Water contrast between Precambrian and Phanerozoic continental lower crust in eastern China

The presence of water, even in small amounts, in the continental lower crust may play a critical role in its physical and chemical properties and behavior. However, the environment and evolution of water in the deep crust remain poorly constrained. Investigation of water, dissolved as H‐related point defects in minerals of lower crustal granulites, may provide clues to clarify this issue. The analyzed and compiled water data of nominally anhydrous clinopyroxene (cpx), orthopyroxene (opx), and plagioclase (plag) in lower crustal granulites from Hannuoba, Nushan, and Daoxian in eastern China reveal significant contrast in water contents (ppm H 2 O by weight) between Precambrian and Phanerozoic samples, e.g., 200–2330 versus 275–720 ppm for cpx, 140–1875 versus 60–185 ppm for opx, 145–900 versus 65–345 ppm for plag, and 155–1120 versus 165–360 ppm for the bulk concentrations. Our data show consistently higher water contents in the Precambrian granulites, implying a more hydrous lower crust in the Precambrian than in the Phanerozoic. Such a difference may reflect variable water contents in the original melts, indicating higher water contents in the Precambrian upper mantle or a plume source for that part of the Precambrian lower crust.