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The Hillabee Greenstone is a mafic metavolcanic sequence at the stratigraphic top of the Talladega Group in the Northern Alabama Piedmont. The Hollins Line fault forms the upper contact of the Hillabee, and an undetermined amount of the Greenstone has been removed by faulting. The igneous protolith consisted of tholeiitic rocks (ash and lava) with minor calc-alkaline dacites. Volcanism was arc-related, based on geochemical evidence and the associated lithologies. Greenschist facies metamorphism and alteration have resulted in changes in the chemistry and mineralogy of the rocks. However, a variety of remnant igneous textures can be observed, and through statistical means, samples that have experienced minimal alteration can be identified, thereby allowing some of the igneous evolution of the Hillabee to be deduced. The chemistry and mineralogy (norm and mode) indicate tholeiitic fractionation representative of relatively shallow crustal depths with typical enrichment in Fe, V, Ti, and quartz and depletion of Mg, Cr, Ni, Co, and olivine. The dacites are associated with more highly fractionated basalts but do not appear to be a direct product of fractionation from the basalts. Some mafic rocks are typically gabbroic in texture and are interpreted to represent lava flows. Geochemical and field evidence indicates that the exposed Hillabee Greenstone represents an immature arc; plagioclase and olivine were highly fractionated prior to extrusion, and early stages of fractionation are not represented in surface exposures. Temporally earlier volcanics may occur downdip to the southeast toward the volcanic source; the exposed Hillabee Greenstone represents volcanics deposited somewhat distally from the volcanic source on the edge of the basin.

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