학술논문
辽东地区赛马碱性杂岩锆石U-Pb年龄、Hf同位素组成及其对构造背景的制约 / Zircon U-Pb age,Hf isotope composition,and their constraints on tectonic setting of the Saima alkaling complex in the eastern Liaoning Province
Document Type
Academic Journal
Author
Source
地质通报 / Geological Bulletin of China. 43(1):76-85
Subject
Language
Chinese
ISSN
1671-2552
Abstract
通过LA-ICP-MS测得辽宁赛马地区浅肉红色霞霓正长岩中的锆石U-Pb年龄为 225.8±1.9 Ma,赛马碱性杂岩的侵位时代为晚三叠世.地球化学分析表明,霞霓正长岩 SiO2 含量为 55.87%～60.88%,Na2O为 0.41%～5.32%,Al2O3 为 17.81%～19.53%,K2O为 9.46%～11.91%,MgO为 0.46%～1.36%,里特曼指数为 7.54～17.01;稀土元素总量较高,高于 300×10-6,强烈富集轻稀土元素,(La/Yb)N值大于 10,个别达到 100 以上;亏损Nb、Ta、P等高场强元素,富集Rb、Th等大离子亲石元素,总体表现出富碱性岩石特征.锆石εHf(t)值为-13.37～-9.30,对应的两阶段Hf模式年龄TDM2 为 2102～1855 Ma.通过岩石成因分析和构造环境判别,赛马碱性杂岩可能形成于由俯冲挤压向陆内伸展、拉张转换的动力背景下的下地壳(或上地幔)部分熔融.赛马碱性杂岩侵位时代(225.8±1.9 Ma)可能代表了华北克拉通北缘岩石圈开始伸展减薄的时间,也是郯庐断裂形成的时间.
The light-red aegirine nepheline syenite in Liaoning Saima area has a LA-ICP-MS U-Pb age of 225.8±1.9 Ma,and the emplacement age of the Saima alkaline complex is the Late Triassic.Aegirine nepheline syenite shows SiO2 of 55.87%～60.88%,Na2O of 0.41%～5.32%,Al2O3 of 17.81%～19.53%,K2O of 9.46%～11.91%,MgO of 0.46%～1.36%,σ43 of 7.54～17.01.The total amount of rare earth elements is higher than 300×10-6,and it is strongly enriched with light rare earth elements.Depletion of high field strength elements such as Nb,Ta,P,and enrichment of large ion lithophilic elements such as Rb,Th,shows the characteristics of alkaline rich rocks.The zircon εHf(t)value is-13.37～-9.30,the corresponding two-stage Hf model age TDM2 is 2102～1855 Ma.The Saima alkaline complex may be formed by the partial melting of the lower crust(or upper mantle)under the dynamic background of subduction-squeezing to inland extension and extension conversion.The age of emplacement(225.8±1.9 Ma)may represent the time when the lithosphere began to stretch and thin on the northern margin of the North China Craton,and also the time when the Tanlu fault was formed.
The light-red aegirine nepheline syenite in Liaoning Saima area has a LA-ICP-MS U-Pb age of 225.8±1.9 Ma,and the emplacement age of the Saima alkaline complex is the Late Triassic.Aegirine nepheline syenite shows SiO2 of 55.87%～60.88%,Na2O of 0.41%～5.32%,Al2O3 of 17.81%～19.53%,K2O of 9.46%～11.91%,MgO of 0.46%～1.36%,σ43 of 7.54～17.01.The total amount of rare earth elements is higher than 300×10-6,and it is strongly enriched with light rare earth elements.Depletion of high field strength elements such as Nb,Ta,P,and enrichment of large ion lithophilic elements such as Rb,Th,shows the characteristics of alkaline rich rocks.The zircon εHf(t)value is-13.37～-9.30,the corresponding two-stage Hf model age TDM2 is 2102～1855 Ma.The Saima alkaline complex may be formed by the partial melting of the lower crust(or upper mantle)under the dynamic background of subduction-squeezing to inland extension and extension conversion.The age of emplacement(225.8±1.9 Ma)may represent the time when the lithosphere began to stretch and thin on the northern margin of the North China Craton,and also the time when the Tanlu fault was formed.