Main Idea Magma Eruption 1. Does all magma erupt at the surface?

Main Idea Magma Eruption 2. Why does it matter where magma erupts or where it cools?

Main Idea Magma Eruption 3. How could you tell if there were an active magma intrusion below the surface?

18.3 – Intrusive Activity

Plutons Intrusive igneous rock body, including batholiths, stocks,sills & dikes Formed through mountain-building processes and oceanic-oceanic collisions Can be exposed at Earth ’ s surface to uplift and erosion

Batholiths & Stocks The largest plutons are called Batholiths. Batholiths are coarse-grained, irregularly shaped, igneous rock mass that covers at least 100 km2 Stocks are irregularly shaped plutons but smaller in size. Both generally form 5-30 km below Earth ’ s surface and are common in the interior of major mountain chains

Laccoliths Relatively small Mushroom-shaped pluton that forms when magma intrudes into parallel rock layers close to Earth ’ s surface Laccoliths have flat bottoms and curved tops.

Sills Pluton that forms when magma intrudes parallel rock layers

Dikes Pluton that cuts across preexisting rocks and often forms when magma invades cracks in surrounding rock bodies

Plutons & Tectonics Many plutons form as the result of mountain-building processes. Plutons are thought to form as a result of continental-continental and oceanic- continental convergence.

Reinforcement T/F Batholiths are common in the interiors of mountain chains. Laccoliths have curved bottoms and flat tops. Sills form when magma is forced between rock layers. Most igneous activity occurs deep within earth.