Eclogites and blueschists of the Pam Peninsula, NE New Caledonia: A reappraisal

Abstract

High-P rocks of the Pam Peninsula, NE New Caledonia, are divided into three zones: (1) an uppermost ferroglaucophane-lawsonite zone of Cretaceous to Eocene metasediments and metavolcanics of the Diahot terrane that experienced peak conditions involving P=7-9 kbar and T=400±58°C; (2) albite-epidote-omphacite zone Diahot terrane rocks that experienced blueschist facies conditions of P=12·6±1·2 kbar and T=570±36°C; (3) lowermost metabasic eclogites of uncertain age that form the Pouébo terrane, which experienced high-P conditions of P=23·9±3·0 kbar and T∼600°C. Eclogite occurs as metre- to kilometre-scale pods in coarse grained hydrous mineral-rich 'glaucophanite' formed during hydration and decompression of the Pouébo terrane. Metamorphism and deformation were consequent to 44-51 Ma Eocene convergence, when sedimentary and ophiolitic nappes were thrust over the eclogites in a SW direction; white mica ages constrain metamorphism to have ended by 37±1 Ma. Large steps in metamorphic grade are coincident with SW-dipping and NE-dipping faults that separate the three zones and were formed during two stages: (1) comparatively slow uplift and hydration of the Pouébo terrane before it was juxtaposed with the albite-epidote-omphacite zone at P∼14 kbar; (2) comparatively rapid uplift of both the Pouébo terrane and the albite-epidote-omphacite zone to form a domal core of eclogite flanked by significantly lower-grade rocks to the SW and NE.