Source to sink relations between the Tian Shan and Junggar Basin (northwest China) from Late Palaeozoic to Quaternary: evidence from detrital U‐Pb zircon geochronology

The tectonic evolution of the Tian Shan, as for most ranges in continental Asia is dominated by north‐south compression since the Cenozoic India‐Asia collision. However, precollision governing tectonic processes remain enigmatic. An excellent record is provided by thick Palaeozoic – Cenozoic lacustrine to fluvial depositional sequences that are well preserved in the southern margin of the Junggar Basin and exposed along a foreland basin associated to the Late Cenozoic rejuvenation of the Tian Shan ranges. U/Pb (LA‐ICP‐MS) dating of detrital zircons from 14 sandstone samples from a continuous series ranging in age from latest Palaeozoic to Quaternary is used to investigate changes in sediment provenance through time and to correlate them with major tectonic phases in the range. Samples were systematically collected along two nearby sections in the foreland basin. The results show that the detrital zircons are mostly magmatic in origin, with some minor input from metamorphic zircons. The U‐Pb detrital zircon ages range widely from 127 to 2856 Ma and can be divided into four main groups: 127–197 (sub‐peak at 159 Ma), 250–379 (sub‐peak at 318 Ma), 381–538 (sub‐peak at 406 Ma) and 543–2856 Ma (sub‐peak at 912 Ma). These groups indicate that the zircons were largely derived from the Tian Shan area to the south since a Late Carboniferous basin initiation. The provenance and basin‐range pattern evolution of the southern margin of Junggar Basin can be generally divided into four stages: (1) Late Carboniferous – Early Triassic basin evolution in a half‐graben or post‐orogenic extensional context; (2) From Middle Triassic to Upper Jurassic times, the southern Junggar became a passively subsiding basin until (3) being inverted during Lower Cretaceous – Palaeogene; (4) During the Neogene, a piedmont developed along the northern margin of the North Tian Shan block and Junggar Basin became a true foreland basin.     

D/O and D/H ratios in the local interstellar medium from FUSE observations

Since HI, OI, and DI have nearly the same ionization potential, the deuterium-to-oxygen ratio (D/O) is an important tracer of the D/H ratio and of its putative spatial variations. D/O is indeed very sensitive to astration, both because of deuterium destruction and oxygen production. Moreover, D/O measurements are less subject to systematic errors than D/H.A survey of D/O in the interstellar medium is performed by the Deuterium Working Group of the FUSE PI Team. The first results show that D/O is a better D/H proxy than D/N, and that D/O is homogeneous in the local interstellar medium, at least within about 100pc. The stability of D/O appears as a strong argument which supports both D/H and O/H spatial stability in the local interstellar medium.     

Significance of OH,F and Cl content in biotite during metamorphism of the Western Adamello contact aureole

The hydroxyl (O(4)) site composition of biotite can in principle be used to retrieve information about fluid composition during fluid–rock interaction; however, due to low F and Cl content, as well as difficulties involved with analyzing the H₂O content using in situ techniques, measuring these species in biotite has remained an elusive goal. Here we present high-precision secondary ion mass spectrometry (SIMS) OH–F–Cl measurements from biotite within metapelites from the Western Adamello Tonalite (WAT) contact aureole, Northern Italy. Fluorine, chlorine and hydrogen are analyzed on the SIMS sequentially by peak-hopping at the same biotite spot; H₂O, F and Cl content were measured with a precision (1σ) οφ 0.06 ωτ%, 50 ανδ 5 ππµ, ρεσπεχτι?ελψ. The compositions of isolated biotite crystals in andalusite are compared with that of biotite in the matrix, documenting that halogens and H₂O behave refractory in biotite during the time scale of contact metamorphism. The H₂O and halogen contents of biotite are mostly locked in during the prograde to peak formation of biotite, and are not reset during further heating or cooling, unless significant biotite recrystallization occurs. It also appears that both Ti content and X_Mg of the biotite from the Western Adamello contact aureole were not significantly reset during cooling. The concentration of F and Cl does not vary systematically with metamorphic grade, which indicates that these species reflect initial compositions. No significant Rayleigh fractionation behavior was observed for these elements. H₂O variations in the biotite from samples throughout the Western Adamello contact aureole suggest that Al-oxy substitution partially controls the variations in OH content through charge balance of the type R^2+,VI + OH^? = Al^3+,VI + O^2? + H₂, while the Ti-oxy substitution does not seem to influence the O(4) site occupation. The main titanium substitution appears to be the Ti-vacancy (\({\text{2}}{{\text{R}}^{{\text{2}}+}}~=~{\text{T}}{{\text{i}}^{{\text{4}}+}}~+\,{\square ^{{\text{VI}}}}\)) exchange. Variations in H₂O and halogen concentrations in biotite define sub mm-scale areas of localized equilibration, even for biotite recrystallized during dehydration reactions that produced large amounts of fluid (chlorite or muscovite breakdown). Similar systematics were observed for Ti⁴⁺ and Al³⁺. These findings further support the increasing number of observations that kinetics control much of the mineralogical reactions occurring in contact aureoles, and hence care is advised in using equilibrium thermodynamics in this environment.     

A high-precision digital astrogeodetic traverse in an area of steep geoid gradients close to the coast of Perth,Western Australia

We present results from a new vertical deflection (VD) traverse observed in Perth, Western Australia, which is the first of its kind in the Southern Hemisphere. A digital astrogeodetic QDaedalus instrument was deployed to measure VDs with \({\sim }\)0.2\(''\) precision at 39 benchmarks with a \({{\sim }}1~\hbox {km}\) spacing. For the conversion of VDs to quasigeoid height differences, the method of astronomical–topographical levelling was applied, based on topographical information from the Shuttle Radar Topography Mission. The astronomical quasigeoid heights are in 20–30 mm (RMS) agreement with three independent gravimetric quasigeoid models, and the astrogeodetic VDs agree to 0.2–0.3\(''\) (north–south) and 0.6–0.9\(''\) (east–west) RMS. Tilt-like biases of \({\sim }1\,\,\hbox {mm}\) over \({\sim }1\,\,\hbox {km}\) are present for all quasigeoid models within \({\sim }20\,\,\hbox {km}\) of the coastline, suggesting inconsistencies in the coastal zone gravity data. The VD campaign in Perth was designed as a low-cost effort, possibly allowing replication in other Southern Hemisphere countries (e.g., Asia, Africa, South America and Antarctica), where VD data are particularly scarce.     

Finite Difference Implicit Structural Modeling of Geological Structures

We introduce a new method for implicit structural modeling. The main developments in this paper are the new regularization operators we propose by extending inherent properties of the classic one-dimensional discrete second derivative operator to higher dimensions. The proposed regularization operators discretize naturally on the Cartesian grid using finite differences, owing to the highly symmetric nature of the Cartesian grid. Furthermore, the proposed regularization operators do not require any special treatment on boundary nodes, and their generalization to higher dimensions is straightforward. As a result, the proposed method has the advantage of being simple to implement. Numerical examples show that the proposed method is robust and numerically efficient.

     

Shifting zonal patterns of the southern boreal forest in eastern Canada associated with changing fire regime during the Holocene

This research aims at uncovering the stand-scale Holocene fire history of balsam fir forest stands from two bioclimatic zones of the boreal forest and assessing the existence of a sub-continental shift in past fire activity that could have triggered a change in the Holocene zonal pattern. In eastern Canada, the extant closed-crown boreal forest corresponds to two ecological regions separated along 49°N, the northern black spruce zone and the southern balsam fir zone. We sampled balsam fir stands from the southern fir zone (n = 7) and among the northernmost patches of fir forest located far beyond the fir zone boundary, into the spruce zone (n = 6). Macrofossil analysis of charcoal in mineral soils was used to reconstruct both the stand-scale and regional Holocene fire histories. Data were interpreted in the context of published palaeoecological evidence. Stands of the balsam fir zone were submitted to recurrent fire disturbances between c. 9000 and 5000 cal. yr B.P. Local fire histories suggested that four sites within the fir zone escaped fire during the Holocene. Such fire protected sites allowed the continuous maintenance of the balsam fir forest in the southern boreal landscape. Stands of the spruce zone have been affected by recurrent fires from 5000 cal. yr B.P. to present. Local fire histories indicated that no site escaped fire in this zone. Published palaeoecological data suggested that balsam fir migrated to its current northern limit sometime between 7300 and 6200 cal. yr B.P. A change of the fire regime 5000 years ago caused the regional decline of an historical northern balsam fir forest and its replacement by black spruce forest. The consequence was a sub-continental reshuffling of the fir and spruce zones within the closed-crown boreal forest. The macrofossil analysis of charcoal in mineral soils was instrumental to the reconstruction of stand-scale Holocene fire history at sites where no other in situ fire proxies were available.     

Spatio-temporal characteristics of the Agulhas Current retroflection

A 12.7-year series of weekly absolute sea surface height (SSH) data in the region south of Africa is used for a statistical characterization of the location of the Agulhas Current retroflection and its variations at periods up to 2 years. The highest probability of presence of the retroflection point is at ～39.5°S/18–20°E. The longitudinal probability density is negatively skewed. A sharp eastward decrease at 22°E is related to detachments of the Agulhas Current from the continental slope at this longitude. The asymmetry in the central part of the distribution might reflect a westward increase of the zonal velocity of the retroflection point during its east–west pulsations. The western tail of the distribution reveals larger residence times of the retroflection at 14°E–15°E, possibly related to a slowing down of its westward motion by seamounts. While the averaged zonal velocity component of the retroflection point increases westward, its modulus exhibits an opposite trend, the result of southward velocity components more intense in the northeastern Agulhas Basin than farther west. These meridional motions likely reflect influences by cyclones adjacent to the Agulhas Current south of the Agulhas Bank, and farther west in the Cape Basin. In the latter area, variations of the meridional motions result in different positions of the westernmost retroflection patterns relative to the neighbouring seamounts, likely influencing the future behaviour of Agulhas rings shed at these locations. Agulhas ring formation at an average yearly rate of 5.8, similar to previous findings, was observed to occur west of ～19°E, in the western half of the retroflection probability domain. A well-defined seasonal signal of the retroflection longitude was found throughout the first 5 years of the time series, characterized by amplitudes of 1–1.3° of longitude, and western (eastern) extremes during austral summer (winter). This annual cycle was strongly phase shifted during and after the upstream retroflection event of 2000–2001.     

Gamma-ray binaries and related systems

After initial claims and a long hiatus, it is now established that several binary stars emit high- (0.1–100 GeV) and very high-energy (>100 GeV) gamma rays. A new class has emerged called “gamma-ray binaries”, since most of their radiated power is emitted beyond 1 MeV. Accreting X-ray binaries, novae and a colliding wind binary (η Car) have also been detected—“related systems” that confirm the ubiquity of particle acceleration in astrophysical sources. Do these systems have anything in common? What drives their high-energy emission? How do the processes involved compare to those in other sources of gamma rays: pulsars, active galactic nuclei, supernova remnants? I review the wealth of observational and theoretical work that have followed these detections, with an emphasis on gamma-ray binaries. I present the current evidence that gamma-ray binaries are driven by rotation-powered pulsars. Binaries are laboratories giving access to different vantage points or physical conditions on a regular timescale as the components revolve on their orbit. I explain the basic ingredients that models of gamma-ray binaries use, the challenges that they currently face, and how they can bring insights into the physics of pulsars. I discuss how gamma-ray emission from microquasars provides a window into the connection between accretion–ejection and acceleration, while η Car and novae raise new questions on the physics of these objects—or on the theory of diffusive shock acceleration. Indeed, explaining the gamma-ray emission from binaries strains our theories of high-energy astrophysical processes, by testing them on scales and in environments that were generally not foreseen, and this is how these detections are most valuable.