On the regional variation of heat flow, geotherms, and lithospheric thickness

Pollack, Henry N.; Chapman, David S.

doi:10.1016/0040-1951(77)90215-3

Cited by 984 publications

(459 citation statements)

References 34 publications

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“…The numerical modeling results suggest, in general, a probability of gravitational instability both at the 1 -continental geotherm (50 mWm -2 ), from [Pollack, Chapman, 1977]. 2 -calculated geotherm provided that the temperature was constant at the lithospheric base (1300 °C) before and after thickening.…”

Section: Oxidesmentioning

confidence: 83%

“…1 -континентальная геотерма (50 мВт/м 2 ), по данным [Pollack, Chapman, 1977]. 2 -рассчитанная геотерма при условии фиксированной температуры (1300 °C) в основании лито-сферы до и после утолщения.…”

Section: рис 2 геотермы до (1) и послеunclassified

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Thinning of the lithosphere by small-scale convective destabilization

Yuen

Fleitout

1985

Nature

134

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Abstract:The lower part of lithosphere in collisional orogens may delaminate due to density inversion between the asthenosphere and the cold thickened lithospheric mantle. Generally, standard delamination models have neglected density changes within the crust and the lithospheric mantle, which occur due to phase transitions and compositional variations upon changes of P-T parameters. Our attention is focused on effects of phase and density changes that may be very important and even dominant when compared with the effect of a simple change of the thermal mantle structure. The paper presents the results of numerical modeling for eclogitization of basalts of the lower crust as well as phase composition changes and density of underlying peridotite resulted from tectonic thickening of the lithosphere and its foundering into the asthenosphere. As the thickness of the lower crust increases, the mafic granulite (basalt) passes into eclogite, and density inversion occurs at the accepted crust-mantle boundary (P=20 kbar) because the newly formed eclogite is heavier than the underlying peridotite by 6 % (abyssal peridotite, according to [Boyd, 1989]). The density difference is a potential energy for delamination of the eclogitic portion of the crust. According to the model, P=70 kbar and T=1300 °C correspond to conditions at the lower boundary of the lithosphere. Assuming the temperature adiabatic distribution within the asthenosphere, its value at the given parameters ranges from 1350 °C to 1400 °C. Density inversion at dry conditions occurs with the identical lithospheric and asthenospheric compositions at the expense of the temperature difference at 100 °C with the density difference of only 0.0022 %. Differences of two other asthenospheric compositions (primitive mantle, and lherzolite KH) as compared to the lithosphere (abyssal peridotite) are not compensated for by a higher temperature. The asthenospheric density is higher than that of the lithospheric base. Density inversion occurs if one assumes the presence of the asthenosphereic material in the composition similar to that of the primitive mantle or lherzolite KH in amounts no less than 1.40 and 0.83 wt. %, respectively, of the conventionally neutral fluid. This amount of the fluid seems to be overestimated and thus does not fully correlate with the current estimates of the fluid content in the mantle. Therefore, the most appropriate material for delamination of the thickened lithosphere is only the fluid-bearing asthenosphere which composition corresponds to that of the depleted mantle of middle-ocean ridges (DMM) being the reservoir existing from the Precambrian. In our model, abyssal peridotite is most similar to DMM as compared with other more fertile compositions of the lithosphere. Heat advection due to uplift of fluid-bearing plumes that occurred much time after collisional events may initiate repeated delamination of gravitationally instable parts of the orogenic and cratonic lithosphere.Key words: delamination, lithosphere, asthenosphere, collisional oro...

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Section: Oxidesmentioning

confidence: 83%

Section: рис 2 геотермы до (1) и послеunclassified

Thinning of the lithosphere by small-scale convective destabilization

Yuen

Fleitout

1985

Nature

134

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“…For uniformity the Al,Cr-in-pyroxene barometer of Nickel and Green (1985, abbreviated P NG85) and the clinopyroxene-solvus thermometer of Nimis and Taylor (2000, abbreviated T NT00) are used in the remainder of this paper. Model conductive geotherms labelled 35, 40, 45 and 50 are after Pollack and Chapman (1977) and terminate in a mantle adiabat with Tp = 1300ºC. The graphite/diamond equilibrium (solid line terminated by diamond symbols) is that of Kennedy and Kennedy (1976).…”

Section: Discussionmentioning

confidence: 99%

The elusive lithosphere–asthenosphere boundary (LAB) beneath cratons

Eaton

Darbyshire

Evans

et al. 2009

Lithos

390

288

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The lithosphere-asthenosphere boundary (LAB) is a first-order structural discontinuity that accommodates differential motion between tectonic plates and the underlying mantle. Although it is the most extensive type of plate boundary on the planet, its definitive detection, especially beneath cratons, is proving elusive. Different proxies are used to demarcate the LAB, depending on the nature of the measurement. Here we compare interpretations of the LAB beneath three The seismic LAB beneath cratons is typically regarded as the base of a high-velocity mantle lid, although some workers infer its location based on a distinct change in seismic anisotropy.Surface-wave inversion studies provide depth-constrained velocity models, but are relatively insensitive to the sharpness of the LAB. The S-receiver function method is a promising new seismic technique with complementary characteristics to surface-wave studies, since it is 2 sensitive to sharpness of the LAB but requires independent velocity information for accurate depth estimation. Magnetotelluric (MT) observations have, for many decades, imaged an "electrical asthenosphere" layer at depths beneath the continents consistent with seismic lowvelocity zones. This feature is most easily explained by the presence of a small amount of water in the asthenosphere, possibly inducing partial melt. Depth estimates based on various proxies considered here are similar, lending confidence that existing geophysical tools are effective for mapping the LAB beneath cratons.

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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). The high geotherm obtained from the spinel lherzolites suggests the presence of high thermal disturbances related to active tectonics in the region.…”

Section: Equilibrium Temperature and Pressure Estimatesmentioning

confidence: 91%

“…The crust thickness is 40 km under the Ethiopian plateau (Dugda et al 2005). Geothermal gradient is based on 40, 60 and 90 mW/m 2 heat flow (Pollack and Chapman, 1977). Spinel and garnet transition is from Köhler and Brey (1990).…”

Section: Equilibrium Temperature and Pressure Estimatesmentioning

confidence: 99%

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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On the regional variation of heat flow, geotherms, and lithospheric thickness

Cited by 984 publications

References 34 publications

Thinning of the lithosphere by small-scale convective destabilization

Thinning of the lithosphere by small-scale convective destabilization

The elusive lithosphere–asthenosphere boundary (LAB) beneath cratons

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

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