Speaker：Prof. Sean Shieh(Department of Earth Sciences, Western University, Canada)
Title: Is diaplectic glass a glass? The untold story of plagioclase
Venue：2nd Floor Lecture Hall
Host：Wen-Pin Hsieh / Research Fellow
《 Abstract 》
Is diaplectic glass a glass? The untold story of plagioclase
Plagioclase feldspar is the most common phase found on the surface of terrestrial planets. Furthermore, diaplectic glass is an optically isotropic, amorphous phase and is believed to be formed by shock transformation of plagioclase. However, the relative scarcity of diaplectic glass was reported from the sample return of Apollo missions. To understand the mechanism of formation of diaplectic glass and also the phase diagram of intermediate plagioclase at pressure >30 GPa in situ high pressure-temperature studies of intermediate plagioclase using the diamond anvil cell were carried out at GeoSoilEnviroCARS, Advanced Photon Source and at Western University.
Our Raman measurements showed that partial amorphization was observed at ~14 GPa for labradorite An51 and full amorphization was observed at >20 GPa. In situ high-pressure X-ray diffraction study supports this observation and found the amorphization of An51 extended to about 1200 K at high pressures. Upon heating, 4 different phase assemblages were observed at pressure from 20 to 62 GPa. A new phase was also observed at >50 GPa and above 1400 K. Importantly, the melting curve of An51 was also determined. Our new findings together with reported shockwave data may explain the formation of diapectic glass and provide shock indicators of lunar and Martian samples.