| 安徽巢湖凤凰山石炭系黄龙组红色灰岩矿物地球化学特征 |
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| 引用本文： | 李根,刘鑫,赵梦琦.安徽巢湖凤凰山石炭系黄龙组红色灰岩矿物地球化学特征[J].高校地质学报,2014,20(4):528. |
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| 作者姓名： | 李根 刘鑫 赵梦琦 |
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| 作者单位： | 内生金属矿床成矿机制研究国家重点实验室，南京大学地球科学与工程学院，南京210023 |
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| 基金项目： | 南京大学地质学理科人才培养基金 |
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| 摘 要： | 安徽巢湖凤凰山晚石炭世黄龙组的地层主体为肉红色生物屑微晶灰岩，顶部为夹灰岩条带的泥岩。矿物学分析显
示，肉红色生物屑微晶灰岩的矿物主要为方解石，含少量针铁矿和赤铁矿。漫反射光谱分析表明，常用的古气候指标“红
度”与灰岩中铁氧化物、氢氧化物的光谱强度具显著的正相关性，而与岩石的全铁含量相关性较低，据此推测铁的氧化物
和氢氧化物是灰岩呈肉红色的重要原因。元素地球化学分析结果显示，黄龙组灰岩相对富Fe，Mn，而贫Co，Ni，在
Al-Fe-Mn，Fe-Mn-(Cu+Co+Ni)以及Cu-Pb-Zn三角判别图上，均靠近或落入热液成因区。综合地球化学特征与前人研究成
果，该文认为巢湖凤凰山黄龙组肉红色灰岩的形成很可能受到海底热液活动的影响。
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| 关 键 词： | 下扬子区 晚石炭世 黄龙组 肉红色灰岩 元素地球化学 热液沉积作用 |
Mineralogical and Geochemical Characteristics of the Red Limestones from the Huanglong Formation in the Fenghuang Shan Area,Anhui Province,East China |
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| LI Gen,LIU Xin,ZHAO Mengqi.Mineralogical and Geochemical Characteristics of the Red Limestones from the Huanglong Formation in the Fenghuang Shan Area,Anhui Province,East China[J].Geological Journal of China Universities,2014,20(4):528. |
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| Authors: | LI Gen LIU Xin ZHAO Mengqi |
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| Abstract: | The Late Carboniferous Huanglong Formation in Chaohu area in the lower Yangtze terrane consisted of red biomicrite
limestone, with a upper belt of mixed mudstone and limestone. The red-colored Huanglong limestone provides a good opportunity for
studying ferric minerals in the limestone and their relationships with the limestone bulk color, and for tracing the influence from
hydrothermal activities. Here we present a comprehensive study on the Huanglong Formation, and discuss the implications for
sedimentary environments and regional hydrothermal episodes. We collected red limestone samples, conducted thin section
microscopical observations and performed instrumental analyses including X-ray powder diffraction (XRD), Diffuse Reflectance
Spectroscopy (DRS), Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS) and Inductively Coupled
Plasma-Optical Emission Spectroscopy (ICP-OES). With DRS, we detected ferric oxide/hydroxide minerals (hematite and goethite) in
the red limestones. We employed “redness”, a widely used paleoclimate index, to quantitatively describe the rocks’red color. Our
data show that for the limestone samples, the hematite/goethite peak intensity on the DRS spectrum correlates well with the measured
redness of the samples, but the bulk iron content shows no such good correlation, which suggests that the ferric oxide/hydroxide
minerals likely control the abnormal red color of the Huanglong red limestones. In various diagrams characterized by distinct elemental
distribution, element data for the limestone samples fall into the zones representing hydrothermal deposits, revealing the potential
influence from hydrothermal activities. Though no direct evidence for hydrothermal systems was observed in the field (e.g.“, black
chimney”relics), findings of Late Carboniferous hydrothermal-associated depositions have been reported in the neighboring area.
Based on our results, the red-colored Huanglong limestones likely indicates a local response to the regional hydrothermal activities: the
hydrothermal systems released ferrous solutes-enriched fluids to surface environments and these ferrous solutes were oxidized to ferric
limestone. We conclude that the Huanglong Formation may record the imprint of the regional hydrothermal activities in the Late
Carboniferous. Our study contributes to the decadal debates on the occurrences of large scale hydrothermal events during the Late
Carboniferous in the lower Yangtze region, South China. Further investigations on sedimentary temperature reconstruction are needed
for unraveling the lower Yangtze hydrothermal episodes. |
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| Keywords: | lower Yangtze region red limestone Huanglong Formation hydrothermal sedimentary process elemental geochemistry |
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