Fabrication and properties of three-dimensional seismic models of the upper mantle

1966 ◽  
Vol 10 (3) ◽  
pp. 290-299 ◽  
Author(s):  
Ludvík Waniek
Keyword(s):  
Upper Mantle ◽  
Three Dimensional ◽  
Seismic Models

Plumbing and architecture of a crustal mineralizing system in the Archean Superior Province, Canada

2021 ◽  
Author(s):  
Eric Roots ◽  
Graham Hill ◽  
Ben M. Frieman ◽  
James A. Craven ◽  
Richard S. Smith ◽  
...  
Keyword(s):  
Upper Mantle ◽  
Spatial Association ◽  
Three Dimensional ◽  
3D Models ◽  
Superior Province ◽  
Seismic Reflection Data ◽  
Reflection Data ◽  
Abitibi Subprovince ◽  
Lower Crustal

<p>The role of melts and magmatic/metamorphic fluids in mineralization processes is well established. However, the role of crustal architecture in defining source and sink zones in the middle to lower crust remains enigmatic. Integration of three dimensional magnetotelluric (MT) modelling and seismic reflection data across the Archean Abitibi greenstone belt of the Superior Province, Canada, reveals a ‘whole-of-crust’ mineralizing system and highlights the controls by crustal architecture on metallogenetic processes. Electrically conductive conduits in an otherwise resistive upper crust are coincident with truncations and offsets of seismic reflections that are mostly interpreted as major brittle-ductile fault zones. The spatial association between these features and low resistivity zones imaged in the 3D models suggest that these zones acted as pathways through which fluids and melts ascended toward the surface. At mid-crustal levels, these ‘conduit’ zones connect to ~50 km long, north-south striking conductors, and are inferred to represent graphite and/or sulphide deposited from cooling fluids. At upper mantle to lower crustal depths, east-west trending conductive zones dominate and display shallow dips. The upper mantle features are broadly coincident with the surface traces of the major deformation zones with which a large proportion of the gold endowment is associated. We suggest that these deep conductors represent interconnected graphitic zones perhaps augmented by sulphides that are relicts from metamorphic fluid and melt emplacement associated primarily with the later stages of regional deformation.  Thus, from the combined MT and seismic data, we develop a crustal-scale architectural model that is consistent with existing geological and deformational models, providing constraints on the sources for and signatures of fluid and magma emplacement that resulted in widespread metallogenesis in the Abitibi Subprovince.</p>

scholarly journals Antarctic Upper Mantle Rheology

2021 ◽  
pp. M56-2020-19
Author(s):  
E. R. Ivins ◽  
W. van der Wal ◽  
D. A. Wiens ◽  
A. J. Lloyd ◽  
L. Caron
Keyword(s):  
Wave Velocity ◽  
Upper Mantle ◽  
Effective Viscosity ◽  
Seismic Velocity ◽  
Imaging Techniques ◽  
Three Dimensional ◽  
Velocity Model ◽  
Mantle Flow ◽  
S Wave ◽  
Velocity Changes

AbstractThe Antarctic mantle and lithosphere are known to have large lateral contrasts in seismic velocity and tectonic history. These contrasts suggest differences in the response time scale of mantle flow across the continent, similar to those documented between the northeastern and southwestern upper mantle of North America. Glacial isostatic adjustment and geodynamical modeling rely on independent estimates of lateral variability in effective viscosity. Recent improvements in imaging techniques and the distribution of seismic stations now allow resolution of both lateral and vertical variability of seismic velocity, making detailed inferences about lateral viscosity variations possible. Geodetic and paleo sea-level investigations of Antarctica provide quantitative ways of independently assessing the three-dimensional mantle viscosity structure. While observational and causal connections between inferred lateral viscosity variability and seismic velocity changes are qualitatively reconciled, significant improvements in the quantitative relations between effective viscosity anomalies and those imaged by P- and S-wave tomography have remained elusive. Here we describe several methods for estimating effective viscosity from S-wave velocity. We then present and compare maps of the viscosity variability beneath Antarctica based on the recent S-wave velocity model ANT-20 using three different approaches.

Electromagnetic images of the Trans-Hudson orogen: the North American Central Plains anomaly revealed

2005 ◽  
Vol 42 (4) ◽  
pp. 457-478 ◽  
Author(s):  
Alan G Jones ◽  
Juanjo Ledo ◽  
Ian J Ferguson
Keyword(s):  
Electrical Properties ◽  
North American ◽  
Upper Mantle ◽  
Lithospheric Mantle ◽  
Three Dimensional ◽  
Conductivity Anomaly ◽  
Central Plains ◽  
Slave Craton ◽  
The North ◽  
Kimberlite Field

Magnetotelluric studies of the Trans-Hudson orogen over the last two decades, prompted by the discovery of a significant conductivity anomaly beneath the North American Central Plains (NACP), from over 300 sites yield an extensive database for interrogation and enable three-dimensional information to be obtained about the geometry of the orogen from southern North Dakota to northern Saskatchewan. The NACP anomaly is remarkable in its continuity along strike, testimony to along-strike similarity of orogenic processes. Where bedrock is exposed, the anomaly can be associated with sulphides that were metamorphosed during subduction and compression and penetratively emplaced deep within the crust of the internides of the orogen to the boundary of the Hearne margin. A new result from this compilation is the discovery of an anomaly within the upper mantle beginning at depths of ~80–100 km. This lithospheric mantle conductor has electrical properties similar to those for the central Slave craton mantle conductor, which lies directly beneath the major diamond-producing Lac de Gras kimberlite field. While the Saskatchewan mantle conductor does not directly underlie the Fort à la Corne kimberlite, which is associated with the Sask craton, the spatial correspondence is close.

Large‐scale three‐dimensional seismic models and their interpretive significance

Geophysics ◽  
1990 ◽  
Vol 55 (9) ◽  
pp. 1166-1182 ◽  
Author(s):  
Irshad R. Mufti
Keyword(s):  
Finite Difference ◽  
Wave Field ◽  
Large Scale ◽  
Three Dimensional ◽  
Synthetic Data ◽  
Real Data ◽  
The Real ◽  
Need To Evaluate ◽  
Zero Offset ◽  
Seismic Models

Finite‐difference seismic models are commonly set up in 2-D space. Such models must be excited by a line source which leads to different amplitudes than those in the real data commonly generated from a point source. Moreover, there is no provision for any out‐of‐plane events. These problems can be eliminated by using 3-D finite‐difference models. The fundamental strategy in designing efficient 3-D models is to minimize computational work without sacrificing accuracy. This was accomplished by using a (4,2) differencing operator which ensures the accuracy of much larger operators but requires many fewer numerical operations as well as significantly reduced manipulation of data in the computer memory. Such a choice also simplifies the problem of evaluating the wave field near the subsurface boundaries of the model where large operators cannot be used. We also exploited the fact that, unlike the real data, the synthetic data are free from ambient noise; consequently, one can retain sufficient resolution in the results by optimizing the frequency content of the source signal. Further computational efficiency was achieved by using the concept of the exploding reflector which yields zero‐offset seismic sections without the need to evaluate the wave field for individual shot locations. These considerations opened up the possibility of carrying out a complete synthetic 3-D survey on a supercomputer to investigate the seismic response of a large‐scale structure located in Oklahoma. The analysis of results done on a geophysical workstation provides new insight regarding the role of interference and diffraction in the interpretation of seismic data.

Deep electrical structure of northern Alberta (Canada): implications for diamond exploration

2009 ◽  
Vol 46 (2) ◽  
pp. 139-154 ◽  
Author(s):  
Erşan Türkoğlu ◽  
Martyn Unsworth ◽  
Dinu Pana
Keyword(s):  
Subduction Zone ◽  
Upper Mantle ◽  
Lithospheric Mantle ◽  
Three Dimensional ◽  
Diamond Formation ◽  
Magnetotelluric Data ◽  
Diamond Exploration ◽  
Upper Mantle Structure ◽  
Resistivity Model ◽  
Northern Alberta

Geophysical studies of upper mantle structure can provide constraints on diamond formation. Teleseismic and magnetotelluric data can be used in diamond exploration by mapping the depth of the lithosphere–asthenosphere boundary. Studies in the central Slave Craton and at Fort-à-la-Corne have detected conductors in the lithospheric mantle close to, or beneath, diamondiferous kimberlites. Graphite can potentially explain the enhanced conductivity and may imply the presence of diamonds at greater depth. Petrologic arguments suggest that the shallow lithospheric mantle may be too oxidized to contain graphite. Other diamond-bearing regions show no upper mantle conductor suggesting that the correlation with diamondiferous kimberlites is not universal. The Buffalo Head Hills in Alberta host diamondiferous kimberlites in a Proterozoic terrane and may have formed in a subduction zone setting. Long period magnetotelluric data were used to investigate the upper mantle resistivity structure of this region. Magnetotelluric (MT) data were recorded at 23 locations on a north–south profile extending from Fort Vermilion to Utikuma Lake and an east–west profile at 57.2°N. The data were combined with Lithoprobe MT data and inverted to produce a three-dimensional (3-D) resistivity model with the asthenosphere at 180–220 km depth. This model did not contain an upper mantle conductor beneath the Buffalo Head Hills kimberlites. The 3-D inversion exhibited an eastward dipping conductor in the crust beneath the Kiskatinaw terrane that could represent the fossil subduction zone that supplied the carbon for diamond formation. The low resistivity at crustal depths in this structure is likely due to graphite derived from subducted organic material.

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