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Item Structural Evolution of the Ubendian Belt: Preliminary Results of a Traverse Between Karema and Mpanda (Tanzania).(1981) Nanyaro, J. T.; Basu, N. K.; Muhongo, S. M.; Mruma, Abdulkarim H.; Djare, S. A.; Mwakalukwa, G. L.; Nduma, I.; Mudiguza, K. M.; Van Straaten, P.; Klerkx, J.; Theunissen, K.Item Petrology of the Marginal Part of Mbozi Syenite—Gabbro Complex, Mbozi District, Mbeya Region, Tanzania(Elsevier, 1984) Basu, Nitin K.; Ikingura, Justinian R.Petrology of the marginal portion of the Mbozi syenite-gabbro complex occurring in southwestern Tanzania was studied. Petrographically, four rock types are recognised: gabbro, nepheline gabbro, nepheline syenite and nepheline-sodalite syenite. Texturally, the rocks exhibit a typical poikilitic texture in gabbro with large plates of undeformed plagioclase enclosing pyroxene and nepheline crystals to a protoclastic nepheline syenite and nepheline-sodalite syenite in which phenocrysts of nepheline, sodalite and pyroxene are set in a groundmass of shattered feldspars. Pyroxene and amphibole are sodic and aluminous in composition and their paragenesis indicates incomplete reaction relation; amphiboles exhibit exsolution of Ti in the form of ilmenite. It is concluded that an initially undersaturated magma favoured crystallization of nepheline and pyroxene in preference to plagioclase feldspars. Later shearing and granulation of the plagioclase and permiation of alkalic fluids may have given rise to the marginal alkaline rocks. Nepheline and mafic crystals are unaffected by the shearing as the strain was absorbed by the host plagioclase crystals. Twinning in pyroxene and amphibole crystals may, however, indicate effect of strain. Straight line variation diagrams of major elements and some of the trace elements and their ratios indicate probable mixing of magmas to produce the observed variation in rock types.Item Mineral Chemistry and Stability Relations of Talc-Piemonitite-Viridine Bearing Quartzite of Mautia Hill, Tanzania(1985) Basu, N. K.; Mruma, Abdulkarim H.Item Zircon U-Pb and Biotite Rb-Sr Dating of the Wami River Granulites, Eastern Granulites, Tanzania; Evidence for Approximately 715 Ma Old Granulite-Facies Metamorphism and Final Pan-African Cooling Approximately 475 Ma Ago(1985) Maboko, Makenya A. H.; Boelrijk, N. A. I. M.; Priem, H. N. A.; Verdurmen, E. A. Th.A UPb investigation of suites of zircons from five granulites in the Wami River area, Tanzania, yields a 17-points discordia with upper and lower intercepts at 714−49+36 Ma and 538−35+49 Ma, respectively. These systematics are interpreted to indicate an age of approximately 715 Ma (Pan African) for the M1 granulite-facies metamorphism, whereas the lower intercept is related to a stage in the uplift and cooling following the M2 amphibolite-facies retrogradation (elsewhere dated at approximately 650 Ma). Three of the granulites contain minor amounts of an inherited, > 1600 Ma old zircon component, probably derived from the igneous precursors of the granulites. A suite of zircons from the adjacent biotite gneisses may signal a provenance age of approximately 2600 Ma (Tanzania craton?), but the U-Pb systematics do not clearly reflect the amphibolitefacies metamorphism (correlated with the M2 partial retrogradation of the granulites) that transformed the sedimentary sequences into gneisses (any petrographic record of a possible older metamorphic influence being absent). Biotite/whole-rock pairs from the same samples yield Rb-Sr ages between about 470 and 485 Ma for the granulites and about 458 Ma for the gneiss. They are interpreted as ‘cooling ages’ and set an age between about 485 and 460 Ma to the final cooling of the crust through the closure temperature of biotite to Rb-Sr. The subsequent granulite-facies and amphibolite-facies events and their chronology are fitted in the continent—continent collision model for the evolution of the Mozambique belt advocated by the first author.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 The Geochemistry of Mafic and Ultramafic Rocks in the Wami River Granulite Complex, Central Coastal Tanzania(1987) Maboko, Makenya A. H.; Basu, N. K.The geochemistry of mafic and ultramafic rocks in the Wami River granulite complex of the central part of the coastal region, Tanzania, suggests that their protolith consisted of basaltic rocks with a calc-alkaline differentiation trend. Some of the ultramafic rocks show primitive chemical characteristics including high (Mg/Mg + Fetot) ratios and high Ni contents. These primary magmas later evolved mainly by olivine fractionation to yield the parent magmas which cooled to form the protolith of the bulk of the mafic granulites. The effect of the granulite facies metamorphism on the geochemistry of the rocks is restricted to depletion of Nb and Rb and possibly the enrichment of Ba.Item Geochemistry of Shallow Groundwater at Kigamboni Peninsula along Dar es Salaam Coastal Strip Tanzania(Elsevier, 1989) Nkotagu, Hudson H.The paper presents types of groundwater, hydrochemical facies, and chemical genesis of shallow groundwater at Kigamboni peninsula. Five types of groundwater have been identified as sodium bicarbonate, sodium sulphate, sodium chloride, calcium bicarbonate and magnesium bicarbonate type of waters. Hydrochemical facies change from calcium-sodium facies near the shore to sodium-calcium facies landward for cations, and from chloride-sulphate-bicarbonate to bicarbonate-chloride-sulphate facies respectively for anions. Calcium and Magnesium in high concentrations near the shore are attributed to dissolution of dolomitic limestone, being indicated by higher ratio of Ca2+/Mg2+ than one for samples K6, K7 and K9. The rest of the samples show low ratios indicating dolomite dissolution with probable calcite precipitation. Whereas the higher alkali metal concentrations than alkaline earths, observed landward, may probably be due to cation exchange process, similar pattern seen for chloride and sulphate concentrations also suggest mixing of fresh recharge water with interstitial marine water and or dissolution of airbone salts by recharging rainwater resulting into oceanic salt recycling. However, the water is observed to be suitable for general domestic and irrigation purposes. It has been concluded that the chemical character of shallow groundwater in the studied area, is a result of the interaction between recharge water with lithology and mixing with probable trapped marine water.Item Metamorphic PT Path of Granulites in the Musgrave Ranges, Central Australia(Elsevier, 1989) Maboko, Makenya A. H.; Mcdougall, Ian; Zeitler, P. K.Item Dating Late Pan-African Cooling in the Uluguru Granulite Complex Of Eastern Tanzania Using the 40Ar_39Ar Technique(Elsevier, 1989) Maboko, Makenya A. H.; Mcdougall, Ian; Zeitler, P. K.Age spectra measured by the 40Ar39Ar technique on hornblende, muscovite and K-feldspar from the Uluguru granulite complex of Eastern Tanzania indicate that following granulite facies metamorphism at ∼ 715 Ma the terrane cooled slowly, reaching a temperature of ∼475°C about 630 Ma ago. Subsequent cooling was even slower, reaching temperatures of ∼170°C about 420 Ma ago. Assuming a simple relationship between cooling rate and thermal gradient, the cooling history translates into an uplift path characterized by a phase of rapid uplift soon after granulite facies metamorphism followed by a period of slow uplift which began about 630 Ma ago. Such a history is consistent with model thermal histories of crustal segments undergoing thermal relaxation and isostatically-driven uplift following tectonic thickening events.Item Interpretation of Aerogeophysical Anomalies of Southwestern Tanzania(1990) Marobhe, Isaac M.This study deals with the interpretation of aeromagnetic data covering an approximate area of 50 000 km2 lying between 8°S to 9°30′S and 32°E to 35°E, Southwest Tanzania. The magnetic anomaly maps presented as contour maps, greytone maps, and stacked profile maps show distinct zones which match the geological units of the basement rocks. The study of magnetic lineaments has shown two prominent trends, one trending NW-SE and the second in the NE-SW. These lineaments have trends that coincide with those of structures in the rift system. Interpretation of digitized data using spectral analysis methods gave spectral depths ranging from 0.50 km to a maximum of 18 km. The shallow spectral depths were interpreted as the depths to the top of magnetic bodies. The application of singular value decomposition method in the automatic optimization of magnetic anomalies using prism, dyke and slope models was studied. The method was then used in the interpretation of prominent anomalies observed in the study area.Item Application of the Hartley Transform to the Interpretation of Magnetic Anomalies Due to Two-Dimensional Dyke Bodies(Elsevier, 1990) Marobhe, Isaac M.This study deals with the application of the Hartley transform in the inversion of total field magnetic anomalies due to a two-dimensional dyke model. The ratio of the Hartley transform to the amplitude spectrum gives the function from which the centre, magnetisation angle and dip may be determined. The depth and width of the dyke are determined from the amplitude spectrum. Tests using theoretical anomalies have shown that most of the estimates of the parameters are in agreement with parameters used to compute the anomalies. Proper scaling of the transform is required to better estimate depth and intensity of magnetisation.Item A Versatile Turbo-Pascal Program for Optimization of Magnetic Anomalies Caused By Two-Dimensional Dike, Prism, or Slope Models(Elsevier, 1990) Marobhe, Isaac M.A Turbo-Pascal program for automatic interpretation of magnetic anomalies caused by a dike, prism, or buried slope model of infinite strike length is presented. The residual between the observed and the calculated anomalies is minimized by adjusting the model parameters automatically. The change in model parameters is determined by decomposing the matrix of partial derivatives into singular values using a compact algorithm.Item Optimisation of Magnetic Anomalies via Singular Value Decomposition(Springer, 1990) Marobhe, Isaac M.A study is made on the application of singular values decomposition of Jacobian rectangular matrix of partial derivatives in the interpretation of magnetic anomalies. The algorithm used in decomposing the matrix is the compact version developed by Nash. The Jacobian matrix is factorised in three matrices, one of which is the diagonal matrix containing singular values. The three matrices together with residual vector are used to calculate the parameter vector change required to account for the observed anomaly. However, tests made using theoretical and field examples have shown that such a solution needs to be smoothed with a factor having a numerical value of between 0.10 and 0.90 before being used to update the initial model parameter vector. The smoothing process was found to increase the rate of convergence and minimises the occurrence of divergences. In addition, the use of a combination of three smoothing factors varying with decrease of the objective function, results in more stable iterations than using single factors. The addition of a small number less than 1.0 on singular values as damping factor, increases the rate of convergence slightly in comparison with no damping, whereas a large factor slows the convergence rate considerably. Once divergence has occurred, the singular values are used successively as damping factors starting with the smallest. This process of overcoming divergence was found to be successful in most cases. A Turbo-Pascal program for IBM/PC’s was developed incorporating the above features to optimise six parameters for dyke and slab models and seven parameters for the prism model. The program has been used to interpret aeromagnetic anomalies observed in S.W.Tanzania of which some are presented here as examples. In some cases, initial errors with values above 20% are reduced to errors of the order of 1% within the first five iterations.Item Zircon UPb Chronometry of the Pressure and Temperature History of Granulites in the Musgrave Ranges, Central Australia(1991) Maboko, Makenya A. H.; Williams, I. S.; Compston, WilliamIon microprobe U-Pb measurements of zircon in the Musgrave Ranges of central Australia date the emplacement of a charnockite, which is cut by a shear zone containing a garnet-clinopyroxene assemblage, M2 (PT conditions {approximately} 11 kb and 720C), at {approximately} 1200 Ma. Veinlets of a post-M2 adamellite cut an M4 assemblage (PT conditions {approximately} 6 kb and 670C) contained in a metadolerite inclusion, suggesting that the adamellite was emplaced during or after M4. Igneous and metamorphic zircons in the adamellite, however, grew at about 1200 Ma, indicating that M2 and M4 were synchronous. At the level of precision of the data, the time interval between the growth of the two assemblages can not have been more than 20 Ma. The authors interpret the pressure, temperature and time (PTt) path obtained by combining the thermobarometric data, and zircon U-Pb ages in terms of magmatic heat input in a thickened crustal segment followed by rapid, possibly tectonically driven, uplift of the lower part of the thickened crust to a depth of 15-20 kmItem Discordant ArAr ages from the Musgrave Ranges, Central Australia: Implications for the Significance of Hornblende ArAr Spectra(1991) Maboko, Makenya A. H.; Mcdougall, Ian; Zeitler, P. K.; Fitzgerald, J. D.Hornblende and biotite from granulites in the Musgrave Ranges, central Australia, yield variable 40Ar39Ar bulk ages even at the scale of a single outcrop. There is no obvious relationship between age, chemical composition, sample location, or textural characteristics of the minerals. We interpret the age variation as due to the incorporation of variable quantities of excess Ar. However, the age spectra of the minerals do not show the typical gain profiles commonly associated with excess Ar and isotope correlation diagrams do not indicate trapped Ar of non-atmospheric composition. Instead, some of the hornblendes and all the biotites show relatively simple age spectra similar to those commonly interpreted in terms of volume diffusion. These observations lead us to argue that, as is commonly the case with biotites, not all hornblende age spectra with simple patterns, similar to those predicted by diffusion theory, can be interpreted unambiguously in terms of geologically significant Ar concentration profiles. More specifically, we conclude that a relatively simple hornblende age spectrum does not necessarily indicate the absence of excess Ar.Despite their complexity, our results show that post-metamorphic cooling of the granulites was very slow. Although the incorporated excess Ar hinders the reconstruction of a more precise thermal history, the data show that following granulite-facies metamorphism ≈ 1200 Ma ago, the terrane did not cool below temperatures at which hornblende and biotite close to Ar diffusion until after ≈ 930 and ≈ 690 Ma, respectively.Item Stratigraphy and Morphotectonics of Karoo Deposits of the Northern Selous Basin, Tanzania(1991-02) Wopfner, H.; Kaaya, Charles Z.ate Permian Karoo deposits of the northern Selous Basin in south-central Tanzania comprise conglomerates and diamictitic boulder beds of alluvial and scarp-foot fan origin. These merge with grey to greenish sandstones, siltstones and black shales of deltaic and lacustrine environments. Microflora assemblages indicate a late Permian age. Lateral changes and interfingering of various lithofacies units are common. Depositional development was controlled by syndepositional faulting and variations of gradients resulting from fault movements. The position of the fault scarp separating the basin area from the elevated basement horst to the west roughly corresponded with the present boundary between the Selous Basin and the Precambrian metamorphics of the Uluguru Mountains. The late Permian Karoo succession of this part of the Selous Basin apparently overlaps older Karoo deposits contained in the north-northeast trending narrow graben structures. It is therefore regarded as a new depositional event which was initiated by renewed tensional tectonism in late Permian time. During this tectonic episode the narrow early Karoo graben structures were expanded into much broader rift basins. Material eroded from the rift shoulders and associated highlands was literally dumped across the fault scarps, forming debris aprons and scarp-foot fans. Rivers emanating from the highlands formed large alluvial fans and, further afield, deltas issued into freshwater lakes. Some of these late Permian faults were rejuvenated by late Cretaceous to early Tertiary tectonism. Thermal waters circulating along fractures converted feldspars, biotites and hornblendes to prehnite. Further tectonic adjustments in mid Tertiary time led to the present-day morphology.Item Depositional Environment of Late Permian Karoo Beds in the Ruhuhu Basin and Mikumi Area of Tanzania(1992) Kaaya, Charles Z.The Middle to Upper Permian Karoo sedimentary rocks in the western part of the Ruhuhu Basin have been stratigraphically redefined. They comprise the Mbuyura, Mhukuru, Ruhuhu and Usili Formations hirtherto known as K3, K4, K5 and K6 units respectively. Mbuyura Formation has further been subdivided into the Scarp Sandstone Member, ..Green Beds" and "Red Beds". Three tectonically controlled depositional cycles are recognized in this succession. The first cycle was initiated by fault movements within the NE - SW trending basin which at that time comprised two half grabens with uneven basin floor. Braided river sands of the Scarp Sandstone Member were deposited from the north and southwest of the basin. They pass upwards and laterally into braid plain mudrocks and sandstones of the "Green Beds". The second cycle was initiated by faulting outside the basin margins which led to overstepping of the "Red Beds" on the Precambrian metamorphics (basement), deposition of braided river sands at the basin margin and formation of mud flats and desiccating shallow ponds towards the basin centre. Amelioration of dry conditions accompanied the deposition of the overlying fluvial-lacustrine sandstones and carbonaceous mudrocks of the Mhukuru Formation. At that time the high grounds in the basin were disappearing under the sediment cover and the depositional area was acquiring a uniform easterly to southeasterly gradient. The overlying Ruhuhu Formation with a total thickness of more than 500 m of calcareous and non-calcareous mudrocks with stromatolite and oolite beds represents an establishment of a broad permanent lake with slightly alkaline waters during most of its history, The 13C isotopic values (+3.457 to -18.251 (PDB)) in the calcareous beds suggest that a great part of the carbon in the carbonates was derived from decomposing plant matter. The third cycle is represented by the Usili Formation. It commenced approximately at the Kazanian/Tatarian boundary as the area with Karoo beds was slowly being uplifted. The uplift coupled with lake level fluctuations resulted in the formation of uplands from which rudaceous sediments (lithic arenites) were eroded and deposited in the low lying mudflats and shallow lakes. The sandstones in the lower three formations are dominated by texturally immature arkoses (up to 70% feldspars) and subarkoses which indicate short transport distances from the basement provenance. Early diagenesis in the sediments as a whole was controlled by climatic conditions and to some extent by depositional environments whereas at the late stages, diagenesis was influenced by temperature, pressure and the type of sediments. A comparison between the Karoo rocks in the Ruhuhu Basin and those in the Mikumi area has been carried out. The available palaeontological data allow a general stratigraphic correlation but are still insufficient for a detailed correlation. A more detailed correlation is nevertheless possible when the palaeontological data are combined with lithostratigraphy. It is concluded that the Karoo succession in the Mikumi area is of the same age as the succession in the Ruhuhu Basin starting from the "Red Beds" to the top of the Usili Formation and both areas were subjected to similar tectonic and climatic patterns, In contrast to the terrestrial depositional environments which prevailed throughout the history of the Ruhuhu Basin. The Mikumi area was for a short period of time within the influence of marginal marine or brackish water conditions.Item Precambrian Tectonics and the Physiochemical Evolution of the Continental Crust. Part I: The Gabbro-eclogite Transition(1992) Ellis, David J.; Maboko, Makenya A. H.We report the first occurrence of retrograde eclogite shear zones cutting Proterozoic granulites from Australia. The Musgrave Range granulites were metamorphosed at about 12 kbar pressure and 850–900°C. The granulites then cooled isobarically and developed a variety of lower-temperature mineral reaction coronas typical of garnet granulites. These rocks are cut by a major shear zone, the Davenport Shear, in which lower-temperature, fine-grained eclogite developed. This demonstrates that mafic rocks in the deep crust can cool down into the thermodynamic stability field of eclogite without undergoing transformation to eclogite. We agree with Harte et al. (1981) that rocks lacking a fluid phase in stable tectonic regions are unlikely to maintain local equilibrium at ambient geotherm conditions until depths well within the upper mantle are reached.Item Geochronological Evidence for ∼ 530–550 Ma Juxtaposition ofTtwo Proterozoic Metamorphic Terranes in the Musgrave Ranges, Central Australia(Taylor and Francis, 1992) Maboko, Makenya A. H.; Mcdougall, Ian; Zeitler, P. K.; Williams, I. S.Contrasting temperature‐time paths from two Proterozoic metamorphic belts in the Musgrave Ranges, central Australia suggest that they represent district tectonothermal terranes. The thermal histories of these terranes converged about 530–550 Ma ago, as they were juxtaposed along the Woodroffe Thrust. Amphibolite fades metamorphism in the gneissic terrane north of the thrust is dated by zircon U‐Pb ages at ∼ 1600 Ma. Subsequently, the gneiss was intruded by granitoid at ∼ 1500 Ma, followed by a second metamorphic event which may be dated by a few zircon ages at ∼ 1400 Ma. Age maxima of ∼ 1300 Ma and ∼ 1260 Ma from steadily rising Ar‐Ar spectra date cooling below closure temperatures of hornblende and K‐feldspar respectively, following the latter metamorphism. In contrast, zircon U‐Pb ages date granulite facies metamorphism in the terrane south of the Woodroffe Thrust at ∼ 1200 Ma. Post‐metamorphic cooling in the granulite terrane was slow with hornblende and biotite remaining open to argon diffusion until after ∼ 930 and ∼ 690 Ma respectively. The thermal histories of the two terranes converged ∼ 530–550 Ma ago, when metamorphism associated with burial of the gneiss under an overriding ∼ 15 km thick thrust sheet of granulite led to the growth of syn‐tectonic muscovite in both terranes and caused near total resetting of Ar‐Ar ages in pre‐existing biotite and K‐feldspar in the gneiss. Cooling from this event was slow with the gneiss dropping below temperatures of ∼ 260° C at ∼ 350 Ma and the granulite cooling below ∼ 200°C at ∼ 400 Ma.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.