Land-use classification using ASTER data and self-organized neutral networks     

《International Journal of Applied Earth Observation and Geoinformation》2005,7(3):183-188

Operationally AVHRR and TM/TM+ data were used and a supervised maximum likelihood classification (MLH) was applied to depict land use changes in Beijing, providing basic maps for planning and development. With rapid growth of the city these are helpful to deal with higher resolution data, whereas new classification algorithms produce land use maps more accurate. In the paper, new sensor ASTER data and the Kohonen self-organized neural network feature map (KSOM) were tested.The TSOM classified 7% more accurately than the maximum likelihood algorithm in general, and 50% more accurately for the classes ‘residential area’ and ‘roads’. The results suggest that ASTER data and the Kohonen self-organized neural network classification can be used as an alternative data and method in a land use update operational system.  相似文献   

Calc-alkaline rear-arc magmatism in the Fuegian Andes: Implications for the mid-cretaceous tectonomagmatic evolution of southernmost South America     

Mauricio González Guillot  Mónica Escayola  Rogelio Acevedo 《Journal of South American Earth Sciences》2011,31(1):1-16

The magmatic arc of the Fuegian Andes is composed mostly of Upper Mesozoic to Cenozoic calc-alkaline plutons and subordinated lavas. To the rear arc, however, isolated mid-Cretaceous monzonitic plutons and small calc-alkaline dykes and sills crop out. This calc-alkaline unit (the Ushuaia Peninsula Andesites, UPA) includes hornblende-rich, porphyritic quartz meladiorites, granodiorites, andesites, dacites and lamprophyres. Radiometric dating and cross-cutting relationships indicate that UPA is younger than the monzonitic suite. The geochemistry of UPA is medium to high K, with high LILE (Ba 500–2000 ppm, Sr 800–1400 ppm), HFSE (Th 7–23 ppm, Nb 7–13 ppm, Ta 0.5–1.1 ppm) and LREE (La 16–51 ppm) contents, along with relatively low HREE (Yb 1.7–1.3 ppm) and Y (9–19 ppm). The similar mineralogy and geochemistry of all UPA rocks suggest they evolved from a common parental magma, by low pressure crystal fractionation, without significant crustal assimilation. A pure Rayleigh fractionation model indicates that 60–65% of crystal fractionation of 60% hornblende + 34% plagioclase + 4% clinopyroxene + 1% Fe-Ti oxide, apatite and sphene (a paragenesis similar of UPA mafic rocks) can explain evolution from lamprophyres to dacites. The UPA has higher LILE, HFSE and LREE, and lower HREE and Y than the calc-alkaline plutons and lavas of the volcanic front. The HREE and Y are lower than in the potassic plutons as well. High concentrations of Th, Nb, Ta, Zr, Hf, LREE and Ce/Pb, and low U/Th, Ba/Th ratios in UPA, even in the least differentiated samples, suggest contributions from subducted sediments to the mantle source. On the other hand, relatively low HREE and Y, high LREE/HREE (La/Yb 11–38) ratios and Nb-Ta contents can be interpreted as mantle metasomatism by partial melts of either subducted garnetiferous oceanic sediment or basalt as well. Additionally, high LILE content in UPA, similar to the potassic plutons, suggests also a mantle wedge previously metasomatized by potassic parental magmas in their route to crustal levels. Therefore, UPA represents a unique suite in the Fuegian arc generated in a multiple hybridized source. UPA generation is related to a transition from normal to flat subduction which additionally caused the widening and landward migration of the magmatic arc, as well as crustal deformation. Rear-arc magmatism endured ca. 22 m.y.; afterwards, calc-alkaline magmatism remained at the volcanic front.  相似文献   

No sedimentary records indicating southerly flow of the paleo-Upper Yangtze River from the First Bend in southeastern Tibet     

《Gondwana Research》2016

It is a long-debated issue whether the Upper Yangtze River once flowed southward from its First Bend as a major tributary of the Red River. The Yangbi valley was assumed as a trough carved by the paleo-Upper Yangtze River. This argument, however, has not been substantiated because of the uncertainty of what is beneath the Quaternary sediments of the valley. We conducted a drilling project in an attempt of resolving this outstanding puzzle. We also studied the Upper Eocene–Lower Oligocene Baoxiangsi and Jinsichang Formations distributed widely to the west of the Yangbi valley because sandstone of the Baoxiangsi Formation were previously regarded as remnants of the south-flowing paleo-Upper Yangtze River. Two drilled holes reveal that the Yangbi valley is entirely filled with Quaternary alluvial-fan and bog deposits and contains no typical fluvial sandstone. The base of the valley is the well-consolidated breccia of the Baoxiangsi Formation. The sedimentary analysis shows that the Baoxiangsi and Jinsichang successions are composed mostly of alluvial-fan, lacustrine, fan-delta and braided-stream facies, and interpreted to have formed in an intermontane rift basin. Facies analysis in conjunction with paleocurrent restoration further shows that the bulk of the Baoxiangsi and Jinsichang sediments were shed from local highlands and debouched to the basin mainly from the south and west. Collectively, our sedimentary investigations of both boreholes and outcrops lend no support of the long-held view that the paleo-Upper Yangtze River flowed to the south through the region south of the First Bend. It, however, remains an unresolved problem how the ancestral Upper Yangtze River evolved during the Tertiary.  相似文献   

Thermo-mechanical modeling of the obduction process based on the Oman Ophiolite case     

《Gondwana Research》2016

Obduction emplaces regional-scale fragments of oceanic lithosphere (ophiolites) over continental lithosphere margins of much lower density. For this reason, the mechanisms responsible for obduction remain enigmatic in the framework of plate tectonics. We present two-dimensional (2D) thermo-mechanical models of obduction and investigate the possible dynamics and physical controls of this process. Model geometry and boundary conditions are based on available geological and geochronological data and numerical modeling results are validated against petrological and structural observations of the Oman (Semail) Ophiolite. Our model reproduces the stages of oceanic subduction initiation away from the Arabian margin, the emplacement of the Oman Ophiolite on top of it, and the domal exhumation of the metamorphosed margin through the ophiolitic nappe. A systematic study indicates that 350–400 km of bulk shortening provides the best fit for both maximum pressure–temperature conditions of the metamorphosed margin (1.5–2.5 GPa/450–600 °C) and the dimension of the ophiolitic nappe (~ 170 km width). Our results confirm that a thermal anomaly located close to the Arabian margin (~ 100 km) is needed to initiate obduction. We further suggest that a strong continental basement rheology is a prerequisite for ophiolite emplacement.  相似文献   

Geochemistry and petrogenesis of Early Carboniferous volcanic rocks in East Junggar,North Xinjiang: Implications for post-collisional magmatism and geodynamic process     

《Gondwana Research》2016,29(4):1466-1481

Early Carboniferous volcanic rocks in the Batamayineishan Formation overlie unconformably the molasse deposits and the ophiolitic mélanges and are restricted in narrow zones along both sides of the Kalamaili orogenic belt in North Xinjiang, southern Central Asian Orogenic Belt. These rocks demonstrate the post-collisional setting in East Junggar commenced in Tournaisian and also mark an important transitional period from the final amalgamation to late Paleozoic voluminous juvenile granitoids in East Junggar. The volcanic rocks are composed of basalt, basaltic andesite, andesite, trachyte and rhyolite. Both mafic and felsic rocks are characterized by enrichments in large ion lithophile elements, light rare earth elements and depletion in Nb and Ta, low initial ⁸⁷Sr/⁸⁶Sr and high, positive ɛ_Nd(t). Three groups of mafic rocks have been identified: Shoshonitic group 1 has the highest MgO, CaO, Ni and Cr and the lowest Na₂O, Al₂O₃, La, Ba, La/Yb and Ba/Th with primary magma features; group 2 calc-alkaline and high-K calc-alkaline mafic rocks have the lowest K₂O, P₂O₅, Th and Th/Nb, and the highest TiO₂; and group 3 (shoshonitic to potassic alkaline) has the highest K₂O, P₂O₅, La, Ba, La/Yb and Th/Nb, and the lowest TiO₂. The A-type-like felsic rocks were derived from the differentiation of the mafic magma. Geological and geochemical evidences indicate that the Batamayineishan Formation was generated from the process of slab breakoff (detachment). Group 1 samples are produced by decompressional melting of the upwelling asthenosphere mainly composed of spinel and garnet (50:50) lherzolite which has been enriched by overlying metasomatized lithosphere during ascent. Group 2 is derived from 5–10% partial melting of shallower spinel-bearing lithospheric mantle induced by the hot rising asthenosphere, where the contribution of slab-derived fluid is predominant. Low partial melting (3–5%) of the mantle wedge and/or thickened lithospheric mantle enriched by slab-derived components generates group 3. Slab breakoff as an important geodynamic process accounts for the post-collisional magmatism between 343.5 Ma–330 Ma, providing a model for post-collisional crust–mantle interaction in the CAOB.  相似文献   

The influence of topography on the forest surface temperature retrieved from Landsat TM,ETM + and ASTER thermal channels     

Martin Hais  Tomáš Kučera 《ISPRS Journal of Photogrammetry and Remote Sensing》2009,64(6):585-591

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Deformation and displacement fields of the Himalayan arc,seismicity and large earthquake hazards in its eastern segment and vicinity     

《Tectonophysics》1987,138(1):93-107

The Himalayan arc is a type of plate margin similar to an island arc and is a world-famous region of tectonic and seismic activities, where a series of large earthquakes have occurred in historical time. In this paper, the vertical deformation and horizontal displacement fields of the Himalayan arc are theoretically derived from the viewpoint of the collision between the Indian and Eurasian plates. In the light of the observed data, the seismicity, earthquake focal mechanism, seismotectonic and geomorphological features of the arc and its vicinity are reasonably explained. The characteristics of seismicity and the possibility of earthquakes with magnitude above 8 occurring in this region in the future are studied.  相似文献   

Circulation patterns inferred from the movement of detached buoys in the eastern Gulf of Mexico     

《Continental Shelf Research》1987,7(8):883-894

The release times of five buoys, which broke free of moorings on the Alabama inner shelf, are known. The locations of subsequent sightings or recoveries of the buoys gave estimated trajectories of the buoys. These results show that the inner-shelf circulation is strongly wind-driven. When the Loop Current penetrates deeply into the northeastern Gulf of Mexico, outer shelf waters are often entrained by the Loop Current.  相似文献   

Distributed,high-resolution modelling of 18O signals in a meso-scale catchment     

《Journal of Hydrology》2007,332(3-4):497-510

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Local oceanic response to atmospheric forcing in the Gulf Stream region     

《Deep Sea Research Part II: Topical Studies in Oceanography》2013

The dominance of shifts in the location of the Gulf Stream (GS) in the local heat balance was observed in an hourly 15-month record of unprecedented surface mooring measurements at a site in the western North Atlantic occupied from November 2005 to January 2007. Instrumentation on the buoy provided a high quality record of air-sea exchanges of momentum, heat, and freshwater flux; and oceanographic sensors recorded ocean variability in the upper 640 m. The mooring was at times in the GS and at other times north of the GS. Our intent was to isolate the local oceanic response to the atmosphere from the influence of the GS shifts. A one-dimensional heat budget analysis indicated that the advective contribution from the GS shifts dwarfed the heat contribution by atmospheric forcing and therefore played the dominant role for upper oceanic thermal variability during the whole time record. A GS case study (i.e., when the surface mooring was in the GS), isolated the upper oceanic response to the atmospheric forcing in the GS and supported the critical role of GS shifts in total oceanic heat content. Through both an Empirical Orthogonal Function (EOF) analysis and by referencing temperatures to that observed at 200 m, the impact of GS shifts and atmospheric forcing were decomposed, allowing the local oceanic thermal response to be isolated. This local oceanic response was particularly prominent during the period of sustained heating during summer. A case study of summer conditions revealed a near surface flow consistent with Ekman dynamics within a shallow, warm ocean mixed layer.  相似文献