A DEEP SCHLUMBERGER SOUNDING TO INVESTIGATE THE ELECTRICAL STRUCTURE OF THE CRUST AND UPPER MANTLE IN SOUTH AFRICA

Geophysics ◽  
1969 ◽  
Vol 34 (3) ◽  
pp. 450-462 ◽  
Author(s):  
J. S. V. Van Zijl
Keyword(s):  
Upper Mantle ◽  
Granite Gneiss ◽  
High Resistivity ◽  
Crust And Upper Mantle ◽  
Current Electrode ◽  
Gneiss Complex ◽  
Final Layer ◽  
Maximum Current ◽  
Electrical Sounding ◽  
Schlumberger Sounding

A deep Schlumberger electrical sounding on the Namaqualand Granite‐Gneiss Complex has been carried out. The sounding center is situated near the middle of this body which measures approximately 500 km by 150 km. Whereas in previous investigations of a similar nature, current electrode spacings have generally been limited to less than 100 km, the use of a telephone line as an emission line has made it possible to extend the maximum current electrode separation to 270 km. Factors which may have influenced the reliability of the measurements include leakage tests, measuring accuracy, lateral effects, and surface electrode effects. The interpretation of the sounding curve which shows the existence of six layers was carried out with the aid of a computer. Some comments are made about the range of the principle of equivalence in the interpretation from the computed results. In particular the results suggest that the lower crust has an extremely high resistivity of approximately 40,000 ohm‐m supposedly due to dehydration. The final layer is conductive.

Electrical conductivity of omphacite and garnet in eclogite: implications for water recycling in the mantle

2020 ◽  
Author(s):  
Hanyong Liu ◽  
Xiaozhi Yang
Keyword(s):  
Electrical Conductivity ◽  
Water Content ◽  
Deep Water ◽  
Upper Mantle ◽  
Critical Role ◽  
High Resistivity ◽  
Water Recycling ◽  
Structural Water ◽  
Crust And Upper Mantle ◽  
Water Contents

<p>Eclogite is an important constituent of subduction slabs and plays a critical role in transporting surface materials (e.g., water) into the deep Earth. Eclogite consists mainly of omphacite and garnet. Although nominally anhydrous, omphacite and garnet contain some amount of structural water (OH) in the lattice, which is up to >1500 ppm wt. H<sub>2</sub>O. This is virtually the highest content in nominally anhydrous minerals (NAMs) derived from the crust and upper mantle (Ingrin and Skogby, 2000). The electrical property of NAMs is very sensitive to water content and a small amount of water could dramatically enhance the conductivity. Thus, laboratory measured conductivity data of omphacite and garnet may help to understand the deep water recycling by eclogitized slab.</p><p>In this study, we have systemically determined the conductivity of omphacite and garnet with different water contents. The experiments were carried out at 350-800 °C, 1 GPa (note that the effect of pressure itself on conductivity is very small) and Ni-NiO buffered conditions. The data show that the conductivity of both omphacite and garnet increases with water content or temperature. The bulk conductivity is then modeled for different mineral compositions and water contents over a range of conditions (Liu et al., 2019). In combination with the geophysically documented high resistivity of the crustal part in deep subducted slabs, we suggest that the water content in omphacite and garnet in the deep-subducted eclogites should not be high at mantle depths. This provides new insights into the deep water recycling by subducted eclogites.</p><p> </p><p><strong>References:</strong></p><p>Ingrin, J., and Skogby, H., 2000, Hydrogen in nominally anhydrous upper-mantle minerals: Concentration levels and implications: European Journal of Mineralogy, 12, 543–570.</p><p>Liu, H., Zhu, Q., and Yang, X., 2019, Electrical conductivity of OH-bearing omphacite and garnet in eclogite: the quantitative dependence on water content: Contributions to Mineralogy and Petrology, 174, doi:10.1007/s00410-019-1593-3.</p><p></p><p></p><p></p><p></p>

scholarly journals Resistivity investigation for well-site definition around Barika Village, Southeast Sulaimany city, Iraqi Kurdistan region.

2016 ◽  
Vol 47 (3) ◽  
pp. 1090
Author(s):  
A. F. Ghaib ◽  
H. Abdulla ◽  
H. Anwar
Keyword(s):  
Electrode Spacing ◽  
High Resistivity ◽  
Kurdistan Region ◽  
Current Electrode ◽  
Vertical Electrical Soundings ◽  
Electrical Resistivity Survey ◽  
Iraqi Kurdistan ◽  
Resistivity Survey ◽  
Maximum Current ◽  
Electrical Soundings

An electrical resistivity survey involving Vertical Electrical Soundings (VES) was carried out in the Barika collective village, southeast of Sulaimany City in the Iraqi Kurdistan Region, to study groundwater characteristics such as depth, thickness and aquifer boundaries. Vertical electrical soundings by Schlumberger array were conducted in this area. The resistivity Schlumberger soundings which have a maximum current electrode spacing (AB) of 800m were carried out at fourteen sites along lines in the NE-SW and NW-SE directions. Interpretation of these soundings showed the presence of three geoelectrical horizons. The upper one is representing the alluvialdeposits with 3Ωm to 60Ωm range of resistivity values reflecting the heterogeneity of the slope deposits. The middle one is taken to be the unconfined jointed aquifer represented by the Tanjero Formation with a resistivity range of 10Ωm to 42Ωm and a thickness range of 24m to 106m. The third horizon is representing the lower part of the TanjeroFormation with a relatively high resistivity range of 51Ωm to 556Ωm. Based on these results and upon our recommendations, a successful water well was drilled yielding quite enough amount of fresh water.

THE CRUST AND UPPER MANTLE STRUCTURES IN CENTRAL ANATOLIA, TURKEY, CONSTRAINED BY GRAVITY AND SEISMIC DATA

2020 ◽  
Author(s):  
Yagmur Yilmaz ◽  
◽  
Alain Plattner ◽  
Rezene Mahatsente ◽  
Ibrahim Çemen ◽  
...  
Keyword(s):  
Upper Mantle ◽  
Seismic Data ◽  
Central Anatolia ◽  
Crust And Upper Mantle

scholarly journals Large-scale variation in seismic anisotropy in the crust and upper mantle beneath Anatolia, Turkey

2021 ◽  
Vol 2 (1) ◽  
Author(s):  
Cédric P. Legendre ◽  
Li Zhao ◽  
Tai-Lin Tseng
Keyword(s):  
Upper Mantle ◽  
Large Scale ◽  
Seismic Anisotropy ◽  
Crust And Upper Mantle ◽  
Wave Splitting ◽  
Mantle Processes ◽  
Open Question ◽  
Subduction System ◽  
Anisotropic Phase ◽  
Regional Tectonics

AbstractThe average anisotropy beneath Anatolia is very strong and is well constrained by shear-wave splitting measurements. However, the vertical layering of anisotropy and the contribution of each layer to the overall pattern is still an open question. Here, we construct anisotropic phase-velocity maps of fundamental-mode Rayleigh waves for the Anatolia region using ambient noise seismology and records from several regional seismic stations. We find that the anisotropy patterns in the crust, lithosphere and asthenosphere beneath Anatolia have limited amplitudes and are generally consistent with regional tectonics and mantle processes dominated by the collision between Eurasia and Arabia and the Aegean/Anatolian subduction system. The anisotropy of these layers in the crust and upper mantle are, however, not consistent with the strong average anisotropy measured in this area. We therefore suggest that the main contribution to overall anisotropy likely originates from a deep and highly anisotropic region round the mantle transition zone.

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