Browsing by Author "Manya, Shukrani"

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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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    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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    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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    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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    Characterization of geochemical alteration halo associated with gold mineralization at the Buzwagi mine, northern Tanzania
    (Elsevier, 2017-05) Manya, Shukrani
    Alteration halo geochemical study was carried out along one transect at the Buzwagi mine which is found in the Neoarchaean Nzega greenstone belt of northern Tanzania. The Buzwagi mine Au mineralization is hosted in quartz veins that are cross-cutting strongly sheared and hydrothermally altered K-granites. Mineralogical studies within the shear zone reveal that sericite, silica and sulphides are the most important hydrothermal mineral assemblages responsible for Au mineralization at the Buzwagi mine. The geochemical alteration halo is characterized by the addition of Au, Cu, Fe, K, Rb, Sn, W and U to wall rocks and simultaneous removal of Na, Sr, Ba, LREE and MREE from the host rocks. The concentrations of Cu (130–870 ppm) which show strong positive correlation with Au (R2 = 0.99) are so high in the alteration halo indicating that Cu is a strong Au pathfinder at the Buzwagi mine. Owing to their immobility during the post-emplacement processes, the HFSE (Zr, Hf, Th, Ta) remained unchanged during the hydrothermal alteration process. The addition of Fe and Cu is attributed to the presence of Fe- and Cu-sulphides (pyrite, chalcopyrite and chalcocite) whereas the addition of K, Rb, Sn, W and U is a function of both primary concentrations of these elements in the host rocks as well as the subsequent strong hydrothermal alteration evidenced by sericitization and silicification which involved the destruction of feldspars into sericites). The destruction of albite and its replacement by sericite accounts for the depletion of Na, Sr (and Ba). The Buzwagi mine Au mineralization mineral association do not include the more known pathfinders like Ag, As, Sb, Bi, Te and Tl and they seem not to have played a role in the mineralization process. These elements, therefore, should not be considered as pathfinders for Au exploration purposes at a Buzwagi-like deposit.
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    Composition and origin of Archean lower crust, Northern Tanzania
    (2008-12) Mansur, A. T.; Manya, Shukrani; Rudnick, R. L.
    Granulite-facies xenoliths from tuff cones erupted on the margin of the Tanzanian craton and within the adjacent Mozambique belt in northern Tanzania offer an opportunity to assess the role of lower crustal processes in the tectonic evolution of these two terranes. Both terranes are Archean, but record very different histories, starting in the Proterozoic and continuing today. Whereas the craton experienced little metamorphism or igneous activity following its stabilization around 2.8 Ga, Archean rocks of the Mozambique belt in the study area experienced at least one episode of high-grade metamorphism during the East African orogeny (ca. 640 Ma). Today, the East African rift exists at the contact between the Mozambique belt and the craton, implying a fundamental lithospheric weakness at this boundary. Granulite xenoliths come from Labait, on the craton margin, and Lashaine and Naibor Soito in the metamorphic belt. Most xenoliths are mafic and all are igneous in origin. Cratonic xenoliths (pl- opx±cpx±gt±hbl) are primarily anhydrous two-pyroxene granulites that likely originated as crystallized high-Ni, Archean basaltic melts. Xenoliths from the Mozambique belt are dominated by mafic granulites (pl-cpx-gt±opx) at Lashaine and banded, mafic to intermediate granulites at Naibor Soito. Positive Sr and Eu anomalies imply that the Lashaine granulites originated as plagioclase cumulates. The wide range in SiO2 (47-65 wt%) and correlation of Ni-MgO in the Naibor Soito xenoliths suggests they may have originated as igneous rocks that subsequently underwent partial melting to form the mafic (pl- opx±cpx±gt±hbl±bt) and felsic bands (pl-qtz-opx±kfs). U-Pb zircon ages for xenoliths from both terranes are Archean, as are most TDM ages, though younger TDM ages are seen in some Lashaine samples that were contaminated by rift magma. High pressures (up to 2.7GPa) are recorded by the Mozambique belt xenoliths, suggesting equilibration in thickened crust during the East African orogeny, but no igneous activity related to metamorphism has been detected and our samples suggest that the Tanzanian lower crust has persisted without significant chemical modification since the Archean. Proterozoic magmatism is also absent from the upper crust in this section of the Mozambique belt, raising the question of the heat source during metamorphism.
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    Composition and thermal history of the lower crust beneath the Tanzania Craton and the adjacent Mozambique Belt
    (2006-05) Mansur, A. T.; Manya, Shukrani; Rudnick, R. L.
    The Tanzanian craton has undergone little deformation since its formation 2.6 Ga ago, but Archaean crust of the adjacent Mozambique Belt (MB) has been reworked by at least two high-grade metamorphic events. An old, thick (~~200-km) lithospheric keel appears to have stabilized the craton during these deformational events. Although a thick keel appears to be absent beneath the MB today, ancient mantle lithosphere is preserved beneath much of the MB and the original thickness of this lithosphere is uncertain. Studies of the present-day lower crust can help to constrain the compositional and thermal evolution of this region. Granulite xenoliths from the Labait volcano (craton margin) are exclusively mafic and are mostly two pyroxene granulites, but also include gt-opx granulites and a gt-cpx-spinel-corundum anorthosite. Most samples also have orthoclase as a major phase. Two-pyroxene thermometry yields temperatures of 710 to 810°C for an estimated lower crustal pressure of 1 GPa; whereas the anorthosite appears to have equilibrated at a somewhat hotter temperature (gt-cpx T = 970°C). All Labait xenoliths exhibit high K2O (0.8 to 2.6 wt., excluding the anorthosite), Ba (530 to 6730 ppm), Sr (440 to 1040 ppm) and Ni contents (100 to 400 ppm) and relatively high Mg# (47 to 63). The combined high Ni, Mg# and alkali and alkaline-earth elements may reflect an unusual igneous protolith (e.g., adakitic magma) or mafic cumulates that have been metasomatically enriched in the lower crust. Granulite xenoliths from Lashaine (MB) are also exclusively mafic and form two groups: 1) anorthositic, high Al2O3 (17 to 23 wt. %) and Mg#, plag-ky-cpx-gt granulites, which are enriched in Sr and have positive Eu anomalies and 2) lower Al2O3 (13 wt. %), two pyroxene ± gt granulites, which are enriched in Ti, K, P and Ni. The latter may be meta-cumulates from alkaline magmas. Temperatures for Lashaine granulites range from 770 to 980°C. Unlike Labait and Lashaine, the Naibor Soito (MB) xenolith suite includes both mafic and intermediate granulites. Mafic granulites from Naibor Soito are similar mineralogically to the Labait xenoliths except that they contain gt. Intermediate xenoliths are two pyroxene garnet granulites. All Naibor Soito samples are LREE-enriched, and two of three intermediate xenoliths exhibit positive Eu anomalies. Like Labait, xenoliths from this locality exhibit high K2O (0.5 to 2.7 wt. %), Ba (207 to 1120 ppm), and Sr (241 to 1146 ppm) contents. Equilibration temperatures of all the xenoliths are significantly hotter than projected present-day lower crustal temperatures, and are probably relicts of the last major orogeny (pan-African). Like elsewhere in the world, lower crustal xenoliths from both the craton and MB are dominated by mafic compositions.
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    Dating basaltic volcanism in the Neoarchaean Sukumaland Greenstone Belt of the Tanzania Craton using the Sm-Nd method: implications for the geological evolution of the Tanzania Craton
    (Elsevier, 2003) Manya, Shukrani; Maboko, Makenya A. H.
    Metabasalts from the Sukumaland Greenstone Belt of north western Tanzania yield a whole rock Sm–Nd isochron age of 2823 ± 44 Ma (initial ε(Nd) = 2.7, MSWD = 1.24). This age, which is interpreted as dating the eruption of the oldest mafic volcanics in the belt, is at the 95% confidence level indistinguishable from 2780 ± 3 and 2808 ± 3Ma single zircon U–Pb ages previously reported from stratigraphically higher rhyolitic pyroclastic rocks from the southern margin of the belt. The age equivalency suggests that the entire∼5–7 km thick greenstone sequence that has been traditionally classified into a predominantly mafic lower part overlain by an upper part in which felsic volcanics and BIF predominate, was emplaced within a relatively short time interval not exceeding ∼44 Ma. The Sm–Nd age of the metabasalts is significantly older than a published zircon U–Pb age of 2680 ± 3Ma obtained from a migmatitic gneiss on the southernmost fringe of the Sukumaland Greenstone Belt. This corroborates previous evidence that high-grade metamorphism in the Tanzania Craton postdates emplacement of the greenstones and is most likely associated with the regional emplacement of the large granitic bodies that intrude and flank the greenstones.
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    A detailed geochronology of the Rungwe Volcanic Province at the southern end of the East African System.
    (2013) Maqway, M.; Class, C.; Mesko, G. T.; Boniface, Nelson; Manya, Shukrani
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    Eruption of kimberlite magmas: physical volcanology, geomorphology and age of the youngest kimberlitic volcanoes known on earth (the Upper Pleistocene/Holocene Igwisi Hills volcanoes, Tanzania)
    (Springer-Verlag, 2012-09-01) Brown, R. J.; Manya, Shukrani; Buisman, I.; Fontana, G.; Field, M.; Mac Niocaill, C.; Sparks, R. S. J.; Stuart, F. M.
    The Igwisi Hills volcanoes (IHV), Tanzania, are unique and important in preserving extra-crater lavas and pyroclastic edifices. They provide critical insights into the eruptive behaviour of kimberlite magmas that are not available at other known kimberlite volcanoes. Cosmogenic 3He dating of olivine crystals from IHV lavas and palaeomagnetic analyses indicates that they are Upper Pleistocene to Holocene in age. This makes them the youngest known kimberlite bodies on Earth by >30 Ma and may indicate a new phase of kimberlite volcanism on the Tanzania craton. Geological mapping, Global Positioning System surveying and field investigations reveal that each volcano comprises partially eroded pyroclastic edifices, craters and lavas. The volcanoes stand <40 m above the surrounding ground and are comparable in size to small monogenetic basaltic volcanoes. Pyroclastic cones consist of diffusely layered pyroclastic fall deposits comprising scoriaceous, pelletal and dense juvenile pyroclasts. Pyroclasts are similar to those documented in many ancient kimberlite pipes, indicating overlap in magma fragmentation dynamics between the Igwisi eruptions and other kimberlite eruptions. Characteristics of the pyroclastic cone deposits, including an absence of ballistic clasts and dominantly poorly vesicular scoria lapillistones and lapilli tuffs, indicate relatively weak explosive activity. Lava flow features indicate unexpectedly high viscosities (estimated at >102 to 106 Pa s) for kimberlite, attributed to degassing and in-vent cooling. Each volcano is inferred to be the result of a small-volume, short-lived (days to weeks) monogenetic eruption. The eruptive processes of each Igwisi volcano were broadly similar and developed through three phases: (1) fallout of lithic-bearing pyroclastic rocks during explosive excavation of craters and conduits; (2) fallout of juvenile lapilli from unsteady eruption columns and the construction of pyroclastic edifices around the vent; and (3) effusion of degassed viscous magma as lava flows. These processes are similar to those observed for other small-volume monogenetic eruptions (e.g. of basaltic magma).
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    Evidence for a record of possible Paleo-Tsunami or storm deposits in the fluviatile Neoproterozoic Malagarasi Supergroup of NorthWestern Tanzania
    (Tanzania Journal of Science, 2020-06-08) Kasanzu, Charles H.; Manya, Shukrani
    Two different localities within the fluviatile Neoproterozoic Malagarasi Supergroup of north-western Tanzania show striking evidence for tsunami related clastic sedimentary deposits. In each locality, the outcrops are characterised by the association of fine grained, thinly laminated shales at the bottom that are overlain by thick deposits of sandstones and conglomerates whose clasts and pebbles vary in size and angularity/roundness. In each case, the two rock units are separated by an erosional surface. The basal shale layers are consistent with deposition in deep shelf environments which are in stark contrast to the immediately overlying conglomerates/sandstones that suggest reworking under high energy conditions. The consistent association of erosional surfaces coupled with the deposition of adjacent low and high energy facies are interpreted as a result of an ancient earthquake triggered tsunami or storm that abruptly changed the depositional energy at the two localities. We propose that a backwash wave transported pebbles and sediments from the shore setting towards the basin interior depositing them on the shale units. Given the limited preservation of such unusual sedimentological deposits in ancient terranes, these two localities in the Neoproterozoic Malagarasi basin provide information on the effects of tsunami or storm impacts in Precambrian basins of Tanzania.
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    Explanatory Notes for the Minerogenic Map of Tanzania
    (Geological Survey of Tanzania (GST), 2015) Leger, C.; Barth, A.; Falk, D.; Mruma, A. H.; Magigita, M.; Boniface, Nelson; Manya, Shukrani; Kagya, M.; Stanek, K. P.
    As one of its efforts to scale up promotional programs for attracting investments in the development and utilization of Tanzania’s mineral resources, the Geological Survey of Tanzania has made major review of the previously existing Mineral Occurrence Map of Tanzania through verification of location of known occurrences of minerals coupled with thorough evaluation and description of geological processes which account for the forͲ mation of these resources as well as their mineral association. The upgrading of this information went hand in hand with the inclusion of the similar data and information for the recently discovered occurrences of some commodities. As a result of these recent reviews and upgrading of information, a new GISͲbased MineroͲ genic Map of Tanzania at a scale of 1:1,500,000 has been developed and published in 2015. The content of this booklet serves as explanatory notes for this newly published map. The aforeͲstated review of information of mineral occurrences and the subsequent publication of the new map was carried out under the implementation of the Sustainable Management of Mineral Resources Project (2009 to 2015), a project that was funded by the World Bank and the Government of Tanzania. Beak Consultants GmbH of Germany was engaged as the consultant for conducting the review and publishing the map and its explanatory notes. Apart from publishing this map using conventional methods (hard and soft copies) the map and all its associated information and explanatory notes are posted in the newly developed web portal of the Geological Survey of Tanzania established in 2015 with address of www.gmisͲtanzania.com, a portal that serves as a platform for online viewing and searching of geoͲdata and information available at the Geological Survey of Tanzania. The Geological Survey of Tanzania is of the opinion that this new map and its explanatory notes, particularly the one placed on the web portal, will facilitate quick and easy disseminaͲ tion of information on the raw materials in the country to potential investors, stakeholders and the general public across the world. This will also allow onͲline quick querying of available geoͲdata related to the extractive industry in Tanzania and hence attracting more investment to the country therefore paving the way to an accelerated economic growth of the country. The Geological Survey of Tanzania encourages all stakeholders to make a good use of the newly developed Minerogenic Map of Tanzania and its explanatory notes and it is committed to providing additional explanations, data and information whenever required in order to ensure thorough understanding of the countryͲwide existing potentials of the minerals to all potential investors, stakeholders and the general public. Let us join hands and efforts to develop the raw materials for the benefit of Tanzania, her people, the investors and the world community at large in line with the “Win – Win” spirit.
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    The First Master Program in Petroleum Geology at the University of Dar es Salaam: Lessons and Challenges
    (2015-11-17) Bertotti, G.; Boniface, Nelson; de Bresser, J. H. P.; Manya, Shukrani; Nkotagu, H.; van Ruitenbeek, F.
    The UDSM, supported by group of geoscientists from Universities of the Netherlands has been able to establish the first Master program in Petroleum Geology of the country. With the crucial financial support of BG-Group 13 students has enrolled for the program. Courses have been given in the first year covering a wide range of relevant disciplines. Students have demonstrated a remarkable dedication to the course and have all performed at high level. The second year of the program will be dedicated to research projects developed in close connection with Industry. Challenges for the future include the development of shared data bases and e-learning facilities, the strengthening of the training the trainers component of the project and the establishment of robust relations with Industry
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    Generation of High-K Granites at the Archaean – Proterozoic Boundary.
    (Nova Science Publishers Inc, 2013-05) Manya, Shukrani
    The Archaean crustal provinces of the world are dominated by the rocks of the Tonalite-Trondhjemite-Granodiorite (TTG) series and account for 50% of the exposed Archaean crust. Towards the end of Archaean, however, TTG magmatism was replaced by the generation of high-K granites which continued into the Proterozoic and Phanerozoic. The late Archaean (~2.65 Ga) high-K granites of the Tanzania Craton some of which intrude the greenstone sequence of northern Tanzania are compared with the early Proterozoic (~ 1.92 - 1.96 Ga) high-K granites from the Ubendian belt of southwestern Tanzania. Granites from both late Archaean and early Proterozoic crustal terranes are pink in colour, and are composed of K-feldspar, plagioclase, quartz, biotite, less hornblende with minor phases including sphene, zircon and chlorite. It is in the Proterozoic granites that muscovite and tourmaline become important phases. The compositional similarities of the high-K granites from both late Archaean and early Proterozoic terranes include high SiO2 (> 70 wt %), high K2O (≥ 4.0 wt %) which leads to K2O/Na2O ratio of > 1, Al2O3 contents lower than those of TTG (< 15 wt %) and low MgO < 1.2 wt % and Ni (< 20 ppm). Trace element compositions reveal that, the high-K granites from both crustal terranes show comparable concentrations of Y, MREE and HREE, and display the negative Eu anomaly (Eu/Eu* = 0.5 - 0.6 on average). The major compositional differences between them are discerned in the most incompatible elements. High-K granites from the Proterozoic terrane consistently show higher concentrations of Zr, Hf, Th, Ba, Sr, K and ΣREE than their late Archaean counterparts. On the basis of the observed compositional similarities and differences, the key trace element ratios employed to distinguish the two magmas involve an incompatible element and middle to heavy REE (i.e. Zr/Sm, Zr/Y, Zr/Nb, Ba/Nb, Th/Ta) as well as the K2O/Na2O ratio. These ratios are a reflection of the primary petrogenetic feature inherent from the source rocks. The field relationships and geochemical features of the high-K granites from both crustal terranes are consistent with their derivation from partial melting at pressures and depths where plagioclase was a residual phase. Whereas the generation of the high-K granites in the Archaean would require partial melting of the juvenile igneous rocks including the TTG and greenstones that were emplaced in previous 10 to 20 Ma, those in the Proterozoic would require partial melting of the more evolved crustal rocks including the Archaean rocks. The generation of high-K granitic magmas at the Archaean-Proterozoic boundary marked a transition from growth of the Neoarchaean continental crust through the addition of juvenile mantlederived material to intra-crustal recycling of pre-existing material. It also marked the final stages of the stabilization of the Archaean Cratons worldwide.
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    Generation of Palaeoproterozoic Tonalites and Associated High-K Granites in Southwestern Tanzania by Partial Melting Of Underplated Mafic Crust in an Intracontinental Setting: Constraints from Geochemical and Isotopic Data
    (Elsevier, 2016-06) Manya, Shukrani; Maboko, Makenya A. H.
    The southwestern part of the 2.0–1.8 Ga Palaeoproterozoic Usagaran Belt in the Njombe area of SW Tanzania is intruded by two types of synchronous granitic rocks with different chemical and petrological characteristics. The first type consists of hornblende-rich tonalites that have major element compositions similar to those of Archaean TTG but differ significantly in their trace element composition. The tonalites are spatially and closely associated with felsic, high-K, I-type granites, some of which are gneissic and/or aplitic. U–Pb zircon geochronology shows that the emplacement of tonalites at 1887 ± 11 Ma was largely contemporaneous with emplacement of high-K granitic gneisses at 1877 ± 15 Ma and aplitic granites at 1857 ± 19 Ma. The data also reveal the presence of Archaean crust of 2648 ± 25 Ma in the zircon cores of some samples in the otherwise Palaeoproterozoic terrane. The tonalites are characterized by MgO contents of 1.60–4.11 wt.% at a SiO2 range of 58.1–67.9 wt.%, the Mg# of 34–55, lower Sr contents (220–462 ppm) and less fractionated REE patterns (La/YbCN = 3.55–12.9) compared to Archaean TTG (Sr > 500 ppm, La/YbCN > 20). These features, coupled with the εNd (1887 Ma) values of + 0.37 to − 0.66 as well as the associated mafic enclaves are suggestive of derivation of the tonalites by low pressure (below the garnet stability) partial melting of a mantle-derived mafic underplate that was subsequently contaminated with small amounts of pre-existing igneous crustal rocks. The evolved nature of the high-K granites (MgO = 0.20–1.30 wt.%, SiO2 = 65.5–73.9 wt.%, Mg# = 25–42, εNd = − 3.20 to − 4.75) coupled with old TDM ages which are 200–1000 Ma older than their emplacement age requires a higher degree of assimilation of older crustal material by the magma derived from partial melting of the underplated mafic crust which was subsequently followed by crystal fractionation involving plagioclase, pyroxene and amphibole. The close spatial and temporal association of the tonalites, mafic enclaves and the high-K granites and gneisses in the Njombe area provides the first direct evidence of the role of magmatic underplating for the regional thermal anomaly that caused widespread crustal anatexis leading to the generation of the 1.8–1.9 Ga granitic rocks (in Njombe area) and/or associated felsic volcanism in the Usagaran (in Ndembera) and Ubendian (in Ngualla) Belts of SW Tanzania.
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    A geochemical constraint on the origin of melts using thermobarometry at Rungwe Volcanic Province, Tanzania
    (2013) Mesko, G. T.; Class, C.; Manya, Shukrani; Maqway, M.; Boniface, Nelson
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    Geochemistry and Geochronology of Neoarchaean Volcanic Rocks of the Iramba–Sekenke Greenstone Belt, Central Tanzania
    (Elsevier, 2008-06-10) Manya, Shukrani; Maboko, Makenya A. H.
    The late Archaean volcanic rocks of the Iramba–Sekenke greenstone belt consist of tholeiitic basalts and basaltic andesites that are associated with a subordinate amount of intermediate to felsic volcanic rocks. Sm–Nd geochronology shows that the entire volcanic suite was emplaced at 2742 ± 27 Ma (MSWD = 1.6, ɛNd = 2.3). REE patterns in the tholeiitic basalts and basaltic andesites are flat or slightly depleted in the LREE and are characterized by La/SmCN and La/YbCN ratios of 0.70–1.17 and 0.74–1.35, respectively. On primitive mantle normalized extended trace element diagrams, two groups of basalts and basaltic andesites can be identified. Rocks of the first group display NMORB-like patterns and are characterized by minor negative Ti anomalies as well as slight depletion of the incompatible elements Th, Nb and Ta relative to the LREE. The second group only differs from the first group in having negative anomalies of Nb and Ta. The intermediate to felsic volcanic rocks are characterized by fractionated REE patterns (La/SmCN = 2.77–6.22 and La/YbCN = 15–103) with only minor to absent Eu anomalies. On primitive mantle- and NMORB-normalized extended trace element diagrams, the samples display large negative anomalies of Nb, Ta and Ti (Nb/Lapm = 0.07–0.21) as well as enrichment of Th relative to the LREE (Th/Lapm = 1.24–3.44). Trace element and isotope geochemistry suggests that crustal contamination did not play a role in the genesis of the Iramba–Sekenke volcanic rocks. Geochemical modelling is consistent with derivation of the tholeiitic basalts and basaltic andesites by 6% non-modal partial melting of a spinel peridotite depleted mantle source. The volumetrically minor intermediate to felsic volcanic rocks are interpreted to have been derived from the parental magmas of the tholeiitic basalts and basaltic andesites by 85–90% Rayleigh fractionation of clinopyroxene, hornblende and minor plagioclase. Tectonic setting discrimination diagrams and trace element ratios in the rocks are consistent with formation of the Iramba–Sekenke greenstone belt in a back-arc setting.
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    Geochemistry and Geochronology of the Bimodal Volcanic Rocks of the Suguti Area in the Southern Part of the Musoma-Mara Greenstone Belt, Northern Tanzania
    (Elsevier, 2009-11-30) Mtoro, Mwache; Maboko, Makenya A. H.; Manya, Shukrani
    The Suguti volcanic rocks of the southern Musoma-Mara greenstone belt in northern Tanzania comprise mainly of a bimodal suite of tholeiitic basalts-basaltic andesites and calc-alkaline rhyolites with a subordinate amount of intermediate rocks. Zircon U–Pb and whole rock Sm–Nd geochronology suggests that the two suites are cogenetic and were emplaced at 2755 ± 1 Ma with a common initial ɛNd value of 2.1. The tholeiitic basalts are characterised by relatively flat chondrite-normalised REE patterns with La/YbCN ratios of 0.8–1.6 (mean = 1.0). The basalts also exhibit negative Ti and Nb anomalies in primitive mantle-normalised multi-element diagrams. The flat REE patterns, the presence of prominent negative Nb anomalies and the positive initial ɛNd value of 2.1 suggest that the basalts were formed by low pressure melting of a mantle wedge in an active continental margin setting. Compared to the tholeiitic basalts, the calc-alkaline rhyolites are characterised by low abundances of the transition elements (Cr < 20 ppm, Ni < 20 ppm) and moderately high HFSE (e.g. Zr = 111–250 ppm) abundances. The rhyolites display strongly fractionated, slightly concave upward chondrite normalised REE patterns that are characterised by a slight depletion of the MREE relative to the HREE and minor to large negative Eu anomalies (Eu/Eu* = 0.3–0.9) and their epsilon Nd values range from +2.05 to +2.33. The depletion of the MREE relative to the HREE is an indication of fractionation of clinopyroxene and hornblende during petrogenesis whereas the negative Eu anomalies indicate plagioclase fractionation. The rhyolites are interpreted to have formed from the parental magma of the basalts by fractional crystallization and/or partial melting of a relatively young basaltic crust.