Has the Yangtze craton lost its root? A comparison between the North China and Yangtze cratons
Graphical abstract
Introduction
Cratons are stable geological regions which are characterized by low density, fast P and S wave velocities, and cold and dry lithospheric roots whose thickness is typically more than 200 km (Body, 1989, James et al., 2001, Jordan, 1975, Morgan, 1984, Peslier et al., 2010). Due to these features, few destructive earthquakes, significant magmatism and deformation events are found within a craton (Windley, 1995). Thus cratons can attain long-term stability and preserve previous geological records (Zhu et al., 2012). However, recent studies indicate that many cratons have been destroyed (Table 1). A study on how these cratons lose their roots is important to make a better understanding of continental formation and evolution (Kusky et al., 2014).
Craton destruction means the process related to loss of its stability and is not equal to lithospheric thinning (Wu et al., 2008, Wu et al., 2014). Table 1 gives a brief introduction to cratons that have been destructed. From the table, it is clear that both the triggering forces and root loss mechanisms corresponding to the destruction of cratons are complex. There are mainly four triggering forces (subduction of oceanic plates beneath the craton, collision events along the marginal regions, mantle plumes, and rifting) and three root loss mechanisms (delamination, thermo-chemical erosion, and melt-peridotite reactions) (e.g., review by Kusky et al., 2007b). The study of cratonic destruction is still in an early stage, thus one has many difficulties determining with certainty the major triggering force and root loss mechanism of the destroyed cratons. The main reason lies in the lack of data and multidisciplinary research results in a variety of interpretations, which makes it hard to make a good understanding of cratonic destruction. It is necessary to choose several cratons to make a further study on the basis of the newest published data and comprehensive analysis of different subjects.
Many studies suggest that the NCC has been destructed in the Mesozoic (Wu et al., 2008, Zhu and Zheng, 2009; Zuo et al., 2013). The current NCC is regarded as a natural Earth Science laboratory for the coexistence of the destroyed Eastern Block and the locally modified Western Block. However, whether the Yangtze craton, which experienced similar tectonothermal events during the Mesozoic, has been destructed is a controversial issue (Zheng and Wu, 2009) for the lack of lithospheric information earlier than the Neoproterozoic. Due to the proximity of these two cratons and their similar tectonic history since the Mesozoic, we choose them as our study objects.
In the last several decades, many scientists concentrated their attention on the study of the destruction of the NCC using geophysical, geological and geochemical data. Four main root loss mechanisms have been proposed, including delamination (Gao et al., 2002, Gao et al., 2004), thermo-chemical erosion (Menzies et al., 2007), melt-peridotite reactions (Zhang, 2009, Zhang et al., 2008a, Zhang et al., 2008b), and delamination of marginal regions and thermo-chemical erosion for interior regions (Gao et al., 2009). As to the dynamic process, some investigations (Zheng and Wu, 2009, Lan et al., 2011, Wu et al., 2014) reveal that the subduction of the Paleo-Pacific (Izanagi) plate during the Mesozoic (190–90 Ma) is one of the main dynamic factors that led to root-loss, and the collision and subduction events along the northern and southern margins have a certain contribution (e.g., Kusky et al., 2007b, Windley et al., 2010), but are not main factors (e.g., Wang et al., 2014b).
Compared to the NCC, relatively fewer studies have been made on the Yangtze craton (Fig. 4). Based on studies which suggest that the Yangtze craton has lost its root, there are mainly two root loss mechanisms: (1) delamination, based on the fast velocity bodies found from tomographic maps (Cai et al., 2003, Jiang et al., 2013a) and outcrops of Mesozoic volcanic rocks with high Mg content beneath the Yangtze craton (Xu et al., 2002a); and (2) thermo-chemical erosion. This idea is based on the fast and slow velocity bodies that are distributed alternatively with a high angle between them (Yuan, 2007). Limited studies reveal that there are three possible dynamic mechanisms for the destruction: the aggregation and breakup of Rodinia (Zheng and Zhang, 2007), the subduction and rollback of the Paleo-Pacific (Izanagi) plate (Kusky et al., 2014), and the collision between the NCC and Yangtze craton (Jiang et al., 2013a).
In this paper, we review and compare the tectonic history and lithospheric structure of the Yangtze and North China cratons using geophysical, geological and geochemical data to solve two questions. First, we test if the Yangtze craton has lost its root. Second, we propose a possible general process for cratonic destruction.
Section snippets
Geological background
The Yangtze craton (Fig. 1), which is located in southeastern China, formed in the Archean (Ge et al., 2013, Wang et al., 2013b, Cheng et al., 2013) with Archean–Paleoproterozoic crystalline basement (Zheng et al., 2006b, Ge et al., 2013) and has a crustal remnant as old as 3.8 Ga (Zhang et al., 2006b). It is surrounded by younger fold belts. To the north, the Triassic Qinling–Dabie–Sulu Belt separates the Yangtze craton from the NCC. To the west, the Mesozoic Longmenshan Orogenic Belt separates
Has the Yangtze craton been destroyed?
Many studies suggest that the Paleo-Pacific (Izanagi) plate subduction in the Mesozoic played an important role in the destruction of the NCC (e.g., Kusky et al., 2007b, Wu et al., 2014). However, whether the Yangtze craton, which experienced similar tectonothermal events in the Mesozoic, has been destroyed has remained controversial. We conclude that the eastern part, middle part and marginal regions of the Yangtze craton have been destructed for the following reasons: (1) The
Conclusions
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Geological, geophysical and geochemical data reveal that the eastern part of the Yangtze craton has been destroyed. The destroyed areas are bounded on the west by the North–South Gravity Lineament and are characterized by the coexistence of both refractory and fertile lithosphere. The destruction was concentrated in two periods. The first period was in the Neoproterozoic. The destructed regions are limited to the marginal regions, and the possible dynamic factor is the aggregation and breakup
Acknowledgments
Two anonymous reviews and Editor Rob Govers are thanked for their constructive comments. We are grateful to Xiaofei Yin and Xu Wang who helped us with the translation calibration for this paper. We appreciate the constructive suggestions on the evolution of the NCC and the Yangtze craton made by Zhensheng Wang. We also thank Xingfu Jiang who provides us the figure of tectonic map of the Yangtze craton. This study was supported by the National Natural Science Foundation of China (No. 91014002).
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