2:15 PM - 2:30 PM
[SCG44-26] Regional silica enrichment in subduction-type metasediments: Evidence from deformed mineral vein sets in the Del Puerto Canyon region, Franciscan Belt, USA
Keywords:Volume change, Deformed vein, Mass transfer
Previously applied methods for estimating rock volume change are based on estimates of absolute stretch, or changes in whole-rock chemical compositions. Estimates based on these approaches give large discrepancies even when applied to the same region. In this study, we develop a largely unexplored method for estimating volume change using the direction and deformation type of deformed mineral veins (Passchier, 1990; Wallis, 1992). The assumptions in this method are few and appropriate uncertainties can be estimated.
Application of the new method to the metagreywacke in the Del Puerto Canyon of the Franciscan belt constrains the syn-metamorphic volume change to be greater than 7%, contrasting with previous proposals for large volume-loss in the same region (Ring, 2008). The results of previous studies can be modified taking into account rigid body rotation of individual grains accommodated by grain boundary sliding and solution transfer. The final result of our approach yields a positive volume change of 7–21vol.% and implies the accretion of silica to the rock. This result is in good accord with the estimate of Audet & Burgmann (2014).
Reference
Audet, P. & Burgmann, R., 2014. Possible control of subduction zone slow-earthquake periodicity by silica enrichment. Nature, 510, 389–392.
Passchier, C. W., 1990. Reconstruction of deformation and flow parameters from deformed vein sets. Tectonophysics, 180, 185–199.
Ring, U., 2008. Deformation and Exhumation at Convergent Margins: The Franciscan Subduction Complex. The Geological Society of America, Special paper, 445
Wallis S. R. 1992. Vorticity analysis in a metachert from the Sanbagawa belt SW Japan. Journal of Structural Geology, 14, 271–80.