University:
Massachusetts Institute of Technology
Course:
12.520 | Geodynamics
Academic year:

2023
Views:

486

Pages:

17
Author:

Lukas Lowery

THE PANAFRICAN OROGENY How Africa was assembled Newly assembled Gondwana ca. 550 Ma Thicker lines possibly assembled at 1 Ga CARBONATITES AND NEPHELINE SYENITES: HOW DISTINGUISHING BETWEEN DEFORMED AND UNDEFORMED VARIETIES OF THESE STRANGE ROCKS IS TEACHING US ABOUT TECTONICS AND ABOUT MANTLE GEOCHEMISTRY Burke et al. (2003) ARCs = Alkaline Rocks & Carbonatites DARCs = Deformed Alkaline Rocks and & Carbonatites • All igneous ARCs and DARCs have mantle isotopic signatures • Many alkaline rocks and carbonatites (ARCs) are strongly associated with rifts Kola Peninsula ARCs are about 400 Ma emplaced during continental collision in Norwegian Caledonides ~300 km away DARCs (yellow) have yielded 2.4 Ga and 2.0 Ga ages Kogarko et al. (1995) This association raises the question: “Could there be DARKs and later kimberlites?” • DARCs (Deformed Alkaline Rocks and Carbonatites) are associated with known/ inferred suture zones • Rifts/suture zones show recurrent nepheline syenite and carbonatite activity • ARCs and DARCs of different ages occur within small distances from each other e.g. Thambani & Salambidwe, southern Malawi Data set AIM: TO DETERMINE A GENETIC LINK BETWEEN OLDER DARCs AND YOUNGER UNDEFORMED ARCs • Rb-Sr • Sm-Nd • Lu-Hf