Gerdes, Axel

Hervé, Francisco

Massonne, Hans-Joachim

Sudo, Masafumi

Thomson, Stuart N.

Willner, Arne

English

Hochschulschriftenserver - Universität Frankfurt am Main

Abstracts and Program, LAK 2009,  Göttingen, 7.4. to 9.4. 2009   309 German Partners Considering the German cooperation partners the following is suggested: Helm-holtz Center for Environmental Research (UFZ) Leipzig and the Technical Uni-versity of Dresden (TU Dresden) as coordinating cooperation partner for the joint project. Related participating institutions are KIT (Karlsruhe Institute of Technol-ogy), the Universität der Bundeswehr – München and the water supply company Sachsenwasser, Leipzig.     Does Chilenia exist? Evidence from the evolution of collisional and coastal accretionary systems between the latitudes 30°S and 35°S Willner AP 1,2, Massonne H-J 2, Gerdes A 3 , Hervé F 4, Sudo M 5, Thomson S 6 1 Inst. Geologie, Mineralogie, Geophysik, Ruhr-Universität Bochum, Germanyy ane.willner@rub.de 2 Institut für Mineralogie und Kristallchemie, Universität Stuttgart, Germany 3 Institut für Geowissenschaften, Mineralogie, J.W.Goethe Universität Frankfurt, Germany 4 Departamento de Geología, Universidad de Chile, Santiago de Chile, Chile 5 Institut für Geowissenschaften, Universität Potsdam, Germany 6 Department of Geology and Geophysics, Yale University, New Haven, CT, USA Within the basement close to the western continental margin of South America between the latitudes 30°S and 35°S the occurrence of a separate microplate, ac-creted to South America in Late Palaeozoic times, has been proposed by Ramos et al. (1984). These authors called the microplate/terrane Chilenia. However, it is not exposed at the surface because of the extensive cover by younger sediments and volcanics. Evidence for the existence of Chilenia can be derived by unravelling the evolution of two contrasting accretionary systems on both sides of the proposed terrane: (1) the Palaeozoic collisional accretionary prism of the Guarguaraz Com-plex at the suture between the Cuyania and Chilenia microplates in western Argen-tina  (longitude  69°W)  and  (2)  the  late  Palaeozoic  coastal  accretionary  complex within the Coastal Cordillera of central Chile (longitude 72°W). Both complexes are composed of continent-derived metasediments including up to 10-15% interca-lations of disrupted oceanic crust and were subjected to high-pressure metamor-phism. According to the age spectrum of detrital zircon, the maximum sedimentation age of the metasediments of the Guarguaraz Complex is about 563 Ma (Willner et al., 2008). Their peak PT-conditions were 13-14 kbar at about 500°C (Massonne and  Calderón,  2008),  which  represent  a  metamorphic  geotherm  of  close  to 10°C/km during this metamorphic stage. A decompresion path to midcrustal con-ditions  at  8  kbar  and  600°C  was  further  derived.  So  far,  such  decompression-heating paths are only known from continent-continent collisional settings. Ages 310                                  Abstracts and Program, LAK 2009,  Göttingen, 7.4. to 9.4. 2009  for the peak of metamorphism (Lu/Hf system) are currently under investigation, cooling ages for the Guarguaraz Complex are at 323Ma (Ar/Ar) and 284-295Ma (zircon fission track). In the coastal accretionary complex, accretion started before 320Ma with frontal accretion  in  upper  levels  leading  to  metamorphic  conditions  of  4-6  kbar,  250-300°C (Willner et al. 2009) after a short period of stable continental margin condi-tions (western margin  of Chilenia). The corresponding geotherms  are relatively high. Chevron folds of bedding planes and reverse faults were formed, indicative of  subhorizontal  shortening  (Richter  et  al.,  2007).  Subhorizontal  flow  paths  at maximum depth  are  proved by a near-isobaric prograde PT-path.  At the  same time,  material  more  deeply  transported  into  a  subduction  channel  was  heated against a  still hot mantle at 12-14 kbar,  600-700°C and subsequently cooled at depth following an anticlockwise PT-path (Willner et al., 2004). Upwards directed forced flow is the predominant process in a subduction channel, but only little material of the subduction channel seems to have been incorporated into the ac-cretionary prism itself.  At ~308 Ma the accretion mode changed from frontal to basal accretion leading to peak PT conditions of 7-10 kbar, 350-400°C (Willner et al., 2005). Maximum sedimentation ages and the ages of the peak of metamorphism are systematically younger in the basal accretionary prism (311 Ma and 279-308 Ma, respectively) than in the frontal accretionary systems (338-345 Ma, > 320 Ma). Deformation after accretion is characterized by pronounced flattening resulting in a penetrative subhorizontal transposition foliation by pressure solution processes (Richter et al., 2007).  Static  recrystallisation  outlasted  deformation  during  decompression  with slight cooling. Erosion at an axial rise of the accretionary wedge balanced accretion at depth leading to recycling of material to the trench as well as filling of retrow-edge basins. Accretion ended after about 100 Ma of duration (Willner et al., 2005).  The contrasting evolution of the collisional and coastal accretionary systems in-dicates collision of the Chilenia Terrane, presumably in Late Devonian-Early Car-boniferous times, before the onset of accretion processes along the Palaeopacific coast.  Chilenia  formed  the  back-stop  system  of  the  extensive  Late  Palaeozoic coastal accretionary system and was first covered by sediments of a wide Late Car-boniferous retrowedge basin that also received detritus from the rising collisional belt (Guarguaraz Complex) and an Early Carboniferous magmatic arc (Willner et al., 2008).  References Massonne H-J, Calderón M (2008) P-T evolution of metapelites of the Guarguaraz Complex,  Argentina  -  evidence  for  Devonian  crustal  thickening  close  to  the western Gondwana margin. Rev Geol Chile 35: 215-231 Ramos VA, Jordan T, Allmendinger R, Kay S, Cortés J, Palma M (1984) Chilenia: un terreno alóctono en la evolución paleozoica de los Andes Centrales. Actas IX Congreso Geológico Argentino 2: 84-106 Abstracts and Program, LAK 2009,  Göttingen, 7.4. to 9.4. 2009   311 Richter P, Ring U, Willner AP, Leiss B (2007) Structural contacts in subduction complexes and their tectonic significance: The Late Paleozoic coastal accretion-ary wedge of central Chile. J Geol Soc London 164: 203-214 Willner AP, Glodny J., Gerya TV, Godoy E, Massonne H-J (2004) A counter-clockwise  PTt-path in high  pressure-low temperature  rocks from  the Coastal Cordillera accretionary complex of South Central Chile: constraints for the earli-est stage of subduction mass flow. Lithos 75: 283-310 Willner, A.P., Thomson, S.N.,  Kröner, A., Wartho, J.A., Wijbrans, J and Hervé, F. (2005). Time markers for the evolution and exhumation history of a late Palaeo-zoic paired metamorphic belt in central Chile (34°-35°30´S). J Pet 46, 1835-1858. Willner AP, Gerdes A, Massonne H-J (2008) History of crustal growth and recy-cling at the Pacific convergent margin of South America at latitudes 29°-36°S re-vealed by a U-Pb and Lu-Hf isotope study of detrital zircon from late Paleozoic accretionary systems. Geochim Cosmochim Acta 253: 114-129 Willner AP, Sepúlveda FA, Hervé F, Massonne H-J, Sudo M (2009) Conditions and timing of pumpellyite-actinolite facies metamorphism in the Early Mesozoic frontal accretionary prism of the Madre de Dios Archipelago (50°20`S; S-Chile). J Petrol: in review.   Transferencia colombiana de conocimientos y experiencias de producción limpia en el beneficio de minerales  auro-argentíferos Wolff Carreño E Proyecto Río Suratá – Convenio CDMB – BGR, erwin.wolf@cdmb.gov.co Desde 1997 se ha venido desarrollando el Proyecto “Reducción de la Contami-nación  Ambiental  Debida  a  la  Pequeña  Minería  en  la  Cuenca  del  Río  Suratá (Proyecto Río Suratá)” en el marco de la Cooperación Técnica Colombo Alemana, cuyos ejecutores han sido por Colombia la Corporación Autónoma Regional para la Defensa de la Meseta de Bucaramanga (CDMB) y por  Alemania el Instituto Federal de Geociencias y Recursos Naturales (BGR) con el fin de aplicar procesos limpios y buenas prácticas ambientales sostenibles para el manejo del mercurio y del cianuro utilizado por la actividad minera auro-argentífera de pequeña escala en los municipios de Vetas y California (Departamento de Santander, Colombia). El desarrollo de este Proyecto ha demostrado reducción de contaminación en forma económicamente sostenible, pues la recuperación del metal valioso ha sido mayor, según los datos recopilados a diciembre 31 de 2007 para las unidades pro-ductivas intervenidas en promedio: Reducción del uso de mercurio en 82%; dis-minución del consumo de cianuro en 36%, e incremento de productividad en 79%. En virtud de los resultados exitosos alcanzados por este proyecto, a partir del año  2005  otras instituciones  ambientales colombianas  que  sufren problemas de 

History of crustal growth and recycling at the Pacific convergent margin of South America at latitudes 29°-36°S revealed by a U-Pb and Lu-Hf isotope study of detrital zircon from late Paleozoic accretionary systems.

in review. Transferencia colombiana de conocimientos y experiencias de producción limpia en el beneficio de minerales auro-argentíferos Wolff Carreño E Proyecto Río Suratá – Convenio CDMB – BGR, erwin.wolf@cdmb.gov.co Desde

P-T evolution of metapelites of the Guarguaraz Complex, Argentina - evidence for Devonian crustal thickening close to the western Gondwana margin. Rev Geol Chile 35: 215-231

Time markers for the evolution and exhumation history of a late Palaeozoic paired metamorphic belt in central Chile (34°-35°30´S).

Does Chilenia exist? : Evidence from the evolution of collisional and coastal accretionary systems between the latitudes 30° S and 35° S

Does Chilenia exist? : Evidence from the evolution of collisional and coastal accretionary systems between the latitudes 30° S and 35° S

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