Quinn, Elizabeth J.

Sessions, Katie J.

Opus: Research and Creativity at IPFW

Indiana University - Purdue University Fort Wayne
Opus: Research & Creativity at IPFW
2002 IPFW Student Research and Creative
Endeavor Symposium
IPFW Student Research and Creative Endeavor
Symposium
4-16-2002
Geochronological Dating Of Monazite Using
Energy Dispersive X-Ray
Elizabeth J. Quinn
Indiana University - Purdue University Fort Wayne
Katie J. Sessions
Indiana University - Purdue University Fort Wayne
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Elizabeth J. Quinn and Katie J. Sessions (2002). Geochronological Dating Of Monazite Using Energy Dispersive X-Ray.
http://opus.ipfw.edu/stu_symp2002/11
GEOCHRONOLOGICAL DATING OF MONAZITE USING ENERGY DISPERSIVE 
X-RAY 
Elizabeth J. Quinn, Katie J. Sessions 
Sponsor: Anne Argast 
Department of Geosciences 
Indiana University-Purdue University Fort Wayne 
Monazite is a mineral rich in rare earth elements as well as uranium and thorium. 
Radiogenic lead accumulates quickly in the mineral and can be analyzed with an electron 
microprobe (EMP) in samples of monazite older than 100 Ma (Mentel et al., 1996). 
Parrish (1990) reports that in conventional U-Pb dating analyses the non-radiogenic lead 
content is always very low, less than 1 ppm. Making the assumption that lead is 
conserved in this mineral, a revised method for geochronological dating of monazite is 
being investigated using energy dispersive x-ray (EDX) rather than EMP. If successful, a 
more generally accessible method of dating monazite would be available. Using the 
recently developed technique, this research attempts to determine the provenance age for 
sedimentary debris in the Fern Creek Formation (2.1 Ga, Chocolay Group, Marquette 
Range Supergroup, UP, Michigan.). The sample was collected at the Sturgeon River 
Dam, two miles northeast of Loretto, Michigan. It was analyzed to determine whether the 
Fern Creek Formation contains monazite derived from underlying Archean gneiss (---2.6 
Ga) or whether the monazite originated from metamorphism associated with the 
Penokean orogeny ( ~1.9 Ga). Lead could not be found in the monazite, despite a high 
concentration of thorium. This monazite, therefore, could not be used for age 
determination by this technique. Because of the absence of lead in the monazite, huttonite 
(ThSi04) from the same sample was investigated. Huttonite is isostructural with monazite 
and contains thorium and lead from its decay (Deer, 1966). Because ofthis, huttonite 
should be similar to monazite in its ability to retain lead. The sample that was tested has a 
formula calculated to be: Th.s6U.o7Ca.10Al.09Mg_o~e.06REE. 11Pb.os(P.19Si_90)04.0· The 
sample was .analyzed using the ISI-DS 160 SEM, Kevex Sigma EDX and Quasar 
Quantitative Software. An 18 kV setting was used with a total count time of 1200 s. The 
age of the sample was computed to be 1.24 Ga using Maple 7 software to solve the 
complex formula presented by Monte! et al. (1996) in his work on chemical aging ofU­
Th minerals. The results of this research were inconclusive. It is conceivable that lead, 
uranium and thorium are not evenly distributed throughout the sample. It is also 
conceivable that lead is not conserved. Further research, probing other sites in samples 
from the same geographic area, needs to be done to substantiate or refute the age that has 
been calculated in this study. 
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Geochronological Dating Of Monazite Using Energy Dispersive X-Ray

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Geochronological Dating Of Monazite Using Energy Dispersive X-Ray

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