ARKANSAS CRUSTAL XENOLITHS: IMPLICATIONS FOR BASEMENT ROCKS OF THE NORTHERN GULF COAST

Crustal xenoliths recovered from the diamondiferous Prairie Creek lamproite province in southwestern Arkansas directly constrain the nature, age and origin of Laurentian basement and indirectly provide a means to test models for development of the southeastern margin of Laurentia and the Ouachita trough. The majority of the crustal xenoliths are near-surface sedimentary rocks, with the rest mainly amphibolite and both fresh and altered granitic rocks. K-Ar dates of four amphibolite samples average ~1.41 Ga and indicate an association with the mid-continent craton.

Xenolith compositions and ages, in conjunction with published geophysical and drill data can be used to evaluate two tectonic models for the development of the southeastern margin of Laurentia and the Ouachita System. One model suggests the Ouachita trough is a failed rift basin essentially contained within the North American craton; while the second model suggests the Ouachita trough is a rifted continental margin with late Paleozoic accretion of an island arc terrane. Application of these data to the two models of Ouachita development suggests that the Ouachita trough is extended and thinned continental lithosphere associated with a Paleozoic rift system that developed separately from the Appalachian continental margin.

Keywords: Ouachita, ages, xenoliths, tectonics, rifting