豫南团山花岗岩LA-MC-ICP-MS锆石U-Pb年龄及其地质意义

LA-MC-ICP-MS Zircon U-Pb Ages of the Tuanshan Granite in Southern Henan Province and Their Geological Significance

豫南团山花岗岩是灵山岩体的一个独立单元,具有含斑细粒黑云二长花岗岩和细粒黑云二长花岗岩两种岩性,是在灵山序列主岩浆期后形成的第一个补充期产物,也是最大规模的补充期产物,基本代表了灵山花岗岩的形成年龄下限。为了限定此年龄和研究灵山岩体与紧邻的肖畈小岩体的关系及其形成的构造背景,对团山花岗岩的两种岩石进行锆石LA-MC-ICP-MS U-Pb年龄测试,并结合前人研究成果综合论述了团山花岗岩的基本地质特征。测试结果显示团山独立单元两种岩性的形成时间分别为129.90±0.63 Ma(MSWD=0.78)和129.92±0.61 Ma(MSWD=0.74),两种岩性形成时间基本一致。灵山岩体晚于肖畈岩体近10 Ma形成,推测两者为两期不同的岩浆活动产物。灵山及其附近早白垩世花岗岩体均具有与区域韧性断裂带形迹方向基本一致的北西-北西西轴线和接触界线,可作为扬子板块与华北板块碰撞事件和断裂事件的岩浆活动响应的证据。此外,通过分析收集到的灵山岩体年龄测试数据发现灵山岩体的形成年龄集中分布于95~110 Ma、120~135 Ma,推测灵山岩体在形成过程中可能经历了两次大的岩浆活动。

Tuanshan granite is a distinct unit of the Lingshan pluton in southern Henan Province.It consists of two lithologies:porphyritic fine-grained biotite monzonite and fine-grained biotite monzonite.It was formed during the first supplementary period after the main magmatic stage of the Lingshan sequence and is the product of the largest supplementary period.Tuanshan granite represents the lower age limit of Lingshan granite.To determine this age and examine the relationship between the Lingshan pluton and the adjacent Xiaofan small pluton,as well as the tectonic setting,zircon LA-MC-ICP-MS U-Pb age tests were conducted on two rocks from the Tuanshan granite.The basic geological characteristics of Tuanshan granite were evaluated in light of previous research results.The test results show that the formation time of the two lithologies in Tuanshan separate unit is 129.90±0.63 Ma(MSWD=0.78)and 129.92±0.61 Ma(MSWD=0.74),essentially the same.Lingshan pluton was formed about 10 Ma later than Xiaofan pluton,which is inferred to be the product of two different magmatic activities.The NW-NWW contact boundary and NW-NWW axis of Lingshan pluton and the nearby Early Cretaceous granite bodies are basically consistent with the direction of structural trace,which can be used as evidence for the magmatic activity response to the collision event between the Yangtze plate and the North China plate and the fault event.Moreover,by analyzing the collected Lingshan pluton age test data,it is found that the formation age of the Lingshan pluton is concentrated at 95~110 Ma and 120~135 Ma,suggesting that Lingshan intrusion may have experienced two large magmatic activities during its formation.