Earth Rocks Lecture 3 Igneous Rocks Chapter 3 Geothermal gradient ...
Earth Rocks Lecture 3 Igneous Rocks Chapter 3 Geothermal gradient : formation of the Earth, core is hot and heat is emanating out to space Granit: popular igneous rock • Pressure increases as we get lower and lower • Produce high temperatures • Melt rock or silicate material near the boundary between the mantle and the core • Magma is lighter than rock – goes up towards the surface through fractures – volcano producing pyroclastic debris • When extrusive material solidifies, lava crystalizes producing volcanic rock • Intrusive material: magma doesn’t reach the surface and crystalizes o As magma cools, crystals form with a mixture of liquid in the magma chamber solidifies: forms a dark igneous rock o Rocks texture: the look of the rock, the size shape and arrangement of crystal as they fit together How Magmas Evolve • Near the crust and mantle body • Norman L. Bowen from Kingston ON, • Through Bowen’s Reaction Series in which crystals settle in a magma chamber • Earlier dark crystals remove heavy elements, leaving melt with lighter ones (magmatic differentiation) – magma changes chemically and composition • Figure 3.16 : temperature scale : discontinuous series of crystilization: olivine forms first (highest melting point) and crystalizes first. As temp drops and reaches melting point of pyroxene •
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calciumrich feldspar forms first, highest crystlization temp composition changes until it’s pure sodiumrock
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non peromagnesium: potassium feldspar, muscovite mica, quartz discontinuous series: different structures cotinours serious (plagioclase) assimilation (host rock melts in magma) magma mixing: when magma is pressing against a host rock, it’s putting pressure on the rocks it’s intruding, of there is a fault or fracture it will form an igneous rock called a dike magma mixing: different magma compositions mixing Figure 4.25: three ways a magma body may be altered Incomplete assimilation : magma cooled before it could completely melt the host rock Igneous compositions: dark versus light mineral (Fe, Mg vs silica) content o Dark minerals are high in iron and mg o Light minerals are based on silica content or number of tetrahedra Igneous textures: size, shape, and the arrangement – how crystals fit together the look of the rock Igneous texture: o Aphanitic: fast cooling magma, small crystals – need a microscope) In volcanic rock Finegrained rock derived from lava flow o Phaneritic: slow cooling magma, large crystals) Magma crystalizing underground Coarsegrained See individual crystals o Porphyritic: large crystals surrounded by smaller ones o Glassy obsidian: Sharpe edges o Glassy: quenches, no crystals: if there is a lot of gas it produces pumice – floats : air holes o Pumice: cools very quickly – no crystals have time to form o Pyroclastic: airborne pieces of magma fell to the ground o Angular fragments, not sediment that’s solidifying
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Naming Igneous Rocks – figure 3.11
• o Felsic (~70% silica) Granit: in cores of mountains, coarsegrained – cools slowly Rhyolite: volcanic aphanitic o Intermediate ~60% silica – melting oceanic crust and the volcanic crust** Andesite: from volcanoes above subduction zones Diorite: in intrusive rocks above subduction zones o Mafic ~50% silica o Basalt: most abundant rock, forms oceanic crust – almost ¾ of our planet is occupied by Oceans: ocean floor is mainly basalt o Gabbro: lower part of oceanic crust, erosion, o Ultramafic ~45% peridotite: makes up the upper part of the mantle
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Intrusive Igneous Bodies
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o Intrude fractures or squeeze between rocks o Forms plutons with two orientations: o Discordant: cut across host rocks o Concordant: parallel to host rocks Types of plutons: o Dykes: discordant, tabular o Sills: concordant, tabular o Laccoliths: concordant, bulge o Batholith: discordant, huge
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calciumrich feldspar forms first, highest crystlization temp composition changes until it’s pure sodiumrock
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non peromagnesium: potassium feldspar, muscovite mica, quartz discontinuous series: different structures cotinours serious (plagioclase) assimilation (host rock melts in magma) magma mixing: when magma is pressing against a host rock, it’s putting pressure on the rocks it’s intruding, of there is a fault or fracture it will form an igneous rock called a dike magma mixing: different magma compositions mixing Figure 4.25: three ways a magma body may be altered Incomplete assimilation : magma cooled before it could completely melt the host rock Igneous compositions: dark versus light mineral (Fe, Mg vs silica) content o Dark minerals are high in iron and mg o Light minerals are based on silica content or number of tetrahedra Igneous textures: size, shape, and the arrangement – how crystals fit together the look of the rock Igneous texture: o Aphanitic: fast cooling magma, small crystals – need a microscope) In volcanic rock Finegrained rock derived from lava flow o Phaneritic: slow cooling magma, large crystals) Magma crystalizing underground Coarsegrained See individual crystals o Porphyritic: large crystals surrounded by smaller ones o Glassy obsidian: Sharpe edges o Glassy: quenches, no crystals: if there is a lot of gas it produces pumice – floats : air holes o Pumice: cools very quickly – no crystals have time to form o Pyroclastic: airborne pieces of magma fell to the ground o Angular fragments, not sediment that’s solidifying
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Naming Igneous Rocks – figure 3.11
• o Felsic (~70% silica) Granit: in cores of mountains, coarsegrained – cools slowly Rhyolite: volcanic aphanitic o Intermediate ~60% silica – melting oceanic crust and the volcanic crust** Andesite: from volcanoes above subduction zones Diorite: in intrusive rocks above subduction zones o Mafic ~50% silica o Basalt: most abundant rock, forms oceanic crust – almost ¾ of our planet is occupied by Oceans: ocean floor is mainly basalt o Gabbro: lower part of oceanic crust, erosion, o Ultramafic ~45% peridotite: makes up the upper part of the mantle
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Intrusive Igneous Bodies
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o Intrude fractures or squeeze between rocks o Forms plutons with two orientations: o Discordant: cut across host rocks o Concordant: parallel to host rocks Types of plutons: o Dykes: discordant, tabular o Sills: concordant, tabular o Laccoliths: concordant, bulge o Batholith: discordant, huge
