Mantle derived crystal-poor rhyolitic ignimbrites: Eruptive mechanism from geochemical and geochronological data of the Piedra Parada caldera,Southern Argentina     

Eugenio Aragon  Antonio Castro  Juan Diaz-Alvarado  Lucio Pinotti  Fernando D'eramo  Manuel Demartis  Jorge Coniglio  Irene Hernando  Carmen Rodriguez 《地学前缘(英文版)》2018,9(5):1529-1553

Trace elements, isotopic modeling and U-Th-Pb SHRIMP zircon age constraints are used to reconstruct the eruption history and magmatic processes of the Piedra Parada Caldera. In the early Eocene, the crystal-poor Barda Colorada ignimbrite(BCI), having 15% micro-porphyritic crystals with respect to magmatic components, erupted a volume estimated in more than 300 km~3. The Piedra Parada caldera is located in the Patagonian Andes foreland, at the southern end of the calderas field of the Pilcaniyeu Volcanic Belt(PVB). This belt is related to an extensional tectonic setting as a result of the collision of the Farallon-Aluk ridge with South America, which enabled the development of a transform ocean/continental plate margin followed by the detachment of the Aluk plate and the opening of a slab window. The BCI extra-caldera Plateau is a 100 m thick deposit, having a lower unit with high silica(Si O_2 76 wt.%),potassium poor rhyolitic composition(trondhjemitic like magma), and an upper unit with normal to high potassium rhyolitic composition(granitic like magma). A trace elements modeling of the BCI units shows that the BCI lower and upper units did not evolve from fractionation or immiscibility in the shallow magma reservoir. The BCI also have a primitive isotopic signature(initial87 Sr/86 Sr =0.7031-0.7049 and ε_(Nd)= +3.4 to +3.65). Thus, tectonic, compositional and isotopic constraints suggest the fast ascent of high silica magmas to a shallow reservoir, and point to an upper mantle origin for these rhyolitic magmas in a transitional(Orogenic-Anorogenic) tectono-magmatic setting. U-Th-Pb SHRIMP zircon crystallization ages of the Syn-caldera stage BCI units(56 -51.5 Ma) show a protracted life of 5 Ma for this caldera reservoir. The age of 52.9 ± 0.3 Ma is considered the best fit for the possible maximum age for the caldera collapse. The Late-caldera magmatism has trachyandesitic and rhyolitic compositions.The trace element modeling suggests that these rhyolites evolve from the trachyandesites and do not evolve from the BCI residual magma. The trachyandesites have U-Th-Pb SHRIMP zircon crystallization ages of 52 ± 1 Ma, suggesting that the caldera eruption was triggered by the arrival of the trachyandesitic magma.  相似文献   

Applicability of the Climate Hazards Group Infrared Precipitation with Stations as Rainfall Input for SWAT Watershed Modeling     

Alejo  Lanie A.  Ella  Victor B.  Saludes  Ronaldo B. 《Water Resources》2021,48(6):925-935

Water Resources - This study assessed the applicability of Climate Hazards Group Infrared Precipitation with Stations (CHIRPS) as rainfall input in watershed modeling using the Soil and Water...  相似文献   

Long-term fluid circulation in extensional faults in the central Catalan Coastal Ranges: P–T constraints from neoformed chlorite and K-white mica     

Irene Cantarero  Pierre Lanari  Olivier Vidal  Gemma Alías  Anna Travé  Vinyet Baqués 《International Journal of Earth Sciences》2014,103(1):165-188

The neoformation of chlorite and K-white mica in fault rocks from two main faults of the central Catalan Coastal Ranges, the Vallès and the Hospital faults, has allowed us to constrain the P–T conditions during fault evolution using thermodynamic modeling. Crystallization of M1 and M2 muscovite and microcline occured as result of deuteric alteration during the exhumation of the pluton (290 °C > T > 370 °C) in the Permian. After that, three tectonic events have been distinguished. The first tectonic event, attributed to the Mesozoic rifting, is characterized by precipitation of M3 and M4 phengite together with chlorite and calcite C1 at temperatures between 190 and 310 °C. The second tectonic event attributed to the Paleogene compression has only been identified in the Hospital fault with precipitation of low-temperature calcite C2. The shortcut produced during inversion of the Vallès fault was probably the responsible for the lack of neoformed minerals within this fault. Finally, the third tectonic event, which is related to the Neogene extension, is characterized in the Vallès fault by a new generation of chlorite, associated with calcite C4 and laumontite, formed at temperatures between 125 and 190 °C in the absence of K-white mica. Differently, the Hospital fault is characterized by the precipitation of calcite C3 during the syn-rift stage at temperatures around 150 °C and by low-temperature fluids precipitating calcites C5, C6 and PC1 during the post-rift stage. During the two extensional events (Mesozoic and Neogene), faults acted as conduits for hot fluids producing anomalous high geothermal gradients (50 °C/km minimum).  相似文献   

http://www.sciencedirect.com/science/article/pii/S1674987112001533     

Eugenio Aragón  Lucio Pinotti  Fernando D’Eramo  Antonio Castro  Osvaldo Rabbia  Jorge Coniglio  Manuel Demartis  Irene Hernando  Claudia E.Cavarozzi  Yolanda E.Aguilera 《地学前缘(英文版)》2013,4(4):377-388

The collision of a divergent ocean ridge may evolve into two end cases:in the continuity of ocean-floor subduction.or in the detachment of the subducted plate.The northern Patagonia active plate margin has the unique situation that in Cenozoic time it has been subjected to two divergent ridge collisions,each one representing one of the end members.The Neogene Antarctica-Nazca divergent ridge collision evolved as a continuous ocean-floor subduction system,promoting a magmatic hiatus at the arc axis,the obduction of part of the ridge ocean-floor in the fore-arc.and basaltic volcanism in the back-arc.In contrast,the Paleogene Farallon-Aluk divergent ridge collision evolved into a transform margin,with the detachment and sinking of the Aluk plate and the development of a large slab window.As in the previous case,this collision promoted a magmatic hiatus at the arc axis,but the tectono-magmatic scenario changed to postorogenic synextensional volcanism that spread to the former fore-arc（basalt,andesite,rhyolite） and former back-arc（bimodal ignimbrite flare-up,basalt）.Geochemistry of this slab window synextensional volcanism shows more MORB-like basalts towards the former fore-arc,and MORB-OIB-like basalts towards the former back-arc.Instead,an isolated undeformable crustal block in the former back-arc,with an "epeirogenic" response to the slab window and extensional regime,was covered by OIB-type basalts after uplift.Major elements show that slab window basalts reach TiCh values up to 3 wt%,as compared with the top value of 1.5 wt%of arc magmas.Besides,the MgO with respect to（FeO^t + Al₂O₃） ratio helps to distinguish slab window magma changes from the former fore-arc to the former back-arc and also with respect to the "epeirogenic" block.Higher contents of HFS elements such as Nb and Ta also help to distinguish this slab window from arc magmas and also,to distinguish slab window magma changes from the former fore-arc to the former back-arc and "epeirogenic" block settings.The isotope compositions of slab window magmatism show a disparate coeval array from MORB to crustal sources,interpreted as a consequence of the lack of protracted storage and homogenization due to the extensional setting.  相似文献   

Neural network simulation of spring flow in karst environments   总被引：2，自引：2，他引：0  

Evan K. Paleologos  Irene Skitzi  K. Katsifarakis  Nektarios Darivianakis 《Stochastic Environmental Research and Risk Assessment (SERRA)》2013,27(8):1829-1837

Daily discharges of two springs lying in a karstic environment were simulated for a period of 2.5 years with the use of a multi-layer perceptron back-propagation neural network. Two models were developed for the springs, one relying on the original data and another where the missing discharge values were supplemented by assuming linear relationships during base flow conditions. For both springs the mean square error of the two models did not differ significantly, with an improvement exhibited at the extremes, during the network’s training phase, by the model that utilized the extended data set, the results of which are reported here. The time lag between precipitation and spring discharge differed significantly for the two springs indicating that in karstic environments hydraulic behavior is dominated, even within a few hundred meters, by local conditions. Optimum training results were attained with a Levenberg–Marquardt algorithm resulting in a network architecture consisting of two input layer neurons, four hidden layer neurons, and one output layer neuron, the spring’s discharge. The neural network’s predictions captured the behavior for both springs and followed very closely the discontinuities in the discharge time series. Under-/over-estimation of observed discharges for the two springs remained below 3 %, with the exception of a few local maxima where the predicted discharges diverged more strongly from observed values. Inclusion of temperature data did not add to the improvement of predictions. Finally, optimum predictions were attained when past discharge data were added to the input record and discharge differentials rather than direct discharges were calculated resulting in elimination of any local maximum discrepancy between observed and predicted discharge values.  相似文献   

THUNDERSTORM CLIMATOLOGY BASED ON LIGHTNING DETECTOR DATA,MANITOBA, CANADA     

Irene Hanuta  Steve LaDochy 《自然地理学》2013,34(2):101-119

Comparisons are made between thunderstorm data collected from a lightning detector network and from conventional climatic stations for the province of Manitoba, Canada. The greater resolution in time and space of lightning detector (direction finder) data makes it a valuable source of thunderstorm information and lends itself to some important applications. Data were collected for the forest fire season of 1985 using a network of 7 lightning direction finders distributed throughout the province. Some 67,912 cloud-to-ground lightning strikes were recorded by time and location during 122 thunderstorm days. July was the most active month with 27,260 strikes over 28 days. Two regions of the province had the greatest concentration of lightning strikes, indicating some influence by topography and position of large lakes. Case studies are presented of the most active lightning storms of 1985 and 1986. These storms are exclusively frontal storms, with most having similar synoptic weather patterns to those of large hailstorms and tornadoes in Manitoba. Relationships between meteorological parameters and lightning strike distribution are presented. These relationships may prove useful in the suppression of lightning-caused forest fires, especially in remote areas of the province. [Key words: lightning, thunderstorm, synoptic climatology, natural hazards, fire prevention.]  相似文献   

Magnetic fabrics and their relationship with the emplacement of the Piracaia pluton,SE Brazil     

M. Irene B. Raposo  Leonardo Frederico Pressi  Valdecir de Assis Janasi 《International Journal of Earth Sciences》2012,101(3):773-786

Magnetic fabric and rock-magnetism studies were performed on the four units of the 578 ± 3-Ma-old Piracaia pluton (NW of São Paulo State, southern Brazil). This intrusion is roughly elliptical (~32 km²), composed of (i) coarse-grained monzodiorite (MZD-c), (ii) fine-grained monzodiorite (MZD-f), which is predominant in the pluton, (iii) monzonite heterogeneous (MZN-het), and (iv) quartz syenite (Qz-Sy). Magnetic fabrics were determined by applying both anisotropy of low-field magnetic susceptibility (AMS) and anisotropy of anhysteretic remanent magnetization (AARM). The two fabrics are coaxial. The parallelism between AMS and AARM tensors excludes the presence of a single domain (SD) effect on the AMS fabric of the units. Several rock-magnetism experiments performed in one specimen from each sampled units show that for all of them, the magnetic susceptibility and magnetic fabrics are carried by magnetite grains, which was also observed in the thin sections. Foliations and lineations in the units were successfully determined by applying magnetic methods. Most of the magnetic foliations are steeply dipping or vertical in all units and are roughly parallel to the foliation measured in the field and in the country rocks. In contrast, the magnetic lineations present mostly low plunges for the whole pluton. However, for eight sites, they are steep up to vertical. Thin-section analyses show that rocks from the Piracaia pluton were affected by the regional strain during and after emplacement since magmatic foliation evolves to solid-state fabric in the north of the pluton, indicating that magnetic fabrics in this area of the pluton are related to this strain. Otherwise, the lack of solid-state deformation at outcrop scale and in thin sections precludes deformation in the SW of the pluton. This evidence allows us to interpret the observed magnetic fabrics as primary in origin (magmatic) acquired when the rocks were solidified as a result of magma flow, in which steeply plunging magnetic lineation suggests that a feeder zone could underlie this area.  相似文献   

A Crustal Model for the Eastern Alps Region and a New Moho Map in Southeastern Europe   总被引：1，自引：0，他引：1  

Irene Molinari  Victor Raileanu  Andrea Morelli 《Pure and Applied Geophysics》2012,169(9):1575-1588

In the last two decades, south-central Europe and the Eastern Alps have been widely explored by many seismic refraction experiments (e.g., CELEBRATION 2000, ALP 2002, SUDETES 2003). Although quite detailed images are available along linear profiles, a comprehensive, three-dimensional crustal model of the region is still missing. This limitation makes this region a weak spot in continental-wide comprehensive representations of crustal structure. To improve on this situation, we select and collect 37 published active-source seismic lines in this region. After geo-referencing each line, we sample them along vertical profiles—every 50?km or less along the line—and derive P-wave velocities in a stack of homogeneous layers (separated by discontinuities: depth of crystalline basement, top of lower crust, and Moho). We finally merge the information using geostatistical methods, and infer S-wave velocity and density using empirical scaling relations. We present here the resulting crustal model for a region encompassing the Eastern Alps, Dinarides, Pannonian basin, Western Carpathians and Bohemian Massif, covering the region within $45^{\circ}\text{--}51^{\circ}\hbox{N}$ and $11^{\circ} \text{--} 22^{\circ}\hbox{E}$ with a resolution of $0.2^{\circ} \times 0.2^{\circ}.$ We are also able to extend and update the map of Moho depth in a wider region within $35^{\circ}\text{--}51^{\circ}\hbox{N}$ and $12^{\circ}\text{--}45^{\circ}\hbox{E},$ gathering Moho values from the collected seismic lines, other published dataset and using the European plate reference EPcrust as a background. All the digitized profiles and the resulting model are available online.  相似文献   

Holocene evolution of a rock‐bounded barrier‐lagoon system,Cíes Islands,northwest Iberia     

Susana Costas  Castor Muñoz Sobrino  Irene Alejo  Marta Pérez‐Arlucea 《地球表面变化过程与地形》2009,34(11):1575-1586

Coastal geomorphology results from the combined effects of contemporary dynamics, sea‐level rise and the inherited geological framework, yet the relative importance of these driving mechanisms may change throughout the evolutionary history of coastal deposits. In this contribution, we analyse the depositional history of the Cíes Islands barrier‐lagoon system, based on lithofacies, radiocarbon ages, and pollen analysis. Our results reveal a sedimentary sequence that provides evidence for striking changes in the dynamical functioning of this complex since the mid‐Holocene. The sedimentary sequence commenced about 7700 cal years bp by fresh‐water ponding of an upland depression located about 4 m below present mean sea‐level. Fresh‐water ponds were infilled by aeolian sediments following a gradual lowering of the water‐table 4000 cal years bp . Post‐3600 cal years bp sea‐level rise allowed water oscillations to reach the elevation of the bedrock causing the inundation of fresh‐water ponds and subsequent lagoonal and marine sedimentation. Subsequently, landward and upward migration of a sand‐barrier led to overwash and deposition of sand in the newly formed lagoon. The resultant sedimentary sequence suggests that climatic conditions played an important role controlling the sedimentation regime during the entire history of the basin; changing water‐table levels during early stages of evolution and increasing storminess during more recent times. In addition, background sea‐level rise related to the Holocene transgression was a key factor in controlling the evolution of the system, yet its influence depended to an extent on the relative elevation of the bedrock topography. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

On the morphological characteristics of overdeepenings in high‐mountain glacier beds          下载免费PDF全文

Wilfried Haeberli  Andreas Linsbauer  Alejo Cochachin  Cesar Salazar  Urs H. Fischer 《地球表面变化过程与地形》2016,41(13):1980-1990

Overdeepenings, i.e. closed topographic depressions with adverse slopes in the direction of flow, are characteristic for glacier beds and glacially sculpted landscapes. Quantitative information about their morphological characteristics, however, has so far hardly been available. The present study provides such information by combining the analysis of (a) numerous bed overdeepenings below still existing glaciers of the Swiss Alps and the Himalaya‐Karakoram region modelled with a robust shear stress approximation and (b) detailed bathymetries from recently exposed lakes in the Peruvian Andes. The investigated overdeepenings exist where glacier surface slopes are low (< 5°–10°), occur in bedrock or morainic material and are most commonly a fraction of a kilometre squared in surface area, hundreds of metres long, about half the length in width and tens of metres deep. They form under conditions of low to high basal shear stresses, at cirque, confluence, trunk valley and terminus positions. The most striking phenomenon, however, is the high variability of their geometries: Depths, surface areas, lengths and widths of the overdeepenings vary over orders of magnitude and are only weakly – if at all – interrelated. Inclinations of adverse slopes do not differ significantly from those of forward slopes and are in many cases higher than so far assumed theoretical limits for supercooling of ascending water and corresponding closure of sub‐glacial channels. Such steep adverse slopes are a robust observation and in support of recently developed new concepts concerning the question about where supercooling of sub‐glacial water and closure of ice channels can or must occur. However, the question of when and under what climatic, topographic and ice conditions the overdeepenings had formed remains unanswered. This open question constitutes a key problem concerning the interpretation of observed overdeepenings, the understanding of the involved glacio‐hydraulic processes and the possibility of realistic predictive modelling of overdeepening formation. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献