Petrogenesis of tonalite-trondhjemite and potassic granite, Geita Greenstone Belt, Tanzania Craton: Implication for crustal evolution during Neoarchean plate tectonic initiation

Journal Publication ResearchOnline@JCU
Gamal-Adeen, I.;Shahien, M.G.;Zayed, A.M.;Bakhit, B.R.;Sanislav, I.V.;Sharib, A.S.A.A. Abu
Ioan Sanislav
Abstract

Geochemical and zircon isotope data reveal a complex petrogenetic history of the Neoarchean granitoids of the Geita Greenstone Belt (GGB), northern Tanzania Craton. Geochemically, the granitoids are categorized into: (1) tonalite-low-silica trondhjemite; (2) high-silica trondhjemite; (3) transitional granitoids; and (4) potassic granite. Compared to tonalite-low-silica trondhjemite, the high-silica trondhjemite displays significant depletion in HREE and HFSE, and have an exceptional high Sr/Y and LaN/YbN ratios. Both categories display similar LREE and LILE patterns. Transitional granitoids comprise dykes and dyke-like bodies of low-silica trondhjemite and quartz monzonite. Characteristically, they have low LaN/YbN and Sr/Y ratios, and are strongly-enriched in LREE and LILE and less depleted in HREE and HFSE. Potassic granite is represented by small intrusions and dykes that exhibit low LaN/YbN and low to moderate Sr/Y ratios, and are moderately-enriched in LREE, strongly-enriched in LILE, and moderately-depleted in HREE and HFSE. The tonalite and low-silica trondhjemite generated (∼2699–2714 Ma) by partial melting of basaltic rock at amphibolite facies metamorphic condition. The high-silica trondhjemite evolved from fractionation of the tonalitic melt. Lithospheric delamination produced high-K mafic magma that fractionated into the transitional granitoids (∼2660–2683 Ma), and caused partial melting of the tonalite-trondhjemites to generate the potassic granite (∼2646–2685 Ma). Geochemical signature of the tonalite-trondhjemites and potassic granite, as indicated by the negative Nb-Ta-Ti anomalies, and strongly-fractionated REEs, supported with the structural style near and at the contact between the felsic gneisses and the greenstone belt infer generation of the gneisses at a convergent plate boundary. Partial melting at the base of an oceanic plateau or a flat subducting slab has been suggested to interpret the evolution of the northern Tanzania Craton (2700–2650 Ma). A metasomatized mantle was introduced by lower crustal delamination/break-off of the down-going slab.

Journal

Geoscience Frontiers

Publication Name

Geoscience Frontiers

Volume

17

ISBN/ISSN

2588-9192

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Pages Count

24

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Publisher

Elsevier

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DOI

10.1016/j.gsf.2026.102279