Geomagnetic disturbance effects on equatorial spreadF

Geomagnetic disturbance effects on the occurrence of range and frequency spread at Huancayo are studied for the period 1957–74. The occurrence of frequency spread is decreased on disturbed days forD-months andE-months while duringJ-months an increase is noted in the post-midnight period. The occurrence of range spread is decreased on disturbed days in the pre-midnight hours duringD andE-months. Post-midnight hours ofD andE-months and all hours of night duringJ-months show an increase of range spread on disturbed days, which is most prominent during low sunspot years. The mean occurrence of frequency spread (2300–0100 LT) and range spread (2000–2300 LT) decrease with increasing ΣKp. On the other hand, occurrence of range spread (0300–0500 LT) increases with increasing ΣKp, and is suggested as the consequence of the changes of the horizontal electric field in theF-region associated with the geomagnetic storms.     

Structural framework for the emplacement of the Bolangir anorthosite massif in the Eastern Ghats Granulite Belt, India: implications for post-Rodinia pre-Gondwana tectonics

Massif type anorthosites at Bolangir, eastern India are emplaced at the vicinity of the proto-Indian craton—Eastern Ghats Granulite belt contact. Micro- and meso-structural evidences indicate that the emplacement of the anorthosite pluton and the adjoining granitoids was syn-tectonic with respect to the D₃ deformation phase (950–1,000 Ma) in the host gneiss. Anisotropy of magnetic susceptibility confirms that magnetic fabrics within anorthosite were dominantly developed during D₃ deformation. Emplacement of felsic melts in the N-S trending dilatant shear zones in the granitoids, Fe-Ti-Zr-REE rich melt bands along N-S trending shear zones and localized N-S magnetic foliation in anorthosite near the Fe-Ti-Zr-REE rich melt bands indicate change in the stress field from NNW-SSE (D₃) to E-W (D₄). Available geochronological and paleogeographic data coupled with the structural analyses of the intrusive and the host gneiss indicate that the emplacement of massif type anorthosite in the EGP is not related to the accretion of Eastern Ghats Granulite Belt over proto-Indian continent during late Neoproterozoic.     

Deformational history of the Precambrian Kolar Schist Belt,South India: Constraints for the tectonic evolution

In the Kolar Schist Belt well-preserved small-scale diastrophic structures suggest four phases of folding (F₁ — F₄). The near coaxial F₁ andF ₂folds are both isoclinal with long-drawn out limbs and sharp hinges. The axial planes of bothF ₁andF ₂folds are subvertical with N-S strikes; these control the linear outcrop pattern of the Schist belt. The later folds (F ₃and F₄) are important in small-to-intermediate scales only and are accommodation structures formed during the relaxation period of the early folding episodes. Mesoscopic shear zones, post-F₂ but pre-F₃ in age, are present in all the rock types in this area. The F₁ and F₂ folds and the mesoscopic shear zones were formed during a continuous E-W subhorizontal compression. Available geochemical and isotopic data show that the Kolar Schist Belt with ensimatic setting is bounded by two granitic terrains of contrasting evolutionary histories. This, together with E-W subhorizontal compression over a protracted period of time, strengthens the recent suggestions that the Kolar Schist Belt represents a suture. This belt then marks the site of a continent-continent collision event of late Archaean-early Proterozoic age.     

Analytical representation of spatial and temporal variations of the geomagnetic field in the Indian region

The magnetic measurements of declination (D), horizontal (H) and vertical (Z) components of earth’s magnetic field, collected from ground surveys between 1962 and 1966, are used to develop an analytical model of geomagnetic field variations over Indian region for the epoch 1965. In order to reflect spatial features with wavelengths of approximately 1000 km, sixth degree polynomial as a function of differential latitude and longitude is calculated by the method of least squares. The root mean square fit of the model to the input data is better than that accounted by the International Geomagnetic Reference Field for 1965.0. Isomagnetic charts drawn forD, H, Z and total force (F) reflect more details than that shown on world magnetic charts. Further, the values of the field at common repeat stations recorded between 1962 and 1974, after eliminating the field values for the epoch 1965.0, are used to get the secular variation as well as its spatial dependence again by means of polynomial which now includes coefficients which are functions of time and of geographical locations. The accuracy of coefficients is tested against the behaviour of secular variation at permanent magnetic observatories. The merits and limitations of the model are discussed.     

Plio-Quaternary geodynamic evolution of a segment of the Peruvian Andean Cordillera located above the change in the subduction geometry: the Cuzco region

The Cuzco region, which is located above a change in subduction geometry, appears to be characterized by a variable Plio-Quaternary tectono-sedimentary evolution essentially located along the major fault system that separates the High Plateaux from the Eastern Cordillera. After the higher surface formation of the High Plateaux, a set of Neogene basins were filled by Miocene “ fluvio-torrential” series and by Plio-Pleistocene fluvio-lacustrine deposits. The Neogene series have been affected by compressional tectonic forces attributed to the Late Miocene. This compression is followed by roughly E-W trending syn-sedimentary extensional tectonics attributed to the Pliocene; it is related to reactivation of the pre-existing major faults, basin evolution, and volcanic activity concentrated along the faults. In the Early Pleistocene, fluvio-lacustrine deposits are affected by syn- and post-sedimentary compressional tectonism it is characterized by shortening that trends both N-S and E-W and produces folding and faulting of the sedimentary cover. Extensional tectonism trending roughly N-S has been taking place from the Middle Pleistocene to the Present; it is coeval with shoshonitic volcanic activity, and with sedimentation of fluvio-lacustrine terraces, torrential fans and moraines. Quaternary and active normal faults due to this tectonism, are located in a narrow zone more than 100 km-long between the High Plateaux and the Eastern Cordillera, and two 15 km-long fault sectors in the Eastern Cordillera. Characteristic Pleistocene scarps, 400 m or more high, are due to the cumulative normal offset, and there are also little scarps, with heights ranging between 2 and 20 m, which are related to Holocene fault reactivations. Recent fault reactivation on the Cuzco fault system, during the April 5, 1986 earthquake (m_b = 5.3), is due to the N-S trending extension. This state of stress, located at a mean elevation of roughly 3730 m, is generally homogeneous to different scales. The active Cuzco normal faults may be a consequence of adjustment between the compensated Western Cordillera and the undercompensated Eastern Cordillera, this latter being uplifted higher than its isostatic equilibrium due to compression acting on its eastern edge. The variation of the state of stress, during the Plio-Quaternary is in agreement with the variations of the compressional boundary forces. It may be explained by variation of the convergence rate or by the variation of pull-slab forces.     

西藏沙拉岗锑矿控矿构造及成矿时代约束

西藏沙拉岗锑矿床位于中国北喜马拉雅地区然巴杂岩穹窿的东南部40km。该地区至少有4种矿床类型被发现:(1)金矿;(2)金锑矿;(3)锑矿;(4)铅锌(银,锑)矿。沙拉岗是该地区代表性的一个以辉锑矿为主要矿石矿物的脉状锑矿床。赋矿围岩为下白垩统甲不拉组板岩、粉砂岩、硅质岩以及辉长岩和闪长岩等侵入体。主要的矿体受控于近东西向和近南北向断裂构造。近东西向的断裂构造多为低角度浅层次的层间断裂,在成矿前和成矿后均有活动。近南北向的构造多为高角度的断裂,切割了矿区的近东西向断裂,闪长岩和辉长岩,是主要的导矿构造和成矿要素,连通了深部含矿热液和浅表近东西向断裂构造。当近东西向和近南北向的构造发生交汇,沿断裂构造分布的蚀变和矿化的规模随之扩大,往往存在较大规模的工业矿体。锆石SHRIMP U-Pb分析说明辉长岩形成于23.6Ma左右,近南北向断裂构造及其伴随的锑矿化的时间,至少要晚于23.6Ma。     

The sheath folds in the Tananao Group between Tienshiang and Tailuko, east-west cross-island highway, Taiwan

Sheath folds or “eye” folds on decimetric to metric scales are well-developed in the metachert-marble-green rock interlayers of the Changchun Formation and in the marble lens of the Tienhsiang Formation, within the Tananao Group between Tienhsiang and Tailuko, along E-W cross-island highway of Taiwan. Closely associated with the sheath folds are the tight to isoclinal folds with rectilinear axes which are parallel to the hinge line of the “eyes”, and the directions of these folds range from N-S to N30°E with gentle plunges to the north or south.The sheath folds are believed to have been formed during the second phase of deformation in this region. The traces of the earlier folding can generally be found at the hinges or limbs of these sheath folds.The explanation presented here is that the sheath fold might be generated episodically during the F₂ deformational phase throughout the entire history of progressive shearing as a result of episodic instability of the flow with successive refolding of metamorphic fabric, during Plio-Pleistocene deformation of Taiwan.     

Die tektonische Baugeschichte von Süd-Devonshire als Beispiel einer mehrphasigen variszischen Prägung

Five movement-phases during the Variscan tectogenesis shaped the structural cast of the Devonian rocks in South Devon. The first movement-phase, i. e. the main tectonic phase, resulted in the mappable fold system trending E-W or ENE-WSW in the west accompanied by related minor folds, and the first cleavage (s ₁) parallel to the axial planes. The cleavage planes dip to the south as far as the line Slapton-Bigbury, while farther to the south they dip to the north and finally to the south again, thus forming a huge fanning. In the second movement-phase a second cleavage (s ₂) with E-W strike associated with minor folds, was superimposed on the older structures south of the line Berry Head-Cornworthy. The trend of these folds is, more or less E-W. Furthermore the second cleavage shows a fanning which does not coincide with that of the first cleavage. South-vergent minor folds of bedding and cleavage planes, associated with small-scale southward thrusts represent structures of a third movement-phase. The fourth movement-phase was the kinking of mainly the first cleavage in the southern part of South Devon. There are two groups: one shows flat-lying kink-bands affecting mainlys ₁; seldoms ₂, and having a southward thrusting sense of movement while the other consists of nearly vertical kink-bands trending N-S which displace to the south on their eastern sides. Subsequently with the commencement of the New Red deposition, repeated tectonic stretching took place, resulting in N-S and WSW--ENE trending faults. The succession of the different tectonic events led to occasionally very complicated superimpositions. The rocks in the middle and southern part of South Devon suffered a regional metamorphosis that increases slowly towards the south. Finally, the tectonic structures of South Devon are compared with those in South Cornwall where the same movements-phases caused a completely different structural style.     

Spatial variability of the Purbeck–Wight Fault Zone—a long-lived tectonic element in the southern UK

New seamless onshore to offshore bedrock (1:10 k scale) mapping for the Lyme Bay area is used to resolve the westward termination of the Purbeck–Wight Fault Zone (PWFZ) structure, comprising one of the most prominent, long-lived (Variscan–Cimmerian–Alpine) structural lineaments in the southern UK. The study area lies south of the Variscan Frontal Thrust and overlays the basement Variscide Rhenohercynian Zone, in a region of dominant E-W tectonic fabric and a secondary conjugate NW-SE/NE-SW fabric. The PWFZ comprises one of the E-W major structures, with a typical history including Permian to early Cretaceous growth movement (relating to basement Variscan Thrust reactivation) followed by significant Alpine (Helvetic) inversion. Previous interpretations of the PWFZ have been limited by the low resolution (1:250 k scale) of the available offshore BGS mapping, and our study fills this gap. We describe a significant change in structural style of the fault zone from east to west. In the Weymouth Bay area, previous studies demonstrate the development of focussed strain associated with the PWFZ, accompanied by distributed strain, N-S fault development, and potential basement uplift in its hangingwall. In the Lyme Bay area to the west, faulting is dominantly E-W, with N-S faulting absent. Comparison of the newly mapped faulting networks to gravity data suggests a spatial relationship between this faulting variation and basement variability and uplift.     

鄂尔多斯盆地东南部中生界地层节理发育特征与古应力场

鄂尔多斯盆地东南部中生代地层中发育有六组节理(E-W、N-S、ENE-WSW、NNW-SSE、WNW-ESE、NNE-SSW),并且构成三期的正交节理系统(E-W与N-S、ENE-WSW与NNW-SSE、WNW-ESE与NNE-SSW).三期正交节理系统形成的先后期次为:E-W向和N-S向两组节理最早形成,WNW-ESE向和NNE-SSW向两组节理为第二期形成,ENE-WSW向和NNW-SSE向两组节理则最晚形成.E-W向、N-S向和ENE-WSW向三组节理的节理间距指数(FSI)分析结果表明,节理间距的发育程度除了受岩层厚度控制外,还受区域应力场的控制.E-W向、N-S向和ENE-WSW向三组节理的节理间距率(FSR)值分布范围指示不同组节理在区域上发育程度具有差异性.此外,E-W向的优势节理组的FSR值有超过间距与层厚比值的临界值,而非优势组的SN向节理的FSR值则全部小于临界值,表明E-W向和N-S向两组节理组成最早一期的正交节理系统.盆内中生代地层中的三期正交节理系统,所对应的古应力场分别为:(1)晚侏罗世盆地处在近E-W向的挤压环境下,形成了第一期正交节理系统,为E-W向和N-S向两组节理;应力来源于古太平洋板块向欧亚板块俯冲所产生的NW-SE向的挤压分量.(2)晚白垩世时,来自于古太平洋板块俯冲产生的NW-SE向挤压应力形成了第二期正交节理系统的WNW-ESE向和NNE-SSW向两组节理.(3)晚白垩世末至新生代,印度板块向欧亚板块下的俯冲产生NE-SW向的远程挤压应力,形成第三期正交节理系统的ENE-WSW向和NNW-SSE向两组节理.     

Spectral observations of ɛ aurigae during the 2009–2011 eclipse

Results of spectral observations of the unique eclipsing binary ? Aur obtained during its recent eclipse are presented. Profile variations of many spectral lines at different eclipse phases can be traced. These variations are partly due to absorption of the stellar radiation in a rotating disk of gas and dust around the second component and partly due to geometric screening of the stellar photosphere and circumstellar region by the disk. A comparison of these results with analogous results obtained by Lambert and Sawyer during the previous (1982–1984) eclipse of ? Aur indicates good agreement, suggesting stability of the gas-dust disk surrounding the invisible component in the binary. The masses of the binary components are estimated using new observational data.     

Intense night-time equatorial radio scintillations by sporadicE layers

Almost saturated scintillations of radio beacons from geostationary satellites received at an equatorial station during night-time have been shown to occur even during complete absence of spreadF on the vertical incidence ionograms at the same location. These scintillation events were observed when the ionograms showed blanketing type of sporadicE layers simultaneously at different heights. It is suggested that strong equatorial radio wave scintillations during night-time are caused by multiple scattering between different levels of large plasma density gradients in theF or sometimes in theE regions of the ionosphere.     

Observations on the processes of sedimentary basin formation at the margins of Southern Africa

Three variants of Atlantic-type continental margin border Southern Africa. On the west is a rifted margin with a rift phase no more than 50 m.y. in length (180–130 m.y. ago). Sedimentary basin formation was by upbuilding of a sediment terrace during the rift phase and the 30 m.y. following, with outbuilding of the terrace dominant during the Cainozoic. Little downwarping of the oceanic crust occurred but the continent—ocean transition zone appears to be wide.To the south of South Africa is an extensive sheared margin. Basin formation began here in mid-Triassic times with intermontane deposition. Local increase in lower crustal density appears to have accompanied subsidence. Truncation of the basins occurred 130–2100 m.y. ago and in places detrital influx was trapped behind a marginal fracture ridge. No continental rise sedimentary apron and characteristic deep structure were formed in these places. A ‘welding’ of the continental edge appears to have taken place.East of 30° E a complex continental margin with a protracted rift phase exists. From Triassic to Cretaceous times sedimentary basin formation was controlled by an E-W tensional stress regime resulting in N-S horsts and grabens. This was accompanied by vol-canicity and crustal thinning. Other stress systems may have prevailed during continental break-up in the Cretaceous while today the region is seismically active and the tensional stress assumed to be E-W. Following break-up sedimentary basins in Natal Valley and Mozambique Channel encroached southwards.     

太白山古冰川地貌与地质构造

太白山分布有更新世冰川地形,其冰川槽谷在平面上呈“十”字型排列;横剖面EW向的呈宽谷形,NS向是呈U型:纵剖面EW向比较平坦,SN向呈阶梯状,其中有许多断裂陡坎。冰斗均位于断裂交汇点,面积不大而深度却相当大。这些地形的形态特征可以用构造加以解释,断裂破碎带是最有利于冰川刨蚀的地段。     

Successive Extensional Tectonic Regimes during the Mesozoic as Evidenced by Neptunian Dikes in the Pontide Magmatic Arc,Northeast Turkey

The eastern Pontide magmatic arc extends ～600 km in an E-W direction along the Black Sea coast and was disrupted by a series of fault systems trending NE-SW, NW-SE, E-W, and N-S. These fault systems are responsible for the formation of diachronous extensional basins, rift or pull-apart, in the northern, southern, and axial zones of the eastern Pontides during the Mesozoic. Successive extensional or transtensional tectonic regimes caused the abortive Liassic rift basins and the Albian and Campanian pull-apart basins with deep-spreading troughs in the southern and axial zones. Liassic, Albian, and Campanian neptunian dikes, which indicate extensional tectonic regimes, crop out within the Paleozoic granites near Kale, Gumushane, and the Malm–Lower Cretaceous platform carbonates in Amasya and Gumushane. These neptunian dikes correspond to extensional cracks that are filled and overlain by the fossiliferous red pelagic limestones. Multidirectional Liassic neptunian dikes are consistent with the general trend of the paleofaults (NE-SW, NW-SE, and E-W), and active dextral North Anatolian fault (NAF) and sinistral Northeast Anatolian fault (NEAF) systems. The Albian neptunian dikes in Amasya formed in the synthetic oblique left-lateral normal faults of the main fault zone that runs parallel to the active North Anatolian fault zone (NAFZ).

Kinematic interpretation of the Liassic and Albian neptunian dikes suggests N-S extensional stress or northward movement of the Pontides along the conjugate fracture zones parallel to the NAFZ and NEAFZ. This northward movement of the Pontides in Liassic and Albian times requires left-lateral and right-lateral slips along the conjugate NAFZ and Northeast Anatolian fault zones (NEAFZ), respectively, in contrast to the recent active tectonics that have been accommodated by N-S compressional stress. On the other hand, mutual relationships between the neptunian dikes and the associated main fault zone of Campanian age extending in an E-W direction in the Kale area, Gumushane suggest the existence of a main left-lateral transtensional wrench zone. This system might be accommodated by the counterclockwise convergence of the Turkish plate with the Afro-Arabian plate relative to the Eurasian plate, and the southward oblique subduction of Paleotethys beneath the eastern Pontide magmatic arc during the Mesozoic.     

On the equatorial spreadF

The post-sunset maximum in virtual height of theF region near the magnetic equator is associated with the general rise of the wholeF region from the base to the height of peak ionisation with little change in the semi-thickness of the layer. This rise ofF region is accentuated on days with large evening peak in the vertical drift velocity or the horizontal electric field in theF region. The range type of equatorial spreadF first occurs only if theF region drift velocity remains significantly upwards after sunset but the maximum intensity of spreadF occurs when the drift velocities are low or even downwards. The range spread first appears at or below the base of theF layer and later spreads into theF layer due to downward movement of the layer and/or upward movement of the irregularity. SpreadF seen on VHF backscatter records corresponds to the range type of spreadF seen on normal ionograms. The frequency type of spreadF does not produce VHF echoes. A strong peak in the electric field seems to be a necessary condition for the generation of equatorial spreadF.     

Activity of the Seyfert galaxy NGC 4151 in the near-IR in 1994–2011

We present the results of our infrared J H K L photometry of the Seyfert galaxy NGC 4151 during its active period in 1995–2011. The variable IR source was still in its active state in 2011, though its observed luminosity had almost halved compared to the maximum of 1995–1996. If the “cool” component of the galaxy’s variable source is a dust shell heated with the central “hot” source, its optical depth at 1.25 µm varied from 0.3 to almost 1.0, its temperature from 700 to 950 K, its size from 20 to 40 pc, and its mass from 2 to 40M _⊙ during our observations. A component with a period of 317 ± 5 days can be revealed in the flux variations observed in 1994–2011.     

Mapping geology in Djelfa District (Saharan Atlas,Algeria), using Landsat 7 ETM+ data: an alternative method to discern lithology and structural elements

Djelfa area in the central Saharan Atlas is characterized by its high lithological diversity with different facies from the Triassic to the Tertiary. The lack of published geological maps of the region (Djelfa) prompted us to test specific processing of satellite images (ratio bands, principal component analysis) in order to establish a lithological discrimination of the region. Several treatments allowed us to map the lineaments highlighting the various tectonic structures of the region. The combination of field and remote sensing data pointed out the double influence of the E-W Eocene and N-S Miocene phases in the structuration of these regions. As a large part of the Djelfa area is inaccessible, the obtained results undeniably contribute to a better understanding of the local geology.     

On the origin of the low energy cosmic rays from stellar sources

The model of stellar origin of the anomalous component in the low energy cosmic rays for He to Fe ions observed in space vehicles is studied in the light of recent results. The model of heliospheric origin by Fisket al which has several attractive features cannot explain the long-term variations of intensity observed during 1974 to 1978 as pointed out by Nagashima and Morishita. The stellar origin model of Durgaprasad and Biswas, on the other hand, can easily account for the sudden appearance of the anomalous component in 1972 and its large decrease in intensity in 1978 on the basis of polarity reversal of the solar magnetic field as discussed by Nagashima and Morishita (1980). In this work, we show that in the stellar model energetic ions of He, C, N, O, etc. could originate in O-type stars which manifest very strong stellar wind with mass loss rate of 3·10^?6 M_⊙ per year. These have terminal velocities of about 1200 to 4000 km/sec and are typically a few times their escape velocity. These velocities correspond to ion energies of 10 to 100 keV/amu. These ions are in partly ionised state and are accelerated in the interstellar shock fronts to about 1 to 50 MeV/amu and thus account for the observed anomalous component of low energy cosmic rays.