Tempo-spatial variations of Mesozoic magmatic rocks in the Gangdise belt, Tibet, with a discussion of geodynamic setting-related issues

The authors used the latest 1:250, 000 regional geological survey data and other relevant research results to compile the first map of distribution of Mesozoic magmatic rocks of the Gangdise belt, Tibet, and preliminarily define the distribution characteristics and tempo-spatial framework of Mesozoic magmatism and used available geochemical data to the nature of magmatism of Early Cretaceous granitoids. When an analysis is performed by placing the Mesozoic magmatism of the Gangdise belt in a tempo-spatial framework, we may find that the Southern Gangdise and Northern Gangdise were mainly affected by subduction during the Jurassic and Cretaceous, while since the Early Jurassic the Gangdise back-arc fault uplift and Central Gangdise also underwent the effects of collision that extended from east to west in addition to the effects of subduction. Based on the aforesaid study, combined with new data of structural and stratigraphic studies, the authors suggest that Mesozoic magmatism in the Gangdise belt may be explained by the model of bidirectional scissors-style subduction (the scissors open toward the west), with the Bangong Co-Nujiang oceanic crust subducted southward and the Neo-Tethys oceanic crust northward. The authors suggest that the conventional “Lhasa block” should be disassembled into the real “Lhasa block” characterized by Paleo- and Mesoproterozoic crustal materials (possibly including the Gangdise back-arc fault uplift and Central Gangdise) and the Southern Gangdise island-arc belt and Northern Gangdise island-arc belt consisting mostly of Neoproterozoic crustal materials that accreted to the south and north sides of the real “Lhasa block” by island-arc accretion during Mesozoic time, respectively. They propose that during the Permian the Gangdise belt might be a fragment of Gondwana that floated in the Paleo-Tethyan Ocean. The subduction and closure of the back-arc oceanic basin represented by the Shiquan River-Lagkor Co-Yunzhug-Nam Co-Lhari ophiolitic mélange zone may not have played a dominant role in the generation of Mesozoic magmas in the Central Gangdise and Northern Gangdise.