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首页> 外文期刊>Contributions to Mineralogy and Petrology >The link between volcanism and plutonism in epizonal magma systems; high-precision U-Pb zircon geochronology from the Organ Mountains caldera and batholith, New Mexico
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The link between volcanism and plutonism in epizonal magma systems; high-precision U-Pb zircon geochronology from the Organ Mountains caldera and batholith, New Mexico

机译：上层岩浆系统中火山作用与水成岩之间的联系;来自新墨西哥州器官山火山口和岩床的高精度U-Pb锆石年代学

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The Organ Mountains caldera and batholith expose the volcanic and epizonal plutonic record of an Eocene caldera complex. The caldera and batholith are well exposed, and extensive previous mapping and geochemical analyses have suggested a clear link between the volcanic and plutonic sections, making this an ideal location to study magmatic processes associated with caldera volcanism. Here we present high-precision thermal ionization mass spectrometry U-Pb zircon dates from throughout the caldera and batholith, and use these dates to test and improve existing petrogenetic models. The new dates indicate that Eocene volcanic and plutonic rocks in the Organ Mountains formed from similar to 44 to 34 Ma. The three largest calderarelated tuff units yielded weighted mean Pb-206/U-238 dates of 36.441 +/- 0.020 Ma (Cueva Tuff), 36.259 +/- 0.016 Ma (Achenback Park tuff), and 36.215 +/- 0.016 Ma (Squaw Mountain tuff). An alkali feldspar granite, which is chemically similar to the erupted tuffs, yielded a synchronous weighted mean Pb-206/U-238 date of 36.259 +/- 0.021 Ma. Weighted mean Pb-206/U-238 dates from the larger volume syenitic phase of the underlying Organ Needle pluton range from 36.130 +/- 0.031 to 36.071 +/- 0.012 Ma, and the youngest sample is 144 +/- 20 to 188 +/- 20 ka younger than the Squaw Mountain and Achenback Park tuffs, respectively. Younger plutonism in the batholith continued through at least 34.051 +/- 0.029 Ma. We propose that the Achenback Park tuff, Squaw Mountain tuff, alkali feldspar granite and Organ Needle pluton formed from a single, long-lived magma chamber/mush zone. Early silicic magmas generated by partial melting of the lower crust rose to form an epizonal magma chamber. Underplating of the resulting mush zone led to partial melting and generation of a highsilica alkali feldspar granite cap, which erupted to form the tuffs. The deeper parts of the chamber underwent continued recharge and crystallization for 144 +/- 20 ka after the final eruption. Calculated magmatic fluxes for the Organ Needle pluton range from 0.0006 to 0.0030 km(3)/year, in agreement with estimates from other well-studied plutons. The petrogenetic evolution proposed here may be common to many small-volume silicic volcanic systems.
机译：器官山破火山口和岩基层揭示了始新世破火山口复合体的火山和上层带古生物记录。破火山口和岩床充分暴露，以前的大量测绘和地球化学分析表明，火山断层和深成岩段之间存在明确的联系，这使其成为研究与破火山口火山作用有关的岩浆作用过程的理想场所。在这里，我们介绍了整个火山口和岩床中的高精度热电离质谱U-Pb锆石日期，并使用这些日期来测试和改进现有的成岩模型。新的日期表明，器官山中的始新世火山岩和深成岩形成于大约44 Ma至34 Ma。与破火山口相关的三个最大凝灰岩单位的加权平均Pb-206 / U-238日期分别为36.441 +/- 0.020 Ma（Cueva Tuff），36.259 +/- 0.016 Ma（Achenback Park凝灰岩）和36.215 +/- 0.016 Ma（Squaw）山凝灰岩）。化学上与喷发的凝灰岩相似的长石长石花岗岩的同步加权平均Pb-206 / U-238日期为36.259 +/- 0.021 Ma。加权平均Pb-206 / U-238可以从下面的器官针质子体的较大体积亚相中获得，范围从36.130 +/- 0.031到36.071 +/- 0.012 Ma，最小的样品是144 +/- 20到188 + //比Squaw Mountain和Achenback Park凝灰岩小20 ka。岩床中的年轻岩体作用持续至少34.051 +/- 0.029 Ma。我们建议Achenback公园凝灰岩，Squaw Mountain凝灰岩，碱性长石花岗岩和器官针状岩体由一个长寿命的岩浆室/糊状区形成。下地壳部分融化产生的早期硅质岩浆上升形成上带岩浆室。所形成的糊状区的欠镀层导致部分熔融并生成了高二氧化硅碱性长石花岗岩盖，喷发形成凝灰岩。最终喷发后，腔室的较深部分继续补给并结晶144 +/- 20 ka。与其他经过深入研究的云母的估计值相符，计算得出的器官针云母的磁通量范围为0.0006至0.0030 km（3）/年。本文提出的成岩演化可能是许多小体积硅质火山岩系统的共同特征。

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