Relationship Between the High-Amplitude Magnetic Anomalies and Serpentinized Fore-Arc Mantle in the Cascadia Subduction Zone

IF 1.9 4区地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS

pure and applied geophysics Pub Date : 2023-09-02 DOI:10.1007/s00024-023-03337-4

Wen-Bin Doo

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Abstract

A zone of significant high-amplitude magnetic anomalies is observed without a comparable gravity high along the Cascadia margin and is spatially correlated with the low-velocity fore-arc mantle wedge. This wedge is interpreted to be serpentinized fore-arc mantle and is further considered to be the main source of the high-amplitude magnetic anomalies. To test this hypothesis, the magnetization-density ratio (MDR) is estimated along the Cascadia margin to highlight the physical characteristics of serpentinization (reduced density and increased magnetization). Interestingly, high MDR values are found only in central Oregon, where slab dehydration and fore-arc mantle serpentinization (50–60% serpentinization) are inferred in conjunction with sparse seismicity. This result may indicate either poorly serpentinized fore-arc mantle (low degree of serpentinization) or that the fore-arc mantle is deeper than the Curie temperature isotherm for magnetite in northern and southern Cascadia. This finding means that magnetic anomaly highs and serpentinized fore-arc mantle may not always be correlated in subduction zones. On the other hand, the MDR pattern suggests segmentation of the Cascadia subduction zone, which is consistent with several previous geological and geophysical observations.

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卡斯卡迪亚俯冲带高振幅磁异常与蛇纹弧前地幔的关系

沿着卡斯卡迪亚边缘观察到一个明显的高振幅磁异常区，没有类似的重力高，并且在空间上与低速弧前地幔楔相关。该楔块被解释为蛇纹石化弧前地幔，并被进一步认为是高振幅磁异常的主要来源。为了验证这一假设，沿着Cascadia边缘估计了磁化密度比（MDR），以突出蛇纹石化的物理特征（密度降低和磁化增加）。有趣的是，高MDR值仅在俄勒冈州中部发现，那里的板块脱水和弧前地幔蛇纹石化（50-60%的蛇纹石化）与稀疏的地震活动相结合。这一结果可能表明，要么是蛇纹石化程度低的弧前地幔（低蛇纹石化），要么是弧前地幔比卡斯卡迪亚北部和南部磁铁矿的居里温度等温线更深。这一发现意味着磁异常高点和蛇纹石化弧前地幔在俯冲带中可能并不总是相关的。另一方面，MDR模式表明对卡斯卡迪亚俯冲带进行了分割，这与之前的几次地质和地球物理观测结果一致。

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来源期刊

pure and applied geophysics 地学-地球化学与地球物理

CiteScore

4.20

自引率

5.00%

发文量

240

审稿时长

9.8 months

期刊介绍： pure and applied geophysics (pageoph), a continuation of the journal "Geofisica pura e applicata", publishes original scientific contributions in the fields of solid Earth, atmospheric and oceanic sciences. Regular and special issues feature thought-provoking reports on active areas of current research and state-of-the-art surveys. Long running journal, founded in 1939 as Geofisica pura e applicata Publishes peer-reviewed original scientific contributions and state-of-the-art surveys in solid earth and atmospheric sciences Features thought-provoking reports on active areas of current research and is a major source for publications on tsunami research Coverage extends to research topics in oceanic sciences See Instructions for Authors on the right hand side.