Marine volcanic rocks
Marine volcanic rocks
Early Cretaceous to Late Triassic
Chiefly greenschist-facies metamorphosed andesite breccias and lava flows, tuff breccia, and ash-flow tuff, and lesser limestone, siltstone, and argillite. Unit locally includes metamorphosed rhyolite flows, breccia, tuff, and volcanogenic sedimentary rocks. Local phyllite, volcaniclastic sedimentary rocks, quartz arenite; slate, limestone. Unit includes Late Jurassic and Early Cretaceous volcanic and volcaniclastic Double Spring Formation, Early Jurassic clastic sedimentary Preachers Formation, Jurassic metavolcanic rocks of Hot Springs Mountain, and Late Triassic and Early Jurassic Gardnerville Formation (siltstone and volcanic conglomerate) at the base in west-central Nevada. Moderately to strongly schistose. Penetrative schistosity locally grades into slaty cleavage. Most of unit metamorphosed to greenschist facies and locally to amphibolite-facies near intrusive contacts.
Includes Middle Jurassic Gold Bug (flow rock over welded tuff) and Veta Grande (volcanic and volcaniclastic rock) Formations (Wyld and Wright, 1993) locally between the Preachers and Double Spring Formations. The Gold Bug and Veta Grande Formations have zircon U-Pb ages of ~162-170 Ma (Wyld and Wright, 1993).
East of Carson City, intruded by the Mount Siegel pluton, which has Pb-Pb age of ~166 Ma (Wooden and others, 1999).
Age diagnostic fossils from the Gardnerville Formation in this unit include: In Topaz Lake 15’ Quadrangle, late early Toarcian to late late Toarcian fossils from Holbrook Junction area (R.W. Imlay <em>in Silberling, 1984); in the Desert Creek Peak 15’ Quadrangle, probably Triassic ammonites and <em>Halobia in Risue Canyon (Halsey, 1953); in the Mount Siegel 15’ Quadrangle, Late Toarcian fossils near Buffalo Canyon (Silberling, 1984); just east of the map area in Dayton 15’ Quadrangle, Late Triassic and Early Jurassic fossils from argillite (equivalent to Gardnerville Formation according to Bingler, 1977) west of Sand Canyon (Stewart, 1997). Sparse fossils of Late Jurassic to Early Cretaceous age have been found in the Double Spring Formation (Noble, 1962).
Unit magmatically linked to the Walker Lake intrusive suite (unit Gwa). Christe (2010) further notes differences with the Middle Jurassic volcanic rocks of the Tuttle Lake Formation in the Northern Sierra terrane (part of unit NSTT) to the west and suggests they were formed well apart.