Archaean basin margin geology and crustal evolution: an East Pilbara traverse

Abstract

A palinspastic reconstruction of a 100 km long traverse through Archaean rocks of the East Pilbara, Western Australia, includes new observations of the deformation preceding the now visible greenstone belt pattern. The restoration is time-calibrated with all available U-Pb datings. Between incompletely preserved basin sequences, two superposed Palaeoarchaean volcano-sedimentary basins (the Coongan and Salgash Basins) are separated by an eastwards time-transgressive interface tentatively interpreted as an onlap surface. For over 140 Ma, the basin margin architecture was structurally controlled by superposed extensional growth fault arrays (D 1) with associated dyke swarms in a curved pattern spatially not related to that of the actual distribution of granite domes and greenstone belts. The basins are interpreted to have formed by collapse after arching above hotspots due to phase transitions by mini-subduction of slabs of cooled water-saturated basalt towards the base of an originally c. 45 km mafic crust. At c. 3.31 Ga, the extension was replaced by plate-driven regional NW-SE compression (D 2) inferred from NW-over-SE shear and ramp-and-flat thrusts, partly reversing offsets of the D 1 extension. The recognition of widespread D 2 pre-doming compression is important because it triggered the c. 3.18 Ga start of formation of the dome-and-keel pattern (D 3) visible today, which culminated at c. 2.9 Ga.

Compressional origin of the Naxos metamorphic core complex, Greece: Structure, petrography, and thermobarometry

“…19) are inconsistent with diapirism being the dominant doming process. Similar features have been documented in Archean granite-greenstone terranes, such as the Pilbara North Pole Dome in Australia (e.g., Nijman et al, 2017). Diapirism or crustal turnover has been proposed as a mechanism to explain these tonalite-trondhjemitegranodiorite (TTG)-cored domes (e.g., Collins et al, 1998), which are associated with larger melt fractions than Naxos migmatites.…”

“…Diapirism or crustal turnover has been proposed as a mechanism to explain these tonalite-trondhjemitegranodiorite (TTG)-cored domes (e.g., Collins et al, 1998), which are associated with larger melt fractions than Naxos migmatites. The pattern of doming and basins with other observed shortening phenomena indicates the importance of regional compression during the formation of these domes, which may have caused a first Raleigh instability, leading to an egg-box pattern of sinking greenstones around the TTG domes (Nijman et al, 2017). N-S horizontal boudinage, and a range of brittle deformation features overprinting these folds, suggests the principal stress axes rotated to a NNE-SSWorientated σ 3 and E-W-oriented σ 1 direction shortly after these folds formed.…”

The Emergence of Life

“…While no modern-style continental landmasses existed before 3.2 Ga, the preserved geological record from the Early Archaean (that can be translated probably back to the Hadean) documents small exposed landmasses on top of submerged ocean plateau-like protocontinents, something like volcanic Iceland surrounded by relatively protected collapse basins (cf. Nijman et al 2017). It is fair to say, however, that our current understanding or knowledge of any kind of exposed terrestrial surface during those early days is hazy (Sleep 2018).…”

Origin, Accretion, and Reworking of Continents

“…Such dome-and-keel structures ZHU ET AL. characterize the structural patterns of major Archean cratons, including the Barberton and Zimbabwe cratons in South Africa (Figure 3a; Anhaeusser & Wilson, 1981;Van Hinsbergen et al, 2011;Van Kranendonk et al, 2014), the Yilgara and Pilbara cratons in Western Australia (Figure 3b; Collins et al, 1998;Hallberg & Glikson, 1981;Nijman et al, 2017;Van Kranendonk et al, 2004), the Superior craton in North America (e.g., Lin, 2005;Lin & Beakhouse, 2013;, and the Eastern Block of the NCC in East Asia (Zhao, 2014;Zhao et al, 2001). In these old cratons, the boundaries between the gneiss domes and the supracrustals (greenstones) are characterized mostly by vertical stretching lineations or L-tectonites, indicating vertical motions (e.g., Lin, 2005;Lin & Beakhouse, 2013;.…”