TY - JOUR
T1 - Felsite-nanogranite inclusions and three Al 2 SiO 5 polymorphs in the same garnet in ultrahigh-temperature granulites from Rundvågshetta, Lützow-Holm Complex, East Antarctica
AU - Hiroi, Yoshikuni
AU - Hokada, Tomokazu
AU - Kato, Mutsumi
AU - Yanagi, Ayahiko
AU - Adachi, Tatsuro
AU - Osanai, Yasuhito
AU - Motoyoshi, Yoichi
AU - Shiraishi, Kazuyuki
N1 - Funding Information:
We thank many collaborative researchers in Antarctica. We are grateful to S. Harley and T. Kawakami for critical and thoughtful reviews that were helpful in improving the manuscript substantially. We also thank M. Satish–Kumar for editorial handling of this manuscript. Funding for this research was from the Japanese Government (Grant– in–Aid for Scientific Research; JP18K03789 to Y. H.; JP17H02976 to T. H.) and the National Institute of Polar Research (General Collaboration Project no. 29–36), Japan. The publication of this paper was supported by an NIPR publication subsidy.
PY - 2019/4/1
Y1 - 2019/4/1
N2 - Ultrahigh-temperature (UHT) granulites characterized by the parageneses of sapphirine + quartz and orthopyroxene + sillimanite + garnet + quartz are found in Rundvågshetta, Lützow-Holm Complex (LHC), East Antarctica. In this study, we report previously undocumented features of the UHT pelitic granulites, including the presence of felsite-nanogranite inclusions (FNIs), which are interpreted to have formed by the supercooling of melt inclusions in garnet, and the presence of three Al 2 SiO 5 polymorphs within the same garnet porphyroblast. Whereas sillimanite is present as inclusions in garnet and in the matrix, kyanite occurs as inclusions in garnet and andalusite appears in FNIs. Porphyroblastic garnet is compositionally zoned with Mg-rich cores surrounded by Fe- and Mn-rich rims, indicating homogenization and later modification of Fe, Mg, and Mn. Ca contents oscillate from core to rim, which may be a remnant of growth zoning and suggests compression before high- temperature decompression. Integration of these new data with those previously documented leads to the inference of a rapid change in pressure-temperature conditions during regional UHT metamorphism in the late Neoproterozoic to early Paleozoic Gondwana-forming collisional orogen. Locally occurring intimate intergrowths of kyanite/sillimanite + sapphirine + garnet ± quartz in garnet may be a breakdown product of Mg-rich staurolite and thus may be a link between high-pressure and UHT metamorphism.
AB - Ultrahigh-temperature (UHT) granulites characterized by the parageneses of sapphirine + quartz and orthopyroxene + sillimanite + garnet + quartz are found in Rundvågshetta, Lützow-Holm Complex (LHC), East Antarctica. In this study, we report previously undocumented features of the UHT pelitic granulites, including the presence of felsite-nanogranite inclusions (FNIs), which are interpreted to have formed by the supercooling of melt inclusions in garnet, and the presence of three Al 2 SiO 5 polymorphs within the same garnet porphyroblast. Whereas sillimanite is present as inclusions in garnet and in the matrix, kyanite occurs as inclusions in garnet and andalusite appears in FNIs. Porphyroblastic garnet is compositionally zoned with Mg-rich cores surrounded by Fe- and Mn-rich rims, indicating homogenization and later modification of Fe, Mg, and Mn. Ca contents oscillate from core to rim, which may be a remnant of growth zoning and suggests compression before high- temperature decompression. Integration of these new data with those previously documented leads to the inference of a rapid change in pressure-temperature conditions during regional UHT metamorphism in the late Neoproterozoic to early Paleozoic Gondwana-forming collisional orogen. Locally occurring intimate intergrowths of kyanite/sillimanite + sapphirine + garnet ± quartz in garnet may be a breakdown product of Mg-rich staurolite and thus may be a link between high-pressure and UHT metamorphism.
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U2 - 10.2465/jmps.181118
DO - 10.2465/jmps.181118
M3 - Article
AN - SCOPUS:85065616996
VL - 114
SP - 60
EP - 78
JO - Journal of Mineralogical and Petrological Sciences
JF - Journal of Mineralogical and Petrological Sciences
SN - 1345-6296
IS - 2
ER -