Browsing by Author "Mruma, Abdulkarim H."
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Item Complex high-strain Deformation in the Usagaran Orogen, Tanzania:Structural Setting of Palaeoproterozoic Eclogites(2003-11) Reddy, S.M; Collins, Alan S.; Mruma, Abdulkarim H.The Palaeoproterozoic Usagaran Orogen of Tanzania contains the Earth's oldest reported examples of subduction-related eclogite facies rocks. Detailed field mapping of gneisses exposed in the high-grade, eclogite-bearing part of the orogen (the Isimani Suite) indicates a complex deformation and thermal history. Deformation in the Isimani Suite can be broadly subdivided into five events. The first of these (D1), associated with formation of eclogite facies metamorphism, is strongly overprinted by a pervasive deformation (D2) at amphibolite facies conditions, which resulted in the accumulation of high strains throughout all of the exposed Isimani rocks. The geometry of foliations and lineations developed during D2 deformation are variable and have different shear directions that enable five D2 domains to be identified. Analysis of these domains indicates a geometrical and kinematic pattern that is interpreted to have formed by strain and kinematic partitioning during sinistral transpression. U–Pb SHRIMP zircon ages from a post-D2 granite and previously published geochronological data from the Usagaran eclogites indicate this deformation took place between 2000 ± 1 Ma and 1877 ± 7 Ma (at 1σ error). Subsequent greenschist facies deformation, localised as shear zones on boundaries separating D2 domains, have both contractional and extensional geometries that indicate post-1877 Ma reactivation of the Isimani Suite. This reactivation may have taken place during Palaeoproterozoic exhumation of the Usagaran Orogen or may be the result of deformation associated with the Neoproterozoic East African Orogen. U–Th–Pb SHRIMP zircon ages from an Isimani gneiss sample and xenocrysts in a “post-tectonic” granite yield ∼2.7 Ga ages and are similar to published Nd model ages from both the Tanzanian Craton and gneiss exposed east of the Usagaran belt in the East African Orogen. These age data indicate that the Isimani Suite of the Usagaran Orogen reflects reworking of Archaean continental crust. The extensive distribution of ∼2.7 Ga crust in both the footwall and hangingwall of the Usagaran Orogen can only be explained by the collision of two continents if the continents fortuitously had the same protolith ages. We propose that a more likely scenario is that the protoliths of the mafic eclogites were erupted in a marginal basin setting as either oceanic crust, or as limited extrusions along the rifted margin of the Tanzanian Craton. The Usagaran Orogen may therefore reflect the mid-Palaeoproterozoic reassembly of a continental ribbon partially or completely rifted off the craton and separated from it by a marginal basin.Item Fault Kinematics and Tectonic Stress in the Seismically Active Manyara–Dodoma Rift Segment in Central Tanzania – Implications for the East African Rift(2008-02) Macheyeki, Athanas S.; Delvaux, Damien; Batista, Marc De; Mruma, Abdulkarim H.The Eastern Branch of the East African Rift System is well known in Ethiopia (Main Ethiopian Rift) and Kenya (Kenya or Gregory Rift) and is usually considered to fade away southwards in the North Tanzanian Divergence, where it splits into the Eyasi, Manyara and Pangani segments. Further towards the south, rift structures are more weakly expressed and this area has not attracted much attention since the mapping and exploratory works of the 1950s. In November 4, 2002, an earthquake of magnitude Mb = 5.5 struck Dodoma, the capital city of Tanzania. Analysis of modern digital relief, seismological and geological data reveals that ongoing tectonic deformation is presently affecting a broad N–S trending belt, extending southward from the North Tanzanian Divergence to the region of Dodoma, forming the proposed “Manyara–Dodoma Rift segment”. North of Arusha–Ngorongoro line, the rift is confined to a narrow belt (Natron graben in Tanzania) and south of it, it broadens into a wide deformation zone which includes both the Eyasi and Manyara grabens. The two-stage rifting model proposed for Kenya and North Tanzania also applies to the Manyara–Dodoma Rift segment. In a first stage, large, well-expressed topographic and volcanogenic structures were initiated in the Natron, Eyasi and Manyara grabens during the Late Miocene to Pliocene. From the Middle Pleistocene onwards, deformations related to the second rifting stage propagated southwards to the Dodoma region. These young structures have still limited morphological expressions compared to the structures formed during the first stage. However, they appear to be tectonically active as shown by the high concentration of moderate earthquakes into earthquake swarms, the distribution of He-bearing thermal springs, the morphological freshness of the fault scarps, and the presence of open surface fractures. Fault kinematic and paleostress analysis of geological fault data in basement rocks along the active fault lines show that recent faults often reactivate older fault systems that were formed under E–W to NW–SE horizontal compression, compatible with late Pan-African tectonics. The present-day stress inverted from earthquake focal mechanisms shows that the Manyara–Dodoma Rift segment is presently subjected to an extensional stress field with a N080°E direction of horizontal principal extension. Under this stress field, the rift develops by: (1) reactivation of the pre-existing tectonic planes of weakness, and (2) progressive development of a new fault system in a more N–S trend by the linkage of existing rift faults. This process started about 1.2 Ma ago and is still ongoing.Item Geology and Geochemistry of Bauxite Deposits in Lushoto District, Usambara Mountains, Tanzania(Elsevier, 2003) Mutakyahwa, M. K. D.; Ikingura, Justinian R.; Mruma, Abdulkarim H.Bauxite deposits in the Usambara Mountains of north eastern Tanzania occur as remnants of residual deposits on two geomorphologically related plateaus of Mabughai-Mlomboza and Kidundai at Magamba in Lushoto, Usambara Mountains. The parent rocks for the deposits are mainly granulites and feldspathic gneisses of Neoproterozoic Mozambique belt. The plateaus represent a preserved Late Cretaceous–Lower Tertiary old land surface (African surface). Other parts of the Usambara Mountains and the neighbouring Pare Mountains are covered mostly by red–brown lateritic soils and impure reddish-brown kaolinitic clays. The bauxite deposits contain mainly Al2O3 (40–69 wt.%), Fe2O3 (3–10 wt.%), SiO2 (0.16–7 wt.%) and other elements occur in quantities not substantial to affect the quality or processing of the bauxite, and are attributed to the presence of relic minerals. Gibbsite makes up to 98 vol.% of the bauxite ore in special cases. Gibbsite is accompanied by goethite in the ore. Boehmite occurs in small amounts and is usually accompanied by hematite. Impurities include goethite, hematite, kaolinite, and minor relic quartz and microcline. Kaolinite is the sole clay mineral encountered in the bauxite ore, suggesting mature soil profiles and a development of the bauxite deposits on a well-drained peneplanation. Ore reserve estimates from the drilling data and surface geological mapping of the deposits yielded bauxite reserves of about 37 million tonnes.Item Geology and Geochemistry of Bauxite Deposits in Lushoto District, Usambara Mountains, Tanzania(2003-08) Mutakyahwa, M.K.D; Ikingura, J.R; Mruma, Abdulkarim H.Bauxite deposits in the Usambara Mountains of north eastern Tanzania occur as remnants of residual deposits on two geomorphologically related plateaus of Mabughai-Mlomboza and Kidundai at Magamba in Lushoto, Usambara Mountains. The parent rocks for the deposits are mainly granulites and feldspathic gneisses of Neoproterozoic Mozambique belt. The plateaus represent a preserved Late Cretaceous–Lower Tertiary old land surface (African surface). Other parts of the Usambara Mountains and the neighbouring Pare Mountains are covered mostly by red–brown lateritic soils and impure reddish-brown kaolinitic clays. The bauxite deposits contain mainly Al2O3 (40–69 wt.%), Fe2O3 (3–10 wt.%), SiO2 (0.16–7 wt.%) and other elements occur in quantities not substantial to affect the quality or processing of the bauxite, and are attributed to the presence of relic minerals. Gibbsite makes up to 98 vol.% of the bauxite ore in special cases. Gibbsite is accompanied by goethite in the ore. Boehmite occurs in small amounts and is usually accompanied by hematite. Impurities include goethite, hematite, kaolinite, and minor relic quartz and microcline. Kaolinite is the sole clay mineral encountered in the bauxite ore, suggesting mature soil profiles and a development of the bauxite deposits on a well-drained peneplanation. Ore reserve estimates from the drilling data and surface geological mapping of the deposits yielded bauxite reserves of about 37 million tonnes.Item Heterogeneous Excess Argon and Neoproterozoic Heating in the Usagaran Orogen, Tanzania, Revealed by Single Grain 40 Ar/39 Ar Thermochronology(Elsevier, 2004) Reddy, Steven M.; Collins, Alan S.; Buchana, Craig; Mruma, Abdulkarim H.Existing tectonic models for the evolution of the Usagaran Orogen place much significance on Palaeoproterozoic K–Ar and Rb–Sr ages. Laser 40Ar/39Ar data from single mica grains from the Isimani Suite near the western margin of the orogen indicate that excess 40Ar is common in micas and this casts considerable doubt on tectonic models that are based on previously published K–Ar ages. Biotites lying within a well-developed S2 foliation (previously constrained at 1999–1991 Ma) yield ages up to 3.3 Ga and contain a significant excess 40Ar component that is variable at an intra- and inter-sample scale. Textural evidence indicates that muscovite grew or recrystallized after the synkinematic biotites and they also record younger 40Ar/39Ar ages with individual steps from 524 to 1055 Ma. It is shown that the mica age variation does not reflect different periods of growth but the preferential partitioning of excess 40Ar into the biotite. The muscovite data also have a component of excess 40Ar and the youngest muscovite 40Ar/39Ar date (535.4 ± 2.3 Ma) indicates a maximum age for greenschist facies metamorphism. This date corresponds to thermal activity associated with the East African Orogen. Greenschist facies deformation (D4 and D5) is interpreted to have been coincident with this thermal event and indicates localized tectonic activity associated with Gondwanan amalgamation. The data are also consistent with greenschist facies deformation, metamorphism and deposition of the Usagaran Konse Group being of Neoproterozoic–Early Palaeozoic age. These new data therefore preclude a solely Palaeoproterozoic tectonic history for the Usagaran Orogen and indicate a complex thermal-tectonic reworking in the Neoproterozoic–Early Palaeozoic.Item Heterogeneous Excess Argon and Neoproterozoic Heating in the Usagaran Orogen, Tanzania, Revealed by Single grain 40Ar/39Ar Thermochronology(2004-09) Reddya, Steven M.; Collins, Alan S.; Buchana, Craig; Mruma, Abdulkarim H.Existing tectonic models for the evolution of the Usagaran Orogen place much significance on Palaeoproterozoic K–Ar and Rb–Sr ages. Laser 40Ar/39Ar data from single mica grains from the Isimani Suite near the western margin of the orogen indicate that excess 40Ar is common in micas and this casts considerable doubt on tectonic models that are based on previously published K–Ar ages. Biotites lying within a well-developed S2 foliation (previously constrained at 1999–1991 Ma) yield ages up to 3.3 Ga and contain a significant excess 40Ar component that is variable at an intra- and inter-sample scale. Textural evidence indicates that muscovite grew or recrystallized after the synkinematic biotites and they also record younger 40Ar/39Ar ages with individual steps from 524 to 1055 Ma. It is shown that the mica age variation does not reflect different periods of growth but the preferential partitioning of excess 40Ar into the biotite. The muscovite data also have a component of excess 40Ar and the youngest muscovite 40Ar/39Ar date (535.4 ± 2.3 Ma) indicates a maximum age for greenschist facies metamorphism. This date corresponds to thermal activity associated with the East African Orogen. Greenschist facies deformation (D4 and D5) is interpreted to have been coincident with this thermal event and indicates localized tectonic activity associated with Gondwanan amalgamation. The data are also consistent with greenschist facies deformation, metamorphism and deposition of the Usagaran Konse Group being of Neoproterozoic–Early Palaeozoic age. These new data therefore preclude a solely Palaeoproterozoic tectonic history for the Usagaran Orogen and indicate a complex thermal-tectonic reworking in the Neoproterozoic–Early Palaeozoic.Item Major Pan-African Imprints in the Ubendian Belt of SW Tanzania(1992) Theunissen, K.; Lenoir, J. L.; Liégeois, J. P.; Delvaux, Damien; Mruma, Abdulkarim H.Item Mechanisms of Inheritance of Rift Faulting in the Western Branch of the East African Rift, Tanzania(1997) Theunissen, K.; Klerkx, J.; Melnikov, A.; Mruma, Abdulkarim H.The western branch of the East African Rift system is commonly cited as a result of Phanerozoic reactivation of the Paleoproterozoic Ubendian belt in western Tanzania. Geological evidence is provided to show that prominent mechanical anisotropies successively appeared during Proterozoic evolution of the Precambrian basement and that their different reactivation behavior contributed to the Phanerozoic rift pattern. The Ubende belt (1950–1850 Ma) is a NW oriented, amphibolite facies ductile lateral shear belt in which older (2100–2025 Ma) and complex granulite facies terranes are included along trend. Retrograde multiphase sinistral strike-slip mylonites developed along the NW oriented ductile shear belt. They reflect persistent Proterozoic wrench fault reactivation of the latter. Shallow level sedimentary basins upon and along the ductile shear belt display deformational structures attributable to the Proterozoic wrench fault reactivation. Neoproterozoic sinistral transpression produced the final geometrical pattern of the wrench fault zone, which appears as an elongate and NW trending positive flower structure, locally enhanced by late Proterozoic contraction. Phanerozoic rifting is demonstrated by others to occur in three distinct episodes, during which the complex rift segment formed upon the multiphase Proterozoic wrench fault zone. The evaluation of the relationship between multiphase rift and multiphase prerift fabrics is reconsidered. The Proterozoic prerift fabrics correspond with a dextral transpressional and ductile deformational pattern, which became selectively reactivated by sinistral transpressional ductile-brittle mylonites. Proterozoic mylonites constitute shallow level mechanical anisotropies and define the general trend of the rift faults. According to the position of these mylonites in the center or in the external parts of their NW oriented Neoproterozoic transpression, they reactivate as complex and multiphase rift faults or as normal and recent faults, respectively. The Paleoproterozoic NW oriented and ductile lateral shear belt constitutes the deep level mechanical anisotropy. Its reactivation in Phanerozoic stress fields is likely dextral oblique transtension, considered as a leading mechanism of the pluriphase and NW oriented deep rift basins.Item Mechanisms of Inheritance of Rift Faulting in the Western Branch of the East African Rift, Tanzania(Wiley, 1996) Theunissen, K.; Klerkx, J.; Melnikov, A.; Mruma, Abdulkarim H.The western branch of the East African Rift system is commonly cited as a result of Phanerozoic reactivation of the Paleoproterozoic Ubendian belt in western Tanzania. Geological evidence is provided to show that prominent mechanical anisotropies successively appeared during Proterozoic evolution of the Precambrian basement and that their different reactivation behavior contributed to the Phanerozoic rift pattern. The Ubende belt (1950–1850 Ma) is a NW oriented, amphibolite facies ductile lateral shear belt in which older (2100–2025 Ma) and complex granulite facies terranes are included along trend. Retrograde multiphase sinistral strike-slip mylonites developed along the NW oriented ductile shear belt. They reflect persistent Proterozoic wrench fault reactivation of the latter. Shallow level sedimentary basins upon and along the ductile shear belt display deformational structures attributable to the Proterozoic wrench fault reactivation. Neoproterozoic sinistral transpression produced the final geometrical pattern of the wrench fault zone, which appears as an elongate and NW trending positive flower structure, locally enhanced by late Proterozoic contraction. Phanerozoic rifting is demonstrated by others to occur in three distinct episodes, during which the complex rift segment formed upon the multiphase Proterozoic wrench fault zone. The evaluation of the relationship between multiphase rift and multiphase prerift fabrics is reconsidered. The Proterozoic prerift fabrics correspond with a dextral transpressional and ductile deformational pattern, which became selectively reactivated by sinistral transpressional ductile-brittle mylonites. Proterozoic mylonites constitute shallow level mechanical anisotropies and define the general trend of the rift faults. According to the position of these mylonites in the center or in the external parts of their NW oriented Neoproterozoic transpression, they reactivate as complex and multiphase rift faults or as normal and recent faults, respectively. The Paleoproterozoic NW oriented and ductile lateral shear belt constitutes the deep level mechanical anisotropy. Its reactivation in Phanerozoic stress fields is likely dextral oblique transtension, considered as a leading mechanism of the pluriphase and NW oriented deep rift basins.Item Mineral Chemistry and Stability Relations of Talc-Piemonitite-Viridine Bearing Quartzite of Mautia Hill, Tanzania(1985) Basu, N. K.; Mruma, Abdulkarim H.Item Neogene-Holocene Rift Propagation in Central Tanzania: Morphostructural and Aeromagnetic Evidence from the Kilombero Area(2003-06) Gall, Bernard L.; Gernigon, Laurent; Rolet, Joel; Ebinger, Cynthia; Gloaguen, Richard; Nilsen, Odd; Dypvik, Henning; Deffontaines, Benoit; Mruma, Abdulkarim H.Based on field studies supplemented by remote sensing and aeromagnetic data from central Tanzania, a Phanerozoic structural history for the region can be developed and placed in a broader rift context. The major contribution of this work is the recognition of rift morphology over an area lying 400 km beyond the southern termination of the Eastern, or Kenya, Rift. The most prominent rift structures occur in the Kilombero region and consist of a wide range of uplifted basement blocks fringed to the west by an east-facing half-graben that may contain 6–8 km of sedimentary strata. Physiographic features and river drainage anomalies suggest that Holocene/Neogene deformation occurs along both rift-parallel and transverse faults, in agreement with the seismogenic character of a number of oblique faults. The present-day rift pattern of the Kilombero extensional province results from the complete overprinting of an earlier (Karoo) rift basin by Neogene- Holocene faults. The Kilombero rift zone is assumed to connect northward into the central rift arm (Manyara) of the Eastern Rift via an active transverse fault zone. The proposed rift model implies that incipient rifting propagates throughout the cold and strong lithosphere of central Tanzania following Proterozoic basement weakness zones (N140°E) and earlier Karoo rift structures (north-south). An eventual structural connection of the Kilombero rift zone with the Lake Malawi rift further south is also envisaged and should imply the spatial link of the eastern and western branches of the East African Rift System south of the Tanzanian craton.Item A New Tectonic and Temporal Framework for the Tanzanian Shield: Implications for Gold Metallogeny and Undiscovered Endowment(2002-03) Kabete, J.M.; Groves, D. I.; McNaughton, N.J.; Mruma, Abdulkarim H.The lack of new gold discoveries in recent times has prompted suggestions that Tanzania is mature or approaching maturity, in terms of gold exploration. New tectonic–metallogenic subdivisions proposed in this study are used to explain gold-endowment, assess gold exploration maturity, and suggest the potential for new discoveries from the following three regions: 1) the Lake Victoria Region, comprising the gold-endowed East Lake Victoria and Lake Nyanza Superterranes of < 2.85 Ga greenschist–amphibolite facies granitoid-greenstone terranes in > 3.11 Ga continental crust. These superterranes are separated by the gold-poor, Mwanza–Lake Eyasi Superterrane, comprising deeply eroded and/or exhumed terranes of gneissic-granulite belts and widespread granitoid plutons; 2) the Central Tanzania Region, comprising the Moyowosi–Manyoni Superterrane, which is largely composed of granitoid and migmatitic–gneissic terranes, and the Dodoma Basement and Dodoma Schist Superterranes, these are underlain by extensive, > 3.2 Ga migmatitic-gneisses and granitoid belts with interspersed, relatively narrow, < 2.85 Ga greenschist–amphibolite facies greenstone and schist belts. The Central Tanzania Region also includes the East Ubendian–Mtera Superterrane, comprising the East Ubendian Terrane of predominantly Paleoproterozoic belts with cryptic Archean age components, and the ~ 2.85–3.0 Ga Isanga–Mtera Terrane of thrust-transported migmatitic ortho- and para-gneisses; and 3) Proterozoic Tanzania Regions, comprising various Archean terranes which were once sutured to the Tanzania Craton prior to later Proterozoic orogenic and tectonic events that separated them from the craton and thermally reworked them. These include the Archean Nyakahura–Burigi Terrane in the Northwestern Tanzania Proterozoic Orogen and the Kilindi–Handeni Superterrane in the Southern East African Orogen of Tanzania. The major metallogenic significance of the new tectonic subdivisions is the recognition of under-explored belts: 1) in the gold-endowed East Lake Victoria and Lake Nyanza Superterranes, Lake Victoria Region. Here deeply weathered belts in the Musoma–Kilimafedha, Kahama–Mwadui and Nzega–Sekenke Terranes and belts, situated in tectono-thermally reworked crustal blocks such as the Iaida–Haidon, Singida–Mayamaya and Mara–Mobrama Terranes, are predicted to be prospective; 2) in the Dodoma Basement Superterrane, Central Tanzania Region, where relatively thin, juvenile granitoid-greenstone belts, similar to the ~ 2815–2660 Ma Mazoka Belt in the Undewa–Ilangali Terrane, contain small-scale gold systems with analogous terrane-scale geologic settings and evolution histories to those of gold-hosting greenstone belts in the Sukumaland Terrane, Lake Victoria Region. The overall geologic–geometric setting of the greenstone belts in the Central Tanzania Region (Mazoka-type) is comparable to those of the gold-hosting juvenile granitoid-greenstone belts in the South West and Youanmi Terranes, Yilgarn Craton, Western Australia, and North Superior and North Caribou Superterrane, northwestern Superior Craton, Canada; and 3) in the Proterozoic Tanzanian Regions, where terranes that lie in close geographic proximity and regional strike extension to the gold-endowed Lake Nyanza Superterrane are likely to be most prospective. They include the Archean Nyakahura–Burigi Terrane in unroofed thrust windows of the Mesoproterozoic Karagwe–Ankolean Belt of northwestern Tanzania, and the Kilindi–Handeni Superterrane where Archean proto-crust has been reworked by Pan-African tectonothermal events in the Southern East African Orogen.Item A New Tectonic and Temporal Framework for the Tanzanian Shield: Implications for Gold Metallogeny and Undiscovered Endowment(Elsevier, 2012) Kabete, J. M.; Groves, D. I.; McNaughton, N. J.; Mruma, Abdulkarim H.The lack of new gold discoveries in recent times has prompted suggestions that Tanzania is mature or approaching maturity, in terms of gold exploration. New tectonic–metallogenic subdivisions proposed in this study are used to explain gold-endowment, assess gold exploration maturity, and suggest the potential for new discoveries from the following three regions: 1) the Lake Victoria Region, comprising the gold-endowed East Lake Victoria and Lake Nyanza Superterranes of < 2.85 Ga greenschist–amphibolite facies granitoid-greenstone terranes in > 3.11 Ga continental crust. These superterranes are separated by the gold-poor, Mwanza–Lake Eyasi Superterrane, comprising deeply eroded and/or exhumed terranes of gneissic-granulite belts and widespread granitoid plutons; 2) the Central Tanzania Region, comprising the Moyowosi–Manyoni Superterrane, which is largely composed of granitoid and migmatitic–gneissic terranes, and the Dodoma Basement and Dodoma Schist Superterranes, these are underlain by extensive, > 3.2 Ga migmatitic-gneisses and granitoid belts with interspersed, relatively narrow, < 2.85 Ga greenschist–amphibolite facies greenstone and schist belts. The Central Tanzania Region also includes the East Ubendian–Mtera Superterrane, comprising the East Ubendian Terrane of predominantly Paleoproterozoic belts with cryptic Archean age components, and the ~ 2.85–3.0 Ga Isanga–Mtera Terrane of thrust-transported migmatitic ortho- and para-gneisses; and 3) Proterozoic Tanzania Regions, comprising various Archean terranes which were once sutured to the Tanzania Craton prior to later Proterozoic orogenic and tectonic events that separated them from the craton and thermally reworked them. These include the Archean Nyakahura–Burigi Terrane in the Northwestern Tanzania Proterozoic Orogen and the Kilindi–Handeni Superterrane in the Southern East African Orogen of Tanzania. The major metallogenic significance of the new tectonic subdivisions is the recognition of under-explored belts: 1) in the gold-endowed East Lake Victoria and Lake Nyanza Superterranes, Lake Victoria Region. Here deeply weathered belts in the Musoma–Kilimafedha, Kahama–Mwadui and Nzega–Sekenke Terranes and belts, situated in tectono-thermally reworked crustal blocks such as the Iaida–Haidon, Singida–Mayamaya and Mara–Mobrama Terranes, are predicted to be prospective; 2) in the Dodoma Basement Superterrane, Central Tanzania Region, where relatively thin, juvenile granitoid-greenstone belts, similar to the ~ 2815–2660 Ma Mazoka Belt in the Undewa–Ilangali Terrane, contain small-scale gold systems with analogous terrane-scale geologic settings and evolution histories to those of gold-hosting greenstone belts in the Sukumaland Terrane, Lake Victoria Region. The overall geologic–geometric setting of the greenstone belts in the Central Tanzania Region (Mazoka-type) is comparable to those of the gold-hosting juvenile granitoid-greenstone belts in the South West and Youanmi Terranes, Yilgarn Craton, Western Australia, and North Superior and North Caribou Superterrane, northwestern Superior Craton, Canada; and 3) in the Proterozoic Tanzanian Regions, where terranes that lie in close geographic proximity and regional strike extension to the gold-endowed Lake Nyanza Superterrane are likely to be most prospective. They include the Archean Nyakahura–Burigi Terrane in unroofed thrust windows of the Mesoproterozoic Karagwe–Ankolean Belt of northwestern Tanzania, and the Kilindi–Handeni Superterrane where Archean proto-crust has been reworked by Pan-African tectonothermal events in the Southern East African Orogen.Item Petrology of the Talc-Kyanite-Yoderite-Quartz Schist and Associated Rocks of Mautia Hill, Mpwapwa District, Tanzania(Elsevier, 1987) Mruma, Abdulkarim H.; Basu, N. K.Talc-kyanite-yoderite-quartz schist and associated rocks belonging to the Proterozoic Usagaran System occurring along the western edge of the Mozambique Orogenic Belt (450–600 Ma) were studied using petrographic, X-ray diffraction, electron-microprobe and fluid inclusion methods. The main rock types studied in the area include talc-kyanite-yoderite-quartz schist, piemontite quartzite, epidote-phogopite quartzite, kyanite-quartz-biotite schist and biotite gneiss. Fluid inclusion studies on the selected rock types indicate the presence of usually two-phased H2O-rich and CO2-rich fluids with a range of filling from 0.6 to 0.95. Some CO2-rich fluids may be one-phased (liquid) at room temperature with their degree of filling ranging from 0.4 to 1.0. Most of the CO2-rich inclusions show negative crystal shapes. Fluid inclusions trapped in kyanite in the talc-kyanite-yoderite-quartz schist with isolated negative crystal shapes are considered primary. The presence of CO2-rich fluids indicates low water fugacity during the formation of the talc-kyanite assemblage, and so pressure was probably lower. Primary fluid inclusions could be trapped at pressures between 5.2 and 5.6 kb and temperatures ranging from 540 to 570°C; this gives the possible P-T range of the peak of the first phase of progressive metamorphism.Item Petrology of the Talc-Kyanite-Yoderite-Quartz Sschist and Asociated Rocks of Mautia Hill, Mpwapwa District, Tanzania(2003) Mruma, Abdulkarim H.; Basu, N. K.alc-kyanite-yoderite-quartz schist and associated rocks belonging to the Proterozoic Usagaran System occurring along the western edge of the Mozambique Orogenic Belt (450–600 Ma) were studied using petrographic, X-ray diffraction, electron-microprobe and fluid inclusion methods. The main rock types studied in the area include talc-kyanite-yoderite-quartz schist, piemontite quartzite, epidote-phogopite quartzite, kyanite-quartz-biotite schist and biotite gneiss. Fluid inclusion studies on the selected rock types indicate the presence of usually two-phased H2O-rich and CO2-rich fluids with a range of filling from 0.6 to 0.95. Some CO2-rich fluids may be one-phased (liquid) at room temperature with their degree of filling ranging from 0.4 to 1.0. Most of the CO2-rich inclusions show negative crystal shapes. Fluid inclusions trapped in kyanite in the talc-kyanite-yoderite-quartz schist with isolated negative crystal shapes are considered primary. The presence of CO2-rich fluids indicates low water fugacity during the formation of the talc-kyanite assemblage, and so pressure was probably lower. Primary fluid inclusions could be trapped at pressures between 5.2 and 5.6 kb and temperatures ranging from 540 to 570°C; this gives the possible P-T range of the peak of the first phase of progressive metamorphism.Item Reconnaissance SHRIMP U–Pb zircon geochronology of the Tanzania Craton: Evidence for Neoarchean granitoid–greenstone belts in the Central Tanzania Region and the Southern East African Orogen(Elsevier, 2012) Kabete, J. M.; McNaughton, N. J.; Groves, D. I.; Mruma, Abdulkarim H.Reconnaissance U–Pb sensitive high-resolution ion microprobe (SHRIMP) zircon dating of gneisses, granitoids and greenstones from well-documented study areas within the Tanzania Craton indicates that: (1) ∼2815–2691 Ma greenschist-amphibolite facies greenstones and associated granitoids are confined within extensive >3600 Ma granitoid–gneisses in the Central Tanzania Region; (2) greenschist-amphibolite facies greenstone rocks from the Singida-Mayamaya Terrane in the south-eastern Lake Nyanza Superterrane, Lake Victoria Region are older than 2681 Ma; (3) greenschist to lower-granulite facies granitoid–greenstone belts from the Kilindi-Handeni Superterrane, within the largely Neoproterozoic Southern East African Orogen are older than 2670 Ma; and (4) the granitoid–greenstone belts within the Dodoma Basement Superterrane, Central Tanzania Region and Kilindi-Handeni Superterrane, Southern East African Orogen are broadly coeval with ∼2823–2671 Ma granitoid–greenstone belts in the Lake Nyanza Superterrane, in the Lake Victoria Region. The basement to juvenile greenstone rocks in the Central Tanzania Region includes E-W-trending orthogneisses. These comprise largely >3140 Ma diorite to granodiorite gneisses with rafts and/or tectonic enclaves of supracrustal rocks, including ∼3600 Ma fuchsitic sericite quartzite, which forms part of the ∼25 km by 5 km Simba-Nguru Hills in the Undewa-Ilangali Terrane. This quartzite contains detrital 4013–3600 Ma zircons that define ancestral cycles of protracted magmatism in their as yet undetected source terranes. In addition to the ∼2815–2670 Ma granitoids and greenstones in the >3000 Ma gneisses and granitoids within the widely accepted marginal zone of the Tanzania Craton, the Lake Nyanza Superterrane extends east into the Kilindi-Handeni Superterrane, in the largely Neoproterozoic Southern East African Orogen. In this Superterrane, Neoarchean igneous and sedimentary rocks in the Mkurumu-Magamba Terrane record ∼620–603 Ma amphibolite-granulite facies metamorphism, ∼585–575 Ma partial-melting, and emplacement of enderbitic-charnockitic granitoids. They also record a short-lived, but significant, 570–560 Ma period of exhumation and emplacement of high-grade metamorphic rocks on to basement rocks of the proto-Archean craton within the Central Tectonic Zone in the Southern East African Orogen.Item Stratigraphy and Palaeodepositional Environment of the Palaeoproterozoic Volcano-Sedimentary Konse Group in Tanzania(Elsevier, 1995) Mruma, Abdulkarim H.The Konse Group is a volcano-sedimentary assemblage of Palaeoproterozoic age located in central Tanzania between the Tanzanian Archaean Craton (to the west) and the high-grade Palaeoproterozoic Isimani Suite (to the east). The Konse Group is unconformably deposited on the high-grade Isimani Suite and it is only mildly metamorphosed to greenschist facies. Although the Konse Group is quite old, its deformational pattern is not complex and the order of superposition of its constituant lithologies can be outlined. There are also abundant primary sedimentary and volcanic structures which are still preserved in it. The Konse Group is therefore one amongst the very few oldest (if not the oldest) sedimentary basins in eastern Africa with preserved stratigraphy and primary structures, hence the basin serves as an important site for palaeodepositional environment, palaeoclimatology, and palaeotectonic studies in Africa and Gondwanaland as a whole. The Konse Group is made up of six lithologically distinct, conformable units. Its basal unit is a well-sorted orthoquartzite (the Mkulula Formation), which is shallow sea or epicontinental sands deposited on the sea shore. The basal orthoquartzite is overlain by a matrix-supported polymictic conglomerate (the Ruaha River Formation), which is either a lag gravel, point bar or channel bar deposit. The conglomerate is, in turn, overlain by thinly laminated silts and muds (the Kilimbe Formation) representing off-shore or shelf zone (distal) facies. The Kilimbe Formation is overlain by the Kikuyu Formation, which is made up of subaqueous volcanics of basic pillow lavas and basic tuffs with lapilli pockets which show low angle, cross-stratification. The subaqueous volcanics are overlain by dolomitic marble (the Ihumbirisa Formation) of the shallow water carbonate shelves fades and they are in turn overlain by the Mhwana Formation, which constitute the top-most unit of the Konse Group. The Mhwana is dominated by fine arenites intercalated with a banded quartz-Fe formation and a Mn-rich quartz formation. The Konse basing is interpreted as a peripheral foreland basin formed at the margin of the Tanzanian Archaean Craton during the :main phase of the Usagaran deformation.Item Stratigraphy and Palaeodepositional Environment of the Palaeoproterozoic Volcano-sedimentary Konse Group in Tanzania(2000-01) Mruma, Abdulkarim H.The Konse Group is a volcano-sedimentary assemblage of Palaeoproterozoic age located in central Tanzania between the Tanzanian Archaean Craton (to the west) and the high-grade Palaeoproterozoic Isimani Suite (to the east). The Konse Group is unconformably deposited on the high-grade Isimani Suite and it is only mildly metamorphosed to greenschist facies. Although the Konse Group is quite old, its deformational pattern is not complex and the order of superposition of its constituant lithologies can be outlined. There are also abundant primary sedimentary and volcanic structures which are still preserved in it. The Konse Group is therefore one amongst the very few oldest (if not the oldest) sedimentary basins in eastern Africa with preserved stratigraphy and primary structures, hence the basin serves as an important site for palaeodepositional environment, palaeoclimatology, and palaeotectonic studies in Africa and Gondwanaland as a whole. The Konse Group is made up of six lithologically distinct, conformable units. Its basal unit is a well-sorted orthoquartzite (the Mkulula Formation), which is shallow sea or epicontinental sands deposited on the sea shore. The basal orthoquartzite is overlain by a matrix-supported polymictic conglomerate (the Ruaha River Formation), which is either a lag gravel, point bar or channel bar deposit. The conglomerate is, in turn, overlain by thinly laminated silts and muds (the Kilimbe Formation) representing off-shore or shelf zone (distal) facies. The Kilimbe Formation is overlain by the Kikuyu Formation, which is made up of subaqueous volcanics of basic pillow lavas and basic tuffs with lapilli pockets which show low angle, cross-stratification. The subaqueous volcanics are overlain by dolomitic marble (the Ihumbirisa Formation) of the shallow water carbonate shelves fades and they are in turn overlain by the Mhwana Formation, which constitute the top-most unit of the Konse Group. The Mhwana is dominated by fine arenites intercalated with a banded quartz-Fe formation and a Mn-rich quartz formation. The Konse basing is interpreted as a peripheral foreland basin formed at the margin of the Tanzanian Archaean Craton during the :main phase of the Usagaran deformation.Item Structural Evolution of the Kilombero Rift Basin in Central Tanzania(2002) Mruma, Abdulkarim H.Detailed geological and structural investigations at the northwestern scarp of the Cenozoic Kilombero Rift allow the drawing of its structural evolution and establishment of stress conditions that prevailed at the different deformational episodes at this rift zone. The structure, where the northwestern scarp of the Cenozoic Kilombero Rift System is located, starts by ductile deformation of granitic and gabbroic rock masses leading to the formation gneissic fabric and b-mineral lineation in the rocks. This deformation is of Precambrian age (most probably a Pan African deformation) and its kinematics are characterized by 320˚/20˚ tectonic transport direction (λ1). Later the area was subjected to at least two brittle deformations (faults and joints) of Permo-Triasic and Cenozoic ages. These brittle deformations developed E-W trending (SET-1) and NE-SW trending (SET-2) conjugate discontinuities (joints and faults). All of them have very high dip angles (about 80˚) and they dip to the south and southeast, respectively. Their configurations imply kinematics with NNW-SSE trending sub-horizontal λ1, sub-vertical λ2, and ENE-WSW trending sub-horizontal λ3 This trend suggests that the stress regime that accounts for their formation had ENE trending sub-horizontal σ1 maximum compressive stress, sub-vertical σ2 intermediate compressive stress and a NNW trending sub-horizontal σ3 minimum compressive stress. Most of these discontinuities show reverse sense of displacement different form the main Kilombero fault (which has a normal throw) though both of them have the same trend. One could argue that the discontinuities with reverse displacement pre-dates the main Cenozoic Kilombero rift, the later being formed by reactivation of the earlier. The discontinuities with reverse displacement could be of Permo-Triasic age associated with Karoo tectonics. It is also possible that the reverse discontinuities and the Kilombero rift are coeval but the reverse sense of displacement in the earlier is induced by large-scale block rotation. In this case, both the reverse discontinuities and the Kilombero rift could be of Permo Triasic age but reactivated during the Cenozoic period particularly along the main Kilombero Rift. However, both the reverse discontinuities and the Kilombero rift could also be of Cenozoic age and that the imprints of Permo-Triasic tectonics are missing in the study area. The Permo-Triastic deformation imprints could be developed further to the southeast of the area where they are not concealed by the Cenozoic cover in the Kilombero plain. Dating of these discontinuities is therefore recommended in order to distinguish those of Permo-Triasic and Cenozoic ages.Item Structural Evolution of the Kilombero Rift Basin in Central Tanzania(2001) Mruma, Abdulkarim H.Detailed geological and structural investigations at the northwestern scarp of the Cenozoic Kilombero Rift allow the drawing of its structural evolution and establishment of stress conditions that prevailed at the different deformational episodes at this rift zone. The structure, where the northwestern scarp of the Cenozoic Kilombero Rift System is located, starts by ductile deformation of granitic and gabbroic rock masses leading to the formation gneissic fabric and b-mineral lineation in the rocks. This deformation is of Precambrian age (most probably a Pan African deformation) and its kinematics are characterized by 320˚/20˚ tectonic transport direction (λ1). Later the area was subjected to at least two brittle deformations (faults and joints) of Permo-Triasic and Cenozoic ages. These brittle deformations developed E-W trending (SET-1) and NE-SW trending (SET-2) conjugate discontinuities (joints and faults). All of them have very high dip angles (about 80˚) and they dip to the south and southeast, respectively. Their configurations imply kinematics with NNW-SSE trending sub-horizontal λ1, sub-vertical λ2, and ENE-WSW trending sub-horizontal λ3 This trend suggests that the stress regime that accounts for their formation had ENE trending sub-horizontal σ1 maximum compressive stress, sub-vertical σ2 intermediate compressive stress and a NNW trending sub-horizontal σ3 minimum compressive stress. Most of these discontinuities show reverse sense of displacement different form the main Kilombero fault (which has a normal throw) though both of them have the same trend. One could argue that the discontinuities with reverse displacement pre-dates the main Cenozoic Kilombero rift, the later being formed by reactivation of the earlier. The discontinuities with reverse displacement could be of Permo-Triasic age associated with Karoo tectonics. It is also possible that the reverse discontinuities and the Kilombero rift are coeval but the reverse sense of displacement in the earlier is induced by large-scale block rotation. In this case, both the reverse discontinuities and the Kilombero rift could be of Permo Triasic age but reactivated during the Cenozoic period particularly along the main Kilombero Rift. However, both the reverse discontinuities and the Kilombero rift could also be of Cenozoic age and that the imprints of Permo-Triasic tectonics are missing in the study area. The Permo-Triastic deformation imprints could be developed further to the southeast of the area where they are not concealed by the Cenozoic cover in the Kilombero plain. Dating of these discontinuities is therefore recommended in order to distinguish those of Permo-Triasic and Cenozoic ages.