四川盆地西部中二叠统白云岩/石的主要结构类型--兼论其与川东北上二叠统-三叠系白云岩/石的差异  

The main texture of dolomite of Middle Permian,western Sichuan basin:Concurrently on the differences with Upper Permian-Triassic,Northeast Sichuan basin

作　　者：黄思静[1,2] 吕杰[1,2] 兰叶芳[1,2] 黄可可[1,2] 王春梅[1,2] 

机构地区：[1]油气藏地质及开发工程国家重点实验室,成都理工大学,成都610059 [2]成都理工大学沉积地质研究院,成都610059

出　　处：《岩石学报》2011年第8期2253-2262,共10页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(40839908、41172099);四川省重点学科“构造地质学”建设基金项目(SZD0408)联合资助

摘　　要：白云岩/石的结构在白云岩成因研究中具有重要意义。四川盆地西部中二叠统栖霞组的白云岩具有与盆地东北部上二叠统长兴组-三叠系不同的结构:盆地西部中二叠统栖霞组除存在一部分斑状晶白云岩以外,总体上缺乏原始结构保存的白云岩,白云石具有特征的非平直晶面他形晶和鞍形晶,且晶体较大;盆地东北部上二叠统长兴组-三叠系非常发育原始结构保存的白云岩,结晶白云岩也以晶体较小的平直晶面自形晶-半自形晶为主。对碳酸盐岩中白云石含量的分布模式而言,盆地西部中二叠统栖霞组出现频率最高的是白云石含量40%～60%的过渡岩石类型,这是一种非经典的分布模式,而盆地东北部上二叠统长兴组-三叠系则缺乏这样的过渡岩石类型,出现频率最高的是白云石含量大于90%和小于10%的端元岩石类型,这是一种经典的分布模式。白云岩/石的结构特征的差异反映盆地西部中二叠统栖霞组白云岩较高的结晶温度、较低的流体Mg/Ca比值、较短的白云化作用持续时间和不彻底的回头白云化作用;盆地东北部上二叠统长兴组-三叠系则主要是相对低温的,高Mg/Ca比值海源流体的彻底白云化作用。The dolomite texture is significant in the study of dolomite genesis.The textures of Middle Permian Qixia dolomite in western Sichuan basin are different from those of Upper Permian-Triassic dolomite in northeastern Sichuan basin.Besides the dolomite with porphyrotopic crystals,the Qixia dolomite,as a whole,is lack of fabric-preserving textures,but characterized by coarser non-planar anhedral to euhedral saddle-like dolomite crystals.However,the fabric-preserving dolomites are well developed in Upper Permian-Triassic carbonates in northeastern Sichuan basin,including predominantly finer planar euhedral to subhedral dolomite crystals.The distribution model of dolomite content of Qixia Formation in western Sichuan basin could be regard as a non-classical one,because the transitional rock type of 40% to 60% dolomite content is dominant;whereas the model of Changxing Formation of Upper Permian-Triassic dolomite in northeastern Sichuan basin could be seen as a classical one that has two dominant end-member rock types of more than 90% or less than 10% dolomite content respectively.The different dolomite textures could reflect the Qixia dolomite experienced the higher crystallization temperature,the lower Mg/Ca ratio of fluids and the shorter duration and incomplete halfway back dolomitization.In contrast,the Upper Permian-Triassic dolomite in northeastern Sichuan basin underwent the complete dolomitization with lower temperatures and marine-derived fluids of high Mg/Ca ratio.

关 键 词：四川盆地西部 中二叠统栖霞组 白云岩结构 白云岩成因 不彻底的回头白云化 

分 类 号：P588.245[天文地球—岩石学]