Average Crustal Composition Research Articles

Crustal Thickness and Vp/Vs Ratio Determination beneath Tangkuban Parahu Volcano, West Java, Indonesia using Receiver Function Analysis

Tangkuban Parahu, an active stratovolcano located approximately 15 km north of Bandung City in Indonesia, is the focal point of this study. The research aims to examine seismic structures within the crust beneath the Tangkuban Parahu Complex. To accomplish this, a teleseismic receiver function method was employed, utilizing broadband seismic stations along a seismological profile within the Tangkuban Parahu Volcano area. Waveform data were collected during the period from October 24, 2021, to March 31, 2022, for analysis. Various seismic wave phases, including P, Ps, PpPs, and PsPs, were identified in the recorded waveforms, within a time window extending from -2 seconds before the onset of the P-wave to 20 seconds after its onset. The analysis and modelling were conducted using the H-κ stacking receiver function technique. The findings of the H-κ stacking receiver function revealed notable variations in crustal structures, encompassing crustal thickness and the average crustal composition, as indicated by the Vp/Vs ratio, within the Tangkuban Parahu Volcano area. Preliminary results suggest that the crust beneath Tangkuban Parahu, estimated based on data from single seismic station, possesses a thickness of approximately 32.3 km, with a corresponding Vp/Vs ratio of around 1.746.

Modelling of crustal composition and Moho depths and their Implications toward seismogenesis in the Kumaon\u2013Garhwal Himalaya

We image the lateral variations in the Moho depths and average crustal composition across the Kumaon–Garhwal (KG) Himalaya, through the H–K stacking of 1400 radial PRFs from 42 three-component broadband stations. The modelled Moho depth, average crustal Vp/Vs, and Poisson’s ratio estimates vary from 28.3 to 52.9 km, 1.59 to 2.13 and 0.17 to 0.36, respectively, in the KG Himalaya. We map three NS to NNE trending transverse zones of significant thinning of mafic crust, which are interspaced by zones of thickening of felsic crust. These mapped transverse zones bend toward the north to form a NE dipping zone of maximum changes in Moho depths, below the region between Munsiari and Vaikrita thrusts. The 1991 Mw6.6 Uttarakashi and 1999 Mw6.4 Chamoli earthquakes have occurred on the main Himalayan thrust (MHT), lying just above the mapped zone of maximum changes in Moho depths. Modelled large values of average crustal Vp/Vs (> 1.85) could be attributed to the high fluid (metamorphic fluids) pressure associated with the mid-crustal MHT. Additionally, the serpentinization of the lowermost crust resulted from the continent–continent Himalayan collision process could also contribute to the increase of the average crustal Vp/Vs ratio in the region.

Underground production of 81Kr detected in subsurface fluids

Radiokrypton dating using the long-lived natural isotope 81Kr has been developed for determining the age of ancient groundwater. 81Kr is attractive for this purpose because it is generally thought to be produced solely in the upper atmosphere. Its 229,000-year half-life, a spatially homogeneous distribution in the atmosphere, and the absence of anthropogenic sources makes it an ideal tracer to determine ages up to ∼1.3 million years. As a noble gas, it is inert and thus not subject to interfering geochemical reactions that may alter the age information. We sought to date groundwater samples collected from deep (0.6–1.9 km) rock fractures in the Kaapvaal Craton, South Africa. Previous studies using other dating methods have estimated groundwater ages at these sites in the 1–100 million year range. Surprisingly, three of the four samples collected from flowing boreholes in gold and diamond mines showed 81Kr isotopic abundances at 2–5 times the atmospheric value. This is the first time that underground production of 81Kr has been detected, indicating that 81Kr can be generated underground in measurable quantities in contrast to the long-held paradigm that such production is insignificant in natural rocks. A radionuclide production and release model is proposed in order to quantify the importance of different factors that affect the concentrations of 81Kr in the groundwater. It is not only the high effective uranium content of the rock but also a higher 81Kr fission yield than previously anticipated that are likely causing the elevated 81Kr values in this case. In less extreme environments with average crustal composition (i.e. moderate U concentration), however, we anticipate that the underground production minimally affects groundwater 81Kr dating as demonstrated.

Crustal structure of the Amazonian Craton and adjacent provinces in Brazil

The study of the crust using receiver functions can provide valuable geological information, such as average crustal composition, its formation dynamics and the tectonic evolution of a region, as well as serve as an initial reference for the generation of seismic wave velocity models to improve earthquake location. To fill in gaps in information on the crust of the Amazonian Craton and adjacent provinces in Brazil, we used receiver functions and H-k stacking to estimate crustal thicknesses and the VP/VS ratios. The results indicate that the crust of the study region is predominantly felsic, with an average VP/VS around 1.73 and an average thickness of 38.2 km, with a range of 27.4–48.6 km. Minimum curvature interpolation of the crustal thickness values has made it possible to delimitate of the Amazonian Craton, which corresponds to the area with an average thickness equal to or greater than 39 km. In addition, it was possible to identify its potential cratonic blocks, as well as the Paranapanema Block of Paraná Basin. The geometry of the craton, defined by its crustal thickness, is corroborated by the distribution of natural seismicity that accompanies its edges. These are related to suture zones between the Amazonian, São Francisco/Congo and Paranapanema paleocontinents. The sedimentary basins that have undergone rifting processes have a thinner crust, usually less than 37 km thick. Due to the great variability of the results, it was not possible to determine a characteristic value of crustal thickness or VP/VS ratio for each structural province located in the study region.

Natural versus anthropogenic influences on the chemical composition of bulk precipitation in the southern Apennines, Italy: A case study of the town of Potenza

This paper presents new data on the chemical composition of precipitation in a selected area of the southern Apennines of Italy; these data are used to assess natural and anthropogenic contributions to the precipitation. The town of Potenza was used as a representative urban site, and the major and minor element (Na+, K+, Ca2+, Mg2+, NH4+, Cl−, NO3−, SO42−, and Li+, NO2−, F−, Br−, PO43−) and trace element (Zn, Fe, Al, Sr, Mn, Ba, Cu, Cr, V, As, Pb, Ni, and Cd) concentrations of bulk precipitation from three different sampling sites within the study area were determined between June 2011 and May 2012. The majority of the collected rainwater has pH values higher than 5.6. The composition of this rainwater was dominated by Ca2+ the element with the highest total volume-weighted mean concentration (TVWA), followed by Cl−, SO42−, Na+, NO3− , K+, Mg2+, and NH4+. The TVWA of the trace metals decreased in the order Zn>Fe>Al>Ba>Sr>Mn>Pb>Cu>As. Neutralising factor (NFXi) values indicate that Ca2+ is the dominant neutralising cation within this rainwater, with lower contribution from NH4+ and Mg2+. The precipitation analysed during this study has a negligible marine influence as determined using Cl− concentrations as a proxy for the abundance of sea salts. Precipitation Fi values (marine fraction of element i) indicate that Na+ is the element with the highest seawater component, and we found partial marine contributions for the SO42−and Mg2+ concentrations within this rainwater. Enrichment factors (EF) of selected elements were calculated to identify the sources of non-crustal elements: K+, Mg2+, Fe, and Ca2+ are the only elements dominantly sourced from the crust, whereas Mn and Ba have highly variable EF values (10–100) suggesting that a small proportion of these elements was derived from anthropogenic sources in addition to a more significant crustal contribution. Sr, Cu, Pb, Zn, and As are highly enriched with respect to average crustal compositions, confirming that the concentrations of these elements within precipitation are significantly controlled by human activities.

Achnanthidium minutissimum (Bacillariophyta) valve deformities as indicators of metal enrichment in diverse widely-distributed freshwater habitats

In the presence of different environmental stressors, diatoms can produce frustules presenting different types of deformities. Metals and trace elements are among the most common causes of these teratological forms. Metal enrichment in water bodies can be attributed to the geological setting of the area or to pollution. The widespread benthic diatom Achnanthidium minutissimum (ADMI) is one of the most metal-tolerant species. In the present study, ADMI teratologies were defined from samples taken from eight very diverse, widely-distributed inland-water habitats: streams affected by active and abandoned mining areas, a metal-contaminated stream, a spring in an old chalcopyrite mine, a mineral-water fountain, and a sediment core taken from a lake affected by metal contamination in the past. Deformed frustules of ADMI were characterised mainly by one (sometimes two) more or less bent off ending, conferring to the specimens a cymbelloid outline (cymbelliclinum-like teratology, CLT). Marked teratologies were distinguished from slight deformities. Hydrochemical analyses, including metals and trace elements, were carried out and enrichment factors (EF) relative to average crustal composition were calculated. To improve our knowledge on the potential of different metals and trace elements to trigger the occurrence of ADMI CLT, we carefully selected 15 springs out of 110 (CRENODAT dataset) where both ADMI and above-average metal or metalloid concentrations occurred, and re-analysed these samples. The results from the eight widely-distributed core sites as well as from the 15 selected CRENODAT springs led to the hypothesis that two metals (copper and zinc) and a metalloid (antimony) were the most likely triggers of ADMI CLT formation. From a quantitative point of view, it is worth noting that the lowest concentrations triggering ADMI CLT can be fairly low, particularly in the case of copper contamination. The antimony-rich site was characterised by a marked-teratology variant where both ends of ADMI were bent off.

Metal concentrations and distribution in the household, stairs and entryway dust of some Egyptian homes

Household, stairs and entryway dust samples were collected from 16 houses distributed across Greater Cairo by using vacuum cleaner and sweeping methods during summer season of 2009. Lead (Pb), nickel (Ni), cadmium (Cd), aluminum (Al), iron (Fe), zinc (Zn), cobalt (Co), chromium (Cr) and copper (Cu) were measured in different dust particle sizes: <38 μm, >38–45 μm and >45–63 μm. The highest average concentrations of Pb, Ni, Cd, Co, Cu, and Cr in different particle sizes were found in entryway followed by household and stairs. Al, Fe and Zn concentrations followed the pattern of entryway > stairs > household. Pb, Ni, Cd, Zn, Co and Cr were found in significantly (p < 0.01) higher concentrations in dust of the small particle size (<38 μm), whereas Al, Fe and Cu were detected in significantly (p < 0.01) higher concentrations in dust of the large particle size (>45–63 μm). The average concentrations of the individual metals in dust of the small particle size (<38 μm) were 268, 196.4 and 254.49 μg gm−1 for Pb, 49.6, 43.5 and 46.66 μg gm−1 for Ni, 2.86, 2.15 and 2.71 μg gm−1 for Cd, 4340, 3796 and 2602 μg gm−1 for Al, 2860, 2200 and 2004 μg gm−1 for Fe, 209.25, 152.3 and 103.26 μg gm−1 for Zn, 4.1, 2.88 and 1.96 μg gm−1 for Co, 85.99, 74.06 and 83.17 μg gm−1 for Cr and 168.2, 156.5 and 122.02 μg gm−1 for Cu in entryway, stairs and household, respectively. The mean concentrations of Cu and Pb in the entryway, stairs and household dust exceeded the maximum permissible limit 100 μg gm−1 for Cu and Pb in soil. The highest concentrations of Pb, Cd, Co and Ni were found in urban areas, Al and Fe in the residential areas, and Cu, Zn and Cr in the residential near to industrial area. Significant positive correlation (p < 0.001) were found between the metal concentrations in household and entryway dust, indicating that the metals in household dust may be derived from outdoor sources in addition to dust generated within the house itself. The contribution of anthropogenic sources, especially traffic emission, to metal levels in household, entryway and stairs dust was reflected by the high values of enrichment factors for Pb, Cd, Zn and Cu and Ni and Cr in fine dust particle compared to the average crustal composition. Insignificant positive correlation coefficients were found between the concentrations of Pb and other metals in household dust. However, the correlation coefficients between the concentrations of Cd, Ni, Cr, Cu, Zn and Fe were statistically significant.

Flood Volcanism in the Northern High Latitudes of Mercury Revealed by MESSENGER

MESSENGER observations from Mercury orbit reveal that a large contiguous expanse of smooth plains covers much of Mercury's high northern latitudes and occupies more than 6% of the planet's surface area. These plains are smooth, embay other landforms, are distinct in color, show several flow features, and partially or completely bury impact craters, the sizes of which indicate plains thicknesses of more than 1 kilometer and multiple phases of emplacement. These characteristics, as well as associated features, interpreted to have formed by thermal erosion, indicate emplacement in a flood-basalt style, consistent with x-ray spectrometric data indicating surface compositions intermediate between those of basalts and komatiites. The plains formed after the Caloris impact basin, confirming that volcanism was a globally extensive process in Mercury's post-heavy bombardment era.

Enriched Basaltic Andesites from Mid-crustal Fractional Crystallization, Recharge, and Assimilation (Pilavo Volcano, Western Cordillera of Ecuador)

The origin of andesite is an important issue in petrology because andesite is the main eruptive product at convergent margins, corresponds to the average crustal composition and is often associated with major Cu^Au mineralization. In this study we present petro- graphic, mineralogical, geochemical and isotopic data for basaltic andesites of the latest Pleistocene Pilavo volcano, one of the most frontal volcanoes of the Ecuadorian Quaternary arc, situated upon thick (30^50km) mafic crust composed of accreted Cretaceous oceanic plateau rocks and overlying mafic to intermediate Late Cretaceous^Late Tertiary magmatic arcs. The Pilavo rocks are bas- altic andesites (54^57·5 wt % SiO2) with a tholeiitic affinity as opposed to the typical calc-alkaline high-silica andesites and dacites (SiO2 59^66wt %) of other frontal arc volcanoes of Ecuador (e.g. Pichincha, Pululahua). They have much higher incompatible element contents (e.g. Sr 650^1350 ppm, Ba 650^1800 ppm, Zr 100^225 ppm, Th 5^25 ppm, La 15^65 ppm) and Th/La ratios (0·28^0·36) than Pichincha and Pululahua, and more primitive Sr (87Sr/86Sr 􏰃0·7038^0·7039) and Nd (eNd 􏰃 þ5·5 to þ6·1) isotopic signatures. Pilavo andesites have geochemical affinities with modern and recent high-MgO andesites (e.g. low-silica ada- kites, Setouchi sanukites) and, especially, with Archean sanukitoids, for both of which incompatible element enrichments are believed to result from interactions of slab melts with peridotitic mantle. Petrographic, mineral chemistry, bulk-rock geochemical and isotopic data indicate that the Pilavo magmatic rocks have evolved through three main stages: (1) generation of a basaltic magma in the mantle wedge region by flux melting induced by slab-derived fluids (aque- ous, supercritical or melts); (2) high-pressure differentiation of the basaltic melt (at the mantle^crust boundary or at lower crustal levels) through sustained fractionation of olivine and clinopyroxene, leading to hydrous, high-alumina basaltic andesite melts with a tholeiitic affinity, enriched in incompatible elements and strongly impoverished in Ni and Cr; (3) establishment of one or more mid-crustal magma storage reservoirs in which the magmas evolved through dominant amphibole and clinopyroxene (but no plagioclase) fractionation accompanied by assimilation of the modified plutonic roots of the arc and recharge by incoming batches of more primitive magma from depth. The latter process has resulted in strongly increasing incompatible element concentrations in the Pilavo basaltic andesites, coupled with slightly increasing crustal isotopic signatures and a shift towards a more calc-alkaline affinity. Our data show that, although ultimately originating from the slab, incompatible element abundances in arc andesites with primitive isotopic signa- tures can be significantly enhanced by intra-crustal processes within a thick juvenile mafic crust, thus providing an additional process for the generation of enriched andesites.

The Neoproterozoic-early Paleozoic metamorphic and magmatic evolution of the Eastern Sierras Pampeanas: an overview

The Eastern Sierras Pampeanas were structured by three main events: the Ediacaran to early Cambrian (580–510 Ma) Pampean, the late Cambrian–Ordovician (500–440 Ma) Famatinian and the Devonian-Carboniferous (400–350 Ma) Achalian orogenies. Geochronological and Sm–Nd isotopic evidence combined with petrological and structural features allow to speculate for a major rift event (Ediacaran) dividing into two Mesoproterozoic major crustal blocks (source of the Grenvillian age peaks in the metaclastic rocks).This event would be coeval with the development of arc magmatism along the eastern margin of the eastern block. Closure of this eastern margin led to a Cambrian active margin (Sierra Norte arc) along the western margin of the eastern block in which magmatism reworked the same crustal block. Consumption of a ridge segment (input of OIB signature mafic magmas) which controlled granulite-facies metamorphism led to a final collision (Pampean orogeny) with the western Mesoprotrozoic block. Sm–Nd results for the metamorphic basement suggest that the T DM age interval of 1.8–1.7 Ga, which is associated with the less radiogenic values of εNd(540) (−6 to −8), can be considered as the mean average crustal composition for the Eastern Sierras Pampeanas. Increasing metamorphic grade in rocks with similar detrital sources and metamorphic ages like in the Sierras de Córdoba is associated with a younger T DM age and a more positive εNd(540) value. Pampean pre-540 Ma granitoids form two clusters, one with T DM ages between 2.0 and 1.75 Ga and another between 1.6 and 1.5 Ga. Pampean post-540 Ma granitoids exhibit more homogenous T DM ages ranging from 2.0 to 1.75 Ga. Ordovician re-activation of active margin along the western part of the block that collided in the Cambrian led to arc magmatism (Famatinian orogeny) and related ensialic back-arc basin in which high-grade metamorphism is related to mid-crustal felsic plutonism and mafic magmatism with significant contamination of continental crust. T DM values for the Ordovician Famatinian granitoids define a main interval of 1.8–1.6, except for the Ordovician TTG suites of the Sierras de Córdoba, which show younger T DM ages ranging from 1.3 to 1.0 Ga. In Devonian times (Achalian orogeny), a new subduction regime installed west of the Eastern Sierras Pampeanas. Devonian magmatism in the Sierras exhibit process of mixing/assimilation of depleted mantle signature melts and continental crust. Achalian magmatism exhibits more radiogenic εNd(540) values that range between 0.5 and −4 and T DM ages younger than 1.3 Ga. In pre-Devonian times, crustal reworking is dominant, whereas processes during Devonian times involved different geochemical and isotopic signatures that reflect a major input of juvenile magmatism.

Enhanced crustal geo-neutrino production near the Sudbury Neutrino Observatory, Ontario, Canada

The geo-neutrino flux at the Sudbury Neutrino Observatory depends on the local level of crustal radio-activity, which is best estimated from surface heat flux data. The surface heat flux records average crustal radio-activity over the whole crustal column and is unaffected by small-scale heterogeneities. We show how the contribution of crustal heat sources to the geo-neutrino flux can be calculated from knowledge of the surface heat flux. We present new heat flux data from two very deep holes (> 2000 m) in the Sudbury structure as well as measurements of U, Th, and K concentrations in the main geological units of the area. With all available data, the average heat flux in the Sudbury basin is ≈ 53 mW m − 2 , higher than the mean value of 42 m W m − 2 for the entire Canadian Shield. The elevated heat flux is due to high heat production in the shallow crust and implies an at least 50% increase of the local crustal component of the geo-neutrino flux relative to that expected for the average crustal composition of the shield.

Compositions of modern dust and surface sediments in the Desert Southwest, United States

Modern dusts across southwestern United States deserts are compositionally similar to dust‐rich Av soil horizons (depths of 0–0.5 cm and 1–4 cm at 35 sites) for common crustal elements but distinctly different for some trace elements. Chemical compositions and magnetic properties of the soil samples are similar among sites relative to dust sources, geographic areas, and lithologic substrates. Exceptions are Li, U, and W, enriched in Owens Valley, California, and Mg and Sr, enriched in soils formed on calcareous fan gravel in southeast Nevada. The Av horizons are dominated by dust and reflect limited mixing with substrate sediments. Modern dust samples are also similar across the region, except that Owens Valley dusts are higher in Mg, Ba, and Li and dusts both there and at sites to the north on volcanic substrates are higher in Sb and W. Thus, dust and Av horizons consist of contributions from many different sources that are well mixed before deposition. Modern dusts contain significantly greater amounts of As, Cd, Cr, Cu, Ni, Pb, and Sb than do Av horizons, which record dust additions over hundreds to thousands of years. These results suggest that modern dust compositions are influenced by anthropogenic sources and emissions from Owens (dry) Lake after its artificial desiccation in 1926. Both modern dusts and Av horizons are enriched in As, Ba, Cu, Li, Sb, Th, U, and W relative to average crustal composition, which we interpret to indicate that the geologic sources of dust in the southwestern United States are geochemically distinctive.

Atmospheric dry deposition fluxes of trace elements measured in Bursa, Turkey

Trace element dry deposition fluxes were measured using a smooth, greased, knife-edge surrogate surface (KSS) holding greased Mylar strips in Bursa, Turkey. Sampling program was conducted between October 2002 and June 2003 and 46 dry deposition samples were collected. The average fluxes of crustal metals (Mg, Ca, and Fe) were one to four orders of magnitude higher than the fluxes of anthropogenic metals. Trace element fluxes ranged from 3 (Cd) to 24 230 (Ca) μg m −2 d −1. The average trace element dry deposition fluxes measured in this study were similar to those measured in other urban areas. In addition, ambient air samples were also collected simultaneously with flux samples and concentrations of trace elements, collected with a TSP sampler, were between 0.7 and 4900 ng m −3 for Cd and Ca, respectively. The overall trace element dry deposition velocities, calculated by dividing the fluxes to the particle phase concentrations ranged from 2.3±1.7 cm s −1 (Pb) to 11.1±6.4 cm s −1 (Ni). These values are in good agreement with the values calculated using similar techniques. The anthropogenic and crustal contributions were estimated by employing enrichment factors (EFs) calculated relative to the average crustal composition. Low EFs for dry deposition samples were calculated. This is probably due to contamination of local dust and its important contribution to the collected samples.

Constraints on the composition of the crust and uppermost mantle in northwestern Canada: Vp/Vs variations along Lithoprobe's SNorCLE transect

Shear-wave seismic data recorded along four profiles during the SNoRE 97 (1997 Slave – Northern Cordillera Refraction Experiment) refraction – wide-angle reflection experiment in northwestern Canada are analyzed to provide S-wave velocity (Vs) models. These are combined with previous P-wave velocity (Vp) models to produce cross sections of the ratio Vp/Vs for the crust and upper mantle. The Vp/Vs values are related to rock types through comparisons with published laboratory data. The Slave craton has low Vp/Vs values of 1.68–1.72, indicating a predominantly silicic crustal composition. Higher values (1.78) for the Great Bear and eastern Hottah domains of the Wopmay orogen imply a more mafic than average crustal composition. In the western Hottah and Fort Simpson arc, values of Vp/Vs drop to ∼1.69. These low values continue westward for 700 km into the Foreland and Omineca belts of the Cordillera, providing support for the interpretation from coincident seismic reflection studies that much of the crust from east of the Cordilleran deformation front to the Stikinia terrane of the Intermontane Belt consists of quartzose metasedimentary rocks. Stikinia shows values of 1.78–1.73, consistent with its derivation as a volcanic arc terrane. Upper mantle velocity and ratio values beneath the Slave craton indicate an ultramafic peridotitic composition. In the Wopmay orogen, the presence of low Vp/Vs ratios beneath the Hottah – Fort Simpson transition indicates the presence of pyroxenite in the upper mantle. Across the northern Cordillera, low Vp values and a moderate-to-high ratio in the uppermost mantle are consistent with the region's high heat flow and the possible presence of partial melt.

Caledonide development offshore–onshore Svalbard based on ocean bottom seismometer, conventional seismic, and potential field data

The western Barents Sea and the Svalbard archipelago share a common history of Caledonian basement formation and subsequent sedimentary deposition. Rock formations from the period are accessible to field study on Svalbard, but studies of the near offshore areas rely on seismic data and shallowdrilling. Offshore mapping is reliable down to the Permian sequence, but multichannel reflection seismic data do not give a coherent picture of older stratigraphy. A survey of 10 Ocean Bottom Seismometer profiles was collected around Svalbard in 1998. Results show a highly variable thickness of pre-Permian sedimentary strata, and a heterogeneous crystalline crust tied to candidates for continental sutures or major thrust zones. The data shown in this paper establish that the observed gravity in some parts of the platform can be directly related to velocity variations in the crystalline crust, but not necessarily to basement or Moho depth. The results from three new models are incorporated with a previously published profile, to produce depth-to-basement and -Moho maps south of Svalbard. There is a 14 km deep basement located approximately below the gently structured Upper Paleozoic Sørkapp Basin, bordered by a 7 km deep basement high to the west, and 7–9 km depths to the north. Continental Moho-depth range from 28 to 35 km, the thickest crust is found near the island of Hopen, and in a NNW trending narrow crustal root located between ∼19°E and 20°E, the latter is interpreted as a relic of westward dipping Caledonian continental collision or major thrusting. There is also a basement high on this trend. Across this zone, there is an eastward increase in the V P, V P/ V S ratio, and density, indicating a change towards a more mafic average crustal composition. The northward basement/Moho trend projects onto the Billefjorden Fault Zone (BFZ) on Spitsbergen. The eastern side of the BFZ correlates closely with coincident linear positive gravity and magnetic anomalies on western Ny Friesland, apparently originating from an antiform with high-grade metamorphic Caledonian terrane. A double linear magnetic anomaly appears on the BFZ trend south of Spitsbergen, sub-parallel to and located 10–50 km west of the crustal root. Based on this correlation, it is proposed that the suture or major thrust zone seen south of Svalbard correlates to the BFZ. The preservation of the relationship between the crustal suture, the crustal root, and upper mantle reflectivity, challenges the large-offset, post-collision sinistral transcurrent movement on the BFZ and other trends proposed in the literature. In particular, neither the wide-angle seismic data, nor conventional deep seismic reflection data south of Svalbard show clear signs of major lateral offsets, as seen in similar data around the British Isles.

Levels of selected metals in ambient air PM10 in an urban site of Zaragoza (Spain)

An assessment of the air quality of Zaragoza (Spain) was performed by determining the trace element content in airborne PM10 in a sampling campaign from July 2001 to July 2002. Samples were collected in a heavy traffic area with a high volume air sampler provided with a PM10 cutoff inlet. The levels of 16 elements (Al, Ba, Ca, Co, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, Pb, Sr, V, and Zn) were quantified after collecting the PM10 on Teflon-coated glass fiber filters (GFF). Regarding the PM10, 32% exceedance of the proposed PM10 daily limit was obtained, some of them corresponding to summer and autumn periods. The limit values of toxic trace elements from US-EPA, WHO, and EC were not exceeded, considering Zaragoza as a moderately polluted city under the current air quality guidelines. The contribution of anthropogenic sources to atmospheric elemental levels was reflected by the high values of enrichment factors for Zn, Pb, and Cu compared to the average crustal composition. Statistical analyses also determined the contribution of different sources to the PM10, finding that vehicle traffic and anthropogenic emissions related to combustion and industrial processes were the main pollutant sources as well as natural sources associated with transport of dust from Africa for specific dates. Regarding the influence of meteorological conditions on PM10 and trace elements concentrations, it was found that calm weather conditions with low wind speed favor the PM10 collection and the pollution for trace elements, suggesting the influence of local sources.

Chemical characterization of ambient aerosol collected during the northeast monsoon season over the Arabian Sea: Labile‐Fe(II) and other trace metals

Ambient aerosol samples were collected over the Arabian Sea during the month of March of 1997, aboard the German R/V Sonne, as part of the German Joint Global Ocean Flux Study (JGOFS) project. This is the third study in a series of analogous measurements taken over the Arabian Sea during different seasons of the monsoon. Dichotomous high‐volume collector samples were analyzed for ferrous iron immediately after collection, while trace metals, anions, and cations were determined upon return to the laboratory. The main crustal component was geochemically well represented by the average crustal composition and amounted to 5.94 ± 3.08 μg m−3. An additional crustal constituent of clay‐like character, rich in water‐soluble Ca and Mg, was seen in the fine fraction in air masses of Arabian origin. Total ferrous iron concentrations varied from 3.9 to 17.2 ng m−3 and averaged 9.8 ± 3.4 ng m−3, with 87.2% of Fe(II) present in the fine aerosol fraction. Fe(II) concentrations accounted for on average 1.3 ± 0.5% of the total Fe. While ferrous iron in the coarse fraction appeared to be correlated with the main crustal component, the fine Fe(II) fraction exhibited a more complex behavior. The anthropogenic contribution to the aerosol, as traced by Pb, Zn, and some anions and cations, was found to be considerably larger, especially during the first 10 days of this cruise, than in previously collected samples from the inter‐monsoon and southwest monsoon of 1995.

Dry atmospheric inputs of trace metals at the Mediterranean coast of Israel (SE Mediterranean): sources and fluxes

This study presents the first detailed data on aerosol concentrations of trace metals (Cd, Pb, Cu, Zn, Cr, Mn, Fe and Al) at the SE Mediterranean coast of Israel, and assesses their sources and fluxes. Aerosol samples were collected at two sampling stations (Tel-Shikmona and Maagan Michael) along the coast between 1994 and 1997. Two broad categories of aerosol trace metal sources were defined; anthropogenic (Cd, Cu, Pb and Zn) and naturally derived elements (Al, Fe, Mn and Cr). The extent of the anthropogenic contribution was estimated by the degree of enrichment of these elements compared to the average crustal composition (EF crust). High values (median >100) were calculated for Cd, Pb and Zn, minor values for Cu and relatively low values (<10) for Fe, Mn and Cr. The crustal-derived elements exhibited a statistically significant seasonal pattern of higher concentrations during spring and autumn (e.g. Al concentrations in some cases during these periods were observed to be in excess of 1500 ng m −3). In the eastern Mediterranean basin crustal-dominated elements are enriched by 2–3 times while others (Cd and Pb) are comparable to the northwestern Mediterranean. The Pb : Cd ratios of ∼150 are higher than in coastal European sites (60–116) or emission materials (∼50). It is speculated that these differences are attributed mainly to the mixing of crustal material with local and European emissions. At present, it is impossible to quantify the latter two fractions. Back trajectory analysis and the subsequent categorization of two main aerosol populations, ‘European’ and ‘North Africa–Arabian’, exhibited a significantly different geochemical imprint on the aerosol chemical composition. ‘European’-derived air masses indicated significantly higher EF crust values for Cd and Pb due to the greater anthropogenic character of the aerosol population, with a dilution by crustal material of this population leading to comparatively lower EF crust values associated with the North African–Arabian air masses.

Geochemistry of ∼1.9 Ga sedimentary rocks from northeastern Labrador, Canada

Fifty-eight rock chips from fifteen samples of sedimentary rocks from the Ramah Group (∼1.9 Ga) in northeastern Labrador, Canada, were analyzed for major and minor elements, including C and S, to elucidate weathering processes on the Earth's surface about 1.9 Ga ago. The samples come from the Rowsell Harbour, Reddick Bight, and Nullataktok Formations. Two rock series, graywacke-gray shales of the Rowsell Harbour, Reddick Bight and Nullataktok Formations, and black shales of the Nullataktok Formation, are distinguishable on the basis of lithology, mineralogy, and major and trace element chemistry. The black shales show lower concentrations than the graywackes-gray shales in TiO 2 (0.3–0.7 wt% vs. 0.7–1.8 wt%), Al 20 3 (9.5–20.1 wt% vs. 13.0–25.0 wt%), and ΣFe (<1 wt% vs. 3.8–13.9 wt% vs FeO). Contents of Zr, Th, U, Nb, Ce, Y, Rb, Y, Co, and Ni are also lower in the black shales. The source rocks for the Ramah Group sediments were probably Archean gneisses with compositions similar to those in Labrador and western Greenland. The major element chemistry of source rocks for the Ramah Group sedimentary rocks was estimated from the Al 2 O 3 TiO 2 ratios of the sedimentary rocks and the relationship between the major element contents (e.g., SiO 2 wt%) and Al 2 O 3 TiO 2 ratios of the Archean gneisses. This approach is justified, because the Al/Ti ratios of shales generally retain their source rock values; however, the Zr/Al, Zr/Ti, and Cr/Ni ratios fractionate during the transport of sediments. The measured SiO 2 contents of shales in the Ramah Group are generally higher than the estimated SiO 2 contents of source rocks by ∼5 wt%. This correction may also have to be applied when estimating average crustal compositions from shales. Two provenances were recognized for the Ramah Group sediments. Provenance I was comprised mostly of rocks of bimodal compositions, one with SiO 2 contents ∼45 wt% and the other ∼65 wt%, and was the source for most sedimentary rocks of the Ramah Group, except for black shales of the Nullataktok Formation. The black shales were apparently derived from Provenance 11 that was comprised mostly of felsic rocks with SiO 2 contents ∼65 wt%. Comparing the compositions of the Ramah Group sedimentary rocks and their source rocks, we have recognized that several major elements, especially Ca and Mg, were lost almost entirely from the source rocks during weathering and sedimentation. Sodium and potassium were also leached almost entirely during the weathering of the source rocks. However, significant amounts of Na were added to the black shales and K to all the rock types during diagenesis and/or regional metamorphism. The intensity of weathering of source rocks for the Ramah Group sediments was much higher than that of typical Phanerozoic sediments, possibly because of a higher Pco 2 in the Proterozoic atmosphere. Compared to the source rock values, the Fe 2+ Ti ratios of many of the graywackes and gray shales of the Ramah Group are higher, the Fe 2+/Ti ratios are lower, and the ΣFe/ Ti ratios are the same. Such characteristics of the Fe geochemistry indicate that these sedimentary rocks are comprised of soils formed by weathering of source rocks under an oxygen-rich atmosphere. The atmosphere about 1.9 Ga was, therefore, oxygen rich. Typical black shales of Phanerozoic age exhibit positive correlations between the organic C contents and the concentrations of S, U, and Mo, because these elements are enriched in oxygenated seawater and are removed from seawater by organic matter in sediments. However, such correlations are not found in the Ramah Group sediments. Black shales of the Ramah Group contain 1.7–2.8 wt%o organic C, but are extremely depleted in ΣFe (< 1 wt% as FeO), S (<0.3 wt%), U (∼1 ppm), Mo (<5 ppm), Ni (<2 ppm), and Co (∼0 ppm). This lack of correlation, however, does not imply that the ∼1.9 Ga atmosphere-ocean system was anoxic. Depletion of these elements from the Ramah Group sediments may have occurred during diagenesis.

Heat flow, gravity and structure of the Abitibi belt, Superior Province, Canada: Implications for mantle heat flow

The results of new heat flow measurements are presented for eleven sites located in the Abitibi greenstone belt of the Archean Superior Province. These new and previously published heat flow data are used with gravity and seismic data to constrain the crustal structure and composition of the Abitibi subprovince, and to determine the mantle heat flow beneath the Canadian Shield. In order to analyze the long-wavelength variations in heat flow and Bouguer gravity anomaly, the crust was divided into three layers with distinctive composition and physical properties. Average density, heat production and thickness for each layer were varied within a range compatible with measurements and yielded crustal models consistent with gravity and heat flow data. The dominant contribution to crustal heat production is that of a tonalitic type layer which has the lowest density. The models require mantle heat flow to range between 10 and 14 mW m −2. The westward increase in heat flow requires the tonalitic layer to thicken from the Grenville Front toward the Kapuskasing uplift at the expense of the greenstone supracrustals. Long-wavelength gravity data are more affected by changes in crustal thickness than by composition, and the low Bouguer anomaly near the eastern Grenville Front is caused by 5–6 km of crustal thickening. In greenstone terranes, the long-wavelength variations in heat flow are more useful for determining average crustal composition and the thickness of supracrustals than the gravity data.