Wu Y.-W.,Chian Aerospace Geophysical Survey and Remote Sensing Center for Land and Resources |
Wu Y.-W.,China University of Geosciences |
Li C.,Jilin University |
Xu M.-J.,Tianjin Chengjian University |
And 4 more authors.
International Geology Review | Year: 2016
A newly discovered Devonian ophiolite located in the Taoxinghu area of central Qiangtang on the Qinhai-Tibet Plateau is described. The ophiolite consists of gabbro and diabasic dikes, and invasive cumulate gabbros-leucogabbros. The ophiolite has undergone greenschist facies metamorphism and minor deformation. Dating of the metagabbro by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) zircon U-Pb techniques yielded a weighted mean age of 367.2 ± 3.3 Ma (Late Devonian). Whole-rock geochemical analyses show that the rocks belong to the tholeiite series, with weak depletion in light rare-earth elements (LREEs), almost no Eu anomalies, weak enrichment in large-ion lithophile elements (LILEs), depletion in Nb and Ta, and weak negative Hf and Ti anomalies. These characteristics are similar to those of back-arc basin basalts. Together, these characteristics suggest that the rocks of the Devonian ophiolite formed by ∼30% partial melting of spinel lherzolite, which was enriched by interaction with aqueous fluids during the late-generation phases; there is no evidence of subduction-related melting. The Devonian ophiolite rocks in the Taoxinghu area were first discovered in the LongmuCo-Shuanghu-Lancang suture zone. Detailed geochemical analyses show that the rocks formed in a back-arc ocean basin environment, indicating that the LongmuCo-Shuanghu-Lancang suture zone in central Qiangtang represents a Late Devonian intra-oceanic subduction zone in the Palaeo-Tethys Ocean. The discovery of the central Qiangtang Devonian ophiolite provides essential data for understanding the evolutionary history of the Palaeo-Tethys Ocean, and for identifying and understanding the roles of the different tectonic units on the Qinghai-Tibet Plateau. © 2015 Taylor & Francis.