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Magmatism in the Context of the Present-Day Tectonic Settings
Published in O.A. Bogatikov, R.F. Fursenko, G.V. Lazareva, E.A. Miloradovskaya, A. Ya, R.E. Sorkina, Magmatism and Geodynamics Terrestrial Magmatism Throughout the Earth’s History, 2020
O.A. Bogatikov, V.I. Kovalenko, E.V. Sharkov, V.V. Yarmolyuk
This suggests that a section of the ancient oceanic lithosphere is represented in ophiolite sequences, which were obducted onto one of the colliding continental forelands during the final stages of ocean closure and formation of fold belts. Their lower part is usually formed by the mantle ultramafites (harzburgites, lherzolites, dunites, etc.); the crustal section starts with a layered complex (dimites, whehrlites, clinopyroxenites, gabbro, etc.); a further dyke-sheeted complex occurs and the upper part is formed by pillow lavas and deep-sea sediments (Coleman, 1977; Nicolas, 1989). Detailed isotope studies of Voykar ophiolite, from the Polar Urals, have shown that oceanic crustal rocks and the mantle harzburgites are complementary and come from a MORB source (Sharma et al., 1995).
Deposits and ore mineralization associated with Ophiolite Complexes in the Sudetes Mts. (Poland)
Published in Adam Piestrzyński, Mineral Deposits at the Beginning of the 21st Century, 2001
W. Olszyński, S.Z. Mikulski, S. Speczik
Ophiolite has been interpreted as oceanic floor fragments obducted into continental margins during orogenic processes. Complete ophiolite suite consists of: serpentinized peridotites, ultramafic cumulates, mafic cumulates and volcanic rocks (sheeted dikes and pillow lavas). Metaultramafic and metamafic rocks of ophiolite complexes may be important metal resources of both hypogene and weathered origin. Metal deposits and occurrences follow rock alternations and are controlled by specific geochemical and tectonic patterns.
Anatomy of an obducted ultramafic unit (Tiébaghi Massif – Peridotite Nappe – New Caledonia): Polyphase brittle tectonics constrained by fault-slip data and crack seal mineralogy
Published in New Zealand Journal of Geology and Geophysics, 2023
Pierre Maurizot, Bernard Robineau, Julie Jeanpert, Marion Iseppi, Stéphane Lesimple, Farid Juillot, Michael Meyer, Patrick Fullenwarth, Vincent Mardhel
Nickel and chromium are essential elements in alloys increasingly used in modern technology. Worldwide, lateritic nickel deposits, which are formed by the surficial weathering of ultramafic ophiolitic rocks has become the most important source for nickel (Mudd and Jowitt 2014). About half of the world’s chromium production is extracted from podiform chromitites (Mosier et al. 2012) which occur in mantle peridotites. New Caledonia hosts considerable resources of both metals (Maurizot et al. 2020b) and is (for nickel mined in supergene laterite) or has been (for chromium mined in podiform chromitites) among the major producing countries. Distribution of these resources is controlled by the tectonic structures of the ultramafic host rock. Therefore, a better knowledge of these structures may help in improving the efficiency of mining of these important mineral resources. In turn, mining works provide a wealth of exposures and data, which can help geologists to better understand the geological evolution of such ophiolitic units. World-class nickel and chromium deposits are hosted in the Peridotite Nappe (Avias 1967; Maurizot and Mortimer 2020) which represents an ophiolite obducted over the continental crust of New Caledonia at the end of the Eocene (Figure 1).
The origin of mafic–ultramafic rocks and felsic plutons along the Clarke River suture zone: implications for porphyry exploration in the northern Tasmanides
Published in Australian Journal of Earth Sciences, 2023
A. Edgar, I. Sanislav, P. Dirks
Positioned along the Clarke River Fault, the Ordovician, Running River Metamorphics comprise strongly deformed, amphibolite facies rocks, which are mostly composed of amphibolite, felsic gneiss and quartzite (Figure 1b). The sequence was intruded by the Falls Creek Tonalite at 456 Ma (Dirks et al., 2021). Dirks et al. (2021) have interpreted the Running River Metamorphics as obducted oceanic crust, which was structurally juxtaposed against basement consisting of S-type granitic gneiss. Metamorphic diamonds have been found within almandine–spessartine garnet-bearing quartzite from the Running River Metamorphics (Edgar et al., 2022b), which indicates that the Running River Metamorphics experienced ultra-high-pressure metamorphism at pressures >3.5 GPa and temperatures >850 °C (Edgar et al., 2022b). The presence of UHP rocks, coupled with the tectonic position of the Running River Metamorphics along a major regional structure, indicates that the Clarke River Fault represents a suture zone between the Charters Towers and Broken River provinces (Edgar et al., 2022b).
Interpreting geology from geophysics in poly-deformed and mineralised terranes; the Otago Schist and the Hyde-Macraes Shear Zone
Published in New Zealand Journal of Geology and Geophysics, 2019
Casey C. Blundell, Robin Armit, Laurent Ailleres, Steven Micklethwaite, Adam Martin, Peter Betts
Throughout both Caples and Rakaia Terranes, semi-continuous, irregularly shaped lenses and podiform bodies of metamorphosed mafic to ultramafic composition occur folded within felsic schist units (Figure 1). These lenses preserve primary emplacement features (pillow structures, porphyritic textures) at low metamorphic grades, appear to be layer concordant with and have normal depositional contacts with enclosing metasedimentary units (Pitcairn et al. 2015; Mortensen et al. 2018). Numerous studies (e.g. Bierlein and Craw 2009; Fagereng and Cooper 2010) have investigated the source of the meta-mafic lenses and conclude that their depositional relationships and geochemical composition (e.g. Pitcairn et al. 2015) are consistent with slivers of oceanic crust being obducted to the overriding plate during subduction. The abundance of these mafic lenses generally increases from east to west, with only one recently identified in the vicinity of the mineralised Hyde-Macraes Shear Zone, and in total comprise less than 10% of outcropping schist basement in Otago, though more is interpreted at depth. Referred to in local literature as ‘greenschists’ (in contrast to quartzo-feldspathic ‘greyschist’), the meta-mafic units contain abundant chlorite and/or epidote, albite, titanite, minor magnetite (or pyrite or pyrrhotite) or hematite (Brown 1963; Craw 1984), and so are visually and petrophysically distinctive among the otherwise homogeneous felsic schist. Consequently, these meta-mafic units are important marker units that can be used to map regional geometries and infer 3-dimensional structure within the Otago Schist using geophysical data (e.g. Martin et al. 2014; MacKenzie et al. 2015).