PTt path of the Boroujerd Complex, northwest Sanandaj?Sirjan Zone, western Iran: Insights from phase equilibrium modelling and thermobarometry

RAHMANI JAVANMARD, SOMAYEH; SEBASTIÁN OSVALDO VERDECCHIA; YAKYMCHUK, CHRIS; BROEKMANS MAARTEN A.T.M.

GEOLOGICAL JOURNAL (CHICHESTER)

JOHN WILEY & SONS LTD

Lugar: LOndres; Año: 2021 vol. 56 p. 3396 - 3414

0072-1050

Variations in the pressures and temperatures of metamorphism reflect the complexity of collisional orogenic systems. In the northwest Sanandaj-Sirjan Zone of western Iran, migmatites in the Boroujerd area record earlier dynamothermal metamorphism followed by the development of a contact metamorphic aureole induced by the Jurassic Boroujerd Batholith. Integrated micro-textural observations, mineral compositions and the results of phase equilibrium modelling indicate that peak metamorphic temperatures reached 640?660°C in andalusite schists and ~700ºC in cordierite-sillimanite migmatites. The pressure does not exceed 3.5 kbar implying a maximum depth of ~13 km. A hairpin clockwise P?T path in the Boroujerd region was inferred from mineral relations (e.g., replacement of andalusite1 by sillimanite in the migmatites in the heating stage, which was followed by a retrograde episode with growth of andalusite2) and P?T pseudosections. Metamorphism of the Boroujerd area was coeval with voluminous intermediate?mafic magmatism, which provided the heat necessary for partial melting. This study demonstrates that metamorphic sequences of the northwest Sanandaj-Sirjan Zone developed under similar metamorphic conditions in the Lower to Middle Jurassic and record an extensional back-arc setting related to the subduction of Neo-Tethys.