Abstract
The crystalline core of the southern Black Hills, South Dakota, exposes an extensive, low-P-high-T aureole of garnet- to second-sillimanite-zone schists centered on the plutonic core of the 1715 Ma Harney Peak Granite (HPG). This paper demonstrates regional patterns of apparent ages observed for 52 40Ar/39Ar dates of muscovite and biotite in diverse rocks from across the ~1000 km2 metamorphic aureole and its plutonic center. About 20 biotite dates, sampled mostly near faults, are influenced by excess 40Ar and obscure the regional trends. The remaining mica dates reveal radial patterns of apparent younging from outer aureole toward inner granite, with previously unrecognized, elliptical age zones centered on the main HPG pluton and its outliers. The regional pattern of 40Ar/39Ar cooling ages indicates non-uniform slow cooling of the mid-crust between ~1600-1250 Ma. This scenario of delayed slow cooling from aureole to pluton is consistent with published cooling ages for muscovite (Rb/Sr) and apatite (U/Pb), which range from 1690 to 1550 Ma and from 1700 to ~1500 Ma, respectively. To explain these results, it is likely that ambient pre-granite temperatures of the country rocks were ≥350 °C at the ~10-14 km depth of granite emplacement, as previously proposed, and that the entire complex resided at this depth and cooled slowly from aureole to granite for hundreds of millions of years. Alternatively, or in addition, the HPG and inner aureole were not uplifted until ~1480-1330 Ma, whereupon they finally cooled through ~300-350 °C.
© 2015 by Walter de Gruyter Berlin/Boston
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Articles in the same Issue
- Hydrothermal synthesis of hematite spherules and jarosite: Implications for diagenesis and hematite spherule formation in sulfate outcrops at Meridiani Planum, Mars
- Concentric slow cooling of a low-P–high-T terrane: Evidence from 1600–1300 Ma mica dates in the 1780–1700 Ma Black Hills Orogen, South Dakota, U.S.A.
- Monazite ages from carbonatites and high-grade assemblages along the Kambam Fault (Southern Granulite Terrane, South India)
- Forward modeling of the effects of mixed volatile reaction, volume diffusion, and formation of submicroscopic exsolution lamellae on calcite-dolomite thermometry
- A low-temperature phase diagram for ilmenite-rich compositions in the system Fe2O3-FeTiO3
- Dehydrogenation of kaersutitic amphibole under electron beam excitation recorded by changes in Fe3+/ΣFe: An EMP and SIMS study
- Protonation in germanium equivalents of ringwoodite, anhydrous phase B, and superhydrous phase B
- Andreyivanovite: A second new phosphide from the Kaidun meteorite
- The crystal chemistry of whitlockite and merrillite and the dehydrogenation of whitlockite to merrillite
- Single-crystal elastic properties of (Mg0.987,Fe0.013)O to 9 GPa
- Stoichiometry of synthetic ulvöspinel single crystals
- Thermal behavior and structural transformation in the chabazite-type zeolite willhendersonite, KCaAl3Si3O12·5H2O
- The kinetics and mechanisms of schwertmannite transformation to goethite and hematite under alkaline conditions
- Crystal chemistry of the mixed-layer sequence talc–talc-smectite–smectite from submarine hydrothermal vents
- Crystal chemical and structural characterization of fibrous tremolite from Susa Valley, Italy, with comments on potential harmful effects on human health
- Thermodynamic properties of CaTh(PO4)2 synthetic cheralite
- A computational study of order-disorder phenomena in Mg2TiO4 spinel (qandilite)
- Mineralogical characterization of silica sinters from the El Tatio geothermal field, Chile
- Influence of multi-electron excitation on EXAFS spectroscopy of trivalent rare-earth ions and elucidation of change in hydration number through the series
- Pressure-induced over-hydration and water ordering in gismondine: A synchrotron powder diffraction study
- 57Fe Mössbauer study of the oxidation state of iron in stilpnomelane from granite pegmatites in Poland
- Constraints on structural models of ferrihydrite as a nanocrystalline material
- Pb+ irradiation of synthetic zircon (ZrSiO4): Infrared spectroscopic investigation
- Equation of state and crystal structure of a new germanate post-titanite phase
- Synthetic hypersilicic Cl-bearing mica in the phlogopite-celadonite join: A multimethodical characterization of the missing link between di- and tri-octahedral micas at high pressures
- The effect of crystal-melt partitioning on the budgets of Cu, Au, and Ag
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- Letter. Identification of randomly interstratified illite/smectite with basal peak widths