Low-pressure isobaric cooling metamorphic P-T paths from Botnnuten in the southern Lutzow-Holm Complex, East Antarctica

This paper reports the metamorphic texture of cordierite megacrysts and the metamorphic P-T path of a newly exposed section of gneiss in East Antarctica. We used mineral textures and pseudosection modeling to reconstruct the metamorphic P-T path of cordierite- and spinel-garnet-bearing gneisses from Botnnuten, an isolated nunatak located similar to 60 km from the southern edge of Lutzow-Holm Bay in East Antarctica. The gneisses underwent low-P granulite-facies metamorphism at 5.0-6.1 kbar and 850 +/- 20 degrees C followed by isobaric cooling. The isobaric cooling path implies long residence in the middle to shallow crustal level without rapid exhumation. This contrasts with the widely recognized clockwise P-T path of basement rocks of the Lutzow-Holm Complex. The rocks at Botnnuten have long been considered part of the Lutzow-Holm Complex based on their petrographical features and geothermobarometric data. However, the present results, combined with a reevaluation of available data, indicate the metamorphic history of the Botnnuten gneisses is more comparable to that of the Yamato Mountains, located southwest of the study area.