Obduction Zones: The Push-Together Boundaries

Obduction Zone

A tectonic boundary where older rocks are pushed over younger rocks due to compressional forces, often forming mountain ranges like the Smokies.

Thrust Fault

A type of fault where rocks are pushed over one another, typically placing older rocks atop younger ones due to horizontal compression.

Push-Together Forces

Compressional stresses that cause rocks to bend, fold, or fault, leading to mountain formation and structural deformation.

Metamorphic Rock

Hard, resistant rock formed under high pressure and temperature, often found deep in mountain ranges and at high peaks.

Sedimentary Rock

Rock formed from accumulated sediments, often deposited in shallow seaways and found beneath metamorphic layers in obduction zones.

Cades Cove (Smokies)

A location in Great Smoky Mountains National Park where older metamorphic rocks lie atop younger sedimentary rocks due to thrust faulting.

Glacier National Park Faults

Faults where compressional forces caused displacement, placing older layers above younger ones, similar to notebook stacking.

Capitol Reef Monocline

A 100-mile-long flexure in Earth's crust formed by thrust faulting and uplift, creating features like arches and canyons.

Waterpocket Fold

A geologic structure in Capitol Reef National Park formed by erosion of younger layers, exposing softer rock that collects water.

Folding

A deformation process where rock layers bend due to compressional forces, like buckling paper or pushing a carpet.

Proto-Atlantic Ocean

An ancient ocean that closed due to push-together forces, forming the Appalachian Mountains through subduction and volcanic activity.

Mid-Atlantic Ridge

A spreading center in the Atlantic Ocean where pull-apart forces create new seafloor, contrasting with push-together zones.

Continental Fit

The jigsaw-like alignment of continents across the Atlantic, supporting the theory of continental drift and shared geologic history.

Glacial Striations

Scratches left by glaciers that indicate flow direction; matching striations across continents support past continental connections.

Newark Basin

A region in New Jersey with sediments from a Death-Valley-type setting, dating to the early formation of the Atlantic Ocean.

Death Valley-Style Extension

A geologic process where previously compressed crust begins to stretch and thin, forming valleys and basins like those seen in Death Valley.

Red Sandstones & Mudstones

Sedimentary rocks formed in arid, valley environments; often found along the U.S. East Coast after Appalachian extension.

Dinosaur State Park (CT)

A site preserving fossilized dinosaur tracks in red sandstone, evidence of ancient life during post-Appalachian extension.

Mantle Convection Cell

A rising flow of hot mantle material triggered by pressure changes, potentially initiating seafloor spreading and ridge formation.

Mid-Atlantic Ridge

A divergent plate boundary formed by mantle upwelling, marking the birth of the Atlantic Ocean as continents drift apart.

Geologic Cycle

The recurring sequence of mountain-building (collision/subduction), extension (valley formation), and ocean basin creation.

Plate Drift

The slow movement of tectonic plates; currently, the Americas are drifting westward while the Atlantic Ocean widens.

Alpine Collision

The ongoing tectonic interaction between Africa and Europe, responsible for the uplift of the Alps.

Himalayan Collision

The tectonic convergence of India and Asia, forming the Himalayas through intense compressional forces.

Subduction Zone Initiation

The process where cold, dense oceanic crust begins to sink beneath continental crust, forming a new subduction zone.

Obduction (Revisited)

A tectonic collision where buoyant continental or island arc crust overrides a subduction zone, forming folds and thrust faults.

Island Arc

A curved chain of volcanic islands formed above a subduction zone, which may later collide with continents during obduction.

Continental Buoyancy

The principle that continents are too light and thick to subduct, causing them to override oceanic crust during collisions.

Blue Ridge & Great Smokies Faulting

Regions where obduction caused older rocks to thrust over younger ones, visible in folded and faulted terrain.

Appalachian Thrust Efficiency

The extensive horizontal displacement of older rocks over younger ones during Appalachian mountain formation—sometimes over hundreds of miles.