The Richtersveld Igneous Complex, South Africa: U‐Pb Zircon and Geochemical Evidence for the Beginning of Neoproterozoic Continental Breakup

• Published in: The Journal of geology Vol. 109; no. 4; pp. 493 - 508
• Main Authors: Frimmel, Hartwig E., Zartman, Robert E., Späth, Andreas
• Format: Journal Article
• Language: English
• Published: Chicago The University of Chicago Press 01-07-2001; University of Chicago, acting through its Press
• Subjects: Alkalies; Chemistry; Crystallization; Geochemistry; Geology; Granite; Neoproterozoic era; Plate tectonics; Prehistoric era; Quartz; Rhyolite; Rocks; Seismology; Syenite; Tectonics; South Africa
• ISSN: 0022-1376; 1537-5269
• DOI: 10.1086/320795

New U‐Pb zircon ages and geochemical data for felsic intrusive and extrusive rocks from the Richtersveld Igneous Complex (RIC) and related rocks in the westernmost part of the 1.03–1.06‐Ga Namaqua‐Natal metamorphic belt, South Africa, indicate that this complex is not related to post‐Namaqua orogenic collapse but is the product of mantle‐derived alkaline magmatism in an extensional stress field that led to the breakup of a Neoproterozoic supercontinent. The oldest age obtained for the crystallization of granitic to syenitic melts is
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Ma. Continued thinning of the crust is reflected by the intrusion of bostonite dikes and a related extrusive phase dated at
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Ma. Magmatism in this igneous province, which stretches for about 200 km along a southwest‐northeast linear trend, lasted at least until
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Ma, which is now the best constraint on the beginning of rifting. Subsequent rift sediment deposition was accompanied by the emplacement of regionally extensive mafic dikes and bimodal, predominantly felsic volcanism along growth faults in the evolving rift basin at
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Ma. Consistent lower intercept ages on concordia diagrams (mean:
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Ma) suggest uplift and possible exposure to groundwater flow in response to late Paleozoic tectonism in the Cape Fold Belt farther south. The genesis of the RIC is in accordance with crustal thinning above a mantle plume that contributed to a mantle‐derived magma addition to the crust over a prolonged period of some 100 m.yr. Comparison with existing geochronological and petrological/geochemical data from elsewhere invites speculation as to the existence of a superplume stretching from southeastern Africa to South China in the heart of a supercontinent Palaeopangea.