UNIVERSITY OF ILLINOIS AT URBANA-CHAMPAIGN, NEWS BUREAU
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 Hu, Illinois 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
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.
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.
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.
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.)
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.
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.
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.
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.
…a new science fiction invention. Science Fiction = “The Science”
Not a methodology but a religion.
Obviously, since the world has gotten warmer, the rocks are expanding. /sarc
Can we just appreciate the lack of a spurious canary-in-the-coal-mine paragraph without bringing climate change up?
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.
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?
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…?
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.
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).
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.
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).
Whoosh
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?
Dean,
We geos do not take kindly to adjustment of data.
Somebody has to maintain standards. Geoff S
Geoff, as a mining engineer I have been exposed to geos for nearly 40 years!!
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.
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.
“You can’t say that. “
A Freudian censorship slip? It does look like it.
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.
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.
Climate change is an ambiguous description, which causes much confusion.
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
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.
Que?
Don’t believe the climate does not change?
“has not always changed”?
Appears to be conflict in the negatives.
The issue is submarine sediment transport and the presence of a tectonic barrier leading to the formation of a sediment starved basin.
Science is not a belief system.
Yes. This is “climate” in its original meaning, ie variations geographically. The Valdivian rain forest has a climate very different from the Atacama Desert.
Seems to cause flooding in Central Valley of California, too.
Hang on. The range is too tall and that is due to sediments lowering the height of the mountains? How does that work?
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
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.
Nope!
They have to prove their concepts and theory.
Throwing ideas back and forth is not science. That is how marketing works.
“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
”the central portion is abnormally tall”
Says who? The mountains are real, it is your idea of normal that must be wrong.
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
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)
If I can just work the word climate into my paper the money trail is astounding!
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’)
Warning this is a playing with computer models. Sort of like Fortnite but not as much fun for kids.
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.
OK, doesn’t this mean that with a later starting date that the southern end hasn’t yet caught up with the initiation point?
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.
First time I read that title, I was trying to figure out what Teutonic models were doing in the Andes.
South America has plenty of Teutonic models. See Gisele Buendchen.
“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.