米仓山区“后河群”的时代及岩石特征

The Houhe Group of the Micangshan area and its characters

专题研究资料表明，米仓山区的中—深变质岩系──“后河组”属前晋宁期“双旋回”喷发的火山建造经深度区域变质作用的产物，原岩类型包括钙碱性—碱钙性—碱性的基性──中性酸性岩类有规律组合的玄武岩—安山岩—流纹岩系列，属下元古界，建议更名为“后河群”。

It is difficult to compare and classify the rocks of the basal structural layers in the Micangshan area because the rocks are varied and complicated and have undergone different degrees of metamorphism. Besides, they were destroyed by structures and invaded by magma. Before 1978, especially the Proterozoic Huodiya Group established by Mr. Yang Jingzhi in 1936 had been used. The rock series of medium and high-grade metamorphism (schistgneiss-migmatite) and epimetamorphic carbonate rocks, phyllite-slate and volcanic rocks, lower part of the Huodiya Group, were grouped into an independent stratigraphic unit. The Second Geological Team of Shaanxi in 1978 established this rock series as a formation and named it the Houhe Formation based on its distribution. This formation was referred to the base of the Sinian subsystem. The writers consider that this Houhe Formation iS the product of the volcanic construction of 'Double-Cycle' of Jinning age. The original rock type includes the regularly mixed basalt-andesite-rhyolite series ranging from ca1cic-alkalic, alkalic-calcic to alkalic or basic-neutral-acid series. Its age is Early Proterozoic era. It is named the Houhe Group.