ORIGIN OF LATE CRETACEOUS IGNEOUS ACTIVITY IN THE NORTHERN GULF OF MEXICO BASIN

The origin of post-rift igneous activity (ca. 108 – 65 Ma) in the northern Gulf of Mexico (GoM) region is a subject of debate. This Late Cretaceous igneous system, characteristically derived from the sublithospheric mantle, consists of alkaline basalts, nepheline syenites, carbonatites, and phonolites. It spans Arkansas, Mississippi, West Texas, and NE Mexico. Existing models include: 1) the Bermuda hotspot track; 2) Edge-driven convection; and 3) Renewed ARCs (alkaline rocks and carbonatites), i.e. reactivation of preexisting alkaline rocks in the lithosphere. These models have several shortcomings. Magmatic age distribution does not match the time-progressive pattern of the hotspot model. Edge-driven convection fails to explain the timing and location of igneous rocks. The renewed ARCs model can explain the location and some lithosphere-derived geochemical signature, but does not predict the timing (30-60 Myr after the cessation of GoM rifting and seafloor spreading) or the predominant asthenosphere-derived geochemical fingerprints.

We hypothesize that tearing of the Farallon slab causes the Late Cretaceous magmatism in northern GoM. A subducting oceanic slab can drag the asthenosphere mantle beneath it into the deeper mantle. Because the subslab asthenospheric mantle is warmer, and more buoyant than the oceanic slab, it can become upwardly mobile through slab gaps, pool at the base of the lithosphere, and result in intraplate volcanism. We speculate that during the middle Cretaceous, a tear initiates at the leading edge of the Farallon slab beneath Arkansas, providing a path for the subslab mantle to upwell and drive alkalic and carbonatitic magmatism. Then the slab tear may propagate orthogonal to the Farallon trench. Such process occur periodically (~ 25 Myr) across the North American continent from Late Cretaceous to Middle Eocene, resulting in the Kansas kimberlites, Montana alkaline province, and kimberlite fields in Saskatchewan. This model correlates the intraplate volcanism with active margins and explains the sublithosphere-derived igneous rocks in a regional tectonic framework. It may also provide boundary constraints for reconstruction of the Farallon slab back to ca. 110 Ma.