Page 89 - Microtectonics

4.2 · Foliations 77

Box 4.2 Continued
entation, but not necessarily a GSPO (Eisbacher 1970; Garcia Celma attractor (Pauli et al. 1996; Herwegh and Handy 1998). DSPO can
1982; Knipe and Law 1987; Lloyd et al. 1992; Law et al. 1990; Herwegh be an active foliation (Sect. 4.2.9.2) if it is defined by shear bands,
and Handy 1998). Such domains can have an elongate shape and but DSPO can also be strain-insensitive. It may form by SGR re-
define a domain shape preferred orientation (DSPO) (Figs. B.4.1, crystallisation of larger grains.
B.4.2) that can form a weak foliation oblique to other fabric ele- All types of shape fabrics can occur combined in a single rock
ments. DSPO have also been referred to as orientation families of fabric, and they may also combine with other foliation and linea-
grains. Individual domains can also change shape by recrystallisa- tion types. A special name for a GSPO oblique to ASPO or mylonitic
tion or rotation of grains. DSPO is usually inclined in the same di- foliation is oblique foliation (Sect. 5.6). Three possible combinations
rection as GSPO in the rock, but at a smaller angle to the fabric of LPO are shown in Fig. B.4.2.

Fig. B.4.1.
Diagram depicting the effect
of an initial fabric on the
development of a shape pre-
ferred orientation (Fig. B.4.2)
with respect to dynamic
recrystallization. The dia-
gram is highly simplified.
Represented polymineralic
rocks are limited to rocks
with two mineral species.
Grain sizes of recrystallised
grains are assumed to be the
same as initially fine grained
phases. (After Piazolo and
Passchier 2002a)

Fig. B.4.2.
Different types of shape
fabrics. a, b and c show sin-
gle shape fabric types,
d, e and f show combina-
tions of shape fabrics