Zircon from gabbroids of the Shaka ridge (South Atlantic): U-Pb age, oxygen i sotope ratios and trace element composition

Rumyantseva N. A., Skublov S. G., Vanshtein B. G., Li X.-H., Li Q.-Li

Zapiski RMO (Proceedings of the Russian Mineralogical Society). 2022. V. 151. N 1. P. 44-73

https://doi.org/10.31857/S0869605522010099

Language: Russian

Abstract

This paper presents the results of dating (U-Pb method, SHRIMP-II) and isotope geochemical data (oxygen δ¹⁸O, rare elements and REE) for zircon xenocrysts from igneous rocks of the Shaka Ridge (South Atlantic) as well as the results of comparative analysis of zircon from the Shaka Ridge with young zircon of oceanic origin from the rocks of Atlantis Bank in the Central Atlantic. Xenogenic zircon grains were found in the gabbroids. For this zircon the U-Pb isotope system recorded the age of crystallization from Proterozoic values of about 1.1 Ga years to Mesozoic values of about 180 Ma. The analyzed zircon has geochemical characteristics of magmatic origin: Th/U ratio (from 0.01 to 19.4), differentiated from LREE to HREE distribution spectra of lanthanides with positive Ce- and negative Eu anomalies. In Yb, U, and Y discrimination diagrams, the zircon under consideration falls into the zircon region of the continental crust rocks, including the granitoid field. The crustal source of xenocrysts is also indicated by the increased Li content in zircon. Data on the isotopic composition of oxygen in zircon indicate either the presence of crustal marks or a possible hydrothermal effect. Most likely, the data obtained as a result of the study reflect the multiplicity of sources of receipt of zircon xenocrysts.

Keywords: zircon, U-Pb dating, REE, oxygen isotopes, Shaka ridge, South Atlantic