Olive Jean-Arthur L.

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Jean-Arthur L.

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Now showing 1 - 7 of 7
  • Article
    Quantifying diffuse and discrete venting at the Tour Eiffel vent site, Lucky Strike hydrothermal field
    (American Geophysical Union, 2012-04-19) Mittelstaedt, Eric ; Escartin, Javier E. ; Gracias, Nuno ; Olive, Jean-Arthur L. ; Barreyre, Thibaut ; Davaille, Anne ; Cannat, Mathilde ; Garcia, Rafael
    The relative heat carried by diffuse versus discrete venting of hydrothermal fluids at mid-ocean ridges is poorly constrained and likely varies among vent sites. Estimates of the proportion of heat carried by diffuse flow range from 0% to 100% of the total axial heat flux. Here, we present an approach that integrates imagery, video, and temperature measurements to accurately estimate this partitioning at a single vent site, Tour Eiffel in the Lucky Strike hydrothermal field along the Mid-Atlantic Ridge. Fluid temperatures, photographic mosaics of the vent site, and video sequences of fluid flow were acquired during the Bathyluck'09 cruise (Fall, 2009) and the Momarsat'10 cruise (Summer, 2010) to the Lucky Strike hydrothermal field by the ROV Victor6000 aboard the French research vessel the “Pourquoi Pas”? (IFREMER, France). We use two optical methods to calculate the velocities of imaged hydrothermal fluids: (1) for diffuse venting, Diffuse Flow Velocimetry tracks the displacement of refractive index anomalies through time, and (2) for discrete jets, Particle Image Velocimetry tracks eddies by cross-correlation of pixel intensities between subsequent images. To circumvent video blurring associated with rapid velocities at vent orifices, exit velocities at discrete vents are calculated from the best fit of the observed velocity field to a model of a steady state turbulent plume where we vary the model vent radius and fluid exit velocity. Our results yield vertical velocities of diffuse effluent between 0.9 cm s−1 and 11.1 cm s−1 for fluid temperatures between 3°C and 33.5°C above that of ambient seawater, and exit velocities of discrete jets between 22 cm s−1 and 119 cm s−1 for fluid temperatures between 200°C and 301°C above ambient seawater. Using the calculated fluid velocities, temperature measurements, and photo mosaics of the actively venting areas, we calculate a heat flux due to diffuse venting from thin fractures of 3.15 ± 2.22 MW, discrete venting of 1.07 ± 0.66 MW, and, by incorporating previous estimates of diffuse heat flux density from Tour Eiffel, diffuse flux from the main sulfide mound of ∼15.6 MW. We estimate that the total integrated heat flux from the Tour Eiffel site is 19.82 ± 2.88 MW and that the ratio of diffuse to discrete heat flux is ∼18. We discuss the implication of these results for the characterization of different vent sites within Lucky Strike and in the context of a compilation of all available measurements of the ratio of diffuse to discrete heat flux.
  • Article
    Rapid rotation of normal faults due to flexural stresses : an explanation for the global distribution of normal fault dips
    (John Wiley & Sons, 2014-04-24) Olive, Jean-Arthur L. ; Behn, Mark D.
    We present a mechanical model to explain why most seismically active normal faults have dips much lower (30–60°) than expected from Anderson-Byerlee theory (60–65°). Our model builds on classic finite extension theory but incorporates rotation of the active fault plane as a response to the buildup of bending stresses with increasing extension. We postulate that fault plane rotation acts to minimize the amount of extensional work required to sustain slip on the fault. In an elastic layer, this assumption results in rapid rotation of the active fault plane from ~60° down to 30–45° before fault heave has reached ~50% of the faulted layer thickness. Commensurate but overall slower rotation occurs in faulted layers of finite strength. Fault rotation rates scale as the inverse of the faulted layer thickness, which is in quantitative agreement with 2-D geodynamic simulations that include an elastoplastic description of the lithosphere. We show that fault rotation promotes longer-lived fault extension compared to continued slip on a high-angle normal fault and discuss the implications of such a mechanism for fault evolution in continental rift systems and oceanic spreading centers.
  • Preprint
    Sensitivity of seafloor bathymetry to climate-driven fluctuations in mid-ocean ridge magma supply
    ( 2015-09) Olive, Jean-Arthur L. ; Behn, Mark D. ; Ito, Garrett T. ; Buck, W. Roger ; Escartin, Javier E. ; Howell, Samuel M.
    Recent studies have proposed that the bathymetric fabric of the seafloor formed at mid-ocean ridges records rapid (23–100 kyr) fluctuations in ridge magma supply caused by sea level changes that modulate melt production in the underlying mantle. Using quantitative models of faulting and magma emplacement, we demonstrate that, in fact, seafloor-shaping processes act as a low-pass filter on variations in magma supply, strongly damping fluctuations shorter than ~100 kyr. We show that the systematic decrease in dominant seafloor wavelengths with increasing spreading rate is best explained by a model of fault growth and abandonment under a steady magma input. This provides a robust framework for deciphering the footprint of mantle melting in the fabric of abyssal hills, the most common topographic feature on Earth.
  • Article
    Hydrothermally-induced melt lens cooling and segmentation along the axis of fast- and intermediate-spreading centers
    (American Geophysical Union, 2011-07-28) Fontaine, Fabrice J. ; Olive, Jean-Arthur L. ; Cannat, Mathilde ; Escartin, Javier E. ; Perol, Thibaut
    The heat output and thermal regime of fast and intermediate spreading centers are strongly controlled by boundary layer processes between the hydrothermal system and the underlying crustal magma chamber (AMC), which remain to be fully understood. Here, we model the interactions between a shallow two-dimensional cellular hydrothermal system at temperatures <700°C, and a deeper AMC at temperatures up to 1200°C. We show that hydrothermal cooling can freeze the AMC in years to decades, unless melt injections occur on commensurate timescales. Moreover, the differential cooling between upflow and downflow zones can segment the AMC into mush and melt regions that alternate on sub-kilometric length scales. These predictions are consistent with along-axis variations in AMC roof depth observed in ophiolites and oceanic settings. In this respect, fine-scale geophysical investigations of the structure of AMCs may help constrain hydrothermal recharge locations associated with active hydrothermal sites.
  • Article
    Mechanism for normal faulting in the subducting plate at the Mariana Trench
    (John Wiley & Sons, 2015-06-02) Zhou, Zhiyuan ; Lin, Jian ; Behn, Mark D. ; Olive, Jean-Arthur L.
    We investigate the mechanisms of normal fault initiation and evolution in the subducting Pacific Plate near the Mariana Trench, through bathymetry analysis and geodynamic modeling. We model the subducting plate as an elastoplastic slab subjected to tectonic forcing at the trench, including vertical load, bending moment, and horizontal tensional force. In our simulations, normal faults initiate within the outer rise region and reach maximum throw toward the trench. This result holds over a wide range of tectonic forcing and is consistent with observations of the Challenger Deep region, where multibeam bathymetry data indicate faults initiate near the outer rise at 70–110 km from the trench and reach maximum throw at 10–35 km from the trench. However, models require a horizontal tensional force with magnitude comparable to axial vertical load to jointly explain the observed seafloor bathymetry, location of maximum normal fault throw, and prevalence of normal faults dipping toward the trench.
  • Article
    Modes of extensional faulting controlled by surface processes
    (John Wiley & Sons, 2014-10-09) Olive, Jean-Arthur L. ; Behn, Mark D. ; Malatesta, Luca C.
    We investigate the feedbacks between surface processes and tectonics in an extensional setting by coupling a 2-D geodynamical model with a landscape evolution law. Focusing on the evolution of a single normal fault, we show that surface processes significantly enhance the amount of horizontal extension a fault can accommodate before being abandoned in favor of a new fault. In simulations with very slow erosion rates, a 15 km thick brittle layer extends via a succession of crosscutting short-lived faults (heave < 5 km). By contrast, when erosion rates are comparable to the regional extension velocity, deformation is accommodated on long-lived faults (heave >10 km). Using simple scaling arguments, we quantify the effect of surface mass removal on the force balance acting on a growing normal fault. This leads us to propose that the major range-bounding normal faults observed in many continental rifts owe their large offsets to erosional and depositional processes.
  • Thesis
    Mechanical and geological controls on the long-term evolution of normal faults
    (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2015-02) Olive, Jean-Arthur L.
    This thesis investigates the long-term evolution of rift-bounding normal faults in extensional environments. My main objective is to develop a theoretical framework that explains the controls on maximum fault offset in terms of a few key mechanical and geological controls. In Chapter 2, I propose that flexural rotation of the active fault plane enables faults to evolve along a path of minimal energy, thereby enhancing their life span. In Chapter 3, I show that surface processes can increase the life span of continental faults by reducing the energy cost of topography build-up. In Chapter 4, I focus on lithospheric bending induced by fault growth. I demonstrate that numerical models that treat the lithosphere as a visco-plastic solid properly predict fault evolution only when the rate-dependent viscous flexural wavelength of the lithosphere is accommodated within the numerical domain. In Chapter 5, I investigate the growth of normal faults in relation to a depth-variable rate of magma emplacement. These models predict both faulting styles and crustal architecture at slow mid-ocean ridges. Finally, in Chapter 6 I use a newly developed 3-D numerical model to establish a relation between along-axis fault continuity and spatial heterogeneities in lithospheric thickness at a ridge segment.