Geochemistry of basement rocks of incoming plate (Cocos Ridge) from Sites U1381 and 1414, IODP Expeditions 334 and 344

Abstract:

The drilling sites of IODP 334 and 344 lie in the being subducted part of Cocos Ridge, offshore Costa Rica. Some seamount clusters distributed in the northwest side of the sites. Most scientists accepted that the Cocos ridge is intimately related to the activity of Galapagos plume (e.g., Hoernle et al., 2000, 2004, 2008). In this study we have selected some basaltic samples from U1381A, U1381C and U1414A (IODP 334 and 344) (Harris et al., 2015a, b) to carry out petrogenetic study. Major element compositions show that these basaltic rocks belong to sub-alkaline rocks, which is consistent with previous study on basalts from northern side of Cocos ridge. The characteristics of trace element composition are similar to that of EMORB, and the compositional differences in trace elements among samples reflect the influence of fractional crystallization. Sr-Nd-Pb isotopic compositions of these basaltic rocks show that there exist mantle heterogeneity beneath the Cocos ridge, and they may be the product of mixing between DMM/GSC and EMII. The new data show more enriched source feature than those from Galapagos hotspot (and its tracks) in previous study (Hoernle et al., 2000,2004), and slightly more enriched than those Miocene to Pliocene arc volcanics from Central America (Gazel et al., 2009). Partial melting model show that the parental basalts for these basaltic rocks may be produced by 13 to 28% partial melting of garnet pyroxenite.

References

Gazel et al., 2009. G-cubed.10, Q02S11, doi:10.1029/2008GC002246.//Harris, R.N., Sakaguchi, A., Petronotis, K., and the Expedition 344 Scientists. 2015a. Input Site U1381. Proceedings of the Integrated Ocean Drilling Program, Volume 344//Harris, R.N., Sakaguchi, A., Petronotis, K., and the Expedition 344 Scientists. 2015b. Input Site U1414.Proceedings of the Integrated Ocean Drilling Program, Volume 344//Hoernle et al., 2000. Geology, 28(5),435-438//Hoernle et al., 2004. Geology, 32,697-700//Hoernle et al., 2008. Nature, 451,1094-1098

(This study was supported by National Natural Science Foundation of China (NSFC nos. 41296030 and 41322036, and IODP-China.)