Departed Suva, Fiji - May 7, 1996
Arrived Pago Pago, Am. Samoa - June 8, 1996
Dynamics of Extensional Convergent Margins the Origin of
Supra-Subduction Zone Ophiolites: Hypothesis Testing in the Tonga Forearc
Sherman Bloomer and Dawn Wright
Co-Chief Scientists Department of Geosciences, Oregon State University
Scientific Summary: The Tonga subduction zone, in the southwestern
Pacific, is the world's most active, extension-dominated convergent margin
system. We conducted a geological and geophysical investigation of selected
portions of the Tonga forearc to test a number of specific
hypotheses about the evolution of these intraoceanic margins. Dawn's
work tested the following hypothesis:
Tonga is the type extensional convergent margin and is undergoing
active tectonic erosion and its forearc is dominated by normal faulting
and movement of material into trench and hence down subduction zone.
The cruise provided essential site survey data for a proposed
Ocean Drilling Program leg.
The Field Program: We designed our shipboard
experiment around nine traverses of the outer Tonga forearc. Data collected
included Sea Beam 2000 swath bathymetry and side-scan sonar, selected single-channel seismic lines,
gravimeter and magnetometer measurements, and dredge sampling. Swath bathymetry was also
collected over three proposed ODP sites on the eastern edge of the
Tonga platform. (SEE FIGURE ABOVE).
