New Method to Obtain Quantified Data on Color of Marine Sediments

Doklady Earth Sciences - A new method of quantitative determination of color using an original photodevice is presented for marine sediments, which are a specific geological object. The advantages...     

Coseismic deformations of the Earth’s surface in Sakhalin related to the August 2, 2007, M w = 6.2 Nevelsk earthquake

The satellite radiointerferometry data revealed deformations of the coastal part of Sakhalin Island caused by the earthquake with M _w = 6.2 that occurred in the Tatar Strait near Nevelsk. Based on the joint analysis of the satellite and seismological data, dislocation models were contrived for the main shock and its strong aftershocks with the western dip of the fault planes. This made it possible to determine the source mechanisms and the geometrical parameters of the seismic ruptures and to calculate the coseismic vertical and horizontal displacements. In contrast to the one-dimensional model of the insular land displacements determined from the satellite radiointerferometry measurements, this provided a three-dimensional model of the surface deformations for the epicentral zone.     

Petrochemical evaluation of the diamond potentials of Yakutian kimberlite fields

The diamond potentials of nine kimberlite bodies occurring in the Mirnyi, Nakyn, AlakitMarkha, and Daldyn fields were studied by examination of 2026 10-m core intervals. Most typical rock samples of about 1 kg were taken from each interval for X-ray fluorescence analysis of silicates. A total of 6715 kimberlite samples were analyzed. Pairwise correlation coefficients between mean compositions of kimberlites and their diamond contents were calculated. Correlations with diamond presence (99%) were found only for TiO₂, Al₂O₃, and K₂O. The negative correlation with TiO₂ and the positive correlation with K₂O can serve as criteria for diamond presence. These dependences are in good agreement with the petrochemical population model. According to this model, the decrease in TiO₂ contents in the range 3.0–0.01% and the increase in K₂O content to 0.85% are related to larger depths of parental melting zones. Contents of K₂O exceeding 0.85% are determined by the presence of garnet pyroxenites, associated with processes accompanying oceanic crust subduction, in magma formation zones. Formation of parental melts at larger depths determines higher diamond potentials of kimberlite bodies. Our results confirm the hypothesis that kimberlite parental melts are selective melts of lithospheric peridotites saturated with water and carbon dioxide.     

Stratigraphy of sediments from the Håkon Mosby Mud Volcano Area

Studies of four gravity cores from the Håkon Mosby Mud Volcano area have shown the existence of three lithologic–stratigraphic units: I – brown clay (0–10?ka), II – gray clay (10–30?ka) and III – gray silt (30–61?ka). The units reflect different paleographic sedimentation and conditions, including the influence of mud volcanic activity. Two periods of mud volcanic activity can probably be discerned: 10–30?ka and Recent. The coexistence of Pleistocene and Late Pliocene benthic foraminifera suggests that the source depth of the volcano is located below the Pliocene–Pleistocene boundary.     

Key processes determining secondary alterations in kimberlites

A variety of hypotheses have been put forward as to the nature of secondary alteration. They were tested by using the amount of insoluble SiO₂ accumulated in the rocks (Q) as the index of secondary alteration degree. This parameter allows any sample to be characterized with the degree of its secondary alteration. By putting Q values together with contents of CaO and rare earth elements, features of diamond crystal size distributions within samples in most altered kimberlites, and the distribution of these parameters over kimberlite bodies, we show that secondary processes occurred when kimberlites were exposed to postmagmatic solutions: fluids containing water and carbon dioxide. Endogenous fluids rose from the bottom of pipes along narrow local zones and spread beyond them at the top, involving larger rock masses. There, they mingled with vadose and phreatic water. The basicity decreased abruptly, inducing profound changes of rock-forming minerals and alteration of diamond crystal weight distribution by recrystallization. The study invokes a great body of factual information, including hundreds and thousands of analyzes of kimberlites from Yakutian diamond pipes: Botuobinskaya, Nyur’inskaya, Maiskaya, Internatsional’naya, Mir, Aikhal, Yubileinaya, Sytykanskaya, Udachnaya-West, and Udachnaya-East.     

Recent geodynamics of the Kuril subduction zone

The collected GPS/GLONASS data allow us to reveal new information on the recent geodynamics of the Kuril Island arc. The maximum deformation stress accumulates in the southern and northern parts of the study area, while a long fading transition process of postseismic motions is observed in the central segment of the Kuril arc as a result of the 2006–2007 great Simushir earthquakes of M _w = 8.3 and M _w = 8.1. We have succeeded in revealing the recent interplate coupling geometry of the Pacific and the North American lithospheric plates and also in estimating the seismic potential of different segments of the Kuril subduction zone.     

The Contemporary Seismic Deficit in the Kuril–Kamchatka Subduction Zone

Doklady Earth Sciences - Based on an analysis of seismicity for the period of 1900–2018, the seismic potential of the Kuril–Kamchatka subduction zone is estimated, and the geometry of...     

A new body of highly diamondiferous kimberlites in the Nakyn field of the Yakutian kimberlite province

We report the first data on the contents of main oxides and REE in rocks and the compositions of pyropes and almandines from the Maiskoe kimberlite body recently discovered in the Nakyn field of the Yakutian kimberlite province.The kimberlites are characterized by low contents of Ti, a slight domination of Mg over Ca, and high contents of K₂O in some samples. The pyropes have high contents of Cr₂O₃ (up to 14.5 wt.%); many of them (～16%) are poor in Ca. In petrochemical and mineralogical features the kimberlites of the Maiskoe body are complementary to the highly diamondiferous kimberlites of the nearby Botuobinskaya and Nyurbinskaya pipes. At the same time, they are not the final link in the evolution of kimberlite magmatism in the Nakyn field, which makes the latter still more promising for diamonds.     

Regional estimation of peak rainflood discharges

Presented are the results of statistical estimation of peak rainflood discharges of the Middle and Lower Amur basin rivers during the period from the beginning of observations to 2007. On the basis of prolonged observation series probable water discharge values were computed and the analysis was carried out of the 1%-probability flow modulus areal reduction. Specified were the 1%-probability peak (maximum) rainfall flow modulus values for the small river catchment areas.