Jurassic detrital zircon U-Pb dating of Langshan area, Inner Mongolia, and its provenance significance

The Jurassic provenance in Langshan area is discussed on the basis of detrital zircon LA-ICP-MS U-Pb dating and geochemical methods. Two sandstone samples were selected from Jurassic Shiguai Group from Dongsheng Temple and Yihejiu area. The statistical data of 111 valid detrital zircons ages reveal that zircon ages have three peaks:the major peak is in Late Paleozoic (259~308Ma) of Hercynian period, followed by the peak in Paleoproterozoic (1.74~2.18Ga) and the peak from Early Paleoproterozoic to Neoarchaean (2.39~2.58Ga). Detrital zircon ages of Hercynian period are close to ages of Langshan large-scale exposed magmatic rocks, the ages of Paleoproterozoic to Neoarchaean are similar in features to the ages of khondalite belt. The sandstone REE distribution characteristics of Jurassic sandstones are similar to those of Hercynian magmatic rocks, Wulashan Group and khondalite belt. Combined with conglomerates and sandstone slices analysis of Shiguai Group, it is held that the Jurassic sedimentation was in a nearsource environment and the provenance was mainly from large-scale Hercynian magmatic rocks in Langshan area. A secondary provenance was derived from khondalite belt in Hetao area. Wulashan Group of Archean, Paleoproterozoic magmatic rocks and Early Mid Triassic magmatic rocks probably provided a small part of the provenance. According to the youngest detrital zircon age of 243Ma in Middle Triassic, the sedimentary age of the strata as Early Middle Jurassic is appropriate, which is in accordance with the fact of total lack of Triassic strata in Langshan area. Based on the provenance analysis, it is concluded that there existed two source areas of north and south on both sides of the Jurassic strata, with the main provenance from Langshan uplift in the north and the secondary provenance from Hetao uplift in the south. There are some differences between different parts of the provenance.