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新疆西天山备战基性-超基性岩年代学和岩石地球化学研究及其对铁成矿背景的制约
Geochronology and geochemistry of the Beizhan basic-ultrabasic pluton in West Tianshan, Xinjiang: Petrogenesis and geodynamical implications
投稿时间:2017-11-17  
中文关键词:金云母氩氩年龄  基性-超基性岩  备战铁矿  西天山  地球动力学背景
英文关键词:phlogopite Ar-Ar age  basic-ultrabasic rock  Beizhan iron deposit  West Tianshan  geodynamic setting
基金项目:国家自然科学基金项目(41503041);中央级公益性科研院所基本科研业务专项资金(K1412);国家重点基础研究发展计划("973"计划)(2012CB416803);中国地质调查局地质调查项目(DD20160124)
作者单位
骆文娟 中国地质科学院 矿产资源研究所, 自然资源部成矿作用与资源评价重点实验室, 北京 100037 
张作衡 中国地质科学院 矿产资源研究所, 自然资源部成矿作用与资源评价重点实验室, 北京 100037 
段士刚 中国地质科学院 矿产资源研究所, 自然资源部成矿作用与资源评价重点实验室, 北京 100037 
蒋宗胜 中国地质科学院 矿产资源研究所, 自然资源部成矿作用与资源评价重点实验室, 北京 100037 
王大川 中国地质大学 地质过程与矿产资源国家重点实验室, 北京 100083 
陈杰 中国地质大学 地质过程与矿产资源国家重点实验室, 北京 100083 
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中文摘要:
      对新疆西天山备战铁矿区附近的基性-超基性岩体——金云母辉石橄榄岩与侵入其中的闪长岩脉进行了年代学和岩石地球化学研究。金云母辉石橄榄岩中金云母40Ar/39Ar坪年龄为298.1±1.9 Ma,该岩石的锆石U-Pb年龄为302.5±1.3 Ma,与备战铁矿的成矿年龄相近。备战金云母辉石橄榄岩具有低SiO2(42.51%~50.82%)、Al2O3(4.87%~7.38%)、TiO2(0.25%~0.77%)和全碱(Na2O+K2O=0.87%~1.87%)含量,而高MgO(26.36%~30.17%)、TFeO(12.33%~15.99%)含量的特征,过渡元素丰度(Cr=523×10-6~7 026×10-6,Ni=906×10-6~1 088×10-6,Co=109×10-6~132×10-6)和Mg#值(0.76~0.79)均较高,表明岩浆经历了橄榄石堆晶作用。由橄榄石最高Fo值(0.79)和岩石的TFeO含量计算得其母岩浆为玄武质岩浆。所有的岩石具有相似的稀土、微量元素配分模式,均呈轻稀土元素富集的右倾型,且重稀土元素较平坦,明显富集大离子亲石元素Rb、Ba、U、K,亏损高场强元素Nb、Ta、Zr、Hf和Ti。总体上Sr、Nd同位素较均一,金云母辉石橄榄岩的(87Sr/86Sr)i=0.704 4~0.704 7,εNd(t)=2.23~3.90,闪长岩(87Sr/86Sr)i=0.704 4,εNd(t)=3.79~4.07,表明金云母辉石橄榄岩和闪长岩为同源演化的岩石。微量元素特征表明金云母辉石橄榄岩起源于尖晶石相,源区为受俯冲流体或熔体交代的软流圈地幔。结合区域构造背景,推测金云母辉石橄榄岩的形成与西天山造山带在晚古生代的山根拆沉引起的软流圈上涌有关,而备战铁矿晚期成矿事件很可能形成于相同的深部动力学背景下。
英文摘要:
      This paper reports the characteristics of the Beizhan phlogopite pyroxene peridotite pluton and diorite veins from West Tianshan, Xinjiang. Laser ablation inductively coupled plasma mass spectrometry (LA ICP-MS) U-Pb zircon dating of the Beizhan phlogopite pyroxene peridotite yielded an age of 302.5±1.3 Ma, and phlogopites from phlogopite pyroxene peridotite yielded a well-defined 40Ar/39Ar plateau age of 298.1±1.9 Ma, which show excellent agreement with the mineralization age of the Beizhan iron deposit. Beizhan phlogolite pyroxene peridotite exhibits relatively lower SiO2 (42.51%~50.82%),Al2O3 (4.87%~7.38%),TiO2 (0.25%~0.77%), Na2O+K2O (0.87%~1.87%),and higher MgO (26.36%~30.17%), TFeO (12.33%~15.99%) content. The high Cr (523×10-6~7 026×10-6), Ni (906×10-6~1 088×10-6), Co (109×10-6~132×10-6) and Mg#(0.76~0.79)values of the Beizhan phlogolite pyroxene peridotite suggest that olivine accumulation occurred in the magma. The calculation based on the highest Fo of olivine from phlogolite pyroxene peridotite and the TFeO content of the whole rocks suggest that its parent magma is basaltic affinity. All the rocks display LREE-enriched and flat HREE patterns,and show the enrichment of large ion lithophile elements (Rb, Ba, U, K) and the depletion of high field-strength elements (Nb, Ta, Zr, Hf, Ti), as well as the positive Pb anomaly. Phlogopite proxene peridotite has low initial 87Sr/86Sr ratios of 0.704 4~0.704 7 and high εNd(t) values of 2.23~3.90,and diorite has initial 87Sr/86Sr ratios of 0.704 4 and εNd(t) values of 3.79~4.07. These homogeneous Sr, Nd isotope compositions suggest that they were derived from the same source region. Furthermore, the trace element signature suggests that phlogolite pyroxene peridotite was derived from a spinel-facies asthenosphere mantle source, which had been modified by subduction-related melts/fluids. Combined with regional tectonic setting, the authors infer that the Beizhan phlogopite pyroxene peridotite was derived from the upwelling of asthenosphere mantle caused by the detachment of the West Tianshan orogenic root zone in Neopaleozoic. It is also suggested that the Beizhan iron deposit was formed under the same geodynamic setting.
骆文娟,张作衡,段士刚,蒋宗胜,王大川,陈杰,2018,新疆西天山备战基性-超基性岩年代学和岩石地球化学研究及其对铁成矿背景的制约[J].岩石矿物学杂志,(5):733~753.
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