| 徐淮地区斑井岩体锆石U-Pb测年、岩石成因及其地质意义 |
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| 引用本文： | 周虎,尚德锋,产思维,陈俊.徐淮地区斑井岩体锆石U-Pb测年、岩石成因及其地质意义[J].矿物岩石,2019,39(3):9-16. |
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| 作者姓名： | 周虎 尚德锋 产思维 陈俊 |
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| 作者单位： | 安徽省地质矿产勘查局325地质队,安徽淮北,235000;安徽省勘查技术院,安徽合肥,230000 |
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| 基金项目： | 萧县前欧盘铜铅锌金矿预查;萧县前欧盘铜铅锌金矿预查 |
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| 摘 要： | 斑井岩体位于徐淮推覆体中北部皇藏峪复背斜北段西翼,由于研究重点和关注度不同,对其成因类型及年代学特征研究较少。故此,本次研究将依托于钻孔XZK01中的7个岩石样品,通过大量的主微量元素地球化学分析及锆石U-Pb年代学分析,深入探讨斑井岩体的成因机制、形成年代及其地质意义。LA-ICP-MS锆石U-Pb年代学分析结果揭示斑井岩体的结晶年龄为126.4Ma±2.1Ma,侵位时代为中生代早白垩世,为地球动力学背景转变期间形成的岩体。本次6个样品的主量元素分析结果中w(SiO2)变化范围为56.54%~59.29%,全碱w(Na2O+K2O)变化范围为4.98%~5.68%,为中性岩;里特曼组合指数σ介于1.77~1.98之间,σ<3.3,属于钙碱性岩。其次,该组样品微量元素w(Sr)介于589×10^-6~728×10^-6之间,平均值为659×10^-6;w(Y)介于11.3×10^-6~12.8×10^-6之间,平均值为12.1×10^-6;w(Yb)介于1.13×10^-6~1.4×10^-6之间,平均值为1.23×10^-6;w(Cr)介于100×10^-6~660×10^-6之间,平均为377×10^-6;Mg#值介于47.17~68.14之间,平均值为58.21。该结果指示斑井岩体具富Sr,Sr/Y,贫Y,Yb的特征,指示其源区具有高压的环境,Mg#的变化特征揭示斑井岩体并非来自下地壳镁铁质岩石部分熔融,且w(Cr)的变化特征指示地幔橄榄岩也可能参与其中。此外,LREE/HREE介于6.91~10.98之间,平均值为8.895;LaN/YbN值在7.68~12.95之间,平均值为10.17,为轻稀土较强富集;大离子亲石元素Rb(23.9×10^-6~44.8×10^-6),K(11373×10^-6~14610.6×10^-6),Ba(513×10^-6~694×10^-6),Th(1.5×10^-6~2.5×10^-6),U(0.51×10^-6~0.79×10^-6)相对富集;高场强元素Nb(3.2×10^-6~4.7×10^-6),Ti(3056.7×10^-6~3536.2×10^-6)等表现出明显负异常。
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| 关 键 词： | 锆石U-PB测年 高镁 高压 岩石成因 地质意义 |
ZIRCON U-Pb DATING,PETROGENESIS AND GEOLOGICAL SINIFICANCE OF THE BANJING PLUTON IN XUHUAI AREA |
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| Zhou Hu,Shang Defeng,Chan Siwei,Chen Jun.ZIRCON U-Pb DATING,PETROGENESIS AND GEOLOGICAL SINIFICANCE OF THE BANJING PLUTON IN XUHUAI AREA[J].Journal of Mineralogy and Petrology,2019,39(3):9-16. |
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| Authors: | Zhou Hu Shang Defeng Chan Siwei Chen Jun |
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| Institution: | (The 325 Geological Team of Anhui Geological and Mineral Exploration Bureau ,Huaibei 235000,China;Anhui Provincial Institute of Exploration Technology , Hefei 230000,China) |
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| Abstract: | 7 samples from the well XZK01 are collected for geochemical and zircon U-Pb dating analysis in order to study the petrogenesis and chronology of the Banjing pluton in the west limb of Huangzhangyu anticline in the Xuhuai nappe.LA-ICP-MS zircon U-Pb dating reveals that the crystallization age of Banjing pluton is 126.4 Ma±2.1 Ma (early Cretaceous emplacement).Major element analysis shows that w(SiO2) ranges from 56.54% to 59.29% and total alkali w(Na2O+ K2O) varies from 4.98% to 5.68%, characteristic of neutral rock.Litman combination index a is in the range of 1.77~1.98,and σ<3.3,characteristic of calc-alkaline rock.Trace element analysis results showed that w(Sr) is in the range of 589×10^6 ^728×10^-6 with an average value of 659 ×10^6;w( Y) ranges from 11. 3×10^-6 ~2.8×10^6 with average value of 12. 1×10^-6;w(Yb) from 1.13×10^-6 to 1.4×10^-6 with average value of 1.23×10^-6;w(Cr) from 100×10^-6 to 660× 10^-6 with the average value of 377×10^-6;Mg# value is in the range of 47. 17~68.14 with the average value of 58.21. Main trace element analysis indicates that Banjing pluton is rich in Sr,Sr/Y and poor in Y, Yb,characteristic of high pressure environment. The variation of Mg# value shows that the pluton is not originated from partial melting of lower crust mafic rock and the variation character of w(Cr) suggests that mantle peridotite is involved in the formation of the pluton. LREE/HREE ranges from 6. 91 to 10. 98 with the average value of 8.895 and LaN/YbN from 7. 68 to 12.95 with the average value of 10.17, indication of strong enrichment of light rare earth elements. The pluton is relatively rich in large ionic lithophile elements, such as Rb(23.9×10^-6 44. 8×10^6),K(11 373×10^-6 ~14 610.6×10^6),Ba(513×10^-6~694×10^6), Th(1.5×10^6~2. 5×10^-6 ) and U(0. 51×10^-6 ~0.79×10^6). High field strength elements, such as Nb(3.2× 10^-6 ~4.7×10^6),Ti(3 056.7×10^6 ~3 536.2×10^-6),exhibit a significant negative anomaly. |
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| Keywords: | zircon U-Pb dating high-Mg high pressure petrogenesis geological significance |
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