Bimodal Volcano-Plutonic Complexes in the Northern Frames of Eastern Section of MongoI-Okhotsk Orogenic Belt

Mongol-Okhotsk orogenic belt was formed during almost all the Phanerozoic period. The bimodal late Paleozoic-early Mesozoic formations were stated in the frames of the western section of Mongol-Okhotsk belt. Their formation is connected with the collision of north Asian and Sino-Korean continents. These collision processes were conjugated with the dimensioned intraplate processes in the region. The rocks of the bimodal volcano-plutonic complex were also stated in the frames of the eastern section of Mongol-Okhotsk orogenic belt. This should proof the identity of geological processes, which accompanied the collision of north Asian and Sino-Korean continents, during all the stage of the formation of the Mongol-Okhotsk belt.

Garnet Growth in the Early Stage of Trachybasalt-Eclogite Transformation

Garnet growth in the early stage of the trachybasalt-eclogite transformation was observed at 2.0 GPa and temperatures of 860 ℃, 940 ℃ and 1020 ℃ for annealing times of 0.66 - 13.6 h. The grain size was determined optically to be increased with increasing annealing time. The growth rate decreased with increasing grain size. The garnet growth law was G^(2.46) = 5.65 × 10^(-15)texp[-27.40 × 10^(3)/RT], where G represents the average grain size after annealing time t, R is the gas constant and T is the absolute temperature.

Elaboration of the Hydro-Geophysics GIS Showing the Volubilis Depression and the Prerifains Ridges Structuration (Morocco North Occidental)

We present a comparative analysis of electrical and gravity data on the Geographic Information System of the prerifaines ridges. At the Meso-Cenozo?c sequence, the geometry of the prerifaines ridges is fairly well known. However, the post-Miocene series remain to be characterized. In this perspective, we use a database composed of gravity and vertical electrical sounding profiles and geo-electrical sections in order to characterize this structuration. These data are calibrated by many oil and hydrogeological boreholes. Preliminary results lead to better understanding of the organization of its underlying structures in this area. The Gravimetric filtering results show that the area may be dissected by tree major faults striking NW-SE, NE-SW and N-S. All these faults have contributed, since Hercynian to Alpines orogenies, to the structuring of this area, being proved to be the deepest and can reach 4500 m. The comparison of gravity maps, geological and structural maps under Geographic Information System allows the identification of major structural directions and trends of the study area. It confirms some structural elements gathered from outcrops and define new ones. Results from this work show the importance of using various filtering and interpretation techniques in the analysis of gravity data. They also provide news insights into the deep structure of the study area.

Early Cretaceous Tectonostratigraphic Evolution of the Southern Tunisian Margin Based on Gravity,Seismic and Potential Field Data:New Insights into a Geodynamic Evolution in a Tethyan and Mesogean Rifting Context

Many geophysical and geological data have been used to interpret the tectonic evolution of the south-eastern part of the Tunisian margin and to analyze the dominant structures in the area.The Menzel Habib Plain(MHP)and surroundings,targeted by this study,exhibits thick siliciclastic and carbonate formations attributed to the Early Cretaceous period.Integration of seismic and gravimetric data coupled with analysis of the syndepositional faults affecting these formations prove that the Tunisian margin is dominated,during this period,by N-S to NE-SW extensional directions.The geodynamic evolution of the MHP is mainly due to the irregular normal movement of the N-S faults,which represents the southernmost branch of the N-S Axis(NSA)and of the NW-SE faults,which constitutes the SE segment of the South Atlasic fault corridor(SAFC).In addition,the NE-SW and E-W oriented faults contributed to this evolution.Over extensive periods,this network of faults determines horst and grabens basin geometry or tilted blocks inducing formation of several distinct areas with different subsidence rates.Simultaneously,the normal activity of the major faults promotes the vertical mobilization of the Triassic salt resulting in the individualization of several diapiric bodies,some of which pierced their sedimentary cover.These dynamics reflect echoes of the sinistral drifting of Africa with respect to Europe,integrated in a long Tethyan rifting cycle,and the beginning of opening of the Mesogean Sea,respectively.

Experimental detection of the inner core translational triplet

The translational oscillation of the solid inner core is one of the Earth’s fundamental normal modes, which is also called Slichter mode. The normal mode should be split to form a triplet due to the Earth’s rotation and ellipticity. In this study, according to the splitting pattern of Slichter mode, an attempt has been made to detect the possibility of Slichter triplet’s existence by using the product spectra of the long-term continuous gravity measurements from the superconducting gravimeters (SG) at 6 glob- ally-distributed permanent stations in the Global Geodynamics Projects network. The results indicate that the background noise level of the global SG observations is 0.0158 nm s–2 and the magnitude threshold of any global harmonic signals, which may be detected by the global SG, is 0.0152 nm s–2 in the subtidal frequency band from 0.162 to 0.285 cph in which Slichter triplet may occur. it implies that the signatures, related to the triplet, may be identified in the global SG observations, if they exist. It is found that there is a group of global harmonic signatures with the periods of 5.310, 4.995 and 4.344 h emerging significantly from the background noise in the global SG observations. They are in good agreement with the splitting pattern of Slichter mode. It implies that this group of signatures may be related to the inner core translational oscillations. The associated density contrast across the inner core boundary may be deduced as between the values provided in the Earth models of the PREM and 1066 A.

Investigation of the Co-seismic Gravity Field Variations Caused by the 2004 Sumatra-Andaman Earthquake Using Monthly GRACE Data

Gravity Recovery and Climate Experiment（GRACE） observations have been used to de-tect the co-seismic and post-seismic gravity field variations due to the Mw=9.3 Sumatra-Andaman earthquake that occurred on December 26,2004.This article focuses on investigating some gravita-tional effects caused by this huge earthquake.We computed the geoid height changes,the equivalent water height（EWH） changes,and the gravity changes using the GRACE Level-2 monthly spherical harmonic（SH） solutions released by University of Texas Center for Space Research（UTCSR）.The GRACE results agree well with the prediction by a dislocation model and are consistent with the results obtained by some previous scholars.In particular,we calculated the three components of the gravity gradient variations and found that they can recover the seismic-related signature more sensitively due to a certain degree of amplification of the signals.A positive-negative-positive mode predominates in the spatial distribution of the horizontal components of the gravity gradient variations,which is possibly attributed to the anomalies in the crustal density distribution caused by the uplift-subduction effect of the dip-slip earthquake.Moreover,the latitude components of the gravity gradient changes show strong suppression of the north-south stripes,which is due to the along-orbit measurements of the two GRACE satellites.We conclude that the posi-tive-negative-positive mode in latitude gravity gradient changes would be a more sensitive fea-ture to detect the deformations of some major dip-slip earthquakes by GRACE data.