Research Student 2012
Project Title: Subcontinental lithospheric mantle evolution of the southern Gondwana margin
Supervisors: Dr Sally Gibson, Dr Chiara M. Petrone (Natural History Museum, London) & Dr Ian Parkinson (University of Bristol)
Xenoliths offer a valauble window into the Earth's normally inaccessible mantle. They record the processes affecting the region: melt depletion events & enrichment processes (metasomatism) as well as indicating lithospheric thickness, oxidation state and lithospheric age.
This project focusses on xenoliths from southern Patagonia, specifically a suite of >200 samples, belonging to the Natural History Museum, London, from the Pali Aike Volcanic Field (PAVF), hosted in alkali basalt. The PAVF is located at the southern tip of South America, and straddles the border between Chile and Argentina. The PAVF spans a region of approximately 4500 km2 above the Magallenes Basin. K-Ar dating gives ages of <5 M.a. for the youngest flows and 5-50 M.a. for older flows (Skewes & Stern 1979). The PAVF occurs in a continental setting. Xenoliths are found in many localities in southern Patagonia, however samples from the PAVF are the only examples of garnet-bearing peridotite found to date. Samples are typically four or five phase lherzolites, containing: orthopyroxene (enstatite), clinopyroxene (diopside), olivine, spinel (+/- garnet (pyrope). Examples of pyroxenites, harzburgites and wehrlites are also present.
The project aims to reconstruct the lithospheric evolution of this area by:
- Constructing and constraining a palaeogeotherm for southern Patagonia
- Constraining the timing and extent of partial melting and/or metasomatism
- Constraining the type and modality of mantle metasomatism and how it relates to Plio-Quaternary subduction-related magmatism.
Comparisons will be made with findings from west Antarctica and other tectonically similar regions (e.g. south-east Australia)