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Section 118-735B-36R-4

Section 118-735B-36R-4


Southwest Indian Ridge (Southeast from Madagascar)

Leg objectives

The aim of the Leg was to drill one or more holes in the Atlantis II Fracture Zone of the Southwest Indian Ridge. The primary goals were to

  • Drill a deep (500 +m) hole in exposed upper mantle peridotite on a median ridge of the fracture zone with the aid of a hard-rock guidebase; and
  • Conduct a major program of geophysical logging and other downhole measurements.
Secondary objectives were to
  • Drill a series of shallow basement holes across the floor of the fracture zone; and
  • Sample basement in active and fossil nodal basins.

Site objectives

The principal objective at Site 735 were

  • Sample a section of basement rock on the wall of the transform;
  • Conduct an array of downhole measurements; and
  • Test the engineering of the hard-rock guidebase and bare-rock drilling capabilities of JOIDES Resolution.

Geologic and tectonic setting

Site 735 is located on a shallow platform in about 700-m of water on the east rim of the Atlantis II Transform. This platform, about 9 km long an a north-south direction and 4 km wide, is one of a series of uplifted blocks that are connected by saddles to form a long, linear ridge parallel to the Atlantis II Transform. The extremely flat surface of this platform suggests that it is a wave-cut feature that has subsided since formation to its present position. The magnetic anomaly pattern on the east wall of the transform suggests a crustal age of about 12 Ma for this site.


Olivine-bearing and olivine gabbro. Fractures are lined with green amphibole and white feldspar (albite?).

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Modified on Friday, 26-Sep-2008 12:39:11 CDT.