Petrogenesis of Triassic Caojian A-type rhyolites and associated I-type granites in the southeastern Tibetan Plateau: rejuvenation of crystal mush

2021 ◽  
pp. 1-20
Author(s):  
Feng Cong ◽  
De-Feng He ◽  
Wei-Qiang Ji ◽  
Liang Huang ◽  
Bo Xiong ◽  
...  
Keyword(s):  
Tibetan Plateau ◽  
Mafic Magma ◽  
Orogenic Belt ◽  
Late Triassic ◽  
Geochemical Data ◽  
Magmatic Evolution ◽  
Crystal Mush ◽  
High Field Strength ◽  
Southeastern Tibetan Plateau ◽  
Age Estimates

Abstract The orogenic process and crustal growth of the Changning–Menglian Palaeo-Tethys orogenic belt in the southeastern Tibetan Plateau is not fully understood. Triassic Caojian rhyolites and granites occur extensively in this orogenic belt and represent important constraints for this issue. This study aims to examine the relationships between the Triassic Caojian rhyolites and granites and to gain a better understanding of their possible petrogenesis. The study used zircon U–Pb geochronology, trace element analyses and Sr–Nd–Hf isotope data to better understand the relationships and possible origin of the rhyolites and granites. Recent zircon U–Pb ages indicated that the Caojian rhyolites were emplaced at 227.2 Ma, whereas age estimates for Caojian granites were slightly older (233.4–236.9 Ma). The Caojian rhyolites are enriched in large-ion lithophile elements and high-field-strength elements, with elevated FeOtot/MgO and Ga/Al ratios. However, they are significantly depleted in Ba, Sr, Eu, P and Ti. These geochemical characteristics indicate that they have an A-type affinity. Furthermore, the Caojian granites comprise biotite monzogranites and granodiorites and show unfractionated composition. Mineralogically, the Caojian granites were found to contain diagnostic I-type minerals such as hornblende. Geochemical data suggest that the petrogenesis of the Triassic Caojian rhyolites is characterized by rejuvenation of crystal mush represented by the Triassic Caojian granites. The necessary thermal input was supplied by mafic magma. This magmatic evolution was likely related to lithospheric delamination and upwelling of the asthenosphere during the Mid- to Late Triassic, forming post-collisional I-type granites and A-type volcanics in the Changning–Menglian Palaeo-Tethys orogenic belt.

Three stages of arc migration in the Carboniferous-Triassic in northern Qiangtang, central Tibet, China: Ridge subduction and asynchronous slab rollback of the Jinsha Paleotethys

2021 ◽  
Author(s):  
Yin Liu ◽  
Wenjiao Xiao ◽  
Brian F. Windley ◽  
Kefa Zhou ◽  
Rongshe Li ◽  
...  
Keyword(s):  
Tibetan Plateau ◽  
Volcanic Rocks ◽  
Late Triassic ◽  
Geochemical Data ◽  
The Tibetan Plateau ◽  
Ridge Subduction ◽  
Temporal Relationships ◽  
Slab Rollback ◽  
Geodynamic Processes ◽  
Central Tibet

Carboniferous-Triassic magmatism in northern Qiangtang, central Tibet, China, played a key role in the evolution of the Tibetan Plateau yet remains a subject of intense debate. New geochronological and geochemical data from adakitic, Nb-enriched, and normal arc magmatic rocks, integrated with results from previous studies, enable us to determine the Carboniferous-Triassic (312−205 Ma), arc-related, plutonic-volcanic rocks in northern Qiangtang. Spatial-temporal relationships reveal three periods of younging including southward (312−252 Ma), rapid northward (249−237 Ma), and normal northward (234−205 Ma) migrations that correspond to distinct slab geodynamic processes including continentward slab shallowing, rapid trenchward slab rollback, and normal trenchward rollback of the Jinsha Paleotethys rather than the Longmuco-Shuanghu Paleotethys, respectively. Moreover, varying degrees of coexistence of adakites/High-Mg andesites (HMAs)/Nb-enriched basalt-andesites (NEBs) and intraplate basalts in the above-mentioned stages is consistent with the magmatic effects of slab window triggered by ridge subduction, which probably started since the Late Carboniferous and continued into the Late Triassic. The Carboniferous-Triassic multiple magmatic migrations and ridge-subduction scenarios provide new insight into the geodynamic processes of the Jinsha Paleotethys and the growth mechanism of the Tibetan Plateau.

scholarly journals Petrogenesis and Geological Implications of the Oligocene Mingze monzodiorites, Southern Lhasa

Minerals ◽  
2020 ◽  
Vol 10 (4) ◽  
pp. 301
Author(s):  
Kailiang Zhang ◽  
Zeming Shi ◽  
Rong Liao ◽  
Feilin Zhu
Keyword(s):  
Tibetan Plateau ◽  
Field Strength ◽  
Lithospheric Mantle ◽  
High Field ◽  
Geochemical Data ◽  
High Field Strength ◽  
Mafic Rocks ◽  
Mafic Enclaves ◽  
Continental Plate ◽  
Geological Implications

The Mingze Cu-Mo deposit is located in the southern margin of the Lhasa block of the Himalayan Tibetan Plateau. Here, we report the geochronological and geochemical data from Mingze monzodiorites, which hosts the Mingze deposit. Zircon dating indicates that the Mingze monzodiorites were emplaced at ca. 31 Ma (i.e., the Oligocene). The monzodiorites have variable SiO2 and MgO contents, strongly negative high field-strength element (HFSE, such as Ta, Nb, Zr and Hf) anomalies on the normalized trace element diagram and show uniform (87Sr/86Sr)i (0.7066–0.7076), εNd(t) (−2.50 to −4.04) and εHf(t) (+1.50 to +7.50). Their geochemical compositions are different from coeval (40–30 Ma) adakite-like rocks but comparable to coeval mafic enclaves and gabbros. We propose that Mingze monzodiorites were derived from partial melting of the lithospheric mantle, which previously metasomatized by the subducted Indian continental plate that probably subducted into the overlying mantle. The concurrency of the genetically related mafic enclaves and associated intermediate to mafic rocks implies the heterogeneity of the Lhasa lower crust.

Origin of the Triassic Lincang granites in the southeastern Tibetan Plateau: Crystallization from crystal mush

Lithos ◽  
2020 ◽  
Vol 360-361 ◽  
pp. 105452 ◽  
Author(s):  
Feng Cong ◽  
Fu-Yuan Wu ◽  
Wen-Chang Li ◽  
Chuan-Long Mou ◽  
Xiao-Ming Huang ◽  
...  
Keyword(s):  
Tibetan Plateau ◽  
Crystal Mush ◽  
Southeastern Tibetan Plateau

Petrogenesis and tectonic implications of the Late Triassic Nangou granodiorite porphyry in the Eastern Kunlun Orogenic Belt, northern Tibetan Plateau

2020 ◽  
Vol 57 (7) ◽  
pp. 801-813
Author(s):  
Jiaming Yan ◽  
Fengyue Sun ◽  
Ye Qian ◽  
Nan Tian ◽  
Zhengping Yan ◽  
...  
Keyword(s):  
Tibetan Plateau ◽  
Oceanic Lithosphere ◽  
Orogenic Belt ◽  
Crustal Thickening ◽  
Late Triassic ◽  
Magma Source ◽  
Isotopic Data ◽  
Heavy Rare Earth Element ◽  
Geological Processes ◽  
Northern Tibetan Plateau

Triassic granitic magmatism is widespread in the Eastern Kunlun Orogenic Belt (EKOB), northern Tibetan Plateau. Some of the granitoids are characterized by high Sr and low Y contents, and consequently high Sr/Y ratios. These high Sr/Y-ratio granitoids are often interpreted as adakitic rocks, originating from the thickened continental lower crust. However, studies have shown that granitoids with high Sr/Y ratios may have formed via other geological processes. This paper reports U–Pb ages, geochemical and Sr–Nd–Hf isotopic data for newly discovered granodiorite porphyries in the Kunlun River area of the Eastern Kunlun Orogenic Belt, and discusses whether the EKOB experienced crustal thickening during the Triassic. The granodiorite porphyries crystallized at 205 Ma. They have some adakitic characteristics with SiO2 = 66.96–69.68 wt.%, Sr/Y ratios = 31–43, La/Yb = 26.9–57.9, Y = 8.47–11.3, Yb = 0.75–1.30, and MgO = 0.44–0.99 wt.%. However, the relatively flat heavy rare earth element patterns indicate that garnet was not the main residue in the magma source. In addition, combined with Nd–Hf isotopic data, these results indicate that the timing of the original generation of the crustal sources of the granodiorites should be Mesoproterozoic, with the involvement of older (Paleoproterozoic) components. The granodiorite porphyries were emplaced in a post-collisional environment after the northward subduction of Paleo-Tethyan oceanic lithosphere, and without thickening of the continental crust.

Rapid cold slab subduction of the Paleo-Tethys: Insights from lawsonite-bearing blueschist in the Changning–Menglian orogenic belt, southeastern Tibetan Plateau

2020 ◽  
Vol 85 ◽  
pp. 189-223
Author(s):  
Huining Wang ◽  
Fulai Liu ◽  
M. Santosh ◽  
Jia Cai ◽  
Fang Wang ◽  
...  
Keyword(s):  
Tibetan Plateau ◽  
Orogenic Belt ◽  
Southeastern Tibetan Plateau

scholarly journals A New HP–UHP Eclogite Belt Identified in the Southeastern Tibetan Plateau: Tracing the Extension of the Main Palaeo-Tethys Suture Zone

2020 ◽  
Vol 61 (8) ◽  
Author(s):  
Huining Wang ◽  
Fulai Liu ◽  
Zaibo Sun ◽  
Lei Ji ◽  
Jianjiang Zhu ◽  
...  
Keyword(s):  
Tibetan Plateau ◽  
Oceanic Crust ◽  
Average Rate ◽  
Peninsular Malaysia ◽  
Ultrahigh Pressure ◽  
Late Triassic ◽  
Metamorphic Belt ◽  
Middle Cambrian ◽  
Southeastern Tibetan Plateau ◽  
Northern Tibetan Plateau

Abstract The Changning–Menglian orogenic belt (CMOB) in the southeastern Tibetan Plateau is an important link between the Longmu Co–Shuanghu suture (LCSS) in the northern Tibetan Plateau and the Chiang Mai–Inthanon and Bentong–Raub sutures in Thailand and Peninsular Malaysia. These belts and sutures are generally regarded as containing the remnants of the oceanic crust of the Palaeo-Tethys that formed by seafloor spreading as a result of the separation of Gondwana- and Eurasia-derived blocks during the Middle Cambrian. In this paper we report the first discovery of abundant unaltered and retrograde eclogites that occur as irregular lenses and blocks in metasedimentary rocks of the CMOB, and these eclogites form an elongate and almost north–south-trending high-pressure (HP)–ultrahigh-pressure (UHP) metamorphic belt that is ∼200 km long and ∼50 km wide. The newly discovered phengite/talc/epidote–glaucophane eclogites, lawsonite–talc–phengite eclogites, dolomite/magnesite–kyanite eclogites and phengite–kyanite-bearing retrograde eclogites have enriched (E-) and normal mid-ocean ridge basalt (N-MORB)-like affinities and mainly positive as well as some negative whole-rock εNd values (–4·34 to +7·89), which suggest an enriched and depleted oceanic lithosphere source for their protoliths. Magmatic zircons separated from the epidote–glaucophane, magnesite–kyanite and (phengite–kyanite-bearing) retrograde eclogites gave protolith ages of 317–250 Ma, which fit well within the time frame of the opening of the Palaeo-Tethys during the Middle Cambrian and its closure during the Triassic. Abundant metamorphic zircons in the eclogites indicate a Triassic metamorphic event related to the subduction of the Palaeo-Tethys oceanic crust from 235 to 227 Ma. Taking into account previous isotopic age data, we now establish the periods of Early–Middle Triassic (246–227 Ma) and Late Triassic (222–209 Ma) as the ages of subduction and exhumation of the Palaeo-Tethyan oceanic crust, respectively. Thermodynamic modelling revealed that the eclogites record distinct HP–UHP peak metamorphic conditions of 23·0–25·5 kbar and 582–610 °C for the phengite–glaucophane eclogites, 24·0–25·5 kbar and 570–586 °C for the talc–glaucophane eclogites, 29·0–31·0 kbar and 675–712 °C for the dolomite–kyanite eclogites, and 30·0–32·0 kbar and 717–754 °C for the magnesite–kyanite eclogites. These P–T estimates and geochronological data indicate that the Palaeo-Tethys oceanic slab was subducted to different mantle depths from 75 km down to 95 km, forming distinct types of eclogite with a variety of peak eclogite-facies mineral assemblages. The eclogites consistently record clockwise metamorphic P–T–t paths characterized by a heating–compression prograde loop under a low geothermal gradient of 5–10 °C km–1, indicating the rapid subduction of cold oceanic crust at a rate of 4·5–6·0 km Ma–1, followed by isothermal or cooling–decompressive retrogression and exhumation at an average rate of 3·2–4·2 km Ma–1. The newly discovered eclogites of the CMOB with their signatures of ocean-crust subduction are petrologically, geochemically and geochronologically comparable with those of the LCSS, providing powerful support for the idea that a nearly 2000 km long HP–UHP eclogite belt extends from the northern Tibetan Plateau to the southeastern Tibetan Plateau, and that it represents the main boundary suture of the Palaeo-Tethyan domain. These results have far-reaching implications for the tectonic framework and complex metamorphic evolution of the Palaeo-Tethyan domain.

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