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Th map of monazite from the Black Hills, South Dakota. "Rosetta" monazite, dating reactions and tectonism in the Black Hills.


The monazite grain is ~ 50 microns wide. The low Th core domains are ca. 1750 Ma, higher Th (and also high Y) rims are ca. 1690 Ma. Sigmoidal inclusion trails in core allow for age constraint for S1 and S2. S3 is constrained by the rim domains which truncate S1-S2, and are correllated with garnet resorption. The rims, therfore, allow direct reaction dating. For more information about this image, contact: Peter Dahl.