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931.
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933.
The Early Cretaceous granitic complex in Highland 1248 of Daxing''anling successively consists of in- truded granodiorite,monzonite granite and syenite granite． Through test analysis on the major,trace and rare earth elements of the intrusive complex,this study focuses on the source characteristics and tectonic environ- ment of the original magma of intrusive complex． The results show that the intrusive rocks in Highland 1248 are meta-aluminous-peraluminous rocks in calc-alkaline series with homologous characteristics in δEu negative anomalies; the complex is enriched in LILE (Ｒb,Cs and K) and depleted in HFSE (lanthanide,Sc,Y,U, Nb and Ta),displaying the geochemical characteristics of I-type granites in active continental-margin subduc- tion zones． The complex also has the characteristics of granites after the collision of plate with rich aluminum and high potassium,but significantly depleted Nb,Ta,Ti,P and other elements,i． e． in the orogenic evolu- tionary stage． The zircon U-Pb SHＲIMP isotopic apparent age of the complex in Highland 1248 is 140． 0--141. 0 Ma,and the formation time is in Early Cretaceous． 相似文献
934.
In conventional seismic exploration,complex overburden prevents us from imaging the deeper under- ground structure,because near-surface velocity model cannot be efficiently simplified and accurately estab- lished． The virtual source method provides a promising solution,which images below a complex overburden without the knowledge of overburden velocities and near-surface changes． In this paper,the authors simulate the forward modeling under complex overburden with sources on the surface and receivers in the horizontal well, and reset the real sources into the horizontal well using the virtual source method,which subtly avoid the distor- tion effects of the complex overburden． Finally the underground structure can be imaged using Kirchhoff migra- tion,so the feasibility and advantages of the virtual source method are verified． 相似文献
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938.
A technique to extract real modes from the identified complex modes is presented in this paper, which enables the normalized
real mode shapes, modal masses, and full or reduced mass and stiffness matrices to be obtained. The theoretical derivation
of the method is provided in detail. An 11-DOF vibration system is used to validate the algorithm, and to analyze the effects
of the number of modes utilized and measurement DOFs on the extraction results. Finally, the method is used to extract real
modes from both experimental modal analysis and operational modal analysis. 相似文献
939.
Post-collisional alkaline magmatism (∼610–580 Ma) is widely distributed in the northern part of the Neoproterozoic Arabian-Nubian Shield (ANS), i.e. the northern part of the Egyptian Eastern Desert and Sinai. Alkaline rocks of G. Tarbush constitute the western limb of the Katharina ring complex (∼593 ± 16 Ma) in southern Sinai. This suite commenced with the extrusion of peralkaline volcanics and quartz syenite subvolcanics intruded by syenogranite and alkali feldspar granite. The mineralogy and geochemistry of these rocks indicate an alkaline/peralkaline within-plate affinity. Quartz syenite is relatively enriched in TiO2, Fe2O3, MgO, CaO, Sr, Ba and depleted in SiO2, Nb, Y, and Rb. The G. Tarbush alkaline suite most likely evolved via fractionation of mainly feldspar and minor mafic phases (hornblende, aegirine) from a common quartz syenite parental magma, which formed via partial melting of middle crustal rocks of ANS juvenile crust. Mantle melts could have provided the heat required for the middle crustal melting. The upper mantle melting was likely promoted by erosional decompression subsequent to lithospheric delamination and crustal uplift during the late-collisional stage of the ANS. Such an explanation could explain the absence or scarce occurrence of mafic and intermediate lithologies in the abundant late- to post-collisional calc-alkaline and alkaline suites in the northern ANS. Moreover, erosion related to crustal uplift during the late-collision stage could account for the lack or infrequent occurrence of older lithologies, i.e. island arc metavolcanics and marginal basin ophiolites, from the northern part of the ANS. 相似文献
940.