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Journal of Petrology | Volume 44 | Number 10 | Pages 1805-1831 | 2003
© Oxford University Press 2003; all rights reserved
LawsoniteOmphacite-Bearing Metabasites of the Pam Peninsula, NE New Caledonia: Evidence for Disrupted Blueschist- to Eclogite-Facies Conditions
1 SCHOOL OF GEOSCIENCES, THE UNIVERSITY OF SYDNEY, SYDNEY, NSW 2006, AUSTRALIA
2 SCHOOL OF EARTH SCIENCES, THE UNIVERSITY OF MELBOURNE, MELBOURNE, VIC., AUSTRALIA, 3052
* Corresponding author. E-mail: joel{at}es.usyd.edu.au
The Diahot terrane of NE New Caledonia contains an interbedded sequence of Cretaceous to Eocene metasediments, felsic and mafic metavolcanics that experienced c. 40 Ma high-P/T metamorphism. Metabasaltic assemblages define two prograde events (M1 and M2) and a tectonically disrupted crustal profile that extends from lawsoniteblueschist conditions in the SW to paragoniteeclogite conditions in the NE. Weakly deformed metabasalts from lowest-grade parts of the Diahot terrane contain M1 omphacite, chlorite, lawsonite and glaucophane-bearing assemblages that partially pseudomorph igneous plagioclase and augite, and reflect P = 0·71·0 GPa and T = 350400°C. M1 assemblages are enveloped by a steeply SW-dipping S2 foliation that becomes progressively more intense towards the NE over a distance of c. 15 km. S2 assemblages are divided into four zones: (1) lawsoniteomphacite; (2) lawsoniteclinozoisitespessartine; (3) clinozoisitehornblendealmandine; (4) almandineomphacite. S2 assemblages reflect a PT gradient that spans the exposed 15 km of the Diahot terrane from P = 0·81·0 GPa and T = 350400°C (Zone 1) to P = 1·61·7 GPa and T = 550600°C (Zone 4). The systematic mineralogical changes reflect parts of a PT array between 1·0 and 1·7 GPa that was extensively disrupted by tectonic thinning during exhumation.
KEY WORDS: blueschist; eclogite; New Caledonia; CNFMASH; pseudosection
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