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Daily QuestionDaily 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

Plate Tectonics and Igneous RocksPlate Tectonics and Igneous Rocks

Fig. 6.6

Ophiolite ComplexOphiolite Complex

Oceanic CrustMarine Sediment

Pillow BasaltsSheeted Dikes

Gabbro

Pillow Basalts in the OceanPillow Basalts in the Ocean

Pillow Basalts on the ContinentsPillow Basalts on the Continents

Sheeted DikesSheeted Dikes

GabbroGabbro

Plate Tectonics and Igneous RocksPlate Tectonics and Igneous Rocks

Fig. 6.6

Cinder ConesCinder 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

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

Plate Tectonics and Igneous RocksPlate Tectonics and Igneous Rocks

Fig. 6.6

Hot SpotsHot 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 ChainsHot Spot Example – Island Chains

Island Chain FormationIsland Chain Formation

Hot Spot Under HawaiiHot Spot Under Hawaii

Notice linear layout of islands

Could determine plate movement rate for data

Island continually being formed

Shield VolcanoesShield 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 VolcanoesShield Volcanoes

Volcano Size ComparisonVolcano Size Comparison

Hot Spot Example – ContinentalHot Spot Example – Continental

Yellowstone

Continental Hot Spot MechanicsContinental Hot Spot Mechanics

Volcanism and Continental Hot SpotsVolcanism and Continental Hot Spots