Surendra P. Verma  Héctor López-Loera  Konduri S. V. Subramanyam  Chakravadhanula Manikyamba 《Geological Journal》2020,55(12):8169-8185

We present new major and trace element geochemical data, including the rare-earth elements (REE), platinum group elements and Au, and combine them with the published information to constrain the highly debated origin of magmas in the Los Tuxtlas Volcanic Field (LTVF) of the Late Miocene to historic age. The LTVF magmas originated in the garnet-bearing mantle as confirmed from the partial melting models of the REE. The mantle-derived magmas may have subsequently undergone fractional crystallization of mainly olivine. The controversial tectonic setting of the LTVF was solved by log-ratio transformed major as well as combined major and trace element data as a continental strike-slip fault setting during the Miocene–Pliocene. During the Pleistocene to Holocene, the more numerous samples having only major elements alone indicated the continental strike-slip fault setting, whereas the lesser number of samples having combined major and trace elements were more consistent with the continental extension. Importantly, no geochemical evidence for the involvement of the subducting slab in the magma genesis of the LTVF could be inferred. The inferences presented in this work were consistent with the entirety of geological, geochemical, and geophysical evidence. The multidimensional models also showed that the monogenetic volcanic field of the Xalapa region of the easternmost part of the Mexican Volcanic Belt represents a continental extension setting.  相似文献   

    

Rachelle B. Turnier  Yaron Katzir  Kouki Kitajima  Ian J. Orland  Michael J. Spicuzza  John W. Valley 《Journal of Metamorphic Geology》2020,38(1):53-70

Corundum (Crn), including sapphire, occurs in emery pods surrounded by marble on the island of Naxos, Greece. The emery formed from bauxite deposited in karst that was metamorphosed to 400–700°C at 20–15 Ma. Many of these rocks initially appeared well suited for refractory accessory mineral (RAM) thermometry, which uses oxygen isotope fractionation between a RAM – corundum – and a modally dominant phase with faster diffusion of oxygen – calcite (Cc) – to determine peak metamorphic temperatures. However, previous attempts at oxygen isotope thermometry were confounded by highly variable fractionations (Δ¹⁸O) measured at mm-scale and the uncertain calibration of Δ¹⁸O(Cc-Crn) versus temperature. Secondary ion mass spectrometry (SIMS) permits in situ analysis of δ¹⁸O in corundum and calcite at the 10-μm scale in adjacent grains where textures suggest peak metamorphic equilibrium was attained. SIMS analyses of adjacent mineral pairs in eight rocks yield values of Δ(Cc-Crn) that systematically decrease from 7.2 to 2.9‰ at higher metamorphic grade. Pairing these data with independent temperature estimates from mineral isograds yields an empirical calibration of 1,000 lnα(Cc-Crn) = 2.72 ± 0.3 × 10⁶/T² (T in K). The new fractionations (2.7‰ at 1,000 K) are significantly smaller than those calculated from the modified increment method (6.5‰ at 1,000 K; Zheng, Geochimica et Cosmochimica Acta, 1991, 55:2299–2307; Zheng, Mineral Mag, 1994, 58A:1000–1001), which yield unreasonably high temperatures of 630 to 1,140°C when applied to the new Naxos data. The new calibration of Δ(Cc-Crn) can be combined with published fractionations to calculate A-factors for corundum versus a range of 14 other minerals. These new fractionation factors can be used for thermometry or to constrain the genesis of corundum. A compilation of gem corundum δ¹⁸O values shows that many igneous sapphires, including important deposits of basalt-associated sapphire, are mildly elevated in δ¹⁸O relative to the calculated range in equilibrium with mantle values (4.4–5.7‰) and formed from evolved magmas.  相似文献   

    

Ramin Pakzad  Shanyong Wang  Scott W. Sloan 《国际地质力学数值与分析法杂志》2020,44(10):1472-1494

A FORTRAN program, consistent with the commercially available finite element (FE) code ABAQUS, is developed based on a three-dimensional (3D) linear elastic brittle damage constitutive model with two damage criteria. To consider the heterogeneity of rock, the developed FORTRAN program is used to set the stiffness and strength properties of each element of the FE model following a Weibull distribution function. The reliability of the program is assessed against available experimental results for granite cylindrical specimens with a throughgoing, flat and inclined fissure. The calibration procedure of the material parameters is explained in detail, and it is shown that the compressive to tensile strength ratio can have a substantial influence on the failure response of the specimens. Numerical simulations are conducted for models with different levels of heterogeneity. The results show a smaller load bearing capacity for models with less homogeneity, representing gradual coalescence of fully damaged elements forming throughout the models during loading. The maximum load bearing capacity is studied for various combinations of inclination angles of two centrally aligned, throughgoing and flat fissures of equal length embedded in cylindrical models under uniaxial and multiaxial loading conditions. The key role of the compressive to tensile strength ratio is highlighted by repeating certain simulations with a lower compressive to tensile strength ratio. It is proven that the peak loads of the rock models with sufficiently small compressive to tensile strength ratios containing two throughgoing fissures of equal length are similar, provided that the minimum inclination angles of the models are the same. The results are presented and discussed with respect to the existing experimental findings in the literature, suggesting that the numerical model applied in this study can provide useful insight into the failure behaviour of rock-like materials.  相似文献   

    

Zuzana Lenďáková  Ondřej Bábek  Balázs Komoróczy  Marek Vlach  Claus-Michael Hüssen  Ján Rajtár 《Geoarchaeology》2020,35(5):729-747

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Trevor H. Booth  Paul R. Muir 《Wiley Interdisciplinary Reviews: Climate Change》2020,11(5)

Two of Australia's most iconic ecosystems have recently sustained heavy damage related to climatic changes: the extensive eucalypt forests from catastrophic bushfires and the Great Barrier Reef from mass coral bleaching. Despite obvious differences, eucalypt trees and reef corals share some similarities in biology and ecology, particularly in relation to climate change impacts and adaptation. Both groups are the focus of an increasing research effort to characterize and respond to climate changes and here we examine how sharing research experiences can benefit both fields. Four key areas of research are considered: (a) modeling current distributions, (b) assessing impacts of climate change on future distributions, (c) using human‐assisted migration to improve survival, and (d) applying genetic enhancement to improve the species’ survival. Examples of each research area are used to examine potential crossovers, limitations of the methods, and future requirements. We conclude that eucalypt and coral researchers, and indeed researchers for many other endangered taxa, can gain much by comparing experiences and methods, despite the apparent differences in their respective taxa. This article is categorized under: Assessing Impacts of Climate Change > Observed Impacts of Climate Change  相似文献   

    

Reynold Chow  Jeremy Bennett  Jürnjakob Dugge  Thomas Wöhling  Wolfgang Nowak 《Ground water》2020,58(1):93-109

Hyporheic exchange is the interaction of river water and groundwater, and is difficult to predict. One of the largest contributions to predictive uncertainty for hyporheic exchange has been attributed to the representation of heterogeneous subsurface properties. Our study evaluates the trade-offs between intrinsic (irreducible) and epistemic (reducible) model errors when choosing between homogeneous and highly complex subsurface parameter structures. We modeled the Steinlach River Test Site in Southwest Germany using a fully coupled surface water-groundwater model to simulate hyporheic exchange and to assess the predictive errors and uncertainties of transit time distributions. A highly parameterized model was built, treated as a “virtual reality” and used as a reference. We found that if the parameter structure is too simple, it will be limited by intrinsic model errors. By increasing subsurface complexity through the addition of zones or heterogeneity, we can begin to exchange intrinsic for epistemic errors. Thus, the appropriate level of detail to represent the subsurface depends on the acceptable range of intrinsic structural errors for the given modeling objectives and the available site data. We found that a zonated model is capable of reproducing the transit time distributions of a more detailed model, but only if the geological structures are known. An interpolated heterogeneous parameter field (cf. pilot points) showed the best trade-offs between the two errors, indicating fitness for practical applications. Parameter fields generated by multiple-point geostatistics (MPS) produce transit time distributions with the largest uncertainties, however, these are reducible by additional hydrogeological data, particularly flux measurements.  相似文献   

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Abdulrahman Th Mohammad  Qassem H Jalut  Nadia L Abbas 《地下水科学与工程》2020,8(1):87-96

Al-Mansourieh zone is a part of Al-Khalis City within the province of Diyala and located in the Diyala River Basin in eastern Iraq with a total area about 830 km2.Groundwater is the main water source for agriculture in this zone.Random well drilling without geological and hydraulic information has led the most of these wells to dry up quickly.Therefore,it is necessary to estimate the levels of groundwater in wells through observed data.In this study,Alyuda NeroIntelligance 2.1 software was applied to predict the groundwater levels in 244 wells using sets of measured data.These data included the coordinates of wells(x,y),elevations,well depth,discharge and groundwater levels.Three ANN structures(5-3-3-1,5-10-10-1 and 5-11-11-1)were used to predict the groundwater levels and to acquire the best matching between the measured and ANN predicted values.The coefficient of correlation,coefficient determination(R2)and sum-square error(SSE)were used to evaluate the performance of the ANN models.According to the ANN results,the model with the three structures has a good predictability and proves more effective for determining groundwater level in wells.The best predictor was achieved in the structure 5-3-3-1,with R2 about 0.92,0.89,0.84 and 0.91 in training,validation,testing and all processes respectively.The minimum average error in the best predictor is achieved in validation and testing processes at about 0.130 and 0.171 respectively.On the other hand,the results indicated that the model has the potential to determine the appropriate places for drilling the wells to obtain the highest level of groundwater.  相似文献   

    

Hauke Wörpel  Axel D. Schwope  Iris Traulsen  Michael J. I. Brown 《Astronomische Nachrichten》2020,341(3):283-290

Optical surveys, such as the MACHO project, often uncover variable stars whose classification requires follow-up observations by other instruments. We performed X-ray spectroscopy and photometry of the unusual variable star MACHO 311.37557.169 with XMM-Newton in April 2018, supplemented by archival X-ray and optical spectrographic data. The star has a bolometric X-ray luminosity of about 1 × 10³² erg s⁻¹ cm⁻² and a heavily absorbed two-temperature plasma spectrum. The shape of its light curve, its overall brightness, its X-ray spectrum, and the emission lines in its optical spectrum suggest that it is most likely a VY Scl cataclysmic variable.  相似文献   

    

Dennis Jack  Klaus-Peter Schröder  Philippe Eenens  Uwe Wolter  José Nicolás González-Pérez  Jürgen H. M. M. Schmitt  Peter H. Hauschildt 《Astronomische Nachrichten》2020,341(8):781-790

With our robotic 1.2 m TIGRE telescope, we were able to obtain eight optical spectra with intermediate resolution (R ≈ 20,000 ) of the Nova V659 Sct during different phases of its outburst. We present a list of the lines found in the Nova spectra. The most common features are H I, O I, Na I, Fe II, and Ca II. Studying the spectral evolution of the strong features, we found that the absorption features move to higher expansion velocities before disappearing, and the emission features show (different) asymmetries. Because of the intermediate spectral resolution, we identified and analyzed the interstellar medium absorption features present in the spectra. We detected atomic absorption features of Na I and Ca II. The sodium D lines show more complex substructures with three main absorption features at a velocity of around −10, 30, and 85 km s⁻¹ . We identified several diffuse interstellar bands (DIBs) in the Nova V659 Sct spectra and determined their velocities and equivalent widths.  相似文献   

    

Mark R. Giovinazzi  Cullen H. Blake  Jason D. Eastman  Jason Wright  Nate McCrady  Rob Wittenmyer  John A. Johnson  Peter Plavchan  David H. Sliski  Maurice L. Wilson  Samson A. Johnson  Jonathan Horner  Stephen R. Kane  Audrey Houghton  Juliana García-Mejía  Joseph P. Glaser 《Astronomische Nachrichten》2020,341(9):870-878

The hot Jupiter HD 217107 b was one of the first exoplanets detected using the radial velocity (RV) method, originally reported in the literature in 1999. Today, precise RV measurements of this system span more than 20 years, and there is clear evidence of a longer-period companion, HD 217107 c. Interestingly, both the short-period planet (P_b ∼ 7.13  d) and long-period planet (P_c ∼ 5059 d) have significantly eccentric orbits (e_b ∼ 0.13 and e_c ∼ 0.40 ). We present 42 additional RV measurements of this system obtained with the MINERVA telescope array and carry out a joint analysis with previously published RV measurements from four different facilities. We confirm and refine the previously reported orbit of the long-period companion. HD 217107 b is one of a relatively small number of hot Jupiters with an eccentric orbit, opening up the possibility of detecting the precession of the planetary orbit due to general relativistic effects and perturbations from other planets in the system. In this case, the argument of periastron, ω , is predicted to change at the level of ∼ 0.8^∘ century⁻¹ . Despite the long time baseline of our observations and the high quality of the RV measurements, we are only able to constrain the precession to be century⁻¹ . We discuss the limitations of detecting the subtle effects of precession in exoplanet orbits using RV data.  相似文献