Single grain argon laser probe dating of phengites from the blueschist to greenschist transition on Sifnos (Cyclades,Greece) |
| |
Authors: | Jan R Wijbrans Manfred Schliestedt Derek York |
| |
Institution: | (1) Geophysics Group, Department of Physics, University of Toronto, M5S 1A7 Toronto, Canada;(2) Institut für Mineralogie, Universität Hannover, Welfengarten 1, D-3000 Hannover, Germany;(3) Present address: NWO Laboratory for Isotope Geology, De Boelelaan 1085, NL-1081 HV Amsterdam, The Netherlands |
| |
Abstract: | Measurements of 40Ar/39Ar age spectra on single white mica crystals of Tertiary age is a new means of obtaining detailed geochronological information of Alpine blueschists. Internal consistency of the data set, as well as excellent agreement with previous conventional K–Ar results, demonstrates that this new technique can be used with confidence to obtain information on the thermal evolution of young metamorphic belts.As mineral grains can be dated individually with this technique, problems related to multiple generations of mica occurring side in the rock can be addressed, potentially yielding much information which cannot be obtained easily by other dating techniques. Ages decrease from 41.7±0.3 Ma in the fresh blueschists and eclogites in northern Sifnos to ca 30 Ma in the more severely overprinted greenschists of central Sifnos. It is argued that this decreasing trend appears gradual, rather than stepwise. This gradual character of the age trend is taken to indicate that it may be caused by differential uplift and cooling, rather than by tectonic juxtaposition of different rock units. In addition, the rocks of central Sifnos contain mica with a plateau age of 18.9±0.3 Ma. This latter age is younger than previous estimates for the age of greenschist overprinting, and more in line with the age of high temperature metamorphism and granite emplacement elsewhere in the Cyclades. |
| |
Keywords: | |
本文献已被 SpringerLink 等数据库收录! |
|