Oceanic crust covers two-thirds of the Earth's solid surface, but scientists still don't entirely understand the process by which it is made. Analysis of more than 600 samples of oceanic crust by a team including Carnegie's Frances Jenner reveals a systemic pattern that alters long-held beliefs about how this process works, explaining a crucial step in understanding Earth's geological deep processes. Their work is published in Nature on November 29.
Magmas generated by melting of the Earth's mantle rise up below the oceanic crust and erupt on the Earth's surface at mid-ocean ridge systems, the longest mountain ranges in the world. When the magma cools it forms basalt, the planet's most-common rock and the basis for oceanic crust.
It has long been assumed that the composition of magmas erupting out of mid-ocean ridges is altered when minerals that form during cooling sink out of the remaining liquid, a process called fractional crystallization. In theory, trace elements that are not included in the crystallizing minerals should be little affected by this process, and their ratios should be the same in the erupting magma as they were in the original magma before cooling.
If this is true, trace element ratios in magmas erupting at mid-ocean ridges should represent those of the original parental magma that formed deep in the Earth's mantle. However, this process doesn't account for the high abundance of trace elements found in samples of basalt from mid-ocean ridges around the world, so the reality of the situation is obviously more complicated than previous theories indicated.
Using the extensive array of samples and advanced modeling, Jenner and her research partner Hugh O'Neill of the Australian National University demonstrated that the concentration of trace elements is due to the process by which the magma is cycled through the oceanic crust prior to being erupted on the sea floor at the mid-ocean ridges.
Magma collects under the Earth's surface in a pool of liquid rock called a magma chamber. Each chamber is frequently flushed with new magma, which mixes with the old magma that was already there, and then this blended magma erupts out onto the ocean floor. Following the influx of new magma and eruption, the remaining magma undergoes fractional crystallization. This means that minerals are separated out from the magma as it cools. However, these minerals contain only minor amounts of the trace elements. As a result, trace elements build up in the magma over time, as the magma chamber is continually replenished by new magma coming in to the system.
"It's a simple idea, but it fits remarkably well," Jenner said. "These new findings will permit us to explore the conditions of mantle melting and production of the Earth's most-common rock."
Carnegie Institution: http://www.ciw.edu
This press release was posted to serve as a topic for discussion. Please comment below. We try our best to only post press releases that are associated with peer reviewed scientific literature. Critical discussions of the research are appreciated. If you need help finding a link to the original article, please contact us on twitter or via e-mail.
The world's most sensitive dark matter detector is poised to join the hunt for WIMPs, the world's most elusive particles
Nearly 20,000 schools may be exposed to ground shaking
On the hundredth anniversary of the first fatal use of chemical weapons, we look back at the scientists who risked their lives to fight a new enemy
The ‘optical lattice’ device is now three times more accurate than previous incarnations
Researchers question the non-hazardous ranking of plastic, saying its environmental impacts are not subject to the same level of scrutiny as other pollutants.
Oklahoma geologists have documented strong links between increased seismic activity in the state and the injection into the ground of wastewater from oil and gas production, a state agency said on Tuesday.
Swallowing a sulfur-rich protoplanet could help explain two lingering mysteries in the story of Earth's formation
In a first-of-its-kind endeavor, electricity-starved Rwanda and the Democratic Republic of Congo are trying to get power from a lake—and avert catastrophe.It’s a Friday afternoon on the Rwandan side of Lake Kivu, and in what was once a quiet cove, a daring venture is taking shape.
The good news is that an eruption there is highly unlikely, but the bad news is that it would be huge
Flame-retardant fabrics normally degrade when washed, but a water-repelling coating could make your flame-proof suit or sofa self-cleaning