40Ar/39Ar age gradients in micas from a high-temperature-low-pressure metamorphic terrain: Evidence for very slow cooling and implications for the interpretation of age spectra

Research Article| January 01, 1994 40Ar/39Ar age gradients in micas from a high-temperature-low-pressure metamorphic terrain: Evidence for very slow cooling and implications for the interpretation of age spectra Kip V. Hodges; Kip V. Hodges 1Department of Earth, Atmospheric, and Planetary Sciences, 54-1120, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 Search for other works by this author on: GSW Google Scholar Willis E. Harries; Willis E. Harries 1Department of Earth, Atmospheric, and Planetary Sciences, 54-1120, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 Search for other works by this author on: GSW Google Scholar Samuel A. Bowring Samuel A. Bowring 1Department of Earth, Atmospheric, and Planetary Sciences, 54-1120, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 Search for other works by this author on: GSW Google Scholar Author and Article Information Kip V. Hodges 1Department of Earth, Atmospheric, and Planetary Sciences, 54-1120, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 Willis E. Harries 1Department of Earth, Atmospheric, and Planetary Sciences, 54-1120, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 Samuel A. Bowring 1Department of Earth, Atmospheric, and Planetary Sciences, 54-1120, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 Publisher: Geological Society of America First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1994) 22 (1): 55–58. https://doi.org/10.1130/0091-7613(1994)022<0055:AAAGIM>2.3.CO;2 Article history First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation Kip V. Hodges, Willis E. Harries, Samuel A. Bowring; 40Ar/39Ar age gradients in micas from a high-temperature-low-pressure metamorphic terrain: Evidence for very slow cooling and implications for the interpretation of age spectra. Geology 1994;; 22 (1): 55–58. doi: https://doi.org/10.1130/0091-7613(1994)022<0055:AAAGIM>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Estimates of the time-temperature history of geologic samples are often based on 40Ar/39Ar ages obtained through incremental-heating experiments on minerals with different Ar retentivities. Laser incre mental heating of single crystals of muscovite and biotite from an ∼1700 Ma monzogranite from a low-pressure- high-temperature metamorphic terrain in central Arizona suggested an essentially uniform distribution of radiogenic 40Ar in each crystal and yielded ages of 1412 ±5 Ma for the muscovite and 1410 ±10 Ma for the biotite. The similarity in these ages implies rapid (∼25 K/m.y.) cooling of the monzogranite after a reheating episode slightly before 1412 Ma. In contrast, detailed age mapping of single crystals from the same samples with the laser microprobe revealed large radiogenic 40Ar gradients indicative of very slow (<1 K/m.y.) cooling and a closure interval for Ar diffusion lasting >400 m.y. Evidence for such low cooling rates has important implications for the longevity of high thermal gradients in the Early-Middle Proterozoic lithosphere. In addition, inconsistency between the laser mapping and incremental-heating results for these micas suggests caution when interpreting incremental-heating data for slowly cooled samples. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.