Characteristics And Genesis From Lingshan Granites In Northeastern Jiangxi,China

In this paper,we studied the granite genesis with the meteorology,mineralogy and geochemistry method,based on the combination of field geological survey and laboratory experiment.At the same time,combined with the basic data of the area and the data of predecessors,the origin of granite,the source of rock formation and its tectonic setting are discussed.The main rock types of the Lingshan granite mainly includes fine-grained pyramidite dextrose monzonite granite,medium-coarse-grained pyrometite mullite monzonite granite,fine-grained pyramid-bearing glaucoma-long granite and medium-Phenonite long granite,occasionally large veins crystal bed alkali long granite,rocky granite porphyry.Contact metamorphic bandwidth is narrow,mainly for the hornfelsed,local weak silicification and skarnization.The characteristics of petrography show that the feldspars of Lingshan granulite are more than 45%-65%,the content of plagioclase is about 25%-35%,and the intergranular double crystals are obvious.The belt structure is more developed,and the mantle fluid metasomatism during the crystallization of the rock mass is mainly silicified and clouded.Mineral chemical characteristics show that The L-feldspar-Or molecule in Lingshan Rock mass is 60.04 ~ 84.45,with sodium feldspar as the main component;plagioclase Ab element end member is 73.69~76.61,An=19.93~23.15,all is oligoclase,the structure of the belt;tibia stone thermometer shows that Lingshan rock solid solution separation of the lower limit temperature(feldspar equilibrium temperature)is437.5 and 433.7?;Lingshan rock mass rich Iron,potassium,low magnesium,poor sodium characteristics,high-iron biotite.The results of rock geochemistry show that the content of SiO2 in Lingshan rock mass is between 68.74 and 76.64%,with an average of 73.09%,which is acidic-super acid rock and Al2O3 is between 12.22% and 14.58%,(Na2O+K2O)is between 8.09%and 9.44%,the total alkali content is higher;the K2O/Na2 O ratio is 1.07~1.70,the rock aluminum saturation index(A/CNK)is 0.95 ~ 1.2 and the rock Ritterman index is1.99~3.02.The Rb,Th,U,Nd and Zr and other elements are enriched in Ta,Hf,Y,Yb and La,which are rich in alkali and alkali.Loss of Ba,Sr,P and Ti and other elements.P,Ti and other incompatible elements of the loss characteristics,indicating the rock subjected to a high degree of separation and crystallization.?REE value is very high,the content of rare earth elements is relatively high,the relative rare enrichment of rare earth elements,heavy rare earth relative loss.The enrichment of light rare earth is animportant sign that deep fluid interaction participates in the alteration of diagenetic processes.Showing that the Lingshan rock mass is metasomatic by the mantle.Through the relevant series to discriminant diagram,showing that Lingshan granite granite body is for the A-type granite,and was formed in the non-orogenic tectonic environment.In summary,the formation of the granite bodies in the Lingshan is inseparable from the evolution of the continental crust.After experiencing the Indosinian tectonic movement,into the early Yanshan period,the region gradually changes from the extrusion dynamic environment to the tensile environment.Over time,in the late Yanshanian period,the lithosphere of this area began to stretch and gradually thinning,which caused the mantle uplift and the mantle part of the melting basaltic magma began to penetrat into the lower crust,triggering deep crustal rock melting,and then forming granitic magma;The basaltic magma and the mantle fluid are mixed in the form of immiscibility.With the rise of magma,the mantle fluid is also rising,and occurs metasomatism during the crystallization process of granitic magma.And then continuously cooling magma underwent crystallization differentiation and evolution,formed the Lingshan porphyritic granite body now.