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Passive obduction and gravity-driven emplacement of large ophiolitic sheets; the New Caledonia Ophiolite (SW Pacific) as a case study?

Yves Lagabrielle, Alain Chauvet, Marc Ulrich and Stephane Guillot
Passive obduction and gravity-driven emplacement of large ophiolitic sheets; the New Caledonia Ophiolite (SW Pacific) as a case study?
Bulletin de la Societe Geologique de France (June 2013) 184 (6): 545-556

Abstract

The 300 km long allochthonous sheet of oceanic mantle forming the New Caledonia ophiolite displays three specific characters: 1) the ophiolite pile lacks concordant sheeted dykes and pillow basalt layers; 2) the ophiolite, referred to as the Peridotite nappe, is thrusted over the basaltic formations of the Poya terrane which are classically thought to originate from a different oceanic environment; 3) The basal contact of the ultramafic sheet is remarkably flat all along New-Caledonia and the Peridotite nappe has not been thickened during obduction, rather it experienced significant extension. This suggests that the peridotites have not been emplaced by a tectonic force applied to the rear. New petrological and geochemical results obtained from mantle rocks finally show that the Poya terrane may originate from the same oceanic basin as the peridotites. In this article, we consider such possible cogenetic links and we propose a simple model for the obduction of the New Caledonia ophiolite in which the Poya basalts represent the original cover of the Peridotite nappe. We infer that continuous uplift of the subducted units buried beneath the oceanic lithosphere in the northern part of New Caledonia drove passive uplift of the ophiolite and led to erosion and to initiation of sliding of the basaltic layer. During the Priabonian (latest Eocene), products of the erosion of the basaltic layer were deposited together with sediments derived from the Norfolk passive oceanic margin. These sediments are involved as tectonic slices into an accretionary wedge formed in response to plate convergence. The volcaniclastic sedimentation ends up with the emplacement of large slided blocks of basalts and rafted mafic units that progressively filled up the basin. Obduction process ended with the gravity sliding of the oceanic mantle sheet, previously scalped from its mafic cover. This process is contemporaneous with the exhumation of the HP-LT units of Pouebo and Diahot. Gravity sliding was facilitated by the occurrence of a continuous serpentine sole resulting from metasomatic hydration of mantle rocks, which developed during the uplift of the Norfolk basement and overlying Diahot and Pouebo units. Progressive emersion of the obducted lithosphere allowed subsequent weathering under subaerial, tropical conditions.


ISSN: 0037-9409
EISSN: 1777-5817
Coden: BSGFAE
Serial Title: Bulletin de la Societe Geologique de France
Serial Volume: 184
Serial Issue: 6
Title: Passive obduction and gravity-driven emplacement of large ophiolitic sheets; the New Caledonia Ophiolite (SW Pacific) as a case study?
Affiliation: Universite Montpellier 2, Geosciences Montpellier, Montpellier, France
Pages: 545-556
Published: 201306
Text Language: English
Summary Language: French
Publisher: Societe Geologique de France, Paris, France
References: 73
Accession Number: 2014-004155
Categories: Igneous and metamorphic petrologySolid-earth geophysics
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. sects., geol. sketch maps
S22°30'00" - S20°00'00", E164°00'00" - E167°00'00"
Secondary Affiliation: Universite Grenoble 1, FRA, France
Country of Publication: France
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, Copyright, Societe Geologique de France. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201404
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