4 research outputs found
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U-Pb isotope geochronologic data from 23 igneous rock units in cental and southeastern Arizona
Geochronologic analyses of igneous rocks were done over the past several years as part of the joint State-Federal STATEMAP program. These analyses were done to determine the age of rocks in areas where Arizona Geological Survey geologists were making geologic maps at 1 :24,000 scale or compiling geologic maps at 1: 100,000 scale. Geochronologic analyses are a basic component of geologic map making in areas where igneous rocks are present but their ages are poorly known. Most ofthe dates reported here are the result of laboratory analyses by Clark Isachsen at the University of Arizona Department of Geosciences, and were determined in most cases by analysis of single zircon crystals from the rock samples. Two dates were produced at the US Geological Survey in Menlo Park, California, by Joe Wooden, and two are from samples collected by Nancy Riggs and analyzed at UC Santa Barbara. These analyses used multiple zircon crystals divided into size fractions for each laboratory analysis. Sample locations and descriptions are reported in Table 1, and basic geochronologic results are reported in Table 2. Concordia diagrams and analytical data are given in Appendix A. ( 40 pages)Documents in the AZGS Document Repository collection are made available by the Arizona Geological Survey (AZGS) and the University Libraries at the University of Arizona. For more information about items in this collection, please contact [email protected]
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U-Pb geochronologic data from zircons from eleven granitic rocks in central and western Arizona
The U-Pb data described in this report were produced to determine the ages of granitic rocks in Arizona and the timing of metamorphic and deformational events. Two developments emerge from the data reported here that are especially significant. Two granites, one from the Mazatzal Mountains east of Phoenix and one from the Santan Mountains southeast of Phoenix, yielded dates between 1630 and 1640 Ma. This is unusually young for early Proterozoic granites in Arizona, although two granites in the Maricopa Mountains southwest of Phoenix have yielded similar dates (Eisele and Isachsen, in review; Joe Wooden, written communication, 1998). Possibly, these dated granites are part of a belt of similar-age granites that roughly occupy the boundary between Pinal Schist on the southeast and metavolcanic and metasedimentary rocks of the Tonto Basin Supergroup to the northwest (Conway and Silver, 1989; Reynolds and Dewitt, 1991).Documents in the AZGS Document Repository collection are made available by the Arizona Geological Survey (AZGS) and the University Libraries at the University of Arizona. For more information about items in this collection, please contact [email protected]