Study Combines Climatic, Tectonic Models to Explain Andean Conundrum


Peer-Reviewed Publication

UNIVERSITY OF ILLINOIS AT URBANA-CHAMPAIGN, NEWS BUREAU

A 3D-relief map of the Andean tectonic setting
IMAGE: A 3D-RELIEF MAP ILLUSTRATING HOW THE SUBMERGED EAST-WEST TRENDING JUAN FERNANDEZ RIDGE MAY ACT AS A BARRIER TO NORTHWARD-MIGRATING TRENCH SEDIMENTS. THE JUAN FERNANDEZ RIDGE IS PART OF THE OCEANIC NAZCA PLATE, LEFT, WHICH IS SUBDUCTING UNDER THE SOUTH AMERICAN CONTINENTAL PLATE, RIGHT. view more 
CREDIT: GRAPHIC COURTESY JIASHUN HU

CHAMPAIGN, Ill. — The Andes Mountains are much taller than plate tectonic theories predict they should be, a fact that has puzzled geologists for decades. Mountain-building models tend to focus on the deep-seated compressional forces that occur when tectonic plates collide and send rocks skyward. A new study demonstrates how modern top-down models that account for climate-related factors combined with traditional bottom-up tectonic models can help uncover the perplexing history of the Andes Mountains.

The study, led by former University of Illinois Urbana-Champaign graduate student Jiashun HuIllinois geology professor Lijun Liu and California Institute of Technology professor Michael Gurnis, is published in the journal Nature Communications.

“The Andes are unique for their tectonic setting,” Liu said. “The central portion of the range is abnormally tall for one formed by the relatively low compressional stress and weak plate interface coupling we think occurs when thin, dense oceanic crust subducts – or slides under – thick continental crust.”

Geochemical and chronological data indicate the most recent Andean Mountain building phase began 40 million years ago, and the most significant crustal shortening – the process of mountain formation – started at the central-to-northern part of the present-day Andes and gradually expanded toward the south.

There is geologic evidence preserved along the Andean coast indicating that the southward expansion of Andean Mountain growth continues today, Liu said, but what is causing this migration and significant crustal deformation is still unclear.

Numerous studies show that higher erosion rates in the southern Andes, due to a warmer and wetter climate than in the north, correspond chronologically with evidence of an increased influx of sediment into the Andean Trench. The researchers said this sediment, which settled along the bottom of the trench along the subducting edge Nazca plate, may have acted as a lubricant atop the subducting plate by reducing compressional forces and resulting in lower mountains.

Liu’s team has taken this climatic-tectonic relationship a step further by uncovering the effect of a curious east-west trending feature known as the Juan Fernandez Ridge – a submerged volcanic hotspot chain that still exists today.

“Today, where the Juan Fernandez Ridge intersects the coast of Chile, it acts as a barrier to the northward-migrating sediments,” said Hu, the lead author of the study. “We hypothesize that this ridge has existed for millions of years, slowly migrating southward with the subducting Nazca Plate, starving the northern Andean Trench of sediments that helped increase the plate coupling and mountain building behind the migrating ridge.”

The team’s new model accounts for the impact of the Juan Fernandez Ridge on sediment transport through time.

“When we use our model to reverse time and reconstruct the subduction history of the Nazca Plate in 3D space, the effects of including the Juan Fernandez Ridge correspond remarkably well with geologic features we see in the Andes today,” Hu said.

The model has yet to be tested with the extensive range of hypotheses that exist for the formation of the Andes Mountains – some of which include incredibly complex plate subduction geometries, the study reports. 

“This study is a critical step forward to have the ability to quantitatively link climate and tectonics – something not well represented in the past studies,” Liu said.  

The National Science Foundation, the National Natural Science Foundation of China and the Center for Computational Science and Engineering at the Southern University of Science and Technology supported this study.

Editor’s notes:

To reach Jiashun Ju, email hujs@sustech.edu.cn.

To reach Lijun Liu, call 217-300-0378; email ljliu@illinois.edu.

The paper “Southward expanding plate coupling due to variation in sediment subduction as a cause of Andean growth” is available online and from the U. of I. News Bureau. DOI: 10.1038/s41467-021-27518-8.


JOURNAL

Nature Communications

DOI

10.1038/s41467-021-27518-8 

METHOD OF RESEARCH

Computational simulation/modeling

SUBJECT OF RESEARCH

Not applicable

ARTICLE TITLE

Southward expanding plate coupling due to variation in sediment subduction as a cause of Andean growth

ARTICLE PUBLICATION DATE

14-Dec-2021

COI STATEMENT

The authors declare that they have no competing interests.

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Ron Long
December 15, 2021 2:11 am

As a geologist that has worked in the Andes Mountains, at elevations up to 18,000 feet), and who now lives in Argentina, with a view of the 5th highest volcano in the world (Tupangato, at more than 20,000 feet), I find this speculation about sediments lubricating subduction zones to be no more than a small part of the very complex factors involved in formation of the Andes. The Himalaya Mountains, where Mt. Everest is, are not due to subduction but to plate collision. This report should be about two paragraphs in a book about the geology of the Andes.

John Tillman
Reply to  Ron Long
December 15, 2021 4:37 am

Friends visiting me in Chile are surprised to learn that Mt. Aconcagua, highest mountain on Earth outside a restricted region of Asia, is not a volcano.

Juan Fernandez ridge points roughly in the direction of Aconcagua, south of which occurs the Southern Andean Volcanic Zone, one of four such zones in the Andes. Others lie in Meso-America, the Cascades and Alaska.

Tupungato is among, if not the most, northerly of the Southern Zone volcanoes.

Last edited 1 month ago by John Tillman
John Tillman
Reply to  John Tillman
December 15, 2021 4:56 am

The Pacific coast of Antarctica is also a volcanic zone, lying with the others on the Ring of Fire. (I know the Southern Ocean is now considered separate, but for volcanic purposes, Antarctica has a Pacific coast.)

Last edited 1 month ago by John Tillman
Duane
Reply to  Ron Long
December 15, 2021 4:55 am

You are creating a straw man argument. The authors of this study never claimed that their theory fully explained the development of the Andes chain. They combined common sense – i.e., that erosional process are greatly affected by climate – and observations about the effects of the transverse ridge that interrupts sediment transport due to ocean currents, with known facts about plate tectonics. Their theory may not be correct, but your tut-tutting and snif-sniffing about their paper is not science, but ignorant dismissal.

Come up with reasons why their theory is wrong, stop it with the straw man arguments.

Scissor
Reply to  Duane
December 15, 2021 5:19 am

I anticipated that they were going to blame the taller than predicted Andes on climate change. Pleasantly surprised.

Furthermore, it appears that their understanding of climate is rational. Progress.

mcswell
Reply to  Scissor
December 15, 2021 6:36 am

Climate, not climate change. This is over a period of tens of millions of years, and there is no link implied to present-day climate change or even present-day climate.

Ron Long
Reply to  mcswell
December 15, 2021 7:10 am

mcswell, the last two surveys of the height of Aconcagua show a 9 foot increase. How will they work this into climate change? However they do it will be a new science invention.

Bill Powers
Reply to  Ron Long
December 15, 2021 7:45 am

…a new science fiction invention. Science Fiction = “The Science”

Not a methodology but a religion.

MarkW
Reply to  Ron Long
December 15, 2021 8:05 am

Obviously, since the world has gotten warmer, the rocks are expanding. /sarc

Last edited 1 month ago by MarkW
To bed B
Reply to  Ron Long
December 15, 2021 10:59 pm

Can we just appreciate the lack of a spurious canary-in-the-coal-mine paragraph without bringing climate change up?

commieBob
Reply to  Duane
December 15, 2021 5:49 am

He doesn’t say it’s wrong. He just doesn’t believe it’s as important as the authors do.

The support for the authors’ theory is models. ‘Nuff said.

If I were looking for evidence that lubrication was a big factor, I would look at the record of earthquakes. Lubrication would mean that stresses would be less likely to build up and suddenly release as earthquakes.

Ron Long
Reply to  Duane
December 15, 2021 7:07 am

Duane, I allowed for their report to be included in a book about the Andes, just not an important part. The Andes are the product of plate collision, with episodes of subduction and collision/obduction. Cerro Aconcagua is composed of Mesozoic marine sedimentary rocks, which shows vertical movement to current height, about 7,000 meters of vertical movement. Interspersed with the fold and thrust marine sedimentary rocks are many volcanoes, around ten of which are the tallest in the world. The impact of a hotspot/rift, and there are several, is worth no more than two paragraphs in the book, in that even if their theory about lubricating and blocks thereof sediments going down a subduction zone is correct, it is a very trivial part of the story. Sniffing?

Red94ViperRT10
Reply to  Ron Long
December 15, 2021 10:01 am

It seems a little more significant than that. What I understand is some “constant” in the models may not be constant at all, it may vary with the amount of available sediment, or…?

Ron Long
Reply to  Red94ViperRT10
December 15, 2021 11:16 am

Red94ViperRT10, the critical issue here is subduction versus collision/obduction. The volcanic arc is produced by subduction. The majority of the Andes, and all of the highest parts, is produced by collision and obduction. The Andes are elevated by folding and over-thrusting, the same as Everest. When you add in the volcanic arc, a small but impressive part of the Andes, you start to speculate about hydrous sediment top load on the subducting plate maybe having some lubricating properties, and if so, what is the observable effect? 2 paragraphs.

Michael S. Kelly
Reply to  Ron Long
December 16, 2021 2:02 am

Before we got together, my wife hiked the Andes. I, however, never hiked more than the Amos’s in Harlem, New York City (elevation 26 feet).

Dean
December 15, 2021 2:16 am

Puzzled for decades over differences between what the model says and what is actually observed?

Take a leaf out of the climate science model and just adjust the heights of the mountains down a bit so it fits with the model.

Should have only take these damn geos about 5 minutes to do this.

Duane
Reply to  Dean
December 15, 2021 4:52 am

Dude – read the damned post. This is not about a climate modeling exercise … it is a reasonably supported geologic theory on how and why the southern Andes are not as tall as the northern Andes.

Sediment transport is a critical element in all sorts of geologic processes, and climate clearly affects sediment transport, all of which is accomplished via water flows and winds (mostly the former).

Dean
Reply to  Duane
December 15, 2021 11:39 pm

Whoosh

Gregory F Lane
Reply to  Duane
December 16, 2021 3:14 am

I am going to the town of Vilcabamba in Ecuador on Christmas Eve. It is very close to Chimbaraazo Volcano (20,600′) … the interesting story we’re reading is that due to the Earth’s “bulge” at the Equator, Chimbarazo’s top is actually closer to the sun than is the summit of Everest. This true Ron Long?

Geoff Sherrington
Reply to  Dean
December 15, 2021 5:13 pm

Dean,
We geos do not take kindly to adjustment of data.
Somebody has to maintain standards. Geoff S

Dean
Reply to  Geoff Sherrington
December 15, 2021 11:40 pm

Geoff, as a mining engineer I have been exposed to geos for nearly 40 years!!

December 15, 2021 2:34 am

The team’s new model accounts for the impact of the Juan Fernandez Ridge on sediment transport through time.

A sediment starved basin is a sedimentary system / tectonic barrier relationship that has zero/zip/zich/nada to do with climate. But hey let’s get the publication/magic money-tree weasel word in there somewhere.

Duane
Reply to  Philip Mulholland.
December 15, 2021 4:48 am

You can’t say that. The postulated process is that the warmer wetter areas to the south of the tallest mountains produce more sediment from erosion – which is indisputably the case – and that the sediment acts as a lubricant on top of the subducting plate thus affecting the resulting height of the Andes Mountains – which is disputable, but certainly not ridiculous.

So climate clearly has at least a potential effect on how plate tectonics functions.

Erosion of landforms is clearly a contributor to the steady but slow rise in sea level since the end of the last glaciation. More sediment transport to the oceans results in a higher sea level. And clearly there is not much sediment transport when the climate is dry and cold, and particularly in the humongous areas in the northern hemisphere covered with a 2 km thick ice sheet, thus hindering the effect of sediment transport on sea level.

fretslider
Reply to  Duane
December 15, 2021 6:54 am

You can’t say that. “

A Freudian censorship slip? It does look like it.

Reply to  Duane
December 15, 2021 9:13 am

Duane,
The issue is the presence of a sediment starved basin. The last time I looked at a map of South America the continental fragment appears to narrow towards the south, so I suggest that the height of the Andes needs to be normalised against the width of the continental fragment before considering the issues of erosion and sediment distribution.

mcswell
Reply to  Philip Mulholland.
December 15, 2021 6:39 am

Like Duane said: how do you think sediment gets into a sedimentary basin? Erosion, obviously. And how does erosion happen? A vertical difference (not much erosion in flat land) plus wind, ice, or water, or some combination of those. And what controls wind, ice and water? Climate.

Just because you don’t believe in climate change doesn’t mean climate does nothing.

Tom Abbott
Reply to  mcswell
December 15, 2021 7:31 am

Climate change is an ambiguous description, which causes much confusion.

Duane
Reply to  Tom Abbott
December 15, 2021 8:40 am

Only idiots don’t believe the climate does not change, has not always changed, and always will change. The only argument is over what causes climate change – natural or man made. In this particular paper that we’re commenting on, they did not attribute the observation that the southern Andes are lower than the norther Andes to “climate change” but rather to the prevailing climate in South America wherein the further south, the more precipitation and therefore more sedimentation

Reply to  Duane
December 15, 2021 9:56 am

Duane,
That the Andes are lower in the south due to climate is an assumption. A structural explanation is more consistent with the overall plate tectonics.

ATheoK
Reply to  Duane
December 17, 2021 6:31 pm

Only idiots don’t believe the climate does not change, has not always changed”

Que?
Don’t believe the climate does not change?
“has not always changed”?

Appears to be conflict in the negatives.

Reply to  mcswell
December 15, 2021 9:47 am

how do you think sediment gets into a sedimentary basin? Erosion, obviously.

The issue is submarine sediment transport and the presence of a tectonic barrier leading to the formation of a sediment starved basin.

Just because you don’t believe in climate change doesn’t mean climate does nothing.

Science is not a belief system.

John Tillman
Reply to  mcswell
December 15, 2021 2:16 pm

Yes. This is “climate” in its original meaning, ie variations geographically. The Valdivian rain forest has a climate very different from the Atacama Desert.

RMoore
December 15, 2021 3:19 am

Seems to cause flooding in Central Valley of California, too.

Ed Zuiderwijk
December 15, 2021 4:57 am

Hang on. The range is too tall and that is due to sediments lowering the height of the mountains? How does that work?

DonK
Reply to  Ed Zuiderwijk
December 15, 2021 8:05 am

Ed, That’s a reasonable question. I’m pretty sure they are discussing sediment flow off the mountains into an offshore trench (subduction zone) in the Pacific which they hypothesize to be blocked by the (submerged) Juan Fernandez ridge which prevents the sediment from migrating North. That, in turn, somehow encourages higher mountains than occur in similar settings elsewhere without that blocking. If so, they could be a lot clearer.

And I, at least, don’t find their concept very persuasive. But I’m not a whiz at geology

Red94ViperRT10
Reply to  DonK
December 15, 2021 10:08 am

Well, we, or at least I, haven’t read the paper. Their theory could be wrong, but it makes logical sense. Now propose an experiment/investigation that could disprove it? That’s how this should work.

ATheoK
Reply to  Red94ViperRT10
December 17, 2021 6:36 pm

Nope!
They have to prove their concepts and theory.
Throwing ideas back and forth is not science. That is how marketing works.

fretslider
December 15, 2021 5:30 am

higher erosion rates in the southern Andes, due to a warmer and wetter climate than in the north”

That needed a climate model? Some say it’s independent of climate

“…data on topographic and fluvial relief, variability of rainfall and discharge, and crustal seismicity suggest that the along-strike pattern of erosion rates in the southern Central Andes is largely independent of climate, but closely relates to the N–S distribution of shallow crustal seismicity and diachronous surface uplift. “

Tectonic control of erosion in the southern Central Andes

https://www.sciencedirect.com/science/article/abs/pii/S0012821X17306404

Thomas Gasloli
December 15, 2021 8:10 am

”the central portion is abnormally tall”

Says who? The mountains are real, it is your idea of normal that must be wrong.

Geoff Sherrington
Reply to  Thomas Gasloli
December 15, 2021 5:20 pm

Thomas,
Thank you for injecting this pertinent observation.
Maybe the authors felt that some practical consequence arose from their observation.
In truth, the few hundred years we have been measuring mountain elevations is a trivial part of the tens of millions of years that plate tectonics are said to be operating in their present form of understanding.
Given that these processes might have continued for hundreds of millions of years, one has to enter the largely unexplored territory of why subduction has not by now consumed all of the material available to get pushed under continents.
Recycling?
Geoff S

Vuk
December 15, 2021 8:29 am

Let me first declare my interest in the matter.
My offspring is a geologist, but I have no more than most superficial knowledge of geology. I know of Gondwana, Laurasia and Pangea.
However, this problem of Andes mountains height could have an explanation in what is happening in the present day geological events and in final analysis could be even related to the Earth’s climate change.
We know that the geographical location of what is the present S. America has moved all over the place.
We also know that in its past there was snowball earth, i.e. that the most of the land mass was covered in hundreds of meters if not km of ice.
If at the point when the ice started melting South America had longitudinal rather than present day latitudinal orientation and that the relevant land mass was nearest to the equator, ice would melt there first and faster than for the rest. This would cause isostatic uplift, which may have been further enhanced by tectonic plates collision, during the final formation of the S. American ‘continent.
(abundance of down votes expected)

Terry
December 15, 2021 9:06 am

If I can just work the word climate into my paper the money trail is astounding!

Peta of Newark
December 15, 2021 9:07 am

Quote:”higher erosion rates in the southern Andes, due to a warmer and wetter climate than in the north”
Why climate – why not just different rock types?

Quote:”The researchers said this sediment, which settled along the bottom of the trench along the subducting edge Nazca plate, may have acted as a lubricant

Again – Rock Types (turning blind eye to the weasel words for a mo’)

  • If this stuff was/is clay, it would be rather slippery – likewise polished and round-grained desert sand
  • Otherwise it would be what you might make Sandpaper or Emery Cloth out of, things not especially noted for slipperiness.
Walter Sobchak
December 15, 2021 9:29 am

Warning this is a playing with computer models. Sort of like Fortnite but not as much fun for kids.

Mike Dubrasich
December 15, 2021 11:28 am

Some observations:

The mountains alter the climate. The climate (temps, rainfall, etc.) at the top is much different than at the base. Besides weather data, the presence of equatorial alpine tundra (called páramo) is ample evidence of the Andean mountains affecting climate.

Paleo páramo floras suggest the high elevations occurred no earlier than the Late Pliocene ~1.7 mya. The Andes may have started rising 40 mya, but they didn’t get so tall until geologically recently.

Topography more than climate controls erosion. Erosion is due to high and growing mountains; flat plains do not erode so readily or voluminously.

The alleged “lubrication” of subducting plates by variable sediments is highly theoretical. Numerous other factors such as fault blocks and plate folding affect uplift rates. Sediment layers are relatively thin veneers on oceanic plates.

Clyde Spencer
December 15, 2021 11:40 am

… the most recent Andean Mountain building phase began 40 million years ago, and the most significant crustal shortening – the process of mountain formation – started at the central-to-northern part of the present-day Andes and gradually expanded toward the south. … There is geologic evidence preserved along the Andean coast indicating that the southward expansion of Andean Mountain growth continues today,

OK, doesn’t this mean that with a later starting date that the southern end hasn’t yet caught up with the initiation point?

Numerous studies show that higher erosion rates in the southern Andes, due to a warmer and wetter climate than in the north, …

This is a simplistic description. Water and warmth favor chemical weathering, whereas cold and higher stream gradients favor mechanical weathering and erosion. That is, frost wedging, glacial scouring, and streams with higher water velocity. The grain size and kinds of minerals in the rocks influence their susceptibility to mechanical and chemical weathering. Inasmuch as the descriptions are simplistic, I suspect that the models are similarly too simplistic.

It might just be that the southern Andes haven’t been growing as long.

MarkW
December 15, 2021 12:21 pm

First time I read that title, I was trying to figure out what Teutonic models were doing in the Andes.

John Tillman
Reply to  MarkW
December 15, 2021 4:16 pm

South America has plenty of Teutonic models. See Gisele Buendchen.

Anton Eagle
December 16, 2021 8:48 am

The Andes Mountains are much taller than plate tectonic theories predict they should be…”

Occam’s Razor…

…if reality doesn’t match your theory, then your theory is probably wrong.

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