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The formation of most jadeitites and other jadeite‐rich rocks (jadeitoids) during subduction is thought to occur by precipitation (P‐type) or metasomatism (R‐type) by infiltration of Na‐Al‐Si‐rich aqueous fluids because of the compositional similarity of the rocks to inferred subduction fluids. Whether these rocks can form by isochemical metamorphism (I‐type) during subduction is still hotly debated. A characteristic of I‐type jadeitoid is that it exhibits a similar prograde metamorphic record as associated eclogite, in contrast to P‐ and R‐type jadeitite and jadeitoids that are typically enclosed in serpentinite derived from the mantle wedge and either lack a prograde metamorphic history (R‐type and P‐type) or probably experience a prograde history (R‐type) that is difficult to discern owing to the high variance of the jadeite‐dominated assemblages and alteration by subduction fluids. The recently discovered Baqing (eastern‐central Tibet) jadeitoid is enclosed by quartzo‐feldspathic schist and has a peak metamorphic assemblage of almandine + jadeite/omphacite + phengite/paragonite + rutile + quartz, similar to eclogite. Abundant mineral inclusions in almandine, especially rutile inclusions with increasing Zr contents from the core to rim of almandine, provide an opportunity to further decode the jadeitoid‐forming processes. In this study, pseudosections and Zr‐in‐rutile thermometry, together with conventional geothermobarometers, were employed to decipher the metamorphic history of Baqing jadeitoids. Two analysed Baqing jadeitoids exhibit a similar clockwise P–T path, starting from early metamorphic conditions of 5–7 kbar, 350–440°C, to different peak conditions (27–29 kbar, 730–760°C, or 20–23 kbar, 670–710°C), followed by relatively consistent retrograde metamorphic conditions of 6–7 kbar, 530–600°C. This result indicates a similar subduction history to the Baqing eclogite. In addition, the Baqing jadeitoids show similar geochemical characteristics to some Na‐rich, K‐depleted and Ca‐depleted sedimentary rocks or plagiogranite. Therefore, we propose an isochemical genesis for the Baqing jadeitoid, rather than a metasomatic origin. [ABSTRACT FROM AUTHOR]

This study illustrates the field relationships of jadeitite-bearing block-in-matrix sequences on Syros and Tinos, Cycladic Blueschist Unit, and adds additional U–Pb zircon ages for jadeitites to the geochronological database. The results confirm the importance of Cretaceous (c. 80 Ma) and Eocene (c. 50 Ma) processes in their geological evolution. Interpretations suggesting that the jadeitites were formed by complete metasomatic replacement of a pre-existing rock are not fully supported by field observations. In at least some cases, the formation of jadeitite is likely due to precipitation from Na-Al-Si-rich aqueous fluids, which also caused variable metasomatic alteration of the host rock. Unambiguous age constraints for formation of the Syros and Tinos jadeitites are not available. A relationship to Eocene blueschist facies metamorphism recorded in the associated metamafic rocks seems plausible. However, since high-pressure overprinting of pre-Eocene jadeitite is also conceivable, there is a much larger time window for jadeitite formation, framed by Cretaceous (c. 80–76 Ma) protolith ages of various mélange blocks and the waning stages of blueschist facies metamorphism (c. 40 Ma). Field observations are consistent with the interpretation that the mélange-like occurrences on Syros and Tinos record, to varying extent, multi-stage processes that include detachment of mafic rocks from the subducting plate, local infiltration of Na-Al-Si-rich aqueous fluids, exhumation via a serpentinitic matrix in a subduction channel and reworking of the primary block-in-matrix fabric by sedimentary or tectonic processes during accretionary wedge formation. [ABSTRACT FROM AUTHOR]

Unique finer-grained interstitial textures, occurring as small blocks or irregular shapes of 0.15–10 mm, were found merging in the coarse-grained textures of Kazakhstan jadeitite. According to the mineral content, the interstitial texture could be classified into two types: Type I, consisting of almost all jadeite crystals, minor omphacite, and little analcime, and Type II, comprising mainly omphacite and analcime, with minor jadeite crystals. They both showed no obvious preferred orientation and have distinct boundaries with the coarse-grained textures but appear more transparent, with finer grain sizes and higher degrees of idiomorphism. The coarse-grained textures include granitoid textures and radial clusters. The granitoid textures formed by euhedral to subhedral prismatic grains usually show rhythmic zoning patterns and parallel intergrowths. Furthermore, fluid inclusions contain H2O and CH4, and it was supposed that the coarse-grained textures were formed by the precipitation of jadeitic fluids. However, perhaps due to the insufficient supply of the fluids or sufficient space, some interspaces were left among the coarser-grained jadeitite. Afterward, these interspaces were filled with precipitation of the successor H2O-richer fluids under a different P–T condition from that of the former coarser-grained jadeitite, and consequently, two kinds of interstitial textures formed. Such interstitial textures seem to appear only in Kazakhstan and therefore could serve as a typical visual identification feature of Kazakhstan jadeitite. [ABSTRACT FROM AUTHOR]

We document the formation of omphacitites in the Monviso Lago Superiore Unit (W. Alps) where eclogite-facies, serpentinite-bearing shear zones host ample evidence for intense intra-slab fluid flow. In the first locality studied, a serpentinite-hosted jadeitite block is rimmed by strained omphacitite (with lawsonite pseudomorphs and minor phengite). U-Th-Pb zircon dating yields a protolith age of c.150 Ma, thus pointing to a burial-related replacement of a former Tethyan seafloor material, and revealed a lack of alpine rims. Multi-mineral Rb-Sr dating of the minerals forming this omphacitite rind yields an isochron age of 41.6 ± 0.7 Ma, corresponding to the early exhumation path still within the eclogite-facies. In this case, omphacitization led to the nearly complete replacement of the former prograde jadeitite through solution-precipitation and was followed by crystal-plastic deformation processes. In various Monviso localities, Fe-Ti metagabbro blocks (commonly exhibiting brecciated garnetite fragments) display evidence for intense fluid-rock interactions leading to the formation of decimeter-thick, weakly strained omphacite-dominated rinds (with minor amounts of lawsonite, clinochlore and talc) around the blocks at the contact with the surrounding serpentinite. Partly dissolved zircon crystals separated from omphacitite rimming an eclogitic Fe-Ti metagabbro block only yielded middle-Jurassic protolith ages. This indicates that omphacitite rinds did not overgrow the eclogite blocks but rather replaced metasomatically the garnet-rich eclogitic assemblage. The omphacitization overprint occurred independently of the nature of the protolith (namely, forming after a jadeitite or after an Fe-Ti eclogite) as a consequence of infiltration of externally-derived fluids and subsequent element sequestration from the incoming fluid phase. These observations highlight the extraordinary ability of eclogite-facies metasomatic fluids to nearly totally overprint rocks as resistant and impermeable as Monviso eclogite breccias or jadeitites. [Display omitted] • Omphacitite forms around eclogite and jadeitite blocks in a subducted meta-ophiolite. • Evidence for metasomatic replacement through dissolution-precipitation processes. • Mutually overprinting fluid-rock interaction events obliterate the previous eclogite / jadeitite matrix. • New insights into fluid percolation processes in serpentinite shear zones and mélanges. [ABSTRACT FROM AUTHOR]

Unique finer-grained interstitial textures, occurring as small blocks or irregular shapes of 0.15–10 mm, were found merging in the coarse-grained textures of Kazakhstan jadeitite. According to the mineral content, the interstitial texture could be classified into two types: Type I, consisting of almost all jadeite crystals, minor omphacite, and little analcime, and Type II, comprising mainly omphacite and analcime, with minor jadeite crystals. They both showed no obvious preferred orientation and have distinct boundaries with the coarse-grained textures but appear more transparent, with finer grain sizes and higher degrees of idiomorphism. The coarse-grained textures include granitoid textures and radial clusters. The granitoid textures formed by euhedral to subhedral prismatic grains usually show rhythmic zoning patterns and parallel intergrowths. Furthermore, fluid inclusions contain H2O and CH4, and it was supposed that the coarse-grained textures were formed by the precipitation of jadeitic fluids. However, perhaps due to the insufficient supply of the fluids or sufficient space, some interspaces were left among the coarser-grained jadeitite. Afterward, these interspaces were filled with precipitation of the successor H2O-richer fluids under a different P–T condition from that of the former coarser-grained jadeitite, and consequently, two kinds of interstitial textures formed. Such interstitial textures seem to appear only in Kazakhstan and therefore could serve as a typical visual identification feature of Kazakhstan jadeitite.

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 (Si3.68), 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 (Si3.55), 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. [ABSTRACT FROM AUTHOR]

Abstract The Hukawng Basin is bounded on its east by splays of the still-active Sagaing Fault. Palinspastically restoring Myanmar's blocks to their positions before the widely-accepted c.400 km dextral strike-slip fault displacement, places the Hukawng Block alongside the Tengchong Block, suggesting they were formerly connected. Additionally the Cretaceous–Paleogene Medial-Myanmar Shear Zone then aligns with the NW-SE Jade Mines Belt. Jadeitite formed there under H P /L T conditions in a Mesozoic subduction zone. It was exhumed at the intersection of the dextral Medial-Myanmar Shear Zone with the subduction-zone at the continental margin of Sundaland. The later Sagaing Fault played no part in that exhumation. [ABSTRACT FROM AUTHOR]

Melt extraction and subduction zone fluid infiltration can produce light Fe isotope compositions of arc lavas relative to the MORBs. However, the Fe isotope signature of subduction zone fluid is poorly constrained, which has hampered our understanding of Fe cycling in the subduction zone. Jadeitite veins in forearc serpentinite provide a unique record for the characteristics of subduction zone fluids. Here we report Fe isotope data for Myanmar jadeitites and associated rocks to constrain the Fe isotope signature of subduction zone fluids. Two types of jadeitites from Myanmar display distinct δ56Fe much lower than typical igneous rocks. White jadeitites, directly precipitated from fluids, have variable δ56Fe from −0.60‰ to −0.04‰, while green jadeitites, formed by fluid-chromite interaction, have δ56Fe (−0.44‰ to −0.19‰) similar to the associated amphibole-rich blackwalls (−0.47‰ to −0.23‰). The light Fe isotope signature of the jadeitites is not induced by weathering, kinetic fractionation, dissolution of Fe-rich carbonate, or mineral dissolution-reprecipitation process. Instead, it most likely reflects the Fe isotope variation of serpentinite-derived fluids. Correlations of δ56Fe with REEs, Sb, and U in white jadeitites suggest that the jadeitite-forming fluid is a mixture of serpentinite-derived and sediment-derived fluids. In contrast, correlations of δ56Fe with Si, Al, and Cr in green jadeitites record the interaction of low-δ56Fe fluids with chromite. Considering the abundance of the serpentinite-derived fluid, it can effectively influence the Fe isotope compositions of the ambient mantle and arc lavas. • Myanmar jadeitites record signature of subduction zone fluids. • Both white and green jadeitites have variably low-δ56Fe. • Low δ56Fe of jadeitites reflect serpentinite-derived fluid signature. • Subduction zone fluid can influence the δ56Fe of ambient mantle and arc lavas. [ABSTRACT FROM AUTHOR]

The key parameter to determine whether jadeitite can be named gem grade jadeitite 'jadeite jade' or not is the content (the mass fraction) of jadeite in jadeitite. So far, most methods to determine the mass fraction of mineral in rock are destructive, which is not suitable in gem detection. Based on the changes of mineral composition and mass fraction of mineral in jadeitite, a non-destructive method by measuring the relative density of jadeitite was established in order to get the mass fraction of jadeite. By Static Water Density Method, 186 pieces of jadeitite samples with relative densities of 3.30-3.24 were divided into groups according to different densities. The main mineral composition and mass fraction of minerals in jadeitite were analyzed by X-ray Powder Diffraction, Manual Heavy-sand Analysis, Electron Probe Microanalysis, Infrared Spectrometry and Raman Spectrometry. The linear relationship between the mass fraction of jadeite and the relative density of jadeitite was statisticstically analyzed. Results show that the main minerals in jadeitite are jadeite, albite, and analcite. As the mass fraction (wA) of jadeite decreases, those of albite and analcime increase, and the measured specific gravities (SG) of jadeitite change accordingly. The relationship between them is wA=1.3454 SG-3.4531 (r=0.9814), showing a good linear dependence relation. Because the measured specific gravity of jadeitite is approximately equal to the theoretical one, mass fraction of jadeite is obtained by measuring the specific gravity of jadeitite. This non-destructive method applies to jadeitite with a specific gravity of 3.3-3.0, jadeite content of 95%-60%, and sum mass fractions of jadeite and albite of 90%-97%.

Abstract Lithium behavior in slab-derived fluids has been constrained using isotope geochemistry of subduction-related metamorphic and volcanic rocks. We investigated a veined jadeitite from the New Idria serpentinite diapir, California, which is regarded as direct precipitates from slab-derived fluids and therefore records slab-derived fluid signatures. We applied an in-situ measurement of Li concentration and δ7Li composition using an ablation volume correction (AVC) LA-MC-ICPMS. This method enabled determinations of millimeter- to submillimeter-scale isotopic variations in the jadeitite veins and host rocks (jadeite matrix), allowing immediate observations on fluid–rock interactions. Multiple-stage jadeite veins and their host rocks showed a wide range of Li concentrations from 4 to 68 μg/g and δ7Li compositions from −11.7 to +6.7‰, with a curvilinear correlation between them. Individual veins formed in different generations also showed wide isotopic variations as large as ~14‰. Those isotopic and compositional variations within/among veins can be readily explained by variable mixing between the matrix and infiltrated fluids. The initial infiltrated fluid compositions were estimated to be between +6.7 and +12.3‰, based on the δ7Li values of jadeites in the veins that were supposed to be unmodified by interactions with their matrices. The estimated fluid composition is mostly consistent with those inferred for slab-derived fluids proposed by previous studies. The New Idria jadeitite provides a line of evidence for the presence of high δ7Li fluids in the mantle wedge at the forearc depth. Our study also demonstrates that the high δ7Li composition of slab-derived fluids can be easily modified by interactions with surrounding rocks along their pathways. Highlights • We applied an in-situ Li isotope study on a veined jadeitite from the New Idria serpentinite body, which is precipitate from slab-derived fluids. • Variations (Li =4-68 μg/g, δ7Li=–11.7 to +6.7‰) within the sample are due to variable mixing between the matrix and infiltrating fluids. • The New Idria jadeitite provides evidence for the presence of high δ7Li fluids in the mantle wedge at sub-forearc depth. [ABSTRACT FROM AUTHOR]

Subduction zone fluids are critical for transporting materials from subducted slabs to the mantle wedge. Jadeitites from Myanmar record fluid compositions and reactions in the forearc subduction channel. Here we present high‐precision Mg isotope data of the Myanmar jadeitites and associated rocks to understand the Mg isotope composition of subduction zone fluids at forearc depths. Two types of jadeitites (white and green) exhibit distinct Mg isotope compositions. The white jadeitites precipitated from Na‐Al‐Si‐rich fluids and have low δ26Mg values, varying from −1.55‰ to −0.92‰, whereas the green jadeitites have higher δ26Mg values (−0.91‰ to −0.74‰) due to metasomatic reactions between fluids and Cr spinel. The amphibole‐rich blackwall in the contact boundaries between jadeitites and serpentinites also exhibits low δ26Mg values (−1.17‰ to −0.72‰). Therefore, the jadeite‐forming fluids have not only high concentrations of Na‐Al‐Si but also low δ26Mg values. The low δ26Mg signature of the fluids is explained by the dissolution of Ca‐rich carbonate in subducted sediments or altered oceanic crust, which is supported by the negative correlation of δ26Mg with CaO/TiO2, CaO/Al2O3, and Sr in the white jadeitites. Given the common occurrence of Ca‐rich carbonates in the subduction channel, the Mg isotope composition of low‐Mg aqueous fluids would be significantly modified by dissolved carbonates. Metasomatism by such fluids along conduits has the potential to generate centimeter‐scale Mg isotope heterogeneity in the forearc mantle wedge. Therefore, Mg isotopes could be a powerful tracer for recycled carbonates not only in the deep mantle but also in the shallow regions of subduction zones. Key Points: The Myanmar jadeitites have δ26Mg values lower than normal mantleJadeite‐forming fluids have high contents of Na‐Al‐Si and low Mg contents and δ26Mg valuesSubduction zone fluids at forearc depths may have low δ26Mg values due to carbonate dissolution [ABSTRACT FROM AUTHOR]

Freezing-point depression was measured in aqueous fluid inclusions to determine salinities in six samples of jadeitite and jadeite-rich rock from the Jagua Clara serpentinite mélange of the Rio San Juan Complex, Dominican Republic. The mélange represents a fossil subduction-zone channel from a cold, mature subduction zone with a geothermal gradient of ~6 °C/km. One hundred and twenty-five determinations of salinity in primary inclusions hosted in jadeite, quartz, apatite and lawsonite range between extremes of 1.2 and 8.7, but yield a well-defined mean of 4.5 ± 1.1 wt% (±1 s.d.) NaCl equiv, slightly higher than mean seawater (3.5 wt%). In one sample, eight additional fluid inclusions in quartz aligned along grain boundaries yield slightly lower values of 2.7 ± 1.3 wt% NaCl equiv. Homogenization temperatures were also measured for 47 fluid inclusions in two samples, but primary entrapment densities are not preserved. It is significant that the suite includes two types of samples: those precipitated directly from an aqueous fluid as well as examples of metasomatic replacement of a pre-existing magmatic rock. Nevertheless, the results indicate identical salinity for both types and suggest a much stronger genetic link between the two types of jadeitite and jadeite-rich rock than has previously been assumed. Based on the results of conductivity measurements in modern subduction zones, we envision a pervasive fluid in the subduction channel that evolved from salinity levels lower than those in sea-water up to the measured values due to on-going but largely completed serpentinization in the subduction channel. The present data represent a reference marker for the subduction channel of the Rio San Juan intra-oceanic subduction zone at 30–50 km depth and after 50–60 Myr of operation. [ABSTRACT FROM AUTHOR]

In the Hellenides Orogen, minerals of various gem quality occur in various rock types from mainly four tectono-metamorphic units, the Rhodope, Pelagonian, and the Attico-Cycladic massifs, and the Phyllites-Quartzites unit of Crete Island. In crystalline rocks, gemstones are related to both regional metamorphic-metasomatic processes (e.g., gem corundums, Mn-andalusite, thulite/clinothulite, spessartine, titanite, jadeite), and to the formation of late alpine-type fissures, such as, for example, quartz, albite, adularia and titanite. The Tertiary (and Mesozoic) magmatic-hydrothermal environments provide gem-quality sapphire, beryl, garnet, vesuvianite, epidote, fluorite, and SiO2 varieties. The supergene oxidation zone of the Lavrion deposit hosts gem-quality smithsonite and azurite. Coloration in the studied material is either due to various chromophore trace elements present in the crystal structure, or due to inclusions of other mineral phases. Future modern exploration methods combined with gemological investigations (such as treatment and faceting of selected stones), are necessary in order to obtain a better knowledge of the gemstone potential of Greece for its possible exploitation.

Jadeitites in serpentinite mélanges are the product of crystallization from and/or metasomatism by aqueous fluids that transfer components from and within a subduction channel—the slab–mantle interaction volume—into discrete rock units, most commonly found within the serpentinized or serpentinizing portion of the channel or the overlying mantle rocks at high pressure (1 to > 2 GPa). Two serpentinite mélanges on either side of the Motagua fault system (MFS) of the Guatemala Suture Zone contain evidence of this process. Whole rock compositional analyses are reported here from 86 samples including jadeitites and the related rocks: omphacitites, albitites and mica rocks. The predominance of a single phase in most of these rocks is reflected in the major element compositions and aspects of the trace elements, such as REE abundances tracking Ca in clinopyroxene. Relative to N-MORB all samples show relative enrichments in the high field strength elements (HFSE) Hf, Zr, U, Th, and the LILE Ba and Cs, contrasted by depletions in K and in some cases Pb or Sr. Most jadeitites are also depleted in the highly compatible elements Cr, Sc and Ni despite their occurrence in serpentinite mélange; however, some omphacitite samples show the opposite. Trace elements in these jadeitite samples show a strong similarity with GLOSS (globally subducted oceanic sediment) and other terrigenous sediments in terms of their trace-element patterns, but are offset to lower abundances. Jadeitites thus incorporate a strong trace-element signature derived from sediments mixed with that from fluid derived from altered oceanic crust. Enrichment in the HFSE argues for mobility of these elements in aqueous fluids at high P/T conditions in the subduction channel and a remarkable lack of fractionation that might otherwise be expected from dissolution and fluid transport. [ABSTRACT FROM AUTHOR]

This contribution presents a geological mapping of the Quaternary succession of the Bulè and low Alpetto tributary valleys (Po Valley, Piedmont), together with preliminary data on its petrography. The investigated area, covering an altitude range between 3015 and 1485 m a.s.l., is located in the Monviso Massif Ophiolite Complex, at the contact with marble and calcschist of the Dora-Maira Massif cover. The Quaternary sequence mainly consists of glacial, outwash, debris and landslide deposits, with local torrential/avalanche and colluvial bodies. The investigation on the petrographic composition of these sediments has allowed to recognize the occasional occurrence of jadeitite boulders, likely exploited during the Neolithic period for axe head production. Four possible jadeitite blocks have been found; one of them is described here for the first time, sizing up to 1 m. In detail, one of the finds is a Neolithic site of jade polishing in the high Bulè Valley that was referred to the middle of V millennium BC (Allisio, La Preistoria e l'alta Valle Po, Lar Editore, Perosa Argentina, ). The jadeitite blocks have been found in the debris (site A), landslide (site B), glacial (site C) and outwash (site d) sediments. The petrographic characterization of the new jadeitite samples might potentially shed light on the still controversial genesis of these peculiar rocks. [ABSTRACT FROM AUTHOR]

• Meta-plagiogranites of the Sistan mélange document Cretaceous igneous activity. • This adakitic magmatism is synchronous to or slightly earlier than the HP/LT event. • Felsic rocks and eclogites shared the same P–T evolution after tectonic mixing. • Melt formation can be reconciled with the subduction of a spreading ridge. • The youngest zircon age of a gabbro from the Birjand ophiolite is 104.2 ± 0.5 Ma. The Sistan suture zone, eastern Iran, exposes a well-preserved accretionary complex that formed by the closure of a Neotethyan ocean basin between the Central Iranian Lut block and the Afghan microcontinent. Mélange sequences include tectonic slices of adakitic plagiogranitic rocks and rare jadeitite. Adakitic whole rock characteristics, compositional zoning of phengites, and matching U–Pb zircon and Rb–Sr isochron ages (c. 87–85 Ma) suggest that the plagiogranites formed before or during the high-pressure/low-temperature (HP/LT) metamorphism that affected other parts of the subduction zone complex. Meta-plagiogranites, eclogites, and blueschists only shared the same P–T evolution after blocks of the felsic intrusions had been tectonically incorporated into the mélange. The suture zone has also been intruded by felsic melts that have largely escaped metamorphic overprinting. The weighted mean U–Pb zircon age of 81.0 ± 1.2 Ma for a newly dated sample of this group is consistent with the 86–71 Ma range previously reported for such rocks. Melt formation is not limited to the forearc region and can be reconciled with a model suggesting subduction of a spreading ridge. A newly dated gabbro yielded a weighted mean U–Pb zircon age of 104.2 ± 0.5 Ma, which is interpreted to represent magmatic crystallization and the youngest protolith age reported so far for the Birjand ophiolite. The geological relevance of an even younger intercept age (91.0 ± 2.7 Ma) of a small zircon subset remains elusive. [ABSTRACT FROM AUTHOR]

In Guatemala, jadeitite occurs as blocks in serpentinite mélange in distinct settings on opposite sides of the Motagua fault. Jadeitites north of the Motagua fault are associated with eclogites, blueschists, and garnet amphibolites and distributed over a 200km E-W area. Omphacitite, omphacite - taramite metabasite, albitite, and phengite rock are found with jadeitite. The assemblages indicate formation at 6-12kbar and 300-400°C, however jadeite - omphacite pairs yield T from ~200 to gt;500ºC for jadeite crystallization. Jadeitites south of the Motagua fault are sourced from three separate fault slices of serpentinite in Jalapa and Zacapa departments and are distinctive: 1) Jadeitite near Carrizal Grande is found in serpentinite with lawsonite eclogites, variably altered to blueschist, and rarely in schists. A large jadeite – omphacite gap and lawsonite suggests T=300-400°C, but at high P as indicated by the presence of quartz: Pgt;12-20kbar. Lawsonite eclogites (P=20-25kbar, T=350-450°C) occur with these jadeitites. 2) At La Ceiba, jadeitites coexist with omphacite blueschists and contain late-stage veins of quartz, diopside, cymrite, actinolite, titanite and vesuvianite. A large jadeite – omphacite gap suggests 300-400°C, but at lower P as indicated by quartz + albite: P=10-14kbar. 3) At La Ensenada jade i tites occur with lawsonite-glaucophane blueschists and chloritite. It is a fine-grained jadeite-pumpellyite rock, intensely deformed and veined with grossular, omphacite, albite and titanite, but no quartz. A large jadeite–omphacite gap and pumpellyite suggest ~200-~300°C at lower P consistent with primary albite: P=6-9kbar. The silicates contain little iron

A detailed electron microscopy analysis of jadeitite celts from the Early Ceramic Age Golden Rock settlement on the small volcanic island of St Eustatius, Lesser Antilles, is presented in an effort to identify the source region(s) of these jadeitite axes and evaluate the extent of trade networks in the Caribbean during pre-Columbian times through which those tools (or source rocks) circulated. Habitation at the site occurred between ca. AD 230–890, and the jadeitite tools most likely date between cal. AD 600 and 825/890. We argue that in provenancing jadeitite emphasis should be placed on the identification of the entire mineral assemblage (including the accessory minerals) and textures, given the complex geological histories and processes that form this quasi-monomineralic rock. Indeed, the mineral assemblages and the characteristics of the individual minerals within the studied jadeitite samples are far from homogenous, suggesting either the source has a high degree of internal variation or there are multiple sources. We have identified three jadeitite groups among the analyzed samples on the basis of mineralogical assemblages: Group 1 consists of samples bearing phlogopite (plus phengite and epidote but without lawsonite or quartz); Group 2 contains lawsonite (plus phengite and quartz but without phlogopite and epidote); and Group 3 is defined by containing hematite. Importantly, we have not identified glaucophane in the analyzed materials. The comparison of these artifact data with those of jadeitites from the four potential known source regions of Caribbean jade, i.e., Guatemala (North and South Motagua Fault mélanges), Cuba (Sierra del Convento mélange) and Dominican Republic (Río San Juan complex) allows us to conclude that both the North and South Motagua Valley mélanges are the most likely sources for artifact groups 2 and 3, and perhaps also for group 1. This identification supports earlier hypotheses on the existence of pan-regional exchange networks, tying the northern Antilles with the Isthmo-Colombian region (Colombia, Panama and Costa Rica) during the Ceramic Age of the Caribbean. [ABSTRACT FROM AUTHOR]

Abstract: The jadeitite that occurs in Myanmar is one of the largest and most important jadeite deposits in the world. However, the formation age of the Myanmar jadeitite remains poorly constrained. Here, we conduct an integrated study using petrology and 40Ar/39Ar geochronology to analyze the Myanmar jadeitite. Petrological observations show that the studied jadeitite consists mainly of jadeite minor sodic–calcic amphibole and analcime and that the jadeitite was cut by late amphibole rock consisting of sodic amphibole and minor chlorite. 40Ar/39Ar laser stepwise heating dating of jadeite from the jadeitite yielded a plateau age of 123.9±3.4Ma, the sodic–calcic amphibole associated with jadeite yielded a plateau age of 134.8±1.4Ma, and the sodic amphibole of late amphibole rock yielded a plateau age of 92.7±1.2Ma. These results indicate that the studied jadeitite was formed during the early Cretaceous from (135Ma) high-pressure (HP) metasomatism and then experienced a late Cretaceous (93Ma) HP metasomatism. Combining our results with previous studies using petrography and geochronology, we suggest that the formation process of Myanmar jadeitite involved multistages of metasomatism. [Copyright &y& Elsevier]

Abstract: High-pressure, low-temperature metamorphic rocks record subduction of oceanic crust and sediments into the mantle, but the timing of subduction initiation is commonly difficult to determine. However, the appearance of fluid activity in the mantle wedge above a subduction zone can be correlated with incipient subduction. Here we describe jadeitite veins up to 5m wide, which are hosted in serpentinites of the Syum-Keu ultramafic complex, Polar Urals, Russia. The jadeitites consist of both jadeite (86–88mol% jd) and omphacite (54–75mol% jd). Multi-stage growth of the jadeite is indicated by variations in color and structure, such as growth zoning and the distribution of fluid inclusions. We consider that the jadeitite veins formed from Na–Al–Si-rich fluids under HP/LT conditions during active subduction, and that the source material was subducted ocean crust. SHRIMP U–Pb dating of zircons from the jadeitite yielded a concordant weighted mean 206Pb/238U age of 404±7Ma, which we interpret as the age of peridotite serpentinization and jadeitite formation in the suprasubduction zone mantle. This age indicates that subduction was initiated about 40Ma earlier than peak metamorphism (360–355Ma) of eclogite in the Polar Urals. [Copyright &y& Elsevier]

Jadeitite is a rare constituent of serpentinite-matrix melange bodies from certain subduction complexes. Most jadeitite crystallizes from Na-, Al-, and Si-bearing fluids that are apparently derived from multiple subduction-zone sources. Even though jadeitite is near-end-member NaAlSi2O6 in major element composition and is volumetrically minor in subduction complexes, its trace elements and stable isotopes appear to record fluid compositions not directly seen in other subduction zone metasomatic systems. Prior to our work, how jadeitite-forming fluids interact with serpentinite host rocks and serpentinizing fluids were largely unknown, because serpentinite-to-jadeitite contacts are generally not exposed. In the Sierra de las Minas, Guatemala, we have studied a 3 m-wide pit transecting the contact between a mined-out jadeitite body and its host serpentinite. An apparent transition zone between the former jadeitite and nearby serpentinite exposed in the mine pit contains four texturally distinct rock types of differing outcrop colours, composed of albitites and meta-ultramafic rocks. (The jadeitite body is now represented only by a large spoil pile.) Seven samples from the contact zone, jadeitite from the spoil pile, a serpentinite outcrop approximately 1 m outside the pit, and a jadeitite nodule within the contact zone albitite were analysed for major, minor, and trace elements. Abundances of Al2O3, Na2O, MgO, FeO, Cr, Ni, and Sc track the contact between sheared albitite and foliated meta-ultramafic rocks. These elements change from values typical of Guatemalan jadeitites in the jadeitite block and albitites in the contact zone to values for Guatemalan meta-ultramafic rocks and serpentinites across the contact zone. In addition, the abundances of SiO2, CaO, Fe2O3, K2O, Rb, Cs, and Y show important features. Of greatest interest, perhaps, approximately 15 cm from the contact with meta-ultramafic rock, Zr, U, Hf, Pb, Ba, Sr, Y, and Cs in albitite are greatly enriched compared to elsewhere in the contact zone. Element enrichments spatially coincide with the appearance, increase in modal abundance, and/or increase in grain sizes of zircon, rare earth element (REE) rich epidote, titantite, and celsian within albitite. All of these 'trace-element-rich' accessory minerals show poikiloblastic inclusions of albite, which suggests that they grew concomitantly in the metasomatic zone. Graphical and computational methods of evaluating mass changes of metasomatites relative to likely protoliths show that, near the contact, fewer minor and trace elements in albitite show 1:1 coordination with presumed protoliths. Most metasomatitites are enriched in large-ion lithophile elements (LILE) and heat-producing elements (HPE) relative to likely protoliths. Albitite near the contact with meta-ultramafic rocks also shows ultramafic components. Except for a Ca-rich actinolite schist zone, the meta-ultramafic rocks are depleted in LILE and HPE relative to serpentinite; host serpentinite is itself under-abundant in these elements relative to average upper mantle or chondrite. In summary, the metasomatic zone shows more evidence for the introduction of components to albitite and actinolitic meta-ultramafic rock than it does for exchange of protolith components between jadeitite and serpentinite. The fluid that presumably formed the metasomatites was sufficiently rich in LILE and high-field-strength elements (HFSE) to both saturate and grow minerals in which Zr, Ba, and Ti are essential structural constituents and/or HFSE, LILE, and HPE minor to moderate substituents. These geochemically diverse element groups were fixed in albitite via the crystallization and growth of new accessory minerals within these rocks during albititization. The amount of LILE and HPE-depleted meta-ultramafic rock appears to be too small to call upon a local source for the LILE and HPE-enrichment seen in albitites. [ABSTRACT FROM AUTHOR]

Abstract: Zircons from one jadeitite sample, collected from serpentinite mélange north of the Motagua fault, Guatemala, were separated for SHRIMP-RG U–Pb dating and trace element analyses. The sub- to anhedral crystal form, lack of typical magmatic oscillatory zoning, the presence of fluid and albite/quartz/jadeite inclusions, and the low Th/U ratios (<0.005) indicate that these zircons would have precipitated from an aqueous solution. The U–Pb concordia intercept age of these zircons is 95.1±3.6Ma, much older than the reported 40Ar/39Ar phengite age (i.e., 77–65Ma) of jadeitites and related rocks from the same area. The 95Ma age is interpreted as the time of jadeitite formation, whereas the 77–65Ma age reflects the time of cooling after isotopic resetting due to superimposed metamorphism at ∼70Ma. The superimposed metamorphic temperature would therefore be higher than the phengite 40Ar/39Ar blocking temperature and probably at 400–450°C. It is further concluded that “metasomatic replacement” and “vein precipitation” are two end-member mechanisms for jadeitite genesis. Both the whole-rock jadeitite and its zircons have very low REE contents, ∼1ppm and 0.5–42ppm, respectively. The whole-rock jadeitite shows a flat and slightly concave REE pattern and a positive Eu anomaly (Eu/Eu*=1.24). Zircons are enriched in HREE and their REE patterns can be divided into two groups: one with negative Eu anomaly and one with positive Eu anomaly. The latter tends to have smaller positive Ce anomalies. The fluid from which jadeitite formed probably evolved over time, becoming more reducing and more dominated by plagioclase decomposition reactions. Alternatively, trace element compositions of zircons simply demonstrate complicated variations of fluid chemistry during jadeitite formation. A reducing fluid with high pH values capable of mobilizing Al, Na, Zr and Hf is inferred to be the media during jadeite/zircon formation. If jadeitite formation was related to serpentinization fluid, the ultramafics must contain olivine as the major primary phase subjected to serpentinization, yielding reducing fluids with high pH values. Two additional requirements are (1) the presence of feldspar/mica-bearing protolithic blocks survived from rodingitization in peridotites to provide Al and Na, and (2) the presence of fluid channels as well as pulses of in/out-flux fluid to trigger metasomatic reactions. These preconditions in subduction zones may contribute to the rare occurrences of jadeitite in global high-P metamorphic belts. [Copyright &y& Elsevier]

A new jadeitite jade locality has been discovered in the serpentinite-matrix subduction mélange of the Sierra del Convento (eastern Cuba) in a context associated with tectonic blocks of garnet-epidote amphibolite, tonalitic-trondhjemitic epidote gneiss and blueschist. The jade outcrops occur as blocks surrounded by serpentinite, as late Miocene-early Pliocene detritic sedimentary deposits formed during erosion of the mélange, and as Recent river and beach deposits related to the Macambo and Guardarraya rivers and their mouths. Jade from these outcrops show gem-quality varieties with colours ranging from greenish white to dark green. Potentially, the deposits may be easily exploited. Former exploitation (probably of the beach deposits) by the pre-Columbian Taino inhabitants of Cuba is documented by a large number of jade artifacts (mostly, petaloid axes) found in eastern Cuba. [ABSTRACT FROM AUTHOR]

Abstract: This study systematically investigated the Lu–Hf isotope signatures of zircons in jadeitite from the North Myanmar, which was formed from jadeite-forming hydrothermal fluids and is always sourced in serpentinite as a mark for the subduction zone. Results show that the three group zircons have positive ε Hf(t) values. Group-I zircons (163.2±3.3 Ma) have relatively higher 176Lu/177Hf ratios (>0.0004) and the corresponding ε Hf(t) values range from 15.5 to 20.0 at t =163 Ma. In contrast, Group-II zircons (146.5±3.4 Ma) exhibit highly variable 176Lu/177Hf ratios from 0.000027 to 0.001398, but still have ε Hf(t) values of 15.6 to 18.5 at t =147 Ma, which resemble to those of the Group-I zircons. The Group-III zircon (122.2±4.8 Ma) has a 176Lu/177Hf ratio of 0.000578 and a ε Hf(t) value of 15.8 at t =122 Ma. Such highly positive ε Hf(t) values for all jadeitite zircons indicate that they were derived from rapid reworking of the very juvenile crust. Therefore, zircon in jadeitite can be used as a valuable mineral to constrain the age of serpentinization/rodingitization, and even the age of formation of ultramafic rock within ophiolites. The results also suggest the presence of the Mesozoic intra-oceanic subduction within the Indo-Burman Range, and further suggest that the hydrothermal fluids were derived from dehydration of seawater-altered oceanic juvenile crust that had been hydrated during and/or after the formation of the oceanic crust, and additionally from serpentine minerals at greater depth. Consequently, the fluids carry the Hf isotope signature of the depleted mantle that can be later imparted to the jadeitite zircons. [Copyright &y& Elsevier]

Trace-element compositions of jadeite (±omphacite) in jadeitites from the Itoigawa-Ohmi district of Japan, analyzed by a laser-ablation inductively coupled plasma mass spectrometry technique showed chemical zoning within individual grains and variations within each sample and between different samples. Primitive mantle-normalized patterns of jadeite in the samples generally showed high large-ion lithophile element contents, high light rare earth element/heavy rare earth element ratios and positive anomalies of high field strength elements. The studied jadeitites have no signatures of the protolith texture or mineralogy. Shapes and distributions of minerals coupled with chemical zoning within grains suggest that the jadeitites were formed by direct precipitation of minerals from aqueous fluids or complete metasomatic modification of the precursor rocks by fluids. In either case, the geochemical characteristics of jadeite are highly affected by fluids enriched in both large-ion lithophile elements and high field strength elements. The specific fluids responsible for the formation of jadeitites are related to serpentinization by slab-derived fluids in subduction zones. This process is followed by dissolving high field strength elements in the subducting crust as the fluids continue to circulate into the subducting crusts and serpentinized peridotites. The fluids have variations in chemical compositions corresponding to various degrees of water–rock interactions. [ABSTRACT FROM AUTHOR]

The Cycladic blueschist belt in the central Aegean Sea has experienced high-pressure (HP) metamorphism during collisional processes between the Apulian microplate and Eurasia. The general geological and tectonometamorphic framework is well documented, but one aspect which is yet not sufficiently explored is the importance of HP mélanges which occur within volcano-sedimentary successions. Unresolved issues concern the range in magmatic and metamorphic ages recorded by mélange blocks and the significance of eventual pre-Eocene HP metamorphism. These aspects are here addressed in a U-Pb zircon study focusing on the block–matrix association exposed on the island of Syros. Two gneisses from a tectonic slab of this mélange, consisting of an interlayered felsic gneiss-glaucophanite sequence, yielded zircon 206Pb/238U ages of 240.1 ± 4.1 and 245.3 ± 4.9 Ma, respectively, similar to Triassic ages determined on zircon in meta-volcanic rocks from structurally coherent sequences elsewhere in the Cyclades. This strongly suggests that parts of these successions have been incorporated in the mélanges and provides the first geochronological evidence that the provenance of mélange blocks/slabs is neither restricted to a single source nor confined to fragments of oceanic lithosphere. Zircon from a jadeitite and associated alteration zones (omphacitite, glaucophanite and chlorite-actinolite rock) all yielded identical 206Pb/238U ages of c. 80 Ma. Similar Cretaceous U-Pb zircon ages previously reported for mélange blocks have been interpreted by different authors to reflect magmatic or metamorphic ages. The present study adds a further argument in favour of the view that zircon formed newly in some rock types at c. 80 Ma, due to hydrothermal or metasomatic processes in a subduction zone environment, and supports the interpretation that the Cycladic blueschist belt records both Cretaceous and Eocene HP episodes and not only a single Tertiary HP event. [ABSTRACT FROM AUTHOR]

Two groups of quarries (Mont Viso and Mont Beigua, Italy) were the source of the Alpine axeheads that circulated throughout western Europe during the Neolithic. The quarries on Mont Viso (Oncino: Porco, Bulè and Milanese), discovered in 2003, have been radiocarbon-dated, and this has revealed that the exploitation of jadeites, omphacitites and eclogites at high altitude (2000–2400 m above sea level) seems to have reached its apogee in the centuries around 5000 BC. The products, in the form of small axe- and adze-heads, were distributed beyond the Alps from the beginning of the fifth millennium, a few being found as far away as the Paris Basin, 550 km from their source as the crow flies. However, it was not until the mid-fifth millennium BC that long axeheads from Mont Viso appeared in the hoards and monumental tombs of the Morbihan, 800 km from the quarries. Production continued until the beginning of the third millennium BC, but at this time the distribution of the products was less extensive, and the process of distribution operated in a different way: tools made from jadeite and eclogite are still found in the French Jura, but the extraction sites at the south-east foot of Mont Viso no longer seem to have been used. The variability in the geographical extent of the distribution at different times seems to be related to the social context of exploitation of the high-altitude quarries, which were only ever accessible for a few months each year. [ABSTRACT FROM AUTHOR]

An increasing number of seismological studies report transient seismicity clusters in the mantle wedge several kilometers above the subduction interface. Their physical significance with respect to subduction zone seismo-tectonics remains poorly understood. Jadeitites are known to form and/or be associated with mantle wedge serpentinites in the c. 30–70 km depth range, and thus may yield information on deformation mechanisms in this region of deep subduction environments. We herein document and compare brittle-viscous features recorded in jadeitites from Polar Urals (Russia), Kashin state (Myanmar) and Motagua fault region (Guatemala) – some of the most important jadeitite occurrences worldwide. In the Polar Urals we identified ultramafic-hosted pristine jadeitite-bearing veins c. 1 km above a Devonian paleo-subduction interface, interpreted as metasomatized former felsic dyke networks crosscutting the mantle wedge peridotites. Here, both jadeitites and associated amphibole-rich dark granofels display widespread brittle-ductile deformation fabrics such as shear bands, foliated cataclasites and breccias, cemented through dissolution-precipitation processes by omphacite and sodic amphiboles, a mineral assemblage typical of high-pressure–low-temperature subduction zone conditions. Electron probe and laser ablation ICP-MS mapping indicate that these brittle-viscous networks display a substantial metasomatic imprint highlighted in the dark granofels by variations in major and trace elements. Switches between viscous and brittle deformation patterns are attested by crystallographic-preferred orientations of jadeite in some of the shear zones that crosscut the host jadeitites. Strikingly similar mineral assemblages and deformation patterns were observed in the Kashin and Motagua samples. Observed deformation features in these localities can be classified into three categories (tectonic breccias, foliated cataclasites and hydraulic breccias), which may occasionally form in sequence and exhibit mutually overprinting textures. Some of the foliated cataclasites contain fine-grained and foliated "shard-like" features forming a radial omphacite-jadeite spherulitic texture, interpreted as former pseudotachylyte that evokes a paleo-seismic origin. We interpret these healed fault networks as recording external fluid influx within fracture zones that repeatedly ruptured along former "dyke" networks. These high permeability drains likely (i) contribute to the transfer of highly pressurized plate-interface metamorphic fluids into the mantle wedge; and (ii) trigger seismic instabilities recorded in the basal part of active mantle wedge sections. These findings provide new insights into the current understanding of the rheology (e.g., serpentinization ratio) and stress state in the mantle wedge, with implications for subduction interface seismogenesis. [Display omitted] • Common evidence for brittle features in exhumed jadeitites • Breccias and foliated cataclasites formed at high pressure in the mantle wedge • Evidence for tightly coupled brittle events and multiple fluid infiltration events • Brittle features in jadeitites form in a serpentinite-poor environment. • They are interpreted as markers of paleo-seismicity along mantle wedge base. [ABSTRACT FROM AUTHOR]

In the Hellenides Orogen, minerals of various gem quality occur in various rock types from mainly four tectono-metamorphic units, the Rhodope, Pelagonian, and the Attico-Cycladic massifs, and the Phyllites-Quartzites unit of Crete Island. In crystalline rocks, gemstones are related to both regional metamorphic-metasomatic processes (e.g., gem corundums, Mn-andalusite, thulite/clinothulite, spessartine, titanite, jadeite), and to the formation of late alpine-type fissures, such as, for example, quartz, albite, adularia and titanite. The Tertiary (and Mesozoic) magmatic-hydrothermal environments provide gem-quality sapphire, beryl, garnet, vesuvianite, epidote, fluorite, and SiO2 varieties. The supergene oxidation zone of the Lavrion deposit hosts gem-quality smithsonite and azurite. Coloration in the studied material is either due to various chromophore trace elements present in the crystal structure, or due to inclusions of other mineral phases. Future modern exploration methods combined with gemological investigations (such as treatment and faceting of selected stones), are necessary in order to obtain a better knowledge of the gemstone potential of Greece for its possible exploitation. [ABSTRACT FROM AUTHOR]