Vertical Axis Rotation Research Articles

The role of active strike-slip faults and opposite vertical axis rotations in accommodating eurasia-arabia shortening in central iran

In Central Iran, most of the Late Cenozoic to Present shortening has been accomplished in the Zagros, in the Alborz, and Kopeh-Dagh mountain ranges. Between these active mountain belts, a minor amount of shortening is observed and the deformation style is characterized by active strike-slip faults that bound relatively aseismic blocks. Two main strike-slip fault systems are presently active in different regions of Central Iran: South of latitude 34°N, active deformation is accommodated on ∼N–S oriented right-lateral strike-slip faults, and north of latitude 34°N, E–W left-lateral strike slip faults prevail.In this work, we investigated two different structures, representative of the two different strike-slip systems occurring in Central Iran: the Yazd fold system located in an area dominated by the occurrence of NNW-SSE oriented right-lateral strike slip faults, and the Ferdows fold system that developed at the western termination of the E–W left-lateral strike-slip Dasht-e-Bayaz fault. Paleomagnetic results show opposite vertical-axis rotations related to the different orientation and sense of movement of strike-slip fault systems, suggesting that in Central Iran the N–S oriented right-lateral and E–W oriented left-lateral strike-slip faults play significant roles in accommodating the Arabia-Eurasia convergence, by rotating counterclockwise and clockwise in the horizontal plane, respectively.

Vertical-axis rotation in East Kopet Dagh, NE Iran, inferred from paleomagnetic data: oroclinal bending or complex local folding kinematics?

The Kopet Dagh Mountains in NE Iran result from Cenozoic tectonic inversion of Triassic and Jurassic rifts that formed along the southern margin of the Eurasian continental plate. The Kopet Dagh defines an arcuate orogen leading to the suggestion that oroclinal bending took place during its formation. We performed a paleomagnetic study including seven sampling sites of Paleocene formations around the Kalat syncline in the East Kopet Dagh to test whether this part of the mountain belt experienced vertical-axis rotation. Paleomagnetic measurements and a reversals test indicate that parts of the collected samples may have been partially remagnetized. Overall paleomagnetic directions of all sample sites show a mean declination of 12.5°, which is the expected direction for stable Europe in the Paleocene and therefore negates any rotation related to regional tectonic events. Directions calculated only from reversely polarized paleomagnetic data, however, suggest clockwise vertical-axis rotations up to 21° since the Paleocene. Numerical modelling of a viscous multi-layer folding mimicking the Kalat syncline stratigraphy suggests that local deviations in overprinted site-mean directions and orientation of the maximum axes of the AMS ellipsoid may be related to complex folding kinematics, acquired after regional vertical-axis rotation, where related viscous flow of relatively weak interlayer is represented by the sampled Paleocene formation.

Dramatic Pliocene–Quaternary subsidence of the southern Rhodes Basin and concomitant north-tilting and uplift of the Anaximander Mountains, the junction of Hellenic and Cyprus arcs, eastern Mediterranean Sea

The Anaximander Mountains and the Rhodes Basin at the junction of Cyprus and Hellenic arcs are one of the tectonically most complex regions in the eastern Mediterranean. Harmonically-tilted Messinian and the uppermost Messinian–Pliocene successions across the northern and eastern margins of the Rhodes Basin showed that these regions experienced dramatic subsidence exceeding ~1500–2500 ms (~1125–1875 m @ 1500 m s−1) during the upper Pliocene–Quaternary. Tilted upper Pliocene–Quaternary growth strata wedges showing apparent north-directed downlap along the northern foothills of the Anaximander Mountain suggested that this region experienced ~1000–2500 ms (~750–1125 m) concomitant uplift. The absence of faults showing extensional stratigraphic separations and the relative subsidence rates calculated using amount of tilting collectively suggest that the Rhodes Basin experienced sagging of its deeper basinal regions, which is attributable to the loading effect of the building of the Tauride Mountains modified by the vertical axis rotations of the Beydağları Block and the Island of Rhodes, and the horizontal axis rotation of the Anaximander Mountain.Messinian and uppermost Messinian–Pliocene were tectonically relatively quiet as shown by the harmonically structured and isopachous successions across the Rhodes Basin and Anaximander Mountain. This interval coincides with the paleomagnetically-determined 9° counterclockwise vertical axis rotation of the Island of Rhodes. The dramatic subsidence observed within the Rhodes Basin and the concommitant uplift of the Anaximander Mountain and its western extension occurred broadly coincident with southeast tilting of the Island of Rhodes and its associated 500–600 m subsidence between 2.5 and 1.8 Ma, the northwest tilting between 1.5 and 1.1 Ma, and the associated re-emergence of the southeastern coast. The large counterclockwise rotation of the Island of Rhodes since 0.8 Ma corresponds with the enormous subsidence observed across the northeastern sector of the Rhodes Basin, which brought the shelf-edge deltas from the near-sea level to their present-day depth of 1200–1500 m.

3D geometric modeling for the Yanjinggou anticline in the Longmen Shan fold-and-thrust belt, China: Oblique thrusting kinematic implications

Three-dimensional (3D) subsurface seismic data acquisition and modeling are rarely undertaken; consequently, the complex effects of oblique thrusting on the 3D morphology and kinematics of folds are still poorly understood. We use 3D seismic data to produce five 3D geometric models and compare our results with structural models of the Yanjinggou anticline in the Longmen Shan fold-and-thrust belt, to investigate the effects of oblique thrusting on 3D fold evolution. 3D geometric modeling results reveal that oblique thrusting may cause fold asymmetry, vertical axis rotation, and a curved fold axis. 3D seismic interpretations and structural modeling suggest that the Yanjinggou anticline developed as a trishear fault-propagation fold and experienced a maximum shortening amount of 1.2 ± 0.1 km. The 3D structural and geometric models are consistent with paleomagnetic results, suggesting that the anticline was affected by oblique thrusting at an angle of 55° above a listric thrust fault with three fault ramps (19°, 30°, and 40°), causing the fold to rotate and develop a curved morphology. The integrated method used in this study to investigate the effects of oblique thrusting on 3D fold morphology and kinematics can be applied to regional oblique thrusting in the Longmen Shan and other fold-and-thrust belts worldwide.

Early-orogenic deformation in the Ionian zone of the Hellenides: Effects of slab retreat and arching on syn-orogenic stress evolution

In this work we report on early-orogenic fracture patterns affecting a Cretaceous to Eocene sedimentary succession exposed in western Greece. These rocks belong to the Cenozoic External Hellenides, which form the western portion of the Aegean orocline. The analysis of fracture type, orientation, and crosscutting relationships provides constraints on the stress and strain patterns during the early stages of orocline formation. The fracture patterns in the study area includes early-orogenic extensional fractures arranged into two mutually orthogonal sets. These developed during progressive burial in the forebulge-foredeep system, ahead of the advancing compressive front. Tectonic solution seams at a high angle to bedding postdate these extensional structures. Solution seams are arranged in different sets, oblique to each other, and developed in the early stages of thrusting and folding. Extensional structures and solution seams are oblique to each other. Their orientation and crosscutting relationships provide evidence for clockwise vertical axis rotation of stress directions with time. This is consistent with the progressive arching of the forebulge-thrust belt system during progressive slab retreat.

Vertical Axis Rotation Across the Eastern Mono Basin and West‐Central Walker Lane Revealed by Paleomagnetic Data From the Jack Springs Tuff

AbstractThe mid‐Miocene Jack Springs Tuff (JST) outcrops from the Bodie Hills of eastern California into the western Mina Deflection, Nevada. Distal outcrops of the JST occur northwest of Mono Lake, CA, on a minimally rotated structural block. This provides a reference location for our paleomagnetic study to estimate relative vertical‐axis rotation. A new 40Ar/39Ar age places the eruption of the JST at 12.114 ± 0.006 Ma. Anisotropy of magnetic susceptibility data, once corrected for local tilt and vertical axis rotation, yields a mean imbrication that trends 178°. The probable source of the JST is located in the Huntoon Valley/Queens Valley region. Eighteen paleomagnetic sites constrain mid‐Miocene to recent vertical axis rotation within the region. All sites are discordant to the reference location with variable amounts of clockwise vertical axis rotation ranging from 25° to 104°. We hypothesize that a previously unrecognized early phase of deformation occurred that predates the deformation in the central Mina Deflection. These new data support the hypothesis that transtensional faulting associated with North American and Pacific plate interaction transferred deformation across the Mono Basin region that was partially accommodated by vertical axis rotation. By late Miocene, deformation had stepped east developing the Silver Peak‐Lone Mountain detachment system followed by the structures that presently define the central Mina deflection. This study further demonstrates that deformation occurred east of the Sierra Nevada Mountains at the latitude of the Mono Basin in western‐most Nevada, a region previously thought to be undeformed in terms of clockwise vertical axis rotation.

Clockwise paleomagnetic rotations in northeastern Iran: Major implications on recent geodynamic evolution of outer sectors of the Arabia-Eurasia collision zone

In this study, an extensive paleomagnetic sampling (70 sites) was carried out in north-eastern Iran with the aim of reconstructing the rotation history of the outer margin of the Eurasia-Arabia collision area represented by the Ala-Dagh, Binalud and Kopeh-Dagh mountain belts. We sampled the red beds units from the Lower Cretaceous Shurijeh Fm. and from the Middle-Upper Miocene Upper Red Fm (URF). Paleomagnetic results from all the sampled areas show a homogeneous amount of CW rotations measured in the above-mentioned Formations. These paleomagnetic results suggest that the oroclinal bending process that caused the curvature of Alborz mountain belt in north Iran after the Middle-Late Miocene, also extended to the Ala-Dagh, Binalud and Kopeh-Dagh mountain belts, at the north-eastern border of the Arabia-Eurasia deforming zone.Based on our paleomagnetic results and on GPS, seismological, geomorphological and structural data available in the area, a hypothesis of tectonic evolution of the northern Iran-South Caspian Basin area, from Middle-Late Miocene to Present, is here proposed. In this model, the initiation of the oroclinal bending processes in northern Iran occurred about 6–4 myr ago, related to the impinging of North Iran between the South Caspian block and the southern margin of the Turan platform, driven by the northward subduction of the South Caspian basement under the Aspheron-Balkhan Sill. As paleomagnetic results from this study show a pattern of vertical axis rotations that is inconsistent with the present-day kinematics of the northern Iranian blocks as described by seismicity and GPS data, we suggest that the tectonic processes responsible for the bending of northern Iran mountain chains are no longer active and that the westward motion of the South Caspian basin, and therefore the initiation of opposite strike-slip motion along the Ashk-Abad and Shahrud faults, occurred very recently (∼2 My ago). We therefore propose that initiation of the northward subduction of the South Caspian basin below the Apsheron-Balkhan Sill and the westward extrusion of the South Caspian block did not occur at the same time, with the former occurring between the late Miocene and the Pliocene, and the latter during the Pleistocene.

Behaviour of minor arcuate shapes hosted in curved fold-and-thrust belts: an example from the Northern Apennines (Italy)

AbstractArcuate fold-and-thrust belts have been extensively studied in the literature. Less attention, however, has been paid to the characteristics of local-scale arcuate structures, meaning 5–10 km long fold or thrust traces that display map-view curvature. Nevertheless, detailed investigation of small arcuate structures hosted in major arcs can contribute to understanding the pervasiveness of deformation mechanisms. We performed a combined geological and palaeomagnetic study on 21 sites from ac. 60 km2area in the Northern Apennines in order to analyse minor arcs at a kilometric scale. As evidenced by the geological and structural analysis performed on the 21 sites, the fold axial trend changes from N–S to NW–SE in the study area. The comparison with palaeomagnetic results shows the lack of correlation between vertical axis rotations and fold axial trends. As a consequence, the minor arcuate shapes of thrusts and related folds are interpreted as mostly primary features inherited from the geometry of the palaeomargin, represented by pre-orogenic faults, according to a context of inversion tectonics.

Major tectonic rotation along an oceanic transform zone, northern Iceland: Evidence from field and paleomagnetic investigations

We provide structural and paleomagnetic evidence for major distributed rotational shear adjacent to and including the active Húsavík-Flatey transform fault in the southern part of the Tjörnes Fracture Zone of north Iceland. In the Flateyjarskagi peninsula immediately south of the fault, dike and bedding trends gradually change over about 11 km in approaching the transform fault main trace. In map view this pattern is seen as a progressive clockwise curvature of structural elements that equals or in some cases exceeds 90°. We present paleomagnetic analyses that verify large clockwise rotations of the same order as the curvature of structural elements observed. We compare our field and paleomagnetic observations with results from careful analog modeling that demonstrate how regional curvature of structures results from distributed strain that dominates the early stages of transform shear deformation, prior to the appearance of a transform fault system comprised of discrete shears. Our paleomagnetic results were obtained from one relatively undisturbed reference site, and three sites of deformed rocks in Flateyjarskagi and two in Tjörnes peninsula. These results indicate large vertical-axis rotations, and the progressive deflection of dike trends throughout northern Flateyjarskagi also serves as a separate quantitative estimate of vertical-axis rotation. The clockwise vertical-axis rotation estimates of 71°–97° from dikes are less than those deduced from paleomagnetism, but the order of magnitude is correct and we attribute the differences as mainly reflecting imperfect bed attitude adjustments used in analyses. The problem is typical for deformed rocks from high-latitude sites with steeply inclined paleomagnetic vectors. We consider our field measurements of dikes as more accurate indicators of true tectonic rotation. This regional deformation of Miocene rocks occurred early in the evolution of the TFZ transform, probably beginning ca. 7 Ma, when an older rift zone present in western North Iceland jumped to its present NVZ location in northeast Iceland. The early deformations involved shear strain distributed over a region about 20-km broad and produced the curved structures. This phase was followed by the sequential development of more narrowly distributed discrete shears, generating the initial Húsavík-Flatey transform fault.

Palinspastic Reconstruction Versus Cross‐Section Balancing: How Complete Is the Central Taurides Fold‐Thrust Belt (Turkey)?

AbstractIn many fold‐thrust belts, cross section–derived shortening estimates are significantly lower than predicted based on plate convergence. This has led to controversial hypotheses that shortening may be largely underestimated due to wholesale underthrusting (convergence without shortening) below far‐traveled continent or ocean‐derived nappes. The Late Cretaceous‐Eocene Taurides fold‐thrust belt (southern Turkey) may contain a highly incomplete shortening record of convergence likely caused by wholesale underthrusting. To estimate this underthrusting, we calculate convergence across the belt using a map‐view palinspastic reconstruction that takes into account major rotations of tectonic units during their accretion. We use paleomagnetic and fault kinematic analysis, timing of accretion, and Africa‐Eurasia convergence to constrain our reconstruction. Our paleomagnetic results confirm an ~40° clockwise vertical axis rotation of the Geyikdağı nappe that forms the core of the belt, which we interpret is accommodated by a lateral gradient in underthrusting on faults structurally above and below the Geyikdağı nappe. We reconstruct ~400–450 km of convergence across the Taurides during their accretion. We compare this predicted convergence to shortening calculated from balanced cross sections, in which we reconstruct a minimum of 154‐km shortening: 57 km within far‐traveled nappes, 70‐km thrusting of far‐traveled nappes over the Geyikdağı nappe, and 27‐km shortening within the Geyikdağı nappe. Shortening in the Taurides created a significant nappe stack, but the majority of convergence was accommodated by wholesale underthrusting with barely a trace at the surface, including ~160 km of convergence by rotation of the belt, and 90–130 km related to missing Africa‐Eurasia convergence.

Clockwise vertical-axis rotation in the West Vardar zone of Serbia: tectonic implications

The Vardar-Tethyan mega-suture between the Eurasian and Adria (Gondwana) margins comprises remnants of oceanic lithosphere of Neotethys and distal parts of the adjacent continental margins including unconformable Late Cretaceous sedimentary cover and Cenozoic igneous rocks of post-obduction age. This study provides kinematic constraints for displacements and rotations affecting the Serbian part of the West Vardar and Jadar-Kopaonik units after the closure of the Neotethyan (= Sava) Ocean. The targets of the paleomagnetic research were Late Cretaceous sediments representing an overstep sequence and a wide variety of Oligocene-Earliest Miocene igneous rocks. The studied 48 sampling points were distributed within two segments of a narrow and 160 km long strip of the Western Vardar zone, namely the wider Rudnik Mts. area to the north and the Kopaonik Mts. area to the south. The results of standard laboratory processing and statistical evaluation suggest that both studied segments of the Western Vardar zone were affected by 30°–46° clockwise vertical-axis rotation which must have taken place after 20 Ma. It is proposed that clockwise vertical-axis rotation documented in the present study on one hand, and the previously documented counterclockwise vertical-axis rotation of Adria, on the other hand are related to large scale extension in the southern Pannonian basin.

Late Paleozoic Iberian Orocline(s) and the Missing Shortening in the Core of Pangea. Paleomagnetism From the Iberian Range

AbstractSupercontinents are usually interpreted to be single and rigid continental plates. How and when Pangea became a rigid supercontinent is disputed, and age estimations vary from ~330 to ~240 Ma. The Gondwana‐Laurussia collision formed the Variscan‐Alleghanian belt, the most prominent witness of Pangea's amalgamation. In Iberia, this orogen draws an “S” shape featured by the Cantabrian Orocline and the Central Iberian curve. The curvature of Central Iberia is particularly evident in Galicia‐Trás‐os‐Montes and in a change of trend that it draws in the Aragonese Branch of the Iberian Range. Recent research showed that both curvatures are not coeval and that the Central Iberian curve had to form prior to ca. 318 Ma (i.e., not a secondary orocline). We report paleomagnetic and structural results from Paleozoic rocks in the Santa Cruz syncline (Aragonese Branch of the Iberian Range) that indicate two main vertical axis rotations events: (1) a Cenozoic (Alpine) clockwise rotation of >20° and (2) a late Carboniferous counterclockwise rotation of ~70°. Once the Cenozoic rotation is restored, the change in structural trend that allegedly evidences the outer arc of the Central Iberian curve disappears. Whereas the Cenozoic rotation is incompatible with a Central Iberian curve, the late Carboniferous rotation is fully compatible with the Cantabrian Orocline, enlarging the area affected by its counterclockwise rotations and the existence of a nonrigid Pangea until, at least, ~295 Ma.

Acceptable Chin–Brow Vertical Angle for Neutral Position Radiography: Preliminary Analyses Based on Parameters of the Whole Sagittal Spine of an Asymptomatic Chinese Population

We sought to acquire the whole sagittal spine parameters and investigated the acceptable chin-brow vertical angle (CBVA) for neutral position radiography in an asymptomatic Chinese population. The parameters measured in 257 asymptomatic volunteers included CBVA, occipital slope, orbital tilt, occipital incidence, C0-C2 Cobb angle, C2-C7 Cobb angle, C1-C7 Cobb angle, C2-C7 sagittal vertical axis and absolute rotation angle, cervical tilt, cranial tilt, T1 slope, and thoracic kyphosis, and others. We used Pearson correlation analyses to find relationships between CBVA and other variables. The subjects were divided into 5 groups according to the CBVA percentile: group A, 0%-20% CBVA; group B, 20%-40% CBVA; group C, 40%-60% CBVA; group D, 60%-80% CBVA; and group E, 80%-100% CBVA. We used analysis of variance to analyze differences among the 5 groups. Orbital tilt, Occipital incidence, C1-C7 Cobb angle, C2-C7 sagittal vertical axis, and cranial tilt all increased with increasing CBVA (P < 0.001). The occipital slope, C2-C7 Cobb angle, C2-C7 absolute rotation angle, cervical tilt, T1 slope, and thoracic kyphosis decreased with decreasing CBVA (P < 0.05). No correlations between other sagittal parameters and the CBVA were found. A slight deviation was found in groups B-D, with a greater deviation in groups A, C, and E. An acceptable range of-1.5° to 5.8° is recommended for the CBVA for cervical radiography in the neutral position. When spinal surgeons evaluate the cervical plane, the effects of the CBVA deviation on cervical curvature must be considered.

Cenozoic Rotation History of Borneo and Sundaland, SE Asia Revealed by Paleomagnetism, Seismic Tomography, and Kinematic Reconstruction.

SE Asia comprises a heterogeneous assemblage of fragments derived from Cathaysia (Eurasia) in the north and Gondwana in the south, separated by suture zones representing closed former ocean basins. The western part of the region comprises Sundaland, which was formed by Late Permian‐Triassic amalgamation of continental and arc fragments now found in Indochina, the Thai Penisula, Peninsular Malaysia, and Sumatra. On Borneo, the Kuching Zone formed the eastern margin of Sundaland since the Triassic. To the SE of the Kuching Zone, the Gondwana‐derived continental fragments of SW Borneo and East Kalimantan accreted in the Cretaceous. South China‐derived fragments accreted to north of the Kuching Zone in the Miocene. Deciphering this complex geodynamic history of SE Asia requires restoration of its deformation history, but quantitative constraints are often sparse. Paleomagnetism may provide such constraints. Previous paleomagnetic studies demonstrated that Sundaland and fragments in Borneo underwent vertical axis rotations since the Cretaceous. We provide new paleomagnetic data from Eocene‐Miocene sedimentary rocks in the Kutai Basin, east Borneo, and critically reevaluate the published database, omitting sites that do not pass widely used, up‐to‐date reliability criteria. We use the resulting database to develop an updated kinematic restoration. We test the regional or local nature of paleomagnetic rotations against fits between the restored orientation of the Sunda Trench and seismic tomography images of the associated slabs. Paleomagnetic data and mantle tomography of the Sunda slab indicate that Sundaland did not experience significant vertical axis rotations since the Late Jurassic. Paleomagnetic data show that Borneo underwent a ~35° counterclockwise rotation constrained to the Late Eocene and an additional ~10° counterclockwise rotation since the Early Miocene. How this rotation was accommodated relative to Sundaland is enigmatic but likely involved distributed extension in the West Java Sea between Borneo and Sumatra. This Late Eocene‐Early Oligocene rotation is contemporaneous with and may have been driven by a marked change in motion of Australia relative to Eurasia, from eastward to northward, which also has led to the initiation of subduction along the eastern Sunda trench and the proto‐South China Sea to the south and north of Borneo, respectively.

Rotations of Normal Fault Blocks Quantify Extension in the Central Tauride Intramontane Basins, SW Turkey

AbstractQuantifying the amount of stretching in extensional basin systems is often challenging in the absence of seismic profiles or boreholes. However, when fault spacing and orientation as well as vertical axis rotation patterns are known, map‐view restoration may provide a good estimate of total extension. This integrated structural and paleomagnetic approach provides a relatively straightforward tool in extensional basin restoration and fault zone kinematic analysis. Here we provide results of an extensive paleomagnetic survey of the Neogene Central Tauride intramontane basins (SW Turkey), where previous work revealed a complex array of basin‐bounding normal faults and relay ramps. In total, 437 oriented cores were sampled at 43 sites distributed within Miocene‐Pliocene continental sedimentary rocks from the Ilgın, Altınapa, Yalvaç, and Beyşehir basins. Despite the more or less coherent overall strike of the mountain belt and basins, rotations vary from ~42° clockwise (Yalvaç) to ~10° (Beyşehir), ~21° (Ilgın), and ~30° (Altınapa) counterclockwise. We show that the rotation pattern is related to normal faults and lateral variations in fault displacement superimposed on regional rotation patterns. We restore these to estimate a minimum NE‐SW horizontal extension of ~30–35 km across the basin system. As a consequence of our reconstruction, it appears that the Sultandağları range that exposes low‐grade metamorphic Paleozoic and Mesozoic rocks of the Geyikdağı and Bolkardağ nappes of the Taurides represents a Miocene extensional core complex.

Paleomagnetic evidence for upper plate response to a STEP fault, SW Anatolia

Pliny-Strabo Trench is a Subduction Transform-Edge Propagator (STEP) Fault developed on the northern edge of the subducted African Oceanic Lithosphere. It connects the Aegean and Cyprian trenches in the Eastern Mediterranean convergent system. Although, deep geometry of the STEP fault and associated slab tear in mantle are imaged, its shallow vertical and lateral continuation in the crust and impact on the over-riding plate are still unknown. Thus, we have studied SW Anatolia, the candidate site where this structure could propagate laterally and vertically, for its vertical axis rotations using paleomagnetic tools.In this study, more than 2000 paleomagnetic samples were collected and analysed from 86 different sites which were later classified into 11 separate geographic domains displaying similar tectonic characteristics. Moreover, available paleomagnetic data in the literature were parametrically resampled, analysed and combined with our data. In the region, there is a positive correlation between rotation amounts and sample ages supporting continuous deformation throughout the Neogene period. The spatial variations of results indicated that the study area can be divided into three main domains based on vertical axis rotations. From the south to the north these domains include SW Anatolian domain with ∼20° counter-clockwise rotation, Burdur–Dinar–Ulubey domain with ∼4° counter-clockwise rotation and northern areas characterized by clockwise rotations. The identified domains of counter-clockwise rotation are separated by a well-defined NW-SE striking Acıpayam Transfer Zone and there is no differential rotation in agreement with the presence of NE-SW striking shear zone in the region. Therefore, we concluded that the Pliny-Strabo STEP Fault have not propagated into the over-riding plate as a shear zone. This implies that there is no evidence to support the presence of alleged Fethiye–Burdur Fault Zone as suggested, and its existence is dubious.

Influence of graviceptor stimulation initiated by off-vertical axis rotation on ventilation.

What is the central question of this study? It is known that respiration is affected by graviceptors, but it remains unclear to what extent labyrinthine and non-labyrinthine graviceptors are involved in this process. What is the main finding and its importance? Our results suggest that the modulation of respiration is not a result of a simple reflex arc, but that it involves a higher integration of different types of receptors with variable contributions of either type of graviceptor among subjects. It has been suggested that the otolith system is involved in the physiological response to changes in body orientation with respect to gravity. In studies on animals, an otolith-respiratory reflex has been observed, but data on humans are scarce and inconclusive, mainly because pure otolithic stimulation is difficult to produce in humans. To assess the otolithic-respiratory reflex in humans, we used an off-vertical axis rotation (OVAR) that produces periodic and pure stimulation of graviceptors. The inspiratory flow was measured during earth vertical axis rotation (EVAR, control conditions) and OVAR in 21 subjects. To distinguish the effects of the labyrinthine and non-labyrinthine graviceptors on ventilation, these measurements were repeated with two different static head positions: head turned leftward and rightward in yaw. The velocity of rotation was individually selected to match spontaneous breathing rate (mean 11.4cyclesmin-1 , 0.19Hz). Average ventilatory flow was higher in OVAR than in EVAR, as was tidal volume. In OVAR, the transition between inspiration and expiration occurred mainly in the forward pitch position. The phase of this transition in most subjects was driven mostly by the body position rather than by the head position, suggesting that respiratory modifications during OVAR mainly involved non-labyrinthine receptors. However, the study demonstrated a high intersubject variability both in the ability of OVAR to synchronize breathing and in the influence of labyrinthine stimulation. We conclude that the respiratory response to changes in orientation of the body with respect to the vertical involves labyrinthine and non-labyrinthine stimulation, with the gain of each signal varying individually.

Vertical axis rotation (or lack thereof) of the eastern Mongolian Altay Mountains: Implications for far-field transpressional mountain building

The Altay Mountains of Western Mongolia accommodate 10–20% of the current shortening of the India-Asia collision in a transpressive regime. Kinematic models of the Altay require faults to rotate anticlockwise about a vertical axis in order to accommodate compressional deformation on the major strike slip faults that cross the region. Such rotations should be detectable by palaeomagnetic data. Previous estimates from the one existing palaeomagnetic study from the Altay, on Oligocene and younger sediments from the Chuya Basin in the Siberian Altay, indicate that at least some parts of the Altay have experienced up to 39 ± 8° of anticlockwise rotation. Here, we present new palaeomagnetic results from samples collected in Cretaceous and younger sediments in the Zereg Basin along the Har-Us-Nuur fault in the eastern Altay Mountains, Mongolia. Our new palaeomagnetic results from the Zereg Basin provide reliable declinations, with palaeomagnetic directions from 10 sites that pass a fold test and include magnetic reversals. The declinations are not significantly rotated with respect to the directions expected from Cretaceous and younger virtual geomagnetic poles, suggesting that faults in the eastern Altay have not experienced a large degree of vertical axis rotation and cannot have rotated >7° in the past 5 m.y. The lack of rotation along the Har-Us-Nuur fault combined with a large amount of rotation in the northern Altay fits with a kinematic model for transpressional deformation in which faults in the Altay have rotated to an orientation that favours the development of flower structures and building of mountainous topography, while at the same time the range widens at the edges as strain is transferred to better oriented structures. Thus the Har-Us-Nuur fault is a relatively young fault in the Altay, and has not yet accommodated significant rotation.

Paleomagnetic constraints on the timing and distribution of Cenozoic rotations in Central and Eastern Anatolia

Abstract. To quantitatively reconstruct the kinematic evolution of Central and Eastern Anatolia within the framework of Neotethyan subduction accommodating Africa–Eurasia convergence, we paleomagnetically assess the timing and amount of vertical axis rotations across the Ulukışla and Sivas regions. We show paleomagnetic results from ∼ 30 localities identifying a coherent rotation of a SE Anatolian rotating block comprised of the southern Kırşehir Block, the Ulukışla Basin, the Central and Eastern Taurides, and the southern part of the Sivas Basin. Using our new and published results, we compute an apparent polar wander path (APWP) for this block since the Late Cretaceous, showing that it experienced a ∼ 30–35° counterclockwise vertical axis rotation since the Oligocene time relative to Eurasia. Sediments in the northern Sivas region show clockwise rotations. We use the rotation patterns together with known fault zones to argue that the counterclockwise-rotating domain of south-central Anatolia was bounded by the Savcılı Thrust Zone and Deliler–Tecer Fault Zone in the north and by the African–Arabian trench in the south, the western boundary of which is poorly constrained and requires future study. Our new paleomagnetic constraints provide a key ingredient for future kinematic restorations of the Anatolian tectonic collage.

Fracture characterization in sigmoidal folds: Insights from the Siah Kuh anticline, Zagros, Iran

Fieldwork and remote-sensing data from the Siah Kuh anticline, simply folded belt, Zagros, Iran indicate that specific structures and fracture systems formed during the development of its sigmoidal shape, and that conceptual fracture models developed for cylindrical folds are inadequate for the correct evaluation and development of hydrocarbon accumulations in this type of anticline. The sigmoidal shape of the Siah Kuh anticline was achieved in the Pliocene due to vertical axis rotations of an already existing anticline. These rotations promoted the development of (1) two systems of normal faults in the outer arcs of the sigmoidal shape, (2) a low-angle thrust, and (3) the north–south Danan anticline in the inner arc of its easternmost bend. The passive margin to syn-folding structures, typically observed in nearby cylindrical and periclinal anticlines, predated the development of the sigmoidal shape and were passively rotated into the segments of the anticline. The sigmoid-related structures are spatially, geometrically, and kinematically related to the bends of the anticline trend, hence they can be predicted and modeled in the subsurface. The sigmoid-related normal faults have a great potential to preserve porosity and promote localized high flow rates or early water breakthrough. However, if they cut through thin reservoir and seal units, sigmoid-related thrusts and normal faults might compromise lateral reservoir continuity and seal integrity. The results of this study can help in reducing risks and uncertainty in the evaluation and development of business opportunities in secondary sigmoidal anticlines within the Zagros or any other fold-thrust belt.