9. Sites 1141 and 11421

Shipboard Scientific Party2

BACKGROUND AND OBJECTIVES

Sites 1141 and 1142 are situated near the crest of Broken Ridge ~350 km east of Deep Sea Drilling Project (DSDP) Site 255 and Ocean Drilling Program (ODP) Sites 752, 753, 754, and 755 (Fig. F1). Flanked to the south by Eocene and earlier oceanic crust of the Australia-Antarctic Basin and to the north by Cretaceous oceanic crust of the Wharton Basin, Broken Ridge appears to have formed during Late Cretaceous time as a result of Kerguelen hot spot magmatism (Duncan, 1991; Duncan and Storey, 1992). Subsequently, Broken Ridge and the Kerguelen Plateau began to separate along the nascent Southeast Indian Ridge at ~40 Ma. Igneous basement of Broken Ridge has not been sampled previously by drilling; dredge samples from three locations along the feature's southern faulted boundary yield dates of ~62, ~83, and 88-89 Ma (Duncan, 1991). Because of the scatter in ages of the dredged rocks and the absence of in situ basement samples from Broken Ridge, knowledge of Broken Ridge's age and composition remains extremely limited. We located Sites 1141 and 1142 on JOIDES Resolution single-channel seismic line JR183-101 (Fig. F2). Sites 1141 and 1142 lie at depths of 1197 and 1201 m, respectively, ~3-4 km north of the crest of Broken Ridge. We chose this location primarily on the basis of its thin sedimentary section (Fig. F3). The top of acoustic basement is flat lying at Site 1141 but has an apparent dip of 2.5° to the north-northeast at Site 1142. A sediment sequence ~100 m thick overlies igneous basement at both sites.

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 eastern Broken Ridge is ~85 Ma, similar to that of the central Kerguelen Plateau (CKP) (Duncan, 1991; Duncan and Storey, 1992; 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;
  9. Determine the paleoceanographic history of this temperate latitude site.

1Examples of how to reference the whole or part of this volume can be found under "Citations" in the preliminary pages of the volume.
2Shipboard Scientific Party addresses can be found under "Shipboard Scientific Party" in the preliminary pages of the volume.

Ms 183IR-109

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