THE MECHANISMS OF PLATE MOTION PLATE TECTONICS THE MECHANISMS OF PLATE MOTION

WHAT CAUSES PLATE MOTION?

THE DRIVING MECHANISM “CONVECTION CURRENTS” Driving force of Plate Tectonics Thermal Convection Flow in mantle Caused by differences in density Warm less dense material rises Cooler more dense material sinks

THE DRIVING MECHANISM “CONVECTION CURRENTS” Heat Sources Heat Gradient & Gravity Contraction causes temperature & pressure to increase with depth Decay of radioactive elements Core heating of Mantle Matierial rises towards the surface Spreads out and drags the lithosphere with it

Whole-Mantle Convection Ocean lithospheric slabs sink into lower mantle Provides downward arm of convection flow Hot mantle plumes at mantle-core boundary move heat toward surface

Mechanisms of Plate Motion - Causes Slab-Pull - Descending Plates: Cooling, older and more dense crust sinks and pulls the trailing lithospheric plate along Cooling, Older and more dense slab of ocean crust sinks at a subduction zone through Asthenosphere pulling trailing lithosphere with it

Mechanisms of Plate Motion - Causes Ridge (slab)-Push - Gravity: Elevated ridge system push plates Ocean slab thickens and becomes more dense as it cools causing it to slide down the sides of the ocean ridges under the influence of gravity, pushing lithosphere ahead of it

Plate Motion Mechanisms Hot Mantle Plumes Caused by CONVECTION CURRENTS Extends from mantle-core boundary Produce Volcanic hot spots Spreads out laterally under the lithosphere Heated mantle material rises & spreads out moving the slabs with it

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Tectonic Settings and Volcanic Activity