Preface: Palaeozoic geodynamics of the southwestern margin of Gondwana: controls on the present architecture of the Argentine-Chilean Andes

Palaeozoic geodynamics of the southwestern margin of Gondwana: controls on the present architecture of the Argentine-Chilean Ande

Stratigraphy, structure and geodynamic evolution of the Paleozoic rocks in the Cordillera del Viento (37º S latitude, Andes of Neuquén, Argentina)

The Pre-Andean Paleozoic substrate from the Cordillera del Viento anticline is a polyorogenic basement composed of two groups of preorogenic rocks with different stratigraphy and deformation. The oldest set consists of pre-Late Devonian metasedimentary rocks belong­ing to the Guaraco Norte Formation. The upper set is formed by the thick volcano-sedimentary sequence of the Carboniferous Andacollo Group. This group is composed from bottom to top of the silicic volcanic rocks of the Arroyo del Torreón Formation (early Carboniferous) and the marine sedimentary rocks of the Huaraco Formation (late Carboniferous) developed in an extensional basin. Both formations are locally separated by minor syn-extensional unconformities. The relationship between the metamorphic rocks of the Guaraco Norte Formation and the volcano-sedimentary sequence of the Anda­collo Group is not observed, but we inferred a major angular unconformity associated with the Late Devonian-early Carboniferous Chanic orogeny. The main Chanic structures are tight vertical and subvertical folds with slight W-WSW vergence, formed under low-grade meta­morphic conditions, with the development of a pervasive axial-plane cleavage (S1), affected by a disjunctive crenulation cleavage (S2). In the early Permian, during the San Rafael orogeny of the Gondwanan orogenic cycle, deformation occurred under very low-grade to non-metamorphic conditions. The main structures are thrusts and associated folds that are re-folded by the Cordillera del Viento anticline, related to the Andean orogeny. The WNW-oriented and SSW-vergent folds are associated with an incipient axial-plane cleavage in the pyroclastic rocks and pencil lineation in shales. The pre-Andean Paleozoic basement rocks are intruded and unconformably covered by early Permian to Early Triassic? granitoids and silicic volcanic rocks from the Huingancó volcanic-plutonic Complex (equivalent to the Choiyoi Group), establishing the beginning of the Andean orogenic cycle in this region.El sustrato paleozoico pre-andino que aflora en el anticlinal de la Cordillera del Viento, es un basamento poliorogénico que está com­puesto por dos conjuntos de rocas preorogénicas con estratigrafía y condiciones de deformación diferentes. El más antiguo tiene una edad devónica superior y está formado por las rocas metasedimentarias de la Formación Guaraco Norte, en tanto que el conjunto superior son las espesas acumulaciones volcano-sedimentarias carboníferas del Grupo Andacollo. Este grupo, integrado en su parte inferior por rocas volcánicas silíceas de la Formación Arroyo del Torreón (Carbonífero inferior) y hacia techo, por las sedimentitas clásticas marinas de la Formación Huaraco (Carbonífero superior) fue desarrollado en el marco de una cuenca extensional y pueden estar separadas localmente por discordancias menores de carácter sin-extensional. Las relaciones entre las rocas metamórficas y la secuencia volcano-sedimentaria del Carbonífero no se observan, pero se infiere una discordancia mayor asociada con la orogenia Chánica, que tuvo lugar entre el Devónico Superior y el Carbonífero inferior. Las estructuras chánicas están asociadas a un metamorfismo de bajo grado y son pliegues apretados sub-verticales a verticales y con ligera vergencia al O-OSO que llevan asociados un clivaje penetrativo (S1) de rumbo N-S a NNO que está afectado por un clivaje subvertical más espaciado (S2). En el Pérmico inferior, durante la orogenia San Rafael del ciclo orogénico Gondwánico, la deformación contraccional se produce en condiciones de metamorfismo de muy bajo grado o en ausencia de éste. Las estructuras principales son cabalgamientos y pliegues asociados que se encuentran plegados por el anticlinal ándico de la Cordillera del Viento. Los pliegues de rumbo ONO y vergencia al SSO llevan asociados un incipiente clivaje de plano axial en los contactos entre limolitas y volcanitas y lineación de tipo lápiz (pencil) en las lutitas. Las rocas del basamento paleozoico pre-ándico están intruidas y cubiertas discordantemente por rocas volcánicas silíceas de edad Pér­mico inferior a Triásico Inferior?, correspondientes al Complejo volcánico-plutónico Huingancó (equivalente al Grupo Choiyoi), unidad que marca el comienzo el ciclo orogénico Andino, en esta región

The Palaeozoic basement of the Andean Frontal Cordillera at 34º S (Cordón del Carrizalito, Mendoza Province, Argentina): Geotectonic implications

The Cordón del Carrizalito is located in the southern sector of the Andean Frontal Cordillera. In this area, the Andean basement is composed of meta-sedimentary rocks (Las Lagunitas Formation) of Ordovician age. In addition, no- or very low grade metamorphism and less deformed rocks also occur in the study area. We call these rocks Selerpe series, whose characteristics are comparable to other series, late Carboniferous in age, described in nearby areas. The Las Lagunitas Formation is affected by west-verging folds, developed under low-grade metamorphic conditions. These structures can be attributed to the Chanic orogeny (Late Devonian – early Carboniferous). The Selerpe series and Las Lagunitas Formation are deformed by east-verging thrusts and folds developed in narrow bands and generated in the absence or under very low metamorphic conditions. These structures always deform the Chanic structures, and are attributed to the Gondwanan deformation (San Rafael orogeny, late Carboniferous – Permian in age). The Chanic structures of the study area can be placed in the western branch and in the hinterland of the Chanic orogen, which was developed as a result of the accretion of the Chilenia terrane at the west Gondwana margin during Late Devonian and early Carboniferous. The eastern branch of this orogen is located in the Andean Precordillera. The Permo-Triassic cover, deformed by the Andean orogenic cycle (Mesozoic – Cenozoic), rests unconformably on the Palaeozoic basement rocks.En el Cordón del Carrizalito, situado en el sector meridional de la Cordillera Frontal de los Andes, afloran metasedimentos ordovícicos pertenecientes a la Formación Las Lagunitas y otro conjunto de rocas menos deformadas, en ausencia de metamorfismo o con metamorfis­mo de muy bajo grado, que hemos denominado serie de Selerpe. Esta última es litoestratigráficamente comparable a series del Carbonífero superior descritas en áreas próximas. La Formación Las Lagunitas está afectada por pliegues apretados, vergentes al oeste y desarrollados bajo condiciones de metamorfismo de bajo grado. Estas estructuras pueden ser atribuidas a la orogenia Chánica (Devónico Superior - Car­bonífero inferior). La deformación Gondwánica, atribuida a la orogenia San Rafael, (Carbonífero superior – Pérmico), afecta tanto a la serie de Selerpe como a la Formación Las Lagunitas y se caracteriza por cabalgamientos y pliegues vergentes al este y generados en ausencia de metamorfismo o bajo condiciones metamórficas de muy grado bajo. Las estructuras chánicas de la zona estudiada se encuentran en las zonas internas de la rama occidental del orógeno del mismo nombre. Estas estructuras se desarrollaron como resultado de la acreción del terreno de Chilenia al margen occidental del antiguo continente de Gondwana durante el Devónico Superior – Carbonífero inferior. La rama oriental del orógeno Chánico se sitúa en la Precordillera andina. La cobertera permo-triásica, deformada durante el Mesozoico y Cenozoico por el ciclo orogénico Andino, se apoya discordantemente sobre las rocas del basamento paleozoico

Loss of strength in Ni3Al at elevated temperatures

Stress decrease above the stress peak temperature (750 K) is studied in h123i single crystals of Ni3(Al, 3 at.% Hf ). Two thermally activated deformation mechanisms are evidenced on the basis of stress relaxation and strain rate change experiments. From 500 to 1070 K, the continuity of the activation volume/temperature curves reveals a single mechanism of activation enthalpy 3.8 eV/atom and volume 90 b3 at 810K with an athermal stress of 330 MPa. Over the very same temperature interval, impurity or solute diffusion towards dislocation cores is evidenced through serrated yielding, peculiar shapes of stress–strain curves while changing the rate of straining and stress relaxation experiments. This complicates the identification of the deformation mechanism, which is likely connected with cube glide. From 1070 to 1270 K, the high-temperature mechanism has an activation enthalpy and volume of 4.8 eV/atom and 20 b3, respectively, at 1250 K

Transition between Variscan and Alpine cycles in the Pyrenean-Cantabrian Mountains (N Spain): Geodynamic evolution of near-equator European Permian basins

In the northern Iberian Peninsula, the Pyrenean-Cantabrian orogenic belt extends E-W for ca. 1000 km between the Atlantic Ocean and Mediterranean Sea. This orogen developed from the collision between Iberia and Eurasia, mainly in Cenozoic times. Lower-middle Permian sediments crop out in small, elongated basins traditionally considered independent from each other due to misinterpretations on incomplete lithostratigraphic data and scarce radiometric ages. Here, we integrate detailed stratigraphic, sedimentary, tectonic, paleosol and magmatic data from well-dated lithostratigraphic units. Our data reveal a similar geodynamic evolution across the Pyrenean-Cantabrian Ranges at the end of the Variscan cycle. Lower-middle Permian basins started their development under an extensional regime related to the end of the Variscan Belt collapse, which stars in late Carboniferous times in the Variscan hinterland. This orogenic collapse transitioned to Pangea breakup at the middle Permian times in the study region. Sedimentation occurred as three main tectono-sedimentary extensional phases. A first phase (Asselian-Sakmarian), which may have even started at the end of the Carboniferous (Gzhelian) in some sections, is mainly represented by alluvial sedimentation associated with calc-alkaline magmatism. A second stage (late Artinskian-early Kungurian), represented by al-luvial, lacustrine and palustrine sediments with intercalations of calc-alkaline volcanic beds, shows a clear up-ward aridification trend probably related to the late Paleozoic icehouse-greenhouse transition. The third and final stage (Wordian-Capitanian) comprised of alluvial deposits with intercalations of alkaline and mafic beds, rarely deposited in the Cantabrian Mountains, and underwent significant pre-and Early Mesozoic erosion in some segments of the Pyrenees. This third stage can be related to a transition towards the Pangea Supercontinent breakup, not generalized until the Early/Middle Triassic at this latitude because the extensional process stopped about 10 Myr (Pyrenees) to 30 Myr (Cantabrian Mountains). When compared to other well-dated basins near the paleoequator, the tectono-sedimentary and climate evolution of lower-middle Permian basins in Western and Central Europe shows common features. Specifically, we identify coeval periods with magmatic activity, extensional tectonics, high subsidence rates and thick sedi-mentary record, as well as prolonged periods without sedimentation. This comparison also identifies some evolutionary differences between Permian basins that could be related to distinct locations in the hinterland or foreland of the Variscan orogen. Our data provide a better understanding of the major crustal re-equilibration and reorganization that took place near the equator in Western-Central Europe during the post-Variscan period

Reactivation of Paleozoic structures during Cenozoic deformation in the Cordón del Plata and Southern Precordillera ranges (Mendoza, Argentina)

The tectonic style of the eastern morphostructural units of the Central Andes between 32°20´ and 33°20´S is strongly influenced by pre- Andean structures, especially those developed during the late Carboniferous-Early Permian San Rafael orogeny of the Gondwanan orogenic cycle. Moreover, in the study area pre-Carboniferous rocks were deformed in Late Devonian-early Carboniferous times by the Chanic orog­eny. In this paper we argue that the Cordón del Plata and the Southern Precordillera ranges, first order features of the eastern ranges of the Andes, have been shaped in large part by the Permian event. Our data suggest that the double verging character of the Andean Precordillera fold- thrust belt is mainly the result of the reactivation of Gondwanan structures which conform a fold-thrust belt with distinct characteristics north and south of 33°S. The northern sector of this belt corresponds to a bivergent system, while the southern sector had a widespread east vergence. The vergence of the Chanic structures is more difficult to determine, but we infer a westward vergence in the Frontal Cordillera and western sector of Precordillera, and an eastern vergence in the eastern sector of the Precordillera. The sharp disappearance of the Precordillera morphostructural unit south of 33°S is inferred here to be related to the distribution of inherited Permian structures.El estilo tectónico del sector oriental de las unidades morfoestructurales de los Andes Centrales entre los 32°20´y 33°20´S se encuentra fuertemente influenciado por estructuras pre-andinas, especialmente aquellas desarrolladas durante el Carbonífero superior-Pérmico Inferior y asociadas al orógeno San Rafael del ciclo orogénico Gondwánico. Además, en el área de estudio, las rocas pre-carboníferas se deformaron durante el Devónico Superior y Carbonífero inferior, en relación con la orogenia Chánica. En este trabajo discutimos los rasgos de primer orden del sector oriental de los Andes, que comprende al Cordón del Plata y a la Precordillera Austral, fueron en gran parte modelados a partir del evento pérmico. Nuestros datos sugieren que la doble vergencia de una faja plegada y corrida en la Precordillera Andina es el resultado principalmente de la reactivación de estructuras gondwánicas que conformaron una faja plegada y corrida con características distintivas al norte y sur de los 33°S. El sector norte de la faja corresponde a un sistema bivergente, mientras que el sector sur posee una vergencia predo­minantemente oriental. La vergencia de las estructuras chánicas es más difícil de predecir, pero se sugiere aquí una vergencia hacia el oeste para las estructuras de la Cordillera Frontal y el sector occidental de la Precordillera y otra hacia el este para las estructuras del sector oriental de la Precordillera. Se infiere que la marcada desaparición de la Precordillera como unidad morfoestructural andina al sur de los 33° está relacionada a la distribución de estructuras chánicas y gondwánicas

Management of Autoimmune Encephalitis in a 7-Year-Old Child With CTLA-4 Haploinsufficiency and AMPA Receptor Antibodies:A Case Report

OBJECTIVES: We report on the therapeutic management of early-onset severe neurologic symptoms in cytotoxic T lymphocyte antigen-4 haploinsufficiency (CTLA-4h) and the presence of antibodies to the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) as an important finding. METHODS: This is a case report from a Dutch academic hospital. Repeated clinical examinations, repeated brain MRI and extended diagnostics on serum and CSF were performed. We used the CARE checklist. RESULTS: A 7-year-old boy was diagnosed with CTLA-4h based on family screening. On diagnosis, he had mild chronic diarrhea and autism spectrum disorder, but no abnormalities in extensive laboratory screening. Six months later, he presented with sudden-onset autoimmune encephalitis. Repeated brain MRI revealed no abnormalities, but immunohistochemistry analysis on serum and CSF showed the presence of AMPAR antibodies. Treatment was initially focused on immunomodulation and targeted CTLA-4 replacement therapy. Because of the persistent fluctuating cerebellar and neuropsychiatric symptoms and the potential clinical significance of the AMPAR antibodies, treatment was intensified with repetition of first-line immunomodulation and rituximab. This combined therapy resulted in sustained clinical improvement and served as a bridge to curative hematopoietic stem cell transplantation. DISCUSSION: This case illustrates the rare early onset of autoimmune encephalitis and presence of AMPAR antibodies in CTLA-4h. Targeted CTLA-4 replacement therapy resulted in a partial response. However, awaiting its optimal therapeutic effect, refractory CNS symptoms required intensification of immunomodulation. The identification of AMPAR antibodies guided our treatment decisions. CLASSIFICATION OF EVIDENCE: This provides Class IV evidence. It is a single observational study without controls.</p

Taxing the Informal Economy: The Current State of Knowledge and Agendas for Future Research

This paper reviews the literature on taxation of the informal economy, taking stock of key debates and drawing attention to recent innovations. Conventionally, the debate on whether to tax has frequently focused on the limited revenue potential, high cost of collection, and potentially adverse impact on small firms. Recent arguments have increasingly emphasised the more indirect benefits of informal taxation in relation to economic growth, broader tax compliance, and governance. More research is needed, we argue, into the relevant costs and benefits for all, including quasi-voluntary compliance, political and administrative incentives for reform, and citizen-state bargaining over taxation

Management of Autoimmune Encephalitis in a 7-Year-Old Child With CTLA-4 Haploinsufficiency and AMPA Receptor Antibodies:A Case Report

OBJECTIVES: We report on the therapeutic management of early-onset severe neurologic symptoms in cytotoxic T lymphocyte antigen-4 haploinsufficiency (CTLA-4h) and the presence of antibodies to the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) as an important finding. METHODS: This is a case report from a Dutch academic hospital. Repeated clinical examinations, repeated brain MRI and extended diagnostics on serum and CSF were performed. We used the CARE checklist. RESULTS: A 7-year-old boy was diagnosed with CTLA-4h based on family screening. On diagnosis, he had mild chronic diarrhea and autism spectrum disorder, but no abnormalities in extensive laboratory screening. Six months later, he presented with sudden-onset autoimmune encephalitis. Repeated brain MRI revealed no abnormalities, but immunohistochemistry analysis on serum and CSF showed the presence of AMPAR antibodies. Treatment was initially focused on immunomodulation and targeted CTLA-4 replacement therapy. Because of the persistent fluctuating cerebellar and neuropsychiatric symptoms and the potential clinical significance of the AMPAR antibodies, treatment was intensified with repetition of first-line immunomodulation and rituximab. This combined therapy resulted in sustained clinical improvement and served as a bridge to curative hematopoietic stem cell transplantation. DISCUSSION: This case illustrates the rare early onset of autoimmune encephalitis and presence of AMPAR antibodies in CTLA-4h. Targeted CTLA-4 replacement therapy resulted in a partial response. However, awaiting its optimal therapeutic effect, refractory CNS symptoms required intensification of immunomodulation. The identification of AMPAR antibodies guided our treatment decisions. CLASSIFICATION OF EVIDENCE: This provides Class IV evidence. It is a single observational study without controls.</p