东昆仑黑石山铜多金属矿床闪长岩锆石U-Pb年代学、地球化学和Sr-Nd-Hf同位素

Zircon U⁃Pb Geochronology,Geochemistry and Sr⁃Nd⁃Hf Isotopes of Diorite in Heishishan Copper Polymetallic Deposit,East Kunlun

黑石山铜铅锌矿床位于东昆仑造山带中段的五龙沟地区,矿区内中三叠世的侵入岩十分发育,与矿体近平行产出的闪长岩为限定东昆仑地区古特提斯洋闭合时间提供了很好的研究对象.对黑石山闪长岩进行了LA‐ICP‐MS锆石U‐Pb定年、全岩地球化学和Sr‐Nd‐Hf同位素分析.定年显示,黑石山闪长岩形成于241.6±1.0 Ma.样品的Si O2含量为52.23%~56.19%,全碱含量为K_(2)O+Na_(2)O=3.99%~6.26%,Na_(2)O=2.79%~3.63%,K_(2)O=1.06%~2.71%,样品富铝、钙、铁,Mg O=2.55%~4.84%,Ti O2=1.11%~1.43%;样品富集大离子亲石元素如Rb、Ba、K,明显亏损Nb、Ta、Ti、P等高场强元素,富集轻稀土元素,亏损重稀土元素,大多具有较为明显的Eu负异常,δEu为0.39~0.59.锆石εHf(t)值为-4.1~+0.7;全岩(^(87)Sr/^(87)Sr)t为0.708860~0.708960,εNd(t)为-4.5~-4.3.综合研究认为,黑石山闪长岩为壳幔混合成因,结合区域构造演化历史,认为其形成于俯冲构造背景,指示东昆仑地区古特提斯洋闭合晚于241.6 Ma.

The Heishishan copper polymetallic deposit is located in Wulonggou area,middle part of the East Kunlun orogen belt.The Middle Triassic intrusions in the mining area are very developed,and the diorite produced nearly parallel to the ore bodies provides a good research object for limiting the closure time of the paleo-Tethys ocean in the East Kunlun area.In this article,investigations in terms of zircon U-Pb dating,geochemistry,and Sr-Nd-Hf isotope data were carried out on the Heishishan diorite.Zircon U-Pb dating of the diorite yields magmatic crystallization ages of 241.6±1.0 Ma.The diorite samples contain SiO2=52.23%-56.19%,K_(2)O+Na_(2)O=3.99%-6.26%,Na_(2)O=2.79%-3.63%,K_(2)O=1.06%-2.71%and MgO=2.55%-4.84%.The diorites are rich in Al,Ca and Fe.Also,they are enriched in light rare earth elements and large ion lithophile elements(Rb,Ba,K),and depleted in heavy rare earth elements and high field strength elements(Nb,Ta,Ti,P).Most samples have obvious negative Eu abnormality(δEu=0.39-0.59).Hf isotopic analysis shows that the zirconεHf(t)values of the diorite are from-4.1 to+0.7.The samples have whole-rock(^(87)Sr/^(86)Sr)t ratios from 0.708860 to 0.708960,εNd(t)of-5.0 to-4.9.The comprehensive analysis shows that the Heishishan diorite is of crust-mantle mixing origin.Based on the regional tectonic evolution history,the diorites were formed in a subduction tectonic setting,indicating that the closure of the paleo-Tethys ocean in the East Kunlun area was later than 241.6 Ma.