Transcript Ophiolite_ppt_presentation

OPHIOLITE
•Ophiolite (Gk. Ophio – snake; lite- stone from
Gk. Lithos)
•Ophiolite- distinctive assemblage of mafic plus
ultramafic rocks; fragments of oceanic crust
emplaced at convergent boundary onto
continental margins and island arcs.
•Ophiolite sequence from bottom to top includes
peridotite, gabbro(often layered), mafic dikes &
pillow basalt, frequently overlain by
pelagic/oceanic sediments of bedded chert,
mudstone, limestone & graywacke sandstone.
Tectonic Regimes – individual
components that interact in plate
tectonic theory.
Six Tectonic Regimes
1. Cratons (Stable Continents) –
composed of light-weight rocks that
float above sea level on hot plastic
interior asthenosphere. Rocks are
felsic & intermediate igneous rocks like
granite & diorite or their equivalents
schist & gneiss
2. Ocean basins – composed of heavy
mafic rocks like basalt & gabbro. Ocean
basins are composed of the ophiolite
suite, a multilayered sequence of rocks.
3. Divergent plate boundaries – new crust
is created – ophiolite suite
4. Convergent plate boundaries – crust is
destroyed by descending into
subduction zone where volcanoes are
associated
5. Transform plate boundaries – plates
slide past one another; faulting occurs
along transform boundaries like
Philippine Fault, San Andreas Fault.
6. Hot Spot – plumes of hot plastic rock
that rise from deep in the mantle;
volcanic activity is associated with hot
spots.
Plate convergence in three different
settings:
• Ocean – Ocean subduction
• Ocean – Continent subduction
• Continent – Continent subduction
Plate Subduction – the denser of the two
plates subducts:
a) older ocean plate
b) always ocean plate
Quake occurs as plates slide past one
another within the plate at Benioff zone.
Volcanic arc – arc-shaped chain of
volcanoes on the margin of overriding
plate at convergent plate boundary.
Island arc – curving series of volcanic
islands created by collision of tectonic
plates in ocean setting. The particular
type of plate boundary that yields
island arcs is called subduction zone.
• Fore-arc basin – located to the “front”
of the volcanic arc; forms toward the
subducted plate side.
• Back-arc basin – associated with island
arc and subduction zone; found at
convergent plate boundaries presently
concentrated in Western Pacific Ocean
Volcanic arcs in continent (Andes,
Cascades)
Island arcs in ocean (Aleutians,
Philippines)
Trenches – deep linear
features/depressions that form the
surface expression of subduction
• Mariana Trench – 11+km
• Philippine Trench – 7+km