Evaluation of effects of chemical reactions on ductile shear deformation

我们评价了中地壳韧性剪切带中形成的花岗岩、辉长岩和橄榄岩糜棱岩中的化学反应对韧性变形的影响。主要研究结果如下：1)角闪岩相花岗岩糜棱岩中存在变形诱导钾长石被紫苏花岗岩交代的现象。细粒反应产物构成了糜棱岩基质中的主要成分，并在很大程度上适应了糜棱岩中的应变。糜棱岩优先发育在富钾长石、贫黑云母的浅色相域或斜长岩脉中，在变形过程中形成的丝光沸石反应比非浅色相域更有利于产生更多的细粒反应产物。随后的反应减弱将有利于白化微区或闪锌矿矿脉的进一步变形，这反过来将有利于进一步的丝光沸石形成反应。这种反馈作用可能是Hatakawa剪切带花岗岩糜棱岩发育的原因。2)应变局部化为单斜辉石分解成角闪石形成的细粒反应产物，斜长石的动态重结晶促进了东达卡变质带麻粒岩相辉长糜棱岩的发育。3)东达卡变质带Uenzaru橄榄岩岩体中的二辉橄榄岩在橄榄岩体内应变定位成斜长石、橄榄石和铬尖晶石组成的斜长岩。

We evaluated the effects of chemical reactions on ductile deformation in granite, gabbro and peridotite mylonites formed within ductile shear zones in the middle crust, the lower crust and the uppermost mantle, respectively. The results are summarized below.1) Deformation-induced K-feldspar replacement by myrmekite occurs in the amphibolite-facies granite mylonites along the eastern margin of the Hatakawa shear zone. The fine-grained reaction products compose the main constituent in the mylonite matrix and largely accommodate the strain in the mylonites. Mylonites are preferentially developed in leucocratic domains or aplite veins which are rich in K-feldspar and poor in biotite, where the myrmekite-forming reaction was more favored to produce more amounts of fine-grained reaction products than non-leucocratic domains during deformation. Subsequent reaction weakening would have favored further deformation in leucocratic domains or aplite veins, which in turn would have favored further myrmekite-forming reaction. Such a feedback process is probably responsible for the development of granite mylonites in the Hatakawa shear zone.2) Strain localization into the fine-grained reaction products formed by decomposition of clinopyroxene into amphibole as well as dynamic recrystallization of plagioclase contributed to the development of granulite-facies gabbroic mylonites in the Hidaka metamorphic belt.3) The lehrzolite mylonite in the Uenzaru peridotite body in the Hidaka metamorphic belt developed by strain localization into the symplectite composed of plagioclase, olivine and chromian spinel when spinel lherzolite was transformed into plagioclase lherzolite during ascent of the peridotite body.