tectonics history

1.7 billion year compression

Early tectonic compression that formed the base rocks of the Grand Canyon and Frenchman Mountain

Rodinia

An ancient supercontinent that later broke apart

Rodinia breakup (~800 mya)

Caused tilting and normal faulting (Grand Canyon Supergroup)

Colorado Plateau stability

Period of little tectonic activity with thick sedimentary rock deposition

Antler Orogeny

Devonian–Late Paleozoic mountain-building event with compression and thrusting

Foreland basin

A deeper region next to mountains where thick sediments accumulate (ex: Arrow Canyon)

Mississippian limestones

Thick marine limestone deposits found in Arrow Canyon

Cyclothems

Repeating sedimentary layers caused by sea-level rise and fall

Pennsylvanian period

Time of alternating environments like shallow seas, rivers, and lakes

Arrow Canyon vs Grand Canyon

Arrow Canyon was deeper; Grand Canyon was shallower and sometimes exposed

Pangea

Supercontinent that existed ~200–300 million years ago

Kaibab Formation

Rock unit formed in a shallow tropical sea

Mesozoic subduction zone

Western North America had subduction with volcanoes and magma formation

Granites

Intrusive igneous rocks formed beneath volcanic arcs

Batholiths

Large bodies of intrusive granite formed underground

Terranes

Pieces of crust (islands or volcanic arcs) added onto continents

Laurentia

Ancient core of North America

Sevier Orogeny

Mid–Late Mesozoic mountain-building event with folding and thrust faulting

Thrust fault

Compressional fault where one block moves over another

Folds

Bending of rock layers due to compression

Basin and Range extension

Stretching of the crust starting ~20–40 million years ago

Cause of Basin and Range

Change in plate motion and subduction of a spreading center

Nevada expansion

Region stretched to about twice its original width

Normal fault

Fault where crust is pulled apart and one block drops down

Fault recognition

Identified by offset layers, shear zones, and fault gouge

Fault gouge

Crushed rock material found along faults

Detachment fault

Low-angle fault where rocks slide over long distances

Turtlebacks

Smooth, curved exposures of deep metamorphic rocks

Strike-slip fault

Fault where blocks slide past each other horizontally

Right-lateral motion

Movement where the opposite side shifts to the right

Owens Valley Fault

Active strike-slip fault with an 1872 earthquake

Shear zone

Area where rocks are deformed by sliding past each other

Modern volcanism

Caused by crustal thinning allowing magma to rise

Long Valley Caldera

Large volcanic depression formed by eruption of Bishop Tuff (~765,000 years ago)

Rhyolite

Silica-rich volcanic rock associated with explosive eruptions

Basaltic volcanism

Low-viscosity lava forming smaller volcanoes

Obsidian domes

Lava domes formed from viscous, silica-rich magma

Coulees

Thick lava flows from viscous magma

Glaciation and drying

Most recent geologic processes shaping the region