熊耳山地区TTG岩石记录大氧化事件及其对岩浆静寂期的启示
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1.中南大学有色金属成矿预测与地质环境监测教育部重点实验室;2.中南大学地球科学与信息物理学院

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国家自然科学基金项目(面上项目,重点项目,重大项目)


Insights from TTG Rock Records on the Great Oxidation Event and its Impact on Tectonic Magma-Limited period in the Xiong'ershan Region
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1.Key Laboratory of Metallogenic Prediction of Nonferrous Metals and Geological Environment Monitoring,Central South University,Changsha;2.School of Geosciences and Info-Physics,Central South University

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    摘要:

    大氧化事件(Great Oxidation Events,简称GOE)的记录主要是来自于沉积岩地球化学特征,岩浆岩方面的证据较少。然而,全球弧岩浆岩的Th/U比值成功指示了两次大氧化事件,开创了利用岩浆岩地球化学指标探索大氧化事件研究的新领域。弧岩浆岩通常产生于俯冲洋壳脱水交代的上覆地幔楔部分熔融,具有重稀土较富集的特点。本研究结合弧岩浆岩相关研究成果,探讨大氧化事件前后不同时期TTG(Tonalite-Trondhjemite- Granodiorite)岩浆岩是否可以记录GOE,以及GOE对TTG的形成会产生哪些影响,特别是后者,前人在考虑大氧化事件期间及之后的TTG形成时,往往忽略了这一影响。通过锆石年代学证明,在2.45-2.20 Ga(全球岩浆静寂期)范围内,针对不同时期(2.43-2.18 Ga)的明显受表壳物质(锆石Hf-O同位素佐证)加入影响的TTG岩石开展研究,包括其锆石Th/U比值和锆石氧逸度异常,为探讨GOE对不同深度岩浆岩的影响提供了新证据。研究表明,三类不同时期的TTG岩石主微量元素与高硅埃达克岩具有相似的地球化学特征。此外,GOE对不同时期岩浆作用的氧同位素和氧逸度变化有一个升高再降低的过程。全岩花岗岩构造图解和锆石微量元素表明这些岩石形成于大洋俯冲带岛弧环境,这一形成过程可能是由于俯冲洋壳脱水和熔融,随后导致TTG岩石氧逸度发生变化。

    Abstract:

    The majority of records regarding the Great Oxidation Events (GOE) are derived from the geochemical characteristics of sedimentary rocks, with minimal involvement of evidence from igneous rocks. However, the Th/U ratio of global arc magmatic rocks has successfully indicated two instances of the GOE, pioneering a new area of study using igneous rock geochemical indicators to explore GOE research. Arc magmatic rocks generally form through the melting of the overlying mantle wedge during subduction-induced dehydration of oceanic crust, exhibiting enrichment in heavy rare earth elements. Combining the results of studies on arc magmatic rocks, this paper explores whether TTG (Tonalite-Trondhjemite-Granodiorite) magmatic rocks from different periods can record GOE and what impact the formation of GOE has on TTG, especially considering that previous studies often overlooked this influence when considering the formation of TTG during and after the Great Oxidation Events. Through zircon geochronology, within the range of 2.45-2.20 Ga (Tectono-Magmatic Lull), this study demonstrates research on TTG rocks influenced by the addition of crustal material during different periods (2.43-2.18 Ga), including evidence from zircon Th/U ratios and zircon oxygen fugacity anomalies. This provides new evidence for exploring the impact of GOE on magmatic rocks at different depths.Research has demonstrated that the main and trace elements in TTG rocks from three distinct periods exhibit similar geochemical characteristics to high silica adakites. Additionally, the Great Oxidation Event (GOE) showcases a pattern of increasing and then decreasing oxygen isotope and oxygen fugacity changes throughout various periods of magmatic activity.Structural diagram of whole rock granite and trace elements of zircon suggests that TTG rocks were formed within an island arc environment situated along an oceanic subduction zone. This formation process is hypothesized to be the result of dehydration and melting of the subducted oceanic crust. Consequently, such processes lead to variances in the oxygen fugacity of TTG rocks.

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  • 收稿日期:2024-01-14
  • 最后修改日期:2024-07-08
  • 录用日期:2024-07-10
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