玄武岩-榴辉岩相变初期的石榴子石生长

GARNET GROWTH IN THE EARLY STAGE OF TRANSFORMATION FROM TRACHYBASALT TO ECLOGITE

在 2 .0 GPa,86 0～ 10 2 0℃ ,加温时间 0 .6 6～ 13.0 7h的条件下 ,粗面玄武岩 -榴辉岩相变初期的石榴子石生长为正常晶体生长。石榴子石粒径随时间而增大 ,其生长速率随粒径增大而减小。界面是控制玄武岩 -榴辉岩相变初期石榴子石生长的主要因素。这一变质作用过程中石榴子石粒径与时间及温度的关系如下 :G2 .4 5=5.6 5× 10 -15t· exp(- 2 7.4 0× 10 3 / RT)式中 G为石榴子石平均粒径 ,t为时间 ,R为气体常数 ,T为绝对温度。

The grain growth kinetics of garnet during the early stage of transformation of trachybasalt to eclogite was investigated at 2.0 GPa. The experimental samples were annealed at temperatures of 860,980 and 1 020℃ for 0.66 to 13 hours. The grain size was determined optically. The normal grain growth of the garnet during the early stage of metamorphism of eclogite facies was observed. The grain size of the garnet increased with increasing annealing time. The rate of garnet growth decreased with increasing grain size. In the early stage of metamorphism of eclogite facies, the interface control mechanism was dominant in garnet growth. The garnet growth law obtained for the early stage of trachybasalt eclogite transformation was: G 2.45 =5.65×10 -15 ·t·exp (-27 40×10 3/RT) , where G represents the average grain size of garnet after annealing time t, R is the gas constant and T is the absolute temperature. In the light of this relationship, the grain growth of garnet in the early stage of eclogite metamorphism can be expounded.