扬子西缘丹巴水子乡辉石岩年代学和岩石成因研究  

Geochronology and petrogenesis of the Shuizi pyroxenite at Danba, western Yangtze Craton

作　　者：赵鹤森 王庆飞[2] 王彦宁 王廷祎 薛胜超 陈威 ZHAO HeSen;WANG QingFei;WANG YanNing;Wang TingYi;XUE ShengChao;CHEN Wei(Chengdu Center,China Geological Survey,Chengdu 610081,China;State Key Laboratory of Geological Processes and Mineral Resources,China University of Geosciences,Beijing 100083,China;Shengtun Mining Group Co.Ltd,Xiamen 361012,China)

机构地区：[1]中国地质调查局成都地质调查中心,成都610081 [2]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 [3]盛屯矿业集团股份有限公司,厦门361012

出　　处：《岩石学报》2022年第1期172-184,共13页Acta Petrologica Sinica

基　　金：国家自然科学青年基金项目(42002107);国家重点研发计划(2020YFA0714802、2016YFC0600307)联合资助。

摘　　要：扬子克拉通西缘在~260Ma发生短期内大规模峨眉山玄武岩溢流喷发。攀西地区发育的镁铁-超镁铁质岩被广泛认为是峨眉山大火成岩省的产物,但在北端松潘-甘孜岩区一直缺乏该类岩石的报道。本文首次报道扬子西缘丹巴水子乡单斜辉石岩的准确年龄,其锆石LA-ICP-MS U-Pb加权平均年龄为260.7±3.3Ma,表明其为峨眉山大火成岩省北端松潘-甘孜岩区镁铁-超镁铁质岩的组成部分。通过与攀枝花钒钛磁铁矿含矿岩体边缘相带苦橄岩和上部相带浅色辉长岩进行锆石微量元素对比显示,水子乡单斜辉石岩具有相近的高氧逸度,其ΔQFM为0~3,Ce_(N)/Ce_(N)平均为~30,该性质可能同样源自扬子西缘洋壳板片俯冲交代形成的较高氧逸度地幔源区。尽管如此,水子乡辉石岩体并未因高氧逸度而有明显的含钛磁铁矿饱和结晶,可能由其较低结晶分异程度造成。相比之下,攀枝花岩体经历了更高程度的含钛磁铁矿和斜长石分离结晶作用,伴随大规模的钒钛磁铁矿成矿。Large-scale eruption of Emeishan flood basalt occurred in the western margin of the Yangtze Craton in a short period during ~260 Ma. Mafic-ultramafic rocks found in the Panxi area are widely considered to be products of the Emeishan Large Igneous Province(ELIP). However, there is a lack of reports on this kind of rocks in the Songpan-Ganzi area in the northern end of the ELIP. This paper first documents a precise age of the Shuizi pyroxenite in the Danba County. The zircon LA-ICP-MS U-Pb weighted mean age is 260.7±3.3 Ma, indicating a representative mafic-ultramafic constituent of the northern end of the ELIP in the Songpan-Ganzi area. Comparing zircon trace elements of the Shuizi pyroxenite with those of picrite in the marginal zone and gabbro in the upper zone of the Panzhihua Fe-Ti-V oxide deposit were conducted. It is found that the Shuizi pyroxenite has similarly high magmatic oxygen fugacity, ΔQFM of 0~3 and average Ce_(N)/Ce_(N) of ~30, to the Panzhihua mafic rocks. The high oxygen fugacity for both is considered to be derived from a mantle lithosphere source which had been metasomatized by subducted oceanic slab materials in the western margin of the Yangtze Craton. Although the Shuizi pyroxenite has high oxygen fugacity, there is less obvious Fe-Ti oxide saturation and precipitation here. This could be attributed to its relatively low degree of crystallization and differentiation. In contrast, the Panzhihua mafic-ultramafic intrusion experienced higher degree of titanomagnetite and plagioclase fractional crystallization, accompanied by a massive Fe-Ti-V oxide mineralization.

关 键 词：峨眉山大火成岩省 松潘-甘孜 辉石岩 锆石微量元素 氧逸度 分离结晶 

分 类 号：P588.125[天文地球—岩石学] P597.3[天文地球—地质学]