The Aguablanca Ni–(Cu) sulfide deposit, SW Spain: geologic and geochemical controls and the relationship with a midcrustal layered mafic complex

The Aguablanca Ni–(Cu) sulfide deposit is hosted by a breccia pipe within a gabbro–diorite pluton. The deposit probably formed due to the disruption of a partially crystallized layered mafic complex at about 12–19 km depth and the subsequent emplacement of melts and breccias at shallow levels (<2 km). The ore-hosting breccias are interpreted as fragments of an ultramafic cumulate, which were transported to the near surface along with a molten sulfide melt. Phlogopite Ar–Ar ages are 341–332 Ma in the breccia pipe, and 338–334 Ma in the layered mafic complex, and are similar to recently reported U–Pb ages of the host Aguablanca Stock and other nearby calc-alkaline metaluminous intrusions (ca. 350–330 Ma). Ore deposition resulted from the combination of two critical factors, the emplacement of a layered mafic complex deep in the continental crust and the development of small dilational structures along transcrustal strike-slip faults that triggered the forceful intrusion of magmas to shallow levels. The emplacement of basaltic magmas in the lower middle crust was accompanied by major interaction with the host rocks, immiscibility of a sulfide melt, and the formation of a magma chamber with ultramafic cumulates and sulfide melt at the bottom and a vertically zoned mafic to intermediate magmas above. Dismembered bodies of mafic/ultramafic rocks thought to be parts of the complex crop out about 50 km southwest of the deposit in a tectonically uplifted block (Cortegana Igneous Complex, Aracena Massif). Reactivation of Variscan structures that merged at the depth of the mafic complex led to sequential extraction of melts, cumulates, and sulfide magma. Lithogeochemistry and Sr and Nd isotope data of the Aguablanca Stock reflect the mixing from two distinct reservoirs, i.e., an evolved siliciclastic middle-upper continental crust and a primitive tholeiitic melt. Crustal contamination in the deep magma chamber was so intense that orthopyroxene replaced olivine as the main mineral phase controlling the early fractional crystallization of the melt. Geochemical evidence includes enrichment in SiO₂ and incompatible elements, and Sr and Nd isotope compositions (⁸⁷Sr/⁸⁶Sr_i 0.708–0.710; ¹⁴³Nd/¹⁴⁴Nd_i 0.512–0.513). However, rocks of the Cortegana Igneous Complex have low initial ⁸⁷Sr/⁸⁶Sr and high initial ¹⁴³Nd/¹⁴⁴Nd values suggesting contamination by lower crustal rocks. Comparison of the geochemical and geological features of igneous rocks in the Aguablanca deposit and the Cortegana Igneous Complex indicates that, although probably part of the same magmatic system, they are rather different and the rocks of the Cortegana Igneous Complex were not the direct source of the Aguablanca deposit. Crust–magma interaction was a complex process, and the generation of orebodies was controlled by local but highly variable factors. The model for the formation of the Aguablanca deposit presented in this study implies that dense sulfide melts can effectively travel long distances through the continental crust and that dilational zones within compressional belts can effectively focus such melt transport into shallow environments.Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users.     

Isotropization in bianchi type-I vacuum cosmology

We have found the most general solution for the Bianchi type-I equations in the Brans-Dicke theory (BDT) for the vacuum case. It is shown that forw > 500 the Universe will become isotropic for any amount of initial anisotropy, secondly it is shown that in the extended inflation scenario, the BDT-scalar field can avoid the inflation in one direction,R ₃. In the other scale factorsR ₁ andR ₂ there is inflationary expansion.     

Star formation and AGN

We analyse the data from narrow band H and [O III] CCD imaging of a sample of nearby spiral galaxies with active nuclei. The results show that the large scale star formation depends on the level of nuclear activity, with Seyfert 2 presenting the strongest disk and circum-nuclear star formation, while Seyfert 1 show very little. We present particular results for the galaxies NGC 3982, NGC 4579, NGC 5427 and NGC 7469.     

P and S Mach Waves Generated by the Detonation of a Cylindrical Explosive Charge - Experiments and Simulations

During blasting operations in a competent rock mass without open joints or faults, the structure of the wave fields generated by the detonation of a cylindrical charge depends mainly on the relation between the velocity of detonation ( c d ) and the velocity of the P and S waves, c P and c S , respectively, in the medium. If c d is larger than c P , detonation is supersonic and Mach P and S waves appear. If c d is between c P and c S , detonation is transonic, and only an S Mach wave is generated. If c d is less than c S , subsonic detonation occurs. In this paper, we describe an experiment conducted at the Andina mine (Chile) in order to demonstrate the differences between the wave fields generated by supersonic and transonic detonation. We also present a simulation of the detonation of a cylindrical charge using the finite differences Itasca software FLAC3.4. In particular, we show how important it is to secure a good adjustment of the rheological behaviour of the medium, in our case, a strain softening elasto-plastic model.     

Integration and influence of paleoseismic and geologic data for the seismic hazard evaluation in the Catalan coastal ranges, Spain

In this study, the influence of paleoseismic and geologic data in the seismic hazard estimation for the Catalan coastal ranges is analysed. We computed the probabilistic seismic hazard using area seismic sources with a Poissonian assumption for the earthquake occurrence. For the computations, a previously published attenuation relationship based on European strong motion data was applied. The resulting hazard estimates show similarities to the previous assessments in the region. These results were then used as a reference for comparison with other new models. In order to analyse the influence of the paleoseismic data three different models were tested. Since the number of faults that are investigated in detail are few, the same area sources that were used in the Poissonian assumption were kept in all three new models. In addition, the new paleoseismic data with faults expressed as line sources were used. In this case, a cyclic earthquake occurrence was assumed. The three models were based on the paleoseismic data with different assumptions on the time elapsed since last event. The time elapsed was set to 0, 10 and 85% of the recurrence interval in each model. The results are presented as maps showing the difference between the three models and the reference model with the Poissonian assumption. The results are given in horizontal peak ground acceleration contour maps for different return periods, also taking into account large return periods as high as 25,000 years. This is done to demonstrate the effect of large recurrence intervals found for some of the active faults. In general, we observe that for short return periods (<1000 years), the Poissonian assumption of earthquake occurrence is probably sufficient and provides a robust estimate of the hazard. However, for longer return periods (>5000 years) the effects of the paleoseismic data become increasingly significant. In order to estimate the true seismic hazard potential of this apparently low seismicity area, long-term behaviour of the possible active faults in the region needs to be investigated systematically.     

Is a small sea turtles rookery doomed to local extinction? Decreasing nesting trends at the Paria Gulf,Venezuela

Small rookeries are rarely evaluated for marine turtles worldwide. Two species of sea turtles (Hawksbill, Eretmochelys imbricata; Leatherback, Dermochelys coriacea) nest on five main beaches of the northeast coast of the Paria Gulf in Venezuela. Population trends using generalized linear models at this rookery were assessed and compared with other small rookeries. Both species showed significant negative nesting trends: Nesting by critically endangered hawksbills decreased over nine seasons 2009–2017 (64–142 nests per year, General Linear Model Slope Value = ?0.061; data pooled for five beaches); similarly, vulnerable leatherback nests decreased across the same period in the main beach Los Garzos (0–69 nests/year; GLMSV = ?0.34). Besides human and natural predation of the nests, no significant environmental impacts affect the beaches except probably on Obispo Isthmus where a gas pipeline installation interrupted the nesting activity in 2014. Observed changes to the nesting trends in these small rookeries have a collective impact on broader conservation concerns for sea turtles in the region.     

Coastal boulder deposit as evidence of an ocean-wide prehistoric tsunami originated on the Atacama Desert coast (northern Chile)

A Late Holocene cliff-top deposit of large boulders well above the limits of modern storm waves is described from the southern coast of the Atacama Desert (northern Chile). The largest moved boulder weighs >40 t and field data point to a flood height >18·5 m above high tide level and an inland penetration greater than 284 m from the cliff edge. The minimum flow velocity needed for particle entrainment was estimated as 10·1 ms⁻¹ and the most likely processes of sediment deposition for different boulders were deduced. The boulder distribution, sorting and orientation of imbricated debris, together with the significant wave height of extreme storms reported and the occurrence of interplate earthquakes in the study area indicate that the deposit records a single event, interpreted here as a tsunami wave train rather than exceptional storm waves. The boulder field was dated to between the 13th and the 16th Centuries ce and possibly correlates with the 1420 Oei orphan tsunami, that affected the eastern coast of Japan. A magnitude of 8·8 to 9·4 has been estimated for the earthquake, which may be one of the larger events of a super-cycle of earthquakes in the southern Atacama Desert. These cycle-ending earthquakes involve large rupture areas (lengths in excess of 600 km) and highly destructive ocean-wide tsunamigenic events.     

Evolution of the star formation rate in galaxies with increasing densities

Some bursts of star formation are thought to be associated with situations in which a galaxy's density is increasing. Examples include protogalaxy collapse, mergers, inflow of gas into a galactic nucleus, or accretion of intergalactic gas. We have examined the evolution of the star formation rate (SFR) and other properties of galaxies with increasing density using one-zone cloud fluid equations describing an extension of the Oort cycle, for which the equilibrium state would give an SFR which increases monotonically with density. However, the calculations show that the energy input associated with the density increase generally dominates the evolution, and forces the system far from its normal equilibrium to a state in which cloud collisions are disruptive rather than coalescent. The calculations predict that starbursts associated with collapse, accretion, or inflow events should be preceded by a long incubation period with a very small SFR. For example, the initial star formation burst in a protogalaxy may be delayed for several billion years until nearly all the infalling material has been accreted onto the growing central object.