Western Limb Research Articles

Rainfall-induced landslide in the active frontal fold–thrust belt of Northwestern Himalaya, Jammu: dynamics inferred by geological evidences and Ground Penetrating Radar

Landslides are the most established geological hazards in the frontal fold–thrust belt of Northwestern Himalaya comprising of Siwaliks and Murree strata. The continuous rainfall from 2 to 6 September, 2014 caused a massive landslide at village Sadal in Udhampur district of Jammu and Kashmir state. The landslide occurred in the early morning of September 6, 2014, destroying entire Sadal habitation comprising 45 houses, and killing 41 people and more than 500 domestic animals. Google earth images of pre and post-landslide events along with the field measurements show the kinematics of upper and lower parts of the slide. Horizontal and vertical components of displacement and mode of failure suggest the landslide as of complex nature. The shallow subsurface geophysical imaging through Ground Penetrating Radar (GPR) survey shows the failure plane composed of friable mudstone bed underlain by massive mudstone and overlain by cross-bedded sandstone. The depth of debris material above the failure plane ranges from 6 m at Site S1a-b to 10 m at Site-S2b and 20 m at Site S3a. The velocity analysis of Site-3 shows four thick layers represented from bottom to surface by L1—sandstone (V = 0.16 m/ns, travel time = 356.36 ns), L2—mudstone (V = 0.17 m/ns, travel time = 288.48 ns), L3—massive mudstone (V = 0.19 m/ns, travel time 220.68 ns), and L4—cross-laminated sandstone (V = 0.20 m/ns, travel time = 77.58 ns) overlaying the failure plane. The study shows the landslide occur along the western limb of a fold identified during the present work. We mapped an old landslide on the same limb which shows 5–6 m-thick subsurface debris material with thick rock fragments involved in the landslide process. The detailed geological and geophysical investigations suggest that both the landslides were triggered by extreme rain fall events.

Radiation Dose Nowcast for the Ground Level Enhancement on 10–11 September 2017

AbstractA ground level enhancement event occurred on 10–11 September 2017, associated with an X8.2 solar flare on the western limb of the Sun. We report the results of our manually conducted nowcast using WArning System for AVIation Exposure to Solar energetic particles. The maximum radiation dose rate at a flight altitude of 12 km was estimated to be approximately 3 μSv/h, which is less than half of the dose rate due to galactic cosmic rays. We also discuss a possible quasi‐parallel shock‐acceleration mechanism that may have led to the exceptionally soft proton energy spectrum as ground level enhancement events.

Analysis of Slope Failure at the Southwestern Limb of Perat Anticline - NE Iraq Using Stereographic Projection

Rock slopes analysis in south western limb of Perat anticline, near Bekhme village, were studied. Seven stations were chosen to study these slopes which distributed along several exposed formations of Bekhme, Shiranish, Tanjero, Kolosh, Khurmala, and Gercus interbeded with Pila Spi according to their existence on the road, beginning from the Iron Bridge of Bekhme. Stereographic projection technique was used in analyzing and classifying these slopes. Plane sliding along bedding planes and joints is the predominant in the formations of Bekhme, Shiranish, Pila Spi and some of khurmala Formation. Clastic rock Formations of Tanjero, Kolosh, and Gercus help to failure in steep and moderate slopes. Because of no distinctive favorable discontinuities to slide along, these slopes are suffering from raveling processes which means granular disintegration into small components by different processes. The rock slopes of Khurmala Formation are affected by wedge sliding along discontinuities intersections with bedding planes.

Vertical Oscillation of a Coronal Cavity Triggered by an EUV Wave

Abstract In this paper, we report our multiwavelength observations of the vertical oscillation of a coronal cavity on 2011 March 16. The elliptical cavity with an underlying horn-like quiescent prominence was observed by the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory. The width and height of the cavity are 150″ and 240″, and the centroid of cavity is 128″ above the solar surface. At ∼17:50 UT, a C3.8 two-ribbon flare took place in active region 11169 close to the solar western limb. Meanwhile, a partial halo coronal mass ejection erupted and propagated at a linear speed of ∼682 km s−1. Associated with the eruption, a coronal extreme-ultraviolet (EUV) wave was generated and propagated in the northeast direction at a speed of ∼120 km s−1. Once the EUV wave arrived at the cavity from the top, it pushed the large-scale overlying magnetic field lines downward before bouncing back. At the same time, the cavity started to oscillate coherently in the vertical direction and lasted for ∼2 cycles before disappearing. The amplitude, period, and damping time are 2.4–3.5 Mm, 29–37 minutes, and 26–78 minutes, respectively. The vertical oscillation of the cavity is explained by a global standing MHD wave of fast kink mode. To estimate the magnetic field strength of the cavity, we use two independent methods of prominence seismology. It is found that the magnetic field strength is only a few Gauss and less than 10 G.

Litho- and chemostratigraphy of the Flatreef PGE deposit, northern Bushveld Complex

The Flatreef is a world-class platinum-group element (PGE) deposit recently discovered down-dip from existing mining and exploration operations on the northern limb of the Bushveld Complex. Current indicated resources stand at 42 Moz PGE (346 Mt with 3.8 g/t Pt+Pd+Rh+Au, 0.32% Ni and 0.16% Cu) which, in the case of Pt, is equivalent to ~ 10 years global annual production, making it one of the largest PGE deposits on earth. The grade and thickness of the Flatreef mineralised interval is highly unusual, with some drill core intersections containing up to 4.5 g/t Pt+Pd+Rh+Au over 90 m in drill core. Here, we document the down-dip and along-strike litho- and chemostratigraphy of the Flatreef and its footwall and hanging wall rocks, based on a diamond drill core database totalling > 720 km. At the base of the sequence intersected in the drill cores are up to 700-m-thick sills of ultramafic rocks (dunite, harzburgite, pyroxenite) emplaced into pelitic, dolomitic, and locally quartzitic and evaporitic rocks belonging to the Duitschland Formation of the Transvaal Supergroup. Next is an approximately 100–200-m sequence of low-grade-sulphide-mineralised, layered mafic-ultramafic rocks containing abundant sedimentary xenoliths and, in places, several chromite seams or stringers. This is overlain by a ~ 100-m-thick sequence of well-mineralised mafic-ultramafic rocks (the Flatreef sensu strictu), overlain by a laterally persistent mottled anorthosite layer at the base of > 1 km of homogenous Main Zone gabbronorite. Based on stratigraphic, lithological and compositional analogies to the layered rocks in the eastern and western Bushveld Complex, we correlate the Flatreef and its chromite bearing footwall rocks with the Upper Critical Zone, notably the interval between the UG2 chromitite and the Bastard Reef as found elsewhere in the Bushveld Complex. This includes recognition of a Merensky Reef correlative. The ultramafic rocks below the main chromitite seam (UG2 correlative) in the Flatreef footwall are correlated with the Lower Critical and Lower zones. However, compared to the western and eastern Bushveld limbs, the studied sequence is strongly enriched in sulphide and PGE, many of the rocks show elevated CaO, K2O, Rb and Zr contents, and lateral continuity of layers between drill cores is less pronounced than elsewhere in the Bushveld, whereas ultramafic units are locally considerably thickened. These compositional and lithological traits are interpreted to result from a range of processes which include contamination with calcsilicate and hornfels, intrusion of granitic magmas, and the influence of multiple structural events such as pre- to syn-emplacement regional-scale open folding and growth faults. Evidence for the existence of potholes also exists. In the shallow, up-dip portions of the project area, the entire magmatic sequence below the Main Zone becomes increasingly contaminated to the extent that individual units are somewhat more difficult to correlate between drill cores. This package represents the Platreef as exposed in outcrop and shallow bore holes across much of the northern limb of the Bushveld Complex. The new data presented here thus indicate that the Platreef is a relatively more contaminated up-dip extension of parts of the Critical and Lower zones.

Association of platinum-group elements with chromitite within the Merensky reef, Western Limb, Bushveld Complex: Results of a high resolution mineralogical and geochemical study

We present the results of a high-resolution mineralogical and geochemical study conducted across three intersections of Merensky reef at Impala Platinum Mines on the Western Limb of the Bushveld Complex. We studied two intersections of non-pegmatoidal Merensky reef and one intersection of pegmatoidal Merensky reef in an attempt to reconstruct the petrogenesis of this economically important ore horizon and in order to establish the relationship between non-pegmatoidal and pegmatoidal reef intersections. Our results indicate a much stronger correlation between PGE and Cr than between PGE and S (or Cu as a proxy for sulfides), which favours a model in which chromite and associated PGEs were introduced from a deeper staging chamber to result in the formation of the chromitite layers of the Merensky reef. The geochemistry of chromite in the Merensky reef is suggestive of the fact that the bottom chromitite layer of the pegmatoidal reef is a lateral correlate of the chromitite of the non-pegmatoidal reef, in which only a single chromitite layer occurs. We propose that the Merensky reef at Impala Platinum Mines is a product of the introduction of chromite-laden basal flows into the Bushveld Complex magma chamber and that the relationship between pegmatoidal and non-pegmatoidal reef intersections is related to non-deposition, rather than erosion, as was shown to be the case at other localities within the Western Limb.

Brightening and Darkening of the Extended Solar Corona during the Superflares of September 2017

Abstract On 2017 September 6 and 10, the strongest X9.3 and X8.2 flares of the decade occurred in the active region NOAA Active Region 12673. During these flares, the Sun Watcher with Active Pixels and Image Processing (SWAP) telescope on board the Project for Onboard Autonomy 2 (PROBA2) satellite registered the unusual alternate brightening and darkening of the western corona at the heliocentric distances ≈1.2–1.7 R ☉. The X9.3 flare on 2017 September 6 was accompanied by coronal brightening up to 30%–45% at distances ≈1.35–1.7 R ☉. Numerical simulations showed that this brightening might be produced by resonant scattering of the flare radiation by the Fe ix–Fe xi ions in the coronal plasma at the temperature T ∼ 0.8–1 MK, and the densities seriously reduced in comparison with the typical values for the quiet background corona probably moving outward with velocities of 30–40 km s−1. At the maximum of the flare and one hour later, two coronal mass ejections (CMEs) originated, which dimmed the coronal emission in the SWAP 174 Å passband above the western limb by 20%–30%. The X8.2 flare on September 10 was accompanied by a CME, which rose up and progressively dimmed the western part of the corona up to 60%. An hour later the darkening, produced by a global rearrangement of the magnetic field structure and an evacuation of a significant part of the coronal plasma, extended over the complete western limb. A differential emission measure (DEM) analysis showed a decrease in the electron density of the background plasma with T ∼ 1–2 MK at distances 1.24–1.33 R ☉ by 2–3.5 times after the CME. At the same time, an additional DEM peak at T ≈ 0.8 MK appeared, which may be associated with an additional emission in the SWAP passband produced by the flare radiation resonantly scattered by the coronal plasma.

Diagnosing the Magnetic Field Structure of a Coronal Cavity Observed during the 2017 Total Solar Eclipse

Abstract We present an investigation of a coronal cavity observed above the western limb in the coronal red line Fe x 6374 Å using a telescope of Peking University and in the green line Fe xiv 5303 Å using a telescope of Yunnan Observatories, Chinese Academy of Sciences, during the total solar eclipse on 2017 August 21. A series of magnetic field models is constructed based on the magnetograms taken by the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory (SDO) one week before the eclipse. The model field lines are then compared with coronal structures seen in images taken by the Atmospheric Imaging Assembly on board SDO and in our coronal red line images. The best-fit model consists of a flux rope with a twist angle of 3.1π, which is consistent with the most probable value of the total twist angle of interplanetary flux ropes observed at 1 au. Linear polarization of the Fe xiii 10747 Å line calculated from this model shows a “lagomorphic” signature that is also observed by the Coronal Multichannel Polarimeter of the High Altitude Observatory. We also find a ring-shaped structure in the line-of-sight velocity of Fe xiii 10747 Å, which implies hot plasma flows along a helical magnetic field structure, in the cavity. These results suggest that the magnetic structure of the cavity is a highly twisted flux rope, which may erupt eventually. The temperature structure of the cavity has also been investigated using the intensity ratio of Fe xiii 10747 Å and Fe x 6374 Å.

Application of gravity and magnetic methods for the crustal study and delineating associated ores in the western limb of Hazara Kashmir Syntaxis, Northwest Himalayas, Pakistan

The present geophysical study deals with the ores and crustal demonstration of southeastern Hazara and its adjoining areas of Azad Jammu and Kashmir, Pakistan, on the basis of terrestrial gravity and magnetic data. Tectonically, the study area lies in the Lesser Himalayas as well as to an extent in the sub-Himalaya, more specifically in the western limb of Hazara Kashmir Syntaxis. In this study, 567 gravity and 508 magnetic stations have been measured with CG-5 gravimeter and proton precession magnetometer, respectively. The collected data have been processed by applying standard corrections and then different types of maps were prepared. The ores in the area have been delineated by the qualitative interpretation of residual Bouguer anomaly and reduction to pole total magnetic intensity maps, whereas regional structures are demarcated by the Bouguer anomaly and regional Bouguer anomaly maps. The positive contour closures on the residual Bouguer anomaly map indicate the iron ore and phosphate, whereas negative contour closures are the effects of low-density material which consists of gypsum and soapstone. The pole-reduced total intensity map also shows the negative and positive contour closures almost in the same localities and confirms the residual Bouguer anomaly map. The geological model computed on the basis of Bouguer anomaly demarcated a series of faults between different rock units in the study area. The Kashmir Boundary Thrust cuts the western limb of Hazara Kashmir Syntaxis near the apex in the north of Muzaffarabad and marks the boundary between Murree Formation and carbonates of Abbottabad Formation. The gravity model also suggests that the thickness of the crust increases towards the northeast.

A distance estimate to the Cygnus Loop based on the distances to two stars located within the remnant

Underlying nearly every quantitative discussion of the Cygnus Loop supernova remnant is uncertainty about its distance. Here we present optical images and spectra of nebulosities around two stars whose mass-loss material appears to have interacted with the remnant's expanding shock front and thus can be used to estimate the Cygnus Loop's distance. Narrow passband images reveal a small emission-line nebula surrounding an M4 red giant near the remnant's eastern nebula NGC 6992. Optical spectra of the nebula show it to be shock-heated with significantly higher electron densities than seen in the remnant's filaments. This along with a bow-shaped morphology suggests it is likely red giant mass-loss material shocked and accelerated by passage of the Cygnus Loop's blast wave. We also identify a B7 V star located along the remnant's northwestern limb which also appears to have interacted with the remnant's shock wave. It lies within a small arc of nebulosity in an unusually complex region of highly curved and distorted filaments along the remnant's northern shock front suggestive of a localized disturbance of the shock front due to the B star's stellar winds. Based on the assumption that these two stars lie inside the remnant, combined with an estimated distance to a molecular cloud situated along the remnant's western limb, we propose a distance to the Cygnus Loop of 1.0 +/- 0.2 kpc. Although larger than several recent estimates of 500 - 800 pc, a distance ~1 kpc helps resolve difficulties with the remnant's postshock cosmic ray and gas pressure ratio and estimated supernova explosion energy.

Possible teleconnections between East and South Asian summer monsoon precipitation in projected future climate change

The present paper examined the teleconnections between two huge Asian summer monsoon components (South and East Asia) during three time slices in future: near-(2010–2039), mid-(2040–2069) and far-(2070–2100) futures under the RCP4.5 and RCP8.5 scenarios. For this purpose, a high-resolution atmospheric general circulation model is used and integrated at 40 km horizontal resolution. To get more insight into the relationships between the two Asian monsoon components, we have studied the spatial displaying correlation coefficients (CCs) pattern of precipitation over the entire Asian monsoon region with that of South Asia and three regions of East Asia (North China, Korea–Japan and Southern China) separately during the same three time slices. The possible factors responsible for these teleconnections are explored by using mean sea level pressure (MSLP) and wind fields at 850 hPa. The CC pattern of precipitation over South Asia shows an in-phase relationship with North China and an out-of-phase relationship with Korea–Japan, while precipitation variations over Korea–Japan and Southern China exhibit an out-of-phase relationship with South Asia. The CCs analysis between the two Asian blocks during different time slices shows the strongest CCs during the near and far future with the RCP8.5 scenario. The CC pattern of precipitation over Korea–Japan and Southern China with the wind (at 850 hPa) and MSLP fields indicate that the major parts of the moisture over Korea–Japan gets transported from the west Pacific along the western limb of NPSH, while the moisture over Southern China comes from the Bay of Bengal and South China Seas for good monsoon activity.

Structure and Stratigraphy of Rumbli and Panjar Areas of Kashmir and Pakistan with the Aid of GIS

ABSTRACT The project area lies in the southern part of the Hazara Kashmir syntaxis. The Hazara Kashmir syntaxis is an antiformal structure. The project area includes Rumbli, Namb, Chatrora, Chachan, Panjar, Barathian and Utrinna areas of Rawalpindi and Sudhnoti districts. The southeastern limb of the Hazara Kashmir syntaxis is imbricated along Punjal thrust, Main Boundary thrust and Riasi fault. The Jhelum fault truncates the western limb of Hazara Kashmir syntaxis. The core of syntaxis comprises of Himalayan molasse deposits. These molasse deposits represent the part of cover sequence of Indian plate. These Himalayan molasse deposits include the Early to Middle Miocene Kamlial Formation, Middle to Late Miocene Chinji Formation, Late Miocene Nagri Formation and Late Miocene Dhok Pathan Formation. The area is highly deformed resulting folds and faults. The major folds in the project area are the Panjar anticline, Barathian syncline, Barathian anticline, Rumbli anticline, Chatrora antiformal syncline and Namb syncline. The folds are either northwest-southeast trending or southwest-northeast trending. The folds are asymmetric, open, and gentle and close in nature. The folds are southwest, northeast or southeast vergent. The Jhelum fault truncates the northeast and northwest trending structures. The folds and faults are the result of northeast-southwest or northwest-southeast Himalayan compression.

The Rio Pardo salient, northern Araçuaí orogen: an example of a complex basin-controlled fold-thrust belt curve

ABSTRACT: The Rio Pardo salient, the large antitaxial curve described by the Aracuai fold-and-thrust belt along the southeastern edge of the Sao Francisco craton, is one of the most prominent and one of the least studied features of the Brasiliano Aracuai-West Congo orogenic system (AWCO). In addition to the Archean/Paleoproterozoic basement, the salient is comprised of metasedimentary rocks mainly from the Neoproterozoic Macaubas Group and the Salinas Formation. Its western limb occupies a portion of the Espinhaco ridge, where the NS-trending structures of the Aracuai belt progressively curve NE and E, thereby defining the hinge zone along the Serra Geral on the Minas-Bahia boundary. The eastern limb is NW-trending and marked by a major shear zone. In models postulated to generate the AWCO through the closure of the Neoproterozoic Macaubas basin, this large curve plays a critical kinematic role. Yet, in spite of this, its development is still not fully understood. How did this curve originate? Which factors controlled its generation? Our field study performed in the northern Aracuai orogen characterized the kinematic picture of the salient, and led to a model that addresses these questions. The results we obtained indicate that the Rio Pardo salient developed in response to four deformation phases. The contractional D1 and D2 phases are coaxial and responsible for a craton-directed tectonic transport along the salient’s outer arc, which is coupled with an overall southward motion of the inner arc, thereby giving rise to a rather complex kinematic picture. Furthermore, structures of the D1/D2 phases define a zigzag pattern with alternating NE- and NW-trending segments along the salient’s leading edge. Along the NE-trending segments, the metasedimentary rocks are thrust northwestwards on top of the craton basement, while along the NW-trending segments, the supracrustal rocks are displaced along dextral to reverse-dextral transpressional shear zones located on the basement/cover contact. Structures of the D3 phase, which are well developed in the hinge zone, record a final WSW-ENE contraction, which was responsible for rotation of the preexistent fabric elements around NNW-trending axes and the enhancement of the salient curvature. The D4 phase is extensional and is recorded by two large-scale structures, the Chapada Acaua and Tingui normal shear zones, as well as by the normal-sinistral reactivation of the Itapebi strike-slip shear zone that marks the salient eastern limb. We interpret the initiation of the Rio Pardo salient during the collisional 565-575 Ma D1/D2 phases essentially as a primary arc that is mainly controlled by the geometry of the Macaubas precursor basin. The thickened internal portion of the Rio Pardo salient was affected by extensional tectonism at c. 530 Ma, and is recorded by the D4 deformation phase, which is currently ascribed to the extensional collapse of the Aracuai-West Congo orogen.

Solar Coronal Loop Dynamics Near the Null Point Above Active Region NOAA 2666

AbstractWe analyse observations of a saddle-like structure in the corona above the western limb of the Sun on 2017 July 18. The structure was clearly outlined by coronal loops with typical coronal temperature no more than 1 MK. The dynamics of loops showed convergence towards the centre of the saddle in the vertical direction and divergence in the horizontal direction. The event is a clear example of smooth coronal magnetic field reconnection. No heating manifestations in the reconnection region or magnetically connected areas were observed. Potential magnetic field calculations, which use as the boundary condition the SDO/HMI magnetogram taken on July 14, showed the presence of a null point at the height of 122 arcsec above the photosphere just at the centre of the saddle structure. The shape of field lines fits the fan-spine magnetic configuration above NOAA 2666.

Early Oligocene calcareous nannofossils, planktonic and larger foraminifera from the United Arab Emirates, Oman Mountains

The Lower Oligocene Asmari Formation occupies the western and eastern flanks of the Jabal Hafit anticline and the western limb of the Jabal Malaqet-Mundassah anticline in the southeast of the United Arab Emirates near the Oman border. In this area the Asmari Formation unconformably overlies the Upper Eocene Dammam Formation. In this study an Early Oligocene characteristic assemblage of calcareous nannofossils, foraminifera, corals, calcareous algae, bryozoa, mollusks and echinoids is described from the carbonate rocks of the Asmari Formation. The Asmari stratigraphic succession is dated by analysis of the calcareous nannofossil assemblages and planktonic and larger foraminifera. The results of this study indicate that the succession falls within the Early Oligocene Zones NP24 and P20-P21. About seventeen nannofossil species are documented for the first time in this formation, along with three planktonic and larger foraminiferal species. The Oligocene rocks in the study area provide results consistent with a shallow-water inner shelf within the photic zone.

Ancient selenophysical structure of the Grimaldi basin: Constraints from GRAIL gravity and LOLA topography

The Grimaldi impact basin is located near the western limb of the moon and lies to the southwest of the Oceanus Procellarum. A clearly visible positive gravity anomaly exists in its low-lying inner wall, implying a subsurface mass concentration beneath the crater. Exploration of this basin could extend our meaningful and fundamental understanding of giant impact processes as well as the structure of mare basins/craters. Limited by the low-resolution of previous gravity field models, it was once impossible to explore the structure beneath Grimaldi. The recent high-resolution gravity data from the Gravity Recovery and Interior Laboratory mission make it possible to break through this barrier. Prior to our investigation of the selenophysical structure around crater Grimaldi, we developed a flexure model that includes surface and subsurface loads. A localized admittance analysis was performed by combining high-resolution gravity data with the high-resolution topography data obtained from Lunar Orbiter Laser Altimeter. Within 2σSTD error constraints, we estimated the best-fit parameters over Grimaldi as well as two other places in its neighborhood. All the predicted admittances show a goodness of fit with their corresponding observations. The large load ratio (∼9.2) found at the Grimaldi is an indirect mirror of the dominant subsurface load, consistent with its large positive gravity anomaly in its low-lying floor. Not only the crustal thickness of 48 km but also the crustal density of 2500 kg m−3 found around Grimaldi shows a great accordance with the recent results of GRAIL. Given the best-fit parameters of f, bc and ρc, the elastic thickness Te is found to be around 28 km over Grimaldi. Taking into account the best-fit values in its neighborhood, a regional elastic thickness of 30 km could be roughly concluded around Grimaldi, which is completely in the previous ranges (20 < Te < 60 km) from Clementine. Our result of the elastic thickness is quite larger than those on the lunar nearside volcanic complexes of the recent GRAIL study. Considering fewer thermal activities occurred on the lunar limb or farside than its nearside, we can then deduce that the lithosphere could be possibly cold and therefore developed a corresponding dense elastic thickness.

Enhanced Polarized Emission from the One-parsec-scale Hotspot of 3C 84 as a Result of the Interaction with the Clumpy Ambient Medium

Abstract We present Very Long Baseline Array polarimetric observations of the innermost jet of 3C 84 (NGC 1275) at 43 GHz. A significant polarized emission is detected at the hotspot of the innermost restarted jet, which is located 1 pc south from the radio core. While the previous report presented a hotspot at the southern end of the western limb, the hotspot location has been moved to the southern end of the eastern limb. Faraday rotation is detected within an entire bandwidth of the 43 GHz band. The measured rotation measure (RM) is at most (6.3 ± 1.9) × 105 rad m−2 and might be slightly time variable on the timescale of a month by a factor of a few. Our measured RM and the RM previously reported by the CARMA and SMA observations cannot be consistently explained by the spherical accretion flow with a power-law profile. We propose that a clumpy/inhomogeneous ambient medium is responsible for the observed RM. Using an equipartition magnetic field, we derive the electron density of 2 × 104 cm−3. Such an electron density is consistent with the cloud of the narrow line emission region around the central engine. We also discuss the magnetic field configuration from the black hole scale to the parsec scale and the origin of low polarization.

The Interrelationship of Micro‐Meso and Macroscopic Structures on the Western Limb of the Hazara Kashmir Syntaxis, Pakistan

AbstractDetailed micro–meso to macroscopic structural analyses reveal two deformation phases in the western limb of the Hazara‐Kashmir Syntaxis (HKS). Bulk top to NW shearing transformed initially symmetrical NNE–SSW trending meso to macroscopic folds from asymmetric to overturned ones without changing their trend. Sigmoidal en‐echelon tension gashes developed during this deformation, that were oblique to bedding parallel worm burrows and bedding planes themselves. Strain analyses of deformed elliptical ooids using the Rf/ϕ method constrain the internal strain patterns of the NNE–SSW structures. The principal stretching axis (S3) defined by deformed elliptical ooids is oriented N27°E at right angles to WNW–ESE shortening. The deformed elliptical ooids in sub‐vertical bedding vertical planes contain ooids that plunge ∼70° SE due to NW‐directed tectonic transport. Finite strain ratios are 1.45 (Rxy) parallel to bedding plane and 1.46 (Ryz) for the vertical plane. From these 2D strain values, we derive an oblate strain ellipsoidal in 3D using the Flinn and Hsu/Nadai techniques. Strains calculated from deformed elliptical ooids average −18.10% parallel to bedding and −18.47% in the vertical plane. However, a balanced cross‐section through the study area indicates a minimum of ∼ −28% shortening. Consequently, regional shortening was only partially accommodated by internal deformation.

On traces of a strong earthquake in walls of the Sary-Bulun medieval sites along the great silk route (western Issyk-Kul Lake region, Northern Tien Shan)

The Sary-Bulun archeological sites located along the Great Silk Route of medieval times are studied. The study revealed a number of the deformations of seismogenic origin: tilts, shifts, and collapse and lateral bends of walls as well as long fissures in corner parts of the rooms. Judging by archeological artifacts, the seismic event occurred at the end of the 12th–beginning of the 13th century AD. Judging by degree of damage, the intensity of this ancient earthquake was I ≥ VIII on the MSK-64. The source of the seismic oscillations was apparently located in the faults cutting the active Boz-Barmak anticline. The studied archeological sites are located on the western limb of this anticline structure. In the medieval period, the Sary-Bulun settlements were the largest metallurgic centers of the Issyk-Kul depression and, thus, they are of a great significance for studying industrial processes of that time.

Pulses of Plagioclase-laden Magmas and Stratigraphic Evolution in the Upper Zone of the Bushveld Complex, South Africa

Cumulate rocks of the Upper Main Zone and Upper Zone (UUMZ) of the Bushveld Complex, South Africa, contain the world's major resources of Fe-Ti-V ±, hosted in Ti-magnetite and apatite, and are commonly considered as having crystallized from the last major injection of magma into the magma chamber. In this study, we present the petrography, modal proportions, whole-rock major element chemistry (260 samples), electron microprobe data (∼10 000 analyses for plagioclase, olivine, and pyroxene), and compiled analyses of Cr in magnetite (239 samples) for the UUMZ sampled over 2.1 km of the Bierkraal drill cores in the western limb of the Complex. The UUMZ section exhibits a broad normal fractionation trend upwards, but a series of reversals to more primitive anorthite contents in plagioclase, Mg# in pyroxenes and olivine, Cr in whole-rocks and Cr in magnetite separates are observed, accompanied by the appearance or disappearance of various minerals. Anorthosite or leucogabbro layers are closely linked to these reversals; the reversals in An % of plagioclase are used as boundaries to divide the UUMZ into 18 cycles. These cycles are interpreted as indications of magma chamber replenishment by plagioclase-laden magmas (up to 20 vol. % plagioclase) and are also marked by spikes in Cr content. In addition, abundant Fe-Ti oxide-bearing plagioclase-rich rocks are identified in the lower half of the UUMZ. These have crystallized from a hybrid melt produced by the mixing of a new plagioclase-bearing magma batch and the resident magma. Further crystallization of this hybrid liquid may lead to the formation of magnetite layers in the lower part of the UUMZ. The Bushveld UUMZ therefore grew by multiple emplacements of crystal-laden magmas coming from deep-seated chambers. Slow cooling in a shallow chamber explains the systematic bottom-up compositional evolution in the cumulate pile within individual cycles. The residual melt reached silicate liquid immiscibility soon after the saturation of apatite. Thereafter, segregation of conjugate Fe-rich and Si-rich melts and crystallization of the paired melts produces cumulates with a smooth upward decrease in Fe-Ti oxides, whereas plagioclase mode increases in each apatite-bearing cycle. A comparison of systematic geochemical analyses and a detailed lithological stratigraphy between the Bushveld limbs demonstrates the possible connectivity between the western and eastern Upper Zone but indicates notable differences from the Bellevue section of the northern limb.