Ophiolites from the Mian-Lue Suture Zone in the Qinling Orogenic Belt: Implications for the Tectonic Evolution of the Central China
The Mian-Lue suture zone in the Qinling erogenic belt, Central China, marks the collision of the North and South China blocks. This suture zone is composed of ophiolitic slices from variable tectono-stratigraphic units. The ophiolites are composed of ultramafic rocks, diabase dyke swarms and basalts, and are well exposed in Lueyang, Pipasi and Derni. In Lueyang, ultramafic rocks include harzburgites and dunites. They exhibit depleted LREE patterns with remarkably positive Eu anomalies. Diabases show slightly negative Eu anomalies. Basalts belong to tholeiite and are depleted in LREE. They show Nb range from 3.9×10-6 to 8.4×10-6, TiO2 range from 0.92％ to 1.86％, Th/Y ratios range from 18.14 to 23.76, Th/Ta ratios from 0.04 to 1.86, Th/Y ratios from 0.01 to 0.02, and Ta/Yb ratios from 0.01 to 0.13, comparable to MORB-type lavas. In Pipasi, the ophiolite is mainly composed of basalts. The basalts show tholeiitic features and (La/Yb)N range from 0.65 to 0.97,Ti/V, Th/Ta, Th/Y, and Ta/Yb ratios are 26.98, 1.06, 0.01 and 0.05 on an average. In Derni, the ophiolite is composed of basalts, gabbros and meta-peridotites. The basalts show LREE depletion without remarkable Eu anomaly, indicating that the rocks are from a mid-ocean ridge tectonic setting. The Mian-Lue ophiolites have the isotopic ages of about 350-245 Ma, suggesting that an ocean basin existed and evolved from Devonian to Permian. These MORB-type ophiolites may represent the fragments of ancient oceanic crust of the Mianlue-Tethyan Ocean that once separated the Qinling and South China blocks during Middle Paleozoic to Early Mesozoic.
ophiolite geochemistry tectonic setting suture zone Qinling orogenic belt.
Lai Shaocong
State Key Laboratory of Continental Dynamics; Department of Geology, Northwest University, Xian 710069, China
国际会议
The IPACES 6th Annual Meeting(“现代地球科学，交流与合作国际学术研讨会暨第六届IPACES学术年会)
武汉
英文
443-445
2007-04-25（万方平台首次上网日期，不代表论文的发表时间）