Exotic Terranes

Ophiolite

A section of oceanic crust and mantle that has been uplifted and exposed above sea level and placed on top of continental crust. 1) Sediment/ silica ooze 2) Pillow basalts 3) Sheeted dykes 4) Gabbro 5) Layered Mafic/Ultramafic 6) Mantle

What is the process of a terrane placement?

1) A micro continent and a volcanic island arc are being carried towards a subduction zone 2) The volcanic island arc is sliced off the subduction plate and thrust onto the continent 3) A new subduction zone forms seaward of the old subduction zone 4) The accretion of the micro continent to the continental margin shoves the remnant island arc further inland and grows the continental margin seaward.

Farallon Plate

A Late Mesozoic-Cenozoic oceanic plate that was largely subducted beneath North America; the Cocos and Juan de Fuca plates are remnants.

What are some examples of accreted terranes in Oregon?

Blue, Klamath, and Coast Range Mountains.

How do we know terranes are exotic?

Fossils assemblages in rocks don't make sense in current locations, paleomagnetism, and radioactive isotope dating.

Terrane

Group of rocks that form together in one area, are unrelated to surrounding rock, bounded by faults, and range in size from 10 to 1000 square miles

How do terranes form?

Rock is rafted in from somewhere else via tectonic movement of plates, docks onto existing land masses, usually at subduction zones or convergent plate boundaries and transform boundaries.

Suture Zone

The zone on Earth's surface where two continents have collided and have been welded together to form a single continent. Divides older North American continent from the newer, 200 million year old rocks. Present at Oregon/Idaho border.