Magma genesis beneath active continental rifts
The East African Rift System (EARS) and the West Antarctic Rift System (WARS) are two of the largest continental rift systems on Earth, but the processes governing rift dynamics remain controversial. The large volume and distinct chemistry of Cenozoic rift-related lavas, combined with geophysical ev...
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University of New Hampshire Scholars' Repository
2017
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| Online Access: | https://scholars.unh.edu/dissertation/139 https://scholars.unh.edu/cgi/viewcontent.cgi?article=1138&context=dissertation |
| Summary: | The East African Rift System (EARS) and the West Antarctic Rift System (WARS) are two of the largest continental rift systems on Earth, but the processes governing rift dynamics remain controversial. The large volume and distinct chemistry of Cenozoic rift-related lavas, combined with geophysical evidence for low-density mantle underlying both rifts, have traditionally been interpreted as evidence for anomalously hot mantle plumes actively rising from the deep mantle beneath both regions. However, in light of increasing evidence that these mantle structures may also be chemical in nature, alternative explanations highlight the role of heterogeneous, easily-fusible mantle components in driving magma genesis in the absence of significant thermal anomalies. These heterogeneous mantle domains may be linked to the complex tectonic histories of continents, which often involve multiple stages of accretion and associated recycling of materials between the crust and the mantle. In this dissertation, detailed chemical investigations of rift-related volcanic rocks provide critical new insight into the nature of the mantle underlying the two active rifts. In particular, the role of volatiles such as water and carbon dioxide is highlighted due to the ability of these components to enhance mantle melting during rift-related decompression. In Chapter II, the first geochemical information from submarine lavas in the Ross Embayment of West Antarctica are reported alongside subaerial lavas from islands and mainland localities, which together provide evidence that volatilized, recycled mantle domains generated during ancient long-lived subduction along the paleo-Pacific margin of Gondwana are key components in the temporally evolving source of Cenozoic magmas (Aviado et al., 2015). In Chapter III, the first rift-wide study of magmatic volatiles recorded in olivine-hosted melt inclusions confirms that the West Antarctic mantle is enriched in water and carbon dioxide on a wide scale, and links the production of hydrated and ... |
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