A double-head photon-counting photometer for fast timing observations

The structure of the electronics of the two-head, high-speed photometer operating on the 152-cm G.D. Cassini telescope of Bologna University has been fully redesigned for high-time-resolution observations of fast variable sources, in particular, of the optical counterparts of X-ray binary systems. The fast photometer now permits sampling times from 0.1 ms to 100 s. The handling of the system clock and I/O configuration have been modified to provide rigorous synchronization of the sampling time with an external high-stability clock and the continuous acquisition of an uninterrupted data stream. The continuous data-acquisition process, which is driven by an external clock, is limited only by the capacity of the hard disk and is supported by a double-buffer SRAM memory designed to overcome any discontinuity in the asynchronous communication with the computer. Real-time monitoring of the data enables continuous evaluation of the weather conditions, and the directly displayed light curve can be used to determine the optimal management of the observations.     

Composition, sources, and mechanism of continental crust growth in the Lake zone of the Central Asian Caledonides: I. Geological and geochronological data

Data on the composition, inner structure, and age of volcanic and siliceous-terrigenous complexes and granitoids occurring in association with them in the Caledonian Lake zone in Central Asia are discussed in the context of major relations and trends in the growth of the Caledonian continental crust in the Central Asian Foldbelt (CAFB). The folded structures of the Lake zone host basalt, basalt-andesite, and andesite complexes of volcanic rocks that were formed in distinct geodynamic environments. The volcanic rocks of the basalt complex are noted for high concentrations of TiO₂ and alkalis, occur in association with fine-grained siliceous siltstone and siliceous-carbonate rocks, are thus close to oceanic-island complexes, and were likely formed in relation to a mantle hotspot activity far away from erosion regions supplying terrigenous material. The rocks of the basalt-andesite and andesite complexes have lower TiO₂ concentrations and moderate concentrations of alkalis and contain rock-forming amphibole. These rocks are accompanied by rudaceous terrigenous sediments, which suggests their origin in island-arc environments, including arcs with a significantly dissected topography. These complexes are accompanied by siliceous-terrigenous sedimentary sequences whose inner structure is close to those of sediments in accretionary wedges. The folded Caledonides of the Lake zone passed through the following evolutionary phases. The island arcs started to develop at 570 Ma, their evolution was associated with the emplacement of layered gabbroids and tonalitetrondhjemite massifs, and continued until the onset of accretion at 515–480 Ma. The accretion was accompanied by the emplacement of large massifs of the tonalite-granodiorite-plagiogranite series. The postaccretionary evolutionary phase at 470–440 Ma of the Caledonides was marked by intrusive subalkaline and alkaline magmatism. The Caledonides are characterized by within-plate magmatic activity throughout their whole evolutionary history, a fact explained by the accretion of Vendian-Cambrian oceanic structures (island arcs, oceanic islands, and back-arc basins) above a mantle hotspot. Indicators of within-plate magmatic activity are subalkaline high-Ti basalts, alkaline-ultrabasic complexes with carbonatites and massifs of subalkaline and alkaline gabbroids, nepheline syenites, alkaline granites, subalkaline granites, and granosyenites. The mantle hotspot likely continued to affect the character of the lithospheric magmatism even after the Caledonian folded terrane was formed.     

http://www.sciencedirect.com/science/article/pii/S1674987111000594

A new model is suggested for the history of the Baikal Rift,in deviation from the classic two-stage evolution scenario,based on a synthesis of the available data from the Baikal Basin and revised correlation between tectonic-lithological-stratigraphic complexes(TLSC) in sedimentary sections around Lake Baikal and seismic stratigraphic sequences(SSS) in the lake sediments.Unlike the previous models,the revised model places the onset of rifting during Late Cretaceous and comprises three major stages which are subdivided into several substages.The stages and the substages are separated by events of tectonic activity and stress reversal when additional compression produced folds and shear structures.The events that mark the stage boundaries show up as gaps,unconformities,and deformation features in the deposition patterns. The earliest Late Cretaceous-Oligocene stage began long before the India-Eurasia collision in a setting of diffuse extension that acted over a large territory of Asia.The NW-SE far-field pure extension produced an NE-striking half-graben oriented along an old zone of weakness at the edge of the Siberian craton.That was already the onset of rift evolution recorded in weathered lacustrine deposits on the Baikal shore and in a wedge-shaped acoustically transparent seismic unit in the lake sediments.The second stage spanning Late Oligocene-Early Pliocene time began with a stress change when the effect from the Eocene India-Eurasia collision had reached the region and became a major control of its geodynamics.The EW and NE transpression and shear from the collisional front transformed the Late Cretaceous half-graben into a U-shaped one which accumulated a deformed layered sequence of sediments.Rifting at the latest stage was driven by extension from a local source associated with hot mantle material rising to the base of the rifted crust.The asthenospheric upwarp first induced the growth of the Baikal dome and the related change from finer to coarser molasse deposition.With time,the upwarp became a more powerful stress source than the collision,and the stress vector returned to the previous NW-SE extension that changed the rift geometry back to a half-graben. The layered Late Pliocene-Quaternary subaerial tectonic-lithological-stratigraphic and the Quaternary submarine seismic stratigraphic units filling the latest half-graben remained almost undeformed.The rifting mechanisms were thus passive during two earlier stages and active during the third stage. The three-stage model of the rift history does not rule out the previous division into two major stages but rather extends its limits back into time as far as the Maastrichtian.Our model is consistent with geological, stratigraphic,structural,and geophysical data and provides further insights into the understanding of rifting in the Baikal region in particular and continental rifting in general.     

Petrogenesis of lamprophyre and associated diabase dykes in Wadi Mandar-Um Adawi area,South Sinai,Egypt

The mafic dykes in Wadi Mandar-Wadi Um Adawi area are as follows: (1) calc-alkaline lamprophyre (i.e., kersantite and spessartite), (2) diabase, and (3) alkaline lamprophyre (i.e., camptonite). The field relations reveal that the emplacement of calc-alkaline lamprophyres preceded the diabase dykes, while alkaline lamprophyres emplaced later than the diabase dykes. Calc-alkaline are basaltic andesite, basaltic trachyandesite to basalt, while the diabase dykes and alkaline lamprophyres are basaltic in composition. These dykes are characterized by metaluminous character. Calc-alkaline lamprophyres and diabase dykes show transitional affinity from calc-alkaline to alkaline, while the alkaline lamprophyres exhibit more strong alkaline character. The mafic dykes were crystallized under temperature 1100–1150 °C and pressure 3–5 kbars in a high oxygen fugacity conditions. Fe-Ti oxides in the dykes are represented by ilmenite and Ti-magnetite. The chemistry of the sulfides hosted in those mafic dykes suggests a magmatic-hydrothermal origin for these minerals. The geochemical behavior of high field strength elements and large ion lithophile elements in these dykes excludes the derivation of diabase or alkaline lamprophyre either by partial melting or fractional crystallization from calc-alkaline lamprophyre. The parental magmatic sources of the studied dykes were generated from crustal material with addition of mantle-derived melt during the post-collisional stage. The mafic dykes in Wadi Mandar-Wadi Um Adawi area were generated from different magmatic sources by partial melting and subsequent fractional crystallization. In addition, the crustal contamination/assimilation process has a prominent role in the magmatic evolution of diabase and alkaline lamprophyre dykes.     

Behavior of Hydrocarbons in the Mouth Parts of Arctic Rivers

The paper reviews data (acquired in 2007–2016) on aliphatic and polycyclic aromatic hydrocarbons in comparison with data on concentrations of lipids, C_org, and chlorophyll a in the water and bottom sediments the river–sea geochemical barrier (for the Northern Dvina, Ob, Yenisei, and Lena rivers). It was established that the concentrations of anthropogenic hydrocarbons decrease and these compounds precipitate like other organic compounds and particulate matter, where riverine and marine waters mix. Relatively pure water flows in the pelagic zones of seas. In spite of low temperatures in the Arctic, anthropogenic hydrocarbons transform so rapidly that natural compounds dominate in the water and bottom sediments: autochthonous in the seawater and allochthonous in the bottom sediments.     

A Kinematic Model of the Formation of the Sim Trough of the Uralian Foredeep

The structural features and mechanism of the formation of the Sim trough within the Uralian Foredeep, as well as the development of the entire Karatau–Suleiman block, are considered. This wedge-shaped block was subject to lateral extrusion to the north along conjugated strike-slip fault zones under a general latitudinal compression. This factor determined the local meridional compression and latitudinal extension of the block. In the central part of the block, the latitudinal extension was compensated by gradual subsidence, which resulted in the formation of the Sim trough.     

Observations of Tilt Deformations in Moscow during the November 12, 2017, Earthquake at the Iran–Iraq Boundary

Doklady Earth Sciences - A residual tilt after a teleseismic earthquake is described in this work. The results of static and dynamic modeling of this event fit the measured values. The conditions...