The occurrence of Precambrian amphibolites from the Xinghuadukou Complex from NE China: Implications for the evolution of the Xinlin-Xiguitu Ocean, the NE branch of the Paleo-Asian Ocean

Abstract

One of the geological attractions of the Xinghuadukou Complex resides in a suite of well exposed amphibolites outcropped locally in the northern part of the Xinlin-Xiguitu Suture zone between the Erguna and the Xing'an blocks in NE China. This suite of amphibolites occurs with gneisses, leptynite, schists, migmatitie and marbles from the Xinghuadukou Complex. Previously, only geochronological studies have been carried out on these amphibolites, suggesting a Late Neoproterozoic to Early Cambrian protolithic age (i.e. 547 ± 46 Ma). However, with only geochronological studies, it is insufficient to solve the controversy surrounding the tectonic settings of these amphibolites, such that the Precambrian evolution of the Xinlin-Xiguitu Suture cannot be further constrained. In this study, our new lithological and geochemical data indicate that these amphibolites are tholeiitic basalts with E-MORB affinities, which were most likely derived from the partial melting of a lithologically-mixed source of fusible eclogite and peridotites within the asthenosphere mantle under lithosphere thinning. Together with the previously reported Mid-Neoproterozoic suprasubudction-related ophiolites (i.e. 620–690 Ma) and ca. 516 Ma Toudaoqiao blueschists from this region, these amphibolites are suggested to be generated on the oceanic crust formed from the back-arc extension due to the intra-oceanic subduction. This interpretation provides new constraints not only on the tectonic implication of the Xinghuadukou Complex, but also the tectonic evolution of the Xinlin-Xiguitu Ocean within the Paleo-Asian Ocean regime.