Tracking changes in crustal thickness during orogenic evolution with Sr/Y: An example from the North American Cordillera


Chapman, James B.
Ducea, Mihai N.
DeCelles, Peter G.
and Profeta, Lucia

Global compilations indicate that the geochemistry of arc magmatism is sensitive to Moho depth. Magmatic products are prevalent throughout the history of Cordilleran orogenesis and can be employed to constrain the timing of changes in crustal thickness as well as the magnitude of those changes. We investigate temporal variations in crustal thickness in the United States Cordillera using Sr/Y from intermediate continental arc magmas. Our results suggest that crustal thickening began during the Late Jurassic to Early Cretaceous and culminated with 55–65-km-thick crust at 85–95 Ma. Crustal thicknesses remained elevated until the mid-Eocene to Oligocene, after which time crustal thicknesses decreased to 30–40 km in the Miocene. The results are consistent with independent geologic constraints and suggest that Sr/Y is a viable method for reconstructing crustal thickness through time in convergent orogenic systems.

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Figure 3. Plot of changes in median Sr/Y in magmatic rocks and calculated crustal thickness through time for Great Basin region. Shaded region and dashed arrows show interpreted trends in data. Timing for events listed at bottom of plot is constrained by independent
geologic studies; see text for discussion. Compiled and plotted data are included in Tables DR1–DR3.

Publication Listing

GEOLOGY, October 2015; v. 43; no. 10; p. 919–922. doi:10.1130/G36996.1