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A J Harding - One of the best experts on this subject based on the ideXlab platform.
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velocity structure from forward modeling of the eastern ridge transform intersection area of the clipperton Fracture Zone east pacific rise
Journal of Geophysical Research, 1997Co-Authors: Michael L Begnaud, James S Mcclain, Ginger A Barth, John A Orcutt, A J HardingAbstract:In the spring of 1994, we undertook an extensive geophysical study of the Clipperton Fracture Zone (FZ) on the fast spreading East Pacific Rise. The Clipperton Area Seismic Study to Investigate Compensation experiment (CLASSIC) included surveys to examine the deep structures associated with the Fracture Zone and adjacent northern ridge segment. In this paper, we report the results from five seismic profiles acquired over the eastern ridge-transform intersection (RTI), including profiles over the RTI high, the northern ridge segment, and the eastern transform region. The travel time data for crustal phases, Moho reflections, and mantle phases were modeled using two-dimensional ray tracing. Seismic profiles reveal that the crust is similar in thickness north and south of the Clipperton FZ, despite differences in axial topography that have previously been interpreted in terms of differences in magma supply. When compared to older crust, the northern ridge axis is characterized by lower seismic velocities and higher attenuation. In our model, a low-velocity Zone exists beneath the ridge axis, probably associated with a Zone of partial melt and/or very high temperatures. Within the transform Zone, we find that the southeastern trough is underlain by nearly normal crustal structure. The crust is slightly thinner than the adjacent aseismic extension but not enough to compensate for the depths of the trough. Toward the RTI, the trough is replaced by an intersection high which appears underlain by a thickened crust, and a thicker upper crustal section. Both characteristics indicate that the intersection high is a volcanic feature produced by excess volcanism at the intersection. The volcanism acts to “fill in” the transform trough, creating the thicker crust that extends under the eastern aseismic extension of the transform. Our results show that the northern ridge segment, often identified as magma-starved, displays the crustal thickness and apparent signal attenuation characteristic of a plentiful, but perhaps episodic, magma supply.
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deepening of the axial magma chamber on the southern east pacific rise toward the garrett Fracture Zone
Journal of Geophysical Research, 1997Co-Authors: Maya Tolstoy, A J Harding, John A OrcuttAbstract:A wide-aperture profile along the ridge axis from 14°29′S to 13°39′S, 120 km to 30 km south of the Garrett Fracture Zone, is analyzed to constrain the thickness of layer 2a and the depth to the axial magma chamber reflector. Five areas along the 90 km line are examined in detail, with several consecutive gathers being analyzed for each area to establish the degree of consistency within each area. A genetic algorithm code is used to find a best fit model from a comparison of the data and WKBJ synthetic seismograms. One hundred starting models are generated using a predefined set of velocity nodes, with a fixed window of allowable depth variations between nodes. An evolutionary process favors the better fitting models in each generation, and a satisfactory misfit is usually obtained within 40 generations. Within individual areas the models were in good agreement with the depth of a given velocity node, generally varying by not more than 20 m, the depth discretization interval for the models. A consistent deepening trend of the axial magma chamber (AMC) is observed across the five areas as the Garrett Fracture Zone is approached. The depth varies from 0.99 km at area 1, which is approximately 100 km south of the Garrett, to 1.23 km at area 5, which is approximately 40 km south of the Garrett. The depth to the axial magma chamber is highly sensitive to any ship wander off axis since layer 2a thickens rapidly off axis with age. For the areas examined here, layer 2a is observed to be relatively constant in thickness along the axis, although it is about 40 m thicker over area 5, where the axial magma chamber is deepest. This variation is within the scatter of previously detailed layer 2a measurements at 13°N on the East Pacific Rise, where an effectively constant thickness is observed. This implies that layer 2a thickening is not a significant factor along this profile and that the AMC deepening is real rather than apparent. Theoretical modeling suggests that the depth to the lid of the axial magma chamber is related to the rate of heat supply at a given location. Thus the gradual consistent deepening of the axial magma chamber can be taken as an indication of a slightly reduced magma supply toward the Garrett Fracture Zone, which marks a major interruption of hundreds of kilometers of continuous ridge axis. The deepening may also be interpreted as a downward limb from a central injection point; however, there is no indication of a similar downward trend in the other (southern) direction. Furthermore, there is no accompanying systematic variation in axial depth or axial volume, both of which are proposed to be indicators of central injection and along-axis flow.
Luisa Ottolini - One of the best experts on this subject based on the ideXlab platform.
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melt migration in the upper mantle along the romanche Fracture Zone equatorial atlantic
Lithos, 2002Co-Authors: P Tartarotti, Sara Susini, Paolo Nimis, Luisa OttoliniAbstract:Textural and petrological data of mantle peridotites sampled in the central and western parts of the Romanche Fracture Zone (Equatorial Atlantic) during the oceanographic expedition PRIMAR-96 (Russian R/V Gelendzhik) are presented. The studied rocks are mantle peridotites carrying patches, pockets and veins/dikes of magmatic origin, interpreted to be the product of various extents of magma impregnation on mantle partial melting residues. Estimated partial melting degrees based on clinopyroxene Ti/Zr ratios are in the ranges 5–13% and 18–20%. In highly impregnated samples, refertilization of residual peridotite minerals precludes a correct evaluation of the degree of melting. Magmatic products occur as pl±cpx±opx±ol±sp aggregates with various textural features. Interstitial pl-rich patches and gabbroic pockets are interpreted to derive from magma migration through the upper mantle by diffusive porous flow in the ductile part of the lithosphere and melt–rock reactions. Metasomatism of the host peridotites is testified by Ti and Cr increase in spinel and Ti, Sr, Zr, Y and LREE increase in clinopyroxene. Veins and dikes reflect channeled magma migration focused by brittle failures at shallower lithospheric levels. Minor or no chemical changes occurred in peridotites impregnated along Fractures. The compositions of magmatic minerals in impregnated peridotites are consistent with derivation from variably fractionated melts of probably MORB type. Barometric estimates suggest that the Romanche peridotites were impregnated at minimum depths of ca. 9–12 km. Thermometric estimates for the peridotite hosts are in the range 750–1050 °C. The spread in temperature values is partly ascribed to localized heating by migrating melts of relatively cold peridotites. Our data and the occurrence of both fertile and depleted peridotites in a neighbouring area along the western Romanche FZ are in accord with the hypothesis of small-scale (<100 km) mantle heterogeneity along this Fracture Zone.
Alain Rabaute - One of the best experts on this subject based on the ideXlab platform.
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Neotectonics of the Owen Fracture Zone (NW Indian Ocean): structural evolution of an oceanic strike-slip plate boundary
Geochemistry Geophysics Geosystems, 2011Co-Authors: Mathieu Rodriguez, Marc Fournier, Philippe Huchon, Nicolas Chamot-rooke, Julien Bourget, M. Sorbier, Sébastien Zaragosi, Alain RabauteAbstract:The Owen Fracture Zone is a 800 km-long fault system that accommodates the dextral strike-slip motion between India and Arabia plates. Because of slow pelagic sedimentation rates that preserve the seafloor expression of the fault since the Early Pliocene, the fault is clearly observed on bathymetric data. It is made up of a series of fault segments separated by releasing and restraining bends, including a major pull-apart basin at latitude 20°N. Some distal turbiditic channels from the Indus deep-sea fan overlap the fault system and are disturbed by its activity, thus providing landmarks to date successive stages of fault activity and structural evolution of the Owen Fracture Zone from Pliocene to Present. We determine the durability of relay structures and the timing of their evolution along the principal displacement Zone, from their inception to their extinction. We observe subsidence migration in the 20°N basin, and alternate activation of fault splays in the vicinity of the Qalhat seamount. The present-day Owen Fracture Zone is the latest stage of structural evolution of the 20-Myr-old strike-slip fault system buried under Indus turbiditic deposits whose activity started at the eastern foot of the Owen Ridge when the Gulf of Aden opened. The evolution of the Owen Fracture Zone since 3-6 Myr reflects a steady state plate motion between Arabia and India, such as inferred by kinematics for the last 20 Myr period. The structural evolution of the Owen Fracture Zone since 20 Myr- including fault segments propagation and migration, pull-apart basin opening and extinction - seems to be characterized by a progressive reorganisation of the fault system, and does not require any major kinematics change.
Enrico Bonatti - One of the best experts on this subject based on the ideXlab platform.
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dolomite formation in pelagic limestone and diatomite romanche Fracture Zone equatorial atlantic
Journal of Sedimentary Research, 2004Co-Authors: Daniel Bernoulli, Luca Gasperini, Enrico Bonatti, Peter StilleAbstract:Abstract Two dredge samples from the Romanche Fracture Zone in the equatorial Atlantic document dolomite formation in pelagic sediments in a deep-sea environment. The samples come from a highly deformed sedimentary succession, the Romanche Sedimentary Sequence, constituting the transverse ridge accompanying the transverse valley of the Fracture Zone to the north. These sediments were folded and uplifted to or near the seafloor prior to the growth of an early Miocene carbonate platform which unconformably overlies them. Dolomitized pelagic limestones of Early Cretaceous age preserve solution molds and unaltered tests of radiolaria (opal-A) and ghosts of calcareous nannoplankton in a dolomicritic groundmass. Carbon isotope data indicate a normal marine source of carbon, and oxygen isotope compositions are consistent with precipitation from cool, marine pore waters at or near the sediment-water interface. The 87/Sr86Sr ratio suggests dolomitization at around 25 Ma, presumably when the sediments were exhumed to or near to the seafloor. In contrast, a dolomite-cemented diatomite of presumably late Eocene age shows no relics of a carbonate precursor. Dolomite crystals grew freely in the originally highly porous rock, cementing it into a tight fabric. The absence of compaction suggests that cementation by dolomite took place soon after deposition and before significant burial of the sediment. Carbon and oxygen isotope compositions of this dolomite suggest that its formation also occurred from cool, marine waters. The 87Sr/86Sr ratio shows the value of seawater around 35 Ma. Under the assumption that dolomite cementation was by seawater, it occurred shortly after deposition at or near the seafloor.
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regional scale melt rock interaction in lherzolitic mantle in the romanche Fracture Zone atlantic ocean
Earth and Planetary Science Letters, 1997Co-Authors: Monique Seyler, Enrico BonattiAbstract:Abstract Mantle-derived peridotites recovered from the Romanche Fracture Zone fall in two compositional groups. Group 1 nearly undepleted lherzolites, indicating a very low degree of melting, are prevalent in the western part of the transform. Group 2 peridotites, with higher Mg/Fe ratio but enriched in Ti and incompatible trace elements and generally containing plagioclase, are common in the eastern part of the transform, where undepleted samples are also present. Group 1 undepleted lherzolites are consistent with a relatively low upper mantle temperature below the Romanche region. Group 2 peridotites can be explained by reaction between melt and lherzolite, at a temperature close to the peridotite solidus, in a still upwelling upper mantle.
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imaging crustal uplift emersion and subsidence at the vema Fracture Zone
Eos Transactions American Geophysical Union, 1994Co-Authors: Enrico Bonatti, Luca Gasperini, Marco Ligi, Gabriela Carrara, E VeraAbstract:Vertical movements of lithospheric slivers due to slow-slip, long-offset transform tectonics may cause major topographic anomalies such as the rough topography of the equatorial Atlantic, where a number of long offset transforms are clustered. These vertical motions even may have caused the intermittent emersion and sinking of islands throughout the evolution of the equatorial Atlantic. We studied a transform-related topographic anomaly observed at the Vema Fracture Zone in the Atlantic at 11°N in the form of a transverse ridge (Figure 1). We used multichannel seismic reflection surveys to image the morphology, thickness, and internal structure of the carbonate platform capping the crest of the transverse ridge. We found that the Vema transverse ridge is actually an uplifted sliver of oceanic crust and—about 3 m.y.a.—its summit was above sea level.
Mathieu Rodriguez - One of the best experts on this subject based on the ideXlab platform.
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Structural reorganization of the India-Arabia strike-slip plate boundary (Owen Fracture Zone; NW Indian Ocean) 2.4 million years ago
2019Co-Authors: Mathieu Rodriguez, Marc Fournier, Philippe Huchon, Nicolas Chamot-rooke, Matthias DelescluseAbstract:The Owen Fracture Zone (OFZ) is the present-day, 800-km-long dextral India Arabia plate boundary, with conspicuous pull-apart basins at stepover areas and at its terminations. We summarize geological evidence documenting the age of formation of the OFZ, based on detailed analysis of geophysical and drilling data in the vicinity of the main pull-apart basins. Although India-Arabia motion started in the Late Cretaceous, we show that the present-day OFZ is a young structure formed at 2.4 Ma. This last structural reorganization of the India-Arabia plate boundary is unrelated to any well-documented kinematic change, leaving questions over its driver.
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structure of the beautemps beaupre pull apart basin at the southern termination of the owen Fracture Zone nw indian ocean from seismic reflection data
EGUGA, 2018Co-Authors: Mathieu Rodriguez, Marc Fournier, Philippe Huchon, Nicolas Chamotrooke, Matthias DelescluseAbstract:The Arabia, Somalia and India tectonic plates meet at the Aden-Owen-Carlsberg triple junction in the NW Indian Ocean. There, strike-slip motion along the Owen Fracture Zone (the current India-Arabia plate boundary) turns into diffuse extension instead of directly connecting to the Sheba spreading center. The main structure of this area of diffuse extension is the 120-km-long, 50-km-wide Beautemps-Beaupre pull-apart basin at the southern end of the Owen Fracture Zone. Here we present a new set of multibeam data, echosounder and seismic profiles crossing the Beautemps-Beaupre Basin acquired in March 2012. Ties of the seismic dataset with ODP Sites located at the top of the Owen Ridge document the stratigraphy of the study area. We investigate how the Beautemps-Beaupre Basin formed in the complex framework of the evolution of the Aden-Owen-Carlsberg triple junction. We show that the BeautempsBeaupre Basin opened 2.4 Myrs ago, coeval with a major structural reorganization of the India-Arabia plate boundary. This 2.4 Myrs-old geological episode is unrelated to any identified kinematic change. This suggests that the opening of the Beautemps-Beaupre Basin reflects a series of transient adjustments of the configuration of the Aden-Owen-Carlsberg triple junction since the last major kinematic change identified in the Indian Ocean between 6 and 8 Ma
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Neotectonics of the Owen Fracture Zone (NW Indian Ocean): structural evolution of an oceanic strike-slip plate boundary
Geochemistry Geophysics Geosystems, 2011Co-Authors: Mathieu Rodriguez, Marc Fournier, Philippe Huchon, Nicolas Chamot-rooke, Julien Bourget, M. Sorbier, Sébastien Zaragosi, Alain RabauteAbstract:The Owen Fracture Zone is a 800 km-long fault system that accommodates the dextral strike-slip motion between India and Arabia plates. Because of slow pelagic sedimentation rates that preserve the seafloor expression of the fault since the Early Pliocene, the fault is clearly observed on bathymetric data. It is made up of a series of fault segments separated by releasing and restraining bends, including a major pull-apart basin at latitude 20°N. Some distal turbiditic channels from the Indus deep-sea fan overlap the fault system and are disturbed by its activity, thus providing landmarks to date successive stages of fault activity and structural evolution of the Owen Fracture Zone from Pliocene to Present. We determine the durability of relay structures and the timing of their evolution along the principal displacement Zone, from their inception to their extinction. We observe subsidence migration in the 20°N basin, and alternate activation of fault splays in the vicinity of the Qalhat seamount. The present-day Owen Fracture Zone is the latest stage of structural evolution of the 20-Myr-old strike-slip fault system buried under Indus turbiditic deposits whose activity started at the eastern foot of the Owen Ridge when the Gulf of Aden opened. The evolution of the Owen Fracture Zone since 3-6 Myr reflects a steady state plate motion between Arabia and India, such as inferred by kinematics for the last 20 Myr period. The structural evolution of the Owen Fracture Zone since 20 Myr- including fault segments propagation and migration, pull-apart basin opening and extinction - seems to be characterized by a progressive reorganisation of the fault system, and does not require any major kinematics change.
