Mesoarchean convergent margin processes and crustal evolution: Petrologic, geochemical and zircon U–Pb and Lu–Hf data from the Mercara Suture Zone, southern India T. Amaldev a, ⁎, M. Santosh b,c , Li Tang c,d , K.R. Baiju a , T. Tsunogae d,e , M. Satyanarayanan f a Department of Marine Geology and Geophysics, Cochin University of Science and Technology, Lakeside Campus, Kochi 16, India b Center for Tectonics, Resources and Exploration, Department of Earth Sciences, University of Adelaide, SA 5005, Australia c School of Earth Sciences and Resources, China University of Geosciences Beijing, 29 Xueyuan Road, Beijing 100083, China d Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8572, Japan e Department of Geology, University of Johannesburg, Auckland Park 2006, South Africa f CSIR — National Geophysical Research Institute, Hyderabad 500007, India abstract article info Article history: Received 18 January 2016 Received in revised form 23 May 2016 Accepted 31 May 2016 Available online 14 July 2016 Handling Editor: Z.M. Zhang The Mercara Shear Zone is sandwiched between the Western Dharwar Craton and the Coorg Block in the South- ern Granulite Terrain of India, and is marked by steep gravity gradients interpreted to suggest the presence of underplated high-density material in the lower crust. Here we present geological, petrological and geochemical data, together with zircon U–Pb ages and Lu–Hf isotopes from a suite of metaigneous (TTG-related gneisses, charnockite, metagabbro, mafic granulite) and metasedimentary (quartz mica schist, khondalite, garnet biotite gneiss, kyanite–sillimanite bearing metapelite) rocks from this zone. Geochemical data on the magmatic suite suggests formation through subduction-related arc magmatism, whereas the metasediments represent volcano-sedimentary trench sequences. Phase equilibrium modeling of mafic granulites from the Mercara Shear Zone suggests P–T range of 10–12 kbar at 700 °C to 900 °C. The zircon data yield weighted mean 207 Pb/ 206 Pb ages of 3229 ± 80 Ma for metagabbro, 3168 ± 25 Ma for the charnockite, and 3181 ± 20 Ma for the mafic granulite. Ages ranging from 3248 ± 28 Ma to 3506 ± 26 Ma were obtained from zircons in the kya- nite/sillimanite bearing metapelite, 3335 ± 44 Ma from khondalite, 3135 ± 14 Ma from garnet biotite gneiss, 3145 ± 17 Ma to 3292 ± 57 Ma from quartz mica schist and 3153 ± 15 Ma to 3252 ± 36 from TTG gneiss. The tightly defined ages of 3.1 to 3.2 Ga from igneous zircons in the magmatic suite suggest prominent Mesoarchean convergent margin magmatism. The timing of high grade metamorphism as constrained from metamorphic overgrowths in zircons is ca. 3.0 Ga which might mark the collisional event between the Western Dharwar Craton and the Coorg Block. Hf isotope features suggest magma derivation mostly from juvenile sources and the Lu–Hf model ages indicate that the crust building might have also involved partial recycling of basement rocks as old as ca. 3.8 Ga. Our study defines the Mercara Shear Zone as a terrane boundary, and possible Mesoarchean suture along which the Coorg Block was accreted to the Western Dharwar Craton. The accretion of these continental fragments might have coincided with the birth of the oldest supercontinent “Ur”. © 2016 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved. Keywords: Petrology and geochemistry Zircon U–Pb geochronology and Lu–Hf isotopes Convergent margin tectonics Mercara Suture Zone southern India 1. Introduction Continents were assembled and broken apart, closing and opening oceans through repeated cycles in Earth history (Reeves et al., 2002; Rogers and Santosh, 2002; Meert, 2003; Murphy and Nance, 2003; Rogers and Santosh, 2003, 2004; Santosh et al., 2009; Meert et al., 2010; Condie and Kröner, 2012; Murphy and Nance, 2012). The birth, evolution and preservation of continental crust have important implica- tions not only in tracing the tectonic history of supercontinents, but also in understanding the formation of mineral resources and in tracing the climatic and biologic evolution (Bradley, 2011; Stern, 2011; Zhai and Santosh, 2011; Strand, 2012; Young, 2012a, b, 2013; Nance et al., 2014; Santosh et al., 2015). The stabilization or cratonization of continental blocks involves juvenile crustal growth, deposition of supracrustal rocks and orogenic processes, together with anorogenic plutonism and deposition of platform sediments (Rogers and Santosh, 2003; Santosh et al., 2009; Nance et al., 2014; Santosh et al., 2014, 2016). Crustal blocks or cratons may thus appear as discrete geologic units bounded by shear zones or sutures and hence the study of this transition zones/terrane boundaries, provide critical information on various geological and tectonic aspects (Daly, 1986; Chetty, 1996; Gondwana Research 37 (2016) 182–204 ⁎ Corresponding author. E-mail address: amaldev302@gmail.com (T. Amaldev). http://dx.doi.org/10.1016/j.gr.2016.05.017 1342-937X/© 2016 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Gondwana Research journal homepage: www.elsevier.com/locate/gr