scholarly journals Tectonic evolution and high-pressure rock exhumation in the Qiangtang Terrane, Central Tibet

2015 ◽  
Vol 7 (1) ◽  
pp. 329-367 ◽  
Author(s):  
Z. Zhao ◽  
P. D. Bons ◽  
G. Wang ◽  
A. Soesoo ◽  
Y. Liu
Keyword(s):  
High Pressure ◽  
Tectonic Evolution ◽  
Late Triassic ◽  
The South ◽  
Metamorphic Belt ◽  
The North ◽  
Ophiolitic Mélange ◽  
Basement Rocks ◽  
Central Tibet ◽  
Qiangtang Terrane

Abstract. Conflicting interpretations of the > 500 km long, east-west trending Qiangtang Metamorphic Belt have led to very different and contradicting models for the Permo-Triassic tectonic evolution of Central Tibet. We define two metamorphic events, one that only affected Pre-Ordovician basement rocks and one subduction-related Triassic high-pressure metamorphism event. Detailed mapping and structural analysis allowed us to define three main units that were juxtaposed due to collision of the North and South Qiangtang terranes after closure of the Ordovician-Triassic ocean that separated them. The base is formed by the Precambrian-Carboniferous basement, followed by non-metamorphic ophiolitic mélange, containing mafic rocks that range in age from the Ordovician to Middle Triassic. The top of the sequence is formed by strongly deformed sedimentary mélange that contains up to > 10 km size rafts of both un-metamorphosed Permian sediments and high-pressure blueschists. We propose that the high-pressure rocks were exhumed from underneath the South Qiangtang Terrane in an extensional setting caused by the pull of the northward subducting slab of the Shuanghu-Tethys. High-pressure rocks, sedimentary mélange and margin sediments were thrust on top of the ophiolitic mélange that was scraped off the subducting plate. Both units were subsequently thrust on top of the South Qiantang Terrane continental basement. Onset of Late Triassic sedimentation marked the end of the amalgamation of both Qiangtang terranes and the beginning of spreading between Qiantang and North Lhasa to the south, leading to the deposition of thick flysch deposits in the Jurassic.

scholarly journals Tectonic evolution and high-pressure rock exhumation in the Qiangtang terrane, central Tibet

Solid Earth ◽  
2015 ◽  
Vol 6 (2) ◽  
pp. 457-473 ◽  
Author(s):  
Z. Zhao ◽  
P. D. Bons ◽  
G. Wang ◽  
A. Soesoo ◽  
Y. Liu
Keyword(s):  
High Pressure ◽  
Tectonic Evolution ◽  
Late Triassic ◽  
The South ◽  
Metamorphic Belt ◽  
The North ◽  
Ophiolitic Mélange ◽  
Basement Rocks ◽  
Central Tibet ◽  
Qiangtang Terrane

Abstract. Conflicting interpretations of the > 500 km long, east–west-trending Qiangtang metamorphic belt have led to very different and contradicting models for the Permo–Triassic tectonic evolution of central Tibet. We define two metamorphic events, one that only affected pre-Ordovician basement rocks and one subduction-related Triassic high-pressure metamorphism event. Detailed mapping and structural analysis allowed us to define three main units that were juxtaposed due to collision of the north and south Qiangtang terranes after closure of the Ordovician–Triassic ocean that separated them. The base is formed by the Precambrian–Carboniferous basement, followed by non-metamorphic ophiolitic mélange containing mafic rocks that range in age from the Ordovician to Middle Triassic. The top of the sequence is formed by strongly deformed sedimentary mélange that contains up to > 10 km size rafts of both unmetamorphosed Permian sediments and high-pressure blueschists. We propose that the high-pressure rocks were exhumed from underneath the south Qiangtang terrane in an extensional setting caused by the pull of the northward subducting slab of the Shuanghu–Tethys. High-pressure rocks, sedimentary mélange and margin sediments were thrust on top of the ophiolitic mélange that was scraped off the subducting plate. Both units were subsequently thrust on top of the south Qiantang terrane continental basement. Onset of Late Triassic sedimentation marked the end of the amalgamation of both Qiangtang terranes and the beginning of spreading between Qiantang and north Lhasa to the south, leading to the deposition of thick flysch deposits in the Jurassic.

scholarly journals Devonian to Triassic tectonic evolution and basin transition in the East Kunlun−Qaidam area, northern Tibetan Plateau: Constraints from stratigraphy and detrital zircon U−Pb geochronology

2021 ◽  
Author(s):  
Jiaopeng Sun ◽  
Yunpeng Dong ◽  
Licheng Ma ◽  
Shiyue Chen ◽  
Wan Jiang
Keyword(s):  
High Pressure ◽  
Tectonic Evolution ◽  
Late Triassic ◽  
The South ◽  
Northern Tibet ◽  
The North ◽  
Northern Tibetan Plateau ◽  
East Kunlun ◽  
North Qaidam ◽  
Tethys Ocean

The late Paleozoic to Triassic was an important interval for the East Kunlun−Qaidam area, northern Tibet, as it witnessed prolonged subduction of the South Kunlun Ocean, a major branch of the Paleo-Tethys Ocean whose closure led to the formation of Pangea. However, the geologic history of this stage is poorly constrained due to the paucity of tectonothermal signatures preserved during a magmatic lull. This article presents a set of new provenance data incorporating stratigraphic correlation, sandstone petrology, and zircon U−Pb dating to depict changes in provenance that record multiple stages of topographic and tectonic transition in the East Kunlun−Qaidam area over time in response to the evolution of the South Kunlun Ocean. Devonian intra-arc rifting is recorded by bimodal volcanism and rapid alluvial-lacustrine sedimentation in the North Qaidam Ultra High/High Pressure Belt, whose sources include the Olongbuluke Terrane and southern North Qaidam Ultra High/High Pressure Belt. Southward transgression submerged the East Kunlun−Qaidam area during the Carboniferous prior to the rapid uplift of the Kunlun arc, which changed the provenance during the Early Permian. This shift in provenance for the western Olongbuluke Terrane and thick carbonate deposition throughout the North Qaidam Ultra High/High Pressure Belt in the late Early Carboniferous indicate that the North Qaidam Ultra High/High Pressure Belt should have been inundated, terminating an ∼95 m.y. erosion history. The closure of the South Kunlun Ocean in the late Triassic generated a retroarc foreland along the Zongwulong Tectonic Belt, which is represented by the development of a deep-water, northward-tapering flysch deposystem that was supplied by the widely elevated Kunlun−Qaidam−Olongbuluke Terrane highland. This new scenario allows us to evaluate current models concerning the assembly of northern Tibet and the tectonic evolution of the Paleo-Tethys Ocean.

scholarly journals 3D density modelling of Gemeric granites of the Western Carpathians

2017 ◽  
Vol 68 (3) ◽  
pp. 177-192 ◽  
Author(s):  
Ján Šefara ◽  
Miroslav Bielik ◽  
Jozef Vozár ◽  
Martin Katona ◽  
Viktória Szalaiová ◽  
...  
Keyword(s):  
Tectonic Evolution ◽  
Lower Boundary ◽  
Western Carpathians ◽  
Mountain Range ◽  
The South ◽  
Geophysical Research ◽  
The North ◽  
Basement Rocks ◽  
Tectonic Contact ◽  
Upper Boundary

Abstract The position of the Gemeric Superunit within the Western Carpathians is unique due to the occurrence of the Lower Palaeozoic basement rocks together with the autochthonous Upper Palaeozoic cover. The Gemeric granites play one of the most important roles in the framework of the tectonic evolution of this mountain range. They can be observed in several small intrusions outcropping in the western and south-eastern parts of the Gemeric Superunit. Moreover, these granites are particularly interesting in terms of their mineralogy, petrology and ages. The comprehensive geological and geophysical research of the Gemeric granites can help us to better understand structures and tectonic evolution of the Western Carpathians. Therefore, a new and original 3D density model of the Gemeric granites was created by using the interactive geophysical program IGMAS. The results show clearly that the Gemeric granites represent the most significant upper crustal anomalous low-density body in the structure of the Gemeric Superunit. Their average thickness varies in the range of 5–8 km. The upper boundary of the Gemeric granites is much more rugged in comparison with the lower boundary. There are areas, where the granite body outcrops and/or is very close to the surface and places in which its upper boundary is deeper (on average 1 km in the north and 4–5 km in the south). While the depth of the lower boundary varies from 5–7 km in the north to 9–10 km in the south. The northern boundary of the Gemeric granites along the tectonic contact with the Rakovec and Klátov Groups (North Gemeric Units) was interpreted as very steep (almost vertical). The results of the 3D modelling show that the whole structure of the Gemeric Unit, not only the Gemeric granite itself, has an Alpine north-vergent nappe structure. Also, the model suggests that the Silicicum–Turnaicum and Meliaticum nappe units have been overthrusted onto the Golčatov Group.

Lithospheric Extension of the Accretionary Wedge: An Example From the Lanling High-Pressure Metamorphic Terrane in Central Qiangtang, Tibet

2021 ◽  
Author(s):  
Xiao Liang ◽  
Genhou Wang ◽  
Wentao Cao ◽  
Marnie Forster ◽  
Gordon Lister
Keyword(s):  
High Pressure ◽  
Subduction Zones ◽  
Hanging Wall ◽  
Late Triassic ◽  
Accretionary Wedge ◽  
Metamorphic Belt ◽  
The North ◽  
Multidisciplinary Study ◽  
Lithospheric Extension ◽  
Tethys Ocean

<p>Deciphering the exhumation mechanism of high-pressure, low-temperature (HP-LT) metamorphic rocks can provide important insights into the tectonic evolution of oceanic subduction zones at active continental margins. Here we present a multidisciplinary study examining the exhumation tectonics of the Permo–Triassic eclogite-bearing Lanling HP-LT terrane within the Central Qiangtang metamorphic belt (CQMB). Field relations and microscopic observations show that the HP-LT rocks are separated from the Permian ophiolite mélange of the hanging wall by low-angle detachments and exhibit five stages of deformation. The pervasive top-to-the-SW and -S shearing structures imply that the Lanling HP-LT terrane was exhumed as a transtensional metamorphic core complex (mcc). The results of the petrological and mineralogical analysis and pseudosection modeling of eclogites indicate that the eclogites and blueschists are characterized by synexhumation mineral growth pulses with decompressional P-T trajectories. A compilation of previous geochronological data and our <sup>40</sup>Ar/<sup>39</sup>Ar dating results of shearing structures in HP-LT rocks indicate a continuous exhumation at ca. 244–210 Ma. Moreover, the CQMB experienced lithospheric transtension, as shown by the Middle–Late Triassic geological events, which include mantle upwelling at ca. 237–230 Ma and abyssal basin development in the Anisian–middle Norian. These observations indicate that the CQMB is likely a autochthonous accretionary wedge resulting from northward subduction of the Paleo-Tethys Ocean beneath the North Qiangtang Block (NQB). Moreover, the transtension of the CQMB occurred in the late stage of the oceanic subduction, which was probably triggered by oceanic slab rollback.</p>

scholarly journals New insights on the early Mesozoic evolution of multiple tectonic regimes in the northeastern North China Craton from the detrital zircon provenance of sedimentary strata

Solid Earth ◽  
2018 ◽  
Vol 9 (6) ◽  
pp. 1375-1397 ◽  
Author(s):  
Yi Ni Wang ◽  
Wen Liang Xu ◽  
Feng Wang ◽  
Xiao Bo Li
Keyword(s):  
North China Craton ◽  
North China ◽  
Early Jurassic ◽  
Orogenic Belt ◽  
Detrital Zircons ◽  
Late Triassic ◽  
Early Triassic ◽  
The South ◽  
The North ◽  
Early Mesozoic

Abstract. To investigate the timing of deposition and provenance of early Mesozoic strata in the northeastern North China Craton (NCC) and to understand the early Mesozoic paleotectonic evolution of the region, we combine stratigraphy, U–Pb zircon geochronology, and Hf isotopic analyses. Early Mesozoic strata include the Early Triassic Heisonggou, Late Triassic Changbai and Xiaoyingzi, and Early Jurassic Yihe formations. Detrital zircons in the Heisonggou Formation yield  ∼ 58 % Neoarchean to Paleoproterozoic ages and  ∼ 42 % Phanerozoic ages and were sourced from areas to the south and north of the basins within the NCC, respectively. This indicates that Early Triassic deposition was controlled primarily by the southward subduction of the Paleo-Asian oceanic plate beneath the NCC and collision between the NCC and the Yangtze Craton (YC). Approximately 88 % of the sediments within the Late Triassic Xiaoyingzi Formation were sourced from the NCC to the south, with the remaining  ∼ 12 % from the Xing'an–Mongolia Orogenic Belt (XMOB) to the north. This implies that Late Triassic deposition was related to the final closure of the Paleo-Asian Ocean during the Middle Triassic and the rapid exhumation of the Su–Lu Orogenic Belt between the NCC and YC. In contrast,  ∼ 88 % of sediments within the Early Jurassic Yihe Formation were sourced from the XMOB to the north, with the remaining  ∼ 12 % from the NCC to the south. We therefore infer that rapid uplift of the XMOB and the onset of the subduction of the Paleo-Pacific Plate beneath Eurasia occurred in the Early Jurassic.

GEOLOGY OF BARROW ISLAND OIL FIELD

1973 ◽  
Vol 13 (1) ◽  
pp. 49 ◽  
Author(s):  
Keith Crank
Keyword(s):  
Oil And Gas ◽  
Water Injection ◽  
Water Source ◽  
Upper Jurassic ◽  
Oil Field ◽  
Late Triassic ◽  
Low Permeability ◽  
High Porosity ◽  
The South ◽  
The North

The Barrow Island oil field, which was discovered by the drilling of Barrow 1 in 1964, was declared commercial in 1966. Since then 520 wells have been drilled in the development of this field which has resulted in 309 Windalia Sand oil producers (from about 2200 feet), eight Muderong Greensand oil wells (2800 feet), five Neocomian/Upper Jurassic gas and oil producers (6200 to 6700 feet), eight Barrow Group water source wells and 157 water injection wells.Production averages 41,200 barrels of oil per day, and 98% of this comes from the shallow Windalia Sand Member of Cretaceous (Aptian to Albian) age. These reserves are contained in a broad north-plunging nose truncated to the south by a major down-to-the-south fault. The anticline is thought to have been formed initially from a basement uplift during Late Triassic to Early Jurassic time. Subsequent periods of deposition, uplift and erosion have continued into the Tertiary and modified the structure to its present form. The known sedimentary section on Barrow Island ranges from Late Jurassic to Miocene.The Neocomian/Jurassic accumulations are small and irregular and are not thought to be commercial in themselves. The Muderong Greensand pool is also a limited, low permeability reservoir. Migration of hydrocarbons is thought to have occurred mainly in the Tertiary as major arching did not take place until very late in the Cretaceous or early in the Palaeocene.The Windalia Sand reservoir is a high porosity, low permeability sand which is found only on Barrow Island. One of the most unusual features of this reservoir is the presence of a perched gas cap. Apparently the entire sand was originally saturated with oil, and gas subsequently moved upstructure from the north, displacing it. This movement was probably obstructed by randomly-located permeability barriers.

Geological mapping of the 1985 Chinese—British Tibetan (Xizang—Qinghai) Plateau Geotraverse route

1988 ◽  
Vol 327 (1594) ◽  
pp. 287-305 ◽  
Keyword(s):  
Strike Slip ◽  
Geological Mapping ◽  
Strike Slip Fault ◽  
Fault System ◽  
Late Triassic ◽  
Clastic Rocks ◽  
The North ◽  
Opposite Sequence ◽  
Geological Map ◽  
Qiangtang Terrane

The 1:500,000 coloured geological map of the traverse route combines observations from the Geotraverse, previous mapping, and interpretation of orbital images. The position of all localities visited by Geotraverse participants and basic geological data collected by them along the traverse route are shown on a set of maps originally drawn at 1:100,000 scale, reproduced on microfiche for this publication. More detailed mapping, beyond a single line of section, was achieved in five separate areas. The relationships between major rock units in these areas, and their significance, are outlined in this paper. Near Gyanco, (Lhasa Terrane) an ophiolite nappe, apparently connected with outcrops of ophiolites in the Banggong Suture about 100 km to the north, was under thrust by a discontinuous slice of Carboniferous—Permian clastic rocks and limestone, contrary to a previous report of the opposite sequence. At Amdo, a compressional left-lateral strike-slip fault zone has modified relationships along the Banggong Suture. Near Wuli, (northern Qiangtang Terrane) limited truncation of Triassic strata at the angular unconformity below Eocene redbeds demonstrates that most of the folding here is of Tertiary age. The map of the nearby Erdaogou region displays strong fold and thrust-shortening of the Eocene redbeds, evidence of significant crustal shortening after the India- Asia collision began. In the Xidatan-Kunlun Pass area, blocks of contrasting Permo—Triassic rocks are separated by east-trending faults. Some of these faults are ductile and of late Triassic — early Jurassic age, others are brittle and part of the Neogene—Quaternary Kunlun leftlateral strike-slip fault system. Some more significant remaining problems that geological mapping might help to solve are discussed briefly, including evidence for a possible additional ophiolitic suture within the Qiangtang Terrane.

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