Multiphase Boudinage: a case study of Amphibolites in Marble in the Naxos Migmatite core

In multiply deformed terrains, multiphase boudinage should be common, but identification and analysis of these is difficult. Here we present an analysis of multiphase boudinage and fold structures in deformed amphibolite layers in marble from the migmatitic center of the Naxos metamorphic core complex. Reconstruction of multiple boudinage generations is possible due to the exceptional 3D outcrop conditions. We identify five distinct generations of boudinage, reflecting the transition from high-strain – high-temperature ductile deformation to medium to low strain brittle boudins on the retrograde path during cooling and exhumation. All boudin generations indicate E-W horizontal shortening and variable directions of bedding parallel extension, evolving from subvertical extension in the earliest boudins to subhorizontal N-S extension during exhumation. Two phases of E-W shortening can be inferred, indicating E-W shortening in the Aegean before activity of the brittle North Anatolian Fault. This study highlights the wealth of information that can be gained from detailed analysis of multiphase boudinage structures.

Basement structure of the Hontomín CO2 storage site (Spain) determined by integration of microgravity and 3D seismic data

A multidisciplinary study has been carried out in Hontomín (Spain) to determine the basement structural setting/ geometry and that of the sedimentary succession of an area aimed to be the first Spanish pilot plant of CO₂ injection. An integration of coincident 3D seismic results, borehole data and unpublished microgravity 5 maps aims to reproduce the deep structure of the basement and to quantify the thickness of the Triassic Keuper evaporites. All datasets manage to clearly identify two main fault systems compartmentalizing the main structural domains into three differentiated blocks. These have been interpreted to be reactivated normal faults that have led to the formation of 10 the Hontomín dome. The general structure is characterized by a half-graben setting filled with thick Keuper evaporites (up to 2000 m thick) forming an extensional forced fold.

The Mohr–Coulomb criterion for intact rock strength and friction – a re-evaluation and consideration of failure under polyaxial stresses

Abstract Darley Dale and Pennant sandstones were tested under conditions of both axisymmetric shortening and extension normal to bedding. These are the two extremes of loading under polyaxial stress conditions. Failure under generalized stress conditions can be predicted from the Mohr–Coulomb failure criterion under axisymmetric compression conditions provided the best form of polyaxial failure criterion is known. The sandstone data are best reconciled using the Mogi (1967) empirical criterion. Fault plane orientations produced vary greatly with respect to the maximum compression direction in the two loading configurations. The normals to the Mohr–Coulomb failure envelopes do not predict the orientations of the fault planes eventually produced. Frictional sliding on variously inclined sawcuts and failure surfaces produced in intact rock samples was also investigated. Friction coefficient is not affected by fault plane orientation in a given loading configuration, but friction coefficients in extension were systematically lower than in compression for both rock types and could be reconciled by a variant on the Mogi (1967) failure criterion. Friction data for these and other porous sandstones accord well with the Byerlee (1977) generalization about rock friction being largely independent of rock type. For engineering and geodynamic modelling purposes, the stress-state dependent friction coefficient should be used for sandstones, but it is not known to what extent this might apply to other rock types.

A simple 3-D numerical model of thermal convection in Earth's growing inner core: on the possibility of the formation of the degree-one structure with lateral viscosity variations

An east-west hemispherically asymmetric structure for Earth's inner core has been suggested by various seismological evidence, but its origin is not clearly understood. Here, to investigate the possibility of an "endogenic origin" for the degree-one thermal/mechanical structure of the inner core, I performed new numerical simulations of thermal convection in the growing inner core. A setup value that controls the viscosity contrast between the inner core boundary and the interior of the inner core, ΔηT, was taken as a free parameter. Results show that the degree-one structure only appeared for a limited range of ΔηT; such a scenario may be possible but is not considered probable for the real Earth. The degree-one structure may have been realized by an "exogenous factor" due to the planetary-scale thermal coupling among the lower mantle, the outer core, and the inner core, not by an endogenic factor due to the internal rheological heterogeneity.

Modeling the contributing factors of desertification and evaluating their relationships to soil degradation process through Geomatic techniques

Desertification is a prolonged stage of land degradation which converts the productive ecosystem to fragile by three crucial events namely evapotranspiration, rainfall and negative human intrusion. The present study concentrates on identifying the causative factors of desertification namely temperature, wind, rainfall and human pressure, distinguishing the desertified land from degraded land and assessing the way from which the soil degradation process gets accelerated by those factors by employing the datasets such as long term (2001–2011) and short term (2012–2015) Meteorological data and Landsat ETM+ and OLI satellite imageries of crop growing period (June–October) into geostatistical methods and newly proposed remote sensing models which yielded good accuracy with in situ observations (R2 = 0.8). In temperature induced desertified region, the rate of increment of the saline affected region was magnified significantly from 16 to 74 % (2001–2015) due to the presence of native fluoride concentration and extreme temperature event over a period of time. The long term exaggeration of soil moisture stress (19 to 90 %) has been notified in the areas that were susceptible to wind induced desertification, due to high evaporation rate invoked by extreme wind event for a substantial period. Similarly rainfall induced desertified regions have also been experiencing high soil moisture stress (4 to 70 %) because of the insufficient reception of rainfall. High human made soil salinity (36 %), human occupancy (16 %), followed by moisture stress (7 %) are observed in the human affected region because of growing population and improper land management of the already fragile land.

Oblique collision and deformation partitioning in the SW Iberian Variscides

Different transpressional scenarios have been proposed to relate kinematics and complex deformation patterns. We apply the most suitable of them to the Variscan orogeny in SW Iberia, which is characterized by a number of successive left-lateral transpressional structures developed at Devonian to Carboniferous times. These structures resulted from the oblique convergence between three continental terranes (Central Iberian Zone, Ossa-Morena Zone and South Portuguese Zone), whose amalgamation gave way to both intense shearing at the suture-like contacts and transpressional deformation of the continental pieces in-between, thus showing strain partitioning in space and time. We have quantified the kinematics of the collisional convergence by using the available data on folding, shearing and faulting patterns, as well as tectonic fabrics and finite strain measurements. Given the uncertainties regarding the data and the boundary conditions modeled, our results must be considered as a semi-quantitative approximation to the issue, though very significant from a regional point of view. The total collisional convergence surpasses 1000 km, most of them corresponding to left-lateral displacement parallel to terrane boundaries. The average vector of convergence is oriented E–W (present-day coordinates), thus reasserting the left-lateral oblique collision in SW Iberia, in contrast with the dextral component that prevailed elsewhere in the Variscan orogen. This particular kinematics of SW Iberia is understood in the context of an Avalonian plate promontory currently represented by the South Portuguese Zone.

Soil indicators to assess the effectiveness of restoration strategies in dryland ecosystems

Soil indicators may be used for assessing both land suitability for restoration and the effectiveness of restoration strategies in restoring ecosystem functioning and services. In this review paper, several soil indicators, which can be used to assess the effectiveness of restoration strategies in dryland ecosystems at different spatial and temporal scales, are discussed. The selected indicators represent the different viewpoints of pedology, ecology, hydrology, and land management. The recovery of soil capacity to provide ecosystem services is primarily obtained by increasing soil rooting depth and volume, and augmenting water accessibility for vegetation. Soil characteristics can be used either as indicators of suitability, that is, inherently slow-changing soil qualities, or as indicators for modifications, namely dynamic, thus "manageable" soil qualities. Soil organic matter forms, as well as biochemistry, micro- and meso-biology, are among the most utilized dynamic indicators. On broader territorial scales, the Landscape Function Analysis uses a functional approach, where the effectiveness of restoration strategies is assessed by combining the analysis of spatial pattern of vegetation with qualitative soil indicators. For more holistic and comprehensive projects, effective strategies to combat desertification should integrate soil indicators with biophysical and socio-economic evaluation and include participatory approaches. The integrated assessment protocol of Sustainable Land Management developed by the World Overview of Conservation Approaches and Technologies network is thoroughly discussed. Two overall outcomes stem from the review: (i) the success of restoration projects relies on a proper understanding of their ecology, namely the relationships between soil, plants, hydrology, climate, and land management at different scales, which is particularly complex due to the heterogeneous pattern of ecosystems functioning in drylands, and (ii) the selection of the most suitable soil indicators follows a clear identification of the different and sometimes competing ecosystem services that the project is aimed at restoring.

Studying local earthquakes in the northern Fennoscandian Shield using the data of the POLENET/LAPNET temporary array

Earthquakes within areas inside continental plates are still not completely understood and the progress in understanding intraplate seismicity is slow due to short history of instrumental seismology and sparse regional seismic networks in seismically non-active areas. However, knowledge about position and depth of seismogenic structures in such areas is necessary, in order to estimate seismic hazard for such critical facilities as nuclear power plants and nuclear waste deposits. In the present paper we address the problem of seismicity in the intraplate area of northern Fennoscandia using the information on local events recorded by the POLENET/LAPNET temporary seismic array during the International Polar Year 2007–2009. We relocate the seismic events by the program HYPOELLIPS and grid search method. We use the first arrivals of P-waves of local events in order to calculate a 3-D tomographic P-wave velocity model of the uppermost crust (down to 20 km) for selected region inside the study area and show that the velocity heterogeneities in the upper crust correlate well with known tectonic units. We compare position of the velocity heterogeneities with the seismogenic structures delineated by epicentres of relocated events and demonstrate that these structures generally do not correlate with the crustal units formed as a result of crustal evolution in Archean and Paleoproterozoic. On the contrary, they correlate well with the post-glacial faults located in the area of the Baltic–Bothnia Megashear (BBMS). Hypocentres of local events have depths down to 30 km. We also obtain focal mechanisms of two selected events with good data quality. Both focal mechanisms are of strike-slip type in which shift prevails over uplift. Our results demonstrate that Baltic–Bothnia Megashear is an important large-scale, reactivated tectonic structure that has to be taken into account in estimating seismic hazard in northern Fennoscandia.

Response of a low subsiding intracratonic basin to long wavelength deformations: the Palaeocene–early Eocene period in the Paris basin

The uppermost Cretaceous to early Palaeogene is a period of major deformations of the western part of the Eurasian plate with prominent basin inversions starting from the Coniacian onwards. These deformations occur in a complex geodynamic setting within both the context of the Africa–Eurasia convergence and the North Atlantic opening. While Mesozoic graben inversions have been extensively studied, particularly in Eastern Europe and the North Sea, more gentle deformations that affect thicker crust areas (intracratonic basins and emerged lands) are not as well documented. The objective of this study is to constrain the exact timing, type and magnitude of the early Palaeogene deformations affecting the intracratonic Paris basin and to integrate them at the Western European scale. Relatively gentle deformations are attempted through a high-resolution reconstitution of its stratigraphic record based on outcrops and well-dated wells, and a high number of well-logs that are correlated using the "stacking pattern" sequence stratigraphic technique. Two orders of sequences are identified (third- and fourth-order) and correlated throughout the basin. Basin geometric and palaeogeographic reconstitutions are based on sediment thickness and facies analysis. Two-dimensional accommodation space measurements were taken in order to quantify the magnitude of the deformations. Three phases of deformation were recognized. 1. An intra-Maastrichtian–pre-Thanetian (59 Ma) deformation, with major uplift and erosion of the Cretaceous strata with two sub-periods of deformation: Maastrichtian–pre-middle-Danian and Upper Danian–pre-Thanetian long wavelength deformations. This period of major deformation is coeval with Upper Cretaceous–pre-Danian compressive deformations linked to the Africa–Eurasia convergence in southern France and with volcanic activity from the North Atlantic to Massif Central and the Rhenish Shield during the Palaeocene; 2. an early Ypresian (55.1–54.3 Ma) medium wavelength deformation (× 10 km), here reported to be a stress rearrangement related to the onset of the North Atlantic opening; 3. an uppermost Ypresian (49.8 Ma) long wavelength deformation (× 100 km), contemporaneous with flexural compressive deformations in the Aquitaine Basin (Pyrenean deformation), and related to the Iberia–Eurasia convergence.

Soil erosion assessment and control in Northeast Wollega, Ethiopia

Soil erosion is the main driver of land degradation in Ethiopia, and in the whole region of East Africa. This study was conducted at the Northeast Wollega in West Ethiopia to estimate the soil losses by means of the Revised Universal Soil Loss Equation (RUSLE). The purpose of this paper is to identify erosion spot areas and target locations for appropriate development of soil and water conservation measures. Fieldwork and household survey were conducted to identify major determinants of soil erosion control. Six principal factors were used to calculate soil loss per year, such as rainfallerosivity, soil erodiblity, slope length, slope steepness, crop management and erosion-control practices. The soil losses have shown spatio-temporal variations that range from 4.5 Mg ha-1 yr-1 in forest to 65.9 Mg ha-1 yr-1 in cropland. Results from the analysis of stepwise multiple linear regression show that sustainable soil erosion control are determined byknowledge of farmers about soil conservation, land tenure security and off-farm income at community level. Thus, policy aim at keeping land productivity will need to focus on terracing, inter-cropping and improved agro-forestry practices.