The Characteristics Of Baiji-Changgai NE Trending Granite Belt From South Anhui Province And Its Relationship With The Origin Of Yanshanian Fault Zone

The Baiji-Changgai NE trending granite belt is located in south Huangshan city, Anhui province. It is mainly composed of(giant) porphyritic granite. Zircon LA-ICP-MS U-Pb dating yields the weighted average age of 148 Ma, 146 Ma and 142 Ma for Wuliting, Guzhu and Changgai plutons in this granite belt. The magmatic rocks were riched in Si, low in Fe、Mg、Ga、Mn、Ti, formed in a post-collision tectonic environment, indicate an island arc granite characteristics and I-type granite properties. The REE pattern of granite is in right dip form with comparatively obvious negative Eu anomalies and depletion in Nb, Ta, P and Ti.A series Yanshanian thrust nappe structures distribute in the study area. They can be divided into two parts with the opposite direction hedge structures by the boundary of NE trending Ningguo-Wucheng fault zone. The nappe structures on the northwest side are formed in early Yanshaninan and thrust form NW to SE, whereas those on the east side may form in late Jurassic to late Cretaceous respectively and from SE to NW. Moreover, the faults in east side should be acted at two periods. Through the comparative analysis, the emplacement age of granite belt is slightly later than the first phase of the SE to NW nappe deformation effect, also obviously controlled by the fracture of rock mass, output in the two groups of different direction of fracture cross area. The Late Jurassic volcanic rock strata(mainly rhyolite) in the study area usually represent extensional tectonic environment. After studing granite petrological and geochemical characteristics, it believed that the tectonic dynamic mechanism had experienced a transition from extension to compression in south Anhui area during the late Jurassic, and ended in late of late Jurassic.