Thermal waters of ‘tectonic origin’: the alkaline,Na‐HCO3 waters of the Rio Valdez geothermal area (Isla Grande de Tierra del Fuego,Argentina)

The geothermal area of Rio Valdez is located in the central portion of the Isla Grande de Tierra del Fuego (South Argentina), ten kilometers south of the southeastern sector of the Fagnano Lake. It consists of a series of thermal springs with low discharge rates (≤1 L/s) and temperatures in the range of 20–33°C distributed in an area of <1 km². The thermal springs are characterized by alkaline, Na‐HCO₃ waters with low salinity (0.53÷0.58 g/L), but relatively high fluoride contents (up to 19.4 mg/L). Their composition is the result of a slow circulation at depth, possibly through deep tectonic discontinuities connected with the Magallanes‐Fagnano Fault (MFF) system. According to geothermometric calculations, thermal waters reach temperatures in the range of 100–150°C and an almost complete chemical equilibrium with the alkali‐feldspars in the metavolcanic country rocks. The relatively high fluorine contents can be explained by the slow ascent and cooling of deep groundwaters followed by a progressive re‐equilibration with F‐bearing, hydrated Mg‐silicates, such as chlorite, which has been recognized as an abundant mineral in the metavolcanics of the Lemaire Formation and metapelites and metagraywackes of the Yahgán Formation. Finally, the isotopic composition of the investigated samples is consistent with the infiltration from local snow melting at altitudes in the range of 610–770 m asl. The comparison of our data with those collected in 1991 seems to suggest a possible progressive decline of the bulk thermal output in the near future. This possibility should be seriously considered before planning a potentially onerous exploitation of the resource. Presently, the only ways to exploit this geothermal resource by the population scattered in the area are the direct use of thermal waters and/or spa structures.     

中国史前玉文化板块论

中国史前玉器有着长达6000余年的历史,遍布东、北、西、南各地,组成相对独立发展的群体及其玉文化区域。其历经玉兵器、玉美器、玉神器以及早期“王室玉”等若干阶段的演进和积淀,为华夏文明的创造奠基了第一块坚实的基石。本文采纳地质学上的“板块”一词以概括说明史前玉文化的宏观性质及其微观特点,史前玉文化板块分为东夷玉文化板块、淮夷玉文化板块、古越玉文化板块等三大玉板块以及海岱玉文化东夷亚板块、陶寺玉文化华夏亚板块、石峁玉文化鬼国亚板块、齐家玉文化氐羌亚板块和石家河玉文化荆蛮亚板块等五个文化亚板块。它们按自身规律运动又互为碰撞、渗透、并存以至融合,终于走向其归宿,熔铸为统一的中华玉文化。     

Salt tectonics and shallow subseafloor fluid convection: models of coupled fluid‐heat‐salt transport

Thermohaline convection associated with salt domes has the potential to drive significant fluid flow and mass and heat transport in continental margins, but previous studies of fluid flow associated with salt structures have focused on continental settings or deep flow systems of importance to petroleum exploration. Motivated by recent geophysical and geochemical observations that suggest a convective pattern to near‐seafloor pore fluid flow in the northern Gulf of Mexico (GoMex), we devise numerical models that fully couple thermal and chemical processes to quantify the effects of salt geometry and seafloor relief on fluid flow beneath the seafloor. Steady‐state models that ignore halite dissolution demonstrate that seafloor relief plays an important role in the evolution of shallow geothermal convection cells and that salt at depth can contribute a thermal component to this convection. The inclusion of faults causes significant, but highly localized, increases in flow rates at seafloor discharge zones. Transient models that include halite dissolution show the evolution of flow during brine formation from early salt‐driven convection to later geothermal convection, characteristics of which are controlled by the interplay of seafloor relief and salt geometry. Predicted flow rates are on the order of a few millimeters per year or less for homogeneous sediments with a permeability of 10^?15 m², comparable to compaction‐driven flow rates. Sediment permeabilities likely fall below 10^?15 m² at depth in the GoMex basin, but such thermohaline convection can drive pervasive mass transport across the seafloor, affecting sediment diagenesis in shallow sediments. In more permeable settings, such flow could affect methane hydrate stability, seafloor chemosynthetic communities, and the longevity of fluid seeps.     

SEISMIC HAZARD ASSESSMENT OF UNITED ARAB EMIRATES AND ITS SURROUNDINGS

This paper presents the seismic hazard assessment and seismic zoning of the United Arab Emirates (UAE) and its surroundings based on the probabilistic approach. The area that has been studied lies between 50°E-60°E and 20°N-30°N and spans several Gulf countries. First, the tectonics of the area and its surroundings is reviewed. An updated catalogue, containing both historical and instrumental events is used. Seismic source regions are modelled and relationships between earthquake magnitude and earthquake frequency is established. A modified attenuation relation for Zagros region is adopted. Seismic hazard assessment is then carried out for 20 km interval grid points. Seismic hazard maps of the studied area based on probable Peak Ground Acceleration (PGA) for 10% probability of exceedance for time-spans of 50, 100 and 200 years are shown. A seismic zone map is also shown for a 475-year return period. Although the results of the seismic hazard assessment indicated that UAE has moderate to low seismic hazard levels, nevertheless high seismic activities in the northern part of UAE warrant attention. The northern Emirates region is the most seismically active part of UAE. The PGA on bedrock in this region ranges between 0.22 g for a return period of 475 years to 0.38 g for a return period of 1900 years. This magnitude of PGA, together with amplification from local site effect, can cause structural damage to key structures and lifeline systems.