大别山超高压榴辉岩流变强度——来自高温高压实验的证据

利用Griggs型 5GPa高压仪器 ,在柯石英稳定域围压条件下 ( >3GPa)完成大别山超高压榴辉岩流变学实验 ,建立了榴辉岩流变状态本构方程 (流动律 ) : ε=Aexp( -Q/RT)σn ,应力指数 (n)为 3 .4 ,活化能 (Q)为 4 80kJ/mol,结构常数 (A)为 10 3.3.实验结果表明 :( 1)作为两相矿物组成的榴辉岩 ,其流变学强度在很大程度上取决于强相矿物 (石榴石 )和弱相矿物 (绿辉石 )含量比例 ;( 2 )天然榴辉岩塑性变形机制是以位错蠕变为主 ;( 3 )根据实验成果比较榴辉岩和上地幔方辉橄榄岩流变学强度相当 ,两者耦合在大陆深俯冲 10 0km左右深度发生拆沉作用可能性很小 ,与上地幔上隆 (upwelling)作用有关的造山期后伸展作用对超高压岩石折返更具有重要意义 .

Rheological strength of UHP eclogite from Dabie Shan: evidences from high p-T experiments

The authors present here experimental study of the rheological properties of UHP eclogite from Dabie at a pressure of 3 GPa by utilizing the 5 GPa Griggs-type piston cylinder apparatus. The rheological constitutive equation of eclogite is determined with a stress exponent of 3.4, an activation energy of 480 kJ/mol and a pre-exponential factor of 10 3.3 . The study shows that: (1) As a typical two-phase rock, the flow strength of eclogite depends on the proportions between the strong phase (garnet) and the weak phase (omphacite); (2) The plastic deformation of eclogite is dominated by dislocation creep; (3) The research result that eclogite has the same strength as does the upper mantle harzburgite suggests that the delamination of the subducting crust component from the underlying upper mantle is unlikely. Therefore, the stretching after the collision orogeny coupled with the upwelling of the upper mantle might play a more important role in the exhumation of UHP rocks.