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(Reference retrieved automatically from Web of Science through information on FAPESP grant and its corresponding number as mentioned in the publication by the authors.)

Changes in the composition of anatectic melt and its complementary residue by forward-modelling using THERMOCALC

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Author(s):
Pavan, Mauricio [1, 2, 3] ; Moraes, Renato [1] ; Sawyer, Edward [3]
Total Authors: 3
Affiliation:
[1] Univ Sao Paulo, Inst Geociencias, Rua Lago 562, BR-05508080 Sao Paulo, SP - Brazil
[2] CPRM Geol Survey Brazil, Rua Costa 55, BR-01304010 Sao Paulo, SP - Brazil
[3] UQAC Univ Quebec Chicoutimi, 555 Blvd Univ, Chicoutimi, PQ G7H 2B1 - Canada
Total Affiliations: 3
Document type: Journal article
Source: LITHOS; v. 396, SEP 2021.
Web of Science Citations: 0
Abstract

This paper presents results from forward modelling of graywacke and shale average bulk compositions assuming closed-system and open-system partial melting processes. For each process, several compositions of anatectic melt and corresponding solid residue are calculated, and the results compared in binary, ternary and normative diagrams to evaluate how their compositions evolve during an isobaric heating path. Melt compositions are peraluminous, with A/CNK increasing from 1.05 to 1.45, as P and T decrease. The mg\# ranges from 0.22 to 0.39, increasing with consumption of biotite and other Fe-Mg phases by melting reactions as T rises. On FeO + MgO, CaO + Na2O, K2O ternary, K2O vs. Na2O binary and chemical normative diagrams, compositions display trends with an increase in the K2O content of melt as T rises, and an increase in FeO + MgO content after the complete consumption of biotite. An increase in orthoclase component along the heating path, followed by an increase in the proportion of quartz component after K-feldspar/plagioclase breakdown is illustrated on mesonorm diagrams. Total melt volume produced by graywacke bulk compositions is in the range 33-53 vol% for closed-system and 21-33 vol% for open-system melting. For the shale bulk composition volumes are in the range 50-70 vol% during closed-systemand 30-45 vol% during open-systemmelting. The rate of melt production varies with the type of melting reaction and is between 0.19 and 4.73 vol%degrees C-1 for water-present melting and 0.01-6.82 vol%degrees C-1 for hydrate-breakdown melting. Retrograde metamorphic assemblages can be formed even with the chemical depletion caused by melt extraction, but an external source of water and other components would make the consumption of the high-T assemblages more efficient. The correlation between data from this study and that from melt inclusions and natural leucosomes indicates that the melt compositions calculated via forward modelling are a useful guide in understanding how leucosome compositions and their mineral assemblages evolve. (C) 2021 Elsevier B.V. All rights reserved. (AU)

FAPESP's process: 13/04007-0 - Metamorphism and partial melting in ancient orogens
Grantee:Renato de Moraes
Support Opportunities: Regular Research Grants