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Geology Seminar Series - Dr. Christine Rasoazanamparany - Chemical and Isotopic Studies Of Monogenetic Volcanic Fields. What have we learned so far?

Wed., Mar. 8, 2023 4:00 p.m. - Wed., Mar. 8, 2023 5:00 p.m.

Location: zoom: https://uregina-ca.zoom.us/j/92774600262?pwd=RlgzR3dDVzloWnpnQldtZmVwNERZdz09

All are welcome to join us for a virtual seminar on March 8, 2023 at 4 pm CST.

Speaker: Dr. Christine Rasoazanamparany, Department of Geology & Environmental Earth Science, Miami University

Topic: Chemical and Isotopic Studies Of Monogenetic Volcanic Fields. What have we learned so far?

Zoom link: https://uregina-ca.zoom.us/j/92774600262?pwd=RlgzR3dDVzloWnpnQldtZmVwNERZdz09

Abstract:

In order to assess the origin and sources of monogenetic volcanism, we conducted detailed field observations, elemental analysis, and Sr-Nd-Pb-Hf-Os-O-U series isotopic studies of young, monogenetic volcanic systems in diverse tectonic settings. The targeted study areas include the Lunar Crater Volcanic Field, Nevada, an area of relatively recent volcanism within the Basin and Range province, western USA; the Michoacán Volcanic Field in the Trans-Mexican Volcanic Belt, which is linked to modern subduction; and the Itasy and Ankaratra Volcanic Fields, Madagascar, which may be associated with intra-continental rifting. In these studies, key questions include: (1) what is the role of crustal assimilation vs. mantle source enrichment in producing chemical and isotopic heterogeneity in the eruptive products, (2) what is the origin of the mantle heterogeneity, and (3) what is the cause of spatial-temporal variability in the sources of magmatism. In all studies we have shown that there is significant compositional variability within individual volcanoes and/or across the volcanic field that cannot be attributed to assimilation of crust during magmatic differentiation, but instead is attributed to mantle source heterogeneity. Although the processes by which the heterogeneities (as well as those in monogenetic volcanic fields globally) are generated may differ depending on tectonic setting, our studies show that there are important commonalties. Despite the distinct tectonic settings of the study areas, all volcanic fields exhibit trace element and isotopic variations that are indicative of mixing of multiple geochemically distinct mantle sources that have resulted from recycling of crustal materials and/or sub-continental lithospheric mantle into the asthenosphere. Our studies further demonstrate that the processes, and in some cases the timing, of the mantle enrichment events can be clearly preserved in mafic monogenetic volcanic systems. It is likely that the small degrees of melting and rapid source to surface transport that prevail in these small, mafic volcanic systems help to preserve detailed evidence of their petrogenetic histories that is often masked or obliterated in more voluminous, silicic volcanic systems. Detailed studies of mafic monogenetic volcanic fields, in which field evidence serves as a foundation for geochemical and isotopic investigations, are therefore key to unraveling processes of mantle source enrichment and heterogeneity in time and space.