BELAJAR LIPATAN Yukkkkk……

January 21, 2008 at 5:37 pm


Lipatan merupakan Struktur berbentuk menyerupai gelombang yang umumnya berkembang pada batuan berlapis yang mengalami gaya kompresi horisontal atau gaya Vertikal.

Bagian Lipatan:

 Sayap Lipatan (Limbs) : Bidang miring yang membangun struktur antiklin atau sinklin

 

Inflection Point-

   limb point where sense of curvature changes

 

 

 

Axial Surface (Axial Plane)-

connects series of hinge lines within a fold

 

Fold Axis-

Imaginary straight line that when moved parallel to itself reproduces the form of a fold

Occurs only with Cylindrical folds

Hinge Line

      connects points of maximum fold curvature

      

Cylindrical vs. Non-Cylindrical Folds

        Cylindrical Folds-

                Straight hinge lines

                Contains fold axes

    

Non-Cylindrical Folds-

                Curved hinge lines

                Does not contain fold axes

 

   Cylindrical        Non-Cylindrical

 

 

 

   Non-Plunging Folds

 

 

 

Plunging Folds

  

Landsat TM image of nortwest trending Mariscal Mountain Anticline, Big Bend National Park

 

                Limestone beds of Torcer Formation in syncline of Malone Mountains, south of Torcer station. Hudspeth County, Texas. Syncline plunging away from observer. USGS photo.

 

Fold Symmetry

Lipatan Simetri Bidang Sumbu Tegak

Non-Simetri Bidang Sumbu Miring 

 

Lipatan Simetrik    Lipatan Asimetrik 

 

 

Form vs Lithologic age relations:

  Antiform– Melipat Cembung keatas

  Synform- Melipat Cekung kebawah

These terms used when stratigraphic age     relations are unclear between folded layers.

 

   

Anticline-convex upward fold  wherein the oldest stratigraphic units occupy core of fold                                              

Synclineconcave upward fold  wherein the youngest stratigraphic units occupy fold core

Sideling Hill Syncline (photo by N. Heywood)

 

 

Green Pond Inlier folds, Newfoundland, NJ

 

 

Fold Classification:

     Dip of Axial Surface                      

          Upright:     700-900   

          Inclined:    100-700.                                  

          Recumbent 00-100.          

   

 

                      

      Interlimb Angle

A. Gentle:          1200-1800

B. Open:             600-1200

C. Tight:              100-600

D. Isoclinal:          0-100.


 

 

Dip Isogon Analysis-

Dip isogons connect points of equal dip on the upper and lower boundary of a folded layer

Measure bed thickness change throughout fold

 

 

Class 1- convergent dip isogons

     

 Class 1A- limb thickening

       

 

Class 1B (Parallel)-

          equal bed thickness throughout the fold

 

 

 

Class 1C- slight hinge thickening

 

    

 

Class 2 (Similar)-

        parallel dip isogon patterns-

        limb thinning; hinge thickening

 

 

 

Class 3:

        divergent dip isogon pattern-

        limb thinning, hinge thickening

 

 

Distinctive Fold types:

Monoclines

 

Basins

 

 

Domes

Chevron Folds

 

Mechanics of Folding:

      Passive Folding  (Shear Folding) 

            slip on surfaces not parallel to rock layering

            rock layering (black layer) does not influence fold development

           black bedding layer merely acts as a “passive” recorder of strain

                card deck analogy in which slip occurs on individual cards;

           the surface of individual card records no strain

           produces similar (Class 2) folds 

 

 

 

 

 

 

 

 

 

Passive folding in layered leucogabbro, Siroua, Morocco

 

 

 

 

 

Flexural Slip Folding

    Folding is controlled by rock layering

    Slip (bending) occurs between rock layers

   No strain on the bedding plan surface

   Circles become ellipses in the profile plane

    Amount of slip increases from the hinge line to the inflection point

    produces parallel (Class 1B) folds

 

                Flexural Slip Folding

 

                

 

Neutral Surface Folding – produces concentric folds

    X-axis is normal to hinge line along top of folded layer

   Neutral surface (no strain) occurs in middle of folded layer

    X-axis is parallel to hinge line along bottom of folded layer

   produces parallel (Class 1B) folds

   

 

Superposed Folds– refolded folds


Specimen of refolded isoclinal folds in schist. Riverside Mountains, Riverside County, California. January 1967. Photo by Warren B. Hamilton, USGS. 

 

Transposed Folds – hinges distended from limbs

 

 

Extensional Folds: folds may also be generated by tension

        Reverse Drag

 

Soft Sediment Deformation- Lastly, folds may occur due to soft sediment deformation, commonly in turbidity current environments

 

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