塔中-巴麦地区下古生界不同结构类型白云岩元素地球化学特征  

Trace-element geochemical characteristics of different textural types of Lower Paleozoic dolomites in the Tazhong-Bamai area

作　　者：黄擎宇[1] 刘伟[1] 石书缘[1] 王坤[1] 孟祥豪[2] 

机构地区：[1]中国石油勘探开发研究院,北京100083 [2]成都理工大学油气藏地质及开发工程国家重点实验室,四川成都610059

出　　处：《地球化学》2016年第2期199-212,共14页Geochimica

基　　金：国家科技重大专项(2011ZX05004);中国石油天然气股份有限公司重大科技专项(2014E-3201)

摘　　要：在岩芯观察、薄片分析、阴极发光分析、全岩微量元素测试以及微组构电子探针分析的基础上,对塔里木盆地塔中-巴麦地区下古生界不同结构类型的基质白云岩和缝洞充填白云石的成因进行了详细研究。结果表明,泥-粉晶白云岩具有较高的Sr、Na含量和低的Fe、Mn含量,结合其多与蒸发岩相伴生的特征认为,该类白云岩主要形成于蒸发海水成岩环境中。颗粒白云岩的Na、Fe、Mn含量与泥粉晶白云岩相似,说明两者形成环境相近,但其Sr含量较低,可能与微生物作用有关。晶粒白云岩中具有平直晶面结构的细晶、自形白云岩和细晶、半自形白云岩的Sr、Na含量相对较低,而Fe、Mn含量略有升高,表明其形成于成岩温度相对较低的浅埋藏阶段;而具有非平直晶面特征的中-粗晶、他形白云岩的Sr、Na含量最低,Fe、Mn含量增加,但Fe-Mn相关性较差,且明显低于其他地区典型深埋藏白云岩的Fe、Mn含量,因此认为其形成环境为温度逐步升高的中埋藏阶段。鞍形白云石充填物Sr含量较低、Fe、Mn、Ba和Zn含量明显增高,反映深部热液活动影响,但由于流体来源不同和后期构造活动存在差异,不同地区鞍形白云石充填物的形成机制各异。The main objective of this paper is to investigate the origin of matrix dolomites and void-filling dolomite cements with different textures in the Lower Paleozoic carbonates in the Tarim Basin, based on the core observation, thin-section analysis, cathodoluminescence, trace-elements and electron microprobe analysis. The results show that micrite dolomite interbedded with evaporitic rocks has high Sr and Na contents but low Fe and Mn contents, suggesting that this type of dolomites was formed in a supersaline seawater enverionment. The Na, Fe and Mn contents of grain dolomites are similar to those of micrite dolomites. The Sr contents, however, are lower than those of other types of dolomites. The reason may be associated with microbial mineralization. Because the grain dolomites are usually overlaid by evaporites, their origin can be interpreted to be of reflux dolomitization during the penecontemporaneous stage. Fine crystalline, enhedral/subhedral dolomites with planar crystal boundaries have relatively low Sr and Na contents and slightly increasing Fe and Mn contents. These features imply that the dolomites were formed at lower temperature during the shallow burial period. Medium to coarse crystalline dolomites with nonplanar crystalline boundaries have the lowest Sr and Na contents and obviously increasing Fe and Mn contents. The co-variation of Fe and Mn, however, is of no positivity and the absolute contents of those trace-elements are lower than those of typical burial dolomites from other basins, showing thatthe dolomitization may occur at relatively high temperature in a medium burial rather than deep burial environment. Void/fracture-filling saddle dolomite cements have low Sr contents but high Fe, Mn, Ba and Zn contents, suggesting the effect of hydrothermal fluids. The formation mechanisms of saddle dolomite cements in different areas are various due to the diverse sources of hot fluids and varying tectonic activities. Different textural types of dolomites have different trace element compositions, th

关 键 词：白云岩 结构类型 元素地球化学 成因 塔里木盆地 

分 类 号：P595[天文地球—地球化学] P588.245[天文地球—地质学]