Geochemistry and tectonic setting of the protolith of eclogites in north Qinling

The protolith of eclogites in north Qinling belongs to tholeiitic basalt.The ratios of Nb/La,Ce/Nb,Th/Yb and Ti/Zr of the eclogites are 0.68～0.92,2.11～3.62,0.42～1.00 and 75.26～125.84, respectively,showing the characteristics of NMORB.However,Their Nb contents of 9～13 μg/g and Zr/Y ratios of 4.24～6.92,together with the enrichment of Ti and Fe,show the affinity of OIB.Therefore the protolith of the eclogites is probably derivation from the source with the mixture of NMORB and OIB members.Based on regionally geological information,the protolith of eclogites is possibly seamount basalt in the oceanic basin,and is of the component of oceanic crust.The basalts subducted downward to the low crust or the mantle,and metamorphized to eclogite at highpressure.