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首页> 外文期刊>Journal of Volcanology and Geothermal Research >The felsic complex of the Vallehermoso Caldera: interior of an ancient volcanic system (La Gomera, Canary Islands)
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The felsic complex of the Vallehermoso Caldera: interior of an ancient volcanic system (La Gomera, Canary Islands)

机译：Vallehermoso破火山口的长石复合体：古代火山系统的内部（加那利群岛戈梅拉）

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摘要

A mid-to-upper Miocene felsic cone sheet dike complex, caldera collapse and dome intrusion, located around the Vallehermoso and Tamargada areas (North of La Gomera Island) is described. It constitutes one of the less-known volcanic episodes in the Canary Archipelago and especially in La Gomera Island. Based on detailed field and structural evidence, it is suggested that the cone sheet shows, at the surface, an almost circular geometry truncated to the NW sector. After the cone sheet dike complex formed, decompression of the interior of an assumed shallow magma chamber occurred due to the subsequent migration of felsic magma throughout the dikes of the cone sheet. This last event caused the roof of the magma chamber to collapse, leading to the formation of a 3- to 4-km-wide caldera. A breccia deposit formed during the collapse and filled a depressed central area which finally was affected by an episode of magmatic resurgence, leading to a later almost circular dome intrusion. The association of cone sheet, breccia deposits and domes constitutes the so-called "Trachytic-Phonolitic Complex" (TPC) and should be viewed as the root of an ancient intensely eroded volcanic edifice made of trachytes, nepheline-phonolites and minor Haueyne phonolites as the dominant materials. A description of the structural, petrological and geochemical features of the Trachytic-Phonolitic Complex and a discussion about their origin are considered in this paper. We also consider the correlation between another felsic intrusion of alkali gabbros and syenites (called Tamargada syenites) that also crops out in the Vallehermoso-Tamargada area with respect to the Trachytic-Phonolitic Complex. Our data suggest that this alkaline intrusion of alkali gabbros and syenites belongs to an earlier intrusive episode. On the basis of petrological, geochemical and detailed field studies, both trachytes and nepheline-phonolites included in the Trachytic-Phonolitic Complex most likely evolved from alkali mafic magmas from the Upper Old Basalt formation through a dominant fractional crystallization process. Additionally, haueyne phonolites could develop from local and later magmatic processes such as gas transfer that altered and changed a small part of the previously mentioned nepheline phonolites to haiiyne phonolites.
机译：描述了位于瓦列赫莫索和塔玛加达地区（戈梅拉岛以北）周围的中新世上新世长英质圆锥形薄片堤防复合体，火山口塌陷和穹顶侵入。它是加那利群岛（尤其是戈梅拉岛）鲜为人知的火山爆发之一。根据详细的领域和结构证据，建议锥表在表面显示出截断为NW扇区的几乎圆形的几何形状。在形成圆锥体薄片堤防复合体之后，由于随后的长英质岩浆在整个圆锥体薄片的堤坝中迁移，假定的浅岩浆室内部发生了减压。最后一个事件导致岩浆房的屋顶坍塌，导致形成了3至4公里宽的火山口。在坍塌过程中形成角砾岩沉积物，并填充了一个凹陷的中央区域，该区域最终受到岩浆回潮的影响，导致后来几乎呈圆形的穹顶侵入。圆锥体薄片，角砾岩沉积物和穹顶的组合构成了所谓的“气管-斜交复合体”（TPC），应被视为由曲奇，霞石-松香和次要的Haueyne沸石制成的古代侵蚀强烈的火山大厦的根源。主导材料。本文考虑了Trachytic-Phonolitic复合体的结构，岩石学和地球化学特征的描述，并对其起源进行了讨论。我们还考虑了长辉岩和正长岩（称为塔玛格达正长岩）的另一次长生侵扰之间的相关性，这些长石岩也出现在Vallehermoso-Tamargada地区，与Trachytic-Phonolitic复杂体有关。我们的数据表明，碱性辉长岩和正长岩的这种碱性侵入属于较早的侵入事件。在岩石学，地球化学和详细的现场研究的基础上，包括在Trachytic-Phonolitic复杂体中的Trachytes和霞石-酚盐很可能是从上古玄武岩地层的碱性镁铁质岩浆经过主要的分步结晶过程演化而来的。另外，海因辉石可以从局部和后来的岩浆作用过程发展而来，例如气体转移，其将先前提到的霞石辉石的一小部分改变并改变为海因辉石。

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