Magma evolution of the East Eifel volcanic field from a perspective based on detrital zircon in modern river sediment

随着大约13000年前Laacher See火山的喷发，第四纪东艾菲尔火山田成为中欧最年轻、最活跃的火山活跃区之一。地震、隆起和气体排放集中发生在这个区域，表明岩浆流体从异常热的上地幔带持续迁移到今天。然而，大地测量学和地球物理方法只能描绘火山覆盖下地壳和地幔的现状。因此，为了更好地了解岩浆从地幔转移到地表的长期过程和时间尺度，研究过去的喷发是必不可少的。通常，从火山沉积物中收集熔岩、火山碎屑碎片或捕虏体样本进行此类研究。然而，这种间断采样是劳动密集型的，容易产生偏差。相反，本文建议研究来自东艾菲尔的现代水系沉积物，从中可以相对容易地提取锆石作为一种特别耐受性和可测定年代的指标矿物。在下降的液态线中，锆石在演化的熔体中结晶，对于东艾菲尔来说，这些熔体主要是在Rieden， Wehr和Laacher See的声质-粗质火山中心被提取出来的。此外，基性火山偶尔含有锆石巨晶，它们代表岩浆上升过程中从深部岩体携带的异晶。在这个项目中，将对Nette和Brohlbach流域的河流沉积物进行取样，利用原位水力分离提取锆石。这两种水系都覆盖了几乎所有东艾菲尔火山中心的区域，因此可以绘制出区域火山沉积物中所有含锆石来源的完整图片。利用铀-钍和铀-铅年代学对具有代表性的300个火山碎屑锆石晶体进行定年，并测定其氧铪同位素组成。结果将有助于澄清关于火山活动空间集中事件的原因的关键问题，这些问题是根据现有的东艾菲尔火山喷发年龄和喷发量而知道的。对位于年轻火山区的现代溪流中的碎屑成分进行分析，可以进行快速和全面的采样，也可以包括已经风化和侵蚀的火山建筑物的矿物。这种新方法具有广泛应用于全球其他火山地区的潜力。

With the eruption of Laacher See volcano ca. 13,000 years ago, the Quaternary East Eifel volcanic field ranks among the youngest and most dynamic volcanically active areas in Central Europe. Earthquakes, uplift, and gas emissions occur focused in this region, suggesting persistent migration of magmatic fluids from anomalously hot upper mantle zones to the present day. Geodetic and geophysical methods, however, can only image the current conditions in the crust and mantle underneath the volcanic cover. To improve the understanding of the long-term processes and timescales of magma transfer from the mantle to the surface, investigations of past eruptions are therefore essential. Conventionally, samples of lava, pyroclastic fragments or xenoliths from volcanic deposits are collected for such investigations. This punctuated sampling, however, is labor intensive and prone to bias. Instead, it is proposed here to investigate modern stream sediments from the East Eifel, from which zircon can be extracted as a particularly resistant and datable index mineral at relative ease. In the liquid line of descent, zircon crystallizes in evolved melts, which for the East Eifel were tapped predominantly in the phonolitic‒trachytic volcanic centers of Rieden, Wehr, and Laacher See. In addition, mafic volcanics occasionally contain zircon megacrysts which represent xenocrysts entrained from plutonic bodies at depth during magma ascent. In this project, stream sediment of the Nette and Brohlbach catchments will be sampled to extract zircon using in-situ hydraulic separation. Both stream systems drain an area that encompasses nearly all East Eifel volcanic centers and thus can yield a complete picture of all zircon-bearing sources in regional volcanic deposits. A representative number (n = 300) of volcanic detrital zircon crystals will be dated using uranium-thorium and uranium-lead geochronology, and their oxygen-hafnium isotopic compositions will be determined. Results will aid in clarifying critical questions regarding the causes for spatially focused episodes in volcanic activity, which are known from existing eruption ages and volumes for the East Eifel. The analysis of detrital components in modern streams located in young volcanic areas allows rapid and comprehensive sampling, which can also include minerals of already weathered and eroded volcanic edifices. This novel approach has potential to be widely applied to other volcanic regions worldwide.