THE IGNEOUS PROVINCIALITY IN TAIWAN - CONSEQUENCE OF CONTINENTAL RIFTING SUPERIMPOSED BY LUZON AND RYUKYU SUBDUCTION SYSTEMS

Geochemical characteristics of late Cenozoic volcanics in Taiwan demon strate that these rocks were produced in diverse tectonic environments . In Taiwan, three igneous provinces, namely, Western, Eastern and Nor thern, respectively (in order of the initiation of volcanic activities ), can be distinguished. The Western Province comprises intraplate bas alts, erupted in the rifted continental margin of southeastern China; whereas the Eastern and Northern Provinces are composed of are volcani cs genetically related to the Luzon and the Ryukyu subduction zones, r espectively. These volcanic rocks were sequentially emplaced on the is land of Taiwan as a result of the collision between the Luzon are and the Asian continent since about 12 Ma. This collision, likewise, induc ed westward migration of the Ryukyu Trench system and subsequent openi ng of the Okinawa Trough. As a consequence, the collision-derived comp ression diminished in northern Taiwan. A post-collisional extension re gime thus formed has generated some recent volcanic rocks in this regi on.