Large-scale distributed deformation controlled topography along the western Africa–Eurasia limit: Tectonic constraints

In the interior of the Iberian Peninsula, the main geomorphic features, mountain ranges and basins, seems to be arranged in several directions whose origin can be related to the N–S plate convergence which occurred along the Cantabro–Pyrenean border during the Eocene–Lower Miocene time span. The Iberian Variscan basement accommodated part of this plate convergence in three E–W trending crustal folds as well as in the reactivation of two left-lateral NNE–SSW strike-slip belts. The rest of the convergence was assumed through the inversion of the Iberian Mesozoic Rift to form the Iberian Chain. This inversion gave rise to a process of oblique crustal shortening involving the development of two right lateral NW–SE shear zones. Crustal folds, strike-slip corridors and one inverted rift compose a tectonic mechanism of pure shear in which the shortening is solved vertically by the development of mountain ranges and related sedimentary basins. This model can be expanded to NW Africa, up to the Atlasic System, where N–S plate convergence seems also to be accommodated in several basement uplifts, Anti-Atlas and Meseta, and through the inversion of two Mesozoic rifts, High and Middle Atlas. In this tectonic situation, the microcontinent Iberia used to be firmly attached to Africa during most part of the Tertiary, in such a way that N–S compressive stresses could be transmitted from the collision of the Pyrenean boundary. This tectonic scenario implies that most part of the Tertiary Eurasia–Africa convergence was not accommodated along the Iberia–Africa interface, but in the Pyrenean plateboundary. A broad zone of distributed deformation resulted from the transmission of compressive stresses from the collision at the Pyrenean border. This distributed, intraplate deformation, can be easily related to the topographic pattern of the Africa–Eurasia interface at the longitude of the Iberian Peninsula.Shortening in the Rif–Betics external zones – and their related topographic features – must be conversely related to more “local” driven mechanisms, the westward displacement of the “exotic” Alboran domain, other than N–S convergence. The remaining NNW–SSE to NW–SE, latest Miocene up to Present convergence is also being accommodated in this zone straddling Iberia and Morocco, at the same time as a new ill-defined plate boundary that is being developed between Europe and Africa.     

Basalts as probes of planetary interiors: Constraints on the chemistry and mineralogy of their source regions

Basalt magmas, derived by the partial melting of planetary interiors, have compositions that reflect the pre-accretionary history of the material from which the planet formed, the planets, subsequent evolutionary history, the chemistry and mineralogy of the source regions, and the intensive thermodynamic parameters operating at the source and emplacement sites. Studies of basalt suites from the Earth, its Moon, and the eucrite parent body reveal compositional differences intrinsic to their source regions which are, in turn, a characteristic of the planet and its formational and evolutionary history.Major interplanetary differences are observed in iron, , TiO₂, Al₂O₃, Na₂O, Cr, Ni, and in volatile element abundances. The most primitive mare basalts have Mg#s 0.6, on the Earth they are 0.70–0.72 for mid-ocean ridge basalts (MORBs) and up to 0.9 for Archean peridotitic komatiites. Eucrites have Mg#s approaching 0.5 (excepting Binda). These differences reflect inherent differences in of their sources. Striking differences in the TiO₂ abundances of the planetary basalts reflect both inter- and intra-planetary variations in source chemistry. Primitive MORBs and primitive oceanic intraplate tholeiites have a factor of 2–3 difference in TiO₂ at comparable Mg# (0.7–1.2 vs 2–3 wt.% respectively). Three major titania groups are recognized in the mare suite; high TiO₂ (8–13 wt.%), low TiO₂ (2–5 wt.%) and very low TiO₂ (<1 wt.%). The eucrites have TiO₂ contents <1 wt.%.The mare basalts and eucrites have pronounced Na₂O depletion relative to all terrestrial basalts. This is a consequence of the preplanetary accretion loss of volatiles from the material that formed the Moon and the eucrite parent bodies.Mare basalts have consistently lower Al₂O₃ contents than the terrestrial basalts. This may be due either to an inherently lower content of Al₂O₃ in the mare sources or it may reflect Al₂O₃ retention in an aluminous phase.The transition metals are fractionated in all three basalt suites. For terrestrial basalts this may reflect core-separation; however, in the case of the Moon and eucrite parent bodies pre-accretionary separation of metal and silicates is a more reasonable explanation. A pronounced Cr anomaly is observed in terrestrial MORBs but not in the mare basalts. This appears to be related to f_O2 differences in the respective mantles.Overall rare earth element abundances are comparable between all three objects. Mare basalts have a pronounced negative Eu anomaly which is inherited from their source region and is record of plagioclase removal from crystallizing magma ocean early in lunar history (4.4–4.6 Ga). Early separation of plagioclase on the Earth appears to have been a relatively unimportant process.     

1.8–1.5-Ga links between the North and South Australian Cratons and the Early–Middle Proterozoic configuration of Australia

The Archaean and Early–Middle Proterozoic (1.8–1.5 Ga) terranes of the North Australian Craton and the South Australian Craton are separated by 400 km of ca. 1.33–1.10-Ga orogenic belts and Phanerozoic sediments. However, there is a diverse range of geological phenomena that correlate between the component terranes of the two cratons and provide evidence for a shared tectonic evolution between approximately 1.8 and 1.5 Ga. In order to honour these correlations, we propose a reconstruction in which the South Australian Craton is rotated 52° counterclockwise about a pole located at 136°E and 25°S (present-day coordinates), relative to its current position. This reconstruction aligns the ca. 1.8–1.6-Ga orogenic belts preserved in the Arunta Inlier and the Gawler Craton and the ca. 1.6–1.5-Ga orogenic belts preserved in the Mount Isa Block and the Curnamona Province. Before 1.5 Ga, the South Australian Craton was not a separate entity but part of a greater proto-Australian continent which was characterised by accretion along a southward-migrating convergent margin (ca. 1.8–1.6 Ga) followed by convergence along the eastern margin (ca. 1.6–1.5 Ga). After 1.5 Ga, the South Australian Craton broke away from the North Australian Craton only to be reattached in its current position during the ca. 1.33–1.10 Ga-Albany–Fraser and Musgrave orogenies.     

Wardrobe matter: the sorting, displacement and circulation of women's clothing

This paper develops a reading of the wardrobe which emphasises the wardrobe's location within the consumption practices of tidying, sorting and the displacement of clothing. Its emphasis is on the circulation of clothing matter and the transience of clothing consumption, not––as recent accounts have stressed––the accumulation, collection and wearing of clothing. Using primarily the example of maternity wear, the paper outlines how clothing matter circulates amongst and between women (between siblings, between friends and amongst neighbours and acquaintances) and accounts for this practice. It argues that maternity wear circulation is both an embodied divestment/recovery ritual and about the making of mothers, through its appeal to thrift, sacrifice and making-do. The paper concludes by reflecting on the significance of the absence of maternity wear from women's wardrobes and by suggesting that wardrobes need to be thought of not just as containers of memory, but as temporary holding places in the lives of clothes, and as pivotally positioned as a fulcrum for clothing movement, between wearing, storage and displacement.     

`Our resistance will be as transnational as capital': Convergence space and strategy in globalising resistance

This paper analyses the emerging globalising networks of communication, solidarity, and information-sharing between social movements and other resistance formations in opposition to neoliberal globalisation. In particular, the paper focuses upon People's Global Action – a network of various social movemnets and grassroots intitiatives from around the world. The paper argues that such a network represents not an organisation, but rather a convergence space – a heterogenous affinity of common ground between resistance formations wherein certain interests, goals, tactics and strategies converge. The paper analyses how space and strategy are negotiated in these globalising terrains of resistance, and argues that place-specific struggles are engaging with alliances and collaborations across diverse boundaries of gender, generation, class, and ethnicity – globalising the common ground between different struggles. Explaining how the internet has been crucial to the development of these networks, the paper argues that the strategies of such networks can be interpreted, in part, through the Taoist text, The Art of War, especially the Taoist notions of terrain, knowing others, and form/lessness. In addition, the paper argues that convergence spaces are fragmented by important issues of language, power, and mobility.     

Late Quaternary faulting along the western margin of the Poronaysk Lowland in central Sakhalin, Russia

Sakhalin Island straddles an active plate boundary between the Okhotsk and Eurasian plates. South of Sakhalin, this plate boundary is illuminated by a series of M_w 7–8 earthquakes along the eastern margin of the Sea of Japan. Although this plate boundary is considered to extend onshore along the length of Sakhalin, the location and convergence rate of the plate boundary had been poorly constrained. We mapped north-trending active faults along the western margin of the Poronaysk Lowland in central Sakhalin based on aerial photograph interpretation and field observations. The active faults are located east of and parallel to the Tym–Poronaysk fault, a terrane boundary between Upper Cretaceous and Neogene strata; the active faults appear to have reactivated the terrane boundary at depth in Quaternary time. The total length of the active fault zone on land is about 140 km. Tectonic geomorphic features such as east-facing monoclinal and fault scarps, back-tilted fluvial terraces, and numerous secondary faults suggest that the faults are west-dipping reverse faults. Assuming the most widely developed geomorphic surface in the study area formed during the last glacial maximum at about 20 ka based on similarities of geomorphic features with those in Hokkaido Island, we obtain a vertical component of slip rate of 0.9–1.4 mm/year. Using the fault dip of 30–60°W observed at an outcrop and trench walls, a net slip rate of 1.0–2.8 mm/year is obtained. The upper bound of the estimate is close to a convergence rate across the Tym–Poronaysk fault based on GPS measurements. A trenching study across the fault zone dated the most recent faulting event at 3500–4000 years ago. The net slip associated with this event is estimated at about 4.5 m. Since the last faulting event, a minimum of 3.5 m of strain, close to the strain released during the last event, has accumulated along the central portion of the active strand of the Tym–Poronaysk fault.     

Detection of petroleum contamination in river sediments from Quebec City region using GC–IRMS

Isotopic analysis by compound specific gas chromatography–isotope ratio mass spectrometry (GC–IRMS) is used to detect and characterize petroleum pollution in surficial sediments along the St Lawrence River, near Quebec City. Unusually mature n-alkane distributions have been found in some recent intertidal sediments in the region. GC–IRMS results suggest that the n-alkanes are not derived from indigenous organic sources because they carry δ¹³C values between −30.0 and −27.0‰, as well as very small isotopic differences between odd and even numbered n-alkanes, which are both typically associated with petroleum products. Comparison of these sediments with bunker fuel, an oil used in the shipping industry, has shown a close isotopic correlation in some sites, which is further supported by biomarkers. Overall, the contamination has been dispersed along the river but is generally localized around the industrial region where hydrocarbon transfer from shore storage to ships takes place. This study illustrates how GC–IRMS can be used effectively in the detection and characterization of petroleum pollutants in sediments.     

Why does the co-seismic slip of the 1999 Chi-Chi (Taiwan) earthquake increase progressively northwestward on the plane of rupture?

The Chi-Chi 1999 earthquake ruptured the out-of-sequence Chelungpu Thrust Fault (CTF) in the fold-and-thrust belt in Western Central Taiwan. An important feature of this rupture is that the calculated slip increases approximately linearly in the SE–NW convergence plate direction from very little at its deeper edge to a maximum near the surface. We propose here a new explanation for this co-seismic slip distribution based on the study of both stress and displacement over the long-term as well as over a seismic cycle. Over the last 0.5 My, the convergence rate in the mountain front belt is accommodated by the frontal Changhua Fault (Ch.F), the CTF and the Shuangtung Fault (Sh.F). Based on previously published balanced cross sections, we estimate that the long-term slip of the Ch.F and of the CTF accommodate 5–30% and 30–55% of the convergence rate, respectively. This long-term partitioning of the convergence rate and the modeling of inter-seismic and post-seismic displacements suggest that the peculiar linear co-seismic slip distribution is accounted for by a combination of the effect of the obliquity of the CTF to the direction of inter-seismic loading, and of increasing aseismic creep on the deeper part of the Ch.F and CTF. Many previous interpretations of this slip distribution have been done including the effects of material properties, lubrication, site effect, fault geometry and dynamic waves. The importance of these processes with respect to the effects proposed here is still unknown. Taking into account the dip angle of the CTF, asperity dynamic models have been proposed to explain the general features of co-seismic slip distribution. In particular, recent works show the importance of heterogeneous spatial distribution of stress prior to the Chi-Chi earthquake. Our analysis of seismicity shows that previous large historic earthquakes cannot explain the amplitude of this heterogeneity. Based on our approach, we rather think that the high stress in the northern part of the CTF proposed by Oglesby and Day [Oglesby, D.D., Day, S.M., 2001. Fault geometry and the dynamics of the 1999 Chi-Chi (Taiwan) earthquake. Bull. Seismol. Soc. Am. 91, 1099–1111] reflects the latitudinal variation of inter-seismic coupling due to the obliquity of the CTF.     

Seismic potential of Southern Italy

To improve estimates of the long-term average seismic potential of the slowly straining South Central Mediterranean plate boundary zone, we integrate constraints on tectonic style and deformation rates from geodetic and geologic data with the traditional constraints from seismicity catalogs. We express seismic potential (long-term average earthquake recurrence rates as a function of magnitude) in the form of truncated Gutenberg–Richter distributions for seven seismotectonic source zones. Seismic coupling seems to be large or even complete in most zones. An exception is the southern Tyrrhenian thrust zone, where most of the African–European convergence is accommodated. Here aseismic deformation is estimated to range from at least 25% along the western part to almost 100% aseismic slip around the Aeolian Islands. Even so, seismic potential of this zone has previously been significantly underestimated, due to the low levels of recorded past seismicity. By contrast, the series of 19 M6–7 earthquakes that hit Calabria in the 18th and 19th century released tectonic strain rates accumulated over time spans up to several times the catalog duration, and seismic potential is revised downward. The southern Tyrrhenian thrust zone and the extensional Calabrian faults, as well as the northeastern Sicilian transtensional zone between them (which includes the Messina Straits, where a destructive M7 event occurred in 1908), all have a similar seismic potential with minimum recurrence times of M ≥ 6.5 of 150–220 years. This potential is lower than that of the Southern Apennines (M ≥ 6.5 recurring every 60 to 140 years), but higher than that of southeastern Sicily (minimum M ≥ 6.5 recurrence times of 400 years). The high seismicity levels recorded in southeastern Sicily indicate some clustering and are most compatible with a tectonic scenario where the Ionian deforms internally, and motions at the Calabrian Trench are small. The estimated seismic potential for the Calabrian Trench and Central and Western Sicily are the lowest (minimum M ≥ 6.5 recurrence times of 550–800 years). Most zones are probably capable of generating earthquakes up to magnitudes 7–7.5, with the exception of Central and Western Sicily where maximum events sizes most likely do not exceed 7.     

Is groundwater in the Tarkwa gold mining district of Ghana potable?

Hand-pump wells in the Tarkwa gold mining district and the geologically similar Bui area were chemically analysed and compared in an effort to determine whether groundwaters in the Tarkwa area have been affected by mining. Significant chemical differences attributed to mine water discharges have been observed in streams in the Tarkwa area. Groundwater chemistry from hand-pump wells in Tarkwa and Bui areas reveal similar hydrochemical facies, predominantly Ca–Na–Mg–HCO₃–Cl. However, except for SO₄^2–, ionic concentrations of groundwaters from Bui are greater than those from Tarkwa probably due to differences in (1) water availability during sedimentation (2) water-rock interactions and/or residence times for water. No demonstrable impact of mining on groundwaters from hand-pumped wells in the Tarkwa area has been noted. Hydrogeological inference suggests that the main streams which receive mine water discharges are both gaining and are groundwater divides. The overwhelming majority of population centres and mining operations are located on opposite sides of these groundwater divides, therefore, it is unlikely aquifers tapped for drinking by these communities would be affected by mining.     

The Tornquist Sea and Baltica–Avalonia docking

Early Ordovician (Late Arenig) limestones from the SW margin of Baltica (Scania–Bornholm) have multicomponent magnetic signatures, but high unblocking components predating folding, and the corresponding palaeomagnetic pole (latitude=19°N, LONGITUDE=051°E) compares well with Arenig reference poles from Baltica. Collectively, the Arenig poles demonstrate a midsoutherly latitudinal position for Baltica, then separated from Avalonia by the Tornquist Sea.Tornquist Sea closure and the Baltica–Avalonia convergence history are evidenced from faunal mixing and increased resemblance in palaeomagnetically determined palaeolatitudes for Avalonia and Baltica during the Mid-Late Ordovician. By the Caradoc, Avalonia had drifted to palaeolatitudes compatible with those of SW Baltica, and subduction beneath Eastern Avalonia was taking place. We propose that explosive vents associated with this subduction and related to Andean-type magmatism in Avalonia were the source for the gigantic Mid-Caradoc (c. 455 Ma) ash fall in Baltica (i.e. the Kinnekulle bentonite). Avalonia was located south of the subtropical high during most of the Ordovician, and this would have provided an optimum palaeoposition to supply Baltica with large ash falls governed by westerly winds.In Scania, we observe a persistent palaeomagnetic overprint of Late Ordovician (Ashgill) age (pole: LATITUDE=4°S, LONGITUDE=012°E). The remagnetisation was probably spurred by tectonic-derived fluids since burial alone is inadequate to explain this remagnetisation event. This is the first record of a Late Ordovician event in Scania, but it is comparable with the Shelveian event in Avalonia, low-grade metamorphism in the North Sea basement of NE Germany (440–450 Ma), and sheds new light on the Baltica–Avalonia docking.     

The role of supergene sulphuric acid during weathering in small river catchments in low mountain ranges of Central Europe: Implications for calculating the atmospheric CO2 budget

The geochemistry of dissolved and suspended loads in river catchments of two low mountain ranges in Central Europe allows comparison of pertinent chemical weathering rates. Distinct differences in lithology, i.e. granites prevailing in the Black Forest compared to Palaeozoic sediments in the Rhenish Massif, provide the possibility to examine the influence of lithology on weathering. Here we determine the origin of river water using the stable isotope ratio δ¹⁸O_H2O and we quantify the geogenic proportions of sulphate from stable isotope ratios δ³⁴S_SO4 and δ¹⁸O_SO4. Particularly in catchments with abundant pyrite, determination of the geogenic amount of sulphate is important, since oxidation of pyrite leads to acidity, which increases weathering. Our results show that spatially averaged silicate weathering rates are higher for the river catchments Acher and Gutach in the Black Forest (10–12 t/km²/yr) compared to the river catchments of the Möhne dam and the Aabach dam in the Rhenish Massif (2–6 t/km²/yr). Correspondingly, the CO₂ consumption by silicate weathering in the Black Forest (334–395 × 10³ mol/km²/yr) is more than twice as high as in the Rhenish Massif (28–151 × 10³ mol/km²/yr). These higher rates for watersheds of the Black Forest are likely due to steeper slopes leading to higher mechanical erosion with respective higher amounts of fresh unweathered rock particulates and due to the fact that the sediments in the Rhenish Massif have already passed through at least one erosion cycle. Carbonate weathering rates vary between 12 and 38 t/km²/yr in the catchments of the Rhenish Massif. The contribution of sulphuric acid to the silicate weathering is higher in the catchments of the Rhenish Massif (9–16%) than in the catchments of the Black Forest (5–7%) due to abundant pyrite in the sediments of the Rhenish Massif. Three times higher long-term erosion rates derived from cosmogenic nuclides compared to short-term erosion rates derived from river loads in Central Europe point to three times higher CO₂ consumption during the past 10³ to 10⁴ years.     

Symplectites in upper mantle peridotites: Development and implications for the growth of subsolidus garnet,pyroxene and spinel

Silicate-oxide symplectites in complex mineral intergrowths are relatively common in upper mantle xenoliths and in xenoliths in the Jagersfontein Kimberlite, South Africa.Harzburgites of olivine and high-Al (1.9–3.6 wt%), Ca (0.6–0.9 wt%) and Cr (0.3–0.9 wt%) enstatite contain symplectites of spinel and diopside, or spinel, diopside and lower-Al (0.8–2.2 wt%), Ca (0.1–0.4 wt%) and Cr (0.02–0.8 wt%) enstatite. From textures and mineral chemistries these symplectites are interpreted to have formed by mineral unmixing and migration from Al–Ca–Cr discrete enstatite to adjoining mineral interfaces.Garnet harzburgites are composed of large (0.5–1 cm) olivine, equally large discrete low-Al (0.6–1.1 wt%), Ca (0.1–0.5 wt%), and Cr (0.1–0.3 wt%) enstatite and smaller interstitial garnet, diopside, and high-Cr and low-Al spinel. Symplectites are composed of either spinel+diopside+garnet, or garnet+spinel. Spinel diopside garnet symplectites have cores of spinel+diopside, resembling symplectites inharzburgites, but surrounded by rims of garnet or garnet+undigested globular spinel. From textures and chemistries we suggest that the spinel+diopside cores formed from Ca-Al-Cr-rich orthopyroxene initially as a nonstoichiometric homogeneous single phase clinopyroxene enriched in Fe, Cr and Al. This was followed by decomposition of the clinopyroxene to diopside+spinel, and subsequent garnet formation in a prograde reaction with olivine or enstatite. In bothharzburgites andgarnet harzburgites the metastable cellular structures may also have formed by the simultaneous precipitation of pyroxene and spinel. In all cases there is a strongly preferred embayment of symplectite bodies into olivine. Olivine appears to have activated adjacent     

Plate collision and paleostress trajectories in a fold-thrust belt: The foothills of Taiwan

Field analyses of compressional faulting and folding in the Foothills of western Taiwan enable us to reconstruct paleostress trajectories over a large area and to establish the relative chronology of tectonic events. Two main compressional events have contributed to the present structure of the fold-thrust belt. Stratigraphic data show that these events are Plio-Pliocene in age. Older normal faulting indicates NNW-SSE extension across the Chinesse passive continental margin during the Neogene. The two main compressional events of the Taiwan collision correspond to similar fan-shaped distributions of maximum compressive stress trajectories, with a counterclockwise shift of 30°–50° between the two events. Using the relationship between recent stress trajectories and the direction of recent plate motion as a guide, we reconstruct the direction of plate convergence for the older event. We suspect that the relative motion Philippine Sea plate-Eurasia has rotated counterclockwise of at least 35°–45° in Taiwan during collision. This conclusion is in agreement with independent plate tectonic reconstructions. Several problems provide objectives to further tectonic and paleomagnetic studies, including the duration and diachronism of compressional events as well as possible clockwise rotation of northernmost Taiwan.     

Coal petrographical characterization of the Mecsek bituminous coal basin, with special reference to the contact metamorphism of coal seams

The bituminous coals of the Mecsek Mountains were formed during the Early Lias and are of paralic origin. The limnic complex of the layers consists of sandstone, aleurite and coal, and the upper layer contains marl of marine origin. The 9–15 minable coal seams have a thickness of 1.2–14.0 m. The Mecsek Coal Field and the coal complex within it show a folded and fractured structure, and with regard to their mechanical behaviour, are strongly stressed.75–90% of the coal material is vitrinite, and 1–14% is inertinite. The quantity of liptinite is smaller than 9%. The coal rank is that of gas coal and fat coal with a reflectivity of 0.85–1.5%, respectively. The coal rank differences and variations according to zones are the consequence of forces of various magnitude that occurred in the course of orogenic movements.During the Early Cretaceous, there was some under-sea-bed volcanic activity in this field, the diabasic material of which appeared in the form of a bed vein along the coal seams, and this has exerted a strong metamorphic influence on the coal. It has resulted in thermo-contact alteration, i.e. in the appearance of natural coke and semicoke of various degrees of metamorphism. This alteration badly affected the quality and technological characteristics, especially the cokability of the coal.     

A study of inherited zircons in granitoid rocks from the South Portuguese and Ossa-Morena Zones, Iberian Massif: support for the exotic origin of the South Portuguese Zone

Trace element and U–Pb isotopic analyses of inherited zircon cores from a sample of Gil Márquez granodiorite (South Portuguese Zone, SPZ) and Almonaster nebulite (Ossa-Morena Zone, OMZ, in the Aracena Metamorphic Belt) have been obtained using laser ablation-inductively coupled plasma-mass spectrometry. These data reveal differences in the age of deep continental crust in these two zones. Inherited zircon cores from the Ossa-Morena Zone range at 600±100 Ma, 1.7–2 Ga and 2.65–2.95 Ga, while those from the South Portuguese Zone range at 400–500 and 700–800 Ma. These data support the “exotic” origin of the South Portuguese Zone basement relative to the rest of Iberian Massif. The young ages of inherited zircon cores and Nd model ages of magmatic rocks of the South Portuguese Zone are comparable to results from granulite facies xenoliths and granitic rocks from the Meguma Terrane and Avalonia and support a correlation between the basement of the southernmost part of the Iberian Massif and the northern Appalachians.     

Contemporary runoff trends in some highland stream basins in Bulgaria

Hydrological changes in four stream basins situated on the northern slopes of the Stara Planina range (North Bulgaria) and in the Rodopi massif (South Bulgaria) have been investigated during the 1951–1989 time period. Parallel analysis of runoff and precipitation mean annual values have been made, calculating the respective annual ratios compared to the mean of the entire range mean value. Curves of runoff and precipitation frequencies have been developed and analyzed. This investigation establishes that during the 1980s a consistent trend towards significant humidity reduction has occurred. Mean annual deviation values of the last decade compared to the entire period mean annual figure amount to 5–20% and 10–25% for the precipitation and runoff, respectively, with humidity reduction of greater amplitude in the North Bulgarian stream basins. Annual Mean deviations are due to significant moisture reduction during the warm half of the year in North Bulgaria and in the cold half in South Bulgaria. Both regions reflect zonal differences caused by climatic patterns of European if not planetary scale.     

U–Pb ages of Neoarchean granitoids from the Black Hills, South Dakota, USA: implications for crustal evolution in the Archean Wyoming province

Zircons in basement rocks from the eastern Wyoming province (Black Hills, South Dakota, USA) have been analyzed by ion microprobe (SHRIMP) in order to determine precise ages of Archean tectonomagmatic events. In the northern Black Hills (NBH) near Nemo, Phanerozoic and Proterozoic (meta)sedimentary rocks are nonconformably underlain by Archean biotite–feldspar gneiss (BFG) and Little Elk gneissic granite (LEG), both of which intrude older schists. The Archean granitoid gneisses exhibit a pervasive NW–SE-trending fabric, whereas an earlier NE–SW-trending fabric occurs sporadically only in the BFG, which is intruded by the somewhat younger LEG. Zircon crystals obtained from the LEG and BFG exhibit double terminations, oscillatory zoning, and Th/U ratios of 0.6±0.3—thereby confirming a magmatic origin for both lithologies. In situ analysis of the most U–Pb concordant domains yields equivalent ²⁰⁷Pb/²⁰⁶Pb ages (upper intercept, U–Pb concordia) of 2559±6 and 2563±6 Ma (both ±2σ) for the LEG and BFG, respectively, which constrains a late Neoarchean age for sequential pulses of magmatism in the NBH. Unzoned (in BSE) patches of 2560 Ma zircon commonly truncate coeval zonation in the same crystals with no change in Th/U ratio, suggesting that deuteric, fluid-assisted recrystallization accompanied post-magmatic cooling. A xenocrystic core of magmatic zircon observed in one LEG zircon yields a concordant age of 2894±6 Ma (±2σ). This xenocryst represents the oldest crustal material reported thus far in the Black Hills. Whether this older zircon originated as unmelted residue of 2900 Ma crust that potentially underlies the Black Hills or as detritus derived from 2900 Ma crustal sources in the Wyoming province cannot be discerned. In the southern Black Hills (SBH), the peraluminous granite at Bear Mountain (BMG) of previously unknown age intrudes biotite–plagioclase schist. Zircon crystals from the BMG are highly metamict and altered, but locally preserve small domains suitable for in situ analysis. A U–Pb concordia upper intercept age of 2596±11 Ma (±2σ) obtained for zircon confirms both the late Neoarchean magmatic age of the BMG and a minimum age for the schist it intrudes. Taken together, these data indicate that the Neoarchean basement granitoids were emplaced at 2590–2600 Ma (SBH) and 2560 Ma (NBH), most likely in response to subduction associated with plate convergence (final assembly of supercontinent Kenorland?). In contrast, thin rims present on some LEG–BFG zircons exhibit strong U–Pb discordance, high common Pb, and low Th/U ratios—suggesting growth or modification under hydrothermal conditions, as previously suggested for similar zircons from SE Wyoming. The LEG–BFG zircon rims yield a nominal upper intercept date of 1940–2180 Ma, which may represent a composite of multiple rifting events known to have affected the Nemo area between 2480 and 1960 Ma. Together, these observations confirm the existence of a Paleoproterozoic rift margin along the easternmost Wyoming craton. Moreover, the 2480–1960 Ma time frame inferred for rifting in the Black Hills (Nemo area) corresponds closely to a 2450–2100 Ma time frame previously inferred for the fragmentation of supercontinent Kenorland.     

Lightning fatalities in Australia, 1824–1991

Information on fatalities from lightning strikes has been extracted from a specially compiled database on natural hazards in Australia. Records dating from 1803–1991 indicate that at least 650 persons have been killed by lightning strikes. Maps and charts show the percentages of victims with respect to age, sex, locality, activity, and other circumstances of the strike. The majority of the 650 fatalities recorded have occurred along the more populous southeastern coast. The overall death rate, from 1910–1989, is 0.08 per 100 000 population. The annual number of lightning fatalities has decreased with time, from a death rate of 0.21 in 1910–1919 to 0.01 in 1980–1989. This trend is more pronounced when population figures are taken into account. The group that has been most at risk in Australia is that of males aged 15–19, followed by males aged 20–34. The male:female ratio of victims has decreased with time but is not approaching equality, being 11.6 in 1910–1919 and 5.3 in 1980–1989. The diurnal and monthly occurrences of lightning fatalities peak at 12.00–18.00 hours and November-February respectively. About 86% of fatalities have occurred outdoors and 14% have occurred indoors. Approximately three-fifths of fatalities have been work-related, and the group of workers that has traditionally been most at risk is that of land-workers. Approximately one-fifth of fatalities have been recreation-related, although this proportion has been increasing with time. The recreational activities of water sports, golf, and cricket have had the greatest number of lightning fatalities. Comparisons are made between these data and the results of other similar studies, both in Australia and overseas.     

Detrital zircon provenance evidence for large-scale extrusion along the Altyn Tagh fault

The question of whether or not the Altyn Tagh fault is a large-scale extrusion boundary is critical for understanding the role of lateral extrusion in accommodating the Indo-Asian convergence and in building the Tibetan Plateau. Oligocene conglomerate clasts in the eastern Xorkol basin are low-grade slate, phyllite, sandstone, dacite and carbonate, and associated paleocurrent indicators evince sediment derivation from the opposing side of the Altyn Tagh fault. Matching these clasts with similar basement rocks in the North Qilian and Tuolainanshan terranes requires post-Oligocene left-lateral offset of 380 ± 60 km on the eastern segment of the Altyn Tagh fault, suggesting large-scale extrusion along the fault in the Cenozoic (Yue, Y.J., Ritts, B.D., Graham, S.A., 2001b. Initiation and long-term slip history of the Altyn Tagh fault. International Geological Review 43, 1087–1094.). In order to further define this piercing point, the detrital zircon pattern of Oligocene sandstone from the Xorkol basin and the zircon ages of basement on the southern side of the fault were established by ion microprobe dating. Characterized by strong peaks between 850 and 950 Ma and the absence of Paleozoic and Mesozoic ages, the detrital zircon age pattern of the Oligocene sandstone matches the age distribution of zircon-bearing rocks of the Tuolainanshan terrane. This match requires 360 ± 40 km of post-Oligocene left-lateral displacement on the eastern segment of the Altyn Tagh fault, supporting as well as refining the previously reported lithology-based cross-fault match. At least one of the following three extrusion scenarios must have existed to accommodate this large offset: (1) northeastward extrusion along the Altyn Tagh–Alxa–East Mongolia fault, (2) eastward extrusion along the Altyn Tagh–North Qilian–Haiyuan fault, and (3) northeastward extrusion of northern Tibet as a Himalaya-scale thrust sheet along the North Qilian–Haiyuan fault. We prefer the first scenario inasmuch as rapidly growing evidence for Cenozoic strike-slip activity on the Alxa–East Mongolia fault and mid-Miocene exhumation of northern Tibet supports it.