The Petrology Of Niuxinshan Granitoids In The North Qilian And Their Zircon SHRIMP Dating

As a product of the crust-mantle interaction, Granites carry a wealth of information on geological processes. However, the studies of the North Qilian Paleozoic granitoids are not enough, which greatly affect understand of the geoscience workers in the area. Based on the above-mentioned problems, the purpose of this study is to determine stages of magmatic activity, to identify the causes of the type and structure of its environment, to analyze its response to orogeny. To achieve the above objectives, this study adopts field geological survey, laboratory analysis and testing and comprehensive analysis of combining research.With the study of the middle of the North Qilian Mountai, we get the following five achievements:(1) Research indicated that, this mixed rock mass is composed by the diorite class and the granite class. The early granite and the diorite nearly simultaneously invade the position; But the later period quartz-diorite class delivers by the arteries shape in the middle of the granite, explained it invades the position to have late in the granite.In the granite rock mass discovered the massive dark color inclusion, showed in the rock mass forming process has certain scale the rock magma mixer action.(2) Zircon SHRIMP U-Pb dating indicate that, the Niuxinshan precipice body granite class age 463±11-481.8±3.2Ma, the diorite for 480.9±4Ma, the quartz-diorite for 434.7±3.5Ma, from this, divides into the Niuxinshan mountainous region area magmatic activity two issues: The early one is for the granite and the diorite combination, both nearly simultaneously invades the position; The later is the quartz-diorite, this is consistent with the field observation phenomenon.(3) Rock geochemistry research indicated that, the early granite is S, the diorite is I, the later period quartz-diorite is I, and has high Sr, the low Y characteristic, which is similar in the Adakites, explained the granite the source rock comes from the earth's crust, but the diorite and the quartz-diorite source rock comes from mixing between crust and mantle.(4) Both the zircon and the rutile thermometer show that, the early granites have temperature to be 779℃and 879℃, the early diorite for 656℃and 844℃, the later quartz-diorite 708℃and 883℃.(5) In the above research foundation, unifies the regional geology characteristic, the author believed that, the early magmatism form when the northern Qilian tectonic plate dives to the south concerns.The dive tectonic plate has the mineral dehydration in the dive process to form the fluid, fluid induction mantle wedge part fusing forms the basic rock magma, the basic rock magma rises to the shell curtain boundary forms the magma chamber, magma chamber own heat and the crystallization latent heat causes the earth's crust part fusing to form the flowered hillock nature rock magma.And the later quartz magmatism is related with orogenic extension function of the mountain building.