Tectonic Quiescence in Actively Extending Back-Arc Regions

IF 3.9 2区地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS

Journal of Geophysical Research: Solid Earth Pub Date : 2024-09-24 DOI:10.1029/2024JB029236

A. Beniest, A. Dannowski, M. Schnabel, H. Kopp, the SO267 Scientist Party

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Abstract

We analyzed refraction and reflection seismic data covering the Central Lau Spreading Center (CLSC) and the Tonga volcanic arc at 18°S in the Pacific Ocean to investigate tectonic inactivity in actively extending back-arc systems. Our P-wave travel time tomography shows a characteristic 6–8 km thick back-arc crust beneath and around the CLSC and a ∼13 km thick arc-crust at the eastern end of our profile, which corresponds to the Tonga volcanic arc. Lower crustal velocities increase to 7.5 km/s toward the volcanic arc, marking the transition from back-arc to arc crust. These high P-wave velocities can be explained by a high pyroxene content in the lower crust originating from depleted melts. Our seismic reflection data show steep normal faults below the CLSC and volcanic structures closer to the volcanic arc, without a tectonically inactive zone (also knows as the “diffuse plate boundary”) in between. Based on our results, we suggest that the Niuafo'ou and Tonga microplates should be treated as one tectonic plate with local zones of intra-plate deformation that are separated by zones that are tectonically quiet.

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积极扩展的后弧区的构造静止

我们分析了位于太平洋南纬 18 度的刘氏中央扩张中心（CLSC）和汤加火山弧的折射和反射地震数据，以研究积极延伸的后弧系统的构造不活跃性。我们的 P 波旅行时间层析成像显示，在刘氏中央扩张中心下方和周围有一个厚达 6-8 千米的后弧地壳，在我们剖面的东端有一个厚达 13 千米的弧形地壳，与汤加火山弧相对应。向火山弧方向的地壳下部速度增加到每秒 7.5 公里，标志着从后弧向弧壳的过渡。这些高 P 波速度可解释为源自贫化熔体的下地壳中的高辉石含量。我们的地震反射数据显示，在 CLSC 下方有陡峭的正断层，在靠近火山弧的地方有火山结构，而在两者之间没有构造不活跃区（也称为 "弥漫板块边界"）。根据我们的研究结果，我们建议将牛佛欧微板块和汤加微板块视为一个构造板块，板块内有局部变形区，而这些变形区又被构造安静区隔开。

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来源期刊

Journal of Geophysical Research: Solid Earth Earth and Planetary Sciences-Geophysics

CiteScore

7.50

自引率

15.40%

发文量

559

期刊介绍： The Journal of Geophysical Research: Solid Earth serves as the premier publication for the breadth of solid Earth geophysics including (in alphabetical order): electromagnetic methods; exploration geophysics; geodesy and gravity; geodynamics, rheology, and plate kinematics; geomagnetism and paleomagnetism; hydrogeophysics; Instruments, techniques, and models; solid Earth interactions with the cryosphere, atmosphere, oceans, and climate; marine geology and geophysics; natural and anthropogenic hazards; near surface geophysics; petrology, geochemistry, and mineralogy; planet Earth physics and chemistry; rock mechanics and deformation; seismology; tectonophysics; and volcanology. JGR: Solid Earth has long distinguished itself as the venue for publication of Research Articles backed solidly by data and as well as presenting theoretical and numerical developments with broad applications. Research Articles published in JGR: Solid Earth have had long-term impacts in their fields. JGR: Solid Earth provides a venue for special issues and special themes based on conferences, workshops, and community initiatives. JGR: Solid Earth also publishes Commentaries on research and emerging trends in the field; these are commissioned by the editors, and suggestion are welcome.