TY - JOUR
T1 - Investigation of magnesium isotope fractionation during basalt differentiation
T2 - Implications for a chondritic composition of the terrestrial mantle
AU - Teng, Fang Zhen
AU - Wadhwa, Meenakshi
AU - Helz, Rosalind T.
N1 - Funding Information:
FZT thanks Nicolas Dauphas, Frank Richter, Paul Tomascak and Rich Walker for very helpful and stimulating discussions, Phil Janney and Liping Qin for their technical assistance and expertise, and Laure Dussubieux for assistance with ordering lab supplies. In addition, N. Dauphas, S. Gao, P. Janney, C. Lundstrom, and F. Richter are thanked for providing several of the samples for this study. Very constructive comments from Albert Galy, Robert Seal, Jeff Grossman and an anonymous reviewer, and the careful and efficient editing by Rick Carlson are greatly appreciated. This work has been supported by NSF and NASA grants to MW.
PY - 2007/9/15
Y1 - 2007/9/15
N2 - To investigate whether magnesium isotopes are fractionated during basalt differentiation, we have performed high-precision Mg isotopic analyses by multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) on a set of well-characterized samples from Kilauea Iki lava lake, Hawaii, USA. Samples from the Kilauea Iki lava lake, produced by closed-system crystal-melt fractionation, range from olivine-rich cumulates to highly differentiated basalts with MgO content ranging from 2.37 to 26.87 wt.%. Our results demonstrate that although these basalts have diverse chemical compositions, mineralogies, crystallization temperatures and degrees of differentiation, their Mg isotopic compositions display no measurable variation within the limits of our external precision (average δ26Mg = - 0.36 ± 0.10 and δ25Mg = - 0.20 ± 0.07; uncertainties are 2SD). This indicates that Mg isotopic fractionation during crystal-melt fractionation at temperatures of ≥ 1055 °C is undetectable at the level of precision of the current investigation. Calculations based on our data suggest that at near-magmatic temperatures the maximum fractionation in the 26Mg/24Mg ratio between olivine and melt is 0.07‰. Two additional oceanic basalts, two continental basalts (BCR-1 and BCR-2), and two primitive carbonaceous chondrites (Allende and Murchison) analyzed in this study have Mg isotopic compositions similar to the Kilauea Iki lava lake samples. In contrast to a recent report [U. Wiechert, A.N. Halliday, Non-chondritic magnesium and the origins of the inner terrestrial planets, Earth and Planetary Science Letters 256 (2007) 360-371], the results presented here suggest that the Bulk Silicate Earth has a chondritic Mg isotopic composition.
AB - To investigate whether magnesium isotopes are fractionated during basalt differentiation, we have performed high-precision Mg isotopic analyses by multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) on a set of well-characterized samples from Kilauea Iki lava lake, Hawaii, USA. Samples from the Kilauea Iki lava lake, produced by closed-system crystal-melt fractionation, range from olivine-rich cumulates to highly differentiated basalts with MgO content ranging from 2.37 to 26.87 wt.%. Our results demonstrate that although these basalts have diverse chemical compositions, mineralogies, crystallization temperatures and degrees of differentiation, their Mg isotopic compositions display no measurable variation within the limits of our external precision (average δ26Mg = - 0.36 ± 0.10 and δ25Mg = - 0.20 ± 0.07; uncertainties are 2SD). This indicates that Mg isotopic fractionation during crystal-melt fractionation at temperatures of ≥ 1055 °C is undetectable at the level of precision of the current investigation. Calculations based on our data suggest that at near-magmatic temperatures the maximum fractionation in the 26Mg/24Mg ratio between olivine and melt is 0.07‰. Two additional oceanic basalts, two continental basalts (BCR-1 and BCR-2), and two primitive carbonaceous chondrites (Allende and Murchison) analyzed in this study have Mg isotopic compositions similar to the Kilauea Iki lava lake samples. In contrast to a recent report [U. Wiechert, A.N. Halliday, Non-chondritic magnesium and the origins of the inner terrestrial planets, Earth and Planetary Science Letters 256 (2007) 360-371], the results presented here suggest that the Bulk Silicate Earth has a chondritic Mg isotopic composition.
KW - Kilauea Iki
KW - isotope fractionation
KW - magma differentiation
KW - magnesium isotopes
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U2 - 10.1016/j.epsl.2007.06.004
DO - 10.1016/j.epsl.2007.06.004
M3 - Article
AN - SCOPUS:34548357163
SN - 0012-821X
VL - 261
SP - 84
EP - 92
JO - Earth and Planetary Science Letters
JF - Earth and Planetary Science Letters
IS - 1-2
ER -