PROVENANCE AND DEPOSITIONAL SETTING OF PALEOZOIC CHERT AND ARGILLITE,SIERRA-NEVADA, CALIFORNIA

The Shoe Fly Complex, the remnants of an early to middle Paleozoic sub duction system, contains the Culbertson Lake allochthon, Included in t he Culbertson Lake allochthon are the post-Cambrian and pre-Upper Devo nian Quartz Hill, Toms Creek, and McMurray Lake cherts. Geochemical da ta derived from these three units plot on the Fe2O3/TiO2 versus Al2O3( Al2O3 + Fe2O3) and La-n/Ce-n versus Al2O3/(Al2O3 + Fe2O3) discriminati on diagrams within either the continental margin-island are field, or that part of the pelagic field overlapping the continental margin-isla nd are field. These relationships are consistent with the presence of argillaceous turbidites interstratified with radiolarite, and suggest a relatively distal continental-island are setting where muddy turbidi ty currents episodically interrupted pelagic deposition. Specimens fro m the Quartz Hill and Toms Creek cherts with Al2O3/TiO2 values > 20 ma ke up Group I samples, whereas specimens with Al2O3/TiO2 values < 10 a re classified as Group II samples. The Al2O3/TiO2 ratios of Group II s pecimens suggest derivation from mafic rock. Mean Th/Sc and Th/U value s, as well as LREE-enriched patterns, are consistent with this interpr etation, and indicate a source area dominated by alkalic seamount or o cean island material. The Al2O3/TiO2 ratios of Group I samples indicat e a source area with an average andesitic to rhyodacitic composition. Chondrite-normalized REE distribution patterns, as well as mean Th/Sc and Th/U values, support such an interpretation. Samples from the McMu rray Lake chert have Al2O3/TiO2 values ranging between similar to 19 a nd similar to 28, and REE patterns characterized by LREE enrichment, n egative Fu anomalies, and slightly fractionated HREE patterns. These f eatures, along with mean Th/Sc and Th/U values, indicate a source area dominated by old upper continental crust. The location of the source area(s) supplying material to cherts and argillites of the Culbertson Lake allochthon is unknown. However, existing tectonic models commonly portray the source of old upper continental crustal material in the S hoe Fly Complex as being located somewhere along the western North Ame rican continental margin, whereas the source of island-are debris is p ortrayed as being located in a fringing are system. Our data suggest t hat a relatively high-standing seamount or ocean island probably resid ed on the subducting oceanic plate. Thus, our work supports the idea t hat Al, Fe, Ti, Th, Sc, and the REEs in chert and argillite deposited in proximal continental-island are settings can be used to assess the characteristics of sources supplying particulate matter to ancient tre nch systems.