See more from this Division: Topical Sessions
See more from this Session: Southwest Pacific Cenozoic Tectonics and Comparisons with Other Orogenic Belts
Abstract:
Protoliths of the amphibolite are metachert and metabasalt. Assemblages range from epidote amphibolite to garnet amphibolite to amphibolite-granulite transition. Grt-Cpx-Phengite thermobarometry and yielded a temperature of 727-740ºC and pressure of 14-17 kbar. Amphibole thermobarometry yielded a temperature of 680 ºC and a pressure of 19 kbar. Based on the field relationship and P-T conditions we interpret the amphibolite to represent a metamorphic sole that formed during the hot initiation of subduction. This implies that a previous subduction zone was present to form the oceanic lithosphere the amphibolite was thrust under. The Feather River ultramafic belt formed under a west-dipping subduction prior to 240 Ma. After blockage of the subduction zone an east-dipping subduction zone formed around 240 Ma with the amphibolite recording the initiation of subduction within young oceanic lithosphere. The peak pressure conditions are much higher than those based on the thickness of the overlying ophiolite indicating that the amphibolite has been exhumed relative to its Feather River ultramafic belt.
See more from this Division: Topical Sessions
See more from this Session: Southwest Pacific Cenozoic Tectonics and Comparisons with Other Orogenic Belts