Lattice preferred orientation, water content, and seismic anisotropy of orthopyroxene

Abstract

Lattice preferred orientation (LPO) and seismic anisotropy of orthopyroxene (enstatite) in mantle xenoliths from Spitsbergen, Svalbard, near the Arctic, are studied. LPOs of enstatite were determined using electron backscattered diffraction (EBSD). We found four types of LPOs of orthopyroxene and defined them as type-AC, -AB, -BC, and -ABC. Type-AC LPO of orthopyroxene is defined as (100) plane aligned subparallel to foliation and [001] axis aligned subparallel to lineation. Type-AB LPO is defined as (100) plane aligned subparallel to foliation and [010] axis aligned subparallel to linea- tion. Type-BC LPO is defined as (010) plane aligned subparallel to foliation and [001] axis aligned subparallel to lineation. Type-ABC LPO is defined as both (100) and (010) planes aligned subparallel to foliation with a girdle distribution of both [100] and [010] axes normal to lineation and [001] axis alignedsubparallel to lineation. We report for the first time the type-AB, -BC, and -ABC LPO of orthopyroxene. We found that the LPO pattern has a correlation with the content of orthopyroxene in the specimen. Nicolet 6700 FTIR (Fourier transformation infrared) study of enstatite showed that type-AC LPO was observed mostly in the samples of enstatite with low water content. It is found that the strength of the LPO of enstatite decreases with increasing water content and has a correlation with the strength of the LPO of olivine: the stronger the LPO of enstatite, the stronger the LPO of olivine. Seismic anisotropy of enstatite was smaller than that of olivine in the same specimen.

Characterization of olivine fabrics and mylonite in the presence of fluid and implications for seismic anisotropy and shear localization

“…In sample 374, the [001] axes of opx are aligned subparallel to lineation, and both [100] and [010] axes are distributed in a girdle shape normal to lineation. These alignments define the ABC-type LPO of opx (Jung et al 2010). Samples 373, 379, 380, and 381 did not have enough opx to properly determine the LPO.…”

“…Sample 372 shows that the [010] axes are aligned subnormal to foliation, the [001] axes of opx are aligned subparallel to lineation, and the [100] axes aligned subnormal to lineation in foliation. This corresponds to the BC-type LPO of opx (Jung et al 2010). In sample 374, the [001] axes of opx are aligned subparallel to lineation, and both [100] and [010] axes are distributed in a girdle shape normal to lineation.…”

Constraints on the rheology of the lower crust in a strike-slip plate boundary: evidence from the San Quintín xenoliths, Baja California, Mexico

“…From the observed CPO patterns, we infer activation of the (010)[100] and (010)[001] slip systems. Glide on the (010)[001] slip system has been documented in naturally deformed orthopyroxene (Hidas et al, 2007;Jung et al, 2010), but alignment of [100] axes with the lineation is not commonly observed. Low-angle misorientation axes in orthopyroxene crystals are abundant and exhibit predominance of [010] rotation axes.…”

Rock Deformation and Formation of LPO of Minerals in the Upper Mantle: Implications for Seismic Anisotropy

“…마지막으로, 감람석의 type-D 격자선호방향은 북극의 스발바드 Spitsbergen지역 스피넬 감람암에서 발견되었다 (Jung et al, 2009c (Fig. 7)으로 정 의되었는데 (Jung et al, 2010), 이는 사방휘석에서 가 장 흔히 발견되는 격자선호방향으로 알려져 왔다 (Hidas et al, 2007;Ishii and Sawaguchi, 2002;Jung et al, 2010;Skemer et al, 2006;Skemer et al, 2010;Soustelle et al, 2009;Tommasi et al, 2008;Xu et al, 2006). 하지만 최근에 북극 스발바 드 Spitsbergen에서 산출하는 맨틀 지놀리스(mantle xenolith, 맨틀포획암)의 연구에서, 그와 다른 세 가지 의 사방휘석의 격자선호방향이 존재한다는 것이 발견 되었다 (Jung et al, 2010).…”

“…7)으로 정 의되었는데 (Jung et al, 2010), 이는 사방휘석에서 가 장 흔히 발견되는 격자선호방향으로 알려져 왔다 (Hidas et al, 2007;Ishii and Sawaguchi, 2002;Jung et al, 2010;Skemer et al, 2006;Skemer et al, 2010;Soustelle et al, 2009;Tommasi et al, 2008;Xu et al, 2006). 하지만 최근에 북극 스발바 드 Spitsbergen에서 산출하는 맨틀 지놀리스(mantle xenolith, 맨틀포획암)의 연구에서, 그와 다른 세 가지 의 사방휘석의 격자선호방향이 존재한다는 것이 발견 되었다 (Jung et al, 2010). (Mainprice et al, 2000;Nicolas and Christensen, 1987;Savage, 1999;Silver, 1996;Smith et al, 2001).…”