China
Africa
Explore chapters and articles related to this topic
General Features of Magmatic Evolution Throughout the Earth’s History
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
Ophiolite assemblages (Fig. 7.1) are typical of the earliest stages of fold-belt evolution. The reconstruction of the initial tectonic position of ophiolites is of major importance for the geodynamic interpretation of the early stages of fold-belt formation. At present, the overwhelming majority of researchers agree that ophiolites were once fragments of oceanic crust and the upper mantle, but there is some controversy about the precise region of the palaeo-ocean floor in which they were formed. Firstly, the ophiolites have been interpreted as the analogues of lithosphere of major oceans formed within mid-oceanic rift zones by large-scale spreading (Coleman, 1977). However, subsequent studies of the petrochemical characteristics of ophiolitic basalts have demonstrated that they are characterized by both tholeiitic and calc-alkaline trends (Fig. 7.2). In this regard, attempts have been made to elaborate the classification of ophiolites (Dobretsov, 1980; Kovalenko 1987; Laz’ko and Sharkov, 1988; Nicolas, 1989; Detrick, 1991; etc.), the ultimate objective being to elucidate the original initial geodynamic environments in which they were formed.
Plutonic Rocks
Published in Dexter Perkins, Kevin R. Henke, Adam C. Simon, Lance D. Yarbrough, Earth Materials, 2019
Dexter Perkins, Kevin R. Henke, Adam C. Simon, Lance D. Yarbrough
New oceanic crust forms at mid-ocean ridges as magma rises to fill space created when plates diverge. The spreading lithosphere, composed of crust and some underlying mantle, cools and becomes denser during spreading. So, the youngest seafloor and highest elevations are at the ridges, and the oldest seafloor and lowest elevations are at ocean margins. The ocean lithosphere may not be the same composition and structure everywhere, but all evidence suggests that there are some standard components. The evidence comes from many sources including drill core, seismic studies, laboratory experiments, grab sampling from the ocean floor, and dredging. The best information, however, may come from studies of ophiolites. Ophiolites are parts of oceanic crust and mantle that were uplifted and added to continental margins or are exposed in islands. The term ophiolite derives from the Greek words ophio (snake) and lite (stone), referring to the commonly green color of the rocks that make up ophiolites. There are many ophiolites around the world, but most are small or very fragmented; Table 6.4 lists some of the best-known and studied ones.
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.
Tectonic setting and mineralisation potential of the Cowley Ophiolite Complex, north Queensland
Published in Australian Journal of Earth Sciences, 2022
A. Edgar, I. V. Sanislav, P. H. G. M. Dirks
Ophiolite complexes have the potential to host substantial, lateritic, Ni–Cr–Co mineralisation, and their occurrence may provide clues about the regional tectonic history (Butt & Cluzel, 2013; Lewis et al., 2006). Ophiolite complexes comprise mafic–ultramafic slices of oceanic lithosphere that were tectonically emplaced onto continental crust during orogenesis (Furnes & Dilek, 2017; Pearce, 2014; Yilmaz & Yilmaz, 2013). Ophiolite complexes are mostly interpreted to have formed along active plate margins. They were traditionally interpreted as sequences of MORB-like oceanic crust that were emplaced along subduction zones during obduction processes atop of an overriding plate. However, most preserved ophiolite complexes have been re-interpreted as being formed within a supra-subduction zone setting (Dilek & Furnes, 2014; Shervais, 2001). Ophiolite complexes are commonly associated with arc–continent or continent–continent collisional terrains (Dilek & Furnes, 2011), although they have also been recognised within backarc basins that experienced extension and subsequent subduction initiation and/or thrusting during basin closure (Božović et al., 2013; Wang et al., 2002). However, ophiolite complexes generated within backarc environments are rarely preserved, owing to the eventual subduction of the backarc and ophiolite sequences during basin closure (Draut & Clift, 2013).
Scientific ocean drilling in the Australasian region: a review
Published in Australian Journal of Earth Sciences, 2022
During the lithospheric destruction stage of the Wilson Cycle, the structure of continent–ocean margins is critical in terms of tectonic and magmatic consequences. For example, the amagmatic character of the plate convergence accompanying formation of the European Alps reflects subduction of a sequence of highly stretched continental ribbons and their intervening serpentinite-floored seas with minor volumes of ultra-slow-spreading-formed crust (McCarthy et al., 2020). In fact, the nature of processes accompanying initiation of subduction have been hard to discover. The results of extensive dredging, submersible, and drilling campaigns (e.g. Expeditions 351, 352, and 371) in the western Pacific arcs have revealed significant insights (Arculus et al., 2019). With respect to the formation of “standard, Penrose-type” oceanic crust, an important conclusion reinforced by these expeditions is that the majority of the world’s ophiolites represent sections of crust generated at convergent margins, especially during subduction inception stages (Ishizuka et al., 2014; Stern et al., 2012; Whattam & Stern, 2011) rather than at mid-ocean ridges (Figure 20). A major international effort has been under way in the past few years to successfully core sections of the terrestrially exposed Oman Ophiolite. Core description and analytical results have been obtained using the Chikyu’s facilities; results are available at: http://publications.iodp.org/other/Oman/OmanDP.html#pgfId-1067936
Geodynamic setting of Ediacaran and Permian–Triassic plagiogranites of the Ust-Bel’sky and Algansky terranes, West Koryak fold belt, NE Russia: insights from U–Pb geochronology and geochemistry
Published in GFF, 2019
Artem Moiseev, Marina Luchitskaya, Sergey Sokolov, Boris Belyatsky
There are different points of view regarding the nature of the ultramafic rocks of the Ust-Bel’sky massif and Ediacaran plagiogranites. According to Palandzhyan (2015), peridotites are similar in composition to the rocks of the subcontinental upper mantle and peridotites of the oceanic lithosphere adjacent to the passive margin. Their formation occurred at the early stage of spreading during extension and thinning of continental lithosphere; the age of mantle cumulates is Tonian–Cryogenian, and the Ediacaran plagiogranites are final phases of the crustal sequence of ophiolite formation (Palandzhyan 2015). Nekrasov et al. (2001) attributed the Otrozhnaya nappe to the crust of the Middle Palaeozoic spreading center, formed within the more ancient oceanic plate. The Ust-Bel’sky massif is a fragment of this plate. Ledneva et al. (2012) regarded ultramafic-mafic rocks of the Ust-Bel’sky massif as the deepest parts of the subcontinental lithospheric mantle that have undergone intense partial melting as a result of its interaction with suprasubduction melts.