USGS Mendenhall postdoc fellowship opportunity: Magmato-tectonic links: ignimbrite calderas, regional dike swarms, and the transition from arc to rift in the Southern Rocky Mountains
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This postdoc opportunity has just been posted (starting March 21) on the USGS website. The focus is on a newly-underway study of the late-emplaced compositionally diverse dikes and other intrusions that radiate outward from the polycyclic Platoro caldera, source of five voluminous ignimbrite sheets (30-28.6 Ma) in the Southern Rocky Mountain volcanic field). These appear to merge in structural trend, composition, and apparent age with the spectacular but virtually unstudied Dulce dike swarm that trends southwest and southward for more than 100 km along the NE margin of the Colorado Plateau (San Juan Basin) from southern Colorado into northern New Mexico). Preliminary observations suggest that the radial Platoro intrusions and Dulce dikes may record the interrelated effects of uplift associated with prolonged late solidification of an arc-related granitoid batholith beneath Platoro caldera, in conjunction with the tectonic transition to weak regional extension along the NE margin of the Colorado Plateau, satellitic to initiation of the Rio Grande rift zone and associated basaltic volcanism farther east.
The research opportunity would include mapping and sampling of selected dike areas for petrologic study and age determinations, especially along the critical transition zone of compositionally diverse dikes that radiate to the SW from the Platoro area and merge with the S-trending Dulce swam of mafic alkalic dikes. Desirable multidisciplinary research efforts could include: polished-section and electron-microprobe petrology and major and trace-element petrochemistry for petrogenetic interpretation; Pb-zircon and/or 40Ar/39Ar geochronology; paleomagnetic-pole and -anisotropy measurements to determine flow directions, timing, and dike-emplacement mechanics; radiogenic isotopic analyses (Sr, Nd) to evaluate mantle versus crustal sources for the intrusions; and thermal and fluid-dynamic modeling to constrain dike-propagation velocities, duration of emplacement processes, and relation to regional tectonic strain.
Joint research advisors for this opportunity are: Peter Lipman (650-329-5295, plipman@xxxxxxxx); Ren Thompson (303-236-0929, rathomps@xxxxxxxx); Kyle Anderson (650-329-5261, kranderson@xxxxxxxx); Margaret Mangan (650-329-5738, mmangan@xxxxxxxx)
Any interested near-completion PhD student should contact one of us directly by phone or email for more information about possibilities (Lipman will be travelling internationally, 3/20-4/3; best available by email). We’re just gearing up for this study, so lots of flexibility exists concerning directions a postdoc could take. Note that the time frame for Mendenhall-16 applications will be brief, about five weeks, closing May 2 (instructions are on USGS website: http://geology.usgs.gov/postdoc/opps/research.html: Research Opportunity #16-4)
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