More Like this

1. Tectonism and Its Relation to Magmatism Around Santorini Volcano From Upper Crustal P Wave Velocity

   https://doi.org/10.1029/2019JB017699  

   Heath, B. A.; Hooft, E. E. E.; Toomey, D. R.; Papazachos, C. B.; Nomikou, P.; Paulatto, M.; Morgan, J. V.; Warner, M. R. (October 2019, Journal of Geophysical Research: Solid Earth)

   Abstract At extensional volcanic arcs, faulting often acts to localize magmatism. Santorini is located on the extended continental crust of the Aegean microplate and is one of the most active volcanoes of the Hellenic arc, but the relationship between tectonism and magmatism remains poorly constrained. As part of the Plumbing Reservoirs Of The Earth Under Santorini experiment, seismic data were acquired across the Santorini caldera and the surrounding region using a dense amphibious array of >14,300 marine sound sources and 156 short‐period seismometers, covering an area 120 km by 45 km. Here aPwave velocity model of the shallow, upper‐crustal structure (<3‐km depth), obtained using travel time tomography, is used to delineate fault zones, sedimentary basins, and tectono‐magmatic lineaments. Our interpretation of tectonic boundaries and regional faults are consistent with prior geophysical studies, including the location of basin margins and E‐W oriented basement faults within the Christiana Basin west of Santorini. Reduced seismic velocities within the basement east of Santorini, near the Anydros and Anafi Basins, are coincident with a region of extensive NE‐SW faulting and active seismicity. The structural differences between the eastern and western sides of Santorini are in agreement with previously proposed models of regional tectonic evolution. Additionally, we find that regional magmatism has been localized in NE‐SW trending basin‐like structures that connect the Christiana, Santorini, and Kolumbo volcanic centers. At Santorini itself, we find that magmatism has been localized along NE‐SW trending lineaments that are subparallel to dikes, active faults, and regional volcanic chains. These results show strong interaction between magmatism and active deformation. 

   more » « less
2. The Impact of Complex Volcanic Plumbing on the Nature of Seismicity in the Developing Magmatic Natron Rift, Tanzania

   https://doi.org/10.3389/feart.2020.609805  

   Reiss, Miriam Christina; Muirhead, James D.; Laizer, Amani S.; Link, Frederik; Kazimoto, Emmanuel O.; Ebinger, Cynthia J.; Rümpker, Georg (February 2021, Frontiers in Earth Science)

   null (Ed.)

   Constraining the architecture of complex 3D volcanic plumbing systems within active rifts, and their impact on rift processes, is critical for examining the interplay between faulting, magmatism and magmatic fluids in developing rift segments. The Natron basin of the East African Rift System provides an ideal location to study these processes, owing to its recent magmatic-tectonic activity and ongoing active carbonatite volcanism at Oldoinyo Lengai. Here, we report seismicity and fault plane solutions from a 10 month-long temporary seismic network spanning Oldoinyo Lengai, Naibor Soito volcanic field and Gelai volcano. We locate 6,827 earthquakes with M L −0.85 to 3.6, which are related to previous and ongoing magmatic and volcanic activity in the region, as well as regional tectonic extension. We observe seismicity down to ∼17 km depth north and south of Oldoinyo Lengai and shallow seismicity (3–10 km) beneath Gelai, including two swarms. The deepest seismicity (∼down to 20 km) occurs above a previously imaged magma body below Naibor Soito. These seismicity patterns reveal a detailed image of a complex volcanic plumbing system, supporting potential lateral and vertical connections between shallow- and deep-seated magmas, where fluid and melt transport to the surface is facilitated by intrusion of dikes and sills. Focal mechanisms vary spatially. T-axis trends reveal dominantly WNW-ESE extension near Gelai, while strike-slip mechanisms and a radial trend in P-axes are observed in the vicinity of Oldoinyo Lengai. These data support local variations in the state of stress, resulting from a combination of volcanic edifice loading and magma-driven stress changes imposed on a regional extensional stress field. Our results indicate that the southern Natron basin is a segmented rift system, in which fluids preferentially percolate vertically and laterally in a region where strain transfers from a border fault to a developing magmatic rift segment. 

   more » « less
3. Unraveling the Connection Between Subsurface Stress and Geomorphic Features

   https://doi.org/10.1029/2025GL116798  

   Kuhasubpasin, B.; Moon, S.; Lithgow‐Bertelloni, C. (October 2025, Geophysical Research Letters)

   Abstract The tectonic stress field induces surface deformation. At long wavelengths, both lithospheric heterogeneity (changes in the thickness and density of crust and lithospheric mantle) and basal tractions from mantle convection contribute to the stress field. Here, we analyze the global alignment of principal horizontal tectonic stresses, fault traces, and river flow directions to infer whether and how deep subsurface stresses control geomorphic features. We find that fault trace orientations are consistent with predictions from Anderson's fault theory. River directions largely align with fault traces and partly with stresses. The degree of alignment depends on fault regime, the source of stress, and river order. Extensional faulting is best predicted by stresses from lithospheric structure variations, while compressive faulting is best predicted by stresses from mantle flow. We propose a metric to quantify the relative influence of mantle flow or lithospheric heterogeneity on surface features, which provides a proxy for lithospheric strength. 

   more » « less
4. How a strong low-angle normal fault formed: The Whipple detachment, southeastern California

   https://doi.org/10.1130/B35386.1  

   Axen, Gary J. (December 2019, GSA Bulletin)

   Abstract Many low-angle normal faults (dip ≤30°) accommodate tens of kilometers of crustal extension, but their mechanics remain contentious. Most models for low-angle normal fault slip assume vertical maximum principal stress σ1, leading many authors to conclude that low-angle normal faults are poorly oriented in the stress field (≥60° from σ1) and weak (low friction). In contrast, models for low-angle normal fault formation in isotropic rocks typically assume Coulomb failure and require inclined σ1 (no misorientation). Here, a data-based, mechanical-tectonic model is presented for formation of the Whipple detachment fault, southeastern California. The model honors local and regional geologic and tectonic history and laboratory friction measurements. The Whipple detachment fault formed progressively in the brittle-plastic transition by linking of “minidetachments,” which are small-scale analogs (meters to kilometers in length) in the upper footwall. Minidetachments followed mylonitic anisotropy along planes of maximum shear stress (45° from the maximum principal stress), not Coulomb fractures. They evolved from mylonitic flow to cataclasis and frictional slip at 300–400 °C and ∼9.5 km depth, while fluid pressure fell from lithostatic to hydrostatic levels. Minidetachment friction was presumably high (0.6–0.85), based upon formation of quartzofeldspathic cataclasite and pseudotachylyte. Similar mechanics are inferred for both the minidetachments and the Whipple detachment fault, driven by high differential stress (∼150–160 MPa). A Mohr construction is presented with the fault dip as the main free parameter. Using “Byerlee friction” (0.6–0.85) on the minidetachments and the Whipple detachment fault, and internal friction (1.0–1.7) on newly formed Reidel shears, the initial fault dips are calculated at 16°–26°, with σ1 plunging ∼61°–71° northeast. Linked minidetachments probably were not well aligned, and slip on the evolving Whipple detachment fault probably contributed to fault smoothing, by off-fault fracturing and cataclasis, and to formation of the fault core and fractured damage zone. Stress rotation may have occurred only within the mylonitic shear zone, but asymmetric tectonic forces applied to the brittle crust probably caused gradual rotation of σ1 above it as a result of: (1) the upward force applied to the base of marginal North America by buoyant asthenosphere upwelling into an opening slab-free window and/or (2) basal, top-to-the-NE shear traction due to midcrustal mylonitic flow during tectonic exhumation of the Orocopia Schist. The mechanical-tectonic model probably applies directly to low-angle normal faults of the lower Colorado River extensional corridor, and aspects of the model (e.g., significance of anisotropy, stress rotation) likely apply to formation of other strong low-angle normal faults. 

   more » « less
5. Density perturbations in the crust indicate potential for blind magmatism beneath magma-poor rifts

   https://doi.org/10.1016/j.tecto.2025.230881  

   Njinju, Emmanuel A; Kolawole, Folarin; Atekwana, Estella A; Ajala, Rasheed; Atekwana, Eliot A; Stamps, D Sarah; Evans, RobL; Katumwehe, Andrew; Barry, Peter H; van_der_Lee, Suzan; et al (October 2025, Tectonophysics)

   Lithospheric weakening mechanisms in non-volcanic segments of active continental rifts remain poorly understood, raising important questions about the geodynamic processes that drive magma-poor rifting. Here, we investigate the crustal and uppermost mantle structure beneath the non-volcanic Albertine-Rhino Graben (ARG) and the adjoining volcanic Edward-George Rift (EGR), East Africa. The ARG exhibits anomalous focusing of intra-rift faulting typically associated with magma-rich, early-stage rifts. Through field observations of rift structures, combined with 3D inversions and 2D forward modeling of gravity data, we investigate the potential controls on intra-rift tectonic strain in a setting with little to no magmatism. Field ground-truthing in the southern ARG reveals prominent rift-axial basement-rooted faulting that post-dates the establishment of border faults. Gravity inversion results show low-density anomalies extending from the surface to about 50 km depth beneath both the EGR and southern ARG, with the strongest anomalies under the ARG at around 15 km. 2D gravity modeling suggests that the lower crust and uppermost mantle are both thinned and less dense beneath these rift segments. In the EGR, crustal thinning and low-density anomalies align with low P-wave velocity zones, suggesting the presence of melt. Given the similar degree of crustal thinning and de-densification in the southern ARG, we infer that trapped lower-crustal melts may also exist beneath the rift, potentially contributing to the early focusing of intra-rift strain. We propose that in non-volcanic rifts, deep, unexposed (‘blind’) melts may play a key role in mechanical weakening of the lithosphere, enabling continued tectonic extension even in the absence of significant surface volcanism. 

   more » « less