CE11 - Lecture 6 - Plate Tectonics

Plate Tectonics

A theory suggesting that Earth's lithosphere is divided into tectonic plates that float on the semi-fluid asthenosphere beneath.

Pangaea

The supercontinent proposed by Alfred Wegener that existed around 280 million years ago, meaning "all land".

Panthalassa

The vast ocean that surrounded Pangaea.

Laurasia and Gondwana

Two landmasses formed when Pangaea split around 180 million years ago.

Evidence for Continental Drift

Includes jigsaw fit of continents, fossil distribution, similar rock types across continents, and paleoclimate indicators.

Wegener’s Mechanism Flaw

Wegener proposed continents float like icebergs on denser crust, but the forces he cited (earth rotation, tidal forces) were too weak.

Alfred Wegener

Proposed the continental drift theory in 1915; initially rejected due to lack of mechanism and political factors.

Harry Hess

Proposed the theory of seafloor spreading in 1962, introducing mantle convection as the driving force.

Seafloor Spreading

The idea that new oceanic crust forms at ridges and old crust is pushed away and subducted into trenches.

Magnetic Striping

Alternating magnetic polarity patterns on the ocean floor that support seafloor spreading.

Paleomagnetism

The record of Earth's magnetic field in rocks, showing periodic geomagnetic reversals.

Mid-Ocean Ridges

Underwater mountain ranges where new oceanic crust is created through volcanic activity.

Magnetite in Basalt

A mineral in basalt that aligns with Earth's magnetic field and records geomagnetic reversals.

Vine and Matthews

Geologists who in 1963 proposed that magnetic striping patterns were due to geomagnetic reversals.

Transform Faults

Plate boundaries where plates slide past each other, causing horizontal displacement (e.g., San Andreas Fault).

Tectonic Plates

Rigid segments of Earth's lithosphere; examples include Eurasian, Pacific, and Philippine Sea Plate.

Plate Motion Rates

Plates move at rates between 1–10 cm per year; Pacific Plate is fastest, North American Plate is slower.

Divergent Boundary

A type of plate boundary where plates move apart and new crust is formed.

Basalt and Gabbro

Mafic igneous rocks created at divergent boundaries, rich in ferromagnesian minerals.

Pillow Lava

Lava that cools quickly upon contact with water, forming rounded structures at mid-ocean ridges.

Sheeted Dykes

Vertical layers of solidified magma formed at divergent boundaries as magma repeatedly intrudes and cools.

Ocean-Ocean Convergent Boundary

One oceanic plate subducts under another, forming trenches and volcanic island arcs.

Ocean-Continental Convergent Boundary

Denser oceanic plate subducts under a continental plate, forming volcanic mountain ranges.

Continental-Continental Convergent Boundary

Both plates collide and uplift into mountain ranges; neither subducts.

Convergent Boundary

A boundary where two plates move toward each other, leading to subduction or mountain formation.

Ridge Push

A force driving plate motion where elevated ridges push plates away due to gravitational forces.

Slab Pull

A force where sinking cold, dense plates pull the rest of the plate down at subduction zones.

Plate Motion Mechanisms

Include mantle convection, ridge push, and slab pull, all working together to move plates.

Unifying Theory of Geology

Plate tectonics, combining evidence from continental drift, seafloor spreading, and paleomagnetism.

Asthenosphere

The semi-fluid layer beneath the lithosphere that allows tectonic plates to move.