Conodont color and textural alteration: An index to regional metamorphism, contact metamorphism, and hydrothermal alteration

Abstract

Research Article| October 01, 1987 Conodont color and textural alteration: An index to regional metamorphism, contact metamorphism, and hydrothermal alteration VIVIAN A. REJEBIAN; VIVIAN A. REJEBIAN 1U.S. Geological Survey, U.S. National Museum of Natural History, E-501, Washington, D.C. 20560 and Georgetown University School of Dentistry, Washington, D.C. 20007 Search for other works by this author on: GSW Google Scholar ANITA G. HARRIS; ANITA G. HARRIS 2U.S. Geological Survey, U.S. National Museum of Natural History, E-501, Washington, D.C. 20560 Search for other works by this author on: GSW Google Scholar J. STEPHEN HUEBNER J. STEPHEN HUEBNER 3U.S. Geological Survey, M.S. 959, Reston, Virginia 22092 Search for other works by this author on: GSW Google Scholar GSA Bulletin (1987) 99 (4): 471–479. https://doi.org/10.1130/0016-7606(1987)99<471:CCATAA>2.0.CO;2 Article history first online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation VIVIAN A. REJEBIAN, ANITA G. HARRIS, J. STEPHEN HUEBNER; Conodont color and textural alteration: An index to regional metamorphism, contact metamorphism, and hydrothermal alteration. GSA Bulletin 1987;; 99 (4): 471–479. doi: https://doi.org/10.1130/0016-7606(1987)99<471:CCATAA>2.0.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 SocietyGSA Bulletin Search Advanced Search Abstract Experimental and field data are used to extend the utility of conodonts as semi-quantitative thermal indices into the regimes of regional and contact metamorphism, as well as hydrothermal alteration. An Arrhenius plot of data from induced conodont color alteration by pyrolysis in air at 1 atm was used to generate the geologic temperatures for conodont color-alteration indices (CAI) above 300 °C, that is, for CAI values of 5½ through 8. Such CAI values occur in very low- to medium-grade, regionally metamorphosed, contact-metamorphosed, and hydrothermally altered rocks. The uniformity or variability of CAI values within a sample, together with conodont texture, can help to distinguish grades and environments of metamorphism, particularly in metacarbonate sequences. Induced CAI by pyrolysis in a water-methane mixture at ½ kbar results in retardation of CAI and in a disparate mixture of both low and high CAI values within each experimental sample. In this system, color-alteration processes, above a CAI of 2 to 3, seem to change from predominantly carbonization to predominantly loss of organic matter, presumably by oxidation and volatilization of oxides. These experiments approximate the type of CAI mixture characteristically found in conodonts recovered from hydrothermally altered rocks. These data indicate that CAI values of 6 to 8 cannot be used to assess precise temperatures of hydrothermally altered rocks but may serve as useful indicators of potential mineralization. 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.