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    南苏鲁高压变质带南岗—高公岛韧性剪切带特征及EBSD石英组构分析

    Characteristics of the Nangang-Gaogongdao ductile shear zone in the South Su-Lu high-pressure metamorphic belt and EBSD fabric analysis of quartz

    • 摘要: 提要:结合地质剖面对南苏鲁高压变质带中的南岗—高公岛韧性剪切带特征进行了研究,结果表明,剪切带上部变形较弱,主要发育S-C组构及拉伸线理;剪切带中部变形较强,发育不对称褶皱、S-C组构、σ型及δ型旋转碎斑以及多米诺骨牌等;剪切带下部变形最强,糜棱质颗粒达80%~90%,并见有同斜褶皱等。EBSD组构分析结果表明,剪切带上部糜棱质石英以中温柱面组构和中低温菱面组构为特征,中、下部以低温底面组构和中低温菱面组构为主,剪切带中石英条带以中温柱面组构为主,石英组构的剪切指向以SE→NW为主,其次为NW→SE,反映本区经历了中温→中低温→低温、以逆冲韧性剪切为主并曾发生韧性滑脱的复杂变形过程。各构造层化学成分及稀土元素变化趋势不明显,可能与原岩成分有关。剪切带中黑云母、白云母的39Ar-40Ar同位素年龄分析表明在253.8~214.2 Ma期间本区曾发生强烈的变形变质作用。

       

      Abstract: Abstract:The characteristics of the Nangang-Gaogongdao ductile shear zone in the south Su-Lu high-pressure metamorphic belt were studied on the basis of the geological section survey. The results reveal that: rocks in the upper part of the shear zone are deformed weakly, in which the S-C fabric and stretching lineation are developed; rocks in the central part are deformed intensely, in which asymmetric folds, S-C fabrics and σ- and δ-type rolled porphyroblasts, as well as domino structure of plagioclase are developed; and rocks in the lower part are deformed most intensely, in which mylonitized grains accounts for up to 80%-90% and congruous tight folds can also be found. EBSD fabric analysis shows that: mylonitized quartz grains in the upper part are characterized by the low- to medium-temperature rhombohedral face fabric and medium-temperature prismatic face fabric, those in the central and lower parts are characterized by low-temperature basal face fabric and low- to medium-temperature rhombohedral face fabric, and banded quartz grains in the shear zone are dominated by medium-temperature prism face fabric, which indicates that the shear zone experienced a complex deformation process from medium-temperature through low-medium temperature to low temperature deformations. The shear sense of the quartz fabrics is mainly from SE to NW and subordinately from NW to SE, reflecting that thrusting shear deformation is dominant, while ductile déollement shear is subordinate in the shear zone. No apparent trend of variations exists in chemical composition and REE patterns of the rocks from the upper part to lower part of the shear zone, so the composition may be determined mainly by the primary compositions of the rocks. 39Ar-40Ar ages of muscovite and biotite from the shear zone indicate that intensive metamorphism and deformation took place in the period of 253.8-214.2 Ma.

       

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