Lab 4A-Porphyroblasts & Shear Zones
VIEPS/Mainz Microstructure Course 
| TOC | Lecture 1 2 3 4 a b  5 a b | Lab 1 a b c 2 a b c 3 a b 4 a b 5 a b | Glossary Table 1 2 3 4 5 Index |

Further Reading:

An introduction to Metamorphic Petrology, 1989. Yardley Chapter 5 170-177

Shear-sense indicators: a review, 1991 Hanmer & Passchier Geol survey of Canada Paper 90-17

1) Experimental deformation of rock analogues

This movie shows the progressive simple shear deformation of a camphor clast in a matrix of OCP grains. This work was carried out by Coen ten Brink at the University of Utrecht. The rig is torsional, so that the shear zone boundaries are curved.

2) Movies of mantled porphyroclasts

The following four movies show computer simulations of the development of mantled porphyroclasts in simple shear, for 2 different flow patterns and for 2 different initial widths of the passive mantle.

Watch the movies and answer the questions below.

For each movie, describe (sketch) and name the wing geometries that develop. If there are transitions of wing geometries with progressive shear strain, describe them. It is best to do this in the form of a table:

For each of the movies, explain the development in wing geometry in terms of flow pattern, initial mantle radius and amount of strain.

For each of the movies and the developing wing geometries, can you use them as sense of shear indicators if (a) you know the orientation of the flow plane and (b) if you don't know the orientation of the flow plane?

Continue with lab 4.B