Ocean Ridges and Oceanic Lithosphere

A series of flashcards covering key vocabulary and concepts related to ocean ridges and oceanic lithosphere as discussed in the lecture.

Oceanic Ridges

Mark the loci of divergent plate margins where new oceanic lithosphere is created.

Spreading Rate

The rate at which oceanic ridges spread, categorized as slow (2.0-5.5 cm/yr), intermediate (5.5-10.0 cm/yr), fast (>10 cm/yr), and ultraslow (<2.0 cm/yr).

Axial Topographic High

The broad topographic high that defines the crest of an oceanic ridge, typically characterized by a deep median rift valley.

Graben

A type of structure formed when tectonic forces cause the ground to sink between normal faults, often found along the central axis of oceanic ridges.

Hydrothermal Circulation

The process involving seawater circulation through the crust, driven by heat from the underlying mantle, which can lead to mineral deposits at ridge crests.

Black Smokers

350-400*C Metal sulfide deposits found at hydrothermal vents on mid-ocean ridges, where superheated water rich in minerals and sulfides is expelled.

MORB

Mid-Ocean Ridge Basalt, a type of volcanic rock that forms from the melting of the mantle at ocean ridges.

Depth-Age Relationship

The consistent observation that ocean floor depth increases with age; younger lithosphere is shallower, and older lithosphere is deeper.

Lithospheric Thickness

The thickness of the lithosphere, which typically increases from a few kilometers at the ridge crest to several tens of kilometers with age.

Seismic Studies

Investigations using seismic data to infer properties about the crust and upper mantle beneath ocean ridges.

what s the structure of the mantle below ridge systems

crust is slightly thinner below oceanic ridges

low upper mantle velocity and anomalous low density

what do we see in axial magma chambers

thin and narrow magma body - sill like

low seismic velocity - surrounded by zone of crystal mush

can be fast or slow spreading

what is the melt experiment and what are the conclusions

Mantle electromagnetic and topography

1) pattern of upwelling + geometry of melt region - asymmetric

3) concentration of melt - around 20% concluding efficient extraction

4) distribution of melt - thin film to sphereoid

5) connectedness of pockets - interconnected allowing for percolation along interfaces