Abstract 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, India’s 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 region’s natural resources and hydrocarbon prospects.

Shallow-marine carbonate facies from volcanic-arc settings provide an important, but commonly overlooked, record of relative sea-level change, differential subsidence-uplift, paleoclimate trends, and other environmental changes. Carbonate strata are thin where volcanic eruptions are frequent and voluminous, unless shallow, bathy-metric highs persist for long periods of time and volcaniclastic sediment and erupted materials are trapped in adjacent depocenters. Carbonate platforms and reefs can attain significant thickness, however, if subsidence continues after volcanic activity ceases or the volcanic front migrates. The areal extent of shallow-marine carbonate sedimentation is likewise affected by differential tectonic subsidence, although carbonate platforms are most laterally extensive during transgressive to highstand conditions and when arc depocenters are filled with sediment. Tectonic controls on shallow-marine carbonate sedimentation in arc depocenters include (1) coseismic fault displacements and associated surface deformation; (2) long-wavelength tectonic subsidence related to dynamic mantle flow, flexure, lithospheric thinning, and thermal subsidence; and (3) large-scale plate deformation related to local conditions of subduction. Depositional controls on carbonate sedimentation in arc depocenters include (1) the frequency, volume, and style of volcanic eruptions; (2) accumulation rates for siliciclastic-volcaniclastic sediment; (3) the frequency, volume, and dispersal paths of erupted material; (4) (paleo)wind direction, which influences both carbonate facies development directly and indirectly by controlling the dispersal of volcanic ash and other pyroclastic sediment, which can bury carbonate-producing organisms; (5) the frequency and intensity of tsunami events; and (6) volcanically or seismically triggered mass-wasting events, which can erode or bury carbonate strata. Regarding platform morphologies in arc-related settings, (1) fringing reefs or barrier reef systems with lagoons may develop around volcanic edifices throughout the long-term evolution of volcanic arcs; (2) local reefs and mounds may build on intrabasinal, fault-bounded highs within underfilled forearc, intra-arc, and backarc basins; (3) isolated platforms with variable platform margin-to-basin transitions are common in “underfilled” and tectonically active depocenters; and (4) broad ramps and rimmed carbonate shelves are typically found in tectonically mature and sediment-filled depocenters.

The Andaman Islands are part of the Andaman-Nicobar Ridge, an accretionary complex that forms part of the outer-arc ridge of the Sunda subduction zone. The Tertiary rocks exposed on the Andaman Islands preserve a record of the tectonic evolution of the surrounding region, including the evolution and closure of the Tethys Ocean. Some of the Paleogene sediments on Andaman may represent an offscraped part of the early Bengal Fan. Through field and petrographic observations, and use of a number of isotopic tracers, new age and provenance constraints are placed on the key Paleogene formations exposed on South Andaman. A paucity of biostratigraphic data poorly define sediment depositional ages. Constraints on timing of deposition obtained by dating detrital minerals for the Mithakhari Group indicate sedimentation after 60 Ma, possibly younger than 40 Ma. A better constraint is obtained for the Andaman Flysch Formation, which was deposited between 30 and 20 Ma, based on Ar-Ar ages of the youngest detrital muscovites at ca. 30 Ma and thermal history modeling of apatite fission-track and U-Th/He data. The latter record sediment burial and inversion (uplift) at ca. 20 Ma. In terms of sediment sources the Mithakhari Group shows a predominantly arc-derived composition, with a very subordinate contribution from the continental margin to the east of the arc. The Oligocene Andaman Flysch at Corbyn's Cove is dominated by recycled orogenic sources, but it also contains a subordinate arc-derived contribution. It is likely that the sources of the Andaman Flysch included rocks from Myanmar affected by India-Asia collision. Any contribution of material from the nascent Himalayas must have been minor. Nd isotope data discount any major input from cratonic Greater India sources.