Origin of the New Caledonian ophiolites based on a French–Australian Seismic Transect

120 to 0 Ma tectonic evolution of the southwest Pacific and analogous geological evolution of the 600 to 220 Ma Tasman Fold Belt System

“…In contrast, Dubois et al (1973) and Collot et al (1987) argued that the South Loyalty Basin formed as a marginal basin prior to 80 Ma above an east-dipping subduction zone, with a trench west of New Caledonia, implying subduction of oceanic crust of the New Caledonia Basin. New seismic interpretations of South Loyalty Basin sediment fill from the southern part of the basin away from the zone of Eocene emplacement of the New Caledonia ophiolite suggest that the South Loyalty Basin formed by extension and later ocean crust accretion around 120 Ma in the Early Cretaceous (Auzende et al 2000), perhaps contemporaneous with the opening of the New Caledonia Basin. Cretaceous oceanic crust in the South Loyalty Basin is also demanded by the model of Sdrolias et al (2002).…”

“…However, there is abundant evidence that commencing around 130-120 Ma, the continental crust of the eastern part of Gondwana passed into a long-lived episode of extension and eventual rifting. This led to fragmentation of continental crust broadly parallel with the present eastern coast of Australia, to form three subparallel marginal basins-from west to east, the Tasman Sea, the New Caledonia Basin and the Loyalty Basin (Symonds et al 1996;Auzende et al 2000;Müller et al 2000)-and two elongate microcontinental ribbons, the Lord Howe Rise and the New Caledonia-Norfolk Ridge (Figure 2). The first sign of eventual rifting and ocean opening was the development of a 2500 km-long continental rift along the eastern margin of Australia mainly between 120 and 95 Ma, characterised by immense volumes of largely felsic magmas (Bryan et al 1997).…”

“…There is no evidence in the Poya Terrane for extensionrelated volcanic rocks as old as the 120 Ma sequences identified seismically in the offshore South Loyalty Basin by Auzende et al (2000). There are several possible reasons for this: (i) it is possible that seismic correlations with sequences west of and on New Caledonia are incorrect or inapplicable; (ii) the Early to Middle Cretaceous sedimentary packages identified seismically in the South Loyalty (Malpas et al 1992;Mortimer et al 1998;Nicholson et al 2000).…”

“…Exhumation and tectonic denudation of these highpressure rocks (Figure 3b) occurred in response to post-collisional extension and development of large detachment faults (Rawling & Lister 2000). Sediments produced during this unroofing process and accumulated in basins on either side of New Caledonia are 1-1.5 s (TWT) thick (Auzende et al 2000). Below them, an erosional break between Middle Eocene, and Late Eocene to Late Oligocene strata reflects emplacement of the ophiolite.…”

Collisional model for rapid fore‐arc block rotations, arc curvature, and episodic back‐arc rifting in subduction settings

“…The opening history of the North Loyalty Basin ($44-35 Ma ago) and its fan shape in map view is consistent with anticlockwise rotational opening about a nearby pole of rotation . Baldwin et al [2007] suggested that both the North Loyalty basin opening and exhumation of blueschist facies rocks in New Caledonia ($44-34 Ma ago) occurred via rapid microplate rotation triggered by a collision that culminated in Late Eocene ophiolite obduction in southern New Caledonia [Aitchison et al, 1995;Auzende et al, 2000;Cluzel et al, 2001]. At the paleosubduction zone, there was also a transition from collision of the Norfolk Rise (starting in the early Eocene [Eade, 1988]) to subduction of normal oceanic crust of the New Caledonia Basin further north.…”