Geologi Struktur(Pengukuran & Analisis Struktur Geologi)

Oleh :Irvani

Referensi :Van Der Pluijm, B. A. and Marshak, S. 2004. Earth Structure. 2nd Edition. W. W. Norton & Company, Inc., USA.Rowland, S.M., Duebendorfer, E.M. and Schiefelbein, I.M. 2007. Structural Analysis and Synthesis : A Laboratory Course in Structural Geology. 3th Edition. Blacwell Publishing Ltd. Voctoria, Australia.Bates, R.L. and Jackson, J.A., 1987. Glossary Geology. 3th Edition. American Geological Institute Elexandria, Virginia.Davis, G.H. 1984. Structural Geology of Rocks and Regions. John Wiley & Sons, New York.Ragan, D.M. 2009. Structural Geology : An Introduction to Geometrical Techniques. 4th Edition. Cambridge University Press, New York.Twiss R.J. And Moores, E.M. 2007. Structural Geology. 2nd Edition. W.H. Freeman and Company, USA.Ramsey J. and Huber, M. 1983. The Techniques of Modern Structural Geology : Strain Analysis. Vol. 1. Academic Press, Inc., London.Ramsey J. and Huber, M. 1987. The Techniques of Modern Structural Geology : Fold and Fractures. Vol. 2. Academic Press, Inc., London.Ramsey J. and Huber, M. 2000. The Techniques of Modern Structural Geology : Applications of Continuum Mechanics in Structural Geology. Vol. 3. Elsevier Academic Press, Inc., California.Cox, A. and Hart, R.B. 1986. Plate Tectonics : How It Works. Blacwell Scienific Publications, Inc., California.Trouw, R.A.J. and Passchier, C.W. 1996. Microtectonics. Springer Verlag Berlin Heidelberg, Germany.DLL.

Pokok Bahasan :

I Pendahuluan (P.1)

II Tektonika & Orogenesa (P.2-3) a. Tektonik lempeng b. Orogenesa III Gaya, Tegangan, Strain & Deformasi (P.4-5) a. Gaya & Tegangan b. Strain & Deformasi IV Struktur Geologi (P.6-9) a. Unsur struktur b. Lipatan c. Kekar d. Sesar/Patahan

V Identifikasi Struk. Geologi (P.10-11)a. Pengukuran dan analisis struktur geologi b. Analisis geofisika struktur geologi

VI Aplikasi Struk. Geologi (P.12-13)a. Mineralisasi b. Migas c. Kebencanaan geologi VII Geologi Struk. Indonesia (P.14)a. Umumb. Sumatra&Jawa c. Bangka Belitung

Arah (bearing): sudut horisontal antara garis dengan arah koordinat tertentu,biasanya utara atau selatan. Azimuth: bearing yang diukur dari utara searah jarum jam. True dip (kemiringan sebenarnya): sudut kemiringan terbesar yang terbentuk olehsuatu bidang dengan bidang datar, diukur tegak lurus perpotongan bidang. Apperent dip (kemiringan semu): sudut yang terbentuk antara suatu bidang dengan bidang horisontal yang diukur tidak tegaklurus perpotongan bidang. Jurus (strike): arah garis horisontal yang terbentuk oleh bidang miring dengan bidang horisontal.

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Stereographic ProjectionObjective : Use stereographic projection to quantitatively represent three-dimensional, orientation data (such as the attitudes of lines and planes) on a two-dimensional piece of paper.Rowland et al., 2007

Nets used for stereographic projection. (a) Stereographic net or Wulff net. (b) Lambert equal-area net or Schmidt net.Rowland et al., 2007

Main elements of the equal-area projection.Rowland et al., 2007

Oblique lower-hemisphere view of the projection of a plane striking northsouth and dipping 50o west. (a) Oblique view. (b) Equal-area projection.Rowland et al., 2007

Pole of a planeProjection of a plane (NS, 40o W) and the pole to the plane. (a) Oblique view. (b) Equal-area projection.Rowland et al., 2007

Projection of a pole to a plane.Rowland et al., 2007

I. LIPATAN

Foto singkapan struktur antiklin pada perlapisan batupasir dan sketsa lapangan yangdibuat untuk mempermudah identifikasi unsur-unsur struktur geologi (McClay, 1987).

An asymmetric, plunging fold (the Sheep Mountain Anticline in Wyoming, USA).Pluijm & Marshak, 2004

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Chevron folds in Franciscan chert of California, USA (Marin County)Pluijm & Marshak, 2004

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Flexural Slip/Flow FoldingPluijm & Marshak, 2004

Shear FoldingPluijm & Marshak, 2004

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(a) Geologic map, (b) corresponding structure section, (c) stratigraphic columnRowland et al., 2007Sambungan.......

Geologic map with two contrasting interpretations of structure section AA. Generalized from Dibblee (1966). (a) Geologic map. (b) Original structure section in which the northern serpentinite block is interpreted as the exposed core of an anticline. (c) Revised structure section in which the northern exposure of serpentinite is interpreted as a landslide block.Rowland et al., 2007

Example of a structure section with intrusive bodies. After Huber and Rinehart (1965)Rowland et al., 2007

Stereographic Analysis of Folded RocksRowland et al., 2007

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Joint Spacing in Sedimentary RocksPluijm & Marshak, 2004II. KEKAR

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III. FaultsRowland et al., 2007

Pengukuran Bidang SesarData Orientasi kemiringan bidang sesar (strike/dip)Data Pitch : merupakan besarnya sudut runcing yang dibentuk antara strike dengan slicken line.

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Shiny slickensided surfaceSlip fibers on a fault surfacePluijm & Marshak, 2004

Analisis struktur geologiAnalisis patahan menggunakan program proyeksi stereografi Dips V-3.0, sehingga diketahui jenis dan pola pergerakan patahan.

Tabel hubungan nilai pitch dengan jenis patahan (Ragan, 1973)

Nilai Pitch

Jenis Patahan

00-100

100-800

800-900

800-900

Patahan Mendatar

Patahan Obliq

Patahan Naik, Slicken line halus ke atas

Patahan Normal, Slicken line halus ke bawah

Fault Geometry and DisplacementPluijm & Marshak, 2004

Extensional and contractional faultingPluijm & Marshak, 2004

(a) Geologic map showing the difference between offset and strike separation. (b) Vertical structure section showing the heave and throw components of dip separationRowland et al., 2007

Diagrams showing the solution of a slip problem. (a) Geologic map. (b) Block diagram. (c) Equal-area plot of the fault plane and bedding plane. (d) Orthographic projection of the fault plane showing the pitch of bedding. The slip is 280 m in the same direction as the dip (direction indicated by slickenside lineations).Rowland et al., 2007

Dynamic and Kinematic Analysis of FaultsDynamic analysisDynamic analysis seeks to reconstruct the orientation and magnitude of the stress field that produced a particular fault or a population of faults.Rowland et al., 2007

Block diagrams and equal-area plots of three classes of faults predicted by E. M. Anderson. The equal-area sterograms show typical fault and slickenline orientation data for a set of faults within each class. For normal faults and thrust faults, the arrows on the great circles of the stereograms point in the direction of the hanging-wall motion. For strike-slip faults, the arrows on the great circles indicate the sense of shear. After Angelier (1979) in Suppe (1985).Rowland et al., 2007

Map view of a mine adit, showing the attitude and sense of motion on eight faults. For use in Problem 10.3. D, down; U, up.Shows a map of a mine adit and a series of minor faults that occur in a homogeneous rock unit. Plot the fault planes on the equal-area net and determine the orientation of the stress ellipsoid.Rowland et al., 2007

Kinematic analysisKinematic analysis is a graphical technique for analyzing fault data (Marrett & Allmendinger, 1990). It allows the structural geologist to quantitatively characterize the overall deformation or movement pattern resulting from cumulative fault motions in a region and to determine the direction of bulk shortening or extension (i.e., strain).As with dynamic analysis, the basic data necessary for kinematic analysis of faults are: (1) the strike and dip of the fault surface, (2) the pitch of slickenlines within the fault plane, and (3) the sense of movement on the fault.Rowland et al., 2007

(a) Cross-section diagram of a normal fault dipping 30o to the east. (b) Equal-area projection, showing the pole to the fault, 90o pitch of slickenlines, and corresponding slip-direction arrow. (c) Cross-section diagram showing the shortening and extension axes, which are perpendicular to one another and 45o from the pole to the fault. (d) Equal-area projection showing the movement plane and projection of the shortening and extension axes. The movement plane lies on the great circle defined by the pole to the fault and the pitch of the slickenlines. The slipdirection arrow points toward the extension axis and away from the shortening axis.Rowland et al., 2007

Equal-area plot of five reverse faults, showing the pitch of slickenlines, slip-direction arrows, extension axes, and shortening axes. The faults dip 20o to 30o to the northwest. The direction of tectonic transport is east-southeast. Consistent with this transport direction, the shortening axes trend east-southeast and are subhorizontal; the extension axes are nearly vertical.Rowland et al., 2007

(a) Equal-area plot of 10 faults, including the fault plane, pitch of slickenlines, and slip direction. (b) Contour diagram of the extension axes; the squares indicate individual extension axes. (c) Contour diagram of the shortening axes; the dots indicate individual shortening axes. Contouring was done following the method of Kamb (1959).Rowland et al., 2007

Two-dimensional relationship between a plane and its state of stressRowland et al., 2007

Mohr circle solution to a sample problem requiring the determination of sn and ss on a particular plane. (a) Block diagram. (b) Mohr circle solution.Rowland et al., 2007

Strain Measurement. Measure longitudinal and shear strain from deformed objects.. Determine the orientation and relative dimensions of the strain ellipse from deformed objects.. Determine in which of three strain fields a particular structure developed.Longitudinal strainShear strainRowland et al., 2007

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Noncoaxial strain demonstrated with a stack of cards. (a) Before deformation. (b) After deformation, showing angular shear.Rowland et al., 2007

Noncoaxial total strain ellipse showing four zones. Notice the asymmetric arrangement of the zones compared with those in the coaxial ellipse. After Ramsay (1967).Rowland et al., 2007

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Common symbols used on geologic mapsRowland et al., 2007

Subsidiary Fault and Fracture GeometriesPluijm & Marshak, 2004

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