Laboratory Manual for Introductory Geology 4e

EXERCISE 5.9
Explaining Features of Igneous Rock Found in the Field (continued )
Name:
Course:
Section:
Date:
(b) The Palisades Sill on the west bank of the Hudson River in New Jersey is a shallow basaltic intrusion. The sill varies
texturally, as shown in the figure below (left). Explain how the observed mineralogical and textural variations were
produced during the crystallization of the sill.
The Palisades Sill on the west bank of the Hudson River
What geologists have discovered about the Palisades Sill
Host rock
Coarse basalt
Fine basalt
Zone of
concentrated
olivine
(c) In the figure below, a thin brown zone of weathering highlights thin iron-rich zones that separate host granite from
mafic xenoliths (inclusions). Based on the magmatic processes described above, suggest an origin for these zones.
Mafic inclusions (xenoliths) in a granitic pluton
Iron-rich zones
Xenoliths
128 CHAPTER 5 USING IGNEOUS ROCKS TO INTERPRET EARTH HISTORY