaceous interpillow sediments and hyaloclastites rich in iron oxydes and intrusive pillow basalt can be found close to our investigated section. (Hetényi et al., 1976) This study was supported by the Developing Competitiveness of Universities in the South Transdanubian Region (SROP-4.2.1.B-10/2/KONV-2010-0002). Dabi, G., Siklósy, Z., Schubert, F., Bajnóczi, B., M. Tóth, T., 2011. The relevance of vein texture in understanding the past hydraulic behaviour of a crystalline rock mass: reconstruction of the palaeohydrology of the Mecsekalja Zone, South Hungary. Geofluids, 11, 309-327. Hetényi, R., Földi, M., Hámor, G., Nagy, I., Bilik, I., Jantsky, B. 1976. Magyarázó a Mecsek hegység földtani térképéhez 10 000-es sorozat. MÁFI Budapest (in hungarian). J�

Large Sanjiang basin groups outside of the Songliao Basin Meso-Senozoic Tectonic-sediment evolution and hydrocarbon accumulation

NASA Astrophysics Data System (ADS)

Zheng, M.; Wu, X.

2015-12-01

The basis geological problem is still the bottleneck of the exploration work of the lager Sanjiang basin groups. In general terms, the problems are including the prototype basins and basin forming mechanism of two aspects. In this paper, using the field geological survey and investigation, logging data analysis, seismic data interpretation technical means large Sanjiang basin groups and basin forming mechanism of the prototype are discussed. Main draw the following conclusions： 1. Sanjiang region group-level formation can be completely contrasted. 2. Tension faults, compressive faults, shear structure composition and structure combination of four kinds of compound fracture are mainly developed In the study area. The direction of their distribution can be divided into SN, EW, NNE, NEE, NNW, NWW to other groups of fracture. 3. Large Sanjiang basin has the SN and the EW two main directions of tectonic evolution. Cenozoic basins in Sanjiang region in group formation located the two tectonic domains of ancient Paleo-Asian Ocean and the Pacific Interchange. 4. Large Sanjiang basin has experienced in the late Mesozoic tectonic evolution of two-stage and nine times. The first stage, developmental stage basement, they are ① Since the Mesozoic era and before the Jurassic; ② Early Jurassic period; The second stage, cap stage of development, they are ③ Late Jurassic depression developmental stages of compression; ④ Early Cretaceous rifting stage; ⑤ depression in mid-Early Cretaceous period; ⑥ tensile Early Cretaceous rifting stage; ⑦ inversion of Late Cretaceous tectonic compression stage; ⑧ Paleogene - Neogene; ⑨ After recently Ji Baoquan Sedimentary Ridge. 5. Large Sanjiang basin group is actually a residual basin structure, and Can be divided into left - superimposed (Founder, Tangyuan depression, Hulin Basin), residual - inherited type (Sanjiang basin), residual - reformed (Jixi, Boli, Hegang basin). there are two developed depression and the mechanism

Plate Tectonics: A Paradigm under Threat.

ERIC Educational Resources Information Center

Pratt, David

2000-01-01

Discusses the challenges confronting plate tectonics. Presents evidence that contradicts continental drift, seafloor spreading, and subduction. Reviews problems posed by vertical tectonic movements. (Contains 242 references.) (DDR)

Geologic map of the Big Delta B-2 quadrangle, east-central Alaska

USGS Publications Warehouse

Day, Warren C.; Aleinikoff, John N.; Roberts, Paul; Smith, Moira; Gamble, Bruce M.; Henning, Mitchell W.; Gough, Larry P.; Morath, Laurie C.

2003-01-01

New 1:63,360-scale geologic mapping of the Big Delta B-2 quadrangle provides important data on the structural setting and age of geologic units, as well as on the timing of gold mineralization plutonism within the Yukon-Tanana Upland of east-central Alaska. Gold exploration has remained active throughout the region in response to the discovery of the Pogo gold deposit, which lies within the northwestern part of the quadrangle near the south bank of the Goodpaster River. Geologic mapping and associated geochronological and geochemical studies by the U.S. Geological Survey (USGS) and the Alaska Department of Natural Resources, Division of Mining and Water Management, provide baseline data to help understand the regional geologic framework. Teck Cominco Limited geologists have provided the geologic mapping for the area that overlies the Pogo gold deposit as well as logistical support, which has lead to a much improved and informative product. The Yukon-Tanana Upland lies within the Tintina province in Alaska and consists of Paleozoic and possibly older(?) supracrustal rocks intruded by Paleozoic (Devonian to Mississippian) and Cretaceous plutons. The oldest rocks in the Big Delta B-2 quadrangle are Paleozoic gneisses of both plutonic and sedimentary origin. Paleozoic deformation, potentially associated with plutonism, was obscured by intense Mesozoic deformation and metamorphism. At least some of the rocks in the quadrangle underwent tectonism during the Middle Jurassic (about 188 Ma), and were subsequently deformed in an Early Cretaceous contractional event between about 130 and 116 Ma. New U-Pb SHRIMP data presented here on zircons from the Paleozoic biotite gneisses record inherited cores that range from 363 Ma to about 2,130 Ma and have rims of euhedral Early Cretaceous metamorphic overgrowths (116 +/- 4 Ma), interpreted to record recrystallization during Cretaceous west-northwest-directed thrusting and folding. U-Pb SHRIMP dating of monazite from a Paleozoic

Phanerozoic geological evolution of Northern and Central Africa: An overview

NASA Astrophysics Data System (ADS)

Guiraud, R.; Bosworth, W.; Thierry, J.; Delplanque, A.

2005-10-01

The principal paleogeographic characteristics of North and Central Africa during the Paleozoic were the permanency of large exposed lands over central Africa, surrounded by northerly and northwesterly dipping pediplanes episodically flooded by epicontinental seas related to the Paleotethys Ocean. The intra-continental Congo-Zaire Basin was also a long-lived feature, as well as the Somali Basin from Late Carboniferous times, in conjunction with the development of the Karoo basins of southern Africa. This configuration, in combination with eustatic sea-level fluctuations, had a strong influence on facies distributions. Significant transgressions occurred during the Early Cambrian, Tremadocian, Llandovery, Middle to Late Devonian, Early Carboniferous, and Moscovian. The Paleozoic tectonic history shows an alternation of long periods of predominantly gentle basin subsidence and short periods of gentle folding and occasionally basin inversion. Some local rift basins developed episodically, located mainly along the northern African-Arabian plate margin and near the West African Craton/Pan-African Belt suture. Several arches or spurs, mainly N-S to NE-SW trending and inherited from late Pan-African fault swarms, played an important role. The Nubia Province was the site of numerous alkaline anorogenic intrusions, starting in Ordovician times, and subsequently formed a large swell. Paleozoic compressional events occurred in the latest Early Cambrian ("Iskelian"), Medial Ordovician to earliest Silurian ("pre-Caradoc" and "Taconian"), the end Silurian ("Early Acadian" or "Ardennian"), mid-Devonian ("Mid-Acadian"), the end Devonian ("Late Acadian" or "Bretonnian"), the earliest Serpukhovian ("Sudetic"), and the latest Carboniferous-earliest Permian ("Alleghanian" or "Asturian"). The strongest deformations, including folding, thrusting, and active strike-slip faulting, were registered in Northwestern Africa during the last stage of the Pan-African Belt development around the

Deformation bands, early markers of tectonic activity in front of a fold-and-thrust belt: Example from the Tremp-Graus basin, southern Pyrenees, Spain

NASA Astrophysics Data System (ADS)

Robert, Romain; Robion, Philippe; Souloumiac, Pauline; David, Christian; Saillet, Elodie

2018-05-01

Strain localization in a porous calcarenite facies of the Aren formation in the Tremp basin was studied. This Maastrichtian syn-tectonic formation exposed in front of the Boixols thrust, in the Central South Pyrenean Zone, hosts bedding perpendicular deformation bands. These bands are organized in two major band sets, striking East-West and N-020 respectively. Both populations formed during early deformation stages linked to the growth of the fold and thrust. A magnetic fabric study (Anisotropy of Magnetic Susceptibility, AMS) was carried out to constrain the shortening direction responsible for the deformation bands development during the upper Cretaceous-Paleocene N-S contraction in the region, which allowed us to define populations of Pure Compaction Bands (PCB) and Shear Enhanced Compaction Bands (SECB) regarding their orientations compared to the shortening direction. Both sets are formed by cataclastic deformation, but more intense in the case of SECBs, which are also thinner than PCBs. The initial pore space is both mechanically reduced and chemically filled by several cementation phases. We propose a geomechanical model based on the regional context of layer parallel shortening, thrusting and strike-slip tectonics considering the burial history of the formation, in order to explain the development of both types of bands at remarkably shallow depths.

Geology of the Sierra de Fiambala, northwestern Argentina: implications for Early Palaeozoic Andean tectonics

USGS Publications Warehouse

Grissom, G.C.; DeBari, S.M.; Snee, L.W.

1998-01-01

This paper is included in the Special Publication entitled 'The proto- Andean margin of Gondwana', edited by R.J. Pankhurst and C.W. Rapela. Field mapping in conjunction with structural, metamorphic, and geochronological data document the tectono-thermal history of exhumed deep crustal rocks in the Sierra de Fiambala, NW Argentina. The range consists of two structural blocks distinguished by different metasedimentary sequences and different grades of metamorphism. Orthogneiss and paragneiss in the northern structural block may have a Precambrian history. Greenschist- to amphibolite-facies metamorphism, intrusion, and injection magmatization affected all rocks at 540-550 Ma. A subsequent event in the Late Cambrian to Ordovician (c.515 to 470 Ma) involved amphibolite- to granulite-facies metamorphism, mafic intrusion, and deformation, followed by cooling through mid-Palaeozoic time. The emplacement of Carboniferous (325-350 Ma) post-tectonic granites caused reheating and retrogression that was strongest toward the northeast part of the range. The Cambrian, Ordovician, and Carboniferous events in the Sierra de Fiambala were of regional extent as indicated by temporal correlations with events reported for other deep crustal rocks of the northern Sierras Pampeanas. Correlations between periods of intrusion and high-grade metamorphism in the northern Sierras Pampeanas and volcanic-sedimentary events in the adjacent supracrustal exposures confirm that rocks in the northern Sierras Pampeanas formed at deep (10-25 km) structural levels in the early Palaeozoic continental margin of Gondwana.

Fold interference pattern in thick-skinned tectonics; a case study from the external Variscan belt of Eastern Anti-Atlas, Morocco

NASA Astrophysics Data System (ADS)

Baidder, L.; Michard, A.; Soulaimani, A.; Fekkak, A.; Eddebbi, A.; Rjimati, E.-C.; Raddi, Y.

2016-07-01

Conflicting views are expressed in literature concerning fold interference patterns in thick-skinned tectonic context (e.g. Central Anti-Atlas and Rocky Mountains-Colorado areas). Such patterns are referred to superimposed events with distinct orientation of compression or to the inversion of paleofaults with distinct strike during a single compressional event. The present work presents a case study where both types of control on fold interference are likely to be combined. The studied folds occur in the Tafilalt-Maider area of eastern Anti-Atlas, i.e. in the E-trending foreland fold belt of the Meseta Variscan Orogen in the area where it connects with the SE-trending, intracontinental Ougarta Variscan belt. Detail mapping documents unusual fold geometries such as sigmoidal and croissant- or boomerang-shaped folds associated with a complex major fault pattern. The folded rock material corresponds to a 6-8 km-thick Cambrian-Serpukhovian sedimentary pile that includes alternating competent and incompetent formations. The basement of the Paleozoic succession is made up of rhomboedric tilted blocks that formed during the Cambrian rifting of north-western Gondwana and the Devonian dislocation of the Sahara platform. The latter event is responsible for an array of paleofaults bounding the Maider and South Tafilalt Devonian-Early Carboniferous basins with respect to the adjoining high axes. The Variscan Orogeny began during the Bashkirian-Westphalian with a N-S direction of shortening that converted the NW-trending Ougnat-Ouzina paleogeographic high into a mega dextral shear zone. Folds developed on top of a moving mosaic of basement blocks, being oriented en echelon on the inverted paleofaults or above intensely sheared fault zones. However, a dominantly NE-SW compression responsible for the building of the Ougarta belt also affected the studied area, presumably during the latest Carboniferous-Early Permian. The resulting fold interference pattern and peculiar geometries

Aeromagnetic anomalies reveal the link between magmatism and tectonics during the early formation of the Canary Islands.

PubMed

Blanco-Montenegro, Isabel; Montesinos, Fuensanta G; Arnoso, José

2018-01-08

The 3-D inverse modelling of a magnetic anomaly measured over the NW submarine edifice of the volcanic island of Gran Canaria revealed a large, reversely-magnetized, elongated structure following an ENE-WSW direction, which we interpreted as a sill-like magmatic intrusion emplaced during the submarine growth of this volcanic island, with a volume that could represent up to about 20% of the whole island. The elongated shape of this body suggests the existence of a major crustal fracture in the central part of the Canary Archipelago which would have favoured the rapid ascent and emplacement of magmas during a time span from 0.5 to 1.9 My during a reverse polarity chron of the Earth's magnetic field prior to 16 Ma. The agreement of our results with those of previous gravimetric, seismological and geodynamical studies strongly supports the idea that the genesis of the Canary Islands was conditioned by a strike-slip tectonic framework probably related to Atlas tectonic features in Africa. These results do not contradict the hotspot theory for the origin of the Canary magmatism, but they do introduce the essential role of regional crustal tectonics to explain where and how those magmas both reached the surface and built the volcanic edifices.

Drainage - Structure Correlation in tectonically active Regions: Case studies in the Bolivian and Colombian Andes

NASA Astrophysics Data System (ADS)

Zeilinger, Gerold; Parra, Mauricio; Kober, Florian

2017-04-01

Interandean Zone and the Subandean Zone (SA), exhibiting a catchment relief of up to 5000 m. While the structural trend in the EC is predominately NW-SE with a uniform (no preferred orientation) distribution of lower order fluvial channels, it changes in the SA into a distinct N-S trend with a pronounced E-W orientation of lower order fluvial channels. A similar pattern is recognized in the Eastern Andes of Colombia, where the structural trend is NE-SW. The Eastern Cordillera comprise a frontal thin-skinned Neogene and Paleogene domain (FR) and the more interior lower Cretaceous an Upper Paleozoic thick-skinned region (IR). The trend of higher order channels is, as expected, parallel to the structures in the interior parts and perpendicular in the frontal part. However, the trend of lower order channels reveal no directional correlation to the structural trend in the interior, but a significant correlation to the structures in the frontal range that suffered relatively to the interior domains younger deformation phases. We therefore postulate a dependency of the directional evolution of drainage patterns on the relative timing of tectonic activity. The only weakly preferred orientation of drainages in the interior parts (EC and IR) suggests a balance between structural control and drainage occupation, and higher maturity of the landscape. In contrast, the distinct pattern of drainages oblique to the structural grain in the frontal ranges (SA and FR) highlights the alignment of tributaries and suggests an ongoing tectonic control on drainage orientation. We test the hypothesis whether the correlation between the direction of small order rivers and the direction of structures can be used as a proxy for relative tectonic activity, which might be relevant in questions on 1) dominance of tectonics over climate, 2) dynamics of deformation propagation in fault-and-thrust-belts and 3) occurrence of higher erosion rates despite "limited" relief or threshold slopes. Ongoing efforts

Plate tectonics on Venus

NASA Technical Reports Server (NTRS)

Anderson, D. L.

1981-01-01

The high surface temperature of Venus implies a permanently buoyant lithosphere and a thick basaltic crust. Terrestrial-style tectonics with deep subduction and crustal recycling is not possible. Overthickened basaltic crust partially melts instead of converting to eclogite. Because mantle magmas do not have convenient access to the surface the Ar-40 abundance in the atmosphere should be low. Venus may provide an analog to Archean tectonics on the earth.

Strontium Isotopic Composition of Paleozoic Carbonate Rocks in the Nevada Test Site Vicinity, Clark, Lincoln, and Nye Counties, Nevada and Inyo County, California.

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

James B. Paces; Zell E. Peterman; Kiyoto Futa

2007-08-07

Ground water moving through permeable Paleozoic carbonate rocks represents the most likely pathway for migration of radioactive contaminants from nuclear weapons testing at the Nevada Test Site, Nye County, Nevada. The strontium isotopic composition (87Sr/86Sr) of ground water offers a useful means of testing hydrochemical models of regional flow involving advection and reaction. However, reaction models require knowledge of 87Sr/86Sr data for carbonate rock in the Nevada Test Site vicinity, which is scarce. To fill this data gap, samples of core or cuttings were selected from 22 boreholes at depth intervals from which water samples had been obtained previously aroundmore » the Nevada Test Site at Yucca Flat, Frenchman Flat, Rainier Mesa, and Mercury Valley. Dilute acid leachates of these samples were analyzed for a suite of major- and trace-element concentrations (MgO, CaO, SiO2, Al2O3, MnO, Rb, Sr, Th, and U) as well as for 87Sr/86Sr. Also presented are unpublished analyses of 114 Paleozoic carbonate samples from outcrops, road cuts, or underground sites in the Funeral Mountains, Bare Mountain, Striped Hills, Specter Range, Spring Mountains, and ranges east of the Nevada Test Site measured in the early 1990's. These data originally were collected to evaluate the potential for economic mineral deposition at the potential high-level radioactive waste repository site at Yucca Mountain and adjacent areas (Peterman and others, 1994). Samples were analyzed for a suite of trace elements (Rb, Sr, Zr, Ba, La, and Ce) in bulk-rock powders, and 87Sr/86Sr in partial digestions of carbonate rock using dilute acid or total digestions of silicate-rich rocks. Pre-Tertiary core samples from two boreholes in the central or western part of the Nevada Test Site also were analyzed. Data are presented in tables and summarized in graphs; however, no attempt is made to interpret results with respect to ground-water flow paths in this report. Present-day 87Sr/86Sr values are compared

Strontium Isotopic Composition of Paleozoic Carbonate Rocks in the Nevada Test Site Vicinity, Clark, Lincoln, and Nye Counties, Nevada, and Inyo County, California

USGS Publications Warehouse

Paces, James B.; Peterman, Zell E.; Futo, Kiyoto; Oliver, Thomas A.; Marshall, Brian D.

2007-01-01

Ground water moving through permeable Paleozoic carbonate rocks represents the most likely pathway for migration of radioactive contaminants from nuclear weapons testing at the Nevada Test Site, Nye County, Nevada. The strontium isotopic composition (87Sr/86Sr) of ground water offers a useful means of testing hydrochemical models of regional flow involving advection and reaction. However, reaction models require knowledge of 87Sr/86Sr data for carbonate rock in the Nevada Test Site vicinity, which is scarce. To fill this data gap, samples of core or cuttings were selected from 22 boreholes at depth intervals from which water samples had been obtained previously around the Nevada Test Site at Yucca Flat, Frenchman Flat, Rainier Mesa, and Mercury Valley. Dilute acid leachates of these samples were analyzed for a suite of major- and trace-element concentrations (MgO, CaO, SiO2, Al2O3, MnO, Rb, Sr, Th, and U) as well as for 87Sr/86Sr. Also presented are unpublished analyses of 114 Paleozoic carbonate samples from outcrops, road cuts, or underground sites in the Funeral Mountains, Bare Mountain, Striped Hills, Specter Range, Spring Mountains, and ranges east of the Nevada Test Site measured in the early 1990's. These data originally were collected to evaluate the potential for economic mineral deposition at the potential high-level radioactive waste repository site at Yucca Mountain and adjacent areas (Peterman and others, 1994). Samples were analyzed for a suite of trace elements (Rb, Sr, Zr, Ba, La, and Ce) in bulk-rock powders, and 87Sr/86Sr in partial digestions of carbonate rock using dilute acid or total digestions of silicate-rich rocks. Pre-Tertiary core samples from two boreholes in the central or western part of the Nevada Test Site also were analyzed. Data are presented in tables and summarized in graphs; however, no attempt is made to interpret results with respect to ground-water flow paths in this report. Present-day 87Sr/86Sr values are compared to values

Silurian extension in the Upper Connecticut Valley, United States and the origin of middle Paleozoic basins in the Québec embayment

USGS Publications Warehouse

Rankin, D.W.; Coish, R.A.; Tucker, R.D.; Peng, Z.X.; Wilson, S.A.; Rouff, A.A.

2007-01-01

Pre-Silurian strata of the Bronson Hill arch (BHA) in the Upper Connecticut Valley, NH-VT are host to the latest Ludlow Comerford Intrusive Suite consisting, east to west, of a mafic dike swarm with sheeted dikes, and an intrusive complex. The rocks are mostly mafic but with compositions ranging from gabbro to leucocratic tonalite. The suite is truncated on the west by the Monroe fault, a late Acadian thrust that carries rocks of the BHA westward over Silurian-Devonian strata of the Connecticut Valley-Gaspe?? trough (CVGT). Dikes intrude folded strata with a pre-intrusion metamorphic fabric (Taconian?) but they experienced Acadian deformation. Twenty fractions of zircon and baddeleyite from three sample sites of gabbrodiorite spanning nearly 40 km yield a weighted 207Pb/206Pb age of 419 ?? 1 Ma. Greenschist-facies dikes, sampled over a strike distance of 35 km, were tholeiitic basalts formed by partial melting of asthenospheric mantle, with little or no influence from mantle or crustal lithosphere. The dike chemistry is similar to mid-ocean ridge, within-plate, and back-arc basin basalts. Parent magmas originated in the asthenosphere and were erupted through severely thinned lithosphere adjacent to the CVGT. Extensive middle Paleozoic basins in the internides of the Appalachian orogen are restricted to the Que??bec embayment of the Laurentian rifted margin, and include the CVGT and the Central Maine trough (CMT), separated from the BHA by a Silurian tectonic hinge. The NE-trending Comerford intrusions parallel the CVGT, CMT, and the tectonic hinge, and indicate NW-SE extension. During post-Taconian convergence, the irregular margins of composite Laurentia and Avalon permitted continued collision in Newfoundland (St. Lawrence promontory) and coeval extension in the Que??bec embayment. Extension may be related to hinge retreat of the northwest directed Brunswick subduction complex and rise of the asthenosphere following slab break-off. An alternative hypothesis is

Geologic Map of the Big Delta B-1 Quadrangle, East-Central Alaska

USGS Publications Warehouse

Day, Warren C.; O'Neill, J. Michael; Aleinikoff, John N.; Green, Gregory N.; Saltus, Richard W.; Gough, Larry P.

2007-01-01

Geologic mapping and U-Pb age dating of rocks from the Big Delta B-1 quadrangle, east-central Alaska, have yielded new insights into the geology and gold mineral resource for the headwater region of the Goodpaster River, northeast of Delta, Alaska. The area lies within the Yukon-Tanana Upland and is underlain by Paleozoic and Cretaceous crystalline bedrock and contains several gold mines and prospects. The Paleozoic units include biotite gneiss, quartzite interlayered with metapelite, and amphibolite gneiss. The Paleozoic units were intruded during the Devonian by tonalitic to granitic plutons, which, as a result of regional Mesozoic metamorphism and tectonism, are now augen gneiss and biotite orthogneiss. The Mesozoic regional metamorphism and ductile deformation of the entire Yukon-Tanana Upland culminated by the Late Cretaceous (about 116 Ma) as a result of northwest-directed regional transpression along the southern margin of the North American craton. This dynamothermal episode was followed by invasion of syn- to post-tectonic granodioritic to granitic batholiths during the Late Cretaceous (about 113-107 Ma), followed by a pulse of 100-95 Ma quartz feldspar porphyry intrusions. Gold mineralization is spatially associated with various post-tectonic Late Cretaceous granitic dikes and batholiths throughout the quadrangle. A northeast-trending structural corridor, described herein as the Black Mountain tectonic zone, both controlled the emplacement of some of the Cretaceous intrusive rocks, gold deposits, and prospects, as well as formed a deep-seated crustal conduit along which a subsequent rhyolite flow-dome complex erupted during the Paleocene. Tertiary uplift and erosion resulted in the development of extensive erosional pediments. Quaternary alpine glaciation carved beautiful, broad valleys in the eastern part of the quadrangle, leaving behind terminal moraines in the headwater region of the Goodpaster river drainage. Continued Holocene to Recent deformation

Preliminary publications Book 1 from Project on Mineral Resources, Metallogenesis and Tectonics of Northeast Asia

USGS Publications Warehouse

Ariunbileg, Sodov; Badarch, Gombosuren; Berzin, Nikolai A.; Bulgatov, Alexander N.; Chimed, Noosoi; Deikunenko, Aleksey V.; Dejidmaa, Gunchin; Diggles, Michael F.; Distanov, Elimir G.; Dorjgotov, Dangindorjiin; Gerel, Ochir; Gordienko, Ivan V.; Gotovsuren, Ayurzana; Hwang, Duk-Hwan; Khanchuk, Alexander I.; Koch, Richard D.; Miller, Robert J.; Nokleberg, Warren J.; Obolenskiy, Alexander A.; Ogasawara, Masatsugu; Orolmaa, Demberel; Oxman, Vladimir S.; Parfenov, Leonid M.; Popeko, Ludmila I.; Prokopiev, Andrey V.; Smelov, Alexander P.; Sotnikov, Vitaliy I.; Sudo, Sadahisa; Timofeev, Vladimir F.; Tret'yakov, Felix F.; Vernikovsky, Valery A.; Ye, Mao; Zadgenizov, Alexander P.

1999-01-01

This report consists of preliminary data tables, maps, and interpretative articles compiled in late 1997 and early 1998 for a new project on the Mineral Resources, Metallogenesis, and Tectonics of Northeast Asia (Eastern and Southern Siberia, Mongolia, North-eastern China, South Korea, and Japan).

Petrogenesis and tectonic setting of the Devonian Xiqin A-type granite in the northeastern Cathaysia Block, SE China

NASA Astrophysics Data System (ADS)

Cai, Da-wei; Tang, Yong; Zhang, Hui; Lv, Zheng-Hang; Liu, Yun-long

2017-06-01

Most Silurian-Devonian granites in South China are S- or I-type granites, which are suggested to be petrogenetically related to the Wuyi-Yunkai orogeny. In this paper, we present the detailed LA-ICP-MS zircon U-Pb dating, major and trace element geochemical, and Nd-Hf isotopic data for Xiqin A-type granites in the northeastern Cathaysia Block, SE China. Zircon U-Pb dating results show that the Xiqin granites were emplaced at about 410 Ma, indicating that they were generated at the end of Wuyi-Yunkai orogeny. These granites are high in K2O + Na2O (6.31-8.79 wt%), high field strength elements (Zr + Nb + Ce + Y = 427-699 ppm), rare earth elements (total REE = 221-361 ppm) as well as high Ga/Al ratios (10,000 Ga/Al = 2.50-3.10), and show characteristics typical of A-type granites. εHf(t) values of the Xiqin granites mainly vary from -0.4 to -3.1 and yield Mesoproterozoic T2DM(Hf) (mainly ranging from 1.29 to 1.45 Ga). The εNd(t) values are from -1.23 to -2.11 and T2DM(Nd) vary from 1.25 to 1.32 Ga. These isotopic data suggest that the Xiqin granites were generated by partial melting of metavolcanic rocks with minor metasedimentary rocks in the lower crust. Our data on the Xiqin granites, coupled with previous studies of Silurian-Devonian magmatism, suggest that the tectonic regime had changed to a strongly post-collisional extension environment in the Wuyi-Yunkai orogen at least since 410 Ma, and that delamination, which accounts for the change in stress from the compression to extension and asthenospheric upwelling during the early Paleozoic, plays a significant role in the generation of Xiqin A-type granites.

Resistant tissues of modern marchantioid liverworts resemble enigmatic Early Paleozoic microfossils

PubMed Central

Graham, Linda E.; Wilcox, Lee W.; Cook, Martha E.; Gensel, Patricia G.

2004-01-01

Absence of a substantial pretracheophyte fossil record for bryophytes (otherwise predicted by molecular systematics) poses a major problem in our understanding of earliest land-plant structure. In contrast, there exist enigmatic Cambrian–Devonian microfossils (aggregations of tubes or sheets of cells or possibly a combination of both) controversially interpreted as an extinct group of early land plants known as nematophytes. We used an innovative approach to explore these issues: comparison of tube and cell-sheet microfossils with experimentally degraded modern liverworts as analogues of ancient early land plants. Lower epidermal surface tissues, including rhizoids, of Marchantia polymorpha and Conocephalum conicum were resistant to breakdown after rotting for extended periods or high-temperature acid treatment (acetolysis), suggesting fossilization potential. Cell-sheet and rhizoid remains occurred separately or together depending on the degree of body degradation. Rhizoid break-off at the lower epidermal surface left rimmed pores at the centers of cell rosettes; these were similar in structure, diameter, and distribution to pores characterizing nematophyte cell-sheet microfossils known as Cosmochlaina. The range of Marchantia rhizoid diameters overlapped that of Cosmochlaina pores. Approximately 14% of dry biomass of Marchantia vegetative thalli and 40% of gametangiophores was resistant to acetolysis. Pre- and posttreatment cell-wall autofluorescence suggested the presence of phenolic compounds that likely protect lower epidermal tissues from soil microbe attack and provide dimensional stability to gametangiophores. Our results suggest that at least some microfossils identified as nematophytes may be the remains of early marchantioid liverworts similar in some ways to modern Marchantia and Conocephalum. PMID:15263095

Late Paleozoic onset of subduction and exhumation at the western margin of Gondwana (Chilenia Terrane): Counterclockwise P-T paths and timing of metamorphism of deep-seated garnet-mica schist and amphibolite of Punta Sirena, Coastal Accretionary Complex, central Chile (34° S)

NASA Astrophysics Data System (ADS)

Hyppolito, T.; García-Casco, A.; Juliani, C.; Meira, V. T.; Hall, C.

2014-10-01

by the non-coaxial exhumation-related foliation S2. During exhumation and retrograde D2 deformation, the garnet-mica schist and amphibolite were tectonically mingled at a depth of ca. 30 km at ca. 315 Ma. We propose that the Punta Sirena unit comprises a “pseudo”-coherent sequence formed by heterogeneous lithologies that followed non-chaotic exhumation mingling, now representing the remnants of the fossil subduction channel developed at the onset of the Late Paleozoic subduction at central Chile.

Depositional systems and stratigraphy of Paleozoic and Lower Mesozoic rocks in outcrop, Tassili region, southwest Algeria

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

Hertig, S.P.; Tye, R.S.; Coffield, D.Q.

1991-08-01

Paleozoic to Lower Mesozoic strata of the southeastern Algerian Tassili are traditionally subdivided by regionally extensive unconformities such as the Pan African, Taconic, Caledonian, and Hercynian. Using outcrop data from southeastern Algeria, this classic approach is modified by reinterpreting the genesis of these unconformities and rock sequences. Five prominent sequences, defined within the Paleozoic and lower Mesozoic section, usually consist of a succession of lowstand, transgressive, and highstand system tracts separated by sequence boundaries or transgressive surfaces. The Pan-African, Taconic, Caledonian, and Hercynian unconformities are sequence boundaries. Important sequence boundaries also occur within the Ordovician and Silurian sections. These sequencesmore » correlate with subsurface data in the Illizi basin and provide a framework for renewed exploration in the subsurface of the Algerian Sahara, where more than 30 billion bbl of recoverable oil and oil equivalent have been generated and trapped.« less

Spiral tectonics

NASA Astrophysics Data System (ADS)

Hassan Asadiyan, Mohammad

2014-05-01

Spiral Tectonics (ST) is a new window to global tectonics introduced as alternative model for Plate Tectonics (PT). ST based upon Dahw(rolling) and Tahw(spreading) dynamics. Analogues to electric and magnetic components in the electromagnetic theory we could consider Dahw and Tahw as components of geodynamics, when one component increases the other decreases and vice versa. They are changed to each other during geological history. D-component represents continental crust and T-component represents oceanic crust. D and T are two arm of spiral-cell. T-arm 180 degree lags behind D-arm so named Retard-arm with respect to D or Forward-arm. It seems primary cell injected several billions years ago from Earth's center therefore the Earth's core was built up first then mantel and finally the crust was build up. Crust building initiate from Arabia (Mecca). As the universe extended gravitation wave swirled the earth fractaly along cycloid path from big to small scale. In global scale (order-0) ST collect continents in one side and abandoned Pacific Ocean in the other side. Recent researches also show two mantels upwelling in opposite side of the Earth: one under Africa (tectonic pose) and the other under Pacific Ocean (tectonic tail). In higher order (order-1) ST build up Africa in one side and S.America in the other side therefore left Atlantic Ocean meandered in between. In order-n e.g. Khoor Musa and Bandar-Deylam bay are seen meandered easterly in the Iranian part but Khoor Abdullah and Kuwait bay meandered westerly in the Arabian part, they are distributed symmetrically with respect to axis of Persian Gulf(PG), these two are fractal components of easterly Caspian-wing and westerly Black Sea-wing which split up from Anatoly. Caspian Sea and Black Sea make two legs of Y-like structure, this shape completely fitted with GPS-velocity map which start from PG and split up in the Catastrophic Point(Anatoly). We could consider PG as remnants of Ancient Ocean which spent up

An intramontane pull-apart basin in tectonic escape deformation: Elbistan Basin, Eastern Taurides, Turkey

NASA Astrophysics Data System (ADS)

Yusufoğlu, H.

2013-04-01

The Elbistan Basin in the east-Central Anatolia is an intramontane structural depression in the interior part of the Anatolide-Tauride Platform. The Neogene fill in and around Elbistan Basin develops above the Upper Devonian to lower Tertiary basement and comprises two units separated by an angular unconformity: (1) intensely folded and faulted Miocene shallow marine to terrestrial and lacustrine sediments and (2) nearly flat-lying lignite-bearing lacustrine (lower unit) and fluvial (upper unit) deposits of Plio-Quaternary Ahmetçik Formation. The former is composed of Lower-Middle Miocene Salyan, Middle-upper Middle Miocene Gövdelidağ and Upper Miocene Karamağara formations whereas the latter one is the infill of the basin itself in the present configuration of the Elbistan Basin. The basin is bound by normal faults with a minor strike-slip component. It commenced as an intramontane pull-apart basin and developed as a natural response to Early Pliocene tectonic escape-related strike-slip faulting subsequent to post-collisional intracontinental compressional tectonics during which Miocene sediments were intensely deformed. The Early Pliocene time therefore marks a dramatic changeover in tectonic regime and is interpreted as the beginning of the ongoing last tectonic evolution and deformation style in the region unlike to previous views that it commenced before that time. Consequently, the Elbistan Basin is a unique structural depression that equates the extensional strike-slip regime in east-Central Anatolia throughout the context of the neotectonical framework of Turkey across progressive collision of Arabia with Eurasia. Its Pliocene and younger history differs from and contrasts with that of the surrounding pre-Pliocene basins such as Karamağara Basin, on which it has been structurally superimposed.

Seismic images of a tectonic subdivision of the Greenville Orogen beneath lakes Ontario and Erie

USGS Publications Warehouse

Forsyth, D. A.; Milkereit, B.; Davidson, A.; Hanmer, S.; Hutchinson, Deborah R.; Hinze, W. J.; Mereu, R.F.

1994-01-01

New seismic data from marine air-gun and Vibroseis profiles in Lake Ontario and Lake Erie provide images of subhorizontal Phanerozoic sediments underlain by a remarkable series of easterly dipping reflections that extends from the crystalline basement to the lower crust. These reflections are interpreted as structural features of crustal-scale subdivisions within the Grenville Orogen. Broadly deformed, imbricated, and overlapping thrust sheets within the western Central Metasedimentary Belt are succeeded to the west by a complex zone of easterly dipping, apparent thrust faults that are interpreted as a southwest subsurface extension of the boundary zone between the Central Metasedimentary Belt and the Central Gneiss Belt. The interpreted Central Metasedimentary Belt boundary zone has a characteristic magnetic anomaly that provides a link from the adjacent ends of lakes Ontario and Erie to structures exposed 150 km to the north. Less reflective, west-dipping events are interpreted as structures within the eastern Central Gneiss Belt. The seismic interpretation augments current tectonic models that suggest the exposed ductile structures formed at depth as a result of crustal shortening along northwest-verging thrust faults. Relatively shallow reflections across the boundary region suggest local, Late Proterozoic extensional troughs containing post-Grenville sediments, preserved possibly as a result of pre-Paleozoic reactivation of basement structures.

Geohistory analysis of the Santa Maria basin, California, and its relationship to tectonic evolution of the continental margin

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

McCrory, P.A.; Arends, R.G.; Ingle, J.C. Jr.

1991-02-01

The Santa Maria basin of central California is a geologically complex area located along the tectonically active California continental margin. The record of Cenozoic tectonism preserved in Santa Maria strata provides an opportunity to compare the evolution of the region with plate tectonic models for Cenozoic interactions along the margin. Geohistory analysis of Neogene Santa Maria basin strata provides important constraints for hypotheses of the tectonic evolution of the central California margin during its transition from a convergent to a transform plate boundary. Preliminary analyses suggest that the tectonic evolution of the Santa Maria area was dominated by coupling betweenmore » adjacent oceanic plates and the continental margin. This coupling is reflected in the timing of major hiatuses within the basin sedimentary sequence and margin subsidence and uplift which occurred during periods of tectonic plate adjustment. Stratigraphic evidence indicates that the Santa Maria basin originated on the continental shelf in early Miocene time. A component of margin subsidence is postulated to have been caused by cessation of spreading on adjacent offshore microplates approximately 19-18 ma. A sharp reduction in rate of tectonic subsidence in middle Miocene time, observed in the Santa Maria basin both onshore and offshore, was coeval with rotation of crustal blocks as major shearing shifts shoreward. Tectonic uplift of two eastern sites, offshore Point Arguello and near Point Sal, in the late Miocene may have been related to a change to transpressional motion between the Pacific and North American plates, as well as to rotation of the western Transverse Ranges in a restraining geometry.« less

A synthesis of mineralization styles and geodynamic settings of the Paleozoic and Mesozoic metallic ore deposits in the Altay Mountains, NW China

NASA Astrophysics Data System (ADS)

Yang, Fuquan; Geng, Xinxia; Wang, Rui; Zhang, Zhixin; Guo, Xuji

2018-06-01

The Altay Mountains within the Xinjiang region of northwestern China hosts major metallic ore deposits. Here we review the geological characteristics, metallogenic features and tectonic settings of these deposits. The metallic ore deposits in the Altay Mountains occur mainly within four regions: North Altay, Central Altay, South Altay and Erqis. We recognize seven types of metallic ore deposits in the Altay Mountains: VMS, submarine volcanogenic iron, magmatic, skarn, pegmatite, hydrothermal vein (Cu-Zn, Fe) and orogenic gold. Among these types, the VMS, pegmatite, orogenic gold and skarn deposits are the most common. Most of the rare metal pegmatite deposits are distributed in Central Altay, with only a few in South Altay. The VMS, submarine volcanogenic type iron and skarn-type deposits are distributed in South Altay, whereas the orogenic-type gold deposits are distributed in the Erqis Fault belt. The hydrothermal vein-type deposits occur in the Erqis Fault belt and Chonghu'er Basin in South Altay. Magmatic-type deposits are mostly in the Erqis Fault belt and Central Altay. Based on isotopic age data, the VMS, submarine volcanogenic-type Fe and skarn-type Cu, Pb, Zn, Fe mineralization occurred during Early-Middle Devonian (∼410-377 Ma), orogenic-type Au, magmatic-type Cu-Ni, and a small number of skarn-type Fe, hydrothermal vein-type Cu-Zn, pegmatite-type rare-metal deposits in Early-Middle Permian (293-261 Ma), pegmatite-type rare-metal deposits, few skarn-type Fe deposit in Early-Middle Triassic (248-232 Ma), and dominantly represented by pegmatite-type rare-metal deposits in Late Triassic-Early Jurassic (223-180 Ma). The metallic ore deposits in the Altay Mountains formed in various tectonic settings, such as the Early-Middle Devonian continental arc and oceanic island arc, Early-Middle Permian post-collisional extensional setting, and Triassic-Early Jurassic intracontinental setting.

Geological and Tectonic Evidence for the Formation and Extensional Collapse of the West Antarctic Plateau: Implications for the Formation of the West Antarctic Rift System and the Transantarctic Mountains

NASA Astrophysics Data System (ADS)

Fitzgerald, P. G.; Studinger, M.; Bialas, R. W.; Buck, W.

2007-12-01

The Transantarctic Mountains (TAM), the world's longest and highest non-contractional intracontinental mountain belt, define the western boundary of the West Antarctic rift system (WARS). The WARS is a broad region of extended continental lithosphere, ca. 750-1000 km wide, lying dominantly below sea-level. A new model (Bialas et al., 2007), proposes that a region of thickened continental crust and high-standing topography, the "West Antarctic Plateau", underwent extensional collapse to leave a remnant edge representing the proto-TAM. Tectonic and paleogeographic reconstructions indicate the plateau formed inboard of a continental arc along the paleo- Pacific margin of Antarctica, active throughout the Paleozoic until the late Mesozoic. This high-standing region was responsible for confining sediments (Beacon Supergroup) to elongate basins along the length of the TAM. Much of the present region of the WARS has been correlated with the Lachlan Fold belt of southeastern Australia. This belt formed from the Ordovician to Carboniferous during back-arc basin formation associated with slab roll- back with short periods of compression. Convergence along the paleo-Pacific margin, perhaps enhanced by subduction of more buoyant oceanic lithosphere as the Phoenix-Pacific ridge was obliquely subducted, resulted in crustal thickening and formation of high-standing terrain (the plateau). Extensional collapse of the plateau most likely began in the Jurassic during initial rifting between East and West Antarctica, but was mainly accomplished during distributed rifting in the Cretaceous (ca. 105-85) following subduction of the Phoenix-Pacific ridge and prior to the separation of New Zealand from Marie Byrd Land. Continued formation of the TAM continued in the Cenozoic concomitant with extension in the WARS that was localized along its western margin adjacent to the TAM. Glacial erosion in the Oligocene and early-Miocene enhanced peak height in the TAM. In this presentation we

Plate tectonics, damage and inheritance.

PubMed

Bercovici, David; Ricard, Yanick

2014-04-24

The initiation of plate tectonics on Earth is a critical event in our planet's history. The time lag between the first proto-subduction (about 4 billion years ago) and global tectonics (approximately 3 billion years ago) suggests that plates and plate boundaries became widespread over a period of 1 billion years. The reason for this time lag is unknown but fundamental to understanding the origin of plate tectonics. Here we suggest that when sufficient lithospheric damage (which promotes shear localization and long-lived weak zones) combines with transient mantle flow and migrating proto-subduction, it leads to the accumulation of weak plate boundaries and eventually to fully formed tectonic plates driven by subduction alone. We simulate this process using a grain evolution and damage mechanism with a composite rheology (which is compatible with field and laboratory observations of polycrystalline rocks), coupled to an idealized model of pressure-driven lithospheric flow in which a low-pressure zone is equivalent to the suction of convective downwellings. In the simplest case, for Earth-like conditions, a few successive rotations of the driving pressure field yield relic damaged weak zones that are inherited by the lithospheric flow to form a nearly perfect plate, with passive spreading and strike-slip margins that persist and localize further, even though flow is driven only by subduction. But for hotter surface conditions, such as those on Venus, accumulation and inheritance of damage is negligible; hence only subduction zones survive and plate tectonics does not spread, which corresponds to observations. After plates have developed, continued changes in driving forces, combined with inherited damage and weak zones, promote increased tectonic complexity, such as oblique subduction, strike-slip boundaries that are subparallel to plate motion, and spalling of minor plates.

Burke new Tectonics editor

NASA Astrophysics Data System (ADS)

Kevin C. Burke, National Academy of Sciences/ National Research Council (NAS/NRC), assumed responsibilities as Editor in Chief of the American Geophysical Union (AGU) journal Tectonics at the beginning of 1990, taking over from Raymond A. Price, Queens University, Kingston, Ontario. Asger Berthelsen, University of Copenhagen, Denmark, continues as the European Editor, and Paul F. Hoffman, Geological Society of Canada, assumes the task of North American Editor. Tectonics is a joint publication of AGU and the European Geophysical Society.

Tectonic and metallogenic model for northeast Asia

USGS Publications Warehouse

Parfenov, Leonid M.; Nokleberg, Warren J.; Berzin, Nikolai A.; Badarch, Gombosuren; Dril, Sergy I.; Gerel, Ochir; Goryachev, Nikolai A.; Khanchuk, Alexander I.; Kuz'min, Mikhail I.; Prokopiev, Andrei V.; Ratkin, Vladimir V.; Rodionov, Sergey M.; Scotese, Christopher R.; Shpikerman, Vladimir I.; Timofeev, Vladimir F.; Tomurtogoo, Onongin; Yan, Hongquan; Nokleberg, Warren J.

2011-01-01

This document describes the digital files in this report that contains a tectonic and metallogenic model for Northeast Asia. The report also contains background materials. This tectonic and metallogenic model and other materials on this report are derived from (1) an extensive USGS Professional Paper, 1765, on the metallogenesis and tectonics of Northeast Asia that is available on the Internet at http://pubs.usgs.gov/pp/1765/; and (2) the Russian Far East parts of an extensive USGS Professional Paper, 1697, on the metallogenesis and tectonics of the Russian Far East, Alaska, and the Canadian Cordillera that is available on the Internet at http://pubs.usgs.gov/pp/pp1697/. The major purpose of the tectonic and metallogenic model is to provide, in movie format, a colorful summary of the complex geology, tectonics, and metallogenesis of the region. To accomplish this goal four steps were taken: (1) 13 time-stage diagrams, from the late Neoproterozoic (850 Ma) through the present (0 Ma), were adapted, generalized, and transformed into color static time-stage diagrams; (2) the 13 time-stage diagrams were placed in a computer morphing program to produce the model; (3) the model was examined and each diagram was successively adapted to preceding and subsequent diagrams to match the size and surface expression of major geologic units; and (4) the final version of the model was produced in successive iterations of steps 2 and 3. The tectonic and metallogenic model and associated materials in this report are derived from a project on the major mineral deposits, metallogenesis, and tectonics of the Northeast Asia and from a preceding project on the metallogenesis and tectonics of the Russian Far East, Alaska, and the Canadian Cordillera. Both projects provide critical information on bedrock geology and geophysics, tectonics, major metalliferous mineral resources, metallogenic patterns, and crustal origin and evolution of mineralizing systems for this region. The major

A superarmored lobopodian from the Cambrian of China and early disparity in the evolution of Onychophora

PubMed Central

Yang, Jie; Ortega-Hernández, Javier; Gerber, Sylvain; Butterfield, Nicholas J.; Hou, Jin-bo; Lan, Tian; Zhang, Xi-guang

2015-01-01

We describe Collinsium ciliosum from the early Cambrian Xiaoshiba Lagerstätte in South China, an armored lobopodian with a remarkable degree of limb differentiation including a pair of antenna-like appendages, six pairs of elongate setiferous limbs for suspension feeding, and nine pairs of clawed annulated legs with an anchoring function. Collinsium belongs to a highly derived clade of lobopodians within stem group Onychophora, distinguished by a substantial dorsal armature of supernumerary and biomineralized spines (Family Luolishaniidae). As demonstrated here, luolishaniids display the highest degree of limb specialization among Paleozoic lobopodians, constitute more than one-third of the overall morphological disparity of stem group Onychophora, and are substantially more disparate than crown group representatives. Despite having higher disparity and appendage complexity than other lobopodians and extant velvet worms, the specialized mode of life embodied by luolishaniids became extinct during the Early Paleozoic. Collinsium and other superarmored lobopodians exploited a unique paleoecological niche during the Cambrian explosion. PMID:26124122

The Chara-Sina dyke swarm in the structure of the Middle Paleozoic Vilyui rift system (Siberian Craton)

NASA Astrophysics Data System (ADS)

Kiselev, A. I.; Konstantinov, K. M.; Yarmolyuk, V. V.; Ivanov, A. V.

2016-11-01

The formation of the Vilyui rift system in the eastern Siberian Craton was finished with breakdown of the continent and formation of its eastern margin. A characteristic feature of this rift system is the radial distribution of dyke swarms of basic rocks. This peculiarity allows us to relate it to the breaking processes above the mantle plume, the center of which was located in the region overlain in the modern structure by the foreland of the Verkhoyan folded-thrust belt. The Chara-Sina dyke swarm is the southern part of a large area of Middle Paleozoic basaltic magmatism in the eastern Siberian Craton. The OIB-like geochemical characteristics of dolerite allow us to suggest that the melting substrate for Middle Paleozoic basaltic magmatism was represented by a relatively homogeneous, mid-depleted mantle of the plume with geochemical parameters similar to those of OIB.

High-Resolution 3D P-Wave Velocity Model in the Trans-European Suture Zone in Poland

NASA Astrophysics Data System (ADS)

Polkowski, M.; Grad, M.; Ostaficzuk, S.

2014-12-01

Poland is located on conjunction of major European tectonic units - the Precambrian East European Craton and the Paleozoic Platform of Central and Western Europe. This conjunction is known as Trans-European Suture Zone (TESZ). Geological and seismic structure under area of Poland is well studied by over one hundred thousand boreholes, over thirty deep seismic refraction and wide angle reflection profiles and other methods: vertical seismic profiling, magnetic, gravity, magnetotelluric, thermal. Compilation of these studies allows creation of detailed, high-resolution 3D P-wave velocity model for entire Earth's crust in the area of Poland. Model provides detailed six layer sediments (Tertiary and Quaternary, Cretaceous, Jurassic, Triassic, Permian, old Paleozoic), consolidated / crystalline crust and uppermost mantle. Continental suturing is a fundamental part of the plate tectonic cycle, and knowing its detailed structure allows understanding plate tectonic cycle. We present a set of crustal cross sections through the TESZ, illustrating differentiation in the structure between Precambrian and Wariscan Europe. National Science Centre Poland provided financial support for this work by NCN grant DEC- 2011/02/A/ST10/00284.

Wet Tectonics: A New Planetary Synthesis

NASA Astrophysics Data System (ADS)

Grimm, K. A.

2005-12-01

Most geoscientists (and geoscience textbooks) describe plate tectonics as a `solid-Earth' phenomenon, with fluids playing an important role in discrete geodynamic processes. As a community of diverse research specialists, the critical role of water is being widely elucidated, however these diverse studies do not address the fundamental origin and operation of the global plate tectonic phenomenon, and its expressions in planetary geodynamics and geomorphology. The Wet Tectonics hypothesis extends well beyond the plate tectonics paradigm, to constitute a new synthesis of diverse geoscience specializations and self-organizing complexity into a simple, internally consistent and explicitly testable model. The Wet Tectonics hypothesis asserts that Earth's plate tectonic system arose from and is the explicit and dynamic result of water interacting with the hot silicate mantle. The tectosphere is defined as an interactive functional (rather than structural, compositional or rheological) entity, a planetary-scale dynamic system of plate formation, plate motion, and rock/volatile recycling. Earth's tectosphere extends from the base of the asthenosphere to the top of the crust, arising and evolving as a dynamic pattern of organization that creates, orders and perpetuates itself. Earth's tectosphere is energetically-open, materially ajar (steady-state operation may not require sub-asthenospheric inputs; shifts between distinct tectonic modes may result from changes in coupling between the tectosphere and subasthenospheric reservoirs) and chemically-closed (i.e. the tectosphere recycles its own wastes). Water is a fundamental requirement in all of the constituent processes of Earth's tectosphere, including seafloor spreading, slab cooling/subsidence, plate motion, asthenosphere rheology, and subduction (where crustal and volatile recycling occur). As a working hypothesis, we suggest that the dynamic and persistent hydrosphere and tectosphere on planet Earth are fully

Earth's glacial record and its tectonic setting

NASA Astrophysics Data System (ADS)

Eyles, N.

1993-09-01

clearly established glacial parentage. The same remarks apply to many successions of laminated and thin-bedded facies interpreted as "varvites". Despite suggestions of much lower values of solar luminosity (the weak young sun hypothesis), the stratigraphic record of Archean glaciations is not extensive and may be the result of non-preservation. However, the effects of very different Archean global tectonic regimes and much higher geothermal heat flows, combined with a Venus-like atmosphere warmed by elevated levels of CO 2, cannot be ruled out. The oldest unambiguous glacial succession in Earth history appears to be the Early Proterozoic Gowganda Formation of the Huronian Supergroup in Ontario; the age of this event is not well-constrained but glaciation coincided with regional rifting, and may be causally related to, oxygenation of Earth's atmosphere just after 2300 Ma. New evidence that oxygenation is tectonically, not biologically driven, stresses the intimate relationship between plate tectonics, evolution of the atmosphere and glaciation. Global geochemical controls, such as elevated atmospheric CO 2 levels, may be responsible for a long mid-Proterozoic non-glacial interval after 2000 Ma that was terminated by the Late Proterozoic glaciations just after 800 Ma. A persistent theme in both Late Proterozoic and Phanerozoic glaciations is the adiabatic effect of tectonic uplift, either along collisional margins or as a result of passive margin uplifts in areas of extended crust, as the trigger for glaciation; the process is reinforced by global geochemical feedback, principally the drawdown of atmospheric CO 2 and Milankovitch "astronomical" forcing but these are unlikely, by themselves, to inititiate glaciation. The same remarks apply to late Cenozoic glaciations. Late Proterozoic glacially-influenced strata occur on all seven continents and fall into two tectonostratigraphic types. In the first category are thick sucessions of turbidites and mass flows deposited along

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

Dallmeyer, R.D.; Gee, D.G.; Beckholmen, M.

In central portions of the Scandinavian Caledonides, greenschist facies volcanosedimentary successions within the Koeli Nappe Complex have been thrust several hundred kilometers eastward onto the Baltoscandian platform. These were derived from eugeoclinal terranes situated outboard (west) of the Baltica continent during the early Paleozoic. The Koeli Nappe Complex is tectonically underlain by higher grade units within the Seve Nappe Complex. These are composed of amphibolite and granulite facies rocks and locally contain eclogites. The Seve Nappes tectonically separate Koeli units from structurally lower allochthons derived from more inboard environments along the Baltoscandian miogeocline. Previous mineral isotopic age-determinations from Seve andmore » Koeli units have been in the 430 to 390 Ma range and have been interpreted to presumably date cooling following Scandian (Middle Silurian to Early Devonian) metamorphism. However, incremental-release /sup 40/Ar//sup 39/Ar dates recorded by minerals within some of the Koeli and Seve Nappes exposed in Jaemtland, Sweden (Taennforsen and Are districts) provide evidence of earlier tectonothermal activity. Hornblendes from the Seve and Koeli Nappe Complexes display variably discordant age spectra as a result of low-temperature, experimental evolution of loosely bound extraneous argon components. However, in most analyses plateau ages of 510 to 475 Ma (Koeli) and 465 to 455 Ma (Seve) are defined. In contrast, muscovite and biotite from all tectonic units record Scandian cooling ages between 245 and 410 Ma. The older events recorded by hornblende within these Seve and Koeli units are evidence of early Caledonian tectonothermal activity and subsequent diachronous cooling during the Early-Middle Ordovician.« less

Basement inheritance and salt tectonics in the SE Barents Sea: Insights from new potential field data

NASA Astrophysics Data System (ADS)

Gernigon, L.; Broenner, M.; Dumais, M. A.; Gradmann, S.; Grønlie, A.; Nasuti, A.; Roberts, D.

2017-12-01

The tectonic evolution of the former `grey zone' between Russia and Norway has so far remained poorly constrained due to a lack of geophysical data. In 2014, we carried out a new aeromagnetic survey (BASAR-14) in the southern part of the new Norwegian offshore territory. Caledonian and Timanian structures, highlighted by the new potential field data, dominate the basement patterns and have exerted a strong influence on the structure and development of the overlying basins and basement highs. Clearly associated with NW-SE-oriented Timanian trends, the Tiddlybanken Basin represents an atypical sag basin that developed at the southern edge of the Fedynsky High. Regional extension and rapid sedimentation initiated the salt tectonics in the Barents Sea in the Early Triassic. Some of the pillows became diapiric during the Early Triassic and rejuvenated during subsequent Jurassic-Tertiary episodes of regional extension and/or compression. At present, quite a few large diapiric salt domes along the Nordkapp and Tiddlybanken basins are relatively shallow, locally reaching the seabed and thus show a clear bathymetric and magnetic signature. Quantitative modelling along 2D seismic transects was also carried out to constrain the structural and basement composition of the study area. The predominant NE-SW Mesozoic trend of the Nordkapp Basin represents a major crustal hinge zone between the Finnmark Platform, poorly affected by major crustal deformation, and the Bjarmeland Platform where Late Palaeozoic rifting controlled the widespread accumulation of salt deposits in Late Carboniferous-Early Permian time. The entire structure and segmentation of the Nordkapp Basin have been influenced by the inherited basement configuration highlighted by the new aeromagnetic data. Both the Nordkapp and the Tiddlybanken basins appear to lie at the edge of a peculiar thick and rigid crustal feature that coincides with a highly magnetic region. The abrupt termination of the eastern Nordkapp

Venus: Mantle convection, hotspots, and tectonics

NASA Technical Reports Server (NTRS)

Phillips, R. J.

1989-01-01

The putative paradigm that planets of the same size and mass have the same tectonic style led to the adaptation of the mechanisms of terrestrial plate tectonics as the a priori model of the way Venus should behave. Data acquired over the last decade by Pioneer Venus, Venera, and ground-based radar have modified this view sharply and have illuminated the lack of detailed understanding of the plate tectonic mechanism. For reference, terrestrial mechanisms are briefly reviewed. Venusian lithospheric divergence, hotspot model, and horizontal deformation theories are proposed and examined.

Ordovician magmatism in the Lévézou massif (French Massif Central): tectonic and geodynamic implications

NASA Astrophysics Data System (ADS)

Lotout, Caroline; Pitra, Pavel; Poujol, Marc; Van Den Driessche, Jean

2017-03-01

New U-Pb dating on zircon yielded ca. 470 Ma ages for the granitoids from the Lévézou massif in the southern French Massif Central. These new ages do not support the previous interpretation of these granitoids as syn-tectonic intrusions emplaced during the Late Devonian-Early Carboniferous thrusting. The geochemical and isotopic nature of this magmatism is linked to a major magmatic Ordovician event recorded throughout the European Variscan belt and related to extreme thinning of continental margins during a rifting event or a back-arc extension. The comparable isotopic signatures of these granitoids on each side of the eclogite-bearing leptyno-amphibolitic complex in the Lévézou massif, together with the fact that they were emplaced at the same time, strongly suggest that these granitoids were originally part of a single unit, tectonically duplicated by either isoclinal folding or thrusting during the Variscan tectonics.

Lasting mantle scars lead to perennial plate tectonics.

PubMed

Heron, Philip J; Pysklywec, Russell N; Stephenson, Randell

2016-06-10

Mid-ocean ridges, transform faults, subduction and continental collisions form the conventional theory of plate tectonics to explain non-rigid behaviour at plate boundaries. However, the theory does not explain directly the processes involved in intraplate deformation and seismicity. Recently, damage structures in the lithosphere have been linked to the origin of plate tectonics. Despite seismological imaging suggesting that inherited mantle lithosphere heterogeneities are ubiquitous, their plate tectonic role is rarely considered. Here we show that deep lithospheric anomalies can dominate shallow geological features in activating tectonics in plate interiors. In numerical experiments, we found that structures frozen into the mantle lithosphere through plate tectonic processes can behave as quasi-plate boundaries reactivated under far-field compressional forcing. Intraplate locations where proto-lithospheric plates have been scarred by earlier suturing could be regions where latent plate boundaries remain, and where plate tectonics processes are expressed as a 'perennial' phenomenon.

Tectonic signatures on active margins

NASA Astrophysics Data System (ADS)

Hogarth, Leah Jolynn

High-resolution Compressed High-Intensity Radar Pulse (CHIRP) surveys offshore of La Jolla in southern California and the Eel River in northern California provide the opportunity to investigate the role of tectonics in the formation of stratigraphic architecture and margin morphology. Both study sites are characterized by shore-parallel tectonic deformation, which is largely observed in the structure of the prominent angular unconformity interpreted as the transgressive surface. Based on stratal geometry and acoustic character, we identify three sedimentary sequences offshore of La Jolla: an acoustically laminated estuarine unit deposited during early transgression, an infilling or "healing-phase" unit formed during the transgression, and an upper transparent unit. The estuarine unit is confined to the canyon edges in what may have been embayments during the last sea-level rise. The healing-phase unit appears to infill rough areas on the transgressive surface that may be related to relict fault structures. The upper transparent unit is largely controlled by long-wavelength tectonic deformation due to the Rose Canyon Fault. This unit is also characterized by a mid-shelf (˜40 m water depth) thickness high, which is likely a result of hydrodynamic forces and sediment grain size. On the Eel margin, we observe three distinct facies: a seaward-thinning unit truncated by the transgressive surface, a healing-phase unit confined to the edges of a broad structural high, and a highly laminated upper unit. The seaward-thinning wedge of sediment below the transgressive surface is marked by a number of channels that we interpret as distributary channels based on their morphology. Regional divergence of the sequence boundary and transgressive surface with up to ˜8 m of sediment preserved across the interfluves suggests the formation of subaerial accommodation during the lowstand. The healing-phase, much like that in southern California, appears to infill rough areas in the

The climatic, biotic and tectonic evolution of the Paleogene Renova formation of southwestern Montana

NASA Astrophysics Data System (ADS)

Lielke, Kevin John

The Renova Formation of southwestern Montana contains an important record of Paleogene floral, faunal, climate and tectonic change in the northern Rocky Mountains. The period between the end of the early Eocene and the early Oligocene (˜49--32 Ma) was a time of rapid and far-reaching climate change. This period saw the end of global greenhouse climate and the establishment of icehouse conditions across the Earth. These changes led to profound alterations in both marine and terrestrial ecosystems. This study examines the late Eocene/early Oligocene history of the northern Rocky Mountains by means of an integrated study of the sedimentology, tectonics and fossil content of the Renova Formation. The first part of this study examines plant fossils found in the Renova Formation in order to examine changes in the composition of the vegetation across the late Eocene/ early Oligocene (E/O) boundary. Plant remains are an effective proxy for climate and are used to estimate multiple climatic parameters across the E/O boundary. The second part of this study examines the paleotopography and paleodrainage patterns of the basins which accumulated the Renova sediments. This is accomplished by a combination of sedimentary facies and detrital zircon analysis. The third part of this study examines the tectonic underpinnings of Paleogene southwestern Montana through a combination of geologic field work and geodynamic modeling. The results of this study indicate that a seasonal summer dry climate became established in the northern Rocky Mountains by early Oligocene time. This is indicated by the elimination of subtropical plant species, the establishment of dry-adapted species and by paleoclimate parameters calculated from leaf physiognomy. Geodynamic calculations and field data indicate that the Renova Formation was deposited in a series of sub-basins separated by relict paleotopography and inverted topography formed by contemporary lava flows. Normal faulting was not active until

Early Permian Pangea `B' to Late Permian Pangea `A'

NASA Astrophysics Data System (ADS)

Muttoni, Giovanni; Kent, Dennis V.; Garzanti, Eduardo; Brack, Peter; Abrahamsen, Niels; Gaetani, Maurizio

2003-10-01

The pre-drift Wegenerian model of Pangea is almost universally accepted, but debate exists on its pre-Jurassic configuration since Ted Irving introduced Pangea 'B' by placing Gondwana farther to the east by ˜3000 km with respect to Laurasia on the basis of paleomagnetic data. New paleomagnetic data from radiometrically dated Early Permian volcanic rocks from parts of Adria that are tectonically coherent with Africa (Gondwana), integrated with published coeval data from Gondwana and Laurasia, again only from igneous rocks, fully support a Pangea 'B' configuration in the Early Permian. The use of paleomagnetic data strictly from igneous rocks excludes artifacts from sedimentary inclination error as a contributing explanation for Pangea 'B'. The ultimate option to reject Pangea 'B' is to abandon the geocentric axial dipole hypothesis by introducing a significant non-dipole (zonal octupole) component in the Late Paleozoic time-averaged geomagnetic field. We demonstrate, however, by using a dataset consisting entirely of paleomagnetic directions with low inclinations from sampling sites confined to one hemisphere from Gondwana as well as Laurasia that the effects of a zonal octupole field contribution would not explain away the paleomagnetic evidence for Pangea 'B' in the Early Permian. We therefore regard the paleomagnetic evidence for an Early Permian Pangea 'B' as robust. The transformation from Pangea 'B' to Pangea 'A' took place during the Permian because Late Permian paleomagnetic data allow a Pangea 'A' configuration. We therefore review geological evidence from the literature in support of an intra-Pangea dextral megashear system. The transformation occurred after the cooling of the Variscan mega-suture and lasted ˜20 Myr. In this interval, the Neotethys Ocean opened between India/Arabia and the Cimmerian microcontinents in the east, while widespread lithospheric wrenching and magmatism took place in the west around the Adriatic promontory. The general

Basement and crustal structure of the Davis Sea region (East Antarctica): implications for tectonic setting and continent to oceanic boundary definition

USGS Publications Warehouse

Guseva, Y.B.; Leitchenkov, G.L.; Gandyukhin, V.V.; Ivanov, S.V.

2007-01-01

This study is based on about 8400 km of MCS, magnetic and gravity data as well as 20 sonobuoys collected by the Russian Antarctic Expedition during 2003 and 2004 in the Davis Sea and adjacent areas between 80°E and 102°E. Major tectonic provinces and features are identified and mapped in the study region including: 1) A marginal rift with a the extended continental crust ranging 130 to more than 200 km in width; 2) The marginal volcanic plateau of the Bruce Bank consisting of the Early Cretaceous igneous rocks; 3) The Early Cretaceous and Late Cretaceous−Paleogene oceanic basins; and 4) The Early Cretaceous igneous province of the Kerguelen Plateau. Four major horizons identified in the sedimentary cover of the Davis Sea region are attributed to main tectonic events and/or paleoenvironmental changes.

Tectonic Storytelling with Open Source and Digital Object Identifiers - a case study about Plate Tectonics and the Geopark Bergstraße-Odenwald

NASA Astrophysics Data System (ADS)

Löwe, Peter; Barmuta, Jan; Klump, Jens; Neumann, Janna; Plank, Margret

2014-05-01

The communication of advances in research to the common public for both education and decision making is an important aspect of scientific work. An even more crucial task is to gain recognition within the scientific community, which is judged by impact factor and citation counts. Recently, the latter concepts have been extended from textual publications to include data and software publications. This paper presents a case study for science communication and data citation. For this, tectonic models, Free and Open Source Software (FOSS), best practices for data citation and a multimedia online-portal for scientific content are combined. This approach creates mutual benefits for the stakeholders: Target audiences receive information on the latest research results, while the use of Digital Object Identifiers (DOI) increases the recognition and citation of underlying scientific data. This creates favourable conditions for every researcher as DOI names ensure citeability and long term availability of scientific research. In the developed application, the FOSS tool for tectonic modelling GPlates is used to visualise and manipulate plate-tectonic reconstructions and associated data through geological time. These capabilities are augmented by the Science on a Halfsphere project (SoaH) with a robust and intuitive visualisation hardware environment. The tectonic models used for science communication are provided by the AGH University of Science and Technology. They focus on the Silurian to Early Carboniferous evolution of Central Europe (Bohemian Massif) and were interpreted for the area of the Geopark Bergstraße Odenwald based on the GPlates/SoaH hardware- and software stack. As scientific story-telling is volatile by nature, recordings are a natural means of preservation for further use, reference and analysis. For this, the upcoming portal for audiovisual media of the German National Library of Science and Technology TIB is expected to become a critical service

Tectonic configuration of the western Arabian continental margin, southern Red Sea, Kingdom of Saudi Arabia

USGS Publications Warehouse

Bohannon, R.G.

1987-01-01

A tectonic reconstruction of pre-Red Sea Afro/Arabia suggests that the early rift was narrow with intense extension confined to an axial belt 20 to 40 km wide. Steep Moho slopes probably developed during rift formation as indicated by published gravity data, two published seismic interpretations and the surface geology.

Playing jigsaw with Large Igneous Provinces—A plate tectonic reconstruction of Ontong Java Nui, West Pacific

NASA Astrophysics Data System (ADS)

Hochmuth, Katharina; Gohl, Karsten; Uenzelmann-Neben, Gabriele

2015-11-01

The three largest Large Igneous Provinces (LIP) of the western Pacific—Ontong Java, Manihiki, and Hikurangi Plateaus—were emplaced during the Cretaceous Normal Superchron and show strong similarities in their geochemistry and petrology. The plate tectonic relationship between those LIPs, herein referred to as Ontong Java Nui, is uncertain, but a joined emplacement was proposed by Taylor (2006). Since this hypothesis is still highly debated and struggles to explain features such as the strong differences in crustal thickness between the different plateaus, we revisited the joined emplacement of Ontong Java Nui in light of new data from the Manihiki Plateau. By evaluating seismic refraction/wide-angle reflection data along with seismic reflection records of the margins of the proposed "Super"-LIP, a detailed scenario for the emplacement and the initial phase of breakup has been developed. The LIP is a result of an interaction of the arriving plume head with the Phoenix-Pacific spreading ridge in the Early Cretaceous. The breakup of the LIP shows a complicated interplay between multiple microplates and tectonic forces such as rifting, shearing, and rotation. Our plate kinematic model of the western Pacific incorporates new evidence from the breakup margins of the LIPs, the tectonic fabric of the seafloor, as well as previously published tectonic concepts such as the rotation of the LIPs. The updated rotation poles of the western Pacific allow a detailed plate tectonic reconstruction of the region during the Cretaceous Normal Superchron and highlight the important role of LIPs in the plate tectonic framework.

Tectonic and climatic control on evolution of rift lakes in the Central Kenya Rift, East Africa

NASA Astrophysics Data System (ADS)

Bergner, A. G. N.; Strecker, M. R.; Trauth, M. H.; Deino, A.; Gasse, F.; Blisniuk, P.; Dühnforth, M.

2009-12-01

The long-term histories of the neighboring Nakuru-Elmenteita and Naivasha lake basins in the Central Kenya Rift illustrate the relative importance of tectonic versus climatic effects on rift-lake evolution and the formation of disparate sedimentary environments. Although modern climate conditions in the Central Kenya Rift are very similar for these basins, hydrology and hydrochemistry of present-day lakes Nakuru, Elmenteita and Naivasha contrast dramatically due to tectonically controlled differences in basin geometries, catchment size, and fluvial processes. In this study, we use eighteen 14C and 40Ar/ 39Ar dated fluvio-lacustrine sedimentary sections to unravel the spatiotemporal evolution of the lake basins in response to tectonic and climatic influences. We reconstruct paleoclimatic and ecological trends recorded in these basins based on fossil diatom assemblages and geologic field mapping. Our study shows a tendency towards increasing alkalinity and shrinkage of water bodies in both lake basins during the last million years. Ongoing volcano-tectonic segmentation of the lake basins, as well as reorganization of upstream drainage networks have led to contrasting hydrologic regimes with adjacent alkaline and freshwater conditions. During extreme wet periods in the past, such as during the early Holocene climate optimum, lake levels were high and all basins evolved toward freshwater systems. During drier periods some of these lakes revert back to alkaline conditions, while others maintain freshwater characteristics. Our results have important implications for the use and interpretation of lake sediment as climate archives in tectonically active regions and emphasize the need to deconvolve lacustrine records with respect to tectonics versus climatic forcing mechanisms.

Tectonic evolution of the Yarlung suture zone, Lopu Range region, southern Tibet

NASA Astrophysics Data System (ADS)

Laskowski, Andrew K.; Kapp, Paul; Ding, Lin; Campbell, Clay; Liu, XiaoHui

2017-01-01

The Lopu Range, located 600 km west of Lhasa, exposes a continental high-pressure metamorphic complex beneath India-Asia (Yarlung) suture zone assemblages. Geologic mapping, 14 detrital U-Pb zircon (n = 1895 ages), 11 igneous U-Pb zircon, and nine zircon (U-Th)/He samples reveal the structure, age, provenance, and time-temperature histories of Lopu Range rocks. A hornblende-plagioclase-epidote paragneiss block in ophiolitic mélange, deposited during Middle Jurassic time, records Late Jurassic or Early Cretaceous subduction initiation followed by Early Cretaceous fore-arc extension. A depositional contact between fore-arc strata (maximum depositional age 97 ± 1 Ma) and ophiolitic mélange indicates that the ophiolites were in a suprasubduction zone position prior to Late Cretaceous time. Five Gangdese arc granitoids that intrude subduction-accretion mélange yield U-Pb ages between 49 and 37 Ma, recording Eocene southward trench migration after collision initiation. The south dipping Great Counter Thrust system cuts older suture zone structures, placing fore-arc strata on the Kailas Formation, and sedimentary-matrix mélange on fore-arc strata during early Miocene time. The north-south, range-bounding Lopukangri and Rujiao faults comprise a horst that cuts the Great Counter Thrust system, recording the early Miocene ( 16 Ma) transition from north-south contraction to orogen-parallel (E-W) extension. Five early Miocene (17-15 Ma) U-Pb ages from leucogranite dikes and plutons record crustal melting during extension onset. Seven zircon (U-Th)/He ages from the horst block record 12-6 Ma tectonic exhumation. Jurassic—Eocene Yarlung suture zone tectonics, characterized by alternating episodes of contraction and extension, can be explained by cycles of slab rollback, breakoff, and shallow underthrusting—suggesting that subduction dynamics controlled deformation.

Unexpected Early Triassic marine ecosystem and the rise of the Modern evolutionary fauna

PubMed Central

Brayard, Arnaud; Krumenacker, L. J.; Botting, Joseph P.; Jenks, James F.; Bylund, Kevin G.; Fara, Emmanuel; Vennin, Emmanuelle; Olivier, Nicolas; Goudemand, Nicolas; Saucède, Thomas; Charbonnier, Sylvain; Romano, Carlo; Doguzhaeva, Larisa; Thuy, Ben; Hautmann, Michael; Stephen, Daniel A.; Thomazo, Christophe; Escarguel, Gilles

2017-01-01

In the wake of the end-Permian mass extinction, the Early Triassic (~251.9 to 247 million years ago) is portrayed as an environmentally unstable interval characterized by several biotic crises and heavily depauperate marine benthic ecosystems. We describe a new fossil assemblage—the Paris Biota—from the earliest Spathian (middle Olenekian, ~250.6 million years ago) of the Bear Lake area, southeastern Idaho, USA. This highly diversified assemblage documents a remarkably complex marine ecosystem including at least seven phyla and 20 distinct metazoan orders, along with algae. Most unexpectedly, it combines early Paleozoic and middle Mesozoic taxa previously unknown from the Triassic strata, among which are primitive Cambrian-Ordovician leptomitid sponges (a 200–million year Lazarus taxon) and gladius-bearing coleoid cephalopods, a poorly documented group before the Jurassic (~50 million years after the Early Triassic). Additionally, the crinoid and ophiuroid specimens show derived anatomical characters that were thought to have evolved much later. Unlike previous works that suggested a sluggish postcrisis recovery and a low diversity for the Early Triassic benthic organisms, the unexpected composition of this exceptional assemblage points toward an early and rapid post-Permian diversification for these clades. Overall, it illustrates a phylogenetically diverse, functionally complex, and trophically multileveled marine ecosystem, from primary producers up to top predators and potential scavengers. Hence, the Paris Biota highlights the key evolutionary position of Early Triassic fossil ecosystems in the transition from the Paleozoic to the Modern marine evolutionary fauna at the dawn of the Mesozoic era. PMID:28246643

Unexpected Early Triassic marine ecosystem and the rise of the Modern evolutionary fauna.

PubMed

Brayard, Arnaud; Krumenacker, L J; Botting, Joseph P; Jenks, James F; Bylund, Kevin G; Fara, Emmanuel; Vennin, Emmanuelle; Olivier, Nicolas; Goudemand, Nicolas; Saucède, Thomas; Charbonnier, Sylvain; Romano, Carlo; Doguzhaeva, Larisa; Thuy, Ben; Hautmann, Michael; Stephen, Daniel A; Thomazo, Christophe; Escarguel, Gilles

2017-02-01

In the wake of the end-Permian mass extinction, the Early Triassic (~251.9 to 247 million years ago) is portrayed as an environmentally unstable interval characterized by several biotic crises and heavily depauperate marine benthic ecosystems. We describe a new fossil assemblage-the Paris Biota-from the earliest Spathian (middle Olenekian, ~250.6 million years ago) of the Bear Lake area, southeastern Idaho, USA. This highly diversified assemblage documents a remarkably complex marine ecosystem including at least seven phyla and 20 distinct metazoan orders, along with algae. Most unexpectedly, it combines early Paleozoic and middle Mesozoic taxa previously unknown from the Triassic strata, among which are primitive Cambrian-Ordovician leptomitid sponges (a 200-million year Lazarus taxon) and gladius-bearing coleoid cephalopods, a poorly documented group before the Jurassic (~50 million years after the Early Triassic). Additionally, the crinoid and ophiuroid specimens show derived anatomical characters that were thought to have evolved much later. Unlike previous works that suggested a sluggish postcrisis recovery and a low diversity for the Early Triassic benthic organisms, the unexpected composition of this exceptional assemblage points toward an early and rapid post-Permian diversification for these clades. Overall, it illustrates a phylogenetically diverse, functionally complex, and trophically multileveled marine ecosystem, from primary producers up to top predators and potential scavengers. Hence, the Paris Biota highlights the key evolutionary position of Early Triassic fossil ecosystems in the transition from the Paleozoic to the Modern marine evolutionary fauna at the dawn of the Mesozoic era.

Lasting mantle scars lead to perennial plate tectonics

PubMed Central

Heron, Philip J.; Pysklywec, Russell N.; Stephenson, Randell

2016-01-01

Mid-ocean ridges, transform faults, subduction and continental collisions form the conventional theory of plate tectonics to explain non-rigid behaviour at plate boundaries. However, the theory does not explain directly the processes involved in intraplate deformation and seismicity. Recently, damage structures in the lithosphere have been linked to the origin of plate tectonics. Despite seismological imaging suggesting that inherited mantle lithosphere heterogeneities are ubiquitous, their plate tectonic role is rarely considered. Here we show that deep lithospheric anomalies can dominate shallow geological features in activating tectonics in plate interiors. In numerical experiments, we found that structures frozen into the mantle lithosphere through plate tectonic processes can behave as quasi-plate boundaries reactivated under far-field compressional forcing. Intraplate locations where proto-lithospheric plates have been scarred by earlier suturing could be regions where latent plate boundaries remain, and where plate tectonics processes are expressed as a ‘perennial' phenomenon. PMID:27282541

Petrology and geochemistry of meta-ultramafic rocks in the Paleozoic Granjeno Schist, northeastern Mexico: Remnants of Pangaea ocean floor

NASA Astrophysics Data System (ADS)

Torres-Sánchez, Sonia Alejandra; Augustsson, Carita; Jenchen, Uwe; Rafael Barboza-Gudiño, J.; Alemán Gallardo, Eduardo; Ramírez Fernández, Juan Alonso; Torres-Sánchez, Darío; Abratis, Michael

2017-08-01

The Granjeno Schist is a meta-volcanosedimentary upper Paleozoic complex in northeastern Mexico. We suggest different tectonic settings for metamorphism of its serpentinite and talc-bearing rocks based on petrographic and geochemical compositions. According to the REE ratios (LaN/YbN = 0.51 -20.0 and LaN/SmN = 0.72-9.1) and the enrichment in the highly incompatible elements Cs (0.1 ppm), U (2.8 ppm), and Zr (60 ppm) as well as depletion in Ba (1 - 15 ppm), Sr (1 -184 ppm), Pb (0.1 -14 ppm), and Ce (0.1 -1.9 ppm) the rocks have mid-ocean ridge and subduction zones characteristics. The serpentinite contains Al-chromite, ferrian chromite and magnetite. The Al-chromite is characterized by Cr# of 0.48 to 0.55 suggesting a MORB origin, and Cr# of 0.93 to 1.00 for the ferrian chromite indicates a prograde metamorphism. We propose at least two serpentinization stages of lithospheric mantle for the ultramafic rock of the Granjeno Schist, (1) a first in an ocean-floor environment at sub-greenschist to greenschist facies conditions and (2) later a serpentinization phase related to the progressive replacement of spinel by ferrian chromite and magnetite at greenschist to low amphibolite facies conditions during regional metamorphism. The second serpentinization phase took place in an active continental margin during the Pennsylvanian. We propose that the origin of the ultramafic rocks is related to an obduction and accretional event at the western margin of Pangea.

Investigation of the Cooling Capacity of Plate Tectonics and Flood Volcanism in the Evolution of Earth, Mars and Venus

NASA Astrophysics Data System (ADS)

van Thienen, P.; Vlaar, N. J.; van den Berg, A. P.

2003-12-01

The cooling of the terrestrial planets from their presumed hot initial states to the present situation has required the operation of one or more efficient cooling mechanisms. In the recent history of the Earth, plate tectonics has been responsible for most of the planetary cooling. The high internal temperature of the early Earth, however, prevented the operation of plate tectonics because of the greater inherent buoyancy of thicker oceanic lithosphere (basaltic crust and depleted mantle) produced from a hotter mantle. A similar argument is valid for Venus, and also for Mars. An alternative cooling mechanism may therefore have been required during a part of the planetary histories. Starting from the notion that all heat output of planets is through their surfaces, we have constructed two parametric models to evaluate the cooling characteristics of two cooling mechanisms: plate tectonics and basalt extrusion / flood volcanism. We have applied these models to the Earth, Mars and Venus for present-day and presumed early thermal conditions. Our model results show that for a steadily (exponentially) cooling Earth, plate tectonics is capable of removing all the required heat at a rate comparable to or even lower than its current rate of operation during its entire history, contrary to earlier speculations. The extrusion mechanism may have been an important cooling agent in the early Earth, but requires global eruption rates two orders of magnitude greater than those of known Phanerozoic flood basalt provinces. This may not be a problem, since geological observations indicate that flood volcanism was both stronger and more ubiquitous in the early Earth. Because of its smaller size, Mars is capable of cooling conductively through its lithosphere at significant rates. As a result may have cooled without an additional cooling mechanism during its entire history. Venus, on the other hand, has required the operation of an additional cooling agent for probably every cooling

New tectonic data constrain the mechanisms of breakup along the Gulf of California

NASA Astrophysics Data System (ADS)

Bot, Anna; Geoffroy, Laurent; Authemayou, Christine; Graindorge, David

2014-05-01

The Gulf of California is resulting from an oblique-rift system due to the separation of the Pacific and the North American plates in the ~N110E to ~N125E trend. The age, nature and orientation of strain which ended with continental break-up and incipient oceanization at ~3.6 Ma, is largely misunderstood. It is generally proposed that early stages of extension began at around 12 Ma with strain partitioning into two components: a pure ENE directed extension in the Gulf Extensional Province (which includes Sonora and the eastern Baja California Peninsula in Mexico) and a dextral strike-slip displacement west of the Baja California Peninsula along the San Benito and Tosco-Abreojos faults. This evolution would have lasted ~5-6 Ma when a new transtensional strain regime took place. This regime, with extension trending ~N110E +/-10° , led to the final break-up and the subsequent individualization of a transform-fault system and subordoned short oceanic ridges. This two-steps interpretation has recently been challenged by authors suggesting a continuous transtensional extension from 12Ma in the trend of the PAC-NAM plates Kinematic. We question both of those models in term of timing and mode of accommodation basing ourselves on field investigations in Baja California Sur (Mexico). The volcano-sedimentary formations of the Comondù group dated 25 to 20 Ma exhibit clear examples of syn-sedimentary and syn-magmatic extensive deformations. This extension, oriented N65° E+/-15° , is proposed to initiate during the Magdalena Plate subduction. It would be related to the GOC initialization. In addition to this finding, we present tectonic and dating evidences of complex detachment-faulting tectonics varying in trend and kinematics with time and space for the development to the south of Baja California Sur. The extension associated with the early detachment-fault system trended ~N110E. From ~17 Ma to, probably, ~7-8 Ma, this extension controlled the early development of the San

Pre-breakup geology of the Gulf of Mexico-Caribbean: Its relation to Triassic and Jurassic rift systems of the region

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

Bartok, P.

1993-02-01

A review of the pre-breakup geology of west-central Pangea, comprised of northern South America, Gulf of Mexico and West Africa, combined with a study of the Mesozoic rift trends of the region confirms a relation between the rift systems and the underlying older grain of deformation. The pre-breakup analysis focuses attention on the Precambrian, Early Paleozoic and Late Paleozoic tectonic events affecting the region and assumes a Pindell fit. Two Late Precambrian orogenic belts are observed in the west central Pangea. Along the northern South American margin and Yucatan a paleo northeast trending Pan-African aged fold belt is documented. Amore » second system is observed along West Africa extending from the High Atlas to the Mauritanides and Rockelides. During the Late Paleozoic, renewed orogenic activity, associated with the Gondwana/Laurentia suture, affected large segments of west central Pangea. The general trend of the system is northeast-southwest and essentially parallels the Gyayana Shield, West African, and eastern North American cratons. Mesozoic rifting closely followed either the Precambrian trends or the Late Paleozoic orogenic belt. The Triassic component focuses along the western portions of the Gulf of Mexico continuing into eastern Mexico and western South America. The Jurassic rift trend followed along the separation between Yucatan and northern South America. At Lake Maracaibo the Jurassic rift system eventually overlaps the Triassic rifts. The Jurassic rift resulted in the [open quotes]Hispanic Corridor[close quotes] that permitted Tethyan and Pacific marine faunas to mix at a time when the Gulf of Mexico underwent continental sedimentation.« less

Iapetus: Tectonic structure and geologic history

NASA Technical Reports Server (NTRS)

Croft, Steven K.

1991-01-01

Many papers have been written about the surface of Iapetus, but most of these have discussed either the nature of the strongly contrasting light and dark materials or the cratering record. Little has been said about other geologic features on Iapetus, such as tectonic structures, which would provide constraints on Iapetus' thermal history. Most references have suggested that there is no conclusive evidence for any tectonic activity, even when thermal history studies indicate that there should be. However, a new study of Iapetus' surface involving the use of stereo pairs, an extensive tectonic network has been recognized. A few new observations concerning the craters and dark material were also made. Thus the geology and geologic history of Iapetus can be more fully outlined than before. The tectonic network is shown along with prominent craters and part of the dark material in the geologic/tectonic sketch map. The topology of crater rims and scarps are quite apparent and recognizable in the different image pairs. The heights and slopes of various features given are based on comparison with the depths of craters 50 to 100 km in diameter, which are assumed to have the same depths as craters of similar diameter on Rhea and Titania.

The Triassic reworking of the Yunkai massif (South China): EMP monazite and U-Pb zircon geochronologic evidence

NASA Astrophysics Data System (ADS)

Chen, Cheng-Hong; Liu, Yung-Hsin; Lee, Chi-Yu; Sano, Yuji; Zhou, Han-Wen; Xiang, Hua; Takahata, Naoto

2017-01-01

Geohistory of the Yunkai massif in South China Block is important in understanding the geodynamics for the build-up of this block during the Phanerozoic orogenies. To investigate this massif, we conduct EMP monazite and U-Pb zircon geochronological determinations on mineral inclusions and separate for seventeen samples in four groups, representing metamorphic rocks from core domain, the Gaozhou Complex (amphibolite facies, NE-striking) and the Yunkai Group (greenschist facies, NW-striking) of this massif and adjacent undeformed granites. Some EMP monazite ages are consistent with the NanoSIMS results. Monazite inclusions, mostly with long axis parallel to the cleavage of platy and elongated hosts, give distinguishable age results for NW- and NE-trending deformations at 244-236 Ma and 236-233 Ma, respectively. They also yield ages of 233-230 Ma for core domain gneissic granites and 232-229 Ma for undefomed granites. Combining U-Pb zircon ages of the same group, 245 Ma and 230 Ma are suggested to constrain the time of two phases of deformation. Aside from ubiquity of Triassic ages in studied rocks, ages of detrital monazite in the meta-sandstone match the major U-Pb zircon age clusters of the metamorphic rock that are largely concentrated at Neoproterozoic (1.0-0.9 Ga) and Early Paleozoic (444-431 Ma). Based on these geochronological data, Triassic is interpreted as representing the time for recrystallization of these host minerals on the Early Paleozoic protolith, and the also popular Neoproterozoic age is probably inherited. With this context, Yunkai massif is regarded as a strongly reactivated Triassic metamorphic terrain on an Early Paleozoic basement which had incorporated sediments with Neoproterozoic provenances. Triassic tectonic evolution of the Yunkai massif is suggested to have been controlled by converging geodynamics of the South China and Indochina Blocks as well as mafic magma emplacement related to the Emeishan large igneous province (E-LIP).

Detrital zircon age distribution from Devonian and Carboniferous sandstone in the Southern Variscan Fold-and-Thrust belt (Montagne Noire, French Massif Central), and their bearings on the Variscan belt evolution

NASA Astrophysics Data System (ADS)

Lin, Wei; Faure, Michel; Li, Xian-hua; Chu, Yang; Ji, Wenbin; Xue, Zhenhua

2016-05-01

In the Southern French Massif Central, the Late Paleozoic sedimentary sequences of the Montagne Noire area provide clues to decipher the successive tectonic events that occurred during the evolution of the Variscan belt. Previous sedimentological studies already demonstrated that the siliciclastic deposits were supplied from the northern part of the Massif Central. In this study, detrital zircon provenance analysis has been investigated in Early Devonian (Lochkovian) conglomerate and sandstone, and in Carboniferous (Visean to Early Serpukhovian) sandstone from the recumbent folds and the foreland basin of the Variscan Southern Massif Central in Montagne Noire. The zircon grains from all of the samples yielded U-Pb age spectra ranging from Neoarchean to Late Paleozoic with several age population peaks at 2700 Ma, 2000 Ma, 980 Ma, 750 Ma, 620 Ma, 590 Ma, 560 Ma, 480 Ma, 450 Ma, and 350 Ma. The dominant age populations concentrate on the Neoproterozoic and Paleozoic. The dominant concordant detrital zircon age populations in the Lochkovian samples, the 480-445 Ma with a statistical peak around 450 Ma, are interpreted as reflecting the rifting event that separated several continental stripes, such as Armorica, Mid-German Crystalline Rise, and Avalonia from the northern part of Gondwana. However, Ediacaran and Cambrian secondary peaks are also observed. The detrital zircons with ages at 352 - 340 Ma, with a statistical peak around 350 Ma, came from the Early Carboniferous volcanic and plutonic rocks similar to those exposed in the NE part of the French Massif Central. Moreover, some Precambrian grains recorded a more complex itinerary and may have experienced a multi-recycling history: the Archean and Proterozoic grains have been firstly deposited in Cambrian or Ordovician terrigenous rocks, and secondly re-sedimented in Devonian and/or Carboniferous formations. Another possibility is that ancient grains would be inherited grains, scavenged from an underlying but not

The Role of Tectonic Stress in Triggering Large Silicic Caldera Eruptions

NASA Astrophysics Data System (ADS)

Cabaniss, Haley E.; Gregg, Patricia M.; Grosfils, Eric B.

2018-05-01

We utilize 3-D temperature-dependent viscoelastic finite element models to investigate the mechanical response of the host rock supporting large caldera-size magma reservoirs (volumes >102 km3) to local tectonic stresses. The mechanical stability of the host rock is used to determine the maximum predicted repose intervals and magma flux rates that systems may experience before successive eruption is triggered. Numerical results indicate that regional extension decreases the stability of the roof rock overlying a magma reservoir, thereby promoting early-onset caldera collapse. Alternatively, moderate amounts of compression (≤10 mm/year) on relatively short timescales (<104 years) increases roof rock stability. In addition to quantifying the affect of tectonic stresses on reservoir stability, our models indicate that the process of rejuvenation and mechanical failure is likely to take place over short time periods of hundreds to thousands of years. These findings support the short preeruption melt accumulation timescales indicated by U series disequilibrium studies.

Pre-lithification tectonic foliation development in a clastic sedimentary rock sequence from SW Ireland

NASA Astrophysics Data System (ADS)

Meere, Patrick; Mulchrone, Kieran; McCarthy, David

2017-04-01

The current orthodoxy regarding the development of regionally developed penetrative tectonic cleavage fabrics in sedimentary rocks is that it postdates lithification of those rocks. It is well established that fabric development under these circumstances is achieved by a combination of grain rigid body rotation, crystal-plastic deformation and pressure solution. The latter is believed to be the primary mechanism responsible for the domainal nature of cleavage development commonly observed in low grade metamorphic rocks. While there have been advocates for the development of tectonic cleavages before host rock lithification these are currently viewed as essentially local aberrations without regional significance. In this study we combine new field observations with strain analysis, element mapping and modelling to characterise Acadian (>50%) crustal shortening in a Devonian clastic sedimentary sequence from the Dingle Peninsula of south west Ireland. Fabrics in these rocks reflect significant levels of tectonic shortening are a product of grain translation, rigid body rotation and repacking of intra- and extra-formational clasts during deformation of an unconsolidated clastic sedimentary sequence. There is an absence of the expected domainal cleavage structure and intra-clast deformation expected with conventional cleavage formation. This study requires geologists to consider the possibility such a mechanism contributing to tectonic strain in a wide range of geological settings and to look again at field evidence that indicates early sediment mobility during deformation.

Tectonic asymmetry of the earth and other planets

NASA Technical Reports Server (NTRS)

Pushcharovskiy, Y. M.; Kozlov, V. V.; Sulidi-Kondratyev, Y. D.

1978-01-01

The structures of Earth, Mars, Venus, and the Moon are examined and compared. Global tectonic characteristics are presented for each. A comparison of the tectonics reveals the structural asymetry of these planets and the moon. Tectonic asymmetry information for the group is used to interpret certain aspects of the earth's geological past.

Creep of phyllosilicates at the onset of plate tectonics

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

Amiguet, Elodie; Reynard, Bruno; Caracas, Razvan

Plate tectonics is the unifying paradigm of geodynamics yet the mechanisms and causes of its initiation remain controversial. Some models suggest that plate tectonics initiates when the strength of lithosphere is lower than 20-200 MPa, below the frictional strength of lithospheric rocks (>700 MPa). At present-day, major plate boundaries such as the subduction interface, transform faults, and extensional faults at mid-oceanic ridge core complexes indicate a transition from brittle behaviour to stable sliding at depths between 10 and 40 km, in association with water-rock interactions forming phyllosilicates. We explored the rheological behaviour of lizardite, an archetypal phyllosilicate of the serpentinemore » group formed in oceanic and subduction contexts, and its potential influence on weakening of the lithospheric faults and shear zones. High-pressure deformation experiments were carried out on polycrystalline lizardite - the low temperature serpentine variety - using a D-DIA apparatus at a variety of pressure and temperature conditions from 1 to 8 GPa and 150 to 400 C and for strain rates between 10{sup -4} and 10{sup -6} s{sup -1}. Recovered samples show plastic deformation features and no evidence of brittle failure. Lizardite has a large rheological anisotropy, comparable to that observed in the micas. Mechanical results and first-principles calculations confirmed easy gliding on lizardite basal plane and show that the flow stress of phyllosilicate is in the range of the critical value of 20-200 MPa down to depths of about 200 km. Thus, foliated serpentine or chlorite-bearing rocks are sufficiently weak to account for plate tectonics initiation, aseismic sliding on the subduction interface below the seismogenic zone, and weakening of the oceanic lithosphere along hydrothermally altered fault zones. Serpentinisation easing the deformation of the early crust and shallow mantle reinforces the idea of a close link between the occurrence of plate tectonics and

Global deglaciation and the re-appearance of microbial matground-dominated ecosystems in the late Paleozoic of Gondwana.

PubMed

Buatois, L A; Netto, R G; Gabriela Mángano, M; Carmona, N B

2013-07-01

The extensive matgrounds in Carboniferous-Permian open-marine deposits of western Argentina constitute an anachronistic facies, because with the onset of penetrative bioturbation during the early Paleozoic microbial mats essentially disappeared from these settings. Abundant microbially induced sedimentary structures in the Argentinean deposits are coincident with the disappearance of trace and body fossils in the succession and with a landward facies shift indicative of transgressive conditions. Deposits of the Late Carboniferous-Early Permian glacial event are well developed in adjacent basins in eastern Argentina, Brazil, South Africa and Antarctica, but do not occur in the western Andean basins of Argentina. However, the deglaciation phase is indirectly recorded in the studied region by a rapid rise in sea level referred to as the Stephanian-Asselian transgression. We suggest that an unusual release of meltwater during the final deglaciation episode of the Gondwana Ice Age may have dramatically freshened peri-Gondwanan seas, impacting negatively on coastal and shallow-marine benthic faunas. Suppression of bioturbation was therefore conducive to a brief re-appearance of matground-dominated ecosystems, reminiscent of those in the precambrian. Bioturbation is essential for ecosystem performance and plays a major role in ocean and sediment geochemistry. Accordingly, the decimation of the mixed layer during deglaciation in the Gondwana basins may have altered ecosystem functioning and geochemical cycling. © 2013 John Wiley & Sons Ltd.

Tectonics of the central Andes

NASA Technical Reports Server (NTRS)

Bloom, Arthur L.; Isacks, Bryan L.; Fielding, Eric J.; Fox, Andrew N.; Gubbels, Timothy L.

1989-01-01

Acquisition of nearly complete coverage of Thematic Mapper data for the central Andes between about 15 to 34 degrees S has stimulated a comprehensive and unprecedented study of the interaction of tectonics and climate in a young and actively developing major continental mountain belt. The current state of the synoptic mapping of key physiographic, tectonic, and climatic indicators of the dynamics of the mountain/climate system are briefly reviewed.

Quaternary landscape evolution of tectonically active intermontane basins: the case of the Middle Aterno River Valley (Abruzzo, Central Italy)

NASA Astrophysics Data System (ADS)