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Diastrophism
Published in Richard J. Chorley, Stanley A. Schumm, David E. Sugden, Geomorphology, 2019
Richard J. Chorley, Stanley A. Schumm, David E. Sugden
With the evidence for movement being so much more secure, the problem of mechanism seems less insuperable to plate tectonics than to continental drift, especially as at least five classes of mechanisms are possible: (a) Viscous drag of the solid lithospheric plates by convection currents in the asthenosphere, rising along the zones of spreading and subsiding along the subduction zones. Earthquake evidence along the Benioff Zone suggests that the mantle below 700 km is too resistant to allow the penetration of subduction plates, which further suggests that convection is in all probability limited to depths above this, and that there is a hierarchy of convection cells of differing size.(b) The plate being pulled by the weight of the relatively cool subducting slab, possibly assisted by an increase in the density of the slab as the gabbro metamorphoses into eclogite at depth.(c) The gravitational sliding of the lithospheric slab away from the oceanic ridge zone raised by rising material in the asthenosphere. It has been estimated that a surface slope of only 1:3000 would produce a movement of the lithosphere of 4 cm/year over the low-velocity top layer of the asthenosphere.(d) Lithospheric plates being pushed apart by magma rising along the axis of the zone of spreading to form wedges of new lithosphere along the trailing-edge of the plate (see Figure 6.2).(e) Mantle plume mechanisms (see Chapter 6) in which magma rising from some twenty-one major hot spots in the mantle and spreading out under the lithosphere plates might provide a horizontal driving-force.
Diamond in the Sky
Published in James C Sung, Jianping Lin, Diamond Nanotechnology, 2019
In addition to the various sources of diamond mentioned, the existence of diamond is known to be deep within Earth as well. This is why volcanic mantle plumes such as kimberlite had been found to bring natural diamond up to the surface here on Earth.
Geochemical patterns of late Cenozoic intraplate basaltic volcanism in northern New Zealand and their relationship to the behaviour of the mantle
Published in New Zealand Journal of Geology and Geophysics, 2021
Ian E. M. Smith, Shane J. Cronin
The nature and origin of small-scale intraplate basaltic volcanic fields in continental settings is an actively researched subject (e.g. McGee and Smith 2016; Smith and Nemeth 2017). Worldwide, small-scale basaltic magmatism has been explained by mantle plumes (e.g. Morgan 1971), passive upwelling of asthenospheric mantle through slab windows (e.g. D’Orazio et al. 2000), lithospheric thinning preceding rifting (e.g. Weaver and Smith 1989) and combinations of low degree melting of lithosphere metasomatised by earlier subduction (e.g. Panter et al. 2006). Explanations for the origin of these small-scale magmatic systems link tectonic setting and precursory events to provide a range of explanations that can be unique to each occurrence. In northern New Zealand the Late Miocene to Recent small-scale basaltic volcano fields which followed arc-type volcanism in the Northland Peninsula and which developed later in the Auckland region show the chemical characteristics of mantle-related intraplate magmatism distinct from the subduction-related mantle sources of the Northland Arc and its associated subsequent bimodal volcanism. Interpretation of their geochemistry reveals two distinct groups, the Kaikohe-Bay of Islands and Whangarei Volcanic Fields (the Northland fields) in the north and the Okete- Ngatutura -South Auckland-Auckland Volcanic Fields (the Auckland fields) to the south (Figure 1). Significantly, the spatial and temporal behaviour of each of these two groups of volcano fields is different and analysis of their chemical compositions reveals a variety of mantle sources and petrogenetic processes. In this paper, we examine these differing compositional patterns and interpret their significance to the behaviour of the mantle beneath northern New Zealand in late Cenozoic times.
Scientific ocean drilling in the Australasian region: a review
Published in Australian Journal of Earth Sciences, 2022
Persistent uprising of a plume of hot, relatively low-density mantle may continue to partially melt as it approaches the Earth’s surface; if the tectonic plate in and upon which the generated magmas are emplaced were moving relative to the more-or-less stationary mantle plume, a chain of volcanoes would develop as the plate is translated over the plume locus (Morgan, 1972). Note however, the assumption of hotspot fixity has been shown to be invalid in the case of the Hawaii (Tarduno et al., 2009) and Indian Ocean hotspots (O’Neill et al., 2003), but not for the Louisville chain, at least for a portion of its life (Koppers et al., 2012). Mantle tomography has confirmed the presence of low-seismic velocity columns of material, extending upwards from the lower mantle and underlying active volcanic loci such as Réunion, Kerguelen, and Amsterdam in the Indian Ocean (Zhao, 2007), and likewise Samoa, Pitcairn and MacDonald in the southern Pacific Ocean (French & Romanowicz, 2015). Ridges linked with respective hotspots include the Chagos-Laccadive with Réunion, Eightyeast Ridge with Crozet, Ninetyeast Ridge with Kerguelen, and multiple tracks in the South Pacific Ocean (Finlayson et al., 2018; Jackson et al., 2010). The Louisville Ridge has no distinct expression at the putative current locus (Koppers et al., 2011) but is probably the tail of the original Ontong Java Nui LIP (Chandler et al., 2012). There are clear southerly younging age progressions along the East Australian volcanic chain (Davies et al., 2015), and the Tasmantid and Lord Howe seamount chains, but no indications at present for deep-seated (low-seismic velocity) mantle plumes underlying any of the respective, nominally active loci (Crossingham et al., 2017; Seton et al., 2019).