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大石桥组是辽河群中一个重要的含矿层位,其岩性主要由白云石大理岩、方解石大理岩、云母片岩组成.在本次研究中,在辽阳南部八会镇辽河群大石桥组地层大理岩中首次发现有一层酸性火山岩夹层,岩性为流纹质角砾凝灰岩.根据野外产状判断,酸性火山岩与大理岩为同时沉积.清晰的振荡环带及比较高的Th/U比值,显示流纹质角砾凝灰岩的锆石为岩浆锆石,对其进行LA-ICP-MS U-Pb测年,结果显示其成岩年龄为2171±11 Ma,首次精确地厘定了大石桥组的形成时代.此年龄也进限定了置于大石桥组之下的浪子山组、里尔峪组、高家峪组等3个地层的沉积时限为2171 Ma之前.
The Dashiqiao Formation is an important ore-bearing layer in the Liaohe Group, and its lithology is mainly composed of dolomite marble, calcite marble and mica schist.Based on this study, in the Dashiqiao Formation of Liaohe Group in Baili Town in southern Liaoyang For the first time, a layer of acidic volcanic interlayer was found in marble, and the lithology is rhyolitic breccia tuff.According to the field production, acidic volcanic rocks and marble are simultaneously deposited.The clear oscillatory zone and the relatively high Th / U ratio, The zircons of rhyolitic brecciated tuff are magmatic zircons, and their LA-ICP-MS U-Pb dating shows that the diagenetic age is 2171 ± 11 Ma. For the first time, the formation of Dashiqiao Formation This age also restricted the setting of the prodigious prodigious prodigies in the Shizishan Formation under the Dashiqiao Formation, with a deposition time before 2171 Ma for three strata, such as Lilleyu Formation and Gaojiayu Formation.