The Arkansas Alkaline Province, Southeastern USA: A Synthesis of New and Existing Chemical and Petrologic Data and Petrogenetic Considerations

The Arkansas alkaline province (AAP), southeastern US, consists of seven intrusions or intrusive complexes that lie along a NE–SW trend that falls on the extension of the Mississippi Valley graben. There are three distinct magmatic events: (1) emplacement of lamproites at ~104 Ma, (2) emplacement of lamprophyres, phonolites, carbonatites, ijolites, and a variety of nepheline syenites between 100 and 98 Ma, and (3) emplacement of a large nepheline syenite body at ~88 Ma. Unpublished and published mineralogical, elemental, and isotope data are used to develop an integrated model for the AAP magmatic activity. The lamproites were derived from ancient enriched subcontinental lithosphere. The carbonatite–lamprophyre–phonolite–ijolite–nepheline syenite association comprises several intrusive complexes (Magnet Cove, Potash Sulphur Springs, V-intrusive) and the Benton lamprophyre–felsic dike swarm. Magmatic evolution is controlled by fractional crystallization of pyroxene and nepheline. The carbonatites may be the result of liquid immiscibility between carbonate and lamprophyric liquids. The large nepheline syenite body (Granite Mountain and Saline County) evolved through fractional crystallization of feldspar and nepheline. Event 2 and 3 magmas were derived from an OIB-like asthenospheric source. The most likely model for the origin of the AAP is the reactivation of a zone of crustal weakness by far field stresses.