Mantle plumes of Central Asia (Northeast Asia) and their role in forming endogenous deposits

The Phanerozoic within-plate magmatism and the related deposits of Siberia are reviewed. The formation of post-perovskite at about 2.5 Ga in the Earth’s interior and the isotope characteristics of within-plate igneous rocks have shown that plate tectonics and deep geodynamics started to operate at about 2–2.5 Ga. The assembly and breakup of supercontinents under the effect of the superplumes formed in layer D″ is considered. Thus, the supercontinent–superplume cycles spanning about 700 Ma are recognized in the Earth’s history.The manifestations of the within-plate magmatic activity are found throughout the whole Phanerozoic. It was demonstrated earlier that between 570 and 160 Ma, the Siberian continent drifted within the African hot mantle field or large low shear velocity province (LLSVP). At least four plumes, excluding the superplume leading to the breakup of Rodinia at 750 Ma, interacted with the Siberian continent. The superplume leading to the breakup of Rodinia was also responsible for the origin of ultramafic intrusions with carbonatites hosting rare-metal (Nb, Ta, REE) mineralization as well as ultramafic–mafic intrusions with Cu–Ni–Pt mineralization localized along the rift zones.The plumes originated in other Phanerozoic cycles formed most likely at the lower-upper mantle boundary, where most of the stagnant slabs is accumulated. Those plumes were responsible for the origin of within-plate igneous rocks. The granitic batholiths formed in the centers of zonal area surrounded by rift zones containing abundant rare-metal intrusions with rare-metal mineralization. Gold, tin, base metal, and porphyry copper deposits are also related to these zonal area.The studies have shown that the formation of folded zones and related deposits which surround these zones as well as the structures of cratons and their metallogenic specialization should be considered in terms of both plate tectonics and plume tectonics.     

亚洲3个大火成岩省(峨眉山、西伯利亚、德干)对比研究

峨眉山(～260 Ma)、西伯利亚(～250 Ma)和德干(～66 Ma)大陆溢流玄武岩是世界上3个重要的大火成岩省.大火成岩省至少具有4个通常被用于识别古地幔柱的标志:(1)先于岩浆作用的地表隆升;(2)与大陆裂谷化和裂解事件相伴;(3)与生物灭绝事件联系密切;(4)地幔柱源玄武岩的化学特征.虽然这3个大火成岩省都是来源于原始地幔柱,但是它们的地球化学特征有本质上的差异,反映其地幔柱曾与不同的上地幔库相互作用.(1)峨眉山和西伯利亚大陆溢流玄武岩的母岩浆,在上升过程中经受了与地球化学上和古老克拉通岩石圈地幔相同的上地幔库(EM1型幔源)的相互作用;(2)而德干大火成岩省没有受到地壳(或岩石圈)混染的原生玄武岩则显示地幔柱和EM2之间的Sr-Nd同位素变化.这种差异有可能制约了3个大火成岩省的成矿潜力.峨眉山和西伯利亚大火成岩省含有世界级岩浆矿床,而德干大火成岩省则不含矿.     

Late paleozoic-Early Mesozoic within-plate magmatism in North Asia: traps, rifts, giant batholiths, and the geodynamics of their origin

A number of large areas of igneous provinces produced in North Asia in the Late Paleozoic and Early Mesozoic include Siberian and Tarim traps and giant rift systems. Among them, the Central Asian Rift System (CARS) has the most complicated structure, evolved during the longest time, and is a large (3000 × 600 km) latitudinally oriented belt of rift zones extending from Transbaikalia and Mongolia to Middle Asia and including the Tarim traps in western China. CARS was produced in the Late Carboniferous, and its further evolution was associated with the lateral migration of rifting zones; it ended in the Early Jurassic and lasted for approximately 110 Ma. CARS was produced on an active continental margin of the Siberian continent and is noted for largest batholiths, which were emplaced simultaneously with rifting. The batholiths are surrounded by rift zones and compose, together with them, concentrically zoned magmatic areas, with crustal (granitoid) magmatism focused within their central portions, whereas mantle (rift-related) magmatism is predominant in troughs and grabens in peripheral zones. The batholiths show geological and isotopic geochemical evidence that their granitoids were produced by the anatexis of the host rocks at active involvement of mantle magmas. Zonal magmatic areas of the type are viewed as analogues of large igneous provinces formed in the environments characteristic of active continental margins. Large within-plate magmatic provinces in North Asia are thought to have been generated in relation to the overlap of at least two mantle plumes by the Siberian continent during its movement above the hot mantle field. In the continental lithosphere, mantle plumes initiated within-plate magmatic activity and facilitated rifting and the generation of traps and alkaline basite and alkali-salic magmatic associations. Because of the stressed states during collision of various type in the continental margin, the mantle melts did not ascend higher than the lowest crustal levels. The thermal effect of these melts on the crustal rocks induced anatexis and eventually predetermined the generation of the batholiths.     

Large igneous provinces (LIPs) and carbonatites

There is increasing evidence that many carbonatites are linked both spatially and temporally with large igneous provinces (LIPs), i.e. high volume, short duration, intraplate-type, magmatic events consisting mainly of flood basalts and their plumbing systems (of dykes, sills and layered intrusions). Examples of LIP-carbonatite associations include: i. the 66 Ma Deccan flood basalt province associated with the Amba Dongar, Sarnu-Dandali (Barmer), and Mundwara carbonatites and associated alkali rocks, ii. the 130 Ma Paraná-Etendeka (e.g. Jacupiranga, Messum); iii. the 250 Ma Siberian LIP that includes a major alkaline province, Maimecha-Kotui with numerous carbonatites, iv. the ca. 370 Ma Kola Alkaline Province coeval with basaltic magmatism widespread in parts of the East European craton, and v. the 615–555 Ma CIMP (Central Iapetus Magmatic Province) of eastern Laurentia and western Baltica. In the Superior craton, Canada, a number of carbonatites are associated with the 1114–1085 Ma Keweenawan LIP and some are coeval with the pan-Superior 1880 Ma mafic-ultramafic magmatism. In addition, the Phalaborwa and Shiel carbonatites are associated with the 2055 Ma Bushveld event of the Kaapvaal craton. The frequency of this LIP-carbonatite association suggests that LIPs and carbonatites might be considered as different evolutionary ‘pathways’ in a single magmatic process/system. The isotopic mantle components FOZO, HIMU, EM1 but not DMM, along with primitive noble gas signatures in some carbonatites, suggest a sub-lithospheric mantle source for carbonatites, consistent with a plume/asthenospheric upwelling origin proposed for many LIPs.     

Mantle Sources and Melting Dynamics in the British Palaeogene Igneous Province

The North Atlantic igneous province offers an unrivalled opportunityto study mantle sources contributing to flood basalt magmatism,and melting dynamics associated with active and passive upwellingof hot mantle beneath the lithosphere. In this study, Palaeogenebasalts sampled at localities across the British Isles (fromthe Hebrides in the north to Lundy Island in the south) areshown to have concentrations of Nb, Zr and Y consistent withderivation from two mantle sources: ‘Icelandic’(plume) mantle and hot N-MORB-like mantle forming an outer envelopeto the plume. These sources were sampled over the period 61–58Ma (chrons 26R–26N). Values of     

Distribution of PGE in Permo-Triassic basalts of the Siberian Large Igneous Province

We have revealed the spatio-temporal regularities of distribution of platinum group elements (PGE) in basaltoids related to the activity of the Siberian mantle plume. As objects of study, we chose rift and flood basalts from the Norilsk district (sampled from the SD-9 borehole), flood basalts from the central part of the Tunguska syneclise (Lower Tunguska), Kuznetsk Basin traps, and subalkalic basalt from the Semeitau volcanoplutonic structure in eastern Kazakhstan. Based on the PGE patterns of basaltoids related to the activity of the Permo-Triassic Siberian plume, we have shown that the rocks that formed in the central part of the Siberian Large Igneous Province (LIP) at the early rift stage have low contents of PGE, whereas picrites and tholeiitic flood basalts have high contents. The rift (Semeitau structure) and flood (Kuznetsk Basin traps) basalts from the peripheral regions are characterized by extremely low PGE contents. The high PGE contents in magmas of the plume head are responsible for the high productivity of ultramafic-mafic trap magmatism. The elevated K contents in magmas and the high PGE contents in the mantle plume head are probably due to the ascent of deep-seated material from the core-lower-mantle boundary, as follows from the thermochemical model of the Siberian plume.     

SHRIMP Zircon U‐Pb Dating of Alkaline Dykes in the Pobei Area,Beishan Rift,Xinjiang Autonomous Region,China: Implications for Tectonic Setting and Mantle Plume Events

In the Beishan rift in the eastern Tianshan orogen, Xinjiang Province, a N-S-trending dyke swarm is present in the Pobei area. The swarm cuts through the 270–290 Ma mafic-ultramafic intrusions associated with Ni-Cu sulphide mineralization. These mafic-ultramafic intrusions are typically found along E-W major faults in the Tianshan orogenic belts. We report SHRIMP U-Pb dating of zircons from a dyke of alkaline composition, which yielded a mean age of 252±9 Ma. Alkaline dykes of the same age are found in the Altay region of Siberia. This age is younger than the 270–290 Ma intraplate magmatic events that produced the mafic-ultramafic intrusions in the region, but in general agreement with the 250–260 Ma Permian plume event that gave rise to the Siberian traps and the Emeishan flood basalts in SW China. We suggest that there is a link between the Emeishan event and the dyke swarm in the Beishan rift and that the intraplate magmatism at 270–290 Ma reflects an early stage of mantle plume activity. The N-S trending dyke swarm in the Beishan rift may represent a later stage in the evolution of mantle plume activity in the NW and SW of China. We also speculate that in Beishan rift and possibly elsewhere in the Tianshan region, the dykes fed basaltic volcanism, whose products have since been eroded due to the strong uplift of the Tianshan orogen as a result of the India-Eurasia collision in the Cenozoic.     

Permo-Triassic plume magmatism of the Kuznetsk Basin,Central Asia: geology,geochronology, and geochemistry

The Kuznetsk Basin is located in the northern part of the Altai–Sayan Folded Area (ASFA), southwestern Siberia. Its Late Permian–Middle Triassic section includes basaltic stratum-like bodies, sills, formed at 250–248 Ma. The basalts are medium-high-Ti tholeiites enriched in La. Compositionally they are close to the Early Triassic basalts of the Syverma Formation in the Siberian Flood basalt large igneous province, basalts of the Urengoi Rift in the West Siberian Basin and to the Triassic basalts of the North-Mongolian rift system. The basalts probably formed in relation to mantle plume activity: they are enriched in light rare-earth elements (LREE; La_n = 90–115, La/Sm_n = 2.4–2.6) but relatively depleted in Nb (Nb/La_PM = 0.34–0.48). Low to medium differentiation of heavy rare-earth elements (HREE; Gd/Yb_n = 1.4–1.7) suggests a spinel facies mantle source for basaltic melts. Our obtained data on the composition and age of the Kuznetsk basalts support the previous idea about their genetic and structural links with the Permian–Triassic continental flood basalts of the Siberian Platform (Siberian Traps) possibly related to the activity of the Siberian superplume which peaked at 252–248 Ma. The abruptly changing thickness of the Kuznetsk Late Permian–Middle Triassic units suggests their formation within an extensional regime similar to the exposed rifts of Southern Urals and northern Mongolia and buried rifts of the West Siberian Basin.     

Late Paleozoic and Early Mesozoic rare-metal magmatism of Central Asia: Stages, provinces, and formation settings

Late Paleozoic and Early Mesozoic epochs in the formation history of the Central Asian Foldbelt are distinguished by high rare-metal productivity. A number of large REE, Ta, Nb, Zr, Be, Sn, Li, Mo, Re, and other deposits were formed at that time. As a rule, they are of the magmatic origin and related to the intrusions of highly evolved igneous rocks varying in composition from alkaline ultramafic with carbonatites to alkali and Li-F granites. In general, the occurrences of rare-metal magmatism are related to the rift zones of the Central Asian Rift System formed 310?C190 Ma ago and conjugated with a consecutive series of the Barguzin, Hangay, and Hentiy zonal igneous provinces characterized by the large batholiths in their centers and rift zones in the framework. Such a structure indicates that these provinces were formed above isometric mantle sources or plumes with participation of large-scale crustal anatexis. The evident links of rare-metal deposits to occurrences of mantle magmatism within the zonal igneous provinces show that plume sources played an important role in their formation.     

Phanerozoic mafic magmatism in the southern Siberian craton: geodynamic implications

The Phanerozoic history of mafic magmatism in the southern Siberian craton included three major events. The earliest event (～500 Ma) recorded in dolerite dikes occurred during accretion and collision at the early stage of the Central Asian orogen. Injection of mafic melts into the upper crust was possible in zones of diffuse extension within the southern Siberian craton which acted as an indenter. The Late Paleozoic event (～275 Ma) produced dikes that intruded in a setting of subduction-related extension at the back of the active continental margin of Siberia during closure of the Mongolia–Okhotsk ocean, as well as slightly older volcanics (290 Ma) in the Transbaikalian segment of the Central Asian orogen. Early Mesozoic magmatism in the southern Siberian craton resulted in numerous 240–250 Ma mafic intrusions in the Angara–Taseeva basin. The intrusions (Siberian traps) appeared as the subducting slab of the Mongolia–Okhotsk ocean interacted with a lower mantle plume. The post-Late Paleozoic ages of flood basalts (290–275 Ma) correspond to progressive northwestward (in present coordinates) motion of the slab beneath the southern craton margin which likely ceased after the slab had reached the zone of the Siberian superplume. Since its consolidation after the Early Mesozoic activity, the crust in the area has no longer experienced extension favorable for intrusion of basaltic magma.     

Early Cretaceous magmatism of Mount Hermon, Northern Israel

 Early Cretaceous (146–115 Ma) magmatism in the region of Mt. Hermon, Northern Israel, is part of an extensive Mesozoic igneous province within the Levant associated with the evolution of the Neotethyan passive margin of Gondwana. The initial stages of activity were characterised by the emplacement of tholeiitic dykes (146–140 Ma) which were uplifted and eroded prior to the eruption of a sequence of alkali basalts, basanites and more differentiated alkaline lavas and pyroclastics from 127 to 120 Ma. The latest stages of activity (120–115 Ma) were highly explosive, resulting in the emplacement of diatreme breccias. Trace element and Sr-Nd-Pb isotope data for the most primitive Early Cretaceous mafic igneous rocks sampled suggest that they were derived by mixing of melts derived by variable degrees of partial melting of both garnet- and spinel-peridotite-facies mantle sources. Though isotopically heterogeneous, the source of the magmas has many similarities to that of HIMU oceanic island basalts. Earlier Liassic (200 Ma) transitional basalts and Neogene–Quaternary (15–0 Ma) alkali basalts erupted within northern Israel also have HIMU affinities. The petrogenesis of the Early Cretaceous and Cenozoic basalts is explained by partial melting of a lithospheric mantle protolith metasomatically enriched during the Liassic volcanic phase, which may be plume-related. Received: 23 July 1998 / Accepted: 6 December 1999     

The Mesoproterozoic mantle plume beneath the northern part of the Siberian craton

The study of the Mesoproterozoic (1473 ± 24 Ma) dolerites of the Olenek uplift of the Siberian craton basement has shown their petrologic and geochemical similarity to typical OIB produced with participation of a mantle plume. The dolerites are characterized by variations in the geochemical composition explained by different degrees of melting of the same source. A conclusion is drawn that the parental melts of the rocks were slightly modified by crustal contamination, as evidenced from their Nd isotope composition (£_Nd(T) = + 0.6 to − 0.8) and the presence of inherited zircons of four ages (2564, 2111, 2053, and 1865 Ma). Since the Siberian craton in the structure of the Nuna supercontinent (Columbia) was located relatively close to the Baltic continent and the Congo and Sao Francisco cratons, we assume that the Early Mesoproterozoic mafic intrusions (1500–1470 Ma) of all these cratons belong to the same large igneous province (LIP). The province formation was related to the activity of superplume (or mantle hot field), which supplied mantle matter to the lithosphere basement. The superplume core was probably located beneath the northern part of the Siberian craton, where basites are compositionally most similar to the primary mantle source.     

The age of unusual xenogenic zircons from Yakutian kimberlites

Several spindle-shaped grains of zircon, which have a small size (<0.25 mm) and a distinct purplish pink coloration were found in the crushed samples of kimberlites from the Aykhal, Komsomolskaya-Magnitnaya, Botuobinskaya (Siberian platform), and Nyurbinskaya (Yakutia) pipes and olivine lamproites of the Khani massif (West Aldan). U-Pb SHRIMP II zircon dating performed at the VSEGEI Center for Isotopic Research yielded the ages of 1870–1890 Ma for the pipes of the Western province (Aykhal and Komsomolskaya) and 2200–2750 Ma for the pipes of the eastern province (Nyurbinskaya and Botuobinskaya), which allowed us to consider these zircons to be xenogenic to kimberlites. Although these zircons resemble in their age and color those from the granulite xenoliths in the Udachnaya pipe [2], no other granulite minerals are found there. Thus, major geological events in the mantle and lower crust, which led to the formation of zircon-bearing rocks, happened at 1800–1900 Ma in the northern part of the kimberlite province, whereas in the Eastern part of the province (Nakyn field) these events were much older (2220–2700 Ma). It is known that the period of 1800–1900 Ma in the Earth’s history was accompanied by intense tectonic movements and widespread alkaline-carbonatite magmatism. This magmatism was related to plume activity responsible for overheating the large portions of the mantle to the temperatures at which some diamonds in mantle rocks would burn (northern part of the kimberlite province). In the Nakyn area, the mantle underwent few or no geological processes at that time, and perhaps for this reason this area hosts more diamondiferous kimberlites. The age of olivine lamproites from the Khani massif is 2672–2732 Ma. Thus, these are some of the world’s oldest known K-alkaline rocks.     

Intraplate geodynamics and magmatism in the evolution of the Central Asian Orogenic Belt

The Central Asian Orogenic Belt (CAOB) was produced as a consequence of the successive closure of the Paleoasian Ocean and the accretion of structures formed within it (island arcs, oceanic islands, and backarc basins) to the Siberian continent. The belt started developing in the latest Late Neoproterozoic, and this process terminated in the latest Permian in response to the collision of the Siberian and North China continents that resulted in closure of the Paleoasian ocean (Metcalfe, 2006; Li et al., 2014; Liu et al., 2009; Xiao et al., 2010; Didenko et al., 2010). Throughout the whole evolutionary history of this Orogenic Belt, a leading role in its evolution was played by convergent processes. Along with these processes, an important contribution to the evolution of the composition and structure of the crust in the belt was made by deep geodynamic processes related to the activity of mantle plumes.Indicator complexes of the activity of mantle plumes are identified, and their major distribution patterns in CAOB structures are determined. A number of epochs and areas of intraplate magmatism are distinguished, including the Neoproterozoic one (Rodinia breakup and the origin of alkaline rock belt in the marginal part of the Siberian craton); Neoproterozoic–Early Cambrian (origin of oceanic islands in the Paleoasian Ocean); Late Cambrian–Early Ordovician (origin of LIP within the region of Early Caledonian structures in CAOB); Middle Paleozoic (origin of LIP in the Altai–Sayan rift system); Late Paleozoic–Early Mesozoic (origin of the Tarim flood-basalt province, Central Asian rift system, and a number of related zonal magmatic areas); Late Mesozoic–Cenozoic (origin of continental volcanic areas in Central Asia).Geochemical and isotopic characteristics are determined for magmatic complexes that are indicator complexes for areas of intraplate magmatism of various age, and their major evolutionary trends are discussed. Available data indicate that mantle plumes practically did not cease to affect crustal growth and transformations in CAOB in relation to the migration of the Siberian continent throughout the whole time span when the belt was formed above a cluster of hotspots, which is compared with the African superplume.     

Proterozoic mafic magmatism in Siberian craton: An overview and implications for paleocontinental reconstruction

We present a summary of late Paleoproterozoic to Neoproterozoic mafic magmatism in the Siberian craton, including recently published U–Pb and ⁴⁰Ar–³⁹Ar dates. These new precise ages suggest that at least some of the previously published K–Ar ages of Siberian mafic bodies should be ignored. The time–space geochronological chart, or the ‘barcode’ of mafic magmatic events shows significant differences between northern and southern Siberia. Both are characterized by ∼1900–1700 Ma magmatic events, but then there was an almost 1 Ga mafic magmatic ‘pause’ in south Siberia until ∼800 Ma. Meanwhile there are indications of multiple mafic magmatic events in North Siberia (Anabar shield and Olenek uplift) between ∼1600 and 1000 Ma. A series of magmatic events probably related to the breakup of Rodinia occurred in southern Siberia after ∼800 Ma. So far, there are no indications of late Neoproterozoic mafic magmatism in North Siberia. Ca. 1000–950 Ma mafic sills were reported from Meso- to Neo-Proterozoic sedimentary successions in the Sette-Daban area on the east side of the Siberian craton, but their tectonic setting is debated. Recent Ar–Ar dates of ∼1750 Ma for NW-trending dykes in the Aldan and Anabar shields, together with similar-age NNE-trending Baikal uplift dykes in south-eastern Siberia suggest the existence of a giant radial dyke swarm possibly related to a mantle plume centred in the Vilyui River area.     

Permo-Triassic hypabyssal mafic intrusions and associated tholeiitic basalts of the Kolyuchinskaya Bay,Chukotka (NE Russia): Links to the Siberian LIP

In order to test tectonic hypotheses regarding the evolution of the Arctic Alaska–Chukotka microplate prior to the opening of the Amerasian basin, we investigated rocks exposed near Kolyuchinskaya Bay, eastern Chukotka. Hypabyssal mafic rocks and associated basaltic flows enclose terrigenous sediments, minor cherts and limestones in pillow interstices. The hypabyssal mafic rock yields a U–Pb zircon age of 252 ± 4 Ma and indicates intrusion of basic magma at the Permo-Triassic boundary, contemporaneous with voluminous magmatism of the Siberian large igneous province (LIP). The lava flows and hypabyssal mafic rocks of the Kolyuchinskaya Bay region have trace elements, Sm–Nd and Rb–Sr isotope compositions identical to the tholeiitic flood basalts of the main plateau stage of the Siberian LIP, but differ from the latter in the major-element variations. We conclude that compositional variations in the hypabyssal rocks studied reflect their generation in an extensional environment that might be related to the Siberian super-plume activity at the time. Although the genetic and temporal links between intrusive mafic rocks and lavas are not well proved, compositional variations of the eruptive rocks still indicate their generation in an extensional environment.     

Ar–Ar ages of intrusions in East Greenland: Rift-to-drift transition over the Iceland hotspot

Sixteen ⁴⁰Ar–³⁹Ar ages are presented for alkaline intrusions to appraise prolonged post-breakup magmatism of the central East Greenland rifted margin, the chronology of rift-to-drift transition, and the asymmetry of magmatic activity in the Northeast Atlantic Igneous Province. The alkaline intrusions mainly crop out in tectonic and magmatic lineaments orthogonal to the rifted margin and occur up to 100 km inland. The area south of the Kangerlussuaq Fjord includes at least four tectonic lineaments and the intrusions are confined to three time windows at 56–54 Ma, 50–47 Ma and 37–35 Ma. In the Kangerlussuaq Fjord, which coincides with a major tectonic lineament possibly the failed arm of a triple junction, the alkaline plutons span from 56 to 40 Ma. To the north and within the continental flood basalt succession, alkaline intrusions of the north–south trending Wiedemann Fjord–Kronborg Gletscher lineament range from 52 to 36 Ma.

We show that post-breakup magmatism of the East Greenland rifted margin can be linked to reconfiguration of spreading ridges in the Northeast Atlantic. Northwards propagation of the proto-Kolbeinsey ridge rifted the Jan Mayen micro-continent away from central East Greenland and resulted in protracted rift-to-drift transition. The intrusions of the Wiedemann Fjord–Kronborg Gletscher lineament are interpreted as a failed continental rift system and the intrusions of the Kangerlussuaq Fjord as off-axis magmatism. The post-breakup intrusions south of Kangerlussuaq Fjord occur landward of the Greenland–Iceland Rise and are explained by mantle melting caused first by the crossing of the central East Greenland rifted margin over the axis of the Iceland mantle plume (50–47 Ma) and later by uplift associated with regional plate-tectonic reorganization (37–35 Ma). The Iceland mantle plume was instrumental in causing protracted rift-to-drift transition and post-breakup tholeiitic and alkaline magmatism on the East Greenland rifted margin, and asymmetry in the magmatic history of the conjugate margins of the central Northeast Atlantic.     

Flood basalts and metallogeny: The lithospheric mantle connection

Continental flood basalts, derived from mantle plumes that rise from the convecting mantle and possibly as deep as the core–mantle boundary, are major hosts for world-class Ni–Cu–PGE ore deposits. Each plume may have a complex history and heterogeneous composition. Therefore, some plumes may be predisposed to be favourable for large-scale Ni–PGE mineralisation (“fertile”).Geochemical data from 10 large igneous provinces (LIPs) have been collected from the literature to search for chemical signatures favourable for Ni–PGE mineralisation. The provinces include Deccan, Kerguelen, Ontong Java, Paraná, Ferrar, Karoo, Emeishan, Siberia, Midcontinent and Bushveld. Among these LIPs, Bushveld, Siberia, Midcontinent, Emei Mt and Karoo are “fertile”, hosting magmatic ore deposits or mineralisation of various type, size and grade. They most commonly intruded through, or on the edges of, Archaean–Paleoproterozoic cratonic blocks. In contrast, the “barren” LIPs have erupted through both continental and oceanic crustal terranes of various ages.Radiogenic isotopic signatures indicate that almost all parental LIP magmas are generated from deep-seated mantle plumes, and not from the more widespread depleted asthenospheric mantle source: this confirms generally accepted plume models. However, several important geochemical signatures of LIPs have been identified in this study that can discriminate between those that are “fertile” or “barren” in terms of their Ni–PGE potential.The fertile LIPs generally contain a relatively high proportion of primitive melts that are high in MgO and Ni, low in Al₂O₃ and Na₂O, and are highly enriched in most of the strongly incompatible elements such as K, P, Ba, Sr, Pb, Th, Nb, and LREE. They have relatively high Os contents (≥ 0.03 to 10 ppb) and low Re/Os (< 10). The fertile LIP basalts display trends of Sr–Nd–Pb isotopic variation intermediate between the depleted plume and an EM1-type mantle composition (and thus could represent a mixing of these two source types), and have elevated Ba/Th, Ba/Nb and K/Ti ratios. These elemental and isotopic signatures suggest that interaction between plume-related magmas and ancient cratonic lithospheric mantle with pre-existing Ni- and PGE-rich sulfide phases may have contributed significantly to the PGE and Ni budget of the fertile flood basalts and eventually to the mineralisation. This observation is consistent with the location of fertile LIPs adjacent to deep old lithospheric roots (as inferred from tectonic environment and also seen in global tomographic images) and has predictive implications for exploration models.Barren LIPs contain fewer high-MgO lavas. The barren LIP lavas in general have low Os contents (mostly ≤ 0.02 ppb) with high Re/Os (10–≥ 200). They show isotopic variations between plume and EM2 geochemical signatures and have high Rb/Ba ratios. These signatures may indicate involvement of deep recycled material in the mantle sources or crustal contamination for barren LIPs, but low degrees of interaction with old lithospheric-type roots.     

Neogene–Quaternary Magmatism of the Çaldıran Plain and its Vicinity (Eastern Turkey): an Example of Post-Collisional Transition from Subduction to Intraplate Type

This paper is aimed at studying the chronological evolution of the Neogene–Quaternary volcanic activity within the Çald?ran plain and its mountainous framing (Eastern Turkey). It is shown that the last pulse of continental-margin magmatism related to the subduction and closure of Neotethys oceanic basin occurred in the Middle Miocene (13.5–12.5 Ma). The post-collision volcanism proceeding simultaneously with large-scale regional tectonic rearrangement and initiation of the long-term Çald?ran fault began in the Late Miocene (7–6 Ma), and reached maximum activity in the Middle Pliocene (4.7–3.6 Ma). The Quaternary period in the region evolution was marked by the abundant within-plate magmatic activity restricted to the regional SW–NE trending zone, and the formation of Eastern Turkey’s largest Tendürek shield volcano (Late Pleistocene–Holocene). Petrological-geochemical data indicate that magmas during the overall evolution of young volcanism of the Çald?ran plain was generated from a single mantle reservoir, whose composition gently one-way evolved with time. Calculations show that melting occurred in the upper part of the asthenosphere (immediately near the boundary with thinned lithospheric mantle), which was metasomatized by pre-existing long-continued subduction. The chemical variations of mantle source with time (from the Middle Miocene to Quaternary) were mainly determined by a decrease of subduction component and the presence of aqueous phases, with a general trend from E-MORB to OIB-type for generated magmas. The composition of Late Quaternary basic lavas of Tendürek Volcano in terms of most petrological-geochemical characteristics corresponds to within-plate alkaline basalts. The main trend of geochemical evolution of mantle source is correlated with a systematic change of the predominant serial affinity of igneous rocks from calcalkaline through moderately alkaline to Na-alkaline varieties. Discrete character of young magmatism within the Çald?ran plain, and its subsequent evolution (sulrasubduction → post-collision → within-plate) were mainly determined by periodical large-scale changes in geotectonic setting within the Eurasian–Arabian collision zone: (1) cessation of subduction, (2) break-up and deepening of oceanic slab with its subsequent break off, (3) inferred emergence of incipient rift setting under conditions of intense submeridional compression.     

Relationship between platinum-bearing ultramafic-mafic intrusions and large igneous provinces (exemplified by the Siberian Craton)

This study aims at summarizing available geological and geochemical data on known Proterozoic platinum-bearing ultramafic-mafic massifs in the south of Siberia. Considering new data on geochemistry and geochronology of some intrusions, it was feasible to compare ore-bearing complexes of different time spans and areas and to follow their relationships with the recognized large igneous provinces. In the south of Siberia, the platinum-bearing massifs might be united into three age groups: Late Paleoproterozoic (e.g., Chiney complex, Malozadoisky massif), Late Mesoproterozoic (e.g., Srednecheremshansky massif), and Neoproterozoic (e.g., Kingash complex, Yoko-Dovyren massif, and massifs in the center of the East Sayan Mts.). In most massifs but Chiney the initial magmas are magnesium-rich. On paleogeodynamic reconstructions, the position of the studied massifs is the evidence that three most precisely dated events in North Canada continued into southern Siberia: In the period 1880-1865 Ma, it was the Ghost-Mara River-Morel LIP; at 1270-1260 Ma, the Mackenzie LIP; and at 725-720 Ma, Franklin LIP. In Siberia, the mostly productive massifs with respect to PGE-Ni-Cu mineralization are those linked with the Franklin LIP: Verkhny Kingash, Yoko-Dovyren, and central part of the Eastern Sayan Mountains, e.g., Tartay, Zhelos, and Tokty-Oy.