ENV 110 Lecture Notes - Lecture 9: Buoyancy, Xenolith, Partial Melting
8 Jun 2018
School
Department
Course
Professor
Environmental Studies – Lecture 9
Magma and Igneous Rock
• Molten rock (melt) is needed to generate volcanic activity and create igneous rock
• Magma – melt under ground
• Lava – elt o earth’s surface
o Lava emerges to surface at volcano (lava lake, foundation, flow (cooled rock))
• Volcano
o Active- still has source for eruption, can build pressure
o Dormant – still has source for eruption, but has not for >1000 years
o Extinct – moved off subduction plate, does not have source
• Igneous Rock
o Intrusive Igneous rock – cools slowly underground (more than extrusive)
▪ Columns and thin sheets
o Extrusive Igneous rock – cools at surface
• Magma formation
o Magma only forms in special tectonic settings (lower crust and upper
asthenosphere)
1. Pressure decreased
a. Decompression melting – decreasing pressure allows atoms to move freely
2. Adding volatiles (flux melting)
a. Lowers melting temp
3. Heat transfer melting
a. Rising magma brings mantle heat with it and melts surrounding rock (like hot
fudge over ice cream)
• Composition of molten rock
o Chemical composition
• Four major melt types based on silica
find more resources at oneclass.com
find more resources at oneclass.com
