华北克拉通中部早白垩世岩石圈地幔性质:来自狐偃山科头钾质正长岩年代学、同位素的限制  

The nature of Early-Cretaceous lithosphere mantle in the central North China craton:constraints from chronological and isotopic data of Ketou potassic syenite in Huyanshan

作　　者：张乔 周俊林[1,2] 李玉宏 陈高潮[1,2] 张慧婷 ZHANG Qiao;ZHOU Junlin;LI Yuhong;CHEN Gaochao;ZHANG Huiting(Key Laboratory for the Study of Focused Magmatism and Giant Ore Deposits,MNR,Xi’an Center of Geological Survey,CGS,Xi’an,710054;Northwest Geological Survey Science and Technology Innovation Center,Xi’an,710054;Xi’an University of Science and Technology,College of Geology and Environment,Xi’an,710054)

机构地区：[1]自然资源部岩浆作用成矿与找矿重点实验室,中国地质调查局西安地质调查中心,西安710054 [2]西北地质调查科技创新中心,西安710054 [3]西安科技大学地质与环境学院,西安710054

出　　处：《地质学报》2020年第3期739-756,共18页Acta Geologica Sinica

基　　金：国家科技重大专项(编号2016ZX05034001-006);国家自然科学基金项目(编号41572131);中国地质调查局地质调查项目(编号20190103)联合资助成果。

摘　　要：华北克拉通东部中生代岩石圈减薄已经取得了大量进展,相比之下对克拉通中部岩石圈演化认识不足。本文对华北克拉通中部狐偃山杂岩体中科头正长岩进行了锆石U-Pb年代学、主量和微量元素、Sr-Nd-Hf同位素地球化学研究。LA-ICP-MS锆石U-Pb定年结果显示,科头正长岩侵位于早白垩世晚期(~111Ma)。岩石样品均为钾质-超钾质,属于碱性系列岩石。这些岩石相对富集轻稀土,亏损重稀土和中稀土,具有明显的正Eu异常(Eu/Eu*=1.22~1.96)、富集大离子亲石元素LILE(Rb、Sr、Ba),亏损高场强元素HFSE(Nb、Ta、Ti)。所有岩石样品具有相对高的初始87Sr/86Sr比值(0.7058~0.7062)和低的εNd(t)(-10.4^-11.1),εHf(t)介于-12.2^-5.2之间。详细的元素和同位素地球化学研究表明科头正长岩的原始岩浆可能来源于富集岩石圈地幔中富金云母的尖晶石二辉橄榄岩源区的部分熔融,岩浆演化过程中经历了地壳混染与结晶分异(AFC)过程。结合华北克拉通中部岩浆资料,将华北克拉通中部早白垩世岩浆作用分为早晚两期:早期(123~135Ma)为岩浆作用高峰期,晚期(~114Ma)为最后一期弱的岩浆期;华北克拉通中部陆下岩石圈地幔是富集的、不均一的,其至少在早白垩世(138~111Ma)一直处于减薄状态。In contrast to the eastern North China craton,limited progress has been made on Mesozoic lithospheric thinning in the central North China craton.This study presents detailed LA-ICP-MS zircon UPb dating,major and trace element geochemical,and Sr-Nd-Hf isotopic data for the Ketou syenite within the Huyanshan alkaline complex in central North China craton.LA-ICP-MS zircon U-Pb dating shows that the Ketou syenite was emplaced in the late stage(111 Ma)of Early-Cretaceous.These samples are all potassic-ultrapotassic and alkaline rocks,which have distinct positive Euanomalies.They also have high initial 87 Sr/86 Sr ratios of 0.7058-0.7062,lowerεNd(t)values of-11.1 to-10.4,and zirconεHf(t)values of-12.2 to-5.2.Detailed research suggests that the primitive magmas of the Ketou syenite were derived from partial melting of the enriched lithosphere mantle with phlogopite-bearing lithosphere mantle at spinel lherzolite zone.The primitive magmas have gone through the process of assimilation and fractional crystallization(AFC).Integrating these results with the published data of magmatism in the central North China,we infer that the late-Mesozoic magmatism in the central North China can be subdivided into two stages:an early one at 123~135 Ma for the peak magmatism and a later one at 114 Ma for the last weak magmatism.Together with the source region for the late-Mesozoic magmatic rocks in the central North China,the results indicate that the lithosphere mantle in central North China was enriched and heterogeneous and began thinning at least between 138 to 111 Ma.

关 键 词：华北克拉通中部 正长岩 早白垩世晚期 钾质 富集岩石圈地幔 岩石圈减薄 

分 类 号：P588.122[天文地球—岩石学] P534.53[天文地球—地质学] P597.3