Journal of Mineralogical and Petrological Sciences, Volume 110, page 111–125, 2015 Crustal assembly of the Antananarivo and Masora domains, central–eastern Madagascar: constraints from U–Pb zircon geochronology and whole–rock geochemistry of meta–granitoids Takashi ICHIKI*, Masahiro ISHIKAWA*, Jun–Ichi KIMURA**, Ryoko SENDA** and Raymond RAKOTONDRAZAFY*** *Graduate School of Environment and Information Sciences, Yokohama National University, 79–7 Tokiwadai, Hodogaya–ku Yokohama 240–8501, Japan **Department of Solid Earth Geochemistry (D–SEG), Japan Agency for Marine–Earth Science and Technology (JAMSTEC), 2–15 Natsushima–cho, Yokosuka 237–0061, Japan ***Department of Earth Sciences, Faculty of Science, University of Antananarivo, PB 906 Antananarivo 101, Madagascar In reconstructions of the Gondwana supercontinent, correlations of Archean domains between Madagascar and India remain debated. In this paper, we aim to establish correlations among these Archean domains using whole–rock geochemistry and U–Pb zircon geochronology of meta–granitoids from the Masora and the Anta- nanarivo domains, central–eastern Madagascar. A meta–granitoid from the central part of Masora domain is dated at 3277 Ma and shows a typical Archean tonalite–trondhjemite–granodiorite composition, whereas a tonalitic gneiss from the southeastern part of the Antananarivo domain gives an age of 2744 Ma. The geo- chemical signature of this tonalitic gneiss differs from that of the ~ 2500 Ma granitoids of the northwestern part of Antananarivo domain. In addition, the geochemical composition of the ~ 760 Ma granitic gneisses is con- sistent with a volcanic–arc origin for the protolith. Based on the geochemical and geochronological results, along with existing data, we identified three episodes of granitic magmatism in central–eastern Madagascar at ~ 3300, 2700, and 2500 Ma. These three magmatic events are consistent with those reported for the Dharwar Craton in India, suggesting that the Archean Masora and Antananarivo domains in Madagascar were part of the Greater Dharwar Craton during the period of 3300–2500 Ma. The 700–800 Ma volcanic arc granites identified in eastern Madagascar have not been reported in India. Therefore, the subduction of the oceanic plate that led to the formation of these granites likely took place at the western margin of the Greater Dharwar Craton, which included part of eastern Madagascar. Keywords: Madagascar, Archean, Meta–granitoids, Whole–rock geochemistry, U–Pb zircon geochronology INTRODUCTION ivo, Betsimisaraka (a possible suture zone), Ikalamavony, Vohibory, Androyan, and Anosyan domains (Fig. 1; Col- Located in the central part of the Gondwana superconti- lins and Windley, 2002; Collins, 2006; Tucker et al., nent, Madagascar is an important area for unraveling the 2011a). Madagascar also hosts a number of crustal–scale history and tectonic processes involved in the formation shear zones, such as the Angavo, Ampanihy, Beraketa, of the Gondwana supercontinent during the late Neopro- Ifanadiana, Ihosy and Zazafotsy shear zones (Fig. 1; terozoic to Cambrian (Stern, 1994; Meert, 2003; Jacobs e.g., Windley et al., 1994; Martelat et al., 2000, 2013; and Thomas, 2004; Collins and Pisarevsky, 2005; Boger, Raharimahefa and Kusky, 2010; Raharimahefa et al., 2011). The present–day landmass of Madagascar contains 2013), that provide tectonic constraints on the assembly four Archean domains and six Proterozoic domains. The of the Gondwana supercontinent. former includes the Antananarivo, Tsaratanana, Antongil, The correlation of Archean domains between Mada- and Masora domains, and the latter includes the Bemar- gascar and India has been extensively studied, especially in the past few years (e.g., Key et al., 2011; Tucker et al., doi:10.2465/jmps.141225 2011a, 2011b, 2014; Ishwar–Kumar et al., 2013; Rekha et T. Ichiki, ichiki–takashi–[email protected] Corresponding author al., 2013, 2014; Brandt et al., 2014; Collins et al., 2014; 112 T. Ichiki, M. Ishikawa, J. Kimura, R. Senda and R. Rakotondrazafy LEGEND et al., 2000; Kröner et al., 2000; Collins and Windley, MADAGASCAR BM Shear zone 2002; Collins, 2006; Raharimahefa and Kusky, 2006, Neoproterozoic 2009, 2010). It is generally accepted that the Masora SHSZ sedimentary rocks Fig. 2(a) Neoproterozoic and Antongil domains belong to an isolated part of the BS Paleo-Mesoproterozoic Western Dharwar Craton of India (e.g., Raval and Veer- TN sedimentary rocks Paleoproterozoic aswamy, 2003, 2011; Collins, 2006; Schofield et al., Neoarchean – AG Meso-Neoarchean 2010; Tucker et al., 2011a, 2014; Ishwar Kumar et al., SMSZ Paleo-Mesoarchean 2013; Rekha et al., 2013, 2014; Collins et al., 2014). AN KSZ INDIA However, the correlation of the Antananarivo domain AGSZ K with the surrounding Archean domains that are now lo- cated in India remains debated. First, Collins and Pisar- SEAN IK M MSZ WDCD ED evsky (2005), Collins (2006), Key et al. (2011), Collins et IHSZ ZSZ CGSZ AD al. (2014), and Plavsa et al. (2014) suggested that the C CHSZ Antananarivo domain was part of Azania, a microconti- V NH IFSZ MYSZ AMSZ nent that consisted of parts of East Africa (Yemen, So- AS BVSZ MKSZ PCSZ NSZ malia, Ethiopia) and the Madurai Block in India (Fig. 1). ESZ TSZ SASZ They also suggested that the Azania microcontinent col- BESZ KKSZCSZ AKSZ MB lided along the Betsimisaraka suture zone with the Ma- 200km sora and Antongil domains that were originally part of EAST the Western Dharwar Craton. However, other researchers AFRICA have demonstrated different models of the Antananarivo domain. A second model demonstrated by Tucker et al. EAST (2011a, 2011b, 2014) suggested that the Antananarivo ANTARCTICA domain was originally part of the Eastern Dharwar Cra- ton of India. A third model proposed by Ishwar–Kumar et Figure 1. Reconstruction of the Greater Dharwar Craton (modi- al. (2013) and Rekha et al. (2014) suggested that the An- fied after Tucker et al., 2011a; Peucat et al., 2013; Collins et al., 2014). Domain names: AD, Androyan domain; AG, Anton- tananarivo domain was contiguous with the Coorg Block. gil domain; AN, Antananarivo domain; AS, Anosyan domain; A fourth model by Brandt et al. (2014) suggested that the BM, Bemarivo domain; BS, Betsimisaraka domain (suture Antananarivo domain and the western part of the Madur- zone); C, Coorg Block; CD, Central Dhawar Craton; ED, East- ai Block formed one contiguous unit. Contrasting models ern Dharwar Craton; IK, Ikalamavony domain; K, Karwar have been proposed for the correlation of the Antananar- Block; M, Masora domain; MB, Madurai Block; NH, Nilgiri Hills; SEAN, Southeastern Antananarivo domain; TN, Tsarata- ivo domain with the surrounding Archean domains in In- nana domain; WD, Western Dharwar Craton; V, Vohibory do- dia in Gondwana reconstructions. main. Shear zone names: AKSZ, Achankovil shear zone; The magmatic ages of meta–granitoids in the Anta- AGSZ, Angavo shear zone; AMSZ, Ampanihy shear zone; nanarivo domain have been determined by Kröner et al. BESZ, Beraketa shear zone; BVSZ, Bhavani shear zone; CSZ, (2000), Tucker et al. (1999, 2007), and Macey et al. Cauvery shear zone; CHSZ, Chitradurga shear zone; CGSZ, Co- – org shear zone; ESZ, Ejeda shear zone; IHSZ, Ihosy shear zone; (2009). These studies mainly analyzed meta granitoids KSZ, Kumta shear zone; KKSZ, Karur–Kambam shear zone; from the north–central and west–central parts of the do- MSZ, Maroala shear zone; MKSZ, Mettur–Kolar shear zone; main (Fig. 2a), revealing ~ 2490–2550 Ma and ~ 730–820 MYSZ, Moyar shear zone; NSZ, Nallamalai shear zone; PCSZ, Ma as pre–collisional magmatic periods in this domain. – – Palghat Cauvery shear zone; SASZ, Salem Attur shear zone; – – SHSZ, Sandrakota–Antsaba shear zone; SMSZ, Southern Maha- These meta granitoids have calc alkaline signatures that rashtra shear zone; TSZ, Tranomaro shear zone; ZSZ, Zazafotsy indicate formation in an arc environment (Kröner et al., shear zone; shear zones are after Ishwar–Kumar et al. (2013), 2000; Macey et al., 2009). However, comparatively little Martelat et al. (2013) and Tucker et al. (2014). research has been undertaken on the southeastern part of the Antananarivo domain. The only age dating of Arche- an meta–granitoids from the Masora domain was per- Plavsa et al., 2014; Kröner et al., 2015; Boger et al., in formed by Tucker et al. (2011a), who dated a meta–gran- press; Ratheesh–Kumar et al., in press). In central–eastern odiorite on the southern margin of this domain. There- Madagascar, the Masora and Antongil domains are sep- fore, both the geological relationship between the south- arated from the Antananarivo domain by the north–south ern and central parts of this domain and the geochemistry trending Betsimisaraka suture zone, which lies almost of these meta–granitoids remain unclear. parallel to the Angavo–Ifanadiana shear zones (Collins Here, we present new whole–rock geochemical re- Crustal assembly of the Antananarivo and Masora domains, Madagascar 113 (a) Central–eastern 50°E (b) Central part of Masora domain 4 km Madagascar BM Quaternary alluvium 15°S Volcanic rock 15°S Paleozoic-Cambrian Granite and migmatite Proterozoic Alkaline granite AMBODILAFA 20°30′S Mafic-ultramafic rock N Metasedimentary rock Archean Metasedimentary rock Meta-granitoid MG08101232 Sampling point AG (with sample number) 48°10′E Road (c) Southern part of Antananarivo domain TN 20°35′S MG07072502 ANTANANARIVO Figure 2. (a) Archean domains in IFANADIANA Madagascar (modified after Tucker BS MG07072201 et al., 2011a) and U–Pb zircon ages Indian Ocean from this and previous studies (Kröner et al., 1999, 2000; Tucker AN et al., 1999, 2007, 2011a; Paquette 21°30′S AGSZ et al., 2003; Kabete et al., 2006; 100km Smith et al., 2008a, 2008b, 2008c; 20 km Raharimahefa and Kusky, 2010; U-Pb igneous 20°S Schofield et al., 2010; Bauer et zircon age Fig.2(b) (700-3400 Ma) Proterozoic al., 2011). Abbreviations are same Alkaline granite 3000-3400 Ma Diorite MG07072010 as in Figure 1. (b) Geological map 2600-2800 Ma Syenite of the central part of the Masora M Metasedimentary rock domain (modified after Randriama- Fig.2(c) 2400-2600 Ma Archean 2000-2200 Ma Metasedimentary rock AMBATOFOTSY nanjara, 2008).