东天山地区黄山东与香山镁铁质- 超镁铁质杂岩体对比

黄山东与香山镁铁质-超镁铁质杂岩体隶属于东天山北部黄山-镜儿泉镁铁质-超镁铁质岩带, 受北东东走向的黄山-镜儿泉韧性剪切带控制, 二者岩石组成差异较大, 黄山东杂岩主要由辉石橄榄岩和辉长岩组成, 主量元素化学组成属钙碱性-拉斑玄武系列, 而香山杂岩主要由辉石橄榄岩、橄榄辉石岩、角闪辉长岩、辉绿岩组成, 属拉斑玄武系列.微量元素地球化学特征显示二者相对富集大离子亲石元素(K、Sr、Ba), 高场强元素(Pb、U), 而相对亏损高场强元素(Nb、P), 适度亏损(Zr、Hf), 但其稀土配分模式不同, 黄山东杂岩显示轻稀土弱富集, 具OIB型的特征, 而香山岩体为平坦型.二者均为尖晶石稳定域不同熔融程度的产物, 侵位过程中主要发生了橄榄石、辉石、斜长石的分离结晶和不同程度的地壳混染.采用LA-ICP-MS法获得黄山东辉长岩与香山角闪辉长岩锆石U-Pb年龄分别为277±1.1 Ma、285±1.1 Ma.二者形成于相同的构造背景下, 是岩石圈地幔根部发生拆沉, 软流圈地幔物质底侵并导致岩石圈地幔发生部分熔融的产物, 构造环境为后碰撞向板内阶段转变的岩石圈间歇性伸展期. 

Contrast of Huangshandong and Xiangshan Mafic-Ultramafic Complex,East Tianshan

Controlled by the NEE-trending Huangshan-Jingerquan ductile sheer zone, the Huangshandong and Xiangshan mafic-ultramafic complex belongs to the Huangshan-Jingerquan mafic-ultramafic rock belt located in the north of East-Tianshan. Huangshandong is characterized by being of calc-alkalic and tholeiitic series and being composed of pyroxene peridotite and gabbro, whereas Xiangshan mafic-ultramafic rocks are made up of pyroxene peridotite, olivine pyroxenite, hornblende gabbro and diabase, belonging to the tholeiitic series. Both rocks are enriched in large ion lithophile elements (such as K, Sr, Ba) and high field strength elements (such as Pb, U), depleted in high field strength elements (such as Nb, P) and slightly depleted in high field strength elements (such as Zr, Hf). However, they are different in the REE pattern, with Huangshandong showing the enrichment of LREE, similar to OIB features, while the Xiangshan rocks presenting the flat pattern of REE. They are the result of partial melting from the spinel source region and magma experienced olivine, pyroxene, plagioclase and amphibole. But they are subject to crust assimilation contamination to a different extent.Using the LA-ICP-MS method, we obtain the age of Huangshandong and Xiangshan at 277±1.1 Ma and 285±1.1 Ma respectively, which demonstrates they generated from the same tectonic setting, resulted from the lithospheric delamination at the root and the upwelling of asthenosphere in the partial melting of lithospheric mantle, corresponding to post-collision intermittent extension setting.