Geomorphic natural hazard on loess terrain: expansion on the gully sidewall

Natural Hazards - Gully sidewall expansion is an important geomorphic natural hazard, and the expansion destroys a large extent of agricultural land in the loess regions every year. The main aim of...     

Granite is an Effective Helium Source Rock: Insights from the Helium Generation and Release Characteristics in Granites from the North Qinling Orogen,China

Global helium(He) shortage is a challenging problem; however, the types of helium source rock and the mechanisms of He generation and release therein remain still poorly understood. In this study, in order to evaluate the potential of granite as an effective helium source rock, we collected granitic samples from the North Qinling Orogen, Central China, in the south of the helium-rich Weihe Basin. The helium generation and release behaviors in granite were studied through analysis of U and Th concentrations, EMPA images, and He and Ar concentrations and isotopic ratios extracted by crushing and stepwise heating. The results indicate that Ar has a better retention and a lower mobility than He. 3 He/4 He ratios released by crushing and stepwise heating are 0.016–0.056 RA and 0.003–0.572 RA, respectively, where RA is the atmospheric 3 He/4 He of 1.4×10-6, reflecting a crustal and radiogenic source. Helium concentrations extracted by the two ways are 0.13–0.95 ucm3 STP/g and 7.82–115.62 ucm3 STP/g, respectively, suggesting that matrix-sited He accounts for more than 98% of total helium preserved in granite. In addition, the total generated He amounts in granites are calculated based on the measured U and Th concentrations in granitic samples. Dividing the preserved He quantities by the generated He amounts, it turned out that less than 10% of He produced since the formation of the granite is preserved in the rock over geological time, suggesting that more than 90% generated He can be transferred to the Weihe Basin. Temperature and fracture are the two critical factors controlling He release. Based on the relationship between He diffusivity of granites and temperature and the He closure temperatures of a variety of U-and Th-rich minerals(27–250°C), we estimate that He can be partially released out of granite at the depths 400 m and totally released at the depths 7800 m. Fractures provide effective transfer of free He from deep source rocks to shallow reservoirs. Finally, a model on granite as an effective helium source rock is established. We suggest exploring He resources in hydrocarbon basins with granitic basement(or adjacent to granite bodies), high geothermal field, and young active fractures.     

复杂3D瞬变电磁场FDTD模拟中需要解决的问题

为了实现缓变瞬态电磁场的时域有限差分(FDTD)模拟,引入了虚拟位移电流,使FDTD随时间步的递推能够进行。在以往较简单模型的计算中,利用时域瞬变场传播需要时间的性质,可将激励源化为初始条件代入,但是对于复杂3D模型,原有的方法不再适用,应当重新考虑源和边界条件的处理方法。由于实际源带有“斜坡”,故可采取将激励源模拟注入的方式;地下边界根据电磁波在导电媒质中快速衰减的特性设定,将改进的完全匹配层用于空中边界。分析表明,对于由空中和地下区域非均匀网格离散引起的时间稳定性问题,交替方向隐式FDTD是可行的解决办法。      

A Review of Study on Fe-C Interaction and Their Adsorption Properties to Soil Heavy Metal

Nowadays, the Fe-C coprecipitate mechanism is recognized by more and more scholars and becomes the hot topic in the environmental science. On the basis of discussing the interaction between iron oxide and organic matter, and the adsorption research progress of Fe-C complexes on heavy metals, the immobilization potential of Fe-C complexes on heavy metals in polluted soil were illustrated. The surface properties and physical characterizations of iron oxide are changed regularly with the interaction of organic matter, which lead to the higher adsorption capacity of Fe-C complexes in contrast to single iron oxide. Besides, the influences of pH values, organic matter types and surface properties of iron oxides on the adsorption capacity of Fe-C complexes on heavy metals were discussed. The excellent adsorption performance of Fe-C complexes in certain conditions will provide important theoretical basis for contaminated soil remediation.     

煎茶岭镍矿床成矿作用特征

煎岭镍矿与同类矿床相比,具有特殊的地质、地球化学物征，是一种特殊类型镍矿。本矿床流体包裹体同位素特征，表现出成矿体为岩浆与地层两端元混合趋势，成矿流体分属于Mg2+-Ca2+-Na+-F-(Cl-)型。根据 Pb、Sr、O、H、C 同位素及 REE资料，作者认为该镍矿的形成与后期酸性岩浆活动有密切关系，后期岩浆活动为成矿提供热力与热液，使成矿元素活化迁移、富集。本文最后提出了初步的成矿模式。     

山西天镇晚白垩世——新恐龙动物君及其地层意义

新发现的山西天镇恐龙动物群是以巨龙类（titanosaurids）和甲龙类（ankylosaurids）为代表，含有鸭嘴龙类及兽脚类化石，其中一具何存较完整的巨龙类骨架（已获骨骼近70%）包括3个甲龙头骨及其头后骨骼.该动物君化石相当丰富，经与蒙古、印度、老挝、加拿大、美国和阿根廷等国晚白垩世恐龙动物君的比较我，实属晚白垩世较为罕见的一新恐龙动物群。由于天镇恐龙动物群的发现不仅将原划归始新世的灰泉堡组的时代归属晚白垩世，而且对白垩系划分和探讨恐龙的分类、演化、迁徒、动物地理区及其绝灭等方面的研究均具有重要意义。     

花岗岩的成岩时代、地球化学特征和成因青海祁漫塔格地区虎头崖矿床Ⅵ矿带

利用 LA ICP MS 锆石 U Pb 法,测得与成矿有关的青海祁漫塔格地区虎头崖矿床Ⅵ矿带花岗岩的成岩年龄为(233.6±1.8)Ma(MSWD=1.2,n=17)。地球化学特征显示：花岗岩属高钾钙碱性、弱过铝质花岗岩;样品的稀土元素组成以总体右倾,轻、重稀土分异明显和具明显的负铕异常为特征;微量元素具有富集 Rb、Th、U、La、Nd 等大离子亲石元素,亏损 Ba、Sr、Nb、P、Ti 等元素的特点。Sr Nd 同位素组成特征显示,花岗岩的源区可能是富集岩石圈地幔。初步研究认为,虎头崖矿床Ⅵ矿带花岗岩可能形成于中、晚三叠世碰撞后碰撞的构造背景下。