Crust-Mantle Transitional Zone beneath SW Tianshan Area Constrained by the Seismic and Calculated Velocities of the Deep-Seated Xenoliths in Tuoyun Basaltic Rocks
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摘要: 对我国西部新疆托云地区中新生代火山岩中的深源岩石包体进行了波速计算, 并与地球物理深部探测技术相结合, 共同限定了西南天山深部壳-幔过渡带的组成和性质.托云地区麻粒岩、橄榄岩的计算波速分别是6.98~7.36 km/s、7.96~8.47 km/s.这些结果与地震反射探测地震波速的对比, 说明在西南天山岩石圈剖面中的40~48km处存在较明显的壳-幔过渡带.过渡带自上而下主要由石英麻粒岩、辉石麻粒岩和橄榄石/石榴石麻粒岩组成, 然后进入尖晶石相二辉橄榄岩组成的上地幔.这样的岩石圈壳-幔结构可以用岩浆底侵-变质作用来解释.Abstract: The velocities of a series of deep-seated xenoliths in Late Mesozoic-Cenozoic basaltic rocks from Tuoyun basin, western Xinjiang (NW China), are calculated.These data, combined with the published seismic velocities for the area, are used to define the composition and structure of the crust-mantle transitional zone beneath southwestern Tianshan.The calculated velocities of peridotite and granulite xenoliths are 6.98-7.36 km/s and 7.96-8.47 km/s, respectively.The comparison of these data with the seismic velocities shows the presence of the crust-mantle transitional zone in 40-48 km beneath southwestern Tianshan.The zone consists of quartz granulite, pyroxene granulite and olivine/garnet granulite from top to bottom, and then transfers into the upper mantle mainly composed of spinel-facies lherzolite with or without volatile component minerals (phlogopite or amphibole).Such crust-mantle structure of lithosphere can be well explained by magma underplating and metamorphism.
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Key words:
- southwestern Tianshan /
- xenolith /
- velocity /
- crust-mantle transitional zone /
- magma underplating
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图 1 研究样品的位置(据Brookfield, 2000略修改)
Fig. 1. The locality map of the studied samples
图 2 西南天山下地壳-上地幔顶部岩石计算波速与地震实测波速的对比(a) 和岩性柱状图(b)
Fig. 2. Comparison of rock calculated velocities of lower crust-top of upper mantle and seismic wave velocities (a), and lithology column of lower crust-top of upper mantle (b), southwestern Tianshan
表 1 麻粒岩、橄榄岩包体的矿物组成与含量(%)
Table 1. The mineral composition and mode of granulite and peridotite xenoliths
表 2 麻粒岩、橄榄岩包体的计算波速
Table 2. The calculated velocities of granulite and peridotite xenoliths
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