Growth of chloritoid and garnet along a nearly isothermal burial path to 70 km depth: an example from the Bughea Metamorphic Complex, Leaota Massif, South Carpathians

摘要

Chloritoid-bearing micaschist occurs in the matrix of a subduction m,lange (Bughea Complex) of the Leaota Massif (South Carpathians) containing blocks of high-pressure rocks such as eclogite and metagabbronorite. Chloritoid is Mg rich and exclusively enclosed together with chlorite, epidote, paragonite, phengite, quartz, and rutile in mm-sized garnet porphyroblasts embedded in a matrix rich in white mica and chlorite. The Mg content of chloritoid inclusions systematically increases outwards from the inner core of garnet porphyroblasts. Modelling using a pressure (P) - temperature (T) pseudosection predicts the growth of chloritoid together with garnet at the expense of chlorite and other Al-rich phases, while following a nearly isothermal P-T path from 13 kbar and 540 A degrees C to 21 kbar and 560 A degrees C. Breakdown of chloritoid occurred along a P-T path characterised by heating and decompression to 600 A degrees C and 15 kbar. The constrained P-T path is compatible with previously determined ones for eclogites in the Bughea Complex, namely burial in a subduction-accretion complex to depths of 70 km, detachment from the subducting slab, tectonic mixing with blocks sampled from different depths, and, thus, exhumation in a subduction channel.