冀西北宣化晚三叠世中期流纹斑岩的发现及其地质意义

Discovery of middle Late Triassic rhyolite porphyry in Xuanhua,northwestern Hebei Province,and its geological significance

冀西北宣化东部地区ZY1井揭露在中元古界下马岭组页岩中,夹有4层流纹斑岩(浅成侵入),本文测得其LA-ICPMS锆石U-Pb年龄为226.5±1.9 Ma,表明其侵入阶段为晚三叠世中期。本区流纹斑岩不含碱性铁镁矿物,应不属于碱性岩。本区发现的晚三叠世中期流纹斑岩,丰富了华北克拉通北缘中晚三叠世构造体制由碰撞后/造山后伸展向板内伸展转变过程中较少的非碱性岩类及其测年数据,对华北地块印支期活动历史的分析研究具有重要理论意义,对寻找矿产资源具有现实意义。

The Well ZY1 in the eastern Xuanhua area of northwestern Hebei Province revealed that there were four layers of rhyolite porphyry intercalated in the shale of the Mesoproterozoic Xiamaling Formation. The LA-ICPMS zircon U-Pb age of 226.5±1.9 Ma is dated in this paper, indicating that the rhyolite porphyry intruded in the middle Late Triassic. The rhyolite porphyry in this area does not contain alkaline femic minerals, so it should not belong to alkaline rock. The middle Late Triassic rhyolitic porphyry discovered in this area enriches non-alkaline rocks and their dating data in the northern margin of the North China Craton(NCC), where the tectonic regime in Middle—Late Triassic is transformed from post collisional/post-orogenic extension to intraplate extension. This study has important theoretical significance for analysis of the Indosinan active history of thr NCC, and has practical significance to search for mineral resources.