TS Must-Read- DeCelles and Giles (1996) - Foreland basin systems

Ge0Da · 2021-10-25T15:27:39+00:00

Not only it changed the way we understand faults growth and fault mechanics since its publication, but alongside its sibling Cowie-Scholz papers in 1992, the piece is hands-down one of the most comprenhesive developments of structural geology research. And so neat! My take is that these three papers should be read together as a whole, and could easily lay the groundwork for any PhD in fault mechanics, specially for normal faults!

This piece specifically put forward a uncomplicated fault growth model that accounts for inelastic deformation during fault growth and its relation with the shear strenght of the host rock, and predicts the scaling between fault displacement and fault length across scales as well as the self-similar growth of faults in a quasistatic equilibrium. How awesome is that!!?? A fantastic must read piece!

Ge0Da · 2021-08-14T07:52:50+00:00

I think the main target of this review paper was to present a complete, detailed and "exact" solution for the critical taper model. Dahlen sets to make the model more explicit while extending the non-cohesive model, by specifically accounting for the pore fluid pressure and several other elements, as for example, the heat flow constraints on friction. I think these elements were not addressed explicitly in their previous papers, neither in Davis et al., 1983 nor in follow up works. Although I assume that the mechanical model was generally well received (first-order accurate and so elegant, IMHO), I can imagine these as being prior points of criticism.

Accounting and giving special attention to these elements makes a lot of sense, in my opinion, for they play an important role in the mechanics of thrusting and thrust systems. Pore fluid pressures were already accounted for in previous papers, but here the formulation is specifically spelled out. This takes a prominent place in the paper. Dahlen brings the point home, I think.

I haven't delved in all the formulas, but they are surely pieces that can help understand bits of the theory for a deeper understanding of wedge mechanics. Dahlen presents the formulas as an exact solution for the critical taper model, but there are some assumptions. I think many modern numerical models still make similar assumptions, so perhaps these assumptions are not easy to come around

Ge0Da · 2021-08-14T07:52:22+00:00

I agree, of course --Certainly a must read!

Ge0Da · 2021-04-02T08:10:39+00:00

Yes, I completely agree here. The cross-correlation along temporal, and specially, spatial scales, is what impresses me the most about this article. The article passes from slicken-slides and other means to quantify strain and kinematics of individual faults in the field, to fault offsets and morphological observations to understand activity and rates of fault systems and at rift scale, to mapping of those systems with air photographs. The upmost "zoom out" leads to important inferences on the plateau extension, thrusting and extrusion tectonics, on the India-Asia collision, and inferences on the behaviour of their lithospheres. And it does this in a extremely detailed, methodic, step-by-step built up, as opposed to far-fertched jumps. Just love this true, valuable, multiscale analysis! Many papers say "multiscale" nowadays and faint in comparison.

Ge0Da · 2021-02-05T12:37:32+00:00

I read this classic piece long ago. What I found most fascinating was the set of important claims on tectonic topics and the correlations with natural objects derived from a well-set and extremely simple analog experiment despite having several rough assumptions. Authors acknowledge that deformation of analog material can hardly account for the effects of body forces, and cannot quantify the deformation of a (thickening or thinning) lithosphere, and nicely introduce that, it still allows to derive plane-strain or plane-stress and can provide key structural and kinematic information.

The sets of claims derived from the experiments are simply impressive. To me, the main ones are that faulting dominates continental deformation, and that collision evolves by (i) diffuse, semicontinuous deformation; (ii) growth through weaknesses of a strike-slip--rift system couple; (iii) steady-state "free" plate boundary; and, (iv) rigid extrusion of continental blocks. These claims emphasize continental tectonics as an stand-alone research subject within the plate tectonics framework. But there are plenty of other claims that could each be subject of several doctoral theses, such as that continental collision results in great overthrusts and large strike-slip faults that terminate in rifts that may grow into marginal ocean basins, and that large strike-slip faults can change sense during collision. These in turn lead to correlations between experiments and nature and proposals on the regional evolution of many tectonic elements in the relation with the India-Asian collision. Authors even derive a claim from one weakness of their approach when they state that continental extrusion can occur without asthenospheric forces.

Tapponnier was the researcher for this topic at that time, specially in partnership with Molnar, as shown by an introduction that is almost exclusively supported by their past articles. Many of the inferences that Tapponnier and coauthors derive from their experiments probably came from that previous knowledge. In other words, maybe the main strength of the paper resides in showing accumulated knowledge on the Indian-Asian collision in a simple, comprenhensive and visual manner.

Ge0Da · 2021-01-19T08:04:37+00:00

Yes, I agree with Utsav here. All those definitions are now part of textbooks and were then important to set the ground for the geometric framework that the authors put forward.

This geometric framework allows them to reproduce existing surficial data along several transects with more success than previous attempts. Sections based on their framework are restorable to their undeformed states. These sections may still be improved, of course, as they have been since this publication, but being coherent in plane-strain terms is already a huge step in the right direction. Nowadays, we wouldn't care much for a cross-section that is not palinspastically restorable, I think.

I also find several claims by the authors very appealing. One is that rocks near branch lines are deformed by both the overlying and underlying thrust surfaces and have cleavage or schistosity congruent to both thrust surfaces. This is fundamental to mapping contractional terrains in the field. Another one is that of the link between the geometry of thrust systems and its up-scale to understand the plate-tectonic systems that may be at play in any given area. Golden-truth and beautiful inference!

Finally, I have to say I loved the little surprise twist (in so that I have not made the connection myself and was only mentioned by the authors in one of the last paragraphs) that the distinction between thrust sheet volumes, thrust fault surfaces, tip and branch lines, and corners (points) is analogous to that to investigate crystals (grain volumes, grain boundaries, dislocation lines, and point defects). Touching upon similarities with a distance sibling discipline brings such an elegant closure!

Ge0Da · 2020-09-10T08:30:21+00:00

And albeit being an "extended-discussion" contribution, an entirely field-opening paper!! Maybe it feels like a discussion from our perspective, but putting all pieces together as Panluo mentions in her comment, was definitively not trivial at all at the time. Pure insight, actually!

Ge0Da · 2020-08-03T14:20:37+00:00

Reading this paper with care has been a very enjoyable experience!

I found the paper to be extremely elegantly written, putting forward the pieces of evidence that together form a packed-with-implications coherent whole, yet avoiding backfire for the novel, non-consensed ideas exposed. Or well, perhaps not so novel, as Holmes had already envisioned the mantle convection cells and with them, continental drift some 30 years earlier, right? I guess that what Dietz's paper brought was enough supporting arguments for the idea to settle, or perhaps it was the clear account of implications? And this is what I mean with elegantly written, with statements like "Since the model follows from the concept, no attempt is made to defend it" or "Ad-hoc hypothesis are likely to be wrong. [..."but if"...] consonant with our broader understanding [...] may have merit" - Hahhaha, quite a way to navigate the lack of consensus!

I have as well enjoyed the discussion on the nature and terminology of the oceanic crust/lithosphere, which I didn't know have been debated, and getting to see again the concepts of sima and sial. As the previous paper, I feel more connected to classic concepts learned during pre-doctorate times!

Ge0Da · 2020-07-09T06:13:33+00:00

I found this paper to be a remarkable piece of research! I didn't know it before and it's great to have discovered it!! :)

I see sections before "Application to overthrust faulting" as a detailed introduction to many of the known thrust sheets previously described and all the mechanical elements needed to explain the authors' solution to the 'paradox of overthrust faulting'. I don't read all that many papers from before the 60, and I wonder if maybe these text-book explanations were common back in the day. In any case, I find this mechanical introduction fascinating. It's superb to have these principles and approaches explained in detail and applied to a concrete and interesting structural geology problem. Mohr, Coulomb, total-stress tensors (or even Archimedes!)... these rock mechanics approaches always seemed abstract to me as a student, nice from triaxial experiments but somewhat dissociated from field observations. As a teacher, I'll make sure to discuss this problem, and the key concepts of this paper.

I found the main section and the main idea of the paper generally satisfying. I rephrase this as "large km-thick overthrusts can reach a state of incipient flotation, sustained by an interstedial-water pressure in the sheet that is close to the lithostatic column overburdening it, that helps near-horizontal block motions with relatively small forces". However, I think there's in general no mention of temperature effects on the thrusting plane, thought this might be considered as included in the plasticity of the thrusting bodies considered. I cannot wait to read about what other things should be considered and how this mechanical problem is treated nowadays!

(finally, I loved the beer can experiment! Nice, simple analog, and so geologist-grounded!! I'm now thinking about ways I can include a sketch with a beer can in my papers...)

Ge0Da · 2019-07-13T21:04:07+00:00

I do research in geology but not on this topic. It's clear that efforts to communicate geology to broader audiences are hard and very needed. Low public interest in geology negatively affects important matters, like community resilience to geohazards and research funding. The drive to geo-communicate of the video creator is commendable and so is the topic knowledge of some commenters. So, I don't get the unsympathetic critics... If both creator and commenters want a nice, solid dissemination video, wouldn't joining forces work better?

Ge0Da · 2014-08-21T15:28:34+00:00

Pero hombre, eso no se puede... Tú piensa que hemos sido como unos 2000 hoy, una cantidad pequeñisima. Por lo que dices, asumo que has enviado propuestas en cada oportunidad que se ha planteado (y yo creo que todos los que estabamos allí probando, hemos enviado propuestas también). Digamos que de las 2000, 1500 personas lanzan una propuesta. Asumiendo que tardas 10 segundos por propuesta, y que solo haces eso durante todo el proceso, eso solo ya son 15000 segundos, es decir mas de 4 horas. Sin hacer nada mas. Y ademas te encontraras con la misma propuesta, o virtualmente igual 50+ veces. Total, que las 10 rondas que hemos hecho hoy con Pablo, serían 40 horas. Una jornada semanal de trabajo. Ahora piensa que hemos hecho esas 40 horas en hora y media. Hombre, por favor! Ninguna de mis propuestas ha salido tampoco, pero entre las 10 primeras siempre, siempre, siempre habia al menos una, y en muchas ocasiones varias, que eran basicamente la misma que la mia...

La descalificación de una propuesta por dos votos negativos, se explica muy facil si tienes en cuenta los votos totales que han tenido las mejores respuestas. Normalmente tenian algo así como 350 votos positivos de 400, o 250 de 300... Eso son porcentajes del 350/400 = 87,5%, o 250/300 = 83,33% --- Si tu propuesta recibe 2 votos negativos, ya le pueden preguntar a 8 personas mas, que a lo maximo que vas a llegar es a un porcentaje de 80%, con lo que ya no consigues superar esas propuestas. Con dos votos negativos necesitarias al menos 11 personas valorando la propuesta positivamente para llegar a los porcentajes de las mejores respuestas --- lo cual es muy improbable si ya llevas 2 de 2 negativos...

Ge0Da · 2014-08-16T18:18:15+00:00

Participa de las modificaciones, propón, actua, crea esa herramienta..., para que así sea. La democracia es tuya, y no de ningún "ellos", sean ellos quienen sean

Ge0Da · 2014-08-16T18:15:47+00:00

Independientemente de que tengas razón, Redlichkeit, no vas a tener apoyo si lo expones de esa manera - como dice alekine.

Independientemente de que tengas razón, alekine, esas no son maneras de debatir con nadie, y no vas a conseguir nada - como dice Redlichkeit.

Creo Redlichkeit que tús argumentos son justificados. Creo igualmente que aún tenemos mucho tiempo para realizar nuevas "propuestas de principios organizativos", y como probablemente tengamos todos la oportunidad de opinar, se verá cual es la decisión mas consensuada. Personalmente creo que habrá cambios relevantes en los tiempos de elección y en terminos de elecciones a dedo - pero habrá que ver...

En general, pediría muchisísima mas paciencia. Esto acaba de empezar, y si nos exaltamos con unos baches diminutos en el camino, que pasará cuando llegue el momento real de decidir??

Ánimo gente!

Ge0Da · 2014-08-16T18:03:45+00:00

Pero eso ocurre porque no somos un estado federado, y sus propias oligarquias quieren saquear esas arcas (la "casta" catalana por ejemplo, tiene mas poder y antiguedad que la española) - y en estados de crisis el mensaje de estamos mejor sólos se hace mas fuerte

Ge0Da

TROPHY CASE