Malaysia Airlines flight MH370 search data reveal geomorphology and seafloor processes in the remote southeast Indian Ocean

© The Author(s), 2017. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Marine Geology 395 (2018): 301-319, doi:10.1016/j.margeo.2017.10.014.A high-resolution multibeam echosounder (MBES) dataset covering over 279,000 km2 was acquired in the southeastern Indian Ocean to assist the search for Malaysia Airlines Flight 370 (MH370) that disappeared on 8 March 2014. The data provided an essential geospatial framework for the search and is the first large-scale coverage of MBES data in this region. Here we report on geomorphic analyses of the new MBES data, including a comparison with the Global Seafloor Geomorphic Features Map (GSFM) that is based on coarser resolution satellite altimetry data, and the insights the new data provide into geological processes that have formed and are currently shaping this remote deepsea area. Our comparison between the new MBES bathymetric model and the latest global topographic/bathymetric model (SRTM15_plus) reveals that 62% of the satellite-derived data points for the study area are comparable with MBES measurements within the estimated vertical uncertainty of the SRTM15_plus model (± 100 m). However, > 38% of the SRTM15_plus depth estimates disagree with the MBES data by > 100 m, in places by up to 1900 m. The new MBES data show that abyssal plains and basins in the study area are significantly more rugged than their representation in the GSFM, with a 20% increase in the extent of hills and mountains. The new model also reveals four times more seamounts than presented in the GSFM, suggesting more of these features than previously estimated for the broader region. This is important considering the ecological significance of high-relief structures on the seabed, such as hosting high levels of biodiversity. Analyses of the new data also enabled sea knolls, fans, valleys, canyons, troughs, and holes to be identified, doubling the number of discrete features mapped. Importantly, mapping the study area using MBES data improves our understanding of the geological evolution of the region and reveals a range of modern sedimentary processes. For example, a large series of ridges extending over approximately 20% of the mapped area, in places capped by sea knolls, highlight the preserved seafloor spreading fabric and provide valuable insights into Southeast Indian Ridge seafloor spreading processes, especially volcanism. Rifting is also recorded along the Broken Ridge – Diamantina Escarpment, with rift blocks and well-bedded sedimentary bedrock outcrops discernible down to 2400 m water depth. Modern ocean floor sedimentary processes are documented by sediment mass transport features, especially along the northern margin of Broken Ridge, and in pockmarks (the finest-scale features mapped), which are numerous south of Diamantina Trench and appear to record gas and/or fluid discharge from underlying marine sediments. The new MBES data highlight the complexity of the search area and serve to demonstrate how little we know about the vast areas of the ocean that have not been mapped with MBES. The availability of high-resolution and accurate maps of the ocean floor can clearly provide new insights into the Earth's geological evolution, modern ocean floor processes, and the location of sites that are likely to have relatively high biodiversity

Shallow seafloor gas emissions near Heard and McDonald Islands on the Kerguelen Plateau, Southern Indian Ocean

© The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Spain, E. A., Johnson, S. C., Hutton, B., Whittaker, J. M., Lucieer, V., Watson, S. J., Fox, J. M., Lupton, J., Arculus, R., Bradney, A., & Coffin, M. F. Shallow seafloor gas emissions near Heard and McDonald Islands on the Kerguelen Plateau, Southern Indian Ocean. Earth and Space Science, 7(3), (2020): e2019EA000695, doi:10.1029/2019EA000695.Bubble emission mechanisms from submerged large igneous provinces remains enigmatic. The Kerguelen Plateau, a large igneous province in the southern Indian Ocean, has a long sustained history of active volcanism and glacial/interglacial cycles of sedimentation, both of which may cause seafloor bubble production. We present the results of hydroacoustic flare observations around the underexplored volcanically active Heard Island and McDonald Islands on the Central Kerguelen Plateau. Flares were observed with a split‐beam echosounder and characterized using multifrequency decibel differencing. Deep‐tow camera footage, water properties, water column δ3He, subbottom profile, and sediment δ13C and δ34S data were analyzed to consider flare mechanisms. Excess δ3He near McDonald Islands seeps, indicating mantle‐derived input, suggests proximal hydrothermal activity; McDonald Islands flares may thus indicate CO2, methane, and other minor gas bubbles associated with shallow diffuse hydrothermal venting. The Heard Island seep environment, with subbottom acoustic blanking in thick sediment, muted 3He signal, and δ13C and δ34S fractionation factors, suggest that Heard Island seeps may either be methane gas (possibly both shallow biogenic methane and deeper‐sourced thermogenic methane related to geothermal heat from onshore volcanism) or a combination of methane and CO2, such as seen in sediment‐hosted geothermal systems. These data provide the first evidence of submarine gas escape on the Central Kerguelen Plateau and expand our understanding of seafloor processes and carbon cycling in the data‐poor southern Indian Ocean. Extensive sedimentation of the Kerguelen Plateau and additional zones of submarine volcanic activity mean additional seeps or vents may lie outside the small survey area proximal to the islands.We thank the Australian Marine National Facility (MNF) for its support in the form of sea time on RV Investigator , support personnel, scientific equipment, and data management. We also thank the captain, crew, and fellow scientists of RV Investigator voyage IN2016_V01. We also thank specifically the following: T. Martin, F. Cooke, S. L. Sow, N. Bax, J. Ford, and F. Althaus, CSIRO (Commonwealth Scientific and Industrial Research Organisation); Echoview Software Pty. Ltd. (Hobart, Australia); C. Dietz and C. Cook, Central Science Laboratory, University of Tasmania; C. Wilkinson and T. Baumberger, National Oceanic and Atmospheric Administration; R. Carey, University of Tasmania; T. Holmes, Institute for Marine and Antarctic Studies, University of Tasmania; N. Polmear; and A. Post, Geoscience Australia. The overall science of the project is supported by Australian Antarctic Science Program (AASP) grant 4338. E.S.' PhD research is supported by the Australian Research Council's Special Research Initiative Antarctic Gateway Partnership (Project ID SR140300001) and by an Australian Government Research Training Program Scholarship. S.C.J. is supported by iCRAG under SFI, European Regional Development Fund, and industry partners, as well as ANZIC‐IODP. J.M.W. is supported by ARC grant DE140100376 and DP180102280. This is PMEL publication number 4910. All IN2016_V01 data and samples acquired on IN2016_V01 are made publicly available in accordance with MNF policy

Large igneous provinces: progenitors of some ophiolites?

Mesozoic and Cenozoic continental flood-basalt provinces, oceanic plateaus, oceanic basin flood basalts, and volcanic passive margins share geologic and geophysical characteristics that indicate an origin distinct from igneous rocks formed at mid-ocean ridges. Such characteristics of mafic large igneous provinces (LIPs) include (1) broad areal extent (>10^5 km^2) of basalts of similar age erupted over ~10^6 yr; (2) lower-crustal bodies characterized by Vp = 7.0–7.6 km·s^–1; (3) some component of intermediate and silicic volcanic rocks; (4) trace element, rare earth element, and isotopic signatures in flood basalts that are distinct from mid-oceanic-ridge basalts (MORBs); (5) thick (10s–100s of meters) individual basalt flows; and (6) long (?750 km) individual basalt flows. In addition, basaltic and gabbroic crustal sections of oceanic LIPs are two to five times thicker than those of “normal” oceanic crust, implying larger magma chambers than at typical mid-ocean ridges and, in the case of some continental flood basalts, resulting in layered intrusive complexes containing chromite. Lastly, some flood-basalt provinces are associated with kimberlites and other ultramafic volcanism. LIPs have formed, on average, every 10 m.y. since 250 Ma. However, despite the lower energy required to obduct relatively high standing oceanic LIPs in contrast to normal oceanic crust, only five obducted oceanic LIPs have been well documented in the Mesozoic and Cenozoic continental and island-arc geologic record. More ophiolite fragments may be obducted sections of volcanic passive margins and oceanic plateaus than we now suppose

Crustal structure of the Ontong Java Plateau: modeling of new gravity and existing seismic data

Seismic refraction and gravity-based crustal thickness estimates of the Ontong Java oceanic plateau, the Earth's largest igneous province, differ by as much as 18 km. In an attempt to reconcile this difference we have evaluated available seismic velocity data and developed a layered crustal model which includes (1) a linear increase in velocity with depth in the Cenozoic sediments and the uppermost extrusive basement and (2) a reinterpretation of deep crustal and Moho arrivals in some deep refraction profiles. Previously, Moho had commonly been interpreted from later arrivals and in some cases constrained by precritical arrivals. However, if first arrivals at distal offsets are interpreted as Moho refractions, the maximum depth to Moho is reduced by about 10 km. Two-dimensional gravity modeling along two transects from well-determined oceanic crust in the Nauru Basin across the central On-tong Java Plateau to the Lyra Basin, based on the reinterpreted crustal model, is regionally consistent with satellite altimetry derived and shipboard gravity fields yielding a 8.0 km/s Moho velocity at a depth of ?32 km under the central plateau. The crust features a thick oceanic, three-layer igneous crust comprising an extrusive upper crust, a 6.1 km/s middle crust and a ?15 km thick 7.1 km/s lower crust. The total Ontong Java Plateau crustal volume is calculated at 44.4 × 106 km3 and 56.7 × 106 km3 for off- and on-ridge emplacement settings, respectively. On the basis of velocities and densities we interpret the lower crust on the plateau to consist of ponded and fractionated primary picritic melts, which due to deformation and/or fluid invasion may have recrystallized to granulite facies mineral assemblages. The melts were emplaced during lithospheric breakthrough of a mantle plume in an oceanic, near-ridge plate tectonic setting

Present-day Plate Boundary Digital Data Compilation

The PLATES Project compiled digital data representing the present-day plate boundaries. This report includes the digital data in three formats: GMT, KMZ and ArcGIS shapefiles.PLATES Project, Institute for Geophysics, The University of Texas at AustinInstitute for Geophysic