Thermal parameters of the oceanic lithosphere estimated from geoid height data

Abstract

Geoid height anomalies derived from SEASAT altimeter data have been analyzed across fracture zones and over ocean ridges in two limited regions of the South Pacific (Eltanin fracture zone system; East Pacific Rise) and southeast Indian Ocean. Observed geoid height‐age and geoid height derivative (with respect to age)‐age relationships have been established. Comparison with theoretical relationships computed for the plate model of lithospheric cooling permits an estimation of the thermal parameters entering into the model. Two quantities can be derived: the product ακTm (α, thermal diffusivity; κ, volume coefficient of thermal expansion; Tm, bottom boundary temperature) and the thickness H of the plate. The best fitting values for the South Pacific and the southeast Indian Ocean are ακTm = 0.52×10−3 cm2 s−1 and H in the range 50–70 km for ages less than 30 m.y., whereas for larger ages (≥30 m.y.), geoid observations are better explained by a larger H value, in the range 70–90 km. The depth‐age relationship observed in the South Pacific region is consistent with these parameters. On the other hand, data for the northeast Pacific argue rather for a lithospheric thickness larger than 100 km. This suggests that local and regional variations exist in the thermal properties of the oceanic lithosphere.

Geoid anomalies across Pacific fracture zones

“…Since a similar hump in the geoid slope-age relationship is also observed at Murray FZ where age offsets are satisfactorily known, we are inclined to think that these features are real. Along Udintsev FZ, the new results presented here are in good agreement with those reported in Cazenave et al (1983) and in . Very large A h / A t values are found at young ages (0-5 Ma), and then a sharp decrease of the geoid slope up to 20Ma is observed, followed by fluctuations at larger ages.…”

“…We had previously analysed Seasat profiles to estimate the geoid step across the Mendocino and Udintsev FZs (Cazenave et al 1982(Cazenave et al , 1983. Since the method used in the previous analyses (visual estimate for the geoid step at Mendocino FZ, no points excluded in the vicinity of the FZ for Udintsev FZ), was somewhat different from the one applied here, we have re-estimated Ah along these two FZ applying the same method as above.…”

New global seamount census from altimetry-derived gravity data

“…This marine gravity anomaly data set has provided uniform and dense data coverage over all oceans and has enabled researchers to investigate both remote bathymetric features unexplored by oceangoing expeditions (e.g. Lazarewicz & Schwank 1982; Cazenave et al 1983; Watts & Ribe 1984; Mammerickx 1992; McAdoo & Marks 1992; Small & Sandwell 1994) as well as large‐scale deep‐seated geophysical phenomena (e.g. Haxby & Weissel 1986; McAdoo & Sandwell 1989; McNutt 1998).…”

Three‐dimensional numerical simulations of mantle flow beneath mid‐ocean ridges

“…Cold blobs sink into the convective mantle and are replaced by hot material, transferring heat upward and limiting the upper thermal boundary layer cooling. This process has been invoked to explain the flattening of the seafloor subsidence, of the heat flow, and of the geoid, observed at old ages [ Parsons and McKenzie , 1978; Stein and Stein , 1992; Doin and Fleitout , 2000], and the rapid decrease of geoid jumps across transform faults as a function of age [ Sandwell and Schubert , 1982; Cazenave et al , 1983; Driscoll and Parsons , 1988; Freedman and Parsons , 1990]. A recent tomographic study, based on surface wave dispersion measurements beneath the Pacific Ocean, provides evidence for a lithosphere reheating from 70 Ma with respect to a purely conductive cooling, that could result from thermal boundary layer instability development [ Ritzwoller et al , 2004].…”