Abstract
Significant volumes of magma are intruded into the crust during
continental break-up, which can influence rift evolution by altering
thermo-mechanical structure of the crust and thereby its response to
extensional stresses. Rift magmas additionally feed surface volcanic
activity and can be globally significant sources of tectonic CO2
emissions. Understanding how magmatism may affect rift development
requires knowledge on magma intrusion depths in the crust. Here, using
data from olivine-hosted melt inclusions, we investigate magma dynamics
for basaltic intrusions in the Main Ethiopian Rift (MER). We find
evidence for a spatially focused zone of magma intrusion at the MER
upper-lower crustal boundary (10-15 km depth), consistent with
geophysical datasets. We propose that ascending melts in the MER are
intruded over this depth range as discrete sills, likely creating a
mechanically weak mid-crustal layer. Our results have important
implications for how magma addition can influence crustal rheology in a
maturing continental rift.