Cathodoluminescence Characterization of Maskelynite and Alkali Feldspar in Shergottite (Dhofar 019)

摘要

Dhofar 019 is classified as an olivine-bearing basaltic shergottite and consists of subhedral grains of pyroxene, olivine, feldspar mostly converted to maskelynite and minor alkali feldspar. The CL spectrum of its maskelynite exhibits an emission band at around 380 nm. Similar UV-blue emission has been observed in the plagioclase experimentally shocked at 30 and 40 GPa, but not in terrestrial plagioclase. This UV-blue emission is a notable characteristic of maskelynite. CL spectrum of alkali feldspar in Dhofar 019 has an emission bands at around 420 nm with no red emission. Terrestrial alkali feldspar actually consists of blue and red emission at 420 and 710 nm assigned to Al-0~--Al and Fe~(3+) centers, respectively. Maskelynite shows weak and broad Raman spectral peaks at around 500 and 580 cm~(-1). The Raman spectrum of alkali feldspar has a weak peak at 520 , whereas terrestrial counterpart shows the emission bands at 280, 400, 470, 520 and 1120 cm~(-1). Shock pressure on this meteorite transformed plagioclase and alkali feldspar into maskelynite and almost glass phase, respectively. It eliminates their luminescence centers, responsible for disappearance of yellow and/or red emission in CL of maskelynite and alkali feldspar. The absence of the red emission band in alkali feldspar can also be due to the lack of Fe3+ in the feldspar as it was reported for some lunar feldspars.