Mantle on EARTH Magazine

Thirsty mantle: Subduction zones swallow more water than thought

Wed, 30 Jan 2019 15:26:27 -0500

A seismic study of part of the Pacific Plate diving beneath the Mariana Trench has revealed that old and cold subducting plates, like the Pacific, likely carry a lot more water into the mantle than previously realized. Credit: K. Cantner, AGI

For all the water stored in oceans, ice and other reservoirs at Earth’s surface, there’s likely even more in the planet’s interior, where it plays important roles in many geological processes, including the formation of magma and the lubrication of earthquake-producing fault zones. Uncovering just how much water is inside Earth — and the extent to which it moves back and forth between the surface and subsurface — has long been a challenge for scientists interested in understanding the planet’s water cycle. A new study peering beneath the Mariana Trench in the Western Pacific has revealed that some subduction zones might pull significantly more water into Earth’s interior than previously thought.

Diamonds reveal water in deep mantle

Tue, 05 Jun 2018 17:05:30 -0400

A new study analyzing the structural and chemical properties of diamonds from various locations in Africa and China found inclusions of ice-VII, a form of crystallized water created under very high pressure that has never before been found in nature. Credit: Marilyn Chung/Berkeley Lab.

Inclusions in diamonds often render them undesirable to consumers, but they can provide researchers with striking insights into Earth’s composition. Recently, scientists probing diamond samples for the presence of carbon dioxide stumbled instead upon inclusions of ice-VII — a type of crystallized water that forms at very high pressures, and has never before been found in nature.

Young Costa Rican lavas might reflect pockets of primordial mantle

Thu, 10 Aug 2017 11:18:53 -0400

Komatiites are commonly found in Archean deposits, but a much younger flow found in Costa Rica may unlock some secrets about Earth's mantle. Credit: Esteban Gazel.

During the Archean, between 4 billion and 2.5 billion years ago, Earth’s super-heated young mantle produced a unique type of lava known as komatiite. In a new study published in Nature Geoscience, researchers looking at 90-million-year-old komatiites in Costa Rica — by far the youngest komatiites ever found — suggest the modern mantle may still harbor pockets of intense heat reminiscent of early Earth.

When and how did plate tectonics begin on Earth?

Mon, 15 May 2017 20:36:52 -0400

Credit: K. Cantner, AGI.

The basic story of Earth’s formation is familiar to most anyone who has taken a geology course: About 4.6 billion years ago, Earth formed when a rocky nucleus accreted dust and debris left over from the formation of our sun.

Moon formed from pulverized Earth mantle

Wed, 18 Jan 2017 14:29:09 -0500

Artist's conception of the violent impact that formed the moon. Credit: K. Cantner, AGI.

Scientists have long thought that the moon was formed when an impactor crashed into Earth, some 100 million years after the planet’s formation. But details of this collision, and how the moon formed in its aftermath, remain puzzling. Now, researchers have found new potassium isotopic evidence that suggests the moon condensed from a superheated cloud of Earth’s mantle material after an extremely violent collision vaporized the impactor and much of the proto-Earth.

Small-scale factors influence mantle flow under the seafloor

Tue, 15 Nov 2016 11:21:27 -0500

Deployment and recovery of an ocean-bottom seismometer (OBS) from the R/V Langseth in the Pacific Ocean more than 1,900 kilometers southeast of Hawaii. The OBS was lowered into the water via crane, where it then fell to the seafloor under its own weight. It stayed on the seafloor for 13 months; researchers then returned to the location, sent the instrument a message to disconnect from its anchor weight, and it rose to the surface where researchers scooped it up. Credit: both: James Gaherty.

In December 2011, scientists and technicians aboard the research vessel Marcus G. Langseth dropped several ocean-bottom seismometers into the deep Pacific more than 1,900 kilometers southeast of Hawaii to measure seismic activity and electrical conductivity to a depth of about 300 kilometers below the seafloor. Now, these measurements are providing new insights into how the mantle flows and deforms below the rigid tectonic plates that make up Earth’s surface.

Junk gem reveals new diamond-forming process

Tue, 13 Sep 2016 13:52:24 -0400

Researchers found a thin magnetite corona — the dappled band shown in (a) and with individual grains colored in (b) — around a sulfide inclusion in a diamond from Botswana, evidence of a diamond-forming process called redox freezing. Scale bars are 0.5 micrometers. Credit: Jacob et al., Nature Communications, June 2016, CC BY 4.0.

Not all diamonds are gems. Those found bearing imperfections or inclusions, known as bort or junk diamonds, are often demoted to industrial uses such as in diamond-tipped drill bits. They also sometimes find their way to scientists interested in using the inclusions to study how such stones form. Now, a team studying a junk diamond from Botswana with a large black sulfide inclusion has uncovered evidence of a previously unrecognized diamond formation process that occurs in the deep mantle.

Mantle convection makes Earth's crust bob

Tue, 16 Aug 2016 13:24:06 -0400

Coral reefs at Cap Miné near the northern end of Madagascar attest to uplift in the area caused by underlying mantle upwelling: While a living reef forms underwater today, the remnants of two former reefs — one upon which the lighthouse sits and one capping the hill at left — were raised out of the water. Credit: Mark Hoggard.

From the earthquake-prone Himalayas and Andes to the volcanically active “Ring of Fire” around the Pacific, the boundaries of Earth’s tectonic plates are often sites of considerable geologic activity. In contrast, the interiors of tectonic plates have been thought to be relatively rigid and quiet.

Stalled slabs sometimes stopped by mineral strengthening

Thu, 16 Jul 2015 13:23:14 -0400

In some subduction zones, the downgoing slabs get stuck at depths of about 1,000 kilometers, held up by some unseen barrier that might be related to high-pressure-induced strengthening of minerals in the rocks surrounding the subducting slabs. Credit: K. Cantner, AGI.

Subduction of tectonic plates into the mantle functions as an eons-long recycling system for Earth’s crust and lithosphere. But in some subduction zones, the downgoing slabs seem to get stuck at depths of about 1,000 kilometers, held up by some unseen barrier on their journey deeper into the lower mantle. Now, scientists propose that this barrier might be related to high-pressure-induced strengthening of minerals in the rocks surrounding subducting slabs at these depths.

A watery surprise from Earth's depths: Mineral provides first direct evidence for water in mantle's transition zone

Thu, 10 Jul 2014 12:58:05 -0400

This half-centimeter-wide diamond contains a speck of ringwoodite, the first known water-bearing mineral from Earth's transition zone. Credit: Graham Pearson, University of Alberta.

Studies of seismic waves traveling through Earth have long suggested that the mantle is like a layer cake, with regions of differing composition. In a layer known as the transition zone, between depths of about 410 to 660 kilometers, much of the rock is thought to be composed of pressure-squeezed variants of the common mineral olivine. One of these hypothesized forms is ringwoodite, which forms blue, cube-shaped crystals. Ringwoodite synthesized in the lab under high pressure can contain up to 2 percent water by weight, suggesting the transition zone could hold massive amounts of water. But direct evidence of this water had been nonexistent as no one had observed ringwoodite from the mantle; the only naturally occurring specimens had come from meteorites.

Corn syrup model splits Yellowstone's plume in two

Thu, 13 Jun 2013 12:48:20 -0400

Yellowstone is renowned for its hot springs, geysers and for hosting one of the world’s most volatile supervolcanoes. Despite its popularity, the origin of all that volcanic activity remains poorly understood. A mantle plume seems like the most obvious source, but traditional plume models can’t explain the jumble of volcanic surface features. Now, a new study using corn syrup to replicate the mantle processes underlying Yellowstone offers a more complicated scenario: a bifurcated mantle plume, split by the Cascadia Subduction Zone.

Beads of water on the moon

Thu, 05 Jan 2012 06:41:58 -0500

Scientists used these small volcanic glass beads to determine that the moon's mantle once held water (and possibly still does). NASA

During the Apollo missions, NASA astronauts shoveled, bagged and sent back to Earth close to 400 kilograms of lunar rocks and soil. But researchers studying these samples never found water. Now, after decades of coming up dry, scientists have found evidence that the moon’s interior once held — and perhaps still holds — water.