Wave velocities and anisotropy of rocks: Implication for origin of low velocity zone of the Qinling Orogenic Belt, China

IF 8.5 1区地球科学 Q1 GEOSCIENCES, MULTIDISCIPLINARY

Geoscience frontiers Pub Date : 2025-01-01 DOI:10.1016/j.gsf.2024.101939

Lei Liu , Ying Li , Tingting Li , Hanyu Wang , Shasha Liu , Panpan Zhao , Gerile Naren , Li Yi , Hong Liu , Fengxia Sun , Jianguo Du

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Abstract

Structure and composition of Earth are fundamental importance in exploring the dynamic evolution of the crust and mantle. The Qinling Orogenic Belt (QOB) is located between the North China plate and the South China Plate, and is one of the main orogenic belts in China. To explore the composition and origin of anisotropy and the low wave velocity zone of the QOB, ten rock samples (gneiss and schist) were collected from the five sites of the QOB and the P- and S-wave velocities of these samples were measured under 0.6 to 2.0 GPa and 100 to 550 °C. The wave velocities increase with increasing pressure and decreasing temperature. The V_P and V_S of the schist and gneiss match the velocity of the middle and lower crust of the QOB, indicating that schist and gneiss are important component of the QOB. All the schist and gneiss samples exhibit obvious seismic anisotropy with 1.64%–17.42% for V_S and 2.93%–14.78% for V_P under conditions of crust and upper mantle. The CPO/LPO and layering distribution of mica in rock samples are the main reasons for this anisotropy. The V_S structures below the five sampled sites from seismic ambient noise tomography were built to explore the effect of schist and gneiss on the composition and structure of the QOB. The results indicate that orientation-arranged gneiss and schist driven by the tectonic stresses might be a new origin of the character of V_P/V_S, seismic anisotropy, and the low velocity zone in the QOB.

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岩石波速与各向异性：对秦岭造山带低速带成因的启示

地球的结构和组成是研究地壳和地幔动态演化的基础。秦岭造山带位于华北板块和华南板块之间，是中国主要的造山带之一。为探讨昆仑山各向异性和低波速带的组成和成因，在昆仑山5个测点采集了10个片麻岩和片岩样品，在0.6 ~ 2.0 GPa和100 ~ 550℃条件下测量了这些样品的横波速度和纵波速度。波速随压力的增大和温度的降低而增大。片岩和片麻岩的VP和VS与QOB中下地壳速度相匹配，表明片岩和片麻岩是QOB的重要组成部分。所有片岩和片麻岩样品在地壳和上地幔条件下均表现出明显的地震各向异性，VS各向异性为1.64% ~ 17.42%，VP各向异性为2.93% ~ 14.78%。岩石样品中云母的CPO/LPO和层状分布是造成这种各向异性的主要原因。在地震环境噪声层析成像的5个采样点下方建立了VS结构，以探讨片岩和片麻岩对QOB组成和结构的影响。结果表明，受构造应力驱动的定向排列片麻岩和片岩可能是形成库区VP/VS特征、地震各向异性特征和低速带的新来源。

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来源期刊

Geoscience frontiers Earth and Planetary Sciences-General Earth and Planetary Sciences

CiteScore

17.80

自引率

3.40%

发文量

147

审稿时长

35 days

期刊介绍： Geoscience Frontiers (GSF) is the Journal of China University of Geosciences (Beijing) and Peking University. It publishes peer-reviewed research articles and reviews in interdisciplinary fields of Earth and Planetary Sciences. GSF covers various research areas including petrology and geochemistry, lithospheric architecture and mantle dynamics, global tectonics, economic geology and fuel exploration, geophysics, stratigraphy and paleontology, environmental and engineering geology, astrogeology, and the nexus of resources-energy-emissions-climate under Sustainable Development Goals. The journal aims to bridge innovative, provocative, and challenging concepts and models in these fields, providing insights on correlations and evolution.