Page 170 - Microtectonics

6

Dilatation Sites –

Veins, Strain Shadows, Fringes and Boudins

6.1 D ilatation sites are voids in a rock filled with fluid, in which material may be
Introduction deposited from solution. They include veins, strain shadows, fringes and
microboudins. Voids can form in rocks at sites of high rheology contrast and/or
6.2 where fluid pressure is high. The filling of such dilatation sites can produce inter-
Veins esting patterns that may contain a lot of information on the way the void opened,
and indirectly on flow in the wall rock.
6.3 Veins can contain blocky, elongate or fibrous material and especially fibres
Fringe Structures carry much information on deformation in the rock. It is possible to obtain infor-
mation on relative motion of vein walls, but even on the relative velocity of vein
6.4 opening and filling using these structures.
Fringes and the Fringes are vein structures that occur on both sides of rigid objects such as
Deformation Path pyrite crystals. Fringes belong to the geometrically most complex microstruc-
tures, and contain detailed information on the progress of deformation in a vol-
6.5 ume of rock. Unfortunately, they are difficult to interpret, but a lot of progress
Non-Fibrous Strain has been made on this subject in recent years. The final sections of this chapter
Shadows and Strain Caps deal with strain caps, strain shadows and microboudinage.

6.6
Microboudinage