File Download
  Links for fulltext
     (May Require Subscription)
Supplementary

Article: Tracking Physicochemical Conditions of Evaporite Deposition by Stable Magnesium Isotopes: A Case Study of Late Permian Langbeinites

TitleTracking Physicochemical Conditions of Evaporite Deposition by Stable Magnesium Isotopes: A Case Study of Late Permian Langbeinites
Authors
KeywordsEvaporite
Fractionation factor
Langbeinite
Mg isotopes
Parent brine
Issue Date2018
PublisherAmerican Geophysical Union.
Citation
Geochemistry, Geophysics, Geosystems, 2018, v. 15 n. 8, p. 2615-2630 How to Cite?
AbstractMagnesium isotopic compositions of evaporite deposits may record information concerning brine evolution during deposition. We report Mg isotopic values (δ26MgDSM3) measured from an evaporite deposit of langbeinite (K2Mg2(SO4)3) found in the Permian Salado Formation. We used these data to model Mg isotope fractionation between langbeinite and its parent brine. In addition, both measured and theoretical results are used to estimate precipitation temperature and interpret depositional environment. The Salado langbeinite δ26Mg values are relatively low and fall within a relatively narrow range (–4.12 ± 0.03‰ to −3.81 ± 0.07‰). Equilibrium fractionation factors between langbeinite and aqueous Mg2+ solutions were calculated using quantum chemical density functional theory. All computations were performed at the B3LYP/6‐31 + G(d,p) level. Solvation effects were addressed using a solvent model (“water‐droplet” approach) and mineral structures were investigated using volume variable cluster models (VVCM). The equilibrium Mg isotopic fractionation factors α between langbeinite and model brine solution we obtained are 1.0005, 1.0004, and 1.0003 (Δ26Mglangb‐water≈103lnα = 0.473‰, 0.390‰, and 0.322‰) at 10°C, 25°C, and 40°C, respectively. These relatively large equilibrium fractionation factors indicate significant Mg isotope fractionation between langbeinite and its parent brine during precipitation, as langbeinite preferentially incorporates the heavier 26Mg and 25Mg isotopes. Rayleigh distillation modeling of the Salado langbeinite's relatively light Mg isotopic composition requires δ26MgDSM3 values of −4‰ for the parent brine. Models favor a precipitation temperature as high as 40°C under equilibrium conditions. Potential disequilibrium precipitation conditions suggested by Mg isotopic data also imply rapid deposition in a hot, arid sedimentary environment prevailing in the southwestern U.S. during the Late Permian.
Persistent Identifierhttp://hdl.handle.net/10722/261755
ISSN
2017 Impact Factor: 2.981
2015 SCImago Journal Rankings: 2.439
ISI Accession Number ID

 

DC FieldValueLanguage
dc.contributor.authorFeng, C-
dc.contributor.authorGao, C-
dc.contributor.authorYin, Q-
dc.contributor.authorJacobsen, B-
dc.contributor.authorRenne, P-
dc.contributor.authorWang, J-
dc.contributor.authorChang, S-
dc.date.accessioned2018-09-28T04:47:16Z-
dc.date.available2018-09-28T04:47:16Z-
dc.date.issued2018-
dc.identifier.citationGeochemistry, Geophysics, Geosystems, 2018, v. 15 n. 8, p. 2615-2630-
dc.identifier.issn1525-2027-
dc.identifier.urihttp://hdl.handle.net/10722/261755-
dc.description.abstractMagnesium isotopic compositions of evaporite deposits may record information concerning brine evolution during deposition. We report Mg isotopic values (δ26MgDSM3) measured from an evaporite deposit of langbeinite (K2Mg2(SO4)3) found in the Permian Salado Formation. We used these data to model Mg isotope fractionation between langbeinite and its parent brine. In addition, both measured and theoretical results are used to estimate precipitation temperature and interpret depositional environment. The Salado langbeinite δ26Mg values are relatively low and fall within a relatively narrow range (–4.12 ± 0.03‰ to −3.81 ± 0.07‰). Equilibrium fractionation factors between langbeinite and aqueous Mg2+ solutions were calculated using quantum chemical density functional theory. All computations were performed at the B3LYP/6‐31 + G(d,p) level. Solvation effects were addressed using a solvent model (“water‐droplet” approach) and mineral structures were investigated using volume variable cluster models (VVCM). The equilibrium Mg isotopic fractionation factors α between langbeinite and model brine solution we obtained are 1.0005, 1.0004, and 1.0003 (Δ26Mglangb‐water≈103lnα = 0.473‰, 0.390‰, and 0.322‰) at 10°C, 25°C, and 40°C, respectively. These relatively large equilibrium fractionation factors indicate significant Mg isotope fractionation between langbeinite and its parent brine during precipitation, as langbeinite preferentially incorporates the heavier 26Mg and 25Mg isotopes. Rayleigh distillation modeling of the Salado langbeinite's relatively light Mg isotopic composition requires δ26MgDSM3 values of −4‰ for the parent brine. Models favor a precipitation temperature as high as 40°C under equilibrium conditions. Potential disequilibrium precipitation conditions suggested by Mg isotopic data also imply rapid deposition in a hot, arid sedimentary environment prevailing in the southwestern U.S. during the Late Permian.-
dc.languageeng-
dc.publisherAmerican Geophysical Union.-
dc.relation.ispartofGeochemistry, Geophysics, Geosystems-
dc.rightsGeochemistry, Geophysics, Geosystems. Copyright © American Geophysical Union.-
dc.rightsPublished version An edited version of this paper was published by AGU. Copyright (2018) American Geophysical Union.-
dc.rightsThis work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.-
dc.subjectEvaporite-
dc.subjectFractionation factor-
dc.subjectLangbeinite-
dc.subjectMg isotopes-
dc.subjectParent brine-
dc.titleTracking Physicochemical Conditions of Evaporite Deposition by Stable Magnesium Isotopes: A Case Study of Late Permian Langbeinites-
dc.typeArticle-
dc.identifier.emailFeng, C: fengcq@hku.hk-
dc.identifier.emailWang, J: wangjun@connect.hku.hk-
dc.identifier.emailChang, S: suchin@hku.hk-
dc.identifier.authorityChang, S=rp01478-
dc.description.naturepublished_or_final_version-
dc.identifier.doi10.1029/2017GC007361-
dc.identifier.scopuseid_2-s2.0-85052518238-
dc.identifier.hkuros292599-
dc.identifier.volume15-
dc.identifier.issue8-
dc.identifier.spage2615-
dc.identifier.epage2630-
dc.identifier.isiWOS:000452122500019-
dc.publisher.placeUnited States-

Export via OAI-PMH Interface in XML Formats


OR


Export to Other Non-XML Formats