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Petrografía y geoquímica del magmatIsmo cretácico superior-eoceno en el área de PichaIhue, provincia de Neuquén Petrography and geochemistry of Upper Cretaceous-Eocene magmatism in the Pichaihue area, Neuquén Province  [cached]
M. Paula Mateo Fernández Caso,Daniel G Montero,Pablo R Leal,Victor A Ramos
Revista de la Asociación Geológica Argentina , 2011,
Abstract: Hacia fines del Mesozoico, en el sector noroeste de la provincia de Neuquén se desarrolló un magmatismo asociado a la evolución y migración del arco andino desde los 36o40' hasta los 38o20' de latitud sur. En base a estudios petrológicos, se caracterizaron facies hipabisales y extrusivas que afloran en el área de Pichaihue. Las primeras están compuestas por andesitas que se emplazan como lacolitos, diques o filones capa intruyendo las secuencias sedimentarias mesozoicas. También se reconocen afloramientos de basaltos. Las facies extrusivas están constituidas principalmente por coladas brechosas, coladas masivas y peque os domos. La geoquímica evidencia una impronta calcoalcalina, de arco volcánico, con una corteza de espesor normal y patrones de elementos traza que sugieren una misma fuente. Dentro del marco regional, se pueden distinguir tres grupos: los diques del cerro Mocho con alto contenido en Ti y mayor relación Sm/Yb, magmatismo cretácico superior-paleoceno al que pertenecen las facies extrusivas (Andesita Rivera) y un evento eoceno al cual corresponden las facies hipabisales (Diques de Colipilli). Por último, la presencia de estas rocas en este segmento de los Andes evidencia una importante migración hacia el este del arco volcánico cretácico superior-eoceno indicando su posición más oriental. Magmatism related to the growth and migration of the Andean arc was developed from the 36o40'S to the 38o20'S latitude, in the northwestern sector of the Neuquén Province, by the end of the Mesozoic. Hypabyssal and extrusive facies, which outcrop in the Pichaihue area, were described based on petrologic studies. The first ones are composed of andesites that are emplaced as lacoliths, dikes or sills intruding the Mesozoic sedimentary sequences. In addition, basalts outcrops were recognized. The extrusive facies consist of breccia or massive lavas and little domes. The geochemistry reveals an arc-like calc-alkaline signature with a normal crust and trace-element patterns which suggest a similar source. Based on regional knowledge, three groups are proposed: Cerro Mocho dikes with Ti anomalies and higher Sm/Yb; extrusive facies of the Upper Cretaceous-Paleocene (Rivera Andesite); and the hypabyssal facies of thr Eocene (Colipilli Dikes). Finally, the occurrences of these rocks in this segment of the Andes indicate an important shift to the East of the Upper Cretaceous-Eocene volcanic arc that reveals its easternmost position.
Mesozoic–Cenozoic Evolution of the Western Margin of South America: Case Study of the Peruvian Andes  [PDF]
O. Adrian Pfiffner,Laura Gonzalez
Geosciences , 2013, DOI: 10.3390/geosciences3020262
Abstract: Based on the structural style and physiographic criteria, the Central Andes of Peru can be divided into segments running parallel to the Pacific coast. The westernmost segment, the Coastal Belt, consists of a Late Jurassic–Cretaceous volcanic arc sequence that was accreted to the South American craton in Cretaceous times. The Mesozoic strata of the adjacent Western Cordillera represent an ENE-vergent fold-and-thrust belt that formed in Eocene times. Tight upright folds developed above a shallow detachment horizon in the West, while more open folds formed above a deeper detachment horizon towards the East and in the neighboring Central Highlands. A completely different style with steeply dipping reverse faults and open folds affecting the Neoproterozoic crystalline basement is typical for the Eastern Cordillera. The Subandean Zone is characterized by mainly NE-vergent imbricate thrusting which occurred in Neogene times. A quantitative estimate of the shortening of the orogen obtained from balanced cross-sections indicates a total shortening of 120–150 km (24%–27%). This shortening was coevel with the Neogene westward drift of South America, occurred at rates between 3 and 4.7 mm/year and was responsible for the high elevation of the Peruvian Andes.
Zeolite assemblages from Northern Patagonian Andes, Argentina: A review
Leal, Pablo Rodrigo;Vattuone, María Elena;Latorre, Carlos Oscar;
Revista mexicana de ciencias geológicas , 2011,
Abstract: in this work very low-grade metamorphic assemblages found in the northern patagonian andes (argentina) are summarized. on the basis of previous studies, several occurrences of zeolites have been delimited. according to their mineralogy, textures and structures, three different alteration stages that evidence a progressive decrease in temperature have been established. the first one (stage i) was the consequence of an event of regional metamorphism that reached the greenschist facies (350 °c and 2 kbar). during this stage, pyroxene, amphibole and feldspar primary phenocrysts broke down to produce an assemblage of actinolite, grossular-andradite, chlorite, albite, prehnite, titanite, clinozoisite, epidote and calcite. in the subsequent stages, direct hydrothermal precipitation took place as the temperature decreased. thus, zeolites, calc-silicates, calcite, quartz and cristobalite started to precipitate as cavity fillings. during stage ii, temperature decreased below 220 °c and wairakite, yugawaralite, laumontite, pectolite, dachiardite, celadonite, thomsonite, pumpellyite and interstratified chlorite/smectite crystallized. prehnite, adularia, titanite and albite were also deposited but only as minor species. these minerals mainly alter feldspar phenocrysts and fill amygdules of basalts and andesites. stage iii is characterized by a temperature drop (below 180 °c) and by the crystallization of hydrothermal secondary minerals within open spaces. most of the alkaline zeolites were deposited during this last event of alteration, filling joints in metabasites and granitoids. although ca-stilbite is the most abundant alteration mineral, analcime, natrolite, barrerite, offretite, chabazite, stellerite, heulandite, mordenite, scolecite, mesolite, quartz, calcite, cristobalite and smectites were also produced.
Magmatic sources, setting and causes of Eocene to Recent Patagonian plateau magmatism (36°S to 52°S latitude) Fuentes magmáticas, ambientes y causas del magmatismo de plateau Eoceno a Reciente en la Patagonia (36°S a 52°S latitud)  [cached]
S.M. Kay,M. Gorring,V.A. Ramos
Revista de la Asociación Geológica Argentina , 2004,
Abstract: Continental back-arc and within-plate basaltic volcanic provinces provide a view into the evolution of the mantle beneath continents and the mass flux of materials that are subducted, but not extracted by arc volcanism. One of the largest continental mafic provinces is the Patagonian province where large mafic plateau volcanic events ranging in age from late Paleocene to Recent have occurred in the absence of major extension. The largest events produced the Eocene Posadas Formation (~ 46°S to 50°S), the late Oligocene to early Miocene Somuncura magmatic province (41°S to 43°S plus similar age magmas up to 46°S), the late Miocene to Pliocene lavas east of the Chile Triple Junction (~46°S to 49°S), and the Payunia magmatic province (36°S to 38.5°S). Tectonically, the Posadas and Triple Junction provinces have been respectively associated with Eocene and Miocene-Recent collisions of the Farallón-Aluk and the Nazca-Antarctic spreading ridges with the Chile trench, the Somuncura province with a mantle thermal anomaly linked to late Oligocene/early Miocene changes in plate convergence vectors, and the Payunia lavas with steepening of a formally shallow subduction zone. Between 45°S-50°S where Tertiary arc volcanism was largely absent, the plateau magmas show almost no trace element affinity with arc rocks as indicated by Ba/La ratios < 20 (arcs > 20) and La/Ta ratios <18 (arcs > 25). The same is true for pre-29 Ma magmas in the Somuncura and pre-20 Ma magmas in the Payunia regions. Associated magmas erupted near the arc can have higher ratios. This situation contrasts with post-29 Ma Somuncura and post-20 Ma Payunia magmas north of 45°S in which Ba/La ratios over 30 and La/Ta ratios < 20 extend far to the east, and lavas with La/Ta ratios > 20 occur to the west. These higher ratios fit with the introduction of arc components into the mantle magma sources as a result of interaction with a Paleogene subducting slab in the Somuncura region and dehydration of a shallowly subducting slab in the Payunia region. At the same time, Nd and Sr isotopic ratios of most of the plateau lavas plot in the OIB field (most eNd = +5 to -1; 87Sr/86Sr = 0.7035 to 0.7048) with Posadas magmas being the most depleted, and Somuncura and some Triple Junction magmas being the most enriched. Across the plateau, these tectonic, chemical, and isotopic data are consistent with the large volume plateau magmas being due to tectonic perturbations that provoke melting in a hot mantle that has been on the verge of melting since the Mesozoic breakup of Gondwana. Las provincias volcánicas basáltica
Fluctuations of Glaciar Esperanza Norte in the north Patagonian Andes of Argentina during the past 400 yr
L. Ruiz, M. H. Masiokas,R. Villalba
Climate of the Past (CP) & Discussions (CPD) , 2012,
Abstract: The number of studies of Little Ice Age (LIA) glacier fluctuations in southern South America has increased in recent years but is largely biased towards sites in the south Patagonian Andes. In this paper we present a detailed record of length and areal fluctuations of Glaciar Esperanza Norte (GEN) in the north Patagonian Andes of Argentina during the past four centuries. The GEN record was reconstructed through the dendro-geomorphological dating of moraines and the analysis of satellite imagery, aerial photographs and documentary material complemented with extensive field surveys. The maximum LIA extent at GEN was associated with an outer moraine dated to the mid 17th century. At least 19 subsequent readvances or standstills evidenced by morainic ridges were identified inside the most extensive LIA moraine. The dating and spacing of these moraines and the additional information available indicate that the ice front retreated much more rapidly during the 20th century than during earlier centuries. Comparison with the record of LIA fluctuations of Glaciar Frías, an ice mass of similar characteristics located 110 km to the north of GEN, shows a similar pattern of recession over the past 400 yr. Both glacier records have the peak LIA event occurring roughly during the same interval (early-mid 17th century) and show a minor readvance during the 1970s, but there are still a few discrepancies in the dating of some inner moraines. These differences may be due to local, specific factors or associated with the inherent uncertainties in the dating of the moraines. The chronologies of GEN and Frías are among the most detailed currently available in Patagonia, but a larger number of study sites is needed to develop robust, regionally representative glacier chronologies. Detailed glaciological, geomorphological and meteorological data are also needed to understand the glacier-climate relationships in this region and develop reliable paleoclimatic reconstructions.
Fluctuations of Glaciar Esperanza Norte in the North Patagonian Andes of Argentina during the past 400 yr  [PDF]
L. Ruiz,M. H. Masiokas,R. Villalba
Climate of the Past Discussions , 2011, DOI: 10.5194/cpd-7-4073-2011
Abstract: The number of studies of Little Ice Age (LIA) glacier fluctuations in Southern South America has increased in recent years but is largely biased towards sites in the South Patagonian Andes. In this paper we present a detailed record of length and areal fluctuations of Glaciar Esperanza Norte (GEN), in the North Patagonian Andes of Argentina, during the past four centuries. The GEN record was reconstructed through the dendro-geomorphological dating of moraines and the analysis of satellite imagery, aerial photographs and documentary material complemented with extensive field surveys. The maximum LIA extent at GEN was associated with an outer moraine dated to the mid 17th century. At least 19 subsequent readvances or standstills evidenced by morainic ridges were identified inside the most extensive LIA moraine. The dating and spacing of these moraines and the additional information available indicate that the ice front retreated much more rapidly during the 20th century than during earlier centuries. Comparison with the record of LIA fluctuations of Glaciar Frías, an ice mass of similar characteristics located 110 km to the north of GEN, shows a similar pattern of recession over the past 400 yr. Both glacier records have the peak LIA event occurring roughly during the same interval and show a minor readvance during the 1970s, but there are still a few discrepancies in the dating of some inner moraines. These differences may be due to local, specific factors or associated with the inherent uncertainties in the dating of the moraines. The chronologies of GEN and Frías are among the most detailed currently available in Patagonia, but a larger number of study sites is needed to develop robust, regionally representative glacier chronologies. Detailed glaciological, geomorphological and meteorological data are also needed to understand the glacier-climate relationships in this region and develop reliable paleoclimatic reconstructions.
Geology and geochemistry of the Eocene zeolite bearing volcaniclastic sediments of Metaxades, Thrace, Greece  [cached]
Koutles, Th.,Kassoli-Fournaraki, A.,Filippidis, A.,Tsirambides, A.
Estudios Geologicos , 1995, DOI: 10.3989/egeol.95511-2280
Abstract: The Eocene zeolite-bearing volcaniclastic sediments (Ca-rich clinoptilolite 51 % on average) of Metaxades, Thrace, Greece, are studied in terms of geology and chemical composition. The alternating formations along a vertical profile in the Metaxades main quarry face are: Discrete horizons of zeolite-bearing volcaniclastic tuffs, zeolite-bearing volcaniclastic tuffs including pebbles, zeolite-bearing volcaniclastic tuffs including thin silica-rich layers, and a calc-clayey horizon. A positive correlation is observed between MgO and CaO in the volcaniclastic tuffs including silica-rich layers. Sr, Rb and Ba are the most abundant trace elements in alllayers; among them, Sr is found to correlate positively with zeolite. The enrichment of sorne trace elements is mainly attributed to mineral abundances, mineral chemistry or leaching processes. The zeolite-bearing volcaniclastic sediments of Metaxades represent an inhomogeneous sequence, which was deposited in a shallow marine environment under turbulent to quiet sedimentary conditions. Los sedimentos eocenos volcanoclásticos con zeolita (51% de media de clinoptilolita rica en Ca) de Metaxades, Tracia, Grecia, se estudian desde el punto de vista geológico y de su composición química. Las formaciones alternantes que se pueden observar en un corte vertical en la cantera principal de Metaxades son: horizontes aislados de tufos volcanoclásticos con zeolita y con delgadas capas ricas en sílice, y un horizonte calco-arcilloso. Se observa una correlación positiva entre MgO y CaO en los tufss volcanoclásticos que presentan capas ricas en sílice. El Sr, el Rb y el Ba son los elementos traza más abundantes en todos los horizontes. Entre ellos, el Sr presenta una correlación positiva con la zeolita. El enriquecimiento en algunos elementos traza se atribuye esencialmente a las abundancias de los minerales, la química mineral, o a fenómenos de lixivinción. Los sedimentos volcanoclásticos con zeolita de Metaxades representan una secuencia inhomogénea, que fue depositada en un ambiente marino somero, bajo condiciones desde turbulentas hasta tranquilas.
Modelling and climatic interpretation of the length fluctuations of Glaciar Frías (north Patagonian Andes, Argentina) 1639–2009 AD
P. W. Leclercq, P. Pitte, R. H. Giesen, M. H. Masiokas,J. Oerlemans
Climate of the Past (CP) & Discussions (CPD) , 2012,
Abstract: We explore the climatic information contained in the record of length fluctuations of Glaciar Frías, in the north Patagonian Andes of Argentina. This record is one of the longest and most detailed glacier records in southern South America, starting in 1639. In order to interpret the length variations of Glaciar Frías since the maximum Little Ice Age extent, we use a combination of a simplified surface energy-balance model to calculate the glacier mass balance, and a flowline model to account for the dynamical response of the glacier to changes in the climatic forcing. The overall retreat of the glacier observed over 1639–2009 is best explained by an annual mean temperature increase of 1.2 °C or a decrease in annual precipitation of 34%, most of which would have occurred during the 20th century. The glacier model is also forced with two independent tree-ring and multi-proxy reconstructions of precipitation and temperature. The uncertainties in these reconstructions are rather large, leading to a wide range in the modelled glacier length that includes most of the observations. However, in both reconstructions, the mid-17th century seems to be too cold and the early 19th century too warm to explain the observed glacier lengths with the glacier model forced with the reconstructions. Forcing with reconstructed precipitation and temperature separately shows that the influence of historical variations in precipitation on the glacier fluctuations of Glaciar Frías is smaller than that of the temperature fluctuations. This suggests that the observed 1639–2009 retreat could be best explained by a warming close to 1.2 °C.
Los Andes Fueguinos: el registro micropaleontológico de los mayores acontecimientos paleooceanográfícos australes del Campaniano al Mioceno
Malumián,Norberto; Jannou,Gabriel;
Andean geology , 2010,
Abstract: the succession of microfossil assemblages in the almost complete marine late cretaceous-miocene stratigraphic column found in the fuegian andes, the orogenic margin of the austral basin, reveals a close relationship with the local tectonic events, the atlantic transgressions-regressions on the patagonian platform, and the most relevant paleoceanographic global events. the fuegian upper campanian-lower eocene sequence, dominated by flysch-type assemblages of agglutinated foraminifers and poorly oxygenated waters of fairly limited depth, is coherent with silled basins in a recently proposed cortical stretching period. the maastrichtian (policarpo formation) has a cosmopolitan agglutinated foraminiferal assemblage contrasting with the coeval austral endemic calcareous assemblages of patagonia. in the paleocene/eocene transition the assemblages of calcareous microfossils, of restricted distribution, exhibit the greatest cenozoic turnover from a cosmopolitan midway-type assemblage (la barca formation) to a strongly endemic early eocene assemblage (punta noguera formation), with the oldest records of the fuegian-patagonian cenozoic most typical genera. the early paleogene has no record of philothermic taxa such as larger foraminifera or morozovelids planktonic foraminifera, and only a short-lived bryozoan limestone (río bueno formation) and the low percentage of the ostracod family hemicytheridae insinuated a warm period. the upper middle-uppermost eocene sequence (la despedida group) starts with a transgression recorded in the austral basin (leticia, man aike, río turbio formations and boltovskoyella beds), and in the colorado basin. this transgression is coeval with a temperature peak of 42 ma, bringing a fuegian retrograde fauna and a foraminiferal assemblage with large-sized nodosarids, which were replaced throughout the late eocene (cerro colorado formation) by typical antarctic genera that reflect the falling global temperature, culminating in the tenuitella insolit
Mineralogy and Geochemistry of the Main Glauconite Bed in the Middle Eocene of Texas: Paleoenvironmental Implications for the Verdine Facies  [PDF]
Sherie C. Harding, Barbara P. Nash, Erich U. Petersen, A. A. Ekdale, Christopher D. Bradbury, M. Darby Dyar
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0087656
Abstract: The Main Glauconite Bed (MGB) is a pelleted greensand located at Stone City Bluff on the south bank of the Brazos River in Burleson County, Texas. It was deposited during the Middle Eocene regional transgression on the Texas Gulf Coastal Plain. Stratigraphically it lies in the upper Stone City Member, Crockett Formation, Claiborne Group. Its mineralogy and geochemistry were examined in detail, and verdine facies minerals, predominantly odinite, were identified. Few glauconitic minerals were found in the green pelleted sediments of the MGB. Without detailed mineralogical work, glaucony facies minerals and verdine facies minerals are easily mistaken for one another. Their distinction has value in assessing paleoenvironments. In this study, several analytical techniques were employed to assess the mineralogy. X-ray diffraction of oriented and un-oriented clay samples indicated a clay mixture dominated by 7 and 14? diffraction peaks. Unit cell calculations from XRD data for MGB pellets match the odinite-1M data base. Electron microprobe analyses (EMPA) from the average of 31 data points from clay pellets accompanied with M?ssbauer analyses were used to calculate the structural formula which is that of odinite: Fe3+0.89 Mg0.45 Al0.67 Fe2+0.30 Ti0.01 Mn0.01) Σ = 2.33 (Si1.77 Al0.23) O5.00 (OH)4.00. QEMSCAN (Quantitative Evaluation of Minerals by Scanning Electron Microscopy) data provided mineral maps of quantitative proportions of the constituent clays. The verdine facies is a clay mineral facies associated with shallow marine shelf and lagoonal environments at tropical latitudes with iron influx from nearby runoff. Its depositional environment is well documented in modern nearshore locations. Recognition of verdine facies clays as the dominant constituent of the MGB clay pellets, rather than glaucony facies clays, allows for a more precise assessment of paleoenvironmental conditions.
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