THE CRUSTAL ORIGIN OF THE SABINE BLOCK IN SOUTH CENTRAL UNITED STATES

This study assesses the origin of the crust under modern day southern Arkansas, Louisiana, western Mississippi, and eastern Texas. The origin of the Sabine Block is not well understood because it was buried by marine and fluvial sediment prior to the Ouachita Orogeny in the late Paleozoic, followed by further deposition of post-orogenic fluvial sediments. Although the origin of the Sabine Block has been studied in the past, no direct sampling of the basement has been done before. The two predominate theories for the origin of the Sabine Block are that this terrane was first rifted from Laurentia during the Cambrian and was later accreted back on to the Laurentia margin during the Ouachita Orogeny. A second model is that the Sabine Block is of an exotic origin (e.g., an oceanic island arc) that is derived from another plate, then accreted on to Laurentia during the Ouachita Orogeny. To gain insight into the origin of the Sabine Block, xenolith samples were collected from two of the Prairie Creek lamproite pipes adjacent to the Crater of Diamonds State Park, located in Murfreesboro, AR. A selection of metamorphic xenoliths were then analyzed for neodymium isotopes to define their crustal model ages. Laser ablation ICP mass spectrometry was also used to date zircons from igneous xenoliths by U–Pb geochronology. The xenoliths were also examined petrographically to better understand petrogenesis and provenance. Xenoliths ranged from meta-sedimentary, amphibolites, and granites. Zircon U-Pb ages range from 1464 to 1783 Ma. This considerable age suggests that the Sabine Block was rifted from Laurentia during the Cambrian.