LA-ICP-MS U-PB DATING AND HF ISOTOPIC COMPOSITIONS OF DETRITAL ZIRCONS FROM THE “PERMIAN” SANDSTONES IN DA HINGGAN MOUNTAINS, NE CHINA: CONSTRAINTS ON THE EVOLUTION OF THE EASTERN SEGMENT OF CENTRAL ASIAN OROGENIC BELT

We present new LA-ICP-MS U-Pb age data and Hf isotopic compositions of detrital zircons from supposed Mid to Upper Permian sandstones from the molasse-type lacustrine-fluviatile Linxi and Zhesi Fms. of the Da Hinggan Mountains (eastern Inner Mongolia, China). Our new data constrain the eastern extension of the Erenhot-Hegenshan suture zone and the plate collision processes between the northern margin of the North China craton and the composite Erguna-Hinggan-Songliao block. The U-Pb ages of detrital zircons indicate ages as young as Late Permian to Early Triassic indicating a younger depositional age as previously assumed. These data also show two uniform age groups of 270–280 Ma and 310–320 Ma, and 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 εHf (t) values of 3.46–10.41. The younger, 270–280 Ma age group is interpreted to derive from a post-orogenic A-type granitoid belt.

Synthesizing this unique information on a magmatic arc of an approximate age of 320 Ma we define a distribution of the Sonidzuoqi–Xilinhot magmatic arc as follows. The arc extends from Solon Obo via Sonidzuoqi, Xilinhot through Ulanhot to Qiqihar, and then it is cut by the sinistral Nenjiang-Balihan slip-strike fault (western boundary fault of the Songliao basin), and ultimately extends to Longzhen in the northern sectors of the Da Hinggan Mountains. The Erenhot-Hegenshan suture zone is located north of this magmatic arc. Further Paleozoic age groups of ~380 Ma, ~430 Ma and ~500 Ma in the samples indicate a mixture of age groups of variable origin and multiple arc-continent accretion during the formation of the composite Erguna-Hinggan-Songliao block. The sample from the uppermost Permian to Lower Triassic Linxi Formation in the Linxi area (in the southern segment of Da Hinggan Mountains) has two age groups of ~1800 Ma and ~2500 Ma, indicating their source from the northern margin of the North China craton located in the south. Therefore, the collision between the North China craton and the Hinggan-Erguna block started during the deposition of the Linxi Formation and the final closure of the intervening oceanic basin occurred during Late Permian-Early Triassic forming the Ondor Sum-Xar Moron suture zone.