试论大箐亚式含铜白云岩的水下火山成因  

A Tentative Discussion on the Submarine Volcanic Genesis of Daqing Subtype Cupreous Dolomite

作　　者：张永北[1] 魏启荣[1] 徐成彦[1] 王豪[1] 

机构地区：[1]中国地质大学地球科学院

出　　处：《岩石矿物学杂志》1998年第1期23-29,T001,共8页Acta Petrologica et Mineralogica

摘　　要：中元古代昆阳裂谷构造性质与东非裂谷相似，其中段武定海盆西缘的观天厂区段有一条ＮＥ向深大断裂通过，是碳酸质岩浆活动的有利地带。区内的大箐亚式含铜白云岩，除含有火山碎屑外，还含有钠长石、更长石、黑云母、金云母等火成矿物，原生白云石也是火成的，成岩物质组分来自幔源碳酸盐岩浆，具有火山岩结构构造，因此，是碳酸质火山岩，包括熔岩和火山碎屑岩。该岩石赋存于因民组（Ｐｔ２ｙ）上部至落雪组（Ｐｔ２ｌ）下部，上、下与海相火山碎屑岩－沉积岩整合，通常在火山洼地较厚，与一套富钠型为主的、相当于与大洋碳酸岩共生的碱性硅酸盐岩共生，因此，岩石形成于水下火山环境。受海水影响，岩石普遍遭受热液蚀变而绿泥石化、绿帘石化、硅化、黑云母暗化边褐铁矿化。Kunyang rift located on the western margin of Yangtze platform is tectonically equivalent to East Africa rift where there exist modern carbonatite volcanos. Guantianchang sector, through which a NE-trending concealed deep fault passes, is just located on the western edge of Wuding sea basin in the middle part of the rift. Therefore, the prerequisite for the formation of carbonatite volcanos exists there. Daqing subtype cupreous dolomite contains several kinds of igneous minerals frequently found in carbonatite such as albite, oligoclase, biotite, phlogopite, arfvedsonite (Guantian), zircon, rutile, fluor-apatite, in addition to plenty of trachytic-trachyandesitic volcaniclastic substances. The primary dolomites were igneous too. Rock constituents were derived from carbonatite once existent there, so rocks show textures and structures of carbonatite lava and volcaniclastic rocks. Therefore, they are a suite of carbonatite volcanic rocks, which include lava and volcaniclastic rocks. The magma that formed them originated from the mantle, and flew from craters to depressions to accumulate and form rocks. Stratified in form, the rocks lie from the upper part of Yinmin Formation (Pt 2y) to the bottom of Luoxie Formation (Pt 2 l ) and are in conformable contact with the overlying and underlying marine facies sedimentary rocks and stratiform volcaniclastic rocks. The rocks are associated with a suite of Na-rich alkaline rocks, equivalent to being associated with oceanic carbonatite. This suggests that they were formed in a submarine environment. Influenced by sea water, they extensively experienced chloritization, epidotization, silicification and limonitization with darkened rims of biotite.

关 键 词：白云岩 含铜 火山成因 水下 火山岩 

分 类 号：P588.245[天文地球—岩石学] P588.14[天文地球—地质学]