Abstract
This work presents an integrated geochronology study combining step-heating Ar-Ar and in-situ Rb-Sr phyllosilicate geochronology with EPMA elemental maps and U-Pb apatite geochronology in order to determine the timing and duration of regional deformation and fluid circulation processes in the Karagwe-Ankole Belt in Central Africa. The Kibuye-Gitarama-Gatumba study area (West Rwanda) forms part of the Western Domain of this Mesoproterozoic belt, where the metamorphic and deformation history, geothermometric evolution and mineralization processes (both genesis and geochronology) have been well-documented in previous studies. Our geochronological results and interpretations show the importance of thermal diffusion throughout the elevated temperature regime present in the Neoproterozoic. During the Ediacaran, metamorphism and fluid alteration in the Gatumba area was associated with deformation, as independently demonstrated by U-Pb apatite and Ar-Ar phyllosilicate geochronology. From the end of the Ediacaran until the Late Cambrian, saline fluid activity is recorded and fluid-induced (re)crystallization processes dominate the Gatumba biotite isotope record. The direct comparison between and Ar-Ar geochronology suggests a parentless 40Ar-component is preserved during this fluid-induced (re)crystallization due to its saline, (earth) alkali-rich composition. Additionally, this multi-method approach allows us to place the history of the Western Domain of the Karagwe-Ankole belt in relation to that of the surrounding areas, i.e. the Eastern Domain and the Congo and Tanzania Cratons. Deformation and epidote-amphibolite facies metamorphism (at ~590–570 Ma), and fluid fluxes (at ~590–495 Ma) occurred in the Kibuye-Gitarama-Gatumba area after the West Gondwana Orogeny but from the onset of the East African Orogeny onwards till after the culmination of the Gondwana amalgamation, demonstrating the progressively eastward-moving orogenic front in this supercontinent assembly.
| Originalsprache | Englisch |
|---|---|
| Seiten (von - bis) | 279-297 |
| Seitenumfang | 19 |
| Fachzeitschrift | Gondwana research |
| Jahrgang | 83.2020 |
| Ausgabenummer | July |
| Frühes Online-Datum | 20 März 2020 |
| DOIs | |
| Publikationsstatus | Veröffentlicht - Juli 2020 |
Bibliographische Notiz
Funding Information:Johanna Van Daele is a research assistant of the Research Foundation - Flanders (FWO) , Belgium. Field work was supported by a grant from the Dirk Vogel Fund (Leuven, Belgium). Additional financial support from the research grant C14/17/056 of the KU Leuven Special Research Fund is acknowledged. Stijn Glorie his contribution was supported through an Australian Research Council Discovery Project ( DP200101881 ). Mr. Francis Gatare (CEO), Dr. Emmanuel Munyengabe, Dr. Michael Biryabarema and Mr. Alain Ntenge of the Rwanda Mines, Petroleum and Gas Board are thanked for the authorization to conduct field work in Rwanda and to export the samples. We are very grateful to Dr. Niels Hulsbosch (KU Leuven) for his help during the fieldwork and to Ms. Ann-Eline Debeer (UGent) for her help in the apatite preparation and carrying out the heavy liquid density separation of the amphibolite samples. We also would like to express our gratitude to Mr. Herman Nijs (KU Leuven) for preparing the high-quality thin and thick sections and to Mr. Pieter L'hoëst (KU Leuven) for his explanation and guidance with the FEG-EPMA. We are very grateful to Associate Editor Tim Johnson for his editorial handling, as well as to two anonymous reviewers for their constructive comments which improved the quality of this manuscript.
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© 2020 International Association for Gondwana Research