Volcanic Debris Avalanche Deposits in the Coastal Range, Eastern Taiwan: Implications for Sedimentation and Tectonics of Arc-Continent Collision

The Coastal Range of eastern Taiwan is located at the plate boundary of Philippine Sea and Eurasia plates, which is the arc-continent collision zone. Abundant huge blocks, especially in Wushihpi area, which are predominantly composed of the volcanic rocks, are interbedded in the Paliwan Formation. Based on the field surveys, different occurrences of volcanic lithofacies have been recognized in outcrops. They are pillow breccias with and without white vesicle fillings, hyaloclastites, peperites rich and poor in zeolite fillings, lahars, lava flows with columnar structures, weathered brownish and reddish blocks in tuffaceous conglomerates and limestones. Those lithofacies can be grouped into three volcanic facies, the shallow marine, transitional from submarine to subaerial facies and subaerial facies. Those facies occur together chaotically and contact sharply. It infers that the volcanic rocks occurred in Wushihpi of Coastal Range is debris avalanche deposits and the source may come from different volcanic sequences of the Tulunshan volcanics, the major eruption products of Luzon Arc. Meanwhile, similar occurrences of debris avalanche deposits as huge blocks are also widely distributed in whole Coastal Range from the north to the south and Lutao. Those observations suggest that the sedimentation of debris avalanche and tectonics of slope failures may play major roles for denudation of volcanic arc during Taiwan arc-continent collision.