Magma:  molten or melted rock; lurks underground and/or comes to surface
     parts of magma: liquid with solids (minerals) and gases  (H2O, CO2, H2S...)
     how primary magma is produced:  decompression (lower the pressure) or heating
       partial melting of the dry mantle-- produces dark/mafic magmas (richer in Fe, Mg, Ca)
            happens at mid-ocean ridges, continental rifts, continental and oceanic hot spots....
       partial melting of the wet mantle-- produces intermediate magmas
            happens at subduction zones only, where water is dragged down into the mantle
       partial melting of the continental crust--produces light/felsic magmas (richer in Si, Na, K)
            continental rifts, continental hot spots, continental arcs, continental collisions
        how secondary magma is produced by modification of the primary magmas
            1. contamination with older rocks
            2. mineral settling from magma
            3. mixing of two magmas

Igneous Rocks: made from magma that's cooled and turned to solid minerals
     only about 10 minerals are commonly found in igneous rocks, almost all are silicates
     mafic/dark minerals (Fe, Mg rich):
        olivine, Ca-feldspar, pyroxene, amphibole, biotite, magnetite
      felsic/pale minerals (Si, Na, K rich):
        quartz, Na-feldspar, K-feldspar, muscovite
     dark minerals grow from dark magma (rich in Fe, Mg....), pale minerals from pale magma

Properties and classification of igneous rocks: only 3 things to classify most igneous rocks
     1.  Gray Scale:  aka "color index";  dark/mafic vs intermediate vs pale/felsic
          gray scale=mineral content, related to chemical composition of magma and hence source
     2.  Mineral Size:  size of minerals; small minerals vs medium vs large minerals
          mineral size related to rate/speed of cooling
                volcanic (fast cooling) vs plutonic (slow cooling)
     3.  Texture:  arrangement of minerals within the rock (not how smooth the rock is)
          porphyritic versus uniform mineral size; glassy to crystalline; vesicular (bubbly) to dense
          pyroclastic = shot into the air during violent eruption:  pumice, ash, bombs...

Plate Tectonics and Igneous Rock Associations:
            where do we find certain magmas/igneous rocks
     Rifts-Oceanic; basalt, diabase, gabbro, etc. of the oceanic crust (mafic/dark rocks only)
     Rifts-Continental; bimodal (mafic and felsic)-- basalt-rhyolite and gabbro-granite
     Hot Spots-Oceanic; basalts and related rocks (mafic/dark rocks only)
     Hot Spots-Continental; bimodal (mafic and felsic), basalt-rhyolite and gabbro-granite
     Subduction Zones; andesite to rhyolite, diorite to granite (mostly intermediate but all kinds)
     Continent-Continent Collisions; rhyolites and granites (felsic/light rocks)

Volcanic and Plutonic Objet d'Igneous: volcanic = formed above ground, plutonic = underground
     Shield volcanoes: made of basaltic/mafic lava flows.  examples: Mauna Kea and Mauna Loa
          runny magma, erupt quietly, flow downhill long distances, form shallow/low angle slopes
     Stratovolcanoes/composite volcanoes: andesitic/intermediate rocks.  Pinatubo, St. Helens.
          sticky magmas,  erupt violently, pyroclastics, pile up close to vent, steep slopes, cones
          Mt. St. Helens: magma caused bulge and earthquake caused landslide caused eruption
     Flood basalts:  big sheets of lava.  columnar basalts on land, pillow basalts form underwater
          lava flows:  flow bottoms and flow tops, vesicles, pahoehoe, aa, etc.
          case study:  Columbia River flood basalts, 15 million years old, all of eastern WA
     Plutons:  large bodies of magma that solidify underground, then later are exposed
          batholiths, dikes, sills, xenoliths
            how does magma push its way through crust and mantle?
 

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