应变-滑劈理的结构分析

应变-滑劈理(Strain-slip cleavage)一词,早在1886年提出。后来的研究者提出了相应的术语,诸如滑劈理(Slip cleavage)、皱劈理(Runzel cleavage)、剪劈理(shearcleavage)、锯齿形劈理(Crenulation cleavage)等。

THE TEXTURAL ANALYSIS OF THE STRAIN-SLIP CLEAVAGE

This article discusses the classification, the textural features and the formation mechanism of the strain-slip cleavage, through megascopic and microscopic analysis of them in the epimetamorphic rocks of the Tongan and Weishan districts.The cleavage planes are closely spaced and parallelly arranged with slips of 0.5mm to several mm. Most of the microlithon’s planes are separated from one another by a width of about 0.02-0.05 mm. Newly formed flaky minerals in the cleavage planes are always oriented and form angles of 5°-15° with the general direction of the cleavage plane, the size of the angle being directly proportional to the width of microlithons and inversely proportional to the lateral stress. There are four ’ kinds of extinction on the cleavage planes.Varieties of plications or microplissements are developed in the microlithons. According to their morphological features the strain-slip cleavage may be classified into six types:1. The slipfold-shaped strain-slip cleavage;2. The chevronfold-shaped strain-slip cleavage;3. The stromatolite-like fold-shaped strain-slip cleavage;4. The undulating fold-shaped strain-slip cleavage;5. The thrustfault-shaped strain-slip cleavage;6. The " S-flexure "-shaped strain-slip cleavage.The strain-slip cleavage is formed not simply through shearing force or compressing force, but results from the compressive force combined with shearing force, that is, it must be formed under the lateral compression by which the cleavage formed in differential shear stress along the direction normal to compressive force, if the beds concerned are laminated or schistose.