【摘要】 查干诺尔辉长岩体由角闪辉长岩和辉长闪长岩组成,呈岩株状侵入于晚石炭世花岗闪长岩和上石炭统宝力高庙组中。角闪辉长岩LA-ICP-MS锆石U-Pb年龄为302 Ma,表明该岩体的形成时代为晚石炭世。查干诺尔辉长岩具有高铝钙、低钛和贫碱的特征,属于钙碱性系列岩石。相对富集大离子亲石元素（LILE）,亏损高场强元素（HFSE）,具明显的Nb、Ta、Ti、Zr、Hf负异常和Pb正异常,与典型的弧岩浆类似。岩石稀土总量较低且变化范围大（∑REE=63.4～135μg/g）,轻、重稀土元素分异程度中等,无明显的Eu异常;稀土元素分布模式表现为轻稀土富集、重稀土平坦且向右缓倾型式。Sr-Nd同位素组成为低(⁸⁷Sr/⁸⁶Sr)_i（0.70407～0.70428）、正ε_Nd（t）（1.62～3.47）,显示了亏损地幔源区的同位素特征;有较高的Pb同位素比值,(²⁰⁶Pb/²⁰⁴Pb)_i为17.816～18.040,(²⁰⁷Pb/²⁰⁴Pb)_i为15.472～15.484,(²⁰⁸Pb/²⁰⁴Pb)_i为37.242～37.534。上述地球化学特征表明查干诺尔辉长岩形成于晚石炭世大陆弧环境,是交代岩石圈地幔含角闪石二辉橄榄岩在低压条件下低程度部分熔融的产物,交代组分来自古亚洲洋闭合期间俯冲板片释放的流体。查干诺尔辉长岩的厘定可能表明内蒙古中部贺根山洋晚石炭世往北俯冲的时间持续至302 Ma,并在早二叠世发生闭合。更多还原

【Abstract】 The Chagannuoer gabbroic pluton is composed of hornblende gabbro and gabbroic diorite and occurs as a stock intruding into the Late Carboniferous granodioritic pluton and the Baoligaomiao Formation.The LA-ICP-MS zircon U-Pb dating suggested that this gabbroic pluton was formed during the Late Carboniferous with an age of ca.302 Ma.The Chagannuoer gabbro is low in titanium and alkali,but high in aluminum and calcium and belongs to the calc-alkali series.It is relatively enriched in large ion lithophile elements（LILE）and depleted in high field strength elements（HFSE）with pronounced negative Nb,Ta,Ti,Zr,and Hf anomalies and positive Pb anomalies similar to typical arc magmas.The Chagannuoer gabbro has low and variable∑REE contents（63.4–135μg/g）and shows a medium REE fractionation with LREE enrichment and no Eu anomalies resulting in parallel gentle right-dipping curves with flat HREE patterns in the chondrite-normalized REE diagrams.Its Sr-Nd-Pb isotopic compositions are characterized by low(⁸⁷Sr/⁸⁶Sr)_i（0.70407–0.70428）and a positiveε_Nd（t）（1.62–3.47）consistent with the DM-like components and by high lead isotopic ratios with(²⁰⁶Pb/²⁰⁴Pb)_i of 17.816–18.040,(²⁰⁷Pb/²⁰⁴Pb)_i of 15.472–15.484,and(²⁰⁸Pb/²⁰⁴Pb)_i of 37.242–37.534.These geochemical characteristics suggest that the Chagannuoer gabbroic pluton was formed in a continental arc setting during the Carboniferous.It was likely generated at low pressures from a small degree of partial melting of an amphibole-bearing lherzolite source in the lithospheric mantle that had been metasomatised by fluids released from a subducted slab during the closure of the Paleo-Asian Ocean.The Chagannuoer gabbroic pluton shows that the Hegenshan Ocean in central Inner Mongolia was subducted northward during the Late Carboniferous at least until 302 Ma and closed in the Early Permian.更多还原