A magneto‐variation array study in the Central Andes of N Chile and SW Bolivia

Soyer, Wolfgang; Brasse, Heinrich

doi:10.1029/2000gl012095

Cited by 49 publications

(18 citation statements)

References 11 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…However, the existence of this conductor is well documented, but because of the three‐dimensionality of the data its vertical position cannot be sufficiently resolved by 2‐D modelling. Lezaeta (2001) and Soyer & Brasse (2001) derive a shallower location for this conductor from 3‐D forward modelling and intersite geomagnetic transfer function analysis.…”

Section: Discussionmentioning

confidence: 99%

Sensitivity studies applied to a two-dimensional resistivity model from the Central Andes

Schwalenberg

Rath²,

Haak

2002

Geophysical Journal International

View full text Add to dashboard Cite

S U M M A R YLong-period magnetotelluric (MT) data have been collected along an E-W profile across the Central Andes in Northern Chile and Southern Bolivia. A 2-D resistivity model explaining these data was found by inverse modelling. The model includes a prominent conductivity anomaly in the backarc of the South American subduction zone below the Bolivian Altiplano. Another, comparatively localized anomaly occurs beneath the Precordillera in the forearc. The enhanced conductivity in the backarc correlates with reflective zones, low seismic velocities and high seismic attenuation. In contrast, no correlation can be found in the forearc. A strong seismic reflector in context with the down-going slab, and another reflector in the middle crust below the Pre-and Western Cordillera do not coincide with anomalous conductivity.Other 2-D models may also be consistent with the data. We applied different techniques to find the range of relevant models. One simple but useful approach is the direct use of the sensitivity matrix containing the partial derivatives of the data with respect to the model parameters. The sensitivity of the model parameters to the data or data subsets can be visualized by calculating columnwise sums from the sensitivity matrix. These sensitivities may be used to indicate model parameters that are less resolved by the data and thus should not form part of an interpretation. Another approach is to perform systematic studies to establish the validity of geologically important features of the model. These studies comprise forward modelling and the use of a priori information. Combining all approaches generates a more complete assessment of the principal model features.We conclude that a minimum depth extent of the Altiplano conductor can be specified as approximately 50 km. Low sensitivity in the forearc beneath the Longitudinal Valley indicates a limited structure resolution, and therefore may explain the absence of a conductive slab in the model. The existence of the localized conductor below the Precordillera can be established by high sensitivity. Finally, we included the two seismic reflectors in the forearc as a priori information in the inversion process. As a result the absence of a conductive slab in the model is probably a result of low sensitivity, but cannot be totally excluded. A conductive zone coinciding with the strong reflector below the Pre-and Western Cordillera is not manifested by the MT data.

show abstract

Section: Discussionmentioning

confidence: 99%

Sensitivity studies applied to a two-dimensional resistivity model from the Central Andes

Schwalenberg

Rath²,

Haak

2002

Geophysical Journal International

View full text Add to dashboard Cite

show abstract

“…A careful examination of model space, including a sensitivity analysis concerning key model features was carried out by Schwalenberg et al [2002]. Additionally, inter‐station magnetic transfer functions were analyzed by Soyer and Brasse [2001], yielding basically similar models of resistivity distribution.…”

Section: Magnetotelluricsmentioning

confidence: 99%

Coincident anomalies of seismic attenuation and electrical resistivity beneath the southern Bolivian Altiplano plateau

Haberland

Rietbrock

Schurr

et al. 2003

Geophysical Research Letters

Self Cite

View full text Add to dashboard Cite

Reassessment of local earthquake data from the ANCORP seismological network allowed the calculation of 3D attenuation (Qp) tomographic images of crust and upper mantle beneath the southern Bolivian Altiplano around 21° S. The images reveal a low‐Qp middle and lower crust and a moderate‐Qp upper mantle beneath the southern Altiplano. Beneath the recent magmatic arc, Qp is not significantly decreased at this latitude. The distribution of crustal Qp coincides with the variation of electrical resistivity, thus limiting the possible mechanisms causing the anomalies. Our findings support the hypothesis that partial melts in middle and lower crust beneath the Altiplano are present on a large scale. We see no evidence for a shallow asthenosphere beneath the southern Altiplano.

show abstract

“…At latitude 21°S the southern Altiplano crust in Bolivia is characterized by large, coincident geophysical anomalies, in particular a broad and deep‐reaching zone of enhanced conductivity [ Soyer and Brasse , 2001; Brasse et al , 2002], high attenuation of seismic waves [ Haberland et al , 2003] and low velocities [ Heit , 2005], all hinting at the occurrence of large volumes of partial melt [ Schilling et al , 2006]. The high‐conductivity zone leads to severe attenuation of electromagnetic fields which aggravates the resolution of deeper structures, particularly in the upper mantle.…”

Section: Introductionmentioning

confidence: 99%

Electrical conductivity beneath the Bolivian Orocline and its relation to subduction processes at the South American continental margin

Brasse¹,

Eydam²

2008

J. Geophys. Res.

Self Cite

View full text Add to dashboard Cite

A long‐period magnetotelluric data set was obtained during 2002 and 2004 in the central Andes to study the deep electrical conductivity structure in the region of the Bolivian Orocline between latitudes 17°S and 19°S. The profile extends from the Coastal Cordillera in northernmost Chile, crosses the volcanic arc and the Altiplano high plateau in central Bolivia, and ends in the Eastern Cordillera. Two‐dimensional inversion revealed several well‐defined conductivity anomalies: in upper crustal levels the conductive sedimentary basins of the central Altiplano and the resistive Arequipa block beneath the western Altiplano are imaged. Earlier seismological and magnetotelluric investigations on the southern Altiplano inferred a large, highly conductive (partially molten) body in the mid to deep crust. It was assumed that this structure would be underlying the entire plateau, but this is not the case according to the new models. Instead, the most prominent feature in the new investigation area is a high‐conductivity zone at upper mantle depths below the high plateau, which may be interpreted as an image of partial melts and fluids triggered by water supply from the subducting Nazca slab. This conductor would be in accordance with the standard subduction scenario; it is, however, laterally offset by almost 100 km from the volcanic arc. In contrast, the deep crust and upper mantle beneath the arc is moderately resistive. Both observations may hint at an emerging shift of the magmatic/fluid system in the central Andes.

show abstract

A magneto‐variation array study in the Central Andes of N Chile and SW Bolivia

Cited by 49 publications

References 11 publications

Sensitivity studies applied to a two-dimensional resistivity model from the Central Andes

Sensitivity studies applied to a two-dimensional resistivity model from the Central Andes

Coincident anomalies of seismic attenuation and electrical resistivity beneath the southern Bolivian Altiplano plateau

Electrical conductivity beneath the Bolivian Orocline and its relation to subduction processes at the South American continental margin

Contact Info

Product

Resources

About