菖蒲盆地早侏罗世火山岩的古地磁研究——对华南晚中生代岩浆热液重磁化与铀成矿的启示  

Paleomagnetism of early Jurassic volcanic rocks from the Changpu Basin:Implications for the late Mesozoic magmatic-hydrothermal remagnetization and uranium mineralization in South China

作　　者：杨思林 易治宇 赵千 刘玉书 王天月 YANG SiLin;YI ZhiYu;ZHAO Qian;LIU YuShu;WANG TianYue(Planetary Environmental and Astrobiological Research Laboratory(PEARL),School of Atmospheric Sciences,Sun Yat-sen University,Zhuhai Guangdong 528478,China;Key Laboratory of Tropical Atmosphere-Ocean System,Ministry of Education,Zhuhai Guangdong 519028,China;Department of Resource and Environment Science,Quanzhou Normal University,Quanzhou Fujian 362000,China;State Key Laboratory of Lithospheric Evolution,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China)

机构地区：[1]中山大学大气科学学院空间与行星科学系,广东珠海528478 [2]热带大气海洋系统科学教育部重点实验室,广东珠海519028 [3]泉州师范学院资源与环境科学学院,福建泉州362000 [4]中国科学院地质与地球物理研究所岩石圈演化国家重点实验室,北京100029

出　　处：《地球物理学报》2025年第4期1394-1416,共23页Chinese Journal of Geophysics

基　　金：国家自然科学基金(42372246,92055205,41672223);广东省自然科学基金(2024A1515010928)资助。

摘　　要：准确厘定中生代东亚陆块群的古地理位置,是重建盘古大陆古地理轮廓和古气候模式的关键基础.由于缺乏可靠的火山岩剩磁记录以及普遍存在的重磁化,华南地块早侏罗世的古地理位置还存在很大的不确定性.本研究选择华南菖蒲盆地早侏罗世火山岩,开展了详细的同位素年代学和古地磁学研究.锆石U-Pb定年结果揭示菖蒲组的同位素年龄为196.4±0.7 Ma.系统热退磁实验分离出三组剩磁分量,其中低温分量为现代黏滞剩磁;从9个采点中获得一组中间分量,全部为正极性,褶皱检验显示其为褶皱后获得的次生剩磁;从17个采点中获得一组呈对趾分布的特征分量,通过了C级倒转检验.虽然正交投影图上特征分量和中间分量之间存在差别,但两者的平均方向在统计上无显著区别,表明两组分量的获得是准同时的.进一步将中间分量和特征分量对应的古地磁极与华北中生代视极移曲线对比,显示其与早白垩世参考极重叠,揭示两者很可能都是早白垩世的重磁化.综合岩相学、岩石磁学和退磁结果表明,热液流体作用下生成的次生磁铁矿是重磁化分量的主要载磁矿物,磁铁矿在形成后期还遭受不同程度的氧化生成磁赤铁矿或赤铁矿,很可能携带了化学剩磁.热液重磁化时间和菖蒲盆地周边岩浆-热液型铀矿的成矿时间相同,表明两者可能由同一期热液活动引起.这一研究结果揭示华南地块在晚中生代期间存在广泛的岩浆-热液重磁化作用,对区域上寻找热液型金属矿床有一定的意义.Determining the paleoposition of the East Asian blocks during the Mesozoic is crucial for reconstructing the paleogeography and climate patterns of Pangea.However,the position of the South China Block within Pangea remains uncertain due to the lack of paleomagnetic data from igneous rocks and widespread remagnetization.To address this,we carried out a detail isotopic geochronological and paleomagnetic study on the early Jurassic volcanic rocks from the Changpu Basin,South China.Laser-ablation–inductively coupled plasma–mass spectrometry U-Pb dating yields an age of 196.4±0.7 Ma.Three components are successfully isolated from a total of 27 sites via stepwise thermal demagnetization.The low-temperature component overlaps the local geomagnetic field,suggestive of a recent viscous overprint.The intermediate component(IC),isolated from 9 sites with exclusive normal polarity,fails a regional fold test,suggesting a post-folding origin.The characteristic remanences(ChRMs)are isolated from 17 sites and pass a reversal test in“C”class.Although the ChRMs and ICs differ in each Zijderveld-plot,the mean direction are statistically indistinguishable,suggesting quasi-simultaneous acquisition.A comparison of paleopoles determined from the ICs and ChRMs with the APWP of North China Block suggests a remagnetization in the Early Cretaceous.A comprehensive analysis of petrology,rock magnetism and demagnetization behavior suggests that magnetites are the main carrier of ICs and ChRMs,which may originate from secondary hydrothermal fluid.Some magnetites underwent further oxidation,forming maghemite and hematite,which may also carry a chemical remanence.The remagnetization is coeval with the regional mineralization of uranium ore,which may result from the same magma-hydrothermal event.These findings support a widespread magmatic hydrothermal remagnetization in southern China during the late Mesozoic and provide clues for searching hydrothermal metal deposits in this area.

关 键 词：古地磁学 华南陆块 重磁化 热液成矿 

分 类 号：P318[天文地球—固体地球物理学]