An analysis of the variation of ocean floor bathymetry and heat flow with age

Abstract

Two models, a simple cooling model and the plate model, have been advanced to account for the variation in depth and heat flow with increasing age of the ocean floor. The simple cooling model predicts a linear relation between depth and t½, and heat flow and 1/t½, where t is the age of the ocean floor. We show that the same t½ dependence is implicit in the solutions for the plate model for sufficiently young ocean floor. For larger ages these relations break down, and depth and heat flow decay exponentially to constant values. The two forms of the solution are developed to provide a simple method of inverting the data to give the model parameters. The empirical depth versus age relation for the North Pacific and North Atlantic has been extended out to 160 m.y. B.P. The depth initially increases as t½, but between 60 and 80 m.y. B.P. the variation of depth with age departs from this simple relation. For older ocean floor the depth decays exponentially with age toward a constant asymptotic value. Such characteristics would be produced by a thermal structure close to that of the plate model. Inverting the data gives a plate thickness of 125±10 km, a bottom boundary temperature of 1350°±275°C, and a thermal expansion coefficient of (3.2±1.1) × 10−5°C−1. Between 0 and 70 m.y. B.P. the depth can be represented by the relation d(t) = 2500 + 350t½ m, with t in m.y. B.P., and for regions older than 20 m.y. B.P. by the relation d(t) = 6400 ‐ 3200 exp (−t/62.8) m. The heat flow data were treated in a similar, but less extensive manner. Although the data are compatible with the same model that accounts for the topography, their scatter prevents their use in the same quantitative fashion. Our analysis shows that the heat flow only responds to the bottom boundary at approximately twice the age at which the depth does. Within the scatter of the data, from 0 to 120 m.y. B.P., the heat flow pan be represented by the relation q(t) = 11.3/t½ μcal cm−2s−1. The previously accepted view that the heat flow observations approach a constant asymptotic value in the old ocean basins needs to be tested more stringently. The above results imply that a mechanism is required to supply heat at the base of the plate.

A global horizontal shear velocity model of the upper mantle from multimode Love wave measurements

“…In the 100 km-depth map the Mid-Atlantic Ocean, Indian Ocean and southern Pacific Ocean spreading ridges appear as a restricted, slow wave-speed feature centred on the bathymetric expression of the ridges. These slow wave speeds give way to fast wave speeds away from the ridges over a few hundred kilometres as the plate forms (Parsons & Sclater 1977). The upper mantle beneath the East Pacific Rise shows as a broad, strong slow wave speed feature in the 100 km depth map with a transition from slow to fast wave speeds toward the older portion of the Pacific Plate, similar to what has been observed in Rayleigh wave models of the Pacific Plate (Forsyth 1977;Zhang & Tanimoto 1991;Ritzwoller et al 2004;Priestley & McKenzie 2006;Maggi et al 2006;Priestley & McKenzie 2013).…”

Jurassic through Early Cretaceous Sedimentation History of the Central Equatorial Pacific and of Sites 800 and 801

“…Paleodepths of the studied sites were estimated following the procedure of Tucholke and Vogt (1979). A uniform thermal subsidence of underlying oceanic crust, which was assumed to have initially formed at ridge depths of 2700 m, and of plateaus was computed by applying an empirical global curve (Parsons and Sclater, 1977, as modified by Marty and Cazenave, 1989-their "Case 2"), where Depth = 2700 m + 283 m Velapsed m.y. Sediment loading was compensated for by raising the sediment surface above the calculated depth of oceanic crust by adding two-thirds of the total thickness of accumulated sediment (Table 5).…”

“…Paleolatitude for sites distant to the Leg 129 region may have been affected by rotation of the Pacific Plate (discussed in text). Depths of seafloor (depositional surface) are computed using the procedure of Tucholke and Vogt (1979), which uses the empirical subsidence curve of oceanic crust (Parsons and Sclater, 1977, as modified by Marty and Cazenave, 1989, in their "Case 2") and assumes an initial ridge crest depth of 2700 m, hence: Depth of sediment surface = (2700 m + 283 m elapsed m.y.) [= crustal subsidence] -2/3 of accumulated thickness of compacted sediment.…”

Lithosphere structure and upper mantle characteristics below the Bay of Bengal

“…3C) In the initial model, the geometry of the Moho was constructed either by utilizing the crustal velocity information (for the N-S transect AA') available from the published seismic refraction data (Curray et al, 1982) or adding 6 km thick normal oceanic crust to the basement (in the case of transects BB' and CC'). The Base of the lithosphere (LAB) was initially chosen based on the plate cooling model for the lithospheric ages in the region (Parsons and Sclater, 1977). Available seismic velocities along transects allowed us to consider the densities 2300 kg/m 3 for the upper sediment layer from present to upper Miocene, 2400 kg/m 3 for the middle layer from middle Miocene to upper Oligocene base and 2550 kg/m 3 for the pre-collision sediment layer.…”

“…9A-C). Additionally, as the N-S rofile (AA') lies across oceanic lithos here of age ranging from 65 to 110 Ma, we incorporated the temperature-dependent lithospheric mantle density structure defined by the global plate cooling models (Parsons and Sclater, 1977;Stein and Stein, 1992) while deriving the lithospheric structure.…”