Detrital zircon from a late Paleozoic accretionary complex of SW Iberia (Variscan Belt): History of crustal growth and recycling at the Rheic convergent margin

In this study we present new U-Pb ages of detrital zircons from greywackes and quartzites of the Pulo do Lobo Anticline (PLA) that have been interpreted to represent a Late Paleozoic accretionary complex in SW Iberia. The PLA separates the Ossa Morena Zone, which has a North- Gondwana affinity throughout Late Ediacaran and Early Paleozoic times, from the South Portuguese Zone, which is considered to be underlain by Laurussia basement. The PLA stratigraphy most likely represents a synorogenic basin that records the closure of the Late Paleozoic Rheic Ocean and the amalgamation of Pangaea. The youngest formations of the PLA contain upper Devonian microfossils.The results obtained indicate that the detrital zircons from the PLA represent a wide range of Precambrian and Paleozoic crystallization ages. Recycling of older sedimentary units of the Late Ediacaran active margin (Cadomian/Pan-African orogenies) as well as of the Early Paleozoic rifting and passive margin (Rheic Ocean) stages, accounts for the older populations with North-Gondwana affinity (Cambrian, Neoproterozoic, Paleoproterozoic and Archean, with a gap of Mesoproterozoic-age). However, the Mesoproterozoic detrital zircon ages found in the greywackes of the Pulo do Lobo Formation (< 7%) that do not correspond to any substantial source within North-Gondwana, could come from recycled sedimentary deposits or from denudation of Grenville-age basement (Laurussia?). The more recent formations present in the northern limb (Ferreira-Ficalho Group) of the PLA show a significant age cluster in the upper Devonian (c. 378 Ma), whereas on the southern limb (Chança Group), samples have from base to top of the stratigraphic sequence: a minor age cluster in the middle Devonian (c. 390 Ma), a significant age cluster in upper Devonian (c. 380 Ma) and very significant age cluster in the upper Devonian (c. 372 Ma). The presence of middle-upper Devonian detrital zircons in combination with very low abundances of Mesoproterozoic detrital zircon suggests that the PLA sedimentary rocks were not derived from exotic sources but rather have a North-Gondwanan origin. The zircon population in the interval c. 390-380 Ma has no identified corresponding magmatic or stratigraphic source in SW Iberia. Considering that, during the development of the upper Devonian basins of SW Iberia, Laurussia basement was not exposed and that there was no magmatic arc on the North-Gondwana margin, we suggest that the c. 390- 380 Ma detrital zircons are most probably derived from denudation of a (intra-oceanic) magmatic arc related to the closure of the Rheic Ocean

Cruise Report W-49 : scientific activities undertaken aboard R/V Westward, St. Thomas - Key West, November 28, 1979 - January 9, 1980

St. Thomas - Key West, FL, November 28, 1979 - January 9, 1980This cruise report outlines the scientific activities for the forty-ninth cruise of the R/V Westward. These activities fall into two categories: a traditional academic program offered purely and directly for the students' scholastic benefit; and, a program of research and student projects in which the students' skill and drive and curiosity determined the scope and benefit of their participation. Emphasis was on study and investigation uniquely available aboard a sailing oceanographic research vessel. The scientific method was emphasized

The asymptotic structure of nearly unstable non-negative integer-valued AR(1) models

This paper considers non-negative integer-valued autoregressive processes where the autoregression parameter is close to unity. We consider the asymptotics of this `near unit root' situation. The local asymptotic structure of the likelihood ratios of the model is obtained, showing that the limit experiment is Poissonian. To illustrate the statistical consequences we discuss efficient estimation of the autoregression parameter and efficient testing for a unit root.Comment: Published in at http://dx.doi.org/10.3150/08-BEJ153 the Bernoulli (http://isi.cbs.nl/bernoulli/) by the International Statistical Institute/Bernoulli Society (http://isi.cbs.nl/BS/bshome.htm

Recent Thermodynamic Data on Vicinal Water and a Model for Their Interpretation

Results of recent measurements on vicinal (i.e. surface modified) water are reported, particularly data for the density, thermal expansion coefficient, and viscosity. The results are discussed and related to previous studies, suggesting that vicinal water extends over large distances, probably in the range of 30 to 100 molecular diameters. It is proposed also that vicinal water is induced not only by proximity to a »solid« interface but may also occur as vicinal hydration of macromolecules larger than a certain minimum size, likely in the range of 1000 to 5000 Daltons. The temperatures (Tk) at which the thermal anomalies in the properties of vicinal water occur have been confirmed by an extensive DSC study. The critical temperatures are found to be independent of the chemical nature of the solid substrate, based on DSC measurements with porous quartz, polystyrene suspensions and diamond powder, thus lending credence to the reality of the »Paradoxical Effect«. Finally, a percolation model of vicinal water, based on the work by Stanley and Teixeira, is discussed. The model leads to a predicted value for the density of vicinal water of 0.97 g/cm3 in good agreement with the observed value. However the model does not predict the occurence of the thermal anomalies

On Calculation of Thermal Conductivity from Einstein Relation in Equilibrium MD

In equilibrium molecular dynamics, Einstein relation can be used to calculate the thermal conductivity. This method is equivalent to Green-Kubo relation and it does not require a derivation of an analytical form for the heat current. However, it is not commonly used as Green-Kubo relationship. Its wide use is hindered by the lack of a proper definition for integrated heat current (energy moment) under periodic boundary conditions. In this paper, we developed an appropriate definition for integrated heat current to calculate thermal conductivity of solids under periodic conditions. We applied this method to solid argon and silicon based systems; compared and contrasted with the Green-Kubo approach.Comment: We updated this manuscript from second version by changing the title and abstract. This paper is submitted to J. Chem. Phy

Dietary and Intraperitoneal Administration of Selenium Provide Comparable Protection in the 6-Hydroxydopamine Lesion Rat Model of Parkinson's Disease

Significant research implicates the involvement of free radicals in the manifestation of Parkinson's disease. The antioxidant, selenium is a vital dietary component for mammals. It is present in the active center of glutathione peroxidase, an antioxidant enzyme that scavenges peroxides and protects membrane lipids and macromolecules from oxidative insult. The purpose of this research was to determine an effective means of delivering selenium as well as an appropriate time frame for antioxidant administration that would elicit a protective response in rats challenged with an intranigral 6-hydroxydopamine (6-OHDA) lesion. In the first part of this study, Fischer 344 rats were placed into one of four groups: selenium enhanced diet, control diet, intraperitoneal injection of selenium as Na2SeO3 or intraperitoneal injection of distilled water. All treatments were delivered prior to an intranigral 6-OHDA lesion. Animals were euthanized two weeks post lesion and their brains processed for tyrosine hydroxylase (TH) immunocytochemistry. Average dopamine neuron survival in the substantia nigra of control animals was less than 22%; whereas nigral dopamine neuron survival in the selenium fed group was 49.7% and 56.0% in the selenium injected group. Based on these results, a subsequent study was designed utilizing the selenium enhanced diet method of antioxidant administration. To examine the neuroprotective effect of long-term selenium treatment, pregnant Fischer 344 rats were exposed to either selenium enhanced or control rat chow. Their pups were treated with the same diet as their mothers and lesioned with 6-OHDA at two months of age. Animals were euthanized and their brains were processed for TH immunocytochemistry. Nigral dopamine neuron survival for the selenium treated animals was significantly protective (59%) when compared to the control chow fed animals (29.6%). However, when compared to the short-term exposure of selenium rat chow in the previous study, there was no significant increase in neuroprotection