Skip to Main content Skip to Navigation
Journal articles

Recycled oceanic crust and marine sediment in the source of alkali basalts in Shandong, eastern China: Evidence from magma water content and oxygen isotopes

Abstract : The magma water contents and cpx δ18O values in alkali basalts from the Fuyanyshan (FYS) volcano in Shandong, eastern China, were investigated by an inverse calculation based on the water content of clinopyroxene (cpx) phenocrysts, the ivAlcpx-dependent water partitioning coefficient Dwatercpx>/melt, and secondary ion mass spectrometer, respectively. The calculated water content (H2O wt.) of magma ranges from 0.58% to 3.89%. It positively correlates with heavy rare earth element concentrations and bulk rock 87Sr/86Sr ratios, and it negatively correlates with Nb/U ratios. However, it is not correlated with bulk Mg# (Mg# = 100 × Mg / (Mg + Fe)) and (La/Yb)n (n represents primitive mantle normalization). Combined with the rather homogenous distribution of water content within cpx grains, these correlations indicate that the water variations among different samples represent the original magma signature, rather than results of a shallow process, such as degassing and diffusion. The δ18O of cpx phenocrysts varies from 3.6‰ to 6.3‰ (±0.5‰, 2SD), which may be best explained by the involvement of components from the lower and upper oceanic crust with marine sediments within the mantle source. The H2O/Ce ratios of the calculated melts range from 113 to 696 and form a positive trend with bulk rock 87Sr/86Sr, which cannot be explained by the recycled Sulu eclogite or by the metasomatized lithospheric mantle. Our modeling calculation shows that the decoupling of ɛHf and ɛNd could be caused by the involvement of marine sediments. Combing the high Ba/Th ratios, positive Sr spikes, and low Ce/Pb ratios for the Fuyanshan basalts, we suggest that the hydrous nature of the FYS basalts was derived from the hydrous mantle transition zone with ancient sediments.
Complete list of metadata

https://hal-insu.archives-ouvertes.fr/insu-03619372
Contributor : Nathalie POTHIER Connect in order to contact the contributor
Submitted on : Friday, March 25, 2022 - 9:44:30 AM
Last modification on : Saturday, March 26, 2022 - 4:21:54 AM
Long-term archiving on: : Sunday, June 26, 2022 - 6:20:52 PM

File

JGR Solid Earth - 2015 - Liu -...
Publisher files allowed on an open archive

Licence

Copyright

Identifiers

Citation

Jia Liu, Qun-Ke Xia, Etienne Deloule, Huan Chen, Min Feng. Recycled oceanic crust and marine sediment in the source of alkali basalts in Shandong, eastern China: Evidence from magma water content and oxygen isotopes. Journal of Geophysical Research : Solid Earth, American Geophysical Union, 2015, 120, pp.8281-8303. ⟨10.1002/2015JB012476⟩. ⟨insu-03619372⟩

Share

Metrics

Record views

145

Files downloads

3