Chapter 4 - Igneous Rocks

6.2 what are igneous rocks 

Igneous rocks: 

• Ignis, meaning fire 

• Magma cools, atoms/ions combine to form solid minerals = crystallization 

  Two types of igneous materials:

  • Magma: molten rock that stays within the crust and/or mantle 

  • Lava: molten rock material that has erupted onto the earth’s surface

6.3.1 igneous rock types 

• Form three general types of igneous rock 

  1. intrusive or plutonic 

     • Magma crystallizes below ground 

     • Large, interlocking crystals 

  • Slow cooling rate 

  • Ex. Granite, gabbro, diorite 

  2. extrusive or volcanic

     Lava crystallizes on or above the surface 

     Small (or no) crystals in a glassy groundmass 

     Fast cooling rate 

6.6.2 Magmatic Differentiation

• magma chamber B can interact with Magma chamber a and mix

6.7 Types of Igneous Intrusions

Pluton: body of magma emplaced into host rock (metamorphic)

Batholith: large igneous body (a group of plutons together)

• ex. Tuolumne batholith, Yosemite, NP, CA

• associated with oceanic continental convergent boundary

Magma’s orientation with host rock:

• sill: concordant; igneous intrusion parallels the structure of the host rock (magma came and wedged in between)

• dike: discordant; igneous intrusion cuts across the host rock (breaks rock for magma to crystalize)

6.8/6.8.1 Igneous Rocks and Plate Tectonics (slide 25)

• magma and volcanoes form at divergent and convergent plate boundaries

• transform and continent/continent = no melting

divergent: seafloor spreading at mid-ocean ridges

• most igneous rocks on Earth are formed here

• partial melting (decompression melting) of upper mantle

• crystalizes as mafic basalt at surface; gabbro at depth

• continental rifts can have felsic rocks, with enough rifting can start erupted basalt

convergent: ocean-continent or ocean-ocean boundaries

• flux melting: water lowers melting temp

• oceanic-continent: melts crystalize as intermediate andesite at surface, diorite at depth

• oceanic-ocean: will have mafic basalt on surface, gabbro at depth

• through magmatic differentiation can form felsic rocks