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近年来对青藏高原中拉萨地块西部中生代岩浆作用的源区、成因和演化等问题的研究较少。本文针对中拉萨地块西部噶尔县左左乡两个中酸性岩体进行了岩石学、锆石U-Pb年代学、微量元素和锆石Hf同位素，以及主量元素和微量元素地球化学研究。左左乡北侧岩体寄主花岗闪长岩和闪长质包体获得同期（163Ma和160Ma）的年龄，属于晚侏罗世；南侧岩体花岗岩年龄为142~147Ma，属于早白垩世。北侧与南侧的中酸性岩石均属于准铝质-弱过铝质高钾钙碱性I型花岗岩，富集大离子亲石元素和轻稀土元素，亏损高场强元素。晚侏罗世岩体寄主岩具有较为富集的锆石Hf同位素成分（eHf（t）=-16.8~-13.6），可能来源于古老下地壳的部分熔融；包体具有相似的Hf同位素成分（eHf（t）=-15.7~-13.6），结合晚侏罗世寄主岩与包体较高的MgO（4.13%~6.90%）、Cr（146×10-6~370×10-6）和Ni（31×10-6~113×10-6）含量，说明包体代表的中基性岩浆可能源于古老富集地幔的熔融，并且在晚侏罗世寄主花岗闪长岩与闪长质包体所代表的两种岩浆间发生过充分的岩浆混合作用。南侧早白垩世花岗岩具有较负且变化范围大的eHf（t）值（-8.2~-4.8和-3.8~+0.2），指示早白垩世岩浆活动中有更多亏损地幔物质或新生地壳物质的加入，并且亏损地幔物质或新生地壳物质与拉萨地块古老地壳物质熔融形成的酸性岩浆发生了岩浆混合，经历岩浆混合后中酸性岩浆又发生了角闪石、长石的分离结晶，最终形成南侧早白垩世岩体的一系列中酸性岩石。研究区早白垩世亏损地幔物质或新生地壳物质的增多可能与南向俯冲的班公湖-怒江板片的回转有关。

The dynamic stability of axially accelerating plates is investigated. Longitudinally 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 governing equations, the initial conditions, and the boundary conditions of the coupled planar vibration. The solvability conditions are established by directly using the method of multiple 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.