Geoscience Reference
In-Depth Information
fold axial plane, and can be readily measured. If the cleavage
orientation is strongly affected by cleavage refraction (Section
8.3.1), estimate the overall orientation of the cleavage across
several beds - this will approximate to the axial plane of the
associated fold. If a later
transecting
cleavage cuts across folds,
it is very unlikely to be axial-planar to them. Intersection or
crenulation lineations may also be useful: the fl owchart below
shows how to discuminate between different lineations (see
8
Distinguishing
lineations
Slickenside
striations
grooves
on bedding or
cleavage plane
Forms of
lineations?
on fault
surface
Location?
mineral fibres
throughout
rock
Defined by
colour bands?
Slickenfibre
lineation
Yes
Defined by
microfold
hinges?
Yes
Crenulation
lineation
No
Cleavage on bedding
intersection lineation
No
Bedding on cleavage
intersection lineation
Form of
grains in
rock?
stretched
Stretching
lineation
merely
aligned
Igneous or
metamorphic
rock?
igneous
Magmatic
lineation
metamorphic
Alignment
lineation
