Crustal assimilation during turbulent magma ascent (ATA); new isotopic evidence from the Mull Tertiary lava succession,N. W. Scotland

Assimilation of crustal rocks with concomitant fractional crystallisation (AFC) is a well documented phenomenon in many igneous suites, but geochemical evidence from the Tertiary Mull lava succession suggests that in these magmas crustal contamination occurred by a distinctly different mechanism. Lavas from the lower half of the Mull Plateau group (MPG) can be divided into two broad sub-types; high (>8%) MgO basalts with elevated Ba and K; and lower MgO (<8%) basaltic-hawaiites with lower Ba and K. The lower crust and most of the upper crust beneath Mull is probably of Lewisian age. The Sr-, Nd-and Pb-isotope compositions of local Lewisian crustal samples yield the following ranges: ⁸⁷Sr/⁸⁶Sr=0.71002–0.72348, ¹⁴³Nd/¹⁴⁴Nd=0.51045–0.51058 and ²⁰⁶Pb/²⁰⁴Pb=14.0–14.6. Ten lavas have also been analysed and yield the following ranges: ⁸⁷Sr/⁸⁶Sr=0.7028–0.7042, ¹⁴³Nd/¹⁴⁴Nd=0.51214–0.51230 and ²⁰⁶Pb/²⁰⁴Pb=15.1–17.9. However, within this range, it is predominantly the more primitive mafic compositions, with elevated Mg, Ba and K, that show the lowest Nd- and Pb-, and the highest Sr-isotope values. Modelling of these isotopic results, in conjunction with major and trace element data, show that: (1) contamination by Lewisian lower crustal material does occur; (2) that the process involved was not one of assimilation with concomitant fractional crystallisation (AFC). The proposed contamination process is one whereby the hottest (most MgO rich) magmas have assimilated acidic partial melts of Lewisian lower crust during turbulent ascent (ATA) through thin, poorly connected dyke- and sill-like magma chambers. The chemical composition of the contaminated lavas can be modelled successfully through addition of 5% acidic Lewisian crust to an uncontaminated lava. In contrast, the more evolved magmas — which probably fractionated at sub-crustal levels — were either not hot enough to molt significant amounts of crust, or did not ascend turbulently because of their higher viscosity, and so are less contaminated with crust.     

Ecological restoration, cultural preferences and the negotiation of ‘nativeness’ in Australia

The paper addresses cultural assumptions about ‘nativeness’ and ‘belonging’ to place as they are implicated in notions of ‘ecological restoration’. Given the centrality of complex notions of ‘indigeneity’ to the issue of what ecological ‘restoration’ means in Australia, this is a rich area for cultural and historical analysis. Case materials illustrate the negotiated and ambiguous nature of Australian ideas about what ‘belongs’ ecologically and culturally across the broad continent of this relatively young post-Settler nation. We seek to foreground these issues through consideration of what ‘restoring’ nature might mean in the context of debates about native plants, the re-introduction of an iconic species of ground dwelling bird, the removal of cane toads that are demonised as highly ‘alien’, and the multiple ways in which the dingo is regarded ambiguously as both native and a ‘pest’ that needs to be controlled and culled. By showing how ‘restoration’ can be understood and mobilised in a variety of ways – in terms of the ‘re-naturing’, ‘re-valuing’ and/or ‘repatriating’ of indigenous species, as well as impassioned rejection of ‘exotics’ – we emphasise the importance of social science for building a well-grounded sense of how environmental management priorities and approaches are informed by a wider set of cultural assumptions.     

Evaluation of the effects of alteration and leaching on Sm–Nd and Lu–Hf systematics in submarine mafic rocks

Nd and Hf isotope systematics of oceanic basaltic rocks are often assumed to be largely immune to the effects of hydrothermal alteration. We have tested this assumption by comparing Nd and Hf isotope data for acid-leached Cretaceous oceanic basalts from Gorgona and DSDP Leg 15 with unleached data on the same rocks. Hf isotope values and Lu/Hf ratios are relatively unaffected by leaching, but ¹⁴³Nd/¹⁴⁴Nd values of leached samples are significantly higher than those of unleached fractions of the same sample in most cases. Furthermore, the Sm/Nd ratios of the majority of leached samples are 10–40% greater than those of unleached samples. X-ray diffraction studies indicate that selective removal of secondary minerals, such as smectite, during the acid leaching process is responsible for the fractionation of Sm/Nd ratios. These results have implications for interpretation of the Hf–Nd isotope systematics of ancient submarine rocks (older than ~ 50 Ma), as (1) the age-corrected ¹⁴³Nd/¹⁴⁴Nd ratio may not be representative of the primary magmatic signature and (2) the uncertainty of the age-corrected ε_Nd value may exceed the assumed analytical precision.     

Inter‐annual variation in the topographic controls on catchment‐scale snow distribution in a maritime alpine catchment,New Zealand

Seasonal snow is a globally important water resource that contributes substantially to upland and lowland water resources. As such, there is a need to understand the controls on the spatial and temporal variation in snow distribution. This study meets this research need by investigating the topographic controls on snow depth distribution in the upper Jollie catchment in the Southern Alps of New Zealand. Furthermore, inter‐annual variation in the importance of the topographic controls is examined and linked to variation in the dominant synoptic‐scale weather patterns over a 4‐year period (2007–2010). Through the use of regression trees, the relative importance of the topographic controls on snow depth was shown to vary between the four study years. In particular, elevation explained the greatest amount of variance in 2007 and 2008 and east‐exposure explained the greatest variance in 2009 and 2010. The other wind exposure variables also had a large effect on the snow depth distribution in 2009 and 2010. Differences in the frequency and duration of synoptic weather patterns were physically consistent with the changing importance of these variables. In particular, a higher frequency of troughing events in 2009 and 2010 is thought to be associated with a reduced importance of elevation and greater influence of wind exposure on snow depth in these years. These findings demonstrate the importance of using multi‐year data sets, and of considering topographic and climatic influences, when attempting to model alpine snow distribution. Copyright © 2014 John Wiley & Sons, Ltd.     

Rupture behavior and deformation localization of the Kunlunshan earthquake (<Emphasis Type="Italic">M</Emphasis><Subscript><Emphasis Type="Italic">w</Emphasis></Subscript>7.8) and their tectonic implications

Earthquake surface rupture is the result of transformation from crustal elastic strain accumulation to permanent tectonic deformation. The surface rupture zone produced by the 2001 Kunlunshan earthquake (M _w 7.8) on the Kusaihu segment of the Kunlun fault extends over 426 km. It consists of three relatively independent surface rupture sections: the western strike-slip section, the middle transtensional section and the eastern strike-slip section. Hence this implies that the Kunlunshan earthquake is composed of three earthquake rupturing events, i.e. the M _w =6.8, M _w =6.2 and M _w ⩽=7.8 events, respectively. The M _w =7.8 earthquake, along the eastern section, is the main shock of the Kunlunshan earthquake, further decomposed into four rupturing subevents. Field measurements indicate that the width of a single surface break on different sections ranges from several meters to 15 m, with a maximum value of less than 30 m. The width of the surface rupture zone that consists of en echelon breaks depends on its geometric structures, especially the stepover width of the secondary surface rupture zones in en echelon, displaying a basic feature of deformation localization. Consistency between the Quaternary geologic slip rate, the GPS-monitored strain rate and the localization of the surface ruptures of the 2001 Kunlunshan earthquake may indicate that the tectonic deformation between the Bayan Har block and Qilian-Qaidam block in the northern Tibetan Plateau is characterized by strike-slip faulting along the limited width of the Kunlun fault, while the blocks themselves on both sides of the Kunlun fault are characterized by block motion. The localization of earthquake surface rupture zone is of great significance to determine the width of the fault-surface-rupture hazard zone, along which direct destruction will be caused by co-seismic surface rupturing along a strike-slip fault, that should be considered before the major engineering project, residental buildings and life line construction. Supported by the National Natural Science Foundation of China (Grant No. 40474037) and the National Basic Research Program of China (Grant No. 2004CB418401)     

The active fault system of SW Alps

Historical and active seismicity in the south-western Alps (France and Italy) shows the recurrence of relatively high-magnitude earthquakes (M ≥ 5.8), like the one that recently affected the Italian Apennine range (M = 6.3 on the 30th March 2009). However, up-to-date detailed mapping of the active fault network has been poorly established. The evaluation of seismological hazard in particular in the highly populated French and Italian coastal region cannot be done without this. Here, we present a detailed study of the main active fault system, based on geological observations along the south-western flank of the Alpine arc. This N140° right-lateral strike-slip active fault system runs along the edge of the Argentera-Mercantour range and can be followed down to the Mediterranean Sea. It is evidenced by (1) Holocene offsets of glacial geomorphology witnessing ongoing fault activity since 10 ka, (2) widespread recent (10–20 Ma) pseudotachylytes featuring long term activity of the faults, (3) active landslides along the main fault zone, (4) geothermal anomalies (hot springs) emerging in the active faults, (5) ongoing low-magnitude seismic activity and (6) localization of the main historical events. In the light of our investigations, we propose a new tectonic pattern for the active fault system in the south-western Alps.     

Measurements of arctic total ozone during the polar winter

Abstract

Ground‐based measurements of total ozone were made during the polar night from Arctic stations in the winters of 1987–88 and 1988–89. The measurements were made with automated Brewer ozone spectrophotometers using the moon as a light source. Data were obtained from Alert and Resolute in Canada for both winters and from Heiss Island, USSR, for the second winter. The method of measurement is briefly reviewed and data from the three stations are presented. The ground‐based total ozone measurements are compared with the integrated values derived from ozonesonde profiles.     

Measurement of stratospheric nitrogen dioxide from the AES stratospheric balloon program

A spectrophotometer which is capable of measuring atmospheric nitrogen dioxide by remote sensing has been included on board the Stratoprobe I and II balloon programs. The results obtained from the Stratoprobe I flight from Churchill, Manitoba, on 22 July 1974, and preliminary results from the Stratoprobe II flights from Yorkton, Saskatchewan on 17–18 August 1975, will be presented here.