干旱区生态环境知识资源中心(Arid): Potassium elemental and isotope constraints on the formation of tektites and element loss during impacts

Arid

DOI	10.1016/j.gca.2021.07.022
	Potassium elemental and isotope constraints on the formation of tektites and element loss during impacts
	Magna, Tomas; Jiang, Yun; Skala, Roman; Wang, Kun; Sossi, Paolo A.; Zak, Karel
通讯作者	Magna, T (corresponding author), Czech Geol Survey, Klarov 3, CZ-11821 Prague 1, Czech Republic.
来源期刊	GEOCHIMICA ET COSMOCHIMICA ACTA
ISSN	0016-7037
EISSN	1872-9533
出版年	2021
卷号	312 页码:321-342
英文摘要	Potassium elemental and isotope systematics were investigated for a suite of central European tektites from three strewn sub-fields in Czech Republic and possible parent sedimentary materials from the vicinity of the Ries impact structure in SE Germany, supplemented by data for several other impact-related materials (bediasites, Ivory Coast tektites, Libyan Desert Glass). This is paralleled by computation of potential K loss and attendant isotope fractionation for physico-chemical conditions typical for formation of tektite precursor melts. These theoretical calculations indicate a <0.1% loss of K from tektite precursor melts up to 2,500 K and <0.002% change in the K-41/K-39 ratio even for a small sphere of 0.002 m at 2,500 K, precluding any significant K loss and isotope fractionation. Numerical modelling also indicates that differential velocities between surrounding gas and liquid are not sufficient to remove the gaseous boundary layer, such that the partial pressure of potassium developed around the molten moldavite beads impedes further evaporation and also contributes to back-condensation of the already evaporated potassium. Central European tektites (moldavites) are enriched in K compared to the assumed sedimentary sources from the wider Ries area whereby the latter materials do not exceed 2.9 wt.% K2O compared to 2.5-4.1 wt.% K2O in moldavites. The apparent K enrichment in moldavites may be explained by a yet unaccounted process during formation of tektite precursor melts and/or unidentified source, such as volcanoclastic deposits that were produced by large Mid-Miocene volcanic centers in the Pannonian Basin. The K isotope compositions of tektites are more variable than those of sediments from the wider Ries area but they largely overlap (delta K-41 from -0.78 +/- 0.03 parts per thousand to -0.13 +/- 0.03 parts per thousand versus -0.72 +/- 0.03 parts per thousand to -0.28 +/- 0.02 parts per thousand, respectively). These ranges mimic K-41/K-39 variations reported for igneous and sedimentary portions of the upper difference among the three investigated strewn sub-fields, depending on their respective distance from the impact. In detail, moldavites from the closest strewn sub-field in the Cheb Basin show predominantly heavy K isotope compositions and those from the farthest strewn sub-field in Western Moravia are uniformly isotopically light. The origin of this difference may reflect lithological heterogeneity of the target area. Potassium contents in bediasites and Ivory Coast tektites range between 1.3 and 1.8 wt.% K2O and their corresponding delta K-41 values vary from -0.57 +/- 0.02 parts per thousand to -0.41 +/- 0.03 parts per thousand. Both ranges are significantly narrower than those observed for moldavites. When compared to data for possible sedimentary precursors in the Chesapeake Bay and Bosumtwi impact structure, respectively, it is apparent that these tektites were neither depleted nor enriched in potassium. The extent of their K isotope fractionation relative to plausible sources remains unconstrained. The Libyan Desert Glass displays invariant delta K-41 of similar to-0.57 +/- 0.06%0 at <= 0.01 wt.% K2O. Given the silica-rich nature of LDG , the lack of possible parent materials, no further constraints can be placed at present to further resolve the source material or reveal details of LDG formation process. (C) 2021 Elsevier Ltd. All rights reserved.
英文关键词	Potassium isotopes Tektite Moldavite Sediment Ries crater Evaporation
类型	Article
语种	英语
收录类别	SCI-E
WOS记录号	WOS:000704172000004
WOS关键词	MODERATELY VOLATILE ELEMENTS ; FRESH-WATER MOLASSE ; MUONG NONG-TYPE ; MC-ICP-MS ; AUSTRALASIAN TEKTITES ; HIGH-TEMPERATURE ; SILICATE MELTS ; BUNTE-BRECCIA ; STREWN FIELD ; TARGET ROCKS
WOS类目	Geochemistry & Geophysics
WOS研究方向	Geochemistry & Geophysics
资源类型	期刊论文
条目标识符	http://119.78.100.177/qdio/handle/2XILL650/363381
作者单位	[Magna, Tomas] Czech Geol Survey, Klarov 3, CZ-11821 Prague 1, Czech Republic; [Jiang, Yun; Wang, Kun] Washington Univ, Dept Earth & Planetary Sci, One Brookings Dr, St Louis, MO 63130 USA; [Jiang, Yun; Wang, Kun] Washington Univ, McDonnell Ctr Space Sci, One Brookings Dr, St Louis, MO 63130 USA; [Jiang, Yun] Chinese Acad Sci, Purple Mt Observ, CAS Key Lab Planetary Sci, CN-210033 Nanjing, Peoples R China; [Skala, Roman; Zak, Karel] Czech Acad Sci, Inst Geol, Rozvojova 269, CZ-16500 Prague 6, Czech Republic; [Sossi, Paolo A.] Swiss Fed Inst Technol, Inst Geochem & Petrol, Clausiusstr 25, CH-8092 Zurich, Switzerland
推荐引用方式 GB/T 7714	Magna, Tomas,Jiang, Yun,Skala, Roman,et al. Potassium elemental and isotope constraints on the formation of tektites and element loss during impacts[J],2021,312:321-342.
APA	Magna, Tomas,Jiang, Yun,Skala, Roman,Wang, Kun,Sossi, Paolo A.,&Zak, Karel.(2021).Potassium elemental and isotope constraints on the formation of tektites and element loss during impacts.GEOCHIMICA ET COSMOCHIMICA ACTA,312,321-342.
MLA	Magna, Tomas,et al."Potassium elemental and isotope constraints on the formation of tektites and element loss during impacts".GEOCHIMICA ET COSMOCHIMICA ACTA 312(2021):321-342.