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首页> 外文期刊>Journal of Volcanology and Geothermal Research >Pre-emptive conditions of dacitic magma erupted during the 21.7 ka Plinian event at Nevado de Toluca volcano, Central Mexico
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Pre-emptive conditions of dacitic magma erupted during the 21.7 ka Plinian event at Nevado de Toluca volcano, Central Mexico

机译：在墨西哥中部内华多·德·托卢卡火山举行的21.7 ka普利尼安事件中爆发了胶质岩浆的先发条件。

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摘要

The Nevado de Toluca volcano in Central Mexico has been active over the last ca. 42 ka, during which tens of km3 of pyroclastic material were erupted and two important Plinian-type eruptions occurred at ca. 21.7 ka (Lower Toluca Pumice: LTP) and ca. 10.5 ka (Upper Toluca Pumice: UTP). Samples from both the LTP and UTP contain plagioclase, amphibole, iron-titanium oxides, and minor anhedral biotite, set in a vesicular, rhy-olitic, glassy matrix. In addition, UTP dacites contain orthopyroxene. Analysis of melt inclusions in plagioclase phenocrysts yields H_2O contents of 2-3.5 wt.% for LTP and 1.3-3.6 wt.% for UTP samples. Ilmenite-ulvospinel geothermometry yields an average temperature of-868℃ for the LTP magma (hotter than the UTP magma, -842℃; Arce et al., 2006), whereas amphibole-plagioclase geothermometry yields a temperature of 825-859℃ for the LTP magma. Water-saturated experiments using LTP dacite suggest that: (i) amphibole is stable above 100 MPa and below 900℃; (ii) plagioclase crystallizes below 250-100 MPa at temperatures of 850-900℃; and (iii) pyroxene is stable only below pressures of 200-100 MPa and temperatures of 825-900℃. Comparison of natural and experimental data suggests that the LTP dacitic magma was stored at 150-200 MPa (5.8-7.7 km below the volcano summit). No differences in pressure found between 21.7 ka and 10.5 ka suggest that these two magmas were stored at similar depths. Orthopyroxene produced in lower temperature LTP experiments is compositionally different to those found in UTP natural samples, suggesting that they originated in two different magma batches. Whole-rock chemistry, petrographic features, and mineral compositions suggest that magma mixing was responsible for the generation of the dacitic Plinian LTP eruption.
机译：墨西哥中部的内华达·德·托卢卡火山在过去约20年间一直活跃。 42 ka，在此期间爆发了数十km3的火山碎屑物质，并且在大约2 a发生了两次重要的Plinian型爆发。 21.7 ka（下Toluca浮石：LTP）和ca。 10.5 ka（托卢卡浮石上层：UTP）。 LTP和UTP的样品都包含斜长石，闪石，氧化铁钛和较小的无角铁黑云母，并置于水疱，流纹岩，玻璃状基质中。此外，UTP数据中还包含邻苯二酚。分析斜长石隐晶石中的熔体夹杂物，LTP的H_2O含量为2-3.5 wt。％，UTP样品的H_2O含量为1.3-3.6 wt。％。钛铁矿-ulspinepine地热法测得的LTP岩浆平均温度为-868℃（比UTP岩浆高-842℃； Arce等，2006），而闪石斜长石岩浆地热法测得的平均温度为825-859℃。 LTP岩浆。用LTP钠铁矿进行的水饱和实验表明：（i）闪石在100 MPa以上和900℃以下均稳定。 （ii）斜长石在850-900℃的温度下在250-100 MPa以下结晶。 （iii）辉石仅在200-100 MPa的压力和825-900℃的温度下才稳定。自然和实验数据的比较表明，LTP胶质岩浆的储存压力为150-200 MPa（火山顶以下5.8-7.7 km）。在21.7 ka和10.5 ka之间没有发现压力差异，表明这两个岩浆以相似的深度存储。低温LTP实验中产生的邻苯二甲酚与UTP天然样品中发现的邻苯二甲醚在成分上有所不同，这表明它们起源于两个不同的岩浆批次。全岩化学，岩石学特征和矿物成分表明，岩浆混合是造成达林普林期LTP爆发的原因。

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