Geochemical Characteristic And Petrogenesis Of Niumaoquan Basic Complex In The Eastern Harlik, Xinjiang, China

There are series of basic-ultrabasic complex which were formed in similar era,adjacent in space and cross-tectonic units in the northen of Xinjiang province with transitional types exist among them.For they contains Cu-Ni-PGE deposits(such as Huangshan, Huangshandong) and V-Ti-Fe deposits(such as Weiya,Xiangshanxi and Niumaoquan),they have got much attentions from geologists who come from domestic and abroad. Niumaoquan complexs located in the eastern of late paleozoic Harlik arc in Junggar plate, open-pit mining has been carried out in it, therefore, we select Niumaoquan complex as theobject of research in this paper.Based on field investigation, petrography,mineralogy,geochemistry and other manners,we analyze the hybrid combination, source of magma and nature of primary magma,prosess of magmatic evolution.Based on these researches we get some achievements as follows:1.Niumaoquan complex have obviously layered property and rhythmical tectonic characteristics, the main rock types include olivine gabbro,olivine-bearing gabbro,gabbro and hornblende gabbro. Alteration are common in complex and the phenomenons of spherical weathering are significant.The main rock-forming minerals are olivine,chrome spinel, pyroxene and amphibole,low-grade magnet occurs in coarse-grained gabbro.2. Major elements indicate that Niumaoquan complex belong to tholeiite series which have experienced the fractional crystallization of olivine clinopyroxene and plagioclase. The m/f values (m/f=(Mg2++Ni2+)/(Fe2++Fe3++Mn2+) of most rocks range from 0.65 to 1.44,so Niumaoquan complex belong to ferruginous rocks.The concentrations of rare earth elements is relatively low,heavy rare earth elements and the whole rare earth elements'fractionation are slightly stronger,light rare earth elements' fractionation are weak,positive Eu anomalies are showed in most rocks.The diagram of trace element which normalized by primitive mantle demonstrate that rocks are enriched large ion lithophile elements(Rb,Ba,Sr,U).The loss of Nb,Ta and high field strength elements(Zr,Hf) are displayed in most rocks with weak enrichment of Ti.3. It can be obtained the MgO content of primitive magma through the Fo molecular of olivine in Niumaoquan complex is 7.3%,but Fo value(76) is not high enough to represent the balance of the original magma liguidus initial phase,so 7.3% of MgO content can only bound it's lower limit.4.Nd-Sr isotopic characteristics indicate that magma derived from the OIB-type source region which was affected by reduction plate,with the evolutionary trend to EMI,therefore,it is inferred that the magmatic source are enriched lithospheric mantle with transformation by subduction fluid.5.Large-scale post-collisional mantle-derived magmatism occurs in the northern of Xinjiang in early Permian(290Ma-270Ma),the symbol of it is a number of mafic-ultramafic rocks array as belts,such as Kalatongke belt,Huangshandong belt in the east of Tianshan,which formed a series of Cu-Ni-PGE and V-Ti-Fe deposits;Niumaoquan complex formed in the postcollisional extension setting background. Delamination of lithospheric mantle is partial melting due to be heated by asthenospheric material.At the same time,the material of enriched lithospheric mantle moved upward though the space which formed by delamination of the lithosphere.