New U-Pb-Hf zircon isotope data for the Paleoproterozoic Ubendian belt in the Chimala area,SW Tanzania |
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| Institution: | 1. Council for Geoscience, 3 Oos Street, Bellville, Cape Town, 7535, South Africa;2. Department of Earth Science, University of Bergen, PO Box 7803, Norway;3. Department of Geology, University of Johannesburg, PO Box 524, Auckland Park, 2006, South Africa;4. Geological Survey of Tanzania, Dodoma, Tanzania |
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| Abstract: | We present new U-Pb and Hf zircon isotope data on a suite of granitoids from a hitherto unstudied area of the Palaeoproterozoic Lupa terrane of the Ubendian belt in SW Tanzania.The major part of the area comprises a sequence of upper amphibolite grade paragneisses and migmatites.Subsequently,the field relations show a complex history of granitoid emplacement from early pre-tectonic strongly foliated diorite-tonalite-granodiorite orthogneiss to late tectonic,weakly deformed ellipsoidal granitoid plutons.These were followed by emplacement of undeformed K-feldspar rich porphyritic alkali granite.U-Pb zircon data on the granitoids show their emplacement ages span the period~1925 Ma to 1890 Ma and constrain the culmination of the Ubendian orogeny in the Lupa terrane to about 1900 Ma.The undeformed K-feldspar rich Chimala granite,previously considered to be unconformably overlain by the Buanji Group volcano-sedimentary rocks(recently shown to be~1675 Ma,not Neoproterozoic as originally thought) was dated at~1407 Ma showing that it must intrude the sedimentary rocks,although the age relationships are not exposed in the mapping area.This is the first record of early Irumide/Kibaran-aged post-tectonic granites in this part of East Africa.Hf isotope data from the zircons show that the granitoids have a long crustal pre-history stretching back to as far as~3.9 Ga,and showing that the Lupa terrane may form part of the "metacratonic" margin of an originally much more extensive Tanzania Craton. |
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| Keywords: | Geochronology Tanzania Ubendian Palaeoproterozoic Mesoproterozoic |
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