Tectonic Transition from Paleo- to Neo-Tethyan Ocean in Tangjia-Sumdo Area, Southern Tibet: Constraints from Early Jurassic Magmatism

AbstractCretaceous–Miocene adakitic rocks in the southern Lhasa sub-terrane have been intensively investigated, while possible Early Jurassic adakitic rocks in this area have been largely neglected. Petrological and geochemical studies revealed adakitic affinities of an Early Jurassic quartz diorite intrusion with mafic enclaves and three tonalite bodies from the Jiacha area in the southern Lhasa sub-terrane. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) zircon U–Pb dating suggests crystallization ages of 199–179 Ma for these rocks. Both quartz diorites and tonalites have typical adakitic geochemical characteristics such as high Al2O3 (15.14–18.22 wt.%) and Sr (363–530 ppm) contents, low Y (4.46–15.9 ppm) and Yb (0.51–1.74 ppm) contents and high Sr/Y ratios of 27–106. The adakitic quartz diorites are further characterized by high MgO (2.63–3.46 wt.%), Mg# (48–54) and εHf(t) (6.6–13.4) values, which were probably produced by partial melting of a subducted oceanic slab with a mantle contribution. The adakitic tonalites have very low abundances of compatible elements and relatively low εHf(t) values (3.5–10.3), and are interpreted to have formed by partial melting of Neoproterozoic mafic lower crust. Upwelling asthenosphere, triggered by rollback of the subducting Bangong–Nujiang (Meso-Tethys) oceanic plate, provided the necessary heat for slab and lower crust melting, resulting in the geochemical diversity of the coexisting felsic intrusive rocks. Contrary to other models, this study further demonstrates that the Bangong–Nujiang oceanic plate was subducted southward beneath the Lhasa terrane during the Early Jurassic.

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Reappraisal of the Mesozoic tectonic transition from the Paleo-Tethyan to Paleo-Pacific domains in South China

Geological Society of America Bulletin ◽

10.1130/b35755.1 ◽

2021 ◽

Author(s):

Chengshi Gan ◽

Yuzhi Zhang ◽

Yuejun Wang ◽

Xin Qian ◽

Yang Wang

Keyword(s):

South China ◽

Middle Jurassic ◽

Late Jurassic ◽

Sedimentary Rocks ◽

Early Jurassic ◽

Igneous Rocks ◽

Late Triassic ◽

Geochemical Data ◽

South China Block ◽

Tectonic Transition

The southeastern (SE) South China Block was mainly influenced by the Paleo-Tethyan and Paleo-Pacific dynamic domains during the Mesozoic. The initial timing of the tectonic transition between these two domains in the SE South China Block still remains debated. The transition would affect the nature of the lithosphere and material provenance of sediments, and, therefore, igneous and sedimentary rocks in the area could record such dynamic processes. In this study, published geochronological and geochemical data of the Triassic and Jurassic igneous rocks and detrital zircon data of contemporaneous sedimentary rocks in the SE South China Block were compiled, aiming to provide constraints on the tectonic transition via tracing the spatial-temporal variations in the nature of the lithosphere and sedimentary provenance signals. The compiled results suggest that the magmatic intensity and volume decreased significantly from the Late Triassic to Early−Middle Jurassic, with an obvious magmatic quiescence between them, and increased from the Early−Middle Jurassic to Late Jurassic. The εNd(t) and zircon εHf(t) values of mafic rocks, granitoids, and shoshonitic rocks remarkably increased from the Late Triassic to Early−Middle Jurassic, indicative of variations in the lithospheric mantle and continental crust. Such variations suggest that the initial tectonic transition occurred at the earliest Early Jurassic. Based on the southward paleocurrents from Early Jurassic sandstone, E-W−trending extension of Early−Middle Jurassic mafic and shoshonitic rocks, and similar sedimentary provenances of Late Triassic and Early−Middle Jurassic sedimentary rocks, these features imply that the SE South China Block was not immediately influenced by the Paleo-Pacific domain during the Early−Middle Jurassic. However, from the Early−Middle Jurassic to Late Jurassic and Early Cretaceous, the spatial distribution, geochemical signatures, magmatic intensity, and magmatic volume of igneous rocks and provenance of sedimentary rocks exhibit obvious variations, and the regional fold hinge direction changed from E-W−trending to NE-trending, suggesting significant effects from Paleo-Pacific subduction on the SE South China Block. Thus, the Mesozoic tectonic transition from the Paleo-Tethyan to the Paleo-Pacific dynamic domain in the SE South China Block likely occurred during the Early−Middle Jurassic.

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Magnetostratigraphic study of a Late Cretaceous−Paleogene succession in the eastern Xining basin, NE Tibet: Constraint on the timing of major tectonic events in response to the India-Eurasia collision

Geological Society of America Bulletin ◽

10.1130/b35874.1 ◽

2021 ◽

Author(s):

Chi-Cheng He ◽

Yue-Qiao Zhang ◽

Shao-Kai Li ◽

Kai Wang ◽

Jian-Qing Ji

Keyword(s):

Late Cretaceous ◽

Accumulation Rate ◽

Foreland Basin ◽

Time Span ◽

Early Miocene ◽

Foreland Basins ◽

Southern Tibet ◽

Tectonic Transition ◽

History Of ◽

Xining Basin

Cretaceous-Cenozoic basins developed in the NE Tibetan Plateau contain key archives to unravel the growth history of the plateau in response to the India-Eurasia collision. Here we present magnetostratigraphic results of a Late Cretaceous to Paleogene succession of the Zhongba section outcropping at the southern margin of the eastern Xining basin. This succession consists of three lithological units punctuated by two stratigraphic unconformities, which best recorded the deformation history of this foreland basin. Detailed magnetostratigraphic investigation show that the lower terrestrial sedimentary rock unit, the Minhe Group, was deposited in latest Cretaceous in the time span of ca. 74.5−69.2 Ma; the middle unit was deposited in Paleogene in the time span of ca. 49.3−22 Ma; and the upper conglomeratic unit, not dated, possibly was deposited in early Miocene. Accordingly, the Cretaceous−Paleogene unconformity, widely observed in the foreland basins of NE Tibet, represents a sedimentary hiatus duration of ∼19.9 m.y., from ca. 69.2 Ma to ca. 49.3 Ma, which possibly recorded the far-field response to the tectonic transition from Neo-Tethys oceanic plate subduction to the India-Eurasia collision in southern Tibet. Changes in provenance, sedimentary accumulation rate, and mean susceptibility value at ca. 33−30 Ma, and the total prolate anisotropy of magnetic susceptibility (AMS) ellipsoids and provenance shifting since ca. 23−19 Ma, point to the pulsed growth of West Qinling, and rapid uplift of Laji Shan, respectively, indicating an enhanced effect of the India-Eurasia collision in Oligocene and early Miocene. AMS results show a clockwise rotation of the shortening direction from NEN-SWS in latest Cretaceous to NE-SW in Paleogene.

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Mesozoic crustal evolution of southern Tibet: Constraints from the early Jurassic igneous rocks in the Central Lhasa terrane

Lithos ◽

10.1016/j.lithos.2020.105557 ◽

2020 ◽

Vol 366-367 ◽

pp. 105557 ◽

Cited By ~ 1

Author(s):

Xin Dong ◽

Yaoling Niu ◽

Zeming Zhang ◽

Zuolin Tian ◽

Zhenyu He

Keyword(s):

Early Jurassic ◽

Igneous Rocks ◽

Crustal Evolution ◽

Southern Tibet ◽

Lhasa Terrane

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Early Jurassic highly fractioned rhyolites and associated sedimentary rocks in southern Tibet: constraints on the early evolution of the Neo-Tethyan Ocean

International Journal of Earth Sciences ◽

10.1007/s00531-018-1646-2 ◽

2018 ◽

Vol 108 (1) ◽

pp. 137-154

Author(s):

Chao Wang ◽

Lin Ding ◽

Li-Yun Zhang ◽

Xiang-Li Ding ◽

Ya-Hui Yue

Keyword(s):

Sedimentary Rocks ◽

Early Jurassic ◽

Early Evolution ◽

Southern Tibet

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Tectonic transition in the Early Jurassic in South China

Geochimica et Cosmochimica Acta ◽

10.1016/j.gca.2006.06.1162 ◽

2006 ◽

Vol 70 (18) ◽

pp. A626

Author(s):

W.D. Sun ◽

X. Ding ◽

Y.H. Hu

Keyword(s):

South China ◽

Early Jurassic ◽

Tectonic Transition

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Exploring Mesozoic Climates - Modeling and Evaluation of Proxy Distributions

10.5194/egusphere-egu2020-9074 ◽

2020 ◽

Author(s):

Jan Landwehrs ◽

Georg Feulner ◽

Matthias Hofmann ◽

Stefan Petri ◽

Benjamin Sames ◽

...

Keyword(s):

Climatic Conditions ◽

Early Jurassic ◽

Late Triassic ◽

Earth System ◽

Tectonic Transition ◽

Climate Indicators ◽

Orbital Configuration ◽

Evolution Of Mammals ◽

High Precipitation ◽

Proxy Reconstructions

The Mesozoic Era (~252-66 Ma) is a decisive period in Earth&#8217;s history. It is marked by a tectonic transition from the Pangea supercontinent towards a modern continental configuration as well as the ecological success of the dinosaurs and the evolution of mammals, flowering plants, stony corals and important groups of planktic calcifiers. The Mesozoic is generally considered as a greenhouse climate period, with especially high global temperatures during the Triassic and the Late Cretaceous. Here, we present novel modeling results on the evolution of global climatic conditions through the Mesozoic.An ensemble of equilibrium climate states for 40 geological timeslices between 255 and 60 Ma is simulated with the CLIMBER-3&#945; Earth System Model of Intermediate Complexity. The influence of changing paleogeography, sea level, vegetation cover, solar luminosity, orbital configuration and atmospheric CO2 concentration is systematically tested based on constraints from published geological proxy reconstructions and previous modeling work.Atmospheric pCO2 is found to be the strongest driver of global mean temperatures, which are generally elevated above the present and reach &#8805;20&#176;C in the Late Triassic to Early Jurassic and the mid-Cretaceous if a recently published pCO2 proxy compilation is employed. The simulated seasonal latitudinal shift of high precipitation zones exhibits a maximum during the mid-Triassic to Early Jurassic and therefore supports the notion of a &#8220;Megamonsoon&#8221; during this time. Simulated humid and arid climate zones generally agree well with spatial distributions of geologic climate indicators like coal and evaporites, although some discrepancies exist. The same applies to the correlation of fossil stony coral reef distributions with regions where seawater temperatures would have been suitable for (modern) coral reefs. We will discuss which changes of Earth System parameters throughout the Mesozoic can best explain shifts in these distributions.

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