Geology Reference
In-Depth Information
(a)
Figure 1.10.
Orthogonal fracture patterns (a) at the subcontinental scale in French Guyana (Choubert, 1974).
and /or the Lincoln Fault but in parallel with the Australian lineament pattern. A similar relation-
ship is discernible in French Guyana (Choubert, 1974) (Fig. 1.10a) where the major fractures trend
NNW-SSE and WNW-ESE, with the minor systems disposed either in parallel or NW-SE and
NE-SW. Such patterns have led some to consider that orthogonal fracture patterns originate as a
result of crustal stresses developed either during the emplacement of the crystalline masses, or
imposed subsequently. Many consider they have developed in relation to horizontal shearing in the
crust, such as that associated with plate migrations, past and present. This suggestion is sustained
by the swarms of minor fractures formed in parallel with the main partings. At a local scale, some
clefts or slots are linear, and run parallel to observed fractures, but are not themselves associated
with partings or at least not throughout their length.
