Provenance and chemostratigraphy of the Neoproterozoic West Congolian Group in the Democratic Republic of Congo (original) (raw)
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Gondwana Research, 2013
The U-Pb data from the volcanic and detrital zircon grains of the Tombador Formation in Chapada Diamantina, Bahia, provide the depositional age of the top of this unit and define the main sedimentary sources of the Archean, Paleoproterozoic and Mesoproterozoic Eras. The lithofacies, petrographic and geochemical data from crystaltuff samples indicated that a volcanic source was located to the east of the Chapada Diamantina region. The available zircon data defined three first-order intracratonic basinal cycles, including the Lower (Statherian), Middle (Calymmian) and Upper (Stenian-early Tonian) Espinhaço basins. These sequences are well exposed at the Espinhaço Supergroup type-section in the Chapada Diamantina region. The zircon Hf isotope data from the 1.4 Ga crystal-tuff in the Middle Espinhaço and the 1.2 Ga tuffaceous rock in the Upper Espinhaço suggested different sources, with model ages of 2.1 to 1.9 Ga and b 1.9 Ga, respectively. The tectonic development of these Paleoproterozoic to Mesoproterozoic intracratonic basins can be explained by the far-field stress at the paleoplate margins, which has been shown in other Phanerozoic intracratonic basins. The data presented here support a tectonic scenario in which the Congo-São Francisco paleoplate interior recorded the main global events related to the geodynamic processes after the Columbia supercontinent collage and the formation and fragmentation of the Rodinia supercontinent.
Journal of South American Earth Sciences, 1992
Arafuaf BeR is a Late Proterozoic (BrasUiano Cycle) ~eotectonic unit which was developed along the southeastem margin of the Sac Francisco Craton (SE Brazil) and was formerly considered as being an ensialic orogen. It is correlated with the Pan-African West Congolian Belt (SW Africa) in many repefts. In the we, stem domain of the belt, the Macafbas Group-the most important supracrostal sequence related to the evolution of the Araquef Belt-comprises the Terra Branca and Carbonita Formations, which consist of littoral glacial sediments to shelf turbidites. These formations grade upward and eastward to the Salinas Formation, consisting of distal turbidites related to submarine fans, pelagic sediments, and a rock association (the Ribeirao da Folha Facies) typical of an ocean-floor environment. Banded iron formations, metacberts, diopsidites, massive anltides, graphite schists, hyperalnminous schists, and ortho-amphibolites, intercalated with quartz-mica schists and impure quartzires, characterize the most distinctive and restricted volcano-sedimentary facies yet found within the Salines Formation. Ultramallc slabs were teotonicatly emplaced within the Ribeirao da Folha Facies. Eight whole rock samples of meta-ultramaflc rocks and ortho-amphibolites yielded a Sm-Nd isuchronic age of 793 + 90 Ma (ENd(T) = 4'4.1:1: 0.6, MSWD ffi 1.76). The structures of the northern Araquaf Belt are marked by a down-dip stretching lineation (western domain) related to frontal thrusts which controlled tectonic transport from east to west; stretching lineation rakes decrease in the eastern tectonic domain, indicating dominant oblique to transcurrent motion; the northern arch of the beR is characterized by major high-dip transcurrent shear zones. Our tectonic model starts with marked fracturing, followed by rifling that took place in the SAo Francisco-Congo Crston around 1000 + 100 Ma (ages of basic intrusions and alkaline anorogenic granites). A sinistral transfer zone was established at the northem boundary of the belt, controlling the enlargement of the Araquaf-West Congoiian rill with the neighbouring northern oratonic region remaining essentially unaffected by compressional stresses. A period of ocesn-flour spreading took place at about 800 M_a. Rift closure started at about 750 Ma and led to the reversal of motion aloug former extensional structures. The main Braslliano-Pan-African orogenic period took place between 700 and 550 Ma and was marked by regional metamorphism and deformation related to both thrusting and lranscurrent movements, and emplacement of synteotonic granites derived from anatectic melts triggered by collisional crustal thickening. In this period, uRramafic slabs were emplaced within the Ribeirlto da Folha Facies, and both may represent an ophiolite-type suite. Late-to post-tectonic (500 to 550 Ma) intrusive granites were generated and emplaced in the Brazilian side along a major zone of crustal thickening in response to the last stages of collision.
Palaeogeography, Palaeoclimatology, Palaeoecology, 2013
The late Mesoproterozoic-middle Neoproterozoic period (ca. 1300 Ma-800 Ma) heralded extraordinary climatic and biological changes related to the tectonic changes that resulted in the assembly (~1.0 Ga) and the break-up of Rodinia (880 Ma-850 Ma). In the Democratic Republic of Congo, these changes are recorded in the Mbuji-Mayi Supergroup which was deposited in the SE-NW trending siliciclastic-carbonate failed-rift Sankuru-Mbuji-Mayi-Lomami-Lovoy Basin. New LA-ICP-MS U-Pb laser ablation data on detrital zircon grains retrieved from the lower arenaceous-pelitic sequence (BI group) together with C and Sr isotopic data on carbonates from the upper dolomitic-pelitic sequence (BII group) and an 40 Ar/ 39 Ar age determination on a dolerite give a new depositional time frame between 1174 ± 22 Ma and ca. 800 Ma for the Mbuji-Mayi Supergroup. The upper age limit is based on the assumption that the transition between the BIIb and BIIc subgroups recorded the Bitter Springs anomaly. In terms of tectonic and paleoclimatic settings, the BII group was deposited in the eastern passive margin of the Congo Craton during warm periods interlaced with temporarily dry and wet seasons, suggesting greenhouse conditions during the fragmentation of Rodinia.
Geological Society, London, Special Publications, 2008
Deposition of Palaeo-Mesoproterozoic sedimentary rocks on the São Francisco-Congo craton started during Statherian taphrogenesis (1.8-1.75 Ga), as verified by ages of c. 1.7 Ga determined for volcanic rocks of the lower part of the Espinhaço Supergroup in the states of Minas Gerais and Bahia (Brazil). These basins contain volcanic rocks and conglomerates alternating with sandstones, argillites and dolomites, deposited in continental, transitional and marine environments. The rocks in the westernmost sector of the Congo Craton (Central Africa) compose the Chela Group, comprising sandstones, argillites and dolomites. In the easternmost region of the Congo Craton the Kibaran, Akanyaru, Kagera and Muva supergroups occur: the first three in the Kibaran Belt and the last in the Irumide Belt and on the Bangweulu Block. They consist predominantly of pelites and schists, sandstones and, in lesser proportion, conglomerates, deposited in shallow marine, fluvial and lacustrine environments. Their sedimentation ages are constrained through ages on felsic tuff layers as follows: Chela Group 1790 + 17 Ma, Kagera Supergroup 1780 + 9 Ma, and Muva Supergroup 1879 + 13 Ma. These data show that broadly coeval and sedimentologically similar epi-continental sedimentary basins occurred on the São Francisco and Congo cratons, suggesting the possible existence of a long-lived wide epi-continental sea covering large areas of these cratons during Statherian times. The São Francisco Craton of South America and the Congo Craton of Africa are stable Archaean blocks of a once coherent landmass (Fig. 1) that broke up during the opening of the Atlantic Ocean. These cratonic nuclei are considered to have become stabilized during the Palaeoproterozoic Trans-Amazonian (South America) and Eburnian (Africa) events, and underwent a succession of later events along their margin including the Mesoproterozoic Espinhaço cycle in South America (Brito Neves et al. 1980), the Kibaran and Irumide orogens in Africa, often associated with the formation of the Rodinia supercontinent, and the Neoproterozoic Pan-African/Brasiliano orogenic events during the agglutination of Gondwana. The Pan-African/Brasiliano orogenesis reworked the edges of both cratons, giving birth to the Brasília, Araçuaí, Sergipano, Rio Preto and Riacho do Pontal belts in Brazil and the West Congo, Kaoko, Damara, Lufilian, Oubanguides and Zambezi belts and the East African orogen in Africa (Fig. 2). The initial coherence of the São Francisco and Congo cratons prior to Gondwana was based largely on the occurrence of comparable Precambrian epi-continental sequences on both sides of the Atlantic Ocean (Trompette 1994). In the São Francisco Craton, the Statherian taphrogenesis (1.8-1.75 Ga) opened a series of intra-continental rifts, some of which expanded into sag basins (Brito Neves 2002), into which volcanic and sedimentary rocks were deposited, collectively called the Espinhaço Supergroup. On the Congo Craton, the Palaeo-/Mesoproterozoic successions comprise the Chela Group on the Angola-Kasai Shield (Torquato & Fogaça 1981), the Kibaran and Akanyaru/Kagera supergroups in the central African Kibaran Belt (Royal Museum for Central Africa 1990; Theunissen et al. 1991) and the Muva Supergroup on the Bangweulu Block and within the Mesoproterozoic Irumide Belt (Daly & Unrug 1982; De Waele & Mapani 2002; De Waele 2005; Fig. 2). In Brazil these successions have been studied in detail and have their stratigraphical nomenclature
Precambrian Research, 2005
A provenance study of Neoproterozoic siliciclastic successions in the stratigraphically and tectonically lowermost and uppermost parts of the Pan-African Gariep Belt (Stinkfontein Subgroup and Oranjemund Group, respectively) in southwestern Africa, as well as in the Rocha Group of the Punta del Este Terrane (Dom Feliciano Belt) in Uruguay, revealed that the Oranjemund and Rocha Groups can be correlated and most likely formed in the same basin. Thus, the Rocha Group is considered to represent the fill of the westernmost part of a reactivated Ediacaran Gariep Basin. The lower parts of the Oranjemund and Rocha Groups reflect erosion of mafic rocks, whereas the upper parts are derived from a predominantly felsic source area. First major and trace element geochemical data are consistent with oceanic islands of within-plate geochemistry in the immediate vicinity as the most likely source of the mafic input into the lower part of the Oranjemund Group, whereas a combination of continental margin and island arc is indicated as source for the bulk of the younger sediments in the upper Oranjemund Group. Age spectra obtained by SHRIMP U-Pb analyses of detrital zircon grains from the Stinkfontein Subgroup (Port Nolloth Group), the Oranjemund Group, and the Rocha Group are very similar, except for a lack of the youngest age group around 600 Ma in the Stinkfontein Subgroup. In all three units, zircon grains of 1000-1200 Ma dominate, with a further peak in the age distribution between 1700 and 2000 Ma. These ages compare well with the pre-Gariep basement geology in southwestern Africa, where the former age range corresponds to magmatic and high-grade metamorphic activity in the Mesoproterozoic Namaqua-Natal Belt and the latter to an extensive Palaeoproterozoic Andean-type volcanic arc (Richtersveld Terrane). Comparable ages are conspicuously absent in the basement of the Rio de la Plata Craton in South America. Derivation of the Rocha Group sediments from a similar source as the contemporaneous Oranjemund Group sediments is therefore suggested. The most likely source of the youngest detrital zircon grains in these two stratigraphic units is the 640-590 Ma magmatic arc of the Dom Feliciano Belt.
The Neoproterozoic West Congo and Katanga Supergroups: Similarities and Differences
2011
The Congo Craton (Fig. 1), which is defined here as the central African large landmass that amalgamated at the time of Gondwana assembly at ~ 550 Ma, consists of several Archaean nuclei supposedly welded together around 2.1 Ga and later exhumed around 1.8 Ga as a result of Eburnean-aged collisional orogeny during the “Columbia” (also called “Nuna”) supercontinent amalgamation (Fernandez et al., 2011; Tait et al., 2010). Since the late Paleoproterozoic, the precursor of the Congo Craton (termed proto-Congo Craton by De Waele et al., 2008) has stabilized and remained a united entity throughout the Meso-Neoproterozoic (Tack et al., 2008). It underwent only intra-cratonic tectonic events (e.g., rifting, basin development, sedimentation, magmatism, etc), which never evolved into the formation of juvenile oceanic crust and break-up of the craton. As a result of Rodinia supercontinent fragmentation, several Neoproterozoic sedimentary basins developed in and around the Congo Craton. During ...
Terra Nova, 2012
U-Pb zircon and Ar-Ar amphibole and biotite ages from rocks of the West Congo Belt of Angola indicate that this area underwent two main deformation events of amphibolite facies grade at c. 540 and 490 Ma, which were followed by tectonically assisted exhumation during eastward thrusting of the hinterland domain onto the foreland domain. High-grade conditions in the West Congo Belt are 20-40 Ma younger than in the Ribeira-Araç uai Belt of Brazil, its South American counterpart, or than in the westernmost Kaoko Belt of Namibia, its African correlative. In the present state of knowledge, a more appropriate counterpart to the southern part of the West Congo Belt may be restricted to the Cabo Frio Terrane in the eastern Ribeira Belt, which yields a broadly similar evolution.
Precambrian Research, 2019
After it had been assembled in the very early Orosirian, the western São Francisco-Congo Paleocontinent experienced several rifting events since the Statherian (ca. 1750 Ma) to Cryogenian (ca. 700 Ma). Records of anorogenic magmatism and/or associated sedimentation from those events have been found in the Neoproterozoic Araçuaí-West Congo orogenic system (AWCO), located between the São Francisco (eastern Brazil) and Congo (central Africa) cratons. Based on detailed field studies and data from lithochemistry, zircon and titanite U-Pb dating, whole-rock Nd and Hf-in-zircon isotopic analyses, we characterize a previously poorly described Early Tonian, riftrelated, volcano-sedimentary succession in order to decipher the evolution of the AWCO precursor basins. That volcano-sedimentary succession, found in the Capelinha Formation type-area, now assigned to the Lower Macaúbas Group, includes quartzites with lenses of ortho-amphibolite (metabasalt) covered by pelitic schists. Zircon grains from ortho-amphibolite samples yielded ages of 957 ± 14 Ma and 576 ± 13 Ma, constraining their magmatic crystallization and regional metamorphism, respectively. These mafic rock show ƐNd (t) from-3.64 to +0.21 and Nd TDM ages from ca. 1.4 to ca. 1.7 Ga. Positive covariation of FeO tot /MgO+FeO tot , TiO 2 , P 2 O 5 , V and Zr, enrichment in light rare earth elements, slightly positive Eu/Eu* anomaly and depletion of high fieldstrenght elements, suggest tholeiitic protolith related to a continental rifting setting. The metasedimentary rocks show broad spectra of detrital zircon ages from the Early Tonian (ca. 940 Ma) to Paleoarchean, with wide-ranging ƐHf values from predominantly negative (as low as-10.76) to positive (+9.94), evoking well-known sediment sources in the São Francisco-Congo Paleocontinent. The youngest age peak (949 ± 12 Ma) constrains a maximum sedimentation age coeval with the basaltic volcanism represented by the ortho-amphibolite. The Capelinha volcano-sedimentary succession nearly correlates in age and origin with other anorogenic units (e.g., Ilhéus and Pedro Lessa dike swarms, Salto da Divisa granitic suite, Gangila basaltic and Mayumbian felsic volcanisms) found in a large region covered by the AWCO and neighbouring cratonic region. However, the Capelinha magmatism seems to preceed by some 20-30 m.y. the main peak (930-900 Ma) of this Early Tonian anorogenic magmatism, suggesting a long-lived and complex rift system.