Yellowstone, Newberry, & lithospheric thickness
Last night at the year's first meeting of the Geological Society of Washington, Derek Schutt of the National Science Foundation gave a talk entitled "The Yellowstone hotspot and how it got that way." Derek mainly focused on the evidence for there indeed being a mantle plume under Yellowstone, possibly caused by the destabilization of the core-mantle boundary layer when subducted Farallon lithosphere sank down to the bottom of the mantle.But the thing that he said that really caught my attention has to do with one of the weird aspects of Yellowstone. Yes, to the southwest of Yellowstone's modern caldera is the Snake River Plain, a series of ancient calderas which overlap one another, getting older and older the further to the southwest you travel, until you get to the oldest one at 17 Ma. That part of it looks pretty much like a classic hotspot track, a la Hawaii. But there's a weird aspect to Yellowstone that doesn't fit the traditional hotspot stereotype: starting at that same 17 Ma caldera/"rift," another series of eruptions propagated away to the west/northwest, including the voluminous Columbia River flood basalts and leading to the Newberry Caldera, which Derek described as "the largest basalt dome in the United States." (See the map above, from Schutt's collaborators Gene Humphreys and John Hernlund.)
So, the question is: What's up with that? It kind of looks like two hotspots heading in different directions. Is this linked to the stretching of the western U.S. via the Basin and Range? Derek pitched another idea, which is based on the thickness of the lithosphere (crust + uppermost mantle). His idea is summarized in the diagram below, which I drew this morning based on my rough sketch of the diagram he put up on the screen at GSW last night. (My apologies to Derek if I've gotten any of the details wrong.)
The basic idea is that the North American lithosphere is thicker to the east, under Yellowstone, which Derek (admittedly loosely) defined as the Wyoming Craton. He suggested that the lithosphere was thinner to the west under Newberry and the Columbia River Plateau, since those were accreted terranes added to North America during the Mesozoic. The mantle plume came up underneath the thicker lithosphere, and punched a hole through right above it (Yellowstone), but part of the plume slid upwards and westwards towards the thinner lithosphere, where it broke through in multiple locations, producing first the Columbia River flood basalts and then later the eruptions culminating in Newberry. I like the idea, and the picture Derek showed is elegant. I can picture this happening, if the suggested lithosphere thicknesses are true. The question is, are they? I don't know enough about that region of the country (yet) to assess the validity of this model. I wanted to use this blog post to share the notion, and see what people think. If you're familiar with that area, please clue me in to the details.
An additional difference between Yellowstone and Columbia River/Newberry (CR/N) is that Yellowstone's magma is rhyolitic and CR/N's magma is basaltic. Rhyolitic magma is a lot more explosive than basalt, and indeed Yellowstone's eruptions have been among the most powerful observed in the geologic record. (The Huckleberry Ridge tuff, which erupted from Yellowstone 2.1 Ma, is deposited over something like half of the Lower 48!) CR/N, on the other hand, appear to be gentler eruptions more like Hawaii's oozing of basalt. I suppose this too can be explained by Derek's model: partial melting of the more-felsic crust under Yellowstone (as hot plume magma heats that thicker slab of continental crust), but a shallower Moho to the west, producing mafic magma a shorter vertical distance from the surface.
PS -I must also add that it was great to meet Tuff Cookie of Magma Cum Laude at the meeting. If there had been one more of us there, it could almost have been a geology blogger's conference.
Labels: gsw, yellowstone
4 Comments:
Aw man! I would have loved to have heard that talk, but I definitely don't in the DC area anymore.
I've been curious about the why the Yellowstone Caldera and Columbia Flood Basalts are the way they are since I knew they existed. I got into a long discussion with one of my professors about how the same system could produce huge amounts of basaltic magma in one place and an enormous rhyolitic caldera in another. He seems to be in the camp that believes a mantle plume is responsible, and seemingly in line with what Schutt presented, we thought that the difference between basalt in one place and rhyolite could be related to lithosphere thickness and the locations existing weaknesses. The V-shaped line of calderas didn't come up in our discussion, though, and I think the idea of the plume breaking through in several places at once is very interesting. I'll be curious to see what additional information Schutt's research in this area turns up.
Has the paper Schutt presented been formally published yet? If so, do you know where I'd be able to find it? I'd like to read it, and to pass it on to the professor with which I had the discussion about Yellowstone. Thanks!
Hi Julian,
It looks like Schutt's been shopping the idea around for a while based on a quick online search. I had to use Google Scholar, http://scholar.google.com/scholar?q=schutt+yellowstone
since Geobase is apparently down this morning. Regardless: Schutt didn't mention a specific paper but he did mention a host of collaborators. I haven't read anything peer-reviewed written by him yet.
Hi Everyone,
This is Derek Schutt. Drop me a line if you have any questions. Regarding the relationship of the CRBs to Yellowstone, a lot of what I mentioned is brought up by Jordan and Grunder: http://www.usd.edu/~Brennan.Jordan/
My work has primarily been on the Snake River Plain and Yellowstone. For peer-reviewed publications, check out: http://welcome.warnercnr.colostate.edu/
~schutt/CSU_web/pubs.htm
I'm glad to send you PDFs, feel free to
email me: Derek.Schutt_at_Colostate.edu
Also, check out Ken Dueker (U of WY), and Bob Smith's (U of UT) web sites.
A little clarification- Newberry is an explosive silicic volcano; not quite sure what a "basalt dome" is. The high lava plains (the younging westward eruptions across OR) are defined by a time-transgressive series of silicic eruptive centers, ala the SRP, culminating at Newberry. Besides the silicics erupted at Newberry, some pretty voluminous rhyolitic magmas were erupted from other HLP calderas- e.g. the Rattlesnake tuff. Also, like the SRP, there are young basalts on the HLP but these generally post-date the HLP silicic activity at any given location. Read Jordan et al. for more details. Also, the crust is much thinner west of basically the Oregon-Idaho border; basalt petrology and other info suggest this... Callan & Julian, remember, there are some major age differences here too- <2 Ma for Yellowstone vs. the big slug of mafic-silicic activity that occurred ~17-14 Ma and this mid-Miocene activty was not just the flood basalts- there was a whole slug of accompanying silicic magmatism (on and off the craton) that occured simultaneously. McDermitt is the most famous of these silicic centers. Essentially, the volcanic and chronologic evidence suggests the plume or whatever initiated ~17 Ma centered around/along E Oregon, then ~12 Ma, you had the SRP and HLP volcanic progressions... I'd like to see more similar aged volcanic rocks around the greater YS-region (there are actually some in Jackson hole) to really make the case for the plume originating as Jordan et al (& Schutt) suggest..great topic though and i wish i would have seen the talk! Check out www.mantleplumes.org for more of the fun...
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