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首页> 外文期刊>Contributions to Mineralogy and Petrology >Reconciliation of discrepant U-Pb, Lu-Hf, Sm-Nd, Ar-Ar and U-Th/He dates in an amphibolite from the Cathaysia Block in Southern China
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Reconciliation of discrepant U-Pb, Lu-Hf, Sm-Nd, Ar-Ar and U-Th/He dates in an amphibolite from the Cathaysia Block in Southern China

机译：差异u-pb，lu-hf，sm-nd，ar-ar和u-th /他/他/他在中国南部的加州街区的倒话中进行了差异

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摘要

We present a combined garnet Lu-Hf and Sm-Nd, zircon and monazite U-Pb, hornblende Ar-Ar, and zircon U-Th/He geochronology study on a garnet-bearing amphibolite from the Cathaysia Block in Southern China. Pseudosection modeling and garnet-clinopyroxene thermometry indicate that the amphibolite attained peak metamorphic conditions of approximately 0.9 GPa and 780 °C. The Lu-Hf garnet date of 402.7 ± 1.0 Ma and Sm-Nd date of 331.6 ± 3.6 Ma define a ~ 70 Myr difference for the same garnet fractions. Reconciling the large discrepancies between these three geochronological systems with the observed major element diffusion profiles in garnet requires that REEs and Hf were fully re-equilibrated at peak temperatures and that subsequent rapid cooling prevented any disruption of the Lu-Hf or Sm-Nd systems throughout cooling from high temperatures. The Sm-Nd garnet age was partially reset during a thermal pulse associated with intrusion of leucocratic veins, which is inferred to have occurred at ca. 226 Ma based on the coinciding hornblende Ar-Ar (222.3 ±0.9 Ma) and monazite U-Pb (226.2 ±2.3 Ma) dates. The T-t path of a reheating event at 226 Ma necessary to produce both the major divalent cation diffusion profiles in garnet and partial resetting of the Sm-Nd garnet age, such that it records an apparent age of ~ 332 Ma, requires an effective diffusion radius of 45-60 um in garnet during reheating, which is in agreement with the observation of pervasive chlorite-filled fractures within single garnet grains. Diffusion kinetics of Lu and Hf in garnet are sufficiently slow that this reheating episode would not impact the Lu-Hf system, and the 402.7 ±1.0 Ma garnet age likely reflects the onset of rapid cooling from peak P-T conditions. The zircon U-Pb date of 434.8 ± 2.7 Ma predates the Lu-Hf garnet date by approximately 30 Myr and is interpreted to reflect zircon crystallization during prograde metamorphism. The ~ 226 Ma reheating event is contemporaneous with the intrusion and crystallization of the widespread Triassic A-type granites and alkaline syenites across the Cathaysia Block, indicating an extensional environment. We interpret the zircon U-Th/He date of 143.1 ±4.2 Ma as reflecting a third thermal pulse based on the concurrence with the early Cretaceous volcanic rocks and granitoids, which overlies the amphibolite.
机译：我们介绍了一名综合的石榴石Lu-HF和SM-ND，锆石和单兆晶石U-PB，Hornblende Ar-Ar和Zircon U-TH / H H H H HINADY南部南部的石榴石倒置的地形学研究。伪质造型和石榴石 - 斜掺温测温仪表明倒角率达到约0.9GPa和780℃的峰变质条件。 LU-HF石榴石日期为402.7±1.0 mA和331.6±3.6 mA的SM-ND日期为相同的石榴石分数定义了〜70的MYR差异。在Garnet中观察到的主要元素扩散型材之间的这三种地理学系统之间的较大差异要求REES和HF在峰值温度下完全重新平衡，随后的快速冷却阻止了整个LU-HF或SM-ND系统的任何破坏从高温冷却。 SM-ND Garnet时效在与人民静脉侵入相关的热脉冲期间部分复位，这被推断出在CA。基于重合角强制Ar-Ar（222.3±0.9 mA）和Monazite U-Pb（226.2±2.3 mA）的226 mA。在Garnet中产生主要二价阳离子扩散谱的226 mA的再加热事件的TT路径以及SM-ND Garnet年龄的部分重置，使得它记录了〜332 mA的明显年龄，需要有效的扩散半径在再加热期间石榴石中的45-60μm，这与观察单一石榴石颗粒内的普华菌灰填充骨折一致。石榴石中LU和HF的扩散动力学足够慢，这种再加热发作不会影响LU-HF系统，402.7±1.0 mA石榴石年龄可能反映出从峰值P-T条件的快速冷却的发作。锆石U-PB日期为434.8±2.7 mA将Lu-HF Garnet日期预测到大约30 myR，并被解释为在镶嵌变质期间反映锆石结晶。 〜226 mA重新加热事件是跨越三叠系A型花岗岩的入侵和结晶的侵扰和结晶，在Cathaysia块上呈碱性延伸，表明延伸环境。我们将Zircon U-Th / He评估为143.1±4.2 mA的日期，因为基于与早期白垩纪火山岩和花岗岩的同时反映第三热脉冲，其覆盖倒角岩。

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