云南镇雄茅口组硅质岩稀土元素地球化学特征及沉积背景浅析
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摘要
镇雄地区二叠系茅口组灰岩中部发育薄层状硅质岩夹层,本次工作对漆树湾及石场坝路线茅口组中部硅质岩夹层采取样品10件,并将样品磨制成薄片10片。对薄片进行镜下观察发现,硅质岩内普遍发育富液相气液两相流体包裹体。通过对所取10块硅质岩进行稀土元素分析测试,结果表明,稀土元素总量较低,LREE/HREE平均值范围为13.47～34.02;Ce/Ce~*平均值变化范围为0.29～0.51,为负异常;Eu/Eu~*平均值变化范围为1.19～1.31,为弱正异常。对比扬子地台南北缘二叠系层状硅质岩稀土元素特征发现,扬子地台西部镇雄地区层状硅质岩稀土元素地球化学特征与扬子南北缘层状硅质岩整体差异较大。但(La/Yb)_N,(La/Ce)_N等部分地球化学参数与扬子南缘相对接近,体现出二者具有一定的亲缘性。综合分析认为,镇雄地区二叠系茅口组硅质岩形成于受峨眉山玄武岩活动影响的陆表海环境背景,硅质岩以热水沉积成因为主。
10 samples of stratiform siliceous rocks in Permian Maokou Formation in Qishuwan and Shichangba area are collected.Microscopic observation shows that liquid-rich gas-liquid two-phase fluid inclusions occur in the siliceous rocks.Geochemical analysis shows that the rock has relatively low ΣREE,LREE/HREE values are 13.47～34.02 on average,Ce/Ce~* values are 0.29～0.51 on average with a negative anomaly;Eu/Eu~* values are 1.19～1.31 on average with a positive anomaly.The characteristics of rare earth elements of the Permian stratiform siliceous rocks in Zhenxiong area are quite different from those in the northern and southern margin of Yangtze platform.However,(La/Yb)_N value,(La/Ce)_N value and other partial geochemical parameters in Zhenxiong area is relatively close to that in the southern margin of Yangtze platform,indicating that there exists some affinity for these siliceous rocks.Comprehensive analysis considers that the Permian Maokou Formation stratiform siliceous rocks in Zhenxiong area are formed in the epicontinental marine environment which is affected by the basalt activity of Emeishan.The siliceous rocks are mainly formed by hot water deposition.
10 samples of stratiform siliceous rocks in Permian Maokou Formation in Qishuwan and Shichangba area are collected.Microscopic observation shows that liquid-rich gas-liquid two-phase fluid inclusions occur in the siliceous rocks.Geochemical analysis shows that the rock has relatively low ΣREE,LREE/HREE values are 13.47～34.02 on average,Ce/Ce~* values are 0.29～0.51 on average with a negative anomaly;Eu/Eu~* values are 1.19～1.31 on average with a positive anomaly.The characteristics of rare earth elements of the Permian stratiform siliceous rocks in Zhenxiong area are quite different from those in the northern and southern margin of Yangtze platform.However,(La/Yb)_N value,(La/Ce)_N value and other partial geochemical parameters in Zhenxiong area is relatively close to that in the southern margin of Yangtze platform,indicating that there exists some affinity for these siliceous rocks.Comprehensive analysis considers that the Permian Maokou Formation stratiform siliceous rocks in Zhenxiong area are formed in the epicontinental marine environment which is affected by the basalt activity of Emeishan.The siliceous rocks are mainly formed by hot water deposition.
引文
[1] 林良彪,陈洪德,朱利东.川东茅口组硅质岩地球化学特征及成因[J].地质学报,2010,84(4):500-507.
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[4] 曹秋香,郭福生,刘向铜,等,浙江江山丁家山组层状硅质岩阴极发光特征及成因[J].沉积学报,2008,26(5):797-803.
[5] 吕炳全,瞿建中.下扬子地区早二叠世海进和上升流形成的缺氧环境沉积[J].科学通报,1989,(22):1 721-1 724.
[6] 方雪,周瑶琪,姚旭,等.四川广元上寺上二叠统硅质岩地球化学特征及成因分析[J].矿物岩石,2017,37(1):93-102.
[7] 马力.中国南方大地构造和海相油气地质[M].北京:地质出版社,2004.
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[9] Shimizu H,Masuda A.Cerium in chert as an indication of marine environment of its formation[J].Nature,1977,266(5600):346-348.
[10] Fleet A J.Hydrothermal and hydrogeneous ferrom anganes deposists [A].In:Rona P A, et al,eds.Hydrothermal Process at sea Floor Spreading Centers[M].New York:Rlenum Press,1983,537-570.
[11] Henderson P.Rare earth element geochemistry[M].Amsterdam:Elsevier Science Publishers B.V.,1984,195-211.
[12] Haskin L A,Haskin M A,Frey F A, et al.Relative and absolute terrestrial abundances of the rare earths,In:L.H.Ahrens (Editor),Origin and Distribution of the Elements,Pergamon,Oxford,1968,889-912.
[13] Murray R W,Buchholtz Ten Brink M R,Gerlach D C, et al.Rare earth,major,and trace elements in chert from the Franciscan complex and Monterey group,Californian:assessing REE sources to fine-grained marine sediments[J].Geochim Cosmochim Acta,1991,55:1 875-1 895.
[14] Murray R W,Buchholtz Ten Brink M R,Jones D L, et al.Rare earth elements as indicators of different marine depositional environments in chert and shale [J].Geology,1990,18:268-271.
[15] Murray R W.Chemical criteria to identify the depositional environment of chert:general principles and applications[J].sedimentary Geology,1994,90:213-232.
(1)杨勤生,马忠义,蔡忠柏,等.中华人民共和国1∶20×104区域地质调查报告镇雄幅[R].云南:云南省地质矿产局第二区域地质测量大队,1976.
[2] 朱同兴.安徽南部下二叠统结核状硅质岩和层状硅质岩的沉积学特征和成因探讨[J].岩相古地理,1989,43(5):1-7.
[3] 夏邦栋,钟立荣,方中,等.下扬子区早二叠世孤峰组层状硅岩成因[J].地质学报,1995,69(2):125-137.
[4] 曹秋香,郭福生,刘向铜,等,浙江江山丁家山组层状硅质岩阴极发光特征及成因[J].沉积学报,2008,26(5):797-803.
[5] 吕炳全,瞿建中.下扬子地区早二叠世海进和上升流形成的缺氧环境沉积[J].科学通报,1989,(22):1 721-1 724.
[6] 方雪,周瑶琪,姚旭,等.四川广元上寺上二叠统硅质岩地球化学特征及成因分析[J].矿物岩石,2017,37(1):93-102.
[7] 马力.中国南方大地构造和海相油气地质[M].北京:地质出版社,2004.
[8] 李红敬,解习农,周炼,等.扬子地区二叠系硅质岩成因分析及沉积环境研究[J].石油实验地质,2009,31(6):564-569.
[9] Shimizu H,Masuda A.Cerium in chert as an indication of marine environment of its formation[J].Nature,1977,266(5600):346-348.
[10] Fleet A J.Hydrothermal and hydrogeneous ferrom anganes deposists [A].In:Rona P A, et al,eds.Hydrothermal Process at sea Floor Spreading Centers[M].New York:Rlenum Press,1983,537-570.
[11] Henderson P.Rare earth element geochemistry[M].Amsterdam:Elsevier Science Publishers B.V.,1984,195-211.
[12] Haskin L A,Haskin M A,Frey F A, et al.Relative and absolute terrestrial abundances of the rare earths,In:L.H.Ahrens (Editor),Origin and Distribution of the Elements,Pergamon,Oxford,1968,889-912.
[13] Murray R W,Buchholtz Ten Brink M R,Gerlach D C, et al.Rare earth,major,and trace elements in chert from the Franciscan complex and Monterey group,Californian:assessing REE sources to fine-grained marine sediments[J].Geochim Cosmochim Acta,1991,55:1 875-1 895.
[14] Murray R W,Buchholtz Ten Brink M R,Jones D L, et al.Rare earth elements as indicators of different marine depositional environments in chert and shale [J].Geology,1990,18:268-271.
[15] Murray R W.Chemical criteria to identify the depositional environment of chert:general principles and applications[J].sedimentary Geology,1994,90:213-232.
(1)杨勤生,马忠义,蔡忠柏,等.中华人民共和国1∶20×104区域地质调查报告镇雄幅[R].云南:云南省地质矿产局第二区域地质测量大队,1976.