Distribution of recycled crust within the upper mantle : insights from the oxygen isotope composition of MORB from the Australian-Antarctic Discordance

Author Posting. © American Geophysical Union, 2009. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 10 (2009): Q12004, doi:10.1029/2009GC002728Geochemical heterogeneity within the mantle has long been recognized through the diversity of trace element and radiogenic isotopic compositions of mantle-derived rocks, yet the specific origin, abundance, and distribution of enriched material within the mantle have been difficult to quantify. In particular, the origin of the distinctive geochemical characteristics of Indian mantle has been debated for decades. We present new laser fluorination oxygen isotope measurements of mid-ocean ridge basalt from the Australian-Antarctic Discordance (AAD), an area where a particularly abrupt transition occurs between Pacific-type mid-ocean ridge basalts (MORB) and Atlantic-type MORB. These data show no distinction in average δ18O between Pacific- and Atlantic-type MORB, indicating that the origin of Indian-type mantle cannot be attributed to the presence of pelagic sediment. The combined radiogenic isotope, δ18O, and trace element characteristics of Indian-type MORB at the AAD are consistent with contamination of the Indian upper mantle by lower crustal material. We also present a compilation of available laser fluorination δ18O data for MORB and use these data to evaluate the nature and percentage of enriched material within the upper mantle globally. Data for each ocean basin fit a normal distribution, with indistinguishable means and standard deviations, implying that the variation in δ18O of MORB reflects a stochastic process that operates similarly across all ocean basins. Monte Carlo simulations show that the mean and standard deviation of the MORB data are robust indicators of the mean and standard deviation of the parent distribution of data. Further, although some skewness in the data cannot be ruled out, Monte Carlo results are most consistent with a normal parent distribution. This similarity in characteristics of the δ18O data between ocean basins, together with correlations of δ18O with radiogenic isotope and trace element characteristics of subsets of the data, suggest that the upper mantle globally contains an average of ∼5–10% recycled crustal material and that the depleted mantle in the absence of this component would have δ18O of ∼5.25‰. The Monte Carlo simulations also suggest that additional oxygen isotope data may be used in the future to test the ability of geodynamical models to predict the physical distribution of enriched domains within the upper mantle

Pre-eruptive magmatic processes re-timed using a non-isothermal approach to magma chamber dynamics

Open Source PaperThis work is licensed under a Creative Commons Attribution 4.0 International License. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in the credit line; if the material is not included under the Creative Commons license, users will need to obtain permission from the license holder to reproduce the material. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/. The attached file is the published version of the article

An extraterrestrial trigger for the Early Cretaceous massive volcanism? Evidence from the paleo-Tethys Ocean

The Early Cretaceous Greater Ontong Java Event in the Pacific Ocean may have covered ca. 1% of the Earth's surface with volcanism. It has puzzled scientists trying to explain its origin by several mechanisms possible on Earth, leading others to propose an extraterrestrial trigger to explain this event. A large oceanic extraterrestrial impact causing such voluminous volcanism may have traces of its distal ejecta in sedimentary rocks around the basin, including the paleo-Tethys Ocean which was then contiguous with the Pacific Ocean. The contemporaneous marine sequence at central Italy, containing the sedimentary expression of a global oceanic anoxic event (OAE1a), may have recorded such ocurrence as indicated by two stratigraphic intervals with 187Os/188Os indicative of meteoritic influence. Here we show, for the first time, that platinum group element abundances and inter-element ratios in this paleo-Tethyan marine sequence provide no evidence for an extraterrestrial trigger for the Early Cretaceous massive volcanism

Personality factors in exercise addiction: a pilot study exploring the role of narcissism, extraversion, and agreeableness

Despite the increased evidence and acceptance of exercise being classed as a behavioral addiction, there is limited research examining personality characteristics within exercise addicts. The purpose of this study was to examine three personality traits (narcissism, extraversion, and agreeableness) and to examine their role in exercise addiction. The sample comprised 114 voluntary participants (74 females and 40 males) who completed the (i) Exercise Addiction Inventory, (ii) Narcissistic Personality Inventory, and (iii) Ten-Item Personality Inventory, as well as demographic questions and questions concerning their engagement and intensity levels of exercise. Results indicated a low incidence of individuals who were classed as at risk of exercise addiction (7%), but a high incidence of symptomatic individuals (75%). Results suggested that extraversion and narcissism may be underlying factors in exercise addiction with no effect for agreeableness. Exercise engagement and intensity were also related to exercise addiction. Further research examining the relationship between personality types and exercise addiction may be useful in identifying individuals at risk for developing exercise addiction

Antiretroviral-naive and -treated HIV-1 patients can harbour more resistant viruses in CSF than in plasma

Objectives The neurological disorders in HIV-1-infected patients remain prevalent. The HIV-1 resistance in plasma and CSF was compared in patients with neurological disorders in a multicentre study. Methods Blood and CSF samples were collected at time of neurological disorders for 244 patients. The viral loads were >50 copies/mL in both compartments and bulk genotypic tests were realized. Results On 244 patients, 89 and 155 were antiretroviral (ARV) naive and ARV treated, respectively. In ARV-naive patients, detection of mutations in CSF and not in plasma were reported for the reverse transcriptase (RT) gene in 2/89 patients (2.2%) and for the protease gene in 1/89 patients (1.1%). In ARV-treated patients, 19/152 (12.5%) patients had HIV-1 mutations only in the CSF for the RT gene and 30/151 (19.8%) for the protease gene. Two mutations appeared statistically more prevalent in the CSF than in plasma: M41L (P = 0.0455) and T215Y (P = 0.0455). Conclusions In most cases, resistance mutations were present and similar in both studied compartments. However, in 3.4% of ARV-naive and 8.8% of ARV-treated patients, the virus was more resistant in CSF than in plasma. These results support the need for genotypic resistance testing when lumbar puncture is performe

Examining the generalizability of research findings from archival data

This initiative examined systematically the extent to which a large set of archival research findings generalizes across contexts. We repeated the key analyses for 29 original strategic management effects in the same context (direct reproduction) as well as in 52 novel time periods and geographies; 45% of the reproductions returned results matching the original reports together with 55% of tests in different spans of years and 40% of tests in novel geographies. Some original findings were associated with multiple new tests. Reproducibility was the best predictor of generalizability—for the findings that proved directly reproducible, 84% emerged in other available time periods and 57% emerged in other geographies. Overall, only limited empirical evidence emerged for context sensitivity. In a forecasting survey, independent scientists were able to anticipate which effects would find support in tests in new samples