Kelyphite Rims on Garnets of Contrast Parageneses in Mantle Xenoliths from the Udachnaya-East Kimberlite Pipe (Yakutia)

A new classification of kelyphitic rims on garnets from xenoliths of peridotitic and eclogitic parageneses of the mantle section under the Udachnaya-East kimberlite pipe (Yakutia) is presented. Five types of rims are identified: Rim1 develops between garnet and olivine/pyroxene (or rim2) and is composed of high-alumina pyroxenes, spinel, phlogopite; rim2, the coarse grain part of rim1, is located between rim1 and olivine/pyroxene, and mainly consists of phlogopite and less aluminous larger pyroxenes and spinel; rim3 develops between garnet and kimberlite, and presents with phlogopite and Fe-Ti spinel; rim4 sometimes presents instead of rim1/rim2 and consists of zoned high-Cr phlogopite with rare fine grains of chromium spinel; rim5, a “pocket” between garnet and rim1, is represented by microcrystalline aggregates of clinopyroxene, mica, spinel, calcite, and feldspar in different variations. Rims 1, 2, and 3 are typical for garnets of all studied parageneses. Rims 4 and 5 develop on high-Cr subcalcic garnets of the most depleted peridotites. Reactions of the formation of all types of rims are given in the article. Each type of kelyphite demonstrates a clear enrichment with a certain component: Rim1—MgO and alkalis; rim2—TiO2; rim3—FeO and TiO2; rim4—Cr2O3; and rim5—СаО, suggesting the multistage injection of different components by mantle fluid.

Pyroxenites of Kukesi Massif, Mirdita Ophiolite – geological record for magmatic system in SSZ environment – preliminary results

<p>Kukesi massif is located in the eastern part of the Mirdita Ophiolite (northern Albania), which marks suture after Neo-Thetyan ocean closure. It is formed of well-preserved mantle and crustal sections which exhibit Supra-Subduction Zone affinity (e.g. Dilek and Furnes 2009, Lithos). Lower part of the mantle section of the Kukesi massif consist mainly of harzburgites, whereas dunites are located close to Moho. Crustal section records transition from lower part formed by peridotites and pyroxenites (so called intermediate zone after Hoxha and Boullier 1995, Tectonophysics) to gabbros. In this study we focus on composition and origin of pyroxenites occurring in the mantle and lower crustal parts of the Kukesi massif.</p><p>In this study we studied 9 samples. They have composition of olivine websterite, clinopyroxenite, orthopyroxenite, hornblende-clinopyroxenite and websterite. Five of the analyzed samples have mantle origin (M): we studied (M)-olivine websterites and (M)-clinopyroxenite from harzburgitic part, as well as two (M)-orthopyroxenitic veins (one with clinopyroxenitic central part - composite vein) with minor amphibole cross-cutting dunites from one locality. From intermediate zone in crustal (C) part we collected (C)-hornblende-clinopyroxenites and (C)-websterite. </p><p>Clinopyroxene composition is homogeneous in (M)-olivine-websterites (Mg#=84.5-87 and 88.8-90.5; Al=0.07-0.1 and 0.05-0.07, respectively), (M)-clinopyroxenite (Mg#=84-86, Al=0.04-0.08), (C)-hornblende-clinopyroxenites (Mg#=88.5-91, Al=0.08-0.12a.p.f.u.) and (C)-websterite (Mg#=87-88; Al=0.13-0.16a.p.f.u.). It differs widely between (M)-orthopyroxenitic veins: from Mg#=85-94 and Al=0.02-0.08 a.p.f.u  in clinopyroxenitic part of composite vein to Mg#=93.6-95 and Al=0.01-0.03 in the purely orthopyroxenitic one. Orthopyroxene from two samples of  (M)-olivine websterites have either Mg#=83 and Al~0.07 a.p.f.u (Fo<sup>olivine</sup>=81.5) or Mg#=87  and Al~0.04 a.p.f.u (Fo<sup>olivine</sup>=86). Orthopyroxene composition in composite(M)-vein varies in wide ranges (Mg#=83-89; Al=0.04-0.08 a.p.f.u.); the other vein is homogeneous (Mg#=90-91, Al=0.02-0.03 a.p.f.u, Fo<sup>olivine</sup>=86.8-90); in (C)-websterite orthopyroxene has Mg#=82.4-84 and Al=0.12-0.14 a.p.f.u. Amphibole has composition of tremolite-actinolite. Spinel, where present, is highly chromian (Cr#=0.59-0.80).</p><p>Clinopyroxene is LREE-depleted in most of the samples, the (La/Lu)<sub>N</sub>=0.03-0.08. It is also LREE-depleted in (M)-clinopyroxenite ((La/Lu)<sub>N</sub>=0.05-0.23), but the contents of trace elements are higher than in other samples (eg. Lu<sub>N</sub>=0.79-2.75 vs. 0.40-0.85). In (M)-veins the LREE contents are approximately at primitive mantle level ((La/Lu)<sub>N</sub>=0.28-1.66).  Clinopyroxene in all samples has positive Th-U, Pb and Sr anomalies and negative Ta and Zr anomalies, but concentrations of trace elements is significantly higher in (M) clinopyroxenite and veins.</p><p>The presence of tremolite and actinolite points to a retrogressive metamorphism which affected the rocks. The LREE-depleted nature of clinopyroxene forming all the pyroxenites and presence of orthopyroxene  point to crystallization of the rocks from tholeiitic melt, but variations in Mg# and REE content in clinopyroxene may reflect formation either from different generations of melts or from melts fractionated due to reactive percolation.  Variations in composition of the parental melts is visible even in a scale of one outcrop, which is demonstrated by (M)-orthopyroxenite veins with various modal composition and mineral major and trace elements compositions.</p><p>This study was financed from scientific funds for years 2018-2022 as a project within program “Diamond Grant” (DI 024748).</p>

Supra-subduction mantle pyroxenites in an infant subduction system: the New Caledonia ophiolite record.

<p>Pyroxenites constitute the major form of heterogeneity in the upper mantle. Their occurrence in supra-subduction zone settings is mostly testified by veins and layers in refractory ophiolitic peridotites, where they represent a crucial witness of melt migration in the forearc/subarc environment [1,2]. The New Caledonia ophiolite hosts one of the largest forearc mantle section worldwide, providing a unique perspective into upper mantle processes. The sequence is dominated by ultra-depleted harzburgites [3], locally overlain by mafic-ultramafic cumulates [4,5,6]. The harzburgites are highly refractory residues that register a multi-phase evolution, including fluid-assisted melting in a forearc environment and contamination by fluid- and melt inputs triggered by Eocene subduction [1]. Pyroxenitic rocks intruding the harzburgites are only known in the Bogota peninsula shear zone, which records HT deformation along a paleotransform fault [7]. In this contribution, we report a comprehensive petrological and geochemical characterization on a new set of pyroxenites from this locality. The pyroxenites (~5-15 cm-thick) generally cut the peridotite foliation at variable angles, but concordant, locally boudinaged, layers also occur. Pyroxenite textures range from cumulitic to porphyroclastic or granoblastic-polygonal. The studied samples mostly consist of amphibole-bearing (5-44 vol.%) websterites, with variable amounts of orthopyroxene (27-67 vol.%) and almost constant clinopyroxene contents (~ 25-29 vol.%). Minor olivine-bearing orthopyroxenites are also present. Accessory phases include high-Ca (An= 82-86 mol%) plagioclase, Cr-rich spinel (Cr# = 50-61), sulfides and, occasionally, apatite. Pyroxenes displays high Mg# (Mg# Opx= 91-92; Mg# Cpx= 84-93), coupled with low Al2O3 contents (0.97-1.92 wt% and 1-2.42 wt% for orthopyroxene and clinopyroxene, respectively). Amphibole is high Mg# edenite. Application of conventional pyroxene thermometry yield equilibration temperatures ranging between 930-1040°C, comparable to the enclosing harzburgites (~ 950°C), whereas amphibole-plagioclase geothermometer provides lower temperatures (~ 800°C). Bulk rock composition of the websterites show variable Mg# (82-91) and REE concentrations ranging between 1 to 10 times chondritic values. They are characterized by flat to LREE-depleted (LaN/SmN 0.28-0.92) patterns, coupled to weak MREE-HREE fractionation (GdN/YbN = 1.73-1.92) and Eu negative anomalies. By contrast, orthopyroxenites display notably lower concentrations (0.1≤REE≤1 chondrite abundances). As a whole, clinopyroxene REE patterns of the websterites mirror bulk rocks at higher absolute values. Putative melts in equilibrium with clinopyroxene indicate strongly enriched compositions (up to 300 times chondritic values) coupled to variable LREE-HREE fractionation (LaN/LuN = 3-19) and flat to fractionated HREE (GdN/LuN 1-2). Such enriched liquids, which show some analogies with pre-obduction adakite-like dikes [8], have never been recorded in the MTZ cumulitic sequence of the New Caledonia ophiolite and shed new light on the magmatic activity in the early stage of subduction. </p><p>[1] Varfalvy, Canad Mineral, 1997, 35 (2), 543-570.<br>[2] Berly et al., J. Petrol., 2006, 47(8), 1531-1555.<br>[3] Secchiari et al., Geosc. Front., 2020, 11(1), 37–55. [4]. <br>[4] Marchesi et al., Chem. Geol., 2009, 266, 171-186.<br>[5] Pirard et al., J. Petrol., 2013, 54, 1759–1792.<br>[6] Secchiari et al., Contrib. Mineral. Petrol., 2018, 173(8), 66.<br>[7] Chatzaras et al., Geology, 2020, 48 (6): 569–573.<br>[8] Cluzel et al., Terra Nova, 2006, 6, 395–402.</p>

New podiform chromitites Occurrence from the Masirah Ophiolite, Oman

<p>The Masirah ophiolite is one of the few true ocean ridge ophiolites that have been preserved (Rollinson, 2017) and lacks any indication that it formed in a subduction environment. The Masirah ophiolite in south-eastern Oman is a different and older ophiolite from the more famous northern Oman ophiolite. Chromite and copper ores comprise large deposits in the Samail ophiolite, northern Oman. In comparison, chromite and copper deposits have not been described in previous reports or previous exploration in Masirah ophiolite. Rollinson (2017) has proposed that the apparent absence of chromitites in the mantle section of Masirah ophiolite is an important discriminant between subduction related and ocean ridge ophiolites.  However, during recent studies on the Batain ophiolite mélange, and Masirah ophiolite, several chromitite pods have been discovered. The chromitites occur as separated small concordant, lenticular pods (3–10 m in thickness), which have been extensively altered and deformed, with the host pyroxenite serpentinites serpentinized harzburgites and dunites. The largest chromitite pods found within the pyroxenite and dunite of Masirah are up to 10 m across.  Unusual minerals and mineral inclusions (orthopyroxene, clinopyroxene, amphibole, phlogopite, serpentine, native Fe, FeO, alloy, sulfide, calcite, laurite, celestine and halite) within chromite have been observed in the chromitites from the  Masirah ophiolites.  The existence of hydrous silicate inclusions in the chromite calls for a role of hydration during chromite genesis. Both  phlogopite and hornblende were possibly formed from alkali-rich hydrous fluids/melts trapped within the chromite during the chromitite formation. High-T green hornblende and phlogopite included in the chromites is evidence of the introduction of water in the magma at the end of the chromite crystallization. Such paragenesis points to the presence of hydrous fluids during the activity of the shear bands. The chromitites parental magmas are rich in K, Na, LREE, B, Cs, Pb, Sr, Li, Rb and U relative to HREE, reflecting the alkalic fluids/melts that prevailed during the chromitites genesis.</p><p>The mineral inclusions  in association with host peridotites may have been brought by the uprising asthenosphere at mid-oceanic ridges due to the mantle convection. It appears that this chromite has been formed through reaction between amid-ocean-ridge basalt-melt with depleted harzburgite in the uppermost mantle.  The chromitite deposits have similar cr# (55-62% Al-chromitites), mg# Al2O3 and TiO2 contents to spinels found in MORB, and have been interpreted as having formed in amid-ocean ridge setting.  This suggests that this chromitites is residual from lower degree, partial melting of peridotite, which produced low-Cr# chromitites at the Moho transition zone, possibly in a mid-ocean-ridge setting. The chemistry of both mineral inclusions and chromite   suggests MORB-related tectonic setting for the chromitites that were crystallized at 1000 °C–1300 °C under pressures <3 GPa . The host peridotites were generated during the proto-Indian Ocean MORB extension and emplaced as a result of the obduction of the ophiolite over the Oman Continental margin during Late Cretaceous-Early Paleocene.</p><p>Rollinson, H., 2017. Geoscience Frontiers, 8: 1253–1262.</p>

Thermobarometry and geochemistry of the mantle section beneath Morkoka pipe Central Yakutia Russia

<p>The Morkoka pipe belonging to the territory of West Daldyn terrane but It has all the features which are characteristic to the Malo- Botuobinsky or Upper MunaThe lower part of mantle section is represented by the depleted lower part of mantle section with the high amount of sub  Ca garnets with the high amount like in Mir pipe and rather long lineal ilmenite trend from the LAB at 7.5 GPA to the Moho at 2 GPA which is also the common feature of most pipe from the Magan terrane an happens in the Upper Muna field  Though the Morkoka pipe itself is barren the nearest territories around contain similar indicator minerals which shot ha there is a group pf pipes and some of them may be diamondiferous. The TRE patterns show mainly S- type which is perspective for the prospecting of diamonds.  But the HFSE for the garnets reveal rather high Zr>Hf peaks which became higher with the HREE level, (Ta>Nb) and higher than La. The LILE and Ba are typically low  but Th U sometimes higher than Nb. The ilmenites reveal slightly concave patterns with the minima near Gd  or  reveal  opposite inclination  similar to garnets but with the elevated LREE part.  The HFSE are rather high an Ta-Nb are higher that Zr Hf Some samples with the high LREE also reveal elevated Th and U, indicating influence of the essentially carbonatitic melts.</p><p>It seems that the mantle beneath the Morkoka pipe wre originally depleted but regenerated but the H2O bearing melts possibly rather oxidized and this may be the reason of the rather low diamond grade.  The ilmenites were generated by the essentially carbonatitic protokimberlite melts which passed through the matrix where garnets prevail  Reaction of the maters with the different REE inclination produced concave REE  patterns</p><p>Grant RBRF 19- 05-00788</p>

Sexual dimorphism in shell morphology of mollusks of the genus Viviparus – important objects of water resources of Ukraine

Bioindication assessment of water bodies of Ukraine can be carried out using the ratio of males and females of mollusks of the genus Viviparus. In practice, it is very convenient to determine the sex of mollusks by the differences in their shell. Male and female freshwater snails Viviparus viviparus (Linnaeus, 1758) and V. contectus (Millet, 1813) are shown to have reliable differences in shell morphology depending on their age. There is almost no sexual dimorphism by shell morphometrics and indices in Viviparus snails aged one to three years. After three years of life, mature females have significantly larger shell width, higher body whorl, and size of the aperture. Females of V. viviparus at the age of two to five years may be differentiated from males by the relationship of mean shell width and shell height, which is statistically significant higher than in males. This difference is explained by the different size of the mantle section genital organs of mature male and female. The obtained results should be taken into consideration in establishing the sex of viviparid snails.