Geochemistry and zircon U-Pb age of the Paleoproterozoic syn-collisional granites in Helanshan region and its geological significance

Helanshan khondalite series,located at the west part of North China craton,are widely intruded by granites. Most of the granites are S-type. The investigated Shabatai granites are characterized by high SiO 2 and Al 2 O 3 contents,71. 96% ～ 73. 87% and 14. 36% ～ 15. 10% ,respectively. The high A / CNK and A / NK values suggest that the granites are peraluminous. The chondrite- normalized REE patterns of the rocks show the enrichment of LREE ( ( La / Yb) N = 12 ～ 191) and strong negative Eu anomalies ( δEu = 0. 15 ～ 0. 32) . The primitive mantle-normalized trace element diagrams show the enrichment of Rb,Th,U and Pb and depletion of Ba,Nb,Ta,Sr and Ti. All above characteristics suggest that they are S-type granites and were probably generated by partial melting of the khondalite in the Helanshan region. The U-Pb dating of zircons from the granites using LA-ICP-MS yields an age of 1958 ± 30Ma, which represents the crystallization age of the S-type granite. According to the published geological data and our new data,it is reasonable to refer that these S-type granites were generated in a Paleoproterozoic collisional tectonic setting between the Yinshan and Ordos blocks.