Normal Fault Movement Research Articles

Lateral displacement during Neogene convergence in the western and central Alps

Although major deformation in the western Alps is clearly the result of north-northwest-directed thrust tectonics, there is evidence suggesting that orogen-parallel deformation may have been important in the late tectonic history of the western Alps. The authors propose that this northeast-trending deformation includes (1) southwest-directed normal-fault movement along the Simplon line; (2) a diffuse zone of northeast-striking dextral strike-slip deformation along the Rhone Valley in Switzerland, between the Mont Blanc and Aiguilles Rouges massifs, and through the Belledonne massif; and (3) southwest-directed thrusting in the Embrunais-Ubaye and Digne nappe systems of southeastern France. The correlation of these three broad regions of deformation is based on similar amounts of minimum displacement, consistent kinematics, and timing of deformation.

A local weakening of the brittle-ductile transition can explain some intraplate seismic zones

A decrease in the strength of a localized area of the lower crust would decrease the depth to the brittle-ductile transition and concentrate stress in the stronger elastic crust around and above the zone of decreased strength. Deformation within the zone of weakened lower crust would occur through viscous or dislocation creep in response to regional plate stress as well as by elastic failure in small earthquakes. Two-dimensional finite-element models of zones of weakness subjected to a regional plate stress predict stress amplification of 10–100% surrounding the local decrease in strength. A finite-element model for an irregular zone of weakness in the lower crust can generate stress directions and relative magnitudes that satisfy the focal mechanisms and seismicity of southeastern Tennessee. An analysis of the displacements and stresses in the central area of decreased crustal strength suggests that strike-slip faulting should dominate. Above this zone the strike-slip faulting should exhibit a strong thrust component. The compression and extension of the crust surrounding the weakened zone at the level of the brittle-ductile transition predicts that the dominant strike-slip faulting should exhibit components of normal faulting on the edges of the weak zone which are near a line through the weak zone parallel to the regional stress and reverse faulting on the edges which are near a line transverse to the regional stress. The seismicity of southeastern Tennessee is diffused over a narrow elliptical zone trending NE. The greatest concentration of activity is near the center. The central zone is characterized by deep-focus strike-slip events with predominantly N or E striking nodal planes. These events are responding directly to compression in the direction of the regional compressive stress and extension perpendicular to the regional compressive stress within the weak zone. The area surrounding the central zone is characterized by focal mechanisms with larger components of reverse or normal fault movements. Events with normal components are dominant on the edges in line with the regional stress as predicted by the stress model for a weak central zone under stress. The agreement between observed earthquake focal mechanisms in southeastern Tennessee and models of crustal stress surrounding a zone of weakness suggests that these events may be caused by a zone of weakness in the lower crust.

Geochronologic studies in central New England II: Post-Acadian hinged and differential uplift

{sup 40}Ar/{sup 39}Ar analyses of muscovite, biotite, and K-feldspar from central New England reveal a remarkable pattern of mineral ages: the ages are progressively younger from central to western New Hampshire and rise sharply near the Vermont border to ages more typical of post-Acadian cooling. This distribution is attributed to differential uplift via isostatic rebound of an anomalously thickened crust at the Bronson Hill anticlinorium. This explanation requires that between 6 and 8 km of normal fault motion has occurred on structures in western New Hampshire, not previously recognized to have accommodated this kind or magnitude of displacement. This hinged, differential uplift occurred from {approximately} 360-170 Ma and is consistent with a time constant for rebound of {approximately} 80 m.y.

Flexural rotation of normal faults

A conceptual model is proposed for the generation of low‐angle normal faults in Metamorphic Core Complexes. The model is based on three assumptions: (1) the isostatic response to normal fault motion is of regional extent; (2) when a fault segment is significantly rotated from the optimum angle of slip, relative to the crustal stress field, it is replaced by a new planar fault oriented in the optimum direction; and (3) the fault cuts the entire upper crust and fault motion always nucleates in the same region at the base of the upper crust. The stress field is considered to be uniform through the crust and the regional isostatic response of the crust to loads is computed using the thin plate flexure approximations. Active low‐angle normal faults are difficult to reconcile with rock mechanics theories, earthquake focal mechanism studies, and geochronologic results indicating rapid cooling of core complex rocks. The model does not require active fault slip on low‐angle faults. The flexural response to normal faulting is shown to be significantly affected by anelastic behavior of the crust and by loading due to sedimentation. The anelastic response to large bending stresses results in significant reduction in the effective elastic rigidity of the upper crust. This can explain the observed short wavelength of topographic response to normal fault loads. The model results in: (1) a nearly flat‐lying abandoned normal fault (or “detachment”) below slices of upper plate rocks and sedimentary infill; (2) a strong contrast in metamorphic grade across the abandoned “detachment”; (3) rapid movement of lower plate rocks from midcrustal depths to shallower depths. These results are qualitatively in agreement with geologic observations for core complexes.

The thrust and normal faults of the Ullapool–Strath Kanaird region and their implications for NW Highland tectonics

Synopsis In the Ullapool to Strath Kanaird region of the NW Highlands the thrusts of the Moine thrust zone generally show a foreland propagating sequence but there are important anomalies. The Moine thrust itself appears to be a late structure, slicing across the earlier thrust stacks. There are several ages of normal fault movement. An early set formed synchronous with thrusting and involved extension in a WNW–ESE direction, parallel to general thrust transport, but also extension NE–SW, perpendicular to thrusting. These variations in movement indicate non-plane strain conditions, with important implications for section restoration. The early normal faults are either cut by or decouple on the Sole thrust to the Moine thrust system. There are late normal faults however, which are well-developed in the Ullapool area, and these are probably Mesozoic in age.

Constraints on the age of movement of the Montsech and Cotiella Thrusts, south central Pyrenees, Spain

Palaeocene to Oligocene thrusting in the Pyrenees was synchronous with the development of the South Pyrenean foreland basin (collectively the Tremp–Graus, Ainsa and Jaca basins). Sedimentological and stratigraphical evidence from the foreland basin is used to constrain the age of movement of the Montsech, Cotiella and External Sierras thrusts. Movement on the emergent imbricate fan at the Montsech front began in the Early Eocene (Illerdian) during an early phase of thrusting that detached in the Triassic evaporites in that region. This phase of thrusting defined the Tremp–Graus basin as a thrust-sheet-top basin. Following the early thrusting, Cuisian age tectonics in the Tremp–Graus and Ainsa basins was dominated by minor normal fault movements during flexural subsidence associated with thrust sheet loading. Growth of the Boltaña anticline to the west of the Ainsa basin indicates that the Ainsa basin had become detached as a thrust-sheet-top basin in the Lutetian. Movement on the Peña Montañesa thrust, and by inference on the Cotiella thrust, began in post-Lutetian times during the propagation of lower thrusts that involved pre-Triassic (Variscan) basement. Thrusting in the External Sierras caused folding and faulting of Oligocene sediments, indicating the continued southward propagation of basement-involved thrusts in the Upper Eocene and Oligocene. Many faults in the Southern Pyrenees have evidence of early normal and later reverse senses of movement indicating reactivation of normal faults during thrusting.

Compressive strains generated by normal faulting

Research Article| August 01, 1984 Compressive strains generated by normal faulting David S. Brumbaugh David S. Brumbaugh 1Department of Geology, Box 6030, Northern Arizona University, Flagstaff, Arizona 86011 Search for other works by this author on: GSW Google Scholar Author and Article Information David S. Brumbaugh 1Department of Geology, Box 6030, Northern Arizona University, Flagstaff, Arizona 86011 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1984) 12 (8): 491–494. https://doi.org/10.1130/0091-7613(1984)12<491:CSGBNF>2.0.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation David S. Brumbaugh; Compressive strains generated by normal faulting. Geology 1984;; 12 (8): 491–494. doi: https://doi.org/10.1130/0091-7613(1984)12<491:CSGBNF>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Hanging-wall blocks of some normal faults located in central and southern Arizona show that both ductile and brittle localized structures formed in response to a compressive stress regime. The structures are believed to result from localized compressive stresses generated within the hanging-wall block during normal fault movement in a regional extensional stress field. Such compressive stresses may be generated by block movement over an irregular normal fault surface or by interactions of sub-blocks in the hanging-wall block. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Reactivation of Mesozoic Thrusts as Normal Faults, Humboldt Range, North-Central Nevada: ABSTRACT

Some low-angle faults in the Humboldt Range of north-central Nevada may be east-verging Mesozoic thrusts that were reactivated as normal faults with westerly displacement. Early deformation in nappes underlain by such faults produced east-verging asymmetric folds of bedding and moderate to steep northwest-dipping penetrative cleavage. These structures, as well as a shallow southeast-plunging Z finite strain axis in nappe rocks, imply west to east compression. Later deformation has younger over older juxtaposition and west-verging asymmetric folds of first foliation. These folds have shallow easterly dipping axial planes whose orientations with respect to adjacent low-angle fault planes and lineations in the fault planes indicate westerly displacement. The later deformatio thus implies reactivation of the low-angle faults as normal faults. Though timing of normal fault motion is uncertain, it appears reasonable to associate it with Cenozoic extension in the Great Basin. Reactivation of thrust faults as low-angle normal faults provides further evidence in support of thin-skinned crustal extension. End_of_Article - Last_Page 938------------

Deltaic Sedimentation and Growth Faulting, Upper Cretaceous, Colorado: ABSTRACT

The upper Pierre, Fox Hills, Laramie, and Arapahoe Formations in the western Denver basin record deltaic sedimentation during the final regression of the Cretaceous sea from eastern Colorado. Prodelta shales and siltstones (Pierre Formation) are overlain by delta-front sandstones (Fox Hills), and delta-plain sandstones, claystones and coals (Laramie Formation). The younger conglomerates of the Arapahoe Formation are braided channel deposits of the fluvial system. Two types of penecontemporaneous (growth) faulting are recognized in 5 mi of outcrop from Golden south to Interstate 70. One type of faulting cuts delta-plain sediments, resulting in a thickness increase of the Laramie Formation from 330 to 530 ft in a horizontal distance of 800 ft. By normal fault movement at the time of sedimentation, an extra 200 ft of lower Laramie sandstone, with minor claystone and thin coal, was deposited on the downthrown side of the fault. The northwest-trending fault plane curved downward toward the south from a dip of about 60° to a low-angle bedding plane fault. A second type of faulting records slumpage on oversteepened prodelta slopes created by seaward progradation of the shoreline. One slide block of shallow-water distributary-mouth sandstone (Fox Hills) about 100 ft thick moved southward down the prodelta slope into water depths estimated to be from 100 to 175 ft and was subsequently buried by prodelta clays (Pierre). The geographic position of these growth faults in the delta sequence appears to have been controlled by recurrent movement of deep-seated faults in the Precambrian basement which at the time of Laramie deposition was at depths in excess of 10,000 ft. Growth faulting heretofore unrecognized in the Cretaceous of the Rocky Mountain area, may be a common occurrence in the areas of deltaic sedimentation. Some abrupt thickness changes may be explained more readily by this process than by the commonly invoked theories of facies change or unconformities. End_of_Article - Last_Page 661------------

Late Paleozoic Structural Directions in Southern Permian Basin, West Texas and Southeastern New Mexico

This study shows the possibility of extensive lateral movement along pre-Permian faults in the Permian basin and determines, largely from subsurface evidence, the direction of the forces responsible for Pennsylvanian and Permian tectonic deformation. A review of the relation of faulting to orthogonal stress axes shows that changes in the geometry and genesis of faults are the consequences of changes in the orientation of the stress axes. Two tectonic systems can be discerned. One consists of folds and faults. The fold axes strike N35°W, whereas the fault systems include one that strikes N55-80°E with indications of right lateral movement and another that strikes N50-65°W with left lateral movement. Thus the fault pattern indicates stress in a nearly east-west direction and the folds indicate direction of stress to be about N65°E. The age of this deformation is thought to be early Late Mississippian to late Middle Pennsylvanian. Another fault system which seems to be younger is composed of faults striking slightly west of north. The most prominent example of this system is the West Platform fault, the movement on which is right lateral with a displacement of tens of miles. The stress giving rise to this system seems to have been nearly north and south and may be related to the force that powered the early and middle Wolfcampian (Permian) thrusting on the south in the Marathon salient of the Ouachita belt. The jagged pattern of the eastern edge of the Central Basin platform may be caused by conjugate faults of this system. The later tectonic history of the region is marked by relaxation of stress and subsequent normal fault movement on the previously formed fault planes. This movement deepened preexisting basins; reefs and other sedimentary features formed around the peripheries of these depressions. Formation of salt pans in later Permian time was related to minor movement along the faults. Remnants of the basins persisted throughout Triassic time, but were obliterated by the great change in geography during Cretaceous time. Renewed movement along the old lines of weakness during Tertiary time caused the eastward tilting of the Delaware basin and the formation of grabens along its west edge. Deep channels in Pleistocene and Holocene sand deposits in the eastern part of the Delaware basin reflect soluti n of the underlying Permian evaporites over these lines.

THE MARYBOROUGH BASIN

The Maryborough Basin, occupying an area of 9,500 square miles, developed as a structural entity in the Mesozoic. Onshore regional mapping has shown that subsidence is controlled by ancient lineaments which have a north-westerly trend. These structural lines are characterised by normal fault movements with downthrow to the east. The eastern margin of the basin has been interpreted from geophysical data as a shallow platform. The sediments of the basin were severely folded in a post-Aptian orogeny.A maximum thickness of 31,000 feet is known in the post-Permian section. Marine conditions prevailed in the Lower Triassic, and again in the Aptian when 7,000 feet of shallow-water quartzose sediments were deposited. The remainder of the section comprises continental sediments. Currents flowing from the east in Aptian time point to an emergent high in this direction. Such a high may have been downfaulted during the post-Aptian orogeny. Four thousand feet of trachyandesitic pyroclastics and tuffaceous sediments which were deposited during the Neocomian may have been derived from an oceanic eruptive zone. This possibly corresponds to the eastern margin of the basin, and also to an interpreted vental belt in the Swain Reefs area immediately to the north-west.Mesozoic and Tertiary marine rocks are possible sources of hydrocarbon. Porous Jurassic orthoquartzite has reservoir potential, but this unit may only be tested by very deep drilling. Much of the onshore Cretaceous section is known to be tight. In the offshore area, the flattening of the northwesterly plunge of the fold structures in the Cretaceous rocks, with the possibility of the development of closures, together with the known thickening of porous, marine Tertiary sediments, enhance the prospect of hydrocarbon accumulation in this area.

Geology of Mescal Range: ABSTRACT

The Mescal Range, approximately 33 miles east of Baker, is in the central Mojave desert region of southeastern California. Here exposed, are rocks ranging in age from Precambrian to Recent. There are, however, no known sedimentary rocks of Tertiary age. Paleozoic sedimentary rocks nearly 11,000 feet thick, complexly folded and faulted, are separated from granitic augen gneiss of Lower Precambrian age by the Clark Mountain normal fault. The Paleozoic formations include: Cambrian, Prospect Mountain quartzite and Pioche shale; Cambrian through Devonian, Goodsprings dolomite and Sultan limestone; Carboniferous, Monte Cristo limestone and Bird Spring formation; Permian, Kaibab formation. The Moenkopi and Chinle formations, of Triassic age, are nearly 850 feet thick. The Aztec sandstone and Delfonte dacite, of Jurassic age, aggregate approximately 1,100 feet. During late Cretaceous time all earlier rocks were deformed by east-west compression. The west-dipping Mescal, Mesquite, and White Line faults represent major thrust faults. Other thrust faults are of an imbricate nature and are exposed on both sides of the Piute Valley. Interphased normal fault movement occurred during the same time interval, as evidenced by the Clark Mountain, Aztec, Piute, and Iron Horse faults, and the Monte Cristo fault system. Widespread zones of breccia, ranging in thickness from 500 feet to a feather edge, probably were formed by tectonic activity. Plutonic rocks of acid and intermediate composition were emplaced during the late stage of the Laramide orogeny. Erosional surfaces may exist between: the Goodsprings dolomite and the Sultan limestone, the Monte Cri to limestone and the Bird Spring formation, the Kaibab formation and the Moenkopi formation, and the Moenkopi formation and the Chinle formation. In Tertiary (?) time a complex system of dikes, ranging in composition from rhyolite to basalt, was emplaced. Older alluvium of Pleistocene age, blankets the lower flanks of the Mescal Range. Recent alluvium occurs in the larger stream courses and as a veneer over the older alluvium in the Shadow and Piute valleys. Geomorphically, the Mescal Range represents a highly dissected upland terrane, which rises about 2,000 feet above a mature surface of moderate relief referred to by Hewett (1956) as the Ivanpah Upland. The maximum elevation found in the Mescal Range is 6,493 feet and is attained just north of the Piute valley on a peak cut in the Bird Spring formation. The area is noted for the Sulphide Queen carbonate body which occurs in the Lower Precambrian basement rocks 3/4 mile east of the settlement of Mountain Pass. This ore body represents the greatest concentration of rare-earth minerals known in the world. In addition, deposits of lead, zinc, End_Page 253------------------------------ silver, gold, and copper ore are found in mineralized zones in the Goodsprings dolomite. Building stone has been quarried from the Aztec sandstone and limestone from the Monte Cristo limestone. A nominal water supply, sufficient for domestic use, is available at Valley Wells Station, Windmill, Clark Mountain Station, the Mountain Pass Mine, and Wheaton Springs. End_of_Article - Last_Page 254------------