UNIVERSITY OF GOTHENBURG Department of Earth Sciences Geovetarcentrum/Earth Science Centre Petrological and mineralogical description of the Sweconorwegian Uddevalla Granite, southwestern Sweden Adi Fazic ISSN 1400-3821 B893 Bachelor of Science thesis Göteborg 2016 Mailing address Address Telephone Telefax Geovetarcentrum Geovetarcentrum Geovetarcentrum 031-786 19 56 031-786 19 86 Göteborg University S 405 30 Göteborg Guldhedsgatan 5A S-405 30 Göteborg SWEDEN Abstract Adi Fazic. University of Gothenburg, Department of Earth Sciences; Geology, Box 460, SE- 405 30 Gothenburg The peculiar positioning and characteristics of the Uddevalla Granite in the Sveconorwegian Province, being situated along a shear zone and cross-cutting the Stora-Le Marstrand Formation, Hisingen and Göteborg Suites has triggered an interest in investigating its origin and giving it a marker in the Swedish geological history. In order to do so, a collaboration studying the granite massif was carried out between me and Erik Jansson where this thesis deals with the petrological aspects and Erik presents the age of the granite. The S-type characteristics, such as the observed amphibolite xenoliths in outcrops, the lack of hornblende as a constituent and the peraluminous composition of samples indicate a syn-collisional tectonic setting for the granite massif. Zircon-dating of the Uddevalla Granite yields a Concordia-age of 1027±9 Ma further supporting the ‘S-type’ character as it fits well within the proposed Agder phase (1050-980 Ma) of the Sveconorwegian orogeny, in which peak metamorphic conditions occurred at 1029±6 Ma. Discovery of the Uddevalla Granite and its properties delivers a strong support for the continent-continent collision theory which is provided for the Sveconorwegian Province. Field relationships of the monzogranitic Uddevalla Granite display a red to light-colored shifting throughout the whole intrusive massif, which may be explained by the mineral modality where a higher K-feldspar amount is present in the red granites. It is suggested that two magma pulses or hydrothermal processes could explain the variations in the incompatible elements. Geothermometric calculations proved unreliable due to an observed post-crystallization alteration. Keywords: Uddevalla Granite, Sveconorwegian, petrology, mineralogy, S-type, birdwing, geothermometry Sammanfattning Adi Fazic. University of Gothenburg, Department of Earth Sciences; Geology, Box 460, SE- 405 30 Gothenburg Den udda positionen och karaktär på Uddevallagraniten i den Sveconorwegiska provinsen, belägen längs en skjuvzon samt att den klipper av Stora-Le Marstrandformationen, Hisingen och Göteborg Suites har väckt ett intresse i att ta reda på dess ursprung samt ge den en markör i Sveriges geologiska historia. För att kunna utföra detta så har ett samarbete mellan mig och Erik Jansson gjorts där detta kandidatarbete handskas med de petrologiska aspekterna och Erik presenterar granitens ålder. Den S-type karaktär, som de observerade amfibolitxenoliterna på hällar, avsaknaden av hornblende och de peraluminösa kompositioner av proverna, indikerar på en syn-kollisional tektonisk miljö. Zirkon-datering på Uddevallagraniten resulterade i en Concordia-ålder på 1027±9 Ma vilket stöder dess ’S-type’ drag men vilken också passar bra in med den föreslådda Agder-fasen (1050-980 Ma) under den Sveconorwegiska orogenesen, där kulmen av metamorfa förhållanden ägde rum 1029±6 Ma. Fyndet ger ett starkt stöd för den en kontinent-kontinent kollisionsteori som är tillhandahållen för den Sveconorwegiska provinsen. Fältobservationer på den monzogranitiska Uddevalla Graniten påvisar ett rött till vitt färgskiftande längs hela intruderande massivet, vilken kan förklaras av mineralmodaliteten där en högre K-fältspat mängd är närvarande i de röda graniterna. Det är föreslaget att två magma pulser eller hydrotermala processer kan förklara variationen i de inkompatibla ämnen. Geotermometriska berkäningar visade sig opålitliga på grund av en observerad post-kristallin ombildning. Nyckelord: Uddevallagranit, Sveconorwegian, petrologi, mineralogi, S-type, birdwing, geotermometer 2 Contents 1. Introduction ......................................................................................................................................... 4 1.1. Geological Setting ........................................................................................................................ 4 2. Samples and methods .......................................................................................................................... 5 2.1. Sample description ....................................................................................................................... 5 2.2. Field Observations ........................................................................................................................ 6 2.3. Whole rock sampling .................................................................................................................... 6 2.4. Thin Sections and petrography ..................................................................................................... 6 2.5. Scanning Electron Microscope (SEM) ......................................................................................... 7 2.6. Garnet-biotite Geothermometer.................................................................................................... 7 3. Results ................................................................................................................................................. 7 3.1. Mineralogy ................................................................................................................................... 7 3.2.1. Alumina Saturation Index ......................................................................................................... 7 3.2.2 Geothermometer ......................................................................................................................... 7 3.2.3. Trace Elements .......................................................................................................................... 7 3.2.4. Pearce Diagram ......................................................................................................................... 8 3.2.5. Spider Diagram .......................................................................................................................... 8 4. Discussion ........................................................................................................................................... 8 Mineralogy .......................................................................................................................................... 8 Geothermometer .................................................................................................................................. 8 Incompatible Elements ........................................................................................................................ 9 Magma Pulses ..................................................................................................................................... 9 Tectonics and timeline ......................................................................................................................... 9 Source rock .......................................................................................................................................... 9 5. Conclusions ....................................................................................................................................... 10 Acknowledgements ........................................................................................................................... 10 References ......................................................................................................................................... 10 Appendix ............................................................................................................................................... 13 Appendix A ....................................................................................................................................... 13 Appendix B ....................................................................................................................................... 13 Appendix C ....................................................................................................................................... 13 3 1. Introduction cutting the N-S trending Stora-Le Marstrand In order to shed light to the origin of the Formation (SLM) and Hisingen Suite. Field Uddevalla Granite, a comprehensive study was observations at Frölandskrossen and Kallsås conducted by Erik Jansson and myself. Erik reveals a contact with the overlying SLM concentrated on the age (Zircon dating of the Formation and late-stage metamorphism along intrusive Uddevalla Granite) whilst the foci of the shear zone. this study are the petrological aspects, 1.1. Geological Setting achieved using geochemistry, mineralogy The recently dated Uddevalla Granite yields a along with geothermometric calculations and Concordia age of 1027±8,7 Ma (Jansson, field observations. 2016) and lies in the Idefjorden Terrane, Previously interpreted as post-orogenic granite southwestern Sweden. The Idefjorden Terrane, dating from 900-1000 Ma, the hereby called sometimes referred to as the Western Segment, Uddevalla Granite is the first syn-collisional