Description
Orbicule-bearin pl.utonio roell:e are exposed approxillltely tour 1111•• southeaet ot Pine Valley, San Diego County, California. Three principal roak unite, a p.bbro, a granodior ite, and a tonalite are apoeed in thia area; the 'tA)nalite ie the youngeet, the granodiorite next youngest, vith the gabbro being the oldest. The orbioul.ea vere •pped •• part or the gabbro body by Merriaa (1958) but preaent study ebov■ them to be aseooiated with an early, more ba■io phue ot the granodiorl.te. The orblculu range from tvo to fifteen inches 1n diameter with ■oae being apherioal and aoae elongate. They haw a dietinct oonaentric, at:ruature and an made up ot alternately tio-rioh and telaio-rioh 11onee vi th 110re ooaraely cryetalline oorea. Solle oaab--layering aesooiated with the orbiaulea eugga■te that the orbioules formed around :nnolitha 1n a IIIOTing aqueou tluid (Moore and Loatvood, 1973).
