Experimental Study on the Crystallographic Preferred Orientation (CPO) of Amphibole and Its Implications for Seismic Anisotropy

amphibolite;hornblende;crystallographic preferred orientation;seismic anisotropy;deformation experiment in simple shear;modified Griggs apparatus;각섬석;단순 전단 변형 실험;격자선호방향;지진파 비등방성;각섬암;550

자연과학대학 지구환경과학부 ;

University:서울대학교 대학원

关键词: amphibolite;    hornblende;    crystallographic preferred orientation;    seismic anisotropy;    deformation experiment in simple shear;    modified Griggs apparatus;    각섬석;    단순 전단 변형 실험;    격자선호방향;    지진파 비등방성;    각섬암;    550;   

Others  :  http://s-space.snu.ac.kr/bitstream/10371/131387/1/000000020879.pdf

美国|英语

来源: Seoul National University Open Repository

【 摘 要 】

Strong seismic anisotropy in the deep crust and upper mantle is considered mainly due to the crystallographic preferred orientation (CPO) of anisotropic minerals, which can be formed by deformation. Inferring seismic properties by using CPO can provide key information on the rheology of the deep Earth. However, experimental studies on the development of CPO of anisotropic minerals in simple-shear deformation has been limited. Simple shear is considered to be the dominant mode of deformation in the crust and uppermost mantle, whereas previous studies have focused on the effects of uniaxial compression. Here, we show the results of simple-shear deformation experiments on amphibolite, conducted at the pressure of 1 GPa and temperatures of 480 to 700 °C which are amphibolite facies conditions. For large strains up to 570 %, our experiments produced three types of CPOs of amphibole, in which (100) poles align subnormal to the shear plane. Type-I CPO shows that [001] axes are aligned nearly parallel to the shear direction, which is commonly observed in highly deformed mid- to lower-crust rocks. Type-I CPO was formed at low temperatures (480 to 550 °C), and at middle temperatures (590 to 600 °C) with low differential stress (below 60 MPa). Type-II CPO represents that [010] axes are aligned nearly parallel to the shear direction. Type-II was formed at middle to high temperatures (590 to 700 °C) with high differential stress (above 110 MPa). Type-III CPO displays that (010) poles and [001] axes form a great circle girdle subparallel to the shear plane. Type-III was observed at high temperatures (640 to 700 °C) with low differential stress (below 130 MPa). Type-II and –III CPOs are rarely found in natural samples. Seismic anisotropy was calculated from the CPO data, finding that seismic anisotropy of amphibole can be sensitive to the temperature, differential stress, and flow geometry in the deep crust and upper mantle where amphibole is stable.