Quantifying Microstructural Evolution in Moving Magma

Many of the grand challenges in volcanic and magmatic research are focused on understanding the dynamics of highly heterogeneous systems and the critical conditions that enable magmas to move or eruptions to initiate. From the formation and development of magma reservoirs, through propagation and arrest of magma, to the conditions in the conduit, gas escape, eruption dynamics, and beyond into the environmental impacts of that eruption, we are trying to define how processes occur, their rates and timings, and their causes and consequences. However, we are usually unable to observe the processes directly. Here we give a short synopsis of the new capabilities and highlight the potential insights that in situ observation can provide. We present the XRheo and Pele furnace experimental apparatus and analytical toolkit for the in situ X-ray tomography-based quantification of magmatic microstructural evolution during rheological testing. We present the first 3D data showing the evolving textural heterogeneity within a shearing magma, highlighting the dynamic changes to microstructure that occur from the initiation of shear, and the variability of the microstructural response to that shear as deformation progresses. The particular shear experiments highlighted here focus on the effect of shear on bubble coalescence with a view to shedding light on both magma transport and fragmentation processes. The XRheo system is intended to help us understand the microstructural controls on the complex and non-Newtonian evolution of magma rheology, and is therefore used to elucidate the many mobilization, transport, and eruption phenomena controlled by the rheological evolution of a multi-phase magmatic flows. The detailed, in situ characterization of sample textures presented here therefore represents the opening of a new field for the accurate parameterization of dynamic microstructural control on rheological behavior

Bivalves from the Olenekian (Early Triassic) of south-western Utah: systematics and evolutionary significance

The recovery from the end-Permian mass extinction event was a key interval in the history of life, but few modern studies provide systematic data on benthic marine faunas from the epoch immediately following the crisis. Here, the bivalve fauna from the early Spathian (Olenekian, late Early Triassic) Virgin Limestone Member of the Moenkopi Formation is comprehensively documented for the first time. The new genus Sementiconcha (Myophoricardiidae), type species Sementiconcha recuperator sp. nov., and the new species Leptochondria nuetzeli, Eumorphotis ericius, E. virginensis and Pleuromya prima, are described. Leptochondriidae is placed in synonymy with Asoellidae, which is revised. With 27 species belonging to 18 genera, the Virgin Limestone Member records the highest bivalve diversity reported so far from this time interval, questioning previous claims that the recovery from the end-Permian mass extinction was delayed until the Middle Triassic. The two bivalve subclasses (Pteriomorphia and Heteroconchia) that are present in the Virgin Limestone Member clearly differ in their evolutionary contexts. Pteriomorphs of the Virgin Limestone are nearly exclusively composed of genera that survived the end-Permian mass extinction event, whereas heteroconchs are highly dominated by genera that evolved in the Early Triassic. This contrasting evolutionary background probably reflects differential effects of the end-Permian mass extinction event and subsequent crises on these two subclasses, possibly related to differences in filter feeding efficiency and shell mineralogy. The high proportion of infaunal heteroconchs, including deep-infaunal Pholodomyoida, is an additional indicator of a relatively advanced recovery stage, further corroborating that recovery of benthic organisms was well underway during the late Early Triassic