CAPTIONS FOR IMAGES SHOWN IN ESS 211 LECTURE
Illustrating flow in fluids and in the solid state.
1. Surface of a pond. The foam on the surface is being passively deformed merely as
a marker in response to flow if the fluid, water.
2. Basaltic magma at Kilauea, Hawaii, flowing as a melt—a true fluid.
3. Surface of a solidified flow at Kilauea; the molten magma has frozen and
crystallized into very fine-grained pyroxene and feldspar
4. Same area as image 3: note the folds in the surface of the flows.
5. Images 5-8 are in the Realmonte salt mine west of Agrigento, Sicily. They
illustrate solid-state flow of halite. Halite is brittle at room temperature (i.e.,
block of salt will fracture when struck by a hammer) but above about 50° C the
crystals allow the rock salt to flow without melting or brittle fracture. This image
was taken in a room in the mine about 100 m below the surface. Note the
banding: the white layers are nearly pure halite [NaCl], and the dark layers are
rich in clay. All the layers were deposited about 7 my ago in dessicated basins
marginal to the Mediterranean as seawater dried up.
6. Layers of halite [and clay] folded by solid-state flow.
7. Close up of folded layers.
8. Another close up. Coin is one euro.
9. An aerial view of folds in the Helvetic Alps, Switzerland. Strata are Cretaceous,
about 80-100 my old. Height of the cliff is estimated at several hundred meters.
This is an example of solid-state flow [about 200° C] of limestone.
10. Images 11 and 12 are of metamorphic rocks, probably originally sandstone and
mudstone, that recrystallized at high temperatures, probably 500-600° C, and
deformed at these temperatures by solid-state flow. White layers are rich in quartz
and plagioclase feldspar; black layers were probably originally basalt dikes and
due to metamorphism now consist of hornblende [amphibole] and plagioclase.
Ventisquero Italia, Cordillera Darwin, Tierra del Fuego.
11. See above.
12. Same locality. Here folded metamorphic rock recording solid-state flow was later
fractured—deformed by brittle failure—and a dike of pegmatite, a coarse-grained
rock consisting of quartz and feldspar, occupied the fracture. The same rock or
material can behave differently as environmental conditions change.
13. Schematic illustrating how metamorphic core complex forms. This is a structural
feature that exposes deep crust exhumed in association with extension and normal
faulting, juxtaposed with rocks that have experienced brittle deformation. Highgrade metamorphic rocks that show ductile deformation features are found in the
footwall, while lower-grade rocks that exhibit evidence of brittle-ductile to brittle
deformationare found in the hanging wall.