Page 255 - Microtectonics

9

Natural Microgauges

9.1 icrostructures have been used in the past to determine a sequence of defor-
Introduction Mmation structures and shear sense. Many microstructures, however, seem to
contain quantitative information as well. Obviously, the chemistry of minerals in
9.2 rocks has long been used to obtain data on metamorphic conditions and isotope
Strain Gauges ratios have been used to determine the age of minerals and rocks, but such data
can often only be obtained from powders or solutions, destroying the microstruc-
9.3 ture in the rock. This chapter presents a collection of microstructures which have
Vorticity Gauges been described in the literature as providing quantitative data from their geom-
etry alone, observed by non-destructive methods. We have named this type of
9.4 structures “microgauges” There are presently microgauges for strain, vorticity, stress
.
The Concept of orientation, differential stress, pressure, strain rate, temperature and rheology. The
Palaeostress Gauges subject is in full development and new tools are added at a regular pace.
Some geologists may wonder if this type of geometric microgauges cannot
9.5 simply be replaced by geochemical tools. Clearly, some types like those for stress
Gauges for the orientation , differential stress and vorticity cannot, but even gauges for pressure
Orientation of and temperature are useful in rocks where the chemistry cannot give a clear an-
Palaeostress swer, such as quartzites, or as a method to check results of geochemical techniques.
Principal Axes

9.6
Differential Stress Gauges
(Palaeopiezometers)
9.7
Pressure Gauges

9.8
Strain Rate Gauges

9.9
Temperature Gauges

9.10
Rheology Gauges