Prograde P-T path of kyanite eclogites from Junan in the Sulu ultrahigh-pressure province, eastern China

Kyanite-bearing ultrahigh-pressure (UHP) eclogites occur as blocks in ortho gneisses at Yangzhuang, in the Junan area of the southwestern Sulu province , eastern China. Eclogites have variable bulk rock compositions, with Al2O3 = 16-27 wt%, FeO* + MgO = 6-22 wt% and CaO = 9-13 wt%. Major minerals are garnet, omphacite, phengitic white mica, zoisite, kyanite, I utile and an S iO2 phase. Fe-rich staurolite (Mg => Mg# = 0.24 +/- 0.01) and paragonite-ma rgarite aggregates are rarely included in the cores of prograde zoned garne t. Metamorphic conditions ranged fi om 520 to 650 degrees C and <1.4 GPa at an early prograde stage, and mostly reached 660-830 degrees C and 2.7-3.5 GPa at the peak UHP stage. The estimated dP/dT of the prograde P-T path is less than 0.25 GPa/100 degrees C at earlier stages and increases to 0.7-1.4 GPa/100 degrees C just before the UHP stage. The kink of the prograde P-T path closely resembles the steady-state P-T paths proposed, assuming a two- parameter brittle-plastic shear str ess model. The estimated P-T path adequ ately explains the absence of prograde lawsonite and sodic amphibole and th e common occurrence of coexisting zoisite, kyanite and sodic-calcic amphibo le in the UHP eclogites throughout the Sulu province. Simple clockwise prog rade P-T paths for Sulu UHP eclogites proposed in earlier studies should be carefully re-examined.