Contents lists available at ScienceDirect Journal of Asian Earth Sciences journal homepage: www.elsevier.com/locate/jseaes Full length article Provenance and paleo–weathering of Tertiary accretionary prism–forearc sedimentary deposits of the Andaman Archipelago, India Neeraj Awasthi ⁎ Physical Research Laboratory, Navrangpura, Ahmedabad 380009, India ARTICLE INFO Keywords: Andaman Islands Provenance Weathering Geochemistry ABSTRACT In order to understand the provenance and tectono–sedimentary processes occurring in the Andaman Subduction Zone (ASZ), the Late Cretaceous to Oligocene sedimentary records from the Andaman Islands have been studied. These sedimentary records are considered to have preserved the history of the India–Asia collision, evolution of the Himalayas, climatic development and palaeo–drainage reorganizations on the Indian and Asian plates. About 47 sandstones and mudstones (shales and siltstones) samples were analyzed for whole rock major, trace, and rare earth element compositions. The geochemical results suggest mixing of sediments derived from the mafic ig- neous sources comprising local ophiolites and volcanic arc of the ASZ and an older Archean to Proterozoic age felsic cratonic source with compositions similar to average granodiorite or upper continental crustal sources. The compositions were dominated by sources of the mafic arc during deposition of the Mithakhari Group, whereas they were controlled by continental sources during deposition of the Andaman Flysch Group. The Hope Town Conglomerate unit of the Mithakhari Group was mainly derived from weathering and erosion of the subaerially exposed local ophiolite thrust sheets, whereas its Namunagarh unit contains significant detritus from volcanic arcs. The Andaman Flysch turbidites were deposited with a greater supply of sediments from first–cycle active continental margin sources probably located in the Tibetan and eastern Myanmar region and recycled quartzose sedimentary sources within the nascent Himalayas. The sediments supplied to both the Mithakhari and the Andaman Flysch Groups were characterized by varying values of CIA, PIA and W. These variable values were either due to non–steady state weathering conditions in the sources or the changing climatic conditions owing to the motion of Indian plate with reference to the equator. The uniformly high CIA and W values in the Andaman Flysch rocks can be related to high precipitation and strong chemical weathering associated with the initiation of the Indian monsoon. 1. Introduction Though confined to the Earth's outer crust, sedimentary rocks and sediments cover nearly three–fourth of the Earth's land surface and most of the ocean floor (Boggs, 2011). On the geological time scale, these sediments and their lithified equivalents range in age from Precambrian to modern and therefore, have been a great source to our existing in- formation about the Earth's history. Various studies on the compositions, textures, structures, and fossils in sedimentary rocks have provided in- sight into the tectonic setting of sedimentary basins, past climates, pa- laeogeography, oceanic environments and ecosystems (e.g., Nesbitt and Young, 1982; Roser and Korsch, 1986; Bhatia and Crook, 1986; McLennan et al., 1993; Fedo et al., 1995; Rieu et al., 2007; Clift et al., 2008). Petrographic, geochemical and geochronological information obtained from clastic sediments is generally used to constrain its pro- venance, tectonic setting, and diagenetic history. Petrographic techniques work well for coarse–grained sediments. However, for the fine–grained sediments, the geochemical studies become more relevant. Geochemical studies take into account distribution of various elements in sedimentary rocks and based on the variations in compositional char- acteristics help to identify different sources, and unravel past sedimen- tary environments by deciphering tectonic settings, variability in the climate, weathering conditions and effects of diagenesis (McLennan et al., 1993; Cullers, 1994; Condie et al., 1995; Cox et al., 1995). Source rock composition primarily controls the bulk geochemical composition but multiple processes and their interaction during the passage from source to sink and after the deposition in the sedimentary basin also equally affect sediment geochemistry (McLennan et al., 1993; Drever and Vance, 1994; Fedo et al., 1995; White and Blum, 1995; Taylor and Howard, 1999; Roy and Roser, 2013). Mobile elements like Na, Ca, Mg, K, Sr, Ba, Rb, Cs help in evaluating and quantifying intensity of chemical weathering and depicting paleoclimatic conditions in source regions http://dx.doi.org/10.1016/j.jseaes.2017.10.005 Received 28 December 2016; Received in revised form 20 September 2017; Accepted 2 October 2017 ⁎ At: Department of Earth Sciences, Indian Institute of Technology Kanpur, 208016, India. E-mail address: aneeraj.geology@gmail.com. Journal of Asian Earth Sciences 150 (2017) 45–62 Available online 05 October 2017 1367-9120/ © 2017 Elsevier Ltd. All rights reserved. MARK