Detrital zircon geochronologic study of upper Paleozoic strata in the eastern Klamath terrane, northern California

Abstract

U-Pb analyses have been conducted on individual detrital zircon grains from Upper Devonian(?)-Carboniferous strata of the Bragdon Formation and UpperCarboniferous-L ower Permian strata of the Baird Formation. These are the two most important clastic units in the Redding section of the eastern Klamath terrane of northern California. There are 31 grains from the Bragdon Formation that yield mainly concordant to slightly discordant ages ranging from ca. 363 Ma to ca. 3.12 Ga. Grains with ages of ca. 363-572 Ma in this sample were apparently shed primarily from the nearby Trinity complex, which contains igneous rocks of these ages. Older grains, ranging from 1.07 to 3.12 Ga, but mostly between 1.76 and 1.99 Ga, were likely recycled from lower Paleozoic strata of the Yreka terrane or the Roberts Mountains allochthon. Six detrital zircons from the Baird Formation are all apparently concordant, with interpreted ages between 320 and 326 Ma. These grains are locally derived and probably record igneous activity represented by the widespread volcanic and volcaniclastic rocks within the Baird Formation.

Mesozoic transpression, transtension, subduction and metallogenesis in northern and central California

“…Although rare in the single analysed metaclastic rock from the southern Klamath Mountains, two North Fork terrane samples from the Sawyers Bar area also exhibit a significant population of 400-460 Ma zircons and a wide range of Proterozoic U-Pb ages. The Paleozoic zircon ages are similar to those of small, isolated Eastern Klamath stocks that intrude the Trinity and Redding subterranes (Irwin and Wooden, 1999;Gehrels and Miller, 2000;Snoke and Barnes, 2006). Neoproterozoic and older zircons may have been derived from the Yreka subterrane (Wallin et al, 2000;Lindsley-Griffin et al, 2006), hence the Eastern Klamath terrane probably was the source of older zircons in the central and southernmost North Fork terrane.…”

“…Reflecting the paucity of blueschists ± eclogites, calcalkaline igneous rocks and multicycle strata, North Fork sedimentary and volcanic units probably formed in a transtensional mafic forearc along the Klamath margin. Evidently the oceanic basin lay farther outboard to the south than the central and northern areas, based on the following: Clastic debris and detrital zircon U-Pb data indicate that the source of fine-grained turbidites in the central and southern North Fork terrane lay in the eastern Klamaths ± nearby North Fork arc (Gehrels and Miller, 2000;Scherer and Ernst, 2008). Strata in the southernmost part of the belt are more distal than argillites in the central North Fork area, and their geochemistry indicates a mixed terrigenous + mafic volcanic provenance .…”

“…At depths approaching c80-120 km, evolution of fluids promotes the partial fusion of entrained sediments + transformed mafic crust and ⁄ or the overlying, metasomatized mantle (DePaolo, 1981;Drummond and Defant, 1990;Hawkesworth et al, 1993;Clift et al, 2001;HickeyVargas et al, 2002). Consequently, deep-seated calcalkaline melts and highly charged aqueous solutions rise into the zone of fracture, forming ore bodies in the upper arc crust (Goldfarb et al, 2001;Groves et al, 2005). The scarcity of metallogenesis coeval Fig.…”

Contrasting early and late Mesozoic petrotectonic evolution of northern California

“…Although rare in the single analyzed metaclastic rock from the southern Klamaths, two North Fork terrane samples from the Sawyers Bar area exhibit a signifi cant population of 400-460 Ma zircons, as well as a wide range of Proterozoic U-Pb ages. The Paleozoic zircon ages are similar to those of minor plutons that intrude the Eastern Klamath Trinity and Redding subterranes (Irwin and Wooden, 1999;Gehrels and Miller, 2000;Snoke and Barnes, 2006); Neoproterozoic and older zircons may have been derived from the Yreka subterrane (Wallin et al, 2000;LindsleyGriffi n et al, 2006). We tentatively conclude that the Eastern Klamath terrane was the source of the older North Fork zircons.…”

“…(1) Minor arc volcanism in the Trinity and Redding subterranes of the eastern Klamaths (Sanborn, 1960;Irwin and Wooden, 1999) was contemporaneous with Triassic-Middle Jurassic chert-argillite deposition and mafi c volcanism in the North Fork terrane. (2) Clastic debris and detrital zircon U-Pb data indicate that the source of distal turbidites in the North Fork terrane was in the Eastern Klamath arc and nearby North Fork volcanic rocks (Gehrels and Miller, 2000;Scherer and Ernst, 2008). (3) To the south, argillaceous and cherty strata deposited along strike of the belt are more distal than argillites in the central North Fork terrane, and their geochemistry indicates provenance from a mixed terrigenous and mafi c volcanic source (Scherer and Ernst, 2008).…”