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首页> 外文期刊>Journal of Volcanology and Geothermal Research >Textural effects of steady state behaviour of the Stromboli feeding system
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Textural effects of steady state behaviour of the Stromboli feeding system

机译：Stromboli进料系统稳态行为的纹理效应

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摘要

The exceptionally persistent activity of Stromboli volcano has lasted for at least 1400 years. The normal strombolian activity is periodically interrupted by more energetic explosions (1-2 per year) and by sporadic effusive episodes (every 10-20 years). Normal activity and effusive episodes are characterized by crystal-rich high-K to shoshonitic basalts issuing from a volatile-poor shallow system. Crystal-poor pumice are emitted only during more violent explosions, and are thought to derive from deep pulses of volatile-rich magma. Shallow level degassing induces massive crystallization of deep pulses of feeding magma that, continuously mixing with the resident one, produces the crystal-rich shoshonite of the persistent activity. We examined the crystallization history of the crystal-rich, shallow reservoir using plagioclase Crystal Size Distribution (CSD) analysis of scoriae and lavas emitted in the past twenty years. CSDs show a linear dependence from crystal size in the size interval 0.06-1.2 mm; number density of larger crystals is biased by right hand truncation effects. CSDs slopes and intercepts are quite constant during the whole considered time span revealing a system that is close to the equilibrium also from a kinetic point of view. The linear crystal size distribution are reached by the system through episodes of growth and resorption, respectively occurring in the degassed and undegassed magma during the continuous mixing in the feeding system. Plagioclase net growth rate (2 x 10~(-11) cm/s) results from a balance of growth (10~(-10) cm/s) and resorption episodes which induce spectacular zoning and resorption textures in crystals larger than 200 μm. CSDs of mafic phases cannot be accurately acquired on each single sample due to poor counting statistics; the evaluation of pyroxene and olivine CSD on the whole data set, however, confirms the conclusions acquired from plagioclase CSDs.
机译：Stromboli火山异常持久的活动至少持续了1400年。正常的血栓形成活动会定期被更多的高能爆炸（每年1-2次）和偶发的散发性发作（每10至20年）打断。正常活动和喷射事件的特征是从贫瘠的浅层系统中发出的富含晶体的高K值至钾生玄武岩。晶体贫化的浮石只有在更剧烈的爆炸中才会散发出来，并且被认为是由富含挥发物的岩浆的深脉冲产生的。浅层除气会引起深部进料岩浆的大量结晶，该岩浆与常驻岩浆连续混合，产生具有持久活性的富含晶体的shoshonite。我们使用斜长石晶体粒度分布（CSD）分析了过去20年排放的石和熔岩，检查了富含晶体的浅层储层的结晶历史。 CSD在0.06-1.2 mm的尺寸区间内显示出与晶体尺寸的线性关系；较大的晶体的数字密度受右手截断效应的影响。在整个考虑的时间范围内，CSD的斜率和截距非常恒定，这从动力学的角度揭示了一个接近平衡的系统。系统通过在进料系统中连续混合期间在脱气和脱气岩浆中分别发生的生长和吸收事件来达到线性晶体尺寸分布。斜长石净生长速率（2 x 10〜（-11）cm / s）是由生长（10〜（-10）cm / s）和吸收事件的平衡所引起的，这些现象在200μm以上的晶体中引起明显的分区和吸收纹理。由于计数统计不佳，无法在每个单个样本上准确获取镁铁质相的CSD；在整个数据集上对辉石和橄榄石CSD的评估证实了从斜长石CSD获得的结论。

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