Laboratory Manual for Introductory Geology 4e

EXERCISE 7.1
Name:
Course:
Responses to Changing Metamorphic Conditions (continued )
Section:
Date:
Rock Polymorph T (°C)
Depth (km) based
on geothermal
gradient
P (kbar)
Depth (km) based
on geobaric gradient
A
B
C
(b) What does the discrepancy between depth estimates based on geothermal and geobaric gradients suggest about
metamorphism?
(c) What mineral changes would occur, and at what temperature and pressure, if
●●
Rock A was heated to 800°C without a change in pressure?
●●
Rock A experienced a drop in pressure to 1.5 kbar without a change in temperature?
●●
Rock B was heated to 700°C and pressure on it was increased to 10 kbar?
●●
Rock C was cooled to 500°C without a change in pressure?
(d) In some cases, it is possible to detect how rocks have changed position in the crust during metamorphism. Suppose
that Rock X has experienced a complex tectonic history in which T-P conditions changed over time as shown by
the dashed arrow.
●●
Describe the sequence of aluminosilicate phase changes in Rock X and the T-P conditions and depths at which
they occurred.
7.3 AGENTS OF METAMORPHISM
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