Geology and Petrology of the Felsic Intrusions in the Metasedimentary
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FACULTEIT WETENSCHAPPEN Opleiding Master of Science in de geologie Geology and petrology of the felsic intrusions in the metasedimentary and metavolcanic rocks of the early Neoproterozoic Zadinian Group around Matadi (Lower-Congo Region, D.R. Congo) Stéphanie Eeckhout Academiejaar 2013–2014 Scriptie voorgelegd tot het behalen van de graad Van Master of Science in de geologie Promotor: Prof. Dr. J. De Grave 1 Co-promotor: Prof. Dr. L. Tack Leescommissie: Prof. Dr. P. Van den haute, Prof. Dr. M. Fernandez-Alonso 2 “Rocks are records of events that took place at the time they formed. They are books. They have a different vocabulary, a different alphabet, but you learn how to read them.” -John McPhee- 3 PREFACE The realization of this thesis would not have been possible without the help of many persons. Therefore I want to thank each and everyone who helped me during this intense and interesting year. First of all I would like to thank Professor Van den haute and Professor De Grave for offering me the opportunity to do my thesis research at the research unit of Mineralogy and Petrology. Their knowledge of petrography and geochronology, respectively, has been of great value. Professor Tack’s knowledge was of great importance to help me understand the study area. I am very grateful for the uncountable hours of work and discussions we have had together. I want to express my appreciation for the time you have sacrificed to correct my drafts and to help improve them with your constructive criticism. I would also like to thank Professor Baudet of the RMCA. His knowledge of the study area and his expertise of GIS and mapping projects has been very helpful. Furthermore I also want to thank Professor Fernandez-Alonso, head of the geology department at the RMCA, for the collaboration with Ghent University. Together with Luc André, I want to thank him for the approval and financial contribution of the geochemical analyses. These analyses were carried out by Laurence Monin and Jacques Navez who also deserve my gratitude for their work and explanatory notes. Feedback “from the outside” on the results of the geochemical analyses was obtained from Sophie Decrée and Ingrid Smet. Their experience helped me in understanding and interpreting the data. I also appreciate the help of Ann-Eline Debeer, who prepared the samples for the geochemical purposes, Elien De Pelsmaeker who helped me embed the zircons and Jan Jurçeka for the preparation of thin sections. Without the help of Stijn Glorie, at the University of Adelaide, it would not have been possible to receive the U-Pb dating results. Last but not least, I would like to thank my boyfriend Jurgen, my sisters and especially my parents for their support throughout my five years of study. 4 1. Introduction ..................................................................................................................................... 9 2. Geological setting .......................................................................................................................... 11 2.1. Geological setting of the West Congo belt ............................................................................ 11 2.1.1. Geographic setting of the Lower-Congo region ............................................................ 11 2.1.2. The West Congo belt in the broader context of the Araçuaí-West Congo orogen ....... 12 2.1.2.1. Araçuaí-West Congo orogen.................................................................................. 15 2.2. The West Congo belt ............................................................................................................. 20 2.3. The West Congo Supergroup................................................................................................. 22 2.3.1. Zadinian Group .............................................................................................................. 23 2.3.2. Mayumbian Group ........................................................................................................ 25 2.3.3. West Congolian Group .................................................................................................. 25 2.4. Geological setting of the Matadi region ................................................................................ 26 2.5. The aim of this study ............................................................................................................. 30 3. Methods ........................................................................................................................................ 32 3.1. Field observations and macroscopic descriptions ................................................................. 32 3.2. Microscopic descriptions ....................................................................................................... 32 3.3. Geochemistry ........................................................................................................................ 33 3.3.1. Sample preparation ....................................................................................................... 33 3.3.1.1. Loss on ignition ...................................................................................................... 33 3.3.1.2. Alkaline fusion ....................................................................................................... 33 3.3.2. Major elements ............................................................................................................. 34 3.3.2.1. ICP-AES................................................................................................................... 34 3.3.3. Trace elements .............................................................................................................. 35 3.3.3.1. ICP-MS ................................................................................................................... 35 3.4. Geochronology ...................................................................................................................... 37 3.4.1. Sample preparation ....................................................................................................... 37 3.4.2. LA-ICP-MS ...................................................................................................................... 38 4. Field observations and macroscopic descriptions ......................................................................... 39 4.1. Field observations ................................................................................................................. 39 4.2. Macroscopic descriptions ...................................................................................................... 44 4.2.1. Felsic magmatic protolith .............................................................................................. 44 4.2.1.1. Massive .................................................................................................................. 44 4.2.1.2. Foliated .................................................................................................................. 44 4.2.1.3. Strongly foliated .................................................................................................... 45 5 4.2.2. Sedimentary protolith ................................................................................................... 45 4.2.2.1. Slightly foliated ...................................................................................................... 45 4.2.2.2. Moderately foliated ............................................................................................... 46 4.2.2.3. Strongly foliated .................................................................................................... 46 4.2.3. Mafic magmatic protolith .............................................................................................. 47 4.2.3.1. Amphibolite ........................................................................................................... 47 4.2.3.2. Metadolerite .......................................................................................................... 47 4.2.3.3. Green phyllite ........................................................................................................ 48 5. Microscopic descriptions ............................................................................................................... 49 5.1. Felsic magmatic protolith ...................................................................................................... 49 5.1.1. Slightly deformed .......................................................................................................... 49 5.1.2. Moderately deformed ................................................................................................... 54 5.1.3. Strongly deformed ......................................................................................................... 60 5.1.4. Summary of observations .............................................................................................. 62 5.2. Sedimentary protolith ........................................................................................................... 63 5.2.1. Slightly deformed .......................................................................................................... 63 5.2.2. Moderately deformed ................................................................................................... 65 5.2.3. Strongly deformed ........................................................................................................