Lithospheric-scale Models Research Articles

Lithospheric Structure and Extensional Style of the Red Sea Rift Segments

Abstract The Red Sea provides an opportunity to study the processes during the transition from continental rifting to early-stage seafloor spreading during ocean initiation. We delineate variations of lithospheric architecture and the nature of extension along the Red Sea region through joint interpretation of gravity and geoid anomalies and gravity-topography transfer functions. We use lithospheric-scale models to compare stretching factors with upper mantle gravity anomaly, residual mantle Bouguer anomaly, and effective elastic thickness. Based on our observations, the Red Sea is divided into four segments; each having distinct lithospheric characteristics and stretching styles. These are: (i) southernmost Red Sea and Danakil having regionally weak and stretched lithosphere, (ii) southern Red Sea with fully developed seafloor spreading and asymmetric lithospheric architecture, (iii) central Red Sea having discontinuous magma accretion with newly formed seafloor spreading, and (iv) northern Red sea with a stronger lithosphere and limited stretching revealing a stage of continental rifting. In these segments, lithospheric stretching correlates with regions of weak lithosphere, including a regime of sublithospheric plume channel beneath the southern Red Sea. The Zabargad fracture zone between the central and northern segments is revealed as a major lithosphere-scale boundary that may act as a barrier to the propagation of seafloor spreading into the northern Red Sea. The weak and highly stretched lithosphere in this region may indicate the onset of a new spreading cell. Our results conclude that the evolution of the Red Sea is more complex than the previously suggested kinematic models of simple “unzipping” and illustrate that several extensional styles can exist within different segments during the initial stages of ocean formation.

Gravity modelling of the Tyrrhenian-Calabrian-Ionian subduction system

This study provides a lithospheric-scale model along the Ionian Subduction zone in Southern Italy, contributing to the seismotectonic investigation of a region which is affected by relevant historical seismicity. The study employs gravity forward modelling to build the geo-structural model along a composite, NW-SE trending transect extending from the Ionian to the Tyrrhenian Sea, including the Aeolian arc and the Calabro-Peloritan onshore. Through a multidisciplinary approach, we propose new interpretations of three 2D deep-seismic reflection profiles across the study area. Such interpretative profiles are used as constraints to model the observed Bouguer gravity anomalies providing upper and lower crust geometries. Whilst a tomographic model provides constraints for the lithospheric and asthenospheric modelling. The entire workflow is constrained by literature data about Moho geometry, deep seismicity and tomographic images that are integrated to determine the subducting slab geometry. The proposed model of the entire subducting system reasonably fits the observed gravity field and is coherent with the first-order geological and geophysical constraints. The modelling results in updated Tyrrhenian and Ionian Moho depth, subducting slab geometry and location, and densities of the main units, providing valuable input about the composition and geometry of the Calabrian arc structures.

The use of «native» wavelet transform for determining lateral density variation of the Volgo-Uralian subcraton

In the last two decades in conjunction with the development of satellite gravimetry, the techniques of regional-scale inverse and forward gravity modeling started to be more actively incorporated in the construction of crustal and lithospheric scale models. Such regional models are usually built as a set of layers and bodies with constant densities. This approach often leads to a certain difference between the initially used measured gravity field and a gravity field that is produced by the model. One of the examples of this kind of models is a recent lithospheric model of the Volgo-Uralian subcraton. In the current study, we are applying the method of «native» wavelet transform to the residual gravity anomaly for defining the possible lateral density variations within the lithospheric layers of Volgo-Uralia. Keywords: wavelet transform; gravity field inversion; forward gravity modeling; Volgo-Uralian subcraton; satellite gravimetry.

A three-dimensional lithospheric-scale thermal model of Germany

Abstract. We present a 3-D lithospheric-scale model covering the area of Germany that images the regional characteristics of the structural configuration and of the thermal field. The structural model resolves major sedimentary, crustal and lithospheric mantle units integrated from previous studies of the Central European Basin System, the Upper Rhine Graben and the Molasse Basin, together with published geological and geophysical data. A combined workflow consisting of 3-D structural, gravity and thermal modelling is applied to derive the 3-D thermal configuration. The modelled temperature distribution is highly variable in response to an imposed heterogeneous distribution of thermal properties assigned to the different units. First order variations in the temperature field are mainly attributed to the thermal blanketing effect from the sedimentary cover, the variability in the amount of radiogenic heat produced within the different crystalline crust compartments and the implemented topology of the thermal Lithosphere-Asthenosphere Boundary.

Tectonostratigraphic evolution and timing deformation in the Miocene Paso del Sapo Basin: Implications for the Patagonian broken foreland

Several segments of the Central and Southern Andes show deformation evidences located far away from the orogenic front. As a result, a landscape constituted by fault-blocks mountains and intermontane basins occurs. The spatial-temporal distribution of the deformation in these Broken Foreland Systems is still uncertain. Some works suggest that change in space and time of rock uplift along the structures is controlled mainly by older crustal discontinuities. However, other authors propose, a particular deformation pattern between the Andean and extra Andean regions, such as eastward-westward migration of the orogenic front related to subduction zone dynamics. In this work we analyse new structural, geomorphological and tectono-stratigraphical data together with previous chronological scheme (based on U-Pb and magnetostratigraphic ages) of one of the Patagonian Broken Foreland depocenters: the Paso del Sapo Basin. The results allow to perform the tectonostratigraphic evolution of the basin and constrain the timing of deformation in Paso del Sapo Basin at 15–11.5 Ma. Different tectonic structures were activated and de-activated in this time interval, while an older crustal discontinuity – the Río Chubut Medio fault, located at the eastern border of the basin – recorded a continuous tectonic activity throughout the entire evolution of the basin. These evidences show a synchronous tectonic activity for the Andean and extra-Andean Patagonian regions at those times. In addition, the presence of a climax deformation constrained to 15–14.6 Ma and the deceleration of the Río Chubut Medio Fault at 12.2 Ma could be related to eastward expansion and westward retraction of the orogenic front respectively. Therefore, our data indicate that both the presence and absence of a deformation pattern in extra-Andean regions should be considered to suggest alternative lithospheric-scale models.

Modelling Rifting Sequence Stratigraphy Coupled with Surface Process and Thermo-Mechanical Modelling

Rift settings preserve high-fidelity records of their depositional history in response to multiple processes, such as climate change that significantly influences the sediment input, and tectonic deformation which contributes to accommodation generation or consuming. Integrated studies of geomorphology, thermochronology, analog experiments and numerical modelling improved our understanding of the rifting processes and associated structural evolution. However, the interplay between climate change, sediment transport from eroding highland to rift basins and rift-related deformation is poorly understood.We present a forward numerical scheme that couples surface process with thermo-mechanical modelling on a rift setting. In the coupling numerical framework, a 2D (potentially 3D) lithospheric scale model is set up. The erosion, sediment transport and deposition are controlled by surface processes with the boundary conditions of climate force (precipitation) and erosion coefficient. The resulting sediment volumes are transferred to the thermo-mechanical system, which has significant effect of crustal deformation. The produced tectonic uplift or subsidence then contributes to the change of surface topography and thus the sediment routing. We focus on investigating the climatic controls on source dynamics, sediment transport, and the deposition in both marine and nonmarine environments. We then quantify the influence of sediment accumulation on crustal deformation and rift evolution. The resulting stratigraphic architecture will be analyzed through evolving stratal stacking patterns and shoreline trajectories to explore the feedbacks between erosion/deposition patterns and the rift structural. We will then apply our modelling to typical rifting examples such as East Africa rift system.

SLIM3D: A tool for three-dimensional thermomechanical modeling of lithospheric deformation with elasto-visco-plastic rheology

We describe a new technique for three-dimensional lithospheric-scale modeling of solid state deformation including strain localization processes. The new code, SLIM3D, includes a coupled thermo-mechanical treatment of deformation processes and allows for an elasto-visco-plastic rheology with diffusion, dislocation and Peierls creep mechanisms and Mohr–Coulomb plasticity. The code incorporates an arbitrary Lagrangian Eulerian formulation with free surface and Winkler boundary conditions. SLIM3D is developed and implemented using the C++ object-oriented programming language. We describe aspects of physical models as well as details of the numerical implementation, including the Newton–Raphson solver, the stress update procedure, and the tangent operator. The applicability of the code to lithospheric-scale modeling is demonstrated by a number of benchmark problems that include: (i) the bending of an elastic plate, (ii) the sinking of a rigid cylinder into a viscous fluid, (iii) the initiation of shear bands in the brittle crust, (iv) triaxial compression test, and (v) lithospheric transpressional deformation. Finally, we discuss possible directions of further development.

Late Mesozoic extensional tectonics in the North China block: a crustal response to subcontinental mantle removal?

Abstract In the North China block, Cretaceous extensional tectonics is expressed by numerous syntectonic plutons bounded by ductile normal faults and several metamorphic core complexes (MCC). Cretaceous half-grabens filled by continental terrigenous deposits are widespread. The examples of MCC from South Liaoning Peninsula, Yiwulüshan, Hohhot as well as the Yunmengshan syntectonic pluton spread along ca 2000 km suggest that the early Cretaceous extensional tectonics in the North China block is globally symmetric. The geodynamics setting of this continental-scale extension remains disputed. It is not satisfactorily explained by back-arc rifting related to the Paleo-Pacific subduction or crustal “unthickening”. Mantle lithosphere removal is, however, considered. Upwelling of asthenosphere may be the origin of heat advection and fluid transfer from mantle to lower crust, thus triggerring the Cretaceous magmatism, crustal softening and diffuse continental stretching. Several possible lithosphere-scale models, such as convective removal of mantle lithosphere and detachment of a large piece of mantle, are discussed.

Numerical modelling of a mantle plume: the plume head–lithosphere interaction in the formation of an oceanic large igneous province

The thermomechanical processes associated with formation of large igneous provinces (LIPs) remain poorly understood owing to fundamental difficulties in simulating plume–lithosphere interactions in current numerical models. These models, which aim to simulate the rise of mantle plume and the spread of plume head material, imply a mechanically over-simplified lithosphere and, commonly, a flat lithosphere (zero vertical displacement) as the upper boundary condition. We propose a new numerical model, derived from lithospheric-scale models. It has a high numerical resolution in the lithospheric domain and explicitly accounts for: (1) free upper surface boundary condition, (2) elastic–plastic–ductile lithospheric rheology, including surface faulting, and (3) vertical strength variations in the lithosphere. We study the final stages of plume ascent and we focus on surface and lithospheric evolution and intra-plate strain localisations. The experiments predict that the first surface elevation occurs in less than 0.2 Ma after plume initiation at 400 km depth. Variation of rheological parameters results in different surface elevations (500–2500 m), ascent (2–10 m/yr) and base plate strain rates (10 −12–10 −15 s −1). Fast (0.2–0.3 m/yr) plume head flattening starts at the moment when the plume head reaches the base of the lithosphere. It leads to large-scale extension and deep normal faulting at the centre of the plateau, and to strong thermomechanical erosion at its base. The erosion is maximal not under the plume centre (as was predicted before), but in two large bordering zones. Our study locally is the igneous province of the Caribbean plate where the pre-existing (Farallon) lithosphere has been affected by the Galapagos hotspot activity that generated thermal perturbations and crustal thickening with two main episodes of volcanism and underplating.

Lithospheric‐scale structure across the Bolivian Andes from tomographic images of velocity and attenuation for P and S waves

We have developed a three‐dimensional, lithospheric‐scale model across the Bolivian Andes at ∼20°S, based on tomographic images of velocity and attenuation for both P and S waves. Observations of travel time and attenuation for this study are from regional, mantle earthquakes in the subducted Nazca plate recorded on a portable, broadband seismic array (Broadband Andean Joint Experiment and Seismic Exploration of the Deep Andes) in Bolivia and Chile. The shallow mantle under the Altiplano from ∼18°S to ∼21°S is high‐velocity and moderately high Q (Vp ≈ 8.3,Vs ≈ 4.7, Qp ≈ 500, and Qs ≈ 200), suggesting lithospheric mantle. High‐velocity material in the Altiplano extends to a depth of ∼125–150 km. The shallow mantle of the Western Cordillera is characterized by high Vp/Vs (∼1.83), suggesting a correlation between Vp/Vs and arc volcanism. Seismic velocity in the Western Cordillera mantle is, on average, only slightly reduced from global averages; however, velocity and attenuation anomalies are locally strong ( Vp ≈ 7.8, Vs ≈ 4.3, Qp ≈ 200, and Qs ≈ 100), consistent with partial melt conditions. Under the Los Frailes volcanic field, in the Eastern Cordillera, shallow mantle velocity and Q decrease drastically from the neighboring Altiplano ( Vp ≈ 7.8, Vs ≈ 4.3, Qp ≈ 300, Qs ≈ 100); however, high Vp/Vs is not as pervasive as it is in the Western Cordillera. We believe that slab‐derived water, and perhaps other volatiles, strongly influence the Western Cordillera, while the Eastern Cordillera low‐velocity region is more affected by partial melt and/or compositional changes. Average velocity and Q in the shallow mantle across the Bolivian Andes, where the tomographic images are best resolved, are significantly higher than in most mantle wedge environments where corresponding images are available. This is likely the result of a compressional “back arc” setting in the Andes. This implies that lithospheric shortening and thickening associated with the formation of the Andes has profoundly influenced the shallow mantle structure across the range. Shallow mantle structure is locally influenced by the subduction processes, particularly under the Western Cordillera; however, the differing volcanism and seismic character under the two Cordilleras suggest that the volcanic process in the Eastern Cordillera may be distinct from arc volcanism. Tertiary volcanism in the Eastern Cordillera is located in the region where mantle shortening is suspected to be greatest. Both the timing and location of volcanism are consistent with upward migration of mantle wedge asthenosphere following the removal of over thickened lithosphere.