TECTONOTHERMAL EVOLUTION OF THE PINALENO-JACKSON MOUNTAIN CORE COMPLEX, SOUTHEAST ARIZONA

Petrologic data, U-Pb analyses of zircon, and Ar-40/Ar-39 analyses wer e used to document the tectonothermal history of two mylonite zones an d the temporal relationship of mylonite formation to movement on detac hment faults in the Pinaleno-Jackson Mountain metamorphic core complex of southeastern Arizona. Mylonite formation in the Pinaleno Mountains is dated at ca. 29 and ca, 19 Ma, The later event possibly is synchro nous with, and structurally related to, the most recent movement on th e Black Rock detachment fault (at <22 Ma) and the Eagle Pass detachmen t fault (at <25 Ma), The detachment surface on the northeast flank of the Pinaleno Mountains may have been active without significant change s in geometry for up to 10 m,y. Heterogeneous age distributions docume nted over relatively short distances in the lower plate of the Pinalen o-Jackson Mountain metamorphic core complex cannot be readily explaine d by a model of simple unroofing through a steady-state geotherm, Mult iple recrystallization events during mylonite formation, and/or transi ent thermal events are required to explain the partial and complete is otopic resetting bf thermochronometers in this area.