Refraction seismic constraints on less extensive CAMP magmatism localized by prior extension in the Southeastern United States

Voluminous magmatism during the emplacement of large igneous provinces is thought to have profound impacts on the tectonic and climatic evolution of Earth. However, the origin of these magmatic events and controls on their emplacement remain debated, in part owing to incomplete information on their volume, distribution and composition. Here we focus on the Central Atlantic Magmatic Province, a large igneous province emplaced across North America, Europe, Africa and South America 201 Ma. Although CAMP is proposed to have been important for the breakup of Pangea and the End-Triassic Extinction, the cause of CAMP magmatism is poorly understood. The widespread distribution of CAMP magmatism at the surface has been interpreted to mean that there are large volumes of magmatic intrusions throughout the crust, but constraints on the latter are limited.

Here we present new constraints on the volume and distribution of CAMP magmatism in the crust from wide-angle seismic reflection/refraction data acquired across Georgia during the SUwanee suture and GA Rift (SUGAR) experiment. Georgia is an ideal location for this study because it lies at the center of CAMP magmatism, and a major Alleghenian suture and Triassic rift basin are in this area, which provide the opportunity to see how these features influence the distribution of magmatism in the crust. SUGAR Lines 1 and 2 cross western and eastern Georgia, respectively. On Line 1, high crustal P-wave velocities of >7.2 km/s are localized beneath the area with the thickest sediments and most concentrated crustal thinning, which we interpret to represent mafic intrusions into the crust. In contrast, most of the crust beneath Line 2 has lower P-wave velocities < 7.0 km/s and lower average VP/VS, consistent with an intermediate composition and limited mafic intrusions. On this profile, synrift sediments are thinner and crustal thinning is less localized. These results suggest either that magmatism resulted from extension or that lithospheric extension prior to CAMP concentrated CAMP magmatic intrusions to areas with greatest thinning. In either case, it indicates that CAMP magmatism is less voluminous and more localized than expected given the widespread distribution of magmatic intrusions at the surface. We explore the implications of these results for the cause of CAMP magmatism.