Hot spots, magma underplating, and modification of continental crust

Abstract

Most common mantle-derived magmas have densities at Moho pressures that exceed the density of average continental crust. Thus, unless the crust is tightly coupled with the mantle, many such magmas should penetrate at or near the Moho interface. The scale of such a phenomenon can be impressive; recent hot spots may have perturbed more than 5% of the planet's surface. The details of the process will depend on the ease of melting of the base of continents.Underplating can explain continental construction from below; Moho structures, or lack thereof; delamination of the continental basement; partial subduction and density cleaning of crust; the formation of massive anorthosite complexes; and major changes of elevation of continental blocks. In the thermally turbulent Archean, the very dense and hot komatiite magmas must have had even more profound influences.Modem studies of the subduction process show that the mantle must be heterogeneous and that volatiles can be carried to great depths in significant volumes.La majorit6 des magmas communCment dCrivCs du manteau ont des densitCs, aux pressions existantes au niveau du Moho, supkrieures B la densite moyenne de la croilte continentale. Ainsi, B moins que la c r o~t e soit Ctroitement accouplCe au manteau, plusieurs de ces magmas doivent ptnCtrer jusqu'h ou prks de l'interface du Moho. Ce phCnombne peut se manifester a une Cchelle impressionnante, et il est probable que les points chauds rCcents aient affect6 plus de 5 % de la surface de la plankte.Les dCtails du processus dCpendent de la facilitC de fusion de la base des continents.Le sous-placage peut expliquer l'edification des continents B mCme leur base, les structures du Moho ou leur absence, la dklamination de la base continentale, la subduction partielle et le nettoiement de la densit6 de la croilte, la formation de complexes d'anorthosite massive et le changement majeur de 1'ClCvation des blocs continentaux. Durant I'ArchCen, thermiquement turbulent, les magmas de komatiite trks denses et chauds ont certainement eu i jouer un r61e encore plus dtterminant.Les Ctudes rCcentes des processus de subduction dCmontrent que le manteau doit &tre hCtCrogbne, et que les substances volatiles peuvent etre transportkes a de grandes profondeurs et en grand volume.[Traduit par la rCdaction]Can. J. Earth Sci. 30, 908-912 (1993)

Field, petrophysical and carbon isotope studies on the Lapland Granulite Belt: implications for deep continental crust

“…Many features in the upper crust are manifestations of deep processes and, vice versa, exposed structures of deep origin may help to understand upper crustal processes. Frost and Bucher 19941, the structure and properties of exposed fragments of presumable deep origin ranging from xenoliths to large granulite terrains (Harley, 1989; Vielzeuf and Vidal, 1990;Fountain et al, 1992) as well as the deformation processes of the deep crust (Fountain, 1989;Kay et al, 1992;Mezger, 1992;Fyfe, 1993; Singh and McKenzie, 1993).…”

Electrical signatures due to thermal anomalies along mobile belts reactivated by the trail and outburst of mantle plume: Evidences from the Indian subcontinent

“…Episodically, reactivated paleo-orogenic (and/or paleo-rift) corridors allow magmatic, metamorphic and metasomatic processes which tend to channelise along them so that underlying crust and sub-crustal lithosphere are renewed periodically by volatiles and associated radiogenic elements, as reflected by the higher radioactive heat generation (Fyfe, 1993). Other factors that may add to higher heat flow along the mobile belts could be the Plume induced mag- Harinarayana et al, 2000).…”

Thoughts on the Jiaodong Gold Province of China: Towards a Tectonic Model

“…3B). Huge granite plutonic and high-grade metamorphic events commence (Fyfe, 1993). Plutons accumulate big drops.…”