Re–Os geochronology of fractions composed of unsized, coarse, and fine molybdenite from a pod of unusual monazite–xenotime gneiss within a granulite facies paragneiss, Hudson Highlands, NY, yielded dates of 950.5 ± 2.5, 953.8 ± 2.6, and 941.2 ± 2.6 Ma, respectively. These dates are not recorded by co-existing zircon, monazite, or xenotime. SEM–BSE imagery of thin sections and separated grains reveals that most molybdenite grains are composed of core and rim plates that are approximately perpendicular. Rim material invaded cores, forming irregular contacts, probably reflecting dissolution/reprecipitation. EPMA and LA-ICP-MS analyses show that cores and rims have different trace element concentrations (for example, cores are relatively enriched in W). On the basis of inclusions of zircon with metamorphic overgrowths, we conclude that molybdenite cores and rims formed after high-grade regional metamorphism. The discovery of cores and rims in individual molybdenite grains is analogous to multi-component U-Pb geochronometers such as zircon, monazite, and titanite; thus, molybdenite should be carefully examined before dating to ensure that the requirement of age homogeneity is fulfilled.
Citation Information
| Publication Year | 2012 |
|---|---|
| Title | Multiple age components in individual molybdenite grains |
| DOI | 10.1016/j.chemgeo.2012.01.011 |
| Authors | John N. Aleinikoff, Robert A. Creaser, Heather Lowers, Charles W. Magee, Richard I. Grauch |
| Publication Type | Article |
| Publication Subtype | Journal Article |
| Series Title | Chemical Geology |
| Index ID | 70038465 |
| Record Source | USGS Publications Warehouse |
| USGS Organization | Central Mineral and Environmental Resources Science Center |
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John N Aleinikoff
Scientist Emeritus
Heather A Lowers
Research Geologist
Richard I Grauch
Scientist Emeritus
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John N Aleinikoff
Scientist EmeritusEmailPhoneHeather A Lowers
Research GeologistEmailPhoneRichard I Grauch
Scientist EmeritusEmailPhone