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老君山组砾岩是北祁连造山带早泥盆世、中泥盆世强烈隆升阶段形成的陆相磨拉石沉积.由西到东,来自肃南、民乐、古浪和靖远的41件砂岩的岩石地球化学特征显著不同:①主量元素显示,西部(肃南、民乐)样品MgO+Fe2O3T值和Al2O3/SiO2值高于东部,而东部样品K2O/Na2O比值高于西部;②在上地壳标准化分布图中,所有样品均亏损Nb,Ta元素.其中西部样品亏损Rb元素,而富集Sc,Co,Ni,V和Cr元素.而东部样品亏损Sr元素且不富集Sc,Co,Ni,V和Cr元素;③稀土元素球粒陨石标准化分配型式均显示右倾型,而LaN/YbN比值和Eu/Eu*值西部样品较低,而东部样品较高.岩石地球化学特征表明,老君山组源岩在东西两段上存在差异.西部肃南一带源岩主要为铁镁质岩石,而东段古浪、靖远一带源岩主要为长英质岩石,民乐一带源岩兼具上述两种岩石特征.根据砾石形态以及沉积地球化学,老君山组沉积物主要以未遭受沉积分选和再循环作用的近源堆积为主,且西部源岩未遭受化学风化而东部遭受了低-中等程度的化学风化.大地构造背景判别和源岩限定,西部肃南一带沉积物可能主要来自于卷入造山带的北祁连岛弧,自民乐向东,沉积物既有来自北祁连岛弧的物质也有来自中祁连变质基底的物质.物源配置的东西差异以及志留系-泥盆系在全区的发育特征暗示,北祁连造山带由于早古生代中祁连地块与阿拉善地块之间的“斜向碰撞或不规则边缘碰撞”作用,导致了泥盆纪早期造山作用在走向上存在不均一造山特点.
The Laosjunshan conglomerate is a continental mylonite deposit formed during the Early Devonian and Middle Devonian uplift in the North Qilian orogenic belt, and from west to east, from Sunan, Minle, Gulang and Jingyuan The geochemical characteristics of 41 sandstones are significantly different: ① The main elements show that the values of MgO + Fe2O3 and Al2O3 / SiO2 in the western (Sunan and Minle) samples are higher than those in the east, while the ratios of K2O / Na2O in the eastern sample are higher than those in the west; In the normal distribution map of the upper crust, all samples depleted Nb and Ta elements, of which western samples depleted Rb elements and enriched elements of Sc, Co, Ni, V and Cr, whereas the eastern samples lost Sr elements and did not enrich for Sc, Co, Ni, V and Cr, respectively; ③The normalized distribution types of REE chondrites all show a right tilting type, while LaN / YbN ratios and Eu / Eu * values are lower in western samples and higher in eastern samples. The source rocks of the Laojunshan source rocks are different in east and west parts.The source rocks in the Sunan area in the west are mainly mafic rocks, while the source rocks in the Gulang and Jingyuan parts of the east part are mainly felsic rocks and source rocks With these two rock characteristics.According to the gravel morphology and sedimentary geochemistry, the Laojunshan Formation sediments mainly Nearly source deposits are not subject to sedimentary sorting and recirculation, and the western source rocks are not subjected to chemical weathering and the eastern part suffered from low to moderate chemical weathering. The tectonic setting of the tectonic setting and source rocks are limited, and the sediments of the western Sunan area The material may come mainly from the North Qilian arc involved in the orogenic belt and eastward from the folk music. The sediment contains both the material from the North Qilian Island arc and the material from the Qilian metamorphic basement. The developmental characteristics of Silurian-Devonian in the whole region imply that the North Qilian orogenic belt, due to the “oblique collision or irregular edge collision” between the Qilian block and the Alxa block in the Early Paleozoic, Which led to the characteristics of uneven orogeny in the early Devonian orogeny.