Cruise Plan

Ship Schedule
8/10: Loading
8/11: 0600 Depart from MARFAC, San Diego
8/12 - 8/19: In-Transit Multibeam Survey (California to Panama)
8/20: 48-hour geophysical survey in NE Panama Basin
8/23: Dock on west side of Panama Canal
*R/V Melville continues to Barbados*

Cruise Objective
The scientific objective is to clarify the present tectonics, resent (post-8 Ma) tectonic history, and origin of 85,000 km "North Nazca" oceanic microplate.  This will be done through a marine geophysical survey of the northeastern Panama Basin.  It will mainly use multibeam, magnetics and acoustic (CHIRP) profiling techniques.  It builds on earlier studies by Dr. Peter Lonsdale in the Panama Basin.

This is testing the following hypotheses:
1) An oceanic microplate intervenes between the Nazca and Carribean plates, with an estimated 50 km/ Myr east-west shear between these plates, partitioned equally between a) a left-lateral continental shear zone along the Panama margin and b) a left-lateral shear zone within the oceanic crust 150 km south of the margin
2) The second shear zone (with east-west motion) occupies the site of a rise crest that was spreading north-south until 7.5 Ma, and then reactivated after a 90 degree rotation of relative plate motion.
3) The oldest part of the microplate includes crust accreted to the Farallon plate prior to 23.5 ma, when the plate split to create Cocos and Nazca plates

This survey would have implications for:
1) The earthquake and volcanic hazard at the microplate margines, especially for the heavily populated Panamanian margin and Columbian subduction zone
2) The ability of microplates to change motion drastically in response to external events (i.e. such as the collision of Central and South America)
3) How new plate boundaries adopt zones of lithospheric weakenss caused by abandonment of other types of plate boundaries
4) The history and processes of a major plate-splitting event.