Asia: a frontier for a future supercontinent Amasia

Abstract

Asia is the world's largest but youngest continent, in which Pacific-type (P-type) and collision-type (C-type) orogenic belts coexist with numerous amalgamated continental blocks. P-type orogens represent major sites of continental growth through tonalite-trondhjemite-granodiorite type (TTG-type) juvenile granitoid magmatism and accretion of oceanic crust and intraoceanic arcs. The Asian continent includes several P-type orogenic belts, of which the largest are the Central Asian and Western Pacific. The Central Asian Orogenic Belt is dominated by P-type fossil orogens arranged with a regular northward subduction polarity. The Western Pacific is characterized by ongoing P-type orogeny related to the westward subduction of the Pacific plate. Asia has a multi-cratonic structure and its post-Palaeozoic history has witnessed amalgamation of the Laurasia composite continent and Pangaea supercontinent. Nowadays, Asia is surrounded by double-sided subduction zones, which generate new TTG-type crust and supply oceanic crust and microcontinents to its active margins. The TTGcrust can be tectonically eroded and subducted down to the mantle transition zone to form a 'second' continent, which may generate mantle upwelling, plumes, and extensive intra-plate volcanism. Moreover, recent plate movements around Asia are dominated by northward directions, which resulted in the India-Eurasia and Arabia-Eurasia collisions beginning at 50-45 and 23-20 Ma, respectively, and will result in Africa-Eurasia collision in the near future. Therefore, Asia is the best candidate to serve as the nucleus for a future supercontinent 'Amasia', likely to form 200-250 Ma in the future. In this paper we unravel a puzzle of continental growth in Asia through P-type orogeny by discussing its tectonic history and geological structure, subduction polarity in P-type orogens, tectonic erosion of TTG-type crust and arc subduction at convergent margins, generation of mantle plumes, and prospects of Asia growth and overgrowth.

Oceanic island basalts in accretionary complexes of SW Japan: Tectonic and petrogenetic implications

“…The CAOB is dominated by Pacific-type orogenic belts (Safonova and Maruyama, 2014), which formed over subduction zones, where oceanic lithosphere was submerged under active continental margins bringing together various fragments of oceanic (oceanic islands, plateaus and ridges) and continental (island arcs and microcontinents) crust to form accretionary complexes with LP-HT blueschist belts. Pacific-type belts are the most important sites of continental growth by tectonic accretion of oceanic crust and intra-oceanic arcs and juvenile mafic to felsic magmatism (e.g., Maruyama et al, 1996;Jahn, 2004;Safonova et al, 2011b;Safonova and Maruyama, 2014).…”

“…We refer to these rocks as OIBs or OIB-type rocks when stressing both their intraplate origin and the specific composition (e.g., Ferrari et al, 2001;Aldanmaz et al, 2006;Safonova et al, 2009Safonova et al, , 2011aSafonova et al, ,c, 2012Safonova and Santosh, 2014). Recognizing OIB-type lavas as elements of OPS is important (i) for reconstructing the evolution of paleo-oceans (Safonova et al, 2009) and the formation of accretionor Pacific-type orogens (e.g., Maruyama et al, 1996Maruyama et al, , 2011Safonova and Maruyama, 2014), (ii) for geological mapping of structurally complicated orogenic belts (e.g., Sano and Kanmera, 1988;Kojima et al, 2000;Nakae, 2000;Safonova et al, 2011a,c) and (iii) for petrogenetic implications (e.g., Komiya et al, 2004;Safonova, 2008;Safonova et al, 2012).…”

“…Worldwide, oceanic rises occur as fragments within accretionary wedges that include oceanic lithosphere fragments, terrigeneous trench sediments, fore-arc flysch, oceanward olistostrome, and tectonic/serpentinite mélanges and record the history of former oceans (Maruyama et al, 1997;Safonova et al, 2009;Safonova and Santosh, 2014). Magmatism producing oceanic islands is widely believed to be related to mantle plumes, which are imaged as columns of heated material ascending from the core-mantle boundary or mantle transition zone (e.g., Morgan, 1971;Maruyama, 1994;Hofmann, 1997;Maruyama et al, 2007Maruyama et al, , 2011Davies, 2011;Safonova and Maruyama, 2014). Oceanic islands are parts of Oceanic Plate Stratigraphy (OPS; e.g., Isozaki et al, 1990;Maruyama et al, 2010;Kusky et al, 2013;Safonova and Santosh, 2014), which represents a regular succession of igneous and sedimentary rocks of the oceanic lithosphere.…”

“…Subduction of oceanic lithosphere brings together various fragments of oceanic (oceanic islands, plateaus and ridges) and continental (island arcs and microcontinents) crust to form accretionary complexes and finally enlarge the continents (e.g., Maruyama et al, 1996;Windley et al, 2007;Safonova et al, 2011a,b,c;Safonova and Maruyama, 2014). Pacific-type belts are most important sites of juvenile crust formation through granitoid magmatism of TTG type, i.e., calc-alkaline andesitic volcanism and M-and I-type granitoid magmatism (Maruyama et al, 1996(Maruyama et al, , 2011.…”

Recognizing OIB and MORB in accretionary complexes: A new approach based on ocean plate stratigraphy, petrology and geochemistry

“…P-type belts form over subduction zones, where oceanic lithosphere is submerged under intra-oceanic arcs or active continental margins. Their identification is of special importance as they represent major sites of continental growth through the formation of juvenile continental crust (tonalite-andesite arc magmatism) and accretion of fragments of oceanic crust (islands, seamounts, plateaus, ridges), intra-oceanic arcs and microcontinents (Bally, 1981;Maruyama et al, 1996;Santosh et al, 2010;Safonova et al, 2011;Safonova and Maruyama, 2014).…”