LA-ICP-MS U-Pb dating and Hf isotopic compositions of detrital zircons from the Permian sandstones in Da Xing'an Mountains, NE China: New evidence for the eastern extension of the Erenhot-Hegenshan suture zone

摘要

The Erenhot-Hegenshan suture zone is located in the eastern segment of the Central Asian Orogenic Belt (CAOB) cutting obliquely through the Da Xing'an Mountains in NE China, and represents the hotly debated boundary of the Xing'an and Songliao blocks. In this study, we present new U-Pb zircon ages and Hf isotopic compositions of zircons from Permian sandstones in the Da Xing'an Mountains (DXAM) of eastern Inner Mongolia, China. Based on the genetic relation of the suggested "Hegenshan Ocean" and the Sonidzuoqi-Xilinhot magmatic arc, we seek the eastern extension of the Erenhot-Hegenshan suture zone by tracing the provenance information of the magmatic arc from our Permian sandstones. LA-ICP-MS U-Pb dating of detrital zircons of the Permian sandstones yield evidence for two age groups of ~280 and ~320 Ma, which represent the Late Paleozoic magmatic arcs. Zircons of the older cluster are considered to derive from the Sonidzuoqi-Xilinhot magmatic arc with its age cluster of 310-320 Ma and similar ε_(Hf(t)) values of 3.46-10.41. Further Paleozoic age groups of ~380Ma, ~430Ma and ~500Ma indicate a mixture of age groups of variable origin. The samples from the central-southern DXAM comprise a mixture of Sonidzuoqi-Xilinhot and Ondon Sum-Xar Moron magmatic arcs, and even include a contribution from the magmatic arc in the northern margin of the North China craton. The samples from the central and northern DXAM contain a mixture of Sonidzuoqi-Xilinhot magmatic arc and post-orogenic magmatic rocks from the Erguna block, respectively. Synthesizing this unique information on a magmatic arc with an approximate age of 320 Ma, we define a distribution of the Sonidzuoqi-Xilinhot magmatic arc as follows: the arc extends from north of Solon Obo, via Sonidzuoqi, Xilinhot through Ulanhot to Qiqihar, and then it is cut by the sinistral Nenjiang-Balihan strike-slip fault (western boundary fault of Songliao basin), and ultimately extends to Longzhen. The Erenhot-Hegenshan suture zone is located north of this magmatic arc.