Rock Density Lab Objectives:

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

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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