24-4 Age and geochemistry of zircon from the Candelaria Formation, western Nevada and eastern California, USA, and implications for correlations of Middle Triassic strata and the effects of the Golconda allochthon on sedimentary provenance

Session: Advances and Applications in Geochronology for Interpreting Stratigraphic and Basin Records, Part I

Presenting Author:

Authors:

Abstract:

The Candelaria Formation (Trc) is exposed throughout western Nevada.  Previous workers have proposed that it is broadly correlative with the Triassic Union Wash Formation (Tru) in the Inyo Mountains, CA, which in turn is correlated with the more-extensive Moenkopi Formation (Trm) and its equivalent lower Buckskin Formation (Trb) on the Colorado Plateau and in western Arizona/southeastern California/northwestern Sonora. Together, these strata have been interpreted to represent sedimentation in the foreland basin that developed in response to emplacement of the Golconda allochthon.  We collected samples of Trc in the type Candelaria Mine section, in the foothills of the Toquima Range, NV, and in the eastern Sierra Nevada at Virginia Lakes, CA, to test correlation of Trc strata with coeval successions through U-Pb geochronology and trace element geochemistry of zircon (LA-ICPMS). Additionally, we sought to investigate provenance contributions of the Golconda allochthon.

Unlike most Trm and Tru strata, all the Trc samples yielded a large percentage of arc-derived zircon grains that range in age from ca. 270 Ma to ca. 245 Ma; the Virginia Lakes sample contains dominantly arc grains. Maximum deposition ages (MDAs) are from ca. 248 Ma (Candelaria, Virginia Lakes) to ca. 259 Ma (Toquima). The younger age matches the MDAs of Tru (247 Ma) and Trb (249 Ma). Trace-element ratios demonstrate a continental-array signature, and comparison of trace elements are similar between Trc, Tru, and Trb. Probability density plot cross-correlation coefficients (CCC) of grains >300 Ma (0.49 – 0.75) indicate that Trc is similar to other Triassic units, especially lower Trm. CCCs that compares Trc with published data from the Schoonover Formation in the Golconda allochthon suggests a poor match (<0.25).

We propose that in early Triassic time, arc magmatism was widespread and magmas were continental and fractionated. Earlier reports speculated that volcanic detritus in Trc was derived from the north, but we find that similarities are strong with arc-magmatic rocks exposed to the west and southwest in California. Wind and wave currents carried ash and crystals from the offshore arc dominantly to the east and northeast, explaining the dominance of arc zircon in Trc in contrast to many units to the south and southeast. Emplacement of the allochthon may have caused more flexure (i.e., foreland basin) than topography (i.e., sediment source).

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

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