Continental Growth and Recycling in Convergent Orogens with Large Turbidite Fans on Oceanic Crust

Abstract

Convergent plate margins where large turbidite fans with slivers of oceanic basement are accreted to continents represent important sites of continental crustal growth and recycling. Crust accreted in these settings is dominated by an upper layer of recycled crustal and arc detritus (turbidites) underlain by a layer of tectonically imbricated upper oceanic crust and/or thinned continental crust. When oceanic crust is converted to lower continental crust it represents a juvenile addition to the continental growth budget. This two-tiered accreted crust is often the same thickness as average continental crustal and is isostatically balanced near sea level. The Paleozoic Lachlan Orogen of eastern Australia is the archetypical example of a tubidite-dominated accretionary orogeny. The Neoproterozoic-Cambrian Damaran Orogen of SW Africa is similar to the Lachlan Orogen except that it was incorporated into Gondwana via a continent-continent collision. The Mesozoic Rangitatan Orogen of New Zealand illustrates the transition of convergent margin from a Lachlan-type to more typical accretionary wedge type orogen. The spatial and temporal variations in deformation, metamorphism, and magmatism across these orogens illustrate how large volumes of turbidite and their relict oceanic basement eventually become stable continental crust. The timing of deformation and metamorphism recorded in these rocks reflects the crustal thickening phase, whereas post-tectonic magmatism constrains the timing of chemical maturation and cratonization. Cratonization of continental crust is fostered because turbidites represent fertile sources for felsic magmatism. Recognition of similar orogens in the Proterozoic and Archean is important for the evaluation of crustal growth models, particularly for those based on detrital zircon age patterns, because crustal growth by accretion of upper oceanic crust or mafic underplating does not readily result in the addition of voluminous zircon-bearing magmas at the time of accretion. This crust only produces significant zircon when and if it partially melts, which may occur long after accretion

Paleoproterozoic S-type granites in the Helanshan Complex, Khondalite Belt, North China Craton: Implications for rapid sediment recycling during slab break-off

“…2.00 and 1.95 Ga (Yin et al, 2011;Dan et al, 2012). As previously noted, the requirements for such rapid sedimentary recycling are only met in a few distinctive tectonic settings that involve processes such as lithospheric delamination, back-arc basin opening, mantle plume ascent or continental rifting Kemp et al, 2007;Zheng et al, 2008;Collins and Richards, 2008;Foster and Goscombe, 2013). A common feature of these tectonic settings is the presence of asthenosphere upwelling, consistent with the generation of high-temperature Stype granites (Sylvester, 1998).…”

“…Several mechanisms have been proposed to explain the rapid formation of S-type granites. For subduction systems or accretionary orogens, the rapid formation of S-type granites and related rocks has been accounted for by models of back-arc basin opening (Cenozoic Hidaka metamorphic belt, Japan; Kemp et al, 2007) and lithospheric delamination (Ordovician Lachlan Fold Belt, Australia; Foster and Goscombe, 2013) or by models that combine both features (Collins and Richards, 2008). The rapid formation of Stype granites in collisional orogenic belts, however, has commonly been attributed to mantle plumes (Jiangnan Orogen, South China Block, Li et al, 2003) or continental rifting (Jiangnan Orogen, Zheng et al, 2008).…”

Late Paleozoic geology of the Queensland Plateau (offshore northeastern Australia)

“…Much of the Paleozoic and Mesozoic metasedimentary successions of eastern Australia and Zealandia (hereinafter basement rocks) are either submerged or concealed under younger sedimentary cover. Basement rocks of these regions typically contain a large component of multi-cycled Gondwanan detritus (Fergusson & Henderson, 2015;Fergusson, Henderson, & Offler, 2017;Foster & Goscombe, 2013;Glen, 2013;Glen, Belousova, & Griffin, 2016). Detrital zircon studies in eastern Australia and the southwestern Pacific region have shown that both sedimentary (Shaanan & Rosenbaum, 2018;Sircombe, 1999) and magmatic (Buys, Spandler, Holm, & Richards, 2014;Tapster, Roberts, Petterson, Saunders, & Naden, 2014) recycling took place.…”

Southern Chile crustal structure from teleseismic receiver functions: Responses to ridge subduction and terrane assembly of Patagonia

“…Alternatively, this crust could also comprise felsic upper crust over a Grenville-age, or even older (see Schilling et al, 2017), mafic lower crust, as we postulated for the crust farther north. We note that such heterogeneous crust was formed ubiquitously in collisional settings around the Gondwana perimeter (Foster and Goscombe, 2013), including, apparently, in Patagonia.…”