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Our Earth, its minerals and ore bodies
Published in Odwyn Jones, Mehrooz Aspandiar, Allison Dugdale, Neal Leggo, Ian Glacken, Bryan Smith, The Business of Mining, 2019
Odwyn Jones, Mehrooz Aspandiar, Allison Dugdale, Neal Leggo, Ian Glacken, Bryan Smith
The main driving force for the movement of the lithospheric plates comes from the Earth’s internal heat energy, which is primarily driven by radioactive decay of elements such as uranium and residual heat from the formation of the planet 4.55 billion years ago. Within the mantle, heat is transferred by convection in which hot rocks rise upwards but as they cool they begin to sink leading to the formation of convection cells. In areas where the litho-sphere is extended or thinned, the asthenosphere will be closer to the earth’s surface which can focus the upwelling hot rocks which leads to the melting of the asthenosphere below the lithosphere boundary and the intrusion of hot primary mantle derived magma. The volume of the intruded magma forces the lithospheric plates to push apart and separate. The episodic nature of ocean basin opening and closing was first noted by John T Wilson in the early 1960s and is known as the Wilson Cycle (Wilson, 1963). Recent, seismic tomography maps of the Earth’s interior show zones of fast and slow seismic S-wave velocity (Wookey and Dobson, 2008). Data collected from depths of ~ 2770 km in the lowermost part of the lower mantle shows two major areas of low S-wave velocity which are interpreted to represent gigantic mantle plumes named Great African and Central Pacific super plumes. It is suggested that the presence and magmatism associated of these super plumes may initiate lithospheric plate movement.
Scientific ocean drilling in the Australasian region: a review
Published in Australian Journal of Earth Sciences, 2022
The creation and destruction of oceanic lithosphere are fundamental consequences of plate tectonics, and an essential part of the “Wilson cycle” (Wilson, 1966). For oceanic lithosphere created by rifting, extension and seafloor spreading between formerly contiguous continental fragments, the nature of the continent–ocean boundary has been explored through many deep-sea drilling expeditions. A dichotomy between magma-rich vs magma-poor margins became recognised for the opening of the Atlantic, characterised by extreme continental lithosphere extension and exposure of the mantle at the seafloor characteristic of the latter (Doré & Lundin, 2015; Tugend et al.,2020). Expeditions 367 and 368 to the South China Sea, while not outlined in this review, discovered an intermediate type of margin between these end-members with a major, very rapid extension of the continental lithosphere (stretching factor of 4) leading to asthenosphere decompression and generation of magma from a mantle of normal potential temperature (Larsen et al.,2018). Creation of rifted continental fragments and ribbons are also typical consequences of the opening of new seas and oceans. An example is the Naturaliste Plateau to the southwest of Australia, explored by Expedition 369. The plateau was formerly located central to the junction between the Antarctic, Indian and Australian continents, and proximal to the initial locus of the Kerguelen Plume. Lee et al. (2020) reported on the recovery of syn-rift volcanic rocks, establishment of the subsidence history and sedimentation record during the fragmentation of continental lithosphere and plume interactions therewith.