Connotea
CiteULike
del.ico.us
BibSonomyAbstract
GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS,
VOL. 10,
Q0AA01,
13 PP., 2009
doi:10.1029/2009GC002497 [Citation]
Improved confidence in (U-Th)/He thermochronology using the laser microprobe: An example from a Pleistocene leucogranite, Nanga Parbat, Pakistan
Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02215, USA
Department of Earth and Space Sciences, University of California, 595 Young Drive East, Los Angeles, California 90095-1567, USA
Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02215, USA
School of Earth and Space Exploration, Arizona State University, Box 871404, Tempe, Arizona 85287, USA
Materials Research Division, Carl Zeiss MicroImaging, Inc., One Zeiss Drive, Thornwood, New York 10594, USA
Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02215, USA
Department of Geosciences, Boise State University, Mailstop 1535, 1910 University Drive, Boise, Idaho 83725-1535, USA
Department of Geosciences, University of Massachusetts, 611 North Pleasant Street, Amherst, Massachusetts 01003-9297, USA
Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02215, USA
Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02215, USA
Department of Earth Sciences, Oxford University, Parks Road, Oxford OX1 3PR, UK
The newly developed laser microprobe (U-Th)/He thermochronometer permits, for the first time, the ability to generate precise (U-Th)/He cooling ages for even very young (<1 Ma) samples with a spatial resolution on the order of tens of micrometers. This makes it possible to test the reproducibility of independent (U-Th)/He age determinations within individual crystals, further increasing the reliability of the method. As an example, we apply it here to a Pleistocene granite from Nanga Parbat, Pakistan, where previous constraints on the thermal history are consistent with rapid exhumation and cooling. Twenty-one (U-Th)/He dates determined on two monazite crystals from a single granite sample yield a mean of 748,000 years with a ∼95% confidence level of ±19,000 years. There is no discernible variation in the distribution of (U-Th)/He ages in the cores of these crystals and therefore no evidence for the development of substantial diffusive-loss 4He zoning over 80% of the interior of the monazite crystals during postcrystallization cooling of the granite. Modeling of these data suggests that cooling at a mean rate of ∼300 K/Ma would be necessary to produce the observed ages and the lack of a 4He gradient, which is consistent with preexisting constraints for Nanga Parbat. Increased precision in thermochronology permits more tightly constrained exhumation models, which should aid geologic interpretation.
Received 13 March 2009; accepted 31 July 2009; published 16 September 2009.
Citation: (2009), Improved confidence in (U-Th)/He thermochronology using the laser microprobe: An example from a Pleistocene leucogranite, Nanga Parbat, Pakistan, Geochem. Geophys. Geosyst., 10, Q0AA01, doi:10.1029/2009GC002497.
Cited By