Kings River ophiolite belt
Kings River ophiolite belt
Early Ordovician, ~484 Ma
Occurs in western slopes of central Sierra Nevada adjacent to the Kings River. Consists of narrow to large fault-bounded masses of dismembered ophiolite, serpentinite, and serpentinite mélange. Belt occurs in a series of tectonic slabs as long as 20 km and separated by serpentinite-matrix mélange zones and crosscutting plutons of the Sierra Nevada batholith. Principal slabs consist of peridotite-cumulate gabbro, sheeted dike-pillow lava slabs, and depleted peridotite-mafic tectonite slabs. Belt interpreted as MORB pillow basalt eruptions that formed the upper crustal levels of an abyssal lithosphere section above a coherent interval of basaltic sheeted dikes. Bounded on the northeastern margin by nonconformably overlying Mesozoic metasedimentary and metavolcanic rocks (unit KSV).
Saleeby and Sharp (1980) report discordant U-Pb zircon ages of ~198-210 Ma from a metadiorite layer within metagabbro, and an amphibole K-Ar age of ~190 Ma for nearby metagabbro. They also report even more discordant U-Pb zircon ages of ~190-305 Ma from plagiogranite pods within metaperidotite. Saleeby (2011), however, reports a multi-rock Sm-Nd isochron age of ~484 Ma for the disrupted ophiolite at Kings River, and states that the Permo-Triassic ages are from later MORB magmatism associated with the Kaweah serpentinite mélange (unit MRKA) emplaced into and on the disrupted Ordovician ophiolite of this unit.