Vorticity analysis in calcite tectonites: An example from the Attico-Cycladic massif (Attica,Greece)

Although calcite tectonites are widespread in nature their use to quantify flow vorticity is limited. We use new (micro-)structural, petrofabric and vorticity data to analyse the kinematics of flow in outcrop-scale calcite mylonite zones. These zones are genetically related to a crustal-scale NE-directed ductile thrust (Basal Thrust) that emplaced the Blueschist over the Basal unit during the exhumation of the Attico-Cycladic Massif. Calcite microstructures reveal that the last stage of deformation occurred at temperatures 200–300 °C achieved by mild heating, which is possibly related with the reburial of the Basal Thrust's footwall. Vorticity analyses were based on the degree of asymmetry of calcite c-axis fabrics as well as on the assumption that the orientation of the long axes of calcite neoblasts within an oblique foliation delineates the direction of instantaneous stretching axis. Both methodological approaches provide consistent estimates with a simple shear component between 55% and 82% (W_n = 0.76–0.96). The use of the stress axis (σ₁) orientation recorded by twin-c-axis-pairs to quantify vorticity generally gives significantly lower simple shear component. Comparison of our vorticity estimates with previous estimates inferred from quartz fabrics and rigid porphyroclasts reveals that exhumation-related deformation in the nappe pile was steady state.     

Topography as a major factor in the development of arcuate thrust belts: insights from sandbox experiments

We have used sandbox experiments to investigate and to illustrate the effects of topography upon the development of arcuate thrust belts. In experiments where a sand pack shortened and thickened in front of an advancing rectilinear piston, the geometry of the developing thrust wedge was highly sensitive to variations in surface topography. In the absence of erosion and sedimentation, the surface slope tended to become uniform, as predicted by the theory of critical taper. Under these conditions, the wedge propagated by sequential accretion of new thrust slices. In contrast, where erosion or sedimentation caused the topographic profile to become irregular, thrusts developed out of sequence. For example, erosion throughout a hinterland caused underlying thrusts to remain active and inhibited the development of new thrusts in the foreland. Where initial topography was irregular in plan view, accreting thrusts tended to be arcuate. They were convex towards the foreland, around an initially high area; concave towards the foreland, around an initially low area. Initial plateaux tended to behave rigidly, while arcuate thrust slices accreted to them. Thrust motions were radial with respect to each plateau. Within transfer zones to each side, fault blocks rotated about vertical axes and thrust motions were oblique-slip. At late stages of deformation, the surface slope of the thrust wedge tended towards a uniform value. Initial mountains of conical shape (representing volcanoes) also escaped deformation, except at depth, where they detached. Arcuate thrust slices accreted to front and back. Where a developing thrust wedge was subject to local incision, accreting thrust slices dipped towards surrounding areas of high topography, forming Vs across valleys.Arcuate structural patterns are to be found around the three highest plateaux on Earth (Tibet, Pamirs and Altiplano) and around the Tromen volcanic ridge in the Neuquén Basin of northern Patagonia. We infer that these areas behaved in quasi-rigid fashion, protected as they were by their high topography.     

Slab behaviour and its surface expression: new insights from gravity modelling in the SE-Carpathians

We use lithosphere-scale gravity models to calculate gravity anomalies resulting from oceanic subduction, continental collision, slab steepening, delamination, and break-off. Local isostasy was assumed for determining vertical movements caused by mass changes related to these tectonic processes. Our results show that subduction is accompanied by basin subsidence on the upper plate caused by the heavy lithospheric root of the subducting slab. The basin evolution goes parallel with the slab evolution and shows considerable modifications when the processes at depth change (slab steepening, delamination, break-off). Characteristic gravity anomaly curves were acquired for the different tectonic scenarios. These curves together with other data (e.g. basin evolution on the upper and the lower plate) were used for the reconstruction of the tectonic evolution of the SE-Carpathians which includes Tertiary subduction and collision followed by slab steepening and delamination.     

From outcrop and petrographic studies to basin-scale fluid flow modelling: The use of the Albanian natural laboratory for carbonate reservoir characterisation

The Albanian fold-and-thrust belt and the Peri-Adriatic Depression are well documented by means of seismic reflection profiles, GPS reference points, potential data, wells and outcrops. The continuous Oligocene to Plio-Quaternary sedimentary records help to constrain both the burial history of Mesozoic carbonate reservoirs, the timing of their deformation, and the coupled fluid flow and diagenetic scenarios.Since the mid-90s, the Albanian foothills were used as a natural laboratory to develop a new integrated methodology and work flow for the study of sub-thrust reservoir evolution, and to validate on real case studies the use of basin modelling tools as well as the application of new analytical methods for the study petroleum systems in tectonically complex areas.The integration of the interactions between petrographic and microtectonic studies, kinematic, thermal and fluid flow basin modelling, is described in detail. The fracturing of the reservoir intervals has a pre-folding origin in the Albanides and relates to the regional flexuring in the foreland. The first recorded cement has a meteoric origin, implying downward migration and the development of an earlier forebulge in the Ionian Basin. This fluid, which precipitates at a maximum depth of 1.5 km, is highly enriched in strontium, attesting for important fluid–rock interaction with the Triassic evaporites, located in diapirs. From this stage, the horizontal tectonic compression increases and the majority of the fluid migrated under high pressure, characterised by brecciated and crack-seal vein. The tectonic burial increased due to the overthrusting, that is pointed out by the increase of the precipitation temperature of the cements. Afterwards, up- or downward migration of SO₄²⁻, Ba²⁺ and Mg²⁺-rich fluids, which migrated probably along the décollement level, allows a precipitation in thermal disequilibrium. This period corresponds to the onset of the thrusting in the Ionian Zone. The last stage characterised the uplift of the Berati belt, developing a selective karstification due likely to the circulation of meteoric fluid.The main results of the fluid flow modelling show that the Upper Cretaceous–Paleocene carbonate reservoirs in the Ionian zone have been charged from the Tortonian onward, and that meteoric fluid migration should have intensely biodegraded the hydrocarbon in place. Concerning the migration paths, it has been demonstrated that the thrusts act principally as flow barriers in Albania, mainly due the occurrence of evaporites (non-permeable), except in the foreland, where they do not occur.     

吉黑东部晚古生代构造体制转换: 来自佳木斯-兴凯地块的双增生杂岩及岛弧岩浆岩带的制约

佳木斯-兴凯地块是吉黑东部地区至关重要的地质组成单元, 其东缘和西缘分别平行对称分布着两条晚古生代岛弧岩浆岩带和中生代增生杂岩带, 它们是古亚洲洋闭合向古太平洋俯冲-增生构造体制转换的关键地质记录。本文对佳木斯-兴凯地块西缘吉黑高压带中的青龙村群斜长角闪岩进行了系统的岩石学、锆石年代学和全岩地球化学研究, 结果表明青龙村斜长角闪岩原岩为拉斑系列玄武岩, 其原岩时代为~260Ma, 具有富集型洋中脊玄武岩(E-MORB)的地球化学特征。同时结合前人对佳木斯地块东缘和西缘分布的大量晚古生代岛弧岩浆岩以及增生杂岩的研究, 本文识别出佳木斯-兴凯地块东、西缘的"双带双弧"结构。"双带"即东缘和西缘平行对称分布的那丹哈达增生杂岩带和吉黑高压变质带, "双弧"则是东缘和西缘同样平行对称分布的早-中二叠世和中-晚二叠世岛弧岩浆岩带。通过对双带双弧的组成、形成时代以及构造背景的研究, 进一步为吉黑东部地区晚古生代时期的古大洋构造体制转换提供新的证据, 并重建了中亚造山带东缘晚古生代到早中生代的构造演化历史。     

In situ study of the $$ R\overline{3} c \to R\overline{3} m $$ orientational disorder in calcite

The temperature dependences of the crystal structure and intensities of the (113) and (211) reflections in calcite, CaCO₃, were studied using Rietveld structure refinements based on synchrotron powder X-ray diffraction data. Calcite transforms from to at about T _c = 1,240 K. A CO₃ group occupies, statistically, two positions with equal frequency in the disordered phase, but with unequal frequency in the partially ordered phase. One position for the CO₃ group is rotated by 180° with respect to the other. The unequal occupancy of the two orientations in the partially ordered phase is obtained directly from the occupancy factor, x, for the O1 site and gives rise to the order parameter, S = 2x − 1. The a cell parameter shows a negative thermal expansion at low T, followed by a plateau region at higher T, then a steeper contraction towards T _c, where the CO₃ groups disorder in a rapid process. Using a modified Bragg–Williams model, fits were obtained for the order parameter S, and for the intensities of the (113) and (211) reflections. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Strain partitioning between the Suruga Trough and the Zenisu Thrust: Neogene to present tectonic evolution in the onland and offshore Tokai district, Japan

The Tokai district in central Japan is located close to the convergent boundary between the Philippine Sea and Eurasian plates, and has experienced not only repeated large interplate earthquakes but also intense aseismic movement. In this paper, the spatial and temporal tectonic evolution of the Tokai district, particularly around the Omaezaki area, is discussed to assess whether the district has been and will be active or inactive. According to a geological survey, the horizontal crustal shortening strain can imply the hypothetical tectonic model that the area has been getting less active and the strain rate since the Neogene can be calculated as 12% and 2×10⁻⁶%/year, respectively. The present interseismic horizontal crustal strain and strain rate around the Omaezaki area are approximately 4×10⁻⁷% and 4×10⁻⁹%/year. By comparing these rates, the decrease since Neogene can imply the hypothetical tectonic model that the area has been getting less active influenced by the strain partitioning between the Suruga Trough and the Zenisu Thrust.     

Exploring the influence of loading geometry on the plastic flow properties of geological materials: Results from combined torsion + axial compression tests on calcite rocks

For technical reasons, virtually all plastic deformation experiments on geological materials have been performed in either pure shear or simple shear. These special case loading geometries are rather restrictive for those seeking insight into how microstructure evolves under the more general loading geometries that occur during natural deformation. Moreover, they are insufficient to establish how plastic flow properties might vary with the 3rd invariant of the deviatoric stress tensor (J₃) which describes the stress configuration, and so applications that use those flow properties (e.g. glaciological and geodynamical modelling) may be correspondingly compromised. We describe an inexpensive and relatively straightforward modification to the widely used Paterson rock deformation apparatus that allows torsion experiments to be performed under simultaneously applied axial loads. We illustrate the performance of this modification with the results of combined stress experiments performed on Carrara marble and Solnhofen limestone at 500°–600 °C and confining pressures of 300 MPa. The flow stresses are best described by the Drucker yield function which includes J₃-dependence. However, that J₃-dependence is small. Hence for these initially approximately isotropic calcite rocks, flow stresses are adequately described by the J₃-independent von Mises yield criterion that is widely used in deformation modelling. Loading geometry does, however, have a profound influence on the type and rate of development of crystallographic preferred orientation, and hence of mechanical anisotropy. The apparatus modification extends the range of loading geometries that can be used to investigate microstructural evolution, as well as providing greater scope for determining the shape of the yield surface in plastically anisotropic materials.     

From the geological to the numerical model in the analysis of gravity-induced slope deformations: An example from the Central Apennines (Italy)

This paper presents the findings from a study on gravity-induced slope deformations along the northern slope of Mt. Nuria (Rieti-Italy). The slope extends from the village of Pendenza to the San Vittorino plain and hosts the Peschiera River springs, i.e. the most important springs of the Central Apennines (average discharge: about 18 m³/s).

Detailed geological-geomorphological and geomechanical surveys, supported by a site stress-strain monitoring system and laboratory tests, led us to define the main evolutionary features of the studied phenomena. Based on the collected data, a “geological-evolutionary model” was developed with a view to identifying a spatio-temporal correlation between relief forms, jointing of the rock mass and its stress conditions. The geological-evolutionary model was expected to improve numerical simulations and to test our assumptions.

The numerical model also allowed us to simulate changes in the stress-strain conditions of the rock mass and correlate them with jointing, seepage, as well as with site-detected and site-monitored forms and deformations. In particular, significant relations between seepage, tensile stresses within the rock mass, karst solution and collapse of cavities were identified.     

Fluid flow record from fracture-fill calcite in the Eocene limestones from the South-Pyrenean Basin (NE Spain) and its relationship to oil shows

The presence of oil shows associated with fractures provides a significant opportunity to a) unravel the type, origin and evolution of fluids involved in fracture-fills, and b) examine how they relate to oil migration. Two stages of calcite cement (C1 and C2) were distinguished in the fractures of the Eocene Armàncies platform carbonates; C1 is characterised by fence-like crystals, exhibits dull red luminescence and contains abundant twin planes, inclusions and δ¹⁸O values that range from − 6.2‰ to − 4.8‰ VPDB. C2 consists of blocky clean crystals, is characterized by dark brown-red luminescence that alternates with yellow bands, and contains hydrocarbon fluid inclusions with homogenisation temperatures of approximately 120 °C. δ¹⁸O values range from − 9.6‰ to − 8.9‰ VPDB. The remaining porosity after C2 precipitation is filled with liquid oil that reached 115 °C. This would seem to indicate that free oil and fluid inclusions oil probably come from the same migration pulse. Oil migration timing was coeval with C2 and continued after calcite cementation was completed.     

湘中锡矿山锑矿床巨量矿石堆积机制: 来自方解石流体包裹体的约束

湘中锡矿山锑矿床目前研究程度已经很高, 但对该矿区锑矿石发生巨量堆积的原因仍不清楚。热液矿床巨量矿石的堆积过程, 实际上就是大规模流体汇聚并发生有效沉淀的过程, 因此, 对锡矿山矿区流体演化过程和沉淀机制的研究有助于解决其巨量矿石的堆积机制问题。锡矿山矿区方解石非常发育, 且与成矿关系密切, 是研究该区流体作用的理想对象。对该区不同期次方解石进行流体包裹体岩相学和显微测温研究, 初步刻画了该区流体演化过程和矿石沉淀机制。研究表明, 不同期次方解石中流体包裹体类型基本相同, 主要为Ⅰ型(纯液相包裹体)和Ⅱ型(富液相两相包裹体), 但流体包裹体的岩相学特征存在明显差异: 主成矿期流体包裹体不发育且个体小, 成矿晚期流体包裹体发育程度中等且个体较大, 成矿后流体包裹体非常发育且个体很大。流体包裹体显微测温分析显示, 该区经历了2次独立的成矿事件: 主成矿期成矿流体为中高温、中低盐度的热液, 这种热液有利于锑的大规模迁移, 矿石沉淀机制为流体混合作用; 成矿晚期流体为中温、低盐度热液, 这种热液中锑的浓度明显小于主成矿期, 矿石沉淀机制为冷却作用; 成矿后还存在一期热液事件, 其流体为一种低温、低盐度热液。锡矿山矿区矿石巨量堆积主要与主成矿期成矿作用有关, 该期成矿流体中锑的浓度高, 流体规模巨大, 且流体混合作用这种矿石沉淀机制非常有利于超大型锑矿床的形成。     

Integration of zircon color and zircon fission-track zonation patterns in orogenic belts: application to the Southern Alps, New Zealand

An exhumed crustal section of the Mesozoic Torlesse terrane underlies the Southern Alps collision zone in New Zealand. Since the Late Miocene, oblique horizontal shortening has formed the northeastern–southwestern trending orogen and exhumed the crustal section within it. On the eastern side, rocks are zeolite- to prehnite–pumpellyite-grade greywacke; on the western side rocks, they have the same protolith, but are greenschist to amphibolite facies of the Alpine Schist. Zircon crystals from sediments in east-flowing rivers (hinterland) have pre-orogenic fission-track ages (>80 Ma) and are dominated by pink, radiation-damaged grains (up to 60%). These zircons are derived from the upper 10 km crustal section (unreset FT color zone) that includes the Late Cenozoic zircon partial annealing zone; both fission tracks and color remain intact and unaffected by orogenesis. Many zircon crystals from sediments in west-flowing rivers (foreland) have synorogenic FT ages, and about 80% are colorless due to thermal annealing. They have been derived from rocks that originally lay in the reset FT color zone and the underlying reset FT colorless zone. The reset FT color zone occurs between 250 and 400 °C. In this zone, zircon crystals have color but reset FT ages that reflect the timing of orogenesis.     

Study of directivity effect on electromagnetic emissions in the HF band as earthquake precursors: Preliminary results on field observations

This work focuses on the use of electromagnetic emissions (EM) in the HF band as a warning event for earthquakes. EM at HF components 41 MHz and 46 MHz were monitored and recorded from eight field stations in Greece and correlated with seismological events. Directivity effect raised since EM emissions at specific station locations were correlated to earthquake events from prescribed regions. EM recordings during 1999 were used and by visual inspection were associated to most of the earthquake events greater than 5R. Using these observations a novel algorithm based on the ratio of short term to long term signal average, together with a prediction rules set derived from 1999's EM emissions study were developed to combine results from several field stations. Performance of the system was promising, but was dependent on the geographic area of interest. Overall performance for earthquakes events of magnitude greater than 5.7 R was 75% of seismic events were correctly predicted by EM activity, while 25% were not predicted.     

Denudation rates of the Quadrilátero Ferrífero (Minas Gerais, Brazil): Preliminary results from measurements of solute fluxes in rivers and in situ-produced cosmogenic Be

This paper investigates the denudation rates in the Quadrilátero Ferrífero, Minas Gerais State (Brazil). The aim is to compare chemical weathering rates from measurements of solute fluxes in rivers and long-term mean erosion rates deduced from in situ-produced cosmogenic ¹⁰Be concentrations measured in fluvial sediments. Both water samples and sediments were collected in fifteen stations (checkpoints) located in four hydrographic basins with low anthropogenic perturbations.Depending of the type of substratum, three degrees of chemical denudation rates from water samples are observed: (i) high rates in marbles; (ii) medium rates in schists, phyllites, granites, gneisses and migmatites; (iii) low rates in quartzites and itabirites. Preliminary results of long-term erosion rates deduced from in situ-produced ¹⁰Be are comparable with those of chemical rates.     

Changes in structural style of normal faults due to failure mode transition: First results from excavated scale models

The effects of failure mode transition from tensile to shear on structural style and fault zone architecture have long been recognized but are not well studied in 3D, although the two modes are both common in the upper crust of Earth and terrestrial planets, and are associated with large differences in transport properties. We present a simple method to study this in physical scale models of normal faults, using a cohesive powder embedded in cohesionless sand. By varying the overburden thickness, the failure mode changes from tensile to hybrid and finally to shear. Hardening and excavating the cohesive layer allows post mortem investigation of 3D structures at high resolution. We recognize two end member structural domains that differ strongly in their attributes. In the tensile domain faults are strongly dilatant with steep open fissures and sharp changes in strike at segment boundaries and branch points. In the shear domain fault dips are shallower and fault planes develop striations; map-view fault traces undulate with smaller changes in strike at branches. These attributes may be recognized in subsurface fault maps and could provide a way to better predict fault zone structure in the subsurface.     

The palaeolatitude controversy in the Silurian of Newfoundland resolved: new palaeomagnetic results from the central mobile belt

A detailed palaeomagnetic investigation of early Silurian volcanics of the Lawrenceton Formation in the Central Mobile Belt (CMB) of Newfoundland reveals primary remanence that places the sampled part of the CMB on the margin of Laurentia in low southerly latitudes in the early Silurian. The palaeomagnetic data indicate large vertical axis (net clockwise) rotations within the CMB and between the CMB and cratonic Laurentia. The volcanics were folded, faulted and in places cleaved in Silurian to Early Devonian times. Anisotropy of magnetic susceptibility measurements on lava flow samples verify field observations of a primary flow-parallel foliation and confirm field measurements of the palaeo-horizontal. A well-developed tectonic fabric was detected at one sampling site near the Reach Fault.Silurian redbeds of the Big Indian Pond Formation were also sampled for palaeomagnetic study. The sediments are folded, faulted and cleaved. A statistically sound syn-folding remanence was identified which, in a tectonically corrected state, is consistent in direction with the remanence in the Silurian volcanics. The sampled sediments are more intensely deformed than the volcanics and magnetic anisotropy measurements indicate both primary layering- and secondary cleavage-related fabrics in varying degrees from site to site. It is possible that cleavage development resulted in remanence reorientation leading to the illusion of syn-folding remanence when, in fact, the remanence was acquired prior to folding.Previously published palaeomagnetic investigations of Silurian rocks in the CMB revealed a discrepancy in palaeofield inclination between volcanic and sedimentary rock types. The sedimentary rocks yielded shallow inclinations and the volcanics intermediate inclinations. Inclination shallowing in the sediments was put forward as an explanation, as well as contamination of the sedimentary results with a shallow overprint. Others argued that the results from the volcanics were in error. The present investigation demonstrates that key volcanics carry a shallower remanence than previously thought, bringing them into approximate agreement with the majority of the results from sediments. Steep results from the Springdale volcanics and very shallow results from the King George IV lake sediments are at variance with the rest of the data. The Springdale result has large error limits that overlap with the other data. The anomalous King George IV result remains an outlier.     

Political ecology in the key of policy: From chains of explanation to webs of relation

Political ecology (PE) is rooted in a combination of critical perspectives and the hard won insights distilled from field work. The theoretical base of political ecology was joined, by Piers Blaikie and others, to an unflinching commitment to empirical observation of biophysical and socio-economic phenomena in place. To this already ambitious mix was added a practical intent to contribute to material as well as social change: a practical political ecology of alternative development ran beneath the surface of much of this work. For many this led to serious encounters with policy and the machinery of policy research institutions. While seemingly contradictory with the critical tenets of political ecology, Blaikie’s pursuit of this pathway led beyond the ivory tower to Political Ecology in the Key of Policy, initially to inform national and international policy and eventually expanding - through the work of second-generation PE - to address internal policy in social movements and alternative development networks. Among recent variations on political ecology that have built partly on the work of Blaikie, Feminist Political Ecology (FPE) expands PE to address women as a group, and gender as a category. FPE and post-structural PE are based on multiple actors with complex and overlapping identities, affinities and interests. An emergent wave of political ecology joins FPE, post-structural theory, and complexity science, to address theory, policy and practice in alternatives to sustainable development. It combines a radical empiricism and situated science, with feminist post-structural theories of multiple identity and “location”, and alternative development paradigms. This approach honors the legacy of Piers Blaikie and other PE founders yet incorporates the insights and political projects of feminism, post-structural critique and autonomous or alternative development movements.     

From public neighbourhoods to multi-tier private neighbourhoods: the evolving ecology of neighbourhood privatization in Calgary

The privatization of urban space, as represented in the trend towards a wide variety of common interest developments and increasing prevalence of gated communities, is an international phenomenon. Recent research has not systematically explored the ways in which these types of developments are collectively re-shaping the public and private realms of the city at large. This empirical study of community areas in a Canadian city describes a number of historical private neighbourhood development trends and their convergence in space and time. Based on the empirical generalizations, a conceptual model is developed to illustrate how the trends may have combined to produce a new geography or ecology of space privatization within the city, one in which the older public city is being circumscribed and bounded by new territories of multi-tiered privatization.     

Relation between "terra rossa" from the Apulia aquifer of Italy and the radon content of groundwater: Experimental results and their applicability to radon occurrence in the aquifer

 The radon-222 (²²²Rn) activity in groundwater of the Apulian karstic aquifer in southern Italy is as great as 500 Becquerel per liter (Bq/L) locally. Normal radium-226 (²²⁶Ra) activity in the limestone and calcareous dolomites of the aquifer is not enough to explain such a high level. Laboratory investigations identified high ²²⁶Ra activity in the "terra rossa," the residuum occupying fissures and cavities in the bedrock, and also the relation between (1) ²²⁶Ra-bearing bedrock and "terra rossa" and (2) ²²²Rn in water. The "terra rossa" is the primary source of the radon in the groundwater. The experimental results show the need to characterize the "terra rossa" of Apulia on the basis of ²²⁶Ra activity and also to study the distribution and variations in ²²²Rn activity over time in the aquifer. Received, January 1996 · Revised, March 1997, September 1997, June 1998 · Accepted, July 1998