Search

Abstract Understanding the physical basics of tectonic events, related fluid flow and ore deposition represents one of the great challenges in modern geosciences. In this contribution, Sm-Nd ages of hydrothermal fluorites and U-Pb ages of carbonates and iron oxides from unconformity-related vein type deposits in the Schwarzwald next to the Upper Rhinegraben rift in SW Germany are used to distinguish different pulses of hydrothermal fluid activity and to understand their relation to large-scale tectonics and magmatism. While the fluorites are of Early Jurassic to Oligocene age, carbonate (calcite, dolomite, siderite) and hematite dated by U-Pb small-scale isochrons records formation from Permian to Quaternary with a clear culmination in the Neogene. These new age-data in combination with microthermometry data of primary fluid inclusions from growth zones in the fluorites and carbonates are used to constrain the timing of fluid signatures. This contribution shows that the ages are correlated with changes in fluid properties and/or tectonic events in the evolving continental crust. Comparison with published thermochronological data, apparent ages of URG-related volcanic rocks and the tectono-sedimentary evolution of the Upper Rhinegraben rift show clear correlations between the intensity of hydrothermal mineralization (and, hence, the intensity of fracture-bound fluid flow) with the U-Pb carbonate ages. This method accordingly provides an excellent tool to date rift-related processes like fluid flow, ore deposition and tectonic activation or reactivation of fractures. Fluid properties changed after the deposition of Middle Triassic Muschelkalk evaporites from low salinity, high temperature (1–6 wt.% NaCl eq , 200–270 °C, cooling late-metamorphic basement fluids) to high salinity, moderate temperature (20–26 wt.% (NaCl + CaCl 2), 50–170 °C, mixture of a modified bittern brine (“basement brine”) with halite dissolution brine). This change led to large scale ore deposition (fluorite-barite-quartz with Pb-Zn-Cu, Bi-Co-Ni-Ag-U, Fe-Mn ores). During the Paleogene and Neogene, previously separated aquifers from various sedimentary units were connected by juxtaposition of the fluid source rocks during Rhinegraben rifting, which resulted in variable salinity and temperature fluids (1–26 wt. % (NaCl + CaCl 2), 50–350 °C) by a multi-component fluid mixing process. Typical mineralization related to this shows barren or Pb-Zn-Cu veins with large amounts of barite. [ABSTRACT FROM AUTHOR]

Abstract: A magma supply system is identified in the upper crust beneath Aso caldera, Japan, appearing as a conductive anomaly via three‐dimensional electrical resistivity modeling. Aso caldera contains numerous postcaldera volcanoes, with Naka‐dake cone recently experiencing eruptions at the first crater, including an explosive eruption that ejected volcanic ash 11,000 m into the air in October 2016. The magma supply system imaged by the resistivity model consists of four key components: a magma reservoir at ~17 km depth that corresponds to the Conrad discontinuity, a magma‐filled crack‐propagation zone that extends obliquely from the magma reservoir, another magma reservoir centered at 6 km depth, and an upright crack‐intrusion zone at 2–4 km depth. The shape of the conductive anomaly is consistent with the regional stress regime, with the locations of the low‐velocity anomalies and a deformation source found beneath the caldera. This anomaly is therefore defined as the magma supply system, which feeds magma to the first crater of the Naka‐dake eruptions. The averaged melt fractions of the upper magma reservoir are estimated to be 3%–4% for 89.3 km3 of the reservoir and 96%–99% for 6.3 km3, with resistivity thresholds of <40 and <1 Ωm, respectively. Furthermore, the resistivity model detects three conductive anomalies in Aso caldera that are associated with an aqueous fluid‐flow system in the region. The resistivity model also suggests that the resistivity distribution can play an important role in characterizing the stress regime based on the distribution of earthquake clusters in the upper crust beneath the caldera. [ABSTRACT FROM AUTHOR]

Fluid mixing is an important process in the formation of many hydrothermal vein-type deposits. Here, we present evidence from hydrothermal fluorite-barite-quartz veins with Pb-Zn-Cu-(Ag)-sulfides and associated mineralization, indicating that mineral precipitation was initiated by mixing of fluids derived from multiple sources, including mixing between more than two end-member fluid compositions. Based on our observations, we relate the diversity of the hydrothermal veins of the Schwarzwald mining district in terms of mineral assemblage and fluid inclusion chemistry to the disturbed and transient geological environment during ongoing rifting. Literature data on the regional geology, current groundwater reservoirs, formation processes and hydraulic features are augmented by new fluid inclusion analyses from post-Cretaceous, hydrothermal vein minerals including microthermometry, crush leach, Microraman and LA-ICP-MS analyses of individual fluid inclusions. Petrography and microthermometry of fluid inclusions show complex sequences of alternating fluid signatures within different growth zones of one crystal. High (20–26 wt% NaCl + CaCl 2 ), moderate (5–20 wt% NaCl + CaCl 2 ) and low salinity (< 5 wt% NaCl + CaCl 2 ), sulfate- and/or CO 2 -bearing primary fluids were trapped during crystal growth. Such variations are commonly observed in minerals from different localities. Bulk crush leach analyses show significant variations in major element composition of the trapped fluids, within the overall Na-Ca-Cl-SO 4 -HCO 3 -system. These variations are caused by mixing of fluids from different aquifers and in various proportions. Ancient fluids show chemical similarities to modern groundwater aquifers that are available for direct sampling, such as granitic basement, Lower Triassic sandstones or Middle Triassic limestones and evaporites. Analyses of individual fluid inclusions by LA-ICP-MS support this interpretation and document the multi-component fluid mixing processes at individual localities recorded on the scale of single crystal growth zones. The latter data are used in a diffusion model to obtain the duration of mineral growth (before the fluid is homogenized), which implies very short-lived fluid events on the order of seconds to hours. By defining end member fluids and their proportions, we show that nearly all fluid mixtures are saturated with respect to barite. By contrast, fluorite-saturated fluids can only be modelled by mixing of a basement brine with fluids from Triassic sandstones. All fluid mixtures are strongly undersaturated with respect to galena, chalcopyrite and sphalerite, the most commonly observed ore minerals in the hydrothermal veins. As the calculated fluid mixtures are typically relatively oxidized and contain high sulfate/sulfide ratios, precipitation of sulfides was probably related to short-lived reduction events caused by an influx of hydrocarbons, by reactions with graphitic wall rocks in fractures by sulfidation related to fluid-rock reaction with the surrounding host rocks or an external influx of hydrocarbon-bearing fluids. The multi-aquifer fluid mixing processes involving aquifers of different chemical and physical constitution were triggered by brittle deformation related to rifting of the Rhine graben. This appears to be essential for the formation of a large number of mineralogically diverse hydrothermal ore deposits. [ABSTRACT FROM AUTHOR]

Fractures generated by internal fluid pressure, for example, dykes, mineral veins, many joints and man-made hydraulic fractures, are referred to as hydrofractures. Together with shear fractures, they contribute significantly to the permeability of fluid reservoirs such as those of petroleum, geothermal water, and groundwater. Analytical and numerical models show that – in homogeneous host rocks – any significant overpressure in hydrofractures theoretically generates very high crack tip tensile stresses. Consequently, overpressured hydrofractures should propagate and help to form interconnected fracture systems that would then contribute to the permeability of fluid reservoirs. Field observations, however, show that in heterogeneous and anisotropic, e.g., layered, rocks many hydrofractures become arrested or offset at layer contacts and do not form vertically interconnected networks. The most important factors that contribute to hydrofracture arrest are discontinuities (including contacts), stiffness changes between layers, and stress barriers, where the local stress field is unfavourable to hydrofracture propagation. A necessary condition for a hydrofracture to propagate to the surface is that the stress field along its potential path is everywhere favourable to extension-fracture formation so that the probability of hydrofracture arrest is minimised. Mechanical layering and the resulting heterogeneous stress field largely control whether evolving hydrofractures become confined to single layers (strata¬bound frac¬tures) or not (non-stratabound fractures) and, there¬fore, if a vertically intercon¬nec¬ted fracture system forms. Non-stratabound hydrofractures may propagate through many layers and generate interconnected fracture systems. Such systems commonly reach the percolation threshold and largely control the overall permeability of the fluid reservoirs within which they develop.

Surgical risk factors for periprosthetic joint infection (PJI) after total knee arthroplasty (TKA) are the subjects of ongoing research. It is unclear if there are specific locations of the surgical area that might act as a pathogen source. Due to the fact that bacterial replication occurs preferably under humid conditions, it was our aim to investigate if irrigation fluid reservoirs on the surgical covers are subject to bacterial colonization. We prospectively observed 40 patients with scheduled aseptic 1-stage TKA revision. At time intervals of 30 min, irrigation samples were tested for microbiological colonization. Additionally, the suction tip was investigated at the end of surgery. Overall, a bacterial detection rate of 25% was found (57/232 samples). Analysis for any positive microbial detection revealed pathogen findings of irrigation fluid in 41.7% of samples after 30 min with a constant increase up to 77.8% after 90 min. Twenty-three percent of suction tips showed bacterial colonization. Coagulase-negative staphylococci, accounting for the majority of PJI, were the predominant pathogens. After an average follow-up of 17 months, no PJI was confirmed. Despite the substantial bacterial load of irrigation fluid, PJI rates were not elevated. Nevertheless, we recommend that irrigation fluid reservoirs should be prevented and not withdrawn by suction. [ABSTRACT FROM AUTHOR]