P. Schmoldt, PhD - MTNet - DIAS
P. Schmoldt, PhD - MTNet - DIAS P. Schmoldt, PhD - MTNet - DIAS
7. Geology of the Iberian Peninsula Fig. 7.28.: Rheological profiles of the Tajo Basin (northern part on the left-hand and southern part on the right-hand side) in terms of tension and compression at a strain rate of 10 −15 s −1 for rheological parameters given in Table 7.4. Outer black lines bind differential stress estimated for dry rock composition; inner black lines denote stress for wet rock composition of the upper crust (quartzite or granite) and lithospheric-mantle (peridotite). Geometric symbols mark the base of competent layers for the upper, middle, and lower crust as well as the lithospheric-mantle, i.e. : wet quartzite, : quartzdiorite, : wet peridotite, ⋄: dry peridotite; note that only wet rock data shown for the upper crust, from Tejero and Ruiz [2002]. Rheological property Thickness (km) Central Spain Central Betic Cordillera Elastic thickness Te 20 - 25 15 - 20 Mechanical strong upper crust (MSUC) ∼18 ∼15 Mechanical strong lower crust (MSLC) 6 - 10 ∼11 Mechanical strong upper mantle (MSL) 8 - 12 ∼6 Tab. 7.5.: Rheological properties of the regions relevant for the PICASSO Phase I investigation of the Iberian subsurface; the values are visually derived from the thermal and rheological European lithosphere model by Tesauro et al. [2009a, Figs. 3, 4]. ties, with characteristic values of the radiogenic heat production for each crustal layer are presented by Tesauro et al. [2009a] and Tesauro et al. [2009b]. The authors use the seismic tomography model by Koulakov et al. [2009], which incorporates teleseismic events as well as travel time data, with a correction of the travel times based on the EuCrust- 07 model [Tesauro et al., 2008]. For the region coinciding with the PICASSO Phase I profile, the authors derive a depth between 120 km and 130 km for the 1200°C isotherm, indicating the lithosphere–asthenosphere transition. In their model, Tesauro et al. [2009a] and Tesauro et al. [2009b] further infer temperatures of approximately 880 – 980°C and 1120°C at 60 km and 100 km depth, respectively. From their thermal model, in combination with the EuCrust-07 model [Tesauro et al., 2008], the authors derive rheological settings for the European lithosphere with properties of the region most relevant for the PI- CASSO Phase I investigation summarised in Table 7.5. However, results by Tesauro et al. [2009a] and Tesauro et al. [2009b] are associated with a higher degree of uncertainty since they are based on seismic data, which have lower resolution in Iberia; aggravated by the fact that the model is of European scale, hence down-weighting local effects. The lower resolution in Iberia is therein due to its location on the edge of the European continent as 164
7.3. Tajo Basin and central Spain Fig. 7.29.: Comparison of estimates for the continental crust in the Spanish Central System (Central Spain) by Villaseca et al. [1999] (using seismic data by Banda et al. [1981]) with the standard profile for the European continental crust derived by Wedepohl [1995] from an integrated 3000 km long geotraverse (seismic velocities in km/s), from Villaseca et al. [1999]. well as the low station coverage on the peninsula. Xenoliths studies Villaseca et al. [1999] studied xenolith-bearing alkaline dykes, intruded into the Variscan basement of the SCS in early Mesozoic times, and conclude that these xenoliths represent lower continental crust material as indicated by thermobarometric calculations based on mineral paragenesis. From their results, revealing a felsic granulite composition of the lower continental crust in Spain in contrast to the more mafic lower-crustal composition estimated in other European Variscan areas, the authors deduce that the crust in this region is not underplated (Fig. 7.29). A non-underplated crust implies the absent of mafic and ultramafic materials in the lithospheric-mantle, which would in turn imply relative low seismic velocity and increased electric resistivity in this region. 7.3.3. Summary and conclusions From previous geophysical studies it can be inferred that the subsurface below the Tajo Basin contains sedimentary cover with a thickness of 3 km on top of three crustal layers, reaching down to depths of 8 – 12 km, 23 – 25 km, and 30 – 33 km, respectively. It has been further proposed, based on results of thermal modelling studies and transformation of seismic tomography data, that the tLAB is located at a depth between 110 km and 130 km beneath the Tajo Basin. The upper crustal layer is thought to be formed from 165
- Page 150 and 151: 6. Using magnetotellurics to gain i
- Page 152 and 153: 6. Using magnetotellurics to gain i
- Page 154 and 155: 6. Using magnetotellurics to gain i
- Page 156 and 157: 6. Using magnetotellurics to gain i
- Page 158 and 159: 6. Using magnetotellurics to gain i
- Page 160 and 161: 6. Using magnetotellurics to gain i
- Page 162 and 163: 6. Using magnetotellurics to gain i
- Page 164 and 165: 6. Using magnetotellurics to gain i
- Page 168 and 169: Part II Geology of the study area I
- Page 170 and 171: 7. Geology of the Iberian Peninsula
- Page 172 and 173: 7. Geology of the Iberian Peninsula
- Page 174 and 175: 7. Geology of the Iberian Peninsula
- Page 176 and 177: 7. Geology of the Iberian Peninsula
- Page 178 and 179: 7. Geology of the Iberian Peninsula
- Page 180 and 181: 7. Geology of the Iberian Peninsula
- Page 182 and 183: 7. Geology of the Iberian Peninsula
- Page 184 and 185: 7. Geology of the Iberian Peninsula
- Page 186 and 187: 7. Geology of the Iberian Peninsula
- Page 188 and 189: 7. Geology of the Iberian Peninsula
- Page 190 and 191: 7. Geology of the Iberian Peninsula
- Page 192 and 193: 7. Geology of the Iberian Peninsula
- Page 194 and 195: 7. Geology of the Iberian Peninsula
- Page 196 and 197: 7. Geology of the Iberian Peninsula
- Page 198 and 199: 7. Geology of the Iberian Peninsula
- 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
- Page 249 and 250: 0 km 10 km 30 km 100 km 300 km Dept
7.3. Tajo Basin and central Spain<br />
Fig. 7.29.: Comparison of estimates for the continental crust in the Spanish Central System (Central Spain) by Villaseca et al. [1999]<br />
(using seismic data by Banda et al. [1981]) with the standard profile for the European continental crust derived by Wedepohl [1995]<br />
from an integrated 3000 km long geotraverse (seismic velocities in km/s), from Villaseca et al. [1999].<br />
well as the low station coverage on the peninsula.<br />
Xenoliths studies<br />
Villaseca et al. [1999] studied xenolith-bearing alkaline dykes, intruded into the Variscan<br />
basement of the SCS in early Mesozoic times, and conclude that these xenoliths represent<br />
lower continental crust material as indicated by thermobarometric calculations based on<br />
mineral paragenesis. From their results, revealing a felsic granulite composition of the<br />
lower continental crust in Spain in contrast to the more mafic lower-crustal composition<br />
estimated in other European Variscan areas, the authors deduce that the crust in this region<br />
is not underplated (Fig. 7.29). A non-underplated crust implies the absent of mafic and<br />
ultramafic materials in the lithospheric-mantle, which would in turn imply relative low<br />
seismic velocity and increased electric resistivity in this region.<br />
7.3.3. Summary and conclusions<br />
From previous geophysical studies it can be inferred that the subsurface below the Tajo<br />
Basin contains sedimentary cover with a thickness of 3 km on top of three crustal layers,<br />
reaching down to depths of 8 – 12 km, 23 – 25 km, and 30 – 33 km, respectively. It has<br />
been further proposed, based on results of thermal modelling studies and transformation<br />
of seismic tomography data, that the tLAB is located at a depth between 110 km and<br />
130 km beneath the Tajo Basin. The upper crustal layer is thought to be formed from<br />
165
Change language