Describe the classic conditions that form coal. Your discussion should include c
ID: 160294 • Letter: D
Question
Describe the classic conditions that form coal. Your discussion should include conditions from deposition to maturation (be sure to include a brief discussion of how the burial history affects coal quality). Explain, with the aid of diagrams, the ore forming processes responsible for three (3) distinct styles/classifications of deposit (e.g. orthomagmatic, placer, hydrothermal, VHMS etc.). Draw a fold indicating the following features: hinge, axial plane, inflexion points, limbs, wavelength. Using diagrams, explain how folds are classified based on their inter-limb angle and closure direction (shape). Explain and distinguish between the concepts of stress and strain. With the aid of suitable diagrams, following Anderson's theory of faulting, describe the relationship between principal stress directions and dykes, thrusts, and sills. Describe, with the aid of sketches, the nature, stress state and typical geological structures of the three (3) principle tectonic boundary settings.Explanation / Answer
6. Answer )
Coal formed millions of years ago when the earth was covered with huge swampy forests where plants - giant ferns, reeds and mosses - grew. As the plants grew, some died and fell into the swamp waters. New plants grew up to take their places and when these died still more grew. In time, there was thick layer of dead plants rotting in the swamp. The surface of the earth changed and water and dirt washed in, stopping to decaying process. More plants grew up, but they too died and fell, forming separate layers. After millions of years many layers had formed, one on top of the other. The weight of the top layers and the water and dirt packed down the lower layers of plant matter. Heat and pressure produced chemical and physical changes in the plant layers which forced out oxygen and left rich carbon deposits. In time, material that had been plants became coal.
Coals are classified into three main ranks, or types: lignite, bituminous coal, and anthracite. These classifications are based on the amount of carbon, oxygen, and hydrogen present in the coal. Coal is defined as a readily combustible rock containing more than 50% by weight of carbon. Coals other constituents include hydrogen, oxygen, nitrogen, ash, and sulfur. Some of the undesirable chemical constituents include chorine and sodium. In the process of transformation (coalification), peat is altered to lignite, lignite is altered to sub-bituminous, sub-bituminous coal is altered to bituminous coal, and bituminous coal is altered to anthracite.
However, the deposits in the Moscow Basin have never gone beyond the lignite stage. It’s too cold!
Finally, recent accumulations (from 10,000 years ago to today) are very rich in fibrous debris known as peat, in which the shapes of branches and roots can still be discerned. This material was not buried deep enough to contain elemental carbon.
The quality of surface and ground water may be affected adversely by the disposal of the ash and sludge that result from the burning of coal and cleaning of flue gases. These are some of the serious problems requiring either improved or new remedies. The affinities of trace elements for either the organic compounds or the minerals in coal affect the quality of the coal. The interplay of the many factors that affect the peat and the resulting coal affects its composition, but the composition is never quite static because it is subject to continuing change.
7 Answer)
As we know, an ore is composed of ore minerals and gangue, which can be utilised for a profitable extraction of one or mere metallic compounds or metals. The entire crust of the earth consists of minerals. They occur as solid masses, or rocks of which the earth's crust is composed, or as local accumulator s of varying size, such as veins, pockets or impregnations in rocks.
The processes of formation of mineral deposits are grouped into three main types:
(A) Magmatic.
(B) Sedimentary.
(C) Metamorphic.
Each type of these processes includes a number of subsidiary processes associated with them. Mineral deposits formed due to the verious processes associated with magmatic activities are called 'Primary-Mineral Deposits'. These are also called 'hypogene-deposits' Mineral deposits arising out of the processes of weathering, and activities of several geological agents are called 'Secondary Mineral Deposits'. These are closely associated with the sedimentary processes of formation. Metamorphic mineral deposits are the outcome of metamorphic processes acting upon an earlier formed mineral deposits or rocks.
(A) The Magmatic process of formation of mineral deposits include the following processes:
1. Magmatic concentration.
2. Pegmatite (pneumatolytic).
3. Contact-metasomatic process.
4. Hydrothermal processes.
5. Sublimation.
Placer deposits
These are made of alluvial, colluvial and eluvial material, which contain economic quantities of some valuable minerals:
Alluvial: Detrital material which is transported by a river and usually deposited along the river's pathway, either in the riverbed itself or on its floodplain.
Colluvial: Weathered material transported by gravity action such as on scree slopes.
Eluvial: Weathered material still at or near its point of formation.
The most common placer deposits are those of gold, platinum, group minerals, gemstones, tin, rutile, monazite and zircon.
- See more at: http://australianmuseum.net.au/geological-ore-deposits#sthash.8q08YmoQ.dpuf
Hydrothermal deposits:
As we know, a magma due to the alteration of physicochemical conditions gradually cools down, producing rock-forming silicate minerals under different conditions of temperature and pressure. It also gives rise to a segregation of residual solutions enclosed within that parent rock which is obvious form the Bowen's reaction series.
Thus towards the end of the process of crystallization, the once widely dispersed gases and metals have collected near the top of the intrusive body. In moving up, the gases ooze and stream through the magma and collect some of the metals in their journey. At this stage pressure may force the gases and their dissolved rare elements to leave the magma chamber and to move along zones of weakness towards the surface. Such fluids may begin their journey upwards as liquids or a gas which later becomes liquid and this hot water solution is known as hydrothermal solution.
8 Answer)
Hinge Fold: : Fold hinges may be abrupt hinge points, such as along kink bands or chevron folds, but are more commonly broader hinge zones, such as within concentric folds.
axial plane fold: The hinge line of a fold may be curved, but where it is a straight line, it is also called the fold axis. If the fold axis is not horizontal, the fold is plunging. If a plane exists that contains the hinge line for each folded layer, it is called the axial plane or axial surface. In cross section view, it is a line that passes through all the hinge points and is called the axial trace.
Inclection Points: Synclines and anticlines consist of two fold limbs that meet along a hinge line. This may be an abrupt change at a hinge point, or a broader hinge zone. The change in curvature along each limb is the inflection line.
Limb: limb point where sense of curvature changes
Wave length: Wave length of the fold is the distance between the hinges on each side of the fold
9 Answer)
There are 5 main concepts with which students struggle when thinking about stress and strain:
rocks deform,
stress causes strain and strain results in structures,
different physical conditions create different structures,
inferring stress from faults, and
the relationship between analogs and reality.
Rocks deform:
Many students have a difficult time realizing that rocks can bend or break. They also may have difficulty imagining the forces necessary to fold or fault rocks or comprehending that the seemingly constant Earth can change dramatically over time.
Stress causes strain, strain results in structures:
Many geologists consider it important for introductory students to understand that visible structures are a record of the stress and physical conditions in the Earth. As a result, the differences between stress, strain and structures formed during strain become key concepts.
A thrust fault is a type of reverse fault in which the fault plane angle is nearly horizontal. Rocks can slip many miles along thrust faults
Two converging continental plates smash upwards to create mountain ranges . Stresses from this uplift cause folds, reverse faults, and thrust faults, which allow the crust to rise upwards.
10 Answer)
The nature stress state and typical geological structure of principle tectonic boundary settings
Like continental volcanoes, submarine volcanoes are most common where tectonic plates move towards or away from each other. In the case of divergent plate boundaries, where plates are spreading away from each other, the rate of plate movement plays an important role in determining the type of volcano that forms and the rate of eruptive activity. Submarine volcanoes at convergent plate boundaries (subduction zones) are much like their subaerial ("under air" or continental) counterparts except that the weight of the overlying water modifies their eruption style. Hot spots leave linear "tracks" of seamounts across the ocean basins and build some of Earth's largest volcanoes.
In essence, plate-tectonic theory is elegantly simple. Earth’s surface layer, from 50 to 100 km (30 to 60 miles) thick, is rigid and is composed of a set of large and small plates. Together these plates constitute the lithosphere, from the Greek lithos, meaning “rock.” The lithosphere rests on and slides over an underlying weaker (but generally denser) layer of plastic partially molten rock known as the asthenosphere, from the Greek asthenos, meaning “weak.” Plate movement is possible because the lithosphere-asthenosphere boundary is a zone of detachment. As the lithospheric plates move across Earth’s surface, driven by forces as yet not fully understood, they interact along their boundaries, diverging, converging, or slipping past each other. While the interiors of the plates are presumed to remain essentially undeformed, plate boundaries are the sites of many of the principal processes that shape the terrestrial surface, including earthquakes, volcanism, and orogeny (that is, formation of mountain ranges).
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