Sm-Nd ISOTOPIC AND ZIRCON U-Pb CONSTRAINTS ON THE AGE OF FORMATION OF THE PRECAMBRIAN CRUST IN SOUTHEAST CHINA
Li Xianhua Zhao Zhenhua Gui Xuntang Yu Jinsheng(Institute of Geochemistry, Guangzhou Branch, Academia Sinica, 510640)
Nd model ages (TDM) of the Pre-Mesozoic crustal rock samples from southeast China range from 1.2 to 3.2 Ga. Two age peaks of 1.4 Ga and 1.8 Ga are observed in the histogram of TDM model ages. Available zircon U-Pb inheritance ages are around 1.2-1.4 Ga, 1.8 Ga and 2.5 Ga, respectively. The combined use of Sm-Nd isotopes and zircon U-Pb inheritance ages suggests that the formation of the Precambrian crust is of episodic character. The oldest crustal nucleus may have been formed during the Late Archaean (2.5 Ga or older?). A rapid production of the crust took place 1.8 Ga ago, consistent with the global crustal formation event at 1.7-1.9 Ga. Another important episode of addition of juvenile crustal material from the mantle in southeast China took place 1.2-1.4 Ga ago, in which the pre-existing crust was strongly reworked and/or remelted.