Rubidium Isotope Fractionation During Chemical Weathering of Granite

Chemical weathering plays a pivotal role in modulating global climate, affecting crustal evolution, and shaping landscapes. Here we carried out the Rb isotopes from a weathering profile developed in granite in tropical environment in South China, aiming to understand the role of continental weathering on controlling the global Rb budget. The samples were dissolved in a mixture of concentrated HF-HNO₃ acids. Rb was completely separated from matrix elements through Sr-spec resin using 3 N HNO₃ as eluent. The Rb isotopes were measured by multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) in standard-sample-bracketing (SSB) mode at at the State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences (GIG-CAS).

Our data show that variations of Rb isotopes are up to 0.4‰ and are gradually shifted to lighter values with increasing degree of weathering of the granite towards the surface, which display that heavy Rb isotope is preferentially released from weathering profile and leaving lighter Rb isotopes in weathered products. However, the limited data on Rb isotopes in river water show that lighter Rb is released into the hydrosphere relative to the data of granite, which makes Rb isotopic fractionation more complicate under surface earth. So, to understand the Rb and its isotopic cycle needs more works to be done.