个旧老厂钾质煌斑岩矿物学特征及其锆石U-Pb和黑云母^(40)Ar-^(39)Ar年龄  

Mineralogical characteristics, zircon U-Pb and biotite ^(40)Ar-^(39)Ar ages of potassic lamprophyres in the Gejiu tin deposit, Yunnan Province

作　　者：曹华文[1,2] 裴秋明 张寿庭[2] 王长明[2] 王光凯 王亮[2] 

机构地区：[1]中国地质调查局成都地质调查中心,四川成都610081 [2]中国地质大学地球科学与资源学院,北京100083 [3]山东正元建设工程有限责任公司,山东济南250100

出　　处：《地球化学》2016年第6期545-568,共24页Geochimica

基　　金：中国地质调查局基础性公益性地质矿产调查项目(DD20160015);国家地质大调查项目(1212011182388)

摘　　要：个旧老厂锡铜多金属矿区出露多条钾质煌斑岩脉,是个旧白垩纪岩浆活动的重要组成部分。本文利用电子探针对煌斑岩进行矿物学特征分析,利用锆石TIMS U-Pb和黑云母^(40)Ar-^(39)Ar进行了煌斑岩年代学研究。煌斑岩辉石斑晶和微晶化学成分近一致,均属普通辉石;黑云母斑晶属壳源铁质-镁质黑云母,而黑云母微晶属壳幔混源型镁质黑云母;中长石斑晶偏基性(An25~40),透长石微晶偏酸性(An1~6)。煌斑岩2颗锆石TIMS U-Pb年龄(87.1±1.3)Ma为捕获的围岩(老卡花岗岩体)锆石的年龄。煌斑岩脉的6个黑云母^(40)Ar-^(39)Ar同位素坪年龄集中在75~70 Ma间(平均72.9 Ma),代表煌斑岩侵位时代,稍晚于个旧中酸性岩浆活动的时代(85~78 Ma)。个旧老厂钾质煌斑岩脉代表壳-幔的相互作用,岩浆起源于古特提斯洋壳板块俯冲的残留板片对地幔楔的交代富集作用而形成的地幔源区。煌斑岩浆侵位的构造背景为俯冲-碰撞后的板内拉伸环境。Exposed in the Laochang Sn-Cu polymetallic ore deposit, Gejiu, Yunnan Province, are various potassic lamprophyre dikes, which are an important part of the Cretaceous magma activity in the Gejiu district. The mineralogical characteristics were studied by means of electron microprobe; the geochronology of lamprophyres was also studied by the zircon TIMS U-Pb and biotite 40Ar-39Ar methods. Both pyroxene phenocryst and microlite are augites with similar chemical composition; biotite phenocryst is ferro-magnesio-biotite, and biotite microlite is magnesio-biotite. Plagioclase phenocryst is andesine （An25-40） while plagioclase microlite is sanidine （An1-6）. TIMS U-Pb ages （（87.1±1.3） Ma） of 2 zircons from lamprophyres suggest that they were captured from wall rocks （the Laoka granite）. The 40Ar-39Ar plateau ages of 6 biotites from lamprophyre dikes range from 75 Ma to 70 Ma （averaging 72.9 Ma）, representing the emplacement age of the lamprophyres, which is slightly yonger than that of intermediate-acidic magma activity （85-78 Ma） in the Gejiu district. The Laochang potassic lamprophyre dikes originated from an enriched mantle source, which was affected by metasomatism between the residual subducted slab of the Paleotethyan oceanic plate and the mantle wedge. The lamprophyric magma was emplaced in the intra-plate extensive tectonic environment after subduction-collision.

关 键 词：钾质煌斑岩 锆石U-Pb年龄 电子探针 黑云母40Ar-39Ar年龄 老厂 

分 类 号：P578.94[天文地球—矿物学] P588.13[天文地球—地质学]