geologic maps

Magnetic Reversals

Periods when Earth’s magnetic field flips polarity, causing the North and South magnetic poles to swap places.

Magnetic Anomalies

Alternating "stripes" of high and low magnetic intensity on the seafloor that represent periods of normal vs. reversed polarity.

Magnetite

The iron-rich mineral found in basalt that aligns with Earth's magnetic field as lava cools, preserving the magnetic record.

Seafloor Magnetic Symmetry

The mirror-image pattern of magnetic stripes on either side of a mid-ocean ridge, proving seafloor spreading.

Transform Boundary

The type of boundary most likely to horizontally offset linear features like roads, fences, and streams.

Wadati-Benioff Zone

The zone of earthquakes that increase in depth away from a trench, following the path of a subducting plate.

Subduction Earthquake Location

Earthquakes always occur on the overriding plate side of a convergent boundary.

Composite Volcanoes

Volcanoes formed at convergent boundaries with subduction; they always appear on the overriding plate.

Hotspot Trail vs. Boundary Volcanoes

A hotspot trail shows a single line of age-progressive volcanoes; boundary volcanoes form an arc parallel to a trench.

Boundary associated with recording Magnetic Reversals

Divergent boundaries (mid-ocean ridges), where new crust cools and locks in the current magnetic polarity.

Lithosphere Production vs. Destruction

Lithosphere is produced at divergent boundaries and destroyed at convergent boundaries (subduction zones).

Continental-Continental Convergence

The boundary type that formed the Himalayas and the Appalachian Mountains.

Mid-Ocean Ridges

Long mountain ridges formed along the seafloor at divergent boundaries.

San Andreas and Alpine Faults

Examples of transform boundaries (specifically in California and New Zealand).

Mantle Plume

A localized column of hot magma rising from deep in the mantle that causes hotspot volcanism.

Hotspot Age Trend

Volcanic features get older as you move away from the active hotspot, reflecting the movement of the plate over a stationary plume.

Subduction

The geologic process where denser plates sink below lighter ones plates in the earths convergent boundaries