Huann-Jih Lo

Lithofacies of volcanic rocks in the central Coastal Range, eastern Taiwan: implications for island arc evolution

Abstract The Miocene igneous rocks in the central Coastal Range, eastern Taiwan, consists of intrusive diabase, andesitic lavas, andesitic to dacitic volcaniclastic rocks, ignimbrites and basaltic lavas. Based on rock characteristics, they can be grouped into ten lithofacies. Furthermore, these lithofacies can be appropriately linked to form five lithofacies associations according to paleoenvironments and type of volcanism. The volcanic eruptions may have commenced on a deep ocean floor in the early Miocene, poured out in a shallowing environment in the middle to late Miocene and, finally, taken place in a subaerial condition at the end of the Miocene. Subaqueous eruptions produced voluminous pillow lavas and breccias, hyaloclastites, massive lavas and thick volcaniclastic deposits. Subaerial eruptions yielded only limited amounts of ignimbrites and basaltic lavas. After the cessation of volcanism due to the arc-continent collision, the volcanoes rapidly subsided and were later overlain by thick terrigenous sediments.