Sharp Contact Research Articles

Barium isotopes reveal the role of deep magmatic fluids in magmatic-hydrothermal evolution and tin enrichment in granites

Although deep magmatic fluids are important for the shallow magmatic-hydrothermal evolution and transport/enrichment of ore-forming elements in transcrustal magmatic system, it is still difficult to identify the influences of such fluids by using conventional geochemical indicators. Here we report Ba isotope compositions for granites from the Jurassic Qitianling batholith in the Nanling Range, South China that hosts several large tin deposits. This composite batholith consists of three stages of granites with an age range of ∼15 Ma and sharp contacts between each other, which suggest an underlying long-lived crystal mush-dominated transcrustal magmatic system. The small variation of δ138/134Ba in the first-stage less evolved granites (−0.24–0.37‰) indicates that fractional crystallization in deep crystal mush of this system does not cause significant Ba isotope fractionation. In contrary, the latter-two stage highly differentiated granites show more variable and overall lower δ138/134Ba (−1.79–0.14‰), which cannot be explained by K-feldspar-controlled fractional crystallization in shallow crystal mush. Instead, the distinctively low Ba contents (<100 μg/g) and magmatic-hydrothermal evolution features of the latter-two stage granites suggest that their low δ138/134Ba are due to modification by magmatic fluids. Further modeling demonstrates that exsolved fluids from deep crystal mush can explain the light Ba isotope compositions of the latter-two stage granites. Because these ascending deep magmatic fluids can efficiently scavenge Sn and other fluid-mobile elements then transport to shallow level, we propose that these fluids could provide critical materials for the Sn-polymetallic mineralization.

Quantifying the densification and shear flow under indentation deformation in borosilicate glasses

AbstractBorosilicate glasses are used ubiquitously for a wide range of applications, where their mechanical properties play a critical role. However, the deformation mechanisms governing the sharp contact response of these glasses remain poorly understood. Herein, we analyze the role of elastoplastic response in determining the indentation deformation mechanisms for a range of borosilicate glass compositions. The series of glasses were made by varying the SiO2‐to‐B2O3 molar ratio while maintaining a constant content of network modifying alkali and alkaline earth oxides. We employed nanoindentation followed by annealing below the glass transition temperature to quantify the contribution of densification and shear flow as a function of glass composition. Interestingly, we observe that the volume recovery upon annealing is inversely proportional to the hardness of the glasses. This suggests that the resistance to permanent deformation is closely related to the network connectivity of the glasses, which in turn governs the mechanism of deformation under sharp contact loading. Overall, we show the important role of alkali and alkaline earth modifiers in governing the composition‐dependent indentation behavior of borosilicate glass series.

Study of simulations of double graded InGaN solar cell structures

The performances of various configurations of InGaN solar cells are compared using nextnano semiconductor simulation software. Here, we compare a flat base-graded wall GaN/InGaN structure, with an InxGa1−xN well with sharp GaN contact layers, and an InxGa1−xN structure with InxGa1−xN contact layers, i.e., a homojunction. The doping in the graded structures is the result of polarization doping at each edge (10 nm from each side) due to the compositional grading, while the well structures and homojunctions are impurities doped at each edge (10 nm from each side) at levels equal to the polarization doping density in the graded structure with similar maximum indium concentration. The solar cells are characterized by their open-circuit voltage, Voc, short circuit current, Isc, solar efficiency, η, and energy band diagram. The results indicate that an increase in Isc and η results from increasing both the fixed and maximum indium compositions, while the Voc decreases. The maximum efficiency is obtained for the InGaN well with 60% In.

A General Approach to Determine the Constitutive Parameter Dependence of Global Quantities at Sharp Contact Testing of Rigid-Plastic Materials

Correlation of sharp contact problems is investigated with the focus on rigid-plastic contact behavior pertinent to engineering metals and alloys. The aim is to determine relations between the contact hardness and constitutive parameters suitable for material characterization. This is performed by using a solution approach where the transition zone between elastoplastic and rigid-plastic contact behavior is analyzed, especially as regards the size of the plastic zone. This approach is applied to three different cases: (1) sharp indentation of von Mises plastic materials; (2) sharp indentation of Drucker–Prager plastic materials; (3) sharp scratching of von Mises plastic materials. Established finite element simulations are used in order to verify the analysis of these three cases. In addition, based on the suggested approach, new results concerning the constitutive parameter dependence of the relative contact area, pertinent to case (2) above, are presented and compared with finite element simulations. All of the results are valid for metals and alloys but also for elastic–plastic crystalline materials where the contact deformation regime is close to the rigid-plastic one.

Modeling and inverse identification method for the characterization of elastic–plastic contact behavior during flat punch indentation

In this work, an inverse identification method is developed for the experimental characterization of the elastic–plastic contact in indentation problem. The method consists of a modeling procedure and an identification procedure. In the modeling, a discrete interfacial stress model is developed and the 2D frictional flat but round punch condition (of which frictionless, sharp corner contact is a special case) is formulated. Only the tendencies of stress distributions are required to be constrained in the model which can highly increase the scope of application. In the identification, an alternative optimization scheme is proposed in which the contact parameters can be inversed by matching the modeled displacement to the experimental data. A displacement-based yield criterion is developed so the plastic domain can be recognized without solving the stress or strain. The proposed method can characterize all of the contact parameters only by using the easy-acquired displacements. Simulation and experiments show that the proposed method can accurately characterize the contact from noisy measurements.

Criteria to identify sedimentary sills intruded during deformation of lacustrine sequences

Although sedimentary dykes have been widely reported across a range of settings, sedimentary sills have received somewhat less attention, perhaps due to the potential difficulties in identifying largely conformable intrusions within bedded sequences. Most outcrop descriptions of clastic intrusions are based on deep-water marine sequences, with few descriptions of sills in lacustrine settings. The recognition of sills in such settings is, however, important because lacustrine sequences are increasingly used as a record of palaeoseismic activity. The misidentification of sills that contain fragments and clasts of host stratigraphy with seismically-generated turbidites and debris flows, may lead to incorrect interpretations of palaeoseismicity. We use the Late Pleistocene Lisan Formation of the Dead Sea Basin as a case study, where laminated lake sediments preserve intricate relationships with sills. This permits us to not only establish a range of criteria used in the identification of sedimentary sills, but also examine relationships with adjacent seismically-triggered slumps and slides. Key criteria we use to recognise sills include marked changes in their thickness together with bifurcation and bridging geometries. Sills may be internally layered, contain lenses of breccia, together with aligned and folded clasts that may be truncated across upper sill contacts. Critical evidence for the interpretation of sills is also preserved along sharp but irregular upper contacts that erode and truncate bedding in the overlying host sequence. Minor apophyses and ‘wedges’ intrude both upwards and downwards from sills, while isoclinal recumbent ‘peel-back’ folds are created in host sediments by shear generated along the lower contacts of sills. We have undertaken anisotropy of magnetic susceptibility (AMS) analysis and find an oblate fabric that suggests flow and intrusion of sills along the strike of the slope, that may also help with their identification in bedded sequences. Sills form along detachments to both extensional and contractional deformation associated with seismically-generated slumps and mass transport deposits, together with sub-surface fold and thrust systems. High fluid pressures associated with injection of sedimentary sills may facilitate near-surface failure and downslope movement of the sedimentary pile.

Mineralogy, geochemistry, and 40Ar/39Ar dating of hornblendite/amphibolite pods in Penjween Ophiolite of northeastern Iraq: Implications for petrogenesis and tectonics

Penjween ophiolite is one of the ophiolitic complexes of northeastern Iraq. The serpentinites within the Penjween Ophiolite hosts many pods of hornblendite and amphibolite, and dikes of diorite among many other igneous bodies. These pods have very sharp contacts with the surrounding mantle serpentinized harzburgites. The hornblendites and amphibolites are usually intimately intergrown together as extremely hard, dark green to black colored, fine-to medium-grained pods with ∼2 x ∼2 x ∼(0.5–1) m dimensions. This study presents petrography, mineral chemistry, whole-rock major and trace element geochemistry, and electron probe microanalyses (EPMA) for the major minerals in the studied rocks. The hornblendite is composed entirely of amphiboles (>99% vol.), meanwhile the amphibolite consists of comparable amounts of amphibole and plagioclase which occasionally occurs as layered rocks with banded texture. The diorite dikes are white in color and consist dominantly of coarse-grained plagioclase and less amphiboles. The amphiboles of these rocks belong to pargasite (Mg# 0.69–0.77) ─ edenite (Mg# 0.74–0.79) endmembers where pargasite is by far the predominant mineral; meanwhile the plagioclase is albite (Ab93.4An6.4Or0.2). The amphiboles are replacement products of pyroxenes indicated from the relict pyroxene within their crystals. The amphiboles are abnormally rich in various dust-like inclusions of transparent minerals like REE-rich epidote, rutile, zircon, apatite, titanite, and ore minerals like ilmenite, and pyrrhotite, oriented along the crystallographic axes and form distinct zones in the core of amphibole crystals. The geochemical characteristics of the studied hornblendite (MgO = 13.07%, Ni = 260 ppm, Mg# = 66.57) as well as the high Sc (33 ppm) and V (254 ppm) concentrations are collectively consistent with a mantle-derived, igneous origin. The primitive-mantle normalized trace elements spidergram showed enrichment (hump) in Ba, Th, U, La, Ce, Pb, and Sr, and depletion (trough) in Nb, Ta, K, and Ti. The chondrite-normalized REE diagram showed enrichment of LREE relative to HREE, indicated from the smooth and steady decrease in the negative slope from LREE towards HREE with a negligible Eu-anomaly. Various tectonic discriminating diagrams showed that the studied hornblendite, amphibolite pods and diorite dikes are of igneous fore-arc origin, formed from calc-alkaline and/or tholeiitic magma within an active continental margin setting. The 40Ar/39Ar laser age of hornblendite is late Paleocene (Thanetian) (57.8 ± 5.1 Ma) which might represent an event during the obduction between the oceanic fore-arc Island and the Arabian Plate during the Late Cretaceous/Paleocene period.

Contourite systems around the northern exit from the Vema Channel

Several drifts of different types and sizes are identified near the northern exit of the Vema Channel, within the projects Neogene-Quaternary contourites of the Central and South Atlantic and Lateral sedimentation in the deep ocean (on the examples from the Central and South-Western Atlantic). Herein, we discuss new results of a multidisciplinary study of sixteen sediment cores and high-resolution sub-bottom (seismoacoustic) profiles, to address the impact of Lower Circumpolar Deep Water (LCDW) and Antarctic Bottom Water (AABW) passing through the Vema gateway on contourite accumulation and erosion. To the west of the northern exit from the Vema Channel, an anticyclonic gyre of LCDW is instrumental in the development of contourite drifts and sediment waves. The contourite origin of generally silty terrigenous sediments in the Santa Catarina Plateau – São Paulo Plateau area is ascertained by both morpho-seismic and sedimentary characteristics. Sedimentary features include: a lack of primary sedimentary structures and pervasive bioturbation; sharp erosional contacts, local hiatuses and stiff mud horizons; some sandy/silty layers and indistinct bedding; mostly fine grain-size, very poor sorting and distinctive bi-gradational sequences; a high degree of correlation between the content of sortable silt (SS) in the total < 63 μm size fraction and SS mean sizes in all eight cores studied. Biostratigraphy, oxygen isotope records and ten new accelerator mass-spectrometry (AMS) 14C dates reveal the mid to late Quaternary age of this mainly terrigenous contourite depositional system (CDS).By contrast, the dominantly calcareous Ioffe Drift, overlying the Florianopolis Fracture Zone (FFZ) ridge to the northeast of the Vema Channel, is far from any source of terrigenous material, and accumulated in an area of low biological productivity. The overall asymmetric geometry, mainly lenticular, upward-convex seismic units separated by erosional unconformities, reflection truncation, small-scale moats dissecting the drift surface collectively indicate its contourite origin. The interpretation of the drift as the CDS is supported by sediment characteristics including common hiatuses corresponding in some cases to erosional contacts, pervasive bioturbation, generally poor sediment sorting, and more or less well-developed bi-gradational sequences. The erosion and deposition in the drift area are mostly controlled by the main LCDW branch following northeastward along the FFZ. Extensive erosion by bottom currents has created numerous hiatuses and markedly reduced the thickness of drift's sediments. The stratigraphic record from the Ioffe Drift sediment cores reveals an Upper Pliocene – Quaternary succession. The results of detailed analyses of six cores from the Ioffe Drift area, compared with two cores and the upper part of DSDP Site 516 from the Rio Grande Rise, notably the use of a SS analogue, provide new information on calcareous biogenic contourites deposited in the pelagic realm of the South Atlantic.

Indicators for identification of lacustrine sandstones of sandy debris‐flow origin: A case study of Es1 Member, Palaeogene Shahejie Formation, Nanpu Sag, Bohai Bay Basin, China

The first member of Shahejie Formation of Eocene–Early Oligocene (Es1, Nanpu Sag) consists of fluvio-deltaic to deep lacustrine shale-sandstone accumulations, and the deep lacustrine deposits include sandy debris flow (SDF), turbiditic and mudrock facies. In the process of hydrocarbon exploration, it was found that that SDF sandstones in the deep lacustrine deposits can constitute excellent hydrocarbon reservoirs. Therefore, the identification of these lithofacies, especially SDF sandstones, is crucial for hydrocarbon exploration. We document here parameters that discriminate lacustrine SDF sandstones from turbiditic and mudrock deposits. Data from cores, wireline logs, and seismic sections are integrated and interpreted. Core-based identification indicators of the SDF sandstones include massive structures with upper and lower sharp contacts with interbedded mudrocks, lateral pinch-outs, locally imbricated to floating pebble-size grains, and elongated (teared) mudrock clasts within the middle and upper parts of normally- or inversely-grading sandstone and poor to high matrix content. These properties are attributed to deposition of non-Newtonian flows with sediment-support mechanism of dispersive pressure, matrix strength and buoyancy, sediment-transportation mechanism, and sediment-settling properties (hindered settling and freezing of the SDF). Log-facies identification indicators of the SDF sandstones are characterized by higher RLLD/RLLS values (40–80 Ω m), higher SP values (35–70 mV), lower Gamma ray (GR) values (70–120 API), and strongly serrated curve motifs. Seismic facies identification indicators of the SDF sandstones have mound-like, lenticular, or wedge-shaped external geometries, and interior worm-like and fusiform chaotic reflections with medium to strong amplitude, medium to high frequency, and medium to low continuity. The results and interpretation of the integrated core-log-seismic data as identification indicators are useful tools for identifying SDF sandstones and effectively distinguishing them from other deep lacustrine deposits.

Geochronology and petrogenesis of granitoids and associated mafic enclaves from Ghohroud in the Urumieh–Dokhtar Magmatic Arc (Iran): Evidence for magma mixing during the closure of the Neotethyan Ocean

The Ghohroud granitoids (GG), containing mafic microgranular enclaves (MMEs) are located in the central part of the Urumieh‐Dokhtar Magmatic Arc (UDMA) in central Iran. They are associated with the subduction‐related magmatism in the Alpine‐Himalayan orogenic belt. The GG are comprised of a variety of intermediate and felsic rocks, including tonalite, granodiorite, granite, diorite porphyry and monzodiorite. The MMEs are gabbroic diorite and tonalite in composition and characterized by a fine‐grained hypidiomorphic microgranular texture with occasional chilled margins. They show rounded, sharp or irregular contact with the host granitoids. The occurrences of quartz, K‐feldspar and corroded plagioclase indicate that MMEs are the products of mixing between mantle and crust‐derived magmas. New ages of zircon U–Pb dating reveal that the GG in the Kashan area emplaced at ca. 19–17 Ma (Burdigalian). All the samples of MMEs and granitoid host rocks in this study are metaluminous and calc‐alkaline with I‐type affinities. They are enriched in light rare earth elements (LREEs) and show slight negative Eu anomalies (Eu/Eu* = 0.36–0.95). These features in a combination with the relative depletion in Nb, Ta, Ti and P, indicate the granitoids and MMEs are closely associated with subduction‐related magmas at an active continental margin. The host rocks yield relatively homogeneous isotopic compositions of initial 87Sr/86Sr ratios ranging from 0.706036 to 0.707055, εNd(t) values varying from −2.25 to 0.8, and the Nd model ages (TDM) vary in a limited range of 0.70–0.96 Ga. The MMEs show similar initial 87Sr/86Sr ratios (0.706420–0.707366), εNd(t) values (−1.32 to −0.27), TDM (0.68–1.09 Ga) and Pb isotopic compositions with host granitoids, which imply they attained isotopic equilibration during magma mingling and mixing. In combination with the petrographic, chemical and isotopic results, we suggest that the origin of MMEs and their host rocks were related to the interaction between crust‐derived melts and mantle‐derived mafic magmas. The magma‐mixing event possibly occurred during the transition from subduction to collision in the UDMA along with the closure of the Neotethyan ocean.

A new paradigm of dissipation-adjustable, multi-scale resolving schemes for compressible flows

The scale-resolving simulation of high speed compressible flow through direct numerical simulation (DNS) or large eddy simulation (LES) requires shock-capturing schemes to be more accurate for resolving broadband turbulence and robust for capturing strong shock waves. In this work, we develop a new paradigm of dissipation-adjustable, shock capturing scheme to resolve multi-scale flow structures in high speed compressible flow. The new scheme employs a polynomial of n-degree and non-polynomial THINC (Tangent of Hyperbola for INterface Capturing) functions of m-level steepness as reconstruction candidates. These reconstruction candidates are denoted as PnTm. From these candidates, the piecewise reconstruction function is selected through the boundary variation diminishing (BVD) algorithm. Unlike other shock-capturing techniques, the BVD algorithm effectively suppresses numerical oscillations without introducing excess numerical dissipation. Then, an adjustable dissipation (AD) algorithm is designed for scale-resolving simulations. This novel paradigm of shock-capturing scheme is named as PnTm−BVD−AD. The proposed PnTm−BVD−AD scheme has following desirable properties. First, it can capture large-scale discontinuous structures such as strong shock waves without obvious non-physical oscillations while resolving sharp contact, material interface and shear layer. Secondly, the numerical dissipation property of PnTm−BVD−AD can be effectively adjusted between n+1 order upwind-biased scheme and non-dissipative n+2 order central scheme through a simple tunable parameter λ. Thirdly, with λ=0.5 the scheme can recover to n+2 order non-dissipative central interpolation for smooth solution over all wavenumber, which is preferable for solving small-scale structures in DNS as well as resolvable-scale in explicit LES. Finally, the under-resolved small-scale can be solved with the dissipation adjustable algorithm through the so-called implicit LES (ILES) approach. Through simulating benchmark tests involving multi-scale flow structures and comparing with other central-upwind schemes, the superiority of the proposed scheme is evident. For instance, the simulation results of the supersonic planar jet show that PnTm−BVD−AD schemes can achieve competitive results as Pn+2Tm−BVD schemes which utilize a higher degree of reconstruction polynomial. Thus, in comparison with the previous work, the proposed PnTm−BVD−AD schemes have the benefit of a more compact stencil and lower cost. In summary, this work provides an alternative scheme for solving multi-scale problems in high speed compressible flows.

Oxide glasses under pressure: Recent insights from experiments and simulations

Deciphering the structure–property relations of densified oxide glasses is a problem of longstanding interest. For example, it is important for understanding the fracture mechanism under sharp contact loading as well as fabricating glasses with tunable physical characteristics. Recent advances in both experimental and simulation techniques have prompted research breakthroughs in understanding the response of glasses to high pressure. In this Perspective, we first briefly discuss the facilities for the high-pressure treatment of glasses, including in situ and ex situ investigations. The recent work on pressure-induced structural changes of archetypical oxide glass families (silicates, germanates, borates, aluminates, phosphates) is discussed and compared to the changes in macroscopic properties induced by densification, as densification treatment can be used to produce oxide glasses with improved hardness, stiffness, and toughness. We also discuss the new insights from atomistic simulations combined with topological analysis tools to unravel the densification mechanism of oxide glasses on the medium-range order length scale. Drawing on these recent studies, we clarify how densification treatment has proved to be an important tool to both understand the disordered nature of glasses and tune their physical properties, although many open questions and challenges remain that require further investigations.

Influence of channelized-flow density structure on the stratal architecture of deep-marine levee deposits

ABSTRACT Deep-water channel and levee deposits are common depositional elements on modern and ancient continental slopes. Unlike their channel counterparts, the spatial and temporal evolution of levee stratigraphy is much less well understood, in part because of the typically more recessive nature of levee deposits in the ancient sedimentary record, and sparse, widely spaced core control or seismic images of insufficient resolution in the modern. Moreover, it is generally inferred that levee development, at least in part, precedes the main phase of channel filling, the reasons for which remain largely unknown. In the Isaac Formation of the Windermere Supergroup (Neoproterozoic) of east-central British Columbia, Canada, well-exposed levee deposits are divided vertically into packages, each consisting of a sand-rich lower part overlain sharply by a mud-rich upper part. The lower part (3–10 m thick) consists mostly of medium- to thick-bedded, upper medium- to coarse-grained, lower-division turbidites intercalated with thin-bedded, fine-grained, upper-division turbidites. Along depositional strike away from channel-fill margins, the thickness of lower-division turbidites exhibit a distinctive thickening and then thinning over a few hundreds of meters that results in a similar thickening and thinning of the entire lower part of a package. The upper part (3–16 m thick) consists mostly of thin-bedded, fine-grained, upper-division turbidites intercalated with uncommon medium- to thick-bedded, medium-grained, lower-division turbidites. Significantly, the thickness of very thin- and thin-bedded turbidites in the upper part generally decreases stratigraphically upward whereas the thickness of intercalated medium- and thick-bedded turbidites changes little. The lateral and vertical changes in these deposits suggest that channelized flows were initially coarse grained and moderately well-sorted, causing them to exhibit negligible density stratification, and therefore high flow efficiency. We interpret that the velocity maximum occurred above the height of the incipient channel margins, thereby allowing the lower, coarse-grained, dense part of flows to easily overspill and deposit thick-bedded, coarse-grained turbidites in the lower part of each package. The sharp contact with the upper part of each package marks the point when relief from channel floor to levee crest exceeded the height of the velocity maximum in average throughgoing turbidity currents. Above this height, density of the flow decreased abruptly and consisted of significantly finer-grained sediment that overspilled to form the upper, finer-grained part of each package. Later the makeup of the sediment supply changed to a more polydispersed grain-size distribution, which caused the throughgoing currents to be more density stratified. This enhanced near-bed stratification and concentration effects, which in addition to intense interfacial mixing, resulted in rapid kinetic energy loss, and promoted deposition in the channel.

Spatial patterns variations of a burrowed carbonate stratum (ramp carbonates), Upper Jurassic Hanifa Formation, central Saudi Arabia

Strata deposited in middle carbonate ramps are often highly burrowed. Such strata are easy to recognize in the stratigraphic record and have been recorded from numerous stratigraphic sections worldwide. However, the spatial patterns of these strata are poorly known, despite being intervals of flow zones in many hydrocarbon reservoirs and water aquifers. In this study, we trace one stratum (in the upper Hanifa Formation, central Saudi Arabia) that was deposited in the middle carbonate ramp of the Late Jurassic for ~21 km, cored it in three localities, and investigated its spatial stratigraphic, sedimentological and ichnological patterns by field investigation and laboratory analysis (petrographic analysis and computer tomography (CT) scanning). The results of the field investigation show that the stratum has a similar spatial stratigraphic pattern over the study area (sharp contacts with the underlying and overlying strata), suggesting one depositional cycle product. Nevertheless, the laboratory analysis revealed that the stratum varies spatially and distinctly in rock composition, burrow percentage (BP), and burrowing style, suggesting various controls on its rock texture. The bottom interval of the stratum comprises wackestone and packstone rock texture which are interpreted as a product of bio-retexturing that took place at the time of the initial flooding stage of the deposition cycle. In the middle (5% to 10% BP) and upper intervals (20% to 40% BP), the stratum has mudstone and wackestone host rock matrix penetrated by a Thalassinoides burrow network (pipe framework) with passive infills (grain-dominated carbonates). The stratum exhibits both vertical and lateral variations in burrow percentage and burrowing styles, which are interpreted to be controlled by variations in bathymetry due to sea-level change and seafloor topography. Such variations influenced the rock texture of the studied stratum and would eventually control the spatial patterns of its petrophysical properties. The results provide insights into the nature and controls on the spatial patterns of burrowed strata of a middle ramp carbonate, patterns that can be similar to many hydrocarbon reservoirs and can be used to predict the distribution of petrophysical properties.

Modern and early Holocene ice shelf sediment facies from Petermann Fjord and northern Nares Strait, northwest Greenland

Based on sediment cores and geophysical data collected from Petermann Fjord and northern Nares Strait, NW Greenland, an Arctic ice shelf sediment facies is presented that distinguishes sub and pro ice shelf environments. Sediment cores were collected from sites beneath the present day Petermann Ice Tongue (PIT) and in deglacial sediments of northern Nares Strait with a focus on understanding the glacial and oceanographic history over the last 11,000 cal yr BP. The modern sub ice shelf sediment facies in Petermann Fjord is laminated and devoid of coarse clasts (IRD) due to strong basal melting that releases debris (debris filtering) from the basal ice at the grounding zone driven by buoyant subglacial meltwater and entrained Atlantic Water. Laminated sediments in the deep basin proximal to the gounding zone comprise layers of fine mud formed by suspension settling from turbid meltwater plumes (plumites) interrupted by normally graded very fine sand to medium silt layers with sharp basal contacts and rip-up clasts of mud, interpreted as turbidites. An inner fjord sill limits distribution of sediment gravity flows from the grounding zone to the deep inner fjord basin, such that sites on the inner sill and beyond the ice tongue largely only comprise plumites. Bioturbation and foraminiferal abundances increase with distance from the grounding zone. The benthic foraminiferal species, Elphidium clavatum is absent beneath the ice tongue, but dominant in the turbid meltwater influenced environment beyond the ice tongue. The very sparse IRD in sediments beneath the PIT and in the fjord beyond the PIT derives mainly from englacial debris in the ice tongue, side valley glaciers, rock falls from the steep fjord walls and sea ice.We use the modern ice shelf sediment facies characteristics to infer the past presence of ice shelves in northern Nares Strait using analyses of sediment cores from several cruises (OD1507, HLY03, 2001LSSL, RYDER19). On bathymetric highs, bioturbated mud with dispersed IRD overlies a 10–15 m thick, distinctly laminated silt and clay unit with rare coarse clasts and sparse foraminifera which forms a sediment drape of nearly uniform thickness. We interpret these laminated sediments to represent glaciomarine deposition by meltwater plumes emanating from ice streams that terminated in floating ice shelves. IRD layers, shifts in sediment composition (qXRD, MS and XRF) and faunal assemblage changes in the laminated unit document periods of ice-shelf instability sometimes, but not always, coupled with grounding zone retreat. Our deglacial reconstruction, including ice shelves, begins ∼10.7 cal ka BP, with confluent ice streams grounded in Hall Basin fronted by the Robeson Channel ice shelf. Ice shelf breakup and grounding zone retreat to relatively stable grounding zones at Kennedy Channel and the mouth of Petermann Fjord was accomplished by 9.4 cal ka BP when the Hall Basin ice shelf was established. This ice shelf broke up and reformed once prior to the final break up at 8.5 to 8.4 cal ka BP marking ice stream collapse, separation of Greenland and Innuitian ice sheets, and the opening of Nares Strait for Arctic-Atlantic throughflow. The Petermann ice shelf remained in Hall Basin until the Petermann Glacier retreated from the fjord mouth ∼7.1 cal ka BP. The resilience of these northern ice streams to strong early Holocene insolation and subsurface Atlantic Water advection is attributed to their northern aspect, buttressing by narrow passages, and high ice flux from the Greenland Ice Sheet (GIS).

Analytical Solution and Shaking Table Test on Tunnels through Soft-Hard Stratum with a Transition Tunnel and Flexible Joints

Tunnels, where they pass through soft-hard strata, are severely damaged during earthquakes. These issues have not yet been well understood. In this study, the seismic performances of a tunnel passing through soft-hard stratum with a transition tunnel and flexible joints under earthquake motion were investigated by proposed analytical solutions and scaled shaking table tests. First, a mechanical model of a tunnel passing through soft-hard stratum with flexible joints is proposed, and it is derived by the Green’s function method. Then, a parametric analysis is conducted to investigate the effects of important variables on tunnels through soft-hard stratum. Finally, shaking table tests are conducted to verify the proposed solution and further investigate the seismic behaviors of the tunnel. The results show that: (1) the analytical solutions are workable and effective; (2) the influence of the soft-hard stratum junction on the tunnel responses is remarkable—the largest bending moment is located at the side of soft rock near the sharp contact area and the maximum shear force appears at the contact; (3) the joints and the transition tunnel could mitigate the potential adverse effects of the sharp contact area—the region affected by the joint is approximately 4.5 times the tunnel diameter on both sides of the stratum interface; and (4) the influence of sharp change of ground layers is more remarkable with a larger excitation amplitude.

When did Goliath collapse? Dating the recent events of a major submarine slide complex, Southeastern Mediterranean margin

Unraveling the failure history of submarine slides and delineating its environmental controls are crucial for practical hazard assessments, but are commonly challenging and costly. Here we address this challenge by investigating the Goliath slide complex, one of the largest documented slide scars on the ~200 km long continental slope offshore Israel. Geophysical evidence suggest that the Goliath complex is a relatively young feature. However, despite its proximity to submarine infrastructure and to one of the most populated coastal areas in the Mediterranean, its recent temporal development was never determined.Based on a detailed analysis of sub-meter resolution multi-channel seismic profiles, four sediment cores were retrieved from the northern head scarp and toe domains of the Goliath slide complex. Selective sedimentological and chronological analyses were carried out following a detailed computed tomography analysis of the cores. The results reveal two generations of deposits on the northern head scarp of Goliath, separated by a detachment surface. Two 14C ages of 7.46 ± 0.13 cal ka BP (core PHS-1) and 7.38 ± 0.16 cal ka BP (core PHS-5) were obtained for the sediments immediately overlying this surface, implying that the Goliath northern head scarp was formed, at least in part, during a substantial ~7.4 cal ka BP event. A ~3.7 kyrs hiatus within the late Holocene sedimentary sequence of core PHS-5 may suggest an additional, more recent and presumably smaller, slide event that occurred at ~2.4 ka BP. The sedimentary succession from Goliath's toe domain (core PTL-3), located ~32 km downslope from the head scarp, show an upper 1.2 m long continuous undisturbed sequence dated to the last ~14 ka BP and including sapropel S1 deposits. This sequence overlies three disturbed units, interpreted as mass transport deposits (MTDs) containing various deformation features, large-scale burrows, sharp contacts and fold structures. A 14C age dates the base of the hemipelagic sequence to 13.91 ± 0.23 cal ka BP, representing the minimum age of the slide event that deposited this MTD. Ages within the MTD units are substantially older (18.21 ± 0.27 to 28.66 ± 0.33 cal ka BP) than in the overlying sequence and an age-inversion within the MTDs supports their interpretation as transported sediments.The timing of the prominent slide events in the Goliath complex corresponds with the late stages of meltwater pulses 1A (~14.6–13.7 ka BP) and 1C (~8.2–7.5 ka BP), periods of accelerated sea level rise and probably increased sediments supply. Our results suggest that climate-driven factors likely contributed significantly to slope instability in this area, while earthquakes on the Dead Sea Transform may have been the triggering factor for the Goliath Slide events.

Geochronology and geochemistry of the Ediacaran orthogneisses from the north Shahrekord (Sadegh‐Abad), Sanandaj‐Sirjan Zone: Insights into magmatic evolution of the Iranian basement

The metamorphosed Sadegh‐Abad granite from the north Shahrekord Metamorphic Complex (NSMC) of Sanandaj‐Sirjan Zone in west Iran shows evidence of ductile deformation. The augen to banded mylonitic granite (orthogneiss) involves sharp contacts with other rock units, including high‐grade metamorphic rocks, such as eclogite, amphibolite, and garnet amphibolite as well as schists. U–Pb zircon dating reveals that the crystallization of the granitic magma occurred at 568 ± 14 Ma (Late Neoproterozoic, Ediacaran). The Sadegh‐Abad mylonitic granite comprises high SiO2 (67–78 wt.%) and Na2O (3.23–7.79 wt.%) contents and low CaO (0.73–1.61 wt.%) and variable K2O concentrations (0.08–4.6 wt.%). The chondrite‐normalized REE diagram shows enrichment in LREE relative to HREE (Ce/Yb)N = 1.90 to 6.12), a negative Eu anomaly (Eu/Eu* = 0.10–0.66), and nearly flat HREE patterns (Tb/Yb)N = 0.94–1.44). These are interpreted to have originated from a continental crustal source. This is further supported by the high concentration of the alkali elements, U, Th, Rb, and the high 87Sr/86Sr(i) isotopic ratios (0.7086 to 0.7163). The lower HREEs abundances, negative Eu anomalies, and the low contents of mafic minerals may infer that partial melting of continental crust has taken place in low‐pressure conditions within the plagioclase stability field, possibly of pre‐existing calc‐alkaline bodies in the lower continental crust. The charge of heating probably occurred via the injection of mafic magmas into the tonalitic and granodioritic continental crust.

Mineralogical and geochemical characteristics of tonsteins from the Middle Jurassic Yan'an Formation, Ordos Basin, North China

Although the Jurassic features a considerable accumulation of coal worldwide, only a few tonsteins within coal seams in this coal-forming period have been investigated. This paper presents the detailed mineralogical and geochemical compositions of six tonstein layers from the Middle Jurassic Yan'an Formation, Ordos Basin, North China. Based on the typical evidence of the distinct field characteristics occurring as paler thin beds with lateral continuity; conchoidal and flint-like fracture planes; sharp contacts with adjacent coals; and the mineralogical compositions, such as vermicular kaolinite, angular quartz, and euhedral zircon crystals with a single UPb age peak, the intra-seam clay beds of the Yan'an Formation were determined to have been mainly derived from a significant pyroclastic source. However, rounded quartz, muscovite, and detrital zircon grains in the tonsteins reflect minor contribution of terrigenous debris from sediment source regions. Moreover, a line of geochemical features including low TiO2/Al2O3 values, Al2O3/TiO2-Nb/Yb, and Al2O3/TiO2-Zr/TiO2 diagrams; low REY concentrations with high fractionation between light REE and heavy REY (REY, rare earth elements and Y; REE, rare earth elements); and pronounced negative Eu anomalies, suggest that the tonsteins have a felsic (rhyolitic) magma origin. A systematic geochemical analysis of enclosing coals of the tonsteins was also conducted to determine the leaching behavior of the trace elements from the tonsteins into the enclosing coals. The results show that Th, U, Nb, Ta, Zr, and Hf tend to be enriched in the overlying and underlying coals and have an enrichment width of up to 30 cm. Similarly, the elevated concentrations of Zn, Rb, Cs, Pb, La, Ce, Pr, and Nd only occur in a relatively narrow zone above and below the tonsteins. The width of the enrichment in the enclosing coals may be mainly related to the properties of the tonsteins, e.g., thickness and original volcanogenic material, the characters of elements including mobility and concentration, and the nature of coals, such as coal rank.

Private Investments, Public Goods: Regulating Markets for Sustainable Development

In the new ecosystem for financing the sustainable development goals (SDGs), private actors are no longer passive bystanders in the development process, nor engaged merely as clients or contractors but as co-investors and co-producers in development projects and programmes. This ‘private turn’ in the financing of international development and other global public goods sees the enmeshment of public and private finance that brings aid and other forms of official development finance into sharp contact with regulatory regimes commonly associated with commercial investments, capital markets and corporate activity. The shift away from public resources for financing (e.g., multilateral sovereign loans) to leveraging financial markets for development capital (e.g., equity and portfolio investments) will insert countries into global financial markets and engagements with corporate actors in ways that will change forms of regulation, accountability and transparency of public finance. Zooming in on the creation of markets for sustainable development investments (SDI), this paper explores how this broader ‘reengineering of public finance’ is establishing new forms of governance that are restructuring the relationship between states and markets and between transnational capital and their host communities. Specifically, the movement towards private investments and financial markets as key drivers of financing for sustainable development has two critical impacts on transnational governance: (a) the use of private markets, in their capital allocation roles, as quasi-regulatory tools for achieving the SDGs and other global public goods; and (b) the deployment of private regulatory regimes (e.g., contracts, codes of conduct, corporate governance codes) as mechanisms to govern the social and environmental externalities of transnational economic activity. These developments have wide-ranging impacts on the domestic legal, political and civic constitution of states that can paradoxically constrain fiscal and policy space for enabling the attainment of the SDGs.