T046-06
How much melt forms in continental rifting and where does it go?
Monday, 14 December 2020: 20:50
Virtual
Molly Margaret Gallahue, Northwestern University, Department of Earth & Planetary Sciences, Evanston, IL, United States, Seth Stein, Northwestern University, Earth & Planetary Sciences, Evanston, IL, United States, Carol A Stein, Univ. of Illinois at Chicago, Chicago, IL, United States, Donna M Jurdy, Northwestern University, Earth and Planetary Science, Evanston, IL, United States, Mitchell Barklage, Nodal Seismic, Saint Charles, MO, United States and Tyrone O Rooney, Department of Earth and Environment Sciences, Michigan State University, East Lansing, MI, United States
Abstract:
The rifting and breakup 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. These rocks appear in two units: shallow seaward dipping reflectors (SDRs) and deeper high velocity lower crust (HVLC). The volume of magmatic rocks is a crucial constraint that can be used in numerical modeling of rift formation. We have compiled the VOLMIR (VOLcanic passive Margin Igneous Rocks) dataset, designed to investigate relationships between the volume of volcanics and other aspects of the rifting process. VOLMIR is based on previously interpreted seismic reflection profiles on which the volumes and geometries of both SDRs and HVLC units can be measured.
We find a relatively consistent ratio of SDR to HVLC volumes, where SDR amounts are approximately 1/3 of that of HVLC. This consistency suggests that the units are directly related during formation and could provide insight into how these units form during the continental rifting breakup process. 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. The relative strength of the correlations suggest that lithospheric processes play more of a role in continental rifting and breakup than hotspot/mantle plume processes. We also investigate the relationship between the volume of volcanics along passive margins and spatially and temporally related large igneous provinces (LIPs) on land. Examining these regions concurrently will provide further insight into the extent and distribution of magmatism along continental rifts prior to and during breakup.
