esci 101: lecture the rock cycle & igneous rocks february 23, 2007 copy of this lecture will be...
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ESCI 101: LectureESCI 101: LectureThe Rock Cycle The Rock Cycle & Igneous Rocks& Igneous Rocks
February 23, 2007February 23, 2007
Copy of this lecture will be found at:http://www.owlnet.rice.edu/~esci101
With Some Graphics from Press et al.,
Understanding Earth, 4th Ed. (Copyright © 2004 by W. H. Freeman & Company)
Enchanted Rock
The Rock The Rock CycleCycle
-Melting & Intrusion-Solidification of melt-Mountain Building-Uplift & Exposure-Weathering-Erosion & Transport-Deposition & Burial-Metamorphism-Melting & Intrusion
Fig 4.9
ESCI 101 - “Pop” Homework #4(Due Wednesday, 2/28/07, 5 PM)
• Assignment:- For this exercise, trace the
alternate pathway of the rock cycle: (1) igneous rocks are formed, (2) become metamorphosed, (3) exposed, and (4) evolve into sandstone. Describe the main processes and events that might take place at each step along the way, and the plate tectonic settings in which they are likely to occur. (Your answer should not exceed one page.)
- See the accompanying plot on the following page.
Pop-HW#4Pop-HW#4 An An
Alternate Alternate Rock Rock CycleCycle
-Melting & Intrusion-Solidification of melt-???-???-???-???-???--> Sandstone
Fig 4.9
X
XX
(a) The Rock (a) The Rock CycleCycle
Fig 4.9
E.g., Convergent
Plate Boundary-Subducting
slab-Mantle melting-Bouyant rise
of melt
(b) The Rock (b) The Rock CycleCycle
Fig 4.9
E.g., Convergent Plate Boundary- Solidification
of melt- Volcanic activity
Intrusive rocks
Extrusive
rocks
Genetic Classification of Genetic Classification of Igneous RocksIgneous Rocks
Granite Gabbro
• IntrusiveIntrusive: crystallized from slowly cooling magma intruded within the Earth’s crust; e.g. granite, gabbro.
Genetic Classification of Genetic Classification of Igneous RocksIgneous Rocks
Rhyolite Basalt
• ExtrusiveExtrusive: crystallized from rapidly cooling magma extruded on the surface of the Earth as lava, …
Rock Rock TexturTextur
eeFig. 5.1
Intrusive: Course-grained,
interlocking
Extrusive: Fine-grained,
discrete crystals, often
glassy
Genetic Classification of Genetic Classification of Igneous RocksIgneous Rocks• ExtrusiveExtrusive: … or erupted as
pyroclastic material, i.e., fragmented pieces of magma ejected and cooled in the air.
Pumice
Scoria
Ash
Formation of Igneous Formation of Igneous RocksRocks
Pyroclasts
Extrusive
Intrusive
Porphyry: partially crystalline
Fig. 5.3
Process of Process of IntrusionIntrusion• Intrusive rocksIntrusive rocks fracture and cross-
cut the “country rock”. • Igneous rocks cool quickly near the intrusive contacts, and cause contact metamorphism.
Fig. 5.2
Composition and Composition and Classification of Classification of Igneous RocksIgneous Rocks
• Chemistry: e.g. % SiO2
• Mineralogy: e.g.–Felsic - high silica–Intermediate - intermediate silica
–Mafic - low silica–Ultramafic - very low silica
(continental crust)
(oceanic crust)
(mantle)
Felsic Igneous Rocks:Felsic Igneous Rocks:
Igneous rocks rich in mineralsIgneous rocks rich in minerals highhigh in silicain silica andand low inlow in iron and magnesium. They iron and magnesium. They
include:include:
GraniteGranite RhyoliteRhyolite
Mafic Igneous Rocks:Mafic Igneous Rocks:
Igneous rocks rich in mineralsIgneous rocks rich in minerals lowlow in silicain silica andand high inhigh in iron and magnesium. They iron and magnesium. They
include:include:GabbroGabbro BasaltBasalt
Intermediate Igneous Intermediate Igneous Rocks:Rocks:
Igneous rocks Igneous rocks intermediateintermediate in in composition between felsic and composition between felsic and
mafic igneous rocks. They mafic igneous rocks. They include:include:
Granodiorite (Dacite)Granodiorite (Dacite)Diorite (Andesite)Diorite (Andesite)
Ultramafic Igneous Ultramafic Igneous Rocks:Rocks:
Igneous rocks with Igneous rocks with very lowvery low silica content, consisting silica content, consisting
dominantly of mafic minerals. dominantly of mafic minerals. The most common ultramafic The most common ultramafic
rock is:rock is:Peridotite (no extrusive equivalent)Peridotite (no extrusive equivalent)
CompositioCompositional nal
ClassificaClassificationtion
Granite
Granite
Quartz
Orthoclase
Biotite
Plagioclase
CompositioCompositional nal
ClassificaClassificationtion
Granite
Granite
Granodiorite
Quartz
Amphibole
Plagioclase
CompositioCompositional nal
ClassificaClassificationtion
Granite
Granite
Granodiorite
Diorite
Plagioclase
Amphibole
CompositioCompositional nal
ClassificaClassificationtion
Granite
Granite
Granodiorite
Diorite
Gabbro
Plagioclase
Pyroxene
CompositioCompositional nal
ClassificaClassificationtion
Granite
Granite
Granodiorite
Diorite
Gabbro
Peridotite
Pyroxene
Olivine
Table. 5.2Felsic Intermediate Mafic
Granite GranodioriteDiorite Gabbro
BasaltAndesiteDaciteRhyolite
Viscosity
Melting Temperature
How do magmas form?How do magmas form?
When rocks melt (or partially melt).
When do rocks melt?When do rocks melt?
When the temperature exceeds the melting point of the rock or
some minerals within the rock.
Factors that Affect Factors that Affect Melting of Minerals (and Melting of Minerals (and
Rocks) Rocks)
• CompositionComposition: Felsic minerals melt at lower temperatures than mafic minerals
• PressurePressure: Increased pressures raises melting points
• Water ContentWater Content: Increased water content lowers melting points
The Formation The Formation of Magma of Magma ChambersChambers
Partial meltingPartial melting
Less dense magmaLess dense magma
Magma risesMagma rises
Magma pools in Magma pools in magma chambermagma chamber
Some minerals melt before others. Results in mixture of melt and solid.
Melt is less dense than solid. Low density minerals tend to melt first.
Buoyant melt migrates through rock pores and fractures.
- Covers 15,400 mi2 !! - Composition
- Granite- Monzonite- Granodiorite- Diorite- Even Gneiss
- All in one “magma chamber”
Why do magmas have such Why do magmas have such different compositions different compositions - - even when derived from a even when derived from a single “parent magma”single “parent magma”
e.g., granite, granodiorite, diorite
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