Diamond Mountains intrusive suite
Diamond Mountains intrusive suite
late Early Cretaceous, Late Jurassic and Early Jurassic, ~104-114 Ma, ~121-128 Ma ~148-163 Ma, and ~178-184 Ma
Occurs in the northeastern Sierra Nevada. Chiefly quartz diorite, granodiorite, quartz monzonite, and granite. Major plutons: Lights Creek, China Gulch, Goodrich, and Genesee-Reward. This unit appears to be composed of plutonic rocks from four or five separate intrusive periods. Sparse older quartz diorite and gabbro associated with Lights Creek quartz monzonite stock, which has zircon U-Pb ages of ~178 and ~184 Ma (Stephens, 2011; Dilles and Stephens, 2010); younger units, such as China Gulch granite have zircon U-Pb ages of ~148-163 Ma (Stephens, 2011; Langenheim and others, 2025); and still younger plutonic rocks, including local porphyritic pegmatite zones, have zircon U-Pb ages from ~104-114 Ma (Van Buer, 2011; Langenheim and others, 2025). Langenheim and others (2025) also report two zircon U-Pb ages of ~121 Ma for this unit, plus an age of ~128 Ma for plutonic rock just north of the map area, indicating a fourth period of intrusion. They also report zircon U-Pb ages of ~94 and ~95 Ma from the southeastern-most part of this unit, but it is likely that these represent small inliers or a previously unmapped body of one of the coeval plutonic units to the south or east (units Glkt or Gwa). Evernden and Kistler (1970) reported biotite K-Ar ages of ~87-100 Ma from the eastern part of this unit, as well as a biotite K-Ar and a hornblende K-Ar age of ~105 Ma from the southwest part of the unit. They also reported a biotite K-Ar age of ~101 Ma and a hornblende K-Ar age of ~102 Ma from just outside this unit (an undescribed lithology probably from an outcrop of this unit too small to map within Cenozoic units roughly in the center of the extent of the intrusive suite). Van Buer (2011) reports apatite fission track ages of ~75-89 Ma, and apatite He ages of ~50-53 Ma, from the northeast part of the unit (colocated with the younger zircon U-Pb ages of ~104-111 Ma). The K-Ar and apatite fission track ages probably represent cooling ages following the final intrusive phase. Lights Creek stock and associated units intrude Kettle Rock terrane (unit KR) to west. The oldest part of the intrusive suite, along with volcanics in the Kettle Rock terrane, are coeval with, and may form a northern extension of, the Tuttle igneous arc that includes older parts of the Tuttle and Emigrant Gap intrusive sequence (unit Gtt and Gegg) and the Tuttle Lake Formation and upper Lake Tahoe sequence (unit NSTT).