重庆石柱吴家坪组硅质岩地球化学特征
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摘要
重庆石柱上二叠统吴家坪组硅质岩广泛发育。通过野外剖面的观察和硅质岩主量、稀土及同位素的分析,认为吴家坪组硅质岩为受到热水影响的生物成因。其化学成份以SiO2为主,质量分数为65.52%~97.76%,富集Fe,Mn等元素,Al/(Al+Fe+Mn)平均值为0.38,但约一半样品的Al/(Al+Fe+Mn)比值接近于纯生物成因的比值;REE总量平均值为38.55×10-6,δCe值为0.48~0.93,为中-弱负异常,δEu值为0.70~1.12,无明显的正负异常;δ30Si的值为0.7‰~1.4‰,更多地接近(或高于)现代放射虫的δ30Si;根据δ18O计算出硅质岩形成时古海水的温度为45℃~95℃。硅质岩的形成与火山活动和断裂有关,下渗的海水与岩浆热液混合,并被加温,溶解了大量SiO2等;然后以热泉形式通过断裂喷出,使附近海水中SiO2含量极大提高,促使放射虫和海绵等硅质生物大量繁殖,最终形成生物硅质岩沉淀下来。
Silicalites are widely distributed in the Wujiaping Formation of Upper Permian in the Shizhu area,Chongqing.Through detailed field observation,combined with the data of macro-analysis,REE and isotope of silicalites,it is indicated that the silicalites of the Wujiaping Formation are characteristic of biogenesis with hydrothermal activity.The contents of SiO2 are relatively high with the value of 65.52%~97.76%.The ratio of Al/(Al+Fe+Mn) is regarded as a helpful criterion for identifying hydrothermal silicalites from other origin silicalites.The average ratio of Al/(Al+Fe+Mn) obtained in the Wujiaping Formation is 0.38.However,about half of the samples are close to the ratio of pure biogenic.The REE contents of silicalites are low(38.55×10-6),with mid enrichment of HREE and weak negative anomaly of Ce,with the value of 0.48~0.93.Eu has a value of 0.70~1.12,showing no evident anomaly.The Silicon(δ30Si) is of a value 0.7‰ ~ 1.4‰,similar to(or above) modern radiolaria δ30Si.Based on the Oxygen isotope(δ18O) fractionation equation of chert and water,the paleo-temperatures of the silicalites in the Wujiaping Formation is 45 ℃~95 ℃.There were many syn-depositional faults and volcanism in the late Permian in eastern Sichuan basin.And the heat source responsible for hydrothermal convection is presented in study area.Present studied section is just located near the Qiyaoshan fault,which could be the pass of hot liquid from deep crust.At that time,sea water encountered and was heated with magmatic liquid,and then dissolved much SiO2 and other elements.The warmer sea water with dissolved SiO2 sprayed out from the faults,which made sea water near the fault contain much more SiO2 and enable radiolarians and siliceous sponges large reproduction.Finally,sea water enriched in SiO2 grew much better and siliceous biology died and set down to form bio-siliceous rock.
Silicalites are widely distributed in the Wujiaping Formation of Upper Permian in the Shizhu area,Chongqing.Through detailed field observation,combined with the data of macro-analysis,REE and isotope of silicalites,it is indicated that the silicalites of the Wujiaping Formation are characteristic of biogenesis with hydrothermal activity.The contents of SiO2 are relatively high with the value of 65.52%~97.76%.The ratio of Al/(Al+Fe+Mn) is regarded as a helpful criterion for identifying hydrothermal silicalites from other origin silicalites.The average ratio of Al/(Al+Fe+Mn) obtained in the Wujiaping Formation is 0.38.However,about half of the samples are close to the ratio of pure biogenic.The REE contents of silicalites are low(38.55×10-6),with mid enrichment of HREE and weak negative anomaly of Ce,with the value of 0.48~0.93.Eu has a value of 0.70~1.12,showing no evident anomaly.The Silicon(δ30Si) is of a value 0.7‰ ~ 1.4‰,similar to(or above) modern radiolaria δ30Si.Based on the Oxygen isotope(δ18O) fractionation equation of chert and water,the paleo-temperatures of the silicalites in the Wujiaping Formation is 45 ℃~95 ℃.There were many syn-depositional faults and volcanism in the late Permian in eastern Sichuan basin.And the heat source responsible for hydrothermal convection is presented in study area.Present studied section is just located near the Qiyaoshan fault,which could be the pass of hot liquid from deep crust.At that time,sea water encountered and was heated with magmatic liquid,and then dissolved much SiO2 and other elements.The warmer sea water with dissolved SiO2 sprayed out from the faults,which made sea water near the fault contain much more SiO2 and enable radiolarians and siliceous sponges large reproduction.Finally,sea water enriched in SiO2 grew much better and siliceous biology died and set down to form bio-siliceous rock.
引文
①王一刚,刘划一,文应初,等.川东上二叠统生物礁气藏形成条件及勘探目标评价研究(报告).中石油西南油气田分公司勘探开发研究院,1998.
②刘文均,郑荣才,张锦泉,等.滇黔桂地区泥盆纪岩相古地理控矿特点研究报告.成都理工学院,1993.
[1]王东安.扬子地台晚元古代以来硅岩地球化学特征及其成因[J].地质科学,1994,29(1):41-54.
[2]李红中,杨志军,周永章,等.秦岭地区硅质岩的特征及研究展望[J].矿物学报,2007,(增31刊):441-443.
[3]Murray Richard W.Chemical criteria toidentify the depositional environment of chert general principles and applications[J].Sedi ment Ge-ol,1994,90:213-232.
[4]夏邦栋,钟立荣,方中,等.下扬子区早二叠世孤峰组层状硅质岩成因[J].地质学报,1995,69(2):125-137.
[5]付伟,周永章,杨志军,等.湘中南二叠系孤峰组硅质岩的成因属性及其地球动力学指示意义[J].矿物岩石地球化学通报,2004,23(4):292-00.
[6]Masao Kametaka,Masamichi Takebe,Hiromi Nagaic,et al.Sedi mentary environments of the Middle Permian phosphorite-chert complexfromthe northeastern Yangtze platform,China;the Gufeng Formation:a continental shelf radiolarian chert[J].Sedi mentary Geology,2005,174:197-222.
[7]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.
[8]王立亭,陆彦邦,赵时久,等.中国南方二叠纪岩相古地理与成矿作用[M].北京:地质出版社,1994,1-147.
[9]罗志立.中国西南地区晚古生代以来地裂运动对石油等矿产形成的影响[J].四川地质学报,1981,2(1):20-39.
[10]冯增昭,杨玉卿,金振奎,等.中国南方二叠纪岩相古地理[J].沉积学报,1996,14(2):1-10.
[11]Adachi M,Yamamoto K,Suigiski R.Hydrothermal chert and associated siliceous rocks fromthe Northern Pacific:Their geological signifi-cance as indication of ocean ridge activity[J].Sedi mentary Geology,1986,47(1/2):125-148.
[12]Yamamoto K.Geochemical characteristics and deposition environment of cherts and associated rocks in the Franciscan and Shi mena terra-nes[J].Sedi ment Geology,1987,52:65-108.
[13]刘岫峰.沉积岩实验室研究方法[M].北京:地质出版社,1991,1-299.
[14]Shi mizu H,Masuda A.Ceriumin chert as anindication of marine environment of its formation[J].Nature,1977,266:346-348.
[15]Fleet AJ.Hydrothermal and hydrogenous ferromanganese deposits.In:P A Ronaet al.Hydrothermal Process at Sea Floor Spreading Cen-tres[M].Amsterdam:Elsevier Science Publishers B V,1983,537-570.
[16]Marchig V,Gundlach H,Moller P,et al.Some geochemistry indictors for discri mination between diagenetic and hydrothermai metallifer-ous sedi ments[J].Marine Geoiogy,1982,50(3):241-256.
[17]Haskin L A,Wildeman T R,Haskin M A.An accurate procedure for the determination of rare earth by neutron activation[J].Journal ofRadioanalytical and Nuclear Chemistry,1968,1(4):337-348.
[18]Clayton R N.High temperature isotope effects in the early solar system[A].In:Valley,et al.eds.Reviews in Mineralogy[C].Houston:Pergamon Press,1986,129-1 391.
[19]宋天锐,丁悌平.硅质岩中的硅同位素(δ30Si)应用于沉积相分析的新尝试[J].科学通报,1989,34(18):1 408-1 411.
[20]丁悌平,蒋少涌,万德芳.硅同位素地球化学[M].北京:地质出版社,1994,1-102.
[21]刘家军,郑明华.热水沉积硅岩的地球化学[J].四川地质学报,1993,13(2):110-118.
[22]Knauth P L,Epstein S.Hydrogen and oxygenisotope rations in nodular and bedded cherts[J].Geoch Cosmoch Acta,1976,40(9):1 095-1 108.
[23]卢武长.稳定同位素地球化学[M].成都:成都地质学院出版发行组,1986,1-334.
②刘文均,郑荣才,张锦泉,等.滇黔桂地区泥盆纪岩相古地理控矿特点研究报告.成都理工学院,1993.
[1]王东安.扬子地台晚元古代以来硅岩地球化学特征及其成因[J].地质科学,1994,29(1):41-54.
[2]李红中,杨志军,周永章,等.秦岭地区硅质岩的特征及研究展望[J].矿物学报,2007,(增31刊):441-443.
[3]Murray Richard W.Chemical criteria toidentify the depositional environment of chert general principles and applications[J].Sedi ment Ge-ol,1994,90:213-232.
[4]夏邦栋,钟立荣,方中,等.下扬子区早二叠世孤峰组层状硅质岩成因[J].地质学报,1995,69(2):125-137.
[5]付伟,周永章,杨志军,等.湘中南二叠系孤峰组硅质岩的成因属性及其地球动力学指示意义[J].矿物岩石地球化学通报,2004,23(4):292-00.
[6]Masao Kametaka,Masamichi Takebe,Hiromi Nagaic,et al.Sedi mentary environments of the Middle Permian phosphorite-chert complexfromthe northeastern Yangtze platform,China;the Gufeng Formation:a continental shelf radiolarian chert[J].Sedi mentary Geology,2005,174:197-222.
[7]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.
[8]王立亭,陆彦邦,赵时久,等.中国南方二叠纪岩相古地理与成矿作用[M].北京:地质出版社,1994,1-147.
[9]罗志立.中国西南地区晚古生代以来地裂运动对石油等矿产形成的影响[J].四川地质学报,1981,2(1):20-39.
[10]冯增昭,杨玉卿,金振奎,等.中国南方二叠纪岩相古地理[J].沉积学报,1996,14(2):1-10.
[11]Adachi M,Yamamoto K,Suigiski R.Hydrothermal chert and associated siliceous rocks fromthe Northern Pacific:Their geological signifi-cance as indication of ocean ridge activity[J].Sedi mentary Geology,1986,47(1/2):125-148.
[12]Yamamoto K.Geochemical characteristics and deposition environment of cherts and associated rocks in the Franciscan and Shi mena terra-nes[J].Sedi ment Geology,1987,52:65-108.
[13]刘岫峰.沉积岩实验室研究方法[M].北京:地质出版社,1991,1-299.
[14]Shi mizu H,Masuda A.Ceriumin chert as anindication of marine environment of its formation[J].Nature,1977,266:346-348.
[15]Fleet AJ.Hydrothermal and hydrogenous ferromanganese deposits.In:P A Ronaet al.Hydrothermal Process at Sea Floor Spreading Cen-tres[M].Amsterdam:Elsevier Science Publishers B V,1983,537-570.
[16]Marchig V,Gundlach H,Moller P,et al.Some geochemistry indictors for discri mination between diagenetic and hydrothermai metallifer-ous sedi ments[J].Marine Geoiogy,1982,50(3):241-256.
[17]Haskin L A,Wildeman T R,Haskin M A.An accurate procedure for the determination of rare earth by neutron activation[J].Journal ofRadioanalytical and Nuclear Chemistry,1968,1(4):337-348.
[18]Clayton R N.High temperature isotope effects in the early solar system[A].In:Valley,et al.eds.Reviews in Mineralogy[C].Houston:Pergamon Press,1986,129-1 391.
[19]宋天锐,丁悌平.硅质岩中的硅同位素(δ30Si)应用于沉积相分析的新尝试[J].科学通报,1989,34(18):1 408-1 411.
[20]丁悌平,蒋少涌,万德芳.硅同位素地球化学[M].北京:地质出版社,1994,1-102.
[21]刘家军,郑明华.热水沉积硅岩的地球化学[J].四川地质学报,1993,13(2):110-118.
[22]Knauth P L,Epstein S.Hydrogen and oxygenisotope rations in nodular and bedded cherts[J].Geoch Cosmoch Acta,1976,40(9):1 095-1 108.
[23]卢武长.稳定同位素地球化学[M].成都:成都地质学院出版发行组,1986,1-334.
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