EXPLORING THE RELATIONSHIP BETWEEN VOLCANIC PASSIVE MARGINS AND ADJACENT LARGE IGNEOUS PROVINCES

The rifting of continents leads to the initiation of seafloor spreading and eventual formation of passive margins. Some margins, termed magma-rich passive margins, are underlain by enormous volumes of igneous rocks, emplaced during continental breakup. The large amount of magmatic material in offshore volcanic passive margins is often compared to onshore large igneous provinces (LIPs), but the relationship between rifting, igneous units along passive margins, and LIPs is presently poorly understood.

We have developed the VOLMIR (VOLcanic passive Margin Igneous Rocks) dataset to investigate some of these relationships. VOLMIR is based on previously interpreted seismic reflection profiles on which the volumes and geometries of both shallow seaward dipping reflector and deeper high velocity lower crustal units can be measured. We find a relatively consistent ratio of SDR to HVLC volumes, with SDR amounts ~1/3 of that of HVLC. This consistency suggests that the units are directly related during formation and provides insight into how these units form during continental rifting and breakup. Presumably, as lower density melt rises to form SDRs, the remaining high-density residuum or cumulate becomes the HVLC. The volumes of SDR units display a moderate positive correlation with distance from the Euler pole, and a weak negative correlation with distance from the nearest hotspot, suggesting that lithospheric processes play more of a role in continental rifting and breakup than hotspot/mantle plume processes.

The North, Mid-, and South Atlantic Ocean breakups (and resulting volcanic passive margins) are temporally and spatially associated with the North Atlantic Igneous Province (NAIP), Central Atlantic Magmatic Province (CAMP), and Paraná-Etendeka LIP. We use VOLMIR to estimate the amount of igneous material along volcanic passive margins in these regions and compare it to estimates from the adjacent LIPs to explore relationships between the onshore LIP and offshore passive margin. Initial results indicate that there is a higher concentration of igneous material along volcanic passive margins than in the adjacent LIP. Further studies will provide insight into the relationship between passive margins and LIPs, and perhaps provide further understanding on the role of magmatism in rifting processes.