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[en] Mount Taftan is a double-peaked stratovolcano, located in southeast of Iran. This volcano constructed a number of calderas among which one of the most important is Anjerk. The magmas erupted from this multi-caldera complex range from andesi-basalt to dacite, but are dominated by andesite and dacite. Two terminal cones, Narkuh and Matherkuh, culminate at 4100 m and 3950 m, respectively. There are three evolutionary stages in the history of the volcanic complex (stage 1: Palaevolcanism, 6.95±0.72Ma, stage 2: Mesovolcanism, 6.01±0.15Ma and stage 3: Neo volcanism, 0.71± 0.03Ma). The eruptive products consist of lava flows, iguimbrites and pyroclastic rocks. The later include tuffs, nuees ardents, breccias and sometimes reworked as lahars. Textural and mineralogical data suggest that both magma mixing and fractional crystallization were involved in the generation of the andesites and dacites. The magmas erupted from this volcano show a calc-alkaline trend. The corresponding lavas are calk-alkaline with a potasic tendency.
[en] The Quaternary volcanic activity manifested within the Kapan block is associated with the activity of five, relatively small, volcanic centers of the areal (monogenic) type: Norashenik, Erkenats, Karmrakar, Kakachsar, and Kakhnut. A link has been established between volcanism and the Quaternary faults of the NW-SE direction parallel to the KhustupGiratakh fault. The age of Kapan lavas, according to our new 40Ar/39Ar data, indicates volcanic activity in the range of the upper Lower Pleistocene prior binging of Middle Pleistocene. All studied rocks are silica-undersaturated rocks and belong to olivine and amphibole basanites, and two samples correspond to picrobasalts. Kapan lavas demonstrate an affinity with some geochemically enriched varieties of the silica-undersaturated lavas of Syunik. Geochemical data indicate the formation of Kapan magmas from mantle sources modified by older subductions in the region. It is shown that in the south of Armenia, where the subduction component increases, in addition to the impact of the Mesozoic subduction, the influence of 'fresher' Andean type Zagros subduction of Paleogene age can be observed
[en] Tephrostratigraphic and chronologic studies in two areas of the North Island have identified a previously unrecorded, thin, distal silicic tephra derived from the Taupo Volcanic Centre. In Taranaki, three radiocarbon ages of the uncorrelated tephra are consistent with the independent radiocarbon chronology obtained from enveloping Egmont-sourced tephras. In western Bay of Plenty, where the uncorrelated tephra is also directly dated, it is overlain by Whakaipo Tephra (c. 2.7 ka) and underlain by Hinemaiaia Tephra (c. 4.5 ka). From these sites in Taranaki and western Bay of Plenty, seven radiocarbon dates obtained on the uncorrelated silicic tephra yield an error-weighted mean age of 3970 ± 31 conventional radiocarbon years B.P. The ages on the uncorrelated tephra (informally referred to as Stent tephra) from both areas are statistically identical but significantly different from those on both Waimihia and Hinemaiaia Tephras. The occurrence of Stent tephra in Taranaki, c. 160 km upwind from the postulated source area, and in western Bay of Plenty, suggests that it represents the product of a moderately large plinian eruption. Until recently, its validity as a discrete eruptive event had been problematical, because a near-source equivalent deposit between Waimihia and Hinemaiaia Tephras was not recognised in the Taupo area. However, a revised stratigraphy proposed by C.J.N. Wilson in 1993 for eastern sectors of the Taupo area shows that multiple tephra layers were erupted from Taupo volcano between c. 3.9 and 5.2 ka. Of these newly recognised layers, unit-Q - the product of a moderately large eruption ( 0.15 km3) at c. 4.0 ka - is tentatively correlated with Stent tephra. Other eruptive units recognised by Wilson are either too old or too small in volume to be considered as likely correlatives. (author). 44 refs., 7 figs., 3 tabs
[en] He cao keng uranium ore field. Located in Wuyishan Mountain metallogenic belt has good uranium geological background, and it has become an important base of volcanic rock type uranium mineral uranium. The area has experienced more than 20 years of exploration work, but there is still a lot geological problems left. In a new round of prospecting breakthrough action, combined with practice to solve 'four is not enough', implement to find the crater, attack red basin, prospect deep, the mine field construction is expected to becoming a large base of uranium. (authors)
[en] The uranium metallogenesis and characteristics have been summarized and discussed based on previous data of Huangnihu district. The early syngenetic sedimentary uranium is regarded as the foundation, and was superimposed and altered by bimodal volcanism-subvolcanism acting as uranium and thermal source, and the volcanism is dominant for uranium concentration. The district is summarized to be composite genetic with multi factors and multi stages, 'diagenesis and metallogenesis to be foundation, and volcanic thermal cover to be the key', so should be ranged into the vocanic thermal cover subtype, volcanic rock type. (authors)
[en] The Galeras Volcano is presently being considered the most active in Colombia. For the last 17 years of constant vigilance, the occurrence of eruptions by Galeras Volcano has been mostly classified as small ones. In the high hazard zone, live 7935 persons who have to be evacuated every time level II to volcanic activity is reached (probable eruption in the course of days or weeks). For the first time in Colombian history, a disaster situation has been declared before its happening. On November 15th, 2005, the National Government, on the basis of the Decreto 4106, declared the existence of an disaster situation within the counties of Pasto, Narino and La Florida, all making part of the Narino Department. This declaration was made considering the serious alteration of the daily life style, to which the population was exposed due to a probable volcanic eruption, is out to come. The present work is an analysis of the emergency procedures which have been carried out with help of the PAR (pressure and release) methodology. This analysis contains some reflexions on how difficulties were solved, and on positive aspects, challenges and advances for a better long term management of evacuations, like those carried out in the high hazard zones of Galeras volcano
[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.