| The southern area of Tieli City lies at the junction of Songnen Terrane and Yichun-Yanshou magma arc.This area is located in the Lesser Xing'an Range-Zhangguangcai Range metallogenic belt,which is an momentous polymetallic metallogenic belt in China.The region has undergone a long geological evolution.The Mesozoic magmatic activitiy continually and form a mass of acid intrusive rocks.In this paper,the petrological characteristics,geochemical characteristics and zircon chronological characteristics have been studied to discuss the genesis,source of diagenetic material,tectonic settings of granite in the southern area of Tieli City.Combined with regional tectonic background and mineral resources,the ore-bearing properties of granite is analyzed.The zircon U-Pb isotope test dating results of granite porphyry and syenogranite samples in the southern area of Tieli city were 114.06±0.95Ma and 101.66±0.93Ma,respectively,which were the products of magmatic activities in the late Yanshanian.Both granite porphyry and syenogranite belong to the high potassium,calcium alkaline and peraluminous magmatic rock.The trace elements showed the enrichment of Rb,Th,Sm,Nd,the depletion of Sr,Ba,Ti,P.Total rare earth elements?REE in granite porphyry is 116.07-237.83×10-6,LREE/HREE=6.79-14.02,?La/Yb?N is5.6520.02.?Eu is 0.02-1.26,which shows the trend from slight positive anomaly to negative anomaly.Total rare earth elements?REE of syenogranite is225.76-237.91×10-6,LREE/HREE=3.86-6.45,which belong to the light rare earth enrichment type.?La/Yb?N is 3.40-5.78,?Eu is 0.04-0.06,the Eu negative anomaly is obvious.Combining the characteristics of Nb/Ta and Zr/Hf ratios,the material sources of the granite porphyry samples in research area are mainly crustal materials,and some of them may come from the mixture of crustal and mantle materials.Syenogranite may formed by asthenosphere material upwelling in large quantities and crust material mixed with remelting.The characteristics of trace and rare earth elements shows that the granite porphyry and syenogranite experienced the fractional crystallization of minerals such as plagioclase,amphibole and biotite.Granite porphyry was formed in the back-arc rift settings and syenogranite was formed in the post collision extensional environment.It is the product of delamination and the thinning of lithospheric after the subduction of the Paleo-Pacific plate to the Eurasian continental plate.The early Cretaceous granite in the south area of Tieli City has a similar diagenetic environment to the ore-forming rocks of the contemporary molybdenum and gold deposits.The geochemical characteristics shows that the rock mass has good ore-bearing property and certain metallogenic potential of molybdenum and gold. |
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