TY - JOUR
T1 - High-precision and high-resolution carbonate 230Th dating by MC-ICP-MS with SEM protocols
AU - Shen, Chuan Chou
AU - Wu, Chung Che
AU - Cheng, Hai
AU - Lawrence Edwards, R.
AU - Hsieh, Yu Te
AU - Gallet, Sylvain
AU - Chang, Ching Chih
AU - Li, Ting Yong
AU - Lam, Doan Dinh
AU - Kano, Akihiro
AU - Hori, Masako
AU - Spötl, Christoph
PY - 2012/12/15
Y1 - 2012/12/15
N2 - To facilitate the measurement of U-Th isotopic compositions suitable for high-precision and high-resolution 230Th dating of coral and speleothem carbonates, secondary electron multiplier (SEM) protocol techniques for multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS) have been developed. The instrumental sensitivities are 1-2%, with a precision of ±1-2‰ (2σ) for abundance determination of 50-200fg 234U (1-4ng 238U) or 230Th. This method features chemistry refinements, improvements to procedural and instrumental blanks, spectral inference reductions, and careful consideration of non-linear SEM behavior. Measurement consistency of this MC-ICP-MS combined with previous mass spectrometric results on U-Th standards and a variety of carbonates demonstrates the validity of the SEM protocol method. For fossil corals, a routine U-Th isotopic determination at permil-level precision requires only 10-50mg of carbonate. As little as 200mg of young coral with an age of less than 20yr can be dated with a precision of ±0.3-0.8yr. About 20-200mg speleothem samples with sub-ppm-to-ppm U are required to earn a 5‰ precision on ages from 5 to 100kyr. Requirement of small sample size, 10-100s mg carbonate, can permit high temporal resolution to date speleothems with slow growth rates, i.e., 1-10mm/kyr. This high-precision 230Th chronology is critical to accurately establish age models, date events and splice geochemical proxy time series records from multiple samples in the fields of paleoclimatology and paleoceanography. The U-Th isotopic determination techniques described here can also be applied to different environmental samples, such as waters, rocks, and sediments.
AB - To facilitate the measurement of U-Th isotopic compositions suitable for high-precision and high-resolution 230Th dating of coral and speleothem carbonates, secondary electron multiplier (SEM) protocol techniques for multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS) have been developed. The instrumental sensitivities are 1-2%, with a precision of ±1-2‰ (2σ) for abundance determination of 50-200fg 234U (1-4ng 238U) or 230Th. This method features chemistry refinements, improvements to procedural and instrumental blanks, spectral inference reductions, and careful consideration of non-linear SEM behavior. Measurement consistency of this MC-ICP-MS combined with previous mass spectrometric results on U-Th standards and a variety of carbonates demonstrates the validity of the SEM protocol method. For fossil corals, a routine U-Th isotopic determination at permil-level precision requires only 10-50mg of carbonate. As little as 200mg of young coral with an age of less than 20yr can be dated with a precision of ±0.3-0.8yr. About 20-200mg speleothem samples with sub-ppm-to-ppm U are required to earn a 5‰ precision on ages from 5 to 100kyr. Requirement of small sample size, 10-100s mg carbonate, can permit high temporal resolution to date speleothems with slow growth rates, i.e., 1-10mm/kyr. This high-precision 230Th chronology is critical to accurately establish age models, date events and splice geochemical proxy time series records from multiple samples in the fields of paleoclimatology and paleoceanography. The U-Th isotopic determination techniques described here can also be applied to different environmental samples, such as waters, rocks, and sediments.
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U2 - 10.1016/j.gca.2012.09.018
DO - 10.1016/j.gca.2012.09.018
M3 - Article
AN - SCOPUS:84867641348
VL - 99
SP - 71
EP - 86
JO - Geochmica et Cosmochimica Acta
JF - Geochmica et Cosmochimica Acta
SN - 0016-7037
ER -