Chapter 7: The Rock Cycle

Question 1

Define ‘Bedding’.

Answer 1

The layered arrangement of strata in a body of sediment or sedimentary rock.

Question 2

Define ‘Biogenic sediment’.

Answer 2

Chemical sediment formed as a result of biochemical reactions in water.

Question 3

Define ‘Burial metamorphism’.

Answer 3

Metamorphism caused solely by the burial of sedimentary or pyroclastic rocks.

Question 4

Define ‘Cementation’.

Answer 4

The joining together of particles in a loose sediment through the addition of a cementing agent.

Question 5

Define ‘Chemical sediment’.

Answer 5

Sediment formed by precipitation (by processes such as evaporation) of minerals from solutions in water.

Question 6

Define ‘Chemical weathering’.

Answer 6

The decomposition of rocks through chemical reactions such as hydration and oxidation.
The principal agent is a weak solution of carbonic acid (H2CO3) that is formed when rainwater and groundwater dissolve carbon dioxide.

Question 7

Define ‘Clastic sediment’.

Answer 7

The loose fragmented debris produced by the mechanical breakdown of older rocks. The four main size classes are gravel, sand, silt, and clay.

Question 8

Define ‘Clay’.

Answer 8

The smallest clastic particles in sediment. The term is also used for a family of minerals.

Question 9

Define ‘Compaction’.

Answer 9

Reduction of the volume of sediment as a result of increased pressure.

Question 10

Define ‘Contact metamorphism’.

Answer 10

Temperature- driven metamorphism adjacent to an intrusive igneous body.

Question 11

Define ‘Correlation (stratigraphic)’.

Answer 11

Determination of the equivalence of age of the succession of strata found in two or more different areas.

Question 12

Define ‘Crystallization (of magma)’.

Answer 12

The set of processes whereby crystals of individual mineral components nucleate and grow in a cooling magma.

Question 13

Define ‘Denudation’.

Answer 13

The sum of the weathering, mass-wasting, and erosional processes that result in the progressive lowering of the Earth’s surface.

Question 14

Define ‘Deposition (of sediment)’.

Answer 14

Accumulation of sediment following transport.

Question 15

Define ‘Diagenesis’.

Answer 15

The various low-temperature and low-pressure changes that happen to a sediment after deposition.

Question 16

Define ‘Erosion’.

Answer 16

The complex group of related processes by which rock is broken down physically and chemically and the products are moved.

Question 17

Define ‘Facies (metamorphic)’.

Answer 17

The assemblage of minerals formed during metamorphism of a rock of a given composition subjected to a given temperature and pressure.

Question 18

Define ‘Foliation’.

Answer 18

The planar texture of mineral grains, principally micas, produced by metamorphism.

Question 19

Define ‘Geologic time scale’.

Answer 19

Numerical time scale fitted to the relative ages of the geologic column.
The geologic column summarizes in chronological order the succession of known rock units determined through the principles of stratigraphy, stratigraphic correlation, and cross-cutting relationships.

Question 20

Define ‘Gravel’.

Answer 20

The coarsest particles of clastic sediment.

Question 21

Define ‘Igneous rock’.

Answer 21

Rock formed by the cooling and consolidation of magma.

Question 22

Define ‘Joint’.

Answer 22

Sheet-like fractures in rock.

Question 23

Define ‘Landslide’.

Answer 23

Any perceptible downslope movement of a mass of bedrock or regolith, or a mixture of the two.

Question 24

Define ‘Lithification’.

Answer 24

The processes by which sediment and soil become rock.
The first stage is burial and compaction. Loose grains of sediment adhere to one another as a result of cementation or recrystallization.

Question 25

Define ‘Lithology’.

Answer 25

Description of a rock on the basis of color, mineralogical composition, and grain size.

Question 26

Define ‘Mass wasting’.

Answer 26

The movement of regolith downslope by gravity without the aid of a transporting medium.
The composition and texture of the sediment involved, the amount of water and air involved, and the steepness of the slope influence the type and velocity of movement.

Question 27

Define ‘Metamorphic rock’.

Answer 27

Rock whose original compounds or textures, or both, have been transformed to new compounds and new textures by reactions in the solid state as a result of high temperature, high pressure, or both.
Metamorphism describes changes in mineral assemblage and texture that occur in the solid state, at temperatures above 150°C and pressures in excess of 300 MPa. The upper limit to metamorphism is reached when rock melting begins.

Question 28

Define ‘Metamorphism’.

Answer 28

All changes in mineral assemblage and rock texture, or both, that take place in sedimentary and igneous rocks in the solid state within the Earth’s crust as a result of changes in temperature and pressure.

Question 29

Define ‘Metasomatism’.

Answer 29

The metamorphic pro- cess in which abundant fluids change the composition and texture of a rock.

Question 30

Define ‘Physical (mechanical) weathering’. Give examples.

Answer 30

The disintegration (physical breakup) of rocks.
Involves processes such as jointing, frost wedging, precipitation of salts in fractures, fire breakage, and wedging by plant roots.

Question 31

Define ‘Recrystallization’.

Answer 31

The formation, in the solid state, of new crystalline minerals grains in a rock.

Question 32

Define ‘Regional metamorphism’.

Answer 32

Metamorphism affecting large volumes of crust and involving both mechanical and chemical changes.

Question 33

Define ‘Regolith’.

Answer 33

The irregular blanket of loose, noncemented rock particles that covers the Earth.

Question 34

Define ‘Rock cycle’.

Answer 34

The cyclic movement of rock material, in the course of which rock is created, destroyed, and altered through the operation of internal and external Earth processes.

Question 35

Define ‘Sand’.

Answer 35

Clastic particles intermediate in size between gravel and silt.

Question 36

Define ‘Sediment’.

Answer 36

Regolith that has been transported by any of the external processes.

Question 37

Define ‘Sedimentary rock’.

Answer 37

Any rock formed by chemical precipitation or by sedimentation and cementation of mineral grains transported to a site of deposition by water, wind, ice, or gravity.
Bedding and the presence of fossils are typical features of sedimentary rock. Sedimentary rock contains information about the environments in which the sediment was formed, transported, deposited, and lithified.

Question 38

Define ‘Silt’.

Answer 38

Fine clastic particle intermediate in size between sand and clay.

Question 39

Define ‘Stratigraphy’.

Answer 39

The study of strata.

Stratigraphy is based on the principles of original horizontality, superposition, and lateral continuity.

Question 40

Define ‘Stratum (pl. strata)’.

Answer 40

A distinct layer of sediment that accumulated at the Earth’s surface.
Each stratum or bed differs from adjacent beds because of changes that occurred in the environment as the sediment accumulated.

Question 41

Define ‘Stress’.

Answer 41

Force per unit area acting on a body.

Question 42

Define ‘Unconformity’.

Answer 42

A substantial break or gap in a stratigraphic sequence that marks the absence of part of the rock record.
The three important kinds of unconformities are nonconformities (sediment deposited on igneous or metamorphic), angular unconformities (uplifting and erosion), and disconformities (erosion).

Question 43

Define ‘Weathering’.

Answer 43

The chemical alteration and mechanical breakdown of rock materials during exposure to air, moisture, and organic matter.

Question 44

The locations where clastic sediment is deposited are largely controlled by plate tectonics. They include …?. The deposition of chemical and biogenic sediment is not as strongly influenced by plate tectonics because it occurs in open aquatic environments.

Answer 44

Low- lying rift valleys, structural basins in mountain ranges, and deep oceanic trenches in subduction zones near continents.

Question 45

The four classes of clastic sedimentary rock are …?, which form from gravel, sand, silt, and clay, respectively.

Answer 45

Conglomerate, sandstone, siltstone (or mudstone), and shale.

Question 46

Chemical sedimentary rock results from the lithification of chemical sediment. ___, which forms from lithified shells and other skeletal material from marine organisms, is the most important rock that forms from the lithification of biogenic sediment.

Answer 46

Limestone.

Question 47

Chemical weathering can turn K-feldspar to …?

Answer 47

Clay. This can happen especially in granite, which is high in k-feldspar.

Question 48

Stratigraphic correlation is …?

Answer 48

The determination of equivalence in age of the succession of strata found in two or more different areas.

Question 49

Using ___ ___to establish the numerical ages of certain rock units, scientists have been able to fit a scale of numerical time to the geologic column.

Answer 49

Radiometric dating.

Question 50

Igneous rock textures form under uniform stress because igneous rocks crystallize from liquids, which cannot sustain differential stress. Is the same true for metamorphic rocks?

Answer 50

In contrast, the textures of many metamorphic rocks record evidence of differential stress, most commonly as foliation, a layered texture that results from the alignment of platy or elongate minerals.

Question 51

What determines the assemblage of minerals that will develop in metamorphic rocks?

Answer 51

The starting composition of a rock, in combination with the temperature and pressure of metamorphism.

Question 52

The three most important kinds of metamorphism are ___, ___, and ___ metamorphism. They differ in conditions of temperature, pressure, and differential stress, and in the relative importance of mechanical deformation and chemical recrystallization.

Answer 52

Contact, burial, and regional.

Question 53

What is Mechanical deformation? Chemical recrystallization?

Answer 53

Mechanical deformation includes grinding, crushing, and the development of foliation.
Chemical recrystallization includes changes in mineral composition, the growth of new minerals, and losses of H2O and CO2 that occur with metamorphism.

Question 54

Metamorphic rocks are named on the basis of texture and mineral assemblage. The products of the metamorphism of ___ are slate, phyllite, schist, and gneiss, in order of increasing metamorphic grade.

Answer 54

Shale.

Question 55

___ undergoes metamorphism under conditions where H2O can enter the rock and form hydrous minerals, resulting in the metamorphic rocks greenschist, amphibolite, and granulite.

Answer 55

Basalt.

Question 56

The metamorphic derivatives of ___ and ___ are marble and quartzite, respectively; they are typically monomineralic and nonfoliated.

Answer 56

Limestone and sandstone.

Question 57

The metamorphic facies concept holds that …?

Answer 57

For a given range of temperature and pressure, and a given rock composition, the assemblage of minerals formed during metamorphism is always the same.
(More in Chapter Summary, point 16?)

Question 58

Melting leads to the development of three main magma types, ___, ___, and ___, the properties of which are mainly determined by their compositions. Partial and fractional melting can lead to variations in magma types.

Answer 58

Basaltic, andesitic, and rhyolitic.

Question 59

Cooling and crystallization, in which crystals nucleate and grow in a cooling magma, combine with composition to determine the properties of igneous rock. What does the rate of cooling influence?

Answer 59

The rate of cooling influences how large the individual mineral grains eventually grow.

Question 60

When magma or lava of a given composition solidifies, the mineral assemblage that forms is the same for intrusive and extrusive rock; the differences are textural. How are volcanic and plutonic textures characterized?

Answer 60

Volcanic rock is characterized by fine grain size or glassy texture, whereas plutonic rock tends to be coarse-grained because the magma cools slowly.

Question 61

What rocks do basaltic, andesitic, and rhyolitic magma yield?

Answer 61

Basaltic magma yields the mafic volcanic rock basalt and its plutonic equivalent, gabbro. Andesitic magma yields the intermediate volcanic rock andesite and its plutonic equivalent, diorite. Rhyolitic magma yields the felsic volcanic rock rhyolite and its plutonic equivalent, granite.

Question 62

What contributes to the diversity of igneous rock types?

Answer 62

Differences in texture that develop during cooling and crystallization, and partly from partial or fractional melting, which can lead to the separation of melt from residual solid rock of a different composition. Fractional crystallization also contributes to the diversification of igneous rock types.

Question 63

What five main factors interact to determine the character of landforms?

Answer 63

Process, climate, lithology, relief, and time.
The constant changes reflect ongoing interactions between the internal forces of plate tectonics, isostasy, and volcanism that uplift the lithosphere, and the external forces of denudation that wear it down. Denudation begins as soon as a mountain range is uplifted, and continues long after active tectonic uplift has ceased.

Question 64

How is basaltic, andesitic and rhyolitic magma formed?

Answer 64

Basaltic: Partial melting of mantle that erupts where curst is splitting, i.e. mid-ocean spreading centres and above mantle hotspots.
Andesitic: Wet partial melting of mantle overlying subducting oceanic plate.
Rhyolitic: Melting at base of continental crust. Assimilates silica-rich crustal material as rising.