Brittle (elastic, competent) solids bend and snap back, and can break. Ductile (

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Brittle (elastic, competent) solids bend and snap back, and can break. Ductile (plastic, incompetent) solids can bend but do not snap back, and can flow, Deformation is the result of directed (differential) pressure (i.e. tension, compression, and shear). Rock deformation can be [] or ductile or both (elastic viscous). Which of these mechanical states exists depends of temperature composition geostatic pressure rate of strain Temperature increase [] rock strength (resistance to breakage) and favors flow. For example, basalt at room Temperature is three times as strong as it is at 700 degree C and six times as strong as it is at 800 degree C. Vise versa, temperature decrease strengthens rock. For example, asthenosphere transitions to lithosphere by [] below a temperature of 400 degree C. Geostatic pressure is all-sided equal pressure like [] pressure that acts on a person under water. In nonporous crystalline rocks its value is positive as it is just the weight of the overburden. In permeable rocks its value is positive as it is the weight of the overburden less the pore pressure which is the weight of the fluid (usually water) that fills [] to the depth. However, in a layer its value will be negative as it is the weight of the overburden less pore pressure that is equal to the weight of the overburden to the bottom of the permeable layer. For this reason, a hole drilled in search for, say, oil is at risk of blowouts when the standard precautionary measure of keeping the hole filled with heavy mud and so under hi hydrostatic pressure proves to be inadequate. Geotectonics refers to the building (coming into being) of internal structures and land forms that result from the deformation of rock masses. Much is now understood in terms of plate tectonics. In this model, Earth's [] (outer rocky shell) is in several pieces that move with respect to each other. Crustal [] exists where plates move apart. Crustal [] exists where plates move toward each other. Crustal shear exits where plates move past each other. Motions are slow and rates of strain are of the order of cm/yr. Continental lithosphere consists of two layers: the upper layer is granitic continental crust (density approximately 2.7 g/cm^3 and thickness 25-70 km) and it floats in the peridotitic rock (density Approximately 3.3 g/cm^3 and thickness 100 km) of the uppermost mantle below. The boundary between the two layers is a detectable [] boundary called the moho. In continental crust, at shallow, less than 10-15 km, depth, rock behaves geotectonically as a brittle solid. Fractures that occur are near-surface joints and through-going faults. At intermediates (15-20 km) depths, and temperatures greater than about 300 degree C, elastic viscous behavior occurs. At greater depth, in caused by sudden slip on faults, generally originate at depths of 20 km less. At greater response to the progressive increase in geostatic pressure and high geothermal-gradient temperatures, [] deformation is the rule. Deformations that produce wave-like structures called folds can occur at any of these levels, however the style of the folding in each is characteristically different as will be described below.

Explanation / Answer

Rock deformation can be BRITTLE or ductile....

Temperature increases WEAKENS rock strength.....

Geostatic pressure is all sided equal pressure like HYDROSTATIC PRESSURE....

in permeable rocks its value is positive as the weight of overburden is less the pore pressure which is the weight of the fluid PORES.....

in this model earths LITHOSPHERE

Crustal WEAKENS When plates move away

Crustal COMPRESSION when plates move toward

The boundary between two layers is a detectable SEISMIC boundary

DUCTILE DEFORMATION

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