F. Rotondo, P. Tartarotti, S. Guerini, G. Porta, N. Campomenosi
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Dehydration, decarbonation and carbonation interplayed from early Alpine subduction up to HP-LT metamorphic peak (T = 550-630°C, P = 1.8-2.5 GPa), to produce a distinctive, pervasive amphibole (tremolite/actinolite) replacement both in carbonate-rich and serpentinite-rich domains pertaining to the MH protoliths, i.e., serpentinite and carbonatebearingmetabreccia of the chaotic rock unit. This characteristic amphibole metasomatism is more pronounced toward the contact with the metaophicarbonates, and the average δ18OVSMOW and δ13CVPDB values of dolomite within the MH (+14.4‰ and +0.7‰ respectively) lie between those of the metaophicarbonates and of calcschist. These results suggest that Mg-H2O-rich fluids from the dehydrating slab, CO2 released by decarbonation and SiO2-rich fluids evolved in calcschists mixed together and circulated mostly along the metaophiolite basement/metasediments interface, where the MH developed and recorded a preferential channel for mixed metamorphic fluid flow. These findings highlight and confirm that the study of metasomatic rocks in convergent systems is crucial to comprehend the behaviour of different","PeriodicalId":54690,"journal":{"name":"Ofioliti","volume":null,"pages":null},"PeriodicalIF":1.2000,"publicationDate":"2021-01-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"4","resultStr":"{\"title\":\"METASOMATIC HORIZON SEALING SERPENTINITE-METASEDIMENTS PAIR IN THE ZERMATT-SAAS METAOPHIOLITE (NORTHWESTERN ALPS): RECORD OF A CHANNEL FOR FOCUSSED FLUID FLOW DURING SUBDUCTION\",\"authors\":\"F. Rotondo, P. Tartarotti, S. Guerini, G. 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Dehydration, decarbonation and carbonation interplayed from early Alpine subduction up to HP-LT metamorphic peak (T = 550-630°C, P = 1.8-2.5 GPa), to produce a distinctive, pervasive amphibole (tremolite/actinolite) replacement both in carbonate-rich and serpentinite-rich domains pertaining to the MH protoliths, i.e., serpentinite and carbonatebearingmetabreccia of the chaotic rock unit. This characteristic amphibole metasomatism is more pronounced toward the contact with the metaophicarbonates, and the average δ18OVSMOW and δ13CVPDB values of dolomite within the MH (+14.4‰ and +0.7‰ respectively) lie between those of the metaophicarbonates and of calcschist. 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引用次数: 4
摘要
在阿尔卑斯西北部泽尔马特-萨斯高压带,在米塞林湖蛇绿岩的变质绿岩(蛇纹岩和变质碳酸盐)基底和变质沉积层(混沌岩和钙片岩)之间形成交代层(MH)。宏观和微观结构分析,结合岩石学和地球化学对MH及其周围岩性的调查,揭示了一个多相的爆破-变形历史,这导致了蛇纹岩基底-沉积界面的复杂结构的形成和矿物化学蚀变。从早阿尔卑斯俯冲到HP-LT变质峰(T = 550-630°C, P = 1.8-2.5 GPa),脱水、脱碳和碳酸作用相互作用,在MH原岩(即蛇纹岩和含碳酸盐的变质砾岩)的富碳酸盐和富蛇纹岩域中形成了独特的、普遍存在的角闪石(透闪石/放光石)替代。这种特征的角闪孔交代作用在与变质碳酸盐接触的方向更为明显,MH内白云岩的平均δ18OVSMOW和δ13CVPDB值(分别为+14.4‰和+0.7‰)介于变质碳酸盐和钙片岩之间。这些结果表明,脱水板的富mg - h2o流体、脱碳释放的CO2以及富sio2流体在混合的钙质岩中演化,主要沿变质岩基底/变质沉积层界面循环,在此形成了混合变质流体的优先通道。这些发现强调并证实了收敛系统中交代岩石的研究对于理解不同成岩作用的行为是至关重要的
METASOMATIC HORIZON SEALING SERPENTINITE-METASEDIMENTS PAIR IN THE ZERMATT-SAAS METAOPHIOLITE (NORTHWESTERN ALPS): RECORD OF A CHANNEL FOR FOCUSSED FLUID FLOW DURING SUBDUCTION
A metasomatic horizon (MH) occurs between the metaophiolite (serpentinite and metaophicarbonates) basement and metasedimentary sequence (chaotic rocks and calcschists) of the Lake Miserin Ophiolite, in the high pressure Zermatt-Saas Zone of the Northwestern Alps. Macro- and microstructural analyses combined with petrological and geochemical investigations of the MH and surrounding lithologies unravelled a polyphase blastesis-deformation history, which led to the formation of a complex fabric and minero-chemical alteration of the serpentinite basement-metasediments interface. Dehydration, decarbonation and carbonation interplayed from early Alpine subduction up to HP-LT metamorphic peak (T = 550-630°C, P = 1.8-2.5 GPa), to produce a distinctive, pervasive amphibole (tremolite/actinolite) replacement both in carbonate-rich and serpentinite-rich domains pertaining to the MH protoliths, i.e., serpentinite and carbonatebearingmetabreccia of the chaotic rock unit. This characteristic amphibole metasomatism is more pronounced toward the contact with the metaophicarbonates, and the average δ18OVSMOW and δ13CVPDB values of dolomite within the MH (+14.4‰ and +0.7‰ respectively) lie between those of the metaophicarbonates and of calcschist. These results suggest that Mg-H2O-rich fluids from the dehydrating slab, CO2 released by decarbonation and SiO2-rich fluids evolved in calcschists mixed together and circulated mostly along the metaophiolite basement/metasediments interface, where the MH developed and recorded a preferential channel for mixed metamorphic fluid flow. These findings highlight and confirm that the study of metasomatic rocks in convergent systems is crucial to comprehend the behaviour of different
期刊介绍:
Since 1976, Ofioliti provides an international forum for original contributions and reviews in the field of the geodynamics, petrology, geochemistry, biostratigraphy, stratigraphy, tectonics and paleogeography applied to ophiolitic terrains and modern oceanic lithosphere, including their sedimentary cover. Studies of topics such as geodynamics of the mantle, the evolution of orogens including ophiolites and paleoceanography are also welcome