| West Junggar Paleozoic accretion-type orogenic belt in central Asia orogenic generation is an important part of central Asia, which is located in the southwest of orogenic belts. West Junggarr in Paleozoic after many subduction and collision, widely developed the Paleozoic sedimentary rocks and magmatic rocks built, and forms a very important Paleozoic tectonic magmatite belts.Based on the field study, this work has carried out Early Permian quartz monzodiorite formed during the Early Permian tectonic environment, formation mechanism and tectonic significance, by analyzing the combination of Early Permian quartz monzodiorite rock types and geochemical characteristics of the West Junggar.1. The age of the quartz monzodiorite LA-ICP-MS zircon U-Pb located in West Junggar bosh Kurt-into the southern magmatic arc old tuyere ranged from286±10Ma to294±4Ma, the weighted average was290.8±6.2Ma, which represent the age of rock formation, the era of the Early Permian.2. The quartz monzodiorite had the characteristics of low silicon (SiO2=58.08-61.57wt.%, mean value=59.40wt.%), high calcium (CaO=4.11-5.23wt.%, mean value=4.75wt.%), Na-rich and poor K (Na2O=5.28-5.73wt.%, mean value=5.51wt.%; K2O=1.67-1.99wt.%, mean value=1.82wt.%; Na2O/K2O=2.76-3.41, Na2O+K2O=6.99-7.67wt.%), high aluminum (Al2O3=16.78-17.42wt.%, mean value=17.20wt.%), low magnesium (MgO=1.71-2.30wt.%, mean value=2.09wt.%), high iron (TFe=6.28-7.56wt.%, mean value=7.12wt.%), the content of TiO2was1-1.2wt.%, mean value=1.11wt.%; the A/CNK was between0.97and1.08, which suggested that it belonged to the aluminum category; the quartz monzodiorite included diopside but not corundum standard mineral, the quartz monzodiorite was falling into the I-type granites both in K2O-Na2O giagram and Nb、(Na2O+K2O)10000×Ga/Al diagram, showing that the quartz monzodiorite should be must aluminum and calcium alkaline I-type granite rock.3. The quartz monzodiorite had the characteristics of low magnesium (Mg#=35-38), Na-rich and poor K, high Sr (Sr=396×10-6-444×10-6, mean value=422×10-6), high Y (Y=31.6×10-6-43.5×10-6, mean value=38.9×10-6), high Yb (2.99×10-6-4.24×10-6), enriching Ba、Rb、 K、 Zr、 Hf、 LREE and lacking Nb、Ta、 P、 Ti in HFSE, slight Eu negative anomaly (δEu=0.8-0.95), high Rb/Sr ratio (Rb/Sr=0.06-0.13), Huck diagram research indicated that the content of Fe2O3, CaO, MgO and K2O decreased while the content of SiO2increased, showing negative linear correlation; on the contrary, the content of Na2O increased while the content of SiO2increased, showing positive linear correlation; the content of A12O3decreased first then increased while the content of SiO2increased, showing V-shape evolution.(La/Yb) N-δ Eu and Pearce discrimination diagrams showed that the quartz monzodiorite was from new partial melting of the earth’s crust, the fractional crystallization of amphibole occurred after magma formed, source area residual mineral should be amphibole, pyroxene, formed in the context of post-collisional extensional collapse tectonic dynamic mechanism, the heat source was mantle basaltic magma underplating.4. West Junggar tectonic magmatic sequence can divide into late Silurian epoch and Lower Devonian (425Ma-405Ma) granite formed under subduction plate melting, Carboniferous granite formed under post-collisional extensional collapse tectonic background, from the partial melting of crustal material, Early Permian Epoch (291Ma) quartz monzodiorite still formed in a post-collisional extension context because of the partial melting of crustal material, but the crustal thinkness might be thicker (35-40kilometres). |
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