Research Article| December 01, 2004 Fluid–metasedimentary rock interactions in subduction-zone mélange: Implications for the chemical composition of arc magmas Christopher M. Breeding; Christopher M. Breeding 1Department of Geology and Geophysics, Yale University, P.O. Box 208109, New Haven, Connecticut 06520-8109, USA Search for other works by this author on: GSW Google Scholar Jay J. Ague; Jay J. Ague 1Department of Geology and Geophysics, Yale University, P.O. Box 208109, New Haven, Connecticut 06520-8109, USA Search for other works by this author on: GSW Google Scholar Michael Bröcker Michael Bröcker 2Institut für Mineralogie, Universität Münster, Corrensstrasse 24, 48149 Münster, Germany Search for other works by this author on: GSW Google Scholar Geology (2004) 32 (12): 1041–1044. https://doi.org/10.1130/G20877.1 Article history received: 09 Jun 2004 rev-recd: 16 Aug 2004 accepted: 31 Aug 2004 first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Christopher M. Breeding, Jay J. Ague, Michael Bröcker; Fluid–metasedimentary rock interactions in subduction-zone mélange: Implications for the chemical composition of arc magmas. Geology 2004;; 32 (12): 1041–1044. doi: https://doi.org/10.1130/G20877.1 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 Elevated concentrations of certain large ion lithophile elements (LILE; e.g., Ba, K, Rb, Cs, Ca, Sr), U, and Pb in arc magmas relative to high field strength elements (HFSE; e.g., Ti, Th, Hf, Nb, Zr) are considered key indicators of fluid addition to arc magma source regions worldwide, but the fluid sources and processes of mass transfer are controversial. Dehydration of downgoing slabs releases fluids that can flow through and react with metamorphosed ultramafic-mafic rock packages in mélange zones near slab-mantle interfaces. New geochemical data from Syros, Greece, reveal that these fluids preferentially leach LILEs, U, and Pb when they infiltrate and react with subducted metasedimentary rocks. Transfer of these LILE-, U-, and Pb-enriched fluids to the mantle wedge at subarc depths could directly trigger partial melting and generate magmas with elevated Ba/Th, Sr/Th, Pb/Th, and U/Th, as well as radiogenic Sr. Alternatively, if fluid transfer occurs at shallower depths (e.g., Syros), the metasomatized mantle could be carried deeper by wedge corner flow to ultimately undergo partial melting in subarc regions. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
deposit of Cu-bearing tourmaline, and the "neon" blue and green shown by the finest stones closely resembles the most sought-after material from Paraíba (figure 1).Mavuco actually produces a wide variety of colors, including unusual deep purple amethyst-like hues and steely violetish blues (figure 2).Of the several hundred kilograms of tourmaline rough mined to date in the Mavuco area, about 10% show blue-to-green Paraíba-like colors without heat treatment (M.Konate, pers.comm., 2007).The Cu-bearing tourmaline from this area may have been sold initially as Brazilian material (in various countries around the world, including Brazil), since the Mozambique origin was not correctly and COPPER-BEARING (PARAÍBA-TYPE) TOURMALINE FROM MOZAMBIQUE
Among fancy-color diamonds, those with saturated blue, green, and red colors are the rarest and generally the most highly valued.Over the last decade, however, diamonds with pure hues in these colors have made up less than one-tenth of one percent of all diamonds examined at GIA, making them virtually unattainable in the marketplace.In recent issues of Gems & Gemology, we have documented the gemological and spectroscopic properties of the rarest of fancy-color diamonds ranging from pink-to-red, blue, and green to the more unusual white and black.This article will address the most common colored diamonds, those with yellow hues, while also examining their much rarer orange cousins (figure 1).This is the last of the fancy color groups in this series, and a brief summary of all the colored diamond groups is provided at the end of the article.Yellow and orange diamonds owe their color primarily to nitrogen impurities that are incorporated in the diamond lattice during growth deep in the earth.Nitrogen is the most common impurity in natural diamond due to the very similar atomic radii of nitrogen and carbon atoms (155 and 170 picometer Van der Waals radii, respectively) as well as the relative abundance of nitrogen in the growth environment.If nitrogen is present when diamond grows, it will inevitably be incorporated.Nitrogen is the sixth most abundant element in the universe and accounts for more than 75% of the earth's atmosphere (Bebout
Vivid blue to green copper-bearing tourmalines, known as Paraíba tourmalines, are recovered from deposits in Brazil, Nigeria, and Mozambique.These tourmalines are sought after for their intense colors.Prices are based, in part, on the geographic origin of a stone, and determining provenance is thus an important aspect for Paraíba tourmaline.However, their geographic origin cannot be established by standard gemological testing and/or qualitative chemical analyses.GIA has established sophisticated criteria requiring quantitative chemical analyses to determine geographic origin for these tourmalines.These criteria were based on several hundred samples from known sources spanning the three countries.Highly accurate and precise quantitative elemental concentrations for Cu, Zn, Ga, Sr, Sn, and Pb are acquired with laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS).These data can then be plotted as a function of elemental concentration for accurate geographic origin determination. In Brief• Geographic origin can have a significant impact on the value of Paraíba tourmaline.• Quantitative chemical analysis with LA-ICP-MS provides a robust tool for origin determination.• The trace elements Cu, Zn, Ga, Sr, Sn, and Pb are the most useful discriminators for Paraíba tourmaline origin.• In limited cases where there are no matching reference data, an "inconclusive" origin determination would be required.
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