Seasonal effects on geophysical–geotechnical relationships and their implications for electrical resistivity tomography monitoring of slopes

Current assessments of slope stability rely on point sensors, the results of which are often difficult to interpret, have relatively high costs and do not provide large-area coverage. A new system is under development, based on integrated geophysical–geotechnical sensors to monitor groundwater conditions via electrical resistivity tomography. So that this system can provide end users with reliable information, it is essential that the relationships between resistivity, shear strength, suction and water content are fully resolved, particularly where soils undergo significant cycles of drying and wetting, with associated soil fabric changes. This paper presents a study to establish these relationships for a remoulded clay taken from a test site in Northumberland, UK. A rigorous testing programme has been undertaken, integrating the results of multi-scalar laboratory and field experiments, comparing two-point and four-point resistivity testing methods. Shear strength and water content were investigated using standard methods, whilst a soil water retention curve was derived using a WP4 dewpoint potentiometer. To simulate seasonal effects, drying and wetting cycles were imposed on prepared soil specimens. Results indicated an inverse power relationship between resistivity and water content with limited hysteresis between drying and wetting cycles. Soil resistivity at lower water contents was, however, observed to increase with ongoing seasonal cycling. Linear hysteretic relationships were established between undrained shear strength and water content, principally affected by two mechanisms: soil fabric deterioration and soil suction loss between drying and wetting events. These trends were supported by images obtained from scanning electron microscopy.     

A new spin on ‘non-rotating’ porphyroblasts: implications of cleavage refraction and reference frames

It has been claimed that rigid porphyroblasts which grow before or during folding and concurrent cleavage development do not rotate with respect to the geographical reference frame (GRF), even if the straining is non-coaxial (Bell, 1985, Bell and Johnson, 1990). The explanation offered is based on strain partitioning. It is argued that the initial orientations of early fabrics included as internal foliations (S_i) in the porphyroblasts have been preserved after polyphase deformation, and even after successive orogenies. According to the strain partitioning model, the porphyroblasts are fixed in domains of coaxial straining (microlithons) and are isolated from the non-coaxial straining associated with the enveloping septa (S_e). This hypothesis, and also its discussions both pro and contra, suffer from insufficient attention to reference frames. We therefore attempt to demonstrate: (a) the need for rigorous treatment of reference frames in geological interpretations; (b) that, in a folding situation, grains that do not rotate with respect to their immediate matrix generally rotate with respect to the GRF; (c) that lack of porphyroblast rotation with respect to the GRF demands a rare folding mechanism (slip fold model); and (d) that the non-rotation hypothesis is in conflict with heterogeneous deformation (cleavage refraction). Finally, we question the validity of the evidence in a study by Fyson (1980), cited in support of non-rotation with respect to the GRF during folding. Fyson reported orientations of S_i that are constant, after folding, over a large area; this scenario is a product of selective data acquisition. In summary, our investigation shows that the lack of porphyroblast rotation with respect to a GRF during folding, while possible, is not universal. The development of microstructures (e.g. curved S_i) is only related to the local deformation path, the characterisation of which does not rely on the GRF.     

Influence of hydrogen on Fe–Mg interdiffusion in (Mg,Fe)O and implications for Earth’s lower mantle

Interdiffusion of Fe and Mg in (Mg,Fe)O has been investigated experimentally under hydrous conditions. Single crystals of MgO in contact with (Mg_0.73Fe_0.27)O were annealed hydrothermally at 300 MPa between 1,000 and 1,250°C and using a Ni–NiO buffer. After electron microprobe analyses, the dependence of the interdiffusivity on Fe concentration was determined using a Boltzmann–Matano analysis. For a water fugacity of ∼300 MPa, the Fe–Mg interdiffusion coefficient in Fe _x Mg_1−x O with 0.01 ≤ x ≤ 0.25 can be described by with and C = −80 ± 10 kJ mol⁻¹. For x = 0.1 and at 1,000°C, Fe–Mg interdiffusion is a factor of ∼4 faster under hydrous than under anhydrous conditions. This enhanced rate of interdiffusion is attributed to an increased concentration of metal vacancies resulting from the incorporation of hydrogen. Such water-induced enhancement of kinetics may have important implications for the rheological properties of the lower mantle.

Equilibrium and kinetic Si isotope fractionation factors and their implications for Si isotope distributions in the Earth’s surface environments

Several important equilibrium Si isotope fractionation factors among minerals, organic molecules and the H₄SiO₄ solution are complemented to facilitate the explanation of the distributions of Si isotopes in Earth’s surface environments. The results reveal that, in comparison to aqueous H₄SiO₄, heavy Si isotopes will be significantly enriched in secondary silicate minerals. On the contrary, quadra-coordinated organosilicon complexes are enriched in light silicon isotope relative to the solution. The extent of ²⁸Si-enrichment in hyper-coordinated organosilicon complexes was found to be the largest. In addition, the large kinetic isotope effect associated with the polymerization of monosilicic acid and dimer was calculated, and the results support the previous statement that highly ²⁸Si-enrichment in the formation of amorphous quartz precursor contributes to the discrepancy between theoretical calculations and field observations. With the equilibrium Si isotope fractionation factors provided here, Si isotope distributions in many of Earth’s surface systems can be explained. For example, the change of bulk soil δ³⁰Si can be predicted as a concave pattern with respect to the weathering degree, with the minimum value where allophane completely dissolves and the total amount of sesqui-oxides and poorly crystalline minerals reaches their maximum. When, under equilibrium conditions, the well-crystallized clays start to precipitate from the pore solutions, the bulk soil δ³⁰Si will increase again and reach a constant value. Similarly, the precipitation of crystalline smectite and the dissolution of poorly crystalline kaolinite may explain the δ³⁰Si variations in the ground water profile. The equilibrium Si isotope fractionations among the quadra-coordinated organosilicon complexes and the H₄SiO₄ solution may also shed light on the Si isotope distributions in the Si-accumulating plants.     

Sulphur isotope patterns from the Bleiberg deposit (Eastern Alps) and their implications for genetically affiliated lead–zinc deposits

Summary A set of 354 sulphur isotope data from the Bleiberg deposit, the type deposit of Alpine low temperature carbonate hosted Pb–Zn deposits (APT deposits), is critically evaluated applying statistical methods. The sulphur isotope patterns vary significantly among the ore horizons. This suggests a long lasting and polyphase mineralisation system. The sulphur isotope composition of barite corresponds to that of Carnian seawater (i.e. 16 ³⁴S). The ³⁴S values of the iron sulphides correspond to data from sedimentary iron sulphides. Pb and Zn sulphides are characterized by three normally distributed ³⁴S populations with mean values of –6 to –8, –13 to –18, and –25 to –29. Heavy sulphur (>–10 ³⁴S) indicates contribution of sulphide sulphur from epigenetic-hydrothermal fluids, whereas light sulphide sulphur (<–21 ³⁴S) was produced by sulphur – reducing bacteria. The intermediate population is explained by mixing of sulphur derived from these two sources. Other sources of local importance, however, can not be excluded. The isotope populations correspond only partly to the paragenetic ore stages. The sulphur isotope patterns in the APT deposits are regionally different. Data from other low-temperature sediment-hosted Pb–Zn deposits support the proposed interpretation. A comparison demonstrates that the sulphur isotope patterns of APT deposits correspond to patterns of the Irish type deposits, but are different to those of Mississippi Valley type deposits.Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1007/s00710-004-0071-3     

First SHRIMP U–Pb zircon dating of granulites from the Kontum massif (Vietnam) and tectonothermal implications

The Kontum massif in Central Vietnam represents the largest continuous exposure of crystalline basement of the Indochina craton. The central Kontum massif is chiefly made of orthopyroxene granulites (enderbite, charnockite) and associated rocks of the Kannack complex. Mineral assemblages and geothermobarometric studies have shown that the Kannack complex has severely metamorphosed under granulite facies corresponding to P–T conditions of 800–850°C and 8±1 kbars. Twenty-three SHRIMP II U–Pb analyses of eighteen zircon grains separated from a granulite sample of the Kannack complex yield ca 254 Ma, and one analysis gives ca 1400 Ma concordant age for a zoned zircon core. This result shows that granulites of the Kannack complex in the Kontum massif have formed from a high-grade granulite facies tectonothermal event of Indosinian age (Triassic). The cooling history and subsequent exhumation of the Kannack complex during Indosinian times ranged from ∼850°C at ca 254 Ma to ∼300°C at 242 Ma, with an average cooling rate of ∼45°C/Ma.     

Characterization of microbial communities associated with African desert dust and their implications for human and ecosystem health

Desert winds aerosolize several billion tons of soil-derived dust each year, including concentrated seasonal pulses from Africa and Asia. Huge dust events create an atmospheric bridge over continents and oceans, and eject a large pulse of soil-associated microorganisms into the atmosphere. These dust events might therefore have a role in expanding the biogeographical range of some microorganisms by facilitating rare long-distance dispersal events. The goal of this study is to characterize the microbes associated with African dust events and determine if they pose a risk to humans or downwind ecosystems. Air samples were collected by vacuum filtration in a source region （Mali, West Africa） during dust events and plated on R2A media to culture microorganisms. These organisms were compared to those in similar samples collected in the Caribbean during Saharan/Sahelian dust events. A high-volume liquid impinger is currently being tested in Barbados, collecting aerosol samples during African dust events. Over 100 bacteria and fungi （19 genera of bacteria and three genera of fungi） have been characterized from source region dust events.     

(Re-)negotiating access: The politics of researching skills and knowledge for ‘sustainable communities’

The last decade has witnessed a surge of interest in ‘sustainable communities’ within the UK. This has stimulated a plethora of research aimed at acquiring a better understanding of what ‘sustainable communities’ might look like and how they can be achieved. However, this has not been accompanied by a reflection and interrogation of the actual processes, challenges and politics of doing ‘sustainable communities’ research. This paper addresses this gap by highlighting the importance of paying attention to the on-going process of negotiating access when carrying out sustainability research at the community level. We draw on a recent study of skills and knowledge for ‘sustainable communities’ in Stroud Gloucestershire, UK, to illustrate the importance of sensitivity to social relationships throughout and beyond the research trajectory within sustainability research. Our experience raises important questions about the politics of research practices when doing sustainability research ‘with’ communities and the challenges associated with participatory approaches as a means to demonstrate research impact. We argue that in developing a fuller understanding of why and how different types of community level initiatives can contribute to the ‘sustainable communities’ agenda, greater consideration needs to be given to how these community practices can be better supported through the process of doing academic research.     

Paying homage to the ‘Heavenly Mother’: Cultural-geopolitics of the Mazu pilgrimage and its implications on rapprochement between China and Taiwan

Much has been researched on tourism across (former) borders of conflict and on pilgrimage as a socio-cultural activity, but the relationship between the two remains poorly understood. Pilgrimage-tours carried out by Taiwanese devotees to the birthplace of Mazu (or Tianshang Shengmu – the Heavenly Mother) in Putian, China offer a significant platform to further our understanding of how religion can play a part in the rapprochement between China and Taiwan. Based on ethnographic fieldwork, this paper goes beyond the conventional state-level analysis to discuss interactions and encounters forged at the levels of the temple organisations and the individual. It utilises Victor Turner’s concept of ‘communitas’ to understand how spiritual spaces are being performed through the pilgrimage rather than already existing before the pilgrimage. Importantly, the Mazu pilgrimage-tour is conceptualised not as a tourism product, but as both a social activity and a socialising one, producing opportunities for different forms of interactions between the Chinese and Taiwanese devotees. These ‘interactions along the side’ as opposed to state-level diplomatic exchanges offer insights into the ‘more-than-state’ and ‘more-than-human’ relationships that bind/divide devotees on both sides of the Taiwan Strait.     

Paleomagnetic dating of ironstone nodules (‘nuts’) from the Yowah opal field,central southern Queensland

To constrain the age of Australian opal formation, we have undertaken a paleomagnetic study of oxidised ironstone ‘nuts’ from Yowah, Queensland. Following standard methods, we have calculated a mean direction of declination D = 191.4°, inclination I = 61.7° (α₉₅ = 4.0°), indicating a paleomagnetic pole position at latitude λ_p = 71.3°S, longitude ?_p = 119.4°E (A₉₅ = 5.3°). The direction comprises both normal and reverse polarities that fail a reversal test most probably owing to contamination by small recent/present-day components. The mean direction should not be significantly affected. A chi-square comparison with paleomagnetic poles for dated Cenozoic rocks in eastern Australia, poles derived from the Global Moving Hotspot Reference Frame and the Cenozoic pole path for North America, appropriately transferred to Australian coordinates, yields a mean age estimate of 35 ± 7 Ma, i.e. late Eocene to early Oligocene. This is interpreted as the age of the ironstone formation, which places a maximum age for the formation of precious Yowah opal. This result confirms and tightens the age for the nearby Canaway weathered profile.     

Change trend of natural gas hydrates in permafrost on the Qinghai-Tibet Plateau (1960–2050) under the background of global warming and their impacts on carbon emissions

Global warming and the response to it have become a topic of concern in today’s society and are also a research focus in the global scientific community. As the world’s third pole, the global warming amplifier, and the starting region of China’s climate change, the Qinghai-Tibet Plateau is extremely sensitive to climate change. The permafrost on the Qinghai-Tibet Plateau is rich in natural gas hydrates (NGHs) resources. Under the background of global warming, whether the NGHs will be disassociated and enter the atmosphere as the air temperature rises has become a major concern of both the public and the scientific community. Given this, this study reviewed the trend of global warming and accordingly summarized the characteristics of the temperature increase in the Qinghai-Tibet Plateau. Based on this as well as the distribution characteristics of the NGHs in the permafrost on the Qinghai-Tibet Plateau, this study investigated the changes in the response of the NGHs to global warming, aiming to clarify the impacts of global warming on the NGHs in the permafrost of the plateau. A noticeable response to global warming has been observed in the Qinghai-Tibet Plateau. Over the past decades, the increase in the mean annual air temperature of the plateau was increasingly high and more recently. Specifically, the mean annual air temperature of the plateau changed at a rate of approximately 0.308–0.420°C/10a and increased by approximately 1.54–2.10°C in the past decades. Moreover, the annual mean ground temperature of the shallow permafrost on the plateau increased by approximately 1.155–1.575°C and the permafrost area decreased by approximately 0.34×10⁶ km² from about 1.4×10⁶ km² to 1.06×10⁶ km² in the past decades. As indicated by simulated calculation results, the thickness of the NGH-bearing permafrost on the Qinghai-Tibet Plateau has decreased by 29–39 m in the past 50 years, with the equivalent of (1.69 – 2.27)×10¹⁰–(1.12–1.51)×10¹² m³ of methane (CH₄) being released due to NGHs dissociation. It is predicted that the thickness of the NGH-bearing permafrost will decrease by 23 m and 27 m, and dissociated and released NGHs will be the equivalent of (1.34–88.8)×10¹⁰ m³ and (1.57–104)×10¹⁰ m³ of CH₄, respectively by 2030 and 2050. Considering the positive feedback mechanism of NGHs on global warming and the fact that CH₄ has a higher greenhouse effect than carbon dioxide, the NGHs in the permafrost on the Qinghai-Tibet Plateau will emit more CH₄ into the atmosphere, which is an important trend of NGHs under the background of global warming. Therefore, the NGHs are destructive as a time bomb and may lead to a waste of efforts that mankind has made in carbon emission reduction and carbon neutrality. Accordingly, this study suggests that human beings should make more efforts to conduct the exploration and exploitation of the NGHs in the permafrost of the Qinghai-Tibet Plateau, accelerate research on the techniques and equipment for NGHs extraction, storage, and transportation, and exploit the permafrost-associated NGHs while thawing them. The purpose is to reduce carbon emissions into the atmosphere and mitigate the atmospheric greenhouse effect, thus contributing to the global goal of peak carbon dioxide emissions and carbon neutrality.©2022 China Geology Editorial Office.     

The relationship between the Neoproterozoic Noonday Dolomite and the Ibex Formation: New observations and their bearing on ‘snowball Earth’

The Neoproterozoic Ibex Formation (Death Valley region, California) is commonly interpreted as a coeval basinal facies to the Noonday Dolomite carbonate platform. However, in some areas (e.g., the Black Mountains, Death Valley), the Ibex Formation is found to rest on the eroded surface of the lower Noonday Dolomite and older units. Sediment-filled grikes root from the top of the eroded lower Noonday Dolomite, followed by the subsequent deposition of the Ibex Formation. Thus, the lower Noonday Dolomite is not considered coeval with all of the Ibex Formation as they are separated by a significant unconformity.At the type section in the Ibex Hills, the basal Ibex Formation commonly consists of polymict conglomerate and laminated mudstone; the upper surface of the mudstone is pierced by large angular clasts of underlying units, including distinctive lower Noonday Dolomite tubestone lithotypes. Here, a finely-laminated pink dolostone that records negative δ¹³C values caps the basal Ibex conglomerate.Several interpretations of the new observations are possible. The erosional unconformity upon which the Ibex is deposited may be glacio-eustatic in origin, the basal conglomerate would represent glaciogenic ice rafted debris, and the overlying dolostone is a classic cap carbonate (noted atop many Neoproterozoic glacial deposits worldwide). Combined with the record from underlying units, the Death Valley succession would then unambiguously record three discrete Neoproterozoic ice ages with cap carbonates in a single succession. Alternatively, the sequence boundary could represent local tectonic activity rather than glacioeustacy.     

‘Nation-states’, ‘quasi-states’, and ‘collapsed-states’ in contemporary Africa

The revival of ethnic identities and the search for historical roots have been significant factors in re-shaping the map of the world in the late twentieth century. Multi-ethnic states have come under increasing strain throughout the century and undermining the concept of the nation-state. However, the successor states to the colonial empires in Africa exhibit the same strains as the often highly fragile successors to the European continental empires earlier in the century. The survival of these quasi-states has been dependent upon the support of the international community for over thirty years as a reaction to the era of colonialism. Anti-colonialism offers little practical support for states in a post-colonial, post-Cold War era. In some cases the result has been disintegration and the emergence of the collapsed state. The revived political movements aimed at democratisation and self-determination have unleashed forces which may be incompatible with the survival of the current state system.     

Evolution of magmatic-hydrothermal system of the Kalaxiange’er porphyry copper belt and implications for ore formation (Xinjiang,China)

The Kalaxiange’er porphyry copper ore belt is situated in the eastern part of the southern Altai of the Central Asian Orogenic Belt and forms part of a broad zone of Cu porphyry mineralization in southern Mongolia, which includes the Oyu Tolgoi ore district and other copper–gold deposits. The copper ore bodies are spatially associated with porphyry intrusions of granodiorite, quartz diorite, quartz syenite, and quartz monzonite and have a polygenetic (polychromous) origin (magmatic porphyry, hydrothermal, and supergene). The mineralized porphyries are characterized by almost identical REE and trace element patterns. The Zr/Hf and Nb/Ta ratios are similar to those of normal granite produced through the evolution of mantle magma. The low initial Sr isotope ratio I_Sr, varying within a narrow range of values (0.703790–0.704218), corresponds to that of primitive mantle, whereas the εNd(T) value of porphyry varies from 5.8 to 8.4 and is similar to that of MORB. These data testify to the upper-mantle genesis of the parental magmas of ore-bearing porphyry, which were then contaminated with crustal material in an island-arc environment. The isotopic composition of sulfur (unimodal distribution of δ34S with peak values of − 2 to − 4‰) evidences its deep magmatic origin; the few lower negative δ³⁴S values suggest that part of S was extracted from volcanic deposits later. The isotopic characteristics of Pb testify to its mixed crust–upper-mantle origin. According to SHRIMP U–Pb geochronological data for zircon from granite porphyry and granodiorite porphyry, mineralization at the Xiletekehalasu porphyry Cu deposit formed in two stages: (1) Hercynian “porphyry” stage (375.2 ± 8.7 Ma), expressed as the formation of porphyry with disseminated and vein–disseminated mineralization, and (2) Indosinian stage (217.9 ± 4.2 Ma), expressed as superposed hydrothermal mineralization. The Re–Os isotope data on molybdenite (376.9 ± 2.2 Ma) are the most consistent with the age of primary mineralization at the Xiletekehalasu porphyry Cu deposit, whereas the Ar–Ar isotopic age (230 ± 5 Ma) of K-feldspar–quartz vein corresponds to the stage of hydrothermal mineralization. The results show that mineralization at the Xiletekehalasu porphyry Cu deposit was a multistage process which resulted in the superposition of the Indosinian hydrothermal mineralization on the Hercynian porphyry Cu mineralization.     

U–Pb isotopic dating of titanite microstructures: potential implications for the chronology and identification of large impact structures

Identifying and dating large impact structures is challenging, as many of the traditional shock indicator phases can be modified by post-impact processes. Refractory accessory phases, such as zircon, while faithful recorders of shock wave passage, commonly respond with partial U–Pb age resetting during impact events. Titanite is an accessory phase with lower Pb closure temperature than many other robust chronometers, but its potential as indicator and chronometer of impact-related processes remains poorly constrained. In this study, we examined titanite grains from the Sudbury (Ontario, Canada) and Vredefort (South Africa) impact structures, combining quantitative microstructural and U–Pb dating techniques. Titanite grains from both craters host planar microstructures and microtwins that show a common twin–host disorientation relationship of 74° about <102>. In the Vredefort impact structure, the microtwins deformed internally and developed high- and low-angle grain boundaries that resulted in the growth of neoblastic crystallites. U–Pb isotopic dating of magmatic titanite grains with deformation microtwins from the Sudbury impact structure yielded a ²⁰⁷Pb/²⁰⁶Pb age of 1851?±?12 Ma that records either the shock heating or the crater modification stage of the impact event. The titanite grains from the Vredefort impact structure yielded primarily pre-impact ages recording the cooling of the ultra-high-temperature Ventersdorp event, but domains with microtwins or planar microstructures show evidence of U–Pb isotopic disturbance. Despite that the identified microtwins are not diagnostic of shock-metamorphic processes, our contribution demonstrates that titanite has great potential to inform studies of the terrestrial impact crater record.     

Dance and wellbeing in Vancouver’s ‘A Healthy City for All’

Through the lens of the dancing body, this paper examines practices of health and wellbeing produced in response to City of Vancouver urban governance policies. In particular, it calls attention to the legislative onslaught by city government in the years abutting the 2010 Winter Olympics to cultivate and manage healthy people, communities, and environments. In an effort to sell Vancouver’s ‘liveability’, I argue City of Vancouver endorsed a new legislative alliance that merged a conspicuously Anglo-American wellbeing lexicon, favouring individual responsibility and self-governance, with the performing arts industries. Drawing upon interviews and performance-based research, the paper illustrates how Karen Jamieson’s community dance project Connect, created for the In the Heart of the City festival, embodies Vancouver’s tri-level legislative ambitions to nurture A Healthy City For All. This materialised through the crafting of a dance-health body practice (healthy people), by choreographing a sense of belonging among ‘at risk’ communities (healthy communities), and in the uniting of the arts and health professions in the process of ‘cleaning up’ disenfranchised neighbourhoods (healthy environments). In bringing together scholarship on cultures of wellbeing and creative dance practice, the article contributes to understandings of how the health-seeking subject is embodied and performed. It also offers a productive critique of the exclusionary nature of urban health legislation, and of the contested role artists and arts festivals can play in nurturing urban wellbeing and normalising inequalities.     

Mid-Cretaceous (Albian–Cenomanian) fossil woods from Hwawon-myeon in Jeollanam-do,Korea, and their palaeoclimatic implications

Two coniferous fossil wood taxa are reported from the Hwawon Formation (middle Cretaceous) at Hwawon-myeon in Jeollanam-do, Korea: Agathoxylon sp. and Taxodioxylon sp. Agathoxylon has a clear affinity with the Araucariaceae and its occurrence in the Hwawon Formation suggests that a dry and tropical–subtropical climate prevailed in this area during the middle Cretaceous. The presence of traumatic resin canals in the Taxodioxylon specimens indicates that flooding occurred repeatedly as part of an alternation between dry and rainy seasons. The low diversity observed for the Cretaceous fossil wood assemblages from the Korean Peninsula could be explained by the palaeoclimatologically stressful environment, as a dry tropical–subtropical climate prevailed over the region at that time.