The Khanka Block, NE China, and its significance for the evolution of the Central Asian Orogenic Belt and continental accretion

Abstract

Sensitive high-resolution ion microprobe and inductively coupled plasma mass spectrometry U-Pb dating of zircons from granitoids and paragneiss in the Chinese segment of the Khanka Block reveals that granite magmatism occurred at 518±7 Ma and was followed shortly after by high-grade metamorphism at c. 500 Ma (timing ranging from 491±4 Ma in medium-grained granitoid, through 499±10 Ma in porphyritic granite, to 501±8 Ma in paragneiss). Such a scenario has previously been established on similar lithologies in the Jiamusi Block to the west, with identical ages. This suggests that the Khanka and Jiamusi blocks form part of a single terrane and that the Dunhua-Mishan Fault, which was previously considered to separate two unique terranes, cannot be a terrane boundary fault. Previous suggestions of a link between the Khanka Block and the Hida Block in Japan are not supported following a comparison of the new zircon data with published ages for the Japanese terranes. A granitoid with an age of 112±1 Ma in the Khanka Block probably records the effect of Pacific plate subduction, as such ages are common further south in the extreme eastern part of the North China Craton, where they have been related to post-collisional extension and lithospheric thinning in the Jiaodong Peninsula. The presence of such young granitoids, and the previous dating of blueschist-facies metamorphism as late Early Jurassic in the Heilongjiang Complex of the Jiamusi Block, supports the view that the current location of the Jiamusi-Khanka terrane is a product of circum-Pacific accretion rather than it being a microcontinental block that was trapped by the northward collision of the North China Craton with Siberia as part of the assembly of the main Central Asian Orogenic Belt. © 2010 The Geological Society of London.