古地理学报2018，Vol.20Issue(1)：33-48,16.DOI:10.7605/gdlxb.2018.01.003
准噶尔盆地吉木萨尔凹陷中二叠统芦草沟组云质岩沉积环境及白云石成因探讨
Sedimentary environment and formation mechanisim of dolomitic rocks in the Middle Permian Lucaogou Formation,Jimusar Depression, Junggar Basin
摘要
Abstract
The Middle Permian Lucaogou Formation of Jimusar Depression,Junggar Basin is characterized by lacustrine fine-grained dolomitic sediments,which are composed of silt-sized to mud-sized terrigenous clasts,tuff clasts,carbonate and hydrothermal minerals.This paper is aimed to understand the sedimentary environment and formation mechanism of dolomitic rocks by studying their petrological,mineralogical and geochemical features.Petrological-mineralogical and major and trace element characteristics of the dolomitic rocks suggest the study area was a shallow salty lake formed under an arid climate during the Middle Permian,and was characterized by intense regional volcanism and active mantle-derived hydrothermal in the basin.The dolomites in the dolomitic rocks mainly present as euhedral-subhedral micritic crystals,forming fine lamination or mixing with other compositions,while fine-crystalline dolomites can only be found occasionally.The micritic dolomites,with low order degrees (0.46) and homogeneous compositions,are usually surrounded by laminations.The fine-crystalline dolomites are featured by welldeveloped metasomatic relict texture and thereby should be the product of diagenesis.Both two kinds of dolomites have high strontium and low magnesium contents,while fine-crystalline dolomites have higher contents of iron and manganese than that of micritic dolomites.The micritic dolomites have a low δ1sOPDs (av.-4.72‰).The forming temperature,54.61 ℃ to 186.46 ℃,is calculated from the δ18OpDB by assuming that the fluid was the mixture of lake water and mantle-derived hydrothermal fluid.The high δ13CPDB (av.8.79‰) of micritic dolomites might be resulted from the gigantic buried organic matter of Lucaogou Formation and metabolic activities of methanogens.In conclusion,the micritic dolomites are contemporaneous-penecontemporaneous protodolomite.Magnesium ion was supplied by the salty lake water,tuff materials as well as mantle-dervied hydrothermal fluid.The dynamic barrier of dolomite formation was broken by the high temperature brought from hydrothermal fluid and the metabolic activities of methanogens.关键词
白云石/成因/幔源热液/芦草沟组/吉木萨尔凹陷/准噶尔盆地Key words
dolomite/origin/mantle-derived hydrothermal fluid/Lucaogou Formation/Jimusar Depression/Junggar Basin分类
天文与地球科学引用本文复制引用
张帅,柳益群,焦鑫,周鼎武,张旭,陆申童,周宁超..准噶尔盆地吉木萨尔凹陷中二叠统芦草沟组云质岩沉积环境及白云石成因探讨[J].古地理学报,2018,20(1):33-48,16.基金项目
国家自然科学基金面上项目(编号:41572086,41272116)资助.[Financially supported by General Program of the National Natural Science Foundation of China (Nos.41572086,41272116)] （编号:41572086,41272116）
