Quartz, jadeite, lawsonite, phengite, glaucophane, and chlorite characterize which metamorphic facies?

Quartz, jadeite, lawsonite, phengite, glaucophane, and chlorite characterize which metamorphic facies?

• A. Greenschist facies
• B. Blueschist facies
• C. Amphibolite facies
• D. Granulite facies

Answer: (B)

Mineral assemblages reveal the pressure–temperature conditions rocks experienced. The combination of blue minerals (glaucophane) with lawsonite, jadeite, phengite, chlorite, and quartz points to a high-pressure, low-temperature setting typical of blueschist metamorphism. This facies forms in subduction zones where rocks are pushed to high pressures while temperatures stay relatively cool, stabilizing those specific minerals. The presence of jadeite and lawsonite, in particular, is a strong indicator of blueschist conditions. By contrast, greenschist facies would show chlorite, epidote, and actinolite without these blueschist minerals; amphibolite facies features hornblende and plagioclase, and granulite facies involves high-temperature minerals like pyroxenes and garnet with little hydrous minerals.

Mineral assemblages reveal the pressure–temperature conditions rocks experienced. The combination of blue minerals (glaucophane) with lawsonite, jadeite, phengite, chlorite, and quartz points to a high-pressure, low-temperature setting typical of blueschist metamorphism. This facies forms in subduction zones where rocks are pushed to high pressures while temperatures stay relatively cool, stabilizing those specific minerals. The presence of jadeite and lawsonite, in particular, is a strong indicator of blueschist conditions. By contrast, greenschist facies would show chlorite, epidote, and actinolite without these blueschist minerals; amphibolite facies features hornblende and plagioclase, and granulite facies involves high-temperature minerals like pyroxenes and garnet with little hydrous minerals.