scholarly journals Destabilization of long-lived Hadean protocrust and onset of pervasive hydrous melting at 3.8 Ga recorded in detrital zircons of the Green Sandstone Bed, South Africa

2021 ◽  
Author(s):  
Nadja Drabon ◽  
Ann Bauer ◽  
Joseph Wooden ◽  
Michael Wiedenbeck ◽  
Donald Lowe ◽  
...  
Keyword(s):  
South Africa ◽  
Detrital Zircons ◽  
Hydrous Melting

Enigmatic provenance signature of sandstone from the Okwa Group, Botswana

2020 ◽  
Vol 123 (3) ◽  
pp. 331-342
Author(s):  
T. Andersen ◽  
M.A. Elburg ◽  
J. Lehmann
Keyword(s):  
South Africa ◽  
Detrital Zircon ◽  
Sedimentary Rock ◽  
Age Distribution ◽  
Sedimentary Rocks ◽  
Detrital Zircons ◽  
Significant Shift ◽  
Zircon Age ◽  
Three Samples ◽  
Isotope Distributions

Abstract Detrital zircon grains from three samples of sandstone from the Tswaane Formation of the Okwa Group of Botswana have been dated by U-Pb and analysed for Hf isotopes by multicollector LA-ICPMS. The detrital zircon age distribution pattern of the detrital zircons is dominated by a mid-Palaeoproterozoic age fraction (2 000 to 2 150 Ma) with minor late Archaean – early Palaeoproterozoic fractions. The 2 000 to 2 150 Ma zircon grains show a range of epsilon Hf from -12 to 0. The observed age and Hf isotope distributions overlap closely with those of sandstones of the Palaeoproterozoic Waterberg Group and Keis Supergroup of South Africa, but are very different from Neoproterozoic deposits in the region, and from the Takatswaane siltstone of the Okwa Group, all of which are dominated by detrital zircon grains younger than 1 950 Ma. The detrital zircon data indicate that the sources of Tswaane Formation sandstones were either Palaeoproterozoic rocks in the basement of the Kaapvaal Craton, or recycled Palaeoproterozoic sedimentary rocks similar to the Waterberg, Elim or Olifantshoek groups of South Africa. This implies a significant shift in provenance regime between the deposition of the Takatswaane and Tswaane formations. However, the detrital zircon data are also compatible with a completely different scenario in which the Tswaane Formation consists of Palaeoproterozoic sedimentary rock in tectonic rather than depositional contact with the other units of the Okwa Group.

Growth of zircon and titanite during metamorphism in the granitoid-gneiss terrane south of the Barberton greenstone belt, South Africa

2005 ◽  
Vol 69 (6) ◽  
pp. 1019-1036 ◽  
Author(s):  
A. Dziggel ◽  
R. A. Armstrong ◽  
G. Stevens ◽  
L. Nasdala
Keyword(s):  
South Africa ◽  
Greenstone Belt ◽  
Regional Metamorphism ◽  
Detrital Zircons ◽  
Geochronological Data ◽  
Weighted Mean ◽  
Barberton Greenstone Belt ◽  
Minimum Age ◽  
Terrane Accretion ◽  
Lower Crustal

AbstractSHRIMP U-Pb zircon and titanite dating have been used to constrain the timing of mid- to lower- crustal metamorphism (∼650—700°C and 8—11 kbar) and syn-kinematic melting in the granitoid gneiss- dominated terrane south of the Barberton greenstone belt, South Africa. This study is concentrated on a clastic metasedimentary unit exposed in one of several greenstone remnants and a late-kinematic trondhjemite intrusive into spatially associated mixed gneisses. Locally, the clastic metasediments show extensive replacement of garnet and plagioclase by epidote and titanite. The titanites yield an upper intercept date of 3229±9 Ma, and provide a minimum age for the peak of metamorphism. Zircons separated from the same unit record a range of concordant and near-concordant 207Pb/206Pb dates between ∼3560 and 3230 Ma, the youngest group yielding a weighted mean date of 3227±7 Ma. This range of dates is interpreted to be due to a combination of metamorphic recrystallization and high- temperature Pb-loss in originally detrital zircons during regional metamorphism. A minimum age for the timing of deformation is given by the emplacement age of 3229±5 Ma for the late-kinematic trondhjemite. Thus, geochronological data support the notion of a major metamorphic episode that coincided with the proposed short-lived terrane accretion event in the centre of the Barberton greenstone belt.

A late Mesozoic – early Cenozoic sedimentary recycling system on the Gondwana rifted margin of southeast Africa

2020 ◽  
Vol 123 (3) ◽  
pp. 343-356
Author(s):  
T. Andersen ◽  
G.A. Botha ◽  
M.A. Elburg
Keyword(s):  
South Africa ◽  
Detrital Zircon ◽  
Distribution Patterns ◽  
Detrital Zircons ◽  
Late Mesozoic ◽  
Mixing Regime ◽  
History Of ◽  
Gondwana Supercontinent ◽  
Rifted Margin ◽  
Early Cenozoic

Abstract Detrital zircons in late Cretaceous – Palaeogene, calcareous sandstone and conglomerate deposited in continental basins on the southeastern African margin after the breakup of Gondwana have characteristic combinations of age and epsilon-Hf that indicate an origin by recycling of Palaeoproterozoic (Waterberg, Soutpansberg and Pretoria groups) and Phanerozoic (Karoo Supergroup) cover successions. The latter is dominant in the south and east (Boane, Mahosi, Chilojo Cliffs), and the Palaeoproterozoic sources in the northwest (Pafuri, Wright’s Tower, Masisi). This recycling and mixing regime was restricted to late Mesozoic and Palaeogene time in northeastern South Africa and adjoining parts of Mozambique and Zimbabwe. Detrital zircon distribution patterns in these deposits reflect the denudation history of the southern African continental surface after breakup of the Gondwana supercontinent.

Provenance and reconnaissance study of detrital zircons of the Palaeozoic Cape Supergroup in South Africa: revealing the interaction of the Kalahari and Río de la Plata cratons

2010 ◽  
Vol 100 (2-3) ◽  
pp. 527-541 ◽  
Author(s):  
Pieter H. Fourie ◽  
Udo Zimmermann ◽  
Nicolas J. Beukes ◽  
Thanusha Naidoo ◽  
Katsuro Kobayashi ◽  
...  
Keyword(s):  
South Africa ◽  
Detrital Zircons ◽  
Rio De La Plata ◽  
Río De La Plata ◽  
La Plata

scholarly journals Heterogeneous Hadean crust with ambient mantle affinity recorded in detrital zircons of the Green Sandstone Bed, South Africa

2021 ◽  
Vol 118 (8) ◽  
pp. e2004370118 ◽  
Author(s):  
Nadja Drabon ◽  
Benjamin L. Byerly ◽  
Gary R. Byerly ◽  
Joseph L. Wooden ◽  
C. Brenhin Keller ◽  
...  
Keyword(s):  
South Africa ◽  
Detrital Zircon ◽  
Detrital Zircons ◽  
Precambrian Geology ◽  
Barberton Greenstone Belt ◽  
Rock Record ◽  
Magma Compositions ◽  
Higher Temperature ◽  
Lower Temperature ◽  
Jack Hills

The nature of Earth’s earliest crust and the processes by which it formed remain major issues in Precambrian geology. Due to the absence of a rock record older than ∼4.02 Ga, the only direct record of the Hadean is from rare detrital zircon and that largely from a single area: the Jack Hills and Mount Narryer region of Western Australia. Here, we report on the geochemistry of Hadean detrital zircons as old as 4.15 Ga from the newly discovered Green Sandstone Bed in the Barberton greenstone belt, South Africa. We demonstrate that the U-Nb-Sc-Yb systematics of the majority of these Hadean zircons show a mantle affinity as seen in zircon from modern plume-type mantle environments and do not resemble zircon from modern continental or oceanic arcs. The zircon trace element compositions furthermore suggest magma compositions ranging from higher temperature, primitive to lower temperature, and more evolved tonalite-trondhjemite-granodiorite (TTG)-like magmas that experienced some reworking of hydrated crust. We propose that the Hadean parental magmas of the Green Sandstone Bed zircons formed from remelting of mafic, mantle-derived crust that experienced some hydrous input during melting but not from the processes seen in modern arc magmatism.

scholarly journals EVOLUÇÃO SEDIMENTAR DO SUPERGRUPO MINAS: 500 MA. DE REGISTRO GEOLÓGICO NO QUADRILÁTERO FERRÍFERO, MINAS GERAIS, BRASIL

1994 ◽  
Author(s):  
Friedrich E. Renger ◽  
Carlos M. Noce ◽  
Antônio W. Romano ◽  
Nuno Machado
Keyword(s):  
South Africa ◽  
Minas Gerais ◽  
Detrital Zircons ◽  
Granitic Rocks ◽  
Iron Formation ◽  
The Third ◽  
Quadrilátero Ferrífero ◽  
Belo Horizonte ◽  
Age Determinations

It is now possible to bracket the age of the Minas Supergroup with reasonable precision between about2580 Ma. (base of the Moeda Formation) and 2050 Ma. (top of the Sabará Formation) on the basis of precisezircon U-Pb age determinations from both granitic rocks of the basement and detrital zircons from quartzitesand graywackes of the Proterozoic metasedimentary sequences of the Quadrilátero Ferrífero.Three major unconformities subdivide the stratigraphic column into three sequences. The first sequencecomprises the Moeda, Batatal, Cauê and Gandarela Formations from 2580 to 2400 Ma.. The second sequencecomprises the Cercadinho, Fecho do Funil, Taboões and Barreiro Formations (the Piracicaba Group) datedat 2400 to 2150 Ma.. The third sequence contains only the synorogenic sediments of the Sabará Formation,deposited during the Transamazonian Event between 2150 and 2050 Ma.. This event folded andmetamorphosed the Minas Supergroup for the first time.The Sabará Formation of the Piracicaba Group has very different sedimentological characteristics fromthe other formations of this group and is exceptionally thick (about 3500 m), we therefore propose to upgradeit to the rank of a Group.Zircon age histograms of the Moeda quartzite (sample QF-1) and Sabará graywacke are similar, indicatinga common Archean source, i.e. the Belo Horizonte Complex north of the Quadrilátero Ferrífero. This impliesthat sedimentation of the Minas Supergroup in the western Quadrilátero Ferrífero is autochthonous.Periods of carbonate and Iron Formation platform sedimentation (Cauê, Gandarela and partly Fecho doFunil Formations) coincide with minor frequency of age plots of detrital zircons, indicating also a stabletectonic environment.Comparison of the Minas Supergroup with the Transvaal Sequence of South Africa revealscorrespondence not only in age but also in thickness, position of the major unconformities, lithologicalcompositions and in the position of gold and pyrite bearing quartz-pebble conglomerates.

Time and Latitude in South Africa

1972 ◽  
Vol 1 ◽  
pp. 27-38
Author(s):  
J. Hers
Keyword(s):  
South Africa ◽  
Cape Town ◽  
Astronomical Observations ◽  
Royal Observatory ◽  
The Republic ◽  
Astronomical Determination ◽  
Limited Accuracy ◽  
Better Than

In South Africa the modern outlook towards time may be said to have started in 1948. Both the two major observatories, The Royal Observatory in Cape Town and the Union Observatory (now known as the Republic Observatory) in Johannesburg had, of course, been involved in the astronomical determination of time almost from their inception, and the Johannesburg Observatory has been responsible for the official time of South Africa since 1908. However the pendulum clocks then in use could not be relied on to provide an accuracy better than about 1/10 second, which was of the same order as that of the astronomical observations. It is doubtful if much use was made of even this limited accuracy outside the two observatories, and although there may – occasionally have been a demand for more accurate time, it was certainly not voiced.

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