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Igneous Petrology and the Nature of Magmas
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
While accounting for only about a quarter of the outcrops at Earth’s surface, igneous rocks make up most of deeper parts of Earth’s crust, in both continental and oceanic regions. So they are both diverse and important. They also make up much of Earth’s mantle, but most igneous rocks that we study formed in the crust, simply because those that originated in the mantle rarely make it to the surface for us to see. The exceptions include (1) slivers of oceanic mantle uplifted and attached to continents through a process called obduction, (2) some xenoliths carried from the mantle to the surface by rising magmas, and (3) tectonic slices that have incorporated into mountain belts during orogenies. Although most igneous rocks that we see originated in the crust, the magmas that produced them often derived initially from the mantle. Consequently, studying igneous rocks gives us important information about the nature of the mantle and the processes that occur there.
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).