Theme 7. Metamorphic rocks. Distinguishing rock types

Theme 7. Metamorphic rocks. Distinguishing rock types 7.1. Metamorphic rocks formation 7.2. Classification of metamorphic rocks 7.3. Distinguishing rock types

7.1. Metamorphic rocks formation

7.2. Classification of metamorphic rocks

7.3. Distinguishing rock types

The Möbius strip or Möbius band is a surface with only one side and only one boundary component. Source: http://en.wikipedia.org

Theme 8. Deformation of rocks 8.1. Layers of uniform dip 8.2. Folds 8.3. Fractures in rocks 8.4. Faults 8.5. Joints

8.1. Layers of uniform dip Most sedimentary rocks were originally deposited as soft horizontal layers at the bottom of the sea and hardened over time. Source: Internet

8.1. Layers of uniform dip Original layering in sediments is called stratification or bedding. Each layer is referred to as a stratum (pl. strata) or bed. Source: http://en.wikipedia.org

8.1. Layers of uniform dip The interfaces between beds are called bedding planes. Source: Internet The outcrops of major bedding planes that separate thick beds of different rock type are depicted on geological maps.

8.1. Layers of uniform dip At the time of deposition, most beds are nearly horizontal. Later, tilting or buckling of the Earth s crust may leave them inclined at an angle to the horizontal. The dip is easily measured with a clinometer. Source: www.geologyclass.org

8.1. Layers of uniform dip The direction of 90 to the dip is the strike of the bed. Source: www.geologyclass.org

Source: Understanding Earth J.Grotzinger, T.H. Jordan, F. Press, R. Siever 8.1. Layers of uniform dip

8.1. Layers of uniform dip Geological compass for measuring the dip direction and strike direction of strata. Source: http://en.wikipedia.org

8.1. Layers of uniform dip Source: www.prog-univers.com

8.1. Layers of uniform dip The principle of superposition(nicolas Steno): Sedimentary layers are deposited in a time sequence, with theoldestonthebottomandtheyoungestonthetop. Source: Internet

8.1. Layers of uniform dip Rocksdeforminresponsetotheforcesactingonthem. Source: www.prog-univers.com Source: Understanding Earth J.Grotzinger, T.H. Jordan, F. Press, R. Siever

8.1. Layers of uniform dip According to the theory of plate tectonics the steady relative motion between two rigid plates of lithosphere causes deformation at the plate boundary. There are three basic types of plate boundary: -spreading centers, where plates diverge and plate area increases; -subduction zones, where plates converge and plate area decreases; -transform-fault boundaries, where two plates slide past eachotherwithnochangeinplatearea. Source: USGS

8.1. Layers of uniform dip Determining whether they respond by folding, faulting, or some combination of the two can be a complex business, depending on the orientation of the forces, the rock type, and the physical conditions during deformation. Source: Internet

8.1. Layers of uniform dip The tectonic forces that act on rocks in plate boundary zones are horizontally directed, and the type of force depends on the relative plate motion: Tensional forces, which stretch and pull formations apart, dominate at divergent boundaries, where plates move away from each other. Compressive forces, which squeeze and shorten rock formations, dominate at convergent boundaries, where plates move toward each other. Shearing forces, which push two sides of a formation in opposite directions, dominate at transform-fault boundaries, where plates slide past each other.

8.1. Layers of uniform dip If subjected to stresses beyond those that their strength can resist, strata are permanently deformed by either buckling or fracturing. Rocks are not brittle, tend to produce folds by buckling or plastic flow. Source: Internet

8.2. Folds The essential characteristic of a fold is a change of dip. Thisoccursatthehingeofthefold. On either side of the hinge is a limb, where the dip is comparatively steady. Source: Internet

8.2. Folds A fold where the limbs diverge downwards(that is, where the dips of the limb are away from the hinge) is an anticline. Afoldwheredipsaretowardsthehingeisasyncline. Source: http://en.wikipedia.org

8.2. Folds Synclines Source: Internet

8.2. Folds Dome Anticlines Source: Internet

8.3. Fractures in rocks Brittle rocks deform by fracturing, especially if stress is applied rapidly. In general, fracturing takes place at shallower levels in the Earth than folding, though both may occur in the same placeatthesametime. Source: Internet

8.3. Fractures in rocks Minor fractures in rocks, both tensional and shear, are called joints. Larger shear fractures, where there are significant displacements of rock bodies across the plane, are called faults Source: Internet

8.4. Faults As with all structural surf aces, the orientationofafault is expressed by its strike and dip. The displacement across a fault is called its slip. Source: Internet

8.4. Faults As with all structural surf aces, the orientation of a fault isexpressedbyitsstrikeanddip. The displacement across a fault is called its slip. Source: Geology for Civil Engineers A.C.McLean, C.D. Gribble

8.4. Faults Tectonic forces determine the style of faulting. Faults are concentrated zones of weakness and of percolation, which may receive local remedial treatment in engineering works.

8.4. Faults Source: Understanding Earth J.Grotzinger, T.H. Jordan, F. Press, R. Siever

8.5. Joints Joints, if frequent, have a considerable effect on the bulk properties of a rock mass. Joints affect the strength and stability of the rock mass, and the voids associated with their presence allow increased circulation of ground water through them. This may be relevant in water supply, in drainage of a deep excavation or in leakage through the sides or floor of a reservoir. Source: Understanding Earth J.Grotzinger, T.H. Jordan, F. Press, R. Siever

Theme 9. The geological timescale. Geological maps and sections 9.1. The geological timescale 9.2. Geological maps and sections

9.1. The geological timescale The principle of uniformitarianism states that the processes that created and moulded the rocks of the Earth in its past are by and large the same as those active today. The principle of superposition states that the sedimentary layers are deposited in a time sequence, withthe oldest onthe bottom andthe youngest onthe top.

9.1. The geological timescale In some layers of sedimentary rock there are traces of the animals and plants that were living at the time the sediment was being deposited and were covered by sediment after their deaths. These remains are called fossils, and their study is palaeontology. The most common fossils are the hard parts of organisms bones, shells, coral skeletons, scales and teeth and the imprints of leaves with the original vegetable matter transformed to a thin, black film of coal.

9.1. The geological timescale Source: Internet

9.1. The geological timescale The idea that rocks and fossils can reveal the past history of the Earth and that rock layers may be understood and interpreted in terms of past environments is an important and central concept in geology. This branch of the science, which studies rocks especially layered rocks as Earth history, is called stratigraphy.

9.1. The geological timescale Source: Internet

9.1. The geological timescale Source: Geology for Civil Engineers A.C.McLean, C.D. Gribble

9.2. Geological maps and sections Source: USGS

9.2. Geological maps and sections Source: Internet