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Lithos
Elsevier Science B.V.
Lithos

Elsevier Science B.V.

0024-4937

Lithos/Journal LithosSCIISTP
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    Dynamics of Early Neoproterozoic accretion, west-central India: I. Geochronology and Geochemistry

    Anwesa BanerjeeNathan CogneNicole Sequeira
    25页
    查看更多>>摘要：The Godhra-Chhota Udepur (GC) sector (west-central India) is the zone of convergence between two crustal-scale accretion zones, i.e. the N/NNE-striking Aravalli Delhi Fold Belt (ADFB) against the E-striking Central Indian Tectonic Zone (CITZ). In this study, we demonstrate the two orogens welded during the Early Neoproterozoic. In the GC sector, recumbently folded basement gneisses, shallow-dipping granitoid mylonites and a suite of allochthonous supracrustal rocks experienced top-to-the south thrusting and nappe formation (D2 deformation). The shallow-dipping crustal domain was modified by the superposition of a network of WNW/W-striking transpressional shear zones and related folds (D3 deformation). The D2-D3 deformations occurred due to oblique crustal convergence marked by the emplacement of pre-D2, post-D2 and syn-D3 granitoids. The post-D2, syn-D3 granite-granodiorites are weakly peraluminous, calc-alkalic, having ferroan to magnesian affinity, and characterised by LREE-enriched moderately fractionated REE patterns with variable negative Eu anomalies. Trace element geochemistry and whole rock Sr-Nd systematics suggest the granitoids were derived from dominantly meta-greywacke precursors. In South-GC, U-Pb zircons in the basement gneisses yield upper intercept/Concordia dates at 1.65-1.60 Ga for high-grade metamorphism. The lower intercept/Concordia dates in the gneisses coincide with the 0.95-0.93 Ga emplacement age of post-D2/syn-D3 granitoids throughout GC. However, the pre-D2 granitoids in South-GC are older, —1.03 Ga. By contrast, pre-D2 granitoids in North-GC yield Late Neoarchean (2.5 Ga) Concordia/upper intercept emplacement ages, identical to the emplacement age of the Archean granites in the ADFB; the lower intercept/Concordia age is 0.95-0.93 Ga. The 2.5 Ga granites did not experience the 1.65-1.60 Ga high-grade metamorphism, but both the lidiodemic units shared the 0.95-0.93 Ga D2-D3 deformation-metamorphism and the emplacement of post-D2 and syn-D3 0.95-0.93 Ga granitoids. The juxtaposition of the —2.5 Ga granitoids and the 1.65-1.60 Ga gneisses is attributed to the 1.03-0.93 Ga ADFB-CITZ oblique accretion that involved contemporaneous emplacement of syn-collisional S-type granitoids..
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    The role of symmetry-breaking strains on quartz inclusions in anisotropic hosts: Implications for Raman elastic geobarometry

    M. MurriJ.P. GonzalezM.L. Mazzucchelli
    10页
    查看更多>>摘要：Raman elastic geobarometry for mineral host-inclusion systems is used to determine the strains acting on an inclusion still entrapped in its host by measuring its Raman wavenumber shifts which are interpreted through the phonon-mode Griineisen tensors of the inclusion phase. The calculated inclusion strains can then be used in an elastic model to calculate the pressure and temperature conditions of entrapment. This method is applied frequently to host inclusion systems where the host is almost elastically isotropic (e.g. garnet) and the inclusion is elastically anisotropic (e.g. quartz and zircon). In this case, when the entrapment occurs under hydrostatic conditions the host will impose isotropic strains on the inclusion which in turn will develop non-hydrostatic stress. In this scenario the symmetry of the inclusion mineral is preserved and the strains in the inclusion can be measured via Raman spectroscopy using the phonon-mode Griineisen tensor approach. However, a more complex situation arises when the host-inclusion system is fully anisotropic, such as when a quartz inclusion is entrapped within a zircon host, because the symmetry of the inclusion can be broken due to the external anisotropic strain field imposed on the inclusion by the host, which in turn will modify the phonon modes. We therefore calculated the strain states of quartz inclusions entrapped in zircon hosts in multiple orientations and at various geologically relevant pressure and temperature conditions. We then performed ab initio Hartree-Fock/Density Functional Theory (HF/DFT) simulations on a-quartz in these strain states. These HF/DFT simulations show that the changes in the positions of the Raman modes produced by strains that are expected for symmetry broken quartz inclusions in zircon are generally similar to those that would be seen if the quartz inclusions remained truly trigonal in symmetry. Therefore, the use of the trigonal phonon-mode Griineisen tensor to determine the inclusion strains does not lead to geologically significant errors in calculated quartz inclusion entrapment pressures in zircon.
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    Evolution of the Paleo-Tethys Ocean in Eastern Kunlun, North Tibetan Plateau: From continental rift-drift to final closure

    Peng WangGuochun ZhaoQian Liu
    15页
    查看更多>>摘要：The dynamic evolution of the Paleo-Tethys Ocean from continental rift-drift and seafloor spreading to initial subduction and final closure has been hotly debated. This paper tries to bring new constraints to this longstanding debate based on the compiled the latest data and investigations into Carboniferous-Triassic magmatism in the westernmost segment of the Eastern Kunlun orogenic belt, North Tibetan Plateau. New results indicate that the ca. 335 Ma appinite stocks were derived from the asthenosphere mantle wedge slightly modified by slab-derived materials. The ca. 244 Ma dioritic appinite stocks were sourced from the partial melting of hydrother-mally altered upper oceanic crust following the closure of the Paleo-Tethys Ocean. The ca. 231 Ma adakitic granite stock originated from the partial melting of the thickened eclogitic lower crust in the syn-collisional setting, and the ca. 219-215 Ma granite batholith had a mafic source in the post-collisional setting. By integrating records available, new scenarios of the evolution of the Paleo-Tethys Ocean in Eastern Kunlun were established. The ca. 390-380 Ma continental rifting leading to the opening of the Paleo-Tethys Ocean is attributed to the post-collisional gravitational instability subsequent to the closure of the Proto-Tethys Ocean and the far-field extensional stress induced by the retreating subduction of the Paleo-Asian Oceanic lithosphere along the northern margin of Tarim-Qaidam. The Paleo-Tethys Oceanic lithosphere initially northward subducted at ca. 366-335 Ma. The closure of the Paleo-Tethys Ocean leading to the "soft" collision between the Eastern Kunlun and Bayanhar terranes occurred at ca. 235-225 Ma followed by the ca. 225-200 Ma post-collisional extension.
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    Origin of gem-quality megacrysts in the Cenozoic alkali basalts from the Muling area, northeastern China

    Linlin HuShaokui PanRen Lu
    12页
    查看更多>>摘要：Megacrysts hosted by mantle-derived volcanic rocks provide valuable information on the chemical evolution and ascending history of the parental magmatic systems. However, the origin of the megacrysts has still been far from consensus. Here, we present systematic major-and trace-element data of a variety of gem-quality megacrysts in the Cenozoic basalts from Muling area, northeastern China, with the aim of investigating the origin and for-mational conditions of these megacrysts. The studied megacrysts are composed of clinopyroxene, garnet and orthopyroxene. All megacrysts are optically and compositionally homogeneous. Clinopyroxene megacrysts, with Mg# of 85.3-87.5, contain Al2O3 of 6.64-8.07 wt%, thus can be ascribed as Al-augites. Garnet megacrysts are rich in pyrope component with Mg# of 74.0-76.0 and contain low Cr2O3 less than 0.05 wt%. All orthopyroxene megacrysts are enstatite in composition. According to the color, they can be further divided into two groups (Group 1: greenish brown; Group 2: dark brown) which are apparently different in chemical composition. Group 2 orthopyroxenes have lower Mg# (85.1-86.3) and Cr2O3 (0.09-0.18 wt%) and higher Al2O3 (6.78-7.71 wt%) and TiO2 (0.20-0.24 wt%), while Group 1 orthopyroxenes are characterized by higher Mg# (89.2-89.8) and Cr2O3 (0.55-0.66 wt%) and lower Al2O3 (5.13-5.93 wt%) and TiO2 (0.11-0.15 wt%). Clinopyroxene, garnet and Group 2 orthopyroxene megacrysts can be easily distinguished with equivalent phases in accompanied peridotite xenoliths or peridotite xenoliths in other locations through eastern China by their major-element compositions. They show good correlations between Mg# and major-oxide contents (such as Al2O3 and TiO2), indicating their derivation from melts which had undergone variable extent of fractional crystallization. Mg# and trace-element compositions of their equilibrium melts are incomparable with those of host basalts. We infer clinopyroxene, garnet and Group 2 orthopyroxene megacrysts from Muling are most likely produced by fractional crystallization of basaltic melts that formed earlier than host basalts. Pressure estimations suggest clinopyroxene and garnet megacrysts from Muling were formed at 2.0-2.5 GPa, corresponding to a depth of 66-80 km, near the boundary between lithosphere and asthenosphere based on local lithosphere thickness. Compared with orthopyroxenes in accompanied peridotites, Group 1 orthopyroxene megacrysts have slightly lower Mg# and higher CaO and Al2O3, similar with those produced by basaltic melts-peridotite interaction experiments in which orthopyroxene precipitated with the expense of olivine and clinopyroxene. A revised model (modified from Liu and Ying (2019): Liu, Y.D., Ying, J.F., 2019. Origin of clinopyroxene megacrysts in volcanic rocks from the North China Craton: a comparison study with megacrysts worldwide. International Geology Review 62,1845-1861.) has been proposed to decipher the formation of variable megacrysts from Muling.
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    Temporal variations in the geochemistry of Mesozoic mafic-intermediate volcanic rocks in the northern Great Xing'an Range, Northeast China, and implications for deep lithospheric mantle processes

    Jie TangWenliang XuFeng Wang
    13页
    查看更多>>摘要：Identifying the composition of the recycled materials in the lithospheric mantle is crucial for establishing links between mantle geochemical 'reservoirs' and deep mantle geodynamic processes. However, studies that focus on deep mantle processes under multiple subduction tectonic regimes have been absent. In this paper, we present 40Ar/39Ar age, whole-rock geochemical, and Sr-Nd-Pb-Hf isotope, zircon Hf-O isotope, and in situ plagioclase Pb isotope data for Mesozoic mafic-intermediate volcanic rocks in the northern Great Xing'an Range, northeast China. These and published data are used to constrain the deep processes that occurred in the lithospheric mantle during the Mesozoic, in the context of the evolution of the Mongol-Okhotsk Ocean and whether subduction of the Paleo-Pacific Plate affected the formation of volcanic rocks in the western part of northeast China. The Mesozoic mafic-intermediate volcanic rocks in the northern Great Xing'an Range can be divided into three stages: Early Jurassic (—180 Ma), Late Jurassic (—155 Ma), and late Early Cretaceous (—120 Ma). These rocks are mainly basalt, basaltic andesite, andesite, and trachyandesite. The Mesozoic mafic-intermediate volcanic rocks have SiO2 = 47.34-60.00 wt%, TFe2O3 = 4.73-11.63 wt%, and Mg# = 26-66, belong to the medium-to high-K calc-alkaline series, exhibit enrichment in light rare earth elements and large-ion lithophile elements, exhibit depletions in heavy rare earth elements and high-field-strength elements (e.g., Nb and Ta), and have no obvious Eu anomalies. These geochemical features are similar to those of arc igneous rocks. Relative to mid-ocean ridge basalts, these mafic-intermediate volcanic rocks exhibit more radiogenic Sr-Pb and less radiogenic Nd-Hf isotopic compositions. The Th/Yb (1.47-3.43) and (Hf/Sm)PM (0.80-1.15) ratios of the Early Jurassic mafic-intermediate volcanic rocks are much lower than those of the Late Jurassic mafic-intermediate volcanic rocks (Th/Yb = 4.31-5.25; (Hf/Sm)PM = 1.49-2.60), whereas the late Early Cretaceous igneous rocks exhibit large variations in these ratios (Th/Yb = 0.37-14.8; (Hf/Sm)PM = 0.59-2.14). The above features show that: (1) the primary magmas of the mafic-intermediate volcanic rocks were mainly derived by partial melting of depleted lithospheric mantle; (2) the lithospheric mantle was mainly metasomatized by sediment-derived fluids related to subduction of the Mongol-Okhotsk oceanic plate during the Early Jurassic, whereas the mantle source was mainly modified by sediment-derived melts triggered by the collapse of thickened lithosphere after closure of the Mongol-Okhotsk Ocean in the Late Jurassic; and (3) sediment-derived fluids associated with subduction of the Paleo-Pacific Plate caused further enrichment of the lithospheric mantle in the western part of northeast China during the late Early Cretaceous.
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    Role of fractional crystallization, fluid-melt separation, and alteration on the Li and B isotopic composition of a highly evolved composite granite pluton: The case of the Eibenstock granite, Erzgebirge, Germany

    Rolf L. RomerHans-Jiirgen ForsterJohannes Glodny
    16页
    查看更多>>摘要：We present a comprehensive Li and B isotope study of granites, aplites, and igneous enclaves from the multiphase Eibenstock granite in the Western Erzgebirge-Vogtland metallogenic province of Germany. The studied samples cover the entire compositional range of the granites from moderately to highly evolved and include variably altered types as obtained by magmatic fractionation, post-magmatic high-to medium-temperature and near-surface low-temperature alteration. Fractionation and alteration processes are unequivocally documented by the chemical variability of the rocks. Despite the marked imprint of these processes on bulk-rock compositions, our granite samples show only little variation in 87Li (-0.52 to 0.75%o) and 8nB (-17.46 to-14.78%o), with surface samples defining the lower end of the 87Li range. The narrow range in 87Li suggests that magmatic fractionation and high-temperature overprint have a very minor effect on 87Li. The B budget of the samples is dominated by tourmaline, which makes δ~(11)B values insensitive for later high-to medium-temperature overprint or surficial low-temperature alteration. Depending on whether tourmaline crystallized before or after exsolution and loss of magmatic fluids, whole-rock samples have higher or lower δ~(11)B values. Granite enclaves have δ~7Li and δ~(11)B values ranging from-1.51 to-0.81%o and-14.55 to-13.89%o, respectively. Some samples have chemical and mineralogical evidence for wall-rock interaction during emplacement or later overprint by external fluids. These samples show broader ranges in δ~7Li (-2.61 to 2.21%o) and δ~(11)B (-21.58 to-9.85%o). These values show that wall-rock interaction via assimilation and external fluids may affect δ~7Li and δ~(11)B to a larger extent than intra-magmatic processes, such as fractional crystallization, fluid-mediated autometasomatic overprinting, or exsolution of fluids from the melt. The offset of δ~7Li and δ~(11)B values towards the compositions of the wall rocks reflects the contrasting composition of granite and country rock and the addition of country-rock material to the granite. The magnitude of the offset reflects both the relative contribution of wall-rock derived Li and B to the granite and the magnitude of the difference in the Li and B isotopic compositions between them.
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    Petrogenesis of mafic rocks from the Xigaze ophiolite, Southern Tibet: Insights into forearc extension induced by Neotethyan rollback

    Shengbiao YangJingsui YangJian Zhang
    20页
    查看更多>>摘要：The Xigaze ophiolite in the central Yarlung Zangbo suture zone (southern Tibet) provides evidence of the tectonic processes that formed the Neotethyan Ocean between the Indian and Eurasian plates. In this study, we present zircon U—Pb geochronological, mineralogical, and geochemical data for mafic rocks from the Xigaze ophiolite to determine their petrogenesis and tectonic environment. The crustal section of the Xigaze ophiolite includes mainly gabbro lenses, amphibolite dikes, dolerite sills or dikes, and basaltic lavas. The absence of a well-developed gabbroic crust and sheeted dike complexes in the ophiolite indicates slow to ultraslow-spreading conditions and a heterogeneous structure of the oceanic lithosphere, which is not atypical for layered ophio-lites. Zircons from the amphibolite and dolerite dike reveal crystallization ages of 125.0 ± 1.8 Ma to 123.8 ± 1.3 Ma, respectively. Geochemically, all mafic rocks have mid-ocean ridge basalt (MORB)-like affinities with enrichment in large ion lithophile elements (LILEs, U) relative to high field strength elements (HFSEs, Nb, Ta and Ti) and light rare earth elements (LREEs). They also exhibit high eNd(t) values ranging from +8.4 to +8.8 at 206Pb/204Pb = 16.75-17.64. Moreover, chromite and clinopyroxene grains from the mafic rocks have a wide compositional spectrum and are mainly plotted in the supra-subduction zone (SSZ) fields. These features indicate that MORB-like magmatism was triggered by decompression melting of the upwelling asthenospheric mantle with minor mass transfer from the subducting slab. The Xigaze ophiolite lacks boninite, high-magnesium an-desites, island arc tholeiites, and calc-alkaline lavas, which indicates that it is incompatible with the complete Izu-Bonin-Mariana forearc sequence. Combined with previous studies, we speculate that the Xigaze ophiolite represents an ancient SSZ-type oceanic lithosphere formed in the Gangdese forearc during the Early Cretaceous, and the upper plate extension is linked to the southward retreat and rollback of the Neotethyan slab. Thus, the Xigaze and other Neotethyan SSZ ophiolites with no systematic change in composition with stratigraphic age provide new insights into the diversity of melt evolution in the forearc crust.
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    Stagnated eclogitic slab-related shoshonitic series volcanic rocks in West Tianshan, Xinjiang, China: Insights from Li-B-Sr-Nd-Hf-Pb isotope and trace element compositions

    Zhen-Hua ZhaoQiang WangXiao-Lin Xiong
    15页
    查看更多>>摘要：This study presents major, trace element and Li-B-Sr-Nd-Pb-Hf isotope compositions of post-collisional (Permian) shoshonitic volcanic rocks (SVRs) from West Tianshan, NW China. Zircon U—Pb dating indicates that the West Tianshan SVRs were mainly formed in the late Early Permian (272-279 Ma). They include absarokites, shoshonites and banakites, which have variable SiO2 (46-63 wt%) and K2O (2.12-8.12 wt%) contents. They display enrichment in light rare earth elements (LREE) and depletion in heavy rare earth elements. They are enriched in large ion lithophile elements (e.g., La, Rb and Ba) and depleted in high field strength elements (e.g., Nb, Ta and Ti) with slightly negative to negligible Eu anomalies, pronounced positive Pb anomalies and low Nb/U (9.32 ± 6.54), Ce/Pb (0.14-10.0, average 5.03 ± 3.02), relatively high Nb/Ta (16.74 ± 2.72) and Zr/Hf (39.56 ± 6.06) ratios. They have relatively high Li contents (26.0-93.0 ppm) and B contents (6.19-84.7 ppm), and low but variable δ~7Li (-4.0%o to +2.4%o). They are characterized by low (~(87)Sr/~(86)Sr); (0.7045-0.7068), positive eNd(t) values (+0.31-+5.53), relatively low ~(206)Pb/~(204)Pb (18.16-18.65), ~(207)Pb/~(204)Pb (15.51-15.63) and ~(208)Pb/~(204)Pb (37.97-39.22) and positive eHf(t) (+5.4-+12.5). These features consistently suggest a met-asomatized enriched mantle source having affinities with an EM Mike reservoir for the SVRs. Source enrichment was generated dominantly by subducted slab related aqueous fluid and altered oceanic crust (AOC) melts. Dehydration modeling of Li and B isotopes and Li, Y, B, Nb trace element fractionation collectively show that the flat, deeply subducted and stagnated, eclogitic slab suffered progressive dehydration(~5-12%)and was distinctly ~7Li-depleted. Based on these compositional features and model calculations, we suggest that West Tianshan SVRs had an enriched mantle source metasomatised by aqueous fluid and hydrous slab melt, and their parental magmas were derived from variable mixing of spinel and garnet peridotite (60Gt:40Sp-80Gt:20Sp). Taking into account petrogenetic and regional tectonic data, we suggest that the West Tianshan SVRs developed in an intraplate setting during the late Early Permian. It is most probable that the Early Permian Tarim mande plume, located in the south side of the study area, promoted Early Permian asthenospheric upwelling that resulted in melting of a fossil subduction-enriched source to produce shoshonitic volcanic rocks in the West Tianshan.
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    The A B C's of metasomatism in the North Atlantic Craton during Pangea breakup; characterized by fluid inclusions in Chidliak diamonds

    Oded ElazarHerman S. GriitterYaakov Weiss
    19页
    查看更多>>摘要：Here we report the nitrogen characteristics and composition of high-density fluid (HDF) trapped in micro-inclusions in a suite of fibrous diamonds from the —142 Ma Chidliak CH-7 kimberlite pipe, the Hall Peninsula, southern Baffin Island, Nunavut. Within these diamonds, we observe three populations based on the chemistry of the encapsulated HDFs, the diamond's nitrogen aggregation states, and the diamond color. 'Chidliak C diamonds contain highly silicic HDFs, have nitrogen in A-and C-centers (with 5-20% in C-centers), and a characteristic intense yellow color. 'Chidliak A' diamonds contain silicic to low-Mg carbonatitic HDFs, carry nitrogen solely in A-centers, and are mostly colorless. A third population, 'Chidliak B', has grey color and distinctive low-K20 silicic to low-Mg carbonatitic HDF compositions and overall smoother and less fractionated trace element pattern relative to 'Chidliak C and 'Chidliak A' diamonds; they carry nitrogen in A-and B-centers (with —15% in B-centers) and are characterized by a grey hue. An eclogitic paragenesis of all diamonds is evident by the HDF compositional variation as well as the presence of omphacitic clinopyroxene inclusions. The appearance of a diamond with A-and B-centers in its octahedral core and A-and C-centers in its coat suggests formation at two distinct events at a similar depth. Combined with pressure and mantle residence estimates based on nitrogen aggregation considerations, we argue that the three diamond populations formed at the relatively shallow region of the lithosphere (likely <180 km) during distinct metasomatic events in the North Atlantic Craton (NAC) since the Proterozoic. The youngest event by silicic HDFs took place close in time to kimberlite activity at 142-157 Ma, as evident by the preservation of nitrogen C-centers in 'Chidliak C diamonds. A link between this event and the mid-lithosphere discontinuity (MLD) in eclogitic portions of the cratonic lithosphere in Chidliak is plausible. The timing of 'Chidliak A' diamonds formation by more carbonatitic HDFs is less well constrained, but can be related to Ca-rich metasomatism observed in local peridotite xenoliths and/or alkaline magmatism between 610 and 550 Ma. A possible link between the formation of 'Chidliak B' diamonds and the timing of Mesoproterozoic olivine lamproite magmatism ca. 1400 Ma is suggested based on the HDF trace element composition and the aggregated nature of nitrogen in these diamonds. The nitrogen systematics and eclogitic source of the fibrous diamonds are comparable with those observed for previously studied gem-quality diamonds from Chidliak. We suggest that these similarities show a temporal connection and mutual crystallization of the two diamond types. This strengthens the involvement of HDFs in the formation of gem-quality diamonds.
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    Diversity of origin and geodynamic evolution of the mantle beneath the Variscan Orogen indicating rapid exhumation within subduction-related melange (Moldanubian Zone, Bohemian Massif)

    Martin KubesJaromir LeichmannJana Kotkova
    22页
    查看更多>>摘要：A variable assemblage of ultrabasic rocks along with minor eclogites investigated on a small area of a few km2 (Gfohl unit, Moldanubian Zone of the Bohemian Massif) reflects incorporation of contrasting mantle domains within a subduction-related tectonic melange during the Variscan orogeny. Based on mineral composition, whole-rock chemistry, isotopic signatures, and pressure-temperature (P-T) estimates, four principal lithological types have been distinguished (1) spinel harzburgite (2) garnet lherzolite (3) spinel websterite and (4) eclogite. Spinel harzburgite, exclusively associated with HT migmatized gneisses, corresponds to the refractory oceanic lithosphere, as demonstrated by whole-rock composition (low AI2O3, CaO), chemistry of spinel (Cr# <0.4) and Al-rich pyroxene (AI2O3 up to 9 wt%). By contrast, garnet lherzolite, predominantly enclosed in HP felsic granulite, represents a fragment of the subcontinental mantle wedge, considering the strong fertile character (high Al2O3, TiO2, Yb) and spinel chemistry (Cr# >0.5). Websterites likely represent products of decompression partial melting of the asthenospheric mantle with a variable input of crustal component, whereas eclogites correspond to HP crystal cumulates from partial melts migrating through the Variscan mantle wedge. Both peridotite protoliths experienced various degrees of secondary refertilization, recorded as a cryptic metasomatic overprint, due to interaction with subduction-related silicate melts, from which numerous websterite and rare eclogite layers crystallized. The secondary mantle refertilization via melt-peridotite reaction is well-documented by decreasing bulk Mg# along with MgO/SiO2, elevated Al2O3/SiO2, TiO2 and FeO_(tot) contents, and isotopic composition (87Sr/86Sr338 ~ 0.7051). Moreover, the positive correlation between highly fluid-immobile incompatible trace elements (e.g. Ti, Sc, V, Zr, Yb) and distribution of REE and Li is consistent with the melt refertilization trend. During the Variscan subduction, lherzolite experienced UHP conditions (42 kbar, 1100 °C). The presence of Cr-spinel relics preserved in garnet suggests that lherzolite was dragged from the shallow mantle wedge to deeper levels of the subduction zone, probably along with the underlying subducting oceanic plate involving refractory harzburgite. This deep burial during the Variscan subduction was closely followed by rapid exhumation dated by the Lu-Hf age of 338.4 ± 6.3 Ma, corresponding to re-equilibration at lower crustal levels or possibly at greater depths, closer to peak P conditions. Decompression-induced partial melting of upwelling asthenosphere with a contribution of crustal material resulted in derivation of primitive to mildly evolved transient melts (87Sr/86Sr338 ~ 0.7049-0.7062) represented by websterites, percolating through and metasomatizing wall-rock peridotites. The rapid exhumation and following juxtaposition of genetically diverse yet closely associated ultrabasic rocks provide a unique insight into the history of Earth mantle, evolving during the formation of the Variscan orogenic belt in Central Europe within contrasting geological settings, from ocean ridge environment to great depths of subduction zone.
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