A Study on the Recovery and Classification of Meteorites from the Mt. Grove Region of Antarctica

The Antarctic Continent has become the largest natural preservatory of meteorites in the world because of its unique geographical position and climatic conditions. Mt. Grove is located in the inland area of the Antarctic Continent where the conditions are favorable for the preservation of meteorites. During China's 15th, 16th and 19th Antarctic Scientific Explorations a large number of meteorites were recovered in the Mt. Grove region. Especially during the 19th Exploration in 2002/03 a total of 4448 meteorites were recovered, which at one stroke put China among countries that have recovered most numbers of meteorites. Here, we report mainly the results of microscope and electron microprobe studies of 28 meteorites recovered during the 16th Exploration. The meteorites are chemically classified based on their mean Fa contents of olivine, mean Fs contents of low-Ca pyroxene and abundances of Fe-Ni metal. We also give a brief account of the meteorite recovery during the three Explorations and of some preli     

Biodiversity and distribution of benthic dinoflagellates in tropical Zhongsha Islands,South China Sea

Journal of Oceanology and Limnology - Benthic dinoflagellates have attracted increasing attention in recent years because of their toxicity and ability to form extensive harmful algal blooms....     

Hydrogeochemistry of karst groundwater for the environmental and health risk assessment: The case of the suburban area of Chongqing (Southwest China)

Karst groundwater is a vital resource for drinking, living and irrigation purposes in karst agricultural areas of the world. Due to the vulnerability of karst aquifers, surface pollutants are easily transferred to the subsurface and make karst groundwater be deteriorated, thereby restricting the rational exploitation of karst groundwater resource. In view of this, 49 karst groundwater samples were collected from spring (SW) and underground river (URW) sites in the suburban area of Chongqing City and analyzed for various hydrochemical components. Particularly, the karst groundwater quality was comprehensively uncovered by combining characteristics of hydrogeochemical evolution and health risks caused by nitrate and fluoride. The results revealed that the karst groundwater was slightly alkaline in nature and the water types were mainly characterized by Ca-HCO₃ accounting for 93.88% of the total samples due to the heavy dissolution of carbonate rock. The relatively high concentrations of Na⁺, SO₄^2? and NO₃^? up to 271.88 mg/L, 277.94 mg/L and 56.94 mg/L were over the corresponding maximum acceptable limits for drinking water, which can be predominately attributed to the emissions of industrial park, dissolution of gypsum and pyrite and excessive application of chemical fertilizers. Although agricultural activities were stopped and chemical fertilizers were no longer applied during the sampling period, long-term application of fertilizers have a persistent adverse effect on the karst groundwater NO₃^?. The pollution index of the karst groundwater (PIG) revealed that the low pollution and potential pollution zones were noticed in the northwestern parts of the study area. With respect of the SW, all the total hazard index (HI) values were below 1 suggesting no significant health risk. On the contrary, HI values of 0.11–1.16 for adults, 0.15–1.61 for children and 0.17–1.83 for infants in the URW indicated significant noncarcinogenic health risks. Particularly, infants and children were more vulnerable to karst groundwater NO₃^? than adults. Furthermore, the noncarcinogenic health risks of karst groundwater can be mainly attributed to NO₃^?, confirmed by the higher contribution ratio (66.55%) to the HI values. Therefore, special and targeted measures need to be taken to decrease the NO₃^? concentration in agricultural area.     

Influence of seismic wave type and incident direction on the dynamic response of tall concrete-faced rockfill dams

Owing to the stochastic behavior of earthquakes and complex crustal structure, wave type and incident direction are uncertain when seismic waves arrive at a structure. In addition, because of the different types of the structures and terrains, the traveling wave effects have different influences on the dynamic response of the structures. For the tall concrete-faced rockfill dam (CFRD), it is not only built in the complex terrain such as river valley, but also its height has reached 300 m level, which puts forward higher requirements for the seismic safety of the anti-seepage system mainly comprising concrete face slabs, especially the accurate location of the weak area in seism. Considering the limitations of the traditional uniform vibration analysis method, we implemented an efficient dynamic interaction analysis between a tall CFRD and its foundation using a non-uniform wave input method with a viscous-spring artificial boundary and equivalent nodal loads. This method was then applied to investigate the dynamic stress distribution on the concrete face slabs for different seismic wave types and incident directions. The results indicate that dam-foundation interactions behave differently at different wave incident angles, and that the traveling wave effect becomes more evident in valley topography. Seismic wave type and incident direction dramatically influenced stress in the face slab, and the extreme stress values and distribution law will vary under oblique wave incidence. The influence of the incident direction on slab stress was particularly apparent when SH-waves arrived from the left bank. Specifically, the extreme stress values in the face slab increased with an increasing incident angle. Interestingly, the locations of the extreme stress values changed mainly along the axis of the dam, and did not exhibit large changes in height. The seismic safety of CFRDs is therefore lower at higher incident angles from an anti-seepage perspective. Therefore, it is necessary to consider both the seismic wave type and incident direction during seismic capacity evaluations of tall CFRDs.     

三维激光扫描技术与断层面形貌量化分析在基岩区古地震研究中的应用

由于对第四纪地层的严重依赖,传统古地震探槽研究方法在基岩区难以发挥作用,导致无法获取基岩区断层的强震活动历史。本研究以山西地堑系的交城断裂为目标断裂,以断裂北段2处基岩断层面为研究对象,通过三维激光扫描技术获取基岩断层面高精度形貌,基于变差函数法结合滑动窗口操作量化断层表面形貌特征,开展在基岩区提取断裂古地震信息的实例研究。结果显示,2处基岩断层面的形貌在高度上具有明显的分段特征,指示了断层面在地震事件作用下的分段出露过程。这种断层面形貌分段特征可以用来识别古地震事件和同震位移量。在思西村基岩断层面上,识别出由老到新的3次古地震事件,同震倾滑位移量依次为2.0 m、1.9 m和2.3 m,在上兰镇基岩断层面上,识别出由老到新的3次古地震事件,同震倾滑位移量依次为1.4 m、2.5 m和2.0 m,指示了交城断裂北、中段具有产生同震位移量大于2 m、震级大于7.5级的破裂型地震的能力。上述研究成果表明,基于三维激光扫描和形貌量化分析方法开展基岩断层面古地震研究,可以准确而高效地识别古地震事件次数和同震位移量,扩展古地震的研究对象,拓宽古地震的研究空间。在未来的研究中,可以适时地开展宇宙成因核素测年以测定断层面的暴露年龄,获得发震年代,给予地震序列年龄框架。     

2022年1月中国大陆地区MS≥4.0地震震源机制解测定

本文利用中国地震台网记录的宽频带波形资料,采用近震全波形反演方法得到2022年1月1—31日发生在中国大陆地区的M_S≥4.0共13次地震的震源机制解。结果显示逆断型1次,走滑型9次,未知型3次。      

XRF半定量分析技术在矿石光片鉴定中的应用

偏光显微镜反光镜下鉴定金属矿物是最常用、最快捷有效的方法,然而鉴定结果容易受到鉴定者主观因素或磨片情况的影响。为了更快速、准确地在反光镜下鉴定矿物,利用XRF半定量分析技术快速、无损、前处理简单等特点,以及磨平抛光的矿石矿物在半定量分析过程中能较好地避免楔入效应和阴影效应的有利因素,采取了先用XRF半定量分析测得的结果去反推矿物,再在显微镜下鉴定矿物的方法。以多金属硫化物矿石、含铀多金属矿石及含微量铀的矿石样品为例进行鉴定,结果表明,在鉴定前知道光片上的元素及其质量分数,通过地球化学方法和经验法反推矿物,结合显微镜观察需要鉴定的矿物,可有效避免忽略掉透明/半透明矿物（锡石）、小粒径矿物（沥青铀矿）、易混淆矿物（铀黑）,提高光片鉴定工作的效率和准确性。