Petrography and petrology of the Hawaii Scientific Drilling Project lavas: Inferences from olivine phenocryst abundances and compositions

The Mauna Loa (ML) and Mauna Kea (MK) lavas recovered by the Hawaii Scientific Drilling Project (HSDP) include aphyric to highly olivine-phyric basalts. The average olivine phenocryst abundance in the reference suite of ML flows is 14.5 vol % (vesicle-free and weighted by the flow thickness), while the average abundances of olivine in the reference suites of the MK alkalic and tholeiitic basalts are 1.1 and 14.0 vol %, respectively. Plagioclase and augite phenocrysts are rare in the ML and MK tholeiites, but the MK alkalic basalts can have up to 4 vol % plagioclase phenocrysts. Strained olivine grains, thought to represent disaggregated dunite xenoliths from the cumulate pile within the magma chamber(s), are ubiquitous in the drill core lavas. These deformed grains can comprise up to 50 % of the modal olivine in a given rock. Olivine core compositions in the lavas span forsterite contents of 80.4–90.7 (median 88.8, ML tholeiites), 75.8–86.6 (median 85.8, MK alkalic basalts), and 76.3–90.5 (median 88.0 mol %, MK tholeiites). Olivines with core compositions in the range Fo_(89–90.5) are present in tholeiitic lavas with a wide range of whole-rock MgO contents (9–30 wt %). Strained and unstrained olivines completely overlap in composition as do the compositions of spinels (100*Cr/(Cr+Al) ∼59–72; Mg# = 100*Mg/(Mg+Fe^(2+)) ∼40–66) present as inclusions in the olivine phenocrysts. The presence of Fo_(90.5) olivine in the HSDP lavas requires magmas with ∼16 wt % MgO in the ML and MK plumbing systems. Rare dunite xenoliths are also present in the drill core lavas. While compositionally homogeneous within a given xenolith, the six xenoliths contain olivines that span a wide range of forsterite contents (78.3–89.2 mol %). Spinels in these xenoliths are chrome-rich, have Mg# between 31 and 66, and define two populations on the basis of TiO_2 contents. Whole-rock compositions for the ML and MK tholeiites define olivine control lines on MgO-oxide diagrams, and the relationship between whole-rock MgO and olivine phenocryst abundance in these lavas suggests that the lavas with >12 wt % MgO have accumulated olivine. Comparing the weighted bulk composition of all of the MK tholeiites in the drill core with a calculated parental magma suggests that, on average, the MK tholeiites entrained most of the olivine phenocrysts that crystallized from their parental liquids. Although deformed olivines in Hawaiian lavas are widely thought to represent disaggregated dunite xenoliths, none of the majoror minor-element data on the strained or unstrained olivine phenocrysts suggest that the strained olivines in the HSDP lavas are exotic. We suggest that most of the olivine phenocrysts in a given flow, whether strained or unstrained, are closely related to the evolved liquid that now forms the groundmass. This is consistent with observed correlations between isotopic systems measured on olivine separates (e.g., O, He) and isotopic systems dominated by groundmass (e.g., Nd, Pb)

Antecedents of the Sharing Economy in a Pandemic Scenario: Prosocial Attitudes, Past Behaviour and Transformation Expectations

The COVID-19 pandemic is expected to have a significant impact on most sharing economy activities, and at present, it is particularly challenging to achieve a consensual model to predict sharing economy behaviour. Based on empirical and theoretical premises established before the pandemic, we intend to explore the association between a set of psychosocial variables (i.e., cooperation, environmental awareness, past behaviour) and sharing economy behaviour, particularly the use of shared assets (i.e., cars and accommodation) during the COVID-19 pandemic. Furthermore, the present study analyses the mediating role of transformation expectations, as the decision to engage or not in sharing behaviour may be influenced by beliefs about the consequences of those actions from the user’s perspective. This study comprised a total of 596 participants. Data was collected through a self-administered questionnaire and was statistically analysed and interpreted using PLS 3.0. Structural Equation Modelling statistical software. Contrary to our predictions, the results show that cooperation negatively influenced the willingness to participate in sharing activities during the COVID-19 pandemic, that environmental awareness was not a significant predictor, and that past sharing behaviour has the strongest influence on the willingness to share during pandemic times. Finally, the mediating effect of transformation expectations was significant in both associations, i.e., pro-environmental consciousness and past sharing experiences, and the willingness to adopt sharing behaviour during COVID-19.Se espera que la pandemia de COVID-19 tenga un impacto importante en la mayoría de las actividades de la economía colaborativa, y en la actualidad, es particularmente difícil lograr un modelo consensual para predecir el comportamiento de la economía colaborativa. Sobre la base de premisas empíricas y teóricas establecidas antes de la pandemia, pretendemos explorar la asociación entre un conjunto de variables psicosociales (es decir, cooperación, consciencia ambiental, comportamiento pasado) y el comportamiento de la economía colaborativa, en particular el uso de activos compartidos (automóviles y alojamiento), durante la pandemia de COVID-19. Además, el presente estudio analiza el papel mediador de las expectativas de transformación, ya que la decisión de participar o no en el comportamiento de compartir puede estar influenciada por creencias sobre las consecuencias de esas acciones desde la perspectiva del usuario. Este estudio comprendió un total de 596 participantes. Los datos se recopilaron a través de un cuestionario autoadministrado y se analizaron e interpretaron estadísticamente utilizando el PLS 3.0., un software estadístico de modelación de ecuaciones estructurales. Contrariamente a nuestras predicciones, los resultados muestran que la cooperación influyó negativamente en la voluntad de participar en actividades compartidas durante la pandemia de COVID-19, que la conciencia ambiental no fue un predictor significativo y que el comportamiento de compartir en el pasado tiene la influencia más fuerte en la voluntad de compartir durante tiempos de pandemia. Finalmente, el efecto mediador de las expectativas de transformación fue significativo en ambas asociaciones, es decir, la conciencia proambiental y las experiencias pasadas de intercambio, y la disposición a adoptar un comportamiento de intercambio durante COVID-19.info:eu-repo/semantics/publishedVersio

Simulated Tempering: A New Monte Carlo Scheme

We propose a new global optimization method ({\em Simulated Tempering}) for simulating effectively a system with a rough free energy landscape (i.e. many coexisting states) at finite non-zero temperature. This method is related to simulated annealing, but here the temperature becomes a dynamic variable, and the system is always kept at equilibrium. We analyze the method on the Random Field Ising Model, and we find a dramatic improvement over conventional Metropolis and cluster methods. We analyze and discuss the conditions under which the method has optimal performances.Comment: 12 pages, very simple LaTeX file, figures are not included, sorr