New In-Situ Geophysical Measurements from Indian Ocean off Northwestern Australia
D. A. Castillo, R. Buffler, B. O'Neill, T. Bolmer
Site 765, drilled during Ocean Drilling Program (ODP) Leg 123 in the eastern
Indian Ocean off northwestern Australia, provided an opportunity to conduct
several in-situ geophysical experiments onboard the JOIDES Resolution. The site
penetrated a 900-m thick Cenozoic and Cretaceous-Upper Jurassic sedimentary
section before penetrating oceanic crust. An extensive suite of Schlumberger
logs and four downhole experiments were conducted. The first experiment, a
vertical seismic profile, recorded detailed velocity
information for a thick
sedimentary column and oceanic crust for the first time during an ODP leg. Data
analyses provide the capability to correlate the borehole information directly
with seismic reflection data at the site, extrapolate the drilling results
regionally, and image the oceanic crust below the borehole.
The second major experiment, another ODP first, was aimed at measuring the
in-situ stresses using hydraulic fracturing and the acoustic borehole televiewer
imaging system to document the nature of interplate stresses. The proximity of
this site to a trench-plate boundary provides an opportunity to examine several
proposed models regarding the origin of stresses in the oceanic lithosphere such
as slab-pull forces (Java Trench) and ridge-push forces (Southeast Indian Ridge).
The third test was a permeability/porosity experiment to study the migration
of
seawater and other pore fluids circulating through the crust. Permeability
experiments provided an opportunity to determine if pore-fluid circulation
exists in this ancient oceanic crust and, if so, to what degree it is dependent
upon th fracture system. The final in-situ measurement documented the thermal
structure within this section of the Indian plate.
AAPG Search and Discovery Article #91022©1989 AAPG Annual Convention, April 23-26, 1989, San Antonio, Texas.