Characteristics and planation surface formation environment of the red weathering crust in Hunan,Guangxi, Yunnan,Guizhou and Tibet

The characteristics of red karst weathering crust in the research region can be divided into three subtypes. The first one includes the silicon to aluminum ratio, the composition of the clay minerals, etc., and reflects the weak action of de-silicon and aluminum enrichment. The second one, for example the granularity, shows that the viscous action is strong. The third one, such as the CaCO₃ content and pH value, has regional difference in a large scale, which is consistent with the condition of modern scenery, so it is not important as for the ancient environment.

     

论中国盐溶角砾岩的特征和分类

中国的蒸发岩矿床非常丰富,与蒸发岩在成因上密切相关的盐溶角砾岩极其发育。本文简述了中国盐溶角砾岩的分布,总结了盐溶角砾岩的一般特征,划分出盐溶角砾岩的主要类型,探讨了盐溶角砾岩与盐泉的关系。     

Time scale of an early to mid-Paleozoic orogenic cycle of the long-lived Central Asian Orogenic Belt, Inner Mongolia of China: Implications for continental growth

We present a detailed, new time scale for an orogenic cycle (oceanic accretion–subduction–collision) that provides significant insights into Paleozoic continental growth processes in the southeastern segment of the long-lived Central Asian Orogenic Belt (CAOB). The most prominent tectonic feature in Inner Mongolia is the association of paired orogens. A southern orogen forms a typical arc-trench complex, in which a supra-subduction zone ophiolite records successive phases during its life cycle: birth (ca. 497–477 Ma), when the ocean floor of the ophiolite was formed; (2) youth (ca. 473–470 Ma), characterized by mantle wedge magmatism; (3) shortly after maturity (ca. 461–450 Ma), high-Mg adakite and adakite were produced by slab melting and subsequent interaction of the melt with the mantle wedge; (4) death, caused by subduction of a ridge crest (ca. 451–434 Ma) and by ridge collision with the ophiolite (ca. 428–423 Ma). The evolution of the magmatic arc exhibits three major coherent phases: arc volcanism (ca. 488–444 Ma); adakite plutonism (ca. 448–438 Ma) and collision (ca. 419–415 Ma) of the arc with a passive continental margin. The northern orogen, a product of ridge-trench interaction, evolved progressively from coeval generation of near-trench plutons (ca. 498–461 Ma) and juvenile arc crust (ca. 484–469 Ma), to ridge subduction (ca. 440–434 Ma), microcontinent accretion (ca. 430–420 Ma), and finally to forearc formation. The paired orogens followed a consistent progression from ocean floor subduction/arc formation (ca. 500–438 Ma), ridge subduction (ca. 451–434 Ma) to microcontinent accretion/collision (ca. 430–415 Ma); ridge subduction records the turning point that transformed oceanic lithosphere into continental crust. The recognition of this orogenic cycle followed by Permian–early Triassic terminal collision of the CAOB provides compelling evidence for episodic continental growth.     

碱消解-高效液相色谱-电感耦合等离子体质谱法测定生物样品中的甲基汞和乙基汞

建立了碱消解-高效液相色谱-电感耦合等离子体质谱联用系统测定生物样品中甲基汞(MeHg)与乙基汞(EtHg)的分析方法。为提高灵敏度,选用微流量的PFA雾化器,在优化的检测条件下,MeHg及EtHg检出限可达到0.036μg/L和0.03μg/L;线性范围达到4个数量级,两条工作曲线线性相关系数为1。对1.78μg/L MeHg、1.65μg/L EtHg的混合标准溶液重复测定7次,色谱峰面积的相对标准偏差(RSD)分别为1.79%和1.44%。对标准物质BCR 464(金枪鱼)的分析结果表明,测定值与标准值基本吻合,但略低于标准值;甲基汞和乙基汞的加标回收率分别为85.9%和84.5%。高效液相色谱与质谱联用技术的高灵敏度和低检出限能够满足生物样品中汞形态定量分析的要求。     

青海南部熔积岩的发现:对寻找VMS型矿床的重要启示

熔积岩指的是侵入、混合到未固结或弱固结的湿沉积物中的熔浆分解、原位形成的一类特殊岩石。正确地认识该类岩石,有利于增进人们对岩浆-水(沉积物)相互作用过程的理解,恢复古环境。在青海南部沱沱河地区发现了一套角砾为撕片状、锯齿状及浑圆状的安山岩,胶结物为铁硅质组合的特殊熔积岩。研究表明,该熔积岩的角砾为岩浆遇水后快速淬火、裂解的产物,铁硅质组合为海底喷气沉积形成的含铁建造;且安山岩与含铁建造发生混合时,含铁建造尚未固结。该套熔积岩的发现,改变了长期以来对开心岭铁矿为火山热液交代安山岩而形成的认识,对于在矿区寻找VMS型矿床、区域内寻找海底热水喷流沉积型矿床具有重要的启示意义。     

西藏驱龙斑岩铜钼矿床中UST石英的发现:初始岩浆流体的直接记录

单向固结结构(UST)是浅成侵位的岩浆出溶过程中形成的一种特殊结构,一般由梳状石英与细晶(斑岩)岩交互生长而成,少数产于斑岩与围岩接触部位,其内的原生包裹体被认为是初始流体出溶的可靠记录.作者在西藏驱龙铜矿床中首次发现了具有单向固结结构的石英.研究表明,驱龙UST石英存在于后期侵位的二长花岗斑岩与花岗闪长岩的接触部位,部分为高温β石英;UST石英中原生包裹体的成分主要为高盐度液相,除石盐子矿物外,还含有硬石膏等其他子矿物.阴极发光及显微测温结果表明,初始流体的出溶发生在高温(t≥573℃)、高压(P≥150～200 MPa)条件下,出溶的流体为高温、高盐度[w(NaCkeq)为44.5%～58%]流体,同时还具有较高的氧逸度.因形成压力较高,判断UST石英不可能由较浅侵位的二长花岗斑岩岩枝冷凝出溶而形成,从而推测驱龙铜矿床深部存在着孕育成矿斑岩的大型岩基.     

藏南白垩系黑-红层沉积岩有机质组成分布特征

对藏南江孜县床得剖面白垩系黑层和红层沉积岩进行的有机地球化学研究表明,黑层有机碳含量高于红层5～10倍,红层和黑层饱和烃主峰碳数分别为nC25和nC23;黑层和红层沉积有机质的母质来源都以水生植物和菌藻类等低等生物为主,陆源有机质的输入非常有限;但饱和烃的分布和主峰碳数的差异可能反映了有机母源物质在种群方面的差异,而这种差异可能主要是水体温度存在差异造成的,即红层发育时期水体温度可能高于黑层沉积时期.而在高温度条件下,水生生物和陆生植物的生长发育受到限制,造成原始有机质产率和有机质沉积保存量低可能是红层沉积岩形成的主要原因.     

Zircon U–Pb ages, Hf and O isotopes constrain the crustal architecture of the ultrahigh-pressure Dabie orogen in China

The crustal structure of the Dabie orogen was reconstructed by a combined study of U–Pb ages, Hf and O isotope compositions of zircons from granitic gneiss from North Dabie, the largest lithotectonic unit in the orogen. The results were deciphered from metamorphic history to protolith origin with respect to continental subduction and exhumation. Zircon U–Pb dating provides consistent ages of 751 ± 7 Ma for protolith crystallization, and two group ages of 213 ± 4 to 245 ± 17 Ma and 126 ± 4 to 131 ± 36 Ma for regional metamorphism. Majority of zircon Hf isotope analyses displays negative ε_Hf(t) values of − 5.1 to − 2.9 with crust Hf model ages of 1.84 to 1.99 Ga, indicating protolith origin from reworking of middle Paleoproterozoic crust. The remaining analyses exhibit positive ε_Hf(t) values of 5.3 to 14.5 with mantle Hf model ages of 0.74 to 1.11 Ga, suggesting prompt reworking of Late Mesoproterozoic to Early Neoproterozoic juvenile crust. Zircon O isotope analyses yield δ¹⁸O values of − 3.26 to 2.79‰, indicating differential involvement of meteoric water in protolith magma by remelting of hydrothermally altered low δ¹⁸O rocks. North Dabie shares the same age of Neoproterozoic low δ¹⁸O protolith with Central Dabie experiencing the Triassic UHP metamorphism, but it was significantly reworked at Early Cretaceous in association with contemporaneous magma emplacement. The Rodinia breakup at about 750 Ma would lead to not only the reworking of juvenile crust in an active rift zone for bimodal protolith of Central Dabie, but also reworking of ancient crust in an arc-continent collision zone for the North Dabie protolith. The spatial difference in the metamorphic age (Triassic vs. Cretaceous) between the northern and southern parts of North Dabie suggests intra-crustal detachment during the continental subduction. Furthermore, the Dabie orogen would have a three-layer structure prior to the Early Cretaceous magmatism: Central Dabie in the upper, North Dabie in the middle, and the source region of Cretaceous magmas in the lower.     

Case history of controlling a landslide at Panluo open-pit mine in China

Controlling of landsides safely and economically is a great challenge to mine operators because landslides are major geological problems especially in open-pit mines. In this paper, a case history at Panluo open-pit mine is presented in detail to share the experiences and lessons with mine operators. Panluo open-pit mine is located in the southwestern Fujian province of China. It is the largest open-pit iron mine in the Fujian province and was planned in 1965 and is in full operation from 1978. In July 1990, an earthquake of magnitude 5.3 in Taiwan Strait and big rainstorms impacted the mine slope, causing tension cracks and rather large-scale failures, and forming a U-shaped landslide. Total potential volume was estimated to be up to 1.0 × 10⁶ m³. This directly threatened the mine production. In order to protect the mine production and the dwellers’ safety around, a dynamic comprehensive method was implemented including geotechnical investigations, in-situ testing and monitoring, stability analysis, and many mitigation and preventive measures. These measures slowed down the development and further occurrence of the landslide. The results showed that the landslides were still active, it was slowed with the control measures and moved rapidly with rainfall and mining down. However, no catastrophic accidents occurred and the pit mining was continued till it was closed at the elevation of 887 m in 2000. As a successful case of landslide control at an open-pit mine for 10 years, this paper reports the controlling measures in details. These experiences of landslide control may be beneficial to other similar mines for landslide control.     

Assessment of frozen-ground conditions for engineering geology along the Qinghai–Tibet highway and railway, China

The Qinghai–Tibet Highway and Railway (the Corridor) across the Qinghai–Tibet Plateau traverses 670 km of permafrost and seasonally frozen-ground in the interior of the Plateau, which is sensitive to climatic and anthropogenic environmental changes. The frozen-ground conditions for engineering geology along the Corridor is complicated by the variability in the near-surface lithology, and the mosaic presence of warm permafrost and talik in a periglacial environment. Differential settlement is the major frost-effect problem encountered over permafrost areas. The traditional classification of frozen ground based on the areal distribution of permafrost is too generalized for engineering purposes and a more refined classification is necessary for engineering design and construction. A proposed classification of 51 zones, sub-zones, and sections of frozen ground has been widely adopted for the design and construction of foundations in the portion of the Corridor studied. The mean annual ground temperature (MAGT), near-surface soil types and moisture content, and active faults and topography are most commonly the primary controlling factors in this classification. However, other factors, such as local microreliefs, drainage conditions, and snow and vegetation covers also exert important influences on the features of frozen ground. About 60% of the total length of the Corridor studied possesses reasonably good frozen-ground conditions, which do not need special mitigative measures for frost hazards. However, other sections, such as warm and ice-rich or -saturated permafrost, particularly in the sections in wetlands, ground improvement measures such as elevated land bridges and passive or proactive cooling techniques need to be applied to ensure the long-term stability of thermally unstable, thick permafrost subsoils, and/or refill with non-frost-susceptible soils. Due to the long-history of the construction and management of the Corridor by various government departments, adverse impacts of construction and operation on the permafrost environment have been resulted. It is recommended that an integrated, executable plan for the routing of major construction projects within this transportation corridor be established and long-term monitoring networks installed for evaluating and mitigating the impact from anthropogenic and climatic changes in frozen-ground conditions.