Oxygen isotope compositions of eclogites in Rongcheng, Eastern China

Abstract

Collected from the Rongcheng region, Shandong Province, the three types of eclogites suffering the UHP (i.e. ultra-high pressure) metamorphism have obviously different oxygen isotope compositions. The eclogites occurring in regional orthogneisses and ultramafic rocks have the oxygen isotope compositions of normal eclogites in the world, but the eclogites existing in marbles are extremely enriched in18O. By applying oxygen isotope geothermometry, for the all types of eclogites, the temperature estimates of quartzgarnet pair, in principle, indicate the formation temperatures of eclogites, so that the peak-metamorphic temperatures are estimated to be averagely little higher than 800°C, which are consistent with the estimates by using other geothermometers according to cation partitioning between coexisting phases. The δ18O values of eclogitic inclusions hosted in marbles from Yangguantun, Rongcheng region, are far higher than the values of eclogites (including eclogitic inclusions in marbles) from the Dabieshan and other places of the Sulu. The oxygen isotope compositions of various minerals indicate that the formation temperatures of eclogites from the Rongcheng region, in general, are higher than that from the Dabieshan and the southwestern part of the Sulu, but the dispersive temperatures estimated by different mineral pairs probably reflect that the UHP eclogites from the Rongcheng region generally suffered overprinted metamorphisms during the exhumation.