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 Regimes1. 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 subductionPlate 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