Validating the existence of the supercraton Vaalbara in the Mesoarchaean to Palaeoproterozoic

Forskningsoutput: AvhandlingDoktorsavhandling (sammanläggning)


title = "Validating the existence of the supercraton Vaalbara in the Mesoarchaean to Palaeoproterozoic",
abstract = "In this thesis, the longevity and continuity of the Vaalbara supercraton is addressed in six papers aimed at placing new temporal and spatial constraints onthe supercraton in the Mesoarchean to Paleoproterozoic. It has been speculated since the 1960’s that the Kaapvaal Craton in southern Africa, together withthe Pilbara Craton in Western Australia existed as a single landmass during the Precambrian – the Vaalbara supercraton. Many studies have demonstrated thegeological similarities between the cratons, particularly in terms of their Mesoarchean to Paleoproterozoic unconformity-bounded sequences. These unconformity-bounded sequences have continuously been refined and developed, especially since the 1990’s. The first main stratigraphic similarities lie in the volcanic and sedimentary successions found in the Neoarchean Fortescue Group and Ventersdorp Supergroup basins on the Pilbara and Kaapvaal cratons, respectively, along with other associated basins. The unconformably overlying Hammersley (and Turee Creek) Group and Transvaal Supergroup on the Pilbara and Kaapvaal cratons, respectively, also show many stratigraphic similarities, and both host world-class deposits of hydrothermally-upgraded iron formations. However, no marker beds or precise age matches have yet been made, especially in the extensive Mesoarchean to Paleoproterozoic mafic dyke swarms and sill provinces present in each craton from the time interval discussed in this thesis. Regardless, the geological discussions has been aided by geochronological and paleomagnetic studies, which have both credited and discredited the existence of the Pilbara and Kaapvaal cratons as nearest neighbours for the time interval between ca. 2.87 Ga and ca. 2.65 Ga.In this thesis, the so-called magmatic barcode record of large igneous provinces (LIPs), which are extensive and short-lived volcanic events, of the KaapvaalCraton is presented together with that of the Pilbara Craton in conjunction with previous geochronological and paleomagnetic studies. This magmatic barcoderecord refines temporal, and through paleomagnetism, spatial constraints, and invalidates the existence of Vaalbara as a distinct continuous supercraton. Magmatic and paleomagnetic linkages between the 2.99-2.98 Ga Usushwana Complex on the Kaapvaal Craton and the ca. 2.87 Ga Millindinna Complex on thePilbara Craton are shown to be incorrect with new ages for the Usushwana Complex and Badplaas dyke swarm presented in Gumsley et al. (2015). Extensivemafic dyke swarms associated with Neoarchean Fortescue volcanism on the Pilbara Craton and Ventersdorp volcanism on the Kaapvaal Craton also show lesssimilarities from new paleomagnetic and geochronological constraints. These constraints are presented in Gumsley et al. (2016) and Evans et al. (2017) for thenewly identified White Mfolozi and Black Range mafic dyke swarms, respectively, on the Kaapvaal and Pilbara cratons. Gumsley et al. (2017) and Kampmannet al. (2015) also present a new LIP, the Ongeluk, on the Kaapvaal Craton which has not been identified on the Pilbara Craton. This new LIP is composed ofthe Ongeluk Formation in the Transvaal Supergroup on the western margin of the Kaapvaal Craton, as well as the Westerberg Sill Province and a north-trendingmafic dyke swarm. The Ongeluk LIP appears to break some of the stratigraphic comparison between the upper Transvaal Supergroup on the Kaapvaal Cratonand the Turee Creek Group on the Pilbara Craton. In addition, a new late Paleoproterozoic mafic dyke swarm, the Tsineng swarm, is presented for the western Kaapvaal Craton in Alebouyeh Semami et al. (2016), which is correlated with Hartley Formation volcanism in the Olifantshoek Supergroup. This magmaticevent may also define a new LIP on the western Kaapvaal Craton. This mafic dyke swarm and its associated volcanism has also not been documented on thePilbara Craton.Instead, it is proposed that the Pilbara and Kaapvaal cratons were part of a much larger continent or supercontinent in the Neoarchean to Paleoproterozoic.This large crustal block likely included the Wyoming, Superior and Hearne cratons of North America, together with the Kola-Karelia Craton located between Russia and Finland, as well as possibly the Singhbhum Craton of India and the Samartia terrane of Russia and Ukraine. This continent or supercontinent, termed ‘Supervaalbara’ here, allows for the Kaapvaal and Pilbara cratons to share many geological similarities without being nearest neighbours, along possiblythe same passive margin. The geological evolution of all these cratons is very similar, particularly in the Paleoproterozoic, and which may have been driven byglobal processes. These global processes may include true polar wander, the submergence and subsequent remergence of continents with sea-level rise and fall, as well as atmospheric oxygenation and global glaciation. Paleomagnetic studies provide further continuity supporting the existence of Supervaalbara, which appears geologically distinct from the Rae family of cratons, suggesting perhaps two different continents in the early Paleoproterozoic before the assembly of the supercontinent Columbia (Nuna) in the late Paleoproterozoic.",
keywords = "Vaalbara, Kaapvaal Craton, Pilbara Craton, U-Pb geochronology, paleomagnetism, supercontinent, large igneous province, dyke swarm, sill province",
author = "Ashley Gumsley",
note = "Defence details Date: 2017-09-22 Time: 13:00 Place: Lecture hall “Pangea”, Geocentrum II, S{\"o}lvegatan 12, Lund External reviewer Name: Hanson, Richard Title: Professor Affiliation: Texas Christian University, Fort Worth, TX, USA ---",
year = "2017",
month = "9",
language = "English",
isbn = "978-91-87847-32-5",
series = "Litholund theses",
publisher = "Lund University, Faculty of Science, Department of Geology, Lithosphere and Biosphere Science",
number = "30",
school = "Department of Geology",