An article in Nature entitled Lithospheric controls on magma composition along Earth’s longest continental hotspot track was published this week and sheds some light on how the thickness of the lithosphere (the Earth’s crust and uppermost portion of the mantle) controls its magma composition.
Hotspots are hot, buoyant material brought up from the Earth’s mantle. These features result in volcanic activity that is not associated with a tectonic plate boundary. For example the Hawaii and Yellowstone hotspots are both located in the middle of a tectonic plate. Over time, the tectonic plate moves while the hotspot stays still. This creates a trail of volcanic rock and features in which geologists can use to track the motion of the tectonic plate.
The longest hotspot track on Earth is known as the Cosgrove track. This track of volcanic activity is located in eastern Australia and spans the entire length of the continent from north to south, covering nearly 2,000 km. The Cosgrove track records volcanic activity dating back 33 to 9 million years.
This newly published article links the thickness of the Earth’s lithosphere to the magma composition of the hotspot. Areas of the lithosphere that are less than 10 km thick result in basaltic composition. A volcanic gap occurs in areas that have a lithosphere thickness of more than 150 km. Finally in the intermediate depths, the composition of the magma is associated with leucite-bearing rocks.
The implications of this study show us that the depth of the lithosphere can be generally mapped by analyzing the magma composition of hotspot tracks.