Abstract
The Chuanlinggou Formation is the lower formation of the Changchengian System, and hosts sedimentary iron deposits (marine oolitic ironstones) of the North China Craton (NCC). To determine the age of the iron deposits, and provide insight into the crustal growth of the craton, laser ablation multiple collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS)U-Pb and in situ Hf isotope analysis were performed on detrital zircon grains. Samples were taken from the roof sand-shale of the sedimentary iron deposits at Jiangjiazhai and Pangjiapbu. Overall, 186 detrital zircon grain U-Pb ages yield three major age populations, with weighted average ages of 2450 Ma, 1848 Ma, and 1765 Ma, respectively. Four younger ages from magmatic zircon grains were obtained, ranging from 1694 to 1657 Ma. Combined with observations from published studies, the results define the lower limit for the age of the Chuanlinggou Formation, and constrain the age of the sedimentary iron deposits (marine oolitic ironstone) close to 1650 Ma. The peak ages of 1848 Ma and 2450 Ma define the major collisional events of the NCC. The age of 1765 Ma can be linked to the age range of the widespread mafic dyke swarms that represent the rifting of the NCC within the Columbia supercontinent. Detrital zircon grains from the Chuanlinggou Formation form two obvious groups, with different εHf (t) values ranging from −1 to −8 and from +1 to +8, which correspond to the U-Pb age ranges of 1.7–1.9 Ga and 2.3–2.6 Ga, respectively. They have a similar two-stage Hf model age peak at 2.65–2.85 Ga, suggesting that the source rocks for each of these events were derived from the recycling of ancient crust. The source rocks of the older group of zircon grains might be derived from juvenile crust with a short reworking period. The critical crust–mantle differentiation event might happen during the period of 2.65–2.85 Ga, marking the most significant stage of the crustal growth in the NCC.
Highlights
The North China Craton (NCC) covers an area of about 1.5 million km2 and is one of the oldest cratons, with age components as old as ~3.8 Ga [1,2,3]
We present U-Pb ages and Hf isotope data from detrital zircon grains from sand-shale samples collected from the roof of the sedimentary iron ores at Jiangjiazhai and Pangjiabu (Figure 1), in order to determine the chronology of the iron deposition, supplying a piece of the picture of the time frame of the distribution of oolitic iron deposits in the global context, and provide further information on the crustal growth and evolution of the NCC
The 200 detrital zircon grains have been subjected to U-Pb age dating, and the most concordant
Summary
The North China Craton (NCC) covers an area of about 1.5 million km and is one of the oldest cratons, with age components as old as ~3.8 Ga [1,2,3]. Qilianshan Orogen and late Palaeozoic Central Asian Orogenic Belt to the west and north, and the Mesozoic Qinling–Dabie and Su–Lu ultrahigh-pressure metamorphic belts to the south and east, Minerals 2018, 8, 547; doi:10.3390/min8120547 www.mdpi.com/journal/minerals Minerals. From the Archean, the craton experienced geological history (Figure 1).and. From the Archean,events the craton experienced geological history manyrespectively recorded tectonic metamorphic [2,4,5,6,7,8,9,10,11,12]. Threea main models for containing the formation recorded tectonic and metamorphic events [2,4,5,6,7,8,9,10,11,12].
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