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Type: Artigo de periódico
Title: Calcic Amphibole Thermobarometry In Metamorphic And Igneous Rocks: New Calibrations Based On Plagioclase/amphibole Al-si Partitioning And Amphibole/liquid Mg Partitioning
Author: Molina
J. F.; Moreno
J. A.; Castro
A.; Rodriguez
C.; Fershtater
G. B.
Abstract: 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.
Subject: In-hornblende Barometer
Spinel-melt Equilibria
Robust Regression
Empirical Calibration
Rights: embargo
Identifier DOI: 10.1016/j.lithos.2015.06.027
Date Issue: 2015
Appears in Collections:Unicamp - Artigos e Outros Documentos

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