Abstract

New 187Os/188Os ratios of Quaternary Mount Adams volcanic rocks from the Cascade arc in southern Washington vary by >300% (187Os/188Os = 0.165–0.564) and fall into high (>0.319) and low (0.166 to 0.281) groups of 187Os/188Os ratios that are substantially more radiogenic than mantle values. These Os isotope compositions and groupings are interpreted to reflect recycling of discrete intracrustal domains with high 187Os/188Os ratios but differing ages, thus recording the process of crustal hybridization and homogenization. Os isotope compositions provide new constraints on amounts of intracrustal recycling in young subduction-zone environments that reflect the magmatic history of the arc. Sr, Nd, Hf, and Pb isotope variations in this young, mafic arc complex are too small to allow such constraints.

You do not currently have access to this article.