PETROLOGIC IMPLICATIONS OF THE PALISADE CREST INTRUSIVE SUITE

The Sierra Nevada batholith forms the intrusive part of a Mesozoic magmatic arc. The Jurassic Tinemaha Granodiorite and granodiorite of McMurry Meadows comprise the Palisade Crest Intrusive Suite in the eastern part of the batholith. These plutons share similar geochemical compositions and record magma reservoir evolution during a time of voluminous ignimbrite eruptions in the overlying volcanic arc. This project serves to link the Palisade Crest Intrusive Suite to the tuff of Sardine Canyon. Comparing whole rock and zircon geochemistry in these rocks helps to better understand the link between intrusive and extrusive arc magmas and the provenance of detrital zircons in nearby fore-arc and retroarc basins. TAS and Harker plots classify the plutons as well as suggest a fractional crystallization process as the magma reservoir formed. Whole rock silica ranges from 57 to 72% and SiO₂ vs. K₂O trend positively with moderately high correlation coefficients; however SiO₂ vs. MgO, CaO, TiO₂, and Al₂O₃ trend negatively with high correlation coefficients. REE plots show that the plutons are light rare earth enriched and are depleted in Eu, with the negative Eu anomaly mostly 0.6 to 0.8. The overlying tuff of Sardine Canyon, erupted during assembly of the Woods Lake mass of Tinemaha Granodiorite, has 68 – 72% SiO₂, and similar REE patterns with negative Eu anomalies (~0.64). Whole rock Nd isotope ratios are identical. Zircons in samples of the tuff and granodiorite have overlapping ranges of Hf (9000-13000 ppm), high Th/U (0.5-1.2) and similar ranges in U/Yb. These observations support the hypothesis that the tuff was erupted from the underlying magma chamber while zircon was crystallizing (T ~750^oC) but before any significant crystallization of sphene.