Dynamical effects of subducting ridges: Insights from 3-D laboratory models

We model the subduction of buoyant ridges and plateaus to study their effect on slab dynamics. Oceanic ridges parallel to the trench have a stronger effect on the process of subduction because they simultaneously affect a longer trench segment. Large buoyant slab segments sink more slowly into the asthenosphere, and their subduction result in a diminution of the velocity of subduction of the plate. We observe a steeping of the slab below those buoyant anomalies, resulting in smaller radius of curvature of the slab, that augments the energy dissipated in folding the plate and further diminishes the velocity of subduction. When the 3D geometry of a buoyant plateau is modelled, the dip of the slab above the plateau decreases, as a result of the larger velocity of subduction of the dense "normal" oceanic plate on both sides of the plateau. Such a perturbation of the dip of the slab maintains long time after the plateau has been entirely incorporated into the subduction zone. We compare experiments with the present-day subduction zone below South America. Experiments suggest that a modest ridge perpendicular to the trench such as the present-day Juan Fernandez ridge is not buoyant enough to modify the slab geometry. Already subducted buoyant anomalies within the oceanic plate, in contrast, may be responsible for some aspects of the present-day geometry of the Nazca slab at depth

Submarine record of volcanic island construction and collapse in the Lesser Antilles arc: First scientific drilling of submarine volcanic island landslides by IODP Expedition 340

IODP Expedition 340 successfully drilled a series of sites offshore Montserrat, Martinique and Dominica in the Lesser Antilles from March to April 2012. These are among the few drill sites gathered around volcanic islands, and the first scientific drilling of large and likely tsunamigenic volcanic island-arc landslide deposits. These cores provide evidence and tests of previous hypotheses for the composition and origin of those deposits. Sites U1394, U1399, and U1400 that penetrated landslide deposits recovered exclusively seafloor-sediment, comprising mainly turbidites and hemipelagic deposits, and lacked debris avalanche deposits. This supports the concepts that i/ volcanic debris avalanches tend to stop at the slope break, and ii/ widespread and voluminous failures of pre-existing low-gradient seafloor sediment can be triggered by initial emplacement of material from the volcano. Offshore Martinique (U1399 and 1400), the landslide deposits comprised blocks of parallel strata that were tilted or micro-faulted, sometimes separated by intervals of homogenized sediment (intense shearing), while Site U1394 offshore Montserrat penetrated a flat-lying block of intact strata. The most likely mechanism for generating these large-scale seafloor-sediment failures appears to be propagation of a decollement from proximal areas loaded and incised by a volcanic debris avalanche. These results have implications for the magnitude of tsunami generation. Under some conditions, volcanic island landslide deposits comprised of mainly seafloor sediment will tend to form smaller magnitude tsunamis than equivalent volumes of subaerial block-rich mass flows rapidly entering water. Expedition 340 also successfully drilled sites to access the undisturbed record of eruption fallout layers intercalated with marine sediment which provide an outstanding high-resolution dataset to analyze eruption and landslides cycles, improve understanding of magmatic evolution as well as offshore sedimentation processes. This article is protected by copyright. All rights reserved

A importância de ser Uros: movimentos indígenas, políticas de identidade e pesquisa genética nos Andes Peruanos

O objetivo deste artigo é explorar as inter-relações entre a pesquisa genética, as lutas políticas de movimentos indígenas e os processos de formação de identidade étnica. Em particular, visa analisar as condições sociais que levaram à colaboração entre os uros, um grupo indígena que habita as ilhas flutuantes do lago Titicaca (Peru), e pesquisadores do projeto Genográfico. Os uros, cujas reivindicações de uma identidade étnica diferenciada eram altamente contestadas no âmbito local, se associaram aos geneticistas com o objetivo de obter um apoio científico para a afirmação dessa identidade e como parte das suas estratégias políticas e demandas territoriais. Assim, esse caso contribui ao maior entendimento da incorporação da pesquisa genética dentro de políticas conceituais travadas em torno das identidades étnicas, bem como da articulação do conhecimento genético com registros preexistentes para definir tais identidadesThe objective of this paper is to explore the interrelations between genetic research with human populations, the political strategies of indigenous movements and processes of identity formation. In particular, it will analyse the social conditions that have resulted in the collaboration between the Uros, an indigenous group living on the floating islands of Lake Titicaca (Peru), and researchers of the Genographic project. The Uros, whose claims to a differentiated ethnic identity were highly contested within the local context, engaged with geneticists with the aim to obtain scientific support for this identity. This was part of their political strategies for their territorial rights. As such, this case offers new insights into the incorporation of genetic research within the conceptual politics waged around ethnic identities, as well as the articulation of genetic knowledge with pre-existing registers to define such identitie

A educação infantil e a questão da escola: o caso da França

Nos últimos trinta anos, a prioridade dada a uma lógica escolar para justificar a pré-escola coincide com uma dupla mudança na instituição. A primeira diz respeito às relações que a escola maternal mantém com a escolarização obrigatória e com as estruturas de cuidados para as crianças pequenas. A outra refere-se às reformas do currículo escolar e ao desenvolvimento dos processos de avaliação. A escola maternal, local de acolhimento, de cuidados e de preparação para a escola, tornou-se institucionalmente uma verdadeira escola. A difusão das comparações internacionais contribuiu para essas mudanças

Heat flow in the Lesser Antilles island arc and adjacent back arc Grenada basin

Using temperature gradients measured in 10 holes at 6 sites, we generate the first high fidelity heat flow measurements from Integrated Ocean Drilling Program drill holes across the northern and central Lesser Antilles arc and back arc Grenada basin. The implied heat flow, after correcting for bathymetry and sedimentation effects, ranges from about 0.1 W/m2 on the crest of the arc, midway between the volcanic islands of Montserrat and Guadeloupe, to 15 km from the crest in the back arc direction. Combined with previous measurements, we find that the magnitude and spatial pattern of heat flow are similar to those at continental arcs. The heat flow in the Grenada basin to the west of the active arc is 0.06 W/m2, a factor of 2 lower than that found in the previous and most recent study. There is no thermal evidence for significant shallow fluid advection at any of these sites. Present-day volcanism is confined to the region with the highest heat flow

Chacras of the pukara: the late occupation (tenth-sixteenth centuries) of Mesada de Andalhuala Banda, Yocavil (Catamarca, Argentina)

This chapter presents the results of archaeological survey undertaken in the Mesada de Andalhuala Banda, Southeast Yocavil Valley, Catamarca, Northwest Argentina (NWA). Three hundred and eighty-two architectural units (AU) were registered, which suggests a prolonged occupation during the first and second millennia AD. In this opportunity, I will focus on the Late Period occupation tenth?sixteenth centuries) and the evidence reflecting activities of the agricultural production cycle, including structures for cultivation, mounds, and longitudinal accumulation of stones that were the product of land clearing, irrigation systems, milling tools, and circular storage structures. Spatially associated with these features are simple and compound residential units with double-faced walls filled with rubble and sediment, morphology assignable to the Santa María culture, which could be the dwelling sector of the population tasked with food production. This information allowed us to hypothesize that the Mesada, as a main productive area, was occupied during the entire Late Period, a time that included climate change and interethnic conflict, and played an important role in relation to the nearby pukara settlement.Fil: Alvarez Larrain, Alina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Saavedra 15. Instituto de las Culturas. Universidad de Buenos Aires. Instituto de las Culturas; Argentina. Universidad Nacional Autónoma de México; Méxic