Slip systems

The atomic plane along which the dislocations loops move is the slip plane ; the direction of the Burgers’s vector is the slip direction. A slip plane and its associated slip direction form a slip system. Usual slip planes are dense atomic planes, such as the basal plane in quartz (0001) or the (001) plane in olivine, and the slip direction is a dense atomic row within the slip plane.

In quartz the low-T slip system is (0001) <a>, and the high-T slip systems are (10-10) <a> and (10-11) <a> in addition to the low-T one :

Examine the consequences in a fabric diagram of quartz

In olivine, the HT-slip system is [100] (001) and [100] (010). In orthopyroxene, the HT-slip system is [001] (100).

Examine the consequences in fabric diagrams of olivine

Figure. Kinematic analysis in a peridotite. Theoretical analysis and fabric diagrams of olivine (ol) and orthopyroxene (opx). The slip direction in olivine is [100] ; in opx, it is [001].

4. Rôle of stress : multiplication of dislocations

No stress, no deformation. The role of stress is to multiply the dislocations. Essentially through the basic mechanism of the Franck-Read mill (Figure).

6. Rôle of temperature: increases the mobility of dislocations

The principal mechanism is, through the increasing mobility of point defects, to help the edges do climb and the screws to change their slip plane.

Date: 2015-01-29; view: 1688