摘要
本文以辽宁省鞍山附近元古宙千枚岩和片岩中的折劈 s为论述的基础。按照简单剪切原理计算出发育折劈的岩石中的γ(剪应变)值。通过γ等值线图及断面图、T_M/T_(QF)-α相关图和变形标志(石英)形态比的研究,初步认为,折劈岩石中矿物组成、结构、微构造和α角等的明显“分异”现象,主要由剪应变和伴随发生的物质迁移所造成。有限应变状态的特点是:剪应变高的带(M)和剪应变较低的带(QF)相间排列。相邻带剪应变差异控制着扩散物质迁移机制,对微构造(如微褶皱)的生成,有重要作用。折劈生成于 T 低于500℃,P 约为5kb 左右的绿片岩相变质环境,它标志着地壳处于区域性抬升状态,相继产生的共轭折劈和膝折带(属于 D,构造),则表明已抬升到足以引起岩石总体体积扩张的高度。
For the crenulation cleavage S_2 in the proterozoic phyllites and schists around Anshan, Liaoning Province,the derailed studies indicate that obvious “differentiation” in mineral con- stituents,texture,microstucture and the a angles,giving rise to alternated M and QF domains parallel to the cleavage surfaces,resulted from shear strain to be accompanied With mass-transfer process.Neccessary factors such as Tin,Tqf and α angle (S,AS_2) are measured,and diagrams showing Tm/Tqf against α are prepared in which a clear linear relation can be expected.Based on principles of simble shear,γ(shear strain)values are calculated for both domains,and the y contour maps (including related sections) of selected areas are also constructed.It is appa- rent that alternated higher and lower shear strain strips or domains (M and QF,respectly) cha- racterizes the finite strain state of rocks with crenulation cleavage.Differences of shear strain (γ) between alternated domains are considered to be the main cause leading to the formation of microstructures and microfolds in the crenulated rocks.High progressive shear strain would en- hance solution of materials in the M domains whereas mineral growth would take place in the QF domains of relatively low γvalues. It is worth to note that y curves plotted for M domains generally exhibit regularly normal distribution pattern,and for QF domains become “undulated”,each crest repre,senting a su- bordinate “shear zone” within QF.This seems to imply that progressive enlargment of these subordinate shear zones which are due to accumulated shear strain,and make QF domains gra- dually “broken-down”,might be a general tendence of development of the crenulation cleavage.
出处
《地质科学》
CAS
CSCD
北大核心
1992年第2期114-123,共10页
Chinese Journal of Geology(Scientia Geologica Sinica)
关键词
造山带
演化
折劈
发育
鞍山市
M-domain
QF-domain
Finite strain state
shear strain
Mass-transfer
