中文摘要:坡北基性-超基性岩带10号岩体位于塔里木板块东北部北山裂谷带内，岩体侵位于下石炭统红柳园组。前人根据岩体侵位地层的时代，间接推断出该岩体形成年龄为晚石炭世—早二叠世。文章对坡北基性-超基性岩带的10号岩体辉长岩和浸染状矿石分别进行了锆石SHRIMP U-Pb、Re-Os定年和Sr-Nd同位素示踪研究，获得岩体的辉长岩锆石SHRIMP U-Pb年龄信息比较分散，其表面年龄信息从古生代—新元古代—古元古代—新太古代均有显示，揭示了新疆塔里木板块东北部北山裂谷带内的基性-超基性岩体的形成经历了复杂的地质演化历史。所获得的主体锆石的年龄为（289±13） Ma（95 %可信度），与岩体侵位于下石炭统红柳园组的地质事实相吻合，可能代表了岩体形成的时间，而年龄信息（2 559～2 589 Ma）暗示了北山地区可能存在古元古代—新太古代的结晶基底。获得浸染状铜镍硫化物矿石的Re-Os等时线年龄为（413±20）Ma （95 %可信度），该年龄不仅大于含矿超基性岩体（289 Ma）的形成时代，而且也老于岩体所侵入的下石炭统红柳园组的地层时代，显然与宏观的地质证据相悖。Sr-Nd和Os同位素特征研究表明，坡北岩带在约280 Ma前成岩成矿时，岩浆在从地幔源区侵入到地壳过程中受到了地壳物质混染，致使浸染状矿石的Re-Os同位素体系呈二元混合体系，因此浸染状矿石Re-Os同位素体系确定的等时线疑为假等时线，其年龄不能代表矿床形成时代或不具有确切的地质意义。铜镍矿化无论从时间上还是空间上都与岩体的侵位密切相关，矿床成因类型又为岩浆熔离型矿床，表明坡北10号铜镍硫化物矿床的成岩成矿时间应发生在晚石炭世—早二叠世期间，是后碰撞构造背景下幔源岩浆上侵的产物。
Abstract:Located in Beishan rift in the northeastern part of Tarim plate, the Pobei No.10 mafic-ultramafic body intruded into Early Carboniferous Hongliuyuan Formation. It is large in size and well differentiated, thus serving as one of the most important intrusive bodies in search for copper-nickel sulfides. According to its emplacement strata, it was previously thought that this intrusive body was formed in Late Carboniferous-Early Permian. The authors performed dating by using such techniques as zircon U-Pb, disseminated ores Re-Os and Sr-Nd isotopic tracer with the purpose of systematic determination of the magmatic and mineralization ages, on such a basis, discussed the metallogenic significance of systematic differences between the ages dated by different isotopic systems. Radiometric dating of the gabbro from the Pobei No.10 mafic-ultramafic body yielded rather scattered zircon age information, but obtained a main body zircon SHRIMP U-Pb age of (289±13) Ma (95% confidence，MSWD=4.9, n=8), which is interpreted as the formation age of the host intrusive. The disseminated ores give an apparent Re-Os isochron age of (413±20) Ma with an initial 187Os/188Os ratio of (0.226±0.032). However, it is found that the apparent Re-Os isochron ages of disseminated ores are older than both the formation age of the host intrusions and the ages of Pobei No.10 mafic-ultramafic emplacement strata, which indicates that the apparent Re-Os isochron ages of disseminated ores are not reliable. It is suggested that the Pobei No.10 mafic-ultramafic body and the deposit were formed at about 280 Ma ago. Because of heterogeneity in initial 187Os/188Os ratios of disseminated ores caused by crust contamination, the apparent dates older than the true age were obtained. Cu-Ni mineraliztion shows a close time-space relationship with the mafic-ultramafic intrusive body, implying a product of magmatic liquation. It is therefore concluded that the intrusion of Pobei No.10 mafic-ultramafic rock body and the related minealization occurred in a post-orogenic dynanmic setting in Late Carboniferous-Early Permion.
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基金项目:国家科技支撑重点项目（编号：2006BAB07B08-01）和地质调查项目（编号：1212010786006、121010633903）
引用文本：
李华芹,梅玉萍,屈文俊,蔡 红,杜国民.2009.新疆坡北基性-超基性岩带10号岩体SHRIMP U-Pb和矿石Re-Os同位素定年及其意义[J].矿床地质,28(5):633~642屈文俊,蔡 红,杜国民.2009.SHRIMP zircon U-Pb and Re-Os dating of No.10 intrusive body and associated ores in Pobei maficultramafic belt of Xinjiang and its significance[J].Mineral Deposits28(5):633~642
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