Tf. Yui et al., UNUSUALLY LOW DELTA-O-18 ULTRA-HIGH-PRESSURE METAMORPHIC ROCKS FROM THE SULU TERRAIN, EASTERN CHINA, Geochimica et cosmochimica acta, 59(13), 1995, pp. 2859-2864
Eclogite and quartzite interlayers, containing ultra-high-pressure (UH
P) metamorphic mineral assemblages, occur at Qinglongshan in the Sulu
terrain, eastern China. These rocks exhibit some of the most negative
oxygen isotope compositions that have ever been reported for metamorph
ic rocks. The delta(18)O value of minerals in eclogite ranges from -10
.4 to -9.0 parts per thousand and in quartzite ranges from -10.2 to -7
.3 parts per thousand. Near isotopic equilibrium between minerals and
rocks suggests that these rocks must have acquired such low oxygen iso
tope compositions before the UHP metamorphism, through near surface me
teoric water-rock interactions. The rocks were then subducted to a gre
at depth during continent-continent collision, forming UHP minerals wi
th concomitant local oxygen isotope redistribution. It is significant
that the rocks have retained such negative oxygen isotope compositions
despite subduction into the upper mantle.