Petrology

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Petrology

• The study of the properties of rocks and the
  processes behind their formation
• Recognition and description of rocks
• Interpretation of their origin and history

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Instructor

• Michael F. Sheridan
• email
• mfs_at_geology.buffalo.edu
• Homepage
• http//www.eng.buffalo.edu/mfs
• Office hours
• We Th 100-200 PM

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Fundamentals

• Classification
• Changing States (Equilibrium)
• Plate Tectonics Petrology
• Thermodynamics
• Kinetics

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Magmatic Rock Bodies

• Study of rocks in hand sample
• Descriptive Petrochemistry
• Origin and evolution of magmas
• Interpretative Petrochemistry

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Study of rocks in hand sample

• Fabric
• Rock forming minerals
• Classification

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Fabric

• Phaneritic
• Aphanitic
• Glassy
• Clastic

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Sequence of mineral formation

• Degree of perfection of form
• Inclusion within other minerals
• Chemical zonation
• Signs of deformation
• Secondary growth
• Alteration to secondary minerals

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Rock forming minerals

• Feldspars
• Quartz
• Pyroxenes
• Olivines
• Amphiboles
• Micas
• Feldspathoids

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Classification

• Leucocratic
• Felsic
• Silicic
• Mafic
• Ultramafic

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Rock Suites

• Mafic and ultramafic
• Calc-alkaline
• Highly alkaline

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Descriptive Petrochemistry

• Chemical analyses
• Major elements
• Trace elements
• Relation of chemistry to mineralogy

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Chemical classification

• Silica concentration
• Acid gt66
• Intermediate 52-66
• Basic 45-52
• Ultrabasic lt45

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Silica saturation

• Oversaturated
• compatible with quartz
• Saturated
• Neither undersaturated minerals nor quartz
• Undersaturated
• undersaturated minerals

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Alkali/Aluminum saturation

• Relative to feldspar composition
• NaAlSi3O8
• Peralkaline
• Peraluminous
• Calc-alkaline

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CIPW norm

• Definition
• How calculated
• Use in classification

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Chemistry of rocks

• Major elements
• Trace elements
• CIPW norm

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From Mineral Composition to Rock Composition

• Determine the minerals present
• estimate their abundance
• Calculate the rock composition using proper
  weightings

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Interpretative Petrochemistry

• Models of crystallization
• Concepts of magma movement
• Secondary alteration

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Ultramafic rock bodies

• Petrography of gabbroic and ultramafic rocks
• Nature of Plutons
• Oceanic subalkaline basaltic to ultramafic
  associations
• Ophiolites

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Petrography of gabbroic and ultramafic rocks

• General
• phaneritic grain size
• may be nearly monomineralic
• Pyroxene
• Olivine
• Plagioclase
• Fabric
• Slow sequential growth
• Hypidiomorphic granular

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Petrography of gabbroic and ultramafic rocks

• Classification
• Alteration
• deuteric and hydrothermal alteration
• Serpentine
• Secondary iron oxide
• brucite talc

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Nature of Gabbroic Plutons

• Dikes, sills, and plugs
• Layered intrusions
• Slow shallow cooling of basaltic magma