DETRITAL ZIRCON AGE OF TURBIDITES FROM THE BEISHAN OROGEN, NW CHINA

The Altaids, as one of the biggest accretionary orogens in the world, is situated between the Siberia and Baltica cratons to the north and the Tarim and North China cratons to the south. Beishan orogenic belt, encompassed the final attachment of the Tarim and North China Cratons to the southern accretionary orogenic collages of the Southern Altaids as far as the Siberian Craton, linked the Tianshan and Xingmeng orogeny. The duration and architecture of the Beishan orogen is controversial and has led to different reconstructions of the Altaids. Proposals of the latest suture in Beishan orogen varies from Devonian to End-Permian.

Turbidites are the most common and archetypal deposits forming deep-marine clastic systems, and those emplaced in an accretionary orogenic belt exhibit younging in the accretionary direction. The Paleozoic turbidites in Beishan are mainly distributed in the Yingmaotuo, Dundunshan, Liuyuan, and Heishankou area from north to south. The εNd(t) values of Yinmaotuo turbidites range from -12.9 to -14.0 Ga, with model ages (TDM) of 2.24-2.28 Ga, indicating they were derived from Proterozoic crust. The εNd(t) values of Dundunshan turbidites range from -5.0 to -9.1, with model ages (TDM) of 1.47-1.82 Ga that are lower than average value (1.9 Ga) of globe sedments. Calculated initial εNd(t) values of the Liuyuan turbidites range from -0.5 to 1.1, and the TDM model ages from 1.06 to 1.22 Ga (Figure 5). The Heishankou turbidites have lower ¹⁴⁷Sm/¹⁴⁴Nd and ¹⁴³Nd/¹⁴⁴Nd ratios, and result in lower εNd(t) values (-4.2 to -2.4) and similar TDM model ages (1.09 to 1.36 Ga). Contrasting isotopic characteristics, together with the sedimentary age, may provide new constrains on the latest suture zone and the architecture of the Beishan orogen.