Geochronological characterization of a transition zone between the Mozambique Belt and Unango-Marrupa Complex in SE Tanzania

• Published in: Precambrian research 2019-02, Vol.321, p.134-153
• Main Authors: Mtabazi, Epiphania G., Boniface, Nelson, Andresen, Arild
• Format: Article
• Language: English
• Subjects: Geochronology; Mandawa-Ruvuma Basin; Monazite; Mozambique Belt; SE Tanzania; Unango-Marrupa Complex; Zircon
• ISSN: 0301-9268; 1872-7433
• DOI: 10.1016/j.precamres.2018.11.017

•We present geochronological data of a transition between Mozambique Belt and the Unango-Marrupa Complex.•Phanerozoic sediments of the Selous-Mandawa-Ruvuma Basin mask the basement exposures.•The area is intruded by granitoids with ages between 790 ± 8.7 Ma and 614 ± 8.1 Ma.•An orthogneiss with a protolith age of 1056 ± 19 Ma occurs as inlier in SE Tanzania.•Metamorphic reworking in SE Tanzania occurred between 606 ± 6.6 and 560 ± 37 Ma.•An alkali granitic pluton postdate metamorphism and intruded the area about 554 ± 3.9 Ma. We present geochronological and petrological data of orthogneisses, granitoids, and supracrustal rocks from SE Tanzania to characterize the transition zone between the Mesoproterozoic Unango-Marrupa Complex and the Neoproterozoic Mozambique Belt. Geochronological data (U-Pb zircon; LA-ICP-MS) indicate that the emplacement of orthogneisses (protolith) and granitoids in SE Tanzania occurred in Stenian, Cryogenian, and Ediacaran Periods. The magmatic emplacement ages are determined between 1056 ± 19 Ma and 554 ± 3.9 Ma. No older ages that that were determined. The Stenian orthogneisses (biotite granitic gneiss dates at 1056 ± 19 Ma and the associated migmatites, charnockites, amphibolite) represents Mesoproterozoic magmatic inliers in the Neoproterozoic rocks and the extension of the Unango-Marrupa Complex in SE Tanzania. Supracrustal rocks (marble and calc-silicate, garnet-biotite (hornblende) gneisses, quartzo-feldspathic gneisses, graphite schists, and quartzites) are interlayered with granitoids dated between 790 ± 8.7 Ma and 614 ± 8.1 Ma. The supracrustal rocks represent the upper part of the Mozambique Belt (Eastern Granulites/Cabo-Delgado nappes), and are possibly relics of continental shelf sedimentary deposits of the Mozambique Ocean. Upon assessing metamorphic ages (U-Pb zircon) in SE Tanzania we determined the Ediacaran metamorphic event dated between 606 ± 6.6 and 560 ± 37 Ma, which reworked the Stenian – Cryogenian crusts. The U-Pb zircon metamorphic ages are supported by a precise U-Th-Pb monazite metamorphic age at 589 ± 5 Ma obtained from a biotite garnet gneiss rock sample (amphibolite facies). The Ediacaran metamorphism in SE Tanzania was followed by the emplacement of biotite alkali granite at 554 ± 3.9 Ma, which probably marks crustal relaxation and extension after metamorphism as the result of collision or accretion. Magmatic rocks of the Mozambique Belt in SE Tanzania were emplaced during the East African Orogeny. M