Journal of Earth Science

High-purity N2 was used to increase the mobile phase flow rate during ion purification of ion-exchange resin. This was performed to improve the efficiency of isotope separation and purification, and to meet the efficiency requirements of rapid multiple-collector-inductively coupled plasma mass spectrometry (MC-ICPMS) analysis. For Cu isotope separation, our results indicated that at a gas flow rate >60 mL/min, the separation chromatographic peaks broadened and the recovery rate decreased to <99.2%. On the other hand, no significant change in the Cu peaks was observed at a gas flow rate of 20 mL/min and the recovery rate was determined to be >99.9%. The Cu isotope ratio, measured by the standard-sample bracketing method, agreed with reference data within a ±2 SD error range. The separation time was reduced from the traditional 10 h (without N2) to 4 h (with N2), indicating that the efficiency was more than doubled. Moreover, Sr and Nd isotope separation in AGV-2 (US Geological Survey andesite standard sample) accelerated with a 20 mL/min gas flow, demonstrating that with the passage of N2, the purified liquid comprised Rb/Sr and Sm/Nd ratios of <0.000 049 and <0.000 001 5, respectively. This indicated an effective separation of Rb from Sr and Sm from Nd. MC-ICPMS could therefore be applied to accurately determine Sr and Nd isotope ratios. The results afforded were consistent with the reference data within a ±2 SD error range and the total separation time was shortened from 2 d to <10 h.

Chahuaqingolepis magniporus gen. et sp. nov., a new taxon of Bothriolepididae (Placoder-mi: Antiarcha), is described from the Middle Devonian in Luquan County, Yunnan Province, South China. The phylogenetic analysis shows that Chahuaqingolepis is the sister group of Wufengshania with the synapomorphy of the large obtected nuchal area. Together with the findings of other associated antiarchs including Dianolepis, Bothriolepis, and Hunanolepis, the new bothriolepid antiarch is assigned to the Bothriolepis sinensis-Hunanolepis fish assemblage, which characterizes the Eifelian of the Middle Devonian in South China. The fish-bearing Tanglishu Formation can be well correlated with the Tiao-majian Formation in Changsha, Shangshuanghe Formation and lower part of the Haikou Formation in Qujing, and Laohutou Formation in Shaoguan and Lechang areas. This discovery not only enriches the Middle Devonian diversity of bothriolepids, but also provides reliable paleoichthyological evidence on the division and correlation of the fish-bearing Devonian strata in South China and deepens the understanding of the biogeography of the Devonian bothriolepids.

Elastic migration has been widely paid attention by employing the vector processing of multicomponent seismic data. Ray based elastic Kirchhoff migration has such properties as high flexibility and high efficiency. However, it has failed to solve many problems caused by multipath. On the other hand, elastic reverse-time migration (RTM) based on the two-way wave equation is known to be capable of dealing with these problems, but it is extremely expensive when applied in 3D cases and velocity model building. Based on the elastic Kirchhoff-Helmholtz integral, we calculate decoupled backward-continued wavefields by introducing elastic Green functions for P- and S-waves, which is expressed by a summation of elastodynamic Gaussian beams. The PP and polarity-corrected PS images are obtained by calculating the correlation between downward and decoupled backward-continued vector wavefields, where polarity correction is performed by analyzing the relation between the polarization direction of converted PS waves and incident angle on the interface. To a large extent, our method combines the high efficiency of ray-based migration with the high accuracy of wave-equation based reverse-time migration. Application of this method to multicomponent synthetic datasets from the fault model and Marmousi 2 model demonstrates the validity, flexibility and accuracy of the new method.

On May 18, 2020, an Mw5.1 earthquake occurred in Qiaojia County, Yunnan Province, China. This moderate-sized event triggered massive coseismic landslides, resulting in some damage. In this work, through visual interpretation of high-resolution (0.8–2 m) Gaofen satellite images before and after the earthquake, 167 landslides were delineated, 18 of which were inspected in the field. Using the landslide number density (LND) and landslide area percentage (LAP), we characterized the spatial distribution of these landslides, and analyzed their possible influence factors and tectonic significance. The results show that these landslides are distributed mostly in the NW-SE direction, roughly parallel to the long axis of seismic intensity zones and the strike of the Xiaohe-Baogunao fault (XBF). The LND and LAP decrease with increasing distances to the fault and from the epicenter to fault ends of the XBF. These permit to suggest that the seismogenic fault of the Qiaojia earthquake is likely a hidden branch of the XBF. All of the landslides induced by this event occurred in the region with the seismic intensity of six degrees or greater of the 2014 Mw6.2 Ludian earthquake. Therefore, it was inferred that the 2020 Qiaojia earthquake was probably the subsequent release of accumulated elastic strain after the 2014 Ludian earthquake in a same tectonic stress regime.

Debris flow forecast is an important means of disaster mitigation. However, the accuracy of the statistics-based debris flow forecast is unsatisfied while the mechanism-based forecast is unavailable at the watershed scale because most of existing researches on the initiation mechanism of debris flow took a single slope as the main object. In order to solve this problem, this paper developed a model of debris flow forecast based on the water-soil coupling mechanism at the watershed scale. In this model, the runoff and the instable soil caused by the rainfall in a watershed is estimated by the distributed hydrological model (GBHM) and an instable identification model of the unsaturated soil. Because the debris flow is a special fluid composed of soil and water and has a bigger density, the density estimated by the runoff and instable soil mass in a watershed under the action of a rainfall is employed as a key factor to identify the formation probability of debris flow in the forecast model. The Jiangjia Gulley, a typical debris flow valley with a several debris flow events each year, is selected as a case study watershed to test this forecast model of debris flow. According the observation data of Dongchuan Debris Flow Observation and Research Station, CAS located in Jiangjia Gulley, there were 4 debris flow events in 2006. The test results show that the accuracy of the model is satisfied.

The shale deposits of Damodar Valley have received great attention since preliminary studies indicate their potential for shale gas. However, fundamental information allied to shale gas reservoir characteristics are still rare in India, as exploration is in the primary stage. In this study, Barakar shale beds of eastern part of Jharia Basin are evaluated for gas reservoir characteristics. It is evident that Barakar shales are carbonaceous, silty, contains sub-angular flecks of quartz and mica, irregular hair-line fractures and showing lithological variations along the bedding planes, signifying terrestrial-fluviatile deposits under reducing environment. The values of TOC varies from 1.21 wt.% to 17.32 wt.%, indicating good source rock potentiality. The vitrinite, liptinite, inertinite and mineral matter ranging from 0.28 vol.% to 12.98 vol.%, 0.17 vol.% to 3.23 vol.%, 0.23 vol.% to 9.05 vol.%, and 74.74 vol.% to 99.10 vol.%, respectively. The ternary facies plot of maceral composition substantiated that Barakar shales are vitrinite rich and placed in the thermal-dry gas prone region. The low values of the surface area determined following different methods point towards low methane storage capacity, this is because of diagenesis and alterations of potash feldspar responsible for pore blocking effect. The pore size distribution signifying the micro to mesoporous nature, while Type II sorption curve with the H2 type of hysteresis pattern, specifies the heterogeneity in pore structure mainly combined-slit and bottle neck pores.

Serpentinization and calcite precipitation of mantle peridotites exhumed along detachment faults at the slow- to ultraslow-spreading centers can provide important clues to the hydrothermal alteration processes. The Tianxiu hydrothermal field is a new-found active and ultramafichosted hydrothermal vent site along the Carlsberg Ridge, Northwest Indian Ocean. Two types of calcite veins are recognized in serpentinized harzburgite samples collected from the seafloor at the water depth of 3 500 m (3.67°N/63.83°E) and 400 m north of Tianxiu hydrothermal field. Calcite veins I occur in the fractures that cut through mesh texture in the highly serpentinized harzburgite, while calcite veins II precipitate within the mesh texture in the relatively weaker serpentinized harzburgite. Both veins show similar δ13CPDB (+0.54‰ and +0.58‰) but different δ18OPDB(−16.67‰ and +4.46‰) values, suggesting that they were derived from the same carbon source but precipitated at different temperatures. Taking the deep seawater temperature of 2 °C as the precipitation temperature of the calcite veins I, the equilibrium δ18OV-SMOW of calcite-precipitating fluid was calculated to be 1.78‰, which is close to the average δ18OV-SMOW value (1.74‰) of vent fluid samples from the ultramafic-hosted hydrothermal systems worldwide. The formation temperature of calcite veins II is inferred to be approximately 134 °C, based on the calculated δ18OV-SMOW above. The temperature differences of calcite precipitation probably resulted from the fluid cooling conductively and mixing with seawater along the presumed fractures during slow upflow. The low-temperature calcite postdates the mesh texture, while the high-temperature calcite may precipitate under relatively low water/rock ratios, alkaline and reduced conditions among the mesh texture, which is revealed by the geochemical models. Therefore, it is suggested that they both have been influenced by hydrothermal fluids and the sampling site is near the discharge zone of hydrothermal circulation.

Deep geothermal from the hot crystalline basement has remained an unsolved frontier for the geothermal industry for the past 30 years. This poses the challenge for developing a new unconventional geomechanics approach to stimulate such reservoirs. While a number of new unconventional brittle techniques are still available to improve stimulation on short time scales, the astonishing richness of failure modes of longer time scales in hot rocks has so far been overlooked. These failure modes represent a series of microscopic processes: brittle microfracturing prevails at low temperatures and fairly high deviatoric stresses, while upon increasing temperature and decreasing applied stress or longer time scales, the failure modes switch to transgranular and intergranular creep fractures. Accordingly, fluids play an active role and create their own pathways through facilitating shear localization by a process of time-dependent dissolution and precipitation creep, rather than being a passive constituent by simply following brittle fractures that are generated inside a shear zone caused by other localization mechanisms. We lay out a new theoretical approach for the design of new strategies to utilize, enhance and maintain the natural permeability in the deeper and hotter domain of geothermal reservoirs. The advantage of the approach is that, rather than engineering an entirely new EGS reservoir, we acknowledge a suite of creep-assisted geological processes that are driven by the current tectonic stress field. Such processes are particularly supported by higher temperatures potentially allowing in the future to target commercially viable combinations of temperatures and flow rates.