Perovskite and Baddeleyite from Kimberlitic Intrusions in the Tarim Large Igneous Province Signal the Onset of an End-Carboniferous Mantle Plume

Earth and Planetary Science Letters 361 (2013) 238–248

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Perovskite and baddeleyite from kimberlitic intrusions in the Tarim large igneous province signal the onset of an end-Carboniferous mantle plume

Dongyang Zhang a, Zhaochong Zhang a,n, M. Santosh a,b, Zhiguo Cheng a, He Huanga, Jianli Kang a,c a State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing 100083, China b Division of Interdisciplinary Science, Kochi University, Kochi 780-8520, Japan c Tianjin Institute of Geology and Mineral Resources, Tianjin 300170, China article info abstract

Article history: Several tens of kimberlitic pipes and dykes are exposed in the Wajilitag area in the western Tarim large Received 22 June 2012 igneous province. Here we report for the first time secondary ion mass spectrometric U–Pb age data on Received in revised form perovskite and baddeleyite grains in a kimberlitic pipe and a kimberlitic dyke from the Tarim Craton. 12 October 2012 The perovskite yielded a well-defined intercept age of 299.874.3 Ma, which is consistent with its Accepted 13 October 2012 corresponding concordia and 206Pb/238U ages, corrected for the common Pb contribution, of about Editor: T.M. Harrison Available online 22 November 2012 300 Ma. The baddeleyite separated from two kimberlitic samples from a dyke display identical concordia U–Pb ages of 300.874.7 Ma and 300.574.4 Ma. Our age data show that the kimberlitic Keywords: intrusions were emplaced at ca. 300 Ma, rather than in the late Permian as previously regarded. These kimberlitic intrusion new ages are slightly older than the eruption ages of Tarim flood basalts (291–273 Ma), offering a geochronology critical regional time marker for the onset of Permo-Carboniferous magmatism in the Tarim Craton. geochemistry mantle plume Detailed petrographic observations did not reveal any ultrahigh pressure mineral assemblage in the Tarim Wajilitag kimberlitic intrusions. Phlogopites from these intrusions show eNd(t) values of þ3.7 to þ4.2. The baddeleyites which are texturally primary and therefore inferred to have crystallized directly from

the kimberlitic magma, yield a range of eHf(t) from þ4.8 to þ8.7. These results combined with previously reported geochemical data, suggest that the Wajilitag kimberlitic intrusions were most likely derived from a moderately refractory and depleted subcontinental lithosphere mantle, metasomatized by subduction components associated with an early-middle Paleozoic convergent regime. The kimberlitic magma was generated by small-degree partial melting of the lithospheric mantle in response to the impingement of the Tarim mantle plume. Thus, our new geochronological data suggest the arrival of the mantle plume beneath the Tarim lithosphere at least 10 million years before the onset of Tarim ﬂood basalt volcanism. The end-Carboniferous Wajilitag kimberlitic intrusions, the oldest known phase associated with Carboniferous magmatism in the Tarim Craton, signals the initial magmatic pulse triggered by mantle plume impingement. & 2012 Elsevier B.V. All rights reserved.

1. Introduction source regions and components invoked for the magmas, including sub-continental lithospheric mantle (SCLM), convective asth- Kimberlites and related rocks have attracted considerable enospheric or sub-asthenospheric mantle and subducted oceanic interest not only because of their economic potential as the main crust (Ringwood et al., 1992; Tainton and McKenzie, 1994; Becker source of diamonds, but also due to their derivation from deep and le Roex, 2006; Paton et al., 2009; Zhang et al., 2010b; domains of the Earth’s mantle with a complex evolutionary Chalapathi Rao et al., 2011). Furthermore, kimberlites provide history, offering valuable insights into the composition of the information on the regional tectonics related to their emplace- sub-continental mantle (Coe et al., 2008; Zhang et al., 2010b; ment, particularly in the context of lithospheric extension (Bailey, Chalapathi Rao et al., 2011). However, owing to their hybrid 1993; Batumike et al., 2008; Tappe et al., 2008). Several kimber- nature and susceptibility to alteration, the origin of kimberlitic lite events around the world broadly coincide with the eruption of magmatism remains enigmatic with a great diversity of different continental ﬂood basalts now being attributed to impact of mantle plumes, which led many researchers to invoke mantle plumes for the genesis of kimberlitic magmatism (e.g., le Roex,

n 1986; Haggerty, 1994; Grifﬁn et al., 2005; Kumar et al., 2007; Corresponding author. Tel.: þ86 10 823 22195; fax: þ86 10 823 23419. E-mail addresses: [email protected], [email protected] Torsvik et al., 2010; Chalapathi Rao et al., 2011). Additional (Z.C. Zhang). support for this cause-and-effect relationship is provided by the

0012-821X/$ - see front matter & 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.epsl.2012.10.034 D.Y. Zhang et al. / Earth and Planetary Science Letters 361 (2013) 238–248 239 track-defining age progressions in kimberlite magmatism from as phlogopite Sr–Nd and baddeleyite Lu–Hf isotopic data for the North America, which coincides with the continental extension of Wajilitag kimberlitic intrusions. Our results provide tight con- the Great Meteor Hotspot track (Heaman and Kjarsgaard, 2000). straints on the emplacement age and plausible mantle source This scenario has been interpreted to be the passage of one or regions of the Wajilitag kimberlitic magma, which in turn have more mantle plumes through this region (Heaman and important implications for the geodynamic evolution in this Kjarsgaard, 2000). However, there are some other kimberlite region. events, such as those in southern Africa and North China, which do not correlate with mantle plume events, suggesting that not all kimberlite events require mantle plume activity and thus alter- 2. Geological setting native models, such as subduction of oceanic lithosphere and lithospheric extension, have also been considered (Haggerty, The TC, located in northwestern China, together with the North 1999; Moore et al., 2008; Jelsma et al., 2009; Chalapathi Rao China and Yangtze Cratons, defines the fundamental tectonic and Srivastava, 2009; Zhang et al., 2010b). The precise determina- collage of China. The Craton is surrounded by the Paleozoic tion of the emplacement age and a tight constraint on the nature Tianshan orogen to the north, the western Kunlun orogen to the of the mantle sources are prerequisites for understanding the south, and the Altyn Tagh orogen to the southeast (Fig. 1a, b). petrogenesis of kimberlites and the regional tectonic implications. The craton has a complex Precambrian basement consisting The kimberlitic intrusions exposed in the Wajilitag area within mainly of late Neoarchean-early Paleoproterozoic tonalitic- the northwestern part of Tarim Carton (abbreviated TC hereafter) trondhjemitic-granodioritic gneisses, late Paleoproterozoic to are located in the well-known Tarim large igneous province (LIP). early Neoproterozoic marine volcano-sedimentary rocks and late This rare occurrence provides an opportunity to evaluate the Neoproterozoic low grade metamorphic volcaniclastic rocks and genesis in the light of recent petrogenetic models developed for glacial deposits, mainly exposed along the margins of the craton other kimberlites worldwide, and to assess the importance of (Long et al., 2011b; Shu et al., 2011; Zhang et al., 2012a). The mantle plumes versus tectonic triggers as causal mechanisms for basement is discordantly overlain by a thick sequence of Phaner- kimberlitic intrusions in the TC. Preliminary studies have sug- ozoic shallow marine and terrestrial volcano-sedimentary strata gested that the Wajilitag kimberlitic intrusions formed during (Guo et al., 2005). Since most of the Phanerozoic rocks are buried late Permian (253 Ma) based on 40Ar/39Ar phlogopite dating, by a thick succession of Neogene aeolian deposits in the central although no information on the analytical procedures or details of part of the craton, the reconstruction of geologic and tectonic the data were reported (Li et al., 2001). Since kimberlitic rocks are elements are based on available exposures along the margins of mineralogically quite complex and are easily susceptible to the craton, together with drill core and geophysical data. The pre- chemical alteration, phlogopite is not an ideal mineral for dating Permian strata are mainly characterized by carbonates, lime- these rocks. Thus 40Ar/39Ar dating of phlogopite separates could stones and sandstones (Guo et al., 2005; Tian et al., 2010). The result in mixed ages or cooling/resetting ages, as groundmass and Permian strata are dominated by clastic rocks, muddy limestones xenocrystic phlogopite may be mixed, and is thus too imprecise to and volcanic rocks (Zhou et al., 2009). Recent studies have constrain the time of emplacement of kimberlitic intrusions revealed widespread early Permian (271.772.2–291.972.2 Ma; (Batumike et al., 2008; Li et al., 2011a). In addition, considering zircon LA-ICPMS, SHRIMP and Cameca U–Pb ages) basalts across the spatial association of the kimberlitic intrusions with the Tarim the Tarim region through drilling and seismic studies (e.g., Tian LIP, many workers broadly interpreted it as a part of the LIP and et al., 2010; Yu et al., 2011). It is estimated that the basalts and correlated it to mantle plume activity (e.g., Jiang et al., 2004; Li other cogenetic igneous units presently occupy an estimated area et al., 2011b). Unfortunately, no direct intrusive relationship of more than 300,000 km2 with a maximum total erupted basalt between the kimberlitic rocks and Tarim flood basalts has been volume of 3.0 105 km3, leading to the suggestion that the found, although several dolerite dykes cut across the kimberlitic Permian Tarim igneous units represent a typical LIP, termed the intrusions. Thus the accurate age of the kimberlite intrusions is Tarim LIP (e.g., Tian et al., 2010; Zhang et al., 2010a, 2010c, poorly constrained. In this contribution, we report for the first 2012d). Although many studies favor a link between the Tarim time precise isotope ages from perovskite and baddeleyite, as well LIP and early Permian mantle plume (e.g., Zhang et al., 2010a;

Fig. 1. (a) Main tectonic units of China. Abbreviations for terranes: WS: West Siberian; TM: Tuva-Mongolia, QD: Qaidam; QT: Qiangtang; GD: Gangdise; MA: Central Mongolis-Argun; BJ: Bureya-Jiamusi; SN: Songnen (modified from Wang et al., 2006). (b) Simplified tectonic map of the TC and surrounding areas showing the distribution of Permian basalts in Tarim. KD: Kuche depression; NTU: northern Tarim uplift; NTD: northern Tarim depression; CTU: central Tarim uplift; SWD: southwestern depression; STU: south Tarim uplift; SED: southeast depression (modified from Tian et al., 2010). (c) Simplified geological map of the Wajilitag area showing the location of kimberlitic intrusions (XJGMR (Xinjiang Bureau of Geology and Mineral Resources), 1984). 240 D.Y. Zhang et al. / Earth and Planetary Science Letters 361 (2013) 238–248

Tian et al., 2010; Qin et al., 2011), an alternative geodynamic 3. Petrography and geochemistry of the Wajilitag kimberlitic model postulated that the Tarim LIP may be linked to lithospheric intrusions extension accompanying passive continental rifting (Yang et al., 2007). The basement and Paleozoic strata are folded and faulted The petrographic features of the Wajilitag kimberlitic pipes by several major Phanerozoic deformational events, resulting in and dykes are markedly similar. The samples examined in this several roughly E-W trending uplifts and depressions (Fig. 1b). study show brecciated nature and inequigranular porphyritic Recent studies have revealed multistage ultramafic-mafic texture, which is characteristic of kimberlitic rocks. The rocks intrusions, mafic dyke swarms and granites exposed along the contain abundant clinopyroxenite, olivine clinopyroxenite, lesser margins of the TC (e.g., Zhang et al., 2008, 2010a, 2012b; Long dunite, and sparse amphibolite xenoliths (Supplementary file 1d– et al., 2011a; Ge et al., 2012). Voluminous Neoproterozoic (0.83– f). They also carry some fragments of the country rocks (mainly 0.62 Ga) ultramafic-mafic intrusions and dykes, as well as gran- sandstone), particularly in the samples collected from along the itoids, are considered to be products of a mantle plume within a edge of the intrusions (Supplementary file 1g). The xenolith suite continental rifting setting, which has been assigned to the shows variation in size and abundance, ranging from 45cmto breakup of the Rodinian continent (Zhang et al., 2009, 2011, 0.1–0.2 mm, and comprises up to 15 vol% of the rock in some 2012b; Zhu et al., 2011; Long et al., 2011a). Arc-like Silurian to places, although they can be extremely rare in other domains. The Devonian granites occur sporadically in the region and are euhedral to rounded macrocrysts and phenocrysts within the interpreted to have formed during the southward (present coor- kimberlitic rocks are dominated by clinopyroxene (10–15 vol%) dinates) subduction of the southern Tianshan ocean beneath the and subordinate olivine (5–10 vol%), with minor phlogopite TC (Jiang et al., 2001; Zhang and Sun, 2010; Ge et al., 2012). (5 vol%), amphibole (1–3 vol%) and apatite (1 vol%), and are The early Permian intrusive complexes, mafic dikes and granites, set in a fine- to micro-grained, interlocking groundmass domi- widely distributed in the northern Tarim, are also interpreted nated by clinopyroxene, phlogopite, olivine, apatite, perovskite, as a part of the Tarim LIP (Yang et al., 2007; Zhang et al., 2008, baddeleyite, garnet, spinel, rutile, magnetite, calcite and graphite 2010a). (Supplementary file 1e, g–l). These macrocrysts and phenocrysts The Wajilitag kimberlitic intrusions are located 40 km south- typically range in length from 0.5 to 5 mm, though some olivine east from the county of Bachu, in the western Tarim LIP, and is and amphibole grains are as large as 10 mm in their longest made up of several tens of pipe and dyke swarms that generated dimension. Some macrocrystal and phenocrystal grains appear some excitement in the past as potentially the first diamond- ragged, highly strained and display undulose extinction or bearing rock reported in Xinjiang (Fig. 1b, c; Du, 1983). kink banding, offering compelling evidence for an origin from The kimberlitic cluster trends NWW-SEE within an area of disaggregated xenoliths (Supplementary file 1i–l). Perovskite and 5km2 and is deeply weathered at the surface to greenish clay. baddeleyite are two important groundmass phases in the Waji- These kimberlitic pipes and dykes intruded the flat-lying and litag kimberlitic rocks. The groundmass perovskite is relatively metamorphosed continental clastic sequences of the upper Devo- abundant, with concentrations up to 3 vol%, while baddeleyite is nian Keziletag and Yimugangtawu Formations, and were in turn relatively rare in the groundmass. Perovskite occurs as brown and cut by late dolerite dykes (Supplementary file 1a–c). Among euhedral or rounded discrete grains, and also co-exists with these, pipe 1, with several microdiamonds separated so far, is clinopyroxene, phlogopite, magnetite and graphite (Fig. 2a). Bad- the most important diamondiferous pipe in the area and is an deleyite occurs as discrete crystals, but is more commonly oval-shaped body with dimensions of ca. 180 m 100 m (Du, associated with apatite and magnetite in late-stage mesostasis 1983; Su, 1991). The Wajilitag kimberlitic intrusions are spatially (e.g., calcite; Fig. 2b). Most baddeleyite grains are surrounded by associated with the Wajilitag early Permian Fe-Ti oxide ore- secondary zircon crystals (Fig. 2b). The presence of such an bearing ultramafic-mafic-syenitic intrusion that is composed of irregular zircon rim may suggest a reaction resulting from the clinopyroxenite, gabbro and syenite and was emplaced at ca. interaction of baddeleyite with deuteric fluids in the kimberlitic 274 Ma (Zhang et al., 2008), but no direct intrusive relationship melt (Heaman and LeCheminant, 1993). The majority of macro- between these rock units has been found in the region (Fig. 1b; Li crysts and phenocrysts and the groundmass are completely or et al., 2001, 2011b). Moreover, numerous felsic and mafic- partially altered to serpentine, chlorite, epidote, Fe-Ti oxides and ultramafic dykes (including some carbonatites) with variable carbonate minerals along their fractures, cleavage planes and strikes intrude either upper Devonian strata or the various crystal margins. Overall, the Wajilitag kimberlitic intrusions intrusions in the area mentioned above (Zhou et al., 2009; show unusually high modal abundance of phenocrysts and Zhang et al., 2010a). microphenocrysts of clinopyroxene and apatite but a low modal

Fig. 2. Back scattered electron (BSE) images of rocks from the Wajilitag kimberlitic intrusions, showing perovskite and baddeleyite crystals in the groundmass. Abbreviations: Cpx¼clinopyroxene; Ph¼phlogopite; Gar¼garnet; Hb¼hornblende; Cc¼calcite; Pv¼perovskite; Gr¼graphite; Mag¼magnetite; Gt¼garnet; Ap¼apatite; Bd¼baddeleyite; Zr¼zircon. D.Y. Zhang et al. / Earth and Planetary Science Letters 361 (2013) 238–248 241 abundance of olivine macrocrysts, relative to other archetypal kimberlites (e.g., Becker and le Roex, 2006; Coe et al., 2008; Chalapathi Rao and Srivastava, 2009). Systematic major and trace element investigations on the Wajilitag kimberlitic rocks were published in recent studies (Jiang et al., 2004; Li et al., 2010b; Supplementary file 2). These kimberlitic samples are all silica-undersaturated (SiO2o 39.84 wt%), and their MgO (15.63–21.52 wt%) and Mg# (0.69– 0.75) contents are slightly lower than those in typical kimberlites (Becker and le Roex, 2006; Coe et al., 2008; Chalapathi Rao and Srivastava, 2009). Primitive mantle-normalized trace element patterns for the kimberlitic samples show systematic negative troughs in Zr, Hf, Ti, Nb and Ta (Supplementary file 2). All samples are characterized by a negative slope of the rare earth elements (REE) patterns with significant light REE/heavy REE fractionation

[(La/Yb)N¼30–59]. The exact nature of the Wajilitag host magma is controversial and has been loosely described as kimberlite (Du, 1983; Wang and Su, 1987; Su, 1991), brecciated phlogopite olivine clinopyroxenite (Li et al., 2001) and kimberlitic brecciated peridotite (Bao et al., 2009). Based on mineralogy and geochemistry, Wang and Su (1987) proposed that the Wajilitag intrusions are similar to typical kimberlites with the exception of slightly lower MgO contents. However, in a more recent study, Bao et al. (2009) argued that the brecciated rock is not a typical kimberlite, and may be described as kimberlitic brecciated peridotite, because the rock does not contain pyrope-garnet and picro- ilmenite, which are common in most typical kimberlites. In conjunction with our petrographic observations and previous studies, we consider that the Wajilitag intrusions are more akin to kimberlite-like rocks based on the overall texture and the mineral assemblage, and we refer to them as kimberlitic rocks in this study.

4. Analytical techniques and results

The sampling and analytical methods, chemical compositions of the perovskite and baddeleyite, U–Pb analytical data on Fig. 3. Representative CL images of perovskite and baddeleyite grains from perovskite and baddeleyite, Sr–Nd analyses of phlogopite Wajilitag kimberlitic rocks. The fragmented nature of the grains is an artifact of and Lu–Hf data on baddeleyite are reported in Supplementary sample preparation. Circles indicate locations of analyzed sites, with numbers in 238 206 ﬁles 3–8, respectively. the circles representing spot numbers. The calculated U/ Pb age for each spot is given.

4.1. Chemical composition of perovskite and baddeleyite weighted average 206Pb/238U age of 299.274.3 (MSWD¼0.62; Fig. 4c). The perovskite grains show limited chemical variation (Supp- lementary file 4)andarecomposedofTiO (51.0–52.5 wt%) and CaO 2 4.3. Baddeleyite U–Pb geochronology (34.9–35.6 wt%) with minor FeO (1.2–2.4 wt%). The analyzed baddeleyites contain ZrO (95.1–97.1 wt%), with minor amounts of TiO 2 2 Baddeleyite grains analyzed in this study were separated from (0.41–2.0 wt%), Nb O (0.34–1.1 wt%) and HfO (0.27–1.0 wt%). 2 5 2 samples DW21-1 and DW21-4, and are mostly subhedral or frag- mental, ranging from 40 to 100 mminlength(Fig. 3). Twenty-one 4.2. Perovskite U–Pb geochronology spot analyses were conducted for each of the two samples analyzed, and the data are reported in the Supplementary file 6. The results Perovskite grains extracted from sample DW31-4, are mostly show variable U contents from 59 to 790 ppm and Th/U from 0.02 to euhedral and fresh and range in size from 15 to 50 mm(Fig. 3). 0.20, with the exception of one analysis (DW21-4@01) which yields a Twenty-three grains of perovskite were analyzed for U–Pb age, and relatively high Th/U¼0.37 due to a significantly high Th content thecompletedatasetisgivenintheSupplementary file 5.The (221 ppm) compared to other studied baddeleyite grains. Our data perovskites show relatively uniform uranium contents of yield identical concordia U–Pb ages of 300.874.7 Ma (MSWD¼1.6, 112729 ppm (1 SD) and Th/U ratio from 8.0 to 35.5. The scattered DW21-1) and 300.574.4 Ma (MSWD¼1.3, DW21-4) (Fig. 5). data points on the Tera-Wasserburg plot give a well-defined lower intercept age at 299.877.5 Ma and an upper intercept with 4.4. Phlogopite Sr–Nd isotope compositions 207Pb/206Pb¼0.8570.03 for the common-Pb composition (Fig. 4a). Using the terrestrial Pb (Stacey and Kramers, 1975)asanestimate The Sr–Nd isotopic data of phlogopite are listed in Supplementary of common-lead composition, the corrected data yield a concordia file 7. The data of the whole-rock kimberlitic samples (Jiang et al., U–Pb age of 299.874.3 Ma (Fig. 4b). 206Pb/238Uindividual 2004; Yu, 2009) are also shown for comparison. Because the dates, following by the 207Pb-based common-Pb correction, yield a phlogopite separates show markedly high calculated 87Rb/86Sr ratios 242 D.Y. Zhang et al. / Earth and Planetary Science Letters 361 (2013) 238–248

4.5. Baddeleyite Hf isotope compositions

The Lu–Hf analyses of baddeleyite were obtained using the same mounts which were previously used for U–Pb dating (Supplementary ﬁle 8). The weighted average value of calculated initial 176Hf/177Hf ratios for DW21-1 baddeleyite obtained as

0.28278770.000013 (2sm, n¼23, MSWD¼5.2), corresponds to eHf (t¼300 Ma) value of þ5.0 to þ8.7. The DW21-4 baddelyites have similar values which are 0.28276670.000013 (2sm, n¼21, MSWD¼5.2) and þ4.8 to þ8.5 (Fig. 6b). The two baddeleyite samples show single-stage Hf model ages of 579–735 Ma, similar to the single-stage Nd model ages of the studied phlogopites.

5. Discussion

5.1. Emplacement age of Wajilitag kimberlitic rocks

Most kimberlites are hybrid rocks and susceptible to secondary alteration, containing a significant proportion of crustal and mantle xenoliths, and therefore the precise determination of their timing of emplacement has remained a challenge (Mitchell, 1986; Li et al., 2010a, 2011a). Previous Ar–Ar isotopic analyses of phlogopite reported a plateau age of 252.7 Ma interpreted to represent the emplacement age of the kimberlitic intrusions (Li et al., 2001, 2011b). Because no information about the analytical details or detailed data were given in these reports, it is difficult to evaluate the quality of these data. Notably, the Ar–Ar age is incompatible with the primary magmatic zircon LA-ICPMS U–Pb age of 27276Ma for a later dolerite dyke in the same region (Li et al., 2007). As mentioned in a previous section, the dolerite dyke cuts across the kimberlitic intrusions and is therefore younger. In addition, post- magmatic alteration and/or crustal contamination processes are widespread in the kimberlitic intrusions. Therefore, the younger Ar–Ar plateau age of the kimberlitic intrusions is likely to be questionable. Moreover, previous studies suggested that most kimberlitic rock-borne clinopyroxenite xenoliths are rock fragments from the Wajilitag ultramafic-mafic intrusions exposed in the same region, because these clinopyroxenite xenoliths show similar field occurrence and close spatial correlation with the intrusive complex (Li et al., 2001; Jiang et al., 2004; Li et al., 2011b). If this proposal is correct, the kimberlitic intrusions should have been emplaced later than the ultramafic-mafic intrusion which formed at ca. 274 Ma (Zhang et al., 2008). However, our recent studies suggest that these clinopyroxene

grains from the clinopyroxenite xenoliths have TiO2 contents between 0.39 and 1.32 wt%, clearly distinct from most clinopyroxene grains from the ca. 274 Ma ultramaﬁc-maﬁc intrusive

Fig. 4. U–Pb age data for the Wajilitag perovskite. Error bars, error ellipses and complex (1.01–2.30 wt%; Li et al., 2012a; Supplementary file 9), uncertainties of weighted average ages are at 2s level. implying that there is no direct genetic relationship between them. The marked contrast in Sr–Nd isotopic composition between clinopyroxenite xenoliths and early Permian (3.703–4.190), their calculated initial 87Sr/86Sr ratios, which yielded ultramafic-mafic intrusive complex further suggest that they are unreasonably low ratios of less than or close to 0.700, may bear not cogenetic (Fig. 6a). Furthermore, no direct intrusive relation- very large uncertainties and are not meaningful to constrain their ship has been found between the kimberlitic intrusions and early petrogenesis (Wu et al., 2002). The age-corrected eNd(t)valuesof Permian ultramafic-mafic intrusion, suggesting that they are not phlogopites show little variation and range from þ3.66 to þ4.18 and cogenetic. single-stage Nd model ages are within 660–710 Ma, whereas the age- Perovskite is considered to be an excellent candidate to corrected eNd(t) values for whole rock samples are þ3.88 to þ5.63. determine the emplacement ages of kimberlites using the U–Pb The slightly wider range of eNd(t) for whole rocks may suggest that isotopic method because the mineral typically contains moderate the Nd isotope composition of these samples has been disturbed by amounts of uranium (50–300 ppm), is one of the late-phase crustal contamination and/or mantle entrainment, as also indicated minerals to crystallize from kimberlitic magma, and is rare in by the petrographic characteristics. Overall, the kimberlitic samples crustal rocks, precluding a xenocrystic origin (Heaman, 1989; (including phlogopite separates) are similar in Sr–Nd isotopic com- Heaman and LeCheminant, 2000; Batumike et al., 2008; Li et al., position to those of Group I kimberlites (Fig. 6a). 2010a). Unfortunately, many perovskite grains from kimberlites, D.Y. Zhang et al. / Earth and Planetary Science Letters 361 (2013) 238–248 243

Fig. 5. U–Pb age data for the Wajilitag baddeleyites. Error bars, error ellipses and uncertainties of weighted average ages are at 2s level.

Fig. 6. Diagram of ISr versus eNd(t) (a) and eHf(t) versus crystal age (b). Data sources: DM, MORB and OIB (Zindler and Hart, 1986); early Permian basalts (Zhou et al., 2009; Li et al., 2012b; Yu et al., 2011; Tian et al., 2010; Zhang et al., 2010a, 2012d); Wajilitag kimberlitic intrusion-hosted xenoliths (Jiang et al., 2004; Yu, 2009); Wajilitag ultramafic-mafic intrusion (Zhang et al., 2008; Li et al., 2012b); Late Neoarchean and early Paleoproterozoic basement (Zhang et al., 2008, 2012a). Fields for northern Tarim basement are based on data from Long et al. (2011a) and references therein. Data for Group I and Group II kimberlite fields are from Becker and le Roex (2006), Coe et al.

(2008), Chalapathi Rao et al. (2011) and references therein. Initial Sr isotope ratios and eNd(t) for these data in (a) recalculated to 300 Ma. such as those in the Mengyin kimberlites, were subjected to LeCheminant, 1993). Furthermore, these studied baddeleyite different levels of alteration after crystallization, which can reset grains have TiO2 contents between 0.41 and 2.0 wt%, quite the U–Pb isotopic system (Yang et al., 2009). In this study, the distinct from the high-Ti (up to 6 wt% TiO2) baddeleyite that narrow compositional range of the Wajilitag perovskites and the typically forms as a subsolidus reaction product along zircon– morphology of the crystals (Fig. 2a), suggest that these perovs- ilmenite interfaces (Heaman and LeCheminant, 1993, 2000). kites did not undergo any significant metasomatic alteration after All these features seem to preclude any possibility of subsolidus crystallization. Therefore, the perovskite U–Pb age of 300 Ma is reactions involved in the formation of the baddeleyite grains in considered to be the best estimate for the emplacement age of the Wajilitag kimberlitic intrusions. The last type of baddeleyite Wajilitag kimberlitic intrusions. which occurs as discrete crystals, has been described in Benfontein, Baddeleyite is rare in kimberlites and similar rock types but Mbuji-Mayi, Wemindji, Mengyin and Fuxian kimberlites (Scatena- can occur as diopside-baddeleyite-zirconolite rims on mantle Wachel and Jones, 1984; Heaman and LeCheminant, 1993; Scharer¨ zircon megacrysts, as subsolidus reaction products along zircon– et al., 1997; Wu et al., 2010; Li et al., 2011a; Zurevinski and ilmenite–rutile interfaces in the presence of calcite (Heaman and Mitchell, 2011). Considering the distinct habit and occurrence of LeCheminant, 1993), or as discrete crystals (Heaman and these baddeleyite grains, they are interpreted as xenocrysts or LeCheminant, 2000; Wu et al., 2010; Li et al., 2011a). The first primary groundmass crystals. The petrographic evidence suggests two baddeleyite types are interpreted as products formed by that most Wajilitag baddeleyite grains are typically small in size reaction between zircon megacrysts and kimberlite melt. In this and are devoid of any twinning, similar to baddeleyites crystallized case, baddeleyite forms fine idiomorphic crystals which are from kimberlitic magma (Scatena-Wachel and Jones, 1984; often oriented perpendicular to the zircon grain boundary. These Mitchell, 1986), although markedly different from the baddeleyite crystals commonly have dark central domains and light marginal mega-xenocrysts (up to 2 cm) from the Mbuji-Mayi kimberlite parts in BSE images, indicating a higher U content in rims than in (Heaman and LeCheminant, 1993; Scharer¨ et al., 1997). A xeno- cores (Heaman and LeCheminant, 1993; Li et al., 2011a). As noted crystic origin from accidental trapping of baddeleyite crystals from above, the Wajilitag baddeleyite grains occur as either individual the mantle can be also ruled out because no fragments of badde- grains or inclusions within late-stage mesostasis. We have not leyite were found in the kimberlitic rock-hosted mantle xenolith found any evidence showing reactions between zircon xenocrysts suite. The fact that these baddeleyites are similar in size to the other and kimberlite melt. Our analyses suggest that the U content in groundmass minerals and occur in close spatial association with the cores is higher than that of the rims, with no residual zircon some of the groundmass phases such as apatite and magnetite core, contrary to what formed by subsolidus reaction between (Fig. 2b) suggests that crystallization of these minerals was macrocrystic zircon and kimberlitic magma (Heaman and near-contemporaneous. Moreover, the Wajilitag baddeleyite is 244 D.Y. Zhang et al. / Earth and Planetary Science Letters 361 (2013) 238–248

2000) and recycled ancient subducted oceanic crust originating from the transition zone or lower mantle (Ringwood et al., 1992; Nowell et al., 2004; Gregorie et al., 2006; Paton et al., 2009). A key aspect of the controversy is whether kimberlites are derived from the lithosphere or the sub-lithosphere. The presence of ultra-deep (4400 km) majorite, ferropericlase, and magnesiowustite¨ inclusions in diamonds and ultra-deep xenoliths entrained within some kimberlites, globally with OIB-like isotopic signatures, led some researchers to suggest that they are convecting mantle melts derived from a transition zone source (Ringwood et al., 1992), or even from the core-mantle boundary (Haggerty, 1994). However, it is widely believed that the isotopic compositions of the kimberlitic rocks are an overprint of the depleted mantle source and the late metasomatic component, which is consistent with a two-stage model of kimberlite formation (Gibson et al., 1995; Becker and le Roex, 2006; Yang et al., 2009; Chalapathi Rao and Srivastava, 2009; Chalapathi Rao et al., 2012). These contrasting models show that the identiﬁcation of a mantle source for kimberlites based on isotope compositions is a formidable task. Indeed, no ultra-deep mineral assemblages (e.g., majorite, ferropericlase, magnesiowustite)¨ have been recognized in the Wajilitag kimberlitic intrusions, indicating that the rock was probably derived from the lithospheric mantle. Furthermore, petrographic observations indicate that almost all samples from the Wajilitag intrusions contain abundant Fig. 7. Histograms of available age data for the Permo-Carboniferous igneous magmatic phlogopite and hornblende. It seems reasonable to rocks in the TC. Data sources: Yu et al. (2011), Tian et al. (2010), Zhang et al. (2010a, 2012d), Qin et al. (2011) and references therein and this study as well as conclude that the primary magma of the Wajilitag intrusions was authors’ unpublished zircon dating results. enriched in volatiles, which might have been derived from a mantle source that had been metasomatized prior to the main melting event that produced the kimberlitic rocks. Additional remarkably pure, containing 95–97 wt% ZrO2, similar to those support for this argument is provided by the wide range in Hf described in a primary groundmass and that crystallized from isotopic compositions (eHf(t)¼þ4.76 to þ8.74) of the Wajilitag kimberlitic magmas (96–98 wt%; Scatena-Wachel and Jones, 1984; baddeleyites, which can be explained by derivation from the Zurevinski and Mitchell, 2011). Thus, the Wajilitag baddeleyite secondary enrichment of depleted mantle source (Scharer¨ et al., appears to be a late-stage primary groundmass phase that crystallized 1997). As noted above, the isotopic characteristics can be directly from the kimberlite magma. These baddeleyites therefore explained by the interaction between the depleted SCLM and an likely record the emplacement age of the kimberlitic magma. Two enriched metasomatic component. Thus, the broadly OIB-like baddeleyite samples from the kimberlitic rocks yielded consistent isotopic signatures of the Wajilitag kimberlitic rocks do not concordia U–Pb ages of 300.874.7 Ma and 300.574.4 Ma, which are necessarily mean that the metasomatic melt was derived from in good agreement with the perovskite U–Pb age of 301.174.1 Ma, the convective asthenospheric mantle. Instead, the negative Nb, further suggesting that the U–Pb age data provide a robust constraint Ta, Hf and Ti anomalies in the kimberlites are commonly inter- on the timing of emplacement of the kimberlitic rocks. preted to represent subduction-related signatures (Coe et al., In summary, the consistency of perovskite and baddeleyite U–Pb 2008; Chalapathi Rao et al., 2010), which are also applicable in ages reported in our study provides reliable and precise constraints to the Wajilitag kimberlitic rocks (Jiang et al., 2004; Li et al., 2010b). infer that the Wajilitag kimberlitic intrusions were emplaced at the We therefore consider that metasomatism of the kimberlitic Carboniferous/Permian boundary (300 Ma) rather than in the late source region was most likely related to subduction-related Permian as previously regarded. Interestingly, there is no clear record events rather than the effect of the convective (asthenospheric) of magmatic events in the TC from late Devonian to late Carbonifer- mantle. For mantle-derived rocks, if the Nd and Hf model ages are ous times (Jiang et al., 2001; Ge et al., 2012). This has been linked to a older than their formation age, it can be inferred that the magma change of the tectonic environment of the northern Tarim from an was derived from enriched mantle sources or was contaminated active continental margin to a passive continental margin during late by crustal materials (Wu et al., 2007; Chalapathi Rao et al., 2011). Devonian (Ge et al., 2012). The ca. 300 Ma Wajilitag kimberlitic Their minimum depleted-mantle Nd and Hf model age could intrusions represent the oldest known magmatic event of the correspond to the age of enrichment of the source (Gibson et al., Carboniferous magmatism, and is therefore estimate prominent 1995; Becker and le Roex, 2006; Chalapathi Rao et al., 2011). signal for the initiation of Permo-Carboniferous magmatic event in In the study, the Hf model ages (TDM ¼579–735 Ma) of badde- the TC (Fig. 7). leyites which are apparently older than their U–Pb ages, provide an important constraint on the timing of source enrichment. 5.2. Mantle source and processes Such an inference is also supported by the Nd model ages

(TDM ¼538–710 Ma). As these samples display extreme incompa- Although it has been widely advocated that the source regions of tible trace elements enrichment (Jiang et al., 2004; Li et al., kimberlitic rocks have a two-stage evolutionary history, comprising 2010b), their mantle Lu/Hf and Sm/Nd ratios may have changed initial melt-depletion with subsequent metasomatic enrichment in during magma genesis, even if this process involved partial incompatible elements, the origin of these rocks is still under debate. melting of pre-enriched source mantle (Gibson et al., 1995; A wide range of sources have been invoked for kimberlitic magmas, Chalapathi Rao et al., 2011). Again, considering that the Nd and including metasomatized SCLM (e.g., Tainton and McKenzie, 1994; Hf isotope signatures of Wajilitag kimberlitic rocks are depleted Becker and le Roex, 2006; Chalapathi Rao and Srivastava, 2009), relative to present-day Bulk Earth, perhaps the most plausible convecting (asthenospheric) mantle (Griffin et al., 2000; Price et al., inference is that the mantle enrichment age does not appear to be D.Y. Zhang et al. / Earth and Planetary Science Letters 361 (2013) 238–248 245 very old, such as late Neoproterozoic, and the metasomatic does not concur with a simple model of post-collisional litho- enrichment of their source region which may relate to an early- spheric extension to explain the large volume of the Tarim middle Paleozoic subduction event, occurred relatively recently. magmatic province, generated during a short period. Instead, we The regional geology of the northern TC also supports this argue for a petrogenetic model that envisages the formation of hypothesis. Some ophiolite me´langes and arc-like magmatic the Wajilitag kimberlitic rocks through melts generated from an events recognized along the northern margin of the TC have ages enriched SCLM, triggered by heat conducted and advected by around 600–418 Ma and 422–363 Ma, respectively, which sug- melts rising from the asthenosphere with high potential tem- gests an active convergent margin along the northern margin of perature. This essentially translates into a mantle plume on the the TC in the early-middle Paleozoic, with southward subduction basis of the following considerations. polarity (Ge et al., 2012 and references therein). We thus conclude Although some workers speculated that the Wajilitag kimber- that the Wajilitag kimberlitic intrusions were derived from litho- litic intrusions is a part of the Tarim LIP, and was also interpreted spheric mantle that has been metasomatized by subduction as being related to the early Permian mantle plume (e.g., Li et al., components prior to the partial melting. 2001, 2011b), the precise magmatic sequence of the Tarim LIP had not been identified because of the lack of precise ages for the 5.3. Implication for the Tarim mantle plume event Wajilitag kimberlitic intrusions. The reliable ages for the kimberlitic intrusions reported in this study indicate a significant pre- Although thermal perturbation of the ambient mantle is flood-basalt event, with magma output in the TC at least essential to trigger kimberlite magmatism, diverse geodynamic 10 million years before the massive outpouring of flood basalts models have been proposed for the trigger of kimberlite volcan- (Fig. 7). This argues against the existing models that consider the ism, involving subduction of oceanic lithosphere (e.g., Sharp, 1974; latter to mark the initial magmatic manifestation of a hot mantle Zhang et al., 2010b; Currie and Beaumont, 2011), impingement of plume. The lack of any obvious age progression for the various mantle plume (e.g., le Roex, 1986; Haggerty, 1994; Heaman and types of magmatic activity also poses limitations on the plume Kjarsgaard, 2000; Torsvik et al., 2010; Chalapathi Rao et al., 2011) model. Isotope geochronological data combined with detailed and regional lithospheric extension (e.g., Batumike et al., 2008; stratigraphic and volcanological studies have revealed a far more Tappe et al., 2008; Moore et al., 2008; Jelsma et al., 2009). complex igneous history for LIPs than previously considered. Two Recently, Han et al. (2011) demonstrated that the complex or three distinct pulses in magmatic output are observable in accretion-collision processes in the Xinjiang region were termi- many continental LIPs (e.g., North Atlantic, Parana´-Etendeka, nated during the late Carboniferous based on the synthesis of Kerguelen and Ontong Java; Gibson et al., 2006; Bryan and existing stratigraphic, geochronologic and geochemical results. Ernst, 2008). The hiatus between pulses varies from case to case, Thus, the TC and surrounding regions were in a post-collisional but can be a few to tens of millions of years. The relative extrusive or intraplate extensional settings during most of the late Carbo- volumes of pulses can be varied, and the volume of magma niferous and the Permian, with no evidence for the existence of a produced during the late pulse(s) may exceed the volume subduction system. Thus, a subduction setting for the formation of produced during the first stage. Furthermore, it has been pro- the kimberlite magma at this time is highly improbable. posed that the effect of a mantle plume on a cratonic lithosphere It has been widely accepted that the post-collisional litho- depends on the distance from the plume (Griffin et al., 2005; spheric extension occurred as a natural consequence of continen- Qin et al., 2011) and also on the thickness of the lithosphere tal collision between the Tarim block and Kazakhstan-Yili block (Gibson et al., 1995; Chalapathi Rao et al., 2011). When a mantle during late Carboniferous (325–316 Ma; Han et al., 2011; Zhang plume impinges on the base of a thick lithosphere, it may cause et al., 2012c). Han et al. (2011) proposed that a significant melting of the readily fusible volatile-rich parts of the metaso- geodynamic change from convergence to extension in the TC matized SCLM due to heat penetrating by conduction and advec- and adjacent tectonic units was initiated at 300 Ma, and tion. Production of some volatile-rich magmas such as kimberlites attributed to delamination of the thickened lithospheric root, could be the only surface expression of mantle melting as in the accompanied by passive upwelling of the asthenosphere, leading case of the Alto Paranaı´ba and Deccan LIPs (Gibson et al., 1995; to concomitant decompressional partial melting of the lower Chalapathi Rao et al., 2011). As noted above, the lithosphere at the crust and underlying lithosphere. This geodynamic scenario time of the kimberlitic magma generation may have been too seems likely for the generation of the small volume of the thick to allow the newly ascended, inflated head of a mantle Wajilitag kimberlitic magma. Yang et al. (2007) also used the starting-plume, to rise sufficiently high to trigger extensive model of lithospheric extension in the passive continental rifting melting of the lithosphere, and therefore only small-volume of to explain the intraplate bimodal magmatism in the NW Tarim volatile-rich magmas such as that of the Wajilitag kimberlitic during early Permian. However, the fact that the kimberlitic intrusions could be the only surface manifestation of SCLM intrusions carry microdiamonds indicates the existence of a thick melting. Likewise, the large time interval (10 Ma) that separates (4140 km) lithospheric mantle in the TC at the time of emplace- the early-phase Wajilitag kimberlitic magma activity from Tarim ment. Furthermore, some workers have proposed that the mod- flood basalts could be related to the widespread presence of a thick ern lithosphere in the TC has a thicknesses of about 140–180 km lithosphere at the time of initial impact of a plume. The extensive (Liu et al., 2004; An and Shi, 2006; Lei and Zhao, 2007). Thus, it effusion of magma may be deferred for several million years until the seems unlikely that large-scale delamination of the thick litho- magma chamber was sufficiently large and hot, the channel of the spheric mantle took place in the TC during most of the late plume magma was unblocked and lithospheric thickness becomes Carboniferous and Permian. Again, in accordance with the model thin enough to permit large-scale melting. Based on these arguments, of McKenzie and Bickle (1988), the composition and volume of it is further proposed that a mantle plume most likely triggered melts is directly related to the amount of lithospheric extension Wajilitag kimberlitic magmatism. If this is true, then it would imply and the potential temperature of the underlying asthenosphere. that the ca. 300 Ma Wajilitag kimberlitic intrusions mark the earliest Therefore, the large volume of Permo-Carboniferous magmatism magmatic manifestation associated with the initial impact of the in the TC would require a relatively large amount of lithospheric Tarim mantle plume. In other words, the Wajilitag kimberlitic extension above a mantle of normal potential temperature. magmatism may represent the arrival of the mantle plume at the However, there is no evidence of widespread late Carboniferous base of the Tarim lithosphere at least 10 million years before the and early Permian faulting in the TC. Thus, the available evidence onset of Tarim flood basalt volcanism that created the LIP. 246 D.Y. Zhang et al. / Earth and Planetary Science Letters 361 (2013) 238–248

Fig. 8. Simpliﬁed geodynamic model showing the evolution of the SCLM beneath the TC and the origin of the Wajilitag kimberlitic intrusions. (a) Early-middle Paleozoic and (b) End-Carbonijerous (300 Ma).

Fig. 8 illustrates our preferred geodynamic model involving (Nos. 2007BAB25B05 and 2011BAB06B02-04) and 111 Project the following events. (1) Subduction occurring along the northern (No. B07011). margins of TC during early-middle Paleozoic provided small- fraction of subduction components that invaded and metasomatized the overlying SCLM (Fig. 8a). (2) Small-degree partial Appendix A. Supplementary materials melting of this previously enriched SCLM by the impingement of a mantle plume produced the Wajilitag kimberlitic magmas Supplementary data associated with this article can be found in (Fig. 8b). Importantly, the data presented in this study demon- the online version at http://dx.doi.org/10.1016/j.epsl.2012.10.034. strate that there is no evidence of significant melt involvement from a convecting mantle in the Wajilitag kimberlitic source region. Therefore, it is likely that the major contribution of the References Tarim mantle plume might have been the heat to trigger partial melting of the metasomatized SCLM, albeit with no substantial An, M.J., Shi, Y.L., 2006. Review on lithospheric thickness research of the Chinese melt input to the Wajilitag magma system (Fig. 8b), similar to the continent. Earth Sci. Front. 13, 23–30. (in Chinese with English abstract). scenario reported for the kimberlites of central India (Chalapathi Bailey, D.K., 1993. Petrogenetic implications of the timing of alkaline, carbonatite and kimberlite igneous activity in Africa. South African J. Geol. 96, 67–74. Rao et al., 2011). Bao, P.S., Su, L., Zhai, Q.G., Xiao, X.C., 2009. Compositions of the kimberlitic brecciated peridotite in the Bachu area, Xijiang and its ore-bearing potential- ities. Acta Geol. Sin. 83, 1276–1301. (in Chinese with English abstract). Batumike, J.M., Griffin, W.L., Belousova, E.A., Pearson, N.J., O’Reilly, S.Y., Shee, S.R., 6. Conclusions 2008. LAM-ICPMS U–Pb dating of kimberlitic perovskite: Eocene–Oligocene kimberlites from the Kundelungu Plateau, D.R. Congo. Earth Planet. Sci. Lett. 267, 609–619. (1) SIMS perovskite and baddeleyite U–Pb dating shows that the Becker, M., le Roex, A.P., 2006. Geochemistry of South African on and off-craton Wajilitag kimberlitic intrusions were emplaced at the Carbo- Group I and II kimberlites: petrogenesis and source region evaluation. J. Petrol. niferous/Permian boundary (300 Ma) rather than in the late 47, 673–703. Bryan, S.E., Ernst, R.E., 2008. Revised definition of large igneous provinces (LIPs). Permian as previously proposed. Earth-Sci. Rev. 86, 175–202. (2) Based on detailed petrographic observations, in conjunction Chalapathi Rao, N.V., Dongre, A.N., Kamde, G., Srivastava, R.K., Sridhar, M., with Nd isotopic data of phlogopite separates and Hf isotope Kaminsky, F.E., 2010. Petrology, geochemistry and genesis of newly discovered compositions for baddeleyites, the Wajilitag kimberlitic rocks Mesoproterozoic highly magnesian, calcite-rich kimberlites from Siddanpalli, Eastern Dharwar craton, Southern India: products of subduction-related are inferred to have been derived from the subcontinental magmatic sources? Mineral. Petrol. 98, 313–328. lithospheric mantle, metasomatized during early-middle Chalapathi Rao, N.V., Lehmann, B., Mainkar, D., Belyatsky, B., 2011. Petrogenesis of Paleozoic by subduction components. the end-Cretaceous diamondiferous Behradih orangeite pipe: implication for mantle plume-lithosphere interaction in the Bastar craton, Central India. (3) The end-Carboniferous kimberlitic magmatism, which is Contrib. Mineral. Petrol. 161, 721–742. volumetrically minor relative to the Tarim flood basalts, Chalapathi Rao, N.V., Srivastava, R.K., 2009. Petrology and geochemistry of may represent the initial surface magmatic expression of diamondiferous Mesoproterozoic kimberlites from Wajrakarur kimberlite field, Eastern Dharwar Craton, Southern India: genesis and constraints on the impingement of a hot mantle plume related to the Tarim mantle source regions. Contrib. Mineral. Petrol. 157, 245–265. LIP, and is interpreted to constrain the arrival of mantle Chalapathi Rao, N.V., Wu, F.Y., Mitchell, R.H., Li, Q.L., Lehmann, B., 2012. plume beneath the thick lithosphere of Tarim. Mesoproterozoic U–Pb ages, trace element and Sr–Nd isotopic composition of perovskite from kimberlites of the Eastern Dharwar craton, southern India: distinct mantle sources and a widespread 1.1 Ga tectonomagmatic event. Chem. Geol. , http://dx.doi.org/10.1016/j.chemgeo.2012.04.023. Coe, N., le Roex, A., Gurney, J., Pearson, D.G., Nowell, G., 2008. Petrogenesis of Swartruggens and Star Group II kimberlite dyke swarms, South Africa: Acknowledgments constraints from whole rock geochemistry. Contrib. Mineral. Petrol. 156, 627–652. Currie, C.A., Beaumont, C., 2011. Are diamond-bearing Cretaceous kimberlites We are grateful to EPSL Editor Prof. Mark Harrison and three related to low-angle subduction beneath western North America? Earth referees for their constructive suggestions which helped in Planet. Sci. Lett. 303, 59–70. Du, P.L., 1983. Brief introduction of geological characters of kimberlite body at improving this manuscript. We thank Prof. Xian-Hua Li, Wajilitag in Bachu County, Xinjiang. Xinjiang Geol. 1, 55–64. (in Chinese with Dr. Qiu-Li Li, Dr. Yue-Heng Yang, Dr. Suo-han Tang and English abstract). Dr. Zhen-yu Chen for technical support. This research work was Ge, R.F., Zhu, W.B., Wu, H.L., Zheng, B.H., Zhu, X.Q., He, J.W., 2012. The Paleozoic northern margin of the Tarim Craton: passive or active? Lithos 142–143, 1–15. financially supported by 973 program (2012CB416806), 305 Gibson, S.A., Thompson, R.N., Day, J.A., 2006. Timescales and mechanisms of Project of the State Science and technology Program of China plume-lithosphere interactions: 40Ar/39Ar geochronology and geochemistry D.Y. Zhang et al. / Earth and Planetary Science Letters 361 (2013) 238–248 247

of alkaline igneous rocks from the Parana´–Etendeka large igneous province. Long, X.P., Yuana, C., Sun, M., Kroner,¨ A., Zhao, G.C., Wilde, S., Hu, A.Q., 2011a. Earth Planet. Sci. Lett. 251, 1–17. Reworking of the Tarim Craton by underplating of mantle plume-derived Gibson, S.A., Thompson, R.N., Leonardos, O.H., Dickin, A.P., Mitchell, J.G., 1995. magmas: evidence from Neoproterozoic granitoids in the Kuluketage area, NW The Late Cretaceous impact of the Trindade mantle plume: evidence China. Precambrian Res. 187, 1–14. from large-volume, mafic, potassic magmatism in SE Brazil. J. Petrol. 36, Long, X.P., Yuan, C., Sun, M., Xiao, W.J., Zhao, G.C., Zhou, K.F., Wang, Y.J., Hu, A.Q., 189–229. 2011b. The discovery of the oldest rocks in the Kuluketage area and its Gregorie, M., Rabinowich, M., Janse, A.J.A., 2006. Mantle mush compaction: a key geological implications. Sci. Chin. Earth Sci. 54, 342–348. to understand the mechanisms of concentration of kimberlite melts and McKenzie, D.P., Bickle, M.J., 1988. The volume and composition of melt generated initiation of swarms of kimberlite dykes. J. Petrol. 47, 631–646. by extension of the lithosphere. J. Petrol. 29, 625–679. Griffin, W.L., Natapov, L.M., O’Reilley, S.Y., van Achterbergh, E., Cherenkova, A.F., Mitchell, R.H., 1986. Kimberlites: Mineralogy, Geochemistry, and Petrology. Cherenkov, V.G., 2005. The Kharamai kimberlite field, Siberia: modification of Plenum Press, New York, p. 442. the lithospheric mantle by the Siberian trap event. Lithos 81, 167–187. Moore, A., Blenkinsop, T., Cotterill, F., 2008. Controls on post-Gondwana alkaline Griffin, W.L., Pearson, N.J., Belousova, E., Jackson, S.E., van Acterberg, E., O’Reilly, S.Y., volcanism in Southern Africa. Earth Planet. Sci. Lett. 268, 151–164. Shee, S.R., 2000. The Hf isotope composition of cratonic mantle: LAM-MC-ICP- Nowell, G.M., Pearson, D.G., Bell, D.R., Carlson, R.W., Smith, C.B., Kempton, P.D.M., MS analysis of zircon megacrysts in kimberlites. Geochim. Cosmochim. Acta 64, Noble, S.R., 2004. Hf isotope systematics of kimberlites and their megacrysts: 133–167. new constraints on their source regions. J. Petrol. 45, 1583–1612. Guo, Z.J., Yin, A., Bobinson, A., Jia, C.Z., 2005. Geochronology and geochemistry of Paton, C., Hergt, J.M., Woodhead, J.D., Phillips, D., Shee, S.R., 2009. Identifying the deep-drill-core samples from the basement of the central Tarim basin. J. Asian asthenospheric component of kimberlitic magmas from the Dharwar craton, Earth Sci. 25, 45–56. India. Lithos 112, 296–310. Haggerty, S.E., 1994. Superkimberlites: a geodynamic diamond window to the Price, S.E., Russell, J.K., Kopylova, M.G., 2000. Primitive magma from the Jericho Earth’s core. Earth Planet. Sci. Lett. 122, 57–69. Pipe, N.W.T., Canada: constraints on primary kimberlite melt chemistry. J. Haggerty, S.E., 1999. Diamond formation and kimberlite clan magmatism. Spec. Petrol. 41, 789–808. Publ.—Geochem. Soc. 6, 105–123. Qin, K.Z., Su, B.X., Sakyi, P.A., Tang, D.M., Li, X.H., Sun, H., Xiao, Q.H., Liu, P.P., 2011. Han, B.F., He, G.Q., Wang, X.C., Guo, Z.J., 2011. Late Carboniferous collision between SIMS zircon U–Pb geochronology and Sr–Nd isotopes of Ni–Cu-bearing mafic- the Tarim and Kazakhstan-Yili terranes in the western segment of the South ultramafic intrusions in eastern Tianshan and Beishan in correlation with flood Tian Shan Orogen, Central Asia, and implications for the Northern Xinjiang, basalts in Tarim Basin (NW China): constraints on a ca. 280 Ma mantle plume. western China. Earth-Sci. Rev. 109, 74–93. Am. J. Sci. 311, 237–260. Heaman, L.M., 1989. The nature of the subcontinentalmantle from Sr–Nd–Pb Ringwood, A.R., Kesson, S.E., Hibberson, W., Ware, N., 1992. Origin of kimberlites isotopic studies on kimberlitic perovskite. Earth Planet. Sci. Lett. 92, 323–334. their related magmas. Earth Planet. Sci. Lett. 113, 521–538. Heaman, L.M., Kjarsgaard, B.A., 2000. Timing of eastern North American kimberlite Scatena-Wachel, D.E., Jones, A.P., 1984. Primary baddeleyite ZrO2 in kimberlite magmatism: continental extension of the Great Meteor hotspot track? Earth from Benfontein, South Africa. Mineral. Mag. 48, 257–261. Planet. Sci. Lett. 178, 253–268. Scharer,¨ U., Corfu, F., Demaiffe, D., 1997. U–Pb and Lu–Hf isotopes in baddeleyite Heaman, L.M., LeCheminant, A.N., 1993. Paragenesis and U–Pb systematics of and zircon megacrysts from the Mbuji-Mayi kimberlite: constraints on the

baddeleyite (ZrO2). Chem. Geol. 110, 95–126. subcontinental mantle. Chem. Geol. 143, 1–16. Heaman, L.M., LeCheminant, A.N., 2000. Anomalous U–Pb systematics in mantle Sharp, W.E., 1974. A plate tectonic origin for diamond-bearing kimberlites. Earth derived baddeleyite xenocrysts from ^lle Bizard: evidence for high temperature Planet. Sci. Lett. 21, 351–354. radon diffusion? Chem. Geol. 172, 77–93. Shu, L.S., Deng, X.L., Zhu, W.B., Ma, D.S., Xiao, W.J., 2011. Precambrian tectonic Jelsma, H., Barnett, W., Richards, S., Lister, G., 2009. Tectonic setting of kimberlites. evolution of the Tarim Block, NW China: new geochronological insights from Lithos 112S, 155–165. the Quruqtagh domain. J. Asian Earth Sci. 42, 774–790. Jiang, C.Y., Mu, Y.M., Zhao, X.N., Bai, K.Y., Zhang, H.B., 2001. Petrology and Stacey, J.S., Kramers, J.D., 1975. Approximation of terrestrial lead isotope evolution geochemistry of an active continental-margin intrusive rock belt on the by a two-stage model. Earth Planet. Sci. Lett. 26, 207–221. northern margin of the Tarim plate. Reg. Geol. Chin. 20, 158–163. (in Chinese Su, L., 1991. A research on magmatic inclusions in minerals from kimberlite in with English abstract). Bachu County, Xinjiang, China. Bull. Xi’an Inst. Geol. Min. Res., Chinese Acad. Jiang, C.Y., Zhang, P.B., Lu, D.R., Bai, K.Y., 2004. Petrogenesis and magma source of Geol. Sci. 32, 15–33. (in Chinese with English abstract). the ultramafic rocks at Wajilitag region, western Tarim Plate in Xinjiang. Acta Tainton, K.M., McKenzie, D., 1994. The generation of kimberlites, lamproites and Petrol. Sin. 20, 1433–1444. (in Chinese with English abstract). their source rocks. J. Petrol. 35, 787–817. Kumar, A., Heaman, L.M., Manikyamba, C., 2007. Mesoproterozoic kimberlites in Tappe, S., Foley, S.F., Kjarsgaard, B.A., Romer, R.L., Heaman, L.M., Stracke, A., south India: a possible link to 1.1 Ga global magmatism. Precambrian Res. Jenner, G.A., 2008. Between carbonatite and lamproite- diamondiferous 154, 192–204. Torngat ultramafic lamprophyres formed by carbonate-fluxed melting of le Roex, A.P., 1986. Geochemical correlation between southern African kimberlites cratonic MARID-type metasomes. Geochim. Cosmochim. Acta 72, 3258–3286. and South-Atlantic hotspots. Nature 324, 243–245. Tian, W., Campbell, I.H., Allen, C.M., Guan, P., Pan, W.Q., Chen, M.M., Yu, H.J., Lei, J., Zhao, D., 2007. Teleseismic P-wave tomography and the upper mantle Zhu, W.P., 2010. The Tarim picrite-basalt-rhyolite suite, a Permian flood basalt structure of the central Tien Shan orogenic belt. Phys. Earth Planet. Inter. 162, from northwest China with contrasting rhyolites produced by fractional 165–185. crystallization and anatexis. Contrib. Mineral. Petrol. 160, 407–425. Li, C.N., Lu, F.X., Chen, M.H., 2001. Research on petrology of the Wajilitag complex Torsvik, T.H., Burke, K., Steinberger, B., Webb, S.J., Ashwal, L.D., 2010. Diamonds body in north edge in the Talimu basin. Xinjiang Geol. 19, 38–42. (in Chinese sampled by plumes from the core-mantle boundary. Nature 466, 352–355. with English abstract). Wang, H.Z., He, G.Q., Zhang, S.H., 2006. The geology of China and Mongolia. Earth Li, Q.L., Li, X.H., Liu, Y., Wu, F.Y., Yang, J.H., Mitchell, R.H., 2010a. Precise U–Pb and Sci. Front. 13, 1–13. (in Chinese with English abstract). Th–Pb age determination of kimberlitic perovskites by secondary ion mass Wang, Y.S., Su, L., 1987. A discussion on petrological and mineralogical character- spectrometry. Chem. Geol. 269, 396–405. istics of kimberlitic rock in Bachu County, Xinjiang, China and a comparison Li, Q.L., Wu, F.Y., Li, X.H., Qiu, Z.L., Liu, Y., Yang, Y.H., Tang, G.Q., 2011a. Precisely dating with some other kimberlitic occurrences. Bull. Xi’an Inst. Geol. Min. Res., Paleozoic kimberlites in the North China Craton and Hf isotopic constraints on the Chinese Acad. Geol. Sci. 15, 47–56. (in Chinese with English abstract). evolution of the subcontinental lithospheric mantle. Lithos 126, 127–134. Wu, F.Y., Li, X.H., Zheng, Y.F., Gao, S., 2007. Lu-Hf isotopic systematics and their Li, Y., Kong, P., Qian, Y.X., Zhang, K.Y., Zhang, M.L., Chen, Y., Cai, X.Y., You, D.H., applications in petrology. Acta Petrol. Sin. 23, 185–220. (in Chinese with 2007. Zircon U–Pb ages of the Early Permian magmatic rocks in the Tazhong- English abstract). Bachu region, Tarim basin by LA-ICP-MS. Acta Petrol. Sin. 23, 1097–1107. (in Wu, F.Y., Sun, D.Y., Li, H.M., Jahn, B.M., Wilde, S., 2002. A-type granites in Chinese with English abstract). northeastern China: age and geochemical constraints on their petrogenesis. Li, Y.Q., Li, Z.L., Sun, Y.L., Chen, H.L., Yang, S.F., Yu, X., 2010b. PGE and geochemistry Chem. Geol. 187, 143–173. of Wajilitag ultramafic cryptoexplosive brecciated rocks from Tarim Basin: Wu, F.Y., Yang, Y.H., Mitchell, R.H., Li, Q.L., Yang, J.H., Zhang, Y.B., 2010. In situ implications for petrogenesis. Acta Petrol. Sin. 26, 3307–3318. (in Chinese with U–Pb age determination and Nd isotopic analysis of perovskites from kim- English abstract). berlites in southern Africa and Somerset Island, Canada. Lithos 115, 205–222. Li, Y.Q., Li, Z.L., Chen, H.L., Yang, S.F., Yu, X., 2012a. Mineral characteristics and XJGMR (Xinjiang Bureau of Geology and Mineral Resources), 1984. Geological Map metallogenesis of the Wajilitag layered mafic-ultramafic intrusion and asso- of Wajilitag area in Bachu County, Xinjiang, Scale 1:5000 (in Chinese). ciated Fe–Ti–V oxide deposit in the Tarim large igneous province, northwest Yang, S.F., Li, Z., Chen, H., Santosh, M., Dong, C.W., Yu, X., 2007. Permian bimodal China. J. Asian Earth Sci. 49, 161–174. dyke of Tarim Basin, NW China: geochemical characteristics and tectonic Li, Z.L., Chen, H.L., Song, B., Li, Y.Q., Yang, S.F., Yu, X., 2011b. Temporal evolution of implications. Gondwana Res. 12, 113–120. the Permian large igneous province in Tarim Basin, Northwest China. J. Asian Yang, Y.H., Wu, F.Y., Wilde, S.A., Liu, X.M., Zhang, Y.B., Xie, L.W., Yang, J.H., 2009. In Earth Sci. 42, 917–927. situ perovskite Sr–Nd–Hf isotopic constraints on the petrogenesis of the Li, Z.L., Li, Y.Q., Chen, H.L., Santosh, M., Yang, S.F., Xu, Y.G., Langmuir, C.H., Chen, Z.X., Ordovician Mengyin Kimberlites in the North China Craton. Chem. Geol. 264, Yu, X., Zou, S.Y., 2012b. Hf isotopic characteristics of the Tarim Permian large 24–42. igneous province rocks of NW China: implication for the magmatic source and Yu, X., Yang, S.F., Chen, H.L., Chen, Z.Q., Li, Z.L., Li, Y.Q., 2011. Permian flood basalts evolution. J. Asian Earth Sci. 49, 191–202. from Tarim Basin, Northwest China: SHRIMP zircon U–Pb dating and geo- Liu, S.W., Wang, L.S., Li, C., Li, H., Han, Y.B., Jia, C.Z., Wei, G.Q., 2004. Thermal- chemical characterizations. Gondwana Res. 20, 485–497. rheological structure of lithosphere beneath the northern flank of Tarim Basin, Yu, X., 2009. Magma evolution and deep geological processes of early Permian western China: implications for geodynamics. Sci. Chin. Earth. Sci. 47, Tarim large igneous province. Ph.D. Thesis, Zhejiang University, Hangzhou, 659–672. pp. 68–69 (in Chinese with English abstract). 248 D.Y. Zhang et al. / Earth and Planetary Science Letters 361 (2013) 238–248

Zhang, C.L., Li, H.K., Santosh, M., Li, Z.X., Zou, H.B., Wang, H.Y., Ye, H.M., 2012a. Zhang, H.F., Zhou, M.F., Sun, M., Zhou, X.H., 2010b. The origin of Mengyin and Precambrian evolution and cratonization of the Tarim Block, NW China: Fuxian diamondiferous kimberlites from the North China Craton: implication petrology, geochemistry, Nd-isotopes and U–Pb zircon geochronology from for Palaeozoic subducted oceanic slab-mantle interaction. J. Asian Earth Sci. Archaean gabbro-TTG-potassic granite suite and Paleoproterozoic meta- 37, 425–437. morphic belt. J. Asian Earth Sci. 47, 5–20. Zhang, Y., Sun, X.M., 2010. 40Ar/39Ar dating on the Late Devonian volcanic rocks Zhang, C.L., Li, X.H., Ye, H.M., 2008. Permian layered ultramafic-mafic-syenite from Kuruktag and its implications for regional geology, Xinjiang. Acta Petrol. intrusive complex in western Tarim block, NW China: genetically related to a Sin. 26, 302–308. (in Chinese with English abstract). Permian mantle plume under Tarim? J. Geol. 116, 263–281. Zhang, Y.T., Liu, J.Q., Guo, Z.F., 2010c. Permian basaltic rocks in the Tarim basin, Zhang, C.L., Xu, Y.G., Li, Z.X., Wang, H.Y., Ye, H.M., 2010a. Diverse Permian NW China: implications for plume–lithosphere interaction. Gondwana Res. 18, magmatism in the Tarim Block, NW China: genetically linked to the Permian 596–610. Tarim mantle plume? Lithos 119, 537–552. Zhang, Z.Y., Zhu, W.B., Shu, L.S., Su, J.B., Zheng, B.H., 2009. Neoproterozoic ages of Zhang, C.L., Yang, D.S., Wang, H.Y., Takahashi, Y., Ye, H.M., 2011. Neoproterozoic the Kuluketage diabase dyke swarm in Tarim, NW China, and its relationship ultramafic-mafic layered intrusion in Quruqtagh of northeastern Tarim Block, to the breakup of Rodinia. Geol. Mag. 146, 150–154. NW China: two phases of mafic igneous activity of different mantle sources. Zhou, M.F., Zhao, J.H., Jiang, C.Y., Gao, J.F., Wang, W., Yang, S.H., 2009. OIB-like, Gondwana Res. 19, 177–190. Zhang, C.L., Zou, H.B., Wang, H.Y., Li, H.K., Ye, H.M., 2012b. Multiple phases of the heterogeneous mantle sources of Permian basaltic magmatism in the western Neoproterozoic igneous activity in Quruqtagh of the northeastern Tarim Block, Tarim Basin, NW China: implications for a possible Permian large igneous NW China: interaction between plate subduction and mantle plume? province. Lithos 113, 583–594. Precambrian Res. http://dx.doi.org/10.1016/j.precamres.2011.08.005. Zhu, W.B., Zheng, B.H., Shu, L.S., Ma, D.S., Wan, J.L., Zheng, D.W., Zhang, Z.Y., Zhu, X.Q., Zhang, D.Y., Zhang, Z.C., Encarnacio´ n, J., Xue, C.J., Duan, S.G., Zhao, Z.D., Liu, J.L., 2011. Geochemistry and SHRIMP U–Pb zircon geochronology of the Korla mafic 2012c. Petrogenesis of the Kekesai composite porphyry intrusion, western dykes: constrains on the Neoproterozoic continental breakup in the Tarim Block, Tianshan, NW China: implications for metallogenesis, tectonic evolution and northwest China. J. Asian Earth Sci. 42, 791–804. continental growth during Late Paleozoic time. Lithos 146–147, 65–79. Zindler, A., Hart, S.R., 1986. Chemical geodynamics. Annu. Rev. Earth Planet. Sci. Zhang, D.Y., Zhou, T.F., Yuan, F., Jowitt, S.M., Fan, Y., Liu, S., 2012d. Source, Lett. 14, 493–571. evolution and emplacement of Permian Tarim Basalts: evidence from U–Pb Zurevinski, S.E., Mitchell, R.H., 2011. Highly evolved hypabyssal kimberlite sills dating, Sr–Nd–Pb–Hf isotope systematics and whole rock geochemistry of from Wemindji, Quebec, Canada: insights into the process of flow differentia- basalts from the Keping area, Xinjiang Uygur Autonomous region, northwest tion in kimberlite magmas. Contrib. Mineral. Petrol. 161, 765–776. China. J. Asian Earth Sci. 49, 175–190.