GEOL 256 Lecture Notes - Lecture 17: Partial Melting, Gneiss, Chemical Evolution

• School: College of Charleston
• Department: Geology and Environmental Geosciences
• Course: GEOL 256
• Professor: Chadwick

Document Summary

Lecture 17: how to make lavas that aren"t basalt (10/16/20) Eutectic melts - finish melting from the eutectic composition to get a non-basaltic magma. All starting peridotite compositions (any combination of typical minerals) starts melting at the eutectic. Partial melting always leads to a near eutectic composition = basalt. 1-25% partial melting leads to basalts in most tectonic environments, even other planets. Rises and pools - less dense than surrounding rock. Magma chamber no longer lower density that surrounding rock - stops rising. Minerals crystalize out and change magma composition. Magma enters continental crust and melts it. Melts continental granite and changes magma composition. Ponded basalt rises and encounters another pooled magma body. Becomes a higher silica overall and creates eruption. Shows which minerals will crystalize and in what order. Higher temps in mantle can melt a higher proportion of magma. Chemical evolution of magmas via fractional crystallization.