A study of brittle-ductile transition in naturally deformed crustal materials

我们利用综合野外观测和构造岩石学分析，研究了自然实例中上下地壳条件下的脆性-韧性转变、变形模式和变形历史。这些例子分别来自日高、云月、良和Higo变质带、Napier杂岩、武道和Gozu花岗岩地块、侏罗纪Toi组以及长越西部和长冈东部的第三纪沉积物。北海道Hidaka变质带北部的辉长岩糜棱岩、伪糜棱岩和调性小糜棱岩带是在麻粒岩相条件下形成的。这些岩石表明地震断裂和脆性破坏发生在下地壳条件下，是由孔隙流体和/或应变速率变化的影响造成的。在Enderby Land的Napier杂岩中，糜棱岩、糜棱岩化伪糜棱岩和伪糜棱岩在同一变形阶段形成于逆行麻粒岩相条件下。伪岩与糜棱岩的关系较为复杂，表明地震断裂和塑性变形在地壳低层交替发生。变形模式的变化可能是由微观结构和/或应变速率的变化引起的。在新泻县武道和谷足花岗岩中，在同一断裂带中依次形成了片理碎裂岩、随机组构碎裂岩和超碎裂岩。序贯地层表明，断裂在构造演化过程中变形机制由破碎向磨碎转变。片理碎裂岩的片理形成于脆性断裂的初始阶段，其片理可以通过伸长的黑云母碎片的排列或由石英或长石等相同矿物碎片组成的伸长透镜的排列来确定。断裂带起源于前碎裂岩，在断裂过程中厚度变宽，后碎裂岩厚度则没有变宽。前碎裂岩与伪岩伴生，表明发生过地震断裂。上述变质带、花岗质地块和沉积盆地的脆性-韧性转变主要由温度变化引起。少

We have investigated brittle-ductile transition, modes of deformation, and deformation histories under the upper to lower crustal conditions in natural examples, using integrated field observations and structural and petrological analyses. The examples are from the Hidaka, Unazuki, Ryoke, and Higo metamorphic belts, Napier Complex, Budo and Gozu granitic massifs, Jurassic Toi Formation, and Tertiary sediments at western Joetsu and eastern Nagaoka cities.Gabbroic mylonites, pseudotachylytes, and tonalitic small mylonite zones in the northern Hidaka metamorphic belt, Hokkaido, formed under granulite facies conditions. These rocks suggest that seismic faulting and brittle failure occurred under lower crustal conditions, resulting from the effects of variations of pore fluids and/or strain rate. In the Napier Complex, Enderby Land, mylonites, mylonitized pseudotachylytes, and pseudotachylytes formed during the same deformation stage under retrograde granulite facies conditions. Complex rel … More ationships of the pseudotachylytes with the mylonites suggest that seismic faulting and plastic deformation alternated at lower crustal levels. The change in mode of deformation would have resulted from the changes in microstructures and/or strain rate. In the Budo and Gozu granites, Niigata Prefecture, foliated cataclasites, random-fabric cataclasites, and ultracataclasites formed in turn in the same fault zones. The sequential formation shows that deformation mechanisms change from breaking to grinding during the structural evolution of the faults. The foliation of the foliated cataclasites, which formed in the initial phase of brittle faulting, is defined either by the alignment of elongated biotite fragments or by the alignment of elongated lenses made of the same kinds of mineral fragments, such as quartz or feldspar. The fault zone originated from the former cataclasite widened in thickness during faulting, but the latter did not. The former cataclasite is associated with pseudotachylyte, indicating that seismic faulting occurred. Mainly temperature change produced the brittle-ductile transition in the above metamorphic belts, granitic massifs, and sedimentary basins. Less