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Early Cambrian magmatic arc flanked by an inverted Cambrian sedimentary basin in the Wilson Terrane of East Antarctica
No full textThe Ross Orogen, in East Antarctica, is linke
d to Cambro-Ordovician subduction and terrane
accretion processes along the paleo-Pacific active margin of Gondwana.
Geological investigations
within the partially exposed basement rocks of
Northern Victoria Land (NVL) have revealed
several major terrane bounding and intra-terrane faul
ts that were active during the Ross Orogen.
However, considerable uncertainty remains regard
ing the deeper crustal architecture and tectonic
evolution of the innermost Wilson Terrane (WT),
the closest recognised tectonic domain to the
East Antarctic Craton. Here we compile and an
alyse enhanced aeromagnetic and gravity anomaly
images from NVL to the Wilkes Subglacial Basin
(WSB) to provide new geophysical constraints on
the crustal architecture and the tect
onic and magmatic evolution of the WT.
Aeromagnetic imaging delineates a major fault system flanking the eastern margin of the Wilkes
Subglacial Basin, which connects to the previously
interpreted Prince Albert Fault System to the
south. Contrary to previous interp
retations, however, this fault syst
em is distinct and lies west of
the Exiles Thrust fault system. Magnetic mode
lling indicates that much larger and thicker
batholiths were emplaced along this fault system
, compared to the thinner sheet-like granitoid
bodies emplaced along the late-Ross Exiles Thrust fault system.
Zircon U–Pb dating over small
exposures of gabbro-diorites within the Prince Al
bert Mountains to the south lead us to propose
that this part of the magmatic arc was emplac
ed in a dominantly transtensional setting along a
major pre-existing fault or suture zone during an earlier phase of subduction (>520 Ma or older),
compared to the intrusions exposed further to
the east. Long-wavelength magnetic lows and
residual Bouguer gravity highs over the central Wi
lson Terrane further to the east are interpreted
with the aid of two-dimensional modelling as refl
ecting several-km thick inverted sedimentary
basins of inferred early Cambrian age. Tectonic inve
rsion likely occurred along major thrust faults,
formed in a dominantly transpressional late stage of
the Ross Orogen. Overall, our interpretations
provide new geophysical evidence in support of a
long-lived and composite WT that experienced
magmatic arc migration and basin inversion in re
sponse to changes in the geometry and dynamics
of the subduction system, much like
several modern subduction systems
Basement faults as a control on crustal architecture and topography at the transiton between Northern Victoria Land and the Wilkes Subglacial Basin (East Antarctica)
No full textMajor terrane bounding and intra-terrane faults have been recognised from extensive geological investigations
within the partially exposed basement rocks of Northern Victoria Land (NVL) in East Antarctica. These major
fault systems were active during the Ross Orogen and are related to several phases of Cambrian to Ordovician age
subduction and crustal accretion along the active paleo-Pacific margin of Gondwana. Here we compile and analyse
enhanced aeromagnetic and gravity anomaly images from NVL to the eastern margin of the Wilkes Subglacial
Basin (WSB) to image the subglacial extent and tectonic architecture of these major fault systems within the base-
ment. Our two-dimensional magnetic and gravity models predict that linear and long-wavelength magnetic lows
and residual Bouguer gravity highs over the central Wilson Terrane reflect several-km thick inverted sedimentary
basins of early Cambrian(?) age. Tectonic inversion occurred primarily along major thrust faults, formed in a dom-
inantly transpressional late stage of the Ross Orogen. Further west, a major fault system flanks the eastern margin
of the Wilkes Subglacial Basin, and connects to the previously interpreted Prince Albert Fault System to the south.
This fault system can now be recognised as lying west of the Exiles Thrust fault system, rather than represent-
ing its southern continuation (e.g. Ferraccioli and Bozzo, 1999, JGR). Relatively thin sheets of mylonitic sheared
granitoids and possible ultramafic lenses are modelled as being associated with the late-Ross (ca 480 Ma) Exiles
Thrust fault system, while significantly larger and thicker batholiths were emplaced along the Prince Albert Fault
System. Recent zircon U–Pb dating over small exposures of gabbro-diorites within the Prince Albert Mountains to
the south lead us to propose that this part of the magmatic arc was emplaced along a major pre-existing fault during
an earlier phase of subduction (>520 Ma or older). This attests to a long-lived and composite magnatic arc system,
which likely migrated in response to changes in the geometry and dynamics of the subduction system, much like
several modern arc systems. Whether the Prince Albert Fault System was indeed a major arc-continent suture in
early Cambrian times, as proposed by Ferraccioli et al., 2002 (GRL), or simply an arc to back-arc, or alternatively
an arc to forearc transition, remains to be more fully understood. Irrespective of possible alternative models for
the original tectonic setting of these faults during the Ross Orogen, we show by combining aeromagnetic inter-
pretation and topographic lineament analyses that these major terrane bounding and intra-terrane basement faults
exerted a key influence both on the tectonic segmentation of the Transantarctic Mountains into discrete Cenozoic
fault-blocks and on the subglacial topography along the eastern margin of the WSB
Phenomenological models of NaV1.5. A side by side, procedural, hands-on comparison between Hodgkin-Huxley and kinetic formalisms
No full textComputational models of ion channels represent the building blocks of conductance-based, biologically inspired models of neurons and neural networks. Ion channels are still widely modelled by means of the formalism developed by the seminal work of Hodgkin and Huxley (HH), although the electrophysiological features of the channels are currently known to be better fitted by means of kinetic Markov-type models. The present study is aimed at showing why simplified Markov-type kinetic models are more suitable for ion channels modelling as compared to HH ones, and how a manual optimization process can be rationally carried out for both. Previously published experimental data of an illustrative ion channel (NaV1.5) are exploited to develop a step by step optimization of the two models in close comparison. A conflicting practical limitation is recognized for the HH model, which only supplies one parameter to model two distinct electrophysiological behaviours. In addition, a step by step procedure is provided to correctly optimize the kinetic Markov-type model. Simplified Markov-type kinetic models are currently the best option to closely approximate the known complexity of the macroscopic currents of ion channels. Their optimization can be achieved through a rationally guided procedure, and allows to obtain models with a computational burden that is comparable with HH models one
Arc Boudinage, Basin Inversion and Obduction in an Evolving Subduction System of East Antarctica
No full textThe paleo-Pacific margin of Gondwana experienced protracted subduction and accretionary tectonics starting in late Neoproterozic-early Cambrian times. Northern Victoria Land (NVL), in East Antarctica, preserves a cryptic record of these active margin processes. Most models indicate that NVL contains three main terranes, namely the Robertson Bay, Bowers and Wilson terranes. Significant debate centres, however, on whether these are far travelled terranes with respect to the East Antarctic Craton, and on the tectonic and magmatic processes that affected its active margin and were ultimately responsible for the formation of the Ross Orogen.
Here we interpret new aeromagnetic, aerogravity and land-gravity compilations that enable us to trace the extent of major subglacial faults in the basement of NVL, examine crustal architecture, and propose a new evolutionary model for the active margin of the craton. Prominent aeromagnetic anomalies at the edge of the Wilkes Subglacial Basin delineate the extent of an early-stage magmatic arc (ca 530 Ma?). This arc may have accreted as an exotic element onto the former Neoproterozoic rifted margin of East Antarctica or (perhaps more likely) developed in situ upon a pre-existing suture.
Remnants of magnetic arc basement are also identified ca 150 km further to the east within the Wilson Terrane (WT). We propose that these were originally adjacent arc segments and that transtension triggered significant arc boudinage separating these segments. Transtension may have created accommodation space for the development of thick Cambrian sedimentary basins, which are marked by regional magnetic lows with an en-echelon geometry. Basin inversion likely occurred in a later traspressional stage of the Ross-Delamerian Orogen (ca. 490-460 Ma) that triggered the development of a major pop-up structure within the WT. Several buried thrusts of the pop-up can be traced in the aeromagnetic images and a prominent residual gravity high delineates its high-grade metamorphic core. High amplitude magnetic and gravity anomalies also delineate buried oceanic basement of the northern Bowers Terrane. Oceanic basement was likely uplifted and obducted onto to the margin either because of oblique subduction or because of docking of a microcontinent inferred to underlie part of the Robertson Bay Terrane
GEOMAGNETIC DEEP SOUNDING INVESTIGATIONS AT THE TRANSITION BETWEEN THE TRANSANTARCTIC MOUNTAINS AND THE WILKES SUBGLACIAL BASIN, NORTHERN VICTORIA LAND
No full textNorth Victoria Land (NVL) features two major tectonic elements: the Transantarctic Mountains (TAM), forming the uplifted flank of the Mesozoic and Cenozoic West Antarctic Rift System, and the Wilkes Subglacial Basin (WSB). Structure of the TAM rift flank has been partially investigated with different geophysical approaches. To the West, the Wilkes Subglacial Basin is present, a broad depression over 400 km wide at the George V Coast and 1200 km long. Geology, lithospheric structure and tectonics of the Basin are only partially known because the Basin is buried beneath the East Antarctic Ice Sheet and is located in a remote region which makes geophysical exploration logistically challenging. Different authors have proposed contrasting hypothesis regarding the origin of the WSB: it could represent a region of rifted continental crust or it may have a flexural origin or might represent an "extended terrane".
Here we present inferences on the electrical conductivity structures at the transition between the TAM and the eastern margin of the WSB, based on Geomagnetic Depth Soundings (GDS) carried out during three different international Antarctic campaigns supported by the Italian Antarctic Projet: the BACKTAM, WIBEM and WISE expeditions. All the data have been processed in the frame of the ISEE project, aimed at evaluate the bias effect of the Polar Electrojet on geomagnetic transfer functions at different high geomagnetic latitudes and to study processing algorithms for magnetotelluric impedance tensor and magnetovariational transfer function estimate with high geomagnetic latitudes data.
The qualitative analysis of the induction arrows, in the period range 20-170 s, reveals an approximately 2D regional electrical conductivity pattern with a clear differentiation between the three Terrains crossed by the GDS transect: the Robertson Bay, the Bowers and the Wilson Terrain. Bi-dimensional models suggest a differentiation of the investigated area in three crustal sectors separated by the Daniels Range and the Bowers Mts., in close relation with main known structural lineaments; to the West, a deep conductivity anomaly is associated with the transition to the Wilkes Subglagial Basin
A new stratigraphic and tectonic model of the South eastern Monte Antola Unit and its relationship with the Monte Gottero Unit (eastern Liguria).
No full textExtent and architecture of major fault systems between northern Victoria Land and the eastern margin of the Wilkes Subglacial Basin (East Antarctica)
No full textTerrane bounding and intra-terrane faults of the Ross Orogen in East Antarctica are linked to several phases of Cambrian to Ordovician age subduction and accretion along the active paleo-Pacific margin of Gondwana. Here we compile and analyse new enhanced aeromagnetic anomaly images over the Northern Victoria Land (NVL) segment of the Ross Orogen and the eastern margin of the Wilkes Subglacial Basin (WSB) that help constrain the extent and structural architecture of these fault systems and enable us re-assess their tectonic evolution. Long-wavelength magnetic lows and residual Bouguer gravity highs are modelled as several-km thick inverted sedimentary basins of early Cambrian(?) age. Tectonic inversion occurred along major thrust faults during the late stages of the Ross Orogen, forming a major high-grade pop-up structure within the central Wilson Terrane, flanked by lower grade rocks. The Prince Albert Fault System can now be recongnised as being located to the west of the Exiles Thrust fault system rather than representing its southern continuation. Relatively thin sheets of mylonitic sheared granitoids and possible ultramafic lenses are associated with the late-Ross (ca 480 Ma) Exiles Thrust fault system, while significantly larger and thicker batholiths were emplaced along the Prince Albert Fault System. Recent zircon U-Pb dating over small exposures of gabbro-diorites within the Prince Albert Mountains to the south lead us to propose that this part of the magmatic arc was emplaced during an earlier phase of subduction (~520 Ma or older?), compared to the late-Ross intrusions to the east. Whether the Prince Albert Fault System was indeed a major cryptic suture in early Cambrian times (Ferraccioli et al., 2002, GRL) remains speculative, but possible. Our aeromagnetic interpretation leads us to conclude that these inherited terrane bounding and intra-terrane fault systems of the Ross Orogen exerted a key influence on Cenozoic tectonic blocks and faults of the Transantarctic Mountains, and that the eastern margin of the WSB adjacent to NVL was also strongly controlled by a complex array of major intraplate strike-slip fault systems
Axon-somatic back-propagation in detailed models of spinal alpha motoneurons
No full textAntidromic action potentials following distal stimulation of motor axons occasionally fail to invade the soma of alpha motoneurons in spinal cord, due to their passing through regions of high non-uniformity.Morphologically detailed conductance-based models of cat spinal alpha motoneurons have been developed, with the aim to reproduce and clarify some aspects of the electrophysiological behavior of the antidromic axon-somatic spike propagation. Fourteen 3D morphologically detailed somata and dendrites of cat spinal alpha motoneurons have been imported from an open-access web-based database of neuronal morphologies, NeuroMorpho.org, and instantiated in neurocomputational models. An axon hillock, an axonal initial segment and a myelinated axon are added to each model.By sweeping the diameter of the axonal initial segment (AIS) and the axon hillock, as well as the maximal conductances of sodium channels at the AIS and at the soma, the developed models are able to show the relationships between different geometric and electrophysiological configurations and the voltage attenuation of the antidromically travelling wave.In particular, a greater than usually admitted sodium conductance at AIS is necessary and sufficient to overcome the dramatic voltage attenuation occurring during antidromic spike propagation both at the myelinated axon-AIS and at the AIS-soma transitions
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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