TY - JOUR
T1 - Rapid determination of initial
87
Sr/
86
Sr and estimation of the Rb-Sr age of plutonic rocks by LA-ICPMS of variably altered feldspars
T2 - An example from the 1.14 Ga Great Abitibi Dyke, Ontario, Canada
AU - Zellmer, G. F.
AU - Kimura, J. I.
AU - Chang, Q.
AU - Shellnutt, J. G.
AU - Sas, M.
AU - Shane, P.
N1 - Funding Information:
The data used are listed in the references and in Table 1 . We thank Yoshiyuki Iizuka and Hui-Ho Hsieh for help with sample preparation, and Hisayoshi Yurimoto and Naoya Sakamoto for access to and assistance with SEM work at the Isotope Imaging Laboratory of Hokkaido University. This contribution benefitted from constructive reviews by two anonymous reviewers, and we thank Xian-Hua Li for editorial handling of this script. G.F. Zellmer acknowledges funding by the Ministry of Business, Innovation, and Employment (MBIE, grant MAUX1507 ). J.-I. Kimura was supported by the Japanese Societry for the Promotion of Science (JSPS, KAKENHI grant numbers JP7162241 , JP15H02148 , and JP16H01123) . J.G. Shellnutt acknowledges funding through the Ministry of Science and Technology, Taiwan (MOST, grant 102-2628-M-003-001MY4 ).
Publisher Copyright:
© 2018 Elsevier B.V.
Copyright:
Copyright 2018 Elsevier B.V., All rights reserved.
PY - 2018/8/1
Y1 - 2018/8/1
N2 -
Sr isotope analysis of plutonic rocks is an important method for deriving the provenance and age of ancient magmatic episodes, and the petrogenetic processes operating during intrusive activity. We determined the
87
Sr/
86
Sr isotopic compositions of fresh and variably altered feldspars from the 1.14 Ga gabbroic Great Abitibi Dyke, Ontario, Canada, through the use of Laser Ablation Inductively-Coupled Plasma Mass Spectrometry (LA-ICPMS). The data show an alteration trend between fresh, low-Rb plagioclase with
87
Sr/
86
Sr ratios of 0.7045 and high-Rb alkali feldspar with
87
Sr/
86
Sr ratios of 0.7059, which may be used to constrain the
87
Sr/
86
Sr ratio of the mantle source. This trend is incompatible with simple mixing and instead has age significance. As post-intrusive alteration through hydrothermal circulation starts immediately following emplacement, LA-ICPMS analysis allows rapid estimation of initial
87
Sr/
86
Sr ratios and intrusive age, suitable for sample screening and selection for more precise dating. For the Great Abitibi Dyke, the Rb-Sr age estimate of emplacement of 1.10 ± 0.23 Ga (2σ) is concordant with the precise U-Pb emplacement age of the dyke (1140.6 ± 2.0 Ma). The most altered high-Rb alkali feldspars return younger ages, suggesting that post-intrusive alteration lasted several hundred million years. This study highlights the need for microanalysis to differentiate between alteration and magmatic processes on basis of Sr isotopic signatures, and outlines a rapid method to determine initial
87
Sr/
86
Sr ratios and to estimate Rb-Sr ages of plutonic rocks in terranes with long histories of multiple intrusive magmatic episodes.
AB -
Sr isotope analysis of plutonic rocks is an important method for deriving the provenance and age of ancient magmatic episodes, and the petrogenetic processes operating during intrusive activity. We determined the
87
Sr/
86
Sr isotopic compositions of fresh and variably altered feldspars from the 1.14 Ga gabbroic Great Abitibi Dyke, Ontario, Canada, through the use of Laser Ablation Inductively-Coupled Plasma Mass Spectrometry (LA-ICPMS). The data show an alteration trend between fresh, low-Rb plagioclase with
87
Sr/
86
Sr ratios of 0.7045 and high-Rb alkali feldspar with
87
Sr/
86
Sr ratios of 0.7059, which may be used to constrain the
87
Sr/
86
Sr ratio of the mantle source. This trend is incompatible with simple mixing and instead has age significance. As post-intrusive alteration through hydrothermal circulation starts immediately following emplacement, LA-ICPMS analysis allows rapid estimation of initial
87
Sr/
86
Sr ratios and intrusive age, suitable for sample screening and selection for more precise dating. For the Great Abitibi Dyke, the Rb-Sr age estimate of emplacement of 1.10 ± 0.23 Ga (2σ) is concordant with the precise U-Pb emplacement age of the dyke (1140.6 ± 2.0 Ma). The most altered high-Rb alkali feldspars return younger ages, suggesting that post-intrusive alteration lasted several hundred million years. This study highlights the need for microanalysis to differentiate between alteration and magmatic processes on basis of Sr isotopic signatures, and outlines a rapid method to determine initial
87
Sr/
86
Sr ratios and to estimate Rb-Sr ages of plutonic rocks in terranes with long histories of multiple intrusive magmatic episodes.
KW - Albitization
KW - Dyke swarms
KW - Gabbros
KW - Laser ablation ICPMS
KW - Sr-isotope analysis
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U2 - 10.1016/j.lithos.2018.05.024
DO - 10.1016/j.lithos.2018.05.024
M3 - Article
AN - SCOPUS:85047883685
VL - 314-315
SP - 52
EP - 58
JO - Lithos
JF - Lithos
SN - 0024-4937
ER -