University of Cambridge
Basalt Magmatism as a Key to Unlocking Cenozoic Dynamic Topography
Abstract
dc:description.abstractReconstructing mantle dynamic topography through space and time remains a significant challenge. Nevertheless, useful insights can be gained by analysing Cenozoic basalt magmatism, which correlate with convectively driven regional uplift across the globe. This dissertation comprises three regional studies. First, Neogene-Quaternary magmatism of the Western Mediterranean region is analysed within a mantle geodynamical framework. Secondly, a petrological and geochemical study of diachronous V-shaped ridges and troughs that flank the Reykjanes Ridge south of Iceland is carried out. Thirdly, the Paleogene Igneous Province that fringes the North Atlantic Ocean is placed in an Icelandic Plume context. The principal objective of this dissertation is to constrain the spatial and temporal thermal structure of the uppermost mantle in these regions by exploiting thermobarometric and geochemical modelling of basalts. Whole-rock samples are analysed for major, trace and rare earth elements, as well as selected radiogenic isotopes. Geochemical concentrations are corrected to approximate primary melt compositions. A suite of complementary geophysical and geomorphic techniques are used to estimate the amplitude, wavelength and depth of mantle thermal anomalies. In this way, independent constraints for mantle dynamic support are used to complement geochemical studies. Neogene-Quaternary magmatism of the Western Mediterranean region is associated with long-wavelength topographic swells underlain by negative shear-wave velocity anomalies, indicative of sub-lithospheric thermal support. 48 newly analysed basalt samples from Spain are combined with legacy databases. Mantle potential temperatures and lithospheric thicknesses are estimated to be 1250–1350◦C and 60–70 km, respectively. These values conform with tomographic predictions and are suggestive of modest asthenospheric warming and lithospheric thinning beneath this region. South of Iceland, a sequence of diachronous V-shaped ridges and troughs records interactions between the Icelandic Plume and the mid-ocean ridge system. Petrological and geochemical analyses of 50 newly drilled samples from a series of ridge-trough pairs reveal systematic differences in major, trace, and rare earth element concentrations. Forward and inverse modelling, based upon polybaric fractional melting, indicate that variations in melt fraction, driven by mantle temperature differences of 25–30◦C, successfully match observations. In this way, resolvable fluctuations in temperature yield significant new insights into the fluid dynamics of mantle convection. The North Atlantic Igneous Province is widely regarded as the product of proto-Icelandic plume activity, which has been tectonically dissected by subsequent opening of the ocean basin. In this study, 19 new whole-rock samples from Arran, Scotland, together with extensive legacy databases are analysed. Minimum mantle potential temperatures, estimated by assuming columnar melting regimes beneath a ∼60-km-thick lithosphere, yield ranges of 1375–1415◦C for the British Isles, 1380–1390◦C for Northeast Greenland, and 1375–1410◦C for a region encompassing the Faroe Islands. These estimates confirm elevated mantle temperatures consistent with plume-related thermal anomalies.
Degree
thesis:*- Name dc:type.qualificationname
- Doctor of Philosophy (PhD)
- Level dc:type.qualificationlevel
- Doctoral
- Grantor dc:publisher.institution
- University of Cambridge
- Year dc:date.issued
- 2025
Author and committee
dc:creator, dc:contributor.*- Author dc:creator
-
- Tien, Chia-Yu
- Advisors dc:contributor.advisor
-
- White, Nicholas
- Maclennan, John
Subjects
dc:subject × 11Rights
dc:rightsIdentifiers
dc:identifier.*- DOI dc:identifier.doi
- https://doi.org/10.17863/CAM.124170
- OAI identifier oai:identifier
- oai:www.repository.cam.ac.uk:1810/394085