Plate Tectonics and Seafloor Spreading Flashcards

Vocabulary flashcards covering plate tectonic boundaries, divergent stages, volcanic behavior, and convergent subduction processes based on lecture notes.

Divergent plate boundary

A tectonic boundary where two plates pull apart or diverge, leading to the creation of an ocean basin.

Asthenosphere

The partially molten, flowable layer of the Earth beneath the lithosphere that exhibits plastic behavior (similar to saltwater taffy) and drives plate motion via convection cells.

Basalt

A fine-grained volcanic rock that forms oceanic crust and oceanic rift floor when lava cools quickly on the Earth's surface.

Diabase

An igneous rock with the same composition as basalt that forms when lava cools intrusively within the Earth, resulting in larger crystal sizes.

Extensional cracks

Cracks (also called tensional cracks) in the Earth's crust caused by tectonic forces pulling a plate apart.

Rift Valley stage

The stage in plate divergence characterized topographically by a long, low, skinny valley floored by basalt, representing the first inkling of an ocean basin.

East African Rift Valley

The premier world-famous example of the Rift Valley stage, featuring a long skinny valley that gets wider on average by a few centimeters every year.

Cornwall, Pennsylvania

A town in Southeastern Pennsylvania featuring extensive iron ore deposits associated with ancient rift magmas and lavas from the Jurassic period, which supplied iron for Revolutionary War cannons.

Linear sea

A narrow body of saltwater formed when rift valley spreading continues long enough for ocean water to flood into the valley.

Red Sea

The primary textbook example of a linear sea, floored by basalt and widening every year as tectonic plates diverge.

Gulf of California

A linear sea located in Baja, Mexico, characterized by a basalt floor and ongoing complex tectonic divergence.

Iceland

An island location where the Mid-Ocean Ridge extends above sea level due to the presence of an underlying stationary volcanic hot spot.

Nonexplosive volcanism

The eruptive style typical of divergent boundaries, where lava oozes or squeezes smoothly out of crustal cracks like toothpaste without forming ash clouds.

Pillow basalts

Distinctive pillowy-shaped rock structures formed when hot basaltic lava erupts underwater and cools rapidly against cold sea water.

Failed rift

A rift zone where tectonic divergence initiated but stopped, leaving ancient buried basalts and pillow formations, such as those found in Northern Wisconsin, Michigan, and Minnesota.

Transform faults

Perpendicular fault lines cutting across mid-ocean ridges that accommodate differences in spreading rates and timing along the Rift Valley.

Magnetic stripes

Invisible ocean-floor patterns recorded in oceanic basalt that document periodic reversals of Earth's magnetic field between normal and reverse polarity.

Convergent boundary

A tectonic boundary where two lithospheric plates move toward one another and collide.

Plate subduction

The tectonic process where a denser lithospheric plate dives or slides beneath a less dense plate into the Earth's interior at a convergent boundary.

Trench

A deep ocean topographic depression caused by the down-warping of a plate as it subducts beneath another plate.

Partial melting

The process where only certain minerals within a subducting plate melt as temperatures increase deeper in the Earth, generating magma that feeds surface volcanism.

Explosive volcanism

The violent style of volcanic eruption characteristic of subduction zones at convergent boundaries, driven by gas pressure within rising magma.