The PORO-CLIM experiment: Did the North Atlantic Igneous Province drive the Paleocene-Eocene Thermal Maximum?

Throughout Earth's history, episodic Large Igneous Province emplacements coincide with remarkable environmental perturbations including mass extinction, global warming, and oceanic anoxia events.  The causal mechanism for this association remains unclear.  An exemplar is the temporal coincidence between the North Atlantic Igneous Province (NAIP) and the Paleocene-Eocene Thermal Maximum (PETM) global warming event.  The NAIP was emplaced over a period of c. 10 million years, whereas the PETM onset spanned c. 10 thousand years.  This discrepancy in pacing has motivated the hypothesis that NAIP-derived carbon-based greenhouse gas emissions slowly changed the background climate until a threshold was reached, triggering positive feedbacks that rapidly released additional non-volcanic carbon emissions that drove the PETM.  Here, we address an alternative hypothesis: that thermal mantle plume pulsing caused a pulse of NAIP magma generation and consequently a pulse of greenhouse gas emissions on the timeframe of the PETM.  To test this hypothesis, the PORO-CLIM experiment has generated an approximately 400 km long wide-angle seismic model of oceanic crust south of the Rockall Plateau, within the outer NAIP.  Crustal thickness and composition along this profile can be interpreted as a tape-recording of asthenospheric mantle temperature throughout NAIP emplacement.  Mantle temperature was cool during late Cretaceous continental break-up, increased through the Paleocene coincident with early NAIP activity, peaked near the Paleocene/Eocene boundary coincident with the most voluminous NAIP activity, and decreased through the early Eocene as NAIP activity waned.  This temperature cycle supports a plume initiation model for the NAIP.  Multiple thermal pulses are superimposed on the long-term temperature cycle.  The crustal morphology of these pulses resembles the V-Shaped Ridges currently forming in oceanic crust south of Iceland, which are thought to reflect thermal pulsing of the modern Icelandic Mantle Plume.  The biggest hot mantle pulse observed on the PORO-CLIM profile is associated with the PETM.  The difference between the age of this pulse recorded here within the outer NAIP and its age recorded within the inner NAIP by kilometre-scale uplift of sedimentary basins shows that the pulse travelled rapidly within the asthenosphere from the centre to the edge of the NAIP.  This pulse of hot, solid mantle travelled sufficiently rapidly to generate a pulse of NAIP magma by decompressional melting on the 10–100 thousand year timeframe of the PETM.  Thus the PORO-CLIM experiment supports a model in which the NAIP supplied a substantial proportion of volcanic greenhouse gases that triggered the PETM.  More generally, we propose that thermal plume pulsing is a key physical process that explains how relatively slow Large Igneous Province emplacements coincide with relatively rapid environmental perturbations.