FAMOUS PROJECT( FRENCH-AMERICAN MID-OCEANUNDERSEA STUDY).James R. Heirtzlerwas the U.S. leaderof Project FAMOUS.
Classic survey of part of the Mid-Atlantic Ridge in 1970s. Provide understanding in pattern of volcanism, fissuring, rifting anddykes injection that occur along ocean ridge axes. Start in 1971. As theory of sea floor spreading and plate tectonic beingaccepted. Right time plate are generate ( oceanic ridge). Area of study: Small segment of Mid-Atlantic Ridge, southwest Azores. Boundary between African and American plate. Reason this area chosen: Aeromagnetic survey show clear central magnetic anomaly. Not far from port of Ponta Delgada . A series of bathymetric survey carried out to produce maps. On maps (Figure 4.5), transform fault can be seen. Figure 4.6Inner rift floor is 2.5km depth and contain small hillssuch as Mount Venus and Mount Pluto.
TECHNIQUE. Almost every marine geological and geophysicalwas used. Many technique not for marine studies and had tobe modified for FAMOUS project.
NAVIGATION SYSTEM. High precision required cause navigation problembecome acute. Solved by: By develop acoustic navigation system. Used acoustic transponder placed on sea floor andlinked to ship and submersible. Equipment proved adaptable. Can be used with other instrument packages thattowed near sea-floor.
SIDE-SCAN SONAR. GLORIA is a side-scan echo-sounding system contribute byBritish. Gave image of sea-floor topography. The topography photo is built up by mosaic the records. For FAMOUS, side-scan sonar mosaic obtained bycombine overlapping sonographs. Useful for: Identify the major fault scarp. Determine the limit extent of fracture zone .
LIBEC(LIGHT BEHIND CAMERA SYSTEM). Overcome field of view (FOV) andunderwater photo quality that cause bylimited light scattering. High intensity LIBEC towed above sea floorand give large area photo. By taking many photo in rapid succession proved possible to build photomosaic ofsea-floor.
The LIBEC system shot 120-foot-wide sections of the seafloor thatwere pieced together. (Courtesy ofU.S. Naval Research Laboratory)Project FAMOUS used the U.S.Navy’s LIBEC camera system, whichsuspended high-intensity electronicflash lamps well above the oceanbottom.
NARROW-BEAM ECHO –SOUNDER.. Conventional echo-sounder beam width about 30º. Inadequate as the resolution more than 1km. Using US navy system (ALVIN) with beam width 2º. Much smaller object can be detect. Give submersible preparation guide. System have same FOV with submersible. Ease the manned submersible survey. Submersible designed with titanium hull for it workunder high pressure. Various sampling devices added: One arm manipulator pick specimen. Bag to collect loose sediment.
INTERPRETATION OF FAMOUSDATA…Assumption… The features on the topographic map is the result ofvolcanism. Thus, each hill-like feature should have volcanicvents at or near the top and flow direction radiatingfrom it.
EVOLUTION OF THE RIFT-VALLEYFLOOR… Figure 4.15 and 4.16 shows the successive stagesin the formation of 2 – 3 km wide strips of newoceanic crust either side of the Mid-Atlantic Ridgeduring the last 200,000 years. The process are consistent with a (half) spreadingrate of 1 - 2cm per year.
EVOLUTION OF THE RIFT-VALLEYFLOOR… The frequency of volcanic events variesappreciably. By the time it was built up, eachvolcano would be underlain by a swarm of dykesemanating from the magma chamber beneath. Subsided and rifting process occurred. Rifts mostlyform beside either to the east or the west of eachvolcano. Each new phase of volcano-buildingdevelops about the latest rift. New volcanoes willtake up space so the older volcanoes are moveaside to accommodate them.
EVOLUTION OF THE RIFT-VALLEYFLOOR… About 100,000 years old, the volcanic hills aresufficiently far from the axis to be uplifted by faultswhich mostly dip inwards from the walls. After 200,000 years, the volcanoes heave beenupfaulted completely out of the valley floor to thetops of the walls.