Beryllium Systematics in Young Volcanic Rocks: Implications for sup10/supBe

<p> <p id="x-x-"> Beryllium is an incompatible trace element that closely parallels neodymium in its geochemical behavior. Be analyses conducted on well-characterized oceanic and arc volcanic rock suites, as well as on marine sediments, suggest a bulk solid/liquid distribution coefficient of 0.03&ndash;0.06 for melting of the mantle and crystallization of basalts. The Be/Nd ratio for many volcanic rocks from diverse tectonic environments is approximately .05, similar to the ratio in chondrites. <p id="x-x-"> Be data for samples from volcanic arcs show that there are significant variations in ¹⁰ Be/ ⁹ Be among different arcs, and that variations in ¹⁰ Be are not due to variations in Be concentration alone. For at least one volcano (Bogoslof), the ¹⁰ Be/ ⁹ Be ratio is constant for samples that vary by a factor of three in both their Be and ¹⁰ Be concentrations, suggesting that ¹⁰ Be is an inherited magmatic signature and not simply a result of contamination near the surface. In addition, the Be, Nd and Pb isotope systems for this volcano are all consistent with a model in which small amounts of sediment were incorporated into the Bogoslof source region&mdash;provided the mantle wedge has the isotopic characteristics of depleted MORB. Since ¹⁰ Be exists only in the uppermost tens of meters of oceanic sediments, the data suggest an efficient return flux of sediment to the mantle at subduction zones. </p> </p></p>