华北克拉通胶莱盆地马山地区早白垩世粗面英安岩岩石成因  

Petrogenesis of the Early Cretaceous trachy-dacite from Mashan in the Jiaolai Basin,North China Craton

作　　者：何登洋 邱昆峰[1] 于皓丞 黄雅琪 丁正江 申颖 HE DengYang;QIU KunFeng;YU HaoCheng;HUANG YaQi;DING ZhengJiang;SHEN Ying(School of Earth Science and Resources,China University of Geosciences,Beijing 100083,China;Shandong Bureau of Geology and Mineral Resources,Jinan 250013,China;Shandong Institute of Geological Sciences,Jinan 250013,China)

机构地区：[1]中国地质大学(北京)地球科学与资源学院,北京100083 [2]山东省地质矿产勘查开发局,济南250013 [3]山东省地质科学研究院,济南250013

出　　处：《岩石学报》2020年第12期3705-3720,共16页Acta Petrologica Sinica

基　　金：国家重点基础研究发展计划项目(2019YFA0708603);国家自然科学基金项目(91962106、41973048);高等学校学科创新引智计划(BP0719021);中国地质大学(北京)创新创业训练计划(202011415006)联合资助。

摘　　要：伸展盆地、拉张断层以及伴生火山岩是华北克拉通中生代岩石圈减薄的地质响应,前两者通常源于中上地壳伸展活动,而后者则可能来自下地壳甚至地幔部分熔融。因此火山岩能够提供来自深部地壳、地幔及壳-幔相互作用的信息。胶莱盆地马山粗面英安岩成因及其与华北克拉通岩石圈减薄的关系仍存在争议。本文对马山粗面英安岩开展岩石学、全岩地球化学、LA-ICP-MS锆石U-Pb年代学以及Lu-Hf同位素研究,查明其Si O2含量为65.73%~66.08%,K2O含量为3.13%~4.03%,全碱含量为7.56%~8.15%,属于高钾钙碱性系列。锆石206Pb/238U年龄为119.3±1.6Ma,与胶莱盆地早白垩世伸展变形时间一致。εHf(t)值为-24.6^-11.5,两阶段Hf模式年龄为2700~1200Ma,表明岩浆源区为改造的古老下地壳并混有富集地幔物质。岩石相对富集K和Sr等大离子亲石元素,亏损Nb、Ta和Ti等高场强元素,LREE/HREE比值较高,无明显的Eu负异常(δEu=0.94~1.02),表明岩浆可能源于下地壳的部分熔融,因此,马山粗面英安岩可能是富集地幔与部分熔融的下地壳相互混染的产物。研究认为早白垩世高角度俯冲的古太平洋板片大规模回撤,胶莱盆地快速伸展断陷伴随青山群火山岩喷发,随后演化形成张性火山盆地。Extensional basin,extensional fault and coeval magmatism represent the most important responses to lithosphere thinning,that are formed by extension of upper crust and partial melting of lower crust or mantle.Volcanic rocks can document evolution processes of magmas that derived from deep crustal/mantle or crust mantle interactions.Petrogenesis of the volcanic rocks in the Jiaolai Basin,however,is debated,and therefore has hampered understanding of the Cretaceous geodynamic of the Jiaolai Basin.In present study,we conducted a study on petrology,geochronology,and geochemistry of trachy-dacite in Mashan area in the eastern North China Craton(NCC).LA-ICP-MS zircon U-Pb geochronology documented that the trachy-dacite erupted at 119.3±1.6 Ma.The dominant negativeεHf(t)values,ranging from-24.6 to-11.5,and tDM2 between 2700 Ma and 1200 Ma,indicate that they were derived from ancient lower crust or lithospheric mantle involved components of the ancient crust.These trachy-dacite rocks in the Jiaolai basin display Si O2=65.73%~66.08%,K2 O=3.13%~4.03%,and total alkali ranging from 7.56%to 8.15%,indicating their affinity of high-K calc-alkaline to shoshonitic in origin.They are characterized by high-moderate LREE/HREE and(La/Yb)Nratios,without significant Eu anomalies(δEu=0.94~1.02),negative Nb-Ta anomalies,and high concentration of LILE than HFSE,demonstrating that they can be derived from partial melting of lower crust and enriched mantle.We therefore proposed that the coeval Cretaceous volcanic rocks exposed in the Jiaolai Basin were derived from partial melting of the ancient lower crust that were contaminated by enriched lithospheric mantle,and fractional crystallization.The Jiaolai Basin and coeval volcanic rocks,corresponding to NCC lithosphere thinning,were products of slab rollback of subduction of the Paleo-Pacific plate during Early Cretaceous.

关 键 词：粗面英安岩 地球化学 地质年代学 LU-HF同位素 岩石圈减薄 胶莱盆地 

分 类 号：P588.142[天文地球—岩石学] P597.3[天文地球—地质学]