Burial dolomitization, the genesis of dolomite in the Dapu Formation (Upper Carboniferous), Guixinan area, Youjiang basin, Southwest China: petrologic and geochemical evidence
Burial dolomitization, the genesis of dolomite in the Dapu Formation (Upper Carboniferous), Guixinan area, Youjiang basin, Southwest China: petrologic and geochemical evidence
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右江盆地贵西南地区大铺组（上石炭统）埋藏白云石化作用及白云石成因：岩石学和地球化学证据
DOI：
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发表时间：
2020
影响因子：
1.4
通讯作者：
Wentao Huang
中科院分区：
文献类型：
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作者：
Zhuowei Miao;Enpu Gong;Yonglin Zhang;Changqing Guan;Wentao Huang
白云石的成因是碳酸盐沉积学领域备受争议和广泛研究的问题。本研究以贵西南地区大铺组白云岩为研究对象，旨在破译大铺组白云石化机制。识别出内匝道开放海相、内匝道受限海相和内匝道浅滩三种沉积环境。研究区发现块状构造的3种白云岩（DI、DII、DIII）与断层构造关系密切，在露头与灰岩呈弯曲扩散接触。以上两点均表明为成岩白云岩。 3种白云石（D1、D2和D3）表现出相似的深-浅紫红色发光，表明其成岩流体特征相似。平面到非平面白云石晶体表明温度超过 50 °C。矿物组合包括D2、D3和硅酸盐矿物（长石、透闪石和阳起石），表明存在接触变质作用，成岩流体富含硅和镁。根据修正后的稀土元素特征，白云石化过程不受地表或浅埋环境中的大气水淋滤和热液的影响。白云岩样品的δ 18 O范围表明，埋藏白云石化作用是在高温环境下发生的。白云岩样品的 87 Sr/ 86 Sr 比值低于同期海水，这意味着成岩流体源自洋中脊玄武岩的蚀变。根据地质背景，推测埋藏白云石化是由被动边缘埋藏成岩水文域的水文构造过程驱动的。简而言之，镁来自海洋玄武岩的低温蚀变、温盐和压实流提供的水动力条件以及同沉积断裂带提供的通道。
The genesis of dolomite is an intensively debated and extensively studied problem in the field of carbonate sedimentology. This study focuses on the dolomite of the Dapu Formation in the Guixinan area, with the aim of deciphering the mechanism of dolomitization in the Dapu Formation. Three types of sedimentary environment, including the open marine of inner ramp, the restricted marine of inner ramp, and the shoal of inner ramp, have been identified. Three types of dolostone (DI, DII and DIII) identified in the study area with massive structure had close relationship with fault structures, and contacted with limestone in curved diffuse way on the outcrop. Both of the above points indicated diagenetic dolomite. Three types of dolomite (D1, D2 and D3) displayed similar dark—light purple red luminescence, indicating that the characteristics of their diagenetic fluids were similar. The planar-s to nonplanar dolomite crystals indicated that the temperature was more than 50 °C. The mineral assemblage including D2, D3, and silicate minerals (feldspar, tremolite and actinolite) suggested contact metamorphism and tht the diagenetic fluid was rich in silicon and magnesium. The dolomitization process was not influenced by the leaching of meteoric water in surface or shallow buried environment and hydrothermal fluids, based on the corrected REE characteristics. The range of the δ 18 O of dolostone samples showed that the burial dolomitization had taken place in high-temperature environment. The lower 87 Sr/ 86 Sr ratio of the dolostone samples than the coeval seawater meant that the diagenetic fluid was derived from the alteration of mid-ocean ridge basalt. Based on the geologic setting, it was speculated that the burial dolomitization was driven by the hydro-tectonic processes in the passive margin burial diagenesis hydrologic realm. In brief, magnesium came from the low-temperature alteration of ocean basalts, the thermohaline and compactional flow supplied hydrodynamic condition, and the synsedimentary fault zones-supplied channels.