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 

    1. 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

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