西南印度洋中脊热液区岩石声学特性

揭天愚; 周建平; 陶春辉; 王汉闯; 李倩宇; 吴涛; 刘隆

doi:10.3969/j.issn.1001-909X.2024.01.001

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海洋学研究 ›› 2024, Vol. 42 ›› Issue (1) : 1-12. DOI: 10.3969/j.issn.1001-909X.2024.01.001

研究论文

西南印度洋中脊热液区岩石声学特性

揭天愚 ¹^,² ,
周建平 ¹^,²^,³^,^* ,
陶春辉 ¹^,² ,
王汉闯 ¹^,² ,
李倩宇 ¹^,²^,⁴ ,
吴涛 ¹^,² ,
刘隆 ⁵

作者信息 +

Acoustic characteristics of rocks from the SWIR hydrothermal fields

JIE Tianyu ¹^,² ,
ZHOU Jianping ¹^,²^,³^,^* ,
TAO Chunhui ¹^,² ,
WANG Hanchuang ¹^,² ,
LI Qianyu ¹^,²^,⁴ ,
WU Tao ¹^,² ,
LIU Long ⁵

Author information +

文章历史 +

摘要

西南印度洋中脊(Southwest Indian Ridge, SWIR)热液区具有潜在发育的大规模硫化物矿床,当前正在开展SWIR硫化物矿产资源评价。测量分析硫化物和不同围岩的声速等物性特征是硫化物近底地震勘探资料处理和解释的基础。该文对西南印度洋中脊热液区的硫化物和围岩等样品进行了系统的物性测量,结合岩石物性(包括密度、孔隙度、P波速度)与矿物组成,深入分析了西南印度洋中脊热液区岩石声速变化特性及其影响因素。结果表明,SWIR热液区围岩的P波速度受到岩石骨架矿物、孔隙和围压的影响。由于岩石孔隙度总体偏小,对P波速度的影响并不显著,但围压的增加使岩石微裂缝和孔隙逐渐闭合,P波速度呈非线性指数变化。蚀变作用导致了矿物成分改变,是影响围岩声速的最关键因素。单一物性参数测量结果可能存在多解性,联合波速、密度、磁性和电性等多物性参数测量有利于岩性区分。该研究成果有助于识别硫化物和围岩,为我国西南印度洋合同区多金属硫化物地震勘探工作提供重要支撑。

Abstract

The hydrothermal fields of the Southwest Indian Ridge (SWIR) have the potential to develop large scale sulfide deposits, and the SWIR sulfide mineral resource evaluation is currently underway. Measurement and analysis of petrophysical characteristics such as P-wave velocity of sulfides and different host rocks are the basis for processing and interpretation of near-bottom seismic exploration data. Through the systematic measurement of the physical properties of sulfides and host rocks in the SWIR hydrothermal areas, we have analyzed the characteristics of rock P-wave velocity variation and its influencing factors by combining rock physical properties (including density, porosity, P-wave velocity) and minerals. The results show that the P-wave velocity of SWIR rocks is influenced by the rock skeleton minerals, pore space and confining pressure. Due to the overall small porosity of the rocks, the effect on P-wave velocity is not significant, but the increase of the confining pressure gradually closes the rock microfractures and pores, and the P-wave velocity varies non-linearly exponentially. The alteration causes the change of mineral composition, which is the most critical factor affecting the P-wave velocity of the confining rocks. The results of single physical parameter measurements may have multiple solutions, and the joint measurement of multiple physical parameters such as wave velocity, density, magnetic and electrical properties is beneficial for lithological differentiation. The research results help identifying sulfides and host rocks, and provide important support for the seismic exploration of polymetallic sulfides in the Southwest Indian Ocean contract area of China.

导出引用

揭天愚, 周建平, 陶春辉, 等. 西南印度洋中脊热液区岩石声学特性[J]. 海洋学研究. 2024, 42(1): 1-12 https://doi.org/10.3969/j.issn.1001-909X.2024.01.001

JIE Tianyu, ZHOU Jianping, TAO Chunhui, et al. Acoustic characteristics of rocks from the SWIR hydrothermal fields[J]. Journal of Marine Sciences. 2024, 42(1): 1-12 https://doi.org/10.3969/j.issn.1001-909X.2024.01.001

中图分类号： P714⁺.8

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摘要

超慢速扩张西南印度洋中脊岩浆的集中供给在空间维度上表现为岩浆扩张段（NVR）与相邻的非转换断层不连续带（NTD）地壳结构的差异，而在时间维度上表现为离轴与沿轴地壳结构的差异.为了进一步揭示岩浆集中供给的时空分布特征，本文选取西南印度洋中脊热液区2010年海底地震仪深部探测中平行于洋中脊距轴部偏北约10 km的离轴测线d0d10，使用射线追踪正演和反演的方法，得到了NVR和NTD北侧离轴区域的地壳及上地幔P波速度结构，并与轴部速度结构进行了对比分析.研究结果表明：（1）NTD北侧离轴区域的地壳厚度约5.2 km，其厚度明显大于轴部NTD下方地壳厚度（~3.2 km），由此推测洋脊轴部NTD区域形成的地壳在不断减薄；（2）NVR北侧离轴区域的地壳厚度约7.0 km，其厚度亦大于轴部NVR地壳厚度（~5.8 km），表明在洋中脊演化过程中洋脊轴区域的岩浆供给在不断减少，其活动性在不断减弱.

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本文引用 [1] 摘要

在超慢速扩张的洋中脊区域，广泛发育的拆离断层将幔源橄榄岩大规模拆离到海底表面，上升出露的橄榄岩发生蛇纹岩化作用，极大地降低了岩石强度，促进了拆离断层的持续滑动，形成独特的光滑地形。本文利用快速拉格朗日连续介质分析法模拟研究蛇纹岩化作用对超慢速洋中脊拆离断层发育的影响。通过对比有蛇纹岩化作用和无蛇纹岩化作用下拆离断层发育的生命周期和力学差异，发现在蛇纹岩化作用下，岩石圈生成断层所需要应力降低了40%，导致断层下盘极易产生与原断层倾向相反的新断层；蛇纹岩化导致断层滑动摩擦力减小，有利于断层的持续滑动。理解蛇纹岩化作用和断层发育的关系对认识超慢速洋脊段末端的扩张机制具有重要意义。

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