MARGINS: Oxygen Isotope Studies of the Central American Arc

在这项拟议的研究中，PI和合作者（Mark Reagan，爱荷华州; Mike卡尔，Rutgers）提议测量中美洲火山弧（CAVA）熔岩中的氧同位素值（d18 O），以区分涉及俯冲上地壳物质的地幔楔过程与上升岩浆与原位上地壳物质的同化/污染。在前一种情况下，d18 O与熔融程度的代用指标（如U/Th、Na 6）和/或地幔源示踪物（如87 Sr/86 Sr）之间可能存在相关性。在后者中，人们会期望d18 O与污染、同化和分化的代理（如MgO或Mg#）相关。对来自CAVA的约30个样品的初步研究显示了非常令人惊讶的结果-d18 O和熔融指数之间存在相关性，然而大范围的熔融和放射成因87 Sr/86 Sr与低d18 O相关，而不是像常见的板片衍生交代剂来源所预期的高d18 O。PI建议收集更多的d18 O数据，以获得更多表征良好的样品，以试图了解试点研究的令人困惑的结果。

In this proposed study the PI and collaborators (Mark Reagan, Iowa; Mike Carr, Rutgers) propose to measure the oxygen isotope values (d18O) in Central America Volcanic Arc (CAVA) lavas in order to distinguish mantle wedge processes involving subducted upper crustal materials, from assimilation/contamination of rising magmas with in situ upper crustal materials. In the former case, one would expect a correlation between d18O and proxies of the extent of melting (e.g. U/Th, Na6) and/or mantle source tracers (e.g. 87Sr/86Sr. In the latter, one would expect correlation of d18O with proxies of contamination, assimilation, and differentiation (like MgO or Mg#). A pilot study of ~30 samples from CAVA show very surprising results- there are correlations between d18O and indices of melting, however large extents of melting and radiogenic 87Sr/86Sr are associated with low d18O, not high d18O as expected for common sources of slab-derived metasomatizing agents. The PIs propose to collect more d18O data for more well-characterized samples in order to try to understand the puzzling results of the pilot study.