Gyarub Zangbo Pallasite: The Outer Solar System Meteorite Found in Tibet

Meteorite Field Guide

Gyarub Zangbo is a pallasite recovered from the Tibetan plateau in 2020. Its oxygen and chromium isotopic signatures place it in the carbonaceous reservoir of the solar system, the same chemical province as bodies that formed in the outer solar system beyond Jupiter. It is officially classified as Pallasite, ungrouped, and represents a parent asteroid with no known match in the meteorite collection.

Discovery on the Roof of the World

In October 2020, a collector named Mr. G. Tulga was exploring the Qiangtang uninhabited region of the Qinghai-Tibet Plateau in western China, northeast of the Gyarub Zangbo River. At an elevation of roughly 4,500 meters above sea level, in one of the most remote landscapes on Earth, he found something that had traveled incomparably further: fragments of an iron-olivine meteorite scattered across the surface.

Several disaggregated pieces composed of olivine crystals and iron-nickel metal were recovered, along with a single much larger metal-rich specimen nearby. Total recovered mass came to approximately 17.6 kg distributed across multiple stones and fragments. The meteorite was named after the river and valley near its findsite, following standard Meteoritical Society nomenclature.

The Tibetan plateau is an exceptional preservation environment for meteorites. The high altitude, aridity, and minimal vegetation mean that stones remain exposed on the surface for extended periods without significant weathering. This is reflected in the relative freshness of Gyarub Zangbo material, which shows well-preserved olivine crystals and a polishable metal matrix despite the extreme environment.

What Is a Pallasite, and Why Is Gyarub Zangbo Different

Pallasites are stony-iron meteorites composed of two phases in intimate contact: crystals of the mineral olivine embedded in a matrix of iron-nickel metal. The metal shows the interlocking kamacite-taenite crystallography called the Widmanstatten pattern, which forms only during extraordinarily slow cooling inside the core of a differentiated asteroid over millions of years. The olivine occupies void spaces between the metal grains, glowing amber, gold, or green when light passes through a polished slice.

The leading formation model for pallasites places their origin at or near the core-mantle boundary of a fully differentiated asteroid, where molten iron-nickel core material contacted the overlying rocky silicate mantle. Some recent research suggests an impact mixing origin, in which a differentiated planetary core was injected into the mantle of a separate body during a collision early in solar system history. Either way, pallasites record a chapter of planetary geology that cannot be studied any other way: the deep interior of a world that no longer exists.

Most pallasites in collections belong to the main group (PMG), which shares a single parent body. The Eagle Station group comprises a small cluster of chemically related specimens. Gyarub Zangbo fits neither. Its olivine composition, metal chemistry, and critically, its isotopic signatures, all point to a body that formed separately from every other known pallasite source.

The Science: A Carbonaceous Signature from Beyond Jupiter

The most scientifically consequential aspect of Gyarub Zangbo is not its rarity as an ungrouped pallasite, but what its isotopic chemistry reveals about where in the solar system its parent body formed.

Planetary scientists have identified a fundamental chemical divide in solar system material called the non-carbonaceous / carbonaceous (NC/CC) dichotomy. Meteorites from the inner solar system, including Earth, Mars, the Moon, ordinary chondrites, and main group pallasites, cluster together in a distinct isotopic field. Meteorites that formed in the outer solar system, beyond what was then proto-Jupiter, cluster in a separate field. These two populations are isotopically non-overlapping across multiple element systems including oxygen, chromium, titanium, and molybdenum.

The prevailing explanation for this divide is Jupiter itself. As proto-Jupiter grew rapidly in the outer disk, it created a pressure barrier that prevented carbonaceous material from drifting inward. Bodies that accreted in the CC reservoir, beyond this barrier, developed a distinct chemical fingerprint that is preserved in the meteorites they produced.

The CC group includes the carbonaceous chondrite families (CI, CM, CO, CV, CK, CR, and others), the Eagle Station pallasites, and several iron meteorite groups (IIC, IID, IIF, IIIF, IVB). What makes Gyarub Zangbo remarkable is that it is the first ungrouped pallasite confirmed to carry a CC isotopic signature while also being compositionally distinct from the Eagle Station group. It represents a separate, previously unsampled differentiated asteroid that originated in the outer solar system.

It is important to distinguish isotopic classification from visual or mineralogical composition. The word "carbonaceous" in this context refers specifically to the CC isotopic reservoir, not to visible carbon content. Gyarub Zangbo slices look like pallasites, not like black carbonaceous chondrites. The carbonaceous designation is a chemical and genetic one, indicating ancestral relationship to the outer solar system population, not a textural description of the meteorite itself.

Mineralogy and Physical Characteristics

Gyarub Zangbo olivine has a fayalite content of approximately 21.6 mol%, which is homogeneous throughout the material. This consistency indicates that the olivine equilibrated thermally inside the parent body rather than being a jumbled mixture of grains from different sources. The iron-nickel metal phase contains approximately 15.8 wt% nickel, with trace amounts of cobalt, copper, and germanium.

The specimens recovered show considerable variation in the ratio of olivine to metal from piece to piece. Some slices are metal-rich with scattered olivine; others show dense concentrations of crystals. This heterogeneity within a single fall is consistent with sampling material from across the core-mantle boundary zone rather than a uniform region.

The olivine crystals in polished slices range in color from olive-green to golden-amber to deep brown, depending on iron content distribution within individual grains and the angle of transmitted light. Under backlighting, translucent crystals glow intensely gold. Crystals showing heavier oxidation or fracturing appear darker, often displaying rich amber and rust tones. No two slices have the same distribution of crystal size, color, and density, which makes each specimen visually distinct even within the same meteorite.

The Widmanstatten pattern in the iron-nickel matrix is well-developed and prominent in etched or polished sections. The intersecting bands of kamacite and taenite are a direct record of the incredibly slow cooling rate inside the parent asteroid, estimated at only a few degrees per million years. This pattern cannot be replicated in any laboratory process and is one of the definitive authentication markers for meteoritic iron.

Frequently asked questions

Collector Significance

Gyarub Zangbo occupies a narrow intersection of scientific importance and visual quality that is difficult to find in a single meteorite. Its aesthetic appeal is genuine: well-prepared slices show the full range of pallasite character, from densely packed olivine fields to expansive etched kamacite regions with sharp Widmanstatten bands. The olivine crystals are translucent and range widely in color, from pale green to deep amber, often within a single slice.

Its scientific significance is not speculative. The 2023 LPSC research by Jiang and colleagues establishes Gyarub Zangbo as a confirmed member of the carbonaceous isotopic reservoir, the first ungrouped pallasite to be so characterized with this combination of chemical and isotopic evidence. It represents a real data point in ongoing research into the structure of the early solar system and the populations of differentiated bodies that formed beyond Jupiter.

For collectors interested in acquiring material that is both displayable and scientifically documented at the highest level, Gyarub Zangbo is one of a very small number of pallasites that delivers both. It is not a common main group specimen. It is a window into a parent asteroid from the outer solar system, recovered from the Tibetan plateau in 2020, documented in the scientific literature, and classified in the Meteoritical Bulletin.

• Sericho Pallasite: Kenya's Iron-Olivine Giant
• Pallasite Meteorites for Sale
• Meteoritical Bulletin Entry #73792 (Gyarub Zangbo)
• Jiang et al. 2023, LPSC: "Gyarub Zangbo: An Anomalous Carbonaceous Pallasite"