干旱区生态环境知识资源中心(Arid): Geochemical insights into formation of enigmatic ironstones from Rio Grande rise, South Atlantic Ocean

Arid

DOI	10.1016/j.margeo.2021.106716
	Geochemical insights into formation of enigmatic ironstones from Rio Grande rise, South Atlantic Ocean
	Benites, Mariana; Hein, James R.; Mizell, Kira; Farley, Kenneth A.; Treffkorn, Jonathan; Jovane, Luigi
通讯作者	Benites, M (corresponding author)，Univ Sao Paulo, Inst Oceanog, Praca Oceanog 191, BR-05508120 Sao Paulo, SP, Brazil.
来源期刊	MARINE GEOLOGY
ISSN	0025-3227
EISSN	1872-6151
出版年	2022
卷号	444
英文摘要	Rio Grande Rise (RGR) is an intraplate oceanic elevation in the South Atlantic Ocean that formed at a hotspot on the Mid-Atlantic Ridge during the Cretaceous. In spreading center and hotspot environments, ironstones form mainly by biomineralization of reduced Fe from hydrothermal fluids or oxidation of sulfide deposits. However, RGR has been considered aseismic and volcanically inactive for the past 46 Ma. Here, we investigate the origin of ironstones collected from the summit of RGR using multiple techniques: petrographic observations, X-ray diffraction, U-Th/He geochronology, and chemical composition. The ironstones from RGR consist of finely laminated goethite containing igneous rock fragments, carbonate fluorapatite, and calcite. Our results suggest that Fe oxyhydroxides were precipitated by Fe-oxidizing bacteria forming bacterial mats. The bacterial Fe mats underwent compaction, dewatering, goethite crystallization, and cementation that created the ironstone deposits. U-Th/He geochronology reveals protracted goethite minimum ages extending from the late Miocene to the Quaternary, probably due to multiple generations of mats, slow mineralization rates, and Fe-oxide dissolution-reprecipitation cycles. Flame-like goethite structures underneath FeMn crusts and a chimney-shaped goethite sample with a central channel indicate that the dewatering fluid flowed upward through the deposits, or a thermal fluid source may have been introduced from below the ironstone deposits. High Fe/Mn ratios, low trace metals contents (Ni + Co + Cu), and very low Fe/REY ratios suggest ironstone precipitation from a hydrothermal fluid; however, REYSN plots and bivariate Ce-SN /Ce-SN* versus Y-SN/Ho-SN and Ce-SN /Ce-SN* versus Nd plots are inconclusive, and a proximal source of magma was unlikely during the period of mat formation. Given this evidence, we hypothesize that a geothermal circulation system may have facilitated ironstone mineralization at RGR.
类型	Article
语种	英语
收录类别	SCI-E
WOS记录号	WOS:000753881700002
WOS关键词	RARE-EARTH-ELEMENTS ; HYDROTHERMAL MANGANESE OXIDE ; IRON-OXIDIZING BACTERIA ; FE-MN CRUSTS ; FERROMANGANESE CRUSTS ; NE ATLANTIC ; BAHARIYA DEPRESSION ; PHASE ASSOCIATIONS ; WESTERN DESERT ; MICROBIAL MATS
WOS类目	Geosciences, Multidisciplinary ; Oceanography
WOS研究方向	Geology ; Oceanography
资源类型	期刊论文
条目标识符	http://119.78.100.177/qdio/handle/2XILL650/376859
作者单位	[Benites, Mariana; Jovane, Luigi] Univ Sao Paulo, Inst Oceanog, Praca Oceanog 191, BR-05508120 Sao Paulo, SP, Brazil; [Hein, James R.; Mizell, Kira] US Geol Survey, PCMSC, 2885 Mission St, Santa Cruz, CA 95060 USA; [Farley, Kenneth A.; Treffkorn, Jonathan] CALTECH, Div Geol & Planetary Sci, Pasadena, CA 91125 USA
推荐引用方式 GB/T 7714	Benites, Mariana,Hein, James R.,Mizell, Kira,et al. Geochemical insights into formation of enigmatic ironstones from Rio Grande rise, South Atlantic Ocean[J],2022,444.
APA	Benites, Mariana,Hein, James R.,Mizell, Kira,Farley, Kenneth A.,Treffkorn, Jonathan,&Jovane, Luigi.(2022).Geochemical insights into formation of enigmatic ironstones from Rio Grande rise, South Atlantic Ocean.MARINE GEOLOGY,444.
MLA	Benites, Mariana,et al."Geochemical insights into formation of enigmatic ironstones from Rio Grande rise, South Atlantic Ocean".MARINE GEOLOGY 444(2022).