Tectonics of Unusual Crustal Accretion in the Parece Vela Basin - Accretionary Prisms and Convergent Margin Tectonics in the Northwest Pacific Basin - page 149

Tectonics of Unusual Crustal Accretion
in the Parece Vela Basin
Yasuhiko Ohara, Kyoko Okino, and Jonathan E. Snow
Abstract Despite its rapid intermediate-spreading rate, the Parece Vela Basin
(PVB) shows unusual characteristics that indicate a depressed magmatic budget,
such as the occurrence of numerous oceanic core complexes (OCCs) and rugged
terrain, exposing abundant peridotites and gabbros. Based on the geologic interpre-
tations of crust with analogous features on global mid-ocean ridges, we propose three
possible mechanisms that can account for these unusual characteristics: (1) presence
of a cold and/or refractory mantle domain, (2) declining spreading rate during
the later phase of the second-stage spreading of the PVB, and (3) a transform sand-
wich effect. Recent numerical modeling for formation of OCC suggests that there
is a minimum as well as a maximum magmatic supply necessary to produce long-
lived detachment fault. In the western PVB, a cold and/or refractory mantle domain
inhibited a large amount of mantle melting within an intermediate-spreading ridge,
attaining the limited window of the condition of magma supply demonstrated in
the numerical model in an otherwise robust magmatic environment. In the central
PVB, a transform sandwich effect and/or declining spreading rate inhibited a large
amount of mantle melting within an intermediate-spreading ridge, also attaining the
limited window of the condition of magma supply demonstrated in the numerical
model in an otherwise robust magmatic environment.