Structural Geology Flashcards
A rule that states that microstructures are keys to mimic the styles and orientation of macrostructures of the same generation within a particular area.
Pumpelly’s rule
An isostasy hypothesis which accounts for regional isostasy created due to flexural folding of the lithosphere. When load on the crust causes downward flexural folding of the crust, with buoyancy forces acting opposite of it, and can possibly create bulging around the load.
Vening Meinesz’ Hypothesis
also called “Uniform pressure”
Hydrostatic pressure
It measures the stiffness or stretcheability of a material, defined as the ratio of stress over strain.
Young’s Modulus
It expresses the relationship between volume change and stress. The ratio of lateral change due to compression or tension.
Poisson’s Ratio
The study of the ability of stressed solid materials, as well as fluids, to flow or deform due to strain rate, elasticity, and viscosity.
a. Speleology
b. Pedology
c. Rheology
d. Palynology
a. Speleology - caves
b. Pedology - soils
c. Rheology - solids/fluids ability to flow due to strain
d. Palynology - nanometer-sized organic-walled fossils
occurs where two subparallel thrusts of approximately equal displacement are separated by a deformed interval that is thin relative to its total area extent.
Duplex
A fault surface parallel to a mechanically weak horizon or layer, or parallel to bedding, that detaches or separates deformed rocks above from undeformed or differently deformed rocks below.
Decollements
Differentiate buckling and bending
Bending - force is applied not parallel to the layer, results in folding
Buckling - force applied is parallel to the layer, resulting in folds
Joints that exhibit feathered structure
a. nonsystematic
b. pinnate
c. plumose
d. Griffith
Answer: Plumose
a. nonsystematic (no common orientation)
b. pinnate (merges with the fault at 30-45-degrees angle)
d. Griffith (pre-existing microcracks/flaws in a rock)
Which among the following are classified as metamorphic rock with inequant grains and foliation?
a. Hornfels
b. Skarn
c. Anthracite
d. Migmatite
Migmatite
Deformation of a rock by extreme microbrecciation, due to mechanical forces applied in a definite direction, without noteworthy chemical reconstitution of granulated minerals.
Mylonitization
is a low temperature, brittle grain fracturing process that involves grain size reduction through the mechanical grinding, rotation and crushing of rock. This process produces small, angular grains that infill between larger grains as in cement mortar
Cataclasis
involves the dissolution of solid grains under high compressive stress conditions so that one grain impinges upon another grain, initiating a soluble phase in the indented grain.
Pressure Solution (e.g. Stylolites)
refers to the nucleation and growth of new minerals as pre - existing minerals become unstable due to temperature/ pressure changes.
Neocrystallization
is an extremely fine-grained to glassy, dark, cohesive rock occurring as veins that form through frictional melting and subsequent quenching during earthquakes,large-scale landslides, and impacts events
Pseudotachylites
is a general term for fine - grained, contact metamorphic rock rich in silicate minerals
Hornfels
wollastonite, tremolite, grossular garnet, spessartine garnet and andradite garnet are common calc - silicate minerals produced by
contact metamorphism of carbonate
is a common alteration product of periclase in marble and is created during serpentinization of Forsterites
Brucite - Mg(OH)2 … (Talc is also a product of serpentinization of pyroxene)
occurs as a result of the exchange of sodium from seawater for calcium in plagioclase, which converts the plagioclase into albite.
Spilitization
is the name for sodium - rich basalts that form along ocean ridges and volcanic arcs
Spilities
refers to the uniform compressive force directed radially inward by the surrounding mass of water.
Hydrostatic stress
refers to a uniform compressive force exerted radially inward due to the mass of surrounding rock.
Lithostatic stress
What is the lithostatic pressure gradient value?
3 kbar for every 10 km
occurs when at least one principal stress has a magnitude not equal to the other principal stresses
deviatoric stress
strain in which parallel lines remain parallel, perpendicular lines remain perpendicular and circles deform to ellipse shapes
Homogeneous
infers that no rotation of the initial to final strain state. Usually described with stress directions normal to the axes.
Coaxial strain
elastic behavior is also referred to as
Hookean behavior
Young ’ s modulus has an average value of for crustal rocks.
∼10 − 11 Pa
in which mesoscopic ductile behavior is facilitated by microscopic fracturing and frictional sliding. It occurs at low lithostatic pressures in the shallow crust.
a. Cataclastic Flow
b. Diffusal Mass Transfer
c. Crystal Defects
d. Twinning and Kinking
Cataclastic Flow
is a high temperature and high pressure process by which solid particles experience translation within a mineral. Crystal lattice vacancies migrate to sites of greatest stress and atoms relocate to sites of minimal stress.
Solid state diffusion/grain boundary diffusion/volume diffusion
The brittle – ductile boundary zone can be generalized as existing at depths and temperatures of?
depths ∼ 10 – 20 km and temperatures of ∼ 300 °C.
Biotite starts to undergo ductile deformation when temperature reaches:
a. ∼ 250 ° C
b. ∼ 300 ° C
c. ∼ 400 ° C
d. ∼ 650 – 700 ° C
Biotite ∼ 250 ° C
Quartz ∼ 300 ° C
Feldspar ∼ 400 ° C
Amphibole ∼ 650 – 700 ° C
Describe the strain direction if you see an en echelon quartz vein array that looks like “S S S S”
Left lateral
the most common type of cleavage in multiple deformed, intermediate to high-grade metapelitic rocks; are linear features that occur as a result of a secondary cleavage imposed upon a fine - grained rock (slate or phyllite) that experienced an earlier cleavage. These represent hinge lines formed by the intersection of two planar surfaces
Crenulation lineations
are formed by shearing of rocks during asymmetric deformation of a rock mass. It develop as elongated mineral or rock grains that define a linear fabric. It also commonly form on metamorphic foliations, on shear surfaces or on mylonitic planes. These lineations may be due to either (1) growth of a crystal in a preferred orientation, or (2) rotation of crystals toward a principal strain direction.
Stretching lineations
are textures inherited from the original rock type (protolith), and which have survived metamorphism
Relict Textures
What is the size of a coarse-grained crystal?
<0.1 mm very fine-grained
0.1-1 mm fine-grained
1-5 mm medium-grained
5-10 mm coarse-grained
> 10 mm very coarse-grained
A metamorphic macrotexture described as: Fine-grained, granular interlocking grains, possibly of variable shapes and sizes. No preferred orientation.
Hornfelsic
Only the durable mineral partly survive the crushing force and the less durable ones are powdered, producing pseudoporphyritic texture.
Cataclastic texture
Among the following, which is the least euhedral group of minerals?
a. Epidote, magnetite, ilmenite
b. Mica, chlorite, dolomite, kyanite
c. Calcite, vesuvianite, scapolite
d. Andalusite, pyroxene, amphibole
Calcite, vesuvianite, scapolite
Conjugate joints are which one of the following?
a., two sets of joints parallel to each other
b. two sets of joints nearly at right angles to one another
c. joints cutting obliquely to one another
d. irregularly disposed joints
two sets of joints nearly at right angles to one another
are elongated openings or fissures that form between blocks of limestone in karst landscapes; defined as a cleft in limestone pavement.
Grike
refers to a situation where different types of sedimentary rocks are juxtaposed against each other, indicating a break in sedimentation that involves contrasting lithologies.
heterolithic unconformity
What is polyphase folding?
a. in which two anticlines of different folds coincide
b. which the axial plane of the folds and their axes intersect at an angle
c. in which anticlines and synclines of different folds coincide
d. in which competent and incompetent beds fold differently
in which anticlines and synclines of different folds coincide
A small fold on the limb or hinge of a larger fold with which it is congruent is known as?
a. daughter fold
b. parasitic fold
c. epidermis fold
d. drape fold
Answer: Parasitic fold
Daughter Fold: This term generally refers to a smaller fold that develops from a larger, more dominant fold, often resulting from further deformation processes.
Drape Fold: A drape fold occurs when sedimentary layers are deposited over an underlying structure, causing the layers to conform to the shape of the structure beneath them, often resulting in a series of folds.
What is the Interlimb angle of tight fold?
30-5 degrees
Gentle: 180-120
Open: 120-70
Close: 70-30
Tight: 30-5
Isoclinal: <5
Notice the interlimb range differences from 60 (180-120), 50, 40, 30…
What is the Interlimb angle of Open fold?
120-70 degrees
Gentle: 180-120
Open: 120-70
Close: 70-30
Tight: 30-5
Isoclinal: <5
Notice the interlimb range differences from 60 (180-120), 50, 40, 30…
What is a monocline?
a. steep angular flexure in bed
b. open fold
c. another term for recumbent fold
d. depression in a flat bed
steep angular flexure in bed
What is the term for a synclinal structure of regional extent composed of smaller folds:
a. synform
b. syneclise
c. synelinorium
d. geosyncline
Answer: Synelinorium
Syneclise: This term refers to a large synclinal basin that may contain sedimentary deposits but does not specifically denote a structure composed of smaller folds.
Geosyncline: A geosyncline is a large-scale depression in the Earth’s crust that can accumulate sediments over geological time, often leading to the formation of mountain ranges but does not specifically refer to a synclinal structure with smaller folds.
What is a slickenside?
a. a type of fold fault
b. any type of grooved surface
c. collapse of a hill slope
d. lineated fault surface
lineated fault surface
What is a fault on which there is increasing separation or offset along the strike known as?
a. wrench fault
b. oblique fault
c. pivot fault
d. scissor fault
Answer: Wrench fault (essentially a strike-slip fault but due to strata orientations, it looks like a dip-slip fault on an outcrop)
What is a fenster?
a. a thrust sheet that displays the rocks beneath it
b. opening under a natural bridge of hard rocks
c. body of water surrounded by ice
d. plateau of denudation
a thrust sheet that displays the rocks beneath it
Possibly the longest, still active and most famous wrenchfault traced so far occurs where?
a. Alpine fault of New Zealand
b. Great Glen fault of Scotland
c. Indus-Tsangpo Suture Zone of Tibet
d. San Andreas fault of North America
San Andreas fault of North America (both transform and wrench)
Dip of a fault plane is the one that it makes in respect of what?
a. its vertical surface
b. its inclined surface
c. its horizontal surface
d. its axial plane
its horizontal surface
Taphrogeny is a term used for which phenomenon?
a. manner of burial and origin of biologic remains
b. formation of a rift
c. formation of a lava flow
d. formation of earth fissures after an earthquake
formation of a rift
According to USCS, this soil group have > 50% of materials retained at No. 4 sieve and consists of 12-50% materials that passes through No. 200 sieve.
a. CL and ML
b. SM and SC
c. SW and SP
d. GM and GC
Answer: Silty Gravel (GM) and Clayey Gravel (GC)
USCS symbols:
G - gravel, S - sand, M - silt, C - clay, O - organic, W - well-graded, P - poorly-graded, H - high liquid limit, L - low liquid limit
What does USCS mean by “fines”?
Clays and Silts, materials that pass through Sieve No. 200
What does USCS mean by “clean”?
are <5% clays and silts composition
According to USCS, this soil group are clean and have ≥ 50% of materials passes through No. 4 sieve.
a. CL and ML
b. SM and SC
c. SW and SP
d. GM and GC
Answer: Well-sorted and Poorly-sorted sand (SW and SP)
USCS symbols:
G - gravel, S - sand, M - silt, C - clay, O - organic, W - well-graded, P - poorly-graded, H - high liquid limit, L - low liquid limit
What is the group symbol for fat clay in USCS?
Answer: CH (High liquid limit clay)
USCS symbols:
G - gravel, S - sand, M - silt, C - clay, O - organic, W - well-graded, P - poorly-graded, H - high liquid limit, L - low liquid limit
