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Oily Pasts and Futures (book review)

Politics and industry make strange bedfellows.  Politics is often short-sighted, with most politicians locked in to the next election, or even the next round of polls, but multifaceted.  Industry, on the other hand, can look over longer timespans but is narrowly focused (“can” is not always “does”). You might hope that the pair could produce public policy that was both broad and longterm, but the reality seems to combine the worst characteristics of each.

Nowhere is this more evident than in peering into the future of oil. Mason Inman’s recent biography of M. King Hubbert, The Oracle of Oil (Amazon link), provides a nice reminder of this interaction from an earlier time. Hubbert’s views on oil, which were made with an eye towards a fully sustainable economy, conflicted with corporate and political motives. Corporations are in a specific business and like to hear that their future is bright, a disastrous approach when the future is changing (see Eastman Kodak’s fall as digital photography bankrupted their film business). Thus there is a tendency within a company to both develop rosy forecasts and believe them (the more pessimistic will tend to leave).  Politicians want happy news about tomorrow–Cassandras don’t tend to get elected. So what happens when unhappy predictions are made?

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My Science Crimes

In keeping with this end-of-the-year theme of what GG is doing wrong, some “crimes against science,” which, as Bob Sharp defined them years ago, was doing some work of interest to the broader community and then not publishing it. (Thankfully, these aren’t the more serious offenses in the expanded criminal ledger GG proposed awhile back).

Now this isn’t an uncommon occurrence: students graduate with thesis chapters not quite ready for publication and discover that life beyond grad school doesn’t provide rewards for getting that stuff into journals.  Some other times things just pile up enough that a paper isn’t completed when everything is handy, and it just gets harder to return to as time goes on.

So, in case anybody out there would benefit from some of this stuff, feel free to nudge GG to take some time and share, either informally or by actually publishing some of this.  And if nobody seems interested, well, then maybe not much of a criminal act :-). Most of these are in some kind of manuscript form (there is other stuff that didn’t even get that far).

  • Geologic map of the Alexander Hills and eastern China Lake basin. Yes, GG mapped while in grad school and actually handed over a copy of his map to Lauren Wright long ago, who included some of it in a never-published update to the SW Tecopa quad (now would be Tecopa 7.5″ quad map). A lot of cool stuff–probably the eastern end of the early Garlock Fault interacting with some low-angle, basin-bottom faults and a pre-China Lake basin history not evident in published maps.
  • Seismicity of the Hansel Valley region.  GG feel really bad about this, as there were a lot of coauthors on the 1983 experiment, which was one of the densest deployments of seismometers in an extending area.  The results are in GG’s PhD thesis but still might merit publication as the data indicates how a low-angle normal fault might interact with ongoing seismic deformation.
  •  Magnetostratigraphy and some additional paleomag in the Lake Mead region. A collaborator dropped out and so the baton was dropped after a single paper. Some of the data is visible here.
  • Paleomagnetic measurements in monoclines of the Colorado Plateau.  Joya Tetreault’s thesis has this; substantial vertical-axis rotations exist in some folds (the Grand Hogback being the most dramatic), though the sampling is far less than ideal and some structures seem to make little sense.
  • Paleomag and micropolar analysis of seismicity in the Coalinga area.  Also part of Tetreault’s thesis. The micropolar work seemed to capture the bending component of folding in the seismicity while the paleomag suggested San Andreas-parallel shear within the fold limbs.
  • Earthquakes in the southern Sierra located with the 1988 experiment. Jason Edwards, a CU BA graduate, did some of this work which was never carried farther. It seemed there were events under one of the Recent cinder cones in the s Golden Trout field as well as some deep events in the westernmost foothills of the southern Sierra.
  • Geophysics of Panamint Valley and the Ivanpah Valley areas.  These were datasets collected by the MIT Geophysics Course in 1987 and 1983, respectively.  Both valley present a major challenge because a large basement gravity gradient exists across these valleys, complicating interpretation.

This is all in addition to various half-done projects still seeming to be active as well as datasets that never were fully exploited (for instance, data from a mixed broadband/short period array at Harrisburg Flat in Death Valley plus some more scattered instruments near Dante’s View, or our inability to get anything sensible out of array recordings of deep local events under the northern end of New Zealand’s South Island).

Mapa Culpa

GG has been rather abrupt in some previous posts with some authors over choices made in making maps for publication, and some of the authors have been insulted, in part because GG seems to have mistaken a conscious choice for laziness or thoughtlessness. Its not like GG is free and clear on making mistakes, so today let’s review a few boo-boos of GG.

First up is one we discussed before, the use of gradient color:

LevandHm

Mantle topography from Vs model of Shen et al, from Levandowski et al. 2014.

GG was the thesis advisor and second author here, and there are two main problems.  One is the rainbow color map, which is widely panned for the challenges it places before those with some level of color blindness. [Alternate color schemes are nicely described here and you can test how images look to the color-blind here. The only good news for this figure is that a continuum of color is more decipherable than separated color blobs]. The other problem is that the colors are continuous.  Can you tell -2.2 from -2.6?  This probably would have been better with discrete color steps. But that’s probably not the complete answer:

This is from Jones et al., 1994, showing travel time residuals with a discrete color bar. On the left is the original, on the right as viewed by a red-blind viewer (as created by Coblis). While the Levandowski et al. image could be deciphered because of smoothly continuous colors, this figure becomes hopeless. (Plate 2 in Jones et al., 1994, is even worse, but GG can’t recover the original file to show this cleanly, and plate 3 is an utter disaster for red-green colorblind). There are similar examples in later tomography papers. Frankly, using some of the better diverging color maps out there would be a better practice.

But this post is inspired more by a comment made by Sara (Carena?) on an earlier snarky post: How about the projection used?   Read More…

The Schist-Melt Conundrum

One of the things that has gotten increasingly glaringly obvious is that there is a big problem lurking in the Mojave Desert. The problem, most simply, is that the dates of plutons in the Mojave overlap rather severely with the dates of emplacement of schists in the lower crust. Dating activity reported at the GSA meeting this past week included a bunch of 72-85 Ma intrusive rocks, mostly metaluminous plutonic rocks that seem likely to have had a mantle melt as a primary source, sitting above the area where the Rand Schist was supposedly being emplaced.  Just as bad for mega-flat slab advocates, the extent of these 70-something plutonic rocks is now extensive enough that it seems awfully hard to sneak in a big flat slab through the Mojave–and even if you do, it is coming in way too late to be starting the Laramide orogeny, which was already chunking along at this point.

So two questions: what is going on in the Mojave? and what are the broader implications inland?

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Dating Stumbles

So Paul Braterman was asking the other day about some advance knowledge of how the new infatuation with detrital zircons and HeFTy plots might be misread in some circles. This is really a question for a real card-carrying geochronologist, but GG will take a swing at it because he’s kind of worried a bit about this and is not staking out any particular terrain.

For the most part both of these are simple variants on classical age-dating techniques (uranium-lead dating and potassium-argon dating), and though rooted in geochronology, most of the applications are elsewhere (e.g., detrital zircons are mainly used as a means of identifying the sources (provenance) of clastic sedimentary rocks, while HeFTy (Helium-Fission Track analysis) is dominantly a means of assessing the thermal or unroofing history of some body of rock through application of multiple geochronometers). But they start pointing at things that could be misleading, so let’s look a bit more….

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The Age of Ages

Not so long ago, you would get a date (one) for some igneous unit.  And that was hard enough that you wouldn’t bother with two or three. Dates were so valuable one well-known scientist had an equally well-known safe to keep them in (we still live with a rule at GSA related to this fellow in that recording or photographing presentations is forbidden). Then there was recognition that some systems closed up shop at different temperatures than others.  So maybe you’d see a U-Pb date and a K-Ar date.  A few labs did this work, often under contract; you (the non-geochronologist) might wrap up a sample and send it on to be dated. Dates, while important, were just some numbers that were part of a geologic story.

Now, however, dates are everything (that, and chemical and isotropic analyses at the tiniest levels, which is a related outgrowth). It seems like more than half the talks at GSA involved dating detrital zircons, or dating zoning in zircons, or dating helium diffusing out of zircons. Dates are used to understand erosion, tectonics, stratigraphy, sedimentology, volcanology, paleoearthquakes, glacial action and more. Arguably this ability is utterly changing geomorphology and sedimentology and it seeps into other fields more slowly.

If you haven’t seen a pdf (probability distribution function, not portable document format) or a HEFTY thermal evolution-o-gram, you haven’t been in a geological talk in some time now.

And so it is about time for the revenge of the grumps.  Not GG so much as others.  For the broad application of these new techniques has excited most geologists, but history tells us that there will be a reckoning.  As GG watched lots of folks who have not themselves sat in front of an LA-ICPMS machine in their lives display plot ofter plot of geochronology-derived stuff, you sense that something will come along to threaten this grand promise.

This has always been the way of new techniques.  They appear, they are exciting and new, they are applied everywhere, and then discrepancies emerge. Look back in olden days and see how potassium-argon dating started; it took awhile for practitioners to recognize that sometimes crystals would lose argon and they got dates that were too young, or that certain materials would introduce an excess of argon from other minerals and a date would be too old. Some early results were discarded, the community identified situations when problems were likely to arise, and early over interpretations were scaled back.

There are hints of this already.  Conflicts between U-Th/He dating and some classic geologic constraints hints at some problems in some places. Some work in the past few years indicated that fission-track thermal histories relying on track length distributions were dependent on specific laboratory practices that are not uniform. Puzzling results are emerging in some sedimentological studies where things that simply cannot be seem to be. On occasion, dates seem backwards, with younger dates from systems that should have closed well before materials yielding older dates.

None of this is really a worry. It is the shake-out that is needed.  And as long as you keep in mind that there might be some landmines out there, the hazards are manageable. It is a kind of “trust, but verify” environment. But there will be reverses ahead, and some promising studies might turn out to be chimera. Don’t be surprised to see some papers saying that a certain technique is wrong when applied under certain conditions. But in the end, we will still come out with a host of tools well suited to consider geologic problems. The age of ages is upon us, like it or not.

How flat is your slab?

Somehow that doesn’t sound good…but it helps to illustrate the problem with “the flat slab” in the western U.S.  If you are interested in the emplacement of the Pelona/Rand/Orocopia Schists, your slab is shallow at shallow depths: basically, it eats into the crust.  It certainly was NOT flat in the crust: there was a definite dip as these schists only go so far inland. You may not care if it is flat or shallowly dipping or anything else farther inland.

If you want your arc to die like the arcs in the Andes have died, you want your slab flat somewhere near 100 km depth.  It doesn’t have to be unusually shallow near the trench, but you need it to go flat for some distance to prevent asthenosphere from creeping in and making volcanoes.

If you want a flat slab to make mountains far inland, the stakes get higher. The most common and physically defensible means of doing this is by imparting a basal shear stress to the continental lithosphere, which carries some consequences.

You could have a subduction system with all these–but there arguably is no such example today (the inland mountains best hope are the Sierras Pampeanas, where the shallow part of the subduction system is pretty normal; if you want the erode the continental lithosphere, Alaska might be your best game).

Things could be pretty complicated.  For instance, subducting some amazingly thick piece of ocean floor under the Mojave Desert makes a lot of sense–but such material will plummet into the deep mantle once the thick pile of basalts gets deep enough to become a thick pile of eclogite.  The Mojave’s flat slab might become a steep slab not very much farther inland. It is even possible that such a scenario would generate a more long-lived flat slab, as it is possible that you have to be disconnected from the deeper parts of a subducting slab for a slab to become shallow and track along the base of the continent. So you might have a “flat slab” in the Mojave 10 or 20 million years before subduction becomes “flat” for purposes of places far inboard.

The point? Say what you mean; “flat slab” is too generic a term to be useful.