The composition and chemical zoning in garnet from high to ultrahigh pressure metamorphic rocks
高压-超高压变质岩石中石榴石的环带和成因

Garnet is common in eclogite and gneiss of high-pressure (HP) to ultrahigh-pressure (UHP) metamorphic origin. It can be well preserved during subduction-zone metamorphism for its high refractoriness and low solubility in fluid and melt. The chemical composition and mineral inclusions preserved in garnet can be used to constrain the P-T conditions, metamorphic evolution, and fluid action. The chemical composition of garnet is related to many factors, such as whole-rock composition, P-T conditions, garnet-forming metamorphic reactions and the assemblage of coexisting minerals. Thus the major elements, trace elements, oxygen isotopes, mineral inclusions and their relations in garnet should all be taken into account when it is used to constrain the metamorphic P-T evolution in UHP metamorphic rocks. In addition, in-situ analyses of U-Pb isotopes and trace elements in accessory minerals such as zircon and/or monazite inclusions in garnet can place a direct constraint on the time of metamorphic garnet growth. Through studying the history of garnet growth during subduction-zone metamorphism, it can not only provide petrologic and geochemical evidence for the processes to produce garnet-bearing metamorphic rocks, but also give clues to the origin of garnet. These are very important to the chemical dynamics of subduction-zone metamorphism.