Abstract

Mylonites from three widely separated localities along the Fries ductile deformation zone in the Blue Ridge province show substantial enrichments in trace and minor elements (TiO2, P2O5, Zr, Y, and V) and depletions in Rb and Sr relative to the protolith. Two end-member hypotheses can explain the enrichments: one involves partitioning to and from an infiltrating fluid and assumes that all the elements were mobile. The second hypothesis assumes that the high-field-strength cations were largely immobile and that their enrichment is due to large volume losses in the mylonites. Modeling indicates that Ti is immobile for fluid/rock ratios as high as 104, and petrographic and modal data support a volume-loss mechanism. Volume loss was accommodated by loss of SiO2 and alkalies during feldspar dissolution. Calculated fluid/rock volume ratios required to produce the observed SiO2 fosses (assuming Ti mobility) range from 70 to 600. Variable enrichments in P, Zr, Y, and V are attributed to selective mobility of these elements during fluid infiltration.

First Page Preview

First page PDF preview
You do not currently have access to this article.