Articles | Volume 9, issue 1
Solid Earth, 9, 139–158, 2018
Solid Earth, 9, 139–158, 2018

Research article 22 Feb 2018

Research article | 22 Feb 2018

Variability of the geothermal gradient across two differently aged magma-rich continental rifted margins of the Atlantic Ocean: the Southwest African and the Norwegian margins

Ershad Gholamrezaie1,2, Magdalena Scheck-Wenderoth2,3, Judith Sippel2, and Manfred R. Strecker1 Ershad Gholamrezaie et al.
  • 1Institute of Earth and Environmental Science, University of Potsdam, Karl-Liebknecht-Str. 24–25, 14476 Potsdam-Golm, Germany
  • 2GFZ German Research Centre for Geosciences, Section 6.1, Telegrafenberg, 14473 Potsdam, Germany
  • 3Faculty of Georesources and Material Engineering, RWTH Aachen, Aachen, Germany

Abstract. The aim of this study is to investigate the shallow thermal field differences for two differently aged passive continental margins by analyzing regional variations in geothermal gradient and exploring the controlling factors for these variations. Hence, we analyzed two previously published 3-D conductive and lithospheric-scale thermal models of the Southwest African and the Norwegian passive margins. These 3-D models differentiate various sedimentary, crustal, and mantle units and integrate different geophysical data such as seismic observations and the gravity field. We extracted the temperature–depth distributions in 1 km intervals down to 6 km below the upper thermal boundary condition. The geothermal gradient was then calculated for these intervals between the upper thermal boundary condition and the respective depth levels (1, 2, 3, 4, 5, and 6 km below the upper thermal boundary condition). According to our results, the geothermal gradient decreases with increasing depth and shows varying lateral trends and values for these two different margins. We compare the 3-D geological structural models and the geothermal gradient variations for both thermal models and show how radiogenic heat production, sediment insulating effect, and thermal lithosphere–asthenosphere boundary (LAB) depth influence the shallow thermal field pattern. The results indicate an ongoing process of oceanic mantle cooling at the young Norwegian margin compared with the old SW African passive margin that seems to be thermally equilibrated in the present day.

Short summary
We examined the thermal gradient as an index of the thermal field in the Atlantic. While the thermal anomaly in the South Atlantic should be equilibrated, the thermal disturbance in the North Atlantic causes thermal effects in the present day. Characteristics of the lithosphere ultimately determine the thermal field. The thermal gradient nonlinearly decreases with depth and varies significantly both laterally and with time, which has implications for methods of thermal history reconstruction.