Was the mantle warmer when Pangea broke up? insights from initial oceanic crustal thickness alongside the rifted margins of the Atlantic and Indian Oceans

Abstract

Insulation by the Pangean supercontinent has been suggested to have resulted in subcontinental mantle thermal anomalies and enhanced magmatic activity that may have influenced continental breakup. However, the thermal state of the mantle during the rifting of Pangea is not well established by geophysical and geochemical data. We present a compilation of oceanic crustal thicknesses next to the rifted margins of the Atlantic and Indian Oceans to investigate the variations of magma budget along the initial spreading centers, and thus the thermal state of the mantle immediately after breakup. We show that the initial oceanic crustal thickness values show a bimodal distribution with two modes centered around ∼5.5 km and ∼6.7 km. The first mode (∼5.5 km) corresponds mostly to initial oceanic crusts from the Equatorial Atlantic and is thinner than present-day normal oceanic crust (∼6.1 km thick). It could result from a cold thermal anomaly related to thick pre-opening equatorial continental lithosphere. The thicker than normal oceanic crusts of the second mode (∼6.7 km) could result from a small positive mantle potential temperature anomaly of 9–15 °C. In the Central Atlantic, which opened in Jurassic time after the Central Atlantic Magmatic Province event, this thermal anomaly could reach ∼60 °C at most to produce ∼9 km thick initial oceanic crust. We thus propose that the insulation effect of Pangea might have controlled locally the thermal state of the asthenosphere but it cannot be considered as a generally ubiquitous effect associated with the breakup of Pangea.