黑龙江省二道坎银矿床三叠纪岩浆岩地球化学特征、构造环境及意义

Geochemical characteristics,tectonic environment and significance of Triassic magmatic rocks in the Erdaokan silver deposit,Heilongjiang Province

为进一步揭示黑龙江省二道坎银矿床三叠纪岩浆活动对成矿的指示作用,本文选取矿区内发育的辉绿岩、玄武安山玢岩、安山玢岩和石英闪长玢岩几类脉岩为研究对象,进行LA-ICP-MS锆石U-Pb年代学和岩石地球化学测试。结果表明,几类脉岩的成岩年龄为235.4~225.7 Ma;轻、重稀土分馏明显,轻稀土相对富集;辉绿岩亏损Th、U,富集Nb、Ta、Sr、Ti;玄武安山玢岩、安山玢岩与石英闪长玢岩富集U,亏损Nb、Ta、Ti;ε_(Hf)(t)值为9.3~11.8,t_(DM1)和t_(DM2)分别为495~408 Ma和841~626 Ma。研究表明,辉绿岩岩浆起源于类似于富集型的地幔源区并受到地壳物质的混染;玄武安山玢岩、安山玢岩及石英闪长玢岩形成于活动大陆边缘岛弧环境,与蒙古-鄂霍次克洋的南东向俯冲相关,岩浆起源于玄武质岩浆底侵新生下地壳的部分熔融。

In order to further reveal the significance of Triassic magmatism to mineralization of the Erdaokan silver deposit in Heilongjiang Province,in this paper,we have selected diabase,basaltic andesite porphyrite,andesite porphyrite and quartz diorite porphyry dikes developed in the deposit as the research objects,and have carried out their LA-ICP-MS zircon U-Pb geochronological and petrogeochemical studies for constrining their diagenetic ages and tectonic environments.The dating results show that diagenetic ages of all kinds of dikes range from 235.4 Ma to 225.7 Ma.The petrogeochemical characteristics of rocks show that their LREE and HREE are obviouly fractionated and their LREE are relatively enriched.Especially,the diabase samples are depleted in Th and U,but enriched in Nb,Ta,Sr and Ti.The basaltic andesite porphyrite,andesite porphyrite and quartz diorite porphyrite samples are enriched in U,but depleted in Nb,Ta and Ti.Their zircon ε_(Hf)(t)values range from 9.3 to 11.8,with tDM1 and t_(DM2) ages ranging from 408 Ma to 495 Ma and from 626 Ma to 841 Ma,respectively.It is believed that the magma of diabase was originated from the enriched mantle source and was contaminated by crustal materials.Basalt andesite porphyrite/andesite porphyrite and quartz diorite porphyrite were formed in the island arc environment of the active continental margin,which was related to the southeastward subduction of the Mongolia-Okhotsk Ocean,and the magma was originated from the partial melting of the juvenile lower crust due to the underplating of basaltic magma.