摘要
四川石棉县石棉蛇绿岩主要由变质橄榄岩和辉长岩组成,玄武岩出露零星.辉长岩中锆石U-Pb年龄为906±46Ma,表明它是新元古代早期岩浆活动产物.变质橄榄岩具有低的Al2O3和CaO含量,高的MgO含量和Mg#值,与世界上典型蛇绿岩中方辉橄榄岩的值一致.玄武岩具有较高的SiO2和TiO2含量,较低的Al2O3和K2O含量;LREE略亏损,基本无Eu异常;在不相容元素方面,玄武岩具有较低的(La/Yb)N,(La/Sm)N,Ce/Zr,Th/Y,Th/La和Ti/Y值,较高的La/Nb,Zr/Nb和Y/Nb值,Nb负异常较为明显;玄武岩的主要地球化学特征与MORB相似,但与IAT和OIB区别明显.在构造环境判别图解中,玄武岩均投影于MORB区域.根据上述特征并结合区域地质构造特征,笔者认为,石棉蛇绿岩可能形成于成熟的弧后盆地环境.
The Shimian ophiolite is mainly composed of metamorphic peridotite and gabbro. The occurences of basalt are very rare. Zircon U-Pb age of the gabbro is 906±46Ma indicating it is product of an early Neoproterozoic magmatic activity. The metamorphic peridotites have low Al2O3. CaO contents, high MgO contents and Mg# values. They are consistent with those of harzburgite from the typical ophiolite of the world. The basalts show higher SiO2 and TiO2 contents, lower Al2O3 and K2O contents, slightly depleted LREE and essentially no Eu anomaly. In the incompatible elements, the basalts have lower (La/Yb) N, (La/Sm) N. Ce/Zr, Th/Y. Th/La and Ti/Y ratios, higher La/Nb, Zr/Nb and Y/Nb ratios. These geochemical characteristics of the basalts are similar to the MORE, but evidently different from IAT and OIB. On the identification diagram of tectonic setting, the basalts are all ploted in the area of MORE. Combining the above-mentioned characteristics with the regional geological data, it is proposed that the Shimian ophiolite was probably formed from the mature back-arc basin.
出处
《地质论评》
CAS
CSCD
北大核心
2003年第1期17-27,共11页
Geological Review
基金
国家自然科学基金(编号49972024)
