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191.
Carl E. Kurt 《Ground water》1979,17(6):550-555
192.
Micrometeorologists have traditionally set aside consideration of horizontal variability and have studied boundary-layer structure with horizontal homogeneity. The numerical forecasting of boundary-layer structures, over normally varying terrain and including normal disturbances such as fronts, requires selection of an appropriate horizontal scale.A simple analysis of steady-state balance between horizontal advection and vertical diffusion provides estimates of the vertical scale (or depth) of surface-induced features. The scale height is a function of the horizontal scale of the variations. Models neglecting important terrain scales of length below ~ 1000 km can predict down to levels of ~ 0.5 to 1 km while those that neglect important terrain scales below ~ 100 km can predict down to ~ 0.2 to 0.6 km. Below these levels, any predicted features will be dominated by the vertical diffusion so that they are solutions of a one-dimensional boundary-value problem.The boundary-induced advection effects dominate free atmosphere advection effects in the lowest few hundred meters as well. This means that if mesoscale advections are resolved and terrain influences are strong, the predictions in the layer ~ 0.2 to 0.8 km can provide mesoscale detail without mesoscale initial conditions above the surface, because the surface forcing will dominate the solution. 相似文献
193.
A biotite dacite that intrudes metamorphic rocks on Okinawa in the Ryukyu island arc has been dated at 12 m.y. by the40Ar/39Ar method. The details of this age measurement and a compilation of radiometric ages for the Ryukyu island arc and adjacent regions are presented. These data suggest that from 65 to 12 m.y. ago the magmatic axis of the Ryukyu arc was confined to a very narrow zone along the arc. In Kyushu and Shikoku, the southern Japanese islands, intrusive and volcanic igneous rocks dated as 21?12 m.y. occur over a much wider zone than in the Ryukyu arc. The apparent difference in width of the magmatic zones may be due to different absolute motions of the overthrust plates of those two regions of subduction. The dissimilarity of available radiometric ages for the Ryukyu arc and for Taiwan suggest different histories for the development of these two features. The occurrence of active volcanoes in association with the Okinawa Trough, northwest of the Ryukyu island arc, may indicate that the trough itself developed in the last 12 m.y. 相似文献
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Three groups of Mesozoic shoshonitic or high-K calc-alkaline intrusive rocks are identified in Dabieshan high-pressure (HP) and ultrahigh-pressure (UHP) metamorphic zone, east-central China and they are related to: (I) slab breakoff; (II) magmatic underplating; and (III) doming. Group-I, the slab breakoff-type, consists of late Triassic (210 Ma) mafic monzodiorites. It has moderate to high Sr, and low Rb and Ba abundances, and moderate light rare earth element (LREE)/heavy rare earth element (HREE) and K/Rb ratios. Group-II, the underplating-type, consists mainly of middle Jurassic–early Cretaceous (160–120 Ma) hornblende quartz monzonitic, biotite monzogranitic, and syenogranitic plutons, characterized by relatively high LREE/HREE and K/Rb ratios, and by a large range in concentration of Sr and Ba, coupled with much smaller range in Rb. Group-III, the doming-type, is represented by Cretaceous (125–95 Ma) granitic stocks and granitic porphyry. Compared with group-II, it has high Rb, Y and HREE abundances, low Sr and Ba abundances and low LREE/HREE and K/Rb ratios. All groups have similar Nd and Sr isotopic compositions. Among the three groups, post-collisional granitoid magmatism (group-II) with ages of 160 to 120 Ma, post-dating the HP and UHP metamorphism at 245 to 220 Ma, is the most abundant in the Dabieshan area. The post-collisional granitoid plutons were initially emplaced at different levels ranging from mid-crust to near-surface. This study shows that the whole-rock chemistry of the granitoids vary systematically with crystallization pressures. For example, K2O, normative Or, Rb and Zr show the strongest increase with decreasing pressure, whereas Ba, Nb, Nd, Yb, MnO, and normative An decrease upward in the Dabie Block. It is suggested that ascent of differentiated, buoyant liquids, combined with fractionation paired with assimilation (AFC), is responsible for the vertical variation. Geological, geochemical and petrological data indicate that group-I could have been generated by partial melting of enriched subcontinental lithosphere mantle due to slab breakoff. Group-II rocks could have been produced mainly from crustal assimilation/melting and fractional crystallization of mantle-derived magmas, whereas group-III magma could have derived from anatexis of the Dabie complex and was highly evolved in a hot doming setting. The late Triassic-early Jurassic slab breakoff may be responsible for the exhumation of UHP rocks through the mantle. The voluminous granitic emplacement together with an episode of rapid denudation suggests that magmatic underplating and inflation could have played a role in the Middle Jurassic–Early Cretaceous rapid exhumation of Dabieshan. 相似文献
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Summary Vein-type barite mineralizations from the Saxothuringian and Moldanubian zone of the NE Bavarian Basement have similar87Sr/86Sr ratios. The different rock types of both tectonic regions are of no influence on those ratios, so that no distinction between barites from the Moldanubian and Saxothuringian zone can be made. The87Sr/86Sr data point to a crustal derivation of ore-bearing fluids rather than to a homogeneous mantle source. Carbonates associated with barite in these veins display similar ratios. The87Sr/86Sr ratios of barites vary with host rocks. From the enclosing wall rocks towards the granitic core zone the ratios tend to increase, while a continuous decrease along with plunge of fold axes (e.g. Berga Anticline) of the host anticline is demonstrated for the Frankenwald vein-type barite occurrences. Based on these isotope data a model on unconformity related barite deposits is discussed for this area.
Strontium-Isotopen-Variationen in Gang-Baryten aus den Nordost-Bayerischen Grundgebirge: Bedeutung für die Herkunft der Elemente und für die Genese von Barytlagerstätten an Diskordanzen
Zusammenfassung Die Strontium-Isotopen-Variation in Gang-Baryten des NE-bayerischen Grundgebirges zeigen87Sr/86Sr-Verhältnisse, die eine krustale Herkunft der Lösungen erkennen lassen. Das Sr-Verhältnis wird durch begleitende Karbonate nicht verändert. Ihre Verhältnisse sind ähnlich denen des Sulfats. Innerhalb der beiden Gruppen (A: nichtmetamorphes Paläozoikum des Frankenwaldes, Bergaer Sattel; B: Granite mit Kristallinhülle des Fichtelgebirges und Oberpfälzer Wald) ist eine Tendenz zu höheren bzw. granittypischen Verhältnissen mit Annäherung an den Sattelkern bzw. zum Granit hin feststellbar. Auf der Grundlage dieser Isotopendaten wird ein Genesemodell für diese Barytvorkommen diskutiert, welches von der Bindung dieser Lagerstätten an die spätvariszische Diskordanz ausgeht.相似文献
200.
Variability of dissolved reactive phosphate flux rates in nearshore estuarine sediments: Effects of groundwater flow 总被引:1,自引:0,他引:1
Theoretical diffusive flux rates for dissolved reactive phosphate (DRP) were determined for sediments in a small area of the Indian River, Florida for the period March–May 1982. Flux rates from the sediment varied from 29 to 70 × 10?6g per m2 per day in seagrass associated sediments to 3–25 × 10?6g per m2 per day for an area devoid of seagrass. Simultaneous measurements of groundwater seepage velocities indicated greater velocities in seagrass associated sediments (1.03 × 10?6m per sec) than an area devoid of grass (0.77 × 10?6m per sec). Measured seepage flux accounted for more than 99% of the combined estimated diffusive and seepage flux of DRP for nearshore seagrass sediments. Also noted was an apparent direct relationship between tidal height, DRP and seepage velocity in nearshore sediments (25 m from shore) which further demonstrates the importance of hydrogeologic variables to these areas. 相似文献