Typical Oxygen Isotope Profile of Altered Oceanic Crust Recorded in Continental Intraplate Basalts

Journal of Earth Science, Vol. 28, No. 4, p. 578–587, August 2017 ISSN 1674-487X Printed in China DOI: 10.1007/s12583-017-0798-5 Invited Article Typical Oxygen Isotope Profile of Altered Oceanic Crust Recorded in Continental Intraplate Basalts Huan Chen 1, 2, 3, Qun-Ke Xia *1, Etienne Deloule4, Jannick Ingrin3 1. School of Earth Sciences, Zhejiang University, Hangzhou 310027, China 2. School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, China 3. UMET, UMR CNRS 8207, Université de Lille1, 59655 Villeneuve d’Ascq, France 4. CRPG, UMR 7358, CNRS Université de Lorraine, 54501 Vandoeuvre-les Nancy, France Huan Chen: http://orcid.org/0000-0003-3524-4163; Qun-Ke Xia: http://orcid.org/0000-0003-1256-7568 ABSTRACT: Recycled oceanic crust (ROC) has long been suggested to be a candidate introducing enriched geochemical signatures into the mantle source of intraplate basalts. The different parts of oceanic crust are characterized by variable oxygen isotope compositions (δ18O=3.7‰ to 13.6‰). To trace the signatures of ROC in the mantle source of intraplate basalts, we measured the δ18O values of clinopyroxene (cpx) phenocrysts in the Cenozoic basalts from the Shuangliao volcanic field, NE China using secondary ion mass spectrometer (SIMS). The δ18O values of the Shuangliao cpx phenocrysts in four basalts ranging from 4.10‰ to 6.73‰ (with average values 5.93‰±0.36‰, 5.95‰±0.30‰, 5.58‰±0.66‰, and 4.55‰± 0.38‰, respectively) apparently exceed those of normal mantle-derived cpx (5.6‰±0.2‰) and fall in the typical oxygen isotope range of altered oceanic crust. The δ18O values display the negative correlations with the Eu, Sr anomalies of whole rocks and erupted ages, demonstrating that (1) the ROC is the main enriched component in the mantle source of the Shuangliao basalts and (2) the contributions of ROC varied with time. The basalt with the lowest δ18O value is characterized by a significant K positive anomaly, 18 highest H2O/Ce and Ba/Th ratios, suggesting that the mantle source of basalts with low δ O can also include a water-rich sediment component that may be the trigger for partial melting. Considering the continuous subduction of the Pacific slab, the temporal heterogeneity of the source components is likely to be caused by the Pacific slab subduction. KEY WORDS: continental basalt, oxygen isotope, recycled oceanic crust, Pacific slab, eastern China. 0 INTRODUCTION al., 2012; Huang and Zhao, 2006). Therefore, the recycled The small-volume continental intraplate basalts are widely oceanic crust (ROC) has increasingly been suggested to be one spread in each continent (e.g., eastern China, western Africa, of the major enriched components in their mantle sources western US, western/central Europe, southeastern Australia), and (Chen et al., 2017, 2015a, b; Liu et al., 2015a, b; Wang et al., the genesis of these basalts are hotly debated (Farmer, 2014). 2015; Xu et al., 2012; Kuritani et al., 2011). Especially in eastern China, the continental basalts extend from Oxygen isotope exchanges between oceanic crust and the northernmost to the southernmost, along the continental mar- seawater occurs during hydrothermal alteration (Muehlenbachs gin (Lei et al., 2013), which form an important part of the volcano and Clayton, 1976). Because the temperature of hydrothermal belt of the western circum-Pacific rim (Fig. 1). These basalts are alteration varied from the lower to the upper part of the oceanic characterized by typical ocean island basalt (OIB)-like trace ele- crust, different layers of altered oceanic crust acquired distinct ment patterns and Sr-Nd-Pb isotopic compositions, which indicate oxygen isotope compositions through hydrothermal exchange the presence of enriched components in the mantle sources (e.g., with seawater (Taylor, 1974). The general profile of oxygen Chen et al., 2007; Zhang et al., 2001; Jung and Hoernes, 2000; isotope compositions of altered oceanic crust exhibits δ18O Marzoli et al., 2000; Zou et al., 2000; Rogers et al., 1995; Zhou values higher than the normal mantle in the upper part and δ18O and Armstrong, 1982). Recently, seismic tomography studies have values lower than the normal mantle in the lower part (Fig. 2) revealed the presence of recycled oceanic slab in the Earth’s man- (Gao et al., 2006; Eiler, 2001; Hoffman et al., 1986; Gregory tle (e.g., Liu et al., 2017; Fichtner and Villaseñor, 2015; Wei et and Taylor, 1981). Therefore, oxygen isotope is a powerful tool to trace ROC component in the mantle source of continental *Corresponding author: [email protected] intraplate basalts (e.g., Chen et al., 2017; Liu et al., 2015a, b; © China University of Geosciences and Springer-Verlag Berlin Wang et al., 2015; Kokfelt et al., 2006; Eiler et al., 2000; Putlitz Heidelberg 2017 et al., 2000; Woodhead et al., 1993). The Shuangliao volcanic field is located in the south part Manuscript received May 24, 2017. of NE China, which consists of eight volcanoes. Xu et al. (2012) Manuscript accepted July 19, 2017. and Chen et al. (2015b) conducted detailed geochemical studies Chen, H., Xia, Q.-K., Deloule, E., et al., 2017. Typical Oxygen Isotope Profile of Altered Oceanic Crust Recorded in Continental Intraplate Basalts. Journal of Earth Science, 28(4): 578–587. doi:10.1007/s12583-017-0798-5. http://en.earth-science.net Typical Oxygen Isotope Profile of Altered Oceanic Crust Recorded in Continental Intraplate Basalts 579 120º 130ºE Cenozoic Marine sediments basalt Russia Pillow basalts 0 450 km Dikes 50ºN Mongolia Fushun- Tan-Lu fault Mishan fault N-MORB Songliao Basin DTGL Shuangliao Gabbros NE China Changbaishan fold belts Beijing Sea of Japan Whole rock 40º North China 3456789102030 18 Craton δ O (‰) (b) Figure 2. Typical oxygen isotope profile of an altered sediment-covered oce- Qinling-Dabie belt anic crust. The blue curve shows the average δ18O values of the altered oceanic Tan-Lu fault crust. The data for the oceanic crust are based on the Samail ophiolite (Taylor, Shanghai 1974), the δ18O values of marine sediments are from Eiler (2001). Yangtze Craton East China Sea 18 30º Here, we measured the δ O values of the clinopyroxene (cpx) phenocrysts in Cenozoic basalts from the Shuangliao vol- Taibei canic field using secondary ion mass spectrometry (SIMS). The typical oxygen isotope profile of altered oceanic crust in the SE China fold system Guangzhou Shuangliao basalts clearly confirms that the recycled oceanic slab was present in the mantle source. The mass balance calculation South China Sea demonstrates that a water-rich sediment component may also be involved in the mantle source although the basalts display the 20º 18 18 (a) lowest δ O, in contrast with intuitively expected elevated δ O. Combined with the erupted ages, the changing source components 110º 120ºE is likely to be caused by the ongoing Pacific slab subduction. (b) N 1 GEOLOGICAL BACKGROUND AND SAMPLES Northeast China (NE China) lies in the Xing’an-Mongolia orogenic belt (XMOB), which belongs to the east part of the Pa- Xinkai River Songliao BasinChangling leozoic Central Asian orogenic belt (Fig. 1a). It is composed of several minor blocks (e.g., Erguna, Xing’an, Songliao, Jiamusi) Changchun Xiaohalabashan amalgamated during subduction and collision among the Siberian Bolishan Dahalabashan Xiliao River Craton, the North China Craton (NCC) and the Pacific Plate (Li, Tongliao Datuerjishan Shitoushan Bobotushan Dongliao 2006; Sengör and Natal’in, 1996; Sengör et al., 1993). The tectonic Xiaotuerjishan Shuangliao Aobaoshan River evolutions of NE China mainly include the closure of the Paleo- Yitong 050 km Asian Ocean, the amalgamation of several minor blocks and the subduction of the Pacific Plate since Late Mesozoic (Maruyama et Figure 1. (a) Simplified tectonic divisions and the distribution of the Ceno- al., 1997; Sengör and Natal’in, 1996; Sengör et al., 1993). zoic intraplate basalts in eastern China as well as the location of the The Shuangliao volcanic field is located in the southeast of Shuangliao volcanic field (modified from Xu et al., 2012); (b) the distribu- the Songliao Basin, which consists of eight volcanoes: Ao- tion and sample locations (red stars) of the Shuangliao basalts. DTGL. baoshan (ABS), Bobotushan (BBT), Bolishan (BLS), Shitoushan Daxin’anling-Taihangshan Gravity Lineament. (STS), Dahalabashan (DHLB), Xiaohalabashan (XHLB), Da- tuerjishan (DTEJ) and Xiaotuerjishan (XTEJ) (Fig. 1b). Seismic including Ar-Ar erupted ages, major and trace elements, tomography has shown the presence of a stagnant subducted Sr-Nd-Pb isotopes and H2O content on these basalts. The Pacific slab in the mantle transition zone beneath the Shuangliao Shuangliao basalts are characterized by high Fe2O3, HIMU volcanic field (Liu et al., 2017; Wei et al., 2012; Huang and Zhao, (high µ)-type trace element patterns and significant correlations 2006). The Shuangliao basalts vary from basanite, alkaline oli- between Ba/Th, Ce/Pb and H2O/Ce ratios, which suggested that vine basalt, and transitional basalts to dolerites (Chen et al., the recycled oceanic slab component may be involved in the 2015b; Xu et al., 2012). Abundant peridotite xenoliths were car- mantle source and the contributions of these source components ried out by the eruption of these volcanoes (Yu et al., 2009). The changed with time. Hence, this area is an appropriate place to Ar-Ar dating results have shown that all volcanoes erupted be- trace oxygen isotopic signatures of ROC in continental basalts. tween 51.0 and 41.6 Ma (Xu et al., 2012). Volcanic cones with 580 Huan Chen, Qun-Ke Xia, Etienne Deloule and Jannick Ingrin high alkalinity erupted between 51 and 48.5 Ma, while transi- 2010; Valley and Kita, 2009; Eiler et al., 1997). tional or subalkaline cones erupted between 43.0 and 41.6 Ma, For the deviation caused by transport and detection proc- indicating that the alkalinity of the Shuangliao volcanic rocks esses, the fractionation factor (δ18O*) could be calculated from 18 decreased with time (Xu et al., 2012).

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