| In this paper,the mineralogy,trace and REE geochemistry,geochronology and HF isotopes of the Laoyaquan granitoid pluton which is in the north of the ophiolite belt in karamaili area of eastern Junggar are studied,and the petrogenetic types,material sources and tectonic setting discussed,in order to provide some evidences for the genetic study of the granite in the Karamaili area.1.Laoyaquan granitoid pluton is located in the north side of karamaili deep fault,with the long axis distributed in NWW,roughly parallel to karamaili suture zone.The pluton is mainly composed of alkali feldspar granite,monzonite granite and porphyritic granite.The LA-ICPMS zircon U-Pb method determines the diagenetic age of zircon crystalline age:alkali feldspar granite 309.9±1.2Ma,monzonite granite 309.3±1.2Ma,porphyritic monzonite granite 314.6±1.1Ma,Formed at the same time,all belong to the Late Carboniferous;The Hf isotopic characteristics are as follows:?Hf(t)of alkali feldspar granite is between+11.387 and+16.258,TDM1 and TDM2 are 497?293Ma and595?284Ma,respectively.The?Hf(t)of monzonite granite is between+12.288 and+15.594,TDM1 and TDM2 are 451?320 Ma and 538?326Ma,respectively.The?Hf(t)of porphyry prophyritic is+11.874?+15.029,and the TDM1 and TDM2 are 476?392Ma and568?367Ma,respectively.;2.The mineralogical characteristics of Laoyaquan granite are as follows:The major minerals are K-feldspar,plagioclase,quartz,amphibole and biotite.Hornblende in Laoyaquan granite belongs to calcium hornblende(Ca B?1.50),The Mg/(Mg+Fe2+)of biotite varies from 0.24 to 0.28,with an average value of 0.25.The variation range of Fe2+/(Fe2++Mg)ratio of biotite is small and concentrated in the range of 0.73?0.76.The results show that the chemical composition of the ore is characterized by poor magnesium and rich iron,suggesting that it has good tin mineralization.3.Laoyaquan granite is peraluminous alkaline rock.The trace elements are characterized by the enrichment of Rb,K and other large ion philophile elements and Hf,Th and other high field strength elements,while the loss of Ba,Sr,Eu,P,Ti and weak loss Nb,Zr,with the characteristics of A-type granite.The total content of rare earth elements is relatively high(129.82×10-6?259.47×10-6),which is relatively enriched in light rare earth(La N/Yb N=2.23?7.63).The rare earth distribution pattern diagram is a flat V-shape with a strong negative Eu anomaly(?Eu=0.02?0.12).4.Laoyaquan alkali feldspar granite,monzonite granite and porphyry monzonite granite all belong to A-type granite with high differentiation.The magma sources of the three may be similar,both of which are lower crust or depleted mantle.The Laoyaquan pluton occurred in the post collisional orogenic setting,indicating that they were emplaced in the post-collision tensional setting,and its formation marked the end of orogeny and the beginning of intraplate tectonic evolution. |
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