p8-9 geologi struktur sesar

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Geologi Struktur(Sesar)

Oleh :Irvani

Universitas Bangka Belitung Jurusan Teknik Pertambangan

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.


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Pokok Bahasan :I Pendahuluan (P.1)

II Tektonika & Orogenesa (P.2-3)a. Tektonik lempengb. Orogenesa

III Gaya, Tegangan, Strain & Deformasi (P.4-5)

a. Gaya & Teganganb. Strain & Deformasi

IV Struktur Geologi (P.6-9)a. Unsur strukturb. 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. Migasc. Kebencanaan geologi

VII Geologi Struk. Indonesia (P.14)a. Umumb. Sumatra&Jawa c. Bangka Belitung


Sesar/Patahan (Fault)Patahan merupakan diskontinuitas memanjang dengan teramati perpindahan posisi. Secara umum patahan membentuk set-set diskontinuitas paralel atau sub-paralel memanjang, atau disebut juga zona patahan. (Pluijm & Marshak, 2004; Davis, 1984; Twiss & Moores, 2007; Jaeger et al., 2007; Giani, 1992; dan Wyllie & Mah, 2004)


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Secara umum sesar dibagi menjadi 3 macam :1. Sesar Normal/Sesar turun2. Sesar Mendatar3. Sesar Naik



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Berdasarkan arah pergerakannya (slip), sesardibagi menjadi :1. Strike Slip Fault2. Dip Slip Fault3. Oblique (strike dip slip fault)



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1. Sesar Normal (Sesar Turun)Yaitu sesar jika blok hangging wall relatif turunterhadap foot wallnya. Atau blok foot wall relatifnaik terhadap hangging wallnya.

Ket : Hangging Wall : merupakan blok yang terletak di atas

bidang sesar.

Foot wall : Merupakan blok yang terletak di bawahbidang sesar.



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2. Sesar NaikYaitu sesar jika blok hangging wall relatif naikterhadap foot wallnya. Atau blok foot wall relatif turunterhadap hangging wallnya.


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Skema terbentuknya sesar naik



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3. Sesar MendatarMerupakan sesar yang kedua blok sesarnyabergerak secara horizontal dengan arah yang berlawanan.

Tidak memiliki blok hangging wall dan blok foot wall.


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Gejala2 (ciri) keterdapatan sesar :1. Kelurusan topografi, air panas, rawa-rawa.2. Perubahan mendadak bidang lapisan/ foliasi3. Perubahan mendadak struktur lain ; lipatan, retas dll4. Perubahan arah dan kemiringan kekar lineasi5. Pergeseran batas satuan peta6. Perulangan dan hilangnya satuan batuan7. Bongkah-bongkah asing pada batuan lain8. Kelurusan jalur mineralisasi, silifikasi dan ubahan9. Metamorfosa10. Pelurusan pd jalur mineralisasi, terbreksikan atau ubahan

dari data geofisika : a. Pelurusan dan perubahan sifatanomali gaya berat dan magnetik. B. Gradien yang curampada peta gaya berat magnetik.



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Komponen-komponen Bidang Sesar :1. Bidang Sesar2. Cermin sesar (slicken side)3. Gores garis (Slicken line)


Pengukuran Bidang Sesar :1. Data Orientasi kemiringan bidang sesar (strike/dip)2. Data Pitch : merupakan besarnya sudut runcing

yang dibentuk antara strike dengan slicken line.


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


Analisis struktur geologiAnalisis patahan menggunakan program proyeksi

stereografi Dips V-3.0, sehingga diketahui jenis dan pola pergerakan patahan.


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Ductile and Brittle Deformation Features

Ductile

Brittle


Diagram dan plotting proyeksi luasan-sama dari tiga kelas patahan (Anderson, 1942 dalam Rowland et al., 2007).


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Sketches illustrating differences between faults, fault zones, and shear zones

Pluijm & Marshak, 2004


Fault Geometry and Displacement



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Block diagram sketches showing the different types of faults





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Extensional and contractional faulting



The geometry of and flats along a thrust fault



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Fault breccia Banded clay gouge



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Pseudotachylyte



Shiny slickensided surface Slip fibers on a fault surface



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slip fibers along a fault



Subsidiary Fault and Fracture Geometries



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Fault-Related Folding





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Fault scarp



Change in fault character with depth for a steeply dipping fault



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Relation of Faulting to Stress



Fault SystemNormal fault systems



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Reverse fault systems



Description of Distributed Deformation in Strike-Slip Zones



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Map-view models of fault bends along strike-slip faults.



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A fracture along which movement takes place is a fault.

Faults

We classify faults based on direction of movement of individual blocks, with reference to a horizontal plane.

acute angle = hanging wall

obtuse angle = foot wall

fault plane

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Dip-Slip Faults

-- primary movement is vertical

reverse fault: old rocks are brought up in hanging wall

normal fault: old rocks are brought up in foot wall

foot wall

foot wallhanging wall

hanging wall

Reverse (Thrust) Faults

Reverse faults form as a result of compressional stresses, which dominate in convergent plate tectonic margins.

Thrust faults can be crustal-scale, as shown in the lower diagram.

Thrust fault: reverse fault with shallowly dipping

fault plane.

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Normal faulting is a result of tension (or extension). Extension is the dominant stress at divergent plate boundaries.

The most classic normal fault valleys are present in the axes of the mid-ocean ridges.

Normal Faults

How a fault is manifested on the surface depends on which is greater: the rate of fault movement or the rate of erosion.

Faults that have not penetrated to the Earth’s surface are blind faults—particularly dangerous from an earthquake hazard

standpoint, since they are hard to detect and map out.

Surface Expressions of Dip-Slip Faults

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Strike-Slip Faults-- primary movement is horizontal, not vertical, meaning no old

rocks are brought up or moved down relative to the Earth’s surface

Strike-slip faults result from shear

stress, like what we see at transform

plate margins. The San Andreas

system is a big strike-slip fault

Identify the Fault

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Identify the Fault

Reverse Fault

older rocks moved upin hanging wall

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Identify the Faults

Normal Faults

older rocks moved down in hanging walls

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Terima Kasih


p8-9 geologi struktur sesar

Documents

analisis struktur geologi

1ii tektonika orogenesa

blok foot wall relatifnaik

strain deformasi p

sesar normalsesar turun2

structural geology