摘要
早古生代加里东造山运动使整个华南板块产生了广泛的岩浆活动,而关于华南早古生代的构造属性是俯冲碰撞还是陆内造山尚存争议。对钦杭结合带的I型花岗岩成因研究对揭示桂东南地区早古生代地球动力学背景及其构造演化具有重要的地质意义。本文对桂东/南莲垌和古龙岩体中的花岗岩样品进行了全岩地球化学分析、LA-ICP-MS锆石U-Pb定年和Lu-Hf同位素分析。莲垌和古龙岩体花岗岩的形成时代相近,分别为435~434和436~435 Ma。莲垌和古龙岩体均为花岗闪长岩,并具有相似的地球化学特征:10000Ga/Al值为2.07,w(Zr+Nb+Ce+Y)值为183×10^(-6),A/CNK为0.87~1.1,平均值为0.97,εHf(t)值为-2.2~1.8,主要集中在0~2,对应的T DM2年龄主要分布在1.6~1.2 Ga,峰值在1.5~1.3 Ga,Nb/Ta值为11.47~14.66,平均值为12.80,Rb/Sr值为0.22~0.52。以上分析结果表明:莲垌和古龙岩体均为钙碱性I型花岗岩,来源于中元古代基底变质火成岩的部分熔融,并可能含一定的幔源物质。其主要形成过程为:华南板块南部与冈瓦纳北缘大规模碰撞所产生的应力,自南向北、自东向西传入华南板块,引发华南板块陆内造山作用。加厚的岩石圈经历了造山后伸展减薄,地幔物质上涌为下地壳部分熔融提供了热量,形成新生地壳熔融型(如古龙岩体)或新生地壳与古老地壳混合熔融型(如莲垌岩体)的母岩浆;在陆内造山作用期后的伸展环境下,母岩浆沿通道上涌,形成了具有俯冲碰撞特征的I型花岗岩。
The Early Paleozoic Caledonian orogeny caused extensive magmatic activities in the South China Block(SCB),but its tectonic attribute is still controversial over weather it was subduction collisional or intracontinental.Study on the petrogenesis of Ⅰ-type granites in the Qin-Hang junction zone is of great geological significance to reveal the Early Paleozoic geodynamic background and tectonic evolution in southeastern Guangxi.In this study,whole-rock geochemical analysis,LA-ICP-MS zircon U-Pb dating and Lu-Hf isotope analysis of granite samples from the Liandong and Gulong plutons in southeastern Guangxi are carried out.The two plutons are granodioites with similar formation ages,at 435434 and 436435 Ma,respectively,and with similar geochemical characteristics(10000Ga/Al value of 2.07;(Zr+Nb+Ce+Y)content of 183×10^(-6);A/CNK ratio of 0.871.1,averaging 0.97;εHf(t)value of-2.2-1.8,mostly between 02;T DM2 age of 1.61.2 Ga,with a peak at 1.51.3 Ga;Nb/Ta ratio of 11.4714.66,averaging 12.80;Rb/Sr ratio of 0.220.52),indicating both are calc-alkaline I-type granite originated from the partial melting of Mesoproterozoic meta-igneous rocks,probably containing some mantle-derived materials.A pluton formation model is proposed as follows:Large-scale collision between the southern SCB and the northern Gondwana margin created S-N and E-W stresses to the SCB triggering intracontinental orogeny.The thickened lithosphere underwent post-orogenic extension and thinning,and upwelling of mantle materials provided heat for the partial melting of the lower crust,forming the parental magma of the melting-type newborn crust(e.g.the Gulong pluton)or the mixed melting-type newborn crust with ancient crust component(e.g.the Liandong pluton).Under extensional environment after the intracontinental orogenic period,the parental magma upwelling along the channel formed the I-type granite with subduction-collision characteristics.
作者
周予茜
时毓
黄椿文
刘希军
蓝媛春
唐源远
翁伯寅
ZHOU Yuxi;SHI Yu;HUANG Chunwen;LIU Xijun;LAN Yuanchun;TANG Yuanyuan;WENG Boyin(Guangxi Key Laboratory of Hidden Metal Mineral Exploration,Guilin University of Technology,Guilin 541004,China;Collaborative Innovation Center for Exploration of Nonferrous Metal Deposits and Efficient Utilization of Resources in Guangxi,Guilin University of Technology,Guilin 541004,China;Hezhou Information Network Center of Science and Technology,Hezhou 542800,China)
出处
《地学前缘》
EI
CAS
CSCD
北大核心
2024年第2期224-248,共25页
Earth Science Frontiers
基金
广西自然科学基金杰出青年基金项目“华南显生宙构造演化(2019GXNSFFA245005)”
国家自然科学基金项目“扬子克拉通古元古代地壳演化:来自崆岭孔兹岩系的证据(42372083)”。
