Abstract

Paleotemperature in the Jurassic Chichibu and the Cretaceous Shimanto accretionary complexes, southwest Japan, increases southward, generally without regard to the early-phase geologic structure. There is an exceptional peak in the Okitsu melange, and the thermal structure probably formed after accretion of the complex. The estimated geothermal gradient is more than 90 °C/km in the Okitsu melange and more than 50 °C/km elsewhere in the complex. The ophiolitic Okitsu melange formed concurrently with Eocene subduction of the Kula-Pacific ridge under the Cretaceous accretionary prism. The previous thermal structure was overprinted by this event.

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