一个造山后花岗岩基:石耳山花岗岩的形成时代和成因

A POST OROGENIC GRANITE BATHOLITH: THE AGE AND GENESIS OF SHIERSHAN GRANITE

根据研究所得新资料，报道了江南造山带东段造山后花岗岩的一个实例：石耳山花岗岩．它的单颗粒锆石Ｕ－Ｐｂ同位素年龄值为０．７７～０．８３Ｇａ，因此该花岗岩形成于晚元古代江南造山带造山运动趋于结束或结束以后（造山运动结束时限被认为是０．８Ｇａ前后［１３］）．它为含绿帘石的碱性长石花岗岩，具高硅、富碱、过铝和较低的Ｚｒ、Ｈｆ、ＨＲＥＥ、Ｌａ／Ｙｂ、Ｒｂ／Ｍ（Ｍ＝ＨＲＥＥ、Ｙ、Ｚｒ、Ｈｆ等），以及趋近于零的εＮｄ（Ｔ）值等特点，起源于有当时年青的含基性岩组分参与的不成熟地壳物质．

Based on the new data from some recent studies, this paper reports an example of Proterozoic post orogenic granites in eastern Jiangnan orogen, Shiershan granite. Single grained zircon U Pb isotope analyses gave ages of 0.77 and 0.83Ga; therefore, Shiershan granite was formed close to or after the termination of orogenesis of Late Proterozoic Jiangnan orogen (0.8Ga ago). Its petrographic and geochemical characteristics indicate that Shiershan granite is epidote bearing granite with higher SiO 2, alkaline and Al 2O 3 contents but lower Zr, Hf, HREE contents and La/Yb, Rb/M ratios (M=HREE, Y, Zr, Hf, etc.). Additionally, its ε ND (T) being nearly equal to zero suggests that the source rocks of Shiershan granite are probably immature crust composed of young mafic igneous rocks.