Measurements link magma melting rate to tectonic plate subduction rate

Nov 08, 2007

Determining the origin and rate of magma production in subduction zone volcanoes is essential to understanding the formation of continental crust and the recycling of subducted materials back into Earth’s mantle.

Now, geologists at the University of Illinois report new measurements of rock samples from Kick’em Jenny, a submarine volcano in the Caribbean, that link the rate at which magma is produced beneath subduction zone volcanoes to the rate at which tectonic plates converge in this plate tectonic setting.

“We can use the geochemical measurements to constrain a geophysical parameter, the melt production rate; we then relate the melting rate at an individual subduction zone to its plate convergence rate, which can also be measured,” said Craig Lundstrom, a UI professor of geology. “We can then use this information in similar situations to understand the rate at which magma is produced in other settings.”

Lundstrom and graduate research assistant Fang Huang report their findings in the November issue of the journal Geology, which is published by the Geological Society of America.

The geochemical technique is based on uranium decaying to lead through a long decay chain of short-lived nuclides. For example, U-235 (a “parent” with a half-life of 700 million years) will decay to Pa-231 (protactinium-231: a “daughter” with a half-life of 33,000 years). By measuring the ratio of parent and daughter species in a rock sample (a technique called uranium-series dating), scientists can determine whether the rock is in secular equilibrium (and quite old), or in uranium series-disequilibrium (and very young).

Using multiple-collector inductively coupled plasma-mass spectrometry, Huang and Lundstrom analyzed 12 rock samples from Kick’em Jenny, a submarine volcano located about 8 kilometers north of Grenada in the southern Lesser Antilles arc.

At Kick’em Jenny, the Atlantic oceanic plate is being pushed beneath the Caribbean plate at a rate of 2-4 centimeters per year, one of the lowest convergence rates of any subduction zone.

In Kick’em Jenny lavas, the researchers found there was twice as much protactinium than should be present if the system was in secular equilibrium. This is the largest protactinium-uranium disequilibrium found in any subduction-zone volcano.

The relationship between melting rate and convergence rate centers on the role of water during melting. “An essential part of all volcanoes at subduction zones is the amount of water involved in the mantle melting process,” Huang said. “During subduction, water is released from the subducting slab into the mantle wedge, which lowers the melting point of the rock. When less water is transported to the mantle, less melt is produced.”

At Kick’em Jenny, water is being added very slowly, because the subducting plate is going down very slowly, Lundstrom said. This results in a slower melting rate, which produces a higher ratio of protactinium to uranium 235.

“This is the first study to show that there is a straightforward relationship between this uranium disequilibrium system and the rate of tectonic plate convergence,” Lundstrom said. “No doubt these short-lived nuclides can be used for a variety of other processes in volcanoes, from determining how fast crystals form to how fast magma moves under mid-ocean-ridge volcanoes.”

Source: University of Illinois at Urbana-Champaign

Explore further: Scientists to explore how ocean nutrients arrive at the surface of the mid-Atlantic ocean

add to favorites email to friend print save as pdf

Related Stories

Great Alaska Earthquake shook Alaska 50 years ago

Mar 26, 2014

Electric clocks on walls in Anchorage shut down at 5:36 p.m. on March 27, 1964. Time stopped at the start of the '64 Great Alaska Earthquake, the second largest ever recorded at magnitude 9.2.

Continents set the pace

Jan 28, 2014

The origin and stimulus behind plate tectonics has been simulated with the aid of high-performance computers. A new study sheds light on the role continents play in the formation of oceanic crust.

Global map to predict giant earthquakes

Dec 12, 2013

A team of international researchers, led by Monash University's Associate Professor Wouter Schellart, have developed a new global map of subduction zones, illustrating which ones are predicted to be capable of generating ...

Recommended for you

Six Nepalese dead, six missing in Everest avalanche

6 hours ago

At least six Nepalese climbing guides have been killed and six others are missing after an avalanche struck Mount Everest early Friday in one of the deadliest accidents on the world's highest peak, officials ...

User comments : 0

More news stories

New research on Earth's carbon budget

(Phys.org) —Results from a research project involving scientists from the Desert Research Institute have generated new findings surrounding some of the unknowns of changes in climate and the degree to which ...

Under some LED bulbs whites aren't 'whiter than white'

For years, companies have been adding whiteners to laundry detergent, paints, plastics, paper and fabrics to make whites look "whiter than white," but now, with a switch away from incandescent and fluorescent lighting, different ...