Tectonic Controls on the Pleistocene–Holocene Wudalianchi Volcanic ﬁeld (Northeastern China)

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Journal of Asian Earth Sciences 24 (2005) 419–431

Tectonic controls on the Pleistocene–Holocene Wudalianchi volcanic ﬁeld (northeastern China)

Yu Wanga,*, Hongzhou Chenb

aGeologic Laboratories Center and Department of Geology, China University of Geosciences, Beijing 100083, China bSeismological Bureau of Heilongjiang Province, Harbin 150036, China

Received 28 May 2002; revised 19 November 2003; accepted 12 December 2003

Abstract The Wudalianchi volcanic field developed during the Pleistocene–Holocene but is dormant at present. Its latest eruption occurred in 1719–1721 AD. The volcanic rocks are high-potassium alkaline basalts derived from the upper mantle (c. 100–120 km depth) as indicated by geochemical data. The field is located in an old tectonic transition zone surrounded by four regional normal faults. The volcanic craters are aligned along NE–NNE-striking fractures and faults, although a NNW-striking sub-surface fracture zone probably controlled the eruptions beginning at 1.33 ^ 0.08 Ma. Beneath the volcanic field, the Moho interface lies at a depth of 33.5–35 km. Eruptions evolved from fissure type to central type eruptions. The field is characterized by an intraplate tectonic setting in a non-orogenic compressional regime which resulted from the subduction of the West Pacific plate beneath the eastern Asian continental margin starting 3–2 Ma ago. q 2004 Elsevier Ltd. All rights reserved.

Keywords: Volcanic ﬁeld; Young alkaline basalts; Northeastern China; Intraplate setting; Compressional tectonic regime; Tectonic control

1. Introduction To the north and south of the Wudalianchi volcanic field, there are other Quaternary volcanoes and volcanic The Wudalianchi volcanic field is located in north- fields, namely the Xiaogulihe (Genghe) Volcano, the eastern China, at 488350 –488510N latitude, 1258570 – Keluo volcanic field, and the Erkeshan Volcano (Fig. 2), 1268310E longitude (Fig. 1), near the NNE-trending with volcanic rocks of similar composition and similar geological age. These volcanoes are distributed along Dahinggan Mountain belt. It is far from the subduction a NNW-trending belt comprising the 320 km long zone of the West Pacific plate. On the southern side of the Wudalianchi volcanic zone. This paper covers mainly Wudalianchi volcanic field, there is the Songliao Basin the Wudalianchi volcanic field. (Fig. 2), a middle Jurassic–early Cenozoic intracontinental Two theories have been put forward to explain the rift-depression which evolved from the middle Jurassic to tectonic setting of the Wudalianchi volcanic field: it occurs early Cenozoic (Heilongjiang Bureau of Geology and (1) in a continental rift environment (Ding, 1988; Qiu et al., Mineral Resources, 1993; Zhang et al., 1997; Wang et al., 1991; Chen and Ren, 1997) and (2) in a hot-spot setting 1999). On the northern side is the Xiaohinggan Mountain formed by intraplate mantle upwelling (Wang, 1997; Gong, belt with a WNW-trending uplift which has evolved since 1997b). Although Cenozoic basalt has been extruded in the late Mesozoic. On the eastern side lies the Songwu intracontinental rift settings in many places in northeastern Graben with NNE–NE-striking normal faults and fractures; China (Whitford-Stark, 1987; Jilin Bureau of Geology and it was formed during the early Cretaceous–middle Mineral Resources, 1988; Chen and Ren, 1997), the Cenozoic (Heilongjiang Bureau of Geology and Mineral tectonic evolution in the Mesozoic and Cenozoic does Resources, 1993). not support the explanation that the eruptions of the Wudalianchi volcanic field have occurred in a continental * Corresponding author. Tel.: þ86-10-8232-1028; fax: þ86-10-8232- rift setting. In fact, the tectonic stress was not extensional 1983. during the eruptions of the Wudalianchi volcanic field E-mail address: [email protected] (Y. Wang). (Wang et al., 1999).

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Fig. 1. Location of the Wudalianchi Volcanic Field (NE China). Abbreviations are as follows: W. V.—Wudalianchi volcanic ﬁeld, C. V.—Changbaishan Tianchi Volcano, QL-DB—Qinling-Dabie, DMT—Dahinggan Mountain Belt, XMT—Xiaohinggan Mountain Belt, YL-YTF—Yilan-Yitong Fault, MS- DHF—Mishan-Dunhua Fault. The area covered by ocean is shown by broken lines. Fig. 2 is shown.

Based on geologic mapping of the Wudalianchi volcanic the field are aligned NE (Fig. 3). These craters are of small field and its surroundings, we analyzed structural styles scale and were formed by flowing basaltic lava. The conical formed in the Cenozoic sediments. Using magnetotelluric craters consist of two parts: the lower part is a shield of sounding results, sequences of volcanic eruptions, seismic- basaltic lava and the upper part is formed by pyroclastic reflection profiles, and seismic focal mechanisms, the crustal rocks. Each volcanic eruption was controlled by basement structure and faulting patterns around and beneath the faults or fissures; the eruptions involved mainly flowing lava Wudalianchi volcanic field were assessed. We also and were either central or fissure type of eruptions. reconstructed the tectonic setting of the Wudalianchi The magma was derived from a depth c. 100–120 km at volcanic eruption centers in order to understand the a source temperature of c. 1068–1100 8C according to relationship between intraplate volcanoes and tectonic stress estimates from mantle source inclusions of websterite and as well as the tectonic control on the passage of magma from clinopyroxenite (Qiu et al., 1991; Gong, 1997a). Radio- the upper mantle to the surface in an intraplate setting. metric (K–Ar) dating of the volcanic products yielded the following age values (Fig. 4): a middle Pleistocene eruption period ,1.33 ^ 0.08–1.27 ^ 0.09 Ma (Miu et al., 1983; 2. Eruption sequences and characteristics Liu, 1987), late Pleistocene eruptions ,0.8 ^ 0.22, of volcanic rocks 0.57 ^ 0.05, 0.52 ^ 0.14 and 0.30–0.65 Ma (Miu et al., 1983; Gong, 1997a,b), and a Holocene eruption—1719– The basaltic lavas from the Wudalianchi volcanic field 1721 AD (mainly from the Laoheishan and Huoshaoshan cover more than 800 km2. The 14 conical volcanic craters of craters). Recently, Li et al. (1999) dated many basaltic rocks 中国科技论文在线 http://www.paper.edu.cn

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Fig. 2. Regional geologic characteristics of the Wudalianchi volcanic field and adjacent areas. Abbreviations are as follows: W. V.—Wudalianchi volcanic field, K. V.—Keluo volcanic field, X. V.—Xiaogulihe Volcano, E. V.—Erkeshan Volcano, DMFF—Dahinggan Mountain Front Fault, NF—Nenjiang Fault, NMF—Nuomoer Fault, CFSB—Central Fault of the Songliao Basin, X-WFZ—Xiaogulihe-Wudalianchi Fault or Fracture Zone (The level of the Moho discontinuity is inferred from mean Bouguer gravity anomaly data on 1 £ 18 grid squares; there is a lack of data near the NW corner of the figure). Figs. 3 and 6 are shown.

using the K–Ar method and demonstrated a similar Hughes, 1982), making it a high-potassium alkali-basalt. sequence. The historic and thermoluminescent dates yielded A special characteristic is that there is no plagioclase, but an age of 278–283 a (Ji and Li, 1998) for the latest eruption, alkali feldspar is found in the basalt (Gong and Xu, 1997). indicating that this is presently a dormant volcano. The lavas are rich in LREE, Ti, Rb, Cs, Sr, Ba and Ta. The K2O content in the Wudalianchi volcanic rocks is The Y/Nb ratio is less than 1 (Gong and Xu, 1997); Sr is 4.28–5.91% with an average of 5.28% (Xu, 1997); it is 1221–1702 ppm, Ba is 1296–2120 ppm, (La/Nb)N is higher than the normal average of 3.65% (Sorensen, 1974; 63.4–45.2, and (Sm/Nd)N is 0.517–0.560 (Wang, 1997). 中国科技论文在线 http://www.paper.edu.cn

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Fig. 3. Distribution, alignment, and age of craters across the Wudalianchi volcanic ﬁeld. Abbreviation of litho-stratigraphic units are as follows: Q—Quaternary sediments, N—Tertiary sediments, K—Cretaceous strata. The isotopic data are from Miu et al. (1983), Liu (1987), Gong (1997a,b) and Li et al. (1999). Unit of isotopic data is Ma.

The petrological evidence, major and trace element Rocks from the other nearby Quaternary volcanoes, such composition, and Sr–Nd–Pb isotopes suggest that the as the Keluo volcanic ﬁeld and the Xiaogulihe Volcano on K-rich volcanic rocks may have been derived from a the eastern side of the Dahinggan Mountain belt and the metasomatic EMI mantle (Fan et al., 1999), and that no Erkeshan Volcano to the south–southeast, have geochem- partial melts of crustal material were added to the magma ical and petrologic characteristics similar to the high- (Zhang et al., 1995; Fan et al., 1999). potassium alkali-basalt from the Wudalianchi volcanic ﬁeld,

Fig. 4. Spectrum of geochronological data from the Wudalianchi, the Keluo, and Erkeshan volcanoes. The data are from Miu et al. (1983), Liu (1987), Gong (1997a,b), and Li et al. (1999). 中国科技论文在线 http://www.paper.edu.cn

Y. Wang, H. Chen / Journal of Asian Earth Sciences 24 (2005) 419–431 423

including leucotephrite and many leucitic minerals (Table 1 and Fig. 4). Together they comprise the NNW-trending Quaternary basalt zone (see Fig. 2), known as the . Wudalianchi volcanic zone. Pattern and type of eruption Conical and shield Central, Conical

3. Geophysical evidence

Several Cenozoic uplifts and depressions occur around the Wudalianchi volcanic field. The Wudalianchi volcanic field is located in a triangular area bounded by different tectonic belts (Fig. 2). These are: (1) the WNW-trending Xiaohinggan Mountain belt, (2) the NNE-trending Dahing- gan Mountain belt, (3) the NE–NNE-trending Songliao rift- depression basin, and (4) the NE–NNE-trending Songwu on the surface Controlled structures ? NE-striking faults or fissureNE-striking faults or Central, fissure Conical Central–fissure, Graben. The geophysical features of the Moho beneath the Wudalianchi volcanic field are distinct from those in other regions of northeastern China and the eastern China continental interior (Ma, 1989; Heilongjiang Bureau of Geology and Mineral Resources, 1993; Dong, 1993). According to interpretations of the Bouguer gravity Miu et al. (1983), Liu (1987), Gong (1997a,b), and Li et al. (1999) anomalies (Heilongjiang Bureau of Geology and Mineral Resources, 1993), the Moho is 33.5–35.0 km deep on the southern side of the Wudalianchi area. On its western side, Main petrology Rich K, high alkalic basalt NS-striking wrench faults Central, Conical in the Dahinggan Mountain belt, the Moho is 45.0–42.5 km deep. On the northern and eastern sides, it is at a depth of 35.5–36.5 km. The Wudalianchi volcanic zone is associated with a NNW-trending wedge-shaped, slightly thinner crust (thickness less than 33.5–35.0 km), with a regional

O% crustal thickness of ,36 km. The updoming of the Moho 2

K interface in the Wudalianchi could be c. 2 km. Within the NE–NNE-trending belts, including the Wudalianchi area, the heat ﬂow can reach 3.55 HFU, although no hot springs have been found. The geothermal gradient in this region is less than 30 8C/km. , 1 cone 9.48% , 23 cones, 14 5.04–5.55% cones 4.28–5.91% High-K, alkalic basalt High-K, alkalic basalt

2 In and around the Wudalianchi volcanic ﬁeld, several 2 2 , 3 cones 5.23–5.50% K, alkalic basalt 2 ¼ . The age data of the Wudalianchi volcanic ﬁeld are from earthquakes with magnitudes between Ms 5.0 and Ms ¼ 5.3 have occurred in recent years (Chen and Xu, Scale and size of cone 13.8 km 350 km 800 km 1995). According to their focal mechanisms, these quakes are controlled mainly by WSW–ENE (mostly E–W)- compression. The focal mechanisms of deep-source and Gong (1997a,b) ^ crustal tectonic earthquakes are similar since they exhibit 0.09, 0.04 53 km ^ ^

^ consistent compressive stresses in an east–west direction (Zhao, 1990; Fu, 1996). According to MT investigations in 0.02–0.10 0.01–0.011 recent years (Zhan et al., 1999), there is a NNW (,3508)- ^ ^ 0.13, 0.36 0.08–1.27 0.02–0.98 striking, high-resistivity, lenticular-shaped body beneath the 0.22–0.20, ^ ^ ^

^ Wudalianchi volcanic ﬁeld, extending down to 15–20 km Eruption ages (Ma) and sequences 1.33 0.8 0.04, 0.43 0.02, 0.06 1719–1721 AD depth; it is 20 km wide in an east–west direction.

4. Regional geology and structural characteristics

The stratigraphic sequence around and below the Wudalianchi volcanic ﬁeld consists of (1) Carboniferous

The age data of the Keluo and Erkeshan are from epimetamorphic phyllites and slates, (2) Jurassic intermedi- Table 1 Volcanoes and their characteristics of the Wudalianchi volcanicVolcanic zone field or volcanoes Xiaogulihe Volcano Holocene Erkeshan Volcano 0.56 Wudalianchi volcanic field Keluo volcanic field 2.98 ate-acidic volcanic rocks, (3) Upper Cretaceous sandstones 中国科技论文在线 http://www.paper.edu.cn

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and clays (Nenjiang Formation), and (4) Upper Tertiary connected to the Songwu Graben along a northeast– sandy gravels (Songwu Formation). There are also many southwest line. granitic plutons which intruded during the Mesozoic period. Some Archean and lower Proterozoic metamorphic rocks 4.1. Nuomoer Fault are also exposed. Based on field geology and magnetotelluric soundings, several structural sections were compiled The Nuomoer Fault strikes E–W and cuts across the (Fig. 5). northern margin of the Songliao Basin. It is a southward- We mapped in detail (scale 1:100000) tectonic struc- dipping, high-angle, normal fault which cuts through the tures, such as NE-striking fractures and normal faults, on the Upper Jurassic–Lower Cretaceous deposits and is covered surface and beneath the Wudalianchi volcanic field and by N3 (Pliocene Series) clay and gravel sediments. It was adjacent areas, using also seismic reflection and MT formed before the Pliocene, but seems to have been inactive profiles. There are different types of faults across and during the eruptions of the Wudalianchi volcanic field around the volcanic craters. These include NE-striking (Heilongjiang Bureau of Geology and Mineral Resources, normal and dextral strike-slip faults, NW-striking trans- 1993). There are no volcanoes along the Nuomoer Fault but tensional faults, and E–W-striking normal faults. More it delineates the southern boundary of the Wudalianchi extensive regional faults around the Wudalianchi volcanic volcanic field. On magnetotelluric sounding profiles field are: (1) the E–W-striking Nuomoer (normal) Fault, (2) (Geophysical Exploration Company of Daqing Bureau of the NE-striking Songwu Graben and related faults, (3) the Petroleum Management, 1993), the Nuomoer Fault extends NNE-striking Nenjiang Fault, and (4) the NNE-striking down to a depth of 500 m. On the southern side of the fault, Dahinggan Mountain Front Fault (Fig. 2). An additional the Erkeshan Volcano erupted during the late Pleistocene. blind fault, the Central Daqing Fault, cuts through the Its petrologic and geochemical characteristics are eastern side of the Wudalianchi volcanic field and may be the same as those of the Wudalianchi volcanic field

Fig. 5. Geological proﬁles across the Wudalianchi volcanic ﬁeld. Abbreviations are as follows: NF—Nenjiang Fault, NMF—Nuomoer Fault, Q—Quaternary,

N-Q—Upper Tertiary–Quaternary, K1n—Nenjiang Formation of the Lower Cretaceous, K—Cretaceous, J—Jurassic. 中国科技论文在线 http://www.paper.edu.cn

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(Qiu et al., 1991; Fan et al., 1999). We believe that restricted the development of the Nenjiang listric fault eruptions of the Wudalianchi volcanic field are not related towards the north or northeast. According to magnetotellu- to any activation of the Nuomoer Fault. ric soundings and recent geophysical monitoring, the Xiaogulihe–Wudalianchi fault zone (X–WFZ) appears to 4.2. Songwu Graben and related faults be a set of NW–NNW-striking fissures or fractures at a depth of 15–20 km in the Wudalianchi and adjacent areas The Songwu Graben and associated NE-striking normal (Zhan et al., 1999). This deep-seated structure is oriented NNW 340–3508. The NNW-striking blind fault zone is faults lie on the eastern side of the Wudalianchi volcanic field. Boundary faults of the graben on the eastern and probably the eastern boundary of the Nenjiang listric fault at western sides are high-angle normal faults dipping west 15–20 km depth. and east, respectively. The graben is filled with sediments such as Upper Cretaceous clays, sandstones, and gravel- 4.4. Dahinggan Mountain Front Fault bearing sandstones, and is covered with Miocene sediments (Wan and Zhong, 1997). Neogene deposits cover faults in The Dahinggan Mountain Front Fault on the western side the region. The faults formed in the late Cretaceous but of the Nenjiang Fault is a NNE-striking normal fault were re-activated during the Tertiary. Local E–W-striking running along the mountain front. It exhibits thrust or N–S-striking normal or dextral strike-slip faults are characteristics, with normal faulting superimposed on limited to the graben. These faults, including the normal some exposed parts of the fault. It dips to the east at angles graben faults, cut across Paleozoic–Mesozoic granites, of 45–658. From field investigations we infer that the thrust Carboniferous–Permian strata and late Jurassic pyroclas- developed during the middle to late Jurassic time, followed tics. On magnetotelluric sounding profiles (Geophysical by normal faulting after the late Cretaceous; perhaps it was Exploration Company of Daqing Bureau of Petroleum accompanied by the uplift of the Dahinggan Mountain belt Management, 1992), the western boundary fault of the during the Cenozoic (Wan and Zhong, 1997). This fault, graben extends down to a depth of 5–6 km and the eastern which only affected the footwall of the Nenjiang Fault, did boundary fault to 8–9 km depth. No volcanic eruptions not control or affect the eruptions of the Wudalianchi occurred along or within the graben. The boundary faults volcanic field. of the graben did not control the ascent of magma beneath the Wudalianchi volcanic field. The graben faults were also not activated during the eruptions of the volcanoes in the 4.5. Central Fault of the Songliao Basin Pleistocene–Holocene. The Central Fault of the Songliao Basin (CFSB) is a NNE-striking blind fault, which is covered by early Tertiary 4.3. Nenjiang Fault and Quaternary sediments. It is a thrust fault dipping east on seismic-reflection profiles and cuts Upper Jurassic–Lower The NNE-striking Nenjiang Fault occurs along the Cretaceous rocks, but is covered, in turn, by Upper Nenjiang River on the western side of the Wudalianchi Cretaceous deposits. This means that the fault formed volcanic field. The fault dips E–ESE and is a normal fault on before the early Cenozoic. The regional evolution of the seismic reflection profiles but on the whole it is poorly Songliao Basin and characteristics of the fault indicate that exposed. In the northern part, the Xiaogulihe Volcano and the the CFSB may be related to the formation of the Yilan- Keluo volcanic field are located on the eastern side of the fault. Yitong Fault on its eastern side. The strike-slip movement On seismic reflection profiles, the Nenjiang Fault appears along the Yilan-Yitong Fault resulted in inversion structures to be a listric fault (Ye et al., 1993). It was active from the of the Songliao Basin during the late Cretaceous (Wang and late Mesozoic to the Tertiary (Zhang, 1983). At the northern Dou, 1997) when this thrust fault may have been margin of the Songliao Basin, it dips east or southeast–east transformed into a normal fault. On seismic reflection at a low angle and has a nearly flat interface in the lower part profiles, the hanging wall of the fault appears to be a normal of the fault (Ye et al., 1993). It extends from the eastern fault in its upper part, but with thrust features in its lower margin of the Dahinggan Mountain belt towards the eastern part. The CFSB extends down to 10–12 km depth. On the margin of the Songliao Basin. This fault cuts late Cretaceous eastern side of the Wudalianchi volcanic field, the fault is strata but is covered by Neogene rocks, principally Lower not obvious on magnetetolluric sounding profiles. Pleistocene and Pliocene deposits. Its most recent activity was during the early to middle Pleistocene (Wan and Zhong, 1997). The western side of the Nenjiang Fault was not 4.6. Structural characteristics of the Wudalianchi activated during stages of volcanic activity according to volcanic field river terrace investigations and seismic records. In the Wudalianchi and adjacent areas, metamorphic In the Wudalianchi volcanic field, the volcanic craters rocks and granites along a NW–NNW-trending zone occur within Pleistocene and Holocene sediments (Fig. 6) 中国科技论文在线 http://www.paper.edu.cn

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Fig. 6. Structural and geologic characteristics of the Wudalianchi volcanic ﬁeld.

which are partly covered by lacustrine–fluvial Quaternary 5. Tectonic stress changes and uplift of the crust sediments. Locally, some NE-striking fractures cut through the Baitushan (0.8–1.0 Ma) and Harbin (0.08–0.2 Ma) In the Wudalianchi volcanic field and adjacent areas, the formations (Miu et al., 1983) but they are covered by black tectonic stress evolved in several stages and was trans- clay sediments (2780 ^ 130 a) (see Figs. 5 and 6). The formed several times. During the middle–early Cenozoic, a faults and fractures are characterized by NW and SE dips at SE-extensional stress field developed in northeastern China high angles (mostly at 75–858, only a few at 25–408). In and its continental margin; it was accompanied by some parts, displacement of the hanging wall of the normal the eruption of alkaline basalts along NE–NNE-striking faults is only 30–35 cm on the fault surface. Even though normal faults, such as the Yilan-Yitong Fault and the there are some large-scale faults, the displacements along Mishan-Dunhua Fault, but there was no volcanic activity the normal faults are less than 1.2 m. in the Wudalianchi area. During the Miocene–Pliocene, 中国科技论文在线 http://www.paper.edu.cn

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the tectonic stress changed to NW–SE, and later E–W almost the same time during the last 50 years (Ma, 1989), compression. From Miocene to early Pleistocene time, a which implies that subduction of the West Pacific plate short-lived extensional stress field developed and produced under the Eurasian plate produced those earthquakes along normal faults in some areas. From the middle–late the continental margin and within the eastern China Pleistocene to Recent, the tectonic stress was compressional continent. The West Pacific plate subducts beneath the with an almost E–W direction but not of such a magnitude Eurasian plate at a rate of 80 mm/a in a direction towards that would result in orogenic belts. N2848 (Ma, 1989; Zhao, 1991). The subduction front of the The focal mechanisms of recent earthquakes also West Pacific plate has reached a depth of 500–600 km indicate an E–W compressive pattern; the fault planes beneath the eastern China continental margin. Furthermore, have two orientations: 17–30 and 278–3038. The main the deep-source earthquakes within the upper mantle of the compressive stress is in the 52–1168 sector with a mean continent also suggest that further towards the west, seismic direction of 848 during the last 50 years. sources are deeper than those occurring in the eastern areas During the eruptions of the Wudalianchi volcanic field in (Zhao, 1988, 1991). The subduction of the West Pacific the Pleistocene–Holocene, the tectonic stress environment plate may have suppressed magmatic activity under the was compressional rather than extensional. It is possible that continental margin, but affects the upper mantle within the the crustal stress field at that time was caused by the continent. This also seems to suggest that regionally or subduction of the West Pacific plate under the Eurasian locally, upwelling of the upper mantle took place beneath plate in a westerly direction since c. 3–2 Ma (Lallemand the continent, such as in the Wudalianchi volcanic field and and Jolivet, 1986; Maruyama and Seno, 1986; Liu et al., related areas. This probably was the main reason why 1989; Zhao, 1991; Otofuji et al., 1994; Meng et al., 1996). basaltic eruptions developed within the northeastern China From the middle Pleistocene on, the Wudalianchi continent, such as in the Wudalianchi area during the volcanic field and its adjacent areas, and indeed the whole Pleistocene–Holocene. northeastern China continent, has been uplifted unevenly. Some geologists have suggested that the eruptions of the According to investigations of river terraces, the uplift rate Wudalianchi volcanic field may have been influenced by was 0.04–0.07 mm/a (10–20 m) during the middle Pleis- the collision of the Indian–Asian plates during the tocene, and 0.03–0.11 mm/a (20–50 m) in the late Cenozoic (Ding, 1988; Gao, 1988). In fact, neither tectonic Pleistocene. In the Wudalianchi volcanic field, the surface stress nor regional structures support this view. According was uplifted 20–50 m during the Quaternary according to to strain monitoring of the motions of intraplate blocks in studies of the river terraces, in the Keluo volcanic field, the recent years (Ma, 1989) on the western side of the lower Pleistocene sediments were uplifted 30 m and middle Dahinggan Mountain belt, the intraplate movement rate is Pleistocene sediments by 10 m. At the same time, in the 0.1–1.5 mm/a towards the northeast, which implies that eastern parts of northeastern China, the uplift rate was even E–W compression from the collision of the Indian–Asian higher than in the Wudalianchi area; for instance, east of the plates is very weak. However, during the eruptions of the Yilan-Yitong Fault, the uplift rate was 0.07–0.09 mm/a Wudalianchi volcanic field, the regional compression was during the middle Pleistocene and 0.21–0.33 mm/a in the from east to west. This is not consistent with the late Pleistocene (Wang et al., 2003). characteristics of tectonic stress in China resulting from collision of the Indian–Asian plates which is characterized by a NNE–NE compressive component (Molnar and 6. Tectonic setting of the Wudalianchi volcanic field Tapponnier, 1975; Tapponnier et al., 1982). On the eastern during the Quaternary side of the Dahinggan Mountain belt, from the Laoyeling (near Yilan-Yitong Fault) to the west, the sites of the The Wudalianchi volcanic field developed in a specific basaltic eruptions migrated 25–30 km from east to west tectonic setting in northeastern China. The change of during the late Tertiary–Holocene. The average horizontal tectonic stress also indicates that during the eruptions of migration rate was 6.8–18 mm/a (Zhao, 1988). We suggest the Wudalianchi volcanic field from 1.33 Ma to 1721 AD, that the Wudalianchi volcanic field was basically not the crust, at least the upper-middle crust, was neither in an influenced by the collision between Indian and Asian plates extensional state, nor in an orogenic compressive state. The during the Cenozoic. timing of the volcanic eruptions (in a similar time interval) The eruptions of the Wudalianchi volcanic field from Erkeshan Volcano, the Wudalianchi volcanic field, correspond to subduction of the West Pacific plate under and the Xiaogulihe Volcano, all lying within a NNW- the Eurasian plate occurring since 3–2 Ma. Both the trending belt, does not support the interpretation that these Wudalianchi area and the West Pacific region were subject volcanoes were controlled by a hot-spot source (Wang, to the same tectonic stress, a compression from east to west 1997; Gong, 1997b; Fan et al., 1999) like the eruptions of (Maruyama and Seno, 1986; Lallemand and Jolivet, 1986; the southeastern Australian volcanoes (Pilger, 1982). Tokyo Institute of Technology, 1989; Zhao, 1991; Meng In northeastern China, the shallow (20–35 km) and deep- et al., 1996). However, the intraplate environment of the source (deeper than 300 km) earthquakes were generated at Wudalianchi volcanic field is far from the West Pacific plate 中国科技论文在线 http://www.paper.edu.cn

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subduction belt. In a normal subduction environment, terrane, but lava could not ascend to the surface although volcanism is commonly attributed to melting of the mantle NE-striking fractures and normal faults extend upwards to wedge, which is distinct from mantle upwelling. The shallow depths. inferred mantle upwelling and eruptions of the Wudalianchi If during the eruptions of the Wudalianchi volcanic field, volcanic field are related to E–W-compression resulting magma from the upper mantle was transferred to the surface from westward subduction of the West Pacific plate. along the NNW-striking deep-seated fault zone, then it Undoubtedly, magma for the Wudalianchi volcanic field erupted at places where NE-striking fractures and faults and adjacent volcanoes was derived from an intraplate existed. Combined with the distribution of other NNW- tectonic environment. In this region, the volcanic rocks do trending volcanoes in the region, but locally NE-trending, not have the characteristics of a typical rift environment, as evidence from structures on the surface suggests that the for example the East African rift zone where bimodal craters of the Wudalianchi volcanic field are along NE- basalt–rhyolite associations occur (Bailey, 1974). A rift striking faults or NE-striking fractures. These structures environment is therefore excluded by the compressive stress occurring at high angles had existed in the volcano area from east to west in the Wudalianchi volcanic field and when the volcanic eruptions were developed. It can be seen adjacent areas. in Fig. 7 that under different tectonic stress, the faults and eruptions of the volcanoes are distinctly inconsistent. Fig. 7a–d illustrate volcanic eruptions in the extensional 7. Discussion tectonic setting. Fig. 7f illustrates the possible tectonic stress and tectonic setting for the volcanic eruptions in the In the Wudalianchi volcanic field, local NE-striking Wudalianchi volcanic field. In an intraplate environment normal faults or fractures are the dominant structures. The with non-orogenic compressional but not extensional stress, relationship between the eruption of the volcanoes and the magmatic upwelling occurs along existing faults or structural features on the surface indicates that faults and fractures. The NNW-striking fracture zone at a depth of fractures influenced the NE-trending distribution of volca- 25–30 km influenced the eruption of the volcanoes, or at nic craters. Faults and fractures seem to have served as the least constrained the magma flowing through the middle- conduits for upwelling of the basaltic magma to the surface, lower crust to the upper crust. although NW- and NNW-striking faults did not constrain Recent studies have addressed crustal magma transfer the volcanic craters. Some NE-striking faults and fractures under different tectonic strain rates, crustal stretching are partly covered by basaltic lava. This proves that these features, and the role of open fractures in a brittle crust structures were formed before eruption of the Wudalianchi (Marquez et al., 2001; Jellinek and Depaolo, 2003; volcanic field. There are other faults distributed around the Nemeth and White, 2003). However, magma transfers volcanoes, but these are of small-scale (and probably did not from the continental margin towards intracontinental areas control the formation and eruption of the volcanoes). Field remains speculative. From petrologic and geochemical and geophysical investigations suggest that the eruptions of data, the basaltic magma was directly derived from the the basaltic magma were not controlled by three regional upper mantle within an intraplate tectonic setting. The faults, the Nuomoer Fault, the Dahinggan Mountain Front Wudalianchi area lies in the region of upwelling mantle. Fault, and the Songwu Graben. The northern and north- The distribution of volcanic craters does not conform to eastern termination of the Nenjiang listric fault strongly sites of mantle upwelling. This inconsistency between influenced the distribution of the Wudalianchi volcanic field mantle swells and the distribution of volcanic clusters or and its related volcanoes. It is possible that the northern and craters in northeastern China suggests that part of the northeastern edges of the Nenjiang listric fault, a NNW- upper mantle probably transferred or migrated from east to striking blind fracture zone, controlled the distribution of west, as deduced from suppressed magmatic activity by the Xiaogulihe-, the Keluo-, the Wudalianchi-, and the subduction of the West Pacific plate. The structural Erkeshan volcanoes. characteristics of the crust and upper mantle are not The Songliao Basin (Fig. 2) was a rift-depression in the consistent with the arrangement of the volcanic clusters Cretaceous, filled with andesitic pyroclastics and volcanic in a NE direction at the surface. Additionally, the product; it was a basin depression in the late Cretaceous and surrounding rocks of the Wudalianchi volcanic field, a large depression during the Cenozoic. So far, there is no such as metamorphic rocks, granites, and even the lower report of basaltic eruption in the Songliao Basin, and no crust were not melted by ascending magma from the upper appearance of the basaltic cones on seismic reflection mantle (Fan et al., 1999). The mantle swell suggests, profiles, although the Wudalianchi volcanic field and perhaps, pressure-release melting in the mantle. This may the Songliao Basin have similar characteristics such as the be the main reason why the Xiaogulihe, Keluo, Wudalianchi, Moho depth (Fig. 2). These features indicate that the and Erkeshan volcanoes are distributed in a NNW-extending NE–NNE-trending rift-depression or graben did not control volcanic belt and have similar characteristics. They were the eruptions of the Wudalianchi volcanic field. Perhaps the probably derived from the same magma reservoir (Qiu et al., volcanism is related to the NE–NNE-trending tectonic 1991; Fan et al., 1999). 中国科技论文在线 http://www.paper.edu.cn

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Fig. 7. Models of tectonic features related to eruptions of the Wudalianchi volcanic ﬁeld. (a–d) illustrate how structural features and volcanic eruptions developed in extensional tectonic settings; (e–h) show features in compressive tectonic settings.

8. Conclusions During the Miocene to Pleistocene, this region was not in a purely extensional or compressional state but rather in a The Wudalianchi volcanic field is characterized by transitional state. From the Pleistocene on, the tectonic olivine basalt derived directly from the upper mantle at a stress has been compressional but in the form of non- depth of 100–120 km at temperatures of ,1068–1100 8C orogenic compression induced by the westward subduction with no associated melting of crustal rocks. The eruptions of the West Pacific plate under the Eurasian plate since occurred in at least three stages. Fissure type to central type 3–2 Ma. The magma of the upper mantle seems to have eruptions developed during these eruption stages. The migrated from east to west. regional faults and the rift-depression which developed Based on (1) non-orogenic E–W compression, (2) from middle Jurassic to early Cenozoic time did not control intraplate basaltic eruptions, (3) existence of NE–NNE- the eruptions. Structural-, petrologic-, and tectonic features striking and high-angle normal faults or fractures on the support the interpretation that the Wudalianchi volcanic surface, and (4) NNW-striking fractures at a depth of field occurs within an intraplate tectonic environment. 15–20 km, it is suggested that the Wudalianchi volcanic 中国科技论文在线 http://www.paper.edu.cn

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field area is part of an intraplate, non-orogenic compressive Gong, J.S., Xu, Y.Q., 1997. Characteristics of petrology and geochemistry regime. Its dynamic feature corresponds to the westward of Wudalianchi Shihlunite. Heilongjiang Geology 8, 73–87.in Chinese with English abstract. subduction of the West Pacific plate under the eastern Asian Heilongjiang Bureau of Geology and Mineral Resources, 1993. Regional continent. Furthermore, volcanism in the Wudalianchi- and geology of Heilongjiang Province. Geological Publishing House, pp. adjacent areas has not noticeably been affected by the 260–346 (in Chinese). collision of the Indian–Asian plates in southwestern China. Hughes, C.J., 1982. Igneous petrology: development in Petrology 7. Elsevier, Amsterdam, pp. 1–551. Jellinek, A.M., Depaolo, D.J., 2003. A model for the origin of large silicic magma chambers: precursors of caldera-forming eruptions. Bulletin of Acknowledgements Volcanology 65, 363–381. Ji, F.J., Li, Q., 1998. The TL chronological evidence of the recent eruption in Wudalianchi volcanic cluster. Seismology and Geology 20, This research was supported by the China Seismological 302–304.in Chinese with English abstract. Bureau. The authors express appreciation to Mr. D.M. Guo Jilin Bureau of Geology and Mineral Resources, 1988. Regional geology of and J.Z. Ren (Seismological Bureau of Heilongjiang Jilin Province. Geological Publishing House, pp. 505–602 (in Chinese). Lallemand, S., Jolivet, L., 1986. Japan Sea: a pull-apart basin? Earth and Province) for help during the field work; Dr D.F. Zhu Planetary Science Letters 76, 375–389. (Institute of Daqing Petroleum Research, Heilongjiang Li, Q., Chen, W.J., Li, D.M., Ji, F.J., Ren, J.Z., Yang, S.L., 1999. A Province) for many seismic-reflection profiles and magne- chronological research on volcanic rocks from the Wudalianchi area. totelluric references. The authors are indebted to Dr J.L. 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