U–Pb zircon dating of post-obduction volcanic-arc granitoids and a granulite-facies xenolith from New Caledonia. Inference on Southwest Pacific geodynamic models |
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Authors: | Jean-Louis Paquette Dominique Cluzel |
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Affiliation: | (1) Laboratoire Magmas et Volcans UMR 6524, CNRS and Université B. Pascal, 5 rue Kessler, Clermont-Ferrand Cedex, 63038, France;(2) Institut des Sciences de la Terre d’Orléans, University of Orléans, UMR 6113, Orléans, BP 6759, 45067, France |
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Abstract: | In New Caledonia, the occurrence of one of the World’s largest and best-exposed subduction/obduction complex is a key point for the understanding of the geodynamic evolution of the whole Southwest Pacific region. Within the ophiolite, pre-and post-obduction granitoids intrude the ultramafic allochthon and provide new time constraints for the understanding of obduction processes. At 27.4 Ma, a new East-dipping subduction generated the active margin magmatism along the western coast of the island (Saint-Louis massif). At 24.3 Ma, the eastward shift of the magma activity and slightly different geochemical features (Koum-Borindi massif) was either related to the older slab break-off; or alternatively, due to the eastward migration of the mantle wedge following the collision of the eastern margin of the Low Howe rise. Finally, the occurrence of a granulite-facies xenolith in the Koum-Borindi massif with comparable 24.5 Ma U–Pb zircon age and isotopic features (initial εNd = 5.1) suggests that these evolved magmas were generated within the lithospheric mantle beneath a continental crust of normal thickness. Geochronological evidence for continuous convergence during the Oligocene infers an East-dipping Eocene-Oligocene subduction/obduction system to have existed in the Southwest Pacific from the d’Entrecasteaux zone to the North Island of New Zealand. |
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Keywords: | Granitoid Granulite U– Pb zircon geochronology New Caledonia Active margin Southwest Pacific |
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