Geochemistry And Implications For Tectonic Evolution Of Mesozoic Granite In Woduhe Area,Northern Daxing’an Mountains

Woduhe area is located in the north of the Daxing’an Mountains, and was influenced by the combination of the Circum-Pacific tectonic domain and the Mongolia-Okhotsk Ocean tectonic domain during Mesozoic. The tectonic evolution in this area is so complex that the analysis of the petrotectonic assemblage to the investigation of the tectonic evolution during Mesozoic in the study area, as well as in the Daxing’an Mountains area. Therefore, based on the land and resources survey project of the China Geological Survey Bureau, this paper carried out detailed petrology, geochemistry and isotope chronology analysis of the Mesozoic granites in the study area. Combined with regional tectonic evolution background. We discussed the tectonic evolution during Mesozoic.The Mesozoic granites in the research area can be divided into three stages, including the Early-Middle Jurassic(181±Ma), the Late Jurassic(156±1Ma) and the Early Cretaceous(141~130Ma).The-Early-Middle Jurassic granites are mainly composed of monzonitic granite, syenitice granite and alkali-feldspar granite, belonging to aluminous-prealuminous, calc-alkaline or high-K calc-alkaline rock series. What’s more magma evolution exists a trend of transformation from the volcanic arc or syn-collision granites(quartz diorite, granite diorite and monzonitic granite) to the granites within the plate or the post-orogenic granites(syenite granite and alkali-feldspar granite), which reflected a transformation from plate collision and extrusion to post-orogenic extensional environment during the Early-Middle Jurassic in Woduhe area. This extensional environment marks the completed closure of Mongolia-Okhotsk Ocean.The lithology of the Late Jurassic granites are mainly quartz diorite ranging from metaluminous to weakly peraluminous, and belonging to calc-alkaline and high-K-alkaline rock series. Magma source area is characterized by obvious volcanic arc and syn-collision granites, which were formed with the partial melting uptrusion and emplacement of the crust as a result of the upwelling of the underlying asthenosphere within the post-orogenic extensional environment.The-Early Cretaceous granites are I-type granites almostly constituted of granite diorite and, monzonitic granite ranging from metaluminous to weakly peraluminous, and belonging to calc-alkaline and higk-K calc-alkaline rock series. Overall, the magma source area are characterized by volcanic arc and syn-collision granites, which are related to the mantle drived melts within extensional environment after the orogenesis and the fragments of the Mongolia-Okhotsk Ocean Crust, as well as the interaction of juvenile crust cased by subduction.Mesozoic granites in some part of the study area possess the nature of Adakite, which is associated with the continental collision of the Siberia plate and the Sino-Korean after the closure of the Mongolia-Okhotsk Ocean. The source region was formed by delamination and melting of thickened crust with the compressional or extensional environment, and has northing to do with the Circus-Pacific tectonic system.