Timing of eclogite facies metamorphism in the North Qinling by U-Pb and Lu-Hf geochronology
Timing of eclogite facies metamorphism in the North Qinling by U-Pb and Lu-Hf geochronology
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DOI：
10.1016/j.lithos.2011.06.003
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发表时间：
2012-04
期刊：
影响因子：
3.5
通讯作者：
Hao Cheng;Chao Zhang;J. Vervoort;Xian‐Hua Li;Qiu-li Li;Y. Wu;Shu Zheng
中科院分区：
文献类型：
--
作者：
Hao Cheng;Chao Zhang;J. Vervoort;Xian‐Hua Li;Qiu-li Li;Y. Wu;Shu Zheng
虽然北秦岭造山带的岩石学资料提供了造山旋回的地球动力学历史的重要信息，但北秦岭造山带内华北陆块与华南陆块之间的大陆碰撞时间仍然基本上没有限制。为完善已有的地球动力学模型，对北秦岭两个榴辉岩进行了U-Pb和Lu-Hf定年。结合常规热压法和假剖面估计，榴辉岩相变质作用期间的压力上限限制在660-710°C温度范围内的石英稳定场内，压力为2.6-2.8GPa。两个地点的石榴绿辉石矿物全岩年龄分别为516.4±5.8Ma（2σ）和494.3±2.7Ma（2σ），相应的加权平均锆石206 Pb/238 U年龄分别为507.0±8.7Ma（2σ）和490.0±4.1（2σ）Ma。石榴石斑晶从两个样品孔的证据，榴辉岩元素分带，但大部分的石榴石晶粒生长专门下榴辉岩相条件下所示的绿辉石包裹体从核心到边缘的发生。因此，这些Lu-Hf年龄被解释为反映高压榴辉岩相变质作用。两个Lu-Hf年龄之间的差异可能代表石榴石生长的最小持续时间，因此括号的开始和关闭的俯冲。这些结果为研究北秦岭造山带的俯冲历史提供了更详细的资料。这些新的U-Pb和Lu-Hf年龄标志着秦岭带华北陆块与华南陆块碰撞开始的时间，表明华南陆块前缘进入华北陆块海沟的时间大约在1980年。北秦岭造山带516 ~ 490 Ma。
Although petrologic data from the North Qinling orogen in central China have provided essential information on the geodynamic history of the orogenic cycle, the timing of the continental collision between the North China block and the South China block in the North Qinling orogen remains essentially unconstrained. To refine existing geodynamic models, two eclogites from the North Qinling were dated by U–Pb and Lu–Hf geochronology. The upper limit of the pressure during the eclogite facies metamorphism was restricted within the quartz stability field at 2.6–2.8GPa within a temperature range of 660–710°C by combining conventional thermobarometry and pseudosection estimates. Mineral–whole rock dating for multi-garnet-(omphacite) fractions from two localities yielded ages of 516.4±5.8Ma (2σ) and 494.3±2.7Ma (2σ) with corresponding weighted mean zircon206Pb/238U ages of 507.0±8.7Ma (2σ) and 490.0±4.1 (2σ) Ma, respectively. Garnet porphyroblasts from the two samples bore evidence of prograde elemental zonation, but the major portion of the garnet grains grew exclusively under eclogite facies conditions as indicated by the occurrence of omphacite inclusions from core to rim. Therefore, these Lu–Hf ages were interpreted to reflect high-pressure eclogite facies metamorphism. The difference between the two Lu–Hf ages likely represents the minimum duration of garnet growth and thus brackets the onset and the closure of the subduction. These results allow for more detailed insight into the subduction history of the North Qinling orogen. These new U–Pb and Lu–Hf ages mark the timing of the onset of the continental collision between the North China block and the South China block in the Qinling belt, suggesting that the entry of the leading edge of the South China block continent into the North China block trench occurred from ca. 516Ma to 490Ma in the North Qinling orogen.