Robert H. Mariner Udo Fehn Glen T. Snyder Shaul Hurwitz 2005 <p><span>This study quantifies the cycling of halogen elements through the Cascadia subduction zone based on the chemistry of thermal springs in the Central Oregon Cascade Range and of a mineral spring in the forearc (Willamette Valley). Considerations based on mass balances, element ratios, and&nbsp;</span>³⁶<span>Cl/Cl and&nbsp;</span>¹²⁹<span>I/I ratios suggest that halogens discharged through the thermal springs in the Cascade Range are probably derived from magma degassing. Our results indicate that &lt;</span><span>&nbsp;</span><span>35% of the subducted Cl and &lt;</span><span>&nbsp;</span><span>20% of the subducted Br and I could be transported through arc volcanism and the thermal springs, a considerably lower percentage than estimated for other volcanic arcs along the Pacific Rim. A likely explanation for this difference is that a large fraction of the halogens is released from the slab at shallow depths into the serpentinized sub-forearc mantle because of the relatively high temperatures in the subducting Juan de Fuca plate. The small fraction of halogens subducted to depth probably also indicates a low rate of water transport, which is consistent with the observation that the Cascade Range sub-arc mantle is relatively dry and has a low degree of volcanic vigor, compared with other arcs.</span></p> application/pdf 10.1016/j.epsl.2005.04.029 en Elsevier Systematics of halogen elements and their radioisotopes in thermal springs of the Cascade Range, Central Oregon, Western USA article