Laboratory Manual for Introductory Geology 4e

FIGURE 7.11 Settings of metamorphism.
Increasing
temperature
Igneous
pluton
Unmetamorphosed
sediment
(a) Contact metamorphism: at contacts between
igneous intrusions and wall rock.
7.5.2 Interpreting the Type of Metamorphism
and Geologic Setting
Geologists recognize six types of metamorphism, each associated
with a different geologic or tectonic setting, and each characterized
by a unique metamorphic agent or combination of agents.
TABLE 7.3 summarizes these relationships.
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Contact metamorphism (also called thermal metamorphism)
occurs where rocks are subjected to elevated temperatures
without changes in pressure or stress. This happens whenever
magma intrudes cooler rock and can occur in any tectonic
setting (FIG. 7.11a).
■■
Burial metamorphism occurs whenever rocks are buried very
deeply by overlying sediments (FIG. 7.11b). Pressure is the dominant
metamorphic agent, but as the geothermal gradient shows,
the deeper the burial, the higher the temperature.
■■
Dynamic metamorphism is caused by shear stress as blocks of rock grind
past one another in fault zones. The role of heat, which causes plastic flow
8 km
(b) Burial metamorphism: in deep sedimentary basins.
Burial metamorphism
Dynamic metamorphism
Sea level
Hot water rises and
reacts with rock.
Cold water sinks into crust.
Water heats up.
(c) Dynamic metamorphism: in transform and other major fault zones.
(d) Metasomatism: at hydrothermal vents along mid-ocean
ridges and at contacts between plutons and wall rock.
(continued)
188 CHAPTER 7 INTERPRETING METAMORPHIC ROCKS