Structural Geology

Question 1

A rule that states that microstructures are keys to mimic the styles and orientation of macrostructures of the same generation within a particular area.

Answer 1

Pumpelly’s rule

Question 2

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.

Answer 2

Vening Meinesz’ Hypothesis

Question 3

also called “Uniform pressure”

Answer 3

Hydrostatic pressure

Question 4

It measures the stiffness or stretcheability of a material, defined as the ratio of stress over strain.

Answer 4

Young’s Modulus

Question 5

It expresses the relationship between volume change and stress. The ratio of lateral change due to compression or tension.

Answer 5

Poisson’s Ratio

Question 6

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

Answer 6

a. Speleology - caves
b. Pedology - soils
c. Rheology - solids/fluids ability to flow due to strain
d. Palynology - nanometer-sized organic-walled fossils

Question 7

occurs where two subparallel thrusts of approximately equal displacement are separated by a deformed interval that is thin relative to its total area extent.

Answer 7

Duplex

Question 8

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.

Answer 8

Decollements

Question 9

Differentiate buckling and bending

Answer 9

Bending - force is applied not parallel to the layer, results in folding
Buckling - force applied is parallel to the layer, resulting in folds

Question 10

Joints that exhibit feathered structure
a. nonsystematic
b. pinnate
c. plumose
d. Griffith

Answer 10

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)

Question 11

Which among the following are classified as metamorphic rock with inequant grains and foliation?

a. Hornfels
b. Skarn
c. Anthracite
d. Migmatite

Answer 11

Migmatite

Question 12

Deformation of a rock by extreme microbrecciation, due to mechanical forces applied in a definite direction, without noteworthy chemical reconstitution of granulated minerals.

Answer 12

Mylonitization

Question 13

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

Answer 13

Cataclasis

Question 14

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.

Answer 14

Pressure Solution (e.g. Stylolites)

Question 15

refers to the nucleation and growth of new minerals as pre - existing minerals become unstable due to temperature/ pressure changes.

Answer 15

Neocrystallization

Question 16

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

Answer 16

Pseudotachylites

Question 17

is a general term for fine - grained, contact metamorphic rock rich in silicate minerals

Answer 17

Hornfels

Question 18

wollastonite, tremolite, grossular garnet, spessartine garnet and andradite garnet are common calc - silicate minerals produced by

Answer 18

contact metamorphism of carbonate

Question 19

is a common alteration product of periclase in marble and is created during serpentinization of Forsterites

Answer 19

Brucite - Mg(OH)2 … (Talc is also a product of serpentinization of pyroxene)

Question 20

occurs as a result of the exchange of sodium from seawater for calcium in plagioclase, which converts the plagioclase into albite.

Answer 20

Spilitization

Question 21

is the name for sodium - rich basalts that form along ocean ridges and volcanic arcs

Answer 21

Spilities

Question 22

refers to the uniform compressive force directed radially inward by the surrounding mass of water.

Answer 22

Hydrostatic stress

Question 23

refers to a uniform compressive force exerted radially inward due to the mass of surrounding rock.

Answer 23

Lithostatic stress

Question 24

What is the lithostatic pressure gradient value?

Answer 24

3 kbar for every 10 km

Question 25

occurs when at least one principal stress has a magnitude not equal to the other principal stresses

Answer 25

deviatoric stress

Question 26

strain in which parallel lines remain parallel, perpendicular lines remain perpendicular and circles deform to ellipse shapes

Answer 26

Homogeneous

Question 27

infers that no rotation of the initial to final strain state. Usually described with stress directions normal to the axes.

Answer 27

Coaxial strain

Question 28

elastic behavior is also referred to as

Answer 28

Hookean behavior

Question 29

Young ’ s modulus has an average value of for crustal rocks.

Answer 29

∼10 − 11 Pa

Question 30

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

Answer 30

Cataclastic Flow

Question 31

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.

Answer 31

Solid state diffusion/grain boundary diffusion/volume diffusion

Question 32

The brittle – ductile boundary zone can be generalized as existing at depths and temperatures of?

Answer 32

depths ∼ 10 – 20 km and temperatures of ∼ 300 °C.

Question 33

Biotite starts to undergo ductile deformation when temperature reaches: a. ∼ 250 ° C b. ∼ 300 ° C c. ∼ 400 ° C d. ∼ 650 – 700 ° C

Answer 33

Biotite ∼ 250 ° C Quartz ∼ 300 ° C Feldspar ∼ 400 ° C Amphibole ∼ 650 – 700 ° C

Question 34

Describe the strain direction if you see an en echelon quartz vein array that looks like "S S S S"

Answer 34

Left lateral

Question 35

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

Answer 35

Crenulation lineations

Question 36

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.

Answer 36

Stretching lineations

Question 37

are textures inherited from the original rock type (protolith), and which have survived metamorphism

Answer 37

Relict Textures

Question 38

What is the size of a coarse-grained crystal?

Answer 38

<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

Question 39

A metamorphic macrotexture described as: Fine-grained, granular interlocking grains, possibly of variable shapes and sizes. No preferred orientation.

Answer 39

Hornfelsic

Question 40

Only the durable mineral partly survive the crushing force and the less durable ones are powdered, producing pseudoporphyritic texture.

Answer 40

Cataclastic texture

Question 41

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

Answer 41

Calcite, vesuvianite, scapolite

Question 42

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

Answer 42

two sets of joints nearly at right angles to one another

Question 43

are elongated openings or fissures that form between blocks of limestone in karst landscapes; defined as a cleft in limestone pavement.

Answer 43

Grike

Question 44

refers to a situation where different types of sedimentary rocks are juxtaposed against each other, indicating a break in sedimentation that involves contrasting lithologies.

Answer 44

heterolithic unconformity

Question 45

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

Answer 45

in which anticlines and synclines of different folds coincide

Question 46

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 46

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.

Question 47

What is the Interlimb angle of tight fold?

Answer 47

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...

Question 48

What is the Interlimb angle of Open fold?

Answer 48

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...

Question 49

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

Answer 49

steep angular flexure in bed

Question 50

What is the term for a synclinal structure of regional extent composed of smaller folds: a. synform b. syneclise c. synelinorium d. geosyncline

Answer 50

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.

Question 51

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

Answer 51

lineated fault surface

Question 52

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 52

Answer: Wrench fault (essentially a strike-slip fault but due to strata orientations, it looks like a dip-slip fault on an outcrop)

Question 53

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

Answer 53

a thrust sheet that displays the rocks beneath it

Question 54

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

Answer 54

San Andreas fault of North America (both transform and wrench)

Question 55

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

Answer 55

its horizontal surface

Question 56

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

Answer 56

formation of a rift

Question 57

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 57

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

Question 58

What does USCS mean by "fines"?

Answer 58

Clays and Silts, materials that pass through Sieve No. 200

Question 59

What does USCS mean by "clean"?

Answer 59

are <5% clays and silts composition

Question 60

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 60

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

Question 61

What is the group symbol for fat clay in USCS?

Answer 61

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