LA-ICP-MS U-Pb zircon geochronology and Hf isotope,geochemistry and kinetics of the Daxigou anorthosite from Kuruqtagh block,NW China

Kuruqtagh block is the best area for Precambrian geology in Xinjiang Autonomous Region, NW China, since it exposed complete Precambrian lithology units. The study of this ancient base will deepen the understanding of the Precambrian evolution of the Tarim Basin. In this paper, we studied the petrology, geochemistry, zircon LA-ICPMS U-Pb chronology and zircon Hf isotope of Daxigou anorthosite （DA） which is located at the northem margin of Tarim craton and discussed the rock formation, tectonic and geological significance. Zircons from the intrusions display oscillatory zoning and high Th/U ratios （0.39-1.35）, implying their magmatic origin. Zircon LA-ICP-MS U-Pb dating results indicate that they formed during the Paleoproterozoic age with the weighted 2~6pb/238U average age of 1818~9 Ma, which is significantly different from former＇s Neoproterozoic age, and is co- incidentally identical with its associated syenite granite age within the error range. Studies on petrogeochemistry suggest that DA belongs to medium-sodium peraluminous alkaline type, rich in Pb, La, Th and LILE, and poor in HFSE （Gd, Nd, and Ta）. The chondrite-normalized REE pattern is slightly to the right form. The average Y~REE is 317.2~ 10-6; HREE show moderate fractionation [average LREE/HREE is 14.71, average （La/Yb）N is 24.77; average （LaJSm）N is 3.85, and average （Gd/Yb）y is 3.46]; and the 6Eu and 8Ce are not obvious. Their initial Hf isotope ratios and Hf two-stage model ages range from -6.6 to -4.43 and 2.63 to 2.74 Ga, respectively. Taken together, it is sug- gested that Daxigou anorthosite is a typical volcanic anorthosite and its primary magma could be contaminated by the partial melt Neoarchaean crust and mainly formed in the arc environment, which recoded the tectonic-magma activities response of the Tarim refers to the amalgamation of the supercontinent Columbia.     

Occurrence and mineral chemistry of chromite and related silicates from the Hongshishan mafic-ultramafic complex,NW China with petrogenetic implications

Mineralogy and Petrology - The Hongshishan mafic-ultramafic complex is located in the western Beishan Terrane, NW China, and hosts an economic Ni-Cu deposit. Chromite as accessory mineral from the...     

东天山-北山镁铁-超镁铁质岩特征、成矿意义及构造背景

东天山-北山地区镁铁-超镁铁质岩体成群成带分布,明显受区域内主干断裂控制,主要分布于东天山、中天山地块和北山裂谷。镁铁-超镁铁质岩体与Cu-Ni矿化密切相关,小岩体成大矿为普遍现象。含矿岩相多集中在橄榄辉长岩、角闪橄榄岩、辉橄岩和各岩相接触带上。岩体低Ti高Mg,高m/s和m/f是评价其含矿性的良好指标。SrNd同位素显示镁铁-超镁铁质岩体整体上源于亏损地幔,在演化过程中经历了同化混染作用,中天山和北山地区较东天山地区混染程度较小。成岩成矿集中在早二叠世约280 Ma,指示其可能是统一地球热力学的产物。镁铁-超镁铁质岩体的构造背景复杂,争议较多,单一的构造背景不能解释所有问题,后碰撞伸展和地幔柱的共同作用可能诱发大规模成岩成矿事件。     

Petrology and Geochemistry of the Banded Iron Formation of the Kuluketage Block,Xinjiang, NW China: Implication for BIF Depositional Setting

The Kuluketage block, located in the northeast Tarim craton, is one of the largest Precambrian blocks in the Xinjiang province. Recently, many banded iron formation (BIF)‐type (Superior‐type) deposits have been discovered in the western part of the Kuluketage block. These deposits occurred in the Paleoproterozoic Shayiti Formation, Xingditage Group, which has a nearly E–W distribution in the southern Xinger and Xingdi faults. Tremolite biotite schist and quartzite are the main wall rocks. The geochemical characteristics of schist indicate that the BIFs occurred in a passive continental margin environment. The LA–ICP–MS zircon ²⁰⁶Pb/²³⁸U ages of BIF and late syenite are 1945 ± 10 Ma(MSWD = 0.77) (weighted average age) and 1974 ± 27 Ma(MSWD = 1.05) (upper intercept age), respectively, indicating that the BIFs occurred in the Paleoproterozoic. In addition, the approximately 1.9 Ga magmatic and metamorphic events are consistent with the global‐scale 2.1–1.8 Ga collisional orogen events which are associated with the assembly of the Columbia supercontinent. The geochemical characteristics show that magnetite and quartz are dominant components (total content, 91.65–98.22 wt.%), and the Zr(Nb) and TiO₂, Zr(Nb) and Al₂O₃ and Zr and Y/Ho display strongly positive correlations, illustrating the addition of crustal materials into the chemical precipitate of the original BIFs. The higher Zr, Nb and Al₂O₃ contents and a lower Y/Ho ratio of the Kuluketage BIFs indicate a higher terrigenous detrital component contaminant compared to BIFs of North China Craton (NCC). The rare earth and yttrium (REY) distribution patterns show a slight LREE enrichment and weak Eu positive anomaly features, indicating that the source of Fe and Si of the Kuluketage BIFs is mainly from the contribution of low‐temperature hydrothermal alteration of the oceanic crust. In addition, along with the decreasing BIF depositional age, the declining of Eu anomaly values reflects the increasing importance of low‐temperature hydrothermal solutions relative to high‐temperature hydrothermal solutions. Moreover, no Ce anomalies in studied BIFs, NCC and Xinyu BIFs are attributed to relative reducing environmental condition when the original BIFs precipitated.