Basic Geologic Problems of Loess in China

The geology of loess in China involves many problems. This paper deals only with the basic ones of the or-igin of loess. the geologic setting and palaeoenvironmental evolution leading to the formation of the Loess Pla-teau. and the regional stratigraphy of loess deposits. particularly the last problem. A better knowledge of theformation and development of the loess deposits in China has been obtained through analysis and correlationof lithostratigraphy. biostratigraphy, magnetostratigraphy. climatostratigraphy and chronostratigraphy.     

Advances in research of the time scales of porphyry deposits: A case study of the Yulong porphyry Cu-Mo deposit in the eastern TibetSCIEI北大核心CSCD

精确限定多期次岩浆-热液活动的时间尺度一直是剖析斑岩矿床形成过程的热点和难点。借助矿物的高精度同位素定年、热力学数值模拟以及石英的钛扩散模型等方法,斑岩矿床中岩浆-热液活动的时间尺度已经被限定在几万年之内。本文以三江特提斯超大型玉龙斑岩铜(钼)矿床为例,重点识别含矿热液脉中普遍存在的石英,利用钛元素的扩散年代学方法,精确限定斑岩矿床中多期岩浆-热液流体活动的时间尺度。扩散模型表明玉龙斑岩矿床热液活动的时间尺度为32000~870000年,有力支持了超大型斑岩矿床可以在几万至几十万年甚至更短时间内形成的观点。此外,为避免钛扩散模型产生较大的误差,需要在精确测定石英中钛含量的基础上,结合矿床地质背景或其他实验方法合理地估测温度和压力条件。研究认为,将矿物的高精度同位素定年与元素的扩散年代学相结合,可以在更为精细的尺度上完善斑岩矿床岩浆-热液活动的时间框架。     

The future of failure: stress or strain?

Strains in rocks can be observed but ancient stresses can only be inferred. We should re-examine the potential of strain geometry as the key to understanding and interpreting common shear structures ranging from faults to plastic shear zones. The concept of failure along zero extension directions can be applied to natural structures in rocks and is predicated on strain compatibility between differently strained volumes. Zero extension directions are considered for two strain configurations, plane strain (k=1) and uniaxial shortening (k=0). The crucial difference between shear fractures, or faults, and plastic yield zones is that the former are preceded by dilatation while the latter are isovolumetric. Volume changes during deformation affect the orientations of zero extension directions and hence of the resulting structures. With isovolumetric strain, yield occurs on planes at 45° to the principal shortening direction in plane strain and at 54.7° to this axis in uniaxial shortening. Uniaxial shortening experiments on rock samples allow estimation of the relative volumetric strains when yield zones initiate. When this volumetric strain is used to estimate the orientation of shear fractures in plane strain, ca 70° dips are predicted for normal faults at high crustal levels, decreasing downwards to 45°.     

Understanding the fate of iron in a modern temperate estuary: Leirárvogur,Iceland

Fluvial dissolved Fe concentrations decrease upon mixing with seawater, resulting in the formation of Fe-floccules. However, a clear understanding of the fate of these floccules has yet to be established. Assessing how tidal processes affect the formation of Fe-colloids in the Leirárvogur estuary, SW Iceland, is an important step in understanding the formation and potential deposition of estuarine Fe-rich minerals within this estuarine system. The Leirárvogur estuary drains predominately Fe-rich basalt, increasing the likelihood of detecting changes in Fe-phases. Fluvial waters and local lake waters that drain into the estuary were compared and the effects of seasonal changes were considered, in an attempt to understand how varying end-members and external factors play a role in Fe-rich mineral formation. Aqueous and colloidal Fe concentrations were found to be greater towards the head of the Leirárvogur estuary, suggesting that potential Fe-rich minerals and complexes are forming at sites of fluvial input. Increasing suspended colloidal Fe towards the estuary mouth suggests that Fe-colloids are readily transported seaward.     

Anatomy of a Cambrian suture in Gondwana: Pacific-type orogeny in southern India?

Southern India occupies a central position in the Late Neoproterozoic–Cambrian Gondwana supercontinent assembly. The Proterozoic mosaic of southern India comprises a collage of crustal blocks dissected by Late Neoproterozoic–Cambrian crust-scale shear/suture zones. Among these, the Palghat–Cauvery Suture Zone (PCSZ) has been identified as the trace of the Cambrian suture representing Mozambique Ocean closure during the final phase of amalgamation of the Gondwana supercontinent. Here we propose a model involving Pacific-type orogeny to explain the Neoproterozoic evolution of southern India and its final amalgamation within the Gondwana assembly. Our model envisages an early rifting stage which gave birth to the Mozambique Ocean, followed by the initiation of southward subduction of the oceanic plate beneath a thick tectosphere-bearing Archean Dharwar Craton. Slices of the ocean floor carrying dunite–pyroxenite–gabbro sequence intruded by mafic dykes representing a probable ophiolite suite and invaded by plagiogranite are exposed at Manamedu along the southern part the PCSZ. Evidence for the southward subduction and subsequent northward extrusion are preserved in the PCSZ where the orogenic core carries high-pressure and ultrahigh-temperature metamorphic assemblages with ages corresponding to the Cambrian collisional orogeny. Typical eclogites facies rocks with garnet + omphacite + quartz and diagnostic ultrahigh-temperature assemblages with sapphirine + quartz, spinel + quartz and high alumina orthopyroxene + sillimanite + quartz indicate extreme metamorphism during the subduction–collision process. Eclogites and UHT granulites in the orogenic core define P–T maxima of 1000 °C and up to 20 kbar. The close association of eclogites with ultramafic rocks having abyssal signatures together with linear belts of iron formation and metachert in several localities within the PCSZ probably represents subduction–accretion setting. Fragments of the mantle wedge were brought up through extrusion tectonics within the orogenic core, which now occur as suprasubduction zone/arc assemblages including chromitites, highly depleted dunites, and pyroxene bearing ultramafic assemblages around Salem. Extensive CO₂ metasomatism of the ultramafic units generated magnesite deposits such as those around Salem. High temperature ocean floor hydrothermal alteration is also indicated by the occurrence of diopsidite dykes with calcite veining. Thermal metamorphism from the top resulted in the dehydration of the passive margin sediments trapped beneath the orogenic core, releasing copious hydrous fluids which moved upward and caused widespread hydration, as commonly preserved in the Barrovian amphibolite facies units in the PCSZ. The crustal flower structure mapped from PCSZ supports the extrusion model, and the large scale north verging thrusts towards the north of the orogenic core may represent a fold-thrust belt. Towards the south of the PCSZ is the Madurai Block where evidence for extensive magmatism occurs, represented by a number of granitic plutons and igneous charnockite massifs of possible tonalite–trondhjemite–granodiorite (TTG) setting, with ages ranging from ca. 750–560 Ma suggesting a long-lived Neoproterozoic magmatic arc within a > 200 km wide belt. All these magmatic units were subsequently metamorphosed, when the Pacific-type orogeny switched over to collision-type in the Cambrian during the final phase of assembly of the Gondwana supercontinent. One of the most notable aspects is the occurrence of arc magmatic rocks together with high P/T rocks, representing the deeply eroded zone of subduction. The juxtaposition of these contrasting rock units may suggest the root of an evolved Andean-type margin, as in many arc environments the roots of the arc comprise ultramafic/mafic cumulates and the felsic rocks represent the core of the arc. The final phase of the orogeny witnessed the closure of an extensive ocean — the Mozambique Ocean — and the collisional assembly of continental fragments within the Gondwana supercontinent amalgam. The tectonic history of southern India represents a progressive sequence from Pacific-type to collision-type orogeny which finally gave rise to a Himalayan-type Cambrian orogen with characteristic magmatic, metasomatic and metamorphic factories operating in subduction–collision setting.     

Major factors influencing boron adsorption in sediments—a case study of modern sediments in Qinghai Lake

Because the boron (B) concentration in water has an apparent positive correlation with salinity, the B content adsorbed in sediments is often regarded as an important indicator to reconstruct the water salinity in a sedimentary environment. The premise of the quantitative reconstruction of paleosalinity is that the B uptake in sediments is proportional to the B concentration in water; however, the study showed that there is no direct relationship. The B absorption in sediments can be affected by both the content of the clay minerals and the total organic carbon content. The data from testing modern sediments and water samples in the Qinghai Lake show that a higher content in clay minerals is beneficial for B adsorption. Furthermore, the organic carbon from halophiles has a strong effect on the enrichment of B. Therefore, the organic carbon content in sediments should be considered when the paleosalinity of water is reconstructed using its B content. It is also thought that the Adams and Couch formulas are not suitable for reconstructing the salinity of water with a high organic carbon content in sediments because they consider only the effect of clay minerals on the adsorbed B without the contribution of organic carbon.     

Comparing the performance of base map scales in GIS-based avalanche simulation: a case study from Palandöken,Turkey

Snow avalanches are very complex and dynamic events that cause serious risk to human lives, infrastructure, and facilities in mountain environments. In this study, GIS-based avalanche simulations were investigated in terms of base map scale over the simulation sensitivity. Study area consisted of the avalanche region from Sultanseki Hill to Hodaklar Hill near the Palandöken skiing site in Erzurum, eastern part of Turkey. In analysis, 1:1,000 (field surveying), 1:5,000 (orthophoto) and 1:25,000 (standard topographic maps) scaled maps were used as base maps. The avalanche simulation was constructed by Triangulated Irregular Network (TIN) extracted from the base maps by using GIS-based ELBA+ simulation model. When 1:1,000-scaled map results were taken as reference simulations at 1:25,000-scaled maps, the best results for the potential area affected by avalanche and the maximum run-out distance were provided. Besides, using 1:5,000-scaled maps showed close correlation with the maximum track width, velocity, flow height, and pressure.     

Time scales and length scales in magma ?ow pathways and the origin ofmagmatic Ni-Cu-PGE ore deposits

Ore forming processes involve the redistribution of heat, mass and momentum by a wide range of processes operating at different time and length scales. The fastest process at any given length scale tends to be the dominant control. Applying this principle to the array of physical processes that operate within magma flow pathways leads to some key insights into the origins of magmatic Ni-Cu-PGE sulfide ore deposits. A high proportion of mineralised systems, including those in the super-giant Noril'sk-Talnakh camp, are formed in small conduit intrusions where assimilation of country rock has played a major role. Evidence of this process is reflected in the common association of sulfides with varitextured contaminated host rocks containing xenoliths in varying stages of assimilation. Direct incorporation of S-bearing country rock xenoliths is likely to be the dominant mechanism for generating sulfide liquids in this setting. However, the processes of melting or dissolving these xenoliths is relatively slow compared with magma flow rates and, depending on xenolith lithology and the composition of the carrier magma, slow compared with settling and accumulation rates. Chemical equilibration between sulfide droplets and silicate magma is slower still, as is the process of dissolving sulfide liquid into initially undersaturated silicate magmas. Much of the transport and deposition of sulfide in the carrier magmas may occur while sulfide is still incorporated in the xenoliths, accounting for the common association of magmatic sulfide-matrix ore breccias and contaminated "taxitic" host rocks. Effective upgrading of so-formed sulfide liquids would require repetitive recycling by processes such as reentrainment, back flow or gravity flow operating over the lifetime of the magma transport system as a whole. In contrast to mafic-hosted systems, komatiite-hosted ores only rarely show an association with externally-derived xenoliths, an observation which is partially due to the predominant formation of ores in lava flows rather than deep-seated intrusions, but also to the much shorter timescales of key component systems in hotter, less viscous magmas. Nonetheless, multiple cycles of deposition and entrainment are necessary to account for the metal contents of komatiite-hosted sulfides. More generally, the time and length scale approach introduced here may be of value in understanding other igneous processes as well as non-magmatic mineral systems.     

Geologic hazards along part of Al-sayl–Alkabeir Al-Jammum road in Saudi Arabia

 The geological hazards along part of Al-Sayl Alkabeir Al-Jammum road, western Saudi Arabia, were studied by the use of the sterographic projection to define the types of possible failures and the magnitude of safety factor on each slope face. The studied area consists of granite and granodiorite rocks that were cut by acidic and basic dikes. There are four sets of structural discontinuities which, besides a few strike slip faults, constitute the planes of weakness that lead to a variety of possible mode failures. The stability analysis indicates that sections of the road are unstable as their cut slopes exceed the maximum safe slope angles which range between 65° and 73°. Received: 16 June 1998 · Accepted: 2 March 1999     

Evaluation of retention properties of a semi-synthetic fractured block from modelling at performance assessment time scales (Äspö Hard Rock Laboratory, Sweden)

Modelling of radionuclide transport in fractured media is a primary task for safety evaluation of a deep nuclear waste repository. A performance assessment (PA) model has been derived from site characterization data with the aim of improving confidence for quantifying transport of sorbing radionuclides at a safety time scale of 10⁶ y. The study was conducted on a 200?×?200?×?200 m semi-synthetic fractured block, providing a realistic system derived from the Äspö Hard Rock Laboratory (Sweden) dataset. The block includes 5,632 fractures ranging from 0.5 to 100 m in length and a heterogeneous matrix structure (fracture coating, gouge, mylonite, altered and non-altered diorite). The PA model integrates steady-state flow conditions and transport of released radionuclides during the safety time scale. An original simulation method was developed involving Eulerian flow and transport within fracture planes with a mixed hybrid finite element scheme and a semi-analytical source term to account for heterogeneous matrix diffusion. Total mass flux of radionuclides (conservative to strongly sorbing) was computed. A method to simplify the system was demonstrated, leading to a major path of 12 fractures. This is mainly due to the low connectivity of the fracture network. Matrix diffusion and sorption proved to have major impact on block retention properties for PA conditions.     

Military uses of groundwater: a driver of innovation?

Military need has been a positive driver to the development of the modern day, and now mature, science of hydrogeology. The important synergy between geology and water supply was appreciated by military men in the mid-nineteenth century but the first real test of this learning only took place in the First World War. German, British and American geologists then mapped water resources and the potential for exploiting groundwater in Belgium and northern France. Technical innovations included deployment of rapid drilling techniques and the promotion of well screens for use in unconsolidated sediments. The mapping techniques were developed further during the Second World War when innovative remote mapping of enemy-occupied territory became an important planning tool to both Allied and German armies. Work in North Africa and other arid and semi-arid terrains promoted insight into the occurrence of groundwater in fresh-water aquifers little replenished by recharge. Mapping of hard rock basement-type environments in the islands of Jersey and Guernsey by German geologists was a concept new to the British Isles. Collectively, these varied initiatives provided part of the foundation for post-Second World War development of modern-day applied hydrogeology.     

Geologic?Features of Yongqu Iron Ore, Nierong County, North Tibet

Please?refer?to?the?attachment(s)?for?more?details.     

Geologic hazards of the Ocoña river valley,Peru and the influence of small-scale mining

Natural Hazards - The Ocoña River Valley, in the Arequipa Department in southern Peru, extends over 150 km from the Pacific coast to its headwaters in the Andes Mountains. While...     

Geochronology of Yanshanian Magmatism and Metamorphism in the Hinterland of the Dabie Mountains and Their Geologic Implications

A strong tectono-magmatic thermal event has been revealed by field observations of granitic, migmatiticand metamorphic rocks in the hinterland of the Dabie Mountains. K-Ar, Ar-Ar and Rb-Sr determinationsshow that the event took place 133-117 Ma ago (Yanshanian). Contemporaneously, a southwestwardthrust-type ductile shearing at multiple levels occurred in the lower crust or at even deeper levels, suggestingthat the Dabie Mountains region was still under the influence ot strong continent-continent overlappingtectonism of the Yangtze block under the Sino-Korean block at depth. Metamorphic rocks of amphibolitefacies, migmatites and deep structural deformations resulting from this tectonothermal event are now exposedto the surface. The present features of the Dabie Mountains thus have appeared only since ca. 100 Ma B.P. Theblock composed of the Dabie Group is not an uplift or shield which would have undergone a long-continuederosion.     

Interhemispheric radio-astrochronological calibration of the time scales from the Andean and the Tethyan areas in the Valanginian–Hauterivian (Early Cretaceous)

An integrated radio-astrochronological framework of the Agrio Formation in the Andean Neuquén Basin of west-central Argentina provides new constraints on the age and the duration of the late Valanginian through Hauterivian stratigraphic interval. A CA-ID TIMS U-Pb age of 126.97 ± 0.04(0.07)[0.15] Ma is presented here from the upper Hauterivian Agua de la Mula Member of the Agrio Formation. Biostratigraphic data from ammonoids and calcareous nannofossils and this high precision new radioisotopic age, together with three former ones from the same Agrio Formation are combined with new astrochronological data in the Andes. These are correlated with modern cyclostratigraphic studies in the classical sections of the Mediterranean Province of the Tethys, supporting detailed interhemispheric correlations for the Early Cretaceous. We also provide new δ¹³C data from the Agrio Formation which are compared with records from the classic Tethyan sections. According to our calibration, the minimum in the values in the mid-Hauterivian appears to be synchronous and, thus, another important stratigraphic marker for global correlation. A new duration of 5.21 ± 0.08 myr is calculated for the Hauterivian Stage, starting at 131.29 ± 0.19 Ma and ending at 126.08 ± 0.19 Ma. The difference between the duration of the Hauterivian in GTS2016 and in this study is 1.32 myr while the base and top of the GTS2016 Hauterivian differ respectively by 3.40 and 4.69 myr.     

A thousand years of loneliness? Globalization from the perspective of a city in a European periphery

Most cities face the challenge of increasing global and local change. Much of what has been said about cities in a globalized world has been concerned with large metropolitan cites. It has been postulated that increased competitiveness is the relevant response, and that urban governance has to change from managerialism to entrepeneurialism in order to cope with this challenge. The first part of the paper discusses some aspects of this body of theory, and the relevance for sub-national regional capitals. It also discusses how the scope of strategies depend on changing national and regional policies. The second part uses the case of Trondheim to discuss how these cities perceive and deal with globalization. Four policy options are discussed; the clientist strategy, the competitive strategy, the isolationist strategy and finally the option of doing nothing at all. The article concludes that global challenges will force local government in small cities to forge new strategies, but the preferred option is a clientist strategy rather than an entrepreneurial one, and the scope of strategy is national rather than global. Thus, when dealing with small peripheral cities and globalization, the range of perspectives must be extended beyond entrepreneurialism and competitiveness.     

The pK1 of TRISH+ in Na-K-Mg-Ca-Cl-SO4 brines—pH scales

The stoichiometric dissociation constant, pK¹ of TRISH⁺ has been determined in NaCl, KCl, MgCl₂ and CaCl₂ solutions to an ionic strength of 6 molal. The results have been used to derive Pitzer coefficients for the interactions of TRIS with Na⁺, K⁺, Mg²⁺ and Ca²⁺ ions. These results can be used to determine the pK¹ of TRISH⁺ in mixed brines which can be used to calibrate pH electrodes. Measurements of pK¹ of TRISH⁺ in mixtures of NaCl-MgCl₂, NaCl-CaCl₂, NaCl-Na₂SO₄, KCl-MgCl₂ and KCl-CaCl₂, artificial seawater and Dead Sea waters were made to determine the reliability of the Pitzer coefficients. The estimated values were found to be in good agreement with the measured values provided corrections were made for the interactions of H⁺ with SO²⁻₄. It now is possible to use dilute solutions of TRIS and TRISH⁺ to make buffers that can be used to make reproducible pH measurements in brines.     

Time scales and length scales in magma flow pathways and the origin of magmatic Ni–Cu–PGE ore deposits

Ore forming processes involve the redistribution of heat, mass and momentum by a wide range of processes operating at different time and length scales. The fastest process at any given length scale tends to be the dominant control. Applying this principle to the array of physical processes that operate within magma flow pathways leads to some key insights into the origins of magmatic Ni–Cu–PGE sulfide ore deposits. A high proportion of mineralised systems, including those in the super-giant Noril'sk-Talnakh camp, are formed in small conduit intrusions where assimilation of country rock has played a major role. Evidence of this process is reflected in the common association of sulfides with vari-textured contaminated host rocks containing xenoliths in varying stages of assimilation. Direct incorporation of S-bearing country rock xenoliths is likely to be the dominant mechanism for generating sulfide liquids in this setting. However, the processes of melting or dissolving these xenoliths is relatively slow compared with magma flow rates and, depending on xenolith lithology and the composition of the carrier magma, slow compared with settling and accumulation rates. Chemical equilibration between sulfide droplets and silicate magma is slower still, as is the process of dissolving sulfide liquid into initially undersaturated silicate magmas. Much of the transport and deposition of sulfide in the carrier magmas may occur while sulfide is still incorporated in the xenoliths, accounting for the common association of magmatic sulfide-matrix ore breccias and contaminated “taxitic” host rocks. Effective upgrading of so-formed sulfide liquids would require repetitive recycling by processes such as re-entrainment, back flow or gravity flow operating over the lifetime of the magma transport system as a whole. In contrast to mafic-hosted systems, komatiite-hosted ores only rarely show an association with externally-derived xenoliths, an observation which is partially due to the predominant formation of ores in lava flows rather than deep-seated intrusions, but also to the much shorter timescales of key component systems in hotter, less viscous magmas. Nonetheless, multiple cycles of deposition and entrainment are necessary to account for the metal contents of komatiite-hosted sulfides. More generally, the time and length scale approach introduced here may be of value in understanding other igneous processes as well as non-magmatic mineral systems.