Petrology

Petrology

the branch of geology that deals with rocks, including their origin, structure, changes, etc.

Applications of Petrology

The fields of engineering, environmental, and urban geology are broadly concerned with applying the findings of geologic studies to construction engineering and problems of land use.

The location of a bridge, for example, involves geologic considerations in selecting sites for the supporting piers. The strength of geologic materials such as rock or compacted clay that occur at the sites of the piers should be adequate to support the load placed on them.

Engineering geology

is concerned with the engineering properties of geologic materials, including their strength, permeability, and compactability, and with the influence of these properties on the selection of locations for buildings, roads and railroads, bridges, dams, and other major civil features.

Urban geology

involves the application of engineering geology and other fields of geology to environmental problems in urban areas.

Environmental geology

is generally concerned with those aspects of geology that touch on the human environment.

Environmental and urban geology

deal in large measure with those aspects of geology that directly influence land use.

Environmental and urban geology

These include the stability of sites for buildings and other civil features, sources of water supply (hydrogeology), contamination of waters by sewage and chemical pollutants, selection of sites for burial of refuse so as to minimize pollution by seepage, and locating the source of geologic building materials, including sand, gravel, and crushed rock.

Since the late 1990s the importance of environmental geology has increased considerably in most developed countries as societies become aware of the environmental impact of humankind.

Metamorphic

Igneous

Sedimentary

3 Subdivision of Petrology

Igneous Petrology

concerned with the identification, classification, origin, evolution, and processes of formation and crystallization of the igneous rocks.

Andesite

is a fine-grained, extrusive igneous rock composed mainly of plagioclase with other minerals such as hornblende, pyroxene, and biotite. The specimen shown is about two inches (five centimeters) across.

Igneous Petrology

Most of the rocks available for study come from the Earth's crust, but a few, such as eclogites, derive from the mantle.

The scope of igneous petrology is very large because igneous rocks make up the bulk of the continental and oceanic crusts and of the mountain belts of the world, and they also include the high-level volcanic extrusive rocks and the plutonic rocks that formed deep within the crust.

Some of the major problems within the scope of igneous petrology are:

form and structure of igneous bodies

crystallization history of the minerals

classification of rocks

fractionation of parent magmas

mechanism of generation of magmas

history of formation and the composition of the present oceanic crust

evolution of igneous rocks

composition of the mantle

conditions of pressure and temperature

Some of the major problems within the scope of igneous petrology are:

form and structure of igneous bodies

crystallization history of the minerals

classification of rocks

fractionation of parent magmas

mechanism of generation of magmas

history of formation and the composition of the present oceanic crust

evolution of igneous rocks

composition of the mantle

conditions of pressure and temperature

Sedimentary Petrology

The field of ___ is concerned with the description and classification of sedimentary rocks, interpretation of the processes of transportation and deposition of the sedimentary materials forming the rocks, the environment that prevailed at the time the sediments were deposited, and the alteration (compaction, cementation, and chemical and mineralogical modification) of the sediments after deposition.

Carbonate Petrology

Clastic Petrology

two main branches of sedimentary petrology

Carbonate Petrology

One branch deals with carbonate rocks, namely limestones and dolomites, composed principally of calcium carbonate (calcite) and calcium magnesium carbonate (dolomite).

Clastic Petrology

The other principal branch of sedimentary petrology is concerned with the sediments and sedimentary rocks that are essentially noncalcareous.

Carbonate Petrology

Much of the complexity in classifying carbonate rocks stems partly from the fact that many limestones and dolomites have been formed, directly or indirectly, through the influence of organisms, including bacteria, lime-secreting algae, various shelled organisms (e.g., mollusks and brachiopods), and by corals.

In limestones and dolomites that were deposited under marine conditions commonly in shallow warm seas, much of the material initially forming the rock consists of skeletons of lime-secreting organisms.

In many examples, this skeletal material is preserved as fossils.

Some of the major problems of carbonate petrology concern the physical and biological conditions of the environments in which carbonate material has been deposited, including water depth, temperature, degree of illumination by sunlight, motion by waves and currents, and the salinity and other chemical aspects of the water in which deposition occurred.

Clastic Petrology

These include sands and sandstones, clays and claystones, siltstones, conglomerates, glacial till, and varieties of sandstones, siltstones, and conglomerates (e.g., the graywacke-type sandstones and siltstones).

These rocks are broadly known as clastic rocks because they consist of distinct particles or clasts.

Clastic petrology is concerned with classification, particularly with respect to the mineral composition of fragments or particles, as well as the shapes of particles (angular versus rounded), and the degree of homogeneity of particle sizes.

Other main concerns of clastic petrology are the mode of transportation of sedimentary materials, including the transportation of clay, silt, and fine sand by wind; and the transportation of these and coarser materials through suspension in water, through traction by waves and currents in rivers, lakes, and seas, and sediment transport by ice.

Metamorphic Petrology

focuses on the composition and texture of metamorphic rocks (rocks such as slate, marble, gneiss, or schist which started out as sedimentary or igneous rocks but which have undergone chemical, mineralogical or textural changes due to extremes of pressure, temperature or both)

Metamorphism

means change in form

In geology the term is used to refer to a solid state recrystallization of earlier igneous, sedimentary, or metamorphic rocks.

Contact Metamorphism

Regional Metamorphism

two main types of metamorphism

Contact Metamorphism

in which changes induced largely by increase in temperature are localized at the contacts of igneous intrusions

Regional Metamorphism

in which increased pressure and temperature have caused recrystallization over extensive regions in mountain belts.

Metamorphism

Other types of ____ include local effects caused by deformation in fault zones, burning oil shales, and thrusted ophiolite complexes; extensive recrystallization caused by high heat flow in mid-ocean ridges; and shock metamorphism induced by high pressure pacts of meteorites and craters on the Earth and Moon.

Metamorphic Petrology is concerned with:

field relations and local tectonic environments;

the description and classification of metamorphic rocks in terms of their texture and chemistry, which provides information on the nature of the pre-metamorphic material;

the study of minerals and their chemistry (the mineral assemblages and their possible reactions), which yields data on the temperatures and pressures at which the rocks recrystallized; and

the study of fabrics and the relations of mineral growth to deformation stages and major structures, which provides information about the tectonic conditions under which regional metamorphic rocks formed.

Metamorphic Petrology is concerned with:

field relations and local tectonic environments;

the description and classification of metamorphic rocks in terms of their texture and chemistry, which provides information on the nature of the pre-metamorphic material;

the study of minerals and their chemistry (the mineral assemblages and their possible reactions), which yields data on the temperatures and pressures at which the rocks recrystallized; and

the study of fabrics and the relations of mineral growth to deformation stages and major structures, which provides information about the tectonic conditions under which regional metamorphic rocks formed.

Metasomatism

A supplement to metamorphism is ___: the introduction and expulsion of fluids and elements through rocks during recrystallization.

Rock Cycle

States of Rock

Igneous

Metamorphic

Sedimentary

Magma

Sediment

Changes of State of the Rock

Melting

Cooling

Heat and Pressure

Weathering and erosion

Compaction and cementation

Rock Cycle

States of Rock

Igneous

Metamorphic

Sedimentary

Magma

Sediment

Changes of State of the Rock

Melting

Cooling

Heat and Pressure

Weathering and erosion

Compaction and cementation