Magnesium isotopic compositions of the Mesoproterozoic dolostones: Implications for Mg isotopic systematics of marine carbonates

Huang, Kangjun; Shen, Bing; Lang, Xian Guo; Tang, Wen; Yang, Peng; Ke, Shaoyong; Kaufman, Alan J.; Hao, Ran; Li, Fang Bing

doi:10.1016/j.gca.2015.05.002

Cited by 89 publications

(46 citation statements)

References 102 publications

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“…26 Mg values ranging from -2.07% to -2.04% (Table 1), which is within error of the accepted value (-2.05% ± 0.05% (2r) (Huang et al 2015;Peng et al 2016). d…”

Section: Mass Spectrometrysupporting

confidence: 77%

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Heterogeneous Mg isotopic composition of the early Carboniferous limestone: implications for carbonate as a seawater archive

Huang

et al. 2017

Acta Geochim

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Carbonate precipitation and hydrothermal reaction are the two major processes that remove Mg from seawater. Mg isotopes are significantly (up (1) micrite samples ranged from -2.86% to -2.97%; (2) pure marine cements varied from -3.40% to -3.54%, while impure cement samples containing small amount of Rugosa coral skeletons showed a wider range (-3.27% to -3.75%); (3) values for the mixture component were -3.17% and -3.49%; and (4) 26 Mg sw was only slightly affected by the faunal composition of carbonate-secreting organisms, even though biogenic carbonate accounts for more than 90% of marine carbonate production in Phanerozoic oceans and there is a wide range (0.2%-4.8%) of fractionation during biogenic carbonate formation.

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“…26 Mg values ranging from -2.07% to -2.04% (Table 1), which is within error of the accepted value (-2.05% ± 0.05% (2r) (Huang et al 2015;Peng et al 2016). d…”

Section: Mass Spectrometrysupporting

confidence: 77%

“…The detailed Mg purification procedures have been reported in previous studies (Shen et al 2009(Shen et al , 2013Huang et al 2015). As such, only a brief description is given in the following.…”

Section: Column Chemistrymentioning

confidence: 99%

Heterogeneous Mg isotopic composition of the early Carboniferous limestone: implications for carbonate as a seawater archive

Huang

et al. 2017

Acta Geochim

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“…The majority of magmatic fractionation processes therefore cannot produce the low levels of δ 26 Mg identified in the carbonatites in this investigation. In contrast, marine dolomite has low δ 26 Mg values of −2.5 to −1‰ over geological time44, and its Mg isotopic composition can be preserved during subduction45. Therefore, the carbonatite mantle sources in the Qinling orogen may contain recycled sediments.…”

Section: Resultsmentioning

confidence: 99%

Origin of unusual HREE-Mo-rich carbonatites in the Qinling orogen, China

Song

Smith

et al. 2016

Sci Rep

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Carbonatites, usually occurring within intra-continental rift-related settings, have strong light rare earth element (LREE) enrichment; they rarely contain economic heavy REE (HREE). Here, we report the identification of Late Triassic HREE-Mo-rich carbonatites in the northernmost Qinling orogen. The rocks contain abundant primary HREE minerals and molybdenite. Calcite-hosted fluid inclusions, inferred to represent a magmatic-derived aqueous fluid phase, contain significant concentrations of Mo (~17 ppm), reinforcing the inference that these carbonatitic magmas had high Mo concentrations. By contrast, Late Triassic carbonatites in southernmost Qinling have economic LREE concentrations, but are depleted in HREE and Mo. Both of these carbonatite types have low δ26Mg values (−1.89 to −1.07‰), similar to sedimentary carbonates, suggesting a recycled sediment contribution for REE enrichment in their mantle sources. We propose that the carbonatites in the Qinling orogen were formed, at least in part, by the melting of a subducted carbonate-bearing slab, and that 10 Ma younger carbonatite magmas in the northernmost Qinling metasomatized the thickened eclogitic lower crust to produce high levels of HREE and Mo.

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“…A notable feature of most Huaziyu magnesite ores is their higher δ 26 Mg values (-0.75 ± 0.26‰, n=18) compared with most Proterozoic dolostones (Huang et al, 2015;Liu et al, 2014;Pokrovsky et al, 2011). Magnesium isotope compositions in bulk magnesite ores may not be significantly altered by regional prograde metamorphic dehydration, recrystallization, early diagenesis, and low-grade metamorphism (e.g., Geske et al, 2012;Higgins and Schrag, 2012;Wang et al, 2014Wang et al, , 2015, but it is possible that fluids metasomatism/dolomitization could produce Mg isotope fractionation (e.g., Geske et al, 2015a;Walter et al, 2015).…”

Section: Interpretation and Discussionmentioning

confidence: 99%

“…The high atmospheric CO 2 level and high seawater alkalinity (e.g., Grotzinger and Kasting, 1993;Kaufman and Xiao, 2003;Ohmoto et al, 2004;Sheldon, 2006), and widespread stromatolites suggesting abundant microbial activity (Grotzinger and Knoll, 1999) In addition, other factors such as the greater alkalinity and possibly different pH (a consequence of higher atmospheric CO 2 partial pressures) of Paleoproterozoic seawater versus modern seawater (Grotzinger and Kasting, 1993;Kaufman and Xiao, 2003;Ohmoto et al, 2004;Sheldon, 2006) (Huang et al, 2015). Similarly, the narrow range of heavier δ 26 Mg values for the magnesite ores (-0.75 ± 0.26‰, n=18) implies that magnesite formation involved a diagenetic brine with heavier δ 26 Mg values and higher Mg concentrations than contemporaneous seawater at the bottom of the lagoon.…”

Section: Evaporative Sedimentation and Brine Diagenesismentioning

confidence: 99%

Genesis of a giant Paleoproterozoic strata-bound magnesite deposit: Constraints from Mg isotopes

Dong

Zhu

et al. 2016

Precambrian Research

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Giant strata-bound magnesite deposits are absent in modern and most Phanerozoic sedimentary environments but occur predominantly in Precambrian strata. These deposits may have formed directly through precipitation of evolved Mg-rich seawater in an evaporative shallow-marine setting or, alternatively, by epigenetic-hydrothermal replacement of the Mg-rich carbonate precursor. To test these hypotheses, we obtained the first Mg isotope data from the world's largest strata-bound magnesite deposit belt, hosted by the ca. 2.1 Ga Dashiqiao Formation in Northeast China. The Mg isotope compositions (δ 26 Mg) of most magnesite ores in the Huaziyu deposit are heavier (-0.75 ± 0.26‰) than most Proterozoic sedimentary dolomite. The Mg isotope compositions and 2 major and trace element data indicate that the magnesites are probably not of hydrothermal origin. Instead, a Mg-rich carbonate precursor precipitated from evaporating seawater in a semi-closed system. Diagenetic brines altered the Mg-rich carbonate precursor to magnesite. Subsequently, recrystallization during regional metamorphism produced coarsely crystalline and saddle magnesite. These interpretations are consistent with the geological features and other geochemical data (element concentrations and C and O isotopes) for the magnesite ores. Hence, we interpret the formation of the Huaziyu magnesite deposit to be dominated by evaporative sedimentation and brine diagenesis.

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Magnesium isotopic compositions of the Mesoproterozoic dolostones: Implications for Mg isotopic systematics of marine carbonates

Cited by 89 publications

References 102 publications

Heterogeneous Mg isotopic composition of the early Carboniferous limestone: implications for carbonate as a seawater archive

Heterogeneous Mg isotopic composition of the early Carboniferous limestone: implications for carbonate as a seawater archive

Origin of unusual HREE-Mo-rich carbonatites in the Qinling orogen, China

Genesis of a giant Paleoproterozoic strata-bound magnesite deposit: Constraints from Mg isotopes

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