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subparallel to the trend of the domain, and microlithons are bounded by the cleavage domains. Spaced cleavages can be categorized based on whether the grains inside the microlithons are randomly oriented or contain microfolds from a previous foliation fabric. Other descriptions for spaced cleavages include the spacing size, the shape and percentage of cleavage domains, and the transition between cleavage domains and microlithons.
176:
130:
103:
There are a variety of definitions for cleavage, which may cause confusion and debate. The terminology used in this article is based largely on
Passchier and Trouw (2005). They state that cleavage is a type of secondary foliation in fine grained rocks characterized by planar fabric elements that form
253:
Cleavage foliations may result due to stress-induced solution transfer by the redistribution of inequant mineral grains by pressure solution and recrystallization. This would also help to increase rotation of elongate and tabular mineral grains. Mica grains undergoing solution transfer will align in
202:
Crenulation cleavage contains microlithons that were warped by a previous foliation. Folding occurs when there are multiple phases of deformation, the latter one causes symmetric or asymmetric microfolds that deform previous foliations. The type of crenulation cleavage pattern that forms depends on
282:
This process occurs either after deformation or in the absence of dynamic deformation. Depending on the intensity of heat during recrystallization, the foliation will either be strengthened or weakened. If the heat is too intense, foliation will be weakened due to the nucleation and growth of new
211:
Disjunctive cleavage describes a type of spaced cleavage where the microlithons are not deformed into microfolds, and formation is independent from any previous foliation present in the rock. A common outdated term for disjunctive cleavage is fracture cleavage. It is recommended that this term be
179:
A thin section depicting spaced cleavage. The cleavage domains are darker biotite grains, and the microlithons between consist of mostly muscovite and quartz. The grains in the microlithons are starting to align in a preferred orientation. A new foliation overprinted an old, showing the beginning
306:
Cleavages display a measurable geometric relationship with the axial plane of folds developed during deformation and are referred to as axial planar foliations. The foliations are symmetrically arranged with respect to the axial plane, depending on the composition and competency of a rock. For
184:
Spaced cleavage occurs in rocks with minerals that are not evenly distributed, and as a result the rock forms discontinuous layers or lenses of different types of minerals. Spaced cleavage contains two types of domains; cleavage domains and microlithons. Cleavage domains are planar boundaries
315:
sequences are folded during very-low to low grade metamorphism, cleavage forms parallel to the fold axial plane, particularly in the clay-rich parts of the sequence. In folded alternations of sandstone and mudstone the cleavage has a fan-like arrangement, divergent in the mudstone layers and
228:
The development of cleavage foliation involves a combination of various mechanisms dependent on the rocks composition, tectonic processes, and metamorphic conditions. The magnitude and orientation of stress coupled with pressure and temperature conditions determine how a mineral is deformed.
197:
Petrographic thin section showing
Crenulation Cleavage within the late Middle Ordovician (Llandeilian Stage) Hendre Shales Formation (Drefach Group) in a roadside exposure along the B4299 Meidrim road heading south towards St Clears, Carmarthenshire, Wales. A first (Caledonoid) and second
273:
stored in deformed grains. Deformed micas can store a sufficient amount of strain energy that can allow recrystallization to occur. This process allows oriented regrowth of both old and new minerals into the damaged crystal lattice during cleavage development.
316:
convergent in the sandstones. This is thought to be because the folding is controlled by buckling of the stronger sandstone beds with the weaker mudstones deforming to fill the intervening gaps. The result is a feature referred to as foliation fanning.
137:
Continuous or penetrative cleavage describes fine grained rocks consisting of platy minerals evenly distributed in a preferred orientation. The type of continuous cleavage that forms depends on the minerals present. Undeformed platy minerals such as
120:
The presence of fabric elements such as preferred orientation of platy or elongate minerals, compositional layering, grain size variations, etc. determines what type of cleavage forms. Cleavage is categorized as either continuous or spaced.
229:
Cleavages form approximately parallel to the X-Y plane of tectonic strain and are categorized based on the type of strain. The mechanisms currently believed to control cleavage formation are rotation of mineral grains, solution transfer,
154:
deform into a grain shape preferred orientation. Continuous cleavage is scale dependent, so a rock with a continuous cleavage on a microscopic level could show signs of spaced cleavage when observed on a macroscopic level.
73:. The degree of deformation and metamorphism along with rock type determines the kind of cleavage feature that develops. Generally, these structures are formed in fine grained rocks composed of minerals affected by
96:, while secondary deals with rocks that undergo metamorphism as a result of deformation. Cleavage is a type of secondary foliation associated with fine grained rocks. For coarser grained rocks,
287:. If minimal heat is applied to a rock with a preexisting foliation and without a change in mineral assemblage, the cleavage will be strengthened by growth of micas parallel to foliation.
163:
Since the nature of cleavage is dependent on scale, slaty cleavage is defined as having 0.01 mm or less of space occurring between layers. Slaty cleavage often occurs after
167:
and is the first cleavage feature to form after deformation begins. The tectonic strain must be enough to allow a new strong foliation to form, i.e. slaty cleavage.
241:
During ductile deformation, mineral grains with a high aspect ratio are likely to rotate so that their mean orientation is in the same direction as the XY plane of
448:
220:
When an older cleavage foliation is erased and replaced by a younger foliation due to stronger deformation and is evidence for multiple deformation events.
88:
element that describes the way planar features develop in a rock. Foliation is separated into two groups: primary and secondary. Primary deals with
269:
occurs when a rock undergoes metamorphic conditions and reequilibrium of a minerals chemical composition. This happens when there is a decrease in
478:
258:
processes, the grain will be extended along the XY-plane of finite strain. This process shapes grains into a preferred orientation.
329:
437:
133:
Metamorphosed shale depicting slaty cleavage. Note the grains of mica, quartz, and ilmenite aligned with a preferred orientation.
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332:
that may have a large influence on the mechanical behavior (strength, deformation, etc.) of rock masses in, for example,
408:
422:
471:
358:
104:
in a preferred orientation. Some authors choose to use cleavage when describing any form of secondary foliation.
506:
302:
in sandstone shale sequences with axial planar cleavage, refraction of cleavage visible on right-hand limb
1165:
1144:
464:
449:
Price, N.J., Cosgrove, J.W., 1990, Analysis of geological structures, Cambridge
University Press, 507pp.
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a preferred orientation. If the minerals grains affected by pressure solution are deformed through
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avoided because of the tendency to misinterpret the formation of a cleavage feature.
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245:. Mineral grains may fold if oriented perpendicular to shortening direction.
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Report of IUGS sub-commission on the systematics of metamorphic rocks.
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198:(Armorican) cleavage are identified. Field of view = 1 cm diam.
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align in a preferred orientation, and minerals such as
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randomly oriented crystals and the rock will become a
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lithology and degree of deformation and metamorphism.
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Different ways in which a cleavage can develop in a
116:
Schematic drawing of continuous and spaced cleavage
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407:Passchier, C. W.; Trouw, R. A. J. (2005).
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100:is used to describe secondary foliation.
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18:
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65:feature that develops as a result of
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107:
722:List of tectonic plate interactions
27:. A: original sedimentary rock; B:
13:
170:
14:
1182:
158:
1140:
1139:
359:Dynamic quartz recrystallization
233:, and static recrystallization.
180:signs of a crenulation cleavage.
1:
364:
237:Mechanical rotation of grains
61:, describes a type of planar
223:
7:
347:
80:Cleavage is a type of rock
10:
1187:
320:Engineering considerations
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1107:
1074:
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868:
825:
807:Thick-skinned deformation
601:
560:
494:
328:a cleavage plane forms a
267:Dynamic recrystallization
262:Dynamic recrystallization
231:dynamic recrystallization
812:Thin-skinned deformation
588:Stereographic projection
326:geotechnical engineering
278:Static recrystallization
578:Orthographic projection
561:Measurement conventions
507:Lamé's stress ellipsoid
303:
216:Transposition cleavage
199:
181:
134:
117:
47:
1089:Paleostress inversion
782:Strike-slip tectonics
652:Extensional tectonics
632:Continental collision
502:Deformation mechanism
298:
291:Relationship to folds
196:
178:
132:
115:
22:
16:Planar fabric in rock
667:Fold and thrust belt
307:example, when mixed
207:Disjunctive cleavage
189:Crenulation cleavage
1099:Section restoration
975:Rock microstructure
637:Convergent boundary
537:Strain partitioning
522:Overburden pressure
512:Mohr–Coulomb theory
125:Continuous cleavage
1166:Structural geology
1076:Kinematic analysis
732:Mountain formation
647:Divergent boundary
612:Accretionary wedge
488:Structural geology
354:Cleavage (crystal)
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182:
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55:structural geology
48:
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1084:3D fold evolution
970:Pressure solution
965:Oblique foliation
845:Exfoliation joint
835:Columnar jointing
495:Underlying theory
249:Solution transfer
108:Types of cleavage
94:sedimentary rocks
75:pressure solution
1178:
1143:
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888:Detachment fault
883:Cataclastic rock
817:Thrust tectonics
787:Structural basin
762:Pull-apart basin
702:Horst and graben
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1023:Detachment fold
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923:Transform fault
898:Fault mechanics
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757:Plate tectonics
707:Intra-arc basin
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568:Brunton compass
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417:. p. 366.
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256:plastic crystal
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171:Spaced cleavage
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29:pencil cleavage
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517:Mohr's circle
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38:(parallel to
37:
34:
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26:
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944:
913:Thrust fault
602:Large-scale
573:Inclinometer
547:Stress field
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71:metamorphism
50:
49:
1094:Paleostress
980:Slickenside
955:Crenulation
908:Fault trace
903:Fault scarp
893:Disturbance
878:Cataclasite
767:Rift valley
687:Half-graben
657:Fault block
642:DĂ©collement
271:free energy
98:schistosity
67:deformation
1160:Categories
1122:Pure shear
1109:Shear zone
1066:Competence
950:Compaction
827:Fracturing
622:Autochthon
617:Allochthon
365:References
338:foundation
165:diagenesis
144:amphiboles
33:diagenetic
1171:Petrology
1058:Boudinage
1038:Monocline
1033:Homocline
1013:Anticline
995:Tectonite
985:Stylolite
960:Fissility
937:lineation
933:Foliation
797:Syneclise
742:Obduction
712:Inversion
604:tectonics
309:sandstone
300:Anticline
224:Formation
82:foliation
59:petrology
46:cleavage.
36:foliation
1145:Category
1117:Mylonite
1048:Vergence
1043:Syncline
945:Cleavage
870:Faulting
415:Springer
348:See also
313:mudstone
285:hornfels
51:Cleavage
1018:Chevron
1005:Folding
850:Fissure
802:Terrane
747:Orogeny
727:MĂ©lange
662:Fenster
552:Tension
152:calcite
90:igneous
40:bedding
792:Suture
777:Saddle
717:Klippe
682:Graben
542:Stress
532:Strain
421:
334:tunnel
148:quartz
86:fabric
42:); D:
1127:Shear
855:Joint
737:Nappe
697:Horst
692:Horse
342:slope
340:, or
140:micas
53:, in
44:slaty
31:; C:
1028:Dome
935:and
860:Vein
840:Dike
772:Rift
583:Rake
419:ISBN
311:and
142:and
92:and
84:, a
69:and
63:rock
57:and
324:In
150:or
1162::
413:.
373:^
336:,
77:.
480:e
473:t
466:v
427:.
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