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3/ Discuss implosion brecciation along strike-slip faults, including where such breccias are likely to form in systems where the strike-slip fault segments are 'stepping' (left or right) or abruptly bending. Discuss the overall interplay of pore fluid pressure, earthquakes/faulting, implosion, brecciation, and mineralization. You might schematically represent some of this on a simple representation of a Mohr circle diagram 2

Answer 1

BRECCIATION:

  Breccias are rocks composed of angular clasts (fragments). In monomictic breccias, clasts have the same composition, whereas polymictic breccias contain clasts of different compositions. Sedimentary breccias comprise more than 30% gravel-size (>2mm) angular clasts produced by mechanical or weathering brittle deformation of nearby rocks. Their angular shape implies minimal transport. Sedimentary breccias develop at the base of talus slopes or in proximity to active faults. Karst breccia forms during erosion, dissolution and collapse of limestone. Pressure solution due to high local stresses at contacts between angular fragments of limestone, marble, or chert can result in the interpenetration of class. Breccias can form during the emplacement of igneous bodies by explosive exsolution of volatile phases and/or explosive interaction of magma with groundwater. Intrusive breccias (such as associated with kimberlite pipes) often contain fragments of both intrusive and host rocks. Igneous breccia dykes may contain a wide range of rock fragments sampled during magma ascent and thus, provide information about the composition of rocks at deeper levels. Volcanic breccias containing lithic (rock) and vitric (glass and pumice ) fragment from near subaerial volcanic vents.

STRIKE SLIP FAULTS:

  A strike-slip fault is a fault zone where two blocks of land move horizontally rather than vertically along a fault plane. These faults can form between two small blocks of land or crustal plates. They also sometimes develop within a continental plate.

ABRUPTLY BENDING:

Strike-slip faults often seem like the least complex faults out of the bunch compared to thrust and normal faults, but it turns out that there’s a lot more to be said, Strike-slip faults are where the crust is sliding past one another and can form linkages between areas experience convergence or divergence. Where strike-slip faults bend things get interesting as it creates zones of compression (called restraining bends) and tension (called releasing bends).

PORE FLUID PRESSURE:

Pore pressure is the pressure of the fluid in the pore space of the rock, and as mentioned above, when it exceeds the hydrostatic pressure, overpressure situation occurs.

  Pore-pressure of seismically activated fractures during hydraulic stimulation of geothermal reservoir at Soultz HDR field, France is estimated based on the high-resolution mapping method of induced microseismic events. The microseismic events with similar waveforms are analyzed, and the seismically activated fracture planes are estimated using the precise source locations determined by the multiple clustering analysis. The tectonic stress measured by hydraulic fracturing method in a borehole is introduced into the calculation of critical pore-pressure for the frictional shear slip of fractures according to Coulomb's law. The estimated critical pore-pressure suggests that the fluid pressure in pre-existing fractures are a higher value near the permeable fracture zones in the well, and declines as the fractures are away from the zones.

EARTHQUAKE:

Movements within the Earth’s crust cause stress to build up at points of weakness and rocks to deform.

Stored energy builds up in the same way as energy builds up in the spring of a watch when it is wound.

When the stress finally exceeds the strength of the rock, the rock fractures along a fault, often at a zone of existing weakness within the rock. The stored energy that is suddenly released as an earthquake!

Intense vibrations, or seismic waves, spread out from the initial point of rupture, the focus, like ripples on a pond. These waves are what makes the ground shake and can travel large distances in all directions.

Near the focus, the waves can be very large, making them extremely destructive

IMPLOSION:

An implosion is simply the opposite of an explosion. In an explosion, matter and energy fly outward, but in an implosion, matter and energy collapse inward. ... So in short, implosions are caused by having a greater pressure on the outside of an object than on the inside. Things collapse intensively in implosion.

MINERALIZATION

  Mineralization is a more restrictive term for the complete conversion of an organic contaminant to its inorganic constituents by a single species or a consortium of microorganisms.

  Mineralization occurs as stockwork of thin quartz veins in granitoids and thick veins emplaced in sheared and mylonitized zones within the pluton. The reef varies with attitude from a single thin tabular body at the northern end to a composite of parallel-sheeted interconnected veins at the central and southern part attaining a maximum width of 200 m. The ore body has been oxidized near the surface at the south with complete removal of copper and reconcentrated as supergene sulfide enrichment at deeper levels. In the northern side, copper is retained in the form of cuprite, chalcocite, covellite and native copper within the oxidation zone without any supergene enrichment. The Cu-Mo mineralization occurs extensively in the entire Malanjkhand pluton in the form of reef-quartz, stringer, pegmatitic and disseminated ore.

Major OFM in the primary zone is chalcopyrite, pyrite, magnetite, molybdenite, sphalerite and gold in order of abundance. Limonite, hematite and goethite commonly occur along fractures in a quartz vein in the oxidation zone. Chloritization, sericitization, epidotization, potassic alteration and silicification are frequently present in order of occurrences.

Mohr circle plot 3.5 case 1 Case 2 case 3 case 4 Failure envelope Tensile cutoff 2.5 1.5 -1 normal stress traction