Department of Geology

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    THE 1994–1995 MANYARA AND KWAMTORO EARTHQUAKE SWARMS: VARIATION IN THE DEPTH EXTENT OF SEISMICITY IN NORTHERN TANZANIA
    (SOUTH AFRICAN JOURNAL OF GEOLOGY,, 2009) Gabriel D. Mulibo
    Seismicity within two earthquake swarms (mb 1.0 to 4.0) in northern Tanzania recorded by the 1994-1995 Tanzania Broadband Seismic Experiment has been investigated through event relocation, modelling of regional depth phases and examination of focal mechanisms. In the Manyara swarm, seismicity is distributed over a region ~20 km wide and extends to >30 km depth. Hypocenters correlate well with the Manyara Rift, and focal mechanisms of many events show normal faulting with nodal planes having the same north-northeast orientation as the Manyara Rift border fault. This result indicates that the events are consistent with slip along the border fault and related faults beneath the Manyara Rift, and shows that the faults extend into the lower crust. Seismicity in the KwaMtoro swarm is distributed over a region ~10 km wide but extends only to ~12 km depth. There are no mapped faults above the swarm, but a strong correlation between the north to south orientation of the swarm, the north to south orientation of nodal planes in focal mechanisms, and north to south striking extensional structures nearby, suggest that events in this swarm could be caused by slip on a system of rift faults. However, a magma-driven origin for either swarm cannot be ruled out either.
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    THE 1994–1995 MANYARA AND KWAMTORO EARTHQUAKE SWARMS: VARIATION INTHE DEPTH EXTENT OF SEISMICITY IN NORTHERNTANZANIA
    (GeoScienceWorld, 2009-12) Mulibo G.D., and Nyblade A.A
    Seismicity within two earthquake swarms (mb 1.0 to 4.0) in northern Tanzania recorded by the 1994-1995 Tanzania Broadband Seismic Experiment has been investigated through event relocation, modelling of regional depth phases and examination of focal mechanisms. In the Manyara swarm, seismicity is distributed over a region ~20 km wide and extends to >30 km depth. Hypocenters correlate well with the Manyara Rift, and focal mechanisms of many events show normal faulting with nodal planes having the same north-northeast orientation as the Manyara Rift border fault. This result indicates that the events are consistent with slip along the border fault and related faults beneath the Manyara Rift, and shows that the faults extend into the lower crust. Seismicity in the KwaMtoro swarm is distributed over a region ~10 km wide but extends only to ~12 km depth. There are no mapped faults above the swarm, but a strong correlation between the north to south orientation of the swarm, the north to south orientation of nodal planes in focal mechanisms, and north to south striking extensional structures nearby, suggest that events in this swarm could be caused by slip on a system of rift faults. However, a magma-driven origin for either swarm cannot be ruled out either.
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    2.67 Ga high-Mg andesites from the Musoma-Mara greenstone belt, northern Tanzania
    (2008-07-01) Manya, Shukrani; Maboko, Makenya A. H.
    Neoarchaean (2.67 Ga) High-Mg andesites occur in the Musoma-Mara greenstone belt, northern Tanzania. They are associated with dacites and Na-granitoids both of which are adakitic in composition. The high-Mg andesites are characterized by higher contents of MgO (2.42 – 9.47 wt %), Cr (41-797 ppm) and Ni (11-254 ppm) than those of normal island arc andesites. Their La/Yb ratios are 9.87 – 22.5 whereas their Sr/Y ratios are 20 – 131.These characteristics are similar to those shown by Cenozoic Setouchi High Magnesian Andesites (HMA). These rocks are characterized by 143Nd/144Nd ratios that range from 0.511062 ± 7 to 0.511308 ± 12 with corresponding εNd (t) of +0.44 and +1.81. The high contents of Mg, Cr and Ni argue in favour of equilibration of their parental magma with mantle peridotite whereas their relatively low La/Yb ratios argue against the involvement of garnet and amphibole as residual phases during partial melting. Thus, the high-Mg andesites are interpreted to have formed by partial melting of the mantle peridotite that has been fluxed by slab-derived fluids. Overall, the geochemical features of high-Mg andesites, their close association with adakitic rocks in the MMGB together with the short time interval taken for their emplacement are interpreted in terms of a ridge-subduction model. It is considered that such a model was important for generation of late Archaean continental crust.
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    The ~4-ka Rungwe Pumice (South-Western Tanzania): A wind-Still Plinian Eruption
    (2011-05) Fontijn, Karen; Ernst, Gerald G. J.; Bonadonna, Costanza; Elburg, Marlina A.; Mbede, Evelyne I.; Jacobs, Patric
    The ~4-ka trachytic Rungwe Pumice (RP) deposit from Rungwe Volcano in South-Western Tanzania is the first Plinian-style deposit from an African volcano to be closely documented focusing on its physical characterization. The RP is a mostly massive fall deposit with an inversely graded base. Empirical models suggest a maximum eruption column height HT of 30.5–35 km with an associated peak mass discharge rate of 2.8–4.8 × 108 kg/s. Analytical calculations result in HT values of 33 ± 4 km (inversion of TEPHRA2 model on grain size data) corresponding to mass discharge ranging from 2.3 to 6.0 × 108 kg/s. Lake-core data allow extrapolation of the deposit thinning trend far beyond onland exposures. Empirical fitting of thickness data yields volume estimates between 3.2 and 5.8 km3 (corresponding to an erupted mass of 1.1–2.0 × 1012 kg), whereas analytical derivation yields an erupted mass of 1.1 × 1012 kg (inversion of TEPHRA2 model). Modelling and dispersal maps are consistent with nearly no-wind conditions during the eruption. The plume corner is estimated to have been ca. 11–12 km from the vent. After an opening phase with gradually increasing intensity, a high discharge rate was maintained throughout the eruption, without fountain collapse as is evidenced by a lack of pyroclastic density current deposits.
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    Acquisition of a Unique Onshore/Offshore Geophysical and Geochemical Dataset in the Northern Malawi (Nyasa) Rift
    (GeoScienceWorld, 2016-12) Donna J. Shillington, James B. Gaherty, Cynthia J. Ebinger, Christopher A. Scholz, Kate Selway, Andrew A. Nyblade, Paul A. Bedrosian, Cornelia Class, Scott L. Nooner, Matthew E. Pritchard, Julie Elliott, Patrick R. N. Chindandali, Gaby Mbogoni, Richard Wambura Ferdinand, Nelson Boniface, Shukrani Manya, Godson Kamihanda, Elifuraha Saria, Gabriel Mulibo, Jalf Salima, Abdul Mruma, Leonard Kalindekafe, Natalie J. Accardo, Daud Ntambila, Marsella Kachingwe, Gary T. Mesko, Tannis McCartney, Melania Maquay, J. P. O’Don- nell, Gabrielle Tepp, Khalfan Mtelela, Per Trin- hammer, Douglas Wood, Ernest Aaron, Mark Gibaud, Martin Rapa, Cathy Pfeifer, Felix Mphepo, Duncan Gondwe, Gabriella Arroyo, Celia Eddy, Brian Kamoga, and Mary Moshi
    The Study of Extension and maGmatism in Malawi aNd Tanzania (SEGMeNT) project acquired a comprehensive suite of geophysical and geochemical datasets across the northern Malawi (Nyasa) rift in the East Africa rift system. Onshore/offshore active and passive seismic data, long‐period and wideband magnetotelluric data, continuous Global Positioning System data, and geochemical samples were acquired between 2012 and 2016. This combination of data is intended to elucidate the sedimentary, crustal, and upper‐mantle architecture of the rift, patterns of active deformation, and the origin and age of rift‐related magmatism. A unique component of our program was the acquisition of seismic data in Lake Malawi, including seismic reflection, onshore/offshore wide‐angle seismic reflection/refraction, and broadband seismic data from lake‐bottom seismometers, a towed streamer, and a large towed air‐gun source.
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    Acquisition of a Unique Onshore/Offshore Geophysical and Geochemical Dataset in the Northern Malawi (Nyasa) Rift
    (Seismological Research Letters, 2016-09-07) Shillington, Donna J.; Gaherty, James B.; Ebinger, Cynthia J.; Scholz, Christopher A.; Selway, Kate; Nyblade, Andrew A.; Bedrosian, Paul A.; Class, Cornelia; Nooner, Scott L.; Pritchard, Matthew E.; Elliott, Julie; Chindandali, Patrick R. N.; Mbogoni, Gaby; Ferdinand, Richard Wambura; Boniface, Nelson; Manya, Shukrani; Kamihanda, Godson; Saria, Elifuraha; Mulibo, Gabriel; Salima, Jalf; Mruma, Abdul; Kalindekafe, Leonard; Accardo, Natalie J.; Ntambila, Daud; Kachingwe, Marsella; Mesko, Gary T.; McCartney, Tannis; Maquay, Melania; O’Donnell, J. P.; Tepp, Gabrielle; Mtelela, Khalfan; Trinhammer, Per; Wood, Douglas; Aaron, Ernest; Gibaud, Mark; Rapa, Martin; Pfeifer, Cathy; Mphepo, Felix; Gondwe, Duncan; Arroyo, Gabriella; Eddy, Celia; Kamoga, Brian; Moshi, Mary
    The Study of Extension and maGmatism in Malawi aNd Tanzania (SEGMeNT) project acquired a comprehensive suite of geophysical and geochemical datasets across the northern Malawi (Nyasa) rift in the East Africa rift system. Onshore/offshore active and passive seismic data, long‐period and wideband magnetotelluric data, continuous Global Positioning System data, and geochemical samples were acquired between 2012 and 2016. This combination of data is intended to elucidate the sedimentary, crustal, and upper‐mantle architecture of the rift, patterns of active deformation, and the origin and age of rift‐related magmatism. A unique component of our program was the acquisition of seismic data in Lake Malawi, including seismic reflection, onshore/offshore wide‐angle seismic reflection/refraction, and broadband seismic data from lake‐bottom seismometers, a towed streamer, and a large towed air‐gun source.
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    Acquisition of a Unique Onshore/Offshore Geophysical and Geochemical Dataset in the Northern Malawi (Nyasa) Rift
    (Seismological Research Letters, 2016) Donna J. Shillington, James B. Gaherty, Cynthia J. Ebinger, Christopher A. Scholz, Kate Selway, Andrew A. Nyblade, Paul A. Bedrosian, Cornelia Class, Scott L. Nooner, Matthew E. Pritchard, Julie Elliott, Patrick R. N. Chindandali, Gaby Mbogoni, Richard Wambura Ferdinand, Nelson Boniface, Shukrani Manya, Godson Kamihanda, Elifuraha Saria, Gabriel Mulibo, Jalf Salima, Abdul Mruma, Leonard Kalindekafe, Natalie J. Accardo, Daud Ntambila, Marsella Kachingwe, Gary T. Mesko, Tannis McCartney, Melania Maquay, J. P. O’Donnell, Gabrielle Tepp, Khalfan Mtelela, Per Trinhammer, Douglas Wood, Ernest Aaron, Mark Gibaud, Martin Rapa, Cathy Pfeifer, Felix Mphepo, Duncan Gondwe, Gabriella Arroyo, Celia Eddy, Brian Kamoga, and Mary Moshi
    The Study ofExtension andmaGmatism inMalawi aNdTanzania (SEGMeNT) project acquired a comprehensive suite of geophysical and geochemical datasets across the northern Malawi (Nyasa) rift in the East Africa rift system. Onshore/offshore active and passive seismic data, long-period and wideband magnetotelluric data, continuous Global Positioning System data, and geochemical samples were acquired between 2012 and 2016. This combination of data is intended to elucidate the sedimentary, crustal, and upper-mantle architecture of the rift, patterns of active deformation, and the origin and age of rift-related magmatism. A unique component of our program was the acquisition of seismic data in LakeMalawi, including seismic reflection, onshore/offshore wide-angle seismic reflection/refraction, and broadband seismic data from lake-bottom seismometers, a towed streamer, and a large towed air-gun source.
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    Active Fault Mapping in Karonga-Malawi after the December 19, 2009 Ms 6.2 Seismic Event
    (Elsevier, 2015) Macheyeki, Athanas S.; Mdala, Hassan; Chapola, Lostina S.; Manhiça, V. J.; Chisambi, Joshua; Feitio, Paulino; Ayele, Atalay; Barongo, J.; Ferdinand, Richard W.; Ogubazghi, G.; Goitom, B.; Hlatywayo, Dumisani J.; Kianji, Gladys; Marobhe, I.; Mulowezi, A.; Mutamina, Daniel; Mwano, J. M.; Shumba, Blessing; Tumwikirize, I.
    The East African Rift System (EARS) has natural hazards – earthquakes, volcanic eruptions, and landslides along the faulted margins, and in response to ground shaking. Strong damaging earthquakes have been occurring in the region along the EARS throughout historical time, example being the 7.4 (Ms) of December 1910. The most recent damaging earthquake is the Karonga earthquake in Malawi, which occurred on 19th December, 2009 with a magnitude of 6.2 (Ms). The earthquake claimed four lives and destroyed over 5000 houses. In its effort to improve seismic hazard assessment in the region, Eastern and Southern Africa Seismological Working Group (ESARSWG) under the sponsorship of the International Program on Physical Sciences (IPPS) carried out a study on active fault mapping in the region. The fieldwork employed geological and geophysical techniques. The geophysical techniques employed are ground magnetic, seismic refraction and resistivity surveys but are reported elsewhere. This article gives findings from geological techniques. The geological techniques aimed primarily at mapping of active faults in the area in order to delineate presence or absence of fault segments. Results show that the Karonga fault (the Karonga fault here referred to as the fault that ruptured to the surface following the 6th–19th December 2009 earthquake events in the Karonga area) is about 9 km long and dominated by dip slip faulting with dextral and insignificant sinistral components and it is made up of 3–4 segments of length 2–3 km. The segments are characterized by both left and right steps. Although field mapping show only 9 km of surface rupture, maximum vertical offset of about 43 cm imply that the surface rupture was in little excess of 14 km that corresponds with Mw = 6.4. We recommend the use or integration of multidisciplinary techniques in order to better understand the fault history, mechanism and other behavior of the fault/s for better urban planning in the area.
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    Aerogeophysical, Geological and Geochemical Investigation of the Late Archaean Granitoids in the Musoma- Mara Greenstone Belt, NE Tanzania
    (2008) Mshiu, Elisante E.; Maboko, Makenya A. H.; Marobhe, I.
    The Musoma Mara Greenstone Belt (MMGB) is intruded with syn-to-post orogenic suites of granitoids which range in composition from Tonalite Trondhjemite Granodiorites (TTG) to granite. High resolution aerogeophysical data surveyed by GST in 2003 has provided aeromagnetic and radiometric data that were used in this study to classify various granitoids existing in MMGB. The individual radioactive element content of K, Th and U, ternary image and K: U: Th composite classification map have been used in data presentation and interpretation. In addition the radioactive element ratios were used to enhance the radiometric signals. Based on the analysis and interpretations made on airborne radiometric, magnetic data and previous geological maps, a geophysical interpretation map was obtained. This map broadly categorized the MMGB granitoids into two types, the first granitoid type is characterized by high contents of all the three elements (K, U and Th) and low magnetic intensity (< 33997 nT). The second granitoid type is characterized by high K relative to U and Th, and higher magnetic intensity (>33997 nT). The aerogeophysical interpretation map was used as a base map for ground follow-up whereby the granite types were sampled accordingly for geochemical analysis. Geochemical classification of the two granitoid types from geophysical data interpretations further subdivided them into three types i.e. biotite granite, calcic granite and TTG. The overall analysis showed high correlation between aerogeophysical and geochemical data whereby the voluminous biotite and calcic granite are the subdivisions from the first granite type and the less voluminous TTG precisely correlated to the second granite type. Their compositional similarity in geochemistry with the northern MMGB high-K and Na-rich granitoids (Manya et al. 2007a, b) suggested tectonic setting and petrogenetic analogy. Biotite and calcic granites are inferred to have been generated from partial melting of pre-existing materials including TTG, intermediate and felsic volcanic rocks whereby TTGs were generated from partial melting of hydrous basaltic crust that transformed into garnet amphibolites.
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    Age and geochemistry of coeval felsic volcanism and plutonism in the Palaeoproterozoic Ndembera Group of southwestern Tanzania: Constraints from SHRIMP U–Pb zircon and Sm–Nd data
    (Elsevier, 2016-01-31) Bahame, Gagao; Manya, Shukrani; Maboko, Makenya A. H.
    The Ndembera metavolcanic rocks represent a continuum of compositions ranging from intermediate to more siliceous calc-alkaline trachyandesites-dacites-trachytes-rhyolites which have been intruded by largely metaluminous, calc-alkaline I-type granites in the Palaeoproterozoic Usagaran Belt of southwestern Tanzania. SHRIMP U–Pb zircon age data show that the Ndembera metavolcanic rocks were extruded at 1871 ± 30 Ma, an event that was largely coeval with the emplacement of cross-cutting microcline-biotite rich granites at 1896 ± 29 Ma. Despite some compositional differences, both the granites and metavolcanic rocks share similar geochemical features including very coherent REE patterns characterized by enrichment of the LREE relative to the HREE (La/YbCN = 13.6–32.8 (average = 23.9) for metavolcanic rocks and La/YbCN = 10.8–38.2 (average = 21.8) for granites), negative Eu anomalies (Eu/Eu* = 0.45–1.01 (average = 0.83) for volcanic rocks and Eu/Eu* = 0.48–0.70 (average = 0.60) for granites), negative Ta, Ti and Nb anomalies (Nb/Lapm = 0.14–0.29 (average = 0.20 for volcanic rocks and Nb/Lapm = 0.01–0.37 (average = 0.16) for granites). The metavolcanic rocks have ɛNd (1871 Ma) values of −0.03 to −4.89 and TDM ages of 2243–2714 which are broadly similar to those of the granites (ɛNd (1896 Ma) values of −3.56 to −4.59 and TDM ages of 2469–2646 Ma). The geochemical similarities between the Ndembera volcanic rocks and granites, coupled with their similar emplacement age, suggest that the two rock suites were derived by the same processes in the same tectonic setting from an isotopically similar source. These geochemical features coupled with the paucity of mafic rocks suggest the derivation of the pluto-volcanic suite by crustal anatexis of basic meta-igneous rocks mixed with a minor metasedimentary component in an intra-continental setting. The more siliceous compositions in the suite may have formed by subsequent fractionation involving hornblende, plagioclase, biotite, titanite and apatite as indicated by the negative correlation between SiO2 and MgO, Fe2O3, Al2O3, CaO, TiO2 and P2O5, low Sr contents and negative Eu and Ti anomalies. The ∼1.87 Ga coeval felsic volcanic and granitic magmatic event documented in the Ndembera Group is also a feature of the nearby Ubendian belt to the west pointing to a Palaeoproterozoic regional thermal event that occurred in southwestern and western Tanzania.
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    The Age of Au–Cu–Pb-bearing Veins in the Poly-orogenic Ubendian Belt (Tanzania): U–Th–total Pb Dating of Hydrothermally Altered Monazite
    (Springer, 2015) Kazimoto, Emmanuel O.; Schenk, Volker; Appel, Peter
    The age of gold–copper–lead mineralization in the Katuma Block of the Ubendian Belt remains controversial because of the lack of radiometric ages that correlate with the age of tectonothermal events of this polyorogenic belt. Previous studies reported whole rock and mineral Pb–Pb ages ranging between 1,660 and 720 Ma. In this study, we report U–Th–total Pb ages of monazite from hydrothermally altered metapelites that host the Au–Cu– Pb-bearing veins. Three types of chemically and texturally distinct types of monazite grains or zones of grains were identified: monazite cores, which yielded a metamorphic age of 1,938 ± 11 Ma (n = 40), corresponding to known ages of a regional metamorphic event, deformation and granitic plutonism in the belt; metamorphic overgrowths that date a subsequent metamorphic event at 1,827 ± 10 Ma (n = 44) that postdates known eclogite metamorphism (at ca. 1,880 Ma) in the belt; hydrothermally altered poikilitic monazite, formed by dissolution–precipitation processes, representing the third type of monazite, constrain the age of a hydrothermal alteration event at 1,171 ± 17 Ma (n = 19). This Mesoproterozoic age of the hydrothermal alteration coincides with the first amphibolite grade metamorphism of metasediments in the Wakole Block, which adjoins with a tectonic contact the vein-bearing Katuma Block to the southwest. The obtained distinct monazite ages not only constrain the ages of metamorphic events in the Ubendian Belt, but also provide a link between the metamorphism of the Wakole metasediments and the generation of the hydrothermal fluids responsible for the formation of the gold– copper–lead veins in the Katuma Block.
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    The Age of Au–Cu–Pb-bearing Veins in the Poly-orogenic Ubendian Belt (Tanzania): U–Th–total Pb Dating of Hydrothermally Altered Monazite
    (Springer, 2015) Kazimoto, Emmanuel O.; Schenk, Volker; Appel, Peter
    The age of gold–copper–lead mineralization in the Katuma Block of the Ubendian Belt remains controversial because of the lack of radiometric ages that correlate with the age of tectonothermal events of this polyorogenic belt. Previous studies reported whole rock and mineral Pb–Pb ages ranging between 1,660 and 720 Ma. In this study, we report U–Th–total Pb ages of monazite from hydrothermally altered metapelites that host the Au–Cu– Pb-bearing veins. Three types of chemically and texturally distinct types of monazite grains or zones of grains were identified: monazite cores, which yielded a metamorphic age of 1,938 ± 11 Ma (n = 40), corresponding to known ages of a regional metamorphic event, deformation and granitic plutonism in the belt; metamorphic overgrowths that date a subsequent metamorphic event at 1,827 ± 10 Ma (n = 44) that postdates known eclogite metamorphism (at ca. 1,880 Ma) in the belt; hydrothermally altered poikilitic monazite, formed by dissolution–precipitation processes, representing the third type of monazite, constrain the age of a hydrothermal alteration event at 1,171 ± 17 Ma (n = 19). This Mesoproterozoic age of the hydrothermal alteration coincides with the first amphibolite grade metamorphismof metasediments in the Wakole Block, which adjoins with a tectonic contact the vein-bearing Katuma Block to the southwest. The obtained distinct monazite ages not only constrain the ages of metamorphic events in the Ubendian Belt, but also provide a link between the metamorphism of the Wakole metasediments and the generation of the hydrothermal fluids responsible for the formation of the gold– copper–lead veins in the Katuma Block.
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    Application of Environmental Isotopes to Groundwater Recharge Studies in a Semi-Arid Fractured Crystalline Basement Area of Dodoma Tanzania
    (Elsevier, 1996) Nkotagu, Hudson H.
    The distribution of 18O and 2H in various water sources indicates that groundwater recharge is due to local rainfall occurring within the basins. Groundwater recharge takes place under a bypass flow mechanism and matrix diffuse flow and is 3% and 2% of the long-term mean annual rainfall of 550 mm for the Makutapora and Hombolo basins, respectively. Chloride mass balance indicates that 60% and 40% of the total groundwater recharge takes place through macropores and matrix flow, respectively. Sporadic variations in 18O, 2H and chloride among adjacent boreholes suggest existence of a discrete fractured aquifer and/or dominance of local recharge. The relationship between δ2H and chloride indicates that groundwater salinization is due to the leaching of surficial and soil salts during high intensity rainfall, which causes high surface runoff and flash floods. It has been concluded that the isotopic and chemical character of groundwater in fractured semi-arid areas may provide the most effective complementary means of groundwater recharge assessment and therefore is very useful in the management of the water resources.
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    Application of environmental isotopes to groundwater recharge studies in a semi-arid fractured crystalline basement area of Dodoma, Tanzania
    (1999-02) Nkotagu, Hamisi H.
    The distribution of 18O and 2H in various water sources indicates that groundwater recharge is due to local rainfall occurring within the basins. Groundwater recharge takes place under a bypass flow mechanism and matrix diffuse flow and is 3% and 2% of the long-term mean annual rainfall of 550 mm for the Makutapora and Hombolo basins, respectively. Chloride mass balance indicates that 60% and 40% of the total groundwater recharge takes place through macropores and matrix flow, respectively. Sporadic variations in 18O, 2H and chloride among adjacent boreholes suggest existence of a discrete fractured aquifer and/or dominance of local recharge. The relationship between δ2H and chloride indicates that groundwater salinization is due to the leaching of surficial and soil salts during high intensity rainfall, which causes high surface runoff and flash floods. It has been concluded that the isotopic and chemical character of groundwater in fractured semi-arid areas may provide the most effective complementary means of groundwater recharge assessment and therefore is very useful in the management of the water resources.
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    Application of Environmental Isotopes to Groundwater Recharge Studies in a Semi-arid Fractured Crystalline Basement Area of Dodoma, Tanzania
    (1999-02) Nkotagu, Hudson H.
    The distribution of 18O and 2H in various water sources indicates that groundwater recharge is due to local rainfall occurring within the basins. Groundwater recharge takes place under a bypass flow mechanism and matrix diffuse flow and is 3% and 2% of the long-term mean annual rainfall of 550 mm for the Makutapora and Hombolo basins, respectively. Chloride mass balance indicates that 60% and 40% of the total groundwater recharge takes place through macropores and matrix flow, respectively. Sporadic variations in 18O, 2H and chloride among adjacent boreholes suggest existence of a discrete fractured aquifer and/or dominance of local recharge. The relationship between δ2H and chloride indicates that groundwater salinization is due to the leaching of surficial and soil salts during high intensity rainfall, which causes high surface runoff and flash floods. It has been concluded that the isotopic and chemical character of groundwater in fractured semi-arid areas may provide the most effective complementary means of groundwater recharge assessment and therefore is very useful in the management of the water resources.
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    Application of Infra-Red Spectral and Multi-Element Analyses in the Gold Exploration in North Mara Mines, Tanzania
    (2008) Kazimoto, Emmanuel O.; Ikingura, Justinian R.; Halley, S.
    A combination of Short Wavelength Infra red (SWIR) spectral and multielement analyses was used to characterize certain hydrothermal alteration, pathfinder elements and their distribution within gold deposits in the Archean Musoma- Mara greenstone belt in Tanzania. The aim was to fingerprint hydrothermal systems responsible for the formation of major gold deposits in the belt. The SWIR spectra of white mica and chlorite from the samples revealed compositional zoning which reflects pH changes associated with hydrothermal fluid- rock interaction during mineralization. White mica crystallinity is variable in the deposits reflecting thermal gradient during hydrothermal alteration. On the other hand, gold pathfinder elements distribution showed extension of pathfinder element signature beyond a distance of 600 m width from the ore zone with either As and Sb association or Ag and Bi association. This suggests that different redox conditions have affected the deposits. This study confirms that a combination of SWIR spectral and multielement data is a cost-effective method in generating mineralization targets and can be applicable in areas with similar styles of mineralization.
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    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.
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    Application of U–Pb detrital zircon geochronology to drill cuttings for age control in hydrocarbon exploration wells: A case study from the Rukwa Rift Basin, Tanzania
    (The American Association of Petroleum Geologists, 2017-02) Hilbert-Wolf, Hannah; Roberts, Eric; Downie, Bob; Mtelela, Cassy; Stevens, Nancy J.; O’Connor, Patrick
    Precise dating and correlation of drilled wells through continental successions is challenging for hydrocarbon exploration, especially where preservation and recovery of age-diagnostic fossils is poor. As a complement or alternative to biostratigraphic dating we demonstrate the effectiveness of U–Pb geochronology via laser ablation–inductively coupled plasma–mass spectrometry on detrital zircon from well cuttings. In basins with syndepositional volcanic input, the youngest zircons in a stratigraphic interval can refine and serve as a proxy for the age of deposition. We demonstrate the reliability of this technique when applied to hydrocarbon exploration wells by analyzing drill cuttings through a continental interval of the Galula-1 well in the Rukwa Rift Basin, East African rift system, Tanzania, which previously yielded conflicting biostratigraphy results. The lower third of the well section reveals a late Miocene to Pliocene up-hole younging trend in the youngest detrital zircon populations, which matches new radioisotopic ages on volcanic tuffs from a correlative outcrop section. This is followed by an interval with recycled young zircons, followed by a zircon-free interval, interpreted to correspond to changes in magma composition of the nearbyRungwe volcanic province. This study provides the first radioisotopic age constraints for the Lake Beds in the Rukwa riftand demonstrates that sedimentation in the basin began by 8.7 Ma, critical for burial and thermal history modeling and establishing the probability of a working hydrocarbon system. Correspondence in age and zircon preservation between well and outcrop samples from the same intervals provides strong support for applying U–Pb detrital zircon geochronology to well cuttings, as a rapid, inexpensive approach for hydrocarbon exploration.
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    Atlas of Gold Deposits in Tanzania, Dar es Salaam.
    (University of Dar Es Salaam, 2010-01) Ikingura, J. R.; Mutakyahwa, M. K. D.; Marobhe, I. M.; Manya, Shukrani; Kazimoto, E.; Kasanzu, C.; Mshiu, Elisante Elisaimon
    The Atlas of gold deposits in Tanzania reviews the geology of significant gold deposits in Tanzania taking into account the new information collected from the exploration and mining companies and research work done in the gold producing regions. The emphasis is placed on the nature and composition of the ore and the geological setting of each of the deposit that include host-rocks, structure, hydrothermal wall-rock alteration and timing of gold mineralization.
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    Average Attenuation of 0.7–5.0 Hz Lg Waves and Magnitude Scale Determination for the Region Bounding the Western Branch of the East African Rift
    (1998) Ferdinand, Richard W.
    The investigation of L G attenuation characteristics in the region bounding the western branch of the East African rift system using digital recordings from a seismic network located along the rift between Lake Rukwa and Lake Malawi is reported. A set of 24 recordings of L G waves from 12 regional earthquakes has been used for the determination of anelastic attenuation, QLg , and regional body‐wave magnitude, MbLg , scale. The events used have body‐wave magnitudes, Mb , between 4.6 and 5.5, which have been determined teleseismically and listed in ISC bulletins. The data were time‐domain displacement amplitudes measured at 10 different frequencies (0.7–5.0 Hz). QLg and its frequency dependence, Η, in the region can be represented in the form QLg = (186.2 ± 6.5) F (0.78±0.05). This model is in agreement with models established in other active tectonic regions. The L G‐wave‐based magnitude formula for the region is given by MbLg = log A + (3.76 ± 0.38) log D − (5.72 ± 1.06), where A is a half‐peak‐to‐peak maximum amplitude of the 1 s L G wave amplitude in microns and D is the epicentral distance in kilometres. Magnitude results for the 12 regional earthquakes tested are in good agreement with the ISC body‐wave magnitude scale.