• RESEARCH PAPER • November 2014 Vol.57 No.11: 2835–2844
doi: 10.1007/s11430-014-4863-y
A thinned lithosphere beneath coastal area of southeastern China as evidenced by seismic receiver functions
YE Zhuo1,2, LI QiuSheng1,2, GAO Rui1,2*, ZHANG HongShuang1,2, HE RiZheng1,2, WANG HaiYan1,2 & LI WenHui1,2
1 Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China; 2 Key Laboratory of Earthprobe and Geodynamics, Ministry of Land and Resources, Beijing 100037, China
Received December 5, 2013; accepted January 25, 2014; published online September 11, 2014
During Mesozoic to Cenozoic time, the large-scale tectono-magmatism had strongly modified the lithosphere beneath the southeastern continent of China, leaving the present-day lithosphere as a new one evolving from the ancient lithosphere that was largely removed and replaced. But this model proposed from geochemical and petrological research is urgently in need of support from seismic observational evidence. In this paper, based on the dataset recorded by the dense stations of two NE ori-ented broadband seismic profiles deployed in the coastal area of southeastern China (SE China), both P-wave (P-RF) and S-wave (S-RF) receiver functions were isolated. We identified Pls phase converted from the Lithosphere-Asthenosphere Boundary (LAB) in P-RFs of individual stations. Migrated Pls phase indicated a depth of 60–70 km for LAB. Inver-sions/comparisons of P-RF (Pls phase) and S-RF (Slp phase) waveforms together with Ps and Sp imaging for the crust and up-per mantle structure further confirmed this result. P-RF and S-RF migrated images exhibit that a flat LAB is positioned at the depth of 60–70 km spreading along the profile, whereas a distinct structural change of lithospheric base appears at the Min River estuary. Both Ps and PpPs migrated images of P-RFs present an abrupt Moho drop across the Min River fault from south to north, which is consistent with previous result obtained from deep seismic sounding. By taking into consideration other ge-ological and geophysical features such as locally high anomalies of crustal Poisson’s ratios and heat flow at the Min River es-tuary, we infer that the Min River fault penetrates down to the Moho and may, furthermore, interfere in the deeper lithospheric structure.
SE China, lithospheric thinning, LAB, Moho, receiver functions, Min River fault
Citation: Ye Z, Li Q S, Gao R, et al. 2014. A thinned lithosphere beneath coastal area of southeastern China as evidenced by seismic receiver functions. Sci-ence China: Earth Sciences, 57: 2835–2844, doi: 10.1007/s11430-014-4863-y
The coastal area of southeastern China (SE China), located in the eastern margin of Eurasian continent, is tectonically situated in the eastern part of Cathaysia Block (Xu et al., 2000; Wang et al., 2003), confronted with Taiwan orogenic belt, one of the youngest ocean-continent convergent oro-gens on the earth, with Taiwan Strait lying between them (Figure 1). This area is featured by the widely spread late
Mesozoic Yanshanian magmatic rocks, a hot topic of many multi-disciplinary studies (e.g., geophysical and petrological) (Xu et al, 2000; Wang et al., 2003; Zhou et al., 2000, 2006; Li, 2000; Wan et al., 2012; Griffin et al., 1998; Li, 1996; Liao et al., 1988, 1990; Xiong et al., 1991). Consequently, despite the controversies about the inducements of the large-scale magmatism in this area (Zhou et al., 2000, 2006; Li, 2000; Wan et al., 2012), a consensus may have been reached from the previous studies, which can be described as that during Mesozoic to Cenozoic time, underplating of a
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Figure 1 Topography map showing the locations of seismic stations and profiles. The black triangles mark the stations deployed along the coastline and midland hilly region of Fujian Province while the fuchsia squares denote the locations of permanent stations from the Fujian Seismic Network. White solid lines AA′ and BB′ represent the two P-RF stacking profiles while the blue solid lines aa′ and bb′ indicate locations of the S-RF stacking profiles. Red crosses denote the surficial locations of piercing points of S-RFs at 70 km depth for profile AA′. Black bold lines are main faults including the Min River fault marked with an arrow. The study area is outlined with a red rectangular box in the lower-left insert map and the top-right corner inset shows the epicenter distribution of teleseismic events of P-RFs (red circles) and S-RFs (blue circles) used in this study.
huge amount of magmatic materials had modified the litho-spheric structures and components beneath the southeastern continent of China, leaving the present-day lithosphere as a new one evolving from the ancient lithosphere that was largely removed and replaced (Xu et al., 2000; Wang et al., 2003; Griffin et al., 1998). However, this geodynamic mod-el derived from petrological studies is urgently in need of confirmation from more direct and exact evidence. Obvi-ously, the pattern of the present-day Lithosphere-Astheno- sphere Boundary (LAB) beneath the southeastern continent of China is one of the direct lines of evidence, which can
verify the above-mentioned model and is definitely of great significance for our understanding of the lithosphere evolu-tion and dynamics of the southeastern continent of China. Seismological method is provided as an efficient approach for the acquisition of the LAB information.
Global map of the depth to the LAB imaged using P-RF method, proposed by Rychert et al. (2009), shows that the LAB beneath the coastal area of SE China is ~70 km; global map of lithospheric thermal thickness based on the typical adiabat of continents (Artemiva et al., 2001) and map of the estimated seismic-thermal lithospheric thickness of the
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Chinese continent (An et al., 2006) show that the litho-sphere beneath SE China is obviously thinner than either the global Archean- Proterozoic cratons or the tectonic domains of middle-western continent of China. The low-velocity and high-conductivity layer was estimated as LAB, which was widely identified beneath eastern China by using regional surface wave tomography (Tsai et al., 2000; Li et al., 2001; Huang et al., 2009) and deep magnetotelluric sounding (Li, 1996). Although the previous studies indicate a thin litho-sphere beneath SE China, a relatively fine pattern of the lithosphere is still lacking due to the low lateral resolutions of previous data. Additionally, many explosive seismic in-vestigations had been carried out in SE China (from the Nanling Range in the south to Zhejiang-Fujian border in the north), whereas they failed to obtain valid LAB information due to the weak energy of penetration for explosive seismic profiling (Liao et al., 1988, 1990; Xiong et al., 1991; Wang et al., 1995). In this article, on the basis of the dense stations of two NE striking broadband seismic profiles, we utilized both P and S receiver functions to jointly constrain the lith-ospheric structure beneath the coastal area of SE China, obtained LAB information with relatively high lateral reso-lution, showed the patterns of LAB along the profiles, and suggested the effects of the Min River fault on the deep lithospheric structure.
1 Data and method
Because of the complications resulted from smearing of reverberations from shallower crustal discontinuities, imag-ing the uppermost mantle discontinuities such as the LAB by using P receiver function is intrinsically limited, whereas S receiver function avoids crustal reverberations because reverberations and direct conversions Sp phases are com-pletely separated, with the former arriving after the incident S wave and the latter arriving before the incident S wave (Rychert et al., 2007; Shen, 2011; Farra et al., 2000; Kumar et al., 2005; Yuan et al., 2006). Therefore, S receiver func-tion has great advantages for detecting signatures like LAB at depths between 50 and 200 km (Kawakatsu et al., 2009). However, S receiver function is not used as much as P re-ceiver function due to its lower lateral resolution and claim for fairly high-quality data (Chen et al., 2006a; Zhang et al., 2010; Shen, 2011). Here we identified Pls phase converted from LAB in P-RFs, combined with Slp phase in S-RFs, to support the reliability of obtained results through joint con-straints between P and S receiver functions (Rychert et al., 2007; Wittlinger et al., 2007).
The waveform data used here are from two NE oriented broadband seismic profiles that were deployed along the coastal area of SE China (in Fujian Province, Figure 1). Profile BB′ was deployed along the coastline of Fujian with 20 portable seismograph stations continuously operating for 32 months (from August 2008 to April 2011). BB′ is 450
km in length, of which the station interval is decreased from ~30 km (for portable stations) to ~15 km by inserting some permanent stations from the Fujian Seismic Network. Pro-file AA′ was deployed along the midland hilly region of Fujian and ~150 km away from BB′ to the northwest, con-tinuously operating for 16 months (from May 2011 to Sep-tember 2012), with a length of 280 km and station interval of ~10 km. Each of the stations was equipped with a Guralp 3T (30 sec to 50 Hz)/3ESP (120 sec to 50 Hz) sensor and a Reftek-130 data acquisition system.
Teleseismic events with Ms>5.5 and epicentral distances of 30°–95° are involved for isolating P-RFs, by using time domain iterative deconvolution method (Ligorria et al., 1999). We adopted a Gaussian filter parameter =2.5 (which largely cut down frequencies higher than ~1 Hz) in the deconvolution of the P-RFs and visually inspected each P-RF carefully. The seismic events finally involved in the selected P-RFs are distributed mainly to the northeast, southeast, and south of study area (top-right corner inset of Figure 1). The isolating of S-RFs for profile AA′ used teleseismic events with Ms>6.0 and epicentral distances of 55°–85° (top-right corner inset of Figure 1) and had similar procedures used for P-RFs. We first rotated the seismic waveforms from their station coordinate system (Z-R-T), which was rotated from the original geographic coordinate system (Z-N-E), to a local ray coordinate system (P-SV-SH) to accommodate the relatively large incident angle of S wave (Wilson et al., 2006). Then S-RFs were extracted from deconvolving the P component by the SV component (Ku-mar et al., 2006) in the frequency domain with a 0.05–0.2 Hz Butterworth bandpass filter adopted in the calculation.
2 Results
2.1 Pls and Slp conversions from an uppermost mantle low-velocity boundary
P-RF traces which were moveout-corrected for a fixed slowness of p0=6.4 s/(°) (corresponding to an epicentral distance of 67°) (Yuan et al., 1997) for two stations TANT (in AA′) and Xiame (in BB′) are sorted by epicentral dis-tances in ascending order, so that the multiply converted phases (PpPs, PsPs+PpSs) migrate to increasing delay time with respect to epicentral distance while the direct convert-ed phases (Ps) do not (Rychert et al., 2009; Shen, 2011) (Figure 2(a)). We can easily identify the Pms phase con-verted from Moho and its two first-order reverberations PpPms and PsPms+PpSms (marked by black dashed lines) in the P-RF trace sections and the corresponding stacked P-RFs for stations TANT and Xiame in Figure 2(a), where PpPms and PsPms+PpSms phases migrate to increasing delay time with respect to epicentral distance while Pms phase does not. Intriguingly, a continuous negative-polarity phase, which appears at a delay time of ~8 s for TANT and ~7.5 s for Xiame, is clearly seen in the P-RF trace sections
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Figure 2 P-RF trace sections for stations TANT and Xiame (a) and the corresponding time-to-depth migrations by P-to-S direct conversion (b). Blue and red colors are used to shade the positive (indicative of velocity increasing downwards) and negative (indicative of velocity decreasing downwards) ampli-tudes, respectively. Red rectangular dots and black triangles exhibit distributions of back azimuths (BAZ) and epicentral distances (Distance) of P-RFs; stacked P-RFs for stations TANT and Xiame are plotted above the P-RF trace sections with the main phases marked by black arrows. P-RFs within 2° epi-central distance are bin-stacked and the Pls phases are marked by blue dashed lines.
and aligned in a straight line. Given that this negative phase does not have the character of migrating with epicentral distance, here we infer it as a direct conversion Pls from an uppermost mantle low-velocity boundary (i.e., a discontinu-ity of which the velocity decreases from upside to under-neath) rather than a crustal reverberation. Then the P-RFs of stations TANT and Xiame were migrated from time domain to depth domain according to the delay time of P-to-S direct conversion, using a local IASP91 velocity model modified from previous deep seismic sounding results (Zhu et al., 2005, 2006). As shown in Figure 2(b), Pls negative phases (marked by blue dashed lines) of TANT and Xiame are mi-grated to ~70 km and ~63 km, respectively.
Furthermore, we made inversions of P-RF waveforms for the S-wave velocity structure under stations TANT and Xiame (Figure 3(a)). In the process, four different Gaussian filter parameters =1.0, 1.5, 2.0, 2.5 were used in the de-convolution, respectively to gain P-RFs with differentiated frequencies for the two stations (Figure 3(b)). Then we jointly inverted the multi-frequency P-RFs for an integrated S-wave velocity structure under the stations. Meanwhile, to avoid the effect of azimuthal anisotropy, we only selected
the P-RFs of which the corresponding seismic events are from southeast and epicentral distances are between 60°–70° for TANT and 80°–90° for Xiame respectively, to be stacked and then used for the inversions, because P-RFs within these back-azimuthal and epicentral ranges have consistent waveforms (as seen in Figure 2(a)). As a result, the synthetic P-RFs simulated from the inverted velocity structures fit fairly well with the observed P-RFs in high degrees of fitting (>90%, Figure 3(b)). Additionally, we also plotted the S-wave velocity structure derived from sur-face wave dispersion analysis (Tsai et al., 2000) of SE Chi-na in Figure 3(a) to be compared with our P-RF inversions.
Inversions from both P-RFs and surface wave analysis in study area coincidently exhibit a relatively large gradient decreasing of S-wave velocity at the depth of 60–70 km, resulting in a low-velocity zone appearing below ~60 km depth, as obviously observed in Figure 3(a). Given this fea-ture, we speculate the top of the low-velocity zone of upper mantle (i.e., LAB) is located at 60–70 km depth, which is consistent with the depth of the migrated negative phase Pls in Figure 2. Furthermore, Figure 3(c) demonstrates that comparisons between synthetic S-RFs simulated from the
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Figure 3 Inversions/comparisons of P-RF and S-RF waveforms for stations TANT and Xiame. (a) S-wave velocity structures from P-RF inversions of stations TANT and Xiame and surface wave dispersion analysis of SE China (Tsai et al., 2000); (b) Observed waveforms (blue lines) and synthetic wave-forms (red lines) of multi-frequency P-RFs. Gaussian filter parameters, percent of fittings (%), and ray parameters are labeled on the left of the P-RF traces. Converted phase Pls from LAB is marked with an arrow; (c) Comparisons between Synthetic S-RFs (red lines) simulated from inverted velocity structures of TANT and Xiame in (a) and observed S-RFs (blue lines). The observed S-RFs are from 25°N in profile bb’. Converted phase Slp from LAB is labeled.
inverted velocity structures of TANT and Xiame in Figure 3(a) and the observed S-RFs exhibit consistent seismic phases of main discontinuities (e.g., Moho and LAB), where converted phase Slp from LAB comes out at 60–70 km depth.
2.2 P-RF and S-RF imaging for the lithospheric struc-ture
We employed Common Conversion Point (CCP) technique (Zhu et al., 2000, 2002) to image the lithospheric structure beneath the study area, exhibiting variations of velocity discontinuities underneath the profiles. Figure 4 shows the P-RF migrated images in depth range of 0–150 km along profiles AA′ and BB′ (as plotted in Figure 1), by using a modified IASP91 model same as used in Figure 2. Similarly, S-RF imaging was done in depth range of 0–150 km along profiles aa′ and bb′, which were properly positioned (see
Figure 1) with respect to the piercing points distribution of S-RFs at 70 km depth (Figure 5).
Figure 4 clearly shows the Moho appearing as a strong and continuous positive signal and fluctuating slightly at the depth of 30 km. But here we focus on a strong and continu-ous negative signal (i.e., Pls phase on P-RF section of indi-vidual stations) appearing below Moho at a depth of 60–70 km, which is considered as an undependent seismic phase converted from a lithospheric low-velocity boundary rather than a crustal reverberation. As described above, this nega-tive phase is aligned in a straight line on time domain P-RF trace sections and does not migrate to increasing delay time with respect to epicentral distance, which suggests it is not provided with any temporal character of reverberations. In addition, negative-polarity direct conversions above the Moho and other positive-polarity reverberations that would be associated with negative reverberation phases are not apparent (Figure 4). So it is unlikely to generate such a
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Figure 4 P-RF migrated images along profile AA′ and BB′ (0–150 km). Stacking bins are set as 150 km in width and 5 km in length along the profile. Blue-black color indicates positive (velocity increasing downwards) while yellow-red negative (velocity decreasing downwards). Bin-stacked P-RF traces are plotted on the images and the bins are defined using piercing points at a depth of 70 km with a moving step of 50 km. LAB and Moho of S-RF imaging (Figure 5) are also projected to profiles AA′ and BB′, as indicated with black and white dashed lines, respectively. Negative phase Pls converted from LAB is clearly seen. Location of the Min River fault is marked by an arrow.
Figure 5 S-RF migrated images along profile aa′ and bb′ (0–150 km). Stacking bins are set as 160 km in width and 10 km in length along the profile. Blue color indicates positive (velocity increasing downwards) while yellow negative (velocity decreasing downwards). LAB and Moho are indicated with black and white dashed lines, respectively. Location of the Min River fault is marked by an arrow.
strong negative-polarity reverberation later. Furthermore, LAB defined by S-RF imaging (Figure 5) along profile aa′ and bb′ is also projected to profiles AA′ and BB′, of which the results demonstrate that the lithospheric low-velocity boundary defined by P-RF is quite coincident with SRF-LAB (Figure 4), especially for coastal line BB′. Be-cause of the approximate superposition of S-RF profile bb′ and P-RF profile BB′ (Figure 1), Pls signal is well fit for SRF-LAB, which further confirms that Pls is converted from LAB. Moho and LAB defined from S-RF along profile aa′ are differentiated from the results of P-RF to a small degree, because aa′ is located slightly far from AA′ (130 km west of AA′, Figure 1). The negative signal below Moho on AA′ section is relatively shallow (<60 km) with double
negative phases appearing at some local sites (e.g., ~25.7°N). Given that Pls is positioned at a depth of ~70 km as presented by P-RF trace section of station TANT, here we speculate that the double negative phases may be re-sulted from multi-layered low-velocity boundaries within lithosphere (Rychert et al., 2007).
LAB defined by P-RF imaging along profile BB’ (Figure 4) is positioned at the depth of 60–65 km, which is con-sistent with S-RF result (Figure 5). It is noticeable and in-triguing that LAB defined by both P-RF and S-RF coinci-dently presents a slight but clear uplift (~5 km) at the inter-section site with the Min River fault (~25.8°N) and some other negative signals also come out at this site below the Moho phase while above the depth of 70 km, appearing
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relatively complex (Figures 4 and 6). In addition, abrupt changing is observed on the Moho here (Figures 4 and 6) (Li et al., 2013; Ye et al., 2013). In order to exhibit a finer lithospheric structure in horizontal and vertical direction, Ps-migrated imaging with smaller stacking bins (2 km in length along the profile) and a smaller depth range of 0–100 km is shown in the left panel of Figure 6. Besides, migra-tion for multiple phases PpPs (Shi et al., 2004; Chen et al., 2006b; Shen et al., 2014), which has a higher vertical reso-lution, was also constructed to support the result of Ps mi-gration, as shown in the right panel of Figure 6. We can clearly observe some changes or offsets of Moho at the in-tersections with the NW striking faults such as the Min River fault from both Ps- and PpPs-migrated images. An abrupt Moho drop (3–4 km) occurs at the Min River estuary, which is consistent with the result obtained from deep seis-mic sounding (Liao et al., 1990). This result indicates the normal slip feature of the Min River fault (Liao et al., 1990; Zhang et al., 2009).
Previous studies have revealed that the crustal Poisson’s ratios (0.28–0.30, Figure 7) (Ai et al., 2007; Ye et al., 2013) and heat flow (Hu et al., 2000) are both presented as rela-tively high anomalies locally at the Min River estuary. Here we present our interpretations for this geological phenome-non through inferring its relationships with the Min River fault. Petrological studies indicate that the tectono-magma- tism in eastern China during the Mesozoic to Cenozoic only originated in very local areas within the lithosphere and was concentrated near the intersections between regional, large-scale faults and the main boundaries of lithosphere. The different penetration depths of faults may have caused different styles of magmatism (Wan et al., 2012, 2008; Wang et al., 2008). The fact that the late Yanshanian high-K calc-alkaline granites are more widespread in the coastal area may indicate that they originate from the mafic mag-mas underplating from asthenosphere (Zhou et al., 2000,
2006). In regional tectonics, the Fuzhou Basin, located at the Min River estuary and the vicinity, is dominated by two regional, large-scale faults, the NE striking Changle-Shaoan fault and NW striking Min River fault which intersects at the Min River estuary (Figures 1 and 7) (Zhang et al., 2009). Thus, the intersections of faults are readily provided as po-tential channels for the intrusion and eruption of basaltic magmas (Zhou et al., 2000, 2006; Wan et al., 2012). More basaltic magmas then intruded into uppermost mantle litho-sphere or crust along the faults and assembled there, result-ing in the locally high anomalies of crustal Poisson’s ratios (Figure 7) and heat flow at the intersection areas of faults (Min River estuary). Moreover, other previous studies have indicated that the NW striking Min River fault is one of the important regional faults in the coastal area of SE China, which remarkably constrains the distributions of earth-quakes, geotherm, and other geological factors in this area and may extend into the Taiwan Strait (Liao et al., 1990; Shao et al., 1993; Chen et al., 1992). Therefore, we infer that the Min River fault penetrates down to the Moho and may, furthermore, interfere in the deeper lithospheric structure.
3 Discussions and conclusions
The old Archean and Proterozoic lithosphere beneath SE China was largely removed and replaced by younger mantle materials during Mesozoic to Cenozoic time, as inferred by geochemical and petrological research (Xu et al., 2000; Wang et al., 2003; Griffin et al., 1998). But this geodynamic model needs to be supported by other more direct evidence, especially the geometry of the present-day lithosphere. Re-sults from surface wave analysis have exhibited that eastern China as a whole is dominated by a thinner lithosphere belt (Tsai et al., 2000; Li et al., 2001; Huang et al., 2009), com-pared with its counterpart beneath middle-western China. In
Figure 6 P-RF migrated images (0–100 km) for direct conversions Ps (a) and multiple conversions PpPs (b). Stacking bins are set as 150 km in width and 2 km in length along the profile. Moho and LAB are marked in the figure. Direct conversion Pms from Moho and its two first-order multiples PpPms and PsPms+PpSms are marked in the right panel. The dashed rectangular in the left panel indicates the distinct structure of Moho and LAB beneath the Min River fault zone.
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Figure 7 Distribution map of crustal Poisson’s ratios in the coastal area of SE China (modified from Ai et al., 2007 and Ye et al., 2013). High anomalies of crustal Poisson’s ratios (0.28–0.30) appear at the Min River estuary where two faults intersect.
this paper, we applied both P-RF and S-RF techniques on our dataset to jointly constrain the lithospheric thickness beneath the coastal area of SE China. Converted signal Pls identified from P-RFs of individual stations and inver-sions/comparisons of P-RF and S-RF waveforms, together with Ps and Sp imaging for the crust and uppermantle structure, jointly confirm a thinned lithosphere with 60–70 km thickness beneath coastal area of SE China. Our result is similar to that observed in the eastern NCC (North China Craton) by Chen et al. (2006a) and Guo et al. (2012) (~60 km thick lithosphere), which supports the point that since Mesozoic to Cenozoic, transition type lithosphere, which was composed of continental crust and oceanic mantle, may have widely existed in the eastern China continent (Wan et al., 2012; Zhou, 2006).
Lithospheric thinning is obviously resulted from regional tectonic extension of which the process, however, is com-plex. Teng et al. (1994) proposed that the lithosphere of southeastern continent of China has been dragged by the eastward and southeastward mantle flow to migrate toward the Pacific, the Philippine Sea, and the Java Trench. This event, which led to a strong tensional field in SE China, coupled with seafloor spreading (spreading of the South
China Sea Basin) and plate collision (collision between the Philippine Sea plate and the Eurasian plate), jointly pro-pelled the lithosphere of SE China toward a complex evolu-tionary experience. Transmitting and upwelling of hot ma-terials from the deep earth brought about the severe litho-spheric thinning beneath SE China. The relatively higher crustal Poisson’s ratios in coastal area of SE China indicate more mantle-originated mafic components in the crust, which is consistent with the inference that the lithosphere beneath study area was largely removed and replaced by asthenospheric mantle materials through underplating dur-ing Mesozoic to Cenozoic time (Xu et al., 2000; Wang et al., 2003).
On the background of the geologic setting above- mentioned, a series of subsidence basins (e.g., the Fuzhou Basin, the Quanzhou Basin, and the Zhangzhou Basin) (Zhang et al., 2009) have formed since Mesozoic to Ceno-zoic in coastal area of SE China (Fujian). The formations of these subsidence basins as well as the high anomalies of crustal Poisson’s ratios and heat flow within the basins are probably related closely to the NW striking faults which have undergone multi-episodic deep tectonic activities. Our receiver function results exhibit an abrupt 3–4 km Moho
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drop and a distinct LAB structural change across the Min River fault from south to north in coastal area of Fujian, which indicate that the Min River fault may not only pene-trate down to the Moho but also interfere in the deeper lith-ospheric structure. As a result, the mantle-originated mag-mas are induced to be assembled and then intrude upwards along the faults, eroding and breaking the lithospheric base (Figures 4, 5 and 6). The upward intrusion of a mass of mafic magmas caused high anomalies of crustal Poisson’s ratios and heat flow at the Min River estuary, which are also strong evidence for the underplating of mantle-originated magmas, modifying the components of lithosphere. How-ever, studies for the NW striking faults such as the Min River fault in coastal area of SE China need to be further improved in the future given that the present-day geological and geophysical data are still poor, especially in the Taiwan Strait.
We are grateful to Earthquake Administration of Fujian Province for greatly helping us with the field work; we also thank Shen Xuzhang from Lanzhou Institute of Seismology and three anonymous reviewers for their constructive suggestions to this paper. This work was supported by Si-noprobe02-03 (Grant No. 201011042) and the National Natural Science Foundation of China (Grant No. 41174081).
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