Distribution of Fenitized Crustal Xenoliths in Carbonatite Intrusions, West-Central Arkansas

Crustal xenoliths from carbonatite intrusions in the Morrilton-Perryville Arkansas area display a variety of mineralogical and textural features that suggest that they are fragments of basement crystalline rock that has undergone sodic metasomatism resulting from their close proximity at depth to a carbonatite complex. With increasing degrees of fenitization, the leucocratic xenoliths range from granolite - syenite - analcite syenite, while the melanocratic xenoliths range from hornblende - biotite to aegerine-apatite. A definite increase in fenitization is observed from Morrilton in the north to Brazil Branch, 16.8 km to the south. Fenitized xenoliths from Brazil Branch are generally quite small (0.5 cm - 1.0 cm) and contain a substantial amount of analcite. At Morrilton Lock and Dam, the fenitized xenoliths are very large (1.0 cm - 2.5 cm), and granolites are common. The xenoliths at Oppello Dump are intermediate in both size and mineralogical character. This area is therefore interpreted as a single alkalic - carbonatitic complex at depth, with its center near the southern extremity of the sampled area