P. C. Bandopadhyay

Provenance analysis of the Oligocene turbidites (Andaman Flysch), South Andaman Island: A geochemical approach

The Oligocene-aged sandstone-shale turbidites of the Andaman Flysch are best exposed along the east coast of the South Andaman Island. Previously undocumented sandstone-shale geochemistry, investigated here, provides important geochemical constraints on turbidite provenance. The average 70.75 wt% SiO2, 14.52 wt% Al2O3, 8.2 wt% Fe2O3t+

Provenance of Oligocene Andaman sandstones (Andaman–Nicobar Islands): Ganga–Brahmaputra or Irrawaddy derived?

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The Andaman–Nicobar Accretionary Ridge: Geology, Tectonics and Hazards

MgO and average 0.20 Al2O3/SiO2 and 1.08 K2O/Na2O ratios in sandstones, compare with quartzwackes. The shale samples have average 59.63 wt% SiO2, 20.29 wt% Al2O3, 12.63 wt% Fe2O3t+

Chapter 11 The Archipelago Group: current understanding

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Chapter 2 Introduction to the geography and geomorphology of the Andaman–Nicobar Islands

MgO and average 2.42 K2O/Na2O and 0.34 Al2O3/SiO2 ratios. Geochemical data on CaO–Na2O–K2O diagram fall close to a granite field and on K2O/Na2O–SiO2 diagram within an active continental margin tectonic setting. The range and average values of Rb and Rb/Sr ratios are consistent with acid-intermediate igneous source rocks, while the values and ratios for Cr and Ni are with mafic rocks. Combined geochemical, petrographic and palaeocurrent data indicate a dominantly plutonic-metamorphic provenance with a lesser contribution from sedimentary and volcanic source, which is possibly the Shan–Thai continental block and volcanic arc of the north-eastern and eastern Myanmar. Chemical index of alteration (CIA) values suggests a moderate range of weathering of a moderate relief terrane under warm and humid climate.

Chapter 6 Geological framework of the Andaman–Nicobar Islands

Abstract Interpretation of the origin of Oligocene Flysch exposed in the Andaman–Nicobar Islands has been the subject of debate. Previous work on the provenance of the Andaman Flysch based on samples from South Andaman has indicated major contributions from Myanmar affected by the India–Asia collision, mixed with subordinate detritus from the nascent Himalayas. This study examines the provenance of a larger suite of samples that extend to North and Middle Andaman islands as well as Great Nicobar Island. Rather monotonous petrographic and heavy-mineral assemblages testify to strong diagenetic imprint, leading to a poorly constrained identification of the sediment source. U–Pb zircon ages provide more robust and diagnostic provenance discrimination between the Myanmar Arc and the growing Himalayan range. Combining petrographic and mineralogical data with detrital zircon U–Pb analyses, we find that most of the Andaman Flysch is dominated by a strong continental-crust signal with only a minor contribution from arc material. Statistical analyses of the data show that most of the samples have a provenance similar to Palaeogene Bengal Fan sediments, although the type section on South Andaman has a closer affinity to the provenance of the modern Irrawaddy. Supplementary material: Sample location (Table A1), the complete petrographic (Table A2), heavy mineral (Table A3) and U–Pb zircon-age datasets (Table A4) are all available at https://doi.org/10.6084/m9.figshare.c.3634328.v1

Paleogene Tectonic and Sedimentation History of the Andaman-Nicobar Accretionary Arc, Northeast Indian Ocean

Rocks exposed across the hundreds of islands that belong to the 800 km long Andaman–Nicobar archipelago provide a condensed window into the active subduction zone that separates the India–Australia plate from the over-riding Burma–Sunda plate. Despite a strategic and seismically active location the Andaman-Nicobar ridge has seen comparatively little research. This Memoir provides the first detailed and comprehensive account of geological mapping and research across the island chain and adjacent ocean basins. Chapters examine models of Cenozoic rifting of the Andaman Sea and the regional tectonic and seismogenic framework. A detailed critical review of the Andaman–Nicobar stratigraphy, supported by new data, includes arc volcanism and a description of Barren Island, Indias only active volcano. Seismic history and hazards and the impacts of the 2004 earthquake and tsunami are also described. The volume ends with an examination of the regions natural resources and hydrocarbon prospects.

Chapter 1 Introduction and history of mapping and research

Abstract The geology and stratigraphy of the Archipelago Group are reviewed and new data presented to improve understanding. Major lithofacies are bioclastic limestones, bioturbated mottled marlstones, micritic limestones, trace fossil-bearing mudstones, quartzose sandstones and reworked volcanic material of Mio-Pliocene and Pleistocene age. The succession overlies the Pre-Neogene submarine fan turbidites and tectonic mélanges of ophiolite derivation and Mithakhari rocks, and is overlain by Quaternary deposits of late Pleistocene–Holocene age. The Neogene sequences were deposited in wave- and current-agitated shallow-marine intertidal and relatively deeper-water subtidal, nearshore and offshore shelfal environments. The existing stratigraphic framework is examined and suggestions made for improvement.

Chapter 14 Seismicity of the Andaman–Nicobar Islands and Andaman Sea

Abstract The geography and the geomorphology of the Andaman–Nicobar accretionary ridge (islands) is extremely varied, recording a complex interaction between tectonics, climate, eustacy and surface uplift and weathering processes. This chapter outlines the principal geographical features of this diverse group of islands.

Chapter 8 Mithakhari deposits

Abstract The Andaman–Nicobar archipelago that forms the western margin of the Andaman Sea is a sediment-dominated accretionary wedge (outer-arc island) associated with a convergent margin tectonic setting. The Andaman accretionary ridge consists of two stratigraphically and structurally distinct terranes, juxtaposed and telescoped into a north–south-trending high-relief fold-thrust belt formed along the obliquely subducting eastern margin of the Indo-Australian oceanic lithospheric plate. The geology and structure of the ridge reflect the complexity of the evolving tectonics and stratigraphy of an accretionary wedge. Pre-Cretaceous meta-sedimentary rocks, Upper Cretaceous ophiolites and Palaeogene–Neogene sedimentary formations indicate rapid, spatial and temporal changes in lithology, sedimentology, sedimentary and tectonic environments, and palaeogeographic setting. This chapter outlines the current geodynamic setting, evidence for the history of accretion and regional geology and introduces the regional stratigraphic framework.