CAJ | 학술논문

柯岗蛇绿岩位于青藏高原北缘,与北部的奥依塔格蛇绿岩、南部的库地蛇及苏巴什绿岩组成青藏高原“第五缝合带”。本文对柯岗蛇绿岩中辉长岩进行了岩石学、地球化学及锆石LA-ICP-MS分析。柯岗辉长岩SiO2含量为43.65%~49.29%,在TAS分类图解上,样品主要落在辉长岩区域,与野外及镜下观察一致。柯岗辉长岩稀土元素总量较低,∑REE范围在12.12~45.45μg/g,经球粒陨石标准化的REE分布模式显示,3个样品显示轻稀土略亏损特征, Eu*为正异常,平均为1.34,1个样品显示轻稀土富集特征, Eu*为0.86,为岩浆分异结晶不同时期的产物。柯岗辉长岩锆石Th/U范围为0.28~0.67,且具有典型岩浆锆石的震荡环带结构或扇形结构特征。22颗锆石206Pb/238U加权平均年龄为(488.8±2.6) Ma, MSWD=0.81,代表柯岗蛇绿岩套中辉长岩结晶年龄。通过柯岗蛇绿岩中辉长岩地球化学特征和构造环境判别图解,并结合前人资料,认为柯岗蛇绿岩形成环境为岛弧或者弧前环境。
가강사록암위우청장고원북연,여북부적오의탑격사록암、남부적고지사급소파십록암조성청장고원“제오봉합대”。본문대가강사록암중휘장암진행료암석학、지구화학급고석LA-ICP-MS분석。가강휘장암SiO2함량위43.65%~49.29%,재TAS분류도해상,양품주요락재휘장암구역,여야외급경하관찰일치。가강휘장암희토원소총량교저,∑REE범위재12.12~45.45μg/g,경구립운석표준화적REE분포모식현시,3개양품현시경희토략우손특정, Eu*위정이상,평균위1.34,1개양품현시경희토부집특정, Eu*위0.86,위암장분이결정불동시기적산물。가강휘장암고석Th/U범위위0.28~0.67,차구유전형암장고석적진탕배대결구혹선형결구특정。22과고석206Pb/238U가권평균년령위(488.8±2.6) Ma, MSWD=0.81,대표가강사록암투중휘장암결정년령。통과가강사록암중휘장암지구화학특정화구조배경판별도해,병결합전인자료,인위가강사록암형성배경위도호혹자호전배경。
Kegang ophiolite is located at the northern Qingzang Plateau. It is part of the Fifth Suture Zone of Qingzang Plateau with Oytag, Kudi and Subashi ophiolite. This paper reports petrology, geochemistry, and zircon LA-ICP-MS analyses of gabbro in Kogang ophiolite. The major elements show that the distribution of SiO2 from 43.65%~49.29%, and in the TAS classification diagram, the samples plot in gabbro area, which is consistent with the field and microscopy observations. The total REE abundances are low, ranging between 12.12~45.45 μg/g, three samples show slightly enrichments in LREE and depletions in HREE, while other samples shows depletions in LREE and enrichments in HREE. Eu* shows slightly positive anomaly in LREE enriched samples, with an average of 1.34, and reflect weak magmatic plagioclase fractional crystallization, while in the LREE depleted samples, the Eu* is 0.86, and reflects strong magmatic plagioclase fractional crystallization. In the cathodoluminescence images, the zircons in Kegang gabbro show crystal morphology and clear oscillatory zoning, which together with the high Th/U (0.28 to 0.67), indicate magmatic origin. 22 single grain zircon U-Pb yielded a weighted mean 206Pb/238U age of (488.8±2.6) Ma (MSWD = 0.81), which represents the crystallizing age of the gabbro. Based on the geological, geochemical characteristics and previous research results, we believe that Kegang ophiolite was formed in an island arc or forearc environment.