Geometry and Emplacement of the Late
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中国科技论文在线 Journal of Asian Earth Sciences 79 (2014) 302–311 http://www.paper.edu.cn Contents lists available at ScienceDirect Journal of Asian Earth Sciences journal homepage: www.elsevier.com/locate/jseaes Geometry and emplacement of the Late Cretaceous mafic dyke swarms on the islands in Zhejiang Province, Southeast China: Insights from high-resolution satellite images ⇑ Ning-hua Chen a, Jin-jin Dong a, Jian-yu Chen a,b, , Chuan-wan Dong a, Zhong-yue Shen a a Department of Earth Sciences, Zhejiang University, Hangzhou 310027, China b State Key Laboratory of Satellite Ocean Environment Dynamics, Second Institute of Oceanography, State Oceanic Administration, Hangzhou 310012, China article info abstract Article history: The geology of Zhejiang coastal area in Southeast China is characterized by numerous Late Mesozoic Received 24 April 2013 intrusive rocks and widespread mafic dyke swarms, which indicate continental lithospheric extensional Received in revised form 1 October 2013 events during the Jurassic and Cretaceous. This work is focused on using multisource high-resolution Accepted 1 October 2013 remote sensing images (Worldview2, Geoeye1 and Quickbird2) to identify the geometry, morphology Available online 9 October 2013 and location of previously undocumented and poorly understood dyke swarms exposed on the islands in Zhejiang Province. The geometry of each dyke is described by its strike, length and thickness. The spa- Keywords: tial distribution of the dyke density and crustal dilation are obtained based on the statistics of 774 Mafic dyke swarms extracted mafic dykes. Field surveys are performed in some islands in order to analyze the detailed geo- High-resolution remote sensing Geometry metric features and assess the interpretative accuracy. The spectral measurement and analysis of mafic Southeastern China dykes are performed as well for remote sensing imagery processing and lithological interpretation. The results show that the frequency distributions of the length and thickness of dykes follow power law curves. The maximum and mean dyke thicknesses are 11.2 m and 1.43 m, respectively. The crustal dila- tion of the islands ranges from 0.09% to 7.4%. From the north to the south islands, the dilation decreases gradually. The dyke frequency and density have the same distribution as the dilation. According to 40Ar–39Ar age (Zhongshanjie archipelago) and U–Pb zircon age (Sijiao Island) of the mafic dyke, the dyke swarms on the eastern Zhejiang islands emplaced at around 87–97 Ma. The cross-cutting relationships of dykes and host rocks show that the mafic dyke swarms have close spatial correlations with granite. The dykes stretch in various directions whereas the NE-trending dykes dominate. Our research reveals four intrusive events that imply the crustal extension and intermittent variation of the regional stress field in the coastal area of southeastern China in the Late Cretaceous. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction of mafic dyke swarms have been extensively studied through mul- tidisciplinary approaches. Mafic dyke swarms occur in a variety of tectonic settings such The geometric and kinematic features of dyke swarms are a as upwelling mantle plumes (e.g. Ernst and Baragar, 1992; Ernst good indicator of magma flow directions, location of magma and Buchan, 2003; Li et al., 2010; Kiselev et al., 2012), backarc source and palaeostress field (e.g. Ernst and Buchan, 2003; Klau- extension (e.g. Xiong et al., 2011), post-orogenic collapse (e.g. Iln- sen, 2006a, 2006b; Annen et al., 2001; Olsson et al., 2011; Kiselev icki, 2010; Liu et al., 2013), intra-continental rifting (e.g. Fahrig, et al., 2012). Multisource remote sensing provides an effective 1987; Smythe et al., 1995; Hou et al., 2005), and constitute a com- way to determine the distribution of dyke swarms on a large mon expression of crustal extension. They serve as major conduits scale (e.g. Babiker and Gudmundsson, 2004; Mège and Korme, for transferring magma to the upper crust, and contain ample 2004), and it is possible to measure the detailed geometric fea- information about the nature of the mantle source. The composi- tures of dyke swarms (including strike, dip, spacing and thick- tion, age, geometry, palaeomagnetism, flow pattern and tectonics ness) through high-resolution satellite imagery. The changes in dyke attitude and rock magnetic fabric can be used to study the propagation modes of dykes, which reveal the overall process of ⇑ the transfer of magma. Corresponding author at: State Key Laboratory of Satellite Ocean Environment Adjacent to the west of Pacific Ocean, the southeastern islands Dynamics, Second Institute of Oceanography, State Oceanic Administration, Hangzhou 310012, China. Tel.: +8657181963116. and coastal areas of China are characterized by numerous Late E-mail address: [email protected] (J.-y. Chen). Mesozoic intrusive rocks and widespread mafic dyke swarms, 1367-9120/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jseaes.2013.10.001 转载 中国科技论文在线 http://www.paper.edu.cn N.-h. Chen et al. / Journal of Asian Earth Sciences 79 (2014) 302–311 303 which indicate continental lithospheric extensional events during appropriate methods for remote sensing interpretation and assess the Jurassic and Cretaceous. Although many models have been pro- the accuracy of measurements, we first conduct field surveys and posed as geodynamical causes to explain this major extensional spectral measurements of dykes on some of the islands that allow event in the last two decades, debates continue (e.g. Martin human access. We used DGPS, compass, tape and laser rangefinder et al., 1994; Li, 2000 and references therein). As a key evidence for the measurements and location. Moreover, 3D point clouds of of extensional events, mafic dyke swarms have been studied in the dyke swarms on Miaozihu Island of Zhongshanjie archipelago lithogeochemistry (e.g. Li et al., 1995; Lapierre et al., 1997; Chen were obtained using high-resolution terrestrial laser scanner (Rie- and Jahn, 1998; Li and McCulloch, 1998; Li, 2000; Zhou and Li, gl-Vz1000), which offers 5 mm point spacing within 100 m dis- 2000; Ren et al., 2002) and palaeomagnetism (e.g. Gilder et al., tance. The geometry of each dyke is described by its strike, 1996; Liu and Morinaga, 1999; Pan et al., 2011) in parts of this re- length and thickness. The lithological spectral were measured gion. However, the distribution, geometry, and kinematics of the using an Analytical Spectrometer Devices (ASD) field-portable mafic dyke swarms largely remain unknown. spectrometer, which records 2151 channels within the 0.4- to Located in the southeast of China, Zhejiang Province has the 2.5-Am-wavelength region. Sample site locations are on Sijiao Is- most islands in China. In spite of the heavy vegetation cover, reefs land and Luhua Island (Fig. 1b). provide completely exposed dyke swarms on most of the islands. In this paper, we use multisource high-resolution remote sensing 3.2. Data and image processing images to identify the geometry, morphology and relative spatial location of previously undocumented and poorly understood dyke Medium resolution images, such as Landsat ETM, ASTER have swarms exposed on the islands where field surveys are difficult. been widely used to extract the length and strike of dyke swarms Based upon the field surveys of representative dyke swarms and in arid and semi-arid areas (e.g. Merged and Brkaiby, 1997; Bilotti the analysis of dyke geometry, we investigated the emplacements et al., 2000; Babiker and Gudmundsson, 2004; Mathieu et al., of the dyke swarms. We also discuss the geodynamic environment 2011). However, it is difficult to use these images for identifying of Late Cretaceous on the islands of the southeastern China. the dyke swarms, which are narrowly and shortly exposed on the island. Thus, we used multisource high-resolution satellite images 2. Geological background (Worldview2, Geoeye1 and Quickbird2) to extract the dyke geo- metric features (i.e., strike, length and thickness) on the islands Zhejiang Province is situated in the south of the Yangtze River in Zhejiang Province. Delta in the southeastern China and constitutes partially the South Because of its very high spatial (0.5 m) and spectral (8-bands) China Block (SCB), which includes the Proterozoic and Paleozoic resolution, Worldview2 imagery is primarily used to extract the terrain of the Yangtze Craton, and South China Fold Belt. The bound- geometric features of dyke swarms. Based on the characters of ary between the Yangtze Craton and South China Fold Belt is the the 8 bands and spectral characters of dykes, we select band 5, 3, sub-EW-trending Jiangshan-Shaoxing Fault (Fig. 1). The geology and 2 for generating false color image. The image is preprocessed of southeast China is characterized by extensive Mesozoic Yansha- for fusion, geometric correction and edge enhancement. All bands nian magmatism (Charvet et al., 1994; Ren et al., 2002; Shu et al., of imagery are geo-referenced to a Transverse Mercator projection 2009; Zhu et al., 2010). SCB has experienced complex and alternate with the root mean square error (RMSE) less than 1 pixel in order extension, compression and strike-slip activities affected by the to minimize the change in the spatial autocorrelation pattern. Geo- interaction of Paleoasian, Tethys and Pacific tectonic domain in eye1 imagery (0.5 m) and Quickbird2 (0.61 m) are used to identify the Mesozoic and Cenozoic eras (Shu et al., 2009). The widespread the dykes as well. Fig. 2 shows the false color and fusion imagery of NE-trending Mesozoic volcanic-intrusive complex area and tec- Wordview2 on Nandingxing Island of Shengsi archipelago. tonic zone formed the basic tectonic framework in Late Mesozoic southeast areas of China (Wang and Zhou, 2002; Hu et al., 2012). 4. Results The geological and geomorphologic characteristics on the islands of the southeastern China are similar to those of the adjacent main- 4.1.