Preface

Preface

Preface     

The Iberian Pyrite Belt: a mineralized system dismembered by voluminous high-level sills

The Iberian Pyrite Belt is a world-ranking massive sulphide province in which a reassessment of the palaeovolcanology has dramatically changed understanding of the source of metals and mechanism of ore formation. In the northern sector, the deposits are hosted by a sill–sediment complex in which more than 90% of the sills post-date the sulphide sheets. Because of a very high sill/sediment ratio, these late intrusions dominate the host succession and have severely disrupted the post-mineralization configuration thus obscuring the true genetic relationships. For example, some oxide deposits have been separated by hectometric sills from sulphide deposits they originally capped, creating seemingly totally independent mineralizing systems. In addition, stratiform sulphide sheets without underlying stockworks are not necessarily allochthonous. An early timing for the mineralization with respect to volcanism means that metals had to be predominantly sourced from the sedimentary basin and the continental crust below the volcanogenic sequence.     

Dike intrusion under shear stress: Effects on magnetic and vesicle fabrics in dikes from rift zones of Tenerife (Canary Islands)

A theoretical model predicting how anisotropy of magnetic susceptibility (AMS) and vesicle fabrics are modified by shear stress resolved on the dike walls prior to the final cooling of magma is developed for vertical dikes. The resulting fabrics are asymmetric with respect to initial fabrics assumed to be symmetric. Application of this model together with collected data on magma flow direction, dike propagation direction and mechanism, and shear sense, allow us to interpret dike fabrics in terms of shear resolved on the dike walls during intrusion (en echelon arrangement, offsetting, and dike curvature). The interpretation of AMS and vesicle fabrics of the margins of four dikes shows a reasonable agreement with the proposed theoretical models, suggesting that asymmetric fabrics can be used to infer magma flow and may provide valuable information on the shear resolved on the dike walls during intrusion.     

The ~AD1315 Tarawera and Waiotapu eruptions, New Zealand: contemporaneous rhyolite and hydrothermal eruptions driven by an arrested basalt dike system?

A series of large hydrothermal eruptions occurred across the Waiotapu geothermal field at about the same (prehistoric) time as the ~AD1315 Kaharoa rhyolite magmatic eruptions from Tarawera volcano vents, 10–20 km distant. Triggering of the Waiotapu hydrothermal eruptions was previously attributed to displacement of the adjacent Ngapouri Fault. The Kaharoa rhyolite eruptions are now recognised as primed and triggered by multiple basalt intrusions beneath the Tarawera volcano. A ~1000 t/day pulse of CO₂ gas is recorded by alteration mineralogy and fluid inclusions in drill core samples from Waiotapu geothermal wells. This CO₂ pulse is most readily sourced from basalt intruded at depth, and although not precisely dated, it appears to be associated with the Waiotapu hydrothermal eruptions. We infer that the hydrothermal eruptions at Waiotapu were primed by intrusion of the same arrested basalt dike system that drove the rhyolite eruptions at Tarawera. This dike system was likely similar at depth to the dike that generated basalt eruptions from a 17 km-long fissure that formed across the Tarawera region in AD1886. Fault ruptures that occurred in the Waiotapu area in association with both the AD1886 and ~AD1315 eruptions are considered to be a result, rather than a cause, of the dike intrusion processes.Editorial responsibility: J. Donnelly-Nolan     

Soil-water behaviour of sandy soils under semi-arid conditions in the Duero Basin (Spain)

This paper examines the soil-water behaviour of sandy soils representative of a broad area in the Duero river basin (Spain), with semi-arid bioclimatic characteristics. Soil-moisture measurements of the first 25 cm of soil profile were taken using time domain reflectometry (TDR) methodology. The infiltration process was studied by means of field experiments combining rainfall simulations and TDR techniques. Finally, a set of hydrodynamic variables was calculated in the laboratory (i.e. available soil-water content, soil-water-retention curves and hydraulic conductivity).The average available soil-water content is 0·07 cm³ cm⁻³, in accordance with the predominance of the sandy textural fraction (85%). The rainfall simulation experiments show that infiltration prevails over overland flow, with a steady-state infiltration rate higher than rainfall application (40mmh⁻¹) in most cases; a low water-retention capacity was also observed. The evolution of soil-moisture over time indicates a close dependence on intra-annual rainfall variability due to the low water-retention capacity of sandy soils. With a maximum water-storage capacity of around 0·18 cm³ cm⁻³, the soils studied show high sensitivity to dry spells and may remain with <50% of the available soil-water content for several months during the year.     

Wet-bulb,dew point,and air temperature trends in Spain

Theoretical and Applied Climatology - This study analyses trends of mean (T m), maximum (T x), minimum (T n), dew point (T d), and wet-bulb temperatures (T w) on an annual, seasonal, and monthly...