Active submarine volcanism on the Society hotspot swell (west pacific): A geochemical study

The present work deals with the petrography and geochemistry of lavas dredged from five active submarine volcanoes (named Mehetia, Moua Pihaa, Rocard, Teahitia, and Cyana) from the southeast end of the Society Islands hotspot trace. Most samples are basic and alkaline, ranging from 16 to 5 wt % MgO, with about 5% normative nepheline. Fractionation modelling based on major and minor compatible element variations suggests that olivine and minor clinopyroxene were the major fractionating phases and implies a maximum range of fractionation of 30–35%. Rocard and Cyana have yielded more evolved, trachy-phonolitic, glassy samples. These evolved samples are thought to be derived by removal of 70% cumulate from the basalts. Both basaltic and phonolitic samples are incompatible-element enriched, with La/YbN ≈ 15 in most of the basalts. The trachy-phonolite patterns show middle rare earth element (REE) depletion and negative Eu anomalies. The Moua Pihaa basalts have flatter patterns than the other basalts (La/YbN = 7.5–12.4). All samples, with the exception of a sample from Moua Pihaa which has elevated 206Pb/204Pb, fall on linear Sr-Nd-Pb isotopic arrays, suggesting two end-member mixing. The most depleted end-member is shown to be a pristine ocean island basalt magma with no detectable contribution from a depleted, mid-ocean ridge basalt (MORB) upper mantle. The flatter REE patterns and higher 206Pb/204Pb of the Moua Pihaa sample are taken to indicate a more depleted, U-enriched (high μ) component in its source. This component may be altered oceanic crust. The Sr isotopic variations in the samples excluding Moua Pihaa correlate positively with Rb/Nb, Pb/Ce, and SiO2 variations, indicating a component of mantle enriched by injection of material from a subducted oceanic slab. Correlation of 207Pb/204Pb with 87Sr/86Sr suggests that the subducted material is geochemically old. Mapping the geochemical variations shows that the contribution to the lavas from the subduction component is greater over the north of the hotspot than in the south. The absence of a MORB component in the Society magmatism, the small volumes of the Polynesian hotspot volcanoes, and the lack of more intense volcanic activity near the center of the Pacific Supers well, all lead us to conclude that the latter is unlikely to be caused by a large convective plume. The Superswell is more probably located above a region in the asthenospheric mantle which, due to its higher content of recycled continental debris, is anomalously hot

Does habitat complexity inluence ish recruitment?

Human activities facilitate coastal habitat transformation and homogenization. The spread of marine invasive species is one example. This in turn may inluence ish recruitment and the subsequent replenishment of adult assemblages. We tested habitat complexity effect on ish (Teleostei) recruitment by experimentally manipulating meadows of the habitat-forming invasive macroalga Caulerpa taxifolia (Chlorophyta). Among the fourteen ish species recorded during the experiment, only two labrids (Coris julis and Symphodus ocellatus) settled in abundance among these meadows. Patterns in the abundance of these juveniles suggested that reduced tri-dimensional meadow complexity may reduce habitat quality and result in altered habitat choices and / or differential mortality of juveniles, therefore reducing ish recruitment and likely the abundance of adults

Campagne Mesopac: Leve de sites de forages ODP en sismique multitraces dans le bassin de Nauru

The Mesopac Cruise was the first multichannel seismic study of the western basins of the Pacific Plate. It was concentrated in the Nauru Basin and in the western area of the Central Pacific Basin. Profiles were calibrated with drilling results from DSDP Sites 462 and 169. For the first time one could observe reflectors within the Cretaceous volcanic complex down to approximately equals 8.5 seconds. Profiles did not allow direct observation of the top of the oceanic crust. After correcting for the load on top of the oceanic crust, results suggest that it cannot lie much deeper than those reflectors. If the oceanic crust lies only a few hundred meters beneath the 2.4 km thick complex, it would be right on the normal thermal subsidence curve corresponding to a Jurassic age

The role of institutional quality in the international trade of a Latin American country: evidence from Colombian export performance

Abstract This paper analyses the relevance of Colombian institutional quality in recent years in terms of the performance of its exports within a framework of trade openness. Based on the trade gravity model, we examine the effect of governance on the evolution of Colombian exports through an econometric approach that identifies, on the one hand, the influence of institutional quality, and on the other hand, the influence of the institutional distance between Colombia and its trading partners. We use a panel data set for 2005–2018, through which the export flows from Colombia to 136 of its trading partners are considered. The findings indicate that Colombian institutional quality and the institutional distance between the country and its partners are statistically significant and affect its foreign sales. Similarly, there is a prominent influence of regulatory quality and the rule of law variables in the performance of Colombian exports in relation to other variables included in the model. We conclude that the Colombian government must improve its institutional quality considerably as a fundamental step towards boosting its overseas sales, not least because the country’s institutional distance from the world average is notable, which also affects its exports