Since flat subduction of the Nazca Plate beneath Peru was first recognized
in the 1970s and 1980s a satisfactory explanation has eluded researchers. W
e present evidence that a lost oceanic plateau (Inca Plateau) has subducted
beneath northern Peru and propose that the combined buoyancy of Inca Plate
au and Nazca Ridge in southern Peru supports a 1500 km long segment of the
downgoing slab and shuts off are volcanism. This conclusion is based on an
analysis of the seismicity of the subducting Nazca Plate, the structure and
geochemistry of the Marquesas Plateau as well as tectonic reconstructions
of the Pacific-Farallon spreading center 34 to 43 Ma. These restore three s
ub-parallel Pacific oceanic plateaus; the Austral, Tuamotu and Marquesas, t
o two Farallon Plate counterparts; the Iquique and Nazca Ridges. Inca Plate
au is apparently the sixth and missing piece in an ensemble of 'V-shaped' h
otspot tracks formed at on-axis positions. We argue the mirror image of the
Inca Plateau, the Marquesas Plateau, is an ancient edifice overprinted by
recent volcanism, in disagreement with the widely accepted young (<5 Ma) ho
tspot model for plateau formation. (C) 1999 Elsevier Science B.V. All right
s reserved.