Subduction-driven shortening and differential exhumation in a Cadomian accretionary wedge: The Teplá–Barrandian unit,Bohemian Massif

The Teplá–Barrandian unit (TBU) of Central Europe's Bohemian Massif exposes perhaps the best preserved fragment of an accretionary wedge in the Avalonian–Cadomian belt, which developed along the northern active margin of Gondwana during Late Neoproterozoic. In the central TBU, three NE–SW-trending lithotectonic units (Domains 1–3) separated by antithetic brittle faults differ in lithology, style and intensity of deformation, magnetic fabric (AMS), and degree of Cadomian regional metamorphism. The flysch-like Domain 1 to the NW is the most outboard (trenchward) unit which has never been significantly buried and experienced only weak deformation and folding. The central, mélange-like Domain 2 is characterized by heterogenous intense deformation developed under lower greenschist facies conditions, and was thrust NW over Domain 1 along a SE-dipping fault. To the SE, the most inboard (arcward) Domain 3 is lithologically monotonous (dominated by graywackes and slates), was buried to depths corresponding up to the lower greenschist facies conditions, where it was overprinted by a pervasive SE-dipping cleavage and then was exhumed along a major NW-dipping normal fault.We interpret these domains to represent allochtonous tectonic slices that were differentially buried and then exhumed from various depths within the accretionary wedge during Cadomian subduction. The NW-directed thrusting of Domain 2 over Domain 1 may have been caused by accretion at the wedge front, whereas the SE-dipping cleavage and SE-side-up exhumation of Domain 3 may record inclined pervasive shortening during tectonic underplating and subsequent horizontal extension of the rear of the wedge. The boundary faults were later reactivated during Cambro–Ordovician extension and Variscan compression.Compared to related terranes of the Cadomian belt, the TBU lacks exposed continental basement, evidence for regional strike-slip shearing, and extensive backarc magmatism and LP–HT metamorphism, which could be interpreted to reflect flat-slab Cadomian subduction. This, in turn, suggests that Cadomian accretionary wedges developed in a manner identical to those of modern settings, elevating the TBU to a key position for understanding the style, kinematics, and timing of accretionary processes along the Avalonian–Cadomian belt.     

Magmatic erosion of the solidification front during reintrusion: the eastern margin of the Tuolumne batholith, Sierra Nevada, California

The Tuolumne batholith, Sierra Nevada, California, consists of several nested granitoid units and is an example of upper-crustal normally zoned intrusions. The two outermost units of the batholith are separated by a wide gradational contact in what is interpreted to represent a large magma chamber. In the Potter Point area near the eastern margin of the batholith, the gradational contact is cross-cut by a network of interconnected mafic–felsic sheets, which grade into zones of magmatic erosion by stoping where the host granodiorite between the sheets was entirely removed and replaced by younger enclave-rich quartz diorite. We interpret these features to record disruption of a steep solidification front, which migrated inwards from the eastern batholith margin and separated the mushy to solidified margin from the remaining active magma chamber. When intersecting the gradational contact, the solidification front started to break up via a network of tectonically driven fractures accompanied by simultaneous injection of localized magma pulses. The solidification front break-up is interpreted here as an initial stage of a “recycling” process, whereby older magma mush is disrupted and incorporated into younger magma batches, a process we propose to have been widespread along internal contacts in the Tuolumne magma chamber.     

Propagation of Interplanetary Coronal Mass Ejections: The Drag-Based Model

We present the “Drag-Based Model” (DBM) of heliospheric propagation of interplanetary coronal mass ejections (ICMEs). The DBM is based on the hypothesis that the driving Lorentz force, which launches a CME, ceases in the upper corona and that beyond a certain distance the dynamics becomes governed solely by the interaction of the ICME and the ambient solar wind. In particular, we consider the option where the drag acceleration has a quadratic dependence on the ICME relative speed, which is expected in a collisionless environment, where the drag is caused primarily by emission of magnetohydrodynamic (MHD) waves. In this paper we present the simplest version of DBM, where the equation of motion can be solved analytically, providing explicit solutions for the Sun–Earth ICME transit time and impact speed. This offers easy handling and straightforward application to real-time space-weather forecasting. Beside presenting the model itself, we perform an analysis of DBM performances, applying a statistical and case-study approach, which provides insight into the advantages and drawbacks of DBM. Finally, we present a public, DBM-based, online forecast tool.     

Comparison and Combination of Coastal and Off-Shore Tide Gauge Measurements from Eivissa Island,Western Mediterranean

Two sea-level records, spanning eight months of simultaneous data in 2002, have been derived from pressure tide gauge measurements at Sant Antoni harbor (Eivissa Island, Western Mediterranean) and off Es Vedrà island, 15 km SW from Sant Antoni. The two time series are compared and used to characterize the sea-level variability in the Balearic Sea. The main forcings for the observed variations, astronomic tides, and meteorologic forcing by the inverse barometer effect are quantified. In a further step, an amplitude transfer function is determined, reflecting the frequency dependent amplification or damping of the nontidal sea-level residuals between both locations due to their local topography. The interpretation of the obtained transfer function indicates sea-level modulating topographic specifics not only for the coastal record at Sant Antoni, but also at the Es Vedrà site. In general, the application of such a transfer function allows the prediction of off-shore sea-level variations from coastal tide gauge measurements. In the present study, ellipsoidal sea-surface heights for Es Vedrà are inferred from Sant Antoni tide gauge data with an accuracy of about 1.5 cm by applying the determined transfer function and a geoid model.     

A spatially resolved high spectral resolution study of Neptune’s stratosphere

Using TEXES, the Texas Echelon cross Echelle Spectrograph, mounted on the Gemini North 8-m telescope we have mapped the spatial variation of H₂, CH₄, C₂H₂ and C₂H₆ thermal-infrared emission of Neptune. These high-spectral-resolution, spatially resolved, thermal-infrared observations of Neptune offer a unique glimpse into the state of Neptune’s stratosphere in October 2007, L_S = 275.4° just past Neptune’s southern summer solstice (L_S = 270°). We use observations of the S(1) pure rotational line of molecular hydrogen and a portion of the ν₄ band of methane to retrieve detailed information on Neptune’s stratospheric vertical and meridional thermal structure. We find global-average temperatures of 163.8 ± 0.8, 155.0 ± 0.9, and 123.8 ± 0.8 K at the 7.0 × 10⁻³-, 0.12-, and 2.1-mbar levels with no meridional variations within the errors. We then use the inferred temperatures to model the emission of C₂H₂ and C₂H₆ in order to derive stratospheric volume mixing ratios (hence forth, VMR) as a function of pressure and latitude. There is a subtle meridional variation of the C₂H₂ VMR at the 0.5-mbar level with the peak abundance found at −28° latitude, falling off to the north and south. However, the observations are consistent within error to a meridionally constant C₂H₂ VMR of at 0.5 mbar. We find that the VMR of C₂H₆ at 1-mbar peaks at the equator and falls by a factor of 1.6 at −70° latitude. However, a meridionally constant VMR of at the 1-mbar level for C₂H₆ is also statistically consistent with the retrievals. Temperature predictions from a radiative-seasonal climate model of Neptune that assumes the hydrocarbon abundances inferred in this paper are lower than the measured temperatures by 40 K at 7 × 10⁻³ mbar, 30 K at 0.12 mbar and 25 K at 2.1 mbar. The radiative-seasonal model also predicts meridional temperature variations on the order of 10 K from equator to pole, which are not observed. Assuming higher stratospheric CH₄ abundance at the equator relative to the south pole would bring the meridional trends of the inferred temperatures and radiative-seasonal model into closer agreement.We have also retrieved observations of C₂H₄ emission from Neptune’s stratosphere using TEXES on the NASA Infrared Telescope Facility (IRTF) in June 2003, L_S = 266°. Using the observations from the middle of the planet and an average of the middle three latitude temperature profiles from the 2007 observations (9.5° of L_S later, the seasonal equivalent of 9.5 Earth days within Earth’s seasonal cycle), we infer a C₂H₄ VMR of at 1.5 × 10⁻³ mbar, a value that is 3.25 times that predicted by global-average photochemical models.     

Bottom-moored acoustic array to monitor density and vertical movement of deep-sea benthopelagic animals

A bottom-moored vehicle, employing a 36-kHz acoustic array, is described. Its purpose is to census benthopelagic populations at abyssal depths and detect vertical movement of these animals. It is argued that an acoustic census offers particular advantages over traditional sampling methods, and when used in conjunction with these methods, offers powerful insight into abyssal community dynamics.     

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Relative sea level changes during the Holocene in the Sisimiut area,south‐western Greenland

Holocene relative sea level (RSL) changes have been investigated by analysing and dating isolation sequences from five lakes near Sisimiut in south‐western Greenland. The transitions between marine and lacustrine sediments were determined from elemental analyses and analyses of macroscopic plant and animal remains. Radiocarbon dating was used to provide minimum ages for the transitions and to construct a RSL curve. Dating of a shell of the marine bivalve Macoma balthica indicates that deglaciation of the lowlands occurred in the early Holocene, at around 10 900 cal a BP. The RSL curve shows initial rapid regression from the marine limit at around 140 m, implying strong glacio‐isostatic rebound. We suggest that the margin of the Greenland Ice Sheet was located at the shelf break during the Last Glacial Maximum. Frequent remains of the ostracode Sarcypridopsis aculeata, which is a thermophilous brackish water species that is unknown from the extant fauna of Greenland, in one of the basins around 8500 cal a BP may mark the beginning of the Holocene thermal maximum in the region. Copyright © 2011 John Wiley & Sons, Ltd.     

A simultaneous X-ray and optical study of TT Arietis

Prelimary results of an extended program of coordinated X-ray and optical observations of TT Ari are presented. The object was observed on August 21/22 1985 both in X-rays (EXOSAT) and optical range, about 100 days after the return to the active state. The first detailed simultaneous study of TT Ari in active state indicates the presence of strongly absorbing structure in the system.Paper presented at the IAU Colloquium No. 93 on Cataclysmic Variables. Recent Multi-Frequency Observations and Theoretical Developments, held at Dr. Remeis-Sternwarte Bamberg, F.R.G., 16–19 June, 1986.