Martinez Fernando

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Martinez
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Fernando
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  • Article
    Variable morphologic expression of volcanic, tectonic, and hydrothermal processes at six hydrothermal vent fields in the Lau back-arc basin
    (American Geophysical Union, 2008-07-26) Ferrini, Vicki L. ; Tivey, Margaret K. ; Carbotte, Suzanne M. ; Martinez, Fernando ; Roman, Christopher N.
    Ultrahigh-resolution bathymetric maps (25 cm grid) are used to quantify the physical dimensions of and spatial relationships between tectonic, volcanic, and hydrothermal features at six hydrothermal vent fields in the Lau back-arc basin. Supplemented with near-bottom photos, and nested within regional DSL-120A side-scan sonar data, these maps provide insight into the nature of hydrothermal systems along the Eastern Lau Spreading Center (ELSC) and Valu Fa Ridge (VFR). Along-axis transitions evident in localized volcanic morphology and tectonic characteristics include a change from broad low-relief volcanic domes (hundreds of meters wide, <10 m tall) that are dominated by pillow and lobate lava morphologies and are cut by faults and fissures to higher aspect ratio volcanic domes (tens of meters wide, tens of meters tall) dominated by aa-type lava morphologies, with finger-like flows, and few tectonic structures. These along-axis differences in localized seafloor morphology suggest differences in hydrothermal circulation pathways within the shallow crust and correlate with regional transitions in a variety of ridge properties, including the large-scale morphology of the ridge axis (shallow axial valley to axial high), seafloor lava compositions, and seismic properties of the upper crust. Differences in morphologic characteristics of individual flows and lava types were also quantified, providing an important first step toward the remote characterization of complex terrains associated with hydrothermal vent fields.
  • Other
    Formation and elimination of segmentation and transform faults on the Reykjanes Ridge
    (Woods Hole Oceanographic Institution, 2021-10) Martinez, Fernando ; Hey, Richard ; Höskuldsson, Ármann
    The objectives of R/V Neil Armstrong cruise AR35-04 (Fig. 1) were to survey the flanks of the Reykjanes Ridge and determine the timing, geometry and associated geophysical characteristics of the large-scale tectonic reorganizations that occurred there in the Paleogene and continue to the present (Fig. 2). The North Atlantic plate boundary between what is today the Bight Fracture Zone and Iceland, a distance of nearly 1000 km, was originally a linear orthogonally-spreading ridge that became abruptly fragmented in a stair-step fashion following a change in plate motion [Smallwood and White, 2002]. Its subsequent evolution involved the systematic and progressive removal of offsets from north to south to re-establish its original linear configuration [Hey et al., 2016; Martinez and Hey, 2017], even though this required the ridge to then spread obliquely, since the new spreading direction remained stable. These tectonic reorganizations took place within the region of influence of the Iceland “hotspot” which creates a strong gradient in mantle melting along the ridge, increasing crustal thicknesses by ~3-4 km and decreasing ridge axis depths by ~ 3000 m between the Bight Fracture Zone and Iceland [Louden et al., 2004]. A mantle gradient in melting properties (compositional and/or thermal) is presumably what results in the regional residual basement depth anomaly that extends throughout this region of the North Atlantic from the Greenland-Iceland-Faroe Ridge to south of the Bight Fracture Zone. This gradient in mantle properties with distance from the Iceland hotspot apparently had strong modulating effects on the tectonic reorganizations: the initial segment lengths and offsets appear in regional magnetic anomaly and satellite-derived gravity maps to be smaller toward Iceland and the segments evolved to re-establish the linear ridge configuration more quickly to the north [Hey et al., 2016]. As both kinematic and “hotspot” effects influence their development, the Reykjanes ridge flanks are key areas for investigating lithospheric and mantle controls on ridge segmentation, formation and elimination of transform faults and the mechanisms controlling their evolution.
  • Article
    Magmatic and tectonic extension at the Chile Ridge : evidence for mantle controls on ridge segmentation
    (John Wiley & Sons, 2016-06-24) Howell, Samuel M. ; Ito, Garrett T. ; Behn, Mark D. ; Martinez, Fernando ; Olive, Jean-Arthur ; Escartin, Javier E.
    We use data from an extensive multibeam bathymetry survey of the Chile Ridge to study tectonomagmatic processes at the ridge axis. Specifically, we investigate how abyssal hills evolve from axial faults, how variations in magmatic extension influence morphology and faulting along the spreading axis, and how these variations correlate with ridge segmentation. The bathymetry data are used to estimate the fraction of plate separation accommodated by normal faulting, and the remaining fraction of extension, M, is attributed primarily to magmatic accretion. Results show that M ranges from 0.85 to 0.96, systematically increasing from first-order and second-order ridge segment offsets toward segment centers as the depth of ridge axis shoals relative to the flanking highs of the axial valley. Fault spacing, however, does not correlate with ridge geometry, morphology, or M along the Chile Ridge, which suggests the observed increase in tectonic strain toward segment ends is achieved through increased slip on approximately equally spaced faults. Variations in M along the segments follow variations in petrologic indicators of mantle melt fraction, both showing a preferred length scale of 50 ± 20 km that persists even along much longer ridge segments. In comparison, mean M and axial relief fail to show significant correlations with distance offsetting the segments. These two findings suggest a form of magmatic segmentation that is partially decoupled from the geometry of the plate boundary. We hypothesize this magmatic segmentation arises from cells of buoyantly upwelling mantle that influence tectonic segmentation from the mantle, up.