东昆仑浪木日镁铁质-超镁铁质岩成因:锆石U-Pb年代学和Sr-Nd-Hf同位素特征  

Genesis of mafic-ultramafic rocks from Langmuri area, East Kunlun: Zricon U-Pb geochronology and Sr-Nd-Hf isotope characteristics

作　　者：张斌武 于淼 杨牧[1] 张琛明 陈海福 ZHANG BinWu;YU Miao;YANG Mu;ZHANG ChenMing;CHEN HaiFu(School of Geosciences and Info-physics,Central South University,Changsha 410083,Hunan,China;Qinghai Provincial Nonferrous Metal Geological and Minerals Exploration Bureau,Xining 810012,Qinghai,China)

机构地区：[1]中南大学地球科学与信息物理学院,湖南长沙410083 [2]青海有色地质勘查局,青海西宁810012

出　　处：《矿床地质》2023年第1期211-228,共18页Mineral Deposits

基　　金：国家自然科学基金项目(编号:41902074;41802080)资助。

摘　　要：浪木日镁铁质-超镁铁质岩体位于东昆仑造山带东段,临近昆中断裂,主要由橄榄岩、橄榄辉石岩、辉石岩和辉长岩组成,且局部发育星点状和浸染状硫化物矿化。辉石岩和橄榄辉石岩获得的锆石U-Pb年龄分别为(421.2±1.2)Ma和(421.10±0.96)Ma,表明岩体侵位于晚志留世。岩石地球化学特征显,浪木日镁铁质-超镁铁质岩具有较高的Mg#(Mg#>80),富集LILE(Rb、Th、U等),亏损HFSE(Nb、Ta、Ti等),轻、重稀土元素分馏程度较强((La/Yb)N=6.28~50.91,(La/Sm)N=1.45~4.15,(Gd/Yb)N=1.43~9.71),具有弱的负Eu异常(δEu=0.226~0.824)。锆石Lu-Hf(εHf(t)=-2.9~-10)和全岩Sr-Nd(εNd(t)=-10.3~-8.9)同位素特征显示,其岩浆源区主要来自富集地幔,与俯冲洋壳脱水交代上覆地幔楔活动有关。综合研究表明,浪木日镁铁质-超镁铁质岩体是原特提斯洋洋壳俯冲晚期的产物,随着俯冲的深入,板片最终断离形成板片窗,导致软流圈上涌促使地幔楔发生部分熔融形成镁铁质-超镁铁质岩浆,岩浆上升过程中与地壳发生混染最终形成浪木日岩体。Langmuri mafic-ultramafic rocks are located in the eastern segment of the East Kunlun orogenic belt,adja‐cent to the East Kunlun central fault.They are mainly composed of peridotite,olivine pyroxenite,pyroxenite and gabbro,and are locally developed with stellate and disseminated sulfide mineralization.Zircon U-Pb geochronol‐ogy of pyroxenite and olivine pyroxenite are(421.2±1.2)Ma and(421.10±0.96)Ma,indicating that the intrusion occurred in the late Silurian.The geochemical characteristics of Langmuri mafic-ultramafic rocks show high Mg#(Mg#>80),enrichment of LILE(Rb,Th,U,etc.),depletion of HFSE(Nb,Ta,Ti,etc.),and strong fractionation de‐gree of light and heavy rare earth elements ((La/Yb)N=6.28~50.91,(La/Sm)N=1.45~4.15,(Gd/Yb)N=1.43~9.71),has a weak negative Eu anomaly (δEu=0.226~0.824).Zircon Lu-Hf(εHf(t)=-2.9~-10) and whole-rock Sr-Nd(εNd(t)=-10.3~-8.9) isotopic characteristics indicate that the magmatic region is mainly derived from the enriched man‐tle,which is related to the activity of the subducted oceanic crust dehydrating and metasomatized upper mantle wedge.Based on the above discussion,we propose that the studied mafic-ultramafic rocks were the product of the late subduction of the Proto-Tethys oceanic crust.With the deepening of subduction,the plate formed a plate win‐dow,which led to asthenosphere upwelling and partial melting of mantle wedge to form basic-ultrabasic magma.During the rising process,the magma mixed with the crust and finally formed Langmuri mafic-ultramafic rocks.

关 键 词：地球化学 镁铁质-超镁铁质岩体 锆石U-PB年代学 SR-ND-HF同位素 浪木日 东昆仑 

分 类 号：P618.52[天文地球—矿床学]