Calcic amphibole thermobarometry in metamorphic and igneous rocks: New calibrations based on plagioclase/amphibole Al-Si partitioning and amphibole/liquid Mg partitioning

Autor(es)

Molina, J. F. ^[1] ; Moreno, J. A. ^{[1, 2]} ; Castro, A. ^[3] ; Rodriguez, C. ^[3] ; Fershtater, G. B. ^[4]

Afiliação do(s) autor(es)

^[1] Univ Granada, Dept Mineral & Petrol, Granada 18002 - Spain

^[2] Univ Estadual Campinas, UNICAMP, Inst Geosci, Dept Geol & Nat Resources, BR-13083970 Campinas, SP - Brazil

^[3] Univ Huelva, CSIC, Fac Ciencias Expt, UA Petrol Expt, Huelva 21071 - Spain

^[4] IGG Russian Acad Sci, Ekaterinburg - Russia

• Tipo de documento: Artigo Científico
• Fonte: LITHOS; v. 232, p. 286-305, SEP 1 2015.
• Citações Web of Science: 38

Resumo

Dependencies of plagioclase/amphibole Al-Si partitioning, D-Al/si(plg/amp), ancramphibole/liquid Mg partitioning, D-Al/si(plg/amp), on temperature, pressure and phase compositions are investigated employing robust regression methods based on MM-estimators. A database with 92 amphibole-plagioclase pairs - temperature range: 650-1050 degrees C amphibole compositional limits: >0.02 apfu (230) Ti and >0.05 apfu Al - and 148 amphibole-glass pairs - temperature range: 800-1100 C; amphibole compositional limit: CaM4/(CaM4 + NaM4)> 0.75 - compiled from experiments in the literature was used for the calculations (amphibole normalization scheme: 13-CNK method). Statistical analysis reveals a significant dependence of D-Al/s(plg/amp) on pressure, temperature, Al fraction in amphibole T1 -site, X-Al(Tl), and albite fraction in plagioclase, X-Ab, leading to the barometric expression: P(kbar) = (8.3144 T(K) InDDAl/siplg/amp -8.7 T(K) + 23377 X-Al(Tl) + 7579X(Ab) - 11302) / - 274) (precision: +/- 1.5 to 2.3 kbar; expressed at 1 s). The D-Al/si(plg/amp) was found to have a significant dependence on temperature and the logarithm of X-ca(liq) + X-Al(liq)) ratio (glass composition expressed as anhydrous mole fraction of cation components) that led to the thermometer: T(degrees C) = 71975-11896 In{[}X-ca(liq)(X-ca(liq) + X-Al(liq))]/8.3144 InDMgamP/liq + 58 - 273 (precision: +/- 35 to +/- 45 degrees C). Amphibole-liquid compositional relationships revealed that the temperature dependence of D(Mg)(amP/liq)was mostly controlled by a positive correlation of X-Mg(liq) with temperature that led to the thermometer: T(degrees C) = 107 InXMGliq - 108 In{[}X-ca(liq)/(X-ca(liq) + X-Al(liq)] + 1184 (precision: +/- 37 to +/- 42 degrees C). The plagioclase-amphibole barometer is suitable for a large diversity of amphibole-plagioclase-bearing assemblages from metamorphic (amphibolites and mafic granulites) and igneous (metaluminous granitoids to gabbros) rocks, whereas the liquid-only and the amphibole-liquid thermometers are applicable to alkaline and suballcaline igneous rocks. The calibrated expressions yield P-T estimates consistent with those obtained with widely used barometers and thermometers. Plagioclase-amphibole barometry extends pressure determinations to quartz-free and/or garnetfree assemblages. (C) 2015 Elsevier B.V. All rights reserved. (AU)

• Processo FAPESP: 14/04920-0 - Investigações geológicas e geoquímicas em terrenos granito-gnaisses arqueanos do Cráton São Francisco
• Beneficiário: Juan Antonio Moreno Moreno
• Modalidade de apoio: Bolsas no Brasil - Pós-Doutorado