Bert De Waele

A review of the Mesoproterozoic to early Palaeozoic magmatic and tectonothermal history of south–central Africa: implications for Rodinia and Gondwana

This paper provides a review of the tectonic evolution of central–southern Africa from Mesoproterozoic to earliest Palaeozoic times, using available geological information and a robust U–Pb zircon database. During the late Mesoproterozoic, the southern margin of the Congo–Tanzania–Bangweulu Craton was characterized by suprasubduction-zone magmatism and the accretion of arc and microcontinental fragments. Magmatism within the adjacent Irumide Belt formed by recycling of older continental crust. Ophiolite blocks, possibly part of an olistostromal mélange, are present in a Neoproterozoic sequence overlying the Irumide Belt, and the occurrence of high-pressure/low-temperature subduction-zone metamorphism and protracted Neoproterozoic suprasubduction-zone magmatism demonstrates that there was an ocean to the south (present-day coordinates) of the Congo–Tanzania–Bangweulu Craton until the amalgamation of Gondwana at 550–520 Ma, indicating that the Congo–Tanzania–Bangweulu Craton was not part of Rodinia. On the basis of their different ages and styles of magmatism, the Mesoproterozoic Kibaran Belt, Choma–Kalomo Block and Irumide Belt are not components of the same orogen, therefore precluding a sub-Saharan-wide, linked ‘Kibaran’ (sensu lato) orogenic event. Evidence is presented to illustrate that the Congo–Tanzania–Bangweulu and Kalahari Cratons developed independently until their final collision during the Pan-African Orogeny along the Damara–Lufilian–Zambezi Orogen at c. 550–520 Ma.

Proterozoic Tectonostratigraphy and Paleogeography of Central Madagascar Derived from Detrital Zircon U-Pb Age Populations

Detrital zircon U‐Pb ages determined by SHRIMP distinguish two clastic sequences among Proterozoic metasedimentary rocks from central Madagascar. The Itremo Group is older: zircon data, stromatolite characteristics, and carbon isotope data all point to a depositional age around 1500–1700 Ma. The Molo Group is younger, deposited between ∼620 Ma (the age of the youngest zircon) and ∼560 Ma (the age of metamorphic overgrowths on detrital cores). Geochronologic provenance analysis of the Itremo Group points to sources in East Africa as well as local sources in central and southern Madagascar but provides no evidence for a detrital contribution from northern and eastern Madagascar nor from southern India. Detrital zircon and sedimentologic similarities between rocks of the Itremo Group and the Zambian Muva Supergroup suggest a lithostratigraphic correlation between the two. The Molo Group has a strong 1000–1100 Ma detrital signature that also indicates an east African provenance and suggests a Neoproterozoic geographic connection with Sri Lanka but shows no indication of input from the Dharwar craton and eastern Madagascar. Central Madagascar was probably juxtaposed with the Tanzanian craton in the Paleo‐ and Mesoproterozoic, whereas northern and eastern Madagascar were connected to India. Internal assembly of Madagascar postdates Neoproterozoic Molo Group sedimentation and is likely to have occurred at about 560 Ma.

Untying the Kibaran knot: A reassessment of Mesoproterozoic correlations in southern Africa based on SHRIMP U-Pb data from the Irumide belt

The Irumide belt is part of a network of late Mesoproterozoic Kibaran-age orogens in south-central Africa. Sensitive high-resolution ion microprobe (SHRIMP) U-Pb zircon ages for gneisses, migmatites, and granitoids indicate that peak Irumide metamorphism was ca. 1020 Ma and that this was associated with widespread granitic magmatism at 1050–950 Ma. Pre-Irumide protoliths are dominated by 1650–1519 Ma granitic gneisses. These data provide the first robust constraint on the timing of Irumide tectonism and show that previous estimates of ca. 1350 and 1100 Ma are incorrect, thereby negating previously proposed correlations of the Irumide belt with nearby Kibaran-aged tectonism. The correlation between the Irumide belt and Choma-Kalomo block of southern Zambia has had a major influence on models for the tectonic assembly of southern Africa because it required that the intervening Neoproterozoic Zambezi belt was intracratonic and associated with minimal horizontal displacements. Our data indicate that both terranes have distinct histories, consistent with lithologic and metamorphic evidence of Neoproterozoic ocean closure along the Zambezi belt. This implies that the Kalahari and Congo cratons assembled during the Neoproterozoic and not during Kibaran-age tectonism, as previously believed. This new outlook on regional African tectonics supports a configuration of the Rodinia supercontinent that places the Congo craton well away from the Kalahari craton ca. 1000 Ma.

The geochronological framework of the Irumide Belt: A prolonged crustal history along the margin of the Bangweulu Craton.

Ion microprobe U-Th-Pb analyses of zircon from 40 granitoid rocks collected from the late Mesoproterozoic Irumide Belt in Central Southern Africa, along the southern margin of the Archean to Paleoproterozoic Bangweulu Block, provide a comprehensive set of age data for this complex orogen. The data indicate that the Irumide Belt is constructed on a basement of principally Paleoproterozoic (ca. 2.05–1.93 Ga) age with a subordinate Neoarchean (ca. 2.73 Ga) component, which is overlain by a platformal quartzite-pelite succession known as the Muva Supergroup. Previously published U-Pb detrital zircon data for the Paleoproterozoic Muva Supergroup, which show age populations that match all of the pre-1.9 Ga basement components identified within the Irumide Belt, suggest that the pre-Muva basement was assembled as a coherent block by ∼1.8 Ga, which we refer to as the Bangweulu Craton. The southern margin of the Bangweulu Craton was then intruded by a previously unrecognized suite of biotite-bearing granitoid rocks between 1.66 and 1.55 Ga, not recorded elsewhere in the region, and was later the site of emplacement of voluminous granitoid magmatism during the Irumide Orogeny at between 1.05 and 1.00 Ga. Hf isotopic data from zircon in these suites indicate variable influence from cryptic Archean rocks in the lower crustal melting zone of the Bangweulu Block. U-Pb analyses of inherited zircon cores in magmatic zircon in these granitoid rocks, directly confirm the presence of this reworked cryptic Archean basement of the Bangweulu Craton. The age data confirm previously proposed tectonic models for the Mesoproterozoic evolution of central Africa, refuting the presence of a continent-spanning Grenvillian-aged Orogen, including the Kibaran Belt, Irumide Belt and Choma-Kalomo Block of central Africa and connecting with Mesoproterozoic terranes further south along the margins of the Kalahari Craton. The data clearly show that the Proterozoic tectonic evolution of the Bangweulu Craton, which became attached to the southern margin of the larger Congo Craton during the Mesoproterozoic, involved a series of distinct convergent orogenic episodes affecting and reworking its southern (passive) margin. The mismatch in timing of Mesoproterozoic orogenic activity along the Bangweulu Craton, compared to that on the margins of the Kalahari, is compatible with the notion that these continental fragments were not juxtaposed along these Mesoproterozoic belts and in their present-day relative positions at the time. Whether either of these central and southern African cratons did form part of Rodinia, however, remains a matter for debate.

Protolith Ages and Timing of Metasomatism Related to the Formation of Whiteschists at Mautia Hill, Tanzania: Implications for the Assembly of Gondwana

Mautia Hill, situated in the Mozambique Belt of East Africa, is a locality famous for its unique high‐pressure whiteschist mineral assemblages. The rocks are located in a complex regional tectonic setting that is critical to understanding the amalgamation history of Gondwana.The timing of the Pan‐African Gondwana collision in this region is still a topic of considerable debate, especially because the age of the Mautia high‐pressure metamorphism/metasomatism has yet to be established. We have extracted detrital zircons with extensive low‐U overgrowths and dated them using the U‐Pb SHRIMP method. Detrital zircon cores indicate that the sediments came from a region identical to the adjacent Tanzania Craton and adjacent Western Mozambique Belt. One detrital grain has a 207Pb/206Pb age of ca. 3.5 Ga and is the oldest dated zircon in the region. The zircon rims provide 207‐corrected 206Pb/238U and 208Pb/232Th weighted mean ages of \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape

Volgo-Uralia: The first U-Pb, Lu-Hf and Sm-Nd isotopic evidence of preserved Paleoarchean crust

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Assembly, configuration, and break-up history of Rodinia: a synthesis

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