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[4D Synthesis Workshop Summary Report]](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
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4D Synthesis Workshop Summary Report
- 1. Results of the EarthScope 4D Evolution of North America workshop: The challenges of connecting surface geology to EarthScope- resolved features
- 2. Workshop report [4D Synthesis Workshop Summary Report]
- 3. Critical considerations forWyoming • Scale and resolution. The challenges in connecting surface geological expressions to EarthScope-resolved features. • Time. Can seismologists, using EarthScope-derived data (3D spatial constraints), help geologists interested in significantly older problems?
- 4. Critical considerations forWyoming • Scale and resolution. The challenges in connecting surface geological expressions to EarthScope-resolved features. [4D Synthesis Workshop Summary Report]
- 5. 0 0 3 6 VP 3 6 % fast% slow VS Body waves (P) Rayleigh waves (S) vertical horizontal 15-25 km 40-70 km 30-50 km 20-30 km Resolution at 80-160 km 160 km 0 25 50 75 100 125 150 175 200 225 250 km Moho 48 ± 4 140 km 225 km RSSD 3 54 VS (km/s) Eilon et al., 2018 Receiver Functions— our best vertical resolution VS from joint Receiver Function and Surface Wave inversion “High-resolution” Tomography Wyoming Craton Cordillera Yellow -stone from Hopper et al. 2014 150 km RSSD 02% VP 2% Scale
- 6. A Pwave RayleighWyoming 0 200 400 600 km Moho 160 AAAAAA 195 km Hearne Craton Juan de Fuca slab old Farallon slab old Farallon slab ocean plateau in old Farallon slab The point here: — 3-D images of lithosphere & asthenosphere reveals unknown and unexpected structures. — It is today’s structure, but was made in the past. — It is hard to interpret without geologic context. — E.g., assuming flat-slab subduction, all this is post-Laramide structure (except maybe the Hearn craton). Seismic velocity is not directly relevant. It needs be interpreted. And, there is less info here than in a thin section, but… it’s our best view of what’s down there Accounting for fast upper mantle seismic structure The thinking goes looks this: > Seismic contrasts are largely due to temperature. > Cool (fast) mantle is created near Earth’s surface. > High lateral contrast is young structure (<100 m.y.) > Beneath western U.S., structure is post-Laramide > Roughly speaking — In upper ~100 km, we see lithosphere shape — In the 100-200 km range, we see - craton root - lithosphere downwellings - slab fragments. — Below 200 km, large volume cool mantle is slab Interpretation
- 7. Critical considerations forWyoming • Time. Can seismologists, using EarthScope-derived data (3D spatial constraints), help geologists interested in significantly older problems? [4D Synthesis Workshop Summary Report]
- 8. Signatures of tectonic processes are preserved through time Wyoming CratonCordillera Yellow- stone 02% VP 2% [Hopperetal.,2014] 150 km LAB MLD Tomography RFs Tomo. RFs [DNA10-S, Obrebski et al., 2011] [courtesy of Gene Humphreys]
- 9. Modern day subduction (Alaska) [Hopper and Fischer, 2015] Wyoming CratonCordillera Yellow- stone [Hopperetal.,2014] LAB MLD Proterozoic subduction? (Slave) [Bostock, 1998] [Rondenay et al., 2008 RFs
- 10. Figures:511 512 Porter et al., 2016 Schmandt and Lin, 2015 Pre-Earthscope modelShen and Ritzwoller, 2016 Svelocities 523 Time since last event dominates the geophysical record
- 11. Porter et al., 2019
- 12. 552 Interpolated fromaveragedSmodels Porter et al., 2019
- 13. Figures:511 512 Porter et al., 2016 Schmandt and Lin, 2015 Pre-Earthscope modelShen and Ritzwoller, 2016 Svelocities
Editor's Notes
- Thoughts on this slide. Introduce the workshop- brought together geologists and geophysicists with the aim of producing a community model for the 4-D evolution of North America. Discussed the idea of generating a Whitmeyer and Karlstrom-esque powerpoint with associated geophysical features. I would argue that the workshop did not complete this goal, but provided good discussions that can hopefully help in constructing a model down the road. So what did we, as a group, learn? And what can we use for the Wyoming craton workshop?
- Email discussions amongst the three of us demonstrated that tangible, concrete results were scarce. No big conclusions generated at the workshop. Instead, we thought about things that were difficult to reconcile at the previous meting but will likely be important considerations for the Wyoming workshop. Describe.
- Notes from Atleigh emphasize the idea that ES was exploratory, and led to discoveries that went beyond what was assumed based on the geology. Atleigh also makes note of the complexity of structure seen in ES, but we should note that the resolution of ES results is still limited relative to the details available from geologic disciplines. This needs to be taken into consideration when we are having discussions. When integrating data from ES and geology, we need to carefully consider what geophysics can and cannot tell us.
- A number of conversations at the 4D workshop centered around time and how it is manifested in observations, both geophysical and geological in nature. How directly can ES results be tied to past tectonic events? Can a 3D image taken of present day structure inform of us past activity? This is a question that is particularly relevant to Wyoming. Many of the talks listed in the program will focus on Precambrian geology, yet the Wyoming craton, from a seismological point of view appears to have been significantly affected by the Laramide.