洋盆封閉后我們有時所忽視的東西：以澳大利亞東部的顯生宇為例

洋盆封閉后我們有時所忽視的東西：以澳大利亞東部的顯生宇為例

The prevailing ‘consensus’ explanation for Phanerozoic development of eastern Australia envisages a‘retreating accretionary orogen’ in which episodic slab retreat resulted in development of offshore island arcs in front of marginal basins. Periodically, this was followed by intervals of plate-coupling during which these basins close and the arcs are retro-thrust back onto the continental margin. Implicit in this model is the notion that all elements developed in an upper plate location upon the accretionary margin and that west-dipping subduction beneath eastern Gondwana was a long-lived phenomenon.

An alternative, testable, hypothesis recently proposed by Aitchison and Buckman (2012) considers eastern Australia to have grown through a series of arc-continent collisions. New crustal material was generated in intra-oceanic island arcs that developedabove east-directed subducting slabs. Elimination of oceanic lithosphere between Gondwana and these arcs because of this subduction led to eventual collision of the arcs with eastern Australia and the additional of new crustal material to the Gondwana continent.

At least four such arc-continent collisions are posited in mid-Cambrian (Mt Stavely arc), Late Ordovician (Macquarie arc), mid-Devonian (Gamilaroi arc)and Late Permian (Gympie arc) times. This process,which we refer to as quantum tectonics, effectively transferred newly generated juvenile crustal material to the continental crust resulting in net growth. When collisions were followed by subduction flip episodes of west-directed subduction beneath the continental margin ensued giving rise to the S- and I-type granites,for which eastern Australia is famous.

AITCHISON J C, BUCKMAN S. 2012. Accordion vs. quantum tectonics: Insights into continental growth processes from the Paleozoic of eastern Gondwana. Gondwana Research, 22:674-680.

Things We Sometimes Overlook after Ocean Closure: Examples from the Phanerozoic of Eastern Australia

Jonathan C. AITCHISON
School of Geosciences, University of Sydney, Australia

arc-continent collision; quantum tectonics; eastern Australia; Phanerozoic

10.3975/cagsb.2012.s1.01

E-mail: jonathan.aitchison@sydney.edu.au.