古地理学报 ›› 2018, Vol. 20 ›› Issue (1): 33-48. doi: 10.7605/gdlxb.2018.01.003

• 岩浆-热液喷流沉积岩 • 上一篇    下一篇

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*

张帅1, 柳益群1, 焦鑫1, 周鼎武2, 张旭1, 陆申童1, 周宁超3   

  1. 1 西北大学大陆动力学国家重点实验室,西北大学地质学系,陕西西安 710069;
    2 山东科技大学地质科学与地质工程学院,山东青岛 266510;
    3 中国地质调查局西安地质调查中心,陕西西安 710069
  • 收稿日期:2017-10-16 修回日期:2017-10-18 出版日期:2018-02-01 发布日期:2018-02-07
  • 通讯作者: 柳益群,女,1951年生,教授,博士生导师,主要从事沉积学、含油气盆地地质学、地幔热液喷流沉积的研究工作。E-mail: liu-yiqun@263.com
  • 作者简介:张帅,男,1993年生,硕士研究生,主要从事沉积学研究工作。E-mail: geologyzs0409@gmail.com。
  • 基金资助:

    *国家自然科学基金面上项目(编号:41572086,41272116)资助

Sedimentary environment and formation mechanisim of dolomitic rocks in the Middle Permian Lucaogou Formation,Jimusar Depression, Junggar Basin

Zhang Shuai1, Liu Yi-Qun1, Jiao Xin1, Zhou Ding-Wu2, Zhang Xu1, Lu Shen-Tong1, Zhou Ning-Chao3   

  1. 1 State Key Laboratory of Continental Dynamics, Department of Geology, Northwest University,Xi'an 710069,Shaanxi;
    2 College of Earth Science & Engineering,Shandong University of Science and Technology,Qingdao 266510,Shandong;
    3 Xi'an Centre of Geological Survey,China Geological Survey,Xi'an 710069,Shaanxi;
  • Received:2017-10-16 Revised:2017-10-18 Online:2018-02-01 Published:2018-02-07
  • Contact: Liu Yi-Qun,born in 1951,is a professor and supervisor of Ph.D. candidate. Now She is mainly engaged in researches of sedimentology,petroliferous basin geology and exhalative rock sediments. E-mail: liu-yiqun@263.com.
  • About author:Zhang Shuai,born in 1993,master degree candidate. He is engaged in sedimentology. E-mail: geologyzs0409@gmail.com.
  • Supported by:

    Financially supported by General Program of the National Natural Science Foundation of China(Nos. 41572086, 41272116)

摘要:

准噶尔盆地吉木萨尔凹陷中二叠统芦草沟组发育一套陆内裂谷背景下,由粉砂级—泥级陆源碎屑、凝灰碎屑、碳酸盐及热液矿物组成的湖相细粒云质岩。本研究以云质岩为研究对象,通过岩石学、矿物学及地球化学研究探讨其形成环境和白云石形成机理。云质岩岩矿特征和主、微量元素特征表明,在中二叠世为处于干旱气候的浅水咸化湖盆,区域火山活动强烈,湖盆内幔源热液活动发育。云质岩中的白云石主要呈自形—半自形的微粉晶颗粒,形成细纹层或与其他组分混合,局部可见自形—半自形的细晶白云石,微粉晶白云石为低有序度白云石(0.46),成分均匀,被纹层包绕,细晶白云石交代残留结构发育,为成岩交代的产物;两类白云石均富锶贫镁,细晶白云石较微粉晶白云石更富铁和锰。微粉晶白云石具有较低的δ18OPDB(平均为-4.72‰),基于白云石的形成流体由湖水和幔源热液混合的假设,所计算得到的形成温度介于54.61~186.46 ℃之间;δ13CPDB偏高(平均为8.79‰),推测其与芦草沟组高的有机质埋藏量及产甲烷古菌的代谢活动有关。微粉晶白云石为同生期—准同生期沉淀或交代的原白云石,其Mg2+来自于咸化湖水、凝灰碎屑和幔源热液,热液带来的高温和产甲烷古菌的代谢活动打破了白云石形成的动力学屏障。

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

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 well-developed 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 δ18OPDB(av.-4.72‰). The forming temperature,54.61℃ to 186.46℃,is calculated from the 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.

Key words: dolomite, origin, mantle-derived hydrothermal fluid, Lucaogou Formation, Jimusar Depression, Junggar Basin

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