GEOL 212 Lecture Notes - Lecture 50: Magma Chamber, Peridotite, Source Rock

• School: University of Maryland
• Department: Geology
• Course: GEOL 212
• Professor: John Merck

Document Summary

Fractional melting: mantle rocks like peridotite consist of several different minerals (mostly olivine and pyroxene), each with its own melting point. Consider that the magma erupting at mid-ocean ridges has moved maybe a mere ten km from its source, but whereas that source was fe and mg rich peridotite, the magma is slightly less. compatible elements like magnesium (mg) tend to remain in the solid phase. The most mg and fe rich minerals in a melt (i. e. those with the highest melting point) will be the first to crystallize out, leaving an increasingly felsic magma. Assimilation: the vast majority of intrusives we see on the continents are felsic, like granite. Remember, in general, continental crust is much more felsic than oceanic. As ultramafic magmas encounter the felsic rocks of the continental crust, they cause the most felsic minerals in those felsic rocks (the ones with the lowest melting point) to melt.