Abstract
The concentration of rare earth elements (REE) in Precambrian sedimentary rocks is widely used to estimate their depositional environment. Specifically, superchondritic Y/Ho is a powerful indicator for determining whether a sedimentary rock was deposited in a marine environment. Currently, superchondritic Y/Ho in seawater is believed to result from the preferential adsorption of Y onto FeMn oxides. In modern oceans, FeMn oxides are considered the sink for subchondritic Y/Ho. On the contrary, Precambrian banded iron formations (BIFs) display superchondritic Y/Ho, suggesting that Precambrian seawater also possessed a superchondritic Y/Ho value. However, Precambrian BIFs cannot account for the sink of subchondritic Y/Ho. Thus, other processes must have been responsible for maintaining the superchondritic Y/Ho of Precambrian seawater. A hydrothermal experiment involving mid-ocean ridge basalt (MORB) and a Cl-rich fluid was conducted at 300 °C and 500 bars to assess the role of basalt-hosted hydrothermal systems on the Y/Ho value of seawater. Over time, the fluid's Ca concentration increased while Na decreased, suggesting plagioclase albitization occurred. The REE pattern of the reacted fluids exhibited superchondritic Y/Ho values up to 63.2. Based on the presence of positive Eu anomaly and the degree of light REE depletion, the REE in the hydrothermal fluids was mainly sourced from plagioclase during albitization. The superchondritic Y/Ho values in the fluids can be explained by the preferential leaching of these elements due to differences in chloride complexing strength between REE. Subchondritic Y/Ho values observed in Precambrian hydrothermally altered basalts may be interpreted as remnants generating superchondritic Y/Ho values in coexisting Precambrian hydrothermal fluids. Therefore, we believe that the superchondritic Y/Ho of Precambrian seawater was maintained by basalt-hosted hydrothermal system.
Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
