Detachments and normal faulting in the Marche fold-and-thrust belt (central Apennines, Italy): inferences on fluid migration paths

In the outermost domains of the central Apennines fold-and-thrust belt, the structural architecture of the late Miocene–early Pliocene contractional edifice was controlled by competence contrasts in the Calcareous–Marly sequences of Mesozoic–Tertiary age, and by a different state of lithification of the rock units at the onset of deformation. Field data on relative chronology of outcrop-scale structures (cleavage, veins, faults, folds) are presented for the three largest thrust-ramp anticlines of the Marche fold-and-thrust belt: Monte Gorzano, Acquasanta and Montagna dei Fiori-Montagnone. The data show that the timing and geometry of deformation structures differ for: (1) the lower Calcareous interval of late Triassic–early Cretaceous age (LCI) bounded on top by the intermediate detachment (ID) of the Fucoidi Marls; (2) the upper Calcareous–Marly interval (UCMI) of late Cretaceous–Oligocene age; (3) the uppermost detachment zone (UDZ) of lower–middle Miocene age; (4) the topmost Messinian Flysch sequence (FS). In the UDZ early episodes of deformation are manifested by compaction of a poorly lithified sequence followed by pervasive development of layer-parallel pressure-solution cleavage. Reverse faults ramp obliquely across the stratigraphic sequence, and are coated by multiple overgrowths of calcite fibers. These structures are deformed by large, eastward-verging asymmetric folds with N–S axial trends, and are cut by late generations of reverse faults. Normal faults started to develop in the fold backlimbs during the final stages of shortening, in middle–late Pliocene times. These early normal faults were reactivated during episodes of late Pliocene–Pleistocene extensional downfaulting, and are now superposed on the compressional edifice. The UDZ is interpreted to have temporarily sealed the upward escape of fluids during the initial episodes of shortening. Pervasive interlayer flow in the poorly lithified sequence was responsible for development of broken beds and scaly fabrics, similar to those observed in accretionary prisms. Only in the latest stages of deformation did propagation of discrete faults provide an interconnected pathway for fluid migration, until the final offset of the UDZ. The structural relationships suggest that fluids trapped within the fold cores and sealed by the UDZ were finally driven upwards due to progressive disruption of the thrust belt by late normal faults of late Pliocene to Pleistocene and Holocene age. Large-scale fluid migration along structurally-controlled pathways was enhanced by the strong components of uplift consequent to the final stages of deformation in the Marche fold-and-thrust belt, and was eventually associated with episodes of normal seismic faulting.     

First evidence of an interglacial lake of Eemian age in northeast Italy

This paper assesses the age of the Tagliamento Morainic Amphitheatre (northeast Italy), one of the largest morainic bodies in the piedmont area of northern Italy, using new stratigraphical and thermoluminescence (TL) data obtained from a site located on the inner flank of the amphitheatre. Two samples from a 12-m-thick stratum of fluviolacustrine, non-varved, fine sand provided TL ages of approximately 110 ± 16 ka BP. This sandy layer lies below a 6-m-thick, massive (non-laminated), clayey stratum. It is hypothesised that a large but short-lived lake formed during the interglacial phase separating the penultimate and last glaciations. Assigning a ‘Riss’ age to the southeastern part of the amphitheatre therefore regains credence. © 1998 John Wiley & Sons, Ltd.     

Triggering processes of deep-seated gravitational slope deformation (DSGSD) in an un-glaciated area of the Cavargna Valley (Central Southern Alps) during the Middle Holocene

Triggering mechanisms and causative processes of deep-seated gravitational slope deformations (DSGSD) in Alpine and high mountain areas include, among others, post-glacial de-buttressing, earthquake-induced ground shaking, or co-seismic surface faulting. Distinguishing between climatic or tectonically driven factors is challenging since faults and fracture systems can play both an active and/or passive role in the process initiation. We applied an integrated approach, including morpho-structural analysis, geologic field survey, a paleoseismological approach applied to trenching, radiocarbon dating and detailed sedimentological analysis, to a DSGSD located in the Cavargna Valley (N Italy), an area that was never occupied by extensive ice tongues in the Upper Pleistocene and Holocene. We were able to document at least two phases of movement from the Middle Holocene onwards and related triggering factors. Thanks to the comparison with dated lacustrine turbidites in the Alpine Lakes, we argue a seismic triggering for the landslide onset, with a possible source located in southern Switzerland, close to the Insubric Line. The later evolution of the landslide was instead driven by climatic predisposing conditions (humid and cold), instead, corresponding to a phase of enhanced slope instability.

     

Physical constraints on impact melt properties from Lunar Reconnaissance Orbiter Camera images

Impact melt flows exterior to Copernican-age craters are observed in high spatial resolution (0.5 m/pixel) images acquired by the Lunar Reconnaissance Orbiter Camera (LROC) Narrow Angle Camera (NAC). Impact melt is mapped in detail around 15 craters ranging in diameter from 2.4 to 32.5 km. This survey supports previous observations suggesting melt flows often occur at craters whose shape is influenced by topographic variation at the pre-impact site. Impact melt flows are observed around craters as small as 2.4 km in diameter, and preliminary estimates of melt volume suggest melt production at small craters can significantly exceed model predictions. Digital terrain models produced from targeted NAC stereo images are used to examine the three-dimensional properties of flow features and emplacement setting, enabling physical modeling of flow parameters. Qualitative and quantitative observations are consistent with low-viscosity melts heated above their liquidii (superheated) with limited amounts of entrained solids.     

Is the Bardeen–Petterson effect responsible for the warping and precession in NGC 4258?

Strong evidence for the presence of a warped Keplerian accretion disc in NGC 4258 (M 106) has been inferred from the kinematics of water masers detected at subparsec scales. Assuming a power-law accretion disc and using constraints on the disc parameters derived from observational data, we have analysed the relativistic Bardeen–Petterson effect driven by a Kerr black hole as the potential physical mechanism responsible for the disc warping. We found that the Bardeen–Petterson radius is comparable to or smaller than the inner radius of the maser disc (independent of the allowed value for the black hole spin parameter). Numerical simulations for a wide range of physical conditions have shown that the evolution of a misaligned disc due to the Bardeen–Petterson torques usually produces an inner flat disc and a warped transition region with a smooth gradient in the tilt and twist angles. Since this structure is similar to that seen in NGC 4258, we propose that the Bardeen–Petterson effect may be responsible for the disc warping in this galaxy. We estimated the time-scale necessary for the disc inside of the Bardeen–Petterson radius to align with the black hole's equator, as a function of the black hole spin. Our results show that the Bardeen–Petterson effect can align the disc within a few billion years in the case of NGC 4258. Finally, we show that if the observed curvature of the outer anomalous arms in the galactic disc of NGC 4258 is associated with the precession of its radio jet/counterjet, then the Bardeen–Petterson effect can provide the required precession period.     

The High Resolution Imaging Science Experiment (HiRISE) during MRO’s Primary Science Phase (PSP)

The High Resolution Imaging Science Experiment (HiRISE) on the Mars Reconnaissance Orbiter (MRO) acquired 8 terapixels of data in 9137 images of Mars between October 2006 and December 2008, covering ∼0.55% of the surface. Images are typically 5-6 km wide with 3-color coverage over the central 20% of the swath, and their scales usually range from 25 to 60 cm/pixel. Nine hundred and sixty stereo pairs were acquired and more than 50 digital terrain models (DTMs) completed; these data have led to some of the most significant science results. New methods to measure and correct distortions due to pointing jitter facilitate topographic and change-detection studies at sub-meter scales. Recent results address Noachian bedrock stratigraphy, fluvially deposited fans in craters and in or near Valles Marineris, groundwater flow in fractures and porous media, quasi-periodic layering in polar and non-polar deposits, tectonic history of west Candor Chasma, geometry of clay-rich deposits near and within Mawrth Vallis, dynamics of flood lavas in the Cerberus Palus region, evidence for pyroclastic deposits, columnar jointing in lava flows, recent collapse pits, evidence for water in well-preserved impact craters, newly discovered large rayed craters, and glacial and periglacial processes. Of particular interest are ongoing processes such as those driven by the wind, impact cratering, avalanches of dust and/or frost, relatively bright deposits on steep gullied slopes, and the dynamic seasonal processes over polar regions. HiRISE has acquired hundreds of large images of past, present and potential future landing sites and has contributed to scientific and engineering studies of those sites. Warming the focal-plane electronics prior to imaging has mitigated an instrument anomaly that produces bad data under cold operating conditions.     

Evidence for Hesperian impact-induced hydrothermalism on Mars

Several hydrated silicate deposits on Mars are observed within craters and are interpreted as excavated Noachian material. Toro crater (71.8°E, 17.0°N), located on the northern edge of the Syrtis Major Volcanic Plains, shows spectral and morphologic evidence of impact-induced hydrothermal activity. Spectroscopic observations were used to identify extensive hydrated silicate deposits, including prehnite, chlorites, smectites, and opaline material, a suite of phases that frequently results from hydrothermal alteration in terrestrial craters and also expected on Mars from geochemical modeling of hydrothermal environments. When combined with altimetry and high-resolution imaging data, these deposits appear associated predominantly with the central uplift and with portions of the northern part of the crater floor. Detailed geologic mapping of these deposits reveals geomorphic features that are consistent with hydrothermal activity that followed the impact event, including vent-like and conical mound structures, and a complex network of tectonic structures caused by fluid interactions such as fractures and joints. The crater age has been calculated from the cumulative crater size-frequency distributions and is found to be Early Hesperian. The evidence presented here provides support for impact-induced hydrothermal activity in Toro crater, that extends phyllosilicate formation processes beyond the Noachian era.     

The nature of recurrent novae

The observational properties and outburst histories of each member of the small class of recurrent novae are reviewed, with the objective of identifying the outburst mechanisms for these systems. Examples are found of both accretion-powered outbursts (T CrB and RS Oph) and thermonuclear-powered outbursts (T Pyx and U Sco). Outburst properties which might be used in future to distinguish between these mechanisms are identified. Many erstwhile recurrent novae (VY Aqr, RZ Leo, V616 Mon, V1195 Oph, V529 Ori, WZ Sge, and V1017 Sgr) appear to be misclassified examples of other types of cataclysmic variables.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.     

Long-term radial velocity variations in some Be stars

All the radial velocities (RV) available in the literature since the beginning of the century for the Be stars EW Lac, 28 Tau, Tau, KX And, KY And, CX Dra and 88 Her, are assembled. When possible, a periodogram analysis has been performed to search for eventual periodic phenomena.The following conclusions have been drawn: EW Lac could be a spectroscopic binary with a period of about 40 years; 28 Tau shows some indications of regular long-term RV variations on the time scale of decades; a probable recurrent shell activity of Tau could be hypothesized. Some useful indications for KX and KY And are given, whereas it is not possible to draw any conclusion for CX Dra and 88 Her owing to the lack of data.     

Spectrographic observations of omicron andromedae from 1967 to 1976

The results of qualitative analysis and radial velocity (RV) determinations from 1967 to 1976 are given. These analyses show sometimes the presence of a thin variable shell also in the years 1967–1974, before the appearance of the envelope. Intensity variations of the metallic lines seem to indicate that in the same period changes of temperature and/or electron pressure may occur in the photospheric layers. In the period 1975–76, the considerable range ofRV and the variability of the shell features show that the shell is rather active. Some conspicuousRV variations seem to be correlated to brightness changes. TheRV do not confirm the periods suggested by the photometric observations. A periodogram analysis givesRV curves with a poor evidence of periodicity. However, the periodP=1^d.5845 obtained from this analysis, close to that of Schmidt, seems to confirm Schmidt's hypothesis of a contact binary system. The periodogram analysis of theRV during the years 1900–1976 and some physical arguments, suggest a probable photospheric activity or an invisible companion with the observed shell period of 30 yr. The duplicity, suggested by Kí and Harmanec (1975) for all the Be stars, could be yet questioned foro And.Thesis for the degree of Applied Physics.