The fluid phase in orogenic settings has a key role in petrology and geochemistry, with implications for deep carbon cycle. We will present some examples from our research group within the Prin project 2010PMKZX7. Fluids enhance metamorphic reactions and re-equilibration of mineral assemblages, determine stability field of metamorphic minerals, and are responsible for metasomatism. Sulu quartzites (China) Dora-Maira whiteschists and marbles (Italy), and Karakorum high-pressure xenoliths (China) represent typical examples of fluid-mineral metamorphic evolution in deeply subducted continental rocks from orogenic settings differing on P/T gradients. Trace element compositions of ultra-high pressure fluids from peak multiphase solid inclusions in quartzite (Sulu) and whiteschists (Dora-Maira) are characterized by significant LILE enrichments and HFSE depletions (Frezzotti & Ferrando, 2015). This selective mass transfer from the subducted continental crust to the mantle wedge by fluid flow deeply modifies the geochemistry of peridotites and, consequently, represents a key for understanding the geochemical variations observed in orogenic magmas (Peccerillo & Frezzotti, 2015). Fluid phases generated during deep subduction are crucial to our understanding for the Earth’s deep carbon cycle (Flesia & Frezzotti, 2015). In collisional contexts characterized by relatively high temperatures such as the Himalayan orogen, deep reactions of decarbonation and of graphite oxidation, as evident in Karakorum xenoliths, are the primary mechanisms to produce CO 2 subsequently released into the atmosphere via tectonic discontinuities. In collisional contexts characterized by deep and cold subduction such as the Western Alps, carbon dissolution (Frezzotti et al., 2014) from both oceanic (Lago di Cignana Mn-nodules) and continental (Dora-Maira marbles) crust is an additional relevant mechanism for the transfer of carbon into the mantle, ultimately outgassed by magmatism and tectonics. Flesia C. & Frezzotti M.L. 2015. The dilemma of the dwarf Earth’s CO 2 degassing: irrelevant or crucial? J. Geochem. Explor., 152, 118-122. Frezzotti M.L. & Ferrando S. 2015. The chemical behavior of fluids released during deep subduction based on fluid inclusions. Am. Mineral., 100, 352-377. Frezzotti M.L., Huizenga J.M., Compagnoni R. & Selverstone J. 2014. Diamond formation by carbon saturation in C- O-H fluids during cold subduction of oceanic lithosphere. Geochim. Cosmochim. Acta, 143, 68-86. Peccerillo A. & Frezzotti M.L. 2015. Magmatism, mantle evolution and geodynamics at the converging plate margins of Italy. J. Geol. Soc., doi:10.1144/jgs2014-085.
Petrological and geochemical role of fluid phases in orogenic settings.
FERRANDO, Simona;
2015-01-01
Abstract
The fluid phase in orogenic settings has a key role in petrology and geochemistry, with implications for deep carbon cycle. We will present some examples from our research group within the Prin project 2010PMKZX7. Fluids enhance metamorphic reactions and re-equilibration of mineral assemblages, determine stability field of metamorphic minerals, and are responsible for metasomatism. Sulu quartzites (China) Dora-Maira whiteschists and marbles (Italy), and Karakorum high-pressure xenoliths (China) represent typical examples of fluid-mineral metamorphic evolution in deeply subducted continental rocks from orogenic settings differing on P/T gradients. Trace element compositions of ultra-high pressure fluids from peak multiphase solid inclusions in quartzite (Sulu) and whiteschists (Dora-Maira) are characterized by significant LILE enrichments and HFSE depletions (Frezzotti & Ferrando, 2015). This selective mass transfer from the subducted continental crust to the mantle wedge by fluid flow deeply modifies the geochemistry of peridotites and, consequently, represents a key for understanding the geochemical variations observed in orogenic magmas (Peccerillo & Frezzotti, 2015). Fluid phases generated during deep subduction are crucial to our understanding for the Earth’s deep carbon cycle (Flesia & Frezzotti, 2015). In collisional contexts characterized by relatively high temperatures such as the Himalayan orogen, deep reactions of decarbonation and of graphite oxidation, as evident in Karakorum xenoliths, are the primary mechanisms to produce CO 2 subsequently released into the atmosphere via tectonic discontinuities. In collisional contexts characterized by deep and cold subduction such as the Western Alps, carbon dissolution (Frezzotti et al., 2014) from both oceanic (Lago di Cignana Mn-nodules) and continental (Dora-Maira marbles) crust is an additional relevant mechanism for the transfer of carbon into the mantle, ultimately outgassed by magmatism and tectonics. Flesia C. & Frezzotti M.L. 2015. The dilemma of the dwarf Earth’s CO 2 degassing: irrelevant or crucial? J. Geochem. Explor., 152, 118-122. Frezzotti M.L. & Ferrando S. 2015. The chemical behavior of fluids released during deep subduction based on fluid inclusions. Am. Mineral., 100, 352-377. Frezzotti M.L., Huizenga J.M., Compagnoni R. & Selverstone J. 2014. Diamond formation by carbon saturation in C- O-H fluids during cold subduction of oceanic lithosphere. Geochim. Cosmochim. Acta, 143, 68-86. Peccerillo A. & Frezzotti M.L. 2015. Magmatism, mantle evolution and geodynamics at the converging plate margins of Italy. J. Geol. Soc., doi:10.1144/jgs2014-085.
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