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Research Article| December 01, 2000 Retrograde net transfer reaction insurance for pressure-temperature estimates Matthew J. Kohn; Matthew J. Kohn 1Department of Geological Sciences, University of South Carolina, Columbia, South Carolina 29208, USA Search for other works by this author on: GSW Google Scholar Frank Spear Frank Spear 2Department of Earth and Environmental Sciences, Rensselaer Polytechnic Institute, Troy, New York 12180, USA Search for other works by this author on: GSW Google Scholar Geology (2000) 28 (12): 1127–1130. https://doi.org/10.1130/0091-7613(2000)282.0.CO;2 Article history received: 13 Mar 2000 rev-recd: 01 Sep 2000 accepted: 20 Sep 2000 first online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Matthew J. Kohn, Frank Spear; Retrograde net transfer reaction insurance for pressure-temperature estimates. Geology 2000;; 28 (12): 1127–1130. doi: https://doi.org/10.1130/0091-7613(2000)282.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search nav search search input Search input auto suggest search filter All ContentBy SocietyGeology Search Advanced Search Abstract Retrograde net transfer reactions significantly affect compositions of metamorphic minerals, yet are rarely considered when determining pressure-temperature (P-T) conditions. Two natural amphibolite facies metapelites from the central Himalaya of Nepal exhibit extremely common compositional patterns, including increases in Mn and Fe/(Fe + Mg) at the rims of garnets, which are the result of retrograde garnet dissolution and Fe-Mg exchange with biotite. However, typical thermobarometric approaches for these rocks result in errors of hundreds of degrees and 3–6 kbar compared with thermobarometry of nearby rocks and petrogenetic grids. These large errors result because dissolution of high-Fe garnet has strongly affected the Fe/Mg ratio of matrix biotite. X-ray maps help evaluate the extent and chemical effects of retrograde reactions in these samples by identifying mineral regions that retain highest-T compositions, or, through a new data-processing approach, by permitting correction of mineral compositions to original high-T values. These approaches ensure against retrograde net transfer reactions and should be applied routinely in thermobarometric studies—they ultimately yield P-T estimates that are more petrologically reasonable, and permit rapid screening of samples for those least affected by retrograde reactions. Reconsideration of thermobarometry in the central and eastern Himalaya indicates that retrograde net transfer reactions are extremely common. Therefore, previous thermobarometric studies based on garnet major element compositions from that region should be reevaluated. You do not currently have access to this article.
Kohn et al. (Sat,) studied this question.