浙江新昌石榴石二辉橄榄岩包体的流变特征及其地质意义

Rheological Features of Garnet Lherzolite Xenoliths from Xinchang, Zhejiang Province,China and their Geological Implications

浙江新昌的石榴石二辉橄榄岩包体以残斑结构为主，并有向粒状变晶结构过渡的趋势。橄榄石组构以［０１０］呈点极密型式，而［１００］和［００１］呈大圆环带为特征。橄榄石的位错亚构造以反映高温位错蠕变的位错壁、亚晶粒构造和滑动位错环为主要特征。利用新的地质温压计计算的平衡温度和压力分别为１１５０℃～１２１０℃和２．１～２．４ＧＰａ。利用显微构造应力计计算流动应力为２２～３０ＭＰａ，利用橄榄岩高温流变律计算的应变速率和等效粘滞度分别为１０－１４～１０－１３ｓ－１和１０１９～１０２０Ｐａ·ｓ，上述数据均已达到软流圈的数值。结合其流变特征认为该区的石榴石二辉橄榄岩代表软流圈的物质，其来源深度为６８～７８ｋｍ。它反映在新生代时期本区存在有软流圈的底辟，它可能控制了该区新生代大地构造的特征及地质演化。

The peridotite xenoliths in Cenozoic basalts in Xinchang, Zhejiang Province, China comprise both spinel and garnet lherzolites. The deformation features of Garnet lherzolites, such as textures,fabrics, and dislocation substructures have been described in detail in this paper. They all reflect high temperature deformation under upper mantle conditions dominated by dislocation creep mechanism. The equilibrium temperature and pressure of the garnet lherzolite as calculated using newly-developed geothermobarometers are 1150℃～1210℃, and 2. 1～2. 4GPa, respectively, indicating that the depth of origin of the xenoliths is 68～78km. The differential stress calculated using microstructural piezometer is within the range of 22～30MPa, while the strain rate and equivalent viscocity inferred from the power law creep of peridotite are 10-14～10-13s-1and 1019～1020pa. s, respectively. It is suggested that the garnet lherzolites should be representative of the asthenosphere in this region, and there should be an asthenospheric diapir during Cenozoic.