Dynamic stability of axially accelerating viscoelastic plates with longitudinally varying tensions

The dynamic stability of axially accelerating plates is investigated. Longitudi- nally varying tensions due to the acceleration and nonhomogeneous boundary conditions are highlighted. A model of the plate combined with viscoelasticity is applied. In the viscoelastic constitutive relationship, the material derivative is used to take the place of the partial time derivative. Analytical and numerical methods are used to investigate summation and principal parametric resonances, respectively. By use of linear models for the transverse behavior in the small displacement regime, the plate is confined by a viscous damping force. The generalized Hamilton principle is used to derive the govern- ing equations, the initial conditions, and the boundary conditions of the coupled planar vibration. The solvability conditions are established by directly using the method of mul- tiple scales. The Routh-Hurwitz criterion is used to obtain the necessary and sufficient condition of the stability. Numerical examples are given to show the effects of related parameters on the stability boundaries. The validity of longitudinally varying tensions and nonhomogeneous boundary conditions is highlighted by comparing the results of the method of multiple scales with those of a differential quadrature scheme.

Petrogenesis of granitic pegmatite veins:Perspectives from major element and B isotope in tourmalines,Chakabeishan,Northern Tibetan Plateau

The petrogenesis of regionally zoned granitic pegmatite veins remains debated.Because of the economic significance,we carried out a study on the Chakabeishan(CKBS)pegmatite-type Li-Be deposit,eastern North Qaidam Tectonic Belt,Northern Tibetan Plateau,by means of in-situ major element and B isotope compositions of tourmalines in the beryl-bearing and spodumene-bearing pegmatite veins.Tourmalines(Tur-Be)from the beryl-bearing pegmatite are homogeneous schorl with low Mg/(Mg+Fe),high Na/(Na+Ca)and Y Al,suggesting that they are of magmatic origin.Two generations of tourmalines(TurLi)from the spodumene-bearing pegmatite are identified:(i)the crystal cores(mostly elbaite and Lirich schorl with subordinate schorl)are consistent with being of magmatic origin crystallized at the magmatic stage;(ii)the crystal rims(schorl)are best understood as the overgrowth at the later hydrothermal stage.Tur-Be and Tur-Li show an obvious difference in core-to-rim B isotopic variation trend with d11B decrease in Tur-Be and increase in Tur-Li.The core-to-rim d11B decrease in Tur-Be results from degassing during its host pegmatitic melt evolution,whereas the core-to-rim d11B increase in Tur-Li is related to fluid exsolution.The estimated d11B values for the initial melts of the beryl-bearing and spodumenebearing pegmatites are10.46‰and10.78‰,respectively,indicating that they most likely originate from protracted fractional crystallization/differentiation of granitic intrusions rather than partial melting of metapelite.Both Mg/(Mg+Fe)ratios and Li abundances in the cores of Tur-Be are lower than those of Tur-Li,suggesting that Tur-Li crystallizes from chemically more evolved melts.

Porphyry mineralization in the Tethyan orogen

The Tethyan metallogenic domain(TMD),as one of the three major domains in the world,extends over 10000 km from east to west,and has developed several world-class metallogenic belts,such as the Gangdese porphyry Cu belt,the Sanjiang metallogenic belt,the Iran porphyry Cu belt,the Pakistan porphyry Cu belt,the southeastern European epithermal gold deposit belt,and the Southeast Asian Sn belt.The formation and evolution of the TMD is mainly controlled by the multi-stage subduction of Tethys oceanic slabs,the opening and closing of several small ocean basins,and continent-continent collision.The Tethys oceans include the Proto-Tethys(Cambrian-Silurian),Paleo-Tethys(Carbonaceous-Triassic)and Neo-Tethys(Jurassic to Cretaceous),which in turn are formed by rifting from the Gondwana land at different times in different micro-continents.With a series of geological processes such as oceanic opening and closing,continental collision and post-collisional reworking with intraplate deformation,various types of ore deposits are developed in the TMD,including porphyry deposits,epithermal deposits,VMS deposits,chromite deposits,Sn deposits and orogenic gold deposits.The metallogenic processes of the TMD can be categorized into three stages.(1)Oceanic subduction:With the subduction of the oceanic slab and dehydration of basalt and sediments,the asthenospheric mantle was metasomatized with preliminary enrichment in metals under oxidized condition.(2)Continental subduction:Continental collision induced partial melting of the mantle wedge enriched the metals and water in mafic melts,which ascended from subarc depths to the lower crust,locally to the shallow crust for hydrothermal mineralization.(3)Post-collisional reworking:Partial melting of the mafic intrusives in the lower crust produced felsic melts under oxidized and water-rich conditions,which underwent crystal fractionation and transferred water and metals into hydrothermal fluids for mineralization.The large-scale porphyry mineralization in the TMD mainly occurs in the Miocene,which is an important scientific issue worthy of further study in the future.How is the metal enriched in the processes of gradual maturity of the crust,and how does large-scale mineralization occur in a collisional orogen where there is no subduction and dehydration of oceanic slabs anymore to supply S and Cl?These are still important questions in the study of porphyry mineralization in the Tethyan orogen.The application of hyperspectral and mineralogical studies of alteration assemblages is beneficial for prospecting and exploration in the TMD.