Geochemistry of the ophiolite and island-arc volcanic rocks in the mianxian-lueyang suture zone, southern qinling and their tectonic significance

摘要

Ultrabasic rocks in the Mianxian-Lueyang ophiolitic melange zone include harzbur- gite and dunite which exhibit LREE depletion with remarkable positive Eu anomaly. The dia- base dike swarm shows LREE enrichment but slightly negative Eu anomaly. Metamorphosed volcanic rocks can be divided into two groups in terms of their REE geochemistry and trace ele- ment ratios of Ti/V, Th/Ta, Th/Yb and Ta/Yb. One is the MORB-type basalt with LREE depletion, representing the fragment of oceanic crust and implying an association of the MORB-type ophiolite and an ancient ocean basin between the Qinling and Yangtze plates dur- Ing the Middle Palezoic-Early Mesozoic era.