Rb–Sr and K–Ar systems of biotite in surface environments regulated by weathering processes with implications for isotopic dating and hydrological cycles of Sr isotopes

Diffusion versus recrystallization processes in Rb–Sr geochronology: Isotopic relics in eclogite facies rocks, Western Gneiss Region, Norway

“…These factors may be either the slight amphibolite-to greenschist-facies alteration, or incipient weathering (cf. Jeong et al, 2006). In any case, since Sr-isotopic signatures of the critical eclogite facies phases omphacite, zoisite, phengite and garnet are consistent with full isotopic equilibration of the rocks during metamorphism we interpret the age of 404 ± 2 Ma as dating eclogitization, at P,T conditions as recorded by the thermobarometric data for these eclogites.…”

Tree-mycorrhiza symbiosis accelerate mineral weathering: Evidences from nanometer-scale elemental fluxes at the hypha–mineral interface

“…This is not surprising as vermiculite is the prime alteration product in acidic dissolution experiments of biotite containing more than $0.8 Mg per O 10 (OH) 2 (Murakami et al, 2003), a value which is close to the Mg content of our biotite ($0.77 Mg per O 10 (OH) 2 ). Other secondary phases that may form during biotite alteration (e.g., Fe 3+ (oxidized-) biotite) are more difficult to distinguish from pristine biotite based solely on high-resolution TEM micrographs because, depending on the extent of oxidation, their (0 0 1) d-spacing range from 10.1 to 10.3 Å (Jeong et al, 2006).…”

The provenance of sediments in the Gulf of Lions, western Mediterranean Sea

“…In many recent studies, the large variations observed in the 87 Sr/ 86 Sr of marine sediments have been attributed to various degree of chemical weathering on the continent [ Cole et al , 2009; Colin et al , 2006; Jung et al , 2004]. During chemical weathering, the radiogenic Sr is preferentially released to the fluid, due to the early breakdown of mica (e.g., mainly biotite) and K‐feldspar which are both minerals with high 87 Sr/ 86 Sr [ Blum and Erel , 1997; Bullen et al , 1997; Jeong et al , 2006; Taylor et al , 2000]. Consequently, the 87 Sr/ 86 Sr of sediment is lowered [ Blum and Erel , 1997; Jeong et al , 2006].…”

“…During chemical weathering, the radiogenic Sr is preferentially released to the fluid, due to the early breakdown of mica (e.g., mainly biotite) and K‐feldspar which are both minerals with high 87 Sr/ 86 Sr [ Blum and Erel , 1997; Bullen et al , 1997; Jeong et al , 2006; Taylor et al , 2000]. Consequently, the 87 Sr/ 86 Sr of sediment is lowered [ Blum and Erel , 1997; Jeong et al , 2006]. However, it must also be noticed that such an evolution critically depends on the amount of altered biotite.…”