Growth rate of continental crust in the northeast margin of the North China Craton: Constraints from the U-Pb dating and Lu-Hf isotopes of detrital zircons from the Laoha River

Abstract

Recently, how to quantitatively estimate the growth rate of continental crust is an enigmatic issue. With the development of ICP-MS technology, the U-Pb dating and Lu-Hf isotopic compositions of detrital zircons from the fluvial sediments can provide an effective and simple approach to constrain the growth rate and evolutionary history of continental crust. In this paper, 189 concordant detrital zircons from the Laoha River have been analyzed for U-Pb ages and Lu-Hf isotopic compositions by excimer LA-MC-ICP-MS. Detrital zircons from samples LH and LH2 show three major age groups, i.e., 2370 Ma~2572 Ma, 1728~2087 Ma, 127~376 Ma and 2374~2598 Ma, 1765~2087 Ma, 119~405 Ma, respectively. They have the common prominent two stage Hf model ages with a peak at ca. 2.7 Ga, which is consistent with the global continental crust. These indicate that the timing of the strongest magmatic events is at ca. 2.5 Ga and 1.8 Ga, and the best estimation age of mantle extraction of the northeast margin of North China Craton is ca. 2.7 Ga. The detrital zircons with U-Pb ages of ~1.8 Ga and ~2.5 Ga have the two stage Hf model ages of ca. 2.7 Ga, whereas ε Hf (t) values are different from those of depleted mantle. These indicate that the majority of continental crust of the northeast margin of North China Craton at time of ~1.8 Ga originated from the reworking of ~2.7 Ga crust. About 5% of the present crustal volume in the northeast margin of North China Craton was formed at 2.9 Ga; whilst ~64% of the present crustal volume in the northeast margin of North China Craton has been formed at 2.5 Ga, which is higher than that of previous studies. It suggests that the continental crust growth in the North China Craton is not uniform, but it is consistent with the episodic growth of global continental crust (60%). Moreover, the majority continental crust of the northeast margin of North China Craton has been formed at 1.8 Ga (84%) as previously interpreted. Finally, we have used formulas to quantitatively calculate the reworking rate and give a suggestion that the time of 2.5 Ga is also the main growth period of continental crust of the North China Craton, and the time of 1.8 Ga is the strongest reworking period of the continental crust in the craton. In addition, the reworking rate began to drop after reactivating in the North China Craton, and the addition of depleted mantle was gradually increased.

Evolutionary history of Precambrian continental crust in the North China Craton

“…We used 207 Pb/ 206 Pb ages for zircons of ≥1000 Ma, and we conducted 440 Lu-Hf isotopic analyses on the concordant spots or similar domains to concordant areas, as guided by CL images. Additionally, we combined our data with other published data (1137 U-Pb ages and Lu-Hf isotopic data from igneous rocks; 1120 U-Pb ages and Lu-Hf isotopic data from detrital zircons) (Yang et al, 2005;Yang, D. B. et al, 2009;Chen et al, 2006;Han et al, 2007;Guo et al, 2008;Luo et al, 2008;Dong et al, 2009;Huang et al, 2010;Jiang et al, 2010;Liu, 2010;Geng et al, 2011;Bao et al, 2013b) for discussion of the formation and evolution of the NCC. As shown in Fig.…”

“…From 2.9 to 2.7 Ga, the average ε Hf (t) value increased significantly from -7 to +5, indicating that a large number of depleted mantle components were Chen et al, 2006;Dong et al, 2009;Geng et al, 2011;Guo et al, 2008;Han et al, 2007;Huang et al, 2010;Jiang et al, 2010;Liu F, 2010;Luo et al, 2008;Yang et al, 2005;and Yang, J. et al, 2009. Data from detrital zircons were compiled from Dong et al, 2009;Geng et al, 2011;Luo et al, 2008;Yang, D. B. et al, 2009;and Bao et al, 2013b. Zhang et al, 2012).…”

“…Zhang et al (2012) systematically collected rock samples from the Songshan area and determined Lu-Hf isotopic composition, and they also suggested that a large amount of magma material originated from the depleted mantle. To quantify continental crustal growth of the NCC, Bao et al (2013b) tested 195 detrital zircons from the Laoha River, which solely drains the NCC, and indicated that the reworking rate was approximately 25% at 2.5 Ga and that the 2.5 Ga magmatic rocks mainly originated from the depleted mantle. Iizuka et al (2010) attempted to quantify the reworking index by using detrital zircons from modern rivers and made a significant advancement.…”

“…Iizuka et al (2010) attempted to quantify the reworking index by using detrital zircons from modern rivers and made a significant advancement. Following this advancement, quantification was used to investigate the evolution of the continental crust (Dhuime et al, 2012;Bao et al, 2013aBao et al, , 2013b. In this paper, we utilized this method, and the relevant formulas are as follows: The initial Hf isotope ratio of the granitoid crust formed during the nth event at time t n was calculated using formula (1), where GC, RC, DM, and α represent the granitoid crust, reworked crustal component, depleted mantle, and the reworking rate, respectively.…”