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.