| 北京密云地区BIF锆石SHRIMP U-Pb定年及其对成矿与变质时代的约束 |
| |
| 关键词:banded iron formation (BIF) zircon SHRIMP U-Pb dating metamorphic events North China Craton |
| 基金项目:本文由天津华北地质勘查局基础地质调查项目“冀北地区一带沉积变质型铁矿成矿规律研究与找矿预测”(编号: HK2024-B13)、市场委托项目“丰宁建宇铁矿有限公司杨营铁矿深部勘查”和华北地质勘查局五一四地质大队科研项目“冀北杨营地区构造复杂环境找矿技术综合研究”(编号: HKWYS2023-C1)联合资助。 |
|
| 摘要点击次数: 174 |
| 全文下载次数: 17 |
| 摘要: |
| Zircon SHRIMP U-Pb Dating of the BIF in Miyun, Beijing and Its Constraints on the Timing of Mineralization and Metamorphism |
| Miyun is a key area of the North China Craton (NCC), where early Precambrian basement and banded iron formations (BIFs) are well developed. To constrain the timing of BIF formation and metamorphism in this area, we conducted zircon SHRIMP U-Pb dating on diopside magnetite hornblendite (sample SY01) from the Shachang iron deposit and magnetite quartzite (sample MF01) from the Fengjiayu iron deposit. Zircons from sample SY01 yield two weighted mean ages of (2 531±7) Ma (MSWD=2.6) and (1 798±15) Ma (MSWD=1.2). Some ca. 2.53 Ga zircons exhibit typical oscillatory zoning with high Th/U ratios (mostly >0.4), interpreted as xenocrystic zircons, suggesting the presence of late Neoarchean crustal material. The ca. 1.80 Ga zircons are recrystallized zircons, recording a late Paleoproterozoic tectonothermal event. Zircons from sample MF01 also yield two weighted mean ages of (2 456±8) Ma (MSWD=1.6) and (1 777±9) Ma (MSWD=1.3). The ca. 2.45 Ga zircons are derived from bright-white residual cores, with weak magmatic zoning and high Th/U ratios; the original magmatic zircon should be ca. 2.5 Ga or older. The age younging is interpreted as ancient lead loss caused by the overprinting of strong late Paleoproterozoic tectonothermal modification. The ca. 1.78 Ga zircons, derived from dark recrystallized domains or metamorphic overgrowths, are homogeneous with low Th/U ratios, typical of metamorphic zircons. This study provides key constraints on the age of BIF mineralization. The ca. 2.53 Ga xenocrystic zircons in the diopside magnetite hornblendite define the oldest age of the BIF, whereas the ca. 2.45 Ga zircons in the magnetite quartzite provide the youngest age. The Miyun BIF is inferred to have been deposited in the late Neoarchean (~2.5 Ga), consistent with the peak BIF mineralization period (2.50–2.55 Ga) in the NCC. Subsequently, the BIF underwent a superimposed modification by a major tectonothermal event during the Late Paleoproterozoic. This study provides new geochronological evidence to better understand the coupled relationship between early Precambrian BIF mineralization and crustal evolution in the NCC. |
| DONG Jinmeng,LÜ Xiangguang,SHI Zhiqiang,WANG Peng,LIANG Jingli,ZHANG Mingyu,YU Wentao,WANG Zhen,SHI Yuruo.2026.Zircon SHRIMP U-Pb Dating of the BIF in Miyun, Beijing and Its Constraints on the Timing of Mineralization and Metamorphism[J].Acta Geoscientica Sinica,47(4):853-867. |
| 查看全文 查看/发表评论 下载PDF阅读器 |
|
|
|
|
|