| Titre | Geochronology and trace element mobility in rutile from a Carboniferous syenite pegmatite and the role of halogens |
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| Auteur | Pe-Piper, G; Nagle, J; Piper, D J W ; McFarlane, C R M |
| Source | American Mineralogist vol. 104, no. 4, 2019 p. 501-513, https://doi.org/10.2138/am-2019-6668 |
| Image |  |
| Année | 2019 |
| Séries alt. | Ressources naturelles Canada, Contribution externe 20180271 |
| Éditeur | Mineralogical Society of America |
| Document | publication en série |
| Lang. | anglais |
| DOI | https://doi.org/10.2138/am-2019-6668 |
| Media | papier; en ligne; numérique |
| Formats | pdf (Adobe® Reader®); html |
| Province | Nouvelle-Écosse |
| SNRC | 21H/08 |
| Région | Clarke Head; Cobequid Highlands |
| Lat/Long OENS | -64.5000 -64.0000 45.5000 45.3333 |
| Sujets | géologie du substratum rocheux; lithologie; roches ignées; roches intrusives; syenites; pegmatites; gabbros; granites; brèches; caractéristiques structurales; zones de failles; failles, décrochement;
rutile; cadre tectonique; magmatisme; mise en place; altération hydrothermale; métasomatose; intrusions; plutons; inclusions; formation de failles; subduction; analyses au microscope électronique à balayage; analyses spectroscopiques; analyses des
éléments en trace; géochimie du titane; géochimie du zirconium; géochimie de l'uranium; anomalies géochimiques; europium; analyse par spectromètre de masse; datation radiométrique; datation au uranium-plomb; datations au plomb-plomb; titanite;
magnetite; chondrites; ilménite; halite; scapolite; morphologie cristalline; manteau terrestre; fusion partielle; conditions de pression-température; géochimie du calcium; géochimie du fer; précipitation; Terrane d'Avalon ; Dissolution;
géochronologie; géochimie; pétrologie ignée et métamorphique; Phanérozoïque; Paléozoïque; Carbonifère; Dévonien; Précambrien; Protérozoïque |
| Illustrations | cartes géolscientiques généralisées; photographies; photomicrographies; tableaux; graphiques; diagrammes Concordia; graphique à barres |
| Programme | Division de la CGC atlantique |
| Diffusé | 2019 04 01 |
| Résumé | (disponible en anglais seulement)
This study investigates Ti mobility in the presence of halogens, as shown by the hydrothermal alteration of magmatic rutile in syenite. The syenite pegmatite
studied intrudes gabbro, is preserved as a tectonic block in a major strike-slip fault zone, and formed in a back-arc environment in which there was widespread A-type granite plutonism. Rutile was studied by SEM and Raman spectroscopy, trace elements
were analyzed by LA-ICP-MS, and age was determined by in situ U-Pb analysis. Magmatic rutile in the syenite forms millimetric-scale crystals rimmed by magmatic titanite and magnetite and also occurs as smaller interstitial crystals. Hydrothermal
alteration occurred preferentially along crystal margins and fractures by a layer-by-layer dissolution-reprecipitation process resulting in high Zr contents (~5000 ppm) in the rutile, together with enrichment in U and depletion in high field strength
elements. The magmatic emplacement age of the syenite was ~360 Ma (dated rutile G) and no younger than 353.9 ± 5.7 Ma (mean Concordia age of interstitial rutile). The syenite was synchronous with the later phases of regional A-type granite plutonism.
Most magmatic rutile has REE patterns either (1) with 1-50 times chondrite enrichment, LREE > HREE and a Eu anomaly, resulting from felsic melt inclusions, or (2) flat patterns with 0.1-10 times chondrite enrichment, present in ilmenite exsolution
lamellae or inclusions. Later hydrothermal halogen-rich fluids, derived from dissolution of halite, produced widespread metasomatic scapolite in the syenite. These fluids also leached Ti and other HFSE, together with REE, from large fractured rutile
crystals. Such fluids resulted in local dissolution-reprecipitation of Ti and Zr and resetting of the U-Pb system in the altered rutile, at 337.4 ± 3.5 Ma. Normalized REE abundances in the hydrothermal rutile show a U-shaped pattern, with the
greatest depletion in the MREE. Variations in dissolution and transport of Zr and Ti by halogen-rich fluids affect the Zr in rutile geothermometer, which yields unrealistic temperatures when applied in this study. More generally, the complexities of
rutile chemistry in this hydrothermal setting could be reproduced in deeper subduction settings as a result of variations in halogen content of fluids released by prograde metamorphism. |
| Sommaire | (Résumé en langage clair et simple, non publié)
Notre étude a permis de dater un corps granitique à Clarke Head près de Parrsboro (Nouvelle-Écosse) ainsi que l'époque de la minéralisation
hydrothermale le long de la zone de la faille de Minas. Elle donne un nouvel aperçu des conditions sous lesquelles le rutile, un minéral, se précipite. |
| GEOSCAN ID | 313031 |
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