- Abstract
- Affiliation
- All
- Authors
- Book Series
- DOI
- EISBN
- EISSN
- Full Text
- GeoRef ID
- ISBN
- ISSN
- Issue
- Keyword (GeoRef Descriptor)
- Meeting Information
- Report #
- Title
- Volume
- Abstract
- Affiliation
- All
- Authors
- Book Series
- DOI
- EISBN
- EISSN
- Full Text
- GeoRef ID
- ISBN
- ISSN
- Issue
- Keyword (GeoRef Descriptor)
- Meeting Information
- Report #
- Title
- Volume
- Abstract
- Affiliation
- All
- Authors
- Book Series
- DOI
- EISBN
- EISSN
- Full Text
- GeoRef ID
- ISBN
- ISSN
- Issue
- Keyword (GeoRef Descriptor)
- Meeting Information
- Report #
- Title
- Volume
- Abstract
- Affiliation
- All
- Authors
- Book Series
- DOI
- EISBN
- EISSN
- Full Text
- GeoRef ID
- ISBN
- ISSN
- Issue
- Keyword (GeoRef Descriptor)
- Meeting Information
- Report #
- Title
- Volume
- Abstract
- Affiliation
- All
- Authors
- Book Series
- DOI
- EISBN
- EISSN
- Full Text
- GeoRef ID
- ISBN
- ISSN
- Issue
- Keyword (GeoRef Descriptor)
- Meeting Information
- Report #
- Title
- Volume
- Abstract
- Affiliation
- All
- Authors
- Book Series
- DOI
- EISBN
- EISSN
- Full Text
- GeoRef ID
- ISBN
- ISSN
- Issue
- Keyword (GeoRef Descriptor)
- Meeting Information
- Report #
- Title
- Volume
NARROW
GeoRef Subject
-
all geography including DSDP/ODP Sites and Legs
-
Atlantic Ocean
-
North Atlantic
-
Gulf of Mexico (1)
-
North Sea (1)
-
-
-
Lewis thrust fault (1)
-
North America
-
Appalachians
-
Southern Appalachians (2)
-
-
-
United States
-
Alabama
-
Calhoun County Alabama (2)
-
Cleburne County Alabama (2)
-
Shelby County Alabama (2)
-
Talladega County Alabama (2)
-
-
Montana
-
Glacier County Montana (1)
-
-
-
-
metamorphic rocks
-
metamorphic rocks
-
cataclasites (1)
-
-
-
minerals
-
carbonates
-
dolomite (1)
-
-
-
Primary terms
-
Atlantic Ocean
-
North Atlantic
-
Gulf of Mexico (1)
-
North Sea (1)
-
-
-
crust (1)
-
deformation (2)
-
faults (4)
-
folds (2)
-
foliation (1)
-
geophysical methods (1)
-
metamorphic rocks
-
cataclasites (1)
-
-
North America
-
Appalachians
-
Southern Appalachians (2)
-
-
-
plate tectonics (1)
-
sedimentary rocks
-
carbonate rocks
-
dolostone (1)
-
-
clastic rocks
-
shale (1)
-
-
-
sedimentation (1)
-
structural analysis (1)
-
structural geology (2)
-
tectonics (4)
-
United States
-
Alabama
-
Calhoun County Alabama (2)
-
Cleburne County Alabama (2)
-
Shelby County Alabama (2)
-
Talladega County Alabama (2)
-
-
Montana
-
Glacier County Montana (1)
-
-
-
-
sedimentary rocks
-
sedimentary rocks
-
carbonate rocks
-
dolostone (1)
-
-
clastic rocks
-
shale (1)
-
-
-
Influence of Growth Strata on the Evolution of Fault-related Folds—Distinct-element Models
ABSTRACT We construct a series of distinct-element models that consist of bonded assemblies of elastic particles that simulate the brittle deformation associated with large-scale, fault-related folding over a rigid footwall. The initial rock mass is simulated by a series of discrete, circular, elastic, frictional particles, bonded in shear and tension and capable of progressive fracture during loading. This produces discontinuities within the simulated rock mass: Regions of intact material are separated by discrete faults or fault zones. The simulations are fully dynamic. Material properties are assigned as microproperties of and between particles; elastic stiffness, friction, and bond strength (shear and tensional) describe particle interactions. Because the macroscopic elastic, failure, and flow properties are not directly determined by the micro-properties, uniaxial and biaxial compression tests must be conducted on a representative specimen to determine macroscopic parameters, such as unconfined compressive strength, Young’s modulus, friction angle, and cohesion. To determine the effect of growth strata on the evolution of the underlying fold, growth strata with thicknesses equivalent to 0%, 25%, 50%, 75%, and 100% of the elevation of the associated anticline above the upper footwall flat are added to the upper surface of the models. The presence or absence of growth strata has a significant effect on the final geometry of the associated fault-related fold. The growth strata provide resistance to forelandward translation, causing folds to tighten from open, gentle ramp anticlines with no or thin growth strata to strongly overturned fault-propagation-type folds with thick growth sequences. The nature and intensity of fracturing is strongly affected by growth-strata thickness. All models have effectively identical early stages, as a result of thin or nogrowth, and initial deformation at the thrust rampisalwaysby back thrusting. This changes with increased burial. (1) With no growth strata, back thrusting continues, although fault dips become shallower with time. (2) With intermediate thicknesses of growth strata, back thrusting gives way to, or alternates with, bedding-parallel shear. (3) With thick growth strata and thus high confining pressure, brittle deformation is inhibited and replaced by elastic deformation of the particles. These models produce realistic-looking packages of growth strata. Well-developed growth triangles are common in backlimbs, and are cut by the faults that originate in the pregrowth strata. The growth strata commonly show angular unconformities and stratigraphic pinch-outs. Overturned forelimb growth strata are significantly deformed, recording brittle deformation associated with progressive growth of the underlying fold.
ABSTRACT We use numerical models to investigate the deformation associated with folding by hinge-zone migration. The model geometry consists of a layer that is displaced over a basal fault with a flat-ramp trajectory. The models use an elastic-plastic Mohr-Coulomb material that allows deformation to be localized as shear bands. Bedding can be simulated as discrete interfaces of slip or as weak layers within the continuum. Two orientations of shear bands are dominant: (1) back thrusts that initiate along the axial surface of the fold and (2) layer-parallel shear bands. The style of deformation in the models is controlled by material properties, degree and type of bedding anisotropy, and geometry of the basal fault. In models with homogeneous, isotropic, elastic–perfectly plastic material properties, shear strain rate is localized in a band along the axial surface that is fixed above the fault bend. A uniform region of high shear strain develops above the ramp in material that has moved through the active axial surface. With cohesion softening, deformation is accentuated in the high-shear-strain-rate band. The active shear band is fixed to the material and moves up the ramp, but its base is pinned to the fault bend. As a result, the band rotates until it reaches an unfavorable orientation relative to the local stress field; then it is abandoned as a new shear band propagates up from the fault bend. This mechanism produces a series of abandoned back-thrust shear bands above the ramp. The introduction of bedding-parallel anisotropy or a rounded fault bend causes layer-parallel shear bands to develop. With increasing anisotropy, there is a transition from back thrusting to layer-parallel shear. The layer-parallel shear bands initiate at the fold’s axial surface, and the propagating tips of the bands remain at the axial surface while inactive parts of the bands are carried up the ramp. The models provide insight into the development of back thrusting and bedding-parallel slip, two mechanisms of hinge-zone migration that are common features in both natural structures and analog models.