Petrological characteristics of altered rocks and apparent hydrothermal fluid circulation at Longqi hydrothermal fields along the Southwest Indian Ridge

Wang Yuan; Li Huaiming; Dong Chuanwan; Yu Zenghui; Tao Chunhui; Li Wei; Yue Xihe; Lü Shihui

doi:10.3969/j.issn.0253-4193.2020.05.008

Volume 42 Issue 5

Nov. 2020

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Wang Yuan，Li Huaiming，Dong Chuanwan, et al. Petrological characteristics of altered rocks and apparent hydrothermal fluid circulation at Longqi hydrothermal fields along the Southwest Indian Ridge[J]. Haiyang Xuebao，2020, 42(5)：77–94，doi:10.3969/j.issn.0253−4193.2020.05.008

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Petrological characteristics of altered rocks and apparent hydrothermal fluid circulation at Longqi hydrothermal fields along the Southwest Indian Ridge

doi: 10.3969/j.issn.0253-4193.2020.05.008

Wang Yuan^{1, 2
,},
Li Huaiming^{1, 2
,
,},
Dong Chuanwan³,
Yu Zenghui⁴,
Tao Chunhui^{1, 2},
Li Wei^{1, 2},
Yue Xihe^{1, 2, 5},
Lü Shihui⁶

1.
Second Institute of Oceanography, Ministry of Natural Resources, Hangzhou 310012, China
2.
Key Laboratory of Submarine Geosciences, Ministry of Natural Resources, Hangzhou 310012, China
3.
College of Earth Science, University of Zhejiang, Hangzhou 310012, China
4.
Key Lab of Submarine Geosciences and Prospecting Techniques, Ministry of Education, Ocean University of China, Qingdao 266100, China
5.
College of Marine Science and Technology, China University of Geosciences, Wuhan 430074, China
6.
School of Ocean Sciences, China University of Geosciences, Beijing 100083, China

Received Date: 2019-03-01
Rev Recd Date: 2019-05-27

Available Online: 2020-11-18

Publish Date: 2020-05-25

Abstract

Abstract

Submarine hydrothermal fields in the vicinity of slow- and ultraslow-spreading oceanic ridges reveal a variety of altered rocks, recording the interaction between the deep crust fluid and the surrounding rock, and providing evidence of the characteristics of the deep hydrothermal fluid and associated cyclic processes. We studied samples of metabasalt, metagabbro, altered pyroxenite, and serpentinite collected by TV-grab during Chinese cruises of DY30, DY34, and DY40 at the Longqi hydrothermal field (areas A, B and C) at the ultraslow-spreading Southwest Indian Ridge. The petrography and mineral chemistry of the rock samples were examined under optical microscope and with an electron microprobe analyzer. The petrographic results show that ～95% of the altered rock samples in the Longqi hydrothermal field exhibited brittle deformation and therefore were probably formed in the upper crust. The remaining 5% of samples, from a deep source close to the Longqi-1 hydrothermal hydrothermal field (Area A) were variable, with brittle and plastic-brittle deformation. The altered rock in the Longqi hydrothermal field exhibited medium-low temperature metamorphism, and was mainly composed of chlorite, epidote, albite, actinolite, and sphene of low green-schist facies. In addition, the chlorite formation temperature (201–341°C) in the altered rocks in Area A, and the Fe content (17.5%–27.5%) of the altered minerals such as serpentine, actinolite and chlorite, were both higher than those for Longqi hydrothermal field areas B and C, where chlorite formation temperature was 239–303°C and the Fe content was 16.8%–26.5%. This is consistent with the high temperature hydrothermal vents observed in Area A. We consider that the detachment fault developed by the ridge section of the Longqi hydrothermal field provides a channel for the upward migration of hydrothermal fluids. The small-scale magmatic intrusion or eruption activity of the magma melt in the axial portion of the shaft during expansion may provide a heat source for the hydrothermal circulation.
- Longqi hydrothermal field,
- Southwest Indian Ridge,
- hydrothermal circulation,
- altered rock,
- detachment fault

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References(40)

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