東台灣蛇綠岩中尖晶石橄欖岩及角閃石輝長岩之礦物化學及全岩化學研究

Abstract

見英文摘要

The South China Sea is one of the youngest marginal ocean basins and is an important feature for reconstructing the tectonic evolution of Southeast Asia. The opening of South China Sea is primarily based on the magnetic anomaly record and is thought to have been active between 32 and 15.5 Ma. The East Taiwan Ophiolite (ETO) is one of the few preserved remnants of South China Sea. The age of ETO is obtained by LA-ICP-MS in situ zircon U/Pb methods and yielded an age of 14.1 ± 0.4 Ma, suggesting that magmatic activity lasted an additional 1.5 million years. New mineral chemistry and bulk rock geochemical data indicate the ETO formed at an oceanic ridge setting. Cr-spinel data (Cr# = 42 – 54) and depleted εNd(t) values (i.e. +9.1) from the peridotites plus the depleted εNd(t) values (i.e. +11.4) and LREE depleted pattern (La/Yb ≦ 1) of the ETO gabbro are consistent with a ridge setting (i.e. N-MORB composition). The East Taiwan Ophiolite is likely a portion of the terminal part of the spreading ridge of South China Sea prior to subduction beneath the Luzon arc.

Key words: ophiolite, geochemistry, East Taiwan Ophilite, peridotite, Taiwan, South China Sea