CORRELATION AND ORIGIN OF UPPER JURASSIC TUFFS AND PLUTONS THROUGH APATITE TRACE ELEMENT GEOCHEMISTRY, SOUTHEASTERN ARIZONA, USA

The Middle to Late Jurassic volcanic suite of southern Arizona has proven in the past to be difficult to correlate due to later Basin and Range and Laramide tectonic events. Recent application of trace mineral geochemistry using single apatite grains from ash-flow tuffs and associated plutons via ICP-MS has allowed for refinement of preliminary correlations. Using the three mapped tuff units in the northern Mustang Mountains as reference (Lipman and Hagstrum, 1992), the Jurassic tuffs can be correlated to tuffs in the Huachuca Mountains and the Canelo Hills. The lowermost of the tuffs has a U-Pb SHRIMP (Stanford University) age of 176 +/- 4 Ma; the middle tuff has an equivalent age of 179 +/- 1Ma.

We correlate the volcanic ranges in southern Arizona using Lipman & Hagstrum's (1992) stratigraphic work in the Mustang Mountains as a starting point. The upper crystal-rich rhyolite of the Mustangs (L&H, 1992) correlates to the upper tuff in the Canelo Hills (20% xls - equal quartz and feldspar including sanidine) and the upper Huachucas (15% xls - 10% feldspar, 5% quartz) as being the Parker Canyon intercaldera tuff (phenocryst-rich rhyolite with abundant quartz and feldspars, L&H, 1992). The middle tuff of the Canelo Hills (~3% xls – very small quartz, some feldspar, possible fiamme), Mustangs (3% xls – biotite and smoky quartz, some feldspars, flattened pumices), and Huachucas (2% xls – few quartz and feldspar crystals) as the same unit, crystal-poor rhyolite intercaldera tuffs sourced from the Turkey Canyon caldera (3-5% xls of quartz and feldspar, characterized by extremely flattened pumices, L&H, 1992). The lower tuffs in the stratigraphic section are not present in the Canelo Hills, however exposures in the Huachucas (3% xls – mostly feldspar, some quartz and biotite, eroded pumices) and Mustangs (1% xls – trace quartz, sanidine, abundant flattened pumice) can be sourced back to the Montazuma caldera exposed as the Huachuca Quartz Monzonite (coarse equigranular potassium feldspar, lesser amounts of quartz, and ~8% biotite, some epidote grains). Trace element concentrations in apatites will be used to confirm these correlations and to correlate tuffs to exposed coeval plutons, such as the Huachuca Quartz Monzonite.