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东天山二叠纪镁铁-超镁铁质成矿岩体造岩矿物特征及其成因意义
Rock-forming mineral features of Permian mineralized mafic-ultramafic intrusions in East Tianshan Mountains and their implications for intrusion generation
投稿时间:2017-01-12  修订日期:2017-03-17
中文关键词:矿物学  镁铁-超镁铁质岩体  铜镍硫化物矿床  岩浆演化  地壳混染  东天山
英文关键词:mineralogy  mafic-ultramafic intrusion  Cu-Ni sulfide deposit  magmatic evolution  crustal contamination  East Tianshan Mountains
基金项目:中国地质调查局地质大调查项目(1212011085061);国家自然科学面上基金(41372101);国家自然科学青年基金(41402070);长安大学中央高校专项基金(CHD310827171007)
作者单位E-mail
冯延清 长安大学 地球科学与资源学院, 陕西 西安 710054  
钱壮志 长安大学 地球科学与资源学院, 陕西 西安 710054;国土资源部岩浆作用成矿与找矿重点实验室, 陕西 西安 710054 zyxyqzz8@chd.edu.cn 
徐刚 长安大学 地球科学与资源学院, 陕西 西安 710054  
段俊 长安大学 地球科学与资源学院, 陕西 西安 710054  
陈炳龙 长安大学 地球科学与资源学院, 陕西 西安 710054  
孙涛 云南大学 资源环境与地球科学学院, 云南 昆明 650091  
姜超 陕西省核工业地质调查院, 陕西 西安 710100  
任萌 长安大学 地球科学与资源学院, 陕西 西安 710054  
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中文摘要:
      东天山造山带与镁铁-超镁铁质岩体有关的铜镍硫化物矿床数量多,分布集中,是我国重要的铜镍成矿带之一。成矿岩体多以小岩体群形式产出,由西向东分布有白鑫滩、黄山和图拉尔根3个岩体群,大型矿床主要赋存在黄山岩体群内。本文对3个岩体群内成矿岩体的主要造岩矿物进行了系统的对比研究。成矿岩体的主要造岩矿物为贵橄榄石、古铜辉石、单斜辉石、斜长石和角闪石以及少量的铬尖晶石和金云母。橄榄石Al温度计计算结果表明,黄山岩体群内成矿岩体的母岩浆结晶温度介于1 143~1 257℃之间,略低于白鑫滩和图拉尔根岩体群(1 283~1 301℃)。单斜辉石压力计算表明成矿岩体的结晶压力相似,介于0.31~0.33 GPa之间。成矿岩体中均富含含水矿物,且单斜辉石结晶早于斜长石,指示成矿岩体的原始岩浆形成于富水环境。成矿岩体的单斜辉石具有较高的Al/Ti值,铬尖晶石和橄榄石具有与岛弧火山岩相似的矿物学特征,结合区域构造演化,认为东天山镁铁-超镁铁质成矿岩体的原始岩浆是被消减板片交代过的地幔部分熔融的产物。矿物学特征对比显示了黄山岩体群内成矿岩体更富斜方辉石和中性斜长石,且具有较低的铬尖晶石Cr#值和橄榄石Ca含量。结合前人研究成果和相关地球化学数据,认为相对高的混染程度导致了黄山岩体群的母岩浆富SiO2和Al2O3,同时降低了岩浆的结晶温度。
英文摘要:
      East Tianshan, one of the important ore concentration belt in China, is characterized by a large number of mafic-ultramafic intrusions with magmatic Cu-Ni sulfide mineralization in a concentrated area. These small mafic-ultramafic intrusions are distributed in three groups, i.e., Baixintan, Huangshan, and Tulaergen, from west to east. The large-sized deposits mainly occur in the Huangshan intrusion group. The rocks mainly consist of olivine, bronzite, clinopyroxene, hornblende and plagioclase together with a small amount of Cr-spinel and phlogopite. Systematic and comparative studies of the mineralogy of rocks from ore-hosting mafic-ultramafic intrusions in East Tianshan were conducted in this paper. The estimated crystallization temperatures based on Cr-spinel and olivine pair from Huangshan intrusion group were from 1 143 to 1 257℃, which are slightly lower than those from Baixintan and Tulaergen groups (1 283~1 301℃). The estimated pressures show similar widths of 0.31~0.33 GPa calculated by clinopyroxene geobarometer for all the three intrusion groups. The characteristics of hydrous minerals and the fact of earlier crystallization of clinopyroxene than plagioclase indicate that the primitive magmas of the intrusions in East Tianshan were substantially hydrous. The clinopyroxenes in sulfide-bearing intrusive rocks have higher Al/Ti ratio, and the compositions of Cr-spinel and olivine crystals are within or close to the field of island arc volcanic basalts. Based on the regional tectonic evolution, the authors hold that the primitive magmas of sulfide-bearing mafic intrusions in East Tianshan were generated by partial melting of a metasomatic mantle, which was modified by slab-derived fluids associated with the previous subdction events. Mineral comparisons indicate that the ore-hosting intrusions in the Huangshan group have more orthopyroxene and andesine as well as lower Cr# of Cr-spinel and Ca content in olivine. The new data obtained from this study, together with previous results, indicate that the higher SiO2 and Al2O3 content in the parental magma of Huangshan intrusions group might have resulted from higher degree of crustal contamination, which also reduced the crystallization temperature of the magma.
冯延清,钱壮志,徐刚,段俊,陈炳龙,孙涛,姜超,任萌,2017,东天山二叠纪镁铁-超镁铁质成矿岩体造岩矿物特征及其成因意义[J].岩石矿物学杂志,36(4):519~534.
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