Late Paleozoic subduction in Xiemisitai:Evidence from the petrology,geochronology and geochemistry of Sailekente pluton, Xinjiang

The Sailekente pluton occurs in the middle-east part of Xiemisitai area. It is mainly composed of the monzonitic granite, quartz diorite and granodiorite. We carried out integrated studies of geology,geochronology,geochemistry and whole rock Sr-Nd and zircon Hf isotopes of the Sailekente pluton,and discuss their petrogenesis and implications on the tectonic evolution. The results show that monzonitic granite (400.9 +/- 4.3Ma)and quartz diorite (398.1 +/- 4.5Ma)are formed in Early Devonian,and granodiorite (381.7 +/- 2.9Ma)is formed in Late Devonian. The whole pluton belongs to metaluminous-weakly peraluminous high-K calc-alkaline granite, and which is characterized by high silicon and enrich of alkali. The pluton has obvious fractionation of LREE and HREE,and is enriched in LREE ((La/Yb)(N) = 5.09 similar to 9.22). The REE patterns show negative Eu anomaly. They are also enriched in LILE and depleted in Nb,Ta and Ti. The monzonitic granite and quartz diorite are characterized by positive epsilon(Nd) (t)(+4.85 similar to +6.18),low (Sr-87/Sr-86)(i) (0.7040 similar to 0.7043)and relatively young model ages t(DM1)(Nd)ranging from 663Ma to 732Ma,the monzonitic granite has epsilon(Hf)(t) values ranging from + 7.94 similar to + 12.12 and t(DM2) (Hf) model ages of zircon between 648Ma and 889Ma,respectively; granodiorite is characterized by positive epsilon(Nd)(t)(+ 4.61 similar to + 4.80),low (Sr-87/Sr-86) i (0.7045 similar to 0.7046)and relatively young model ages t(DM1)(Nd)ranging from 731Ma to 749Ma,and the epsilon(Hf)(t)values and t(DM2)(Hf)model ages of zircon are ranging from + 4.26 to + 11.69,and between 631Ma and 1103Ma,respectively. In conclusion,Sailekente pluton is formed in the environment of continental margin arc under the subductional background,which could be a product of emplacement and condensation crystallization of magma which is derived from partial melting of the juvenile crust. Both monzonitic granite and quartz diorite originate from the partial melting of the juvenile crust;the granodiorite mainly comes from the partial melting of the juvenile crust with the addition of a small amount of mantle-derived materials. The dark microgranular enclaves may be the product of the mantle-derived material and the partially molten magma of the juvenile crust not being completely mixed,and finally condensed and crystallized. The medium-acid magmatism is associated with subduction continuing at least from the Late Ordovician to the Late Devonian in the Xiemisitai area.