IgneousRocks1

Slide1 : ESCI 101: Lecture The Rock Cycle andamp; Igneous Rocks February 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 andamp; Company) Enchanted Rock


The Rock Cycle : The Rock Cycle Melting andamp; Intrusion Solidification of melt Mountain Building Uplift andamp; Exposure Weathering Erosion andamp; Transport Deposition andamp; Burial Metamorphism Melting andamp; Intrusion Fig 4.9


Slide3 : 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#4 An Alternate Rock Cycle : Pop-HW#4 An Alternate Rock Cycle Melting andamp; Intrusion Solidification of melt ??? ??? ??? ??? ??? -andgt; Sandstone Fig 4.9 X X X


(a) The Rock Cycle : (a) The Rock Cycle Fig 4.9 E.g., Convergent Plate Boundary Subducting slab Mantle melting Bouyant rise of melt


(b) The Rock Cycle : (b) The Rock Cycle Fig 4.9 E.g., Convergent Plate Boundary Solidification of melt Volcanic activity Intrusive rocks Extrusive rocks


Genetic Classification of Igneous Rocks : Genetic Classification of Igneous Rocks Granite Gabbro Intrusive: crystallized from slowly cooling magma intruded within the Earth’s crust; e.g. granite, gabbro.


Rock Texture : Rock Texture Fig. 5.1 Intrusive: Course-grained, interlocking


Genetic Classification of Igneous Rocks : Genetic Classification of Igneous Rocks Rhyolite Basalt Extrusive: crystallized from rapidly cooling magma extruded on the surface of the Earth as lava, …


Rock Texture : Rock Texture Fig. 5.1 Intrusive: Course-grained, interlocking Extrusive: Fine-grained, discrete crystals, often glassy


Genetic Classification of Igneous Rocks : Genetic Classification of Igneous Rocks Extrusive: … or erupted as pyroclastic material, i.e., fragmented pieces of magma ejected and cooled in the air. Pumice Scoria Ash


Formation of Igneous Rocks : Formation of Igneous Rocks Pyroclasts Extrusive Intrusive Porphyry: partially crystalline Fig. 5.3


Process of Intrusion : Process of Intrusion Intrusive 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 Classification of Igneous Rocks : Composition and Classification of Igneous 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:Igneous rocks rich in minerals high in silica and low in iron and magnesium. They include: : Felsic Igneous Rocks: Igneous rocks rich in minerals high in silica and low in iron and magnesium. They include: Granite Rhyolite


Mafic Igneous Rocks:Igneous rocks rich in minerals low in silica and high in iron and magnesium. They include: : Mafic Igneous Rocks: Igneous rocks rich in minerals low in silica and high in iron and magnesium. They include: Gabbro Basalt


Common Minerals : Common Minerals


Intermediate Igneous Rocks:Igneous rocks intermediate in composition between felsic and mafic igneous rocks. They include: : Intermediate Igneous Rocks: Igneous rocks intermediate in composition between felsic and mafic igneous rocks. They include: Granodiorite (Dacite) Diorite (Andesite)


Ultramafic Igneous Rocks:Igneous rocks with very low silica content, consisting dominantly of mafic minerals. The most common ultramafic rock is: : Ultramafic Igneous Rocks: Igneous rocks with very low silica content, consisting dominantly of mafic minerals. The most common ultramafic rock is: Peridotite (no extrusive equivalent)


Slide20 : Fig. 5.4


Compositional Classification : Compositional Classification Granite Granite Quartz Orthoclase Biotite Plagioclase


Compositional Classification : Compositional Classification Granite Granite Granodiorite Quartz Amphibole Plagioclase


Compositional Classification : Compositional Classification Granite Granite Granodiorite Diorite Plagioclase Amphibole


Compositional Classification : Compositional Classification Granite Granite Granodiorite Diorite Gabbro Plagioclase Pyroxene


Compositional Classification : Compositional Classification Granite Granite Granodiorite Diorite Gabbro Peridotite Pyroxene Olivine


Slide26 : Table. 5.2 Felsic Intermediate Mafic Granite Granodiorite Diorite Gabbro Basalt Andesite Dacite Rhyolite Viscosity Melting Temperature


How do magmas form? : How do magmas form? When rocks melt (or partially melt). When do rocks melt? When the temperature exceeds the melting point of the rock or some minerals within the rock.


Factors that Affect Melting of Minerals (and Rocks) : Factors that Affect Melting of Minerals (and Rocks) Composition: Felsic minerals melt at lower temperatures than mafic minerals Pressure: Increased pressures raises melting points Water Content: Increased water content lowers melting points


The Formation of Magma Chambers : The Formation of Magma Chambers Partial melting Less dense magma Magma rises Magma pools in magma 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.


Slide30 : Covers 15,400 mi2 !! Composition Granite Monzonite Granodiorite Diorite Even Gneiss All in one 'magma chamber'


Why do magmas have such different compositions - even when derived from a single “parent magma” : Why do magmas have such different compositions - even when derived from a single 'parent magma' e.g., granite, granodiorite, diorite


Magma Differentiation : Magma Differentiation The process by which rocks of various compositions can arise from a uniform parent magma Occurs because different minerals crystallize at different temperatures (i.e., the opposite of partial melting) Tune in Wednesday for the exciting conclusion!