上地幔的变形和熔岩相互作用:日本Horoman橄榄岩层状结构的启示

IF 2.7 3区 地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS
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引用次数: 0

摘要

为了更好地了解上地幔中熔岩与岩石之间的相互作用,研究人员对日本北海道Horoman橄榄岩群的变形地幔橄榄岩进行了微结构和岩石学分析。霍罗曼橄榄岩群岩性多变,包含各种超基性岩和黑云母岩。我们研究了一个面积为 3 × 70 米的露头,其中包含层状尖晶石哈兹伯格岩、斜长石蛭石和黑云母岩。研究结果表明,反应熔体在已经变形的橄榄岩中优先沿着褶皱迁移,这些熔体富集区特别容易进一步变形。支持这一推论的因素包括:(1)变形橄榄岩中岩层和褶皱边界的平行性,以及橄榄岩中橄榄石的形状和晶体学优选取向(SPOs 和 CPOs);(2)橄榄岩和黑云母岩层边界附近的镁扩散趋势和钠长石晶粒的模态成分;(3) 橄榄石晶体中 NiO 含量的变化;(4) 橄榄石 CPOs 的正交(010)[100] 滑移系统模式和弱纤维-[010] 模式的变化;以及 (5) 强烈的副长石 SPOs、副长石的尖齿形状以及晶体间无变形。这些结果与之前报道的霍罗曼橄榄岩复合体的P-T条件相结合,表明具有层状结构的变形橄榄岩和黑云母岩代表了1050-1150 °C的温度和0.7-1.5 GPa的压力。我们的研究结果表明,压力的降低导致了无熔体系统向含熔体系统的转变,变形机制随之发生变化,从无熔体系统中的位错蠕变转变为含熔体系统中的扩散蠕变,并在富含熔体的细粒层中出现应变局部化。变形机制的变化很可能发生在大洋中脊下方的最上层地幔中,那里强烈的流变对比是由熔融分量的空间变化控制的。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Deformation and melt–rock interaction in the upper mantle: Insights from the layered structure of the Horoman peridotite, Japan

To obtain a better understanding of melt–rock interactions in the upper mantle, microstructural and petrological analyses were conducted on deformed mantle peridotites from the Horoman peridotite complex, Hokkaido, Japan. The Horoman peridotite complex is lithologically heterogeneous and contains various kinds of ultramafic and mafic rocks. We studied an outcrop of 3 × 70 m in size that contains layered spinel harzburgite, plagioclase lherzolite, and mafic rocks. The results indicate that reactive melts migrated preferentially along the foliation in the already deformed peridotite, and that these melt-rich zones became especially prone to further deformation. This inference is supported by (1) the parallelism of the boundaries of rock layers and foliation in the deformed peridotite, and the shape and crystallographic preferred orientations (SPOs and CPOs) of olivine in the peridotites; (2) the diffusive trends of magnesium and modal compositions of pargasite grains near the boundaries between peridotite and mafic layers; (3) variations in the NiO content of olivine crystals; (4) variations in olivine CPOs with orthorhombic (010)[100] slip system patterns and weak fiber-[010] patterns; and (5) the strong pargasite SPOs, the cuspate shapes of the pargasites, and the absence of intercrystallite deformation. The results, combined with previously reported P–T conditions for the Horoman peridotite complex, indicate that the deformed peridotites and mafic rocks with a layered structure represent temperatures of 1050–1150 °C and pressures of 0.7–1.5 GPa. Our results suggest that a decrease in pressure led to the transition from a melt-free to a melt-bearing system with a consequent change in the deformation mechanism, from dislocation creep in the melt-free system to diffusion creep in the melt-bearing system, with strain localization in the fine-grained melt-rich layers. The change in deformation mechanism is likely to have occurred in the uppermost mantle beneath a mid-ocean ridge, where strong rheological contrasts are controlled by spatial variations in the melt fraction.

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来源期刊
Tectonophysics
Tectonophysics 地学-地球化学与地球物理
CiteScore
4.90
自引率
6.90%
发文量
300
审稿时长
6 months
期刊介绍: The prime focus of Tectonophysics will be high-impact original research and reviews in the fields of kinematics, structure, composition, and dynamics of the solid arth at all scales. Tectonophysics particularly encourages submission of papers based on the integration of a multitude of geophysical, geological, geochemical, geodynamic, and geotectonic methods
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