Rheological behavior of high temperature garnet-bearing migmatites: The Khondalite Belt example (North China Craton)

The contribution presents microstructural and petrological results obtained on garnet-bearing felsic migmatites from the Khondalite Belt (North China Craton). The study focused on low-melt fraction felsic migmatites in which peritectic garnet are strongly elongated and show plastic deformation. These peritectic garnet grains show different typology depending on their petrographic location within the layered migmatite. An elongated shaped garnet with sillimanite and biotite inclusion lies within Al-rich layer whereas poecilithic garnets are located within S-rich layers, forming a garnet-quartz aggregate. The study presents petrological, microstructural observation and EBSD analyses of the garnet grains and garnet-quartz aggregates. Phase diagram sections modeling allows to constrain the P-T conditions of the deformation at 850-1000 degrees C and 0.6-1.1 GPa. At such high-to ultra-high temperature conditions, a low melt fraction was produced, between 1 and 12% (generally under 7%). Forescattered diffraction and misorientation maps with Orientation Pole Figure argue for dislocation creep with development of subgrains in garnets. Our results suggest that at high-to ultra-high temperature, the quartz-feldspar-garnet solid framework of felsic migmatites strongly accommodate the deformation and contribute to weakening of migmatite even at low melt fraction.