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Geochemistry and Mineralogy of Basalts from the South Mid-Atlantic Ridge (18.0°–20.6°S): Evidence of a Heterogeneous Mantle Source

by Yun Zhong 1,2, Weiliang Liu 1,2,*, Zhilei Sun 1,2, Chris Yakymchuk 3, Kefa Ren 4, Jinnan Liu 1,5,6, Wei Li 1,5,6, Yaoliang Ma 1,5,6 and Bin Xia 1,5,6
1
School of Marine Sciences, Sun Yat-sen University, Guangzhou 510006, China
2
The Key Laboratory of Gas Hydrate, Ministry of Natural Resources, Qingdao Institute of Marine Geology, Qingdao 266071, China
3
Department of Earth and Environmental Sciences, University of Waterloo, Waterloo, ON N2L 3G1, Canada
4
School of Earth Sciences, Chengdu University of Technology, Chengdu 610059, China
5
Guangdong University Key Laboratory of Offshore Oil Exploration and Development/Guangdong Provincial Key Laboratory of Marine Resources and Coastal Engineering, School of Marine Sciences, Sun Yat-sen University, Guangzhou 510006, China
6
Southern Laboratory of Ocean Science and Engineering (Zhuhai, Guangdong), Zhuhai 519000, China
*
Author to whom correspondence should be addressed.
Minerals 2019, 9(11), 659; https://doi.org/10.3390/min9110659
Received: 27 September 2019 / Revised: 22 October 2019 / Accepted: 24 October 2019 / Published: 27 October 2019
(This article belongs to the Section Mineral Geochemistry and Geochronology)
The South Mid-Atlantic Ridge is a typical slow-spreading ridge that represents a modern example to understand mantle composition and the evolution of mid-ocean ridge magmatism. In this paper, we investigate basalt samples dredged from four locations along the South Mid-Atlantic Ridge ranging from 18.0° to 20.6°S. The basalts belong to the tholeiitic series and exhibit normal mid-ocean ridge basalt (N-MORB) geochemical features with variable enrichments of Rb, Th, U, and Pb and depletions of Ba and Sr relative to primitive mantle. Some samples have negative Nb–Ta anomalies whereas others have positive Na–Ta anomalies to average N-MORBs. Plagioclase phenocrysts, microphenocrysts, and microlites occur in the in the matrix; phenocrysts and microphenocrysts are bytownite and labradorite in composition. Olivine phenocrysts are forsterite (Fo87 to Fo96). Chemical zoning in phenocrysts are interpreted to record crystal fractionation and magma mixing. Cores of plagioclase phenocrysts have higher anorthite values (An72–83) and estimated crystallization temperatures (~1180–1240 °C) that may suggest a xenocrystic origin. The lower anorthite proportions of rims of plagioclase phenocrysts (An65–71) and microphenocrysts (An54–72) yield lower estimated crystallization temperatures of ~1090–1120 °C and ~980–1060 °C, respectively. Rims of plagioclase phenocrysts and microphenocrysts may be generated in different environments such as magma chambers or magma channels, respectively. The basalt samples probably originated from partial melting of a depleted mantle spinel lherzolite source with a minor contribution of enriched materials possibly derived from the Saint Helena plume and subcontinental lithospheric mantle in the asthenosphere. Variable compositions of the basalt samples suggest heterogeneous mantle that includes depleted and enriched components at the South Mid-Atlantic Ridge between 18.0°–20.6°S. View Full-Text
Keywords: basalt; mineralogy; geochemistry; petrogenesis; South Mid-Atlantic Ridge basalt; mineralogy; geochemistry; petrogenesis; South Mid-Atlantic Ridge
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Zhong, Y.; Liu, W.; Sun, Z.; Yakymchuk, C.; Ren, K.; Liu, J.; Li, W.; Ma, Y.; Xia, B. Geochemistry and Mineralogy of Basalts from the South Mid-Atlantic Ridge (18.0°–20.6°S): Evidence of a Heterogeneous Mantle Source. Minerals 2019, 9, 659.

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  • Supplementary File 1:

    ZIP-Document (ZIP, 132 KB)

  • Externally hosted supplementary file 1
    Doi: 10.5281/zenodo.3515763
    Link: https://zenodo.org/record/3515763#.Xa6uoegzaUk
    Description: Appendix Tables Table S1 Whole-rock major element (wt.%) and trace element (ppm) compositions of the SMAR basalt samples Table S2 Electron probe microanalytical data of typical plagioclases in the SMAR basalt samples Table S3 Electron probe microanalytical data of typical olivines in the SMAR basalt samples
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