Original paper

A clockwise P-T path of anatectic metapelites from Wadi Shiban: implication for crustal evolution in southwestern Yemen

Abu El-Rus, Mohamed A.; Andresen, Arild; Ahmed, Abd-Elmohsen A.; Malek, Abdul-Hamid

Abstract

Microstructural relations and the inferred sequence of mineral reactions indicate that Wadi Shiban metapelites in southwestern Yemen developed in response to continuous P-T changes during a single metamorphic event. The rocks followed a clockwise P-T path involving decompression during cooling. The prograde evolution was characterized by muscovite and biotite volatile phase absent-melting reactions. Retrograde metamorphism involved formation of intergrowths of plagioclase + biotite + quartz ± muscovite or chlorite + plagioclase + quartz + biotite + magnetite on garnet grains in proximity to leucosomes as well as formation of late muscovite after sillimanite, alkali feldspar and garnet. Geothermobarometric calculations indicate 813°C and ∼ 7.5 kbar for the metamorphic peak followed by decompression at ∼ 751°C. The high T/P ratio (>100° C/kbar) inferred for the Wadi Shiban metapelites close to the metamorphic peak suggests an additional heat input, probably due to significant thinning of the mantle lithosphere causing rapid heating of the overlying crust. However, the P-T path indicates that the crust in southwestern Yemen involved initial crustal thickening and burial of the sediments (∼ 22 km deep), followed by rapid tectonic exhumation during cooling to a shallower level (∼ 7 km deep).

Keywords

metapelitescrustal evolutionprograde metamorphismretrograde metamorphismmigmatitesp-t path