Arc-continent collisions, sediment recycling and the maintenance of the continental crust
Arc-continent collisions, sediment recycling and the maintenance of the continental crust
Date
2008-02-13
Authors
Clift, Peter D.
Schouten, Hans A.
Vannucchi, Paola
Schouten, Hans A.
Vannucchi, Paola
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Abstract
Subduction zones are both the source of most new continental crust and the
locations where crustal material is returned to the upper mantle. Globally the total amount of
continental crust and sediment subducted below forearcs currently lies close to 3.0 Armstrong
Units (1 AU = 1 km3/yr), of which 1.65 AU comprises subducted sediments and 1.33 AU
tectonically eroded forearc crust. This compares with average ~0.4 AU lost during
subduction of passive margins during Cenozoic continental collision. Individual margins may
retreat in a wholesale, steady-state mode, or in a slower way involving the trenchward
erosion of the forearc coupled with landward underplating, such as seen in the central and
northern Andean margins. Tephra records of magmatism evolution from Central America
indicate pulses of recycling through the roots of the arc. While this arc is in a state of long-
term mass loss this is achieved in a discontinuous fashion via periods of slow tectonic erosion
and even sediment accretion interrupted by catastrophic erosion events, likely caused by
seamount subduction. Crustal losses into subduction zones must be balanced by arc
magmatism and we estimate global average melt production rates to be 96 and 64
km3/m.y./km in oceanic and continental arc respectively. Key to maintaining the volume of
the continental crust is the accretion of oceanic arcs to continental passive margins. Mass
balancing across the Taiwan collision zones suggests that almost 90% of the colliding Luzon
Arc crust is accreted to the margin of Asia in that region. Rates of exhumation and sediment
recycling indicate the complete accretion process spans only 6–8 m.y. Subduction of
sediment in both erosive and inefficient accretionary margins provides a mechanism for
returning continental crust to the upper mantle. Sea level governs rates of continental erosion
and thus sediment delivery to trenches, which in turn controls crustal thicknesses over 107–
109 yrs. Tectonically thickened crust is reduced to normal values (35–38 km) over timescales
of 100–200 Ma.
Description
Author Posting. © Geological Society of London, 2009. This is the author's version of the work. It is posted here by permission of Geological Society of London for personal use, not for redistribution. The definitive version was published in Geological Society, London, Special Publications 318 (2009): 75-103, doi:10.1144/SP318.3.