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Mafic vs. Felsic Magmas: Determine Eruption Pattern at Volcanoes Explosive or Quiet?
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Rock Density LabObjectives:(1)Compare the densities of continental and oceanic crust(2)Relate rock density to the process of subduction at plate boundaries.
Mafic vs. Felsic Magmas: Determine Eruption Pattern at VolcanoesExplosive or Quiet?
Differences in density drive sea-floor recycling and plate tectonics:
Mafic vs. Felsic Igneous RocksMafic Characteristics Felsic Characteristics
Igneous Rocks of the Ocean
CrustMafic
~ 50 % silicaHigh in Magnesium (Mg) and Iron (Fe)
Dark color DenseBasalt & Gabbro
Rock of the ocean crust and upper mantle
Mafic Igneous Rocks have heavy minerals with IRON & Magnesium
Elements• Iron• Magnesium• Calcium
Minerals•Olivine•Amphiboles•Ca feldspars
“MAFIC” and are dark in color due to the iron & magnesium.
http://whatonearth.olehnielsen.dk/rocks/volcanicrocks.asp
make
Igneous Rocks of Continental Crust
Felsic~70% silicaLight color
Light
Granites, Rhyolites, Andesites• High silica
Felsic Igneous Rocks have light minerals with silicon & oxygen
Elements• silicon• oxygen
Minerals•Quartz (silica)•Feldspars
“Felsics” and are light in color because they lack iron and are rich in silica.
http://whatonearth.olehnielsen.dk/rocks/volcanicrocks.asp
make
Mafic vs. Felsic Densities: Ocean vs. Continental Crust
Made of… Mafic/Felsic Density Age Thickness
Ocean CrustContinental Crust
Differences in density drive sea-floor recycling & plate tectonics: •The ocean floor is made of basalt (mafic magma). Continental crust is made of granite (from felsic magmas). •Ocean crust is denser than continental crust.•When ocean and continental crust collide … the denser ocean crust sinks back into the mantle (Subduction). This recycles the ocean floor.
Mafic vs. Felsic Magma: Volcano Shape
Mafic vs. Felsic Magma: Volcanic Activity