Late Cretaceous Adakitic Granites of the Southeastern Tibetan Plateau: Garnet Fractional Crystallization of Arc‐Like Magmas at the Thickened Neo‐Tethyan Continental Margin

Abstract

The tectonic setting of Cretaceous granitoids in the southeastern Tibet Plateau, east of the Eastern Himalaya Syntax, is debated. Exploration and mining of the Laba Mo-Cu porphyry-type deposit in the area has revealed Late Cretaceous granites. New and previously published zircon U-Pb dating indicate that the Laba granite crystallized at 89-85 Ma. Bulk-rock geochemistry, Sr-Nd isotopic data and in situ zircon Hf isotopic data indicate that the granite is adakitic and was formed by partial melting of thickened lower crust. The Ca, Fe, and Al contents decrease with increasing SiO 2 content.These and other geochemical characteristics indicate that fractional crystallization of garnet under high-pressure conditions resulted in the adakitic nature of the Laba granite. Cretaceous granitoids are widespread throughout the Tibetan Plateau including its southeastern area, forming an intact curved belt along the southern margin of Eurasia. This belt is curved due to indenting by the Indian continent during Cenozoic, but strikes parallel to both the Indus-Yarlung suture zone and the Main Frontal Thrust belt. It is therefore likely that Cretaceous granitoids in both the Gangdese and southeastern Tibetan Plateau areas resulted from subduction of Neo-Tethyan lithosphere.

Early Cretaceous back‐arc basin basalt‐type gabbros in the southeastern Tibetan Plateau: Implications for Neo‐Tethyan oceanic slab subduction

“…The limited data available from the Western Myanmar Arc (WMA) in the western Sibumasu Block suggest a geochemical similarity to Andean-type magmatic arcs (Mitchell et al, 2012;Wang et al, 2014a;Li et al, 2019). In addition, numerous data are now available for the syn-and post-collisional magmatism within the Baoshan-Tengchong blocks (the northern fragments of the Sibumasu Block) and adjacent areas (Lin et al, 2012;Xu et al, 2012;Zhu et al, 2017;Xiang et al, 2019;Xie et al, 2020). However, knowledge of the pre-collisional mafic magmatism resulting from subduction of the Neo-Tethyan oceanic slab is poor, which in turn has hindered our understanding of Neo-Tethyan tectonics in the SE Tibetan Plateau.…”