华南前寒武纪地壳形成时代的Sm-Nd和锆石U-Pb同位素制约

Sm-Nd ISOTOPIC AND ZIRCON U-Pb CONSTRAINTS ON THE AGE OF FORMATION OF THE PRECAMBRIAN CRUST IN SOUTHEAST CHINA

华南前中生代地壳岩石的Nd模式年龄分布在1.2—3.2Ga之间,并且在1.8Ga和1.4Ga出现明显的峰值。各类岩石的残留锆石U-Pb年龄主要集中在1.2—1.4Ga、1.8Ga和2.5Ga。Sm-Nd同位素体系和锆石U-Ph年龄的综合制约表明,华南前寒武纪地壳主要以幕式增生的方式形成,形成时代为晚太古(2.5Ga或更老)、中元古早期(～1.8Ga)和中元古晚期(1.2～1.4Ga)。

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.