昭通巧家玄武岩中灯笼状葡萄石聚集体的形貌特征及成因
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摘要
借助显微镜和扫描电镜、电子背散射衍射仪、电子探针、拉曼探针等现代仪器,对云南昭通巧家杏仁斑状玄武岩晶洞中灯笼状葡萄石聚集体的形貌和成因进行系统研究。葡萄石主要与水晶、绿帘石等矿物共生。葡萄石中普遍含有0.03%~0.06%的SrO,与其共生的绿帘石中SrO的含量(0.18%~1.70%)明显高于葡萄石;与葡萄石共生的水晶中气液包裹体主要成分为H_2O及少量CH_4。灯笼状聚集体由板柱状葡萄石单晶呈扇形密集分布,大多数晶粒的[010]方向垂直于灯笼状聚集体的横切面,[100]方向和[001]方向均平行于灯笼状葡萄石聚集体横切面且按一定的角度呈发散状。分析表明,葡萄石形成于低温(151.5℃~169.1℃)、低盐度(10.11%~11.81%)的热液环境中,成矿热液中少量甲烷等有机成分的存在,使葡萄石聚集体倾向于生长成整体具有更小比表面积的球形。晶洞中锶的来源与玄武岩层下的下二叠统(P1)富含锶的碳酸岩层密切相关。
Morphology and formation of the lantern-shaped prehnite aggregates in amygdaloidal and porphyritic basaltic druse,Qiaojia in Yunnan Province,China,are systematically studied by optical microscope,scanning electron microscope,electron back scatter diffraction,electron probe,Raman probe and other modern instruments.It shows that the prehnite is associated with quartz and epidote with Sr contents varying from 0.03% to 0.06% in prehnite grains,and 0.18% to1.70%in epidote grains.The analysis also indicates that the hydrothermal fluids in quartz are enriched in H_2O and CH_4.Single prehnite crystal appears as plate columnar and the prehnite aggregates occur as lantern shape with fan-shaped morphology.The[010]direction of most prehnite crystals is perpendicular to the cross section of the lantern-shaped aggregates,while[100]and[001]directions of prehnite crystals are parallel to the cross section of the lantern-shaped aggregate with certain angle rotation around the center.It reveals that prehnite formed in low temperature(151.5 ℃~169.1 ℃)and low salinity(10.11%~11.81%)hydrothermal solutions with a small amount of organics in the hydrothermal solution,such as methane,which makes prehnite crystals form as aggregates of pellets with smaller specific surface area.It is considered that sources of strontium in miarolitic cavity are closely related to Lower Permian strontium carbonate formation directly below the basalt rock.
Morphology and formation of the lantern-shaped prehnite aggregates in amygdaloidal and porphyritic basaltic druse,Qiaojia in Yunnan Province,China,are systematically studied by optical microscope,scanning electron microscope,electron back scatter diffraction,electron probe,Raman probe and other modern instruments.It shows that the prehnite is associated with quartz and epidote with Sr contents varying from 0.03% to 0.06% in prehnite grains,and 0.18% to1.70%in epidote grains.The analysis also indicates that the hydrothermal fluids in quartz are enriched in H_2O and CH_4.Single prehnite crystal appears as plate columnar and the prehnite aggregates occur as lantern shape with fan-shaped morphology.The[010]direction of most prehnite crystals is perpendicular to the cross section of the lantern-shaped aggregates,while[100]and[001]directions of prehnite crystals are parallel to the cross section of the lantern-shaped aggregate with certain angle rotation around the center.It reveals that prehnite formed in low temperature(151.5 ℃~169.1 ℃)and low salinity(10.11%~11.81%)hydrothermal solutions with a small amount of organics in the hydrothermal solution,such as methane,which makes prehnite crystals form as aggregates of pellets with smaller specific surface area.It is considered that sources of strontium in miarolitic cavity are closely related to Lower Permian strontium carbonate formation directly below the basalt rock.
引文
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[2]张立飞.含钙铝榴石的葡萄石-绿纤石相平衡:以新疆萨尔托海蛇绿岩中变基性岩石为例[J].岩石学报,1997,13(3):406-417.
[3]赵爱醒,张学俊,薛成秀,等.湖北大冶铁山铁矿床葡萄石和硅硼钙石矿物学特征及形成条件[J].地球科学,1991,16(6):681-686.
[4]Marcia M,Luis A,Mario V,et al.Prehnite-pumpellyite facies metamorphism in the Cenozoic Abanico Formation,Andes of central Chile(33°50′S):chemical and scale controls on mineral assemblages,reaction progress and the equilibrium state[J].Andean Geology,2010,37(1):54-77.
[5]张良钜,饶灿,阮青锋.球粒状緑帘石的结构特征与成因[J].矿物学报,2010,30(2):174-178.
[6]彭志忠,周公度,唐有祺.葡萄石的晶体结构[J].科学通报,1957,2(8):330-331.
[7]Papike J J,Zoltai T.Ordering of tetrahedral aluminum in prehnite Ca2(Al,Fe3+)[Si3AlO10](OH)2[J].American Mineralogist,1965,52(7-8):974-984.
[8]Werner B H,Werner J,Dethard K,et al.Prehnite:structural similarity of the monoclinic and orthorhombic polymorphs and their Si/Al ordering[J].Journal of Solid State Chemistry,1990,86(2):330-333.
[9]Akasaka M,Hashimoto H,Makino K,et al.57Fe Mssbauer and X-ray Rietveld studies of ferrian prehnite from Kouragahana,Shimane Peninsula,Japan[J].Journal of Mineralogical and Petrological Sciences,2003,98:31-40.
[10]Pan Y M,Mao M,Lin J R.Single-crystal EPR study of Fe3+and VO2+in prehnite from the Jeffrey mine,Asbestos,Quebec[J].The Canadian Mineralogist,2009,47(4):933-945.
[11]Zhao W Y,Liu X W,Wang Q Y,et al.Space symmetry of prehnite,Ca2Al[Si3AlO10](OH)2,from the Tieshan iron mineral deposit,central China[J].Mineralogical Magazine,2003,67(1):73-77.
[12]Theresa A D,Nancy L R,Ross J A,et al.Equation of state and structure of prehnite to 9.8GPa[J].European Journal of Mineralogy,2009,21(3):561-570.
[13]徐海军,金淑燕,郑伯让.岩石组构学研究的最新技术——电子背散射衍射(EBSD)[J].现代地质,2007,21(2):213-225.
[14]张云湘,骆耀南.攀西裂谷[M].北京:地质出版社,1988.
[15]王吉平,胡墨田,周建民,等.论华蔡山地区天青石矿石的两种成因[J].地质学报,2000,74(4):325-332.
[16]郭峰.碳酸盐沉积学[M].北京:石油工业出版社,2008.
[17]徐义刚,钟孙霖.峨眉山大火成岩省:地幔柱活动的证据及其熔融条件[J].地球化学,2001,30(1):1-9.
[18]郑海飞,郝瑞霞.普通地球化学[M].北京:北京大学出版社,2007.
[19]黄思静,Qing H R,黄培培,等.晚二叠世-早三叠世海水的锶同位素组成与演化——基于重庆中梁山海相碳酸盐的研究结果[J].中国科学(D辑:地球科学),2008,38(3):273-283.
[20]戴塔根,龚铃兰,张起钻.应用地球化学[M].湖南:中南大学出版社,2005.
[21]董元彦,路福綄,唐树戈.物理化学[M].北京:科学出版社,2008.