| Titre | Nature of the hydrothermal alteration of the Miocene Sigri Petrified Forest and host pyroclastic rocks, western Lesbos, Greece |
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| Auteur | Pe-Piper, G; Imperial, A; Piper, D J W ; Zouros, N C; Anastasakis, G |
| Source | Journal of Volcanology and Geothermal Research vol. 369, 2018 p. 172-187, https://doi.org/10.1016/j.jvolgeores.2018.11.018 |
| Année | 2018 |
| Séries alt. | Ressources naturelles Canada, Contribution externe 20180269 |
| Éditeur | Elsevier BV |
| Document | publication en série |
| Lang. | anglais |
| DOI | https://doi.org/10.1016/j.jvolgeores.2018.11.018 |
| Media | papier; en ligne; numérique |
| Référence reliée | Cette publication est reliée à Mineral data (SEM,
electron microprobe, Raman spectroscopy) from epithermal hydrothermal alteration of the Miocene Sigri Petrified Forest and host pyroclastic rocks, Western Lesbos, Greece |
| Formats | pdf (Adobe® Reader®) |
| Région | Sigri; Lesbos Island |
| Lat/Long OENS | 25.8333 26.1667 39.2500 39.1667 |
| Sujets | Néogène; Miocène; vulcanologie; géologie du substratum rocheux; lithologie; roches ignées; roches volcaniques; pyroclastiques; ignimbrites; argiles; caractéristiques structurales; zones de failles;
paléosols; fossiles; plantes fossiles; bois silicifié; antécédents tectoniques; système hydrothermal; filons; filons rocheux; laccolithes; intrusions; volcanisme; eaux atmosphériques; fluage; analyses minéralogiques; analyses au microscope
électronique à balayage; analyses microscopiques; analyses par microsonde électronique; analyses spectroscopiques; analyses par diffraction des rayons x; altération; altération hydrothermale; silicification; argilisation; couleur; diagenèse;
tectonique; paléontologie; minéralogie; géochimie; Phanérozoïque; Cénozoïque; Tertiaire |
| Illustrations | cartes géolscientiques généralisées; coupes transversales; tableaux; photographies; photomicrographies; spectres; dessins |
| Programme | Division de la CGC atlantique |
| Diffusé | 2018 11 30 |
| Résumé | (disponible en anglais seulement)
The early Miocene Sigri Pyroclastic Formation in western Lesbos Island hosts the famous petrified forest of silicified tree fossils, protected as a UNESCO
Geopark. The formation consists primarily of flow tuffs, mud flow deposits and stream conglomerate. Hydrothermal veins rich in silica, iron, and manganese are preferentially developed in major fault zones and along paleosols. The purpose of this
study is to understand the nature of the hydrothermal system and its relationship to the preservation of tree fossils. Samples were collected from fresh and altered pyroclastic rocks, hydrothermal veins and petrified wood. Rock mineralogy and
chemistry were investigated using a petrographic microscope, scanning electron microscope, electron microprobe, Laser Raman spectroscopy, and X-ray powder diffraction. Early devitrification of volcanic glass in tuffs formed opaline silica and locally
resulted in smectite. At the same time, fossil trees were partly replaced by amorphous silica. Epithermal alteration and hydrothermal veins include (1) adularia + silica + kaolinite; (2) jarosite + hematite + amorphous silica; and (3) 'Fe-oxide'
and/or 'Mn-oxide' + amorphous silica. The MnSi mixture and Mn-oxides comprise structurally amorphous romanechite with some more crystalline grains of todorokite, ramsdellite and/or nsutite. The mixtures of Fe-oxides and silica are also largely
amorphous and include alpha-cristobalite. Such mixtures replace parts of the petrified wood including cell walls. The various colors observed from the petrified wood are principally related to the abundance of iron and organic matter. Faulting and
complex hydrothermal alteration was related to the emplacement of laccoliths and dykes around 18 Ma, 1-3 Ma after deposition of the Sigri Pyroclastic Formation. The observed types of low temperature epithermal alteration are compared with that
produced by different circulating waters in the modern Taupo volcanic zone of New Zealand. Hydrothermal deposition of Fe-oxides and silica played an important role in the preservation of the petrified forest. |
| Sommaire | (Résumé en langage clair et simple, non publié)
Description minéralogique et interprétation des altérations hydrothermales des roches de la célèbre forêt pétrifiée de Lesbos (Grèce). |
| GEOSCAN ID | 313029 |
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