Title: Zircon U–Pb age and Sr–Nd–Hf isotopic constraints on the age and origin of Triassic mafic dikes, Dalian area, Northeast China
Abstract: Abstract Post-orogenic mafic rocks from Northeast China consist of swarms of dolerite dikes. We report a new U–Pb zircon age, as well as whole-rock geochemical and Sr–Nd–Hf isotopic data. Laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS) U–Pb zircon analysis yielded an age of 210.3 ± 1.5 million years (i.e. Triassic) for these mafic dikes. Most Dalian mafic rocks exhibit low K2O + Na2O contents, and span the border between alkaline and calc-alkaline rock associations in the total alkali–silica diagram. The investigated dikes are also characterized by relatively high (87Sr/86Sr)i ratios (0.7061–0.7067) and negative ϵNd (t) (−4.7 to −4.3) and ϵHf (t) values (−4.1 to −1.1), implying that they were derived from an enriched lithospheric mantle source. The mafic dikes are characterized by relatively low MgO (4.65–5.44 wt.%), Mg# (41–44), and compatible element content [such as Cr (89.9–125 ppm) and Ni (56.7–72.2 ppm)], which are the features of an evolved mafic magma. No evidence supports the idea that the mafic rocks were affected by significant assimilation or crustal contamination during emplacement. We conclude that the dolerites formed in a post-orogenic extensional setting, related to lithospheric delamination or ‘collapse’ of the Central Asian Orogenic Belt (CAOB), also termed the Xingmeng Orogenic Belt in China. Keywords: post-orogenicTriassic magmatismmafic dikeslithospheric delaminationcrustal extensionNortheast China Acknowledgements This research was supported by the National Nature Science Foundation of China (40673029 and 40773020). We are grateful to Dr Lian Zhou and Jinhui Yang for their help with the Sr, Nd, and zircon Hf isotopic analysis, and we thank Yong-sheng Liu and Zhao-Chu Hu for their help with LA–ICP–MS zircon U–Pb dating. The authors also thank Hu-jun Gong for helping with cathodoluminescence image handling.
Publication Year: 2012
Publication Date: 2012-07-17
Language: en
Type: article
Indexed In: ['crossref']
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Cited By Count: 20
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