Hans Niemeyer - Academia.edu (original) (raw)
Papers by Hans Niemeyer
Andean Geology, Jul 1, 1989
El complejo Igneo-Sedimentario del Cordón de Lila, de probable edad ordovícica, está formado por ... more El complejo Igneo-Sedimentario del Cordón de Lila, de probable edad ordovícica, está formado por 3.000 m de lavas y volcanoclastitas básicas, intermedias y ácidas con intercalaciones de limolitas y grauwacas turbidíticas. Las lavas presentan un quimismo de arco volcánico. La secuencia se habría depositado en ambiente marino de poca profundidad, mientras que hacia el techo la sedimentación pudo haberse realizado en condiciones subaéreas. Los efusivos se encuentran genéticamente ligados a numerosos cuerpos gabrodioríticos y riolíticos que penetran la secuencia, en distintos lugares. Este complejo se integra dentro de lo que se conoce como Faja Eruptiva de la Puna Occidental, un arco magmático relacionado con subducción de polaridad oriental, probablemente oblicua, que consumía, durante el Ordovícico, corteza oceánica bajo el bloque continental de Arequipa-Mejillones. La colisión de éste con el continente sudamericano habría ocurrido durante la fase orogénica Oclóyica en el Ifmite ordovícico-silúrico. La oblicuidad de la subducción se infiere sobre la base de indicios de transcurrencia a lo largo de la Falla Tucúcaro y otras fallas de rumbo submeridiano en el Cordón Lila. El soldamiento definitivo del Macizo de Arequipa-Mejillones al continente habría producido una cratonización de las zonas del arco y de tras-arco, con un alzamiento general y consecuente erosión y arrasamiento de los relieves, lo cual explica la ausencia del Silúrico en el norte de Chile. Sobre esa superficie de erosión se depositaron secuencias marinas devónicas.
Andean Geology, Aug 30, 2010
La Formación Trapa-Trapa está constituida por rocas volcánicas y volcanoclásticas del Mioceno, qu... more La Formación Trapa-Trapa está constituida por rocas volcánicas y volcanoclásticas del Mioceno, que afloran entre los 36° y 39" Lat. S, en la Cordillera Principal de los Andes de Chile. Esta unidad está formada por andesitas, andesitas basálticas y escasos basaltos y dacitas, junto a rocas epi y piroc1ásticas, e intrusivos subvolcánicos asociados. Mineralógicamente, estas rocas se componen de plagioclasa (andesina-labradorita), clinopiroxeno, ortopiroxeno y menor cantidad de hornblenda (dacitas) y olivino (basaltos). Las rocas volcánicas de la Formación Trapa-Trapa son calco alcal bas, con cantidades normales de potasio y razón K, O/Na. O menor que uno. Tienen contenidos menores de K. O que las rocas de la Formación Farellones (32 0-35 0 Lat. S) y K, O, Ba, Rb y Sr menores que la Formación Cerro de Las Tórtolas (29 0-31 0 Lat. S). Su composición química es similar a la de las rocas volcánicas del Plio-Cuaternario de este sector de los Andes, y son más pobres en Nb, Ni, Cr y Ti, que los ba
Andean Geology
The southern part of the Mid-Permian Chinquilchoro pluton consits of two approximately concentric... more The southern part of the Mid-Permian Chinquilchoro pluton consits of two approximately concentric lithofacies: an A lithofacies, external melanocratic and a leucocratic internal B lithofacies. The A lithofacies is formed by quartz diorite and quartz monzonite, and the B lithofacies lies in the limit between quartz monzodiorite and quartz monzonite. The contact between the two lithofacies is transitional and difuse. The two lithofacies are calcalkaline, metaluminous and ferric. The coexistence of both lithofacies can be explained by fractional crystallization from the same parental magma in an anorogernic tectonic environment.
Journal of South American Earth Sciences, 2018
A continental magmatic arc (the Famatinian magmatic arc) was developed on the western margin of G... more A continental magmatic arc (the Famatinian magmatic arc) was developed on the western margin of Gondwana during the Early to Middle Ordovician. This has a northwestern orientation in the northern Chile-Argentina Andes between 21° and 26° south latitude with a northeastern directed subduction zone and developed on a continental crust represented by a metamorphic basement. A paleogeographical scheme for the Ordovician magmatic arc is proposed and two tectonic environments can be recognized from our own data and data from the literature: forearc and arc. The Cordón de Lila Complex can be assigned to a forearc position. Here the turbiditic flows become paralell to the northwestern elongation of the magmatic arc. The sedimentation in the frontal-arc high platform of the forearc is represented by stromatolitic limestones and a zone of phosphate production.The internal structure of the arc can be inferred from the petrographic composition of the turbidites: basaltic and andesitic lavas, dacitic and/or rhyolitic lavas and ash fall tuffs. Also the Quebrada Grande Formation was developed on the forearc. Plutonic Ordovician rocks testify the continuity of the magmatic arc. The data about the basement exposed in the present paper do not support the existence of the Arequipa-Antofalla Terrane.
Journal of Paleontology, 1995
Fossiliferous marine Devonian has been known in Chile for less than a decade. The initial discove... more Fossiliferous marine Devonian has been known in Chile for less than a decade. The initial discovery from south of the Salar de Atacama region, in the Sierra de Almeida, northern Chile is described together with its brachiopods. The brachiopods indicate an age span of Emsian–Eifelian or Givetian, shallow-water conditions in the Benthic Assemblage 2 range, and a biogeographic boundary region between the cool climate Malvinokaffric Realm and warmer region extra-Malvinokaffric Realms, including the Eastern Americas Realm and the Rhenish-Bohemian Region of the Old World Realm. The recent discovery of a Malvinokaffric Realm trilobite far to the south in Chile, at Buill in the Andes of Chiloe, serves to underline our very preliminary knowledge of the Chilean Devonian, whereas the alleged Devonian brachiopods from the Chonos Archipelago far to the south are probably bivalves of uncertain age.
Geoscience Frontiers, 2017
The Middle Member of the Zorritas Formation in the Antofagasta region of northern Chile, yielded ... more The Middle Member of the Zorritas Formation in the Antofagasta region of northern Chile, yielded terrestrial and marine palynomorph assemblages which span the Devonian/Carboniferous boundary. The assemblages show a clear predominance of terrestrial palynomorphs with 70 miospore species, 18 marine phytoplankton species, two non-marine algae and one chitinozoan species, all coming from 15 productive levels. Palynomorphs are poorly preserved and most of them are reworked. Three palynological associations are recognized based on miospores. These are assigned to the TournaisianeVisean, Tournaisian and probable latest Famennian. Age assignments are discussed in the frame of the spore zonal schemes established for Euramerica and western Gondwana. The stratigraphical distribution of spores allows the identification of the probable position of the Devonian/Carboniferous boundary within the Zorritas Formation. This system boundary is proposed for the first time in Palaeozoic sedimentary rocks of northern Chile. The presence of Gondwanan typical miospore species indicates affinities with this palaeocontinent even though the Tournaisian and TournaisianeVisean miospore associations support the cosmopolitanism already suggested for the early Carboniferous flora. The significant number of reworked palynomorphs together with the sedimentological analysis of the studied sections, suggest that these deposits were severely impacted by the climatic change and major sea level fluctuations. Similar conditions were recorded in coeval western Gondwana basins.
Andean Geology, Jun 29, 2010
... Tanto utilizando la relación (I 002 +I 004 )/(I 001 +I 003 ) (Brown y Brindley, 1984) como la... more ... Tanto utilizando la relación (I 002 +I 004 )/(I 001 +I 003 ) (Brown y Brindley, 1984) como la relación (I 002 +I 004 )/I 003 (Petruk, 1964), se obtuvieron valores del orden de 3,2 átomos de Fe. Tanto este valor como los determinados mediante microsonda (ca. ... Petruk, W. 1964. ...
Andean Geology, 2015
In the present study a first found of agates in Chile is reported from the Cordón de Lila region ... more In the present study a first found of agates in Chile is reported from the Cordón de Lila region in northern Chile. The agates occur as veins and lenses in altered Permian volcanic rocks. The rock composition is rhyodacitic/ dacitic consisting of a fine-grained K-feldspar-quartz groundmass with phenocrysts of plagioclase (An 50-60) and pyroxene (augite). The volcanic host rocks show strong features of alteration and brecciation. Results of XRD, polarizing microscopy and cathodoluminescence (CL) microscopy and spectroscopy point to a late-to postvolcanic formation of the agates by hydrothermal f luids and SiO 2 which was released during the alteration of unstable minerals and volcanic glass. Strongly varying agate micro-textures and the appearance of euhedral quartz crystals with µm-sized growth lamellae (so called Bambauer quartz) indicate fluctuations in the physico-chemical conditions (SiO 2 concentration, pH) during alteration and agate formation. Another indication for the alteration processes is the occurrence of secondary calcite in the agate-bearing rocks.
Earth-Science Reviews, 2016
Supposed pre-Mesozoic igneous and metamorphic rocks from northern Chile are reviewed in the light... more Supposed pre-Mesozoic igneous and metamorphic rocks from northern Chile are reviewed in the light of twentyone new SHRIMP U-Pb zircon age determinations. Metamorphic rocks from the precordillera upthrust belt mostly show a wide spectrum of zircon ages, indicating derivation from sedimentary protoliths. Youngest detrital zircon ages (i.e., maximum depositional ages) range from c. 850 Ma at Belén to 1000-1100 Ma in Sierra de Moreno and Cordón de Lila. Late Proterozoic provenance throughout the region corresponds to a c. 1 Ga igneous and metamorphic event. The main source region could have been the Proterozoic MARA block or Laurentia to the west. Early Ordovician plutonic rocks (465-485 Ma) correlated with the Famatinian magmatism of NW Argentina are recognised in all three outcrop areas, and contemporaneous volcanic rocks in Cordón de Lila. Hfand O-isotope data for Ordovician zircon in these rocks, and for c. 1450 detrital zircon in the metasedimentary rocks, are consistent with ultimate derivation from Early Mesoproterozoic to Paleoproterozoic lithosphere. A depositional age younger than 400 Ma is determined for the Quebrada Aroma metamorphic complex, indicating post-Early Silurian metamorphism and folding. Carboniferous igneous and deformational events occur in the Coast Range, where metasedimentary complexes are mostly related to Late Paleozoic subduction-accretion; deformation and metamorphism continued near the present Pacific shore line until Triassic and earliest Jurassic times. The underlying crust of much of Norte Grande is considered to be Proterozoic (Arequipa-Antofalla block or MARA), although there are no igneous rock outcrops of this age.
Andean Geology, Dec 1, 1997
... Niemeyer et al. (1985), los cuales deben considerarse erróneos. Page 9. H. Niemeyer, R. Veneg... more ... Niemeyer et al. (1985), los cuales deben considerarse erróneos. Page 9. H. Niemeyer, R. Venegas, CR González y FG Aceñolaza En cuanto a ... al. , 1963). Qm-cuarzo monocristalino; F-fel·jespato; Lt-Iíticos tota-les. 1-interior ...
Journal of the Geological Society, 2015
The palaeo-Pacific margin of Gondwana in the present-day south–central Andes is marked by tectoni... more The palaeo-Pacific margin of Gondwana in the present-day south–central Andes is marked by tectonic activity related to subduction and terrane accretion. We present detrital zircon U–Pb data encompassing the Palaeozoic era in northern Chile and northwestern Argentina. Cathodoluminescence images reveal dominantly magmatic zircon barely affected by abrasion and displaying only one growth phase. The main age clusters for these zircon grains are Ediacaran to Palaeozoic with an additional peak at 1.3–0.9 Ga and they can be correlated with ‘Grenvillian’ age, and the Brasiliano, Pampean, and Famatinian orogenies. The zircon data reveal main transport from the nearby Ordovician Famatinian arc and related rocks. The Silurian sandstone units are more comparable with Cambrian units, with Brasiliano and Transamazonian ages (2.2–1.9 Ga) being more common, because the Silurian deposits were situated within or east of the (extinct) Famatinian arc. Hence, the arc acted as a transport barrier throughout Palaeozoic time. The complete suite of zircon ages does not record the accretions of exotic terranes or the Palaeozoic glacial periods. We conclude that the transport system along the palaeo-Pacific margin of Gondwana remained stable for c. 0.3 byr and that provenance data do not necessarily reflect the interior of a continent. Hence, inherited geomorphological features must be taken into account when detrital mineral ages are interpreted. Supplementary material: U–Pb data, CL images, and detailed geological maps are available at www.geolsoc.org.uk/SUP18796.
Journal of South American Earth Sciences, 2014
International Journal of Earth Sciences, 2010
Andean Geology, 2009
es paralelo a la fosa chileno-peruana en el norte de Chile. Se analizaron los desplazamientos en ... more es paralelo a la fosa chileno-peruana en el norte de Chile. Se analizaron los desplazamientos en el rumbo y en la vertical de una de sus fallas maestras: la Falla Sierra de Varas (FSV). Ésta se estudió en el segmento entre Aguada del Hornito y Aguada del Cerro Alto de Varas, sobre la base del desplazamiento en el rumbo de dos porciones de la unidad de Granitoides paleozoicos con idéntica petrografía, estructura interna y edad. Se determinó una separación sinistral horizontal de 15,6±1 km con una componente vertical de 4,9±0,1 km, lo cual implica un rechazo neto sinistral-inverso de 16,4±1 km. El alzamiento vertical está de acuerdo con el espesor estratigráfi co erosionado del bloque oriental. Se investigó, además, la dinámica y cinemática de la FSV mediante el análisis de mesofallas asociadas a sus desplazamientos. Se determinó así un sistema estructural sinistral-inverso, que tuvo lugar durante el Eoceno medio tardío. Un segundo sistema estructural dextral, con desplazamiento de 0,6 km se sobrepuso sobre el anterior y ocurrió con posterioridad al Mioceno. Los desplazamientos simultáneos, tanto en el rumbo como según fallas inversas, dados por la existencia de una 'fl or inversa' en el segmento estudiado, indican que éste fue afectado primeramente por una transpresión. El desplazamiento sinistral demostrado para la FSV y su cambio de rumbo hacia el SE, inmediatamente al sur de Aguada de Alto de Varas, son compatibles con la vergencia hacia el oeste de pliegues y fallas inversas asociadas del cinturón plegado y corrido de El Profeta, el cual también habría resultado de la transpresión.
Revista geológica de Chile, 2007
La interacción entre magmas ácidos y básicos ha sido ampliamente documentada en plutones y batoli... more La interacción entre magmas ácidos y básicos ha sido ampliamente documentada en plutones y batolitos de arcos magmáticos. El Plutón Sierra de Varas (PSV), un cuerpo granítico elíptico zonado expuesto en el norte de Chile, y que se emplazó durante el límite Carbonífero-Pérmico (~300 Ma), muestra evidencias de interacción sinmagmática con magmas básicos durante el emplazamiento. Esta interacción se manifiesta en la presencia de intrusiones de gabro, enclaves máficos y diques segmentados, los que exhiben bordes enfriados, contactos lobulados e intercambio de xenocristales con la roca granítica. Los datos termobarométricos en rocas del Plutón Sierra de Varas indican temperaturas de ~750ºC para el equilibrio anfíbola-plagioclasa y de 0,26 a 0,36 GPa (Al total en hornblenda), estimándose una profundidad de emplazamiento de entre 7 y 10 km. La termobarometría de anfíbolas en diques diabásicos sinmagmáticos entrega temperaturas de 785 a 840ºC y presiones de 0,20-0,45 GPa (barómetro semicuantitativo de Al 2 O 3-TiO 2) para los centros de los cristales. El paso progresivo desde diques segmentados a enclaves elípticos se atribuye a un proceso de 'mingling' entre el magma ácido y los magmas básicos que intruyeron episódicamente durante el enfriamiento del plutón, en el nivel de emplazamiento del Plutón Sierra de Varas en la corteza superior.
Revista geológica de Chile, 2007
Revista geológica de Chile, 1999
espanolSe estudio la Falla Sierra Castillo y sus estructuras mesoscopicas conexas en Quebrada del... more espanolSe estudio la Falla Sierra Castillo y sus estructuras mesoscopicas conexas en Quebrada del Carrizo y sus alrededores, donde al este yuxtapone terrenos triasicos y paleozoicos, con terrenos bajocianos al oeste. en dicha falla juega el papel de falla maestra respecto de sus estructuras conexas. Se infiere que sus movimientos eoceno-oligocenos estuvieron dominados por 'stresses' transpresivos con transcurrencia sinistral. Esta inferencia surge del estudio de estructuras S-C en rocas de falla, y en la vergencia de un pliegue de arrastre, directamente observados sobre la traza de la falla. Sus estructuras conexas son compatibles con dicho sentido de movimiento y estan formadas por fallas inversas, pliegues ptigmaticos, grietas de tension, clivaje; ademas de vetas y fallas subverticales en posicion T (tension) y R (Riedel). Se determinaron las direcciones y sentidos del transporte tectonico sobre la base de la cinematica de fallas inversas y la interseccion de estas con el clivaje. Se deduce una rotacion de 65° en el sentido horario de la direccion de acortamiento, desde un rumbo oeste hasta uno nor-noroeste. Por otro lado, se considero la alternativa que las rocas hayan rotado en sentido antihorario, conservandose constante la direccion de acortamiento. EnglishThe Sierra Castillo Fault and its associated mesoscopic structures were studied at Quebrada del Carrizo. Here the fault juxtaposes Triassic and Paleozoic rocks on the east with Bajocian rocks on the west. The Sierra Castillo Fault serves as a master fault of its associated mesoscopic structures. It is inferred that a sinistral traspression occurred along it during the Eocene-Oligocene. This inference is based on S-C structures and a drag fold directly observed on the trace of the fault. This deduction is also based on other associated structures such as reverse faults, ptygmatic folds, tensional gashes and cleavage. Subvertical veins and faults in positions T (tension) and R (Riedel) were also identified. Transport directions and sense were determined studying the kinematics of reverse faults and the intersection between reverse faults and cleavage. A 65° clockwise rotation of the shortening direction from a west position to a north-northwest position is detected. An alternative solution considered is the anticlockwise rotation of the rocks, with the shortening direction remaining constant.
Revista geológica de Chile, 2008
In this contribution, we present a reassessment of the Pular Formation age (Sierra de Almeida, An... more In this contribution, we present a reassessment of the Pular Formation age (Sierra de Almeida, Antofagasta) that in previous papers was attributed to either the Late Paleozoic or Triassic. At Quebrada del Medio, the Pular Formation includes a 379-meter-thick stratigraphic section formed from base to top by conglomerates, sandstones, black bituminous shales and limestones, tuffaceous sandstones and a poorly welded ignimbrite that accumulated in fl uvial and lacustrine environments. A multidisciplinary study of the fl ora and fauna was undertaken. The existence of diagnostic Gondwana microfl ora and macrofl ora allows attributing a Middle Triassic to early Late Triassic age to the Pular Formation.
Andean Geology, Jul 1, 1989
El complejo Igneo-Sedimentario del Cordón de Lila, de probable edad ordovícica, está formado por ... more El complejo Igneo-Sedimentario del Cordón de Lila, de probable edad ordovícica, está formado por 3.000 m de lavas y volcanoclastitas básicas, intermedias y ácidas con intercalaciones de limolitas y grauwacas turbidíticas. Las lavas presentan un quimismo de arco volcánico. La secuencia se habría depositado en ambiente marino de poca profundidad, mientras que hacia el techo la sedimentación pudo haberse realizado en condiciones subaéreas. Los efusivos se encuentran genéticamente ligados a numerosos cuerpos gabrodioríticos y riolíticos que penetran la secuencia, en distintos lugares. Este complejo se integra dentro de lo que se conoce como Faja Eruptiva de la Puna Occidental, un arco magmático relacionado con subducción de polaridad oriental, probablemente oblicua, que consumía, durante el Ordovícico, corteza oceánica bajo el bloque continental de Arequipa-Mejillones. La colisión de éste con el continente sudamericano habría ocurrido durante la fase orogénica Oclóyica en el Ifmite ordovícico-silúrico. La oblicuidad de la subducción se infiere sobre la base de indicios de transcurrencia a lo largo de la Falla Tucúcaro y otras fallas de rumbo submeridiano en el Cordón Lila. El soldamiento definitivo del Macizo de Arequipa-Mejillones al continente habría producido una cratonización de las zonas del arco y de tras-arco, con un alzamiento general y consecuente erosión y arrasamiento de los relieves, lo cual explica la ausencia del Silúrico en el norte de Chile. Sobre esa superficie de erosión se depositaron secuencias marinas devónicas.
Andean Geology, Aug 30, 2010
La Formación Trapa-Trapa está constituida por rocas volcánicas y volcanoclásticas del Mioceno, qu... more La Formación Trapa-Trapa está constituida por rocas volcánicas y volcanoclásticas del Mioceno, que afloran entre los 36° y 39" Lat. S, en la Cordillera Principal de los Andes de Chile. Esta unidad está formada por andesitas, andesitas basálticas y escasos basaltos y dacitas, junto a rocas epi y piroc1ásticas, e intrusivos subvolcánicos asociados. Mineralógicamente, estas rocas se componen de plagioclasa (andesina-labradorita), clinopiroxeno, ortopiroxeno y menor cantidad de hornblenda (dacitas) y olivino (basaltos). Las rocas volcánicas de la Formación Trapa-Trapa son calco alcal bas, con cantidades normales de potasio y razón K, O/Na. O menor que uno. Tienen contenidos menores de K. O que las rocas de la Formación Farellones (32 0-35 0 Lat. S) y K, O, Ba, Rb y Sr menores que la Formación Cerro de Las Tórtolas (29 0-31 0 Lat. S). Su composición química es similar a la de las rocas volcánicas del Plio-Cuaternario de este sector de los Andes, y son más pobres en Nb, Ni, Cr y Ti, que los ba
Andean Geology
The southern part of the Mid-Permian Chinquilchoro pluton consits of two approximately concentric... more The southern part of the Mid-Permian Chinquilchoro pluton consits of two approximately concentric lithofacies: an A lithofacies, external melanocratic and a leucocratic internal B lithofacies. The A lithofacies is formed by quartz diorite and quartz monzonite, and the B lithofacies lies in the limit between quartz monzodiorite and quartz monzonite. The contact between the two lithofacies is transitional and difuse. The two lithofacies are calcalkaline, metaluminous and ferric. The coexistence of both lithofacies can be explained by fractional crystallization from the same parental magma in an anorogernic tectonic environment.
Journal of South American Earth Sciences, 2018
A continental magmatic arc (the Famatinian magmatic arc) was developed on the western margin of G... more A continental magmatic arc (the Famatinian magmatic arc) was developed on the western margin of Gondwana during the Early to Middle Ordovician. This has a northwestern orientation in the northern Chile-Argentina Andes between 21° and 26° south latitude with a northeastern directed subduction zone and developed on a continental crust represented by a metamorphic basement. A paleogeographical scheme for the Ordovician magmatic arc is proposed and two tectonic environments can be recognized from our own data and data from the literature: forearc and arc. The Cordón de Lila Complex can be assigned to a forearc position. Here the turbiditic flows become paralell to the northwestern elongation of the magmatic arc. The sedimentation in the frontal-arc high platform of the forearc is represented by stromatolitic limestones and a zone of phosphate production.The internal structure of the arc can be inferred from the petrographic composition of the turbidites: basaltic and andesitic lavas, dacitic and/or rhyolitic lavas and ash fall tuffs. Also the Quebrada Grande Formation was developed on the forearc. Plutonic Ordovician rocks testify the continuity of the magmatic arc. The data about the basement exposed in the present paper do not support the existence of the Arequipa-Antofalla Terrane.
Journal of Paleontology, 1995
Fossiliferous marine Devonian has been known in Chile for less than a decade. The initial discove... more Fossiliferous marine Devonian has been known in Chile for less than a decade. The initial discovery from south of the Salar de Atacama region, in the Sierra de Almeida, northern Chile is described together with its brachiopods. The brachiopods indicate an age span of Emsian–Eifelian or Givetian, shallow-water conditions in the Benthic Assemblage 2 range, and a biogeographic boundary region between the cool climate Malvinokaffric Realm and warmer region extra-Malvinokaffric Realms, including the Eastern Americas Realm and the Rhenish-Bohemian Region of the Old World Realm. The recent discovery of a Malvinokaffric Realm trilobite far to the south in Chile, at Buill in the Andes of Chiloe, serves to underline our very preliminary knowledge of the Chilean Devonian, whereas the alleged Devonian brachiopods from the Chonos Archipelago far to the south are probably bivalves of uncertain age.
Geoscience Frontiers, 2017
The Middle Member of the Zorritas Formation in the Antofagasta region of northern Chile, yielded ... more The Middle Member of the Zorritas Formation in the Antofagasta region of northern Chile, yielded terrestrial and marine palynomorph assemblages which span the Devonian/Carboniferous boundary. The assemblages show a clear predominance of terrestrial palynomorphs with 70 miospore species, 18 marine phytoplankton species, two non-marine algae and one chitinozoan species, all coming from 15 productive levels. Palynomorphs are poorly preserved and most of them are reworked. Three palynological associations are recognized based on miospores. These are assigned to the TournaisianeVisean, Tournaisian and probable latest Famennian. Age assignments are discussed in the frame of the spore zonal schemes established for Euramerica and western Gondwana. The stratigraphical distribution of spores allows the identification of the probable position of the Devonian/Carboniferous boundary within the Zorritas Formation. This system boundary is proposed for the first time in Palaeozoic sedimentary rocks of northern Chile. The presence of Gondwanan typical miospore species indicates affinities with this palaeocontinent even though the Tournaisian and TournaisianeVisean miospore associations support the cosmopolitanism already suggested for the early Carboniferous flora. The significant number of reworked palynomorphs together with the sedimentological analysis of the studied sections, suggest that these deposits were severely impacted by the climatic change and major sea level fluctuations. Similar conditions were recorded in coeval western Gondwana basins.
Andean Geology, Jun 29, 2010
... Tanto utilizando la relación (I 002 +I 004 )/(I 001 +I 003 ) (Brown y Brindley, 1984) como la... more ... Tanto utilizando la relación (I 002 +I 004 )/(I 001 +I 003 ) (Brown y Brindley, 1984) como la relación (I 002 +I 004 )/I 003 (Petruk, 1964), se obtuvieron valores del orden de 3,2 átomos de Fe. Tanto este valor como los determinados mediante microsonda (ca. ... Petruk, W. 1964. ...
Andean Geology, 2015
In the present study a first found of agates in Chile is reported from the Cordón de Lila region ... more In the present study a first found of agates in Chile is reported from the Cordón de Lila region in northern Chile. The agates occur as veins and lenses in altered Permian volcanic rocks. The rock composition is rhyodacitic/ dacitic consisting of a fine-grained K-feldspar-quartz groundmass with phenocrysts of plagioclase (An 50-60) and pyroxene (augite). The volcanic host rocks show strong features of alteration and brecciation. Results of XRD, polarizing microscopy and cathodoluminescence (CL) microscopy and spectroscopy point to a late-to postvolcanic formation of the agates by hydrothermal f luids and SiO 2 which was released during the alteration of unstable minerals and volcanic glass. Strongly varying agate micro-textures and the appearance of euhedral quartz crystals with µm-sized growth lamellae (so called Bambauer quartz) indicate fluctuations in the physico-chemical conditions (SiO 2 concentration, pH) during alteration and agate formation. Another indication for the alteration processes is the occurrence of secondary calcite in the agate-bearing rocks.
Earth-Science Reviews, 2016
Supposed pre-Mesozoic igneous and metamorphic rocks from northern Chile are reviewed in the light... more Supposed pre-Mesozoic igneous and metamorphic rocks from northern Chile are reviewed in the light of twentyone new SHRIMP U-Pb zircon age determinations. Metamorphic rocks from the precordillera upthrust belt mostly show a wide spectrum of zircon ages, indicating derivation from sedimentary protoliths. Youngest detrital zircon ages (i.e., maximum depositional ages) range from c. 850 Ma at Belén to 1000-1100 Ma in Sierra de Moreno and Cordón de Lila. Late Proterozoic provenance throughout the region corresponds to a c. 1 Ga igneous and metamorphic event. The main source region could have been the Proterozoic MARA block or Laurentia to the west. Early Ordovician plutonic rocks (465-485 Ma) correlated with the Famatinian magmatism of NW Argentina are recognised in all three outcrop areas, and contemporaneous volcanic rocks in Cordón de Lila. Hfand O-isotope data for Ordovician zircon in these rocks, and for c. 1450 detrital zircon in the metasedimentary rocks, are consistent with ultimate derivation from Early Mesoproterozoic to Paleoproterozoic lithosphere. A depositional age younger than 400 Ma is determined for the Quebrada Aroma metamorphic complex, indicating post-Early Silurian metamorphism and folding. Carboniferous igneous and deformational events occur in the Coast Range, where metasedimentary complexes are mostly related to Late Paleozoic subduction-accretion; deformation and metamorphism continued near the present Pacific shore line until Triassic and earliest Jurassic times. The underlying crust of much of Norte Grande is considered to be Proterozoic (Arequipa-Antofalla block or MARA), although there are no igneous rock outcrops of this age.
Andean Geology, Dec 1, 1997
... Niemeyer et al. (1985), los cuales deben considerarse erróneos. Page 9. H. Niemeyer, R. Veneg... more ... Niemeyer et al. (1985), los cuales deben considerarse erróneos. Page 9. H. Niemeyer, R. Venegas, CR González y FG Aceñolaza En cuanto a ... al. , 1963). Qm-cuarzo monocristalino; F-fel·jespato; Lt-Iíticos tota-les. 1-interior ...
Journal of the Geological Society, 2015
The palaeo-Pacific margin of Gondwana in the present-day south–central Andes is marked by tectoni... more The palaeo-Pacific margin of Gondwana in the present-day south–central Andes is marked by tectonic activity related to subduction and terrane accretion. We present detrital zircon U–Pb data encompassing the Palaeozoic era in northern Chile and northwestern Argentina. Cathodoluminescence images reveal dominantly magmatic zircon barely affected by abrasion and displaying only one growth phase. The main age clusters for these zircon grains are Ediacaran to Palaeozoic with an additional peak at 1.3–0.9 Ga and they can be correlated with ‘Grenvillian’ age, and the Brasiliano, Pampean, and Famatinian orogenies. The zircon data reveal main transport from the nearby Ordovician Famatinian arc and related rocks. The Silurian sandstone units are more comparable with Cambrian units, with Brasiliano and Transamazonian ages (2.2–1.9 Ga) being more common, because the Silurian deposits were situated within or east of the (extinct) Famatinian arc. Hence, the arc acted as a transport barrier throughout Palaeozoic time. The complete suite of zircon ages does not record the accretions of exotic terranes or the Palaeozoic glacial periods. We conclude that the transport system along the palaeo-Pacific margin of Gondwana remained stable for c. 0.3 byr and that provenance data do not necessarily reflect the interior of a continent. Hence, inherited geomorphological features must be taken into account when detrital mineral ages are interpreted. Supplementary material: U–Pb data, CL images, and detailed geological maps are available at www.geolsoc.org.uk/SUP18796.
Journal of South American Earth Sciences, 2014
International Journal of Earth Sciences, 2010
Andean Geology, 2009
es paralelo a la fosa chileno-peruana en el norte de Chile. Se analizaron los desplazamientos en ... more es paralelo a la fosa chileno-peruana en el norte de Chile. Se analizaron los desplazamientos en el rumbo y en la vertical de una de sus fallas maestras: la Falla Sierra de Varas (FSV). Ésta se estudió en el segmento entre Aguada del Hornito y Aguada del Cerro Alto de Varas, sobre la base del desplazamiento en el rumbo de dos porciones de la unidad de Granitoides paleozoicos con idéntica petrografía, estructura interna y edad. Se determinó una separación sinistral horizontal de 15,6±1 km con una componente vertical de 4,9±0,1 km, lo cual implica un rechazo neto sinistral-inverso de 16,4±1 km. El alzamiento vertical está de acuerdo con el espesor estratigráfi co erosionado del bloque oriental. Se investigó, además, la dinámica y cinemática de la FSV mediante el análisis de mesofallas asociadas a sus desplazamientos. Se determinó así un sistema estructural sinistral-inverso, que tuvo lugar durante el Eoceno medio tardío. Un segundo sistema estructural dextral, con desplazamiento de 0,6 km se sobrepuso sobre el anterior y ocurrió con posterioridad al Mioceno. Los desplazamientos simultáneos, tanto en el rumbo como según fallas inversas, dados por la existencia de una 'fl or inversa' en el segmento estudiado, indican que éste fue afectado primeramente por una transpresión. El desplazamiento sinistral demostrado para la FSV y su cambio de rumbo hacia el SE, inmediatamente al sur de Aguada de Alto de Varas, son compatibles con la vergencia hacia el oeste de pliegues y fallas inversas asociadas del cinturón plegado y corrido de El Profeta, el cual también habría resultado de la transpresión.
Revista geológica de Chile, 2007
La interacción entre magmas ácidos y básicos ha sido ampliamente documentada en plutones y batoli... more La interacción entre magmas ácidos y básicos ha sido ampliamente documentada en plutones y batolitos de arcos magmáticos. El Plutón Sierra de Varas (PSV), un cuerpo granítico elíptico zonado expuesto en el norte de Chile, y que se emplazó durante el límite Carbonífero-Pérmico (~300 Ma), muestra evidencias de interacción sinmagmática con magmas básicos durante el emplazamiento. Esta interacción se manifiesta en la presencia de intrusiones de gabro, enclaves máficos y diques segmentados, los que exhiben bordes enfriados, contactos lobulados e intercambio de xenocristales con la roca granítica. Los datos termobarométricos en rocas del Plutón Sierra de Varas indican temperaturas de ~750ºC para el equilibrio anfíbola-plagioclasa y de 0,26 a 0,36 GPa (Al total en hornblenda), estimándose una profundidad de emplazamiento de entre 7 y 10 km. La termobarometría de anfíbolas en diques diabásicos sinmagmáticos entrega temperaturas de 785 a 840ºC y presiones de 0,20-0,45 GPa (barómetro semicuantitativo de Al 2 O 3-TiO 2) para los centros de los cristales. El paso progresivo desde diques segmentados a enclaves elípticos se atribuye a un proceso de 'mingling' entre el magma ácido y los magmas básicos que intruyeron episódicamente durante el enfriamiento del plutón, en el nivel de emplazamiento del Plutón Sierra de Varas en la corteza superior.
Revista geológica de Chile, 2007
Revista geológica de Chile, 1999
espanolSe estudio la Falla Sierra Castillo y sus estructuras mesoscopicas conexas en Quebrada del... more espanolSe estudio la Falla Sierra Castillo y sus estructuras mesoscopicas conexas en Quebrada del Carrizo y sus alrededores, donde al este yuxtapone terrenos triasicos y paleozoicos, con terrenos bajocianos al oeste. en dicha falla juega el papel de falla maestra respecto de sus estructuras conexas. Se infiere que sus movimientos eoceno-oligocenos estuvieron dominados por 'stresses' transpresivos con transcurrencia sinistral. Esta inferencia surge del estudio de estructuras S-C en rocas de falla, y en la vergencia de un pliegue de arrastre, directamente observados sobre la traza de la falla. Sus estructuras conexas son compatibles con dicho sentido de movimiento y estan formadas por fallas inversas, pliegues ptigmaticos, grietas de tension, clivaje; ademas de vetas y fallas subverticales en posicion T (tension) y R (Riedel). Se determinaron las direcciones y sentidos del transporte tectonico sobre la base de la cinematica de fallas inversas y la interseccion de estas con el clivaje. Se deduce una rotacion de 65° en el sentido horario de la direccion de acortamiento, desde un rumbo oeste hasta uno nor-noroeste. Por otro lado, se considero la alternativa que las rocas hayan rotado en sentido antihorario, conservandose constante la direccion de acortamiento. EnglishThe Sierra Castillo Fault and its associated mesoscopic structures were studied at Quebrada del Carrizo. Here the fault juxtaposes Triassic and Paleozoic rocks on the east with Bajocian rocks on the west. The Sierra Castillo Fault serves as a master fault of its associated mesoscopic structures. It is inferred that a sinistral traspression occurred along it during the Eocene-Oligocene. This inference is based on S-C structures and a drag fold directly observed on the trace of the fault. This deduction is also based on other associated structures such as reverse faults, ptygmatic folds, tensional gashes and cleavage. Subvertical veins and faults in positions T (tension) and R (Riedel) were also identified. Transport directions and sense were determined studying the kinematics of reverse faults and the intersection between reverse faults and cleavage. A 65° clockwise rotation of the shortening direction from a west position to a north-northwest position is detected. An alternative solution considered is the anticlockwise rotation of the rocks, with the shortening direction remaining constant.
Revista geológica de Chile, 2008
In this contribution, we present a reassessment of the Pular Formation age (Sierra de Almeida, An... more In this contribution, we present a reassessment of the Pular Formation age (Sierra de Almeida, Antofagasta) that in previous papers was attributed to either the Late Paleozoic or Triassic. At Quebrada del Medio, the Pular Formation includes a 379-meter-thick stratigraphic section formed from base to top by conglomerates, sandstones, black bituminous shales and limestones, tuffaceous sandstones and a poorly welded ignimbrite that accumulated in fl uvial and lacustrine environments. A multidisciplinary study of the fl ora and fauna was undertaken. The existence of diagnostic Gondwana microfl ora and macrofl ora allows attributing a Middle Triassic to early Late Triassic age to the Pular Formation.