Possible seismogenic origin of changes in the ULF EM resonant structure observed at Teoloyucan geomagnetic station, Mexico, 1999-2001

International audienceThe evolution of the ULF resonant structure observed at Teoloyucan geomagnetic station has been provisionally studied in a possible relation with seismic activity in Mexico in the period 1999-2001. Two resonant lines were observed in the H-component (linear polarization) in the frequency bands fR2=10.2?11.1 mHz and fR2=13.6?14.5 mHz, sometimes accompanied by other harmonics. The source of the observed resonances is possibly related with the geomagnetic location of the station (geomagnetic latitude ?=29.1°) and its proximity to the equatorial electrojet (?~30°). An enhancement of the carrier frequency of both resonances in the period 1 month?2 weeks was found before the strongest EQs. Also, a depression of the resonant structure just a few days before and a few days after some EQs seems to be correlated with seismic activity

Isotopic and geochemical features of newly formed zircon rims as a criterion for identification of feeding sources of Ti-Zr placers

Zircons were studied from the Ti-Zr placers of the Murray Basin (Mindarie and WIM-150 deposits) and metamorphic rocks of the adjacent Kanmantoo Belt and the Ballarat Trough in Southeast Australia, and from Russian basins with Ti-Zr placers: the Cenomanian-Turonian and Poltavian basins in the East European Platform and the Sarmatian basin in the northern Caucasus, Stavropolye, and Kalmykia. The study of the primary source → weathering mantle → intermediate reservoir rock → economic placer system includes (1) morphostructural and paleofacies reconstructions of the studied territories; (2) quantitative analysis of ore mineral distribution in each element of this system; and (3) study of zircon typomorphism from the feeding source to the basin, where Ti-Zr placers have been deposited. In all elements of the system studied, zircons were examined using optical and cathodoluminescence microscopy, an electron microprobe, mass spectrometry (laser ablation and SHRIMP II), including U-Pb dating, Lu and Hf isotopes, distribution of trace elements (REE, Y, P), and comparative analysis of indicative ratios: Th/U, HfO2/ZrO2, Y2O3/(Y2O3 + REE2O3), (La + Sm)/(Gd + Yb), etc. Newly formed rims replacing detrital zircon g rains and marking the time of late geological events were identified. The rims differ from the cores in distribution of trace elements. Genetic typification of diverse newly formed rims is based on discrimination of them by internal structure, isotopic and geochemical characteristics, which are used as a criterion of relationships between Ti-Zr placers and their inferred feeding sources. Based on these data, a prospecting model of the buried Ti-Zr placers with estimation of their resource potential has been produced.19 page(s

ULF geomagnetic anomalies of possible seismogenic origin observed at Teoloyucan station, Mexico, in 1999-2001: Intermediate and short-time analysis

The analysis of ULF geomagnetic field measured at Teoloyucan station (Central Mexico, 11'35.735" W, 19 4445.100" N, 2280 m height) is presented in an intermediate (+/- 15 days) and short time scale (the day of the EQ occurrence) in relation to 7 major earthquakes occurred in Mexico in 1999-2001. Local changes in the fractal dynamics of the magnetic field are found to be important: a pronounced fall of the fractal index is frequently observed prior to the main shock. The study of the ULF resonant structure recently discovered in the frequencies f(R1) = 10.2-11.1 mHz and f(R2) = 13.6-14.5 mHz reveals changes in their character probably related to the processes of the earthquakes preparation. The success of the observation of the mentioned anomalies (specially the fractal index decrease) strongly depends on how close is the station from the epicenter, and what is the magnitude of the earthquake. (c) 2006 Published by Elsevier B.V