Copper isotope fractionation during magma differentiation: Evidence from lavas on the East Pacific Rise at 10 degrees 30'N

doi:10.1016/j.gca.2023.07.016

IOCAS-IR > 海洋地质与环境重点实验室

	Copper isotope fractionation during magma differentiation: Evidence from lavas on the East Pacific Rise at 10 degrees 30'N
	Sun, Pu1,2 ; Niu, Yaoling 3,4; Chen, Shuo 1,2; Guo, Pengyuan 1,2; Duan, Meng 1,2; Chen, Yanhong 4; Gong, Hongmei 1,2; Xiao, Yuanyuan 1,2; Wang, Xiaohong 1,2
	2023-09-01
发表期刊	GEOCHIMICA ET COSMOCHIMICA ACTA
ISSN	0016-7037
卷号	356 页码:93-104
通讯作者	Sun, Pu([email protected])
摘要	Redox-driven copper (Cu) isotope fractionation has been widely observed in low-temperature weathering and hydrothermal processes. However, how Cu isotopes may fractionate during magmatic processes remain unknown. To address this issue, we studied MORB samples from the East Pacific Rise (EPR) at 10. 30'N to explore the Cu isotope behavior during magma differentiation. These samples are globally ideal because they are generated from a uniformly depleted sub-ridge mantle source but have experienced varying extents of fractional crystallization and sulfide segregation with large variations of MgO (1.76-7.38 wt%) and Cu (16.0-75.2 mu g/g). Lavas with MgO >= 4.9 wt% involving olivine, clinopyroxene and plagioclase as the major liquidus minerals show homogeneous delta Cu-65 of 0.05 +/- 0.03%, suggesting little Cu isotope fractionation at this stage of magma differentiation. However, after Fe-Ti oxides appear on the liquidus, melt delta Cu-65 values first decrease rapidly to -0.41% at MgO of 3.9 wt% and then increase with the most evolved sample having delta Cu-65 of 0.08%. Such a significant Cu isotope fractionation during magma differentiation has never been reported before. We suggest the large Cu isotope variation at MgO < 4.9 wt% reflect a redox change of MORB melt resulting from fractional crystallization of Fe-Ti oxides. The crystallization of ilmenite (Fe2+TiO3), which is the first Fe-Ti oxide phase during MORB differentiation, causes a sudden increase of Fe3+/Sigma Fe in the residual melt and drives the redox reaction Fe3+ + Cu1+ -> Fe2+ + Cu2+. As a result, sulfides segregated from the MORB melts have high Cu2+ content and heavy Cu isotope compositions with Delta 65Cu(Sulfide- Silicate melt) > 0 because of the preferential bonding of heavy Cu isotopes (65Cu vs. 63Cu) with Cu2+, whose fractionation rapidly decreases delta Cu-65 of the residual melts. The increase of Fe3+/Sigma Fe will quickly drive the melt to be saturated in titanomagnetite (magnetite-Ulv ospinel solid solutions), whose crystallization decreases melt Fe3+/Sigma Fe and drives the redox reaction Fe2+ + Cu2+ -> Fe3+ + Cu1+. As a result, the segregated sulfides after titanomagnetite saturation have decreasing Cu2+ content. These sulfides are also predicted to have low Ni content and exhibit Delta 65Cu(Sulfide- Silicate melt) < 0, whose segregation raises delta Cu-65 in the residual melts. Therefore, we suggest a significant influence of redox states of Cu and abundance of Ni in the segregated sulfides on the Cu isotope fractionation during MORB differentiation. During mantle melting for MORB at.FMQ < 0, Cu isotope fractionation between melt and mantle sulfide is inferred to be limited, and the upper mantle has primitive MORB-like delta Cu-65 of 0.06 +/- 0.05%.
关键词	Copper isotopes Isotope fractionation East Pacific Rise Mid-ocean ridge basalts Magma differentiation Magma redox state
DOI	10.1016/j.gca.2023.07.016
收录类别	SCI
语种	英语
资助项目	National Natural Science Foundation of China (NSFC)[91958215]; National Natural Science Foundation of China (NSFC)[41630968]; National Natural Science Foundation of China (NSFC)[ZR2020MD029]; Shandong Provincial Natural Science Foundation[B18048]; 111 Project; [42006049]
WOS研究方向	Geochemistry & Geophysics
WOS类目	Geochemistry & Geophysics
WOS记录号	WOS:001059489400001
出版者	PERGAMON-ELSEVIER SCIENCE LTD
WOS关键词	OXIDATION-STATE ; PARTITION-COEFFICIENTS ; OXYGEN FUGACITY ; MORB GLASSES ; ELEMENT GEOCHEMISTRY ; CHALCOPHILE ELEMENTS ; SULFIDE SATURATION ; PRECISE ANALYSIS ; SILICATE MELTS ; ARC BASALTS
引用统计	被引频次：5[WOS] [WOS记录] [WOS相关记录]
文献类型	期刊论文
条目标识符	http://ir.qdio.ac.cn/handle/337002/181836
专题	海洋地质与环境重点实验室
通讯作者	Sun, Pu
作者单位	1.Chinese Acad Sci, Inst Oceanol, Key Lab Marine Geol & Environm, Qingdao 266071, Peoples R China 2.Laoshan Lab, Lab Marine Geol, Qingdao 266061, Peoples R China 3.Laoshan Lab, Qingdao 266237, Peoples R China 4.China Univ Geosci, Sch Ocean Sci, Beijing 100083, Peoples R China
第一作者单位	中国科学院海洋研究所
通讯作者单位	中国科学院海洋研究所
推荐引用方式 GB/T 7714	Sun, Pu,Niu, Yaoling,Chen, Shuo,et al. Copper isotope fractionation during magma differentiation: Evidence from lavas on the East Pacific Rise at 10 degrees 30'N[J]. GEOCHIMICA ET COSMOCHIMICA ACTA,2023,356:93-104.
APA	Sun, Pu.,Niu, Yaoling.,Chen, Shuo.,Guo, Pengyuan.,Duan, Meng.,...&Wang, Xiaohong.(2023).Copper isotope fractionation during magma differentiation: Evidence from lavas on the East Pacific Rise at 10 degrees 30'N.GEOCHIMICA ET COSMOCHIMICA ACTA,356,93-104.
MLA	Sun, Pu,et al."Copper isotope fractionation during magma differentiation: Evidence from lavas on the East Pacific Rise at 10 degrees 30'N".GEOCHIMICA ET COSMOCHIMICA ACTA 356(2023):93-104.