Constraints from P-T pseudosections （MnNCKFMASH system）, foliation intersection/ inflection axes preserved in porphyroblasts （FIAs）, mineral assemblages and textural relationships for rocks containing all three Al...Constraints from P-T pseudosections （MnNCKFMASH system）, foliation intersection/ inflection axes preserved in porphyroblasts （FIAs）, mineral assemblages and textural relationships for rocks containing all three Al2 SiO5 polymorphs indicate a kyanite→ andalusite→ sillimanite sequential formation at different times rather than stable coexistence at the Al2SiO5 triple point. All three Al2SiO5 polymorphs grew in the Chl, Bt, Ms, Grt, St, Pl and Crd bearing Ordovician Clayhole Schist in Balcooma, northeastern Australia separately along a looped P-T-t-D path that swaps from clockwise to anticlockwise in the tectono-metamorphic history of the region. Kyanite grew during crustal thickening in an Early Silurian Orogenic event followed by decompression/heating, andalusite and fibrolitic sillimanite growth during Early Devonian exhumation.展开更多
The garnet-muscovite geothermometer and garnet-muscovite-Al2SiO5 -quartz （GMAQ） geobarometer have been empirically calibrated under P-T conditions of 1-12 kbar and 460-760 ℃ using natural metapelitic rocks. The che...The garnet-muscovite geothermometer and garnet-muscovite-Al2SiO5 -quartz （GMAQ） geobarometer have been empirically calibrated under P-T conditions of 1-12 kbar and 460-760 ℃ using natural metapelitic rocks. The chemical compositions of the calibrant muscovite are in the ranges of Fe=0.03-0.21 atoms, Mg=0.02-0.32 atoms and AI VI=1.62-1.96 atoms, respectively, on the ll-oxygen basis per formula unit. The garnet-muscovite thermometer yields similar temperature estimates to the well calibrated garnet-biotite thermometer within error of 4-55 ℃, and successfully discriminates the systematic temperature change of the different zones of either the prograde or inverted metamorphic terranes or thermal contact aureoles. The six formulations of GMAQ barometry yield similar pressure estimates to the well calibrated GASP barometer within error of ±1.2 kbar, and plot the Al2SiOs-bearing metapelite into the correct stability field of the AI2SiOs polymorphs. Moreover, the GMAQ thermobarometers show that the pressure is almost constant for every thermal contact aureole within limited geographic region, which reflects geological condition. The random errors are estimated to be of ca. 4-60 ℃ and 4-1.4 kbar for the geothermometer and geobarometer, respectively. A spreadsheet for applying GMAQ geothermo- barometry is supplied in the Electronic Supplementary Materials.展开更多
文摘Constraints from P-T pseudosections （MnNCKFMASH system）, foliation intersection/ inflection axes preserved in porphyroblasts （FIAs）, mineral assemblages and textural relationships for rocks containing all three Al2 SiO5 polymorphs indicate a kyanite→ andalusite→ sillimanite sequential formation at different times rather than stable coexistence at the Al2SiO5 triple point. All three Al2SiO5 polymorphs grew in the Chl, Bt, Ms, Grt, St, Pl and Crd bearing Ordovician Clayhole Schist in Balcooma, northeastern Australia separately along a looped P-T-t-D path that swaps from clockwise to anticlockwise in the tectono-metamorphic history of the region. Kyanite grew during crustal thickening in an Early Silurian Orogenic event followed by decompression/heating, andalusite and fibrolitic sillimanite growth during Early Devonian exhumation.
基金supported by the Key Research Program of Frontier Sciences of Chinese Academy of Sciences (No. QYZDJ-SSW-DQC036)the National Natural Science Foundation of China (No. 41730215)
文摘The garnet-muscovite geothermometer and garnet-muscovite-Al2SiO5 -quartz （GMAQ） geobarometer have been empirically calibrated under P-T conditions of 1-12 kbar and 460-760 ℃ using natural metapelitic rocks. The chemical compositions of the calibrant muscovite are in the ranges of Fe=0.03-0.21 atoms, Mg=0.02-0.32 atoms and AI VI=1.62-1.96 atoms, respectively, on the ll-oxygen basis per formula unit. The garnet-muscovite thermometer yields similar temperature estimates to the well calibrated garnet-biotite thermometer within error of 4-55 ℃, and successfully discriminates the systematic temperature change of the different zones of either the prograde or inverted metamorphic terranes or thermal contact aureoles. The six formulations of GMAQ barometry yield similar pressure estimates to the well calibrated GASP barometer within error of ±1.2 kbar, and plot the Al2SiOs-bearing metapelite into the correct stability field of the AI2SiOs polymorphs. Moreover, the GMAQ thermobarometers show that the pressure is almost constant for every thermal contact aureole within limited geographic region, which reflects geological condition. The random errors are estimated to be of ca. 4-60 ℃ and 4-1.4 kbar for the geothermometer and geobarometer, respectively. A spreadsheet for applying GMAQ geothermo- barometry is supplied in the Electronic Supplementary Materials.
