Low-pressure melting of metapelitic rocks and the role of H2O: insights from phase equilibria modelling

Kód výsledku v IS VaVaI

<a href="https://www.isvavai.cz/riv?ss=detail&h=RIV%2F00025798%3A_____%2F17%3A00000111" target="_blank" >RIV/00025798:_____/17:00000111 - isvavai.cz</a>

Výsledek na webu

<a href="http://onlinelibrary.wiley.com/doi/10.1111/jmg.12279/full" target="_blank" >http://onlinelibrary.wiley.com/doi/10.1111/jmg.12279/full</a>

DOI - Digital Object Identifier

<a href="http://dx.doi.org/10.1111/jmg.12279" target="_blank" >10.1111/jmg.12279</a>

Jazyk výsledku

angličtina

Název v původním jazyce

Low-pressure melting of metapelitic rocks and the role of H2O: insights from phase equilibria modelling

Popis výsledku v původním jazyce

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 field area exhibits a condensed metamorphic field gradient, from greenschist to amphibolite facies suprasolidus conditions, recording a low-P 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-P 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. 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.

Název v anglickém jazyce

Low-pressure melting of metapelitic rocks and the role of H2O: insights from phase equilibria modelling

Popis výsledku anglicky

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 field area exhibits a condensed metamorphic field gradient, from greenschist to amphibolite facies suprasolidus conditions, recording a low-P 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-P 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. 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.

Druh

J_imp - Článek v periodiku v databázi Web of Science

CEP obor

—

OECD FORD obor

10505 - Geology

Projekt

<a href="/cs/project/GAP210%2F12%2F2205" target="_blank" >GAP210/12/2205: Růst kontintální kůry a konstrukce kontinentu na příkladu Centrálního asijského orogenního pásu</a><br>

Návaznosti

P - Projekt vyzkumu a vyvoje financovany z verejnych zdroju (s odkazem do CEP)

Rok uplatnění

2017

Kód důvěrnosti údajů

S - Úplné a pravdivé údaje o projektu nepodléhají ochraně podle zvláštních právních předpisů

Název periodika

Journal of Metamorphic Geology

ISSN

0263-4929

e-ISSN

—

Svazek periodika

35

Číslo periodika v rámci svazku

9

Stát vydavatele periodika

GB - Spojené království Velké Británie a Severního Irska

Počet stran výsledku

28

Strana od-do

1131–1159

Kód UT WoS článku

000414597400009

EID výsledku v databázi Scopus

2-s2.0-85030470353