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31.
变泥质岩的深熔作用与具铈（Ce）负异常熔体的成因 总被引：6，自引：0，他引：6
对美国加州南Sierra Nevada岩基中一个典型的中生代变质表壳岩及其混合岩带进行了详细的野外观察和元素地球化学研究。研究发现:在持久(约为150Ma)的花岗岩侵位作用下,早白垩世变泥质岩发生达角闪岩相的中高级变质作用和部分熔融,导致Isabella混合岩的形成;浅色体具有和变泥质岩及混合岩近平行的REE分布模式,但浅色体的LREE含量相对较低;和变泥质岩相似,混合岩中的浅色体具有显著的Ce负异常。野外观测、岩相观察及元素地球化学特征表明,浅色体显著的Ce负异常是继承了原岩的Ce负异常特征,而不是由于副矿物(磷灰石、独居石或锆石)的差异溶解或结晶分异作用造成的。早白垩世变泥质岩(浅色体的原岩)主要由泥质及沙质海相沉积物组成,局部夹基性火山灰和火山碎屑,形成于与大陆岛弧密切相关的浅海环境。原岩的Ce负异常反映了较还原的浅海沉积环境。具有Ce负异常浅色体的产出表明,如果俯冲带上的沉积岩在俯冲过程中发生部分熔融作用并且所产生的熔体参与大洋型岛弧岩浆作用,最终可以导致具有Ce异常的基性岩浆生成。 相似文献
32.
Conceptual model for millennial climate variability: a possible combined solar-thermohaline circulation origin for the ~1,500-year cycle 总被引：1，自引：0，他引：1
Dansgaard-Oeschger and Heinrich events are the most pronounced climatic changes over the last 120,000 years. Although many of their properties were derived from climate reconstructions, the associated physical mechanisms are not yet fully understood. These events are paced by a ~1,500-year periodicity whose origin remains unclear. In a conceptual model approach, we show that this millennial variability can originate from rectification of an external (solar) forcing, and suggest that the thermohaline circulation, through a threshold response, could be the rectifier. We argue that internal threshold response of the thermohaline circulation (THC) to solar forcing is more likely to produce the observed DO cycles than amplification of weak direct ~1,500-year forcing of unknown origin, by THC. One consequence of our concept is that the millennial variability is viewed as a derived mode without physical processes on its characteristic time scale. Rather, the mode results from the linear representation in the Fourier space of nonlinearly transformed fundamental modes. 相似文献
33.
Climate Dynamics - Variations of the global sea level pressure (SLP) field reflect atmospheric and oceanic influences and have a profound influence on temperature, precipitation and the global... 相似文献
34.
Jasim?Al-KhalidiEmail author Mihai?Dima Sabina?Stefan 《Theoretical and Applied Climatology》2018,133(1-2):179-190
The impact of large-scale modes on Iraq climate is investigated here based on winter and spring fields of temperature and precipitation. The temperature data (1971–2010) was recorded at 8 stations whereas the precipitation fields (1981–2010) were recorded at 18 locations. Empirical orthogonal function analyses were performed in order to characterize the spatial variability of the Iraq climatological parameters. The relationships between the global sea surface temperature, sea level pressure, and geopotential height fields with the dominant modes of Iraq temperature and precipitation were also investigated. Correlation and regression maps emphasize links between Iraq climate and large-scale modes, like the Atlantic Multidecadal Oscillation and the El Niño Southern Oscillation phenomenon. 相似文献
35.
The applicability of resistivity methods to ground water investigations is well recognized. As water-saturated rock formations
have a lower electrical resistivity than dry ones, an electrical resistivity survey should result in low resistivity anomalies. Normally, such anomalies are interpreted to indicate areas of potentially significant ground water flows. In karst areas,
however, interpretation may not be as straightforward: for example, large electrically conductive domains can represent water bearing zones, whose fluid-permeability may be poor; alternatively, fast flow conduits, which
may be unsaturated, occur as slender objects, and not as clear anomalous features. In order to deal with such extreme heterogeneities,
resistivity investigations require some specific adjustments. One example is the so-called “mise à la masse” method. In Romania,
it was used to trace the cold karst water inflows that detrimentally affected the commercial exploitation of a thermal spring,
Hercules at Baile Herculane. Conventional geoelectrical approaches––such as using resistivity highs to detect air-filled cave passages,
are proved to be less efficient in the considered karst investigations. 相似文献
36.
Patriche Cristian Valeriu Irimia Liviu Mihai 《Theoretical and Applied Climatology》2022,148(3-4):1035-1056
Theoretical and Applied Climatology - Climate change affects the viticulture sector worldwide in different ways, some countries reporting negative impacts, other positive effects, depending on the... 相似文献
37.
The authors present synthetically the great variety of the forms of relief in Romania, which create a real natural attraction, satisfying any side of tourist demand. The most significant poles of Romanian tourism, represented by the Carpathians, the unique Danube Delta, the Black Sea offer great possibilities for winter sports, hiking, climbing, water sports, fishing and hunting, sun bathing and medical treatment, owing to the immense balneary potentialities of the country.In the development of Romanian tourism an important part has had and is still having the scientific research activity achieved in the Tourism Department of a specialized institute of researches. The studies worked out in this field are divided into several categories, dealing with subjects of conjuncture and prognosis, economic efficiency, revaluation of territory, improvement of activity in various resorts, launching of new produces, sociology investigations, new iteneraries etc.The authors also present a selective bibliography. 相似文献
38.
We present evidence for a thick (∼100 km) sequence of cogenetic rocks which make up the root of the Sierra Nevada batholith
of California. The Sierran magmatism produced tonalitic and granodioritic magmas which reside in the Sierra Nevada upper-
to mid-crust, as well as deep eclogite facies crust/upper mantle mafic–ultramafic cumulates. Samples of the mafic–ultramafic
sequence are preserved as xenoliths in Miocene volcanic rocks which erupted through the central part of the batholith. We
have performed Rb-Sr and Sm-Nd mineral geochronologic analyses on seven fresh, cumulate textured, olivine-free mafic–ultramafic
xenoliths with large grainsize, one garnet peridotite, and one high pressure metasedimentary rock. The garnet peridotite,
which equilibrated at ∼130 km beneath the batholith, yields a Miocene (10 Ma) Nd age, indicating that in this sample, the
Nd isotopes were maintained in equilibrium up to the time of entrainment. All other samples equilibrated between ∼35 and 100
km beneath the batholith and yield Sm-Nd mineral ages between 80 and 120 Ma, broadly coincident with the previously established
period of most voluminous batholithic magmatism in the Sierra Nevada. The Rb-Sr ages are generally consistent with the Sm-Nd
ages, but are more scattered. The 87Sr/86Sr and 143Nd/144Nd intercepts of the igneous-textured xenoliths are similar to the ratios published for rocks outcroping in the central Sierra
Nevada. We interpret the mafic/ultramafic xenoliths to be magmatically related to the upper- and mid-crustal granitoids as
cumulates and/or restites. This more complete view of the vertical dimension in a batholith indicates that there is a large
mass of mafic–ultramafic rocks at depth which complement the granitic batholiths, as predicted by mass balance calculations
and experimental studies. The Sierran magmatism was a large scale process responsible for segregating a column of ∼30 km thick
granitoids from at least ∼70 km of mainly olivine free mafic–ultramafic residues/cumulates. These rocks have resided under
the batholith as granulite and eclogite facies rocks for at least 70 million years. The presence of this thick mafic–ultramafic
keel also calls into question the existence of a “flat” (i.e., shallowly subducted) slab at Central California latitudes during
Late Cretaceous–Early Cenozoic, in contrast to the southernmost Sierra Nevada and Mojave regions.
Received: 27 December 1997 / Accepted: 11 June 1998 相似文献
39.
Olivier Féménias Tudor Berza Mihai Tatu Hervé Diot Daniel Demaiffe 《International Journal of Earth Sciences》2008,97(3):479-496
The Motru Dyke Swarm intrudes the Precambrian Danubian basement of the Southern Carpathians (Romania). It is a marker of a
sub-volcanic event that occurred during the early Palaeozoic (Cambrian to Ordovician). The geographical distribution of dykes
on a ∼2,000 km2 area is heterogeneous; several areas of high dyke density have been the subject of a detailed petrological and geochemical
study. Taken altogether, the 150 samples define a single complete magmatic series, from basaltic andesite to rhyolite. Whole-rock
major element variations show a medium- to high-K, calc-alkaline magmatic suite. The compositional variations and the general
decrease of trace element contents (both compatible and incompatible, including REEs) from basaltic andesite to rhyolite are
consistent with 1) the fractionation of the observed phenocryst assemblages, Ca-amphibole (Ti-pargasite to magnesiohornblende)
followed by intermediate plagioclase, clinopyroxene and accessory biotite and quartz and 2) the absence of lower and/or upper
crustal contamination. Trace elements diagrams display typical arc patterns (LILE, Pb and LREE enrichment and relative depletion
in Nb-Ta, Zr-Hf and Ti). The Th/U, Nb/Ta and Zr/Hf ratios are constant and close to the mantle values throughout the whole
series, which argues that the parental magma was generated from a single and homogeneous enriched lithospheric mantle source.
The field regional evidence implies that melting occurred during a late- to post-orogenic period of lithospheric extension,
and thus took place quite lately after the cessation of Pan-African subduction. 相似文献
40.
Jean-Clair Duchesne Jean-Paul Liègeois Viorica Iancu Tudor Berza Dmitry I. Matukov Mihai Tatu Sergei A. Sergeev 《International Journal of Earth Sciences》2008,97(4):705-723
The Sichevita and Poniasca plutons belong to an alignment of granites cutting across the metamorphic basement of the Getic
Nappe in the South Carpathians. The present work provides SHRIMP age data for the zircon population from a Poniasca biotite
diorite and geochemical analyses (major and trace elements, Sr–Nd isotopes) of representative rock types from the two intrusions
grading from biotite diorite to biotite K-feldspar porphyritic monzogranite. U–Pb zircon data yielded 311 ± 2 Ma for the intrusion
of the biotite diorite. Granites are mostly high-K leucogranites, and biotite diorites are magnesian, and calcic to calc-alkaline.
Sr, and Nd isotope and trace element data (REE, Th, Ta, Cr, Ba and Rb) permit distinguishing five different groups of rocks
corresponding to several magma batches: the Poniasca biotite diorite (P1) shows a clear crustal character while the Poniasca granite (P2) is more juvenile. Conversely, Sichevita biotite diorite (S1), and a granite (S2*) are more juvenile than the other Sichevita granites (S2). Geochemical modelling of major elements and REE suggests that fractional crystallization can account for variations within
P1 and S1 groups. Dehydration melting of a number of protoliths may be the source of these magma batches. The Variscan basement, a
subduction accretion wedge, could correspond to such a heterogeneous source. The intrusion of the Sichevita–Poniasca plutons
took place in the final stages of the Variscan orogeny, as is the case for a series of European granites around 310 Ma ago,
especially in Bulgaria and in Iberia, no Alleghenian granitoids (late Carboniferous—early Permian times) being known in the
Getic nappe. The geodynamical environment of Sichevita–Poniasca was typically post-collisional of the Variscan orogenic phase. 相似文献