北山造山带尖山子新元古代早期似斑状花岗岩年代学、地球化学特征及地质意义  

Age,Geochemistry and Geological Significance of an Early Neoproterozoic Porphyritic Granite in the Jianshanzi Area of the Beishan Orogenic Belt

作　　者：王必任 滕超[3] 白相东 关成尧 袁四化 张晓飞 杨欣杰 WANG Biren;TENG Chao;BAI Xiangdong;GUAN Chengyao;YUAN Sihua;ZHANG Xiaofei;YANG Xinjie(School of Earth Sciences,Institute of Disaster Prevention,Sanhe 065201,Hebei,China;Hebei Key Laboratory of Earthquake Dynamnics,Sanhe 065201,Hebei,China;Cores and Samples Center of Natural Resources,China Geological Survey,Sanhe 065201,Hebei,China;Development and Research Centre,China Geological Survey,Beijing 100037,China)

机构地区：[1]防灾科技学院地球科学学院,河北三河065201 [2]河北省地震动力学重点实验室,河北三河065201 [3]中国地质调查局自然资源实物地质资料中心,河北三河065201 [4]中国地质调查局发展研究中心,北京100037

出　　处：《西北地质》2024年第6期44-57,共14页Northwestern Geology

基　　金：廊坊市科学技术研究与发展计划自筹经费项目“三河市段甲岭-邦均断裂断层泥石英微形貌及其年代学研究”(2021013165);中央高校基本科研业务费专项自主申报项目“北山微地块前寒武纪地层对比及其对构造亲缘性的制约”(ZY20215119)联合资助。

摘　　要：笔者报道了北山造山带东缘尖山子地区新元古代早期似斑状花岗岩年代学、地球化学特征,结合已发表的同期花岗质岩石地球化学数据,讨论其源区性质及北山南部前寒武纪基底与塔里木克拉通的亲缘性。似斑状花岗岩两件样品锆石U-Pb年龄分别为(901±5)Ma,(935±3)Ma,表明其形成于新元古代早期。似斑状花岗岩样品发育钾长石斑晶,显示高的SiO2含量(70.41%~76.05%)和过铝质特征(A/CNK=1.01~1.21);具有相似的球粒陨石标准化稀土元素配分曲线并显示轻稀土富集、Eu负异常(δEu=0.30~0.46)和在原始地幔标准化多元素图解上显示Rb、Th、U和K正异常,Ba、Nb、Ta、Sr、P和Ti负异常;具有富集的锆石Hf同位素组成,其ε_(Hf)(t)值为-5.0~-1.4和相应的两阶段Hf模式年龄为2.08~1.86 Ga。这些地球化学特征共同反应似斑状花岗岩为壳源花岗岩,并指示早期地壳的再造事件。结合前人发表的地球化学数据,北山造山带南部前寒武纪基底经历了中元古代地壳新生事件和新元古代早期地壳再造事件,花岗质岩石锆石ε_(Hf)(t)值主要落在2.2~1.3 Ga地壳物质Hf同位素演化区内,指示北山南部不存在太古代基底,因此与具有太古代结晶基底的塔里木克拉通可能不具有构造亲缘性。The geochronological and geochemical data of an early Neoproterozoic porphyritic granite in the Jianshanzi Area of the Beishan Orogenic Belt has been present.Combined with published geochemical data of contemporaneous granitic rocks,their magma sources and the tectonic affinity between the Precambrian basement in the southern Beishan and Tarim Cration are discussed.Two samples from the porphyritic granite have zircon U-Pb ages of(901±5)Ma and(935±3)Ma,respectively,indicating that it was formed during the early Neoproterozoic.Samples from the porphyritic granite contain K-feldspar phenocrysts with high SiO2 contents(70.41%~76.05%)and peraluminous characteristics(A/CNK=1.01~1.21),and exhibit similar chondrite-normalized REE patterns with LREE-enrichment and pronounced negative Eu anomalies(δEu=0.30~0.46),and show positive Rb,Th,U and K anomalies,negative Ba,Nb,Ta,Sr,P and Ti anomalies in the primitive mantlenormalized trace-element diagram,and have evolved zirconε_(Hf)(t)values of−5.0 to−1.4 and two-stage Hf model ages of 2.08~1.61 Ga.All these geochemical characteristics suggest that the porphyritic granite is a typical crustal-derived granite,indicating an older crustal reworking event.Together with the reported data,the Precambrian basement of the southern Beishan experienced both Mesoproterozoic crustal growth and early Neoproterozoic crustal reworking events with the zirconε_(Hf)(t)values of granitic rocks plotting within the crustal evolution trend defined by 2.1~1.3 Ga crustal material,indicating the absence of an Archean basement in the southern Beishan,and therefore it may not have tectonic affinity with the Tarim craton with an Archean crystalline basement.

关 键 词：新元古代 花岗质岩石 地壳再造 北山造山带 

分 类 号：P597[天文地球—地球化学]