Some remarks on heat flow and gravity anomalies

McKenzie, Dan

doi:10.1029/jz072i024p06261

Cited by 681 publications

(178 citation statements)

References 21 publications

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“…This cooling is reflected on the dependence of geophysical observables on the age of the plate t [2,3]. For plates younger than about 70 My, both seafloor topography and surface heat flow (SHF) decrease linearly as ffiffi t p , consistent with predictions from the half-space cooling model [4].…”

Section: Introductionsupporting

confidence: 58%

“…Since these observables reflect the thermal structure of the lithosphere, their flattening implies a similar behaviour for the isotherms within the plate. These features are included in the popular plate model [2], which considers the lithosphere as a cooling plate with an isothermal lower boundary. Although this model can explain the observed flattening of both seafloor topography and SHF, it does not propose any particular mechanism by which the horizontal isotherm is maintained at constant depth.…”

Section: Introductionmentioning

confidence: 99%

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Small-scale gravitational instabilities under the oceans: Implications for the evolution of oceanic lithosphere and its expression in geophysical observables

Zlotnik

Afonso

Dı́ez

et al. 2008

Philosophical Magazine

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Sublithospheric small-scale convection (SSC) is thought to be responsible for the flattening of the seafloor depth and surface heat flow observed in mature plates. Although the existence of SSC is generally accepted, its ability to effectively produce a constant lithospheric thickness (i.e. flattening of observables) is a matter of debate. Here we study the development and evolution of SSC with a 2D thermomechanical finite-element code. Emphasis is put on (i) the influence of various rheological and thermophysical parameters on SSC, and (ii) its ability to reproduce geophysical observables (i.e. seafloor depth, surface heat flow, and seismic velocities). We find that shear heating plays no significant role either in the onset of SSC or in reducing the lithospheric thickness. In contrast, radiogenic heat sources and adiabatic heating exert a major control on both the vigour of SSC and the thermal structure of the lithosphere. We find that either dislocation creep, diffusion creep, or a combination of these mechanisms, can generate SSC with rheological parameters given by laboratory experiments. However, vigorous SSC and significant lithospheric erosion are only possible for relatively low activation energies. Well-developed SSC occurs only if the first $300 km of the mantle has an average viscosity of &10 20 Pa s; higher values suppress SSC, while lower values generate unrealistic high velocities. Seismic structures predicted by our models resemble closely tomography studies in oceanic mantle. However, the fitting to observed seafloor topography and surface heat flow is still unsatisfactory. This puts forward a fundamental dichotomy between the two datasets. This can be reconciled if most of the observed flattening in seafloor topography is influenced by processes other than SSC.

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Section: Introductionsupporting

confidence: 58%

Section: Introductionmentioning

confidence: 99%

Small-scale gravitational instabilities under the oceans: Implications for the evolution of oceanic lithosphere and its expression in geophysical observables

Zlotnik

Afonso

Dı́ez

et al. 2008

Philosophical Magazine

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“…Hager and Richards [1989] described the shallow seafloor at mid-ocean ridges as "familiar examples of convectively maintained topography." Yet, neither they nor Moucha and Forte [2011] question the view, dating from the early days of plate tectonics, that isostatic equilibrium of the cooling lithosphere at mid-ocean ridges accounts for the variation in depth and is a process largely isolated from sublithospheric mantle dynamics [e.g., Lambeck, 1972;McKenzie, 1967;Morgan, 1968;Sclater et al, 1971]. None of those authors misunderstands the physical issues involved, and all of them would provide essentially the same description of the dependence of ocean depth on the age of the ocean floor (at least out to 80 Ma).…”

Section: Terminologymentioning

confidence: 99%

Mantle dynamics, isostasy, and the support of high terrain

2015

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Dynamic topography is commonly understood to be deflection of the Earth's surface that results from convection of the mantle. Because different authors use the words "dynamic topography" differently, topography designated as dynamic may amount to only a few hundred meters or may exceed 2000 m. For most regions, however, surface heights computed on the assumption that the lithospheric column is in isostatic equilibrium provide good approximations to observed topography. The small free-air gravity anomalies and still smaller isostatic anomalies (<~30-50 mGal) associated with long-wavelength topography suggest that deflections of the Earth's surface induced by flow-induced normal tractions applied to the base of the lithosphere do not exceed~300 m. Little evidence exists to show that such tractions support more than~100 m of high terrain in regions like southern Africa, the Rocky Mountains and Colorado Plateau of the USA, eastern Asia, or the Aegean-Anatolian region, where some have argued for many hundreds to >2000 m of dynamic topography. Moreover, simple examples show that if flow-induced stresses maintain a given density distribution, then the resultant surface deflections can be smaller than those that would exist in isostatic equilibrium. In light of confusion over the term "dynamic topography," we offer readers simple tools that we hope will enable them to diagnose the component of topography that results from flow-induced stresses and to distinguish it from topography that is compensated isostatically.

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“…However, such an approach is misleading because (i) most data that represent the flattening are "abnormal" [e.g., as "distance criterion" of (4, 6)] and (ii) ffiffi ffi x p cannot be simply translated to ffi ffi t p to address heat input. Plotting z º ffi ffi t p ( old lithosphere (14) or some other way of counteracting the effects of a conductively cooling halfspace (15). The fundamental omission of Adam and Vidal (1) is the lack of a physically justifiable model: Even if z º ffiffi ffi x p trends were to be accepted, they do not demonstrate causally that "mantle flow drives the subsidence of oceanic plates."…”

mentioning

confidence: 99%