Abstract
Bodies of rock that are detached (recovered) from subducting oceanic
plates, and exhumed to Earth’s surface, become invaluable records of the
mechanical and chemical processing of rock along subduction interfaces.
Exposures of interface rocks with high-pressure (HP) mineral assemblages
provide insights into the nature of rock recovery, yet various
interpretations concerning thermal gradients, recovery rates, and
recovery depths arise when directly comparing the rock record with
numerical simulations of subduction. Constraining recovery rates and
depths from the rock record presents a major challenge because small
sample sizes of HP rocks makes statistical inference weak. As an
alternative approach, this study implements numerical simulations of
oceanic-continental convergence and applies a classification algorithm
to identify rock recovery. Over one million markers are classified from
64 simulations representing a large range of subduction zones. We find
recovery P’s (depths) correlate strongly with convergence velocity and
moderately with oceanic plate age, while PT gradients correlate strongly
with oceanic plate age and upper-plate thickness. Recovery rates
strongly correlate with upper-plate thickness, yet show no correlation
with other boundary conditions. Likewise, PT distributions of recovered
markers vary among numerical experiments and generally show poor overlap
with the rock record. A significant gap in predicted marker recovery is
found near 2 GPa and 550 ˚C, coinciding with the highest density of
exhumed HP rocks. Implications for such a gap in marker recovery include
numerical modeling uncertainties, petrologic uncertainties, selective
sampling of exhumed HP rocks, or natural geodynamic factors not
accounted for in numerical experiments.