5. Site 11371

Shipboard Scientific Party2

BACKGROUND AND OBJECTIVES

Site 1137 lies on Elan Bank (Houtz et al., 1977), the Kerguelen Plateau's large western salient, which is flanked on three sides by presumed Cretaceous oceanic crust of the Enderby Basin (Fig. F1). Before we drilled Site 1137, no basement samples had been retrieved from Elan Bank; hence, the age and geochemistry of the igneous crust, and its relationship to the contiguous central and southern Kerguelen Plateau, were unknown. We located Site 1137 on Australian Geological Survey Organisation Rig Seismic multichannel seismic (MCS) line RS179/601 (Fig. F2). The site lies at a depth of 1005 m on Elan Bank's eastern crest. We chose this location as representative of the entire Elan Bank on the basis of its relatively simple structural setting and thin sedimentary section (Fig. F3). Interpreted igneous basement contains some internal reflections. The top of the basaltic basement has an apparent dip of 1.5° to the east (assuming a sediment velocity of 1.9 km/s), and a strong intrabasement reflection beneath has an apparent dip of 4.8° to the east (assuming a basement velocity of 3.8 km/s). Overlying basement, we observed two seismic sequences, an extremely thin (~25 m, or 0.02 s two-way traveltime [TWT]) lower sequence characterized by a velocity of 2.3 km/s, and an thicker (~200 m, or 0.21 s TWT) upper sequence with a velocity of 1.9 km/s (Fig. F3).

Summary of Objectives

The main objectives at this site were to

  1. Characterize the petrography and compositions of the lavas;
  2. Determine the age of the lavas, testing the hypothesis that the uppermost igneous basement of Elan Bank is ~85 Ma, the age yielded by basalts from Site 747 on the central Kerguelen Plateau (Pringle et al., 1994; Storey et al., 1996);
  3. Determine the physical characteristics of the lava flows;
  4. Identify the environment of eruption (subaerial or submarine);
  5. Obtain minimum estimates for the age of basement from overlying sediment;
  6. Estimate the duration of possible subaerial and shallow marine environments from the sedimentary and igneous record;
  7. Determine the facies of the seismic stratigraphic sequences;
  8. Define the ages of seismic sequence boundaries; and
  9. Determine the paleoceanographic history of this high latitude site.

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2Shipboard Scientific Party addresses can be found under "Shipboard Scientific Party" in the preliminary pages of the volume.

Ms 183IR-105

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