Petrographic and Trace Element Geochemistry of Rocks Dredged from the Aves Ridge: Examples of Mixed Basalt Signatures

The origin of the Aves Ridge formation, and its relationship to the anomoalously thick Caribbean plate remains enigmatic. The Aves Ridge shows characteristics of both an island arc and traditional back arc spreading center and yield petrography similar to other back arc volcanism, such as in the Sea of Japan, South Sandwich Islands Back Arc and Taiwan-­Luzon arc. Unlike mid­ocean ridge magmatism which produces a limited variety of basalts, the front arc volcanism in the Lesser Antilles east of the Aves Ridge produce a wide variety of igneous rocks. Recent work from IODP Leg 350 suggests that the back arc is rifted arc material. In this work we show that the Aves Ridge produces chemically diverse magmas. Here we examine detailed petrography and trace element geochemistry of dredged samples. Samples display felty texture with abundant plagioclase and minor clinopyroxene. Larger euhedral grains of plagioclase were reasonably evolved (An55-­65), while other samples contain serpentinized olivine and plagontized glass, +/- Magnetite. Quick cooling was exhibited by fine grained plagioclase matrix and flow textures were apparent in a number of sections. Combined, the abundance of plagioclase, clinopyroxene, olivine, and magnetite indicate that studied samples are pillow basalts rather than areally and subareally deposited arc rocks. Trace element geochemistry show a diverse history. The rare earth element trends are those of ocean island basalt where LREE are enriched 10-100 times over cohondrite owing to subduction influence. Based on Cr vs Y, Zr vs Zr/Y and Cr vs Ce/Sr plots, among others, samples are classified as ocean island basalts but a number of samples distinctly trend toward MORB with minor overlap of arc boninite field. In general, we believe that the Aves Ridge Dredge samples represent basalt at the transition between ocean island basalt and mid ocean ridge basalt.