Research on protolith of eclogite in main hole of Chinese Continental Scientific Drill project and its genetic instructions

Eclogite was the most common metamorphic rock in orogenic belt, it contained abundant geodynamic information. According to the contact relationship of country rocks, the eclogite from 0~2 000 m in the main hole of the Chinese Continental Scientific Drill (CCSD) could be classified into three types: symbiotic eclogite gneiss;eclogite adjacent to ultrabasic rocks and symbiotic eclogite ultrabasic rocks. Compared to the geochemical differences with the three types of eclogites, the authors considered that the protoliths of these rocks were probably the basic-untrabasic complex evolved from the single magma chamber by cumulation and fractional crystallization. The main source materials of these protoliths were derived from the enriched mantle by partial melting in subduction zone of oceanic crust downthrusted to the mainland under a back-arc extensional magmatism.