Zeolites in Fissures of Crystalline Basement Rocks
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ZEOLITES IN FISSURES OF CRYSTALLINE BASEMENT ROCKS INAUGURALDISSERTATION zur Erlangung des Doktorgrades der Fakultät für Chemie, Pharmazie und Geowissenschaften der Albert-Ludwigs-Universität Freiburg im Breisgau vorgelegt von TOBIAS WEISENBERGER aus Emmendingen 2009 Vorsitzender des Promotionsausschusses: Prof. Dr. Rolf Schubert Referent: Prof. Dr. Kurt Bucher Korreferent: Prof. Dr. Reto Gieré Tag des Promotionsbeschlusses: 9.. Juli 2009 Saint Barbara statue in the Arvigo quarry– Patron saint of geologists and firemen Saints day: 4th December Der Tag der heiligen Barbara! - Feierlich stehen sie alle da, die Männer, die aus des Berges Nacht - das schwarze Gestein zu Tage gebracht, das dort gelegen seit Urweltzeit; - bald wird es vom roten Feuer gefreit. Feierlich stehen sie alle da.- Es ist 4. Dezember: St. Barbara! Du Schutzpatronin, St. Barbara, - Im Schmucke treten sie alle dir nah'; An dem Tschako wiegt sich die schwarze Feder, - Schwarz ist ja alles, Anzug und Leder. Dort sind die weißen, Musik trägt rot. - In Ordnung und Würde, wie nach Gebot beginnt der Zug, und wer ihn sah',- weiß, es ist heute St. Barbara! Zurück von der Kirche St. Barbara. - Und es geschieht, was immer geschah, Musik spielt lustig, die Federn winken, - in Oberschlesien will man auch trinken, sorglos sich freuen, den Tag genießen, - wen sollte das heitere Volk verdrießen? Und es geschieht, was immer geschah! - Nur einmal im Jahr ist St. Barbara! St. Barbara; Poem after Käthe Gutwein ABSTRACT I ABSTRACT The goal of the thesis is to study the occurrences and formation of zeolites hosted in crystalline basement rocks. The low-grade fissure mineral assemblages including zeolites are the key to the appreciation of water-rock interaction in hydrothermal and geothermal systems at relatively low temperatures (< 250 °C) located in granites and gneisses of the crystalline basement. Extensive work is done on zeolite occurrences in sedimentary rocks often pyroclastic origin and volcanic rocks, whereas elements necessary for zeolite formation derive from primary glass of from feldspar. In contrast the formation of zeolites in granites and gneisses is poorly studied and no systematic of evaluation and spatial distribution are carried out either chemical studies on zeolites or formation consideration are done. Therefore a systematic evaluation of zeolites in the Central Swiss Alps is presented. Ca-zeolites occur in various assemblages in late fissures and fractures in granites and gneisses. The systematic study of zeolite samples showed that the majority of finds originate from three regions particularity rich in zeolite-bearing fissures: (1) in the central and eastern part of the Aar- and Gotthard Massif, including the Gotthard road tunnel and the Gotthard-NEAT tunnel, (2) Gibelsbach/Fiesch, in a fissure breccia between Aar Massif and Permian sediments, and (3) in Penninic gneisses of the Simano nappe at Arvigo (Val Calanca). The excavation of tunnels in the Aar- and Gotthard massif give an excellent overview of zeolite frequency in Alpine fissures, whereas 32 % (Gotthard NEAT) and 18 % (Gotthard road tunnel) of all fissures are filled with zeolites. The number of different zeolites is limited to 6 species: laumontite, stilbite and scolecite are abundant and common, whereas heulandite, chabazite and epistilbite occur occasionally. Ca is the dominant extra- framework cations, with minor K and Na. Heulandite and chabazite additionally contain Sr up to 29 and 10 mole%, respectively. Na and K content of zeolites tends to increase during growth as a result of systematic changes in fluid composition and/or temperature. The K enrichment of stilbite found in surface outcrops compare to stilbite in the subsurface may indicate late cation exchange during interaction with surface water. Texture data, relative age sequences derived from fissure assemblages and equilibrium calculations shows that the Ca-dominated zeolites precipitated from fluid with decreasing temperature in the order (old to young = hot to cold): scolecite, ABSTRACT II laumontite, heulandite, chabazite and stilbite. The components necessary for zeolite formation are derived from dissolving primary granite and gneiss minerals. The nature of these minerals depends on the metamorphic history of the host rock. Zeolites in the Aar Massif derived from the dissolution of epidote or calcite and albite that were originally formed during Alpine greenschist metamorphism. Whereas albitization of plagioclase in higher grade rocks releases the necessary components for zeolite formation, a process that is accompanied by a distinct porosity increase. Zeolite fissures occur in the zone where fluid inclusions in earlier formed quartz contain H2O dominated fluids. This is consistent with equilibrium calculations that predict a low CO2 tolerance of zeolite assemblages particularly at low temperature. Pressure decrease along the uplift and exhumation can increase zeolite stability. The major zeolite forming reaction consumes calcite and albite; it increases pH and the total of dissolved solids. The produced Na2CO3 waters are in accord with reported deep groundwater (thermal water) in the continental crust, which are typically oversaturated with respect to Ca-zeolites. A detailed local study of the mineralogical, chemical and petrological evolution of crystalline basement rocks in Arvigo was performed to assess information about the evolution of fluid-rock interaction during uplift of the Alpine orogen. The Arvigo fissures contain the assemblage epidote, prehnite, chlorite and various species of zeolites. Fluid rock interaction takes place along a retrograde exhumation path which is characterized with decreasing temperature by: (1) coexisting prehnite/epidote, that reveals temperature conditions of 330 – 380 °C, (2) chlorite formation at temperature of 333 ± 32 °C and (3) formation of zeolites <250 °C. The formation of secondary minerals is related to the hydrothermal replacement reaction during albitization and chloritization that releases components for the formation of Ca-Al silicates and form a distinct reaction front. The fluid-rock interaction is associated with a depletion of Al2O3, SiO2, CaO, Fe2O3 and K2O in the altered wall rock. The reaction is associated with an increase in porosity up to 14.2 ± 2.2 %, caused by the volume decrease during albitization and the removal of chlorite. The propagation of the sharp reaction front through the gneiss matrix occurred via a dissolution-reprecipitation mechanism. Zeolite formation is tied to the plagioclase alteration reaction in the rock matrix, which releases components for zeolite formation to a CO2-poor, alkaline aqueous fluid. ABSTRACT III A combined study of 40Ar/39Ar age dating, apatite fission track (FT) and chemical characterization of tunnel and surface samples are present to carry out the position of low-temperature water-rock interaction in respect to the Alpine history. Apatite FT analysis yields an exhumation rate of 0.45 mm a-1, a cooling rate of 13 °C Ma-1 and a geothermal gradient of 28 °C km-1. Combining these with the 40Ar/39Ar plateau age for apophyllite of ∼2 Ma, a minimum formation temperature and depth of 70 °C and 2800 m, respectively can be assumed. Temperature-time evolution of fissures in the Aar Massif and thermodynamic mineral evolution indicate that laumontite were formed between 7 and 2 Ma before present at temperatures between 150 and 70 °C. ACKNOWLEDGMENTS IV ACKNOWLEDGMENTS It is a great pleasure for me to thank the many people who made this thesis possible. I am most thankful to my advisor Prof. Dr. Kurt Bucher. I thank him for awarding the topic of this thesis and an outstanding supervision. I am glad that he gave me the opportunity to continue my research interests on zeolites that I experience during my diploma thesis. I always appreciated the discussion and constructive criticism with him. A special appreciation has to be mentioned that he gave me the freedom to develop and follow my own ideas. He enhanced me to educate myself during numerous DMG workshops and teached me to deal with thermodynamic calculations, which was not even easy with me. During theses years Kurt must have used up a lifetime supply of red ink pens to teach me geological common sense. This thesis would not have been possible without the great advise and trust in me. Thank you! Also, I want to thank Prof. Dr. Reto Gieré for the additional supervision, numerous discussions and the takeover of the co-referee. I want to thank my parents, who always gave me the liberty to follow my interest and supported me during my education in a loving environment. A special thank to all the people who supported me during my search for Alpine zeolites and supplied samples: Peter Amacher, mineral representative of the NEAT Amsteg-Sedrun section who provided high-quality minerals specimen and who was always easy to contact for discussion. Beda Hoffmann and Peter Vollenweider from the Swiss Natural History Museum in Bern, giving me the possibility to study their mineral collection and their encourage during my work in the “dungeon”. Giovanni Polti and Alfredo Polti SA for permission to do field work in the active quarry in Arvigo, especially Luigi who took care about me during blasting, even we conduct our conversion by signs, due to my lack in Italian language. I appreciate all the help and support that I get by using technical equipment in external research institutes: Prof. Dr. Stefan Graeser form the Mineralogical Institute Basel, who provided me the possibility to use the FTIR instrument; Dr. Egbert Keller from the Crystallographic Institute Freiburg, who guided me through DSC-TGA measurements and Andreas Leemann from the Swiss Federal Laboratories for ACKNOWLEDGMENTS V Materials Testing and Research for impregnation of rock samples. Roelant van der Lelij from the Department of Mineralogy in Geneva for the apophyllite dating and helpful discussion and PD Dr. Meinert Rahn for helping with the apatite fission track analysis and the always profitable conversations. I wish to thank Zeng Lu, Fleurice, Siggi, Zhou Wei, Hiltrud and Duy Anh Dao for their always open doors, where I find a sympathetic ear for discussion.