T221 Getting to the Root of It—Metamorphism, Tectonics, and Crustal Evolution

Wednesday, 7 November 2012
8:00 AM - 12:00 PM
208B

LOW P-T KYANITE GROWTH ASSOCIATED WITH ALUMINUM METASOMATISM AND QUARTZ-SULFIDE VEINING, SENTINEL CU DEPOSIT, NORTHWESTERN ZAMBIA

Paper number: T221-6
Program: Technical Sessions
Time: 9:30 AM – 9:45 AM

Authors

Abstract

The Lufilian Arc, south-central Africa, is Pan-African aged metamorphic belt interpreted to be associated with the assembly of Gondwana . The area is known for extensive occurrences of whiteschists (kyanite-quartz-talc schists), commonly associated with high-pressure subduction zone metamorphism. In addition, the area hosts mineral enrichments associated with the Zambian and Congolese Copper Belts. Previous work in the Domes Region of the Lulfilian Arc (John et al., 2004) suggests that Pan African metamorphism occurred at peak metamorphic conditions of ~750⁰C and ~13 kbar.

New, detailed petrographic work on samples taken from drill core at the Sentinel Cu deposit, located on the northeast margin of the Kabompo Dome, northwestern Zambia, suggests a much lower P-T evolution. The Sentinel deposit is hosted in the Katangan Supergroup, which also hosts the extensive occurrences of whiteschists, and consists of kyanite-bearing graphitic phyllite within quartz-feldspar-biotite schist that overlies a sequence of marbles and quartzites. Phyllite occurs as a single ~400m layer where deformation is more intense on its upper and lower margins in comparison to a lower strain core. Within the low-strain domain 0.5-1cm, un-aligned kyanite is directly associated with weakly deformed quartz-chalcopyrite veins that cut bedding and also occur parallel to axial planes of folds. In high-strain domains quartz-sulfide-kyanite veins are dismembered, with kyanite occurring as porphyroclasts in a mylonitic matrix. These textural relationships suggest that veining occurred either prior to, or early in deformation. Moreover, kyanite-vein association and the grain size difference between kyanite and the sub-millimeter phyllite matrix, suggests that kyanite growth is related to aluminum metasomatism during the veining event. Critically, no assemblage evidence exists in the kyanite-bearing phyllites or surrounding quartz-feldspar-biotite schist for high-pressure and/or high-temperature metamorphism as suggested by earlier workers. We suggest a much lower P-T evolution for metasediments of the domes region, and therefore a contrasting tectonometamorphic evolution of the Lufilian Arc relative to the High-P rocks of the Zambezi Belt.

John, T., Schenk, V., Mezger, K., Tembo, F., 2004. Journal of Geology, 112, 71-90.