Eclogite from the Qianliyan Island in the Yellow Sea: a missing link between the mainland of China and the Korean peninsula

摘要

At Qianliyan Island, about 80 km East of Qingdao in the northern part of the South Yellow Sea of China, lenses and layers of eclogite and two-mica epidote-plagioclase gneiss occur within granitic gneiss. From the eclogite, peak metamorphic conditions of 775 degrees C, 2.6 GPa were defined using compositions of garnet mantle zones, omphacite inclusions, and homogeneous phengite cores with high Si contents. During exhumation, the eclogite underwent different stages of retrogression, i.e. at eclogite-facies (740-790 degrees C, 1.60-1.75 GPa), amphibolite-facies (640-690 degrees C, 0.8-1.0 GPa), and, finally, at greenschist-facies conditions. Relics of omphacite and garnet in pyrite of the two-mica epidote-plagioclase gneiss, although obliterated in the rock matrix, prove this rock also to have experienced high-pressure (HP) metamorphic conditions. Similar HP metamorphic rocks occur at Sulu and Dabie in the west and at the Hongseong complex of South Korea in the east, enhancing the probability of a coherent HP/(UHP) belt ranging from Qinlin in the west towards the Korean peninsula in the east.