%AScoggin, Shane [Department of Geosciences University of Arizona Tucson AZ USA, Now at Department of Geology and Geophysics University of Wyoming Laramie WY USA]%AReiners, Peter [Department of Geosciences University of Arizona Tucson AZ USA]%AShuster, David [Department of Earth and Planetary Science University of California Berkeley CA USA]%ADavis, George [Department of Geosciences University of Arizona Tucson AZ USA]%AWard, Lauren [Department of Geosciences University of Arizona Tucson AZ USA, Now at Department of Earth Sciences University of Hawai'i Honolulu HI USA]%AWorthington, James [Department of Geosciences University of Arizona Tucson AZ USA, Now at Geosciences Research Division Scripps Institution of Oceanography University of California San Diego La Jolla CA USA]%ANickerson, Phillip [Department of Geosciences University of Arizona Tucson AZ USA, Now at Rio Tinto Exploration Salt Lake City UT USA]%AEvenson, Nathan [Department of Geosciences University of Arizona Tucson AZ USA, Now at Kane Environmental Inc. Seattle WA USA]%BJournal Name: Geochemistry, Geophysics, Geosystems; Journal Volume: 22; Journal Issue: 12; Related Information: CHORUS Timestamp: 2023-08-27 03:56:21 %D2021%IDOI PREFIX: 10.1029 %JJournal Name: Geochemistry, Geophysics, Geosystems; Journal Volume: 22; Journal Issue: 12; Related Information: CHORUS Timestamp: 2023-08-27 03:56:21 %K %MOSTI ID: 10363559 %PMedium: X %T(U‐Th)/He and 4 He/ 3 He Thermochronology of Secondary Oxides in Faults and Fractures: A Regional Perspective From Southeastern Arizona %XAbstract

Fe‐ and Mn‐oxides are common secondary minerals in faults, fractures, and veins and potentially record information about the timing of fluid movement through their host rocks. These phases are difficult to date by most radioisotopic techniques, but relatively high concentrations of U and Th make the (U‐Th)/He system a promising approach. We present new petrographic, geochronologic and thermochronologic analyses of secondary oxides and associated minerals from fault zones and fractures in southeastern Arizona. We use these phases in attempt to constrain the timing of fluid flow and their relationship to magmatic, tectonic, or other regional processes. In the shallowly exhumed Galiuro Mountains, Fe‐oxide (U‐Th)/He dates correspond to host‐rock crystallization and magmatic intrusions from ca. 1.6 to 1.1 Ga. Step‐heating4He/3He experiments and polydomain diffusion modeling of3He release spectra on these samples are consistent with a crystallite size control on He diffusivity, and little fractional loss of radiogenic He since formation in coarse‐grained hematite, but large losses from fine‐grained Mn‐oxide. In contrast to Proterozoic dates, Fe‐ and Mn‐oxides from the Catalina‐Rincon and Pinaleño metamorphic core complexes are exclusively Cenozoic, with dates clustering at ca. 24, 15, and 9 Ma, which represent distinct cooling or fluid‐flow episodes during punctuated periods of normal faulting. Finally, a subset of Fe‐oxides yield dates of ca. 5 Ma to 6 ka and display either pseudomorphic cubic forms consistent with oxidative retrogression of original pyrite or magnetite, or fine‐grained botryoidal morphologies that we interpret to represent approximate ages of recrystallization or pseudomorphic replacement at shallow depths.

%0Journal Article