Geodynamic Setting of Recent Volcanism in North Eurasia

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ISSN 0016-8521, Geotectonics, 2009, Vol. 43, No. 5, pp. 337–357. © Pleiades Publishing, Inc., 2009.Original Russian Text © V.I. Kovalenko, V.V. Yarmolyuk, O.A. Bogatikov, 2009, published in Geotektonika, 2009, No. 5, pp. 3–24.

INTRODUCTION

The project “Recent Volcanism: Its Evolution and Cat-astrophic Consequences” is one of the pivotal projects inthe program of the Presidium of the Russian Academy ofSciences entitled “Changes in the Environment and Cli-mate: Natural Catastrophes.” The most important objec-tive of this project is to ascertain the principles of spa-tiotemporal evolution of recent volcanism in North Eur-asia. In this paper, we present original data and the resultsof integration of extensive available information in form ofthe GIS layout of the map of recent volcanism of NorthEurasia (Fig. 1) compiled by V.V. Akinin, O.A. Braitseva,O.A. Bogatikov, V.M. Gazeev, A.G. Gurbanov,A.N. Evdokimov, V.I. Kovalenko, E.A. Korago,E.A. Kudryashova, A.B. Leksin, I.V. Melekestsev,M.A. Pevzner, V.V. Ponomareva, V.G. Sakhno, F.M. Stu-pak, E.V. Sharkov, and V.V. Yarmolyuk and edited byV.I. Kovalenko, V.V. Yarmolyuk, and O.A. Bogatikov. Themap is based on the results of investigations of many geol-ogists integrated and supplemented by executors of theprogram. The demarcation of the mapped territory takes

into account the type of volcanism, composition of igne-ous rocks, the staged evolution of volcanic activity, and itsgeodynamic setting. The relationships of recent volcanismnot only to geodynamics but also to neotectonics andmountain building are characterized for particular regions.It should be noted that this paper is based on new K–Arand radiocarbon age determinations published in the col-lective monograph [14] with the same title as the afore-mentioned project and as a short summary in [18]. Thegreat body of new factual data cannot be considered in ajournal article, so that only a brief overview sufficient forestablishing the geodynamic setting of recent volcanism inNorth Eurasia is presented in this paper. Readers can getacquainted with the full available information in [14].

THE MAP OF RECENT VOLCANISM OF NORTH EURASIA:

DEMARCATION AND GEODYNAMIC SETTING

Contrary to the previous views that only Kamchatkaand the Kuril Islands are hazardous with respect to

Geodynamic Setting of Recent Volcanism in North Eurasia

V. I. Kovalenko, V. V. Yarmolyuk, and O. A. Bogatikov

Institute of Geology of Ore Deposits, Petrography, Mineralogy, and Geochemistry, Russian Academy of Sciences, 35 Staromonetnyi per., Moscow, 119017 Russia

e-mail: [email protected]

Received March 17, 2009

Abstract

—A GIS layout of the map of recent volcanism in North Eurasia is used to estimate the geodynamicsetting of this volcanism. The fields of recent volcanic activity surround the Russian and Siberian platforms—the largest ancient tectonic blocks of Eurasia—from the arctic part of North Eurasia to the Russian Northeastand Far East and then via Central Asia to the Caucasus and West Europe. Asymmetry in the spatial distributionof recent volcanics of North Eurasia is emphasized by compositional variations and corresponding geodynamicsettings. Recent volcanic rocks in the arctic part of North Eurasia comprise the within-plate alkaline and sub-alkaline basic rocks on the islands of the Arctic Ocean and tholeiitic basalts of the mid-ocean Gakkel Ridge.The southern, eastern, and western volcanic fields are characterized by a combination of within-plate alkalineand subalkaline basic rocks, including carbonatites in Afghanistan, and island-arc or collision basalt–andesite–rhyolite associations. The spatial distribution of recent volcanism is controlled by the thermal state of the mantlebeneath North Eurasia. The enormous mass of the oceanic lithosphere was subducted during the formation ofthe Pangea supercontinent primarily beneath Eurasia (cold superplume) and cooled its mantle, having retainedthe North Pangea supercontinent almost unchanged for 200 Ma. Volcanic activity was related to the develop-ment of various shallow-seated geodynamic settings and deep-seated within-plate processes. Within-plate vol-canism in eastern and southern North Eurasia is controlled, as a rule, by upper mantle plumes, which appearedin zones of convergence of lithospheric plates in connection with ascending hot flows compensating submer-gence of cold lithospheric slabs. After the breakdown of Pangea, which affected the northern hemisphere of theEarth insignificantly, marine basins with oceanic crust started to form in the Cretaceous and Cenozoic inresponse to the subsequent breakdown of the supercontinent in the northern hemisphere. In our opinion, theyoung Arctic Ocean that arose before the growth of the Gakkel Ridge and, probably, the oceanic portion of theAmerasia Basin should be regarded as a typical intracontinental basin within the supercontinent [48]. Mostlikely, this basin was formed under the effect of mantle plumes in the course of their propagation (expansion,after Yu.M. Pushcharovsky) to the north of the Central Atlantic, including an inferred plume of the North Pole(HALIP).

DOI:

10.1134/S001685210905001X

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young volcanic activity, the performed study has shownthat potential volcanic hazard threatens more extensiveterritories at the northeastern, arctic, and southern mar-gins of the Russian Federation. This hazard is related tothose types of volcanic activity which are not character-istic of Kamchatka and the Kuril Islands and develop inthe within-plate and collision geodynamic settings. Thecenters of such volcanic activity are situated withinRussia and close to its borders. Therefore, it hasbecome necessary to depict the occurrences of recentvolcanism over the entire territory of North Eurasia.

The elaboration of this problem in the framework ofthe program “Changes in the Environment and Climate:Natural Catastrophes” resulted in the compilation of amap of recent volcanism of North Eurasia using GIStechnology (Fig. 1). The main objective of this map isdelineating the regions of volcanic activity that devel-oped in the Pleistocene and Holocene, i.e., those that arenot older than 1.8 Ma and are related to recent variationsof tectonic and geodynamic regimes. The latter conditionimplies that the nature of volcanic activity in specificneovolcanic provinces has remained unchanged untilnow and the settings of recurrent volcanic eruptionsremain the same. Because of this, the map is focused onthe attributes pertaining to the last stages of the evolutionof volcanic regions. These stages differ in age in particu-lar regions. For example, the present-day structural graincontrolling volcanic activity in Kamchatka started toevolve about 50 ka ago, and volcanism of precisely thisage is shown in the map (Fig. 1). In contrast, the geody-namic and tectonic regimes of volcanism in the within-plate regions of Central Asia did not change during theentire Late Cenozoic (>25 Ma ago), and the volcanicattributes of this time interval are reproduced in the map.

The topographic and neotectonic [12] maps, as wellas the maps of active faults [11] and earthquake sources[28], were used as a structural base of the GIS layoutshown in Fig. 1. The volcanic areas projected on thesemaps in the form of separate layers allowed us to con-sider the links of volcanic activity with many parame-ters of recent endogenic activity and to provide insightsinto the general evolutional trends of recent volcanismin North Eurasia. The particular volcanic regions differin the composition of igneous rocks and geologicalconditions of volcanic eruptions. The map demon-strates localization of active volcanic fields in the sys-tem of orographic elements of Eurasia and their distinctrelations to young mountains, i.e., zones of neotectonicactivity characterized by numerous microplates smallerin size in comparison with common lithospheric plates.These zones differ in geodynamics and occur at theperiphery of the Eurasian lithospheric plate.

The concentrically asymmetric spatial distributionof recent volcanism is characteristic of North Eurasia.On examination of the map (Fig. 1), the concentricarrangement of the volcanic fields is noteworthy. Theregions with recent volcanism make up the belts sur-rounding the Russian and Siberian platforms as the

largest ancient tectonic blocks. Beginning from thewestern Arctic Region and moving eastward, recentvolcanism is traced from Spitsbergen Archipelago,Franz Josef Land, and Novaya Zemlya to the New Sibe-rian Islands, Gakkel Ridge, the islands that mark theDe Long Dome, and finally, to the northeastern prov-ince of within-plate volcanism of the Chukchi Penin-sula and Alaska. In the east of North Eurasia, recentvolcanism develops as a chain of island arcs, includingthe Aleutian, Kamchatka, Kuril, and Japan arcs, and theadjacent within-plate volcanic province of the easternmargin of the Far East. The system of recent volcanicregions that frames the southern part of North Eurasiais traced westward from the Amur region via the Baikalregion, Mongolia, Afghanistan, Iran, Turkey, and theCaucasus to the eastern and central Mediterranean andWest Europe. Via the north of West Europe, the westernEuropean segment of the belt of recent volcanism isconnected with the western Arctic segment.

The asymmetry in the spatial distribution of recentvolcanism in North Eurasia is expressed in the composi-tional zoning of igneous rocks and variation in their geo-dynamic setting. The arctic segment of the recent volca-nic belt in North Eurasia is distinguished by alkaline andsubalkaline basic rocks on the islands of the ArcticOcean and tholeiitic basalts of the Gakkel Ridge. Suchrock associations are referred to within-plate provincesand mid-ocean ridges, respectively. The volcanic regionsin the eastern segment of the belt related to island arcs arecharacterized by a predominance of basaltic andesite andandesite in the complete range of basalt to rhyolite. Thesouthern and the western segments of the volcanic beltare distinguished by a combination of alkaline and sub-alkaline basic rocks, including carbonatites in Afghani-stan and basalt–andesite–rhyolite associations of colli-sion-related volcanic rocks.

The spatial distribution of recent volcanism in NorthEurasia is nonuniform: igneous rocks concentrate insome regions and are sporadic in others. The volcanicregions are not only spatially separated but differ fromone another in tectonic control of volcanic activity, itsage, and evolutional trend. Volcanic regions of the mid-ocean ridges, island arcs, zones of continental collision,within-plate regions related to mantle hot spots, conti-nental rifts, and transcontinental belts are distinguishedin North Eurasia (Fig. 2).

Volcanic regions of mid-ocean ridges

are illus-trated by the Gakkel Ridge, about 1800 km in extent(Fig. 2, region I). This ridge is an arctic continuation ofthe Mid-Atlantic Ridge in the global system of Mid-Atlantic ridges. The spreading rate in the Gakkel Ridgeis not high (1.0–1.3 cm/yr); however, its structure istypical of MORs. Linear volcanic edifices extend alongthe axial rift valley. At the continental framework of thenewly formed oceanic lithosphere, Late Cenozoicalkali basalts erupted on the New Siberian, NovayaZemlya, and Spitzbergen islands (Fig. 2, region VI),which, probably, mark the region of rifting in the Arctic

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Eurasia Basin. Recent volcanism is suggested in theMakarov Basin [2] and even at the North Pole, thoughother authors are in doubt about this inference [4].

Volcanic regions of suprasubduction island arcs

are exemplified in the Kuril, Kamchatka, and other vol-canic arcs of East Asia (Fig. 2, region II). The recentstage of their evolution is characterized by volcanoesthat appeared during the last 40–50 Ma. Almost allmorphological types of volcanoes are known: lava pla-teau and plains, shield volcanoes and statavolcanoes,and calderas. Andesites are the most abundant, how-ever, the composition of rocks ranges from basalt torhyolite, including lavas, tuffs, and ingnimbrites. Vol-canic rocks of the calc-alkaline series are the most fre-quent; the tholeiitic and subalkaline series are lessabundant.

Volcanic regions of continental collision zones

arerelated to the Alpine–Himalayan Orogenic Belt thatwas formed in the zone of collision between the Ara-bian–African and Indian plates. Recent volcanic activ-

ity proceeded with variable intensity along its entireextent from Central Tibet in the east to the PyreneanPeninsula in the west. The Asian and Europeanbranches of the Alpine–Himalayan volcanic belt, alsocalled Tethyan, are distinguished.

The Asian branch

(Fig. 2, region III) combines thevolcanic regions that are related to the part of the colli-sion belt located in the Asian continent and; it formedabove the zone of collision and subduction of the Ara-bian and Indian plates under the Eurasian Plate. Recentvolcanism is related to the late orogenic stage andstarted mainly in the Pliocene [19, 53, 54]. The largelava plateaus, shield volcanoes, and stratovolcanoesformed at that time are grouped into volcanic chainsextending along the mountain ranges. The igneousrocks vary in composition from alkaline to calc-alka-line basalts via andesites to rhyolites, and even carbon-atite volcanic edifices in Afghanistan.

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(Fig. 2, region IV) of the col-lision volcanic belt is traced along the northern conti-

I

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Geodynamic demarcation of recent volcanic regions in North Eurasia. (

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) boundary of volcanic region. Volcanic regions (numerals in figure): I, Gakkel Mid-Ocean Ridge;II, Kamchatka, Kuril, Aleutian, and other island arcs; (III, IV)Tethyan Collision Belt: III, Asian Branch; IV, Anatolian–BalkanBranch; (V, VI) within-plate provinces: V, East and Central Asia (subprovinces: Va, Maritime, Vb, Central Asian); VI, NortheasternRussia; (VII, VIII) transcontinental rift belts: VII, Central African–Central European, VIII, East African–Transcaucasus.

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nental framework of the Mediterranean Sea and charac-terized by relations to subduction zones. The volcanicactivity developed during the whole Cenozoic. ThePliocene–Pleistocene volcanism is related to recentmountain building. Andesites, dacites, and rhyolitescompose stratovolcanoes and pyroclastic fields. Thepresent-day island-arc volcanism is related to theAegean and Eolian arcs with a number of central volca-noes consisting of andesites, dacites, and rhyolites(lavas and pyroclastic rocks). The volcanoes of theVesuvius group stand out by high-K alkaline igneousrocks.

Volcanic regions of within-plate volcanism

makeup spatially separate groups regarded as within-platevolcanic provinces;

the province of East and CentralAsia

is the largest one. This province comprises a num-ber of spatially separate and structurally unrelated vol-canic regions that evolved during, at least, the last30 Ma [36, 38]. The Maritime and Central Asian sub-provinces are distinguished in geological structure andcomposition of igneous rocks. The Maritime subprov-ince (Fig. 2, region Va) is characterized by NE-trendinggrabens, which are traced along the continental marginand determine the linear distribution of the rift-relatedvolcanic fields. Tholeiitic, subalkali, and alkali basaltsassociated with locally occurring trachyrhyolites,comendites, and pantellerites are predominant.

The volcanic regions of the Central Asian subprov-ince (Fig. 2, region Vb) are scattered between the Sibe-rian and Chinese platforms. Systems of grabens (rifts),for example, the Baikal Rift System, are conjugatedwith some volcanic regions. In general, however, volca-nic activity was unrelated to graben formation andlargely developed beyond the rift basins [35, 36].Melanephelinite, basanite, trachybasalt, and basaltictrachyandesite are typical. This volcanic subprovinceextends into Southeast Asia up to the western margin ofthe Pacific Ocean.

The Northeastern within-plate volcanic province

(Fig. 2, region VI) is characterized by sporadic occur-rences of late Miocene to Holocene volcanic rocks inthe form of separate lava flows, cinder cones,melanephelinitic, basanitic, and basaltic stocks anddikes known from Chukchi Peninsula and Alaska.Some of the volcanic centers are controlled by plateboundaries with high present-day seismicity, e.g., theMoma Graben at the Asian continental extension of theGakkel Ridge. Other centers are located far from theplate boundaries.

The Central African–Central European (CACE) andthe East African–Transcaucasus (EATC)

transconti-nental near-meridional rift belts

are selected as a spe-cial group of within-plate volcanic regions. These beltsare characterized by cross-cutting orientation withrespect to the Eurasian, African, and Arabian lithos-pheric plate boundaries and the Tethyan collision vol-canic belt [19, 34]. The CACE Belt (Fig. 2, region VII)is marked by Late Cenozoic volcanic fields and grabens

of the Central Europe Rift System, in particular, theRhine Graben; the Mediterranean region (Pantelleria,Sardinia, Roman Province); and Northwest Africa(Tibesti, Jabal Haraji, Air, Ahaggar) up to the Gulf ofGuinea.

The EATC Rift Belt (Fig. 2, region VIII) is tracedfrom the Forecaucasus (Mineral’nye Vody district) toTanzania. In the Alpine Fold System, this belt is markedby volcanic fields of the Transcaucasus TransverseRise, where more than half of the total volume of lateorogenic igneous rocks of the Mediterranean Belt wereformed from the late Miocene to Quaternary [19]. Tothe south, in the Arabian Shield, the belt is traced byvolcanic fields and grabens of the Levant System andRed Sea Graben passing further southward into the EastAfrican Rift System.

In conclusion of this section, it should be noted thatthe occurrences of recent volcanism in North Eurasiaare controlled by the boundaries of the lithosphericplates. In the arctic segment of the belt of volcanicregions, these boundaries are of divergent character,whereas in the eastern and southern segments they aremainly related to convergent plate boundaries in theform of island arcs and zones of continental collision.

GEODYNAMIC SETTING OF RECENT VOLCANISM AND A GENERAL MODEL

OF VOLCANIC ACTIVITY IN NORTH EURASIA

The relationship of recent volcanism in North Eur-asia to various types of lithospheric plate boundaries israther evident and in some regions does not contradictthe dependence of igneous rock compositions on thegeodynamic mechanisms of magmatic melt formation.For example, magmatism of the Gakkel Ridge corre-sponds to the MOR setting, while the igneous associa-tions of the Aleutian, Kamchatka, and Kuril island arcsare typical of subduction zones. The magmatism of theAlpine–Himalayan Belt of continental collision fits, toa great extent, the mechanisms inherent to convergentplate boundaries. At the same time, the evolution ofrecent volcanism in North Eurasia raises questions,which are left without answers in terms of commonlyaccepted geodynamic systematics. (1) Why does therecent volcanism that makes up the marginal belt ofEurasia practically not enter into the Russian and Sibe-rian platforms as its ancient core? (2) Why are volcanicrocks different in composition and commonly formedin different geodynamic settings closely associated inspace and time? (3) What are the geological and geody-namic implications of the within-plate volcanic associ-ations widespread in zones of recent magmatism?(4) What geological and geodynamic processes areresponsible for the formation of recent volcanism inNorth Eurasia?

When discussing these and some other questions,we will issue from the available general and regionalschemes of geological and tectonic correlation and

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from the principles of deep geodynamics (plume tec-tonics), plate tectonics, and the data of global seismictomography [5, 15, 25, 31, 32, 35, 36].

The neotectonic evolution of North Eurasia.

Aswas mentioned above, recent volcanism in North Eur-asia was formed in different geodynamic settings con-trolled by plate and plume tectonics [5, 15, 24, 25, 35,37]. We cannot consider the entire tectonic history ofNorth Eurasia in this paper, and this is hardly necessary,because a great number of publications concerning thissubject are available [2, 4, 22, 48, 49, to name only afew]. Only the aspects of tectonic evolution related torecent volcanism are pointed out here.

The continent of Eurasia was formed in the LatePaleozoic (about 250 Ma ago) by amalgamation of thecontinental blocks of Baltia, Siberia, Kazakhstan,Tarim, and some smaller blocks during the closure ofthe Asian and Ural paleooceans in the course of theVariscan and Indosinian orogenies [48, 51] (Fig. 3).The closure of the Iapetus paleoocean in the LateOrdovician to the Early Silurian resulted in the amal-gamation of the North American and Baltic cratonswith Greenland. The amalgamation of all of the afore-mentioned continents together with the continents of thesouthern hemisphere gave rise to the creation of the Pan-gea supercontinent at the end of the Paleozoic (Fig. 3).

During the formation of Pangea, the arctic shelf wasconsolidated into a single continental block by the Mid-dle Triassic as a result of the collision of numerous ter-ranes of West Siberia from the Spitsbergen islands tothe eastern boundary of the Laptev Sea. At that time, avast epicontinental shallow-water basin with numerous

islands separated by rifts filled with plateau basaltsoccupied the place of the present-day Arctic Ocean [2].

Pangea was broken up approximately 200 Ma agointo Laurasia and Gondwana. In the Mesozoic andEarly Cenozoic, Gondwana disintegrated into Africa,South America, India, Australia, and Antarctica,whereas Laurasia broke up into Eurasia and NorthAmerica. This breakup eventually led to the closure ofthe South Anyui Basin, which corresponded in the Cre-taceous to the northern Pacific Ocean that divided theEurasian and North American plates in the east. Thelithosphere of this basin was subducted beneath EastEurasia in the Early Cretaceous with the formation ofthe South Anyui Suture Zone [2].

The enormous mass of the oceanic lithosphere wassubducted when Eurasia was being formed (Fig. 4). Inthe East Mediterranean, the African Plate was sub-ducted beneath the European continent; the ArabianPlate, beneath Asia Minor and the Caucasus; the Indo-Australian Plate, beneath Central Asia. In this way, theEurasian continent expanded to the south. In the east,Eurasia has grown during the last 180 Ma largely bysubduction of the oceanic crust because of the absenceof large continental masses in this part of the Pacific,except Kamchatka, which collided with East Asia. Thesubduction and related cooling of the mantle beneathEurasia continue to the present day. The calculatedlengths of the subducted lithosphere for Japan were10000 km over the last 100 Ma and 15000 km over thelast 150 Ma; 6500 km of the Tethys were consumedover the last 100 Ma and 4500 km of the Himalayasover the last 50 Ma. Similar estimates for the WesternAlps are 1100 km over the last 150 Ma and 500 km over100 Ma [42, 46, 49]. This mass of the oceanic lithos-pheric plates is established beneath the continent byseismic tomography as a

cold superplume

, or a

slab

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Continents of (a) present-day Earth and (b) Pangea(200 Ma ago).

0

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Lithospheric plates buried during the last 180 Ma:results of calculation, after [49]. (

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) subducted plates;(

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) plates subducted beneath Eurasia; (

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) vectors and lineardisplacements of lithospheric plates during their conver-gence. The origin of the arrow indicates the plate margin atthe beginning of convergence and the end of arrow, thepresent-day position of the plate margin. Numerals are thetime intervals when the plates were displaced. According tothe reconstructions, deepwater trenches migrated towardthe Pacific Ocean and to the north in the territory of Tethys.

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graveyard

(high-velocity seismic anomaly) almostthroughout the mantle from discontinuities at 410–660 kmdown to layer D'' at the mantle–core interface [48, 49].Low-velocity seismic anomalies (hot mantle regions)are noted largely in the upper mantle at depths above410–660 km. The aforementioned cold superplumeembraces practically the whole of Eurasia up to thenorthern Urals and the North Sea and the Tethyan Med-iterranean province (Fig. 5).

A quite different situation occurred in the ArcticRegion. The Canada Basin, as a part of the larger Amer-asia Basin, opened here in the Early Cretaceous alongwith the formation of the Franz Josef volcanic plateau,which is combined with dike swarms and volcanicflows of the arctic islands of Canada and Greenland intothe High Arctic Large Igneous Province (HALIP) [39,44, 45, 47]. The center of the dike swarms recon-structed at the moment predating the breakdown of

Greenland, Svalbard, and Franz Josef Land is outlinedat the northeastern margin of Queen Elizabeth Islandand referred to the effect of a mantle plume. Accordingto preliminary data, the formation of dike swarmslasted through the Cretaceous and Cenozoic. TheMakarov Basin, with spreading in its axial zone andsubduction at its eastern margin, opened 120–90 Maago [2]. Subduction was accompanied by island-arcvolcanism. The Alpha–Mendeleev volcanic plateauarose above this subduction zone at the end of the Cre-taceous [2]. Within-plate basic volcanic rocks wereformed at the same time at the continental shelf of Eur-asia: the Hyperborean (De Long) Dome in the CanadaArctic Archipelago and Cape Washington in the northof Greenland. Spreading in the Gakkel Ridge started inthe Paleocene 53 Ma ago contemporaneously with theopening of the Eurasia Basin [3], which continues to

Fig. 5.

Regions of high-velocity cold mantle of North Eurasia in the transitional zone at a depth of ~600 km, after [59]. View fromthe North Pole. (

1, 2

) Continental plates: (

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) continents proper and (

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) continental shelf; (

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) high-velocity cold mantle; (

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) conver-gent boundary. A–B–C is the line of the schematic section shown in Fig. 6.

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expand currently, with the development of tholeiiticbasaltic volcanism.

Thus, the geological history of the arctic part of NorthEurasia, on the one hand, and its eastern, southern, andwestern portions, on the other hand, are different. Theeastern, southern, and western portions were character-ized by long-term subduction that gave rise to the forma-tion of the cold middle and lower mantle [26, 27],whereas the geodynamics of the active arctic regions wasclose to extension. Comparison of the northern andsouthern groups of continents pertaining to Pangea, how-ever, indicates that local extension in the northern part ofthis supercontinent was weak. In the southern (Gond-wana) part of Pangea, practically all present-day conti-nents had been separated by that time, whereas in the arc-tic part, the Atlantic spreading system expanded into theArctic Region with the formation of an insignificantinner oceanic basin and the Gakkel Mid-Ocean Ridgeonly in the Cenozoic [23, 33] (Fig. 1). Rifting in Arcticawas a local rather than a global phenomenon. As wasemphasized in [33], rifting and spreading in Arctica is ofincomplete character with repeated jumping of thespreading axes. The geodynamic difference of the north-ern and the southern parts of Pangea probably testifies tothe general retention of the supercontinental character ofits northern block. This was possible only if the astheno-sphere and the mantle as a whole were relatively cold andthe lithospheric plates were retained as in a trap from theLate Paleozoic until the present. If this was actually thecase, the incomplete rifting in Arctica, accompanied byspreading, reflected local invasions of hot mantlethrough the prevalent cold mantle material. Such expan-sion of the hot mantle into Arctica had global conse-

quences only from the side of the Atlantic. Thus, therecent geodynamic evolution of North Pangea supportsthe data of global seismic tomography, indicating thepredominance of cold mantle in this part of the Earth.

In general, the Cenozoic geological history of Arc-tica resembles the late stages of evolution of the super-continents (Fig. 6). Eurasia, North America, and Green-land with their shelves can be referred to such a super-continent, where oceanic basins occupy less than 50%of the Arctic Ocean and only a negligible portion of theaforementioned continents (Fig. 7). If this suggestion isvalid, the Arctic Ocean itself should be regarded as anintracontinental sedimentary basin typical of the evolvedsupercontinent (cf. Fig. 6 and Fig. 15 from [48]). Theorigination of a basin with oceanic crust and its connec-tion with the Atlantic Ocean, as well as the separation ofNorth America and Greenland, are indications of thesubsequent breakdown of this supercontinent.

Within-plate magmatism of North Eurasia andmantle plumes.

The regions of recent volcanism inNorth Eurasia are delineated on the map shown inFig. 1. These regions are related to the plate boundariesand the territories situated beyond these boundaries,i.e., the areas of within-plate reactivation. In addition tothese regions, magmatism with intraplate isotopicgeochemical and volcanological signatures is wide-spread in the unusual setting, first of all, in the volcanicregions of the collisional Alpine–Himalayan Belt. Thisis an important point, and we will dwell on it below.

Let us estimate which volcanic occurrences shownin the map are related to mantle plumes documented byseismic tomography [60]. Only a few hotspots, charac-

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Geodynamic settings that control formation of North Pangea supercontinent.

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terized in [60], are related to the occurrences of recentvolcanism in North Eurasia. A whole-mantle plumethat extends from the mantle–core interface is estab-lished beneath the Eifel volcanic region in WestEurope. A low-velocity seismic anomaly is traced fromthe mantle–core interface upward to the discontinuityof 660 km, where it spreads in the northwestern direc-tion. In the depth interval between 660 and 410 km, this

anomaly is interrupted by high-velocity cold mantle,which is correlated with the subducted African Plate.Low-velocity hot mantle material appears again abovea depth of 410 km.

Low-velocity seismic anomalies (hot mantle) aredetected above 410 km, in the transitional zone between410–660 km, and below this zone beneath active within-

EA

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Continents and regions of recent magmatism in the northern hemisphere of the Earth (view from the North Pole). (

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) microplate boundary. Tectonic elements (abbreviations in circles): Can, Canada Basin; M, Makarov Basin;EA, Eurasia Basin; FJ, Franz Josef Islands; SA, South Anyui Suture.

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plate volcanoes in the eastern part of North Eurasia(Changbaishan, Pektusan, and Wudalianchi volcanoes).

A great number of mantle plumes are established inSoutheast and East Asia [49, 59]. Some occurrences ofrecent volcanism shown in the map are related to theseplumes. The location of such plumes is demonstrated inFig. 8. They are traced from the Aleutian arc, along theeastern margin of Eurasia up to New Zealand. The rela-tion of plumes to several island arcs attracts attention.In some cases, the plumes are confined to marginalseas; however, as was emphasized by Maruyama [49],a number of plumes cannot be referred to marginalbasins (Caroline, Fuji, Woodlark) because they occurbeyond the trench or are unrelated to shallow plate tec-tonics. These plumes are characterized by low-velocityS-wave anomalies that indicate hot mantle in the transi-tional zone (410–660 km) [58] and deeper [59]. Near

the surface, especially in the continental part, theseanomalies are marked by occurrences of alkali and sub-alkali basalts with OIB signatures [29] and, occasion-ally, by tholeiitic basalts close to MORB in composi-tion. This recent volcanism of East and Southeast Asiahas been called remarkable [50] because it is confinedto the region of a cold superplume [49] and requires aspecial explanation of its geodynamic setting. Theauthors mentioned above deemed that the occurrence ofa deep cold superplume in combination with highendogenic activity, manifested not only in within-platevolcanism but also in the formation of many micro-plates (Fig. 8), often with marginal basins, is the maingeodynamic contradiction of this region. Both the vol-canism in such basins and the within-plate characteris-tics of the igneous rocks are explained by spreading.The seismic tomography in the system of the Tonga

?

1 2 3 4 5 6 7

?

Fig. 8. Regions of low-velocity hot mantle (mantle plumes) in the upper mantle of North Pangea, after [7–9, 59, 60]. The hatchedcircles are projections of mantle plumes. See Fig. 6 for other symbols.

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island arc and marginal sea shows, however, that thisinterpretation is dubious because the low-velocityanomaly beneath the marginal sea extends to a depthgreater than 500 km, whereas the sources of spreading-related magmas are commonly detected at a depthabove 100 km. We will return to this contradictionbelow.

We should make separate mention of the deep struc-ture of the Central Asian within-plate province, which,in the opinion of some authors, is genetically related tothe processes that occur along the eastern convergentboundary of the continent [7–9, 20, 59]. The idea of theexistence of hot mantle at the bottom of this province isconfirmed by geophysical data. The territory where theasthenospheric mantle of South Siberia and Mongoliarises to a depth of less than 100 km [6, 61, 63] is con-toured in Fig. 9. In addition, the local juts of theasthenophere, which attain the bottom of the crust at adepth of about 50 km, e.g., in the South Baikal Basin,are shown; they are interpreted as mantle plumes[36, 63]. The location of these plumes coincides withregions of Late Cenozoic volcanism (Fig. 9). In partic-ular, the South Hangay, South Baikal, and Udokanhotspots and the Vitim Plateau in the marginal part ofthe North Baikal mantle salient correspond to theplumes in their localization.

Zorin et al. [7–9] have established the location ofplume stems, which previously remained uncertain.The gravity models of plume stems beneath the BaikalRift Zone and the highlands of Central Mongolia(Figs. 10a, 10b) are consistent with the seismic data onthe distribution of group velocity of long-period Ray-leigh waves (Fig. 10c) and azimuthal seismic anisot-ropy (Fig. 10d) [7–9].

It turned out that the plume stems are locatedbeneath the thinned lithosphere, i.e, within the previ-ously established asthenospheric salient [6, 62]. Thereduced thickness of the lithosphere above the plumesis a rather typical phenomenon related to the thermaleffect [55]. As was stated in [9, 63], the asthenosphericsalient is composed of merging plume heads. Becausethe plumes are melted as a result of decompressionlargely in their head portions at a depth of 60–150 km[10], the location of the fields of Neogene basalts isdetermined, to a greater extent, by configuration ofasthenospheric salient rather than by the position of theplume stem (Fig. 9). The existence of mantle plumes atthe bottom, at least of the South Hangay and SouthBaikal regions was corroborated by seismic tomogra-phy [17, 21, 22]. As a result, the thinned stem segmentsof the plumes have been traced to a depth greater than600 km. The geophysical data allow us to speak aboutstreams of low-velocity mantle beneath the volcanicregions of Central Asia. These streams are mushroom-shaped, as is typical of plumes, and ascend at least fromthe upper and lower mantle boundaries up to the loweredge of the lithosphere.

A low-velocity region of the mantle interpreted as ahot or water-enriched mantle plume is detected at thebottom of the western Mediterranean and in centralWest Europe [43]. Such a mantle underlies almost theentire western European region of recent within-platevolcanism, including, first of all, the Central EuropeanRift Belt, as well as other districts of West Europe, theEast Atlantic, North Africa, and the West Mediterra-nean (to the west of Italy). The mantle of this territoryis characterized by anomalously low velocities of P-and S-waves over an area of 2500 × 4000 km2 and morethan 500 m in depth, mainly localizing in the transi-tional zone. The occurrence of hot mantle is confirmedby the high heat flow beneath the Central European RiftZone. As is suggested in [43], the occurrence of a strat-iform hot plume in this region explains the develop-ment of local extension against the background ofregional compression caused by subduction of the Afri-can Plate beneath Eurasia. The lower temperature ofthis plume in comparison with the superplumes isexplained by its shallow-seated position in the transi-tional zone between the upper and lower mantle. Thesame cause limits the spreading of recent volcanism inWest Europe and the Mediterranean and explains thelocal rifting characterized by insignificant opening ofextension structural elements. This plume is similar tothe anomalous mantle of Central and East Asia in thecomposition of igneous rocks (alkali, subalkali, andless frequent tholeiitic basalts), localization in the tran-sitional zone (410–660 km), and ambiguous relation-ships to subduction zones. The control of particular vol-canic fields by mantle anomalies is similar as well.Thus, the relatively narrow mantle juts (hot fingers) atthe bottom of the Central French, Rhine, and Bogemianmassifs and the Panonian Basin ascend from the transi-tional zone to the crust bottom [56, 67], like the afore-mentioned salients at the bottom of the volcanic regionsin Central Asia.

Unfortunately, data of seismic tomography in thearctic part of North Eurasia are lacking, so that somesuggestions stated below are based on analogy with theregions underlain by mantle plumes.

The Jan Mayen plume located between the NorthAtlantic and the Arctic Region and proved by seismictomography [60] is close to the Iceland plume in mor-phology. This plume is traceable from the core–mantleinterface to the upper mantle (with several gaps) andexpands below the discontinuity of 660 km. It is evidentthat volcanism is fed here by this plume.

Using the correlation between surface geology andglobal seismic tomography for the substantiation of theconcept of plume tectonics, Maruyama [48, pp. 26 and30] mentioned a plume beneath the North Pole amongstthe deep mantle plumes of the Atlantic. Unfortunately,this plume was not shown in any of numerous figurespresented in the papers by Maruyama and other authorsengaged in global seismic tomography. If it is assumedthat the opening of the Atlantic Ocean during the break-



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Fig. 9. Mountain systems and regions of recent volcanism in the south of Eastern Siberia and Central Mongolia with structural elementsof the lithosphere, after [63]. (1) Lava field, (2) plate and microplate boundaries, (3) asthenospheric rise at a depth of <100 km,(4) asthenospheric salient (mantle plume) at a depth of <50 km, (5) dominating mountain peaks. Lithospheric plates and microplates(inscriptions in figure): Sib, Siberian; Mon, Mongolian; Am, Amur; volcanic regions: SH, South Hangay, SB, South Baikal;NB, North Baikal; Ud, Udokan; Vit, Vitim Plateau; Dar, Dariganga Plateau.

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down of Pangea was controlled by a chain of mantleplumes, it should be suggested that one of these plumeswas located at the northern end of the mid-ocean ridgein the vicinity of the North Pole or, more likely, near thespreading Gakkel Ridge.

The available geological data on the formation his-tory of the arctic portion of North Eurasia do not con-tradict this suggestion. Judging from paleomagnetic

data and paleodynamic reconstructions [41, 51], thispart of Eurasia was located at the polar latitudes andperiodically involved in within-plate reactivationbeginning from the Late Permian. The Siberian flood-basalt province, which started to form in the Late Per-mian–Early Triassic, embraced, in addition to the Sibe-rian Platform, the Taimyr and New Siberian Islands,and the Chukchi Peninsula. Basaltic eruptions in the

Fig. 10. Interpretation of geophysical data for territory of Central Asia, after [7–9]. (a, b) Gravity models of plume stems: (a) long-wave isostatic anomaly, (b) theoretical gravity effect of a set of cylindrical bodies whose upper and lower edges are located at depthsof 150 km and 420 km, respectively; (c) group velocity of Rayleigh waves for a period of 100 s. Projections of plume stems fall intolow-velocity regions; (d) seismic azimuthal anisotropy in the upper 200 km of the mantle. The directions of seismic anisotropy cor-responding to the directions of material flow in the asthenosphere reveal a tendency to radial orientation relative to the plume stems.(1) Projection of plume stem, (2) Late Cenozoic lava fields, (3) seismic stations and fast directions of anisotropy.

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Kara Sea occurred in the Triassic and Early Jurassic.Rifting and formation of the Franz Josef volcanic pla-teau took place in the Late Jurassic and the Early Cre-taceous. The Cretaceous and Cenozoic history of theArctic Basin characterized above was also marked byepisodic within-plate activity. One such episode wasrelated to the formation of the large HALIP igneousprovince, which comprised the Early Cretaceousspreading magmatism of the Makarov Basin. The sec-ond episode was the formation of the Late CretaceousAlpha–Mendeleev lava plateau; the third episodestarted 53 Ma ago and led to the rise of the GakkelRidge. Thus, the geological data testify to the activemantle beneath the arctic territories, which affected thelithosphere in a pulsatory manner and periodically gaverise to the formation of large igneous provinces relatedto the activity of mantle plumes.

This concept does not contradict the localization ofvolcanic rocks of elevated alkalinity in Arctica. Suchvolcanics are localized in the continental framework ofthe Gakkel Ridge beyond the active spreading center,similarly to the same rocks in the framework of the RedSea and the Gulf of Aden, which opened above the Afarplume. Finally, submarine eruptions dated at the secondhalf of the 15th century, the first half of the 18th cen-tury, and 1957 are noted along the Lomonosov Ridge ata distance of 192 km to the southwest of the North Pole[45]. The center of these eruptions was located at88°16′ N and 65°36′ W near a seamount at the spurs ofthe Lomonosov Ridge, which towers by 1500 m abovea bottom depth of 3000 m. Seismic activity is recordedhere, and fragments of basaltic hornblende and volca-nic glass have been found. This seamount is an inferredactive volcano. The De Long Rise [30] and the eastern-most part of the Chukchi Peninsula are also regarded aspresumable sites of plume location [1, 48, 49].

Kamchatka is characterized by a predominance ofisland-arc recent volcanism. At the same time, in thecentral part of the eastern shore of Kamchatka, wherethe Emperor Ridge is approaching, the indications ofCretaceous within-plate volcanism are pointed out asevidence for the initial formation of this block in thevicinity of the Hawaiian hotspot and its subsequenttraveling along with the Pacific Plate toward East Asia[16]. If this was the case, the Kamchatka Block withoccurrences of within-plate volcanism was formedunder the effect of the Hawaiian mantle plume.

A general model of recent volcanic activity ofNorth Eurasia. As was mentioned above, the regionsof recent volcanism in North Eurasia are broadly con-trolled by boundaries of lithospheric plates. In the Arc-tic Region, a divergent-type boundary and related mag-matism are localized in the spreading Gakkel Ridge andits continental framework.

Recent volcanic regions are mostly controlled byconvergent boundaries of lithospheric plates thatencompass North Eurasia in the south as a semiring.The character of the magmatism at these boundaries is

consistent with the mechanisms of magma generationcorresponding to such boundaries. Some differencesare likely determined by a special regime of boundaryformation. Their peculiarities are caused by the subduc-tion of an enormous volume of lithospheric materialbeneath North Eurasia in the Late Cretaceous and Cen-ozoic (Figs. 4, 5) in combination with relatively con-stant location of subduction zones. It may be suggestedthat the storage of giant masses of cold subducted mate-rial exceeding the overlying continental lithosphere involume must be accompanied by certain geologicaleffects and reflected in recent volcanic activity. Thisspecific character is expressed, first of all, in the abun-dance of volcanic rocks having within-plate signaturesbut occurring under atypical, as is supposed now, con-ditions of convergent boundaries. The possible mecha-nisms controlling such specificity are consideredbelow.

To characterize these mechanisms, it is necessary todiscern the geodynamic settings of shallow-seated platetectonics (down to a depth of 660 km) and deep geody-namics that embraces the entire mantle down to layer D''at the mantle–core interface. Deep geodynamics, cur-rently called plume tectonics, is governed by whole-mantle convection, which assumes sinking of the coldsubducted lithosphere deep into the mantle down to itsboundary with the Earth’s core and compensatingascent of hot mantle flows in the form of superplumesand smaller plumes. The subducted lithosphere candrown in the lower mantle only when the density of theburied mass exceeds the mantle density. This possibil-ity is realized not always and not immediately after sub-duction of the lithosphere into the transitional zone410–660 km deep. Judging from the high-velocity seis-mic anomalies established by global seismic tomogra-phy in the mantle beneath Eurasia and, to a lesserextent, beneath America, considerable time is requiredfor transformation of the subducted lithosphere intohigh-density aggregations. For example, the subductionbeneath Asia on the side of Pacific Ocean lasted for noless than 450 Ma. In some localities, this processstarted much earlier, during the breakdown of the Rod-inia supercontinent and the formation of the PacificOcean. The last supercontinent, Pangea, formed largelyin the Permian and Triassic (Fig. 3), is retained in thenorthern hemisphere until now (in its broad outlines)with amalgamation of North America, Greenland, andEurasia. Indeed, the breakdown of North Pangea ismanifested not only in the appearance of newly formedoceanic crust [33] but also in the separation of NorthAmerica and Greenland (rift of the Nares Strait) orNorth America and Eurasia (rift of the Bering Strait).This disintegration, however, does not compare inscope with the separation of South America, Australia,and Antarctica, and this difference allows us to suggestthe retention of the North Pangea supercontinent as anintact mass. The Upper Paleozoic sediments of someformerly existing basins have probably been retainedsince Panthalassa on the shelf of the Arctic Ocean [4,

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33]. The Barents Sea Basin, filled with Upper Paleozoicand Triassic sequences of immense thickness, is anexample [33]. Precisely at that time, the lithosphericplates subducted to the transitional zone beneath thispart of the supercontinent became able to sink at themantle’s bottom with formation of a huge high-velocityseismic anomaly, or cold superplume [48, 49]. Sincethis moment, the system of global mantle convectionhas changed.

For reasons so far ambiguous, cold superplumesgave way to hot plumes and are followed by breakdownof supercontinents. The breakdown of Pangea is a strik-ing example in this respect (Fig. 3). It is evident thatthis process is controlled by the thermal state of themantle beneath the supercontinent. Judging from thedata of seismic tomography, North Pangea is underlainmainly by cold mantle, whereas the piece of Pangealocated in the southern hemisphere is underlain by hotmantle and therefore was fragmented into South Amer-ica, India, Australia, and Antarctica. The northern partof the supercontinent remained relatively calm becauseof ceaseless subduction of enormous masses of the coldlithosphere, which suppressed the hot mantle thatexisted beneath this part of the supercontinent as well.The occurrence of the hot mantle related to the lowermantle plume made itself felt by periodic breaching tothe surface at arctic latitudes. As was mentioned above,such breaches resulted in the formation of Siberian pla-teau basalts; the Jurassic rifting and magmatism in theEast Siberian and Chukchi seas and the arctic margin ofAlaska [33]; and the Cretaceous activity with formationof the HALIP (see above).

The ongoing subduction beneath North Eurasiafrom the east to the south did not permit progress inthese processes. The prevalence of compression overextension was most obvious during the formation of theSiberian flood basalt province. Despite the vigorouswithin-plate processes in North Eurasia 250 Ma ago,they did not lead to the breakup of the lithosphere andformation of a new ocean. Spreading was suppressed atthat time, as well as later, in the Early Cretaceous, whenthe evolution of the HALIP did not give rise to theopening of a new ocean. Spreading reactivated only inthe Early Cenozoic in connection with opening of theNorth Atlantic and development of the Iceland and JanMayen plumes. A new Eurasia Basin with the spreadingGakkel Ridge was opened about 53 Ma ago and theyoung Arctic Ocean started to evolve at that time [4].Taking into account that the zones of continentalbreakup are formed between mantle plumes [40], itshould be supposed that one more plume existed nearthe eastern end of the Gakkel Ridge. As was suggestedabove, it could have been a younger mantle plumebeneath the North Pole or a new pulse of the HALIPplume probably accompanied by other smaller plumes(De Long, Bering, etc.). In contrast to other spreadingbasins of the world, the Arctic oceanic basin is smallerin size and characterized by a low spreading rate, prob-ably as a result of ongoing accumulation of cold lithos-

pheric material beneath the continent. Nevertheless, itis more reasonable to refer recent arctic volcanism tothe activity of the aforementioned plumes (Fig. 8),which gave birth to the Gakkel Ridge. Thus, recentbasic volcanism of elevated alkalinity in the arctic partof North Pangea is most likely caused by within-plateactivity of mantle plumes, whereas tholeiitic volcanismis related to zones of shallower spreading.

A more complicated situation arises with interpreta-tion of the geodynamic nature of recent volcanism inthe southern tract of volcanic regions in North Eurasia.The main point of contention regarding this interpreta-tion is the cause of the formation of the mantle plumesthat produce basic magmatism of elevated alkalinity inthe part of North Eurasia underlain by a cold super-plume. The simplest possible explanation is related tothe mass balance in the lower mantle, when the coldmaterial of subducted plates sinks to the mantle–coreinterface or another deep-seated discontinuity. It is evi-dent that this material must squeeze out a deep-seatedhot material, and the latter will ascend as lighter hotplumes through the cooled mantle. As follows from thestructure of the mantle at the convergent boundaries inEast and Southeast Asia [59], a part of compensatingmaterial ascends immediately near the convergentboundary (Fig. 11), and the remainder is involved inwhole-mantle convection, compensating the consump-tion of material for the formation of a new crust inMOR and activity of mantle hot spots. If the cold litho-spheric plates actually accumulated beneath CentralEurasia, North America, and Greenland at the mantle–core interface (slab graveyard, after Maruyama), it isnatural to assume that the hot material of the lowermantle or layer D'' would be squeezed out to the periph-ery of this graveyard, that is, to the southern peripheryof North Eurasia, North America, and Greenland, i.e.,to the margin of the North Pangea supercontinent.Miyashiro [50] referred this volcanism (remarkable, inhis terms) to a hot region of the mantle. As follows fromthe data of global seismic tomography, this suggestioncomes into conflict with the actual occurrence of coldmantle beneath Asia. Zhao [49, 59] supposed that Ter-tiary and Quaternary volcanism of East Asia is relatedto the formation of a big mantle wedge, whose dimen-sions are determined not only by the zone of subductionof the Pacific Plate beneath Asia but also by near-hori-zontal extension of this zone in the transitional mantleat a depth of 410–660 km for almost 1500 km west-ward. This idea in application to the Baikal region wasdeveloped by Zorin [7–9] (Fig. 12). It is inferred thatdehydration of hydrosilicates retained in a stagnant slabresulted in entering of fluids into the asthenosphere andbrought about its upwelling [61], which, in turn, gaverise to the generation of basaltic magmas and rifting.Because Central Mongolia and the Baikal region aresituated more than 1500 km to the west of the gentlydipping stagnant slab, it is assumed that subduction isaccompanied by development of a convective cell elon-gated in the horizontal direction in the asthenosphere of



the mantle wedge [5]. It is suggested that the ascendingbranch of this convective cell may be taken outside thestagnant slab and, in particular, extend to the bottom ofthe Baikal Rift System and the highland of CentralMongolia [7–9]. The batches of material emerging as anascending branch of convective flow must acquire an ener-getically advantageous droplike or columnar [55] config-uration, in other words, behave as plumes (Fig. 12).

This model does not rule out the aforementionedmechanism of balanced cold and hot mantle during thesinking of slabs. The model assumes a certain relation-ship between the plunging oceanic lithospheric plateand intracontinental volcanic regions, which is notobservable in the surface regional geology. This model,however, meets a number of contradictions. Thus, it ishard to imagine how the composition and character ofmagmatism and the unchanged location of volcanicregions in the structure of the lithosphere could havebeen retained for 150 Ma if the configuration of the

subduction zones in East Asia was changed repeatedlywith substantial recession for more than 1500 km fromthe Lesser Khingan in the Early Cretaceous to Japan at

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Fig. 12. Structure of the mantle in East Eurasia and a modelof the formation of mantle plumes beneath the Baikal RiftZone and the highland of Central Mongolia: (a) section line;(b) mantle section, after [61]; and (c) a model, after [7–9].According to the model, the batches of heated and fertilizedperidotite are detached from a stagnant slab sinking into thelower mantle. After separation, these batches emergethrough the upper part of the transitional zone and areinvolved in convection. The ascending branch of this con-vection breaks into particular streams, which are regardedas upper mantle plumes.

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–1% 0% +1%

Fig. 11. (a) Deep structure of the mantle at convergentboundaries of the western Pacific Ocean, after [59], and(b) a model of convective flows at these boundaries.

duction

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present. It should also be kept in mind that igneousrocks typically have within-plate compositional signa-tures without indication of island-arc specificity.Finally, the concentration of volcanic activity in severalregions could not have been related to a single convec-tive system in the asthenosphere of a big mantle wedge.

It has been suggested that the mantle plumes in EastAsia bear a hydrous (0.2 wt % H2O in mantle source)rather than thermal character owing to the intense dehy-dration of a huge mass of subducted plates [49]. Smith[52] explained this magmatism by its links to a DUPALsource that arose in the metasomatized mantle wedgeformed as a result of subduction or ascent of hydrousmantle plumes due to the exsolution of wadsleyite intoolivine and hydrous melt enriched in LILE at a depth of410 km. This idea is not yet supported by direct obser-vations concerning the water content in basic magmas.The first available data on melt inclusions show that themelts were dry and the water content therein was nothigher than the average H2O concentration in OIB [13].

Thus, the aforesaid allows us to accept the model ofmass balance in the mantle.

In summary, the model of recent volcanism in NorthEurasia may be presented as follows (Fig. 13). In thecourse of breakup of Pangea, its northern part wasretained as a large aggregation of continents, which canbe considered a supercontinent. The subduction alongtheir common framework determined the stability ofthis group of landmasses and prevented their fragmen-tation. The volume of the supercontinent increasesalong the convergent boundaries surrounding the stableplatform of North Eurasia, and these boundaries werecrucial for the localization of volcanic regions. Thecomposition and mode of occurrence of recent volcanicrocks (except within-plate varieties) were controlled, toa great extent, by the processes occurring at plateboundaries and by sublithospheric processes related tothe activity of mantle plumes. The long-term subduc-tion of lithospheric plates beneath Eurasia and NorthAmerica led to the accumulation of cold lithospheric

material and the cessation of convection in the hot man-tle. The activity of the mantle plume in the Polar Regionof the Earth has been suppressed since the Late Per-mian; the material of the hot mantle has reached theEarth’s surface only sporadically. The recent phase ofplume activity has given rise to the formation of theGakkel Spreading Ridge and to eruptions of within-plate alkali basalts scattered at the periphery of the oce-anic basin. The low spreading rate in the Arctic Oceantestifies to the locking effect of the buried cold mantleon the activity of the hot mantle. We suggest that thespecificity of the magmatic processes at the convergentboundaries of North Eurasia was related to compensat-ing convective motions of the mantle in the zonesaffected by subduction boundaries. The sinking lithos-pheric plates are components of whole-mantle convec-tion. At the same time, the nonsteady state of the sub-duction branch of the convection loop and the occur-rence of stagnant and fragmented slab segments giverise to the formation of additional convective cells andthe ascent of hot mantle flows, which compensate thesinking lithospheric slabs.

The formation of mantle plumes as a result of deepmantle convection was accompanied by collision- andsubduction-related shallow-seated magmatism in thesouthern and eastern parts of North Eurasia. In the Arc-tic Region, deep-seated plume magmatism (basic rocksof elevated alkalinity) was accompanied by shallowspreading magmatism (tholeiitic basalts).

CONCLUSIONS

(1) A GIS layout of the map of recent volcanism ofNorth Eurasia has been compiled. Topographic andneotectonis maps, as well as maps of active faults anddistribution of earthquake sources presented as separatelayers served as a structural base of the layout. Regionsof recent volcanism projected on these maps provideinsights into the links of volcanic activity with indepen-dent parameters of recent endogenic processes and

North AmericaEurasia Pacific

superplume

0

500

1000

1500

2000

2500km

Continental lithosphere

Transitional mantle

Low-velocity hot mantle

Standard mantleSubducted lithosphere andhigh-velocity cold mantleMantle flow

EurasiaBasin

Fig. 13. A geodynamic model of the formation of the North Pangea supercontinent.



have allowed us to estimate the main trends in the evo-lution of recent volcanism in North Eurasia.

(2) Recent volcanism in North Eurasia occursaround the Russian and Siberian platforms—the largestancient tectonic blocks of Eurasia—embracing the Arc-tic Region of Eurasia and extending in its southern partfrom the Northeast and Far East of Russia via CentralAsia and the Caucasus toward West Europe.

(3) The asymmetry in the spatial distribution ofrecent volcanism in North Eurasia is expressed in vari-ation of the composition and geodynamic setting ofigneous rocks. The arctic part of North Eurasia is char-acterized by the occurrence of within-plate alkali andsubalkali basalts on the islands of the Arctic Ocean andthe tholeiitic basalts in the Gakkel Ridge. The southern,eastern, and western segments of the tract of recent vol-canism are characterized by a combination of within-plate alkali and alkaline basalts (including carbonatitesin Afghanistan), and collision basalt–andesite–rhyoliteassociations.

(4) In the course of the formation of the Pangeasupercontinent, an enormous mass of oceanic lithos-phere was subducted, first of all, beneath Eurasia. Thismass of oceanic lithospheric plates is recorded by seis-mic tomography as a cold superplume (high-velocityseismic anomaly) for the entire depth interval from thediscontinuity of 410–660 km to layer D'' at the mantle–core interface. At that time, an epicontinental basinexisted on the place of the Arctic Ocean, as is typical ofsupercontinents. After the breakdown of Pangea, sub-duction beneath Eurasia has proceeded from the southand the east until the present day with ongoing growthof the cold superplume.

(5) In brief terms, our model of the formation ofrecent volcanism in Eurasia is stated as follows. In gen-eral, the volcanic activity is controlled by the bound-aries of the lithospheric plates that limit the territory ofNorth Eurasia and determined by the geodynamicregimes at these boundaries. The eastern and southernlimitations correspond to convergent boundaries andthe related volcanic regions are characterized by supra-subduction setting. The widespread within-plate volca-nic rocks are controlled by mantle plumes, whichappear in convergent zones owing to ascending flowsfrom deep hot mantle that compensated plunging of thelithospheric slabs.

Since the breakdown of Pangea, which affected thissupercontinent in the northern hemisphere of the Earthonly a little, marine basins with oceanic crust started toform in the Cretaceous and Cenozoic as manifestationsof further breakdown of the supercontinent. In ouropinion, the young ocean that existed before theappearance of the Gakkel Ridge and, probably, the oce-anic portion of the Amerasia Basin can be regarded asforming a typical basin within the supercontinent [48].Most likely, this basin was formed under the effect ofmantle plumes, including an inferred plume beneath theNorth Pole, which developed to the north of the Central

Atlantic and was responsible for the eruptions of tholei-itic and alkali basalts in Arctica. In southern and easternNorth Eurasia, the within-plate plume magmatism wasaccompanied by shallow-seated collision- and subduc-tion-related magmatism, whereas shallow-seatedspreading magmatism (eruptions of tholeiitic basalts)accompanied deep plume magmatism in Arctica.

ACKNOWLEDGMENTS

This study was supported by the Russian Founda-tion for Basic Research (project nos. 08-05-00347,08-05-00472) and the Presidium of the Russian Acad-emy of Sciences (program no. 16).

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Reviewers: V. E. Khain and S. V. Ruzhentsev

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Geodynamic Setting of Recent Volcanism in North Eurasia