Assessment of the 187Re decay constant by cross calibration of Re–Os molybdenite and U–Pb zircon chronometers in magmatic ore systems

Metrology and Traceability of U-Pb Isotope Dilution Geochronology (EARTHTIME Tracer Calibration Part I)

“…This approach requires a priori assumption that the radio-isotopic dates for minerals A and B should be equivalent and/or have an established systematic relationship. This approach has contributed to calibrations of the 40 Ar/ 39 Ar (Renne et al, 2010), Re-Os (Selby et al, 2007), Lu-Hf (Sö derlund et al, 2004), Rb-Sr (Nebel et al, 2011) radio-isotopic dating systems, and also U-Th, which uses the same principle but involves calibration against secular equilibrium ratios (Cheng et al, 2000(Cheng et al, , 2013. Improvements in the accuracy of the U-Pb system as a result of the EARTHTIME tracer calibration experiment (e.g., reduced uncertainty in the purity of NBS 981 and 982 Pb metals, isotopic composition of U reference materials) can now be used to inform these previous experiments (excluding the U-Th system) where the input data are fully documented and permit full re-processing of the raw mass spectrometric data using new input parameters and data reduction algorithms.…”

“…Traceability is critical for quantifying the accuracy of absolute U/Pb geochronology and comparing U/Pb dates with other isotope dating systems, whose ages are determined using an independent set of experiments (e.g., 40 Ar/ 39 Ar) or using numerical models of solar system orbital dynamics (i.e., astrochronology). Decay constants for several other isotopic systems have been calibrated with respect to, or informed by, the U-Pb system through 'inter-calibration' experiments as a means to augment first-principles counting or ingrowth experiments (e.g., Rb-Sr, Re-Os K-Ar, Lu-Hf; Nebel et al, 2011;Scherer et al, 2001;Selby et al, 2007;Renne et al, 2010). For these cases, the ability to trace the U-Pb system back to SI units means that these other decay systems can also be traced back, within limits, through assumptions about the samples used for inter-calibration.…”

Mantle Sulfides and their Role in Re–Os and Pb Isotope Geochronology

“…Critically, sulfide exposed in a thin section or grain mount that may appear to be distant from any grain boundary in the two observable dimensions may in fact intersect a grain boundary in the third dimension. ; Shen et al 1996;Smoliar et al 1996;Selby et al 2007) is the primary control on the long term evolution of 187 Os/ 188 Os in the mantle. Therefore, undisturbed Type-1 BMS may preserve important geochronological information pertaining to ancient melt depletion events, as the lack of subsequent 187 Os ingrowth due to the near absence of Re that was partitioned into the melt preserves the original 187 Os/ 188 Os of the BMS in presumed isotopic equilibrium with the silicate melt at the time of melt depletion.…”

U-Pb, Re-Os, and Ar/Ar Geochronology of Rare Earth Element (REE)-Rich Breccia Pipes and Associated Host Rocks from the Mesoproterozoic Pea Ridge Fe-REE-Au Deposit, St. Francois Mountains, Missouri

“…Although insignificant, the Re (1.4 pg/g) and Os (0.2 pg/g, with 187 Os/ 188 Os = ~0.28) data are blank-corrected using the average Re-Os blank values at the time of analysis. The Re-Os data are presented with a total of three different uncertainties (at 2-sigma level): (1) error that includes mass spectrometry uncertainties only; (2) error that includes all sources of analytical uncertainty (Re and Os mass spectrometer measurements, blank abundances and isotopic compositions, spike calibrations and reproducibility of standard Re and Os isotopic values); and (3) error that includes all sources of analytical uncertainty (#2 above), plus uncertainty in the decay constant (0.35%; Smoliar et al, 1996;Selby et al, 2007; Table 2). 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 36 Ar/Ar analysis 40 Ar/ 39 Ar data were acquired at the USGS in Denver, CO.…”