Rutiles in eclogite from the Sulu UHPM Terrane: A preliminary study

In recent years more than 40 rutile-bearing eclogite ore bodies have been discovered among the thousands of eclogite bodies in the Sulu Utra-High Pressure Metamorphic (UHPM) terrene. Rock- and ore-cores obtained by the Chinese Continental Scientific Drilling (CCSD) Project revealed the presence of several hundred meters of rutile-bearing eclogites. This paper presents a preliminary petrographic,trace element, and Pb isotope study of rutile ores in eclogite. Rutiles occur as inclusions, intergranular infillings, remnant replacements, and hydrothermal infillings in the host rocks. The ore minerals define four stages of rutile mineralization and metamorphic evolution in the eclogites. Electron microprobe (EMP) trace element analysis of three rutile specimens show that different occurrences of eclogite also have different trace element compositions in rutile. These compositional differences may reflect different source rocks for the eclogites. Peak metamorphic temperatures were calculated using the Zr geothermometer in rutile. The Pb isotopic compositions of rutile obtained by step-fuse analysis of single grains of rutile did not fall on one growth line, but show similar variation between different samples. This implies that the Pb isotopic compositions of rutile may have been disturbed during its growth. This variation could be used to trace the growth history of the rutile, and further to trace the process of continental subduction-exhumation.