The growth of the Zimbabwe Craton during the late Archaean: an ion microprobe U–Pb zircon study

2011 ◽  
Vol 168 (4) ◽  
pp. 941-952 ◽  
Author(s):  
Hugh R. Rollinson ◽  
Martin Whitehouse
Keyword(s):  
Ion Microprobe ◽  
Late Archaean ◽  
Zimbabwe Craton

A terrane interpretation of the Archaean Limpopo Belt

1993 ◽  
Vol 130 (6) ◽  
pp. 755-765 ◽  
Author(s):  
H. R. Rollinson
Keyword(s):  
Shear Zones ◽  
Kaapvaal Craton ◽  
Late Archaean ◽  
The North ◽  
Zimbabwe Craton ◽  
Marginal Zones ◽  
Limpopo Belt

AbstractThe Limpopo Belt is a zone of thickened Archaean crust whose origin is currently explained by a late Archaean continent-continent collision between the Kaapvaal and Zimbabwe cratons. This review shows that the two cratons have fundamentally different geological histories and that the Zimbabwe Craton was unlikely to have behaved as a stable ‘cratonic’ block at the time of the Limpopo Belt collision. The geological histories of the Zimbabwe Craton, the North Marginal, Central and South Marginal zones of the Limpopo Belt and the Kaapvaal Craton are shown to be sufficiently different from one another to warrant their consideration as discrete terranes. The boundaries between the five units outlined above are all major shear zones, further supporting a terrane model for the Limpopo Belt. The five units were all intruded by late- to syn-tectonic granites c.2.6 Ga, constraining the accretion event to c. 2.6 Ga.

scholarly journals Configuration of Late Archaean Chilimanzi and Razi Suites of Granites, South-Central Zimbabwe Craton, From Gravity Modelling: Geotectonic Implications

2019 ◽  
Vol 177 (2) ◽  
pp. 1043-1069
Author(s):  
Rubeni T. Ranganai ◽  
Oswald Gwavava ◽  
Cynthia J. Ebinger ◽  
Kathryn A. Whaler
Keyword(s):  
Gravity Modelling ◽  
Late Archaean ◽  
South Central ◽  
Zimbabwe Craton

A SHRIMP ion microprobe study of inherited and magmatic zircons from four Scottish Caledonian granites

1992 ◽  
Vol 83 (1-2) ◽  
pp. 473-483 ◽  
Author(s):  
R. T. Pidgeon ◽  
W. Compston
Keyword(s):  
Source Rocks ◽  
Magmatic Zircon ◽  
Ion Microprobe ◽  
Age Composition ◽  
Chemical Changes ◽  
Zircon Age ◽  
Late Archaean ◽  
Late Proterozoic ◽  
Detailed Assessment ◽  
Middle Proterozoic

ABSTRACTUsing the ion microprobe SHRIMP we have analysed zircons from the Ben Vuirich, Glen Kyllachy, Inchbae and Vagastie Bridge granites from the Scottish Caledonides, in an attempt to resolve the ages of inherited zircons shown to be present in these granites by previous conventional multigrain analyses. Middle Proterozoic age components were found in inherited zircons from all four granites. Late Proterozoic (900–1,100 Ma) components have been identified in zircons from the Glen Kyllachy and Ben Vuirich granites in the Grampian Highlands. A Late Archaean age has only been detected in one zircon from the Glen Kyllachy granite. The distribution of inherited components in the granite zircon populations could reflect fundamental divisions in the age composition of granite source rocks; however, detailed assessment of this possibility must await further ion microprobe analyses on zircons from many more granites.SHRIMP isotopic and U, Th and Pb analyses were made on successive shells of zoned zircon surrounding inherited cores from the Glen Kyllachy granite to monitor chemical changes during magmatic zircon growth. Results show that zircon shells have characteristic but significantly different Th, U and Pb concentrations. Magmatic zircon from the Vagastie Bridge granite also forms as clearly defined oscillatory zoned shells around unzoned nuclei of inherited zircon. However, the distinction between magmatic and inherited zircon in zircons from the Inchbae granite is less clear. Zircons from the Ben Vuirich granite occur as euhedral, magmatic zircons, or as rounded, subhedral, inherited zircon grains. A SHRIMP age of 597 ± 11 (2σ) Ma for euhedral magmatic zircon from this granite is identical, within the uncertainty, to the conventional multigrain zircon age of 590 ± 2 (2σ) Ma reported by Rogers et al. (1989) and confirms the conclusions of those authors that sedimentation of the Dalradian sequence took place in the Precambrian.

scholarly journals Tectonostratigraphic terranes within Archaean gneiss complexes: examples from Western Australia and southern West Greenland

1991 ◽  
Vol 39 ◽  
pp. 199-211
Author(s):  
Allen P. Nutman
Keyword(s):  
Western Australia ◽  
Field Work ◽  
Ion Microprobe ◽  
Late Archaean ◽  
West Greenland ◽  
Tectonic Processes ◽  
Gneiss Complex ◽  
Northwestern Margin ◽  
Geological Boundaries ◽  
Orogenic Belts

New field work and isotopic data show that the Godthabsfjord region of West Greenland consists of a collage of tectonostratigraphic terranes, which evolved separately prior to tectonic juxtaposition in the late Archaean. In Western Australia the Narryer Gneiss Complex, which lies on the northwestern margin of the Yilgarn Craton, is, unlike the Godthabsfjord region, very poorly exposed (less than 1 % ). In consequence it is impossible to follow geological boundaries in this complex, and instead the complex has been studied by a very extensive use of within-grain zircon U-Pb geochronology on the ion microprobe SHRIMP. The zircon geochronology suggests that the Narryer Gneiss Complex also consists of several discrete terranes of early to mid Archaean gneisses. In both the Godthabsfjord region and the Narryer Gneiss Complex, late Archaean juxtaposition of terranes was accompanied by intrusion of crustally­derived granites, deformation, and amphibolite facies metamorphism. Thus some Archaean high grade gneiss complexes consist of terranes that underwent independent evolution until they were brought together at a later time. In this respect their anatomy resembles post-Archaean orogenic belts that formed as a consequence of plate tectonic processes.

U–Pb ages of single zircons within "Upernavik" metasedimentary rocks and regional implications for the tectonic evolution of the Archaean Nain Province, Labrador

1992 ◽  
Vol 29 (2) ◽  
pp. 260-276 ◽  
Author(s):  
L. Schiøtte ◽  
A. P. Nutman ◽  
D. Bridgwater
Keyword(s):  
Granulite Facies ◽  
Detrital Zircons ◽  
Ion Microprobe ◽  
Granulite Facies Metamorphism ◽  
Late Archaean ◽  
Metasedimentary Rocks ◽  
Bay Area ◽  
Single Grain ◽  
Different Sources ◽  
Rock Complex

Detrital zircons and their postdepositional overgrowths from three units of the "Upernavik" supracrustal association in the northern (Saglek) block of the Archaean Nain Province have been dated with the ion microprobe SHRIMP. In one unit, from the granulite-facies area in inner Saglek Fiord, the zircon population is dominated by early Archaean grains thought to be derived from the Uivak gneisses. Recrystallization and growth of new zircon within this metasediment took place during granulite-facies metamorphism at 2761 ± 12 Ma (2σ), which is also a younger limit on the age of deposition.In a second unit, from the amphibolite-facies area in outer Saglek Fiord, detrital zircons have predominantly mid- and late Archaean ages. The mid-Archaean zircons are comparable in age to the 3235 Ma Lister gneisses. The ages of the late Archaean detrital zircons (2800–2960 Ma) do not correspond to any known rock complex in the Saglek block, but plutonic rocks associated or correlative with the ca. 2840 Ma Kanairiktok Plutonic Suite of the southern (Hopedale) block are a possible source for many of the grains. Overgrowths were dated at 2690–2730 Ma in this sample.A third metasedimentary unit from the Okak Bay area, 100 km south of Saglek Fiord, also contains detrital zircons with ages comparable to that of the Lister gneisses (3235 Ma). The age of recrystallization and zircon overgrowths was dated at ca. 2560 Ma in this sample. A single grain dated at ca. 2780 Ma is considered most likely to be detrital, which would imply an age of deposition between ca. 2780 and 2560 Ma for this unit.The results show that although late Archaean depositional ages are possible for all three units, the "Upernavik" supracrustal association is composite and sediments in different units have widely different sources and metamorphic histories. These conclusions support a new model for the Nain Province according to which separate terranes were tectonically juxtaposed in the late Archaean. In this model, the age of plutonic and supracrustal rocks and their metamorphic histories prior to juxtaposition differ from one terrane to another.

Microchemistry of ZnO Varistors

1992 ◽  
Vol 50 (2) ◽  
pp. 1694-1695
Author(s):  
K. K. Soni ◽  
J. Hwang ◽  
V. P. Dravid ◽  
T. O. Mason ◽  
R. Levi-Setti
Keyword(s):  
Grain Boundaries ◽  
Multiple Roles ◽  
Grain Boundary Engineering ◽  
Ion Microprobe ◽  
Dopant Distribution ◽  
Important Ingredient ◽  
Zno Varistor ◽  
Zno Varistors ◽  
Zno Powder ◽  
The University

ZnO varistors are made by mixing semiconducting ZnO powder with powders of other metal oxides e.g. Bi2O3, Sb2O3, CoO, MnO2, NiO, Cr2O3, SiO2 etc., followed by conventional pressing and sintering. The non-linear I-V characteristics of ZnO varistors result from the unique properties that the grain boundaries acquire as a result of dopant distribution. Each dopant plays important and sometimes multiple roles in improving the properties. However, the chemical nature of interfaces in this material is formidable mainly because often trace amounts of dopants are involved. A knowledge of the interface microchemistry is an essential component in the ‘grain boundary engineering’ of materials. The most important ingredient in this varistor is Bi2O3 which envelopes the ZnO grains and imparts high resistance to the grain boundaries. The solubility of Bi in ZnO is very small but has not been experimentally determined as a function of temperature.In this study, the dopant distribution in a commercial ZnO varistor was characterized by a scanning ion microprobe (SIM) developed at The University of Chicago (UC) which offers adequate sensitivity and spatial resolution.

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