Does the core contribute to deep mantle sourced plumes?
Abstract
Mantle plumes represent a major component of heat transfer within the mantle. They are thought to be instrumental in the process of continental break-up, and are likewise considered responsible for the associated voluminous outpourings of the basic lavas, which make up continental flood basalt provinces. The 660 km discontinuity and the core-mantle boundary have been tentatively proposed as possible source regions for mantle plumes, nevertheless their source remains a matter of active debate. High 3He/4He ratios for plume related lavas from the Ethiopian Flood Basalt Province suggest an origin in the undegassed lower mantle; furthermore, high resolution tomography has revealed a meandering plume-like structure that extends down to the core-mantle boundary beneath Afar. Variably fractionated, mixed and differentiated high-Ti lavas from the North West Plateau show consistent major and trace element trends that indicate a common evolutionary origin from a mantle plume. High iron (12 16 % Fe2O3), magnesium (5.5 22% MgO) and titanium (3 7% TiO2) contents imply that they were derived from a high temperature small melt-fraction, and comparison plots for CaO/Al2O3 versus Al2O3 and Fe15 versus Na15 suggest that this was generated at between 5 and 6 GPa. Homogeneous trace element patterns with enriched LREE and depleted HREE indicate the presence of garnet in the source and derivation from a small melt fraction (< 5 %); furthermore they illustrate that the lavas have not been extensively contaminated by crustal material. The geochemical characteristics of these lavas, together with the fact that they are geographically localised, suggest that they represent the outpourings from the hot uncontaminated core of the plume from which they were derived. In this sense they represent the primary magma from the plume, and are therefore likely to contain fingerprints of its origin or source. We will present Os isotope data to fingerprint this source.
- Publication:
-
EGS - AGU - EUG Joint Assembly
- Pub Date:
- April 2003
- Bibcode:
- 2003EAEJA......363D