High-precision Mg isotope analyses of low-Mg rocks by MC-ICP-MS

An, Yajun; Wu, Fei; Xiang, Yuan-Xin; Nan, Xiao-Yun; Yu, Xun; Yang, Jin‐Hui; Yu, Haiying; Xie, Lie‐Wen; Huang, Fang

doi:10.1016/j.chemgeo.2014.09.014

Cited by 170 publications

(94 citation statements)

References 64 publications

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“…The standard materials were also analysed, with d 26 Mg = À0.20 ± 0.09‰ for BCR-2, d 26 Mg = À0.27 ± 0.01‰ for BHVO-2 and d 26 Mg = À0.48 ± 0.03‰ for GSR-3. These values are consistent with previously published data (À0.36 to À0.16‰ for BCR-2 and À0.32 to À0.16‰ for BHVO-2; Teng et al, 2007Teng et al, , 2015Huang et al, 2009Huang et al, , 2011Huang et al, , 2015An et al, 2014).…”

Section: Methodssupporting

confidence: 94%

Origin of low δ26Mg basalts with EM-I component: Evidence for interaction between enriched lithosphere and carbonated asthenosphere

Tian

Yang

et al. 2016

Geochimica et Cosmochimica Acta

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This study presents stable Mg isotopic data for Cenozoic potassic basalts from Wudalianchi and Erkeshan in northeastern China to determine the interactions between upwelling carbonated asthenosphere and enriched lithospheric mantle. Although the Wudalianchi and Erkeshan basalts have variable MgO contents of 4.45 to 9.47 wt.%, they exhibit a homogeneous Mg isotopic composition with d 26 Mg values ranging from À0.57‰ to À0.46‰ and averaging À0.51 ± 0.06‰ (2SD, n = 18). This Mg isotopic composition is lighter than that of the average mantle (d 26 Mg = À0.25 ± 0.07‰) but similar to late Cretaceous (<110 Ma) and Cenozoic basalts from the North China Craton and the South China Block (d 26 Mg = À0.60 to À0.35‰). The high CaO/Al 2 O 3 and Ba/Rb, and low Hf/Hf * ratios of the Wudalianchi and Erkeshan basalts are typical characteristics of carbonatitic metasomatism, suggesting that the light Mg isotopic composition could derive from involvement of recycled sedimentary carbonates in the mantle source. The high Dy/Er ratios (2.55 to 2.75) and excess of 230 Th ( 230 Th/ 238 U = 1.24 to 1.33) suggest presence of garnet in a relatively deep mantle source. Additionally, the seismic tomographic observations show the existence of the stagnant Pacific slab in the mantle transition zone (410-660 km) under eastern China. This carbonated mantle source should be located in the asthenosphere. However, compared to other low d 26 Mg basalts from eastern China with MORB-like Sr-Nd-Pb isotopic compositions and OIB-like trace element features, the Wudalianchi and Erkeshan basalts exhibit EM-I Sr-Nd-Pb isotopic compositions combined with high SiO 2 , Ba, K, Pb and LREE contents, high Ba/Th and low Ce/Pb ratios. These geochemical features require a contribution from another mantle source, most likely an EM-I lithospheric mantle. Therefore, an asthenosphere-lithosphere interaction model is proposed for determine the origin of the Wudalianchi and Erkeshan basalts. The original melt was derived from partial melting of the carbonated asthenospheric mantle that was metasomatized by carbonate melt from the stagnant Pacific slab in the mantle transition zone. This ascending melt with a low d 26 Mg signature subsequently interacted with the EM-I lithospheric mantle. The interaction dissolved pyroxene and crystallized olivine, releasing LILE, REE, Sr and Pb from dissolved minerals into the melt. Simultaneously, Mg was inherited by newly formed olivine. Therefore, this interaction modified the trace elements and the Sr-Nd-Pb isotopic compositions of the melt toward EM-I geochemical features but preserved the light Mg isotope signatures.

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Section: Methodssupporting

confidence: 94%

Origin of low δ26Mg basalts with EM-I component: Evidence for interaction between enriched lithosphere and carbonated asthenosphere

Tian

Yang

et al. 2016

Geochimica et Cosmochimica Acta

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“…The total procedural Mg blank was lower than 20 ng, negligible relative to the 50 μg loaded into the column. The standards in this study yielded δ 26 Mg = −0.26 ± 0.01‰ (2SD, n = 4) for BHVO‐2 and −0.22 ± 0.02‰ (2SD, n = 4) for BCR‐2 (Table ), which were consistent with published values within error (e.g., An et al, ; Teng et al, , ; Teng, Li, Ke, et al, ; Teng, Li, Rudnick, et al, ).…”

Section: Methodssupporting

confidence: 91%

Marine Carbonate Component in the Mantle Beneath the Southeastern Tibetan Plateau: Evidence From Magnesium and Calcium Isotopes

Liu

Wang

et al. 2017

JGR Solid Earth

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Tracing and identifying recycled carbonates is a key issue to reconstruct the deep carbon cycle. To better understand carbonate subduction and recycling beneath the southeastern Tibetan Plateau, high‐K cal‐alkaline volcanic rocks including trachy‐basalts and trachy‐andesites from Tengchong were studied using Mg and Ca isotopes. The low δ26Mg (−0.31 ± 0.03‰ to −0.38 ± 0.03‰) and δ44/40Ca (0.67 ± 0.07‰ to 0.80 ± 0.04‰) values of these volcanic rocks compared to those of the mantle (−0.25 ± 0.07‰ and 0.94 ± 0.05‰, respectively) indicate the incorporation of isotopically light materials into the mantle source, which may be carbonate‐bearing sediments with low δ26Mg and δ44/40Ca values. In addition, no correlations of δ26Mg and δ44/40Ca with either SiO2 contents or trace element abundance ratios (e.g., Sm/Yb and Ba/Y) were observed, suggesting that limited Mg and Ca isotopic fractionation occurred during cal‐alkaline magmatic differentiation. A binary mixing model using Mg–Ca isotopes shows that 5–8% carbonates dominated primarily by dolostone were recycled back into the mantle. Since Tengchong volcanism is still active and probably related to ongoing plate tectonic movement, we propose that the recycled carbonates are derived from oceanic crust related to the ongoing subduction of the Indian plate.

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“…The results are reported in the conventional δ notation that is defined as δ X Mg = [( X Mg/ 24 Mg) sample / ( X Mg/ 24 Mg) DSM3 − 1] × 1000, where X = 25 or 26, and DSM3 is an international reference of solution made from pure Mg metal . Analyses of the well-characterized USGS standard BHVO-2 in this study yielded δ 26 Mg = − 0.28 ± 0.04‰ (2SD, n = 6, Table 1), in agreement with previously reported values Huang et al, 2009;Pogge von Strandmann et al, 201 l;An et al, 2014).…”

Section: Methodssupporting

confidence: 88%

Magnesium isotopic compositions of altered oceanic basalts and gabbros from IODP site 1256 at the East Pacific Rise

Huang

Gao

et al. 2015

Lithos

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High-precision Mg isotope analyses of low-Mg rocks by MC-ICP-MS

Cited by 170 publications

References 64 publications

Origin of low δ26Mg basalts with EM-I component: Evidence for interaction between enriched lithosphere and carbonated asthenosphere

Origin of low δ26Mg basalts with EM-I component: Evidence for interaction between enriched lithosphere and carbonated asthenosphere

Marine Carbonate Component in the Mantle Beneath the Southeastern Tibetan Plateau: Evidence From Magnesium and Calcium Isotopes

Magnesium isotopic compositions of altered oceanic basalts and gabbros from IODP site 1256 at the East Pacific Rise

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