内蒙古正镶白旗火山杂岩基本特征及形成机制

正镶白旗火山杂岩为一不规则的穹丘状地质体,它是由渐变过渡的火山碎屑岩、流纹质碎斑熔岩和次火山岩构成的一个整体.可初步划分出三个近似同心环带.中环的流纹质碎斑熔岩是火山杂岩的主体,它的众多特征反映出初始岩浆含有较多的挥发分.岩浆在地下经过了较好的结晶分异,在地下——地上某个范围内存在隐爆——侵出区.火山作用是以小规模隐爆伴随缓慢的向上侵出为主.作用时间长,形成了规模较大的火山岩.正镶白旗火山杂岩属太平洋岩系钙碱质系列,原始岩浆由来源于上地幔和下地壳熔体的混熔作用形成.

THE ELEMENTARY FEATURES AND FORMATION MECHANISM OF VOLCANIC COMPLEX IN ZHEN XIANG BAI QI AREA, INNER MONGOLIA

Volcanic complex in Zhen Xiang Bai Qi area is an unregular dome-shaped geologic body. It is a whole body, consisted transitional pyroclastic rock, rhyo-porphyroclastic lava and sub-volcanic rock. It is preliminary classified into three concentric rings. Rhyo-porphyroclastic lava is a principal portion in volcanic complex. Its numerous features show there are many volatile components in primary magma with full underground crystallization-differentiation. Then is a sub-explosion-slow-extrusion district in a certain region between underground and land surface. Volcanic action is mainly small scale sub-explosion accompanying up slow extrusion. Time of action is longer, forming into bigger scale volcanic complex. The volcanic complex in Zhen Xiang Bai Qi area belongs to the Pacific cale-alkaline rock series. Its original magma is from the Xixed melting of upper mantle and deep crust.