Types of Brittle Deformation

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Pelatnas IESO Geologi Struktur 2013 Pelatnas IESO Geologi Struktur 2013

Deformasi Rapuh

Salahuddin

Salahuddin Husein

Husein

Jurusan

Jurusan TeknikTeknik GeologiGeologi Fakultas

Fakultas TeknikTeknik UniversitasUniversitas GadjahGadjah MadaMada 2013

2013

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Types of Brittle Deformation

Pluijm & Marshak (2004)

Types of Brittle Deformation

Fossen (2010) common during shallow deformation of

porous rocks and sediments

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Types of Brittle Deformation

Fossen (2010)

Intragranular fractures (restricted to single grains) in cataclastically deformed porous sandstone

Intergranular fractures (extend across a number of grains) in metamorphic rock

Tensile Cracks

A crack in a crystal lattice. The crack is a plane of finite extent across which all atomic bonds are broken.

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Tensile Cracks

Pluijm & Marshak (2004) The importance of preexisting cracks in creating stress concentrations.

Tensile Cracks

Pluijm & Marshak (2004) Development of a throughgoing crack in a block under tension.

• When tensile stress (σ_t) is applied, Griffith cracks open up. • The largest, properly oriented cracks propagate to form a

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Tensile Cracks

Pluijm & Marshak (2004) Longitudinal splitting.

Modes of Crack Displacement

Mode IV (closing mode) is sometimes used for

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Modes of Crack Displacement

Fossen (2010) Extension fractures:

•Joints; have little or no macroscopically detectable displacement.

•Fissure; when filled with air or fluid.

•Veins; mineral-filled extension fractures. •Dikes; magma-filled

fractures.

Stylolites: contraction fracturesor closing fractures (anticracks)

Fracture Growth

Pluijm & Marshak (2004) Propagating shear-mode crack and

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Fracture Growth

Fossen (2010)

Fault Surface Veins

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Fault Surface Veins

Fracture formation

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Joints

Joint Morphology

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Joint Morphology

Fossen (2010)

Joint Morphology

Fossen (2010)

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Joint Morphology

Fossen (2010)

Elliptically arranged arrest lines

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Plumose Structures

Pluijm & Marshak (2004) Straight plume

Curvy plume Multiple

arrest

Joint Arrays

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Joint Arrays

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Joint Formation Sequence

Pluijm & Marshak (2004) Joints form in a random sequence, but with regular spacing.

Stress Shadow

Pluijm & Marshak (2004) Stress shadow defines the joint interval.

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Joint Origins: Unroofing Joints

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Joint Origins: Fault-related Joints

Pluijm & Marshak (2004) Formation of joints in the

hanging-wall block of a

region in which normal faulting is taking place.

Formation of joints

above an irregularity in a (reverse) fault surface.

Pinnate joints along a fault.

Joint Termination

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Joint Termination

Fossen (2010) Compressive stress

Extenxional stress

Joint Termination

Joints terminating without curving when they approach one another.

Joints curving into each other and linking.

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Vein Arrays

Pluijm & Marshak (2004) Simple en echelonarray.

Sigmoidal en echelon veins.

Vein Fills

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Vein Fills

Deformation Bands

Cataclastic deformation band, Navajo Sandstone

Cataclastic deformation band, Nubian Sandstone

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Mechanism of Deformation Bands

Fossen (2010)

• Develop by shear-related disaggregation of grains by means of grain rolling, grain boundary sliding and breaking of grain bonding cements.

• Disaggregation bands can be almost invisible in clean sandstones, but may be detected where they cross and offset laminae.

Deformation Bands

Fossen (2010)

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Deformation Bands

Fossen (2010)

Conjugate (simultaneous and oppositely dipping) sets of cataclastic deformation bands in Entrada Sandstone, Utah.

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Fault Terminology

Pluijm & Marshak (2004) Fault

Fault zone

Fault splay

Anastomosing fault

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Fault Terminology

Fossen (2010)

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Fault Terminology

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Identifikasi Sesar

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Fault Sets

Footwall

Hangingwall

Normal fault (extensional) • Older rocks in HW

over younger rocks in the FW.

• Stratigraphic omission

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Footwall

Hangingwall

Reverse (thrust fault)

Reverse (Thrust) Fault Characteristics

• Younger rocks in HW over older rocks in the FW.

• Stratigraphic repetition

Slip and Separation

•Slip - actual relative displacement between two points that occupied the same location before faulting

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Fault Terminology

Fossen (2010)

Fault Terminology

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Fault Symbols

Normal faults sense of drag

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Normal Fault Zone

Chiang Muan, Thailand

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Rotational Faults

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Duplexes are imbricate fault systems linked on both sides by major faults, all faults must have been active synchronously

Duplex Faults

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Fault Offsets

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Fault Bends

Pluijm & Marshak (2004) Restraining

bend

Releasing bend

Fault Anatomy

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Fault Anatomy

Fossen (2010)

Fault Anatomy

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Fault Displacement

Pluijm & Marshak (2004) Fault displacement is about 3% of fault length.

Stick-Slip Behaviour

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Fault Displacement

Fossen (2010)

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Fault Terminations

Pluijm & Marshak (2004) A. Fault merging

B. Fault horsetailing

C. Transfer onto ductile deformation

Fault Terminations

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Fault Terminations

Pluijm & Marshak (2004) Tip line: boundary between the slipped and unslipped region at the end of a fault.

Damage Zone

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Damage Zone

Fossen (2010)

Hanging-wall rollover (fault-bend fold) related to bend in the main fault. The damage zone is unusually wide due to the complications posed by the fault bend. Synthetic and antithetic shear bands are separated by color.

Damage Zone

Fossen (2010)

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Subsidiary Faults

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Fault Systems

Pluijm & Marshak (2004) Imbricate

Duplex

Fault Systems

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Fault Population

Fossen (2010)

The development of curved fault systems in unconsolidated sand.

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Fault Population

Fossen (2010)

• The Wasatch fault zone near Salt Lake City, Utah, crudely indicated by white dashed line.

• Note the curved fault geometry, indicating a history of segment linkage.

• Sketches of various stages of plaster extension experiment indicate how such fault zones can form.

Overlap Zones

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Fault Rocks

Sibson (1977)

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Fault-related Folds

Pluijm & Marshak (2004) Folding in a fault zone Folding in a fault zone

Detachment fold Drape fold over faulted basement

Change with Depth

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Fault and Stress

Pluijm & Marshak (2004) Anderson’s theory of faulting

(high-angle) normal faults (low-angle) reverse faults (vertical) strike-slip faults

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Conjugate Fractures

Norway

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Conjugate Faults

Jerudong, Brunei Darussalam

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Listric Faults

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Listric Fault Geometry

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Listric Fault Geometry

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Fault Growth

• Faulting preferentially initiated in sandstone unit.

• Mechanical contrasts due to changes in lithology are enormously important to

understanding structural style in numerous ways.

Fault Growth

Two end members for fault growth:

• Radial tip propagation (a) • Segment linkage (b)

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Growth of Boundary Fault

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