北京昌平地区串岭沟组沉积岩中独居石、金红石赋存状态及其成因

摘要

Monazite and rutile grains are found in the contribution by using energy spectrum analysis to study the silty mudstones,which are collected from the lower part of Chuanlinggou Formation in Changping area of Beijing.The maximum particle size of the monazite is up to 88μm while the largest rutile is 20 μm.According to lots of backscattered images,the monazites show jagged edges and irregular shapes,appeared as fishes,birds,flowers,worms,and so on, while the rutiles are arranged as a string of beads.An overwhelming majority of the monazites and rutiles are distributed in quartz or hematite veins.However,monazites or rutiles are hardly found in the places far away from the veins.These monazites with the age of (152 ±1 1)Ma are dated using SHRIMP Ⅱ at Beijing SHRIMP Center.According to the preliminary age data,it is suggested that these monazites belong to secondary monazites,which are associated with the late hydrothermal event,not formed in the diagenetic stage.%对采自北京昌平地区串岭沟组下部层位粉砂质泥岩中的矿物进行了详细的能谱分析,发现了独居石和金红石颗粒.独居石最大粒径为88μm,金红石最大粒径为20μm.背散射图像显示独居石边缘不平整,形状不规则,呈现出“鱼形”、“鸟形”、“花形”、“虫形”等各种形状；金红石则呈串珠状分布.大量的观察发现,独居石和金红石绝大多数都分布在石英脉或赤铁矿细脉里,远离脉的地方几乎没有独居石和金红石的分布.独居石初步 SHRIMP U-Pb 原位定年结果为(152±11) Ma,表明这些独居石颗粒并非成岩期形成,而为次生独居石,其形成与后期的热液事件有关.