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[en] Two ultrabasic-basic rocks-bearing units occur in the Vizcaino Peninsula of Southern Baja California (Mexico): the Vizcaino Layered Complex (VLC) and the San Hipolito Zone (SHZ). The VLC consists of two sequences: the lower Puerto Nuevo Sequence (serpentinite breccia, harzburgite, dunite, cyclic units), and the upper La Pintada Sequence (cyclic units, gabbros, diorites). The SHZ consists of serpentinite, actinote schists. microgabbros, spilitic pillow lavas, ophicalcites, radiolarites, tuffs, greywackes, interbedded limestone and dolomite, siliceous sandstones, and volcano sedimentary strata). The VLC is an autochtonous complex generated by a magma under plating, which is intrusive into the San Pablo Metamorphic Complex (SPMC) (amphibole-biotite gneiss with lenses of granite, migmatitic amphibolitic gneiss, orthoamphibolites). Originally, together with its metamorphic roof, the SPMC, it constituted a continental magmatic arc .The SHZ, a former Late Triassic marginal sea, is an allochthonous Carnian (?)-Norian ophiolitic unit, emplaced as a nappe upon the VLC during the Liassic. During the Late Triassic (starting at ±220 Ma) this zone underwent a long lived extensional event, during which plagiogranite dykes and dolerite/albitite dykes were emplaced into it, whereas the San Hipolito Basin opened behind it. Then, different units of the VLC were exhumed and exposed by low angle normal listric faults. It seems that the upper part of the VLC, La Pintada Sequence and the SPMC were then displaced to their present position of San Pablo-La Pintada. During the Liassic compressional phase the plagiogranite dykes were boudinaged, and slices of the SHZ Nappe came to rest upon every one of the units of the Puerto Nuevo Sequence, including the serpentinite breccia (which gave way to the erroneous notion of the so-called Puerto Nuevo melange of previous literature).
[en] In the present report results of content, distribution, variation of Se gross content and its compound forms in soils of different texture as well organic matter evidence in different kinds of crops are presented. A number of data for Se content and distribution in soils in Serbia was obtained. The Se content in the soils in Serbia varies in a broad range 39-440 μg/kg. The available Se (after extraction with NH4OAc and EDTA) showed the range 1.2-27.6% of the total Se content. The geographical distribution of Se in the soils in Serbia indicates that Se occurs in inadequate amounts in many agricultural regions. Its low status in soils has been thought to be associated with a higher incidence of some diseases. It seems that a moderate dificiency of Se is widespread in many parts of Serbia. Severe cases of deficiency were not reported so far, but a moderate deficiency can cause quite serious health problems because of some difficulties in their identification. The study of the Se content in Astragalus onobrychis growing in low Se soils (258-289 μg/kg) in southeastern Serbia showed that this species is not high Se-accumulator plant. However, these soils are characterized by a high available Se (27.1-28.2% of total Se after extraction with 0.05M EDTA). The Se content in the various parts of the plant varies in the range of 94-222 μg/kg. Selenium content in wheat in Serbia shows the range from 3.6 to 65.6 μg/kg (mean value 20.5 μg/kg; n=58), in corn 2.8-82 μg/kg (mean value 13.7 μg/kg; n=79), and in garlic 2.1-85.5 μg/kg (mean value 13.7 μg/kg; n=66). In the Zlatibor district (western Serbia) Se content in soils varies depending on parent rock: over ultramafic rocks 228 ± 33 μg/kg (n=16), over limestone 322 ± 80 μg/kg (n=6), over schists 219 ± 44 μg/kg (n=5) and over Neogene sediments 322 ± 63 μg/kg (n=2). The lowest Se content in grass was found over schists (21.6 ± 2.5 μg/kg), but the highest one in grass over Neogene sediments (54.9 μg/kg). The grass over ultramafic rocks contains 25.9 ± 10.3 μg/kg. The Se status in soils and plants in Serbia is not fully known. There is a great need to make a systematic geochemical mapping for Se and the other trace elements in soils and plants
[en] Mitu complex migmatites rocks correlates with the province of Rio Negro - Juruena (Brazil). Mitu on the plategeologic 443 in an area of 1,115 km2 approximately where divided into three units called monzogranite of Mitu, pringamosa's granofels and gneiss Del Yi; units with macroscopic textural and structural differences, and similar mineralogical composition. The rocks from Mitu's monzogranite are classified petrographically as monzogranite with syenogranites, granodiorites and subordinated quartz feldspar granofels. The pringamosa's granofels groups, granofels and gneisses with homophonous migmatitic structures, nebulite, ophthalmic, schlieren and banded, of granitic composition and gneiss del Yi groups quartz tube feldspathic gneisses with biotite and large porphyroblasts alkaline feldspar by way of augen together with quartz-feldspar granofels bands with biotite. The essential minerals found in these units are quartz, potassium feldspar (microcline), plagioclase (andesine-oligoclase) and biotite. Accessory minerals are apatite, zircon, monazite, opaque, rutile, allanite, fluorite and hastingsite. Rocks from Mitu's migmatites complex are high potassium sub-alkaline, metaluminous and peraluminous affinity; correspond to grains of a type affinity ferrous and magnetite series, with enrichment of REE in samples with monazite.
[en] New bulk-rock oxygen isotope data indicate a complicated history of fluid-rock interactions in the upper few kilometers of a basaltic arc. attending its Mesozoic accretion to the western margin of North America. Folded, multiply recrystallized, weakly metasomatized mafic volcanics and interstratified sediments of the Sawyers Bar terrane, an eastern segment of the western Triassic and Paleozoic belt, were investigated. The following scenario can now be reconstructed: (1) island-arc tholeiites (IATs), ocean-island basalts (OIBs), and distal turbidites were deposited in a subsea environment during Permian and Early Mesozoic time (170-245 Ma). Basaltic rocks underwent low-temperature alteration by seawater; recrystallization occurred at 100-200 degrees C and < 1 kbar. Alkali exchange and variable Mg-enrichment were accompanied by increases in bulk-rock δ18O values of the greenstones from 6 to approximately 10 per-thousand, preceeding initial stages of island-arc formation. (2) Middle Jurassic (165-170 Ma) suturing of the seaward oceanic arc structurally beneath a landward, 227 Ma blueschist terrane resulted in regional deformation and greenschist-facies metamorphism. Pervasive overprinting took place without important chemical or isotopic exchange under conditions of 300-425 degrees C, 3 ± 1 kbar. (3) Granitoid plutons, emplaced during late-Middle Jurassic time (160-165 Ma), heated adjacent wallrocks to ∼500-600 degrees C at pressures of approximately 2-3 kbar; thermal upgrading resulted in devolatilization of isotopically heavy metasediments and in the exchange of high δ18O fluids with intercalated greenstones. δ18O values in IAT and OIB metavolcanics increased from 9 to 10 per-thousand alone axial portions of NS-trending folds to more than 15 per-thousand where metabasalts are intimately interlayered with the metasediments. 72 refs., 5 figs., 1 tab
[en] This review of the Canadian Shield is primarily concerned with the part (such as in the Lake Superior region) that is seismically the least active of the North American continent. The crystalline metamorphic and igneous rocks of the more stable elements of the shield provide excellent possibilities for dry excavations suitable for long-term storage of radioactive waste materials
[en] The possibility to use radiogeochemical characteristics of sedimentary and ingneous rocks, metamorphized in amphibolitic and epidote-amphibolitic facies (Lower Proterozoic) is shown. Using the known techniques the uranium (general and mobile) in rocks was determined. Uranium extractability coefficient the ratio of the mobile uranium quantity to the general one-is calculated. A considerable difference for the formations in the value of uranium extractability coefficient, which is 2-3 times higher for metavolcanites than for terrigenous sedimentary rocks, metamorphized in the same facies is established. Approximately the same ratio of the parameter between initially chemogenic and clastogene rocks is observed. The above-mentioned permits to consider uranium extractability coefficient as criterion for initial genesis of metamorphic formations
[en] An investigation into the concentrations of the main heat producing radioactive elements, uranium, thorium and potassium in various rock samples was carried out by gamma ray spectrometry. The samples included igneous, metamorphic and sedimentary rocks of different ages. They were collected mainly from the northern part of the country. Results of the investigation show relatively high concentrations of radioactive elements in most rock types, comparing to the average values commonly cited. However, for granitic rocks the values obtained are, more or less, comparable to those obtained by Amnuaychai Thienprasert and his colleagues, who worked in the same area using different method of investigation. Apart from that granitic samples of triassic and cretaceous ages also have radioactive elements concentration similar to those of the Darby pluton in Southeastern Seward Peninsular, Alaska, the Granite Mountain in Wyoming and the Conway Granite of New Hampshire which has been cited as a low-grade uranium-thorium resource. As a consequence of such high radioactive elements concentrations, heat generations of most rock samples investigated are much higher than reported average values. The heat generations seem to have some influence on the nature of heat sources of hot springs in northern Thailand, especially at Ban Pong, Nam Ron hot spring Amphoe Mae Chan. Furthermore the radiogenic heat productions also affect to a great extent surface heat flow in the region provided that the radioactive elements concentrations do not decrease with depth. Surface heat flow in northern Thailand was recently reported to be very high comparing to the average value of the earth. This high heat flow was suspected to be caused by extensional tectonics resulting indirectly from sea-floor spreading in the Andaman Sea during the last 10 million years. However, from this study it can be shown that heat generations could be another factor which has much influence on the value of the surface heat flow
[en] The volcaniclastic sequence of Aranzazu (VSA, late Pliocene - early Pleistocene?) was sourced from the northernmost sector of the Machin - Cerro Bravo volcanic complex. The volcaniclastic accumulations filled the pre-existing fault-bend depressions in the surroundings of Aranzazu town (Caldas department, Colombia). A new classification of volcaniclastic deposits is proposed, in which the lahars are defined as volcaniclastic resedimented deposits, and differentiated from the primary volcaniclastic and epiclastic deposits. The updating the sedimentology and rheology of the deposits related with the laharic events is aimed. The VSA stratigraphy is based on the lithofacies identification and the definition of the architectural elements for syn- and inter-eruptive periods. The VSA lower member corresponds to the successive aggradation of syneruptive lahars (SV and SB elements) resulted from re-sedimentation of pumice-rich pyroclastic deposits and transported as debris and hyperconcentrated stream/flood flows. The VSA middle and upper members defined by coal contents were formed during the dominion of inter-eruptive (FF element) over the syn-eruptive (SV and SB elements) periods. They were formed during the reestablishment of the fluvial condition after the syn-eruptive laharic activity. Once the fluvial deposition was strengthened, the necessary conditions for the peat formation were propitious and the coal-bearing bed sets were developed.
[en] Anisotropy Magnetic susceptibility indicated a differences of Magnetic susceptibility value of a sample due to the direction or orientation of magnetic field on it. The 22 sample's were taken from lour area around Merapi mountain in central Java and their Anisotropy Magnetic susceptibility were measured by using MS2 Bartington. The 22 sample's shown a high susceptibility value about 8037.5 x 105. Eleven sample's have high anisotropy ( it's anisotropy degree about 16% ). The rest of the sample have an anisotropy degree less than 6% (sample's from pasar bubar, Kali Kuning, Kali Gendong, Kali Gendol Utara). This result give an indication that a part of the sample's can be used for paleomagnetic