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

Maars代表了引人注目和具有旅游吸引力的火山口（例如艾菲尔火山场），火山口碎片主要是近地表岩石碎片。火星最初被认为是岩浆气体（CO2）爆炸的陨石坑，自20世纪70年代初以来，火星被普遍解释为是上升的岩浆和（地下）水之间物理相互作用的结果。对艾菲尔西部著名的粉状火山边缘沉积物的仔细观察表明，暴露在边缘的火成岩大约有50%是由缓慢冷却的火成岩的圆形熔岩包裹碎片组成的，这些火成岩最初位于地表以下约20公里处，这是由斜辉石中的流体包裹体推断出来的。深部深部深部深部深部深部深部深部深部深部变质寄主岩可能被注入的高磷二氧化碳破碎，这些碎屑被新岩浆包裹，呈圆形，并可能被高速湍流二氧化碳射流输送到最上层地壳。在这里，它们促成了上地壳泥盆纪砂岩/板岩的破碎，而加热的地下水可能加剧了这种破碎。南部内火山口壁上有10 m宽的凝集物露头，表明岩浆岩浆参与了侵位过程。这一假设表明岩浆CO2在大部分固体火成岩颗粒的破碎、向上运输和喷发过程中起着重要作用。这个模型，如果被提议的研究证实，将代表关于海洋成因的范式的一个基本变化。这也意味着，至少在艾菲尔的一些泥岩结构的起源类似于金伯利岩系统的多阶段侵位过程的流行模式，而不是热液岩浆形成的模式，主要的能量来源和破碎地点是来自地壳/地幔深处的岩浆（CO2）。将进行高分辨率的现场和实验室分析来测试所提出的模型。

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.