Si rich minerals melt first Si poor minerals melt last Partial melting yields a

Si rich minerals melt first si poor minerals melt

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Si-rich minerals melt first / Si-poor minerals melt last - Partial melting, yields a silica rich magma - Removing the partial melt from its source create Assimilation - Magma melts the wall rock it passes through - Blocks of wall rock fall into magma - Assimilation of these rocks alters magma composition Magma Mixing - Different magmas may blend in a magma chamber - The result combines the characteristic of the 2 - Often magma mixing is incomplete, resulting in blobs of one rock type suspended within the other Magma Movement - Magma doesn’t stay put; it tends to rise upward - Magma may move upward in the crust - Magma may breach the surface - a volcano - This transfers mass from deep to shallow parts of Earth - A crucial process in the Earth System - Provides the raw material for soil, atmosphere and ocean - Why does magma rise? - It is less dense than surrounding rocks - Magma is more buoyant - Buoyancy lifts magma upward - Weight of overlying rock creates pressure - Pressure squeezes magma upward - It is like mud squeezed between your toes - Speed of magma flow governed by viscosity - Lower viscosity eases movement - Lower viscosity is generated by - Higher T - Lower SiO2 content - Higher volatile content - Viscosity depends on temperature, volatiles, and silica - Temperature - Hot = lower viscosity; cooler = higher viscosity - Volatile content: - More volatiles - lower viscosity - Less volatiles - higher viscosity
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- Silica content - Less SiO2 (mafic) - lower viscosity - More SiO2 (felsic) - higher viscosity Making Igneous Rock - Cooling rare - Depth - deeper is hotter; shallower is cooler - Shape - spherical bodies cool slowly; tabular faster - Groundwater - circulating water removes heat - Changes with cooling - Fractional crystallization - early crystal settle by gravity - Melt composition changes as a result Bowen’s Reaction Series - N.L. Bowen - devised experiments cooling melts - He discovered that minerals solidify in a specific series - Continuous - plagioclase changed from Ca-rich to Na-rich - Discontinuous - minerals start and stop crystallizing - Olivine - Pyroxene - Amphibole - Biotite Igneous Environment - 2 major categories - based on cooling locale - Extrusive settings - cool at or near the surface - Cool rapidly - Chill too fast to grow big crystals - Intrusive settings - cool at depth - Lose heat slowly - Crystals grow slowly and large Extrusive Settings - Lava flows cool as blankets that often stack vertically - Lava flows exit volcanic vents and spread outward - Low-viscosity lava (basalt) can flow long distance - Lava cools as it flows - Explosive ash eruption: Mt. St-Helens - High-viscosity felsic magma erupts explosively - Yield huge volumes of ash that can cover large regions - Pyroclastic flow - Pyroclastic flows are often augmented by glacial melt water debris flows that can travel many kilometres from the volcano
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Intrusive Setting - Magma invades preexisting wall rock by - Percolating upward between grains -
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  • Fall '09
  • Basalt

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