Publication Date:
2017-12-19
Description:
Thin oceanic crust is formed by decompression melting of the upper mantle at mid-ocean ridges, but the origin of the
thick and buoyant continental crust is enigmatic. Juvenile continental crust may form from magmas erupted above intraoceanic
subduction zones, where oceanic lithosphere subducts beneath other oceanic lithosphere. However, it is unclear
why the subduction of dominantly basaltic oceanic crust would result in the formation of andesitic continental crust at the
surface. Here we use geochemical and geophysical data to reconstruct the evolution of the Central American land bridge,
which formed above an intra-oceanic subduction system over the past 70Myr. We find that the geochemical signature
of erupted lavas evolved from basaltic to andesitic about 10Myr ago - coincident with the onset of subduction of more
oceanic crust that originally formed above the Galápagos mantle plume. We also find that seismic P-waves travel through
the crust at velocities intermediate between those typically observed for oceanic and continental crust. We develop a
continentality index to quantitatively correlate geochemical composition with the average P-wave velocity of arc crust
globally. We conclude that although the formation and evolution of continents may involve many processes, melting
enriched oceanic crust within a subduction zone - a process probably more common in the Archaean - can produce juvenile continental crust.
Type:
Article
,
PeerReviewed
Format:
text
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