Melt inclusions as a record of mantle heterogeneity and melt-crust interaction
Dr Jason Harvey (SEE), Dr David Fergusson (SEE), Dr Dan Morgan (SEE), Dr John Maclennan (University of Cambridge, Dr Eduardo Morgado (SEE)Contact email: firstname.lastname@example.org
In the absence of representative mantle samples, melt inclusions trapped within early crystallizing minerals, such as olivine, provide a snapshot of primary mantle melt composition before such homogenisation occurs - the olivine crystal protects the melt inclusion from being incorporated into the pooled melt - therefore preserving evidence of any compositional heterogeneity in the mantle source. In addition, heterogeneity can be introduced through interaction of a homogeneous melt with the lithosphere while a magma is either stored within or transits through the region between its source and its eruption site.
However, melt inclusions are small (sub-mm diameter) and, until recently, analysis of more than one potential tracer of mantle source in a melt inclusion has been challenging. This project, using a powerful combination of major, trace and volatile elements with Sr, Nd and Pb isotope measurements, and using methods recently developed by the supervisors and collaborators (see Harvey et al., 2009; Reinhard et al., 2017, 2018) will fingerprint the nature of the chemical and isotopic heterogeneities in individual melt inclusions that are representative of the ingredients that formed the melts erupted in the Southern Volcanic Zone of Chile (Morgado et al., 2015), the Afar Rift (Ferguson et al., 2013), and Iceland (Maclennan et al., 2008). This combination of tracers will provide a unique perspective on the scale, magnitude and distribution of mantle heterogeneities beneath these regions. The information derived will inform on processes relating to melt production and transport in the mantle sources that feed continental rifts, plumes and subduction-related magmas. The depth at which a melt inclusion becomes trapped within its host can be determined by its CO2 and H2O abundances; coupled with the chemical and isotopic composition of a population of melt inclusions, the chemical heterogeneity at depth and hence the complexity of magmatic plumbing within the mantle plume can also be determined.
Related undergraduate subjects:
- Earth science
- Natural sciences