大别山超高压岩石的流变学研究  

Reological Study on the Dabie Ultrahigh-Pressure Rocks

作　　者：焦述强[1] 金振民[2] 金淑燕[2] 谭子珊[1] 

机构地区：[1]福州大学工程地质与水文地质勘察研究所,350002 [2]中国地质大学地学院,武汉430074

出　　处：《地质学报》2001年第3期353-362,共10页Acta Geologica Sinica

基　　金：国家自然科学基金(编号49672144)和福建省教委科技项目(编号KZ0001)联合资助的成果

摘　　要：本文利用野外构造解析、透射电镜、岩组等手段,对大别山地区超高压岩石的变形表象及变形机制进行了详细的观察和研究,从而动态地建立了超高压岩石折返的PTtD轨迹。结果表明:超高压石榴橄榄岩经历了高温和低温两种变形,其中橄榄石中发育高温[001](100)和中低温[010](100)两种滑移系。超高压榴辉岩中绿辉石的位错构造发育,位错密度为4.98×10~7/cm^2。绿辉石亚颗粒的特征显示存在颗粒边界迁移和扩散蠕变。绿辉石的组构测定表明,绿辉石晶内塑性流动形成了[001]极密,该极密平行于线理,属L型收缩组构。组构对称型显示本区榴辉岩以共轴变形为主,由于应变分解,部分地区含非共轴成分。付林图解表明,绿辉石和石榴子石的变形均属于收缩型椭球,拉伸型应变,这与绿辉石组构测定结果一致。石榴子石位错密度为3.54×10~7/cm^2,部分地区的石榴子石发育动态重结晶及核幔构造等,形成榴辉岩相糜棱岩。另外根据不同超高压岩石中石英的位错密度或亚颗粒大小,计算了超高压岩石折返时各个阶段的应力大小。By means of field structure analysis, TEM and fabric, we have studied carefully the deformation feature and mechanism of the ultrahigh-pressure rocks in Dabie, thus having dynamically constructed the exhumation PTtD path of ultrahigh-pressure rocks. The Dabie ultrabasic rocks coexisted with ultrahigh-pressure eclogites have undergone high-temperature deformation as well as lower one, of which the olivins have developed high-temperature glide-system[001] (100) and low-temperature one [010](100). The well-developed dislocation structure of omphacite in eclogite means that the eclogite has undergone dislocation creep. The dislocation density of ompahcite is 4. 98× 107/cm2. The subgrains of omphacite, the boundary of which is often uneven and intertwined with the mother grains, have rotated to dynamic recrystallization grains. Fabric of omphacite indicates that the intracrystalline ductile flow has formed [001] pole, which is parallel to lineation and belongs to L-type constriction fabric. The main-phase deformation of eclogite is co-axial, but some asymmetry strain has also existed due to the strain partitioning in Dabie erogenic belt. The Flinn plots indicate that the omphacite strain is belongs to constriction ellipsoid denoting stretching strain, being similar with the result of omphacite fabric analysis. The garnet has a dislocation density of 3. 54× 107/cm2 and some of the garnet in certain eclogites have developed recrystallization. The stresses of ultrahigh-pressure rocks during different exhumation stages have been deduced from the subgrain or dislocation density of deformation quarltzs in different ultrahigh-rocks.

关 键 词：榴辉岩 组构 流变学 超高压岩石 石榴子石 石榴橄榄岩 古应力 

分 类 号：P588.3[天文地球—岩石学]