P-T-t Evolution of Ultrahigh-Temperature Granulites from the Saxon Granulite Massif, Germany. Part I: Petrology |
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Authors: | ROTZLER JOCHEN; ROMER ROLF L |
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Institution: | 1INSTITUT FÜR GEOWISSENSCHAFTEN, UNIVERSITÄT POTSDAM, POSTFACH 60 15 53, 14415 POTSDAM, GERMANY
2GEOFORSCHUNGSZENTRUM POTSDAM, TELEGRAFENBERG, 14473 POTSDAM, GERMANY |
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Abstract: | The granulites of the Saxon Granulite Massif equilibrated athigh pressure and ultrahigh temperature and were exhumed inlarge part under near-isothermal decompression. This raisesthe question of whether PTt data on the peak metamorphismmay still be retrieved with confidence. Felsic and mafic granuliteswith geochronologically useful major and accessory phases haveprovided a basis to relate PT estimates with isotopicages presented in a companion paper. The assemblage garnet +clinopyroxene in mafic granulite records peak temperatures of10101060°C, consistent with minimum estimates ofaround 967°C and 22·3 kbar obtained from the assemblagegarnet + kyanite + ternary feldspar + quartz in felsic granulite.Multiple partial overprint of these assemblages reflects a clockwisePT evolution. Garnet and kyanite in the felsic granulitewere successively overgrown by plagioclase, spinel + plagioclase,sapphirine + plagioclase, and biotite + plagioclase. Most ofthis overprinting occurred within the stability field of sillimanite.Garnet + clinopyroxene in the mafic granulite were replacedby clinopyroxene + amphibole + plagioclase + magnetite. Thehigh PT conditions and the absence of thermal relaxationfeatures in these granulites require a short-lived metamorphismwith rapid exhumation. The ages of peak metamorphism (342 Ma)and shallow-level granitoid intrusions (333 Ma) constrain thetime span for the exhumation of the Saxon granulites to |
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