Fluid inclusions in the salt minerals from the Permian Fengcheng Formation in the Urho region, Junggar Basin, Xinjiang
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摘要: 二叠系风城组为准噶尔盆地乌尔禾地区重要的勘探层系,也是成因非常特殊的深湖相含盐火山-沉积建造。通过钻井岩心观察、薄片鉴定、扫描电镜、X衍射、电子探针和包裹体显微测温等技术手段,较为详细地研究了风城组盐类矿物流体包裹体特征及成因。确定盐类矿物成矿流体属中-低温度(51.2~125.7℃)、中-高盐度(13.72%~24.93% NaCl)、中偏高密度(1.06~1.16g/cm3)的H2O-NaCl体系、并含有CH4气体的高碱性热卤水;提出风城组深湖相含盐火山-沉积建造与湖底热液喷流活动有关,推测下渗湖水与幔源岩浆水混合形成的深部高碱性热卤水失衡回返,萃取易溶盐类物质,最终通过湖底喷流口以热卤水形式喷发,与湖盆底部低浓度水混合"兑卤成盐",形成罕见、复杂盐类矿物组合。Abstract: The Permian Fengcheng Formation as the important hydrocarbon exploration target in the Urho region, Junggar Basin, Xinjiang is built up of the genetically special deep-lake salt-bearing volcanic-sedimentary formations. The detailed study of characteristics and genesis of the fluid inclusions in the salt minerals from the Permian Fengcheng Formation is based on the techniques such as core observation, thin-section examination, scanning electron microscopy, X-ray diffraction analysis, microprobe analysis and microthermometry of the inclusions. The ore-forming fluids of the salt minerals are assigned to the H2O-NaCl systems with the moderate to low temperature (51.2 to 125.7℃), moderate to high salinity (13.72% to 24.93% NaCl), moderate to high density (1.06 to 1.16 g/cm3), and high-alkaline thermal brines with CH4 gases. The deep-lake salt-bearing volcanic-sedimentary formations are thought to be associated with the sublacustrine hydrothermal effusion in the Fengcheng Formation. It is speculated that the genetic mechanisms for the salt minerals are involved into the disequilibrium and inversion of the deep-seated high-alkaline thermal brines caused by the mixing of sinking lake water and mantle-derived magmatic water, extraction of soluble salts during the upward migration of the mixed hydrothermal brines, and the eruption of the hydrothermal brines from the sublacustrine vents and then mixing with the low-concentration lacustrine water at the bottom of the lakes, and the formation of the compositionally complicated salt minerals at last.
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Keywords:
- Junggar Basin /
- Urho /
- Fengcheng Formation /
- salt mineral /
- fluid inclusion /
- ore-forming hydrothermal fluid
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