Artículo
Low- P melting of metapelitic rocks and the role of H 2 O: Insights from phase equilibria modelling
Sola, Alfonso Manuel
; Hasalová, Pavlina; Ferrez Weinberg, Roberto; Suzaño, Nestor Omar
; Becchio, Raul Alberto
; Hongn, Fernando Daniel
; Botelho, Nilson
Fecha de publicación:
10/2017
Editorial:
Wiley Blackwell Publishing, Inc
Revista:
Journal Of Metamorphic Geology
ISSN:
0263-4929
Idioma:
Inglés
Tipo de recurso:
Artículo publicado
Clasificación temática:
Resumen
Water‐fluxed melting has long been thought to have a minor influence on the thermal and chemical structure of the crust. We report here on amphibolite facies metasedimentary rocks from the 490–450 Ma Famatinian Orogen, in northwest Argentina, that have undergone water‐fluxed incongruent biotite melting at relatively low temperature, which have produced and lost a significant volume of melt. The protoliths consist of the turbiditic Puncoviscana Formation (Neoproterozoic to Early Cambrian). The field area exhibits a condensed metamorphic field gradient, from greenschist to amphibolite facies suprasolidus conditions, recording a low pressure almost isobaric path, reaching peak conditions estimated at 700°C at 4 kbar. Thermodynamic modelling in the MnNCKFMASHTO system is applied to investigate melting at such low pressure as a function of water content. Calculations using a typical turbidite composition show how small amounts of added free H2O may increase significantly the melt fraction with little or no change in either the melt or residual phase compositions. They indicate negligible difference in normative An–Ab–Or proportions and ferromagnesian contents between melts derived by dehydration and water‐fluxed melts. The same is true for the content of H2O dissolved in melts, which remains constant and the melt produced is granitic whether or not aqueous fluids are present. Thus, neither the residue nor the melt composition are indicators of the presence of aqueous fluids during anatexis. Recognizing the impact of small additions of H2O to an anatectic terrane may therefore be difficult. The most significant change related to water‐fluxing is the relative proportions of minerals and melt fraction, rather than the actual mineral assemblage. The modal proportion of feldspar decreased while those of cordierite and biotite increased in the residual assemblages, as <5 mol.% of free H2O was added. The impact of this addition is to more than double the proportion of water‐undersaturated melt to 25–30 mol.%. We have also developed a simple way to estimate how much melt a residual rock has lost, if the compositional trends of the protoliths are known. In summary, we find that even though the addition of small amounts of free H2O impacts significantly on rock fertility, there is little obvious record in the field. The combined application of careful petrological investigation and thermodynamic modelling is the key to identify the influence of aqueous fluids, and exploit systems that became open not only to fluid influx but also to the extraction of melt.
Palabras clave:
Famatinian Orogen
,
Migmatite
,
Nw Argentina
,
Thermocalc
Archivos asociados
Licencia
Identificadores
Colecciones
Articulos(IBIGEO)
Articulos de INST.DE BIO Y GEOCIENCIAS DEL NOA
Articulos de INST.DE BIO Y GEOCIENCIAS DEL NOA
Articulos(INENCO)
Articulos de INST.DE INVEST.EN ENERGIA NO CONVENCIONAL
Articulos de INST.DE INVEST.EN ENERGIA NO CONVENCIONAL
Articulos(SEDE CENTRAL)
Articulos de SEDE CENTRAL
Articulos de SEDE CENTRAL
Citación
Sola, Alfonso Manuel; Hasalová, Pavlina; Ferrez Weinberg, Roberto; Suzaño, Nestor Omar; Becchio, Raul Alberto; et al.; Low- P melting of metapelitic rocks and the role of H 2 O: Insights from phase equilibria modelling; Wiley Blackwell Publishing, Inc; Journal Of Metamorphic Geology; 00; 10-2017; 1-29
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