内蒙古赤峰早白垩世多斑流纹斑岩岩相学特征及成因

PETROGRAPHY AND GENESIS OF THE EARLY CRETACEOUS DOSEMIC RHYOLITE PORPHYRY IN CHIFENG CITY,INNER MONGOLIA

内蒙古赤峰双胜地区早白垩世多斑流纹斑岩,发育气孔构造,具多斑状结构,斑晶含量高达70%,成分为透长石(30%)、石英(35%)及斜长石(5%).斑晶透长石呈半自形宽板状且具有梳状反应边,反应边成分为Na-正长石,反应边中含针柱状矿物雏晶.斑晶石英边缘或内部被强烈熔蚀,并发育碎斑结构,具有“裂而不离”或“离而不散”的特点,碎斑石英之间被基质成分充填.岩石兼具熔岩及碎斑熔岩的双重结构.岩石中含气孔.岩石结构特征反映岩浆经历了绝热-减压快速上升过程,可能指示成岩时期区域伸展构造背景的开始.

The Early Cretaceous dosemic rhyolite porphyry in Shuangsheng area of Chifeng,Inner Mongolia,is characterized by vesicular structure and multi-porphyritic texture,with 70% of phenocryst content,including sanidine(30%),quartz(35%)and plagioclase(5%). The sanidine phenocryst shows subhedral wide tabular structure with comblike reaction rim,which is composed of Na-orthoclase and contains needle-columnar mineral crystallite. The edge or interior of the quartz phenocryst is strongly corroded, where porphyroclastic texture is developed, with the characteristics of “cracked or dispersed but not separated”. Matrix components are filled in between the quartz porphyroclasts. The rock contains vesicles,showing the dual structure of lava and porphyroclastic lava. The structure characteristics of the rock reflect a rapid uplift process with adiabatic-decompression of magma,probably indicating the beginning of regional extensional tectonic setting in diagenetic period.