The geochemistry of sulphur in a mixed allogenic–autogenic karst catchment,Castleton, Derbyshire,UK

Analyses are presented of anion chemistry and sulphur isotopic compositions of sulphate in sinking streams and groundwaters in a mixed allogenic–autogenic karst catchment. Using the sulphur isotopic data, sources of sulphate from agriculture and the effects of sulphate reduction arising from slurry application can be distinguished from natural rock weathering sources. Within the aquifer, sulphate in known autogenic waters has isotopic compositions distinct from allogenic waters, the autogenic waters being dominated by sulphate from rainfall and rock weathering in these low agricultural intensity catchments. On this basis, water rising at low flow from Whirlpool Rising, Speedwell Cavern, has been identified as dominantly autogenic. Groundwater flow between the sinks and risings in Speedwell Cavern is believed to be along conduits following mineralized faults (rakes). During transit SO42−/Cl− in the water increases. Isotopic mass balance shows that this must be due to addition of sulphate from the oxidation of ore minerals by groundwater. Mass balance considerations show that the present rate of sulphide oxidation must be the result of enhancement by lead mining operations on the rakes. Copyright © 2000 John Wiley & Sons, Ltd.     

An Appraisal of the 2001 Bhuj Earthquake (Mw 7.7, India) Source Zone: Fractal Dimension and b Value Mapping of the Aftershock Sequence

We examined seismic characteristics, b value and fractal dimension of the aftershock sequence of the January 26, 2001 Bhuj earthquake (Mw 7.7) that occurred in the Kutch failed rift basin, western margin of the Stable Continental Region (SCR) of India. A total of about 2,000 events (M?≥?2.0) were recorded within two and a half months, immediately after the main shock. Some 795 events were precisely relocated by simultaneous inversion. These relocated events are used for mapping the frequency-magnitude relation (b value) and fractal correlation dimension (Dc) to understand the seismic characteristics of the aftershocks and the source zone of the main shock. The surface maps of the b value and Dc reveal two distinct tectonic arms or zones of the V-shaped aftershock area, western zone and eastern zone. The b value is relatively higher (~1.6) in the western zone compared to a lower value (~1.4) in the eastern zone. The Dc map also shows a higher value (1.2–1.35) in the western zone compared to a lower Dc (0.80–1.15) in the eastern zone; this implies a positive correlation between Dc and b value. Two cross sections, E–W and N–S, are examined. The E–W sections show similar characteristics, higher b value and higher Dc in the western zone and lower in the eastern zone with depth. The N–S sections across the fault zones, however, show unique features; it imaged both the b and Dc characteristics convincingly to identify two known faults, the Kutch Mainland fault and the South Wagad fault (SWF), one stepping over the other with a seismogenic source zone at depth (20–35?km). The source zone at depth is imaged with a relatively lower b and higher Dc at the ‘fault end’ of the SWF showing a negative correlation. These observations, corroborated with the seismic tomography as well as with the proposed geological/tectonic model, shed a new light to our understanding on seismogenesis of the largest SCR earthquake in India in the recent years.     

Volcano-tectonic controls and emplacement kinematics of the Iriga debris avalanches (Philippines)

Mt Iriga in southeastern Luzon is known for its spectacular collapse scar that was possibly created in 1628 ad by a 1.5-km³ debris avalanche. The debris avalanche deposit (DAD) covered 70?km² and dammed the Barit River to form Lake Buhi. The collapse has been ascribed to a non-volcanic trigger related to a major strike-slip fault under the volcano. Using a combination of fieldwork and remote sensing, we have identified a similar size, older DAD to the southwest of the edifice that originated from a sector oblique to the underlying strike-slip fault. Both deposits cover wide areas of low, waterlogged plains, to a distance of about 16?km for the oldest and 12?km for the youngest. Hundreds of metre-wide and up to 50-m-high hummocks of intact conglomerate, sand and clay units derived from the base of the volcano show that the initial failure planes cut deep into the substrata. In addition, large proportions of both DAD consist of ring-plain sediments that were incorporated by soft-sediment bulking and extensive bulldozing. An ignimbrite unit incorporated into the younger DAD forms small (less than 5?m high) discrete hummocks between the larger ones. Both debris avalanches slid over water-saturated soft sediment or ignimbrite and spread out on a basal shear zone, accommodated by horst and graben formation and strike-slip faults in the main mass. The faults are listric and flatten into a well-developed basal shear zone. This shear zone contains components from the substrate and has a diffuse contact with the intact substrata. Long, transport-normal ridges in the distal parts are evidence of compression related to deceleration and bulldozing. The collapse orientation and structure on both sectors and DAD constituents are consistent with collapse being a response to combined transtensional faulting and gravity spreading. Iriga can serve as a model for other volcanoes, such as Mayon, that stand in sedimentary basins undergoing transtensional strike-slip faulting.     

The geology of split butte — A maar of the south-central snake river plain,Idaho

Split Butte is a volcanic crater of Quaternary age consisting of a tephra ring which at one time retained a lava lake. The tephra is thinly bedded and is composed of partially palagonitized sideromelane clasts and subordinate lithic fragments. The beds typically dip radially away from the center of the crater, but locally dip toward the crater center. The tephra ring resulted from phreatomagmatic eruptions as a result of interaction of groundwater with rising basaltic magma, evidenced by glassy and granulated pyroclastic debris, the presence of abundant palagonite and other secondary minerals, numerous armored lapilli, and plastically deformed ash layers below ejecta blocks. Statistical analysis of the grain size distribution of the ash also indicates a phreatomagmatic origin of Split Butte tephra. In addition, the analysis reveals that the stratigraphically lowest tephra was deposited primarily by pyroclastic flow mechanisms while the upper tephra layers, comprising the bulk of the deposits, were deposited dominantly by airfall and pyroclastic surge. The lava lake and four en echelon basalt dikes were emplaced when phreatomagmatic activity at the vent ceased. Subsequent collapse caused a broad, shallow pit crater to form in the laval lake, and minor spattering occurred at one point along the pit crater scarp. Partial erosion of the tephra, deposition of aeolian sediments and encroachment of the Butte by later lava flows completed the development of Split Butte.     

The effect of oxygen fugacity on the solubility of carbon-oxygen fluids in basaltic melt

The solubility of CO₂CO fluids in a mid-ocean ridge basalt (morb) has been measured at 1200°C, 500–1500 bar, and oxygen fugacities between NNO and NNO-4. High oxygen fugacities, and thus CO₂-rich fluids, were produced by using a starting material equilibrated at NNO, and Ag₂C₂O₄ as the fluid source. Low oxygen fugacities were achieved by using graphite capsules, and MgCO₃ as the fluid source. These graphite-saturated fluids have the lowest possibleC/O₂CO ratio for a given pressure and temperature.

Experiments were run in a rapid-quench internally heated pressure vessel. Fluid compositions were measured using a simple vacuum technique and by Raman spectroscopy of fluid inclusions. The two techniques yielded comparable results. Fourier transform micro-infrared spectroscopy was used to identify and measure concentrations of dissolved volatiles in double-polished wafers of the quenched glasses. Carbonate was the only carbon-bearing species identified. Raman spectroscopic analysis of inclusion-free areas of glass confirmed the absence of dissolved molecular CO₂, CO and carbon. The measured concentrations of dissolved CO₂ in the glasses were proportional to the fugacity of CO₂ during the experiments, calculated from the measured fluid compositions. The data were fit to the equationX_CO2^melt(ppm)= 0.492 fCO₂ (bar).

The insolubility of CO, compared to CO₂, may be related to the fact that dissolution of CO requires reduction of another species in the melt, whereas dissolution of CO₂ does not. Due to the fact that CO will be an important component of natural CO fluids at low pressures and low oxygen fugacities, equilibrium dissolved CO₂ contents will be less than calculated assuming pure CO₂ fluids, but as theC/O₂CO ratio in a pure CO fluid at fixed pressure and temperature is a direct function of oxygen fugacity, measurement of the oxygen fugacity of quenched glasses or trapped fluids in natural samples should allow saturation concentrations to be calculated. Dissolved CO₂ contents of somemorb are less than expected if they were in equilibrium with pure CO₂. These samples must, therefore, have been more reduced than average if they were fluid-saturated. Together with results from other studies of CO₂ and H₂O solubilities in basalt, the results of this study provide a comprehensive framework for modelling CO₂ solution inmorb.     

Evaluation of rainfall-runoff performance using the stochastic integral equation method

The stochastic integral equation method (S.I.E.M.) is used to evaluate the relative performance of a set of both calibrated and uncalibrated rainfall-runoff models with respect to prediction errors. The S.I.E.M. is also used to estimate confidence (prediction) interval values of a runoff criterion variable, given a prescribed rainfall-runoff model, and a similarity measure used to condition the storms that are utilized for model calibration purposes.Because of the increasing attention given to the issue of uncertainty in rainfall-runoff modeling estimates, the S.I.E.M. provides a promising tool for the hydrologist to consider in both research and design.     

Caribbean hurricanes: changes of intensity and track prediction

The meteorological conditions of hurricanes passing near Puerto Rico (18N, 68W) are analyzed using composite daily reanalysis and satellite data. When an intense hurricane is present, the regional circulation is dominated by upper easterly flow over the Caribbean and central Atlantic and a surge of low-level westerly anomalies across the tropics. Warm SST anomalies extend along the coast of Venezuela, doubling the convective energy available to Caribbean hurricanes. Intensifying hurricanes tend to propagate westward with an atmospheric ridge over the Gulf Stream, in an environment with aerosol optical depth <0.6. Hurricanes form and strengthen in the east-shear phase of the Madden Julian Oscillation. Sinking motions and dry air appear in an anti-cyclonic gyre behind intensifying hurricanes. Numerical model 48-h forecasts of Caribbean hurricane tracks are analyzed over the period 2000–2010. A “slow right” bias is found east of Puerto Rico in comparison with observed.     

Late Quaternary paleo sea level geomorphological markers of opposite vertical movements at Salina volcanic island (Aeolian Arc)

Raised marine terraces and submerged insular shelves are used through an integrated approach as markers of relative sea level changes along the flanks of the Salina volcanic island (Aeolian Arc, southern Italy) for the purpose of evaluating its crustal vertical deformation pattern through time. Paleo sea level positions are estimated for the terrace inner margins exposed subaerially at different elevations and the erosive shelf edges recognized offshore at different depths. Compared with the eustatic sea levels at the main highstands (for the terraces) and lowstands (for the shelf edges) derived from the literature, these paleo sea level markers allowed us to reconstruct the interplay among different processes shaping the flanks of the island and, in particular, to quantify the pattern, magnitudes and rates of vertical movements affecting the different sectors of Salina since the time of their formation. A uniform uplift process at rates of 0.35 m ka⁻¹ during the Last Interglacial is estimated for Salina (extended to most of the Aeolian Arc) as evidence of a regional (tectonic) vertical deformation affecting the sub-volcanic basement in a subduction-related geodynamic context. Before that, a dominant subsidence at rates of 0.39–0.56 m ka⁻¹ is instead suggested for the time interval between 465 ka (MIS 12) and the onset of the Last Interglacial (MIS 5.5, 124 ka). By matching the insular shelf edges with the main lowstands of the sea level curve, a relative age attribution is provided for the (mostly) submerged volcanic centres on which the deepest (and oldest) insular shelves were carved, with insights on the chronological development of the older stages of Salina and the early emergence of the island. The shift from subsidence to uplift at the Last Interglacial suggests a major geodynamic change and variation of the stress regime acting on the Aeolian sub-volcanic basement. © 2019 John Wiley & Sons, Ltd.     

中国西南天山西域砾岩的磁性地层年代与地质意义*

西域组是我国西部一重要并广泛引用的晚新生代地层,关于其年代和成因至今尚存争议。在西南天山喀什远源盆地喀什-阿图什褶皱带不同构造部位选择有代表性的5~6个晚新生代地层剖面开展了详细的沉积学、磁性地层年代学对比研究,据此限定了不同构造的起始变形时间以及西域砾岩的沉积年代。西域砾岩并非一年代地层单位,作为一岩石地层单位,其底界具有穿时特征,从山体(北)向喀什前陆盆地(南)逐渐变新。其底界年龄在盆地北部近源区约为15.5Ma^[1],在盆地中部中源区约为8.6Ma^[1],在盆地南部远源区的阿图什背斜为1.9Ma,喀什背斜为1.6~0.7Ma。这一穿时的砾岩沉积楔体的起始堆积起因于盆地北部边界逆冲断层(KBT)的活动。构造变形是由北南脉冲式迁移扩展的,其速率是非均匀的,在约15.5Ma至4.0Ma期间为1.4~3.4mm/a,在约4.0Ma以来剧增至>10mm/a。西域砾岩沉积前缘向南进积速率与构造变形前缘迁移速率有很好的一致性,但在时间上较构造变形可能滞后2.0Ma。这表明构造变形前缘向南的脉冲式扩展是西域砾岩进积并发生侧向和垂向上岩相突变的主因。     

Laboratory kinetics of C2H radical reactions with ethane, propane, and n-butane at T = 96-296 K: implications for Titan

The kinetics of the reactions of C₂H radical with ethane (k₁), propane (k₂), and n-butane (k₃) are studied over the temperature range of T = 96-296 K with a pulsed Laval nozzle apparatus that utilizes a pulsed laser photolysis-chemiluminescence technique. The C₂H decay profiles in the presence of both the alkane reactant and O₂ are monitored by the CH(A²Δ) chemiluminescence tracer method. The results, together with available literature data, yield the following Arrhenius expressions: k₁(T) = (0.51 ± 0.06) × 10⁻¹⁰ exp[(−76 ± 30)K/T] cm³ molecule⁻¹ s⁻¹ (T = 96-800 K), k₂(T) = (0.98 ± 0.32) × 10⁻¹⁰exp[(−71 ± 60)K/T] cm³ molecule⁻¹ s⁻¹ (T = 96-361 K), and k₃(T) = (1.23 ± 0.26) × 10⁻¹⁰ cm³ molecule⁻¹ s⁻¹ (T = 96-297 K). At T = 296 K, k₁ is measured as a function of total pressure and has little or no pressure dependence. The results from this work support a direct hydrogen abstraction mechanism for the title reactions. Implications to the atmospheric chemistry of Titan are discussed.