The same in-run precision was obtained from a 30 μm × 20 μm crater using a 200 fs laser beam of 20 μm in diameter rastered along the circumference of a circle with a 7 μm radius at 25 Hz for 15 s.With an enhanced sensitivity ion interface, the sensitivity for the total amount of Pb was ∼2 m V ppm Ω register enabled the determination of the U–Pb age of zircon and monazite crystals with an internal and intermediate precision comparable to that obtained from sensitive high resolution ion microprobe (SHRMP) techniques.Therefore, it is assumed that all lead found within a grain is due to radioactive decay of uranium and thorium.Estimates of monazites closure temperature are ~820 ± 30 degrees C (Parrish, 1990; Spear and Parrish, 1996).
Zircon and monazite ages are accurate given the small offsets from ID-TIMS ages, 0.15–0.7% for zircons and 0.2–0.7% for monazite well within internal precision from the primary standard in the analytical session and competitive with an internal precision of 0.43–0.6% for zircon and 0.2–0.8% for monazite.
A total of 30 points on 7 grains were analyzed for sample ARR96-106. 2) defined by the leucosomes, and they occured in both the leucosomes and the selvages.
35 total points on 9 matrix monaztite grains plus 5 single points on 5 small monazite inclusions in garnet were analyzed for sample ARR96-117. All electon microprobe analyses were done on a JEOL 733 Superprobe by Dr. Monazite inclusions in garnet porphyroblasts were generally aligned in sigmoidal inclusion trails that represent an earlier fabric.
It is useful for geochronology because it contains relatively large amounts of uranium and thorium, which decay radioactively to lead.
Typically, there is negligible non-radiogenic lead in monazite.