Crustal reworking and growth during India–Asia continental collision: Insights from early Cenozoic granitoids in the central Lhasa Terrane, Tibet

2021 ◽  
Author(s):  
Changqi Yang ◽  
Feng Huang ◽  
Jifeng Xu ◽  
Yunchuan Zeng ◽  
Qian Liu ◽  
...  
Keyword(s):  
Continental Collision ◽  
Lhasa Terrane ◽  
Crustal Reworking ◽  
Early Cenozoic

Magmatic record of continuous Neo-Tethyan subduction after initial India-Asia collision in the central part of southern Tibet

2020 ◽  
Author(s):  
Feng Huang ◽  
Tyrone O. Rooney ◽  
Ji-Feng Xu ◽  
Yun-Chuan Zeng
Keyword(s):  
Mantle Wedge ◽  
Leading Edge ◽  
Continental Collision ◽  
Southern Tibet ◽  
Mafic Rocks ◽  
Lhasa Terrane ◽  
Slab Breakoff ◽  
Geodynamic Processes ◽  
Generation Mechanisms ◽  
Transitional Phase

The Lhasa Terrane in southern Tibet is the leading edge of the Tibet-Himalaya Orogen and represents a fragmentary record of terminal oceanic subduction. Thus, it is an ideal region for studying magmatism and geodynamic processes that occurred during the transition from oceanic subduction to continental collision and/or oceanic slab breakoff. Here we examine a suite of early Cenozoic mafic rocks (ca. 57 Ma) within the central part of Lhasa Terrane, southern Tibet, which erupted during a transitional phase between the onset of India-Asia continental collision and Neo-Tethyan slab breakoff. These rocks display a geochemical affinity with magmas produced by fluid-fluxed melting of the mantle wedge within a subduction zone environment. The whole-rock element and Sr-Nd isotope compositions of these mafic rocks are similar to those of Cretaceous subduction-related magmatism in southern Tibet, demonstrating the sustained influence of the Neo-Tethys Ocean slab on the mantle wedge during the onset of the collision of India and Asia. The results of our geochemical forward modeling constrain the conditions of melt generation at depths of 1.3−1.5 GPa with significant fluid additions from the Neo-Tethyan slab. These results provide the first petrological and geochemical evidence that slab flux-related magmatism continued despite the commencement of continental collision. While existing studies have suggested that magmas were derived from melting of the Neo-Tethyan slab during this period, our new results suggest that additional magma generation mechanisms were active during this transitional phase.

Isotope geochemistry of the 1985 Tibet Geotraverse, Lhasa to Golmud

1988 ◽  
Vol 327 (1594) ◽  
pp. 263-285 ◽  
Keyword(s):  
Tibetan Plateau ◽  
Isotope Geochemistry ◽  
Active Continental Margin ◽  
The Tibetan Plateau ◽  
Crustal Assimilation ◽  
Lhasa Terrane ◽  
Kunlun Mountains ◽  
Source Regions ◽  
Crustal Reworking ◽  
Granite Magmatism

Geochronological data from the Golmud —Lhasa section across the Tibetan Plateau indicate progressively younger periods of magmatism from north to south associated with successively younger ocean closures. Pre -collision Eocene magmatism (50—4 0 Ma) exposed along the southern margin of the Lhasa Terrane in the Gangdise Belt resulted from anatexis of mid -Proterozoic crust (~ 1000 Ma) at depths greater than 10 km, but at higher crustal levels subduction-related intrusions were predominantly mantle-derived with ~ 30 % crustal assimilation . Intrusions from the northern Lhasa Terrane are early Cretaceous in age (130 —110 Ma). These form a bimodal suite comprised of two-mica granites derived from anatex is of Mid -Proterozoic crust and of biotite -hornblende granodiorites from about 60 % crustal assimilation by mantle magmas above a post-collision subduction zone. They place a minimum constraint on collision between the Lhasa and Qiangtang Terranes of 130 Ma . Granite magmatism from the Kunlun Mountains is late P ermian -early Jurassic in age (260—190 Ma). The Kunlun batholith represents reworked mid-Proterozoic crust (1400 —1000 Ma) at an active continental margin from 260 —2 4 0 M a . Post-tectonic granites were emplaced in a post-collision setting (200 -190M a). Collision between the Qiangtang and Kunlun Terranes is dated as end -Triassic. Nd model ages of sediments from across the plateau record up lift and erosion of young source regions throughout the Phanerozoic confirming that the Tibetan Plateau is the site of multiple continental collision through time. Phanerozoic magmagenesis throughout the plateau requires considerable crustal reworking and limited crustal growth which suggests thickened continental crust in the region may predate the most recent Eocene collision.

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