Late Palaeozoic Tectonic Evolution Of Kalamaili In Eestern Junggar, Xinjiang:Evidences From Isotopic Chronology And Geochemistry

Central Asian orogenic belt (C AOB) is one of the largest hyperplastic orogenic belts in the Phanerozoic. The Kalamaili suture zone in the east junggar is very important in the central Asia Paleozoic tectonic framework structure unit, and its evolution process has very important significance for the study of the central Asia orogenic belt. In this article by studying the plagioclase granite, gabbro in the Kalamaili ophiolite belt and biotite quartz-syenite, biotite granite on the west edge of the Kalamaili fault zone, isotopic chronology and petrogeochemistry, the following understanding have been reached:1. The plagioclase granite in the Kalamaili ophiolite LA-ICP-MS zircon U-Pb age was 356.0±5.9 Ma, gabbro LA-ICP-MS zircon U-Pb age was 354.4±3.4 Ma; biotite quartz-syenite in south area of Kalamaili fracture LA-ICP-MS zircon U-Pb age was 345.7±4.0 Ma, biotite granite LA-ICP-MS zircon U-Pb age was 317.9±3.6 Ma.2. Early Early Carboniferous biotite quartz-syenite has high Si content(SiO2= 68.34-69.62 wt%), medium aluminium content(Al2O3= 14.74-15.23 wt%), rich in alkali(Na2O+K2O= 7.92-9.11 wt%, K2O/Na2O= 0.76-0.87), CaO= 1.67-2.35 wt%, low magnesium(MgO= 0.80-0.97 wt%, Mg#= 33-34);TiO2= 0.45-0.51 wt%, aluminium high potassium calcium alkali(A/NKC= 0.95-0.99, average value is 0.97); depleted Ba, Nb, Sr, P and Ti, rich in Rb, Th, U, K and Pb elements, the rare earth element distribution figure shows a weak Eu negative anomaly (5Eu= 0.71-0.80), indicating I-type granite geochemical characteristics. Combined with regional geological background, It formed in the later collision orogeny, derived from the partial melting of crust because of the mantle upwelling, and mixed with a small amount of mantle material.3. Early the late carboniferous biotite granite have characteristics of the main elements, with high Si(SiO2= 75.78-76.51 wt%), low aluminum(Al2O3= 12.48-12.73 wt%), rich in alkali(Na2O +K2O= 8.62-8.93 wt%), K2O/Na2O= 1.09-1.20, low CaO(0.26-0.57 wt%), low MgO(0.06-0.09 wt%, Mg#= 10-12), TiO2(0.08-0.10 wt%), weakly peraluminous high potassium calcium alkali (A/NKC= 0.98-1.02, average value is 1.01); depleted Ba, Nb, Ta, Sr, P, Ti and other elements, rich Rb, Th, U, K and Pb element, Y/Nb= 1.74-2.51; the Rare earth element distribution diagram shows a strong Eu negative anomaly(8Eu= 0.12-0.18), with A2-type granite geochemical characteristics. In combination with regional geological background, it formed in the post-collision, result of the partial melting of the earth's crust material.4. Black mica quartz-syenite and biotite granite formed in the post-collision, in combination with plagioclase granite and gabbro in the Kalamaili ophiolite zircon U-Pb age, indicating the old basin that the Kalamaili ophiolite represent closure time limit should be limited about 354.4-345.7 Ma.