Iron isotope fractionation during transcrustal magmatic differentiation: Implications for continental crustal formation in subduction zones

doi:10.1130/B37831.1

	Xu, Jian 1,2; Xia, Xiao-Ping 3; Wang, Qiang1,2 ; Zhang, Le 1,2; Cui, Ze-Xian 1,2; Yang, Qing 1,2; Zhang, Wan-Feng 1,2
	Iron isotope fractionation during transcrustal magmatic differentiation: Implications for continental crustal formation in subduction zones
刊名	GEOLOGICAL SOCIETY OF AMERICA BULLETIN
ISSN号	0016-7606
	2025-03-01
卷号	137 期号:3-4 页码:1843-1854
DOI	10.1130/B37831.1
语种	英语
WOS研究方向	Geology
摘要	Earth's continental crust is hypothesized to originate from mantle melting in subduction zones. However, mantle melts are typically Fe-rich, with light Fe isotopes (delta Fe-56 = 0.05 parts per thousand), unlike the Fe-depleted and heavy Fe isotope (delta Fe-56 can be up to 0.2 parts per thousand) compositions of continental crust. The mechanisms responsible for this paradox remain elusive. Here, we report Fe isotope data from a suite of co-magmatic Middle Triassic continental arc rocks in the Ailaoshan tectonic zone (Yunnan, SW China). Gabbroic diorites have light Fe isotopes (delta Fe-56 = 0.04 parts per thousand-0.09 parts per thousand), while granodiorites and normal-arc granites have slightly heavier values (delta Fe-56 = 0.07 parts per thousand-0.14 parts per thousand). Adakitic granites, with high Sr/Y (61-183) and La/Yb (47-90) ratios, exhibit the heaviest delta Fe-56 (0.16 parts per thousand-0.19 parts per thousand). Rayleigh fractionation modeling results suggest that fractionation of isotopically light Fe minerals (e.g., olivine, pyroxene, and amphibole) can reproduce the Fe isotopic variations in most samples, but fails to explain the high Sr/Y, La/Yb, and delta Fe-56 values of adakitic granites, which would require Fe-rich garnet fractionation. Notably, the different Fe isotopes of the adakitic granites and non-adakitic rocks reveal two distinct transcrustal magmatic differentiation pathways: lower crustal, high-pressure, garnet-dominated fractionation; and middle-upper crustal, amphibole-dominated fractionation. The heavy Fe isotopic and Fe-depleted characteristics of the Ailaoshan magmatic arc suites are more comparable to the calc-alkaline arc magmas from normal to thick crust arcs (e.g., the Andean arc), but remarkably different from the tholeiitic arc magmas from thin crust arcs (e.g., the Mariana arc). This study highlights the role of amphibole and garnet fractionation in magmatic calc-alkaline differentiation. We propose that a thickened crust would permit a longer magmatic differentiation column, thus facilitating felsic and Fe-depleted continental crustal formation. The fractionated Fe-rich, garnet-bearing arc cumulates with light Fe isotopes are density-unstable and may be recycled into the mantle by lower crustal foundering.
WOS记录号	WOS:001438304600002
收录类别	SCI
引用统计	被引频次：1[WOS] [WOS记录] [WOS相关记录]
文献类型	期刊论文
条目标识符	http://ir.gig.ac.cn/handle/344008/83008
专题	同位素地球化学国家重点实验室
通讯作者	Xu, Jian
作者单位	1.Chinese Acad Sci, Guangzhou Inst Geochem, State Key Lab Isotope Geochem, Guangzhou 510640, Peoples R China 2.Chinese Acad Sci, Ctr Excellence Deep Earth Sci, Guangzhou 510640, Peoples R China 3.Yangtze Univ, Coll Resources & Environm, Wuhan 430100, Peoples R China
推荐引用方式 GB/T 7714	Xu, Jian,Xia, Xiao-Ping,Wang, Qiang,et al. Iron isotope fractionation during transcrustal magmatic differentiation: Implications for continental crustal formation in subduction zones[J]. GEOLOGICAL SOCIETY OF AMERICA BULLETIN,2025,137(3-4):1843-1854.
APA	Xu, Jian.,Xia, Xiao-Ping.,Wang, Qiang.,Zhang, Le.,Cui, Ze-Xian.,...&Zhang, Wan-Feng.(2025).Iron isotope fractionation during transcrustal magmatic differentiation: Implications for continental crustal formation in subduction zones.GEOLOGICAL SOCIETY OF AMERICA BULLETIN,137(3-4),1843-1854.
MLA	Xu, Jian,et al."Iron isotope fractionation during transcrustal magmatic differentiation: Implications for continental crustal formation in subduction zones".GEOLOGICAL SOCIETY OF AMERICA BULLETIN 137.3-4(2025):1843-1854.