New Caledonia Obducted Peridotite Nappe: Offshore Extent and Implications for Obduction and Postobduction Processes

摘要

One of the largest ophiolitic peridotite masses in the world covers a quarter of the island of Grande Terre, New Caledonia. The Peridotite Nappe was obducted during the Eocene, is weakly deformed, and corresponds to the highest of a structurally simple pile of thrust nappes. We present new marine seismic data that allow us to track the offshore continuation of the Peridotite Nappe along strike for a distance of more than 500 km south of New Caledonia and to image its preobduction, synobduction, and postobduction sedimentary records. Offshore, the Peridotite Nappe underlies a similar to 150 km wide and 2 km deep basin. Flat-topped horsts of peridotite are clearly bounded by major normal faults; in contrast, faults are obscure onland. To the east, the Peridotite Nappe roots along the eastern margin of the Felicite Ridge (new name), a similar to 300 x 25 km dome-shaped ridge, which we interpret as being the southern extension of the high-pressure/low-temperature metamorphic core complex observed in New Caledonia. Two alternative tectonic models address the relative timing and relationships between Peridotite Nappe emplacement, uplift of a metamorphic core complex, and extensional tectonics. These models provide new ideas for the understanding the formation of the eastern margin of the Zealandia continent. Our results contribute to an understanding of how oceanic mantle is emplaced onto continental margins.