甘肃红石山北泥盆纪雀儿山群火山岩锆石U-Pb年龄及其岩石地球化学特征

U-Pb zircon age and petrogeochemical characteristics of the Devonian volcanic rocks in the northern Queershan Group, Hongshishan, Gansu Province

泥盆纪雀儿山群火山岩位于甘肃红石山北地区,主要为一套中性—中酸性火山岩,以安山岩、英安岩、流纹岩等岩石为主。根据雀儿山群火山岩的分布与接触关系、火山岩中英安岩的锆石U-Pb年龄(365.4±1.5)Ma,并结合前人研究成果,可以判定该火山岩形成时代为泥盆纪。岩石地球化学分析表明该火山岩属钙碱性系列。微量元素呈现明显Ba、U、Sm、La、Ce相对富集和Nb、Ti、P相对亏损,具有火山弧花岗岩特征,稀土元素具有轻稀土富集、重稀土亏损的右倾型配分模式。综合认为雀儿山群火山岩的构造背景为与俯冲汇聚型板块边界有关的大陆边缘火山弧。

The study area is located in the north area of the Hongshishan, Gansu Province. The volcanic rocks of the Devonian Quershan Group are mainly a set of intermediate-basic and intermediate-acid volcanic rocks, mainly consisting of andesite, dacite, rhyolite and other rock combinations. According to the distribution and contact relationship of volcanic rocks in the Quershan Group, the zircon U-Pb age of dacite in the volcanic rocks is(365.4±1.5) Ma, and the formation age of the volcanic rocks can be determined as early-Late Devonian. Petrogeochemical analysis shows that the volcanic rocks belong to calc-alkaline series. The trace elements are relatively enriched in Ba, U, Sm, La, Ce and depleted in Nb, Ti, P, which are characteristic of volcanic arc granite. The REE distribution pattern is right-leaning with LREE enrichment and HREE depletion. The tectonic setting of volcanic rocks in the Quershan group is a continental margin volcanic arc related to subduction convergent plate boundary.