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首页> 外文期刊>Journal of Volcanology and Geothermal Research >The temporal evolution of three magmatic systems in the West Eifel volcanic field, Germany
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The temporal evolution of three magmatic systems in the West Eifel volcanic field, Germany

机译：德国西埃菲尔火山场中三种岩浆系统的时间演化

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摘要

The Quaternary West Eifel volcanic field is the surface expression of a mantle plume that is thought to contain ～1% melt. The volcanoes range in age from 0.7 Ma to ～10 000 yr BP and the average recurrence rate of volcanism is around 3.5 X 10~(-4) eruptions per year, giving a mean time between eruptions of 2875 years, assuming that the field is monogenetic. The presence of mafic and ultramafic xenoliths is taken as evidence for rapid, single-stage emplacement of magmas at velocities around 0.5 km/h. However, the presence of clinopyroxene that preserves evidence of polybaric crystallisation belies this simple model. This study uses variations in the Fo content of olivine in mantle-derived xenoliths and in olivine xenocrysts enclosed in cumulate xenoliths to calculate the time scale of evolution of three volcanic centres in the Eifel field. Core-rim variations in olivine are interpreted to result from Fe-Mg interdiffusion between it and a surrounding melt. Using experimental determinations of the interdiffusion coefficient and approximations of magma temperature, contact times have been calculated using planar and radial diffusion models. The three volcanic centres studied were Meerfelder Maar, Gemuendener Maar and Baarley. The cumulate xenoliths at Meerfelder Maar formed at a depth of ～13 km and record a magma emplacement event at between 1 and 3 years prior to eruption. Two suites of mantle-derived olivine clinopyroxenites record a further two events at 1-8 days and ～3 h prior to eruption. The final event is interpreted to record the eruption of this volcano and the 3-h contact time records the time required for transport of peridotite xenoliths from the mantle to surface, giving an average emplacement velocity of around 15 km/h. The cumulate xenoliths at Gemuendener Maar crystallised at depths of between 4 and 22 km. There are four distinct events recorded by the zoned olivine grains in the clinopyroxene-rich cumulates from this locality. The maximum residence time is similar to that at Meerfelder Maar. However, in this case the final magma resided in the chamber for between 23 days and 2.7 months prior to eruption, allowing enough time for any entrained peridotite xenoliths to be filtered out. The cumulate xenoliths from the Baarley locality record a much longer history than those at the other localities. In this case, initially peridotitic olivine has been completely re-equilibrated over > 175 years prior to eruption. In common with the other two localities, there is evidence of multiple intrusive events, at depths up to 7 km, prior to final eruption. The duration of the final eruption event and the interpreted depth to source of the xenoliths indicate an emplacement velocity of around 3 km/h. The data derived from modelling of diffusion profiles in olivine from cumulate xenoliths indicate that the magmatic systems feeding these three volcanoes were dynamic and very short-lived. In addition, these data can be used to place constraints on the rate of cumulate formation in subvolcanic magma chambers. On the basis of the data presented here, it would seem that an appreciable thickness of cumulates can form over relatively short time spans (days to a few years).
机译：西埃菲尔第四纪火山场是地幔柱的表面表达，被认为含有〜1％的熔体。火山的年龄范围从0.7 Ma到〜10000 BP，火山的平均复发率每年约为3.5 X 10〜（-4）次喷发，假设该场为2875年，则平均喷发时间为2875年。单基因的。镁铁质和超镁铁质的异质岩的存在被证明以大约0.5 km / h的速度快速，单一阶段地沉积岩浆。但是，保留了多晶结晶证据的斜柏基的存在掩盖了这个简单的模型。这项研究利用地幔衍生的异种岩中橄榄石的Fo含量变化以及堆积在异种积石中的橄榄石异种结晶的Fo含量来计算埃菲尔气田中三个火山中心演化的时间尺度。橄榄石中芯缘的变化被解释为是由于Fe-Mg与周围熔体之间的相互扩散造成的。通过实验确定互扩散系数和岩浆温度的近似值，已使用平面和径向扩散模型计算了接触时间。研究的三个火山中心是Meerfelder Maar，Gemuendener Maar和Baarley。 Meerfelder Maar处的堆积异岩在约13 km的深度形成，并在喷发前1至3年记录了一次岩浆侵位事件。两套来自地幔的橄榄石斜辉石在喷发前的1-8天和〜3 h记录了另外两个事件。最终事件被解释为记录了该火山的喷发，而3小时的接触时间记录了橄榄岩异种岩从地幔到地表的运输所需的时间，平均进位速度约为15 km / h。 Gemuendener Maar上的累积异种岩在4至22 km的深度结晶。来自该地区的富含次生环戊烯的堆积物中的带橄榄石的颗粒记录了四个不同的事件。最长停留时间类似于Meerfelder Maar的停留时间。但是，在这种情况下，最终岩浆在喷发前在室内停留了23天至2.7个月，从而有足够的时间将夹带的橄榄岩异种岩滤出。来自Baarley地方的累积异种石的历史比其他地方的历史更长。在这种情况下，火山喷发前的橄榄石橄榄石在超过175年的时间里已经完全重新平衡。与其他两个地方一样，有证据表明在最终喷发之前，在深度达7 km处有多次侵入事件。最终喷发事件的持续时间和对异种岩源的解释深度表明了大约3 km / h的侵袭速度。从累积的异种岩中橄榄石中的扩散剖面建模得到的数据表明，这三个火山的岩浆系统是动态的，寿命很短。此外，这些数据可以用来限制火山岩浆下腔积聚的速率。根据此处提供的数据，似乎可以在相对较短的时间跨度（几天到几年）内形成一定数量的堆积物厚度。

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