Preferential retrogression of high-P metasediments and the preservation of blueschist to eclogite facies metabasite during exhumation, Diahot terrane, NE New Caledonia

Abstract

High-P metabasites of the Diahot terrane, NE New Caledonia occur as spatially restricted (cm to km-scale) lenses, boudins and layers in psammitic to pelitic metasediments. Although interlayered, the two rock types preserve distinct, tectonically disrupted metamorphic profiles in the transition from lawsonite blueschist in the SW to low-T eclogite in the NE. As the metabasites experienced comparatively low strain, igneous textures, and, more rarely, igneous minerals are preserved. Metamorphic assemblages in the metabasites range from lawsonite-omphacite-glaucophane-bearing assemblages (Zone 1; P=7-10 kbar, T=350-400 °C) in the SW, through clinozoisite-almandine-bearing assemblages (Zone 2; P=..