This age was confirmed by isotopic U–Pb SHRIMP dating (341.6 ± 2.8 Ma).
These results are in agreement with previous estimates for the timing of durbachitic intrusions into the root of the Variscan orogen and from the Variscan basement incorporated into Western Alps, between 343 and 332 Ma.
Zircon grains are commonly partially or completely metamict, and therefore susceptible to Pb loss and common Pb contamination.
Using Ca and K contents as indicators of damaged or contaminated zircon, a CHIME (Chemical U–Th–total Pb method) age of 347.8 ± 18 Ma was obtained from data with 0.0062 wt.% of Pb O.
One particular reaction that has received attention in pelitic rocks is the staurolite-in reaction at which garnet is commonly consumed (Pyle and Spear, 2003). H., (2006) Geochronological constraints on the evolution of high-pressure felsic granulites from an integrated electron microprobe and ID-TIMS geochemical study.
The loss of garnet may be partly or even dominantly responsible for the appearance of monazite that has been observed at the staurolite-in isograd.
Our research focuses on I- and S-type granites of the Lachlan Fold Belt (LFB), Australia, for which petrology and zircon chronology have been thoroughly characterized.
We are documenting textural relationships, morphology and zoning of monazite in these granitic rocks.
These comparisons will allow further evaluation of the role played by basement type and source rocks in the petrogenesis of these granitic rocks.In addition trace element concentrations have been measured for a number of zircons from the same source.The present work supports the view that in general the apparent age decreases as the amount of U and Th increases, possibly due to radiation damage within the crystal.Monazite is a lanthanum-cerium light rare earth element phosphate that is common in many igneous rocks and metamorphic rocks.It is useful for geochronology because it contains relatively large amounts of uranium and thorium, which decay radioactively to lead.