The Arequipa Massif of Peru: New SHRIMP and isotope constraints on a Paleoproterozoic inlier in the Grenvillian orogen     

C. Casquet  C.M. Fanning  C. Galindo  R.J. Pankhurst  C.W. Rapela  P. Torres 《Journal of South American Earth Sciences》2010,29(1):128-142

The enigmatic Arequipa Massif of southwestern Peru is an outcrop of Andean basement that underwent Grenville-age metamorphism, and as such it is important for the better constraint of Laurentia–Amazonia ties in Rodinia reconstruction models. U–Pb SHRIMP zircon dating has yielded new evidence on the evolution of the Massif between Middle Paleoproterozoic and Early Paleozoic. The oldest rock-forming events occurred in major orogenic events between ca. 1.79 and 2.1 Ga (Orosirian to Rhyacian), involving early magmatism (1.89–2.1 Ga, presumably emplaced through partly Archaean continental crust), sedimentation of a thick sequence of terrigenous sediments, UHT metamorphism at ca. 1.87 Ga, and late felsic magmatism at ca. 1.79 Ga. The Atico sedimentary basin developed in the Late-Mesoproterozoic and detrital zircons were fed from a source area similar to the high-grade Paleoproterozoic basement, but also from an unknown source that provided Mesoproterozoic zircons of 1200–1600 Ma. The Grenville-age metamorphism was of low-P type; it both reworked the Paleoproterozoic rocks and also affected the Atico sedimentary rocks. Metamorphism was diachronous: ca. 1040 Ma in the Quilca and Camaná areas and in the San Juán Marcona domain, 940 ± 6 Ma in the Mollendo area, and between 1000 and 850 Ma in the Atico domain. These metamorphic domains are probably tectonically juxtaposed. Comparison with coeval Grenvillian processes in Laurentia and in southern Amazonia raises the possibility that Grenvillian metamorphism in the Arequipa Massif resulted from extension and not from collision. The Arequipa Massif experienced Ordovician–Silurian magmatism at ca. 465 Ma, including anorthosites formerly considered to be Grenvillian, and high-T metamorphism deep within the magmatic arc. Focused retrogression along shear zones or unconformities took place between 430 and 440 Ma.  相似文献   

The last major earthquakes along the Magallanes–Fagnano fault system recorded by disturbed trees (Tierra del Fuego,South America)     

Antonio Pedrera  Jesús Galindo‐Zaldívar  Ana Ruiz‐Constán  Fernando Bohoyo  Pablo Torres‐Carbonell  Patricia Ruano  Adolfo Maestro  Lourdes González‐Castillo 《地学学报》2014,26(6):448-453

Forests situated above active fault zones may record hillslope evolution, thus holding information about recent seismic events. Lenga trees (Nothofagus pumilio) extend across the Magallanes–Fagnano fault system (MFFS), the active transform boundary between the South American and Scotia plates. Coseismic surface ruptures along the fault scarp tilt trees located uphill. During the interseismic period, tree growth curves the trunks. Annual tree rings from the study area show abrupt changes from concentric to asymmetric, allowing the timing of major historical earthquakes to be established. In this case, tree‐ring analysis suggests rupture on the MFFS fault scarp in 1883 ± 5 and 1941 ± 10, coinciding with the February 1, 1879 (Modified Mercalli Scale, VI) and the December 17, 1949 (Ms 7.8) earthquakes in Tierra del Fuego. Our results provide evidence that this fault system was the source of these earthquakes, which has implications for seismic hazard in the study region.  相似文献   

The Palaeocene/Eocene boundary section at Zumaia (Basque‐Cantabric Basin) revisited: new insights from high‐resolution magnetic susceptibility and carbon isotope chemostratigraphy on organic matter (δ13Corg)     

Jean‐Yves Storme  Xavier Devleeschouwer  Johann Schnyder  Geoffrey Cambier  Juan Ignacio Baceta  Victoriano Pujalte  Antonietta Di Matteo  Paola Iacumin  Johan Yans 《地学学报》2012,24(4):310-317

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Links between topography,moisture fluxes pathways and precipitation over South America     

Ramiro Ignacio Saurral  Inés Angela Camilloni  Tércio Ambrizzi 《Climate Dynamics》2015,45(3-4):777-789

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Petrographic studies of the impact melts from Meteor Crater,Arizona, USA     

Friedrich Hrz  David W. Mittlefehldt  Thomas H. See  Charles Galindo 《Meteoritics & planetary science》2002,37(4):501-531

Abstract— We investigated the ballistically dispersed melts from Meteor Crater, Arizona, USA to determine the stratigraphic extent of its melt zone from the compositional relationship of melts and target rocks. Most melt particles are crystallized, hydrated, and oxidized; pristine glasses are rare. Hydration and oxidation occurred at ambient temperatures long after the impact. The preserved glasses are generally clear and texturally homogeneous, but unlike typical impact melts, they have unusually heterogeneous compositions, both within individual particles and from sample to sample. For example, the average SiO₂ for individual particles ranges from 43 to 65%. The projectile content is unusually high and it is distributed bimodally, with specific samples containing either 5–10% or 20–30% FeO. These compositional heterogeneities most likely reflect the high carbonate content of the target rocks and the release of copious CO₂ that dispersed the melts, thereby terminating melt flow and mixing. The high projectile content and the CO₂ depleted residue of purely sedimentary rocks produced mafic melts that crystallized fine‐grained olivine and pyroxene. The melts fall into three compositional groups reflecting variable proportions of the major target formations, Moenkopi, Kaibab, and Coconino. Least‐square mixing calculations revealed one group to contain 55% Moenkopi, 40% quartz‐rich, upper Kaibab, and 5% meteorite, suggesting a source depth of <30 m from the pre‐impact surface. The other two melt groups have higher contents of meteorite (15–20%) and Kaibab (50–70%) and contain more SiO₂ than average Kaibab. The additional quartz may have been derived from Coconino or the upper Kaibab, implying melt depths >90 m or <30 m, respectively. Additional studies, especially hydrocode calculations, are needed to better understand the source depth of these melts and their exceptionally high projectile content.  相似文献   

Double-barred galaxies at intermediate redshifts: a feasibility study     

Thorsten Lisker  Victor P. Debattista †  Ignacio Ferreras  Peter Erwin 《Monthly notices of the Royal Astronomical Society》2006,370(1):477-487

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A principal component analysis approach to the star formation history of elliptical galaxies in compact groups   总被引：1，自引：0，他引：1  

Ignacio Ferreras  Anna Pasquali  Reinaldo R. de Carvalho  Ignacio G. de la Rosa  Ofer Lahav 《Monthly notices of the Royal Astronomical Society》2006,370(2):828-836

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Decoupling the host and nuclear spectra of type I AGNs using integral field spectroscopy: A test on 3C 120     

Sebastin F. Snchez  Begoa García-Lorenzo  Knud Jahnke  Evencio Mediavilla  Jos Ignacio Gonzlez-Serrano  Lise Christensen  Lutz Wisotzki 《New Astronomy Reviews》2006,49(10-12):501

We have developed a new technique to decouple the spectra of the host and the nucleus of type I AGNs using integral field spectroscopy data. The technique is a simple extension of methods widely tested in 2D imaging. We present here the results from applying the technique to data taken with INTEGRAL at the 4.2 m William Herschel Telescope on the Seyfert 1 radio-galaxy 3C 120. We obtained, for the first time, a clean spectrum of the host galaxy, without contamination from the nuclear source.  相似文献   

The formation history of the Galactic bulge     

Ignacio Ferreras  Rosemary F. G. Wyse  Joseph Silk 《Monthly notices of the Royal Astronomical Society》2003,345(4):1381-1391

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Recovery simulations of grossly polluted sediments in the Bilbao Estuary     

Antonio González Oreja J  Ignacio Saiz Salinas J 《Marine pollution bulletin》2003,46(1):42-48

The Bilbao Estuary is one of the most contaminated estuaries on the north coast of Spain, and vast efforts have been made to abate pollution there. In fact, the local water authority has forecast a biological recovery of the native fauna after a substantial increase in dissolved oxygen to normoxic levels. In order to assess this prediction by evaluating the extent of natural regeneration of these polluted sediments, two long-term bioassays (t=90 d) were performed. In both of them, lethal (differences in survival) and sublethal (differences in length and weight growth) effects were measured by using juvenile individuals of the autochthonous clam, Scrobicularia plana (Da Costa, 1778). The sediments tested differed in pollution levels, as measured by a set of indicators including PAHs, PCBs, heavy metals, volatile organic matter and coprostanol. All sediments were finally exposed to normoxic conditions in situ in the Bilbao Estuary (DO approximately 6.3 mg l(-1)). In the first experiment, concerning moderately polluted sediments from the Bilbao Estuary and reference sediments from the "pristine" Plentzia Estuary, no significant differences (P>0.05) were found regarding animal survival (approximately 94.5%) or growth in length or weight between the sediments tested. In the second experiment, also involving grossly polluted sediments (GPS) from the Bilbao Estuary, survival (24.5%) was statistically lower (P<0.05) than in the other sediments (approximately 93%). No significant differences were found in growth (length, weight) between animals exposed to moderately polluted or reference sediments. We interpret this dramatic difference in survival as the lethal effect on the animals tested of the GPS of the Bilbao Estuary, indicating a situation where biological recovery is not possible due to the adverse consequences of contaminants sorbed into sediments. The extensive use of this inexpensive bioassay could help to distinguish sediments in which homeostatic recovery is possible from grossly polluted "hot spots", which need costly remedial actions.  相似文献