投稿时间：2023-12-08
修订日期：2024-08-20
网络发布日期：2024-11-05
中文摘要:新疆巴楚县小海子杂岩体是中国西北部早二叠世塔里木大火成岩省的一部分，由镁铁-超镁铁质侵入体及碱性岩体和岩脉组成。为了更好地约束小海子杂岩体的成因及相关Fe-Ti氧化物的成矿条件，作者对第一期镁铁-超镁铁质侵入体（辉长岩、辉石岩）、第二期碱性岩体（辉石正长岩、钾长花岗岩）及后期脉岩（辉绿岩脉、闪长岩脉和正长岩脉）进行了矿物学、地球化学和锆石U-Pb定年的综合研究。锆石测年结果表明，辉长岩年龄286.1~285.8 Ma，辉石岩年龄约282.3 Ma，辉石正长岩年龄约279.4 Ma，钾长花岗岩年龄约275.3 Ma，辉绿岩脉年龄为284.9 Ma、闪长岩脉年龄约274 Ma、正长岩脉年龄约（275.5±1.8）Ma，与地质观察的先后侵入关系吻合，并说明小海子杂岩体（274~286 Ma）为塔里木大火成岩省第二期岩浆活动的产物，演化时限大约12 Ma。地球化学数据显示小海子杂岩具有类似OIB的成分亲和性，类似于巴楚地区同时代的玄武岩。铁钛氧化物矿体主要赋存于辉石岩和辉长岩中，推测由深处的岩浆分异和随后的分离结晶作用形成。小海子杂岩的镁铁质-超镁铁质岩石具有与巴楚地区玄武岩相似的微量元素模式，表明它们可能具有相似的地幔源区，来源于俯冲相关过程所指示的陆下岩石圈地幔源区。小海子辉石正长岩和钾长花岗岩的微量元素模式近乎相同且Th/U和Zr/Nb比值分别为3.6~4.7和4.6~6.0，暗示它们可能来源于同一地幔源区，且是由镁铁质岩石或具有相同母岩浆的深源岩浆部分熔融或分离结晶形成的。本区各种岩脉均具有板内拉张环境玄武岩的微量元素地球化学特征。在岩浆分异的晚期阶段，Fe-Ti氧化物的积累可能伴随着高f(O2)和富挥发分条件下Fe-Ti熔体的结晶,大部分Fe-Ti氧化物在晚期以不规则集合体的形式结晶，浸染状和填隙状磁铁矿的聚集可能是由于液相Fe2O3/FeO比值、f(O2)和压力的变化，或者分离结晶过程中硅酸盐岩浆的挥发分含量变化引起的。
Abstract:The Xiaohaizi complex in Bachu County, Xinjiang, is a part of the Early Permian Tarim Large Igneous Province in northwestern China. It is composed of mafic-ultramafic intrusions, alkaline intrusions and dykes. In order to better constrain its genesis and the metallogenic conditions of associated Fe-Ti oxides, we conducted a comprehensive study of mineralogy, geochemistry and zircon U-Pb dating of the first-stage mafic-ultramafic intrusions (gabbro, pyroxenite), the second-stage alkaline intrusions (pyroxene syenite, K-feldspar granite) and the later dikes (diabase dikes, diorite dikes and syenite dikes). Zircon dating results show that the age of gabbro is 286.1~285.8 Ma, the age of pyroxenite is 282.3 Ma, the age of pyroxene syenite is 279.4 Ma, the age of K-feldspar granite is 275.3 Ma, the age of diabase dyke is 284.9 Ma, the age of diorite dyke is 274 Ma, and the age of syenite dyke is (275.5±1.8) Ma, which are consistent with the successive intrusion relationship from geological observation, and indicates that the Xiaohaizi complex (274~286 Ma) was formed in the second stage of magmatic activity in the Tarim Large Igneous Province, and the evolution time is about 12 Ma.The geochemical data show that the Xiaohaizi igneous rock has a composition affinity similar to OIB, similar to the contemporary basalt in the Bachu area. The iron-titanium oxide ore is mainly hosted in pyroxenite and gabbro, which may be formed by deep magmatic differentiation and subsequent fractional crystallization. The mafic-ultramafic rocks of the Xiaohaizi complex have similar trace element patterns to basalts in the Bachu area, indicating that they may have similar mantle sources, which may derive from the subcontinental lithospheric mantle source indicated by subduction-related processes. The trace element patterns of the Xiaohaizi pyroxene syenite and K-feldspar granite are nearly the same, and the Th/U and Zr/Nb ratios are 3.6~4.7 and 4.6~6.0, respectively, suggesting that they may derive from the same mantle source and formed by partial melting or fractional crystallization of mafic rocks or deep-seated magmas with the same parent magma. All kinds of dikes in this area have the trace element geochemical characteristics of basalt formed in intraplate extensional environment. In the late stage of magmatic differentiation, the accumulation of Fe-Ti oxides may be accompanied by the crystallization of Fe-Ti melts under high f(O2) and volatile-rich conditions. Most of the Fe-Ti oxides crystallize in the form of irregular aggregates in the late stage. The aggregation of disseminated and interstitial magnetite may be caused by the change of Fe2O3/FeO ratio, f(O2) and pressure in the liquid phase, or the volatile content of silicate magma in the process of separation and crystallization.
keywords:Tarim Large Igneous Province mafic-ultramafic intrusion chronology magma evolution Fe-Ti oxide Xinjiang
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基金项目:本文得到地质调查项目“南疆铁多金属矿产地质调查评价”（编号:DD20240117）和“大宗紧缺战略性矿产重点远景区矿产地质调查”（编号:DD20221684）联合资助
引用文本：
张磊,陈懋弘,陈港,安鹏,杨成栋,任程昊.2024.新疆巴楚县小海子杂岩体岩浆演化及成矿：年代学和地球化学约束[J].矿床地质,43(5):1054~1080ZHANG Lei,CHEN MaoHong,CHEN Gang,AN Peng,YANG ChengDong,REN ChengHao.2024.Magmatic evolution and mineralization of Xiaohaizi complex in Bachu County, Xinjiang: Constraints from geochronology and geochemistry[J].Mineral Deposits43(5):1054~1080
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