Magma formation, transport and evolution in an oceanic ultraslow extensional setting
Final Report Abstract
The project targeted the evolution of intraplate magmatic systems in the Azores, Central Northern Atlantic that are situated in a divergent, regional stress field. Our new geochemical and petrological, bathymetric and seismic data show that the magmatic activity in the Azores is the result of the arrival of a small, compositionally anomalous plume head underneath the mid-Atlantic Ridge. The alkaline lavas associated with this magmatic period display slightly elevated degrees of partial melting. Magmatic activity from 10-4 Ma occurs widespread and forms the major volumes of the submarine Princesa Alice Bank and the basement underneath the islands of Corvo and Flores west of the mid-Atlantic Ridge. The ecological impact of the plume head was mostly regional due to the submarine nature and relatively small size of the mantle plume compared to e.g., Iceland or Hawaii. Most of the oceanic crust west of Princesa Alice bank has not been affected by the initial activity of the plume head but displays a shallower water depth compared to similar age oceanic crust. We interpret this to reflect a lithospheric uplift due to the impingement of the mantle plume. A stratigraphic profile at the western Princesa Alice bank consists of lavas that show evidence for slightly higher degrees of partial melting but also display the highest water-rock ratios observed in oceanic crust to date. We interpret these signatures to be an effect of a long-lasting magmatic activity and hydrothermal alteration along rifting features in which the extreme degree of alteration results from long-lasting activity rather than extremely high temperatures. Lavas <2 Ma erupt along structural weak zones that formed due to extension at the slow spreading Terceira Rift axis and its precursors. Magmas ascent through dikes and form distinct ridges. In the case of the Serreta Ridge, west of the island of Terceira we can show that the older magmas are being fed from a magma reservoir underneath the volcano of Santa Barbara, while the youngest eruption is geochemically distinct and bypasses the central volcano’s magma reservoir and rises from the mantle. We conclude that the youngest eruption (1998-2001) may indeed reflect the initiation of a new magma plumbing system which is independent from the magma reservoir underneath Santa Barbara. Generally, we observe that the magmatic activity from 2 Ma to recent is largely focused towards smaller tectonic structures and lineaments (e.g., west of Faial and Terceira). The transition from individual ridges to a submarine seamount, which may ultimately lead to a large central volcano, was observed at Dom João de Castro seamount and suggests that the basement of the larger, subaerial volcanoes could consist of several ridges, with varying orientation. Our new data from a stratigraphic profile on the northern Terceira Rift axis shoulder suggest that the edifices in the Azores alternate between phases of tectonic activity with less dominant magmatic activity and vice versa over periods of 100 kyrs. The results from our project stress the importance of combining constraints on the local and regional stress field with the geochemistry in intraplate environments. The distribution of distinct geochemical signatures along individual ridges suggests an interaction between the source geochemical signatures and the overlying tectonic stress regime with limited interaction and mixing between different ridges. We can show that the preferential extraction of magmas along structural weak zones may also preserve much of the mantle geochemical heterogeneity, whereas mixing and assimilation in the reservoirs of the large central volcanoes may homogenize the source heterogeneity and reflects the evolution of the shallow magma reservoir.
Publications
- 2018. Correlated Changes Between Volcanic Structures and Magma Composition in the Faial Volcanic System, Azores. Frontiers in Earth Science 6, 78
Romer, R.H.W., Beier, C., Haase, K.M., Hübscher, C.
(See online at https://doi.org/10.3389/feart.2018.00078) - 2019. Extreme intensity of fluid-rock interaction during extensive intraplate volcanism. Geochimica et Cosmochimica Acta 257, 26-48
Beier, C., Bach, W., Busch, A.V., Genske, F.S., Hübscher, C., Krumm, S.H.
(See online at https://doi.org/10.1016/j.gca.2019.04.017) - 2019. Progressive Changes in Magma Transport at the Active Serreta Ridge, Azores. Geochemistry, Geophysics, Geosystems 20, 5394-5414
Romer, R.H.W., Beier, C., Haase, K.M., Klügel, A., Hamelin, C.
(See online at https://doi.org/10.1029/2019GC008562) - 2020. Rifting of the oceanic Azores Plateau with episodic volcanic activity. Scientific Reports 10, 19718
Storch, B., Haase, K.M., Romer, R.H.W., Beier, C., Koppers, A.A.P.
(See online at https://doi.org/10.1038/s41598-020-76691-1) - 2021. The evolution of central volcanoes in ultraslow rift systems: Constraints from D. João de Castro seamount, Azores. Tectonics 40, e2020TC006663
Romer, R.H.W., Beier, C., Haase, K.M., Eberts, A., Hübscher, C.
(See online at https://doi.org/10.1029/2020TC006663) - Shipboard Scientific Party R/V Meteor M128, 2022. The submarine Azores Plateau: Evidence for a waning mantle plume? Marine Geology 451, 106858
Beier, C., Genske, F., Hübscher, C., Haase, K.M., Bach, W., Nomikou, P.
(See online at https://doi.org/10.1016/j.margeo.2022.106858)
