Revista Geologica De Chile最新文献

{"title":"A Miocene toxodontid (Mammalia: Notoungulata) from the sedimentary series of the Cura-Mallín Formation, Lonquimay, Chile","authors":"D. Croft, J. Radic, Enrique Zurita, R. Charrier, J. J. Flynn, A. Wyss","doi":"10.4067/S0716-02082003000200008","DOIUrl":"https://doi.org/10.4067/S0716-02082003000200008","url":null,"abstract":"Estratos fluvio-lacustres del Mioceno medio del Miembro Rio Pedregoso de la Formacion Cura-Mallin estan ampliamente expuestos al este y al sur de la ciudad de Lonquimay, Chile. Estos estratos se acumularon en la cuenca extensional de Cura-Mallin, la cual posteriormente sufrio una inversion tectonica. En esta region esta cuenca se interpreta como un sistema de subcuencas diacronico compuesto por dos half-graben. En estratos de la Formacion Cura-Mallin expuestos en la ladera occidental del Cerro Tallon, en la orilla oeste del rio Biobio se encontro una mandibula izquierda incompleta de un notoungulado toxodontido. Comparaciones morfologicas y morfometricas indican que el ejemplar pertenece a Nesodon conspurcatus. Este es el primer hallazgo de Nesodon conspurcatus que se realiza fuera de Patagonia y una de las pocas ocurrencias bien documentadas de Nesodon en regiones de alta latitud fuera de Argentina. La amplia distribucion geografica de Nesodon y su restringido rango de distribucion temporal, sugieren que este taxon podria ser uno de los indicadores mas utiles para las faunas pertenecientes a la edad Mamifero Santacrucense.La ausencia de Nesodon en la fauna tipo de la Edad Mamifero Friasense en Rio Frias/Cisnes, en la Patagonia chilena, parece confirmar lo anterior y sugiere la posibilidad de establecer una distincion faunistica entre la Edad Mamifero Santacrucense y el Friasense.","PeriodicalId":140719,"journal":{"name":"Revista Geologica De Chile","volume":"212 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2015-04-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132194987","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A Toarcian retro-arc basin of Central Patagonia (Chubut), Argentina: Middle Jurassic closure,arc migration and tectonic setting","authors":"M. Suárez, M. Marquéz","doi":"10.4067/S0716-02082007000100004","DOIUrl":"https://doi.org/10.4067/S0716-02082007000100004","url":null,"abstract":"La Cuenca de Chubut (nuevo nombre para la Cuenca Liasica de Chubut Occidental de otros autores), desarrollada durante el Jurasico Inferior en la parte occidental de la region extra-Andina de la Patagonia central, en Argentina (42°30S y 44°30S), acumulo sedimentos continentales y de mar somero, con aporte piroclastico, de la Formacion Osta Arena y unidades equivalentes. Esta cuenca estuvo limitada al oeste por un arco magmatico (Faja Plutonica Subcordillerana) y un complejo de subduccion del Triasico tardio-Jurasico temprano (Complejo Metamorfico Los Chonos). A su vez, la parte oriental del fondo de la cuenca se desarrollo sobre un arco remanente de edad triasica superior-jurasica inferior (Batolito de Patagonia Central) y sobre las sedimentitas neopaleozoicas de un prisma de acrecion. Hacia el este, la cuenca estaba limitada por un sistema volcanico toarciano asociado a la pluma de Karroo (Formacion Marifil). El arco continuaba hacia el norte, donde esta representado por el Miembro Icalma de la Formacion Nacientes del Biobio, que bordeaba por el oeste a la Cuenca de Neuquen. El cierre de la Cuenca de Chubut ocurrio durante el Jurasico Medio y coincide en el tiempo con una brusca migracion al suroeste del arco magmatico toarciano, desde una posicion en la Patagonia central extra-Andina, con una orientacion NNW, a una ubicacion en la Cordillera Patagonica con una orientacion norte-sur. Sincronicamente, se desarrollo volcanismo silicico anatectico asociado a tectonismo extensional al este del arco. En consecuencia, durante el Jurasico Medio hubo un cambio tectonico mayor en la region patagonica. Se propone que la migracion del arco estuvo relacionada con el crecimiento de una pluma bajo Patagonia nororiental.","PeriodicalId":140719,"journal":{"name":"Revista Geologica De Chile","volume":"40 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2015-04-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124093657","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Deformación compresiva cuaternaria en la Cordillera Principal de Chile central (Cajón del Maipo, este de Santiago)","authors":"A. Lavenu, José Cembrano","doi":"10.4067/S0716-02082008000200003","DOIUrl":"https://doi.org/10.4067/S0716-02082008000200003","url":null,"abstract":"El estudio geologico y estructural detallado de sedimentos recientes en el valle del rio Maipo (Cajon del Maipo), al este de Santiago, muestra la existencia de una deformacion en compresion con fallas inversas y pliegues de arrastre contemporaneos. Estas estructuras son cinematicamente compatibles con una direccion de esfuerzo cercana a N-S (N338°E) que afecta tambien a las unidades de roca mas antiguas (Formacion Abanico), que constituyen el sustrato de las terrazas aluviales cuaternarias. En estas rocas del sustrato, se superponen dos episodios de deformacion, el primero de edad neogena (post 9 Ma), caracterizado por un al de direccion E-O; el segundo cuaternario y con un al cercano a N-S. Este ultimo episodio de deformacion resultaria de la particion regional del vector de convergencia oblicua entre las placas de Nazca y Sudamerica; un 'buttress' a los 33°S produciria el gradiente de velocidad latitudinal necesario en el antearco para conducir a un acortamiento norte-sur. La sismicidad cortical superficial en la parte interna del antearco (Cordillera Principal) es -al menos en parte- compatible con la direccion de compresion obtenida a partir del analisis cinematico de las fallas mesoscopicas.","PeriodicalId":140719,"journal":{"name":"Revista Geologica De Chile","volume":"33 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2008-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128130923","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Un nuevo espécimen de cocodrilo marino del Jurásico Medio del norte de Chile: revalidación de Metriorhynchus westermanni (Crocodyliformes: Metriorhynchidae)","authors":"Z. Gasparini, A. Paulina-Carabajal, G. Chong","doi":"10.4067/S0716-02082008000200008","DOIUrl":"https://doi.org/10.4067/S0716-02082008000200008","url":null,"abstract":"Se revalida la especie Metriorhynchus -westermanni Gasparini a partir de un nuevo especimen de cocodrilo marino caloviano (Metriohrynchidae) hallado en el curso medio de quebrada Cherejara, Sierra del Medio, Region de Antofagasta, Chile. El analisis del neurocraneo y de los huesos asociados demuestra que el holotipo de M. westermanni no es unjuvenil deMetriohrynchus casamiquelai Gasparini y Chong, como anteriormente se propuso. Varias diferencias morfologicas tales como frontal y parietal en el mismo plano, ausencia de depresion medial en el sector interorbital del frontal, piso de la fosa supratemporal plano y horizontal, narinas internas con forma de lagrima con la base mas ancha caudalmente y separadas por un septo completo, justifican revalidar a M. westermanni. De esta manera aumenta la diversidad de cocodrilos marinos jurasicos en el oeste del Gondwana, con predominio de registros chilenos en el Jurasico Medio.","PeriodicalId":140719,"journal":{"name":"Revista Geologica De Chile","volume":"93 44 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2008-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129021763","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Depósitos sinorogénicos en el antepaís neopaleozoico del cinturón de Famatina, centro-oeste de Argentina: implicancias paleoambientales, paleogeografías y tectonosedimentarias","authors":"Miguel Ezpeleta, R. Astini, F. M. Dávila","doi":"10.4067/S0716-02082008000200004","DOIUrl":"https://doi.org/10.4067/S0716-02082008000200004","url":null,"abstract":"RESUMEN:En el cinturon de Famatina, ubicado entre las provincias geologicas argentinas de Sierras Pampeanas y Precordillera, se describe y analiza una sucesion de conglomerados de -400 m, considerada en trabajos previos como la seccion superior del intervalo postglacial neopaleozoico del Grupo Paganzo (Pensilvaniano tardio). En este trabajo estos conglomerados (Formacion Las Pircas nom.nov.), extensamente desarrollados en Famatina, son separados como una unidad litoestratigrafica diferente asociada a un episodio de deformacion, sobre la base de: 1. la presencia de una discordancia angular en su base, 2. un fuerte contraste litofacial con la unidad glacial subyacente y 3. su organizacion estratigrafica interna. El analisis de facies indica un predominio de depositos de abanicos aluviales proximales, que pasan en transicion hacia sistemas fluviales entrelazados y desarrollo local de depositos lacustres. La recurrencia de megacapas con bloques y conglomerados de composicion granitica indica una significativa exhumacion de basamento, sugiriendo actividad tectonica coetanea. Asimismo, los estudios de procedencia indican participacion de clastos de areniscas fluviales pensilvanianas y volcanitas acidas ordovicicas que actualmente se exponen en la sierra de Famatina. Esto es compatible con el analisis de paleocorrientes, que muestra una dispersion de los sedimentos hacia el oeste. La posicion de los altos topograficos de basamento al este del arco principal, junto con evidencias de plegamiento, sugieren una etapa de deformacion de zocalo dentro del antepais no descrita con anterioridad. Esto permite explicar la fuente principal de esta cuna clastica depositada de este a oeste parcialmente equivalente a la Formacion Tupe en el ambito de Precordillera. Este modelo de antepais puede ser comparado con el antepais fragmentado moderno de los Andes Centrales.ABSTRACT:In the Famatina belt, western Argentina, a -400 m thick conglomerate succession is extensively developed and has been previously considered as the uppermost section of a postglacial interval (late Pennsylvanian) of the Paganzo Group. Here we separate it as a different lithostratigraphic unit (Las Pircas Formation, nom. nov.) with a significant tectonic meaning based on: 1. the angular discordance at its base; 2. the strong lito facial contrast with the underlying glacial unit and 3. its internal stratigraphic organization. Facies analyses indicate topographically controlled proximal alluvial fans succeeded by braided fluvial systems, and local development of lacustrine deposits. Granite bearing-megaboulder beds and conglomerates indicate significant basement exhumation and tectonic unroofing. Clast composition also depicts early Pennsylvanian sandstones and Ordovician volcanic rocks mainly exposed in the central part of Famatina (at present). Paleocurrent analyses are compatible with a dispersal pattern mostly to the west. The position of basement topographic high further east from the main contem","PeriodicalId":140719,"journal":{"name":"Revista Geologica De Chile","volume":"3 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2008-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"117050412","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"P-T evolution of metapelites from the Guarguaraz Complex, Argentina: evidence for Devonian crustal thickening close to the western Gondwana margin","authors":"H. Massonne, Mauricio Calderón Nettle","doi":"10.4067/S0716-02082008000200002","DOIUrl":"https://doi.org/10.4067/S0716-02082008000200002","url":null,"abstract":"In the Guarguaraz Complex of the Argentine Frontal Cordillera (latitude 33.3°S) serpentinite lenses, metabasites, and garnet-bearing metasedimentary rocks occur. The corresponding Devonian metamorphic event was assigned to the formation of an accretionary wedge by previous authors. We have tested this hypothesis by investigating the metamorphic evolution of a pelite from this complex. Garnet in this rock shows a well evolved prograde zoning. Potassic white mica with Si contents between 3.38 (core) and 3.12 (rim) per formula unit, biotite, quartz and plagioclase, which have formed late blasts at the expense of amphibole, coexist with this phase. On the basis of P-T pseudosections and water-absent equilibria, we have estimated the subsequent P-T path for the studied metapelite. The garnet core formed at about 8 kbar and 470-500°C. After nearly isothermal burial to 45 km (13.5 kbar) where Si-rich phengites grew, temperatures increased followed by exhumation and an overprint stage at 8 kbar and 565°C. This P-T path is not compatible with the idea of an accretionary wedge complex. It is more likely that the high-pressure conditions were attained by thickening of continental crust when the hypothetical Chilenia terrane collided with the continental margin of western Gondwana in Devonian times.","PeriodicalId":140719,"journal":{"name":"Revista Geologica De Chile","volume":"74 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2008-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129262484","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Edades de metamorfismo en las unidades con bajo grado de la región central del Famatina: la impronta del ciclo orogénico oclóyico (Ordovícico)","authors":"Gilda Collo, R. Astini, A. Cardona, M. D. Campo, Umberto G. Cordani","doi":"10.4067/S0716-02082008000200001","DOIUrl":"https://doi.org/10.4067/S0716-02082008000200001","url":null,"abstract":"Muchos de los episodios de metamorfismo y deformacion asociados a las rocas de bajo grado del NO argentino fueron tradicionalmente vinculados con orogenos antiguos como el pampeano (Cambrico) y el ocloyico (Ordovicico). En el cinturon del Famatina, la falta de dataciones precisas y de un analisis estratigrafico de detalle en las sucesiones con bajo grado, condujeron a interpretaciones ambiguas respecto a la evolucion paleozoica del segmento sur de los Andes Centrales. Estudios recientes establecen que el 'basamento metamorfico' de bajo grado de dicha region estaria conformado por las formaciones Negro Peinado y Achavil, cuyos analisis de procedencia las vinculan con la finalizacion del ciclo pampeano. Por su parte, la Formacion La Aguadita, tambien afectada por metamorfismo de bajo grado, corresponderia a depositos sinorogenicos ordo vicieos (ocloyieos). En consecuencia, el conjunto seria mas joven que la FormacionPunco viscana (prepampeana) con la que fue habitualmente correlacionado. Las edades K-Ar presentadas en este trabajo permiten establecer que el metamorfismo y la deformacion de estas unidades son Ordovicicos y no mas antiguos (Proterozoico-Cambrico Medio) como se interpreto durante muchos anos. Edades de 457±9 Ma (roca total) y 463±14 Ma (fraccion <2µm) obtenidas para la Formacion Negro Peinado, permiten su vinculacion con el climax de la orogenia ocloyiea, desarrollada en el margen occidental de Gondwana durante el Paleozoico inferior. Las edades de 435±12 Ma (fraccion <2µm) en la Formacion La Aguadita y de 444±8 Ma (roca total) en filonitas de la faja de deformacion angulos, son consistentes con la extension de este ciclo orogenico hasta el Silurico Inferior. Adicionalmente, se obtuvo una edad de 359±7 Ma (fraccion <2µm) en rocas de la Formacion Negro Peinado (faja de deformacion Las Trancas), que evidencia un reequilibrio local del sistema isotopico K-Ar parcialmente coincidente con el rango temporal asignado para la orogenia achaliana (Silurico Tardio-Carbonifero temprano).ABSTRACT:Many of the metamorphic and deformational events associated to low-grade units in NW Argentina have been linked with ancient orogenies, like the Pampean (Cambrian) and the Ocloyic (Ordovician) cycles. The lack of specific ages in the low-grade metamorphic rocks of the Famatina belt, as well as the absence of a detailed stratigraphic analysis, have led to ambiguous interpretations respect to the Paleozoic evolution of the southern segment of the Central Andes. Recent work allows recognition of two units within the low-grade 'metamorphic basement'; the Negro Peinado and the Achavil formations. Provenance analysis relates deposition of both units to the final stages of the Pampean cycle during the Cambrian, whereas an Ordovician (Ocloyic) synorogenic nature is suggested for the La Aguadita Formation, also traditionally included within the low-grade 'metamorphic basement'. Thus, as a whole, these units areyounger than the traditionally correlated pre-Pampean ","PeriodicalId":140719,"journal":{"name":"Revista Geologica De Chile","volume":"241 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2008-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133456199","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Depositional environments and hydrocarbon potential of the Middle Jurassic Los Molles Formation, Neuquén Basin, Argentina: palynofacies and organic geochemical data","authors":"M. Martínez, M. Prámparo, M. Quattrocchio, C. Zavala","doi":"10.4067/S0716-02082008000200005","DOIUrl":"https://doi.org/10.4067/S0716-02082008000200005","url":null,"abstract":"A multidisciplinary analysis of palynofacies in a sequence-stratigraphical framework, TOC (total organic carbon) and TAI (thermal alteration index) analyses, has been applied to outcrop samples of the uppermost Los Molles Formation (Middle Jurassic), Neuquen Basin, Argentina, in order to characterise the palaeoenvironmental and palaeo-climatic conditions during the deposition of this unit. Five types of palynofacies (P-l to P-5) have been identified and are interpreted to indicate a restricted marine to inner neritic environment. In P-1 and P-4, a marine environment close to the terrestrial source area with moderate oxidizing conditions and energy, is suggested. In P-2, the assemblage of freshwater algae, acritarchs and prasinophytes suggest a marginal marine environment influenced by fluvial discharge. In P-3, the marine microplankton content reflects conditions ranging from a marginal-marine (sub-normal salinity) to an inner neritic environment. In P-5, a dysoxic marine environment (probably marginal) is suggested. Warm and relatively humid (abundance of Cheirolepidiaceae in association withAraucariaceae) and locally humid (presence of swamps or ponds, on the alluvial plains) conditions are inferred. TOC content (65% of the analyzed samples reach TOC values over 1%), TAI values (2 to 2+, transitional between an immature phase and the window of liquid petroleum generation) and kerogen type (P-1, P-2 and P-5 show transitional characteristics between kerogen type II and III, while P-3 and P-4 show characteristics of kerogen type III and occasionally type IV), suggest that, in the studied area, the Los Molles Formation has some hydrocarbon potential. However, kerogen state suggests that the anoxic-dysoxic conditions of the site of deposition were not optimum for its preservation.","PeriodicalId":140719,"journal":{"name":"Revista Geologica De Chile","volume":"84 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2008-06-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124849292","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Depositional environment of Stelloglyphus llicoensis isp. nov.: a new radial trace fossil from the Neogene Ranquil Formation, south-central Chile","authors":"J. P. Roux, S. Nielsen, Á. Henríquez","doi":"10.4067/S0716-02082008000200006","DOIUrl":"https://doi.org/10.4067/S0716-02082008000200006","url":null,"abstract":"Stelloglyphus llicoensis isp. nov. is a large radial, discoidal to ellipsoidal trace fossil with a central shaft and single to bifurcating branches radiating from different levels. A 30 m thick measured section of the Ranquil For- mation at Punta Litre contains an associated trace fossil assemblage including Zoophycos, Chondrites, Phycosiphon, Nereites missouriensis, Lockeia siliquaria, Psammichnites(?), Parataenidium, Ophiomorpha, and Rhizocorallium, some of which reworked the Stelloglyphus traces. The sedimentology, together with micro- and macrofossils and the associated trace fossil assemblage, suggest that the succession was deposited in an outer continental shelf to slope environment in subtropical to tropical waters.","PeriodicalId":140719,"journal":{"name":"Revista Geologica De Chile","volume":"58 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2008-06-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132756994","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Jurassic to Early Cretaceous subduction-related magmatism in the Coastal Cordillera of northern Chile (18°30'-24°S): geochemistry and petrogenesis","authors":"V. Oliveros, D. Morata, L. Aguirre, G. Féraud, M. Fornari","doi":"10.4067/S0716-02082007000200003","DOIUrl":"https://doi.org/10.4067/S0716-02082007000200003","url":null,"abstract":"Jurassic to Early Cretaceous magmatism in the Coastal Cordillera of northern Chile is represented by thick sequences of mostly basaltic-andesitic to andesitic lava flows and minor sedimentary rocks. The volcanic sucession was intruded by large plutonio bodies and smaller stocks and dikes. New geochemical data, including major and trace elements for a suite of Middle to Upper Jurassic volcanic and plutonio rocks from six localities in the Coastal Cordillera (18°30'-24°S), are presented here. The volcanic rocks are characterized by their petrological and chemical homogeneity; they are highly porphyritic basaltic-andesites and andesites with calc-alkaline to high-K calc-alkaline affinities, higher LILE than HFSE abundances, negative Nb and Ti anomalies, and LREE/HREEfractionation, which are the typical compositional features of subduction-related igneous rocks. No significant differences are observed in rocks from different areas or ages, but the plutonio rocks show subparallel, less and more enriched patterns respectively compared to volcanic rocks. The evolution and differentiation of the parental magmas is mainly due to fractional crystallization dominated by plagioclase, olivine and clinopyroxene. Assimilation of the continental crust was not important, although Th and La contents would indicate increasing sediment contribution or crustal contamination of the magmas with time. The magma source is likely to be a depleted mantle metasomatized by fluids, which originated from dehydration of the subducted oceanic crust. No evidence of slab melting was found in the studied rocks. The extensional tectonic setting that dominated the evolution of the Jurassic-Early Cretaceous arc in northern Chile would have favoured the extrusion of huge amounts of volcanic rocks during a relatively short period of time, avoiding thus a mayor interaction with the continental crust.","PeriodicalId":140719,"journal":{"name":"Revista Geologica De Chile","volume":"50 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2007-12-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115619760","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}