贺兰山北段贺兰山岩群富铝片麻岩碎屑锆石LA-ICP-MS U-Pb定年及区域对比

贺兰山北段贺兰山岩群中发育一套富铝片麻岩，Al2O3含量较高，总体与粘土质岩石化学成分相似，显示孔兹岩系的特征，变质矿物组合主要为石榴子石、堇青石、硅线石、十字石、紫苏辉石等，变质级别达角闪岩相—麻粒岩相。从宗别立岩组含石榴矽线黑云二长片麻岩中选取100粒各种类型的锆石进行了LA-ICP-MS U-Pb同位素测年，获得47个测年数据，锆石年龄多数介于1.80~2.15Ga之间，峰值为2.00~2.05Ga。碎屑锆石年龄频谱图与鄂尔多斯地块北缘的集宁岩群和乌拉山岩群十分相似，总体与吕梁构造运动的时限一致，为华北克拉通成熟陆壳演化阶段的产物，证明孔兹岩系形成于古元古代，之后长期处于稳定状态，很少受到构造热事件的干扰。

LA-ICP-MS U-Pb detrital zircon geochronology of alumina-rich gneiss of the Helanshan complex-group in the northern segment of Helanshan Mountains and regional comparison

The Helanshan Group exposed in the northern segment of Helangshan mountains is high-grade metamorphosed rocks which are mainly composed of grey-biotite-sillimanite-cordierite-monzonitic-gneiss, sillimanite-garnet-biotite-plagioclase-gneiss,garnet-biotite-plagioclase-leptynite, sillimanite-garnet-monzonitic-leptite, sillimanite-biotite- plagioclase-leptynite, graphite-marble and hypersthene-plagioclase-gneiss. The gneiss of Helanshan Group belongs to khondalite series characterized by rich in Al2O3 and similar geochemistry to clay rocks, and its protolith rocks assemblages are alumina rich pelite and siltstone, which indicate that the gneiss is a suite of stable continental margin terrigenous clastic rock, the metamorphosed mineral assemblages of gneiss consist of garnet, cordierite, sillimanite, staurolite, hypersthene and so on. Forty-seven U-Pb data were obtained by LA-ICP-MS method for the detrital zircons of four garnet- sillimanite-biotite-monzonitic-gneiss from the Helanshan Group in this study. The majority ages of the grains from these four samples are clustered in the 1.80-2.15Ga, with characteristic age probability peaks at 2.00-2.05Ga. The detrital zircons ages of the Helanshan Group are similar to Jining complex and Wulashan Group in the western margin of E'erduosi massif that were related to Lüliang movement. We interpret these gneiss as the evolution of mature crust of the North China craton. Based on distributing age range of detrital zircons of the Helanshan Group. We suggest that the khondalite series of the Helanshan Group formed in the Paleoproterzoic, less to the effect of later period tectonic-thermal events of the North China.