Lawsonite-Omphacite-Bearing Metabasites of the Pam Peninsula, NE New Caledonia: Evidence for Disrupted Blueschist- to Eclogite-Facies Conditions |
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Authors: | FITZHERBERT J A; CLARKE G L; POWELL R |
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Institution: | 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 |
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Abstract: | The Diahot terrane of NE New Caledonia contains an interbeddedsequence of Cretaceous to Eocene metasediments, felsic and maficmetavolcanics that experienced c. 40 Ma high-P/T metamorphism.Metabasaltic assemblages define two prograde events (M1 andM2) and a tectonically disrupted crustal profile that extendsfrom lawsoniteblueschist conditions in the SW to paragoniteeclogiteconditions in the NE. Weakly deformed metabasalts from lowest-gradeparts of the Diahot terrane contain M1 omphacite, chlorite,lawsonite and glaucophane-bearing assemblages that partiallypseudomorph 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 foliationthat becomes progressively more intense towards the NE overa distance of c. 15 km. S2 assemblages are divided into fourzones: (1) lawsoniteomphacite; (2) lawsoniteclinozoisitespessartine;(3) clinozoisitehornblendealmandine; (4) almandineomphacite.S2 assemblages reflect a PT gradient that spans the exposed15 km of the Diahot terrane from P = 0·81·0GPa and T = 350400°C (Zone 1) to P = 1·61·7GPa and T = 550600°C (Zone 4). The systematic mineralogicalchanges reflect parts of a PT array between 1·0and 1·7 GPa that was extensively disrupted by tectonicthinning during exhumation. KEY WORDS: blueschist; eclogite; New Caledonia; CNFMASH; pseudosection |
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