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Magma mixing is a widespread magmagenic process. However, its significance in the formation of ultrapotassic magmas has been largely overlooked so far as they are commonly thought to originate directly from the mantle and ascend rapidly through the crust. The Hezhong ultrapotassic lavas in Western Yunnan (SW China) are (basaltic) trachy-andesitic in composition. These rocks display porphyritic textures with olivine, clinopyroxene (Cpx), spinel, and phlogopite occurring as both phenocryst and glomerocryst. Disequilibrium textures and complex zonation of crystals are commonly observed. Specifically, based on the textural and compositional characteristics, olivines can be classified into three different populations: two populations are characterized by highly to moderately magnesian olivines with normal chemical core-rim zonation (Fo~94–86 to Fo~89–79 and Fo~91–89 to Fo~86–84, respectively). The third population lacks obvious crystal zonation, but individual crystals exhibit some compositional variety at lower Fo contents (Fo83–76). Similarly, four populations of Cpx and two populations of spinel phenocrysts are recognized in terms of texture and composition. Notably, Cpx with reverse zoning contains a 'green-core' surrounded by a colourless mantle and rim. Hence, based on the variations of mineral assemblage, types of inclusions, and chemical compositions, all phenocryst/glomerocryst minerals can be divided into three groups. Mineral Group I (MG I) consists of high Fo cores of olivine, cores of the zoned spinel, and phlogopite. MG II only includes the green cores of reversed zoned Cpx (green-core Cpx), and MG III is composed of micro phenocrysts without obvious zoning and rims of large phenocrysts. Comparing these mineral groups with relevant minerals occurring in typical temporally and spatially associated igneous rocks, we suggest that the MG I and II could have been derived from magmas with compositions resembling an olivine lamproite and a trachyte, respectively. The overall bulk-rock geochemical and isotopic features of Hezhong lavas also agree with a mixing process between these two endmembers. Hence, we infer that mixing between these two magmas played a key role in the petrogenesis of the ultrapotassic Hezhong lavas and that the MG III crystallized from the mixed magmas. Our study highlights the complex formation of ultrapotassic magmas inferring that caution must be taken when using bulk chemical magma compositions are to deduce source signatures. [ABSTRACT FROM AUTHOR]

Cratonic lamproites are diamondiferous ultrapotassic rocks that are emplaced through thick continental lithosphere and thought to derive from melting of metasomatized (i.e., geochemically enriched) regions of the subcontinental lithospheric mantle (SCLM). We explored the alternative hypothesis that melts sourced from sublithospheric (i.e., convective mantle) sources dominate the genesis of cratonic lamproites. Supporting evidence includes a robust linear correlation between the Mg/Fe ratios of xenocrystic and magmatic olivine in lamproites worldwide, overlapping the trend observed for kimberlite olivine. This indicates that, similar to kimberlites, primary lamproite melts originate from broadly similar sublithospheric mantle sources before assimilating SCLM material of variable composition. The lamproites are also characterized by a direct correlation between olivine Mg/Fe ratio and bulk-lamproite K2O/Al2O3, an index of potassium enrichment in the melt that is independent of mantle-xenocryst entrainment and magmatic differentiation. Quantitative modeling indicates that this correlation results from the interaction between carbonate-bearing sublithospheric melt and phlogopite-rich wall rocks in the SCLM. Our data show that cratonic lamproites and kimberlites have similar mantle sources in the convective mantle, with lamproites acquiring their peculiar enrichment in K by interaction with metasomatized SCLM en route to the surface. Modification of sublithospheric melts during transit through the continental lithosphere might represent a common process for the genesis of alkaline mafic/ultramafic magmas. [ABSTRACT FROM AUTHOR]

The dynamic properties and melting behavior of the Earth's mantle are strongly influenced by the presence of volatile species, including water, carbon dioxide, and halogens. The role that halogens play in the mantle has not yet been fully quantified: their presence in only small quantities has dramatic effects on the stability of mantle minerals, melting temperatures, and in generating halogen-rich melts such as lamproites. Lamproites are volumetrically small volcanic deposits but are found on every continent on the planet: they are thought to be melts generated from volatile-rich mantle sources rich in fluorine and water. To clarify the mantle sources of lamproites, we present experimentally determined mineral/melt partition coefficients for fluorine and barium between phlogopite and lamproite melts. Both fluorine and barium are compatible in phlogopite [ D F (Phl/Melt) 0.96 ± 0.02 − 3.44 ± 0.33 , D Ba (phl/Melt) 0.52 ± 0.05 − 3.68 ± 0.43 ] at a range of pressures (5–30 kbar), temperatures (1000–1200 °C), and fluid compositions (C-O-H mixtures). Using our partition coefficients, we model the melt compositions produced by potential lamproite sources, including phlogopite garnet lherzolite, phlogopite harzburgite, and hydrous pyroxenite. The results demonstrate that hydrous pyroxenites and phlogopite garnet lherzolite can produce melts with F and Ba contents similar to lamproites, but only hydrous pyroxenites fully reproduce other geochemical characteristics of lamproites including high K2O, low CaO contents, and high F/H2O ratios. [ABSTRACT FROM AUTHOR]

The Marepalli dyke of the Vattikod cluster of the Ramadugu Lamproite Field, Nalgonda district, Telangana, India consists of pseudomorphed leucite, phlogopite (Al-poor, Ti-rich zoned phlogopite micas), pseudomorphed olivine, fluorapatite and Al-poor diopside embedded in groundmass consisting mainly of poikilitic Fe-rich titanian phlogopite and potassic amphibole. Other groundmass minerals are Al-Na-poor diopside, Al-poor spinels (titanian magnesian chromites to titanian chromites), Sr-rich fluorapatite and late-stage interstitial anhedral crystals of titanite and K-feldspar. The late-stage deuteric minerals present are REE-rich allanite, pyrite, magnetite, chalcopyrite, galena, hydro-zircon, carbonates (calcite, witherite and strontianite), baryte and cryptocrystalline SiO2. Apatite is an early crystallising phase and is present as inclusions in phlogopite and pyroxene. Phlogopite and amphibole occur as inclusions in titanite and K-feldspar. The compositional trends of phlogopite are of almost constant Al2O3 content with FeOT and TiO2 enrichment, and are typical of lamproitic micas. The FeOT enrichment is accompanied additionally by MgO depletion (reflecting VIFe2+ enrichment) from core to rim together with a slight increase in the tetraferric iron component. Diopside is characterised by <0.4 wt.% alumina and <0.6 wt.% sodium contents and exhibits typical lamproitic affinity. The spinels are alumina-poor with un-evolved titanian magnesian chromite to titanian chromite compositions. The presence of K-richterite, as an abundant amphibole, indicates a lamproite affinity, and on the basis of the typomorphic mineralogy, this rock is classified as a 'pseudoleucite-amphibole-phlogopite lamproite'. The Marepalli lamproite shows significant difference in compositional ranges of phlogopite, amphibole, pyroxene and spinel in comparison to those reported from the Vattikod, Gundrapalli, Ramadugu, Somavarigudem and Yacharam lamproites of Ramadugu Lamproite Field. These lamproites are considered to form from a common parent magma under reducing conditions as evidenced from: (1) low tetraferric iron content in phlogopite; (2) low Fe3+# and Ti# in spinels; and (3) high F content in phlogopite and apatite. [ABSTRACT FROM AUTHOR]

[Display omitted] • Trace elements in melts of mica-K-richterite pyroxenites are not strongly enriched. • Accessory phases apatite and Ti-oxides are essential in lamproite sources. • MARID lacks apatite and cannot be the sole source of alkaline melts. • Phlogopite, but not clinopyroxene or K-richterite, explains high 87Sr/86Sr signature. The trace element compositions of melts and minerals from high-pressure experiments on hydrous pyroxenites containing K-richterite are presented. The experiments used mixtures of a third each of the natural minerals clinopyroxene, phlogopite and K-richterite, some with the addition of 5% of an accessory phase ilmenite, rutile or apatite. Although the major element compositions of melts resemble natural lamproites, the trace element contents of most trace elements from the three-mineral mixture are much lower than in lamproites. Apatite is required in the source to provide high abundances of the rare earth elements, and either rutile and/or ilmenite is required to provide the high field strength elements Ti, Nb, Ta, Zr and Hf. Phlogopite controls the high levels of Rb, Cs and Ba. Since abundances of trace elements in the various starting mixtures vary strongly because of the use of natural minerals, we calculated mineral/melt partition coefficients (D Min/melt) using mineral modes and melting reactions and present trace element patterns for different degrees of partial melting of hydrous pyroxenites. Rb, Cs and Ba are compatible in phlogopite and the partition coefficient ratio phlogopite/K-richterite is high for Ba (1 3 6) and Rb (12). All melts have low contents of most of the first row transition elements, particularly Ni and Cu ((0.1–0.01) × primitive mantle). Nickel has high D Min/melt for all the major minerals (12 for K-richterite, 9.2 for phlogopite and 5.6 for Cpx) and so behaves at least as compatibly as in melting of peridotites. Fluorine/chlorine ratios in melts are high and D Min/melt for fluorine decreases in the order apatite (2.2) > phlogopite (1.5) > K-richterite (0.87). The requirement for apatite and at least one Ti-oxide in the source of natural lamproites holds for mica pyroxenites that lack K-richterite. The results are used to model isotopic ageing in hydrous pyroxenite source rocks: phlogopite controls Sr isotopes, so that lamproites with relatively low 87Sr/86Sr must come from phlogopite-poor source rocks, probably dominated by Cpx and K-richterite. At high pressures (>4 GPa), peritectic Cpx holds back Na, explaining the high K 2 O/Na 2 O of lamproites. [ABSTRACT FROM AUTHOR]

Dynamic metasomatism experiments were performed by reacting a lamproite melt with garnet peridotite by drawing melt through the peridotite into a vitreous carbon melt trap, ensuring the flow of melt through the peridotite and facilitating analysis of the melt. Pressure (2–3 GPa) and temperature (1050–1125 °C) conditions were chosen where the lamproite was molten but the peridotite was not. Phlogopite was formed and garnet and orthopyroxene reacted out, resulting in phlogopite wehrlite (2 GPa) and phlogopite harzburgite (3 GPa). Phlogopites in the peridotite have higher Mg/(Mg + Fe) and Cr2O3 and lower TiO2 than in the lamproite due to buffering by peridotite minerals, with Cr2O3 from the elimination of garnet. Compositional trends in phlogopites in the peridotite are similar to those in natural garnet peridotite xenoliths in kimberlites. Changes in melt composition resulting from the reaction show decreased TiO2 and increased Cr2O3 and Mg/(Mg + Fe). The loss of phlogopite components during migration through the peridotite results in low K2O/Na2O and K/Al in melts, indicating that chemical characteristics of lamproites are lost through reaction with peridotite so that emerging melts would be less extreme in composition. This indicates that lamproites are unlikely to be derived from a source rich in peridotite, and more likely originate in a source dominated by phlogopite-rich hydrous pyroxenites. Phlogopites from an experiment in which lamproite and peridotite were intimately mixed before the experiment did not produce the same phlogopite compositions, showing that care must be taken in the design of reaction experiments.

In this study, we show how veined lithospheric mantle is involved in the genesis of ultrapotassic magmatism in cratonic settings. We conducted high pressure experiments to simulate vein + wall rock melting within the Earth's lithospheric mantle by reacting assemblages of harzburgite and phlogopite-rich hydrous mantle xenoliths. These comprised a mica-, amphibole-, rutile-, ilmenite-, diopside (MARID) assemblage at 3–5 GPa and 1325–1450 °C. Melting of the MARID assemblages results in infiltration of melt through the harzburgite, leading to its chemical alteration. At 3 and 4 GPa, melts are high in K 2 O (> 9 wt%) with K 2 O/Na 2 O > > 2 comparable to anorogenic lamproites. Higher pressures and temperatures (5 GPa/1450 °C) lead to increasing MgO contents of the melt and to some extent lower K 2 O contents (5–7 wt%) at equally high K 2 O/Na 2 O ratios. Our experiments provide insights into the role of alkalis in nickel-partitioning (D Ni ) between olivine and ultrapotassic melt. We observe that the high contents of Na, K, and Al are indicative of high D Ni values, implying that the melt polymerization is the dominant factor influencing the olivine/melt nickel partitioning. The change of D Ni as a function of melt composition results in a pressure independent, empirical geothermometer: T ° C = − 88.14 · ln liq ( Na 2 O + K 2 O · liq 1 + SiO 2 TiO 2 · liq Al 2 O 3 liq MgO + FeO · D Ni + 1906.2 Element oxides represent the composition of the glass (in wt%), and D Ni is the liquid/olivine Ni-partitioning coefficient. We propose that this geothermometer is applicable to all natural silicate melts that crystallized olivine in a temperature interval between 1000 and 1600 °C. Application to glass-olivine pairs from calc-alkaline settings (Mexico), MORB (East Pacific Rise), and OIB (Hawaii) yielded reasonable values of 996–1199 °C, 1265 °C, and 1330 °C, respectively. [ABSTRACT FROM AUTHOR]

Micas from mafic ultrapotassic rocks with lamproitic affinity from several localities of the Central Mediterranean region were studied through single-crystal X-ray diffraction (SC-XRD), electron microprobe analysis (EMPA) and Secondary Ion Mass Spectrometry (SIMS); Mössbauer Spectroscopy (MöS), when feasible, was also applied to minimise the number of unknown variables and uncertainties. Analysed lamproitic samples cover the most important Central Mediterranean type localities, from Plan d'Albard (Western Alps) to Sisco (Corsica), Montecatini Val di Cecina and Orciatico (Tuscany, Italy) and Torre Alfina (Northern Latium, Italy). The studied crystals show distinctive chemical and structural features; all of them belong to the phlogopite-annite join and crystallise in the 1 M polytype, except for micas from Torre Alfina, where both 1 M and 2 M 1 polytypes were found. Studied micas have variable but generally high F and Ti contents, with Mg/(Mg + Fe) ranging from ~ 0.5 to ~ 0.9; 2 M 1 crystals from Torre Alfina radically differ in chemical composition, showing high contents of Ti and Fe as well as of Al in both tetrahedra and octahedra, leading to distinctive structural distortions, especially in tetrahedral sites. SIMS data indicate that studied micas are generally dehydrogenated with OH contents ranging from ~ 0.2 apfu (atoms per formula unit) for Orciatico and Torre Alfina to ~ 1.4 for Plan d'Albard crystals; this feature is also testified by the length of the c parameter, which decreases with the loss of hydrogen and/or the increase of the F → OH substitution. Chemical and structural data suggest that the entry of high charge octahedral cations is mainly balanced by an oxy mechanism and, to a lesser extent, by a M 3 +,4 + -Tschermak substitution. Our data confirm that Ti preferentially partitions into the M2 site and that different Ti and F contents, as well as different K/Al values, are both dependant upon f H2O and the composition of magma rather than controlled by P and T crystallisation conditions. The obtained data help to discriminate among lamproite-like rocks formed within a complex geodynamic framework but still related to a destructive tectonic margin and evidence different trends for micas from the youngest Torre Alfina (Northern Latium) lamproites, referred to the Apennine orogeny and those of the older lamproites from Orciatico, Montecatini Val di Cecina (Tuscany), Western Alps, and Corsica, the latter referred to the Alpine orogeny. Phlogopite crystals from the older lamproites fall within the compositional and structural field of worldwide phlogopites from both within-plate and subduction-related settings. Phlogopite from the Plio-Pleistocene lamproite-like occurrence in Tuscany and Northern Latium, despite crystals with low Mg# of the Torre Alfina rock plot well within the general field of the other crystals in less evolved samples, follows a different evolution trend similar to that of shoshonites from Tuscany and Northern Latium. On this basis, we argue that the observed differences are inherited by slight differences in the magma compositions that are related to different genetic and evolution pathways. [ABSTRACT FROM AUTHOR]

A mineralogical study of the hypabyssal facies, late Cretaceous macrocrystic pulse of TK1 intrusion and the Mesoproterozoic aphanitic pulse of TK4 intrusion in the Wajrakarur Kimberlite Field of southern India shows that the rocks contain macrocrysts of forsteritic olivine, phenocrysts and microphenocrysts of Al–Na-poor diopside and phlogopite set in a groundmass mainly of Al–Na-poor diopside and phlogopite. Other groundmass minerals are spinel, perovskite and fluorapatite in TK1, and spinel, titanite, chlorite, calcite and gittinsite in TK4. K-richterite and perovskite occur only as inclusions in phlogopite and titanite, respectively in TK4. Late-stage deuteric phases include pyrite and barite in TK1, and strontianite, chalcopyrite, galena and pentlandite in TK4. Diopside microphenocrysts in TK4 exhibit oscillatory zoning with characteristics of diffusion controlled magmatic growth. TK1 spinels show magmatic trend 2 that evolves from magnesiochromite and culminates in titaniferous magnetite, whereas TK4 spinels are less evolved with magnesiochromite composition only. TK1 phlogopites show a simple compositional trend that is typical of lamproite micas, while four distinct growth zones are observed in TK4 phlogopites with the following compositional characteristics: zone I: high Cr 2 O 3 and TiO 2 and low BaO; zone II: low Cr 2 O 3 ; zone III: low TiO 2 and high BaO; zone IV: low BaO. Forsterite contents and trace element concentrations reveal two xenocrystic core populations and one magmatic rim population for TK1 olivines. Mineralogically, both TK1 and TK4 are classified as diopside–phlogopite lamproites rather than archetypal kimberlites. The two lamproites are considered to have formed from the same parent magma but crystallised under distinct oxygen fugacity conditions. With elevated content of Fe 3 + in phlogopite, spinel and perovskite, TK1 appears to have crystallised in a relatively high oxygen fugacity environment. Multiple growth generations of phlogopite, spinel and fluorapatite in TK4 indicate a complex evolutionary history of the magma. Close spatial and temporal associations of Mesoproterozoic kimberlites and lamproites in southern India can possibly be explained by a unifying model which accounts for the generation of diverse magmas from a range of geochemical resevoirs in a continental rift setting. [ABSTRACT FROM AUTHOR]

Two early Cretaceous potassic sill intrusions from Ramnagore and Rajpura in the Raniganj Gondwana Sedimentary Basin of eastern India consist of macrocrysts and microcrysts of olivine, together with phenocrysts and microphenocrysts of mica, apatite and diopside set in a groundmass of mica, diopside, K-feldspar, apatite and rutile. Titanian magnesian aluminous chromite occurs as a groundmass phase in the Ramnagore rocks. The compositional characteristics of olivine are similar to those of peridotite-derived mantle xenocrysts in terms of their high forsterite and Ni contents coupled with low Mn, Ca, Al and Ti. Mineralogically, the sill intrusions are classified as phlogopite–diopside–K-feldspar–apatite olivine lamproites. Mica and apatite crystals commonly show core–overgrowth rim textures with up to three distinct compositional zones. The mica zones are M-I core: high Ti, low-to-high Cr and moderate Ba; M-II inner rim: moderate Ti, low Cr and high Ba; and M-III outer rim: low Ti, Cr and Ba. Rajpura mica show a fourth zone (M-IV), which occurs as patches at the crystal margins, characterized by higher Fe T and lower K compared to the other three zones. M-I phlogopite is interpreted to be "antecrystic", whereas M-II and M-III mica represent magmatic growth zones. M-IV mica has probably developed during hydrothermal alteration. Both the Rajpura and Ramnagore mica exhibit a trend of decreasing Al 2 O 3 with increasing FeO T , which is typical for bona fide lamproites. Rajpura apatite crystals show three distinct compositional zones, viz. Ap-I core: high-Sr–low-LREE; Ap-II inner rim: high-Sr–high-LREE; and Ap-III microporous outer rim: moderate-Sr–low-LREE and considerable quantities of Ba and Na. The Ap-I and Ap-II generations represent two distinct magmatic growth zones, whereas Ap-III developed during hydrothermal alteration. Ramnagore apatite exhibit oscillatory zoning with fluctuations in Sr and LREE contents. Diopside has Al–Na-poor compositions, typical of lamproitic clinopyroxene. The study demonstrates how the mineralogy of lamproites records crystallization from multiple pulses of mantle-derived K-rich magmas, with protracted magmatic differentiation and late-stage hydrothermal evolution. • Two phlogopite–diopside–K-feldspar–apatite olivine lamproites from eastern India. • High-Fo olivine grains are peridotite mantle-derived xenocrysts. • High Cr Ti phlogopite record earlier failed lamproite activity at mantle depths. • Magmatic mica and apatite zones reflect different stages of magma differentiation. • Metasomatic mica and apatite record late-stage hydrothermal alteration. [ABSTRACT FROM AUTHOR]

Kimberlitic rocks are known in the São Francisco Craton, Brazil, since the 1980s when the De Beers started a prospective work in the Itapicuru River Greenstone Belt. However, 40 years later, the scientific knowledge about these occurrences is still very restricted. This paper presents new geological and petrographical data for the pipes of the "Brauna Kimberlitic Field". These rocks are exposed in a strongly eroded cratonic area of Northeastern São Francisco Craton and as expected, represent the deepest parts of these bodies, showing textural aspects and components typical of coherent volcanic rocks emplaced at deep crustal levels. The kimberlitic magmatic event resulted not only in the emplacement of macrocrystalline hypabyssal olivine archetypal kimberlites, here represented by the B3 (678–682 Ma) and B4 pipes (s.s. Former type 1 kimberlites), but also in hypabyssal macrocrystalline pyroxene-phlogopite- lamproite intrusions, as exposed in the B7 (641 Ma) pipe of the Brauna Field. Both magmas are rich in mantle-xenoliths and have potential for diamond ores. The observed features suggest the presence of multiple magmatic pulses – which acted as deep samplers, recorded in the diversity of xenoliths and xenocrysts – thus demonstrating the potential of these rocks for the comprehension of the first stages of evolution of the Early Earth as well as for understanding the formation of the metasomatized lithospheric mantle below the São Francisco Craton. The new data for these hypabyssal facies, macrocrystic pulse of kimberlitic rocks in the Brauna Field, São Francisco Craton, Brazil, can be used to characterize the petrographic and mineralogical heterogeneities of a Neoproterozoic alkaline-ultrapotassic magmatic event that shows a kimberlite-lamproite transitional nature. The petrogenetic knowledge presented for the São Francisco Craton kimberlites and lamproites – accordingly to the most recent classifications for these rocks – include textural-genetic data, geotectonic environment, and intrusive-spatial context, setting these rocks at the stage 5 of present-day kimberlite classification scheme. Moreover, the integration of such data and the close spatial associations of kimberlites, lamproites, lamprophyres, syenites and shoshonites allowed to create a solid interpretation of the rock formation processes that correlates these Neoproterozoic alkaline ultrapotassic magmas to the reactivation of ancient mantle conduits in a thick lithosphere that overlies a previously metasomatized mantle and intrude a metal-rich craton environment. • Current models and nomenclature of kimberlite-lamproite rocks highlight the importance of detailed petrogenetic studies. • Detailed petrographic studies points to the usefulness of deepening the discussion on kimberlite rocks nomenclature. • The pipes of the BKF present textural characteristics and components typical of massive coherent rocks emplaced at deep crustal levels. • B3/B4 are classified as coherent coarse-grained, macrocrysts-rich, hypabyssal-facies, mega-graded, diamondiferous-olivine-kimberlite. • Otherwise, B7 is interpreted as an intrusive plug of a massive coherent coarse-grained, hypabyssal, diamondiferous-phlogopite-lamproite. • The petrogenetic and textural classification of BKF, presented in this paper, contribute to understanding of kimberlite and lamproite magmas. • BKN petrogenesis contribute to understand the metasomatized mantle and ore deposits of the Sao Francisco Craton. [ABSTRACT FROM AUTHOR]

New high precision 40Ar/39Ar ages are presented which more tightly constrain the eruption ages of the West Kimberley lamproites of northwestern Western Australia. The data show a southward progression in ages of the lamproites over a distance of ∼135 km, from ∼22.5 Ma in the northernmost lamproites of the Ellendale Field to ∼19 Ma in the Noonkanbah Field in the south, excluding the Walgidee Hill lamproite. The large (∼490 ha) zoned Walgidee Hills lamproite at the northern edge of the Noonkanbah Field is the youngest of the West Kimberley lamproites and represents a later pulse of lamproite magmatism at 17.4 Ma, >1 Ma after the main lamproite magmatism. The southward progression of lamproite ages extends across a wide swath from the Proterozoic King Leopold Orogen at the southern margin of the Kimberley Craton to the Phanerozoic Fitzroy Trough in the Canning Basin. The magmatism does not appear to be the result of the migration of a mantle plume, but more likely reflects small degrees of partial melting of old, thick, metasomatised lithosphere extending from the craton margin beneath the basin, with melting triggered by regional uplift and/or small-scale mantle convection at the craton margin. Emplacement of the lamproites likely exploited ancient trans-lithospheric structures associated with the Proterozoic orogen at the craton margin and structures associated with the formation of the Canning Basin in the Phanerozoic. • New high precision 40Ar/39Ar ages determined for West Kimberley lamproite province • Southward progression of lamproite ages, but no evidence of mantle plume source • Lamproite genesis by small degree partial melting of metasomatized lithosphere • Magmatism triggered by regional uplift and/or plate margin mantle convection • Crustal emplacement controlled by ancient trans-lithospheric structures [ABSTRACT FROM AUTHOR]

The Lentiira-Kuhmo-Kostomuksha triangle, along the Finland – Russian border and within the central part of the Archean Karelian craton, contains numerous examples of phlogopite-rich, ultramafic, mantle-xenocryst-bearing and, in some cases, diamond-bearing dike rocks. Laser probe Ar-Ar data on phlogopite from 3 dike rocks on the Finnish side (Lentiira, Kuhmo) all gave ages within error of each other, 1202 ± 3 Ma (2σ), 1199 ± 3 Ma (2σ) and 1204 ± 4 Ma (2σ) while a fourth sample produced mixed ages. Published Rb-Sr dates on mineralogically and chemically similar dikes from the Russian side (Kostomuksha) are 1232 ± 5 Ma. The question remains open whether these represent two distinct age populations or whether differences in isotopic system behavior are the reason for the 30 m.y. age difference.

Sierra Leone contains two Jurassic-aged diamondiferous kimberlite clusters, namely Koidu and Tongo-Tonguma (hereafter referred to as Tongo), consisting of eruptive pipes and NE-SW trending dikes. In this study, a combination of detailed petrography, and phlogopite, spinel, and olivine compositions in hypabyssal samples is presented to classify and constrain the petrogenesis of these kimberlites. Both the Koidu and Tongo rocks are predominantly macrocrystic and highly micaceous with phlogopite abundances, normalised to olivine-free, of 36–65 vol% in the groundmass. These phlogopite contents are comparable to those of some cratonic lamproites and significantly higher than any other kimberlites. Other groundmass minerals include spinel, perovskite, and apatite set in a base of carbonate and serpentine. Phlogopite and spinel have similar compositions in the Koidu and Tongo samples, displaying evolutionary trends consistent with those observed in worldwide kimberlites. Olivine macrocrysts and microcrysts display complex zoning with distinct cores, internal zones, and rims. The core compositions display a range in Mg# (81–95) and are interpreted to be derived from the disaggregation of lithospheric mantle xenoliths and proto-kimberlite related megacrysts. The Tongo olivine rims, interpreted to be primary magmatic crystallisation products, have similar compositions from various locations within the cluster whereas the Koidu samples display a range in rim compositions (Mg# 87–89) from different locations within the cluster. The average Koidu rim compositions display a strong positive correlation with the average core compositions, consistent with the trend formed by kimberlites worldwide and indicative of a strong control by melt-lithosphere interaction on melt compositions. Previously, it has been shown that the Mg# of olivine rim's negatively correlates with the abundance of groundmass phlogopite (± oxide minerals) in kimberlites. However, the Koidu and Tongo kimberlites are exceptionally phlogopite-rich given their olivine Mg#, fall outside of the worldwide kimberlite array and have olivine compositions and phlogopite abundances like some cratonic lamproites. This leads us to suggest that Koidu and Tongo represent a rare style of highly micaceous kimberlite magmatism, not previously reported in other cratonic regions, and are genetically linked to the assimilation of K 2 O-rich, metasomatic mantle lithologies. We further suggest that the K 2 O content, reflected by groundmass phlogopite abundances, of worldwide kimberlite and cratonic lamproite parent magmas ascending to the surface may be related to assimilation of craton-specific styles of metasomatic lithologies in the SCLM. • Unique highly micaceous kimberlites from Sierra Leone. • Olivine compositions constraining melt-SCLM interactions. • Craton-specific melt-SCLM assimilation and K2O enrichment. [ABSTRACT FROM AUTHOR]

This study reports a petrographic and crystal chemical analysis of three types of micas (yangzhumingite, light brown phlogopite and dark brown phlogopite) found in a lamproitic dyke at the Kvaløya Island (North Norway). The study was carried out integrating different analytical techniques: electron microprobe, single crystal X-ray diffraction, inductively coupled plasma mass spectrometry, Mössbauer and micro-Fourier Transform infrared spectroscopy. Kvaløya yangzhumingite (second occurrence in nature) was characterized for the first time in detail via single crystal X-ray diffraction. The different mica types are distinguishable on the basis of the VI Fe and Mg versus Si content. Yangzhumingite composition is intermediate between those of KMg 2.75 (Si 3.5 Al 0.5 )O 10 F 2 and KMg 2.50 Si 4 O 10 F 2 synthetic compounds reported in the literature. Light and possibly dark brown phlogopite is a Mg-rich fluorotetraferriphlogopite, the latter having a greater Fe content. The infrared spectra of yangzhumingite and the light brown phlogopite show the occurrence of OH − absorption bands respectively at: ~ 3586 cm − 1 which correlates well with the measured F content; 3707 cm − 1 and 3686 cm − 1 assigned mainly to 3Mg 2 + –K + –OH − (phlogopitic) environment. Structural analyses, performed only on yangzhumingite and light brown phlogopite show that both samples are 1 M polytypes with the expected space group C 2/ m . Crystal chemical details are compatible with the following major substitution mechanisms: 2 XII K + + VI [] ↔ 2 XII [] + VI R 2 + (where R 2 + = Mg, Fe), OH − ↔ F − for yangzhumingite and 2 VI R 2 + ↔ VI Ti 4 + + VI [] (Ti-vacancy), OH − ↔ F − for light brown phlogopite. All three types of micas formed at relatively constant low pressure, but over a large temperature range in equilibrium with a grain boundary fluid that underwent significant changes in composition during reaction progress. Light brown phlogopite cores and dark brown phlogopite rims formed during crystallization from the lamproitic magma, while yangzhumingite formed as a result of reactions between the already formed phlogopite and the highly reactive fluid that was derived from the volatile-rich lamproite magma. [ABSTRACT FROM AUTHOR]

[Display omitted] • Experimental partial melts of K-richterite-bearing mica pyroxenites produce lamproite melts. • Melting of mica pyroxenites without amphibole produce more calcium-rich melt compositions. • Melts of hydrous pyroxenites in the lower cratonic lithosphere instigate mantle metasomatism. Melting experiments on ultramafic rocks rich in the hydrous minerals phlogopite or phlogopite + K-richterite, some including 5% of accessory phases, have been conducted at 15 and 50 kbar. The assemblages represent probable source components that contribute to melts in cratonic regions, but whose melt compositions are poorly known. A main series of starting compositions based on MARID xenoliths consisted of a third each of clinopyroxene (CPX), phlogopite (PHL) and K-richterite (KR) with or without 5% ilmenite, rutile or apatite. Additional experiments were run without KR and with higher proportions of accessory phases. Melt traps were used at near-solidus temperatures to facilitate accurate analysis of well-quenched melts, for which reversal experiments demonstrate equilibrium. Results show that KR melts rapidly and completely within 50 °C of the solidus, so that melts reflect the composition of the amphibole and its melting reaction. Melts have high SiO 2 and especially K 2 O but low CaO and Al 2 O 3 relative to basaltic melts produced from peridotites at similar pressures. They have no counterparts amongst natural rocks, but most closely resemble leucite lamproites at 15 kbar. KR and PHL melt incongruently to form olivine (OL) and CPX at 15 kbar, promoting SiO 2 contents of the melt, whereas orthopyroxene OPX is increasingly stable at lower lithosphere pressures, leading to an increase in MgO and decrease in SiO 2 in melts, which resemble olivine lamproites. Melts of mica pyroxenites without KR are richer in CaO and Al 2 O 3 and do not resemble lamproites. These experiments show that low CaO and Al 2 O 3 in igneous rocks is not necessarily a sign of a depleted peridotite source. Accessory phases produce melts exceptionally rich in P 2 O 5 or TiO 2 depending on the phases present and are unlike any melts seen at the Earth's surface, but may be important agents of metasomatism seen in xenoliths. The addition of the 5% accessory phases ilmenite, rutile or apatite result in melting temperatures a few ten of degrees lower; at least two of these appear essential to explain the compositions of many alkaline igneous rocks on cratons. Melting temperatures for CPX + PHL + KR mixtures are close to cratonic geotherms at depths > 130 km: minor perturbations of the stable geotherm at >150 km will rapidly lead to 20% melting. Melts of hydrous pyroxenites with a variety of accessory phases will be common initial melts at depth, but will change if reaction with wall-rocks occurs, leading to volcanism that contains chemical components of peridotite even though the temperature in the source region remains well below the melting point of peridotite. At higher temperatures, extensive melting of peridotite will dilute the initial alkaline melts: this is recognizable as alkaline components in basalts and, in extreme cases, alkali picrites. Hydrous pyroxenites are, therefore, components of most mantle-derived igneous rocks: basaltic rocks should not be oversimplified as being purely melts of peridotite or of mixtures of peridotite and dry pyroxenite without hydrous phases. [ABSTRACT FROM AUTHOR]

The extensional Thrace basin (NW Anatolia) contains an association of early Miocene diopside--leucite--phlogopite (Doğanca) and diopside--phlogopite (Korucuköy) lamproites with Oligocene medium-K calc-alkaline andesites (Keşan volcanics), early Miocene shoshonitic rocks (Altınyazı trachyte) and middle Miocene Na-alkaline basalts (Beğendik basalts). The Doğanca lamproite (K2O = 5.1-5.5 wt.%; K/Na = 2.78-2.89; MgO = 11.4-11.8 wt.%) consists of olivine (Fo71-86), diopside (Al2O3 = 1.0--5.0, Na2O = 0.2-0.6), phlogopite (TiO2 = 1.1-9.4, Al2O3 = 11.1-13.9), spinel (Mg# = 22.9-32.6; Cr# = 6483.4), leucite, apatite, zircon, Fe--Ti-oxides and magnetite in a poikilitic sanidine matrix. The potassic volcanic units (lamproites and trachytes) in the region have similarly high Sr and low Nd isotopic compositions (87Sr/86Sr(i) = 0.70835-0.70873 and 143Nd/144Nd(i) = 0.51227-0.51232). The major and trace element compositions and Sr--Nd--Pb isotopic ratios of the shoshonitic, ultrapotassic and lamproitic units closely resemble those of other Mediterranean ultrapotassic lamproites (i.e., orogenic lamproites) from Italia, Serbia, Macedonia and western Anatolia. The Beğendik basalts show intraplate geochemical signatures with an Na-alkaline composition, an absence of Nb negative anomalies on primitive mantle-normalized multi-element diagrams, as well as low Sr (~ 0.70416) and high Nd (0.51293) isotopic ratios; and include olivine (Fo72-84), diopside, spinel, Fe--Ti-oxides and magnetite. The Oligocene Keşan volcanics were emplaced in the earlier stages of extension in Thrace, and represent the typical volcanic products of post-collisional volcanism. The continental crust-like trace element abundances and isotopic compositions of the most primitive early Miocene ultrapotassic rocks (Mg# up to 74) indicate that their mantle sources were intensely contaminated by the continental material. By considering the geodynamic evolution of the region, including oceanic subduction, crustal accretion, crustal subduction and post-collisional extension, it is suggested that the mantle sources of the potassic volcanic units were most likely metasomatized by direct subduction of continental blocks during accretion and assemblage of various Alpine tectono-stratigraphic units. Overall, the magma production occurred in an extensional tectonic setting that controlled the core-complex formation and related basin development, with the middle Miocene Beğendik basalts being derived from asthenospheric sources during the late stages of extension. [ABSTRACT FROM AUTHOR]

A cluster of lamproite dykes are located 1 km west of Vattikod village at the NW margin of the Cuddapah basin, Eastern Dharwar craton, southern India, during the pursuit for locating primary diamond source rocks by adapting multifarious applications. These exotic rocks are emplaced along WNW-ESE to NW-SE trending fractures in the granitic rocks belonging to the Peninsular Gneissic Complex. Ten out of twelve lamproites occur near Vattikod village and one each is located in the vicinity of Marepalli and Gundrapalli villages respectively. These lamproites, though highly altered, contain microphenocrysts of altered olivine, clinopyroxene, phlogopite, leucite and sanidine and translucent to opaque, amoeboid shaped patches of glass set in a groundmass rich in carbonate, phlogopite, serpentine, and chlorite. This new cluster of lamproites constitutes a part of the recently discovered Ramadugu lamproite field. The Vattikod and Ramadugu lamproites, together with those from Krishna lamproite field and the Cuddapah basin, constitute, a wide spectrum of ultrapotassic magmatism emplaced in and around the Palaeo-Mesoproterozoic Cuddapah basin in southern India. [ABSTRACT FROM AUTHOR]

The Paleocene ultraferrous Mn-rich phlogopite-olivine rocks of the Taukha terrane belong to the alkaline ultrabasic rocks of the potassic series. The olivine is represented by hortonolite, while the phlogopite is enriched in Cl. Other minerals are represented by Ti-magnetite, Mn-rich ilmenite, Zn-rich pleonaste, apatite, and zircon. There are also epigenetic serpentine, talc, carbonates, magnetite, breithauptite, nickeline, hedleyite, cobaltite, tsumoite, auricupride, cuproauride, and other minerals. The phlogopite-olivine rocks possibly represent a part of a magmatic complex previously unknown in Sikhote Alin, the rocks of which are associated with fluidolites of a large diatreme. There are grounds to suggest that they were formed by the injection of fluid-rich (mainly, HO, Cl, F, and S) deep magmas into the upper lithosphere. Based on these specific features, as well as the sharp K predominance over Na and the enrichment in some incompatible elements (Sn, Ta, Nb, and Zr), the phlogopite-olivine rocks are the most close to lamproites but differ in the high contents of Fe, Mn, Au, Pt, and Pd and in the olivine's composition. The manifestation of such magmatism in the Taukha terrane records the transition from subduction to transform continental margin settings. [ABSTRACT FROM AUTHOR]

Abstract: Lamproites are among the most enigmatic mantle generated melts, and are typically abundant in phlogopite. We investigated the major and trace element chemistry of phlogopite crystals from Mediterranean lamproite occurrences in Spain, Serbia and Turkey. The most primitive lamproite samples were selected in order to evaluate the generation of the different phlogopite populations in their distinct mantle setting(s). Phlogopite hosted in Mediterranean lamproites can be grouped into different compositional arrays on the basis of their major element chemistry using Al2O3, FeOT and TiO2 concentrations. Contents of Cr, F and presumably Ti allow discrimination of the macrocrysts into phlogopite phenocrysts, which are liquidus and near-liquidus phases, and mantle xenocrysts. Further distinction among different populations of mantle-derived phlogopite can be achieved, considering trace element and isotopic ratios. The latter also distinguish between crustal and asthenospheric imprints on the source of the lamproitic parental melt. [Copyright &y& Elsevier]

The rocks of the Jasra intrusive complex (Shillong Plateau, northeastern India) include phlogopite clinopyroxenites (with olivine or perovskite relics), alkali gabbros/monzodiorites, syenites and nepheline syenites. They have a potassic affinity (Na2O/K2O ∼1), and their mineralogy is dominated by clinopyroxene with which phlogopite, olivine, amphibole, feldspars, feldspathoids, oxides, orthopyroxenes, perovskite, titanite and other accessory phases are variably associated. The Jasra intrusive rocks are cumulates derived from at least two distinct magmatic liquids. The potassic affinity of the Jasra rocks differs from the nearby Sung Valley ijolitic-carbonatitic complex and from the ultrapotassic lamproitic rocks of the Damodar Valley, which are of approximately the same age. This suggests major variability in the mantle sources of small-volume alkaline volcanism in the Early Cretaceous of northeastern India. [ABSTRACT FROM AUTHOR]

The article presents information on the phlogopite which are the olivine rocks of the Taukha terrane and are most similar to lamproites that are the products of deep rooted magmatism with a peculiar chemical composition. It informs that the practical and scientific interest in the lamproites is due to their capacity of bearing diamond and information on the geological processes, composition, and physicochemical conditions at different levels of the lithosphere. It further informs that the terrane represents a fragment of the Neocomian accretionary wedge composed of Jurassic and Lower Cretaceous terrigenous of sedimentary rocks.

Baotite occurs as a late phase in the Kvaløya lamproite dyke and in the fenitized granite adjacent to the dyke, suggesting that baotite formed during reactions between rock and fluids derived from a volatile-rich lamproitic magma. Most of the analyzed grains of baotite from the Kvaløya lamproite show compositions close to the ideal Nb-free end-member BaTiSiOCl. Compilation of all published baotite analyses suggests that the major compositional variations of baotite occur between the Nb-free end member BaTiSiOCl, and a Nb-rich end member BaTiFe²NbSiOCl. However, a Pb-bearing baotite, showing significant concentrations of Ca, Sr, Pb and K, and approximately 3 Ba p.f.u., was also identified from the Kvaløya lamproite. Euhedral fluorapatite formed as an early phase during crystallization of the lamproite magma, while anhedral REE-rich fluorapatite overgrowths on the euhedral grains formed during reactions with the late magmatic fluid. Fluorapatite contains up to 1.2 F p.f.u., but only traces of Cl. Other F-rich, but Cl-poor minerals of the lamproite include fluoro-potassic-magnesio-arfvedsonite, fluoro-phlogopite, and yangzhumingite. The presence of baotite together with a range of high-F, but low-Cl mineral phases suggests that the minerals formed in equilibrium with a high-F, Cl-bearing hydrous fluid. The high Cl-content of baotite demonstrates that Cl is strongly partitioned into this mineral in the presence of a Cl-bearing F-rich hydrous fluid. We suggest that a combination of high a, a, a, and f, but low a of the fluid enabled baotite formation. [ABSTRACT FROM AUTHOR]

Abstract: report new 40Ar/39Ar age results for two kimberlites (Muligiripalle pipe 5 and Tummatapalle pipe 13) and one lamproite (Pochampalle), from the Archaean Dharwar craton in southern India. Previous studies indicate that kimberlites and related rocks are highly susceptible to extraneous argon contamination, leading to anomalously old ages; although reliable 40Ar/39Ar ages can be obtained from step-heating analyses of groundmass phlogopite grains. carried out single-step 40Ar/39Ar fusion analyses on phlogopite phenocrysts and xenocrysts. This approach is not favoured, because it does not allow identification of argon loss/gain effects, thus complicating data interpretation and reducing confidence in the reliability of the reported ages. In particular, it is suggested that the Pochampalle lamproite was emplaced <1400Ma ago, rather than ca.1500Ma, as suggested by . It is recommended that 40Ar/39Ar geochronology of kimberlite and lamproites include step-heating analyses of matrix phlogopite grains, with anomalous or contentious results verified using other dating methods. [Copyright &y& Elsevier]

The geochemistry and mineralogy of lamproites from south-western Anatolia can be used as a snapshot of the lithospheric composition beneath the Menderes Massif. High and near-constant KO contents, the presence of mantle xenocrystic phlogopite and olivine, highly magnesian olivine phenocrysts and Cr-rich spinel inclusions all indicate that the lithospheric mantle was phlogopite-bearing ultradepleted harzburgite at the time of lamproite eruption (20-4 Ma). This mantle assemblage most probably originated in a complex multistage process, including (intra-oceanic) supra-subduction zone depletion during the final stages of southern Neotethyan ocean closure, and accretion of the forearc oceanic lithosphere as shallowly subducted material to the already assembled Anatolia. The data presented here support shallow subduction of the oceanic lithosphere as a cause of the uplift of the Menderes Massif, in contrast to the traditional core-complex model. Terra Nova, 00, 000-000, 2010 [ABSTRACT FROM AUTHOR]

Abstract: In this study we experimentally determine phlogopite/melt partition coefficients of Ra and other trace elements in a lamproitic system. This work was achieved using an analytical technique (LA-ICP-MS) with low detection limits (~0.01 fg) permitting the measurement of the very low Ra concentrations feasible in experiments (~1 ppb). D Ra phlogopite/melt was determined to 2.28±0.44 and 2.84±0.47 in two experiments, the ratio D Ra/D Ba is around 1.6. The compatibility of Ra in phlogopite results from an ionic radius being close to the apex of the lattice strain parabola for earth alkalis in the large XII-coordinated interlayer site of phlogopite. A re-evaluation of D Ra and D Ra/D Ba for magmatic minerals containing appreciable Ra, yields D Ra mineral/melt ranging from ~2.6 for phlogopite down to 2–3•10−5 for pyroxenes, and D Ra/D Ba mineral/melt from ~4 for leucite to 2•10−2 for orthopyroxene. The influence of melt composition on D Ra/D Ba is less than 10%. All investigated minerals have different D Ra/D Ba, strongly fractionating Ra from Ba. Thus, for magmatic systems, (226Ra)/Ba in the various minerals is not constant, these minerals do not form a straight line in the (226Ra)/Ba–(230Th)/Ba system at the time of crystallization and thus, there is no (226Ra)/Ba–(230Th)/Ba isochron at t 0. 226Ra–230Th–Ba mineral dating is thus applicable only to model ages calculated from mineral–glass pairs with known D Ra. [Copyright &y& Elsevier]

Kaapvaal lamproites, also known as orangeites, are H 2 O-rich, diamondiferous, highly micaceous, ultrapotassic rocks. Olivines in kimberlites have been shown to be extremely useful in tracking melt evolution, highlighting the importance of the chemical effects of SCLM assimilation on asthenosphere-derived melts. Kaapvaal lamproites are derived from melting metasomatised SCLM and may be expected to form an endmember to the asthenosphere melt-SCLM trend defined by kimberlites. In this contribution, we use olivine composition in Kaapvaal lamproites to further understand melt evolution in the SCLM and assess the similarity between Kaapvaal lamproite, other diamondiferous lamproites, and kimberlite petrogenesis in cratonic regions. We present olivine composition for representative on- and off-craton Kaapvaal lamproites from Finsch and Melton Wold, respectively. Olivines from these Kaapvaal lamproites are characterized by distinct core and rim zones, regardless of the size of individual grains. Polycrystalline grains are abundant at Finsch but relatively rare at Melton Wold. The olivine cores from both occurrences are predominantly Mg-rich (Fo >89) whereas Fe-rich cores (Fo <89) are rare. Mg-rich cores are interpreted to be derived from the disaggregation of mantle peridotites, including sheared peridotites, whereas Fe-rich cores are derived from olivines of the Cr-poor megacryst suite. The average Fo and NiO concentrations of the Melton Wold cores are lower than Finsch cores, likely related to less refractory off-craton mantle. The olivine rims at Finsch and Melton Wold are characterized by reverse zoning with ranges of Fo 89-92 and Fo 90-91 , respectively. The rims are interpreted to represent crystallisation related to a complex interplay between increasing oxidation, assimilation of orthopyroxene, and increasing alkali content of the melt during evolution. The average core and rim compositions of Finsch and Melton Wold, in conjunction with data from diamondiferous lamproites of other cratonic regions, define a broad positive correlation. Kaapvaal lamproites have Mg-rich core and rim compositions, similar to that of Lac de Gras kimberlites, and interpreted to reflect sampling and equilibration of low volume Kaapvaal lamproite melt with refractory mantle. In contrast to Lac de Gras kimberlites, Kaapvaal lamproites have high abundances of groundmass phlogopite that reflect metasomatic material in the SCLM source, likely present as veins within refractory peridotite. This suggests that increasing proportions of melt-metasomatised SCLM interactions are not always linked with increasing Fe content of melts. We show that the petrogenesis of Kaapvaal lamproites is similar to that of kimberlites and lamproites from other cratonic regions, however, the high abundance of phlogopite and Fo-rich olivine rims suggest a distinct metasomatic lithology in the source and that olivine composition ; i.e., a proxy for melt composition, may be strongly controlled by melt volume during melt-SCLM interactions. • Orangeites have olivine zoning similar to kimberlites. • In contrast to Kimberley kimberlites, olivine rims are Mg-rich. • In contrast to Kimberley kimberlites, Fe-rich cores are rare. • Olivine average core-rim compositions in addition to high phlogopite groundmass abundance suggests refractory yet metasomatised source. • Olivine in orangeites suggests similar petrogenesis to diamondiferous lamproites and kimberlites worldwide. [ABSTRACT FROM AUTHOR]

Abstract: Historically, phlogopite and olivine have been mined in the Silver City Dome District in Kansas, USA, from lamproite ultra-potassic igneous rock for use as a supplement in cattle feed. Micro-Lite LLC is now evaluating processing techniques for recovery of phlogopite to be used for reinforcement in plastics, high temperature applications, and electrical insulators, which requires a higher grade phlogopite product. To determine the purity of the processed ore, QEMSCAN® was utilised to identify and quantify phlogopite and impurities, including olivine, pyroxenes, feldspars, titanium phases (mainly titanite and perovskite), apatite, magnetite, chromite, and other phases. Samples were prepared and analysed in a manner to decrease or eliminate preferred orientation of phlogopite to provide accurate quantitative results. The results show that the flotation product has a higher concentration of phlogopite at 87% (by mass), compared to 78% in the hydrosizer product. The main impurity phase in both products is olivine (10% in the flotation product and 18% in the hydrosizer product). In the hydrosizer product, 15% of the sample consists of liberated phlogopite particles, while in the flotation product 58% of the sample occurs as pure, liberated phlogopite particles. [Copyright &y& Elsevier]

Middle Miocene volcanic activity in the Afyon volcanic province (eastern part of Western Anatolia) is characterized by multistage potassic and ultrapotassic alkaline volcanic successions. The volcanism is generally related to the northward subduction of the African plate beneath the Eurasian Plate. In Afyon, the Middle Miocene volcanic products consist of melilite leucitite, tephriphonolite, trachyte, basaltic-trachyandesite, phonolite, phonotephrite, tephriphonolite and lamproite rocks. Near- surface emplacement and relatively quiescent subaerial eruptions of lamproitic magma produced different emplacement forms such as dome/plug-shaped bodies and lava flows, showing variation in volume and texture. The mineralogical constituents of the lamproites are sanidine, olivine (77 < Mg no. < 81), phlogopite (74 < Mg no. < 78), K-richterite, clinopyroxene (74 < Mg no. < 78), with accessory apatite, calcite and opaque minerals. Afyon lamproites resemble Mediterranean-type Si-rich lamproites. Their compositional range is 50-52 wt % SiO2, 4-8 wt % MgO, and they display a typical lamproitic affinity. Chondrite-normalized REE patterns exhibit enrichment in LREE relative to HREE ((La/Yb)CN = 15.3-17.0). They show extreme enrichment in LILE relative to primitive mantle values and troughs of Nb and Ti. The lamproites give a range of high initial 87Sr/86Sr ratios and low 143Nd/144Nd ratios. The geochemical and isotopic characteristics suggest that lamproitic magma is derived from highly metasomatized mantle. The enrichment history may include metasomatic events related to subduction, as in other active orogenic areas of the Mediterranean. [ABSTRACT FROM AUTHOR]

Phlogopite lamproites occur in the Inner Arc Tectono-Magmatic Domain of the Eastern Altiplano (southern Peru, Andean Cordillera), a geotectonic setting characterizing lamproites at destructive plate margins. One sample free from contamination by crustal felsic melts displays many diagnostic features of «Mediterranean» lamproites as regards mineral assemblages and the bulk-rock composition [56.6 wt.% SiO2, 12.9 wt.% Al2O3, K2O/Al2O3<0.8, MgO<8 wt.%, CaO<3.5 wt.%, very strong LILE enrichment (La/YbN=27) and Sr, Nb, Ta and Ti negative anomalies (Sr/NdN=0.49, La/NbN=0.38)]. In thin sections, the rock shows a volumetrically dominant fluidal groundmass (82 vol.%) enclosing 1–3 mm olivine-rich polycrystalline aggregates [Mg–Ni-rich olivine, (88

Dynamic metasomatism experiments were performed by reacting a lamproite melt with garnet peridotite by drawing melt through the peridotite into a vitreous carbon melt trap, ensuring the flow of melt through the peridotite and facilitating analysis of the melt. Pressure (2–3 GPa) and temperature (1050–1125 °C) conditions were chosen where the lamproite was molten but the peridotite was not. Phlogopite was formed and garnet and orthopyroxene reacted out, resulting in phlogopite wehrlite (2 GPa) and phlogopite harzburgite (3 GPa). Phlogopites in the peridotite have higher Mg/(Mg + Fe) and Cr2O3 and lower TiO2 than in the lamproite due to buffering by peridotite minerals, with Cr2O3 from the elimination of garnet. Compositional trends in phlogopites in the peridotite are similar to those in natural garnet peridotite xenoliths in kimberlites. Changes in melt composition resulting from the reaction show decreased TiO2 and increased Cr2O3 and Mg/(Mg + Fe). The loss of phlogopite components during migration through the peridotite results in low K2O/Na2O and K/Al in melts, indicating that chemical characteristics of lamproites are lost through reaction with peridotite so that emerging melts would be less extreme in composition. This indicates that lamproites are unlikely to be derived from a source rich in peridotite, and more likely originate in a source dominated by phlogopite-rich hydrous pyroxenites. Phlogopites from an experiment in which lamproite and peridotite were intimately mixed before the experiment did not produce the same phlogopite compositions, showing that care must be taken in the design of reaction experiments. [ABSTRACT FROM AUTHOR]

A suite of potassium‐bearing minerals from the Walgidee Hills lamproite intrusion in the Kimberley region of Western Australia was selected for 39Ar/40Ar dating. These included wadeite, jeppeite, priderite, potassium richterite, and phlogopite. All recorded excellent plateau ages, with the mean age of the combined data set being 17.3±0.3 Ma. Phlogopite recorded the largest uncertainty, whereas, of the other minerals, wadeite gave the best precision. Although rare to absent in common magmatic rocks, these minerals are widely distributed in alkaline complexes and in lamproite, kimberlite and orangeite intrusions. The results indicate this suite of minerals is excellent for 39Ar/40Ar dating and that they can be used singly or in combination to obtain the precise magmatic crystallization ages of ultra‐alkaline rocks. Because of the stability of potassium richterite at mantle depths, 39Ar/40Ar dating of MARID (mica‐amphibole‐rutile‐ilmenite‐diopside) xenoliths should be a more widely‐applied technique to investigating mantle geodynamics. [ABSTRACT FROM AUTHOR]

Diamondiferous rock types worldwide are broadly divided into kimberlite and lamproite, the latter of which have unique characteristics in different regions and include carbonate-rich varieties (formerly orangeites/Group II kimberlites). Diamondiferous rocks in West Africa are typically micaceous and share petrographic, mineralogical, and geochemical characteristics with both kimberlites and lamproites. To further constrain the classification and petrogenesis of diamondiferous rocks worldwide and their variability between different cratonic regions, in this study we combine detailed petrographic observations with olivine, phlogopite, and spinel chemistry for hypabyssal samples from the Jurassic Tongo dike (Sierra Leone) and the Neoproterozoic Weasua cluster (Liberia). The Tongo dike contains macrocrysts of olivine and phlogopite in a groundmass of olivine, abundant phlogopite, spinel, perovskite, and apatite with a base of calcite, dolomite, and lesser serpentine. The phlogopite is characterised by concurrent FeO and Al 2 O 3 enrichment, which is typical of kimberlites and unlike lamproites. These features and the kimberlite-like spinel compositions allow us to classify the Tongo samples as micaceous kimberlites. The Weasua rocks comprise macrocrysts of olivine in a groundmass of olivine, phlogopite, diopside (zoned towards aegirine-rich rims), spinel, perovskite, and apatite with a base of serpentine and less common calcite. The composition of Weasua phlogopite trends to significant FeO enrichment and Al 2 O 3 depletion, i.e. towards tetraferriphlogopite. The enrichment in mica, phlogopite chemistry and presence of magmatic diopside indicates that these rocks are olivine lamproites. The populations of olivine macrocrysts and microcrysts at Tongo and Weasua are similar and characterised by distinct core and rim zones. Two distinct olivine core populations are observed. 1) forsterite-rich (Fo > 90) olivine interpreted to reflect xenocrysts from typical mantle peridotites. Al-in-olivine thermometry suggests that these cores have P-T equilibration within diamond stability at Weasua and Tongo. 2) Al-, Ca- and Na- rich cores with P-T formation conditions extending beyond the mantle adiabat. These cores are interpreted to reflect metasomatic and thermal perturbation linked with the infiltration of kimberlite/lamproite melts in the deep lithosphere shortly before entrainment in the ascending magma. The olivine rims at Tongo and Weasua show limited variations in Fo contents at similar values of 88.9 ± 0.8 for Tongo and 89.6 ± 1.2 for Weasua, as well as similar minor and trace element concentrations. Thus, whereas the Tongo and Weasua rock types are classified as kimberlite and olivine lamproite, respectively, the olivine chemistry suggests a similar petrogenetic evolution. • Here we classify unusual transitional kimberlite-lamproites from West Africa. • Tongo rocks are micaceous transitional kimberlites. • Weasua rocks are diopside-bearing olivine lamproites. • West African diamondiferous rocks defy clear classification. • Olivine chemistry indicates similar petrogenesis both localities. [ABSTRACT FROM AUTHOR]