Rock cleavage, foliation and lineation and their various types of formations

Presentation focuses on the types of Rock cleavagrs, foliations and lineations. These types are also explained in brief.

1. ROCK CLEAVAGE, FOLIATION AND LINEATION Sharik Shamsudhien 183104008 Manipal Institute of Technology

2. ROCK CLEAVAGE   Rock Cleavage describes a type of planar rock feature that develops as a result of deformation and metamorphism.  The degree of  deformation and metamorphism along with rock type determines the kind of cleavage feature that develops. Mostly these structures are formed in fine grained rocks composed of minerals affected by pressure solution. Cleavage is a type of rock  foliation , a  fabric  element that describes the way planar features develop in a rock. Cleavage is a type of secondary foliation associated with fine grained rocks. For coarser grained rocks,  schistosity  is used to describe secondary foliation. The terminology that Passchier and Trouw (2005) states that cleavage is a type of secondary foliation in fine grained rocks characterized by planar fabric elements that form in a preferred orientation

3. Types of Rock cleavages Slaty Cleavage or schistosity Slaty cleavage or is caused by the parallel arrangement of platy minerals, such as mica or by the parallel arrangement of ellipsoidal grains , such as quartz and feldspar. A rock possessing slaty cleavage can be split into an indefinite number of thin sheets parallel to the cleavage . The term slaty cleavage is used if the rock is less intensely metamorphosed rocks, such as slate where as schistocity is used if the rock is recrystallised into minerals that are readily recognized by the naked eye. Cleavage and schistocity may or may not be parallel to bedding.

4. Fracture cleavage Fracture cleavage is essentially closed spaced jointing. The minerals in the rock are not parallel to the cleavage The distance between the individual planes of cleavage can be measured and is mostly in millimeters and centimeters

5. Slip Cleavage Cleavage along which there has been some displacement is called slip cleavage. Older cleavage, bedding or Schistosity is commonly displaced one to several millimeters. The platy cleavage, such as micas or chlorites may be dragged into positions that are nearly parallel to the slip cleavage. This ype of cleavage consist of closely spaced faults.

6. Bedding Cleavage Cleavage or schistosity that is parallel to the bedding is commonly referred to as bedding cleavage or bedding schistosity . It is commonly similar to slaty cleavage in that it is caused by parallel platy minerals

7. FOLIATIONS  Foliation is the result of the parallel arrangement  in a plane(mica) perpendicular to the maximum principal applied stress or it’s the  repetitive layering in metamorphic rocks.   Each layer can be as thin as a sheet of paper where the foliation derived from the word folium which means leaf, or over a meter in thickness. The types of foliations are primary and secondary foliations. Foliations and lineations are primary if they originate by primary sedimentary or igneous process. Foliations and lineations are secondary if they originate by secondary process such as tectonic deformation or metamorphism Types of Foliations 1.Spaced Foliations A) Compostional B) Disjunctive C) Crenulation 2.Contineous Foliations A) Fine B) Coarse

8. Compositional foliations Compositional foliations are marked by layers or laminae of different mineralogical composition. A planar alignment of platy or needle-shaped crystals may also be present, but the rock has weak tendancy to cleave parallel to the foliation. The structures are sub divided on the basis of mineralogical variation, spacing and the relative thickness of the compostiional layers into Diffuse and Banded foliations. Diffuse foliations are widely spaced weak concentrations of a mineral in a rock of predominantely one lithology , Whereas banded foliations are composed of relatively closely spaced compositional layers that are mineralogically distinct and of comparable abundance.

9. Disjunctive foliations These foliations are characterised by thin domains, called cleavage domains or seams The word disjunctive is derived from the word “ disjunctus ” means disjoined or detached. Disjuctive foliations commonly form in previously unfoliated rocks such as limestones or mudstones, although in some foliated rocks they may also develop cross-cutting the earlier foliation Disjunctive foliations on the basis of smoothness are divided into four groups:- Styolitic Long, continuous and irregular cleavage that have distictive tooth like geometry Anastomosing Long, continuous and wavy cleavage domains that form irregular network Rough Short, discontinuous, concentrations of highly oriented platy minerals that envelope the coarse grains Smooth Long, continuous and smooth cleavage which have concentrations of highly oriebted platy crystals

10. Styolitic Anastomosing Rough Smooth

11. Crenulation Foliation Crenulation foliation are formed by harmonic wrinkles or chevron folds that develop in a preexisting foliation The new foliation occurs across the old foliation and is defined by both limbs of symmetric crenulations or one of the limbs of asymmetric crenulations. The old foliations is preserved in the microlithons either as hinges of symmetric crenulations On the basis of orienatation of platy minerals in the cleavage domain the further subdivision of crenulations are:- Zonal crenulation The platy minerals in the new cleavage domain are oriented at a small angle to the domain and form a continuous variation of orientations from the platy minerals. Discrete Crenulation The Orientation of platy minerals in the new cleavage domains is parallel to the domains and sharply discordant with the orientation of platy minerals in the microlithons

12. Continuous Foliations Continuous foliations are defined either by domains with a spacing less than 10 microns They are divided by grain size into fine and coarse continuous foliations. Fine Microcrenulation Microdisjunctive Microcontinuous Coarse Fine continuous Fine continuous foliations may be either microdominal or microcontinuous The microdominal fine foliations may be microcrenulation or microdisjunctive and they have the same characteristics as their macroscopic counterparts. Coarse Continuous Coarse continuous foliations are characterized by the complete orientation of homogeneously distributed platy minerals or the alignment of flattened mineral grains. They have no dominal structure, which would be easily revealed by the coarse grain size.

13. LINEATIONS Lineations   are linear structural features within rocks( hornblede ). In short its the Homogeneous distributed linear structure Described as any repeated , commonly penetrative and parallel alignment of linear elements within a rock A lineation is caused by a similar growth of elongate minerals in the plane.  Lineation field measurements are recorded as map lines with a plunge angle and azimuth. There are several types of lineations Intersection lineations Crenulation lineation Mineral lineations Stretching lineations Slickensides Mullion Boundinage

14. Intersection Lineation Intersection lineations are linear structures formed by the intersection of any two surfaces in a three-dimensional space. Intersection of two planar features is an "apparent" lineation in that there is no fabric that is linear Intersection lineations can be formed by the intersection of any two foliations Bedding and cleavage (parallel to the fold axis) Cleavage and a second cleavage

15. Crenulation lineation Intersection between fold hinges and foliation Small scale rippling of an earlier foliation (and occasionally bedding) produces an obvious linear array parallel to the closely spaced and regular wrinkle hinges. Many schists exhibit this type of lineation. It generally is a good indication of superposed deformation

16. Mineral lineation Preferred alignment of minerals due to deformation and/or Recrystallization during deformation Aligned needle shaped grains (hornblende) Streaked or smeared mineral fibers Long axes of platy minerals like micas

17. Stretching lineation Elongation of minerals due to "stretching" deformation, and it can be visualised as a result of pulling, causes to form a cigar-shaped rod parallel to the direction to which is being pulled. This lineation is formed by the parallel alignment of individual detrital grains, aggregates or fragments of any size that have been elongated and/or rotated during deformation.

18. Mullions, Slickensides and Boudins Mullions Mullions structure consist a series of parallel column structures, which may be several inches in diameter and several feet long Slickenside Slickensides are rock surfaces naturally polished by motion on faults. They often display linear structures due to frictional sliding on the fault surfaces. Boudins French for Sausage; another form of lineation, where in cross section a competent thickens and thins, in such a way to simulate a string of sausages Boudins Slickenside Mullions

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