Chapter 1 Introduction to New Caledonia: geology, geodynamic evolution and mineral resources

Abstract

This Memoir summarizes our current knowledge of New Caledonia geology, geodynamics and mineral resources based on published and unpublished information. Except for a short paper timed for the 34th International Geological Congress (Cluzel et al. 2012b), there has been no review of the geology of New Caledonia since Paris (1981)that is, for more than 35 years. As such, it is timely that this Memoir is published.This Memoir comprises a collection of ten self-contained chapters written by 28 researchers from New Caledonia, France, New Zealand, Australia and Papua New Guinea. This work is not simply a summation of the factual material acquired since Paris (1981). The purpose of each chapter is to present: (1) a data synthesis from which the reader can make his or her own interpretations and (2) an interpretation by the authors incorporating contemporary datasets and geoscientific concepts. Onshore-offshore connections are emphasized, as are the geological relations with New Zealand, Australia and Papua New Guinea, although this Memoir certainly is not a synthesis of the geodynamics of the SW Pacific.This introductory chapter is a starting point for understanding how the current state of geoscientific knowledge of New Caledonia was reached. It includes a small-scale geological map and proposes a general stratigraphic scheme for New Caledonia. It reviews the advances in knowledge of the geology of the country since the last synthesis of Paris (1981). It also summarizes current problems and issues and the analyses strengths and weaknesses in the state of knowledge of the country's geology.Chapter 2 reviews the geodynamics of the SW Pacific and its relations with New Caledonian geology (Collot et al. 2020). The onshore geology of New Caledonia cannot be separated from its regional and offshore context. This chapter identifies the major geological structures of the SW Pacific from the eastern Australian coast to the Tonga-Kermadec Trench. This mostly submerged system of basins, ridges and seamounts of various ages is interpreted as oceanic and thinned continental crust, continental ridges, volcanic arcs, intra-plate volcanic chains and oceanic plateaus. Part of this region, including New Caledonia, is a submerged continent referred to as Zealandia (Mortimer et al. 2017). This chapter presents and compares tectonic models that attempt to explain the formation and development of this complex area.Chapter 3 considers the Pre-Late Cretaceous basement terranes of the Gondwana active margin (Maurizot et al. 2020a).

Testing the Reliability of Sedimentary Paleomagnetic Datasets for Paleogeographic Reconstructions

“…The southwest Pacific area went through a complex tectonic and paleogeographic evolution during the Eocene, related to the inception of the Tonga-Kermadec subduction system (recent reviews can be found in Cluzel et al, 2012;Collot et al, 2020;Dallanave et al, 2018b, Dallanave et al, 2020Maurizot et al, 2020a, Maurizot et al, 2020bSutherland et al, 2020). The Tonga-Kermadec subduction initiated in the middle Eocene immediately to the east of the Norfolk Ridge, the northernmost part of which is The eigenvector are oriented as the average eigenvector of the anisotropy of magnetic susceptibility (AMS), shown in Figure 8B.…”

“…The complete sets of directions are given in supporting Supplementary Table S2 available online. emerging to form the New Caledonia archipelagos ( Figures 7C). The history of the eastern margin of northern Zealandia before the Tonga-Kermadec subduction is still debated, because the geology of New Caledonia suggests the presence of a pre-Tonga east-dipping subduction zone (Cluzel et al, 2012;Collot et al, 2020;Maurizot, 2011;Maurizot et al, 2020a, Maurizot et al, 2020b, which is, however, difficult to reconcile with the geologic history derived from seismic profiles acquired in the Tasman area (Sutherland et al, 2017). Zealandia is separated from continental Australia by the oceanic crust of the Tasman Ocean basin, which ended its spreading activity during magnetic anomaly 24 in the early Eocene (∼53 Ma; Gaina et al, 1998;Figures 7C).…”

On the Influence and Correction of Water Content on pXRF Analysis of Lateritic Nickel Ore Deposits in the Context of Open Pit Mines of New-Caledonia

“…The obduction of the peridotite layer on sedimentary formations and the basaltic unit of Poya is attributed to the Late Eocene [28][29][30][31][32]. Originally covering a large part of Grande-Terre in New-Caledonia, the formation was gradually stripped by a succession of episodes of chemical and mechanical alteration.…”

Extrusion of subducted crust explains the emplacement of far-travelled ophiolites

“…For detailed explanation and references regarding the datasets (c-e) see Supplementary Note 1 and Supplementary Tables 1 and 2. Simplified cross sections showing the structure of the Oman 13 (a) and New Caledonia 56,57 (b) ophiolites and their structural relationship to the underlying continental rocks. The far-travelled ophiolite sheets are separated from their oceanic root by exhumed continental units, which show a transition from non-metamorphic to high metamorphic grade.…”