271 / 2019-07-04 07:37:04

Detrital zircon trace elements, U-Pb geochronology and its geological significance of "Huoshan Sandstone" in Xiweikou area of eastern margin of Ordos basin

Eastern margin of Ordos basin；Xiweikou；Huoshan sandstone；U-Pb dating；Geochemistry；Geological significance

It is of great geological significance to determine the "Huoshan sandstone" for the division of Precambrian strata in the North China Craton, the analysis of provenance, the evolution of sedimentary and structure and the restoration of the Precambrian strata. In this paper, petrology, zircon U-Pb dating and zircon microarea geochemistry of the "Huoshan sandstone" have been studied. It is shown that the "Huoshan sandstone" is quartzite which is composed by 77.0-85.5% quartz. The main size of quartz grains are 0.30-0.50mm with well rounded. The type of cementation is mosaic, and the siliceous secondary growth is particularly well developed. The contact edge of quartz grains is relatively straight, indicating that it is a metamorphic rock that original rocks are medium-grained quartz sandstone. The Th/U ratio of zircon proves that the zircon in "Huoshan sandstone" are mainly magmatic zircon but no metamorphic zircon, and their chondrite-normalized REE patterns of most zircon are characterized by HREE enrichment relative to LREE and MREE with distinctive positive Ce anomalies (Ce/Ce*: 5.9-187.1) and negative Eu anomalies (Eu/Eu* : 0.071-0.61), which are typical of magmatic zircon. The age of zircon 207Pb/206Pb is 1770±20 - 2732±16Ma and there are two obvious peaks of 1800 and 2500Ma in the U-Pb age frequency histogram. The age of the intersection on the harmonic line is 2524±41Ma, while the lower is 1842±28Ma.These shows that "Huoshan sandstone" should be attributed to Proterozoic, and the source of materials of "Huoshan sandstone" is derived from the Precambrian strata exposed in zhongtiaoshan area of central North China Craton. Therefore, it can be inferred that the Precambrian strata were involved in the subduction, collage and collision of the two continental blocks in the east and west of North China. The above results have confirmed the central orogenic belt was formed in the late paleoproterozoic.