P. Schmoldt, PhD - MTNet - DIAS

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9. Data collection and processing constraint at greater depth given their limited period range and larger errors. The multistrike analysis yields directions of N30.0E and N29.4E (0.8 av. RMS misfit) for the Tajo Basin of the lithospheric-mantle with depth down to 100 km and 120 km, respectively; as well as a direction of N20.2E (0.7 av. RMS misfit) for the asthenosphere. The significantly different values indicate that the geoelectric strike below the Tajo Basin varies between lithospheric and asthenospheric parts of the mantle, and that the LAB is likely to be found at depth below 120 km. The latter assumption is based on the fact that the observed strike direction is similar for the depth ranges with and without the interval 100 – 120 km, indicating that this interval agrees with structures of the region above. This observation, however, is not well constraint since structures for such a thin layer at this depth are not well resolved. The true strike directions for the lithosphericmantle can be assumed to possess an orientation between 0 and 90 degrees, rather than the orthogonal direction, considering the results of seismic tomography studies in this regions, indicating a NE-SW geological strike (cf. Section 7.3.2). Lithospheric depth Finally, despite indications for different strike directions of crust and mantle by previous analyses and seismic results (cf. Sec. 7.3.2), it is tested whether a reasonable, common strike direction can be found for the depth range spanning from intermediate crust to LAB. The multi-strike analysis yields a direction of N37.2E (1.1 av. RMS misfit) and N35.3E (1.1 av. RMS misfit) for the Tajo Basin lithosphere with an assumed LAB depth of 100 km and 120 km respectively; coincident with a range of low RMS misfit in the main plot of Figure 9.11. For the whole profile a direction of N15.0E is determined, which however does not fit with the RMS distribution of stations in the Betic Cordillera. In principle, a common geoelectric strike direction of intermediate crust, lower crust and lithospheric-mantle can be found: However, certain aspects favour a separate treatment of the two regions, namely the higher average RMS misfit for the combined range indicating an inferior fit of local structures and, more importantly, results of the other geophysical methods that are in favour of two different strike directions at crust and mantle depths (cf. Sec. 7.3.2). Conclusions Thorough investigation of the geoelectric strike direction beneath the PICASSO Phase I profile presented in the previous paragraphs results in the following conclusions: 216 • Strike characteristics differ between the southern region of the profile associated with the Betic Cordillera, and the northern region associated with the Tajo Basin. The Betic Cordillera exhibits complex subsurface structures for the whole depth range for which no distinct geoelectric strike direction can be identified, whereas for the Tajo Basin common geoelectric strike directions can be fitted to the majority of the different depth layers.
0 km 10 km 30 km 100 km 300 km Depth range Depth: 12 – 100 km (lithosphere) 90 75 60 45 30 15 0 pic041 pic040 pic037 pic035 pic033 pic031 9.6. Compensating for distortion of the impedance tensor pic029 pic027 pic025 Depth: 12 – 120 km (lithosphere) 90 75 60 45 30 15 0 pic041 pic040 pic037 pic035 pic033 pic031 Betic Cordillera pic029 pic027 pic025 pic023 pic023 CIZ pic022 pic022 pic020 pic020 pic019 pic019 pic017 pic017 pic015 pic015 Multi-strike (Av. RMS-misfit in brackets) pic013 pic013 pic011 pic011 pic009 pic009 pic007 Multi-strike (Av. RMS-misfit in brackets) pic007 Tajo Basin pic006 pic006 All stations Tajo Basin 15.0 (1.2) 37.2 (1.1) pic005 pic005 pic004 pic004 pic003 pic003 pic002 All stations Tajo Basin 15.0 (1.2) 35.9 (1.1) Fig. 9.11.: RMS misfit for different geoelectric strike directions of stations recorded during PICASSO Phase I, using data in the Niblett-Bostick depth ranges 12 – 100 and 12 – 120 km; shown in the inset. Empty spaces are due to lack of data for this depth range at the respective station. Also shown in the top right corner is the optimal common geoelectric strike direction clockwise from North calculated for all stations and for stations in the Tajo Basin only; indicated by dashed and dotted white lines in the main plot, respectively. Assignment of stations to the different geological regions, displayed on the bottom of the plot, is based on their location in respect to geological units of the USGS EnVision map for Europe (Fig. 9.1), CIZ: Central Iberian Zone, part of the Iberian Massif. See text for further details. • Beneath the Tajo Basin, four groups of layers are derived according to their preferential geoelectric strike direction, namely upper crust (≤ 10 km), combined intermediate and lower crust (12 - 30 km), lithospheric-mantle (35 - 120 km), and asthenosphere (≥ 140 km). Among these, structures in the upper crust are found to be relatively heterogeneous, and structures of the asthenosphere are less constrained due to their greater depth. • Layers in the Tajo Basin subsurface can be grouped into two bands: crustal layers with a geoelectric strike direction of N40.9W, determined for the structures of the intermediate and lower crust; and mantle layers with a geoelectric strike direction of N29.4E, associated with the lithospheric-mantle. The strike direction of the lithospheric-mantle is similar to the direction of the asthenosphere (N20.2E) and can be expected to provide a suitable estimation for the upper mantle given that constraints on the asthenosphere are weaker due to decreasing resolution of the MT method with depth. • The determined geoelectric strike direction at mantle depth is not in agreement with derived plate motion of Eurasia (at Long: 3W, Lat: 40N), i.e. N50.6E (2.5 cm/a) [Argus and Gordon, 1991] and N50.5E (2.4 cm/a) [De Mets et al., 1994]. It is therefore unlikely that the mantle geoelectric strike direction originates from processes in connection with relative plate motion. Thus, it is unlikely that effects of anisotropic structures, caused by lattice preferred orientation from drag along alignment pic002 pic001 pic001 RMS misfit 4 3 2 1 0 RMS misfit 4 3 2 1 0 217
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Multidimensional isotropic and anis
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Contents 2.3. Deviation from plane
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Contents 8.3. Inversion of 3D model
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List of Figures 2.1. Amplitude of t
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List of Figures 4.17. Visual repres
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List of Figures 8.2. Ambient noise
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List of Figures 10.10.RMS misfit va
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List of Figures A.15.Result of anis
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List of Tables xviii 5.5. Parameter
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List of Acronyms FE finite element
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List of Symbols Below is a list of
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Symbol SI unit Denotation φ · pha
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Abstract The Tajo Basin and Betic C
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Publications Poster presentations x
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Acknowledgements Team, namely Colin
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Introduction 1 The Iberian Peninsul
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ections from enhanced one-dimension
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Part I Theoretical background of ma
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2. Sources for magnetotelluric reco
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Mathematical description of electro
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yields 3.2. Deriving magnetotelluri
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3.2. Deriving magnetotelluric param
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3.3. Magnetotelluric induction area
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Depth d s d 1 d 2 d n-2 d n-1 t 1 t
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3.4. Boundary conditions materials
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3.5. The influence of electric perm
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Distortion of magnetotelluric data
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4.1. Types of distortion Fig. 4.1.:
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J s 0 s 0 4.1. Types of distortion
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Scale Type Terminology Example Atom
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4.1. Types of distortion the use of
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4.2. Dimensionality Fig. 4.12.: The
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1D 2D local 3D/1D 3D/2D regional 4.
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4.3. General mathematical represent
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4.4. Removal of distortion effects
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Parameter Geoelectrical application
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4.4.5. Caldwell-Bibby-Brown phase t
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Method Applicability Swift angle 2D
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5. Earth’s properties observable
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6. Using magnetotellurics to gain i
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Part II Geology of the study area I
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7. Geology of the Iberian Peninsula
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Page 202 and 203: 7. Geology of the Iberian Peninsula
Page 205 and 206: Recovering a synthetic 3D subsurfac
Page 207 and 208: direction direction Depth: 12 - 30
Page 209 and 210: 8.2. Generating synthetic 3D model
Page 211 and 212: Distance from the centre of the mes
Page 213 and 214: 3D N45W 3D-crust TE Rho TE Phi Peri
Page 215 and 216: 8.3. Inversion of 3D model data sch
Page 217 and 218: Model variation RMS misfit Optimal
Page 219 and 220: Profile: 3D-crust (TM-only) Depth (
Page 221 and 222: Parameter Value 8.3. Inversion of 3
Page 223 and 224: Depth (km) 10 -2 10 -1 10 0 10 1 10
Page 225 and 226: Depth (km) 10 -2 10 -1 10 0 10 1 10
Page 227 and 228: Step 1: Isotropic 2D inversion Step
Page 229 and 230: 8.3. Inversion of 3D model data par
Page 231 and 232: 8.4. Summary and conclusions bution
Page 233 and 234: Regularisation order Smoothing para
Page 235 and 236: S N 1% 0 Depth (km) 3% Depth (km) 1
Page 237 and 238: 9.1. Profile location Data collecti
Page 239 and 240: Location (degrees) Recording period
Page 241 and 242: Geological region Stations Geologic
Page 243 and 244: 9.4. Segregation of data acquired w
Page 245 and 246: Phase (degrees) 135 90 45 0 Z xy -4
Page 247 and 248: 0 km 10 km 30 km 100 km 300 km Dept
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Page 255 and 256: Pseudo-sections crustal strike dire
Page 257 and 258: 9.8. Analysis of vertical magnetic
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Page 262 and 263: 10. Data inversion WinGLink softwar
Page 264 and 265: a (horizontal smoothing) 10. Data i
Page 266 and 267: 10. Data inversion Short period ran
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Page 274 and 275: 10. Data inversion Depth (km) S N 0
Page 276 and 277: Depth (km) 10. Data inversion S N 0
Page 278 and 279: 10. Data inversion Group velocity m
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Page 290 and 291: 10. Data inversion isotropic 2D lay
Page 292 and 293: 10. Data inversion Depth (km) Depth
Page 298 and 299: 10. Data inversion tigation is usua
Page 300 and 301: Depth (km) Depth (km) 10. Data inve
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Modelled Observed Modelled Observed
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Depth (km) 10. Data inversion 0 30
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10. Data inversion Depth off LAB (k
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10. Data inversion Depth (km) S 0 5
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10. Data inversion 10.3. Summary an
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10. Data inversion owing to availab
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11 Summary and conclusions The key
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11.2. PICASSO Phase I investigation
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A. Appendix Eocene 54 Ma 42 Ma 36 M
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A. Appendix A.2. Auxiliary informat
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A. Appendix 292 Fig. A.3.: Issues i
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A. Appendix A.2.4. Computation time
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296 3D-mantle profile Inversion res
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298 07-centre profile The profile 0
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300 3D-crust profile The profile 3D
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302 J-centre profile The J-centre p
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A. Appendix Anisotropy Resistivity
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A. Appendix A.4. Auxiliary figures
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A. Appendix 314 ρ TE(Ω−m) φ T
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A. Appendix 320 pic003 (off-diagona
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A. Appendix 322 pic013 (off-diagona
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Bibliography Abalos, B., J. Carrera
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Bibliography Artemieva, I. M. (2006
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Bibliography Berdichevsky, M., V. D
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Bibliography Cebriá, J.-M., and J.
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Bibliography de Vicente, G., J. Gin
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Bibliography Egbert, G. D., and J.
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Bibliography Ganapathy, R., and E.
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Bibliography Haak, V., and R. Hutto
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Bibliography Hutton, R. (1972), Som
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Bibliography Jones, A. G., and R. W
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Bibliography Kurtz, R. D., J. A. Cr
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Bibliography Lviv Centre of Institu
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Bibliography Merrill, R. T., and M.
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Bibliography Newman, G., and G. Hoh
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Bibliography Pádua, M. B., A. L. P
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Bibliography Prácser, E., and L. S
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Bibliography Ritter, J. R. R., M. J
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Bibliography Serson, P. H. (1973),
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Bibliography Spitzer, K. (2006), Ma
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Bibliography Tikhonov, A. N., and V
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Bibliography Wanamaker, B. J., and
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Bibliography Xu, Y., C. McCammon, a
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P. Schmoldt, PhD - MTNet - DIAS

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