21 research outputs found
Compositional characteristics and spatial distribution of enriched Icelandic mantle components
Author Posting. © The Authors, 2010. This is the author's version of the work. It is posted here by permission of Oxford University Press for personal use, not for redistribution. The definitive version was published in Journal of Petrology 51 (2010): 1447-1475, doi:10.1093/petrology/egq025.We present compositional data on a suite of 18 primitive neovolcanic alkali basalts from three
flank zone regions in Iceland (Vestmannaeyjar in the south, Snæfell in the east, and Snæfellsnes
in the west) that are peripheral to the main rift zones that are dominated by tholeiitic basalts. This
study integrates He isotope data with radiogenic isotope data (Sr-Nd-Pb-Hf), stable isotope data
(δ18O), and trace element data to characterise the compositional features of the trace-elementenriched
components of the Icelandic mantle. We also present high-precision Pb isotope data on
an additional 57 lava samples from the flank zones (including Öræfajökull in the south-east) and
the Northern and Eastern rift zones. Most Icelandic lavas have negative Δ207Pb (–4 to –1), with
higher values (–1 to +4) found only in samples from Öræfajökull, Snæfell, and parts of the
Reykjanes Peninsula. At Snæfell, this EM1-type component is characterised by a low δ18Oolivine
signature (+4.1‰ to +4.6‰), moderate 206Pb/204Pb values (18.4-18.6) and MORB-like 3He/4He
(6.9-7.5 R/RA). Samples from Vestmannaeyjar and Snæfellsnes have mantle-like δ18Oolivine
(+4.9‰ to +5.0‰), and radiogenic 206Pb/204Pb values (18.9-19.3) that fall on the NHRL for
208Pb/204Pb (Δ208Pb –5 to +5). Compared to the Vestmannaeyjar lavas, Snæfellsnes lavas have
higher La/YbN (5-11 vs. 3-5), lower εNd (5.5-6.5 vs. 6.8-7.6) and lower 3He/4He (6.3-8.6 R/RA vs.
11.4-13.5 R/RA). Therefore, the most trace element enriched components in the Icelandic mantle
are not the carriers of the high 3He/4He values (> 15 R/RA) found in some lavas on Iceland and
the adjacent ridges, and instead are consistent with degassed, recycled components. Even after
excluding the EM1-type high Δ207Pb samples, high-precision Pb isotope data produce a kinked
array on an 206Pb/204Pb vs. 208Pb/204Pb plot, which is not consistent with simple binary mixing
between two end-members. This requires significant lateral heterogeneity within the Icelandic
mantle and the presence of more than just two compositionally-distinct local mixing end-member
components. Samples from each of the main axial rift zones define different trends. Despite the
tectonic continuity between the Northern Volcanic Zone and the Eastern Volcanic Zone, lavas
from these two rift zones define separate sub-parallel linear arrays. Lavas from the adjacent
Western Volcanic Zone and the Eastern Volcanic Zone define oblique linear arrays that converge
on a common local end-member that is not involved in the magmatism of the Northern Volcanic
Zone. Therefore, there is a distinct NE-SW compositional heterogeneity within the Icelandic
mantle.work was funded primarily by the Danish National Research
Foundation through a grant to the former Danish Lithosphere Centre, with additional funding
from the University of Iowa for the oxygen isotope analyses
The Pondicherry interpretation of quantum mechanics: An overview
An overview of the Pondicherry interpretation of quantum mechanics is
presented. This interpretation proceeds from the recognition that the
fundamental theoretical framework of physics is a probability algorithm, which
serves to describe an objective fuzziness (the literal meaning of Heisenberg's
term "Unschaerfe," usually mistranslated as "uncertainty") by assigning
objective probabilities to the possible outcomes of unperformed measurements.
Although it rejects attempts to construe quantum states as evolving ontological
states, it arrives at an objective description of the quantum world that owes
nothing to observers or the goings-on in physics laboratories. In fact, unless
such attempts are rejected, quantum theory's true ontological implications
cannot be seen. Among these are the radically relational nature of space, the
numerical identity of the corresponding relata, the incomplete spatiotemporal
differentiation of the physical world, and the consequent top-down structure of
reality, which defies attempts to model it from the bottom up, whether on the
basis of an intrinsically differentiated spacetime manifold or out of a
multitude of individual building blocks.Comment: 18 pages, 1 eps figure, v3: with corrections made in proo
Quantum discreteness is an illusion
I review arguments demonstrating how the concept of "particle" numbers arises
in the form of equidistant energy eigenvalues of coupled harmonic oscillators
representing free fields. Their quantum numbers (numbers of nodes of the wave
functions) can be interpreted as occupation numbers for objects with a formal
mass (defined by the field equation) and spatial wave number ("momentum")
characterizing classical field modes. A superposition of different oscillator
eigenstates, all consisting of n modes having one node, while all others have
none, defines a nondegenerate "n-particle wave function". Other discrete
properties and phenomena (such as particle positions and "events") can be
understood by means of the fast but smooth process of decoherence: the
irreversible dislocalization of superpositions. Any wave-particle dualism thus
becomes obsolete. The observation of individual outcomes of this decoherence
process in measurements requires either a subsequent collapse of the wave
function or a "branching observer" in accordance with the Schr\"odinger
equation - both possibilities applying clearly after the decoherence process.
Any probability interpretation of the wave function in terms of local elements
of reality, such as particles or other classical concepts, would open a
Pandora's box of paradoxes, as is illustrated by various misnomers that have
become popular in quantum theory.Comment: 18 pages. v2: Some text and two references added. v3: Minor changes,
one reference added. v4: 21 pages. Submitted to AmJP (not accepted). v5:
Minor changes (mainly formulations). v6: Accepted by Found.Phys. Final
version is available at http://www.springerlink.co
Origin and geochemical evolution of the Madeira-Tore Rise (eastern North Atlantic)
The Madeira-Tore Rise, located ∼700 km off the NW African coast, forms a prominent ridge in the east Atlantic. The age and origin of the rise are controversial. This study presents major and trace element, Sr, Nd, Pb, Hf isotope and 40Ar/39Ar age determinations from volcanic rocks dredged from different sites along the rise. In addition, isotopic compositions of rock samples from Great Meteor Seamount in the central Atlantic are presented. The new radiometric and paleontologically constrained ages identify two major episodes of volcanism: The first is the base of the rise (circa 80 to >95 Ma) and the second is seamounts on the rise (0.5–16 Ma). It is proposed that interaction of the Canary hot spot with the Mid-Atlantic spreading center formed the deep basement of the Madeira-Tore Rise and the J-Anomaly Ridge west of the Atlantic spreading center in the Mid-Cretaceous. Age and geochemical data and plate tectonic reconstructions suggest, however, that the recovered Late Cretaceous volcanic rocks represent late stage volcanism from the time when the Madeira-Tore Rise was still close to the Canary hot spot. Long after moving away from the influence of the Canary hot spot, the Madeira-Tore Rise was overprinted by late Cenozoic volcanism. Miocene to Pleistocene volcanism at the northern end of the rise can be best explained by decompression mantle melting beneath extensional sectors of the Azores-Gibraltar Fracture Zone (African-Eurasian plate boundary). The geochemical compositions of these volcanic rocks suggest that the magmas were variably contaminated by enriched material within or derived by melting of enriched material underplated at the base of the lithosphere, possibly originating from the Cretaceous Canary plume. Alternatively, these late Cenozoic volcanic rocks may have derived from decompression melting of enriched pyroxenitic/eclogitic material in the upper mantle. Isotopically more depleted Pliocene to Pleistocene volcanism at the southern end of the Madeira-Tore Rise may be related to the nearby Madeira hot spot
Medical Malpractice : How Legal Liability Affects Medical Decisions
In health care, overuse and underuse of medical treatments represent equally dangerous deviations from an optimal use equilibrium and arouses concerns about possible implications for patients\u2019 health, and for the healthcare system in terms of both costs and access to medical care. Medical liability plays a dominant role among the elements that can affect these deviations. Therefore, a remarkable economic literature studies how medical decisions are influenced by different levels of liability. In particular, identifying the relation between liability and treatments selection, as well as disentangling the effect of liability from other incentives that might be in place, is a task for sound empirical research. Several studies have already tried to tackle this issue, but much more needs to be done. In the present chapter, we offer an overview of the state of the art in the study of the relation between liability and treatments selection. First, we reason on the theoretical mechanisms underpinning the relationship under investigation by presenting the main empirical predictions of the related literature. Second, we provide a comprehensive summary of the existing empirical evidence and its main weaknesses. Finally, we conclude by offering guidelines for further research
A new digestion and chemical separation technique for rapid and highly reproducible determination of Lu/Hf and Hf isotope ratios in geological materials by mc-ICP-MS
Change from thrusting to syn-orogenic extension at a mid-crustal level: an example from the Palaeoproterozoic Nagssugtoqidian Orogen (West Greenland).
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