The Study On Granite And Its Enclaves At Mishuling In Western Qinling

The granite is located in the south of the Mianlue suture zone in the Qinling orogenic belt and the south-eastern margin of the western Qinling,which is an important geological information for the junction between the east and west Qinling.Mi Shuling area of the West Qinling Mountains exposed the porphyaceous adamelite,and there are a lot of microgranular enclaves.The granite rocks in Mafic microgranular enclaves(Mafic Micro-granular Enclave,referred to as MME)as an important symbol of granite crust mantle mixed origin,many scholars and geology research has been in the area.But the previous research area focused on field observation of rock mass and its microgranular enclaves,study on tectonic environment analysis and rock geochemistry,analysis of mafic microgranular enclaves in itself of some weak.Based on the theory of experimental petrology,through the microgranular enclave of mafic minerals:clinopyroxen and ring of plagioclase by electron probe microanalysis(EPMA)data analysis,combination of geochronology,geochemistry and their host rocks from the characteristics of the study and further demonstrate the crust mantle magma mixing,comprehensive study of granite is one of the most important Geodynamic Significance(crustal thickness).The main findings are as follows:1.The area of the granite is mainly composed of mid-coarse grained adamellite and dark mafic rock inclusions in host rock.2.The host granite in the area is a typical quasi-aluminum high-K calc-alkaline I-type granite.Mineral composition in the amphibole and biotite,no garnet and other aluminous minerals.The main rock geochemical characteristics:(1)SiO2 content is higher(59.71%-68.82%),K2O(2.66%-4.14%),K2 O / Na2 O 0.44-1.30,mainly shows K2 O / Na2 O equivalence,Al2O3(15.32%(0.13%-5.11%),showing the evolution trend of high potassium and alkaline;(2)MgO(0.75%-2.94%)is high,A / CNK average of 0.83,the performance of quasi-aluminum granite;(3)P2O5 with the increase in SiO2 and a downward trend,and CIPW standard minerals almost no corundum molecules,which show a typical type I granite characteristics.The development of a large number of dark rock inclusions in the emerald rock,with a typical igneous rock structure and high content of needle-like apatite.Compared with the host rock,there are obvious characteristics such as high magnesium,high iron and high calcium,and the alkalinity,differentiation index and consolidation index are significant,which show the material properties of different source areas.3.The development of a large number of dark rock inclusions in the emerald rock,with a typical igneous rock structure and high content of needle-like apatite.Compared with the host rock,there are obvious characteristics such as high magnesium,high iron and high calcium,and the alkalinity,differentiation index and consolidation index are significant,which show the material properties of different source areas.4.The analysis of rare earth and trace element data shows that the host granite has the characteristics of enrichment of large ion lithophile elements,enrichment of light rare earth(LREE),Sr tank,Eu negative anomalies(showing positive anomalies individually),In the process of different evolution,the host granite is the product of early evolution of magma,and the crystallization separation phenomenon of plagioclase may exist in the process of differentiation.Based on the results of comprehensive rock geochemical analysis,the characteristics of crust-mantle magma mixing are revealed.5.The oblique feldspar in the dark rock inclusions is 26 <An <46,showing acidic plagioclase-neutral plagioclase,that is,the plagioclase with the annulus in the inclusions.The results show that the edge to the core is acidic to neutral,with the gradual evolution of the basic plagioclase gradient,revealing the possibility of mixing the basic magma and acid magma;calculated in the body of the clinopyroxene crystallization depth of 27 km to 46 km,which is close to the crustal bottom of the crust-mantle boundary,and it is inferred that the depth of the crust-mantle magma is at least 46 km,that is,the depth of the host granite formation is 46 km or less.The two petrophysical characteristics,which are typical of the magmatic mixture,and the typical igneous rock structure and the higher content of acicular apatite,are favorable to demonstrate the role of the mixed crust and mantle in the region.There is reasonableness.6.The geologic background and the tectonic environment of the combined area show that the granite in the west area of the West Qinling Formation should be formed after the collision(extrusion environment)to the post-collision(extension environment)Period,belonging to post-orogenic granite.