南秦岭旬阳志留系热水沉积钠长石岩地质地球化学特征  

GEOLOGY AND GEOCHEMISTRY OF SILURIAN HYDROTHERMAL SEDIMENTARY ALBITITE IN THE XUNYANG BASIN,SOUTHERN QINLING

作　　者：刘淑文[1] 王涛[2] 曾荣[1] 薛春纪[3] 唐永忠 

机构地区：[1]长安大学资源学院地质系,西安710054 [2]西北有色地质勘查局地勘院,西安710054 [3]中国地质大学地学院,北京100083 [4]陕西地质调查研究院,西安725007

出　　处：《地质与勘探》2008年第3期40-46,共7页Geology and Exploration

基　　金：中国地质调查局综合研究项目(编号:200310200040);教育部优秀青年教师计划项目联合资助

摘　　要：热水沉积钠长石岩在南秦岭上古生界中颇具特点,与南秦岭众多的大型超大型铅锌矿成矿关系密切。最近,在南秦岭旬阳下古生界铅锌矿集区内的志留系梅子垭组地层中首次识别出一条近东西方向延伸长达10余千米的钠长石沉积岩带,与地层整合产出,渐变过渡,厚层块状、条带状、角砾状构造,均粒微-细晶结构、内碎屑结构;矿物成分以石英和钠长石为主,铁白云石、镁电气石常见;化学组成以富含SiO2、Al2O3及Na2O为特征;富Fe、Mn,贫Co、Ni、Cu等微量元素;稀土元素配分曲线与围岩类似,但总量较围岩偏低。钠长石岩中锆石形态、图像及SH IRMPU-Pb测年结果反映锆石为热液上升过程中捕获的基底及下伏地层柱中的碎屑锆石。结合该区下古生界属于扬子北缘被动陆缘裂谷环境,认为该钠长石岩属于热水沉积成因。Hydrothermal sedimentary albitite in the upper Paleozoic is closely related with many large and superlarge Pb - Zn deposits in the south Qinling orogenic belt. Recently, a nearly E - W striking over 10 km long albitite zone has be recognized for the first time in the lower Silurian Meiziya Formarion in a lower Paleozoic Pb - Zn ore concentration region of Xunyang area, southern Qinling. The albitite zone shows a conformable contacting and gradational relationship with the county rocks, and exists as thick - bedded and massive, banded, or brecciated structures, and fine to very fine equigranular and intraclastic textures. Albitite is composed primary of albite （70% -75% ± ） and quartz （ 15 % ± ）, and dravite and ankerite occur quite often. Chemically composition of albitite is rich in SiO2, Al2 O3 , and Na2 O, and also rich in the Fe and Mn, poor in Co, Ni and Cu. ∑ REE of albitite are lower than those of county rocks, but their chondrite normalized REE distribution patterns are quite similar. Shapes, cathodol photos and SHRIMP U - Pb dating of zircons from albitite indicate a complicated origin of clastic zircons captured from the basement and lower Paleozoic sediments by the uplifting hotwater. All the geological and geochemical characteristics of albitite prove that, combining with the fact that its lower Paleozoic belongs to a passive continental margin rift environment on the northern margin of the Yangtze plate, the lower Paleozoic albitite is of hydrothermal sedimentary origin.

关 键 词：热水沉积 钠长石岩 南秦岭 旬阳盆地 志留系 

分 类 号：P512.2[天文地球—地质学] P632