STRUCTURE OF THE HYDROTHERMAL ROOT ZONE OF THE SHEETED DIKES IN FAST-SPREAD OCEANIC CRUST: A CORE-LOG INTEGRATION STUDY OF ODP HOLE 1256D, EASTERN EQUATORIAL PACIFIC

Authors

  • Marie Violay* Géosciences Montpellier, Université Montpellier 2, - CNRS, Montpellier, France. now at INGV - Istituto Nazionale di Geofisica e Vulcanologia, Roma, Italy.
  • Philippe A. Pezard Géosciences Montpellier, Université Montpellier 2, - CNRS, Montpellier, France
  • Benoit Ildefonse Géosciences Montpellier, Université Montpellier 2, - CNRS, Montpellier, France
  • Bernard Célérier Géosciences Montpellier, Université Montpellier 2, - CNRS, Montpellier, France
  • Agathe Deleau Géosciences Montpellier, Université Montpellier 2, - CNRS, Montpellier, France

Keywords:

ODP, IODP, Hole 1256D, mid-oceanic ridge, upper oceanic crust, sheeted dike complex, electrical borehole images, hydrothermal system, fractures, dikes, veins

Abstract

Ocean Drilling Program Hole 1256D reached for the first time the transition zone between the sheeted dike complex and the uppermost gabbros. The recovered crustal section offers a unique opportunity to study the deepest part of the hydrothermal system in present-day oceanic crust. We present a structural analysis of electrical borehole wall images. We identified, and measured the orientations of four categories of structures: major faults, minor fractures, possibly hydrothermal veins, and dikes. All structures tend to strike parallel to the paleo-ridge axis. Three major fault zones (meter thick) and dikes are steeply dipping (~ 75° on average) outward the ridge. Centimeter-thick moderately conductive planar features are interpreted as hydrothermal veins, are organized in arrays of consistent spacing, thickness, and orientation, and are dipping about 15-20° toward the ridge. This structural pattern is interpreted as an on-axis paleohydrothermal circulation system, with vertical, dike-parallel fractures, and sub-horizontal high-temperature hydrothermal veins at the base of the sheeted dike, which was subsequently rotated ~ 15° westward around a ridge-parallel, sub-horizontal axis. This rotation can be caused by upper-crustal block rotation along a listric normal fault, and/or subsidence at the ridge axis.

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Published

2012-06-30

How to Cite

Violay*, M., Pezard, P. A., Ildefonse, B., Célérier, B., & Deleau, A. (2012). STRUCTURE OF THE HYDROTHERMAL ROOT ZONE OF THE SHEETED DIKES IN FAST-SPREAD OCEANIC CRUST: A CORE-LOG INTEGRATION STUDY OF ODP HOLE 1256D, EASTERN EQUATORIAL PACIFIC. Ofioliti, 37(1), 1-11. Retrieved from https://www.ofioliti.it/index.php/ofioliti/article/view/402

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