The collision of the Luzon Arc with southern China
represents the best example of arc-continent collision in the modern oceans,
and compares closely with the Early Ordovician (480-470 Ma) accretion of
the Lough Nafooey Arc of Connemara, Ireland, to the passive margin of Laurentia
(North America). Together with colleagues
I have been developing
a general model for steady-state arc-continent collision in which arc crust
is progressively added to a passive margin during a process of compression,
metamorphism and magmatism lasting 3–10 million years at any one location
on the margin. This tectonic process is likely the principle origin
of continental convergent margins and the dominent process for building
the continental crust, at least during Phanerozoic times (<600 Ma).
Depending on the obliquity of the angle of collision, the timing of active
collision may be diachronous and long-lived along the margin. Magmatism
accompanying accretion is more enriched in incompatible trace elements than
average continental crust, contrasting with more depleted magmatism prior
to collision. Accretion of a mixture of depleted and enriched arc lithologies
to the continental margin allows the continental crust to grow through time
by arc-passive margin collision events.
During arc-continent collision the upper and middle arc crust are detached
from the depleted ultramafic lower crust, which is subducted along with
the mantle lithosphere on which the arc was founded. Rapid (2–3 million
years) exhumation and gravitational collapse of the collisional orogen forms
the Okinawa and South Mayo Troughs in Taiwan and western Ireland, respectively.
These basins are filled by detritus eroded from the adjacent collision zone.
During subsequent subduction polarity reversal, continuous tearing and retreat
of the oceanic lithosphere along the former continent-ocean transition provides
space for the new subducting oceanic plate to descend without need for breaking
of the original slab.
Schematic model showing how the new Ryukyu subduction system is able to
along the Chinese margin due to lithospheric tearing along the continent-ocean
transition of the South China Sea (Clift et al., 2003).
Draut, A.E., and Clift, P.D. 2002. The origin and significance
of the Delaney Dome Formation, Connemara, Ireland. Journal of the Geological
Society, London, 159, 95–103.
Draut, A.E., Clift, P.D., Hannigan, R., Layne, G.D. and Shimizu, N., 2002.
A model for continental crust genesis by arc accretion: rare earth element
evidence from the Irish Caledonides. Earth and Planetary Science Letters,
Clift, P.D., Schouten, H., and Draut, A.E., A general model of arc-continent
collision and subduction polarity reversal from Taiwan and the Irish Caledonides.
In Larter, R. and Leat, P., (Editors), Intra-Oceanic Subduction Systems;
Tectonic and Magmatic Processes, Geological Society of London, special
publication, in press.
Clift, P.D., Draut, A.E., Layne, G., and Blusztajn, J., Trace element and
Pb isotopic constraints on the provenance of the Rosroe and Derrylea Formations,
South Mayo, Ireland. Transactions of the Royal Society of Edinburgh,
Earth Science, 93 (2), in press.
Draut, A.E., and Clift, P.D., 2001. Geochemical evolution of arc magmatism
during arc-continent collision, South Mayo, Ireland. Geology, 29,
Clift, P.D., and Ryan, P.D., 1994. Geochemical evolution of an Ordovician
Island Arc, South Mayo, Ireland. Journal of the Geological Society,
London, 151, 329–342.
Page created by Peter Clift
Last Updated October 2002