General characteristics of the geochemical evolution of silicic melts during the development of massive sulfide magmatic ore systems: Evidence from the investigation of melt inclusions

The investigation of melt inclusions in the minerals of volcanic rocks from the massive sulfide deposits of Siberia and the Urals revealed some specific features in the development of their magmatic ore systems. It was shown that the petrochemical and rare earth element compositions of melt inclusions reflect the geodynamic conditions of their formation: island arc conditions for the massive sulfide deposits of Rudny Altai, eastern Tuva, and the Salair Range and a back arc basin environment for the Yaman-Kasy deposit. The silicic melts of inclusions from the volcanic rocks of massive sulfide deposits show some specific features with respect to the contents of volatile components. In all of the ore deposits studied, fluorine content was always low (0.03–0.08 wt %), whereas chlorine content (0.13–0.28 wt %) was higher than the average value for silicic melts (0.17 wt %). There is a strong differentiation of water content in melt inclusions, both between deposits and between various volcanics from a single deposit. Ore-bearing melts show the highest water contents of 3.34–4.07 wt %. High Cu contents in the silicic melts of the Yubileinoe and Kyzyl-Tashtyg deposits (up to 7118 and 3228 ppm, respectively) may indicate the affinity of some ore components to particular silicic magmas. This is supported by the elevated contents of Cu in the porphyry Cu deposits of Romania (Valea Morii), Mongolia (Bayan Ula), and Bolivia. On the other hand, the silicic melts of inclusions from the molybdenum-uranium deposit of the Strel’tsovka ore field show high contents of another group of ore components (U and F).     

Conditions of Quaternary magmatism at Spitsbergen Island

Petrological and geochemical data obtained on the Quaternary lavas of volcanoes at Spitsbergen Island indicate that the rocks were produced via the deep-seated crystallization of parental alkaline magmas at 8–10 kbar. The character of clinopyroxene enrichment in incompatible elements indicates that the mineral crystallized from more enriched melts than those inferred from the composition of the host lavas. These melts were close to the parental melts previously found as veinlets in mantle hyperbasite xenoliths in the lavas. According to the character of their enrichment in Pb and Sr radiogenic isotopes and depletion in Nd, the basalts from Spitsbergen Island define a single trend with the weakly enriched tholeiites of the Knipovich Ridge, a fact suggesting the closeness of the enriched sources beneath the continental margin of Spitsbergen and beneath the spreading zone. Magmatic activity at Spitsbergen was related to the evolution of the Norwegian-Greenland basin, which evolved in pulses according to the shift of the spreading axes. The most significant of the latter events took place in the Neogene, when the Knipovich Ridge obtained its modern position near the western boundary of Spitsbergen. Early in the course of the evolution, the emplacement of alkaline melts generated at Spitsbergen into the oceanic mantle could form the enriched mantle, which was later involved in the melting process beneath the spreading zone.     

Low-pressure,water-assisted anatexis of basic dykes in a contact metamorphic aureole,Fuerteventura (Canary Islands): oxygen isotope evidence for a meteoric fluid origin

Migmatites produced by low-pressure anatexis of basic dykes are found in a contact metamorphic aureole around a pyroxenite–gabbro intrusion (PX2), on Fuerteventura. Dykes outside and inside the aureole record interaction with meteoric water, with low or negative δ¹⁸O whole-rock values (+0.2 to −3.4‰), decreasing towards the contact. Recrystallised plagioclase, diopside, biotite and oxides, from within the aureole, show a similar evolution with lowest δ¹⁸O values (−2.8, −4.2, −4.4 and −7.6‰, respectively) in the migmatite zone, close to the intrusion. Relict clinopyroxene phenocrysts preserved in all dykes, retain typically magmatic δ¹⁸O values up to the anatectic zone, where the values are lower and more heterogeneous. Low δ¹⁸O values, decreasing towards the intrusion, can be ascribed to the advection of meteoric water during magma emplacement, with increasing fluid/rock ratios (higher dyke intensities towards the intrusion acting as fluid-pathways) and higher temperatures promoting increasing exchange during recrystallisation. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Geomorphological hazards related to deep dissolution phenomena in the Western Italian Alps: Distribution, assessment and interaction with human activities

Deep dissolution affects great part of soluble rocks (e.g. gypsum and anhydrite) of the Western Italian Alps. The related superficial phenomena (sinkholes, gravity-induced processes and a local worsening of geomechanical rock properties) are not limited to typical karsts landscape and cause slope instability also affecting populated sites and infrastructures. The paper aims to describe general characteristic of dissolution phenomena, to interpret their conditioning factors and evolutionary stages and to assess possible hazards due to their superficial effects.The search for evidences of deep dissolution leads to the selection of representative sites in the central part of the Western Italian Alps (Piemonte and Valle d'Aosta Region). Detailed geological and geomorphological studies have been used to classify the selected sites by type, size and variable state of activity. Very different evolutionary stages of dissolution phenomena have been interpreted by comparison of case-studies: some are early “embryonic”; others are more evolved, up to typical sinkholes, or even remodelled by other phenomena. Some cases show an extreme complexity in the interactions between corrosion phenomena and other geomorphic processes: slope deformations, from one side, and karst, fluvial and glacial phenomena, to the other. A wide range of movement rates on slope instabilities induced by deep dissolution have been estimated by topographic and geomorphic data. Geochemical data on removed rocks by dissolution indicate 0.4 mm/year values for local subsidence. Historical and technical data indicate low frequency of major dissolution-induced collapses, but highlight widespread damages to tunnels, roads and buildings, especially along slopes.     

Development and morphometry of sinkholes in coastal plains of Apulia, southern Italy. Preliminary sinkhole susceptibility assessment

Evolution of coastlines in karst areas may be strongly controlled by dissolution processes which favour the development of surface and subsurface landforms. The generation of caves in these environments is commonly favoured by the mixing between fresh and brackish waters. The sinkholes resulting from the upward propagation of the caves may interfere with the anthropogenic environment and cause damage to human elements (property and activities). To highlight the often underestimated importance of karst phenomena in coastal areas, we have analyzed a coastal stretch of Apulia, in southern Italy. The study area, covering an extension of about 6 km², is situated in the Ionian coast, and presents several interesting karst landforms that are generally connected to caves. Tens of sinkholes were mapped through field surveys, multi-year aerial-photographs (dating back to the 1940s) and archival research. We have performed a morphometric analysis of the sinkholes. The analysis describes the main parameters of the sinkholes (area, length, width, and depth), and the control exerted by the main discontinuity systems in the area. The detrimental effects derived from interaction between human environment and these karst landforms is also under consideration. A sinkhole susceptibility map, which may provide useful information for planners, developers and the insurance industry has eventually been produced through application of a decision tree model.     

A transdisciplinary analysis of water problems in the mountainous karst areas of Morocco

Water management and engineering in the karstic High Atlas of Morocco are difficult tasks under the prevailing geological, hydrogeological, geomorphological, vegetational and climatic conditions. It is important to be able to understand and predict the characteristics and availability of water for future water planning in the region under changing climatic and agricultural conditions. An interdisciplinary analysis of problems and adequate hydrological modelling tools developed by geologists, hydrologists and biologists are necessary. The karst areas of the High Atlas Mountains are characterised by impermeable triassic basalt underlying substantial subsurface reservoirs with high potential discharge rates. The karst groundwater aquifers are extensive but largely unknown in dimension, probably with a hierarchical network of groundwater flow paths. It is estimated that approximately 70% of the surface water is directly lost to groundwater. Steep landslide- and debris flow prone slopes exist next to coarse-grained, highly porous river beds. Infrequent, high intensity rainfall or snowmelt causes a particularly high flood risk to these karst areas. In addition, agriculture and land use changes have degraded the karst areas. The most important driving forces for degradation include permanent overgrazing even during droughts and the use of firewood by a continually growing population. Large scale degradation of vegetation has occurred in the oro-mediterranean (mountainous Mediterranean) zone, between 2600 and 3400 m which coincides with the most important zone for karstic groundwater creation. The combination of high amounts of groundwater flow and rapid surface flow due to sparse vegetation has increased the problems of flood flow.     

Oxygen isotopic compositions of Allende Type C CAIs: Evidence for isotopic exchange during nebular melting and asteroidal metamorphism

In situ oxygen isotopic measurements of primary and secondary minerals in Type C CAIs from the Allende CV3 chondrite reveal that the pattern of relative enrichments and depletions of ¹⁶O in the primary minerals within each individual CAI are similar to the patterns observed in Types A and B CAIs from the same meteorite. Spinel is consistently the most ¹⁶O-rich (Δ¹⁷O = −25‰ to −15‰), followed by Al,Ti-dioside (Δ¹⁷O = −20‰ to −5‰) and anorthite (Δ¹⁷O = −15‰ to 0‰). Melilite is the most ¹⁶O-depleted primary mineral (Δ¹⁷O = −5‰ to −3‰). We conclude that the original melting event that formed Type C CAIs occurred in a ¹⁶O-rich (Δ¹⁷O  −20‰) nebular gas and they subsequently experienced oxygen isotopic exchange in a ¹⁶O-poor reservoir. At least three of these (ABC, TS26F1 and 93) experienced remelting at the time and place where chondrules were forming, trapping and partially assimilating ¹⁶O-poor chondrule fragments. The observation that the pyroxene is ¹⁶O-rich relative to the feldspar, even though the feldspar preceded it in the igneous crystallization sequence, disproves the class of CAI isotopic exchange models in which partial melting of a ¹⁶O-rich solid in a ¹⁶O-poor gas is followed by slow crystallization in that gas. For the typical (not associated with chondrule materials) Type C CAIs as well for as the Types A and B CAIs, the exchange that produced internal isotopic heterogeneity within each CAI must have occurred largely in the solid state. The secondary phases grossular, monticellite and forsterite commonly have similar oxygen isotopic compositions to the melilite and anorthite they replace, but in one case (CAI 160) grossular is ¹⁶O-enriched (Δ¹⁷O = −10‰ to −6‰) relative to melilite (Δ¹⁷O = −5‰ to −3‰), meaning that the melilite and anorthite must have exchanged its oxygen subsequent to secondary alteration. This isotopic exchange in melilite and anorthite likely occurred on the CV parent asteroid, possibly during fluid-assisted thermal metamorphism.     

Kinetics of Cd sorption, desorption and fixation by calcite: A long-term radiotracer study

Time-dependent sorption and desorption of Cd on calcite was studied over 210 days utilizing ¹⁰⁹Cd as a tracer to distinguish between ‘labile’ and ‘non-labile’ forms of sorbed Cd. Stabilizing the calcite suspensions for 12 months under atmospheric P_CO2 and controlled temperature was necessary to reliably follow Cd dynamics following initial sorption. Results revealed time-dependant Cd sorption and marked desorption hysteresis by calcite under environmentally relevant conditions. Data obtained were fitted to a first-order kinetic model and a concentric shell diffusion model. Both models described the progressive transfer of Cd²⁺ to a less reactive form within calcite and subsequent desorption of Cd subject to different initial contact times. The kinetic model provided a better fit to the combined sorption and desorption data (R² = 0.992). It differentiates between two ‘pools’ of sorbed Cd²⁺ on calcite, ‘labile’ and ‘non-labile’, in which labile sorbed Cd is in immediate equilibrium with the free Cd²⁺ ion activity in solution whereas non-labile Cd is kinetically restricted. For the diffusion model (R² = 0.959), the rate constants describing Cd dynamics in calcite produced a half-life for Cd desorption of ∼175 d, for release to a ‘zero-sink’ solution. Results from this study allow comment on the likely mechanisms occurring at the calcite surface following long-term Cd sorption.     

Metallographic cooling rates and origin of IVA iron meteorites

We have determined the metallographic cooling rates for 13 IVA irons using the most recent and most accurate metallographic cooling rate model. Group IVA irons have cooling rates that vary from 6600 °C/Myr at the low-Ni end of the group to 100 °C/Myr at the high-Ni end of the group. This large cooling rate range is totally incompatible with cooling in a mantled core which should have a uniform cooling rate. Thermal and fractional crystallization models have been used to describe the cooling and solidification of the IVA asteroid. The thermal model indicates that a metallic body of 150 ± 50 km in radius with less than 1 km of silicate on the outside of the body has a range of cooling rates that match the metallographic cooling rates in IVA irons in the temperature range 700-400 °C where the Widmanstätten pattern formed. The fractional crystallization model for Ni with initial S contents between 3 and 9 wt% is consistent with the measured variation of cooling rate with bulk Ni and the thermal model. New models for impacts in the early solar system and the evolution of the primordial asteroid belt allow us to propose that the IVA irons crystallized and cooled in a metallic body that was derived from a differentiated protoplanet during a grazing impact. Other large magmatic iron groups, IIAB, IIIAB, and IVB, also show significant cooling rate ranges and are very likely to share a similar history.