Slab geometry controls Paleo-Tethyan post-collisional tectonomagmatism: Insights from Late Triassic ultrapotassic rocks in Peninsular Malaysia

Post-collisional ultrapotassic magmas are generally formed by partial melting of a subduction-metasomatized mantle source in response to continental collision and subduction. This paper presents new geochronological, geochemical, and Sr−Nd−Hf−Pb isotopic data for a suite of potassic and ultrapotassic rocks from the Raub Complex in Peninsular Malaysia. Zircon U−Pb dating shows the ultrapotassic rocks were emplaced at 225−222 Ma and the potassic rocks at 216 Ma. The elemental and isotopic data suggest the ultrapotassic rocks were derived from melt-metasomatized, subcontinental lithospheric mantle, and the potassic rocks were derived from subducted continental sediments. The occurrence of the ultrapotassic rocks, along with spatiotemporal variations in the geochemistry of igneous rocks in Peninsular Malaysia, indicate that continental collision began at ca. 235 Ma, followed by progressive shallow continental subduction and slab breakoff at ca. 225 Ma. Two distinct post-collisional tectonomagmatic events occurred along the eastern Paleo-Tethyan suture, characterized by rapid exhumation associated with the formation of low-K mafic rocks and limited exhumation associated with ultrapotassic rocks. We propose that high- and low-angle continental subduction can account for these different post-collisional events. The results provide insights into the Late Triassic geological evolution of the eastern Paleo-Tethyan suture and enhance our understanding of the effect of slab geometry on post-collisional tectonomagmatism.