Some of the tridymite in the monomict Northwest Africa (NWA) 11591 eucrite are found to have sulfide‐rich replacement textures (SRTs) to varying degrees. The SRTs of tridymite in NWA 11591 are characterized by the distribution of loose porous regions with aggregates of quartz and minor troilite grains along the rims and fractures of the tridymite, and we propose a new mechanism for the origin of this texture. According to the volume and density conversion relationship, the quartz in the SRT of tridymite with a hackle fracture pattern was transformed from tridymite. We suggest that the primary tridymite grains are affected by the S‐rich vapors along the rims and fractures, leading to the transformation of tridymite into quartz. In addition, the S‐rich vapors reacted with Fe2+, which was transported from the relict tridymite and/or the adjacent Fe‐rich minerals, and/or the S‐rich vapors react with the exotic metallic Fe to form troilite grains. The sulfurization in NWA 11591 most likely occurred during the prolonged subsolidus thermal metamorphism in the shallow crust of Vesta and might be an open, relatively high temperature (>800 °C) process. Sulfur would be an important component of the metasomatic fluid on Vesta. 相似文献
Fifty cases of regional yearly extreme precipitation events(RYEPEs)were identified over the Yangtze-Huaihe River Valley(YHRV)during 1979–2016 applying the statistical percentile method.There were five types of RYEPEs,namely Yangtze Meiyu(YM-RYEPE),Huaihe Meiyu(HM-RYEPE),southwest-northeast-oriented Meiyu(SWNE-RYEPE)and typhoon I and II(TC-RYEPE)types of RYEPEs.Potential vorticity diagnosis showed that propagation trajectories of the RYEPEs along the Western Pacific Subtropical High and its steering flow were concentrated over the southern YHRV.As a result,the strongest and most frequently RYEPEs events,about 16–21 cases with average rainfall above 100 mm,occurred in the southern YHRV,particularly in the Nanjing metropolitan area.There have been 14 cases of flood-inducing RYEPEs since 1979,with the submerged area exceeding 120 km~2as simulated by the Flood Area hydraulic model,comprising six HM-RYEPEs,five YM-RYEPEs,two TC-RYEPEs,and one SWNE-RYEPE.The combination of evolving RYEPEs and rapid expansion of urban agglomeration is most likely to change the flood risk distribution over the Nanjing metropolitan area in the future.In the RCP6.0(RCP8.5)scenario,the built-up area increases at a rate of about 10.41 km~2(10 yr)~(-1)(24.67 km~2(10 yr)~(-1))from 2010 to 2100,and the area of high flood risk correspondingly increases from 3.86 km~2(3.86 km~2)to 9.00 km~2(13.51 km~2).Areas of high flood risk are mainly located at Chishan Lake in Jurong,Lukou International Airport in Nanjing,Dongshan in Jiangning District,Lishui District and other low-lying areas.The accurate simulation of flood scenarios can help reduce losses due to torrential flooding and improve early warnings,evacuation planning and risk analysis.More attention should be paid to the projected high flood risk because of the concentrated population,industrial zones and social wealth throughout the Nanjing metropolitan area. 相似文献
The food consumption and ecological conversion efficiency of a species marine pelagic andsmall size fish, Hyporhamphus sajori, were determined by using in situ stomach content method presented by Eggers. The results showed that: (1) the fish was taken in food all day, so empty-stomach rate was very low, taking up about 4.5% of the total determined fish number. However, the fish still has significant daily feeding rhythm. A feeding peak was found 0:00 o'clock at night, but feeding level was always high in the daytime; (2) relationship between instantaneous food content in stomach and corresponding time could be described as S_t = a ·e ~(-b ·t). There was not significant difference of instantaneous gastric evacuation rate between two determinations, with average value being 0.13 × 10~(-2)g/ (g·d) (wet weight); (3) the daily food consumption tended to change in irregular waving form, with average value being (10.16×l0~(-2)±1.19×l0~(-2) g/ (g·d) (wet weight) or (55.56 × 10~(-2) ±6.51 × 10~(-2) kJ/ 相似文献