INVESTIGATIONS OF GRANITOIDS IN THE NORTHERN PIEDMONT OF ALABAMA

Granitic rocks were shown on the first geologic map of Alabama in 1858. On the 1927 geologic map 18 granitic bodies were collectively called the Pinckneyville Granite. A body of augen gneiss was shown, just southeast of the Pinckneyville. Gault (1945) published a systematic study of the Pinckneyville, which he renamed the Pinckneyville Quartz Diorite Complex. He considered it to comprise three overlapping intrusive stages, probably of late Paleozoic age.

Systematic geologic mapping, begun in the 1960's, led to the recognition of seven groups of granitic rocks, differentiated on the bases of composition and structural setting. They were informally called the Kowaliga Augen Gneiss, the Almond Plutons, the Bluff Springs Granite, the Elkahatchee Quartz Diorite Gneiss, the Hissop Granite(s) and the Rockford Granite(s).

Geochronologic, petrographic and geochemical studies, begun in the 1970's, further refined, but also complicated, the groupings. Radiometric age groupings led Deininger (1975) to call the Kowaliga, Elkahatchee, and Zana the older granites and the rest the younger granites. Cluster analyses and zircon morphologies indicate a threefold division of the "younger granites" not totally correlative with the abovementioned groupings.

Continued work in the 1980's contributed to theories on the petrogenesis of the granites, supported the threefold division and cast doubt on the Zana. Nearly twenty years of field-based studies culminated in the 1987 publication of "Granites of Alabama" edited by Drummond and Green. Unfortunately, that also seems to have marked the end of a productive period of granite studies in the northern piedmont.