Late Paleozoic retrograded eclogites from within the northern margin of the North China Craton: Evidence for subduction of the Paleo-Asian ocean

摘要

Retrograded eclogites from the central part of the northern margin of the North China Craton, Hebei Province, China occur as separate tectonic lenses or boundins within garnet-biotite-plagioclase gneisses of the Paleoproterozoic Hongqiyingzi Complex characterized by amphibolite facies paragneisses. The petrographic features and mineralogical compositions represent three main metamorphic stages: (1) the peak eclogite facies stage (P > 1.40-1.50 GPa, T=680-730 degrees C), (2) the granulite facies stage and (3) the amphibolite facies stage (P=0.67-0.81 GPa, T=530-610 degrees C) formed during decompression. The major and trace element and Sm-Nd isotopic data suggest that most of the retrograded eclogite samples had protolitlis of tholeiitic oceanic crust with geochemical characteristics of mid-ocean ridge basalt (MORB) or island arc tholeiite (IAT) environment, and were contaminated by crustal components during subsequent subduction. Zircon SHRIMP isotopic dating of two different textural varieties of retrograded eclogite defines a weighted mean age of similar to 325 Ma, which is interpreted as the peak metamorphic age of the eclogites and reflects the occurrence of eclogite facies metamorphism related to subduction of Paleo-Asian Oceanic crust beneath the North China Craton during the Late Paleozoic. Finally, we show that the retrograded eclogite from Hebei Province is not related to the Baimashi retrograded eclogite at the northern foot of the Heng Mountains, approximately, 300 km to the southwest. (c) 2006 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.