1887

oa South African Journal of Geology - A palaeomagnetic test of the Kaapvaal - Pilbara (Vaalbara) connection at 2.78 Ga

Volume 101 Number 4
  • ISSN : 1012-0750
  • E-ISSN: 1996-8590

 

Abstract

Integrated U-Pb geochronology and palaeomagnetic study of mafic to felsic volcanic rocks of the Derdepoort Belt of South Africa are employed to test the hypothesis that the Pilbara and Kaapvaal Cratons were joined as part of a Late Archaean 'Vaalbara' supercontinent. An age of 2782 ± 5 Ma is deduced for eruption of the Derdepoort basalts, bracketed by a concordant SHRIMP zircon age of 2781 ± 5 Ma for overlying felsic volcanics and a concordant isotope dilution zircon age of 2783 ± 2 Ma for underlying granite of the Gabarone Complex. Based on the low (subgreenschist) metamorphic grade of the basalts, the presence of highly stable single domain magnetite, and a positive conglomerate test, the magnetization of the Derdepoort basalts is inferred to date from the time of their emplacement and cooling at 2782 Ma. Results yield a primary palaeopole at 005° E, 40° S (A95 = 18° ), and indicate a palaeolatitude of 64.5 ± 17.5° for the Kaapvaal Craton at 2782 Ma. Published palaeomagnetic data for the Mount Roe Basalts of the Pilbara Craton indicate a palaeolatitude of 34.3 ± 6.4° at 2772 ± 2 Ma. The latitudinal separation of 30° implies that the cratons were not contiguous at 2.77 to 2.78 Ga, although the possibilities that the cratons could have been joined during other intervals of time, or that they were non-contiguous parts of a larger continent, are not ruled out.

Die hipotese dat die Pilbara- en Kaapvaalkraton aanmekaar verbind was as 'n dee] van 'n Laat-Argeïese 'Vaalbara' - superkontinent, word getoets deur gebruik te maak van geïntegreerde U-Pb-geochronologie en paleomagnetiese studie van mafiese tot felsiese gesteentes van die Derdepoortgordel in Suid-Afrika. 'n Ouderdom van 2782 ± 5 Ma word vir die erupsie van die Derdepoortbasalte afgelei. Hierdie ouderdom val binne die grense van 'n konkordante 'SHRIMP'-sirkoonouderdom van 2781 ± 5 Ma vir die oorliggende felsiese vulkaniese gesteentes en 'n konkordante isotoopverdunningsirkoonouderdom van 2783 ± 2 Ma vir die onderliggende graniet van die Gabaronekompleks. Gebaseer op die Jae metamorfiese graad (subgroenskis) van die basalte, die teenwoordigheid van hoogs stabiele enkeldomeinmagnetiet, en 'n positiewe konglomeraattoets, word afgelei dat die magnetisasie van die Derdepoortbasalte dateer vanaf die tyd van hul inplasing en afkoeling 2782 Ma gelede. Die resultate toon 'n primêre paleopool by 005° E, 40° S (A95 = 18° ), en dui op 'n paleobreedte van 64.5 ± 17.5° vir die Kaapvaalkraton teen 2782 Ma. Gepubliseerde paleomagnetiese data vir die Mount Roe-basalte van die Pilbarakraton dui aan 'n paleobreedte van 34.3 ± 6.4° teen 2772 ± 2 Ma. Alhoewel die breedteskeiding van 30° impliseer dat die kratons nie 2.77 tot 2.78 Ga gelede aangrensend was nie, word die moontlikheid dat die kratons tydens ander tydintervalle aangrensend was, of dat hulle nie-aangrensende dele van 'n grater kontinent was, nie uitgesluit nie.

Loading full text...

Full text loading...

Loading

Article metrics loading...

/content/journal/10520/EJC-1ac373c954
1998-12-01
2020-09-27

This is a required field
Please enter a valid email address
Approval was a Success
Invalid data
An Error Occurred
Approval was partially successful, following selected items could not be processed due to error