Vein fluorite U-Pb dating demonstrates post–6.2 Ma rare-earth element mobilization associated with Rio Grande rifting
Vein fluorite U-Pb dating demonstrates post–6.2 Ma rare-earth element mobilization associated with Rio Grande rifting
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DOI：
10.1130/ges02139.1
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发表时间：
2019-12
期刊：
影响因子：
2.5
通讯作者：
G. Piccione;E. Rasbury;Brent A. Elliott;J. Richard Kyle;Stephen J. Jaret;Alvin S. Acerbo;A. Lanzirotti;P. Northrup;Kathleen M. Wooton;Randall R. Parrish
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文献类型：
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作者：
G. Piccione;E. Rasbury;Brent A. Elliott;J. Richard Kyle;Stephen J. Jaret;Alvin S. Acerbo;A. Lanzirotti;P. Northrup;Kathleen M. Wooton;Randall R. Parrish
许多研究已经记录了热液和变质流体中稀土元素 (REE) 的迁移性，但稀土元素迁移的过程和时间很少受到很好的限制。德克萨斯州西部跨佩科斯岩浆省的圆顶石岩是一个稀土矿产区，其横切裂缝中充满了萤石和方解石以及各种不寻常的矿物。其中最值得注意的是钇和重稀土元素 (YHREE) 碳酸盐矿物，根据元素分析，推测其为洛凯特石。虽然根据黑云母中的 K/Ar 确定圆顶石石的年龄为 36.2 ± 0.6 Ma，但这里提供的 U-Pb 萤石和珍珠陶年龄清楚地表明这些矿脉中的矿化年龄小于 6.2 ± 0.4 Ma（最古老萤石的年龄）。这种日期上的差异表明，流体与石石相互作用，动员稀土元素超过 30 m.y.火成岩就位后。观察到的稀土元素动员的时间与格兰德河裂谷扩张重叠，我们认为与扩张相关的含氟流体可能是最初动员的原因。后来的一代流体能够溶解萤石，我们假设后来的历史涉及硫酸。记录这些流体的矿物的同步加速器光谱和激光烧蚀电感耦合等离子体质谱 (LA-ICP-MS) U-Pb 定年法为更基本地了解过程提供了巨大的潜力，这些过程不仅对稀土元素而且对其他矿床都很重要。
Numerous studies have documented rare-earth element (REE) mobility in hydrothermal and metamorphic fluids, but the processes and timing of REE mobility are rarely well constrained. The Round Top laccolith in the Trans-Pecos magmatic province of west Texas, a REE ore prospect, has crosscutting fractures filled with fluorite and calcite along with a variety of unusual minerals. Most notably among these is an yttrium and heavy rare-earth element (YHREE) carbonate mineral, which is hypothesized to be lokkaite based on elemental analyses. While the Round Top laccolith is dated to 36.2 ± 0.6 Ma based on K/Ar in biotite, U-Pb fluorite and nacrite ages presented here clearly show the mineralization in these veins is younger than 6.2 ± 0.4 Ma (the age of the oldest fluorite). This discrepancy in dates suggests that fluids interacted with the laccolith to mobilize REE more than 30 m.y. after igneous emplacement. The timing of observed REE mobilization overlaps with Rio Grande rift extension, and we suggest that F-bearing fluids associated with extension may be responsible for initial mobilization. A later generation of fluids was able to dissolve fluorite, and we hypothesize this later history involved sulfuric acid. Synchrotron spectroscopy and laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) U-Pb dating of minerals that record these fluids offer tremendous potential for a more fundamental understanding of processes that are important not only for REE but other ore deposits as well.