Q-1 What is the term used to describe a crystal with no rational faces? Q- 2Why
ID: 234748 • Letter: Q
Question
Q-1 What is the term used to describe a crystal with no rational faces?
Q- 2Why are the eons colloquialy collected under the title" Pre-Cambrian" not Subdivided into many periods?
Q-3What do the 3 Al3siO2 polymorphs tell us about the rock they are in?
Q-4How do P-wave Shadows Formed?
Q-5What can you tell about the depositional Envirment of a fine grained sandstone with micas in it?
Q-6 under what condition does oxidation occur and how can it be indentified?
Q-7What Does Digenesis mean?
Q-8 How do sediments vary Along the course of River?
Q9-What is geothermal gradient and why is it important?
Q-10 What are the 4 Buchan zones and what are they used for?
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Explanation / Answer
1.
2. The Precambrian Era means: "before the Cambrian period." This is an old and common term was originally used to refer to the whole period of earth's history before the formation of the oldest rocks with recognizable fossils in them. In the last few decades, however, geologists have found that there are some hard-to-discern fossils in some Precambrian rocks, so this period is now also known as the Cryptozoic or "obscure life" Eon (i.e., "crypt" = "hidden," and "zoon" = "life").
The Precambrian covers almost 90% of the entire history of the Earth. It has been divided into three eras: the Hadean, the Archean and the Proterozoic
3. The Al2SiO5 polymorphs (andalusite, kyanite, and sillimanite) are common in metasedimentary rocks, and are very useful for determining pressure-temperature conditions of metamorphism.
Kyanite occurs in gneiss, schist, pegmatite, and quartz veins resulting from high pressure regional metamorphism of principally pelitic rocks. It occurs as detrital grains in sedimentary rocks.It occurs associated with staurolite, andalusite, sillimanite, talc, hornblende, gedrite, mullite and corundum. Kyanite occurs schist, formed under extreme pressure as a result of the two landmasses that formed supercontinent Pangaea.
4. A seismic shadow zone is an area of the Earth's surface where seismographs cannot detect an earthquake after its seismic waves have passed through the Earth.
Almost all the information available on the structure of the Earth's deep interior is derived from observations of the travel times, reflections, refractions and phase transitions of seismic body waves, or normal modes. P-waves travel through the fluid layers of the Earth's interior, and yet they are refracted slightly when they pass through the transition between the semisolid mantle and the liquid outer core. As a result, there is a P-wave "shadow zone" between 103° and 142° from the earthquake's focus. In contrast, S-waves do not travel through.
5. The deposition would have been ocured in the reducing environment as mica are associated with the Sandstone.
6. When an element object undergoes oxidation, it is transformed because it has lost electrons. It can be identified by change in the colour of the substance as Fe change to red in colour by oxiidation.
7. Diagenesis is the change of sediments or existing sedimentary rocks into a different sedimentary rock during and after rock formation i.e.,lithification, at temperatures and pressures less than that required for the formation of metamorphic rocks.It does not include changes from weathering.[1] It is any chemical, physical, or biological change undergone by a sediment after its initial deposition, after its lithification. This excludes surface alteration i.e., weathering and metamorphism. These changes happen at relatively low temperatures and pressures and result in changes to the rock's original mineralogy and texture.
8. The size of the sediments will go on decreasing as it moves toward the sea or ocean.
9. Geothermal gradient is the rate of increasing temperature with respect to increasing depth in the Earth's interior.
The geothermal gradient is important for the oil, gas, and geothermal energy industries.
10. Buchan series is a another metamorphic facies series that sees a fast increase in temperature but a relatively small increase in pressure. Characteristic minerals include andalusite, biotite and cordierite.The metamorphic prograde sequence of the Buchan zone series is:
biotite - cordierite - andalusite - sillimanite
Buchan metamorphism occurs often in extensional settings, for example at rift basins.
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