我国东部近百年夏季雨型的大气环流和海温场特征     

杨永胜  施能 《南京气象学院学报》2001,24(4):513-519

根据新划分的1900－1998年东部夏季雨型序列，分析了与各类雨型相对应的北球海平面气压场和海表温度距平均的行征。指出不同雨型对应着不同的环流场和海表温度距平场，而且存在着差异的强信号区。  相似文献   

Evolution of Moldanubian rocks in Austria: review and synthesis   总被引：7，自引：1，他引：7  

K. PETRAKAKIS 《Journal of Metamorphic Geology》1997,15(2):203-222

The Moldanubian zone in Austria comprises three major lithological units. Despite general agreement that nappe tectonics contributed to its current structure, the number and position of tectonic boundaries, or continental pieces that were involved in its evolution, as well as the age, extent and position of oceanic sutures are disputed. Recent models ascribe the Moldanubian tectonostratigraphic structure to its oblique, N- to NE-directed collision with Moravia only. The rocks of the Moldanubian Bunte series and Gföhl unit experienced a common, intensive overprint in the range 700–800 °C and 8–11 kbar. Textural evidence suggests that this overprint was attained during nearly isothermal decompression, so the rocks experienced higher pressures prior to this overprint. These conditions constrain a continent–continent collision environment that contributed to the formation of the Moldanubian granulites. The estimated metamorphic temperatures are close to <i>T</i><sub>max</sub>. During this Hercynian, high-<i>T </i> overprint, the minerals underwent extensive diffusion-controlled homogenization of elements. The early stages of retrogression of these units were characterized by isobaric cooling at <i>c</i>. 6 kbar in the range 650–500 °C that is related to the oblique collision of the Moldanubian and Moravian zones. Cooling to <i>c</i>. 400 °C is demonstrated by unstrained, diasporized corundum inclusions in garnet of common Moldanubian granulites. The available age data (including cooling ages) from metamorphic rocks show a very wide variation between 490 and 280 Ma that depends on sample characteristics and the dating method used. They demonstrate clearly, however, that the metamorphic overprint is Hercynian. The possibility that the large variation in ages reflects homogenization, resetting and closure of the isotopic systems attained at different, sample- and method-specific times is discussed. Age data varying between <i>c</i>. 370 and <i>c</i>. 346 Ma tentatively date different stages during the Hercynian, high-<i>T </i> decompression. The majority of zircon and monazite U/Pb ages as well as the hornblende and muscovite Ar/Ar cooling ages cluster between <i>c</i>. 345 and <i>c</i>. 326 Ma and date the effective closure conditions and the onset of rapid, nearly isobaric cooling. The continent–continent collision that formed the granulites pre-dates <i>c</i>. 370 Ma. The intra-Moldanubian nappe-stacking pre-dates thrusting of the Moldanubian zone over the Moravian zone. The range <i>c</i>. 340–335 Ma is the lower limit for completion of tectonic activity in the Moldanubian zone. The Moldanubian series are post-tectonically intruded by granitoids of the Southern Bohemian Pluton. Recent age determinations and geochemical evidence suggest that the formation of the early granitoid types took place in the lower crust in connection with the Hercynian high-grade overprint. The Moldanubian Monotone series in Austria is separated from the other Moldanubian units by a conspicuous tectonic horizon. It also differs from them by its characteristic high-<i>T </i>, low-<i>P</i> overprint, which is best demonstrated by a widespread cordierite gneiss.  相似文献   

The Alpine geodynamic evolution of Penninic nappes in the eastern Central Alps   总被引：1，自引：0，他引：1  

U. RING 《Journal of Metamorphic Geology》1992,10(1):33-53

The eastern Central Alps consist of several Pennine nappes with different tectonometamorphic histories. The tectonically uppermost units (oceanic Avers Bündnerschiefer, continental Suretta and Tambo nappes, oceanic Vals Bündnerschiefer) show Cretaceous/early Tertiary W-directed thrusting with associated blueschist facies metamorphism related to subduction of the Pennine units beneath the Austroalpine continental crust. This event caused eclogite facies metamorphism in the underlying continental Adula nappe. The gross effect was crustal thickening. The tectonically lower, continental Simano nappe is devoid of any imprint from this event. In the course of continent-continent collision, high- T metamorphism and N-directed movements occurred. Both affected the whole nappe pile more or less continuously from amphibolite to greenschist facies conditions. Crustal thinning commenced during the regional temperature peak. A final phase is related to differential uplift under retrograde P–T conditions. Further thinning of the crust was accommodated by E- to NE-directed extensional deformation.  相似文献   

Verteilung ausgewählter toxischer Spurenelemente im Sediment des Breitlingsees bei Brandenburg     

Georg Schettler 《洁净——土壤、空气、水》1992,20(3):142-149

Distribution of Selected Toxic Trace Elements in the Sediment of Lake Breitling near Brandenburg. Considerable enrichments of several heavy metals in relation to the local geological background were found in the surface sediments of Lake Breitling (Havel lake system) (Zn: 50-fold, Cd: 25-fold, Cu: 14-fold, Pb: 13-fold), whereas Be, Co and V are remarkably unchanged if the increased clay mineral content in the more recent sediments is considered. – The heavy metal distribution patterns indicate a high percentage of atmospheric input of these elements, and according to geochemical profiles heavy metal deposition has been constant on a high level for years. – Especially the most enriched Zn which was found to some extent NH<sub>4</sub>Ac-exchangeable deserves ecotoxic attention.  相似文献   

Timing of low-temperature metamorphism and cooling of the Paleozoic and Mesozoic formations of the Bükkium,innermost Western Carpathians,Hungary     

P. Árkai  K. Balogh  I. Dunkl 《International Journal of Earth Sciences》1995,84(2):334-344

K-Ar ages of illite-muscovite and fission track ages of zircon and apatite were determined from various lithotypes of the Bükkium, which forms the innermost segment of the Western Carpathians. The stratigraphic ages of these Dinaric type formations cover a wide range from the Late Ordovician up to the Late Jurassic. The grade of the orogenic dynamo-thermal metamorphism varies from the late diagenetic zone through the <img src="/content/p548584w3m12784t/xxlarge8216.gif" alt="lsquo" align="BASELINE" BORDER="0">anchizone<img src="/content/p548584w3m12784t/xxlarge8217.gif" alt="rsquo" align="BASELINE" BORDER="0"> up to the <img src="/content/p548584w3m12784t/xxlarge8216.gif" alt="lsquo" align="BASELINE" BORDER="0">epizone<img src="/content/p548584w3m12784t/xxlarge8217.gif" alt="rsquo" align="BASELINE" BORDER="0"> (chlorite, maximally biotite isograd of the greenschist facies). The K-Ar system of the illite-muscovite in the < 2 <img src="/content/p548584w3m12784t/xxlarge956.gif" alt="mgr" align="MIDDLE" BORDER="0">m grain-size fraction approached equilibrium only in <img src="/content/p548584w3m12784t/xxlarge8216.gif" alt="lsquo" align="BASELINE" BORDER="0">epizonal<img src="/content/p548584w3m12784t/xxlarge8217.gif" alt="rsquo" align="BASELINE" BORDER="0"> and high-temperature <img src="/content/p548584w3m12784t/xxlarge8216.gif" alt="lsquo" align="BASELINE" BORDER="0">anchizonal<img src="/content/p548584w3m12784t/xxlarge8217.gif" alt="rsquo" align="BASELINE" BORDER="0"> conditions. The orogenic metamorphism culminated between the eo-Hellenic (160-120 Ma) phase connected to the beginning of the subduction in the Dinarides, and the Austrian (100-95 Ma) phase characterized by compressional crustal thickening. No isotope geochronological evidence was found for proving any Hercynian recrystallization. The stability field of fission tracks in zircon was approached using the thermal histories of the different tectonic units. A temperature less than 250°C and effective heating time of 20–30 Ma had only negligible effects on the tracks, whereas total annealing was reached between 250 and 300°C. Apatite fission track ages from the Paleozoic and Mesozoic formations show that the uplift of the Bükk Mountains occurred only in the Tertiary (not earlier than ca. 40 Ma ago). Thermal modeling based on apatite fission track length spectra and preserved Paleogene sediment thickness data proved that the Late Neogene burial of the recently exhumed plateau of the Bükk Mountains exceeded 1 km.  相似文献   

Hard X-ray all-sky imaging with BATSE/CGRO     

S. N. Zhang  B. A. Harmon  G. J. Fishman  W. S. Paciesas 《Experimental Astronomy》1995,6(4):57-62

The large Area Detectors (LADs) of the BATSE experiment aboard the Compton Gamma-ray Observatory have been used recently as the first hard X-ray all-sky imager at energies between 20 keV and 300 keV. The Earth occultation process is formulated in terms of a curved Radon transform convoluted by a step transform in a selected field of view (FOV) ranging from 5°×5° to 40°×40°. The Maximum Entropy Method is then used to reconstruct an image in the hard X-ray sky. Multiple images of different regions of the sky can be produced simultaneously. A source location accuracy of 0.1° for strong sources and a sensitivity limit of 100 mCrab have been achieved in an one-day integration period.Invited Paper on <img src="/content/t31r3462927148p0/xxlarge8220.gif" alt="ldquo" align="MIDDLE" BORDER="0">Imaging in High Energy Astronomy<img src="/content/t31r3462927148p0/xxlarge8221.gif" alt="rdquo" align="MIDDLE" BORDER="0">, Sept., 1994, Capri, Italyalso Universities Space Research Association  相似文献   

Cretaceous amber inclusions of Spain and Myanmar demonstrate early diversification and wide dispersal of Cephenniitae (Coleoptera: Staphylinidae: Scydmaeninae)     

《Cretaceous Research》2016

The taxonomic status of previously misplaced species of an ant-like stone beetle from Spanish amber (Albian) is clarified. Specimens of <em>Kachinus magnificus</em> (originally placed as incertae sedis within Scydmaenitae) were re-examined and their characters were found different from those of the type species of <em>Kachinus</em> from Myanmar amber. Consequently, <em>Archeutheia</em> gen. nov. is proposed to accommodate the Spanish species, resulting in <em>Archeutheia magnifica</em> comb. nov. Moreover, in a comprehensive phylogenetic analysis <em>Archeutheia</em> was placed as a sister group to extant <em>Eutheia</em>, within the tribe Eutheiini of Cephenniitae. A specimen of an undetermined genus from Myanmar amber clearly belonging in Cephenniini is also recorded. Both taxa represent the first definite Cretaceous Cephenniitae, a supertribe whose recent members are distributed on all continents but are especially diverse in the Oriental and East Palaearctic regions. This finding demonstrates a diversification of two presently most species-rich tribes of Cephenniitae already in Early Cretaceous. <em>Archeutheia</em> is strikingly similar to the extant species of <em>Eutheia</em> and <em>Veraphis</em>, showing male dimorphic characters (modified protrochanters) and antennal cavities characteristic of Palaearctic Eutheiini. This fact suggests a long morphological stability in the supertribe. A previously proposed hypothesis of an early presence of the Cephenniitae in the Northern Hemisphere is for the first time supported by the fossil record, and the palaeolocalities (western Europe and Southeast Asia) demonstrate a wide distribution of Cephenniitae in the Cretaceous and an early split of its ancestral lineage.  相似文献   

Gravity anomalies and deep structure of the Ninetyeast Ridge north of the equator,eastern Indian Ocean — a hot spot trace model     

Manoj Mukhopadhyay  M. B. R. Krishna 《Marine Geophysical Researches》1995,17(2):201-216

The Ninetyeast Ridge north of the equator in the eastern Indian Ocean is actively deforming as evidenced by seismicity and its eastward subduction below the Andaman Trench. Basement of the ridge is elevated nearly 2 km with respect to the Bengal Fan; seismic surveys demonstrate continuity of the ridge beneath sediment for 700 km north of 10° N where the ridge plunges below the Fan sediment. The ridge is characterised by a free-air gravity high of 50 mgal amplitude and 350 km wavelength, and along-strike continuity of 1500 km in a north-south direction, closely fringing (locally, even abutting) the Andaman arc-trench bipolar gravity field. Regression analysis between gravity and bathymetry indicates that the ridge gravity field cannot be explained solely by its elevation. The ridge gravity field becomes gradually subdued northwards where overlying Bengal Fan sediments have a smaller density contrast with the ridge material. Our gravity interpretation, partly constrained by seismic data, infers that the ridge overlies significant crustal mass anomalies consistent with the hot spot model for the ridge. The anomalous mass is less dense by about 0.27 g cm<sup>–3</sup> than the surrounding oceanic upper mantle, and acts as a <img src="/content/t231l8j55038r16j/xxlarge8216.gif" alt="lsquo" align="BASELINE" BORDER="0">cushion<img src="/content/t231l8j55038r16j/xxlarge8217.gif" alt="rsquo" align="BASELINE" BORDER="0"> for isostatic compensation of the ridge at the base of the crust. This <img src="/content/t231l8j55038r16j/xxlarge8216.gif" alt="lsquo" align="BASELINE" BORDER="0">cushion<img src="/content/t231l8j55038r16j/xxlarge8217.gif" alt="rsquo" align="BASELINE" BORDER="0"> is up to 8 km thick and 400–600 km wide. Additional complexities are created by partial subduction of the ridge below the Andaman Trench that locally modifies the arc-trench gravity field.  相似文献   

The P–T–t evolution of the exhumed Himalayan metamorphic core in the Likhu Khola region,East Central Nepal          下载免费PDF全文

S. Shrestha  K. P. Larson  C. Guilmette  M. A. Smit 《Journal of Metamorphic Geology》2017,35(6):663-693

The recent identification of multiple strike‐parallel discontinuities within the exhumed Himalayan metamorphic core has helped revise the understanding of convergence accommodation processes within the former mid‐crust exposed in the Himalaya. Whilst the significance of these discontinuities to the overall development of the mountain belt is still being investigated, their identification and characterization has become important for potential correlations across regions, and for constraining the kinematic framework of the mid‐crust. The result of new phase equilibria modelling, trace element analysis and high‐precision Lu–Hf garnet dating of the metapelites from the Likhu Khola region in east central Nepal, combined with the previously published monazite petrochronology data confirms the presence of one of such cryptic thrust‐sense tectonometamorphic discontinuities within the lower portion of the exhumed metamorphic core and provides new constraints on the <i>P–T</i> estimates for that region. The location of the discontinuity is marked by an abrupt change in the nature of <i>P–T–t</i> paths of the rocks across it. The rocks in the footwall are characterized by a prograde burial <i>P–T</i> path with peak metamorphic conditions of ~660°C and ~9.5 kbar likely in the mid‐to‐late Miocene, which are overlain by the hanging wall rocks, that preserve retrograde <i>P–T</i> paths with <i>P–T</i> conditions of >700°C and ~7 kbar in the early Miocene. The occurrence of this thrust‐sense structure that separates rock units with unique metamorphic histories is compatible with orogenic models that identify a spatial and temporal transition from early midcrustal deformation and metamorphism in the deeper hinterland to later deformation and metamorphism towards the shallower foreland of the orogen. Moreover, these observations are comparable with those made across other discontinuities at similar structural levels along the Himalaya, confirming their importance as important orogen‐scale structures.  相似文献   

Interaction of deformation and metamorphism during subduction and exhumation of hydrated oceanic mantle: Insights from the Western Alps     

G. REBAY  M. I. SPALLA  D. ZANONI 《Journal of Metamorphic Geology》2012,30(7):687-702

Petrological investigations supported by multi‐scale structural analysis of eclogitized serpentinite in the Zermatt–Saas Zone of the Western Alps allows for the determination of mineral assemblages related to successive fabrics, upon which the <i>P–T–d–t</i> path of these hydrated mantle rocks can be inferred. Serpentinites of the upper Valtournanche, with lenses and dykes of metagabbro and meta‐rodingite, display an Alpine polyphase metamorphic evolution from eclogite to epidote‐amphibolite facies conditions associated with three successive foliations having different parageneses in these rocks. Serpentinite mainly consists of serpentine with minor magnetite; however, where S1 and S2 foliations are pervasive, metamorphic olivine, together with Ti‐clinohumite and clinopyroxene, are also found. The mineral assemblage associated with D1 includes serpentine1, clinopyroxene1, opaque minerals, titanite ± olivine1, Ti‐clinohumite1 and ilmenite; the D2 assemblage is the same (±chlorite) but minerals have different compositions. The assemblage associated with D3 comprises serpentine3, opaque minerals, ±chlorite3, ilmenite and amphibole3. Ti‐clinohumite is associated with veins that are older than D2 and pre‐date D3. Veins that post‐date D3 are characterized by amphibole + chlorite or by serpentine. <i>P</i>–<i>T</i> conditions for S2 parageneses evaluated using two pseudosections for different bulk compositions suggest that these rocks experienced pressures >2.5 ± 0.3 GPa at temperatures slightly higher than 600 °C. The late epidote–amphibolite facies re‐equilibration associated with D3 and D4 developed during late syn‐exhumation deformation related to folding and testifies to a small temperature decrease. These results, which were integrated in the regional framework, suggest that different portions of the Zermatt–Saas Zone registered different <i>P</i>–<i>T</i> peak conditions and underwent different exhumation paths. In addition, the inferred <i>P</i>–<i>T</i>–<i>d</i>–<i>t</i> path suggests that the Valtournanche serpentinites re‐equilibrated close to the UHP conditions registered by the Cignana meta‐cherts. These results imply that tectonic slices exhumed after UHP metamorphism might be wider than previously reported or that small‐size UHP units, tectonically sampled during the Alpine convergence, are more abundant than those that have been detected to date.  相似文献