SR-BEARING ZOISITE AND EPIDOTE IN ULTRA-HIGH PRESSURE (UHP) METAMORPHIC ROCKS FROM THE SU-LU PROVINCE, EASTERN CHINA - AN IMPORTANT SR RESERVOIR UNDER UHP CONDITIONS

Sr-bearing zoisite and epidote are common constituents of eclogites an d associated paraschists throughout the Su-Lu ultra-high pressure (UHP ) province, eastern China. The SrO content of prograde zoisite and epi dote reaches 3.2 wt% in crystal cores and generally decreases toward c rystal margins. Retrograde epidote is poorer in SrO (<0.1 wt%). Prelim inary rare earth element (REE) analyses of epidote give La2O3 (up to 2 .9 wt%), Ce2O3 (5.9 wt%), and Nd2O3 (3.0 wt%). REE contents of zoisite are distinctly lower (La2O3 up to 0.16 wt%, Ce2O3 up to 0.26 wt%, and Nd2O3 up to 0.16 wt%) than coexisting epidote. Apatite is always more depleted in SrO (0.10-0.59 wt% on average) than coexisting zoisite an d epidote, and Sr-Ca partition coefficients for zoisite and epidote an d apatite [(Sr/Ca)(zo/ep-ap)] range from 5 to 20. SrO content of K-whi te mica (0.012-0.044 wt%) is an order of magnitude lower than that of apatite. An evaluation of the SrO content in zoisite and epidote and t heir modal abundances in seven samples indicates that >70% of the whol e-rock SrO is contained in these minerals. Apatite and K-white mica at e only minor reservoirs for SrO in these rocks. Zoisite and epidote ar e thus regarded as the most important Sr reservoirs at UHP conditions where calcic plagioclase and titanite are unstable.