Evidence for multiple dynamic events and subsequent decompression stage recorded in a shock vein

We investigated a shock vein of the Yamato 791384 L6 chondrite to clarify the nature and sequence of the dynamic processes that resulted from the shock events. The chondritic host-rock of Y-791384 mainly consists of olivine (Fa24–25), low-Ca pyroxene (Fs18–22), albitic feldspar (An9–10Ab84–86Or5–7), troilite and metallic Fe–Ni. The shock vein contains majorite (or majorite-pyropess) and magnesiowüstite (+ minor jadeite) as high-pressure polymorphs. Two different dynamic events were recorded in the shock vein. The majorite grain contained vitrified (Mg,Fe)SiO3-perovskite inclusions. The (Mg,Fe)SiO3-perovskite was crystallized from a chondritic melt, and is a remnant of a first dynamic event. The majorite and magnesiowüstite were also crystallized directly from a chondritic melt but induced by a second dynamic event. The pressure condition for the first and second dynamic events would be >~24 GPa and <~22 GPa, respectively. Pervasive feather-shaped olivine (Fa16) nucleated on the magnesiowüstite and majorite. This feather-shaped olivine is evidence for rapidly grown olivine from the melt related to the shock event. Phase relations deduced from high-pressure melting experiments of the Allende meteorite and peridotite indicate that the magnesiowüstite and majorite + olivine pair cannot coexist at equilibrium condition. The disequilibrium assemblage reflects a decompression stage. These features demonstrate the complexity of events during a natural dynamic process.

Research Highlights► Complex history of a shock vein in Yamato 791384 L6 chondrite. ► Evidence for multiple planetesimal collisions in the shock vein. ► Further evidences for melting during a dynamic event in the shock vein. ► Record of decompression stage in the shock vein.