The geology and tectonic evolution of the northwest part of the Barberton Greenstone Belt, South Africa: A review

2019 ◽  
Vol 122 (4) ◽  
pp. 421-454
Author(s):  
C.R. Anhaeusser
Keyword(s):  
Greenstone Belt ◽  
Structural Evolution ◽  
Structural Complexity ◽  
Strike Slip ◽  
Schist Belt ◽  
Progressive Deformation ◽  
Barberton Greenstone Belt ◽  
Wide Range ◽  
Area North ◽  
Granitoid Intrusions

AbstractFormations on the northwestern flank of the Barberton Greenstone Belt have hosted over 85% of all the gold recovered from the ca. 3550 to 3000 Ma Barberton Supergroup since early discoveries in 1872. This sector of the greenstone belt also happens to coincide with a complex tectonic architecture resulting from successive stages of folding and faulting superimposed onto a complex lithostratigraphy. Of particular importance has been the influence of two diapiric granitoid intrusions that caused added structural complexity following their emplacement ca. 3227 to 3250 Ma. Of these the larger Kaap Valley Pluton invaded the area north of present day Barberton town causing the separation of the greenstones into a northern arm (Jamestown Schist Belt) and a southern sector which remained attached to the main greenstone belt (Moodies Hills). The ballooning pluton produced vertical as well as horizontal flattening stresses, the latter reactivating earlier high-angle faults and resulting in subhorizontal strike-slip movements, particularly along the Barbrook Fault Zone, which acted as a right-lateral strike-slip fault. Formations north of this fault were buckled, following progressive deformation in the region known as the Sheba Hills, into major synclinal folds (Eureka and Ulundi Synclines) with folded axial planes that dip steeply to the south, southeast or east. The second granitoid intrusion (Stentor Pluton), which has been extensively modified by subsequent magmatic events, caused significant flattening of greenstone belt rocks in the northeastern part of the Barberton Greenstone Belt (Three Sisters region) as well as in other areas rimming the granitic body. Combined, the two plutons produced a wide range of interference and reactivated structures particularly affecting a triangular region extending from the Jamestown Schist Belt into the area occupied by the New Consort Gold Mine and areas to the east. This paper attempts to outline, in the simplest manner, the geological and structural evolution of the main gold-producing region of the Barberton Goldfield. The principal aim is therefore to highlight the structural influence of the diapiric plutonism and the manner in which the plutons contributed significantly to the horizontal reactivation of pre-existing regional faults, which in turn, resulted in the progressive deformation of a heterogeneous lithological terrane.

Colloidal Plasmonic Nanostar Antennas with Wide Range Resonance Tunability

2019 ◽  
Author(s):  
Theodoros Tsoulos ◽  
Supriya Atta ◽  
Maureen Lagos ◽  
Michael Beetz ◽  
Philip Batson ◽  
...  
Keyword(s):  
Single Particle ◽  
Structural Complexity ◽  
Field Enhancement ◽  
Hot Electron ◽  
Structure Property ◽  
Plasmon Band ◽  
Gold Nanostars ◽  
Wide Range ◽  
Particle Level ◽  
Spectrally Resolved

<div>Gold nanostars display exceptional field enhancement properties and tunable resonant modes that can be leveraged to create effective imaging tags or phototherapeutic agents, or to design novel hot-electron based photocatalysts. From a fundamental standpoint, they represent important tunable platforms to study the dependence of hot carrier energy and dynamics on plasmon band intensity and position. Toward the realization of these platforms, holistic approaches taking into account both theory and experiments to study the fundamental behavior of these</div><div>particles are needed. Arguably, the intrinsic difficulties underlying this goal stem from the inability to rationally design and effectively synthesize nanoparticles that are sufficiently monodispersed to be employed for corroborations of the theoretical results without the need of single particle experiments. Herein, we report on our concerted computational and experimental effort to design, synthesize, and explain the origin and morphology-dependence of the plasmon modes of a novel gold nanostar system, with an approach that builds upon the well-known plasmon hybridization model. We have synthesized monodispersed samples of gold nanostars with finely tunable morphology employing seed-mediated colloidal protocols, and experimentally observed narrow and spectrally resolved harmonics of the primary surface plasmon resonance mode both at the single particle level (via electron energy loss spectroscopy) and in ensemble (by UV-Vis and ATR-FTIR spectroscopies). Computational results on complex anisotropic gold nanostructures are validated experimentally on samples prepared colloidally, underscoring their importance as ideal testbeds for the study of structure-property relationships in colloidal nanostructures of high structural complexity.</div>

scholarly journals Quantifying Understory Complexity in Unmanaged Forests Using TLS and Identifying Some of Its Major Drivers

2021 ◽  
Vol 13 (8) ◽  
pp. 1513
Author(s):  
Dominik Seidel ◽  
Peter Annighöfer ◽  
Christian Ammer ◽  
Martin Ehbrecht ◽  
Katharina Willim ◽  
...  
Keyword(s):  
Laser Scanning ◽  
Structural Equation Models ◽  
Light Availability ◽  
Structural Complexity ◽  
Basal Area ◽  
Ecosystem Functions ◽  
Canopy Openness ◽  
Seasonal Precipitation ◽  
Wide Range ◽  
Precipitation And Temperature

The structural complexity of the understory layer of forests or shrub layer vegetation in open shrublands affects many ecosystem functions and services provided by these ecosystems. We investigated how the basal area of the overstory layer, annual and seasonal precipitation, annual mean temperature, as well as light availability affect the structural complexity of the understory layer along a gradient from closed forests to open shrubland with only scattered trees. Using terrestrial laser scanning data and the understory complexity index (UCI), we measured the structural complexity of sites across a wide range of precipitation and temperature, also covering a gradient in light availability and basal area. We found significant relationships between the UCI and tree basal area as well as canopy openness. Structural equation models (SEMs) confirmed significant direct effects of seasonal precipitation on the UCI without mediation through basal area or canopy openness. However, annual precipitation and temperature effects on the UCI are mediated through canopy openness and basal area, respectively. Understory complexity is, despite clear dependencies on the available light and overall stand density, significantly and directly driven by climatic parameters, particularly the amount of precipitation during the driest month.

Paleomagnetism of 3.5-4.0 Ga zircons from the Barberton Greenstone Belt, South Africa

2021 ◽  
Vol 567 ◽  
pp. 116999
Author(s):  
Roger R. Fu ◽  
Nadja Drabon ◽  
Michael Wiedenbeck ◽  
Alec R. Brenner ◽  
Donald R. Lowe ◽  
...  
Keyword(s):  
South Africa ◽  
Greenstone Belt ◽  
Barberton Greenstone Belt

Salt thickness and heterogeneity control the degree of coupling between sub- and supra-salt structure during salt-detached translation: evidence from physical models

2021 ◽  
Author(s):  
Sian Evans ◽  
Christopher Jackson ◽  
Sylvie Schueller ◽  
Jean-Marie Mengus
Keyword(s):  
Structural Evolution ◽  
Structural Complexity ◽  
Vertical Movement ◽  
Sediment Supply ◽  
Physical Models ◽  
Structural Development ◽  
Salt Structure ◽  
Regional Tectonic ◽  
Base Salt ◽  
Strain Coupling

&lt;p&gt;Salt flows like a fluid over geological timescales and introduces significant structural complexity to the basins in which it is deposited. Salt typically flows seaward due to tilting of the basin margins, and is therefore influenced by the geometry of the surface that it flows across (e.g. fault scarps or folds on the base-salt surface). This can lead to coupling of sub- and supra-salt structures, with the orientation and distribution of base-salt structures reflected in the structure of the overburden. However, precisely what controls the degree of strain coupling during salt-detached translation is still poorly understood, in particular the role played by salt thickness and lithological heterogeneity. This partly reflects the fact that it can be difficult to deconvolve the relative contributions of natural variables such as the magnitude of relief, sediment supply, and regional tectonic regime. In addition, seismic data provide only the present structural configuration of salt basins, from which their formative kinematics must be inferred. If we can develop a better understanding of how sub-salt structure controls the types and patterns of supra-salt deformation, we can produce better kinematic (structural) restorations of salt basins and, therefore, have a better understanding of the related mechanics.&lt;/p&gt;&lt;p&gt;In order to isolate the influence of salt thickness and heterogeneity on sub- to supra-salt strain coupling during salt-detached horizontal translation, we present a series of physical analogue models with controlled boundary conditions. We use a simple base-salt geometry comprising three oblique base-salt steps, and vary the thickness and composition of the ductile salt analogue in each experiment. X-ray tomography allows us to image the internal structure during model evolution and therefore gain a 4D picture of its structural development.&lt;/p&gt;&lt;p&gt;Results show that thicker and more homogeneous salt units experience more vertical movement (i.e. minibasin subsidence and diapiric rise) and the overburden structure is less explicitly coupled with the underlying base-salt relief. Conversely, thinner and more heterogeneous salt units restrict vertical movement, and therefore the resulting overburden structure is dominated by lateral movement and more closely coupled to the geometry of the base-salt surface. These results highlight the important role of base-salt relief in the subsequent structural evolution of salt basins and why, despite broad similarities between different salt basins, there is significant variability in their structural styles.&lt;/p&gt;

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