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Dating of Guperas Formation rhyolites changes the stratigraphy of the Mesoproterozoic Sinclair Supergroup of Namibia

D. H. Cornell, M. Harris, B. S. Mapani, T. Malobela, D. Frei, M. Kristoffersen, K. Lehman Francko and R. Hanson
Dating of Guperas Formation rhyolites changes the stratigraphy of the Mesoproterozoic Sinclair Supergroup of Namibia
South African Journal of Geology (November 2020) 123 (4): 633-648

Abstract

The volcanosedimentary Guperas Formation contains the youngest volcanic rocks of the Sinclair Supergroup in the Konkiep Terrane of southern Namibia. Precise U-Pb zircon microbeam dating shows that the Guperas Formation as mapped includes felsic volcanic rocks which belong to both the first (1.37 to 1.33 Ga) and the third (1.11 to 1.07 Ga) magmatic cycle of the Sinclair Supergroup. Volcanic rocks of the "true" Guperas Formation are dated by three samples, with a combined age of 1108 + or - 10 Ma. The sedimentary rocks mapped as Guperas Formation are also distinguished by two different detrital age spectra into the approximately 1100 Ma true Guperas Formation and the Aruab Member of the approximately 1217 Ma Barby Formation. Geochronology now resolves the previous stratigraphic separation of the very similar Nubib and Rooiberg (Sonntag) Granites. The two small outcrops of 1334 + or - 5 Ma Rooiberg Granite are now shown to be part of the regional 1334 + or - 8 Ma Nubib Granite batholith. The Konkiep Terrane was affected by faulting and shear zones, but was only gently folded and not involved in regional metamorphism, despite its proximity to the Namaqua-Natal Province to the southwest. This is due to the Konkiep Terrane having a thick and strong continental basement which may have formed as part of the mainly Palaeoproterozoic Rehoboth Province. However no Palaeoproterozoic rocks are exposed in the Konkiep Terrane, which is now interpreted as an unaffiliated terrane. The three cycles of extrusive and plutonic magmatism in the Sinclair Supergroup formed in chronologically distinct periods and different tectonic settings, which requires revision of the stratigraphic nomenclature. The Konkiep Group is replaced by three new groups which are separated by >100 million-year unconformities. The Betta Group, represented by the mainly volcanic Kumbis, Nagatis and Welverdiend formations in the first magmatic cycle, probably formed in a passive continental rift setting due to breakup of the Rehoboth Province between 1374 and 1334 Ma. The Vergenoeg Group, represented by the sedimentary Kunjas and volcanic Barby and Haiber Flats formations, formed in a subduction setting at the margin of the Konkiep Terrane. This approximately 1217 to 1204 Ma magmatic cycle ended with the accretion of Namaqua-Natal terranes to the Kalahari Craton. The approximately 1100 Ma Ganaams Group, represented by the volcanic Guperas Formation and sedimentary Aubures Formation, was the result of interplay between the continental-scale Umkondo mantle heating event and movements between crustal blocks following the Namaqua-Natal collisional orogeny.


ISSN: 1012-0750
EISSN: 1996-8590
Serial Title: South African Journal of Geology
Serial Volume: 123
Serial Issue: 4
Title: Dating of Guperas Formation rhyolites changes the stratigraphy of the Mesoproterozoic Sinclair Supergroup of Namibia
Affiliation: University of Gothenburg, Department of Earth Sciences, Gothenburg, Sweden
Pages: 633-648
Published: 20201110
Text Language: English
Publisher: Bureau for Scientific Publications, Pretoria, South Africa
References: 29
Accession Number: 2021-006832
Categories: Igneous and metamorphic petrologyGeochronology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 3 tables, geol. sketch maps
S35°00'00" - S20°00'00", E15°00'00" - E25°00'00"
Secondary Affiliation: University of Namibia, NAM, NamibiaUniversity of Stellenbosch, ZAF, South AfricaUniversity of Oslo, NOR, NorwaySouthern Methodist University, USA, United StatesTexas Christian University, USA, United States
Country of Publication: South Africa
Secondary Affiliation: GeoRef, Copyright 2021, American Geosciences Institute. Abstract, Copyright, Geological Society of South Africa. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 202105
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