Scientists unearth 20 million years of 'hot spot' magmatism under Cocos
plate

Date:
June 20, 2023
Source:
Georgia Institute of Technology
Summary:
A team of scientists has observed past episodic intraplate magmatism
and corroborated the existence of a partial melt channel at the
base of the Cocos Plate. Situated 60 kilometers beneath the Pacific
Ocean floor, the magma channel covers more than 100,000 square
kilometers, and originated from the Gala'pagos Plume more than 20
million years ago, supplying melt for multiple magmatic events --
and persisting today.


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FULL STORY ==========================================================================
Ten years ago, Samer Naif made an unexpected discovery in Earth's
mantle: a narrow pocket, proposed to be filled with magma, hidden some
60 kilometers beneath the seafloor of the Cocos Plate.

Mantle melts are buoyant and typically float toward the surface -- think underwater volcanoes that erupt to form strings of islands. But Naif's
imaging instead showed a clear slice of semi-molten rock: low-degree
partial melts, still sandwiched at the base of the plate some 37 miles
beneath the ocean floor.

Then, the observation provided an explanation for how tectonic plates
can gradually slide, lubricated by partial melting. The study also
"raised several questions about why magma is stored in a thin channel --
and where the magma originated from," says Naif, an assistant professor
in the School of Earth and Atmospheric Sciences at Georgia Institute
of Technology.

Fellow researchers went on to share competing interpretations for the
cause of the channel -- including studies that argued against magma
being needed to explain the observation.

So Naif went straight to the source.

"I basically went on a multiyear hunt, akin to a Sherlock Holmes detective story, looking for clues of mantle magmas that we first observed in the
2013 Naturestudy," he says. "This involved piecing together evidence
from several independent sources, including geophysical, geochemical,
and geological (direct seafloor sampling) data." Now, the results of
that search are detailed in a new Science Advances article, "Episodic intraplate magmatism fed by a long-lived melt channel of distal plume
origin," authored by Naif and researchers from the U.S. Geological
Survey at Woods Hole Coastal and Marine Science Center, Northern Arizona University, Lamont-Doherty Earth Observatory of Columbia University,
the Department of Geology and Geophysics at Woods Hole Oceanographic Institution, and GNS Science of Lower Hutt, New Zealand.

Zeroing in A relatively young oceanic plate -- some 23 million years
old -- the Cocos Plate traces down the western coast of Central America, veering west to the Pacific Plate, then north to meet the North American
Plate off the Pacific coast of Mexico.

Sliding between these two plates caused the devastating 1985 Mexico City earthquake and the 2017 Chiapas earthquake, while similar subduction
between the Cocos and Caribbean plates resulted in the 1992 Nicaragua
tsunami and earthquake, and the 2001 El Salvador earthquakes.

Scientists study the edges of these oceanic plates to understand the
history and formation of volcanic chains -- and to help researchers and agencies better prepare for future earthquakes and volcanic activity.

It's in this active area that Naif and fellow researchers recently set out
to document a series of magmatic intrusions just beneath the seafloor,
in the same area that the team first detected the channel of magma back
in 2013.

Plumbing the depths For the new study, the team combined geophysical, geochemical, and seafloor drilling results with seismic reflection
data, a technique used to image layers of sediments and rocks below the surface. "It helps us to see the geology where we cannot see it with
our own eyes," Naif explains.

First, the researchers observed an abundance of widespread intraplate magmatism. "Volcanism where it is not expected," Naif says, "basically
away from plate boundaries: subduction zones and mid-ocean ridges."
Think Hawaii, where "a mantle plume of hot, rising material melts during
its ascent, and then forms the Hawaii volcanic chain in the middle of
the Pacific Ocean," just as with the Cocos Plate, where the team imaged
the volcanism fed by magma at the lithosphere-asthenosphere boundary --
the base of the sliding tectonic plates.

"Below it is the convecting mantle," Naif adds. "The tectonic plates
are moving around on Earth's surface because they are sliding on the asthenosphere below them." The researchers also found that this channel
below the lithosphere is regionally extensive -- over 100,000 square
kilometers -- and is a "long-lived feature that originated from the
Gala'pagos Plume," a mantle plume that formed the volcanic Gala'pagos
islands, supplying melt for a series of volcanic events across the past
20 million years, and persisting today.

Importantly, the new study also suggests that these plume-fed melt
channels may be widespread and long-lived sources for intraplate magmatism itself -- as well as for mantle metasomatism, which happens when Earth's
mantle reacts with fluids to form a suite of minerals from the original
rocks.

Connecting the (hot spot) dots "This confirms that magma was there in
the past -- and some of it leaked through the mantle and erupted near
the seafloor," Naif says, "in the form of sill intrusions and seamounts: basically volcanoes located on the seafloor." The work also provides compelling supporting evidence that magma could still be stored in the
channel. "More surprising is that the erupted magma has a chemical
fingerprint that links its source to the Gala'pagos mantle plume."
"We learned that the magma channel has been around for at least 20
million years, and on occasion some of that magma leaks to the seafloor
where it erupts volcanically," Naif adds.

The team's identified source of the magma, the Gala'pagos Plume, "is more
than 1,000 kilometers away from where we detected this volcanism. It is
not clear how magma can stay around in the mantle for such a long time,
only to leak out episodically." Plume hunters wanted The evidence that
the team compiled is "really quite subtle and requires a detailed and
careful study of a suite of seafloor observations to connect the dots,"
Naif says. "Basically, the signs of such volcanism, while they are quite
clear here, also require high resolution data and several different
types of data to be able to detect such subtle seafloor features." So,
"if we can see such subtle clues of volcanism here," Naif explains, "it
means a similar, careful analysis of high resolution data in other parts
of the seafloor may lead to similar discoveries of volcanism elsewhere,
caused by other mantle plumes." "There are numerous mantle plumes dotted across the planet. There are also numerous seamounts -- at least 100,000
of them! -- covering the seafloor, and it is anyone's guess how many of
them formed in the middle of the tectonic plates because of magma sourced
from distant mantle plumes that leaked to the surface." Naif looks
forward to continuing that search, from seafloor to asthenosphere.

* RELATED_TOPICS
o Earth_&_Climate
# Volcanoes # Geology # Earthquakes # Natural_Disasters
o Fossils_&_Ruins
# Fossils # Origin_of_Life # Early_Climate # Paleontology
* RELATED_TERMS
o Mantle_plume o Oceanic_trench o Yellowstone_Caldera o
Ice_sheet o Ocean o Mid-ocean_ridge o Tunguska_event o River

========================================================================== Story Source: Materials provided by Georgia_Institute_of_Technology. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Samer Naif, Nathaniel C. Miller, Donna J. Shillington, Anne Be'cel,
Daniel Lizarralde, Dan Bassett, Sidney R. Hemming. Episodic
intraplate magmatism fed by a long-lived melt channel of distal
plume origin.

Science Advances, 2023; 9 (23) DOI: 10.1126/sciadv.add3761 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2023/06/230620174452.htm

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