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  • 1
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    Arc-continent collision and orocline formation: Closing of the Central American seaway (2012)
    Wiley
    Details
    Publication Date: 2012-04-18
    Description: Closure of the Central American seaway was a local tectonic event with potentially global biotic and environmental repercussions. We report geochronological (six U/Pb LA-ICP-MS zircon ages) and geochemical (19 XRF and ICP-MS analyses) data from the Isthmus of Panama that allow definition of a distinctive succession of plateau sequences to subduction-related protoarc to arc volcaniclastic rocks intruded by Late Cretaceous to middle Eocene intermediate plutonic rocks (67.6 ± 1.4 Ma to 41.1 ± 0.7 Ma). Paleomagnetic analyses (24 sites, 192 cores) in this same belt reveal large counterclockwise vertical-axis rotations (70.9° ± 6.7°), and moderate clockwise rotations (between 40° ± 4.1° and 56.2° ± 11.1°) on either side of an east-west trending fault at the apex of the Isthmus (Rio Gatun Fault), consistent with Isthmus curvature. An Oligocene-Miocene arc crosscuts the older, deformed and segmented arc sequences, and shows no significant vertical-axis rotation or deformation. There are three main stages of deformation: 1) left-lateral, strike-slip offset of the arc (∼100 km), and counterclockwise vertical-axis rotation of western arc segments between 38 and 28 Ma; 2) clockwise rotation of central arc segments between 28 and 25 Ma; and 3) orocline tightening after 25 Ma. When this reconstruction is placed in a global plate tectonic framework, and published exhumation data is added, the Central American seaway disappears at 15 Ma, suggesting that by the time of northern hemisphere glaciation, deep-water circulation had long been severed in Central America.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 2
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    Effects of rapid global warming at the Paleocene-Eocene boundary on neotropical vegetation (2010)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2010-11-13
    Description: Temperatures in tropical regions are estimated to have increased by 3 degrees to 5 degrees C, compared with Late Paleocene values, during the Paleocene-Eocene Thermal Maximum (PETM, 56.3 million years ago) event. We investigated the tropical forest response to this rapid warming by evaluating the palynological record of three stratigraphic sections in eastern Colombia and western Venezuela. We observed a rapid and distinct increase in plant diversity and origination rates, with a set of new taxa, mostly angiosperms, added to the existing stock of low-diversity Paleocene flora. There is no evidence for enhanced aridity in the northern Neotropics. The tropical rainforest was able to persist under elevated temperatures and high levels of atmospheric carbon dioxide, in contrast to speculations that tropical ecosystems were severely compromised by heat stress.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Jaramillo, Carlos -- Ochoa, Diana -- Contreras, Lineth -- Pagani, Mark -- Carvajal-Ortiz, Humberto -- Pratt, Lisa M -- Krishnan, Srinath -- Cardona, Agustin -- Romero, Millerlandy -- Quiroz, Luis -- Rodriguez, Guillermo -- Rueda, Milton J -- de la Parra, Felipe -- Moron, Sara -- Green, Walton -- Bayona, German -- Montes, Camilo -- Quintero, Oscar -- Ramirez, Rafael -- Mora, German -- Schouten, Stefan -- Bermudez, Hermann -- Navarrete, Rosa -- Parra, Francisco -- Alvaran, Mauricio -- Osorno, Jose -- Crowley, James L -- Valencia, Victor -- Vervoort, Jeff -- New York, N.Y. -- Science. 2010 Nov 12;330(6006):957-61. doi: 10.1126/science.1193833.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Smithsonian Tropical Research Institute, Box 0843-03092, Balboa, Ancon, Republic of Panama. jaramilloc@si.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/21071667" target="_blank"〉PubMed〈/a〉
    Keywords: Angiosperms ; Atmosphere ; Biodiversity ; Carbon Dioxide ; Colombia ; *Ecosystem ; Extinction, Biological ; *Global Warming ; *Plants ; Pollen ; Spores ; Temperature ; Time ; *Trees ; *Tropical Climate ; Venezuela
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 3
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    Middle Miocene closure of the Central American Seaway (2015)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2015-04-11
    Description: Uranium-lead geochronology in detrital zircons and provenance analyses in eight boreholes and two surface stratigraphic sections in the northern Andes provide insight into the time of closure of the Central American Seaway. The timing of this closure has been correlated with Plio-Pleistocene global oceanographic, atmospheric, and biotic events. We found that a uniquely Panamanian Eocene detrital zircon fingerprint is pronounced in middle Miocene fluvial and shallow marine strata cropping out in the northern Andes but is absent in underlying lower Miocene and Oligocene strata. We contend that this fingerprint demonstrates a fluvial connection, and therefore the absence of an intervening seaway, between the Panama arc and South America in middle Miocene times; the Central American Seaway had vanished by that time.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Montes, C -- Cardona, A -- Jaramillo, C -- Pardo, A -- Silva, J C -- Valencia, V -- Ayala, C -- Perez-Angel, L C -- Rodriguez-Parra, L A -- Ramirez, V -- Nino, H -- New York, N.Y. -- Science. 2015 Apr 10;348(6231):226-9. doi: 10.1126/science.aaa2815.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Universidad de los Andes, Bogota, Colombia. cmontes@uniandes.edu.co. ; Universidad Nacional de Colombia, Medellin, Colombia. ; Smithsonian Tropical Research Institute, Ciudad de Panama, Panama. ; Universidad de Caldas, Manizales, Colombia. ; University of Houston, Houston, TX 77004, USA. ; Washington State University, Pullman, WA 99164, USA. ; Corporacion Geologica Ares, Bogota, Colombia. ; Universidad de los Andes, Bogota, Colombia. ; Ecopetrol, Bogota, Colombia.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/25859042" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 4
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    Constraints on trenchward arc migration and back‐arc magmatism in the North Patagonian Andes in the context of Nazca plate rollback (2019)
    Wiley
    In: Tectonics
    Details
    Publication Date: 2019
    Description: Abstract Geochemical and geochronological data reveal that late Oligocene‐early Miocene time is a break point in the evolution of Andean magmatism. The Patagonian Andes registered the onset of arc volcanism since the late Eocene forming part of the El Maitén Belt, whose development was driven by the subduction of the Farallon/Nazca plates beneath the Andean margin. During the Oligocene, the El Maitén Belt shows a change in the geochemical signature of its magmas from tholeiitic to calc‐alkaline compositions, reflecting a more mature stage in the magmatic arc evolution. Toward the early Miocene, a striking event is registered in Andean volcanic sequences as mafic tholeiitic lava flows of the El Maitén are interbedded with marine deposits, suggesting their development in the context of a fast subsiding regime. Geochemical analyses presented in this paper show that these rocks resemble E‐MORB‐like and OIB compositions, isotopically depleted, which strongly contrast with previous arc products. By this time, a global plate reorganization event had caused an increase in convergence rates, accelerated roll back and a more orthogonal geometry of subduction, triggering widespread magmatism and the development of extensional basins in the overriding plate. Arc‐related volcanism during the early Miocene can be found only in the western slope of the Andes, suggesting the retreat of the volcanic front toward the trench. The proposed model highlights a strong linkage between the geochemical signature of magmatic products and changes in the subduction zone configuration and mantle dynamics during the evolution of the Patagonian Andes (41°–44°S).
    Print ISSN: 0278-7407
    Electronic ISSN: 1944-9194
    Topics: Geosciences
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 5
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    Deep Crustal Faults, Shear Zones, and Magmatism in the Eastern Cordillera of Colombia: Growth of a Plateau From Teleseismic Receiver Function and Geochemical Mio‐Pliocene Volcanism Constraints (2019)
    Wiley
    Details
    Publication Date: 2019
    Description: Abstract The Eastern Cordillera of Colombia, in the northern Andes, is an example of an orogen in which Mesozoic basins were compressed during the Cenozoic, forming a ~2,500‐m‐high plateau in its northern portion. Significant shortening and crustal thickening have contributed to the construction of the present topography and elevation. In this contribution, we combine the use of teleseismic receiver functions, Hf isotopes, whole‐rock geochemistry, and U‐Pb dating to help elucidate the main mechanisms that played a role in the crustal thickening and uplift of the cordillera. Receiver functions calculated for three stations on top of the plateau are consistent with the presence of thrusts that converge into major crustal interfaces at upper‐middle crustal depths; they also suggest the existence of two crustal anisotropic layers beneath the western flank of the cordillera, which we interpret to have formed as a result of shearing. In the northern portion of the plateau, in the area where two Mio‐Pliocene volcanic domes and their related deposits outcrop, a lower crustal high seismic velocity layer is suggested by the receiver functions; we propose magmatic underplating for the origin of this layer. The geochemical characteristics of the volcanic rocks in the area are consistent with partial melt in a mantle influenced by slab‐related fluids; this magma could have been added to the crust and portions of it ascended and reached the surface, experiencing assimilation and differentiation during the process. We hypothesize that this Mio‐Pliocene volcanism was related to flattening of the Nazca subducting slab.
    Print ISSN: 2169-9313
    Electronic ISSN: 2169-9356
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 6
    Electronic Resource
    Electronic Resource
    Periodic Multilayers of Perylene-3,4:9,10-Tetracarboxylic Dianhydride and Chloroindium Phthalocyanine: Limitations to Long-Term Stability (1995)
    s.l. : American Chemical Society
    Chemistry of materials 7 (1995), S. 657-662 
    Details
    ISSN: 1520-5002
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/cm00052a009
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  • 7
    Electronic Resource
    Electronic Resource
    Electron and hole mobility in tris(8-hydroxyquinolinolato-N1,O8) aluminum (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 66 (1995), S. 3618-3620 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have measured the drift mobility of electrons and holes in thin, vapor-deposited films of tris(8-hydroxyquinolinolato-N1,O8) aluminum using a time of flight photoconductivity technique. The drift of mobility of both carriers is dispersive and strongly electric field and temperature dependent. At ambient temperature and an electric field of 4×105 V cm−1, the effective mobility of electrons and holes is 1.4×10−6 and 2×10−8 cm2 V−1 s−1, respectively, in a 400 nm thick sample. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.113806
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  • 8
    Electronic Resource
    Electronic Resource
    Femtosecond phase spectroscopy of multi-level systems: Phthalocyanines (1996)
    Springer
    Applied physics 63 (1996), S. 255-264 
    Details
    ISSN: 1432-0649
    Keywords: PACS: 07.60.Ly; 42.65.Re; 78.47.+p
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract.  A femtosecond frequency-domain interferometer is applied to metal-free and vanadyl phthalocyanine (H2Pc and VOPc) thin films to measure time-resolved difference phase and transmission spectra simultaneously. For both samples, the phase-change dynamics is different from the transmission-change dynamics at 620 nm, reflecting that the phthalocyanines (Pc) cannot be modeled with a two-level system but by a multi-level or inhomogeneously broadened system, in which each level pair exhibits different relaxation dynamics. Because of this dynamical difference, a phase-change measurement is required to correct distortion of the transient spectra due to induced phase modulation of probe pulses. Near zero time delay, the phase and transmission changes show different growth behavior. This behavior is explained by antisymmetric amplitude and phase gratings which are produced by coherent coupling between frequency-chirped pump and probe pulses.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01833795
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  • 9
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    Cenozoic paleogeography of the Andean foreland and retroarc hinterland of Colombia (2015)
    American Association of Petroleum Geologists (AAPG)
    Details
    Publication Date: 2015-08-04
    Description: New biostratigraphic zonations, core descriptions, sandstone petrography, facies analysis, and seismic information are compared with published detrital and bedrock geo- and thermochronology to build a Cenozoic paleogeographic reconstruction of the Andean retroarc region of Colombia, encompassing the ancestral Central Cordillera, Middle Magdalena Valley, Eastern Cordillera, and Llanos basin. We identify uplifted sediment source areas, provenance domains, depositional environments, and thickness changes to propose a refined paleogeographic evolution of eastern Colombia. We conclude that Cenozoic evolution of the northernmost Andes includes (1) a period of contractional deformation focused in the Central Cordillera and Middle Magdalena Valley that may have started by the Late Cretaceous, although thermochronological data points to maximum shortening and exhumation during the late Paleocene; (2) a period of slower deformation rates or even tectonic quiescence during the middle Eocene; and (3) a renewed phase of contractional deformation from the late Eocene to the Pleistocene/Holocene expressed in provenance, bedrock thermochronology, and increased subsidence rates in the Llanos foreland. The sedimentary response in the Llanos foreland basin is controlled by source area proximity, exhumation and shortening rates, relationships between accommodation and sediment supply, as well as potential paleoclimate forcing. This new reconstruction changes the picture of Cenozoic basin evolution offered by previous reconstructions, providing an updated chronology of deformation, which is tied to a more precise understanding of basin evolution.
    Print ISSN: 0149-1423
    Electronic ISSN: 0149-1423
    Topics: Geosciences
    Published by American Association of Petroleum Geologists (AAPG)
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  • 10
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    Evidence for middle Eocene and younger land emergence in central Panama: Implications for Isthmus closure (2012)
    Geological Society of America (GSA)
    Details
    Publication Date: 2012-05-01
    Description: The rise of the Isthmus of Panama, linked to a number of climatic, paleoceanographic, and biological events, has been studied mostly from indirect, often distal, geochemical and biotic evidence. We have upgraded existing geologic mapping in central Panama with more than 2000 field stations, over 40 petrographic analyses, and more than 30 new geochronological and thermochronological analyses. This data set suggests that the isthmus was an uninterrupted chain above sea level from late Eocene until at least late Miocene times. The basement complex of central Panama is a folded-faulted, ∼3-km-thick arc sequence, intruded by granitoid bodies and onlapped by mildly deformed upper Eocene and Oligocene strata. Six U/Pb zircon ages in the granitoids—along with published geochronological data—reveal intense late Paleocene to middle Eocene magmatism (58–39 Ma), a temporary cessation of magmatic activity between 38 and 27 Ma, and renewed magmatism between 25 and 15 Ma in a position ∼75 km south of the former magmatic axis. Thermochronological analyses in zircon (eight U-Th/He ages), and in apatite crystals (four U-Th/He ages and nine fission-track ages) obtained from a subset of 58–54 Ma granitoid bodies record a concordant Lutetian-age (47–42 Ma) cooling from ∼200 °C to ∼70 °C in ∼5 m.y., and cooling below ∼40 °C between 12 and 9 Ma. Cooling is linked to exhumation by an angular unconformity that separates the deformed basement complex below from mildly deformed, upper Eocene to Oligocene terrestrial to shallow-marine strata above. Exhumation and erosion of the basement complex are independently confirmed by lower Miocene strata that have a detrital zircon signature that closely follows the central Panama basement complex age distribution. These results greatly restrict the width and depth of the strait separating southern Central America from South America, and challenge the widely accepted notion that the Central American Seaway closed in late Pliocene time, when the ice age began.
    Print ISSN: 0016-7606
    Electronic ISSN: 1943-2674
    Topics: Geosciences
    Published by Geological Society of America (GSA)
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