铜陵焦冲金矿岩浆作用过程:来自闪长玢岩的证据
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摘要
本文主要针对安徽铜陵焦冲金矿区的闪长玢岩进行了详细的岩相学观察和矿物电子探针分析。岩相学观察表明,岩石内发育独特的石英斑晶、斜长石斑晶及其中的角闪石包裹体和角闪石斑晶。石英斑晶呈港湾状或次圆形,由溶蚀的次圆形内核和生长边构成,在内核与边部之间有熔融包裹体产出;斜长石斑晶具明显的"核-幔-边"环带结构,幔部发育明显的溶蚀界面,溶蚀界面处大量熔融包裹体呈环带分布;角闪石包裹体分别包裹于斜长石斑晶的核部和幔部,后者的边部被溶蚀呈次圆形;角闪石斑晶呈长条形,包裹有细针状的磷灰石。电子探针分析结果表明,斜长石中An含量自核部至边缘呈降低趋势,幔部出现多个An峰值;而来自斜长石斑晶核部、幔部和基质中的角闪石Al2O3含量从核部至基质也逐渐下降。采用角闪石-斜长石温压计和角闪石全铝压力计,分别对斜长石斑晶核部及包裹的角闪石、斜长石斑晶幔部及包裹的角闪石和基质中共生的角闪石-斜长石微晶的结晶温度和压力进行估计,结果表明,温度为806.84~808.75、791.00~797.86和660.3~683.9℃,压力为675~706、463~487和206~212 MPa,对应的形成深度为25.52~26.70、17.50~18.40和7.79~8.02km。角闪石斑晶的结晶压力和深度为448~483MPa和16.93~18.25km,与包裹于斜长石幔部的角闪石包裹体一致。根据以上岩相学和角闪石-斜长石矿物化学分析结果,本文提出一个多重岩浆房模型:来自深部幔源的流体(透岩浆流体)将不同层位的岩浆房串联活化,活化后的中基性岩浆和花岗闪长质岩浆混合形成中性岩浆,最后中性富流体的岩浆快速上侵冷却就位于地表,同时释放大量的挥发分(含矿物质),后期的减压排气作用可能是主要的成矿机制。
This paper presents new petrographic observations and microprobe analyses for the dioritic porphyrite from the Jiaochong gold deposit.Petrographic observations indicate the existence of unique quartz,plagioclase and hornblend phenocrysts in the rock.The quartz phenocryst is composed of resorbed core and growth rim,with melt inclusions along the border between core and rim.The plagioclase phenocrysts consist of resorbed core,resorbed growth mantle,and growth rim,with melt inclusions along resorption surfaces in the mantle.Hornblende poikilotopes are observed within core and mantle of the plagioclase phenocrysts.Hornblend phenocrysts are elongated in shape and contain acicular apatite poikilotopes.Microprobe analyses show that the An content of plagioclase from core to rim presents a reduced tendency and appears some An peaks at mantle,the aluminum content of hornblende from core of plagioclase to the matrix is decreasing.Using Amp-Pl geothermobarometry and whole-Al content of hornblende geobarometry the crystallization temperature and pressure of plagioclase phenocryst core and hornblende inclusions within it,the mantle of plagioclase and its hornblende inclusions,and co-existing Hbl-Pl micolites in the matrix are calculated respectively.The results show that the temperatures are 806.84-808.75,791.00-797.86 and 660.3-683.9 ℃,respectively.The pressures are 6.75-7.06 kb,4.63-4.87 kb,and 2.06-2.12 kb respectively.The corresponding formation depths are 25.52-26.70,17.50-18.40,and 7.79-8.02 km,respectively.Besides,the crystallization conditions of hornblende phenocryst are similar to those of embedded hornblende in the mantle of plagioclase phenocryst,the pressure of crystallization and corresponding depths are 4.48-4.83 kb and16.93-18.25 km,respectively.On the basis of the petrographic and geochemical analytical results,the present paper proposes the model of multiple magma chambers:the deep mantle-derived transmagmatic fluids activate different-level magma chambers,as a result,forming intermediate-basic and granodioritic magmas,and the magma mixing between them has occurred.Finally,the mixing intermediate melt-fluid flow driven by fluid pressure emplace rapidly near the surface,meanwhile,large amounts of volatile(ore-bearing fluid)are released.The exhalation process caused by decompression is probably the main mineralization mechanism.
This paper presents new petrographic observations and microprobe analyses for the dioritic porphyrite from the Jiaochong gold deposit.Petrographic observations indicate the existence of unique quartz,plagioclase and hornblend phenocrysts in the rock.The quartz phenocryst is composed of resorbed core and growth rim,with melt inclusions along the border between core and rim.The plagioclase phenocrysts consist of resorbed core,resorbed growth mantle,and growth rim,with melt inclusions along resorption surfaces in the mantle.Hornblende poikilotopes are observed within core and mantle of the plagioclase phenocrysts.Hornblend phenocrysts are elongated in shape and contain acicular apatite poikilotopes.Microprobe analyses show that the An content of plagioclase from core to rim presents a reduced tendency and appears some An peaks at mantle,the aluminum content of hornblende from core of plagioclase to the matrix is decreasing.Using Amp-Pl geothermobarometry and whole-Al content of hornblende geobarometry the crystallization temperature and pressure of plagioclase phenocryst core and hornblende inclusions within it,the mantle of plagioclase and its hornblende inclusions,and co-existing Hbl-Pl micolites in the matrix are calculated respectively.The results show that the temperatures are 806.84-808.75,791.00-797.86 and 660.3-683.9 ℃,respectively.The pressures are 6.75-7.06 kb,4.63-4.87 kb,and 2.06-2.12 kb respectively.The corresponding formation depths are 25.52-26.70,17.50-18.40,and 7.79-8.02 km,respectively.Besides,the crystallization conditions of hornblende phenocryst are similar to those of embedded hornblende in the mantle of plagioclase phenocryst,the pressure of crystallization and corresponding depths are 4.48-4.83 kb and16.93-18.25 km,respectively.On the basis of the petrographic and geochemical analytical results,the present paper proposes the model of multiple magma chambers:the deep mantle-derived transmagmatic fluids activate different-level magma chambers,as a result,forming intermediate-basic and granodioritic magmas,and the magma mixing between them has occurred.Finally,the mixing intermediate melt-fluid flow driven by fluid pressure emplace rapidly near the surface,meanwhile,large amounts of volatile(ore-bearing fluid)are released.The exhalation process caused by decompression is probably the main mineralization mechanism.
引文
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[2]罗照华,卢欣祥,陈必河,等.透岩浆流体成矿作用导论[M].北京:地质出版社,2009:1-177.
[3]Rutherford M J.Magma ascent rates[J].Reviews in Mineralogy and Geochemistry,2008,69:241-271.
[4]魏海泉.长白山火山岩浆柱岩浆上升作用过程[J].地学前缘,2010,17(1):11-23.
[5]罗照华,杨宗峰,代耕,等.火成岩的晶体群与成因矿物学展望[J].中国地质,2013,40(1):176-180.
[6]常印佛,刘湘培,吴言昌.长江中下游铜铁成矿带[M].北京:地质出版社,1991:1-379.
[7]吴才来,周珣若,黄许陈,等.铜陵地区中酸性侵入岩锆石群结晶特征及其成因[J].岩石矿物学杂志,1994,13(3):239-247.
[8]吴才来,陈松勇,史仁灯,等.铜陵中生代中酸性侵入岩特征及成因[J].地球学报,2003,24(1):41-48.
[9]储玲林,张瑞生,廖群安,等.辽西建昌—凌源地区早侏罗世水泉沟组底部英安岩中斜长石环带特征的解释[J].岩石学报,2006,22(9):2325-2330.
[10]Dempster T J,Jolivet M,Tubrett M N,et al.Magmatic zoning in apatite:A monitor of porosity and permeability change in granites[J].Contributions to Mineralogy and Petrology,2003,145:568-577.
[11]Schmidt M W.Amphibole composition in tonalite as a function of pressure:An experimental calibration of the Al-inhornblende barometer[J].Contributions to Mineralogy and Petrology,1992,110:304-310.
[12]Holland T J B,Blundy J D.Non-ideal interactions in calcic amphiboles and their bearing on amphibole plagioclase geothermometry[J].Contributions to Mineralogy and Petrology,1994,116:433-447.
[13]Leake B E.Nomenclature of amphibole[J].American Mineralogist,1978,63:1023-1052.
[14]Bowen N L.The melting phenomena of the plagioclase feldspars[J].American Journal of Science,1913,4:577-599.
[15]Phemister J.Zoning in plagioclase felspar[J].Mineralogical Magazine,1934,23:541-555.
[16]Hills E S.Reverse and oscillatory zoning in plagioclase felspars[J].Geological Magazine,1936,73:50-56.
[17]Grove T L.Coupled CaAl-NaSi diffusion in plagioclase feldspar:Experiments and applications to cooling rate speedometry[J].Geochimica et Cosmochimica Acta,1984,48:2113-2121.
[18]Tsuchiyama A.Dissolution kinetics of plagioclase in melt of the system diopside-albite-anorthite,and the origin of dusty plagioclase in andesites[J].Contributions to Mineralogy and Petrology,1985,89:1-16.
[19]Rutherford M J,Sigurdson H,Carey S,et al.The May 18,1980eruption of Mount St.Helens:1.Melt composition and experimental phase equilibria[J].Journal of Geophysical Re-search,1985,90:2929-2947.
[20]Blundy J,Cashman K,Humhreys M.Magma heating by decompression-driven crystallization beneath andesite volcanoes[J].Nature,2006,443:76-80.
[21]覃峰,徐晓霞,罗照华.北京房山岩体形成过程中的岩浆混合证据[J].岩石学报,2006,22(12):2957-2970.
[22]Allegre C J,Provost A,Jaupart C.Oscillatory zoning:A pathological case of crystal growth[J].Nature,1981,294:223-228.
[23]Ginibre C,Kronz A,Worner G.High resolution quantitative imaging of plagioclase composition using accumulated backscattered electron images:New constrains on oscillatory zoning[J].Contributions to Mineralogy and Petrology,2002,142:436-438.
[24]Nakamura M,Shimakita S.Dissolution origin and syn-entrapment compositional change of melt inclusion in plagioclase[J].Earth and Planetary Science Letters,1998,161:119-133.
[25]唐永成,吴言昌,储国正,等.安徽沿江地区铜金多金属矿床地质[M].北京:地质出版社,1998:1-349.
[26]LU Q T,Hou Z Q,Zhao J H,et al.Deep seismic reflection profiling reveals complex crustal structure of Tongling ore district[J].Science in China:Series D,2003,33:442-449.
[27]Wu C L,Wang Z H,Qiao D W,et al.Types of enclaves and their features and origins in intermediate-acid intrusive rocks from Tongling district,Anhui,China[J].Acta Geologica Sinica,2000,74(1):54-67.
[28]黄雄飞,莫宣学,喻学惠,等.西秦岭印支期高Sr/Y花岗岩类的成因及动力学背景:以同仁地区舍哈力吉岩体为例[J].岩石学报,2014,30(11):3255-3270.
[29]罗照华,刘翠,苏尚国.理解岩浆系统的物理过程[J].岩石学报,2014,30(11):3113-3119.
①娄尤华.安徽铜陵县焦冲金硫矿1∶1000详查报告:安徽省铜陵市狮子山区.合肥:安徽省地质矿产勘查局321地质队,2005.
[2]罗照华,卢欣祥,陈必河,等.透岩浆流体成矿作用导论[M].北京:地质出版社,2009:1-177.
[3]Rutherford M J.Magma ascent rates[J].Reviews in Mineralogy and Geochemistry,2008,69:241-271.
[4]魏海泉.长白山火山岩浆柱岩浆上升作用过程[J].地学前缘,2010,17(1):11-23.
[5]罗照华,杨宗峰,代耕,等.火成岩的晶体群与成因矿物学展望[J].中国地质,2013,40(1):176-180.
[6]常印佛,刘湘培,吴言昌.长江中下游铜铁成矿带[M].北京:地质出版社,1991:1-379.
[7]吴才来,周珣若,黄许陈,等.铜陵地区中酸性侵入岩锆石群结晶特征及其成因[J].岩石矿物学杂志,1994,13(3):239-247.
[8]吴才来,陈松勇,史仁灯,等.铜陵中生代中酸性侵入岩特征及成因[J].地球学报,2003,24(1):41-48.
[9]储玲林,张瑞生,廖群安,等.辽西建昌—凌源地区早侏罗世水泉沟组底部英安岩中斜长石环带特征的解释[J].岩石学报,2006,22(9):2325-2330.
[10]Dempster T J,Jolivet M,Tubrett M N,et al.Magmatic zoning in apatite:A monitor of porosity and permeability change in granites[J].Contributions to Mineralogy and Petrology,2003,145:568-577.
[11]Schmidt M W.Amphibole composition in tonalite as a function of pressure:An experimental calibration of the Al-inhornblende barometer[J].Contributions to Mineralogy and Petrology,1992,110:304-310.
[12]Holland T J B,Blundy J D.Non-ideal interactions in calcic amphiboles and their bearing on amphibole plagioclase geothermometry[J].Contributions to Mineralogy and Petrology,1994,116:433-447.
[13]Leake B E.Nomenclature of amphibole[J].American Mineralogist,1978,63:1023-1052.
[14]Bowen N L.The melting phenomena of the plagioclase feldspars[J].American Journal of Science,1913,4:577-599.
[15]Phemister J.Zoning in plagioclase felspar[J].Mineralogical Magazine,1934,23:541-555.
[16]Hills E S.Reverse and oscillatory zoning in plagioclase felspars[J].Geological Magazine,1936,73:50-56.
[17]Grove T L.Coupled CaAl-NaSi diffusion in plagioclase feldspar:Experiments and applications to cooling rate speedometry[J].Geochimica et Cosmochimica Acta,1984,48:2113-2121.
[18]Tsuchiyama A.Dissolution kinetics of plagioclase in melt of the system diopside-albite-anorthite,and the origin of dusty plagioclase in andesites[J].Contributions to Mineralogy and Petrology,1985,89:1-16.
[19]Rutherford M J,Sigurdson H,Carey S,et al.The May 18,1980eruption of Mount St.Helens:1.Melt composition and experimental phase equilibria[J].Journal of Geophysical Re-search,1985,90:2929-2947.
[20]Blundy J,Cashman K,Humhreys M.Magma heating by decompression-driven crystallization beneath andesite volcanoes[J].Nature,2006,443:76-80.
[21]覃峰,徐晓霞,罗照华.北京房山岩体形成过程中的岩浆混合证据[J].岩石学报,2006,22(12):2957-2970.
[22]Allegre C J,Provost A,Jaupart C.Oscillatory zoning:A pathological case of crystal growth[J].Nature,1981,294:223-228.
[23]Ginibre C,Kronz A,Worner G.High resolution quantitative imaging of plagioclase composition using accumulated backscattered electron images:New constrains on oscillatory zoning[J].Contributions to Mineralogy and Petrology,2002,142:436-438.
[24]Nakamura M,Shimakita S.Dissolution origin and syn-entrapment compositional change of melt inclusion in plagioclase[J].Earth and Planetary Science Letters,1998,161:119-133.
[25]唐永成,吴言昌,储国正,等.安徽沿江地区铜金多金属矿床地质[M].北京:地质出版社,1998:1-349.
[26]LU Q T,Hou Z Q,Zhao J H,et al.Deep seismic reflection profiling reveals complex crustal structure of Tongling ore district[J].Science in China:Series D,2003,33:442-449.
[27]Wu C L,Wang Z H,Qiao D W,et al.Types of enclaves and their features and origins in intermediate-acid intrusive rocks from Tongling district,Anhui,China[J].Acta Geologica Sinica,2000,74(1):54-67.
[28]黄雄飞,莫宣学,喻学惠,等.西秦岭印支期高Sr/Y花岗岩类的成因及动力学背景:以同仁地区舍哈力吉岩体为例[J].岩石学报,2014,30(11):3255-3270.
[29]罗照华,刘翠,苏尚国.理解岩浆系统的物理过程[J].岩石学报,2014,30(11):3113-3119.
①娄尤华.安徽铜陵县焦冲金硫矿1∶1000详查报告:安徽省铜陵市狮子山区.合肥:安徽省地质矿产勘查局321地质队,2005.
目录
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