Formation of the Olyutorsky–Kamchatka foldbelt: a kinematic model

The Olyutorsky–Kamchatka foldbelt formed as a result of two successive collisions of the Achaivayam–Valaginsky and Kronotsky–Commander island arcs with the Eurasian margin where the two terranes docked after a long NW transport. We model their motion history from the Middle Campanian to Present and illustrate the respective plate margin evolution with ten reconstructions. In this modeling the arcs are assumed to travel on the periphery of the large plates of Eurasia, North America, Pacific, and Kula, for which the velocities and directions of motion are known from published data. The model predicts that the Achaivayam–Valaginsky arc was the leading edge of the Kula plate from the Middle Campanian to the Middle Paleocene and then moved slowly with the Pacific plate as long as the Middle Eocene when it accreted to Eurasia. The Kronotsky arc initiated in the Middle Campanian on the margin of North America and was its part till the latest Paleocene when the terrane changed polarity to move northwestward with the Pacific plate and eventually to collide with Eurasia in the Late Miocene. The predicted paleolatitudes of the Achaivayam–Valaginsky and Kronotsky–Commander island arcs for the latest Cretaceous and Paleogene are consistent with nine (out of eleven) reliable paleomagnetic determinations for samples from the two arcs. Additional changes imposed on the initial model parameters (kinematics of the large plates, relative position of the Kula–Pacific Ridge and the Emperor seamount chain, or time of active volcanism within the arcs) worsen the fit of the final reconstructions to available geological and paleomagnetic data. Therefore, the suggested model appears to be the most consistent one at this stage of knowledge.     

Thermal thickness of the Earth’s lithosphere: a numerical model

A technique is suggested and the thermal thickness of the lithosphere is calculated, as well as the temperature distribution in the lithosphere on the basis of data on topography, the age of the oceanic bottom, crustal composition and structure, gravity anomalies, and mean annual surface temperatures. The bottom of the lithosphere is determined as the 1300°C isotherm. The calculation resolution is 0.5°×0.5°. All first-order tectonic structures, such as mid-ocean ridges and plume areas in oceans, continental rifts, cratons, and orogenic belts, are expressed in the computed thermal thickness. The comparative analysis of the thermal thickness of oceanic and continental lithosphere, lithosphere of cratons and young platforms, ancient and young orogens, remnant oceanic basins and adjacent continental areas can be used in geodynamical analysis of the corresponding regions.     

Identifying key environmental and building features affecting the outcome of a seismic event: a case study of the “921” earthquake

Natural Hazards - Major earthquakes in a given location are unpredictable, infrequent, and often fatal. Using data from a previous earthquake disaster, this study explores the relationship between...     

Gated communities,heterotopia and a “rights” of privilege: a `heterotopology' of the South African security-park

This paper attempts a two-tiered analysis of what has come to be referred to as the `security-park', i.e., that South African variation of the `gated community' which combines Blakely and Snyder's [Fortress America: Gated communities in the United States, Brookings Institution Press, Washington, 1999] typically separable `lifestyle', `prestige' and `security zone' gated community types. The first part of this analysis reviews the existing literature on gated communities and relates it back to the South African situation. The second part, both theoretical and empirical, draws on Foucault's [Utopias and heterotopias, in: N. Leach (Ed.), Rethinking Architecture: A Reader in Cultural Theory, Routledge, London, 1997] notion of the heterotopia, and on a variety of textual representations of Dainfern. The heterotopia, as an `analytics of difference' becomes a particularly important means of critique here, drawing attention to security-parks as: (1) possessing a precise and well-defined function within society (a function which typically coalesces around points of social crisis), (2) operating distinctive systems of admission and exclusion, (3) containing certain `juxtaposed incompatibilities' (of which a paradoxical `heterochroneity' is one of the most pronounced elements), (4) embodying – via the espousal of a certain `utopics' – an `alternate mode of social ordering' (in Hetherington's [The Badlands of Modernity: Heterotopia and Social Ordering, Routledge, New York, 1997] term). Each of these analytical strands constitutes a discursive relay through which one might deduce wider networks of social power or in the case of Dainfern or security-parks more generally, historical structures of the race- and class-structuring of privilege and poverty. Representations and practices of the security-park are in this way indicative of a far larger political rationality – a self-justificatory set of entitlements, warrants and exclusionary prerogatives which we have labelled a “rights” of privilege.     

From the plutonic root to the volcanic roof of a continental magmatic arc: a review of the Neoproterozoic Araçuaí orogen,southeastern Brazil

International Journal of Earth Sciences - The Araçuaí-West Congo orogen (AWCO) is one of the various components of the Brasiliano/Pan-African orogenic network generated during the...     

Reinterpretation of the Ordovician rotations in NW Argentina and Northern Chile: a consequence of the Precordillera collision?

Early Paleozoic paleomagnetic data from NW Argentina and Northern Chile have shown large systematic rotations within two domains: one composed of the Western Puna that yields very large (up to 80°) counter-clockwise rotations, and the other formed by the Famatina Ranges and the Eastern Puna that shows (~40°) clockwise rotations around vertical axes. In several locations, lack of significant rotations in younger rocks constrains this kinematic pattern to have occurred during the Paleozoic. Previous tectonic models have explained these rotations as indicative of rigid-body rotations of large para-autochthonous crustal blocks or terranes. A different but simple tectonic model that accounts for this pattern is presented in which rotations are associated to crustal shortening and tectonic escape due to the collision of the allochthonous terrane of Precordillera in the Late Ordovician. This collision should have generated dextral shear zones in the back arc region of the convergent SW Gondwana margin, where systematic domino-like clockwise rotations of small crustal blocks accommodate crustal shortening. The Western Puna block, bordering the Precordillera terrane to the north, might have rotated counterclockwise as an independent microplate due to tectonic escape processes, in a fashion similar to the present-day relationship between the Anatolia block and the Arabian microplate.     

Implications of gravity data from East Kalimantan and the Makassar Straits: a solution to the origin of the Makassar Straits?

Recent free-air gravity data covering the Makassar Straits is integrated with Bouguer gravity data from onshore East Kalimantan to provide new insights into the basement structure of the region. Onshore Kalimantan, gravity highs on the northern margin of the Kutai Basin trend NNE–SSW and N–S and correspond with the axes of inverted Eocene half-grabens. NW–SE trending lows correspond to deep seated basement weaknesses reactivated as normal faults during the Tertiary. An intra-basin gravity high trending NNE–SSW, the Kutai Lakes Gravity High, is modelled as folded high density Paleogene sediments flanked by syn-inversion synclines infilled with low density sediments. Offshore Kalimantan, the Makassar Straits include two basins offset by an en-echelon fault zone, suggestive of an extensional origin. The regional signature of the free-air anomaly data mirrors the bathymetry, but this effect can be reduced by the use of filters in order to examine the basin architecture. The free-air gravity minimum in the Makassar Strait is only −20 mGal, much smaller than that appropriate for a foreland basin, and more indicative of an extensional basin. The steepness of the gradients on the flanks of the basins indicates fault control of their margins. A regional 2D profile across the North Makassar Basin suggests the presence of attenuated crust (<14 km) in the basin axis at the present day, whereas flexural backstripping implies the presence of oceanic crust of middle Eocene age. The presence of oceanic crust in the North Makassar Straits Basin has implications for regional plate tectonic models.     

Groundwater flow in a transboundary fault-dominated aquifer and the importance of regional modeling: the case of the city of Querétaro,Mexico

The city of Querétaro, located near the political boundary of the Mexican states of Querétaro and Guanajuato, relies on groundwater as it sole water supply. Groundwater extraction in the city increased from 21?×?10⁶ m³/yr in 1970 to 104?×?10⁶ m³/yr in 2010, with an associated drawdown of 100 m in some parts of the aquifer. A three-dimensional numerical groundwater-flow model has been developed that represents the historical evolution of the aquifer’s potentiometric levels and is used to simulate the effect of two scenarios: (1) a 40 % reduction in the extraction rate from public water supply wells in early 2011 (thus reducing the extraction to 62?×?10⁶ m³/yr), and (2) a further reduction in 2021 to 1?×?10⁶ m³/yr. The modeling results project a temporary recovery of the potentiometric levels after the 40 % reduction of early 2011, but a return to 2010 levels by 2020. If scenario 2 is implemented in 2021, the aquifer will take nearly 30 years to recover to the simulated levels of 1995. The model also shows that the wells located in the city of Querétaro started to extract water from part of the aquifer beneath the State of Guanajuato in the late 1970s, thus showing that the administrative boundaries used in Mexico to study and develop water resources are inappropriate, and consideration should be given to physical boundaries instead. A regional approach to studying aquifers is needed in order to adequately understand groundwater flow dynamics.     

Reply to “Oxygen isotope heterogeneity of the mantle beneath the Canary Islands: a discussion of the paper of Gurenko et al.”

The comment by Day et al. (Contrib Mineral Petrol, 2012) (1) discusses the validity of the previously obtained oxygen isotope data for El Hierro and La Palma (Canary Island) olivines, (2) questions the approach by Gurenko et al. (Contrib Mineral Petrol 162:349–363, 2011) of using weakly correlated variations of δ¹⁸O_olivine values with X _px (proportion of pyroxenite-derived melt in the parental magma), and (3) provides reasons why oxygen isotope data by secondary ion mass spectrometry (SIMS) “offer sensitive means for detecting melt-crust interactions.” We respond these comments and report a new set of oxygen isotope measurements performed by SIMS and single-grain laser fluorination methods. These measurements confirm our previous data and conclusions and demonstrate the ability of the SIMS technique to analyze O isotopes in terrestrial samples with 2-sigma uncertainty better than ±0.25 ‰.     

The Cretaceous-Tertiary boundary in a sector of the south limb of the Miranda-Treviño synclinal: the first appearance of chelonia and archosauria in the Basque country

This paper presents a study of the Cretaceous-Tertiary boundary in the Miranda-Treviño Synclinorium (Basque-Cantabric basin) where two main sequences have been recognised; the lower is regressive and theupper one has a marked transgressive trend. They are separated by a low angled un-conformity which is indicative of the Maastrichtian-Danian boundary.The lower sequence (S1) indicates a clear transition between the shoreface and backshore sub-environments. Bone accumulations are located in the sandy sediments of the upper foreshore and backshore, associated with ferrugenous hardgrounds and gypsum efflorescences.The upper sequence (S2) indicates the beginning of a marine transgression. It is composed a dominantly carbonate-rich sediments and the fauna suggests a deposition in environmental conditions ranging from stenohaline, to littoral, and to a coastal lagoon and inner carbonaterich platform.In the lower sequence (Maastrichtian Unit S₁ U₃), the following herpetofauna have been identified; an eusuchian alligator, and two dinosaurs (an ornithopod and a sauropod). Several plates of chelonia have been identified as? Adocus sp.     

Knowledge, power, and tribal mapping: a critical analysis of the “return of the Truku people”

Over the past decade, Indigenous peoples in Taiwan have shown a strong desire for the ??return of the Native??; this includes the Truku people in eastern Taiwan. Seizing a favorable climate of political opportunity structure in 2004, the Truku people first succeeded in obtaining the Taiwanese government??s recognition as an independent Indigenous nation??formerly considered a subgroup of the Atayal Nation. Then, riding on accumulated political resources, a few Truku elites started to engage in a government-initiated tribal mapping project. However, while tribal mapping originated in some North American Indigenous communities with a bottom-up process and spirit, the Taiwanese government sent both money (through the municipal government) and an academic expert team into the community to initiate and to assist (the elite group) with the tribal mapping project. These top-down government initiatives resulted in at least two major ill effects. First of all, two other subgroups of the Atayal Nation living in the same region were systematically excluded from the tribal mapping project, to the extent that their own traditional territories became part of the traditional territory of the newly formed Truku Nation. Secondly, possibly expecting a high political payoff on the part of elites, elite competition arose during the process of tribal mapping, with the interests of other community members largely ignored. As such, instead of establishing a decolonizing force, the ??return of the Truku?? appears to have achieved ??colonialism from within.?? This paper analyzes this process and considers ways to develop a more democratic strategy for the ??return of the Truku.??     

Spots on the Surface of a Star: An Influence on the Estimates of Star–Exoplanet Binary System Parameters

Astronomy Reports - We developed an algorithm to model a light curve observed in a binary system that contains an exoplanet and a host star, on the surface of which there are spots. The spot-caused...     

Numerical Modeling of the Effects of Major Elements on the Solubility of Chrome–Spinel and a Likely Solution of the Problem of the Origin of Chromitite

Doklady Earth Sciences - The influence of variations in fo-, fa-, en-, fs-, di-, an-, and ab-components in a high-Mg basaltic melt on the topology of the spinellide liquidus was analyzed using the...     

Hornblende–garnet–plagioclase thermobarometry: a natural assemblage calibration of the thermodynamics of hornblende

Calibrations are presented for an independent set of four equilibria between end-members of garnet, hornblende, plagioclase and quartz. Thermodynamic data from a large internally-consistent thermodynamic dataset are used to determine the ΔG° of the equilibria. Then, with the known mixing properties of garnet and plagioclase, the non-ideal mixing in amphibole is derived from a set of 74 natural garnet–amphibole–plagioclase–quartz assemblages crystallised in the range 4–13 kbar and 500–800 °C. The advantage of using known thermodynamic data to calculate ΔG° is that correlated variations of composition with temperature and pressure are not manifested in fictive derived entropies and volumes, but are accounted for with non-ideal mixing terms. The amphibole is modelled using a set of ten independent end-members whose mixing parameters are in good agreement with the small amount of data available in the literature. The equilibria used to calibrate the amphibole non-ideal mixing reproduce pressures and temperatures with average absolute deviations of 1.1 kbar and 35 °C using an average pressure–temperature approach, and 0.8 kbar with an average pressure approach. The mixing data provide not only a basis for thermobarometry involving additional phases, but also for calculation of phase diagrams in complex amphibole-bearing systems. Received: 8 November 1999 / Accepted: 7 July 2000     

Pseudo- and real-inverted metamorphism caused by the superposition and extrusion of a stack of nappes: a case study of the Southern Brasília Orogen,Brazil

International Journal of Earth Sciences - The Southern Brasília Orogen is a Neoproterozoic belt that occurs along the southernmost border of the São Francisco Craton where the...     

Geothermobarometry of a stilpnomelane–garnet-bearing metapegmatite: P–T constraints on the Eo-Alpine metamorphic overprint of the Austroalpine nappes north of the Tauern Window

The Ordovician Kellerjochgneiss (Schwaz Augengneiss) is a polymetamorphic orthogneiss-bearing unit and is part of the Austroalpine basement nappes north of the Tauern Window. Within the Kellerjochgneiss a small, strongly deformed metapegmatite dike occurs. The pegmatite crosscuts the gneiss discordantly and contains the mineral assemblage muscovite 1,2+plagioclase+K-feldspar+chlorite+quartz+garnet 1 (Alm_67–76Andr_0.9–2Sps_17–28Prp_0.4–5)+garnet 2 (Grs_36–46Alm_24–32Andr_8–21Sps_15–17Prp_0–1)±stilpnomelane±biotite±clinozoisite. The magmatic protolith assemblage is comprised of relict K-feldspar, quartz and garnet 1. Textural observations indicate that biotite and muscovite cores (muscovite 1) are either part of the magmatic- or an earlier (Variscan?) metamorphic assemblage. Geothermobarometry of the metapegmatite was done on the latest-stage (Eo-Alpine) mineral assemblage garnet 2+muscovite 2+chlorite+stilpnomelane+plagioclase+quartz. Calculations of H₂O-absent intersections in the system [KCNFMAS] with the multi-equilibrium program THERMOCALC v.3.1 yielded P–T estimates of 4.4 to 6.7 kbar and 321°C to 376°C. Calculations of the P–T conditions by using the assemblage muscovite 2+chlorite+stilpnomelane+quartz yielded slightly higher pressures of 6.4 to 7.2 kbar at temperatures of 310–325°C. Correlating these P–T data with geochronological data from the neighbouring lithologies (Kellerjochgneiss, Innsbruck Quartzphyllite, Wildschönau Schists) and with structural investigations from these units indicate that the P–T estimates obtained in this investigation represent the Eo-Alpine metamorphic overprint. Hence, these unusual rocks provide important information on the Eo-Alpine P–T conditions since most samples studied from the investigated Austroalpine basement nappes north of the Tauern Window rarely contain mineral assemblages suitable for geothermobarometry.     

A review of the pressure–temperature–time evolution of the Limpopo Belt: Constraints for a tectonic model

Published literature argues that the Limpopo Belt can be subdivided into three zones, each with a distinctive geological character and tectono-metamorphic fingerprint. There are currently two contrasting schools of thought regarding the tectono-metamorphic evolution of the CZ. One camp argues that geochronological, structural and prograde pressure–temperature (P–T) evidence collectively indicate that the CZ underwent tectono-metamorphism at ca. 2.0 Ga which followed a clockwise P–T evolution during a transpressive orogeny that was initiated by the collision of the Kaapvaal and Zimbabwe cratons. Deformation and metamorphism consistent with this scenario are observed in the southern part of the NMZ but are curiously absent from the whole of the SMZ. The opposing view argues that the peak metamorphism associated with the collision of the Kaapvaal and Zimbabwe cratons occurred at ca. 2.6 Ga and the later metamorphic event is an overprint associated with reactivation along Archean shear zones. Post-peak-metamorphic conditions, which at present cannot be convincingly related to either a ca. 2.6 or 2.0 Ga event in the CZ reveal contrasting retrograde paths implying either near-isothermal decompression and isobaric cooling associated with a ‘pop-up’ style of exhumation or steady decompression–cooling linked to exhumation controlled by erosion. Recent data argue that the prograde evolution of the ca. 2.0 Ga event is characterised by isobaric heating prior to decompression–cooling. Contrasting P–T paths indicate that either different units exist within the CZ that underwent different P–T evolutions or that some P–T work is erroneous due to the application of equilibrium thermobarometry to mineral assemblages that are not in equilibrium. The morphology of the P–T path(s) for the ca. 2.6–2.52 Ga event are also a matter of dispute. Some workers have postulated an anticlockwise P–T evolution during this period whilst others regard this metamorphic event as following a clockwise evolution. Granitoid magmatism is broadly contemporaneous in all three zones at ca. 2.7–2.5 suggesting a possible causal geodynamic link. P–T contrasts between and within the respective zones prevent, at present, the construction of a coherent and inter-related tectonic model that can account for all of the available evidence. Detailed and fully-integrated petrological and geochronological studies are required to produce reliable P–T–t paths that may resolve some of these pertinent issues.     

The miarolitic pegmatites from the K?nigshain: a contribution to understanding the genesis of pegmatites

In this paper, we show that the crystallization of miarolitic pegmatites at K?nigshain started at about 700°C, in melts containing up to 30 mass% water. Such high water concentration at low pressures (1–3 kbar) is only possible if the melts are peralkaline. Such peralkaline melts are highly corrosive, and reacted with the wall rock—here the granite host—forming the graphic granite zone, in part via a magmatic–metasomatic reaction. With cooling, the water concentration in some melt fractions increased up to 50 mass% H₂O. The melt-dominated system ends below 600°C and passes into a fluid-dominated system, the beginning of which is characterized by strong pressure fluctuations, caused by the change of OH and CO₃ ²⁻ in the melt, to molecular water and CO₂. We note two generations of smoky quartz, one crystallized above the β–α-transition of quartz (≈573°C), and one below, both of which contain melt inclusions. This indicates that some melt fraction remains during at least the higher-temperature portion of the growth of minerals into the miarolitic cavity, contradicting the view that minerals growing into a pegmatite chamber only do so from aqueous fluids. We show that the K?nigshain miarolitic pegmatites are part of the broad spectrum of pegmatite types, and the processes active at K?nigshain are representative of processes found in most granitic pegmatites, and are thus instructive in the understanding of pegmatite formation in general, and constraining the composition and characteristics of pegmatite-forming melts. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

The Sarmatia megablock as a fragment of the Vaalbara supercontinent: Correlation of geological events at the Archean‒Paleoproterozoic transition

The results of correlation between geological events in the period of 2.8?2.0 Ga provide grounds to assume that the Sarmatia lithospheric megablock definable in the southern part of the East European Craton belonged to the ancient Vaalbara supercontinent consisting of the Pilbara and Kaapvaal cratons. In the period of 2.8?2.6 Ga, all of them represented fragments of the continental crust consolidated at approximately 2.8 Ga and subjected to continental rifting, which was accompanied by intense basite volcanism. In the period of 2.50?2.45 Ga, these three cratons were characterized by similar tectonic settings and accumulation of banded iron formations. Precisely these banded iron formations of the largest Transvaal, Hamersley, Kursk, and Kremenchug?Krivoi Rog iron ore basins accumulated in the period of 2.50?2.45 Ga in a single oceanic basin serve as a basis for adequate paleotectonic reconstructions of the Vaalbara supercontinent. In the period of 2.45?2.20 Ga, all three cratons were subjected to a long-lasting break in sedimentation followed by activation of continental rifting with terrigenous sediment deposition, which terminated with basite volcanism ca. 2.2 Ga. These events gave start to the Vaalbara breakup, which represented a multistage process with alternating divergence and convergence phases of supercontinent fragments until the Kaapvaal and Zimbabwe, Pilbara and Yilgarn, and Sarmatia and Volgo-Uralia cratons, respectively, became eventually united.     

Early Mesozoic sedimentary‒tectonic evolution of the Central-East Iranian Microcontinent: Evidence from a provenance study of the Nakhlak Group

In Central Iran, the mixed siliciclastic?carbonate Nakhlak Group of Triassic age is commonly seen to have a Cimmerian affinity, although it shows considerable resemblances with the Triassic Aghdarband Group in far northeastern Iran, east of Kopeh-Dagh area, with Eurasian affinity. The Nakhlak Group is composed of the Alam (Late Olenekian?Anisian), Baqoroq (Late Anisian??Early Ladinian), and Ashin (Ladinian??Early Carnian) formations consisting mainly of volcanoclastic sandstone and shale and fossiliferous limestone. The Baqoroq Formation contains also metamorphic detritus. Sandstone petrofacies reflect the detrital evolution from active volcanism to growing orogen and again active volcanism. Textural and modal analyses of volcanic lithic fragments from the Alam Formation reflect the eruption style and magma composition of a felsic to intermediate syn-sedimentary arc activity. The detrital modes of the Baqoroq Formation sediments suggest a recycled orogenic source followed by arc activity in a remnant fore-arc basin. The sandstone samples from the Ashin Formation demonstrate a continuity of felsic to intermediate arc activity. Major and trace element concentrations of the Nakhlak Group clastic samples support sediment supply from first-cycle material and felsic magmatic arc input. The enrichment in LREE, the negative Eu anomalies, and the flat HREE patterns indicate origination from the old upper continental crust and young arc material. The chemical index of alteration (CIA ～51–70 for sandstone and 64–76 for shale samples) indicates medium degrees of chemical weathering at the source. Petrographical and geochemical evidence together with facies analysis constructed the following depositional conditions for the Nakhlak Group sediments: In the Olenekian, a fore-arc shallow to deep marine depositional basin developed that later was filled by recycled and arc-related detritus and changed into a continental basin in the Anisian. Ladinian extension let to a deepening of the basin. With respect to the similarities between the Nakhlak and Aghdarband (NE Iran) groups and unusual present-day position of the Nakhlak Group with no stratigraphic connection to the surrounding area, the development of first a fore-arc basin and later change into a back-arc depositional basin in close relation with the Aghdarband basin at the southern Eurasian active margin in the Triassic are here proposed. Understanding the basin development recorded in the Nakhlak Group provides constraints on the closure history of Palaeotethys and of the tectonic evolution of early Mesozoic basins at the southern Eurasian margin before the Cimmerian Orogeny.