Structural and strain analysis in the Late Paleozoic coastal accretionary wedge of central Chile

Abstract In this study structural and finite strain data are used to explore the tectonic evolution and the exhumation history of the Chilean accretionary wedge. The Chilean accretionary wedge is part of a Late Paleozoic subduction complex that developed during subduction of the Pacific plate underneath South America. The wedge is commonly subdivided into a structurally lower Western Series and an upper Eastern Series. This study shows the progressive development of structures and finite strain from the least deformed rocks in the eastern part of the Eastern Series of the accretionary wedge to higher grade schist of the Western Series at the Pacific coast. Furthermore, this study reports finite-strain data to quantify the contribution of vertical ductile shortening to exhumation. Vertical ductile shortening is, together with erosion and normal faulting, a process that can aid the exhumation of high-pressure rocks. In the east, structures are characterized by upright chevron folds of sedimentary layering which are associated with a penetrative axial-plane foliation, S1. As the F1 folds became slightly overturned to the west, S1 was folded about recumbent open F2 folds and an S2 axial-plane foliation developed. Near the contact between the Western and Eastern Series S2 represents a prominent subhorizontal transposition foliation. Towards the structural deepest units in the west the transposition foliation became progressively flat lying. Finite-strain data as obtained by Rf/Phi and PDS analysis in metagreywacke and X-ray texture goniometry in phyllosilicate-rich rocks show a smooth and gradual increase in strain magnitude from east to west. There are no evidences for normal faulting or significant structural breaks across the contact of Eastern and Western Series. The progressive structural and strain evolution between both series can be interpreted to reflect a continuous change in the mode of accretion in the subduction wedge. Before ~320-290 Ma the rocks of the Eastern Series were frontally accreted to the Andean margin. Frontal accretion caused horizontal shortening and upright folds and axial-plane foliations developed. At ~320-290 Ma the mode of accretion changed and the rocks of the Western Series were underplated below the Andean margin. This basal accretion caused a major change in the flow field within the wedge and gave rise to vertical shortening and the development of the penetrative subhorizontal transposition foliation. To estimate the amount that vertical ductile shortening contributed to the exhumation of both units finite strain is measured. The tensor average of absolute finite strain yield Sx=1.24, Sy=0.82 and Sz=0.57 implying an average vertical shortening of ca. 43%, which was compensated by volume loss. The finite strain data of the PDS measurements allow to calculate an average volume loss of 41%. A mass balance approximates that most of the solved material stays in the wedge and is precipitated in quartz veins. The average of relative finite strain is Sx=1.65, Sy=0.89 and Sz=0.59 indicating greater vertical shortening in the structurally deeper units. A simple model which integrates velocity gradients along a vertical flow path with a steady-state wedge is used to estimate the contribution of deformation to ductile thinning of the overburden during exhumation. The results show that vertical ductile shortening contributed 15-20% to exhumation. As no large-scale normal faults have been mapped the remaining 80-85% of exhumation must be due to erosion.

A structural and metamorphic study of the southern Menderes Massif (Western Turkey)

P-T conditions, paragenetic studies and the relation between mineral growth, deformation and - when possible- isograd minerals have been used to describe the type of metamorphism involved within lower units of the southern Menderes Massif of the Anatolide Belt in western Turkey. The study areas mainly consist of Proterozoic orthogneiss and surrounding schists of presumed Paleozoic age. Both units are seen as nappes in the southern study area, the Çine and the Selimiye nappe, on the whole corresponding to Proterozoic orthogneiss and surrounding schists, respectively. The Çine and Selimiye nappes are part of a complex geological structure within the core series of the Menderes Massif. Their emplacement under lower greenschist facies conditions, would result from closure of the northern Neo-Thethys branch during the Eocene. These two nappes are separated by a major tectonic structure, the Selimiye shear zone, which records top-to-the-S shearing under greenschist facies conditions. Amphibolite to upper amphibolite facies metamorphism is widely developed within the metasedimentary rocks of the Çine nappe whereas no metamorphism exceeding lower amphibolite facies has been observed in the Selimiye nappe. In the southern margin of the Çine Massif, around Selimiye and Millas villages, detailed sampling has been undertaken in order to map mineral isograds within the Selimiye nappe and to specify P-T conditions in this area. The data collected in this area reveals a global prograde normal erosion field gradient from south to north and toward the orthogneiss. The mineralogical parageneses and P-T estimates are correlated with Barrovian-type metamorphism. A jump of P-T conditions across the Selimiye shear zone has been identified and estimated c. 2 kbar and 100 °C which evidences the presence of amphibolite facies metasedimentary rocks near the orthogneiss. Metasedimentary rocks from the overlying Selimiye nappe have maximum P-T conditions of c. 4-5 kbar and c. 525 °C near the base of the nappe. Metasedimentary rocks from the Çine nappe underneath the Selimiye shear zone record maximum P-T conditions of about 7 kbar and >550 °C. Kinematic indicators in both nappes consistently show a top-S shear sense. Metamorphic grade in the Selimiye nappe decreases structurally upwards as indicated by mineral isograds defining the garnet-chlorite zone at the base, the chloritoid-biotite zone and the biotite-chlorite zone at the top of the nappe. The mineral isograds in the Selimiye nappe run parallel to the regional SR foliation. 40Ar/39Ar mica ages indicate an Eocene age of metamorphism in the Selimiye nappe and underneath the Çine nappe in this area. Metasedimentary rocks of the Çine nappe 20-30 km north of the Selimiye shear zone record maximum P-T conditions of 8-11 kbar and 600-650 °C. Kinematic indicators show mainly top-N shear sense associated with prograde amphibolite facies metamorphism. An age of about 550 Ma could be indicated for amphibolite facies metamorphism and associated top-N shear in the orthogneiss and metasedimentary rocks of the Çine nappe. However, there is no evidence for polymetamorphism in the 6 metasedimentary rocks of the Çine nappe, making tectonic interpretations about late Neoproterozoic to Cambrian and Tertiary metamorphic events speculative. In the western margin of the Çine Massif metamorphic mineral parageneses and pressure– temperature conditions lead to similar conclusion regarding the erosion field gradient, prograde normal toward the orthogneiss. The contact between orthogneiss and surrounding metasedimentary rocks is mylonitic and syn-metamorphism. P-T estimates are those already observed within the Selimiye nappe and correlated with lower amphibolite facies parageneses. Finally additional data in the eastern part and a general paragenetic study within the Menderes Massif lower units, the Çine and the Selimiye nappes, strongly suggest a single Barrovian-type metamorphism predating Eocene emplacement of the high pressure–low temperature Lycean and Cycladic blueschist nappes. Metamorphic mineral parageneses and pressure–temperature conditions do not support the recently proposed model of high pressure–low temperature metamorphic overprinting, which implies burial of the lower units of the Menderes Massif up to depth of 30 km, as a result of closure of the Neo-Tethys. According to the geochronological problem outlined during this thesis, there are two possible schemes: either Barrovian-type metamorphism is Proterozoic in age and part of the sediments from Selimiye nappe (lower amphibolite facies) has to be proterozoic of age too, or Barrovian-type metamorphism in Eocene of age. In the first case the structure observed now in the core series would correspond to simple exhumation of Proterozoic basement. In the latter case a possible correlation with closure of Neo-Tethys (sensu stricto, southern branch) is envisaged.

Friend of the police: Polizei in Nord-Ghana (Upper West Region) /// Arbeitspapiere / Institut für Ethnologie und Afrikastudien ; 93

Korruption, Gewalt, Machtmissbrauch – im medialen, aber auch im wissenschaftlichen Diskurs wird die afrikanische Polizei oft als dysfunktionale staatliche Institution dargestellt. Dabei erscheinen Polizisten und zivile Akteure als klar voneinander abgegrenzte Akteursgruppen, wobei die Polizisten einseitig das staatliche Gewaltmonopol durchsetzen. Ein Blick auf den Alltag polizeilichen Handelns in Nordghana eröffnet jedoch eine andere Perspektive: Wegen der niedrigen Legitimität, konkurrierenden alternativen Rechtsinstanzen und den Widersprüchen innerhalb ihrer Institution sind Polizisten mit massiven Unsicherheiten konfrontiert. Ihre Praktiken können als situative Anpassungen der Polizeiarbeit an dieses Umfeld verstanden werden. Dabei übertragen Polizisten oft Kernaufgaben ihrer Institution an zivile Akteure, die sogenannten „friends of the police“. Auch zivile Akteure verfügen jedoch durch physischen Widerstand, Beziehungen, Status und Geld über beträchtliche Beeinflussungsmöglichkeiten. Die öffentliche Ordnung ergibt sich erst aus den Verhandlungen zwischen den Polizisten und unterschiedlichen zivilen Akteuren unter Einbeziehung ihrer sozialen Ressourcen und moralischer Vorstellungen.

"Talking about Marriage ..." : Polizeiarbeit in Upper West, Ghana /// Arbeitspapiere / Institut für Ethnologie und Afrikastudien ; 102

Polizei in Afrika ist korrupt und schlecht ausgebildet und eine „Marionette“ der Regierungen − so das nicht nur im populären, sondern auch sozialwissenschaftlichen Diskurs vermittelte Bild. Eine ethnographische Perspektive, die Polizeiarbeit im Alltag beobachtet und auf die Interaktionsstrategien der Polizisten mit Klienten und ihre Deutungen und Selbstbilder fokussiert, erlaubt neue Einsichten in das alltägliche Funktionieren der Organisation. Die vorliegende Arbeit basiert auf einem dreimonatigen Aufenthalt in der domestic violence unit der Police Headquarters in der Upper West Region Ghanas. Sie zeigt unter anderem, wie die Akteure die Ausbildung zum Polizisten, Gehaltsfragen, Versetzungen, Geschlechterverhältnis und Beförderungen konzeptionalisieren und wo sie sich in ihrer Arbeitswelt positionieren. Die besondere Aufmerksamkeit der Arbeit gilt der Interaktion der Polizisten mit Akteuren außerhalb ihrer Organisation, den „Klienten“. Eine zentrale Erkenntnis ist, dass die Klienten erst mit Hilfe typischer bürokratischer Praktiken und Redensarten als solche von den Polizisten konstruiert werden. Dabei sind die Klienten aber weder passiv polizeilicher Willkür ausgeliefert noch können einflussreiche Klienten die Polizei nach ihrem Gusto manipulieren. In zwei Fallstudien von Verhandlungssituationen wird deutlich, wie Polizisten Autorität in der Interaktion mit Klienten herstellen und legitimieren und welche Maßnahmen Klienten ihrerseits ergreifen, um die Situation zu ihren Gunsten zu gestalten.

Aircraft-based in-situ aerosol mass spectrometry: Chemical characterization and source identification of submicron particulate matter in the free and upper troposphere and lower stratosphere

The composition of the atmosphere is frequently perturbed by the emission of gaseous and particulate matter from natural as well as anthropogenic sources. While the impact of trace gases on the radiative forcing of the climate is relatively well understood the role of aerosol is far more uncertain. Therefore, the study of the vertical distribution of particulate matter in the atmosphere and its chemical composition contribute valuable information to bridge this gap of knowledge. The chemical composition of aerosol reveals information on properties such as radiative behavior and hygroscopicity and therefore cloud condensation or ice nucleus potential. rnThis thesis focuses on aerosol pollution plumes observed in 2008 during the POLARCAT (Polar Study using Aircraft, Remote Sensing, Surface Measurements and Models, of Climate, Chemistry, Aerosols, and Transport) campaign over Greenland in June/July and CONCERT (Contrail and Cirrus Experiment) campaign over Central and Western Europe in October/November. Measurements were performed with an Aerodyne compact time-of-flight aerosol mass spectrometer (AMS) capable of online size-resolved chemical characterization of non-refractory submicron particles. In addition, the origins of pollution plumes were determined by means of modeling tools. The characterized pollution episodes originated from a large variety of sources and were encountered at distinct altitudes. They included pure natural emissions from two volcanic eruptions in 2008. By the time of detection over Western Europe between 10 and 12 km altitude the plume was about 3 months old and composed to 71 % of particulate sulfate and 21 % of carbonaceous compounds. Also, biomass burning (BB) plumes were observed over Greenland between 4 and 7 km altitude (free troposphere) originating from Canada and East Siberia. The long-range transport took roughly one and two weeks, respectively. The aerosol was composed of 78 % organic matter and 22 % particulate sulfate. Some Canadian and all Siberian BB plumes were mixed with anthropogenic emissions from fossil fuel combustion (FF) in North America and East Asia. It was found that the contribution of particulate sulfate increased with growing influences from anthropogenic activity and Asia reaching up to 37 % after more than two weeks of transport time. The most exclusively anthropogenic emission source probed in the upper troposphere was engine exhaust from commercial aircraft liners over Germany. However, in-situ characterization of this aerosol type during aircraft chasing was not possible. All long-range transport aerosol was found to have an O:C ratio close to or greater than 1 implying that low-volatility oxygenated organic aerosol was present in each case despite the variety of origins and the large range in age from 3 to 100 days. This leads to the conclusion that organic particulate matter reaches a final and uniform state of oxygenation after at least 3 days in the free troposphere. rnExcept for aircraft exhaust all emission sources mentioned above are surface-bound and thus rely on different types of vertical transport mechanisms, such as direct high altitude injection in the case of a volcanic eruption, or severe BB, or uplift by convection, to reach higher altitudes where particles can travel long distances before removal mainly caused by cloud scavenging. A lifetime for North American mixed BB and FF aerosol of 7 to 11 days was derived. This in consequence means that emission from surface point sources, e.g. volcanoes, or regions, e.g. East Asia, do not only have a relevant impact on the immediate surroundings but rather on a hemispheric scale including such climate sensitive zones as the tropopause or the Arctic.