G Model PRECAM-3373; No. of Pages 25 ARTICLE IN PRESS Precambrian Research xxx (2011) xxx–xxx Contents lists available at ScienceDirect Precambrian Research journa l homepage: www.elsevier.com/locate/precamres Provenance and tectonic significance of the Palaeoproterozoic metasedimentary successions of central and northern Madagascar a,b,∗ b c b e b B. De Waele , R.J. Thomas , P.H. Macey , M.S.A. Horstwood , R.D. Tucker , P.E.J. Pitfield , b d b d e f g D.I. Schofield , K.M. Goodenough , W. Bauer , R.M. Key , C.J. Potter , R.A. Armstrong , J.A. Miller , h h h h i T. Randriamananjara , V. Ralison , J.M. Rafahatelo , M. Rabarimanana , M. Bejoma a SRK Consulting, Level 1, 10 Richardson Street, West Perth, WA 6005, Australia b British Geological Survey, Keyworth, Notts NG12 5GG, United Kingdom c Council for Geoscience, Western Cape, South Africa d British Geological Survey, Murchison House, Edinburgh, United Kingdom e United States Geological Survey, Reston, VA 20192, USA f Australian NationalUniversity, Canberra, Australia g Stellenbosch University, Stellenbosch, South Africa h Projet de Gouvernance des Ressources Minières, Antananarivo, Madagascar i Université de Antananarivo, Antananarivo, Madagascar a r t i c l e i n f o a b s t r a c t Article history: New detrital zircon U–Pb age data obtained from various quartzite units of three spatially separated Received 9 July 2009 supracrustal packages in central and northern Madagascar, show that these units were deposited between Received in revised form 19 April 2011 1.8 and 0.8 Ga and have similar aged provenances. The distribution of detrital zircon ages indicates an Accepted 26 April 2011 overwhelming contribution of sources with ages between 2.5 and 1.8 Ga. Possible source rocks with an Available online xxx age of 2.5 Ga are present in abundance in the crustal segments (Antananarivo, Antongil and Masora Domains) either side of a purported Neoproterozoic suture (“Betsimisaraka Suture Zone”). Recently, Keywords: possible source rocks for the 1.8 Ga age peak have been recognised in southern Madagascar. All three U–Pb dating supracrustal successions, as well as the Archaean blocks onto which they were emplaced, are intruded Detrital provenance by mid-Neoproterozoic magmatic suites placing a minimum age on their deposition. The similarities in East African Orogen Gondwana detrital pattern, maximum and minimum age of deposition in the three successions, lend some support Palaeoproterozoic to a model in which all of Madagascar’s Archaean blocks form a coherent crustal entity (the Greater Tectonics Dharwar Craton), rather than an amalgamate of disparate crustal blocks brought together only during Neoproterozoic convergence. However, potential source terranes exist outside Madagascar and on either side of the Neoproterozoic sutures, so that a model including a Neoproterozoic suture in Madagascar cannot be dispelled outright. © 2011 Elsevier B.V. All rights reserved. 1. Introduction and references therein). However, new data have been obtained for the northern half of Madagascar through a concerted phase Madagascar occupies a critical, central position within the East of geological mapping and research undertaken by teams from African Orogen (EAO; Fig. 1). Consequently, an understanding of the British and United States Geological Surveys (BGS-USGS) and the geological history of its component terranes is important for the Council for Geoscience of South Africa (CGS), in conjunc- constraining the palaeogeography of the entire region through tion with Malagasy geologists from the Projet du Governance time and elucidating the assembly history of Gondwana. Many des Ressources Minérales (PGRM), as part of a multi-disciplinary, recent studies of the geology of Madagascar have focused on World Bank-sponsored project which ran between 2004 and comparisons between the three component Archaean cratonic 2008 (see BGS-USGS-GLW, 2008 and CGS, 2009a,b). This study domains and intervening paragneiss assemblages (Collins, 2006 facilitated re-interpretations of the tectonic framework of the northern half of Madagascar. In this paper we focus on a poorly understood aspect of the Precambrian shield: the age and prove- ∗ nance of the enigmatic metasedimentary units of Proterozoic Corresponding author at: SRK Consulting, Level 1, 10 Richardson Street, West age that rest upon the Archaean cratons of central and eastern Perth, WA 6005, Australia. E-mail addresses: [email protected], [email protected] (B. De Waele). Madagascar. 0301-9268/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.precamres.2011.04.004 Please cite this article in press as: De Waele, B., et al., Provenance and tectonic significance of the Palaeoproterozoic metasedimentary successions of central and northern Madagascar. Precambrian Res. (2011), doi:10.1016/j.precamres.2011.04.004 G Model PRECAM-3373; No. of Pages 25 ARTICLE IN PRESS 2 B. De Waele et al. / Precambrian Research xxx (2011) xxx–xxx Proto-Tethys Arabian-Nubian Shield (ANS) High-grade rocks of EAO Other Late Neoproterozoic belts Cratonic building blocks Arab i a Suture zoneand terrane boundaries of theEAO Shear Zone of the EAO Subduction zone A N S Collision A f rica AMB Aravalli Mobile Belt AMB W-Gondwana M India Fig. 2 EAO ? Australia E-Gondwana S-America East Antarctica Fig. 1. Palaeoposition of Madagascar in Gondwana (after Thomas et al., 2009). The ancient shield of Madagascar is composed of distinctive Of the three successions described here, the Itremo Group, Archaean crustal blocks: the dominantly Meso- to Neoarchaean which locally overlies the western Antananarivo Craton, is blocks of east Madagascar (Antongil and Masora cratons) and the the best-studied (Figs. 2, 3). It comprises a thick succession exclusively Neoarchaean block of central Madagascar (Antana- of quartzite, metapelite and metacarbonate, affected by (sub-) narivo Craton, Fig. 2). Two very different hypotheses attempt greenschist facies metamorphism, and has yielded detrital zircon to explain their present-day juxtaposition. A widely-accepted age data with the largest modes at ca. 2500 and 1850 Ma (Cox hypothesis (e.g. Collins, 2006 and references therein) portrays et al., 1998, 2004a; Fitzsimons and Hulscher, 2005). On the basis of 13 them as disparate fragments of peninsular India and central East the geochronological data, carbonate ␦ C compositions and the Africa, respectively, joined along a convergent margin boundary morphology of stromatolites in the succession, the Itremo Group – the “Betsimisaraka suture” – active throughout Neoprotero- is regarded as having been deposited during the Late Palaeopro- zoic time (ca. 800–550 Ma). The “Betsimisaraka suture” comprises terozoic (Cox et al., 1998, 2004a; Fitzsimons and Hulscher, 2005), a belt of Neoproterozoic metasedimentary rocks, intruded by although a younger age cannot be ruled out. As yet, bedrock of voluminous Neoproterozoic to Cambrian granitoids, which has Palaeoproterozoic age (ca. 2.0–1.8 Ga) has only been identified been named as the Anaboriana-Manampotsy belt (Fig. 2). Another in southern Madagascar (Tucker et al., 2010a). Nevertheless, a hypothesis (Tucker et al., 2010a,b) portrays them as different close match of detrital zircon ages from the Itremo Group with parts of a common craton (the Greater Dharwar Craton) joined the Ubendian-Usagaran belts of east Africa (e.g. marginal to the by a Neoarchaean accretion event (ca. 2.5 Ga). Both perspectives Tanzania Craton), led Cox et al. (1998, 2004a) and Fitzsimons acknowledge that the disparate Archaean cratons are overlain by and Hulscher (2005) to conclude that the Antananarivo Craton metasedimentary rocks of Proterozoic age: the eastern Antongil was derived from East Africa. In their view, the Itremo Group and Masora cratons by the Sahantaha and Maha groups respec- was deposited unconformably on the East African margin, and a tively, and the western Antananarivo Craton by the Itremo Group piece of it (the future Antananarivo Craton) rifted away to form (Fig. 2). The metasedimentary rocks represent either remnants a microcontinent, “Azania” (Collins and Pisarevsky, 2005). The of discrete sedimentary basins deposited on the Archaean cra- Antananarivo Craton and overlying supracrustal rocks were then tons, and/or dissected parts of one or more parautochthonous metamorphosed and deformed during an early Neoproterozoic to allochthonous sheets that were structurally emplaced dur- orogenesis (ca. pre-800 Ma, Collins et al., 2003b; Collins, 2006) ing post-depositional orogenic events (e.g. De Waele et al., prior to its rifting away, and subsequent amalgamation with east 2008). Madagascar. Please cite this article in press as: De Waele, B., et al., Provenance and tectonic significance of the Palaeoproterozoic metasedimentary successions of central and northern Madagascar. Precambrian Res. (2011), doi:10.1016/j.precamres.2011.04.004 G Model PRECAM-3373; No. of Pages 25 ARTICLE IN PRESS B. De Waele et al. / Precambrian Research xxx (2011) xxx–xxx 3 43°E 44°E 45°E 46°E 47°E 48°E 49°E 50°E 51°E 52°E 12°S Phanerozoic cover rocks 0 100 km Vohibory (V), Androyen (And), Anoysen (Ano) AM Anaboriana - Manampotsy Neoproterozoic domains and belts NB North Bemarivo 13°S SB South Bemarivo Neo-to Mesoproterozoic Ik Ikalama vony sub-domain NB terrane SSZ 14°S It Itremo Group Palaeoproterozoic SB S Sahantaha Group cover sequences S M Maha Group AM Andraparaty thrust TS Tsaratanana 15°S Archaean AN Antananarivo domains and cratons Ant Antongil-Masora Ant 16°S ANTONGIL CRATON KT 17°S Ts Bekodoka Mesoarchaean Inlier nucleus 18°S N AN 19°S ANTANANARIVO CRATON INDIAN OCEAN MD 20°S A-I It M IK MASORA 21°S CRATON 22°S Major thrusts Kalonja thrust 23°S KT Ano Angavo-Ifanadiana A-I Shear Zone V 24°S AnD Maroala MD Deformation Zone 25°S Sandrakota ShearZone SSZ Fig. 2. Tectonic architecture of Madagascar showing the location of successions described in the text. The less well-studied Sahantaha Group of northern Madagascar taha Group yielded a U–Pb detrital zircon signature comparable to has been variably metamorphosed up to amphibolite-/granulite- the Itremo Group (Cox et al., 2003).