Does Large‐Scale Crustal Flow Shape the Eastern Margin of the Tibetan Plateau? Insights From Episodic Magmatism of Gongga‐Zheduo Granitic Massif.

The mechanisms driving crustal deformation and uplift of orogenic plateaus are fundamental to continental tectonics. Large‐scale crustal flow has been hypothesized to occur in eastern Tibet, but it remains controversial due to a lack of geologic evidence. Geochemical and isotopic data from Cenozoic igneous rocks in the eastern Tibet‐Gongga‐Zheduo intrusive massif, provide a way to test this model. Modeling results suggest that Cenozoic magmas originated at depths of ∼30–40 km, the depth that crustal flow has been postulated to occur at. Detailed isotopic analyses indicate that the igneous rocks are derived from partial melting of the local Songpan‐Ganzi crust, arguing against a long‐distance crustal flow. Episodic magmatism during the Cenozoic showing a repeated shifting of magmatic sources can be correlated with crustal uplift. The continued indentation of the Indian Block and upwelling of the asthenosphere contribute to the crustal deformation, magmatism, and uplift. Plain Language Summary: How the Tibetan Plateau grows outward and deformed remains controversial. A large‐scale crustal flow model has been favored for the expansion of the southeast Tibetan Plateau, arguing that crustal materials could flow hundreds of km resulting in crustal thickening and uplift. Detailed geochemical and isotopic investigations on the largest intrusion (Gongga‐Zheduo) in the eastern margin of the Tibetan Plateau show that their magmatic source is local crustal rocks of the Songpan‐Ganzi terrane without the input of crustal materials from central Tibet. Thermodynamic and trace element modeling results show that the Cenozoic magma is derived from ∼30 to 40 km depth, similar to the depth of postulated crustal flow. The results are inconsistent with the large‐scale eastward crustal flow model. A repeated shifting of magmatic sources during the Cenozoic is correlated with crustal uplift. Mantle‐crust interaction plays a primary role in the formation of magmatism and modifying crustal rheology. The continued collision between the Indian and Asian blocks and upwelling of the asthenosphere contribute to the crustal deformation and uplift. Key Points: Isotopic and thermodynamic modeling results indicate that Gongga‐Zheduo granitic rocks in eastern Tibet are sourced from the local crustNo crustal materials from central Tibet are observed in eastern Tibet arguing against the large‐scale crustal flow modelCenozoic episodic magmatism in eastern Tibet with a repeated vertical shifting of sources is correlated with staged crustal uplift [ABSTRACT FROM AUTHOR]