The role of extension in the Miocene denudation of the Nevado-Filábride Complex, Betic Cordillera (SE Spain)

The Internal Zone of the Betic Cordillera, SE Spain, consists of a nappe stack of three complexes, the deepest of which is the Nevado-Filábride Complex. The zone is separated from the overlying Alpujárride Complex by a crustal scale shear zone that has variously been interpreted as a thrust or an extensional detachment. A suite of 74 new apatite and zircon fission track results have been obtained from the Nevado-Filábride Complex and these have been used to define regional cooling patterns for the complex. Rapid cooling (105°C–200°C Ma−1) is spatially related to the tectonic contact with the overlying Alpujárride Complex-Cooling to near-surface temperatures occurred first in the east (Sierra de los Filabres) during the mid-Serravallian (12±1 Ma) and was completed by the early Tortonian (9–8 Ma) in the west (Sierra Nevada). There is no correlation between fission track age and sample elevation. These results are consistent with tectonic unroofing of this complex, a finding that favors extension as the mechanism by which the two complexes were brought into contact. Extension spans the middle and earliest upper Miocene (12–8 Ma) in the study area and therefore lasted much longer than previously documented. A hypothesis is advanced which links oblique convergence between the Iberian plate and the Betic Internal Zones, resulting in crustal contraction at depth, with orogen parallel extension in the middle and upper crust

Statistics for Fission-Track Thermochronology

This chapter introduces statistical tools to extract geologically meaningful information from fission-track (FT) data using both the external detector and LA-ICP-MS methods. The spontaneous fission of 238U is a Poisson process resulting in large single-grain age uncertainties. To overcome this imprecision, it is nearly always necessary to analyse multiple grains per sample. The degree to which the analytical uncertainties can explain the observed scatter of the single-grain data can be visually assessed on a radial plot and objectively quantified by a chi-square test. For sufficiently low values of the chi-square statistic (or sufficiently high p values), the pooled age of all the grains gives a suitable description of the underlying ‘true’ age population. Samples may fail the chi-square test for several reasons. A first possibility is that the true age population does not consist of a single discrete age component, but is characterised by a continuous range of ages. In this case, a ‘random effects’ model can constrain the true age distribution using two parameters: the ‘central age’ and the ‘(over)dispersion’. A second reason why FT data sets might fail the chi-square test is if they are underlain by multimodal age distributions. Such distributions may consist of discrete age components, continuous age distributions, or a combination of the two. Formalised statistical tests such as chi-square can be useful in preventing overfitting of relatively small data sets. However, they should be used with caution when applied to large data sets (including length measurements) which generate sufficient statistical ‘power’ to reject any simple yet geologically plausible hypothesis

Molecular basis of structure and function of the microvillus membrane of intestinal epithelial cells

Correlation of molecular structure with biochemical functions of the plasma membrane of the microvilli of intestinal epithelial cells has been investigated by biochemical and electron microscopic procedures. Repeating particles, measuring approximately 60 &#197;in diameter, were found on the surface of the microvilli membrane which had been isolated or purified from rabbit intestinal epithelial cells and negatively stained with phosphotungstic acid. These particles were proved to be inherent components of the microvillus membrane, attached to the outer surface of its trilaminar structure, and were designated as the elementary particles of the microvilli of intestinal epithelial cells. Biochemical and electron microscopic identification of these elementary particles has been carried out by isolation of the elementary particles with papain from the isolated microvillus membrane, followed by purification of the particles by chromatographies on DEAE-cellulose and Sephadex columns. The partially purified particles containing invertase and leucine aminopeptidase are similar in size and structure to those of the elementary particles in the microvillus membrane. Evidence indicates that each of the elementary particles coincide with or include an enzyme molecule such as disaccharidase or peptidase, which carry out the terminal hydrolytic digestion of carbohydrates and proteins, respectively, on the surface of the microvillus membrane. Magnesium ionactivated adenosine triphosphatase and alkaline phosphatase cannot be solubilized with papain but remains in the smooth-surface membrane after the elementary particles have been removed. Cytochemical electron microscopic observation revealed that the active site of magnesium ion-activated adenosine triphosphatase is localized predominantly in the inner surface of the trilaminar structure of the microvillus membrane.</p

Sustainable drainage system site assessment method using urban ecosystem services

The United Kingdom's recently updated approach to sustainable drainage enhanced biodiversity and amenity objectives by incorporating the ecosystem approach and the ecosystem services concept. However, cost-effective and reliable methods to appraise the biodiversity and amenity values of potential sustainable drainage system (SuDS)sites and their surrounding areas are still lacking, as is a method to enable designers to distinguish and link the amenity and biodiversity benefits that SuDS schemes can offer. In this paper, therefore, the authors propose two ecosystem services- and disservices-based methods (i.e. vegetation structure cover-abundance examination and cultural ecosystem services and disservices variables appraisal) to aid SuDS designers to distinguish and link amenity and biodiversity benefits, and allow initial site assessments to be performed in a cost-effective and reliable fashion. Forty-nine representative sites within Greater Manchester were selected to test the two methods. Amenity and biodiversity were successfully assessed and habitat for species, carbon sequestration, recreation and education ecosystem services scores were produced,which will support SuDS retrofit design decision-making. Large vegetated SuDS sites with permanent aquatic features were found to be most capable of enhancing biodiversity- and amenity-related ecosystem services. Habitat for species and recreation ecosystem services were also found to be positively linked to each other. Finally, waste bins on site were found to help reduce dog faeces and litter coverage. Overall, the findings presented here enable future SuDS retrofit designs to be more wildlife friendly and socially inclusive

Spatial correlation bias in late-Cenozoic erosion histories derived from thermochronology

International audienceThe potential link between erosion rates at the Earth's surface and changes in global climate has intrigued geoscientists for decades1,2 because such a coupling has implications for the influence of silicate weathering3,4 and organic-carbon burial5 on climate and for the role of Quaternary glaciations in landscape evolution1,6. A global increase in late-Cenozoic erosion rates in response to a cooling, more variable climate has been proposed on the basis of worldwide sedimentation rates7. Other studies have indicated, however, that global erosion rates may have remained steady, suggesting that the reported increases in sediment-accumulation rates are due to preservation biases, depositional hiatuses and varying measurement intervals8-10. More recently, a global compilation of thermochronology data has been used to infer a nearly twofold increase in the erosion rate in mountainous landscapes over late-Cenozoic times6. It has been contended that this result is free of the biases that affect sedimentary records11, although others have argued that it contains biases related to how thermochronological data are averaged12 and to erosion hiatuses in glaciated landscapes13. Here we investigate the 30 locations with reported accelerated erosion during the late Cenozoic6. Our analysis shows that in 23 of these locations, the reported increases are a result of a spatial correlation bias—that is, combining data with disparate exhumation histories, thereby converting spatial erosion-rate variations into temporal increases. In four locations, the increases can be explained by changes in tectonic boundary conditions. In three cases, climatically induced accelerations are recorded, driven by localized glacial valley incision. Our findings suggest that thermochronology data currently have insufficient resolution to assess whether late-Cenozoic climate change affected erosion rates on a global scale. We suggest that a synthesis of local findings that include location-specific information may help to further investigate drivers of global erosion rates

The Parameters That Govern the Accuracy of Fission-Track Age Determinations: A Re-Appraisal

Since the generalized use of the zeta-calibration method, research on fission-track age calibration and the parameters that govern the accuracy of fission-track ages has become limited to a few laboratories. The present paper gives a review of the research that has been carried out on these problems in our laboratory during the last decade. The results of these investigations demonstrate that absolute thermal neutron fluence measurements and the determination of the U-235 fission rate during sample irradiation no longer present a problem. The only parameter that would seem to remain to be determined is therefore the spontaneous fission decay constant of U-238 (lambda(f)). However, the results of our experiments also re-emphasize the importance of the techniques of track analysis that are used in an FT age determination, They can be responsible for systematic differences up to 15-20% in the final age result if the absolute approach is used. The parameters that play a role are the track registration efficiency and the combined etching-observation efficiency. These parameters have to be properly dealt with if hf is determined through the analysis of samples of known age. By applying the same analytical techniques to the age standards and the unknown samples, the zeta-method eliminates the systematic effects of these parameters and intrinsically ensures accurate ages. When a value of lambda(f) is agreed by consensus and/or as a result of new experimentation, it will still be essential to perform age standard analyses for determining a procedure factor (Q) that yields direct information on the systematic effect of the technique of track analysis. This routine will nevertheless be a significant improvement on the calibration based on the determination of the all-embracing zeta-factor

Age of crustal melting, emplacement and exhumation history of the Shivling leucogranite, Garhwal Himalaya

We report a U-Pb monazite age of 23.0 ± 0.2 Ma for the Shivling leucogranite, a tourmaline + muscovite ± biotite leucogranite at the top of the High Himalayan slab in the Garhwal Himalaya, north India. The Shivling-Bhagirathi leucogranite is a viscous near-minimum melt, emplaced as a foliation parallel laccolith via a dyke network not far from its source region. Prograde heating occurred soon after the India-Asia collision at c. 50 Ma up to melting at 23 Ma and high temperatures (&gt;550 °C) were maintained for at least 15 Ma after garnet growth. The leucogranite was emplaced at mid-crustal depths along the footwall of the Jhala fault, a large-scale low-angle normal fault, part of the South Tibetan Detachment system, above kyanite and sillimanite grade gneisses. The geometry of the leucogranite laccolith shows biaxial extension and boudinage both perpendicular (north-northeast-south-southwest) and parallel to the strike (west-northwest-east-southeast) of the mountain range. Unroofing occurred by underthrusting beneath the High Himalayan slab along the Main Central Thrust zone, progressively 'jacking up' the leucogranites, removal of material above by low-angle normal faulting, and erosion. Very rapid cooling at rates of 200-350 °C/Ma between 23-21 Ma immediately followed crystallization, as tectonic unroofing and erosion removed 24-28 km of overburden during this time. K-Ar muscovite ages are 22 ± 1.0 Ma and fission track ages of zircons from &gt;5000 m on the North Ridge of Shivling are 14.2 ± 2.1 and 8.8 ± 1.2 Ma and apatites are 3.5 ± 0.79 and 2.61 ± 0.23 Ma. Slow steady state cooling at rates of 20-30 °C/Ma from 20-1 Ma shows that maximum erosion rates and unroofing of the leucogranite occurred during the early Miocene. This timing coincides with initiation of low-angle, north-dipping normal faulting along the South Tibetan Detachment system

Improved modeling of fission-track annealing in apatite

This paper seeks to explain the mechanism of transmission of failures from the financial sector to the real economy. We consider the tightening of firms' financial conditions as an engine of such a transmission. In order to investigate this mechanism we construct a dynamic stochastic general equilibrium model focusing on the production side of the economy as a channel of the transition of the crisis. The debt cutting is modeled as a negative shock to the lending mechanism through an increase in the level of collateral required by financial institutions in order to provide a loan. We conclude that deleveraging might be one of the main reasons for the drop in both consumption and investment during the recent financial crisis