New paper by group members – sampling the mantle in Antarctica

*article written by Dr. Michael Broadley and Prof. Ray Burgess.

The Earth’s mantle makes up more than 80% of the Earth by volume and has controlling influence on the generation of the Earth’s crust, the oceans and the atmosphere. The mantle therefore plays a dominant role in sustaining the habitable environment of our Planet. Volatile element and compounds vital to life such as water, carbon and nitrogen are released through from the mantle to the surface through volcanic eruptions but what is less well known is whether these volatiles species are taken back down into the mantle through the subduction of old crustal material together with seawater and sediments.

 Attempting to study the volatile composition of the Earth’s mantle is incredibly difficult and we therefore rely on the analysis of samples which originate from the mantle but have now been brought to the surface through volcanic eruptions, so called mantle xenoliths. Our study combined detailed noble gas isotopic and halogen elemental analysis of the volatiles trapped within mantle xenoliths erupted within Western Antarctica, to try and better understand the distribution of volatiles throughout the Earth.

Mt Overlord

View from the south of Mount Overlord an eroded stratovolcano in Victoria Land, Antarctica. Most of the cone is ice-covered but just below the summit there is a small area of abundant mantle xenoliths that were used in the study. (Image: Ray Burgess)

 Noble gases and halogens are concentrated on the surface of the Earth within the atmosphere, seawater and sediments and have unique signatures within each of these reservoirs, allowing them to be used as geochemical fingerprints for tracing the movement of volatiles throughout the Earth. Within the Western Antarctic xenoliths we have found signatures within these trapped fluids similar to air and marine sediments, as well as the background mantle signature. This indicates that the mantle beneath Western Antarctica has been infiltrated with volatiles from the Earth’s surface during a previous subduction event.  

Victoria land

Baker Rocks is another xenolith locality along the coast of Victoria Land Antarctica, about 150km south of Mount Overlord. The image shows co-author Luigi Dallai collecting xenoliths from well-bedded basalt tuffs. (Image: Ray Burgess)

The new data confirm that the volatiles can be introduced to the mantle through subduction and can remain trapped there over millions of years. This implies that the mantle is a much larger reservoir for volatiles than was previously thought and needs to be taken in to account when considering the global volatile cycle.

 

 

 

 

thin section

Thin section image of Western Antarctic xenolith showing individual minerals (a) and trapped fluid inclusions (b + c). (Image: Ray Burgess)

 —————————————

Full citation:

MW Broadley, CJ Ballentine, D Chavrit, L Dallai, R Burgess (2016) Sedimentary halogens and noble gases within Western Antarctic xenoliths: Implications of extensive volatile recycling to the sub continental lithospheric mantle Geochimica et Cosmochimica Acta 176, 139-156 doi:10.1016/j.gca.2015.12.013 

See also University of Manchester holdings here 

Fieldwork in Antarctica was supported by the Italian Programma Nazionale di Ricerche in Antartide, and laboratories and staff in the UK by the NERC and the ERC.

Advertisements

About Katherine Joy

Hello! I am Katherine Joy. I am part of the University of Manchester Isotope Geochemistry and Cosmochemistry group. More details about my research interests can be found at http://www.seaes.manchester.ac.uk/people/staff/profile/?ea=katherine.joy
Gallery | This entry was posted in Earth, Laboratory and tagged , , , . Bookmark the permalink.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s