Evolution Of Subcontinental Lithospheric Mantle Research Articles

Multistage evolution of subcontinental lithospheric mantle of northwestern Deccan volcanic province, India: Constraints from the ultramafic xenoliths in alkali magma

Multistage evolution of subcontinental lithospheric mantle of northwestern Deccan volcanic province, India: Constraints from the ultramafic xenoliths in alkali magma

Lithospheric mantle refertilization by DMM-derived melts beneath the Cameroon Volcanic Line\u2014a case study of the Befang xenolith suite (Oku Volcanic Group, Cameroon)

The origin and evolution of subcontinental lithospheric mantle (SCLM) are important issues of Earth’s chemical and physical evolution. Here, we report detailed textural and chemical analyses on a mantle xenolith suite from Befang (Oku Volcanic Group, Cameroon Volcanic Line), which represents a major tectono-magmatic structure of the African plate. The samples are sourced from spinel-facies mantle and are dominated by lherzolites. Their texture is cataclastic to porphyroclastic, and foliation defined by grain-size variation and alignment of spinel occurs in part of peridotites. Spinel is interstitial and has amoeboidal shape. Clinopyroxene REE patterns are similar to those of Depleted MORB Mantle (DMM) except LREEs, which vary from depleted to enriched. The A-type olivine fabric occurs in the subset of one harzburgite and 7 lherzolites studied by EBSD. Orthopyroxene shows deformation consistent with olivine. The fabric of LREE-enriched clinopyroxene is equivalent to those of orthopyroxene and olivine, whereas spinel and LREE-depleted clinopyroxene are oriented independently of host rock fabric. The textural, chemical and thermobarometric constraints indicate that the Befang mantle section was refertilised by MORB-like melt at pressures of 1.0–1.4 GPa and temperatures slightly above 1200–1275 °C. The olivine-orthopyroxene framework and LREE-enriched clinopyroxene preserve the protolith fabric. In contrast, the LREE-depleted clinopyroxene, showing discordant deformation relative to the olivine-orthopyroxene protolith framework, and amoeboidal spinel crystallized from the infiltrating melt. The major element and REEs composition of minerals forming the Befang peridotites indicate subsequent reequilibration at temperatures 930–1000 °C. This was followed by the formation of websterite veins in the lithospheric mantle, which can be linked to Cenozoic volcanism in the Cameroon Volcanic Line that also brought the xenoliths to the surface. This study therefore supports the origin of fertile SCLM via refertilization rather than by extraction of small melt fractions, and further emphasizes the involvement of depleted melts in this process.

Sr-Nd isotopic study of dolerite dykes in the Western Dharwar craton, southern India: Implications for the evolution of the subcontinental lithospheric mantle in late Archean

Mafic dyke swarms are one of the major geologic features that represent crustal extension and rifting episodes which result in the transfer of large volumes of mantle materials to the crust. The rapid emplacement of dykes within a short span of time helps to preserve the composition of subcontinental lithospheric mantle (SCLM) and understand its evolution over time. Here we report major and trace element geochemistry and Sr-Nd isotopic characteristics of dykes from the Tiptur area in the late Archean Western Dharwar craton of southern India. The studied mafic dykes are un-metamorphosed and preserve pristine igneous textures and mineralogy. Three different groups of dykes were identified and categorized as olivine dolerites, dolerites and REE enriched dolerites, based on the distinct petrographical and geochemical characteristics. Olivine dolerites are having a high Mg# suggesting a lower degree of fractionation and is indicative of a less evolved magma. Dolerites have comparatively lower Mg# than the olivine dolerites indicating that the former have undergone significant fractional crystallization as confirmed by the higher Ni contents. The low initial Sr isotopic ratio for olivine dolerites (87Sr/86Sr = 0.70088) with negative epsilon Nd values are suggesting a late Archean enriched subcontinental lithospheric mantle (SCLM) in the source region. The dolerites (87Sr/86Sr = 0.70132 to 0.70327) and REE enriched dolerites (87Sr/86Sr = 0.70405 to 0.70653) show signatures of a more enriched source. The evolution of SCLM from a DMM source enriched by the subduction of the mafic oceanic crust in the late Archean to a mantle enriched by continent-derived sediments towards the early Proterozoic are reflected in the dolerite and REE enriched dykes.

He and Ar isotope geochemistry of pyroxene megacrysts and mantle xenoliths in Cenozoic basalt from the Changle–Linqu area in western Shandong

We performed a combined study of He–Ar isotopes and element geochemistry for pyroxene megacrysts and mantle xenoliths from Cenozoic basalt in the Changle–Linqu area in western Shandong. The results are used to trace the evolution of subcontinental lithospheric mantle after destruction of the North China Craton. The 3He/4He ratios of pyroxene megacrysts, websterite, and dunites are 7.0–7.7 Ra, 7.4 Ra, and 7.0–7.7 Ra, respectively. They are related to the origin of host basalts, and are slightly lower than that of mid-ocean ridge basalts (MORB). Their 40Ar/36Ar ratios are much lower than that of MORB and close to that of air. The lherzolites and wehrlites represent the fragments of the newly accreted lithospheric mantle, and their REE and trace elements indicate that they experienced melt metasomatism and partial melting. The 3He/4He ratios of their olivine are slightly lower than that of MORB, but 3He/4He ratios of their clinopyroxene are low (2.3–7.1 Ra) and display an inverse correlation with (La/Yb)N. The 40Ar/36Ar ratios of these clinopyroxene are much lower than that of MORB and close to the air ratio. Combining existing studies of petrology, Sr–Nd–Pb isotopes, O isotopes, trace elements, and Mg isotopes, we infer that the juvenile lithospheric mantle in the Changle–Linqu area was metasomatized by oceanic crust-derived melts, which transfer the supracrustal Ar isotope signatures to the mantle sources. The low 4He abundance and low 3He/4He ratios of clinopyroxene in the lherzolites and wehrlites are ascribed to metasomatism by crustal melts from the subducted Pacific plate.

Variations in carbon isotopic composition in the subcontinental lithospheric mantle beneath the Yangtze and North China Cratons: Evidence from in-situ analysis of diamonds using SIMS

The components and evolution of subcontinental lithospheric mantle beneath the North China Craton and the Yangtze Craton is a current topic in the geological study of China and the carbon isotopic composition of diamond is one of the most direct probes into cratonic lithospheric mantle processes. In this paper, in-situ SIMS (Secondary Ion Mass Spectrometry) techniques were used to analyze the carbon isotope compositions at different internal growth zones of diamonds from Shandong and Liaoning in the North China Craton and Hunan in the Yangtze Craton. It was found that the carbon isotopic range of diamonds from the North China Craton are rather distinct from those of the Yangtze Craton; the former has a range of −6.0/‰ to −2.0‰ (relative to VPDB) with an average value of −3.0‰ in their core areas, which is consistent with global peridotitic diamonds; the diamonds from the Yangtze Craton, however, have a carbon isotopic range from −8.6‰ to −3.0‰ with an average value of −7.4‰ in their core areas, being more consistent with global eclogitic diamonds. The variations of carbon isotope ratios between different internal growth zones in individual diamonds were different in the three diamond localities studied. There was a clear correlation between changes in carbon isotopic composition and phases of diamond dissolution and new growth, while no correlation was observed between δ 13C and internal inclusions. The variations suggest that the carbon isotopic compositions of mantle fluids were changing during the process of diamond crystallization, and that the heterogeneity of the carbon isotopic composition in mantle carbon reservoirs was a more important factor than carbon isotope fractionation in controlling the carbon isotopic compositions and their variation in diamonds. In addition, the preliminary results of in-situ nitrogen analyses demonstrated that the variation of carbon isotopic compositions between the core and outer growth zones does not correlate with nitrogen abundances, implying either that diamonds crystallized in an open environment or that the carbon isotopic composition and nitrogen contents in mantle fluids were controlled by other, not yet understood factors. The experimental results provide hints that the isotopic composition of carbon and its original sources were different in metasomatic fluids controlling diamond formation in the mantle beneath the North China Craton and the Yangtze Craton.

Precisely dating Paleozoic kimberlites in the North China Craton and Hf isotopic constraints on the evolution of the subcontinental lithospheric mantle

Kimberlite, a deep-sourced ultramafic potassic rock, carries not only diamond, but also invaluable mantle xenoliths and/or xenocrysts, which are important for tracking the evolution of subcontinental lithospheric mantle (SCLM). However, it is challenging to accurately determine the emplacement age of kimberlite and its compositions of primary magma because of modifications by crustal and/or mantle contamination and post-emplacement alteration. This paper reports emplacement ages of diamondiferous kimberlites in Mengyin and Fuxian of the North China Craton (NCC) using three different dating methods. For Mengyin kimberlite, single-grain phlogopite Rb–Sr dating yields an isochron age of 485 ± 4 Ma, U–Th–Pb analyses on perovskite give a 238U– 206Pb age of 480.6 ± 2.9 Ma and a 232Th– 208Pb age of 478.9 ± 3.9 Ma, and baddeleyite yields a 207Pb– 206Pb age of 480.4 ± 3.9 Ma. For Fuxian kimberlite, baddeleyite gives a 207Pb– 206Pb age of 479.6 ± 3.9 Ma, indicating that the Paleozoic kimberlites in the NCC were emplaced at ~ 480 Ma. Numerous lines of evidence indicate that the studied baddeleyites are xenocrysts from the SCLM, and can be used to constrain Hf isotope compositions ( ε Hf(t) ~ − 6) of the SCLM when kimberlite erupted. Combined with data from Mesozoic–Cenozoic mantle-derived rocks and xenoliths, the Hf isotope evolution trend of the SCLM beneath NCC before craton destruction was tentatively constructed, which suggested that the Archean SLCM was enriched by metasomatism at ~ 1.3 Ga. Further Hf isotope investigations on additional SCLM-derived materials could be used to compare with the constructed Hf isotope evolution trend before craton destruction to determine when lithospheric thinning occurred.

Osmium isotope and highly siderophile element geochemistry of mantle xenoliths from NW Turkey: implications for melt depletion and metasomatic history of the sub-continental lithospheric mantle

Ultramafic xenoliths entrained in the late Miocene alkali basalts and basanites from NW Turkey include refractory spinel-harzburgites and dunites accompanied by subordinate spinel-lherzolites. Whole-rock major and trace element characteristics indicate that the xenoliths are mostly the solid residues of varying degrees of partial melting (∼4–∼15%), but some have geochemical signatures reflecting the processes of melt/rock interaction. Mantle-normalized trace element patterns for the peridotites vary from LREE-depleted to strongly LREE-enriched, reflecting multistage mantle processes from simple melt extraction to metasomatic enrichment. Rhenium and platinum group element (PGE) abundances and 187Os/188Os systematics of peridotites were examined in order to identify the nature of the mantle source and the processes effective during variable stages of melt extraction within the sub-continental lithospheric mantle (SCLM). The peridotites are characterized by chondritic Os/Ir and Pt/Ir ratios and slightly supra-chondritic Pd/Ir and Rh/Ir ratios, representing a mantle region similar in composition to the primitive mantle (PM). Moderate enrichment in PPGE (Pd–Pt–Rh)/IPGE (Ir–Os–Ru) ratios with respect to the PM composition in the metasomatized samples, however, reflects compositional modification by sulphide addition during possible post-melting processes. The 187Os/188Os ratios of the peridotites range from 0.11801 to 0.12657. Highly unradiogenic Os isotope compositions (γOs at 10 Ma from –7.0 to –3.2) in the chemically undisturbed mantle residues are accompanied by depletion in Re/Os ratios, suggesting long-term differentiation of SCLM by continuous melt extraction. For the metasomatized peridotites, however, systematic enrichments in PPGE and Re abundances, and the observed positive covariance between 187Re/188Os and γOs can most likely be explained by interaction of solid residues with basaltic melts produced by melting of relatively more radiogenic components in the mantle. Significantly, the wide range of 187Os/188Os ratios characterizing the entire xenolith suite seems to be consistent with multistage evolution of SCLM and suggests that parts of the lithospheric mantle contain materials that have experienced ancient melt removal (∼1.3 Ga) which created time-integrated depletion in Re/Os ratios; in contrast, some other parts display evidence indicative of recent perturbation in the Re–Os system by sulphide addition during interaction with metasomatizing melts.

Geochemistry and Evolution of Subcontinental Lithospheric Mantle in Central Europe: Evidence from Peridotite Xenoliths of the Kozakov Volcano, Czech Republic

Neogene basanite lavas ofKoza¤ kov volcano, located along the Lusatian fault in the northeastern Czech Republic, contain abundant anhydrous spinellherzolitexenolithsthatprovidean exceptionallycontinuoussampling of the upper two-thirds of central European lithospheric mantle. The xenoliths yield a range of two-pyroxene equilibration temperatures from 6808C to 10708C, and are estimated to originate from depths of 32^70 km, based on a tectonothermal model for basaltic underplating associated with Neogene rifting.The sub-Koza¤ kov mantle is layered, consisting ofan equigranular upper layer (32^43 km), a protogranular intermediate layer that contains spinel^pyroxene symplectites after garnet (43^67 km), and an equigranular lower layer (67^70 km). Negative correlations of wt % TiO2, Al2O3, and CaO with MgO and clinopyroxene mode with Cr-number in the lherzolites record the effects of partial fusion and melt extraction;YandYb contents of clinopyroxene and the Cr-number in spinel indicate 5 to 15% partial melting. Subsequent metasomatism of a depleted lherzolite protolith, probably by a silicate melt, produced enrichments in the large ion lithophile elements, light rare earth elements and high field strength elements, and positive anomalies in primitive mantle normalized trace element patterns for P, Zr, and Hf. Although there are slight geochemical discontinuitiesat theboundariesbetween the three textural layers of mantle, there tends to be an overall decrease in the degree of depletion with depth, accompanied by a decrease in the magnitude of metasomatism. Clinopyroxene separates from the intermediate protogranular layer and the lower equigranular layer yield Nd/Nd values of 0 51287^0 51307 (eNd1⁄4þ4 6 to þ8 4) and Sr/Sr values of 0 70328^0 70339. Such values are intermediate with respect to the Nd^Sr isotopic array defined by anhydrous spinel peridotite xenoliths from central Europe and are similar to those associated with the present-day low-velocity anomaly in the upper mantle beneath Europe. The geochemical characteristics of the central European lithospheric mantle reflect a complex evolution related to Devonian to Early Carboniferous plate convergence, accretion, and crustal thickening, Late Carboniferous to Permian extension and gravitational collapse, and Neogene rifting, lithospheric thinning, and magmatism.

Refertilization of ancient lithospheric mantle beneath the central North China Craton: Evidence from petrology and geochemistry of peridotite xenoliths

The petrology and geochemistry of peridotite xenoliths in the Cenozoic basalts from Fanshi, the central North China Craton (NCC), provide constraints on the evolution of sub-continental lithospheric mantle. These peridotite xenoliths are mainly spinel-facies lherzolites with minor harzburgites. The lherzolites are characterized by low forsterite contents in olivines (Fo < 91) and light rare earth element (LREE) enrichments in clinopyroxenes. In contrast, the harzburgites are typified by high-Fo olivines (> 91), high-Cr# spinels and clinopyroxenes with low abundances of heavy REE (HREE). These features are similar to those from old refractory lithospheric mantle around the world, and thus interpreted to be relics of old lithospheric mantle. The old lithospheric mantle has been chemically modified by the influx of melts, as evidenced by the Sr–Nd isotopic compositions of clinopyroxenes and relatively lower Fo contents than typical Archean lithospheric mantle (Fo > 92.5). The Sr–Nd isotopic compositions of harzburgites are close to EM1-type mantle, and of the lherzolites are similar to bulk silicate earth. The latter could be the result of recent modification of old harzburgites by asthenospheric melt, which is strengthened by fertile compositions of minerals in the lherzolites. Therefore, the isotopic and chemical heterogeneities of the Fanshi peridotite xenoliths reflect the refertilization of ancient refractory lithospheric mantle by massive addition of asthenospheric melts. This may be an important mechanism for the lithospheric evolution beneath the Central NCC.

Evolution of subcontinental lithospheric mantle beneath eastern China: Re–Os isotopic evidence from mantle xenoliths in Paleozoic kimberlites and Mesozoic basalts

The ages of subcontinental lithospheric mantle beneath the North China and South China cratons are less well-constrained than the overlying crust. We report Re–Os isotope systematics of mantle xenoliths entrained in Paleozoic kimberlites and Mesozoic basalts from eastern China. Peridotite xenoliths from the Fuxian and Mengyin Paleozoic diamondiferous kimberlites in the North China Craton give Archean Re depletion ages of 2.6–3.2 Ga and melt depletion ages of 2.9–3.4 Ga. No obvious differences in Re and Os abundances, Os isotopic ratios and model ages are observed between spinel-facies and garnet-facies peridotites from both kimberlite localities. The Re–Os isotopic data, together with the PGE concentrations, demonstrate that beneath the Archean continental crust of the eastern North China Craton, Archean lithospheric mantle of spinel- to diamond-facies existed without apparent compositional stratification during the Paleozoic. The Mesozoic and Cenozoic basalt-borne peridotite and pyroxenite xenoliths, on the other hand, show geochemical features indicating metasomatic enrichment, along with a large range of the Re–Os isotopic model ages from Proterozoic to Phanerozoic. These features indicate that lithospheric transformation or refertilization through melt-peridotite interaction could be the primary mechanism for compositional changes during the Phanerozoic, rather than delamination or thermal-mechanical erosion, despite the potential of these latter processes to play an important role for the loss of garnet-facies mantle. A fresh garnet lherzolite xenolith from the Yangtze Block has a Re depletion age of ∼1.04 Ga, much younger than overlying Archean crustal rocks but the same Re depletion ages as spinel lherzolite xenoliths from adjacent Mesozoic basalts, indicating Neoproterozoic resetting of the Re–Os system in the South China Craton.

中国Hannoubaカンラン岩ゼノリスのRe-Os鉱物アイソクロン年代：大陸下リソスフェアマントルの進化

中国Hannoubaカンラン岩ゼノリスのRe-Os鉱物アイソクロン年代：大陸下リソスフェアマントルの進化

U–Th–Pb and Lu–Hf isotopic constraints on the evolution of sub-continental lithospheric mantle, French Massif Central

We have carried out a Pb double-spike and Lu–Hf isotope study of clinopyroxenes from spinel-facies mantle xenoliths entrained in Cenozoic intraplate continental volcanism of the French Massif Central (FMC). U–Th–Pb and Lu–Hf isotope systematics verify the existence of different lithospheric domains beneath the northern and southern FMC. Northern FMC clinopyroxenes have extreme Lu/Hf ratios and ultra-radiogenic Hf ( ε Hf = +39.6 to +2586) that reflect ∼15–25% partial melting in Variscan times (depleted mantle model ages ∼360 Ma). Zr, Hf and Th abundances in these clinopyroxenes are low and unaffected by hydrous/carbonatitic metasomatism that overprinted LILE and light REE abundances and caused decoupling of Lu/Hf–Sm/Nd ratios and Nd–Hf isotopes ( ε Nd = +2.1 to +91.2). Pb isotopes of northern FMC clinopyroxenes are radiogenic ( 206Pb/ 204Pb > 19), and typically more so than the host intraplate volcanic rocks. 238U/ 204Pb ratios range from 17 to 68, and most samples have distinctively low 232Th/ 238U (<1) and 232Th/ 204Pb (3–22). Clinopyroxenes from southern FMC lherzolites are generally marked by overall incompatible trace element enrichment including Zr, Hf and Th abundances, and have Pb isotopes that are similar to or less radiogenic than the host volcanic rocks. Hf isotope ratios are less radiogenic ( ε Hf = +5.4 to +41.5) than northern FMC mantle and have been overprinted by silicate-melt-dominated metasomatism that affected this part of FMC mantle. Major element and Lu concentrations of clinopyroxenes from southern FMC harzburgites are broadly similar to northern FMC clinopyroxenes and suggest they experienced similar degrees of melt extraction as northern FMC mantle. 238U/ 204Pb (53–111) and 232Th/ 204Pb ratios (157–355) of enriched clinopyroxenes from the southern FMC are extreme and significantly higher than the intraplate volcanic rocks. In summary, mantle peridotites from different parts of the FMC record depletion at ∼360 Ma during Variscan subduction, followed by differing styles of enrichment. Northern FMC mantle was overprinted by a fluid/carbonatitic metasomatic agent that carried elements like U, Pb, Sr and light REE. In contrast, much of the southern FMC mantle was metasomatised by a small-degree partial silicate melt resulting in enrichment of all incompatible trace elements. The extreme mantle 238U/ 204Pb (northern and southern FMC), 232Th/ 238U (northern FMC) and 232Th/ 204Pb ratios (southern FMC), coupled with unremarkable present-day Pb isotope ratios, constrain the timing of enrichment. Mantle metasomatism is a young feature related to melting of the upwelling mantle responsible for Cenozoic FMC volcanism, rather than subduction-related metasomatism intimately associated with mantle depletion during the Variscan orogeny. The varying metasomatic styles relate to pre-existing variations in the thickness of the continental lithospheric lid, which controlled the extent to which upwelling mantle could ascend and melt. In the northern FMC, a thicker and more refractory lithospheric lid (⩾80 km) only allowed incipient degrees of melting resulting in fluid/carbonatitic metasomatism of the overlying sub-continental lithospheric mantle. The thinner lithospheric lid of the southern FMC (⩽70 km) allowed larger degrees of melting and resulted in silicate-melt-dominated metasomatism, and also focused the location of the volcanic fields of the FMC above this region.

Nature and evolution of Mesozoic–Cenozoic lithospheric mantle beneath the Cathaysia block, SE China

Mantle-derived garnet and spinel peridotite xenoliths and xenocrysts from the Daoxian basalts (151–131 Ma) and the Anyuan lamprophyres (∼44 Ma) provide insights into the nature and evolution of subcontinental lithospheric mantle beneath the Cathaysia block, SE China. The Daoxian area lies astride the translithospheric Ningyuan–Jianghua fault zone in western Cathaysia, whereas the Anyuan area lies east of the fault zone. The peridotite xenoliths from both localities have experienced melt extraction (generally 3–10% fractional or batch melting) and subsequent silicate melt metasomatism. Depleted coarse-textured spinel peridotites from Anyuan and localities in East Cathaysia have relatively magnesian olivine (Mg #≥91) and may be relics of the Proterozoic lithospheric upper mantle, preserved locally at shallow levels away from the translithospheric fault. At Daoxian coarse-textured xenoliths are absent, and some xenoliths have sheared microstructures. The minerals of the Daoxian xenoliths have lower Cr # and Mg # than those from Auyuan. The Daoxian xenoliths also have higher bulk CaO+Al 2O 3 contents and FeO/MgO, suggesting more pronounced metasomatism. The differences between the Daoxian and Anyuan xenolith suites reflect their spatial relationship to the translithospheric Ningyuan–Jianghua fault zone, which played an important role in the Mesozoic replacement of Proterozoic lithospheric mantle. The lithospheric mantle information from these localities is combined with published data from other localities to provide the first comprehensive survey of the evolution of the lithospheric mantle beneath the Cathaysia block. The xenolith suites of West and East Cathaysia are interpreted as sampling mixtures of older and newly accreted lithospheric mantle that replaced the Proterozoic lithosphere through extension, thermal erosion and melt metasomatism.

Isotope and trace elemente geochemistry of mantle xenolith from Eastern Yangtze Craton: Implications for persistence and multistage evolution of subcontinental lithospheric mantle

Isotope and trace elemente geochemistry of mantle xenolith from Eastern Yangtze Craton: Implications for persistence and multistage evolution of subcontinental lithospheric mantle