MAGMA RESERVOIR DEPTHS AND MAGMA TRANSPORT IN THE CENTRAL ATLANTIC MAGMATIC PROVINCE OF EASTERN NORTH AMERICA, WESTERN NEWARK BASIN, PENNSYLVANIA, USA, ASSOCIATED WITH RIFTING OF PANGAEA

Volcanic eruptions are thought to be fed by crust-spanning magmatic systems with connected magma reservoirs that may be mostly crystal mush (>30% crystals). We test this paradigm in the Central Atlantic Magmatic Province, Earth’s largest areal eruption of basaltic magma. The presence of larger crystals (antecrysts) in CAMP basalt requires an established reservoir system at the time of eruption. We focus on the earliest phase at 201.52 Ma in the Morgantown and Jacksonwald intrusive complexes (MJIC), western Newark basin. Pyroxene and whole-rock compositions from basalt and intrusion chill margins are used in thermobarometers (Putirka, 2008; Neave and Putirka, 2017) to estimate P-T conditions of antecryst formation and infer magma reservoir depths (first for ENA-CAMP). We compare relative P-T values within our restricted dataset supported by textural evidence and in good agreement with rhyolite-MELTS models and interpret results in the context of the reconstructed MJIC (Withjack, this session) and ENA-CAMP system.

Surprisingly, while P-T results indicate reservoirs throughout the crust, orthopyroxene (OPX) and augite (AUG) core results are significantly different: OPX crystallized from more primitive liquids above 1215°C at 0.9-0.4 GPa, 33-16 km in lower to mid-crust; AUG cores grew in mid- to upper crust at 1208-1156°C, 0.35-0 GPa, 13-0 km from slightly more evolved liquids. Deep reservoirs are consistent with seismic reflections at 24-33 km beneath the rift (Sheridan et al., 1991). Characteristics of crystal histories include growth at different P; partial resorption during ascent; capture by different basaltic magmas; and rapid ascent from middle to upper crust. Crystals in clusters formed at different P-T; textures help distinguish mush from clusters aggregated by transport/emplacement. Possible mush clusters in basalt formed in liquid-rich environments (>85% liquid) at P corresponding to rift basin intrusions. In sum, antecrysts formed at depth with < 10% fractionation before ascent with little evidence for crystal-rich mush at any level of the system at the time of flood basalt eruptions. Results are consistent with low-viscosity, liquid-rich magmas and a reservoir system that facilitated large volume transport and eruption under conditions of accelerated extension (Withjack et al., 2020).