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Journal of Geodynamics 49 (2010) 39–53

Contents lists available at ScienceDirect

Journal of Geodynamics

journa l homepage: ht tp : / /www.e lsev ier .com/ locate / jog

antle dynamics of the Paleoproterozoic North China Craton: A perspectiveased on seismic tomography

. Santosha,∗, Dapeng Zhaob, Timothy Kuskyc

Department of Natural Environmental Science, Faculty of Science, Kochi University, Kochi 780-8520, JapanDepartment of Geophysics, Tohoku University, Sendai 980-8578, JapanThree Gorges Geohazards Research Center, and State Key Laboratory for Geological Processes and Mineral Resources, China University of Geosciences, Wuhan 388, China

r t i c l e i n f o

rticle history:eceived 19 June 2009eceived in revised form1 September 2009ccepted 21 September 2009

eywords:orth China Cratonantle tomographyantle dynamics

ectonicsectospherealeoproterozoicolumbia

a b s t r a c t

We investigate the mantle dynamics beneath the North China Craton (NCC) and surrounding regionsbased on a synthesis of recent P-wave mantle tomographic data down to depths of 600–800 km andtheir correlation with the surface geological features, with particular reference to the Paleoproterozoictectonic events associated with the incorporation of the NCC within the Columbia supercontinent amal-gam. From the tomographic images, we identify a hot corridor in the mantle transition zone beneath thecentral region of the Western Block of the NCC sandwiched between two cold corridors. This scenario issimilar to the donut-shaped high-velocity anomaly surrounding a region of low-velocity anomaly in thelowermost mantle under the Pacific and suggests that the cold regions might represent slab graveyardswhich provide the fuel for the plumes rising from the center. A tomographic transect along the collisionalsuture of the NCC with the Columbia supercontinent, covering the Yinshan-Ordos Blocks in the WesternBlock through the Central Orogenic Belt and into the Eastern Block of the NCC reveals a ca. 250 km thicklithospheric keel below the Ordos Block defined by a prominent high-velocity anomaly. We identify slabbreak-off and asthenospheric upwelling in this region and suggest that this process probably initiated thethermal and material erosion of the tectosphere beneath the Eastern Block from the Paleoproterozoic,which was further intensified during the Mesozoic when a substantial part of the sub-continental mantlelithosphere was lost. We visualize heat input from asthenosphere and interaction between astheno-sphere and overlying carbonated tectosphere releasing CO2-rich fluids for the preservation of ultra-hightemperature (ca. 1000 ◦C) metamorphic rocks enriched in CO2 as well as high-pressure mafic granulitesas a paired suite in this region. We also identify a hot swell of the asthenosphere rooted to more than200 km depth and reaching up to the shallow mantle in the tomographic section along 35◦N latitude

at a depth of 800 km. This zone represents a cross-section through the southern part of the NCC. Thesurface distribution of Paleoproterozoic Xiong’er lavas and mafic dykes in this region would indicate thatthis region might have evidenced similar upwellings in the past. Our study has important implicationsin understanding the evolution of the NCC and suggests that the extensive modification of the mantlearchitecture and lithospheric structure beneath one of the fundamental Precambrian nuclei of Asia hada prolonged history probably dating from the Paleoproterozoic suturing of the NCC within the Columbia

.

supercontinent amalgam

. Introduction

The North China Craton (NCC) constitutes the oldest continen-al fragment in China bounded by Phanerozoic orogenic belts along

ts southern and northern margins (Fig. 1, inset). Together with theouth China and Tarim cratons, the NCC constitutes one of the fun-amental Precambrian nuclei of Asia (e.g., Zhao et al., 2002, 2005;.C. Zhao et al., 2007, 2009; Wilde et al., 2002, 2004; Kröner et

∗ Corresponding author. Tel.: +81 88 844 8278; fax: +81 88 844 8278.E-mail address: santosh@cc.kochi-u.ac.jp (M. Santosh).

264-3707/$ – see front matter © 2009 Elsevier Ltd. All rights reserved.oi:10.1016/j.jog.2009.09.043

© 2009 Elsevier Ltd. All rights reserved.

al., 2005; Kusky et al., 2007a; Santosh et al., 2006, 2007a,b, 2008,2009a,b,c, among others). The NCC occupies an important positionin the Paleoproterozoic supercontinent Columbia (Fig. 1). Globalsimilarities of ages of major tectonic events associated with conti-nental collision suggest that there was a peak in the amalgamationof landmasses into a supercontinent in the late Paleoproterozoic(Rogers and Santosh, 2002, 2009; Condie, 2002; Zhao et al., 2002;

G.C. Zhao et al., 2007; Kusky et al., 2007a; Kusky and Santosh,2009). Rogers and Santosh (2002) proposed the framework of asupercontinent, Columbia, that formed and was broken up duringthe period between 1.9 and 1.5 billion years ago. They proposedthat Columbia may have contained nearly all of the Earth’s conti-

40 M. Santosh et al. / Journal of Geodynamics 49 (2010) 39–53

F ter Kut

naNsptwTiCCseC

iAehrtNzsi2m

ig. 1. North China Craton within the Paleoproterozoic Columbia supercontinent (afhe major Precambrian cratons and younger orogens (after Zhao et al., 2005).

ental blocks during this period when eastern India, Australia andttached parts of Antarctica were apparently sutured to westernorth America, and the eastern margin of North America to the

outhern margin of Baltica. Zhao et al. (2002) identified the criticalosition of NCC within Columbia. Kusky et al. (2007a) proposed thathe Inner Mongolia–Northern Hebei orogen (NHO) of North Chinaas a major Paleoproterozoic orogen that links Baltica, North China,

arim, West Africa and the western margin of the Amazon shieldn a continuous zone of continental outbuilding making the Northhina Craton a keystone block in matching different elements ofolumbia. Hou et al. (2008) also proposed a model for the Columbiaupercontinent where the ‘North Hebei Orogen’ along the north-rn margin of the NCC was linked with other cratons within theolumbia supercontinent.

The North China Craton is also considered as a typical arean the globe where a craton developed a continental root in therchean, and subsequently lost half of that root during later tectonicvents. Numerous geological, geophysical and geochemical studiesave addressed the geometry and timing of loss of the cratonicoot of the NCC (see review by Kusky et al., 2007b and referencesherein). Mantle xenoliths delivered by Devonian kimberlites in theCC clearly show the presence of tectosphere in the Late Paleo-

oic. However, the xenoliths in strongly alkaline basalts eruptedince the Tertiary show the disappearance of the tectosphere, andnstead, the appearance of an iron rich oceanic mantle (Gao et al.,002). Evidence for the loss of the Archean keel and its replace-ent by a more fertile lithospheric mantle in the eastern part of

sky and Santosh, 2009). The inset shows the tectonic framework of China illustrating

the NCC sometime after the Paleozoic has been provided from sev-eral petrologic, geochemical, isotopic and geophysical techniques(e.g., Gao et al., 2002, 2004; Yang et al., 2008; Chen et al., 2008; Liet al., 2009, among various others).

The mantle dynamics associated with the Paleoproterozoicsubduction-accretion-collision tectonics of the NCC and theMesozoic–Cenozoic decratonization process in the eastern parthave significant importance in understanding the tectonic evolu-tion of this region, and have so far been addressed largely frompetrological and geochemical studies. Seismic tomography offersa powerful technique to image the three-dimensional (3-D) struc-ture of the Earth’s crust and underlying mantle (e.g., Zhao, 2004,2009). Recently, Tian et al. (2009) and Xu and Zhao (2009) appliedthe tomographic method of Zhao et al. (1994) and D. Zhao et al.(2007) to a large number of arrival time data from local, regionaland teleseismic events to determine high-resolution 3-D P-wavevelocity structure down to 800 km depth beneath the NCC and sur-rounding regions. They used the best data sets recorded by over 500permanent seismic stations of the China Seismic Network in addi-tion to some portable seismic stations. More than 150,000 P-wavearrival times from local earthquakes and travel-time residuals fromteleseismic events were used for imaging the 3-D crust and upper

mantle structures.

In this study, we present a detailed evaluation of the seismictomography beneath the NCC and adjacent regions and attempt tocorrelate it with the major geological and tectonic events. Amongthe various features discussed, we demarcate the presence of a

M. Santosh et al. / Journal of Geodynamics 49 (2010) 39–53 41

Fig. 2. Geologic and tectonic map of the North China Craton (compiled after Zhao et al., 2005; G.C. Zhao et al., 2009; Kusky et al., 2007a; Santosh et al., 2007a), showing thedistribution of the main tectonic subdivisions. The locations of ultrahigh-temperature and high-pressure orogens along the zone of collision of the Ordos and Yinshan Blocksa Chinat ween

ttumsspaitttimlc

2

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nd its extension into the northern part of the Central Orogenic Belt (Trans-Northhe Khondalite Belt (Kusky et al., 2007a). This study identifies the collision zone bet

hick tectospheric keel beneath the western part of the NCC and itshermal and material erosion towards the eastern part. We spec-late that the erosion of the sub-continental lithosphere was aulti-stage process that was initiated from the Paleoproterozoic

ubduction-collision history with an increasing intensity of ero-ion towards the Eastern Block of NCC through younger tectonicrocesses. Although we identify a marked correlation between hotsthenospheric windows with surface geological manifestationsncluding the occurrence of paired high-pressure and ultrahigh-emperature granulite belts in the northern margin of the NCC,he voluminous Xiong’er volcanics in the southern domain andhe series of mafic dyke swarms distributed all along the cratonicnterior, it is difficult to predict a direct link with the present day

antle dynamics from the tomographic images due to the intenseithospheric reactivation along the boundary zones surrounding theratonic nucleus through younger geological events.

. Geological and tectonic framework of NCC

The NCC is considered to incorporate three discrete crustallocks namely, the Eastern Block, Western Block and the inter-ening Central Orogenic Belt also known as the Trans-North Chinarogen (e.g., Zhao et al., 2002, 2005; G.C. Zhao et al., 2009; Wildet al., 2002, 2004; Kröner et al., 2005; Kusky et al., 2007a; Trapt al., 2009, among several others) (Fig. 2). Since this intervening

one is not a single orogen and carries several orogenic belts ofifferent tectonic styles and evolutionary history, the term Centralrogenic Belt would be more appropriate. The Central Orogenicelt is believed to represent a collision zone resulting from themalgamation of the Eastern and Western Blocks, although the

Orogen) are also shown. The ‘North Hebei Orogen’ includes the Yinshan Block andthe Yinshan and Ordos Blocks as the Inner Mongolia Suture Zone.

timing of the collision is debated (Zhao et al., 2002, 2006; G.C.Zhao et al., 2007; Kusky et al., 2007a). The Late Paleoproterozoictectonic evolution and continental growth in the NCC have beenaddressed in a number of recent works (Wilde et al., 2002, 2004;Kröner et al., 2005; Zhao et al., 2005; G.C. Zhao et al., 2009; Kuskyet al., 2007a; Santosh et al., 2006, 2007a,b, 2008, 2009a,b,c, amongseveral others). One of the models proposes that the basement ofthe North China Craton was involved in at least two Paleoprotero-zoic collisional events: the first one at 1.95–1.92 Ga forming theKhondalite Belt along which the Yinshan Block in the north andthe Ordos Block in the south amalgamated to form the WesternBlock (Zhao et al., 2005; Santosh et al., 2006, 2007a, 2007b; shownas Inner Mongolia Suture Zone in Fig. 2). The second collisionalevent occurred at ∼1.85 Ga, forming the Central Orogenic Belt alongwhich the Western and Eastern Blocks collided to form the coher-ent basement of the North China Craton (Zhao et al., 2005; Wildeet al., 2002, 2004; Kröner et al., 2005; Faure et al., 2007). Thesetwo collisional events were within the time span (2.1–1.8 Ga) ofthe global-scale collisional events that led to the assembly of theColumbia supercontinent (Rogers and Santosh, 2002, 2009; Zhao etal., 2002; G.C. Zhao et al., 2009). An alternate model (Kusky and Li,2003; Kusky et al., 2007a) proposes that a single high-grade orogen(termed the ‘North Hebei Orogen’, and correlating with the term‘Yinshan Block’ as used here) developed along the northern marginof the NCC which represents the collisional orogen along which the

NCC in a series of collisons from 2.3 to 1.85 Ga, culminating in thecontinent–continent collision when the NCC was incorporated intothe Columbia supercontinent amalgam (Kusky and Santosh, 2009).

The timing of collision between the Ordos and Yinshan Blocksand the formation of ultra-hot orogens within the Inner Mongo-

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2 M. Santosh et al. / Journal o

ia Suture Zone (Fig. 2) at the time of incorporation of NCC withinhe Columbia supercontinent has been addressed in some recenttudies. Santosh et al. (2007b) reported SHRIMP U–Pb ages of zir-ons in khondalites and ultrahigh-temperature (UHT) granulitesrom the Jining Complex. The oldest detrital cores in their studyevealed 207Pb/206Pb ages up to 2090 ± 22 Ma, although the dom-nant age population was noted to be around 1970 Ma. The oldest

etamorphic zircons are around ca. 1.95 Ga in this belt. Zircon fromhe highest grade sample in their study with a sapphirine-bearingHT assemblage belong to a single population with a weightedean 207Pb/206Pb age of 1919 ± 10 Ma. In another recent study,

antosh et al. (2009b) reported SHRIMP U–Pb, rare earth element,f isotope, and laser Raman spectroscopic data on zircons from the

apphirine + quartz bearing UHT granulites from the Jining Com-lex. Despite the core-rim textures displayed by some of the UHTircons, their age values sharply converge within error, yieldingeighted mean 207Pb/206Pb ages of ca. 1.92 Ga, indicating growth

y recrystallization under extreme thermal conditions. In general,he zircons show moderate heavy rare earth element enrichmentith sharp positive Ce and negative Eu anomalies. The Hf isotopeata from the UHT zircons also display a fairly uniform character,ith the majority of them characterized by positive �Hf values,ithout any indication of mixing between reworked crust and

uvenile material. The majority of mineral inclusions in the UHTircons, as revealed by laser Raman study, also support a magmaticource. Their results demonstrate that the collision between theinshan and Ordos blocks occurred at around 1.92 Ga, which coin-ides with the global collision event at 2.0–1.8 Ga recognized as theiming of the assembly of the Paleo-Mesoproterozoic superconti-ent Columbia (Rogers and Santosh, 2002, 2009; Zhao et al., 2002;.C. Zhao et al., 2009; Kusky and Santosh, 2009). The ca. 1.92-Ga agebtained from zircons in rocks within an ultrahot orogen developedlong the collisional zone of the NCC indicates the extreme ther-al conditions to which the crust was subjected as the NCC was

ncorporated within the Columbia amalgam.Several studies have characterized the occurrence of a number

f major mafic dyke swarms in the NCC which, together with anoro-enic rapakivi granites and anorthosites have been correlated to aominant extension in the period 1.85–1.75 Ga (Kusky and Li, 2003;usky et al., 2007a; Hou et al., 2008). Some of these works consider

hat the mafic dyke swarms intruded northward from the Xiong’erolcanic belt. Peng et al. (2005, 2007) interpreted the mafic dykewarm as feeder of the Xiong’er large igneous province that wasmplaced in the Late Paleoproterozoic and correlated to a mantlelume. About 640 undeformed and unmetamorphosed mafic dykesave been mapped extending for about 1000 km long with an areaf over 2.8 Mkm2 in the Precambrian basement across the Northhina Craton (Hou et al., 2008; Peng et al., 2007). The dominantrientation of the mafic dyke swarm is N-NW, where as few dykeshow E–W and NE trends. Peng et al. (2005) reported a SHRIMP zir-on U–Pb age of 1778 ± 3 Ma and zircon/baddeleyite 207Pb/206Pbge of 1803 ± 7 Ma for a mafic dyke at Datong in the Western Block.hao et al. (2005) also obtained an 39Ar–40Ar age of 1804 ± 16 Ma formafic dyke at Mt Hengshan in the Western Block. A diabase dyke att Hengshan in the Central Orogenic Belt has yielded a single-grain

ircon U–Pb age of 1770 ± 3 Ma (Halls and Heaman, 2000). Hou etl. (2006) obtained a SHRIMP zircon U–Pb age of 1837 ± 18 Ma for aarge NNW-trending mafic dyke at Mt Taishan in the Eastern Block.

ang et al. (2007) also obtained zircon U–Pb upper intercept age of841 ± 18 Ma and a concordia age of 1853 ± 24 Ma for a mafic dyke

n the Eastern Block. These geochronological data suggest a major

antle magmatic event within the NCC during 1.85–1.77 Ga.The Xiong’er volcanic belt, covering an area of more than

0,000 km2 along the southern margin of the North China Cra-on, has long been considered an intra-continental rift zone andnterpreted as part of a large igneous province formed by a man-

ynamics 49 (2010) 39–53

tle plume that led to the break-up of the Paleo-Mesoproterozoicsupercontinent Columbia. In a recent overview, G.C. Zhao et al.(2009) provided an alternate model for their origin. Lithologically,the Xiong’er volcanic belt is dominated by basaltic andesite andandesite, with minor dacite and rhyolite, as against the commonrock associations related to continental rifts or mantle plumes,which are generally bimodal and dominated by mafic compo-nents. Based on a synthesis of the petrological and geochemicalcharacteristics of the Xiong’er volcanics, G.C. Zhao et al. (2009) pro-posed that they are remarkably similar to those rock associationsin modern continental margin arcs. The Nd-isotope composi-tions of the Xiong’er volcanic rocks suggest that 5–15% oldercrust has been transferred into the upper lithospheric mantle bysubduction-related recycling during Archean to Paleoproterozoictime. Available SHRIMP and LA-ICP-MS U–Pb zircon age data indi-cate that the Xiong’er volcanic rocks erupted intermittently over aprotracted interval from 1.78 Ga, through 1.76–1.75 Ga and 1.65 Ga,to 1.45 Ga, though the major phase of the volcanism occurred at1.78–1.75 Ga. G.C. Zhao et al. (2009) proposed that the Xiong’ervolcanic belt most likely represents a Paleo-Mesoproterozoic con-tinental magmatic arc that formed at the southern margin ofthe North China Craton and might represent subduction-relatedepisodic outbuilding on the continental margins of the Paleo-Mesoproterozoic supercontinent Columbia.

3. Interpretation of seismic tomographic data from NCC

3.1. Upper mantle tomography defines hot and cold corridorsbeneath NCC

Tian et al. (2009) presented seismic images of the North ChinaCraton and adjacent regions centered on the Ordos Block at variousdepth layers (Fig. 3). In general, the crust and the upper mantledown to 300 km depth are dominated by high P-wave velocity(hereafter high-velocity) anomalies, particularly towards the cen-tral, southern and western domains. This might suggest blocksof the crustal and lithospheric materials sinking down to vari-ous depths (e.g., Maruyama et al., 2007; D. Zhao et al., 2007). Thecold anomalies in the southern and western regions might corre-late mostly with the Phanerozoic subduction-collision events andslabs sinking to various depths. However, in all these depth lay-ers, the northern part surrounding the junction between the Ordosand Yinshan Blocks as well as all along the eastern margin of theOrdos Block along the Central Orogenic Belt, low-velocity anoma-lies dominate suggesting hot regions extending from shallow todeeper levels. At 500 km depth, within the mantle transition zone,the major part of the region beneath the Ordos Block, extending fur-ther north as well as south, shows prominent low-velocity zones(Fig. 3d). An interpretative cartoon sketch of the P-wave velocityimage of the NCC and adjacent regions at the 500 m depth layer isshown in Fig. 4. Four prominent low-velocity zones are identified(H1, H2, H3 and H4 in Fig. 4a, ‘H’ denoting hot region). Several high-velocity zones are distributed towards the west as well as east of theOrdos Block (identified as C1–C9 in Fig. 4a, ‘C’ denoting cold region).In general the mantle transition zone (410–660 km depth) beneaththe North China Craton and adjacent regions can be divided into acentral ‘hot corridor’ bound on both sides by two ‘cold corridors’.The cold corridor beneath the Eastern Block and further towardsthe east may correspond to the stagnant Pacific slab (Zhao, 2004;Huang and Zhao, 2006; D. Zhao et al., 2009).

Previous studies have correlated the distribution of high-velocity anomalies in the circum-Pacific and Tethyan domains overthe world (Grand, 1994, 2002; Zhao, 2004) with the subductionhistory of the Earth, suggesting that these anomalies are causedby subducted oceanic lithosphere (Maruyama et al., 2007; Zhao,

M. Santosh et al. / Journal of Geodynamics 49 (2010) 39–53 43

Fig. 3. P-wave tomographic images at depths of 60, 160, 300 and 500 km beneath the North China Craton and adjacent regions (modified from Tian et al., 2009). Red andb elocitv nces to

2iewmd2aacNbsIrltasbdzfsuePrlab

ip

lue colors denote lower and higher velocity perturbations relative to the average velocity perturbation scale is shown at the bottom. (For interpretation of the refere

009). The strongest high-velocity anomaly, both in intensity andn size, within the mantle occurs in the western Pacific and east-rn Asia and coincides with the circum-Pacific subduction zonehere it meets with the Tethyan domain, forming an overlappingega-scale subduction zone which has been termed as a super-

ownwelling zone, or Asian cold superplume (Maruyama et al.,007; Santosh et al., 2009a). The whole-mantle tomographic imagelong the Beijing–Tokyo cross-section by Zhao (2004) shows that1200 km-long stagnant slab floats right above the 660-km dis-

ontinuity that separates the upper mantle from the lower mantle.ear the bottom of the mantle, immediately above the core–mantleoundary, high-velocity anomalies are present, suggesting that alab graveyard was once stagnant in the mantle transition zone.n between there are no high-velocity anomalies in the depthange of 660–2000 km. This might suggest the catastrophic col-apse of stagnant slabs once in the mantle transition zone downo the bottom of the mantle. The Pacific superplume is defined byconcentric large-scale structure with a core characterized by low

eismic velocity (extending about 3000 km across), and surroundedy a donut-shaped high-velocity anomaly with steep velocity gra-ients (Maruyama et al., 2007). This surrounding high-velocityone has been interpreted as a slab graveyard resulting from theormation of the Rodinia supercontinent. Slab graveyards are con-idered to provide the fuel for the generation of plumes which risep and ultimately coalesce to produce superplumes (Maruyamat al., 2007; Santosh et al., 2009a). In the case of the Westernacific region, low-velocity anomalies representing a number ofising plumes are present only along the peripheral region in theower mantle, suggesting the recycled slab material is depleted

t the center of the superplume rising from the core–mantleoundary.

In the present case, the low-velocity zones identified as H1–H4n Fig. 4a below the North China Craton might represent risinglumes from the mantle transition zone. These zones H1–H4 are

y at each depth. The red triangle represents the location of the Datong volcano. Thecolor in this figure legend, the reader is referred to the web version of the article.)

enveloped on both sides by relatively hot regions together defininga hot corridor (Fig. 4b). This region is surrounded on both sides bycold domains. This scenario is similar to the donut-shaped high-velocity anomaly surrounding a region of low-velocity anomalyin the Pacific and suggests that the cold regions represent slabgraveyards which provide the fuel for the plumes rising from thecenter. Similar to the case of the Western Pacific region, some ofthe subducted slabs, particularly those towards the northern andeastern domains of NCC may correspond to slab debris derivedfrom older subduction-collision events in Earth history, probablyrelated to the Paleoproterozoic evolution of the North China Cra-ton.

In a recent study, Kawai et al. (2009) investigated thebulk density variations in the lower mantle based on thepressure–volume–temperature equation of state of the con-stituent mineral phases. Their computations and modeling showthat the subducted felsic materials (TTG—tonalite–trondhjemite–granodiorite) become stagnant at the mantle transition zone,whereas the other materials including the dense anorthositic crustwould sink down into the core–mantle boundary. The TTG-derivedmaterial is lighter than the average composition of the mantle inthe lower mantle, but at domains deeper than 300 km, the mate-rial becomes much denser than the surrounding mantle throughthe polymorphic transformation of SiO2 into denser phases. SinceSiO2 is a dominant constituent of the TTG, this transformationand density change will allow the material to sink deep into themantle. Kawai et al. (2009) proposed that significant subductedmaterial could therefore remain stagnant in the mantle transi-tion zone, constituting a second ‘continental layer’ in this zone.

The TTG-derived material is also important in terms of mantlegeodynamics because the radiogenic elements contained in themwould provide a heat source for the mantle plumes (Senshu et al.,2009). Stagnant TTG in the mantle transition zone could there-fore produce mantle plume from the 410 km boundary on the

44 M. Santosh et al. / Journal of Geodynamics 49 (2010) 39–53

F h bena See te

ttpmpicth

ig. 4. Interpretative sketch map of the P-wave tomographic image at 500 km depthot corridor in the middle sandwiched between two cold corridors on both sides.

op of mantle transition zone. The zones H1–H4 at the center ofhe North China Craton (Fig. 4b) may also probably correspond tolumes derived by the subduction of large amounts of TTG-derivedaterial. However, we do not exclude the possibility that the

lumes are generated in the lower mantle, and remains to be clar-fied by further studies. In summary, the regions surrounding theratonic nucleus of the NCC illustrate complex deep mantle archi-ecture, probably reflecting an intense lithospheric reactivationistory.

eath the North China Craton. The P-wave velocities define two prominent regions:xt for discussion.

3.2. Transect across Yinshan and Ordos blocks

Fig. 5a shows a vertical cross-section of P-wave tomographicimage down to 600 km depth along longitude 108◦E across the

Ordos and Yinshan Blocks of the NCC, and Fig. 5b illustrates acartoon sketch that interprets the mantle tomography under thisregion with a prominent asthenospheric upwelling along the cross-section. We have chosen this section since this region is of criticalinterest to the models on the history of evolution of the NCC as well

M. Santosh et al. / Journal of Geodynamics 49 (2010) 39–53 45

F gitudd ach dei op of6 or in t

aCalga(2toaPtcssuafr

3

it

ig. 5. (a) Vertical cross-section of P-wave velocity tomography along East 108◦ lonenote lower and higher velocity perturbations relative to the average velocity at e

ndicates Moho and the lower one denotes the 410 km discontinuity defining the t00 km depth along East 108◦ longitude. (For interpretation of the references to col

s the tectonics of accretion of the Paleoproterozoic supercontinentolumbia (e.g., Zhao et al., 2002; G.C. Zhao et al., 2007; Santosh etl., 2007a,b, 2008, 2009a,b; Kusky et al., 2007a). The timing of col-ision between the Yinshan and Ordos blocks coincides with thelobal collision event at 2.0–1.8 Ga recognized as the timing of thessembly of the Paleo-Mesoproterozoic supercontinent ColumbiaRogers and Santosh, 2002, 2009; Zhao et al., 2002; G.C. Zhao et al.,009). Notwithstanding the debate over the evolution of the NCC,he Khondalite Belt sandwiched along the region of amalgamationf the Ordos and Yinshan blocks, represents an accretionary belt,long with extruded UHT and HP orogens within the trace of thealeoproterozoic Columbia suture. The cartoon interpretation ofhe P-wave velocity image shown in Fig. 5b illustrates partly erodedold lithospheric roots below the Ordos Block and the remnants ofubducted slabs floating at various levels up to the mantle tran-ition zone. Importantly, zones of low-velocity anomalies definepwelled asthenosphere. Whereas this section shows an enlargedrea at the boundary between the Yinshan and Ordos blocks, weurther evaluate in the next section the mantle dynamics in a moreegional context within the NCC.

.3. Mantle dynamics beneath NCC

Fig. 6a shows a vertical cross-section of P-wave tomographicmage along 37◦N latitude which approximately traces an E–W sec-ion from the Ordos-Yinshan collision zone into Central Orogenic

e down to a depth of 600 km (modified from Tian et al., 2009). Red and blue colorspth. The velocity perturbation scale is shown at the bottom. The upper dashed line

the mantle transition zone. (b) Interpretative sketch map of tomographic image athis figure legend, the reader is referred to the web version of the article.)

Belt and further into the Eastern Block (Xu and Zhao, 2009). Notethat we use the image by Xu and Zhao (2009) for the E–W tran-sect, instead of the data in Tian et al. (2009) because of the higherresolution for this region in the tomographic images presented byXu and Zhao (2009). However, in order to interpret the mantledynamics of the Ordos Block, we have used the tomographic imagespresented by Tian et al. (2009) as they provide a more regionalcoverage.

An interpretative cartoon sketch of the tomographic image ofFig. 6a is shown in Fig. 6b. An approximately 250 km thick litho-spheric keel occurs below the Ordos Block. A huge section of thesubducted slab is floating on top of the mantle transition zone.Deep subducted fragments of remnant slabs that are sinking belowthe mantle transition zone can also be traced up to depths of800 km. Apparently, slab graveyards extend below this zone, andprobably down to the core–mantle boundary, similar to the casedescribed from the Rodinia and Gondwana slab graveyards (e.g.,Maruyama et al., 2007). In the present case, it is difficult to pre-dict whether these subducted slab debris represent the remnantsof the subduction history during the amalgamation of the Columbiasupercontinent, or those from younger geological events such as

subduction beneath the NCC during closure of the Paleoasian andPaleotethys oceans (Kusky et al., 2007b). Below the Eastern Block,a thin and flat lithospheric root is traced which is underlain by athin asthenosphere. Obviously, this part of the continental root hasbeen substantially eroded, and the presence of the prominent low-

46 M. Santosh et al. / Journal of Geodynamics 49 (2010) 39–53

F ituded t eachr sitiond ces to

va

dtfBhgeot

atMaot

ig. 6. (a) Vertical cross-section of P-wave velocity tomography along North 37◦ latenote lower and higher velocity perturbations relative to the average velocity aepresent the region between 410 and 660 km depths representing the mantle tranown to a depth of 800 km. See text for discussion. (For interpretation of the referen

elocity zone immediate below confirms upwelling asthenospherend continued lithospheric erosion.

The P-wave velocity image from the surface down to 600 kmepth along N40◦ latitude cross-section (Fig. 7a) and its interpreta-ive sketch (Fig. 7b) provide an important window extending fromarther west and into the Ordos Block through the Central Orogenicelt and entering into the Eastern Block. The presence of a remnantigh-velocity zone beneath the western part of the Ordos Block sug-ests the presence of a thick lithospheric keel. Its continuity furtherast is abruptly terminated by a prominent low-velocity anomalyriginating far below the mantle transition zone and reaching upo the bottom of the crust.

The zone of upwelling that spreads across the shallow mantlend lower crustal regions correlates directly with the surface dis-

ribution of UHT granulites within the Columbia suture in the NCC.

g–Al granulites discovered from this belt display metamorphicssemblages of sapphirine + quartz, spinel + quartz, high aluminarthopyroxene coexisting with sillimanite and quartz, and high-emperature mesoperthites, all diagnostic of UHT metamorphism

down to a depth of 800 km (modified after Xu and Zhao, 2009). Red and blue colorsdepth. The velocity perturbation scale is shown at the bottom. The dashed lines

zone. (b) Interpretative sketch map of tomographic image along North 37◦ latitudecolor in this figure legend, the reader is referred to the web version of the article.)

at temperatures of ca. 1000 ◦C and pressures of 10–12 kbar (Santoshet al., 2006, 2007a,b, 2009b,c). Detailed fluid inclusion petrography,microthermometry and laser Raman spectroscopy revealed thepresence of high density pure CO2-rich fluids suggesting that theUHT metamorphism occurred under water-deficient and CO2-richconditions which aided in stabilizing the dry mineral assemblages(Santosh et al., 2008). Several high-pressure (HP) granulite occur-rences are reported further east (e.g., Zhao et al., 2001; Guo et al.,2004; O’Brien et al., 2005) within the Central Orogenic Belt, along anextension of the collision zone between Ordos and Yinshan Blocks(Fig. 1). Both the UHT and HP granulites are distributed directlyabove the wide zone of upwelling traced in the present study.Although the mantle region beneath the UHT–UHP belts definesa heat window within the Columbia suture, this upwelling of the

present day mantle may have no direct relationship with the devel-opment of the Paleoproterozoic ultrahot metamorphic orogens.

A hot swell of the asthenosphere rooted to more than 200 kmdepth and reaching up to the shallow mantle is also visible in thetomographic section along 35◦N latitude down to a depth of 800 km

M. Santosh et al. / Journal of Geodynamics 49 (2010) 39–53 47

Fig. 7. (a) Vertical cross-section of P-wave velocity tomography along North 40◦ latitude down to a depth of 600 km (modified from Tian et al., 2009). Red and blue colorsdenote lower and higher velocity perturbations relative to the average velocity at each depth. The velocity perturbation scale is shown at the bottom. The upper dashed linei of thN etatiov

(ewspfsTbAtat

4

4

aadaapisp

ndicates Moho and the lower one denotes the 410 km discontinuity defining the toporth 37◦ latitude down to a depth of 800 km. See text for discussion. (For interprersion of the article.)

Fig. 8). This zone represents a cross-section through the south-rn part of the NCC where the Paleoproterozoic Xiong’er lavas areidely distributed (e.g., G.C. Zhao et al., 2009). Several mafic dyke

warms also radiate from this zone (Hou et al., 2008). An inter-retative sketch of this anomaly as well as the surface geologicaleatures are shown in a combined diagram in Fig. 8 illustrating pos-ible subducted slabs floating in the deep part of the upper mantle.his region again defines a hot window with a possible correlationetween the asthenospheric upwelling and mantle magmatismgain, the apparent correlation with the surface distribution of

he Xiong’er rocks as well as the mafic dyke swarms needs to bepproached with caution due to the intense reactivation history ofhe NCC and surrounding regions.

. Discussion

.1. Correlating seismic anomalies with geological history

Seismic velocity perturbations result from both temperaturend chemical (compositional) anomalies. Here we interpret thenomalies as cold lithospheric root at shallow levels, as dense sub-ucted slab materials at deeper levels, and as hot and less densesthenospheric upwelling. The implications of velocity anomalies

nd distinguishing thermal and chemical anomalies from velocityerturbations alone are not straightforward. Indeed, tomographic

mages provide only a snapshot of the current mantle althoughome frozen-in information in the crust and upper mantle couldrovide clues to understand the past geodynamics. However, com-

e mantle transition zone. (b) Interpretative sketch map of tomographic image alongn of the references to color in this figure legend, the reader is referred to the web

pared to the crust and uppermost mantle, the deep upper mantleis easier to be rewritten by the later geodynamic events or man-tle convection. The regions surrounding the cratonic nucleus ofthe NCC were intensely affected by younger tectonic processes,and there is little possibility that the underlying mantle haskept coupled continuously from the Paleoproterozoic to Cenozoic.In addition, the temperature anomaly instead of compositionalanomaly could be the major cause of velocity anomaly withinthe upper mantle depth, and such temperature anomalies wouldeventually disappear even in the absence of subsequent geologicalevents. Therefore, to what extent the upper mantle anomalies canbe linked with older geological processes remains uncertain.

4.2. Modification of mantle architecture

Recent receiver-function studies suggest that the Cenozoiccrustal rifting in areas surrounding the cratonic nucleus of west-ern NCC is a manifestation of a late thermal event that affectedthe entire upper mantle of the region (e.g., Chen and Ai, 2009;Chen et al., 2008; Chen, in press). Low-velocity anomalies havebeen identified in the shallow upper mantle surrounding the north-ern margin of NCC and parts of the central NCC representing ahotter mantle transition zone (e.g., Huang and Zhao, 2006) and

correlating with lateral asthenospheric mantle flow driven by theIndia–Eurasia collision (Liu et al., 2004). The thinned lithospherearound the northern margin of the western NCC could also reflectfeatures produced by Paleozoic-to-early Mesozoic events relatedto the formation of the Central Asian Orogenic Belt (Chen, in

48 M. Santosh et al. / Journal of Geodynamics 49 (2010) 39–53

Fig. 8. (a) The distribution of mafic dykes in North China craton (after Hou et al., 2008). The thickness of the dykes in the map is not to scale. (b) The distribution of theXiong’er volcanic suite at the southern margin of North China Craton (after G.C. Zhao et al., 2009). (c) Vertical cross-section of P-wave velocity tomography along North 35◦

l e coloa ashedt imagi to the

ptwtEpgptsaemuu

atitude down to a depth of 600 km (modified from Tian et al., 2009). Red and blut each depth. The velocity perturbation scale is shown at the bottom. The upper dhe top of the mantle transition zone. (d) Interpretative sketch map of tomographicnterpretation of the references to color in this figure legend, the reader is referred

ress). Thus, successive tectonic events from the final cratoniza-ion of the NCC in the Paleoproterozoic to the early Mesozoicere instrumental in the modification of the mantle architec-

ure beneath and surrounding the NCC. From Late Mesozoic toarly Cenozoic, mantle processes other than stable convection,robably including thermo-mechanical–chemical erosion and/orravitational instability-induced lithospheric delamination, tooklace under the eastern part of the NCC (Chen, in press) aided byhe deep dehydration of the subducting Pacific slab and vigorousubduction-induced convective circulations in the mantle wedge

bove the stagnant slab (see also Zhao and Ohtani, 2009; Maruyamat al., 2009; D. Zhao et al., 2009). The central and western NCC wereuch less affected by the Pacific subduction, and the lithosphere

nder a large part of these regions may have remained relativelyndisturbed.

rs denote lower and higher velocity perturbations relative to the average velocityline indicates Moho and the lower one denotes the 410 km discontinuity defininge along North 37◦ latitude down to a depth of 800 km. See text for discussion. (Forweb version of the article.)

4.3. The tectosphere and its role

Tomographic images below old cratons have revealed high-velocity roots extending to over 200 km depth (e.g., Grand, 1994;Zhao, 2004). The thickness of the continents, defined by the depth towhich the rigid crust and upper mantle extends before reaching theconvecting mantle below that drives the plates, has been debated(e.g., Kennet, 2003). Based on information from heat flow, geo-chemistry and the relative delay times of seismic waves in differentsettings, Jordan (1988) proposed the ‘tectosphere’ (highly depleted

relatively low density upper mantle layer) model, in which a zonemoves with the motion of the plate lying beneath the old con-tinental shields and is considered to extend up to 300–400 kmdepth. More recent assessments of heat-flow data and geochem-istry favour a zone no thicker than 250 km and the depth factor has

M. Santosh et al. / Journal of Geodynamics 49 (2010) 39–53 49

Fig. 9. Cartoon sketch correlating the surface geological distribution of the high-pressure and ultrahigh-temperature orogens in the northern margin of the North ChinaCraton with the tectosphere and rising asthenosphere as interpreted from vertical cross-section of P-wave velocity tomography along North 40◦ latitude down to a deptho 2 inpua ision tP

bsrsktmosbats

b2etatu

fbfSpmtmodctCt

f 600 km. The model visualizes that a similar tectonic scenario with heat and COnd ultra-hot orogens which developed and extruded during the subduction-collaleoproterozoic supercontinent Columbia.

een debated (cf. Polet and Anderson, 1995). Higher seismic wavepeeds in this zone (Gung et al., 2003) indicate the presence of aegion possessing distinct properties, particularly, cooler than itsurroundings, and with a distinct composition. Tectosphere, alsonown as continental keel, is thus a rigid, cold and chemically dis-inct raft that supports the continental crust (Jordan, 1988) and

ostly occurs only in Archean and Proterozoic cratons. The volumef tectosphere was gradually reduced by thermal and material ero-ion by rising plumes during the break-up of supercontinents andy subsequent intrusion by high-temperature plumes. Santosh etl. (2009c) proposed that tectosphere plays a key role in continen-al fragmentation, dispersion, and amalgamation and correlated theupercontinental cycle with a super-tectosphere cycle.

We interpret the prominent high-velocity layer extendingeneath the Ordos block and which defines large zone of over00 km thickness as the remnant of North China Craton’s partlyroded tectosphere, but firmly preserved as the continental keel inhe Western Block. The hot upwelling immediately below this zonend which rises up through a window up to shallow levels providehe key for probable tectospheric erosion caused by asthenosphericpwelling.

The tectosphere may also function as an important fluidactory (Santosh et al., 2009a). The carbonation of tectosphereeneath many sub-continental mantle regions has been inferredrom the occurrence of carbonate minerals in mantle xenoliths.antosh and Omori (2008a,b) used the Proterozoic palaeogeogra-hy of continents to trace the possible “windows” of CO2 fromantle to the atmosphere, speculated from the presence of tec-

osphere. If high-temperature, adiabatic upwelling (plumes) orantle decompression beneath divergent plate margins impinge

n the tectosphere, small CO2-rich melt fractions would be can-

idate parent melts for relatively rare magma types such asarbonatites, kimberlites and lamproites. We show in Fig. 9 car-oon sketch of the erosion of the tectosphere beneath the Northhina Craton by the rising hot asthenosphere. This would lead tohe release of CO2-rich fluids. Santosh et al. (2008) reported the

t from hot asthenosphere impinging the tectosphere probably preserved the dryectonics associated with the incorporation of the North China Craton within the

common presence of high density pure CO2-rich fluid inclusionsin sapphirine-bearing UHT granulites of Tuguiwula in the JiningComplex of the Khondalite Belt in North China Craton. This regionis located within the trace of the Columbia suture, at the junctionbetween the Ordos and Yinshan Blocks and immediately above thehot asthenosphere that fills the eroded segment of the continentalkeel. Although the major upwelling traced from the tomographicimage represents the present day mantle architecture with contin-uing tectospheric erosion, it might provide an important clue fora similar process that prevailed in the Paleoproterozoic when theheat required for the UHT and HP metamorphism at 900–1000 ◦Cwas supplied by the hot asthenosphere which also supplied theCO2-rich fluids through eroding the carbonated tectosphere andpreserved the dry UHT metamorphic assemblages.

4.4. Lost keel and retained keel

Many sections of tectosphere have seismic shear waveanisotropy patterns suggesting that they contain a zone thatdeforms according to the current motion of the craton in the platetectonic mosaic, while others may record fossil deformation fabrics(e.g., Silver and Chan, 1991). The depth to which the tectosphericmantle extends is debated (Polet and Anderson, 1995), althoughmost tomographic images of the cratons show high-velocity rootsextending to at least 200 km depth, and in some cases to depthsgreater than 300 km (e.g., Grand, 1994). Some global tomographicmodels show a zone extending to 400 km, based on the depthsat which seismic waves travel at elevated speeds (e.g., Gung etal., 2003; Zhao, 2004). The formation of tectosphere is a complexprocess and is considered by some workers as a restite of man-tle magmas, predominantly komatiites. In the Archean, extensive

slab melting is thought to have occurred generating felsic magmaswhich reacted with mantle olivine in the hanging wall resultingin the formation of orthopyroxene-enriched mantle peridotiteswhich characterize the tectosphere. Geophysical observations (e.g.,Grand, 2002; Zhao, 2004) indicate that the size of the tectosphere

5 f Geod

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0 M. Santosh et al. / Journal o

orresponds to a maximum depth limit of 300 km underneath cra-ons formed by 2.0 Ga.

The average thickness of continental crust is around 35 km withpredominantly felsic upper crust and a mafic lower crust, which

s only one tenth of the thickness attributed to the tectosphere.he rigidity and buoyancy of the continental crust in old cratonsre therefore possible functions of an underlying thick tectosphere.hus, recent speculations consider that the tectosphere which func-ions as the buoyant keel of continental crust plays a crucial rolen the supercontinental cycle, including continental fragmenta-ion, dispersion and amalgamation (Santosh et al., 2009a). Theectosphere is generally confined to continental cratonic regionsormed before 2.0 Ga. Due to long term cooling, the Archean man-le was of comparatively slightly higher temperature than in thehanerozoic, such that a cold mass would be expected to sink.owever, the chemically distinct buoyant nature of the refrac-

ory (melt-depleted) tectosphere appears to have allowed for itsevelopment and preservation as a thick sub-continental keel. Thepatial distribution of tectosphere mantle on the globe (Santosht al., 2009a) based on the present day images from S-wave and-wave tomography (e.g., Grand, 2002; Zhao, 2004, 2009) showshe presence of tectosphere under most cratonic domains, withhe largest one underneath North America. However, followingts formation during the Archean and early Proterozoic, the vol-me of tectosphere is presumed to have been gradually reduced inesponse to thermal and material erosion, possibly through risingigh-temperature plumes during and subsequent to the break-upf ancient supercontinents (e.g., Santosh et al., 2009a). Thermalnd material erosion of tectosphere, its replacement by oceanicantle by plume activity and the formation of a series of back-

rc basins is characteristic of the Western Pacific and Asian regionse.g., Maruyama et al., 2007; D. Zhao et al., 2007, 2009).

The North China Craton is considered as a type locality in thelobe where a craton developed a continental root in the Archean,nd subsequently lost half of that root during later tectonic events.umerous geological, geophysical and geochemical studies haveddressed the geometry and timing of loss of the cratonic root ofhe NCC and provided geological, geophysical and geochemical datahat help constrain the geometry and timing of root loss (see reviewy Kusky et al., 2007a and references therein). Mantle xenolithselivered by Devonian kimberlites in the NCC clearly show the pres-nce of tectosphere in the Late Paleozoic. However, the xenolithsn strongly alkaline basalts erupted since the Tertiary show the dis-ppearance of the tectosphere, and instead, the appearance of anron rich oceanic mantle (Gao et al., 2002). Evidence for the loss ofhe Archean keel and its replacement by a more fertile lithospheric

antle in the eastern part of the NCC sometime after the Paleozoicas been provided from several petrologic, geochemical, isotopicnd geophysical techniques (e.g., Gao et al., 2002, 2004; Yang et al.,008; Chen et al., 2008; Li et al., 2009, among various others).

The P-wave tomographic images and their interpretativeketches down to a depth of 600–800 km along two traverses whichogether cover the region from west of Ordos Block, through the col-ision zone between Ordos-Yinshan Blocks and Central Orogenicelt into the Eastern Block in the NCC discussed in this studyrovide important clues on the mantle dynamics of this criticalegion. Indeed, information on the ages of the subducted slabs is notvailable from the tomographic images. Geochemical studies havehown that the mantle lithospheres beneath some of the old cratonsave survived for periods more than 3 billion years in spite of vari-us tectonic activities (Carlson et al., 2005). A cold and up to 250 km

hick lithospheric root occurs below the Ordos Block, indicating thathe NCC preserves its keel below the Western Block. Thermal and

aterial erosion of the tectosphere is interpreted from prominentow-velocity regions adjacent to this block rising from depths below00 km and spreading across the collision zone between the Ordos-

ynamics 49 (2010) 39–53

Yinshan Blocks and extending to the northern part of the CentralOrogenic Belt.

The mantle beneath the northern part of the Central OrogenicBelt is also heated by an asthenospheric swell at relatively shallowlevels (less than 150 km depth). In contrast, moving eastward belowthe Eastern Block of the North China Craton, the thickness of thetectosphere is drastically reduced and the thin floating layer at thewestern edge of the Eastern Block is immediately underlain by ahot region.

The growth of the continental crust in North China Craton isconsidered to have occurred mainly in the Archean (see reviewby Kusky et al., 2007b) with a major continent–continent colli-sion occurring in the Paleoproterozoic when the NCC joined theColumbia supercontinent amalgam (Zhao et al., 2002, 2005; G.C.Zhao et al., 2007; Kusky and Santosh, 2009; Rogers and Santosh,2009; Santosh et al., 2009a). Phanerozoic events were mostlyrestricted to the surrounding orogenic belts, although subduc-tion around the margins of the NCC has been suggested to havesignificantly hydro-weakened the remaining tectosphere, leadingto the second stage of root-loss in the Mesozoic (e.g., Kusky etal., 2007a). Cratons are traditionally considered as ancient, sta-ble regions of the continental lithosphere which have not beendisturbed by intense magmatic, metamorphic or other tectonicevents after their stabilization. Kusky et al. (2007b) described theformation and destruction of the NCC as the “orogen-to-craton-to-orogen” cycle. Recently, Begg et al. (2009) analyzed the lithosphericarchitecture of Africa based on synthesis of petrologic, geochemicaland geophysical data. The larger cratons in this region are underlainby geochemically depleted, rigid, and mechanically robust sub-continental lithospheric mantle (designated as tectosphere in ourstudy). They identified that these cratonic roots have steep sides,extending in some cases to over 300 km depth. Beneath smallercratons extensive refertilization has reduced the lateral and verti-cal extent of strongly depleted tectosphere. Their analysis indicatesthat an extensive Archean tectosphere was present beneath Africaand that where continental crust and the sub-continental litho-spheric mantle have remained connected, there is a strong linkagebetween the tectonic evolution of the crust and the compositionand modification of its underlying tectosphere.

A number of studies have addressed the evidence and processesassociated with the thinning of the sub-continental mantle beneaththe eastern part of the NCC in the Mesozoic (see Zhai et al., 2007and papers therein). In a recent work, Yang et al. (2008) focusedon the eastern part of the North China craton where large volumesof Mesozoic igneous rocks occur with widespread metamorphiccore complexes and pull-apart basins. They presented Hf isotopecompositions of magmatic zircon grains from igneous rocks in theLiaodong Peninsula which indicate the widespread formation oflate Mesozoic granitoids through partial melting of ancient crust,with substantial input of a mantle component via magma mix-ing and crustal assimilation. Yang et al. (2008) considered thatthe magmatism resulted from removal and modification of litho-spheric mantle, accompanied by asthenospheric upwelling. TheirHf isotope data record the addition of juvenile crust beneath theeastern part of the North China craton which they correlated to amajor extensional event and possibly slab rollback of the Pacificplate. They concluded that at around 200 Ma, the ancient litho-sphere beneath the eastern North China craton was progressivelyreactivated and replaced, resulting in “decratonization.” This pro-cess was termed the “orogen–craton–orogen” cycle by Kusky et al.(2007b).

In an earlier study, Gao et al. (2002) reported Re–Os data for peri-dotite xenoliths carried in Paleozoic kimberlites and Tertiary alkalibasalts which confirmed that the refractory and chemically buoy-ant lithospheric keel present beneath the eastern block of the NorthChina craton is of Archean age. This Archean keel was replaced

f Geod

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pbffosrOd

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M. Santosh et al. / Journal o

y more fertile lithospheric mantle sometime after the Paleozoic.hey also suggested that the lithospheric mantle beneath the cen-ral portion of the craton (Ordos Block in our study) formed atround 1900 Ma ago, which is the last major Precambrian orogenyn this region. Gao et al. (2002) proposed that since this age is sig-ificantly younger than the overlying crust (2700 Ma), the originalrchean lithosphere was replaced in the Proterozoic. In the Easternlock, the timing of lithospheric replacement is constrained to thehanerozoic (Jurassic or Cretaceous) based on the Re–Os resultsresented by Gao et al. (2002) which was correlated to an eventfter the collision of the Yangtze and North China cratons in the Tri-ssic, and related subduction and extrusion of ultrahigh-pressureetamorphic rocks. Thus, Gao et al. (2002) suggested two major

ithospheric replacement events in the North China Craton, one ata. 1900 Ma and the other at ca. 220 Ma.

Gao et al. (2004) examined the geochemical characteristics ofate Jurassic high magnesium andesites, dacites and adakites fromhe North China Craton and showed that they were derived fromn ancient mafic lower crust that foundered into the convectingantle. The also provided evidence for the presence of inheritedrchean zircons in these magmas, and the neodymium and stron-

ium isotopic compositions of these rocks overlap with those ofclogite xenoliths derived from the lower crust of the North Chinaraton. They correlated the foundering of the mafic lower conti-ental crust in the Late Jurassic as the timing when lithosphericemoval occurred beneath the North China Craton.

Rudnick et al. (2004) reported mineralogical and chemical com-ositions of spinel peridotite xenoliths from two Tertiary alkaliasalt localities, one from the Central Orogenic Belt and the otherrom the Eastern Block. Their compositions are markedly differentrom typical cratonic lithosphere, and correlate with the suggestionf Gao et al. (2002) on the removal of the Archean mantle litho-phere beneath this region. They suggested that the lithosphereeplacement occurred in the Paleoproterozoic beneath the Centralrogenic Belt where as in the Eastern Block the removal occurreduring Phanerozoic.

The lithospheric thinning in NCC has also been detected byeophysical techniques. In a recent study on the thickness ofhe lithosphere in the northeastern part of the NCC, Chen et al.2008) applied receiver-function analysis which identified that theithosphere–asthenosphere boundary is as shallow as 60–70 kmn the southeast basin and coastal areas and deepens to around40 km in the northwest mountain ranges and continental interior.hen et al. (2008) interpreted these results to indicate widespread

ithospheric thinning in the region as compared to the >180-kmithospheric thickness typical of most cratonic regions and con-luded that a complex modification of the lithosphere occurreduring the tectonic reactivation of the old craton. In another recenttudy, Li et al. (2009) applied a Rayleigh wave inversion techniqueo image the velocity structure of the lithosphere across the centralegion and eastern block of the North China Craton. They identi-ed a prominent lateral variation in the velocity structure betweenhe central and Eastern block and confirmed that the lithosphereemoval through tectonic processes in the Mesozoic–Cenozoicimes in the eastern part of the NCC is more intense than the centralegion.

The question of why only the eastern half of the root was lost,nd not the root from beneath the whole craton has remained annigma. Several proposals have been put forward, including theoncept that the root grew independently, by tectonic underplatingf subducted buoyant oceanic lithosphere, beneath the previously

eparate eastern and western halves of the craton by 2.5 Ga, withodification at around 1.8 Ga associated with the Paleoproterozoic

ratonization event (Kusky et al., 2007b). The loss of the root fromnly the eastern half during younger tectonism was attributed inheir model to some physical or geometric difference between the

ynamics 49 (2010) 39–53 51

two halves. It is also possible that the collisional or subduction-related tectonic processes acting only on the Eastern Block mayhave caused the disruption of the tectosphere there during theMesozoic. Among the possible triggering mechanisms are colli-sion of the South China (Yangtze) and North China Cratons inthe Triassic, the India–Asia collision, closure of the Solonker andMongol–Okhotsk oceans, Mesozoic subduction of the Pacific platebeneath Eastern China, impingement of mantle plumes, mantlehydration from long-term subduction, and several rifting events(Kusky et al., 2007b).

The interpretation of P-wave tomographic data in the presentstudy provides more insights into this intriguing topic. Large-scalemantle replacement requires intense and continued erosion of thecratonic root, either associated with the subduction-collision his-tory of supercontinents, or involving superplumes rising from deepmantle domains. A recent study by Chen and Ai (2009) shows thatthe mantle transition zone in the central and western NCC displayssmoother structural features and weaker thermal anomalies thanthat in the eastern part of the craton which suggests a relativelyweak effect of deep mantle dynamics on the Cenozoic tectonicsof the central and western parts of the craton. The lithosphericreactivation might have been more intense in the boundary zonessurrounding the cratonic nucleus as also indicated by the significantthinning, rift magmatism, active faulting and seismicity surround-ing the Ordos Block (Zhang et al., 2002). The northern boundary ofthe NCC witnessed the progressive subduction of the Paleo-Asianocean and the amalgamaton of terranes that produced the Cen-tral Asian Orogenic Belt in Paleozoic to early Mesozoic (Buslov etal., 2001; Xiao et al., 2003). As an active continental margin duringthis period, the lithosphere in this region might have also under-gone significant modification, as compared to the cratonic interiorof the Ordos Block. We speculate that the erosion of the sub-lithospheric mantle beneath the Eastern Block of the NCC mighthave been initiated from the Paleoproterozoic, associated with thesubduction-collision tectonics and asthenospheric upwelling. Pro-longed thermal and material erosion of the tectosphere beneaththe Eastern Block was further intensified by the Mesozoic–Cenozoictectonic activity in this region, in particular, the deep subductionof the Pacific plate and its stagnancy in the mantle transition zoneunder East Asia.

Acknowledgments

We thank two anonymous referees for constructive and help-ful reviews on an earlier version, and Editor-in-Chief Prof. RandellStephenson for encouragement.

References

Begg, G.C., Griffin, W.L., Natapov, L.M., O’Reilly, S.Y., Grand, S.P., O’Neill, C.J., Hron-sky, J.M.A., Djomani, Y.P., Swain, C.J., Deen, T., Bowden, P., 2009. The lithosphericarchitecture of Africa: seismic tomography, mantle petrology, and tectonic evo-lution. Geosphere 5, 23–50.

Buslov, M.M., Saphonova, I.Yu., Watanabe, T., Obut, O.T., Fujiwara, Y., et al., 2001.Evolution of the Paleo-Asian ocean (Altai-Sayan region, central Asia) and colli-sion of possible Gondwana-derived terranes with the southern marginal part ofthe Siberian continent. Geoscience Journal 5, 203–224.

Carlson, R.W., Pearson, D.G., James, D.E., 2005. Physical, chemical, and chronolog-ical characteristics of continental mantle. Reviews in Geophysics 43, RG1001,doi:10.1029/2004RG000156.

Chen, L., in press. Concordant structural variations from the surface to the base ofthe upper mantle in the North China Craton and its tectonic implications. Lithos.

Chen, L., Ai, Y., 2009. Discontinuity structure of the Mantle Transition Zone beneaththe North China Craton from receiver function migration. Journal of Geophysical

Research 114, B06307, doi:10.1029/2008JB006221.

Chen, L., Wang, T., Zhao, L., Zheng, T., 2008. Distinct lateral variation of lithosphericthickness in the Northeastern North China Craton. Earth and Planetary ScienceLetters 267, 56–68.

Condie, K.C., 2002. Breakup of a Paleopreoterozoic supercontinent. GondwanaResearch 5, 41–43.

5 f Geod

F

G

G

G

G

G

G

H

H

H

H

J

K

K

K

K

K

K

K

L

L

M

M

O

P

P

P

R

R

R

S

2 M. Santosh et al. / Journal o

aure, M., Trap, P., Lin, W., Monie, P., Bruguier, O., 2007. Polyorogenic evolution of thePaleoproterozoic Trans-North China Belt, new insights from the Luliangshan-Hengshan-Wutaishan and Fuping massifs. Episodes 30, 1–12.

ao, S., Rudnick, R.L., Carlson, R.W., McDonough, W.F., Liu, Y.-S., 2002. Re–Os evi-dence for replacement of ancient mantle lithosphere beneath the North Chinacraton. Earth and Planetary Science Letters 198, 307–322.

ao, S., Rudnick, R.L., Yuan, H.-L., Liu, X.-M., Liu, Y.-S., Xu, W.-L., Ling, W.-L., Ayres, J.,Wang, X.-C., Wang, Q.-H., 2004. Recycling lower continental crust in the NorthChina craton. Nature 432, 892–897.

rand, S.P., 1994. Mantle shear structure beneath the Americas and surroundingoceans. Journal of Geophysical Research 99, 11591–11621.

rand, S.P., 2002. Mantle shear-wave tomography and the fate of subducted slabs.Philosophical Transactions of the Royal Society of London (Series A) 360,2475–2491.

ung, Y., Panning, M., Romanowicz, B., 2003. Global anisotropy and the thickness ofcontinents. Nature 422, 707–711.

uo, J.H., Sun, M., Chen, F.K., Zhai, M.G., 2004. Sm–Nd and SHRIMP U–Pb zircongeochronology of high-pressure granulites in the Sanggan area, North ChinaCraton: timing of Paleoproterozoic continental collision. Journal of Asian EarthSciences 24, 629–642.

alls, H.C., Heaman, L.M., 2000. The paleomagnetic significance of new U-Pb age datafrom the Molsen dyke swarm, Cauchon Lake area, Manitoba. Canadian Journalof Earth Sciences 37, 957–966.

ou, G., Liu, Y., Li, J., 2006. Evidence for ∼1.8 Ga extension of the Eastern Block of theNorth China Craton from SHRIMP U-Pb dating of mafic dyke swarms in ShandongProvince. Journal of Asian Earth Sciences 27, 392–401.

ou, G., Santosh, M., Qian, X., Lister, G.S., Li, J., 2008. Configuration of the LatePaleoproterozoic supercontinent Columbia: insights from radiating mafic dykeswarms. Gondwana Research 14, 395–409.

uang, J., Zhao, D., 2006. High-resolution mantle tomography of Chinaand surrounding regions. Journal of Geophysical Research 111, B09305,doi:10.1029/2005JB004066.

ordan, T., 1988. Structure and formation of the continental tectosphere. Journal ofPetrology, Special Lithosphere Issue, 11–37.

awai, K., Tsuchiya, T., Tsuchiya, J., Maruyama, S., 2009. Lost primordial continents.Gondwanda Research 16, 581–586.

ennet, B.L.N., 2003. The Seismic Wavefield—Volume 2, Interpretation of Seismo-grams on Regional and Global Scales. Cambridge University Press, 546 pp.

röner, A., Wilde, S.A., Li, J.H., Wang, K.Y., Zhao, G.C., 2005. Age and evolution of alate Archaean to early Palaeozoic upper to lower crustal section in the Wutais-han/Hengshan/Fuping terrain of north China. Journal of Asian Earth Sciences 24,577–595.

usky, T.M., Li, J., 2003. Paleoproterozoic tectonic evolution of the North ChinaCraton. Journal of Asian Earth Sciences 22, 383–397.

usky, T., M., Santosh M., 2009. The Columbia connection in North China GeologicalSociety, London, Special Publication 323, 49–71.

usky, T.M., Li, J.H., Santosh, M., 2007a. The Paleoproterozoic North Hebei Oro-gen: North China craton’s collisional suture with the Columbia supercontinent.Gondwana Research 12, 4–28.

usky, T.M., Windley, B.F., Zhai, M.G., 2007b. Tectonic evolution of the NorthChina block: from Orogen to Craton to Orogen. In: Zhai, M.G., Windley, B.F.,Kusky, T.M., Meng, Q.R. (Eds.), Mesozoic Sub-Continental Lithospheric ThinningUnder Eastern Asia, vol. 280. Geological Society of London Special Publication,pp. 1–34.

i, Y., Wu, Q., Zhang, R., Pan, J., Zhang, F., Zheng, R., 2009. The lithospheric thinningof the North China Craton inferred from Rayleigh waves inversion. GeophysicalJournal International 177, 1334–1342.

iu, M., Cui, X., Liu, F., 2004. Cenozoic rifting and volcanism in eastern China: a mantledynamic link to the Indo–Asian collision? Tectonophysics 393, 29–42.

aruyama, S., Santosh, M., Zhao, D., 2007. Superplume, supercontinent, and post-perovskite: Mantle dynamics and anti-plate tectonics on the core-mantleboundary. Gondwana Research 11, 7–37.

aruyama, S., Hasegawa, A., Santosh, M., Kogiso, T., Omori, S., Nakamura, H., Kawai,D., Zhao, D., 2009. The dynamics of the big mantle wedge, magma factory, andmetamorphic-metasomatic factory in subduction zones. Gondwana Research16, 414–430.

’Brien, P.J., Walte, N., Li, J.H., 2005. The petrology of two distinct granulite typesin the Hengshan Mts, China, and tectonic implications. Journal of Asian EarthSciences 24, 615–627.

eng, P., Zhai, M.G., Zhang, H.F., Guo, J.H., 2005. Geochronological constraints on thePaleoproterozoic evolution of the North China Craton: SHRIMP zircon ages ofdifferent types of mafic dikes. International Geology Review 47, 492–508.

eng, P., Zhai, M.G., Guo, J.H., Kusky, T.M., Zhao, T.P., 2007. Nature of mantle sourcecontributions and crystal differentiation in the petrogenesis of the 1.78 Ga maficdykes in the central North China Craton. Gondwana Research 12, 29–46.

olet, J., Anderson, D.L., 1995. Depth extent of cratons as inferred from tomographicstudies. Geology 23, 205–208.

ogers, J.J.W., Santosh, M., 2002. Configuration of Columbia, a Mesoproterozoicsupercontinent. Gondwana Research 5, 5–22.

ogers, J.J.W., Santosh, M., 2009. Tectonics and surface effects of the supercontinent

Columbia. Gondwana Research 15, 373–380.

udnick, R.L., Gao, S., Ling, W-.L., Liu, Y.-S., McDonough, W.F., 2004. Petrology andgeochemistry of spinel peridotite xenoliths from Hannuoba and Qixia, NorthChina craton. Lithos 77, 609–637.

antosh, M., Omori, S., 2008a. CO2 flushing: a plate tectonic perspective. GondwanaResearch 13, 86–102.

ynamics 49 (2010) 39–53

Santosh, M., Omori, S., 2008b. CO2 windows from mantle to atmosphere: modelson ultrahigh-temperature metamorphism and speculations on the link withmelting of snowball Earth. Gondwana Research 14, 82–96.

Santosh, M., Sajeev, K., Li, J.H., 2006. Extreme crustal metamorphism duringColumbia supercontinent assembly: evidence from North China Craton. Gond-wana Research 10, 256–266.

Santosh, M., Tsunogae, T., Li, J.H., Liu, S.J., 2007a. Discovery of sapphirine-bearingMg-Al granulites in the North China Craton: implications for Paleoproterozoicultrahigh-temperature metamorphism. Gondwana Research 11, 263–285.

Santosh, M., Wilde, S., Li, J.H., 2007b. Timing of Paleoproterozoic ultrahigh-temperature metamorphism in the North China Craton: evidence from SHRIMPU-Pb zircon geochronology. Precambrian Research 159, 178–196.

Santosh, M., Tsunogae, T., Ohyama, H., Sato, K., Li, J.H., Liu, S.J., 2008. Carbonic meta-morphism at ultrahigh-temperatures: evidence from North China Craton. Earthand Planetary Science Letters 266, 149–165.

Santosh, M., Maruyama, S., Yamamoto, S., 2009a. The making and breaking of super-continents: some speculations based on superplumes, superdownwelling andthe role of tectosphere. Gondwana Research 15, 324–341.

Santosh, M., Sajeev, K., Li, J.H., Liu, S.J., Itaya, T., 2009b. Counterclockwise exhumationof a hot orogen: the Paleoproterozoic ultrahigh-temperature granulites in theNorth China Craton. Lithos 110, 140–152.

Santosh, M., Wan, Y., Liu, D., Chunyan, D., Li, J., 2009c. Anatomy of zircons from anultrahot Orogen: the amalgamation of North China Craton within the supercon-tinent Columbia. Journal of Geology 117, 429–443.

Senshu, H., Maruyama, S., Rino, S., Santosh, M., 2009. Role of tonalite-trondhjemite-granite (TTG) crust subduction on the mechanism of supercontinent breakup.Gondwana Research 15, 433–442.

Shao, J.A., Zhai, M.G., Zhang, D.M., Zhang, L.Q., 2005. Identification of 5 time-groupsof dike swarms in Shanxi-Hebei-Inner Mongulia border area and its tectonicimplications. Acta Geologica Sinica 79, 56–67.

Silver, P.G., Chan, W.W., 1991. Shear wave splitting and sub-continental mantledeformation. Journal of Geophysical Research 96, 16, 429-16, 454.

Tian, Y., Zhao, D., Sun, R., Teng, J., 2009. Seismic imaging of the crust and upper mantlebeneath the North China Craton. Physics of the Earth and Planetary Interiors 172,169–182.

Trap, F., Faure, M., Lin, W., Moine, P., Meffre, S., Melleton, J., 2009. The ZanhuangMassif, the second and eastern suture zone of the Paleoproterozoic Tran-NorthChina Orogen. Precambrian Research 172, 80–98.

Wang, Y.J., Zhao, G.C., Fan, W.M., Peng, T.P., Sun, L.H., Xia, X.P., 2007. LA-ICP-MS U–Pbzircon geochronology and geochemistry of Paleoproterozoic mafic dykes fromwestern Shandong Province: implications for back-arc basin magmatism in theEastern Block, North China Craton. Precambrian Research 154, 107–124.

Wilde, S.A., Zhao, G.C., Sun, M., 2002. Development of the North China craton duringthe Late Archaean and its final amalgamation at 1.8 Ga: some speculations on itsposition within a global Palaeoproterozoic supercontinent. Gondwana Research5, 85–94.

Wilde, S.A., Zhao, G.C., Wang, K.Y., Sun, M., 2004. First precise SHRIMP U-Pb zirconages for the Hutuo Group, Wutaishan: further evidence for the Paleoprotero-zoic amalgamation of the North China Craton. Chinese Science Bulletin 49, 83–90.

Xiao, W.J., Windley, B.F., Hao, J., Zhai, M., 2003. Accretion leading to collision andthe Permian Solonker suture, Inner Mongolia, China: termination of the centralAsian orogenic belt. Tectonics 22, 1069, doi:10.1029/2002TC001484.

Xu, P., Zhao, D., 2009. Upper mantle velocity structure beneath the North ChinaCraton: implications for lithospheric thinning. Geophysical Journal International177, 1279–1283.

Yang, J.-H., Wu, F.W., Wilde, S.A., Belousova, E., Griffin, L., 2008. Mesozoic decra-tonization of the North China block. Geology 36, 467–470.

Zhai, M.G., Windley, B.F., Kusky, T.M., Meng, Q.R., 2007. Mesozoic Sub-ContinentalLithospheric Thinning Under Eastern Asia, vol. 280. Geological Society of LondonSpecial Publication, 352 pp.

Zhang, H.F., Sun, M., Zhou, X.H., Fan, W.M., Zhai, M.G., Ying, J.F., 2002. Mesozoiclithosphere destruction beneath the North China Craton: evidence from major,trace element, and Sr-Nd-Pb isotope studies of Fangcheng basalts. Contributionsto Mineralogy and Petrology 144, 241–253.

Zhao, D., 2004. Global tomographic images of mantle plumes and subducting slabs:insight into deep earth dynamics. Physics of the Earth and Planetary Interiors146, 3–34.

Zhao, D., 2009. Multiscale seismic tomography and mantle dynamics. GondwanaResearch 15, 297–323.

Zhao, D., Ohtani, E., 2009. Deep slab subduction and dehydration and theirgeodynamic consequences: evidence from seismology and mineral physics.Gondwana Research 16, 401–413.

Zhao, D., Hasegawa, A., Kanamori, H., 1994. Deep structure of Japan subduction zoneas derived from local, regional and teleseismic events. Journal of GeophysicalResearch 99, 22313–22329.

Zhao, D., Maruyama, S., Omori, S., 2007. Mantle dynamics of western Pacific to EastAsia: new insight from seismic tomography and mineral physics. GondwanaResearch 11, 120–131.

Zhao, D., Tian, Y., Lei, J., Liu, L., Zheng, S., 2009. Seismic image and origin of the

Changbai intraplate volcano in East Asia: role of big mantle wedge abovethe stagnant Pacific slab. Physics of the Earth and Planetary Interiors 173,197–206.

Zhao, G.C., Wilde, S.A., Cawood, P.A., Sun, M., 2001. Archean blocks and their bound-aries in the North China Craton: lithological, geochemical, structural and P-Tpath constraints and tectonic evolution. Precambrian Research 107, 45–73.

f Geod

Z

Z

Z

M. Santosh et al. / Journal o

hao, G.C., Cawood, P.A., Wilde, S.A., Sun, M., 2002. Review of global 2.1–1.8 Gacollisional orogens and accreted cratons: a pre-Rodinia supercontinent? EarthScience Reviews 59, 125–162.

hao, G.C., Sun, M., Wilde, S.A., Li, S.Z., 2005. Late Archean to Paleoproterozoic evolu-tion of the North China Craton: key issues revisited. Precambrian Research 136,177–202.

hao, G.C., Sun, M., Wilde, Li, S.Z., Liu, S.W., Zhang, J., 2006. Composite nature ofthe North China Granulite-Facies Belt: tectonothermal and geochronologicalconstraints. Gondwana Research 9, 337–348.

ynamics 49 (2010) 39–53 53

Zhao, G.C., Kroner, A., Wilde, S.A., Sun, M., Li, S., Li, X., Zhang, J., Xia, S., He, Y., 2007.Lithotectonic elements and geological events in the Hengshan-Wutai-Fupingbelt, Trans–North China Orogen: a synthesis and implications for the evolu-

tion of a long lived (2560–1850 Ma) magmatic arc. Geological Magazine 144,753–775.

Zhao, G.C., He, Y., Sun, M., 2009. The Xiong’er volcanic belt at the southern margin ofthe NorthChina Craton: petrographic and geochemical evidence for its outboardposition in the Paleo-Mesoproterozoic Columbia Supercontinent. GondwanaResearch 16, 170–181.