Direct inversion of the Longitudinal Ray Transform for 2D residual elastic strain fields

We examine the problem of Bragg-edge elastic strain tomography from energy resolved neutron transmission imaging. A new approach is developed for two-dimensional plane-stress and plane-strain systems whereby elastic strain can be reconstructed from its Longitudinal Ray Transform (LRT) as two parts of a Helmholtz decomposition based on the concept of an Airy stress potential. The solenoidal component of this decomposition is reconstructed using an inversion formula based on a tensor filtered back projection algorithm whereas the potential part can be recovered using either Hooke's law or a finite element model of the elastic system. The technique is demonstrated for two-dimensional plane-stress systems in both simulation, and on real experimental data. We also demonstrate that application of the standard scalar filtered back projection algorithm to the LRT in these systems recovers the trace of the solenoidal component of strain and we provide physical meaning for this quantity in the case of 2D plane-stress and plane-strain systems.Comment: 30 pages, 9 figure

Magnetotelluric monitoring of geodynamic processes

Electromagnetic (EM) monitoring of geodynamic processes can be based on the two different seismo-electrical phenomena: a change in resistivity of some geological cross-sections and a generation of EM fields of internal (geodynamic) origin. Continuous observation of the natural magnetotelluric (MT) field simultaneously provides information on both such phenomena. The transfer functions between components of the MT field reflect geoelectrical section and the residual field includes the EM field of internal origin. Their variations in time give independent information on geodynamic processes. The transfer functions and the residual field can be determined by known deterministic methods, although it appears more convenient to apply the methods of adaptive data processing. They elicit information on both phenomena in real time. Continuous MT observations were carried out at the Bishkek geodynamic testing ground (Kirgizia) during 1993. Their results show how informative MT monitoring is

Magnetotelluric monitoring of geodynamic processes

Electromagnetic (EM) monitoring of geodynamic processes can be based on the two different seismo-electrical phenomena: a change in resistivity of some geological cross-sections and a generation of EM fields of internal (geodynamic) origin. Continuous observation of the natural magnetotelluric (MT) field simultaneously provides information on both such phenomena. The transfer functions between components of the MT field reflect geoelectrical section and the residual field includes the EM field of internal origin. Their variations in time give independent information on geodynamic processes. The transfer functions and the residual field can be determined by known deterministic methods, although it appears more convenient to apply the methods of adaptive data processing. They elicit information on both phenomena in real time. Continuous MT observations were carried out at the Bishkek geodynamic testing ground (Kirgizia) during 1993. Their results show how informative MT monitoring is

Zircons from Collisional Granites, Garhwal Himalaya, NW India: U–Th–Pb Age, Geochemistry and Protolith Constraints

In the present work, we studied zircons from the less foliated granites of the Chail Group, which form a thrust sheet of the Lesser Himalayan Sequences, Garhwal region. Compositionally, these granites are S–type, formed in a collisional tectonic setting. Zircons possess an internal structure, mineral inclusions, and geochemical characteristics typical of magmatic origin. The U–Th–Pb geochronology and geochemistry were assessed using the laser ablation multi–collector inductively coupled plasma spectrometry (LA–ICP–MS) technique. U–Th–Pb isotope dating of zircons from two different samples revealed their age, estimated from the upper intersection of the discordia, to be 1845 ± 19 Ma. Zircons from one sample contained inherited cores belonging to three age groups: Paleoarchean (3.52 Ga), Neoarchean (2.78 Ga and 2.62 Ga), and Paleoproterozoic (2.1 Ga). Zircons with ages of 3.52, 2.62, and 2.1 Ga were interpreted as magmatic based on their geochemical characteristics. The 2.78 Ga core was interpreted as metamorphic. The observed inheritance is consistent with the melting of sedimentary rocks. The inherited zircons could have originated from Aravalli and Bundelkhand Craton and Paleoproterozoic Aravalli Fold Belt rocks. This confirms that the studied granites are S–type and could have been formed in a collisional environment at 1.85 Ga on the western flank of the Columbia Supercontinent