The structure of magma plumbing systems controls a variety of processes that are critical to keeping people safe, secure, and prosperous. These processes include the: (i) location, threat, and early warning signals of volcanic eruptions; (ii) accumulation of magma-related ore deposits; and (iii) distribution of subsurface heat. Yet magma plumbing systems are themselves controlled by a multitude of geological factors, such as host rock lithology and structure, and magma dynamics, each of which unique to different geological settings. Deciphering how entire magma plumbing systems are constructed is thus challenging: at active volcanoes we cannot see the subsurface geology at a high resolution, and exposed ancient intrusions only provide a snapshot of the systems evolution. We therefore have to infer how magma plumbing systems are constructed, and use various modelling approaches to test these interpretations. These models underpin many recent advances in volcanology but, by necessity, are simplified compared to natural magmatic systems and their host rock.

In this presentation, we will explore how ground deformation is used to understand the structure and growth of subsurface magma plumbing systems. In particular, we will demonstrate how seismic reflection data, which provides ultrasound-like images of Earth’s crust, and structural geological mapping of active and ancient systems can be integrated to test model-based hypotheses concerning how magma emplacement translates into ground deformation. For example, graben-bounding, dyke-induced faults are commonly observed on Earth and many planetary bodies, but can we assume that their surficial graben properties (e.g. width and cumulative extension) reflect the underlying dyke depth and thickness? Similarly, how do surface uplift patterns relate to subsurface magma plumbing system structure? Overall, this presentation will emphasise the need to integrate geological, geophysical, and modelling-based approaches to advance our understanding of plumbing system construction.

How to cite: Magee, C. and Jackson, C.: Constructing magma plumbing systems, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13156, https://doi.org/10.5194/egusphere-egu23-13156, 2023.

Until recently, early Carboniferous volcanic activity along the SW edge of the East European Craton (EEC) in Poland has been documented only by wells and, to some degree, by magnetic data. Recently, regional PolandSPAN seismic reflection survey, acquired by ION Geophysical above the entire cratonic edge in Poland, provided unique subsurface insight into this very important event of an extensive volcanic activity. This onshore seismic survey was acquired with ultra-long offsets (12 kms), tight station spacing (25 m), high fold (480) and was processed up to PSDM. 12 seconds record lengths of uncorrelated data provided imaging down to 60 km, with superior data resolution for the entire Phanerozoic sedimentary cover.

In N Poland, within the Mazury High, where Palaeozoic sedimentary cover has been eroded prior to the Permo-Mesozoic deposition within the marginal part of the Polish Basin, the Tajno pyroxenite-syenite-carbonatite complex, the Ełk syenite massif, the Pisz gabbro-syenite massif and Mława syenite massif, all of early Carboniferous age, have been drilled by numerous wells. In the Baltic Basin, where the Ediacaran – Silurian sedimentary cover has been preserved, numerous wells documented doleritic sills of the same age. In this area, a complex system of strong amplitude seismic reflectors of length reaching up to 100 km has been detected using PolandSPAN seismic data. These seismic features are located within the crystalline basement of the Baltic Basin at depth of 7-14 km, and closely resemble lower-crustal reflections (LCR) documented e.g. within the basement of the North Sea basin.

Another type of seismic features related to the lower Carboniferous volcanic intrusives has been documented in SE Poland within the Lublin Basin, where EEC crystalline basement is overlain by thick Ediacaran – Paleozoic – Mesozoic sedimentary cover. In this area, numerous wells encountered lower Carboniferous doleritic intrusions hosted by the Upper Devonian carbonates, and lower Carboniferous basaltic effusives. PolandSPAN data from the Lublin Basin revealed numerous saucer-shaped, strong amplitude seismic reflectors, characterized by lobate morphology and located at depths of 4-7 km, within the topmost Silurian–Lower Devonian section. Collectively, they form ca. 70 km long network of seismic reflectors. They were interpreted as saucer-shaped igneous sills, similar to igneous intrusions imaged by seismic data in other sedimentary basins. Some of these sills have been incorporated into the late Carboniferous compressional deformations of the frontal Variscan fold and thrust belt.

This study was supported by NCN grant UMO-2021/41/B/ST10/03550.

How to cite: Krzywiec, P. and Poprawa, P.: Seismic imaging of lower Carboniferous volcanic intrusions along the SW edge of the East European Craton in Poland, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3601, https://doi.org/10.5194/egusphere-egu23-3601, 2023.

Available globally gridded topography and free-air gravity anomaly are used to compute the Bouguer gravity anomaly over the southern Bundelkhand region and its boundary with the Vindhyan basin. The Bouguer anomaly map displays a large E-W trending gravity high in the central region of the anomaly map, which is majorly covered by the sedimentary Vindhyan rocks, south of the Bundelkhand craton and Deccan trap outcrops, southwest of the craton. The existence of this high in 30 km upward continued regional Bouguer gravity anomaly and the corresponding residual gravity map indicates the large depth as well as spatial extent of the high-density source giving the gravity high. The deep crustal source yielding the high gravity anomaly is backed by the depth estimates obtained for three interfaces (~30.2 km, ~11.9 km, ~2.7 km) from the radially averaged power spectrum analysis. Moho topography obtained as the result of 3D inversion of the Bouguer gravity data using the Parker-Oldenburg iterative algorithm exhibits a shallow Moho of ~32 km below the region covered by the Vindhyan rocks, giving the high gravity signatures. A 2D forward model is developed along the AA’ profile using density and thickness constraints from prior studies, along with the depth estimates obtained from the radially averaged power spectrum analysis. The resulting crustal model exhibits a thick high-density layer above the Moho interface, being the thickest beneath the region covered by the Vindhyan basin rocks underlain by the Bijawar rocks and Bundelkhand basement rocks. Correlating the Moho depths obtained from the inversion with the forward model, it is observed that the shallow Moho below the Vindhyan rocks in the inverted Moho topography is depicting the top surface of the high-density layer modelled over the Moho beneath the region. This high-density layer is theorized to be magmatic underplating arising from crustal extension induced by subduction-led extension tectonics involving the Bundelkhand cratonic block in the Proterozoic times. The presence of the underplated layer below the Vindhyan basin can be correlated with the proposed initiation of the Central Indian Tectonic Zone (CITZ) within the Paleo-Mesoproterozoic period. This points to the tentative formation mechanism of the Vindhyan basin, that is rifting, with the crustal thinning being compensated by the magmatic emplacement above the Moho. This probably resulted due to the onset of oblique collision between the northern and southern Indian blocks along the CITZ at around ~2 Ga, up to ~1Ga, which is said to be the closure age of the Upper Vindhyan rocks. Thus, the obtained results and inferences from the present study deciphers the Moho topography and the underplated high-density layer below the region covered by Vindhyan rocks, south of the Bundelkhand craton, providing a preliminary understanding of the crustal structure beneath the study area and paving the way to undertake further studies to comprehend the implications of the geodynamics of the region with respect to supercontinent reconstructions.

How to cite: Mukherjee, A. and Mandal, A.: Utilizing global gravity data to delineate magmatic underplating and its implications: A case study from Proterozoic Vindhyan basin, south of Bundelkhand craton, India, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6239, https://doi.org/10.5194/egusphere-egu23-6239, 2023.

Appinites are a suite of plutonic rocks, ranging from ultramafic to felsic in composition, that are characterized by idiomorphic hornblende as the dominant mafic mineral in all lithologies and by spectacularly diverse textures, including planar and linear magmatic fabrics, mafic pegmatites and widespread evidence of mingling between mafic and felsic compositions. These features suggest crystallization from anomalously water-rich magma which, according to limited isotopic studies, has both mantle and meteoric components.

Appinites typically occur as small (~2 km diameter) complexes emplaced along the periphery of granitoid plutons and commonly adjacent to major deep crustal faults, which they preferentially exploit during their ascent. Several studies emphasize the relationship between intrusion of appinites, granitoid plutonism and termination of subduction. However, recent geochronological data suggest a more long-lived genetic relationship between appinites and granitoid magma generation and subduction.

Appinites may represent aliquots of hydrous basaltic magma derived from variably fractionated mafic underplates that were originally emplaced during protracted subduction adjacent to the MOHO, triggering generation of voluminous granitoid magmas by partial melting in the overlying MASH zone. The hydrous mafic magmas from this underplate may have ascended, accumulated, and differentiated at mid-to-upper crustal levels (ca. 3-6 kbar, 15 km depth) and crystallized under water-saturated conditions.  The granitoid magmas were emplaced in pulses when transient stresses activated favourably oriented structures which became conduits for magma transport. The ascent of late mafic magmas, however, is impeded by the rheological barriers created by the structurally overlying granitoid magma bodies. Magmas that form appinite complexes evaded those rheological barriers because they preferentially exploited the deep crustal faults that bounded the plutonic system. In this scenario, appinite complexes may be a direct connection to the mafic underplate and so its most mafic components may provide insights into processes that generate granitoid batholiths and, more generally, into crustal growth in arc systems. 

How to cite: Murphy, J. B., Collins, W. J., and Archibald, D. B.: Appinite complexes, granitoid batholiths and crustal growth: a conceptual model, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4334, https://doi.org/10.5194/egusphere-egu23-4334, 2023.

How to cite: Möri, A. and Lecampion, B.: Magmatic Intrusions From a Hydraulic Fracture Modeling Perspective, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4313, https://doi.org/10.5194/egusphere-egu23-4313, 2023.

Magma intrusions ascending through the upper crust induce a displacement of the Earth’s surface, the amplitude of which  increases as the magma approaches the surface. Most geodetic observations of ground displacements induced by magma transport are interpreted using static elastic models of open dislocations or pressurized surfaces without any a priori knowledge on the surface shape of the magma intrusion. Furthermore, the numerical models currently developed for the propagation of fluid-filled cracks, which are also elastic, do not generally resolve the 3D displacement field induced at the free surface. Our aim is to bridge these two distinct approaches by using fluid-filled crack propagation models to derive the evolution of the surface displacement over time, thus providing a useful tool for the assimilation of geodetic data based on dynamic models.

In a first step, we use Weertman crack theory, which provides the shape of a non-viscous fluid-filled crack to derive the surface displacement field from a finite element model. This solution is then compared to the classical dislocation model (OKADA formulation) and to 2D displacement field inferred from the simulation of the propagation of the fluid filled using a 2D boundary element model. Eventually, the results are validated using analogue experiments injecting a finite volume of air inside a transparent gelatin characterised by elastic behaviour. In the experiments, the position and shape of the crack are monitored by cameras while the surface displacement field is recovered by photogrammetry (3D components) and by scanner measurements (only the vertical component).

How to cite: Pinel, V., Galland, O., Furst, S., Métral, L., Camus, B., and Maccaferri, F.: Surface displacement field induced by an ascending Weertman crack: numerical modeling versus analogue experiments., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5645, https://doi.org/10.5194/egusphere-egu23-5645, 2023.

Magmatic overpressure in shallow- and mid-crustal magma chambers (MC) can deform the crustal host rocks. Stress field produced by such deformation often control the nucleation and subsequent crack formation for magma emplacement. A direction of physical volcanology is concerned with determination of the volcanotectonic ground surface displacements that can aid in monitoring and sometimes forecasting magmatic eruptions. The existing Mogi Model can analytically calculate surface displacements due to overpressure in a single MC by considering elastic deformation of a finite crustal section. Many geological and geophysical studies report that magma plumbing systems represent an array of randomly placed interconnected MCs, and there is a need of theoretical estimation of their ground surface displacement. In this study we present a new analytical formulation to estimate surface displacement in terms of both vertical as well as horizontal directions above a dual MC setting. Our analytical solution finds support from finite element (FE) models performed with the same set of geometrical and physical parameters. The off-axis chambers considered in our model are separated along both vertical and horizontal directions. The present study suggests that with increasing horizontal chamber separation (S_h) the vertical ground displacement above the two chambers gradually changes from a single peak into an indistinct double-peak, and finally two prominent independent, high-amplitude peaks. On the other hand, on increasing the vertical separation (S_v) between two off-axis chambers we observed that the initial double peaks merged to produce a single peak situated roughly above the middle of the two chambers. Stress map obtained from the FE models shows that the deformation of two MCs can only interact when located within a critical distance, else their deformation remains independent. Interestingly, our study suggests that the magnitude of stress field strongly depends on the strength of the mechanical interaction between two neighboring chambers.

How to cite: Hazarika, P. J., Baruah, A., Dasgupta, R., and Mandal, N.: Analytical and numerical model estimates of ground surface displacements in dual magma chamber setting, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-767, https://doi.org/10.5194/egusphere-egu23-767, 2023.

Only a fraction of the magma generated in the earth finds its way to the surface during volcanic eruptions, while most of it will cool down and crystallize at different depths in the crust. Of particular interest is the pre-eruptive level, typically between 10km to 2km. Here, understanding the ratio erupted vs non-erupted magma has implications for volcanic eruption forecasting, long-term magmatic evolution, pluton formation, volcanic cyclicity, and post-eruptive geophysical monitoring. With a special focus on crystal-rich or mushy magmas, we address this problem by exploring, once a conduit reaches the surface, how efficiently the magma reservoir gets depleted and what regions of the reservoir are affected. We address those questions here using an unstructured finite element code, Gridap, written in Julia (Badia et al. 2020).

Results show that several modes of magma advection exist including the classical pipe flow mode where a new batch of magma added to a mush chamber moves through a dike to the surface. Yet, several other modes also exist, which include a Stokes flow mode where magma does not make it to the surface despite a pre-existing open connection, and various intermediate modes. We use the numerical simulations to determine how magma rising speeds depends on the material and geometrical parameters such as magma and mush viscosities, or sizes of the magma batch, mush chamber or dike widths. As the numerical simulations cannot be performed for the full range of realistic magma viscosities, we use them to derive scaling laws for each of the mechanical deformation modes. These scaling laws can be used to extrapolate results to natural conditions, and highlight the key controlling parameters that determine whether melt buoyancy will result in an eruption or not. Importantly, it shows that there are physical limits to the volume of magma that can be erupted from a newly added batch of magma in a mush chamber. We will discuss the application of the results to natural cases.

References cited

Badia, S., & Verdugo, F. (2020). Journal of Open Source Software, 5(52), 2520.

How to cite: Berlie, N., Kaus, B. J. P., and de Silva, S. L.: Constraining the limits to magma chamber evacuation during explosive eruptions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12817, https://doi.org/10.5194/egusphere-egu23-12817, 2023.

We illustrate GALES, a finite element C++ code that we developed during last >10 years. GALES solves the time-dependent 3D thermo-fluid dynamics (4D space-time) of non-Newtonian multicomponent flows (magma) and 2-way coupled elastic structure (rocks). GALES accounts from incompressible to compressible flow regimes, and it is therefore suited to simulate from under-saturated magma conditions deep into the crust to the rapidly accelerating conditions along volcanic conduits including transonic flow regimes leading to explosive volcanic eruptions. The code is implemented with a suite of models describing the real properties of multi-component multiphase magmas, which are locally (in space and time) computed. Magma dynamics are fully coupled with rock elasto-dynamics, allowing computation of the transient signals (deformation, gravity) associated with magmatic flows by accounting for rock heterogeneities, free surface and real topography. Geometrical complexities associated with multiple magmatic reservoirs, connecting dykes, volcanic conduits etc. can all be accounted for, in separate or individual simulations. Typical computational time steps of 0.01 s and simulation lengths of order hours allow confident computation of signal frequencies in the range 0.001 – 10 Hz, which is still under-investigated for magmatic and volcanic systems. The results illustrate several original aspects of magma dynamics and associated signals, such as the association between magma convection and generation of Ultra-Long-Period ground displacement dynamics; the ground deformation patterns associated with complex distributions of overpressure, both negative and positive, reflecting magma transfer across separate reservoirs; the decoupling of gravity and deformation sources associated with buoyancy-driven ascent of magma; the generation of transient explosive events associated with deep arrivals of gas-rich magmas in basaltic open system volcanoes; and many others.

How to cite: Papale, P., Garg, D., Longo, A., and Montagna, C.: Modeling the 4D coupled dynamics of magma propagation, ground deformation, and gravity changes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2671, https://doi.org/10.5194/egusphere-egu23-2671, 2023.