五台地区雁门关早元古代镁铁-超镁铁岩体的岩石地球化学特征、成因及其大地构造意义

本文对五台地区侵入于原北金岗库组的雁门关镁铁-超镁铁岩体进行了详细的岩石学、矿物学和岩石地球化学分析研究.雁门关岩体在矿物成份上,特别是单斜辉石、尖晶石和角闪石,具有阿拉斯加型侵入岩体和俯冲带或弧相关的岩浆特征,其元素地球化学特征也可与阿拉斯加型侵入杂岩体类比,具有明显的Nd (Ta),Zr (Hf),Y和Ti负异常.从构造环境判别图来看,雁门关岩体主要为与俯冲相关的成因,具大陆边缘弧的性质.因此,雁门关岩体是侵入在大陆边缘弧环境的岩浆经历了橄榄石和单斜辉石的分离结晶作用的产物.它与恒山-五台-阜平地区广泛分布的同时代花岗岩和火山岩一起,构成了华北克拉通中部造山带内一期重要的古元古代大陆边缘岛弧岩浆活动.

Geochemistry, petrogenesis and tectonic setting of the Paleoproterozoic Yanmenguan mafic-ultramafic intrusion in the Hengshan-Wutai-Fuping area

A detailed study of petrology, mineralogy, geochemistry and petrogenesis on the Paleoproterozoic Yanmenguan mafic-ultramafic intrusion in the Hengshan-Wutai-Fuping area is presented here. The intrusion is akin to Alaskan-type or arc-related magmatism in mineral geochemistry, especially in the compositions of spinel, clinopyroxene, and amphibole. The rock geochemistry is also comparative to those of Alaskan-type mafic-ultramafic complexes, as characterized by pronounced Nd (Ta), Zr (Hf), Y and Ti trough in primitive mantle normalized trace element patterns. In trace element discrimination diagrams, the Yanmenguan rocks plot in the field of subduction zone-related magmas, indicating a tectonic setting of continental arc. Therefore, we propose that the magma of the Yanmenguan mafic-ultramafic intrusion originated from lithospheric mantle in a continent marginal arc, and experienced fractional crystallization of olivine and clinopyroxene. This intrusion, together with contemporary granitic and volcanic rocks in this area, signifies an important stage of Paleoproterozoic magmatism developed in continent margin of the Trans-North China Orogen.