The explosive origin of Pulvermaar in the West Eifel Volcanic Field (WEVF): H2O or CO2?

西埃菲尔火山场 (WEVF) 的 Pulvermaar 爆炸源：H2O 还是 CO2？

• 批准号: 445046755
• 负责人: Professor Dr. Hans-Ulrich Schmincke
• 金额: --
• 依托单位: Department of Earth Science
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2020
• 资助国家: 德国
• 起止时间: 2019-12-31 至 2022-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/445046755?language=en
• 关键词: explosive; origin; Pulvermaar; West; Eifel

Maars represent striking and touristically attractive (e.g. Eifel volcanic field) tephra-rimmed volcanic craters, tephra fragments being dominated by near-surface rock fragments. Originally thought to represent magmatic gas (CO2) explosion craters, maars have been generally interpreted since the early 1970ies as having resulted from physical interaction between rising magma and (ground-) water. Closer inspection of the rim deposits of the prominent Pulvermaar in the western Eifel shows that the tephra exposed at the rim consist to ca 50 % of round lava-coated fragments of a slowly cooled igneous rock originally emplaced at ca. 20km beneath the surface as deduced from fluid inclusions in clinopyroxene. Following fragmentation of the plutonic rocks and surrounding metamorphic host rocks at depth possibly by injected high-p CO2, the fragments were rounded, coated by new magma and likely transported by high velocity turbulent CO2-jets to the uppermost crust. Here they contributed to fragmentation of upper crustal Devonian sandstones/slates, fragmentation possibly enhanced by heated groundwater. A 10 m-wide outcrop of agglutinates at the southern inner crater wall shows that fluid melilite-nephelinite magma participated in the emplacement process. This hypothesis suggests a fundamental participation of magmatic CO2 in the fragmentation, upward transport and eruption of largely solid igneous pellets. This model, if substantiated by the proposed research, would represent a basic change in paradigm with respect to maar genesis. It would also imply that the origin of at least some maar structures in the Eifel resembles that of prevailing models of multistage emplacement processes of kimberlite systems rather than of phreatomagmatic maar formation, the main source of energy and site of fragmentation being magmatic (CO2) sourced deep in the crust/mantle. High-resolution field and lab analyses will be carried out to test the proposed model.

Maars代表了引人注目的和具有旅游吸引力的（例如Eifel火山场）火山灰边缘的火山口，火山灰碎片主要是近地表的岩石碎片。最初被认为是代表岩浆气体（CO2）爆炸的陨石坑，自20世纪70年代初以来，maars通常被解释为上升的岩浆和（地下）水之间的物理相互作用。对艾弗尔山西部著名的普尔弗玛尔火山的边缘沉积物进行更仔细的检查表明，暴露在边缘的火山灰由大约50%的圆形熔岩覆盖的缓慢冷却的火成岩碎片组成，最初位于大约1000米处。根据单斜辉石中的流体包裹体推断，可能是由于注入高p二氧化碳，在深处的深圳岩和周围的变质寄主岩发生碎裂后，碎片变圆，被新岩浆覆盖，并可能被高速湍流二氧化碳喷流输送到地壳最上层。在这里，他们促成了上地壳泥盆纪砂岩/板岩的破碎，破碎可能会被加热的地下水增强。一个10米宽的凝集物在南部的火山口内壁露头表明，流体黄长石霞岩岩浆参与了侵位过程。这一假设表明，岩浆CO2的基本参与的破碎，向上运输和喷发的主要固体火成岩丸。这个模型，如果被提议的研究所证实，将代表一个关于maar起源的基本范式变化。这也意味着，至少有一些玛珥结构在艾菲尔的起源类似于金伯利岩系统的多阶段侵位过程的流行模型，而不是phreatomagmatic玛珥形成，能量的主要来源和网站的碎片是岩浆（CO2）来源于地壳/地幔深处。将进行高分辨率的现场和实验室分析，以测试所提出的模型。