Las sierras de Palermo, Cachi y Molinos, de la provincia de Salta, forman parte de la Cordillera Oriental, que está integrada por un basamento meta-sedimentario que se asigna a la Formación Puncoviscana, con edad de sedimentación y leptometamorfismo que corresponde al lapso Ediacarano-Terreneuviano. Las psamitas y pelitas están representadas esencialmente por grauvacas, litarenitas, lutitas y wackes, las cuales se habrían depositado en ambientes de arco de islas continental a margen continental activo. Las áreas de proveniencia habrían estado constituidas esencialmente por sedimentos cuarzosos y rocas ígneas félsicas a intermedias, que son típicas de la Corteza Continental Superior (UCC), las cuales habrían sufrido transporte hidráulico relativamente breve que permitió su alteración pero no una selección granulométrica eficiente. Las edades y caracteres morfológicos de los circones detríticos evidencian distintos orígenes y edades, unos volcánicos euhedrales de 527 Ma y otros redondeados por erosión con edades de 583 Ma. Las trazas fósilescorrespondientes a las asociaciones de Nereites saltensis que se desarrollan, son coherentes con las edades >540 Ma obtenidas a partir de los circones, mientras que no se encontró hasta ahora en esta región Oldhamia radiata. La Formación Puncoviscana,es afectada con posterioridad, por un evento metamórfico regional que culmina con la orogenia Tilcárica (~520 Ma), que desarrolla condiciones de Facies Sub-esquistos Verdes alcanzando eventualmente Facies Esquistos Verdes. Otro evento dinámicotérmico posterior ocurre entre los 488 y 453 Ma (Cámbrico superior – Ordovícico superior) que da lugar a la intrusión de los plutones tonalítico-trondhjemíticos y granodiorítico-graníticos de la Formación Cachi, con los que se asocian los gneises, migmatitas, filitas y esquistos moteados del Complejo La Paya, en Facies de Anfibolitas a Granulitas. Dichas edades U-Pb fueron determinadas en circones y monacitas,como así también mediante los isótopos de estroncio.

“Provenance of the Puncoviscana Formation meta-sediments and geochemical interpretation of its tectonic-setting in Cordillera Oriental and Sierras Pampeanas, Argentina”. The Puncoviscana Formation sl. is an important lithostratigraphic sequence consisted of dominantly psammites and mudstones, interbedded with subordinate conglomerate, carbonates and volcanics deposited in a shallow basin between the Neo-Proterozoic and Terreneuvian on the western edge of Gondwana, which for some authors would have behaved as foreland basin and for others as a passive continental margin, a thesis we interpret like sequences of one same evolutionary process. In Puncoviscana formation sl. ichnofóssils are grouped into two associations with different distributions: an area with Nereites saltensis, which correspond to the highest levels of the Ediacaran and another one with Oldhamia radiata, which would fit on Terreneuvian levels. On another side, detrital zircons giving a wide range of ages, indicate provenances from Paleo-Proterozoic, Meso-Proterozoic and Neo-Proterozoic terranes to which are summoned those of Terreneuvian. The available radiometric values correspond to different cratonic areas recognized in the South American continent from 2,300 to 950 Ma. There are also detected zircon ages between 850 and 600 Ma, which indicate igneous activity between the end of the Sunsas and the beginning of the Pampean cycle. We propose the name of Ancajano Complex for this interval. Clastic sequences of the Puncoviscana formation, begin over the Ancajan Complex and comforms a continuous sequence from meta-sediments to Greenschists and Amphibolites metamorphic facies developed within the Pampean cycle and it ends with the Tilcaric orogeny occurred at 520 Ma, evidenced by the unconformity that separates the Puncoviscana Formation from Meson Group. The development of an extensional marginal basin between 580 and 540 Ma, led to the extrusion of basic alkaline, ultrabasic to a tholeiitic magmatism; whereas the culmination of the sedimentary sequence, and in a subduction environment, between 540 and 520 Ma, it generates significant calc-alkaline and a per-aluminous magmatism in the Eastern Cordillera and Precordillera of Catamarca, Santiago del Estero and Córdoba provinces. Geochemical analyzes on representative outcrops of different metamorphic levels, allowed us to use major, minor and trace element diagrams to characterize environments of deposition of sediments, which generally correspond to “Active Continental Margin” and “Oceanic and Continental Arc Islands”. In addition, it could be shown that sedimentary debris which contributed to the Puncoviscana basin, essentially correspond to siliceous sediments and igneous felsic, which are typical of Upper Continental Crust (UCC), being very similar sedimentary processes in all the studied samples, as evidenced by the overall chemical composition and behavior of the Rare Earth Elements.

Hf-isotope data of >1100 detrital zircon grains from the Palaeozoic, south-central Andean Gondwana margin record the complete crustal evolution of South America, which was the predominant source. The oldest grains, with crustal residence ages of 3.8-4.0Ga, are consistent with complete recycling of existing continental crust around 4Ga. We confirm three major Archaean, Palaeoproterozoic (Transamazonian) and late Mesoproterozoic to early Neoproterozoic crust-addition phases as well as six igneous phases during Proterozoic to Palaeozoic time involving mixing of juvenile and crustally reworked material. A late Mesoproterozoic to early Neoproterozoic, Grenville-age igneous belt can be postulated along the palaeo-margin of South America. This belt was the basement for later magmatic arcs and accreted allochthonous microcontinents as recorded by similar crustal residence ages. Crustal reworking likely dominated over juvenile addition during the Palaeozoic era, and Proterozoic and Archaean zircon was mainly crustally reworked from the eroding, thickened Ordovician Famatinian arc.

The Puncoviscana Formation is an important stratigraphic sequence of sandstones and shales, with intercalated conglomerates, limestones and volcanic rocks. It was deposited at the Neoproterozoic-Cambrian boundary in a shallow basin on the western margin of Gondwana. Trace fossils of the Puncoviscana Formation s.l. are represented by the Oldhamia and Nereites ichnoassociations and the geographical distribution of assemblages are aligned as parallel belts, with a shallower eastern Nereites association and a deeper western Oldhamia association. They represent different temporal levels on the evolution of the basin. Detrital zircon spectra display a wide range of ages, which indicate their provenance from Neoproterozoic to Cambrian source areas as well as Meso- to Paleoproterozoic basement units, exhibiting typical Gondwanan ages. Thick limestone banks are interbedded in the Puncoviscana Formation s.l. that included the siliciclastic sequences, with very low- to medium-metamorphic grade. delta C-13 values for the limestones vary from -1.57 to + 3.4 parts per thousand VPDB, while in the Sierras Pampeanas, delta C-13 values vary from +2.6 to +8 parts per thousand VPDB. Also, reported Sr-87/Sr-86 values allow a clear differentiation of two rock sets. The limestones interbedded with the Puncoviscana Formation yielded values typical for the Neoproterozoic-Cambrian transition, between 0.70868 and 0.70896; while the limestones of the Sierras Pampeanas display values between 0.70748 and 0.70756, common in the Middle to Late Ediacaran. Deformation and uplift of the Puncoviscana Formation is clearly represented in northern Argentina by the Tilcarian unconformity, which is overlain by the Meson Group.

The evolution of the provenance areas for Late Neoproterozoic, Cambrian and Early Ordovician sedimentary and meta-sedimentary rocks of north central and northwest Argentina is discussed using 123 maximum ages of detrital zircons from 42 samples from this and previously published studies. Most detrital zircon ages fall into two groups: 1,200–900 Ma and 670–545 Ma. These ages are essentially identical for the non- to very low grade metamorphic late Neoproterozoic to Early Cambrian Puncoviscana Formation and the low to high grade metamorphic rocks of Eastern Sierras Pampeanas. Hence, both units are related to similar provenance areas at the same time of sedimentation. The time span from zircon crystallization in the Earth’s crust to exhumation and erosion may be very long. This is important when determining maximum ages of sedimentary rocks. Variation of zircon maxima may also be influenced by concurrent sedimentary cover of proposed provenance areas. For the late Mesoproterozoic to early Neoproterozoic zircon age group, an active mountain range of the southwest Brazilian Sunsás orogen is the most probable provenance area. The younger, late Neoproterozoic zircons are related to the continuously developing mountains of the Brasiliano orogen of southwest and south central Brazil. Young zircons, up to 514 Ma, from fossil-bearing Puncoviscana and Suncho Formation outcrops are related to late Early Cambrian volcanism contemporaneous with sedimentation. This situation continues through the Late Cambrian to the Early Ordovician, but the Sunsás orogen provenance diminishes as possible Río de la Plata craton origins become important.

Fil: Acenolaza, Florencio Gilberto. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Tucuman. Instituto Superior de Correlacion Geologica. Universidad Nacional de Tucuman. Facultad de Ciencias Naturales e Instituto Miguel Lillo. Departamento de Geologia. Catedra Geologia Estructural. Instituto Superior de Correlacion Geologica; Argentina

U-Pb ages of detrital zircons from greywacke, and Rb-Sr metamorphic ages of slate from the Puncoviscana Formation of northwest Argentina are reported, and used to constrain the depositional age, metamorphic history, and sedimentary provenance of these rocks. The detrital zircon ages define mainly Late Mesoproterozoic-Early Neoproterozoic (1150-850 Ma) and Late Neoproterozoic-Early Cambrian (650-520 Ma) populations, the relative proportions of which vary inversely with the age of the youngest zircons in the samples. The 1150-850 Ma population is present in all samples and dominates in those with relatively old grains (> 600 Ma) in the Late Neoproterozoic-Early Cambrian population. However, the Late Mesoproterozoic-Early Neoproterozoic population is substantially smaller in those samples in which the Late Neoproterozoic-Early Cambrian population dominates and contains relatively young grains (> 520 Ma). The youngest zircons, c. 520 Ma, are in the Rancagua (Cachi, Salta province) sample. They form a narrow, unimodal peak and may have originated from volcanic sources active during deposition, in which case these youngest zircons would constrain the depositional age of the sample to the late Early Cambrian. This is consistent with Rb-Sr ages of 550-500 Ma for samples of slate from the Puncoviscana Formation. The detrital zircon age populations suggest a sedimentary provenance in a continental hinterland with a stabilized, extensive Late Mesoproterozoic orogen (with minor Paleoproterozoic and Archean precursors) and a more variable Late Neoproterozoic orogen containing an evolving sequence of less extensive subcomponents. A direct relationship with the Brazilian Shield is thus suggested with sedimentary detritus originating within the active-margin orogens of the interior, but with ultimate deposition in the passive-margin environment of western Gondwanaland.

The Sierra de Velasco is formed of large plutons that are related to each other by intrusive contacts and separated by generally aligned deformation zones. The plutons are composed of calc-alkaline, syn-, late- and post-kinematic granitoids of different ages and intrusion levels. They are grouped in three large batholiths: Aimogasta, Bazan and Patquia. On the northeastern flank, the metamorphic country rock is represented by micaschists, phyllites and quartzites with hornfels (La Cebila Formation), to the north by tonalitic porphyries that in all cases demonstrate a shallow level of the granitoid intrusions. Shape of the plutons, as well as structural characters and grade of deformation indicate that the intrusive sequences began in Ordovician times and culminated in the Carboniferous, with deformation periods during Silurian and Devonian times.

Small, strata-bound copper sulfide deposits are found associated with bitumen in Lower Cretaceous basaltic andesite flows of the Pabellon Formation near Copiapo, north Chile. The physical characteristics of the bitumen and hydrocarbon biomarkers provide clues to the genesis, evolution, and possible role during copper mineralization. Biomarker analysis reveals a predominantly bacterial origin, with minor contributions from phytoplankton and higher plants, which were deposited in a shallow marine environment. An expulsion temperature between 64° and 87°C was determined, typical for low maturity petroleum. This petroleum was altered during migration by mixing with brines, increasing its viscosity by aromatization and sulfurization. At the moment of the accumulation, the temperature of the brine was under 150°C. The viscous oil filled the primary and secondary porosity of the basaltic andesite, which acted as an oil trap. After the oil accumulation, a hotter, hydrothermal influx resulted in thermal alteration of the petroleum and a further decrease of light alkane concentrations. High sulfur concentrations in the hydrothermal fluids led to further aromatization of the organic compounds, generating highly alkylated benzonaptho- and dinaphthothiophenes. Copper in the sulfur-rich solutions was reduced, triggering the precipitation of bornite, chalcopyrite, digenite, chalcocite, and covellite through thermochemical sulfate reduction. The bitumen interacted with metals by virtue of its inherent reducing characteristics (activated carbon) and was itself oxidized to form a pyrobitumen residue.

The Antarctic Peninsula has been part of a magmatic arc since at least Jurassic times. The South Shetland Islands archipelago forms part of this arc, but it was separated from the Peninsula following the Pliocene opening of the Bransfield Strait. Dikes are widespread throughout the archipelago and are particularly accessible on the Hurd Peninsula of Livingston Island. The host rocks for the dikes are represented by the Miers Bluff Formation, which forms the overturned limb of a large-scale fold oriented 63/23 NW. The orientation of minor structures indicates a fold axis oriented NNE-SSW (24/0). Structural analysis of the dikes and their host rocks shows that the tectonic regime was similar to other parts of the archipelago and that only minor changes of the stress field occurred during dike emplacement.Based on crosscutting field relationships and geochemical data, six early Paleocene to late Eocene intrusive events can be distinguished on Hurd Peninsula. In contrast to calc-alkaline dikes from other parts of the South Shetland Islands, the majority of the Hurd Peninsula dikes are of tholeiitic affinity. Nd and Pb isotope data indicate a significant crustal component, particularly during initial magmatic activity.Plagioclase Ar-40/Ar-39 and whole rock K-Ar ages show that dike emplacement peaked during the Lutetian (48.3 +/- 1.5, 47.4 +/- 2.1, 44.5 +/- 1.8 and 43.3 +/- 1.7 Ma) on Hurd Peninsula and also further northeast on King George Island. Dike intrusion continued on Livingston Island at least until the Priabonian (37.2 +/- 0.9 Ma). The type of magma sources (mantle, slab, crust and sediment) did not change, though their relative magmatic contributions varied with time.During Cretaceous and Early Paleogene times, the Antarctic Peninsula including the South Shetland Islands was situated southwest of Patagonia; final separation from South America occurred not before the Eocene. Thus, the geological evolution of Livingston Island is related as much to the development of Patagonia as of Antarctica, and needs to be considered within the history of southernmost South America. (C) 2008 Elsevier Ltd. All rights reserved.

Discussion of continental drift around Antarctica began nearly 100 years ago. While the Gondwana connections of Antarctica to Africa and Australia have been well defined for decades, the relative pre-drift positions of the Antarctic Peninsula and Patagonia continue to be subjects of controversy. Certainly older figures, which showed a paleo-position of the Peninsula crossing over continental crust of the Falkland Plateau or even South Africa or Patagonia, are out of consideration now. But contradictory opinions remain over the relative paleo-position of the Peninsula as a more or less straight prolongation of the Patagonian Andes, versus a position parallel to Patagonia along the Pacific coast. Geological reasons are found for both opinions, but geophysical observations on the adjacent ocean floors, particularly the evolution of the Weddell Sea crust, speak for the last-mentioned reconstruction.

This paper concerns sedimentary, volcanic, metamorphic and igneous rocks of the Sierra de Famatina and adjacent rock series in NW Argentina, for which the name 'Famatina system' has been used widely in the literature. It is suggested that this is renamed the 'Famatina complex', since 'system' is an internationally defined stratigraphical term. The Famatina complex is considered to have formed as an island arc on continental crust, represented in its diversity by metasediments and meta-volcanic rocks of the Sierra de Famatina, with a corresponding back-arc basin exposed in the medium- to high-grade metamorphic rocks of the adjacent Las Termas belt to the east. The Famatina complex was deposited in contact with the eastern Pampean complex ('Pampia terrane') at the western active continental margin of Gondwana in latest Proterozoic and Ordovician times. Deposition was, in part, accompanied by voluminous Ordovician magmatism of calc-alkaline composition. NNW-SSE-striking shear zones, dated previously at 402 +/- 2 Ma, are interpreted as marking the final stage of collision of the island-arc/back-arc/continent complex. The dynamics of crustal block movements along the most prominent (TIPA) shear zone indicate overthrusting of the eastern Pampean series onto the western Famatina series and, hence, uplift and cooling of the eastern block must have occurred earlier than cooling of the western one. The composition of inherited components in Famatina metasediments and meta-granitoids argues for autochthonous arc-continent convergence rather than accretion of an exotic terrane.

The hypothesis of exotic terranes in Peru, Bolivia, Argentina and Chile generated discussions on the mode of transfer and extent of accretional events that may have occurred in the southern Andes during the Late Proterozoic-Early Paleozoic. Initially, a tectogenesis based on autochthonous mobile fold belts was discussed. Following ideas emphasised the fragmentation of the supercontinent Rodinia, Laurentia moving along the West Gondwana border and colliding with the Gondwana western margin. The most important effect of this Laurentia/Gondwana relationship was attributed to the Argentine Precordillera. (or Cuyania) terrane splitting off from Laurentia and docking to Gondwana in the Early Paleozoic. In this study, the most cited arguments for this Laurentia/Precordillera relationship are discussed, emphasising paleontological considerations. It is shown that these arguments do not exclude a close original vicinity of the Precordillera terrane to Gondwana.The Precordillera terrane is suggested to be part of a hypothetical platform, which developed between South America, Africa and Antarctica (SAFRAN platform), and which was displaced to its actual position by transcurrent faults. The collisional events in the Sierras Pampeanas ensued from strike-slip movements and were responsible for the S and I type transpressional magmatism along the Pampean and Famatinian terranes. The final result of this continent-parallel movement of terrane slices is similar to that of a terrane split off from Laurentia, but the first-named way of formation easier explains the general continuity of plate convergence at the western border of Gondwana than the Laurentia/Precordillera connection does. (C) 2002 Elsevier Science B.V. All rights reserved.

The sedimentary sequences outcropping in Hurd Peninsula, Livingston Island, are formally defined as members of the Miers Bluff Fonna­ tion (MBF): Johnsons Dock and Napier Peak Members and Moores Peak breccias. The lowermost strata (Johnsons Dock Member) are studied in detail, while the investigations of the upper part of the sedimentary sequences crop­ ping out at Napier Peak and Cerro Mirador are of a reconnaissance nature only. The sediments in castern Hurd Peninsula are studied in three sedimentological and geological scctions (Napier Peak, Cerro Mirador and Moores Peak). Meas­ urcments of the orientation of thc axes of small-scale folds represented in the sections suggest that phases 3a and 3b of MUNoz et al, (1992) can be unificd in one final phase. Their orientations are in the frame of normal deviations usu­ ally within the developmcnt of a fold system. Thc Moores Peak breccias are a component and an inseparable part of the whole sedimentary sequence in Hurd Peninsula. They are the upper lithostratigraphical division of the MBF and rep­ resent the final stage of sedimentation in the Carboniferous(?)-Triassic Miers Bluff depositional basin. The dominant transport of the Moores Peak breccias has been by dcbris flows.

For the last two hundred years many German scientists followed ALEXANDER VON HUMBOLDT in geoscientifically researching Latin America. In this study their main activities and the influences on the development of the Latin-American geoscientific research are outlined also depicting changes in the German-Latin-American research cooperation during the second half of the twentieth century. Analyzing the reasons for the altered conditions the authors consider a nexus to the international research projects to be the essential basis for a successful future cooperation between German geologists and their colleagues in Latin America.

RESUMEN Las serpentinitas del area de La Cabana forman parte de la Serie Occidental del Basamento Metamorfico de la Cordillera de la Costa de la IX Region y corresponden a dunitas de grano grueso parcial a totalmente serpentinizadas. Contienen cromita como mineral accesorio, la que generalmente esta alterada en grado variable a ferricromita. En cambio, las cromitas presentes en las cromititas de Centinela Bajo, preservan su composicion original con un minimo grado de alteracion, lo que permite su uso como indicadores petrotectonicos. Sus valores de 'numero de cromo' (#Cr= Cr/Cr+Al) entre 0,65 y 0,90, de 'numero de magnesio' (#Mg=Mg/ Mg+Fe+2) entre 0,40 y 0,70, indican un ambito de arco de islas para el emplazamiento de las peridotitas estudiadas.

A Holy Alliance? The Church and the Left in Costa Rica, 1933-1948. By Eugene Miller. (London: M.E. Sharpe, 1996. Pp. 228. Illustrations. Notes. Appendix. Bibliography. Index. No Price.) - Volume 55 Issue 1