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A Review of the Neoproterozoic to Cambrian Tectonic Evolution

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A Review of the Neoproterozoic to Cambrian Tectonic Evolution Accepted Manuscript Orogen styles in the East African Orogen: A review of the Neoproterozoic to Cambrian tectonic evolution H. Fritz, M. Abdelsalam, K.A. Ali, B. Bingen, A.S. Collins, A.R. Fowler, W. Ghebreab, C.A. Hauzenberger, P.R. Johnson, T.M. Kusky, P. Macey, S. Muhongo, R.J. Stern, G. Viola PII: S1464-343X(13)00104-0 DOI: http://dx.doi.org/10.1016/j.jafrearsci.2013.06.004 Reference: AES 1867 To appear in: African Earth Sciences Received Date: 8 May 2012 Revised Date: 16 June 2013 Accepted Date: 21 June 2013 Please cite this article as: Fritz, H., Abdelsalam, M., Ali, K.A., Bingen, B., Collins, A.S., Fowler, A.R., Ghebreab, W., Hauzenberger, C.A., Johnson, P.R., Kusky, T.M., Macey, P., Muhongo, S., Stern, R.J., Viola, G., Orogen styles in the East African Orogen: A review of the Neoproterozoic to Cambrian tectonic evolution, African Earth Sciences (2013), doi: http://dx.doi.org/10.1016/j.jafrearsci.2013.06.004 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. 1 Orogen styles in the East African Orogen: A review of the Neoproterozoic to Cambrian 2 tectonic evolution 3 H. Fritz1, M. Abdelsalam2, K. A., Ali3, B. Bingen4, A. S. Collins5, A. R. Fowler6, W. 4 Ghebreab7, C. A. Hauzenberger1, P. R. Johnson8, T. M. Kusky9, P. Macey10, S. Muhongo11, 5 R. J. Stern12, G.Viola4,13 6 7 1 Department of Earth Sciences, University of Graz, Austria. 8 2 Boone Pickens School of Geology, Oklahoma State University, Noble Research Center, 9 Stillwater, OK, 74078, USA. 10 3 Faculty of Earth Sciences King Abdulaziz University Jeddah 21589, Saudi Arabia . 11 4 Geological Survey of Norway, Trondheim, Norway. 12 5 Tectonics Resources and Exploration (TRaX), Geology and Geophysics, School of Earth 13 and Environmental Sciences, The University of Adelaide, Australia. 14 6 Geology Department, Faculty of Sciences, United Arab Emirates University, P.O Box 15 17551, Al-Ain, Abu Dhabi, United Arab Emirates. 16 7 University of Asmara, Department of Earth Sciences, P.O. Box 1220, Asmara, Eritrea 17 8 6016 SW Haines Street, Portland, Oregon 97219, USA. 18 9 Three Gorges Research Center for Geohazards, State Key Laboratory of Geological 19 Processes and Mineral Resources, China University of Geosciences, Wuhan, China. 20 10 Council for Geoscience (CGS), South Africa. 21 11 University of Dar es Salaam, Department of Geology, Tanzania. 22 12 Geosciences Department, University of Texas at Dallas, Richardson, Texas, USA. 23 13 Norwegian University of Science and Technology, Trondheim, Norway. 24 25 Abstract 26 27 The East African Orogen, extending from southern Israel, Sinai and Jordan in the north to 28 Mozambique and Madagascar in the south, is the world´s largest Neoproterozoic to Cambrian 29 orogenic complex. It comprises a collage of individual oceanic domains and continental 30 fragments between the Archean Sahara-Congo-Kalahari Cratons in the west and 31 Neoproterozoic India in the east. Orogen consolidation was achieved during distinct phases of 32 orogeny between ~850 and 550 Ma. The northern part of the orogen, the Arabian-Nubian 33 Shield, is predominantly juvenile Neoproterozoic crust that formed in and adjacent to the 34 Mozambique Ocean. The ocean closed during a protracted period of island-arc and 35 microcontinent accretion between ~850 and 620 Ma. To the south of the Arabian Nubian 36 Shield, the Eastern Granulite-Cabo Delgado Nappe Complex of southern Kenya, Tanzania 37 and Mozambique was an extended crust that formed adjacent to the Mozambique Ocean and 38 experienced a ~650-620 Ma granulite-facies metamorphism. Completion of the nappe 39 assembly around 620 Ma is defined as the East African Orogeny and was related to closure of 40 the Mozambique Ocean. Oceans persisted after 620 Ma between East Antarctica, India, 41 southern parts of the Congo-Tanzania- Bangweulu Cratons and the Zimbabwe-Kalahari 42 Craton. They closed during the ~600–500 Ma Kuungan or Malagasy Orogeny, a 43 tectonothermal event that affected large portions of southern Tanzania, Zambia, Malawi, 44 Mozambique, Madagascar and Antarctica. The East African and Kuungan Orogenies were 45 followed by phases of post-orogenic extension. Early ~600–550 Ma extension is recorded in 46 the Arabian-Nubian Shield and the Eastern Granulite - Cabo Delgado Nappe Complex. Later 47 ~550–480 Ma extension affected Mozambique and southern Madagascar. Both extension 48 phases, although diachronous, are interpreted as the result of lithospheric delamination. Along 49 the strike of the East African Orogen, different geodynamic settings resulted in the evolution 50 of distinctly different orogen styles. The Arabian-Nubian Shield is an accretion-type orogen 51 comprising a stack of thin-skinned nappes resulting from the oblique convergence of 52 bounding plates. The Eastern Granulite - Cabo Delgado Nappe Complex is interpreted as a 53 hot- to ultra-hot orogen that evolved from a formerly extended crust. Low viscosity lower 54 crust resisted one-sided subduction, instead a sagduction-type orogen developed. The regions 55 of Tanzania and Madagascar affected by the Kuungan Orogeny are considered a Himalayan- 56 type orogen composed of partly doubly thickened crust. 57 58 Keywords: East African Orogen, Mozambique Belt, Arabian - Nubian Shield, Tectonics, 59 Metamorphism, Magmatism. 60 61 1. Introduction 62 The East African Orogen (EAO; Stern, 1994) is a Neoproterozoic–early Cambrian mobile 63 belt that today extends south along eastern Africa and western Arabia from southern Israel, 64 Sinai and Jordan in the north to Mozambique and Madagascar in the south. A southern 65 continuation of the EAO, from Mozambique to Antarctica, was proposed by Jacobs et al., 66 (1998), Jacobs and Thomas (2004) and Grantham et al. (2011), but this is challenged by 67 Collins and Pisarevsky (2005). Crust similar to the EAO is likely present in the northern 68 Arabian plate buried under Phanerozoic sedimentary cover (Stern and Johnson, 2010) , and 69 also in terranes now found in Asia Minor. In its southern portion, between the Congo- 70 Tanzania-Bangweulu Cratons and the Zimbabwe-Kalahari Craton (Fig. 1), the EAO devides 71 into the E–W trending Damara-Zambesi Belt (Johnson et al., 2005) that continues to the 72 Southern Granulite Terrane of India (Plavsa et al., 2012, Collins et al., in press) and further 73 into Sri Lanka and East Arctica at Ltzow-Holm Bay (Shiraishi et al., 1994). All these belts 74 were part of an orogenic cycle spanning the period between breakup of Rodinia (870–800 Ma; 75 Li et al., 2008) and final amalgamation of Gondwana (~500 Ma: Collins and Pisarevsky, 76 2005; Pisarevsky et al., 2008). Here we review the tectonometamorphic evolution of the EAO. 77 Extending ~6000 km N–S, the EAO forms the largest continuous Neoproterozoic–Cambrian 78 orogen on Earth, comparable in extent to the ~7500 km long Cenozoic Alpine–Himalayan 79 orogenic system. The EAO is considered a “Transgondwanan supermountain range” whose 80 formation and destruction had important implications for atmospheric oxygenation (Och and 81 Shields-Zhou, 2012) and thus for the evolution of higher organized organisms on Earth 82 (Squire et al., 2006). 83 Traditionally, the EAO is subdivided into the Arabian–Nubian Shield (ANS) in the north, 84 composed largely of juvenile Neoproterozoic crust (e.g. Stern, 1994, 2002; Johnson and 85 Woldehaimanot, 2003; Johnson et al., 2011), and the Mozambique Belt (MB) in the south 86 comprising mostly pre-Neoproterozoic crust with a Neoproterozoic–early Cambrian 87 tectonothermal overprint (Fig. 1) (e.g., Fritz et al., 2005; Collins, 2006; De Waele et al., 88 2006a; Viola et al., 2008; Bingen et al., 2009). Although the focus of this review is on 89 Neoproterozoic to early Cambrian mountain building and destruction processes that shaped 90 the EAO, relevant precursor EAO orogenies are also briefly described. We avoid using the 91 term “Pan-African” to describe the orogenies outlined below. This term was originally applied 92 to describe a widespread ~500 Ma tectonothermal event in Africa (Kennedy, 1964) but was 93 subsequently used widely to encompass any Neoproterozoic thermal or tectonic event. Hence, 94 we believe that this term has lost any use as defining a particular tectonic event. Instead, we 95 herein refer to ~650–620 Ma tectonothermal events as the East African Orogeny and ~600– 96 500 Ma events as the Kuunga Orogeny. The term Kuunga was originally used as a time frame 97 of global orogenies (Meert et al., 1995) and subsequently linked with the collision of 98 Australia-Antarctica with southern India and the Kalahari Craton (Meert, 2003). Collins and 99 Pisavervsky (2005) then introduced the term Malagasy Orogeny to specify the ~600-500 Ma 100 orogeny caused by the collision of India with the already amalgamated Congo and Azania 101 terranes, the latter constituting much of Madagsacar. Here we use the broader term Kuunga 102 Orogeny for a common ~600-500 Ma tectonometamorphic event in East Africa. 103 The ~6000 km length of the EAO makes it is unlikely that it has similar tectonic styles 104 along its entire length. Even a cursory inspection suggests that different processes were active 105 in the ANS in the north and the MB in the south. Additional differences in temporal and 106 geometric relations are seen in Tanzania and Mozambique where the E–W trending Damara- 107 Zambesi-Irumide Belt intersects the N–S trending MB.
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