Series Of Thrust Faults Research Articles

Growth of the northeastern Tibetan plateau since the Middle Miocene as revealed by syn-tectonic growth strata

Syn-tectonic deposition of sediments (growth strata) preserves a direct record of mountain building-erosion and basin deformation. When and how these sediments incorporated into forward propagating fold-and-thrust (FTB) belts can shed light on the above processes. Despite many years of research, there is still ongoing debate about the timing and mechanisms of the southern Qaidam fold-and-thrust belt in the northeastern Tibetan Plateau. Here, we provide insight into the deformation of the Qaidam Basin and the broader tectonic processes of the northeastern Tibetan Plateau through detailed analysis of the Dafengshan (DFS), Jiandingshan (JDS) and Heiliangzi (HLZ) anticlines along the southern Qaidam FTB. Identification of the growth strata by Area-Depth analysis and age determination indicate that deformation of the DFS anticline initiated in the mid-Miocene (∼15 Ma), and has successively experienced lateral growth (∼15–8.0 Ma) and uplift (∼8.0 Ma-present). This timeline of deformation coincides with periods of mountain building in the northeastern Tibetan Plateau and might be related to the removal of mantle beneath northern Tibet. The synchronization of growth strata with an increase in sedimentation and exhumation rates reveals the reactivation of the tectonic belt around the basin in the mid-Miocene, creating the current basin-range landform; since ∼8 Ma, compression has expanded rapidly into the interior of the Qaidam Basin, leading to incorporation of basin deposits into the FTB. Geomorphological analyses coupled with 3-D fold modeling demonstrate that the JDS and HLZ-fold train with S-shaped configuration is a coherent fold system developed by lateral growth and linkage of two different fold segments in the context of the N–S directional compression of the plateau. Considering the prevalent S-shaped constructions within the basin and the current seismicity, we propose that the dominant structures in the southwestern Qaidam Basin are a series of thrust faults and folds controlled by the compression component of the East Kunlun Fault, with a limited influence from the Altyn Tagh Fault.

Tectonostratigraphy and major structures of the Georgian Greater Caucasus: Implications for structural architecture, along-strike continuity, and orogen evolution

AbstractAlthough the Greater Caucasus Mountains have played a central role in absorbing late Cenozoic convergence between the Arabian and Eurasian plates, the orogenic architecture and the ways in which it accommodates modern shortening remain debated. Here, we addressed this problem using geologic mapping along two transects across the southern half of the western Greater Caucasus to reveal a suite of regionally coherent stratigraphic packages that are juxtaposed across a series of thrust faults, which we call the North Georgia fault system. From south to north within this system, stratigraphically repeated ~5–10-km-thick thrust sheets show systematically increasing bedding dip angles (<30° in the south to subvertical in the core of the range). Likewise, exhumation depth increases toward the core of the range, based on low-temperature thermochronologic data and metamorphic grade of exposed rocks. In contrast, active shortening in the modern system is accommodated, at least in part, by thrust faults along the southern margin of the orogen. Facilitated by the North Georgia fault system, the western Greater Caucasus Mountains broadly behave as an in-sequence, southward-propagating imbricate thrust fan, with older faults within the range progressively abandoned and new structures forming to accommodate shortening as the thrust propagates southward. We suggest that the single-fault-centric “Main Caucasus thrust” paradigm is no longer appropriate, as it is a system of faults, the North Georgia fault system, that dominates the architecture of the western Greater Caucasus Mountains.

The Holocene Activity Evidence of the Yema River‐Daxue Mountain Fault in Western Qilian Mountain

AbstractAltyn Tagh fault controls the deformation characteristics of the northern margin of the Qinghai‐Tibet Plateau. The sinistral slip rate of the eastern segment of the fault reduces gradually where the reduction transforms into the deformation within Qilian Mountain, forming a series of thrust faults and strike‐slip faults. Among them, the Yema River‐Daxue Mountain fault is one of the important structural transform faults in the study area. Based on the differences of the geometrical characteristics and activities, the fault is divided into four segments, the Yema River segment, the Shibandun segment, the Liushapo segment and the Baishitougou segment, among which the former three are Holocene active faults, and the Baishitougou segment belongs to late Pleistocene fault. The excavated trenches imply a total of 6 paleoearthquake events, and at least 4 events have occurred during Holocene, whose occurrence times are 8300±700 yr BP, 6605±140 yr BP, 4540±350 yr BP, 2098±47 yr BP, respectively. The recurrence interval is 2600±600 yr BP that is close to the lapsed time of the last one, 2098±47 yr BP, which suggests that the Yema River‐Daxue Mountain fault is in a high risk of major earthquakes in the future. The vertical coseismic displacements of the four Holocene paleoearthquake events are 100 cm, 42 cm, 40 cm and 50 cm, respectively, the horizontal coseismic displacements are 5 m, 4.5–5.5 m, 5–8 m and 4–5.5 m, separately, and then the reference magnitude of the paleoearthquake events is conjectured to be M7.6±0.1.

S and Pb Isotopic Constraints on the Relationship between the Linong Granodiorite and the Yangla Copper Deposit, Yunnan, China

Abstract:The Yangla copper deposit, located in western Yunnan Province, China, is a typical giant, newly started mining copper deposit with an estimated Cu reserves of about 1,200,000 tons. The deposit is spatially and temporally associated with the Linong granodiorite, which is rich in SiO2 (SiO2=58.25 wt%–69.84 wt%) and alkalis (Na2O+K2O=5.98 wt%–8.34 wt%), indicating an association with shoshonitic series to high‐K calc‐alkaline series granites, and shows low contents of TiO2 (0.35 wt%–0.48 wt%), MgO (1.51 wt%–1.72 wt%), and Al2O3 (13.38 wt%–19.75 wt%). The δ34S values of sulfides of the main ore stage from copper ores vary range from −4.2‰ to −0.9‰, indicating a much greater contribution from the mantle to the ore‐forming fluids. The δ34S values of the late ore stage is −9.8‰, indicating enrichment of biogenic sulfur which may derive from the crustal hydrothermal fluid. The 208pb/204pbj 207pb/204pb and 206pb/204pb of sulfides of the main ore stage from copper ores range within 38.66–38.73, 15.71–15.74 and 18.35–19.04, respectively, implying that the Pb was derived from the mantle, with the crustal component, probably representing mixtures of mantle lead and crustal lead. Sulfide of the late ore stage in their Pb isotopic composition, 208Pb/204Pb= 38.69, 207Pb/204Pb=15.70, 206Pb/204Pb=18.35, implying that the Pb was derived from the crust. The Linong granodiorite is syncollisional, produced by partial melting of thickened lower crust, which was triggered by the westward subduction of the Jinshajiang Oceanic plate. During a transition in geodynamic setting from collision‐related compression to extension, gently dipping ductile shear zones (related to subduction) were transformed to brittle shear zones, consisting of a series of thrust faults in the Jinshajiang tectonic belt. The tensional thrust faults would have been a favorable environment for ore‐forming fluids. The ascending magma provided a channel for the ore‐forming fluid from the mantle wedge. After the magma arrived at the base of the early‐stage Linong granodiorite, the platy granodiorite at the base of the body would have shielded the late‐stage magma from the fluid. The magma would have cooled slowly, and some of the ore‐forming fluid in the magma would have entered the gently dipping thrust faults near the Linong granodiorite, resulting in mineralization.

Subsurface compressional structures and facies transitions imaged by seismic reflection data, eastern margin of Richardson Trough, Peel Plateau, Yukon

Abstract Knowledge of the deformation front of the Richardson Anticlinorium is an important component of assessments for regional hydrocarbon potential; but sparse outcrop in the Peel Plateau, Yukon has made geological interpretations difficult and the results of reconnaissance mapping uncertain. To date, a single fault has been inferred to define the eastern limit of deformation. In this paper, we present stratigraphic and structural interpretations of multi-channel seismic reflection data collected in an early phase of hydrocarbon exploration. Early Tertiary deformation is expressed as a series of thrust faults, folds and back thrusts, not a single through-going fault. Deformation has been concentrated on several lithologic transitions: a pinch out of syn-rift sandstones and the transition from carbonate platform to basinal shales. The Middle Ordovician to Middle Devonian eastern margin of the Richardson Trough is imaged as clinoforms and a carbonate buildup; clinoforms can be mapped about 75 km along strike. Integration with aeromagnetic data allows us to construct a map of subsurface structures along the eastern deformation front associated with the Richardson Anticlinorium. Faulted anticlines and facies pinch outs are potential traps although any play in this region remains hypothetical.

Structural cross-section based on the Mt Isa deep seismic transect

The Mt Isa deep seismic transect images a regional detachment surface and basement-cutting faults associated with Mesoproterozoic, east – west shortening in the Mt Isa Inlier, Queensland. New mapping along the trace of the transect is combined with interpretations of seismic-reflection data to derive a structural cross-section for the top 12 km of the crust. A regional detachment surface is imaged beneath the eastern half of the inlier leading to a fold and thrust belt interpretation for this region, where supracrustal units were decoupled from basement and translated west or northwest. The detachment is imaged across most of the Eastern Fold Belt in the reflection data, and it emerges as a series of thrust faults along the western margin of this belt. This detachment is cross-cut by reverse faults related to a regional, basement-involved style of deformation that involved the entire inlier. Shortening in the Western Fold Belt is dominantly east-vergent and was accommodated by a complex interplay of local thrusts, folds and reverse faults.

Holocene faulting on a tectonic margin: Georgia Basin, British Columbia, Canada

Multibeam bathymetric data collected in the Strait of Georgia, British Columbia, have revealed two areas of seabed disturbance, interpreted to be faults. The easterly fault zone (Fraser Delta Fault) is demarked by a pockmark chain extending along strike of a southwesterly-dipping fault offset 1 km to the northeast and having a throw of over 50 m. The pockmarks occur in a region of high sedimentation, located in the Fraser River prodelta. The eastern strait fault zone (Porlier Pass Fault) occurs within a fold of the Cretaceous Nanaimo Group. Here, a series of thrust faults displace sediments from Cretaceous to Holocene by up to 40 m with over 2 km of surface expression. Based on Holocene stratigraphic displacement in an area of significant sedimentation, these fault zones are considered to be active.

Tectonic implications of early silurian thrust imbrication of the northern exploits subzone, Central Newfoundland

Central Newfoundland's Dunnage Zone contains a composite assemblage of island arc and oceanic rocks formed in the Paleozoic Iapetus Ocean. Two different and perhaps unrelated Late Cambrian-Middle Ordovician volcanic belts (Lush's Bight and Robert's Arm belts, and their correlatives) are preserved in the Notre Dame Subzone, and are interpreted to represent arc and back-arc basin sequences developed; (1) adjacent to the Laurentian margin of Iapetus and (2) in the intraoceanic realm of the 4000 km wide Paleozoic ocean. Paleozoic paleogeographic reconstructions suggest that the Exploits Subzone contains volcanic and sedimentary rocks originally deposited in a third arc located between the intraoceanic arc (Robert's Arm Belt) and the Peruvian promontory of Gondwana. The New Bay Pond area is located within the northern Exploits Subzone, and preserves an imbricate thrust stack formed during Late Ordovician/Early Silurian southeastward-directed thrusting. Thrust-load related subsidence led to deposition of cherts and argillites overlain by a southeastward-prograding wedge of orogenic flysch and molasse in a foreland trough. Late Ordovician-Early Silurian structural disruption of the flysch/molasse sequence and older strata of the northern Exploits Subzone, by a series of thrust faults, place Middle Ordovician rocks over the younger flysch, and formed a new, southeast-vergent accretionary wedge. This event records the emplacement of the Exploits Subzone over Gondwanan continental margin rocks of the Gander Zone, soon after the Notre Dame Subzone collided with the Appalachian margin of Laurentia. Continued closure of Iapetus brought together the collisionally modified margins of Gondwana and Laurentia. The Exploits Subzone is cut by numerous Silurian-mid Devonian predominantly dextral strike-slip faults, suggesting that this convergence involved a significant component of dextral transpression. Several pull-apart basins are located along these strike-slip faults, and are filled by Silurian volcano-sedimentary sequences. These faults formed in response to the counter-clockwise rotation of Gondwana, juxtaposing the Avolonian margin of Gondwana with the Appalachian margin of Laurentia by the Carboniferous.

Reservoir models in the Junggar Basin, Xin-jiang, north-west China

The Junggar Basin in north-west China is an Upper Palaeozoic-Middle Cenozoic sedimentary basin, asymmetric in the N-S direction. It consists of an E-W striking foredeep basin in the south, where a series of anticlines are developed near the Tianshan Mountains, and a northern part comprising a northward rising slope where a series of thrust faults have developed. These two different tectonic settings have resulted in two types of oil and gas reservoir models that can be used in exploration for new reservoirs in similar geological settings.

Seismic modelling by Fresnel diffraction theory with application to wide-aperture data from SW Oklahoma

SUMMARY A numerical, 2-D modelling algorithm for seismic P-waves, based on Fresnel diffraction theory, has been developed. This algorithm uses Huygens’ principle: every point on the wavefront may act as an independent secondary source for the subsequent behaviour of the wave. Huygens’ principle implies that a seismogram, which is the seismic response of a medium to a source, can be calculated as the sum of responses of secondary sources on a wavefront. The Fresnel approximation of diffraction is used to calculate the seismic responses. This modelling algorithm is an integral method that is applicable to laterally inhomogeneous models. Ray tracing is used to determine the travel time from each individual secondary source to the receiver. Since the response at the receiver is the accumulation of responses from all secondary sources instead of that from a single source, diffractions and caustics can be modelled in addition to reflections and transmissions. The algorithm is verified by comparison with acoustic finite difference computations, and applied to modelling of data from a wide-aperture seismic survey conducted in SW Oklahoma in 1985. The structure in the survey area is highly laterally inhomogeneous with igneous rocks to the SW, sedimentary rocks to the NE, and a series of thrust faults between.

Polyphase deformation in Sierra del Cuervo, Chihuahua, Mexico: Evidence for Ancestral Rocky Mountain tectonics in the Ouachita foreland of northern Mexico

Sierra del Cuervo is a north-northwest–trending mountain range ∼30 km northeast of Chihuahua City, Chihuahua, Mexico. Rocks exposed in the sierra range from late Precambrian to Quaternary. It has long been recognized that Sierra del Cuervo contains one of the most lithologically different Paleozoic outcrops in Chihuahua, and the recent discovery of Precambrian rocks in the south-central part of the range distinguishes Sierra del Cuervo as one of only two known Precambrian outcrops in the state. Mapping and structural analysis in the south-central part of Sierra del Cuervo reveal that at least five major periods of deformation, ranging from Precambrian to late Tertiary, are represented. The most dramatic structures are a series of thrust faults and associated folds. Thrusting involved both Precambrian basement and Paleozoic sedimentary rocks, with tectonic transport toward the east-southeast. Stratigraphic relationships in Sierra del Cuervo restrict the age of this deformation only to post-Early Permian and pre-Cretaceous, but regional considerations suggest that it occurred during the middle Permian. The origin of these late Paleozoic structures has previously been related to the westward extension of the Ouachita frontal zone; however, their orientation is oblique to the postulated trace of the frontal zone and suggests a much more complex relationship with the Ouachita system. Paleocurrents and compositional variations in sandstones of the Rara Formation indicate the presence of a basement-involved uplift in west-central Chihuahua during the Late Pennsylvanian and Early Permian. This apparent unroofing of a western basement-cored block, followed by east-southeast–directed thrusting, is inconsistent with the tectonic style of the Ouachita frontal zone and suggests that the late Paleozoic structures in Sierra del Cuervo are related to Ancestral Rocky Mountain deformation. Additional evidence for this southern extension of the Ancestral Rocky Mountains is found in other parts of northern and central Chihuahua and indicates that most of the region was in the Ouachita foreland during the late Paleozoic.

Late Cretaceous stratigraphy, deformation, and intrusion in the Madison Range of southwestern Montana

Dating of orogenic rock units in the central part of the Madison Range shows that Laramide deformation was virtually completed by the end of the Cretaceous. Early Campanian K-Ar dates of about 79 m.y. were obtained from welded tuffs in the basal part of the Livingston Formation, a volcanic and volcaniclastic assemblage that is conformable with underlying Cretaceous clastic rocks and with the overlying Sphinx Conglomerate. No datable materials were obtained from the Sphinx, but both it and the Livingston were deformed by the Hilgard fault system, a series of thrust faults and associated folds which extend along the western side of the southern two-thirds of the range. This north-trending fault system represents the culmination of Laramide shortening within the range. K-Ar and 40 Ar/ 39 Ar dating of hornblende from dacitic laccolithic rocks that intruded the Hilgard fault system in the central part of the range indicates an approximate date of 68–69 m.y. B.P. for emplacement of the igneous suite. The dacite postdates movement along faults of the Hilgard fault system, and postdates the synorogenic Sphinx Conglomerate.

STRATIGRAPHY AND STRUCTURE OF THE OAK HILL SUCCESSION IN VERMONT

North of the Winooski River, Vermont, the Oak Hill succession occupies the region between the eastern margin of the Champlain Lowland and the western foot of the Green Mountains. The lithologic units are traceable into southern Quebec, and some are traceable southward into west-central Vermont. Lower and middle Cambrian ages have been assigned to all units. The strata below the Gilman quartzite are tentatively correlated with the Mendon series in the Rutland-Brandon region. All units above the Gilman have stratigraphic equivalents in the adjoining Rosenberg succession. The earliest recorded differential downwarping of the local geosynclinal area immediately preceded the beginning of deposition of the Pinnacle sediments. The distribution of the shaly, sandy, and conglomeratic facies of the Pinnacle and West Sutton formations indicate a western source for the sediments and also that the sea was encroaching westward. The Gilman quartzite marks the first occurrence of reworked sands; reworked sediments formed practically all of the elastics sediments thereafter. A prominent anticlinorium occupies much of the southern part of the area. Northward it fades into a westward-dipping homocline. The western margin of the succession is formed in most places by a series of thrust faults, which may be continuous. The Oak Hill thrust, considered the western boundary of the succession in southern Quebec, has not been recognized in Vermont. The strata were strongly folded before thrusting; the thrusts are subsequent shear thrusts. Several klippen, related genetically to the thrusts, form prominent hills west of the western margin of the succession.