华北克拉通新太古代板块俯冲作用:来自山西云中山地区变质高镁火成岩组合的证据  

Neoarchean subduction in North China Craton: New evidence from the metamorphic high-Mg igneous assemblage in Yunzhognshan area, Shanxi Province

作　　者：王惠初 康健丽 肖志斌 相振群[1] 李建荣[2] 孙义伟 施建荣 张家辉 WANG HuiChu;KANG JianLi;XIAO ZhiBin;XIANG ZhenQun;LI JianRong;SUN YiWei;SHI JianRong;ZHANG JiaHui(Tianfin Center, China Geological Survey, Tianfin 300170, China;Shanxi Institute of Geological Survey, Taiyuan 030006, China)

机构地区：[1]中国地质调查局天津地质调查中心,天津300170 [2]山西省地质调查院,太原030006

出　　处：《岩石学报》2018年第4期1099-1118,共20页Acta Petrologica Sinica

基　　金：国土资源部公益性基础地质调查项目(DD20160042)资助

摘　　要：在华北克拉通中部的山西云中山地区,新太古代花岗闪长质片麻岩中存在一些超镁铁质岩-镁铁质岩块及由斜长角闪岩、角闪变粒岩、石英岩和石榴夕线黑云片岩等岩石类型构成的变质表壳岩残片,其中的超镁铁质-镁铁质岩、斜长角闪岩和角闪变粒岩构成一套高镁火成岩组合。超镁铁质岩已变质为橄榄绿泥阳起片岩等岩石类型,呈变余斑状结构,橄榄石斑晶仍有保存;岩石SiO_2含量为39.22%～44.99%,Al_2O_3为8.82%～13.47%,Mg O为19.24%～22.13%,Na_2O+K_2O=0.71%～1.11%,CaO为5.75%～8.42%;Al_2O_3/TiO_2=14.8～17.4,CaO/Al_2O_3=0.60～0.84;化学成分上与科马提岩有一定的相似性。与之紧密伴生的斜长角闪岩也具有高镁特征,Mg O含量为11.28%～15.09%,铝、硅和碱质均偏低,具正铕异常,显示堆晶辉长岩的特征。非高镁斜长角闪岩有相对高的铝、硅和碱质,其原岩应为钙碱性玄武岩。角闪变粒岩样品的SiO_2含量为54.21%～55.71%,Al_2O_3为14.24%～15.49%,Mg O为6.26%～8.28%,Fe OT/Mg O=1.11～1.58,高钠低钾,Na_2O+K_2O=3.7%～4.78%,Na_2O/K_2O=5.15%～13.13,Mg#=53.0～61.5,属于高镁安山岩。由超镁铁质质岩-斜长角闪岩-角闪变粒岩构成的变质高镁火山岩组合具有钙碱性系列趋势。超镁铁质岩稀土元素含量总量较低,具有轻稀土富集和重稀土亏损的稀土型式;斜长角闪岩与超镁铁质岩比较,除富集大离子亲石元素和Cr、Ni明显较低外,具有相似的微量元素图谱形态。三种岩石类型在微量元素蛛网图上均显示出Ta、Nb、Ti负异常和Pb正异常。野外产状和岩石地球化学特征表明超镁铁质岩和高镁斜长角闪岩属于阿拉斯加型杂岩体,角闪变粒岩属于赞岐岩质高镁安山岩。在Zr/Nb-Nb/Th和Nb/Y-Zr/Y构造环境判别图解上显示出与俯冲相关的演化趋势,在Hf-Th-Ta、Nb/La-(La/Sm)N和Th/Yb-Nb/Yb图解上也落在岛弧钙碱性岩石区域。以上特征表明高镁火成岩组合形成于与Some mafic-ultramafic rock fragments and metamorphosed supracrustal rock fragments consisting of amphibolites,Hbleptynite,quartzite and garnet-mica-schist were found as residues occur in the Neoarchean augen granodioritic gneiss,in Yunzhongshan area,the central North China Craton（ NCC）. The mafic-ultramafic rocks,amphibolite and Hb-leptynite constitute a metamorphic highMg igneous assemblage. Ultramafic rocks that metamorphosed into olivine-chlorite-actinolite-schists preserve remnant porphyritic texture with olivine-phenocryst,and which are characterized by high contents of MgO（ 19. 24% - 22. 13%）,Cr（ 1935 × 10^-6- 3345 ×10^-6） and Ni（ 706 × 10^-6- 988 × 10^-6）,and low contents of SiO2（ 39. 22% - 44. 99%） and alkalis（ Na2O ＋ K2O = 0. 71% -1. 11%）,with relative low Al2O3/TiO2（ 14. 8 - 17. 4） as well as CaO/Al2O3（ 0. 60 - 0. 84）. In major element compositions ultramafic rocks are somewhat similar to the komatiitic rocks. Amphibolites can be divided into two groups of high-MgO and non high-MgO,the MgO content of the former is 11. 28% - 15. 08%,and of the latter 7. 68% - 9. 07%. The high-MgO amphibolites coexist closely with ultramafic rocks,and are characterized by relative low contents of SiO2,Al2O3 and alkalis,high Mg#（ 65. 7 - 72. 7）,with positive Eu anomalies. These features suggest that the high-MgO amphibolites are metamorphic gabbro from fractional crystallization of mantle-derived magma. The non high-MgO amphibolites have relative high contents of SiO2,Al2O3 and alkalis,with very weak positive Eu anomalies,which infer that their protolith are calc-alkali basalts. The chemical composition of Hb-leptynite（ SiO254. 21% -55. 71%,Al2O314. 24% - 15. 49%,MgO 6. 26% - 8. 28% and Fe OT/MgO = 1. 11 - 1. 58） reveal the character of high-Mg andesite. The high-Mg igneous assemblage shows a calc-alkaline series trend. REE patterns of light REE enrichment and traceelements spider diagram with Nb,Ta,Ti negative anomalies,Pb positive anomaly imply crustal material contamination

关 键 词：云中山 高镁火成岩组合 新太古代 岛弧构造环境 华北克拉通 

分 类 号：P588.124[天文地球—岩石学] P588.125[天文地球—地质学]