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首页> 外文期刊>Contributions to Mineralogy and Petrology >Multiple ways of producing intermediate and silicic rocks within Thingmúli and other Icelandic volcanoes
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Multiple ways of producing intermediate and silicic rocks within Thingmúli and other Icelandic volcanoes

机译：在Thingmúli和其他冰岛火山中产生中层和硅质岩的多种方法

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Major and trace element compositions of rocks and coexisting phenocrysts of the Thingmúli volcano suggest a revision of the existing models for the formation of intermediate and silicic melts in Iceland. The new data define two compositional tholeiitic trends with a significant gap between them. A high-iron trend (HFe) contains 6–14 wt% total FeO in silicic rocks with c. 1 wt% MgO, as well as sodic plagioclase and hedenbergite phenocrysts. A low-iron trend (LFe) contains 3–5 wt% FeO at c. 1 wt% MgO, which is typical of Iceland but higher than MORB compositions. The most evolved phenocrysts of the LFe trend do not reach iron-rich end members. The HFe trend is interpreted as a result of fractional crystallization; numerical modelling using the MELTS algorithm suggests that crystallization took place under redox conditions constrained to one-log unit below the fayalite-magnetite-quartz oxygen buffer (FMQ-1). The LFe trend is explained by a combination of mixing between rhyolite and ferrobasalt, assimilation of hydrated crust and fractional crystallization under higher redox conditions (FMQ). The two trends and the gap are best defined in a plot of Mg# versus SiO2 that is useful to unravel petrogenetic processes. For example, intermediate and silicic rocks of the Holocene volcanic systems of spreading rifts (e.g. Krafla), propagating rifts (e.g. Hekla) and off-rifts (Öræfajökull) also fall into high- and low-iron fields and outline a gap similar to Thingmúli. The identification of two compositional trends in erupted intermediate and silicic volcanic products shows that processes in the deep roots of single volcanic systems are highly diverse and likely controlled by local variations in the thermal gradients and the extend of hydrothermal alteration. Generalizations about the relationship between the compositions of intermediate and silicic rocks and plate tectonic setting, therefore, should be avoided.
机译：Thingmúli火山的岩石和共生的表观晶体的主要和微量元素组成表明，对冰岛中，硅质熔体形成的现有模型进行了修订。新数据定义了两个成分性趋势，它们之间存在明显差距。高铁趋势（HFe）在硅酸盐岩石中含有6-14 wt％的总FeO。 1wt％的MgO以及钠斜长石和黑钙石隐晶石。低铁趋势（LFe）在c处含有3-5wt％的FeO。 1wt％的MgO，这是冰岛的典型特征，但高于MORB的组成。 LFe趋势中演化最剧烈的表晶未达到富铁末端成员。 HFe趋势被解释为分步结晶的结果。使用MELTS算法进行的数值建模表明，结晶是在氧化还原条件下发生的，该条件被限制在方铁石-磁铁矿-石英氧缓冲液（FMQ-1）下方的一个对数单位。 LFe趋势是由流纹岩和铁玄武岩的混合，水合硬壳的同化和在较高的氧化还原条件（FMQ）下的分步结晶的组合所解释的。在Mg＃与SiO2的关系图中可以最好地定义这两个趋势和差距，这对于揭示成岩过程很有用。例如，全新世火山系统的裂谷（如克拉夫拉），裂谷（如海克拉）和裂谷（Öræfajökull）的中，硅质岩也属于高铁和低铁领域，并勾勒出类似于Thingmúli的空隙。对火山喷发的中，硅质火山产物的两种成分趋势的识别表明，单个火山系统深层根部的过程高度多样化，并可能受热梯度的局部变化和水热蚀变的扩展的控制。因此，应该避免对中，硅质岩成分与板块构造环境之间关系的概括。

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