Ninetyeast Ridge Research Articles

Contrasting vertical distribution between prokaryotes and fungi in different water masses on the Ninety-East Ridge, Southern Indian Ocean

Contrasting vertical distribution between prokaryotes and fungi in different water masses on the Ninety-East Ridge, Southern Indian Ocean

Enhanced Late Miocene Chemical Weathering and Altered Precipitation Patterns in the Watersheds of the Bay of Bengal Recorded by Detrital Clay Radiogenic Isotopes

AbstractThe late Miocene was a period of declining CO2levels and extensive environmental changes, which likely had a large impact on monsoon strength as well as on the weathering and erosion intensity in the South Asian Monsoon domain. To improve our understanding of these feedback systems, detrital clays from the southern Bay of Bengal (International Ocean Discovery Program Site U1443) were analyzed for the radiogenic isotope compositions of Sr, Nd, and Pb to reconstruct changes in sediment provenance and weathering regime related to South Asian Monsoon rainfall from 9 to 5 Ma. The 100 kyr resolution late Miocene to earliest Pliocene record suggests overall low variability in the provenance of clays deposited on the Ninetyeast Ridge. However, at 7.3 Ma, Nd and Pb isotope compositions indicate a switch to an increased relative contribution from the Irrawaddy River (by ∼10%). This shift occurred during the global benthic δ13C decline, and we suggest that global cooling and increasing aridity resulted in an eastward shift of precipitation patterns leading to a more focused erosion of the Indo‐Burman Ranges. Sr isotope compositions were decoupled from Nd and Pb isotope signatures and became more radiogenic between 6 and 5 Ma. Grassland expansion generating thick, easily weatherable soils may have led to an environment supporting intense chemical weathering, which is likely responsible for the elevated detrital clay87Sr/86Sr ratios during this time. This change in Sr isotope signatures may also have contributed to the late Miocene increase of the global seawater Sr isotope composition.

Biodiversity of radiolarians in surface sediments from the East Indian Ocean and their implication for water masses

This study focused on radiolarian diversity in the deep-sea sediments of the East Indian Ocean (EIO) to demonstrate their potential as a paleoceanogrpahic proxy. Radiolarians are in general abundant in deep-sea sediment of the EIO. However, around Sri Lanka, their abundances decrease potentially because of terrigenous matter inputs. The significantly high abundance of radiolarians in the northern Ninety-East Ridge (NER) area may indicate high levels of productivity in the overlying waters. Further, redundancy analysis (RDA) demonstrated that, in the EIO, Tetrapyle group and Phorticium group mainly inhabited the water depth between 25 m and 100 m; Acanthodesmia vinculata, Botryostrobus scutum and Dictyocoryne group can potentially be a nutrient indicator; the distribution of Didymocryrtis tetrathalamus tetrathalamus may possibly be related to the dissolved oxygen concentration; the distributions of Cornutella profunda, Cycladophora sp., and Cycladophora cornuta may be mainly influenced by flows of AAIW. Our analysis documented that the distribution of an Equatorial Undercurrent (EUC) assemblage, including A. vinculata, B. scutum, Dictyocryphalus hispidus, D. tetrathalamus tetrathalamus, Tetrapyle group, Phorticium group and Dictyocoryne group, may be controlled by the eastward-flowing EUC with the salinity-high and dissolved oxygen-rich waters. The Antarctic Intermediate Water may also affect the distribution pattern of Intermediate-Deep assemblage, including Cycladophora sp., C. profunda, Clathrocanium diadema and C. cornuta, with a possible northward spread along the NER into the southern Bay of Bengal.

The Nature and Evolution of the Ninetyeast Ridge: A Key Tectonic and Magmatic Feature of the East Indian Ocean

The Nature and Evolution of the Ninetyeast Ridge: A Key Tectonic and Magmatic Feature of the East Indian Ocean

Andaman–Nicobar–Sumatra Margin Revisited: Analysis of the Lithospheric Structure and Deformation Based on Gravity Modeling and Distribution of Seismicity

The Andaman–Nicobar–Sumatra subduction margin, with a well-developed Benioff zone down to ~ 200 km depth, extends over 1300 km along strike and has a lateral extent of ~ 200 km. Two-dimensional (2D) profiles based on generalized inversion of free-air gravity anomaly data across different segments of the Andaman–Nicobar sector of the margin were analyzed by reconstructing the geometry of the converging India–Eurasia lithospheric plates. Detailed 2D structures of the Ninetyeast Ridge (NER), fore-arc basin, volcanic arc, back-arc basin, spreading ridge, Sewell Rise, Mergui Ridge and Mergui Basin, and depths of Moho and the lithosphere–asthenosphere boundary were delineated. The volcanic arc is located at a distance of ~ 150–200 km from the trench and is marked by a zone of positive gravity anomaly separated from the trench by the fore-arc basin with a zone of gravity low. The topographic and gravity anomaly patterns show complex geometrical patterns over the volcanic arc due to the presence of a number of regional faults striking parallel to the trench axis developing a series of pull-apart (transtensional) basins as well as the interaction of the spreading ridges on the overriding plate. A narrow zone of negative gravity anomaly (~ − 185 to − 110 mGal) observed in the gravity model of the margin is interpreted to be associated with fore-arc shear fault above a zone of fractured oceanic crust with a thick sedimentary layer, located above a zone of sharp bending of the eastward converging Indian lithosphere in the fore-arc basin. A high concentration of seismicity and a trench-parallel band of moderate moment energy release along this fault might have been caused by concentrated deformation within the zone of flexing of the descending plate. A wide fore-arc (> 200 km) and the enhanced deformation of the subducting Indian oceanic plate in central sectors possibly resulted from increased interaction between the NER and the Andaman trench and extension in the Andaman back-arc. Appearance of a second moderate energy band and shifting of seismicity toward the trench axis following the 2004 MW 9.2 mega-event are apparently caused by the migration of the stress field from deeper to shallower part of the Indian lithosphere. A similar type of seismicity migration toward shallower part of the descending plate has been recorded along other subduction margins around the globe.

Exploring structured scripting cartographic technique of GMT for ocean seafloor modeling: A case of the East Indian Ocean

This paper examines spatial variations in the geomorphology of the Ninety East Ridge (NER), located in the Indian Ocean. The NER is an extraordinary long linear bathymetric feature with topography reflecting complex geophysical setting and geologic evolution. The research is based on a compilation of high-resolution bathymetric, geological, and gravity datasets clipped for the study area extent (65° - 107°E, 35°S - 21°N): General Bathymetric Chart of the Oceans (GEBCO), Earth Gravitational Model (EGM2008, EGM96). The submarine geomorphology of the NER was modeled by digitized cross-sectional profiles using Generic Mapping Tools (GMT). The availability of the method is explained by 1) the free datasets; 2) the open source GMT toolset; 3) the available tutorials of the GMT and the codes explained in this work. Three segments of the NER were selected, digitized, and modeled: 1) northern 89°E, 7°S to 90°E, 7°N; 2) central 88.4°E, 14.7°S to 88.8°E, 8.2°S; 3) southern 87.9°E, 17°S to 87.5°E, 27°S. Measured depths were visualized in graphs, compared, and statistically analyzed by the histograms. The northern segment has a steepness of 21.3° at the western slopes, and 14.5° at the eastern slope. The slopes on the eastern flank have dominant SE orientation. The central segment has a bell-shaped form, with the highest steepness comparing to the northern and southern segments. The eastern flank has a steepness of 49.5°. A local depression at a distance of 50 km off from the axis (90°E) continues parallel to the NER, with the shape of the narrow minor trench. The western slope has a steepness of 57.6°, decreasing to 15.6°. The southern segment has a dome-like shape form. Compared to the northern and central segments, it has a less pronounced ridge crest, with a steepness of 24.9° on the west. The eastern flank has a steepness of 36.8° until 70 km, gradually becoming steeper at 44.23°. A local minor trench structure can be seen on its eastern flank (100 km off the axis). This corresponds to the very narrow long topographic depressions stretching parallel to this segment of the NER at 90.5°E. The study contributes to regional geographic studies of Indian Ocean geomorphology and cartographic presentation of GMT functionality for marine research and oceanographic studies.

Provenance and Weathering of Clays Delivered to the Bay of Bengal During the Middle Miocene: Linkages to Tectonics and Monsoonal Climate

AbstractTectonics and regional monsoon strength control weathering and erosion regimes of the watersheds feeding into the Bay of Bengal, which are important contributors to global climate evolution via carbon cycle feedbacks. The detailed mechanisms controlling the input of terrigenous clay to the Bay of Bengal on tectonic to orbital timescales are, however, not yet well understood. We produced orbital‐scale resolution geochemical records for International Ocean Discovery Program Site U1443 (southern Bay of Bengal) across five key climatic intervals of the middle to late Miocene (15.8–9.5 Ma). Our new radiogenic Sr, Nd, and Pb isotope time series of clays transported to the Ninetyeast Ridge suggest that the individual contributions from different erosional sources overall remained remarkably consistent during the Miocene despite major tectonic reorganizations in the Himalayas. On orbital timescales, however, high‐resolution data from the five investigated intervals show marked fluctuations of all three isotope systems. Interestingly, the variability was much higher within the Miocene Climatic Optimum (around 16–15 Ma) and across the major global cooling (~13.9–13.8 Ma) until ~13.5 Ma, than during younger time intervals. This change is attributed to a major restriction on the supply of High Himalayan erosion products due to migration of the peak precipitation area toward the frontal domains of the Himalayas and the Indo‐Burman Ranges. The transient excursions of the radiogenic isotope signals on orbital timescales most likely reflect climatically driven shifts in monsoon strength.

Геоморфология хребта Девяностого градуса

This paper explores the geomorphological features of the Ninety East Ridge (NER), Indian Ocean. NER presents especially long and linear topographic structure formed as a result of complex regional geophysical and geologic development. The research is based on high precision bathymetric, geological and gravity data. The submarine geomorphology of NER was digitized as three cross-sectional profiles. The profiles were selected in northern, central and southern segments. The depths were visualized in graphs, compared and statistically analyzed by histograms. The study contributes to the geophysical studies of the Indian Ocean.

Распределение потоков метана на границе вода–атмосфера в различных районах Мирового океана

For the first time, methane fluxes at the water-atmosphere interface were calculated for the water area of Pacific, Indian, and Atlantic oceans (for the area about 30,000 miles) on the basis of the expeditionary measurements of methane concentrations in the surface layer of water and subsurface layer of the atmosphere along the entire course of the vessel. Methane fluxes at the water-atmosphere interface were calculated for the water areas of the Pacific, Indian and Atlantic oceans. In the result of the studies carried out in various regions of the World Ocean, an uneven spatial distribution of methane fluxes from strong absorption to emission of anomalous intensity was observed. The article presents the results of a detailed study for the deepwater area of the Indian Ocean open waters in the northern part of the Ninetyeast Ridge. Both supersaturation and undersaturation of seawater respectively to its concentrations in the atmosphere have been revealed on the basis of the direct measurements of methane concentrations in the ocean surface water layer. The distribution of dissolved methane in the water column of the Indian Ocean has been considered.

Sedimentary provenance of the Plio-Pleistocene Nicobar Fan: Complex sourcing revealed through Raman spectroscopy heavy mineral analysis

The Nicobar Fan lies within the north-eastern Indian Ocean between the Ninety-East Ridge and Sunda Arc. The fan forms part of the Bengal–Nicobar Fan System and is among the oldest and largest submarine fans on Earth. Previous U–Pb zircon studies of the Nicobar and Bengal fans indicate the Himalaya as the dominate sediment source, making these fans a major Cenozoic sink for uplifted Himalayan sediment. However, the northwards moving Indian Plate, coupled with mid-Pleistocene collision of the Ninety-East Ridge with the Sunda Arc, has shutdown many sediment pathways linking the Himalaya and Nicobar Fan. Here we use big data Raman spectroscopy heavy mineral analysis along with U–Pb zircon data to better define sediment source regions for the Nicobar Fan during the Plio-Pleistocene following the shutdown of sediment delivery. The detrital zircon spectra for the Plio-Pleistocene Nicobar Fan from this study are consistent with previous work indicating that the original sources of these zircons can be found within both the Greater and Tethyan Himalaya, the Gangdese Arc, and the Indo-Myanmar Ranges. However, the heavy mineral data indicate that a large proportion of sediment has been derived from a more complex array of sources. This is coupled with an abundance of low- and moderate-stability minerals (e.g., amphibole, apatite, clinopyroxene), which are unlikely to have been transported large distances. Suggesting that proximal sources have delivered the majority of lower-stability heavy minerals into the Plio-Pleistocene Nicobar Fan. We show that from the Pleistocene onwards direct sediment delivery into the Nicobar Fan from the Himalaya was largely shutdown, with sediment instead shedding off the uplifting Indo-Myanmar Ranges, the Andaman–Nicobar Accretionary Ridge, and the westwards propagating Ayeyarwady River. This study shows that extensive uplift along the northern Sunda Arc is recorded in the Nicobar Fan alongside the previously reported Himalayan record.

Composition of Volcanic Tuffs, Neotectonics, and Structure of the Upper Sedimentary Cover of the Osborn Plateau (Indian Ocean)

The Osborn Plateau is a large intraplate elevation in the eastern Indian Ocean, which has been poorly studied by geological and geophysical methods. On cruise SO258/1 aboard the R/V Sonne, new data were collected by Parasound seismic processing, multibeam survey, and, for the first time, dredging. Faults in the sedimentary cover, which extend to the seafloor surface, indicate high neotectonic activity in the area of the Osborn Plateau. It may have continued up to the present, as well as in the adjacent segment of the Ninetyeast Ridge, where strong earthquakes are recorded. Two reflectors A and C in the upper part of the sedimentary cover mark global regressive changes in the World Ocean level at the Pliocene–Pleistocene and Miocene–Pliocene and boundaries. Reflector B in sediments at the Lower–Upper Pliocene boundary is associated with a change in the regional hydrodynamic regime at the time in the eastern Indian Ocean. Reflector B at the Lower–Upper Pliocene boundary is associated with a change in the local hydrodynamic regime in the region of the plateau and was caused by uncompensated sedimentation. As a result of dredging, strongly altered vitroclastic tuffs were obtained, consisting of palagonized ash particles and lapilli. Analysis of geochemical data on the composition of palagonite made it possible to reconstruct the main geochemical features of the primary composition of glass in tuffs, in particular, high enrichment in incompatible elements (Nb, Zr, Ti, La, etc.). The results of studying the dredged rocks suggest that tuffs dredged on the Osborn Plateau were formed as a result of explosive volcanic eruptions of alkaline basalts under subaerial or relatively shallow conditions and represent the latest eruption products in the region.

Bacterial and archaeal communities in deep sea waters near the Ninetyeast Ridge in Indian Ocean

Depth-dependent distribution patterns of bacterial and archaeal communities in deep sea water column around the Ninetyeast Ridge in the Indian Ocean were investigated using 16S rRNA gene profiling. Sampling was conducted at the northern Ninetyeast Ridge (1°59.89′N–9°59.70′S, 87°58.90′E–88°00.03′E) from September to November 2016 where samples were collected from the bathyal (1 000 m) to bathypelagic depths (>4 000 m) in four different stations. A total of 1 565 405 clean data falling into 6 712 bacterial OTUs and 1 452 727 clean data falling into 806 archaeal OTUs based on 97% similarity level were analyzed. Most of the bacterial 16S rRNA gene sequences were affiliated with Gammaproteobacteria, followed by Alphaproteobacteria and Bacteroidia. The archaeal 16S rRNA gene sequences mostly affiliated to Nitrososphaeria (Thaumarchaeota) dominated with relative abundances ranging from 52.68% to 97.2%, followed by Thermoplasmata (Euryarchaeota). Vertical partitioning of bacterial and archaeal communities among different water layers was observed. Canonical correspondence analysis (CCA) and Spearman’s correlations revealed that depth (P=0.003), dissolved oxygen (P=0.019), and nitrite (P=0.033) were the main environmental factors affecting bacterial community structure at genus level in the Ninetyeast Ridge. On the other hand, the first two CCA axes accounted for 74.4% of the explained total variance, it seems that the archaeal communities at genus level were heavily influenced by the environmental variables including depth, dissolved oxygen (DO), nitrite, salinity, phosphate, ammonia, nitrate, and silicate, but none of them exhibited any significant correlation on the structuring (P>0.1).

A complete structural model and kinematic history for distributed deformation in the Wharton Basin

The equatorial eastern Indian Ocean hosts a diffuse plate boundary, where widespread deformation accommodates the relative motion between the Indian, Australian and Capricorn sub-plates. We integrate IODP Expedition 362 borehole data, which for the first time provides an accurate, ground-truthed chronostratigraphy of the sedimentary sequence east of the Ninety East Ridge (NER), with 2D seismic reflection profiles and multibeam bathymetry to assess the styles of faulting between the NER and the Sunda subduction zone, timing of activity and comparison with physical and rheological properties. We identify four distinct fault sets east of the NER in the northern Wharton Basin. N-S (350-010°) orientated faults, associated with the N-S fracture zones formed at the now extinct Wharton spreading centre, are still active and have been continuously active since at least 10 Ma. NNE- and WNW-trending fault fabrics develop between the fracture zones. The orientations and likely sense of displacement on these three sets of faults defines a Riedel shear system responding to ∼NNE-SSW left-lateral strike-slip activity at depth, demonstrated by the recent 2012 great intraplate earthquakes. We also find evidence of ∼NE-SW reverse faults, similar in style to E-W reverse faults observed west of the NER, where reverse faulting is more dominant. We show that the activity of this strike-slip system increased ca. 7-9 Ma, contemporaneous with reverse faulting and intraplate deformation west of the NER.

Two-stage eastward diachronous model of India-Eurasia collision: Constraints from the intraplate tectonic records in Northeast Indian Ocean

The onset of timing and the model of the India-Eurasia collision are strongly debated based on continental works, without systematic marine tectonic constraints. Two aseismic ridges, the Laccadives-Maldives-Chagos Ridge (LMCR) formed after the Deccan volcanism in western India and the Ninetyeast Ridge (NER) formed after the emplacement of the Rajmahal Traps in eastern India are prominent features in the Northeast Indian Ocean. The onset of a major and steady increase in magma production rates along the aseismic ridge associated with the significant slowdown of the northward moving Indian Plate is a likely indicator of the onset of the India-Eurasia collision. Using gravity-derived crustal thickness, we calculated the magma production rates along the LMCR and the NER, respectively. The steady increasing magma production rate along the LMCR and a southwestward jump of the Central Indian Ridge constrained the “soft” (India-island arc) and “hard” (India-Eurasia) collisions between western India and Eurasia to 50–52 Ma and ~41 Ma, respectively. The steady increasing magma production rate along the NER and the formation of the Mammerickx Microplate constrained the soft collision between eastern India and Eurasia to 47–49 Ma, and the extinction of the Wharton Ridge constrained the hard collision between eastern India and Eurasia to 38 Ma. Both the soft and hard collisions between western India and Eurasia are ~3 Myr earlier than the soft and hard collisions between eastern India and Eurasia, respectively. With systematic marine tectonic constraints, a two-stage eastward diachronous model of the India-Eurasia collision was proposed.

New data on geology of the Osborn Knoll, Indian ocean

The Osborne Plateau is a large intraplate elevation in the eastern part of the Indian Ocean, which has been poorly studied by geological and geophysical methods. In cruise SO258/1 on RV Sonne, were collected new data with Parasound seismic profiling and multi-beam echo sounder survey. Fractures in the sedimentary cover, which extend to the bottom surface, indicate on high neotectonic activity in the area of the Osborne Plateau. It can continue up to the present, as well as in the adjacent segment of the Ninetyeast Ridge, where strong earthquakes are recorded. Two reflectors in the upper part of the sedimentary cover mark global regressive changes in the World Ocean level at the boundary of the Miocene / Pliocene and Pliocene / Pleistocene. The reflector in the sediments at the boundary of the Lower / Upper Pliocene is associated with a change in the regional hydrodynamic regime at the time in the eastern Indian Ocean. The rocks dragged on the Osborn Knoll are identical to volcanic rocks of the Ninetyeast Ridge, confirming their assumed genetic similarity, but they are more identical to basalts of the Kerguelen plateau. Extremely modified vitroclastic tuffs appear to have been formed as a result of explosive volcanic eruptions of alkaline basalts or foidites in subaeral or relatively shallow water conditions and represent the most recent eruption in the region.

A New Model of the Ninety East Ridge Formation, Indian Ocean

The comprehensive analysis of geological, geophysical, and geochemical data makes it possible to obtain the most complete picture of the geological structure of the central part of the Ninety East Ridge (NER), the Osborn Plateau, and the adjacent part of the Central Basin. This region has been established to be a complex tectonic structure. In respect of the revealed structural features of the major near-NS faults of Indrani, Indira, and Lanka, they are not transform faults. Based on the generalization of all available data on the northern and southern parts of the NER, supplemented by the studies of the NER’s central part, it is found out that the NER was constructed on the continental crust of an ancient continent, likely Lemuria. According to a new formation model, the NER is a relict fragment of this continent, preserved in the form of a block or an escarp, as an extended horst structure. This paper involves the primary data obtained by different Russian scientific and production organizations in the course of expeditions in the Central Basin during the 1980–1990s, as well as other data, including those obtained from foreign sources.

New Data on the Geology of Osborn Plateau, Indian Ocean

The Osborn Plateau is a large intraplate rise in the eastern part of the Indian Ocean, which has been poorly studied by the geological and geophysical methods. In cruise SO258/1 on the R/V Sonne, new data were collected using Parasound seismic profiling and a multibeam echo-sounder survey. Faults in the sedimentary cover, which extend to the bottom surface, indicate high neotectonic activity in the Osborn Plateau area. It may continue up to the present, as well as in the adjacent segment of the Ninetyeast Ridge, where strong earthquakes have been recorded. Two reflectors in the upper part of the sedimentary cover mark the global lowering of the World Ocean level at the Miocene/Pliocene and Pliocene/Pleistocene boundaries. The reflector in the sediments at the Lower/Upper Pliocene boundary is associated with a change in the regional hydrodynamic regime that occurred at that time in the eastern Indian Ocean. The rocks dredged on Osborn Plateau are identical to some volcanic rocks of the Ninetyeast Ridge, confirming their assumed genetic link, but they are more similar to the basalts of the Kerguelen Plateau. Extremely altered vitroclastic tuffs appear to have been formed as a result of explosive volcanic eruptions of alkali basalts or foidites under subaeral or relatively shallow water conditions and represent the most recent eruptions in the region.

Seismicity and seismotectonics in and around Sri Lanka: a synoptic review

Seismicity and seismotectonics in and around Sri Lanka are reviewed, considering the country in both the local and regional contexts. Seismic activity reported within the country indicates a close correlation with the local geotectonic setup that comprises certain active features such as lineaments and faults, bedrock fractures, thrust/shear zones and tectonic movements of individual mini-plates. Seismicity in the regional context is discussed, evaluating identified active zones in the northern Indian Ocean surrounding the country. A large area of diffuse seismicity located south-southeast of Sri Lanka enclosing the northern part of the Ninetyeast Ridge, could be a dominant source of strong shallow intraplate earthquakes, and could render direct threats of striking large-magnitude events in close proximity to the country. The oceanic region west of Sri Lanka and continental region of southern peninsular India are not as active, more like dormant areas with sparse seismicity. However, seismogenic potential of these regions may not be completely ruled out, given evidence of previous isolated strong events.

Geological studies in the Eastern Indian Ocean: cruise SO258/1 of the R/V Sonne (Germany) with the participation of Russian researchers

New geological-geophysical data were obtained during Cruise SO258 leg 1 of the R/V SONNE carried out in the eastern part of the Indian Ocean in 2017. This expedition was part of the research project INGON, which is a collaboration between the Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research (AWI) and the GEOMAR Helmholtz Centre for Ocean Research Kiel. Multibeam echo-sounder bathymetry, seismic reflection profiling and rock sampling were done on 3 areas on 85° E Ridge and close to the Ninetyeast Ridge. The paper describes the first results.

The geotectonic features of the Southeast Indian Ridge and its current research progress

The Southeast Indian Ridge (SEIR) is the fastest spreading ridge in the Indian Ocean, with an average half spreading rate of 25−50 mm/a. The crust produced by the SEIR accounts for more than half of the total Indian oceanic crust. It represents a pivotal element in shaping the current tectonic settings of the Indian Ocean. Compared with the Southwest Indian Ridge (SWIR) and Northwest Indian Ridge (NWIR), the temporal and spatial evolution of the SEIR has been more complex, as reflected by the present-day tectonic and geomorphological diversity of its segmentation pattern. In this study, we integrate the topographic and geomorphological features, the gravimetric and geomagnetic signatures, and the MORB geochemical characteristics from the SEIR and the adjacent areas, in order to define the segmentation of the ridge, to trace its evolution through time, to characterize the heterogeneity degree of the mantle source beneath the ridge and to explore potential genetic links between regional intraplate volcanisms and the spreading ridge. The study shows that the axial bathymetry of SEIR undulates along the ridge, with the shallowest depth at the Amsterdam-St. Paul Plateau (ASP) and the deepest ones at the Australian-Antarctic Discordance (AAD). Using bathymetric, gravity and geomagnetic data, thirty-one first-order ridge segments can be distinguished. The boundaries of each segment coincide with transform faults. The eastern Indian Ocean expanded owing to three main successive phases of oceanic accretion each characterized by a distinct orientation: northwestward phase before 84 Ma, a north-south one between 84 and 38 Ma and a northeastward phase after 38 Ma. The mantle source of the SEIR is heterogeneous, especially in ASP and AAD regions. While the ASP results from a hotspot-ridge interaction, the AAD represents the isotopic boundary between Indian and the Pacific Ocean mantle domains. In the eastern Indian Ocean, there are many off-axis oceanic plateaux, such as the Kerguelen Plateau, Broken Ridge, Ninetyeast Ridge, Naturaliste Plateau and Wallaby-Cuvier Plateau. The buildings of these off-axis oceanic plateaux are either related to plume activity, and/or to presence of remnants of continental crust material embedded in the shallow mantle. The SEIR integrated with the NWIR at ~38 Ma, while the SWIR wedged into the NWIR-SEIR sometime after or before 38 Ma at the Rodrigues Triple Junction. The heavy isotopic compositions of SEIR are similar to NWIR and the northeast end of SWIR. Compared with Pacific-Antarctic Ridge, the Indian ridge systems show obvious Dupal anomaly, indicating the larger-scale mantle heterogeneities. This study can help better understand the evolution of the eastern Indian Ocean, the ridge systems and tectonic patterns of the entire Indian Ocean. It can also enhance our knowledge on Gondwana continent rifting and the evolution of Indian Ocean.