Geochemical investigations of continental rift magmatism: a case study in East Africa's Western Rift
Open Access
- Author:
- Pitcavage, Erica
- Graduate Program:
- Geosciences
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- December 18, 2019
- Committee Members:
- Tanya Furman, Dissertation Advisor/Co-Advisor
Tanya Furman, Committee Chair/Co-Chair
Maureen Feineman, Committee Member
Christelle Wauthier, Committee Member
Danny Glynn Sykes, Outside Member
Mark E Patzkowsky, Program Head/Chair - Keywords:
- East African Rift
geochemistry
petrology
isotope geochemistry
geochronology
Uganda
magmatism
volcanism - Abstract:
- The Cenozoic East African Rift System (EARS) is the earth’s largest continental divergent boundary and an important case study for understanding magmatic processes related to continental rifting. The EARS consists of several major segments: the Main Ethiopian Rift, the Eastern (or Kenya) Rift, the Western Rift, and the Malawi Rift. In the Western Rift, volcanism is located in distinct volcanic provinces and is typically restricted to intrabasin accommodation zones rather than aligned along border faults. Lava compositions require significant input from metasomatized sub-continental lithospheric mantle (SCLM), which has been modified by late Proterozoic-early Phanerozoic tectonic events (~450-500 Ma). Major element, trace element and isotopic compositions of primitive magmas from the Bufumbira, Katwe-Kikorongo, and Bunyaruguru volcanic fields in the Virunga and Toro Ankole Volcanic Provinces indicate that they are derived from mixing of metasomatic sources dominated by the regional common lithospheric mantle (CLM) as one endmember with contributions from locally varying metasomes. The mineralogy of these metasomes influences the trace element systematics of early-crystallizing phenocrysts from the melts derived from them. Bulk rock and mineral geochemistry indicate that small-volume melts are derived from deep lithospheric mantle and undergo small amounts of fractionation, which exerts control on both bulk magma and mineral compositions. The primitive lavas were dated with eruption ages of 21-662 ka, overlapping temporally with other occurrences of recent volcanism in the region.