大兴安岭南部红山子盆地花岗斑岩SHRIMP锆石U-Pb年龄、地球化学特征及其地质意义

SHRIMP zircon U-Pb Dating and Geochemistry Characteristics of Granite-porphyrys from Hongshanzi Basin and Its Geological Significance in South Great Hingan Range

大兴安岭南部红山子盆地火山岩中赋存小型铀钼矿床,并有花岗斑岩侵入。花岗斑岩和火山岩中的锆石具有明显的振荡环带,Th/U值高,属典型的岩浆成因锆石。锆石SHRIMP U-Pb测年结果显示,花岗斑岩锆石10个分析点的年龄变化范围较小,为142～130 Ma,加权平均值为（134.79±0.92）Ma,MSWD为1.17,而火山岩的年龄为158～155 Ma,指示红山子盆地内的花岗斑岩与火山岩是不同时期岩浆作用的产物。花岗斑岩具有高硅、碱,富钾特征;稀土元素总量较低,轻稀土明显富集,重稀土分馏不明显,Eu负异常明显;富集Ba、Sr、K等大离子亲石元素和Th、U、Zr等高场强元素,贫Nb、Ta、P等元素,具高Ba-Sr流纹岩的特征,为下地壳中上部岩石部分熔融的产物,与盆地内低Ba-Sr流纹岩的特征不一致,显示两者物质来源不同。红山子盆地内的花岗斑岩与盆地内火山岩不是同期岩浆作用的产物,但与我国东部和我国北方邻国主要铀矿赋矿火山岩、次火山岩的形成时代一致,为探讨红山子盆地铀矿的成因和指导铀矿勘查打开了新的窗口。

Hongshanzi Basin volcanic rocks occurred a small U-Mo deposit in southern Great Hingan Range and granite-porphyry formed in Hongshanzi Basin. Granite-porphyrys and volcanic rock of zircon from Hongshanzi Basin has obvious oscillatory belt,high Th / U ratio,and they belong to typical magma genesis. Our ziron SHRIMP U-Pb dating results show that the apparent ages of 10 analysis points is 142 ~ 130 Ma,the weighted average is（ 134. 9 ± 0. 92） Ma and MSWD is 1. 17. However,the age of volcanic rocks is 158 ~ 155 Ma indicating the granite-porphyrys and volcanic rock isnot the product of contemporaneous magmatism in Hongshanzi basin. Chemically,this pluton shows high contents of silica and alkalies,rich potassium; The total amount of REE is relatively low. The rocks showing rich LREE obviously and HREE fractionation was not,with obvious negative Eu anomaly,are enriched in LILEs such as Ba,Sr,K and HFSEs such as Th,U,Zr,and depeted in Nb,Ta,P,consistent with high Ba-Sr rhyolites in Great Hingan Range,it formed by partial melting of the middle-upper part of lower crust rocks through crystallization differentiation,had different from the low Ba-Sr rhyolites in Hongshanzi Basin,reflecting the inconsistency of their material sources. The granite-porphyrys isnot the product of contemporaneous volcanic magmatism in Hongshanzi basin,consistent with the age of subvolcanic rock and volcanic rock which the rocks as the ore-bearing host rocks of uranium deposit in eastern China and northern country of China,The new window had suppied by the genesis of uranium deposits and uranium exploration in Hongshanzi Basin.