Search

El Norte de Chile es conocido por la importante explotación cuprífera contemporánea. Las evidencias arqueológicas indican que tal explotación no es un fenómeno moderno, sino que ha existido en el Norte Grande desde al menos el Período Arcaico Tardío. Para identificar las materias primas minerales usadas en los procesos minero-metalúrgicos prehispánicos, hemos desarrollado un nuevo protocolo analítico basado en la mineralogía automatizada (QEMSCAN). Las muestras provienen del distrito minero-metalúrgico prehispánico de Collahuasi, ubicado en la actual región de Tarapacá. A partir de este estudio, se determinó que la mineralogía de las menas utilizadas en las fundiciones metalúrgicas de los sitios del Distrito Collahuasi corresponde a brocantita, malaquita y crisocola; a su vez, se ha podido poner en evidencia cuál fue el “metal Collahuasi” que circuló en tiempos prehispánicos tardíos.

Paniri volcano, in northern Chile, belongs to a volcanic chain trending across the main orientation of the Central Andean volcanic province. Field work mapping, stratigraphic sequences, and one new 40Ar/39Ar and eleven previous published 40Ar/39Ar, and K/Ar ages, indicate that the evolution of Paniri involved eruption of seven volcanic units (Malku, Los Gordos, Las Lenguas, Las Negras, Viscacha, Laguna, and Llareta) during four main stages occurring over more than 1 Myr: Plateau Shield (>800 ka); Main Edifice (800–400 ka); Old Cone (400–250 ka); and New Cone (250–100 ka). Considering glacial and fluvial action, an estimated 85.3 km3 of volcanic material were erupted during the eruptive history of Paniri volcano, giving a bulk eruption rate of 0.061 km3/ka, with major activity in the last 150 kyr (eruption rate of 0.101 km3/ka). Lava flows from Paniri show abundant plagioclase together with subordinate ortho-, and clino-pyroxene, and amphibole as main phenocrysts. Moreover, although true basalts are scarce in the Central Andes, olivine-bearing lavas were erupted at Paniri at ∼400 ka. Also, scarce phenocrysts of biotite, quartz, rutile, and opaque minerals (Fe-Ti oxides) were identified. The groundmass of these flows is composed mainly of glass along with pyroxene and plagioclase microlites. Consolidated and unconsolidated pyroclastic deposits of dacitic composition are also present. The consolidated deposits correspond to vitreous tuffs, whilst unconsolidated deposits are composed of pumice clasts up to 5 cm in diameter. Both pyroclastic deposits are composed of glassy groundmass (up to 80% vol.), and subordinated plagioclase, hornblende, and biotite phenocrysts up to 1 cm in length. Results of twenty-four new, coupled with previous published compositional analyses show that volcanic products of Paniri vary from 57% (basaltic-andesite) to 71% (rhyolite) vol. SiO2, with significant linear correlations between major element-oxide and trace-element concentrations. 87Sr/86Sr isotope ratios range from 0.7070 to 0.7075, indicating that Paniri, similar to other volcanoes of the San Pedro – Linzor volcanic chain, have undergone significant crustal contamination of its parental magmas. However, the almost constant Sr-isotope compositions of the different volcanic units defined for Paniri volcano, suggested later fractional crystallization of magmas at upper crustal levels.

Because of its flexibility and ability to respond to nuance, group analytic praxis is valuable for ‘tweaking’ culture in larger organizations, and for assisting leaders in resolving conflict and harnessing resistance to change to achieve better outcomes. Are these systems ‘closed’ or ‘open’? This first of a pair of chapters on working with whole organizations explains how the group analytic concept ‘matrix’ relates to autopoiesis, a concept from systems theory, to offer a coherent framework for understanding whole organizations as social systems with sub-groupings and a distinct identity. Concepts of identity as patterns of relating link group analytic theory and autopoiesis. There are examples of how group analytic thinking is applied practically in consultation, including two vignettes about mergers. We discuss the need for translucent, non-rigid boundaries and the anthropological lens of tribalism (‘us and them’ thinking) which opens the next chapter.

Das Ehepaar Balint revolutionierte die Medizin mit ihren Selbsterfahrungsgruppen fur Arzte. Sie legten den Mitgliedern ihrer Gruppen nahe, nicht mehr sich selbst als das handelnde Subjekt bzw. den Patienten als das zu behandelnde Objekt zu betrachten. Ihr Ideal war eine Beziehung zwischen zwei verantwortlichen und erwachsenen Menschen. Solange der Arzt eine wirkliche Beziehung mit dem Patienten und dessen Familie herstellte, machte es Sinn, die Supervision auf Fallprobleme und die Ubertragungsbeziehung zwischen Arzt und Patient zu fokussieren.

The UK Primary Health Care Reforms dating from 1990 have resulted in traumatic stress for General Practitioners (GPs) within the UK National Health Service (NHS). Previously, their first task had always been to provide care. Now the objectives are purely economic, focusing on cost-effectiveness and meeting Government targets. This article compares the Balint Model, set out by Michael and Edna Balint in the 1950s, to what is required in the current situation, and shows how group analysis can help GPs come to terms with their new professional identity and how they see their future.

Exposures of metamorphic basement in the Central Andes are scarce and reconstructions of the history of the Pacific margin of Gondwanaland must rely on a few isolated outcrops. We studied two areas of exposed basement in northernmost Chile (Belen) and westernmost Bolivia (Cerro Uyarani). The Belen metamorphic complex has been known for some time and consists of fault-bounded amphibolites, gneisses, schists, and minor quartzites overlain by folded Mesozoic to Cenozoic strata. The Cerro Uyarani is the only basement outcrop on the Bolivian Altiplano and has only recently been found and studied by geological reconnaissance. It consists of foliated mafic and felsic granulites, charnockites, and amphibolites. How do these basement occurrences compare and how do they relate to the other Precambrian crustal domains in the Central Andes? To answer these questions, we used geothermobarometers to reconstruct the P–T conditions of metamorphism, as well as geochemical analyses and petrological methods to study these rocks. The two basement blocks were found to have distinct geological histories and are probably separated by a major crustal domain boundary. Isotopic fingerprinting by Pb-isotopes clearly exclude Laurentian crustal components either in the protoliths or as reworked material. This signature is quite distinct from basement rocks farther south in Chile and northwestern Argentina.

In a context of rapid change, outbreaks of sibling rivalry in organizations act as a defence against the inability to mourn and feel remorse. When changes are imposed on work-teams, sibling preoccupations surface to prevent the working through of the breakdown of relations between the institutional parents and their dependants. Siblings also adopt envy-preventing strategies, engaging in collective self-idealization by forming sisterhoods or brotherhoods to protect themselves from disillusionment and individuation. Each succeeding generation has to face the fact that a primus inter pares will have to be chosen to inherit the mantle of power from the parental generation and restore the world to its `normal' state of inequality. In the context of recent structural changes in organizations the new managers have acted like borderline parents and fostered sibling rivalry. This dynamic has functioned to deny the guilt and the fear of retaliation associated with fratricide and matricide committed during the `re-engineering' process, when the youngsters sent their parents into early retirement. I want to explore the central importance of authority, disillusionment and mourning and show that the outbreak and suppression of sibling rivalry is connected with the problem of transition and succession in organizations.

SUMMARY Teleseismic data recorded during one and a half years are investigated with the receiver function technique to determine the crustal and upper-mantle structures underneath the highly elevated Altiplano and Puna plateaus in the central Andes. A series of converting interfaces are determined along two profiles at 21 ◦ S and 25.5 ◦ S, respectively, with a station spacing of approximately 10 km. The data provide the highest resolution gained from a passive project in this area, so far. The oceanic Nazca plate is detected down to 120 km beneath the Altiplano whereas beneath the Puna, the slab can unexpectedly be traced down to 200 km depth at longer periods. A shallow crustal low-velocity zone is determined beneath both plateaus exhibiting segmentation. In the case of the Altiplano, the segments present vertical offsets and are separated by inclined interfaces, which coincide with major fault systems at the surface. An average depth to Moho of about 70 km is determined for the Altiplano plateau. A strong negative velocity anomaly located directly below the Moho along with local crustal thinning is interpreted beneath the volcanic arc of the Altiplano plateau between 67 ◦ W and 68.5 ◦ W. A deep section of the Puna profile reveals thinning of the mantle transition zone. Although poorly resolved, the detected anomaly may suggest the presence of a mantle plume, which may constitute the origin of the anomalous temperatures at the depth of the upper-mantle discontinuities.

A set of seismological stations was deployed in the Central Andes region along a ∼600 km long profile at 21°S between Chile and Bolivia and operated for a period of almost two years, from March 2002 to January 2004. Here we present the results of the tomographic inversion for P -wave velocity anomalies, based on teleseismic data recorded at the stations. The reliability of the results has been checked by a series of synthetic tests. The tomographic images show high-velocities on the west of the profile that are indicative of cold material from the fore-arc. A low-velocity anomaly is detected at the border between the fore- and the volcanic arc where the Quebrada Blanca seismic anomaly was previously described. This anomaly might be related to the presence of fluids that originate at the cluster of earthquakes at a depth of ∼100 km in the subducted plate. A strong low-velocity anomaly is detected beneath the entire Altiplano plateau and part of the Eastern Cordillera, in agreement with previous receiver function results. The Brazilian Shield is thought to be responsible for the strong high-velocity anomaly underneath the Interandean and Subandean regions.

The Jurassic to Early Cretaceous magmatic arc of the Andes in northern Chile was a site of major additions of juvenile magmas from the subarc mantle to the continental crust. The combined effect of extension and a near stationary position of the Jurassic to lower Cretaceous arc favoured the emplacement and preservation of juvenile magmatic rocks on a large vertical and horizontal scale. Chemical and Sr, Nd, and Pb isotopic compositions of mainly mafic to intermediate volcanic and intrusive rock units coherently indicate the generation of the magmas in a subduction regime and the dominance of a depleted subarc mantle source over contributions of the ambient Palaeozoic crust. The isotopic composition of the Jurassic (206Pb/204Pb: ∼ 18.2; 207Pb/204Pb: ∼ 15.55; 143Nd/144Nd: ∼ 0.51277; 87Sr/86Sr: ∼ 0.703–0.704) and Present (206Pb/204Pb: ∼ 18.5; 207Pb/204Pb: ∼ 15.57; 143Nd/144Nd: ∼ 0.51288; 87Sr/86Sr: ∼ 0.703–0.704) depleted subarc mantle beneath the Central and Southern Andes (18°–40°S) was likely uniform over the entire region. Small differences of isotope ratios between Jurassic and Cenozoic to Recent of subarc mantle-derived could be explained by radiogenic growth in a still uniform mantle source.

Active continental margins are considered as the principal site for growth of the continental crust. However, they are also sites of recycling and destruction of continental crust. The Andean continental margin has been periodically active at least since the early Paleozoic and allows the evaluation of the long-term relevance of these processes. The early Paleozoic orogeny at ca. 0.5 Ga recycled and homogenized the ∼2 Ga old early Proterozoic crust of the Brazilian Shield, which was previously orogenized at ca. 1 Ga, consistent with global models of prominent crustal growth at 2 Ga and a near constant mass of continental crust in the Phanerozoic. The metamorphic and magmatic evolution and the isotopic signatures of the early Paleozoic rocks do not indicate significant crustal growth, either by accretion of exotic terranes and island arcs or by juvenile additions from a mantle source. The dominant inferred mode of crustal evolution in the Paleozoic was recycling of older crust. Destruction of continental crust by subduction erosion is prominent in sections of the present active margin and is also likely to have occurred in the past orogens. Voluminous juvenile magmatism is only observed in the Jurassic — lower Cretaceous extensional magmatic arc. Compositions of mantle-derived magmas from the early Paleozoic to the Cainozoic, as well as late Cretaceous mantle xenoliths, indicate that depleted mantle was already present beneath the early Paleozoic orogen. The old subcontinental, enriched mantle related to the Brazilian shield and bordering Proterozoic mobile belts was modified by asthenospheric mantle in the younger subduction systems. In summary, this transect of the Andes is not a site of major continental growth, but a site where long-term processes of growth, recycling and destruction balance out.