Synchronous Emplacement of the Anorthosite Xenolith‐Bearing Beaver River Diabase and One of the Largest Lava Flows on Earth.

New geochronologic and paleomagnetic data from the North American Midcontinent Rift (MCR) reveal the synchronous emplacement of the Beaver River diabase, the anorthosite xenoliths within it, and the Greenstone Flow—one of the largest lava flows on Earth. A U‐Pb zircon date of 1091.83 ± 0.21 Ma (2σ) from one of the anorthosite xenoliths is consistent with the anorthosite cumulate forming as part of the MCR and provides a maximum age constraint for the Beaver River diabase. Paired with the minimum age constraint of a cross‐cutting Silver Bay intrusion (1091.61 ± 0.14 Ma; 2σ), these data tightly bracket the age of the Beaver River diabase to be 1091.7 ± 0.2 Ma (95% CI), coeval with the eruption of the Greenstone Flow (1091.59 ± 0.27 Ma; 2σ)—which is further supported by indistinguishable tilt‐corrected paleomagnetic pole positions. Geochronological, paleomagnetic, mineralogical and geochemical data are consistent with a hypothesis that the Beaver River diabase was the feeder system for the Greenstone Flow. The large areal extent of the intrusives and large estimated volume of the volcanics suggest that they represent a rapid and voluminous ca. 1,092 Ma magmatic pulse near the end of the main stage of MCR magmatism. Key Points: New geochronology on an anorthosite xenolith tightly constrains the timing of the Beaver River diabase intrusionsPaleomagnetic and geochronological data support that the Beaver River diabase is comagmatic with the very high‐volume Greenstone FlowWide conduits of magma to the surface are indicated by large anorthosite xenoliths [ABSTRACT FROM AUTHOR]