Sm-Nd and Zircon U-Pb Isotopic Constraints on the Age of Formation of the Precambrian Crust in Southeast China

Nd model ages(T;)of the Pre-Mesozoic crustal rock samples from Southeast China rangefrom 1.2 to 3.2Ga.Two age peaks of 1.4Ga and 1.8Ga are observed in the histogram of T;model ages.Available U-Pb zircon inheritance ages are concentrated around 1.2-1.4Ga,1.8Ga and2.5Ga,respectively.The combined use of Sm-Nd and U-Pb zircon inheritance ages suggests that theformation of the Precambrian crust is of episodic character.The oldest crustal nucleus may havebeen formed during the Late Archean（2.5Ga or older?）.A rapid production of the crust tookplace 1.8Ga ago,consistent with the global crust formation event at 1.7-1.9Ga.Another importantepisode of the addition of juvenile crustal material from the mantle in Southeast China took place1.2-1.4Ga ago,during which the pre-existing crust was strongly reworked and/or remelted.