Plate tectonics and magma genesis

Wyllie, Peter J.

doi:10.1007/bf01764318

Cited by 90 publications

(32 citation statements)

References 24 publications

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“…The calculated Simon-type fit along c-e [Griggs, 1972] is probably a better representation of a peridotite solidus, and it matches more closely the recent experimental determination (Figure 34). The peridotite melting interval in Figures 33b and 33c was estimated by Wyllie [1981]. The geotherms in Figure 33 are from various sources, and these merit comparison with Figure 7.…”

Section: Convection Geotherms and Solidus Curvesmentioning

confidence: 99%

Magma genesis, plate tectonics, and chemical differentiation of the Earth

Wyllie¹

1988

Reviews of Geophysics

130

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Magma genesis, migration, and eruption have played prominent roles in the chemical differentiation of the Earth. Plate tectonics has provided the framework of tectonic environments for different suites of igneous rocks and the dynamic mechanisms for moving masses of rock into melting regions. Petrology is rooted in geophysics. Petrological and geophysical processes are calibrated by the phase equilibria of the materials. The geochemistry of basalts and mantle xenoliths demonstrates that the mantle is heterogeneous. The geochemical reservoirs are related to mantle convection, with interpretation of a mantle layered or stratified or peppered with blobs. Seismic tomography is beginning to reveal the density distribution of the mantle in three dimensions, and together with fluid mechanical models and interpretation of the geoid, closer limits are being placed on mantle convection. Petrological cross sections constructed for various tectonic environments by transferring phase boundaries for source rocks onto assumed thermal structures provide physical frameworks for consideration of magmatic and metasomatic events, with examples being given for basalts, andesites, and granites at ocean-continent convergent plate boundaries, basalts and nephelinites from a thermal plume beneath Hawaii, kimberlites in cratons, nephelinites from continental rifts, and anorogenic granites. The fluid dynamics of rock-melt-vapor systems exerts strong control on igneous processes and chemical differentiation. Unravelling the processes during subduction remains one of the major problems for understanding mantle heterogeneities and the evolution of continents. INTRODUCTIONThe Union Lecture on which this review is based was pre- the magmatic processes occurring nearer the source of magma generation. There remains a gap between volcanoes, their plutonic roots, and the magma sources which has to be filled by indirect studies including geophysics, geochemistry, and fluid dynamics. Lavas reach the surface through volcanoes, and lavas can provide information about the source rocks from which they were derived if the materials and processes can be suitably calibrated in the laboratory. The calibration involves the geochemistry of major, minor, and trace element distributions (including isotopes) between minerals and melts and the conditions for melting of the various source materials under various conditions. Some lavas also bring to the surface samples of the host rocks from which they were derived by partial melting or of the rocks through which they rose. The lavas release gases to the atmosphere and hydrosphere which also provide clues about the nature of the source material at depth.The theme common to the different parts of this review relates to the conditions for melting, transfer, storage, and eruption of melts. The approach is as follows. Plate tectonics provides a framework of tectonic environments and internal processes, which can be calibrated by laboratory experiments at high pressures. Within this framework I next outline the developm...

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Section: Convection Geotherms and Solidus Curvesmentioning

confidence: 99%

Magma genesis, plate tectonics, and chemical differentiation of the Earth

Wyllie¹

1988

Reviews of Geophysics

130

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“…10) in the stability field of spinel (e.g., Wyllie, 1981;Köhler and Brey, 1990). Furthermore, as shown in Figure 10, the temperature and pressure range of the spinel lherzolites display a higher geothermal gradient with heat flow (~70-90 mW/m 2 ) than the normal continental gradient (40 mW/m 2 , Pollack and Chapman, 1977).…”

Section: Equilibrium Temperature and Pressure Estimatesmentioning

confidence: 93%

Geochemical and Sr–Nd–Pb isotopic compositions of lithospheric mantle: Spinel lherzolites in alkaline basalts from the northwestern Ethiopian plateau

Meshesha¹,

Shinjo

Orihashi

2014

Journal of Mineralogical and Petrological Sciences

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The geochemical characteristics of mantle xenoliths (spinel lherzolites) in Quaternary alkaline basalts from the northwestern Ethiopian plateau provide new insight into the conditions of melting associated with the Afar plume. The major element compositions of the spinel lherzolites are in the range of those of the primitive mantle. The high modal content of the clinopyroxene (14-23%) indicate that the mantle xenoliths are fertile spinel lherzolites that have experienced insignificant partial melting. However, enrichment in highly incompatible elements (LREE, Ba, Pb, Th, and U) and the absence of any typical metasomatic minerals indicate that the spinel lherzolites underwent an event of later cryptic metasomatic enrichment induced by plume-related, hydrous fluid-rich silicate melts. The

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“…But pyrope-rich garnet is about 10% more dense than the other mantle silicates, and only a few percent increase in overall garnet content of the mantle within the stability field of garnet peridotite would be enough to produce the calculated mass excess. This mass excess would only affect the mantle below about 60 km, since above that depth, given normal mantle temperatures, garnet peridotite transforms to spinel peridotite [Wyllie, 1981].…”

Section: Thickening the Crust Is Not Possible Under The 45øn Area Sincementioning

confidence: 99%

“…The transformation from garnet peridotite to spinel peridotite takes place at greater depths at higher temperatures [Wyllie, 1981]. The transition within hot plume mantle must thus take place at greater depths than in mantle of normal temperature, and no density anomaly would result.…”

Section: Thickening the Crust Is Not Possible Under The 45øn Area Sincementioning

confidence: 99%

Anomalous mantle at 45°N Mid‐Atlantic Ridge?

Mello¹,

Cann²,

Fowler³

1999

J. Geophys. Res.

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Abstract. The Mid-Atlantic Ridge at 45øN has a ridge crest depth close to normal for slow spreading ridges and a crustal thickness of 6 km. However, the free-air gravity over the region is higher than expected for such axial depths, and erupted basalts are enriched in incompatible trace elements and radiogenic isotopes, which could be taken to indicate the presence of a mantle plume beneath the spreading axis. But the ridge is at normal depths and the crust is of normal thickness. We model free-air gravity across and parallel to the strike of the ridge. A density structure derived from a cooling model provides a good fit for gravity across the ridge axis. A gravity model along the ridge axis indicates that most of the gravity signal over the Azores and Reykjanes Ridge is related to thicker crust, while the gravity signal over 45øN can be modeled by a density anomaly, which extends along the spreading axis from about 43øN to 50øN and from zero age to 35 m.y. Such a mass excess can be explained by an increase in the garnet content of the mantle within the stability field of garnet peridotite. The enriched basalts occur in the same region as the mass anomaly. We interpret them as originating from cool hotspot mantle. This anomalous mantle may derive from a hotspot that existed at the North America-Africa-Eurasia triple junction when it was at 45øN between 59 and 26 m.y. The King's Trough Complex is the remnant of that hotspot. We consider that this cool hotspot mantle still underlies the spreading axis and contributes to crustal construction.

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Plate tectonics and magma genesis

Cited by 90 publications

References 24 publications

Magma genesis, plate tectonics, and chemical differentiation of the Earth

Magma genesis, plate tectonics, and chemical differentiation of the Earth

Geochemical and Sr–Nd–Pb isotopic compositions of lithospheric mantle: Spinel lherzolites in alkaline basalts from the northwestern Ethiopian plateau

Anomalous mantle at 45°N Mid‐Atlantic Ridge?

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