Sm-Nd data for granitoids across the Namaqua sector of the Namaqua-Natal Province, South Africa.

• Sm–Nd data for rocks of granitic composition in an east–west traverse across the Namaqua Sector of the Mesoproterozoic c. 1.2 Ga Namaqua–Natal Province of southern Africa provide new evidence about the timing of crustal extraction from the mantle. Recent ion probe zircon dating has shown that, contrary to previous indications that pre-Namaqua basement had been preserved in parts of the Namaqua Sector, the majority of the magmatic rocks were emplaced during the 1.4–1.0 Ga Namaqua tectogenesis and very little U–Pb evidence of older precursors remains. Sm–Nd model ages show that Mesoproterozoic crustal extraction did occur, but was also strong in the Palaeoproterozoic, with local evidence for the existence of Archaean crust. The distribution of model ages generally corresponds with the established terranes, subdivided using lithostratigraphic and structural criteria. The northern part of the Bushmanland Terrane shows early Palaeoproterozoic to Archaean model ages and is clearly different from the southern part, which has Mesoproterozoic model ages. This supports the previously published results of a north–south traverse and justifies the separation of the Garies Terrane from the Bushmanland Terrane, though further subdivisions are not supported. The continuation of the Richtersveld Province east of Pofadder is supported by one sample, and the terrane boundary between the Bushmanland and Kakamas terranes is marked by an abrupt change from Palaeoproterozoic to Mesoproterozoic model ages. Model ages for the Kakamas and Areachap terranes do not distinguish them well. They suggest a Mesoproterozoic to late Palaeoproterozoic origin for both terranes, neither of which has a purely juvenile character. The influence of Palaeoproterozoic crust-forming events is clear in the Kaaien Terrane to the east, possibly reflecting reworking of the Kaapvaal Craton. The Namaqua Sector of the Province thus has a history of crustal extraction and evolution which reaches back locally to the Archaean, with major Palaeoproterozoic and Mesoproterozoic crust-forming events. This differs from the Natal Sector, which has a largely juvenile character related to a Mesoproterozoic Wilson cycle. Attempts to reconstruct the Mesoproterozoic Supercontinent Rodinia will have to take into account the extensive Nd-isotopic evidence for older crustal events in the Namaqua sector.

Ämnesord

NATURVETENSKAP  -- Geovetenskap och miljövetenskap (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences (hsv//eng)

Nyckelord

Nd model ages

granitoids

Namaqua-Natal Province

South Africa

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