Upload
ainun-fatihah
View
138
Download
4
Embed Size (px)
DESCRIPTION
formation of volcanic layer- a case study-> FAMOUS Project ( French-American Mid-Ocean Undersea Study).
Citation preview
FAMOUS PROJECT( FRENCH-AMERICAN MID-OCEAN UNDERSEA STUDY).
James R. Heirtzler was the U.S. leader of Project FAMOUS.
Classic survey of part of the Mid-Atlantic Ridge in 1970s. Provide understanding in pattern of volcanism, fissuring, rifting and
dykes injection that occur along ocean ridge axes. Start in 1971.
As theory of sea floor spreading and plate tectonic being accepted.
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 hills
such as Mount Venus and Mount Pluto.
TECHNIQUE.
Almost every marine geological and geophysical was used.
Many technique not for marine studies and had to be modified for FAMOUS project.
NAVIGATION SYSTEM. High precision required cause navigation problem become
acute. Solved by:
By develop acoustic navigation system. Used acoustic transponder placed on sea floor and
linked to ship and submersible. Equipment proved adaptable.
Can be used with other instrument packages that towed near sea-floor.
SIDE-SCAN SONAR. GLORIA is a side-scan echo-sounding system contribute by
British. Gave image of sea-floor topography. The topography photo is built up by mosaic the records.
For FAMOUS, side-scan sonar mosaic obtained by combine 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) and underwater photo quality that cause by limited light scattering.
High intensity LIBEC towed above sea floor and give large area photo.
By taking many photo in rapid succession proved possible to build photomosaic of sea-floor.
The LIBEC system shot 120-foot-wide sections of the seafloor that were pieced together.
(Courtesy of U.S. Naval Research Laboratory)
Project FAMOUS used the U.S. Navy’s LIBEC camera system,
which suspended high-intensity electronic flash lamps well above
the ocean bottom.
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 work
under high pressure. Various sampling devices added:
One arm manipulator pick specimen. Bag to collect loose sediment.
Alvin
French submersible Cyana
INTERPRETATION OF FAMOUS DATA…
Assumption…
The features on the topographic map is the result of
volcanism.
Thus, each hill-like feature should have volcanic
vents at or near the top and flow direction radiating
from it.
EVOLUTION OF THE RIFT-VALLEY FLOOR…
Figure 4.15 and 4.16 shows the successive stages
in the formation of 2 – 3 km wide strips of new
oceanic crust either side of the Mid-Atlantic Ridge
during the last 200,000 years.
The process are consistent with a (half) spreading
rate of 1 - 2cm per year.
EVOLUTION OF THE RIFT-VALLEY FLOOR…
The frequency of volcanic events varies appreciably. By the time it was built up, each volcano would be underlain by a swarm of dykes emanating from the magma chamber beneath.
Subsided and rifting process occurred. Rifts mostly form beside either to the east or the west of each volcano. Each new phase of volcano-building develops about the latest rift. New volcanoes will take up space so the older volcanoes are move aside to accommodate them.
EVOLUTION OF THE RIFT-VALLEY FLOOR…
About 100,000 years old, the volcanic hills are sufficiently far from the axis to be uplifted by faults which mostly dip inwards from the walls.
After 200,000 years, the volcanoes heave been upfaulted completely out of the valley floor to the tops of the walls.
PLAY
Thank you…