内蒙古北山造山带小红山地区三叠纪花岗岩成因——来自锆石U-Pb年龄和Hf同位素的约束  

Petrogenesis of Triassic granites in Xiaohongshan area,Beishan orogenic belt:Constraints from zircon U-Pb ages and Hf isotopes

作　　者：李敏[1,2] 任邦方 段霄龙 田健 段连峰 牛文超 LI Min;REN Bangfang;DUAN Xiaolong;TIAN Jian;DUAN Lianfeng;NIU Wenchao(Tianjin Center,China Geological Survey,Tianjian 300170,China;North China Center for Geoscience Innovation,Tianjian 300170,China)

机构地区：[1]中国地质调查局天津地质调查中心,天津300170 [2]华北地质科技创新中心,天津300170

出　　处：《地质通报》2020年第9期1422-1435,共14页Geological Bulletin of China

基　　金：中国地质调查局项目《全国陆域及海区地质图件更新与共享(中国地质调查局天津地质调查中心)》(编号:DD20190371);《温都尔庙和镶黄旗地区区域地质调查》(编号:DD20190038);《阴山成矿带小狐狸山和雅布赖地区区域地质矿产调查》(编号:DD20160039)。

摘　　要：对北山造山带小红山地区三叠纪花岗斑岩锆石U-Pb年龄、锆石Hf同位素和全岩地球化学组成进行了研究。LA-MC-ICP-MS锆石U-Pb测年结果显示,2个花岗斑岩样品的锆石206 Pb/238 U年龄为211.8±1.6 Ma和205.9±1.7 Ma,显示花岗斑岩的侵位时代为晚三叠世晚期。花岗斑岩具有高硅、富碱、准铝,贫钙、镁、铁的特征,属于高钾钙碱性至钾玄岩系列,分异程度较高,属高分异I型花岗岩,富集Rb、Th、U、La、Ce等大离子亲石元素,亏损Nb、P、Ti等高场强元素和Ba、Sr,表现出低Sr,高Yb和Y的特点,并具有明显的负Eu异常。εHf(t)值较高(-1.43~9.93),Hf同位素地壳模式年龄T C DM为610~1335 Ma,指示花岗斑岩均源于具有幔源烙印的新生地壳并混有重熔的古老地壳。结合最近获得的数据及区域地质资料,提出在后造山伸展体制下,基性岩浆底侵带来的热导致新元古代—古生代新生地壳的部分熔融,并遭受了下元古界古老地壳重熔的岩浆混染,形成的岩浆经过分离结晶作用,最终在中上地壳侵位形成了晚三叠世花岗斑岩。In this paper,zircon U-Pb ages,Hf isotopes and whole rock geochemical compositions of Triassic granite-porphyry in Xiaohongshan area of Beishan orogenic belt were systematically studied.Zircon LA-MC-ICP-MS U-Pb dating results show that the two ages of granite-porphyry are 211.8±1.6 Ma(the confidence value is 95%,n=24,MSDW=2.4)and 205.9±1.7 Ma(the confidence value is 95%,n=23,MSDW=2.9)respectively,which intruded at the late stage of Late Triassic.The granite-porphyry in the study area is characterized by high silicon,rich alkali,quasi-aluminum,and poor calcium,magnesium,and iron.It belongs to the series of high potassium calc-alkaline to potassic basanite with high degree of differentiation.It belongs to highly differentiated I-type granite.It is enriched in Rb,Th,U,La,Ce and other large ion lithophile elements and depleted in Nb,P,Ti,Ba and Sr.It is characterized by low Sr,high Yb and Y with obvious negative europium anomaly.TheεHf(t)values range from-1.43 to 9.93,which are relatively high,and the Hf isotopic crustal model ages range from 610 Ma to 1335 Ma,indicating that the granite-porphyry was derived from the juvenile crust with mantle imprint mixed with remelting old crust.According to the data obtained in this paper and other regional geological data acquired recently,it is proposed that,under the post-orogenic extension system,the heat brought by the underplating of basic magma caused the partial melting of the juvenile crust from Neoproterozoic to Paleozoic,and suffered magma contamination of the remelting of the old crust of Lower Proterozoic.In addition,the magma was finally emplaced in the middle and upper crust after fractional crystallization,forming the the Late Triassic granite-porphyry in the study area.

关 键 词：三叠纪 花岗岩 后造山伸展 锆石U-PB年龄 锆石HF同位素 北山造山带 

分 类 号：P534.51[天文地球—古生物学与地层学] P588.12[天文地球—地质学]