Shock-metamorphic features in amphiboles from the Xiuyan crater of China

Abstract

Amphibole-bearing gneiss fragments are common in the impact breccias of the Xiuyan crater, China. Three kinds of amphibole-bearing gneiss fragments with different shock-metamorphic levels have been identified. Shock-metamorphic features of amphiboles in these gneisses were investigated in situ by optical microscope, electron microprobe, Raman spectroscopy, and X-ray diffraction. Amphiboles in the weakly shocked gneiss (shock pressure less than 10 GPa) basically remain intact. Amphiboles in the moderately shocked gneiss (shock pressure range between 35 and 45 GPa) show strong deformation, reduced optical interference color, and partial loss of OH -. In the strongly shocked gneiss (shock pressure above 50 GPa), amphiboles are completely melted and dendritic pyroxenes crystallize from the melt. The formation of dendritic pyroxenes shows nearly complete loss of water in the amphibole melt at shock-induced high temperature above 1,500°C. The occurrence of both diopside and pigeonite dendrites crystallized in the same amphibole melt shows inhomogenous melt composition and rapid cooling of the melt.

Nanotextures and formation process of coesite in silica glass from the Xiuyan impact crater

“…(2018) recently proposed an updated classification system of shock metamorphism of silicate rocks and sediments, which classify crystalline rocks into F (felsic), M (mafic), A (anorthositic), and U (ultramafic). The gneiss clast from the suevite in this study belongs to the F type, in which the feldspar was completely transformed into vesicular feldspar glass, the quartz was completely transformed into diaplectic glass, and the amphibole was completely melted and decomposed (Yin and Chen 2014), but whole rock melts were not observed. The lack of a mixed whole‐rock melt suggests that the SiO 2 was not liquid during shock.…”

“…The opaque polyphase masses in transmitted light are constituted of tabular pyroxene and oxide crystals (Figs. 1c and 1d), which are the result of the melting and recrystallization of amphibole (Yin and Chen 2014).…”

Kinetic and Thermodynamic Transition Pathways of Silica by Machine Learning: Implication for Meteorite Impacts

“…Journal of Geophysical Research: Solid Earth 10.1029/2024JB028656 Direct monitoring intermediate structures or phase transition mechanism during meteorite impacts are extremely challenging. Previous geological records employed the extrapolation of melting temperature of minerals, for example, quartz or amphibole (Chen et al, 2023;Yin & Chen, 2014) to derive the impact pressure. However, such estimations of pressure are rough.…”