--> Post-Rift Magmatism at Passive Margins: An Integrated Study of Late Cretaceous Igneous Activity in the Northern Gulf of Mexico

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Post-Rift Magmatism at Passive Margins: An Integrated Study of Late Cretaceous Igneous Activity in the Northern Gulf of Mexico

Abstract

The pre-Cenozoic tectonic history of the Gulf of Mexico (GoM) can be broadly described as Triassic rifting, followed by Jurassic seafloor spreading, and post-rift igneous activity as well as rapid subsidence during the Late Cretaceous. The igneous system, emplaced ca. 108 – 65 Ma, mainly consists of alkaline basalts, as well as nepheline syenites, carbonatites and phonolites, of which some are characteristically derived from the sublithospheric mantle. They span the entirety of the Northern GoM from the Uvalde and Balcones volcanic fields in Texas, through Louisiana and Arkansas, to the Jackson Dome in Mississippi. How this widespread magmatism affected the structural framework and thermal history of the basement and the overlying sedimentary package is still not clear. Competing hypotheses regarding the post-rift magmatism in the Gulf of Mexico include: 1) Magmatism in the Northern GoM was a consequence of the Bermuda hotspot as the North America plate moved over it; 2) Extensional reactivation of Ouachita-Appalachian and Grenville structures led to low-degree melting, due to crustal flexure induced by increased sediment load and/or compression in the western US; 3) Edge-driven mantle convection produced melts at the continent-ocean boundary; and 4) Tearing of stagnant Farallon slabs caused asthenospheric upwelling, decompression melting, and magma emplacement. Preliminary results show that there is no eastward age progression as predicted by the Bermuda hotspot hypothesis. Our S-wave tomography in Texas area reveals an overlap of the Uvalde-Balcones Igneous Province with the boundary between S-wave velocity anomalies in the crust and upper mantle, as well as the remnant of the Ouachita suture. While the spacing among igneous provinces matches the predicted size of edge-driven convection cells, this model does not readily explain the timing of the magmatism. It is also possible that tearing of a Farallon slab could trigger magmatism ca. 1200 km from the trench along the western margin of North America; a modern analog is the Changbai volcano associated with the stagnant Pacific slab in northeast Asia. We are acquiring new igneous rock ages and geochemical data, and integrating seismic reflection, tomography, and potential field data. This study aims to unravel the Late Cretaceous lithospheric structure and thermal evolution of the northern GoM, and to better understand the influence of post-rift magmatism on petroleum systems at passive margins.