TESTING THE UTILITY OF DETRITAL ZIRCON HAFNIUM SIGNATURES FOR SEDIMENTARY PROVENANCE: THE NORTHERN GREAT VALLEY GROUP, CALIFORNIA

The Great Valley Group (GVG) of California is an ideal area to test the utility of Hf for sedimentary provenance because the sediment source of the GVG is well-established in the Klamath-Sierran magmatic arc and the geochronology and geochemistry of the arc is well-studied. We sampled five 134-138 Ma plutons in the Klamath Mountains (KM) and northern Sierran terranes (SN) to establish a basis for comparison with GVG detrital zircon Hf signatures. The weighted mean εHf values for the KM plutons are 9.0 ± 1.1 (MSWD 0.4), 11.4 ± 1.4 (0.2), and 12.1 ± 1.4 (0.6), and the weighted mean εHf values for the SN plutons are 11.2 ± 1.5 (0.3) and 11.1 ± 0.7 (0.8). The small standard deviation of εHf for each pluton and the overlap in εHf between plutons suggest that these plutons had a similar juvenile magma source with minimal crustal contamination. These Hf results are consistent with the plutons’ emplacement west of increasingly positive εNd values recorded in SN plutons, and west of the ⁸⁷Sr/⁸⁶Sr 0.706 line.

We completed εHf analysis of 130-152 Ma detrital zircon in seven GVG sandstone samples, and our results reveal higher ranges, standard deviations, and MSWD values for εHf in most of the detrital zircon samples relative to similar-age plutons. Two Platina petrofacies samples have weighted mean εHf values of 7.3 ± 1.1 (MSWD 0.5) and 13.4 ± 1.8 (4.1) and an εHf range of 13 units (3-16). One sample from the Chico Formation has a range in εHf of 9 units (12-21), with a weighted mean of 14.2 ± 1.5 (0.9). Two samples from the Lower Cretaceous Stony Creek Petrofacies have an εHf range of 9 units (8 -17), with weighted means of 13.3 ± 3.8 (0.5; excludes outlier with εHf of -24) and 13.4 ± 1 (1.0). Finally, two samples from the Venado Formation of the Boxer petrofacies with nearly unimodal Lower Cretaceous detrital zircon age distributions have an εHf range of 14 units (2-16), with weighted means in εHf of 10.5 ± 1.8 (1.9) and 11.0 ± 1.3 (1.0). These results suggest that sediment mixing is occurring even within samples with unimodal detrital zircon age signatures and show that Hf signatures in detrital zircon may reveal greater detail and variation in sedimentary provenance than conventional methods alone. Integrated with detrital zircon age dating, Hf analysis of zircon may provide more detailed provenance information and better delineate sediment transport pathways.