Geochronology of the Arkansas Alkaline Province, Southeastern United States

• Published in: The Journal of geology 2009-11, Vol.117 (6), p.615-626
• Main Authors: Eby, G. Nelson, Vasconcelos, Paulo
• Format: Article
• Language: English
• Subjects: Age distribution; Apatites; Geological time; Granite; Inlets; Isotopes; Magnets; Mica; Minerals; Nepheline; Petrology; Prairies; Rocks; Syenite
• ISSN: 0022-1376; 1537-5269
• DOI: 10.1086/605779

The Arkansas alkaline province (AAP) consists of intrusive bodies ranging in lithology from carbonatite and lamproite through nepheline syenite. Apatite and titanite fission‐track ages fall into two groups—101–94 Ma and ∼88 Ma. New40Ar/39Ar ages and those reported in the literature define a third age group of ∼106 Ma. Apatite and titanite fission‐track ages are concordant, indicating rapid cooling due to the emplacement of these intrusions at high levels during a time of regional uplift. There is a relationship between age and petrology: (1) lamproites are emplaced at ∼106 Ma, (2) carbonatites and associated silica‐undersaturated rocks are emplaced between 101 and 94 Ma, and (3) large nepheline syenite bodies are emplaced at ∼88 Ma. Chemical and isotopic data support the inference that the lamproites are derived from subcontinental lithosphere, while the other sequences are derived from the asthenosphere. The ages for the AAP and other conflicting information do not support the hypothesis that the AAP was formed by the passage of the North American plate over the Bermuda hotspot. A more likely explanation is that the magmatism was related to extension and reactivation of faults associated with the Mississippi graben.