Multiple sources and magmatic evolution of the Late Triassic Daocheng batholith in the Yidun Terrane: Implications for evolution of the Paleo-Tethys Ocean in the eastern Tibetan Plateau

Granitoids with diverse composition and tectonic settings provide important tools for exploring crustal evolution and regional geodynamic history. Here we present an integrated study using petrological, mineralogical, zircon U-Pb geochronological, whole-rock geochemical, and isotopic data on the Late Triassic Daocheng batholith in the Yidun Terrane with a view to understanding the petrogenesis of a compositionally diverse batholith and its implications for the evolution of the Paleo-Tethys Ocean in the eastern Tibetan Plateau. The different lithological units of the batholith, including granodiorite, monzogranite, and quartz diorite, with abundant mafic microgranular enclaves in the granodiorite (MME I) and monzogranite (MME II), show identical crystallization ages of 218−215 Ma. The mineral assemblage and chemical composition of the granodiorite are identical to those of tonalitic-granodioritic melts generated under water-unsaturated conditions. The insignificant Eu anomalies and low magmatic temperatures indicate hydrous melting in the source. The relatively narrow range of whole-rock chemical and Sr-Nd isotopes, as well as the zircon trace element and Hf isotopic compositions of the granodiorite, suggest a homogeneous crustal source for the magma. Our modeling suggests that the rock was produced by 20−50% of lower crustal melting. The Daocheng monzogranites display more evolved compositions and larger variations in Sr-Nd-Hf isotopes than the granodiorite, which are attributed to assimilation and the fractional crystallization process. This is evidenced by the presence of metasedimentary enclave and inherited zircon grains with Neoproterozoic and Paleozoic ages, a non-cotectic trend in composition, and the trend shown by the modeling of initial 87Sr/86Sr ratios and Sr. The quartz diorites and MMEs showing composition similar to that of andesitic primary magma have high zircon εHf(t) values and are characterized by enrichment in LILEs and depletion of HFSEs. They were derived from the partial melting of lithospheric mantle that had been metasomatized by slab melts and fluids. The MMEs in both rocks display typical igneous texture and higher rare earth element (REE) and incompatible element concentrations than their host granites. The presence of fine-grained margins, acicular apatite, and plagioclase megacrysts suggests a magma mingling process. The overgrowth of amphibole around the pyroxene, quartz ocelli rimmed by biotite, and oscillatory zones of plagioclase are all indicative of chemical diffusion. Their enriched Sr-Nd isotopes imply isotopic equilibrium with the host granites. Based on a comparison with the coeval subduction-related magmatism, we propose that subduction and subsequent rollback of the Paleo-Tethys (Garzê-Litang Ocean) oceanic slab was the possible mechanism that triggered the diverse Triassic magmatism within the eastern Tibetan Plateau.

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Supplemental Material: Multiple sources and magmatic evolution of the Late Triassic Daocheng batholith in the Yidun Terrane: Implications for evolution of the Paleo-Tethys Ocean in the eastern Tibetan Plateau

10.1130/gsab.s.16652782.v1 ◽

2021 ◽

Author(s):

Pengsheng Dong ◽

Guochen Dong

Keyword(s):

Trace Elements ◽

Geochemical Modeling ◽

Major And Trace Elements ◽

Late Triassic ◽

Magmatic Evolution ◽

Eastern Tibetan Plateau ◽

Isotopic Data ◽

Multiple Sources ◽

Icp Ms ◽

Tethys Ocean

Table S1: Mineral association of samples from the Daocheng batholith; Table S2: LA-ICP-MS U-Pb isotopic data for zircons from the Daocheng batholith; Table S3: Hf isotopic data for zircons from the Daocheng batholith; Table S4: Trace elements data for zircons from the Daocheng batholith; Table S5: Major and trace elements data for the Daocheng batholith; Table S6: Whole-rock Sr-Nd isotopic data of the Daocheng batholith; Table S7: Representative microprobe analyses of amphibole from the Daocheng batholith; Table S8: Partition coefficient for minerals used in geochemical modeling.

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Supplemental Material: Multiple sources and magmatic evolution of the Late Triassic Daocheng batholith in the Yidun Terrane: Implications for evolution of the Paleo-Tethys Ocean in the eastern Tibetan Plateau

10.1130/gsab.s.16652782 ◽

2021 ◽

Author(s):

Pengsheng Dong ◽

Guochen Dong

Keyword(s):

Trace Elements ◽

Geochemical Modeling ◽

Major And Trace Elements ◽

Late Triassic ◽

Magmatic Evolution ◽

Eastern Tibetan Plateau ◽

Isotopic Data ◽

Multiple Sources ◽

Icp Ms ◽

Tethys Ocean

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Quantifying the contribution of upper‐middle crustal shortening and lower crustal thickening to surface uplift in the south‐eastern Tibetan Plateau

Geological Journal ◽

10.1002/gj.4113 ◽

2021 ◽

Author(s):

Chaoyang Li ◽

Xiaodian Jiang ◽

Wei Gong

Keyword(s):

Tibetan Plateau ◽

Crustal Thickening ◽

Eastern Tibetan Plateau ◽

The South ◽

Crustal Shortening ◽

South Eastern ◽

Surface Uplift ◽

Lower Crustal

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Source and pressure effects in the genesis of the Late Triassic high Sr/Y granites from the Songpan-Ganzi Fold Belt, eastern Tibetan Plateau

Lithos ◽

10.1016/j.lithos.2020.105584 ◽

2020 ◽

Vol 368-369 ◽

pp. 105584

Author(s):

Qiong-Yao Zhan ◽

Di-Cheng Zhu ◽

Qing Wang ◽

Roberto F. Weinberg ◽

Jin-Cheng Xie ◽

...

Keyword(s):

Tibetan Plateau ◽

Pressure Effects ◽

Late Triassic ◽

Eastern Tibetan Plateau ◽

Fold Belt

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Late Triassic orogenic assembly of the Tibetan Plateau: constraints from magmatism and metamorphism in the east Lhasa terrane

Journal of Petrology ◽

10.1093/petrology/egab032 ◽

2021 ◽

Author(s):

Yanfei Chen ◽

Zeming Zhang ◽

Richard M Palin ◽

Zuolin Tian ◽

Hua Xiang ◽

...

Keyword(s):

Crustal Thickening ◽

Late Triassic ◽

The Tibetan Plateau ◽

Plate Convergence ◽

Lhasa Terrane ◽

The North ◽

Tectonic History ◽

Peak Metamorphism ◽

Tethys Ocean ◽

Lower Crustal

Abstract The early Mesozoic evolution of the Lhasa terrane, which represents a major component of the Himalayan-Tibetan orogen, remains highly controversial. In particular, geological units and events documented either side of the eastern Himalayan syntaxis (EHS) are poorly correlated. Here, we report new petrological, geochemical and geochronological data for co-genetic peraluminous S-type granites and metamorphic rocks (gneiss and schist) from the Motuo–Bomi–Chayu region of the eastern Lhasa terrane, located on the eastern flank of the EHS. Zircon U–Pb dating indicates that these units record both Late Triassic magmatic (216–206 Ma) and metamorphic (209–198 Ma) episodes. The granites were derived from a Paleoproterozoic crustal source with negative zircon εHf(t) values (–5.5 to –16.6) and TDM2 model ages of 1.51–1.99 Ga, and are interpreted to have formed by crustal anatexis of nearby metasediments during collisional orogeny and crustal thickening. The gneisses and schists experienced similar upper amphibolite-facies peak metamorphism and associated partial melting, followed by decompressional cooling and retrograde metamorphism. These rocks were buried to lower-crustal depths and then exhumated to the surface in a collisional orogenic setting during plate convergence. From comparison of these data to other metamorphic belts with similar grades and ages, and association of coeval granitic magmatism widespread in the central-east Lhasa terrane, we propose that the studied co-genetic magmatism and metamorphism in the Motuo–Bomi–Chayu region records Late Triassic accretion of the North Lhasa and South Lhasa terranes, which represents the first evidence of the Paleo-Tethys ocean (PTO) closure in this part of Asia. These data provide new constraints on the spatial and temporal evolution of the Paleo-Tethyan Wilson Cycle and provide a ‘missing link’ to correlate the geology and tectonic history of the Lhasa terrane continental crust on either side of the EHS.

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Imaging the Late Triassic lithospheric architecture of the Yidun Terrane, eastern Tibetan Plateau: Observations and interpretations

Geological Society of America Bulletin ◽

10.1130/b35778.1 ◽

2021 ◽

Author(s):

Qiong-Yao Zhan ◽

Di-Cheng Zhu ◽

Qing Wang ◽

Peter A. Cawood ◽

Jin-Cheng Xie ◽

...

Keyword(s):

Tibetan Plateau ◽

Oceanic Lithosphere ◽

Late Triassic ◽

Eastern Tibetan Plateau ◽

Magmatic Differentiation ◽

Isotopic Compositions ◽

Magmatic Rocks ◽

Mantle Sources ◽

Magma Sources ◽

Nonlinear Trends

The present-day lithospheric architecture of modern and ancient orogens can be imaged by geophysical techniques. For ancient orogens, unravelling their architecture at the time of formation is hindered by later tectono-magmatic events. In this paper, we use spatial variations in radiogenic isotopic compositions of Late Triassic magmatism from the Yidun Terrane, eastern Tibetan Plateau, to establish its lithospheric architecture during the Triassic. Comprehensive geochemical and isotopic data of Late Triassic magmatic rocks from four transects across the Yidun Terrane document eastward enrichment in whole-rock Nd, Sr, and zircon Hf isotopic compositions. Mafic and felsic rocks of major plutons show coherent and nonlinear trends in the Zr and P2O5 systematics and have limited variation of isotopic compositions. This indicates that Late Triassic magmatic differentiation was dominated by fractionation of mantle-derived mafic magmas. The spatial isotopic trends result from changing mantle sources, including variable contributions of isotopically depleted asthenospheric mantle and isotopically enriched subcontinental lithospheric mantle (SCLM) to magma sources. The spatial variation of mantle sources suggests a westward thinning of the SCLM during the Triassic. We propose that this architecture is most likely associated with eastward subduction of oceanic lithosphere of the Jinshajiang Ocean located at the west of the Yidun Terrane, immediately prior to the Late Triassic magmatism.

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