摘要
为探讨狮泉河左左地区林子宗群典中组火山岩成因及其动力学背景,本文进行了年代学、岩石地球化学以及Lu-Hf同位素研究。结果显示,锆石U-Pb年龄为57.1±0.8 Ma和55.8±0.7 Ma,将原属于则弄群拖称组火山岩重新厘定为古新世典中组。地球化学特征显示过铝质、高钾钙碱性,具高SiO_(2)、低TiO_(2)、低MgO、低Cr、Ni和Mg^(#) (均值22),富集K、Rb、Pb等大离子亲石元素,亏损Nb、Ta、Ti、P等高场强元素,反映弧岩浆特征。轻重稀土元素分馏明显,相对富集轻稀土,Eu、Ba、Sr负异常显著,指示较强的分离结晶作用。锆石Hf同位素ε_(Hf)(t)介于+2.61~+9.51,T_(DM)^(C)年龄为965~514 Ma,指示新生地壳物质的重熔。综合分析认为印度大陆和亚洲大陆初始碰撞于70 Ma,随后板片持续回转并伴随典中组弧火山岩的形成;在56 Ma左右新特提斯洋板片断离,形成了年波组和帕那组大规模火山作用(时间持续到40 Ma)。
To investigate the petrogenesis and tectonic setting of the Dianzhong Formation volcanic rocks in the Shiquanhe area,we present detailed zircon U-Pb geochronology,whole-rock geochemistry,and Lu-Hf isotopic data for volcanic rocks from the Dianzhong Formation(Linzizong Group).The results reveal zircon U-Pb ages of 57.1±0.8 Ma and 55.8±0.7 Ma,demonstrating that these volcanic rocks,previously assigned to the Tuocheng Formation(Zenong Group),should be reclassified as the Paleocene Dianzhong Formation.Geochemical analyses indicate the samples are peraluminous,high-K calc-alkaline series characterized by high SiO_(2) and low TiO_(2) contents,along with low MgO,Cr,and Ni concentrations and low Mg^(#) values(mean=22).These rocks show distinct enrichment in large ion lithophile elements(LILE;e.g.,K,Rb and Pb),coupled with depletion in high field strength elements(HFSE;e.g.,Nb,Ta,Ti and P),indicative of an arc magmatic affinity.The fractionation of light and heavy rare earth elements is obvious,with relative enrichment in LREE and significant negative Eu,Ba,and Sr anomalies,indicative of extensive fractional crystallization processes.Zircon Hf isotopes yield ε_(Hf)(t)values ranging from+2.61 to+9.51,with two-stage model ages(T_(DM)^(C))between 965 and 514 Ma,indicating derivation from the remelting of juvenile crustal material.These data suggest that following the initial India-Asia continental collision(~70 Ma),continued rollback of the Neo-Tethyan slab resulted in the formation of the Dianzhong Formation volcanics.The subsequent slab breakoff at~56 Ma triggered the large-scale Nianbo and Pana Formation volcanism,which lasted until about 40 Ma.
作者
俞嘉嘉
陈伟
唐菊兴
马旭东
李阳
王承洋
刘青枰
刘畅
邸梦想
YU Jiajia;CHEN Wei;TANG Juxing;MA Xudong;LI Yang;WANG Chengyang;LIU Qingping;LIU Chang;DI Mengxiang(State Key Laboratory of Deep Earth and Mineral Exploration,Institute of Mineral Resources,Chinese Academy of Geological Sciences,Beijing 100037,China;School of Earth Science and Resource,China University of Geosciences,Beijing 100083,China)
出处
《地质学报》
北大核心
2025年第10期3357-3371,共15页
Acta Geologica Sinica
基金
中国地质调查项目(编号DD20230359)
西藏自治区科技计划项目(编号XZ202401YD0006)
中国地质科学院基本科研业务费项目(编号JKYQN202325,KK2407)联合资助的成果。
关键词
典中组
林子宗群
新特提斯洋
印度-亚洲大陆碰撞
Dianzhong Formation
Linzizhong Group
Neo-Tethys
Indian-Asian continent collision
