Presentation on theme: "10.2 Intrusive Igneous Activity. Plutons Structures that result from the cooling & hardening of magma at depth Form deep down Can only be studied once."— Presentation transcript:
10.2 Intrusive Igneous Activity
Plutons Structures that result from the cooling & hardening of magma at depth Form deep down Can only be studied once they are uplifted and erosion have exposed them Variety of shapes & sizes Sills & Laccoliths Dikes Batholiths
Sills & Laccoliths Plutons that form when magma is intruded close to the surface Sills & Laccoliths vary in shape & composition Sills form when magma is injected along sedimentary bedding surfaces, parallel to the bedding planes. Horizontal Sills are the most common To form, the overlying sedimentary rock is lifted to equal height of the sill. Both have the same thickness.
Sills & Laccoliths Laccoliths are formed when magma is intruded between sedimentary layers close to the surface Similar to Sills Magma that makes Laccoliths are more viscous
Dikes Form when magma is injected into fractures, cutting across preexisting rock layers Sheet-like structure Thickness ranges from 1 km Many dikes form when magma from a large magma chamber invades fractures in the surrounding rocks
Batholiths Largest intrusive igneous bodies Very thick An intrusive igneous body must have a surface exposure > 100 km to be considered a batholith Uplift and erosion have removed the surrounding rock that then exposes the batholith
Origin of Magma Geologists conclude that magma originates when essentially solid rock partially melts by raising the temperature Heat Hotter the further in you go Pressure Pressure = rock’s melting temp. Water Causes rocks to melt at temps.
3 Ways Magma Can Form… 1. Heat 2. Pressure 3. Water can the melting temp. of mantle rock
10.3 Plate Tectonics & Igneous Activity
Convergent Plate Boundaries The main connection between plate tectonics & volcanism is that plate motions provide the mechanisms by which mantle rocks melt to generate magma Ocean – Ocean Ocean – Continent
Divergent Plate Boundaries Most magma is produced along the oceanic ridges during seafloor spreading
Intraplate Igneous Activity Intraplate volcanism occurs within a plate, NOT AT A PLATE BOUNDARY Most intraplate volcanism occurs where a mass of hotter than normal mantle material called mantle plume rises toward the surface.