Fold their geometry and classifications
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The document defines and describes different types of folds based on their geometry and classification. It discusses key aspects of fold geometry including hinge, axis, axial plane, crest, trough, and limbs. It then covers general classifications of folds such as anticline, syncline, dome, and basin. Specific fold types like chevron, box, and fan folds are also defined. The document concludes by discussing geometric classifications of symmetrical and asymmetrical folds and special fold types associated with faults.
Fold their geometry and classifications
- 1. Prepared byPrepared by Azhar MahmoodAzhar Mahmood TopicTopic Fold their geometry andFold their geometry and classificationclassification
- 2. Fold DefinitionFold Definition ►FoldsFolds are wave-like structures that resultare wave-like structures that result from deformation of bedding, foliation, orfrom deformation of bedding, foliation, or other originally planar surfaces in rocks.other originally planar surfaces in rocks.
- 3. Geometry of FoldGeometry of Fold ► •• HingeHinge: points of maximum curvature within a single: points of maximum curvature within a single ► folded surface.folded surface. ► •• AxisAxis: a line when moved parallel to itself “sweeps out” a: a line when moved parallel to itself “sweeps out” a ► folded surface. The fold axis and fold hinge line have thefolded surface. The fold axis and fold hinge line have the ► same attitude.same attitude. ► •• Axial Plane or SurfaceAxial Plane or Surface : the plane or surface defined by: the plane or surface defined by ► connecting fold hinge lines in multiple folded surfacesconnecting fold hinge lines in multiple folded surfaces ► •• Inflection pointInflection point : a point on a folded surface where the: a point on a folded surface where the ► curvature changes direction. This is half the distancecurvature changes direction. This is half the distance ► between hinge points.between hinge points.
- 4. Geometry of FoldsGeometry of Folds ►CrestCrest – The highest point on the cross– The highest point on the cross section of a foldsection of a fold ►TroughTrough – The lowest point on the cross– The lowest point on the cross section of a foldsection of a fold ►LimbsLimbs – The straighter portion of the– The straighter portion of the fold connecting the hinge zonesfold connecting the hinge zones ►Hinge ZonesHinge Zones – Exhibit the greatest– Exhibit the greatest curvature of a foldcurvature of a fold
- 5. Geometry of FoldsGeometry of Folds
- 6. Geometry of FoldsGeometry of Folds ►Hinge LineHinge Line – The line joining points– The line joining points of greatest curvature on a foldedof greatest curvature on a folded surfacesurface ►Axial SurfaceAxial Surface – When many hinge– When many hinge lines (from multiple foldedlines (from multiple folded surfaces) connect forming a planesurfaces) connect forming a plane ►PlungePlunge – When the fold hinge is– When the fold hinge is inclined to the horizontalinclined to the horizontal
- 7. Geometry of FoldsGeometry of Folds ►WavelengthWavelength – The distance between– The distance between subsequent crests or troughssubsequent crests or troughs ►AmplitudeAmplitude – Half the distance from a– Half the distance from a crest to the subsequent troughcrest to the subsequent trough ►VergenceVergence – The direction of leaning of– The direction of leaning of the axial surfacethe axial surface
- 8. Geometry of FoldsGeometry of Folds ►First-Order FoldsFirst-Order Folds – The master (largest)– The master (largest) foldfold ►Second-Order FoldsSecond-Order Folds – Smaller folds on– Smaller folds on the flanks of first-order foldsthe flanks of first-order folds ►Enveloping SurfaceEnveloping Surface – Enables the– Enables the relation of small to large scale foldsrelation of small to large scale folds
- 9. Fold ClassificationFold Classification ►General ClassificationGeneral Classification ►Morphological ClassificationMorphological Classification ►Geometric ClassificationGeometric Classification ►Special ClassificationSpecial Classification
- 11. Kinds of FoldsKinds of Folds ►AnticlineAnticline – A folds that is concave– A folds that is concave towards older rocks in its centertowards older rocks in its center ►AntiformAntiform – A fold that is concave– A fold that is concave downwarddownward ►SynclineSyncline – A folds that is concave– A folds that is concave towards younger rocks in its centertowards younger rocks in its center ►SynformSynform – A folds that is concave upward– A folds that is concave upward ►DomeDome – An antiform where bedding dips– An antiform where bedding dips away from the central pointaway from the central point ►BasinBasin – A synform where bedding dips– A synform where bedding dips towards a central pointtowards a central point
- 12. ►Antiformal SynclineAntiformal Syncline Have a syncline characterHave a syncline character Younger rock in coreYounger rock in core Older rock on limbOlder rock on limb Syncformal AnticlineSyncformal Anticline Have a anticline characterHave a anticline character Younger rock on the limbYounger rock on the limb Older rock in coreOlder rock in core
- 13. ►DomesDomes Half cut structure of circle Dip away fromHalf cut structure of circle Dip away from center,convex upwardcenter,convex upward Example. Salt forms,Doms structureExample. Salt forms,Doms structure ►BasinBasin Dip toward centerDip toward center These structure occur on regionalThese structure occur on regional level,convex downwadlevel,convex downwad
- 14. Kinds of FoldsKinds of Folds
- 15. ClassificationClassification ►SyntaxisSyntaxis It is antiformal structure convex toward theIt is antiformal structure convex toward the interlad and concave toward the forelandinterlad and concave toward the foreland HomoclineHomocline Have uniformaly limbs which dip is sameHave uniformaly limbs which dip is same direction , regional folddirection , regional fold MonoclineMonocline Both limbs sometime parallal and someBoth limbs sometime parallal and some time gental to steeptime gental to steep
- 17. Overturned FoldsOverturned Folds ►•• Overturned folds possess an overturnedOverturned folds possess an overturned limb- the limb must belimb- the limb must be ►rotated more than 90° to bring it back to itsrotated more than 90° to bring it back to its original positionoriginal position ►•• Note that the overturned limb dips steeperNote that the overturned limb dips steeper than the axial planarthan the axial planar ►cleavagecleavage
- 19. Recumbent FoldRecumbent Fold ► This type of fold isThis type of fold is compressed so much thatcompressed so much that it is no longer vertical.it is no longer vertical. ► There is a large extent ofThere is a large extent of overlapping and it canoverlapping and it can take the form of an “s”.take the form of an “s”. ► To the right is a diagramTo the right is a diagram that shows the process ofthat shows the process of recumbent folding.recumbent folding.
- 21. Chervan FoldChervan Fold ►ChevronChevron andand Kink FoldsKink Folds – Have straight– Have straight limbs and sharp angular hingeslimbs and sharp angular hinges
- 22. Hormonic FoldHormonic Fold ►Hormonic FoldHormonic Fold ► A fold which maintains its geometric form,A fold which maintains its geometric form, integral wavelength, and symmetryintegral wavelength, and symmetry throughout a sequence of layersthroughout a sequence of layers ►Disharmonic FoldsDisharmonic Folds – Shape or wavelength– Shape or wavelength changes from one layer to anotherchanges from one layer to another
- 24. Box FoldBox Fold ►Crust flate Trough also flateCrust flate Trough also flate ►Having two hingesHaving two hinges
- 25. Fan foldFan fold ►Fan shape structureFan shape structure ►Both limbs are over turnedBoth limbs are over turned ►Having two FormsHaving two Forms ►A.. Anticlinal Fan foldA.. Anticlinal Fan fold Both limb over turn,older in core and youngerBoth limb over turn,older in core and younger on limbson limbs ►B.. Synclinal Fan foldB.. Synclinal Fan fold Both limbs overturnd,younger in core older onBoth limbs overturnd,younger in core older on limbslimbs
- 26. Isoclined FoldIsoclined Fold ►Dip of limb is one either anti or syncline,Dip of limb is one either anti or syncline, axial plane is verticalaxial plane is vertical TypesTypes Inclined Isoclined FoldInclined Isoclined Fold Horizental Isoclined foldHorizental Isoclined fold
- 30. Special ClassificationSpecial Classification ►Drag FoldDrag Fold ►Fault Progated foldFault Progated fold ►Fault bend foldFault bend fold ►Detechment foldDetechment fold ►Decollement foldDecollement fold
- 31. Drag FoldDrag Fold ►Related to faultRelated to fault ►Z type fold are developed in thrust orZ type fold are developed in thrust or reverse faultreverse fault ►Z type shows thrusted, dip is north thrust orZ type shows thrusted, dip is north thrust or reverse also called updip faultreverse also called updip fault
- 32. Fault Progated FoldFault Progated Fold ►Fold develop with faultFold develop with fault
- 33. Fault bend FoldFault bend Fold ►Formed as a result of the geometry of faultFormed as a result of the geometry of fault planeplane
- 34. Detechment FoldDetechment Fold ►Fold formed on the ramFold formed on the ram
- 35. Decollement FoldDecollement Fold ►Fold formed due to decollmaFold formed due to decollma
- 37. Symmetrical foldSymmetrical fold ►is a fold that is concave upward. Anis a fold that is concave upward. An anticlinorium is a large anticline on whichanticlinorium is a large anticline on which minor folds are superimposed, and aminor folds are superimposed, and a synclinorium is a large syncline on whichsynclinorium is a large syncline on which minor folds are superimposed.minor folds are superimposed. A A symmetrical foldsymmetrical fold is one in which the is one in which the axial plane is vertical. An aaxial plane is vertical. An asymmetricalsymmetrical foldfold is one in which the axial plane is is one in which the axial plane is inclinedinclined
- 38. Asymmetrical foldAsymmetrical fold ►.anticline on which minor folds are.anticline on which minor folds are superimposed, and a synclinorium is asuperimposed, and a synclinorium is a large syncline on which minor folds arelarge syncline on which minor folds are superimposed. A symmetrical fold is onesuperimposed. A symmetrical fold is one in which the axial plane is vertical.in which the axial plane is vertical. An An asymmetrical foldasymmetrical fold is one in which is one in which the axial plane is inclined. An overturnedthe axial plane is inclined. An overturned fold, or overfold, has the axial planefold, or overfold, has the axial plane inclined to such an extent that the stratainclined to such an extent that the strata on one limb are overturnedon one limb are overturned
- 40. UprightUpright FoldFold ►Upright Upright folds (Have vertical, or nearlyfolds (Have vertical, or nearly vertical, axial surfacesvertical, axial surfaces