Tarim Plume Research Articles

Lower Crustal Rheology Controls Strain Partitioning and Mode of Intracontinental Deformation

AbstractThe factors that control strain partitioning along plate boundaries and within continental interiors remains poorly resolved. Plate convergence may be accommodated via distributed crustal shortening or discrete crustal‐scale strike‐slip faulting, but what controls these differing modes of deformation is debated. Here we address this question by examining the actively deforming regions that surround the Tarim Basin in central Asia, where deformation is uniquely partitioned into predominately strike‐slip faults in the east and distributed fold‐thrust belts in the west to accommodate Cenozoic India‐Asia plate convergence. We present integrated geological and geophysical observations to elucidate patterns in crustal deformation and compositional structure in and around the Tarim Basin. The thrust‐dominated western Tarim Basin correlates with a strongly‐magnetic lower crust, whereas strike‐slip faulting along the eastern margins of the Tarim Basin lack such magnetic signals. We suggest that the lower crust of the western Tarim is more mafic and stronger than in the east, which impacts intra‐plate strain partitioning. A stronger lower crust results in vertical decoupling to drive mid‐crust horizontal detachments and facilitate thrust faulting, whereas a more homogenized crust favored vertical transcrustal strike‐slip faulting. These rheological differences likely originated from the impingement of the Permian Tarim plume focused in the west. A comparison with the Longmen Shan of eastern Tibetan Plateau reveals remarkably similar strain partitioning that correlates with variations in foreland rheology. Our results highlight how variations in lower‐crust viscosity impact strain partitioning in an intra‐plate setting and how plume processes exert a strong control on later continental tectonic processes.

Circum-cratonic mantle archives the cumulative effects of plume and convergence events

The cumulative effects of heating, various melts/fluids, and tectonic stress from plume and convergent events can produce complex geochemical signatures in circum-cratonic mantle domains. The lithospheric mantle beneath the northwestern Tarim Craton witnessed the Tarim plume and multi-stage convergent events, thus providing a good opportunity to investigate the depletion and enrichment of circum-craton mantle driven by their cumulative effects. Here, we present the in-situ mineral major/trace elements, clinopyroxene Sr isotopic and whole-rock analyses of platinum group elements and Re-Os isotopes for peridotite xenoliths from Piqiang in the northwestern Tarim Craton. Combined with peridotite xenoliths from Tuoyun (South Tianshan Belt) and Xikeer (inner Tarim), we established a lithospheric mantle profile to constrain the formation and subsequent evolution of the circum-Tarim mantle in response to the subduction of the archipelagic ocean and the impingement of the Tarim plume. The Piqiang peridotites have moderately refractory compositions (Mg# in Ol: 90.1–90.9; average values) and can be divided into Group A lherzolites (subgroups A1, A2 and A3) and Group B wehrlite. Group A1 lherzolites contain copper-poor sulfides and clinopyroxenes depleted in incompatible elements, and are interpreted as melting residua that experienced negligible metasomatism. Group A2 lherzolites have disequilibrium textures and are depleted in Nb and Ta with high Ti/Eu but low (La/Yb)N ratios in clinopyroxene, demonstrating recent volatile-rich melt metasomatism. Carbonatitic metasomatism from a mixed crust-mantle source is recorded in the Group A3 lherzolites, as their clinopyroxenes have highly variable 87Sr/86Sr ratios (0.7028–0.7057) with low Ti/Eu and high (La/Yb)N. Overall, Group A lherzolites display high initial 187Os/188Os ratios (0.1198–0.1271, excluding suprachondritic values), yielding the Neoproterozoic peak (∼650 Ma) TRD eruption model ages and the minimum estimate for the age of lithospheric mantle formation of 1.1 Ga. Their high-Na clinopyroxenes, low-Ca orthopyroxenes, and low melting pressures (<3 GPa) suggest that the initial melt extraction of these peridotites was the result of lateral mantle accretion triggered by multi-stage subduction of the Neoproterozoic Pan-Rodina Ocean. In this case, the greater fertility of the Tuoyun peridotites compared to those from Piqiang defines a trend of lateral accretion, while the low whole-rock Al2O3 but high 187Os/188Os ratios of the Xikeer peridotites point to a second melt extraction event. This melt extraction event is interpreted as reflecting low-flux plume melts that heated and melted the overlying lithospheric mantle at the edge of the early Permian Tarim plume. Meanwhile, the Piqiang peridotites, further from the center of the Tarim plume, underwent carbonatitic metasomatism originating from the lower-flux plume melts that involved the high-density components from recycled oceanic crustal materials. The mantle melt activity and faulting related to the India-Eurasia collision provided the reactive melts to form the Group B wehrlite and prepared migration pathways for volatile-rich melts to metasomatize Group A2 lherzolites. Collectively, the accretion, re-extraction, and metasomatic modification of circum-craton mantle reflected a response to the cumulative effects of the plume and convergence events. Our study reveals that the mechanical, thermal, and chemical effects from different dynamic events interacted with each another and worked together to affect the circum-craton mantle evolution.

A Mantle Plume Connection for Alkaline Lamprophyres (Sannaites) from the Permian Tarim Large Igneous Province: Petrological, Geochemical and Isotopic Constraints

AbstractThe origin of lamprophyres associated with large igneous provinces (LIPs) remains controversial, particularly whether they are derived by direct melting of mantle plumes, or from previously metasomatized domains in thermally perturbed subcontinental lithosphere. Here, we report the petrological and geochemical characteristics of a recently identified suite of alkaline lamprophyres (sannaites) that represent the final pulse of magmatism in the Permian Tarim LIP in NW China. The sannaites display porphyritic texture with phenocrysts of olivine, clinopyroxene, hornblende, phlogopite, and titanomagnetite in a groundmass of plagioclase, clinopyroxene, nepheline, hornblende, biotite, and titanomagnetite with minor pyrite and apatite. Carbonate ocelli and almost pure albite in the groundmass are interpreted to have crystallized from immiscible carbonate and hydrous fluids, respectively, produced by late-stage magmatic segregation. The rocks show low to moderate SiO2 (37.7–49.3 wt.%) and MgO (2.74–9.91 wt.%), together with high Fe2O3T (up to 22.7 wt.%) and alkali contents (up to 9.02 wt.% Na2O + K2O). They are characterized by high incompatible element abundances, especially a marked enrichment in large-ion lithophile elements (Rb and Ba) and light rare-earth elements (e.g. La and Ce) relative to P and high-field-strength elements (e.g. Ti). They show a relatively restricted range of δ66Zn values between 0.22‰ and 0.46‰ with an average of 0.37 ± 0.04‰ (2SE, n = 10), which is marginally heavier than that of MORBs (0.27 ± 0.05‰). Their (87Sr/86Sr)t values range from 0.7035 to 0.7061, εNd(t) from −0.97 to +5.62, and δ26Mg from −0.36‰ to −0.17‰ (n = 8), the latter being consistent with those of global MORBs. Based on the correlation between Zn isotopes and TiO2–FeO concentrations, we infer that the heavy Zn isotopes in some of the sannaites resulted from fractional crystallization of Fe–Ti oxide minerals. The whole rock geochemical features of these rocks (negative K anomalies and enrichment in large-ion lithophile elements) and rhyolite–MELTS simulations suggest that the primary magmas of the sannaites were derived from an amphibole-bearing enriched lithospheric mantle source. Metasomatism and related formation of amphibole-bearing metasomatized mantle may be linked to sublithospheric melts/fluids derived from the Tarim plume in the earlier stages of plume activity, rather than slab-derived fluids or carbonate melts as suggested in previous studies for other alkaline mantle-derived magmas. Partial melting may have been triggered by the thermal input from the Tarim plume during a later stage. This study suggests that exotic, alkali-rich magmas can be produced during the multi-stage evolution of large mantle plumes, involving complex cycles of lithospheric mantle metasomatism and later melting of previously enriched domains.

Hydrogen Concentrations and He Isotopes in Olivine From Ultramafic Lamprophyres Provide New Constraints on a Wet Tarim Plume and Earth's Deep Water Cycle

AbstractWater enters Earth's mantle via subduction of hydrated oceanic slab and largely returns to the ocean‐atmosphere system through arc volcanism. However, the extent to which H2O is transferred into the deep mantle is poorly constrained. Here, we address this question by combining mineral chemistry and bulk‐rock geochemistry data for aillikites related to the deep mantle plume which generated the Permian Tarim large igneous province (NW China). The water contents of olivine phenocrysts are 75–168 ppm H2O and positively correlated with Ti contents. These results, combined with infrared hydroxyl peaks at 3,572 and 3,525 cm−1, suggest that H is mainly present in the form of Ti‐clinohumite‐like point defects. Hydrogen concentration profiles across olivine reveal that H loss during decompression was limited to the outermost rims, and yield dehydration durations of 15–417 min. Based on the water contents of the highest‐Fo olivine cores, the water contents of the primitive aillikite melts and their mantle source are estimated as 1.6–4.7 wt% and 150–1,200 ppm H2O, respectively. 3He/4He ratios (5.31–5.84 Ra) of olivine phenocrysts are slightly lower than MORBs and suggest involvement of recycled slab containing U (and hence radiogenic 4He) in the plume source. This interpretation is consistent with Pb isotope compositions of the aillikites which are intermediate between PREMA (Prevalent Mantle) and EM (Enriched Mantle) compositions. These lines of evidence combined with the depleted Sr‐Nd isotopes and moderately radiogenic Os isotopes of the aillikites suggest that water in these rocks derived from a plume source marginally contaminated by deeply subducted hydrated material.

New insights into the mantle source of a large igneous province from highly siderophile element and Sr-Nd-Os isotope compositions of carbonate-rich ultramafic lamprophyres

Despite being volumetrically minor components, carbonate-rich ultramafic magmas like aillikites represent good candidates to investigate the compositional variations in plume and/or lithospheric mantle sources because they represent low-degree melts which preferentially sample highly fusible components including recycled crustal material. To gain new insights into the composition of the plume-related magmas and, more broadly, the petrogenesis of ultramafic lamprophyres, we have undertaken the first comprehensive study of bulk rock and mineral (olivine and Ti-magnetite) highly siderophile element (HSE) abundances and Re-Os isotopes combined with in situ major-, trace-element and Sr-Nd isotope analyses of apatite and perovskite from the Permian Wajilitag aillikites of the Tarim large igneous province, China. The Wajilitag aillikites have high PPGE (Pt and Pd) contents relative to IPGE (Os, Ir and Ru), which can be ascribed to low-degree partial melting and/or fractionation of olivine and laurite. Measured 187Os/188Os ratios are moderately to highly radiogenic (0.186–0.313) with age-corrected γOs values up to +113. In situ Sr and Nd isotope analyses of apatite phenocrysts (87Sr/86Sr(i) = 0.70349–0.70384; εNd(i) = +1.3 to +4.9) and fresh perovskite grains (87Sr/86Sr(i) = 0.70340–0.70390; εNd(i) = +1.3 to +3.8) exhibit limited variability both within and across samples from different aillikite dykes and the only volcanic pipe in the area. These Nd isotopic values resemble those from bulk-rock samples (εNd(i) = +1.9 to +5.2), whereas Sr in apatite and perovskite extends to marginally less radiogenic values than the bulk-rock compositions (87Sr/86Sr(i) = 0.70362–0.70432). The moderately depleted Sr-Nd isotope compositions of magmatic apatite and perovskite, and the previously reported mantle-like C isotope values of these samples suggest that the aillikites and their carbon probably derived from a sub-lithospheric (plume) source with minimal contribution of deeply subducted material. Conversely, the radiogenic Os isotope compositions of the Tarim aillikites and separated minerals require some contribution from recycled crustal material in the plume source. Mass balance calculations suggest that the radiogenic Os isotopes and moderately depleted Sr-Nd isotopes can be reproduced by less than one third of eclogite component addition to a moderately depleted mantle source. We conclude that the combination of complementary isotopic systems can enlighten contributions from different components to mantle-derived magmas and, in this case, clarifies the occurrence of carbon-free subducted oceanic crust in the Tarim plume.

Petrogenesis of Early Permian basalts in the Turpan-Hami basin, NW China: Implications for the spatial limits of the Tarim mantle plume

Controversies remain as to the area of the Tarim Large Igneous Province (TLIP), in particular, the relationship between extensive Permian magmatism in the Central Asian Orogenic Belt (CAOB) and the activity of Tarim plume. Here we report the geochronological, mineralogical and geochemical characteristics of the Permian basalts from the Turpan-Hami (Tu-Ha) basin, located in southwestern CAOB. LA-ICP-MS zircon U-Pb dating yielded an age of 298.4 ± 2.6 Ma, temporally close to that of the Tarim plume. The basalts could be classified into lower porphyritic basalt with phenocrysts of plagioclase, olivine, minor clinopyroxene, and upper aphyric basalts. Geochemically, the former is characterized by relatively higher Na2O + K2O (3.97–5.13 wt%), low (La/Yb)N (∼2) and depleted Sr-Nd values [εNd(t)= +8.2 to +8.7; (87Sr/86Sr)i = 0.7032–0.7034], whereas the latter have lower Na2O + K2O (4.19–4.43 wt%) content, higher (La/Yb)N (∼4–6) and more enriched Sr-Nd values [εNd(t)= +4.6 to +6.2; (87Sr/86Sr)i = 0.7033–0.7048]. The compositional variation of plagioclase phenocrysts and pressure estimation (∼7kbar) indicate that Tu-Ha magmas were stored and evolved in a lower crustal magma chamber which experienced at least one-time magma replenishment. The estimated mantle potential temperature (1270–1480 °C) in Tu-Ha basin is similar to MOR, with no obvious thermal anomaly. Furthermore, higher Na/Ti ratio of quartz-normative Tu-Ha basalts suggest a shallower melting depth for Tu-Ha basin than central area of TLIP, which against a typical plume model. These characteristics alongside regional geologic records collectively suggest that the formation of Permian Tu-Ha basalts is more closely linked post-orogenic extension, implying that the extensive Permian magmatism in the CAOB is unrelated to the Tarim plume.

Tarim Large Igneous Province Caused by a Wide and Wet Mantle Plume

AbstractLarge igneous provinces (LIPs) can form by interactions between a hot mantle plume and the lithosphere. The Tarim LIP between ~300 and 280 Ma, located in Northwest China, has been investigated by geochemistry and sedimentology studies. However, the factors controlling Tarim LIP formation and the ancient Tarim plume characteristics remain unclear. Here, a series of 3‐D geodynamic models are combined with geological observations to constrain the Tarim LIP evolution and the features of the related Tarim plume. Our results show that (1) an ancient plume produced abundant melts attributed to decompression melting, excess temperature, high water contents, and slow plate motion velocities to form the banded Tarim LIP. (2) The simulated pre‐eruption topography coincides with the stratigraphic records from the late Carboniferous to early Permian. Specifically, the swell area of pre‐eruption topography is sensitive only to the plume radius and enables us to constrain the ancient mantle plume size well. (3) Based on the volcanic activity and pre‐eruption topography, we infer that the ancient Tarim plume had a very large radius of ~200 km, a high excess temperature of ~250 K, and a high water content of ~5 wt.%. (4) Our parameter tests and global plate reconstruction results show that high water contents and slow plate motion velocities facilitate continental flood basalts to form with thick lithosphere. Our geodynamic modeling not only provides new constraints for the Tarim LIP evolution but also first quantificationally demonstrates that water in the mantle plays a key role in continental flood basalt formation.

Carbonatites of Tarim (NW China): First evidence of crustal contribution in carbonatites from a large igneous province

Many carbonatites are associated both spatially and temporally with large igneous provinces (LIPs), and considered to originate from a mantle plume source lacking any contribution from recycled crustal materials. Here, we report an occurrence of carbonatite enriched in rare-earth elements (REE) and associated with the Tarim LIP in northwestern China. The Tarim LIP comprises intrusive and volcanic products of mantle plume activity spanning from ~300 to 280Ma. The carbonatites at Wajilitage in the northwestern part of Tarim are dominated by calcite and dolomite varieties, and contain abundant REE minerals (principally, monazite and REE-fluorcarbonates). Th–Pb age determination of monazite yielded an emplacement age of 266±5.3 Ma, i.e. appreciably younger than the eruption age of flood basalts at ~290Ma. The carbonatites show low initial 87Sr/86Sr (0.7037–0.7041) and high εNd(t) (1.2–4) values, which depart from the isotopic characteristics of plume-derived basalts and high-Mg picrites from the same area. This indicates that the Wajilitage carbonatites derived from a mantle source isotopically distinct from the one responsible for the voluminous (ultra)mafic volcanism at Tarim. The carbonatites show δ26MgDSM3 values (−0.99 to −0.65‰) that are significantly lower than those in typical mantle-derived rocks and rift carbonatites, but close to marine sediments and orogenic carbonatites. We propose that the carbonatites in the Tarim LIP formed by decompressional melting of recycled sediments mixed with the ambient mantle peridotite. The enriched components in the Tarim plume could be accounted for by the presence of recycled sedimentary components in the subcontinental mantle.

Disseminated gold–sulfide mineralization at the Zhaima deposit, eastern Kazakhstan

The Zhaima gold–sulfide deposit is located in the northwestern part of the West Kalba gold belt in eastern Kazakhstan. The mineralization is hosted in Lower Carboniferous volcanic and carbonate rocks formed under conditions of marginal-sea and island-arc volcanic activity. The paper considers the mineralogy and geochemistry of primary gold–sulfide ore and Au-bearing weathering crusts. Au-bearing arsenopyrite–pyrite mineralization formed during only one productive stage. Disseminated, stringer–disseminated, and massive rocks are enriched in Ti, Cr, V, Cu, and Ni, which correspond to the mafic profile of basement. The main ores minerals are represented by finely acicular arsenopyrite containing Au (up to few tens of ppm) and cubic and pentagonal dodecahedral pyrite with sporadic submicroscopic inclusions of native gold. The sulfur isotopic composition of sulfides is close to that of the meteoritic standard (δ34S =–0.2 to +0.2). The 40Ar/39Ar age of three sericite samples from ore veinlets corresponds to the Early Permian: 279 ± 3.3, 275.6 ± 2.9, and 272.2 ± 2.9 Ma. The mantle source of sulfur, ore geochemistry, and spatial compatibility of mineralization with basic dikes allow us to speak about the existence of deep fluid–magmatic systems apparently conjugate with the Tarim plume.

Plume‐orogenic lithosphere interaction recorded in the Haladala layered intrusion in the Southwest Tianshan Orogen, NW China

AbstractThe plume‐orogenic lithosphere interaction may be common and important for the generation of large igneous provinces. The information regarding such a process is recorded by the Haladala gabbroic intrusion (~300 Ma), the largest layered ultramafic‐mafic intrusion hosting V‐Ti magnetite deposits in the Southwest Tianshan Orogen, NW China. The Haladala gabbros exhibit unfractionated chondrite‐normalized rare earth element patterns with negative Nb and Ta anomalies and positive Pb anomaly on the primitive mantle‐normalized multielement variation diagram. They are characterized by low initial Sr isotopes, slightly decoupled but high positive bulk rock εNd(t) and εHf(t), and high 207Pb/204Pb and 208Pb/204Pb relative to 206Pb/204Pb, delineating a DUPAL signature in the sources. The Haladala gabbros cannot be arc or postcollisional magmatism, given the lack of hydrous minerals and low K contents, respectively. This is further supported by the relatively low oxygen fugacity required for the gradual enrichment of V‐Ti magnetite during the magma fractionation and by an overall anhydrous mantle source suggested by troctolite mineral assemblage (olivine + plagioclase). The emplacement age of the Haladala gabbros is identical to that of the Wajilitag kimberlites in the Tarim's interior, which have been interpreted as the first magmatic expression of the Tarim mantle plume. We thus propose that the Haladala gabbroic intrusion was generated in a hybrid geodynamic setting in which the Southwest Tianshan Orogen was impacted by an upwelling mantle plume. In this sense, the Haladala layered gabbroic intrusion records the early phase of magmatism of the Tarim plume, which was preferentially emplaced in a lithospheric weak zone.

The impact of early sulfur saturation and calc-crustal contamination on ore-forming process in the Posan mafic–ultramafic complex: Derived from the shallow depleted mantle, Beishan region, NW China

The Posan ultramafic intrusion is one of the ~280Ma Pobei mafic–ultramafic complexes located in the Beishan rift, on the northeastern margin of the Tarim Craton. Given that three finished drill holes reveal less economic mineralization, it is necessary to understand the ore potential of this little ultramafic intrusion. Detailed fieldwork shows that it is comprised of five stages of magma events. Among them, stages I, II and III are the mafic bodies dominated by gabbro, gabbronorite and olivine gabbro, and stages IV and V are the ultramafic bodies characterized by layered intrusions. Theoretically, the Posan ultramafic intrusion meets the first requirement of ore mineralization because of its high MgO contents (14.76%) of the parental magma. Moreover, the low Ni content (less than 1900ppm) in olivine and the paragenesis of sulfides and spinel demonstrate that the Posan intrusion experienced early sulfur saturation before or during the fractional crystallization of spinel and olivine. This part of the sulfide, which may contain Ni–Cu or PGE mineralization, deserves to be the focus of future work. In stage IV, the continuous decrease of Ni contents in olivine with the fractional crystallization, the calc-crustal contamination (irregular distributed plagioclase, high Th/Yb ratios, Nb and Zr depletion and K, Rb, Ba, U, Th and Pb enrichment) instead of sulfur-rich crustal contamination, and the high level of oxygen fugacity (+2.1<fO2QFM<+3.0) result in no obvious disseminated sulfides created in this stage. A clinopyroxene TiO2-Alz diagram confirms that the Beishan mafic–ultramafic complexes were formed in a rift-related circumstance rather than the arc-related cumulus. Low TiO2/Yb and Nb/Yb ratios reflect that the Beishan complexes were derived from the shallow depleted mantle without garnet. Considering the temporal and spatial relationship of the Tarim large igneous province and the large numbers of mafic–ultramafic intrusions in the Beishan region, it is reasonable to speculate that the Beishan mafic–ultramafic complexes, including the Posan intrusion (275.8±2.7Ma), have a genetic affiliation with, but were not directly formed by, the early Permian Tarim Plume.

The migration of Tarim plume magma toward the northeast in Early Permian and its significance for the exploration of PGE-Cu–Ni magmatic sulfide deposits in Xinjiang, NW China: As suggested by Sr–Nd–Hf isotopes, sedimentology and geophysical data

It is well known that a genetic link exists between the formation of ultramafic-rocks-hosted PGE-Cu–Ni sulfide deposits and the eruption of associated continental flood basalts. We here present a new model for the relationship between the Cu–Ni deposits located along the northeastern margin of Tarim and the internal Tarim basalt. Sr–Nd isotope and Hf isotope two-stage crust model ages TDMc indicate that whereas the Cu–Ni deposits along the northeastern margin of Tarim have Neoproterozoic and Mesoproterozoic lithology contamination, the surrounding rocks of Cu–Ni deposits in Beishan (Pobei) and Central Tianshan do not have Neoproterozoic lithologies. We propose that this is the result of mixing with the Neoproterozoic rocks in the interior of Tarim block. There is also an east–west trending positive magnetic anomaly belt in the central Tarim Basin, while Early Permian mafic–ultramafic rocks found along the northeastern margin of Tarim probably have a relationship with the Tarim Basin basalt. According to the Bouguer gravity map, the Bachu area near the center of Early Permian plume has high gravity values, with the northeastern high gravity belt in the central Tarim Basin possibly the result of a tilt of the mantle plume to the southwest below the Tarim block, which could be consistent with the earlier uplift and denudation in northeastern Tarim and later in southwestern Tarim from the Early Carboniferous to the Late Permian, as well as with observed uplift in the Bachu area in the Permian. We infer that the tilt of a mantle plume to the southwest below the Tarim block led to the inclined attitude of overlying rocks, with Early Permian magma flowing toward the northeast margin of Tarim. Based on this model, new PGE-Cu–Ni magmatic sulfide deposits related to Early Permian mafic–ultramafic intrusions may be found in the southwest area of Beishan, although this area is covered by Mesozoic and Cenozoic sediments.

Geochemistry and age of rare-metal dyke belts in eastern Kazakhstan

The results of studies of the Chechek and Akhmirovo dyke belts (the Kalba-Narym zone of Eastern Kazakhstan) constituted by rare-metal Li-F-granitoids (ongonites) are presented. The results of geochemical mapping of dyke belts are given, as are the first-obtained data on the rare-metal composition of rock-forming minerals and melt inclusions. The data on precision dating of rocks by means of the 40Ar/39Ar-isotope technique are presented. It is shown that the dyke belts were formed from the melts of three different geochemical types. The existence of these types might be caused by differentiation within the deep-seated magma chambers. The data of geochronology permit us to conclude that the centers of rare-metal Li-F-magmatism characteristic of the large magma provinces that appeared under the impact of mantle plumes on the arisen continental crust might have been formed at the final stages of the formation of the Kalba-Narym batholith. This allows one to assume the rare-metal Li-F-granitoids (ongonites) of the dyke belts in Eastern Kazakhstan belong to the large Late-Paleozoic magma province that appeared in the region of Central Asia as a result of the activity of the Tarim plume.

Origin of Permian gabbroic intrusions in the southern margin of the Altai Orogenic belt: A possible link to the Permian Tarim mantle plume?

Abstract Zircon U–Pb dating and Hf isotopic compositions, whole-rock and mineral geochemistry, as well as field and petrographic observations, are reported for the Permian gabbroic intrusions in the southern margin of the Altai orogenic belt. Similar zircon ages (~ 280 Ma) of these intrusions to that of the Permian Tarim mantle plume suggest a possible link to the Tarim plume. Olivine grains from the intrusions have Fo contents ranging from 69 to 81 and NiO from 0.05 to 0.21 wt.%, indicating the crystallization from evolved mafic magmas. Clinopyroxene grains from the intrusions have 0.3 to 1.5 wt.% TiO 2 and display a rift- to arc-like affinity. The intrusions are tholeiitic and have slightly LREE-depleted to LREE-enriched chondrite-normalized rare earth element (REE) patterns. Zircons from the intrusions have e Hf (t) values higher than + 8.0, whereas the whole-rock e Nd (t) values range from + 2.7 to + 7.0. Rocks from the intrusions have Nb/La of 0.2 to 0.8, consistent with the derivation from a depleted sub-lithospheric mantle with variable degrees of crustal contamination. The presence of primary hornblende and/or biotite in the rocks indicates metasomatism by slab-derived fluids/melts in the mantle source. We propose that upwelling of asthenospheric mantle in the Permian Tarim mantle plume along the Irtish suture zone, resulted in partial melting of the sub-continental lithospheric mantle. Based on a comparison between the Ni–Cu sulfide-bearing Kalatongke complex and un-mineralized intrusions, we suggest that Ni–Cu sulfide mineralized intrusions in the Altai orogenic belt are characterized by the enrichments of LREEs and LILEs and by the presence of primary water-bearing minerals.

The Erbutu Ni-Cu Deposit in the Central Asian Orogenic Belt: A Permian Magmatic Sulfide Deposit Related to Boninitic Magmatism in An Arc Setting

The Erbutu Ni-Cu sulfide deposit is hosted in a small ultramafic intrusion located at the southern margin of the Central Asian orogenic belt, Inner Mongolia. This deposit is the first case of a magmatic sulfide deposit related to boninitic magmatism in an arc setting. The host intrusion is composed of orthopyroxenite and olivine orthopyroxenite. More than three quarters of the intrusion contains economic, disseminated sulfide mineralization. SHRIMP U-Pb dating of zircons from the intrusion gives a crystallization age of 294.2 ± 2.7 Ma, similar to the age of the Permian Tarim plume in northwest China. Olivine orthopyroxenite is characterized by olivine crystals with relatively high Fo contents (85–88 mol %) and extremely low Ca contents (<250 ppm). Coexisting orthopyroxene crystals have clinoenstatite composition with enstatite from 86 to 88 mol %. Whole-rock data show characteristic enrichments of light REE relative to heavy REE, pronounced negative Nb-Ta anomalies, and moderately positive Hf anomaly. The δ 34S values of sulfide separates are 4 to 5‰, significantly higher than the typical mantle value (0 ± 2‰). The ɛ Hf values of zircons are from −4 to −9. These data indicate that the parental magma was a boninite. Crustal contamination was involved during magma evolution and ore formation.

Petrology and geochemistry of gabbro and picrites from the Altai collisional system of Hercynides: Evidence for the activity of the Tarim plume

We present petrological, isotopic, and geochronological data on gabbro-picrite plutons from the Altai collisional system of Hercynides (eastern Kazakhstan). The geological, geochemical, and geochronological data suggest that these rocks are indicators of the activity of the Tarim plume. The gabbro and picrites formed in two stages (~293 and 280 Ma) in an acid-to-basic succession, explained by a model for the interaction of thermochemical plumes with the lithosphere. Early igneous activity, which gave rise to subalkalic gabbro plutons, reflects the first interaction between the ascending plume and the lithosphere, with low-melting sublithospheric protoliths. Further interaction was characterized by the sublithospheric spread of the plume head with intense heating of the lithospheric base and possible intrusion of deep melts, which resulted in the formation of Cu–Ni–PGE gabbro-picrite plutons in the Altai collisional system and Northwest China.

U-Pb isotopic age, composition, and sources of the plagiogranites of the Kalba range, Eastern Kazakhstan

Of special importance in the evolution of the Paleoasian ocean is the Carboniferous‐Permian stage, which reflects the closure of the oceanic basin and formation of the structure of the Central Asian fold belt (CAFB) in its present-day form [1]. This is also the time (320‐280 Ma) when the largest Angara‐Vitim granitoid batholith and conjugate synplutonic basite dikes in Transbaikalia, granitoid intrusions and bimodal basalt‐rhyolite series of the Gobi‐Tien Shan zone of South Mongolia, and the Kalba‐Narym and ZharmaSaur batholithic bodies and preceding subalkaline gabbroids, picritoids, high-Al plagiogranitoids, and paleovolcanic structures of the central type in Eastern Kazakhstan were formed. Unlike the Permian‐Triassic stage, which was proved to be related to the Siberian superplume [2], the geodynamic nature of the Carboniferous‐Permian magmatism of the CAFB remains controversial. The plume model was proposed for the Angara‐Vitim batholith [3], and break-off of lithospheric plates in the collision zone between the Kazakhstan and Siberian paleocontinents was suggested for the batholithic belts of Eastern Kazakhstan [4]. These models believe that the collision-related mantle was supplied either with autonomous plumes or with asthenospheric fingers produced by mantle extinction at the divergent margins of lithospheric plates. The solution of this problem consists in studying key magmatic complexes (composition, structure, age), with a special emphasis on the sources of magmatic melts. One such key complex is the plagiogranite of the Kalba Range traditionally distinguished in the Kunush Complex. One group of researchers suggested an Early Carboniferous age and island arc affinity [5], while others consider them as collision-related Late Carboniferous rocks [6, 7], or as products of the Tarim plume [8]. The analysis of the tectonic position of the magmatic complexes of Great Altai (according to N.A. Eliseev) and their correlation with sources [8, 9] sheds no light on this controversary. This article is aimed at accurate dating of the plagiogranites of the Kalba‐Narym zone for refining their position in the magmatic scheme, as well as for estimating the formation conditions and sources of plagiogranite magmas based on their composition and geochemical modeling of the protolith‐melt system. We studied the plagiogranites from the Zhilandy and Tochka massifs (Fig. 1). The Zhilandy Massif forms an isometric body, with medium-grained biotite granites in the central part and fine-grained porphyritic varieties and plagiogranite porphyry dikes in the marginal parts. The plagiogranites consist of large biotite, short-prismatic zoned andesine‐oligoclase, and single grains of orthoclase‐microperthite and green hornblende. The Tochka Massif is made up of NW-extended minor bodies and dikes of fine-grained porphyritic biotite plagiogranites and plagiogranite porphyries. The plagiogranites of the Tochka Massif differ macroscopically from the Zhilandy rocks owing to superimposed processes of mylonitization; however, microscopically, they have similar petrographic and mineral composition. The dikes of plagiogranite porphyries of both the massifs contain phenocrysts of short-prismatic zoned plagioclase, quartz, and biotite embedded in the microcrystalline groundmass. In both cases, the plagiogranites intrude black shales of the Takyr Formation ( D 3 –C 1 ) and are cut by the Early Permian granitoids of the Kalba batholithic belt [5‐7, 10].

Mantle sources of Permian-Triassic Siberian traps (West Siberian Plate and Siberian craton)

We investigate the dynamics of multilevel subcontinental melting beneath a lithosphere of variable thickness as a model simulating generation of melts that produced flood basalt in the Siberian Trap province. The inferred sequence of volcanic events correlates with upper mantle decompression melting above hotspots and related conductive melting of metasomatized depleted lithosphere. Numerical experiments show that complex mafic magmatic systems of this kind are at least two-stage with a zone of decompression melting in upwelling mantle flow and a sub-Moho lithospheric melting region; the shallower lithospheric melting region can be disconnected from the mantle zone of decompression melting along the edges of the magmatic system; the lithospheric melting region has a particular layered structure with its top at a depth of 60–70 km and a maximum size exceeding the length of the erupted lava field; mafic melts produced at different levels of the system have different compositions. In the area of influence of the Tarim plume, including the Zaisan-Gobi zone and other structures of the Gobi-Tien Shan belt, diverse Cu-Ni-PGE, Ni-Co-As, Au-Hg, Cu-Mo, and ore deposits related to plume magmatism formed. Their composition, formation conditions, and relationship with magmatism are discussed.

Permian ultramafic-mafic magmatism and accompanying Cu-Ni mineralization in the Gobi-Tien Shan belt as a result of the Tarim plume activity

The paper reports data on the age, composition, and geodynamic environments of Permian ultramafic-mafic complexes in the Zaisan-Gobi zone in the eastern Gobi-Tien Shan rift belt. The synchronous formation of these complexes with Early Permian lava alkali and tholeiitic basalts discovered beneath the cover of the Tarim and Junggar platform blocks suggests that they are derivates of the Tarim plume related to the Permo-Triassic Siberian superplume. This is evidenced from the composition and metallogeny of the complexes similar to those of magnesian trap intrusions on the western periphery of the Siberian Platform. In the area of influence of the Tarim plume, including the Zaisan-Gobi zone and other structures of the Gobi-Tien Shan belt, diverse Cu-Ni-PGE, Ni-Co-As, Au-Hg, Cu-Mo, and ore deposits related to plume magmatism formed. Their composition, formation conditions, and relationship with magmatism are discussed.