Refractory Element Fractionations in the CV3 Carbonaceous Chondrite Allende: What Role do CAIs Play?

Several studies, primarily Kornacki and Fegley (1986) and Munker et. al. (2003), suggested that calcium-aluminum-rich inclusions (CAIs) common to the CV3 subclass of chondritic meteorites contain significantly lower Nb-Ta ratios than the accepted bulk solar system value. These studies have lead me postulate that; CV3 carbonaceous chondrites display, on average, low Nb/Ta values because of the low Nb/Ta values in the CAIs. Calcium, titanium, niobium, tantalum, zirconium, and hafnium abundances were obtained via LA-ICP-MS analysis on five chondrules, two CAIs, and the matrix from the CV3 carbonaceous chondrite Allende. The matrix displayed Nb/Ta and Zr/Hf values that encompass around the accepted bulk solar system values of 19.9 ± 2 and 34.3 ± 3.5 respectively. The chondrules extracted from Allende displayed variable Nb/Ta values that ranged from 3.8 to 24.2 (1σ = 10%), and Zr/Hf values that ranged from 30.4 to 41.0 (1σ = 10%). The CAIs displayed consistently low Nb/Ta values that ranged from 0.9 to 12.7 (1σ = 10%), and erratic Zr/Hf values that ranged from 12 to 73 (1σ = 10%). The Nb-Ta ratios in comparison with the Zr-Hf ratios show evidence that fractionation of Nb and Ta occurred independently of any Zr and Hf fractionation. Furthermore, within CAIs, there is evidence that as the Nb/Ta values decrease, the Zr/Hf values become more erratic. I cannot say that I know the reasons behind these low Nb/Ta values, nor the erratic Zr/Hf values found within these CAIs, I speculate that any inaccuracy in the currently accepted 50 % condensation temperatures of these refractory elements may provide insight into the mechanisms behind the findings in this study