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This study presents data of in-situ mineral major and trace element chemistry, whole-rock major and trace element and Sr–Nd isotope geochemistry, as well as zircon U–Pb dating and Lu–Hf isotope studies of andesite dykes from the Sulu orogenic belt of eastern China to evaluate their petrogenesis and thus to provide insights into crust–mantle interactions in a tectonic terrane that underwent continental subduction and was then overprinted by oceanic subduction. The andesites mainly comprise plagioclase, hornblende, clinopyroxene and magnetite as phenocrysts that are embedded in a groundmass of fine-grained quartz and K-feldspar, with minor amounts of biotite, magnetite, titanite, apatite and zircon. They possess intermediate concentrations of SiO2 (54.97–62.24 wt.%), Na2O + K2O (6.35–7.24 wt.%) and MgO (3.37–7.12 wt.%) with high Mg# values [Mg# = 100 × Mg/(Mg + Fe2+) molar] of 54–64, and are characterized by arc-like trace element patterns that are enriched in light rare earth elements (LREE) and large ion lithophile elements (LILE) but depleted in high field strength elements (HFSE). The hornblende and clinopyroxene phenocrysts exhibit enrichment in Th and U but an obvious depletion of HFSE. The andesites have high initial 87Sr/86Sr ratios of 0.7073–0.7086 and negative ɛNd(t) values of −15.7 to −14.4 for whole-rock, and newly crystallized magmatic zircons show negative ɛHf(t) values of −27.0 to −17.6. U–Pb dating on syn-magmatic zircons yields consistent ages of 124 ± 2 to 116 ± 1 Ma, indicating eruption of the andesitic lavas during the Early Cretaceous. Inherited zircons are present and yield Neoproterozoic, Paleoproterozoic and Archean U–Pb ages. Taking into account all these geochemical and geochronological data, and the compositional features of contemporaneously formed mafic–andesitic igneous rocks from the Sulu belt and the adjacent continental crust of the North China Craton, we propose that the andesites crystallized from primary andesitic magmas derived from partial melting of enriched metasomatites in the subcontinental lithospheric mantle. The enriched metasomatites are inferred to be formed by a two-step process: firstly by crust–mantle interactions during the Triassic collisional orogeny and secondly by a subsequent modification by fluids/melts that mainly derive from seafloor sediments during subduction of the paleo-Pacific plate in eastern Asia. Slab rollback of the subducted paleo-Pacific slab and concomitant asthenosphere upwelling are an appropriate geodynamic mechanism for the generation of extensive arc-like magmatism during the Early Cretaceous in the Sulu belt.

In Western Himalayan Syntaxis, the India‐Asia continental collision occurred at ca. 50 Ma, while its uplift history and exhumation mechanism are still in dispute despite decades of studies. A new type of eclogite was found in Naran, located ca. 30 km southwest of the Upper Kaghan Valley. Phase equilibrium calculations and thermobarometer performed on the Naran eclogite documented the peak‐P metamorphic condition of 720–780°C at 2.4–2.8 GPa. Two further exhumation stages were identified with the first one at high‐P granulite‐facies conditions of 750–800°C at 1.6–1.9 GPa, and the second at amphibolite‐facies conditions of 550–630°C at 0.5–0.8 GPa. SIMS U‐Pb dating of metamorphic zircons yielded an age of 46 ± 2 Ma, which is interpreted to constrain the high‐P metamorphism age along the northwestern margin of the Indian plate. SIMS U‐Pb dating of rutile yielded a cooling age of 26 ± 3 Ma, which is interpreted as cooling age in the amphibolite facies. The average speculated exhumation rate of the Naran massif (∼3 mm a−1) was much lower than that recovered from the Upper Kaghan Valley massif (86–143 mm a−1). The tectonic and metamorphic evolution of the whole Western Himalayan Syntaxis shows the difference in temporal and spatial change within the Paleogene era, indicating the inconsistent exhumation histories of the continental slices. Such a multi‐slice exhumation process was probably related to the closure of the Neo‐Tethys ocean and the break‐off of the Indian lithospheric slab. Key Points Naran eclogite underwent peak metamorphism at ca. 46 Ma with PT conditions of 710–770°C, 2.2–2.8 GPa U‐Pb dating of rutile indicated cooling age of ca. 26 Ma with PT conditions of 580–630°C and 0.6–0.8 GPa Naran eclogite represents a new type of HP rock sequence with a much lower exhumation rate (3 mm a−1) than Kaghan eclogite (30–143 mm mm a−1)

The Purang ophiolite, which crops out over an area of about 650 km2 in the western Yarlung–Zangbo suture zone, consists chiefly of mantle peridotite, pyroxenite and gabbro. The mantle peridotite is comprised mainly harzburgite and minor dunite. Locally, the latter contains small pods of chromitite. Pyroxenite and gabbro occur as veins of variable size within the peridotite; most of them strike northwest, parallel to the main structure of the ophiolite. Three types of dunite occur in the Purang ophiolite: dunite that envelopes podiform chromitite (1) and lenses of dunite with either Cr-rich spinel (2) or Cr-poor spinel (3) in a harzburgite host. The constituent minerals of dunite envelopes around podiform chromitite are similar in composition to those of transition-zone dunite (Fo91.01−91.87 in olivine; Cr/(Cr+Al) (Cr#) =41.5–47.0 and Mg/(Mg+Fe2+) (Mg#) =58.9–63.0 in Cr-spinel). Forsterite contents in olivine decrease from type 2 lenses with Cr-rich spinel (91.9–93.0) to type 1 dunite enveloping chromitite (91.7–93.7) to type 3 lenses with Cr-poor spinel (95.3–96.0). Similarly, Cr# in spinel decreases from type 2 (66.9–67.9) to type 1 (41.5–47.0) to type 3 (19.8–20.6). In addition, Al2O3 in clinopyroxene is highest in type 2 (3.48–5.24 wt %) and decreases to type 1 (1.56–3.29 wt %) and type 3 (0.78–0.86 wt %). Olivine in type 1 dunite enveloping podiform chromitite has Li concentrations and δ7Li values of 1.48–1.71 ppm and 6.19 ‰–7.98 ‰, respectively. Type 2 dunite lenses with Cr-rich spinel contain olivine with Li =0.98–1.64 ppm and δ7Li =6.77 ‰–10.99 ‰. The type 3 dunite lenses with Cr-poor spinel show the highest values of Li =0.94–1.40 ppm and δ7Li =10.25 ‰–14.20 ‰. Exsolution lamellae of clinopyroxene and magnetite occur as oriented intergrowths in olivine of type 3 dunite lenses with Cr-poor spinel. We suggest that the Purang ophiolite developed during two main stages of formation. In the first stage, abyssal peridotites formed in a mid-ocean-ridge environment. During the second stage, hydrous high-Mg boninitic melts were produced by high degrees of partial melting in a supra-subduction zone mantle wedge, which reacted with peridotite to form type 2 dunite pods with high-Cr# spinel. At lower degrees of partial melting in the same mantle wedge, Al-rich melts were produced, which reacted with peridotite to form type 3 dunite pods that contain low-Cr# spinel. These Al-rich melts were also relatively rich in Ti4+, Ca2+ and Fe3+, which were incorporated into the olivine structure by appropriate substitutions. During cooling, these elements exsolved as lamellae of magnetite and clinopyroxene.

This paper shows how a faulty approach to the study of mineral inclusions in zircon can lead to misleading interpretations of the geological context. We present and discuss two well-documented examples. Zircon grains separated from HP metamorphic jadeitite of the Rio San Juan Complex, Dominican Republic, and from UHP pyrope quartzite of the Dora Maira Massif, northern Italy, were studied using cathodoluminescence (CL) techniques, in combination with mineral inclusion and age data. In general, zircon from both localities shows inherited magmatic core domains with oscillatory zoning and metamorphic rims. The magmatic cores of zircon from the jadeitite yield ages of 115–117 Ma and host jadeite and omphacite which are of metamorphic origin and formed at about 78 Ma. Zircon from lawsonite blueschist, representing the country rock of the jadeitite, contains domains with oscillatory zoning that are nearly identical in age to the zircon cores from the adjacent jadeitite, and also contains younger metamorphic minerals such as lawsonite, albite, phengite (Si 3.68 ), chlorite, and omphacite. Similar observations were made on the magmatic cores of zircon from the pyrope quartzite. These are about 275 Ma in age and host pyrope, phengite (Si 3.55 ), talc, and kyanite, all of which formed during UHP metamorphism at about 35 Ma. Zircon from the biotite-phengite-gneiss country rock (metagranite) shows oscillatory zoning and yields ages that are identical to those of the magmatic cores of zircon from pyrope quartzite, which thus reflect granitic intrusion ages. The country-rock zircon also encloses metamorphic minerals with ages of about 35 Ma. Such minerals are, for example, garnet and phengite, as well as a polymineralic assemblage of clinopyroxene+garnet+phengite+quartz, that point to formation at UHP metamorphic conditions around 40 kbar/750 °C. Based on these examples we suggest an effective approach centered on key evidence from CL studies to show that magmatic domains of zircon may actually contain pseudo-inclusions which were not entrapped during an early stage of formation, but were instead introduced during later metamorphic or metasomatic events along microcracks representing pathways for fluid influx. Cathodoluminescence microscopy is thus an excellent tool for avoiding such pitfalls by allowing distinction between true inclusions and pseudo-inclusions in zircon.

Four Cenozoic, rhönite-bearing alkali-olivine basalt samples from the Changle area (Shandong Province, China) show an intracontinental character and were generated in an extensional setting. Petrographic studies document different generations of rhönite. In three samples, rhönite occurs either as a reaction product surrounding coarse-grained corundum, spinel and phlogopite or along cleavage planes in phlogopite. In one sample rhönite forms disseminated crystals in a mantle xenolith, possibly formed by a reaction of coarse-grained orthopyroxene or spinel with a melt. Rhönite exhibits a wide range of compositions: 22.9 wt %–33.0 wt % SiO2, 13.3 wt %–19.0 wt % Al2O3, 9.4 wt %–19.9 wt % MgO and 10.210.2 wt %–24.5 wt % FeO. The derived primary substitutions include (1) SiIV + NaVII = (Al, Fe3+)IV + CaVII, (2) MgVI = (Fe2+, Mn2+)VI and (3) TiVI + (Mg + Fe2+ + Mn2+)VI = 2Fe3+VI. Rare-earth-element (REE) patterns of euhedral rhönite crystals from the mantle xenolith (sample SS17) and those surrounding spinel (sample CL04) have a concave-upward shape for the heavy rare-earth elements (HREEs) and are slightly enriched in the light rare-earth elements (LREEs). These patterns resemble those of kaersutitic amphibole and kaersutite reported from basanite, olivine nephelinite, transitional alkali-olivine basalt and hawaiite. In contrast, REE patterns of the other two samples containing fine-grained, anhedral and acicular rhönite crystals (samples CL01 and EGS03) are relatively steep, with lower HREE and higher LREE abundances, similar to those of ocean island basalts (OIBs). All types of Changle rhönite show positive Nb, Ti and V anomalies in spidergrams normalized to primitive mantle. Mineral assemblages of the studied samples indicate that rhönite crystallized at different stages within a temperature range from about 950 to 1180 ∘C and at pressures below 0.5 kbar, with fO2 below the NNO buffer. The chemical composition of Changle rhönite is interpreted to depend on the composition of the initial silicate melt, the redox conditions during crystallization and the composition of the minerals involved in reactions to form rhönite. Similar to metasomatic mantle amphibole, the compositions of Changle rhönites cover the I-Amph (I-amphibole) and S-Amph (S-amphibole) fields, indicating that they may have formed due to an intraplate metasomatic event, overprinting an older metasomatic subduction episode.

Paleoproterozoic banded iron formation (BIF) iron ore of the Zhengjiapo region of the Changyi metallogenic belt, Eastern Block of North China Craton contains abundant coexisting antiperthite and mesoperthite textures. The antiperthite and mesoperthite occur in felsic domains of the Zhengjiapo BIF ore and enable derivation of peak temperature metamorphic conditions. Thermodynamic phase modeling shows that equilibrium conditions of corresponding textures, considering the related mineral assemblage of Pl + Qz + Kfs + Mag + Opx + L, are in the range of 870–940 °C and 5.0–6.8 kbar. Ternary feldspar thermometry using reintegrated compositions of antiperthite and mesoperthite in the felsic domain of the studied BIF iron ore reveals even higher peak metamorphic temperatures of 1045–1080 °C. The ultra-high temperature–low pressure conditions of Precambrian BIF have not yet been reported from the North China Craton. The documented ultra-high temperature metamorphism of the Zhengjiapo BIF iron ore in the Changyi metallogenic belt indicates that the BIF was involved in the collision-related tectonic process during Paleoproterozoic to have occurred in the Jiao-Liao-Ji orogenic belt.

This study utilizes zircon SIMS U–Pb dating, REE and trace-element analysis as well as oxygen isotope ratios of zircon to distinguish jadeite-rich rocks that formed by direct crystallization from a hydrous fluid from those that represent products of a metasomatic replacement process. Zircon was separated from a concordant jadeitite layer and its blueschist host, as well as from loose blocks of albite-jadeite rock and jadeitite that were all collected from the Jagua Clara serpentinite-matrix mélange in the northern Dominican Republic. In the concordant jadeitite layer, three groups of zircon domains were distinguished based on both age as well as geochemical and oxygen isotope values: age groups old (117.1 ± 0.9 Ma), intermediate (three dates: 90.6, 97.3, 106.0 Ma) and young (77.6 ± 1.3 Ma). Zircon populations from the blueschist host as well as the other three jadeite-rich samples generally match zircon domains of the old age group in age as well as geochemistry and oxygen isotope ratios. Moreover, these older zircon populations are indistinguishable from zircon typical of igneous oceanic crust and hence are probably inherited from igneous protoliths of the jadeite-rich rocks. Therefore, the results suggest that all investigated jadeite-rich rocks were formed by a metasomatic replacement process. The younger domains might signal actual ages of jadeitite formation, but there is no unequivocal proof for coeval zircon-jadeite growth.

The Beloretsk Metamorphic Complex in the SW Urals formed at a convergent eastern margin of Baltica during the Neoproterozoic-Early Cambrian Timanide orogeny. It comprises three major units with lenses of facies-critical metabasites within metasedimentary rocks: A lowermost eclogite unit, an intermediate garnet amphibolite unit and an upper amphibolite-greenschist unit. Pressure ( P )-temperature ( T )-paths of four rocks from the two lowermost units were determined mainly by PT pseudosection techniques showing similar clockwise loops at different peak metamorphic, water-saturated conditions: A phengite-bearing eclogite shows peak PT conditions of 16.5–18.5 kbar/525–550 °C (stage I) followed by stage II at 11.5–13.0 kbar/585–615 °C. A garnet amphibolite from the intermediate unit yields lower peak conditions of 11.7–14.5 kbar/480–510 °C (stage I) followed by stage II at 9.5–11.0 kbar/535–560 °C. However, a granite gneiss in the eclogite unit shows similar maximum pressures as the eclogite, but higher temperatures at 15.6–16.2 kbar/660–675 °C, whereas a garnet micaschist contains comparable high pressure relicts, but underwent an advanced midcrustal reequilibration at 7.5–9.0 kbar/555–610 °C. We dated the eclogite by a 7-point Rb/Sr mineral isochron (phengite, omphacite, apatite) at 532.2±9.1 Ma interpreted as age of crystallisation of the eclogitic peak PT assemblage. This age is the youngest compared to the known Timanide metamorphic and magmatic ages.

Whiteschists from the Dora-Maira massif (Western Alps, Italy) are Mg and K-rich metasomatised granites which experienced ultra-high-pressure metamorphism and fluid–rock interaction during Alpine continental subduction. The sources and timing of fluid infiltration are a source of significant debate. In this study, we present boron (B) isotopes and other fluid-mobile trace-element (FME) concentrations in various generations of phengite from whiteschists and their country rock protoliths to investigate the sources and timing of metasomatic fluid influx. Reconstructed bulk rock concentrations based on modal data and mineral compositions indicate that significant amounts B and other FME were added to the rock during prograde metamorphism, but that this fluid influx postdates the main Mg metasomatic event. High B concentrations (150–350  μ g/g) and light δ 11 B values (− 16 to −4 ‰) recorded in phengite point to a B-rich sediment-derived fluid as the main source of B in the whiteschists. Further redistribution of FME during metamorphism was associated with breakdown of hydrous minerals, such as talc, phlogopite, and ellenbergerite. The source of the Mg-rich fluids cannot be constrained based on the B data in phengite, since its signature was overprinted by the later main B metasomatic event. Rare tourmaline-bearing whiteschists record additional information about B processes. Tourmaline δ 11 B values (− 6 to +1 ‰) are in isotopic equilibrium with similar fluids to those recorded in most phengite, but phengites in tourmaline-bearing samples record anomalous B isotope compositions that reflect later redistribution of B. This study demonstrates the utility of in situ analyses in unravelling complex fluid–rock interaction histories, where whole-rock analyses make it difficult to distinguish between different stages of fluid–rock interaction. Polymetasomatism may result in decoupling of different isotopic systems, thus complicating their interpretation. The Dora-Maira whiteschists interacted with multiple generations of fluids during subduction and therefore may represent a long-lived fluid pathway.

Garnet is one of the most significant minerals in metamorphic rocks, that provides key information on prograde, peak-metamorphic and retrograde parts of the pressure-temperature ( PT ) path. Such results require a detailed knowledge of its different growth domains. For iron-poor compositions, the cathodoluminescence (CL) microscopy is an important and often overlooked method and allows to identify the internal structures of all garnet grains in one thin section within only a few seconds. The advantage of the CL-microscope is to deliver low magnification images in true color, not only of garnet but also, for instance, of other rock forming silicates, carbonates, sulfates, etc., of metamorphic, but also of sedimentary and magmatic origin, using polished thin sections. Internal structures of grossular from Mexico and pyrope from the Italian Alps were characterized and visualized by CL-microscopy. The different growth domains were additionally studied using CL-spectra and electron microprobe (EMP) analysis. Grossular shows a patchy zonation in its core while in mantle and rim zones oscillatory zoning is observed. It contains zones of anomalous birefringence, zones of orange and bluish luminescence and zones lacking luminescence. Different but low amounts of the activator elements Mn 2+ and Eu 2+ are responsible for the orange and bluish luminescent domains. Pyrope is also characterized by oscillatory growth zones, shows a dull luminescent core with a change of crystal morphology during growth, and displays an increase of brightness from core towards rim—the outermost rim, however, is lacking luminescence. The different luminescent zones are characterized by different amounts of Dy 3+ , Tb 3+ , Sm 3+ and Sm 2+ as activator elements. Because of slow diffusion rates of activators such as the REEs Sm, Dy and Tb, it can be still possible to visualize possible prograde and/or peak pressure stage growth domains of garnet, even if later high temperature events may have homogenized the major element profiles. Such domains may help to identify respective assemblages of mineral inclusions, and hence these results can represent an integral part of a detailed PT path. Thus the CL-information can be used as an important pathfinder prior to supplementary investigations, as for instance EMP, ion probe, mineral or fluid inclusion studies.