On the thermal stability of Rb-Sr and K-Ar biotite systems: Evidence from coexisting Sveconorwegian (ca 870 Ma) and Caledonian (ca 400 Ma) biotites in SW Norway

Surprisingly young Rb/Sr ages from the Simav extensional detachment fault zone, northern Menderes Massif, Turkey

“…The presence of both brown and green biotites in the same thin section indicates the role of retrogressive processes during which the brown biotites have been transformed into green biotites (cf. Verschure et al, 1980;Veblen and Ferry, 1983;Edwards and Essene, 1988;Shau et al, 1991;Pitra and Guiraud, 1996;Ikeda, 1998;Thomson, 2001;Brown, 2002;Waters and Charnley, 2002;Henry et al, 2005). The transformation of brown biotite to green biotite is evidenced by Ti-exsolution (±chloritization) in the form of titanite and rutile where sagenitic texture is very characterisitic (Fig.…”

LA-MC-ICPMS Pb–Pb dating of rutile from slowly cooled granulites: Confirmation of the high closure temperature for Pb diffusion in rutile

“…Willigers et al, 2004), and the following closure temperatures would perhaps be more appropriate for the constructing the T-t history of the Adirondack Highlands: (1) U-Pb in monazite (P800°C; Kamber et al, 1998); (2) U-Pb in sphene (670 ± 45°C; Cherniak, 1993;Mezger et al, 1993); (3) Ar in hornblende (580°C; Cherniak et al, 1991;Kamber et al, 1995); and (4) Ar in biotite (ca. 400°C; Verschure et al, 1980;Del Moro et al, 1982;Harrison et al, 1985). Using these closure temperature estimates, we calculate a T c for Pb diffusion in the rutile from the study of Mezger et al (1989a) to be 500°C and 540°C for rutile with a diameter of 0.14-0.18 and 0.18-0.42 mm, respectively.…”

Nonmonotonic thermal histories and contrasting kinetics of multiple thermochronometers

“…Rb/Sr ages of micas in metamorphic rocks are commonly observed to be ''too old" to be consistent the inferred metamorphic history of their host rocks. Examples include highgrade metamorphic rocks in western Norway (e.g., Verschure et al, 1980;Kü hn et al, 2000;Glodny et al, 2008), the central and eastern Alps (von Blanckenburg et al, 1989;Steck and Hunziker, 1994), and the Urals (Glodny et al, 2003). The preservation of pre-metamorphic or too-old Rb/Sr mica ages has been suggested to reflect (1) previously overestimated diffusivity of Sr in micas (e.g., von Blanckenburg et al, 1989);…”