Chemical evolution at surface condition in the Zermatt-Saas area (Swiss Alps): A geo-hydrochemistry study on surface water-rock interaction Dissertation Zur Erlangung des Doktorgrades der Geowissenschaftlichen Fakultät der Albert-Ludwigs Universität Freiburg i. Br Vorgelegt von ZHOU Wei aus Nanjing, Jiangsu, P. R. China 2010 Vorsitzender des Promotionsausschusses: Professor Dr. Rolf Schubert Referent: Professor Dr. Kurt Bucher Koreferent: Professor Dr. Ingrid Stober Tag des Promotionsausschusses: 07. July, 2010 PhD Thesis ZHOU Wei 2010 Steter Tropfen höhlt den Stein 水滴石穿 „Es gibt in der Welt nichts, was sich mehr seinem Grunde einfügt und weicher ist als Wasser, zugleich nichts, was stärker ist und selbst das Härteste besiegt; es ist unvergleichbar und unbezwingbar.“ Lao-tse, Tao Te King, Kapitel 78-642 600 v. Chr. To my parents Acknowledgements ACKNOWLEDGEMENTS I would especially like to thank my first supervisor, Prof. Dr. Kurt Bucher. During the following three years PhD studies, he gave the prevalent and benevolent supports on tutoring lectures, managing field trips and organizing laboratory works. During this thesis writing, his rigorous scientific approach, enlightened guidance, creativity, and encouragement are much appreciated. I greatly benefited from regular discussion with him on scientific topics that not only stick to my miniature geo/hydrology interests but also quite broaden to entire geosciences by his wisdom and extensive experience and knowledge on the subjects. My thanks also go to my second supervisor, Prof. Dr. Ingrid Stober, for her patience and numerous help during my research work. Her strong support on field trips and extensive hydrologic knowledge are greatly valuable. Particularly thanks also to Dr. Fleurice Parat, Dr. Tobias Weisenberger and Xiaoyan Li for scientific discussion help with problem solving, during the writing of this thesis, they provided plenty of helpful comments and offered warmly encourages that are deeply thankful. Many thanks to Dr. Ulrike Seelig, Dr. Zeng Lv, Dr. DuyAnh Dao and Sebastian Weber for providing all kinds of help. I owe my thanks to Sigrid Hirth-Walther for her many hours of patient tuition with laboratory works on water analyses. Thanks to Dr. Hiltrud Müller-Sigmund for her patient tuition with the operation of the electron microprobe. I would also like to thank Isolde Schmidt for assistance with the XRD and XRF measurements; Melanie Schrage for the sample preparation; Dagmar Flemming for all supports of computer apparatuses and Susanne Schuble for literature searches. Thanks to all the colleges at the Institute of Mineralogy and Geochemistry for all the pleasant moments. This thesis was conducted at Institute of Mineralogy and Geochemistry, University of Freiburg, Germany from October 2007 to July 2010. The author was financial supported by China Scholarship Council and the scientific activities, like fieldwork and conference, were funded by the Rinne Foundation. The supports are gratefully acknowledged. I Abstract ABSTRACT Chemical evolution at mountainous area in the Zermatt-Saas is predominantly driven by water and rock interaction. Surface water acquires the dissolved solids by reaction of precipitation water with the minerals in the bedrock. The chemical characteristics of the surface water have been studied first to understand the mechanisms of the solute acquisition. Total dissolved solids (TDS) of the surface water varies from 6 to 244 mg L-1. The low TDS (e.g. 6–10 mg L-1 ) water are the high altitude ponds underlain by silicate bedrocks. All the collected water samples show the clear chemical signatures of the bedrock mineralogy. The chemical compositions of the three main types of water represent the mineralogy of the dominant bedrock lithology. Specifically, Ca-HCO3 waters develop from metamorphic mafic rocks such as greenschists, blueschists and eclogites and from carbonate-bearing schists. Mg-HCO3 water originates from serpentinites and peridotites. Ca-SO4 water derives from continental basement rocks such as sulphide-rich granites and gneisses containing Ca- bearing plagioclase. The sulfuric acid, which released from the sulfide alternation, primarily controls the calcite and silicate dissolution then limits TDS for the chemical characteristic of surface waters. If calcite is present in the bedrock, dissolution of the mineral neutralizes the acid produced by sulphide weathering and buffers pH to near neutral to weakly alkaline conditions. If calcite is absent, the process produces low-pH waters in gneiss and granite catchments. It is also confirmed that in the Zermatt-Saas area, natural low-pH waters (pH < 6) in a pristine high-altitude environment have a geogene origin and do not suggest anthropogenic damages (industrial acid rain). The intensive chemical weathering forms weathering rinds (WRs) on the surface of exposed serpentinite and metabasaltic greenschist. These outcrops are widespread in the high alpine Zermatt area and located nearby the surface water. In the serpentinite, weathering process acts on two primary minerals, forsterite (Fo) and antigorite (Atg). The weathering products in WRs are secondary chrysotile (Ctl) from Fo and a metastable secondary Atg phase (S-Atg) from the primary one. In the metabasaltic greenschist, the weathering process mainly acts by oxidation-reduction reaction on chlorite and sulfide minerals. The newly formed oxidized Chl is detected at the expanded cleavages of primary Chl. Sulfide minerals are mainly pyrite, pyrrhotite and chalcopyrite. The weathered sulfide presents distinctive lamellar structures and contains fewer metals than the primary sulfides. Iron films have been observed on the greenschist surface, chemically associated with the dissolution of II Abstract sulfide minerals and silicates. In additional, clay minerals, which are considered as the newly formed phases with respect to water-rock interaction, are located under surface water. It is found that the clay mineralogy presents the variation with respect to their localities as well. Generally, chlorite appears in each mud deposition in the study area, while no kaolinite appears in the deposits under run offs in the Findeln Platform area. A profound study of the chemical evolution has been established in the Lichenbretter, SE Zermatt. Two inverse models are used to explain the chemical evolution from atmospheric precipitation by the chemical reaction with exposed carbonate or/and silicate rocks than transferred to the Ca-HCO3 and Mg-HCO3 types of surface water. The chemical weathering rate in Lichenbretter have been estimated. The weathering rinds forming rates is about 30 ± 5 mm kyr-1 that observed weathering rinds with the thickness of 5mm on the outcrops and are formed over 150 yrs. The overall chemical weathering rate in Lichenbretter area is estimated to be 9 to 11 t km-2 yr-1. III Introduction INTRODUCTION The aim of study The aim of this study is to explain the chemical evolution in the mountainous Zermatt-Saas area. The observed chemical characteristics of atmospheric precipitation, weathering rinds on outcrops and surface water have been considered as inputs, reactants and outputs for the interaction processes, respectively. In the study area, these water and rock interactions are mainly occurs as the chemical weathering, which acts on the rocks with water serving, decomposes minerals, weakens rock structures, then removes ions dissolved in the water. Nowadays, numerous studies have been established to explain the chemical weathering processes in the surface condition. However there still exist large amount of uncertainties to examine the field observation either of the chemical characteristics of surface water (e.g. Bassett, 1997; O´Brien et al., 1997; Bricker et al., 2003; Velbel and Price, 2007; Schnoor, 1990; White and Brantley, 2003) or the chemical weathering mechanisms of exposed rocks (e.g. Dorn, 1998; Dixon et al., 2002; Gordon and Dorn, 2005; Nicholson, 2008). The most critical aspects are: 1) the disturbances from un-geogene source of solutes, for example biomass inputs from plants (e.g. Drever and Hurcomb, 1986; Brown et al., 1994; Drever, 1994; Aquilina, et al., 1997; Drever, 1997); 2) the vagueness from lithological complexities in the watershed (e.g. Bassett, 1997; O´Brien et al., 1997; Bricker et al., 2003; Velbel and Price, 2007), and 3) the incongruent dissolution occurs in bedrocks that caused by differential of solubility and kinetics between rock-forming minerals (e.g. White and Brantley, 1995; White et al., 2001; Bowser and Jones, 2002). All of these uncertainties turn out the essential demand for the accurate assessment on both surface water and exposed rocks in the catchment. In this study, the high elevation (most of sampling sites are located over 2700m above see level) Zermatt area has been chosen with regard to two reasons. Firstly, the water catchments of the Zermatt area (Swiss Alps) are characterized by thin or lacking biomass and soil cover. In pervious studies, it has been emphasized that in high mountainous catchments, surface water chemistry is generally dominated by minerals dissolution and precipitation in bedrock with meteoric water serving (Drever and Hurcomb, 1986; Giovanoli et al., 1988; Drever and Zobrist, 1992; Gragnani and Torcini, 1992; Oliva et al., 2004; Blum et al., 1998; Dalai et al., 2002a,b; Jacobson et al., 2002). Secondly, although the study area is characterized by four major geologic IV Introduction units (details are described in Chapter I; Beather, 1953, 1967; Pfeifer et al.,