MINERAL INCLUSIONS IN ZIRCONS FROM UHP ECLOGITE AND HP GRANULITE AND CONSTRAINTS ON THE P-T CONDITIONS OF ZIRCON GROWTH, NORTH QAIDAM TERRANE, CHINA

Ultra high-pressure eclogites from the North Qaidam terrane, near the Dulan region of Western China, contain zircons with a variety of inclusions that can be used to constrain timing of ultra-high pressure metamorphism in the region.

Zircons were mechanically separated from whole rock samples, mounted in epoxy, and imaged with SEM. CL, BSE, and EDS maps were used to pinpoint where inclusions are located in the zoned zircons. Inclusions were identified by their EDS spectra. Initial analysis was conducted with three zircons with inclusions each from seven samples of eclogite. The inclusion phases identified include rutile, omphacite, hornblende, calcic and low Na clinopyroxenes, quartz, garnet, epidote, zoisite, and apatite. Most of the inclusions were monophase, and there were plenty examples of intermediate compositions in solid solution phases, predominately between omphicite and less sodic clinopyroxenes. Rutile inclusions primarily occur in more euhedral zircons. Many zircons that are subhedral have inclusions showing atypical morphologies for the minerals present, including narrow, needle-like inclusions of minerals that do not typically present with that habit.

Using the data collected here and the location of the inclusions relative to the zoning in the zircons, we can constrain the timing of the development of the inclusion.