Subduction Denialism, Part 1: The Backstory
I recently had an exchange with some Earth hypothesizers* on a blog that claims convergent plate boundaries are a “myth” and in fact the Earth has expanded significantly (about double the size it was ~200 m.y. ago). The post in question can be found here and has all the information you need to learn about the expanding Earth hypothesis.
Here’s the gist: since subduction doesn’t occur but crustal generation at spreading centers does, the result is net growth of the Earth. There is all sorts of theoretical evidence for expansion as argued by subduction denialists — geometric constraints, that the universe is also expanding, lack of Earth-like plate tectonics on other planetary bodies, claims that subduction violates fundamental laws of physics, and — every denialists favorite — emphasizing and amplifying any and every uncertainty or anomaly in plate tectonic theory^.
I’m really not that interested in discussing speculative theoretical constraints. I’m also not interested in arguing about whether or not the size of the Earth has remained exactly constant (to some unmentioned level of precision). There might be some interesting discussions to be had in this regard and perhaps a topic for the future, but for these posts I will focus on the claim that plate convergence does not occur. This is a specific claim that we can address by investigating observable patterns. Theoretical discussions and “thought experiments” can indeed be entertaining and, in some cases, intellectually rewarding — but for this specific claim I’d rather stick to data and observations.
The specific context for my posts is in the comment thread on that blog. It’s quite long and has several off-topic tangent discussions, so I will provide you the highlights:
(1) After reading the contents of the post, I inquired about the Nazca plate specifically (to help focus discussion) and the blog owner, called ‘Oil Is Mastery’ (whom I will hereafter refer to as OIM and make his comments this color), replied by saying:
The Nazca plate cannot possibly be subducting as zircon data shows conclusively that it is spreading in all directions
OIM is referring to this map from NOAA’s NGDC website showing ages of oceanic crust. I replied (my comments shown in this color):
The Nazca plate is older (the yellowish color on the NGDC map) right near the ‘armpit’ of the South American continent. If it was “spreading in all directions” … then where is the eastern divergent boundary?
OIM then replied by saying:
The eastern so-called “divergent boundary” of the Nazca Plate is the Andes Mountain Range.
Interesting. The Andes Mountain Range is a spreading center? Hmm. I was confused so I asked for clarification. At first I got some other stats, so I asked again, and then OIM proclaimed his position clearly and succinctly:
Of course it [Nazca and South American plate boundary] is a divergent boundary since those are the only kind that exist. Convergence and subduction are myths.
Emphasis mine. I then asked:
Can you draw a sketch cross section showing that spreading center in relation to the Chile-Peru trench and the Andes? I’m interested in how fold-thrust belts form w/out compression. Thanks.
OIM was never to be heard from again on that thread — I assume that means he either can’t or is unwilling to expand on his Andes divergent boundary hypothesis. He did, however, go on to post about his calculations proving increase in Earth’s diameter since the ancient Greeks, showing biogeographical evidence that subduction does not occur, and a rather bizarre conflation of fascism and plate tectonics (?).
(2) It is at this point that I then engaged with a loyal follower and prolific commenter on OIM’s blog … a commenter named ‘Anaconda’. Anaconda’s comments on OIM are typically quite lengthy and comprehensive. I’ve sparred with Anaconda in the past on a different topic, but that’s a story for another day.
To his credit, Anaconda initiated the discussion with a short review of some of the information on Wikipedia’s page on subduction, which you can read for yourself. Wikipedia may be useful for trivia, but is more often than not unsatisfying when it comes to scientific topics. But, it does typically come up first in searches and can sometimes be a good place to start. After that brief review Anaconda started his assault on plate convergence by saying (I’ll put Anaconda’s comments in this color):
An interesting note is that the Wikipedia entry for subduction offers little scientific evidence in its favor.
Oh, there is a long description, but these descriptions are based on the presumption that subduction does exist.
It seems to be held “self evident” that subduction occurs.
So, it’s interesting that the best scientific evidence for subduction is not listed under subduction, itself, but as a counter-argument to Expanding Earth theory.
In reponse to this, I replied:
In many scientific ideas, it’s difficult to point to a single, or even a handful, of papers that provide all the evidence. The evidence comes from the totality of decades of work. The very fact that there is so much work done makes it challenging to show the work.
In that spirit I’ve listed below enough references about subduction to give you a taste (i.e., this is not a “complete” list). These include geophysical (especially seismic tomography and seismologic), geochemical, petrological, mapping/observational, and experimental studies. Not all, but many, of the Earth’s subduction zones are covered in this list. At the end I’ve also included a list of textbooks … these are the best place to start. As bonus, I’ve included some relevant websites.
I’m not here to defend each and every one of these studies … Take some time and familiarize yourself with the literature and the concepts. There’s a wealth of data presented in these papers that need reinterpreation and re-evaluation if you disagree with their conclusions.
I won’t reproduce the list here, but you can see it in my comment on that thread (in case it gets deleted, I’ve reproduced the list here). It includes nearly 70 peer-reviewed papers, five textbooks, and several websites. At first, Anaconda appreciated this list … later he dismissed it as a “laundry list” and was upset that he didn’t have access, which I’ll discuss more below.
(3) The thread went off-topic for a few comments, but then came back to subduction. Earlier in the thread I asked OIM how fold-thrust belts (i.e., large-scale compressional tectonics) develop in the absence of convergence. I never received and answer from OIM, but Anaconda stated:
An issue has been brought forth that one must explain the presence of thrust-fold belts without subduction for Expanding Earth theory to have any merit at all.
And among the list [Wikipedia’s list of fold-thrust belts] are many areas that are not and never have been associated with subduction.
So the idea that without subduction zones you can’t have thrust-fold belts is inaccurate.
I asked Anaconda which fold-thrust belts from that list were not or were never associated with subduction zones, to which he responded with a list of major orogenic belts from the North American Cordillera. I honestly don’t know as much about the geology of mountains in Mexico or Canada — just my own location bias. If others do, please comment below. But, the “Wyoming-Utah Thrustbelt”, called the Sevier in the literature, is Cretaceous in age and associated with the convergent western margin of the continent at the time (which also produced the now-partially-exhumed magmatic arc of the Sierra Nevada).
The Rocky Mountains are on this list, although I’ve never thought of them as a typical fold-thrust belt, but I suppose they can be considered as such within this very general context. The Rockies are a bit younger, involve thick- vs. thin-skinned deformation, high-angle reverse faults, basement uplifts, reactivation and/or inversion of older tectonic features, and are interpreted to be a result of a shallowing of the subducting slab. The details of this interpretation are still hotly debated and more work is always being done.
But, this post isn’t about explaining every detail of these fold-thrust belts. There are entire books and entire series of books written on the subject (GSA’s DNAG series from the 1980s comes to mind). The fundamental question in my mind is how compressional deformation of rocks over large regions (i.e., reverse faulting, thrust faulting, folding) can even occur without convergence? If there is only divergence and extension, how is something like this, for example, produced? What is the mechanism?
When Anaconda wondered what geologists thought the mechanism for orogenesis (i.e., mountain building) was pre-plate tectonics and I told him it was geosynclinal theory, to which he replied:
Briefly, [geosynclinal theory] held that vertical crustal movement was primarily responsible for orogeny development.
Do I hear echoes of an expanding Earth?
Huh? And then:
Yet, each and every Geosynclinal theory paper was cast aside, never the less. Apparently today’s geologists don’t feel the need evaluate each and every paper because they are derivative of a theory today’s geologists think is wrong.
Wrong. The papers weren’t cast aside, the idea was. The sign of a good paper is a clear separation of data, observations, and measurements from the interpretation and implications. When plate tectonics concepts were being postulated and discussed in the literature and at conferences in the 1950s and 1960s researchers went back to these old papers and re-evaluated them. They revisited the old datasets and saw them in a different light. In many cases, new papers were written. As for the suggestion that modern geologists don’t evaluate old papers, Anaconda couldn’t be more wrong. Look at the list of references for papers that deal with surface geology and I bet that the majority of them have a reference to a pre-plate tectonic paper or, in many cases, a published geologic map. For my master’s degree, I leaned heavily on P.B. King’s classic 1940s work on west Texas geology. A lot of his ideas about how the patterns came about have been revised over the years, but the documentation of the patterns themselves are robust and everlasting. In other words, I was able to use his data and observations to support a different interpretation.
So, do I think Anaconda (or any other subduction denialist) needs to debunk each and every single paper in the literature that documents compressional features? No, of course not. But, they should be able to explain the data and observations presented in these papers within the context of their mechanism for their formation.
(4) Okay … now on to what dominated the remainder of the thread and what is the focus of Part 3 in this series — the Cascadia subduction zone (Pacific Northwest of the United States).
In addition to fold-thrust belts that Anaconda thought were unassociated with convergence, he also wondered about trenches:
The Cascadia Subduction Zone doesn’t have a trench, other alleged subduction zones have a trench.
The suggestion being that since not all subduction zones have a distinct physiographic trench expressed on the sea floor (i.e., linear trough-like bathymetric depression between the subducting plate and the overriding plate) then there must be something erroneous about the whole concept. For the time being, let’s put aside the question of how trenches develop in some places and not in others on an Earth with no convergence … we’ll let the subduction denialists explain that (as they should). But, this is a great question — I responded:
Cascadia trench is over-filled with sediment, does not have sea-floor expression … also has significant accretionary complex.
That is my unedited comment … in retrospect, it’s incomplete and oversimplified. I thought it required more explanation so I offered to do some research on the particular topic of the Cascadia subduction zone, especially with respect to sedimentation, and put together a post (which you are reading right now). Anaconda agreed that would be a good idea:
Yes, the Cascadia Subduction Zone is a good place to start.
But a bit later he got peeved at me when I suggested he conduct some of his own research in the meantime. With regards to not having internet access to some journals, he stated:
Laundry lists of papers that aren’t available on the internet are not helpful. One must also be careful that laundry lists are not a substitute for actually presenting a case.
Lists without ready access for the reader tend to be a substitute for substantive scientific argument.
We, unwashed groundlings patiently await your return from the great ivory tower. Master of the academy have forbearance, not all the little people of the internet have access to the great libraries hosted in the hollowed halls of academia.
We humbly await your discerning directions to the great trench of Cascadia.
Your most obedient internet groundling,
Anaconda of the little people
Clever. A bit of a persecution complex I think … as if “we” are keeping the truth from “them” … very conspiratorial. Open access is a much talked about issue and continues to be debated in academia. That is beyond the scope of this post but, in this case, it would be valuable if more peer-reviewed articles were freely and openly available to the public.
Finally, I told Anaconda multiple times that it would take some time to do this — real research takes a lot of work and I’ve got other things going on, so I end up working on this stuff bit by bit in the evenings:
This may not be posted for another week or two due to other things going on in my life…
Less than 90 minutes later, Anaconda replied:
I’m still patiently waiting for a paper demonstrating a “trench overfilled w/ sediment”
First of all — I said a week or two, not an hour or two. Secondly, even though earlier in the thread I described how it’s often difficult to point to a single paper for specific questions, Anaconda now twists the words as if I claimed I was going to give him a single paper. Typically, researchers need to spend the time searching and reading what’s already been done and do some synthesis on their own. We all know this.
Well, sorry Anaconda … I never claimed there would be a single paper neatly addressing the topic on hand. Compiling and synthesizing existing research requires referring to numerous studies. I will, however, try my best to high-grade the list to the most relevant and not just inundate you with a long list.
* I‘m not sure what else to call them, they aren’t scientists (by their own admission) – I don’t know, perhaps “enthusiasts”?
^ I’m not saying that anomalous observations that challenge our understanding shouldn’t be investigated … in fact, quite the opposite. That’s what makes an interesting research project and that’s how science progresses. But the subduction denialists aren’t doing any actual analysis — they don’t take it the next step and propose mechanisms SPECIFIC TO THAT DATA — they generalize and claim that the anomaly once and for all disproves plate tectonics and, by default, supports their hypothesis.