北秦岭罗汉寺岩群锆石SHRIMP U-Pb年龄及其构造地质意义

North Qinling Luohansi Rock Group SHRIMP U-Pb Zircon Age and Its Tectonic Significance

摘要: 对出露于北秦岭周至黑河小王涧黄草坪南罗汉寺岩群(弧前盆地沉积楔形体)中的英安质晶屑凝灰岩,进行了锆石SHRIMP U-Pb同位素测年研究,获得该群晶屑凝灰岩形成时代为(491±5)Ma,反映该岩群跨及早奥陶世.结合商丹带北侧广泛发育的加里东期岛弧花岗岩带和前人在其他地区测定该岩群的最新年代信息,认为本次测年数据为北秦岭古生代洋盆消减及板块汇聚过程,提供了重要的同位素年代学依据.同时,为研究商丹蛇绿构造混杂岩带俯冲碰撞的增生造山过程,提供了有力的时代佐证.

Abstract: The paper presents SHRIMP U-Pb dating results of zircon from south Luohansi group(the sedimentous wedge of forearc basin),cropping out from the north Qinling to Heihe River Xiaowangjian Huangcaoping.The age of crystal tuff obtained was 491±5 Ma.The obtained age indicates that this group is through Ordovician.Combined to granite belt of Caledonian stage widely grown in northern side of Shangdan belt,and the newest age information measured by predecessors in other places,the important evidence of isotopes chronology was offered to subduction of northern Qinling Paleozoic Oceanic basin and plate convergence.At the same time,the powerful evidence was provided to research subduction collision age of ophiolitic mixtite belt.