HR: 0800h
AN: V41C-0722    [Abstracts]
TI: First Discovery of Eclogite in West Papua (Wandamen Peninsula)
AU: * de Sigoyer, J
EM: sigoyer@geologie.ens.fr
AF: Ecole Normale Superieure, 24 rue Lhomond, Paris, 75005, France
AU: Pubellier, M
EM: manu_pub@geologie.ens.fr
AF: Ecole Normale Superieure, 24 rue Lhomond, Paris, 75005, France
AU: Bailly, V
EM: bailly@geologie.ens.fr
AF: Ecole Normale Superieure, 24 rue Lhomond, Paris, 75005, France
AU: Rigenbach, J
EM: Jean-Claude.RINGENBACH@total.com
AF: Total SA, Tour Coupole, Paris La Defense, 92078, France
AB: Exceptional boulders of fresh eclogites and large garnets (up to 10 cm) were discovered in schist in the Wandamen peninsula (West Papua) The eclogites are located in a context of very active oblique convergence between the Pacific plate and the Australian plate. The Wandamen peninsula is located in the Cenderawasih bay (West Papua). An EW metamorphic gradient is observed from the western unmetamorphosed Lengguru sedimentary prism to the Wandamen peninsula. The metamorphic Wandamen peninsula may therefore represent the inner part of the Lengguru belt, and may also be in the continuation of the inner part of the Central range of Papua New Guinea farther east. The eclogite occurs as centimetric lenses within garnet bearing metasedimentary rocks. Sediments look like the Cenozoic sediments of the internal zone of the Lengguru FTB. The eclogites are medium to coarse grained. The eclogitic paragenesis consists of clinopyroxenes, garnets, amphiboles, rutiles, quartz and accessory minerals like apatites. Clinopyroxenes have omphacitic composition, they are poecilitic, and very fresh as rare textures of retrogression (symplectite) are observed. Garnets are micrometric to centimetric. They present atoll shapes, with a core often filled by slightly green amphibole, or by quartz. They contain minute inclusions of omphacite, amphibole, apatite, quartz. Many rutiles exsolutions are observed within the garnets, suggesting high metamorphic conditions. Inclusions of quartz in the garnet or in the omphacite are surrounded by many fractures suggesting the previous occurrence of coesite. The sodic calcic greenish amphiboles and rutiles are also important minerals of these eclogites. Migmatites and resulting leucogranite cross cut the eclogite indicating a later HT event. The leucogranite is rich in tourmaline and muscovite that suggest their anatectic origin (melting of the black micashists metamorphosed under migmatitic conditions). Miocene pebbles were found within an unmetamorphosed conglomerate (no metamorphic or magmatic pebbles were in the conglomerate) that overlies the eastern flank of the Wandamen massif suggesting that exhumation of eclogite was active after Miocene.
DE: 3651 Thermobarometry
DE: 3656 Ultra-high temperature metamorphism
DE: 3660 Metamorphic petrology
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting