Making it thick: a volcanic plateau origin of Palaeoarchean continental lithosphere of the Pilbara and Kaapvaal cratons

Abstract

How and when continents grew and plate tectonics started on Earth remain poorly constrained. Most researchers apply the modern plate tectonic paradigm to problems of ancient crustal formation, but these are unsatisfactory because diagnostic criteria and actualistic plate configurations are lacking. Here, we show that 3.5-3.2 Ga continental nuclei in the Pilbara Craton, Australia, and the eastern Kaapvaal Craton, southern Africa, formed as thick volcanic plateaux built on a substrate of older continental lithosphere and did not accrete through horizontal tectonic processes. These nuclei survived because of the contemporaneous development of buoyant, nonsubductable mantle roots. This plateau-type of Archean continental crust is distinct from, but complementary to, Archean gneiss terranes formed over shallowly dipping zones of intraoceanic underplating (proto-subduction) on a vigorously convecting early Earth with smaller plates and primitive plate tectonics.

The zircon archive of continent formation through time

“…Some key constraints from other types of data also agree with this estimate, for example, diamond compositions suggest a change in geodynamics at 3 Ga (Shirey & Richardson 2011), the metamorphic record at 2.7 Ga (Brown 2006(Brown , 2007 and the geochemistry of the rock record at 2.5 Ga (Keller & Schoene 2012). The many publications that cite the lithological and geochemical signatures of Archaean rocks as being related to subduction provide ambiguous evidence to build on this topic, as the origins of these have multiple interpretations (see Van Kranendonk et al 2014).…”

“…The black bars below represent hypothesized timing of global geodynamic regimes based upon this review, and arrows show the record of metamorphic conditions: UHP, ultra-high pressure; UHT, ultra-high temperature; E-HP, eclogite-high pressure. Kranendonk et al 2014;Van Kranendonk 2010). After c. 4.0 Ga, there is no obvious marked change in a global record until c. 3.0 Ga that may reflect the onset of subduction and/or plate tectonics.…”

“…Hence, a flat growth curve is derived for the last 2.5 Ga. Third, the crustal volume must have increased to its present-day value at some point since 4.5 Ga. For this to happen, growth must have outweighed destruction; this may have been assisted through the existence of differing tectonic processes compared with today. An increase in the role of plume-related and/or other vertical tectonic processes in the Archaean (see Van Kranendonk et al 2014), particularly the earlier Archaean, may be (Sizova et al 2010;Nutman et al 2013), which may limit crustal destruction, is also another factor governing growth rate. In summary, at some point in Earth history, the crustal growth rate must have changed from a regime dominated by growth to a regime with balanced growth and destruction.…”

Reconstruction of the physical volcanological processes and petrogenesis of the 3.5Ga Warrawoona Group pillow basalt of the Warralong Greenstone Belt, Pilbara Craton Western Australia

“…Such terranes have been studied in Australia, South Africa, North America, South America, Asia, Europe and Canada, (Condie, 1981;Furnes et al, 2011;Hickman, 2012;Dostal and Mueller, 2013;Furnes et al, 2013;Kröner et al, 2013;Puchtel et al, 2013;Hepple, 2014;Van Kranendonk et al, 2015). Granite-greenstone terranes are characterized by dome-and-keel structures, where volcanic and sedimentary rocks are wedged between dome-shaped granite-gneiss-pegmatitic structures (Marshak et al, 1992), and are a classic map pattern seen in Archean terranes (Van Kranendonk et al, 2004b).…”

“…The East Pilbara Terrane (3.53 -3.22 Ga), is thought to cover an area of about 100 000 km 2 although much of it does not outcrop Van Kranendonk et al, 2004a;Van Kranendonk, 2006;Yuan, 2015). The EPT has undergone six stages of regional deformation (D1-D6 1998;Van Kranendonk et al, 2002;Van Kranendonk, 2010;Van Kranendonk et al, 2015).…”