Sixteen 40Ar/39Ar geochronology analyses from southeastern Arizona

The results of 40 Ar/39 Ar analyses of 15 samples of rhyolitic ash-flow tuffs and one sample of a dacitic dome from Mid-Tertiary and Cretaceous volcanic successions in the Tucson area are presented in this report. Most of the samples were collected from variably tilted Mid-Tertiary supracrustal successions surrounding the Catalina metamorphic core complex in the Tortolita Mountains, Black Mountain, San Pedro trough, and Cienega Gap areas. Four samples of Upper Cretaceous ash-flow tuffs from the Santa Rita and Roskruge Mountains were also collected. Ten samples (FO-660, FO-927, FL-354, FK-1336, FK-1702, FK-1706, FK-1707, FK-1832, FK-3062 and FK-3277) were submitted in the fall of 200 1. Sanidine was separated from all but samples FK-3062 and FK-3277 from which biotite was separated (sample preparation in Table 1). In May of 2002, six additional rhyolites were submitted (CAF-02-1680, CAF-02-3628, T02-715, JES-3-26-02-1, WRD-CPH-l and WRD-CPH-2). Sanidine was separated from all of these samples. (4 pages)