Low-angle Normal Fault System Research Articles

Crustal flow driving twin domes exhumation and low-angle normal faulting in the Menderes Massif of western Anatolia

Lower crustal flow in regions of post-orogenic extension has been inferred to explain the exhumation of metamorphic core complexes and associated low-angle normal (detachment) fault systems. However, the origin of detachment faults, whether initially formed as high-angle or low-angle shear zones, and the extension is symmetric or asymmetric remains enigmatic. Here, we use numerical modeling constrained by geophysical and geological data to show that symmetric extension in the central Menderes Massif of western Anatolia is accommodated by the crustal flow. Our geodynamic model explains how opposite dipping Gediz and Büyük Menderes detachment faults are formed by ∼40° footwall rotation. Model predictions agree with seismic tomography data that suggests updoming of lower crust beneath the exhumed massifs, represented as “twin domes” and a flat Moho. Our work helps to account for the genetic relation between the exhumation of metamorphic core complexes and low-angle normal faulting in both Cordillera and Aegean orogenic regions and has important implications on crustal dynamics in extensional provinces.

Mode of continental breakup of marginal seas

AbstractWe investigated the continent-ocean transition (COT) structure of three main marginal seas in the western Pacific Ocean (South China Sea, Coral Sea, and Woodlark Basin) to determine the tectono-magmatic processes acting during continental breakup. The COT formed from the activity of a low-angle normal fault system localizing deformation during final rifting. Extension was contemporaneous with magmatic activity, including volcanic edifices, dikes, and sills in the distalmost parts of these basins. The COT shows a sharp juxtaposition in space and time of continental crust against igneous oceanic crust, and its overall structure differs from that of magma-poor or magma-rich passive-margin archetypes. We propose that this mode of breakup is characteristic of marginal seas due to the high extension rates imposed by kinematic forces of nearby subduction zones. Revealed in the context of marginal seas, this mode of breakup and the resulting COT structures highlight the underestimated diversity of continental breakup mechanisms.

Deep External Fluid Source Along the Gubbio Normal Fault (Italy): Implications for Slip Along the Altotiberina Active Low-Angle Normal Fault System

Fluids play a critical role in fault slip, fault and damage zone development, and the distribution of seismicity in regional fault systems; however, determining the source of fluids within fault damage zones is complicated by superposition of fluid-related fabrics. Clumped isotopes applied to tectonic studies offer an opportunity to distinguish between fluid sources based on temperature and stable isotopic composition. Here we use the clumped isotope geothermometer and field observations and compare them with microstructural analysis to investigate the Gubbio normal-fault (GuF) core, a major SW-dipping epidetachment fault conjugate to the active Altotiberina low-angle normal fault in central Italy. Several distinct calcite vein sets reveal the incorporation of multiple generations of fluids during development of the damage zone. Clumped isotope results from these various precipitation phases record crystallization temperatures ranging from 87–154°C. These temperatures are broadly consistent with the presence of calcite deformation twin types II and III and are higher than estimates of regional peak burial temperatures. Additionally, stable isotope compositions within vein calcite are distinct from published isotopic values of the Apennine sedimentary succession, which constitutes the local bedrock. We propose that these observations suggest hydrothermal fluids migrated from depths greater than 6 km, which requires hydraulic connectivity along structural pathways between the shallow and deep crust, and fluid overpressures. These fluids reach the GuF via migration along the Altotiberina low-angle normal fault plane ​​and they may be either of diagenetic or of deeper subduction origin. We suggest they possibly originated from the proximal retreating Apennine subduction system, implying that subduction processes exert spatial control on the distribution of fluid-assisted normal faulting and related seismicity which is consistent with the co-migration of closely coupled subduction and hinterland extension in the Apennines from Miocene to Present.

Meteoric fluid infiltration in crustal-scale normal fault systems as indicated by δ18O and δ2H geochemistry and40Ar/39Ar dating of neoformed clays in brittle fault rocks

Both the sources and pathways of fluid circulation are key factors to understanding the evolution of low-angle normal fault (LANF) systems and the distribution of mineral deposits in the upper crust. In recent years, several reports have shown the presence of meteoric waters in mylonitic LANF systems at mid-crustal conditions. However, a mechanism for meteoric water infiltration to these mid-crustal depths is not well understood. Here we report paired δ 18 O and δ 2 H isotopic values from dated, neoformed clays in fault gouge in major detachments of the southwest United States. These isotopic values demonstrate that brittle fault rocks formed from exchange with pristine to weakly evolved meteoric waters at multiple depths along the detachment. 40 Ar/ 39 Ar dating of these same neoformed clays constrains the Pliocene ages of fault-gouge formation in the Death Valley area. The infiltration of ancient meteoric fluids to multiple depths in LANFs indicates that crustal-scale normal fault systems are highly permeable on geologic timescales and that they are conduits for efficient, coupled flow of surface fluids to depths of the brittle-plastic transition.

Rolling open Earth’s deepest forearc basin

The Weber Deep—a 7.2-km-deep forearc basin within the tightly curved Banda arc of eastern Indonesia—is the deepest point of the Earth’s oceans not within a trench. Several models have been proposed to explain the tectonic evolution of the Banda arc in the context of the ongoing (ca. 23 Ma–present) Australia–Southeast Asia collision, but no model explicitly accounts for how the Weber Deep achieved its anomalous depth. Here we propose that the Weber Deep formed by forearc extension driven by eastward subduction rollback. Substantial lithospheric extension in the upper plate was accommodated by a major, previously unidentified, low-angle normal fault system we name the “Banda detachment.” High-resolution bathymetry data reveal that the Banda detachment is exposed underwater over much of its 120 km down-dip and 450 km lateral extent, having produced the largest bathymetric expression of any fault discernable in the world’s oceans. The Banda arc is a modern analogue for highly extended terranes preserved in the many regions that may similarly have “rolled open” behind migrating subduction zones.

Assembling the world’s type shallow subduction complex: Detrital zircon geochronologic constraints on the origin of the Nacimiento block, central California Coast Ranges

Temporal and spatial patterns in the architecture of the Franciscan Complex provide valuable insights into the subduction processes through which such patterns arise. The Nacimiento Franciscan belt is an allochthonous sliver of subduction assemblages in the central California Coast Ranges displaced either: (1) from southern California by >300 km of Neogene dextral slip along the San Andreas fault system or (2) from central California to southern California and back again, by >500 km of Late Cretaceous–Paleocene sinistral slip along the Sur-Nacimiento fault followed by San Andreas–related motion. New U-Pb detrital zircon data from 20 (meta)clastic samples indicate that the Nacimiento Franciscan section was assembled between ca. 95 and 80 Ma. Abundant Cretaceous (particularly Late Cretaceous) and diminishing amounts of Jurassic and Proterozoic zircon grains point to a southern California origin for Nacimiento Franciscan protoliths, precluding significant sinistral strike-slip along the Sur-Nacimiento fault. Furthermore, the suite of detrital zircon ages reported here bears a strong resemblance to new and existing data from subduction complexes in southern California that were emplaced during Laramide shallow subduction (i.e., Sierra de Salinas, Portal Ridge, Quartz Hill, Rand, San Emigdio, and Tehachapi schists). Hence, the Nacimiento Franciscan is distinct from Franciscan rocks in central and northern California and more likely represents an outboard element of the Late Cretaceous southern California low-angle subduction system. Upon restoring the Nacimiento block to its Late Cretaceous position, an inboard-younging trend is apparent in the composite Nacimiento–southern California schist belt, suggesting that progressively younger accretionary materials were underplated farther inboard by tectonic erosion. We posit that arc and forearc elements absent from southern California were removed by a combination of physical and tectonic erosion attending shallow subduction, interleaved in the subduction complex, and recycled into the mantle. Steepening of the Laramide slab was marked by a phase of crustal extension in the overriding plate. During this phase, the Sur-Nacimiento fault likely functioned as a segment of a low-angle normal fault system spanning the southern Sierra Nevada batholith to the Nacimiento accretionary system.

Detrital zircon geochronology of Neoproterozoic–Lower Cambrian passive-margin strata of the White-Inyo Range, east-central California: Implications for the Mojave–Snow Lake fault hypothesis

Correlation of lithotectonic packages across major transcurrent structures is critical to understanding the tectonic evolution of the North American continental margin. Detrital zircon geochronology of uppermost Proterozoic to Lower Paleozoic miogeoclinal strata from the White-Inyo Mountains permits evaluation of: (1) the age and provenance of these metasediments and (2) a model for truncation of the passive margin along a postulated large-magnitude Cretaceous dextral shear zone, i.e., the Mojave–Snow Lake fault. U-Pb ages of detrital zircons from the Neoproterozoic Wyman Formation, the uppermost Proterozoic Reed Dolomite (Hines Tongue Member), and clastic strata of the Lower Cambrian Deep Springs, Campito (Montenegro Member), Poleta, and Harkless formations reflect ultimate derivation from the adjacent 1.7–pre-1.8 Ga Mojavia terrane and/or 1.7–1.8 Ga Yavapai continental basement, with subsidiary sources in both the ca. 1.4 Ga Yavapai-Mazatzal anorogenic granitoids and the >2.5 Ga North American craton, and a small proportion of 1.0–1.3 Ga grains, most likely reworked from Grenville clastic wedge deposits. Detrital zircon age spectra from the Lower Cambrian Andrews Mountain Member of the Campito Formation are unique in comparison with the remainder of the studied section, containing a major age peak centered at ca. 1.1 Ga and a subsidiary Lower Cambrian age peak, permitting calculation of a ca. 527 ± 12 (2σ) Ma maximum depositional age. These features, in addition to abundant detrital magnetite-ilmenite grains, reflect a distal source for these rocks, most likely from the ca. 1.1 Ga Pikes Peak batholith and/or the Midcontinent rift and ca. 0.53 Ga bimodal intrusions of the Oklahoma-Colorado aulacogen. In terms of zircon age distribution, allochthonous metamorphic pendants in the Snow Lake terrane of the central Sierra Nevada batholith are most similar to those of stratigraphically equivalent units in the Death Valley region and, to lesser degrees, the White-Inyo section, and the Mojave Desert region. Given the similarity and relative proximity of Death Valley facies assemblages to the Snow Lake terrane, we suggest that the latter was not transported northward from the Mojave Desert region and instead represents footwall assemblages of a late Early to early Middle Jurassic low-angle normal fault system, probably along the outer transform-truncated margin of the Last Chance thrust stack. This model implies a few tens of kilometers of offset, in contrast to the hundreds of kilometers required by the Mojave–Snow Lake fault hypothesis.

Extensional deformation structures within a convergent orogen: The Val di Lima low-angle normal fault system (Northern Apennines, Italy)

A low-angle extensional fault system affecting the non metamorphic rocks of the carbonate dominated Tuscan succession is exposed in the Lima valley (Northern Apennines, Italy). This fault system affects the right-side-up limb of a kilometric-scale recumbent isoclinal anticline and is, in turn, affected by superimposed folding and late-tectonic high-angle extensional faulting.The architecture of the low-angle fault system has been investigated through detailed structural mapping and damage zone characterization. Pressure-depth conditions and paleofluid evolution of the fault system have been studied through microstructural, mineralogical, petrographic, fluid inclusion and stable isotope analyses. Our results show that the low-angle fault system was active during exhumation of the Tuscan succession at about 180°C and 5 km depth, with the involvement of low-salinity fluids. Within this temperature - depth framework, the fault zone architecture shows important differences related to the different lithologies involved in the fault system and to the role played by the fluids during deformation. In places, footwall overpressuring influenced active deformation mechanisms and favored shear strain localization.Our observations indicate that extensional structures affected the central sector of the Northern Apennines thrust wedge during the orogenic contractional history, modifying the fluid circulation through the upper crust and influencing its mechanical behavior.

Salinia revisited: a crystalline nappe sequence lying above the Nacimiento fault and dispersed along the San Andreas fault system, central California

Salinia revisited: a crystalline nappe sequence lying above the Nacimiento fault and dispersed along the San Andreas fault system, central California

Miocene bivergent crustal extension in the Aegean: Evidence from the western Cyclades (Greece)

Current models for Miocene backarc extension of the Aegean region generally suggest that stretching was accommodated mainly by NE-dipping low-angle normal faults with N to NE sense of shear. A crustal-scale low-angle normal fault system trending over a length of more than 200 km forms the North Cycladic detachment system, which records a NE-directed normal shear sense separating the Cycladic Blueschist unit in the footwall from the Upper Cycladic unit in the hanging wall. Based on new structural field data, we propose the existence of another large-scale low-angle normal fault system, the West Cycladic detachment system, which is exposed on Kea, Kythnos, and Serifos, strikes over a length of at least 100 km, and has a possible extension to the SE, where the existence of a South Cycladic detachment system has been recently postulated. The West Cycladic detachment system shares many similarities with the North Cycladic detachment system, with the notable exception that the structure dips toward the SW with top-to-the-SSW kinematics. New 40 Ar/ 39 Ar and U-Th/He thermochronological data suggest that the West Cycladic detachment system accommodated extension throughout the Miocene. Since both the North and the West Cycladic detachment systems were active until the late Miocene but exhibit opposing shear sense, we propose that a large part of the stretching of the Aegean crust was accommodated by these two bivergent crustal-scale detachment systems.

Miocene south directed low‐angle normal fault evolution on Kea Island (West Cycladic Detachment System, Greece)

New structural, petrologic, and thermochronologic data from Kea, West Cyclades, define a crustal‐scale ductile shear zone and ductile/brittle low‐angle normal fault (LANF) system. Both the greenschist‐facies shear zone forming the footwall and the overlying LANF zone formed during constrictional strains, with a consistent top‐to‐SW‐S shear sense, with increasing finite strains toward higher structural levels but decreasing temperatures from footwall to hanging wall. The tectonostratigraphy comprises a ∼450 m thick footwall of shallowly dipping schists and calcite marbles representing the Intermediate Unit of the Attic‐Cycladic Crystalline (ACC). Above the footwall is a ∼60 m thick highly strained LANF zone, consisting of phyllonites, cataclastic schists, ultramylonitic calcite marbles, (proto) mylonitic calcite marbles, and cohesive cataclasites that arch over the whole island. These fault rocks exhibit multistage LANFs, evolving from ductile to brittle conditions. An up to ∼50 m thick brecciated limestone and dolostone sequence forms the unmetamorphosed hanging wall which is most probably part of the Upper Unit of the ACC. Multiequilibrium P‐T estimates on chlorite‐white mica pairs in the footwall yield 7–5.5 kbar/360°C–450°C for inclusions in albite and epidote, 5.5–3 kbar/400°C–350°C for the main foliation, and 3–2 kbar/350°C–280°C in localized shear bands (C and C′ foliations). The 40Ar/39Ar white mica footwall cooling ages demonstrate that greenschist‐facies retrogression occurred between ∼21 and 17 Ma. Localized, late decimeter thick shear zones were active and dynamically recrystallized before ∼15 to 13 Ma. The LANF on Kea, together with similar structures in South Attica and the West Cyclades define the West Cycladic Detachment System, characterized by ductile to brittle top‐SW‐S shear sense.

Strain and kinematic vorticity analysis of the Louzidian low-angle ductile shear detachment zone in Chifeng, Inner Mongolia, China

The Louzidian low-angle ductile shear detachment zone at the south of Chifeng is a SE-dipping, low-angle normal fault system. It is composed mainly of ductile shear zone, ductile-brittle shear zone and brittle fault zone. The ductile shear zone consists of, from bottom to top, mylonitic rocks, protomylonites and mylonites. Finite strain measurement of feldspar strain markers from those rocks using the R f /ϕ method shows that strain intensities (Es) of the mylonite at core of the ductile shear zone (Es=0.65–0.96) are higher than those of the mylonitic rocks close to the granite intrusions (Es=0.59–0.62) and of the protomylonites at top of the ductile shear zone (Es= 0.47–0.70), and the strain types of the protomylonites and mylonties are elongate strain and plane-flattening strain, respectively. The kinematic vorticity values (W k ) estimated by the Polar Mohr diagram and the Rigid Grain Net range from 0.81 to 0.90 with an average of 0.85 for the protomylonites, and from 0.53 to 0.80 with 0.66 on average for the mylonites; Wk values of the extensional crenulation cleavage, i.e., C′, estimated by C′ method range from 0.63 to 0.37 with an average of 0.50. The angles between the maximum principal stress and shearing direction determined using the Maximum effective moment criterion evolved from 61° to 69° and to 75°, and finally normal to shearing direction. The results of strain and kinematic vorticity measurements suggest that high strain corresponds to low kinematic vorticity. Kinematic vorticity measurements show that the Louzidian low-angle ductile shear detachment zone is a result of a combination of simpledominated general shearing at the early stage and pure-dominated general shearing at the late stage. All these, together with isotope geochronology and regional tectonic background, suggest that the Louzidian ductile shear detachment zone resulted from a combination of crust extension and magma intrusion. The model of simple shear at the early stage and pure shear at the late stage in the formation of metamorphic core complex has probably general significance.

Present activity and seismogenic potential of a low-angle normal fault system (Città di Castello, Italy): Constraints from surface geology, seismic reflection data and seismicity

We present new constraints on an active low-angle normal fault system in the Città di Castello–Sansepolcro basin (CSB) of the northern Apennines of Italy. New field data from the geological survey of the Carta Geologica d' Italia (CARG project) define the surface geometry of the normal fault system and lead to an interpretation of the CROP 03 deep-crust seismic reflection profile (Castiglion Fiorentino–Urbania segment), with particular attention paid to the geometry of the Plio-Quaternary extensional structures. Surface and sub-surface geological data are integrated with instrumental and historical seismicity in order to define the seismotectonics of the area. Low-angle east-dipping reflectors are the seismic expression of the well-known Altotiberina Fault (AF), a regional extensional detachment on which both east- and west-dipping high-angle faults, bounding the CSB, sole out. The AF breakaway zone is located ∼ 10 km west of the CSB. Within the extensional allochthon, synthetic east-dipping planes prevail. Displacement along the AF is ∼ 4.5 km, which agrees with the cumulative offset due to its synthetic splays. The evolution of the CSB has mainly been controlled by the east-dipping fault system, at least since Early Pleistocene time; this system is still active and responsible for the seismicity of the area. A low level of seismic activity was recorded instrumentally within the CSB, but several damaging earthquakes have occurred in historical times. The instrumental seismicity and the intensity data points of the largest historical earthquakes (5 events with maximum MCS intensity of IX to IX–X) allow us to propose two main seismogenic structures: the Monte Santa Maria Tiberina (Mmax = 5.9) and Città di Castello (Mmax up to 6.5) normal faults. Both are synthetic splays of the AF detachment, dipping to the NE at moderate (45–50°) to low (25–30°) angles and cutting the upper crust up to the surface. This study suggests that low-angle normal faults (at least with dips of 25–30°) may be seismogenic.

Development of active low-angle normal fault systems during orogenic collapse: Insight from Tibet

Development of active low-angle normal fault systems during orogenic collapse: Insight from Tibet

Development of active low-angle normal fault systems during orogenic collapse: Insight from Tibet

Research Article| January 01, 2008 Development of active low-angle normal fault systems during orogenic collapse: Insight from Tibet Paul Kapp; Paul Kapp 1Department of Geosciences, University of Arizona, 1040 E 4th Street, Tucson, Arizona 85721, USA Search for other works by this author on: GSW Google Scholar Michael Taylor; Michael Taylor 2Department of Geology, University of Kansas, 1475 Jayhawk Boulevard, Lawrence, Kansas 66045, USA Search for other works by this author on: GSW Google Scholar Daniel Stockli; Daniel Stockli 2Department of Geology, University of Kansas, 1475 Jayhawk Boulevard, Lawrence, Kansas 66045, USA Search for other works by this author on: GSW Google Scholar Lin Ding Lin Ding 3Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100029, China Search for other works by this author on: GSW Google Scholar Geology (2008) 36 (1): 7–10. https://doi.org/10.1130/G24054A.1 Article history received: 03 May 2007 rev-recd: 13 Aug 2007 accepted: 17 Aug 2007 first online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Paul Kapp, Michael Taylor, Daniel Stockli, Lin Ding; Development of active low-angle normal fault systems during orogenic collapse: Insight from Tibet. Geology 2008;; 36 (1): 7–10. doi: https://doi.org/10.1130/G24054A.1 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 Active north-trending rifts in Tibet vary significantly in their character as a function of extension magnitude. Most rifts are characterized by internally drained basins bounded by high-angle normal faults with Paleogene or older rocks in the footwall. However, the central part of the Yadong-Gulu Rift (near Lhasa) and the newly documented Lunggar Rift in west-central Tibet are bounded by low-angle normal faults (detachments) with mylonitic rocks and Miocene granites in the footwall, and exhibit active basin incision and intrabasin topographic highs in areas of inferred maximum extension. We suggest that Tibetan rifts initiate as high-angle normal fault and half-graben or graben basin systems and evolve in response to increasing extension and footwall isostatic rebound into detachment systems that are active at uppermost crustal levels and above which rift basin fill is being uplifted and eroded. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Structural evolution of the Gurla Mandhata detachment system, southwest Tibet: Implications for the eastward extent of the Karakoram fault system

Field mapping and geochronologic and thermobarometric analyses of the Gurla Mandhata area, in southwest Tibet, reveal major middle to late Miocene, east-west extension along a normal-fault system, termed the Gurla Mandhata detachment system. The maximum fault slip occurs along a pair of low-angle normal faults that have caused significant tectonic denudation of the Tethyan Sedimentary Sequence, resulting in juxtaposition of weakly metamorphosed Paleozoic rocks and Tertiary sedimentary rocks in the hanging wall over amphibolite-facies mylonitic schist, marble, gneisses, and variably deformed leucogranite bodies in the footwall. The footwall of the detachment fault system records a late Miocene intrusive event, in part contemporaneous with top-to-the-west ductile normal shearing. The consistency of the mean shear direction within the mylonitic footwall rocks and its correlation with structurally higher brittle normal faults suggest that they represent an evolving low-angle normal-fault system. 4 0 Ar/ 3 9 Ar data from muscovite and biotite from the footwall rocks indicate that it cooled below 400 °C by ca. 9 Ma. Consideration of the original depth and dip angle of the detachment fault prior to exhumation of the footwall yields total slip estimates between 66 and 35 km across the Gurla Mandhata detachment system. The slip estimates and timing constraints on the Gurla Mandhata detachment system are comparable to those estimated on the right-slip Karakoram fault system, to which it is interpreted to be kinematically linked. Moreover, the mean shear-sense direction on both the Karakoram fault and the Gurla Mandhata detachment system overlap along the intersection line between the mean orientations of the faults, which further supports a kinematic association. If valid, this interpretation extends previous results that the Karakoram fault extends to mid-crustal depths.

Abstract: Structural model of thrust inversion of low-angle normal fault systems: The Oceanside - San Diego faults, Inner California Borderland, USA

Abstract: Structural model of thrust inversion of low-angle normal fault systems: The Oceanside - San Diego faults, Inner California Borderland, USA

The role of low-angle normal faulting and isostatic response in the evolution of the Suez rift, Egypt

A new geometric model for the Suez rift suggests that isostatic uplift of an underlying low-angle normal fault system accompanying early block faulting localized subsequent deep-seated extension. This, in turn, created a superimposed late-stage graben system offset to the east from an earlier locus of extension. Initial extension in the Oligocene and earliest Miocene drove minor rotation on wide tilt blocks over an eastward-dipping low-angle normal fault system and formed a series of wide half-grabens. With increasing extension, more closely spaced faults formed smaller rotating tilt blocks, fragmenting the larger, earlier half grabens and creating numerous sub-basins. In response to this brittle thinning of the upper crust, isostatic uplift of the lower crust arched the underlying low-angle fault surface, limiting gravity-driven tilt-block movement in the west by flattening the low-angle fault surface and creating a broad gulf-parallel high in the fault surface and Moho under the eastern portions of the rift. This process diminished faulting in the west and localized continuing deep-seated extension under the crest of the arch, possibly through induced mantle convection. Through-going faults thus initiated cut the old low-angle fault system and bound a system of down-dropped grabens offset to the east of the most extended portions of the older tilt-block array. In the Red Sea, immediately to the south, this process has continued, with the increased separation allowing the formation of mantle-derived oceanic crust. This model suggests that early movement over low-angle detachments and accompanying isostatic response may play an important role in localizing deformation within rifts, and are probably critical elements in the early formation of passive margins.

Detached strata in a Tertiary low-angle normal fault terrane, southeastern California: A sedimentary record of unroofing, breaching, and continued slip

Research Article| July 01, 1988 Detached strata in a Tertiary low-angle normal fault terrane, southeastern California: A sedimentary record of unroofing, breaching, and continued slip Julia M.G. Miller; Julia M.G. Miller 1Department of Geology, Vanderbilt University, Nashville, Tennessee 37235 Search for other works by this author on: GSW Google Scholar Barbara E. John Barbara E. John 2Department of Earth Sciences, Cambridge University, Cambridge CB2 3EQ, England Search for other works by this author on: GSW Google Scholar Geology (1988) 16 (7): 645–648. https://doi.org/10.1130/0091-7613(1988)016<0645:DSIATL>2.3.CO;2 Article history first online: 02 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 Julia M.G. Miller, Barbara E. John; Detached strata in a Tertiary low-angle normal fault terrane, southeastern California: A sedimentary record of unroofing, breaching, and continued slip. Geology 1988;; 16 (7): 645–648. doi: https://doi.org/10.1130/0091-7613(1988)016<0645:DSIATL>2.3.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 Miocene sedimentary strata exposed in the eastern Chemehuevi Mountains, southeastern California, record development of an evolving low-angle normal fault system. The sequence includes more than 1 km of conglomerate and sandstone with rare interbedded monolithologic breccia and volcanic flows. Clasts of Peach Springs Tuff in basal units indicate that this succession is younger than 18 Ma. These rocks have been displaced by a regionally extensive low-angle normal fault, the Chemehuevi detachment, and are folded and faulted. Structural reconstructions and the character of associated fault rocks indicate that the Chemehuevi fault was initiated at a low angle and that the footwall was progressively unloaded through thinning and displacement of its cover during extensional deformation. The syntectonic sedimentary rocks described here provide evidence that movement continued on the gently dipping (< 15°) fault even after part of the fault was breached and the footwall eroded.The conglomerates and sandstones were deposited by stream flow and debris flow on alluvial fans. Synsedimentary faulting is suggested by angular discordance below one monolithologic breccia bed and by local coarsening-upward sequences. Clast types reveal progressive unroofing of hanging-wall rocks to expose the Chemehuevi fault zone, from which chloritic, brecciated granite clasts were derived. Clasts were then derived from both the hanging wall and the footwall, footwall debris being dominant high in the section. Distinctive clasts show that late displacement on this evolving fault system was on the order of 1 to 5 km. 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.

Low-angle normal-fault system along the range front of the southwestern Galiuro Mountains in southeastern Arizona

Neogene erosion along the southwestern flank of the Galiuro Mountains in the Basin and Range province of southeastern Arizona has exposed multiple strands of a mid-Tertiary low-angle normal-fault system that offsets Oligocene-Miocene and older strata. This fault system along the range front is overlain unconformably by onlapping Miocene-Pliocene basin fill but forms the structural boundary between the Galiuro range and the adjacent San Pedro trough, and it served as the breakaway zone for the extensional detachment system associated with the nearby Catalina-Rincon core complex. Younger high-angle normal faults of comparatively modest displacement cut various strands of the low-angle normal-fault system and locally displace basin fill. The antiquity and nature of the Galiuro range front challenge the common assumption that all morphologically prominent blocks of the Basin and Range province are young relief features bounded by high-angle normal faults.