Archean Sedimentation Adjacent To An Orogenic Belt-Examples From Zimbabwe With Implications For Archean Tectonics

点击翻译按钮获取中文摘要

The Limpopo Province in southern Africa is a high-grade metamorphic belt that represents the exhumed root of a continent- continent collision zone. Granite-greenstone terranes of the Zimbabwe Province, to the north, and Kaapvaal Province to the south, flank the Limpopo Province. On the Kaapvaal craton, the Witwatersrand Supergroup is interpreted as a foreland-basin fill, representing the sedimentary response to collisional events in the Limpopo orogeny. A sedimentary succession of comparable lateral extent, thickness, and lithology to the Witwatersrand Supergroup is not present in the Zimbabwe Craton adjacent to the northern marginal zone of the Limpopo Province. Instead, five local and lithologically distinct stratigraphic successions of different age are present in the greenstone belts. At least four of these successions, developed in the lower and upper greenstones, are of comparable age to the Witwatersrand Supergroup. The absence of a Witwatersrand equivalent in Zimbabwe raises several important questions regarding the evolution of the southern African Archean in specific, and Archean tectonics and sedimentation patterns in general: 1) What are the detailed characteristics of two of the 3.0-2.7 Ga Zimbabwean basins, including source-area composition, source-area age, source-area location, sediment dispersal patterns, depositional environments, basin configuration, basin evolution, and tectonic setting? 2) What was the genetic relationship of the Zimbabwe sedimentary basins with respect to the evolution of the Limpopo orogeny? 3) Was the Limpopo orogeny of Pyrenean or Himalayan type? A multidisciplinary approach, involving detailed field mapping, structural analysis, sedimentologic-stratigraphic analysis, and geochemistry, will be applied to two of the stratigraphic successions to address the above questions.