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1.
The Shah-Kuh granitic pluton of eastern Central Iran was emplaced 165 Ma ago, in an active continental margin setting. It is made of two main units: a granodioritic unit (SiO2=63–71 wt%) to the north–west and a syenogranitic unit (SiO2=73–77 wt%) to the south–east. The former unit displays seriate medium-grained textures and contains locally abundant mafic enclaves. The latter unit is medium- to coarse-grained and porphyritic, with 0.5–3 cm long K-feldspar megacrysts. Fine-grained granitic bodies are present in both units. The rocks are metaluminous to slightly peraluminous (I-type) and peraluminous (S-type) and belong to the ilmenite-series granites. Fractional crystallization appears to have been a very effective differentiation process in both units, and the fractionated mineral assemblages are determined by mass balance calculations. Isotopic data (Sri=0.7065 and εNdt=−2.5) are consistent with a young upper crustal protolith. Tin mineralization in sheeted quartz-tourmaline (-cassiterite) veins is spatially associated with the granodioritic unit. The veins formed by hydraulic fracturing when the granodioritic to monzogranitic magma became water-saturated and exsolved a fluid phase during crystallization. The reduced nature of this magma is responsible for the incompatible behaviour of Sn, likely to favour Sn concentration in the residual melt and then in the exsolved fluid. Another fluid phase was exsolved by the syenogranitic magma and was responsible for local greisenized granites, characterized by high Y and HREE-contents and non-fractionated REE distribution patterns. Field and mineralogical data show that the (B, Sn) vein-forming fluid was different from the (F, Li) greisen-forming fluid.  相似文献   
2.
The Malayer–Boroujerd plutonic complex (MBPC) in western Iran, consists of a portion of a magmatic arc built by the northeast verging subduction of the Neo-Tethys plate beneath the Central Iranian Microcontinent (CIMC). Middle Jurassic-aged felsic magmatic activity in MBPC is manifested by I-type and S-type granites. The mafic rocks include gabbroic intrusions and dykes and intermediate rocks are dioritic dykes and minor intrusions, as well as mafic microgranular enclaves (MMEs). MBPC Jurassic-aged rocks exhibit arc-like geochemical signatures, as they are LILE- and LREE-enriched and HFSE- and HREE-depleted and display negative Nb–Ta anomalies. The gabbro dykes and intrusions originated from metasomatically enriched garnet-spinel lherzolite [Degree of melting (fmel) ~ 15%] and exhibit negative Nd and positive to slightly negative εHf(T) (+ 3.0 to ? 1.6). The data reveal that evolution of Middle Jurassic magmatism occurred in two stages: (1) deep mantle-crust interplay zone and (2) the shallow level upper crustal magma chamber. The geochemical and isotopic data, as well as trace element modeling, indicate the parent magma for the MBPC S-type granites are products of upper crustal greywacke (fmel: 0.2), while I-type granites formed by partial melting of amphibolitic lower crust (fmel: 0.25) and mixing with upper crustal greywacke melt in a shallow level magma chamber [Degree of mixing (fmix): 0.3]. Mixing between andesitic melt leaving behind a refractory dense cumulates during partial crystallization of mantle-derived magma and lower crustal partial melt most likely produced MMEs (fmix: 0.2). However, enriched and moderately variable εNd(T) (? 3.21 to ? 4.33) and high (87Sr/86Sr)i (0.7085–0.7092) in dioritic intrusions indicate that these magmas are likely experienced assimilation of upper crustal materials. The interpretations of magmatic activity in the MBPC is consistent with the role considered for mantle-derived magma as heat and mass supplier for initiation and evolution of magmatism in continental arc setting, elsewhere.  相似文献   
3.
The Aligoodarz granitoid complex (AGC) is located in the Sanandaj-Sirjan Zone (SSZ), western Iran and consists of quartz-diorites, granodiorites and subordinate granites. Whole rock major and trace element data mostly define linear trends on Harker diagrams suggesting a cogenetic origin of the different rock types. (87Sr/86Sr)i and εNdt ratios are in the ranges 0.7074-0.7110 and −3.56 to −5.50, respectively. The trace elements and Sr-Nd isotopic composition suggest that the granitoids from the AGC are similar to crustal derived I-type granitoids of continental arcs. The whole rock suite was produced by assimilation and fractional crystallization starting from a melt with intermediate composition likely possessing a mantle component. In situ zircon U-Pb data on the granites with LA-ICP-MS yield a crystallization age of ∼165 Ma. Inherited grains spanning in age from ∼180 Ma up to 2027 Ma were also found and confirm that assimilation of country rock has occurred.Chemical and chronological data on the AGC were compared with those available for other granitoid complexes of the central SSZ (e.g., Dehno, Boroujerd and Alvand). The comparison reveals that in spite of the different origins that have been proposed, all these granitoid complexes are likely genetically related. They share many chemical features and are derived from crustal melts with minor differences. Alvand granites have the most peculiar compositions most likely related to the presence of abundant pelitic component. All these intrusions are coeval and reveal the presence of an extensive magmatic activity in the central sector of the SSZ during middle Jurassic.  相似文献   
4.
Microgranular enclaves are common in the Jurassic Aligoodarz granitoids of western Iran. Enclaves Enclosed in Granodiorite (EEG) and Enclaves Enclosed in Tonalite (EET) are different but they overlap their hosts on variation diagrams. The EEG is compositionally intermediate between tonalite and granodiorite. Mixing between tonalitic and granodioritic magmas and fractional crystallization are two models examined as the origin of the EEG. Field, textural, mineralogical and chemical observations suggest that chemical equilibration, common in magma mixing, was not attained between the EEG and its host. This, together with other observations does not support magma mixing as a mechanism for forming the EEG. Alternatively, excessive nucleation of biotite ± Fe-Ti-oxides ± amphibole by rapid cooling at borders of a shallow magma chamber and later fragmentation and dispersal by dynamic arc plutonism best explains the EEG. However, channeling of a new magma into the nearly solid tonalitic host explains formation of the EET.  相似文献   
5.
The Middle Jurassic Boroujerd Granitoid Complex of the Sanandaj-Sirjan Zone (with a U–Pb zircon age of 169–172 Ma) was emplaced in an active continental margin setting. This complex consists of three main units: an elongate NW–SE extending granodioritic unit (SiO2 = 58–71 wt%), which is widespread throughout the area, a quartz-dioritic unit (SiO2 = 52–63 wt%), exposed as small stocks within the granodioritic body, and a monzogranitic unit (SiO2 = 70–75 wt%), widely scattered as separate small outcrops through the southern part of the area. A series of NW trending aplites and pegmatites are present in the granodioritic unit and its aureole.Geochemically this complex is metaluminous to slightly peraluminous, typical of I-type granites. It belongs to high-K calc-alkaline series and displays the geochemical characteristics typical of volcanic arc granites related to an active continental margin (e.g. significant Nb, Ti, P and Sr depletion). Isotopic data (Sri = 0.7062–0.7074 and εNdt = −3.02 to −3.62) are consistent with a crustal protolith. In addition, fractional crystallization may have played an important role in the formation of the whole spectrum of the granitoid types that occur in the Boroujerd area.  相似文献   
6.
Recently, new theories on underground geophysical and geochemical interactions which had been reported to occur during the preparation stages of earthquakes and the remotely measurable variations have been put to test and some warning factors were suggested as earthquake precursors. Data vendors are providing daily basis information from the earth's surface by combining remote sensing data and in situ observations. In this paper, we analyze atmospheric, oceanic, and surface changes in the ocean, coast, and land lying near the epicenters of two recent major earthquakes. The changes are studied in terms of the regional fault locations which have been reported by the U.S. Geological Survey as the shake triggering geological structures. Our detailed analyses showed anomalous increases of surface latent heat flux (SLHF) for both the earthquakes. Meaningfully limited to the geographical extents of the regional active faults, the SLHF variation patterns suggest pre-seismic activity 2–3 weeks before the main events. The agreement of these variations with abnormalities in other climatic and surface factors like relative humidity and temperature represents an unusual situation during the same period as well. Spatiotemporal variations of chlorophyll-a was also studied as another earthquake indicator. Abnormal rises in these factors are possibly caused by the formation of micro-cracks, heat production, evaporation, ionization, and upwelling of nutrient-rich water produced by pre-seismic activity prior to the main events.  相似文献   
7.
Theoretical and Applied Climatology - Evapotranspiration is one of the main components of water balance and its accurate estimation is of great importance in planning and optimizing water...  相似文献   
8.
A bench scale study was conducted to assess the possibility and extent of biological clogging in compacted clayey soil exposed to high-strength leachate simulating conditions in a landfill. In two series of experiments, distilled–deionized water, slightly acidic water and fresh high-strength leachate were permeated through compacted clayey soil and the rate of infiltration was recorded. Colony-forming units per unit mass of soil were counted, and scanning electron microscope photographs were taken before and after termination of experiments. Results indicated that infiltration of leachate containing a very high concentration of organic matter followed a logistic fit indicating hydraulic clogging of the porous media. This was in agreement with a five order of magnitude greater bacterial growth compared to the original state of the soil and to cases where distilled–deionized and acidified water was used as the permeant. Water and acidified water infiltration followed a power fit indicating persistent infiltration through the end of experiments with no sign of clogging. Bacterial counts in these cases were similar to that of the original state of the soil. Photographs taken by scanning electron microscope also indicated formation of plate-like material within the soil texture in contrast to no change when water was used as the permeating fluid and to formation of holes when acidified water was infiltrated through the soil. It was concluded that biological clogging considerably reduced the rate of infiltration within compacted clayey soil shortly after exposure to high-strength leachate.  相似文献   
9.
The preparation process of an impending earthquake may leave fingerprints on the earth??s surface. Elastic strain in rocks, formation of micro-cracks, gas releases and other chemical or physical activities in the earth??s crust before and during earthquakes has been reported to cause rises in temperature, surface latent heat flux (SLHF), upwelling index and chlorophyll-a (Chl-a) concentration on the ground or sea surface. Changes in surface temperature can be monitored with thermal infrared sensors such as NOAA-AVHRR and microwave radiometers like AMSR-E/Aqua. SLHF data and upwelling indices are provided by National Centers for Environmental Prediction (NCEP) Reanalysis Project and Pacific Fisheries Environmental Laboratory, respectively. This study examines behaviors of the above four factors prior to the past three oceanic and coastal earthquakes occurred at the Pacific Ocean (Northern California of June 15, 2005, Central California of September 28, 2004, and December 22, 2003). We were successful in detecting pre-earthquake anomalies prior to all three earthquakes. Our detailed analysis revealed 1?C5?°C rises in surface temperature in epicentral areas. Considerable anomalies in Chl-a concentration, 1?C2?weeks before the day of the main earthquakes, were spotted, which are attributed to the rise in upwelling index. Time series of SLHF showed meaningful rises from 1?month to a fortnight before the earthquake events. One problem in our research was the low resolution of the data which makes the graphs that are generated from NCEP database affected by all sources of anomalies, other than seismic activities, within an about 1.8°?C2.5° (200?km) area.  相似文献   
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