Monazite, crystallization

Monazite crystals within the ferrocarbonatite sample were dated using CHIME U-Th-Pb, and an age of 165 8 Ma was calculated. This age was used to evaluate the Sm-Nd ( nci= -6.0) and Rb-Sr ( Sr/ Sri65 = 0.71061) data these values are considerably different than the syenites and the sannaites. The high initial "sr/ Sr and low nci indicate that the... 

A monazite crystal in a metamorphic rock is about 100 pm across. It is estimated that the peak metamorphic temperature was 700°C and monazite formed near peak metamorphism. The metamorphic event lasted for about 20 Myr. Find the diffusion distance and evaluate whether the monazite grain lost a significant amount of Pb. That is, evaluate whether monazite grain can be used to determine the age of peak metamorphism. 

The diffusion coefficient of Pb in monazite depends on temperature as D = exp(-0.06-71,200/7) m /s (Cherniak et al., 2004). You found a 100-/rm-diameter monazite crystal in a metamorphic rock. Assume that the monazite crystal formed at peak metamorphic temperature. 

Objections against these findings were soon raised. The strongest peak attributed to element 126 could experimentally be accounted for [55] by a prompt y-ray from the (p,n) nuclear reaction with natural 140Ce, a major component of the monazite crystals. The weaker peaks were shown to stem from to K x-rays from traces of ordinary elements such as antimony and tellurium [56]. When a more specific technique for the excitation of x-ray spectra was applied to the inclusions, namely by monochromatic synchrotron radiation tuned to the x-ray absorption edges, the evidence for superheavy elements vanished [57,58]. Furthermore, attempts failed [59] to detect them in bulk monazites through isolation of an A>294 fraction with a mass... 

Figure 28 Backscattered electron image and age measurements for complexly zoned monazite crystals from contact metamorphosed Ireteba granite, Nevada. Crystallization age of the pluton is 65 Ma. Subsequent infiltration of fluids perhaps as young as 16 Ma apparently dissolved and reprecipitated new monazite in an extremely complex fashion. Ages determined via ion microprobe, and have t)fpical uncertainties of a few percent...

More recently, Morgan and Marshall have suggested that compounds having the monazite crystal structure may be useful oxidation interface coatings. Specifically, they recommend the compound LaP04. Their sol-gel experiments with this compound are encouraging. 

The correlation of Th and U with Si is shown dramatically in the X-ray maps of Figure 14. An intermediate zone in this monazite crystal has a euhedral outline with initially high Th, which decreases steadily outward. Si zoning (Fig. 14b) matches the Th zoning perfectly. U is only weakly zoned, but shows a similar pattern. Y zoning is indistinct, and does not show the sharp chemical zones seen in Th and Si. 

Compositionally distinct material observed in the cores of some migmatite zone monazite crystals (e.g.. Figs. 15g,h,i) could readily be interpreted as representing the initially-formed monazite core. However, Pyle et al. (2001) have suggested that this texture, in some instances, may arise from an extremely irregular crystal shape and the orientation of the thin section cut through the crystal (Fig. 16). Monazite at low grades is... 

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