A large weathered pallasite mass along with about a hundred disaggregated fragments, having a combined weight of 17.614 kg, were found by Mr. G. Tulga on the Qinghai-Tibet Plateau in China. The total mass of this pallasite was subsequently sold to Z. Wang. A type sample was submitted to the University of Washington in Seattle (A. Irving) and Washington University in St. Louis (P. Carpenter) for analysis and classification, and Gyarub Zangbo was classified as an ungrouped pallasite.
The Gyarub Zangbo pallasite is composed of small rounded to angular, mostly dark brown olivines (~60 vol%) embedded in an FeNi-metal host (~36 vol%), together with minor troilite, schreibersite, chromite (Fe-rich, Al-poor), phosphate, and pyroxene (Jiang et al., 2023 #1183). Gyarub Zangbo has an olivine Fa value of ~21.6, a high Ir and Ni concentration, and a positive ε54Cr isotope value of 3.05 (±0.32), which are all consistent with formation in the CC reservoir.
Subsequent analyses of both the Gyarub Zangbo and Bordji Badji Mokhtar 001 pallasites were conducted by Boesenberg et al. (2023 #2392). A chemical analysis of the metal in Gyarub Zangbo shows a trace element composition that is anomalous relative to other pallasites, with a high Ir content indicative of an early crystallized core unit (see diagrams below).
Ga vs. Au and Ir vs. Au Concentrations for Gyarub Zangbo, Pallasites, and Iron Groups
Diagrams credit: Boesenberg et al., 54th LPSC, #2392 (2023)
Triple Oxygen Isotopes for Ungrouped Pallasites and Irons
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Diagram credit: Jiang et al., 54th LPSC, #1183 (2023)
Chromite Fe/(Fe+Mg) vs. Al/(Al+Cr) for Pallasites
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Diagram credit: Boesenberg et al., 54th LPSC, #2392 (2023)
Some proposed scenarios for pallasite formation can be found on the Imilac page. The specimen of Gyarub Zangbo shown above is a 5.1 g interior slice, compliments of Shun-Chun Yang.
Gyarub Zangbo Etched Slice
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Photo courtesy of Shun-Chun Yang
Gyarub Zanbo 29.25 kg Slice
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Photo courtesy of Yin Shu
