Geochemical Constraints for the Genesis of Post-collisional Magmatism and the Geodynamic Evolution of the Northern Taiwan Region

Taiwan is an active mountain belt created by the oblique collision of the northern Luzon arc with Asia. Late Pliocene extensional collapse of the northern Taiwan mountain belt (NTMB) was accompanied by magmatism that formed the Northern Taiwan Volcanic Zone (NTVZ; 28---02Ma). The geochemical characteristics of the NTVZ magmas can thus provide constraints both for the mantle source composition and the geodynamic processes operating in the late orogenic stage of the region. The NTVZ volcanic rocks consist dominantly of calc-alkaline andesites and basalts, along with sub-ordinate but heterogeneous lavas including low-K, shoshonitic and ultrapotassic magmas. From the NE to the SW in the NTVZ, the magmas show systematic compositional variations from low-K to calc-alkaline and then shoshonitic. This spatial geochemical varia-tion, characterized by southwesterly increase in potassium and incompatible trace elements, appears to be subparallel to the south-