CAJ | 학술논문

为了研究水化岩石圈地幔和地幔楔的地震波速、各向异性及其与蛇纹石化程度及应变状态的关系,作者实验测量了8块叶蛇纹岩(采自辽宁的岫玉)标本在不同构造主方向(X, Y和Z)上的纵、横波速度随围压(0~600 MPa)的变化规律,详细研究了叶蛇纹石在塑性变形过程中通过(001)[010]位错滑移形成很强的晶格优选定向和高达21%的纵波速度各向异性与24%的剪切波分裂的特征,发现高温叶蛇纹岩与低温利蛇纹岩具有截然不同的地震波性质,例如,在围压600 MPa 下,高温叶蛇纹岩的 Vp=6.73 km/s、Vs=3.74 km/s, Vp/Vs=1.80,而低温利蛇纹岩的Vp=5.10 km/s、Vs=2.32 km/s, Vp/Vs=2.20。前人利用低温蛇纹石化橄榄岩的波速数据解释温度高于300℃的水化地幔楔和岩石圈地幔的地震波速不可避免地要低估研究区域内蛇纹石化的程度和水含量。本研究查明叶蛇纹岩的地震波性质及其各向异性特征亦为解释全球大洋板块俯冲带乃至青藏高原地区的剪切波分裂资料提供了新的思路。
위료연구수화암석권지만화지만설적지진파속、각향이성급기여사문석화정도급응변상태적관계,작자실험측량료8괴협사문암(채자료녕적수옥)표본재불동구조주방향(X, Y화Z)상적종、횡파속도수위압(0~600 MPa)적변화규률,상세연구료협사문석재소성변형과정중통과(001)[010]위착활이형성흔강적정격우선정향화고체21%적종파속도각향이성여24%적전절파분렬적특정,발현고온협사문암여저온리사문암구유절연불동적지진파성질,례여,재위압600 MPa 하,고온협사문암적 Vp=6.73 km/s、Vs=3.74 km/s, Vp/Vs=1.80,이저온리사문암적Vp=5.10 km/s、Vs=2.32 km/s, Vp/Vs=2.20。전인이용저온사문석화감람암적파속수거해석온도고우300℃적수화지만설화암석권지만적지진파속불가피면지요저고연구구역내사문석화적정도화수함량。본연구사명협사문암적지진파성질급기각향이성특정역위해석전구대양판괴부충대내지청장고원지구적전절파분렬자료제공료신적사로。
Antigorite is a main contributor to the formation of anomalously low seismic velocities and high anisotropy in subducting oceanic slabs, forearc mantle wedges and subcontinental mantle shear zones. Here we report new results on P- and S-wave velocities and anisotropy in 8 antigorite serpentinite samples (“Xiuyan jade” from Liaoning, China), measured at pressures up to 600 MPa. The results combined with previous experimental data allow us to distinguish the effects of low and high temperature (LT and HT) serpentinization on seismic velocities in the upper mantle. Serpentine contents in hydrous subducting slabs, mantle wedges and subcontinental mantle shear zones where temperature is>300 ℃should be at least twice as large as previous estimates based on LT serpentinization. The intrinsic Vp and Vs anisotropy of serpentinites, formed by plastic flow-induced lattice-preferred orientation (LPO) of antigorite, can be as high as 21%and 24%, respectively. Our results provide a new explanation for various anisotropy patterns observed in subduction systems worldwide. For a steeply subducting slab, antigorite is most likely deformed by nearly coaxial flattening and thus the trench-parallel seismic velocity is much faster than the trench-normal velocity. For a shallowly subducting slab, however, antigorite is most likely deformed by simple shear. Within the horizontal plane, the trench-normal velocity can be smaller, equal to, or larger than the trench-parallel velocity, depending on the dip angle of subduction. The geophysical characteristics of the Tibetan Plateau such as strong heterogeneities in seismic velocities and attenuation, shear wave splitting and electric conductivity can be equally explained by the presence of serpentinized shear zones within the subcontinental mantle.