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Petrogenesis and 40Ar/39Ar Geochronology of the Brandberg Complex, Namibia: Evidence for a Major Mantle Contribution in Metaluminous and Peralkaline Granites |
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| Authors: | SCHMITT A K; EMMERMANN R; TRUMBULL R B; BUHN B; HENJES-KUNST F |
| Institution: | 1GEOFORSCHUNGSZENTRUM POTSDAM, TELEGRAFENBERG B124, 14473 POTSDAM, GERMANY 2INSTITUT FÜR GEOWISSENSCHAFTEN UND LITHOSPHÄRENFORSCHUNG, UNIVERSITÄT GIESSEN, 35390 GIESSEN, GERMANY 3BUNDESANSTALT FÜR GEOWISSENSCHAFTEN UND ROHSTOFFE, 30655 HANNOVER, GERMANY |
| Abstract: | Anorogenic granites of the Brandberg igneous complex in NW Namibiaformed during early Cretaceous rifting and continental break-upof Gondwana. A metaluminous series SiO2 = 62–77 wt %,molar (Na + K)/Al = 0·8–0·95] includes anearly monzonite body, major biotite–hornblende granite,late biotite granite segregations and peripheral dykes of trachydacite.Volumetrically minor peralkaline granites of the Amis complexSiO2 = 72–77 wt %, (Na + K)/Al = 1·0–1·5]intrude the main granite and adjacent country rocks. Comparedwith the metaluminous main granite, these are in part highlyenriched in Zr, Nb, Y, U and Th. Initial Nd and Sr isotope ratiosof the metaluminous suite are |
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