Nature Of The Songliao Block:Evidence From The Detrital Zircon U-Pb Dating Of Paleozoic Sedimentary Rocks

The Songliao block is located in the transitional parts of the eastern section of the Central Asian Orogenic Belt and Pacific tectonic domain, now there are a lot of controversy on the properties of the tectonic.This article rely on the investigation and evaluation subjection of the National oil-gas resource stratagem precinct:The Songliao Basin and the periphery of Upper Paleozoic petroleum geology,which belongs to the subjection:Strategic constituencies of the Songliao Basin and the periphery of Upper Paleozoic oil and gas resources, A large number of comprehensive geological study was carried on exposed basement rocks of the Songliao block, more than60pieces of rock samples were collected in northern and western of the Songliao block,during the field geologic survey and the measurement of typical section. a typical samples of more than20were carried on Petrological, geochemical analysis. And sub-elected detrital zircons was testing in LA-ICP-MS zircon U-Pb geochronology. Songliao basement of the Upper Paleozoic detrital zircons is not only widespread, but the strong stability of these detrital zircon geochronology is an important method of extraction of sediment age.In this paper, we report the detrital zircon age data by measured the Upper Paleozoic Zhesi Formation in southern Songliao Block and the Upper Paleozoic Tumen Ridge Formation in the northern Songliao Block, Combined with the Upper Paleozoic Benbatu Formation in the western Songliao Block and the Upper Paleozoic Heilongong Formation in the eastern Songliao Block, comprehensive discuss the geotectonic setting of the Songliao block. detrital zircon of the Zhesi Formation U-Pb dating by LA-ICP MS technique. some important data and cognitions are gotten:1. The basement rocks are widely outcrop in the north part of the Songliao Block, which mainly composed of high-grade gneiss, Paleozoic strata and Mesozoic granites. The Paleozoicsedimentary strata of a sequence of schist, phyllite, slate, quartzite and meta-sandstone, isremarkably similar to the basement rocks beneath the Songliao basin; Xiwu areas in the west part of the Songliao Block developed in a Late Ancient Carboniferous-Permian shallow marine strata, and the calc-alkaline volcanic rocks, the main rock types include mudstone, siltstone, sandstone, carbonate rocks, andesite, basalt.2. The detrital zircon age from Zhesi Formatio show four major age groups:263～378Ma, the peak age of274Ma;405-547Ma, peak515Ma;660～974Ma, peak923Ma;1165Ma,1369Ma,1465Ma,1517Ma. The youngest zircon age of263±2Ma represents lower age limit the deposition age of Zhesi Formation. The zircons with the peak age at～515Ma show the age information of the Pan-African metamorphic complex in NE China. The rest old ages reflect the information of basement in the Songliao Block.3.Four samples of Tieli metasedimentary rocks in the Songliao Block yield apparent ages ranging from2690to501Ma, with four age populations at:2071-2690Ma, with a peak at2585Ma;1776-1997Ma, with a peak at1890Ma;991-719Ma, with a peak at800Ma; and592-501Ma, with a peak at518Ma. The results show similar age populations to the CAOB,indicates that the long collision-accretion history of the CAOB equated with the global event.4.There are age information with peak ages of800Ma、943Ma、1476Ma、1890Ma、2585Ma, from the basement rocks in the Songliao Block, indicates that these Archean-Proterozoic zircons were derived from a local source close to the basins. When compared with neighboring the Jiamusi-Khanka Block to the east and Xing’an lock to the west, the Tieli metasedimentary rocks contain more abundant Archean and Proterozoicdetrital zircons, implying that the remnants of the Archean and Proterozoic basement couldmainly occur in the Songliao Block. This supports the view that the nature of the Songliao Block should be a microcontinent and not the orogenic belt developed in the CAOB. 5.According to the data results of the age of the different regions of the Songliao Block, The Songliao Block regions contain a wealth of Archean and Proterozoic detrital zircons. This suggest that the Songliao plots have Archean and Proterozoic metamorphic basement, and provides a rich source of material for the Paleozoic sediment. The results indicate that the Songliao Block is more likely the stable micro continental block, rather than long-term activities of the orogenic belt.