Preliminary results from a search for regional tectonomagnetic effects in California and western Nevada

Physical theory and laboratory experiments both indicate that tectonomagnetic effects in seismically active areas should be detected with highly sensitive drift-free differential magnetometers. By using a pair of synchronized 0.25 7 absolute magnetometers to measure precisely field differences between 70 adjacent sites with a 10–15 km separation, more than 1,000 km of faults in California and western Nevada have been monitored for anomalous changes in the local magnetic field. Over a nine-month period, four sets of mea surements have been completed along 350 km of the San Andreas and two sets along the Excelsior Mountains, Mono Lake, and Owens Valley. Preliminary results show that significant changes have occurred between each subsequent data set and that these changes appear to be related to tectonic structure and seismicity. This method looks promising as a simple inexpensive scheme for indicating some hazardous sections of active faults, particularly in countries where extensive geophysics programs are not feasible.     

Estimation of groundwater recharge in a major sand and gravel aquifer in Ireland using multiple approaches

Groundwater recharge was investigated in the most extensive sand and gravel aquifer (area of approximately 200 km²) in the Republic of Ireland as part of a wider study seeking to derive recharge estimates using aquifer vulnerability mapping. The proportion of effective rainfall (total rainfall minus actual evapotranspiration) that leads to recharge is known as the recharge coefficient. The recharge investigation involved a variety of approaches, including soil moisture budgeting, well hydrograph analysis, numerical modelling and a catchment water balance. The adoption of multiple techniques provided insights on recharge and also on aquifer properties. Comparison of two soil moisture budgeting approaches (FAO Penman-Monteith with Penman-Grindley) showed how variations in the effective rainfall values from these methods influence groundwater levels simulated in a numerical groundwater model. The catchment water balance estimated the recharge coefficient to be between 81 and 85%, which is considered a reasonable range for this aquifer, where overland flow is rarely observed. The well hydrograph analysis, using a previous estimate of specific yield (0.13), gave recharge coefficients in the range of 40–80%, considered low for this aquifer: a revised specific yield of 0.19 resulted in a more reasonable range of recharge coefficients of between 70 and 100%.     

An examination of the use of the logratio transformation for the testing of endmember hypotheses

Given a compositional dataset in the absence of any prior information on any mixing process which may have formed it, a complete analysis of mixtures determines three distinct types of estimates in order. These are: (i) the estimate of the number of endmembers or fixed source compositions, of which all the sample compositions of the dataset must be approximate mixtures; (ii) the estimated compositions for each of these chosen number of endmembers; and (iii) the estimated contributions of each of these endmember estimates to each sample. Traditionally, the estimate for the number of endmembers has been assessed either by mapping or by inspection of the coefficients of determination between the observed and estimated variables. Mapping entails the plotting on a map of the region from which the samples were taken, either the contours of the contributions of each endmember to each sample, or some other portrayal of the distribution of endmember abundances. Because it requires the complete analysis, assessment by this method is too elaborate except for final confirmation and display. Alternatively, choosing a number of endmembers, which result in suitability high coefficients of determination for all or most variables, may account for elements which are not part of the conjectured mixing process or, worse, may result in the identification of endmembers which may never in fact have existed. Such an error is similar to overspecifying a multiple regression model. So, the obvious starting point from which to assess the validity, or otherwise choice of endmember numbers, is to examine the matrix of residuals. The differences between the logratio-transformed observed and estimated data form an array of residual logratios. A linear combination of these may be formed for each sample, which, under a random perturbation assumption, should follow a univariate normal distribution. Whether or not this scalar is normal can be readily tested. It can also be examined graphically for such desirable qualities as symmetry when the test for normality may be too severe. This procedure is employed to assess the decompositions of the U.S.G.S. Mid-Pacific data and the Nazca Plate Surface sediments.This paper was presented at the 18th Geochautauqua, Newark, Delaware, 13–14 October 1989.     

Origin of the Nchanga copper–cobalt deposits of the Zambian Copperbelt

The Zambian Copperbelt forms the southeastern part of the 900-km-long Neoproterozoic Lufilian Arc and contains one of the world’s largest accumulations of sediment-hosted stratiform copper mineralization. The Nchanga deposit is one of the most significant ore systems in the Zambian Copperbelt and contains two major economic concentrations of copper and cobalt, hosted within the Lower Roan Group of the Katangan Supergroup. A Lower Orebody (copper only) and Upper Orebody (copper and cobalt) occur towards the top of arkosic units and within the base of overlying shales. The sulfide mineralogy includes pyrite, bornite, chalcopyrite, and chalcocite, although in the Lower Orebody, sulfide phases are partially or completely replaced by malachite and copper oxides. Carrollite is the major cobalt-bearing phase and is restricted to fault-propagation fold zones within a feldspathic arenite. Hydrothermal alteration minerals include dolomite, phlogophite, sericite, rutile, quartz, tourmaline, and chlorite. Quartz veins from the mine sequence show halite-saturated fluid inclusions, ranging from ~31 to 38 wt% equivalent NaCl, with homogenisation temperatures (Th_TOT) ranging between 140 and 180°C. Diagenetic pyrites in the lower orebody show distinct, relatively low δ ³⁴S, ranging from −1 to −17‰ whereas arenite- and shale-hosted copper and cobalt sulfides reveal distinctly different δ ³⁴S from −1 to +12‰ for the Lower Orebody and +5 to +18‰ for the Upper Orebody. There is also a clear distinction between the δ ³⁴S mean of +12.1±3.3‰ (n=65) for the Upper Orebody compared with +5.2±3.6‰ (n=23) for the Lower Orebody. The δ ¹³C of dolomites from units above the Upper Orebody give δ ¹³C values of +1.4 to +2.5‰ consistent with marine carbon. However, dolomite from the shear-zones and the alteration assemblages within the Upper Orebody show more negative δ ¹³C values: −2.9 to −4.0‰ and −5.6 to −8.3‰, respectively. Similarly, shear zone and Upper Orebody dolomites give a δ ¹⁸O of +11.7 to +16.9‰ compared to Lower Roan Dolomites, which show δ ¹⁸O of +22.4 to +23.0‰_. Two distinct structural regimes are recognized in the Nchanga area: a weakly deformed zone consisting of basement and overlying footwall siliciclastics, and a moderate to tightly folded zone of meta-sediments of the Katangan succession. The fold geometry of the Lower Roan package is controlled by internal thrust fault-propagation folds, which detach at the top of the lowermost arkose or within the base of the overlying stratigraphy and show vergence towards the NE. Faulting and folding are considered to be synchronous, as folding predominantly occurred at the tips of propagating thrust faults, with local thrust breakthrough. The data from Nchanga suggests a strong link between ore formation and the development of structures during basin inversion as part of the Lufilian Orogeny. Sulfides tend to be concentrated within arenites or coarser-grained layers within shale units, suggesting that host-rock porosity and possibly permeability played a role in ore formation. However, sulfides are also commonly orientated along, but not deformed by, a tectonic fabric or hosted within small fractures that suggest a significant role for deformation in the development of the mineralization. The ore mineralogy, hydrothermal alteration, and stable isotope data lend support to models consistent with the thermochemical reduction of a sulfate- (and metal) enriched hydrothermal fluid, at the site of mineralization. There is no evidence at Nchanga for a contribution of bacteriogenic sulfide, produced during sedimentation or early diagenesis, to the ores.Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users.Editorial handling: H. Frimmel     

The petrology and petrogenesis of the Tertiary anorogenic mafic lavas of Southern and Central Queensland,Australia — Possible implications for crustal thickening

The Miocene-Oligocene volcanism of this region is part of the larger Tertiary volcanic province found throughout E. Australia. Within the S.E. Queensland region, the volcanism is strongly bimodal, and has emanated from six major centres, and many additional smaller centres. The mafic lavas (volumetrically dominant) range continuously from ne-normative through to Q-normative and are predominantly andesine-normative; Mg/Mg+Fe (atomic ratios range from 30–60; K₂O ranges from 0.42–2.93%, and TiO₂ from 0.81–3.6%.Phenocryst contents are low (averaging 6.7 vol.%), and comprise olivine (Fa_18–75; Cr-spinel inclusions occur locally in Mg-rich phenocrysts), plagioclase (An_25–68), and less commonly augite, which is relatively aluminous in lavas of the Springsure volcanic centre. Very rare aluminous bronzite occurs in certain Q-normative lavas. Groundmass minerals comprise augite, olivine (Fa_33–77), feldspar (ranging from labradorite through to anorthoclase and sanidine), Fe-Ti oxides, and apatite. Within many of the Q-normative lavas, extensive development of subcalcic and pigeonitic pyroxenes occurs, and also relatively rarely orthopyroxene. Mineralogically, the ne- and ol-normative lavas, and some of the Q-normative lavas are indistinguishable, and in view of the gradations in chemistry, the term hawaiite has been extended to cover these lavas. The term tholeiitic andesite is used to describe the Q-normative lavas containing Ca-poor pyroxenes as groundmass phases.Megacrysts of aluminous augite, aluminous bronzite, olivine, ilmenite, and spinel sporadically occur within the lavas, and their compositions clearly indicate that they are not derived from the Upper Mantle. Rare lherzolite xenoliths are also found.The petrogenesis of these mafic lavas is approached by application of the thermodynamic equilibration technique of Carmichael et al. (1977), utilizing three parental mineral assemblages that could have been in equilibrium with the magmas at P and T. The models are: (a) standard upper mantle mineralogy; (b) an Fe-enriched upper mantle model (Wilkinson and Binns 1977); (c) lower crust mineralogy, based on analysed megacryst compositions. The calculations suggest that these mafic magmas were not in equilibrium with either mantle model prior to eruption, but show much closer approaches to equilibrium with the lower crust model. Calculated equilibration temperatures and pressures (for the lower crust model) range from 995°–l,391° C (average 1,192), and 7.2–16.3 kb (average 12.4). These results are interpreted in terms of a model of intrusion and magma fractionation within the crust-mantle interface region, with consequent crustal underplating and thickening beneath the Tertiary volcanic regions. Some support for the latter is provided by regional isostatic gravity anomalies and physiographic considerations.     

Refining the ice flow chronology and subglacial dynamics across the migrating Labrador Divide of the Laurentide Ice Sheet with age constraints on deglaciation

The Laurentide Ice Sheet was characterized by a dynamic polythermal base. However, important data and knowledge gaps have led to contrasting reconstructions in areas such as the Labrador Ice Divide. In this study, detailed fieldwork was conducted at the southeastern edge of a major landform boundary to resolve the relative ice flow chronology and constrain the evolution of the subglacial dynamics, including the migration and collapse of the Labrador Ice Divide. Surficial mapping and analysis of 94 outcrop‐scale ice flow indicators were used to develop a relative ice flow chronology. ¹⁰Be exposure ages were used with optical ages to confine the timing of deglaciation within the study area. Four phases of ice flow were identified. Flow 1 was a northeasterly ice flow preserved under non‐erosive subglacial conditions associated with the development of an ice divide. Flow 2 was a northwest ice flow, which we correlate to the Ungava Bay Ice Stream and led to a westward migration of the ice divide, preserving Flow 2 features and resulting in Flow 3's eastward‐trending indicators. Flow 4 is limited to sparse fine striations within and around the regional uplands. The new optical ages and ¹⁰Be exposure ages add to the regional geochronology dataset, which further constrains the timing of ice margin retreat in the area to around 8.0 ka. Copyright © 2019 The Authors. Journal of Quaternary Science Published by John Wiley & Sons Ltd.     

Electrochemical strengthening of clayey sandy soils

Most previous studies and applications of electrochemical stabilization of soils through electroosmosis have been made on clayey soils. The object of this investigation was to find out if relatively small amounts of clay (1.5%–3.5%, by weight) present in a sandy soil would be enough for stabilization and strengthening to be possible. The results indicate increases of cohesion of the order of 100–200 lb./sq.ft. X-ray analyses of treated soils indicate that sheet structures of clays are reduced and silicates destroyed upon treatment by electroosmosis. Newly-formed minerals also cement the soil. These neoformations include gibbsite, limonite, calcite, hydrohematite, hydrogoethite (hydrolepidocrocite), hisingerite, allophane, allophanoid, gypsum, hematite, magnetite, nontronite, trona and natron (Na₂ CO₃, 10H₂O). The process seems to be irreversible.     

Closed Circuit Television (CCTV) Earthquake Behaviour Coding Methodology: analysis of Christchurch Public Hospital video data from the 22 February Christchurch earthquake event

Earthquake epidemiological research indicates that the behavioural response influences the nature and severity of injuries sustained. However, there is no observational evidence of the actions individuals engage in during and immediately following earthquake shaking, and the context in which earthquake injuries and deaths are caused. Closed Circuit Television Earthquake Behaviour Coding Methodology has been developed as a tool to classify human behaviour during and immediately following earthquake shaking using real event video data. The coding methodology was applied to security video data captured during the 22 February 2011 M_w6.3 ‘Christchurch’ earthquake event from the Christchurch Public Hospital which experienced shaking intensity of MM9 lasting approximately 12–15 s. We applied this coding methodology to determine: demography, trans-event behavioural responses, post-event behavioural responses, influence of social context on behaviour, and influence of behaviour on injuries. A total of 213 individuals from 31 different camera views were analysed. Sixty-six per cent of the individuals were adult-aged females. The primary trans-event responses were to hold (26%) onto furniture, walls, and/or other people close to them and to look around (30%). No individuals were observed to perform all ‘Drop, Cover, Hold’ actions, the recommended action during strong earthquake shaking in New Zealand. Post-event behaviour included: running, walking, providing assistance, moving towards others, visual communication, and some individuals gave instructions. Social contextual behaviour varied depending on the role of the adult. There were no serious injuries linked to behaviour. The results of this initial study indicate the coding methodology can record the distribution of and variation in human behaviours. Therefore, objective observation of earthquake video data can provide a useful quantitative measure of human behaviour. Significantly, the process will enable researchers to look more closely at behaviours, as well as the social and physical contexts associated with injury risk during and immediately following earthquake shaking.     

Platinum-group elements (Ir,Pd, Pt and Rh) in road-deposited sediments in two urban watersheds,Hawaii

This study represents the first detailed investigation of platinum-group elements (PGEs) in road-deposited sediment (RDS) in Hawaii, USA. Thirty-three sample locations, in two urban watersheds in Honolulu, Oahu, Hawaii were sampled. The <63 μm fraction of RDS was digested with aqua regia, followed by matrix separation with Dowex AG50-X8 cation exchange resin. PGEs were analyzed with inductively coupled plasma-mass spectrometry (ICP-MS) equipped with a desolvating nebulizer. Concentrations of Rh, Pd and Pt in residential streets reached 64, 105 and 506 ng/g, respectively. Maximum enrichment ratios, computed as RDS concentrations relative to baseline values, exceeded 400, indicating a significant anthropogenic signal with the sequence Rh > Pt > Pd. Iridium concentrations were uniformly low <1 ng/g, and enrichment ratios support a geogenic source. Significant interelement PGE correlations (Pd–Pt–Rh), combined with the magnitude of PGE pair-wise ratios (Pt/Pd, Pt/Rh and Pd/Rh), and relative percentages comparable to European RDS and roadside soil in Indiana, USA all suggest an automobile source. Attrition of PGE-loaded automobile catalytic converters and subsequent loss to the environment by exhaust emissions explains the significant environmental signal of PGEs in road environments of Hawaii. Further PGE work is required to quantify urban transport paths as PGEs are known to bioaccumulate, cause cellular damage and may have detrimental human health effects.