The Final Collision Of The Xra Moron-Changchun Suture

The northeast China located among the North China Craton, the Siberia Craton andthe Pacific plate. As this region was not only influenced by the collision of Paleo-AsianOcean during the Paleozoic, but also influenced by the subduction of Pacific plate alongthe eastern margin of Asian Continent. In this paper, we focus on the provenancecharacteristics, geochemistry, and U-Pb detrital ages of the Linxi Formation, combinedwith the current age data and Paleontology data to discuss the final collision of theSiberia Craton and the North China Craton.The study area geographically exposed in southeastern Inner-Mongolia, southmargin of the Songnen block, north to the Hengenshan-Heihei suture, south to the XarMoron suture, belonging to the eastern segment Central Asian Orogenic Belt（CAOB）.The samples of sandstones were collected from the upper and middle part of the standardsection-“the Linxi town Guandi-Qujiagou section”. They are fine-mediun grained impuresandstone and made up of quartz grains （30%-35%）, plagioclase （20%）, lithicclasts（25%）and micas （5%）, with a few of accessory minerals（e.g. magentite, limonite,pyronxene, titanite, and zircon）.The sandstones from the Linxi Formation were characterised by greywacke in themajor elements and their radios（especially, Na₂O/K₂O）. The upper crust-normalized traceelements patterns patterns of the Linxi Formation have the parallel trends in the spiderdiagram, indicating the similar provenances related to the rocks of the upper crust. According to the analyses of the rare earth elements（REE）, the REE in thechondrite-normalized patterns mainly describe consistent features. They are enriched inLREE and slightly depleted in HREE（LREE/HREE=6.29-8.36ppm）, with weak negativeanomalies of Eu, illustrating an origin of felsic upper continent crustal rocks.The geochemical discrimation diagrams show that the tectonic setting for theprovenance of the Linxi Formation is mainly characterised by the Continental Island Arc（CIArc）.As shown by cathodoluminescence （CL） images, the detrital zircons are mostly thelong columnar euhedral grains with magmatogenic oscillatory zonings. Theirchondrite-normalized patterns mostly share similar characteristics, with enriched LREEand flat HREE and the Th/U ratios ranging from0.1¹.72, indicating the magmaticorigin as well. The LA-ICPMS U-Pb data of detrital zircons from the Linxi Formationshow the whole detrital zircon age between238Ma and1801Ma, peaking at252Ma，472Ma，1325Ma，1714Ma. A younger population shows peaks at252This suggests thatdeposition of the Linxi Formation was later than²52Ma. A few older zircons withU-Pb ages at1689-1801,1307-1414Ma,593-978Ma are also present, suggesting theNeoproterozoic history of the CAOB.Based on the tectonic setting and our recent U-Pb ages of the Linxi Formation in thestudy area, combined with the published geological data, we conclude that the finalcollision of the Siberia Craton and the North China Craton is located at the southernLinxi area （Solonker-Xar Monron suture）, and can be extended to the eastern along theChangchun-Yanji suture. The timing for the final collision should be probably at earlyTriassic...