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首页> 外文期刊>Journal of Volcanology and Geothermal Research >Episodic construction of batholiths: Insights from the spatiotemporal development of an ignimbrite flare-up
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Episodic construction of batholiths: Insights from the spatiotemporal development of an ignimbrite flare-up

机译：岩基的偶发式构造：从火成岩爆发的时空发展中得出的见解

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Using the canon that large silicic volcanic fields are the surface manifestation of batholith formation at depth as a departure, we examine what the spatiotemporal pattern of the 10-1 Ma ignimbrite flare-up of the Altiplano-Puna Volcanic Complex of the Central Volcanic Zone of the Andes reveals about the formation of its upper-crustal plutonic underpinnings. The volume-time relations of major ignimbrite eruptions reveal an episodic pattern of eruptions at rates much higher than those typical of continental arcs. At least 10,000 km~3 of dacitic magma were erupted in four pulses of eruptions at ～ 10, 8, 6, and 4 Ma that show increasing intensity and definition with time and then catastrophic diminution after 4 Ma. Calculated rates of extrusion during the pulses (0.004 to 0.012 km~3 yr~(-1)) are up to an order of magnitude higher than the average rate for the flare-up and continental silicic volcanic provinces in general (0.001 km~3 yr~(-1)). Peak intrusion rates of 0.012 to 0.06 km~3 yr~(-1)) calculated assuming a range of 3:1 to 5:1 plutonic: volcanic ratio are consistent with calculated rates of granite pluton formation. These spatiotemporal patterns suggest that a composite upper-crustal granodiorite batholith was built episodically in pulses characterized by episodic rates of intrusion that became more intense and defined in time. This pattern can be understood in the framework of a model where the mechanical strength of the crust evolves in response to magmatism through time. We propose that the APVC flare-up records a positive feedback between the mantle input, magma production, and upward migration of the magmatic system that results in a thermomechanical evolution that promotes the accumulation of larger bodies of dacite magma in the upper crust with time. The record from long-lived nested calderas suggests that locally the sub-volcanic batholith may be constructed of plutons that themselves are composite bodies built over several million years. We find support for our ideas in the Mesozoic Sierra Nevada Batholith of California.
机译：利用大的硅质火山场是深度上的岩基形成的表面表现的规律，我们研究了中部火山区高原-普纳火山复合体的10-1 Ma着火闪耀的时空格局。安第斯山脉揭示了其上地壳古生代基础的形成。主要火成岩喷发的时空关系揭示出一种爆发性的喷发模式，其速率远高于大陆弧典型的喷发速率。在〜10、8、6和4 Ma的四个喷发脉冲中，至少喷出了10,000 km〜3的达喀尔岩浆，这些脉冲显示出强度和清晰度随时间增加，然后在4 Ma之后发生灾难性的减小。脉冲期间（0.004至0.012 km〜3 yr〜（-1））的计算挤出速率比一般爆发和大陆硅质火山岩省的平均速率（0.001 km〜3）高一个数量级。 yr〜（-1））。假设岩体与火山岩的比例为3：1至5：1，则计算得出的峰值入侵率为0.012至0.06 km〜3 yr〜（-1））与计算得出的花岗岩岩体的形成速率一致。这些时空模式表明，复合上壳花岗闪长岩基岩以脉冲状构造，其特征是侵入性的侵入速率越来越强，并在时间上得到了确定。可以在模型的框架中理解这种模式，在该模型中，地壳的机械强度会随时间流逝的岩浆作用而变化。我们建议APVC爆发在地幔输入，岩浆产生和岩浆系统的向上迁移之间记录一个正反馈，从而导致热机械演化，随着时间的推移促进较大的达菲岩岩浆体在上地壳中的积累。长期存在的嵌套火山口的记录表明，局部火山岩下的岩基可能是由自身构成为数百万年的复合体的岩体构造而成的。我们在加利福尼亚的中生代内华达山脉基底区找到了支持我们观点的支持。

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