A New Higher Order Displacement Discontinuity Method Based on the Joint Element for Analysis of Close-Spacing Planar Fractures

Summary The 2D displacement discontinuity method (DDM) has been widely used to characterize the hydraulic fracture geometry and the induced in-situ stresses in the oil and gas industry owing to its simplicity and accuracy. As smaller fracture spacing is used by multistage fracturing, the constant DDM (CDDM) loses its accuracy in predicting the fracture behaviors, especially for the inner fractures in a stage where they are subjected to the strong stress shadowing effect. In this paper, the 2D higher order DDM (HDDM) based on the joint elements was developed to overcome this limitation. The higher order displacement discontinuity intensively increases the accuracy of CDDM but maintains the same amount of computation time by using patched-element pattern. The joint elements are introduced to simultaneously determine the opening, shearing, and closing of each fracture element based on the stress boundary condition, which can avoid the “negative width” of the inner fractures given by CDDM which are mechanically closed under the strong stress shadowing effect. The developed 2D joint element HDDM (JE-HDDM) gives the same results with the CDDM when the fracture spacing is relatively large, but shows its outperformance in both efficiency and accuracy over the CDDM in predicting the displacement discontinuities and induced in-situ stresses in close fracture-spacing case.

Rapid Test Method for Multi-Beam Profile of Phased Array Antennas

The testing requirements of the active phased array antennas are very different from those of traditional passive antennas, due to its beam steering capability. Usually, each beam profile of the active phased array needs a separate radiation pattern test, which makes the overall testing time extremely long. Thus the traditional antenna test method can no longer meet the efficiency and cost requirements of new active phased array antennas test. In this paper, a fast test method tailored for phased array antennas is proposed that offers significantly reduced testing time at the expense of slight sacrifice of the accuracy. Using the simulated element pattern in array and ideal port excitation, the beam profile in any direction can be predicted by testing only a certain beam profile. Through theoretical derivation and experiments, the effectiveness of the method is verified, and the testing efficiency of the phased array antenna is demonstrated to be improved by ten times or even more.

Global implication of mesoproterozoic (~ 1.4 Ga) magmatism within the Sette-Daban Range (Southeast Siberia)

Mesoproterozoic period included several global tectonic events like break-up of Nuna and formation of Rodinia. However, although Siberia is a significant piece of both supercontinents, Mesoproterozoic time is marked by quiescence of magmatic and tectonic activity in it. We report here a mafic dyke (named Gornostakh dyke) in the southeastern Siberian Craton dated at 1419 ± 32 Ma by LA-ICPMS U–Pb geochronology of apatite. The dyke has tholeiitic compositions with high MgO and alkaline content, low-Ti, and arc-like trace element pattern. Due to the absence of subduction tectonics in the study area, geochemical data could be attributed to a significant contribution from metasomatically enriched subcontinental lithospheric mantle previously modified by subduction processes. That kind of composition is common for low-Ti dykes of intraplate flood basalt provinces similar to, for example, Permian–Triassic Siberian large igneous province (LIP). Paleogeographic reconstructions suggest that Siberia was connected to Laurentia and Baltica and their reconfiguration interrupts a prolonged tectonic quiescence in the Siberian Craton from ca. 1.88 Ga reflecting a transition from Nuna to Rodinia configuration. The mafic magmatism on 1419 Ma on the southeastern margin of the Siberian Craton together with coeval extensional tectonics observed in the structure of the Sette-Daban ridge proposes a hypothetical LIP which may be a direct consequence of the beginning of this transition.

An Early Bronze Age Burial with a Golden Spiral Ring from Ammerbuch-Reusten, Southwestern Germany

A women’s burial of the Early Bronze Age that was uncovered near Ammerbuch-Reusten, Tübingen district in autumn 2020 shows clear relations to burial rites of the Final Neolithic in central Europe. The only grave good was in the rear of the burial. A small spiral ring made of gold wire at the left side of the burial at hip level, which can be considered to be the earliest securely dated precious metal find in southwestern Germany. The find fits into a small series of early spiral rings made of gold wire, which are among the oldest precious metal finds in central Europe. Its composition with c. 20 % silver and less than 2 % copper as well as traces of platinum and tin indicates the use of a naturally occurring gold alloy, most likely from so-called alluvial deposits obtained by panning from rivers. The trace element pattern strongly suggests that this type of gold derives from Cornwall, specifically from River Carnon. The burial matches a group of other burials from the Bronze Age on the plateau and is apparently related to a hilltop settlement on the nearby Kirchberg of Reusten.

The Fluid Mobilities of K and Zr in Subduction Zones: Thermodynamic Constraints

A subduction zone plays a critical role in forging continental crust via formation of arc magmas, which are characteristically enriched in large ion lithophile elements (LILEs) and depleted in high field strength elements (HFSEs). This trace element pattern results from the different mobilities of LILEs and HFSEs during slab-to-wedge mass transfer, but the mechanisms of trace element transfer from subducting crusts are not fully understood. In this study, thermodynamic simulations are carried out to evaluate the mobilities of K and Zr, as representative cases of LILE and HFSE, respectively, in slab fluids. The fluids buffered by basaltic eclogite can dissolve > 0.1 molal of K at sub-arc depths (~3 to 5.5 GPa). However, only minor amounts of K can be liberated by direct devolatilization of altered oceanic basalt, because sub-arc dehydration mainly takes place at temperatures < 600 °C (talc-out), wherein the fluid solubility of K is very limited (<0.01 molal). Therefore, serpentinite-derived fluids are required to flush K from the eclogite. The solubility of K can be enhanced by the addition of NaCl to the fluid, because fluid Na+ can unlock phengite-bonded K via a complex ion exchange. Finally, it is further confirmed that Zr and other HFSEs are immobile in slab fluids.

Global Implication of Mesoproterozoic (1.4 Ga) Magmatism Within Sette-Daban Range (Southeast Siberia)

Mesoproterozoic period included several global tectonic events like break-up of Nuna and formation of Rodinia. However, although Siberia is a significant piece of both supercontinents, Mesoproterozoic time is marked by quiescence of magmatic and tectonic activity in it. We report here a mafic dyke (named Gornostakh dyke) in the southeastern Siberian Craton dated at 1419 ± 32 Ma by LA-ICPMS U-Pb geochronology of apatite. Paleogeographic reconstructions suggest that Siberia was connected to Laurentia and Baltica and their reconfiguration interrupts a prolonged tectonic quiescence in the Siberian Craton from ca. 1.88 Ga reflecting a transition from Nuna to Rodinia configuration. The 1419 Ma Gornostakh dyke and coeval deformation observed in the structure of the region may be a direct consequence of this transition. The dyke has tholeiitic compositions with high MgO and alkaline content, low-Ti, and arc-like trace element pattern. Due to the absence of subduction tectonics in the study area, geochemical data could be attributed to a significant contribution from metasomatically enriched subcontinental lithospheric mantle previously modified by subduction processes. Such mafic magmatism on the margin of the Siberian Craton could be related to a hypothetic large igneous province, which initiated the continental break-up.