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John Walter 《Journal of Historical Geography》1976,2(2):176-177
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Long‐term chemical evolution and modification of continental basement brines – a field study from the Schwarzwald,SW Germany
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Highly saline, deep‐seated basement brines are of major importance for ore‐forming processes, but their genesis is controversial. Based on studies of fluid inclusions from hydrothermal veins of various ages, we reconstruct the temporal evolution of continental basement fluids from the Variscan Schwarzwald (Germany). During the Carboniferous (vein type i), quartz–tourmaline veins precipitated from low‐salinity (<4.5wt% NaCl + CaCl2), high‐temperature (≤390°C) H2O‐NaCl‐(CO2‐CH4) fluids with Cl/Br mass ratios = 50–146. In the Permian (vein type ii), cooling of H2O‐NaCl‐(KCl‐CaCl2) metamorphic fluids (T ≤ 310°C, 2–4.5wt% NaCl + CaCl2, Cl/Br mass ratios = 90) leads to the precipitation of quartz‐Sb‐Au veins. Around the Triassic–Jurassic boundary (vein type iii), quartz–haematite veins formed from two distinct fluids: a low‐salinity fluid (similar to (ii)) and a high‐salinity fluid (T = 100–320°C, >20wt% NaCl + CaCl2, Cl/Br mass ratios = 60–110). Both fluids types were present during vein formation but did not mix with each other (because of hydrogeological reasons). Jurassic–Cretaceous veins (vein type iv) record fluid mixing between an older bittern brine (Cl/Br mass ratios ~80) and a younger halite dissolution brine (Cl/Br mass ratios >1000) of similar salinity, resulting in a mixed H2O‐NaCl‐CaCl2 brine (50–140°C, 23–26wt% NaCl + CaCl2, Cl/Br mass ratios = 80–520). During post‐Cretaceous times (vein type v), the opening of the Upper Rhine Graben and the concomitant juxtaposition of various aquifers, which enabled mixing of high‐ and low‐salinity fluids and resulted in vein formation (multicomponent fluid H2O‐NaCl‐CaCl2‐(SO4‐HCO3), 70–190°C, 5–25wt% NaCl‐CaCl2 and Cl/Br mass ratios = 2–140). The first occurrence of highly saline brines is recorded in veins that formed shortly after deposition of halite in the Muschelkalk Ocean above the basement, suggesting an external source of the brine's salinity. Hence, today's brines in the European basement probably developed from inherited evaporitic bittern brines. These were afterwards extensively modified by fluid–rock interaction on their migration paths through the crystalline basement and later by mixing with younger meteoric fluids and halite dissolution brines. 相似文献
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This paper examines changes in the commercial cleaning industry in Australasia which are occurring against a backdrop of significant transformation in the mode of labour market regulation in both countries. Specifically, whereas for most of the twentieth century both Aotearoa/New Zealand and Australia had systems of labour market regulation in which the state provided minimum wage and work protections through the interventions of arbitration courts, in the past few years these courts have either been abolished (in the case of New Zealand) or severely restricted in their ambit (in the case of Australia), all as part of a neoliberal effort to introduce “flexibility” into labour markets. The result has been an erosion of wages and a worsening of conditions of employment for cleaners and many other groups of workers. At the same time, this transformation in the architecture of labour market regulation poses significant challenges to unions seeking to represent cleaners and other low‐paid service sector workers. 相似文献
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Ancient Maya settlement patterns exhibit fractal geometry both within communities and across regions. Fractals are self-similar sets of fractional dimension. In this paper, we show how Maya settlement patterns are logically and statistically self-similar. We demonstrate how to measure the fractal dimensions (or Hausdorff–Besicovitch dimensions) of several data sets. We describe nonlinear dynamical processes, such as chaotic and self-organized critical systems, that generate fractal patterns. As an illustration, we show that the fractal dimensions calculated for some Maya settlement patterns are similar to those produced by warfare, supporting recent claims that warfare is a significant factor in Maya settlement patterning. 相似文献