Shocked titanite records Chicxulub hydrothermal alteration and impact age
Shocked titanite records Chicxulub hydrothermal alteration and impact age
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DOI：
10.1016/j.gca.2020.04.031
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发表时间：
2020-07
影响因子：
5
通讯作者：
N. Timms;C. Kirkland;A. Cavosie;A. Rae;W. Rickard;N. Evans;T. Erickson;A. Wittmann;L. Ferrière;G. Collins;S. Gulick
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文献类型：
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作者：
N. Timms;C. Kirkland;A. Cavosie;A. Rae;W. Rickard;N. Evans;T. Erickson;A. Wittmann;L. Ferrière;G. Collins;S. Gulick
热液活动是撞击事件发生后的一种常见现象，但确定撞击热液系统并确定其年代可能具有挑战性。这项研究提供了第一个详细的评估冲击微观结构和影响有关的蚀变的影响的U-Pb系统学和微量元素的钛铁矿（CaTiSiO 5），重点是从峰环的希克苏鲁布的冲击结构，墨西哥的花岗岩目标岩石。> 1 mm长的冲击孪晶钛铁矿颗粒保留了密集的不规则微裂纹网络，其中一些利用了冲击孪晶界面。次生微晶硅和黄铁矿沿沿着某些微裂隙不均匀分布。原位激光烧蚀多收集器电感耦合等离子体质谱（LA-MC-ICPMS）分析揭示了三个端元铅成分的混合物。Pb组分为：1）普通铅，与邻近碱性长石的铅同位素特征一致; 2）自岩浆结晶以来积累的放射成因铅; 3）由于与撞击相关的完全放射成因铅损失而产生的次级、较年轻的铅特征。最年轻的推断年龄定义了一个回归从共同铅相交Concordia在67 ± 4 Ma，与确定的年龄为66.04 ± 0.05 Ma的希克苏鲁布的影响事件。LA-MC-ICPMS数据的等值线图显示，年轻的年龄在空间上被限制到与微量元素（REE-Y-Zr-Nb-Mo-Sn-Th）和Eu/Eu* 异常的幅度减少显着亏损的微观结构复杂的域。飞行时间二次离子质谱法（ToF-SIMS）显示，钛铁矿中局部元素贫化的模式与微裂纹在空间上相关，年龄和微量元素丰度的空间相关性与Pb和其他微量元素通过流体从裂缝域中的快速流体通道的普遍网络中的局部去除是一致的。介导的与撞击事件相关的元素运输过程。在这里，我们解释了67 ± 4 Ma的U-Pb年龄代表的热液铅的损失在希克苏鲁布峰环的影响事件。这些结果突出了我们的分析方法的潜力，使用钛铁矿地质年代学和地球化学的约会后的影响热液活动在其他地方的影响结构。
Hydrothermal activity is a common phenomenon in the wake of impact events, yet identifying and dating impact hydrothermal systems can be challenging. This study provides the first detailed assessment of the effects of shock microstructures and impact-related alteration on the U-Pb systematics and trace elements of titanite (CaTiSiO5), focusing on shocked granite target rocks from the peak ring of the Chicxulub impact structure, Mexico. A > 1 mm long, shock-twinned titanite grain preserves a dense network of irregular microcracks, some of which exploit shock twin interfaces. Secondary microcrystalline anatase and pyrite are heterogeneously distributed along some microcracks. In situ laser ablation multi-collector inductively-coupled plasma mass spectrometry (LA-MC-ICPMS) analysis reveals a mixture of three end-member Pb components. The Pb components are: 1) common Pb, consistent with the Pb isotopic signature of adjacent alkali feldspar; 2) radiogenic Pb accumulated since magmatic crystallization; and 3) a secondary, younger Pb signature due to impact-related complete radiogenic Pb loss. The youngest derived ages define a regression from common Pb that intersects Concordia at 67 ± 4 Ma, in agreement with the established age of 66.04 ± 0.05 Ma for the Chicxulub impact event. Contour maps of LA-MC-ICPMS data reveal that the young ages are spatially restricted to microstructurally-complex domains that correlate with significant depletion in trace elements (REE-Y-Zr-Nb-Mo-Sn-Th) and reduction in magnitude of the Eu/Eu* anomaly. Mapping by time-of-flight secondary ion mass spectrometry (ToF-SIMS) show that patterns of localised element depletion in titanite are spatially related to microcracks, which are enriched in Al. The spatial correlation of ages and trace element abundance is consistent with localised removal of Pb and other trace elements from a pervasive network of fast fluid pathways in fractured domains via a fluid-mediated element transport process associated with the impact event. Here we interpret the 67 ± 4 Ma U-Pb age to represent hydrothermal Pb-loss in the Chicxulub peak ring in the wake of the impact event. These results highlight the potential of our analytical approach using titanite geochronology and geochemistry for dating post-impact hydrothermal activity in impact structures elsewhere.