MKG-0301 | GEOLOGI STRUKTUR
Dosen pengampu: Efrina Chandra Agusti Putri, S.T., M.Sc.
Kontrak Perkuliahan
Kriteria penilaian:
Kehadiran/keaktifan 10%
Tugas/Quiz 15%
Praktikum 20%
UTS 25%
UAS 30%
*Keterlambatan > 20 menit dianggap tidak hadir (1x absen)
*Izin dilakukan paling lambat 1 jam sebelum jam kuliah dengan alasan yang jelas
Untuk pertanyaan/pengumpulan tugas, silakan kirim via e-mail [email protected]
Lingkup pembelajaran
• Analisis kinematika dan dinamika
• Unsur struktur dan mekanisme deformasi
• Rekahan (fractures)
• Sesar (faults)
• Lipatan (folds)
• Foliasi, cleavage, lineasi
• Shear zone dan deformasi progresif
• Struktur geologi dan tektonik
• Analisis struktur geologi
• Aplikasi geologi struktur pada
bidang migas, tambang dan
geologi teknik
Referensi Davis, G. H., Reynolds, S. J., and Kluth, C. F., 2012, Structural Geology of Rock and
Regions, 3rd edition, John and Wiley and Sons, Inc.
Fossen, H., 2010, Structural Geology, Cambrige University Press.
Groshong, R. H. Jr., 2006, 3-D structural
Geology, Springer, The Netherlands.
Apa itu geologi struktur?
Geologic structures provide part of the basis for
recognizing and reconstructing the profound changes
that have marked the physical evolution of the Earth’s outermost layers, as observed from the scale of the
plates down to the microscopic.
A geologic structure is a geometric configuration of
rocks, and structural geology deals with the geometry,
distribution and formation of structures.
Plate tectonics provides a backdrop for understanding the origin and significance of geologic structures, especially regional structures. Plate tectonic analysis is the essential basis for interpreting the dynamic circumstances that give rise to deformational movements (Davis, 2012)
Geologi struktur berperan penting dalam sejarah geologi suatu daerah, terutama di batas lempeng, dimana pergerakan
deformasi paling mengubah susunan dan kontak batuan.(A) Oceanic lithosphere is being subducted from right to left beneath volcanic arc of basalt and andesite.
(B) Continental margin makes contact with the volcanicarc. Profound deformation takes place at location of collision.
Structural geology significance
MINERAL AND MINING
Most ore deposits owe their existence to the movement of hydrothermal solutions through fractured bedrock, where precipitation of precious metals (gold, silver) and base metals (copper, lead, zinc) creates structurally controlled veins.
OIL AND GAS EXPLORATION
Petroleum geologists are experts on the migration of hydrocarbons traveling through permeable
rocks (including fractured rocks), with trapping of hydrocarbons not uncommonly structurally controlled (e.g., in an anticline, or along a fault).
HYDROGEOLOGY
Hydrogeologists study fracture-induced permeability and overall shapes, sizes, and orientations of basins of sedimentary rocks in order to model the flow of groundwater, to estimate water reserves, and to site wells.
Tektonik Lempeng
Pergerakan lempeng pada masanya bertanggungjawab pada
pembentukan rangkaian
pegunungan, dataran tinggi plateau dan daerah terdeformasi lainnya di bumi akibat aktivitas deformasi kerak bumi secara mekanik maupun
termal. Beberapa diantaranya yang dapat kita lihat kini adalah rangkaian pegunungan Appalachians, Alpen, Andes dan Himalaya.
Litosfer
Merupakan penyusun lempeng bumi, terdiri dari kerak benua dan samudera, serta mantel bagian atas.Pergerakan lempeng
Plate boundaries are the edges of plates, the contacts between adjacent plates.
Depth levels of earthquakes at or near plate boundaries vary from very shallow to very deep, depending on the nature of the plate boundary and the
mechanical conditions of the plates brought into contact.
Jenis pergerakan lempeng
Pergerakan lempeng konvergen mengakibatkan subduksi
(penunjaman lempeng) dan kolisi (membentuk pegunungan lipatan).
Pergerakan lempeng saling
menjauh (divergen) menyediakan
“void” atau ruang untuk intrusi batuan beku menjadi gunung vulkanik atau sebagai cekungan akumulasi sedimen.
Batas transform lempeng
menghasilkan steeply dipping fault zones and shear zones.
The Fundamental Structures
Contacts are the boundaries that separate one rock body from another. They include normal depositional contacts, unconformities, intrusive contacts, fault contacts, and shear-zone contacts.
Primary structure, typically outcrop-scale features that develop during the formation of a rock body, for example, in sediment before the sediment become sedimentary rock, or in lava or magma before it
becomes volcanic or intrusive igneous rock.
Secondary structures form in sedimentary or igneous rocks after lithification, and in metamorphic rocks during or after metamorphism, e.g: joints, faults, folds, metamorphic fabrics, and shear zones.
Structural Datasets
• Field observation data
• Satellite images → aerial photo
• DEM (Digital
Elevation Model), GIS, Google Earth
• Seismic data
• Core data
Skala geologi struktur
Analisis geologi struktur
Descriptive analysis
Characterization of the shape and appearance of geologic structures, incl. development of a precise vocabulary (jargon) that any geologist can understand. Describing the
orientation of a structure in 3D space.
Kinematic analysis
Define the direction of movement on a structural features from the undeformed to the deformed state.
Strain analysis
Search for features in rock that can be measured to define strain
Dynamic analysis
Measuring the present-day state of stress in Earth, interpreting the state of stress responsible for microstructure in rocks.
Mechanism analysis
The study of processes on the atomic to grain scale that allow structures to develop.
Tectonic analysis
Regional scale or megascopic study to find relationship between structures and global tectonic processes, and their relation to other discipline like stratigraphy and petrology
Deformasi
dapat diartikan sebagai perubahan yang terjadi pada suatu volume batuan.
Describing “deformation” is geometric analysis. It requires comparing
(1) the final location of a volume of rock to where it started out;
(2) the present orientation of a volume of rock to its original orientation;
(3) the present shape of a volume of rock to its original shape; and
(4) the present size of a volume of rock to its original size
Deformasi
Deformation of rock bodies results from the loading by gravitational, tectonic, thermal, and/or impact forces, which generate
stresses that may exceed rock strength.
When rock strength is exceeded, the rock body will behave in a brittle manner (by fracturing) or a ductile manner (by flowing in the solid state), depending on how the conditions of the physical environment have affected the rock’s capacity to resist
stress.
Komponen deformasi
Deformation is the transformation from an initial to a final geometry by means of rigid body translation, rigid body rotation, strain (distortion) and/or volume change.
Rotation involves a uniform physical rotation of a rock volume (such as a shear zone) relative to an external coordinate system.
Translation moves every particle in the rock in the same direction and the same distance, and its
displacement field consists of parallel vectors of equal length.
Any change in shape, with or without change in volume, is referred to as strain, and it implies that particles in a rock have changed positions relative to each other.
Volume change, also referred to as dilation, or
volumetric strain. Even if the shape of a rock volume is unchanged, it may have shrunk or expanded.
Deformasi = Translasi + Rotasi + Distorsi + Dilasi
Tahapan deformasi
When a rock is subjected to increasing stress it passes through 3 successive stages of deformation.
Elastic Deformation
— wherein the strain is reversible
Ductile Deformation
— wherein the strain is irreversible
Fracture
— irreversible strain wherein
the material breaks
Stress vs. Strain
Stress Strain
Compression Shortening (contraction)
Tension Lengthening
(extension)
Faktor yang mempengaruhi respon batuan terhadap deformasi
Temperature - At high temperature molecules and their bonds can stretch and move, thus materials will behave in more ductile manner. At low temperature, materials are brittle.
Confining Pressure - At high confining pressure materials are less likely to fracture because the
pressure of the surroundings tends to hinder the formation of fractures. At low confining stress, material will be brittle and tend to fracture sooner.
Strain rate -- At high strain rates material tends to fracture. At low strain rates more time is available for individual atoms to move and therefore ductile behavior is favored.
Composition -- Some minerals, like quartz, olivine, and feldspars are very brittle. Others, like clay minerals, micas, and calcite are more ductile. This is due to the chemical bond types that hold them
together. Thus, the mineralogical composition of the rock will be a factor in determining the deformational behavior of the rock. Another aspect is presence or absence of water. Water appears to weaken the
chemical bonds and forms films around mineral grains along which slippage can take place. Thus wet rock tends to behave in ductile manner, while dry rocks tend to behave in brittle manner.
