Frank Zwaan

The call for an “energy transition” undeniably requires finding low-emission energies, among which serpentinization-sourced natural hydrogen (H2) is one potential candidate. However, the knowledge needed to successfully explore for this new energy source, i.e., to understand when and where natural H2 forms during the Wilson cycle, is yet incomplete. Answering these questions is challenging and requires not only a much-improved understanding of serpentinization processes, but also a deep understanding of the geological systems in which serpentinization occurs. The aim of this contribution is not only to focus on how natural H2 forms, migrates and is trapped, but also to investigate the characteristics and evolution of the geological systems that hosted, or host, serpentinization and potential natural H2 production. More specifically, we examine the evolution of mantle rocks during their emplacement in ocean continent transitions (OCTs) and their later reactivation and emplacement in rift-inversion orogens. To do so, we review the evolution of OCT-derived ophiolites located in the Alpine system. We focus on two settings: the Western Pyrenean fossil OCT exposed in SW-France and the Grischun-Malenco fossil OCTs exposed in SE-Switzerland and northern Italy. Their choice is linked to the fact that they are not only the best documented and exposed examples of OCT-derived ophiolites worldwide, but also to the fact that they bear active H2 systems. Compared with ophiolites derived from Mid Ocean Ridges (MOR) or Supra-Subduction Zones (SSZ), OCT-derived ophiolites are substantially different in terms of mantle rock composition, emplacement mechanisms during collision, and potential for natural H2 production. In this study, we review the characteristics of OCTs based on the well calibrated distal Iberian margin and the Grischun-Malenco fossil OCT. We then synthesize the state-of-the art knowledge on these well described OCTs and OCT-derived ophiolites and their potential for natural H2 systems. Finally, we discuss how far this knowledge can be used to explore for native H2 along the Tethyan suture zones in Eastern Europe, and in collisional orogens in general.

Natural hydrogen gas (H ₂ ) generated through the serpentinization of mantle rocks is a possible source of clean energy. For efficient serpentinization and large‐scale H ₂ generation to occur, mantle rocks need to be brought near the surface (exhumed) into a favorable temperature range (the serpentinization window) and in contact with water. Rift‐inversion orogens that form when rift basins are closed and tectonically inverted provide promising environments for serpentinization‐related H ₂ generation and the accumulation of economical H ₂ volumes. Erosion is known to impact exhumation processes, but how erosion efficiency influences serpentinization and associated H ₂ resource potential in rift‐inversion orogens remains poorly understood. We use numerical geodynamic models with varying rifting phase durations to address this question. We find that, on the one hand, efficient erosion can cause a shift from a typical symmetric orogenic style to an asymmetric style in systems with limited preceding rifting, thus promoting mantle exhumation and creating favorable conditions for efficient serpentinization that may lead to bulk natural H ₂ generation. Independent of erosion efficiency, advanced rifting facilitates the formation of asymmetric orogens and the mantle exhumation needed for efficient serpentinization, showing that rift duration is a dominant factor to consider. On the other hand, highly efficient erosion can limit serpentinization potential in all settings as rapid exhumation of hot material narrows the serpentinization window's vertical extent. Moreover, the removal of potential reservoir and seal rocks diminishes the likelihood of natural H ₂ accumulations forming. Using these insights, we present a speculative first‐order application to the Pyrenees, Alps, and Betics.

Partially molten lower-crustal domains are key features of many large hot orogens, including the Altai tract of the CAOB, Tibet, and the Altiplano–Puna, where seismic imaging reveals extensive low-velocity, high-temperature regions interpreted as crustal mush zones. These regions form and evolve under the combined influence of crustal thickening, mantle–lithosphere removal, and thermally driven weakening, which together promote melt generation, rheological softening, and decoupling between crustal levels, thereby enabling lateral and vertical redistribution of material. Yet, the feedback between melt migration, deformation, and mechanically anisotropic, layered mush systems remains insufficiently quantified.In this contribution, we compare different types of models that approximate the crustal evolution of hot orogens: semi-scaled thermal paraffin-wax analogue models with visco-plastic finite-element numerical models that respect the laboratory scale and employ similar material properties. In addition, orogen-scale control numerical models were performed to mimic natural prototypes. The models were designed to explicitly address (i) crustal strength, shortening, and basal heating, and (ii) how these parameters govern internal deformation, melt coalescence, and plumbing-system architecture.Analogue experiments successfully reproduced melt migration and its coalescence in buckled and folded layers, suggesting that mechanically layered mush domains can localize melt along fold hinges, shear zones, and evolving permeability pathways, with potential transitions from dominantly lateral to buoyancy-driven melt transfer as deformation proceeds. However, the analogue models lack rigorous and precise quantification of the thermal field, and melt migration is tracked approximately, using image analysis based on DIC and X-ray CT-scanning methods. Furthermore, precise dynamical scaling is currently limited by the absence of a representative rheological law based on the complex rheometry of the paraffins used, restricting us to discrete viscosity measurements for different velocities and temperatures.The first step in the numerical approach was to reproduce the analogue model geometry and melt distribution. Simulations successfully mimic the development of melt-rich regions at both laboratory and orogen scales within a range of natural parameter values, but they do not reproduce the degree of melt coalescence within crustal layers that occurs naturally in the analogue models; nevertheless, these weak zones promote further strain distribution and strongly influence the overall crustal deformation response. An important advantage of the numerical approach is the well-constrained control on the thermal regime and temperature–melt evolution in the system. For the tested parameters, however, the numerical models yield a more homogeneously thickened crust without significant buckling of the lower crust, and a major limitation is the absence of porous melt flow, which may play a key role in melt coalescence and ascent.The discrepancy between analogue and numerical results suggests more complex rheological coupling between deformed and partially molten crustal layers than can be captured by either method alone. This motivates a re-evaluation of the dynamical and thermal scaling of analogue experiments and the implementation of porous flow and anisotropic permeability in future numerical models.

Natural hydrogen gas (H2) generated through the serpentinization of mantle rocks is a promising source of clean energy. For large-scale serpentinization and natural H2 generation to occur, the mantle rocks need to be brought into a optimal temperature range (the serpentinization window) and into contact with water. Alpine-style rift-inversion orogens, formed during the closure of rift basins, provide excellent environments for serpentinization-related natural H2 generation, while also harbouring extensive volumes of sediments in which natural H2 accumulation could form. In such orogens, erosion is known to have an important impact on exhumation processes and sediment distribution, but to what degree erosion efficiency influences natural H2 resource potential remains poorly understood. We use numerical geodynamic models of rift-inversion to explore and, importantly, quantify the relative roles of erosion and tectonic processes by applying different erosion efficiencies and initial rift phase durations.Our modelling shows that, regardless of erosion efficiency, initial rift duration is a dominant factor during both the extension and inversion phase. Prolonged rifting causes increased mantle exhumation and thus higher natural H2 generation potential. Erosion efficiency exerts only a secondary effect, in that more efficient erosion modestly reduces H2 generation potential by narrowing the serpentinization window. Inversion of advanced rift basins results in asymmetric orogens in which mantle material is incorporated into the overriding wedge, a configuration that is critical for generating high natural H2 generation potential in these systems. Nevertheless, efficient erosion of otherwise symmetric orogens formed after limited rifting allows for a shift to an asymmetric style, with significant mantle exhumation and natural H2 generation potential.However, efficient erosion and associated fast exhumation of relatively hot material in orogens can also decrease the vertical extent of the serpentinization window, reducing natural H2 generation potential. Moreover, rapid erosion can remove the otherwise abundant potential reservoir rocks and seals needed for exploitable natural H2 accumulations to form. Still, these negative effects of erosion on “conventional” natural H2 resources (involving H2 accumulation in reservoir rocks), may be favourable for “unconventional” natural H2 resources. Systems with relatively hot mantle material close to the surface may in fact be suitable for stimulated natural H2 exploitation efforts, involving direct drilling of the mantle source rock itself.Thus, although erosion efficiency is not the dominant factor, it can still have a considerable impact on natural H2 potential in rift-inversion orogens. Therefore, a thorough understanding of the evolution of those orogens targeted for exploration, will be of great importance. This challenge can be aided by numerical geodynamic models such as those presented here, with which we perform a first-order analysis of natural examples from the Pyrenees, Alps, and Betics.

A key challenge in the 21st century is the successful implementation of the energy transition, which hinges on the development of sustainable (energy) resources. In this context, hydrogen gas (H2) generated by natural processes is a promising source of clean energy. However, we urgently need to develop the concepts and exploration strategies for this promise of natural H2 energy to become a reality.The most likely mechanism of large-scale natural H2 generation in nature is the serpentinization of ultramafic mantle rocks during their chemical reaction with water. In order to predict the bulk serpentinization and natural H2 generation that may lead to the development of exploitable H2 deposits, we consider the following “recipe” for efficient serpentinization, which involves three main ingredients: (1) (fresh) mantle rocks that need to be at (2) optimal temperatures between ca. 200-350˚C (the serpentinization window), and (3) in contact with ample water for the reaction to take place. The serpentinization window can be expected at 8-12 kilometers below the Earth’s surface. However, mantle rocks are normally found at much greater depth; thus these rocks must be brought closer to the surface (exhumed) through geodynamic processes. Moreover, water needs to reach such depths along large faults or other structures that cut into the exhumed mantle. The challenge we are faced with is to understand where (and when) these ingredients may come together in nature, and how much natural H2 may be generated.Numerical geodynamic modelling is an ideal means to tackle this issue since it allows us not only to test how mantle rocks can be exhumed, but also to trace the temperature conditions and potential water availabilitiy (Zwaan et al. 2025). By combining this information, we assess favorable settings and timing of bulk natural H2 generation in different geodynamic systems. Subsequently, we consider where the natural H2 could be exploited. The serpentinizing mantle source rocks at 8-12 km depth cannot be directly targeted. Ideally, the natural H2 would instead migrate and accumulate in sedimentary reservoir rocks at depths of only a couple of kilometers that are connected with the mantle source rocks via migration pathways (e.g., faults). Importantly, all key elements need to be in place for the system to work.Our first-order modelling work and the development of natural H2 system concepts greatly helps to direct natural H2 resource exploration efforts, for example in the Alps and Pyrenees. Moreover, substantial opportunity lies in refining both the geodynamic modelling and natural H2 system analysis, in field- and laboratory testing of our H2 system concepts, and in extending such a “mineral system” modelling approach to other types of natural resources that are crucial to the energy transition. Reference:Zwaan, F., Brune, S., Glerum, A.C., Vasey, D.A., Naliboff, J.B., Manatschal, G., & Gaucher, E.C. 2025: Rift-inversion orogens are potential hot spots for natural H2 generation, Science Advances, 11, eadr3418. https://doi.org/10.1126/sciadv.adr3418

Extensional tectonic settings may undergo time‐dependent kinematic changes, causing a multiphase evolution of the resulting fault networks. Yet, the spatial and temporal evolution of fault networks during triaxial and biaxial strain remains underexplored. Here we present scaled analogue models to investigate fault geometry, activity, and patterns across multiple phases of triaxial (constrictional) and biaxial (plane) strain. Our models show that (a) during the shift from biaxial to triaxial strain, first‐phase normal faults are fully reactivated and new conjugate sets of oblique‐slip faults develop during the subsequent triaxial phase. (b) During the shift from triaxial to biaxial strain, first‐phase conjugate sets of oblique‐slip faults either become inactive or are partly reactivated, while being cut across and linked up by new faults during subsequent biaxial strain. Our results illustrate kinematic interactions within multiphase fault networks, showing how perturbations in stress domains control the geometry of new faults and how earlier dominant faults create mechanical obstacles that hinder fault propagation. Finally, we compare the fault network evolution in our models to natural examples. The transition from biaxial to triaxial strain reflects the two‐phase deformation observed in the Aegean Sea, where pre‐existing normal faults were reactivated and new oblique‐slip normal faults developed. Similarly, a shift from triaxial to biaxial strain explains the faulting patterns in the Barents Sea during the Late Mesozoic to Early Cenozoic, which exhibit abandoned, reactivated, and newly developed faults.

As the energy transition gathers steam, naturally occurring hydrogen gas (H2) generated by the serpentinization of mantle rocks is a highly promising sustainable alternative to fossil fuels. To undergo serpentinization, mantle rocks that are normally situated at great depth need to be brought closer to the surface by plate tectonics and other geodynamic processes. Here, they may react with water to be efficiently serpentinized and generate natural H2, which can accumulate in reservoirs as it migrates to the surface (as part of a natural H2 system).Exploring natural H2 systems requires a solid understanding of their geodynamic history, which can be informed by numerical geodynamic modelling. Through such modelling we can trace how, when, and where mantle material enters the serpentinization window, as well as when active, large-scale faults penetrate exhumed mantle bodies allowing for water circulation, as well as serpentinization and H2 generation, to occur.Our recent modelling of rifting and subsequent rift inversion (Zwaan et al., in press) shows that, although serpentinization-related natural H2 generation is a phenomenon best known from (magma-poor) rifted margins and oceanic spreading ridges, annual volumes of natural H2 generated during inversion may be up to 20 times higher than during rifting, due to the colder thermal regime in rift-inversion orogenic environments. Moreover, suitable reservoir rocks and seals required for natural H2 accumulations to form are readily available in rift-inversion orogens, whereas they may not be present when serpentinization occurs in deep marine continental rift or oceanic spreading settings.Our model results thus provide a first-order motivation to turn to rift-inversion orogens for natural H2 exploration and are supported by indications of natural H2 generation in rift-inversion orogens such as the European Alps and Pyrenees.REFERENCE CITED: Zwaan, F., Brune, S., Glerum, A.C., Vasey, D.A., Naliboff, J.B., Manatschal, G., Gaucher, E.C (in press). Rift-inversion orogens are potential hotspots for natural H2 generation. Science Advances. Link to preprint: https://doi.org/10.21203/rs.3.rs-3367317/v

Serpentinization-sourced H2 has become a promising source of decarbonated energy. It can be generated in fiver tectonic settings, namely: (1) intra-craton settings, (2) divergent settings such as hyperextended rifts, ocean continent transitions and mid ocean ridges, (3) subduction systems, (4) obduction, and (5) rift-inverted orogens. Most recently, many studies have been focusing on parts of the H2-system, i.e., the kitchen, plumbing system, reservoir, cap rock and trapping and preservation mechanisms or on the detection of leaking natural H2 systems at or near the surface. However, a holistic understanding of a serpentinization-sourced H2 system is still in its infancy and an exploration protocol tailored to the different tectonic settings is missing to date. In our study, we aim to develop a protocol to predict, quantify and explore serpentinization-sourced H2 systems in rift-inverted orogens. To do so, we use the Grisons area (SE Alps in Switzerland) as a field analogue. In this area all play-elements of the serpentinization-sourced H2 system exist and can be accessed and the rift and convergent structures are well exposed and investigated. This allows us to examine the interplay, in time and space, between the play-elements of a serpentinization-sourced H2 system and to develop a predictive exploration protocol. In this perspective, we first seek to define a serpentinization-sourced H2 system in a rift-inversion orogen and second to address when and where the serpentinization-sourced H2 forms, what are the essential play-elements and how they interact in time and space, impacting the location and timing of H2 production by considering the two dominant parameters, temperature and access to water, which determine entry into the serpentinization window (kitchen) for mantle rocks. In our presentation, we show the first preliminary results of our holistic, geological approach aiming to integrate different data sets from the Grisons area. We are aware that to develop a predictive play-element based exploration protocol for a serpentinization-sourced H2 system in rift-inverted orogens, similar to that developed in oil and gas systems, further studies will be necessary.

Rift-inversion orogens such as the High Atlas, Pyrenees, and Greater Caucasus exhibit strain localization primarily due to contractional reactivation of lithospheric weaknesses inherited from continental rifting, rather than from long-lived subduction leading to continental collision along a major plate boundary. These orogens thus experience a transition from extension to compression distinct from their plate-boundary counterparts that impacts georesource development and seismic hazard. It is widely recognized that the initial conditions prior to rift inversion strongly control the structural and thermal evolution of such orogens, yet it is difficult to derive initial conditions from available structural and thermochronologic data.Here, we present geodynamic numerical modeling designed to capture the structural and thermal evolution of rift-inversion orogens. We complement our study with new Python routines to calculate synthetic low-temperature thermochronometric ages from the model results. This enables directly comparing our numerical results with thermochronometric data collected in natural rift-inversion orogens. Our initial results (Vasey et al., 2024) indicate three end-member structural styles in model orogens: 1) asymmetric underthrusting reminiscent of the Pyrenees and Greater Caucasus, 2) distributed thickening reminiscent of the High Atlas, and 3) polarity flip in which the vergence of the orogen varies over time. Synthetic apatite (U-Th)/He and fission track thermochronometric ages record regions of focused exhumation on the flanks of the initial rifts and in the hanging walls of major thrust faults in the final orogens, mirroring similar relationships between major structures and areas of greater exhumation observed in natural orogens.These results demonstrate how geodynamic modeling can extend the ability of structural data and low-temperature thermochronology to help distinguish between competing models of pre-orogenic initial conditions.Reference Cited:Vasey, D.A., Naliboff, J.B., Cowgill, E., Brune, S., Glerum, A., and Zwaan, F., 2024, Impact of rift history on the structural style of intracontinental rift-inversion orogens. Geology, v. 52, no. 6, 429-434, doi:10.1130/G51489.

Analogue modeling for Earth Sciences started over two centuries ago as an explorative technique that allowed for the first time unfolding and visualizing a wide range of tectonic processes. While this character remains a compelling feature of analogue models, this experimental methodology has evolved over the last few decades into a quantitative, reproducible and reliable method. Most recent developments aredispersed across scientific journal articles, many behind pay-walls and sometimes hidden in appendices, but no open-access overview exists that brings all this knowledge together.In the context of the EU research infrastructure EPOS, we are preparing the first comprehensive guide (SPRINGER will publish that as open access) on the state-of-the-art in analogue modeling of geologic processes. This community-built book will be organized into three sections. The first section will serve as a “cookbook” for building analogue models, offering up-to-date guide on scaling down models, selecting suitable analog materials, collecting experimental data, and interpreting those results. The second section will focus on a variety of tectonic processes that can be reproduced in the lab and analyzed using analogue modelling. The final section will emphasize the importance of sharing experimental research data through Open Access data publications and illustrate how analogue models can enhance the Earth Science teaching experience in classrooms. This book will fill a significant gap in the scholarly literature and will serve as a reference and guide for both early-career and experienced researchers as well as reaching out to a broader community of educational and academic teachers. In this presentation, we will share our journey toward this community-effort and give examples of the different sections of the book.