干旱区生态环境知识资源中心(Arid): Characteristics of desert varnish from nanometer to micrometer scale: A photo-oxidation model on its formation

Arid

DOI	10.1016/j.chemgeo.2019.05.016
	Characteristics of desert varnish from nanometer to micrometer scale: A photo-oxidation model on its formation
	Xu, Xiaoming 1; Li, Yan1 ; Li, Yanzhang 1; Lu, Anhuai 1; Qiao, Ruixi 2; Liu, Kaihui 2; Ding, Hongrui 1; Wang, Changqiu 1
通讯作者	Li, Yan ; Lu, Anhuai
来源期刊	CHEMICAL GEOLOGY
ISSN	0009-2541
EISSN	1872-6836
出版年	2019
卷号	522 页码:55-70
英文摘要	Rock varnish is a widespread Mn-rich rock coating commonly developed in arid environments, but the mechanism for its formation is still under debate. In this study, rock varnish and adjacent soil dust collected from Gobi Desert were analyzed for exploring the possible abiotic oxidation mechanism of Mn oxides. The occurrence of rock varnish shows a direct and close relationship with strong irradiation of sunlight, giving the first evidence of photochemical genesis. Abundant caves and tunnels with average diameter of similar to 1-5 mu m are observed on varnish surface regions, which facilitate the penetration of sunlight and water. Metal (oxyhydr)oxides, including birnessite, hematite, goethite, ruffle and anatase, account for the major components of rock varnish, which are all solar light-responsive semiconducting minerals. The trace elements enrichment patterns revealed by LA-ICP-MS provide the indication of an aqueous origin. The positive Ce anomalies in varnish in contrast to the rock substrate, as well as the positive correlation between Ce and Mn suggest a strong oxidizing environment in the genesis of rock varnish. Therefore, the photo-generated holes and reactive oxygen species (ROSs) on metal oxides in varnish can promote Mn(II) oxidation, which are further demonstrated from thermodynamic and kinetic considerations. ROSs including O-1(2) and OH center dot with strong oxidizing capability are detected by EPR in varnish suspension, providing the direct evidence for Mn(II) oxidation. Laboratory experimental simulations show the photocatalysis of metal oxides in rock varnish greatly promote Mn(II) oxidation by 2.10-7.97 times in comparison with homogenous solution oxidation. All these lines of evidence suggest that light-induced abiotic process may play important roles in the formation of rock varnish together with other abiotic and biotic pathways, which can even provide implications for the evolution of Mn oxides on surface of terrestrial planets.
英文关键词	Rock varnish Solar light Photocatalysis Abiotic oxidation Manganese
类型	Article
语种	英语
国家	Peoples R China
收录类别	SCI-E
WOS记录号	WOS:000480330600005
WOS关键词	ROCK-VARNISH ; MANGANESE-OXIDE ; ELECTRONIC-STRUCTURES ; MN(II) OXIDATION ; RAMAN-SPECTRA ; MOJAVE DESERT ; NEGEV DESERT ; IRON ; COATINGS ; ANATASE
WOS类目	Geochemistry & Geophysics
WOS研究方向	Geochemistry & Geophysics
来源机构	北京大学
资源类型	期刊论文
条目标识符	http://119.78.100.177/qdio/handle/2XILL650/214871
作者单位	1.Peking Univ, Sch Earth & Space Sci, Key Lab Orogen Belts & Crustal Evolut, Beijing Key Lab Mineral Environm Funct, Beijing 100871, Peoples R China; 2.Peking Univ, Sch Phys, Beijing 100871, Peoples R China
推荐引用方式 GB/T 7714	Xu, Xiaoming,Li, Yan,Li, Yanzhang,et al. Characteristics of desert varnish from nanometer to micrometer scale: A photo-oxidation model on its formation[J]. 北京大学,2019,522:55-70.
APA	Xu, Xiaoming.,Li, Yan.,Li, Yanzhang.,Lu, Anhuai.,Qiao, Ruixi.,...&Wang, Changqiu.(2019).Characteristics of desert varnish from nanometer to micrometer scale: A photo-oxidation model on its formation.CHEMICAL GEOLOGY,522,55-70.
MLA	Xu, Xiaoming,et al."Characteristics of desert varnish from nanometer to micrometer scale: A photo-oxidation model on its formation".CHEMICAL GEOLOGY 522(2019):55-70.