Evolution of the mantle source mineralogy during continental rifting
E001
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Abstract
As a continental rift progresses towards an oceanic spreading center, three categories of rifted margins can be produced: magma poor, normal, and magma-rich margins. Despite decades of studies, controls on magmatic production in these regions remain poorly understood. IODP Expedition 396 sampled the continent-ocean transition of the magma-rich Mid-Norwegian Margin, formed during the last break-up phase of Pangea. The presence of a mantle plume has been suggested to explain the excess magmatism. However, mantle potential temperatures obtained from basalt compositions collected during the expedition suggest that a pure thermal anomaly is insufficient to explain the amount of excess magmatism. Using a newly developed geochemical model, we show that the source mineralogy changed during the rifting process. We interpret this change for thermal destabilization of the metasomatic subcontinental lithosphere due to significant stretching.