New U-Pb-Hf zircon isotope data for the Paleoproterozoic Ubendian belt in the Chimala area,SW Tanzania  

作　　者：Robert J.Thomas Joachim Jacobs Marlina A.Elburg Abdul Mruma Godson Kamihanda Anthony Kankila Alex Masanja Hamisi Saidi 

机构地区：[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

出　　处：《Geoscience Frontiers》2019年第6期1993-2006,共14页地学前缘（英文版）

基　　金：supported by the research funding agencies of Denmark,Iceland,Norway and Sweden,and the Swedish Museum of Natural History;funded by an NRF-NEP grant(No.93208)

摘　　要：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.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.

关 键 词：Ceochronology Tanzania Ubendian PALAEOPROTEROZOIC Mesoprorerozoic 

分 类 号：P59[天文地球—地球化学]