Temperature effects and their geological consequences at transform margins

Abstract

A thermal model of transform-margin evolution, including both shear heating and lateral conduction of heat from hot oceanic to colder lithosphere, was developed to gain insight into transform-margin crustal structure. Results indicate that over 2 km of crustal uplift may occur at the fault trace for a modelled transform fault 500 km in length with spreading half-rates of 1.0 and 4.0 cm/year. This uplift decreases away from the fault over a distance of 60–80 km. The viscosity of the lower continental crust and upper mantle adjacent to the transform margin is reduced by a factor of more than 100. In response to plate motion and asthenospheric upwelling at the spreading ridge, flow of this thermally weakened material may also play a role in continental crustal thinning.Thermal model predictions are compared with geological observations and crustal structure across transform margins. In particular, we show that the geology of the Southwest Newfoundland Transform Margin, eastern Canada, and the Cape Range fracture zone, Western Australia, supports the model predictions of uplift, erosion, and crustal thinning.

The Cote d'Ivoire-Ghana Transform Margin Eastern Equatorial Atlantic

“…At this stage, the vertical motion is estimated to have been on the order of 1 km, 20 km north of the continent/ocean boundary. This uplift is comparable to the thermal uplift estimated and reported by Todd and Keen (1989) for the southern Newfoundland Transform Margin.…”

“…Moreover, the contact between hot oceanic lithosphere and colder continental crust should have induced strong thermal gradients and resulted in subsequent marginal ridge uplift (Todd and Keen, 1989;Lorenzo and Vera, 1992). Within the Ivorian Basin, coeval sedimentation (D sequence) recorded such an uplift, while the previous sedimentary units were tilted northward.…”

“…Margin and its conjugate, the Falkland Margin (Ewing et al, 1971;Emery et al, 1975;Scrutton, 1976Scrutton, , 1979Scrutton, , 1982Lorenzo and Mutter, 1989); b) southern Newfoundland Margin (Hayworth and Keen, 1979;Todd et al, 1988;Keen et al, 1990); c) southern margin of the Exmouth Plateau (Lorenzo et al, 1991); d) Spitzbergen Margin (Lowell, 1972;Eldholm and Talwani, 1982;Eldholm et al, 1987); and e) equatorial African transform margins (Fail et al, 1970;Arens et al, 1971;Machens, 1973;Delteil et al, 1974;Emery et al, 1975;Mascle, 1976;Klingebiel, 1976;Blarez, 1986;Blarez et al, 1987;Mascle and Blarez, 1987;Mascle et al, 1988;Mascle, Auroux, et al, 1989;Basile, 1990;Basile et al, 1992;Mascle et al, 1993;Basile et al, 1993) and their conjugate, the northern Brazilian Margin (Ponte and Asmus, 1978 ;Zalan et al, 1985 ;Costa et al, 1990). Scientific drilling was conducted adjacent to transform margins during DSDP Leg 36 (Barker, Dalziel et al, 1976) and ODP Leg 114 (Ciesielski, Kristofferson, et al, 1988) in the Falkland area and ODP Leg 122 in the Exmouth Plateau (Haq, von Rad, O'Connell, et al, 1990).…”

Transform margins: development, controls and petroleum systems – an introduction

“…Early studies of the thermal expansion-driven uplift (e.g. Todd & Keen 1989;Lorenzo et al 1991;Lorenzo & Vera 1992;Basile et al 1993;Gadd & Scrutton 1997;Vågnes 1997), drawing from thermomechanical finiteelement and finite-difference modelling compared with crustal thinning and erosion estimates constrained by the refraction and reflection seismic, gravity and well data, interpreted a distinct uplift. Subsequent models (e.g.…”

Geodynamic evolution of the Côte d'Ivoire-Ghana transform margin: an overview of Leg 159 results

“…Uplift has been tentatively explained according to three main mechanisms: (1) tectonics, which implies either a compressional component (e.g., Blarez and Mascle, 1988) or sharp differences in tectonic subsidence ; (2) thermally induced uplift via heating of the continental lithosphere by the adjacent oceanic lithosphere (Mascle and Blarez, 1987;Todd and Keen, 1989;Lorenzo and Vera, 1992); and (3) magmatic effects such as underplating, which are unlikely along the CIG area because of the lack of any evidence of magmatic rocks or associated magnetic anomaly coeval with the rifting. Finally, more recently, mechanical modeling has been proposed (Lorenzo and Wessel, 1997) potentially associated with thermal modeling (Gadd and Scrutton, 1997;Vågnes, 1997).…”