Dynamic Background And Significance Of Mengentaolegai Intrusion At Mid-triassic In Middle Daxinganling Mountain

This paper studied the Mengentaolegai intrusion in Wulanhaote area, middle Daxinganling mountain, with a purpose to provide new evidences for discussing the tectonic evolution of Xingmeng orogenic belt from the end of late Paleozoic to the early Mesozoic, the time of final suture of Siberia plate and the North China plate, and the conversion time of ancient Asian tectonic domain and west Pacific tectonic domain. Based on detailed research of petrology, mineralogy, rock geochemistry and isotope of Mengentaolegai intrusion, the following conclusions are obtained:1. Field survey revealed that, the Mengentaolegai intrusion can be divided into three map unit, which are medium-fine grained tonalite (locally visible secondary muscovite), medium-fine grained granodiorite and fine-grained biotite monzogranite (locally containing muscovite).2. The Mengentaolegai intrusion is collision-related S-type or curstal derived granite: high SiO2content (average71.89%), relatively rich in potassium (Average K2O/Na2O ratio is1.19), average A/CNK is1.09(0.73-1.27), all of the data points projected in the S-type or shell source granite area in ACF diagram, there are corundum in the standard minerals (average1.48); strong fractionation between LREE and HREE,((La/Yb)N=3.2-32.5, average14), rich in LREE and depleted in HREE, right-tilt distribution pattern, very similar to those of the S-type granites in northern margin of North China Craton; moderate negative anomaly of Eu(from0.2to0.8, average0.4), in addition to one sample is projected in crust-derived granite, the rest falls in crust-derived granite in (La/Yb)N-δEu diagram; all the electron probe data of biotite indicate per-aluminous (including S-type granites).3. The magma source for Mengentaolegai intrusion is made of Metapelite and Metamorphic sandstone, but no mantle material involvement.4. The rock geochemistry and isotopic composition of Mengentaolegai intrusion indicate that:it is formed in collision setting in mid-triassic (with zircon LA-ICPMS U-Pb age of 224±1Ma,230±1Ma and234±1Ma). The mengentaolegai intrusion records the geodynamic evolution information at the convergence area of Siberia and North China Cration after collision. This thesis just made a preliminary study, there’s far more work need to do to reveal the tectono-magmatic evolution process of the northern region of North China Craton.