Geodynamics of the Amirante Ridge and Trench Complex, Western Indian Ocean
TL;DR: The formation and evolution of the arcuate Amirante Ridge and Trench Complex (ARTC) is a significant geomorphic-structural feature in the Western Indian Ocean (WIO).
Abstract: The formation and evolution of the ∼600 km long arcuate Amirante Ridge and Trench Complex (ARTC) is a significant geomorphic–structural feature in the Western Indian Ocean (WIO). The WIO contains evidence of at least two major magmatic episodes followed by continental rifting within the span of a little more than 20 million years. This involved the splitting of Madagascar from India at around 85 Ma and then separation between India and the Seychelles at 64–63 Ma as a possible consequence of two powerful volcanic eruptions from the Marion and Reunion hot spots, respectively. Formation and evolution of the ARTC represents this tumultuous period in the Indian Ocean, approximately between 85 and 60 Ma (Late Cretaceous–Early Tertiary). We integrated geophysical, palaeomagnetical, and petrological data to examine three existing models that attempt to explain the formation of ARTC. In contrast, our study hints at several stages of extension and compression responsible for its formation. Our integrated data also ...
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01 Jan 2015
TL;DR: In this article, a plausible model for the early evolution of plate-tectonic evolution is proposed using constraints of several recently mapped regional scale tectonic features, which is better constrained than the preceding period of its early evolution.
Abstract: The available plate-tectonic evolution models suggest that the deep ocean basins adjoining the western continental margin of India have evolved largely due to break-up and dispersal of India, Seychelles and Madagascar continental blocks since Late Cretaceous. Mainly owing to the availability of large number of well identified magnetic anomaly picks, the evolution of the region from chron C28ny (~62.5 Ma) and younger times is better constrained than the preceding period of its early evolution. Using constraints of several recently mapped regional scale tectonic features, a plausible model for that early evolution is proposed in this paper. Around 88.0 Ma the involved continental blocks were in their immediate pre-drift configuration where a wide continental rift zone existed between India and Madagascar. Seafloor spreading in the Mascarene Basin commenced shortly before 83.0 Ma. A ternary rift system off Saurashtra peninsula of western India, formed shortly before 68.5 Ma, reached seafloor spreading stage in the Laxmi and Gop basins around 67.6 and 64.7 Ma respectively. Around 62.5 Ma the ancestor of the Carlsberg Ridge spreading center developed between the Seychelles Plateau and the Laxmi Ridge while spreading in the northern Mascarene Basin ceased and spreading in the Laxmi and Gop basins continued at very slow rate. Between 60.9 and 57.9 Ma the spreading in the southern Mascarene Basin also ceased and the spreading center jumped north between the Laccadive Plateau and the northern boundary of the Mascarene Basin. The divergence regimes of the Gop, Laxmi and Laccadive basins ceased between 57.6 and 56.4 Ma, and the Laccadive Plateau and the Laxmi Ridge got welded to the Indian plate.
62 citations
01 Jan 2014
TL;DR: The nearly 7,500 km long coastline of India is remarkably varied and dynamic and displays diverse rock-based, sediment-based and coral-based landforms as mentioned in this paper, which is controlled largely by monsoons.
Abstract: The nearly 7,500 km long coastline of India is remarkably varied and dynamic and displays diverse rock-based, sediment-based and coral-based landforms. Coastal processes along the Indian coasts are controlled largely by monsoons. The Arabian Sea coast differs from the Bay of Bengal coast in several respects. The east coast is wider, with several large deltas, large lagoons, one of the world’s largest mangrove wetland (Sundarbans) and long stretches of sandy beaches backed by dunes or ridges. In comparison, the west coast is more indented with rocky headlands, intervening sandy bays and multiple estuaries. Cliffs and associated features are relatively more common. A large saline marshland and lagoon-barrier complexes (kayals) are some of the noteworthy features along the west coast.
24 citations
TL;DR: In this article, the authors present new estimates of crustal thickness and V P /V S from H-κ stacking of receiver functions from a year long deployment of seismic stations across the Seychelles covering the topographic plateau, the Amirante Ridge and the northern Mascarene Basin.
16 citations
Cites background from "Geodynamics of the Amirante Ridge a..."
...There has been much debate in the literature about the origin of the Amirantes, with mechanisms ranging from subduction (Miles, 1982; Masson, 1984; Mart, 1988; Damuth and Johnson, 1989; Mukhopadhyay et al., 2012): transpression along a strike-slip fault formed during the opening of the West Somali Basin prior to the separation of Madagascar– Seychelles–India (Plummer, 1996) to a bolide impact (Hartnady, 1986)....
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TL;DR: In this article, a ship-borne gravity-magnetic and satellite-derived free-air gravity (FAG) data was used to derive the crustal structure of Laxmi Ridge and adjacent areas.
Abstract: In this study, we undertake analysis of ship-borne gravity-magnetic and satellite-derived free-air gravity (FAG) data to derive the crustal structure of Laxmi Ridge and adjacent areas. 2D and 3D crustal modelling suggests that the high resolution FAG low associated with the ridge is due to underplating and that it is of continental nature. From Energy Spectral Analysis, five-depth horizons representing interface between different layers are demarcated that match those derived from 2D models. Magnetic sources from EMAG2 data, various filtered maps and absence of underplating in the EW section suggest that the EW and NW–SE segment of the Laxmi Ridge is divided by the Girnar fracture zone and probably associated with different stages of evolution. From the derived inclination parameters, we infer that the region to the north of Laxmi Ridge, between Laxmi and Gop Basins, is composed of volcanic/basaltic flows having Deccan affinity, which might have been emplaced in an already existing crust. The calculated inclination parameters derived from the best fit 2D model suggests that the rifting in the Gop Basin preceded the emplacement of the volcanics in the region between Laxmi and Gop Basins. The emplacement of volcanic/basaltic flows may be associated with the passage of India over the Reunion hotspot.
14 citations
TL;DR: In this paper, the authors provided a paleogeographic reconstruction of the NW India margin for the Late Cretaceous-Paleocene interval, compiling information from ophiolites surrounding the Arabian Sea and data collected at sea.
6 citations
Cites background from "Geodynamics of the Amirante Ridge a..."
...…the nature and origin of the fossil plate boundary preserved at the Amirante Ridge and Trench System remain unclear [Damuth and Johnson, 1989, Mukhopadhyay et al., 2013], as the structure ambiguously shares some morphological and structural characteristics of subduction zones [Johnson et…...
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...…System is still one of the most enigmatic features of the Indian Ocean, with various origins proposed so far, from an extinct plate boundary [Masson, 1984, Damuth and Johnson, 1989, Mart, 1988, Mukhopadhyay et al., 2013, Eagles and Hoang, 2014] to a remnant of a meteorite impact [Hartnady, 1986]....
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References
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TL;DR: A hypothesis is suggested which accounts for the extinctions and the iridium observations, and the chemical composition of the boundary clay, which is thought to come from the stratospheric dust, is markedly different from that of clay mixed with the Cretaceous and Tertiary limestones, which are chemically similar to each other.
Abstract: Direct physical evidence is presented for an unusual event at exactly the time of extinctions in the planktonic realm. Deep-sea limestones exposed in Italy, Denmark, and New Zealand indicate iridium increases of about 30, 160, and 20 times, respectively, above the background level at precisely the time of the Cretaceous-Tertiary extinctions, 65 million years ago. Reasons are given that this iridium is of extraterrestrial origin, but did not come from a nearby supernova. A hypothesis is set forth which accounts for the extinctions and the iridium observations. One prediction of this hypothesis is verified, that the chemical composition of the boundary clay, which is thought to come from the stratospheric dust, is markedly different from that of clay mixed with the chemically similar Cretaceous and Tertiary limestones.
3,357 citations
"Geodynamics of the Amirante Ridge a..." refers background in this paper
...Extensive chaotic slump structures on the East African continental margin indicate proximity to mega-earthquake and/or giant tsunamis probably triggered by the bolide impact (Alvarez et al. 1980; Chatterjee et al. 2003)....
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TL;DR: In this article, a combination of high-density data from the dense mapping phases of Geosat and ERS 1 along with lower-density but higher-accuracy profiles from their repeat orbit phases is used to construct gravity anomalies from the two vertical deflection grids.
Abstract: Closely spaced satellite altimeter profiles collected during the Geosat Geodetic Mission (-6 km) and the ERS 1 Geodetic Phase (8 km) are easily converted to grids of vertical gravity gradient and gravity anomaly. The long-wavelength radial orbit error is suppressed below the noise level of the altimeter by taking the along-track derivative of each profile. Ascending and descending slope profiles are then interpolated onto separate uniform grids. These four grids are combined to form comparable grids of east and north vertical deflection using an iteration scheme that interpolates data gaps with minimum curvature. The vertical gravity gradient is calculated directly from the derivatives of the vertical deflection grids, while Fourier analysis is required to construct gravity anomalies from the two vertical deflection grids. These techniques are applied to a combination of high-density data from the dense mapping phases of Geosat and ERS 1 along with lower-density but higher-accuracy profiles from their repeat orbit phases. A comparison with shipboard gravity data shows the accuracy of the satellite- derived gravity anomaly is about 4-7 mGal for random ship tracks. The accuracy improves to 3 mGal when the ship track follows a Geosat Exact Repeat Mission track line. These data provide the first view of the ocean floor structures in many remote areas of the Earth. Some applications include inertial navigation, prediction of seafloor depth, planning shipboard surveys, plate tectonics, isostasy of volcanoes and spreading ridges, and petroleum exploration.
1,695 citations
TL;DR: A detailed study of ship and aeroplane tracks across the Indian Ocean was carried out in this paper, and it was shown that Africa is now moving northward at 2 cm/y relative to Antarctica in the South West Indian Ocean.
Abstract: Summary
All available ship and aeroplane tracks across the Indian Ocean were searched for identifiable magnetic anomalies and transform faults, and hence the age and direction of motion at the time of formation of about two-thirds of the floor of the ocean established. The magnetic lineations show that India moved away from Antarctica at about 18 cm/y for 20 My in the Early Tertiary. This rapid motion ceased in the Eocene and was followed by a period in which little or no spreading took place west of the Ninety East Ridge. Australia separated from Antarctica during this period. The present spreading episode began about 36 My ago. This detailed study has permitted instantaneous poles of rotation to be obtained, and has established that Africa is now moving northward at 2cm/y relative to Antarctica in the South West Indian Ocean. The evolution of the triple junction between the South East, South West and Central Indian Ridges is clearly reflected in the topography and magnetic lineations. The depth of parts of the ocean formed since the Late Cretaceous increases with age in the manner expected from the temperature structure of a cooling plate, and supports the evolution determined from the magnetic lineations in a most remarkable way. Heat flow observations are more scattered but also consistent with the same thermal model. The proposed evolution agrees with the distribution of known continental fragments and with the Late Cretaceous palaeomagnetic poles from surrounding continents and one obtained from the shape of the magnetic lineations south of India. It is, however, not yet clear how to reconstruct Gondwanaland from the Late Cretaceous reconstructions.
850 citations
"Geodynamics of the Amirante Ridge a..." refers background in this paper
...Phase I: India–Madagascar split (90–85 Ma) It is now known that at the beginning of the Cretaceous (M11 = 130 Ma), Gondwanaland began to break into four continental blocks: South America, Africa– Arabia, India–Madagascar, and Australia–Antarctica (Veevers et al. 1980)....
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...In the first episode, the break-up led to the establishment of seaways between South America and Africa in the west, and Antarctica, Australia, India, and New Zealand in the east....
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...Finally, in the Late Cretaceous (90–100 Ma), the break-up of Gondwanaland was completed when Australia and New Zealand separated from Antarctica, and India–Seychelles–Madagascar (Greater India) got separated from Africa and Antarctica (McKenzie and Sclater 1971; Veevers et al. 1980; Beutel et al. 2005)....
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...The ocean between India and Australia–Antarctica was about 800 km wide at this time, as was the South Atlantic Ocean (Lawver et al. 1992)....
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...…in the Late Cretaceous (90–100 Ma), the break-up of Gondwanaland was completed when Australia and New Zealand separated from Antarctica, and India–Seychelles–Madagascar (Greater India) got separated from Africa and Antarctica (McKenzie and Sclater 1971; Veevers et al. 1980; Beutel et al. 2005)....
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TL;DR: In this article, the authors used magnetic anomaly and fracture zone information to develop a self-consistent tectonic history of the Indian and South Atlantic oceans and made three reasonably well constrained (39, 53, and 65 Ma) and two speculative (80 and 115 Ma) reconstructions of the positions of the Gondwana continents.
Abstract: Magnetic anomaly and fracture zone information is used to develop a self-consistent tectonic history of the Indian and South Atlantic oceans. Working backward in time we have made three reasonably well constrained (39, 53, and 65 Ma) and two speculative (80 and 115 Ma) reconstructions of the positions of the Gondwana continents (Ma is m.y.B.P.). Our final fit, which is constrained by the recognition of Mesozoic anomalies off Antarctica and in the Mozambique Basin, places Dronning Maud Land against southern Mozambique and Madagascar in the northern position against Kenya. We suggest that after the initial rifting, Antarctica moved away from Africa in a southerly direction relative to present-day Africa. This started the formation of the Southwest Indian Ridge. Most of the present length and geometry of the ridge result from migration of triple junctions so do not reflect predrift continental outlines. India and Madagascar moved with Antarctica until India separated from first Antarctica then Madagascar, when it started moving north toward Asia. In our reconstructions we find no necessity for significant relative motion between the Antarctic Peninsula and South America from the early Cretaceous to the Oligocene. From the breakup of Gondwanaland to the present we identify seven significant events. These are (1) first break in the late Triassic/early Jurassic between East and West Gondwanaland with initial motion along long transform faults parallel to the present African east coast, (2) early Cretaceous separation of Africa and South America and possibly simultaneous separation between India and Australia-Antarctica, (3) cessation of motion between Africa and Madagascar, (4) break between India and Madagascar in the late Cretaceous, (5) Paleocene reorganization in the northwest Indian Ocean when the Seychelles left India, (6) Eocene separation between Australia and Antarctica with Australia joining the Indian plate, and (7) India's collision with Asia and subsequent commencement of spreading on the Central Indian Ridge, and later opening of Drake Passage.
653 citations
"Geodynamics of the Amirante Ridge a..." refers background or methods in this paper
...ically resembling a subduction system (Norton and Sclater 1979); (2) its 75 km-long wavelength of free-air gravity anomaly that may suggest some degree of subduction...
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...Some of the arguments are based on (1) the ARTC’s arcuate, concave morphology typically resembling a subduction system (Norton and Sclater 1979); (2) its 75 km-long wavelength of free-air gravity anomaly that may suggest some degree of subduction (Miles 1982; Masson 1984); (3) some amount of…...
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10 Feb 1995
TL;DR: The evidence suggests that the thick lava pile at Volcan de l'Androy in the south of the island marks the focal point of the Marion hot spot at ∼88 million years ago and that this mantle plume was instrumental in causing continental breakup.
Abstract: Widespread basalts and rhyolites were erupted in Madagascar during the Late Cretaceous. These are considered to be related to the Marion hot spot and the breakup of Madagascar and Greater India. Seventeen argon-40/argon-39 age determinations reveal that volcanic rocks and dikes from the 1500-kilometer-long rifted eastern margin of Madagascar were emplaced rapidly (mean age = 87.6 ± 0.6 million years ago) and that the entire duration of Cretaceous volcanism on the island was no more than 6 million years. The evidence suggests that the thick lava pile at Volcan de l'Androy in the south of the island marks the focal point of the Marion hot spot at 88 million years ago and that this mantle plume was instrumental in causing continental breakup.
617 citations
"Geodynamics of the Amirante Ridge a..." refers background in this paper
...…part of the Indian Ocean was beginning to form when the development ISSN 0020-6814 print/ISSN 1938-2839 online © 2012 Taylor & Francis http://dx.doi.org/10.1080/00206814.2010.504076 http://www.tandfonline.com of the Indian Ocean Ridge system commenced (Storey et al. 1995; Parson and Evans 2005)....
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...It is now accepted that Madagascar was separated from India during 89–85 Ma (Agarwal et al. 1992; Storey et al. 1995), probably triggered by the volcanic eruption through Marion hot spot....
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...of the Indian Ocean Ridge system commenced (Storey et al. 1995; Parson and Evans 2005)....
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