Geochemistry of the Ophiolite and Island-Arc Volcanic Rocks in the Mianxian Lueyang Suture Zone, Southern Qinling and Their Tectonic Significance  

作　　者：赖绍聪 张国伟 杨永成 陈家义 

出　　处：《Chinese Journal Of Geochemistry》1999年第1期39-50,共12页中国地球化学学报

基　　金：ThisprojectwasjointlysupportedbytheNationalNaturalScienceFoundationofChina!(No .492 90 10 0 );theSpecialSci enceFoundationofS

摘　　要：Ultrabasic rocks in the Mianxian Lueyang ophiolitic melange zone include harzburgite and dunite which exhibit LREE depletion with remarkable positive Eu anomaly. The diabase 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 element ratios of Ti/V, Th/Ta, Th/Yb and Ta/Yb. One is the MORB type basalt with LREE depletion, representing the fragments of oceanic crust and implying an association of the MORB type ophiolite and an ancient ocean basin between the Qinling and Yangtze plates during the Middle Paleozoic Early Mesozoic era. The other comprises the island arc volcanic rocks including tholeiitic basalt and a large amount of calc alkaline intermediate acid volcanic rock, which could not be the component of the ancient oceanic crust but the result of magmatism at the continental margin. This indicates that the Mianxian Lueyang limited ocean basin had undergone a whole process of development, evolution and vanishing from Devonian Cretaceous to Permian. And the Qinling area had become an independent lithospheric microplate, on the southern side of which there were exhibited the tectonic characteristics of active continental margins during the Late Paleozoic Early Mesozoic. That is to say, the Qinling cannot be simply considered as a result of collision between the Yangtze and North China plates.Ultrabasic rocks in the Mianxian Lueyang ophiolitic melange zone include harzburgite and dunite which exhibit LREE depletion with remarkable positive Eu anomaly. The diabase 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 element ratios of Ti/V, Th/Ta, Th/Yb and Ta/Yb. One is the MORB type basalt with LREE depletion, representing the fragments of oceanic crust and implying an association of the MORB type ophiolite and an ancient ocean basin between the Qinling and Yangtze plates during the Middle Paleozoic Early Mesozoic era. The other comprises the island arc volcanic rocks including tholeiitic basalt and a large amount of calc alkaline intermediate acid volcanic rock, which could not be the component of the ancient oceanic crust but the result of magmatism at the continental margin. This indicates that the Mianxian Lueyang limited ocean basin had undergone a whole process of development, evolution and vanishing from Devonian Cretaceous to Permian. And the Qinling area had become an independent lithospheric microplate, on the southern side of which there were exhibited the tectonic characteristics of active continental margins during the Late Paleozoic Early Mesozoic. That is to say, the Qinling cannot be simply considered as a result of collision between the Yangtze and North China plates.

关 键 词：地球化学 蛇绿岩 秦岭地区 火山岩 稀土元素 缝合带 

分 类 号：P588.1[天文地球—岩石学] P588.14[天文地球—地质学]