北山石板泉一带石炭纪双峰式火山岩地球化学特征及构造意义

北山造山带南缘石板泉一带的石炭纪火山岩(红柳园组)在时空上构成独特的双峰式火山岩组合,具有较短的Daly间断及大量酸性火山岩夹少量中基性火山岩为主要特征,其中安山岩具有富钠贫钾、高Al低Mg的过铝质高钾钙碱性系列特征,并含有相当数量亏损地幔物质,指示了安山岩源区可能源于亏损地幔,显示板内安山岩的特征;流纹岩属于低Ti流纹岩类,指示岩石可能是基性岩浆底侵作用下地壳物质发生部分熔融,源区存在有斜长石残留,形成于大陆裂谷环境,其动力学体制可能与陆内伸展拉张作用有关,表明从晚古生代形成的裂谷在早石炭世晚期-晚早石炭世早期发展到鼎盛时期,晚石炭世由伸展拉张到逐步进入碰撞挤压这个地球动力学环境的重大转折时期,二叠世末进入碰撞造山演化阶段。

Geochemical Characteristics of Carboniferous Bimodal Volcanic Rocks in Shibanquan,Beishan and Its Tectonic Significance

Located in the southern margin of Beishan orogenic belt, the carboniferous volcanic rocks(Hongliuyuan Group) have constituted a unique bimodal volcanic rock combination in time and space, which are mainly characterized byshorter Daly discontinuous and a large number of acidic volcanic rock, with a small amount of intermediate and basic volcanic rocks. In which, the andesites are rich in sodium and poor in potassium, with high Al values and low Mg contents, belonging to the peraluminous high potassium calc-alkaline series, containing substantial amount of depleted mantle materials, and indicating that these andesites may be derived from depleted mantle, with geochemical characteristics of intraplate andesite. The rhyolites belong to the low Ti type, indicating that they may be formed by partial melting of lower crust materials under theinfluence from the underplating of basic magma, with some plagioclaseresidued inmagmatic source.And, these rhyolites were formed in a continental rift environment, its dynamics system may be associated with intracontinental stretching tension effect, suggesting that the late Paleozoic rift were developed to the peak stage in the late period of Early Carboniferous and/or the early period of Late Carboniferous. Thus, the Late Carboniferous serves as the major turning point for the the geodynamic environment gradually changing from the extension and tension to the collision and compression, and this studying area was steped into the ollision orogenic evolution stage at the end of Permian.