超高压变质流体的组成与演化：中国大陆科学钻探工程主孔岩心的流体包裹体研究
Composition and evolution of ultrahigh-pressure metamorphic fluids: a fluid inclusion study of the drill cores from the main hole of Chinese Continental Scientific Drilling Program
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摘要: 中国大陆科学钻探工程主孔位于大别-苏鲁超高压变质带东段的江苏东海县,孔深为5100m,其上部2050m钻遇的岩石主要为榴辉岩,其次是正、副片麻岩、石榴橄榄(辉石)岩以及少量片岩和石英岩。它们经历了超高压变质作用和随后的角闪岩相退变质作用。通过对上述各种岩石的详细流体包体观察和RAMAN光谱分析,发现了五种不同成分的流体包裹体:(1)中-低盐度水溶液包裹体(Ⅰ型),呈原生的孤立和小群存在于榴辉岩和片麻岩锆石的岩浆核和超高压变质边缘,或存在于绿辉石、黝帘石和被绿辉石包裹的方解石和石英中,偶尔呈出溶包裹体产于磷灰石中,而主要沿绿辉石、石榴石、蓝晶石、黝帘石和石英等矿物的穿颗粒裂隙分布;也呈孤立和小群产于切穿榴辉岩的方解石脉和片麻岩重结晶石榴石和绿帘石中;(2)CO2(±CH4)-H2O包裹体(Ⅱ型),存在于锆石的岩浆核和变质边缘,或沿石英裂隙分布;(3)含石盐±SiO2±CaCO3的复杂盐水包裹体(Ⅲ型),呈原生流体包裹体产在榴辉岩的绿辉石中,与石英出溶棒一起平行于绿辉石的C轴分布,或产在石榴辉石岩透辉石的晶内裂隙中;(4)富CO2包裹体(Ⅳ型),在榴辉岩的石英中随机分布;(5)单气相包裹体(Ⅴ型),沿各种矿物穿颗粒裂隙分布。流体包裹体产状及其与捕获时代关系表明,Ⅰ型和Ⅱ型包裹体可以出现在超高压变质岩原岩、峰期变质和退变质各阶段。Ⅲ型包裹体出现在超高压变质岩的早期减压退变质阶段。而Ⅳ型和Ⅴ型包裹体主要形成于角闪岩相及更晚的退变质阶段。本研究的主要认识是:(1)低盐度H2O和CO2流体在进变质、超高压变质和退变质作用各阶段均有存在,这表明在整个超高压变质演化过程中流体具有继承性。(2)超高压变质岩原岩和角闪岩相退变质岩中存在较丰富的流体包裹体,但在超高压峰期捕获的流体包裹体却很少见,这表明丰富的原岩流体或在超高压进变质过程中被排出岩石体系,或进入含水超高压矿物和结合进名义无水矿物。(3)复杂成分原生流体包裹体的发现证明在超高压变质峰期后的早期减压退变质阶段存在一种高盐度似熔体流体,名义上的无水矿物在超高压条件下可以保存相当量的流体,并在退变质过程中分离出来,产生流体-岩石相互作用。(4)角闪岩阶段的流体包裹体具有各种不同的化学组成,且在局部富集,推测可能有部分外部加入的流体。(5)流体包裹体类型、丰度和成分在不同岩石类型中和不同钻孔深度都存在明显差异,表明超高压变质作用过程中没有大规模的透入性流体活动。(6)根据超高压变质峰期包裹体等容线得到的压力值大大低于根据矿物温压计获得的近峰期变质压力,这表明包裹体的密度在捕获后发生了改变。这些改变是由于流体渗漏、部分爆裂和流体-岩石相互作用所引起。
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[1] Andersen T, Burke E A J and Austrheim H. 1989. Nitrogen-bearing,aqueous fluid inclusions in some eclogites from the Western Gneiss Region of the Norwegian Caledonides. Contrib. Mineral. Petrol. ,103:153 - 165.
[2] Andersen T, Austrheim H and Burke E A J. 1991. Mineral-fluid-melt interactions in high-pressure shear zones in the Bergen Arcs nappe complex, Calidonides of W. Norway: Implications for the fluid regime in Caledonian eclogite-facies metamorphism. Lithos, 27:187- 204.
[3] Andersen T, Austrheim H, Burke E A J and Elvevold S. 1993. N2 and CO2 in deep crustal fluids: evidence from the Caledonides of Norway. Chem. Geol., 108:113-132.
[4] Andersen T, Burke E A J and Austrheim H. 1989. Nitrogen-bearing, aqueous fluid inclusions in some eclogites from the Western Gneiss Region of the Norwegian Caledonides. Contrib. Mineral. Petrol. ,103:153 - 165.
[5] Ayers J C, Eggler D H. 1995. Partition of elements between silicate melt and H2 O-NaCl fluids at 1.5 and 2.0 GPa pressure: Implications for mantle metasomatism. Geochim. Cosmochim. Acta, 59: 4237-4246.
[6] Bakker R J. 2003. Package FLUIDS 1. Computer programs for analysis of fluid inclusion data and for modeling bulk fluid properties. Chem.Geol. , 194:3-23.
[7] Bebout G E. 1991. Field-based evidence for devolatization in subduction zones: implications for arc Magmatism. Science, 251: 413 -416.
[8] Bebout G E. 1996. Volatile transfer and recycling at convergent margins: mass-balance and insights from high P/T metamorphic rocks. In:Bebout G E, Scholl D W, Kirby S H et al. (eds.). Subduction:Top to Bottom. Geophys. Momograph, 96:179-1.
[9] Bischoff J L. 1991. Densities of liquids and vapors in boiling NaCl-H2Osolutions: a PVTX summary from 300°to 500℃. Amer. J. Sci.291: 309 -338.
[10] Bodnar R J. 1993. Revised equation and table for determining the freezing point depression of H2 O-NaCl solutions. Geochim.Cosmochim. Acta, 49:1861 - 1873.
[11] Chen B, Zheng Y F, Wu Y B. 2004. A study of oxygen isotopes and hydroxyl content in minerals of UHP metamorphic rocks from CCSD core 734 to 933m. Acta Petrolgica Sinica, 20(5): 1116 - 1132 (in Chinese with English abstract).
[12] Franz L, Romer R L, Klemd R, Schmid R, Oberh nsli R, Wagner T and S Dong. 2001. Eclogite-facies quartz veins within metabasites of the Dabie Shan (eastern China):pressure-temperature-timedeformation path, composition of the fluid phase and fluid flow during exhumation of high-pressure rocks. Contrib. Mineral.Petrol. , 141: 322- 346.
[13] Fu B, Touret J L R and Zheng Y F. 2001. Fluid inclusions in coesitebearing eclogites and jadeite quartzite at Shuanghe, Dabie Shan (China). J. Metamorphic Geol. , 19: 529 -545.
[14] Fu B, J L R Touret, Zheng Y F. 2003. Remnants of premetamorphic fluid and oxygen isotopic signatures in eclogites and garnet clinopyroxenite from the Dabie-Sulu terranes, eastern China. J.Metamorphic Geol. , 21:561 -578.
[15] Holland T J B. 1979. Experimental determination of the reaction paragonite = jadeite kyanite water, internally consistent thermodynamic data for part of the system Na2 O - Al2 O3 - SiO2 -H2 O, with application to eclogites and blueschists. Contrib.Mineral. Petrol. , 68:293-301.
[16] Hollistar L S. 1990. Enrichment of CO2 in fluid inclusions in quartz by removal of H2 O during crystal-plastic deformation. J. Structural Geology, 7:895-901.
[17] Johnson E L and Hollister L S. 1995. Syndeformational fluid trapping in quartz: determining the pressure-temperature conditions of deformation from fluid inclusions and the formation of pure CO2 fluid inclusions during grain boundary migration. J. Metamorphic Geol. ,13: 239 - 249.
[18] Kerrick D M. 1990. The Al2 SiO5 polymorphs.In: Robie P H (ed.).Reviews in Mineralogy, vol. 22, Mineral. Soc. Am. , Washington,DC, pp 406.
[19] Klemd R, van der Kerkhof A M and Horn E E. 1992. High-density CO2 - N2 inclusions in eclogite-facies metasediments of the Muncheberg gneiss complex, SE Germany. Contrib. Mineral. Petrol. , 111:409-419.
[20] Liou J G, Zhang R Y, Ernst W G. 1995. Occurrence of hydrous and carbonate phases in ultrahigh-pressure rocks from east-central China: Implications for the role of volatiles deep in cold subduction zones.Island Arc, 4: 362 - 375.
[21] Liou J G, Zhang R Y, Ernst W G, Rumble D, Maruyama S. 1998. High-pressure minerals from deeply subducted metamorphic rocks.In: Ultrahigh-pressure Mineralogy ( Eds. ) Reviews In Mineralogy,33 - 96.
[22] Lui F L, Xu Z Q. 2004. Fluid inclusions in coesite-bearing zircons from UHP rocks in southern Su-Lu terrain. Chinese Science Bulletin, 49(2): 181 -189 (in Chinese).
[23] Liu J, Bohlen S R, Ernst W G. 1996. Stability of hydrous phases in subducting oceanic crust. Earth Planet. Sci. Lett. , 143: 161 - 171.
[24] Peacock S M. 1990. Fluid processes in subduction zones. Science, 248: 329 - 337.
[25] Peacock S M. 1993. Large scale hydration of the lithosphere above subducting slabs. In: J L R Touret and A B Thompson (Guest eds.) Fluid-Rock Interactions in the Deeper Continental Lithosphere. Chem. Geol. , 108: 49 - 59.
[26] Philippot P. 1993. Fluid-melt-rock interaction in mafic eclogites and coesite-bearing metasediments: constraints on volatile recycling during subduction. Chem. Geol., 108: 93-112.
[27] Philippot P. 1996. The Chemistry of high-pressure fluids ( 1 to 3 GPa):natural observations vs. experimental constraints. Earth Sci. Front. ,China Univ. Geosci. , Beijing, 3:39 -52.
[28] Philippot P, Chevallier P, Chopin C and Dubessy J (1995) Fluid composition and evolution in coesite-bearing rocks (Dora-Maira massif, Western Alps): implications for element recycling during subduction. Contrib. Mineral. Petrol. , 121:29-44.
[29] Philippot P and Selverstone J. 1991. Trace element-rich brines in eclogitic veins: implications for fluid composition and transport during subduction. Contrib. Mineral. Petrol., 106:417-430.
[30] Scambellury M, Philippot P. 2001. Deep fluids in subduction zones. Lithos, 55:213 -227.
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