Download Igneous Rocks and Intrusive Igneous Activity

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Daily Question
 At which type of plate boundary would you find
mafic igneous rocks? Explain
 Would the rocks be basalt, gabbro, or could both
rock types occur? Explain
Fig. 6.6
Plate Tectonics and Igneous Rocks
Ophiolite Complex
Oceanic Crust
Marine Sediment
Pillow Basalts
Sheeted Dikes
Gabbro
Pillow Basalts in the Ocean
Pillow Basalts on the Continents
Sheeted Dikes
Gabbro
Fig. 6.6
Plate Tectonics and Igneous Rocks
Cinder Cones
Built from ejected lava
fragments
 Have steep slopes
(controlled by angle of
repose – the steepest
angle at which material
remains stable)
 Small – 300 m (1000 ft)
high, 2 km in diameter

Composite Cones Stratovolcano
Most encircle the pacific
ocean (ring of fire) as part
of magmatic arcs
 Large – ~1 km high, 5 - 25
km wide
 Symmetrical structure
 Composed of alternating
lava flows and pyroclastic
deposits
 Product of high viscosity
magma
 Have violent eruptions

Mount Rainer
Fig. 6.6
Plate Tectonics and Igneous Rocks
Hot Spots
 Produced by rising plume of mantle material (mantle
plume)
 They are stationary – plates move over the hotspots
 Basalts produced by hot spots are chemically
different from basalts produced at MOR
Hot Spot Example – Island Chains
Island Chain Formation
Hot Spot Under Hawaii
Notice linear layout of
islands
 Could determine plate
movement rate for data
 Island continually being
formed

Shield Volcanoes
 Broad, slightly domed strucutre
 Large structure 9 km (~6 miles) high & 50 km
(~30 miles) wide
 Produced by fluid (low viscosity) lava
 Example: Mauna Loa, Kilauea, other island
chains
Shield Volcanoes
Volcano Size Comparison
Hot Spot Example – Continental
 Yellowstone
Continental Hot Spot Mechanics
Volcanism and Continental Hot Spots