Depending on time constraints and depth of penetration, the logging program will be divided into two or three parts. At the beginning of the leg, the Triple-combo will be used for obtaining a temperature profile, assessing borehole conditions, and determining possible variations in alteration. The FMS will provide information regarding the ellipticity of the borehole as well as high-resolution images of stratigraphic boundaries and structural features. The second and third logging runs will include the triple-combo, FMS/sonic, magnetometer, and VSP deployments. Pending funding, the sonic probe (digital array sonic tool [SDT]) commonly used in the FMS/Sonic combination will be substituted with the Dipole Shear Sonic Imager (DSI). The DSI will produce a full set of waveforms (P-, S-, and Stoneley waves); the shear-wave velocity and amplitude measured at different azimuths in the borehole may indicate preferred mineral and/or fracture orientations as well as paleostress directions. During Leg 176, the verification of depth/seismic ties by means of a VSP and synthetic seismograms will be essential for identifying deep crustal reflectors. The location and abundance of Fe-Ti oxide intervals will be determined by using the magnetometer.
A core-log integration program will be essential for the reorientation of cored samples recovered
from Hole 735B. Correlation of digital core images obtained with a DMT Color Scanner and FMS
images potentially will provide the opportunity for the reorientation of structural and stratigraphic
features. The reorientation of the core from Hole 735B may prove to be essential for the
determination of the lateral extent of structural features as well as the association of local strikes
and dips with the regional tectonic environment. In addition, the FMS high-resolution images will
vastly improve the determination of the fracture and alteration zone distribution in the crust and
correlations between geophysical logs and discrete laboratory data will provide information
regarding compositional variations with depth.
Depending on hole conditions and depth of penetration the approximate time estimates for the logging program during Leg 176 will be as follows:
|No Hole Conditioning||Hole Conditioning|
|Time Estimate||121.8 hrs (5.1 days)||147.7 hours (6.2 days)|
To 176 Sampling Strategy
176 Table of Contents