Uplift and volcanism of the SE Colombian Andes in relation to Neogene sedimentation in the Upper Magdalena Valley

The present study deals with the relation between Neogene uplift and volcanism of the SE Colombian Andes and sedimentation processes in the Upper Magdalena Valley. The southernmost part of the Upper Magdalena Valley, the S. Neiva Basin, is located between latitudes 2°08'-2°31 N and longitudes 75°22'-75°37'W. To the east, the basin borders the Garzón Massif, the southernmost part of the Eastern Cordillera. To the west, the basin borders the terrain of a fold and thrust belt that was active from the Eocene to the L.Miocene. The Central Cordillera is located W of the fold and thrust belt.Three subinvestigations were carried out. A fission track study was performed on rocks from the Garzón Massif. Sedimentological, stratigraphical and geochronological investigations were accomplished in the S. Neiva Basin as well as in the area of the fold and thrust belt and part of the Central Cordillera. For the sake of clarity, these subinvestigations are discussed in different parts of the thesis.In part 1 (chapter I) the goals of the investigation are presented. Furthermore, information is given on the regional geology and tectonic setting and on published literature, aerial photographs and topographical sheets, used during the present study.Part 2 (chapter II) discusses the results of the fission track study of the Precambrian Garzón Massif. Fission track age determinations of apatites, zircons and sphenes revealed that three major uplift and cooling phases occurred. Around 900 Ma ago, an orogeny resulted in ≥10 km uplift. Some 100 Ma ago block faulting and differential uplift took place and between ≥12 Ma ago and the present time, the Garzón Massif was uplifted some 6.5 km.Part 3 (chapters III to VIII) deals with the Neogene deposits in the S. Neiva Basin. In chapter III the stratigraphy of the different rock units is discussed. Emphasis is on the Honda Formation, the Gigante Formation and the informal Las Vueltas formation.In chapter IV the age of these formations is given, established by means of K-Ar and fission track age determinations. The age of the Honda Formation ranges approximately from ≥16 Ma to 10-9 Ma; the age of the Gigante Formation from 10-9 Ma to ≤6 Ma. The age of the volcaniclastic middle member of the Gigante Formation could be more accurately determined and ranges from 8 Ma to 6.4 Ma. The age of the Las Vueltas formation could not be established, because the rocks do not contain volcanic material. On the grounds of the age of the Gigante Formation and a K-Ar age of ±1 Ma for the oldest Quaternary terrace, the formation is thought to have an Upper Miocene to Pliocene age.Chapter V is dedicated to the petrology of the three formations mentioned above. Pebble and point counts show that the sandstones and conglomerates of the Honda Formation and the lower two members of the Gigante Formation have a western provenance. The upper member of the Gigante Formation, however, shows strong admixing of material with an eastern provenance and the Las Vueltas formation consists entirely of erosional products from the Garzón Massif. These facts suggest that the first Neogene uplift phase of the massif ≥12 Ma ago had little influence on the deposits of the Honda Formation. They also suggest that a second uplift phase took place, which started during deposition of the upper member of the Gigante Formation and culminated during deposition of the Las Vueltas formation.In chapter VI the sedimentological characteristics of the Honda Formation are discussed. It appears that during periods of active uplift or volcanism, sediments were deposited by different alluvial fan systems and volcanic aprons, prograding on a broad alluvial plain. During intervening periods of greater volcanic and tectonic quiescence, the alluvial fans or volcanic aprons became much reduced in size, and sediments were laid down by braided and meandering river systems, flowing toward the east on the alluvial plain.In chapter VII the sedimentological characteristics of the Gigante Formation are treated. The lower and upper members of the formation were deposited by an ancestral Magdalena River, flowing toward the N. During deposition of the middle member, enormous quantities of volcaniclastics flooded the basin, forcing the paleo-Magdalena River to a more eastward position.Chapter VIII deals with the tectonics of the S. Neiva Basin. The second Neogene uplift pulse of the Garzón Massif, which started around 6.4 Ma ago, coincided with strong SE-NW compression, leading to folding and faulting of the basinal sediments. It is likely that deposition of the upper unit of the Las Vueltas formation resulted from strike-slip movements along the faults in the massif. On the basis of the approximate age of the sediments that underwent wrench-faulting, it is concluded that these movements began in the Pliocene. Wrench faulting appears to have had little influence on the faults within the S. Neiva Basin.Part 4 of the thesis (chapters IX to XI) is dedicated to deposits outside the S.Neiva Basin, which were investigated during the present study. These deposits comprise two small outcrops of fluvial and volcaniclastic sediments of Gigante age (chapter IX) as well as Pliocene to Quaternary volcaniclastic sediments of the fold and thrust belt area and the Central Cordillera (chapters X and XI).In chapter IX it is shown that the geological history of the S.Neiva Basin and the Garzón Massif is compatible with the geological history of the Suaza Valley, further to the S, and the Miocene history of the fold and thrust belt area.Chapter X deals with the Pliocene volcaniclastic deposits in the fold and thrust belt area and the Central Cordillera. These deposits comprise the informal fluvio-volcanic El Carmen formation, with an age of ≥3.3 Ma, and the ignimbrites of the Guacacallo Formation, with an age of 2.5±0.2 Ma. The stratigraphical relation between the ignimbrites and the Gigante Formation further to the E, in the S. Neiva Basin, suggests that the basin mainly underwent erosion in the period between *6 Ma and 2.5±0.2 Ma.Chapter XI treats the volcaniclastic terraces along the Páez River and the downstream part of the La Plata River. The deposits resulted from two separate influxes of volcaniclastic material, probably from the Nevado del Huila. The older deposits have an age of ±1 Ma; the younger deposits are dated at <1 Ma. After deposition, erosional terraces were formed in the sediments. The terraced deposits are lateral equivalents of similar terraces along the part of the Magdalena River, located between Gigante and El Hobo.In part 5 (chapter XII) a synthesis of the data from the previous chapters is given, and the geological histories of the different areas are integrated in a single model. Furthermore, uplift of the Garzón Massif is discussed in the light of the plate tectonic setting. Neogene uplift phases of the Garzón Massif coincided with cessation of activity of the Central Cordillera volcanic arc. Volcanism was resumed during periods of tectonic quiescence. The fact that Laramide-style uplift was contemporaneous with absence of volcanic activity, suggests that low-angle subduction of part of the Nazca Plate took place. Beside low-angle subduction, however, crustal predisposition to a certain style of uplift probably played a role in determining the style of mountain building. Thus it is likely that Laramide-style uplift of the massif was also influenced by the presence of inherited zones of structural weakness

Fractional plateaus in the Coulomb blockade of coupled quantum dots

Ground-state properties of a double-large-dot sample connected to a reservoir via a single-mode point contact are investigated. When the interdot transmission is perfect and the dots controlled by the same dimensionless gate voltage, we find that for any finite backscattering from the barrier between the lead and the left dot, the average dot charge exhibits a Coulomb-staircase behavior with steps of size e/2 and the capacitance peak period is halved. The interdot electrostatic coupling here is weak. For strong tunneling between the left dot and the lead, we report a conspicuous intermediate phase in which the fractional plateaus get substantially altered by an increasing slope.Comment: 6 pages, 4 figures, final versio

Quantum phase transition in a two-channel-Kondo quantum dot device

We develop a theory of electron transport in a double quantum dot device recently proposed for the observation of the two-channel Kondo effect. Our theory provides a strategy for tuning the device to the non-Fermi-liquid fixed point, which is a quantum critical point in the space of device parameters. We explore the corresponding quantum phase transition, and make explicit predictions for behavior of the differential conductance in the vicinity of the quantum critical point

Quantum phase transitions in the Bose-Fermi Kondo model

We study quantum phase transitions in the Bose-Fermi Kondo problem, where a local spin is coupled to independent bosonic and fermionic degrees of freedom. Applying a second order expansion in the anomalous dimension of the Bose field we analyze the various non-trivial fixed points of this model. We show that anisotropy in the couplings is relevant at the SU(2) invariant non Fermi liquid fixed points studied earlier and thus the quantum phase transition is usually governed by XY or Ising-type fixed points. We furthermore derive an exact result that relates the anomalous exponent of the Bose field to that of the susceptibility at any finite coupling fixed point. Implications on the dynamical mean field approach to locally quantum critical phase transitions are also discussed.Comment: 13 pages, 9 figures, some references added/correcte

Malnutrition assessment methods in adult patients with tuberculosis:A systematic review

OBJECTIVES: Malnutrition is associated with a twofold higher risk of dying in patients with tuberculosis (TB) and considered an important potentially reversible risk factor for failure of TB treatment. The construct of malnutrition has three domains: intake or uptake of nutrition; body composition and physical and cognitive function. The objectives of this systematic review are to identify malnutrition assessment methods, and to quantify how malnutrition assessment methods capture the international consensus definition for malnutrition, in patients with TB. DESIGN: Different assessment methods were identified. We determined the extent of capturing of the three domains of malnutrition, that is, intake or uptake of nutrition, body composition and physical and cognitive function. RESULTS: Seventeen malnutrition assessment methods were identified in 69 included studies. In 53/69 (77%) of studies, body mass index was used as the only malnutrition assessment method. Three out of 69 studies (4%) used a method that captured all three domains of malnutrition. CONCLUSIONS: Our study focused on published articles. Implementation of new criteria takes time, which may take longer than the period covered by this review. Most patients with TB are assessed for only one aspect of the conceptual definition of malnutrition. The use of international consensus criteria is recommended to establish uniform diagnostics and treatment of malnutrition. PROSPERO REGISTRATION NUMBER: CRD42019122832

Cortical phase changes measured using 7-T MRI in subjects with subjective cognitive impairment, and their association with cognitive function

FSW - Self-regulation models for health behavior and psychopathology - ou

Spin Exciton in quantum dot with spin orbit coupling in high magnetic field

Coulomb interactions of few ($N$) electrons confined in a disk shaped quantum dot, with a large magnetic field $B=B^*$ applied in the z-direction (orthogonal to the dot), produce a fully spin polarized ground state. We numerically study the splitting of the levels corresponding to the multiplet of total spin $S=N/2$ (each labeled by a different total angular momentum $J_z$) in presence of an electric field parallel to $B$, coupled to $S$ by a Rashba term. We find that the first excited state is a spin exciton with a reversed spin at the origin. This is reminiscent of the Quantum Hall Ferromagnet at filling one which has the skyrmion-like state as its first excited state. The spin exciton level can be tuned with the electric field and infrared radiation can provide energy and angular momentum to excite it.Comment: 9 pages, 9 figures. submitted to Phys.Rev.

Kondo effect in transport through Aharonov-Bohm and Aharonov-Casher interferometers

We derive the extension of the Hubbard model to include Rashba spin-orbit coupling that correctly describes Aharonov-Bohm and Aharonov-Casher phases in a ring under applied magnetic and electric fields. When the ring is connected to conducting leads, we develop a formalism that is able to describe both, Kondo and interference effects. We find that in the Kondo regime, the spin-orbit coupling reduces strongly the conductance from the unitary limit. This effect in combination with the magnetic flux, can be used to produce spin polarized carriers.Comment: 6 pages, 4 figures, presented at SCES2008, Buzios, Brasi

Vegetation responses to abrupt climatic changes during the Last Interglacial Complex (Marine Isotope Stage 5) at Tenaghi Philippon, NE Greece

The discovery that climate variability during the Last Glacial shifted rapidly between climate states has intensified efforts to understand the distribution, timing and impact of abrupt climate change under a wide range of boundary conditions. In contribution to this, we investigate the nature of abrupt environmental changes in terrestrial settings of the Mediterranean region during the Last Interglacial Complex (Marine Isotope Stage [MIS] 5) and explore the relationships of these changes to high-latitude climate events. We present a new, temporally highly resolved (mean: 170 years) pollen record for the Last Interglacial Complex from Tenaghi Philippon, north-east Greece. The new pollen record, which spans the interval from 130,000 to 65,000 years ago, forms part of an exceptionally long polleniferous sediment archive covering the last 1.35 million years. The pollen data reveal an interglacial followed by alternating forest and steppe phases representing the interstadials and stadials of the Early Glacial. Superimposed on these millennial-scale changes is evidence of persistent sub-millennial-scale variability. We identify ten high-amplitude abrupt events in the pollen record, characterised by rapid contractions of closed forest to open steppe environment and interpreted to indicate major changes in moisture availability and temperature. The contractions in forest cover on millennial timescales appear associated with cooling events in the Mediterranean Sea, North Atlantic and Greenland regions, linked to the Dansgaard-Oeschger (DO) cycles of the Early Glacial. On sub-millennial timescales, the pattern of changes in forest cover at Tenaghi Philippon display a structure similar to the pattern of short-lived precursor and rebound-type events detected in the Greenland ice-core record. Our findings indicate that persistent, high-amplitude environmental variability occurred throughout the Early Glacial, on both millennial and submillennial timescales. Furthermore, the similarity of the pattern of change between Tenaghi Philippon and Greenland on sub-millennial timescales suggests that teleconnections between the high-latitudes and the Mediterranean region operate on sub-millennial timescales and that some terrestrial archives, such as Tenaghi Philippon, are particularly sensitive recorders of these abrupt climate changes

Low temperature transport in AC-driven Quantum Dots in the Kondo regime

We present a fully nonequilibrium calculation of the low temperature transport properties of a quantum dot in the Kondo regime when an AC potential is applied to the gate voltage. We solve a time dependent Anderson model with finite on-site Coulomb interaction. The interaction self-energy is calculated up to second order in perturbation theory in the on-site interaction, in the context of the Keldysh non-equilibrium technique, and the effect of the AC voltage is taken into account exactly for all ranges of AC frequencies and AC intensities. The obtained linear conductance and time-averaged density of states of the quantum dot evolve in a non trivial way as a function of the AC frequency and AC intensity of the harmonic modulation.Comment: 30 pages,7 figure