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首页> 外文期刊>Lithos: An International Journal of Mineralogy, Petrology, and Geochemistry >Microgeochemistry of rutile and zircon in eclogites from the CCSD main hole: Implications for the fluid activity and thermo-history of the UHP metamorphism
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Microgeochemistry of rutile and zircon in eclogites from the CCSD main hole: Implications for the fluid activity and thermo-history of the UHP metamorphism

机译：CCSD主孔榴辉岩中金红石和锆石的微地球化学：对UHP变质流体活动和热史的影响

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摘要

Rutile and zircon in eclogites from the main hole of the Chinese Continental Scientific Drilling (CCSD-MH) were analyzed by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and electron microprobe (EMP). Both single spot and profile analyses of large matrix rutiles (>60 μm) generally demonstrate core-rim variability of Pb, Sr, Zr and U. Pb and Sr show enrichment at the rims, while Zr and U decrease in concentration from the cores to the rims. Correspondingly, temperatures estimated by Zr-in-rutile geothermometers are higher within the cores (mainly in the range of 680-740 °C) than at the rims by 10-30 °C. We note that estimated temperatures within the cores of matrix rutiles correlate positively with grain diameter. This suggests that the Zr content in rutiles is not only dependent on temperature and pressure, but is also affected by fluid activity and Zr diffusion. Estimated temperatures within the cores of matrix rutiles merely represent lower limits of the peak ultra-high pressure (UHP) metamorphic temperatures. Combined with Th/U and Ce/Lu ratios, rare earth element (REE) patterns and ~(206)Pb/~(238)U ages, Ti-in-zircon geothermometers can be used to distinguish the thermal evolution of eclogites during the UHP metamorphism Zircons of 745 ±8.0 Ma (2σ, n = 3) show evidence of the temperatures at which they crystallized from the original magma. Zircons of 240 ± 7.0 Ma (2σ, n = 11) with flat HREE patterns suggest a definite temperature range (689 ± 18 °C (2σ, n = 11)) for the prograde metamorphism Although 226 Ma is generally considered the time of the peak UHP metamorphism for the Dabie-Sulu orogen, except for a few grains with a maximum temperature of 744 °C, most of the 226±2.0 Ma (2σ, n = 12) zircons indicate lower temperatures (average = 698 ± 12°C (2σ, n = 12)). These data imply that the 226 Ma zircons were probably not products of the peak UHP metamorphism, but might instead be associated with the pressure decrease in the post-peak metamorphism. The youngest zircons (<220 Ma) provide evidence for temperatures (682 ±14 °C (2σ, n = 11)) associated with the retrograde metamorphism. Geothermometers that incorporate both rutile and zircon indicate that there may have been experienced a locally short-lived heating event for eclogites from the CCSD-MH.
机译：通过激光烧蚀-电感耦合等离子体质谱法（LA-ICP-MS）和电子探针（EMP）分析了中国大陆科学钻探公司（CCSD-MH）主孔榴辉岩中的金红石和锆石。大基质金红石（> 60μm）的单点分析和轮廓分析通常都表明Pb，Sr，Zr和U的芯-边缘变异性。Pb和Sr在边缘处富集，而Zr和U的浓度从芯部降低到轮辋。相应地，金红石型地热仪估算的岩心内温度（主要在680-740°C范围内）比边缘温度高10-30°C。我们注意到，基体金红石型核芯内的估计温度与晶粒直径呈正相关。这表明金红石中的Zr含量不仅取决于温度和压力，而且还受流体活度和Zr扩散的影响。基体金红石芯中的估计温度仅代表峰值超高压（UHP）变质温度的下限。结合Th / U和Ce / Lu比值，稀土元素（REE）模式和〜（206）Pb /〜（238）U年龄，Ti-in-Zircon地热仪可用于区分榴辉岩在高温下的榴辉岩热演化。 UHP变质锆石为745±8.0 Ma（2σ，n = 3），显示了它们从原始岩浆中结晶出来的温度。具有平坦HREE模式的240±7.0 Ma（2σ，n = 11）锆石表明前移变质作用的确定温度范围（689±18°C（2σ，n = 11））尽管通常认为226 Ma除少数最高温度为744°C的晶粒外，大别-苏鲁造山带的UHP峰值变质，大多数226±2.0 Ma（2σ，n = 12）锆石表明温度较低（平均= 698±12°C） （2σ，n = 12））。这些数据表明，226 Ma锆石可能不是超高压变质峰的产物，而可能与峰后变质的压力下降有关。最年轻的锆石（<220 Ma）提供了与逆行变质作用有关的温度（682±14°C（2σ，n = 11））的证据。结合了金红石和锆石的地热仪表明，对于来自CCSD-MH的榴辉岩，可能经历了局部短暂的加热事件。

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