Fine Gold intrusive suite
Fine Gold intrusive suite
Early Cretaceous, ~101-128 Ma
Occurs in western part of central Sierra Nevada. Originally defined by Bateman (1992). Chiefly tonalite, trondhjemite, granodiorite, and granite, with small bodies of diorite and gabbro. Zircon U-Pb ages from this unit range from ~101-128 Ma (Saleeby and Sharp, 1980; Stern and others, 1981; Chen and Moore, 1982; Wooden and others, 1999; Lackey and others, 2008, 2012; Ardill and others, 2018). This age range excludes one age of 91 Ma from a locality in the northeast corner of the unit reported by Wooden and others (1999), which is ~10 Ma younger than any other in the unit, and probably belongs to the adjacent ~84-98 Ma Sonora Pass intrusive suite (unit Gso) or ~91-102 Ma Jack Main Canyon intrusive suite (unit Gja). This unit has also yielded biotite K-Ar ages of ~83-113 Ma and hornblende K-Ar ages of ~88-128 Ma (Kistler and others, 1965; Evernden and Kistler, 1970; Saleeby and Sharp, 1980; Tobisch and others, 1995), excluding one hornblende K-Ar age of ~144 Ma (Evernden and Kistler, 1970), which is at least ~16 Ma older than any other hornblende K-Ar age from this unit and is also older than the zircon U-Pb ages. This unit has also yielded a muscovite K-Ar age of ~110 Ma (Evernden and Kistler, 1970), apatite fission track ages of ~78-125 Ma, and sphene fission track ages of ~96 Ma and ~99 Ma (Naeser and Dodge, 1969). Major plutons: tonalite of Ross Creek, Bass Lake Tonalite, Poopenaut Valley granodiorite, and granite porphyry of Star Lakes. May include granodiorite of Arch Rock, Ward Mountain Trondhjemite, Knowles Granodiorite, granodiorite of Sawmill Mountain, and the northern part of the granite of Shuteye Peak. As mapped, this unit includes deformed and altered gabbro, diorite, tonalite, and local peridotite, locally named the tonalite of Millerton Lake by Bateman (1992) with an optimal U-Pb zircon age of ~134 Ma, too small to be mapped separately. This unit intrudes across the Melones fault which separates the Cosumnes terrane and Yuba River superterrane from the rest of the Sierra Nevada.