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SUMMARY:Raising the Colorado Plateau – tales from xenoliths and petrolog
 ical modeling - Richard Palin\, University of Oxford
DTSTART:20221108T120000Z
DTEND:20221108T130000Z
UID:TALK176966@talks.cam.ac.uk
CONTACT:Oscar Branson
DESCRIPTION:High-elevation\, low-relief continental plateaus are major top
 ographic features and profoundly influence atmospheric circulation\, sedim
 ent transport and storage\, and biodiversity. Although orogenic surface-up
 lift mechanisms for modern continental plateaus near to plate margins\, su
 ch as Tibet\, are well-characterized\, they cannot account for examples in
  intracontinental settings\, such as the Colorado Plateau\, southwestern U
 SA. While strongly debated\, most competing hypotheses that account for Ce
 nozoic uplift of the Colorado Plateau acknowledge the importance of northw
 est-directed subduction of the Farallon oceanic plate beneath North Americ
 a since c. 100 Ma. Here\, I will describe the results of two in-depth inve
 stigations into mechanisms that may have caused uplift of the plateau\; on
 e being primarily tectonic\, and the other being primarily petrological in
  nature. First\, I show via study of lawsonite-bearing eclogite xenoliths 
 collected from diatremes in the center of the plateau that the shallow-dip
 ping Farallon slab may have penetrated through the proto-plateau SCLM at r
 elatively shallow depth (~120 km)\, shearing away ~80 km of its mantle roo
 t. This removal likely caused asthenospheric upwelling and isostatic rebou
 nd of the plateau region during the Late Cretaceous to the Eocene. Secondl
 y\, I report on the results of recent petrological modelling that has inve
 stigated whether broad-scale hydration-induced metasomatism of continental
  lower crust can reduce its density and increase its buoyancy sufficiently
  to drive isostatic uplift. With reference to devolatilization of the subd
 ucting Farallon slab\, we have applied open-system reactive transport flui
 d-rock interaction models to determine the spatial and temporal scales ove
 r which mineralogic transformations would have taken place following the i
 nfiltration of aqueous fluids into the proto-plateau lower crust. These da
 ta show that cumulative surface uplift of over 1\,000 m can be achieved by
  metasomatism of an initial 40-km-thick continental crust\, even at relati
 vely modest fluid infiltration rates compared to modern-day subduction zon
 es worldwide. This petrological effect should also be considered alongside
  purely tectonic arguments when accounting for anorogenic uplift in intrac
 ontinental regions\, without the need to invoke contributions from extrane
 ous mechanisms that lack a priori evidence\, such as mantle plume impingem
 ent.
LOCATION:Department of Earth Sciences\, Tilley Lecture Theatre
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