浙闽前寒武纪基底地壳的形成和增长时代

THE FORMATION AND ACCRETION AGES OF THE PRECAMBRIAN CRUSTAL BASEMENT IN ZHEJIANG AND FUJIAN PROVINCES

对浙闽地区变质岩Sm-Nd及锆石U-Pb年龄资料研究后认为,浙闽地区存在前寒武纪地壳基底,还可能存在晚太古代古陆核。基底地壳具有幕式增长的特点,经历了2400Ma(早元古代)、1800Ma(中无古代)和1400Ma(中元古代)三个主要的地壳增长时期。

Metamorphic rocks in Zhejiang and Fujian Provinces have Rb-Sr isochronic ages in the range of 650-1970 Ma, U-Pb zircon ages of 890-2760 Ma and Sm-Nd wholerock isochronic ages of 1380-2120 Ma, which suggests that there exists Precambrian crustal basement in this region. Three peaks of Nd model ages of the metamorphic rocks ( - 1400, -1800, -2400 Ma) hint that the basement crust underwent three accretion episodes in the Early-Middle Proterozoic. Nd model ages of the Phanerozoic granitoids and volcanic rocks (2000-1000 Ma) also fall into the Early-Middle Proterozoic period and their εNd(T) values are all negative ( -1. 7--11. 4, average of -6. 0). This indicates that beneath the granitoids and volcanics appears to be the Early - Middie Proterozoic continental crust from which rock-forming materials of the granitoids and volcanic rocks were derived.