Anatomy of an obducted ultramafic unit (Tiébaghi Massif – Peridotite Nappe – New Caledonia): Polyphase brittle tectonics constrained by fault-slip data and crack seal mineralogy

ABSTRACT

New data collected in the mining areas of the Tiébaghi Massif, a klippe of the Peridotite Nappe located in the north of New Caledonia, are presented. Data were collected in open cast nickel mine pits and chromite underground works, notably along a 1.2-km long tunnel which penetrates the deep geological structure of the massif. Surface and sub-surface geology, microtectonic observations and kinematic analysis of fracture planes, Electrical Resistivity Tomography, micron-scale Raman spectroscopy and Transmission Electron Microscopy were used to characterise the different tectonic regimes and associated mineralisations. Three stages of deformation and their kinematic axes are identified. Fractures coated with antigorite-tremolite minerals are associated to supra-subduction melt intrusions in a compressional regime characterised mainly by thrust and transcurrent faults. They are followed by fractures coated with polygonal serpentine formed in an extensional regime. The two former mineral phases are commonly superimposed on the same plane. Third-stage consist of fractures associated with supergene minerals deposited in an extensional regime, associated with gravity driven normal faulting. Fractures associated with this supergene stage have reactivated the former hypogene network.

KEYWORDS:

• Ophiolite
• peridotite
• serpentine
• polygonal
• chromite
• nickel
• supergene
• laterite
• ferricrete
• electric resistivity tomography

Acknowledgements

This work was funded by the Geological Survey of New Caledonia (Government of New Caledonia). ‘Société Le Nickel’ mining company is gratefully acknowledged for having supported this study, giving access to the operating areas, and providing extensive sets of data. We thank Henri Reuillard and the Tiébaghi Association (Association for the preservation of the mining and historical heritage of North Caledonian) for arranging access to the Chromical mine as well as providing local accommodation.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

The authors confirm that the data supporting the findings of this study are available within the article and its supplementary materials. The data that support the findings of this study are openly available in figshare at https://doi.org/10.6084/m9.figshare.c.6764184.v2.