Segmentation of the Andean margin by isostatic models and gradients

Schaller, Theresa; Andersen, Jasmin; Götze, Hans‐Jürgen; Koproch, Nicolas; Schmidt, Sabine; Sobiesiak, M.; Splettstößer, S.

doi:10.1016/j.jsames.2015.01.008

Cited by 13 publications

(4 citation statements)

References 52 publications

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“…The resistivity structure of the continental plate forearc between the coast and the Precordillera is dominated by resistivities >1,000 Ωm (the FHRZ), aside the presence of some LRZs (see next paragraph). The east‐west extent of the FHRZ coincides with a domain of the forearc characterized by higher density (Schaller et al, ), higher P ‐ and S ‐wave velocities (Koulakov et al, ), and lower seismic attenuation (Schurr et al, ) in comparison to the Precordillera. Based on seismic properties of the western forearc and complemented with thermal models of the subduction zone (Springer, ), it was suggested that this region embodies a rigid and cold block (e.g., Schurr et al, ).…”

Section: Discussionmentioning

confidence: 95%

Fluid Distribution in the Central Andes Subduction Zone Imaged With Magnetotellurics

et al. 2019

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We present a model of the electrical resistivity structure of the lithosphere in the Central Andes between 20°and 24°S from 3-D inversion of 56 long-period magnetotelluric sites. Our model shows a complex resistivity structure with significant variability parallel and perpendicular to the trench direction. The continental forearc is characterized mainly by high electrical resistivity (>1,000 Ωm), suggesting overall low volumes of fluids. However, low resistivity zones (LRZs, <5 Ωm) were found in the continental forearc below areas where major trench-parallel faults systems intersect NW-SE transverse faults. Forearc LRZs indicate circulation and accumulation of fluids in highly permeable fault zones. The continental crust along the arc shows three distinctive resistivity domains, which coincide with segmentation in the distribution of volcanoes. The northern domain (20°-20.5°S) is characterized by resistivities >1,000 Ωm and the absence of active volcanism, suggesting the presence of a low-permeability block in the continental crust. The central domain (20.5°-23°S) exhibits a number of LRZs at varying depths, indicating different levels of a magmatic plumbing system. The southern domain (23°-24°S) is characterized by resistivities >1,000 Ωm, suggesting the absence of large magma reservoirs below the volcanic chain at crustal depths. Magma reservoirs located below the base of the crust or in the backarc may fed active volcanism in the southern domain. In the subcontinental mantle, the model exhibits LRZs in the forearc mantle wedge and above clusters of intermediate-depth seismicity, likely related to fluids produced by serpentinization of the mantle and eclogitization of the slab, respectively.

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Section: Discussionmentioning

confidence: 95%

Fluid Distribution in the Central Andes Subduction Zone Imaged With Magnetotellurics

et al. 2019

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“…Two hypotheses have been suggested to explain the locking mechanism of the Peru-Chile subduction zone. The first hypothesis states that a high-density structure, within the forearc, produces a downward buoyancy force, locking the overriding and subducting plates [8,24]. The second hypothesis is that low-density oceanic features on the subducting slab pull the slab upwards during the subduction process and thereby lock the plate interfaces [9,25,26].…”

Section: Introductionmentioning

confidence: 99%

Lithospheric Structure of the Central Andes Forearc from Gravity Data Modeling: Implication for Plate Coupling

Gushurst

Mahatsente

2020

Lithosphere

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Geodetic and seismological data indicates that the Central Andes subduction zone is highly coupled. To understand the plate locking mechanism within the Central Andes, we developed 2.5-D gravity models of the lithosphere and assessed the region’s isostatic state. The densities within the gravity models are based on satellite and surface gravity data and constrained by previous tomographic studies. The gravity models indicate a high-density (~2940 kg m-3) forearc structure in the overriding South American continental lithosphere, which is higher than the average density of the continental crust. This structure produces an anomalous pressure (20-40 MPa) on the subducting Nazca plate, contributing to intraplate coupling within the Central Andes. The anomalous lithostatic pressure and buoyancy force may be controlling plate coupling and asperity generation in the Central Andes. The high-density forearc structure could be a batholith or ophiolite emplaced onto the continental crust. The isostatic state of the Central Andes and Nazca plate is assessed based on residual topography (difference between observed and isostatic topography). The West-Central Andes and Nazca ridge have ~0.78 km of residual topography, indicating undercompensation. The crustal thickness beneath the West-Central Andes may not be sufficient to isostatically support the observed topography. This residual topography may be partially supported by small-scale convective cells in the mantle wedge. The residual topography in the Nazca ridge may be attributed to density differences between the subducting Nazca slab and the Nazca ridge. The high density of the subducted Nazca slab has a downward buoyancy force, while the less dense Nazca ridge provides an upward buoyancy force. These two forces may effectively raise the Nazca ridge to its current-day elevation.

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“…This is due to the fact that the VGG are especially sensitive to shallow density variations, while the gravity anomalies are more useful in the study of deeper density contrasts (Álvarez et al, , ). Recently, more researchers are giving attention to the use of satellite gravity gradients for modeling purposes (Álvarez et al, , ; Ebbing et al, ; Götze & Pail, ; Oruc, ; Schaller et al, ). However, most of the studies interpret the signal with simple (Bouguer) density corrections, without considering the heterogeneities of the different layers of the lithosphere.…”

Section: Introductionmentioning

confidence: 99%

3‐D Modeling of Vertical Gravity Gradients and the Delimitation of Tectonic Boundaries: The Caribbean Oceanic Domain as a Case Study

Gómez-García

Meeßen

Scheck‐Wenderoth

et al. 2019

Geochem Geophys Geosyst

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Geophysical data acquisition in oceanic domains is challenging, implying measurements with low and/or nonhomogeneous spatial resolution. The evolution of satellite gravimetry and altimetry techniques allows testing 3‐D density models of the lithosphere, taking advantage of the high spatial resolution and homogeneous coverage of satellites. However, it is not trivial to discretise the source of the gravity field at different depths. Here, we propose a new method for inferring tectonic boundaries at the crustal level. As a novelty, instead of modeling the gravity anomalies and assuming a flat Earth approximation, we model the vertical gravity gradients (VGG) in spherical coordinates, which are especially sensitive to density contrasts in the upper layers of the Earth. To validate the methodology, the complex oceanic domain of the Caribbean region is studied, which includes different crustal domains with a tectonic history since Late Jurassic time. After defining a lithospheric starting model constrained by up‐to‐date geophysical data sets, we tested several a‐priory density distributions and selected the model with the minimum misfits with respect to the VGG calculated from the EIGEN‐6C4 data set. Additionally, the density of the crystalline crust was inferred by inverting the VGG field. Our methodology enabled us not only to refine, confirm, and/or propose tectonic boundaries in the study area but also to identify a new anomalous buoyant body, located in the South Lesser Antilles subduction zone, and high‐density bodies along the Greater, Lesser, and Leeward Antilles forearcs.

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Segmentation of the Andean margin by isostatic models and gradients

Cited by 13 publications

References 52 publications

Fluid Distribution in the Central Andes Subduction Zone Imaged With Magnetotellurics

Fluid Distribution in the Central Andes Subduction Zone Imaged With Magnetotellurics

Lithospheric Structure of the Central Andes Forearc from Gravity Data Modeling: Implication for Plate Coupling

3‐D Modeling of Vertical Gravity Gradients and the Delimitation of Tectonic Boundaries: The Caribbean Oceanic Domain as a Case Study

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